An off-grid inverter based on quasi-proportional resonant control

Abstract

The present invention discloses an off-grid inverter based on quasi-proportional resonance control, including a DC power supply, a three-phase inverter full-bridge circuit and a filter. The three-phase inverter full-bridge circuit is composed of six power switch tubes. The three-phase inverter full-bridge circuit is connected to the DC power supply through a DC bus, and is used to invert the DC power supply into a three-phase AC voltage. The filter is connected to the three-phase inverter full-bridge circuit, and is used to filter out the high-frequency harmonic components in the output voltage of the three-phase inverter full-bridge circuit to obtain a three-phase balanced AC output voltage. Beneficial effect: The filter is connected to the three-phase inverter full-bridge circuit of the present invention, so that the three-phase inverter full-bridge circuit connection saves the three-phase output voltage / current positive and negative sequence separation and positive and negative sequence loop separate control required in the traditional inverter load unbalanced control, greatly simplifies the system control structure, and suppresses the output voltage imbalance under unbalanced load conditions.

Description

Technical Field

[0001] The invention relates to the technical field of power electronic conversion, and in particular to an off-grid inverter based on quasi-proportional resonance control. Background Art

[0002] An off-grid inverter is a device that converts direct current into alternating current, also known as an inverter power supply. It can output 50Hz sinusoidal alternating current that is consistent with the requirements of the national power grid and provide it to places that require mobile power supply or areas without electricity. It is usually used in conjunction with photovoltaic or other new energy inverters to convert the direct current generated by new energy into alternating current and provide it to the load.

[0003] When the inverter works in off-grid mode, the three-phase load asymmetry is common, which will cause the three-phase imbalance of the support voltage generated by the three-phase inverter, resulting in more energy loss and affecting the stability of the system. At the same time, when the voltage at the common connection point is seriously unbalanced, it may even affect the normal operation of induction motors, power electronic conversion devices, etc. Therefore, a three-phase inverter that can correct the balance is urgently needed. Summary of the invention

[0004] In order to solve the above problems, especially to address the deficiencies in the prior art, the present invention provides an off-grid inverter based on quasi-proportional resonance control that can solve the above problems.

[0005] To achieve the above purpose, the present invention adopts the following technical means:

[0006] An off-grid inverter based on quasi-proportional resonance control includes a DC power supply, a three-phase inverter full-bridge circuit and a filter. The three-phase inverter full-bridge circuit is composed of six power switch tubes. The three-phase inverter full-bridge circuit is connected to the DC power supply through a DC bus and is used to invert the DC power supply into a three-phase AC voltage. The filter is connected to the three-phase inverter full-bridge circuit and is used to filter out high-frequency harmonic components in the output voltage of the three-phase inverter full-bridge circuit to obtain a three-phase balanced AC output voltage.

[0007] A further solution of the present invention is that the DC power supply is a distributed DC power supply or a battery.

[0008] A further solution of the present invention is that two ends of the DC bus are connected to support capacitors C1.

[0009] A further solution of the present invention is that the six power switch tubes of the three-phase inverter full-bridge circuit are insulated gate bipolar transistors IGBT.

[0010] A further solution of the present invention is that the three-phase inverter full-bridge circuit is controlled using a quasi-proportional resonance control strategy.

[0011] A further solution of the present invention is that the filter is composed of a filter inductor L, a filter inductor parasitic resistor r and a filter capacitor C2, the three groups of voltage output ends of the three-phase inverter full-bridge circuit are all connected to the filter inductor L, the filter inductor L is connected to an external load through the filter inductor parasitic resistor r, the ends of the three groups of filter inductor parasitic resistors r away from the filter inductor L are all connected to the filter capacitor C2, and the three groups of filter capacitors C2 are all connected to the DC bus.

[0012] Beneficial effects of the present invention:

[0013] The filter is connected to the three-phase inverter full-bridge circuit of the present invention, so that the three-phase inverter full-bridge circuit connection eliminates the links of three-phase output voltage / current positive and negative sequence separation and positive and negative sequence loop separate control required in the traditional inverter load unbalance control, greatly simplifies the system control structure, and suppresses the output voltage imbalance under unbalanced load conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 This is a topological diagram of the inverter of the present invention. DETAILED DESCRIPTION

[0015] The technical solution of the present invention will be described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0016] The technical solution of the present invention will be described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0017] Example 1

[0018] like Figure 1 As shown, an off-grid inverter based on quasi-proportional resonance control includes a DC power supply 1, a three-phase inverter full-bridge circuit 3 and a filter 4. The three-phase inverter full-bridge circuit 3 is composed of six power switch tubes. The three-phase inverter full-bridge circuit 3 is connected to the DC power supply 1 through a DC bus 2 and is used to invert the DC power supply 1 into a three-phase AC voltage. The filter 4 is connected to the three-phase inverter full-bridge circuit 3 and is used to filter out high-frequency harmonic components in the output voltage of the three-phase inverter full-bridge circuit 3 to obtain a three-phase balanced AC output voltage.

