Control method for limiting photovoltaic output voltage, current and power

Abstract

The invention discloses a control method for limiting photovoltaic output voltage, current and power, relates to the technical field of photovoltaic converter control strategies, and solves the problems of overlarge photovoltaic output voltage and current, excessive power and overlarge output voltage of a converter under specific requirements. According to the technical scheme, the method is characterized in that control under an MPPT mode, a power limiting mode and a converter output voltage limiting mode is converted into control over inductive current, the minimum value is selected as an inductive current given value, and therefore automatic switching under all the modes is achieved; wherein the power limiting mode can limit the photovoltaic output power according to the frequency change of the power grid to realize the primary frequency modulation of the power grid; and an MPPT restarting strategy is provided for solving the problem that the system cannot recover the MPPT mode due to sudden change of the power of the photovoltaic panel, so that the power of the system cannot be continuously tracked.

Description

Technical Field

[0001] The present application relates to the technical field of photovoltaic converter control strategies, and in particular to a control method for limiting photovoltaic output voltage, current, and power. Background Art

[0002] In order to reduce power loss and improve energy utilization, traditional photovoltaic output is mainly committed to achieving maximum power output. When abnormalities occur in the photovoltaic or power grid, it is impossible to make independent judgments based on the abnormalities and restore the system to normal. To address these problems, this application designs a control method for limiting photovoltaic output voltage, current, power and converter output voltage under abnormal photovoltaic or power grid conditions. Summary of the invention

[0003] The present application provides a control method for limiting photovoltaic output voltage, current, and power. Its technical purpose is to solve the problems of excessive photovoltaic output voltage and current and excess power under specific requirements and excessive output voltage of the converter, making photovoltaic output more flexible.

[0004] The above technical objectives of this application are achieved through the following technical solutions:

[0005] A control method for limiting photovoltaic output voltage, current and power, the control method is implemented by a control system, the control system includes an MPPT control unit, a voltage controller, a current controller, a limiter, a comparison 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 given value under different working modes; wherein the working modes include MPPT mode, power limiting mode and converter output voltage limiting mode; the limiters include a first limiter, a second limiter and a third limiter.

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

[0007] In the MPPT control unit, the maximum photovoltaic output voltage V PV_max When |ΔV| is greater than the preset value, the MPPT control unit stops running; where ΔV = V PV -V MPPT_ref , V PV Represents photovoltaic output voltage; V MPPT_ref Indicates the maximum photovoltaic output power voltage reference value;

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

[0009] Furthermore, the output range of the voltage controller is 0~i max , the first limiter limits the range of i min ~i max ; where i max Indicates the maximum photovoltaic output current; i min Indicates the minimum photovoltaic output current.

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

[0011] According to the deviation of the grid frequency from the operating frequency, the power limit given value P is obtained. max , P max / V PV Input to the second limiter to obtain the inductor current reference given value i in the power limiting mode p_ref , to achieve the primary frequency regulation of the power grid; where the power limit given value P max for:

[0012] P max =P N -k·Δf

[0013] Among them, P max Indicates the maximum power output under power limitation conditions; P N represents the maximum photovoltaic output power; k represents the frequency modulation coefficient; Δf represents the change in the grid frequency from the operating frequency.

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

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

[0016] Set the maximum output voltage limit of the converter to V o_max The actual value of the converter output voltage V o The difference is obtained by subtracting, and the difference is input to the voltage controller, and then passes through the third limiter to obtain the inductor current reference given value i under the converter output voltage limiting mode. o_ref .

