Power conversion device

Abstract

The inverter (408) converts the power output from the distributed power source (40) into AC power and outputs it to the AC system. The inverter control circuit (409) generates a target AC voltage value for controlling the inverter (408) and generates a command value for controlling the inverter (408) as a voltage source. When the inverter (408) is connected to the AC system, the inverter control circuit (409) makes the frequency of the target AC voltage value the frequency of the AC voltage detected by the AC frequency detection circuit (4091), and when the target AC power value is in the direction of power operation, it controls the phase of the target AC voltage value to be at least the leading phase relative to the AC voltage of the AC system.

Description

Technical Field

[0001] This disclosure relates to power conversion devices. Background Technology

[0002] In recent years, to reduce environmental impact, there has been a rapid increase in the adoption of power generation systems using static inverters that utilize natural energy sources such as solar cells, which do not emit carbon dioxide. To address power shortages following the Great East Japan Earthquake, products such as systems with built-in batteries, systems that use electric vehicles as batteries, and systems combining solar cells and batteries have been developed. Static inverters are also used in these systems.

[0003] On the other hand, in thermal power plants, which act as a regulator, the cost of generating electricity, including management costs, is increasing as the amount of electricity generated from renewable energy sources rises, leading to predictions of their gradual closure. Synchronous generators in thermal power plants, for example, potentially have a suppressive effect on system frequency variations (inertial forces, synchronization forces, etc.). As thermal power plants gradually close (reducing the number of synchronous generators), it will be difficult to ensure system stability.

[0004] To address the aforementioned issues, companies have been continuously developing virtual synchronous generator control technology that enables static inverters to function as synchronous generators. Japanese Patent Application Publication No. 2011-193606 (Patent Document 1) discloses a control method and control device for a static inverter equipped with virtual synchronous generator control technology. Specifically, Patent Document 1 describes a control method for virtual synchronous generator control during stable operation in interconnected systems. The inverter unit described in Patent Document 1 consists of a speed governor control unit, a mass system calculation unit, and an AVR (Automatic Voltage Regulator) unit required for virtual synchronous generator control. The mass system calculation unit calculates the angular frequency output from the static inverter based on the difference between the effective power output from the static inverter and the command value (power target value) output from an energy management device (hereinafter referred to as EMS). Based on the calculated angular frequency, current value, and set voltage, the inverter unit controls the target AC voltage to become an advancing phase when the frequency of the power system decreases.

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: Japanese Patent Application Publication No. 2011-193606 Summary of the Invention

[0008] Patent Document 1 describes a static inverter equipped with virtual synchronous generator control function that generates AC voltage for an AC system and operates as a voltage source. This static inverter calculates the angular frequency (frequency and phase of the AC voltage) of the AC system output from the static inverter based on the difference between the target output power value notified from the EMS and the effective power output by the static inverter. The static inverter generates an offset value added to the target output power value notified from the EMS based on the difference between the frequency of the AC voltage and the target frequency value (e.g., 60Hz) of the AC voltage notified from the EMS. When the frequency of the power system decreases, the control is implemented to make the target AC voltage an advancing phase, so the static inverter outputs more effective power than the target output power value notified from the EMS in the power operation direction (discharge direction). In the following description, the control that enables the static inverter to operate as a voltage source is described as voltage control. On the other hand, the control that enables the static inverter to operate as a current source synchronously with the input AC voltage is described as current control.

[0009] In a power distribution system equipped with static inverters controlled by multiple virtual synchronous generators, the EMS manages the number of static inverters connected to the distribution system through power demand management. For example, in a power distribution system with three static inverters, if the power demand can be supplied by the output of one static inverter, considering the efficiency of the power conversion device including the static inverter, it is better to supply all the power with one inverter than to share the power with three static inverters. However, when the required power increases and it is difficult to supply the power demand with one inverter, the EMS outputs an instruction to add another static inverter to the distribution system. The static inverter, receiving the instruction as a new participant in the distribution system, detects the frequency, phase, and amplitude of the AC voltage of the AC system at its end, based on the AC voltage of the AC system of its local distribution system. Furthermore, the static inverter generates a target value for the AC voltage of the AC system when using the measured frequency, phase, and amplitude for voltage control, and outputs power to the AC system.

[0010] On the other hand, there is an error in the AC voltage of the AC system measured by the voltage sensor. When the frequency and phase are detected by detecting the zero-crossing point of the AC voltage waveform at this terminal using a static inverter, for example, consider a case where the AC voltage of the AC system, which is 0V, is output as -2V due to the error. When the static inverter generates a target AC voltage value based on the zero-crossing point detected by the voltage sensor, this target value is generated with a phase lag compared to the actual AC voltage of the AC system. Even if the static inverter starts voltage control based on the zero-crossing point information detected by the voltage sensor, because the target AC voltage value is lags behind, power flows from the AC system towards the static inverter immediately after voltage control begins. This flowing power varies according to the phase difference.

[0011] This phenomenon is eliminated in a few seconds to a dozen seconds by using the virtual synchronous generator control of the aforementioned particle system calculation unit and speed controller control unit. However, if the power demanded exceeds the power capacity of the previously operating static inverter, the previously operating static inverter stops due to overload. The control circuit for controlling the static inverter is often composed of a microcomputer. The microcomputer samples the AC voltage and AC current of the AC system synchronously with the carrier wave during the PWM (Power Width Modulation) conversion, which serves as the reference for controlling the static inverter. More specifically, the microcomputer generates an interrupt signal based on the carrier signal and calculates a command value based on the generated interrupt signal. In this case, the sampling position of the AC voltage of the AC system changes according to the timing of the input carrier interruption. This results in an error in the time axis direction caused by sampling. Furthermore, errors occur in the linearity and amplitude direction of the aforementioned voltage sensor. Due to these errors, errors occur in the frequency, phase, and voltage amplitude of the output AC voltage of the newly switched-on static inverter. In particular, when the output AC voltage of a static inverter is lagging, the static inverter draws unnecessary power from the system (charging) when it is newly turned on. When this unnecessary power exceeds the power capacity of the already turned-on static inverter, the already turned-on static inverter stops due to overload.

[0012] As explained above, in a power system with multiple static inverters equipped with virtual synchronous generator control, when a static inverter is newly connected to and then disconnected from the power system, the connected static inverter draws in power in the regenerative (charging) direction. When a static inverter originally connected to the system outputs power to compensate for the drawn-in power, this power exceeds the static inverter's power capacity, causing the static inverter to stop. The object of this disclosure is to provide a power conversion device that can suppress the stopping of static inverters originally connected to the AC system when an inverter is newly connected to and then disconnected from the AC system.

[0013] The power conversion device disclosed herein includes: an inverter that converts power output from a distributed power source into AC power and outputs it to an AC system; an AC voltage meter that measures the AC voltage of the AC system; an AC frequency detection circuit that detects the frequency and phase of the AC voltage of the AC system based on the output of the AC voltage meter; and an inverter control circuit that generates a target AC voltage value for controlling the inverter and generates a command value for controlling the inverter as a voltage source. When the inverter is switched on to the AC system, the inverter control circuit makes the frequency of the target AC voltage value the frequency of the AC voltage detected by the AC frequency detection circuit, and when the target AC power value is in the direction of power operation, it controls the phase of the target AC voltage value to be at least the leading phase relative to the AC voltage of the AC system.

[0014] According to the power conversion device disclosed herein, when a new inverter is connected to or stopped in an AC system, it is possible to suppress the shutdown of a static inverter that was originally connected to the AC system. Attached Figure Description

[0015] Figure 1 This is a block diagram showing the structure of a power distribution system (AC system) connected to the power conversion device according to Embodiment 1.

[0016] Figure 2 This is for further explanation including with Figure 1 The diagram shows a portion of the equipment connected to the power distribution system 24 battery 40 and a block diagram of the structure of the power distribution system 24.

[0017] Figure 3 yes Figure 1 The block structure diagram of the megawatt-class solar power conversion device 27 is shown.

[0018] Figure 4 yes Figure 1 The diagram shows the block structure of the power conversion device 41 for the battery in the power distribution system.

[0019] Figure 5 This is an explanation Figure 3The diagram shown is a block diagram of the structure of the first control circuit 204 of the first DC / DC conversion circuit 203 that controls the megawatt-class solar power conversion device 27.

[0020] Figure 6 This is an explanation Figure 3 The diagram shown is a block diagram of the structure of the first DC / AC conversion circuit 208 and the second control circuit 209 that control the megawatt-class solar power conversion device 27.

[0021] Figure 7 This is an explanation Figure 4 The diagram shown is a block diagram of the structure of the third control circuit 404 of the second DC / DC conversion circuit 403 of the power conversion device 41 for controlling the power distribution system battery.

[0022] Figure 8 This is an explanation Figure 4 The diagram shown is a block diagram of the structure of the fourth control circuit 409 of the second DC / AC conversion circuit 408 of the battery power conversion device 41 for controlling the power distribution system.

[0023] Figure 9 This is a diagram that schematically illustrates the function of the speed controller.

[0024] Figure 10 This is an explanation Figure 8 The diagram shown is a block diagram of the structure of the AC frequency detection circuit 4091.

[0025] Figure 11 This is an explanation Figure 8 The diagram shown is a block diagram of the inverter voltage control circuit 4095.

[0026] Figure 12 This is an explanation Figure 8 The diagram shown is a block diagram of the structure of the virtual synchronous generator control circuit 4093.

[0027] Figure 13 This is a diagram used to illustrate the operation of the target power generation circuit 40931.

[0028] Figure 14 This diagram illustrates the operation of the target frequency generation circuit 40934.

[0029] Figure 15 It is used for explanation Figure 12 The diagram shown is a block diagram of the structure of the speed controller control circuit 40933.

[0030] Figure 16 This is an explanation Figure 12 The diagram shown is a block diagram of the structure of the particle system operational circuit 40937.

[0031] Figure 17This is a simplified diagram illustrating the structure of a power distribution system used to explain the effect of the battery power conversion device 41 when the new power distribution system is connected.

[0032] Figure 18 (a) is a diagram showing the AC voltage waveform of the power distribution system 24 at the connection point of the load 31 when the power distribution system battery power conversion device 41b is switched on with a delayed phase, and the AC voltage waveform of the AC system output by the power distribution system battery power conversion device 41b. (b) is a diagram showing the output current waveform of the power distribution system battery power conversion device 41b.

[0033] Figure 19 This is a diagram showing the charging and discharging power (effective value) of the two power conversion devices 41a and 41b of the power distribution system battery when the AC voltage phase of the newly connected power distribution system battery power conversion device 41b is lagging.

[0034] Figure 20 (a) is a diagram showing the AC voltage waveform of the power distribution system 24 at the connection point of the load 31 when the power distribution system battery power conversion device 41b is turned on with the leading phase, and the AC voltage waveform of the AC system output by the power distribution system battery power conversion device 41b. (b) is a diagram showing the output current waveform of the power distribution system battery power conversion device 41b.

[0035] Figure 21 This is a diagram showing the charging and discharging power (effective value) of the two power conversion devices 41a and 41b of the power distribution system battery when the AC voltage phase of the newly connected power distribution system battery power conversion device 41b is in the leading phase.

[0036] Figure 22 This is a flowchart showing the operation of DSO21 when the power conversion device 41b for the power distribution system battery is newly connected to the power distribution system.

[0037] Figure 23 This is a flowchart illustrating the operation of the power conversion device 41a for batteries in the power distribution system interconnected with the system.

[0038] Figure 24 This is a flowchart illustrating the control process during the disconnection of the power conversion device 41 for batteries in the power distribution system.

[0039] Figure 25 This is a flowchart illustrating the control process when a new power conversion device 41 for a battery in a power distribution system is added.

[0040] Figure 26This is a flowchart showing the control process of the fourth control circuit 409 when the power conversion device 41 for the battery of the newly connected power distribution system is activated.

[0041] Figure 27 This is a flowchart illustrating the control process when a new addition (new connection for charging direction (regeneration direction) is made to the power conversion device 41 for the battery in the power distribution system in Embodiment 2.

[0042] Figure 28 This is a flowchart illustrating the control process when the power conversion device 41 for the battery of the new power distribution system is connected in the fourth control circuit 409 of Embodiment 2.

[0043] Figure 29 (a) to (c) are diagrams illustrating the method for detecting the zero-crossing point (phase) of a delayed phase.

[0044] Figure 30 This is a diagram showing the charging and discharging power (effective value) of the two power distribution system battery power conversion devices 41 when the AC voltage phase of the newly connected power distribution system battery power conversion device 41 in Embodiment 2 is lagging.

[0045] (Symbol Explanation)

[0046] 20: Substation; 21: Distribution Automation System (DSO); 22: Voltmeter; 23: Automatic Voltage Regulator (SVR); 24: Distribution System; 25: Communication Line; 26: Megawatt-class Solar Power; 27: Megawatt-class Solar Power Conversion Device; 28: Switch; 29: Impedance; 30: Synchronous Generator; 31: Load; 40: Distribution System Battery; 41: Distribution System Battery Power Conversion Device; 100: Town; 101: Factory; 102: Building; 103: Apartment; 201, 206, 210, 401, 406, 410: Voltmeter; 202, 207, 211, 402, 407, 411: Ammeter; 203: First DC / DC Conversion Circuit; 2 04: First control circuit; 205: DC bus; 208: First DC / AC conversion circuit; 209: Second control circuit; 212: Communication interface circuit; 403: Second DC / DC conversion circuit; 404: Second control circuit; 405: DC bus; 408: Second DC / AC conversion circuit; 409: Fourth control circuit; 412: Communication interface circuit; 998: Generator rotor; 999: Valve; 2041: MPPT control circuit; 2042: Voltage control circuit; 2043: Switching circuit; 2044: Fifth control circuit; 2090: Current control circuit; 2091: Phase detection circuit; 2092: First sine wave generation circuit; 2093: Subtractor; 2094: 1st PI control circuit; 2095: Multiplier; 2096: Subtractor; 2097: 6th control circuit; 2098: 2nd PI control circuit; 2099: 1st PWM converter circuit; 4041: Charging control circuit; 4042: Discharging control circuit; 4043: 2nd switching circuit; 4044: 7th control circuit; 4091: AC frequency detection circuit; 4092: Effective power calculation circuit; 4093: Virtual synchronous generator control circuit; 4094: Inverter current control circuit; 4095: Inverter voltage control circuit; 4096: 3rd switching circuit; 4097: 8th control circuit; 40910: Phase detection circuit; 40911: Frequency detection circuit; 40912: 40931: Target power generation circuit; 40932: Subtractor; 40933: Speed ​​controller control circuit; 40934: Target frequency generation circuit; 40935: Adder; 40936: Subtractor; 40937: Particle system operation circuit; 40951: 3rd sine wave generation circuit; 40952: Subtractor; 40953: 3rd PI control circuit; 40954: 2nd PWM conversion circuit; 409331: Multiplier; 409332: First-order delay system model; 409333: Limiting circuit; 409371: Subtractor; 409372: Integrator; 409373: Multiplier; 409374: Divider; 409375: Adder;409376: Phase calculation circuit. Detailed Implementation

[0047] Hereinafter, embodiments will be described in detail with reference to the accompanying drawings. Furthermore, the same or equivalent parts in the drawings will be referred to by the same symbols, and their descriptions will generally not be repeated.

[0048] The following implementation relates to virtual synchronous generator control, which enables power conversion devices that interconnect in an AC system, such as energy generation devices utilizing renewable energy sources like solar cells and energy storage devices like batteries, to have the characteristics of a synchronous generator, thereby improving the stability of the system.

[0049] Implementation method 1.

[0050] Figure 1 This is a block diagram showing the structure of the power distribution system (AC system) connecting the power conversion device according to Embodiment 1. In Embodiment 1, for the sake of simplicity, a single-phase system is used as an example, but it can also be applied to a three-phase system.

[0051] Reference Figure 1 The power distribution system 24 (24a-24d) is connected to the substation 20, and multiple automatic voltage regulators 23 (23a-23c) are connected in series in the power distribution system 24. In Embodiment 1, each automatic voltage regulator 23 is composed of an SVR, and the automatic voltage regulator 23 will be referred to as SVR23 below. The power distribution system 24 is connected to towns 100 (towns A100a, B100b, C100c, D100d), factories 101, buildings 102, apartments 103, megawatt-class solar power conversion devices 27, and power conversion devices 41 for power distribution system batteries (hereinafter, these are sometimes referred to as "consumers").

[0052] Multiple voltmeters 22 are connected to the power distribution system 24. The measurement results of the voltmeters 22 are sent to the power distribution automation system 21 (hereinafter referred to as DSO21) at a predetermined period. The tap position information, primary side voltage information and secondary side voltage information of the SVR23 are also notified to the power distribution automation system 21. In Embodiment 1, the SVR23 notifies the power distribution automation system 21 of the tap position information, primary side voltage information and secondary side voltage information at a predetermined period, and notifies it irregularly when the tap is switched. The DSO21 collects various measurement results and other information from various consumers (building 102, apartment 103, town 100, factory 101, megawatt-class solar power conversion device 27, synchronous generators 30a, 30b and power distribution system battery power conversion devices 41a, 41b, 41c) at a predetermined period. A CEMS (Community Energy Management System), not shown, collects data from smart meters (not shown) installed at each consumer's location at predetermined intervals (e.g., 30-minute intervals) on the power consumption of consumers in towns A100a, B100b, C100c, and D100d, as well as the power generated by energy-generating devices, and notifies DSO21 of the collection results. A megawatt-level solar power conversion device 27 is connected to a megawatt-level solar panel 26. Similarly, power conversion devices 41a, 41b, and 41c for the distribution system batteries are connected to distribution system batteries 40a, 40b, and 40c.

