Control circuit and inverter device including the same

Abstract

To provide a control circuit capable of suppressing a rapid increase in output of an inverter circuit due to a rapid increase in sunlight, and an inverter device including the control circuit.SOLUTION: In a control circuit 6 for controlling an inverter circuit 2 for converting DC power output from a DC power supply 1 into AC power, a three phase current signal obtained by detecting a three phase output current of the inverter circuit 2 is converted into a d-axis current signal and a q-axis current signal which are two orthogonal components of a rotating coordinate system. A d-axis upper limit setting unit 34 that calculates a first upper limit power value that is larger than the present output power of the inverter circuit 2 and changes according to the output power, and sets a first upper limit value corresponding to the first upper limit power value as an upper limit value Idmax, and a d-axis target limiting unit 33 that limits the target value Id * to the upper limit value Idmax or less.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a control circuit for controlling an inverter circuit that converts DC power output by a solar cell or the like into AC power, and to an inverter device including the control circuit. [Background technology]

[0002] Self-consumption solar power generation systems have been developed. These systems are equipped with an inverter that converts DC power generated by solar cells into AC power and outputs it. Self-consumption solar power generation systems are not permitted to reverse power flow to the power grid, so the inverter must suppress the output power so that it does not exceed the power consumed by the load.

[0003] Patent Document 1 discloses an inverter device that converts DC power output from a DC power source into AC power using an inverter circuit and supplies the AC power to a power grid. The control circuit of the inverter device includes a current control unit that converts detected three-phase output currents into orthogonal d-axis and q-axis current signals in a rotating coordinate system and controls each of them to a target value. The control circuit can suppress the output power by limiting the target value of the d-axis current signal to a predetermined range. Patent Document 1 limits the target value of the d-axis current signal to an upper limit value of the d-axis current signal corresponding to the upper limit value of the inverter circuit's output active power (hereinafter referred to as the "d-axis upper limit value"). This allows the control circuit to suppress the output active power of the inverter circuit to an upper limit value. The control circuit can control the output active power of the inverter circuit so that it does not exceed the rated power by setting the d-axis upper limit value to a value corresponding to the rated power of the inverter circuit. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 6437807 Summary of the Invention [Problem to be solved by the invention]

[0005] Photovoltaic power generation systems have the problem of output instability due to fluctuations in solar radiation. For example, if clouds block sunlight and the intensity of solar radiation suddenly decreases, output drops sharply. Conversely, if the clouds blocking the sunlight move and the intensity of solar radiation suddenly increases, output rises sharply. A sudden increase in output due to fluctuations in solar radiation is particularly problematic for self-consumption photovoltaic power generation systems, which do not allow reverse power flow. When the load on the facility is low, such as on holidays, the system must limit output to below the power consumption of the facility's load to prevent reverse power flow to the power grid. If the intensity of solar radiation suddenly increases and the output of the photovoltaic power generation system rises sharply, reverse power flow may occur because the output is not limited if it is below a set upper limit. In reality, the reverse power relay (RPR) activates before reverse power flow occurs, shutting down the photovoltaic power generation system.

[0006] The present invention has been devised in light of the above circumstances, and aims to provide a control circuit that can suppress a sudden increase in inverter circuit output due to a sudden increase in solar radiation, and an inverter device equipped with such a control circuit. [Means for solving the problem]

[0007] A control circuit provided by a first aspect of the present invention is a control circuit for controlling an inverter circuit that converts DC power output by a DC power supply into AC power, and includes: a current control unit that converts three-phase current signals that detect the three-phase output current of the inverter circuit into a d-axis current signal and a q-axis current signal, which are two orthogonal components of a rotating coordinate system, and controls each of them to a target value; a d-axis current target value generation unit that generates a d-axis current target value that is a target value of the d-axis current signal; a d-axis upper limit setting unit that calculates a first upper limit power value that is greater than the current output power of the inverter circuit and changes depending on the output power, and sets the first upper limit value corresponding to the first upper limit power value as a d-axis upper limit value; and a d-axis target limiting unit that limits the d-axis current target value to be equal to or less than the d-axis upper limit value.

[0008] In a preferred embodiment of the present invention, the d-axis upper limit setting unit calculates the first upper limit power value by adding an increase value greater than "0" to the output power.

[0009] In a preferred embodiment of the present invention, the d-axis upper limit setting unit calculates the first upper limit power value by multiplying the output power by an increase coefficient greater than "1".

[0010] In a preferred embodiment of the present invention, the d-axis upper limit setting unit sets the smaller of a second upper limit value corresponding to a second upper limit power value that does not change according to the output power and the first upper limit value as the d-axis upper limit value.

[0011] In a preferred embodiment of the present invention, the power supply control system further includes a DC voltage target value setting unit that sets a DC voltage target value that is a target value for an output voltage of the DC power supply, wherein the DC voltage target value setting unit changes the DC voltage target value to adjust the DC voltage target value so as to increase the output power of the DC power supply, and the d-axis current target value generation unit generates, as the d-axis current target value, a DC voltage compensation value for controlling the output voltage of the DC power supply to the DC voltage target value.

[0012] An inverter device provided by a second aspect of the present invention includes the control circuit provided by the first aspect of the present invention and the inverter circuit. [Effects of the Invention]

