JP2014042381A - Control circuit for controlling inverter circuit, and inverter device having the control circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a control circuit for an inverter circuit which keeps from causing or increasing a power oscillation of a power system.SOLUTION: A control circuit 3 for controlling via a PWM signal an inverter circuit 2 for converting DC power to AC power to be supplied to a power system includes: a DC voltage control section 31 for generating a DC voltage compensation signal for controlling an input voltage of the inverter circuit 2; a power oscillation component attenuation section 32 for attenuating a frequency component of power oscillation in outputting the DC voltage compensation signal input thereinto; a current control section 35 for generating a current compensation signal for controlling an output current of the inverter circuit 2 by using the signal output from the power oscillation component attenuation section 32 as a desired d axis current; and a PWM signal generation section 36 for generating the PWM signal on the basis of the current compensation signal. The compensation signal, which controls the output power, has the frequency component of power oscillation suppressed, so that the output power also has the frequency component suppressed.

Description

  The present invention relates to a control circuit that controls an inverter circuit, and an inverter device including the control circuit.

  The Western Japan power system (60 Hz system) is a skewered system that exceeds 1000 km from east to west by connecting the power systems of each power company with a 500 kV transmission line. It is known that in a skew-shaped system, weakly-damping long-period power fluctuations (period 2 to 5 seconds) are generated in the entire power system due to its structure. Hereinafter, the long-period power fluctuation is simply referred to as “power fluctuation”. In addition, the instability of power fluctuations may increase due to heavy power flow and the liberalization of power due to power trading. A system monitoring method has been developed for accurately grasping the state of the power fluctuation and performing operation and control of the power system (see Non-Patent Document 1).

  In recent years, research using natural energy has progressed. Since the electric power generated by the solar cell is DC power, when it is supplied to the power system, it is necessary to convert it into AC power by an inverter circuit. A grid-connected inverter system has been developed as a system that converts DC power output from a DC power source into AC power by an inverter circuit and supplies the AC power to the power system (see, for example, Patent Document 1).

“Estimation of Inertial Center Frequency Based on Multipoint Synchronous Measurement Data”, Hashiguchi et al., Denki Theory B, Vol. 130, No. 1, 2010, pp. 106-113

JP2011-188665A

  Since the solar cell changes the output power depending on the solar radiation state, the output power of the inverter circuit also changes. This output change may increase the power fluctuation of the power system. In addition, when a large number of grid-connected inverter systems are connected to the power system, power fluctuations may be caused by these output changes.

  The present invention has been conceived under the circumstances described above, and it is an object of the present invention to provide a control circuit for an inverter circuit that can suppress causing or increasing the power fluctuation of the power system. .

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

  A control circuit provided by the first aspect of the present invention is a control circuit that controls, by a PWM signal, an inverter circuit that converts DC power into AC power and supplies the power to the power system, and outputs power from the inverter circuit. A power control unit that generates a compensation signal for control, a predetermined frequency attenuation unit that receives the compensation signal, attenuates and outputs a component of a predetermined frequency, and a signal output from the predetermined frequency attenuation unit is a current target. And a current control means for generating a current compensation signal for controlling the output current of the inverter circuit, and a PWM signal generation means for generating the PWM signal based on the current compensation signal. .

  In a preferred embodiment of the present invention, the predetermined frequency is a frequency of power fluctuation of the power system.

  In a preferred embodiment of the present invention, the power control means generates a DC voltage compensation signal for controlling an input voltage of the inverter circuit as the compensation signal.

  In a preferred embodiment of the present invention, the apparatus further comprises active power calculating means for calculating the output active power of the inverter circuit, and the power control means is an active power compensation signal for controlling the output active power of the inverter circuit. Is generated as the compensation signal.

  In a preferred embodiment of the present invention, the predetermined frequency attenuation means receives the predetermined frequency from the outside of the control circuit.

  In a preferred embodiment of the present invention, frequency detection means for detecting a system frequency of the power system and a system frequency signal continuously detecting the system frequency are input, and components other than a predetermined frequency band are attenuated. Predetermined band pass means for outputting, FFT processing means for calculating an output level for each frequency of the signal output from the predetermined band pass means, and predetermined frequency detection means for detecting a frequency at which the output level is equal to or higher than a threshold value. The predetermined frequency attenuating means receives the frequency detected by the predetermined frequency detecting means as the predetermined frequency.

  In a preferred embodiment of the present invention, the predetermined frequency attenuation means is a notch filter.

  In a preferred embodiment of the present invention, the inverter circuit outputs three-phase alternating current power, and the current control means is for a three-phase current signal respectively detecting the three-phase output current of the inverter circuit. Conversion means for performing three-phase / two-phase conversion and rotational coordinate conversion to convert two axis component signals, and two for controlling the deviation signal between the two axis component signals and the respective target signals to zero Two-phase control means for generating a signal, and inverse conversion means for performing a stationary coordinate transformation and a two-phase / three-phase transformation on the two signals to convert them into the three-phase current compensation signal. The signal output from the predetermined frequency attenuating means is set as one target signal of the two axis component signals.

