A new photovoltaic inverter main circuit topology structure for inhibiting harmonics

Abstract

The application discloses a novel photovoltaic inverter main circuit topology structure for inhibiting harmonics, which comprises a photovoltaic direct-current power supply, an inverter, an alternating-current output filter circuit, a detection circuit and a controller; a Q1 is connected in series on a capacitor C1 of the alternating-current output filter circuit; the detection circuit detects a current value Ig from a power grid side and outputs the current value Ig to the controller; an output end of the controller is connected with the Q1 and a Q2; the controller processes data of the Ig value, and then sends a control signal 1 and a signal 2 according to a processing result; the signal 1 is used for controlling the controllable device Q1 to be disconnected or closed; and the signal 2 is used for controlling the controllable device Q2 to be disconnected or closed. Compared with the prior art, the application has the beneficial effects that when the Q1 and the Q2 are closed, a pair of LC filter circuits are formed; when the Q1 and the Q2 are disconnected, a pair of L filter circuits are formed; and the current passing through the Q1 and the Q2 is reduced.

Description

Technical Field

[0001] This invention relates to a novel photovoltaic inverter main circuit topology for suppressing harmonics, belonging to the field of inverter circuit technology. Background Technology

[0002] With the advancement of global energy structure transformation and energy conservation and emission reduction goals, the installed capacity of photovoltaic power generation continues to grow rapidly. As the core energy conversion device between the photovoltaic power generation system and the power grid, the output power quality of the photovoltaic grid inverter directly affects grid connection safety and grid operation quality. Photovoltaic inverters generally employ pulse width modulation (PWM) to convert the direct current output from the photovoltaic array into alternating current (AC) with the same frequency and phase as the grid. However, due to the high-frequency switching characteristics of power switching devices and the inherent nonlinearity of PWM modulation, the inverter output voltage and current inevitably contain a large number of harmonics. These are mainly high-frequency harmonics near the switching frequency and its integer multiples, as well as low-order harmonics caused by dead-time effects, device voltage drops, and DC bus voltage fluctuations. If these harmonics are not suppressed, they will lead to distortion of the grid-connected current waveform, increasing the total harmonic distortion rate and making it difficult to meet grid-connected power quality standards. Summary of the Invention

[0003] To overcome the above-mentioned shortcomings, the purpose of this invention is to provide a novel photovoltaic inverter main circuit topology for suppressing harmonics.

[0004] To achieve the above objectives, the technical solution adopted by this invention is: a novel photovoltaic inverter main circuit topology for suppressing harmonics, comprising a photovoltaic DC power supply, an inverter, an AC output filter circuit, a detection circuit, and a controller. The AC output filter circuit adopts an LC or L filter circuit structure, and a Q1 is connected in series with the capacitor C1 of the AC output filter circuit. The detection circuit detects the current value Ig from the grid side and outputs the current value Ig to the controller. The output terminal of the controller is connected to Q1 and Q2. The controller processes the Ig value, and then the controller issues control signals 1 and 2 according to the processing result. Signal 1 is used to control the controllable device Q1 to open or close, and signal 2 is used to control the controllable device Q2 to open or close.

[0005] The present invention is further configured such that the control method of the controller includes the following steps:

[0006] Step 1: When the inverter starts to connect to the grid, the controller first closes the controllable devices Q1 and Q2;

[0007] Step 2: The detection circuit detects the grid-connected current value Ig in real time, and sends the detected current value Ig directly to the controller. The controller simultaneously calculates the current total harmonic distortion rate THDi of the current value Ig, and compares the calculated current total harmonic distortion rate THDi with a preset THDinom value. When THDi > THDinom, it indicates that the power grid itself contains relatively large current harmonics at this time, and the controller controls the controllable devices Q1 and Q2 to close; when THDi < THDinom, it indicates that the power grid itself contains relatively small current harmonics at this time, and the controller controls the controllable device Q1 or Q2 to open.

[0008] The present invention is further configured as: a DC harmonic pre-suppression buffer circuit is connected in parallel to the photovoltaic DC power supply, and the DC harmonic pre-suppression buffer circuit includes an inductor L3, a filter capacitor C3 and a bleeder resistor R1 connected in series.

[0009] The DC harmonic pre-suppression buffer circuit is used to suppress low-frequency harmonics on the DC side and switching-coupled high-frequency harmonics caused by operating condition fluctuations of the photovoltaic DC power supply, and at the same time attenuate common-mode harmonic leakage current generated by the stray capacitance of the photovoltaic DC power supply.

[0010] Compared with the prior art, the beneficial effects of the present invention are: since the controller performs data processing on the Ig value, the controller then outputs control signal 1 and signal 2 according to the processing result. Signal 1 is used to control the controllable device Q1 to open or close, and signal 2 is used to control the controllable device Q2 to open or close. When Q1 and Q2 are closed, a pair of LC filter circuits is formed; when Q1 and Q2 are open, a pair of L filter circuits is formed, which reduces the current passing through Q1 and Q2, increases the conversion efficiency of the output current, and reduces the disturbance to the power grid caused by switching. Brief Description of the Drawings

[0011] Figure 1 is a schematic structural diagram of the novel photovoltaic inverter main circuit topology for harmonic suppression shown in a preferred embodiment of the present invention.

[0012] In the figures: PV, photovoltaic DC input power supply; 1, inverter; 2, detection circuit; 3, controller; 4, power grid. Detailed Description of the Preferred Embodiments

[0013] The preferred embodiments of the present invention are described in detail below with reference to the accompanying drawings, so that the advantages and features of the present invention can be more easily understood by those skilled in the art, thereby making a clearer and more definite definition of the protection scope of the present invention.

