Classifications

• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02J—ELECTRIC POWER NETWORKS; CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
  • H02J3/00—Circuit arrangements for AC mains or AC distribution networks
  • H02J3/38—Arrangements for feeding a single network from two or more generators or sources in parallel; Arrangements for feeding already energised networks from additional generators or sources in parallel
• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
  • H02M7/00—Conversion of AC power input into DC power output; Conversion of DC power input into AC power output
  • H02M7/42—Conversion of DC power input into AC power output without possibility of reversal
  • H02M7/44—Conversion of DC power input into AC power output without possibility of reversal by static converters
  • H02M7/48—Conversion of DC power input into AC power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode

Definitions

• Patent Document 1 discloses a power conversion device (power conditioner). Specifically, when the negative-phase voltage on the AC side of the inverter is equal to or greater than a predetermined value, the power conditioner determines that the inverter is in isolated operation and controls the inverter to stop.
• the negative-phase voltage on the AC side of the inverter may exceed a predetermined value, and the inverter may be erroneously determined to be in islanding operation.
• One objective of this disclosure is to provide technology that can appropriately determine whether an inverter is operating in islanded mode.
• a first aspect of the present disclosure relates to a power conditioner.
• the power conditioner includes an inverter that converts DC power supplied from a DC power source into AC power and supplies the AC power to a power grid, and a control device that controls the inverter.
• the control device generates a negative-phase current command for causing a negative-phase AC current to flow from the inverter based on a first differential voltage, which is the difference between a negative-phase voltage on the AC side of the inverter and a voltage from which high-frequency components of the negative-phase voltage have been removed.
• the control device then controls the inverter to stop when a second differential voltage, which is the difference between the negative-phase voltage and a negative-phase voltage command obtained by multiplying the negative-phase current command by the characteristics of the impedance between the inverter and the power grid, satisfies a threshold condition.
• a second aspect of the present disclosure relates to a power conditioner.
• the power conditioner includes an inverter that converts DC power supplied from a DC power source into AC power and supplies the AC power to a power grid, and a control device that controls the inverter. If a first differential voltage, which is the difference between the negative-phase voltage on the AC side of the inverter and a voltage from which high-frequency components have been removed, is greater than zero, the control device determines whether the positive-phase voltage on the AC side of the inverter is within a predetermined range. If it is determined that the positive-phase voltage is within the predetermined range, the control device controls the inverter to stop.
• a third aspect of the present disclosure relates to a power conditioner.
• the power conditioner includes an inverter that converts DC power supplied from a DC power source into AC power and supplies the AC power to a power grid, and a control device that controls the inverter.
• the control device calculates a first differential voltage, which is the difference between the negative-phase voltage on the AC side of the inverter and a voltage from which high-frequency components of the negative-phase voltage have been removed, and controls the inverter to stop when the positive-phase voltage and negative-phase voltage on the AC side of the inverter satisfy predetermined conditions.
• a fourth aspect of the present disclosure relates to a power control method.
• the power control method includes using an inverter to convert DC power into AC power and supplying the AC power to a power grid; generating a negative-phase current command for causing a negative-phase AC current to flow from the inverter based on a first differential voltage, which is the difference between a negative-phase voltage on the AC side of the inverter and a voltage from which high-frequency components of the negative-phase voltage have been removed; and controlling the inverter to stop when a second differential voltage, which is the difference between the negative-phase voltage and a negative-phase voltage command obtained by multiplying the impedance characteristics between the inverter and the power grid, satisfies a threshold condition.
• a fifth aspect of the present disclosure relates to a power control method.
• the power control method includes converting DC power to AC power using an inverter and supplying the AC power to a power grid; determining whether a first differential voltage, which is the difference between a negative-phase voltage on the AC side of the inverter and a voltage from which high-frequency components have been removed from the negative-phase voltage, is greater than zero; if it is determined that the first differential voltage is greater than zero, determining whether a positive-phase voltage on the AC side of the inverter is within a predetermined range; and if it is determined that the positive-phase voltage is within the predetermined range, controlling the inverter to stop.
