Power converter

Abstract

To provide a power conversion device that can achieve stable operation even when the DC power changes. [Solution] The power converter 1 converts DC power to AC power and outputs it. The controller 18 of the power converter 1 calculates the active power command value from the detected DC power value (panel output detected value) and the active power correction command value (adder 105). The controller 18 calculates the frequency command value of the AC voltage from the active power command value and the active power detected value (frequency command calculator 107). The controller 18 outputs a PWM signal based on the frequency command value (integrator 108, voltage command calculator 109, PWM calculator 110). The controller 18 calculates the active power correction command value using the deviation between the DC voltage detected value and the DC voltage command value and a control gain corresponding to the detected DC power value (DC voltage controller 104).

Description

Technical Field

[0001] The present invention relates to a power conversion device.

Background Art

[0002] In order to achieve carbon neutrality, the introduction of renewable energy such as solar power is progressing. Along with this, it is expected that the proportion of synchronous generators connected to the power grid will decrease, while the proportion of inverters connecting renewable energy to the power grid will increase. A synchronous generator has a rotating body and the ability to supply inertia to the power grid, but a conventional inverter does not have such an ability. Therefore, when the proportion of inverters connected to the power grid increases, there is a concern that the inertia of the power grid will be insufficient, the grid frequency will be likely to fluctuate, and the power grid will become unstable.

[0003] Therefore, the concept of virtual inertia that simulates the ability to supply inertia to the power grid by inverter control has been proposed. Inverters with the ability to supply virtual inertia to the power grid have attracted attention, and such inverters are called grid-forming inverters. As an example of such a grid-forming inverter, Patent Document 1 is known. Patent Document 1 shows an example of a grid-forming inverter provided with a DC power source in a DC circuit.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, when applying grid-forming inverters to solar power generation, if the DC circuit is equipped with an unstable DC power source such as a solar panel, it becomes difficult to maintain a stable DC voltage in the grid-forming inverter, thus posing a challenge to stable operation of the grid-forming inverter. When an imbalance occurs between the power input to the DC section of the grid-forming inverter from the solar panel and the power output by the grid-forming inverter to the power grid, the DC voltage of the grid-forming inverter fluctuates according to the amount of this imbalance. As a result, if the fluctuation in DC voltage is large, the grid-forming inverter may shut down due to DC overvoltage or DC undervoltage. In addition, in general, MPPT (Maximum Power Point Tracking) control is applied to inverters for solar power generation in order to maximize the generated power, but such control becomes difficult to apply when the DC voltage fluctuates.

[0006] As mentioned earlier, solar panels are unstable power sources, mainly because the irradiance of sunlight hitting the panels is easily altered. When weather conditions change suddenly, the irradiance of sunlight can change in a short time. When the irradiance of sunlight changes, the output characteristics of the solar panel change, and this change affects the stability of the DC voltage. If the inverter could understand the information on the irradiance of sunlight, it would be possible to adjust the control of the DC voltage in accordance with the changes in the irradiance of sunlight. However, this is difficult in practice because it requires a sensor to detect the irradiance of sunlight and the inverter to obtain the irradiance of sunlight in real time.

[0007] The object of the present invention is to provide a power conversion device that can achieve stable operation even when the DC power changes. [Means for solving the problem]

[0008] To achieve the above objective, the present invention provides a power conversion device that converts DC power to AC power and outputs it, comprising a controller that calculates an active power command value from the detected value of the DC power and the active power correction command value, calculates an AC voltage frequency command value from the active power command value and the active power detection value, outputs a PWM signal based on the frequency command value, and calculates the active power correction command value using the deviation between the DC voltage detection value and the DC voltage command value and a control gain corresponding to the detected value of the DC power. [Effects of the Invention]

[0009] According to the present invention, stable operation can be achieved even when the DC power changes. Other problems, configurations, and effects will be clarified by the following description of embodiments. [Brief explanation of the drawing]