[0019] How it works

[0020] The working principle of the three-phase inverter full-bridge circuit 3 is to achieve the conversion from DC to AC by controlling the on and off of the power switch tube.

[0021] When the power switch tube is turned on and off in a specific order and time, the DC bus 2 voltage is chopped and recombined to generate an alternating polarity AC voltage at the three-phase output end. For example, in a switching cycle, for the A-phase output, when the upper bridge arm power switch tube is turned on and the lower bridge arm is turned off, the output voltage is the positive half cycle; when the lower bridge arm power switch tube is turned on and the upper bridge arm is turned off, the output voltage is the negative half cycle. By accurately controlling the on-time and off-time of the power switch tube, the amplitude and frequency of the output AC voltages uoa, uob, and uoc can be adjusted.

[0022] The DC bus half voltages Udc1 and Udc2 are mainly used to analyze the voltage and other parameters of the power switch tube in the circuit. Taking the common structure as an example, the collector of the power switch tube of the upper half bridge arm is connected to the positive end of the DC bus (the voltage can be represented by Udc1, etc.), and the emitter of the power switch tube of the lower half bridge arm is connected to the negative end of the DC bus (the voltage can be represented by Udc2, etc.). The power switch tube uses the voltage of Udc1-Udc2 to generate an AC output voltage.

[0023] The main function of the filter 4 is to filter out the high-frequency harmonic components in the inverter output voltage to obtain a relatively balanced three-phase AC output voltage.

[0024] Quasi-proportional resonant control

[0025] The quasi-proportional resonant control strategy is used to control the three-phase inverter, and its transfer function is: Where K p is the proportionality coefficient, K r is the resonance coefficient, ω0 is the fundamental angular frequency.

[0026] First, the output voltage uoa, uob, uoc and output current iLa, iLb, iLc of the three-phase inverter are obtained through the sampling circuit. Then the output voltage signal is compared with the given reference voltage signal to obtain the voltage error signal.

[0027] Proportional coefficient K p Its function is to provide fast dynamic response. When a voltage error occurs, it can quickly adjust the control signal like traditional proportional control, so that the output voltage quickly approaches the reference value. Resonance coefficient K r It is mainly used to achieve zero-static error tracking for AC signals of a specific frequency. Through the high gain characteristics at the fundamental frequency, it can effectively eliminate steady-state errors and ensure the accuracy of the output voltage.

[0028] Finally, the control signal adjusted by the quasi-proportional resonant controller is input into the driving circuit of the three-phase inverter full-bridge circuit 2 to control the on and off of the power switch tube, thereby realizing accurate control of the output voltage of the three-phase inverter. Through this control method, the system can achieve high-precision output voltage control under different load conditions, and has strong adaptability to grid frequency fluctuations and system parameter changes, and the total harmonic distortion of the output voltage is low, and the dynamic response characteristics are good.

[0029] Example 2

[0030] like Figure 1 As shown, an off-grid inverter based on quasi-proportional resonance control includes a DC power supply 1, a three-phase inverter full-bridge circuit 3 and a filter 4. The three-phase inverter full-bridge circuit 3 is composed of six power switch tubes. The three-phase inverter full-bridge circuit 3 is connected to the DC power supply 1 through a DC bus 2 and is used to invert the DC power supply 1 into a three-phase AC voltage. The filter 4 is connected to the three-phase inverter full-bridge circuit 3 and is used to filter out high-frequency harmonic components in the output voltage of the three-phase inverter full-bridge circuit 3 to obtain a three-phase balanced AC output voltage.

[0031] The DC power source 1 is a distributed DC power source or a battery. Distributed DC power sources can integrate a variety of renewable energy sources, such as solar panels, small wind turbines, etc., so that the off-grid inverter can better adapt to different environments and energy supply conditions; the battery can provide a relatively stable DC voltage and provide a stable DC bus voltage for the off-grid inverter, which is conducive to the inverter outputting high-quality AC power and reducing the fluctuation and distortion of the output voltage.

