Photovoltaic system MPPT analog circuit based on PO algorithm

Abstract

The invention discloses a method based on Pamp; the photovoltaic system MPPT analog circuit based on the O algorithm comprises a photovoltaic array, a Boost circuit, a voltage and current acquisition module, an analog multiplier, a differentiator, a hysteresis comparator, an XNOR gate circuit, a sampling hold circuit, an integrator and a PWM generator. The input end of the analog multiplier is respectively connected with the output voltage and current of the voltage and current acquisition module; one differentiator is connected with the output of the analog multiplier, and the other differentiator is connected with the output voltage of the voltage and current acquisition module; the input end of the XNOR gate circuit is respectively connected with the outputs of the two hysteresis comparators; and the output of the PWM generator is connected to a base electrode of a switching tube in the Boost circuit and is used for controlling the switching tube. The maximum power point tracking circuit has the advantage that maximum power point tracking of the photovoltaic system is achieved through the analog circuit.

Description

Technical Field

[0001] The present application relates to the field of photovoltaic technology, and in particular to a photovoltaic system MPPT simulation circuit based on a P&O algorithm. Background Art

[0002] Solar energy is a clean energy with great potential. Due to its abundant resource availability, wide distribution, low greenhouse gas emissions and environmental pollution, it has been widely used to replace traditional energy. Solar photovoltaic power generation has great potential in the development of renewable energy. Its universality, low pollution and low maintenance cost have attracted people's attention. However, the output power characteristics of solar photovoltaic arrays are nonlinear. Under the condition of changing atmospheric conditions and load variables, it is difficult to utilize all available solar energy without a controlled system. In order to obtain the best performance, it is necessary to force the system to operate at the optimal power point. The common method to solve this problem is the maximum power point tracking (MPPT) system, which enables the system to output at maximum power.

[0003] The maximum power point tracking algorithm is the MPPT algorithm. The P&O algorithm is a commonly used algorithm in the MPPT algorithm of photovoltaic systems. The MPPT algorithm is usually implemented digitally to achieve the same response time for solar panels when the environment changes. The digital implementation of the MPPT algorithm is more complicated than the analog algorithm. In addition, when environmental conditions change rapidly, the digital MPPT algorithm cannot operate well. Summary of the invention

[0004] The present application provides a photovoltaic system MPPT simulation circuit based on the P&O algorithm, which has the advantage of realizing maximum power point tracking of the photovoltaic system through an analog circuit, so that it can be integrated with a DC-DC controller to make up for the defects of structural complexity and high cost of traditional digital MPPT controllers. Under the conditions of changes in ambient temperature and irradiance, it can quickly track the maximum power point and has a better tracking effect.

[0005] The above-mentioned object of the present application is achieved through the following technical solutions, a photovoltaic system MPPT simulation circuit based on the P&O algorithm, comprising:

[0006] Photovoltaic arrays;

[0007] Boost circuit, connected to the output of the photovoltaic array and used to supply power to the load or battery;

[0008] Voltage and current acquisition module, used to collect the output voltage and current of the photovoltaic array;

[0009] An analog multiplier, whose input terminals are respectively connected to the output voltage and current of the voltage and current acquisition module;

[0010] Differentiator: There are two differentiators, one of which is connected to the output of the analog multiplier, and the other is connected to the output voltage of the voltage and current acquisition module;

[0011] A hysteresis comparator, comprising two hysteresis comparators, connected to the output ends of the two differentiators respectively, for determining changes in output signals of the differentiators;

[0012] An XNOR gate circuit, whose input terminals are respectively connected to the outputs of two hysteresis comparators;

[0013] A sample-and-hold circuit is connected to the output end of the XNOR gate circuit;

[0014] an integrator connected to the output end of the sample-and-hold circuit;

[0015] And a PWM generator is used to generate high and low level signals according to the output of the integrator, and the output of the PWM generator is connected to the base of the switch tube in the Boost circuit for controlling the switch tube.

[0016] Furthermore, the Boost circuit includes an inductor L1, a switch tube Q1, a diode D1 and a capacitor C1. The switch tube Q1 is connected in parallel with a second diode whose conduction direction is opposite to that of the switch tube Q1.

[0017] Furthermore, in the Boost circuit, a capacitor C2 is connected in parallel between the positive and negative electrodes of the circuit.

[0018] Furthermore, the PWM generator includes a second comparator and a sawtooth signal generator, one input terminal of the second comparator is connected to the output of the integrator, and the other input terminal of the second comparator is connected to the output of the sawtooth signal generator.