  In a preferred embodiment of the present invention, the system further comprises a reactive power control means for generating a reactive power compensation signal for controlling the reactive power output of the inverter circuit, and the reactive power compensation signal is transmitted between the two axis component signals. The other target signal is used.

  The inverter device provided by the second aspect of the present invention includes the control circuit provided by the first aspect of the present invention and the inverter circuit.

  According to the present invention, the compensation signal generated by the power control unit is input to the current control unit after the component of the predetermined frequency is attenuated. The current control unit generates a current compensation signal using this as a current target, and the PWM signal generation unit generates a PWM signal based on the current compensation signal. The inverter circuit performs power conversion based on the PWM signal and outputs AC power. Since the predetermined frequency component of the compensation signal is attenuated, the predetermined frequency component is also suppressed in the output power output from the inverter circuit. By using the power oscillation frequency as the predetermined frequency, the inverter circuit can suppress outputting the same frequency component as the power oscillation frequency, and can suppress increasing the power oscillation of the power system. it can.

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

It is a figure for demonstrating the grid connection inverter system provided with the control circuit which concerns on 1st Embodiment. It is a functional block diagram for demonstrating the internal structure of the control circuit which concerns on 1st Embodiment. It is a Bode diagram which shows the characteristic of a notch filter. It is a functional block diagram for demonstrating the internal structure of the current control part which concerns on 1st Embodiment. It is a figure which shows the one machine infinite bus model. It is a model that adds a model showing a grid interconnection inverter system to the one machine infinite bus model. It is a figure which shows a simulation result (in the case of frequency "0.1 * _fSW "). It is a figure which shows a simulation result (in the case of frequency " _fSW "). It is a figure which shows a simulation result (in the case of frequency "10 * _fSW "). It is a figure which shows a simulation result (in the case of a step-like change). It is a functional block diagram for demonstrating the internal structure of the control circuit which concerns on 2nd Embodiment. It is a figure for demonstrating the high capacity | capacitance system which concerns on 3rd Embodiment. It is a functional block diagram for demonstrating the internal structure of the control circuit which concerns on 4th Embodiment.

  Hereinafter, embodiments of the present invention will be specifically described with reference to the drawings, taking as an example the case where a control circuit according to the present invention is used in a grid-connected inverter system.

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

  The grid-connected inverter system A is a distributed power source, and includes a DC power source 1, an inverter circuit 2, a control circuit 3, a current sensor 4, a voltage sensor 5, and a DC voltage sensor 6. The grid interconnection inverter system A is linked to the three-phase power grid B. Hereinafter, the three phases are referred to as a U phase, a V phase, and a W phase. The grid interconnection inverter system A converts the DC power output from the DC power source 1 into AC power by the inverter circuit 2 and supplies it to a load (not shown). The load is also supplied with power from the power system B. The grid interconnection inverter system A is a system with a reverse power flow, and supplies AC power to the power system B. Although not shown, a transformer for boosting (or stepping down) the AC voltage is provided on the output side of the inverter circuit 2. A combination of the inverter circuit 2, the control circuit 3, the current sensor 4, the voltage sensor 5, and the DC voltage sensor 6 is an inverter device, which is called a so-called power conditioner.

  The DC power supply 1 outputs DC power and includes 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 circuit 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 circuit 2 converts DC power input from the DC power source 1 into AC power and outputs the AC power. The inverter circuit 2 includes a PWM control inverter and a filter (not shown). The PWM control inverter is a three-phase inverter provided with three sets of six switching elements (not shown). Based on the PWM signal input from the control circuit 3, each switching element is switched on and off to generate DC power. Convert to AC power. The filter removes high frequency components due to switching. Since the positive and negative electrodes on the input side of the inverter circuit 2 are respectively connected to the positive and negative electrodes of the DC power supply 1, the input voltage of the inverter circuit 2 matches the output voltage of the DC power supply 1.

The current sensor 4 detects an instantaneous value of the three-phase output current of the inverter circuit 2. The current sensor 4 converts the detected instantaneous value into a digital signal, and controls the control circuit 3 as current signals i _u , i _v , i _w (the three current signals may be collectively described as “current signal i”). Output to. The voltage sensor 5 detects an instantaneous value of the three-phase output voltage of the inverter circuit 2. The voltage sensor 5 converts the detected instantaneous value into a digital signal and outputs it as a voltage signal v _u , v _v , v _w (the three voltage signals may be collectively described as “voltage signal v”). Output to.

  The DC voltage sensor 6 detects an instantaneous value of the input voltage of the inverter circuit 2 (that is, the output voltage of the DC power supply 1). The DC voltage sensor 6 digitally converts the detected instantaneous value and outputs it to the control circuit 3 as a DC voltage signal e. The DC voltage sensor 6 detects a voltage between terminals of an electrolytic capacitor (not shown) provided between a positive electrode and a negative electrode on the input side of the inverter circuit 2. As will be described later, since the control circuit 3 performs DC voltage control, the DC voltage is controlled to a constant voltage, and the electric power stored in the electrolytic capacitor is also constant. Therefore, the power input to the inverter circuit 2 matches the power output from the DC power source 1.

