Power conversion device

Abstract

The present application provides a load power supply using its own AC system, and simultaneously synchronously connects the AC system to a power conversion device of another AC system. The power conversion device includes a power conversion circuit and a power command correction unit. The power conversion circuit converts DC power of a DC power source into AC power to form a first AC system. The power command correction unit determines an active power command correction amount and a reactive power command correction amount of the first AC system for controlling the power conversion circuit. The first AC system is configured to be connectable to a second AC system via a relay. The power command correction unit calculates an angular frequency deviation, a phase deviation, and a voltage deviation between the first AC system and the second AC system. The power command correction unit determines the active power command correction amount and the reactive power command correction amount so that the angular frequency deviation is below an angular frequency deviation threshold value, the phase deviation is below a phase deviation threshold value, and the voltage deviation is below a voltage deviation threshold value.

Description

Technical Field

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

[0002] Patent Document 1 describes a power conversion device. This device includes: an inverter that converts power output from a distributed power source into AC power and outputs it to an AC system; an AC voltmeter 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 voltmeter; 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 connected to the AC system, the inverter control circuit uses the frequency of the target AC voltage value as the frequency of the AC voltage detected by the AC angular frequency detection circuit, and, when the target AC power value is the direction of power operation, controls the AC voltage to ensure that the phase of the target AC voltage value is at least one phase ahead of the AC voltage of the AC system.

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent Document 1: International Publication No. 2021 / 220488 Summary of the Invention

[0006] The technical problem that the invention aims to solve

[0007] The aforementioned power conversion device is used in power distribution systems with multiple static inverters equipped with virtual synchronous generator control, from the perspective of power supply and demand, when an additional static inverter is connected. This power conversion device is used to suppress the shutdown of the already connected static inverter in the power flow immediately following the addition. The aforementioned power flow is caused, for example, by errors in the angular frequency, phase, and voltage amplitude of the output AC voltage of the added static inverter. These errors arise from sampling errors, voltage measurement errors, etc.

[0008] However, when the aforementioned power conversion device connects a stopped inverter to the AC system, it prevents the stationary inverter that is already connected to the AC system from stopping. Therefore, the aforementioned power conversion device cannot handle situations such as connecting its own AC system to a commercial system, i.e., connecting an operating AC system to another operating AC system.

[0009] The purpose of this invention is to provide a power conversion device that can simultaneously supply power to the load through its own AC system while also connecting its own AC system to other AC systems.

[0010] Technical means for solving technical problems

[0011] As an example, a power conversion device is used, comprising: a power conversion circuit that converts DC power from a DC power source into AC power to form a first AC system; and a power command correction unit that determines an active power command correction amount and a reactive power command correction amount for controlling the power conversion circuit, wherein the first AC system is configured to be connected to a second AC system via a relay, the power command correction unit calculates an angular frequency deviation, a phase deviation, and a voltage deviation between the first AC system and the second AC system, and determines the active power command correction amount and the reactive power command correction amount such that the angular frequency deviation is below an angular frequency deviation threshold, the phase deviation is below a phase deviation threshold, and the voltage deviation is below a voltage deviation threshold.

[0012] Invention Effects

[0013] According to one embodiment, a power conversion device can be provided that can simultaneously supply power to a load through its own AC system while synchronously connecting its own AC system to other AC systems. Attached Figure Description

[0014] Figure 1 This is a diagram showing a structural example of the power conversion device according to the first embodiment.

[0015] Figure 2 This is a diagram illustrating an example of the hardware structure of the inverter control device according to the first embodiment.

[0016] Figure 3 This is a diagram illustrating a first example of the calculation method for the active power command correction amount and the reactive power command correction amount in the first embodiment.

[0017] Figure 4 This diagram shows the access determination unit of the power command correction unit in the first embodiment.

[0018] Figure 5 This is a diagram illustrating a second example of the calculation method for the active power command correction amount and the reactive power command correction amount in the first embodiment.

[0019] Figure 6 This is a diagram illustrating an example of the calculation method for the active power command correction amount and the reactive power command correction amount in the second embodiment.

[0020] Explanation of reference numerals in the attached figures

[0021] 1...DC power supply, 2...AC load, 3...inverter, 4...filter, 5...current sensor, 6...first voltage sensor, 7...relay, 8...AC power supply, 9...second voltage sensor, 10...inverter control unit, 10a...processor, 10b...volatile memory, 10c...non-volatile memory, 10d...storage device, 10e...interface, 10f...bus, 11...power calculation unit, 12...active power command unit, 13...reactive power command unit, 1 4…First voltage command generation unit, 15…Angular frequency command generation unit, 16…Phase command generation unit, 20…Current command generation unit, 21…Current command limiting unit, 23…Current control unit, 24…Main circuit control unit, 31…Power command correction unit, 32…Access judgment unit, 40…Autonomous AC system, 50…Operation panel, 51…Operation device, 52…Display device, 61…Information processing terminal, 62…Upper-level control device, 100…Power conversion device, PR…Program. Detailed Implementation

[0022] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. However, the present invention is not limited to the following embodiments. Furthermore, various additions or modifications can be made to the embodiments without departing from the spirit of the present invention.