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

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

[0019] When the system works in MPPT mode, if the grid frequency is less than or equal to the power frequency, P max ≥P MPPT , then i p_ref ≥i MPPT_ref , the given value of the inductor current is i MPPT_ref , the system is still in MPPT mode; when the grid frequency is greater than the power frequency, P max <P MPPT , then i p_ref <i MPPT_ref , the given value of the inductor current is 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 , the voltage controller in MPPT mode enters saturation; when the grid frequency gradually recovers, i p_ref Gradually increases until |ΔV|<A, the MPPT control unit starts to work, the voltage controller in the MPPT mode starts to desaturate, and the system switches to the MPPT mode; MPPT Indicates the maximum photovoltaic output power;

[0020] When the system works in power limiting mode, when the photovoltaic output voltage drops to the threshold, it exits the power limiting mode. 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 in MPPT mode is i PI is 0, the output i of the first limiter MPPT_ref for i min The system uses i from the photovoltaic output side min The minimum current output power is when the photovoltaic output voltage does not drop to the minimum output voltage value V set by the photovoltaic device. PV_min When the PV is still generating power, the system cannot be restored to the MPPT mode. Stop the system and restart it to restore the MPPT working mode, otherwise stop the system.

[0021] When the system works in MPPT mode, if the photovoltaic condition is enhanced, V o >V o_max At this time, the voltage controller in the converter output voltage limiting mode quickly desaturates 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, and the system switches to converter output voltage limiting mode;

[0022] As the photovoltaic conditions recover, V o <V o_maxAt this time, the voltage controller in the converter output voltage limiting mode quickly saturates. At this time, when |ΔV|<A, the MPPT control unit starts to work, the MPPT voltage controller starts to desaturate, and the system switches to MPPT mode.

[0023] A computer-readable storage medium stores a computer program, wherein the program, when executed by a processor, implements a control method for limiting photovoltaic output voltage, current, and power.

[0024] A computer device comprises a memory, a processor and a computer program stored in the memory and executable on the processor, wherein when the processor executes the program, the control method for limiting photovoltaic output voltage, current and power as claimed in any one of claims 1 to 8 is implemented.

[0025] The beneficial effects of this application are:

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

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

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

[0029] (4) When an abnormality occurs in the photovoltaic or power grid, the system can be restored to normal by making independent judgments based on the abnormality. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0031] Figure 2 A schematic diagram of a simulation waveform for realizing primary frequency modulation of a power grid from MPPT mode to power limiting mode and then to MPPT mode;

[0032] Figure 3 for Figure 2 MPPT reference voltage V under working conditions MPPT_ref Schematic diagram of simulation waveform;

[0033] Figure 4 This is the change diagram of photovoltaic curve under extreme working conditions;

[0034] Figure 5 MPPT reference voltage V under extreme conditions MPPT_ref Schematic diagram of simulation waveform;

[0035] Figure 6 The output i of the MPPT voltage regulator under extreme conditionsPI Schematic diagram of simulation waveform;

[0036] Figure 7 The inductor current i is given in the MPPT mode under extreme working conditions. MPPT_ref Schematic diagram of simulation waveform;

[0037] Figure 8 The photovoltaic output voltage V is when the photovoltaic can still generate power under extreme conditions. PV Schematic diagram of simulation waveform;

[0038] Fig. 9 The photovoltaic output voltage V is when the photovoltaic power cannot generate power under extreme conditions. PV Schematic diagram of simulation waveform;

[0039] Fig.10 It is a schematic diagram of simulation waveforms from MPPT mode to converter output voltage limiting mode and then to MPPT mode;

[0040] Fig.11 for Fig.10 MPPT reference voltage V under working conditions MPPT_ref Schematic diagram of simulation waveform. DETAILED DESCRIPTION

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

[0042] Figure 1 This is a schematic diagram of the structure of the control method for limiting the photovoltaic output voltage, current, power and converter output voltage of the present application. The control method described in the present application is as follows: Figure 1 The control system shown in the figure is implemented. The control system includes an MPPT control unit, a voltage controller, a current controller, a limiter, a comparison unit and a PWM unit.

[0043] This control method is mainly a voltage and current dual closed-loop control. The whole system has three working modes, namely MPPT mode, power limiting mode and converter output voltage limiting mode. In particular, the inductor current setting of this control method is obtained by comparing the current reference values ​​corresponding to the limiting conditions in each mode, and the minimum value is selected as the current setting, so that automatic switching between different modes can be achieved. In the process of controlling the inductor current, the feedforward control strategy is used, and the current i L The deviation is fed forward by the current controller and the input voltage V PV Add them together to get the given value of the PWM unit, and after passing through the PWM unit, get the duty cycle D of the switch tube.