  The control circuit 3 controls the inverter circuit 2 and is realized by, for example, a microcomputer. The control circuit 3 generates a PWM signal based on the current signal i input from the current sensor 4, the voltage signal v input from the voltage sensor 5, and the DC voltage signal e input from the DC voltage sensor 6. To the inverter circuit 2.

  FIG. 2 is a functional block diagram for explaining the internal configuration of the control circuit 3.

  The control circuit 3 includes a DC voltage control unit 31, a power fluctuation component attenuation unit 32, a reactive power calculation unit 33, a reactive power control unit 34, a current control unit 35, and a PWM signal generation unit 36. Although not shown, the control circuit 3 includes a protection mechanism that detects an overvoltage, an overcurrent, an isolated operation, and the like and disconnects the grid-connected inverter system A from the power system B.

The DC voltage control unit 31 is for controlling the input voltage of the inverter circuit 2. The DC voltage control unit 31 receives a deviation Δe (= e ^* −e) between the DC voltage signal e output from the DC voltage sensor 6 and the DC voltage target value e ^*, and makes the deviation zero. The DC voltage compensation signal is output to the power fluctuation component attenuation unit 32. The DC voltage control unit 31 performs, for example, PI control (proportional integration control).

In the grid-connected inverter system A, maximum power point tracking (MPPT) control is performed using the power-voltage characteristics of the DC power supply 1. The MPPT control is to control the output voltage so that the output power is maximized. In the present embodiment, the direct current voltage target value e ^* is slightly changed to perform direct current voltage control, thereby changing the output voltage of the direct current power source 1 so that the output power of the direct current power source 1 becomes larger. Change e ^* . Thus, the DC voltage target value e ^* becomes the maximum output operating voltage, and the power output from the DC power supply 1 is maximized. Note that a DC / DC converter circuit is provided in front of the inverter circuit 2 so that the inverter circuit 2 controls the output voltage of the DC / DC converter circuit to be constant, and the DC / DC converter circuit performs maximum power point tracking control. May be.

  The power fluctuation component attenuating unit 32 removes the same frequency component as the power fluctuation frequency (hereinafter referred to as “power fluctuation component”) from the DC voltage compensation signal. The power fluctuation component attenuating unit 32 is a so-called notch filter having an amplitude characteristic as shown in the Bode diagram of FIG. 3, attenuates a predetermined frequency component and passes other frequency components as they are without being attenuated. FIG. 3 shows a Bode diagram when a frequency component of 0.918 [Hz] is removed. The power fluctuation component attenuating unit 32 receives the DC voltage compensation signal from the DC voltage control unit 31 and outputs a signal obtained by removing the power fluctuation component from the DC voltage compensation signal to the current control unit 35.

The transfer function F _N (s) of the power fluctuation component attenuation unit 32 is expressed by the following equation (1). f ₀ is the center frequency of the frequency band to be attenuated, and a and b are parameters that determine the attenuation characteristics. The parameters a and b are appropriately determined based on actual machine verification based on the stability of the control system and the efficiency of MPPT control. As the center frequency f ₀ , a power fluctuation frequency f _SW is set. In the present embodiment, the frequency f _SW is received from the electric power company that manages the power system B. If the power fluctuation frequency f _SW is known in advance, it may be set in advance. In this case, the power fluctuation component attenuation unit 32 may be an adaptive notch filter so as to cope with a change in the frequency f _SW . Further, the power fluctuation component attenuating unit 32 is not limited to the transfer function F _N (s) expressed by the following equation (1), and may be any unit that attenuates a predetermined frequency component.

The power oscillation component attenuating unit 32 may be configured by connecting a plurality of notch filters in multiple stages so as to cope with a case where there are a plurality of power oscillation frequencies f _SW .

  The reactive power calculator 33 calculates reactive power output from the inverter circuit 2. The reactive power calculator 33 calculates and outputs a reactive power value Q based on the current signal i input from the current sensor 4 and the voltage signal v input from the voltage sensor 5.

The reactive power control unit 34 is for controlling the reactive power output from the inverter circuit 2. The reactive power control unit 34 receives a deviation (Q ^* −Q) between the reactive power value Q output from the reactive power calculation unit 33 and the reactive power target value Q ^*, and is used to make the deviation zero. The power compensation signal is output to the current control unit 35. The reactive power control unit 34 performs PI control, for example. In this embodiment, “0” is set as the reactive power target value Q ^* so that the power factor becomes “1”.

  The current control unit 35 is for controlling the output current of the inverter circuit 2. The current control unit 35 generates a compensation signal based on the current signal i input from the current sensor 4 and outputs the compensation signal to the PWM signal generation unit 36.

  FIG. 4 is a functional block diagram for explaining the internal configuration of the current control unit 35.

  The current controller 35 includes a three-phase / two-phase converter 35a, a rotation coordinate converter 35b, an LPF 35c, an LPF 35d, a PI controller 35e, a PI controller 35f, a stationary coordinate converter 35g, and a two-phase / three-phase converter. 35h.