[0053] Figure 2 This is for further explanation including with Figure 1 The diagram shows a portion of the equipment connected to the power distribution system 24 battery 40 and a block diagram of the structure of the power distribution system 24.

[0054] Reference Figure 2 The power distribution system 24 is connected to a load 31, a power distribution system impedance 29, a power distribution system battery 40, and a power conversion device 41 for the power distribution system battery. The impedance 29 is simplified and described in a centralized manner. In Embodiment 1, the impedance 29 of the power distribution system consists of a reactor component and a resistive component.

[0055] Figure 3 yes Figure 1 The block structure diagram of the megawatt-class solar power conversion device 27 is shown.

[0056] Reference Figure 3The megawatt-class solar power conversion device 27 includes a voltmeter 201, a current meter 202, a first DC / DC conversion circuit 203, a first control circuit 204, a DC bus 205, a voltmeter 206, a current meter 207, a first DC / AC conversion circuit 208, a second control circuit 209, a voltmeter 210, a current meter 211, and a communication interface circuit 212.

[0057] Voltmeter 201 measures the first DC voltage output from the megawatt-class solar panel 26. Ammeter 202 measures the DC current output from the megawatt-class solar panel 26. A first DC / DC converter circuit 203 converts the DC power from the first DC voltage output from the megawatt-class solar panel 26 into a second DC voltage. A first control circuit 204 controls the first DC / DC converter circuit 203. A DC bus 205 supplies the second DC voltage output from the first DC / DC converter circuit 203 to the first DC / AC converter circuit 208. Voltmeter 206 measures the second DC voltage from the DC bus 205. Ammeter 207 measures the DC current output from the first DC / DC converter circuit 203.

[0058] The first DC / AC converter circuit 208 converts the DC power output from the first DC / AC converter circuit 203 into AC power and outputs it to the power distribution system 24. The second control circuit 209 controls the first DC / AC converter circuit 208. A voltmeter 210 measures the AC voltage output from the first DC / AC converter circuit 208. A current meter 211 measures the AC current output from the first DC / AC converter circuit 208. A communication interface circuit 212 communicates with the DSO 21.

[0059] Figure 4 yes Figure 1 The diagram shows the block structure of the power conversion device 41 for the battery in the power distribution system.

[0060] Reference Figure 4 The power conversion device 41 for the battery in the power distribution system includes a voltmeter 401, a current meter 402, a second DC / DC conversion circuit 403, a third control circuit 404, a DC bus 405, a voltmeter 406, a current meter 407, a second DC / AC conversion circuit 408, a fourth control circuit 409, a voltmeter 410, a current meter 411, and a communication interface circuit 412.

[0061] Voltmeter 401 measures the third DC voltage output from the power distribution system battery 40. Ammeter 402 measures the DC current output from the power distribution system battery 40. A second DC / DC converter circuit 403 converts the DC power from the third DC voltage output from the power distribution system battery 40 into a fourth DC voltage. A third control circuit 404 controls the second DC / DC converter circuit 403. A DC bus 405 supplies the fourth DC voltage output from the second DC / DC converter circuit 403 to the second DC / AC converter circuit 408.

[0062] Voltmeter 406 measures the fourth DC voltage of DC bus 405. Ammeter 407 measures the DC current output from the second DC / DC converter circuit 403. The second DC / AC converter circuit 408 converts the DC power output from the second DC / DC converter circuit 403 into AC power and outputs it to the power distribution system 24. The fourth control circuit 409 controls the second DC / AC converter circuit 408. Voltmeter 410 measures the AC voltage output from the second DC / AC converter circuit 408. Ammeter 411 measures the AC current output from the second DC / AC converter circuit 408. The communication interface circuit 412 enables communication between the power distribution system battery power conversion device 41 and DSO21.

[0063] The structures of the first DC / DC converter 203 and the second DC / DC converter 403 can be adapted to use known DC / DC converter structures. The structures of the first DC / AC converter 208 and the second DC / AC converter 408 can be adapted to use known inverter structures.

[0064] exist Figure 3 as well as Figure 4 In the structure, the first DC / AC conversion circuit 208 and the second DC / AC conversion circuit 408 each correspond to an embodiment of an inverter that converts power output from a distributed power source into AC power and outputs it to an AC system. Furthermore, the second control circuit 209 is an inverter control circuit that generates a command value for controlling the inverter as a current source based on the input AC voltage. Similarly, the fourth control circuit 409 corresponds to an embodiment of an inverter control circuit that generates a target AC voltage value for controlling the inverter and generates a command value for controlling the inverter as a voltage source.

[0065] Figure 5 This is an explanation Figure 3 The diagram shown is a block diagram of the structure of the first control circuit 204 of the first DC / DC conversion circuit 203 that controls the megawatt-class solar power conversion device 27.

[0066] Reference Figure 5The first control circuit 204 includes an MPPT (Maximum Power Point Tracking) control circuit 2041, a voltage control circuit 2042, a first switching circuit 2043, and a fifth control circuit 2044.

[0067] The MPPT control circuit 2041 performs so-called maximum power point tracking control. To maximize the extraction of power generated from the megawatt-class solar panel 26, the MPPT control circuit 2041 searches for the maximum power point of the megawatt-class solar panel 26 based on measurements from voltmeter 201 and ammeter 202. Specifically, the MPPT control circuit 2041 generates control command values ​​for controlling the first DC / DC converter circuit 203 in a manner that makes the DC voltage measured by voltmeter 201 correspond to the voltage of the maximum power point.

[0068] The voltage control circuit 2042 generates a control command value for the first DC / DC converter circuit 203 to maintain the DC voltage (second DC voltage) of the DC bus 205 at a predetermined voltage target value based on the measurement value of the voltmeter 206.

[0069] The fifth control circuit 2044 outputs control parameters and target values ​​to the MPPT control circuit 2041 and the voltage control circuit 2042 based on the current status information of the first DC / DC conversion circuit 203 and the information of the second control circuit 209, and manages the power generation status of the megawatt-level solar panel 26. The fifth control circuit 2044 also outputs control signals to the first switching circuit 2043.

[0070] The first switching circuit 2043 selects one of the outputs of the MPPT control circuit 2041 and the voltage control circuit 2042 as the control command value output of the first DC / DC conversion circuit 203 according to the control signal from the fifth control circuit 2044.

[0071] The first DC / DC converter circuit 203 is controlled using either MPPT mode or voltage control mode. When the first DC / DC converter circuit 203 is in MPPT mode, the first switching circuit 2043 outputs the control command value generated by the MPPT control circuit 2041. When the first DC / DC converter circuit 203 is in voltage control mode, the first switching circuit 2043 is controlled by outputting the control command value generated by the voltage control circuit 2042.

[0072] Figure 6 This is an explanation Figure 3 The diagram shown is a block diagram of the structure of the first DC / AC conversion circuit 208 and the second control circuit 209 that control the megawatt-class solar power conversion device 27.

[0073] Reference Figure 6 The second control circuit 209 includes a phase detection circuit 2091, a first sine wave generation circuit 2092, a current control circuit 2090, and a sixth control circuit 2097. The current control circuit 2090 includes a subtractor 2093, a first PI control circuit 2094, a multiplier 2095, a subtractor 2096, a second PI control circuit 2098, and a first PWM converter 2099. The current control circuit 2090 operates in a control mode similar to that of a typical solar power conversion device installed in a home. In this control mode, the power conversion device is controlled to output power synchronously with the AC voltage of the AC system.

[0074] Phase detection circuit 2091 detects the phase of the AC voltage waveform measured by voltmeter 210. In Embodiment 1, phase detection circuit 2091 detects zero-crossing points from the AC voltage waveform and detects the frequency of the AC voltage from the zero-crossing point detection result. Phase detection circuit 2091 outputs the frequency of the AC voltage and the zero-crossing point information as phase information to first sine wave generation circuit 2092.

[0075] The first sine wave generation circuit 2092 generates a sine wave that is synchronized with the AC voltage waveform measured by the voltmeter 210, based on the amplitude of the AC voltage measured by the voltmeter 210 and the phase information detected by the phase detection circuit 2091.

[0076] The current control circuit 2090 generates a control command value for the first DC / AC converter circuit 208 based on the DC voltage of the DC bus 205 output from the voltmeter 206. The subtractor 2093 subtracts the DC voltage of the DC bus 205 output from the voltmeter 206 from the target value of the DC bus voltage output from the sixth control circuit 2097, and inputs the subtraction result to the first PI control circuit 2094. The first PI control circuit 2094 outputs a voltage command value in a manner that ensures the DC voltage of the DC bus 205 reaches a predetermined value, based on the control parameters (proportional gain and integral time) output from the sixth control circuit 2097 and the output of the subtractor 2093.

[0077] Multiplier 2095 multiplies the voltage command value output from the first PI control circuit 2094 by a sine wave synchronized with the AC voltage waveform output from the first sine wave generation circuit 2092 to generate a current command value. Subtractor 2096 subtracts the AC system current value measured by ammeter 211 from the current command value output from multiplier 2095 and outputs the subtraction result to the second PI control circuit 2098. The second PI control circuit 2098 outputs the current command value to the first PWM converter circuit 2099 in a manner that makes the subtraction result output from subtractor 2096 zero, based on the control parameters (proportional gain and integral time) output from the sixth control circuit 2097. The first PWM converter circuit 2099 performs PWM conversion on the current command value from the second PI control circuit 2098 to generate a control command value, and outputs the control command value to the first DC / AC converter circuit 208.

[0078] The sixth control circuit 2097 controls the current control circuit 2090. The sixth control circuit 2097 collects measurement results related to the DC bus 205 from voltmeter 206 and ammeter 207, measurement results related to the AC system from voltmeter 210 and ammeter 211, and status information of the first DC / DC converter circuit 203 from the first control circuit 204. The sixth control circuit 2097 notifies the DSO 21, etc., of the collected information via the communication interface circuit 212.

[0079] As described above, the control parameters for the first PI control circuit 2094 and the second PI control circuit 2098 are also notified from the sixth control circuit 2097. Furthermore, the effective voltage of the AC system measured by the AC system effective voltage measurement circuit (not shown) or the effective power and ineffective power information measured by the AC system effective power measurement circuit (not shown) and ineffective power measurement circuit are also notified to the DSO21 via the communication interface circuit 212 through the sixth control circuit 2097. The sixth control circuit 2097 also notifies the fifth control circuit 2044 of the measurement results such as the effective voltage and effective power of the AC system. For example, if the effective value of the AC voltage of the AC system exceeds a predetermined value, the fifth control circuit 2044 switches the control of the megawatt-level solar panel 26 from MPPT mode to voltage control mode to suppress the rise of the AC voltage of the AC system.

[0080] Figure 7 This is an explanation Figure 4 The diagram shown is a block diagram of the structure of the third control circuit 404 of the second DC / DC conversion circuit 403 of the power conversion device 41 for controlling the power distribution system battery.

[0081] Reference Figure 7The third control circuit 404 includes a charging control circuit 4041, a discharging control circuit 4042, a second switching circuit 4043, and a seventh control circuit 4044.

[0082] The charging control circuit 4041 generates control command values ​​for the second DC / DC converter circuit 403 when performing charging control of the power distribution system battery 40 based on the outputs of the ammeter 402, the voltmeter 401, and the voltmeter 406.

[0083] The discharge control circuit 4042 generates control command values ​​for the second DC / DC converter circuit 403 when discharging the battery 40 from the power distribution system based on the outputs of the ammeter 402, the voltmeter 401, and the voltmeter 406.

[0084] The 7th control circuit 4044 outputs control parameters and target values ​​to the charging control circuit 4041 and the discharging control circuit 4042, and manages the charging amount, charging current, and discharging power of the power distribution system battery 40. The 7th control circuit 4044 outputs control signals to the 2nd switching circuit 4043.

[0085] The second switching circuit 4043 selects one of the outputs of the charging control circuit 4041 and the discharging control circuit 4042 as the control command value output of the second DC / DC conversion circuit 403 according to the control signal from the seventh control circuit 4044.

[0086] The second switching circuit 4043 is controlled to output the control command value generated by the charging control circuit 4041 when the battery 40 of the power distribution system is being charged, and to output the control command value generated by the discharging control circuit 4042 when the battery 40 of the power distribution system is being discharged.

[0087] Figure 8 This is an explanation Figure 4 The diagram shown is a block diagram of the structure of the fourth control circuit 409 of the second DC / AC conversion circuit 408 of the battery power conversion device 41 for controlling the power distribution system.

[0088] Reference Figure 8 The fourth control circuit 409 includes an AC frequency detection circuit 4091, an effective power calculation circuit 4092, a virtual synchronous generator control circuit 4093, an inverter current control circuit 4094, an inverter voltage control circuit 4095, and a third switching circuit 4096.

[0089] The AC frequency detection circuit 4091 detects the phase of the AC voltage waveform measured by the voltmeter 410. In Embodiment 1, the AC frequency detection circuit 4091 detects zero-crossing points from the AC voltage waveform and detects the frequency from the time interval between the detected zero-crossing points. Furthermore, the AC voltage frequency detection method is not limited to methods using the detection results of zero-crossing points.

[0090] The effective power calculation circuit 4092 calculates the effective power output from the second DC / AC conversion circuit 408 (inverter) based on the AC voltage and AC current information measured by the voltmeter 410 and the ammeter 411. In Embodiment 1, the effective power calculation circuit 4092 also uses the zero-crossing detection information and AC frequency information output from the AC frequency detection circuit 4091 to accumulate the power of one cycle of the AC voltage waveform and calculate the effective power. Furthermore, the method for calculating the effective power is not limited to the above-described manner; for example, in the case of a three-phase AC system, a DQ converter or similar method can be used to calculate the effective power.

[0091] The virtual synchronous generator control circuit 4093 uses the frequency information of the AC voltage and the actual power information output from the AC frequency detection circuit 4091 and the actual power calculation circuit 4092 to enable the second DC / DC conversion circuit 408 (static inverter) to perform virtual synchronous generator control in a manner that gives it the inertial force, synchronization force, and braking force of a synchronous generator. The following is a brief explanation of virtual synchronous generator control technology. Synchronous generators, exemplified by thermal power plants, have functions such as adjusting the output power according to the frequency (speed governor function), maintaining angular velocity (inertial force), synchronizing with the AC voltage of the AC system (synchronization force), regulating the voltage of the base system (AVR (Automatic Voltage Regulator) function), and continuing operation even when the AC voltage of the AC system momentarily drops during a system fault. In virtual synchronous generator control technology, the static inverter simulates the functions of a synchronous generator by controlling the transient response of the static inverter. Specifically, the functions include three aspects: the static inverter simulating a speed governor, simulating a particle system model based on oscillation equations (dynamic characteristics of a rotating machine), and the AVR function.

[0092] In Embodiment 1, the case where a speed governor function and a function simulating a particle system model based on oscillatory equations are specifically described. Furthermore, the AVR function of the synchronous generator is primarily controlled based on output voltage commands or invalid power command values ​​notified from the host system (DSO21 in Embodiment 1), so it is not installed in Embodiment 1. Hereinafter, the speed governor function and the function simulating a particle system model based on oscillatory equations will be explained in detail.

[0093] First, let's explain the function of the speed governor. In a power plant, the speed governor controls the output power of the generator by controlling the output of the gas turbines or steam turbines in thermal or nuclear power plants, and the guide vanes of the turbines in hydroelectric power plants. In an AC power system, when demand exceeds supply, the frequency of the AC voltage decreases. In thermal or hydroelectric generators where output can be controlled, the speed governor has a droop characteristic, controlling the frequency by increasing the generated power. Conversely, when supply exceeds demand, the frequency of the AC voltage increases. Even in this case, in thermal or hydroelectric generators where output can be controlled, the speed governor again has a droop characteristic, controlling the frequency by decreasing the generated power.

[0094] Figure 9 This is a diagram schematically illustrating the function of the speed controller. For example... Figure 9 As shown, when the angular velocity ω of the synchronous generator increases, the valve 999 regulating the energy inflow moves to the right. As a result, the energy supplied to the synchronous generator decreases. On the other hand, when the angular velocity of the synchronous generator decreases, the valve 999 regulating the energy inflow moves to the left. As a result, the energy supplied to the synchronous generator increases. Thus, the synchronous generator can individually control the energy output from the synchronous generator by the frequency of the AC voltage of the AC system at the synchronous generator's terminals (the angular velocity of the synchronous generator). Even when the synchronous generators perform the above actions separately, since the above actions are managed by the frequency of the AC voltage of the AC system, load sharing can be achieved among multiple generators. For the speed governor, a standard model composed of a single-order delay form is provided by the "General Incorporated Association of Electrical Engineering".

[0095] In Embodiment 1, the operation of the speed governor is described when the model composed of the above-described primary delay system is used to approximate the speed governor (refer to Equation (1)). Furthermore, in Equation (1), -1 / Kgd represents the proportional gain of the speed governor, and Tg represents the time constant of the primary delay system.

