JP2011217442A - Single operation detector, method of detecting single operation, and system-interconnected inverter system equipped with single operation detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a reactive power change system of single operation detector, which can properly detect a single operation without increasing the quantity of input reactive power even when a reactive power load is included in a load.SOLUTION: The single operation detector 6, which detects a single operation state, is provided with a reactive power input unit 61 which periodically inputs a reactive power where a current gains, and a reactive power where a current delays to the output power of an inverter device 2, and a single operation detector 64 which determines whether the phase of an interconnection point voltage signal Vo at an interconnection point (a) has changed. The single operation detector 64 detects the system is in a single operation state when it is determined that the phase of the interconnection point voltage signal Vo has changed. Even when a reactive power load is included in a load B, it can detect a single operation properly because it is determined that the phase of the interconnection point voltage signal Vo has changed in case any reactive power has been input.

Description

  The present invention relates to an isolated operation detection device, an isolated operation detection method, and a grid-connected inverter system including the isolated operation detection device, and more particularly, to an active isolated operation detection.

  2. Description of the Related Art Conventionally, a grid-connected inverter system has been developed that converts DC power generated by a solar cell or the like into AC power and supplies it to a connected load or power system. When an accident occurs in the power system, etc., the circuit breaker is activated by a protective device provided on the power system side, so that the grid-connected inverter system is disconnected from the power system (power failure). In this case, the load connected to the grid interconnection inverter system is in a state where power is supplied from the grid interconnection inverter system (single operation). Under conditions where the output power and load power of the grid-connected inverter system are balanced, the grid-connected inverter system cannot detect a power system power failure. In order to ensure the safety of maintenance workers, the grid-connected inverter system is provided with a function of detecting isolated operation, disconnecting the load from the grid-connected inverter system, and automatically stopping the power conversion operation.

  FIG. 6 is a diagram illustrating an example of a grid-connected inverter system including a conventional isolated operation detection device.

  The grid interconnection inverter system A includes an isolated operation detection device 6 'for detecting an isolated operation. The isolated operation detection device 6 ′ outputs an open signal to the switch 8 and outputs a stop signal to the inverter control device 3 when detecting the isolated operation. The switch 8 to which the open signal is input disconnects the connection between the grid interconnection inverter system A and the load B. Further, the inverter control device 3 to which the stop signal is input stops generating the PWM signal and stops the power conversion operation. Thereby, the independent operation state of the grid connection inverter system A is avoided.

  The method for detecting the isolated operation by the isolated operation detection device 6 ′ includes a passive method for detecting the isolated operation state by detecting a change in voltage waveform or phase that occurs when the isolated operation is changed to the isolated operation, and a cycle. There is an active method in which a fluctuation factor is given and a single operation state is detected when a voltage waveform or phase changes correspondingly. Among these, the active method includes a stand-alone operation detection method of a reactive power fluctuation method.

  In the reactive power fluctuation type isolated operation detection method, reactive power is periodically injected, and the voltage at the connection point a detected by the voltage sensor 5 at this time (hereinafter referred to as “connection point voltage”). ) The islanding operation is detected by the change of the phase of Vo.

  FIG. 7 is a diagram for explaining the reactive power fluctuation type isolated operation detection method, and shows waveforms of the interconnection point voltage Vo and the output current Io of the inverter device 2 before and after the reactive power injection.

  FIG. 4A shows waveforms of the interconnection point voltage Vo and the output current Io during the interconnection operation. As shown in the figure, the phase of the output current Io is advanced while reactive power is being injected. The reactive power injected at this time is hereinafter referred to as “advanced reactive power” and is set to a positive value (reversely, the reactive power that delays the phase of the output current Io is referred to as “delayed reactive power” below, and is negative. Value). On the other hand, the phase of the interconnection point voltage Vo does not change because the system C absorbs the system power even if reactive power is injected (the system voltage does not change).

  FIG. 2B shows waveforms of the interconnection point voltage Vo and the output current Io during the single operation. The phase of the output current Io is advanced while reactive power is injected, as in FIG. Further, since the system C for absorbing the injected reactive power is disconnected, the phase of the interconnection point voltage Vo follows the output current Io and advances. In the figure, the phase of the interconnection point voltage Vo is advanced by θ as compared with the time of interconnection operation.

  Therefore, it can be determined whether the operation state is the single operation state or the connection operation state depending on whether the phase of the connection point voltage Vo advances when reactive power is injected. The isolated operation detection device 6 ′ outputs a reactive power injection signal to the inverter control device 3 to periodically inject reactive power, and the phase change amount θ of the interconnection point voltage Vo input from the voltage sensor 5 at this time When the value exceeds a predetermined threshold value θ ′, it is determined that the phase of the connection point voltage Vo has changed, and it is determined that the vehicle is in the single operation state.

