JP5770610B2 - Isolated operation detection device, grid-connected inverter system, and isolated operation detection method - Google Patents

Description

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

  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.

  FIG. 13 is a block diagram for explaining a grid-connected inverter system provided with a conventional isolated operation detection device.

  The grid-connected inverter system A100 converts the DC power generated by the DC power source 1 into AC power and supplies it to the connected load C and the three-phase power system B. Hereinafter, the three phases are referred to as a U phase, a V phase, and a W phase.

  The inverter device 2 converts a DC voltage input from the DC power source 1 into an AC voltage by switching a switching element (not shown). The inverter control device 3 receives the current signal and the voltage signal detected by the current sensor 4 and the voltage sensor 5, generates a PWM signal based on the current signal and the voltage signal, and outputs the PWM signal to the inverter device 2. The inverter device 2 performs switching of the switching element based on the PWM signal input from the inverter control device 3.

  When an accident occurs in the power system B, etc., the circuit breaker D is activated by the protective device provided on the power system B side, so that the grid-connected inverter system A100 is disconnected from the power system B (power failure). In this case, a single operation state in which power is supplied to the load C only from the grid-connected inverter system A100 is obtained. Under the condition where the output power of the grid interconnection inverter system A100 and the power consumption of the load C are balanced, the grid interconnection inverter system A100 cannot detect a power failure of the power grid B. In order to ensure the safety of maintenance workers, the grid interconnection inverter system A100 is provided with a function of detecting an isolated operation, disconnecting the load C from the grid interconnection inverter system A100, and automatically stopping the power conversion operation. ing. Further, when reclosing is performed immediately after being disconnected by the circuit breaker D, there is a case where a large overcurrent flows due to connection in a state where the phase is shifted. In this case, the circuit breaker D is disconnected again, and an upper substation of the electric power system B is also affected. In the worst case, there is a possibility that a wide-area power failure occurs. In order to prevent this, it is necessary to detect isolated operation appropriately and at high speed.

  The isolated operation detection device 600 is for detecting an isolated operation of the grid interconnection inverter system A100. When the isolated operation detection device 600 detects an isolated operation, the isolated operation detection device 600 outputs an open signal to the switch 8 and outputs a stop signal to the inverter control device 3. The switch 8 to which the open signal is inputted disconnects the connection between the grid interconnection inverter system A100 and the load C. 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 grid connection inverter system A100 is avoided.

  The islanding operation detection device 600 detects the islanding operation by a passive method for detecting the islanding state by detecting a change in voltage waveform or phase that occurs when the islanding operation is changed to the islanding operation. There is an active method in which a fluctuation factor is given to the device, and when the voltage waveform or phase changes correspondingly, it is detected that the state is in an isolated operation state. Among these, as an active method, an isolated operation detection method using an inter-order harmonic detection method has been developed. The isolated operation detection method of the inter-order harmonic detection method is a harmonic that is not normally included in the power system B, and is a harmonic having a frequency that is a non-integer multiple of the fundamental wave of the power system B (hereinafter referred to as “inter-order harmonics”). In this case, the impedance or admittance of the harmonics of the power system B as viewed from the interconnection point is detected and the islanding operation is detected from the change. is there.

  The islanding operation detection device 600 periodically issues a command to the current injection device 7 to convert a single-phase current of inter-order harmonics (for example, 2.4-order harmonics) between predetermined phases (for example, U-phase) of the power system B. Between V phases). Then, from the current signal input from the current sensor 4 and the voltage signal input from the voltage sensor 5, the signal for the positive phase and the signal for the reverse phase of the interharmonic harmonic are obtained by discrete Fourier transform and symmetrical coordinate transformation. And are extracted respectively. The isolated operation detection device 600 calculates the admittance for the normal phase from the voltage signal and current signal for the normal phase, and calculates the admittance for the reverse phase from the voltage signal and current signal for the reverse phase. Then, when the single operation is detected from the change in the admittance for the positive phase and the single operation is also detected from the change in the admittance for the reverse phase, it is determined that the single operation has been detected. When it is determined that the isolated operation is detected, the isolated operation detection device 600 outputs an open signal to the switch 8 and outputs a stop signal to the inverter control device 3.

JP 2003-250226 A

  However, in the case of the method described above, when extracting the signal for the positive phase and the signal for the negative phase of the inter-order harmonic component from the current signal and the voltage signal, respectively, first, for each coefficient that is expanded in the Fourier series, It is necessary to extract a signal of inter-order harmonic components by using discrete Fourier transform, and further to perform a symmetrical coordinate transformation to extract a signal for the positive phase and a signal for the reverse phase.

  The present invention has been conceived under the circumstances described above, and is capable of extracting a single phase operation signal and a positive phase signal of the injected harmonics by simple processing. Its purpose is to provide a device.

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

An isolated operation detection device provided by the first aspect of the present invention is an isolated operation detection device that detects an isolated operation of a grid-connected inverter system that is linked to a three-phase AC power system. Current injection instruction means for single-phase injection of a harmonic current of a predetermined angular frequency; voltage signal conversion means for converting the detected three-phase voltage signal into a first voltage signal and a second voltage signal; Current signal conversion means for converting a three-phase current signal into a first current signal and a second current signal; processing the first voltage signal with a first transfer function; and converting the second voltage signal into Signal processing is performed by the second transfer function, and the first positive phase divided voltage signal is extracted by adding them, the first voltage signal is signal-processed by the third transfer function, and the second voltage Signal to the first transfer function Signal processing, and adding these, positive phase divided voltage signal extraction means for extracting a second positive phase divided voltage signal, signal processing the first voltage signal by the first transfer function, The second voltage signal is signal-processed by the third transfer function, and these are added to extract a first negative phase voltage signal, and the first voltage signal is signaled by the second transfer function. Processing, processing the second voltage signal according to the first transfer function, and adding them to extract a second negative phase voltage signal, and the first phase voltage signal extracting means, Current signal is processed by the first transfer function, the second current signal is signal processed by the second transfer function, and these are added to extract a first positive phase current signal. , The first current signal according to the third transfer function. Positive-phase current signal extraction means for extracting the second positive-phase current signal by adding the signals, processing the second current signal with the first transfer function, The first current signal is signal-processed by the first transfer function, the second current signal is signal-processed by the third transfer function, and these are added to obtain the first negative-phase current signal. Extracting, signal-processing the first current signal with the second transfer function, signal-processing the second current signal with the first transfer function, and adding them to form a second anti-phase A negative phase divided current signal extracting means for extracting a divided current signal, the first positive phase divided voltage signal and the second positive phase divided voltage signal, the first positive phase divided current signal and the second Positive phase to calculate the positive phase system circuit constant from the positive phase current signal From the distribution circuit constant calculation means, the first negative phase divided voltage signal and the second negative phase divided voltage signal, the first negative phase divided current signal and the second negative phase divided current signal. A negative phase system circuit constant calculating means for calculating a system circuit constant for the reverse phase, and an independent operation for determining the single operation based on a change in the system circuit constant for the positive phase and the system circuit constant for the negative phase Determination means, where the predetermined angular frequency is ω and the time constant is T, the first transfer function is
G ₁ (s) = (T · s + 1) / {(T · s + 1) ² + (T · ω) ² }
And the second transfer function is
G ₂ (s) = − T · ω / {(T · s + 1) ² + (T · ω) ² }
And the third transfer function is
G ₃ (s) = T · ω / {(T · s + 1) ² + (T · ω) ² }
It is characterized by being.

An isolated operation detection apparatus provided by the second aspect of the present invention is an isolated operation detection apparatus that detects an isolated operation of a grid-connected inverter system that is linked to a three-phase AC power system. Current injection instruction means for single-phase injection of a harmonic current of a predetermined angular frequency; voltage signal conversion means for converting the detected three-phase voltage signal into a first voltage signal and a second voltage signal; Current signal conversion means for converting a three-phase current signal into a first current signal and a second current signal; processing the first voltage signal with a first transfer function; and converting the second voltage signal into Signal processing is performed by the second transfer function, and the first positive phase divided voltage signal is extracted by adding them, the first voltage signal is signal-processed by the third transfer function, and the second voltage Signal to the first transfer function Signal processing, and adding these, positive phase divided voltage signal extraction means for extracting a second positive phase divided voltage signal, signal processing the first voltage signal by the first transfer function, The second voltage signal is signal-processed by the third transfer function, and these are added to extract a first negative phase voltage signal, and the first voltage signal is signaled by the second transfer function. Processing, processing the second voltage signal according to the first transfer function, and adding them to extract a second negative phase voltage signal, and the first phase voltage signal extracting means, Current signal is processed by the first transfer function, the second current signal is signal processed by the second transfer function, and these are added to extract a first positive phase current signal. , The first current signal according to the third transfer function. Positive-phase current signal extraction means for extracting the second positive-phase current signal by adding the signals, processing the second current signal with the first transfer function, The first current signal is signal-processed by the first transfer function, the second current signal is signal-processed by the third transfer function, and these are added to obtain the first negative-phase current signal. Extracting, signal-processing the first current signal with the second transfer function, signal-processing the second current signal with the first transfer function, and adding them to form a second anti-phase A negative phase divided current signal extracting means for extracting a divided current signal, the first positive phase divided voltage signal and the second positive phase divided voltage signal, the first positive phase divided current signal and the second Positive phase to calculate the positive phase system circuit constant from the positive phase current signal From the distribution circuit constant calculation means, the first negative phase divided voltage signal and the second negative phase divided voltage signal, the first negative phase divided current signal and the second negative phase divided current signal. A negative phase system circuit constant calculating means for calculating a system circuit constant for the reverse phase, and an independent operation for determining the single operation based on a change in the system circuit constant for the positive phase and the system circuit constant for the negative phase Determination means, where the predetermined angular frequency is ω and the time constant is T, the first transfer function is
G ₁ (s) = (T ² · s ² + T · s + T ² · ω ² ) / {(T · s + 1) ² + (T · ω) ² }
And the second transfer function is
G ₂ (s) = − T · ω / {(T · s + 1) ² + (T · ω) ² }
And the third transfer function is
G ₃ (s) = T · ω / {(T · s + 1) ² + (T · ω) ² }
It is characterized by being.

