A method for controlling the output voltage, current, and power of photovoltaic power.

Abstract

This invention discloses a control method for limiting the output voltage, current, and power of photovoltaic (PV) power supplies, relating to the field of PV converter control strategy technology. It solves the problems of excessive PV output voltage and current, excessive power, and excessive converter output voltage under specific requirements. The key technical point is to transform the control in MPPT mode, power limiting mode, and converter output voltage limiting mode into the control of inductor current, selecting the minimum value as the inductor current setpoint, thereby achieving automatic switching between modes. The power limiting mode can limit PV output power based on grid frequency changes, achieving primary grid frequency regulation. Furthermore, to address the problem that sudden changes in PV panel power prevent the system from resuming MPPT mode, thus causing the system power to lose tracking, an MPPT restart strategy is provided.

Description

Technical Field

[0001] This application relates to the field of photovoltaic converter control strategy technology, and in particular to a control method for limiting photovoltaic output voltage, current and power. Background Technology

[0002] To reduce power loss and improve energy efficiency, traditional photovoltaic output mainly focuses on achieving maximum power output. When photovoltaic or grid abnormalities occur, it is unable to make autonomous judgments based on the abnormalities and restore the system to normal. To address these issues, this application designs a control method for limiting photovoltaic output voltage, current, power, and converter output voltage under abnormal photovoltaic or grid operating conditions. Summary of the Invention

[0003] This application provides a control method for limiting the output voltage, current, and power of photovoltaics. Its technical purpose is to solve the problems of excessive photovoltaic output voltage and current, excessive power, and excessive output voltage of the converter under specific requirements, so as to make photovoltaic output more flexible.

[0004] The above-mentioned technical objective of this application is achieved through the following technical solution:

[0005] A control method for limiting the output voltage, current, and power of a photovoltaic system is disclosed. This control method is implemented through a control system comprising an MPPT control unit, a voltage controller, a current controller, a limiter, a comparator unit, and a PWM unit. The control method controls the photovoltaic output voltage, current, power, and converter output voltage by controlling the inductor current reference setpoint under different operating modes. The operating modes include MPPT mode, power limiting mode, and converter output voltage limiting mode. The limiter comprises a first limiter, a second limiter, and a third limiter.

[0006] Furthermore, the control in the MPPT mode includes:

[0007] The maximum output voltage V of the photovoltaic system is controlled within the MPPT control unit. PV_max A limit is imposed, and when |ΔV| exceeds a preset value, the MPPT control unit is stopped; where ΔV = V PV -V MPPT_ref V PV V represents the photovoltaic output voltage. MPPT_ref This indicates the reference value for the maximum output power voltage of the photovoltaic system.

[0008] Photovoltaic output voltage V PV and photovoltaic output current I PV After passing through the MPPT control unit, the maximum output power voltage reference value V of the photovoltaic system is obtained. MPPT_ref V PV With VMPPT_ref The difference is input to the voltage controller, and then passes through the first limiter to obtain the inductor current reference setpoint i in MPPT mode. MPPT_ref .

[0009] Furthermore, the output range of the voltage controller is 0 to i. max The limiting range of the first limiter is i min ~i max ; where i max Indicates the maximum output current of the photovoltaic system; i min This indicates the minimum output current of the photovoltaic system.

[0010] Furthermore, the control in the power limiting mode includes:

[0011] The power limiting setpoint P is obtained based on the magnitude of the deviation of the grid frequency from the operating frequency. max , will P max / V PV The input to the second limiter yields the inductor current reference setpoint i in power limiting mode. p_ref This enables primary frequency regulation of the power grid; where the power limiting setpoint P max for:

[0012] P max =P N -k·Δf

[0013] Among them, P max P represents the maximum power output under power limiting conditions. N Δf represents the maximum output power of the photovoltaic system; k represents the frequency regulation coefficient; and Δf represents the amount of change in the grid frequency from the operating frequency.

[0014] Furthermore, the limiting range of the second limiter is 0 to i. max .