[0013] According to the present invention, the d-axis upper limit setting unit sets a first upper limit corresponding to the first upper limit power value as the d-axis upper limit value. The d-axis target limiting unit limits the d-axis current target value to be equal to or less than the d-axis upper limit value. This allows the control circuit according to the present invention to limit the output power of the inverter circuit to be equal to or less than the first upper limit power value. The first upper limit power value is greater than the current output power of the inverter circuit and varies depending on the output power. Therefore, even if solar radiation suddenly increases, the control circuit according to the present invention can prevent a sudden increase in output power by limiting the output power of the inverter circuit to be equal to or less than the first upper limit power value and gradually increasing the first upper limit power value. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a block diagram showing the overall configuration of an inverter device according to a first embodiment. [Figure 2] FIG. 2(a) is a block diagram showing the internal configuration of a control unit of a control circuit, and FIG. 2(b) is a block diagram showing the internal configuration of a current control unit. [Figure 3] 10A and 10B are diagrams for explaining suppression control by a control circuit for suppressing a sudden increase in the output active power of an inverter circuit. [Figure 4] FIG. 10 is a block diagram showing the internal configuration of a control circuit of an inverter device according to a second embodiment. [Figure 5] 10 is a flowchart illustrating a maximum power point search process performed by a DC voltage target value setting unit according to the second embodiment. [Figure 6] FIG. 10 is a block diagram showing the overall configuration of an inverter device according to a third embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0015] Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0016] FIG. 1 is a block diagram showing the overall configuration of an inverter device A1 according to a first embodiment. The inverter device A1 is a so-called power conditioner that converts DC power input from a DC power source 1 into AC power and supplies it to a load L. The DC power source 1 outputs DC power and, in this embodiment, includes a solar cell. The solar cell generates DC power by converting solar energy into electrical energy. The DC power source 1 outputs the generated DC power to the inverter device A1. The combination of the DC power source 1 and the inverter device A1 constitutes a so-called photovoltaic power generation system. Note that the photovoltaic power generation system may also include a storage battery system. The photovoltaic power generation system (inverter device A1) is connected to a three-phase power grid B. Hereinafter, the three phases are referred to as U-phase, V-phase, and W-phase. Power is also supplied to the load L from the power grid B. However, the photovoltaic power generation system is a self-consumption type, and the inverter device A1 is not permitted to perform reverse power flow to the power grid B. The inverter device A1 includes an inverter circuit 2, a control circuit 6, a current sensor 71, a voltage sensor 72, a DC current sensor 81, and a DC voltage sensor 82. In reality, the inverter device A1 also includes a transformer and other components for electrically insulating the inverter circuit 2 from the power system B, but these components are not shown or described here.

[0017] The inverter circuit 2 converts DC power input from the DC power source 1 into AC power and outputs it. The inverter circuit 2 includes a PWM-controlled inverter and a filter (not shown). The PWM-controlled inverter is a three-phase full-bridge inverter with three sets of six switching elements (not shown), and converts DC power into AC power by switching each switching element on and off based on a PWM signal input from a control circuit 6. The filter removes high-frequency components caused by switching. The positive and negative terminals of the input side of the inverter circuit 2 are connected to the positive and negative terminals of the DC power source 1, respectively, so that the input voltage of the inverter circuit 2 matches the output voltage of the DC power source 1, and the input current of the inverter circuit 2 matches the output current of the DC power source 1.

[0018] The current sensor 71 detects the instantaneous values ​​of the three-phase output currents of the inverter circuit 2. The current sensor 71 converts the detected instantaneous values ​​into digital signals to generate current signals i u ,i v ,i w (The three current signals may be collectively referred to as "current signal i") and output to the control circuit 6. The voltage sensor 72 detects the instantaneous values ​​of the output voltages of the three phases of the inverter circuit 2. The voltage sensor 72 converts the detected instantaneous values ​​into digital signals to generate voltage signals v u ,v v ,v w (The three voltage signals may be collectively referred to as "voltage signal v") and output them to the control circuit 6. The voltage sensor 72 also calculates the effective value Vrms of the line voltage from the detected instantaneous value and outputs it to the control circuit 6.

[0019] The DC current sensor 81 detects the instantaneous value of the input current of the inverter circuit 2 (i.e., the output current of the DC power supply 1). The DC current sensor 81 converts the detected instantaneous value into digital form and outputs it to the control circuit 6 as a DC current signal Idc. The DC voltage sensor 82 detects the instantaneous value of the input voltage of the inverter circuit 2 (i.e., the output voltage of the DC power supply 1). The DC voltage sensor 82 converts the detected instantaneous value into digital form and outputs it to the control circuit 6 as a DC voltage signal Vdc. The DC voltage sensor 82 detects the voltage between the terminals of an electrolytic capacitor (not shown) provided between the positive and negative electrodes on the input side of the inverter circuit 2.

[0020] The control circuit 6 controls the inverter circuit 2 and is realized by, for example, a microcomputer. The control circuit 6 generates a PWM signal based on the current signal i input from the current sensor 71, the voltage signal v and the line voltage effective value Vrms input from the voltage sensor 72, the DC current signal Idc input from the DC current sensor 81, and the DC voltage signal Vdc input from the DC voltage sensor 82. The control circuit 6 then outputs the generated PWM signal to the inverter circuit 2. The control circuit 6 includes a control unit 3, a DC voltage target value setting unit 4, and a power calculation unit 5.

[0021] The DC voltage target value setting unit 4 sets a voltage target value Vdc, which is a target value of the DC voltage signal Vdc. * The DC voltage target value setting unit 4 is configured to perform so-called maximum power point tracking control (MPPT control), and sets the voltage target value Vdc * is changed to maximize the input power from DC power supply 1, and the voltage target value Vdc * Specifically, the DC voltage target value setting unit 4 calculates the input power input from the DC power supply 1 based on the DC current signal Idc input from the DC current sensor 81 and the DC voltage signal Vdc input from the DC voltage sensor 82. Then, the voltage target value Vdc * If the calculated input power increases when Vdc is changed, * is changed in the same direction, and if the calculated input power is reduced, it is assumed that the maximum power point has been exceeded, and the voltage target value Vdc * By repeating this process, the operating point is positioned near the maximum power point, and the input power input from the DC power supply 1 is kept as maximum as possible. The DC voltage target value setting unit 4 changes the set voltage target value Vdc * is output to a DC voltage control unit 31 of the control unit 3, which will be described later.

[0022] The process of searching for the maximum power point performed by the DC voltage target value setting unit 4 is not limited to the above. * The input power is calculated for each case when Vdc is decreased by a predetermined value and increased by a predetermined value, and the voltage target value Vdc is increased in the direction of the larger value. * It is also possible to change the amount of increase or decrease, or to use a genetic algorithm to solve the so-called "two-hill problem." In addition, the method is not limited to the hill-climbing method, and any algorithm used in maximum power point tracking control can be used.