  In a preferred embodiment of the present invention, the predetermined angular frequency is a non-integer multiple angular frequency of the fundamental wave of the power system.

  In a preferred embodiment of the present invention, the islanding determination means can determine that the islanding operation is based on a change in the system circuit constant for the positive phase and based on a change in the system circuit constant for the reverse phase. Only when it can be determined as an isolated operation, it is determined as an isolated operation.

  In a preferred embodiment of the present invention, the current injection instructing unit instructs the grid interconnection inverter system to inject a harmonic current having the predetermined angular frequency.

  In a preferred embodiment of the present invention, the system circuit constant is an absolute value of admittance.

  The grid-connected inverter system provided by the third aspect of the present invention includes the islanding detection device provided by the first or second aspect of the present invention.

An islanding operation detection method provided by the fourth aspect of the present invention is an islanding operation detection method for detecting islanding operation of a grid-connected inverter system linked to a three-phase AC power system. A first step of single-phase injection of a harmonic current of a predetermined angular frequency; a second step of converting the detected three-phase voltage signal into a first voltage signal and a second voltage signal; A third step of converting a three-phase current signal into a first current signal and a second current signal; signal processing of the first voltage signal by a first transfer function; Signal processing is performed by the second transfer function, and the first positive phase divided voltage signal is extracted by adding them, the first voltage signal is signal-processed by the third transfer function, and the second voltage The signal is processed by the first transfer function, A fourth step of extracting a second positive phase divided voltage signal by adding the first and second signals, processing the first voltage signal with the first transfer function, and converting the second voltage signal to the first Signal processing is performed using a transfer function of 3, and a first negative-phase voltage signal is extracted by adding them, and the first voltage signal is signal-processed using the second transfer function, and the second voltage A signal is processed by the first transfer function, and a second negative phase voltage signal is extracted by adding the signals, and the first current signal is converted by the first transfer function. Signal processing, signal processing of the second current signal by the second transfer function, and adding them to extract a first positive phase current signal, and converting the first current signal to the third current signal And processing the second current signal with the second transfer function. A sixth step of extracting a second positive phase current signal by adding the signals, and signal processing the first current signal with the first transfer function, The second current signal is signal-processed by the third transfer function, and these are added to extract a first negative-phase current signal, and the first current signal is signaled by the second transfer function. Processing, processing the second current signal with the first transfer function, and adding them to extract a second negative-phase current signal, and the first positive phase A system circuit constant for the positive phase is calculated from the divided voltage signal and the second positive phase divided voltage signal, and the first positive phase divided current signal and the second positive phase divided current signal. A step, and the first negative phase voltage signal and the second negative voltage signal A ninth step of calculating a system circuit constant for the negative phase from the first negative phase component current signal and the second negative phase component current signal, and the positive phase system circuit constant and the reverse phase And a tenth step of determining isolated operation based on a change in system circuit constant of a phase, and when the predetermined angular frequency is ω and a time constant is T, the first transfer function is
G ₁ (s) = (T · s + 1) / {(T · s + 1) ² + (T · ω) ² }
And the second transfer function is
G ₂ (s) = − T · ω / {(T · s + 1) ² + (T · ω) ² }
And the third transfer function is
G ₃ (s) = T · ω / {(T · s + 1) ² + (T · ω) ² }
It is characterized by being.

  According to the present invention, a positive phase signal and a negative phase signal having a predetermined angular frequency are extracted from each voltage signal and each current signal, respectively, and a system circuit for the positive phase is extracted using the extracted positive phase signal. A constant is calculated, and a system circuit constant for the negative phase is calculated using the extracted signal for the negative phase. Then, the isolated operation is detected based on the change in the calculated system circuit constant for the positive phase and the system circuit constant for the reverse phase. Since only the signal processing is performed using the first to third transfer functions, the signals for the positive phase and the negative phase having a predetermined angular frequency can be extracted by simple processing.

  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 block diagram for demonstrating the grid connection inverter system which concerns on 1st Embodiment. It is a block diagram for demonstrating the internal structure of the isolated operation detection apparatus which concerns on 1st Embodiment. It is a block diagram for demonstrating the method to convert the process accompanied by a rotation coordinate transformation and a stationary coordinate transformation into a linear time invariant process. It is a block diagram for demonstrating the method to convert the process accompanied by a rotation coordinate transformation and a stationary coordinate transformation into a linear time invariant process, and is represented by the matrix. It is a block diagram for demonstrating the calculation of a matrix. It is a block diagram which shows the process which performs a static coordinate transformation after performing a low-pass filter process after performing a rotational coordinate transformation. It is a Bode diagram for analyzing a transfer function which is each element of matrix G _LPF . It is a figure for demonstrating the signal for a positive phase, and the signal for a reverse phase. It is a block diagram which shows the process which performs a static coordinate transformation after performing a high-pass filter process after performing a rotational coordinate transformation. It is a Bode diagram for analyzing a transfer function which is each element of matrix G _HPF . It is a block diagram for demonstrating the internal structure of the positive phase divided voltage signal extraction part which concerns on 2nd Embodiment. It is a figure which shows the frequency characteristic of the part for the positive phase (reverse phase) voltage (current) signal extraction part which concerns on 2nd Embodiment. It is a block diagram for demonstrating the grid connection inverter system provided with the conventional isolated operation detection apparatus.

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

  FIG. 1 is a block diagram for explaining a grid-connected inverter system according to the first embodiment.

  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, a current injection device 7, and a switch. 8 is provided. The DC power source 1 is connected to the inverter device 2. The inverter device 2 is connected to a three-phase AC power system B via an output line of U-phase, V-phase, and W-phase output voltages via a switch 8. The current sensor 4 and the voltage sensor 5 are installed on the output side of the inverter device 2. The inverter control device 3 is connected to the inverter device 2. The grid-connected inverter system A converts the DC power output from the DC power supply 1 into AC power and supplies it to the power system B and the load C. In addition, the structure of the grid connection inverter system A is not restricted to this. For example, other sensors necessary for controlling the inverter device 2 may be provided.

  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 C and the power system B. The inverter device 2 includes a PWM control type three-phase inverter circuit including three sets and six switching elements (not shown). The inverter circuit converts the DC voltage input from the DC power source 1 into an AC voltage by switching each switching element on and off based on the PWM signal input from the inverter control device 3. Further, the inverter device 2 removes a high-frequency component due to switching by a built-in filter circuit (not shown), and boosts or steps down the AC voltage to a level substantially equal to the system voltage by a built-in transformer circuit. In addition, the structure of the inverter apparatus 2 is not restricted to this. For example, the inverter circuit may be a multi-level inverter circuit. Also, a so-called transformer-less system without a transformer circuit may be used. Further, a DC / DC converter circuit may be provided between the DC power source 1 and the inverter device 2.

  The inverter control device 3 controls the inverter device 2 and is realized by, for example, a microcomputer. The inverter control device 3 commands the waveform of the output voltage output from the grid-connected inverter system A based on the current signal I input from the current sensor 4 and the voltage signal V input from the voltage sensor 5. The command value signal is generated, and a pulse signal generated based on the command value signal is output as a PWM signal. The inverter device 2 outputs an alternating voltage having a waveform corresponding to the command value signal by switching each switching element on and off based on the input PWM signal.

  The inverter control device 3 includes a command value signal generation unit 31 and a PWM signal generation unit 32.

  The command value signal generator 31 receives the current signal I from the current sensor 4 and the voltage signal V from the voltage sensor 5 to control the output power and the output current of the grid-connected inverter system A. A compensation signal is generated, and a command value signal is generated based on the compensation signal. The generated command value signal is output to the PWM signal generation unit 32. A description of each control and the command value signal generation method is omitted.

  The PWM signal generation unit 32 generates a PWM signal by a triangular wave comparison method based on an input command value signal and a carrier signal generated as a triangular wave signal having a predetermined frequency (for example, 4 kHz). In the triangular wave comparison method, a command value signal and a carrier signal are respectively compared. For example, a pulse signal that is high when the command value signal is larger than the carrier signal and low when it is smaller is generated as a PWM signal. The generated PWM signal is output to the inverter device 2. Moreover, the PWM signal generation part 32 stops the production | generation of a PWM signal, when the isolated operation detection signal (stop signal) is input from the isolated operation detection apparatus 6. FIG. Thereby, the power conversion operation of the inverter device 2 is stopped.

  The current sensor 4 detects a current flowing through each phase at a connection point with the power system B (that is, an output current of the system connection inverter system A). The detected current signal I (Iu, Iv, Iw) is input to the inverter control device 3 and the isolated operation detection device 6. The voltage sensor 5 detects the voltage of each phase at the connection point with the power system B. The detected voltage signal V (Vu, Vv, Vw) is input to the inverter control device 3 and the independent operation detection device 6. Note that, when the grid-connected inverter system A is linked to the power grid B, the voltage at the grid point substantially matches the grid voltage.