[0015] Furthermore, the control in the converter output voltage limiting mode includes:

[0016] Maximum output voltage limit V of the converter o_max The actual value of the converter output voltage V o The difference is obtained by subtracting the input values. This difference is then input to the voltage controller and passed through the third limiter to obtain the inductor current reference setpoint i in the converter output voltage limiting mode. o_ref .

[0017] Furthermore, the limiting range of the third limiter is 0 to i. max .

[0018] Furthermore, the switching between the aforementioned working modes includes:

[0019] When the system operates in MPPT mode, if the grid frequency is less than or equal to the power frequency, P is obtained. max ≥P MPPT , then i p_ref ≥i MPPT_ref The inductor current is given by i. MPPT_ref The system is still in MPPT mode; when the grid frequency is greater than the power frequency, P is obtained. max <P MPPT , then i p_ref <i MPPT_ref The inductor current is given by i p_ref The system switches to power limiting mode. At this time, |ΔV|>A, the MPPT control unit stops working, and the output remains at V. MPPT_ref In MPPT mode, the voltage controller enters saturation; as the grid frequency gradually recovers, i p_ref The voltage gradually increases until |ΔV| < A, at which point the MPPT control unit starts working, the voltage controller in MPPT mode begins to desaturate, and the system switches to MPPT mode; where P MPPT Indicates the maximum output power of the photovoltaic system;

[0020] When the system operates in power limiting mode, it exits power limiting mode when the photovoltaic output voltage drops to a threshold. At this time, |ΔV| is greater than the preset value, and the output of the MPPT control unit is V. MPPT_ref Then the voltage controller output i in MPPT mode PI The output i of the first limiter is 0. MPPT_ref For i min The system outputs i from the photovoltaic output side min The minimum current output power, when the photovoltaic output side voltage does not drop to the minimum output voltage value V set by the photovoltaic device. PV_min If the photovoltaic system still generates power, it cannot return to MPPT mode. In this case, stop and restart the system to restore MPPT working mode; otherwise, stop the system.

[0021] When the system operates in MPPT mode, if the photovoltaic conditions are enhanced, causing V o >V o_max At this point, the voltage controller in the converter output voltage limiting mode quickly desaturates and controls the photovoltaic output voltage. Since |ΔV| > A, the MPPT control unit stops working, and the output remains at V. MPPT_ref If the voltage controller in MPPT mode saturates, the system switches to converter output voltage limiting mode.

[0022] With the recovery of photovoltaic conditions, V o <V o_maxAt this point, the voltage controller in the converter output voltage limiting mode quickly saturates. When |ΔV| < A, the MPPT control unit starts to work, the MPPT voltage controller begins to desaturate, and the system switches to MPPT mode.

[0023] A computer-readable storage medium having a computer program stored thereon, characterized in that, when executed by a processor, the program implements a control method for limiting the output voltage, current, and power of a photovoltaic system.

[0024] A computer device includes a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor, when executing the program, implements a control method for limiting photovoltaic output voltage, current, and power as described in any of claims 1 to 8.

[0025] The beneficial effects of this application are as follows:

[0026] (1) The MPPT algorithm with dual closed-loop control has good dynamic response performance when the external environment changes;

[0027] (2) This control method transforms each control condition into the control of the inductor current, making the control more convenient and enabling smooth switching between modes.

[0028] (3) The power limiting mode of this control method can achieve primary frequency regulation of the power grid;

[0029] (4) When photovoltaic or power grid malfunctions, the system can make an independent judgment based on the malfunction and restore the system to normal. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the control method described in this application;

[0031] Figure 2 This is a simulation waveform diagram illustrating the primary frequency regulation of the power grid from MPPT mode to power limiting mode and back to MPPT mode.

