Self-adaptive anti-overload droop control method of photovoltaic direct current converter

Abstract

The invention discloses a self-adaptive anti-overload droop control method of a photovoltaic direct current converter, which aims at the overload problem of a photovoltaic system under traditional droop control, and realizes effective overload suppression of the photovoltaic system under illumination fluctuation by introducing dp / dv as a droop control correction. Compared with an existing method, the method has the advantages that mode switching and capacity prediction are not needed, and a droop control curve can be adaptively adjusted according to output voltage and current; (2) under the sudden change of illumination, the voltage adjustment is relatively stable, and the control performance is good; and (3) the control system is simpler. In conclusion, the method has very high engineering practical value.

Description

Technical Field

[0001] The present invention belongs to the technical field of power electronics, and in particular relates to an adaptive anti-overload droop control method for a photovoltaic DC converter. Background Art

[0002] Photovoltaic power generation, as a clean and renewable energy form, has been widely used around the world. Among them, DC microgrids based on large-scale photovoltaic power sources have gradually become a current research hotspot due to their high efficiency in energy conversion and convenient networking.

[0003] Photovoltaic panels are generally connected to the DC bus through a DC converter, which controls the energy output of the photovoltaic panels. Droop control is widely used as the underlying control method because it can achieve passive power sharing. Traditional droop control is generally based on a fixed droop coefficient control method with fixed capacity, so that the power supply can achieve power sharing in proportion to capacity within the safe operating range. However, since the available capacity of photovoltaics is affected by environmental conditions (light / temperature), under traditional droop control, photovoltaic power supplies may be overloaded due to the decrease in available capacity. Therefore, photovoltaic power supplies need to be supplemented with overload prevention strategies under droop control.

[0004] Traditional overload prevention strategies generally use mode switching, that is, when the output power of the photovoltaic power source is less than the available capacity, it operates in the droop control mode; when the output power of the photovoltaic power source reaches the maximum, it switches to the maximum power output mode. However, mode switching depends on the accurate judgment of the available photovoltaic capacity, and the switching process often brings energy fluctuations and deteriorates the power quality. Therefore, finding an efficient overload protection droop control method has become an urgent problem to be solved. Summary of the invention

[0005] The purpose of the present invention is to provide a simple and efficient overload protection droop control method. The method corrects the reference voltage of the droop control based on the real-time dp / dv value of the photovoltaic panel, without mode switching and measurement of available capacity.

[0006] In order to achieve the above-mentioned invention object, the present method adopts the following technical scheme:

[0007] An adaptive anti-overload droop control method for a photovoltaic DC converter, characterized in that the method comprises the following steps:

[0008] The voltage of the photovoltaic panel v pv , the output port voltage V is sampled, and the photovoltaic panel current i pv Take samples;

[0009] Calculate the dp / dv value based on the collected photovoltaic panel voltage and current;

[0010] The voltage controller controls the output port voltage at the voltage reference value according to the voltage reference value given by the adaptive droop control;

[0011] The pulse width modulation signal is generated according to the duty cycle given by the voltage controller to control the IGBT.

[0012] The method of the present invention adds a correction value based on dp / dv to the traditional droop control method, so that the photovoltaic power source passively participates in power sharing and prevents overload under sudden changes in light intensity. Moreover, the overload protection of the photovoltaic system does not require mode switching and capacity prediction, and the droop control curve can be adaptively adjusted according to the output voltage and current.

[0013] Furthermore, in the voltage controller, the voltage reference value V is calculated according to the following method: ref .

[0014]

[0015] Where: V ref is the reference value of the photovoltaic power supply output voltage, V * is the voltage rating, R is the droop factor, It is obtained based on the real-time output voltage and current of the photovoltaic panel, and k is the correction proportional coefficient.

[0016] Furthermore, the correction proportional coefficient is specifically set as follows:

[0017]

[0018] Where: V max and V min are the maximum and minimum values ​​of the DC bus voltage, dp / dv max It is the maximum value of dp / dv.

[0019] Due to the adoption of the technical solution of the present invention, the present invention can enable the photovoltaic power source to passively participate in power sharing, while preventing overload under sudden changes in light intensity; the photovoltaic system's overload protection does not require mode switching and capacity prediction, and the droop control curve can be adaptively adjusted according to the output voltage and current. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a photovoltaic power generation control block diagram of the present invention.

[0021] Figure 2 The photovoltaic output characteristic curve of the present invention, wherein (a) is the voltage-power curve, and (b) is the dp / dv-power curve.

[0022] Figure 3 This is the change diagram of the system droop control output curve under the change of photovoltaic available capacity. DETAILED DESCRIPTION

[0023] In order to describe the present invention more specifically, the technical solution of the present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0024] like Figure 1 As shown in the figure, it is a control structure diagram of the photovoltaic panel under the present invention. The photovoltaic panel is connected to the DC microgrid through the Buck circuit. The present invention is mainly applied to the control part (in the dotted box). By collecting the photovoltaic output voltage v pv and current i pv Value calculation After correcting the proportional coefficient k, the reference value of the traditional VI droop is corrected to obtain a new voltage reference value V ref Then, the voltage reference value passes through the voltage control loop to generate a duty cycle signal to drive the power device.

