Power System

Abstract

To suppress harmonic resonance in a power conversion device.SOLUTION: A power system comprises a plurality of power conversion devices for performing conversion between AC power and DC power. In a harmonic reference excessive state, the power system outputs a predetermined operating state change command for movement from the harmonic reference excessive state to a harmonic normal state to the plurality of power conversion devices. During this process, the power system gradually increases the number of target power conversion devices for which the operating state change command is issued until they reach the harmonic normal state.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] FIELD OF THE DISCLOSURE Embodiments of the present invention relate to power systems. [Background technology]

[0002] The power system includes, for example, a plurality of power conversion devices that convert AC power and DC power. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 6157880 Summary of the Invention [Problem to be solved by the invention]

[0004] In power conversion equipment connected to a grid, harmonic resonance occurs due to the interaction between the grid impedance caused by the wiring on the grid side, power load, etc. and the control of the power conversion equipment, causing the operation to become unstable and, in some cases, leading to a protective shutdown. For example, in systems such as microgrids and offshore wind power generation systems in which many power conversion equipment are linked, there is a high risk of serious resonance troubles due to their interactions.

[0005] Furthermore, although the power conversion device is equipped with a harmonic filter, when the operating state changes, the system function of the harmonic filter changes, and there is a risk of harmonic resonance occurring.

[0006] Therefore, an object of this embodiment is to provide a power system capable of suppressing harmonic resonance in a power conversion device. [Means for solving the problem]

[0007] A power system according to an embodiment includes a plurality of power conversion devices that convert AC power and DC power. The power conversion devices include a switch that switches between conduction and non-conduction with an AC power source, a power converter including a switching element that switches a connection with a DC device that is a device that operates with DC power, and a converter control unit that gives an operation command to the switching element. The power system includes a harmonic detection unit that is connected to the power conversion devices and detects whether the state is a harmonic standard exceeding state in which harmonic components in a predetermined frequency range of an AC voltage and / or an AC current exceed a predetermined standard, or a harmonic normal state in which the harmonic components are equal to or lower than the predetermined standard, and a command function unit that outputs a predetermined operating state change command to the plurality of power conversion devices in the case of the harmonic standard exceeding state to transition from the harmonic standard exceeding state to the harmonic normal state, and at that time, gradually increases the number of the power conversion devices to which the operating state change command is output until the harmonic normal state is reached. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is an overall configuration diagram of a power system according to a first embodiment. [Diagram 2] FIG. 2 is a flowchart showing the process performed by the power system of the first embodiment. [Diagram 3] FIG. 3 is an explanatory diagram of a switching operation in the first embodiment. [Figure 4] FIG. 4 is a graph relating to the voltage control mode and the current control mode in the first embodiment. [Diagram 5] FIG. 5 is a diagram illustrating a functional configuration of the harmonic detection unit according to the first embodiment. [Figure 6] FIG. 6 is a diagram illustrating a functional configuration of the converter control unit according to the first embodiment. [Figure 7] FIG. 7 is a diagram illustrating a functional configuration of the AC information calculation unit according to the first embodiment. [Figure 8] FIG. 8 is a diagram showing a functional configuration of the converter control unit in the voltage control mode in the first embodiment. [Figure 9]FIG. 9 is a diagram illustrating a functional configuration of the voltage control unit in the first embodiment. [Figure 10] FIG. 10 is an overall configuration diagram of a power system according to the second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments (first and second embodiments) of the power system of the present invention will be described with reference to the accompanying drawings. Note that, hereinafter, the power load will be simply referred to as the load.

[0010] (First embodiment) 1 is an overall configuration diagram of a power system S of a first embodiment. The power system S includes an AC power source 1, a system configuration 2, a plurality of power conversion devices 3, a DC device 4 provided for each of the power conversion devices 3, and a control system 5.

[0011] The AC power supply 1 generates AC power.

[0012] The system configuration 2 is wiring, loads, etc. on the system side, and generates a system impedance.

[0013] The power conversion device 3 is provided at an interconnection point between the AC system and the DC device 4, and converts AC power supplied by the AC system into DC power supplied by the DC device 4, and vice versa. The power conversion device 3 includes a voltage transformer VT, a switch CB, an interconnection inductor I, a harmonic filter F, an instrument current transformer CT, a converter control unit 31, and a power converter 32.

