MPPT control system based on PWM

Abstract

The invention discloses a PWM-based MPPT control system, and relates to the field of photovoltaic power generation, the PWM-based MPPT control system comprises an MCU controller, a photovoltaic panel, a driving circuit and an energy storage circuit, the energy storage circuit is connected with two electrodes of the photovoltaic panel, and the photovoltaic panel generates power to store energy for a battery in the energy storage circuit; the energy storage circuit comprises a triode, an inductor and a sampling resistor, an MPPT state machine control strategy is built in the MCU controller, PWM waves are output according to the state machine control strategy, and the drive circuit is controlled; the output of the driving circuit is connected with the grid of the triode to control the on-off of the energy storage circuit, the source of the triode is connected with the positive output of the photovoltaic panel, the drain of the triode is connected with one end of the inductor, and the other end of the inductor is connected with the positive end of the battery. An MPPT algorithm control strategy of positive and negative disturbance regulation and control can be realized by using a low-performance 8-bit MCU (Microprogrammed Control Unit); a large number of multipliers and filtering algorithms are omitted, and the control logic is simple; an automatic correction function is achieved, and the maximum output power of the photovoltaic panel is tracked in real time.

Description

Technical Field

[0001] The embodiments of the present application relate to the field of photovoltaic power generation, and in particular to a PWM-based MPPT control system. Background Art

[0002] Maximum Power Point Tracking (MPPT) is an electronic tracking technology. This application mainly focuses on the application of MPPT algorithm in controlling solar photovoltaic power generation. MPPT technology is used to track the maximum output power of photovoltaic panels at any time to avoid energy waste to the greatest extent.

[0003] In related technologies, there are many MPPT control algorithms, but the core principles all require accurate sampling of current and voltage. However, sampling in general engineering always has errors, especially in low-cost scenarios. It is impossible to completely eliminate the accumulated errors, resulting in tracking failure. Summary of the invention

[0004] The embodiment of the present application provides a PWM-based MPPT control system to solve the problems of complex traditional MPPT control algorithms and large sampling and tracking cumulative errors. The system includes an MCU controller, a photovoltaic panel, a drive circuit, and an energy storage circuit. The energy storage circuit is connected to the two poles of the photovoltaic panel, and the photovoltaic panel generates electricity to store energy in the battery in the energy storage circuit;

[0005] The energy storage circuit includes a transistor, an inductor and a sampling resistor, and the MCU controller has a built-in MPPT state machine control strategy, which outputs a PWM wave and controls the drive circuit according to the state machine control strategy;

[0006] The output of the driving circuit is connected to the gate of the transistor to control the on and off of the energy storage circuit. The source of the transistor is connected to the positive output of the photovoltaic panel, the drain of the transistor is connected to one end of the inductor, and the other end of the inductor is connected to the positive terminal of the battery.

[0007] Specifically, a sampling resistor is connected in series between the negative electrode of the photovoltaic panel and the negative electrode of the battery, and the MCU controller samples the current of the sampling resistor and outputs a PWM wave according to the sampled current value;

[0008] The energy storage circuit is also provided with a unidirectional conducting diode, the cathode of the diode is connected to the drain of the transistor, and the anode of the diode is connected to the negative electrode of the photovoltaic panel and is grounded.

[0009] Specifically, the MCU controller obtains the sampling current value of the sampling resistor and the output voltage of the photovoltaic panel, and when the output voltage of the photovoltaic panel is higher than the set threshold, starts the MPPT state machine control; when the output voltage of the photovoltaic panel is lower than the set threshold, exits the MPPT state machine control strategy.

