No abstract

Utilizing high order passive filters for the voltage source converters is becoming attractive in industrial applications due to the excellent attenuation performance, smaller size and lower cost. The LCL, the multituned traps and recently the combined LCL with multituned traps (LCL-mT) are the most popular high order filters. However, the increased number of elements and the inherent resonances complicate both filter parameter design and current control loop stabilization, especially, in presence of parameter uncertainties and wide variations of the grid inductance. Hence, in this paper a straightforward and robust design procedure for the LCL-mT filter is proposed. Compared to the existing methods, the proposed technique is not iterative and satisfies the traditional practical limits on filter parameters, while ensures stability even in presence of wide grid inductance variations and filter parameter uncertainties. The validity and effectiveness of the proposed method is proved by simulation and experimental results. Index Terms-Delay based stabilization, LCL and traps filters, single loop control, voltage source converter.

Compared with the traditional L filters, the high order LCL and LLCL filters for grid integration of voltage source converters offer better switching harmonic attenuation even with smaller passive elements. However, the inherent resonance of the high order filters complicates the control of the converter and also the design of filter parameters, especially at presence of digital delays and grid impedance variations. This study proposes a simple design procedure for the LCL and the LLCL filters of a delay-based stabilised converter that satisfies the predefined constraints on the converter current ripple, grid current harmonics and the reactive power of the capacitor and at the same time, ensures adequate stability of the simple single loop current control against the resonance. Moreover, the effect of grid impedance on the filter performance and controller stability is taken into account, thus the proposed method is robust against a wide range of grid impedance variations. Experimental results for a 3 kW test rig under steady state and transient conditions confirm the effectiveness of the proposed filter design algorithm.

Rapid development of high-speed trains confronts the power grid with serious power quality problems. In this study, to compensate power quality, an improved grid voltage sensorless control method for the railway power conditioner (RPC) is proposed. The proposed control strategy utilises a moving average filter to better detect the compensating currents and a proportional-resonant controller to control the compensating currents. Moreover, a sensorless virtual flux method based on second order low-pass filters is presented to replace the AC voltage sensors. Using the proposed strategy, the dynamic and steady-state characteristic of the RPC is significantly enhanced. Through simulation tests, the effectiveness of the proposed methods is confirmed.

This study proposes a simple digital current control technique for single-phase grid-connected voltage source converters. Unlike conventional strategies, the proposed method does not require any proportional-integral or proportionalresonant controller, fictitious phase generation, reference frame transformation and decoupling network; thus, it has the advantages of simplicity and reduced computational efforts. The suggested digital technique only uses a simple proportional controller in its structure and can be directly implemented on available digital signal processors. A digital controller parameter design procedure is proposed which ensures stability and near-zero steady-state error under all circumstances. Simulation and experimental results confirm that the proposed technique provides a fast and accurate current tracking with minimum harmonic distortions.