[0023] [First Implementation Method]

[0024] Figure 1 This is a diagram illustrating a structural example of the power conversion device according to the first embodiment. (See diagram below.) Figure 1 As shown, the power conversion device 100 of this embodiment converts the DC power supplied by the DC power source 1 into AC power to form an autonomous AC system 40. An autonomous AC system is an AC system that determines the frequency, phase, and amplitude of the system's output voltage itself.

[0025] The power conversion device 100 first determines the frequency and phase of the output voltage of the autonomous AC system 40 to operate. The amplitude of the output voltage of the autonomous AC system 40 is determined based on the reactive power of its own inverter. The frequency of the output voltage of the autonomous AC system 40 and the phase, which is the integral value of the frequency, are determined based on the active power of its own inverter.

[0026] The autonomous AC system 40 outputs AC power to the AC load 2. Thus, the power conversion device 100 provides power from the DC power source 1 to the AC load 2. Here, the AC load 2 is a conceptual load. Therefore, specifically, the AC load 2 includes, for example, a power regulation circuit that regulates at least one of the voltage and frequency of the AC power from the autonomous AC system 40, and a load from which power is supplied. The AC load 2 is, for example, an induction motor device, a commercial air conditioning device, etc.

[0027] The power conversion device 100 includes an inverter 3, a filter 4, a current sensor 5, a first voltage sensor 6, and an inverter control device 10. The autonomous AC system 40 in the power conversion device 100 corresponds to the output side of the inverter 3. However, the filter 4, current sensor 5, and first voltage sensor 6 are not essential components of the autonomous AC system 40. Furthermore, at the AC output of the power conversion device 100, in addition to connecting the AC load 2, other power conversion devices, power conditioners (PCS), etc., that perform the same control as the power conversion device 100 can be connected. Here, the autonomous AC system 40 is an example of the "first AC system" in this application. Additionally, the inverter 3 is an example of the "power conversion circuit" in this application. The current sensor 5 is an example of the "first current sensor" in this application.

[0028] The power conversion device 100 also includes an operation panel 50. The operation panel 50 accepts various input information through user operation. The operation panel 50 includes an operation device 51 and a display device 52. The operation device 51 may be, for example, a touch panel, or an input device composed of physical components such as keys, switches, and buttons. The display device 52 may be, for example, a liquid crystal monitor, an organic EL monitor, etc.

[0029] The power conversion device 100 can also be communicatively connected to an external information processing terminal 61 via wired or wireless means, and accept input information through the operation of the operating unit of the information processing terminal 61. The information processing terminal 61 can be, for example, a computer, smartphone, or tablet terminal. The operating unit of the information processing terminal 61 can be, for example, a touch panel, touchpad, keyboard, or mouse. The operating panel 50 is not a necessary component of the power conversion device 100, but it is generally installed on the power conversion device 100. Furthermore, the power conversion device 100 can also be communicatively connected to a higher-level control device 62, receiving various input information from the higher-level control device 62. The higher-level control device 62 can be, for example, a computer, server, or a processor integrated into other power conversion devices or PCS.

[0030] DC power source 1 can be, for example, a secondary battery or capacitor such as a lithium-ion battery, nickel-metal hydride battery, or lead-acid battery, or a renewable energy source such as a solar power generation device, compressed air energy storage (CAES), or a flywheel. Alternatively, DC power source 1 can also be, for example, a DC transmission equipment, a DC microgrid, or a DC system.

[0031] Inverter 3 is constructed, for example, using a three-phase full-bridge circuit. Inverter 3 operates under the control of inverter control device 10, converting DC power input from DC power source 1 into AC power, which is then output to AC load 2 via filter 4. Filter 4 removes unwanted high-frequency components from the AC power output from inverter 3. Filter 4 is, for example, an LCL filter.

[0032] The current sensor 5 outputs a signal representing the current value of the AC power output from the inverter 3. That is, the current sensor 5 outputs a signal representing the measured current of the autonomous AC system 40. The first voltage sensor 6 outputs a signal representing the voltage value of the AC power output from the inverter 3 after passing through the filter 4. That is, the first voltage sensor 6 outputs a signal representing the measured voltage of the autonomous AC system 40. The measurement results of the current sensor 5 and the first voltage sensor 6 are input to the inverter control device 10 as the measured current value Iout and the measured voltage value Vout of the AC power output from the power conversion device 100, respectively. The measured current value Iout is an example of the "first measured current" in this application. The measured voltage value Vout is an example of the "first measured voltage" in this application.

[0033] The inverter control device 10 initiates various control processes upon receiving an input signal based on user operations on the operating device 51. For example, upon receiving a first input signal, the inverter control device 10 initiates control processes to form the autonomous AC system 40. Additionally, upon receiving a second input signal, the inverter control device 10 initiates control processes to synchronize the connection to the AC power supply 8. Furthermore, the inverter control device 10 may also initiate control processes upon receiving a user-operated input signal from an external information processing terminal 61 communicatively connected to the power conversion device 100. Alternatively, the inverter control device 10 may also initiate control processes upon receiving a control signal from an upstream control device 62 communicatively connected to the power conversion device 100.