[0014] See Figure 1As shown in the figure, a novel photovoltaic inverter main circuit topology for harmonic suppression in this embodiment includes a photovoltaic DC power supply PV, an inverter 1, an AC output filter circuit, a detection circuit 2 and a controller 3. The AC output filter circuit adopts an LC or L filter circuit structure, and Q1 is connected in series on the capacitor C1 of the AC output filter circuit. The detection circuit 2 detects the current value Ig from the grid 4 side, and outputs the current value Ig to the controller 3. The output end of the controller 3 is connected to Q1 and Q2. The controller 3 performs data processing on the Ig value, and then the controller 3 sends out control signal 1 and signal 2 according to the processing result. Signal 1 is used to control the turn-off or turn-on of the controllable device Q1, and signal 2 is used to control the turn-off or turn-on of the controllable device Q2.

[0015] Since the controller 3 performs data processing on the Ig value, and then the controller 3 sends out control signal 1 and signal 2 according to the processing result, signal 1 is used to control the turn-off or turn-on of the controllable device Q1, and signal 2 is used to control the turn-off or turn-on of the controllable device Q2. When Q1 and Q2 are turned on, a pair of LC filter circuits is formed. When Q1 and Q2 are turned off, a pair of L filter circuits is formed, which reduces the current passing through Q1 and Q2. The conversion efficiency of the output current is increased, and the disturbance caused by switching to the grid 4 is reduced.

[0016] The control method of the controller 3 includes the following steps: Step 1: When the inverter 1 starts to connect to the grid, the controller 3 first turns on the controllable devices Q1 and Q2. Step 2: The detection circuit 2 detects the grid-connected current value Ig in real time, and sends the detected current value Ig directly to the controller 3. The controller 3 simultaneously calculates the current total harmonic distortion rate THDi of the current value Ig, and compares the calculated current total harmonic distortion rate THDi with the preset THDinom value. When THDi > THDinom, it indicates that the grid 4 itself contains large current harmonics at this time, and the controller 3 controls the controllable devices Q1 and Q2 to be turned on, forming a pair of LC filter circuits to enhance filtering. When THDi < THDinom, it indicates that the grid 4 itself contains small current harmonics at this time, no strong filtering capability is required, and only the inductor L1 and the inductor L2 are needed, and the controller 3 controls the controllable device Q1 or Q2 to be turned off.

[0017] A DC harmonic pre-suppression buffer circuit is connected in parallel to the photovoltaic DC power supply PV. The DC harmonic pre-suppression buffer circuit includes an inductor L3, a filter capacitor C3 and a bleeder resistor R1 connected in series. The DC harmonic pre-suppression buffer circuit is used to suppress low-frequency harmonics on the DC side and switching-coupled high-frequency harmonics caused by working condition fluctuations of the photovoltaic DC power supply PV, and at the same time weaken the common-mode harmonic leakage current generated by the stray capacitance of the photovoltaic DC power supply PV.

[0018] Preferably, inverter 1 is an H-bridge inverter 1. During the high-speed switching process of the power devices in inverter 1, C1 and C2 are used to absorb the noise interference generated by the power devices. Together with inductors L1 and L2, they form two pairs of filter circuits to significantly filter out harmonics and output clean electrical energy to the power grid 4.

[0019] The above embodiments are only for illustrating the technical concept and features of the present invention. Their purpose is to enable those skilled in the art to understand the content of the present invention and implement it. They should not be used to limit the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A novel photovoltaic inverter main circuit topology for suppressing harmonics, comprising a photovoltaic DC power supply, an inverter, an AC output filter circuit, a detection circuit, and a controller, characterized in that: The AC output filter circuit adopts an LC or L filter circuit structure, and Q1 is connected in series on the capacitor C1 of the AC output filter circuit; the detection circuit detects the current value Ig from the grid side and outputs the current value Ig to the controller; the output end of the controller is connected to Q1 and Q2; the controller performs data processing on the Ig value, and then the controller sends out control signal 1 and signal 2 according to the processing result. Signal 1 is used to control the turn-off or turn-on of the controllable device Q1, and signal 2 is used to control the turn-off or turn-on of the controllable device Q2.

2. The novel harmonic-suppressing photovoltaic inverter main circuit topology according to claim 1, characterized in that, The control method of the controller includes the following steps: Step 1: When the inverter starts grid connection, the controller first turns on the controllable devices Q1 and Q2; Step 2: The detection circuit detects the grid-connected current value Ig in real time, and sends the detected current value Ig directly to the controller. The controller simultaneously calculates the total harmonic distortion rate THDi of the current value Ig, and compares the calculated total harmonic distortion rate THDi with the preset THDinom value. When THDi>THDinom, it indicates that the power grid itself contains large current harmonics at this time, then the controller controls the controllable devices Q1 and Q2 to be turned on; when THDi<THDinom, it indicates that the power grid itself contains small current harmonics at this time, then the controller controls the controllable device Q1 or Q2 to be turned off.

3. The novel harmonic-suppressing photovoltaic inverter main circuit topology according to claim 1, characterized in that, A DC harmonic pre-suppression buffer circuit is connected in parallel to the photovoltaic DC power supply, and the DC harmonic pre-suppression buffer circuit includes an inductor L3, a filter capacitor C3 and a bleeder resistor R1 connected in series.

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