• a sixth aspect of the present disclosure relates to a power control method.
• the power control method includes using an inverter to convert DC power into AC power and supplying the AC power to a power grid; calculating a first differential voltage that is the difference between a negative-phase-sequence voltage on the AC side of the inverter and a voltage from which high-frequency components have been removed from the negative-phase-sequence voltage; and controlling the inverter to stop when the positive-phase-sequence voltage and negative-phase-sequence voltage on the AC side of the inverter satisfy predetermined conditions.
• a negative-phase current command for causing a negative-phase AC current to flow from the inverter is generated based on a first differential voltage, which is the difference between the negative-phase voltage on the AC side of the inverter and the voltage from which the high-frequency components of the negative-phase voltage have been removed.
• a second differential voltage which is the difference between the negative-phase voltage and the negative-phase voltage command obtained by multiplying the impedance characteristics between the inverter and the power grid by the negative-phase current command, satisfies a threshold condition
• control is performed to stop the inverter. This makes it possible to appropriately determine whether the inverter is operating in islanding mode. Furthermore, if the inverter does enter islanding mode, it becomes possible to stop the inverter early. Therefore, safety is ensured.
• a first differential voltage which is the difference between the negative-phase voltage on the AC side of the inverter and the voltage from which high-frequency components have been removed, is greater than zero
• a first differential voltage is calculated, which is the difference between the negative-phase voltage on the AC side of the inverter and a first voltage obtained by removing high-frequency components from the negative-phase voltage. Furthermore, if the positive-phase voltage and negative-phase voltage satisfy predetermined conditions, the inverter is controlled to stop. This makes it possible to appropriately determine whether the inverter is operating in islanded mode. Furthermore, if the inverter does enter islanded mode, it becomes possible to stop the inverter early. Therefore, safety is ensured.
• the fourth perspective achieves the same effect as the first perspective.
• the fifth perspective achieves the same effect as the second perspective.
• FIG. 1 is a diagram for explaining an overview of a power conversion system according to a first embodiment
• 2 is a block diagram showing an example of functions of a control device according to the first embodiment
• FIG. FIG. 2 is a block diagram showing an example of detection of an isolated operation according to the first embodiment.
• FIG. 10 is a diagram for explaining a specific example of the characteristics of the isolated operation according to the first embodiment.
• 4 is a flowchart showing an example of processing by the control device according to the first embodiment;
• FIG. 10 is a block diagram showing an example of detecting an isolated operation according to the second embodiment.
• 10 is a flowchart showing an example of processing by a control device according to a second embodiment;
• FIG. 11 is a block diagram showing an example of detecting an isolated operation according to the third embodiment. 11 is a flowchart illustrating an example of processing by a control device according to a third embodiment.
• the DC power source 11 is a power storage device (e.g., a solar cell module) that stores electricity generated by renewable energy.
• renewable energy include solar power, wind power, and hydropower.
• the inverter 12 is a device that converts the DC power output from the DC power source 11 into AC power and supplies the AC power to the power grid 30 via the transformer 20.
• Examples of inverters 12 include a current-controlled GFL (Grid Following) inverter and a voltage-controlled GFM (Grid Forming) inverter.
• the control device 100 is connected to the inverter 12 and controls the inverter 12.
• the output voltage Vs and output current Io output from the inverter 12 are input to the control device 100.
• the output voltage Vs includes a positive-phase voltage Vps and a negative-phase voltage Vns.
• the output current Io includes a positive-phase current Ipo and a negative-phase current Ino.
• the output voltage Vs input to the control device 100 is, for example, the detected value of the output voltage Vs (hereinafter referred to as the Vs detected value).
• the Vs detected value includes the detected value of the positive-phase voltage Vps (also referred to as the Vps detected value) and the detected value of the negative-phase voltage Vns (also referred to as the Vns detected value).