[0034] The inverter control device 10 includes functional blocks comprising a power calculation unit 11, a reactive power command unit 13, a first voltage command generation unit 14, an angular frequency command generation unit 15, a phase command generation unit 16, a current command generation unit 20, a current command limiting unit 21, a current control unit 23, and a main circuit control unit 24. These functional blocks may also be circuit units composed of circuits. Alternatively, a processor such as a CPU or MPU may execute a predetermined program, causing the processor to function as these functional blocks. In this embodiment, the latter example will be used for explanation.

[0035] Figure 2 This section illustrates an example of the hardware structure of the inverter control device 10 according to the first embodiment. The inverter control device 10 is, for example, composed of a microcomputer or a microcontroller. The inverter control device 10 includes, for example, a processor 10a, volatile memory 10b, non-volatile memory 10c, storage device 10d, interface 10e, and bus 10f. The processor 10a, volatile memory 10b, non-volatile memory 10c, storage device 10d, and interface 10e are electrically connected to the bus 10f and can exchange data with each other. A predetermined program PR is stored in the non-volatile memory 10c. The processor 10a can implement these functional blocks by executing the program PR stored in the non-volatile memory 10c.

[0036] The program PR can be stored in storage device 10d. Additionally, volatile memory 10b is, for example, RAM. Non-volatile memory 10c is, for example, ROM, PROM, etc. Storage device 10d is, for example, SSD, HDD, etc. Processor 10a can obtain the program PR from an external source via interface 10e and store the program PR in non-volatile memory 10c or storage device 10d. Some or all of these functional blocks can also be implemented using hardware circuits such as logic ICs, FPGAs, etc.

[0037] The power calculation unit 11 calculates the active power P and reactive power Q, which represent the active and reactive components of the AC power actually output by the power conversion device 100, based on the measured current value Iout obtained from the current sensor 5 and the measured voltage value Vout obtained from the first voltage sensor 6. Furthermore, the active power P is an example of "output active power" in this application. The reactive power Q is an example of "output reactive power" in this application.

[0038] The reactive power command unit 13 generates a command value for the reactive component of the AC power output from the power conversion device 100 based on the measured voltage value Vout obtained from the first voltage sensor 6, and outputs the reactive power command value corrected by the reactive power command correction amount described later as a reactive power command (value) Q*. Specifically, the reactive power command unit 13 generates the reactive power command Q* by adding the reactive power command correction amount to the value obtained by multiplying the deviation (V0-Vout) between the rated voltage V0 (e.g., V0 = 200V) and the measured voltage value Vout by a predetermined proportional gain KQ. In addition, the reactive power command unit 13 may, for example, determine the reactive power input from an external source as the reactive power command Q*.

[0039] The first voltage command generation unit 14 generates a first voltage command E* based on the reactive power Q calculated by the power calculation unit 11 and the reactive power command Q* output from the reactive power command unit 13, which is the voltage command value before superimposing higher harmonics on the AC power output from the power conversion device 100. Specifically, the first voltage command generation unit 14 generates a first voltage command E* based on the rated voltage V0 by performing proportional-integral control (PI control) on the deviation (Q*-Q) between the reactive power command Q* and the reactive power Q.

[0040] The active power command unit 12 determines the active power command P0 of the power conversion device 100. For example, the active power command unit 12 determines the active power as an externally input value. The active power command unit 12 outputs the active power command value obtained by adding the active power command correction amount (described later) to the active power command (value) P0 as the active power command P*.

[0041] The angular frequency command generation unit 15 generates a command value for the angular frequency of the AC power output from the power conversion device 100 based on the active power P and active power command P* obtained by the power calculation unit 11, and outputs this command value as the angular frequency command ω*. Specifically, the angular frequency command generation unit 15 calculates the value obtained by multiplying the deviation (P*-P) between the active power command P* and the active power P by the reciprocal of a predetermined proportional gain, 1 / KP. The angular frequency command generation unit 15 calculates the angular frequency deviation Δω, which is given virtual inertia, by performing first-order lag and first-order lead compensation on the calculated value. Furthermore, the angular frequency command generation unit 15 generates the angular frequency command ω* by adding the angular frequency deviation Δω to the rated angular frequency ω0 (e.g., 2π×50Hz).

[0042] The phase command generation unit 16 generates a phase command θ*, which is a command value for the phase of the AC power output from the power conversion device 100, based on the angular frequency command ω* output from the angular frequency command generation unit 15. Specifically, the phase command generation unit 16 generates the phase command θ* by integrating the angular frequency command ω*. Thus, the phase command θ* based on the angular frequency command ω* can be obtained. Furthermore, the phase command θ* can be the remainder when the value obtained by integrating the angular frequency command ω* is divided by 2π.

[0043] The current command generation unit 20 generates a current command I* for the AC power output from the power conversion device 100 based on a first voltage command E* based on the rated voltage V0 generated by the first voltage command generation unit 14, a phase command θ* based on the angular frequency command ω* obtained by the phase command generation unit 16, and the measured voltage value Vout of the first voltage sensor 6. Specifically, it calculates the deviation between the value obtained by performing a dq conversion on the measured voltage value Vout based on the phase command θ* and the first voltage command E*, and calculates the current command I* based on this deviation. Thus, the current command generation unit 20 can generate a current command I* for AC power based on the angular frequency command ω* generated by the angular frequency command generation unit 15 and the predetermined rated voltage V0.