[0019] Furthermore, the integrator is used to generate a reference voltage Vref according to the output of the sample and hold circuit, and the reference voltage Vref satisfies:

[0020] When the XNOR gate circuit outputs a high level signal, the reference voltage Vref is higher than the sawtooth signal Vsawtooth;

[0021] When the XNOR gate circuit outputs a low level signal, the reference voltage Vref is lower than the sawtooth signal Vsawtooth;

[0022] The output of the integrator is connected to the positive input terminal of the second comparator.

[0023] To sum up, the beneficial effects of the present application are: the maximum power point tracking of the photovoltaic system is realized through analog circuits, which can be integrated with a DC-DC controller to make up for the defects of the traditional digital MPPT controller's structural complexity and high cost. Under the conditions of changes in ambient temperature and irradiance, the maximum power point can be quickly tracked, and a better tracking effect can be achieved. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is the structure diagram of the MPPT simulation circuit of the photovoltaic system based on the P&O algorithm in this application. Figure 1 Among them, 1. Photovoltaic array; 2. Voltage and current acquisition module; 3. Analog multiplier; 4. Differentiator; 5. Hysteresis comparator; 6. XNOR gate circuit; 7. Sample and hold module; 8. Integrator; 9. PWM generator;

[0025] Figure 2 This embodiment is a schematic diagram of the working process of the MPPT simulation circuit of the photovoltaic system based on the P&O algorithm in this application;

[0026] Figure 3 This is an experimental diagram of the S&H working mode in a specific embodiment of the present application. XNOR is used as the input signal, which is sampled and held by the S&H module. The rising edge of the S&H clock activates the sampling mode, and the falling edge activates the holding mode.

[0027] Figure 4 This is a PWM working mode experimental diagram of a specific embodiment of the present application. The output signal of the S&H module circuit is input into the integrator to generate a reference voltage, which is compared with the sawtooth signal. When Vref>Vsawtooth, the PWM output is a high level '1', and when Vref<Vsawtooth, the PWM output is a low level '0'. Using this working principle, the analog MPPT control circuit adjusts the switch device in the BOOST circuit through the PWM wave to track the maximum power of the photovoltaic panel.

[0028] Figure 5 This is an experimental diagram of the MPPT tracking effect in a specific embodiment of the present application, which is an experimental result of a photovoltaic MPPT simulation circuit based on the P&O algorithm under a standard steady-state (irradiance 1000, standard temperature 25°C) test; the results show that the tracking power Power has reached the maximum output power Pmax of the photovoltaic panel, indicating that the maximum power tracking circuit has good performance under minimum oscillation conditions. DETAILED DESCRIPTION

[0029] The specific implementation of the present application is described in detail below with reference to the accompanying drawings.

[0030] Embodiment: A photovoltaic system MPPT simulation circuit based on P&O algorithm, such as Figure 1 , including a photovoltaic array 1, a Boost circuit, a voltage and current acquisition module 2, an analog multiplier 3, a differentiator 4, a hysteresis comparator 5, an XNOR gate circuit 6, a sample and hold circuit 7, an integrator 8 and a PWM generator 9.

[0031] The Boost circuit is connected to the output of the photovoltaic array and is used to supply power to the load or battery. The Boost circuit includes an inductor L1, a switch tube Q1, a diode D1 and a capacitor C1. The switch tube Q1 is connected in parallel with a second diode whose conduction direction is opposite to that of the switch tube Q1. In the Boost circuit, the positive and negative poles of the circuit are connected in parallel with a capacitor C2.

[0032] The voltage and current acquisition module is used to collect the output voltage and current of the photovoltaic array.

[0033] The input ends of the analog multiplier are respectively connected to the output voltage and current of the voltage and current acquisition modules.

[0034] There are two differentiators, one of which is connected to the output of the analog multiplier, and the other is connected to the output voltage of the voltage and current acquisition module.

[0035] The hysteresis comparator includes two, which are respectively connected to the output ends of the two differentiators and are used to judge the change of the output signal of the differentiator.

[0036] The input ends of the XNOR gate circuit are respectively connected to the outputs of the two hysteresis comparators.

[0037] The sample-and-hold circuit is connected to the output end of the XNOR gate circuit.