[0023] The power calculation unit 5 calculates the active power and reactive power output by the inverter circuit 2. Based on the current signal i input from the current sensor 71 and the voltage signal v input from the voltage sensor 72, the power calculation unit 5 calculates the active power P and reactive power Q and outputs them to the control unit 3. The power calculation unit 5 extracts only the positive-phase components from the current signal i and the voltage signal v, respectively, and then calculates the active power P and reactive power Q. The calculated active power P and reactive power Q are input to the control unit 3. Generally, the power system B contains not only the positive-phase component of the fundamental AC signal but also the negative-phase component and AC signals with harmonic components. These components other than the positive-phase component make it difficult to accurately measure the active power and reactive power of the AC signal. Therefore, the power calculation unit 5 removes components such as the negative-phase component and harmonic components from the current signal i and the voltage signal v, extracts only the positive-phase component, and then calculates the active power P and reactive power Q. Note that a detailed description of the power calculation unit 5 is omitted.

[0024] The control unit 3 controls the inverter circuit 2, and receives a current signal i input from the current sensor 71, an effective value Vrms of the line voltage input from the voltage sensor 72, an active power P and a reactive power Q input from the power calculation unit 5, a DC voltage signal Vdc input from the DC voltage sensor 82, and a voltage target value Vdc input from the DC voltage target value setting unit 4. * The PWM signal is generated based on the above and output to the inverter circuit 2.

[0025] 2(a) is a block diagram showing the internal configuration of the control unit 3. The control unit 3 includes, as functional components, a DC voltage control unit 31, a reactive power control unit 32, a d-axis target limiting unit 33, a d-axis upper limit setting unit 34, a q-axis target limiting unit 35, a q-axis range setting unit 36, a current control unit 37, and a PWM signal generating unit 38.

[0026] The DC voltage control unit 31 is a functional component for controlling the output voltage of the DC power supply 1. The DC voltage control unit 31 controls the DC voltage signal Vdc input from the DC voltage sensor 82 and the voltage target value Vdc input from the DC voltage target value setting unit 4. *Deviation ΔVdc (=Vdc * -Vdc) and calculate the DC voltage compensation value to make the deviation zero. * and outputs it to the current control unit 37. In this embodiment, the DC voltage control unit 31 performs PI control (proportional-integral control). Note that control other than PI control (for example, PID control) may also be performed.

[0027] The reactive power control unit 32 is a functional component for controlling the reactive power output by the inverter circuit 2. The reactive power control unit 32 calculates the reactive power Q input from the power calculation unit 5 and a preset reactive power target value Q * Deviation ΔQ(=Q * -Q) is calculated, and the reactive power compensation value to make the deviation zero is set to the target value Iq of the q-axis current. * The reactive power target value Q is output to the current control unit 37. * is set to a fixed value (for example, "0"). In this embodiment, the reactive power control unit 32 performs PI control. Note that control other than PI control (for example, PID control) may also be performed.

[0028] As described above, the DC voltage control unit 31 and the reactive power control unit 32 perform PI control. In control that includes integral action, if a limit is placed on the output compensation value, a problem known as windup occurs. Therefore, it is necessary to take measures against this windup. As a conventionally known method can be used to take measures against windup, detailed explanation will be omitted.

[0029] The d-axis target limiting unit 33 is configured to limit the target value Id output from the DC voltage control unit 31. * is set by the d-axis upper limit setting unit 34. max The d-axis target limiting unit 33 is a functional configuration for limiting the upper limit value Id max Target value Id limited to: * is output to the current control unit 37.

[0030] The d-axis upper limit setting unit 34 sets the target value Id * Upper limit Id max The d-axis upper limit setting unit 34 includes a first upper limit calculation unit 341, a second upper limit calculation unit 342, and a comparison unit 343.

[0031] The second upper limit value calculation unit 342 calculates a second upper limit value Id for suppressing the output active power of the inverter circuit 2 to a second upper limit power value P2 or less. max The second upper limit value calculation unit 342 calculates the second upper limit value Id 2 using the following equation (1) based on the effective value Vrms of the line voltage input from the voltage sensor 72 and the second upper limit power value P2: max 2 is calculated sequentially. The second upper limit power value P2 is set to a preset power value according to the rated power of the inverter circuit 2 or a suppression power value received from a higher-level device (not shown). The second upper limit value calculation unit 342 may receive a preset power value according to the rated power of the inverter circuit 2 and a suppression power value received from a higher-level device, and set the smaller power value as the second upper limit power value P2. The coefficient a is a predetermined coefficient for conversion to a d-axis value set in the d-axis target limiting unit 33, and is calculated and set in advance based on the CT ratio of the current sensor 71, the VT ratio of the voltage sensor 72, the AD ratio at the time of digital conversion, etc. In this way, the second upper limit power value P2 (second upper limit value Id max 2) is a value calculated regardless of the current output power of the inverter circuit 2, and is the first upper limit power value P1 (first upper limit value Id max Unlike 1), it does not change depending on the output power. Id max 2 = a P2 / Vrms (1)

[0032] The second upper limit value Id calculated by the second upper limit value calculation unit 342 max For example, if the output current of the inverter circuit 2 is to be suppressed to a current upper limit value I2 or less, the second upper limit value Id max2 may be calculated. The current upper limit value I2 is set in advance, and the power factor K is calculated from the active power P and reactive power Q calculated by the power calculation unit 5. Furthermore, the coefficient b is a predetermined coefficient for conversion to a d-axis value set in the d-axis target limiting unit 33, and is calculated in the same way as the coefficient a and set in advance. Id max 2 = b K I2 (2)