[0044] When the current command I* generated by the current command generation unit 20 exceeds a predetermined limit value, the current command limiting unit 21 limits the current command I* to bring the current command I* below the limit value. Alternatively, if it is not necessary to suppress the current command I* to below the limit value, the current command limiting unit 21 can be omitted from the inverter control device 10.

[0045] The current control unit 23 generates a voltage command V* for the AC power output from the power conversion device 100 based on the limited current command I* input from the current command limiting unit 21 and the measured current value Iout from the current sensor 5. Specifically, the current control unit 23 calculates the deviation between the value obtained by performing a dq conversion on the measured current value Iout based on the phase command θ* and the limited current command I*, and calculates the voltage command V* based on this deviation. Thus, in the current control unit 23, a voltage command V* for AC power can be generated based on the current command I* generated by the current command generation unit 20. Furthermore, the current control unit 23 is an example of a "second voltage command generation unit" in this application. Additionally, the voltage command V* is an example of a "second voltage command" in this application.

[0046] The main circuit control unit 24 controls the operation of the inverter 3 based on the voltage command V* generated by the current control unit 23 and the phase command θ* obtained by the phase command generation unit 16. At this time, the main circuit control unit 24 generates gate signals for each switching element of the inverter 3 by performing PWM control based on the voltage command V* and the phase command θ*, and outputs these gate signals to the inverter 3. Thus, the inverter 3 can be driven to perform power conversion from DC to AC power in a manner that changes the voltage and phase of the AC power output from the inverter 3 to the AC load 2 according to the voltage command V* and the phase command θ*.

[0047] Therefore, the power conversion device 100 can operate autonomously in a virtually inertial state, supplying power to the AC load 2. Here, inertia in the power conversion device refers to the ability to maintain a constant frequency relative to changes in the power system's supply and demand balance. Inertial force is the force that maintains the original frequency for a certain period even if the balance between power consumption and generation is disrupted. As renewable energy increases and the number of synchronous generators connected in parallel with the system decreases, the system's inertia decreases. By enabling the inverter to have a pseudo-inertia function, it is possible to simulate inertial action corresponding to large changes in frequency / voltage, ensuring the stability of the power system.

[0048] Such virtual inertia functionality also promises applications as follows. Virtual inertia PCS, by modifying the software of existing PCS, can cope with sharp decreases in the overall system frequency. Furthermore, inverters with virtual inertia monitor frequency / voltage and output active / reactive power corresponding to their large changes.

[0049] The AC output of the autonomous AC system 40 in the power conversion device 100, in addition to connecting to the AC load 2, can also be connected to the AC power source 8 via relay 7. The AC power source 8 is a power source whose output angular frequency, phase, and voltage cannot be controlled by the owner or user of the power conversion device 100; for example, it is a commercial power source, a diesel generator, etc. That is, the connection point of the AC power source 8 serves, for example, as the receiving point of a commercial power source or the output point of a generator. This connection point is not within the power conversion device 100 but is located externally, generally at a distance from the power conversion device 100. Furthermore, the AC power source 8 is an example of the "second AC system" in this application.

[0050] Relay 7 is either in an open state or controlled to be in an open state before the autonomous AC system 40 is synchronized with the AC power supply 8. On the other hand, relay 7 is either in a closed state or controlled to be in a closed state when the autonomous AC system 40 is synchronized with the AC power supply 8. Through this action, relay 7 serves to electrically connect the autonomous AC system 40 and the AC power supply 8 when they are in a state where they can be synchronously connected.

[0051] Here, from the perspective of power supply and demand, consider the case where an autonomous AC system, consisting of a power conversion device 100, an AC load 2, and a power conversion device or PCS that performs the same control as the power conversion device 100, is added to the AC power supply 8. In this case, to prevent overcurrent, overvoltage, etc., it is desirable to synchronously connect the autonomous AC system 40 in the power conversion device 100 to the AC power supply 8. However, the AC power supply 8 cannot control the output angular frequency, phase, and voltage. Therefore, while continuing to supply power to the AC load 2, the power conversion device 100 adjusts the frequency, phase, and voltage (amplitude) output of its own autonomous AC system 40 to match the frequency, phase, and voltage (amplitude) of the AC power supply 8, thus synchronously connecting the autonomous AC system 40 to the AC power supply 8.

[0052] Figure 3 This represents the first example of the calculation method for the active power command correction amount and the reactive power command correction amount in the first embodiment.

[0053] The power command correction unit 31 calculates the active power command correction amount ΔP* and the reactive power command correction amount ΔQ* based on the deviations in the angular frequency, phase, and voltage of the output of the autonomous AC system 40 and the AC power supply 8, and sends them to the active power command unit 12 and the reactive power command unit 13, respectively. Specifically, the power command correction unit 31 calculates the output angular frequency ωout, phase θout, and voltage amplitude |Vout| of the power conversion device 100 based on the output of the first voltage sensor 6, i.e., the measured voltage value Vout. Here, the output angular frequency ωout is an example of the "first measured angular frequency" in this application. The phase θout is an example of the "first measured phase" in this application. The measured voltage value Vout is an example of the "first measured voltage" in this application.