• the output current Io input to the control device 100 is the detected value of the output current Io (also referred to as the Io detected value).
• the Io detection value includes a detection value of the positive-phase current Ipo (also referred to as the Ipo detection value) and a detection value of the negative-phase current Ino (also referred to as the Ino detection value). These detection values are detected, for example, by a detector (not shown) provided between the inverter 12 and the transformer 20.
• the control device 100 generates a current command for controlling the output current Io of the inverter 12 based on the Vs detection value and the Io detection value.
• the control device 100 then generates a pulse width modulation signal (PWM signal) based on the current command and issues an instruction ins to the inverter 12 to operate in accordance with the PWM signal.
• PWM signal pulse width modulation signal
• the load 50 is, for example, a device connected to the power conditioner 10 and consumed in a factory or the like where the power conditioner 10 is installed.
• the load 50 is typically composed of a resistive load R, an inductive load L, and a capacitive load C.
• the control device 100 generates a negative-phase current command for causing the inverter 12 to flow a negative-phase AC current based on a first differential voltage, which is the difference between the negative-phase voltage Vns on the AC side of the inverter 12 and the voltage from which high-frequency components have been removed from the negative-phase voltage Vns.
• the control device 100 then controls the inverter 12 to stop when a second differential voltage, which is the difference between the negative-phase voltage command obtained by multiplying the impedance characteristics between the inverter 12 and the power grid 30 by the negative-phase current command, satisfies a threshold condition. This makes it possible to appropriately determine whether the inverter 12 is operating in islanded mode. Furthermore, if the inverter 12 does enter islanded mode, it is possible to quickly stop the inverter 12. Therefore, safety is ensured. Details of the processing by the control device 100 will be described later.
• the control device 100 has hardware that realizes various functions.
• the hardware includes a processing circuit capable of high-speed calculations. Examples of the processing circuit include an FPGA (Field Programmable Gate Array) and an ASIC (Application Specific Integrated Circuit).
• the hardware may also include a storage device and a computing unit (e.g., a CPU or GPU) that executes a program stored in the storage device.
• the control device 100 includes an inverter operation control unit 110, a power control unit 120, a current control unit 130, and an output control unit 140.
• the inverter operation control unit 110 Based on the Vns detection value, the inverter operation control unit 110 generates a negative-phase current command for causing a negative-phase AC current to flow from the inverter 12.
• the negative-phase current command includes at least one of a d-axis component negative-phase current command Indref (hereinafter referred to as the d-axis negative-phase current command Indref) and a q-axis component negative-phase current command Inqref (hereinafter referred to as the q-axis negative-phase current command Inqref).
• the inverter operation control unit 110 also executes islanding operation detection processing.
• the islanding operation detection processing the inverter operation control unit 110 determines whether the inverter 12 is in islanding operation based on the negative-phase-sequence current command, the Vs detection value, and the Io detection value. If it is determined that the inverter 12 is in islanding operation, the inverter operation control unit 110 outputs a gate block signal gtb to the output control unit 140 to stop the inverter 12. Details of the islanding operation detection processing will be described later.
• the Vs detection value input to the inverter operation control unit 110 may be obtained, for example, via a PLL (Phase Locked Loop) provided in the control device 100.
• PLL Phase Locked Loop
• a PLL is a circuit that synchronizes the phase of the input voltage signal and the output voltage signal. This makes it possible to synchronize the Vs detection value with the phase of the output voltage Vs of the inverter 12, thereby properly connecting the inverter 12 to the power grid 30.
• the power control unit 120 calculates an active power command value Pref (hereinafter referred to as the active power command value Pref) and a reactive power command value Qref (hereinafter referred to as the reactive power command value Qref) based on a preset reference power.
• the current control unit 130 generates a current command Iref for controlling the output current Io of the inverter 12 based on the negative-phase-sequence current command (at least one of the d-axis negative-phase-sequence current command value Indref and the q-axis negative-phase-sequence current command value Inqref), the active power command value Pref, and the reactive power command value Qref.