[0096] -1 / (Kgd×(1+s×Tg))…(1)

[0097] Next, we will explain the functionality of the simulation model based on the oscillating equations for a particle system. Synchronous generators, such as... Figure 9The diagram shows a generator rotor 998 with an inertial constant m. For example, in the case where the power generated by a megawatt-level solar power system 26 decreases rapidly due to drastic changes in solar radiation, the insufficient power cannot be supplied instantaneously under the control of the aforementioned speed governor. The synchronous generator converts the rotational energy stored in the generator rotor 998 into electricity and outputs it to the AC system. At this time, the angular velocity (rotation speed) of the generator rotor 998 decreases. When the angular velocity of the generator rotor 998 decreases, the energy supplied is increased by controlling the speed governor to support demand and supply. Equation (2) is the oscillation equation of the simulated mass system model (generator rotor 998) (converting energy P by angular velocity ω into torque T). In Equation (2), Dg represents the braking coefficient, and M represents the aforementioned inertial constant.

[0098] Tin-Tout=M×dω / dt+Dg×ω…(2)

[0099] In Implementation 1, by incorporating Equations (1) and (2) into the control of the static inverter (second DC / AC conversion circuit 408), the static inverter simulates the inertial force, synchronization force and braking force of the synchronous generator.

[0100] Refer again Figure 8 The inverter current control circuit 4094 generates control command values ​​when the second DC / AC conversion circuit 408 is controlled by current control. The circuit structure and operation of the inverter current control circuit 4094 are described below. Figure 6 The current control circuit 2090 in the inverter is the same. The inverter current control circuit 4094 is the same as... Figure 6 The only difference between the current control circuit 2090 and the one in the middle is the control parameters used.

[0101] The inverter voltage control circuit 4095 generates control command values ​​when the second DC / AC conversion circuit 408 is controlled by voltage control (control mode of AC voltage output from the second DC / AC conversion circuit 408).

[0102] The third switching circuit 4096 switches the control command value from the inverter current control circuit 4094 and the control command value from the inverter voltage control circuit 4095 according to the output of the eighth control circuit 4097.

[0103] The 8th control circuit 4097 collects measurement results related to the DC bus 405 from voltmeter 406 and ammeter 407, measurement results related to the AC system from voltmeter 410 and ammeter 411, and status information of the 2nd DC / DC converter circuit 403 from the 3rd control circuit 404. The 8th control circuit 4097 notifies the DSO21 and others of the collected information via the communication interface circuit 412.

[0104] The various control parameters of the aforementioned virtual synchronous generator control circuit 4093, inverter current control circuit 4094, and inverter voltage control circuit 4095 are also notified from the 8th control circuit 4097. Furthermore, the effective voltage of the AC system measured by the effective voltage meter circuit of the AC system (not shown) or the effective and ineffective power information measured by the effective and ineffective power measurement circuit of the AC system (not shown) is also notified to DSO21 via the communication interface circuit 412. The measurement results of the effective voltage and effective power of the AC system are also notified to the 7th control circuit 4044.

[0105] Figure 10 This is an explanation Figure 8 The diagram shown is a block diagram of the structure of the AC frequency detection circuit 4091.

[0106] Reference Figure 10 The AC frequency detection circuit 4091 includes a phase detection circuit 40910, a frequency detection circuit 40911, and a second sine wave generation circuit 40912.

[0107] The phase detection circuit 40910 detects zero-crossing points on the AC voltage waveform output from the voltmeter 410. The phase detection method in the phase detection circuit 40910 is not limited to zero-crossing point detection. Regarding actual zero-crossing point detection, errors occur, such as detection errors in the voltmeter 410 (mainly offset errors), amplitude detection errors in the voltmeter 410 (mainly linearity errors), and sampling period errors when sampling the AC voltage waveform. Furthermore, when sampling using a microcomputer, errors in the sampling period occur due to the time deviation from carrier interruption to actual sampling.

[0108] The frequency detection circuit 40911 detects the frequency of the AC voltage in the AC system by measuring the period of the zero-crossing point output from the self-phase detection circuit 40910. The method for detecting the frequency of the AC voltage in the AC system is not limited to period detection from the zero-crossing point.

[0109] The second sine wave generation circuit 40912 generates a sine wave synchronized with the AC voltage of the AC system based on the zero-crossing point detection result in the phase detection circuit 40910, the frequency detection result in the frequency detection circuit 40911, and the AC voltage amplitude of the AC system output from DSO21.

[0110] The AC frequency detection circuit 4091 outputs the zero-crossing detection result, frequency detection result, and sine wave information.

[0111] Figure 11 This is an explanation Figure 8 The diagram shown is a block diagram of the inverter voltage control circuit 4095.

[0112] Reference Figure 11 The inverter voltage control circuit 4095 includes a third sine wave generation circuit 40951, a subtractor 40952, a third PI control circuit 40953, and a second PWM conversion circuit 40954.

[0113] The inverter voltage control circuit 4095 outputs control command values ​​for controlling the second DC / AC conversion circuit 408 based on the frequency and phase information output from the virtual synchronous generator control circuit 4093 (described in detail later) and the amplitude information of the AC voltage of the AC system output from the eighth control circuit 4097.

[0114] The sinusoidal wave information from the AC frequency detection circuit 4091 is input to the third sine wave generation circuit 40951. The sinusoidal wave information includes frequency information, phase information, and amplitude information. In Embodiment 1, the amplitude information may also be excluded from the sinusoidal wave information. This is because QV control is not performed in the virtual synchronous generator control circuit 4093.

[0115] The third sine wave generation circuit 40951 generates the target value of the AC voltage of the AC system output from the second DC / AC conversion circuit 408 based on the input frequency information, phase information, and amplitude information.

[0116] Subtractor 40952 subtracts the AC voltage measured by voltmeter 410 from the output of the third sine wave generation circuit 40951, and outputs the subtraction result to the third PI control circuit 40953.

[0117] The third PI control circuit 40953 generates a voltage command value through PI control to make the input subtraction result zero, and outputs it to the second PWM conversion circuit 40954. The control parameters (control gain and integral time) of the third PI control circuit are output from the eighth control circuit 4097.

[0118] The second PWM conversion circuit 40954 performs PWM conversion on the voltage command value output from the third PI control circuit 40953 and outputs the control command value to the third switching circuit 4096.

[0119] Figure 12 This is an explanation Figure 8 The diagram shown is a block diagram of the structure of the virtual synchronous generator control circuit 4093.

[0120] Reference Figure 12The virtual synchronous generator control circuit 4093 includes a target power generation circuit 40931, a subtractor 40932, a speed governor control circuit 40933, a target frequency generation circuit 40934, an adder 40935, a subtractor 40936, and a particle system operation circuit 40937.

[0121] The target power generation circuit 40931 generates a target power value for the virtual synchronous generator control circuit 4093 (as the target value of the AC power output by the second DC / AC conversion circuit 408 of the inverter). The target power value is input to the mass system operation circuit 40937 via adder 40935 and subtractor 40936. Specifically, in Embodiment 1, the target power generation circuit 40931 outputs charging and discharging power from the distribution system battery 40 based on the power command value (target power value) output from DSO21. When the power conversion device 41 for the distribution system battery is interconnected with the system for charging and discharging control, the target power generation circuit 40931 outputs the power command value from DSO21. However, in the case of the inverter (second DC / AC conversion circuit 408) of the power conversion device 41 for connecting the AC system to the power distribution system battery, in order to minimize the oscillation of the system immediately after connection, in Embodiment 1, the target power generation circuit 40931 outputs a power command value of zero immediately after connection, and then changes it to the power command value (power target value) Pref specified by DSO21 after a predetermined time. In the following description, the inverter (second DC / AC conversion circuit 408) for connecting the AC system and interconnecting the power distribution system battery is sometimes referred to as the power conversion device 41 for connecting the system and interconnecting the power distribution system battery.

[0122] Figure 13 This is a diagram used to illustrate the operation of the target power generation circuit 40931. (Refer to...) Figure 13 This explains the operation of the target power generation circuit 40931 when the power conversion device 41 for the battery of the power distribution system is newly connected to the system.

[0123] Upon new connection, with the power command value from DSO21 set to Pref, the target power generation circuit 40931 outputs zero. This is because, when the newly connected power distribution system battery converter 41, which is controlled to not be charged or discharged, outputs the target power value Pref immediately after connection, the following problem exists: Power is supplied in a balanced manner to the load through the generator already connected to the system. Even if the newly connected power distribution system battery converter 41 is controlled by voltage, it does not immediately output power. Therefore, the virtual synchronous generator control circuit 4093 determines that the load power consumption is low and controls it to increase the frequency of the AC voltage output from the AC system. As a result, the newly connected power distribution system battery converter 41 exerts unnecessary interference on the AC system.

[0124] Regarding the power conversion device 41 for a power distribution system battery that is already interconnected with the system and supplies power to the load, in Embodiment 1, the target power generation circuit 40931 can also receive an instruction to change the aforementioned power target value from Pref_b to Pref_a. At this time, in Embodiment 1, new connection information for the power conversion device 41 for the power distribution system battery is also input to the target power generation circuit 40931. During the new connection of the power conversion device 41 for the power distribution system battery, interference occurs during the connection timing and immediately after connection due to uncontrolled power supply from the power conversion device 41 for the power distribution system battery. This causes unnecessary interference to the frequency of the AC voltage of the AC system output from the power conversion device 41 for the power distribution system interconnected with the system. Furthermore, when the power target value of the power conversion device 41 for the power distribution system interconnected with the system is changed, the magnitude of the interference further increases. Therefore, in Embodiment 1, as... Figure 13 As shown by the solid line, the target power generation circuit 40931, regarding the newly connected power conversion device 41 for the battery of the distribution system, immediately sets the target power value to zero after connection. After confirming the convergence of system interference, it gradually increases the target power value from zero (e.g., at a certain rate of change) to Pref over a predetermined time. On the other hand, regarding the power conversion device 41 for the battery of the distribution system already interconnected with the system, the target power generation circuit 40931 maintains the target power value (Pref_b) before the new connection until the system interference converges. After the system interference converges, it... Figure 13 The dashed line indicates that the target power value is gradually reduced from Pref_b to Pref_a over a predetermined period of time (e.g., at a certain rate of change).

[0125] Furthermore, in Implementation 1, the control involves changing the power target value after the interference convergence of the AC voltage of the AC system is detected, but it is not limited to this. For example, even if the power target value is changed after a predetermined time has elapsed since the new turn-on command is received from DSO21, the same effect can be obtained.

[0126] In Implementation 1, the case where a new connection information is notified to the power conversion device 41 for the battery in the power distribution system interconnection, is described, but it is not limited to this. For example, when the target power generation circuit 40931 receives an instruction to change the power target value from Pref_b to Pref_a, it maintains the current power target value without switching it for a predetermined time. If a large system disturbance occurs during this time, the target power generation circuit 40931 determines that the power conversion device 41 for the battery in the power distribution system has been newly connected, and waits for the power target value to switch until the system disturbance converges. Afterwards, the target power generation circuit 40931 controls the power target value according to the above points. Thus, the same effect can be achieved even if no new additional information is exchanged from DSO21.

[0127] The target frequency generation circuit 40934 generates the frequency (target frequency value) of the target AC voltage of the virtual synchronous generator control circuit 4093. The frequency of the target AC voltage is used as the frequency of the AC voltage that serves as a reference, and is input to the speed governor control circuit 40933 via the subtractor 40932.

[0128] Figure 14 This diagram illustrates the operation of the target frequency generation circuit 40934. Generally, the target value of the AC voltage frequency of the AC system is fixed (e.g., 50Hz or 60Hz). Therefore, in Embodiment 1, the target frequency generation circuit 40934 sets the target frequency value of the newly connected power distribution system battery power conversion device 41 to the frequency (Fmesure) of the AC voltage of the AC system detected by the frequency detection circuit 40911 immediately before the connection is established, and maintains this value until the interference after the connection is established converges (see reference). Figure 14 (Solid line in the diagram). When interference convergence is detected, the target frequency generation circuit 40934 gradually (e.g., at a certain rate of change) changes the target frequency value from Fmesure over a predetermined time to become the frequency of the AC voltage of the predetermined AC system (e.g., 60Hz or 50Hz).

[0129] In Implementation 1, the target frequency value is roughly controlled using the system frequency (e.g., 60Hz or 50Hz) without significant variation. Therefore, the target frequency generation circuit 40934 sets the target frequency value of the power conversion device 41 for the power distribution system battery, which is already interconnected with the system, to the target frequency value output from the 8th control circuit 4097. This also results in, as explained in the target power generation circuit 40931, that after the control of the frequency of the AC voltage of the AC system output by the power conversion device 41 for the power distribution system battery, which is already connected to the system, begins immediately after power-on, it does not cause unnecessary interference to the balanced power supply to the power generation equipment and load, which is already connected to the system. Therefore, the target frequency generation circuit 40934, after power-on, can control the AC system without causing unnecessary interference by setting the target frequency value to the frequency (Fmesure) of the detected AC voltage of the AC system.

[0130] Refer again Figure 12 The subtractor 40932 subtracts the output of the target frequency generation circuit 40934 from the measured frequency output from the self-frequency detection circuit 40911. The output of the subtractor 40932 is then input to the speed controller control circuit 40933.

[0131] The speed controller control circuit 40933 outputs the offset of the target value of the AC power output from the inverter, which is added to the target power generation circuit 40931, based on the difference between the frequency (target frequency value) of the AC voltage output by the target frequency generation circuit 40934 (which serves as a reference) and the frequency (measured frequency) of the AC voltage output by the AC frequency detection circuit 4091.

[0132] The detailed operation of the speed controller control circuit 40933 will be described later.

[0133] Adder 40935 generates the control power target value of particle system operation circuit 40937 by adding the offset value output from speed controller control circuit 40933 and the power target value output from target power generation circuit 40931.

[0134] Subtractor 40936 subtracts the target control power value output from adder 40935 from the effective power output from effective power calculation circuit 4092. The output of subtractor 40936 is input to particle system operation circuit 40937.

[0135] The particle system operation circuit 40937 takes as input the difference between the sum of the offset output from the adder 40935 and the target value of the AC power value and the output of the actual power calculation circuit 4092 (the output of the subtractor 40936) and calculates the frequency and phase of the AC voltage output from the inverter of the power conversion device 41 for the distribution system battery to make the difference (the output of the subtractor 40936) zero.

[0136] The particle system operation circuit 40937 has an inertial force simulation unit that simulates the inertial force of a synchronous generator and a braking force simulation unit that simulates braking force.

[0137] When the inverter of the particle system is newly connected to the AC system, the particle system operation circuit 40937 sets the value of the inertial constant provided to the inertial force simulation unit to be greater than the value of the inertial constant during normal operation, at least for a predetermined time immediately after connection or until the effective power output from the inverter enters a predetermined range.

[0138] When a new power conversion device is connected to the AC system, the particle system calculation circuit 40937, after the communication interface circuit 412 receives information related to the new connection with the other power conversion device, sets the value of the inertial constant provided to the inertial force simulation unit to be at least greater than the value of the inertial constant under normal operation for a predetermined time after a predetermined time after the communication interface circuit 412 receives information related to the new connection with the other power conversion device, or until the effective power output from the inverter enters a predetermined range. Details of the particle system calculation circuit 40937 will be described later.

[0139] The 8th control circuit 4097 notifies the target power generation circuit 40931 of the power target value (Pref) and the interference convergence judgment result, the speed governor control circuit 40933 of the control parameters (proportional gain and time constant, etc.), the target frequency generation circuit 40934 of the frequency target value association information (Fmesure and AC system frequency), and the mass system operation circuit 40937 of the control parameters (inertia constant, braking coefficient, etc.).

[0140] Figure 15 This is an explanation Figure 12 The diagram shown is a block diagram of the structure of the speed controller control circuit 40933.

[0141] Reference Figure 15 The speed controller control circuit 40933 includes a multiplier 409331, a first-order delay system model (represented in the figure as 1 / (1+s×Tg)) 409332, and a limiting circuit 409333.

[0142] Multiplier 409331 multiplies the output of subtractor 40932 and the proportional gain (denoted as -1 / Kgd in the figure) output from the 8th control circuit 4097. The output of multiplier 409331 is then output to the primary delay model 409332. In Embodiment 1, the case of speed controller control using the standard primary delay model suggested by the "General Incorporated Association of Electrical Engineering" is described. Therefore, the primary delay model 409332 is as follows: Figure 15 The model of the first-order delay system (1 / (1+s×Tg)) is installed as described. The output of the first-order delay system model 409332 is limited by the limiting circuit 409333. The output of the limiting circuit 409333 is sent as an offset value to the adder 40935.

[0143] Figure 16 This is an explanation Figure 12 The diagram shown is a block diagram of the structure of the particle system operational circuit 40937.

[0144] Reference Figure 16 The particle system operation circuit 40937 includes a subtractor 409371, an integrator (referred to as 1 / (M×s) in the figure) 409372, a multiplier 409373, a divider 409374, an adder 409375, and a phase calculation circuit 409376.

[0145] Subtractor 409371 subtracts the output of multiplier 409373 from the output of subtractor 40936 (the subtraction result of measured effective power and power target value). The subtraction result is then input to integrator 409372.

[0146] Integrator 409372 generates the output of subtractor 409371 by integrating the output of subtractor 409371. Figure 9 The target angular velocity of the generator rotor 998 (2×π×60Hz: in Embodiment 1, the target frequency is set to 60Hz) and the difference (Δω) between the angular velocity of the generator rotor 998 are shown. The output of the integrator 409372 is input to the multiplier 409373.