[0033] The first upper limit value calculation unit 341 calculates the first upper limit value Id max The first upper limit value calculation unit 341 calculates a first upper limit power value Id 1 for suppressing the output active power of the inverter circuit 2 to be equal to or less than the first upper limit power value P1, by setting a value greater than the current output power of the inverter circuit 2 as the first upper limit power value P1. max The first upper limit value calculation unit 341 calculates the first upper limit value Id max In this embodiment, the first upper limit value calculation unit 341 calculates the first upper limit power value P1 by adding an increase value ΔP to the active power P input from the power calculation unit 5. The increase value ΔP is a value greater than "0" and is set in advance. The increase value ΔP varies depending on the calculation period, rated power, etc., and is set appropriately based on experiments and simulations. Then, the first upper limit value calculation unit 341 calculates the first upper limit value Id using the following equation (3) based on the effective value Vrms of the line voltage input from the voltage sensor 72 and the first upper limit power value P1. max 1 is calculated sequentially. In this way, the first upper limit power value P1 (first upper limit value Id max 1) changes depending on the current output power of the inverter circuit 2. Id max 1 = a P1 / Vrms (3)

[0034] The first upper limit value calculation unit 341 may calculate the first upper limit power value P1 by multiplying the active power P input from the power calculation unit 5 by an increase coefficient α. The increase coefficient α is a value greater than "1" (for example, "1.1") and is set in advance. The increase coefficient α differs depending on the calculation cycle, rated power, etc., and is set appropriately based on experiments or simulations.

[0035] The comparison unit 343 compares the first upper limit value Id calculated by the first upper limit value calculation unit 341. max 1 and the second upper limit value Id calculated by the second upper limit value calculation unit 342 max 2 is input and the two are compared. max 1 and the second upper limit Id max The smaller of the two values ​​is the upper limit Id max and set it in the d-axis target limiting unit 33.

[0036] The d-axis upper limit setting unit 34 determines the upper limit value Id using the same formulas as the above formulas (1) and (3) based on the smaller value of the set second upper limit power value P2 and the calculated first upper limit power value P1. max and set it in the d-axis target limiting unit 33. Also, the d-axis upper limit setting unit 34 does not include the second upper limit calculating unit 342 and the comparing unit 343, and may use the first upper limit value Id calculated by the first upper limit calculating unit 341. max 1 is the upper limit Id max may be set in the d-axis target limiting unit 33 as

[0037] The q-axis target limiting unit 35 limits the target value Iq output from the reactive power control unit 32. * is a functional configuration for limiting the target value Iq * is output to the current control unit 37.

[0038] The q-axis range setting unit 36 ​​sets the target value Iq *In this embodiment, in order to limit the power factor of the output power of the inverter circuit 2 to a range equal to or greater than Kmin and equal to or less than "1.00", the q-axis range setting unit 36 ​​sets the target value Iq * An upper limit value Iqmax and a lower limit value Iqmin are set in the q-axis target limiting unit 35 as the upper and lower limits of the target value Iq. The upper limit value Iqmax is calculated sequentially using the following equation (4) based on the effective value Vrms of the line voltage input from the voltage sensor 72 and the active power P input from the power calculation unit 5. Kmin is set in advance. Furthermore, coefficient c is a predetermined coefficient for converting to a q-axis value set in the q-axis target limiting unit 35, and is calculated in the same way as the coefficient a and set in advance. Note that the following equation (4) is derived based on the relational expression between the active power P, the reactive power Q, and the power factor K. The lower limit value Iqmin is "0". The q-axis target limiting unit 35 calculates the target value Iq * is limited to a range equal to or less than the upper limit value Iqmax and equal to or greater than the lower limit value Iqmin. Note that the range set by the q-axis range setting unit 36 ​​is not limited to this.

number

[0039] The current control unit 37 is a functional component for controlling the output current of the inverter circuit 2. The current control unit 37 generates a current compensation value based on the current signal i input from the current sensor 71, and outputs the current compensation value to the PWM signal generation unit 38.

[0040] FIG. 2(b) is a block diagram showing the internal configuration of the current control unit 37.

[0041] The current control unit 37 has, as its functional configuration, a three-phase / two-phase conversion unit 371, a rotating coordinate conversion unit 372, an LPF 373, an LPF 374, a PI control unit 375, a PI control unit 376, a stationary coordinate conversion unit 377, and a two-phase / three-phase conversion unit 378.

[0042] The three-phase / two-phase conversion unit 371 is a functional component that performs so-called three-phase / two-phase conversion processing (αβ conversion processing). The three-phase / two-phase conversion processing is a process of converting a three-phase AC signal into an equivalent two-phase AC signal, and converts the three-phase AC signal into an AC signal of an α-axis component and an AC signal of a β-axis component by decomposing the three-phase AC signal into components of the α-axis and β-axis that are orthogonal to each other in a stationary orthogonal coordinate system (hereinafter referred to as the "stationary coordinate system") and adding up the components of each axis. The three-phase / two-phase conversion unit 371 converts the three-phase current signal i input from the current sensor 71 into an AC signal of an α-axis component and an AC signal of a β-axis component. u ,i v ,i w α-axis current signal i α and β-axis current signal i β and outputs it to the rotation coordinate conversion unit 372.

[0043] The conversion process performed by the three-phase / two-phase conversion unit 371 is expressed by the determinant shown in the following equation (5).

number

[0044] The rotating coordinate conversion unit 372 is a functional component that performs so-called rotating coordinate conversion processing (dq conversion processing). The rotating coordinate conversion processing is processing that converts a two-phase signal in a stationary coordinate system into a two-phase signal in a rotating coordinate system. The rotating coordinate system has orthogonal d- and q-axes, and is an orthogonal coordinate system that rotates in the same direction as the fundamental wave of the interconnection point voltage at the same angular velocity. The rotating coordinate conversion unit 372 converts the α-axis current signal i α and β-axis current signal i β Based on the phase θ of the fundamental wave of the interconnection point voltage, the d-axis current signal i d and q-axis current signal i q Convert it to and output it.

[0045] The conversion process performed by the rotation coordinate conversion unit 372 is expressed by the determinant shown in the following equation (6).

number

[0046] LPF373 and LPF374 are low-pass filters, and are used to filter the d-axis current signal i d and the DC component of the q-axis current signal iq. α and β-axis current signal i β The fundamental wave components of the d-axis current signal i d and q-axis current signal i q That is, LPF 373 and LPF 374 remove unbalanced components and harmonic components and pass only the fundamental component.