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

[0045] Limiting 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 two values ​​is greater than a preset value (here the preset value is A, which is determined according to the parameters of the photovoltaic device), the MPPT control unit stops running.

[0046] Photovoltaic output voltage V PV and current I PV After passing through the MPPT control unit, the maximum photovoltaic output power voltage reference value V is obtained MPPT_ref , the actual value of photovoltaic output voltage V PV Subtract V MPPT_ref Then enter the voltage controller, the output range of the voltage controller is 0~i max (i max is the maximum photovoltaic output current), and then passes through a limiter (limit range is i min ~i max ,i min is the minimum photovoltaic output current), and the inductor current reference given value i in MPPT mode is obtained MPPT_ref .

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

[0048] According to the deviation of the grid frequency from the operating frequency, the power limit given value P is obtained. max , P max Divide by V PV After passing through a limiter (limit range is 0~i max ) to obtain the inductor current reference given value i in power limiting mode p_ref .P max The relationship with the change in grid frequency is:

[0049] P max =P N -k·Δf;

[0050] Among them, P max P is the maximum power output under power limitation conditions; N is the rated power of photovoltaic power; k is the frequency modulation coefficient; Δf is the change of grid frequency from the operating frequency.

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

[0052] Converter output voltage maximum limit value V o_max Subtract the actual value V o , enter the voltage controller and a limiter (limit range is 0~i max), the inductor current reference given value 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 is not reached o_max , so the voltage controller limiting the converter output voltage is in saturation):

[0055] When working in MPPT mode, if the grid frequency is less than or equal to the power frequency, the P max ≥P MPPT , so i p_ref ≥i MPPT_ref , the given value of the inductor current is i MPPT_ref , the system is still in MPPT mode; when the grid frequency is greater than the power frequency, the P max <P MPPT , so i p_ref <i MPPT_ref , the given value of the inductor current is i p_ref , the system enters the 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 grid frequency gradually recovers, i p_ref Gradually increases until |ΔV|<A, the MPPT control unit starts to work, the MPPT voltage controller starts to desaturate, and the system works in MPPT mode. The simulation results are as follows Figure 2 , Figure 3 It can be seen that the simulation results are basically consistent with the above analysis.

[0057] If the system works in power limiting mode, the light intensity and temperature will drop sharply. Under this extreme condition, the photovoltaic output voltage will drop rapidly to a very small value, such as Figure 4 As shown, the power limit mode is exited at this time. Since |ΔV|>A at this time, the MPPT control unit still does not work, and the output is still the previous V MPPT_ref ,like Figure 5 As shown, the voltage regulator output in MPPT mode is PI is 0, the limiter output i MPPT_ref for i min ,like Figure 6 , Figure 7 As shown, the system starts from the photovoltaic output side with i 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 device PV_min ,like Figure 8 As shown, it means that the photovoltaic equipment can still provide energy, but the system cannot be restored to MPPT mode. At this time, it is necessary to stop the system and restart it to restore the MPPT working mode. Otherwise, it means that the lighting conditions are not enough to make the photovoltaic output power (such as at night). Fig. 9 As shown, the system needs to be stopped.

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

[0059] When working in MPPT mode, if the photovoltaic condition is enhanced, V o >V o_max At this time, 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] As the photovoltaic conditions recover, V o <V o_max At this time, 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 starts to desaturate, and the system works in the MPPT mode. The simulation results are as follows Fig.10 , Fig.11 It can be seen that 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 principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A control method for limiting photovoltaic output voltage, current and power, the control method is implemented by a control system, the control system includes an MPPT control unit, a voltage controller, a current controller, a limiter, a comparison unit and a PWM unit, characterized in that: The control method realizes the control of photovoltaic output voltage, current, power and converter output voltage by controlling the inductor current reference given value under different working modes; wherein the working modes include MPPT mode, power limiting mode and converter output voltage limiting mode; and the limiter includes a first limiter, a second limiter and a third limiter.