[0014] The switch CB switches between conduction and non-conduction with the AC power source 1 .

[0015] The converter control unit 31 executes various controls such as giving operation commands to the switching elements of the power converter 32. The converter control unit 31 generates a gate command gate for controlling the switching operation of the power converter 32, using an AC voltage Vs obtained by a voltage transformer VT connected to a system interconnection point P between the system configuration 2 generating a system impedance and the interconnection inductor I, an AC current Is obtained by a current transformer CT provided between the interconnection inductor I and the power converter 32, and a command signal from a command function unit 52 of the control system 5.

[0016] The converter control unit 31 realizes each function by, for example, a hardware processor such as a CPU (Central Processing Unit) executing a program (software) stored in a storage unit (not shown). Also, some or all of the functions may be realized by hardware such as an LSI (Large Scale Integration), an ASIC (Application Specific Integrated Circuit), or an FPGA (Field Programmable Gate Array), or may be realized by a combination of software and hardware.

[0017] The power converter 32 includes a switching element that switches the connection with the DC device 4. The power converter 32 converts AC power and DC power mutually based on the control of the converter control unit 31. The power converter 32 is a circuit configured using self-extinguishing switching elements such as IGBTs (Insulated Gate Bipolar Transistors) and MOSFETs (Metal-Oxide-Semiconductor Field Effect Transistors).

[0018] The DC device 4 is a device that operates on DC power, and is, for example, a storage battery, a generator, a load, or the like.

[0019] The control system 5 is a system that executes control of the power conversion device 3, and includes a harmonic detection unit 51 and a command function unit 52.

[0020] The harmonic detection unit 51 inputs information such as voltage, current, and values ​​based on the voltage and current as the system state. This information may be obtained by communication from each power conversion device 3, or may be obtained from a separate detector.

[0021] The harmonic detection unit 51 detects, based on the input information, whether the power electronics devices 3 are in a harmonic exceeding standard state, in which the harmonic components in a predetermined frequency range of the AC voltage and / or AC current exceed a predetermined standard, or in a harmonic normal state, in which the harmonic components are equal to or lower than the predetermined standard. Note that the threshold value for determining whether the harmonic exceeding standard state has occurred and the threshold value for determining whether the harmonic normal state has occurred may be the same or different (details will be described later).

[0022] In the case of a harmonic standard exceeding state, the command function unit 52 outputs a predetermined operating state change command to the multiple power electronics devices 3 to transition from the harmonic standard exceeding state to a harmonic normal state, and at that time, gradually increases the number of power electronics devices 3 to which the operating state change command is output until the harmonic normal state is reached. In other words, the number of power electronics devices 3 to which the operating state change command is output is not increased all at once, but is increased stepwise if the transition has not occurred while successively determining whether the transition has occurred from the harmonic standard exceeding state to the harmonic normal state.

[0023] For example, in the case of a harmonic standard exceeding state, the command function unit 52 outputs a switching operation command for switching the switching element as an operation state change command to the power conversion device 3 in which the switch CB is conductive and the switching operation of the connection with the DC device 4 by switching of the switching element is stopped. The power conversion device 3 that has received the switching operation command is operated, for example, substantially at zero power.

[0024] When the harmonic standard is exceeded, the command function unit 52 outputs a switching operation command to a power conversion device selected from among the power conversion devices 3 in which the switch CB is conductive and the switching operation of the connection to the DC device 4 by switching of the switching element has stopped, based on a priority corresponding to the state of the connected DC device 4.

[0025] When the DC device 4 is a storage battery, the command function unit 52 calculates charging / discharging needs based on the current state of charge of the connected storage battery and deterioration characteristics related to the state of charge, selects a power conversion device 3 with a higher priority as the charging / discharging needs are higher, and outputs a switching operation command to the selected power conversion device 3 to execute a charging / discharging operation. For example, if deterioration is low at a charging rate of 80% in a storage battery, the charging needs (priority) are higher the charging rate is lower than 80%, and the discharging needs (priority) are higher the charging rate is higher than 80%.

[0026] When the DC device 4 is a generator, the command function unit 52 calculates the power generation efficiency from the current operating state of the generator, selects the power conversion device 3 with a higher power generation efficiency as the higher the priority, and outputs a switching operation command to the selected power conversion device 3. For example, in the case of PV (Photovoltaic: solar power generation) or wind power generators, the closer to the maximum efficiency operating point, the higher the priority.