[0054] Furthermore, the power command correction unit 31 calculates the angular frequency ωgrid, phase θgrid, and voltage amplitude |Vgrid| of the AC power supply 8 based on the measured voltage value Vgrid obtained from the output of the second voltage sensor 9 installed on the AC power supply 8 side of the relay 7. Then, the power command correction unit 31 calculates the angular frequency deviation Δω = ωgrid - ωout, the phase deviation Δθ = θgrid - θout, and the voltage deviation ΔV = |Vgrid| - |Vout|. The value obtained by proportional-integral control (PI control) of the sum of the phase deviation Δθ and the angular frequency deviation Δω is used as the active power command correction amount ΔP*, and the value obtained by proportional-integral control of the voltage deviation ΔV is used as the reactive power command correction amount ΔQ*. Here, the angular frequency ωgrid is an example of the "second measured angular frequency" in this application. The phase θgrid is an example of the "second measured phase" in this application. The measured voltage value Vgrid is an example of the "second measured voltage" in this application.

[0055] Furthermore, the angular frequency deviation Δω is the difference between the angular frequency ωgrid and the output angular frequency ωout. The phase deviation Δθ is the difference between the phase θgrid and the phase θout. The voltage deviation ΔV is the difference between the measured voltage (amplitude) value |Vgrid| and the output voltage (amplitude) value |Vout|. Additionally, the measured voltage value Vgrid is an example of the "second measured voltage" in this application. The phase θgrid is an example of the "second measured phase" in this application. Furthermore, the angular frequency ωgrid is an example of the "second measured phase" in this application.

[0056] As described above, the active power command unit 12 performs corrections using the active power command correction amount ΔP*. Specifically, the active power command unit 12 calculates the active power command P* based on P* = P0 + ΔP* and outputs it. As a result, for example, when ΔP* > 0, the power conversion device 100 increases the active power output. Therefore, the output angular frequency ωout increases, the phase θout increases, and thus the angular frequency deviation Δω and the phase deviation Δθ decrease.

[0057] As described above, the reactive power command unit 13 performs a correction using the reactive power command correction amount ΔQ*. Specifically, the reactive power command unit 13 calculates the reactive power command (value) Q* based on Q* = KQ(V0 - Vout) + ΔQ* and outputs it. As a result, for example, when ΔQ* > 0, the power conversion device 100 increases the reactive power output. Therefore, the voltage amplitude |Vout| increases, and the voltage deviation ΔV decreases.

[0058] Here, we consider the case where relay 7 has an automatic synchronization connection function. That is, we imagine that relay 7 detects the angular frequency or frequency, phase, and voltage at its two ends, and automatically closes when the frequency difference, phase difference, and voltage difference at both ends are within a specified range. Through the power command correction unit 31 described above, the frequency difference, phase difference, and voltage difference between the output of the autonomous AC system 40 (i.e., the power conversion device 100) and the AC power supply 8 decrease. When the specified connection conditions are met, relay 7 automatically closes. Thus, the autonomous AC system 40 in the power conversion device 100 is synchronously connected to the AC power supply 8.

[0059] The access conditions are that the angular frequency deviation Δω, phase deviation Δθ, and voltage deviation ΔV between the output of the autonomous AC system 40 and the output of the AC power supply 8 are all below a preset threshold. That is, the access conditions are that the angular frequency deviation Δω is below the angular frequency deviation threshold Δωth, the phase deviation Δθ is below the phase deviation threshold Δθth, and the voltage deviation ΔV is below the voltage deviation threshold ΔVth.

[0060] On the other hand, consider the case where relay 7 does not have an automatic synchronization connection function, but is configured to be in a closed state when a connection signal is received. In this case, when the connection conditions are met, the power conversion device 100 sends a connection signal to relay 7. Specifically, as follows... Figure 4 As shown, the power command correction unit 31 includes an access determination unit 32. The access determination unit 32 monitors the angular frequency deviation Δω, phase deviation Δθ, and voltage deviation ΔV. When all these deviations are below a preset threshold, it determines that the access conditions are met (hereinafter also referred to as access conditions met). When the access determination unit 32 determines that the access conditions are met, it outputs and sends an access signal to the relay 7.

[0061] As a specific example of the access conditions, regarding angular frequency deviation, |Δω|≤2π×0.05 [rad / s] is considered; regarding phase deviation, |Δθ|≤0.1 [rad] is considered; and regarding voltage deviation, |ΔV|≤5 [V] is considered. That is, the angular frequency deviation threshold Δωth ​​is, for example, 2π×0.05 [rad / s], the phase deviation threshold Δθth is, for example, 0.1 [rad], and the voltage deviation threshold ΔVth is, for example, 5 [V].

[0062] Furthermore, when determining whether the access conditions are met and sending the access signal, the determination and sending can also be performed when the angular frequency deviation Δω, phase deviation Δθ, and voltage deviation ΔV are all below a predetermined threshold for a predetermined period of time (e.g., 1 second). That is, the access determination unit 32 can determine that the access conditions are met and send the access signal to the relay 7 when the access conditions are met, such that the angular frequency deviation Δω is below the angular frequency deviation threshold Δωth, the phase deviation Δθ is below the phase deviation threshold Δθth, and the voltage deviation ΔV is below the voltage deviation threshold ΔVth, or when the state of meeting the access conditions has lasted for a predetermined time.