[0147] Multiplier 409373 multiplies the output of integrator 409372 and the braking coefficient Dg output from the 8th control circuit 4097. By subtracting the output of multiplier 409373 from the output of subtractor 40936, the particle system operation circuit 40937 simulates the braking force of a synchronous generator under the control of the 2nd DC / AC converter circuit 408.

[0148] The output (Δω) of the integrator 409372 is divided by 2×π by the divider 409374 to transform it into frequency difference information (Δf).

[0149] Adder 409375 adds the frequency difference information (Δf) and the target frequency value (60Hz) to obtain the frequency (rotation frequency) of generator rotor 998, and outputs it as the voltage control phase target value to inverter voltage control circuit 4095. The output of adder 409375 is input to phase calculation circuit 409376.

[0150] The phase calculation circuit 409376 calculates the phase of the generator rotor 998 based on the output of the adder 409375 and the information from the 8th control circuit 4097, and uses it as the voltage control phase target value. This value is then output to the inverter voltage control circuit 4095 via the second sine wave generation circuit 40912 in the AC frequency detection circuit 4091.

[0151] Next, use Figures 17-21 The following is a summary of the operation of Implementation Method 1. Figure 17 This is a simplified diagram illustrating the structure of a power distribution system used to explain the effect of the battery power conversion device 41 when a new power distribution system is connected. Figure 17 In this embodiment, the power conversion device 41a for the battery of the power distribution system is interconnected with the AC system and supplies power to the load 31 via impedance 29a. The impedance 29 of the power distribution system 24 is actually a combination of resistive and capacitive components, but in Embodiment 1, for simplicity, it is only represented as a reactor component. Additionally, the newly connected power conversion device 41b for the battery of the power distribution system is connected to the load 31 via impedance 29b.

[0152] This describes the operation in this structure when the power conversion device 41b for the power distribution system battery is instructed by DSO21 to be interconnected with Pref as the power target value. At this time, the power conversion device 41a for the power distribution system battery is also notified to be newly connected and to switch the power target value from Pref_b to Pref_a. When the fourth control circuit 409 receives the new connection instruction via the communication interface circuit 412, it outputs a start instruction for the second DC / DC converter circuit 403 to the third control circuit 404 and starts the second DC / AC converter circuit 408. Specifically, after the fourth control circuit 409 connects a relay (not shown) to boost the DC bus 405 to a predetermined voltage, it connects the output of the second DC / AC converter circuit 408 to the AC system.

[0153] After the second DC / DC converter circuit 403 and the second DC / AC converter circuit 408 have started up, the eighth control circuit 4097 in the fourth control circuit 409 begins to handle the newly activated control. Similarly, the third control circuit 404 also begins to handle the newly activated control.

[0154] After the control circuit 409 initiates control for the newly connected circuit, the initial AC frequency detection circuit 4091 detects the frequency and phase of the AC voltage in the AC system based on the output of the voltmeter 410. At this time, no power (current) is output from the power conversion device 41b for the power distribution system battery, so the AC voltage waveform at the interconnection point of the power conversion device 41b for the power distribution system battery (the point between the power conversion device 41b for the power distribution system battery and the impedance 29b) is equal to the voltage waveform of the AC system input to the load 31. Therefore, if the power conversion device 41b for the power distribution system battery can be newly connected with the frequency and phase of the AC voltage in the AC system at the interconnection point of the power distribution system battery, the power conversion device 41b for the power distribution system battery can be newly connected without interfering with the AC system. However, as mentioned above, the measurement result of the voltmeter 410 contains errors. Specifically, the measurement result of the voltmeter 410 includes the offset error of the voltmeter 410 and the error caused by linearity, etc.

[0155] Thus, when the AC voltage of the AC system is generated based on the output of the voltmeter 410 (which includes error), for example, when a zero-crossing point is detected, when the offset error is, for example, -5V relative to the effective voltage of 200V, and when the zero-crossing point information detected by the AC frequency detection circuit 4091 is used, the AC voltage of the AC system output by the power conversion device 41b for the power distribution system battery becomes lagging behind the AC voltage of the AC system supplied to the load 31.

[0156] The following uses Figure 18 as well as Figure 19 This section provides an overview of the operation of the AC system of the battery power conversion device 41 in the power distribution system when the AC voltage is supplied with a delayed output. Figure 18 This is a diagram showing the relationship between AC voltage and output AC current when the voltage phase of the AC system of the newly connected power distribution system battery power conversion device 41b is lagging. Figure 19 This is a diagram showing the charging and discharging power (effective value) of the two power conversion devices 41a and 41b of the power distribution system battery when the AC voltage phase of the newly connected power distribution system battery power conversion device 41b is lagging. Furthermore, Figure 18 and Figure 19 The timeline scales are different. Figure 18 The horizontal axis is in the millisecond range; in contrast, Figure 19 The horizontal axis is in seconds (s).

[0157] Figure 18(a) is a diagram showing the AC voltage waveform of the power distribution system 24 at the connection point of the load 31 when the power distribution system battery power conversion device 41b is switched on with a delayed phase, and the AC voltage waveform of the AC system output by the power distribution system battery power conversion device 41b. Figure 18 (b) is a diagram showing the output current waveform of the power conversion device 41b for battery in the power distribution system.

[0158] like Figure 18 (a) The phase of the AC voltage output from the power conversion device 41b for the battery in the power distribution system is delayed. Therefore, the current flowing through impedance 29b (the current output from the power conversion device 41b for the battery in the power distribution system) is as follows: Figure 18 As shown in (b). Therefore, when the power conversion device 41b for the battery in the power distribution system is newly connected with a delayed phase, as Figure 18 (b) shows that in the power conversion device 41b for the battery in the power distribution system, electricity flows in the direction of charging power (regeneration direction).

[0159] Therefore, upon new connection, the power conversion device 41b for the power distribution system battery is charged, so the power conversion device 41a for the power distribution system battery increases its discharge power to supply the charging power to the power conversion device 41b for the power distribution system battery. Figure 19 The diagram illustrates the temporal progression of the actual power output from the power conversion devices 41a and 41b of the power distribution system battery. (Example) Figure 19 As shown, the power conversion device 41a for the power distribution system battery supplies the charging power to the power conversion device 41b for the power distribution system battery with its own discharge power.

[0160] Generally speaking, the closer the efficiency of a power conversion device including a battery is to its rated power, the better the efficiency. Therefore, DSO21 starts the power conversion device 41b of the power distribution system battery when it predicts that the power supplied to the load 31 through the power conversion device 41a of the power distribution system battery is insufficient. In Embodiment 1, when the charging and discharging power exceeds 90% of the rated capacity of the power conversion device 41a of the power distribution system battery, it is controlled to add a new power conversion device 41b of the power distribution system battery. In this case, when the newly connected power conversion device 41b of the power distribution system battery starts by charging, as Figure 19 The diagram shows a situation where the rated capacity of the power conversion device 41a for the power distribution system battery is exceeded. In this case, the power conversion device 41a for the power distribution system battery stops due to overload, thus ceasing to supply power to the power distribution system 24.

[0161] The power supplied by the power conversion device 41b for charging the battery in the power distribution system is determined by the voltage phase difference (the magnitude of the lag phase) of the AC voltage waveform of the AC system at the interconnection point between the power conversion device 41b and the load 31. Specifically, the greater the phase difference, the greater the charging power.

[0162] Similarly, using Figure 20 as well as Figure 21 This section provides an overview of the operation of the AC system of the battery power conversion device 41 in the power distribution system when the AC voltage is supplied by the AC system. Figure 20 This is a diagram showing the relationship between AC voltage and output AC current when the voltage phase of the AC system of the newly connected power distribution system battery power conversion device 41b is leading. Figure 21 This is a diagram showing the charging and discharging power (effective value) of the two power conversion devices 41a and 41b of the power distribution system battery when the AC voltage phase of the newly connected power distribution system battery power conversion device 41b is in the leading phase. Figure 20 and Figure 21 The timeline scales are different. Figure 20 The horizontal axis is in the millisecond range; in contrast, Figure 21 The horizontal axis is in seconds (s).

[0163] Figure 20 (a) is a diagram showing the AC voltage waveform of the power distribution system 24 at the connection point of the load 31 when the power distribution system battery power conversion device 41b is turned on with the leading phase and the AC voltage waveform of the AC system output by the power distribution system battery power conversion device 41b.

[0164] Figure 20 (b) is a diagram showing the output current waveform of the power conversion device 41b for battery use in the power distribution system. For example... Figure 20 As shown in (a), the phase of the AC voltage output from the power conversion device 41b for the battery in the power distribution system is leading, so the current flowing through impedance 29b (the current output from the power conversion device 41b for the battery in the power distribution system) is as follows: Figure 20 As shown in (b). Therefore, when the power conversion device 41b for the battery in the power distribution system is newly connected with the leading phase, as Figure 20 (b) shows that in the power conversion device 41b for the battery in the power distribution system, electricity flows in the direction of discharge electricity (power operation direction).

[0165] Therefore, in Embodiment 1, when the second DC / AC conversion circuit 408 (inverter) is connected to the AC system, the fourth control circuit 409 (inverter control circuit) makes the frequency of the AC voltage target value become the frequency of the AC voltage detected by the AC frequency detection circuit 4091, and when the AC power target value is the power operation direction, the phase of the AC voltage target value is controlled so that the AC voltage relative to the AC system is at least the leading phase.

[0166] Therefore, upon reconnection, the power is discharged in the power conversion device 41b of the power distribution system battery, so the power conversion device 41a of the power distribution system battery reduces the discharge power of the power conversion device 41b of the power distribution system battery. Figure 21 The diagram illustrates the temporal progression of the actual power output from the power conversion devices 41a and 41b of the power distribution system battery. (Example) Figure 21 As shown, the discharge power of the power conversion device 41a and the power conversion device 41b for the power distribution system battery is combined and supplied to the load 31.

[0167] like Figure 21 The power conversion devices 41a and 41b of the power distribution system battery share the power supply to the load 31, so problems such as overload shutdown that would occur when the power is newly connected with a later phase will not happen.

[0168] Furthermore, the power discharged by the power conversion device 41b for the power distribution system battery is determined by the phase difference (the magnitude of the leading phase) between the phase of the voltage of the power conversion device 41b for the power distribution system battery and the phase of the AC voltage of the AC system at the system interconnection point of the load 31. Specifically, the greater the phase difference, the greater the discharge power.

[0169] When the power converter is used as a voltage source to reconnect the system as described above, and when the power converter is used as an energy-generating device, the AC voltage output from the power converter is switched on in a manner where the phase of the AC voltage at the interconnection point before the new connection is made advanced. Therefore, even if errors occur in the detection results of zero-crossing points due to sensor errors such as voltmeter errors, the newly connected power converter outputs power in the power operation direction (discharge direction), thus preventing the power converter operating as a voltage source before connection from stopping due to overload. Furthermore, when the interconnected power converters are operating in the charging direction (charging remaining power), the power converter is switched on in a delayed phase. Therefore, the newly connected power converter operates in the regeneration direction (charging direction), thus preventing the power converter operating as a voltage source before connection from stopping due to overload. The delayed phase switching will be described later.

[0170] In Implementation Method 1, a power distribution system was used as an example, but it is not limited to this; the same effect can be achieved even when applied to a power transmission system. Furthermore, the same effect is achieved even when connected to a dedicated power distribution line. In addition, the same effect is achieved even in independent systems such as microgrids.

[0171] Next, refer to Figures 1 to 26 This explains the specific operation of the power conversion device in Embodiment 1. Refer again... Figure 1 This describes the power distribution system of the power conversion device involved in Embodiment 1. In Embodiment 1, in order to control the power distribution system voltage within a predetermined voltage range, three SVRs 23 are connected in series between the substation 20 and the megawatt-class solar power conversion device 27 (or the power distribution system battery power conversion device 41, town D100d). A power distribution system battery power conversion device 41a is installed near the megawatt-class solar power conversion device 27. In Embodiment 1, the power distribution system battery power conversion device 41a operates as a voltage source. The power generated by the megawatt-class solar power 26 is de-slackened by activating the virtual synchronous generator control circuit 4093.

[0172] The loads include towns A100a, B100b, C100c, and D100d, factory 101, building 102, and apartment 103. Power is supplied to the loads from substation 20, megawatt-class solar power 26, and distribution system battery 40a. Distribution system battery 40c and power conversion device 41c for distribution system batteries are located near substation 20. Distribution system battery 40b and power conversion device 41b for distribution system batteries are located near town B100b. Furthermore, a synchronous generator 30a is located in factory 101. A synchronous generator 30b is located in building 102 for emergency use.

[0173] Here, we will explain the operation of a newly added distribution system battery 40b that supports the distribution system 24 by the power supplied from the substation 20, the generated power from the megawatt-class solar power 26 (the megawatt-class solar power conversion device 27 operates via a current source), and the discharged power output from the distribution system battery 40a.

[0174] Figure 22 This is a flowchart showing the operation of DSO21 when the power conversion device 41b for the power distribution system battery is newly connected to the power distribution system.

[0175] Reference Figure 22 In step S101, DSO21 confirms whether the current time is the time for collecting various measurement results. If the current time is not the time for collecting various measurement data, DSO21 will remain on standby until the current time becomes the time for collecting data.

[0176] If the current moment is the time when various measurement data are collected, the process proceeds to step S102.

[0177] In Implementation 1, in step S102, DSO21 collects the equipment operation information of substation 20, the measurement information of voltmeter 22, the information of SVR23, the measurement information of megawatt-class solar power conversion device 27 (power generation, etc.), and the measurement information of power conversion device 41 for distribution system battery (charging and discharging power, SOC (State of Charge), current status information, etc.) at 1-minute intervals.

[0178] In step S103, DSO21 re-evaluates the operating plan of each power distribution system battery 40.

[0179] In step S104, DSO21 determines whether a new power distribution system battery 40 needs to be added. Specifically, DSO21 determines that an addition is needed if the current power distribution system battery 40a cannot supply power based on collected data. The situation where the current power distribution system battery 40a cannot supply power refers to situations such as the current power distribution system battery power conversion device 41a operating at more than 90% of its rated capacity or the state of charge (SOC) being less than 10%.

[0180] If it is determined that additional data is needed, the process proceeds to step S105; if it is not determined that additional data is needed, the process proceeds to step S106.

[0181] In step S105, DSO21 notifies the newly added power conversion device 41b for the power distribution system battery of the new addition request (instruction) and the power target value Pref. Afterwards, the process proceeds to step S108.

[0182] In step S106, DSO21 determines whether to disconnect the power distribution system battery 40. Specifically, DSO21 determines to disconnect the power distribution system battery 40 using the power conversion device 41 if the power supplied to the power distribution system 24 is sufficient and disconnecting the power distribution system battery 40a will not affect the power distribution system 24, or if the SOC of the power distribution system battery 40 is below a predetermined value (there is a possibility of over-discharge). If it is determined that the power distribution system battery 40 should be disconnected, the process proceeds to step S107. If it is not determined that the power distribution system battery 40 should be disconnected, the process returns to step S101.

[0183] In step S107, DSO21 notifies the power conversion device 41 for the disconnected power distribution system batteries of the disconnection instruction. Afterwards, the process proceeds to step S108.

[0184] In step S108, DSO21 notifies other power conversion devices 41 in the power distribution system that it is newly connected or disconnected for those that have not been added or disconnected, and notifies all power conversion devices 41 in the power distribution system interconnected with the system of the newly added power target value Prefa or the power target value after disconnection. After step S108, the process returns to step S101.

[0185] Figure 23 This is a flowchart illustrating the operation of the power conversion device 41a for batteries in the power distribution system interconnected with the system.

[0186] In step S121, the power conversion device 41a for the power distribution system battery collects various measurement data. Specifically, the power conversion device 41a collects the measured voltages from voltmeters 401, 406, and 410. The measurement result of voltmeter 410 is AC voltage, so the fourth control circuit 409 calculates the effective voltage and uses it as the measured voltage. The power conversion device 41a collects the measured currents from ammeters 402, 407, and 411. The measurement result of ammeter 411 is AC current, so the fourth control circuit 409 calculates the effective current as the measured current. The power conversion device 41a collects the current status information (SOC, etc.) of the power distribution system battery 40a.

[0187] In step S122, if the communication interface circuit 412 receives data from DSO21, the process proceeds to step S123. If the communication interface circuit 412 does not receive data from DSO21, the process continues with step S121.

[0188] In step S123, the fourth control circuit 409 within the power conversion device 41a for the battery in the power distribution system determines whether the received data is a data transmission request. If it is determined that the received data is a data transmission request, the process proceeds to step S124. If it is determined that the received data is not a data transmission request, the process proceeds to step S125.

[0189] In step S124, the fourth control circuit 409 sends the measurement results to DSO21 via the communication interface circuit 412. Afterwards, the process returns to step S121.

[0190] In step S125, the fourth control circuit 409 determines whether it has received a disconnection request from DSO21 or a notification that a distribution system battery 40 has been disconnected. If a disconnection request or a notification that a distribution system battery 40 has been disconnected is received, the process proceeds to step S126. If no disconnection request or notification that a distribution system battery 40 has been disconnected is received, the process proceeds to step S127.

[0191] In step S126, the power conversion device 41a for the power distribution system batteries begins the disconnection process. Afterwards, the process returns to step S121.

[0192] The processing steps S127 to S130 will be described later.

[0193] Figure 24 This is a flowchart illustrating the control process during the disconnection of the power conversion device 41 for batteries in the power distribution system.

