Power conversion device

Abstract

The invention provides a power conversion device (1) capable of realizing stable operation even if DC power changes, wherein the power conversion device (1) converts DC power into AC power and outputs the AC power. A controller (18) of a power conversion device (1) calculates an active power command value (adder (105)) on the basis of a DC power detection value (panel output detection value) and an active power correction command value. The controller (18) calculates the frequency command value of the AC voltage on the basis of the active power command value and the active power detection value (frequency command calculator (107)). The controller (18) outputs PWM signals (an integrator (108), a voltage command arithmetic unit (109), and a PWM arithmetic unit (110)) on the basis of the frequency command value. A controller (18) calculates an active power correction command value (DC voltage controller (104)) using a deviation between a DC voltage detection value and a DC voltage command value and a control gain corresponding to a DC power detection value.

Description

Technical Field

[0001] This invention relates to power conversion devices. Background Technology

[0002] To achieve carbon neutrality, renewable energy sources such as solar power are being gradually adopted. It is predicted that the proportion of synchronous generators connected to the power system will decrease accordingly, while the proportion of inverters connecting renewable energy sources to the power system will increase. Synchronous generators have rotating bodies, providing inertia to the power system, but existing inverters do not possess this capability. Therefore, as the proportion of inverters connected to the power system increases, there are concerns about insufficient inertia in the power system, susceptibility to frequency fluctuations, and increased instability.

[0003] Therefore, the concept of virtual inertia—the ability to simulate inertia in a power system using inverter control—was proposed. Inverters capable of providing virtual inertia to a power system have attracted attention; such inverters are called system-forming inverters (grid-forming inverters). Patent Document 1 is known as an example of such a system-forming inverter. Patent Document 1 shows an example of a system-forming inverter with a DC power supply in a DC circuit.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Application Publication No. 2024-36973 Summary of the Invention

[0007] The problem that the invention aims to solve

[0008] However, when using system-forming inverters in solar power generation, the DC voltage of the system-forming inverter is difficult to maintain stability when there is an unstable DC power source such as a solar panel in the DC circuit. Therefore, there is a problem with the system-forming inverter's stable operation. When an imbalance occurs between the power input to the DC section of the system-forming inverter from the solar panel and the power output of the system-forming inverter to the power system, the DC voltage of the system-forming inverter fluctuates accordingly. As a result, if the DC voltage fluctuation is large, there is a risk that the system-forming inverter will stop due to DC overvoltage or DC undervoltage. Furthermore, while MPPT (Maximum Power Point Tracking) control is generally used in solar-facing inverters to maximize power generation, it is difficult to apply such control when the DC voltage fluctuates.

[0009] As mentioned above, solar panels are unstable power sources, primarily because the irradiance of sunlight illuminating them is highly variable. During rapid weather changes, the irradiance can fluctuate within a short period. This variation in irradiance alters the output characteristics of the solar panel, consequently affecting the stability of the DC voltage. While an inverter could theoretically adjust the DC voltage accordingly if it knew the irradiance, the practicality of adjusting the DC voltage in real-time is limited by the need for sensors to detect irradiance and the inverter's requirement for real-time irradiance monitoring.

[0010] The purpose of this invention is to provide a system that can achieve stable operation even when the DC power changes.

[0011] Technical solutions for solving the problem

[0012] To achieve the above objectives, the present invention provides a power conversion device that converts DC power into AC power and outputs it. The device has a controller that calculates an active power command value based on the detected value of the DC power and an active power correction command value, calculates a frequency command value of the AC voltage based on the active power command value and the detected value of the active power, outputs a PWM signal based on the frequency command value, and calculates the active power correction command value using the deviation between the detected value of the DC voltage and the DC voltage command value, and a control gain corresponding to the detected value of the DC power.

[0013] Invention Effects

[0014] According to the present invention, stable operation can be achieved even with changes in DC power. Other issues, structures, and effects not described above will be explained through the following description of embodiments. Attached Figure Description

[0015] Figure 1 This describes the structure of a first embodiment of a power conversion device for solar power generation.

[0016] Figure 2 This represents an example of the output characteristics of a solar panel.

[0017] Figure 3 This represents an example of the output characteristics of a frequency instruction arithmetic unit.

[0018] Figure 4 This represents an example of the output characteristics of a gain regulator.

[0019] Figure 5 This shows an example of the structure of a DC voltage controller.

[0020] Figure 6This represents an example of the action waveform in the first embodiment.

[0021] Figure 7 This represents an example of the action waveform in the first embodiment.