  The isolated operation detection device 6 detects an isolated operation, and is realized by, for example, a microcomputer. The islanding operation detection device 6 periodically outputs a current injection instruction signal to the current injection device 7, and causes the current injection device 7 to inject a current of interharmonics into the power system B. The isolated operation detection device 6 detects an isolated operation based on the voltage signal and the current signal detected when the current injection device 7 injects a current of interharmonic harmonics. Details of the detection method of the isolated operation will be described later. The isolated operation detection device 6 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 PWM signal generation unit 32 of the inverter control device 3 as a stop signal and input to the switch 8 as an open signal.

  The current injection device 7 injects a single-phase current of inter-order harmonics into the power system B, and is configured by an inverter circuit, a transformer, and the like. The current injection device 7 injects a single-phase current of inter-order harmonics between predetermined phases (for example, between the U phase and the V phase) of the power system B in response to the instruction signal input from the isolated operation detection device 6. In the present embodiment, for example, 2.4 order harmonics are used as interharmonics to be injected. Hereinafter, the harmonics between orders injected by the current injection device 7 are referred to as “harmonics between injection orders”.

  The switch 8 disconnects the connection between the grid-connected inverter system A and the load C. The switch 8 disconnects the connection between the grid-connected inverter system A and the load C 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.

  Next, details of the isolated operation detection device 6 will be described with reference to FIGS.

  FIG. 2 is a block diagram for explaining the internal configuration of the isolated operation detection device 6.

  As shown in the figure, the isolated operation detection device 6 includes a voltage signal three-phase / two-phase converter 61, a positive-phase divided voltage signal extractor 62a, a reverse-phase divided voltage signal extractor 62b, a current signal three-phase / two-phase. A conversion unit 63, a positive phase component current signal extraction unit 64a, a negative phase component current signal extraction unit 64b, a positive phase component system circuit constant calculation unit 65, a negative phase component system circuit constant calculation unit 66, an isolated operation determination unit 67, and A determination instruction unit 68 is provided. 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 voltage signal three-phase / two-phase converter 61 converts the three voltage signals Vu, Vv, Vw input from the voltage sensor 5 into an α-axis voltage signal Vα and a β-axis voltage signal Vβ. The voltage signal three-phase / two-phase conversion unit 61 performs so-called three-phase / two-phase conversion processing (αβ conversion processing), and converts the voltage signals Vu, Vv, Vw into orthogonal α-axis components and β-axis components. Respectively, and the α-axis voltage signal Vα and the β-axis voltage signal Vβ are generated by combining the axis components.

The conversion process performed by the voltage signal three-phase / two-phase converter 61 is expressed by a determinant represented by the following equation (1).

  The positive-phase divided voltage signal extraction unit 62a and the negative-phase divided voltage signal extraction unit 62b are based on the α-axis voltage signal Vα and the β-axis voltage signal Vβ input from the voltage signal three-phase / two-phase conversion unit 61, and the harmonics between the injection orders. A signal for the positive phase and a signal for the negative phase of the wave are extracted. The positive phase divided voltage signal extraction unit 62a and the negative phase divided voltage signal extraction unit 62b are linear time invariant processes (hereinafter, referred to as an improved rotation coordinate conversion process (dq conversion process) developed by the inventors of the present application). A low-pass filter using “DQ-LTI conversion processing”) is used.

  The DQ-LTI conversion processing can perform processing equivalent to performing static coordinate conversion (inverse dq conversion) after performing predetermined processing after performing rotational coordinate conversion (dq conversion), and linearity. And signal processing with time invariance. Since rotational coordinate transformation and stationary coordinate transformation are nonlinear time-varying processes, linear control theory cannot be used for designing a control system using these, and system analysis cannot be performed. The DQ-LTI conversion process has been developed to solve this problem, and a process equivalent to performing a static coordinate conversion after performing a predetermined process after performing a rotational coordinate conversion is performed as a transfer function. This is a calculation process using a matrix.

  First, a method for converting processing involving rotational coordinate transformation and stationary coordinate transformation into linear time-invariant processing will be described.

  FIG. 3A is a diagram for explaining processing involving rotational coordinate conversion and stationary coordinate conversion. In this processing, first, the signals α and β are converted into signals d and q by rotational coordinate conversion. The signals d and q are each processed by a predetermined transfer function F (s), and signals d 'and q' are output. Next, the signals d ′ and q ′ are converted into signals α ′ and β ′ by stationary coordinate transformation. The nonlinear time-varying process shown in FIG. 3A is converted into a process using a matrix G of linear time-invariant transfer functions shown in FIG.

The rotational coordinate transformation shown in FIG. 3A is represented by a determinant of the following equation (2), and the stationary coordinate transformation is represented by a determinant of the following equation (3).

  Therefore, the process shown in FIG. 3A can be expressed as shown in FIG. 4A using a matrix. The matrix G shown in FIG. 3B can be calculated by calculating the product of the three matrices shown in FIG. 4A and making the calculated matrix a linear time-invariant matrix. At this time, the calculation is performed after converting the matrix of the stationary coordinate conversion and the rotation coordinate conversion into a matrix product.

The matrix of rotational coordinate conversion can be converted into a product of the right-hand side matrix shown in the following equation (4).
Where j is the imaginary unit, exp () is the exponential function of the base e of the natural logarithm,
It is. T ⁻¹ is an inverse matrix of T.

From the Euler's formula, calculating by substituting exp (jθ) = cos θ + jsin θ and exp (−jθ) = cos θ−jsin θ,
It can be confirmed that

Further, the matrix of the static coordinate conversion can be converted into the product of the matrix on the right side shown in the following equation (5). The matrix in the middle of the matrix product is a linear time-invariant matrix.
Where j is the imaginary unit, exp () is the exponential function of the base e of the natural logarithm,
It is. T ⁻¹ is an inverse matrix of T.

From the Euler's formula, calculating by substituting exp (jθ) = cos θ + jsin θ and exp (−jθ) = cos θ−jsin θ,
It can be confirmed that

When the product of the three matrices shown in FIG. 4A is calculated using the above equations (4) and (5) and the matrix G is calculated, the following equation (6) is obtained.

When attention is paid to the element in the first row and the first column of the three matrixes in the center of the above equation (6) and this is represented by a block diagram, the block diagram shown in FIG. 5 is obtained. When calculating the input / output characteristics of the block diagram shown in FIG.
It becomes. Where F (s) is a one-input one-output transfer function having an impulse response f (t).

  Here, assuming that θ (t) = ωt, θ (t) −θ (τ) = ωt−ωτ = ω (t−τ) = θ (t−τ), and therefore the block diagram shown in FIG. Is equal to that of a linear time invariant system having an impulse response f (t) exp (-jωt). When the impulse response f (t) exp (−jωt) is Laplace transformed, a transfer function F (s + jω) is obtained. The input / output characteristics when exp (jθ (t)) and exp (−jθ (t)) in the block diagram shown in FIG. 5 are interchanged are the input / output characteristics of the transfer function F (s−jω). Become.

Therefore, if the calculation is further advanced from the above equation (6),
Is calculated.

  Thereby, the process shown to Fig.4 (a) can be converted into the process shown to FIG.4 (b). The process shown in FIG. 4B is equivalent to the process of performing the stationary coordinate conversion after performing the process represented by the predetermined transfer function F (s) after performing the rotational coordinate conversion. This system is a linear time-invariant system.

The transfer function of the low-pass filter is represented by F (s) = 1 / (Ts + 1), where T is the time constant. Therefore, the transfer function matrix G _LPF showing the process shown in FIG. 6, that is, the process equivalent to the process of performing the static coordinate conversion after the low-pass filter process after performing the rotary coordinate conversion, And is calculated as shown in the following equation (8).

FIG. 7 is a Bode diagram for analyzing a transfer function that is each element of the matrix G _LPF . FIG. 5A shows a 1-row and 1-column element of matrix G _LPF (hereinafter referred to as “(1,1) element”. Other elements are also described in the same manner) and (2,2) element. It shows a transfer function, Fig. (b) shows a transfer function of (1,2) element of the matrix G _LPF, FIG. (c) the transfer function of the (2,1) element of the matrix G _LPF Is shown. The figure shows the case where the center frequency is the frequency of the fundamental wave of the system voltage (for example, 60 [Hz]) (that is, the center angular frequency ω = 120π [rad / sec]). In this case, “0.1”, “1”, “10”, and “100” are shown.

The amplitude characteristics shown in FIGS. 4A, 4B, and 5C all have a peak at the center frequency, and the peak of the amplitude characteristic is −6 dB (= 1/2). Further, as the time constant T increases, the pass band decreases. The phase characteristic shown in FIG. 5A is 0 degree at the center frequency. That is, the transfer function of the (1, 1) element and the (2, 2) element of the matrix G _LPF passes the signal of the center frequency (center angular frequency) without changing the phase. The phase characteristic shown in FIG. 5B is 90 degrees at the center frequency. That is, the transfer function of the (1,2) element of the matrix G _LPF passes the phase of the signal of the center frequency (center angular frequency) by 90 degrees. On the other hand, the phase characteristic shown in FIG. 4C is −90 degrees at the center frequency. That is, the transfer function of the (2, 1) element of the matrix G _LPF passes the signal of the center frequency (center angular frequency) delayed by 90 degrees. Hereinafter, processing shown in the transfer function matrix G _LPF for the two signals after the three-phase / two-phase conversion will be discussed with reference to FIG.

  FIG. 8 is a diagram for explaining the signal for the positive phase and the signal for the negative phase. FIG. 4A shows the signal for the positive phase, and FIG. 4B shows the signal for the reverse phase.

  In FIG. 9A, positive phase signals of harmonics between injection orders (center angular frequency ω) included in the voltage signals Vu, Vv, Vw are indicated by vectors u, v, w of broken line arrows. The vectors u, v, and w have directions different from each other by 120 degrees, and are arranged in a clockwise order and rotated counterclockwise at the central angular frequency ω. The α-axis signal and β-axis signal obtained by converting the positive phase signal into three-phase / two-phase signals are indicated by vectors α and β of solid arrows. The vectors α and β are different in the direction of 90 degrees in the clockwise order, and are rotated in the counterclockwise direction at the central angular frequency ω.