[0038] The integrator is connected to the output end of the sample-and-hold circuit;

[0039] A PWM generator is used to generate high and low level signals according to the output of the integrator, and the output of the PWM generator is connected to the base of the switch tube in the Boost boost circuit for controlling the switch tube. The PWM generator includes a second comparator and a sawtooth signal generator, one input end of the second comparator is connected to the output of the integrator, and the other input end is connected to the output of the sawtooth signal generator.

[0040] The integrator is used to generate a reference voltage Vref according to the output of the sample-and-hold circuit. The reference voltage Vref satisfies:

[0041] When the XNOR gate circuit outputs a high level signal, the reference voltage Vref is higher than the sawtooth signal Vsawtooth;

[0042] When the XNOR gate circuit outputs a low level signal, the reference voltage Vref is lower than the sawtooth signal Vsawtooth;

[0043] The output of the integrator is connected to the positive input terminal of the second comparator.

[0044] refer to Figure 1, the output voltage and current of the photovoltaic panel are multiplied to obtain power, and the output power and panel voltage signals are sent to differentiators ① and ② respectively. The trend of power and panel output voltage is obtained through differentiators ① and ②. The output signals after the differentiators are dPpv / dt and dVpv / dt. The derivatives of power and voltage are input to the hysteresis comparator to obtain the sign signals of dPpv / dt and dVpv / dt. The sign signal is the input signal of the XNOR gate circuit, which is used to determine whether the two signs are in phase or in opposite phase. The output of the XNOR gate circuit is the input of the sample and hold circuit (S&H). The S&H with fast acquisition time reduces the sampling interval time and power failure cycle. In addition, the S&H has a low drop rate, which can reduce the deviation between the working point and MPP of the photovoltaic panel during the sampling period. An integrator is placed after the output of the S&H module circuit to generate the Vref voltage signal, and then a parallel capacitor is used to reduce the voltage oscillation. Finally, Vref is compared with the 200kHz sawtooth wave to generate a PWM waveform to drive the switch tube of the DC / DC boost converter. The duty cycle of the BOOST boost circuit is changed by controlling the on and off of the switch tube, and finally MPPT is achieved.

[0045] The P&O perturbation observation method is used to track the change in the output power of the photovoltaic cell after each voltage perturbation at any time in the MPPT in order to obtain the maximum power. When the output voltage is higher, the output power is greater, and the next perturbation will further increase the voltage until the maximum power point is reached. When the output voltage decreases, the output power will decrease as the output voltage decreases, and the next perturbation will be an increase in the voltage level. When the output voltage increases, if the output power decreases, the next perturbation will reduce the output voltage. When the output voltage decreases and the output power increases, the next perturbation will be to further reduce the voltage until the maximum power point is reached. The P&O algorithm perturbation rules in Table 1 are converted into the logical conversion truth table in Table 2, where an increase in the change is represented by state 1 and a decrease in the change is represented by state 0.

[0046] Table 1 P&O algorithm rules

[0047]

[0048] Table 2 P&O logic conversion truth table

[0049]

[0050] In Table 2, when the next disturbance output is state 1, the two inputs are the same, and when the next disturbance output is state 0, the two inputs are opposite. The MPPT based on the P&O algorithm works on the XOR logic.

[0051] Combine the following Figure 2-5 Specific introduction to the implementation methods and implementation results of the present invention:

[0052] First, after the BOOST boost circuit is connected to the photovoltaic array and powered on, the PWM generator generates a high-level signal, the switch tube Q1 is turned on, the photovoltaic array current Ipv increases, the output voltage Vpv decreases, and the output power of the photovoltaic array gradually increases. The voltage and current acquisition module collects the output voltage and current signals of the photovoltaic array in real time, and obtains the power Ppv through the analog multiplier product operation. Ppv and Ipv are respectively sent to differentiators ① and ② to obtain the output signals dPpv / dt and dVpv / dt. The sign signals of dP / dt and dVpv / dt are further judged through the hysteresis comparator output.