[0010] Specifically, the MPPT state machine includes the following control states:

[0011] Update the reference current state: use the current value sampled at the current moment as the reference current;

[0012] First PWM state: increase the PWM duty cycle by one unit and obtain the corresponding sampled current;

[0013] Second PWM state: increase the PWM duty cycle by two units and obtain the corresponding sampled current;

[0014] The third PWM state: increase the PWM duty cycle by three units to obtain the corresponding sampled current;

[0015] Fourth PWM state: reduce the PWM duty cycle by one unit and obtain the corresponding sampled current;

[0016] Fifth PWM state: reduce the PWM duty cycle by two units and obtain the corresponding sampled current;

[0017] Sixth PWM state: reduce the PWM duty cycle by three units and obtain the corresponding sampled current.

[0018] Specifically, when the MCU controller detects that the output voltage of the photovoltaic panel is greater than 4V, the MPPT control strategy is started and the disturbance flag is set to high level 1; when the effective disturbance flag is detected to be 1, the PWM value and the first current value at the current moment are recorded, and the state is switched to the first PWM state.

[0019] Specifically, when the sampled current obtained in the first PWM state is greater than the first current value, the current PWM value and the second current value are recorded, and the state is switched to the second PWM state;

[0020] When the sampled current obtained in the second PWM state is greater than the second current value, the current PWM value and the third current value are recorded, and the state is switched to the third PWM state;

[0021] When the sampled current values ​​acquired multiple times in the third PWM state show an increasing trend, the cycle is set in the third PWM state.

[0022] Specifically, when the sampled current obtained in the first PWM state is less than the first current value, the PWM value in the current state is reduced by one duty cycle, and the reference current state is switched to be updated, and the disturbance flag is set to a low level 0;

[0023] When the sampled current obtained in the second PWM state is less than the second current value, the PWM value in the current state is reduced by two duty cycles, and the reference current state is switched to be updated, and the disturbance flag is set to 0;

[0024] When the sampled current obtained in the third PWM state is less than the third current value, the PWM value in the current state is reduced by three duty cycles, and the state is switched to update the reference current state, and the disturbance flag is set to 0.

[0025] Specifically, when it is detected that the disturbance flag is set to 0 in the updating reference current state, the PWM value and the fourth current value in the current state are recorded, and the state is switched to the fourth PWM state;

[0026] When the sampled current obtained in the fourth PWM state is greater than the fourth current value, the current PWM value and the fifth current value are recorded, and the process turns to the fifth PWM state;

[0027] When the sampled current acquired in the fifth PWM state is greater than the fifth current value, the current PWM value and the sixth current value are recorded, and the state is turned to the sixth PWM state.

[0028] Specifically, when the sampled current obtained in the fourth PWM state is less than the fourth current value, the PWM value in the current state is increased by one duty cycle, and the reference current state is switched to be updated, and the disturbance flag is set to 1;

[0029] When the sampled current obtained in the fifth PWM state is less than the fifth current value, the PWM value in the current state is increased by two duty cycles, and the reference current state is switched to be updated, and the disturbance flag is set to 1;

[0030] When the sampled current obtained in the sixth PWM state is less than the sixth current value, the PWM value in the current state is increased by three duty cycles, and the state is switched to update the reference current state, and the disturbance flag is set to 1.

[0031] Specifically, when the sampled current values ​​acquired multiple times in the sixth PWM state show an increasing trend, the cycle is set in the sixth PWM state.

[0032] The beneficial effects brought by the technical solution provided by the embodiment of the present application include at least:

[0033] The MPPT algorithm control strategy for positive and negative disturbance regulation can be implemented using a low-performance 8-bit MCU;

[0034] It saves a lot of multipliers and filtering algorithms, and the control logic is simple;

[0035] With automatic correction function, it can track the maximum output power of photovoltaic panels in real time. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 It is a structural schematic diagram of a PWM-based MPPT control system provided in an embodiment of the present application;

[0037] Figure 2It is a state diagram of the MPPT control algorithm state machine provided in an embodiment of the present application. DETAILED DESCRIPTION

[0038] In order to make the objectives, technical solutions and advantages of the present application clearer, the implementation methods of the present application will be further described in detail below with reference to the accompanying drawings.