[0032] Support capacitors C1 are connected to both ends of the DC bus 2. Changes in the load in the three-phase inverter full-bridge circuit 3, the switching action of the power switch tube and other factors will cause fluctuations in the voltage of the DC bus 2, and the support capacitor C1 can play a buffering role; when the load suddenly decreases and the energy provided by the DC power supply 1 is relatively excessive in a short period of time, the support capacitor C1 will absorb this excess energy, store charge, and prevent the DC bus 2 voltage from rising sharply; on the contrary, when the load suddenly increases and the energy provided by the DC power supply 1 is temporarily insufficient, the support capacitor C1 will release the stored charge to replenish energy for the circuit, thereby stabilizing the DC bus 2 voltage.

[0033] Example 3

[0034] like Figure 1As shown, an off-grid inverter based on quasi-proportional resonance control includes a DC power supply 1, a three-phase inverter full-bridge circuit 3 and a filter 4. The three-phase inverter full-bridge circuit 3 is composed of six power switch tubes. The three-phase inverter full-bridge circuit 3 is connected to the DC power supply 1 through a DC bus 2 and is used to invert the DC power supply 1 into a three-phase AC voltage. The filter 4 is connected to the three-phase inverter full-bridge circuit 3 and is used to filter out high-frequency harmonic components in the output voltage of the three-phase inverter full-bridge circuit 3 to obtain a three-phase balanced AC output voltage.

[0035] The six power switches of the three-phase inverter full-bridge circuit 3 are insulated gate bipolar transistors IGBT. This configuration enables the three-phase inverter full-bridge circuit 3 to have good driving characteristics, excellent switching characteristics, excellent conduction characteristics, stable overall performance, high integration and low cost.

[0036] The three-phase inverter full-bridge circuit 3 is controlled by a quasi-proportional resonance control strategy, which has high-precision output voltage control and good harmonic suppression capability, and can effectively improve the working efficiency and working effect of the three-phase inverter full-bridge circuit 3.

[0037] The filter 4 is composed of a filter inductor L, a filter inductor parasitic resistor r and a filter capacitor C2. The three voltage output terminals of the three-phase inverter are all connected to the filter inductor L, and the filter inductor L is connected to an external load through the filter inductor parasitic resistor r. The ends of the three groups of filter inductor parasitic resistors r away from the filter inductor L are all connected to the filter capacitor C2, and the three groups of filter capacitors C2 are all connected to the DC bus. This arrangement is relatively simple, which is convenient for connecting the filter 4 to the three-phase inverter full-bridge circuit 3, and can effectively improve the working efficiency and working effect of the filter 4.

[0038] The examples given in the present invention are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here, and the obvious changes or modifications derived therefrom are still within the protection scope of the present invention.

Claims

1. An off-grid inverter based on quasi-proportional resonant control, characterized in that: The invention comprises a direct current power supply (1), a three-phase inverter full-bridge circuit (3) and a filter (4); the three-phase inverter full-bridge circuit (3) is composed of six power switch tubes; the three-phase inverter full-bridge circuit (3) is connected to the direct current power supply (1) via a direct current bus (2) and is used to invert the direct current power supply (1) into a three-phase alternating current voltage; the filter (4) is connected to the three-phase inverter full-bridge circuit (3) and is used to filter out high-frequency harmonic components in the output voltage of the three-phase inverter full-bridge circuit (3) to obtain a three-phase balanced alternating current output voltage.

2. The off-grid inverter based on quasi-proportional resonance control according to claim 1, characterized in that: The DC power source (1) is a distributed DC power source or a battery.

3. The off-grid inverter based on quasi-proportional resonant control according to claim 1, characterized in that: Two ends of the DC bus (2) are connected to a supporting capacitor C1.

4. The off-grid inverter based on quasi-proportional resonant control according to claim 1, characterized in that: The six power switch tubes of the three-phase inverter full-bridge circuit (3) are insulated gate bipolar transistors (IGBT).

5. The off-grid inverter based on quasi-proportional resonance control according to claim 4, characterized in that: The three-phase inverter full-bridge circuit (3) is controlled by adopting a quasi-proportional resonance control strategy.

6. The off-grid inverter based on quasi-proportional resonant control according to claim 1, characterized in that: The filter (4) is composed of a filter inductor L, a filter inductor parasitic resistor r and a filter capacitor C2. The three groups of voltage output ends of the three-phase inverter full-bridge circuit (3) are all connected to the filter inductor L. The filter inductor L is connected to an external load via the filter inductor parasitic resistor r. The ends of the three groups of filter inductor parasitic resistors r away from the filter inductor L are all connected to the filter capacitor C2. The three groups of filter capacitors C2 are all connected to the DC bus (2).

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