[0010] [Figure 1] The configuration of the first embodiment of a power conversion device for solar power generation is shown. [Figure 2] An example of the output characteristics of a solar panel is shown. [Figure 3] An example of the output characteristics of a frequency command calculator is shown. [Figure 4] An example of the output characteristics of a gain adjuster is shown. [Figure 5] An example configuration of a DC voltage controller is shown. [Figure 6] An example of the operating waveform of the first embodiment is shown. [Figure 7] An example of the operating waveform of the first embodiment is shown. [Figure 8] The configuration of a second embodiment of a power conversion device for solar power generation is shown. [Figure 9] The configuration of a third embodiment of a power conversion device for solar power generation is shown. [Figure 10] The configuration of the fourth embodiment of the power conversion device for solar power generation is shown. [Modes for carrying out the invention]

[0011] Hereinafter, embodiments of the power conversion device for solar power generation according to the present invention will be described with reference to the drawings. The purpose of this embodiment is, for example, to stabilize the operation of a grid-forming inverter for solar power generation by stabilizing the DC voltage, and to achieve compatibility with MPPT (Maximum Power Point Tracking) control in order to maximize the generated power. Another purpose of this embodiment is, for example, to stabilize the DC voltage by adjusting the DC voltage control without using information on the irradiance of sunlight, even when the irradiance of sunlight changes.

[0012] [First example] Figure 1 shows the configuration of a first embodiment of a solar power conversion device. The solar power conversion device 1 in this embodiment is connected to a three-phase AC power system 2. The solar power conversion device 1 includes an AC / DC converter 12, a DC capacitor 13, a DC voltage detection sensor 14, a DC current detection sensor 15, an AC voltage detection sensor 16, an AC current detection sensor 17, and a controller 18.

[0013] The solar panel 11 is connected to the DC side of the AC / DC converter 12, and the AC side of the AC / DC converter 12 is connected to the 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 detection sensor 14 detects the DC voltage of the DC capacitor 13. A DC current detection sensor 15 is connected between the solar panel 11 and the AC / DC converter 12 and detects the DC current output by the solar panel 11. An AC voltage detection sensor 16 is connected to the AC side of the AC / DC converter 12 and detects the three-phase AC voltage on the AC side of the AC / DC converter 12. An AC current detection sensor 17 is connected between the AC / DC converter 12 and the power system 2 and detects 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 input and outputs pulse signals to drive the switching elements that make up the AC / DC converter 12.

[0014] The controller 18 has a multiplier 100, a gain adjuster 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.

[0015] The multiplier 100 takes as inputs 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, multiplies them to calculate the panel output power, and outputs it as a panel output detection value.

[0016] The gain adjuster 101 takes as input the panel output detection value output by the multiplier 100 and outputs a gain adjustment command value for adjusting the control gain of the DC voltage controller 104.

[0017] The MPPT controller 102 takes as inputs 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, and calculates a DC voltage command for the AC / DC converter 12 such that the power output by the solar panel 11 is maximized by MPPT (maximum power point tracking) control, and outputs it as a DC voltage command value.

[0018] The subtractor 103 takes as inputs 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, and outputs the difference value.

[0019] The DC voltage controller 104 takes as inputs the difference value output by the subtractor 103 and the gain adjustment command value output by the gain adjuster 101, and outputs an active power correction command value by, for example, proportional integral calculation so that the difference value output by the subtractor 103 becomes zero.

[0020] The adder 105 takes as inputs the panel output detection value output by the multiplier 100 and the active power correction command value output by the DC voltage controller 104, and outputs the added value as an active power command value.

[0021] 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.

[0022] The frequency command calculator 107 takes the active power command value output by the adder 105 and the active power detection value output by the active power calculator 106 as inputs and outputs the frequency command value of the AC voltage that the AC / DC converter 12 outputs to the AC side.

[0023] The integrator 108 takes the frequency command value output by the frequency command calculator 107 as input and outputs the phase command value of the AC voltage that the AC / DC converter 12 outputs to the AC side through integration.