[0039] The term "multiple" as used herein refers to two or more than two. "And / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can mean: A exists alone, A and B exist at the same time, and B exists alone. The character " / " generally indicates that the related objects are in an "or" relationship.

[0040] Figure 1 It is a structural diagram of a PWM-based MPPT control system provided by an embodiment of the present application. The system includes an MCU controller, a photovoltaic panel, a drive circuit and an energy storage circuit. The energy storage circuit is connected to the two poles of the photovoltaic panel, and the photovoltaic panel generates electricity to store energy for the battery BT1 in the energy storage circuit. The energy storage circuit includes a transistor Q3, an inductor L1 and a sampling resistor R3. The MCU controller can be a conventional eight-bit MCU, and only needs to use its basic functions, in conjunction with the built-in MPPT state machine control strategy or control algorithm, to output PWM waves and control the drive circuit through the state machine control strategy during actual regulation. The output of the drive circuit is connected to the gate of the transistor Q3 to control the on and off of the energy storage circuit. The source of Q3 is connected to the positive output of the photovoltaic panel, the drain of Q3 is connected to one end of L1, and the other end of L1 is connected to the positive end of BT1. This circuit structure constitutes a basic asynchronous buck circuit, which generates PWM wave by MPPT algorithm, and then controls Q3 by PWM. Since MPPT algorithm controls the duty cycle of PWM, the asynchronous buck circuit composed of Q3, L1 and D1 can generate different voltages on BT1, thereby obtaining different currents on R3, and MPPT algorithm samples this current. That is, one duty cycle corresponds to one current value, so as long as the duty cycle of PWM is controlled, it is equivalent to controlling the output current.

[0041] Figure 2 It is the state diagram of the MPPT control algorithm state machine. The MCU controller is set with the triggering condition of the MPPT state machine control mechanism, that is, the output voltage threshold of the photovoltaic panel. When the output voltage of the photovoltaic panel is higher than the set threshold, the MPPT state machine control is started; when the output voltage of the photovoltaic panel is lower than the set threshold, the MPPT state machine control strategy is exited. After starting the adjustment mechanism, refer to the following control states for dynamic transformation:

[0042] Update the reference current state: use the current value sampled at the current moment as the reference current;

[0043] First PWM state: increase the PWM duty cycle by one unit and obtain the corresponding sampled current;

[0044] Second PWM state: increase the PWM duty cycle by two units and obtain the corresponding sampled current;

[0045] The third PWM state: increase the PWM duty cycle by three units to obtain the corresponding sampled current;

[0046] Fourth PWM state: reduce the PWM duty cycle by one unit and obtain the corresponding sampled current;

[0047] Fifth PWM state: reduce the PWM duty cycle by two units and obtain the corresponding sampled current;

[0048] Sixth PWM state: reduce the PWM duty cycle by three units and obtain the corresponding sampled current.

[0049] It is specially noted that the state machine only defines the system working state and specific adjustment means, but not the current value and PWM value, that is, each time the state is switched, the PWM duty cycle is increased or decreased by several units relative to the previous state. In particular, the reference current state is updated, and the reference current value is uncertain each time it is switched to this state, which is also the key to the dynamic adjustment of positive and negative disturbances in this application.

[0050] When the system starts normally and detects that the output of the photovoltaic panel is greater than 4V, the MPPT control strategy is started and the disturbance flag is set to high level 1. The reference current can be set based on this state and switched to the update reference current state, corresponding to Figure 2 Follow the procedure in step 1 of .

[0051] When the effective disturbance flag is detected to be 1, the current PWM value and the first current value are recorded, and the state is switched to the first PWM state. Assuming that the initial state is PWM(0), it becomes PWM(1) after switching, indicating an increase of one duty cycle unit, corresponding to Figure 2 Follow step 2 of the procedure.