JP 2009-136096 A

  However, when the reactive power load (capacitive load and inductive load) is included in the load B, the isolated operation detection device 6 'may not be able to detect the isolated operation appropriately. For example, when the load B includes a capacitive load, even if the advance reactive power is injected, the phase of the output current Io is delayed by the capacitive load of the load B, and the amount by which the phase advances is reduced. In this case, the amount by which the phase of the interconnection point voltage Vo that follows the output current Io advances is also small. Therefore, the voltage phase change amount θ does not exceed the threshold value θ ′, and no isolated operation is detected.

  FIG. 8 shows the phase change amount θ of the interconnection point voltage Vo when reactive power is injected, and the isolated operation detection signal output from the isolated operation detection device 6 ′ (when it is detected that the operation is in the isolated operation state, This is a signal that is output to convey that effect to other means, and corresponds to an open signal that is output to the switch 8 and a stop signal that is output to the inverter control device 3.) Timing for explaining the relationship It is a chart. In the figure, the isolated operation detection device 6 'outputs a reactive power injection signal for proceeding between t1 and t2 and injecting reactive power.

  (A) of the same figure is a thing at the time of interconnection operation. In this case, since the voltage phase change amount θ does not change even when reactive power is injected, the isolated operation detection signal remains a low level signal indicating that it has not been detected.

  FIG. 6B shows a case where the load B is only a resistive load (or a case where a capacitive load and an inductive load are balanced) at the time of single operation. In this case, when the advance reactive power is injected, the voltage phase change amount θ changes and exceeds the threshold value θ ′. Therefore, the isolated operation detection signal changes to a high level signal indicating the isolated operation detection.

  FIG. 6C shows a case where a capacitive load is included in the load B during a single operation (when the capacitive load is larger than the inductive load). In this case, when the advance reactive power is injected, the voltage phase change amount θ changes, but does not exceed the threshold value θ ′. Therefore, the isolated operation detection signal remains as a low level signal indicating non-detection.

  As a method for detecting an isolated operation in the case of FIG. However, in this case, there is a high possibility that the isolated operation is erroneously detected due to fluctuations in the system voltage. In addition, when the injected reactive power and the reactive power load of the load B completely coincide with each other, the voltage phase change amount θ becomes “0”, so that it cannot be determined by comparison with the threshold value θ ′. .

  A method of increasing the voltage phase change amount θ by gradually increasing the reactive power to be injected is also conceivable. FIG. 4D shows a case where the reactive power is further injected after the reactive power is injected between t1 and t2. When the reactive power is injected first, the voltage phase change amount θ does not exceed the threshold value θ ′. However, since the larger reactive power is injected, the voltage phase change amount θ exceeds the threshold value θ ′, and the isolated operation detection signal changes to a high level signal indicating the isolated operation detection. However, injecting a large amount of reactive power at the time of the interconnection operation deteriorates the power factor or greatly distorts the waveform of the output current Io.

  The present invention has been conceived under the circumstances described above, and even when a reactive power load is included in a load, it is possible to appropriately detect an isolated operation without increasing the amount of reactive power injection. It is an object of the present invention to provide a stand-alone operation detection device of a reactive power fluctuation method capable of

  In order to solve the above problems, the present invention takes the following technical means.

  The isolated operation detection device provided by the first aspect of the present invention is a power conversion in a state where a grid-connected inverter system that converts DC power into AC power and outputs it to a load and a power system is disconnected from the power system. A single operation detection device that detects that an operation is in an isolated operation state, and periodically injects reactive power that advances current and reactive power that delays current into the output power of an inverter device that performs power conversion operation. Reactive power injection control means; and judgment means for judging whether or not an electrical signal at a connection point between the grid-connected inverter system and the power system has changed. When it is determined that there has been a change, it is detected that the vehicle is in a single operation state.

  In a preferred embodiment of the present invention, the determination means determines whether or not the phase of the voltage signal has changed.

  In a preferred embodiment of the present invention, the determination means determines the phase of the voltage signal when the amount of change of the phase of the detected voltage signal from the phase during the interconnection operation exceeds a predetermined threshold value. Is determined to have changed.

  In a preferred embodiment of the present invention, the determination means determines whether or not the amount of change is greater than a predetermined first threshold when reactive power that advances current is injected, and the current is It is determined whether or not the amount of change has become smaller than a predetermined second threshold value when delayed reactive power is injected, and the determination means has determined that the change amount has become larger than the first threshold value. If it is determined that the value is smaller than the second threshold value, it is detected that the vehicle is in a single operation state.

  In a preferred embodiment of the present invention, the reactive power injection control means alternately injects reactive power in which current advances and reactive power in which current is delayed.

  In a preferred embodiment of the present invention, the reactive power injection control means continuously injects reactive power in which the current advances and reactive power in which the current is delayed, a plurality of times.

  In a preferred embodiment of the present invention, when the number of times that the electrical signal has been determined to have changed by the determination means reaches a predetermined number, it is detected that the vehicle is in a single operation state.