[0024] The voltage command calculator 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.

[0025] The PWM calculator 110 takes the output voltage command value output by the voltage command calculator 109 as input and outputs a pulse signal to drive the switching elements that make up the AC / DC converter 12 through PWM calculation.

[0026] Figure 2 shows an example of the output characteristics of a solar panel 11. With the horizontal axis representing panel voltage and the vertical axis representing panel output, the output characteristics of the solar panel 11 generally exhibit an upward-convex shape. By operating the solar panel at its maximum power point, the power generated by 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 in accordance with such a DC voltage command value, the power generated can be maximized. Furthermore, as irradiance decreases, the solar panel output decreases, and the change in solar panel output in response to changes in solar panel voltage also becomes smaller.

[0027] Figure 3 shows an example of the output characteristics of the frequency command calculator 107. When the horizontal axis represents the effective power detection value output by the AC / DC converter 12 on the AC side and the vertical axis represents the frequency command value of the voltage output by the AC / DC converter 12 on the AC side, a downward characteristic with a right-down slope is obtained. When the AC / DC converter 12 outputs an effective power equal to the effective power command value on the AC side, the frequency command value is set to the reference value (50 Hz or 60 Hz). On the other hand, when an effective power greater than the effective power command value is being output, the frequency command value is set to a value smaller than the reference value, so as to reduce the phase difference between the AC terminal of the AC / DC converter 12 and the power grid and have a characteristic such that the effective power output decreases. Also, when an effective power smaller than the effective power command value is being output, the frequency command value is set to a value larger than the reference value, so as to increase the phase difference between the AC terminal of the AC / DC converter 12 and the power grid and have a characteristic such that the effective power output increases.

[0028] Figure 4 shows an example of the output characteristics of the gain adjuster 101. When the horizontal axis is the panel output detection value and the vertical axis is the gain adjustment command value, for example, when the panel output detection value is P1 or less, the gain adjustment command value is G1, and when the panel output detection value exceeds P1, the gain adjustment command value monotonically increases with an increase in the panel output detection value. For example, when the panel output detection value is P2, the gain adjustment command value is G2, and when the panel output detection value is P3, the gain adjustment command value is G3. It can be set as P1 < P2 < P3, G1 < G2 < G3.

[0029] When the solar irradiance is small, the output detection value of the solar panel also becomes small. By having such characteristics, when the solar irradiance is small, the value of the gain adjustment command value becomes small, and the control gain of the DC voltage controller 104 can be reduced. As described above, when the solar irradiance decreases, the solar panel output decreases, and the change in the solar panel output with respect to the change in the solar panel voltage also becomes small. 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 solar irradiance. Note that the configuration of the DC voltage controller 104 will be described later.

[0030] However, when the power converter 1 is started, the output of the solar panel 11 starts from zero. If the control gain of the DC voltage controller 104 is set to zero at that time, it becomes difficult to control the panel voltage of the solar panel 11. Therefore, 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.

[0031] Figure 5 shows the configuration of the DC voltage controller 104. The DC voltage controller 104 consists of multipliers 1040, 1041, 1042, 1043, integrator 1044, and adder 1045.

[0032] Multiplier 1040 takes the reference value KP of the proportional gain and the gain adjustment command value output by the gain adjuster 101 as inputs, multiplies them, and outputs the adjusted proportional gain. Multiplier 1041 takes the reference value KI of the integral gain and the gain adjustment command value output by the gain adjuster 101 as inputs, multiplies them, and outputs the adjusted integral gain. Multiplier 1042 takes the output of the 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 the 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 an integral operation, and outputs the calculated value. Adder 1045 takes the output of multiplier 1042 and the output of integrator 1044 as inputs, outputs the value obtained by adding them together, and outputs it as the active power correction command value.

[0033] This configuration allows the proportional and integral gains of the DC voltage controller 104 to be adjusted according to the gain adjustment command value output by the gain adjuster 101.