[0047] The PI control section 375 outputs the d-axis current signal i d PI control is performed based on the deviation between the DC component of and the target value, and the current compensation value x d The target value Id output from the DC voltage control unit 31 and limited to the range set by the d-axis target limiting unit 33 is output. * is the d-axis current signal i d The PI control section 376 uses the q-axis current signal i q DC component and target value Iq * PI control is performed based on the deviation from the current compensation value x q The target value Iq output from the reactive power control unit 32 and limited to the range set by the q-axis target limiting unit 35 is * is the q-axis current signal i q is used as the target value for the DC component of

[0048] The stationary coordinate conversion unit 377 converts the current compensation values ​​x d ,x q is the current compensation value x in the stationary coordinate system. α ,x β The stationary coordinate conversion unit 377 performs a so-called stationary coordinate conversion process (inverse dq conversion process) to convert the current compensation value x d ,x q Based on the phase θ, the current compensation value x in the stationary coordinate system is calculated. α ,xβ Convert to.

[0049] The conversion process performed by the stationary coordinate conversion unit 377 is expressed by the determinant shown in the following equation (7).

number

[0050] The two-phase / three-phase conversion unit 378 converts the current compensation value x α ,x β , the three-phase current compensation value x u ,x v ,x w The two-phase / three-phase conversion unit 378 performs a so-called two-phase / three-phase conversion process (inverse αβ conversion process) to perform a conversion process that is the reverse of that performed by the three-phase / two-phase conversion unit 371.

[0051] The conversion process performed by the two-phase / three-phase conversion unit 378 is expressed by the determinant shown in the following equation (8).

number

[0052] The PWM signal generating unit 38 is a functional component that generates a PWM signal. The PWM signal generating unit 38 generates a three-phase current compensation value x u ,x v ,x w Based on the carrier signal, the PWM signal generator 38 generates a command signal for commanding the waveform of the output voltage of each phase of the inverter circuit 2, and generates a PWM signal using a triangular wave comparison method based on the command signal and the carrier signal. For example, a pulse signal that goes high when the command signal is greater than the carrier signal and goes low when the command signal is equal to or less than the carrier signal is generated as the PWM signal. The generated PWM signal is output to the inverter circuit 2. Note that the PWM signal generator 38 is not limited to generating a PWM signal using the triangular wave comparison method, and may also generate a PWM signal using a hysteresis method, for example.

[0053] In this embodiment, the control circuit 6 is implemented as a digital circuit, but it may be implemented as an analog circuit. The processing performed by each unit may be designed as a program, and a computer may function as the control circuit 6 by executing the program. The program may also be recorded on a recording medium and read by a computer.

[0054] FIG. 3 is a diagram for explaining suppression control by the control circuit 6 for suppressing a sudden increase in the output active power of the inverter circuit 2. Each diagram in FIG. 3 shows the voltage-power characteristics of the DC power supply 1 (solar cell). The horizontal axis indicates the output voltage of the DC power supply 1, and the vertical axis indicates the output power of the DC power supply 1. In each diagram, point M indicates the operating point. For simplicity of explanation, FIG. 3 will be described assuming that the output active power of the inverter circuit 2 is equal to the output power of the DC power supply 1.

[0055] FIG. 3(a) shows the voltage-power characteristics when the solar radiation intensity is relatively low, and only a power sufficiently small relative to the second upper limit power value P2 can be output. In this case, the DC voltage target value setting unit 4 performs MPPT control, and the operating point M is located near the maximum power point. Because the second upper limit power value P2 is large, the output power of the DC power supply 1 is not limited, and the maximum power can be output. The first upper limit power value P1 is calculated by adding an increase value ΔP to the active power P detected as the output active power of the inverter circuit 2, and the d-axis upper limit setting unit 34 calculates the first upper limit value Id corresponding to the first upper limit power value P1. max 1 is the upper limit Id max and set it in the d-axis target limiting unit 33.

[0056] FIG. 3(b) shows the voltage-power characteristics when the solar radiation intensity suddenly increases compared to FIG. 3(a). The dashed curve shows the voltage-power characteristics in FIG. 3(a). As the voltage-power characteristics change from the dashed curve to the solid curve, the curve showing the voltage-power characteristics intersects with the line showing the first upper limit power value P1. In this case, the target value Id output from the DC voltage control unit 31 * is the upper limit value Id set by the d-axis upper limit setting unit 34.max (First upper limit Id max 1), the output active power of the inverter circuit 2 is restricted to be equal to or less than the first upper limit power value P1. As a result, the operating point M cannot move to the maximum power point, but moves to the intersection of the curve showing the voltage-power characteristics and the line showing the first upper limit power value P1.

[0057] Figure 3(c) shows a state in which the first upper limit power value P1 has been recalculated, compared to Figure 3(b). The voltage-power characteristics remain unchanged from Figure 3(b), but the line representing the first upper limit power value P1 has changed. The first upper limit power value P1 is recalculated at each predetermined calculation cycle and is calculated by adding an increase value ΔP to the active power P detected as the output active power of the inverter circuit 2 at that time, so it has increased by the increase value ΔP. As a result, the operating point M has moved to the intersection of the curve representing the voltage-power characteristics and the line representing the first upper limit power value P1.

[0058] Figure 3(d) shows a state in which the first upper limit power value P1 has been recalculated, as compared to Figure 3(c). The voltage-power characteristics remain unchanged from Figure 3(c), but the line representing the first upper limit power value P1 has changed. The first upper limit power value P1 has increased by an increase value ΔP. As a result, the operating point M has moved to the intersection of the curve representing the voltage-power characteristics and the line representing the first upper limit power value P1.