The three-phase / two-phase converter 35a performs a so-called three-phase / two-phase conversion process (αβ conversion process). The three-phase / two-phase conversion process is a process that converts a three-phase AC signal into an equivalent two-phase AC signal. The three-phase AC signal is a stationary orthogonal coordinate system (hereinafter referred to as “static coordinate system”). In this case, the signals are decomposed into orthogonal α-axis and β-axis components and the components of the respective axes are added to each other, thereby converting into an AC signal of the α-axis component and an AC signal of the β-axis component. The three-phase / two-phase converter 35a converts the three-phase current signals i _u , i _v , i _w input from the current sensor 4 into an α-axis current signal iα and a β-axis current signal iβ, and rotates coordinates It outputs to the conversion part 35b.

The conversion process performed by the three-phase / two-phase conversion unit 35a is represented by a determinant represented by the following equation (2).

The rotation coordinate conversion unit 35b performs a so-called rotation coordinate conversion process (dq conversion process). The rotation coordinate conversion process is a process of converting a two-phase signal in the stationary coordinate system into a two-phase signal in the rotation coordinate system. The rotating coordinate system is an orthogonal coordinate system having orthogonal d-axis and q-axis and rotating in the same rotational direction at the same angular velocity as the fundamental wave of the system voltage of the power system B. The rotation coordinate conversion unit 35b converts the α-axis current signal iα and β-axis current signal iβ of the stationary coordinate system input from the three-phase / two-phase conversion unit 35a into rotation coordinates based on the phase θ of the fundamental wave of the system voltage. System d-axis current signal i _d and q-axis current signal i _q are converted and output.

The conversion process performed by the rotation coordinate conversion unit 35b is represented by a determinant represented by the following expression (3).

LPF35c and LPF35d is a low-pass filter, to pass only the DC component of the d-axis current signal i _d and the q-axis current signal i _q, respectively. By rotating the coordinate transformation process, the fundamental wave component of the α-axis current signal iα and β-axis current signal iβ has been converted into a DC component of the d-axis current signal i _d and the q-axis current signal i _q, respectively. That is, the LPF 35c and the LPF 35d remove the unbalanced component and the harmonic component, and pass only the fundamental wave component.

The PI control unit 35e performs PI control (proportional integration control) based on the deviation between the DC component of the d-axis current signal i _d and the target signal, and outputs a compensation signal x _d . Signal input from the power fluctuation component attenuation unit 32 (signal to remove power fluctuation component from a DC voltage compensation signal) is used as a target signal of the d-axis current signal i _d.

The PI control unit 35f performs PI control based on the deviation between the DC component of the q-axis current signal i _q and the target signal, and outputs a compensation signal x _q . The reactive power compensation signal input from the reactive power control unit 34 is used as a target signal for the q-axis current signal _iq .

The stationary coordinate conversion unit 35g converts the compensation signals x _d and x _q respectively input from the PI control unit 35e and the PI control unit 35f into the compensation signals xα and xβ of the stationary coordinate system. 35b is the reverse of the conversion process. The stationary coordinate conversion unit 35g performs a so-called stationary coordinate conversion process (inverse dq conversion process). The compensation signal x _d , x _q of the rotating coordinate system is used as the compensation signal xα of the stationary coordinate system based on the phase θ. , convert to xβ.

The conversion process performed by the stationary coordinate conversion unit 35g is expressed by a determinant represented by the following expression (4).

The two-phase / three-phase conversion unit 35h converts the compensation signals xα, xβ input from the stationary coordinate conversion unit 35g into three-phase compensation signals x _u , x _v , x _w . The two-phase / three-phase conversion unit 35h performs a so-called two-phase / three-phase conversion process (reverse αβ conversion process), and performs a reverse conversion process to the three-phase / two-phase conversion unit 35a.

The conversion process performed by the two-phase / three-phase conversion unit 35h is represented by a determinant represented by the following equation (5).

Returning to FIG. 2, the PWM signal generation unit 36 generates a PWM signal. The PWM signal generator 36 is a command signal for instructing the waveform of the output voltage of each phase of the inverter circuit 2 based on the three-phase compensation signals x _u , x _v , x _w input from the current controller 35. And a PWM signal is generated by a triangular wave comparison method based on the command signal and the carrier signal. For example, a pulse signal that is high when the command signal is larger than the carrier signal and low when the command signal is equal to or less than the carrier signal is generated as a PWM signal. The generated PWM signal is output to the inverter circuit 2. Note that the PWM signal generation unit 36 is not limited to the case where the PWM signal is generated by the triangular wave comparison method. For example, the PWM signal generation unit 36 may generate the PWM signal by a hysteresis method.

  In the present embodiment, the case where the control circuit 3 is realized as a digital circuit has been described, but it may be realized as an analog circuit. Further, the processing performed by each unit may be designed by a program, and the computer may function as the control circuit 3 by executing the program. The program may be recorded on a recording medium and read by a computer.

In the present embodiment, the current control unit 35, the removed signal power fluctuation component from a DC voltage compensation signal output from the DC voltage control unit 31 as a target signal of the d-axis current signal i _d, from the reactive power control unit 34 Current control is performed using the input reactive power compensation signal as a target signal for the q-axis current signal _iq . Then, the PWM signal generation unit 36 generates a PWM signal based on the compensation signals x _u , x _v , x _w generated by the current control unit 35 and outputs the PWM signal to the inverter circuit 2. The inverter circuit 2 performs power conversion based on the PWM signal.