[0052] When the sampled current obtained in the first PWM state is greater than the first current value, the current PWM value and the second current value are recorded, and the second PWM state is switched. After switching, it becomes PWM(1+2), which means that two duty cycle units are added on the basis of the previous PWM(1) state, corresponding to Figure 2 Follow step 2 of the procedure.

[0053] When the sampled current obtained in the second PWM state is greater than the second current value, the current PWM value and the third current value are recorded, and the state is switched to the third PWM state; after the switch, it becomes PWM (1+2+3), which means that three duty cycle units are added on the basis of the previous PWM (1+2) state, corresponding to Figure 2 Follow step 4 of the procedure.

[0054] In particular, if the system disturbance is serious and the current increasing trend cannot be effectively curbed after switching to the third PWM state, the state will not be switched, but the third PWM state will be maintained in a cycle. The cycle process here is changed according to the step size of increasing the duty cycle by three units at a time until the current maintains a normal trend and starts to decrease.

[0055] The above steps 1 to 3 are extreme cases. Under normal circumstances, if the current drops after adjustment in step 2, and the sampled current obtained in the first PWM state is less than the first current value, the PWM value in the current state is reduced by one duty cycle, and the reference current state is switched to be updated, and the disturbance flag is set to low level 0. This step corresponds to Figure 2 The process of step 5 in the above diagram is the state logic of step 1-step 2-step 5. The disturbance flag includes two states: 1 and 0, which correspond to the states of increasing and decreasing PWM duty cycle, that is, positive disturbance adjustment and negative disturbance adjustment. After entering the state of updating the reference current, the subsequent dynamic adjustment will be based on the latest PWM value and current value, so the current and PWM are both fluctuating, not constant.

[0056] When the sampled current obtained in the second PWM state starts to decrease and is less than the second current value, the PWM value in the current state is reduced by two duty cycles, and the reference current state is switched to be updated, and the disturbance flag is set to 0. This step corresponds to Figure 2 The process of step 6 in the above diagram is the state logic of step 1-step 2-step 3-step 6. In terms of PWM value, the process of step 6 actually changes PWM(1+2) to PWM(1), not to PWM(0).

[0057] When the sampled current obtained in the third PWM state starts to decrease and is less than the third current value, the PWM value in the current state is reduced by three duty cycles, and the reference current state is switched to be updated, and the disturbance flag is set to 0. This step corresponds to Figure 2 The process of step 6 in the above diagram is the state logic of step 1-step 2-step 3-step 4-step 7. In terms of PWM value, the process of step 7 actually changes PWM(1+2+3) to PWM(1+2), and it is not restored to PWM(0).

[0058] The above is about the situation where the PWM duty cycle increases, because after switching back to the updated reference current state, it does not necessarily become PWM(0), and dynamic adjustment needs to continue when the voltage has not yet recovered, so the present application also introduces a negative disturbance state adjustment mechanism.

[0059] When the disturbance flag is detected to be set to 0 in the updating reference current state, the PWM value and the fourth current value in the current state are recorded, and the state is switched to the fourth PWM state. This step corresponds to Figure 2 In step 8 of the process, it is assumed that the initial state is PWM(0). In terms of PWM value, step 8 actually changes PWM(0) to PWM(0-1).

[0060] When the sampled current obtained in the fourth PWM state is greater than the fourth current value, the current PWM value and the fifth current value are recorded, and the fifth PWM state is switched. This step corresponds to Figure 2 In step 9 of the process, in terms of PWM value, PWM(0-1) is actually changed to PWM(0-1-2).

[0061] When the sampled current obtained in the fifth PWM state is greater than the fifth current value, the current PWM value and the sixth current value are recorded, and the sixth PWM state is switched; this step corresponds to Figure 2 In step 10 of the process, in terms of PWM values, PWM(0-1-2) actually becomes PWM(0-1-2-3).

[0062] When the negative disturbance is large, after switching to the sixth PWM state, the current increasing trend still cannot be effectively curbed, and the state is no longer switched, but the sixth PWM state is maintained in a cycle. The cycle process here is changed according to the step size of reducing the duty cycle by three units at a time until the current maintains a normal trend and starts to decrease.