[0027] When the DC device is the load, the command function unit 52 calculates the power supply needs from the current operating state of the load, selects the power conversion device 3 as the higher the power supply needs are, and outputs a switching operation command to the selected power conversion device 3. For example, when the load is a temperature adjustment device, the greater the difference between the current temperature and the set temperature, the higher the power supply needs (priority).

[0028] The above describes the case where the operating state change command is a switching operation command. Next, a description will be given of the case where the operating state change command is a command to change from the current control mode to the voltage control mode.

[0029] The converter control unit 31 is capable of switching between a current control mode in which the current of the AC power supply 1 is feedback-controlled and a voltage control mode in which the phase of the voltage output to the AC power supply side is adjusted in synchronization with the voltage of the AC power supply 1 without directly feedback-controlling the current of the AC power supply 1. In this case, when the harmonic standard is exceeded, the command function unit 52 outputs an operating state change command from the current control mode to the voltage control mode to the power conversion device 3 operating in the current control mode.

[0030] Furthermore, as an emergency measure, the command function unit 52 may open the switch CB when the number of power electronics devices 3 to which the operation state change command is output due to the harmonic standard exceeding state is equal to or greater than a predetermined threshold value and the harmonic standard exceeding state does not transition to a harmonic normal state within a predetermined period. In other words, if harmonic resonance continues even after changing the operation states of a certain number of power electronics devices 3, some or all of the multiple switches CB are opened to prevent the unstable state from continuing. This prevents the harmonic filter F from acting on the system side, for example, and the harmonic stability of the system can be restored.

[0031] 2 is a flowchart showing processing by the power system S of the first embodiment. In step S1, the harmonic detection unit 51 of the control system 5 determines whether or not the harmonic standard is exceeded, and if Yes, the process proceeds to step S2, and if No, the process returns to step S1.

[0032] In step S2, the command function unit 52 outputs an operating state change command to one power electronics device 3. In this case, for example, the target power electronics device 3 is selected according to the various priorities described above.

[0033] Next, in step S3, the command function unit 52 determines whether or not a predetermined time has elapsed, and if Yes, the process proceeds to step S4, and if No, the process returns to step S3.

[0034] In step S4, the harmonic detection unit 51 determines whether the harmonic normal state has been reached. If Yes, the process ends; if No, the process returns to step S2.

[0035] After the process ends, it returns to start, step S1 again, and continuously monitors whether the harmonic reference exceeding state exists.

[0036] FIG. 3 is an explanatory diagram of the switching operation in the first embodiment and is an equivalent circuit diagram of the power conversion device 3, system impedance, etc. As shown in FIG. 3, the AC system is composed of, for example, an equivalent inductance Lgrid from the AC power supply 1 to the system connection point P. Also, the impedance when looking from the system connection point P to the AC power supply 1 side is referred to as the system impedance Zgrid.

[0037] Also, the impedance when looking from the system connection point P to the power converter 32 side is referred to as the converter impedance Zvsc. Zvsc is an impedance based on the connection inductor I (Lvsc), the harmonic filter F, the characteristics of the converter control, etc.

[0038] For example, when the switch CB is conducting and the power converter 32 is in the switching (Zsw) stop state, the current Is of the power converter 32 becomes 0, and resonance occurs due to Lgrid and the harmonic filter F.

[0039] On the other hand, when the switch CB is conducting and the power converter 32 is in the switching (Zsw) operation state, the current Is of the power converter 32 is not equal to 0, and with the resistance action on the power converter 32 side (-90 degrees < the phase of Zvsc < +90 degrees), the resonance due to Lgrid and the harmonic filter F is mitigated.

[0040] Note that even when the power conversion device 3 is in a substantially zero-power operation state, the resistance action on the power converter 32 side can be obtained.

[0041] 4 is a graph relating to the voltage control mode and the current control mode in the first embodiment. In the current control mode, the converter impedance Zvsc has a phase outside the range of ±90 degrees (−90 degrees to 90 degrees), and the harmonic resonance is amplified by the negative resistance.

[0042] On the other hand, the converter impedance Zvsc' in the voltage control mode does not deviate from the phase range of ±90 degrees (-90 degrees to 90 degrees) and the negative resistance can be made small, so that harmonic resonance is less likely to be amplified.

