A Method for Measuring Line Impedance of Inverter Parallel System

Abstract

The invention provides a line impedance measurement method for an inverter parallel system. Through sampling bus voltage and output current of each inverter in a microgrid central controller, a specific subharmonic component with a highest content is extracted to estimate line impedance. The method comprises the steps of (1) carrying out system initialization and setting the virtual output impedance of each inverter, (2) sampling bus voltage and the output current of each inverter, (3) carrying out fast Fourier transform or other similar algorithms on the bus voltage and determining a harmonicorder h with a highest harmonic content, (4) extracting the bus voltage and the h-order harmonic component in the output current of each inverter, (5) calculating the line impedance of each inverter,and (6) filtering a calculation result. The method does not cause any disturbance to an original system, the construction cost of the system is not increased, the calculation method is simple, and agood solution is provided for engineering application.

Description

Technical field [0001] The invention belongs to the measurement technology of power grid line impedance, and in particular relates to a method for measuring the line impedance of an inverter parallel system. Background technique [0002] In recent years, with the development of renewable energy power generation technology, distributed power generation models have been widely used. Primary energy sources such as photovoltaics and wind power are usually delivered to the grid through power electronic interface devices such as inverters. In order to increase the capacity of the system and improve the reliability of the system, each inverter usually adopts a parallel operation mode. Therefore, the distributed power generation system (also called microgrid) can be simplified to a structure of multiple inverters in parallel. For such systems, droop control is usually used to achieve coordinated control between parallel inverters. Because droop control can achieve synchronization and ...

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Problems solved by technology

However, the droop control has the following disadvantages: the reactive power is affected by the line impedance difference and cannot be shared among the inverters; the output power has control coupling when the line impedance is not purely inductive or purely resistive; nonlinear load Causes the reduction of bus voltage quality, etc.

All these methods will bring certain disturbance or distortion to the original system, so they are all intrusive measurement methods, which affect the performance and stability of the system to a certain extent.

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