[0059] FIG. 3(e) shows a state in which the first upper limit power value P1 has been recalculated compared to FIG. 3(d). The voltage-power characteristics remain unchanged from FIG. 3(d), but the line representing the first upper limit power value P1 has changed. The first upper limit power value P1 has increased by an increase value ΔP. In FIG. 3(e), the first upper limit power value P1 has become sufficiently large, and the line representing the first upper limit power value P1 is located above the curve representing the voltage-power characteristics. In this case, the output power of the DC power supply 1 is not limited, and MPPT control positions the operating point M near the maximum power point, allowing the DC power supply 1 to output maximum power.

[0060] When the solar radiation intensity suddenly increases and no limitation according to the first upper limit power value P1 is applied (when only a limitation according to the second upper limit power value P2 is applied), the state changes from that of FIG. 3(a) to that of FIG. 3(e). In this case, the output active power of the inverter circuit 2 increases rapidly, instantaneously exceeding the power consumed by the load L and causing a reverse power flow. In reality, the RPR is activated just before the reverse power flow occurs, and the inverter device A1 is stopped. Meanwhile, by applying a limitation according to the first upper limit power value P1, the state changes from that of FIG. 3(a) through the states of FIGS. 3(b) to 3(d) to the state of FIG. 3(e). As a result, the output active power of the inverter circuit 2 increases stepwise, preventing a sudden increase.

[0061] Figure 3(f) shows a case where the second upper limit power value P2 is smaller than the case of Figure 3(e). The first upper limit power value P1 is recalculated from the state of Figure 3(d) and increased by an increment ΔP, so that the recalculated first upper limit power value P1 is greater than the second upper limit power value P2. In this case, the target value Id output from the DC voltage control unit 31 * is the upper limit value Id set by the d-axis upper limit setting unit 34. max (Second upper limit Id max 2), the output active power of the inverter circuit 2 is restricted to be equal to or less than the second upper limit power value P2. As a result, the operating point M cannot move to the maximum power point, but moves to the intersection of the curve showing the voltage-power characteristics and the line showing the second upper limit power value P2.

[0062] Next, the operation and effects of the control circuit 6 and the inverter device A1 according to this embodiment will be described.

[0063] According to this embodiment, the current control unit 37 receives the three-phase current signal i input from the current sensor 71. u ,i v ,i w The d-axis current signal i d and q-axis current signal i q and convert it into the d-axis current signal i d and q-axis current signal i qThe DC components of the d-axis current signal i are controlled to their target values. d The target value Id of the DC component * is output from the DC voltage control unit 31 and is limited to the range set by the d-axis target limiting unit 33. The d-axis upper limit setting unit 34 sets the first upper limit value Id max 1 and the second upper limit Id max The smaller of the two values ​​is the upper limit Id max The d-axis target limiting unit 33 sets the target value Id * Upper limit value Id max The control circuit 6 limits the output power of the inverter circuit 2 to be equal to or less than the first upper limit power value P1. This limits the output active power of the inverter circuit 2 to be equal to or less than the smaller of the first upper limit power value P1 and the second upper limit power value P2. The first upper limit power value P1 is greater than the current output power of the inverter circuit 2 and varies depending on the output power. Therefore, when the solar radiation intensity increases suddenly, the control circuit 6 can prevent the output power from increasing suddenly by limiting the output power of the inverter circuit 2 to be equal to or less than the first upper limit power value P1 and gradually increasing the first upper limit power value P1.

[0064] Furthermore, according to this embodiment, the first upper limit value calculation unit 341 calculates the first upper limit power value P1 by adding an increase value ΔP greater than "0" to the active power P input from the power calculation unit 5. Therefore, the first upper limit value calculation unit 341 can gradually increase the first upper limit power value P1. Furthermore, the first upper limit value calculation unit 341 can gradually increase the first upper limit power value P1 even when calculating the first upper limit power value P1 by multiplying the active power P input from the power calculation unit 5 by an increase coefficient α greater than "1" (for example, "1.1").

[0065] According to this embodiment, the d-axis upper limit setting unit 34 sets the first upper limit value Id max 1 and the second upper limit Id max The smaller of the two values ​​is the upper limit Id max is set in the d-axis target limiting unit 33. max 1 is the second upper limit Id max When the value becomes larger than 2, the d-axis upper limit setting unit 34 sets the second upper limit value Id max 2 is the upper limit Id maxTherefore, the control circuit 6 can suppress the output active power of the inverter circuit 2 to be equal to or less than the second upper limit power value P2.

[0066] In the present embodiment, the case where the output voltage of the DC power supply 1 is controlled has been described, but the present invention is not limited to this. The output current of the DC power supply 1 may be controlled. That is, the DC voltage target value setting unit 4 may be replaced by a DC current target value setting unit that sets a target value of the DC current, and the DC voltage control unit 31 may be replaced by a DC current control unit that calculates the deviation between the DC current signal Idc input from the DC current sensor 81 and the target value of the DC current and outputs a compensation value to make the deviation zero.

[0067] In the first embodiment, the DC voltage target value setting unit 4 sets the voltage target value Vdc by MPPT control so that the input power from the DC power supply 1 is maximized. * However, the present invention is not limited to this. For example, the voltage target value Vdc is adjusted so that the output active power of the inverter circuit 2 is maximized. * An example of this case will be described below as a second embodiment.

[0068] 4 is a block diagram showing the internal configuration of the control circuit 6 of the inverter device A2 according to the second embodiment. In the figure, elements that are the same as or similar to those in the control circuit 6 according to the first embodiment (see FIG. 1) are given the same reference numerals.

[0069] The control circuit 6 according to the second embodiment, instead of the DC voltage target value setting unit 4, sets the voltage target value Vdc so that the output power of the inverter circuit 2 is maximized. * The control circuit 6 according to the first embodiment differs from the control circuit 6 according to the first embodiment in that it includes a DC voltage target value setting unit 4' that adjusts the DC voltage target value.

[0070] The DC voltage target value setting unit 4' sets the voltage target value Vdc * is changed so that the effective power P input from the power calculation unit 5 is maximized. *The DC voltage target value setting unit 4 according to the first embodiment performs so-called maximum power point tracking control to control the output power of the DC power supply 1 to a maximum, whereas the DC voltage target value setting unit 4′ controls the output effective power of the inverter circuit 2 to a maximum.

