A variable clamping control method for maximum power tracking access transient

Abstract

The application is suitable for the field of power electronics, and provides a variable clamping control method for maximum power tracking access transient state, which comprises the following steps: S1, setting a voltage collected and sent to an MPPT as a clamping value of an output MPPT voltage reference; S2, setting a fixed deviation for a voltage feedback quantity and a voltage reference value according to the clamping value; and S3, eliminating unreasonable clamping value setting and accelerating an MPPT loop takeover process through a pressure difference existing between the feedback quantity and the voltage reference value. The clamping value is dynamically changed through a simple hardware circuit, the transient state of the MPPT loop takeover process is improved, the system robustness is improved, the SA curve change can be arbitrarily adapted, and the problem that the MPPT cannot be entered due to unreasonable clamping value setting is solved.

Description

Technical Field

[0001] This invention belongs to the field of power electronics technology, and in particular relates to a variable clamping control method for improving the transient state of maximum power point tracking access. Background Technology

[0002] Maximum power point tracking (MPPT) technology is widely used in photovoltaic power generation, stratospheric airships, and spacecraft. It's a method to improve energy efficiency based on the output characteristics of solar cells. According to energy supply and demand balance, when energy demand is less than the maximum output power of the solar cell, MPPT is not needed. In this case, the circuit operates in other control loops, such as the output voltage loop (OVR) or the output current loop (OCR), determined by the load demand. When the energy demand is greater than or equal to the maximum output power of the solar cell, to achieve maximum energy utilization, the system controls the input at the maximum power point of the solar cell. This is often achieved through input voltage loop (IVR), input current loop (ICR), or power IPR control, hereinafter referred to as the MPPT loop. This means that in systems with MPPT functionality, most have at least two control loops, and loop switching may occur during load increases or decreases. MPPT technology can be implemented using two methods: digital circuits and analog circuits, which obtain the maximum power point through algorithms and hardware, respectively. Digital circuits are more expensive but more flexible, while analog circuits are cheaper but have relatively poorer steady-state and dynamic characteristics. This patent aims to optimize the loop switching process of analog circuits. Summary of the Invention

[0003] The purpose of this invention is to provide a variable clamping control method for maximum power point tracking access transients, aiming to solve the above-mentioned technical problems.

[0004] This invention is implemented as follows: a variable clamping control method for maximum power point tracking (MPPT) access transients, the variable clamping control method for MPPT access transients includes the following steps:

[0005] S1. Set the voltage acquired and fed into the MPPT to the clamping value of the output MPPT voltage reference;

[0006] S2. Set a fixed deviation between the voltage feedback value and the voltage reference value based on the clamping value;

[0007] S3. Eliminate unreasonable clamping value settings and accelerate the MPPT loop takeover process by using the voltage difference between the feedback quantity and the voltage reference value.

[0008] A further technical solution of the present invention is to add an operational amplifier and a diode to the variable clamping control to accelerate the takeover of the MPPT.

[0009] A further technical solution of the present invention is: the MPPT circuit with dynamic clamping in the accelerated MPPT loop control includes an MPPT circuit and a resistor R.i Capacitor C i Operational amplifier CMP and diode D, input k v U SA Connect the input terminal of the MPPT circuit and the positive input of the operational amplifier CMP respectively. Connect the output terminal of the operational amplifier CMP to the anode of the diode D. Connect the output terminal of the MPPT circuit to the resistor R. i One end, resistor R i The other end is combined with the cathode of the diode D to output U. MPyef resistance R i Also via the capacitor C i Grounding.

[0010] A further technical solution of the present invention is that when the load power is small, the variable clamping control method operates in the output voltage loop, and the output voltage is stable.

[0011] A further technical solution of the present invention is: when the load increases, the energy required by the variable clamping control method is greater than the maximum power. As the Enable signal is set high, the system enters the MPPT clamping transient state for a short time and the output voltage overshoot is lower.

[0012] A further technical solution of the present invention is: when the output characteristics change, the input voltage is controlled by the MPPT loop, and the operating point gradually decreases.

[0013] A further technical solution of the present invention is: when the load decreases, the system exits MPPT and the output voltage is re-stabilized under OVR control.

[0014] A further technical solution of the present invention is: in the case of increased load, the variable clamping control method expects the MPPT loop to eventually take over, and the energy utilization rate is optimal when entering the MPPT loop control according to the set reference voltage.