[0034] Figure 6 shows an example of the operating waveform in the first embodiment. This case is an example where the power converter 1 is started up, the operating point moves to the maximum power point, and the irradiance of sunlight decreases during steady-state operation. Up to time T1, the power converter 1 has not yet been started up, and the output of the solar panel is zero. Therefore, the gain adjustment command value is the lower limit value G1, the adjusted proportional gain of the DC voltage controller 104 is KP × G1, and the adjusted integral gain is KI × G1.

[0035] At time T1, the power converter 1 starts up and the solar panel output begins to increase. However, until the solar panel output reaches P1, the gain adjustment command value remains at the lower limit G1, and the adjusted proportional gain of the DC voltage controller 104 remains KP × G1, and the adjusted integral gain remains KI × G1.

[0036] When time T2 arrives and the solar panel output exceeds P1, the gain adjustment command value begins to increase, and consequently, the adjusted proportional gain and adjusted integral gain of the DC voltage controller 104 also begin to increase.

[0037] At time T3, the operating point moves to the maximum power point, and the solar panel output reaches a steady state at P3. At this time, the gain adjustment command value also becomes constant at G3, and the adjusted proportional gain of the DC voltage controller 104 becomes constant at KP × G3, and the adjusted integral gain becomes constant at KI × G3.

[0038] As time T4 approaches and the irradiance of sunlight begins to decrease, the output of the solar panels also decreases, causing the gain adjustment command value to start to decrease. Consequently, the adjusted proportional gain and adjusted integral gain of the DC voltage controller 104 also begin to decrease.

[0039] At time T5, the decrease in solar irradiance ends, and the solar panel output reaches a steady state at P2. At this time, the gain adjustment command value also becomes constant at G2, and the adjusted proportional gain of the DC voltage controller 104 becomes constant at KP × G2, and the adjusted integral gain becomes constant at KI × G2.

[0040] As described above, it is possible to adjust the proportional and integral gains of the DC voltage controller 104 in accordance with changes in the irradiance of sunlight. Furthermore, when the power converter 1 is started up and the panel output of the solar panel 11 is zero, a lower limit can be set for the gain adjustment command value to prevent the adjusted proportional and integral gains from becoming zero, thereby preventing the panel voltage of the solar panel 11 from becoming uncontrollable.

[0041] Figure 7 shows an example of the operating waveform in the first embodiment. This case is an example where the power converter 1 is started up and the solar panel output increases. Up to time T1, the power converter 1 has not yet been started up, and the solar panel output is zero. Therefore, the gain adjustment command value is the lower limit value G1.

[0042] At time T1, power converter 1 starts up and the solar panel output begins to increase. However, the gain adjustment command value remains at the lower limit G1 until the solar panel output reaches P1, and the rate of change of the active power correction command value is gradual.

[0043] At time T2, when the solar panel output exceeds P1, the gain adjustment command value begins to increase, and consequently, the rate of change of the active power correction command value also gradually increases. The active power command value to the AC / DC converter 12 is obtained by adding the active power correction command value to the solar panel output. Since the AC / DC converter 12 operates according to the active power command value, the difference between the active power detection value of the power output by the AC / DC converter 12 and the solar panel output behaves similarly to the active power correction command value, resulting in a waveform with a gradually increasing rate of change.

[0044] In this way, the gain adjustment command value is changed according to the magnitude of the solar panel output, and an active power correction command value is calculated to stabilize the DC voltage. The AC / DC converter 12 operates according to the active power command value obtained by adding the active power correction command value to the solar panel output.