  The control circuit 3 controls the DC voltage input to the inverter circuit 2 and the reactive power output from the inverter circuit 2. In addition, the control circuit 3 controls the DC power input by controlling the DC voltage, thereby controlling the output power. Therefore, the control circuit 3 also controls the output power by controlling the DC voltage.

Since the signal obtained by attenuating the frequency component of the power fluctuation from the DC voltage compensation signal for controlling the output power is used as the target signal of the d-axis current signal _id , the output power of the inverter circuit 2 also suppresses the frequency component. It will be done. Therefore, the inverter circuit 2 can suppress causing or increasing power fluctuation.

  Below, the simulation for confirming that the grid connection inverter system A can suppress causing electric power fluctuation is demonstrated.

  First, a simulation for examining the occurrence of power fluctuation will be described.

FIG. 5A is a diagram showing a one-machine infinite bus model. The one-machine infinite bus model is a model in which one generator C is connected to a large power system (infinity bus D) via a transmission line. A simulation was performed using the model. In this simulation, in order to investigate the occurrence of power fluctuations, a model in which the generator C and the infinite bus D are connected by two lines Z1 and Z2 is assumed. Went. The rated capacity of the generator C is 60 [MVA], the rated output is 50 [MW], the system frequency is 60 [Hz], and the system voltage is 22 [kV _rms ].

  FIG. 5B shows the internal phase of the generator C. FIG. 5C shows a change in the rotational speed of the generator C. With reference to the rotational speed corresponding to the reference frequency (for example, 60 [Hz]) of the power system, the rotational speed and the reference Is shown as a percentage of the baseline. When the time Time was 1 [s] and the line Z2 was disconnected and reclosed, the internal phase and the rotational speed thereafter fluctuated. This fluctuation was power fluctuation, and the frequency of fluctuation (frequency of power fluctuation) was about 0.918 [Hz].

  Next, it will be described with reference to FIGS. 6 to 10 that the conventional grid-connected inverter system may cause power fluctuation and that the grid-connected inverter system A can suppress the occurrence of this power fluctuation. .

  FIG. 6 is a model obtained by adding a model showing the grid interconnection inverter system A to the one-machine infinite bus model shown in FIG. Other conditions are common to the model shown in FIG.

  First, in the control circuit 3 (see FIG. 2) of the grid interconnection inverter system A, the power fluctuation component attenuation unit 32 is not provided (that is, a conventional grid interconnection inverter system, hereinafter, “grid interconnection inverter system A100”). In this way, the output of the grid interconnection inverter system A100 was varied. The model of the grid interconnection inverter system A100 corresponds to a d-axis output (corresponding to the output of the DC voltage control unit 31 in FIG. 2) and a q-axis output (output of the reactive power control unit 34 in FIG. 2). ) And a current source that outputs a three-phase current corresponding thereto. The output fluctuation was verified as the following four patterns.

7A to 7C are diagrams in which the output fluctuates at a frequency 0.1 times the frequency of power fluctuation (f _SW = 0.918 [Hz]) generated in the previous simulation. . The amplitude of the output fluctuation is set to 0.5 [MW]. FIG. 7A shows the amount of change in active power output from the grid-connected inverter system A100 from the steady state (hereinafter referred to as “active power output change amount”) ΔP and reactive power from the steady state. A change amount (hereinafter referred to as “reactive power output change amount”) ΔQ is shown. Since the reactive power is controlled to “0”, the active power output change amount ΔP indicates the output fluctuation. 7 (b) and 7 (c) show fluctuations in the internal phase and rotational speed of the generator C, as in FIGS. 5 (b) and 5 (c). 8 to 10 below, (a) shows the active power output change amount ΔP and the reactive power output change amount ΔQ when varied in each pattern, and (b) shows the internal phase of the generator C. (C) shows the fluctuation of the rotational speed of the generator C.

As shown in FIG. 7A, the active power output change amount ΔP fluctuates at a frequency “0.1 · f _SW ” (= 0.0918 [Hz], a period of about 10.9 [s]). . On the other hand, as shown in FIGS. 7B and 7C, the internal phase and the rotational speed of the generator C hardly change. That is, even if the output of the grid-connected inverter system A100 fluctuates at the frequency “0.1 · f _SW ”, the power fluctuation component is not output, and thus no power fluctuation occurs.

FIGS. 8A to 8C show an output that fluctuates at a frequency f _SW . As shown in FIG. 8A, the active power output change amount ΔP fluctuates at a frequency f _SW (= 0.918 [Hz], a cycle of about 1.09 [s]). Further, as shown in FIGS. 8B and 8C, the internal phase and the rotational speed of the generator C also fluctuate at the same frequency. That is, when the output of the grid interconnection inverter system A100 fluctuates at the frequency f _SW , a power fluctuation component is output and power fluctuation occurs.

FIGS. 9A to 9C show an output that fluctuates at a frequency 10 times the frequency f _SW . As shown in FIG. 9A, the active power output change amount ΔP fluctuates at a frequency “10 · f _SW ” (= 9.18 [Hz], a period of about 0.109 [s]). On the other hand, as shown in FIGS. 9B and 9C, the internal phase and the rotational speed of the generator C hardly change. That is, even if the output of the grid-connected inverter system A100 fluctuates at the frequency “10 · f _SW ”, the power fluctuation component is not output, so the power fluctuation does not occur.