[0032] Figure 3 for Figure 2 MPPT reference voltage V under operating conditions MPPT_ref A schematic diagram of the simulation waveform;

[0033] Figure 4 This is a graph showing the changes in photovoltaic curves under extreme operating conditions;

[0034] Figure 5 V is the MPPT reference voltage under extreme operating conditions. MPPT_ref A schematic diagram of the simulation waveform;

[0035] Figure 6 For the MPPT voltage regulator output i under extreme operating conditionsPI A schematic diagram of the simulation waveform;

[0036] Figure 7 For the inductor current given i in MPPT mode under extreme operating conditions MPPT_ref A schematic diagram of the simulation waveform;

[0037] Figure 8 The photovoltaic output voltage V is the voltage V that the photovoltaic system can still generate power under extreme operating conditions. PV A schematic diagram of the simulation waveform;

[0038] Figure 9 V is the photovoltaic output voltage when the photovoltaic system fails to generate power under extreme operating conditions. PV A schematic diagram of the simulation waveform;

[0039] Figure 10 This is a simulation waveform diagram showing the transition from MPPT mode to converter output voltage limiting mode and back to MPPT mode.

[0040] Figure 11 for Figure 10 MPPT reference voltage V under operating conditions MPPT_ref A schematic diagram of the simulation waveform. Detailed Implementation

[0041] The technical solution of this application will be described in detail below with reference to the accompanying drawings.

[0042] Figure 1 This is a schematic diagram of the control method for limiting photovoltaic output voltage, current, power, and converter output voltage as described in this application. The control method described in this application uses... Figure 1 The control system shown is used to achieve this. This control system includes an MPPT control unit, a voltage controller, a current controller, a limiter, a comparator unit, and a PWM unit.

[0043] This control method primarily employs dual closed-loop control of voltage and current. The entire system has three operating modes: MPPT mode, power limiting mode, and converter output voltage limiting mode. Specifically, the inductor current setpoint is obtained by comparing the current reference values ​​corresponding to the limiting conditions in each mode, selecting the minimum value as the current setpoint, thus enabling automatic switching between different modes. During the inductor current control process, a feedforward control strategy is used, where the current i... L The deviation, after passing through the current controller, is fed forward by the input voltage V. PV The sums are used to obtain the given parameters for the PWM unit, and the duty cycle D of the switching transistor is obtained after passing through the PWM unit.

[0044] (1) The control in the MPPT mode includes:

[0045] Limit the maximum photovoltaic output voltage V in the MPPT control unit PV_max And when |ΔV| (ΔV is V) PV With V MPPT_ref When the difference between the values ​​is greater than a preset value (here, the preset value is set to A, which depends on the parameters of the photovoltaic equipment), the MPPT control unit is ordered to stop operating.

[0046] Photovoltaic output voltage V PV and current I PV After passing through the MPPT control unit, the maximum output power voltage reference value V of the photovoltaic system is obtained. MPPT_ref Actual value of photovoltaic output voltage V PV Subtract V MPPT_ref Then it enters the voltage controller, whose output range is 0 to i. max (i max (to the maximum output current of the photovoltaic system), then passes through a limiter (limiting the range to i). min ~i max i min (For the minimum photovoltaic output current), the inductor current reference setpoint i in MPPT mode is obtained. MPPT_ref .

[0047] (2) The control under the power limiting mode includes:

[0048] The power limiting setpoint P is obtained based on the magnitude of the deviation of the grid frequency from the operating frequency. max P max Divide by V PV Then it passes through a limiter (limiting the range to 0~i). max The inductor current reference setpoint i in power-limited mode is obtained. p_ref P max The relationship with the change in power grid frequency is as follows:

[0049] P max =P N -k·Δf;

[0050] Among them, P max P represents the maximum power output under power limiting conditions. N Δf represents the rated power of the photovoltaic system; k is the frequency regulation coefficient; and Δf is the change in grid frequency from the operating frequency.

[0051] (3) The control in the converter output voltage limiting mode includes:

[0052] Maximum output voltage limit of converter V o_max Subtract the actual value V o It enters the voltage controller and a limiter (limiting the range from 0 to i). maxAfter that, the inductor current reference setpoint i in the converter output voltage limiting mode is obtained. o_ref .

[0053] Switching between different modes:

[0054] (1) Switching between MPPT mode and power limiting mode (default output voltage V) o The maximum limit value V was not reached. o_max Therefore, the voltage controller limiting the converter output voltage is in saturation.