[0043] That is, in the current control mode, a frequency range in which negative resistance is exhibited may occur mainly due to the effects of high gain and control delay. On the other hand, in the voltage control mode, the negative resistance can be reduced because the current is not directly controlled.

[0044] Therefore, by using a command to change from the current control mode to the voltage control mode as the operating state change command, it is possible to suppress harmonic resonance.

[0045] 5 is a diagram showing a functional configuration of the harmonic detection unit 51 of the first embodiment. The conversion unit 511 inputs information on three-phase (R phase, S phase, T phase) voltage or current as the system state. The conversion unit 511 also converts the reference phase theta=2πf s ×t(f s A conversion unit 511 converts the system frequency component into a DC amount and outputs an effective axis component D and a reactive axis component Q.

[0046] The digital filter 512 is, for example, a high-pass filter that removes the direct current and outputs only the harmonic components. By devising the characteristics of the digital filter 512, signals in any frequency range can be detected.

[0047] The sum of harmonics in a specified frequency range is obtained by taking the sum of squares (symbol 513) of the output of the digital filter 512. This is compared with the square value (symbol 515) of the reference (symbol 514) in a comparator 516 to determine whether the harmonic standard is exceeded or the harmonic normal state is present.

[0048] In addition, there may be only one harmonic reference as shown in the figure, or comparator 516 may have a hysteresis characteristic so that a first threshold value used to determine whether the harmonic normal state is changed to an over-harmonic reference state and a second threshold value used to determine whether the harmonic normal state is changed to an over-harmonic reference state are different.

[0049] Furthermore, the present invention is not limited to the example shown in FIG. 5, and other harmonics detection methods may be used, such as a method of calculating and comparing the amplitude of a predetermined frequency using a Fourier transform or the like.

[0050] Fig. 6 is a diagram showing a functional configuration of the converter control unit 31 of the first embodiment. An example of the current control mode will be described with reference to Fig. 6. First, the AC information calculation unit 311 acquires the AC system voltage phase (system interconnection point voltage). This allows the execution of calculation control synchronized with the AC system at high speed.

[0051] The current control unit 312 executes, for example, a general non-interfering current control, for example, feedback control of the AC current by a control calculation synchronized with the AC system voltage phase.

[0052] A current control unit 312 compares the AC current with an AC current command value based on active power and reactive power command values, and outputs a voltage command value based on a value obtained by multiplying the deviation by an AC current control gain.

[0053] In this way, active power and reactive power are adjusted by controlling the AC current. Note that, depending on the design of the AC current control gain and the control error due to the delay time of the current control calculation, negative resistance occurs in the converter impedance, leading to high-frequency resonance.

[0054] The gate signal generating unit 313 generates a gate signal for controlling the switching element based on the voltage command value, for example, by a triangular wave carrier comparison method.

[0055] Next, Fig. 7 is a diagram showing a functional configuration of the AC information calculation unit 311 (Fig. 6) of the first embodiment. First, the conversion unit 81 acquires information indicating the grid interconnection point voltages (R-phase voltage Vsr, S-phase voltage Vss, and T-phase voltage Vst) detected by the voltage detector. The conversion unit 81 converts (calculates) the acquired R-phase voltage Vsr, S-phase voltage Vss, and T-phase voltage Vst into an AC grid effective voltage Vsd and an AC grid reactive voltage Vsq using equation (1). Note that the AC grid voltage phase theta is a value output by an oscillator 85 described later, and is a value indicating the voltage phase of a certain reference phase (in this example, the R phase) of the AC grid.

[0056]

number

[0057] The PI calculation unit 82 calculates a frequency difference (hereinafter, frequency difference Δfpll) between the frequency of the AC system voltage to which the power converter 32 is connected and a reference AC system frequency fs0 (reference symbol 83) based on the AC system reactive voltage Vsq converted by the conversion unit 81. The frequency difference Δfpll takes a positive value when the frequency of the AC system voltage is higher than the reference AC system frequency fs0, and takes a negative value when the frequency is lower than the reference AC system frequency fs0. The reference AC system frequency fs0 is the rated frequency of the connected AC system, and is a constant of, for example, 50 [Hz] or 60 [Hz]. The frequency difference Δfpll continues to increase or decrease until the calculated value of the AC system reactive voltage Vsq input to the PI calculation unit 82 becomes zero, and converges to the value of the difference between the actual AC system frequency and the reference AC system frequency fs0.