• the output control unit 140 generates a PWM signal according to the current command Iref.
• the output control unit 140 issues an instruction ins to the inverter 12 to stop the inverter 12.
• the output control unit 140 issues an instruction ins to the inverter 12 to operate according to the PWM signal.
• the process for detecting islanding operation executed by the inverter operation control unit 110 includes a high-frequency component removal unit 111, a current command calculation unit 112, an impedance calculation unit 113, a negative-phase voltage command generation unit 114, a threshold determination unit 115, and a delay processing unit 116.
• the high-frequency component removal unit 111 removes high-frequency components from the negative-phase voltage Vns on the AC side of the inverter 12.
• the voltage from which the high-frequency components of the negative-phase voltage Vns have been removed is also referred to as the first voltage.
• a low-pass filter (LPF) for example, is used as a method for removing the high-frequency components of the negative-phase voltage Vns.
• the current command calculation unit 112 generates a negative-phase current command (at least one of a d-axis negative-phase current command value Indref and a q-axis negative-phase current command value Inqref) for flowing a negative-phase AC current from the inverter 12 based on a first differential voltage, which is the difference between the negative-phase voltage Vns and the first voltage.
• the impedance calculation unit 113 calculates the impedance between the inverter 12 and the power grid 30 based on the positive-sequence voltage Vps and the positive-sequence current Ipo.
• the impedance is the value obtained by dividing the positive-sequence voltage Vps by the positive-sequence current Ipo.
• the impedance may also be the value obtained by dividing the negative-sequence voltage Vns by the negative-sequence current Ino. In this case, the negative-sequence voltage Vns and the negative-sequence current Ino are input to the impedance calculation unit 113.
• the threshold determination unit 115 determines whether a threshold condition is satisfied based on a second differential voltage, which is the difference between the negative-phase voltage command obtained by the negative-phase voltage command generation unit 114 and the negative-phase voltage Vns.
• the threshold condition is a condition for determining whether the inverter 12 is in islanding operation. If it is determined that the threshold condition is satisfied, i.e., if the inverter 12 is in islanding operation, the threshold determination unit 115 generates a gate block signal gtb to stop the inverter 12. On the other hand, if it is determined that the threshold condition is not satisfied, i.e., if the inverter 12 is not in islanding operation, the threshold determination unit 115 disables the gate block signal gtb.
• the delay processing unit 116 delays the timing of outputting the gate block signal gtb to the inverter 12 in order to stabilize the operation of the inverter operation control unit 110.
• the delay processing unit 116 imposes a delay of, for example, several ms.
• FIG. 4 is a diagram for explaining a specific example of the characteristics of islanding operation. Specifically, (A) in FIG. 4 shows the observation point of the output voltage waveform of the high-frequency component removal unit 111. (B) in FIG. 4 shows an example of the output voltage waveform at the observation point when the impedance of the three-phase line on the system side is unbalanced, and (C) in FIG. 4 shows an example of the output voltage waveform at the observation point during islanding operation. As shown in (A) in FIG. 4, there are two observation points: voltage Va and voltage Vb. Voltage Va is a first voltage output from the high-frequency component removal unit 111. Voltage Vb is a first differential voltage obtained by subtracting the first voltage from the negative-phase voltage Vns.
• the negative-phase voltage Vns rises. Specifically, the negative-phase voltage Vns becomes greater than 0 V. In this case, the voltage Vb (first differential voltage) rises to a value greater than 0 V, then falls and transitions to 0 V.
• FIG. 5 is a flowchart showing an example of processing by the control device 100 according to embodiment 1. Specifically, Fig. 5 shows an outline of an example of detecting islanding.
• step S100 the control device 100 removes high-frequency components from the negative-phase voltage Vns to generate a first voltage. Then, processing proceeds to step S110.
• step S110 the control device 100 calculates a first differential voltage, which is the difference between the negative-phase voltage Vns and the first voltage. Then, processing proceeds to step S120.
