Robust current control design of a three phase voltage source converter

Abstract

In this paper, a robust design method for current control is proposed to improve the performance of a three phase voltage source converter (VSC) with an inductorcapacitor-inductor (LCL) filter. The presence of the LCL filter complicates the dynamics of the control system and limits the achievable control bandwidth (and the overall performance), particularly when the uncertainty of the parameters is considered. To solve this problem, the advanced H? control theory is employed to design a robust current controller in stationary coordinates. Both control of the fundamental frequency current and suppression of the potential LC resonance are considered. The design procedure and the selection of the weight functions are presented in detail. A conventional proportional-resonant PR controller is also designed for comparison. Analysis showed that the proposed H? current controller achieved a good frequency response with explicit robustness. The conclusion was verified on a 5 kW VSC that had a LCL filter.

Comprehensive comparison of the delta- and wye-connected autotransformer applied to 12-pulse rectifier

“…In addition, from (4), (5) and Fig. 1, it is also obtained that the switching functions of the 12-pulse rectifier with delta-connected autotransformer are the same with that of the 12-pulse rectifier with wye-connected autotransformer, that is…”

“…Because of its simple system configuration, low EMI at input ac mains and reduced voltage rippled dc side, multipulse rectifier (MPR) is widely used in adjustable speed drives, electro-chemical processes, aircraft converter systems and renewable energy conversion systems [1][2][3][4][5][6]. A MPR comprises a phase-shifting transformer and several three-phase diode bridge rectifiers, where the harmonics generated by one rectifier can be cancelled by other rectifiers [7].…”

“…The function of the IPR (IPR: Inter-phase Reactor) is to absorb the output voltage difference of two bridge rectifiers, which can ensure the independent operation of the two bridge rectifiers. The ZSBT (Zero-sequence Blocking Transformer) exhibits high impedance to zero-sequence currents, which is used to promote 120 o conduction for each rectifier diode [5]. Figure 2 shows the winding connection of delta-connected autotransformer and its phase diagram.…”

Balance control of grid currents for UPQC under unbalanced loads based on matching-ratio compensation algorithm

“…The mechanism of DC bus voltage fluctuations can be revealed by (15) and (16). That is, the DC bus voltage u dc and u dc± will fluctuate with the changes of the power p ser , currents i serabc and neutral current i dco .…”

“…Therefore, a resonant (R) controller is employed to achieve zero steady-state error in [15]. The nonlinear loads may cause the output voltages of the inverter to be distorted, and thus multi-resonant (MR) controllers are employed to effectively control several low-order harmonics with high content in the nonlinear load currents in [16], so as to improve the waveform quality of the inverter voltage.…”