[0022] Figure 8 This illustrates the structure of a second embodiment of a power conversion device for solar power generation.

[0023] Figure 9 This describes the structure of a third embodiment of a power conversion device for solar power generation.

[0024] Figure 10 This illustrates the structure of a fourth embodiment of a power conversion device for solar power generation. Detailed Implementation

[0025] Hereinafter, embodiments of the power conversion device for solar power generation of the present invention will be described with reference to the accompanying drawings. The objective of this embodiment is, for example, to achieve stable operation of the system-forming inverter for solar power generation by stabilizing the DC voltage, and further to simultaneously achieve MPPT (Maximum Power Point Tracking) control in order to maximize power generation. Another objective of this embodiment is, for example, to stabilize the DC voltage by adjusting the DC voltage control without using information about the solar irradiance, even when there are changes in solar irradiance.

[0026] [First Embodiment]

[0027] Figure 1 This diagram illustrates the structure of a first embodiment of a power conversion device for solar power generation. In this embodiment, the power conversion device 1 for solar power generation is connected to a three-phase AC power system 2. The power conversion device 1 for solar power generation includes an AC / DC converter 12, a DC capacitor 13, a DC voltage sensor 14, a DC current sensor 15, an AC voltage sensor 16, an AC current sensor 17, and a controller 18.

[0028] A solar panel 11 is connected to the DC side of an AC / DC converter 12, and the AC side of the AC / DC converter 12 is connected to a three-phase AC power system 2. A DC capacitor 13 is connected to the DC side of the AC / DC converter 12, and a DC voltage sensor 14 detects the DC voltage of the DC capacitor 13. A DC current sensor 15 is connected between the solar panel 11 and the AC / DC converter 12 to detect the DC current output by the solar panel 11. An AC voltage sensor 16 is connected to the AC side of the AC / DC converter 12 to detect the three-phase AC voltage on the AC side of the AC / DC converter 12. An AC current sensor 17 is connected between the AC / DC converter 12 and the power system 2 to detect the three-phase AC current output by the AC / DC converter 12. The controller 18 takes the DC voltage detection value output by the DC voltage detection sensor 14, the DC current detection value output by the DC current detection sensor 15, the AC voltage detection value output by the AC voltage detection sensor 16, and the AC current detection value output by the AC current detection sensor 17 as inputs, and outputs pulse signals that drive the switching elements constituting the AC / DC converter 12.

[0029] The controller 18 includes a multiplier 100, a gain regulator 101, an MPPT controller 102, a subtractor 103, a DC voltage controller 104, an adder 105, an active power calculator 106, a frequency command calculator 107, an integrator 108, a voltage command calculator 109, and a PWM calculator 110.

[0030] The multiplier 100 takes the DC voltage detection value output by the DC voltage detection sensor 14 and the DC current detection value output by the DC current detection sensor 15 as inputs, multiplies them to calculate the output power of the panel, and outputs it as the panel output detection value.

[0031] The gain regulator 101 takes the panel output detection value of the multiplier 100 as input and outputs a gain adjustment command value to adjust the control gain of the DC voltage controller 104.

[0032] The MPPT controller 102 takes the DC voltage detection value output by the DC voltage detection sensor 14 and the DC current detection value output by the DC current detection sensor 15 as inputs, and calculates the power output by the solar panel 11 to become the DC voltage command of the AC / DC converter 12 through MPPT (Maximum Power Point Tracking) control, and outputs it as the DC voltage command value.

[0033] The subtractor 103 takes the DC voltage detection value output by the DC voltage detection sensor 14 and the DC voltage command value output by the MPPT controller 102 as inputs and outputs the difference between them.

[0034] The DC voltage controller 104 takes the difference output by the subtractor 103 and the gain adjustment command value output by the gain regulator 101 as inputs, and outputs the active power correction command value by making the difference output by the subtractor 103 zero, for example by proportional-integral operation.

[0035] Adder 105 takes the panel output detection value from multiplier 100 and the active power correction command value from DC voltage controller 104 as inputs, and adds them together as the active power command value output.

[0036] The active power calculator 106 takes the AC voltage detection value output by the AC voltage detection sensor 16 and the AC current detection value output by the AC current detection sensor 17 as input, and outputs the active power output by the AC / DC converter 12 to the AC side as the active power detection value.

[0037] The frequency command arithmetic unit 107 takes the active power command value output by the adder 105 and the active power detection value output by the active power arithmetic unit 106 as inputs, and outputs the frequency command value of the AC voltage output by the AC / DC converter 12 to the AC side.