[0058] The adder 84 adds the frequency difference Δfpll calculated by the PI calculator 82 to the reference AC system frequency fs0. In the following description, the frequency obtained by adding the frequency difference Δfpll to the reference AC system frequency fs0 will be referred to as an AC frequency fpll.

[0059] The oscillator 85 outputs the AC system voltage phase theta, which repeatedly and monotonically increases between a minimum value of 0 and a maximum value of 2π, based on the frequency of the AC frequency fpll calculated by the adder 84. As described above, the AC system voltage phase theta is used for the conversion of the AC system effective voltage Vsd and the AC system reactive voltage Vsq of the converter 81 and for the AC current control. In the AC current control, when non-interfering current control based on variables on a general rotating coordinate system is applied, the AC system voltage phase theta is used for the rotating coordinate conversion or inverse conversion (fixed coordinate conversion) of the voltage and current values. By the above-mentioned process, the AC information calculation unit 311 obtains the AC system voltage phase theta by repeating the calculation of the AC system voltage phase theta so that the calculated value of the AC system reactive voltage Vsq in the converter 81 becomes zero.

[0060] Next, FIG. 8 is a diagram showing the functional configuration of the converter control unit 31 (FIG. 1) in the voltage control mode (virtual generator control) in the first embodiment.

[0061] The power calculation unit 314 calculates the active power and reactive power flowing into and out of the power converter 32 .

[0062] The voltage control unit 315 performs pseudo-inertia control that simulates the characteristics of, for example, a synchronous generator. The oscillation frequency of the voltage command value is calculated from the frequency deviation obtained by multiplying the difference between the active power command value and the active power by the pseudo-inertia characteristic.

[0063] The amplitude of the voltage command value is calculated from the reactive power command value, the reactive power, and the voltage amplitude command value. No feedback control of the current control is performed.

[0064] The active power and reactive power are adjusted by controlling the phase and amplitude of the voltage command value rather than controlling the AC current. Synchronization to the AC system is gradual based on the difference between the active power command value and the active power, resulting in dynamic characteristics similar to those of a synchronous generator.

[0065] The gate voltage generating unit 316 generates and outputs a gate signal based on a voltage command value from the voltage control unit 315 .

[0066] In this way, in the voltage control mode, there is no feedback control of the AC current and it is slowly synchronized with the AC system, so negative resistance characteristics caused by delay time in current control calculations are unlikely to occur. This makes it possible to suppress harmonic resonance.

[0067] 9 is a diagram showing the functional configuration of the voltage control unit 315 (FIG. 8) in the first embodiment. A calculator 901 calculates an active power command value p * Subtract and add active power p.

[0068] The pseudo inertia Δf is calculated using a function based on the output from the calculator 901. * The adder 904 outputs Δf * and the reference AC system frequency (constant) f s Add 0 (code 903) to get the oscillation frequency f * Output.

[0069] The oscillator 905 has an oscillation frequency f * Based on the voltage command phase theta * Output.

[0070] The calculator 906 calculates the reactive power command value q * and subtract reactive power q.

[0071] Based on the output from the calculator 906, a function is used to output a value of the drooping characteristic (reference numeral 907). The adder 909 multiplies the value of the drooping characteristic and the AC system voltage command value Vs * The PI control 911 performs PI (Proportional Integral) control using the output from the calculator 910. The adder 912 adds the voltage command value amplitude V * Output.

[0072] The sine wave calculation 913 calculates the voltage command value phase theta * and the voltage command amplitude V * The sine wave calculation is performed based on the above and a voltage command value is output.

[0073] In the above calculation, the positive polarity of the active power is the direction in which the active power flows from the grid to the power converter 32. In that case, for example, when the active power command value>active power, the pseudo inertia output Δf * <0, and the oscillation frequency f * becomes smaller.

[0074] In addition, the voltage command value Vr * , Vs * , Vt * Since the phase of the inverter 10 lags behind the grid, active power flows into the power converter 32.

[0075] In addition, the positive polarity of the reactive power is set to the direction in which the power converter 32 performs capacitive operation. In that case, for example, when the AC system voltage command value>AC system voltage, the voltage command value amplitude V * increases, and capacitive reactive power is output, which has the effect of raising the AC system voltage.