  In a preferred embodiment of the present invention, the determination means has a time difference between a detected zero-cross timing of the voltage signal and a corresponding zero-cross timing of the voltage signal at the time of interconnection operation exceeding a predetermined threshold value. In this case, it is determined that the phase of the voltage signal has changed.

  In a preferred embodiment of the present invention, the determination means determines whether or not the frequency of the voltage signal has changed.

  The grid interconnection inverter system provided by the second aspect of the present invention includes the inverter device and the isolated operation detection device provided by the first aspect of the present invention.

  The isolated operation detection method provided by the third aspect of the present invention is a power conversion in a state in which a grid-connected inverter system that converts DC power into AC power and outputs it to a load and a power system is disconnected from the power system. A single operation detection method for detecting that an operation is in an isolated operation state, the first step of injecting reactive power in which current advances into output power of an inverter device that performs power conversion operation, and the grid interconnection A second step of determining whether or not an electrical signal at an interconnection point between the inverter system and the power system has changed; and a third step of injecting reactive power whose current is delayed into the output power of the inverter device. And a fourth step of determining whether or not the electrical signal has changed, and it is determined that the electrical signal has changed in the second step or the fourth step. If, and detects that the islanding state.

  According to a fourth aspect of the present invention, there is provided a program for converting power in a state where a grid-connected inverter system that converts a DC power into an AC power and outputs it to a load and a power system is disconnected from the power system. A program for causing a computer to function as an isolated operation detection device for detecting that an operation is in an isolated operation state, wherein the reactive power and current that advances current are output to the output power of the inverter device that performs power conversion operation Reactive power injection control means for periodically injecting delayed reactive power, determination means for determining whether or not an electrical signal at a connection point between the grid-connected inverter system and the power system has changed, and When the determination means determines that the electrical signal has changed, it is a detection means for detecting that the vehicle is in an isolated operation state. Make.

  The recording medium provided by the fifth aspect of the present invention is a computer-readable recording medium on which the program provided by the fourth aspect of the present invention is recorded.

  According to the present invention, the reactive power in which the current advances and the reactive power in which the current is delayed are periodically injected into the output power of the inverter device, and the single operation state is determined when it is determined that the electrical signal at the interconnection point has changed. Is detected. Therefore, even if reactive power load is included in the load, and it is not determined that the electrical signal has changed even if injecting reactive power is injected and isolated operation cannot be detected, the electrical signal when injecting reactive power that is delayed It is determined that has changed, and the isolated operation can be detected. On the contrary, even if the reactive power that is delayed is injected, it is determined that the electrical signal has not changed and the isolated operation cannot be detected. Can be detected. Therefore, even when the reactive power load is included in the load, the isolated operation can be detected appropriately. Further, since the amount of reactive power injected is not increased, it is possible to suppress deterioration of the power factor and significant distortion of the output current waveform.

  Other features and advantages of the present invention will become more apparent from the detailed description given below with reference to the accompanying drawings.

It is a figure for demonstrating the grid connection inverter system provided with the isolated operation detection apparatus which concerns on 1st Embodiment of this invention. It is a figure which shows an example of the waveform of a reactive power injection signal. It is a flowchart for demonstrating the isolated operation detection process which an isolated operation detection apparatus performs. It is a timing chart for demonstrating the relationship between the phase change amount of a connection point voltage when a reactive power is inject | poured, and an independent operation detection signal. It is a figure which shows the other example of the waveform of a reactive power injection signal. It is a figure which shows an example of the grid connection inverter system provided with the conventional isolated operation detection apparatus. It is a figure for demonstrating the independent operation detection method of a reactive power fluctuation system. It is a timing chart for demonstrating the relationship between the variation | change_quantity of the phase of a connection point voltage when a reactive power is inject | poured, and an independent operation detection signal.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments of the present invention will be specifically described with reference to the drawings, taking as an example the case where the isolated operation detection apparatus according to the present invention is used in a grid-connected inverter system.

  FIG. 1 is a diagram for explaining a grid-connected inverter system including an islanding detection device according to a first embodiment of the present invention.

  As shown in the figure, the grid-connected inverter system A includes a DC power source 1, an inverter device 2, an inverter control device 3, a current sensor 4, a voltage sensor 5, an isolated operation detection device 6, and a switch 8. . The grid-connected inverter system A converts DC power output from the DC power source 1 into AC power by the inverter device 2 and supplies the AC power to the load B and the power system C.

  The DC power source 1 outputs DC power and includes, for example, a solar battery. A solar cell generates direct-current power by converting solar energy into electrical energy. The DC power source 1 outputs the generated DC power to the inverter device 2. Note that the DC power source 1 is not limited to one that generates DC power from a solar cell. For example, the DC power source 1 may be a fuel cell, a storage battery, an electric double layer capacitor, a lithium ion battery, or AC power generated by a diesel engine generator, a micro gas turbine generator, a wind turbine generator, or the like. It may be a device that converts to DC power and outputs it.