[0063] Upon receiving a synchronization access preparation command, the power command correction unit 31 calculates the active power command correction amount ΔP* and the reactive power command correction amount ΔQ*, as described above, and continuously sends them to the active power command unit 12 and the reactive power command unit 13, respectively. The calculation / sending cycle is, for example, the control cycle of the inverter control device 10. The synchronization access preparation command is sent to the power command correction unit 31 by the user of the power conversion device 100 using the operation panel 50 of the power conversion device 100, the operation unit of the information processing terminal 61 that can communicate with the power conversion device 100, etc. Alternatively, the synchronization access preparation command is sent to the power command correction unit 31 from the upper-level control device 62 that can communicate with the power conversion device 100. The synchronization access preparation command can also be sent through control processing in the upper-level control device 62 that can communicate with the power conversion device 100.

[0064] When the power command correction unit 31 receives the synchronization completion information of the AC power source 8 from the relay 7, it ends the calculation and transmission of the active power command correction amount ΔP* and the reactive power command correction amount ΔQ*. Alternatively, the power command correction unit 31 may end the calculation and transmission of the active power command correction amount ΔP* and the reactive power command correction amount ΔQ* after a certain period of time has elapsed since receiving the synchronization completion information of the AC power source 8. Or, the power command correction unit 31 may end the calculation and transmission of the active power command correction amount ΔP* and the reactive power command correction amount ΔQ* while continuously receiving the synchronization completion information of the AC power source 8 for a certain period of time. This allows for more stable synchronization. Furthermore, if the relay 7 does not have an automatic synchronization connection function, and the power conversion device 100 sends a relay connection signal to the relay 7, the calculation and transmission may end when the connection judgment unit 32 sends a relay connection signal, or after a certain period of time has elapsed since sending the relay connection signal.

[0065] Figure 5 This is a diagram illustrating a second example of the calculation method for the active power command correction and reactive power command correction in the first embodiment. (See diagram for example.) Figure 5As shown, in the calculation method of the second example of the first embodiment, the angular frequency command ω*, phase command θ*, and voltage command amplitude |V*| of the power conversion device 100 are used instead of the output angular frequency ωout, phase θout, and voltage amplitude |Vout| of the power conversion device 100. Therefore, with... Figure 3 Similarly, the calculation method of the first example in the first embodiment shown can also calculate the active power command correction amount ΔP* and the reactive power command correction amount ΔQ*.

[0066] According to this first embodiment of the power conversion device 100, it is possible to continue supplying power to the AC load 2 while simultaneously connecting the autonomous AC system 40 included in the power conversion device 100 to the AC power source 8.

[0067] [Second Implementation]

[0068] In the second embodiment, the hardware structure of the power conversion device 100 is the same as that of the first embodiment, but the calculation methods of the active power command correction amount and the reactive power command correction amount in the power command correction unit 31 are different.

[0069] Figure 6 This section illustrates an example of the calculation method for the active power command correction and reactive power command correction in the second embodiment. In this embodiment, descriptions of parts identical to those in the first embodiment are appropriately omitted.

[0070] The autonomous AC system 40 included in the power conversion device 100, similar to that in the first embodiment, continuously supplies power to the AC load 2 while simultaneously connecting to the AC power source 8. In the case of a large-scale user-side device such as a microgrid or factory, the AC power source 8 and the relay 7 are sometimes located far from the power conversion device 100. For example, in the case where the AC power source 8 is a commercial system, the relay 7 is a grid-connected relay at the power receiving point, and the power conversion device 100 is installed inside a user building, it is assumed that the power conversion device 100 and the relay 7 are several meters to several hundred meters apart.

[0071] At this time, as shown in the first embodiment, a delay occurs until the power conversion device 100 receives the output of the second voltage sensor 9, i.e., the measured voltage value Vgrid, which is provided on the AC power supply 8 side of the relay 7. Furthermore, in order to avoid providing a dedicated wiring directly connecting the power conversion device 100 and the second voltage sensor 9, and instead communicate the measured voltage value Vgrid of the second voltage sensor 9 to the power conversion device 100 via the upper-level control device 62, a delay corresponding to that via the upper-level control device 62 occurs.

[0072] When such a delay occurs, at the moment when the power conversion device 100 receives the measured voltage value Vgrid from the second voltage sensor 9, the actual phase of the AC power supply 8 is ahead of the phase θgrid obtained from the received measured voltage value Vgrid. Therefore, even if the power conversion device 100 is phase synchronized with the phase θgrid, a phase difference will actually occur. If the relay 7 is closed in this state, undesirable power reception may occur.

[0073] Therefore, in Figure 6 In the example of the calculation method for the active power command correction and reactive power command correction in the second embodiment shown, in order to correct the phase θ by an amount corresponding to the reception delay, a term for the leading phase correction θadj is added based on the first example of the first embodiment. By performing leading phase correction on the phase θgrid, the active power command correction ΔP* that takes into account the aforementioned delay is determined. Specifically, the leading phase correction θadj is used to make the phase deviation Δθ = (θgrid + θadj) - θout. Furthermore, the leading phase correction θadj is an example of the "phase correction amount" in this application.