10 (a) to 10 (c) show the output greatly changing in a stepped manner. As shown in FIG. 10A, the active power output change amount ΔP greatly changes in a stepped manner from 0 [MW] to 2 [MW] when the time Time is 1 [s]. Further, as shown in FIGS. 10B and 10C, the internal phase and rotational speed of the generator C fluctuate at a frequency f _SW (= 0.918 [Hz], a cycle of about 1.09 [s]). ing. That is, when the output of the grid-connected inverter system A100 changes in a step shape, since all frequency components are included in the step change, the power fluctuation component is output and the power fluctuation occurs.

As described above, and when the output of the system interconnection inverter system A100 varies in power oscillation frequency f _SW, when large changes stepwise, it was confirmed that power oscillations is caused.

  Next, using the grid-connected inverter system A instead of the conventional grid-connected inverter system A100, the output is varied in four patterns as in FIGS. 7 to 10 (a) to (c). Verification was performed. In the model of the grid interconnection inverter system A, the d-axis output is given through a notch filter (corresponding to the power fluctuation component attenuation unit 32 in FIG. 2). FIGS. 7 to 10 (d) to (f) are obtained by performing the same verifications as FIGS. 7 to 10 (a) to (c), respectively. 7D to 10D show the active power output change amount ΔP and the reactive power output change amount ΔQ in each pattern, respectively, similarly to FIGS. 7A to 10A. Moreover, (e) of FIGS. 7-10 shows the internal phase of the generator C in each pattern similarly to (b) of FIGS. 7-10, respectively, (f) of FIGS. Similarly to FIG. 7 to FIG. 10C, the fluctuations in the rotational speed of the generator C in each pattern are shown.

FIG. 7D is almost the same as FIG. 7A, and the active power output change ΔP fluctuates at the frequency “0.1 · f _SW ”. 7 (e) and 7 (f) are substantially the same as FIGS. 7 (b) and 7 (c), and there is no power fluctuation. That is, the output fluctuation of the frequency “0.1 · f _SW ” is the same as that of the grid interconnection inverter system A100 even in the grid interconnection inverter system A.

On the other hand, FIG. 8D differs from FIG. 8A in that the active power output change amount ΔP does not fluctuate. This is because the component of the frequency f _SW from a DC voltage compensation signal (power fluctuation component) is removed by the power fluctuation component attenuation unit 32 (see FIG. 2). In this case, as shown in FIGS. 8E and 8F, the internal phase and the rotational speed of the generator C hardly change. That is, the grid interconnection inverter system A can suppress the occurrence of power fluctuation by removing the power fluctuation component by the power fluctuation component attenuation unit 32.

FIG. 9D is almost the same as FIG. 9A, and the active power output variation ΔP fluctuates at the frequency “10 · f _SW ”. Also, FIGS. 9E and 9F are almost the same as FIGS. 9B and 9C, and no power fluctuation occurs. That is, the output fluctuation of the frequency “10 · f _SW ” is the same as that of the grid interconnection inverter system A100 even in the grid interconnection inverter system A.

The active power output change amount ΔP shown in FIG. 10D varies when the time Time is 1 to 2 [s], and changes to 2 [MW]. This is because the power fluctuation component attenuation unit 32 has removed the component of the frequency f _SW (power fluctuation component) from the DC voltage compensation signal. In this case, as shown in FIGS. 10E and 10F, the internal phase and the rotational speed of the generator C hardly change. That is, the grid interconnection inverter system A can suppress the occurrence of power fluctuation by removing the power fluctuation component by the power fluctuation component attenuation unit 32.

  As described above, it was confirmed that the use of the grid interconnection inverter system A can suppress the occurrence of power fluctuation.

  In the first embodiment, control is performed after the current control unit 35 performs three-phase / two-phase conversion of the current signal i and rotational coordinate conversion, but is not limited thereto. For example, the α-axis current signal iα and the β-axis current signal iβ output from the three-phase / two-phase conversion unit 35a may be controlled. In this case, the signal input from the power fluctuation component attenuating unit 32 (the signal obtained by removing the power fluctuation component from the DC voltage compensation signal) and the reactive power compensation signal input from the reactive power control unit 34 are subjected to stationary coordinate conversion, and the target is converted. What is necessary is just to use as a signal. Alternatively, the three-phase current signal i may be directly controlled. In this case, the signal input from the power fluctuation component attenuating unit 32 and the reactive power compensation signal may be subjected to two-phase / three-phase conversion by stationary coordinate conversion and used as a target signal.

In the first embodiment, the case where the frequency f _{SW of} power fluctuation is given from the outside has been described, but the present invention is not limited to this. For example, the frequency f _SW may be detected and used. The case where the frequency f _SW is detected and the center frequency of the notch filter is set will be described below as a second embodiment.

  FIG. 11 is a functional block diagram for explaining the internal configuration of the control circuit according to the second embodiment. In the figure, the same or similar elements as those of the control circuit 3 (see FIG. 2) according to the first embodiment are denoted by the same reference numerals. As shown in FIG. 11, the control circuit 3 ′ is different from the control circuit 3 according to the first embodiment in that it includes a power fluctuation frequency detection unit 37.