[0063] Similar to the regulation mechanism of the forward disturbance, when the sampled current obtained in the fourth PWM state is less than the fourth current value, the PWM value in the current state is increased by one duty cycle, and the reference current state is switched to be updated, and the disturbance flag is set to 1. This step corresponds to Figure 2 In step 11 of the process, in terms of PWM value, PWM(0-1) is actually changed to PWM(0).

[0064] When the sampled current obtained in the fifth PWM state is less than the fifth current value, the PWM value in the current state is increased by two duty cycles, and the reference current state is switched to be updated, and the disturbance flag is set to 1. This step corresponds to Figure 2 In step 12 of the process, in terms of PWM value, PWM(0-1-2) is actually changed to PWM(0-1).

[0065] When the sampled current obtained in the sixth PWM state is less than the sixth current value, the PWM value in the current state is increased by three duty cycles, and the reference current state is switched to be updated, and the disturbance flag is set to 1. This step corresponds to Figure 2 In step 13 of the process, in terms of PWM values, PWM(0-1-2-3) actually becomes PWM(0-1-2).

[0066] This solution is mainly aimed at the problem that the current MPPT algorithm has too high hardware requirements and cannot be implemented in engineering. It can be implemented with only 8-bit PWM and 10-bit ADC, eliminating overly complex algorithms. It only needs to perform simple filtering on the sampled current value and use the comparison method to achieve it. Even if an error occurs, it can be automatically corrected. After the above state processing, the PWM output is always disturbed up and down at the maximum output current. Even if it is disturbed, the sampling is wrong, and the output power of the photovoltaic panel changes, it can be automatically calibrated to the maximum output current, maintaining the system stability and efficient output effect.

[0067] In summary, the beneficial effects brought about by this application include the following:

[0068] The MPPT algorithm control strategy for positive and negative disturbance regulation can be implemented using a low-performance 8-bit MCU;

[0069] It saves a lot of multipliers and filtering algorithms, and the control logic is simple;

[0070] With automatic correction function, it can track the maximum output power of photovoltaic panels in real time.

[0071] The preferred embodiments of the present invention are described above; it should be understood that the present invention is not limited to the above-mentioned specific embodiments, and the devices and structures not described in detail should be understood to be implemented in a common manner in the art; any technician familiar with the art can make many possible changes and modifications without departing from the technical solution of the present invention, or modify them into equivalent embodiments with equivalent changes, which does not affect the essential content of the present invention; therefore, any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention are still within the scope of protection of the technical solution of the present invention.

Claims

1. A PWM-based MPPT control system, characterized in that: It includes an MCU controller, a photovoltaic panel, a drive circuit and an energy storage circuit. The energy storage circuit is connected to the two poles of the photovoltaic panel, and the photovoltaic panel generates electricity to store energy in the battery in the energy storage circuit. The energy storage circuit includes a transistor, an inductor and a sampling resistor, and the MCU controller has a built-in MPPT state machine control strategy, which outputs a PWM wave and controls the drive circuit according to the state machine control strategy; The output of the driving circuit is connected to the gate of the transistor to control the on and off of the energy storage circuit. The source of the transistor is connected to the positive output of the photovoltaic panel, the drain of the transistor is connected to one end of the inductor, and the other end of the inductor is connected to the positive terminal of the battery.

2. The PWM-based MPPT control system according to claim 1, characterized in that: A sampling resistor is connected in series between the negative electrode of the photovoltaic panel and the negative electrode of the battery, and the MCU controller samples the current of the sampling resistor and outputs a PWM wave according to the sampled current value; The energy storage circuit is also provided with a unidirectional conducting diode, the cathode of the diode is connected to the drain of the transistor, and the anode of the diode is connected to the negative electrode of the photovoltaic panel and is grounded.