[0038] The integrator 108 takes the frequency command value output by the frequency command arithmetic unit 107 as input, and outputs the phase command value of the AC voltage output by the AC / DC converter 12 on the AC side through integration.

[0039] The voltage command arithmetic unit 109 takes the voltage amplitude command value of the AC voltage output by the AC / DC converter 12 to the AC side and the phase command value output by the integrator 108 as inputs, and outputs the output voltage command value of the AC voltage output by the AC / DC converter 12 to the AC side.

[0040] The PWM arithmetic unit 110 takes the output voltage command value output by the voltage command arithmetic unit 109 as input, and outputs pulse signals to drive the switching elements constituting the AC / DC converter 12 through PWM calculation.

[0041] Figure 2 This illustrates an example of the output characteristics of the solar panel 11. When the horizontal axis is set to panel voltage and the vertical axis to panel output, the output characteristics of the solar panel 11 generally exhibit an upward convexity. By operating at the maximum power point where the panel output is at its maximum, the power generation of the solar panel 11 can be maximized. Therefore, the MPPT controller 102 calculates the panel voltage at the maximum power point and outputs this panel voltage as a DC voltage command value. By controlling the panel voltage according to this DC voltage command value, the power generation can be maximized. Furthermore, when the irradiance decreases, the solar panel output decreases, and the change in solar panel output also decreases relative to the change in solar panel voltage.

[0042] Figure 3 This shows an example of the output characteristics of the frequency command calculator 107. When the horizontal axis is set to the detected value of the active power output from the AC / DC converter 12 to the AC side, and the vertical axis is set to the frequency command value of the voltage output from the AC / DC converter 12 to the AC side, it has a droop characteristic that slopes downward to the right. When the AC / DC converter 12 outputs active power equal to the active power command value to the AC side, the frequency command value is the reference value (50 Hz or 60 Hz). On the other hand, when the output active power is greater than the active power command value, by setting the frequency command value to a value smaller than the reference value, the phase difference between the AC terminal of the AC / DC converter 12 and the power system is reduced, and the active power output is reduced. Additionally, when the output active power is smaller than the active power command value, by setting the frequency command value to a value greater than the reference value, the phase difference between the AC terminal of the AC / DC converter 12 and the power system is increased, and the active power output is increased.

[0043] Figure 4 This shows an example of the output characteristics of the gain regulator 101. When the horizontal axis is set to the panel output detected value and the vertical axis is set to the gain adjustment command value, for example, when the panel output detected value is below P1, the gain adjustment command value is set to G1, and when the panel output detected value exceeds P1, it has a characteristic that the gain adjustment command value monotonically increases with the increase of the panel output detected value. For example, when the panel output detected value is P2, the gain adjustment command value is set to G2, and when the panel output detected value is P3, the gain adjustment command value is set to G3, and it is only necessary to set P1 < P2 < P3 and G1 < G2 < G3.

[0044] When the irradiance of sunlight is small, the output detected value of the solar panel also decreases. Therefore, by having such characteristics, when the irradiance of sunlight is small, the value of the gain adjustment command value decreases, and the control gain of the DC voltage controller 104 can be reduced. As described above, when the irradiance of sunlight decreases, the output of the solar panel decreases, and the change in the solar panel output with respect to the change in the solar panel voltage also decreases. Therefore, the control gain of the DC voltage controller 104 can be reduced accordingly. That is, the control gain of the DC voltage controller 104 can be appropriately adjusted according to the irradiance of sunlight. In addition, the structure of the DC voltage controller 104 will be described later.

[0045] However, when the power conversion device 1 starts, the output of the solar panel 11 starts from zero. Therefore, when the control gain of the DC voltage controller 104 is set to zero at this time, it is difficult to control the panel voltage of the solar panel 11. Therefore, in order to prevent the control gain of the DC voltage controller 104 from becoming zero, a lower limit value G1 is set for the gain adjustment command value.

[0046] Figure 5 This shows the structure of the DC voltage controller 104. The DC voltage controller 104 consists of multipliers 1040, 1041, 1042, 1043, an integrator 1044, and an adder 1045.

[0047] Multiplier 1040 takes the reference value KP of the proportional gain and the gain adjustment command value output by gain regulator 101 as inputs, and outputs the adjusted proportional gain by multiplying them. Multiplier 1041 takes the reference value KI of the integral gain and the gain adjustment command value output by gain regulator 101 as inputs, and outputs the adjusted integral gain by multiplying them. Multiplier 1042 takes the output of subtractor 103 and the adjusted proportional gain output by multiplier 1040 as inputs, and outputs the value obtained by multiplying them. Multiplier 1043 takes the output of subtractor 103 and the adjusted integral gain output by multiplier 1041 as inputs, and outputs the value obtained by multiplying them. Integrator 1044 takes the value output by multiplier 1043 as input, performs integration operation and outputs its operation value. Adder 1045 takes the output of multiplier 1042 and the output of integrator 1044 as inputs, and outputs the value obtained by adding them, which is output as the active power correction command value.

