Circulating current control strategy for parallel full‐scale wind power converters

Abstract

Converter parallel techniques can increase the power rating, but there is a circulating current problem. Therefore, this study focuses on the circulating current problem in parallel full-scale wind power converter systems. The general definition of circulating currents is first introduced. The concept of circulating current percentage is then defined to quantitatively analyse the relatively serious situation of circulating currents for parallel converter systems. Then, the generation mechanisms of circulating currents are analysed based on the mathematical model of circulating currents. Actually, circulating currents can be regarded as a kind of disturbance to the load currents of a parallel system. Thereby, a novel control strategy, based on circulating current feed-forward compensation for parallel converter systems, is proposed and a feed-forward controller is designed. Finally, simulations based on MATLAB/ Simulink and hardware-in-loop experiments based on RT-LAB are carried out. Both simulation and experimental results validate the proposed circulating current control method.

Experimental Study of the Parameter Mismatch Effects on the Low Frequency Circulating Currents of Parallel Three Phase Inverters

“…However, when the converters are connected in parallel, circulating currents appear that can produce undesirable effects in the system [14]. They are produced due to hardware mismatches (filter inductors, power delivered by each inverter), or differences in the control parameters, such as the modulators of the inverters connected in parallel [15].…”

Parallel‐connected buck converters controlled by capacitor current feedback based PT with current‐sharing ability

“…For the application scenarios required high power, high current is brought in flowing through switching devices from the power supply side to the load, which could result in high current pressure on the switching devices. The parallel-connected power converters possess the advantages of large capacity, high efficiency and high reliability, and hence have been used to resolve the issues of power conversion with high currents [1][2][3]. Although the parallelconnected power converters allow the use of low-power devices for high-power applications, each power module might be accompanied with the issue of imbalanced current distribution.…”

Series‐connected multi‐half‐bridge modules converter for integrating multi‐megawatt wind multi‐phase permanent magnet synchronous generator with dc grid

“…To meet the requirement of the low-voltage bulk-power generation peculiarity of the WECS, a single power converter cannot be used. Therefore, parallel-converters configuration has been proposed in the literature [3][4][5][6][7][8][9][10][11]. The main drawbacks of the parallel operation are the low-voltage operation, which requires a step-up stage through a transformer or a direct current (dc)-dc boost converter in order to be able to connect to a medium-voltage dc grid, and the presence of circulating currents, which do not only increase the power losses but also challenge the power sharing control of different converters [7,11].…”