The power oscillation frequency detection unit 37 detects the power oscillation frequency f _SW from the system frequency of the power system B and sets it to the center frequency f ₀ of the attenuation frequency band of the power oscillation component attenuation unit 32. The power fluctuation frequency detection unit 37 includes a frequency detection unit 37a, a bandpass filter 37b, an FFT processing unit 37c, and a comparison unit 37d.

  The frequency detection unit 37a detects the system frequency of the power system B. The frequency detection unit 37 a detects the frequency of the voltage signal v input from the voltage sensor 5. The voltage signal v is obtained by detecting the voltage at the output end of the inverter circuit 2, that is, the voltage at the connection point between the grid connection inverter system A and the power system B. Therefore, the system frequency of the power system B can be detected by detecting the frequency of the voltage signal v. The frequency detector 37a continuously detects the system frequency and outputs it as a frequency signal f to the bandpass filter 37b.

  The band pass filter 37b extracts a component in a predetermined frequency band (0.2 [Hz] to 1 [Hz]). The band-pass filter 37b passes a predetermined frequency band component of the frequency signal f input from the frequency detector 37a as it is, attenuates other frequency components, and outputs the attenuated frequency component to the FFT processor 37c. It is known that the frequency of power fluctuation is 0.2 [Hz] to 1 [Hz], and the frequency of power fluctuation accompanying changes in power demand is known to be included in 0.2 [Hz] or less. ing. The bandpass filter 37b removes the frequency component of fluctuation due to power demand and extracts only the frequency component of power fluctuation.

  The FFT processing unit 37c performs a fast Fourier transformation process. The FFT processing unit 37c performs a fast Fourier transform process on the signal input from the bandpass filter 37b (extracting a frequency component of a predetermined frequency band from the frequency signal f), and calculates an output level for each frequency. Output to the comparison unit 37d.

The comparison unit 37d compares the output level of each frequency input from the FFT processing unit 37c with a threshold value. The comparison unit 37d outputs the frequency at which the output level is equal to or higher than the threshold value to the power fluctuation component attenuation unit 32 as the power fluctuation frequency _fSW .

The configuration of the power fluctuation frequency detection unit 37 is not limited to this. For example, a fast Fourier transform process may be performed on the frequency signal f output from the frequency detection unit 37a, and only the output level of a frequency in a predetermined frequency band may be input to the comparison unit 37d. Further, the comparison unit 37d may detect the frequency having the maximum output level among the frequencies at which the output level is equal to or higher than the threshold as the frequency f _SW .

  Also in the second embodiment, as in the first embodiment, a signal obtained by removing the power fluctuation component from the DC voltage compensation signal is used as a current target by the current control unit 35. Therefore, also in 2nd Embodiment, there can exist an effect similar to 1st Embodiment.

In addition, it is more efficient that each of the grid-connected inverter systems A detects the frequency f _SW instead of detecting the frequency f _{SW of the} power fluctuation, but the remote monitoring control device that monitors a plurality of grid-connected inverter systems A detects the frequency f _SW. Good. A case where the remote monitoring control device detects the frequency f _SW and transmits it to each grid-connected inverter system A will be described below as a third embodiment.

  FIG. 12 is a diagram for explaining a large-capacity system according to the third embodiment.

The large-capacity system E includes a plurality of grid-connected inverter systems A connected in parallel, and a remote monitoring control device F that remotely monitors each grid-connected inverter system A. The remote monitoring control device F monitors the power generation state of each grid-connected inverter system A and includes a power fluctuation frequency detection unit 37. The power oscillation frequency detection unit 37 is the same as the power oscillation frequency detection unit 37 (see FIG. 11) according to the second embodiment, and the power oscillation frequency f is based on the voltage signal v input from the voltage sensor 5. _SW is detected and transmitted to each grid-connected inverter system A. Each grid-connected inverter system A sets the received frequency f _SW to the center frequency f ₀ of the power fluctuation component attenuation unit 32 (see FIG. 2).

  In the third embodiment, the same effect as that of the first embodiment can be obtained.

  In the first to third embodiments, the case where the control circuit 3 (3 ') performs DC voltage control has been described. However, the present invention is not limited to this. For example, a case where the control circuit performs active power control will be described below as a fourth embodiment.

  FIG. 13 is a functional block diagram for explaining the internal configuration of the control circuit according to the fourth embodiment. In the figure, the same or similar elements as those of the control circuit 3 (see FIG. 2) according to the first embodiment are denoted by the same reference numerals. As shown in FIG. 13, the control circuit 3 ″ differs from the control circuit 3 according to the first embodiment in that active power control is performed instead of DC voltage control.

  The active power calculator 33 ′ calculates the active power output from the inverter circuit 2. The active power calculation unit 33 ′ calculates and outputs an active power value P based on the current signal i input from the current sensor 4 and the voltage signal v input from the voltage sensor 5.