[0015] The beneficial effects of this invention are: by dynamically changing the clamping value with minimal hardware circuitry, the transient response of the MPPT loop takeover process is improved; simultaneously, it can arbitrarily adapt to changes in the SA curve, thereby enhancing system robustness. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the traditional MPPT circuit implementation without clamping.

[0017] Figure 2 This is a schematic diagram of the traditional MPPT circuit with clamping.

[0018] Figure 3 This is a schematic diagram of an MPPT circuit with dynamic clamping provided in an embodiment of the present invention.

[0019] Figure 4 This is a schematic diagram of the circuit model provided in an embodiment of the present invention.

[0020] Figure 5 This is a schematic diagram of key waveforms provided in an embodiment of the present invention. Detailed Implementation

[0021] OVR Output voltage regulator Output voltage loop regulator OCR Outputcurrentregulator Output current loop regulator IVR Input voltage regulator Input voltage loop regulator ICR Input currentregulator Input current loop regulator SA Solararray Solar cells

[0022] like Figure 1-5 As shown, the variable clamping control method for improving the transient state of maximum power point tracking provided by the present invention includes: S1, setting the voltage collected and fed into the MPPT as the clamping value of the output MPPT voltage reference; S2, setting a fixed deviation between the voltage feedback quantity and the voltage reference value according to the clamping value; S3, eliminating unreasonable clamping value settings and accelerating the MPPT loop takeover process by the voltage difference between the feedback quantity and the voltage reference value.

[0023] In the MPPT function circuit implemented by hardware circuit, the initial value is often 0V or a fixed clamping value. This is because the maximum power point of the solar cell is affected by many factors, so it is impossible to make a simple prediction of the maximum power point. Figure 1-2 The traditional MPPT circuit implementation is given. The "MPPT circuit" can use methods such as conductance increment, and its input is the voltage and current of the solar cell: k v U SA k i I SA This function is enabled by the Enable signal (Disable and Enable signals are not logically related), and its output typically passes through R, which acts as an integrator. i C i A stable reference voltage U at the maximum power point is obtained. MPref Clearly, for the MPPT circuit configuration without clamping, U MPref The voltage increases from 0V, and the transient process is longer.

[0024] Because changes in illumination are slow and rarely abrupt, the tracking period of MPPT is generally low, ranging from hundreds of hertz to thousands of hertz. However, the system load exacerbates the transient process.

[0025] It should be noted that since maximum power point tracking technology is mostly implemented by dynamically operating near (or on either side of) the maximum power point, the reference voltage U MPref The initial value, or (lower) clamping value, cannot be higher than the maximum power point voltage that may occur during the operation of the solar cell, and a certain margin needs to be reserved, otherwise it will lead to failure of MPPT.

[0026] Therefore, this patent proposes a method of clamping via input voltage to accelerate the takeover process of the MPPT loop. The improved circuit diagram is shown below. Figure 4 As shown, the voltage of the solar cell fed into the MPPT is used as the clamping value for the output MPPT voltage reference. Only a few circuits, such as operational amplifiers and diodes, are needed to accelerate the MPPT function takeover. The operational amplifier is configured as a follower or proportional amplifier, and the diode acts as a lower clamp, while maintaining a fixed deviation between the voltage feedback (the solar cell voltage fed into the MPPT) and the voltage reference value to ensure that the clamping does not affect the normal closed-loop operation of the MPPT circuit. Because there is always a diode voltage difference V between the feedback and the voltage reference clamping value... D Therefore, there will be no problem of being unable to enter MPPT due to an unreasonable clamp value setting.

[0027] The circuit was built and verified in the SIMetrix simulation circuit, such as... Figure 4 As shown, two identical Buck circuits are connected in parallel, namely module 1 and module 2. The Buck circuit parameters are given in Table 1. The Buck output voltages are connected in parallel to form a bus, which is connected to the step load. R is composed of S8 connected in parallel with S1. load The Buck input is connected to two SAs respectively. To simulate different operating conditions, the input and output will change. The Buck is controlled by the output voltage loop. When the load is less than the maximum output power of the solar cell, it outputs a stable 90V bus voltage. When the output load demand exceeds the maximum power of the input solar cell, the circuit will be taken over by the MPPT loop, which is implemented through the input voltage loop. The change in the input SA represents the sudden impact of factors such as shading on the solar cell, and the change in the output load represents the impact of a step load. The parameters are given in Table 2. Since the expected output voltage is 90V, the circuit is a buck circuit. Therefore, the clamping voltage in the traditional MPPT circuit form for comparison is set to 90V * voltage sampling factor. Here, the voltage sampling factor is 0.1, and the MPPT uses the incremental conductance method.