That is, the α-axis signal is 90 degrees ahead of the β-axis signal. When the processing shown in the transfer function of the (1, 1) element of the matrix G _LPF is performed on the α-axis signal, the amplitude becomes half and the phase does not change (see FIG. 7A). Further, when the process indicated by the transfer function of the (1,2) element of the matrix G _LPF is performed on the β-axis signal, the amplitude is halved and the phase is advanced by 90 degrees (see FIG. 7B). Therefore, since both phases are the same as the α-axis signal, the α-axis signal is reproduced by adding both. On the other hand, when the processing indicated by the transfer function of the (2, 1) element of the matrix G _LPF is performed on the α-axis signal, the amplitude is halved and the phase is delayed by 90 degrees (see FIG. 7C). Further, when the process indicated by the transfer function of the (2, 2) element of the matrix G _LPF is performed on the β-axis signal, the amplitude becomes half and the phase does not change. Therefore, since both phases are the same as the β-axis signal, the β-axis signal is reproduced by adding both.

The reverse phase component is a component whose phase sequence is opposite to the normal phase component. In FIG. 8B, the reverse phase signal of the harmonics between injection orders (center angular frequency ω) included in the voltage signals Vu, Vv, and Vw is indicated by vectors u, v, and w of broken line arrows. The vectors u, v, and w are different in direction from each other by 120 degrees, and are arranged in the counterclockwise order and rotated in the counterclockwise direction at the central angular frequency ω. An α-axis signal and a β-axis signal obtained by three-phase / two-phase conversion of the antiphase signal are indicated by vectors α and β of solid arrows. The vectors α and β are different in the direction of 90 degrees in the counterclockwise order, and rotate in the counterclockwise direction at the angular frequency ω ₀ .

That is, the α-axis signal is 90 degrees behind the β-axis signal. When the processing indicated by the transfer function of the (1, 1) element of the matrix G _LPF is performed on the α-axis signal, the amplitude becomes half and the phase does not change. Further, when the process indicated by the transfer function of the (1,2) element of the matrix G _LPF is performed on the β-axis signal, the amplitude becomes half and the phase advances by 90 degrees. Therefore, since the phases of both are reversed, adding them together cancels each other. On the other hand, when the processing indicated by the transfer function of the (2, 1) element of the G _LPF is performed on the α-axis signal, the amplitude is halved and the phase is delayed by 90 degrees. Further, when the process indicated by the transfer function of the (2, 2) element of the matrix G _LPF is performed on the β-axis signal, the amplitude becomes half and the phase does not change. Therefore, since the phases of both are reversed, adding them together cancels each other. That is, the transfer function matrix G _LPF passes the positive phase signal of the harmonics between the injection orders and blocks the negative phase signal. In addition, since signals of frequencies other than the harmonics between injection orders (harmonics other than harmonics between injection orders, fundamental waves, etc.) are attenuated by harmonics between injection orders, the processing shown in the transfer function matrix G _LPF is as follows: It can be confirmed that this is a band-pass filter process for extracting the positive phase signal of the center frequency.

When the (1, 2) element and the (2, 1) element of the transfer function matrix G _LPF are interchanged, conversely to the above, the positive phase signal is cut off and the negative phase signal is passed. Therefore, when extracting the antiphase signal of the center frequency, a matrix obtained by exchanging the (1, 2) element and the (2, 1) element of the transfer function matrix G _LPF may be used.

Returning to FIG. 2, the positive phase divided voltage signal extraction unit 62 a determines the positive of the inter-injection order harmonics from the α axis voltage signal Vα and the β axis voltage signal Vβ input from the voltage signal three-phase / two-phase conversion unit 61. The signal for the phase is extracted. The extracted positive phase divided voltage signals Vαp and Vβp are output to the positive phase divided system circuit constant calculation unit 65. The positive phase divided voltage signal extraction unit 62a performs the processing represented by the transfer function matrix G _LPF shown in the above equation (8). That is, the process shown in the following equation (9) is performed. As the center angular frequency ω, the angular frequency of the harmonics between the injection orders is set in advance. For example, when the harmonic between injection orders is a 2.4 harmonic, if the angular frequency of the fundamental wave of the system voltage is ω ₀ = 120π [rad / sec] (60 [Hz]), the center angular frequency ω = 2. 4ω ₀ = 288π [rad / sec] (144 [Hz]) is set. The time constant T is designed in advance.

The positive phase divided voltage signal extraction unit 62a performs the filtering process in the stationary coordinate system without performing the rotation coordinate conversion and the stationary coordinate conversion. The process performed by the positive phase divided voltage signal extraction unit 62a is a linear time invariant process because it is represented by a transfer function matrix G _LPF . Since the system is a linear time invariant system that does not include the rotating coordinate transformation process and the static coordinate transformation process, which are nonlinear time-varying processes, control system design and system analysis using linear control theory are possible. Further, the positive phase divided voltage signals Vαp and Vβp are easily calculated by the above equation (9).

The anti-phase voltage signal extraction unit 62b extracts the anti-phase signal of the harmonics between the injection orders from the α-axis voltage signal Vα and β-axis voltage signal Vβ input from the voltage signal three-phase / two-phase conversion unit 61. To do. The extracted negative phase divided voltage signals Vαn and Vβn are output to the negative phase divided system circuit constant calculation unit 66. The negative phase divided voltage signal extraction unit 62b performs processing represented by a matrix in which the (1,2) and (2,1) elements of the matrix G _LPF of the transfer function shown in the above equation (8) are interchanged. That is, the process for extracting the reverse phase signal is performed, and the process shown in the following equation (10) is performed. Similar to the positive phase divided voltage signal extraction unit 62a, the angular frequency of the harmonics between the injection orders is preset as the center angular frequency ω. The time constant T is designed in advance.

The negative phase divided voltage signal extraction unit 62b performs the filtering process in the stationary coordinate system without performing the rotation coordinate conversion and the stationary coordinate conversion. The processing performed by the negative phase divided voltage signal extraction unit 62b is represented by a matrix in which the (1,2) element and the (2,1) element of the transfer function matrix G _LPF are interchanged. is there. Since the system is a linear time invariant system that does not include the rotating coordinate transformation process and the static coordinate transformation process, which are nonlinear time-varying processes, control system design and system analysis using linear control theory are possible. Further, the negative phase divided voltage signals Vαn and Vβn are easily calculated by the above equation (10).

  The current signal three-phase / two-phase converter 63 converts the three current signals Iu, Iv, Iw input from the current sensor 4 into an α-axis current signal Iα and a β-axis current signal Iβ. The current signal three-phase / two-phase conversion unit 63 performs a so-called three-phase / two-phase conversion process (αβ conversion process). The current signals Iu, Iv, and Iw are converted into an α-axis component and a β-axis component that are orthogonal to each other. To generate the α-axis current signal Iα and the β-axis current signal Iβ.

The conversion process performed by the current signal three-phase / two-phase conversion unit 63 is represented by a determinant represented by the following equation (11).

The positive phase current signal extraction unit 64a extracts the positive phase signal of the harmonics between the injection orders from the α-axis current signal Iα and β-axis current signal Iβ input from the current signal three-phase / two-phase conversion unit 63. To do. The extracted positive-phase current signals Iαp and Iβp are output to the positive-phase current system circuit constant calculation unit 65. The positive-phase current signal extraction unit 64a performs the processing represented by the transfer function matrix G _LPF shown in the above equation (8). That is, the process shown in the following equation (12) is performed. As the central angular frequency ω, the angular frequency of the harmonics between the injection orders is set in advance, and the time constant T is designed in advance.

The anti-phase current signal extraction unit 64b extracts the anti-phase signal of the harmonics between the injection orders from the α-axis current signal Iα and the β-axis current signal Iβ input from the current signal three-phase / two-phase conversion unit 63. To do. The extracted negative phase current signals Iαn and Iβn are output to the negative phase system circuit constant calculation unit 66. The reversed-phase current signal extraction unit 64b performs processing represented by a matrix in which the (1,2) and (2,1) elements of the matrix G _LPF of the transfer function shown in the above equation (8) are interchanged. That is, the process shown in the following equation (13) is performed. As the central angular frequency ω, the angular frequency of the harmonics between the injection orders is set in advance, and the time constant T is designed in advance.

The positive phase system circuit constant calculation unit 65 calculates system circuit constants for the positive phase. In this embodiment, the absolute value of admittance is calculated as the system circuit constant for the positive phase. The positive phase distribution system circuit constant calculation unit 65 includes the positive phase divided voltage signals Vαp and Vβp input from the positive phase divided voltage signal extraction unit 62a and the positive phase divided current signal input from the positive phase divided current signal extraction unit 64a. The absolute value Yp of the admittance for the positive phase is calculated from Iαp and Iβp by the following equation (14). The calculated absolute value Yp of the admittance for the positive phase is output to the isolated operation determination unit 67.

The anti-phase system circuit constant calculation unit 66 calculates system circuit constants for the anti-phase. In this embodiment, the absolute value of the admittance is calculated as the system circuit constant for the reverse phase. The negative-phase component system circuit constant calculation unit 66 includes the negative-phase divided voltage signals Vαn and Vβn input from the negative-phase divided voltage signal extraction unit 62b and the negative-phase divided current signal input from the negative-phase divided current signal extraction unit 64b. From Iαn and Iβn, the absolute value Yn of the admittance for the reverse phase is calculated by the following equation (15). The calculated absolute value Yn of the reversed phase admittance is output to the isolated operation determination unit 67.