[0194] In step S141, when the fourth control circuit 409 receives a disconnection request or when a disconnected distribution system battery 40 is detected, it changes the control parameters in the speed governor control circuit 40933 and the mass system calculation circuit 40937 within the virtual synchronous generator control circuit 4093. The fourth control circuit 409 of the distribution system battery power conversion device 41 that is not disconnected also performs the same process. Specifically, in order to suppress system interference caused by disconnection, the fourth control circuit 409 sets the values ​​of the time constants or inertial constants of the control parameters in the speed governor control circuit 40933 and the mass system calculation circuit 40937 to be greater than their normal operating values. In Embodiment 1, the fourth control circuit 409 sets different values ​​for the control parameters of the disconnected distribution system battery power conversion device 41 and the control parameters of the distribution system battery power conversion device 41 that continues to operate without disconnection. More specifically, compared to the power conversion device 41 for the battery of the power distribution system that continues to operate without being disconnected, the fourth control circuit 409 sets the time constant Tg in the speed controller control circuit 40933 to be larger in the disconnected power conversion device 41 for the battery of the power distribution system.

[0195] The reason for this setting is as follows. When the power conversion device 41 for the distribution system battery is disconnected, the distribution system 24 is supported by distributed power sources including the power conversion device 41 for the distribution system battery that is not disconnected. Therefore, the power for discharging or charging the power conversion device 41 for the distribution system battery that has received the disconnection instruction is provided by the power conversion device 41 for the distribution system battery that is not disconnected or by the distributed power source. In Embodiment 1, DSO21 notifies each distributed power source (including the power conversion device 41 for the distribution system battery) connected to the distribution system 24 of the power target value after disconnection, along with the disconnection information of the power conversion device 41 for the distribution system battery that is not disconnected. In Embodiment 1, in the power conversion device 41 for the distribution system battery that has received the disconnection instruction, the target power generation circuit 40931 reduces the target value (power target value) of the AC power output by the inverter from the target value before the disconnection instruction is received to "zero" at a predetermined time or a predetermined slope.

[0196] On the other hand, in the power conversion device 41 for battery storage in the power distribution system that has not received a disconnection instruction, the target power generation circuit 40931 makes the target power value change from the target value before receiving the disconnection instruction to the target power value notified when the disconnection information is received, at a predetermined time or a predetermined slope.

[0197] By controlling as described above, when the power conversion device 41 for the battery of the power distribution system is disconnected, the oscillation of the power distribution system 24 caused by the disconnection can be minimized.

[0198] However, even with the control measures implemented as described above, the frequency and phase of the system AC voltage still change due to factors such as the timing of changes in the power target value. Even when the load and the power generated by the megawatt-class solar panels 26 remain unchanged during the disconnection of the power conversion device 41 for the distribution system batteries, the frequency and phase of the system AC voltage still change. As each power conversion device 41 for the distribution system batteries changes the frequency and phase of the system AC voltage, unnecessary interference is applied to the distribution system 24. Therefore, in Embodiment 1, the eighth control circuit 4097 sets the values ​​of the control parameters (proportional gain and time constant) in the speed governor control circuit 40933 and the control parameters (inertia constant and braking coefficient) in the mass system calculation circuit 40937 to values ​​greater than those under normal control. This suppresses interference to the distribution system 24 (changes in the frequency and phase of the AC voltage of the AC system) that accompany changes in the power target value.

[0199] Furthermore, even when there are fluctuations in the load and the generated power of the megawatt-level solar panel 26, the eighth control circuit 4097 sets the values ​​of the time constant Tg in the speed governor control circuit 40933 and the inertial constant m in the mass system calculation circuit 40937 to be larger than those in the non-disconnected power distribution system battery power converter 41. Therefore, compared to the non-disconnected power distribution system battery power converter 41, the offset value added to the power target value output from the speed governor control circuit 40933 can be suppressed smaller in the disconnected power distribution system battery power converter 41, thus enabling smooth disconnection. In other words, the output fluctuations of the load 31 and the megawatt-level solar panel 26 can be almost completely covered by the non-disconnected power distribution system battery power converter 41, thus minimizing the output fluctuations of the disconnected power distribution system battery power converter 41. Furthermore, by increasing the inertial constant m within the operational circuit 40937 of the particle system, the frequency of the AC voltage generated by the AC system of the battery power conversion device 41 in the disconnected power distribution system remains almost unchanged. Therefore, no unnecessary interference is provided to the power distribution system during disconnection.

[0200] Reference Figure 24 After the processing in step S141 is completed, the process proceeds to step S142.

[0201] In step S142, the eighth control circuit 4097 in the fourth control circuit 409 confirms whether the effective power output from the effective power calculation circuit 4092 falls within a predetermined range. If the effective power does not fall within the predetermined range, the process remains in standby mode until it falls within the predetermined range. If the effective power falls within the predetermined range, the process proceeds to step S143.

[0202] In step S143, the 8th control circuit 4097 instructs the communication interface circuit 412 to disconnect the DSO21 notification.

[0203] In step S144, the eighth control circuit 4097 disconnects the second DC / AC conversion circuit 408 from the power distribution system 24. Specifically, the eighth control circuit 4097 outputs a command value to the second DC / AC conversion circuit 408 to make the output "zero", and instructs the third control circuit 404 to stop the second DC / AC conversion circuit 403.

[0204] After the third control circuit 404 outputs a stop instruction to the second DC / DC converter circuit 403 (specifically, outputting a command value to make the charging / discharging power "zero"), it notifies the fourth control circuit 409 of its intention. The third control circuit 404 and the second DC / DC converter circuit 403 then switch to a low-power mode. On the other hand, upon receiving the stop information from the second DC / DC converter circuit 403 from the third control circuit 404, the fourth control circuit 409 switches some of its functions, except for the communication interface circuit 412, to a low-power mode, thus ending the decoupling process.

[0205] Refer again Figure 23 In step S127, the power conversion device 41a for the power distribution system's battery determines whether new additional information has been received. If new additional information is received, the process proceeds to step S128. If no new additional information is received, the process returns to step S121.

[0206] In step S128, the power conversion device 41a for the power distribution system battery changes the control parameters in the speed governor control circuit 40933 and the mass system calculation circuit 40937 within the virtual synchronous generator control circuit 4093.

[0207] The reason for changing the control parameters is as follows. The reason is the same as when disconnecting the power conversion device 41 for the battery in the power distribution system described above, to suppress large interference (frequency changes) in the power distribution system 24. When reconnected, as mentioned above, due to measurement errors (linearity, offset, etc.) of the voltmeter 410, especially in the phase of the AC voltage in the AC system, errors occur. Therefore, when the power conversion device 41 for the battery in the power distribution system is reconnected, even if the target power value is "zero" due to the phase error, power is charged and discharged from the reconnected power conversion device 41 based on the magnitude of the phase error. This charging and discharging power becomes very large due to the phase difference and continues to flow until the phase difference converges. As a result, a large interference is introduced into the frequency of the AC voltage in the AC system of the power distribution system 24. Therefore, in order to suppress the magnitude of this interference, the power conversion device 41a for the power distribution system battery sets the values ​​of the control parameters in the speed governor control circuit 40933 within the virtual synchronous generator control circuit 4093 and the mass system calculation circuit 40937 to be greater than the values ​​during normal operation. As a result, the inertial force of the synchronous generator simulated by the mass system calculation circuit 40937 increases, thus suppressing the interference of frequency and phase of the AC voltage of the AC system output from the second DC / AC conversion circuit 408.

[0208] In step S128, after the changes to the control parameters in the speed governor control circuit 40933 and the mass system calculation circuit 40937 within the virtual synchronous generator control circuit 4093 are completed, the process proceeds to step S129.

[0209] In step S129, the interconnected power distribution system battery power conversion device 41 suppresses changes to control parameters until the frequency oscillation of the AC voltage of the AC system caused by the new connection of the power distribution system battery power conversion device 41 converges. In Embodiment 1, the interconnected power distribution system battery power conversion device 41 determines that the oscillation has converged by suppressing changes to control parameters for a predetermined time. The convergence determination of oscillation is not limited to this; the interconnected power distribution system battery power conversion device 41 can also determine that convergence has occurred when the frequency amplitude of the AC voltage of the AC system measured by the voltmeter 410 enters a predetermined range. After confirming that the predetermined time has elapsed, the process proceeds to step S130.

[0210] In step S130, the power conversion device 41 for the power distribution system battery returns the control parameters in the speed governor control circuit 40933 and the mass system calculation circuit 40937 within the virtual synchronous generator control circuit 4093 to their normal operating values. Afterward, the process returns to step S121.

[0211] Next, the operation of the power conversion device 41 for the battery of the newly connected power distribution system will be explained. Figure 25 This is a flowchart illustrating the control process when a new power conversion device 41 for a battery in a power distribution system is added.

[0212] In step S161, the power conversion device 41 for the power distribution system battery, which is in low-power mode standby, remains in standby mode until a start request is received from DSO21. When a start request is received from DSO21, the process proceeds to step S162.

[0213] In step S162, the eighth control circuit 4097 within the fourth control circuit 409 instructs the third control circuit 404 to start the second DC / DC converter circuit 403. The third control circuit 404 starts the second DC / DC converter circuit 403. Specifically, the eighth control circuit 4097 sets a relay (not shown) connecting the power distribution system battery 40 and the second DC / DC converter circuit 403 to open, charging the DC bus 405 until a predetermined voltage is reached. At this time, the third control circuit 404 collects various information from the power distribution system battery 40 and notifies the fourth control circuit 409 of the results. Specifically, the eighth control circuit 4097 collects information such as SOC and degradation progress by communicating with a battery management unit (not shown).

[0214] When the fourth control circuit 409 receives various information, including information about the power distribution system battery 40 (such as start-up information of the second DC / DC converter circuit 403), from the third control circuit 404, the eighth control circuit 4097 within the fourth control circuit 409 sets the values ​​of various control parameters in the speed governor control circuit 40933 within the virtual synchronous generator control circuit 4093 and the mass system calculation circuit 40937 to values ​​used when the circuit is newly switched on. In Embodiment 1, in order to enable the power conversion device 41 for the power distribution system battery to operate as an AC voltage source, the third switching circuit 4096 is controlled to select the output of the inverter voltage control circuit 4095.

[0215] Here, the various control parameters during the new connection are explained. In Embodiment 1, similar to the disconnection process described above, the values ​​of the control parameters in the speed governor control circuit 40933 within the virtual synchronous generator control circuit 4093 and the mass system calculation circuit 40937 are set to values ​​greater than those during normal operation. In Embodiment 1, the various control parameters are set to values ​​larger than those during disconnection. Specifically, at least the time constant (Tg) in the speed governor control circuit 40933 and the inertia constant (M) in the mass system calculation circuit 40937 are set to large values. As a result, by delaying the response time of the speed governor control and seemingly increasing the inertial force of the generator rotor based on the oscillation equation, the frequency variation of the AC voltage in the AC system of the power distribution system 24 is suppressed.

[0216] Therefore, when the power conversion device 41 for the newly connected power distribution system battery is activated, even if the output power is not controlled by the newly activated power conversion device 41, the frequency of the AC voltage of the AC system will not be significantly disturbed and it can continue to operate. The power not controlled by the newly activated power conversion device 41 refers to the charging and discharging power caused by the phase difference between the phase of the AC voltage of the AC system and the phase of the AC voltage output by the power conversion device 41, as detailed above.

[0217] The rationale for this control method is explained below. The power conversion device 41 for the power distribution system battery is connected (interconnected) to the power distribution system 24 via voltage control, as described above. Therefore, as long as the power shortage within the power distribution system 24 is below the power capacity of the power conversion device 41, supply and demand balance can be ensured without any particular problem. Normally, in the event of a power shortage, support from a power conversion device (e.g., a megawatt-class solar power conversion device 27) controlled as a current source interconnected with the power distribution system 24 can be received by controlling the frequency of the AC voltage in the AC system. However, the time from the occurrence of an event to its convergence is limited in cases such as the new connection or disconnection of the power conversion device 41. Therefore, even if the power supply (discharging or charging power) from the power conversion device 41 is insufficient, the impact on the overall system control is very small. Specifically, the influence here refers to the effect of the state of charge (SOC) of the power distribution system battery 40. Therefore, in Embodiment 1, priority is given to reducing the frequency disturbance (frequency interference) of the AC voltage of the AC system compared to ensuring the SOC of the power distribution system battery 40. Therefore, by increasing the inertia constant m, the inertial force of the synchronous generator simulated by the mass system operation circuit 40937 increases, so the frequency and phase interference of the AC voltage of the AC system output from the second DC / AC conversion circuit 408 can be suppressed. Similarly, by increasing the time constant (Tg) in the speed governor control circuit 40933, after the power conversion device 41 for the power distribution system battery is reconnected, the accumulated value of the frequency deviation stored in the integrator (not shown) at the time point when the speed governor control is started to normal control will not increase, and normal control can be restored. As a result, the time for frequency stabilization of the AC voltage of the AC system in the reconnection to normal interconnection control can be shortened. This explains the case of increasing the time constant (Tg) in the speed governor control circuit 40933 and the inertia constant m in the particle system calculation circuit 40937, but it is not limited to this. Even if, as described above, the frequency of the AC voltage in the AC system and the offset value of the target power applied by the speed governor control are not significantly changed, the same effect can be achieved by changing the control parameters such as the proportional gain Kgd in the speed governor control circuit 40933 and the braking coefficient Dg in the particle system calculation circuit 40937.

[0218] After the processing in step S162 is completed, the fourth control circuit 409 detects the frequency and phase of the AC voltage of the AC system.

[0219] In step S163, the phase detection circuit 40910 detects the zero-crossing point from the measurement result of the AC voltage of the AC system output from the voltmeter 410. Specifically, the phase detection circuit 40910 uses the time information of the time when the output of the voltmeter 410 changes from negative to positive and each amplitude to perform linear interpolation on the time of the zero-crossing point.

[0220] The phase detection circuit 40910 can also be configured to calculate the time information of the zero-crossing point from positive to negative according to the above points, calculate the offset error of the voltmeter 410 based on the calculation result of the zero-crossing point time information, and calculate the zero-crossing point time again based on the calculation result of the offset error.

[0221] The following explains the method for calculating the offset error. The phase detection circuit 40910 calculates the lengths of the positive and negative AC voltage periods of the AC system based on the zero-crossing point information from negative to positive and from positive to negative. When the positive time is longer than the negative time, the phase detection circuit 40910 adds a negative offset value to the output of the voltmeter 410. Similarly, when the positive time is shorter than the negative time, the phase detection circuit 40910 adds a positive offset value to the output of the voltmeter 410. The phase detection circuit 40910 repeats this process until the time difference between the positive and negative times falls within a predetermined range, at which point a correction is applied to the offset value. This control reduces the offset error of the voltmeter 410. Furthermore, the method for calculating the offset error is not limited to this; for example, the same effect can be achieved even if the offset value is calculated in a way that makes the absolute values ​​of the positive and negative peak voltages of the AC system approximately the same.

[0222] In step S164, the frequency detection circuit 40911 uses zero-crossing point information to detect the frequency. Specifically, the frequency detection circuit 40911 calculates the frequency based on zero-crossing point time information of two consecutive points. In Embodiment 1, the frequency of the AC voltage of the AC system is determined using only zero-crossing point time information of two consecutive points, but it is not limited to this. The frequency detection circuit 40911 may also determine the frequency of the AC voltage of the AC system based on multiple zero-crossing point information, and calculate the average value of the frequencies of the AC voltages of multiple AC systems.

[0223] After the frequency detection is completed, the AC frequency detection circuit 4091 performs phase detection. In Embodiment 1, the phase detection circuit 40910 determines the zero-crossing point when the output of the latest voltmeter 410 changes from negative to positive at the time when the frequency detection is completed, and uses this as phase information.

[0224] In step S165, the frequency and phase information of the AC voltage of the AC system are input to the second sine wave generation circuit 40912.

[0225] The second sine wave generation circuit 40912 generates a sine wave as a reference for voltage control based on the detected frequency and phase information and the frequency and phase information output from the particle system calculation circuit 40937 in the virtual synchronous generator control circuit 4093. The second sine wave generation circuit 40912 outputs the generated sine wave information to the third sine wave generation circuit 40951 in the inverter voltage control circuit 4095.

[0226] The detection information (frequency and phase information of the AC voltage of the AC system) from the AC frequency detection circuit 4091 is also input to the virtual synchronous generator control circuit 4093 and the eighth control circuit 4097. The detection information input to the virtual synchronous generator control circuit 4093 is then input to the target frequency generation circuit 40934. Furthermore, the detection information from the AC frequency detection circuit 4091 is input to the particle system calculation circuit 40937 via the eighth control circuit 4097. Specifically, the initial values ​​of the integrator 409372 within the particle system calculation circuit 40937 and the register (not shown) within the phase calculation circuit 409376 are set.

[0227] After the frequency and phase information of the AC voltage of the AC system are set in step S165, the process proceeds to step S166.

[0228] In step S166, the 8th control circuit 4097 sets the initial values ​​of the frequency target value and the initial values ​​of the power target value for the target power generation circuit 40931 and the target frequency generation circuit 40934 within the virtual synchronous generator control circuit 4093.

[0229] In step S167, the target power generation circuit 40931 sets the time shift for the target power value. The target frequency generation circuit 40934 sets the time shift for the target frequency value.

