Virtual-impedance-based inverter parallel running method

Abstract

A virtual impedance based method for parallel operation inverters comprises: introducing an AND virtual generator for each inverter, the virtual generator being connected to a point (B) where the inverter is through virtual impedance, and the magnitude of the virtual impedance being capable of being set as required; enabling control of the inverter to be equivalent to control, through the virtual generator, of the state of the point where the inverter is; applying droop control to the virtual generator, adjusting the frequency and voltage amplitude of the virtual generator respectively through active and reactive operations of the inverter, thereby obtaining a voltage instruction value of the virtual generator; on this basis, further obtaining an output voltage instruction value of the inverter, controlling the voltage output by the inverter to track the instruction value, thereby implementing the control on the voltage of the virtual generator, and finally implementing decoupling adjustment on the active and reactive operations. Compared with the conventional control method, the control policy of wireless parallel operation of the inverters is implemented through the virtual impedance, no obvious hardware investment is additionally required, and the line equivalent impedance can be changed as required, thereby improving the using effect of the droop feature, and being applicable to a resistive environment.

Description

technical field [0001] The invention relates to a control method for parallel operation of inverters, in particular to a control method for realizing wireless parallel operation of inverters by using virtual impedance. Background technique [0002] With the deepening of the energy crisis and the prominence of environmental problems, distributed generation (DG), which mainly utilizes renewable energy, is developing rapidly. Microgrids control many DGs as an organism and have broad prospects. Since most DGs are inverter-type, it is necessary to study the parallel operation technology of inverters. In addition, parallel operation of inverters is also involved in uninterruptible power supply UPS. The parallel operation technology of inverters based on droop characteristics does not require communication, has good robustness, and is widely used. [0003] The droop characteristic control principle is indirectly as follows: For such as figure 1 In the system shown, the line impe...

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Problems solved by technology

[0024] Adding an isolation transformer between the inverter and the line can make the line inductive, but greatly increases the cost

The article "Current Sharing Control of Uninterruptible Power Supply Parallel System Based on Virtual Impedance" (Proceedings of the Chinese Society for Electrical Engineering, 2009, 29(24): 32-39) published by Yu Wei et al. The circulating current of inverters in parallel operation, but did not study the power (especially reactive power) coordination of inverters in detail; "Multi-loop feedback control strategy of DG inverter in microgrid" published by Wang Chengshan et al. The output impedance of the control converter disclosed in the article of Chinese Journal of Electrotechnical Society, 2009, 24(2): 100-107 is inductive, but the virtual impedance of this method is limited by the control parameters

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