Computer-aided design (CAD) method for droop characteristic of distributed power supply of microgrid isolated network during running

Abstract

The invention discloses a computer-aided design (CAD) method for a droop characteristic of a distributed power supply of a microgrid isolated network during running, and belongs to the field of running and control of microgrids. The CAD method is characterized in that the frequency of an inverter is fixed at 50Hz; a charge voltage amplitude value and an active power drop curve as well as a component ratio of a load voltage d axis to a load voltage q axis and a reactive power drop curve are designed; an active power reference value and a reactive power reference value of the inverter are obtained through calculation; by adopting performance qualification (PQ) control, the inverter can transmit appointed active power and reactive power, so that in the isolated network, the change of system loads is borne by each inverter according to the capacity; and therefore, voltage and frequency of the microgrid during running in the isolated network can be kept stabilized. By the method, the limitation that the frequency is required to be introduced into drop control according to the conventional drop characteristic is avoided, and the microgrid can stably run under the isolated network state.

Description

technical field [0001] The droop characteristic design method belongs to the field of microgrid operation and control. [0002] A microgrid is a low-voltage grid that combines various small distributed power sources to provide electrical energy for local loads. It has two operation modes of grid-connected and isolated grid, which can improve the reliability of power supply at the load side. Most of the microgrids use PQ control when they are connected to the grid. The frequency and voltage of the system are maintained by the large grid. However, in the isolated grid state, the frequency and voltage support of the large grid is lost, and the microgrid needs to adjust the voltage and frequency by itself. [0003] Therefore, it is necessary to design a good control strategy to keep the voltage and frequency of the microgrid stable during the isolated grid operation. [0004] The present invention proposes a new droop characteristic design method for the isolated grid operation ...

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Problems solved by technology

[0021] In the traditional synchronous generator system, the frequency is determined by the rotor speed, but in the inverter system, there is no rotor, and the frequency is determined by the controller, so the traditional droop characteristic introduces the frequency into the droop curve, which is unreasonable

It should be pointed out that the above droop control strategy works well for the single-inverter isolated grid system, but for the multi-inverter isolated grid system, since each inverter will calculate its own frequency reference value, they jointly participate in the system It is easy to make the system unstable when the frequency adjustment of the

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