[0048] By adopting such a structure, the proportional gain and integral gain of the DC voltage controller 104 can be adjusted in accordance with the gain adjustment command value output by the gain regulator 101.

[0049] Figure 6 This illustrates an example of the operating waveform in the first embodiment. This example describes the situation where the power conversion device 1 starts up, the operating point moves to the maximum power point, and the solar radiation intensity decreases during steady-state operation. Until time T1, before the power conversion device 1 starts up, the solar panel output is zero. Therefore, the gain adjustment command value is the lower limit G1, the adjusted proportional gain of the DC voltage controller 104 is KP×G1, and the adjusted integral gain is KI×G1.

[0050] At time T1, the power conversion device 1 starts, and the output of the solar panel begins to increase, but the gain adjustment command value remains at the lower limit G1 until the output of the solar panel reaches P1. The adjusted proportional gain of the DC voltage controller 104 remains at KP×G1, and the adjusted integral gain remains at KI×G1.

[0051] When time T2 is reached, and the output of the solar panel exceeds P1, the gain adjustment command value begins to increase, and the adjusted proportional gain and adjusted integral gain of the DC voltage controller 104 also begin to increase accordingly.

[0052] At time T3, the operating point moves to the maximum power point, and the output of the solar panel becomes stable at P3. At this time, the gain adjustment command value is also fixed at G3, the adjusted proportional gain of the DC voltage controller 104 is fixed at KP×G3, and the adjusted integral gain is fixed at KI×G3.

[0053] When the solar radiation intensity begins to decrease at time T4, the output of the solar panel also decreases, so the gain adjustment command value begins to decrease, and the adjusted proportional gain and adjusted integral gain of the DC voltage controller 104 also begin to decrease accordingly.

[0054] At time T5, the decrease in solar irradiance ends, and the solar panel output reaches a stable state at P2. At this time, the gain adjustment command value is also fixed at G2, the adjusted proportional gain of the DC voltage controller 104 is fixed at KP×G2, and the adjusted integral gain is fixed at KI×G2.

[0055] As described above, the proportional gain and integral gain of the DC voltage controller 104 can be adjusted in accordance with changes in the irradiance of sunlight. In addition, when the power conversion device 1 starts up, a lower limit value is also set for the gain adjustment command value when the panel output of the solar panel 11 is zero. This can suppress the situation where the adjusted proportional gain and the adjusted integral gain become zero, and prevent the panel voltage of the solar panel 11 from becoming uncontrollable.

[0056] Figure 7 This illustrates an example of the operating waveform in the first embodiment. This example shows the situation where the power conversion device 1 starts up and the output of the solar panel gradually increases. Until time T1, before the power conversion device 1 starts up, the output of the solar panel is zero. Therefore, the gain adjustment command value is the lower limit value G1.

[0057] At time T1, power conversion device 1 starts up, and the output of the solar panel begins to increase, but the gain adjustment command value remains at the lower limit G1 until the output of the solar panel reaches P1. The rate of change of the active power correction command value is gradual.

[0058] When time T2 is reached, and the output of the solar panel exceeds P1, the gain adjustment command value begins to increase, and the rate of change of the active power correction command value also gradually increases accordingly. Adding the solar panel output to the active power correction command value yields the active power command value for the AC / DC converter 12. Since the AC / DC converter 12 operates according to the active power command value, the difference between the active power detected value of the AC / DC converter 12 output and the solar panel output also exhibits the same change as the active power correction command value, showing a waveform with a gradually increasing rate of change.

[0059] In this way, the gain adjustment command value is changed in accordance with the size of the solar panel output to calculate the active power correction command value in a way that makes the DC voltage stable, and the AC / DC converter 12 operates according to the active power command value obtained by adding the solar panel output and the active power correction command value.

[0060] The main features of the first embodiment can also be summarized as follows.