3. The PWM-based MPPT control system according to claim 2, characterized in that: The MCU controller obtains the sampling current value of the sampling resistor and the output voltage of the photovoltaic panel, and starts the MPPT state machine control when the output voltage of the photovoltaic panel is higher than the set threshold; when the output voltage of the photovoltaic panel is lower than the set threshold, exits the MPPT state machine control strategy.

4. The PWM-based MPPT control system according to claim 3, characterized in that: The MPPT state machine includes the following control states: Update the reference current state: use the current value sampled at the current moment as the reference current; First PWM state: increase the PWM duty cycle by one unit and obtain the corresponding sampled current; Second PWM state: increase the PWM duty cycle by two units and obtain the corresponding sampled current; The third PWM state: increase the PWM duty cycle by three units to obtain the corresponding sampled current; Fourth PWM state: reduce the PWM duty cycle by one unit and obtain the corresponding sampled current; Fifth PWM state: reduce the PWM duty cycle by two units and obtain the corresponding sampled current; Sixth PWM state: reduce the PWM duty cycle by three units and obtain the corresponding sampled current.

5. The PWM-based MPPT control system according to claim 4, characterized in that: When the MCU controller detects that the output voltage of the photovoltaic panel is greater than 4V, the MPPT control strategy is started and the disturbance flag is set to high level 1; when the effective disturbance flag is detected to be 1, the PWM value and the first current value at the current moment are recorded, and the state is switched to the first PWM state.

6. The PWM-based MPPT control system according to claim 5, characterized in that: When the sampled current obtained in the first PWM state is greater than the first current value, the current PWM value and the second current value are recorded, and the state is switched to the second PWM state; When the sampled current obtained in the second PWM state is greater than the second current value, the current PWM value and the third current value are recorded, and the state is switched to the third PWM state; When the sampled current values ​​acquired multiple times in the third PWM state show an increasing trend, the cycle is set in the third PWM state.

7. The PWM-based MPPT control system according to claim 6, characterized in that: When the sampled current obtained in the first PWM state is less than the first current value, the PWM value in the current state is reduced by a duty cycle, and the reference current state is switched to be updated, and the disturbance flag is set to a low level 0; When the sampled current obtained in the second PWM state is less than the second current value, the PWM value in the current state is reduced by two duty cycles, and the reference current state is switched to be updated, and the disturbance flag is set to 0; When the sampled current obtained in the third PWM state is less than the third current value, the PWM value in the current state is reduced by three duty cycles, and the state is switched to update the reference current state, and the disturbance flag is set to 0.

8. The PWM-based MPPT control system according to claim 4, characterized in that: When it is detected that the disturbance flag is set to 0 in the updating reference current state, the PWM value and the fourth current value in the current state are recorded, and the state is switched to the fourth PWM state; When the sampled current obtained in the fourth PWM state is greater than the fourth current value, the current PWM value and the fifth current value are recorded, and the process turns to the fifth PWM state; When the sampled current acquired in the fifth PWM state is greater than the fifth current value, the current PWM value and the sixth current value are recorded, and the state is turned to the sixth PWM state.

9. The PWM-based MPPT control system according to claim 8, characterized in that: When the sampled current obtained in the fourth PWM state is less than the fourth current value, the PWM value in the current state is increased by a duty cycle, and the reference current state is switched to be updated, and the disturbance flag is set to 1; When the sampled current obtained in the fifth PWM state is less than the fifth current value, the PWM value in the current state is increased by two duty cycles, and the reference current state is switched to be updated, and the disturbance flag is set to 1; When the sampled current obtained in the sixth PWM state is less than the sixth current value, the PWM value in the current state is increased by three duty cycles, and the state is switched to update the reference current state, and the disturbance flag is set to 1.

10. The PWM-based MPPT control system according to claim 9, characterized in that: When the sampled current values ​​acquired multiple times in the sixth PWM state show an increasing trend, the cycle is set in the sixth PWM state.

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