[0045] The main features of the first embodiment can also be summarized as follows:

[0046] The power converter 1 shown in Figure 1 converts DC power to AC power and outputs it. The controller 18 of the power converter 1 calculates the active power command value from the detected DC power value (panel output detected value) and the active power correction command value (adder 105). The controller 18 calculates the frequency command value of the AC voltage from the active power command value and the active power detected value (frequency command calculator 107). The controller 18 outputs a PWM signal based on the frequency command value (integrator 108, voltage command calculator 109, PWM calculator 110). The controller 18 calculates the active power correction command value using the deviation between the DC voltage detected value and the DC voltage command value and a control gain corresponding to the detected DC power value (Figures 4 and 5) (DC voltage controller 104).

[0047] By using a control gain corresponding to the detected DC power value, the operation of the power converter 1 remains stable even when the DC power changes. As a result, the operation of the power converter 1 remains stable even when the irradiance of sunlight changes.

[0048] As shown in Figure 1, the controller 18 includes a gain adjuster 101 that takes a detected DC power value (panel output detected value) as input and outputs a gain adjustment command value to adjust the control gain. By taking the detected DC power value as input and outputting a gain adjustment command value, the control gain can be easily adjusted according to the irradiance of sunlight.

[0049] As shown in Figure 4, the gain adjuster 101 outputs a gain adjustment command value that increases monotonically in response to an increase in the detected DC power (panel output detected value). This allows the control gain to be increased as the irradiance of sunlight increases.

[0050] As shown in Figure 4, the gain adjuster 101 has a positive lower limit G1 and outputs a gain adjustment command value greater than or equal to the lower limit G1. This prevents the control gain from becoming zero and allows for control of the DC voltage (panel voltage).

[0051] The power converter 1 shown in Figure 1 converts DC power to AC power and outputs it. The controller 18 of the power converter 1 calculates an active power correction command value using a control gain corresponding to the detected DC power value (DC voltage controller 104). As shown in Figure 7, 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 increases. As a result, the operation of the power converter 1 remains stable even when the DC power changes.

[0052] In detail, as the detected DC power increases, the control gain increases, and the rate of change of the difference between the detected active power and the detected DC power increases (Figure 7). As a result, the operation of the power converter 1 remains stable even when the DC power changes.

[0053] [Second example] Figure 8 shows the configuration of a second embodiment of a solar power conversion device. In this embodiment, the solar power conversion device 3 is connected to a three-phase AC power system 2. The solar power conversion device 3 includes a DC / DC converter 20, a DC capacitor 13, a DC voltage detection sensor 14, a DC current detection sensor 15, an AC / DC converter 12, a DC capacitor 21, a DC voltage detection sensor 22, an AC voltage detection sensor 16, an AC current detection sensor 17, and a controller 19.

[0054] The solar panel 11 is connected to the primary side of the DC / DC converter 20, the secondary side of the DC / DC converter 20 is connected to the DC side of the AC / DC converter 12, and the AC side of the AC / DC converter 12 is connected to the 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 detection sensor 14 detects the DC voltage of the DC capacitor 13. A DC current detection sensor 15 is connected between the solar panel 11 and the DC / DC converter 20 and detects 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 detection sensor 22 detects the DC voltage of the DC capacitor 21. An AC voltage detection sensor 16 is connected to the AC side of the AC / DC converter 12 and detects the three-phase AC voltage on the AC side of the AC / DC converter 12. An AC current detection sensor 17 is connected between the AC / DC converter 12 and the power system 2 and detects the three-phase AC current output by the AC / DC converter 12. The controller 19 takes as input the primary DC voltage detection value output by the DC voltage detection sensor 14, the primary DC current detection value output by the DC current detection sensor 15, the secondary 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, and outputs pulse signals to drive the switching elements constituting the AC / DC converter 12 and the DC / DC converter 20.

[0055] The controller 19 includes a multiplier 111, a gain adjuster 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.

[0056] The multiplier 111 takes the primary DC voltage detection value output by the DC voltage detection sensor 14 and the primary DC current detection value output by the DC current detection sensor 15 as inputs, multiplies them to calculate the panel's output power, and outputs it as the panel output detection value.