[0074] The leading phase correction θadj is expressed, for example, by the signal transmission delay time T1 from the second voltage sensor 9 to the power conversion device 100, according to the following equation (1), and updated over a period of T1. That is, the power command correction unit 31 can obtain θadj according to equation (1) over a period of T1. That is, for the angular frequency ωgrid of the voltage of the AC power supply 8, the advancing phase is obtained by integrating the amount of the transmission delay time T1 over the time t = 0 to T1, and this is used as the leading phase correction θadj. Regarding the signal transmission delay time T1, for example, the required time for actual signal transmission and reception is measured multiple times, and representative values ​​of the measured required times, such as average value, median value, etc., are selected.

[0075] [Formula 1]

[0076]

[0077] However, if the above method is used, the signal transmission and reception delay time T1 needs to be measured in advance. Therefore, as an alternative, consider the method in which the power command correction unit 31 changes the phase correction amount θadj according to the following formula (2) to find an appropriate value for the phase correction amount θadj.

[0078] [Equation 2]

[0079]

[0080] Here, relay 7 has an automatic synchronization function. That is, relay 7 is configured to automatically become closed when the angular frequency deviation Δω, phase deviation Δθ, and voltage deviation ΔV are all below their respective threshold values. Furthermore, consider the scenario where relay 7 outputs a response signal when it becomes closed.

[0081] The leading phase correction θadj can be expressed, for example, using the elapsed time t from when the access determination unit 32 determines that the access condition is met, and the leading phase correction gain Kθ, by equation (2). When the access determination unit 32 does not determine that the access condition is met, t = 0.

[0082] The power conversion device 100 first synchronizes its phase with the phase θgrid before phase advance correction. If the angular frequency deviation Δω, phase deviation Δθ, and voltage deviation ΔV meet the access conditions, the access judgment unit 32 determines that the access conditions are met. Then, after the moment when the power command correction unit 31 makes this judgment, it starts to perform phase advance correction on the phase θgrid according to formula (2). That is, after a predetermined time period, when the angular frequency deviation Δω is below the angular frequency deviation threshold Δωth, the phase deviation Δθ is below the phase deviation threshold Δθth, and the voltage deviation ΔV is below the voltage deviation threshold ΔVth, the power command correction unit 31 adds a phase advance correction amount θadj to the phase θgrid to perform phase advance correction. The power command correction unit 31 increases the phase advance correction amount θadj according to the length of the elapsed time t from the start of phase advance correction. In addition, at the moment when the phase advance correction amount θadj is added to the phase θgrid, as described above, a phase difference is generated between the output phase of the power conversion device 100 and the phase of the AC power supply 8, and the relay 7 will not be in a closed state.

[0083] By adding the leading phase correction θadj, the output phase of the autonomous AC system 40 in the power conversion device 100 begins to lead, and the actual phase difference between the autonomous AC system 40 and the AC power supply 8 gradually decreases. When the angular frequency deviation Δω, phase deviation Δθ, and voltage deviation ΔV meet the automatic connection conditions of the relay 7, the relay 7 itself becomes closed, and the autonomous AC system 40 in the power conversion device 100 is synchronously connected to the AC power supply 8. At this time, the relay 7 sends a response signal to the inverter control device 10.

[0084] When the inverter control device 10 receives a response signal from the relay 7, the power command correction unit 31 can maintain the value of the leading phase correction amount θadj at this time, stop the calculation of ΔP* and ΔQ*, and set ΔP* and ΔQ* to 0 respectively.

[0085] Furthermore, the power command correction unit 31 can also provide a margin of time for maintaining the value of θadj, so that the output of the inverter 3, i.e., the autonomous AC system 40, can be stably connected to the AC power supply 8. That is, the power command correction unit 31 can also maintain the value of θadj for a period of time, such as several seconds, after receiving the response signal from the relay 7, and then stop the calculation of ΔP* and ΔQ*, setting ΔP* and ΔQ* to 0 respectively.

[0086] In addition, after stopping the calculation of ΔP* and ΔQ*, the power command correction unit 31 continuously or at intervals monitors ΔV, Δω, and Δθ. When ΔV, Δω, and Δθ no longer meet the access conditions, the power command correction unit 31 restarts the calculation of ΔP* and ΔQ* by making θadj change according to the time t elapsed, as per equation (2).

[0087] Furthermore, the phase advance correction θadj increases monotonically from 0 to 2π (rad) based on the elapsed time t, but 2π is the upper limit. When the value of θadj reaches the upper limit of 2π, the power command correction unit 31 considers that the relay 7 has been closed during this period and stops the calculation of ΔP* and ΔQ*. If the relay 7 does not send the response signal when synchronization is activated to the inverter control device 10, the power command correction unit 31 cannot detect the open or closed state of the relay 7. In this case, even if the relay 7 is closed, the power command correction unit 31 adds the phase advance correction θadj and continues to perform the calculation of ΔP* and ΔQ*, and stops the calculation of ΔP* and ΔQ* when the value of θadj reaches the upper limit of 2π.

