Abstract
An integral plus resonant sliding mode direct power control (IRSMC DPC) strategy for voltage source converter high voltage direct current (VSC-HVDC) systems under unbalanced grid voltage conditions is proposed in this paper. Through detailed instantaneous power flow analysis, a generalized power compensation method, by which the ratio between the amplitude of active and reactive power ripples can be controlled continuously, is obtained. This enables the system to provide flexible power control, so that the desired performance of the system on both the ac and dc sides can be attained under different operating conditions. When the grid voltage is unbalanced, one or both of the active and reactive power terms contain ripples, oscillating at twice the grid frequency, to obtain non-distorted ac current. A power controller consisting of the proportional, integral and resonant control laws is designed using the sliding mode control approach, to achieve accurate power control objective. Simulation studies on a two-terminal VSC-HVDC system using MATLAB/SIMULINK (R2013b, Mathworks, Natick, MA, USA) are conducted to verify the effectiveness of the IRSMC DPC strategy. The results show that this strategy ensures satisfactory performance of the system over a wide range of operating conditions.
Highlights
Voltage source converter high voltage direct current (VSC-HVDC) technology is playing an ever-increasing role in power transmission systems all over the world [1,2,3]
This paper proposes an integral plus resonant sliding mode direct power control (IRSMC DPC)
The generalized power compensation method presented enables the VSC-HVDC system to provide flexible power control compensation method presented enables the VSC-HVDC system to provide flexible power control functions, so that the desired system performance on both the ac and dc sides can be obtained under different operating conditions
Summary
Voltage source converter high voltage direct current (VSC-HVDC) technology is playing an ever-increasing role in power transmission systems all over the world [1,2,3]. Three-phase voltage unbalance is common in practical power systems When this happens, the performance of various control strategies for VSC-based systems will be affected. Many control methods are studied to improve the performance of the DPC strategies under unbalanced grid voltage conditions. The sliding mode control (SMC)-based DPC strategies for doubly fed induction generator (DFIG) rotor side converter and VSC inverter (VSI) are proposed in [15,16], respectively. An integral plus resonant SMC-based DPC (IRSMC DPC) strategy for a VSC-HVDC system under unbalanced grid voltage conditions is proposed. As one or both of the active and reactive power terms contain ripples to obtain non-distorted ac current, and considering the impacts of time delays on system performance, a SMC-based power controller, consisting of the proportional, integral, and resonant control laws, is designed to achieve accurate power control objective.
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