  The isolated operation determination unit 67 determines whether or not the grid interconnection inverter system A is in an isolated operation state. The isolated operation determination unit 67 performs determination when a determination instruction signal is input from the determination instruction unit 68, and outputs an isolated operation detection signal when it is determined that the vehicle is in the isolated operation state. The isolated operation determination unit 67 has a positive phase admittance absolute value Yp input from the normal phase distribution system circuit constant calculation unit 65 smaller than a predetermined value set in advance and a reverse phase distribution system circuit constant calculation unit 66. When the absolute value Yn of the admittance for the reverse phase calculated by is smaller than a predetermined value set in advance, it is determined that the vehicle is in the single operation state.

  The absolute value Yp of the admittance for the positive phase calculated by the positive phase system circuit constant calculation unit 65 indicates the magnitude of the admittance for the positive phase with respect to the harmonics between the injection orders of the power system B as viewed from the interconnection point. Yes. Also, the absolute value Yn of the admittance for the antiphase component calculated by the antiphase system circuit constant calculation unit 66 represents the magnitude of the admittance for the antiphase component of the harmonics between the injection orders of the power system B viewed from the interconnection point. Show. The absolute value of the admittance of the electric power system B viewed from the connection point when the system connection inverter system A is in the single operation state is smaller than that in the connection state. Therefore, when the detected absolute value of the admittance becomes smaller than a predetermined value set in advance, it can be determined that the vehicle is in the single operation state. Injecting a single-phase current between the phases of the three-phase AC power system B is equivalent to injecting a positive-phase and a reverse-phase three-phase current of the same magnitude at the same time. In the present embodiment, the detection based on the absolute value of the admittance for the positive phase of the harmonics between the injection orders and the determination based on the absolute value of the admittance for the reverse phase are performed to prevent erroneous detection. ing.

  Note that the method for determining the isolated operation state is not limited to that described above. In addition to the determination method described above, a determination based on the difference between the absolute value Yp of the admittance for the normal phase and the absolute value Yn of the admittance for the reverse phase may be added. In the determination, the absolute value Yp of the admittance for the positive phase and the absolute value Yn of the admittance for the reverse phase are substantially equal during normal operation, and the absolute value Yp of the admittance for the positive phase and the admittance of the reverse phase during system transient. The fact that the absolute value Yn is different is used. Further, when it is determined that the single operation is performed by either the determination based on the absolute value Yp of the admittance for the normal phase or the determination based on the absolute value Yn of the admittance for the reverse phase, it may be determined that the state is the single operation. Alternatively, it may be determined that the vehicle is in the single operation state only by the determination based on the absolute value Yp of the admittance for the positive phase. Moreover, you may make it determine combining each determination mentioned above.

  The system circuit constants calculated by the normal phase system circuit constant calculation unit 65 and the reverse phase system circuit constant calculation unit 66 are not limited to the absolute value of admittance but may be the absolute value of impedance. In this case, the isolated operation determination unit 67 may determine whether or not the calculated absolute value of the impedance is greater than a predetermined value set in advance.

  The determination instruction unit 68 instructs determination of the single operation state, periodically outputs a current injection instruction signal to the current injection device 7, and sends a determination instruction signal to the single operation determination unit 67. Output. Instead of providing the determination instruction unit 68, the current injection device 7 may periodically inject current, and the isolated operation determination unit 67 may perform determination in synchronization therewith. Further, the inverter device 2 may inject a single-phase current of inter-order harmonics without providing the current injection device 7. In this case, the determination instruction unit 68 periodically outputs a current injection instruction signal to the command value signal generation unit 31 of the inverter control device 3, and the command value signal generation unit 31 superimposes the inter-order harmonics to generate the command value. A signal may be generated.

In the present embodiment, the three voltage signals Vu, Vv, Vw are converted into an α-axis voltage signal Vα and a β-axis voltage signal Vβ orthogonal to each other, and the three current signals Iu, Iv, Iw are orthogonal to each other. It is converted into Iα and β-axis current signal Iβ. Then, from the α-axis voltage signal Vα and the β-axis voltage signal Vβ, the positive-phase divided voltage signals Vαp and Vβp and the negative-phase divided voltage signals Vαn and Vβn of the harmonics between the injection orders are extracted, respectively, and α-axis current signals Iα and β From the axial current signal Iβ, positive phase current signals Iαp, Iβp and negative phase current signals Iαn, Iβn of the harmonics between the injection orders are extracted. Then, the absolute value Yp of the admittance for the normal phase and the absolute value Yn of the admittance for the reverse phase are calculated from the extracted signal, and the isolated operation is determined based on this. Since signal processing is simply performed using the matrix of the transfer function G _LPF or the matrix in which the (1, 2) and (2, 1) elements of the transfer function matrix G _LPF are interchanged, the positive phase component of the harmonics between the injection orders The signals for the opposite phase and the opposite phase can be extracted by simple processing.

  In the present embodiment, the case where the absolute value Yp of the positive phase admittance is calculated from the positive phase divided voltage signals Vαp, Vβp and the positive phase divided current signals Iαp, Iβp using the above equation (14) will be described. However, it is not limited to this. For example, the positive phase divided voltage signals Vαp and Vβp and the positive phase divided current signals Iαp and Iβp are converted into three-phase positive phase signals by two-phase / three-phase conversion processing (reverse αβ conversion processing), respectively. It may be used to calculate the absolute value Yp of the admittance for the positive phase. In this case, the product of the matrix of the three-phase / two-phase conversion process shown in the equation (1), the matrix shown in the equation (9), and the matrix of the two-phase / three-phase conversion process is calculated, A three-phase positive phase voltage signal may be directly calculated from the voltage signals Vu, Vv, Vw using a matrix of products. Further, the product of the matrix of the three-phase / two-phase conversion process shown in the above equation (11), the matrix shown in the above equation (12), and the matrix of the two-phase / three-phase conversion process is calculated, and the matrix of the product The current signals Iu, Iv, and Iw may be used to directly calculate the three-phase positive current signals. The same applies to the reverse phase. Further, in the first embodiment, instead of the calculation shown in the equation (1) and the calculation shown in the equation (9), the product of each matrix is calculated and the calculation using the matrix of the product is performed. It may be. The same applies to the current signal and the reverse phase component.

  In the present embodiment, the case where the time constants of the elements of the transfer function matrix are the same has been described. However, different values may be used for each element. For example, it can be designed to provide additional characteristics such as improving the quick response of the α-axis component and increasing the stability.

  In the present embodiment, the case where the positive phase divided voltage signal extraction unit 62a, the negative phase divided voltage signal extraction unit 62b, the positive phase divided current signal extraction unit 64a, and the negative phase divided current signal extraction unit 64b are individually designed. Although explained, it is not limited to this. Any two or more may be designed at a time so that the time constant T is shared.

  In the first embodiment, the case where the process for replacing the low-pass filter is performed to extract the signal for the positive phase and the signal for the reverse phase of the harmonics between the injection orders has been described. However, the process for replacing the high-pass filter is performed. Thus, these signals may be extracted. Hereinafter, a case where a process replacing the high-pass filter is performed will be described as a second embodiment.

The transfer function of the high-pass filter is represented by F (s) = Ts / (Ts + 1), where T is the time constant. Therefore, the transfer function matrix G _HPF showing the process shown in FIG. 9, that is, the process equivalent to the process of performing the static coordinate conversion after performing the high-pass filter process after performing the rotation coordinate conversion is expressed by the above equation (7). And is calculated as shown in the following equation (16).

FIG. 10 is a Bode diagram for analyzing a transfer function that is each element of the matrix G _HPF . FIG (a) shows a transfer function of (1, 1) element and (2,2) element of the matrix G _HPF, FIG (b) the transfer function of the (1,2) element of the matrix G _HPF FIG. 4C shows the transfer function of the (2, 1) element of the matrix G _HPF . This figure shows the case where the center frequency is 60 Hz, and the time constant T is “0.1”, “1”, “10”, “100”.

The amplitude characteristic shown in FIG. 6A is attenuated in the vicinity of the center frequency, and the amplitude characteristic at the center frequency is −6 dB (= ½). Further, as the time constant T increases, the cutoff band decreases. The amplitude characteristics shown in FIGS. 5B and 5C both have a peak at the center frequency, and the peak of the amplitude characteristics is −6 dB (= ½). Further, as the time constant T increases, the pass band decreases. Further, the phase characteristic shown in FIG. 5A is 0 degree at the center frequency. That is, the transfer function of the (1, 1) element and the (2, 2) element of the matrix G _HPF passes the signal of the center frequency without changing the phase. The phase characteristic shown in FIG. 5B is −90 degrees at the center frequency. That is, the transfer function of the (1,2) element of the matrix G _HPF passes the signal of the center frequency signal delayed by 90 degrees. On the other hand, the phase characteristic shown in FIG. 4C is 90 degrees at the center frequency. That is, the transfer function of the (2, 1) element of the matrix G _HPF passes the phase of the signal at the center frequency by 90 degrees. The processing shown in the matrix G _{HPF of the} transfer function for the two signals after the three-phase / two-phase conversion will be discussed below with reference to FIG.