[0061] Figure 1 The power conversion device 1 shown converts DC power to AC power and outputs it. The controller 18 of the power conversion device 1 calculates the active power command value (adder 105) based on the detected DC power value (panel output detected value) and the active power correction command value. The controller 18 calculates the AC voltage frequency command value (frequency command arithmetic unit 107) based on the active power command value and the detected active power value. The controller 18 outputs a PWM signal based on the frequency command value (integrator 108, voltage command arithmetic unit 109, PWM arithmetic unit 110). The controller 18 uses the deviation between the detected DC voltage value and the DC voltage command value, and the control gain corresponding to the detected DC power value (…). Figure 4 , 5 The active power correction command value is calculated using the DC voltage controller 104.

[0062] By using a control gain corresponding to the detected DC power value, the operation of the power conversion device 1 remains stable even when the DC power changes. As a result, the operation of the power conversion device 1 remains stable even when the solar radiation intensity changes.

[0063] like Figure 1 As shown, the controller 18 has a gain regulator 101 that uses the detected value of DC power (panel output detected value) as input and output to adjust the control gain. By using the detected value of DC power as the input and output gain adjustment command value, the control gain can be easily adjusted in accordance with the irradiance of sunlight.

[0064] Gain regulator 101 Figure 4 As shown, the output gain adjustment command value increases monotonically as the detected value of DC power (panel output detected value) increases. Therefore, the control gain can be increased as the solar radiation intensity increases.

[0065] Gain regulator 101 Figure 4 As shown, a positive lower limit value G1 is provided, and a gain adjustment command value above the lower limit value G1 is output. Therefore, the control gain will not become zero, enabling control of the DC voltage (panel voltage).

[0066] Figure 1The power conversion device 1 shown converts DC power to AC power and outputs it. The controller 18 of the power conversion device 1 uses a control gain corresponding to the detected DC power value to calculate the active power correction command value (DC voltage controller 104). For example... Figure 7 As shown, when the detected DC power value increases, the rate of change of the difference between the detected active power value and the detected DC power value also increases. Therefore, even if the DC power changes, the operation of the power conversion device 1 remains stable.

[0067] In detail, as the detected DC power value increases, the control gain increases, and the rate of change of the difference between the detected active power value and the detected DC power value increases. Figure 7 Therefore, even if the DC power changes, the operation of the power conversion device 1 remains stable.

[0068] [Second Embodiment]

[0069] Figure 8 This illustrates the structure of a second embodiment of a power conversion device for solar power generation. In this embodiment, the power conversion device 3 for solar power generation is connected to a three-phase AC power system 2. The power conversion device 3 for solar power generation includes a DC / DC converter 20, a DC capacitor 13, a DC voltage sensor 14, a DC current sensor 15, an AC / DC converter 12, a DC capacitor 21, a DC voltage sensor 22, an AC voltage sensor 16, an AC current sensor 17, and a controller 19.

[0070] A solar panel 11 is connected to the primary side of a DC / DC converter 20. The secondary side of the DC / DC converter 20 is connected to the DC side of an AC / DC converter 12. The AC side of the AC / DC converter 12 is connected to a three-phase AC power system 2. A DC capacitor 13 is connected to the primary side of the DC / DC converter 20, and a DC voltage sensor 14 detects the DC voltage of the DC capacitor 13. A DC current sensor 15 is connected between the solar panel 11 and the DC / DC converter 20 to detect the DC current output by the solar panel 11. A DC capacitor 21 is connected to the DC side of the AC / DC converter 12, and a DC voltage sensor 22 detects the DC voltage of the DC capacitor 21. An AC voltage sensor 16 is connected to the AC side of the AC / DC converter 12 to detect the three-phase AC voltage on the AC side of the AC / DC converter 12. An AC current sensor 17 is connected between the AC / DC converter 12 and the power system 2 to detect the three-phase AC current output by the AC / DC converter 12. The controller 19 takes the primary side DC voltage detection value output by the DC voltage detection sensor 14, the primary side DC current detection value output by the DC current detection sensor 15, the secondary side DC voltage detection value output by the DC voltage detection sensor 22, the AC voltage detection value output by the AC voltage detection sensor 16, and the AC current detection value output by the AC current detection sensor 17 as inputs, and outputs pulse signals to drive the switching elements constituting the AC / DC converter 12 and pulse signals to drive the switching elements constituting the DC / DC converter 20.

[0071] The controller 19 includes a multiplier 111, a gain regulator 112, an MPPT controller 113, a subtractor 114, a DC voltage controller 115, an adder 116, an active power calculator 117, a frequency command calculator 118, an integrator 119, a voltage command calculator 120, a PWM calculator 121, a primary voltage controller 122, and a PWM calculator 123.