The active power control unit 34 ′ is for controlling the active power output from the inverter circuit 2. The active power control unit 34 ′ receives a deviation (P ^* −P) between the active power value P output from the active power calculation unit 33 ′ and the active power target value P ^* and sets the deviation to zero. Are output to the power fluctuation component attenuating unit 32. The active power control unit 34 ′ performs, for example, PI control.

Power fluctuation component attenuation unit 32 removes the power fluctuation component from the effective power compensation signal input from the effective power control unit 34 ', and outputs to the current control unit 35 as a target signal of the d-axis current signal i _d.

  In the fourth embodiment, the output power is controlled by controlling the reactive power and the active power. A signal obtained by removing the power fluctuation component from the active power compensation signal is used as a current target by the current control unit 35. Therefore, also in the fourth embodiment, the same effect as in the first embodiment can be obtained.

  In this embodiment, although the case where the grid connection inverter system A was a three-phase system was demonstrated, a single phase system may be sufficient. In the case of a single-phase system, for example, the current control unit 35 (see FIG. 2) is based on a deviation between a single-phase current signal input from the current sensor 4 and a signal input from the power fluctuation component attenuation unit 32. A phase compensation signal may be output, and the PWM signal generator 36 may generate a PWM signal based on the compensation signal. Alternatively, the single-phase current signal may be converted into two orthogonal current signals by Hilbert transform or the like and input to the rotation coordinate conversion unit 35b (see FIG. 4).

  The control circuit according to the present invention and the inverter device including the control circuit are not limited to the above-described embodiments. The design of the control circuit according to the present invention and the specific configuration of each part of the inverter device including the control circuit can be varied in design in various ways.

A Grid-connected inverter system 1 DC power supply 2 Inverter circuit 3, 3 ′, 3 ″ Control circuit 31 DC voltage control unit (power control means)
32 Power fluctuation component attenuation unit (predetermined frequency attenuation means)
33 reactive power calculation unit 33 'active power calculation unit 34 reactive power control unit 34' active power control unit (power control means)
35 Current control part 35a Three-phase / two-phase conversion part (conversion means)
35b Rotating coordinate converter (converter)
35c, 35d LPF
35e, 35f PI controller (two-phase control means)
35g Static coordinate converter (inverse conversion means)
35h Two-phase / three-phase converter (inverse conversion means)
36 PWM signal generator 37 Power oscillation frequency detector 37a Frequency detector 37b Band pass filter (predetermined band pass means)
37c FFT processing unit 37d comparison unit (predetermined frequency detection means)
4 Current sensor 5 Voltage sensor 6 DC voltage sensor B Power system C Generator D Infinite bus E Large capacity system F Remote monitoring and control device

Claims (10)

A control circuit that controls an inverter circuit that converts DC power into AC power and supplies the power to the power system using a PWM signal,
Power control means for generating a compensation signal for controlling the output power of the inverter circuit;
A predetermined frequency attenuating means for inputting the compensation signal and attenuating and outputting a predetermined frequency component;
Current control means for generating a current compensation signal for controlling the output current of the inverter circuit, using the signal output from the predetermined frequency attenuating means as a current target;
PWM signal generating means for generating the PWM signal based on the current compensation signal;
A control circuit comprising: The predetermined frequency is a frequency of power fluctuation of the power system.
The control circuit according to claim 1. The power control means generates a DC voltage compensation signal for controlling the input voltage of the inverter circuit as the compensation signal.
The control circuit according to claim 1 or 2. Active power calculating means for calculating the output active power of the inverter circuit is further provided,
The power control means generates an active power compensation signal for controlling the output active power of the inverter circuit as the compensation signal.
The control circuit according to claim 1 or 2.   The control circuit according to claim 1, wherein the predetermined frequency attenuating unit receives the predetermined frequency from the outside of the control circuit. A frequency detection means for detecting a system frequency of the power system;
A system band signal that continuously detects the system frequency is input, a predetermined band passing means that attenuates and outputs a component other than the predetermined frequency band, and
FFT processing means for calculating an output level for each frequency of the signal output from the predetermined band passing means;
Predetermined frequency detecting means for detecting a frequency at which the output level is equal to or higher than a threshold;
Further comprising
The control circuit according to claim 1, wherein the predetermined frequency attenuating unit receives the frequency detected by the predetermined frequency detecting unit as the predetermined frequency.   The control circuit according to claim 1, wherein the predetermined frequency attenuation means is a notch filter. The inverter circuit outputs three-phase AC power,
The current control means includes
Conversion means for performing three-phase / two-phase conversion and rotational coordinate conversion on the three-phase current signals respectively detecting the three-phase output currents of the inverter circuit, and converting them into two axis component signals;
Two-phase control means for generating two signals for controlling the deviation signal between the two axis component signals and the respective target signals to zero;
Inverse conversion means for performing static coordinate conversion and two-phase / three-phase conversion on the two signals to convert the two signals into the three-phase current compensation signal;
With
The signal output from the predetermined frequency attenuating means is set as one target signal of the two axis component signals.
The control circuit according to claim 1. Reactive power control means for generating a reactive power compensation signal for controlling the output reactive power of the inverter circuit,
The reactive power compensation signal is set as the other target signal of the two axis component signals.
The control circuit according to claim 8.   An inverter device comprising the control circuit according to claim 1 and the inverter circuit.