In FIG. 8 (a), the α-axis signal (vector α) obtained by three-phase / two-phase conversion of the positive phase signal of the harmonics between injection orders (center angular frequency ω) is converted into the (1, 1) element of the matrix G _HPF . When the process indicated by the transfer function is performed, the amplitude is halved and the phase does not change (see FIG. 10A). Further, when the process indicated by the transfer function of the (1,2) element of the matrix G _HPF is performed on the β-axis signal (vector β), the amplitude is halved and the phase is delayed by 90 degrees (see FIG. 10B). ). Therefore, since the phases of both are reversed, adding them together cancels each other. On the other hand, when the process indicated by the transfer function of the (2, 1) element of the matrix G _HPF is performed on the α-axis signal, the amplitude is halved and the phase is advanced by 90 degrees (see FIG. 10C). Further, when the process indicated by the transfer function of the (2, 2) element of the matrix G _HPF is performed on the β-axis signal, the amplitude becomes half and the phase does not change. Therefore, since the phases of both are reversed, adding them together cancels each other.

In FIG. 8 (b), the α-axis signal (vector α) obtained by three-phase / two-phase conversion of the anti-phase component signal of the harmonics between injection orders (center angular frequency ω) is converted into the (1, 1) element of the matrix G _HPF . When the process indicated by the transfer function is performed, the amplitude is halved and the phase does not change. Further, when the process indicated by the transfer function of the (1,2) element of the matrix G _HPF is performed on the β-axis signal (vector β), the amplitude is halved and the phase is delayed by 90 degrees. Therefore, since both phases are the same as the α-axis signal, the α-axis signal is reproduced by adding both. On the other hand, when the processing indicated by the transfer function of the (2, 1) element of the matrix G _HPF is performed on the α-axis signal, the amplitude becomes half and the phase advances by 90 degrees. Further, when the process indicated by the transfer function of the (2, 2) element of the matrix G _HPF is performed on the β-axis signal, the amplitude becomes half and the phase does not change. Therefore, since both phases are the same as the β-axis signal, the β-axis signal is reproduced by adding both.

In other words, the transfer function matrix G _HPF passes the anti-phase signal of the harmonics between the injection orders, and blocks the positive signal. In addition, signals of frequencies other than the harmonics between the injection orders (harmonics other than the harmonics between the injection orders, fundamental waves, etc.) are transferred to the transfer functions of the (1,1) and (2,2) elements of the matrix G _HPF. When the processing shown in FIG. 10 is performed (see FIG. 10A), the processing shown in the transfer function of the (1,2) element and the (2,1) element is attenuated (FIG. 10 ( b) and (c)), and passes almost as it is. Therefore, it can be confirmed that the process shown in the matrix G _HPF of the transfer function is a notch filter process that removes only the positive phase signal of the center frequency.

When the (1,2) element and the (2,1) element of the matrix G _HPF of the transfer function are interchanged, the reverse phase signal is cut off and the positive phase signal is passed, contrary to the above. Therefore, in order to remove only the antiphase signal of the center frequency, a matrix in which the (1,2) element and the (2,1) element of the transfer function matrix G _HPF are exchanged may be used.

  The block diagram for explaining the internal configuration of the isolated operation detection device according to the second embodiment is the same as that of the isolated operation detection device 6 according to the first embodiment shown in FIG. The negative phase divided voltage signal extracting unit 62b, the positive phase divided current signal extracting unit 64a, and the negative phase divided current signal extracting unit 64b are respectively converted into a positive phase divided voltage signal extracting unit 62a ′ (see FIG. 11 described later) and a negative phase. The divided voltage signal extracting unit 62b ′, the positive phase divided current signal extracting unit 64a ′, and the reverse phase divided current signal extracting unit 64b ′ are changed (not shown except for the positive phase divided voltage signal extracting unit 62a ′). .) The positive phase component voltage signal extraction unit 62a ′, the negative phase component voltage signal extraction unit 62b ′, the positive phase component current signal extraction unit 64a ′, and the negative phase component current signal extraction unit 64b ′ pass components other than the components to be extracted. The desired component is extracted by suppressing.

  FIG. 11 is a block diagram for explaining the internal configuration of the positive phase divided voltage signal extraction unit 62a '.

The positive phase divided voltage signal extraction unit 62a ′ shown in the figure includes a fundamental wave positive phase blocking unit NF1, a fundamental wave negative phase blocking unit NF2, an injection order harmonic anti-phase blocking unit NF3, and a fifth harmonic blocking. Part NF4, 7th harmonic cutoff part NF5, and 11th harmonic cutoff part NF6. The fundamental wave positive phase cutoff unit NF1 suppresses the passage of the signal of the fundamental wave in the positive phase, and performs the processing represented by the transfer function matrix G _HPF shown in the above equation (16). As the center angular frequency ω, the angular frequency ω ₀ = 120π [rad / sec] (60 [Hz]) of the fundamental wave of the system voltage is set in advance.

The fundamental wave anti-phase component cut-off unit NF2 suppresses the passage of the signal of the anti-phase component of the fundamental wave. The (1, 2) element of the matrix G _HPF of the transfer function shown in the above equation (16) and (2 , 1) Perform processing represented by a matrix with elements replaced. As the center angular frequency ω, the angular frequency ω ₀ = 120π [rad / sec] (60 [Hz]) of the fundamental wave of the system voltage is set in advance. In this case, in the transfer function matrix G _HPF , this is equivalent to setting “−ω ₀ ” as the central angular frequency ω.

The inter-injection-order harmonic anti-phase component blocking unit NF3 suppresses the passage of the anti-phase signal of the inter-injection-order harmonic, and the transfer function matrix G _HPF (1, 1, 2) Perform processing represented by a matrix in which elements and (2,1) elements are interchanged. As the central angular frequency ω, the angular frequency “2.4ω ₀ ” of the harmonics between the injection orders is set in advance. In this case, in the transfer function matrix G _HPF , this is equivalent to setting “−2.4ω ₀ ” as the central angular frequency ω.

The fifth harmonic cutoff unit NF4, the seventh harmonic cutoff unit NF5, and the eleventh harmonic cutoff unit NF6 are respectively a fifth harmonic (positive phase), a seventh harmonic (positive phase), and an eleventh order. It suppresses the passage of harmonics (positive phase), and performs the processing represented by the transfer function matrix G _HPF shown in the above equation (16). Around angular frequency omega, respectively, the angular frequency "-5Omega _0" of the fifth harmonic, the angular frequency "7Omega _0" of the seventh harmonic, the angular frequency "-11Omega _0" of the 11 harmonics is preset Yes.

FIG. 12A is a diagram illustrating frequency characteristics of the positive phase divided voltage signal extraction unit 62a ′. Basic wave positive phase cutoff unit NF1, Fundamental wave negative phase cutoff unit NF2, Injection order harmonics negative phase cutoff unit NF3, 5th harmonic cutoff unit NF4, 7th harmonic cutoff unit NF5, 11th harmonic The blocking unit NF6 includes the normal phase component of the fundamental wave, the reverse phase component, the anti-phase component of the harmonics between the injection orders, the fifth harmonic component (positive component), the seventh harmonic component (positive component), and the eleventh component, respectively. Since it has a frequency characteristic that suppresses the passage of harmonics (positive phase component), the frequency characteristic of the positive phase component voltage signal extraction unit 62a ′ as a whole is as shown in FIG. According to the figure, the fundamental wave component (angular frequency “ω ₀ ”), the anti-phase component of the fundamental wave (angular frequency “−ω ₀ ”), and the anti-phase component of the fourth harmonic (angular frequency “−2. 4ω ₀ ”), the fifth harmonic component (angular frequency“ −5ω ₀ ”), the seventh harmonic component (angular frequency“ 7ω ₀ ”), and the eleventh harmonic component (angular frequency“ −11ω ₀ ”) are suppressed. The other components (the positive phase component of the 2.4th harmonic) are passed. Therefore, the positive phase divided voltage signal extraction unit 62a ′ can suitably pass only the positive phase component of the 2.4th harmonic, and the 2.4th harmonic from the α axis voltage signal Vα and the β axis voltage signal Vβ. The positive phase divided voltage signals Vαp and Vβp obtained by extracting only the positive phase component of the wave are output.

In general, since the harmonics superimposed on the power system B are many fifth, seventh, and eleventh harmonics, in this embodiment, the positive and negative phase components of these and the fundamental wave, and injection The reverse phase component of the 2.4th harmonic, which is the interharmonic harmonic, is suppressed. In addition, what is necessary is just to design positive phase divided voltage signal extraction part 62a 'according to the order of the harmonic which needs to be suppressed. For example, when it is desired to suppress only the 5th harmonic as the harmonic, it is not necessary to provide the 7th harmonic cutoff unit NF5 and the 11th harmonic cutoff unit NF6, and further to suppress the 13th harmonic. In the transfer function matrix G _HPF shown in the above equation (16), a 13th-order harmonic cutoff unit in which “13ω ₀ ” is set as the central angular frequency ω may be further provided.

  The positive phase divided voltage signal extraction unit 62a 'performs the filtering process in the stationary coordinate system without performing the rotation coordinate conversion and the stationary coordinate conversion. Since the system is a linear time invariant system that does not include the rotating coordinate transformation process and the static coordinate transformation process, which are nonlinear time-varying processes, control system design and system analysis using linear control theory are possible. Further, the positive phase divided voltage signals Vαp and Vβp are easily calculated by determinants of transfer functions.

Similarly to the positive phase divided voltage signal extraction unit 62a ′ (see FIG. 11), the negative phase divided voltage signal extraction unit 62b ′ also includes six blocking units. The negative phase component voltage signal extraction unit 62b ′ includes an injection order harmonic positive phase block unit NF3 ′ (not shown) instead of the injection order harmonic reverse phase block unit NF3. Different from the positive phase divided voltage signal extraction unit 62a ′. The inter-injection order harmonic positive phase blocking unit NF3 ′ suppresses the passage of the positive phase signal of the inter-injection order harmonic, and is represented by the transfer function matrix G _HPF shown in the above equation (16). Process. As the central angular frequency ω, the angular frequency “2.4ω ₀ ” of the harmonics between the injection orders is set in advance.