[0053] Before the operating power of the photovoltaic system reaches the MPPT, if the tracking direction is correct, the dPpv / dt sign signal is positive, the power change signal Vp increases, the dVpv / dt sign signal is positive, the voltage change signal Vv increases, and the XNOR gate circuit output determines that the next disturbance is an increase, that is, XNOR_output increases. The output signal of the S&H module circuit is input to the integrator to generate a reference voltage Vref, which is compared with the sawtooth signal Vsawtooth. At this time, Vref>Vsawtooth, the PWM generator output is high, Q1 is turned on, and the high-level signal driving the switch tube Q1 during the S&H sampling period will be maintained until the next S&H hold signal appears;

[0054] After the operating power of the photovoltaic system exceeds the MPPT, if the tracking direction is wrong, the dPpv / dt sign signal is negative, the power change signal Vp decreases, the dVpv / dt sign signal is positive, the voltage change signal Vv increases, and the XNOR gate circuit output determines that the next disturbance is a decrease, that is, XNOR_output decreases. The output signal of the S&H module circuit is input to the integrator to generate a reference voltage Vref, which is compared with the sawtooth signal Vsawtooth. At this time, Vref<Vsawtooth, the PWM generator output is low, Q1 is turned off, and the low-level signal driving the switch tube Q1 during the S&H hold period will be maintained until the next S&H sampling signal appears;

[0055] Before the operating power of the photovoltaic system reaches the MPPT, if the tracking direction is wrong, the dPpv / dt sign signal is negative, the power change signal Vp decreases, the dVpv / dt sign signal is negative, the voltage change signal Vv decreases, and the XNOR gate circuit output determines that the next disturbance is an increase, that is, XNOR_output increases. The output signal of the S&H module circuit is input to the integrator to generate a reference voltage Vref, which is compared with the sawtooth signal Vsawtooth. At this time, Vref>Vsawtooth, the PWM generator output is high, Q1 is turned on, and the high-level signal driving the switch tube Q1 during the S&H sampling period will be maintained until the next S&H hold signal appears;

[0056] After the operating power of the photovoltaic system exceeds the MPPT, if the tracking direction is correct, the dPpv / dt sign signal is positive, the power change signal Vp increases, the dVpv / dt sign signal is negative, the voltage change signal Vv increases, and the XNOR gate circuit output determines that the next disturbance is a decrease, that is, XNOR_output decreases. The output signal of the S&H module circuit is input to the integrator to generate a reference voltage Vref, which is compared with the sawtooth signal Vsawtooth. At this time, Vref<Vsawtooth, the PWM generator output is low, Q1 is turned off, and the low-level signal driving the switch tube Q1 during the S&H hold period will be maintained until the next S&H sampling signal appears. The S&H circuit module clock is set to: D=0.5, F sh =500Hz, T sh =0.002s, T on =T off =0.001s.

[0057] The photovoltaic system executes in the above four modes cyclically. The working process of the system is as follows: Figure 2 The output power of the system will oscillate around the maximum power point to achieve maximum power point tracking. By selecting appropriate device parameter indicators and sawtooth wave signals, smaller oscillations will be generated, and the system will have good adjustability and dynamics.

[0058] In order to verify the effectiveness of the analog circuit of the present invention in realizing MPPT, the Chromas 62150H-600s photovoltaic simulator is used as the photovoltaic array input to simulate and verify the circuit. The models and specifications of each component in the circuit are as follows: Figure 1 As shown, the following experimental results are obtained:

[0059] (1) After the circuit is powered on, the photovoltaic system only takes 600us to track the MPPT and remain stable;

[0060] (2) The output power reaches 58W, and the MPPT control circuit is relatively well designed for irradiance changes. The average MPPT efficiency at different irradiance levels reaches 99.99%.

[0061] Figure 3 The experimental diagram of S&H working mode is shown, with XNOR as the input signal, sampled and held by the S&H module. The rising edge of the S&H clock activates the sampling mode, and the falling edge activates the holding mode.

[0062] Figure 4 The experimental diagram of PWM working mode is shown. The output signal of the S&H module circuit is input into the integrator to generate a reference voltage, which is compared with the sawtooth signal. When Vref>Vsawtooth, the PWM output is high level '1', and when Vref<Vsawtooth, the PWM output is low level '0'. Using this working principle, the analog MPPT control circuit adjusts the switch device in the BOOST circuit through the PWM wave to track the maximum power of the photovoltaic panel.

[0063] Figure 5 The MPPT tracking effect experimental diagram is shown. The photovoltaic MPPT simulation circuit based on the P&O algorithm is in the standard steady state (irradiance 1000W / m 2 The experimental results under the test of standard temperature (25℃) are shown. The results show that the tracking power Power has reached the maximum output power Pmax of the photovoltaic panel, indicating that the maximum power tracking circuit has good performance under the minimum oscillation condition. Compared with other methods, this method has higher advancement.