[0071] 5 is a flowchart for explaining the process of searching for the maximum power point performed by the DC voltage target value setting unit 4'. The execution of this search process starts when the inverter circuit 2 starts the power conversion operation.

[0072] First, the voltage target value Vdc * An initial value V0 is set to Vdc, and a search direction is set (S1). In this embodiment, the open circuit voltage is set as the initial value V0. In addition, as the search direction, the target voltage value Vdc * The direction of decrease is set to decrease the voltage target value Vdc. Note that the settings are not limited to this. * is output (S2), and the output voltage of DC power supply 1 reaches the voltage target value Vdc * Then, the active power P calculated by the power calculation unit 5 is acquired (S3) and set as the previous active power P0 (S4).

[0073] Next, it is determined whether the currently set search direction is a decreasing direction (S5). If the search direction is a decreasing direction (S5: YES), the target voltage value Vdc * is decreased by ΔV (S6), and if the search direction is not a decreasing direction (S5: NO), that is, if it is an increasing direction, the voltage target value Vdc * is increased by ΔV (S7). Then, the voltage target value Vdc * is output (S8), and the active power P is obtained (S9). Note that if the increase / decrease width ΔV is too small, it takes too long to search for the maximum power point, and if it is too large, accuracy and stability will decrease, so it is necessary to set an appropriate value.

[0074] Next, it is determined whether the active power P is greater than the previous active power P0 (S10). If the active power P is greater than the previous active power P0 (S10: YES), the search direction is not changed, and the previous active power P0 is set to the active power P (S12), and the process returns to step S5. On the other hand, if the active power P is equal to or less than the previous active power P0 (S10: NO), the maximum power point has been exceeded, and the search direction is reversed (S11). That is, if the search direction was decreasing, the search direction is changed to increasing, and if the search direction was increasing, the search direction is changed to decreasing, and the previous active power P0 is set to the active power P (S12), and the process returns to step S5. Thereafter, steps S5 to S12 are repeated.

[0075] The process of searching for the maximum power point performed by the DC voltage target value setting unit 4' is not limited to the above. For example, when the voltage target value Vdc * When the voltage is decreased by ΔV and increased by ΔV, the active power P is obtained, and the voltage target value Vdc is increased. * It is also possible to change the increase / decrease amount ΔV or to use a genetic algorithm to solve the so-called "two-hill problem." In addition, the method is not limited to the hill-climbing method, and any algorithm used in maximum power point tracking control can be used. In any algorithm used in conventional maximum power point tracking control, it is sufficient to track the output power of the inverter circuit 2 to its maximum, rather than tracking the output power from the DC power source 1 to its maximum.

[0076] In this embodiment, the output active power of the inverter circuit 2 is also limited to the smaller of the first upper limit power value P1 and the second upper limit power value P2. The first upper limit power value P1 is greater than the current output power of the inverter circuit 2 and varies depending on the output power. Therefore, when solar radiation suddenly increases, the control circuit 6 limits the output power of the inverter circuit 2 to the first upper limit power value P1 or less and gradually increases the first upper limit power value P1, thereby preventing a sudden increase in output power. Furthermore, according to this embodiment, the inverter device A2 has a common configuration with the inverter device A1 and achieves the same effects as the inverter device A1. Furthermore, according to this embodiment, the DC voltage target value setting unit 4′ controls the output active power of the inverter circuit 2 to approximately maximize it. Therefore, even if the output active power of the inverter circuit 2 is not approximately maximized when the DC power output from the DC power source 1 is approximately maximized, the output power of the system can be approximately maximized. This improves power generation efficiency compared to when the DC power output from the DC power source 1 is controlled to approximately maximize it.

[0077] The present invention can also be applied to a case where a DC / DC converter circuit is provided between the DC power supply 1 and the inverter circuit 2. A case where a DC / DC converter circuit is provided will be described below as a third embodiment.

[0078] 6 is a block diagram showing the overall configuration of the inverter device A3 according to the third embodiment, in which elements that are the same as or similar to those in the inverter device A1 according to the first embodiment (see FIG. 1) are given the same reference numerals.

[0079] The inverter device A3 shown in FIG. 6 differs from the inverter device A1 according to the first embodiment in that a DC / DC converter circuit 2′ is provided in the preceding stage of the inverter circuit 2, and a control circuit 6′ is provided for controlling the DC / DC converter circuit 2′.

[0080] The DC / DC converter circuit 2' boosts or drops the output voltage of the DC power supply 1 and outputs it to the inverter circuit 2. The DC / DC converter circuit 2' boosts or drops the input voltage and outputs it by switching on and off a switching element (not shown) based on a PWM signal input from the control circuit 6'. The positive and negative electrodes of the input side of the DC / DC converter circuit 2' are connected to the positive and negative electrodes of the DC power supply 1, respectively, so the input voltage of the DC / DC converter circuit 2' matches the output voltage of the DC power supply 1, and the input current of the DC / DC converter circuit 2' matches the output current of the DC power supply 1.

[0081] The DC current sensor 81' detects the instantaneous value of the input current to the DC / DC converter circuit 2' (i.e., the output current of the DC power supply 1). The DC current sensor 81' converts the detected instantaneous value into a digital signal and outputs it to the control circuit 6' as a DC current signal I'dc. The DC voltage sensor 82' detects the instantaneous value of the input voltage to the DC / DC converter circuit 2' (i.e., the output voltage of the DC power supply 1). The DC voltage sensor 82' converts the detected instantaneous value into a digital signal and outputs it to the control circuit 6' as a DC voltage signal V'dc. The DC voltage sensor 82' detects the voltage between the terminals of an electrolytic capacitor (not shown) provided between the positive and negative electrodes on the input side of the DC / DC converter circuit 2'.

[0082] The control circuit 6' controls the DC / DC converter circuit 2' and is realized by, for example, a microcomputer. The control circuit 6' generates a PWM signal based on the DC current signal I'dc input from the DC current sensor 81' and the DC voltage signal V'dc input from the DC voltage sensor 82', and outputs the PWM signal to the DC / DC converter circuit 2'. The control circuit 6' includes a control unit 3' and a DC voltage target value setting unit 4'.

