Zhuohui Tan

High-performance complex controller for high-power converters with low pulse ratios

For high-power converters with low pulse ratios (e.g. 80 Hz load frequency with 600Hz carrier frequency for a 27 MVA Variable Frequency Drive), the current control loop design has been a challenge due to the large signal delay and potentially higher-order plant (LCL filter between the converter and machines). The stability issue and cross-coupling effect is a problem in such application. In this paper, a complex current controller with excellent dynamic performance is proposed. The design is done by using the “double-sided frequency modeling” methodology. The stability, decoupling-effect, dynamic response and the robustness of the control loop are analyzed, which provides a design guideline for such applications. The performance of the proposed strategy and the improved state feedback method are compared. And finally simulation results are presented to validate the controller design and analysis.

Control strategies for a high-performance 2×27 MVA machine test bench with multilevel IGCT converters

In this paper, control strategies of a 22 MW / 27 MVA machine test bench using pumpback topology are introduced. The current loop design at extremely low pulse ratios (e.g. 600 Hz carrier frequency / 80 Hz load frequency) is developed. The system stability and dynamic response are analyzed. The challenges for high-power machine control with a sine filter and a transformer connected between the voltage-source-inverter and the machine are listed and solutions are given. Afterwards, some specific test modes are introduced as well. Finally, the control strategy is validated with the motor test at the customer site.

Position sensorless vector control of the brushless synchronous motor

The position sensorless vector control scheme for the brushless excited synchronous motor based on the IGCT converter is presented in this paper. Since the instantaneous excitation current cannot be directly measured in this application, an adaptive rotor position and speed observer, which does not rely on the explicit estimation of the excitation current, is developed for the brushless excited synchronous motor. The roughly estimation of the excitation current is based on the average model of the excitation machine and the rotating rectification diode. The control algorithms are implemented and validated in a 2*27MVA motor pump-back test bench.