[0230] Specifically, as described above, the target power generation circuit 40931 is as follows: Figure 13 The solid line indicates that the target power value is set to "zero" upon initial connection, and then adjusted to Pref after a predetermined time following the convergence of the disturbance in the distribution system 24 caused by the initial connection. Therefore, when Pref is input, the target power generation circuit 40931 calculates... Figure 13The slope of the straight line shown. Furthermore, when the target power generation circuit 40931 confirms the convergence of interference in the power distribution system 24 after a new connection via the 8th control circuit 4097, it generates and outputs a power target value based on the calculated slope of the aforementioned straight line. This is because, as described above, when the control is set to output the power target value Pref immediately after the newly connected power distribution system battery power converter 41 (which has not yet undergone charging or discharging) is connected, power is supplied from each power distribution system battery power converter 41 in a state of supply and demand balance through the power distribution system battery power converter 41 and synchronous generator 30, which are already connected to the system and supplied with power. The power distribution system battery power converter 41 (operating with the power target value as before the new connection) and synchronous generator 30, which are already connected to the system, are controlled in a way that the load is lightened, causing the frequency of the output AC voltage of the AC system to increase. Similarly, when the newly connected power distribution system battery power converter 41 outputs less AC power (effective power) than the pref output power, it controls the AC frequency to increase. The rate of frequency increase is determined by the impedance of the power distribution system 24, so the rate of frequency increase differs for each power distribution system battery power converter 41 and synchronous generator 30. This causes unnecessary interference to the power distribution system 24. Therefore, the target power generation circuit 40931 within the newly connected power distribution system battery power converter 41 is controlled as described above.

[0231] On the other hand, regarding the power conversion device 41 for batteries in the already interconnected power distribution system, as described above, the target power generation circuit 40931 is as follows: Figure 13 As shown by the dashed line, the power target value is generated in such a way that, after a predetermined time has elapsed since the interference in the power distribution system 24 converges, the power target value Pref_b before reconnection becomes the power target value Pref_a after reconnection. In Embodiment 1, the predetermined time in the target power generation circuit 40931 on the newly connected side and the predetermined time in the target power generation circuit 40931 in the system interconnection are set to be the same. As a result, unnecessary interference (frequency interference) that occurs in the power distribution system 24 when the power conversion device 41 for the battery in the power distribution system is reconnected is suppressed.

[0232] In implementation method 1, the target power generation circuit 40931 is as follows: Figure 13As shown by the solid line, for the newly connected power distribution system battery power conversion device 41, immediately after connection, the target power value is controlled to zero. After confirming system interference convergence, the target power value is gradually increased from zero to Pref over a predetermined time. On the other hand, for the power distribution system battery power conversion device 41 already interconnected with the system, the target power generation circuit 40931 maintains the target power value (Pref_b) before the new connection until the system interference converges. After confirming system interference convergence, as shown by the solid line, the target power generation circuit 40931 maintains the target power value (Pref_b) before the new connection. Figure 13 As shown by the dashed line, the power target value is gradually reduced from Pref_b to Pref_a over a predetermined period of time.

[0233] Similarly, the operation of the target frequency generation circuit 40934 will be explained. When the frequency (Fmesure) and Fref detected by the frequency detection circuit 40911 are input, the target frequency generation circuit 40934 outputs Fmesure as the target frequency value until the interference in the power distribution system 24 converges. Furthermore, when the target frequency generation circuit 40934 detects system interference convergence through the 8th control circuit 4097, it outputs the target frequency value (refer to) that changes from Fmesure to Fref after a predetermined time. Figure 14 Furthermore, in the virtual synchronous generator control, the frequency of the target AC voltage is controlled approximately at the system frequency (e.g., 60Hz or 50Hz) without significant variation. Therefore, the target frequency generation circuit 40934 outputs the target frequency value from the eighth control circuit 4097 to the power conversion device 41 of the distribution system battery, which is already interconnected with the system. Thus, as explained regarding the target power generation circuit 40931, when controlling the frequency of the AC voltage output from the power conversion device 41 of the distribution system battery immediately after power-on, unnecessary interference is introduced into the balanced power supply state between the power generation equipment already connected to the system and the load. Therefore, after the power conversion device of the distribution system battery is immediately powered on, control can be performed using the detected frequency (Fmesure) of the AC voltage of the AC system, without providing unnecessary interference to the AC system.

[0234] Refer again Figure 25 After step S167, the process proceeds to step S168. In step S168, initialization processing is performed when controlling the second DC / AC converter circuit 408. Hereinafter, using... Figure 26 This explains the operation of the second DC / AC conversion circuit 408. Figure 26 This is a flowchart showing the control process of the fourth control circuit 409 when the power conversion device 41 for the battery of the newly connected power distribution system is activated.

[0235] In step S181, after the control of the second DC / AC conversion circuit 408 begins, the effective power calculation circuit 4092 within the fourth control circuit 409 calculates the effective power. Specifically, the effective power calculation circuit 4092 calculates the effective power by accumulating the electrical force of one cycle of the AC voltage of the AC system based on the zero-crossing point information detected by the AC frequency detection circuit 4091 and the frequency detection information. More specifically, the effective power calculation circuit 4092 calculates the electrical force of one cycle of the AC voltage of the AC system based on the zero-crossing point detection information indicating that the AC voltage of the AC system has switched from negative to positive. More specifically, the effective power calculation circuit 4092 calculates the unit effective power by multiplying the output of the voltmeter 410 and the output of the ammeter 411 and dividing the multiplication result by the sampling period. Furthermore, the effective power calculation circuit 4092 accumulates the unit effective power with respect to one cycle of the AC voltage of the AC system. The effective power calculation circuit 4092 calculates the effective power by multiplying the accumulated result with the frequency information output from the AC frequency detection circuit 4091.

[0236] In step S182, the eighth control circuit 4097 confirms whether the current time is within the control cycle. In Embodiment 1, one cycle of the AC voltage of the AC system is used as the control cycle. Furthermore, the control cycle can be an integer multiple of the AC voltage cycle of the AC system or a predetermined cycle such as 1 second. If the current time is within the control cycle, the process proceeds to step S183.

[0237] In step S183, the eighth control circuit 4097 outputs an instruction to the target power generation circuit 40931 within the virtual synchronous generator control circuit 4093 to generate an initial value for the target power value. Upon receiving the instruction, the target power generation circuit 40931 follows the points described above. Figure 13 The initial values ​​for generating the power target value are shown.

[0238] In step S184, the eighth control circuit 4097 outputs an instruction to the target frequency generation circuit 40934 within the virtual synchronous generator control circuit 4093 to generate an initial value for the target frequency value. Upon receiving the instruction, the target frequency generation circuit 40934 follows the points described above. Figure 14 The initial value for generating the target frequency is shown.

[0239] In step S185, the eighth control circuit 4097 outputs an instruction to the virtual synchronous generator control circuit 4093 to generate frequency and phase information when generating the target value of AC voltage for controlling the second DC / AC conversion circuit 408. Upon receiving the instruction, the virtual synchronous generator control circuit 4093 outputs instructions to the phase detection circuit 40910 and frequency detection circuit 40911 within the AC frequency detection circuit 4091 to detect the frequency and phase of the AC voltage in the AC system of the power distribution system 24.

[0240] In Embodiment 1, upon new connection, the zero-crossing point information detected by the AC frequency detection circuit 4091 includes an error caused by the sensor error present in the voltmeter 410. Therefore, for example, when the power conversion device 41 for the battery of the power distribution system is newly connected for use in the discharge direction (power operation direction), if the phase of the AC voltage of the AC system output from the second DC / AC conversion circuit 408 is lagging behind the phase of the AC voltage of the power distribution system 24, as in... Figure 19 The description states that the newly connected power conversion device 41 for the distribution system's battery operates in the charging direction (regeneration direction) immediately after being connected. As a result, other interconnected power conversion devices 41 for the distribution system's battery, as well as the synchronous generator 30, need to discharge to replenish the power charged by the newly connected power conversion device 41. Due to this additional discharge power, the output of the power conversion device 41 exceeds its power capacity. Consequently, there are instances where the power conversion device 41 stops due to over-power.

[0241] Therefore, in Embodiment 1, when the power conversion device 41 for the distribution system battery is reconnected to the power conversion device 41 for the purpose of discharging in DSO21, the fourth control circuit 409 controls the addition of a predetermined offset to the phase information detected by the AC frequency detection circuit 4091 (the zero-crossing point time information when the AC voltage of the AC system switches from negative to positive in Embodiment 1), so that the phase of the AC voltage of the AC system output from the power conversion device 41 for the distribution system battery at the time of reconnection becomes an advancing phase relative to the phase of the AC voltage of the distribution system 24. Specifically, the output is obtained by subtracting a predetermined time from the zero-crossing point time detected by the AC frequency detection circuit 4091. Furthermore, the method of controlling in a manner that becomes the advancing phase is not limited to this method. For example, even if the system is configured such that, when interconnected, the offset provided at the aforementioned new turn-on is calculated based on the zero-crossing point time information of the sine wave waveform that becomes the target value of the voltage control output from the second sine wave generation circuit 40912 when controlling the second DC / AC conversion circuit 408 and the zero-crossing point time information detected by the phase detection circuit 40910, the same effect can be obtained.

[0242] When the power conversion device 41 for the battery of the power distribution system is newly connected for the purpose of discharging in DSO21, if the fourth control circuit 409 controls the second DC / AC conversion circuit 408 in such a way that the phase of the AC voltage of the output AC system is leading, then as follows Figure 21 As shown, the newly connected power distribution system battery power conversion device 41 outputs power in the discharge direction (power operation direction) immediately after being connected. Other interconnected power distribution system battery power conversion devices 41 and synchronous generator 30 operate in the direction of suppressing the discharge power, thus controlling the power output without exceeding the power capacity of the power distribution system battery power conversion device 41. Therefore, the power distribution system battery power conversion devices 41 in the interconnected system can continue to operate.

[0243] exist Figure 26 In step S185, after the calculation of the frequency and phase of the AC voltage of the target AC system is completed, the processing proceeds to... Figure 25 Step S169. In step S169, the 8th control circuit 4097 starts virtual synchronous generator control. After the virtual synchronous generator control starts, the inverter voltage control circuit 4095, according to the... Figure 26 The frequency and phase (zero-crossing point detection time information) detected in step S185 are used by the third sine wave generation circuit 40951 to generate a target value for the AC voltage of the AC system output from the power conversion device 41 for the power distribution system battery. Based on the generated target value of the AC voltage of the AC system, the inverter voltage control circuit 4095 generates and outputs a control signal for the second DC / AC conversion circuit 408. After the control of the second DC / AC conversion circuit 408 begins, the virtual synchronous generator control circuit 4093 begins virtual synchronous generator control.

[0244] Specifically, in the virtual synchronous generator control circuit 4093, the subtractor 40932 subtracts the output of the target frequency generation circuit 40934 from the frequency of the measured AC voltage of the AC system output from the self-frequency detection circuit 40911, and sends the subtraction result to the speed governor control circuit 40933. In the speed governor control circuit 40933, the multiplier 409331 multiplies the output of the subtractor 40932 with the control parameter (-1 / Kgd) output from the 8th control circuit 4097, and sends the multiplication result to the first-order delay system model 409332. The first-order delay system model 409332 uses the time constant Tg output from the 8th control circuit 4097 to perform a simulation of the first-order delay system (1 / (1+s×Tg)), and sends the calculation result to the limiting circuit 409333. The limiting circuit 409333 imposes a limit on the input data. Specifically, the limiting circuit 409333 limits the output in a manner that does not exceed the power capacity of the second DC / AC conversion circuit 408.

[0245] The output of the speed controller control circuit 40933 is added to the target power value output from the target power generation circuit 40931 via adder 40935. Subtractor 40936 subtracts the output of adder 40935 from the measured effective power output from the effective power calculation circuit 4092. The output of subtractor 40936 is input to the mass system operation circuit 40937.

[0246] In the particle system operation circuit 40937, subtractor 409371 subtracts the output of multiplier 409373 from the output of subtractor 40936, and sends the subtraction result to integrator 409372. Integrator 409372 divides the subtraction result by the inertial constant m output from the 8th control circuit 4097 and integrates the division result. The output of integrator 409372 (Δω: the difference between the angular velocity (2×π×60Hz) of the AC system frequency) is input to multiplier 409373 and divider 409374. Multiplier 409373 multiplies the output Δω of integrator 409372 and the braking coefficient Dg output from the 8th control circuit 4097, and outputs the multiplication result to subtractor 409371. Divider 409374 divides the output Δω of integrator 409372 by 2×π, transforming Δω into Δf (the difference from the AC system frequency (60Hz)). The output of divider 409374 is then added to 60Hz, the reference frequency for the AC system voltage, via adder 409375, thereby generating the frequency for voltage control in inverter voltage control circuit 4095.

[0247] The frequency information output from adder 409375 is input to phase calculation circuit 409376. The operation of phase calculation circuit 409376 is explained below. The operation of phase calculation circuit 409376 differs between new power-on and system interconnection. During system interconnection, phase calculation circuit 409376 integrates the frequency information output from adder 409375 and calculates the phase when inverter voltage control circuit 4095 performs voltage control based on the integration result. The calculated phase information and frequency information are input to third sine wave generation circuit 40951 within inverter voltage control circuit 4095 via second sine wave generation circuit 40912 in AC frequency detection circuit 4091. Third sine wave generation circuit 40951 uses the received phase and frequency information to generate a target value for the AC voltage of the AC system output from power conversion device 41 for the power distribution system battery.

[0248] Return to Figure 24 In step S170, the eighth control circuit 4097 confirms whether a predetermined time has elapsed. The predetermined time refers to the time taken for the interference in the power distribution system to converge after the newly connected battery power conversion device 41 is activated. Specifically, in Figure 13 or Figure 14 In this process, the predetermined time is the time required until the output of the target power generation circuit 40931 becomes Pref and the output of the target frequency generation circuit 40934 becomes Fref. If the predetermined time has not elapsed, the process proceeds to step S171. If the predetermined time has elapsed, the process proceeds to step S172.

[0249] In step S171, the 8th control circuit 4097 collects various measurement data. Afterwards, the process proceeds to step S169.

[0250] In step S172, the eighth control circuit 4097 changes the various parameters used for controlling the virtual synchronous generator, which were set in S162 for new general connection, to control parameters used for normal system interconnection. Afterwards, processing transitions to normal control (see [reference]). Figure 23 ).

[0251] As described above, in Embodiment 1, when the power distribution system 24 is newly connected to the power distribution system battery converter 41 via a voltage source (voltage control) in the discharge direction (power operation direction), the phase of the AC voltage of the AC system output from the power distribution system battery converter 41 becomes an advancing phase compared to the phase information detected by the phase detection circuit 40910. Therefore, even if there are phase overlap measurement errors in the AC voltage waveform of the AC system of the power distribution system 24 due to sensing errors of the voltmeter 410, since the connection is at least an advancing phase, the power distribution system battery converter 41 will not needlessly charge the power from the power distribution system 24 immediately after connection. Thus, it has the effect of not unnecessarily increasing the discharge power of the power distribution system battery converter 41 in the interconnected system, and can reliably continue to operate.

[0252] In Embodiment 1, when the power conversion device 41 for the distribution system battery is newly connected or disconnected, the values ​​of the control parameter (time constant Tg) of the speed governor control circuit 40933 within the virtual synchronous generator control circuit 4093 and the control parameter (inertia constant m) of the mass system calculation circuit 40937 are made greater than the values ​​under normal control. This is implemented not only in the newly connected or disconnected power conversion device 41 for the distribution system battery, but also in the continuously interconnected power conversion devices 41 for the distribution system battery. As a result, the new connection or disconnection can be performed without unnecessary large interference to the frequency of the AC voltage of the AC system of the distribution system 24. This is because the impact of the new connection or disconnection of the power conversion device 41 for the distribution system battery on the distribution system 24 does not last for a long time. Through the control described above, unnecessary interference in the frequency of the AC voltage of the AC system of the distribution system 24 can be prevented.

[0253] Compared to the newly connected power distribution system battery power converter 41, the inertia constant m within the mass system operation circuit 40937 is set to be larger in the continuously operating power distribution system battery power converter 41. Specifically, to suppress the influence of the sensing error of the voltmeter 410, the phase of the AC voltage of the AC system of the newly connected power distribution system battery power converter 41 is made leading. To supply power to the power distribution system 24 using the newly connected power distribution system battery power converter 41, the phase of the AC voltage of the AC system of the newly connected power distribution system battery power converter 41 needs to be controlled by a virtual synchronous generator to a phase suitable for system interconnection. Therefore, regarding the newly connected power distribution system battery power converter 41, compared to the power distribution system battery power converter 41 in the system interconnection, the response performance is set higher by utilizing the frequency and phase control of the mass system operation circuit 40937, thereby shortening the time of frequency interference.

[0254] Furthermore, in implementation method 1, such as Figure 13 as well as Figure 14 The target power generation circuit 40931 and target frequency generation circuit 40934 are shown in the control circuit 4093 for the virtual synchronous generator. Therefore, when the power conversion device 41 for the battery in the new power distribution system is connected, various controls of the speed governor control circuit 40933 and the mass system operation circuit 40937 can be smoothly implemented. As a result, unnecessary frequency interference in the power distribution system 24 can be prevented.

[0255] Implementation method 2.