2. The control method according to claim 1, characterized in that: The control under the MPPT mode includes: In the MPPT control unit, the maximum photovoltaic output voltage V PV_max When |ΔV| is greater than the preset value, the MPPT control unit stops running; where ΔV = V PV -V MPPT_ref , V PV Represents photovoltaic output voltage; V MPPT_ref Indicates the maximum photovoltaic output power voltage reference value; Photovoltaic output voltage V PV and photovoltaic output current I PV After passing through the MPPT control unit, the maximum photovoltaic output power voltage reference value V is obtained MPPT_ref , V PV With V MPPT_ref After the difference is made, it is input to the voltage controller and then passes through the first limiter to obtain the inductor current reference given value i in MPPT mode. MPPT_ref .

3. The control method according to claim 2, characterized in that: The output range of the voltage controller is 0~i max , the first limiter limits the range of i min ~i max ; where i max Indicates the maximum photovoltaic output current; i min Indicates the minimum photovoltaic output current.

4. The control method according to claim 1, characterized in that: The control in the power limiting mode includes: According to the deviation of the grid frequency from the operating frequency, the power limit given value P is obtained. max , P max / V PV Input to the second limiter to obtain the inductor current reference given value i in the power limiting mode p_ref , to achieve the primary frequency regulation of the power grid; where the power limit given value P max for: P max =P N -k·Δf Among them, P max Indicates the maximum power output under power limitation conditions; P N represents the maximum photovoltaic output power; k represents the frequency modulation coefficient; Δf represents the change in the grid frequency from the operating frequency.

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

6. The control method according to claim 1, characterized in that: The control in the converter output voltage limiting mode includes: Set the maximum output voltage limit of the converter to V o_max The actual value of the converter output voltage V o The difference is obtained by subtracting, and the difference is input to the voltage controller, and then passes through the third limiter to obtain the inductor current reference given value i under the converter output voltage limiting mode. o_ref .

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

8. The control method according to any one of claims 1 to 7, characterized in that: Switching between working modes includes: When the system works in MPPT mode, if the grid frequency is less than or equal to the power frequency, P max ≥P MPPT , then i p_ref ≥i MPPT_ref , the given value of the inductor current is i MPPT_ref , the system is still in MPPT mode; when the grid frequency is greater than the power frequency, P max <P MPPT , then i p_ref <i MPPT_ref , the given value of the inductor current is 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 , the voltage controller in MPPT mode enters saturation; when the grid frequency gradually recovers, i p_ref Gradually increases until |ΔV|<A, the MPPT control unit starts to work, the voltage controller in the MPPT mode starts to desaturate, and the system switches to the MPPT mode; MPPT Indicates the maximum photovoltaic output power; When the system works in power limiting mode, when the photovoltaic output voltage drops to the threshold, it exits the power limiting mode. 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 in MPPT mode is i PI is 0, the output i of the first limiter MPPT_ref for i min The system uses i from the photovoltaic output side min The minimum current output power is when the photovoltaic output voltage does not drop to the minimum output voltage value V set by the photovoltaic device. PV_min When the PV is still generating power, the system cannot be restored to MPPT mode. Stop the system and restart it to restore MPPT mode, otherwise stop the system. When the system works in MPPT mode, if the photovoltaic condition is enhanced, V o >V o_max At this time, the voltage controller in the converter output voltage limiting mode quickly desaturates 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, and the system switches to converter output voltage limiting mode; As the photovoltaic conditions recover, V o <V o_max At this time, the voltage controller in the converter output voltage limiting mode quickly saturates. At this time, when |ΔV|<A, the MPPT control unit starts to work, the MPPT voltage controller starts 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 the program is executed by a processor, the control method for limiting photovoltaic output voltage, current and power as described in any one of claims 1 to 8 is implemented.

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, the control method for limiting photovoltaic output voltage, current and power as described in any one of claims 1 to 8 is implemented.

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