[0088] According to this second embodiment of the power conversion device 100, it is possible to continuously supply power to the AC load 2 while simultaneously connecting the autonomous AC system 40 included in the power conversion device 100 to an AC power source 8 located at a remote distance. Furthermore, in this embodiment, the phase correction amount θadj can also be the remainder when θadj is divided by 2π.

[0089] Furthermore, the control of the power conversion device 100 in the above embodiment can also be performed, for example, to control its operation in parallel with a commercial system. Therefore, the AC system within the power conversion device 100 is not limited to an autonomous AC system of autonomous operation.

Claims

1. A power conversion device, characterized in that, include: A power conversion circuit that converts DC power from a DC power source into AC power to form a first AC system; and The power command correction unit determines the active power command correction amount and reactive power command correction amount of the first AC system used in the control of the power conversion circuit. The first AC system is configured to be connected to the second AC system via a relay. The power command correction unit calculates the angular frequency deviation, phase deviation, and voltage deviation between the first AC system and the second AC system. The power command correction unit determines the active power command correction amount and the reactive power command correction amount so that the angular frequency deviation becomes below the angular frequency deviation threshold, the phase deviation becomes below the phase deviation threshold, and the voltage deviation becomes below the voltage deviation threshold.

2. The power conversion device according to claim 1, characterized in that, include: A first voltage sensor that outputs a signal representing the first measured voltage of the first AC system; A first current sensor that outputs a signal representing the first measured current of the first AC system; The power calculation unit calculates and outputs active power and reactive power based on the first measured voltage obtained from the first voltage sensor and the first measured current obtained from the first current sensor. The active power command unit determines the active power command of the power conversion device; An angular frequency command generation unit generates an angular frequency command based on the output active power and the active power command. The phase command generation unit generates a phase command based on the angular frequency command; The reactive power command unit determines the reactive power command based on the first measured voltage or the external input value; The first voltage command generation unit generates a first voltage command based on the output reactive power and the reactive power command; The current command generation unit generates a current command based on the first measured voltage and the first voltage command; A current command limiting unit that limits the current command and outputs it; and The second voltage command generation unit generates a second voltage command based on the current command limited by the current command limiting unit and the first measured voltage. The power conversion circuit is controlled based on the second voltage command. The active power command unit will use the active power command correction amount to correct the active power command value as the active power command output. The reactive power command unit will use the reactive power command correction amount to correct the reactive power command value as the reactive power command output.

3. The power conversion device according to claim 2, characterized in that: The power command correction unit performs the following processing: Based on the first measured voltage, the first measured angular frequency and the first measured phase of the first AC system are calculated. Based on the second measured voltage of the second AC system obtained from the second voltage sensor of the second AC system, the second measured angular frequency and the second measured phase are calculated. The difference between the first measured angular frequency and the second measured angular frequency is calculated as the angular frequency deviation. The difference between the first measurement phase and the second measurement phase is calculated as the phase deviation. The difference between the amplitude of the first measured voltage and the amplitude of the second measured voltage is calculated as the voltage deviation.

4. The power conversion device according to claim 1, characterized in that: The power command correction unit calculates the active power command correction amount based on the phase deviation and the angular frequency deviation, and Based on the voltage deviation, the reactive power command correction amount is calculated.

5. The power conversion device according to claim 4, characterized in that: The power command correction unit obtains the active power command correction amount by performing proportional control or proportional-integral control on the sum of the value obtained by proportional control of the phase deviation and the angular frequency deviation. The reactive power command correction amount is obtained by performing proportional control or proportional-integral control on the voltage deviation.

6. The power conversion device according to claim 3, characterized in that: The power command correction unit calculates the phase deviation and the active power command correction amount based on the phase obtained by performing a phase correction on the second measurement phase.

7. The power conversion device according to claim 6, characterized in that: The power command correction unit performs phase correction by adding a phase correction amount to the second measured phase after the predetermined time period, when the angular frequency deviation falls below the angular frequency deviation threshold, the phase deviation falls below the phase deviation threshold, and the voltage deviation falls below the voltage deviation threshold. The phase correction amount is increased based on the elapsed time since the start of the phase correction.

8. The power conversion device according to claim 2, characterized in that: The power command correction unit performs the following processing: Based on the second measured voltage of the second AC system obtained from the second voltage sensor of the second AC system, the second measured angular frequency and the second measured phase are calculated. The difference between the frequency of the calculated angular frequency command and the second measured angular frequency is taken as the angular frequency deviation. The difference between the phase of the phase command and the second measured phase is taken as the phase deviation. The difference between the amplitude of the first voltage command or the second voltage command and the amplitude of the second measured voltage is calculated as the voltage deviation.

9. The power conversion device according to claim 1, characterized in that: The relay is configured to automatically close when the angular frequency deviation, the phase deviation, and the voltage deviation fall below their respective threshold values.

10. The power conversion device according to claim 1, characterized in that: When the access conditions are met, namely, the angular frequency deviation is below the angular frequency deviation threshold, the phase deviation is below the phase deviation threshold, and the voltage deviation is below the voltage deviation threshold, or when the access conditions are met for a predetermined time, the power command correction unit outputs an access signal to the relay.

11. The power conversion device according to claim 10, characterized in that: The relay is configured to become closed when it receives the access signal.

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