[0072] The multiplier 111 takes the primary side DC voltage detection value output by the DC voltage detection sensor 14 and the primary side DC current detection value output by the DC current detection sensor 15 as inputs, multiplies them to calculate the output power of the panel, and outputs it as the panel output detection value.

[0073] The MPPT controller 113 takes the primary-side DC voltage detection value output by the DC voltage detection sensor 14 and the primary-side DC current detection value output by the DC current detection sensor 15 as inputs. Through MPPT (Maximum Power Point Tracking) control, it calculates the power output by the solar panel 11 to become the primary-side DC voltage command of the DC / DC converter 20 with the maximum power, and outputs it as the primary-side DC voltage command value.

[0074] The subtractor 114 takes the secondary side DC voltage detection value output by the DC voltage detection sensor 22 and the specified secondary side DC voltage command value as input, and outputs the difference between them.

[0075] The DC voltage controller 115 takes the difference output by the subtractor 114 and the gain adjustment command value output by the gain regulator 112 as inputs, and outputs the active power correction command value by making the difference output by the subtractor 114 zero, for example by proportional-integral operation.

[0076] Adder 116 takes the panel output detection value from multiplier 111 and the active power correction command value from DC voltage controller 115 as inputs, and adds them together as the active power command value output.

[0077] The active power calculator 117 takes the AC voltage detection value output by the AC voltage detection sensor 16 and the AC current detection value output by the AC current detection sensor 17 as inputs, and outputs the active power output by the AC / DC converter 12 to the AC side as the active power detection value.

[0078] The frequency command arithmetic unit 118 takes the active power command value output by the adder 116 and the active power detection value output by the active power arithmetic unit 117 as inputs, and outputs the frequency command value of the AC voltage output by the AC / DC converter 12 to the AC side.

[0079] The integrator 119 takes the frequency command value output by the frequency command arithmetic unit 118 as input, and outputs the phase command value of the AC voltage output by the AC / DC converter 12 on the AC side through integration.

[0080] The voltage command arithmetic unit 120 takes the voltage amplitude command value of the AC voltage output by the AC / DC converter 12 to the AC side and the phase command value output by the integrator 119 as inputs, and outputs the output voltage command value of the AC voltage output by the AC / DC converter 12 to the AC side.

[0081] The PWM arithmetic unit 121 takes the output voltage command value output by the voltage command arithmetic unit 120 as input, and outputs a pulse signal to drive the switching elements constituting the AC / DC converter 12 through PWM calculation.

[0082] The primary-side voltage controller 122 takes the primary-side DC voltage detection value output by the DC voltage detection sensor 14, the primary-side DC voltage command value output by the MPPT controller 113, and the secondary-side DC voltage detection value output by the DC voltage detection sensor 22 as inputs. It calculates the duty cycle command value of the DC / DC converter 20 by having the primary-side DC voltage of the DC / DC converter 20 follow the primary-side DC voltage command value. The PWM operator 123 takes the duty cycle command value output by the primary-side voltage controller 122 as input and outputs pulse signals that drive the switching elements constituting the DC / DC converter 20 through PWM calculation.

[0083] In this embodiment, the output characteristics of the solar panel 11 are the same as those in the first embodiment. Figure 2 The same. Furthermore, the output characteristics of the frequency instruction arithmetic unit 118 are the same as those in the first embodiment. Figure 3 The same. Furthermore, the output characteristics of the gain regulator 112 are the same as those in the first embodiment. Figure 4 The same. Furthermore, the structure of the DC voltage controller 115 is the same as in the first embodiment. Figure 5 same.

[0084] In this structure, similar to the first embodiment, the proportional gain and integral gain of the DC voltage controller 115 can be adjusted in response to changes in solar irradiance. Furthermore, when the power conversion device 3 starts up, a lower limit is set for the gain adjustment command value when the panel output of the solar panel 11 is zero. This suppresses the situation where the adjusted proportional gain and adjusted integral gain become zero, preventing the panel voltage of the solar panel 11 from becoming uncontrollable.

[0085] [Third Embodiment]

[0086] Figure 9 This describes the structure of a third embodiment of a power conversion device for solar power generation. In addition to the structure of the first embodiment, the power conversion device 4 for solar power generation in this embodiment includes an external controller 5 and an interface 124 capable of communicating with a gain regulator 101 and a DC voltage controller 104. The interface 124 can output the input / output characteristics of the gain regulator 101 to the external controller 5, or set the input / output characteristics of the gain regulator 101 given by the external controller 5. Furthermore, it can output the reference value KP of the proportional gain and the reference value KI of the integral gain of the DC voltage controller 104 to the external controller, or set the reference value KP of the proportional gain and the reference value KI of the integral gain given by the external controller 5 to the DC voltage controller 104.