• step S130 the control device 100 calculates the second differential voltage. Processing then proceeds to step S140.
• the second differential voltage is the voltage obtained by subtracting the negative-phase-sequence voltage Vns from the negative-phase-sequence voltage command obtained by multiplying the impedance characteristics between the inverter 12 and the power grid 30 by the negative-phase-sequence current command.
• step S140 the control device 100 determines whether the second differential voltage satisfies the threshold condition. If the second differential voltage satisfies the threshold condition (step S140; Yes), processing proceeds to step S150. Otherwise (step S140; No), processing ends.
• step S150 the control device 100 determines that the inverter 12 is in isolated operation and executes control to stop the inverter 12.
• a negative-phase current command for causing a negative-phase AC current to flow from the inverter 12 is generated based on a first differential voltage, which is the difference between the negative-phase voltage on the AC side of the inverter 12 and a first voltage obtained by removing high-frequency components from the negative-phase voltage Vns.
• the power conditioner 10 controls the inverter 12 to stop when a second differential voltage, which is the difference between the negative-phase voltage command obtained by multiplying the impedance characteristics between the inverter 12 and the power grid 30 by the negative-phase current command, satisfies a threshold condition. This allows appropriate determination of whether the inverter 12 is in islanding operation. Furthermore, when the inverter 12 is in islanding operation, the inverter 12 can be stopped early. Therefore, safety is ensured.
• Fig. 6 is a block diagram showing an example of detection of islanding operation according to embodiment 2. Specifically, Fig. 6 shows an example of detection of islanding operation utilizing the characteristic that the voltage Vb (first differential voltage) is greater than 0 V when islanding operation is detected.
• Vb first differential voltage
• the inverter operation control unit 110 includes a high-frequency component removal unit 111, a current command calculation unit 112, an isolated operation determination unit 117, a condition determination unit 118, and a delay processing unit 116.
• the high-frequency component removal unit 111, the current command calculation unit 112, and the delay processing unit 116 perform the same processing as in embodiment 1 described above, and therefore their explanations are omitted.
• the isolated operation determination unit 117 and the condition determination unit 118 are explained.
• the islanding operation determination unit 117 determines whether the voltage Vb (first differential voltage) is greater than zero. If it is determined that the voltage Vb (first differential voltage) is greater than zero, the islanding operation determination unit 117 determines that the inverter 12 is in islanding operation. The islanding operation determination unit 117 may also monitor the state of the voltage Vb (first differential voltage) for a certain period of time, and then determine whether the voltage Vb (first differential voltage) is greater than zero. For example, if the voltage Vb (first differential voltage) has transitioned to zero after the certain period of time has elapsed (see Figure 4 (B)), the islanding operation determination unit 117 determines that the inverter 12 is not in islanding operation.
• the islanding operation determination unit 117 determines that the inverter 12 is in islanding operation. Therefore, it is possible to appropriately determine whether the inverter 12 is in islanding operation.
• the condition determination unit 118 determines whether the positive-sequence voltage Vps on the AC side of the inverter 12 is within a predetermined range.
• the predetermined range refers, for example, to the estimated voltage range of the positive-sequence voltage Vps when the impedance of the three-phase line on the grid side is balanced (hereinafter referred to as the estimated positive-sequence voltage range).
• the predetermined range is determined, for example, by the design specifications of the power conversion system 1 (control device 100).
• the condition determination unit 118 determines that the inverter 12 is in islanding operation.
• the condition determination unit 118 determines that the inverter 12 is not in islanding operation. This allows for a more appropriate determination of whether the inverter 12 is in islanding operation.
• condition determination unit 118 determines that the inverter 12 is in islanding operation, it activates the gate block signal gtb to stop the inverter 12. If it determines that the inverter 12 is not in islanding operation, the condition determination unit 118 disables the gate block signal gtb.
• FIG. 7 is a flowchart showing a processing example of the control device 100 according to embodiment 2. Specifically, Fig. 7 shows an outline of an example of detecting islanding.
