A Zero-Sequence Voltage Injection-Based Control Strategy for a Parallel Hybrid Modular Multilevel HVDC Converter System
This paper proposes a zero-sequence voltage injection (ZSVI)-based model predictive control (MPC) strategy to control the dc current/power flow and simultaneously minimize the dc current ripple. The proposed strategy takes advantage of a cost function minimization technique to determine and inject the optimal zero-sequence voltage components into the dc- bus voltage of a PHMMC system. This paper derives a discrete-time dynamic model of the dc transmission-line current and, correspondingly, develops a predictive model. The predictive model is used to inject the appropriate amount of zero-sequence voltage components to the dc bus reference voltage waveform. Compared with the existing triplen harmonics injection method, the proposed ZSVI-MPC strategy improves the performance of a PHMMC system in terms of minimization of the dc current/voltage ripple.
One of the main technical challenges associated with the control of a PHMMC-HVDC system is to simultaneously control the dc current/power flow and the real and reactive power. The existing method proposed to resolve this issue is based on third harmonic component injection where a third harmonic component is introduced to the reference phase voltages. Although this method controls the dc bus voltage, it cannot eliminate the magnitude of the sixth-order harmonic component in the dc current. Further reduction of the dc current/voltage ripple necessitates injection of higher order harmonics to the dc bus voltage, which will add to the complexity in control.
In this project, a zero-sequence voltage injection (ZSVI)-based model predictive control (MPC) strategy is proposed to simultaneously regulate the dc current/power flow and reduce the dc current/voltage ripple of a PHMMC-HVDC system. The MPC strategy is a promising control strategy applied to power-electronic converter systems due to its fast dynamic response, flexibility to include constraints and nonlinearities of the system, and ease in digital implementation.
This project takes the advantages of the features of the MPC strategy and develops a discrete-time predictive model of the dc current of a PHMMCHVDC station. Based on the developed model, an MPC strategy is proposed to: 1) control the dc current/power flow through the dc transmission lines by regulating the dc bus voltage and 2) minimize the dc current/voltage ripple. The capability of the overall controller with the proposed MPC strategy in terms of dc current/power flow control and real/reactive power control for a 21-level PHMMC-HVDC station is presented.
TOOLS AND SOFTWARE USED:
- MP LAB
Jiangchao Qin, Student Member, IEEE, and Maryam Saeedifard, Senior Member, IEEE, “A Zero-Sequence Voltage Injection-Based Control Strategy for a Parallel Hybrid Modular Multilevel HVDC Converter System”, IEEE TRANSACTIONS ON POWER DELIVERY, VOL. 30, NO. 2, APRIL 2015