FIG. 12B is a diagram illustrating frequency characteristics of the negative phase divided voltage signal extraction unit 62b ′. Basic wave positive phase cutoff unit NF1, fundamental wave negative phase cutoff unit NF2, injection order harmonics negative phase cutoff unit NF3 ', 5th harmonic cutoff unit NF4, 7th harmonic cutoff unit NF5, 11th harmonic The wave cut-off unit NF6 includes the normal phase component of the fundamental wave, the reverse phase component, the positive phase component of the harmonics between the injection orders, the fifth harmonic component (positive phase component), the seventh harmonic component (positive phase component), 11 Since it has a frequency characteristic that suppresses the passage of the second harmonic (positive phase component), the frequency characteristic of the positive phase component voltage signal extraction unit 62b ′ as a whole is as shown in FIG. According to the figure, the fundamental wave component (angular frequency “ω ₀ ”), the negative phase component of the fundamental wave (angular frequency “−ω ₀ ”), and the positive phase component of the fourth harmonic (angular frequency “2.4ω). ₀ ”), the fifth harmonic component (angular frequency“ −5ω ₀ ”), the seventh harmonic component (angular frequency“ 7ω ₀ ”), and the eleventh harmonic component (angular frequency“ −11ω ₀ ”) are suppressed. , And other components (the reverse phase component of the 2.4th harmonic) are passed. Therefore, the negative phase divided voltage signal extraction unit 62b ′ can suitably pass only the negative phase component of the 2.4th order harmonic, and the 2.4th order harmonic can be obtained from the α axis voltage signal Vα and the β axis voltage signal Vβ. The negative phase voltage signals Vαn and Vβn obtained by extracting only the negative phase component of the wave are output.

  Similarly to the positive phase voltage signal extraction unit 62a ′, the positive phase component current signal extraction unit 64a ′ is a fundamental wave positive phase blocking unit NF1, a fundamental wave negative phase blocking unit NF2, and a harmonic phase blocking between injection orders. A part NF3, a fifth harmonic cutoff part NF4, a seventh harmonic cutoff part NF5, and an eleventh harmonic cutoff part NF6. Since the frequency characteristics of the positive phase current signal extraction unit 64a ′ also show the characteristics shown in FIG. 12A, the positive phase component and the negative phase component of the fundamental wave, the negative phase component of the 2.4th harmonic, and the fifth harmonic. The component, the seventh harmonic component, and the eleventh harmonic component are suppressed, and the other components (the positive phase component of the 2.4 harmonic) are passed. Therefore, only the positive phase component of the 2.4th harmonic can be suitably passed, and only the positive phase component of the 2.4th harmonic is extracted from the α-axis current signal Iα and the β-axis current signal Iβ. Divided current signals Iαp and Iβp are output.

  The negative-phase component current signal extraction unit 64b ′ is similar to the negative-phase component voltage signal extraction unit 62b ′, and the fundamental wave positive-phase component cutoff unit NF1, the fundamental wave negative-phase component cutoff unit NF2, and the harmonic positive-phase component between injection orders. Part NF3 ′, a fifth harmonic cutoff part NF4, a seventh harmonic cutoff part NF5, and an eleventh harmonic cutoff part NF6. Since the frequency characteristic of the negative phase current signal extraction unit 64b ′ also shows the characteristic shown in FIG. 12B, the positive phase component and negative phase component of the fundamental wave, the positive phase component of the 2.4th harmonic, and the fifth harmonic. The component, the seventh harmonic component, and the eleventh harmonic component are suppressed, and the other components (the reverse phase component of the 2.4 harmonic) are passed. Therefore, only the reverse phase component of the 2.4th harmonic can be suitably passed, and the reverse phase component in which only the reverse phase component of the 2.4th harmonic is extracted from the α axis current signal Iα and the β axis current signal Iβ. The phase divided current signals Iαn and Iβn are output.

  The negative phase component voltage signal extraction unit 62b ′, the positive phase component current signal extraction unit 64a ′, and the negative phase component current signal extraction unit 64b ′ also perform the filtering process in the stationary coordinate system without performing the rotation coordinate transformation and the stationary coordinate transformation. It is carried out. Since the system is a linear time invariant system that does not include the rotating coordinate transformation process and the static coordinate transformation process, which are nonlinear time-varying processes, control system design and system analysis using linear control theory are possible.

  Also in the second embodiment, the positive phase divided voltage signals Vαp and Vβp, the negative phase divided voltage signals Vαn and Vβn, the positive phase divided current signals Iαp and Iβp, and the negative phase divided current signals Iαn and Iβn are represented by determinants of transfer functions. Thus, it is possible to easily extract each of them, and it is possible to determine whether the islanding operation is performed using these. Therefore, the same effect as that of the first embodiment can be obtained.

  In the second embodiment, as in the case of the first embodiment, different values may be used for the time constant of each element of the transfer function matrix, or the time constant T may be shared. The positive phase divided voltage signal extraction unit 62a ′, the negative phase divided voltage signal extraction unit 62b ′, the positive phase divided current signal extraction unit 64a ′, and the negative phase divided current signal extraction unit 64b ′. You may make it design at once.

In the second embodiment, each block of the positive phase divided voltage signal extraction unit 62a ′, the negative phase divided voltage signal extraction unit 62b ′, the positive phase divided current signal extraction unit 64a ′, and the negative phase divided current signal extraction unit 64b ′. Although the case where a fixed value is set in advance as the central angular frequency ω used in the section has been described, the present invention is not limited to this. When the sampling period of the signal processing is a fixed sampling period, the fundamental wave positive phase cutoff unit NF1, the fundamental wave reverse phase cutoff unit NF2, the fifth harmonic cutoff unit NF4, the seventh harmonic cutoff unit NF5, and the 11th harmonic. In the cutoff unit NF6, the angular frequency ω ₀ of the fundamental wave of the system voltage may be detected by a frequency detection device or the like, and the central angular frequency ω may be set based on the detected angular frequency ω ₀ . In addition, since the angular frequency of the harmonics between the injection orders is fixed, the angular frequency between the injection order harmonics anti-phase component blocking unit NF3 and the inter-injection order harmonics positive phase component blocking unit NF3 ′ is a fixed value. Can be set as Similarly, in the first embodiment, the angular frequency of the harmonics between the injection orders may be set as a fixed value, so that it is not necessary to detect the angular frequency ω ₀ of the fundamental wave of the system voltage with a frequency detection device or the like.

  In the first or second embodiment, the positive phase divided voltage signal extracting unit 62a, the negative phase divided voltage signal extracting unit 62b, the positive phase divided current signal extracting unit 64a, and the negative phase divided current that use processing instead of the low-pass filter are used. When the signal extraction unit 64b is provided, the positive phase divided voltage signal extraction unit 62a ′, the negative phase division voltage signal extraction unit 62b ′, the positive phase division current signal extraction unit 64a ′, and the negative phase component, which use processing instead of the high pass filter, are used. Although the case where the current signal extraction unit 64b ′ is provided has been described, the present invention is not limited to this. For example, a positive-phase divided voltage signal extraction unit 62a and a positive-phase divided current signal extraction unit 64a are provided, which are extracted by passing a signal for the positive phase using processing instead of a low-pass filter, and a negative phase divided voltage signal extraction unit. 62b ′ and a negative phase current signal extraction unit 64b ′ may be provided, and a negative phase signal may be extracted using a process in place of the high-pass filter. In addition, a positive phase divided voltage signal extraction unit 62a is provided for extraction by passing a signal for the positive phase using processing instead of the low pass filter, and a reverse phase divided voltage signal extraction unit 62b is provided for processing instead of the low pass filter. Is extracted by passing the signal of the reverse phase using the signal, and the signal of the positive phase is extracted using a process replacing the high-pass filter with the positive phase current signal extraction unit 64a ′. An extraction unit 64b ′ may be provided to extract the signal for the reverse phase using processing in place of the high-pass filter.

  In the first or second embodiment, a case has been described in which 2.4-order harmonics are injected into the power system B and 2.4-order harmonic components are extracted from the detected voltage signal and current signal. However, the present invention is not limited to this, and harmonics between orders other than the 2.4 order may be used. Moreover, you may make it utilize the harmonic which is not a harmonic between orders. The reason why inter-order harmonics are used is that, by using harmonics that do not substantially exist in the power system B, it is possible to accurately extract even if the injected current is reduced. Therefore, if the amount existing in the electric power system B is a very small harmonic (for example, the 10th harmonic), it can be used instead of the interharmonic harmonic. By setting the central angular frequency ω according to the angular frequency of the harmonic to be used, it is possible to extract a signal for the positive phase and a signal for the negative phase of the desired harmonic.

  In the first or second embodiment, the isolated operation detection device according to the present invention has been described as a configuration different from the inverter control device. However, the single operation detection device is included in the inverter control device and realized by a single microcomputer or the like. May be.

  In the said 1st or 2nd embodiment, although the case where the isolated operation detection apparatus which concerns on this invention was used for the grid connection inverter system was demonstrated, it is not restricted to this. The isolated operation detection device according to the present invention can also be used in a grid interconnection device such as a synchronous generator.