• step S200 the control device 100 removes high-frequency components from the negative-phase voltage Vns to generate a first voltage. Then, processing proceeds to step S210.
• step S210 the control device 100 calculates a first differential voltage, which is the difference between the negative-phase voltage Vns and the first voltage. Then, processing proceeds to step S220.
• step S220 the control device 100 determines whether the first differential voltage is greater than zero. If it is determined that the first differential voltage is greater than zero (step S220; Yes), processing proceeds to step S230. Otherwise (step S220; No), processing ends.
• step S230 the control device 100 determines whether the positive-phase voltage Vps is within a predetermined range. If it is determined that the positive-phase voltage Vps is within the predetermined range (step S230; Yes), processing proceeds to step S240. Otherwise (step S230; No), processing ends.
• step S240 the control device 100 determines that the inverter 12 is operating independently and executes control to stop the inverter 12.
• Fig. 8 is a block diagram showing an example of islanding operation detection according to embodiment 3. Specifically, Fig. 8 shows an example of islanding operation detection using the characteristics of the positive-phase voltage Vps or the negative-phase voltage Vns.
• the inverter operation control unit 110 includes a high-frequency component removal unit 111, a current command calculation unit 112, a condition determination unit 118, and a delay processing unit 116.
• the high-frequency component removal unit 111, the current command calculation unit 112, and the delay processing unit 116 perform the same processing as in embodiment 1 described above, and therefore their explanations are omitted. Below, the condition determination unit 118 will be explained.
• the condition determination unit 118 inputs the positive-sequence voltage Vps and the negative-sequence voltage Vns.
• the condition determination unit 118 determines whether the positive-sequence voltage Vps and the negative-sequence voltage Vns on the AC side of the inverter 12 satisfy predetermined conditions.
• the predetermined conditions include the positive-sequence voltage Vps on the AC side of the inverter 12 being within a predetermined range and the negative-sequence voltage Vns on the AC side of the inverter 12 being greater than zero.
• the predetermined range refers, for example, to the estimated voltage range (estimated positive-sequence voltage range) of the positive-sequence voltage Vps when the impedance of the three-phase line on the grid side is balanced.
• the predetermined range is determined, for example, by the design specifications of the power conversion system 1 (control device 100).
• FIG. 9 is a flowchart showing a processing example of the control device 100 according to embodiment 3. Specifically, Fig. 9 shows an outline of an example of detecting islanding.
• step S300 the control device 100 removes high-frequency components from the negative-phase voltage Vns to generate a first voltage. Then, processing proceeds to step S310.
• step S310 the control device 100 calculates a first differential voltage, which is the difference between the negative-phase voltage Vns and the first voltage. Then, processing proceeds to step S320.
• step S320 the control device 100 determines whether the positive-phase voltage Vps and the negative-phase voltage Vns satisfy predetermined conditions. If it is determined that the positive-phase voltage Vps and the negative-phase voltage Vns satisfy the predetermined conditions (step S320; Yes), processing proceeds to step S330. Otherwise (step S320; No), processing ends.
• step S330 the control device 100 determines that the inverter 12 is operating independently and executes control to stop the inverter 12.
• step S320 may be executed before step S300 or step S310.
• the control device 100 may be configured to execute steps S300 and S310, and steps S320 and S330 independently.
• a first differential voltage is calculated, which is the difference between the negative-phase-sequence voltage Vns on the AC side of the inverter 12 and a first voltage obtained by removing high-frequency components from the negative-phase-sequence voltage Vns. Furthermore, when the positive-phase-sequence voltage Vps and the negative-phase-sequence voltage Vns satisfy predetermined conditions, the power conditioner 10 determines that the inverter 12 is in isolated operation and controls the inverter 12 to stop. This provides the same effects as those of the first embodiment described above.

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  • 2024-05-08 WO PCT/JP2024/017070 patent/WO2025234014A1/ja active Pending
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