[0256] In Embodiment 1, the case where the power conversion device 41 for the power distribution system battery is newly connected in the discharge direction (power operation direction) is described. However, in Embodiment 2, the case where the power conversion device 41 for the power distribution system battery is newly connected in the charging direction (regeneration direction) is described. Therefore, the structure of the power conversion device 41 for the power distribution system battery in Embodiment 2 is the same as that in Embodiment 1 (see [reference]). Figure 4 as well as Figure 7 , 8 (10-12, 15, 16). The only difference is in the control of the particle system operation circuit 40937 within the newly added power distribution system battery power conversion device 41. Hereinafter, the operation of the different parts will be explained.

[0257] The following uses Figures 27-30 This explains the operation of the power conversion device 41 for the battery in the power distribution system of Embodiment 2. Figure 27This is a flowchart illustrating the control process when a new addition (new connection for charging direction (regeneration direction) is made to the power conversion device 41 for the battery in the power distribution system in Embodiment 2.

[0258] use Figure 27 This describes the operation of the power conversion device 41 for the battery in the power distribution system that makes a new connection in the charging direction (regeneration direction).

[0259] Similar to Embodiment 1, the power conversion device 41 for the power distribution system battery, which is in low-power standby mode, remains in standby mode until a start request is received from DSO21 (S161). In step S161, upon receiving a start request from DSO21, the eighth control circuit 4097 within the fourth control circuit 409 outputs to the third control circuit 404 to start the second DC / DC converter circuit 403. Furthermore, the control during startup of the third control circuit 404 is the same as in Embodiment 1, so a detailed explanation of its operation will not be repeated.

[0260] After completing the startup process including the power distribution system battery 40, the third control circuit 404 notifies the fourth control circuit 409 along with the information it has collected. Upon receiving the completion of the startup process from the third control circuit 404, the eighth control circuit 4097 within the fourth control circuit 409 sets the various control parameters of the speed governor control circuit 40933 within the virtual synchronous generator control circuit 4093 and the mass system calculation circuit 40937 to the parameters used during the new connection. At this time, in order to enable the power distribution system battery to operate as an AC voltage source using the power conversion device 41, the third switching circuit 4096 controls the selection of the output of the inverter voltage control circuit 4095. If "Yes" is selected in step S161, in step S162, the control parameters of each control circuit within the virtual synchronous generator control circuit 4093 are changed to the parameters used during the new connection.

[0261] Here, the various control parameters during the new connection are explained. Similar to Embodiment 1, the eighth control circuit 4097 makes the values ​​of the control parameters in the governor control circuit 40933 within the virtual synchronous generator control circuit 4093 and the mass system calculation circuit 40937 greater than their values ​​during normal operation. At this time, similar to Embodiment 1, the eighth control circuit 4097 further makes the values ​​of these control parameters greater than the values ​​of the control parameters set during disconnection. Specifically, the eighth control circuit 4097 increases at least the time constant (Tg) in the governor control circuit 40933 and the inertia constant (M) in the mass system calculation circuit 40937. As a result, the response time of the governor control is delayed, and the apparent increase in the oscillation equation-based response time is also increased. Figure 9The generator rotor shown has inertial force. Therefore, similar to Embodiment 1, frequency variations in the AC voltage of the AC system of the power distribution system 24 can be suppressed. Specifically, when the power conversion device 41 for the power distribution system battery is newly connected, even if power not controlled by the newly connected power conversion device 41 is output, the frequency of the AC voltage of the AC system will not be significantly disturbed, and operation can continue. Uncontrolled power refers to charging and discharging power caused by the phase difference between the phase of the AC voltage of the AC system and the phase of the AC voltage output by the power conversion device 41 for the power distribution system battery. The principle and effect of this method are the same as in Embodiment 1, so they will not be explained again.

[0262] Return to Figure 27 After completing step S162, the process proceeds to step S163. In step S163, similar to embodiment 1, the fourth control circuit 409 detects the phase (zero-crossing point moment) of the AC voltage of the AC system and outputs the zero-crossing point moment information to the frequency detection circuit 40911.

[0263] In step S164, the frequency detection circuit 40911 detects the frequency of the AC voltage of the AC system based on the zero-crossing point time information.

[0264] Specifically, similar to Embodiment 1, the phase detection circuit 40910 in the AC frequency detection circuit 4091 uses the time information of the voltmeter 410's output changing from negative to positive and each amplitude to linearly interpolate the zero-crossing point time to obtain the value. Furthermore, the frequency detection circuit 40911 calculates the frequency of the AC voltage of the AC system based on the zero-crossing point time information of two consecutive points. In Embodiments 1 and 2, the frequency detection circuit 40911 is configured to use only the zero-crossing point time information of two consecutive points to determine the frequency of the AC voltage of the AC system, but it is not limited to this. Alternatively, the frequency detection circuit 40911 can determine the frequency of the AC voltage of the AC system based on multiple zero-crossing point information and take the average value. Alternatively, similar to Embodiment 1, the phase detection circuit 40910 can calculate the time information of the zero-crossing point changing from positive to negative according to the above points, calculate the offset error of the voltmeter 410 based on the calculation result (see Embodiment 1 for details), and recalculate the zero-crossing point time based on the offset error.

[0265] After detecting the frequency of the AC voltage in the AC system, the AC frequency detection circuit 4091 performs phase detection of the AC voltage in the AC system. Similar to Embodiment 1, the AC frequency detection circuit 4091 uses the zero-crossing point when the output of the latest voltmeter 410 changes from negative to positive after frequency detection as the phase information. After the detection of the frequency and phase information of the AC voltage in the AC system is completed in step S164, the process proceeds to step S165.

[0266] In step S165, the frequency information and phase information detected by the AC frequency detection circuit 4091 are input to the second sine wave generation circuit 40912.

[0267] The second sine wave generation circuit 40912 generates a sine wave as a reference for voltage control based on the detected frequency and phase information and the frequency and phase information output from the particle system calculation circuit 40937 within the virtual synchronous generator control circuit 4093. This sine wave is then output to the third sine wave generation circuit 40951 in the inverter voltage control circuit 4095. The detection information from the AC frequency detection circuit 4091 is also input to the virtual synchronous generator control circuit 4093 and the eighth control circuit 4097. The frequency and phase of the AC voltage of the AC system input to the virtual synchronous generator control circuit 4093 are input to the target frequency generation circuit 40934. The detection information from the AC frequency detection circuit 4091 is input to the particle system calculation circuit 40937 via the eighth control circuit 4097. Specifically, the detection information is set as the initial value of the integrator 409372 within the particle system calculation circuit 40937 and the register (not shown) within the phase calculation circuit 409376.

[0268] After the frequency and phase information of the AC voltage of the AC system are set in step S165, the process proceeds to step S166. In step S166, the 8th control circuit 4097, similar to Embodiment 1, sets the initial values ​​of the frequency target value and the initial values ​​of the power target value for the target power generation circuit 40931 and the target frequency generation circuit 40934 within the virtual synchronous generator control circuit 4093.

[0269] In step S167, the target power generation circuit 40931 sets the time shift of the power target value. The specific operations (target value generation operations) and effects of the target power generation circuit 40931 and the target frequency generation circuit 40934 are the same as in embodiment 1, so they will not be described again.

[0270] Next, in step S202, the fourth control circuit 409 begins to control the second DC / AC conversion circuit 408. Figure 28 This is a flowchart illustrating the control process when the power conversion device 41 for the battery in the newly connected power distribution system is activated using the fourth control circuit 409 in Embodiment 2. Hereinafter, using... Figure 28 This explains the operation of the second DC / AC conversion circuit 408.

[0271] In step S181, after the control of the second DC / AC conversion circuit 408 begins, the effective power calculation circuit 4092 within the fourth control circuit 409 calculates the effective power. The calculation method for the AC effective power is the same as in embodiment 1.

[0272] In step S182, the eighth control circuit 4097 confirms whether the current time is within the control cycle. In Embodiment 2, similarly to Embodiment 1, one cycle of the AC voltage of the AC system is used as the control cycle. The control cycle can also be an integer multiple of the AC voltage cycle of the AC system or a predetermined cycle such as 1 second.

[0273] If it is determined that the current moment is within the control cycle, the process proceeds to step S183. In step S183, the 8th control circuit 4097 outputs an instruction to the target power generation circuit 40931 within the virtual synchronous generator control circuit 4093 to generate an initial value for the power target value.

[0274] In step S184, the eighth control circuit 4097 outputs an instruction to the target frequency generation circuit 40934 within the virtual synchronous generator control circuit 4093 to generate an initial value for the target frequency value. Upon receiving the instruction, the target frequency generation circuit 40934 generates the initial value for the target frequency value according to the points described above. After generating the initial value, once virtual synchronous generator control begins in the virtual synchronous generator control circuit 4093, the target power generation circuit 40931 and the target frequency generation circuit 40934, similar to Embodiment 1, proceed as follows: Figure 13 as well as Figure 14 The target voltage and frequency values ​​are shown.

[0275] In step S210, the eighth control circuit 4097 outputs an instruction to the AC frequency detection circuit 4091 to generate a target value for the AC voltage of the AC system output from the power conversion device 41 of the power distribution system battery when the second DC / AC conversion circuit 408 is newly connected to the power distribution system 24. Upon receiving the instruction, the AC frequency detection circuit 4091 outputs instructions to the phase detection circuit 40910 and the frequency detection circuit 40911 to generate information on the frequency and zero-crossing point of the AC voltage input from the power distribution system 24. Details of the method for detecting the frequency and zero-crossing point of the AC voltage input from the power distribution system 24 in Embodiment 2 will be described later.

[0276] Implementation 2 differs from Implementation 1 in that, in order to charge the remaining power of the megawatt-level solar panel 26, the power conversion device 41 for the distribution system battery is reconnected to operate in the charging direction (regeneration direction). As explained in Implementation 1, immediately after the power conversion device 41 for the distribution system battery is connected to the distribution system 24, the output power is determined by the phase difference between the phase of the AC voltage of the AC system of the distribution system 24 and the phase of the AC voltage of the AC system output by the power conversion device 41 for the distribution system battery.

[0277] In implementation method 1, in order to make the phase of the target AC voltage value advance relative to the AC voltage of the AC system, such as Figure 20 as well as Figure 21 As shown, in the discharge direction (power operation direction), the output power is determined by the phase difference. On the other hand, when the phase of the target AC voltage value is delayed relative to the AC voltage of the AC system, such as... Figure 18 as well as Figure 19 As shown, in the charging direction (regeneration direction), the output power is determined by the phase difference. In fact, this power, apart from the magnitude of the phase difference, is determined by the magnitude of the difference between the amplitude of the AC voltage of the AC system of the power distribution system 24 and the amplitude of the AC voltage of the AC system output by the power conversion device 41 for the battery of the power distribution system.

[0278] Therefore, in Embodiment 2, when the second DC / AC conversion circuit 408 (inverter) is connected to the AC system, the fourth control circuit 409 (inverter control circuit) makes the frequency of the AC voltage target value become the frequency of the AC voltage detected by the AC frequency detection circuit 4091, and when the AC power target value is in the regeneration direction, it controls the phase of the AC voltage target value to be at least lagging behind the AC voltage of the AC system.

[0279] Specifically, the fourth control circuit 409 adds a predetermined offset to the phase information detected by the AC frequency detection circuit 4091, or controls the zero-crossing detection time by adding an offset. Here, in Embodiment 2, similarly to Embodiment 1, the phase information is the zero-crossing time information when the AC voltage of the AC system switches from negative to positive.

[0280] In Embodiment 2, the fourth control circuit 409 adds a predetermined time to the zero-crossing point time detected by the AC frequency detection circuit 4091 and outputs the result. Furthermore, the method for controlling the phase of the target AC voltage value to be a delayed phase relative to the AC voltage of the AC system is not limited to this method. In Embodiment 2, phase information (zero-crossing point time information) is generated as shown below. Specifically, as described in the operation description of the AC frequency detection circuit 4091, the AC frequency detection circuit 4091 calculates three consecutive zero-crossing point times based on the measurement data from the voltmeter 410. The three consecutive zero-crossing point times refer to the zero-crossing point time t1 when the AC voltage of the AC system switches from negative to positive, the zero-crossing point time t2 when it switches from positive to negative, and the zero-crossing point time t3 when it switches from negative to positive. Moreover, the AC frequency detection circuit 4091 calculates Tu_d = t2 - t1 (the time when the AC voltage of the AC system is positive) and Td_u = t3 - t2 (the time when the AC voltage of the AC system is negative) based on the calculation results.

[0281] Figure 29 Figures (a) to (c) illustrate the method for detecting the zero-crossing point (phase) of a delayed phase. Figure 29 (a) to (c) show the voltage information output from voltmeter 410. Figure 29 In (a) to (c), the vertical axis represents voltage and the horizontal axis represents time.

[0282] This explains the case where the voltmeter 410 has a primary component of offset error, which is the main cause of error during phase detection. Figure 29 The sine wave waveform shown by the solid line in (a) represents the data measured by voltmeter 410. Figure 29 In example (a), voltmeter 410 has a negative offset error. Therefore, regarding the zero-crossing time t1, the detection occurs before the actual zero-crossing time (leading phase). In this case, in Tu_d and Td_u, which are the results of the above calculations, as... Figure 29 (a) shows the following relationship.

[0283] Tu_d>Td_u…(3)

[0284] Next, use Figure 29 (a) to (c) illustrate the method for detecting the zero-crossing point time in Embodiment 2. The phase detection circuit 40910 within the AC frequency detection circuit 4091 calculates the zero-crossing point times t1, t2, and t3 according to the points described in Embodiment 1. For example, the phase detection circuit 40910 uses the time information between two consecutive samples from the output of the voltmeter 410 that switch from negative to positive, and the two sample values ​​(positive and negative), to perform linear interpolation on the zero-crossing point times t1, t2, and t3 to calculate them.

[0285] The phase detection circuit 40910 calculates Tu_d and Td_u based on the calculated zero-crossing point time information. Furthermore, in Embodiment 2, when the phase of the AC voltage output from the power conversion device 41 for the AC system of the distribution system battery becomes an advancing phase, the phase detection circuit 40910, when setting Tstatic_max and Tstatic_min to predetermined values ​​for detecting the advancing phase, determines the offset value (advancing phase) in a manner that makes the following formula true (see [reference]). Figure 29 (b)).

[0286] Tstatic_max>Tu_d-Td_u>Tstatic_min…(4)

[0287] In implementation method 2, Figure 29 (b) is set as the zero-crossing detection time of the advancing phase.

[0288] Similarly, when the phase of the AC voltage output from the power conversion device 41 for the battery in the power distribution system is made to be a delayed phase, when Tlaggin_max and Tlaggin_min are set to predetermined values ​​for detecting the delayed phase, the offset value (delayed phase) is determined in such a way that the following formula holds (see reference). Figure 29 (c)).

[0289] Tlaggin_max>Tu_d-Td_u>Tlaggin_min…(5)

[0290] In implementation method 2, Figure 29 (c) is set as the zero-crossing point detection time of the delayed phase. As described above, the same effect can be obtained even if the phase of the AC voltage of the AC system output from the power conversion device 41 for the battery of the power distribution system is controlled. In addition, even if the system is configured to calculate the offset provided at the above-mentioned new turn-on based on the zero-crossing point time information of the sine wave waveform that becomes the target value of voltage control output from the second sine wave generation circuit 40912 when controlling the second DC / AC conversion circuit 408 and the zero-crossing point time information detected by the phase detection circuit 40910 when the system is interconnected, the same effect can be obtained.

[0291] The zero-crossing point time information t1 and t3 detected by the phase detection circuit 40910 are input to the frequency detection circuit 40911. The frequency detection circuit 40911 calculates the frequency fx of the AC voltage of the AC system of the power distribution system 24 using the following formula.

[0292] fx=1 / (t3-t1)…(6)

[0293] Similar to Implementation 1, the detected zero-crossing point time information t3 and frequency information are used as sine wave information and are notified from the second sine wave generation circuit 40912 to the third sine wave generation circuit 40951.

[0294] The third sine wave generation circuit 40951 generates a target value for the AC voltage output from the power conversion device 41 for the power distribution system battery based on the notified sine wave information. In Embodiment 2, the timing for connecting the power conversion device 41 for the power distribution system battery to the power distribution system 24 is set to the zero-crossing point of the target value of the AC voltage generated by the third sine wave generation circuit 40951. Therefore, a very large discharge or charging power is not output immediately after connection, allowing the power conversion device 41 for the power distribution system battery to be connected to the power distribution system 24 anew.

[0295] In step S210, after calculating the frequency and phase information (zero-crossing point time information) of the AC voltage of the AC system according to the above points, the processing proceeds to... Figure 27 Step S169. In step S169, the 8th control circuit 4097 outputs an instruction to the virtual synchronous generator control circuit 4093 to start virtual synchronous generator control. After the virtual synchronous generator control starts, the 3rd sine wave generation circuit 40951 of the inverter voltage control circuit 4095 generates a target value for the AC voltage of the AC system output from the power conversion device 41 for the power distribution system battery, based on the frequency and phase (zero-crossing point detection time information) information detected in step S210. The inverter voltage control circuit 4095 generates and outputs a control signal for the 2nd DC / AC conversion circuit 408 based on the generated target value of the AC voltage of the AC system. After the control of the 2nd DC / AC conversion circuit 408 starts, the virtual synchronous generator control circuit 4093 starts virtual synchronous generator control.