  The isolated operation detection device, the grid interconnection inverter system, and the isolated operation detection method according to the present invention are not limited to the above-described embodiments. The specific configuration of each part of the isolated operation detection device, the grid interconnection inverter system, and the isolated operation detection method 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 Command value signal generator 32 PWM signal generator 4 Current sensor 5 Voltage sensor 6 Independent operation detector 61 Voltage signal three-phase / two-phase converter (voltage Signal conversion means)
62a, 62a 'Positive phase divided voltage signal extraction unit 62b Reverse phase divided voltage signal extraction unit 63 Current signal three-phase / two-phase conversion unit (current signal conversion means)
64a Positive phase current signal extraction unit 64b Reverse phase current signal extraction unit 65 Positive phase system circuit constant calculation unit 66 Reverse phase system circuit constant calculation unit 67 Independent operation determination unit 68 Determination instruction unit (current injection instruction means)
7 Current injection device 8 Switch B Power system C Load D Breaker

Claims (8)

An isolated operation detection device for detecting isolated operation of a grid-connected inverter system linked to a three-phase AC power system,
Current injection instruction means for single-phase injection of harmonic current of a predetermined angular frequency into the power system;
Voltage signal conversion means for converting the detected three-phase voltage signal into a first voltage signal and a second voltage signal;
Current signal conversion means for converting the detected three-phase current signal into a first current signal and a second current signal;
The first voltage signal is signal-processed by a first transfer function, the second voltage signal is signal-processed by a second transfer function, and these are added to extract a first positive-phase voltage signal Then, the first voltage signal is signal-processed by a third transfer function, the second voltage signal is signal-processed by the first transfer function, and these are added to obtain a second positive phase divided voltage. Positive phase divided voltage signal extracting means for extracting a signal;
The first voltage signal is signal-processed by the first transfer function, the second voltage signal is signal-processed by the third transfer function, and these are added together to produce a first negative phase voltage signal. And the first voltage signal is signal-processed by the second transfer function, the second voltage signal is signal-processed by the first transfer function, and these are added together to obtain a second inverse. A negative phase divided voltage signal extracting means for extracting a phase divided voltage signal;
The first current signal is signal-processed by the first transfer function, the second current signal is signal-processed by the second transfer function, and these are added to form a first positive-phase current signal And the first current signal is signal-processed by the third transfer function, the second current signal is signal-processed by the first transfer function, and these are added to obtain a second positive signal. A positive phase current signal extracting means for extracting a phase current signal;
The first current signal is signal-processed by the first transfer function, the second current signal is signal-processed by the third transfer function, and these are added to obtain a first negative-phase current signal. Is extracted, and the first current signal is signal-processed by the second transfer function, the second current signal is signal-processed by the first transfer function, and these are added together to obtain a second inverse. A negative phase current signal extracting means for extracting a phase current signal;
From the first positive phase divided voltage signal and the second positive phase divided voltage signal, and from the first positive phase divided current signal and the second positive phase divided current signal, a system circuit constant for the positive phase is obtained. Positive phase distribution system circuit constant calculation means for calculating
From the first negative phase divided voltage signal and the second negative phase divided voltage signal, and the first negative phase divided current signal and the second negative phase divided current signal, a system circuit constant for the negative phase is obtained. A negative phase distribution system circuit constant calculating means for calculating
Isolated operation determination means for determining isolated operation based on changes in the system circuit constant for the positive phase and the system circuit constant for the reverse phase;
With
When the predetermined angular frequency is ω and the time constant is T,
The first transfer function is:
G ₁ (s) = (T · s + 1) / {(T · s + 1) ² + (T · ω) ² }
And
The second transfer function is
G ₂ (s) = − T · ω / {(T · s + 1) ² + (T · ω) ² }
And
The third transfer function is
G ₃ (s) = T · ω / {(T · s + 1) ² + (T · ω) ² }
Is,
An isolated operation detection device. An isolated operation detection device for detecting isolated operation of a grid-connected inverter system linked to a three-phase AC power system,
Current injection instruction means for single-phase injection of harmonic current of a predetermined angular frequency into the power system;
Voltage signal conversion means for converting the detected three-phase voltage signal into a first voltage signal and a second voltage signal;
Current signal conversion means for converting the detected three-phase current signal into a first current signal and a second current signal;
The first voltage signal is signal-processed by a first transfer function, the second voltage signal is signal-processed by a second transfer function, and these are added to extract a first positive-phase voltage signal Then, the first voltage signal is signal-processed by a third transfer function, the second voltage signal is signal-processed by the first transfer function, and these are added to obtain a second positive phase divided voltage. Positive phase divided voltage signal extracting means for extracting a signal;
The first voltage signal is signal-processed by the first transfer function, the second voltage signal is signal-processed by the third transfer function, and these are added together to produce a first negative phase voltage signal. And the first voltage signal is signal-processed by the second transfer function, the second voltage signal is signal-processed by the first transfer function, and these are added together to obtain a second inverse. A negative phase divided voltage signal extracting means for extracting a phase divided voltage signal;
The first current signal is signal-processed by the first transfer function, the second current signal is signal-processed by the second transfer function, and these are added to form a first positive-phase current signal And the first current signal is signal-processed by the third transfer function, the second current signal is signal-processed by the first transfer function, and these are added to obtain a second positive signal. A positive phase current signal extracting means for extracting a phase current signal;
The first current signal is signal-processed by the first transfer function, the second current signal is signal-processed by the third transfer function, and these are added to obtain a first negative-phase current signal. Is extracted, and the first current signal is signal-processed by the second transfer function, the second current signal is signal-processed by the first transfer function, and these are added together to obtain a second inverse. A negative phase current signal extracting means for extracting a phase current signal;
From the first positive phase divided voltage signal and the second positive phase divided voltage signal, and from the first positive phase divided current signal and the second positive phase divided current signal, a system circuit constant for the positive phase is obtained. Positive phase distribution system circuit constant calculation means for calculating
From the first negative phase divided voltage signal and the second negative phase divided voltage signal, and the first negative phase divided current signal and the second negative phase divided current signal, a system circuit constant for the negative phase is obtained. A negative phase distribution system circuit constant calculating means for calculating
Isolated operation determination means for determining isolated operation based on changes in the system circuit constant for the positive phase and the system circuit constant for the reverse phase;
With
When the predetermined angular frequency is ω and the time constant is T,
The first transfer function is:
G ₁ (s) = (T ² · s ² + T · s + T ² · ω ² ) / {(T · s + 1) ² + (T · ω) ² }
And
The second transfer function is
G ₂ (s) = − T · ω / {(T · s + 1) ² + (T · ω) ² }
And
The third transfer function is
G ₃ (s) = T · ω / {(T · s + 1) ² + (T · ω) ² }
Is,
An isolated operation detection device.   The isolated operation detection device according to claim 1 or 2, wherein the predetermined angular frequency is an angular frequency that is a non-integer multiple of a fundamental wave of the power system.   The isolated operation determination means can be determined as isolated operation based on a change in the system circuit constant for the positive phase, and only when it can be determined as isolated operation based on a change in the system circuit constant for the reverse phase. The isolated operation detection device according to claim 1, wherein the isolated operation is determined as isolated operation.   The islanding operation detection device according to any one of claims 1 to 4, wherein the current injection instruction means instructs the grid interconnection inverter system to inject a harmonic current having the predetermined angular frequency.   The isolated operation detection device according to any one of claims 1 to 5, wherein the system circuit constant is an absolute value of admittance.   A grid-connected inverter system comprising the isolated operation detection device according to any one of claims 1 to 6. An isolated operation detection method for detecting isolated operation of a grid-connected inverter system linked to a three-phase AC power system,
A first step of injecting a single-phase harmonic current of a predetermined angular frequency into the power system;
A second step of converting the detected three-phase voltage signal into a first voltage signal and a second voltage signal;
A third step of converting the detected three-phase current signal into a first current signal and a second current signal;
The first voltage signal is signal-processed by a first transfer function, the second voltage signal is signal-processed by a second transfer function, and these are added to extract a first positive-phase voltage signal Then, the first voltage signal is signal-processed by a third transfer function, the second voltage signal is signal-processed by the first transfer function, and these are added to obtain a second positive phase divided voltage. A fourth step of extracting a signal;
The first voltage signal is signal-processed by the first transfer function, the second voltage signal is signal-processed by the third transfer function, and these are added together to produce a first negative phase voltage signal. And the first voltage signal is signal-processed by the second transfer function, the second voltage signal is signal-processed by the first transfer function, and these are added together to obtain a second inverse. A fifth step of extracting a phase divided voltage signal;
The first current signal is signal-processed by the first transfer function, the second current signal is signal-processed by the second transfer function, and these are added to form a first positive-phase current signal And the first current signal is signal-processed by the third transfer function, the second current signal is signal-processed by the first transfer function, and these are added to obtain a second positive signal. A sixth step of extracting a phase split current signal;
The first current signal is signal-processed by the first transfer function, the second current signal is signal-processed by the third transfer function, and these are added to obtain a first negative-phase current signal. Is extracted, and the first current signal is signal-processed by the second transfer function, the second current signal is signal-processed by the first transfer function, and these are added together to obtain a second inverse. A seventh step of extracting a phase split current signal;
From the first positive phase divided voltage signal and the second positive phase divided voltage signal, and from the first positive phase divided current signal and the second positive phase divided current signal, a system circuit constant for the positive phase is obtained. An eighth step of calculating
From the first negative phase divided voltage signal and the second negative phase divided voltage signal, and the first negative phase divided current signal and the second negative phase divided current signal, a system circuit constant for the negative phase is obtained. A ninth step of calculating
A tenth step of determining an isolated operation based on a change in the system circuit constant for the positive phase and the system circuit constant for the reverse phase;
With
When the predetermined angular frequency is ω and the time constant is T,
The first transfer function is:
G ₁ (s) = (T · s + 1) / {(T · s + 1) ² + (T · ω) ² }
And
The second transfer function is
G ₂ (s) = − T · ω / {(T · s + 1) ² + (T · ω) ² }
And
The third transfer function is
G ₃ (s) = T · ω / {(T · s + 1) ² + (T · ω) ² }
Is,
An isolated operation detection method characterized by the above.