[0087] By adopting this structure, the control gain of the DC voltage controller 104 can be optimized even when the output characteristics of the solar panel 11 change. Furthermore, the external controller 5 can be, for example, an operation panel housed within the casing of the power conversion device 4, but it can also be any terminal (computer, smartphone, etc.). The external controller 5 has at least an input device and a display device, but the input device and display device can also be integrated, such as a touch panel.

[0088] The main features of the third embodiment can also be summarized as follows.

[0089] like Figure 9 As shown, the power conversion device 4 has an interface section 124 for the input / output characteristics and control gain of the output gain regulator 101, as well as instructions for changing the input / output characteristics and control gain. The controller 18 changes the input / output characteristics and control gain according to the instructions. Therefore, the user can easily confirm and change the input / output characteristics and control gain of the gain regulator 101.

[0090] [Fourth Embodiment]

[0091] Figure 10 This describes the structure of a fourth embodiment of a solar power conversion device. In addition to the structure of the second embodiment, the solar power conversion device 6 of this embodiment includes an external controller 5 and an interface 125 capable of communicating with a gain regulator 112 and a DC voltage controller 115. The interface 125 can output the input / output characteristics of the gain regulator 112 to the external controller 5, or set the input / output characteristics of the gain regulator 101 given by the external controller 5. Furthermore, it can output a reference value KP for the proportional gain and a reference value KI for the integral gain of the DC voltage controller 115 to the external controller, or set the reference values ​​KP for the proportional gain and KI for the integral gain given by the external controller 5 to the DC voltage controller 115.

[0092] By adopting such a structure, the control gain of the DC voltage controller 115 can be optimized even when the panel output characteristics of the solar panel 11 change.

[0093] This invention is not limited to the above embodiments, but includes various modifications. For example, the above embodiments are described in detail for ease of understanding of the invention and are not limited to having all the structures described. Furthermore, a portion of the structure of one embodiment can be replaced with the structure of another embodiment, and structures of other embodiments can be added to the structure of one embodiment. Additionally, for a portion of the structure of each embodiment, other structures can be added, deleted, or replaced.

[0094] Furthermore, the aforementioned structures and functions can be partially or entirely implemented in hardware, for example, through design in integrated circuits. Alternatively, these structures and functions can be implemented in software by a controller (processor) interpreting and executing programs that implement each function. The programs, tables, files, and other information implementing these functions can be stored in memory, hard disks, SSDs (Solid State Drives), or recording media such as IC cards, SD cards, or DVDs.

[0095] Embodiments of the present invention may be as follows.

[0096] (1). A power conversion device that converts DC power into AC power and outputs it to a power system, characterized in that the control unit of the power conversion device calculates an active power command value based on the detected value of DC power and an active power correction command value calculated by taking the deviation between the detected value of DC voltage and the command value of DC voltage as input; calculates a frequency command for the AC voltage output by the power conversion device based on the active power command value and the detected value of active power; outputs a PWM signal for generating the AC voltage based on the frequency command; and uses a control gain that changes accordingly to the detected value of DC power in the calculation of the active power correction command value.

[0097] (2). The power conversion device as described in (1) is characterized in that it has a gain regulator, which takes the detected value of the DC power as input and outputs a gain adjustment command value for changing the control gain.

[0098] (3). The power conversion device as described in (2) is characterized in that: the gain regulator outputs a gain adjustment command value that increases monotonically as the detected value of the DC power increases.

[0099] (4). The power conversion device as described in (3) is characterized in that: the gain regulator has a lower limit limiter and the gain adjustment command value is not less than a specified value.

[0100] (5) The power conversion device as described in (4) is characterized in that: the power conversion device has an interface for communicating with the outside, and is able to output the input-output characteristics and control gain of the gain regulator to the outside, and change the input-output characteristics and control gain according to the instructions from the outside.

[0101] (6) A power conversion device that converts DC power into AC power and outputs it to a power system, characterized in that: the control unit of the power conversion device calculates an active power command value based on the detected value of DC power and an active power correction command value calculated by taking the deviation between the detected value of DC voltage and the command value of DC voltage as input; calculates a frequency command for the AC voltage output by the power conversion device based on the active power command value and the detected value of active power; outputs a PWM signal for generating the AC voltage based on the frequency command; and increases the rate of change of the difference between the detected value of active power output by the power conversion device to the power system and the detected value of DC power as the detected value of DC power increases.