  The inverter device 2 converts a DC voltage input from the DC power source 1 into an AC voltage and outputs the AC voltage to the load B and the power system C. The inverter device 2 is a so-called PWM control inverter device, and based on the PWM signal input from the inverter control device 3, the switching device (not shown) is switched on and off to convert the input DC voltage to an AC voltage. Convert. Moreover, the inverter apparatus 2 removes the high frequency component by switching by the built-in filter circuit (not shown).

  The inverter control device 3 controls the inverter device 2, and includes an output current signal Io input from the current sensor 4, a connection point voltage signal Vo input from the voltage sensor 5, and an independent operation detection device 6. Based on the input reactive power injection signal, a PWM signal is generated and output to the inverter device 2. The inverter control device 3 performs feedback control on the output current Io and the reactive power Q output from the inverter device 2.

  The inverter control device 3 includes a reactive power detection unit 31, a target reactive power setting unit 32, a reactive power control unit 33, a current control unit 34, and a PWM signal generation unit 35.

  The reactive power detection unit 31 calculates the reactive power Q output from the inverter device 2 from the output current signal Io input from the current sensor 4 and the interconnection point voltage signal Vo input from the voltage sensor 5 and outputs the calculated reactive power Q. To do.

The target reactive power setting unit 32 sets and outputs a target reactive power Q ^* based on a reactive power injection signal input from a reactive power injection unit 61 (described later) of the isolated operation detection device 6. When the reactive power injection signal indicates that reactive power is not injected, the target reactive power setting unit 32 sets the target reactive power Q ^* to “0” and outputs it. If the reactive power injection signal is advanced and indicates that reactive power is to be injected, the target reactive power Q ^* is set to a positive positive value and output, and the reactive power injection signal indicates that the reactive power injection is delayed and injected. In the state shown, the target reactive power Q ^* is set to a negative predetermined value and output. Note that the positive predetermined value and the negative predetermined value are sufficiently small so that the power factor is not significantly deteriorated by the injected reactive power and the waveform of the output current signal Io is not significantly distorted. Is preset as follows. Further, the positive predetermined value and the negative predetermined value are set such that a phase change of the interconnection point voltage signal Vo can be detected by injecting reactive power during the single operation.

The reactive power control unit 33 receives a deviation between the reactive power Q input from the reactive power detection unit 31 and the target reactive power Q ^* input from the target reactive power setting unit 32, and sets the deviation to “0”. The correction value for this is output as a correction value signal.

  The current control unit 34 receives a deviation between the output current signal Io input from the current sensor 4 and the correction value signal input from the reactive power control unit 33, and a correction value for setting the deviation to “0”. Is output to the PWM signal generator 35 as a command value signal.

  The PWM signal generation unit 35 generates a PWM signal by a triangular wave comparison method based on a command value signal input from the current control unit 34 and a carrier signal generated as a triangular wave signal having a predetermined frequency (for example, 4 kHz). To do. For example, a pulse signal that is high when the command value signal is larger than the carrier signal and low when the command value signal is smaller than the carrier signal is generated as a PWM signal. The generated PWM signal is output to the inverter device 2. Further, the PWM signal generation unit 35 stops generating the PWM signal when an isolated operation detection signal (stop signal) is input from the isolated operation detection device 6. Thereby, the power conversion operation of the inverter device 2 is stopped.

The inverter control device 3 controls the output reactive power of the inverter device 2 to be “0” while the target reactive power setting unit 32 sets the target reactive power Q ^* to “0”. Further, the inverter control device 3 performs control so that the output reactive power of the inverter device 2 becomes the positive predetermined value while the target reactive power setting unit 32 sets the target reactive power Q ^* to a positive predetermined value. To do. Thereby, advance reactive power is inject | poured. On the other hand, the inverter control device 3 performs control so that the output reactive power of the inverter device 2 becomes the predetermined negative value while the target reactive power setting unit 32 sets the target reactive power Q ^* to a predetermined negative value. To do. Thereby, delayed reactive power is injected. Note that the configuration of the inverter control device 3 is not limited to the above, and any configuration that can control the reactive power Q and generate the PWM signal may be used. For example, the PWM signal may be generated by a method other than the triangular wave comparison method. Further, feedback control of other than the output current Io and reactive power Q (for example, output voltage Vo and active power) may be performed.

  The current sensor 4 detects the output current Io output from the inverter device 2. The output current Io detected by the current sensor 4 is output to the inverter control device 3 as an output current signal Io. The voltage sensor 5 detects a connection point voltage Vo which is a voltage at the connection point a. The connection point voltage Vo detected by the voltage sensor 5 is output to the inverter control device 3 and the isolated operation detection device 6 as the connection point voltage signal Vo.

  The switch 8 disconnects the connection between the grid-connected inverter system A and the load B. The switch 8 disconnects the connection between the grid-connected inverter system A and the load B when an isolated operation detection signal (open signal) is input from the isolated operation detection device 6. Thereby, the independent operation state of the grid connection inverter system A is avoided.