[0076] In this way, according to the power system S of the first embodiment, when an operating state change command is output to multiple power conversion devices 3 in the event of a harmonic standard exceeding state, by gradually increasing the number of target power conversion devices 3, it is possible to suppress harmonic resonance in the power conversion devices 3 while avoiding the occurrence of power conversion devices 3 making unnecessary operating changes.

[0077] Furthermore, since the harmonic detection unit 51 is provided in the control system 5, there is no need to modify the power conversion device 3.

[0078] Moreover, as the operation state change command, specifically, a switching operation command for switching the switching elements of the power converter 32 can be used. Here, if an operation change is made to a number of power conversion devices 3 more than necessary, this leads to an increase in power loss due to switching, but this can be avoided. Furthermore, when the DC device 4 is a storage battery, a generator, or a load, the power conversion device 3 suitable for the operation change is selected based on the priority of each device, and the operation change is made to achieve both the operation required for the operation of the power system and the suppression of harmonic resonance, which is efficient.

[0079] Moreover, if a command to change from the current control mode to the voltage control mode is used as the operation state change command, harmonic resonance can be suppressed more effectively. Here, if an operation state change is made to a number of power conversion devices 3 that is greater than necessary, this leads to a decrease in the responsiveness of the power system due to the characteristics of the voltage control mode that slowly synchronizes with the AC system, but this can be avoided.

[0080] In addition, in the event of an emergency in which the harmonic standard exceeding state continues, by opening a part or all of the switches CB of the power conversion device 3, it is possible to prevent the harmonic resonance from expanding further.

[0081] Second embodiment Next, a second embodiment will be described. Descriptions of the same matters as those in the first embodiment will be omitted as appropriate.

[0082] 10 is an overall configuration diagram of a power system S of the second embodiment. This is different from the first embodiment (FIG. 1) in that a harmonic detector 51 is not provided in the control system 5, and a harmonic detector 319 is provided for each converter control unit 31. Each of the multiple harmonic detectors 319 has the same function as the harmonic detector 51.

[0083] In this case, the command function unit 52 of the control system 5 determines whether the current state is a harmonic standard exceeding state or a harmonic normal state based on the information on the harmonic standard exceeding state and the harmonic normal state received from multiple harmonic detection units 319.

[0084] For example, when it is determined that even one of the power electronics devices 3 is in a harmonic standard exceeding state, the command function unit 52 aggregates and judges the harmonic state, for example, by outputting an operation state change command.

[0085] In this way, according to the second embodiment, it is possible to obtain the same effects as those of the first embodiment, even when each converter control unit 31 has a harmonic detection unit 319. The technique of the second embodiment is effective in simplifying the configuration of the control system 5, including the interface with the voltage transformer VT and the current transformer CT, by utilizing the function of the converter control unit 31, for example.

[0086] Although some embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included in the scope and spirit of the invention, and are included in the scope of the invention and its equivalents described in the claims.

[0087] Furthermore, the program executed by the power system S of this embodiment can be provided by recording it in an installable or executable file format on a recording medium readable by a computer device, such as a CD (Compact Disc)-ROM (Read Only Memory), a flexible disk (FD), a CD-R (Recordable), or a DVD (Digital Versatile Disk). The program may also be provided or distributed via a network such as the Internet. [Explanation of symbols]

[0088] 1...AC power source, 2...system configuration, 3...power conversion device, 4...DC device, 5...control system, 31...converter control unit, 32...power converter, 51...harmonic detection unit, 52...command function unit, S...power system

Claims

1. A power system including a plurality of power conversion devices that convert AC power and DC power, The power conversion device is A switch for switching between conduction and non-conduction with respect to the AC power source; A power converter including a switching element for switching a connection with a DC device that is a device that operates with DC power; A converter control unit that issues an operation command to the switching element, The power system includes: a harmonic detection unit connected to the power conversion device, which detects whether a harmonic standard exceeding state is in a state in which harmonic components in a predetermined frequency range of an AC voltage and / or an AC current exceed a predetermined standard, or a harmonic normal state in which the harmonic components are equal to or lower than the predetermined standard; a command function unit that, in the event of the harmonic standard exceeding state, outputs a switching operation command to switch the switching element as an operating state change command to the power conversion device in which the switch is conductive and the switching operation of the connection to the DC device by switching the switching element has stopped, and operates the power conversion device so that the phase of the impedance seen from the switch to the power converter approaches a range of less than ±90 degrees and the resistive action of the impedance increases, and at that time, gradually increases the number of the power conversion devices to which the operating state change command is output until the harmonic normal state is reached.

