New control strategy for DSTATCOM without current sensors and its engineering application

This paper analyses the negative sequence equivalent circuit of DSTATCOM in unbalanced distribution networks. A new control model of negative sequence voltage without current sensors based on instantaneous power balancing algorithm is deduced. To compensate for balanced and unbalanced voltages, a new cascade voltage loop control strategy, in which the negative sequence voltage control loop is parallel to the positive sequence voltage loop, is proposed. Then the mathematical model of the new cascade loop voltage control method is discussed. The DSTATCOM output voltage command is directly obtained from the bus voltage at the Point of Common Coupling (PCC) and the DC-side voltage via a simple algebraic algorithm based on power balance equation. In addition, the implementation costs can be reduced since current sensors are not required in the proposed control strategy. Simulation and industrial application results are presented to verify the validity of the proposed control strategy. It is successfully implemented in the DSTATCOM installed in the Lianyuan Iron and Steel Corporation in Hunan province of China.