[0025] like Figure 2 As shown in (a), it is a photovoltaic output characteristic curve. From (a), it can be seen that there is a nonlinear relationship between the photovoltaic output voltage and power. The curve can be divided into two sections according to the positive and negative of dp / dv: the rising section dp / dv>0 and the falling section dp / dv<0. At the maximum power point, dp / dv=0. As shown in (b), there is a specific relationship between dp / dv and power: i. When dp / dv=0, the maximum power is output; ii. When dp / dv<0, a certain power is withdrawn. The adaptive anti-overload droop control strategy of the present invention is based on this characteristic.

[0026] According to the photovoltaic panel voltage and current collected by the sampling module and the output port voltage, the control formula of the present invention is:

[0027]

[0028] Where: V ref is the reference value of the photovoltaic power supply output voltage, V * is the voltage rating, R is the droop factor, It is obtained based on the real-time output voltage and current of the photovoltaic panel, and k is the correction proportional coefficient.

[0029] The correction ratio coefficient is related to the dp / dv value, and the specific settings are as follows:

[0030]

[0031] Where: V max and V min are the maximum and minimum values ​​of the DC bus voltage, dp / dv max It is the maximum value of dp / dv.

[0032] like Figure 3As shown in Figure 1, the output curve of the system droop control changes when the available photovoltaic capacity changes under the change of light. Assuming that under the initial conditions, the available photovoltaic capacity is At this time, the droop control curve is shown as a solid line. In the safe voltage range [V min ,V max ], the output power is less than the maximum photovoltaic power, the photovoltaic panel works in the descending section dp / dv<0, there is no overload, and the steady-state working point is A. At a certain moment, the light drops suddenly, and the available photovoltaic capacity drops to The maximum power cannot support the power required at point A. At this time, the output voltage of the photovoltaic panel decreases until it exceeds the maximum power point. At this time, dp / dv>0. According to the proposed control strategy, the output voltage reference value decreases, resulting in a decrease in output power until a new steady-state equilibrium point B is reached.

[0033] In the present invention, the above data collection, calculation and control steps can be performed through a sampling module, a dp / dv calculation module, a voltage controller and a PWM module.

[0034] Wherein, the sampling module includes:

[0035] Voltage sampling module, for photovoltaic panel voltage v pv , sample the output port voltage V;

[0036] Current sampling module, photovoltaic panel current i pv Take samples;

[0037] The dp / dv calculation module calculates the dp / dv value according to the collected photovoltaic panel voltage and current. The calculation method is as follows: Current Multiply to get the power at the current moment Combined with the voltage at the previous moment power Available

[0038] The voltage controller, according to the reference voltage V given by the adaptive droop control ref , and the difference is made with the port voltage V, and the difference is passed through the proportional integrator to generate the duty cycle d;

[0039] The PWM module generates a pulse width modulation signal to control the IGBT according to the duty cycle d given by the voltage controller.

[0040] The above description of the embodiments is to facilitate the understanding and application of the present invention by those skilled in the art. It is obvious that those skilled in the art can easily make various modifications to the above embodiments and apply the general principles described herein to other embodiments without creative work. Therefore, the present invention is not limited to the above embodiments, and improvements and modifications made to the present invention by those skilled in the art based on the disclosure of the present invention should be within the scope of protection of the present invention.

Claims

1. An adaptive anti-overload droop control method for a photovoltaic DC converter, characterized in that: The method comprises the following steps: The voltage of the photovoltaic panel v pv , the output port voltage V is sampled, and the photovoltaic panel current i pv Take samples; Calculate the dp / dv value based on the collected photovoltaic panel voltage and current; The voltage controller controls the output port voltage at the voltage reference value according to the voltage reference value given by the adaptive droop control; The pulse width modulation signal is generated according to the duty cycle given by the voltage controller to control the IGBT.

2. The method for adaptive overload protection and droop control of a photovoltaic DC converter according to claim 1, characterized in that: In the voltage controller, the voltage reference value V is calculated according to the following method ref . Where: V ref is the reference value of the photovoltaic power supply output voltage, V * is the voltage rating, R is the droop factor, It is obtained based on the real-time output voltage and current of the photovoltaic panel, and k is the correction proportional coefficient.

3. The method for adaptive overload protection and droop control of a photovoltaic DC converter according to claim 2, characterized in that: The specific settings of the correction ratio coefficient are as follows: Where: V max and V min are the maximum and minimum values ​​of the DC bus voltage, dp / dv max It is the maximum value of dp / dv.

4. The method for adaptive overload protection and droop control of a photovoltaic DC converter according to claim 1, 2 or 3, characterized in that: The method adds a correction value based on dp / dv to the traditional droop control method, so that the photovoltaic power source passively participates in power sharing, while preventing overload under sudden changes in light intensity; moreover, the overload protection of the photovoltaic system does not require mode switching and capacity prediction, and the droop control curve can be adaptively adjusted according to the output voltage and current.

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