[0102] (7) A power conversion device that converts DC power into AC power and outputs it to a power system, characterized in that: the control unit of the power conversion device calculates an active power command value based on the detected value of DC power and an active power correction command value calculated by taking the deviation between the detected value of DC voltage and the command value of DC voltage as input; calculates a frequency command for the AC voltage output by the power conversion device based on the active power command value and the detected value of active power; outputs a PWM signal for generating the AC voltage based on the frequency command; and increases the control gain for calculating the active power correction command value when the detected value of DC power increases.

[0103] According to (1)-(7), in a system-forming inverter for solar power generation, DC voltage stabilization can be achieved, enabling stable operation of the system-forming inverter. Furthermore, by stabilizing the DC voltage, MPPT (Maximum Power Point Tracking) control can also be achieved simultaneously, maximizing power generation. Moreover, even if solar irradiance changes, DC voltage stabilization can be achieved without using information about solar irradiance.

[0104] Explanation of reference numerals in the attached figures

[0105] 1: Power conversion device for solar power generation

[0106] 2: Power System

[0107] 3: Power conversion device for solar power generation

[0108] 4: Power conversion device for solar power generation

[0109] 5: External controller

[0110] 6: Power conversion device for solar power generation

[0111] 11: Solar panels

[0112] 12: AC / DC converter

[0113] 13: DC capacitor

[0114] 14: DC voltage detection sensor

[0115] 15: DC current detection sensor

[0116] 16: AC voltage detection sensor

[0117] 17: Alternating Current Detection Sensor

[0118] 18: Controller

[0119] 19: Controller

[0120] 20: DC / DC converter

[0121] 21: DC capacitor

[0122] 22: DC voltage detection sensor

[0123] 100: Multiplier

[0124] 101: Gain Adjuster

[0125] 102: MPPT Controller

[0126] 103: Subtractor

[0127] 104: DC Voltage Controller

[0128] 105: Adder

[0129] 106: Active power calculator

[0130] 107: Frequency Instruction Arithmetic Unit

[0131] 108: Integrator

[0132] 109: Voltage Command Arithmetic Unit

[0133] 110: PWM Calculator

[0134] 111: Multiplier

[0135] 112: Gain Adjuster

[0136] 113: MPPT controller

[0137] 114: Subtractor

[0138] 115: DC Voltage Controller

[0139] 116: Adder

[0140] 117: Active power calculator

[0141] 118: Frequency Instruction Arithmetic Unit

[0142] 119: Integrator

[0143] 120: Voltage Command Arithmetic Unit

[0144] 121: PWM Calculator

[0145] 122: Primary side voltage controller

[0146] 123: PWM Calculator

[0147] 124: Interface Section

[0148] 125: Interface Section

[0149] 1040: Multiplier

[0150] 1041: Multiplier

[0151] 1042: Multiplier

[0152] 1043: Multiplier

[0153] 1044: Integrator

[0154] 1045: Adder.

Claims

1. A power conversion device that converts DC power into AC power and outputs it, characterized in that: It has a controller, the controller, The active power command value is calculated based on the detected DC power value and the active power correction command value. The frequency command value of the AC voltage is calculated based on the active power command value and the active power detection value. A PWM signal is output based on the frequency command value. The active power correction command value is calculated using the deviation between the DC voltage detection value and the DC voltage command value, and the control gain corresponding to the DC power detection value.

2. The power conversion device as described in claim 1, characterized in that: The controller has a gain regulator that takes the detected value of the DC power as input and outputs a gain adjustment command value for adjusting the control gain.

3. The power conversion device as described in claim 2, characterized in that: The gain regulator outputs a gain adjustment command value that increases monotonically as the detected value of the DC power increases.

4. The power conversion device as described in claim 3, characterized in that: The gain regulator has a positive lower limit value and outputs a gain adjustment command value above the lower limit value.

5. The power conversion device as described in claim 4, characterized in that: It has an interface section that outputs the input-output characteristics of the gain regulator and the control gain, and inputs instructions for changing the input-output characteristics and the control gain. The controller changes the input / output characteristics and the control gain according to the instructions.

6. A power conversion device that converts DC power into AC power and outputs it, characterized in that: A controller is provided that calculates the active power correction command value using a control gain corresponding to the detected value of the DC power. When the detected value of DC power increases, the rate of change of the difference between the detected value of active power and the detected value of DC power also increases.

7. The power conversion device as described in claim 6, characterized in that: When the detected value of DC power increases, the control gain increases, and the rate of change of the difference between the detected value of active power and the detected value of DC power increases.

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