2. A power system including a plurality of power conversion devices that convert AC power and DC power, The power conversion device is A switch for switching between conduction and non-conduction with respect to the AC power source; A power converter including a switching element for switching a connection with a DC device that is a device that operates with DC power; A converter control unit that issues an operation command to the switching element, The power system includes: a harmonic detection unit connected to the power conversion device, which detects whether a harmonic standard exceeding state is in a state in which harmonic components in a predetermined frequency range of an AC voltage and / or an AC current exceed a predetermined standard, or a harmonic normal state in which the harmonic components are equal to or lower than the predetermined standard; A command function unit that outputs a predetermined operating state change command to a plurality of the power electronics devices in the case of the harmonic standard exceeding state, for transitioning from the harmonic standard exceeding state to the harmonic normal state, and at that time, gradually increases the number of the power electronics devices to which the operating state change command is output until the harmonic normal state is reached; The command function unit outputs, in the case of the harmonic standard exceeding state, a switching operation command to switch the switching element as the operation state change command to the power conversion device in which the switch is conductive and a switching operation of the switching element to switch the connection with the DC device is stopped; The power conversion device that receives the switching operation command is operated with substantially zero power.

3. A power system including a plurality of power conversion devices that convert AC power and DC power, The power conversion device is A switch for switching between conduction and non-conduction with respect to the AC power source; A power converter including a switching element for switching a connection with a DC device that is a device that operates with DC power; A converter control unit that issues an operation command to the switching element, The converter control unit includes: a current control mode in which the current of the AC power supply is feedback-controlled; a voltage control mode in which the phase of a voltage output to the AC power source is adjusted in synchronization with the voltage of the AC power source without directly feedback controlling the current of the AC power source; The power system includes: a harmonic detection unit connected to the power conversion device, which detects whether a harmonic standard exceeding state is in a state in which harmonic components in a predetermined frequency range of an AC voltage and / or an AC current exceed a predetermined standard, or a harmonic normal state in which the harmonic components are equal to or lower than the predetermined standard; a command function unit that, when the harmonic standard exceeding state occurs, outputs an operating state change command from the current control mode to the voltage control mode to the power conversion device operating in the current control mode, and at that time, gradually increases the number of the power conversion devices to which the operating state change command is output until the harmonic normal state is reached.

4. The power system according to claim 1 , wherein the harmonic detection unit and the command function unit are provided in a control system that controls a plurality of the power conversion devices.

5. The harmonic detection unit is provided for each converter control unit, 4. The power system according to claim 1, wherein the command function unit is provided in a control system that controls a plurality of the power conversion devices, and determines whether the state is the harmonic standard exceeding state or the harmonic normal state based on information on the harmonic standard exceeding state and the harmonic normal state received from a plurality of the harmonic detection units.

6. 3. The power system according to claim 1, wherein, in the case of the harmonic standard exceeding state, the command function unit outputs the switching operation command to a power conversion device selected from the power conversion devices in which the switch is conductive and switching operation of the connection to the DC device by switching of the switching element has stopped, based on a priority corresponding to a state of the connected DC device.

7. The DC device is a storage battery; 7. The power system according to claim 6, wherein the command function unit calculates charging / discharging needs based on a current charging state of the connected storage battery and a deterioration characteristic related to the charging state, selects the power conversion device as having a higher priority as the charging / discharging needs are higher, and outputs the switching operation command to the selected power conversion device.

8. the DC device is a generator; 7. The power system according to claim 6, wherein the command function unit calculates a power generation efficiency from a current operating state of the generator, selects the power conversion device with a higher priority as the power generation efficiency is higher, and outputs the switching operation command to the selected power conversion device.

9. The DC device is a load of power; 7. The power system according to claim 6, wherein the command function unit calculates power supply needs from a current operating state of the load, selects the power conversion device as having a higher priority as the power supply needs are higher, and outputs the switching operation command to the selected power conversion device.

10. The command function unit includes:

4. The power system according to claim 1, wherein the switch is opened when a number of the power conversion devices to which the operation state change command is output due to the harmonic standard exceeding state is equal to or greater than a predetermined threshold value, and when the harmonic standard exceeding state does not transition to the harmonic normal state within a predetermined period of time.

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