[0064] The present invention will be further described below in conjunction with the accompanying drawings:

[0065] Figure 1 The structure diagram of a photovoltaic system MPPT simulation circuit implementation method based on the P&O algorithm is shown. Figure 1 As shown, the components of the present invention mainly include: a photovoltaic array 1, a Boost circuit, a voltage and current acquisition module 2, an analog multiplier 3, a differentiator 4, a hysteresis comparator 5, an XNOR gate circuit 6, a sampling and holding module 7, an integrator 8, and a PWM generator 9.

[0066] Figure 2 A control flow chart of the MPPT simulation circuit implementation method for a photovoltaic system based on the P&O algorithm is shown.

[0067] Figure 3 This is the experimental diagram of the S&H working mode. The XNOR is used as the input signal, which is sampled and held by the S&H module. The rising edge of the S&H clock activates the sampling mode, and the falling edge activates the holding mode.

[0068] Figure 4 The experimental diagram of PWM working mode is shown in Figure 1. The output signal of the S&H module circuit is input into the integrator to generate a reference voltage, which is compared with the sawtooth signal. When Vref>Vsawtooth, the PWM output is a high level '1', and when Vref<Vsawtooth, the PWM output is a low level '0'. Using this working principle, the analog MPPT control circuit adjusts the switch device in the BOOST circuit through the PWM wave to track the maximum power of the photovoltaic panel.

[0069] Figure 5 This is the MPPT tracking effect experimental diagram. The photovoltaic MPPT simulation circuit based on the P&O algorithm is in the standard steady state (irradiance 1000W / m 2 The experimental results under the test of standard temperature (25℃) are shown. The results show that the tracking power Power has reached the maximum output power Pmax of the photovoltaic panel, indicating that the maximum power tracking circuit has good performance under the minimum oscillation condition. Compared with other methods, this method has higher advancement.

[0070] The above is only a preferred implementation of the present application. It should be pointed out that a person skilled in the art can make several modifications and improvements without departing from the inventive concept of the present application, and these all fall within the scope of protection of the present application.

Claims

1. A photovoltaic system MPPT simulation circuit based on P&O algorithm, characterized in that: include: Photovoltaic arrays; Boost circuit, connected to the output of the photovoltaic array and used to supply power to the load or battery; Voltage and current acquisition module, used to collect the output voltage and current of the photovoltaic array; An analog multiplier, whose input terminals are respectively connected to the output voltage and current of the voltage and current acquisition module; Differentiator: There are two differentiators, one of which is connected to the output of the analog multiplier, and the other is connected to the output voltage of the voltage and current acquisition module; A hysteresis comparator, comprising two hysteresis comparators, connected to the output ends of the two differentiators respectively, for determining changes in output signals of the differentiators; An XNOR gate circuit, whose input terminals are respectively connected to the outputs of two hysteresis comparators; A sample-and-hold circuit is connected to the output end of the XNOR gate circuit; an integrator connected to the output end of the sample-and-hold circuit; And a PWM generator is used to generate high and low level signals according to the output of the integrator, and the output of the PWM generator is connected to the base of the switch tube in the Boost circuit for controlling the switch tube.

2. The photovoltaic system MPPT simulation circuit based on the P&O algorithm according to claim 1, characterized in that: The Boost circuit includes an inductor L1, a switch tube Q1, a diode D1 and a capacitor C1. The switch tube Q1 is connected in parallel with a second diode whose conduction direction is opposite to that of the switch tube Q1.

3. The photovoltaic system MPPT simulation circuit based on the P&O algorithm according to claim 2, characterized in that: In the Boost circuit, capacitor C2 is connected in parallel between the positive and negative poles of the circuit.

4. The photovoltaic system MPPT simulation circuit based on the P&O algorithm according to claim 1, characterized in that: The PWM generator includes a second comparator and a sawtooth signal generator, wherein one input terminal of the second comparator is connected to the output of the integrator, and the other input terminal of the second comparator is connected to the output of the sawtooth signal generator.

5. The photovoltaic system MPPT simulation circuit based on the P&O algorithm according to claim 4, characterized in that: The integrator is used to generate a reference voltage Vref according to the output of the sample-and-hold circuit. The reference voltage Vref satisfies: When the XNOR gate circuit outputs a high level signal, the reference voltage Vref is higher than the sawtooth signal Vsawtooth; When the XNOR gate circuit outputs a low level signal, the reference voltage Vref is lower than the sawtooth signal Vsawtooth; The output of the integrator is connected to the positive input terminal of the second comparator.

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