  The isolated operation detection device 6 detects an isolated operation, and outputs an isolated operation detection signal when an isolated operation is detected. The isolated operation detection signal output from the isolated operation detection device 6 is input to the inverter control device 3 as a stop signal and input to the switch 8 as an open signal.

  The islanding operation detection device 6 includes a reactive power injection unit 61, a voltage phase detection unit 62, a phase change amount detection unit 63, and an islanding operation detection unit 64. Since the present invention relates to an active type isolated operation detection method, only the configuration for detecting the active type isolated operation is described. Actually, the isolated operation detection device 6 also includes a configuration for passive isolated operation detection, but the description and explanation thereof are omitted in the present embodiment.

  The reactive power injection unit 61 generates a reactive power injection signal and outputs it to the target reactive power setting unit 32 in order to cause the inverter device 2 to periodically inject reactive power. The reactive power injection signal has three states: a state indicating that reactive power is not injected, a state indicating that advanced reactive power is injected, and a state indicating that delayed reactive power is injected. For example, in the present embodiment, the reactive power injection signal has three values “0”, “1”, and “−1”, which indicates that reactive power is not injected, and that advanced reactive power is injected. This corresponds to the state shown and the state showing that the delayed reactive power is injected.

  FIG. 2 is a diagram illustrating an example of a waveform of the reactive power injection signal.

  As shown in the figure, the reactive power injection signal becomes “1” in a predetermined cycle T, and “1” continues to be “0” for a predetermined period Δt. Further, “−1” is obtained in the middle of the period T, and “−1” continues to be “0” for a predetermined period Δt. The predetermined period T is set to be within 0.5 seconds, which is the active isolated operation detection time limit. Further, the period Δt is as short as possible in order to minimize the influence on the power factor by the injected reactive power.

  When the reactive power injection signal is input to the target reactive power setting unit 32, the reactive power is advanced only at the timing of the period T and injected during the period Δt, and the delayed reactive power is generated at the intermediate timing of the advanced reactive power injection. Injected only during period Δt. Note that the delay reactive power injection timing does not necessarily have to be an intermediate timing of the advance reactive power injection.

  The reactive power injection signal is not limited to this. For example, a first reactive power injection signal composed of a low level signal indicating that reactive power is not injected and a high level signal indicating advance reactive power is injected, and a low level signal indicating that reactive power is not injected Two signals may be used as a second reactive power injection signal including a high level signal indicating that delayed reactive power is injected. The reactive power injection unit 61 also outputs a reactive power injection signal to the isolated operation detection unit 64.

  The voltage phase detector 62 detects the phase of the interconnection point voltage signal Vo input from the voltage sensor 5 and is, for example, a PLL (Phase-Locked Loop) circuit. The voltage phase detection unit 62 outputs the detected phase of the interconnection point voltage signal Vo to the phase change amount detection unit 63.

  The phase change amount detection unit 63 detects the phase change amount θ when the phase of the interconnection point voltage signal Vo input from the voltage phase detection unit 62 is compared with the phase during the interconnection operation. When the phase of the interconnection point voltage signal Vo is advanced as compared with that during interconnection operation, the phase change amount θ is detected as a positive value, and the phase of the interconnection point voltage signal Vo is delayed compared with that during interconnection operation. The phase change amount θ is detected as a negative value.

The isolated operation detection unit 64 detects the isolated operation by comparing the phase change amount θ input from the phase change amount detection unit 63 with a predetermined threshold value. The isolated operation detection unit 64 sets a threshold value to be compared with the phase change amount θ at a timing when the reactive power injection signal input from the reactive power injection unit 61 advances and enters a state indicating injection of reactive power. The threshold value θ ₁ is switched, and the threshold value to be compared with the phase change amount θ is switched to a predetermined threshold value θ ₂ at a timing when the reactive power injection signal indicates that the reactive power injection is delayed. (See (b)). The threshold value θ ₁ is a positive value indicating that the phase is advanced, and the threshold value θ ₂ is a negative value indicating that the phase is delayed, and is set in advance.

The isolated operation detection unit 64 compares the phase change amount θ with the threshold value θ ₁ when the advanced reactive power is injected, and is in the isolated operation state when the phase change amount θ is larger than the threshold value θ _1. The phase change amount θ is compared with the threshold value θ ₂ when the delayed reactive power is injected, and it is determined that the single operation state is obtained when the phase change amount θ is smaller than the threshold value θ _2. . The isolated operation detection unit 64 outputs the determination result as a detection signal to the PWM signal generation unit 35 and the switch 8 of the inverter control device 3. In the present embodiment, the isolated operation detection unit 64 outputs a connected operation detection signal (low level signal) when it is not determined that it is in the isolated operation state (when it is determined that it is in the connected operation state). An independent operation detection signal (high level signal) is output when it is determined that the state is present. The PWM signal generation unit 35 to which the isolated operation detection signal (stop signal) is input stops generating the PWM signal. Thereby, the power conversion operation of the inverter device 2 is stopped. Further, the switch 8 to which the isolated operation detection signal (open signal) is input disconnects the connection between the grid-connected inverter system A and the load B. Thereby, the independent operation state of the grid connection inverter system A is avoided.