[0057] The MPPT controller 113 takes the primary DC voltage detection value output by the DC voltage detection sensor 14 and the primary DC current detection value output by the DC current detection sensor 15 as inputs, and uses MPPT (Maximum Power Point Tracking) control to calculate the primary DC voltage command for the DC / DC converter 20 that maximizes the power output by the solar panel 11, and outputs it as the primary DC voltage command value.

[0058] The subtractor 114 takes the secondary DC voltage detection value output by the DC voltage detection sensor 22 and a predetermined secondary DC voltage command value as input and outputs the difference between them.

[0059] The DC voltage controller 115 takes the difference value output by the subtractor 114 and the gain adjustment command value output by the gain adjuster 112 as inputs, and outputs an active power correction command value, for example, by proportional-integral operation, so that the difference value output by the subtractor 114 becomes zero.

[0060] The adder 116 takes the panel output detection value output by the multiplier 111 and the active power correction command value output by the DC voltage controller 115 as inputs, and outputs the sum of them as the active power command value.

[0061] 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.

[0062] The frequency command calculator 118 takes the active power command value output by the adder 116 and the active power detection value output by the active power calculator 117 as inputs and outputs the frequency command value of the AC voltage that the AC / DC converter 12 outputs to the AC side.

[0063] The integrator 119 takes the frequency command value output by the frequency command calculator 118 as input and outputs the phase command value of the AC voltage that the AC / DC converter 12 outputs to the AC side through integration.

[0064] The voltage command calculator 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.

[0065] The PWM calculator 121 takes the output voltage command value output by the voltage command calculator 120 as input and outputs a pulse signal to drive the switching elements that make up the AC / DC converter 12 through PWM calculation.

[0066] The primary voltage controller 122 takes the primary DC voltage detection value output by the DC voltage detection sensor 14, the primary DC voltage command value output by the MPPT controller 113, and the secondary DC voltage detection value output by the DC voltage detection sensor 22 as inputs and calculates the duty cycle command value for the DC / DC converter 20 so that the primary DC voltage of the DC / DC converter 20 follows the primary DC voltage command value. The PWM calculator 123 takes the duty cycle command value output by the primary voltage controller 122 as input and outputs pulse signals to drive the switching elements constituting the DC / DC converter 20 by PWM calculation.

[0067] In this embodiment, the output characteristics of the solar panel 11 are the same as those in Figure 2 of the first embodiment. The output characteristics of the frequency command calculator 118 are the same as those in Figure 3 of the first embodiment. The output characteristics of the gain adjuster 112 are the same as those in Figure 4 of the first embodiment. Furthermore, the configuration of the DC voltage controller 115 is the same as that in Figure 5 of the first embodiment.

[0068] In this configuration as well, similar to the first embodiment, it is possible to adjust the proportional and integral gains of the DC voltage controller 115 in accordance with changes in the irradiance of sunlight. Furthermore, when the power converter 3 is started up and the panel output of the solar panel 11 is zero, a lower limit can be set for the gain adjustment command value to prevent the adjusted proportional and integral gains from becoming zero, thereby preventing the panel voltage of the solar panel 11 from becoming uncontrollable.

[0069] [Third example] Figure 9 shows the configuration of a third embodiment of a solar power conversion device. In addition to the configuration of the first embodiment, the solar power conversion device 4 of this embodiment includes an interface unit 124 that can communicate with an external controller 5, a gain adjuster 101, and a DC voltage controller 104. The interface unit 124 can output the input / output characteristics of the gain adjuster 101 to the external controller 5, or set the input / output characteristics provided by the external controller 5 to the gain adjuster 101. 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 provided by the external controller 5 to the DC voltage controller 104.

[0070] This configuration makes it possible to optimize the control gain of the DC voltage controller 104 even when the panel output characteristics of the solar panel 11 change. The external controller 5 is, for example, an operation panel provided on the housing of the power converter 4, but it may be any terminal (computer, smartphone, etc.). The external controller 5 is equipped with at least an input device and a display device, but the input device and display device may be integrated, such as a touch panel.