[0055] When operating in MPPT mode, if the grid frequency is less than or equal to the power frequency, the obtained P max ≥P MPPT Therefore i p_ref ≥i MPPT_ref The inductor current is given by i. MPPT_ref The system is still in MPPT mode; when the grid frequency is greater than the power frequency, the obtained P max <P MPPT Therefore i p_ref <i MPPT_ref The inductor current is given by i. p_ref The system enters power limiting mode. At this time, |ΔV|>A, the MPPT control unit stops working, and the output remains at V. MPPT_ref The voltage controller in MPPT mode enters saturation.

[0056] As the power grid frequency gradually recovers, i p_ref The voltage is gradually increased until |ΔV| < A, at which point the MPPT control unit starts working, the MPPT voltage controller begins to desaturate, and the system operates in MPPT mode. Simulation results are as follows: Figure 2 , Figure 3 As shown in the figure, the simulation results are basically consistent with the above analysis.

[0057] If the system operates in power-limited mode, the light intensity and temperature drop drastically. Under this extreme condition, the photovoltaic output voltage will rapidly decrease to a very low level, such as... Figure 4 As shown, at this point, the power limiting mode is exited. Since |ΔV| > A, the MPPT control unit is still not working, and the output remains the previous V. MPPT_ref ,like Figure 5 As shown, this causes the voltage regulator output i in MPPT mode. PI The output i of the limiter is 0. MPPT_ref For i min ,like Figure 6 , Figure 7 As shown, the system outputs i from the photovoltaic output side. minThe minimum current output power; after a certain period of time, if the photovoltaic output side voltage does not drop to the minimum output voltage value V set by the photovoltaic equipment. PV_min ,like Figure 8 As shown, this indicates that the photovoltaic equipment can still provide energy, but the system cannot return to MPPT mode. In this case, the system needs to be stopped and restarted to restore the MPPT working mode. Otherwise, it means that the lighting conditions are insufficient for the photovoltaic output power (such as at night). Figure 9 As shown, the system needs to be stopped at this point.

[0058] (2) Switching between MPPT mode and converter output voltage limiting mode (the current setpoint of the default power limiting mode reaches the maximum limit value i) max ):

[0059] When operating in MPPT mode, if photovoltaic conditions are enhanced, causing V o >V o_max At this point, the voltage controller in the converter output voltage limiting mode quickly exits saturation and controls the photovoltaic output voltage. At this time, |ΔV|>A, the MPPT control unit stops working, and the output remains at V. MPPT_ref The voltage controller in MPPT mode enters saturation.

[0060] With the recovery of photovoltaic conditions, V o <V o_max At this point, the voltage controller in the converter output voltage limiting mode rapidly saturates. When |ΔV| < A, the MPPT control unit starts working, the MPPT voltage controller begins to desaturate, and the system operates in MPPT mode. Simulation results are as follows: Figure 10 , Figure 11 As shown in the figure, the simulation results are basically consistent with the above analysis.

[0061] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A control method for limiting the output voltage, current, and power of a photovoltaic system, wherein the control method is implemented through a control system, the control system comprising an MPPT control unit, a voltage controller, a current controller, a limiter, a comparator unit, and a PWM unit, characterized in that, This control method controls the photovoltaic output voltage, current, power, and converter output voltage by controlling the inductor current reference setpoint under different operating modes; wherein, the operating modes include MPPT mode, power limiting mode, and converter output voltage limiting mode; the limiter includes a first limiter, a second limiter, and a third limiter.

2. The control method as described in claim 1, characterized in that, The control in the MPPT mode includes: The maximum value of the photovoltaic output voltage in the MPPT control unit V PV_max Apply restrictions, and when |Δ V When | is greater than A, the MPPT control unit is stopped; where Δ V for V PV and V MPPT_ref The difference, Δ V=V PV - V MPPT_ref , V PV Indicates the photovoltaic output voltage; V MPPT_ref This indicates the maximum output power voltage reference value of the photovoltaic system; A represents the preset value. Photovoltaic output voltage V PV and photovoltaic output current I PV The maximum output power voltage reference value of the photovoltaic system is obtained after passing through the MPPT control unit. V MPPT_ref ,Will V PV and V MPPT_ref The difference is input to the voltage controller, and then passes through the first limiter to obtain the inductor current reference setpoint in MPPT mode. i MPPT_ref .