When the absolute values of the threshold value θ ₁ and the threshold value θ ₂ are set to the same value, the isolated operation detection unit 64 may compare the absolute value of the phase change amount θ with the threshold value θ ₁ . In this case, since it is not necessary to switch the threshold value to be compared, it is not necessary to input a reactive power injection signal to the isolated operation detection unit 64.

  FIG. 3 is a flowchart for explaining an isolated operation detection process performed by the isolated operation detection device 6.

The isolated operation detection process is always executed while the inverter device 2 is performing the power conversion operation, that is, while the inverter control device 3 is outputting the PWM signal. First, advance reactive power is injected (S1). That is, the reactive power injection signal generated by the reactive power injection unit 61 is “1” (a state indicating that the advanced reactive power is injected). As a result, the target reactive power Q ^* set by the target reactive power setting unit 32 is set to a positive predetermined value and output, so that the reactive power Q output from the inverter device 2 is the target reactive power Q ^* (positive To a predetermined value).

  Next, the phase change amount θ is detected (S2). That is, the phase of the interconnection point voltage signal Vo input from the voltage sensor 5 is detected by the voltage phase detection unit 62, and the phase change amount θ when compared with the phase during the interconnection operation is calculated by the phase change amount detection unit 63. Detected.

Next, it is determined whether or not the phase change amount θ is larger than the threshold value θ ₁ (S3). When the phase change amount θ is larger than the threshold value θ ₁ (S3: YES), an isolated operation detection signal is output (S4), and the isolated operation detection process is ended.

On the other hand, when the phase change amount θ is equal to or less than the threshold value θ ₁ (S3: NO), the isolated operation detection signal is not output, and delayed reactive power is injected after a predetermined time has elapsed (S5). That is, the reactive power injection signal generated by the reactive power injection unit 61 is “−1” (a state indicating that delayed reactive power is injected). As a result, the target reactive power Q ^* set by the target reactive power setting unit 32 is set to a negative predetermined value and output, so that the reactive power Q output from the inverter device 2 is the target reactive power Q ^* (negative To a predetermined value).

  Next, the phase change amount θ is detected (S6). That is, the phase of the interconnection point voltage signal Vo input from the voltage sensor 5 is detected by the voltage phase detection unit 62, and the phase change amount θ when compared with the phase during the interconnection operation is calculated by the phase change amount detection unit 63. Detected.

Next, it is determined whether or not the phase change amount θ is smaller than the threshold value θ ₂ (S7). When the phase change amount θ is smaller than the threshold value θ ₂ (S7: YES), an isolated operation detection signal is output (S4), and the isolated operation detection process is ended.

On the other hand, when the phase change amount θ is equal to or larger than the threshold value θ ₂ (S7: NO), the isolated operation detection signal is not output, and the process returns to step S1 and proceeds after a predetermined time to inject reactive power (S1). . Whether the phase variation theta is larger than the threshold value θ ₁ (S3: YES), smaller than the threshold value theta _2: to (S7 YES), step S1 to S3, S5 to S7 are repeated Kaee.

  The isolated operation detection device 6 may be realized as an analog circuit or a digital circuit. Further, the processing performed by each unit may be designed by a program, and the computer may function as the isolated operation detection device 6 by executing the program. The program may be recorded on a recording medium and read by a computer.

In this embodiment, the leading reactive power and the delayed reactive power are alternately injected, and the phase change amount θ is compared with the threshold value θ ₁ and the threshold value θ ₂ to detect the single operation state. ing. When the capacitive load of the load B is larger than the inductive load, the amount of advancement of the phase of the connection point voltage signal Vo is reduced even when the advance reactive power is injected, and the voltage phase change amount θ is larger than the threshold value θ _1. It may not be possible. However, in this case, when delayed reactive power is injected, the amount of phase delay of the interconnection point voltage signal Vo increases, and the voltage phase change amount θ becomes smaller than the threshold value θ ₂ . Therefore, even if the isolated operation state cannot be detected when the advanced reactive power is injected, the isolated operation state can be detected when the delayed reactive power is injected.

  FIG. 4 is a timing chart for explaining the relationship between the phase change amount θ of the interconnection point voltage signal Vo and the independent operation detection signal when reactive power is injected.

FIG. 5A shows a change in the reactive power injection signal. As shown in FIG. 6A, the reactive power injection signal becomes “1” (a state indicating that the advanced reactive power is injected) between t1 and t2, and “−1” (a state between t3 and t4). The state shows that the delayed reactive power is injected). FIG. 4B shows the change of the voltage phase change amount θ and the switching of the threshold value (threshold value θ ₁ or threshold value θ ₂ ) compared with the change. In this example, the case where the capacitive load of the load B is larger than the inductive load is shown. FIG. 3C shows the change in the isolated operation detection signal.