[0296] Specifically, in the virtual synchronous generator control circuit 4093, the speed governor control circuit 40933 subtracts the output of the target frequency generation circuit 40934 from the frequency of the measured AC voltage of the AC system output by the self-frequency detection circuit 40911, and outputs the subtraction result to the speed governor control circuit 40933.

[0297] The multiplier 409331 of the speed controller control circuit 40933 multiplies the output of the subtractor 40932 and the control parameter (-1 / Kgd) output from the 8th control circuit 4097, and outputs the multiplication result to the first delay system model 409332.

[0298] The first-order delay system model 409332 uses the time constant Tg output from the 8th control circuit 4097 to perform the calculation of the first-order delay system (1 / (1+s×Tg)), and outputs the calculation result to the limiting circuit 409333.

[0299] Limiting circuit 409333 imposes a limit on the input data. Specifically, limiting circuit 409333 limits the output in a manner that does not exceed the power capacity of second DC / AC converter circuit 408.

[0300] Adder 40935 adds the output of speed controller control circuit 40933 to the target power value output from target power generation circuit 40931. Subtractor 40936 subtracts the output of adder 40935 from the measured effective power output from effective power calculation circuit 4092. The output of subtractor 40936 is input to mass system operation circuit 40937.

[0301] In the particle system operation circuit 40937, the subtractor 409371 subtracts the output of the multiplier 409373 from the output of the subtractor 40936 and outputs the subtraction result to the integrator 409372.

[0302] Integrator 409372 divides the subtraction result by the inertia constant m output from control circuit 8 4097 and integrates the result. The output of integrator 409372 (Δω: the difference between the angular velocity (2×π×60Hz) of the AC system frequency) is input to multiplier 409373 and divider 409374.

[0303] Multiplier 409373 multiplies the output Δω of integrator 409372 and the braking coefficient Dg output from the 8th control circuit 4097, and outputs the multiplication result to subtractor 409371.

[0304] Divider 409374 divides the output Δω of integrator 409372 by 2×π, transforming Δω into Δf (the difference from the AC system frequency (60Hz)). Adder 409375 adds the output of divider 409374 to 60Hz, which serves as the reference frequency for the AC system voltage. This generates the frequency used for voltage control in inverter voltage control circuit 4095.

[0305] The frequency information output from adder 409375 is input to phase calculation circuit 409376. The operation of phase calculation circuit 409376 is explained below. The operation of phase calculation circuit 409376 differs during initial power-on and system interconnection. During system interconnection, phase calculation circuit 409376 integrates the frequency information output from adder 409375 and calculates the phase for voltage control by inverter voltage control circuit 4095 based on the integration result. The calculated phase and frequency information are input to third sine wave generation circuit 40951 within inverter voltage control circuit 4095 via second sine wave generation circuit 40912 in AC frequency detection circuit 4091. Third sine wave generation circuit 40951 generates a target value for AC voltage of the AC system output from power conversion device 41 for battery in the power distribution system based on the phase and frequency information.

[0306] Return to Figure 27 In step S203, the eighth control circuit 4097 confirms whether the effective power calculated by the effective power calculation circuit 4092 is within a predetermined power range. That is, the eighth control circuit 4097 confirms whether the interference with the charging and discharging power of the newly connected power conversion device 41 for the power distribution system battery in the power distribution system 24 converges within a predetermined range. If the effective power does not converge within the predetermined range, the process proceeds to step S171. If the effective power converges within the predetermined range, the process proceeds to step S204.

[0307] In step S171, the 8th control circuit 4097 collects various measurement data. Afterwards, the processing returns to step S169. In step S169, the 8th control circuit 4097 again controls the virtual synchronous generator control circuit 4093. At this time, in Embodiment 2, unlike in Embodiment 1, the target power generation circuit 40931 and the target frequency generation circuit 40934 within the virtual synchronous generator control circuit 4093 maintain their initial values ​​(see reference) until the interference converges. Figure 13 as well as Figure 14 ).

[0308] In step S204, the eighth control circuit 4097 confirms whether the output of the target power generation circuit 40931 within the virtual synchronous generator control circuit 4093 is Pref and whether the output of the target frequency generation circuit 40934 is Fref. If the output of the target power generation circuit 40931 is Pref and the output of the target frequency generation circuit 40934 is Fref, the process proceeds to step S172. If the output of the target power generation circuit 40931 is not Pref or the output of the target frequency generation circuit 40934 is not Fref, the process proceeds to step S205.

[0309] In step S205, the 8th control circuit 4097 collects various measurement data. Afterwards, the processing returns to step S204.

[0310] In step S172, the eighth control circuit 4097 changes the various parameters used for controlling the virtual synchronous generator, which were configured in step S162 for the new general connection, to control parameters used for normal system interconnection. Afterwards, processing transitions to normal control (see reference). Figure 23 ).

[0311] As described above, in Embodiment 2, when the power conversion device 41 for the power distribution system battery is newly connected to the power distribution system 24 in the charging direction (regeneration direction) using a voltage source (voltage control), the phase of the AC voltage of the AC system output from the power conversion device 41 for the power distribution system battery is made to be a delayed phase compared to the phase information detected by the phase detection circuit 40910. Therefore, even if there are phase overlap measurement errors in the AC voltage waveform of the power distribution system 24 due to sensing errors of the voltmeter 410, since the connection is at least a delayed phase, it is possible to prevent unnecessary power discharge from the newly connected power conversion device 41 for the power distribution system battery to the power distribution system 24 immediately after connection.

[0312] Figure 30 This is a diagram showing the charging and discharging power (effective value) of the two power distribution system battery power conversion devices 41 when the AC voltage phase of the newly connected power distribution system battery power conversion device 41 in Embodiment 2 is lagging.

[0313] like Figure 30 As shown, immediately after a new connection is made, the power conversion device 41b for the power distribution system battery operates in the charging direction, thus increasing the charging power of the interconnected power distribution system battery power conversion device 41a. This prevents the output power of the power distribution system battery power conversion device 41a from exceeding the maximum charging power, causing it to stop due to overcapacity. Therefore, it has the effect of preventing unnecessary increases in the discharge power of the interconnected power distribution system battery power conversion device 41a, and ensuring reliable continued operation.

[0314] In Embodiment 2, similarly to Embodiment 1, when the power conversion device 41 for the distribution system battery is newly connected, the values ​​of the control parameter (time constant Tg) of the speed governor control circuit 40933 within the virtual synchronous generator control circuit 4093 and the control parameter (inertia constant m) of the mass system calculation circuit 40937 are made greater than their normal control values. This is implemented not only for the newly connected power conversion device 41 for the distribution system battery, but also for the continuously interconnected power conversion devices 41 for the distribution system battery.

[0315] Therefore, a new connection can be made without unnecessarily causing significant interference to the frequency of the AC voltage of the AC system in the power distribution system 24. This is because the impact on the power distribution system 24 caused by the new connection of the power conversion device 41 for the power distribution system battery will not last for a long time. Through the control described above, it is possible to prevent unnecessary interference in the frequency of the AC voltage of the AC system in the power distribution system 24.

[0316] Compared to the newly connected power conversion device 41 for the distribution system battery, the inertia constant m in the control parameters, at least within the mass system operation circuit 40937, is set larger in the continuously operating power conversion device 41 for the distribution system battery. The reason is as follows: Regarding the phase of the AC voltage of the AC system of the newly connected power conversion device 41 for the distribution system battery, it becomes lagging to suppress the influence of the sensing error of the voltmeter 410. In order to supply power to the distribution system 24 using the newly connected power conversion device 41 for the distribution system battery, the phase of the AC voltage of the AC system of the newly connected power conversion device 41 for the distribution system battery needs to be controlled by a virtual synchronous generator to a phase suitable for system interconnection. Therefore, regarding the newly connected power conversion device 41 for the distribution system battery, compared to the power conversion device 41 for the distribution system in system interconnection, the frequency and phase response performance based on the mass system operation circuit 40937 is set higher. This shortens the time when frequency interference occurs.

[0317] Furthermore, in implementation method 2, such as Figure 13 as well as Figure 14 The target power generation circuit 40931 and target frequency generation circuit 40934 are shown in the control circuit 4093 for the virtual synchronous generator. Therefore, when the battery power conversion device 41 of the new power distribution system is connected, various controls of the speed governor control circuit 40933 and the mass system operation circuit 40937 can be smoothly implemented. As a result, unnecessary frequency interference can be avoided in the power distribution system 24.

[0318] Furthermore, in embodiments 1 and 2, even when the offset error and linearity during sensing are not guaranteed in the voltmeter 410, an offset is applied to the voltmeter 410 at the zero-crossing point time detected by the phase detection circuit 40910 (applying an offset such that it becomes an advancing phase when the indication from DSO21 is discharge, and a lagging phase when charging) or an offset is applied to the voltmeter 410 at the time point of phase detection when the indication from DSO21 is discharge, and a lagging phase when charging, to calculate the zero-crossing point time. Therefore, it has the effect that when the system is newly turned on, the battery power conversion device 41 of the interconnected power distribution system can reliably continue to operate without unnecessarily increasing the charging and discharging power.

[0319] In Embodiment 1, the cases of connecting or disconnecting the power conversion device 41 for the power distribution system battery in the power distribution system 24 are described, but this is not a limitation. For example, the same effect can be obtained by similarly controlling the power conversion device 41 for the power distribution system battery installed inside a factory or building that is composed of a power transmission system or dedicated distribution lines.

[0320] The power conversion device 41 for the battery in the power distribution system was described in embodiments 1 and 2, but is not limited thereto. For systems that supply power to the system from sources such as solar cells, wind turbines, or fuel cells, where a static inverter is controlled as a voltage source, the same effect can be achieved if the same control is performed when the system is newly connected or disconnected. Furthermore, on-board batteries from vehicles such as electric vehicles (EVs), plug-in hybrid electric vehicles (PHEVs), or fuel cell vehicles (FCVs) can also be used.

[0321] In embodiments 1 and 2, a single-phase AC case was used as an example for simplification, but this is not a limitation; for example, three-phase AC could also be used. Furthermore, the method for calculating the effective power is not limited to this; for example, in the case of three-phase AC, arithmetic methods such as DQ transformation can be used for calculation. Additionally, the method for detecting the frequency and phase of the AC voltage input from the distribution system 24 is not limited to this; particularly regarding the phase, when a new connection is made, it is sufficient to control the phase in the discharge direction with the advancing phase and the phase in the charging direction with the lagging phase.

[0322] In embodiments 1 and 2, the speed governor model within the speed governor control circuit 40933 is modeled as a first-order delay system, but this is not a limitation. The same effect can be achieved even if a second-order delay system or an LPF (Low Pass Filter) is used to construct the speed governor model. In embodiments 1 and 2, the particle system operation circuit is modeled using an integrator and a feedback loop, but this is not a limitation. For example, the particle system operation circuit can also be modeled using a first-order delay system, a second-order delay system, or an LPF. In embodiments 1 and 2, VQ control, which is widely implemented in virtual synchronous generator control, is omitted for simplicity, but the same effect can be obtained even if this method is used in a power conversion device that also implements VQ control as virtual synchronous generator control.

[0323] Explanation of variations.

[0324] Furthermore, in embodiments 1 to 3, for ease of explanation, the following description is provided: Figures 3 to 13 The control circuits for the megawatt-class solar power conversion device 27 and the power conversion device 41 for the power distribution system battery are shown in the hardware (H / W) configuration. However, even if the functions of each or a portion of the blocks described in each block are implemented using software (S / W) installed on the CPU (Central Processing Unit), the same control functions can be achieved. Alternatively, the same control functions can be achieved through functional division of software and hardware for at least a portion of the blocks.

[0325] The embodiments disclosed herein should be considered illustrative and not restrictive in all respects. The scope of this disclosure is set forth in the claims, not in the foregoing description, and is intended to include all modifications within the meaning and scope equivalent to the claims.

Claims

1. A power conversion device comprising: an inverter that converts electric power output from a distributed power source into alternating-current electric power and outputs the electric power to an alternating-current system; an alternating-current voltage measurer that measures an alternating-current voltage of the alternating-current system; an alternating-current frequency detection circuit that detects a frequency and a phase of the alternating-current voltage of the alternating-current system based on an output of the alternating-current voltage measurer; and an inverter control circuit that generates an alternating-current voltage target value at the time of controlling the inverter and generates an instruction value for controlling the inverter as a voltage source, wherein the inverter control circuit makes the frequency of the alternating-current voltage target value the frequency of the alternating-current voltage detected by the alternating-current frequency detection circuit at the time of turning on the inverter to the alternating-current system, and controls the phase of the alternating-current voltage target value to be at least leading phase with respect to the alternating-current voltage of the alternating-current system in a case where a target value of the alternating-current electric power is a motoring direction.

2. The power conversion device according to claim 1, wherein the inverter control circuit controls the phase of the alternating-current voltage target value in different manners in a case where the target value of the alternating-current electric power is the motoring direction and in a case where the target value of the alternating-current electric power is a regenerative direction at the time of turning on the inverter to the alternating-current system.

3. The power conversion device according to claim 2, wherein the inverter control circuit makes the frequency of the alternating-current voltage target value the frequency of the alternating-current voltage detected by the alternating-current frequency detection circuit at the time of turning on the inverter to the alternating-current system, and controls the phase of the alternating-current voltage target value to be at least lagging phase with respect to the alternating-current voltage of the alternating-current system in a case where the target value of the alternating-current electric power is the regenerative direction.

4. The power conversion device according to any one of claims 1 to 3, wherein the inverter control circuit calculates the phase of the alternating-current voltage output from the inverter based on a target value of the alternating-current electric power output from the inverter.

5. The power conversion device according to claim 4, further comprising: an effective power calculation circuit that calculates and outputs an effective power output from the inverter, wherein the inverter control circuit comprises: a governor control circuit that outputs an offset amount added to the target value of the alternating-current electric power based on at least a difference between a frequency of an alternating-current voltage serving as a reference and the frequency of the alternating-current voltage output from the alternating-current frequency detection circuit; and a mass system operation circuit that calculates the frequency and the phase of the alternating-current voltage output from the inverter based on a difference between a sum of the offset amount and the target value of the alternating-current electric power and the output of the effective power calculation circuit.

6. The power conversion device according to claim 5, wherein the mass system operation circuit has an inertia force simulation section that simulates an inertia force that a synchronous generator has and a brake force simulation section that simulates a brake force that the synchronous generator has. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ The mass system operation circuit sets, at least, a value of an inertia constant provided to the inertia force simulation section to a value larger than a value of an inertia constant at the time of normal operation, until the effective power output from the inverter enters a predetermined range, or until a predetermined time elapses after the connection to the AC system is newly made.

7. The power conversion device according to claim 5, wherein The power conversion device has a communication interface circuit, The mass system operation circuit has an inertia force simulation section that simulates an inertia force that a synchronous generator has, and a braking force simulation section that simulates a braking force that the synchronous generator has, The mass system operation circuit sets, at least, a value of an inertia constant provided to the inertia force simulation section to a value larger than a value of an inertia constant at the time of normal operation, until the effective power output from the inverter enters a predetermined range, or until a predetermined time elapses after the connection to the AC system is newly made.

8. The power conversion device according to any one of claims 5 to 7, wherein The inverter control circuit further has a target frequency generation circuit that, at the time of the connection to the AC system is newly made, makes a frequency of an AC voltage that is input to the governor control circuit to be a frequency detected by the AC frequency detection circuit immediately after the connection is made, and thereafter, changes to a predetermined frequency after a predetermined time elapses.

9. The power conversion device according to claim 8, wherein The target frequency generation circuit makes the frequency of the AC voltage that is input to the governor control circuit to be a frequency detected by the AC frequency detection circuit before the connection is to be made, immediately after the connection is made.

10. The power conversion device according to any one of claims 5 to 7, 9, wherein The inverter control circuit further has a target power generation circuit that, at the time of the connection to the AC system is newly made, makes a target value of the AC power output from the inverter that is input to the mass system operation circuit to be zero immediately after the connection is made, and thereafter, increases to a target value of the AC power specified by a power distribution automation system after a predetermined time elapses.

11. The power conversion device according to claim 8, wherein The inverter control circuit further has a target power generation circuit that, at the time of the connection to the AC system is newly made, makes a target value of the AC power output from the inverter that is input to the mass system operation circuit to be zero immediately after the connection is made, and thereafter, increases to a target value of the AC power specified by a power distribution automation system after a predetermined time elapses.

12. The power conversion device according to claim 10, wherein The target power generation circuit makes the target value of the alternating-current power of the inverter output input to the mass system operation circuit zero at a predetermined time after the turn-on is just performed.

13. The power conversion device according to claim 11, wherein The target power generation circuit makes the target value of the alternating-current power of the inverter output input to the mass system operation circuit zero at a predetermined time after the turn-on is just performed.

14. The power conversion device according to claim 10, wherein The target power generation circuit makes the target value of the alternating-current power of the inverter output input to the mass system operation circuit zero when the inverter is de- synchronized from the alternating-current system, The inverter control circuit de-synchronizes the inverter from the alternating-current system after the effective power output from the effective power calculation circuit enters a predetermined range.

15. The power conversion device according to any one of claims 11 to 13, wherein The target power generation circuit makes the target value of the alternating-current power of the inverter output input to the mass system operation circuit zero when the inverter is de- synchronized from the alternating-current system, The inverter control circuit de-synchronizes the inverter from the alternating-current system after the effective power output from the effective power calculation circuit enters a predetermined range.

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