[0083] The DC voltage target value setting unit 4' is the same as the DC voltage target value setting unit 4 according to the first embodiment, and sets the voltage target value V'dc, which is the target value of the DC voltage signal V'dc. * The voltage target value V'dc* is changed so that the input power from DC power supply 1 is maximized. * Adjust.

[0084] The control unit 3' includes a DC voltage control unit 31 and a PWM signal generation unit 38. The DC voltage control unit 31 has the same functional configuration as the DC voltage control unit 31 according to the first embodiment, and is a functional configuration for controlling the output voltage of the DC power supply 1. The DC voltage control unit 31 controls the DC voltage signal V'dc output from the DC voltage sensor 82' and the voltage target value V'dc input from the DC voltage target value setting unit 4. * Deviation ΔV'dc (=V'dc * -V'dc) and outputs a DC voltage compensation value for making the deviation zero to the PWM signal generating unit 38. In the inverter device A3, the DC / DC converter circuit 2' performs MPPT control.

[0085] The PWM signal generating unit 38 has the same function as the PWM signal generating unit 38 according to the first embodiment, and is configured to generate a PWM signal to be output to the DC / DC converter circuit 2'. The PWM signal generating unit 38 generates a PWM signal by a triangular wave comparison method based on the signal input from the DC voltage control unit 31 and the carrier signal. The generated PWM signal is output to the DC / DC converter circuit 2'. The PWM signal generating unit 38 also generates a PWM signal by a triangular wave comparison method based on the target value Id * While the target value Id is limited by the setting range, a PWM signal with a fixed duty cycle is generated. * While the voltage is limited by the set range, MPPT control is stopped.

[0086] The configuration of the control circuit 6' is not limited to the above. In this embodiment, the control circuit 6' is implemented as a digital circuit, but it may be implemented as an analog circuit. The processing performed by each unit may be designed by a program, and a computer may function as the control circuit 6' by executing the program. The program may also be recorded on a recording medium and read by a computer.

[0087] The inverter circuit 2 converts the DC power input from the DC / DC converter circuit 2' into AC power. The positive and negative poles of the input side of the inverter circuit 2 are connected to the positive and negative poles of the output side of the DC / DC converter circuit 2', respectively, so that the input voltage of the inverter circuit 2 matches the output voltage of the DC / DC converter circuit 2', and the input current of the inverter circuit 2 matches the output current of the DC / DC converter circuit 2'. The control circuit 6 does not include the DC voltage target value setting unit 4 (see FIG. 1), and the voltage target value Vdc * is set to a fixed value. As a result, the output voltage of the DC / DC converter circuit 2' is set to the voltage target value Vdc * is fixed at

[0088] In this embodiment as well, the output active power of the inverter circuit 2 is limited to or below the smaller of the first upper limit power value P1 and the second upper limit power value P2. The first upper limit power value P1 is greater than the current output power of the inverter circuit 2 and varies depending on the output power. Therefore, when solar radiation increases suddenly, the control circuit 6 limits the output power of the inverter circuit 2 to or below the first upper limit power value P1 and gradually increases the first upper limit power value P1, thereby preventing a sudden increase in output power. Furthermore, according to this embodiment, the inverter device A3 has a common configuration with the inverter device A1 and therefore achieves the same effects as the inverter device A1.

[0089] In the first to third embodiments, the DC power supply 1 generates DC power using a solar cell, but the present invention is not limited to this. For example, the DC power supply 1 may be a device that converts AC power generated by a wind turbine generator or the like into DC power and outputs it. The present invention is particularly effective when efficiently extracting power from a system that converts energy such as natural energy, the output of which cannot be controlled, into power.

[0090] The control circuit and inverter device according to the present invention are not limited to the above-described embodiment, and the specific configurations of the control circuit and inverter device according to the present invention can be freely designed in various ways. [Explanation of symbols]

[0091] A1, A2, A3: inverter device, 1: DC power supply, 2: inverter circuit, 4: DC voltage target value setting unit, 6: control circuit, 31: DC voltage control unit, 33: d-axis target limit unit, 34: d-axis upper limit setting unit, 37: current control unit

Claims

1. A control circuit for controlling an inverter circuit that converts DC power output from a DC power supply into AC power, a current control unit that converts three-phase current signals obtained by detecting three-phase output currents of the inverter circuit into a d-axis current signal and a q-axis current signal, which are two orthogonal components of a rotating coordinate system, and controls each of the d-axis current signal and the q-axis current signal to a target value; a d-axis current target value generating unit that generates a d-axis current target value that is a target value of the d-axis current signal; a d-axis upper limit setting unit that calculates a first upper limit power value that is greater than a current output power of the inverter circuit and that varies depending on the output power, and sets the first upper limit value corresponding to the first upper limit power value as a d-axis upper limit value; a d-axis target limiting unit that limits the d-axis current target value to be equal to or less than the d-axis upper limit value; Equipped with Control circuit.

2. the d-axis upper limit setting unit calculates the first upper limit power value by adding an increase value greater than “0” to the output power. The control circuit of claim 1 .

3. the d-axis upper limit setting unit calculates the first upper limit power value by multiplying the output power by an increase coefficient greater than "1." The control circuit of claim 1 .

4. the d-axis upper limit setting unit sets the smaller of a second upper limit value corresponding to a second upper limit power value that does not change according to the output power and the first upper limit value as the d-axis upper limit value. The control circuit of claim 1 .

5. a DC voltage target value setting unit that sets a DC voltage target value that is a target value of an output voltage of the DC power supply, the DC voltage target value setting unit adjusts the DC voltage target value by changing the DC voltage target value so that the output power of the DC power supply becomes larger; the d-axis current target value generation unit generates, as the d-axis current target value, a DC voltage compensation value for controlling the output voltage of the DC power supply to the DC voltage target value. The control circuit of claim 1 .

6. a control circuit according to any one of claims 1 to 5; the inverter circuit; An inverter device comprising:

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