The reactive power injection signal is “1” between t1 and t2, and the reactive power is injected during this time. The threshold value to be compared with the voltage phase change amount θ is switched to the threshold value θ ₁ at t1. At this time, the voltage phase change amount θ changes from “0” and becomes a positive value. However, since the capacitive load of the load B is larger than the inductive load, it is smaller than the threshold value θ ₁ . . Therefore, the isolated operation detection signal remains as a low level signal indicating non-detection.

The reactive power injection signal is “−1” between t3 and t4, and delayed reactive power is injected during this time. The threshold value to be compared with the voltage phase change amount θ is switched to the threshold value θ ₂ at t3. At this time, the voltage phase change amount θ changes from “0” to a negative value, and since the capacitive load of the load B is larger than the inductive load, the voltage phase change amount θ is smaller than the threshold value θ ₂ . Therefore, the isolated operation detection signal changes to a high level signal indicating the isolated operation detection. In the present embodiment, since the voltage phase change amount θ is compared with the threshold value at the timing (t2, t4) of the reactive power injection end, the isolated operation detection signal changes to a high level signal at the timing t4. . Note that the timing of comparison between the voltage phase change amount θ and the threshold value is not limited to this.

On the contrary, when the inductive load of the load B is larger than the capacitive load, the amount of delay of the phase of the connection point voltage signal Vo becomes small even when the delayed reactive power is injected, and the voltage phase change amount θ becomes the threshold θ May not be smaller than ₂ . However, in this case, when advance reactive power is injected, the amount by which the phase of the interconnection point voltage signal Vo advances is increased, and the voltage phase change amount θ becomes larger than the threshold value θ ₁ . Therefore, even if the isolated operation state cannot be detected when the delayed reactive power is injected, the isolated operation state can be detected when the advanced reactive power is injected.

  As described above, in this embodiment, the reactive power load is included in the load B because the advanced reactive power and the delayed reactive power are alternately injected to determine whether or not each is in the single operation state. Even in the case where the vehicle is operated, the isolated operation can be detected appropriately. Further, since the amount of reactive power injected is not increased, it is possible to suppress deterioration of the power factor and significant distortion of the waveform of the output current Io.

  In the first embodiment, the case has been described in which the advance reactive power and the delayed reactive power are alternately injected. However, the present invention is not limited to this. For example, after the reactive reactive power is continuously injected a plurality of times, the delayed reactive power may be continuously injected the same number of times.

FIG. 5 shows another example of the waveform of the reactive power injection signal. FIG. 5A shows a reactive power injection signal for continuously injecting the leading reactive power and the delayed reactive power three times each. Yes. In this case, if the phase change amount θ exceeds the threshold even once, it may be determined that the vehicle is in the single operation state, or if the phase change amount θ exceeds the threshold value three times in succession (for example, , T2, t4, and t6, the phase change amount θ may be larger than the threshold value θ ₁ ). When it is determined that the single operation state is reached when the phase change amount θ exceeds the threshold value a plurality of times, erroneous detection of the single operation due to fluctuations in the system voltage or the like can be suppressed. In this case, the period T from t1 to t13 needs to be within 0.5 seconds, which is the active isolated operation detection time limit. Further, in this case, a counter is provided in the isolated operation detection unit 64 to count the number of times the phase change amount θ exceeds the threshold value, and the isolated operation is performed when the counter reaches a predetermined number (for example, “3” times). A detection signal may be output.

  Further, even when the forward reactive power and the delayed reactive power are alternately injected, it may be determined that the vehicle is in the single operation state if the phase change amount θ exceeds the threshold value three times, for example. FIG. 6B illustrates an example in which the advanced reactive power and the delayed reactive power are alternately injected, and the phase change amount θ is determined to be in the single operation state if the phase change amount exceeds the threshold value three times. Is to do. In this case, the period T from t1 to t13 needs to be within 0.5 seconds, which is the active isolated operation detection time limit.

  In the first embodiment, the phase change is detected by detecting the phase of the interconnection point voltage signal Vo and comparing it with the phase during the interconnection operation. However, the present invention is not limited to this. For example, from the injection of reactive power to the timing (hereinafter referred to as “zero cross”) when the interconnection point voltage signal Vo changes from a negative value to a positive value (or from a negative value to a positive value). The phase change may be detected on the basis of the time.

  Since the phase changes when reactive power is injected during single operation, the time from the start of reactive power injection to zero crossing is different from that during interconnection operation (see FIG. 7). Therefore, the time from the zero cross to the zero cross (for example, one cycle) at the time of interconnection operation is timed and recorded, the reactive power injection is started at the zero cross timing, and the time to the corresponding zero cross is timed. When the difference between the measured time and the measured time during the interconnection operation exceeds a predetermined threshold value, it is determined that the phase of the interconnection point voltage signal Vo has changed, and it is determined that it is in the single operation state. May be.