[0071] The main features of the third embodiment can also be summarized as follows:

[0072] As shown in Figure 9, the power converter 4 includes an interface unit 124 that outputs the input / output characteristics and control gain of the gain adjuster 101 and receives commands to change the input / output characteristics and control gain. The controller 18 changes the input / output characteristics and control gain according to the commands. This allows the user to easily check and change the input / output characteristics and control gain of the gain adjuster 101.

[0073] [Fourth embodiment] Figure 10 shows the configuration of a fourth embodiment of the solar power conversion device. In addition to the configuration of the second embodiment, the solar power conversion device 6 of this embodiment includes an interface unit 125 that can communicate with an external controller 5, a gain adjuster 112, and a DC voltage controller 115. The interface unit 125 can output the input / output characteristics of the gain adjuster 112 to the external controller 5, or set the input / output characteristics provided by the external controller 5 to the gain adjuster 101. 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 115 to the external controller, or set the reference value KP of the proportional gain and the reference value KI of the integral gain provided by the external controller 5 to the DC voltage controller 115.

[0074] This configuration makes it possible to optimize the control gain of the DC voltage controller 115 even when the panel output characteristics of the solar panel 11 change.

[0075] The present invention is not limited to the embodiments described above, and includes various modifications. For example, the embodiments described above are explained in detail to make the present invention easier to understand, and are not necessarily limited to those having all the configurations described. Furthermore, it is possible to replace parts of the configuration of one embodiment with the configuration of another embodiment, and it is also possible to add configurations from other embodiments to the configuration of one embodiment. In addition, it is possible to add, delete, or replace parts of the configuration of each embodiment with other configurations.

[0076] Furthermore, some or all of the above configurations and functions may be implemented in hardware, for example, by designing them as integrated circuits. Alternatively, the above configurations and functions may be implemented in software by having a controller (processor) interpret and execute programs that implement each function. Information such as programs, tables, and files that implement each function can be stored in memory, a recording device such as a hard disk or SSD (Solid State Drive), or a recording medium such as an IC card, SD card, or DVD.

[0077] The embodiments of the present invention may also be as follows.

[0078] (1) A power converter that converts DC power to AC power and outputs it to a power grid, wherein the control unit of the power converter calculates an active power command value from the detected value of the DC power and an active power correction command value calculated using the deviation between the detected DC voltage and the DC voltage command value as input, calculates a frequency command for the AC voltage output by the power converter from the active power command value and the active power detected value, outputs a PWM signal that generates the AC voltage based on the frequency command, and uses a control gain that changes according to the detected value of the DC power in calculating the active power correction command value.

[0079] (2) A power conversion device characterized by comprising a gain adjuster that takes the detected value of the DC power as input and outputs a gain adjustment command value for changing the control gain as described in (1).

[0080] (3)(2) The power conversion device characterized in that, in response to an increase in the detected value of the DC power, the gain adjuster outputs a gain adjustment command value that increases monotonically.

[0081] (4)(3) The power conversion device is characterized in that the gain adjuster is equipped with a lower limit limit so that the gain adjustment command value does not fall below a predetermined value.

[0082] (5)(4) The power converter is characterized in that it includes an interface unit for communicating with the outside, outputs the input / output characteristics of the gain adjuster and the control gain to the outside, and can change the input / output characteristics and the control gain according to commands from the outside.

[0083] (6) A power converter that converts DC power to AC power and outputs it to a power system, wherein the control unit of the power converter calculates an active power command value from the detected value of the DC power and an active power correction command value calculated using the deviation between the detected DC voltage and the DC voltage command value as input, calculates a frequency command for the AC voltage output by the power converter from the active power command value and the active power detected value, outputs a PWM signal that generates the AC voltage based on the frequency command, and when the detected value of the DC power increases, the rate of change of the difference between the detected value of the active power output by the power converter to the power system and the detected value of the DC power increases.