[0028] Table 1 Key parameters of the simulation circuit

[0029]

[0030] Table 2 Input / Output Parameters

[0031]

[0032] Based on the changes in input and output, the 150ms of circuit simulation can be divided into 5 stages, P1 to P5, as shown in the figure, corresponding to Table 2. The waveforms of the key points are shown in... Figure 5 The information is provided in the text.

[0033] Figure 5The P1 stage is the circuit setup process. At this time, the load power is relatively small, and the system eventually operates in the output voltage loop. The output voltage uBUS stabilizes at 90V. At this point, the clamping voltage of the traditional MPPT circuit has completed its pre-charge and is 9V-V. D V D This represents the diode voltage drop.

[0034] In Phase P2, the load increases, and the energy demand exceeds the maximum power of the solar cells. As the Enable signal goes high, the system enters MPPT (Multi-Level Transmission). It can be seen that the variable clamping control method proposed in this patent has a shorter transient time and lower output voltage overshoot compared to the traditional fixed clamping method. After the loop take-off transient...

[0035] In the P3 stage, the output characteristics of the solar cell in Buck module 1 change. As can be seen, the input voltage is controlled by the MPPT loop, and the operating point gradually changes from 115V to 100V.

[0036] During the P4 phase, the load decreases, the system exits MPPT, and the output voltage uBUS stabilizes again at 90V under OVR control.

[0037] In the P5 stage, the load increases, and it is expected that the MPPT loop will eventually take over to achieve optimal energy utilization. In the traditional Buck module 1, the maximum power point voltage of the solar cell drops to 100V, approaching the set fixed clamping value. The MPPT circuit cannot find the maximum power point, causing the system to fail to enter the MPPT loop. The variable clamping control method proposed in this patent does not limit the initial reference voltage, thus it can still successfully enter the MPPT loop and achieve MPPT control.

[0038] In summary, this patent demonstrates how dynamically changing the clamping value with minimal hardware circuitry improves the transient response of the MPPT loop takeover process, while also adapting arbitrarily to changes in the SA curve, thereby enhancing system robustness.

[0039] 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, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A variable clamping control method for maximum power point tracking (MPPT) with transient response, characterized in that, The maximum power point tracking access transient variable clamping control method includes the following steps: S1. Set the voltage collected and fed into the MPPT circuit to the clamping value of the output MPPT voltage reference; S2. Set a fixed deviation between the voltage feedback value and the voltage reference value based on the clamping value; the voltage feedback value is the voltage fed into the MPPT circuit. S3. By utilizing the voltage difference between the voltage feedback value and the voltage reference value, the situation of unreasonable clamping value setting is eliminated, and the MPPT loop takeover process is accelerated. In this variable clamping control method, an operational amplifier CMP and a diode D are added to accelerate the takeover of the MPPT; The MPPT circuit with dynamic clamping in the accelerated MPPT loop connection includes the MPPT circuit and resistors. R i ,capacitance C i Operational amplifiers (CMPs) and diodes D ,enter k v U SA Connect the input terminal of the MPPT circuit and the positive input of the operational amplifier CMP respectively. The negative input of the operational amplifier CMP is connected to the diode. D The anode of the operational amplifier CMP is connected to the diode. D The anode of the MPPT circuit is connected to the resistor. R i One end, resistor R i The other end is connected to the diode D cathode merging output U MPyef ,resistance R i The other end is also via the capacitor C i Grounding.

2. The variable clamping control method for maximum power point tracking access transients according to claim 1, characterized in that, When the load power is low, this variable clamping control method operates in the output voltage loop, resulting in a stable output voltage.

3. The variable clamping control method for maximum power point tracking access transients according to claim 2, characterized in that, When the load increases, the energy required by this variable clamping control method is greater than the maximum power. As the Enable signal goes high, the system enters the MPPT clamping transient state for a short time and the output voltage overshoot is lower. The Enable signal is an enable signal used to enable the MPPT control circuit.

4. The variable clamping control method for maximum power point tracking access transients according to claim 3, characterized in that, When the output characteristics change, the input voltage is controlled by the MPPT loop, and the operating point gradually decreases.

5. The variable clamping control method for maximum power point tracking access transients according to claim 4, characterized in that, In this variable clamping control method, when the load decreases, the system exits MPPT and the output voltage stabilizes again under the control of the output voltage loop OVR. In this variable clamping control method, the MPPT loop ultimately takes over when the load increases, achieving optimal energy utilization. It enters the MPPT loop control based on the set voltage reference value.

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