  Moreover, although the said 1st Embodiment demonstrated the case where isolated operation was detected based on the change of the phase of the connection point voltage signal Vo, it is not restricted to this. For example, the isolated operation may be detected based on a change in the frequency of the interconnection point voltage signal Vo.

  The isolated operation detection device, isolated operation detection method, and isolated operation detection system according to the present invention are not limited to the above-described embodiments. The specific configuration of each part of the grid-connected inverter system including the isolated operation detection device, the isolated operation detection method, and the isolated operation detection device according to the present invention can be varied in design in various ways.

A grid-connected inverter system 1 DC power supply 2 inverter device 3 inverter control device 31 reactive power detection unit 32 target reactive power setting unit 33 reactive power control unit 34 current control unit 35 PWM signal generation unit 4 current sensor 5 voltage sensor 6 independent operation Detector 61 Reactive power injection unit (Reactive power injection control means)
62 Voltage Phase Detection Unit 63 Phase Change Amount Detection Unit 64 Independent Operation Detection Unit (Judgment Unit)
8 Switch B Load C Power system D Breaker

Claims (13)

An isolated operation detection device that detects that the grid-connected inverter system that converts DC power into AC power and outputs it to the load and the power system is an isolated operation state in which the power conversion operation is performed in a state disconnected from the power system. There,
Reactive power injection control means for periodically injecting reactive power in which the current advances and reactive power in which the current is delayed into the output power of the inverter device that performs the power conversion operation;
Judgment means for judging whether or not the electrical signal at the interconnection point between the grid interconnection inverter system and the power system has changed,
With
When it is determined by the determination means that the electrical signal has changed, it is detected that the vehicle is in a single operation state.
An isolated operation detection device.   The isolated operation detection device according to claim 1, wherein the determination means determines whether or not the phase of the voltage signal has changed.   The determination unit determines that the phase of the voltage signal has changed when the amount of change from the phase of the phase of the detected voltage signal from the phase during the linked operation exceeds a predetermined threshold value. The isolated operation detection device according to 1. The determination means determines whether or not the amount of change is greater than a predetermined first threshold when injecting reactive power in which current advances, and injecting reactive power in which current is delayed Determine whether the amount of change is less than a predetermined second threshold;
When it is determined by the determination means that the value is larger than the first threshold value, or when it is determined that the value is smaller than the second threshold value, it is detected that the vehicle is in a single operation state.
The isolated operation detection device according to claim 3.   5. The isolated operation detection device according to claim 1, wherein the reactive power injection control unit alternately injects reactive power in which current advances and reactive power in which current is delayed. 6.   5. The isolated operation detection device according to claim 1, wherein the reactive power injection control unit continuously injects the reactive power in which the current advances and the reactive power in which the current is delayed, respectively, several times continuously.   The isolated operation detection device according to any one of claims 1 to 6, wherein when the number of times that the electrical signal is determined to be changed by the determination means reaches a predetermined number, the isolated operation state is detected. .   The determination means changes the phase of the voltage signal when the time difference between the detected zero-cross timing of the voltage signal and the corresponding zero-cross timing of the voltage signal during interconnection operation exceeds a predetermined threshold value. The isolated operation detection device according to claim 2, wherein it is determined that the operation has been performed.   The isolated operation detection device according to claim 1, wherein the determination means determines whether or not the frequency of the voltage signal has changed. The inverter device and the isolated operation detection device according to any one of claims 1 to 9,
A grid-connected inverter system. A single operation detection method for detecting that a grid-connected inverter system that converts DC power into AC power and outputs it to a load and a power system is a single operation state in which power conversion operation is performed in a state disconnected from the power system. There,
A first step of injecting reactive power in which current advances into output power of an inverter device that performs power conversion operation;
A second step of determining whether or not an electrical signal at a connection point between the grid-connected inverter system and the power system has changed;
A third step of injecting reactive power whose current is delayed into the output power of the inverter device;
A fourth step of determining whether the electrical signal has changed;
With
When it is determined that the electrical signal has changed in the second step or the fourth step, it is detected that the vehicle is in a single operation state.
An isolated operation detection method characterized by the above. Computer
As an isolated operation detection device for detecting that the grid-connected inverter system that converts DC power into AC power and outputs it to the load and the power system is in an isolated operation state in which the power conversion operation is performed in a state disconnected from the power system A program for functioning,
The computer,
Reactive power injection control means for periodically injecting reactive power in which the current advances and reactive power in which the current is delayed into the output power of the inverter device that performs the power conversion operation;
Judgment means for judging whether or not the electrical signal at the interconnection point between the grid interconnection inverter system and the power system has changed,
Detecting means for detecting that the electric signal is changed by the determining means to detect that it is in a single operation state;
Program to make it function.   The computer-readable recording medium which recorded the program of Claim 10.

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