3. The control method as described in claim 2, characterized in that, The output range of the voltage controller is 0~ i max The limiting range of the first limiter is i min ~ i max ; in, i max Indicates the maximum output current of the photovoltaic system; i min This indicates the minimum output current of the photovoltaic system.

4. The control method as described in claim 3, characterized in that, The control in the power limiting mode includes: The power limit setpoint is obtained based on the magnitude of the deviation of the grid frequency from the operating frequency. P max ,Will P max / V PV The inductor current reference setpoint in power-limiting mode is obtained by inputting to the second limiter. i p_ref This enables primary frequency regulation of the power grid; whereby the power limiting setpoint... P max for: ； in, P max This indicates the maximum power output under power limiting conditions; P N Indicates the maximum output power of the photovoltaic system; k Indicates the frequency modulation coefficient; Δ f It represents the amount of change in the power grid frequency from the operating frequency.

5. The control method as described in claim 4, characterized in that, The limiting range of the second limiter is 0~ i max .

6. The control method as described in claim 5, characterized in that, The control in the converter output voltage limiting mode includes: Maximum limit of converter output voltage V o_max Actual value of converter output voltage V o The difference is obtained by subtracting the input values. This difference is then input to the voltage controller and passed through the third limiter to obtain the inductor current reference setpoint in the converter output voltage limiting mode. i o_ref .

7. The control method as described in claim 6, characterized in that, The limiting range of the third limiter is 0~ i max .

8. The control method as described in claim 7, characterized in that, Switching between working modes includes: When the system operates in MPPT mode, if the grid frequency is less than or equal to the power frequency, the following is obtained: P max ≥ P MPPT ,but i p_ref ≥ i MPPT_ref The system's inductor current setpoint is taken as i MPPT_ref The system is still in MPPT mode; when the grid frequency is greater than the power frequency, the following is obtained: P max < P MPPT ,but i p_ref < i MPPT_ref The system's inductor current setpoint is taken as i p_ref The system switches to power limiting mode, at which point |Δ V |>A, the MPPT control unit stops working, and the output remains at 0. V MPPT_ref The voltage controller in MPPT mode enters saturation; as the grid frequency gradually recovers, i p_ref Gradually increase until |Δ V When | < A, the MPPT control unit starts working, the voltage controller in MPPT mode begins to desaturate, and the system switches to MPPT mode; where, P MPPT Indicates the maximum output power of the photovoltaic system; When the system is operating in power-limited mode, it exits power-limited mode when the photovoltaic output voltage drops to a threshold. At this time, |Δ V If the value is greater than the preset value, the output of the MPPT control unit is... V MPPT_ref The output of the voltage controller in MPPT mode i PI The output of the first limiter is 0. i MPPT_ref for i min The system outputs photovoltaic power from the photovoltaic output side. i min The minimum current output power when the photovoltaic output side voltage does not drop to the minimum output voltage value set by the photovoltaic device. V PV_min If the photovoltaic system still generates power, it cannot return to MPPT mode. In this case, stop and restart the system to restore MPPT mode; otherwise, stop the system. When the system operates in MPPT mode, if the photovoltaic conditions are enhanced, it will cause... V o > V o_max At this point, the voltage controller in the converter output voltage limiting mode quickly desaturates and controls the photovoltaic output voltage. V |>A, the MPPT control unit stops working, and the output remains at... V MPPT_ref If the voltage controller in MPPT mode saturates, the system switches to converter output voltage limiting mode. With the recovery of photovoltaic conditions, V o < V o_max At this point, the voltage controller in the converter output voltage limiting mode quickly saturates, and at this time |Δ V When | < A, the MPPT control unit starts working, the MPPT voltage controller begins to desaturate, and the system switches to MPPT mode.

9. A computer-readable storage medium having a computer program stored thereon, characterized in that, When executed by the processor, the program implements the control method for limiting the output voltage, current, and power of photovoltaic power as described in any one of claims 1 to 8.

10. A computer device, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that, When the processor executes the program, it implements the control method for limiting the output voltage, current, and power of photovoltaic power as described in any one of claims 1 to 8.

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