[0084] (7) A power converter that converts DC power to AC power and outputs it to a power grid, wherein the control unit of the power converter calculates an active power command value from the detected value of the DC power and an active power correction command value calculated using the deviation between the detected DC voltage and the DC voltage command value as input, calculates a frequency command for the AC voltage output by the power converter from the active power command value and the active power detected value, outputs a PWM signal that generates 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 the DC power increases.

[0085] According to (1)-(7), in grid-forming inverters for solar power generation, DC voltage stabilization can be achieved, enabling stable operation of the grid-forming inverter. Furthermore, by stabilizing the DC voltage, compatibility with MPPT (Maximum Power Point Tracking) control can be achieved, maximizing the generated power. Moreover, even if the irradiance of sunlight changes, the DC voltage can be stabilized without using information on the irradiance of sunlight. [Explanation of Symbols]

[0086] 1: Power conversion device for solar power generation 2: Power system 3: Power conversion device for solar power generation 4: Power conversion device for solar power generation 5: External controller 6: Power conversion device for solar power generation 11: Solar panels 12: AC / DC converter 13: DC Capacitor 14: DC voltage detection sensor 15: DC current detection sensor 16: AC voltage detection sensor 17: AC current detection sensor 18: Controller 19: Controller 20: DC / DC Converter 21: DC Capacitor 22: DC voltage detection sensor 100: Multiplier 101: Gain Adjuster 102: MPPT Controller 103: Subtractor 104: DC voltage controller 105: Adder 106: Active Power Calculator 107: Frequency command calculator 108: Integrator 109: Voltage command calculator 110:PWM calculator 111: Multiplier 112: Gain Adjuster 113: MPPT Controller 114: Subtractor 115: DC voltage controller 116: Adder 117: Active Power Calculator 118: Frequency command calculator 119: Integrator 120: Voltage command calculator 121:PWM calculator 122: Primary voltage controller 123:PWM calculator 124: Interface section 125: Interface section 1040: Multiplier 1041: Multiplier 1042: Multiplier 1043: Multiplier 1044: Integrator 1045: Adder

Claims

1. In a power conversion device that converts DC power to AC power and outputs it, The active power command value is calculated from the detected DC power value and the active power correction command value. The frequency command value of the AC voltage is calculated from the active power command value and the detected active power value. Based on the aforementioned frequency command value, a PWM signal is output. The active power correction command value is calculated using the difference between the detected DC voltage value and the DC voltage command value, and a control gain corresponding to the detected DC power value. A power converter equipped with a controller.

2. In the power conversion device according to claim 1, The aforementioned controller The system includes a gain adjuster that takes the detected DC power as input and outputs a gain adjustment command value for adjusting the control gain. A power conversion device characterized by the following features.

3. In the power conversion device according to claim 2, The aforementioned gain adjuster is In response to an increase in the detected DC power, the gain adjustment command value, which increases monotonically, is output. A power conversion device characterized by the following features.

4. In the power conversion device according to claim 3, The aforementioned gain adjuster is It has a positive lower limit, Outputs the gain adjustment command value that is equal to or greater than the lower limit. A power conversion device characterized by the following features.

5. In the power conversion device according to claim 4, The interface unit outputs the input / output characteristics and the control gain of the gain adjuster, and receives commands to change the input / output characteristics and the control gain. The aforementioned controller The input / output characteristics and the control gain are changed in accordance with the above command. A power conversion device characterized by the following features.

6. In a power conversion device that converts DC power to AC power and outputs it, The system includes a controller that calculates an active power correction command value using a control gain corresponding to the detected value of the DC power, As the detected value of the DC power increases, the rate of change of the difference between the detected value of the active power and the detected value of the DC power increases. A power conversion device characterized by the following features.

7. In the power conversion device according to claim 6, When the detected value of the DC power increases, the control gain increases, and the rate of change of the difference between the detected value of the active power and the detected value of the DC power increases. A power conversion device characterized by the following features.

Images