The authors discuss high-voltage power conversion. Conventional series connection and three-level voltage source inverter techniques are reviewed and compared. A novel versatile multilevel commutation cell is introduced: it is shown that this topology is safer and more simple to control, and delivers purer output waveforms. The authors show how this technique can be applied to either choppers or voltage-source inverters and generalized to any number of switches.<<ETX>>

Multi-level conversion : high voltage choppers and voltage-source inverters

This paper presents a nonlinear control technique for a three-phase shunt active power filter (SAPF). The method provides compensation for reactive, unbalanced, and harmonic load current components. A proportional-integral (PI) control law is derived through linearization of the inherently nonlinear SAPF system model, so that the tasks of current control dynamics and dc capacitor voltage dynamics become decoupled. This decoupling allows us to control the SAPF output currents and the dc bus voltage independently of each other, thereby providing either one of these decoupled subsystems a dynamic response that significantly slower than that of the other. To overcome the drawbacks of the conventional method, a computational control delay compensation method, which delaylessly and accurately generates the SAPF reference currents, is proposed. The first step is to extract the SAPF reference currents from the sensed nonlinear load currents by applying the synchronous reference frame method, where a three-phase diode bridge rectifier with R-L load is taken as the nonlinear load, and then, the reference currents are modified, so that the delay will be compensated. The converter, which is controlled by the described control strategy, guarantees balanced overall supply currents, unity displacement power factor, and reduced harmonic load currents in the common coupling point. Various simulation and experimental results demonstrate the high performance of the nonlinear controller.

Correction to “Experimental Design of a Nonlinear Control Technique for Three-Phase Shunt Active Power Filter”

This paper proposes a combined system of a thyristor-controlled reactor (TCR) and a shunt hybrid power filter (SHPF) for harmonic and reactive power compensation. The SHPF is the combination of a small-rating active power filter (APF) and a fifth-harmonic-tuned LC passive filter. The tuned passive filter and the TCR form a shunt passive filter (SPF) to compensate reactive power. The small-rating APF is used to improve the filtering characteristics of SPF and to suppress the possibility of resonance between the SPF and line inductances. A proportional-integral controller was used, and a triggering alpha was extracted using a lookup table to control the TCR. A nonlinear control of APF was developed for current tracking and voltage regulation. The latter is based on a decoupled control strategy, which considers that the controlled system may be divided into an inner fast loop and an outer slow one. Thus, an exact linearization control was applied to the inner loop, and a nonlinear feedback control law was used for the outer voltage loop. Integral compensators were added in both current and voltage loops in order to eliminate the steady-state errors due to system parameter uncertainty. The simulation and experimental results are found to be quite satisfactory to mitigate harmonic distortions and reactive power compensation.

A Combination of Shunt Hybrid Power Filter and Thyristor-Controlled Reactor for Power Quality

This work presents an analysis and a new control design of a voltage-source converter (VSC) transmission system operating under unbalanced network conditions. The system is analyzed in the positive and negative synchronous reference frames. The proposed control strategy contains a main controller and an auxiliary controller. The main controller is implemented in the positive d-q frame using decoupling control without involving positive/negative-sequence decomposition. The auxiliary controller is implemented in the negative-sequence d-q frame using cross-coupling control of negative-sequence current. Simulation results using the SIMULINK power system blockset show good performance of the proposed control strategy for a 300-MW 300-kV dc VSC transmission system during both balanced conditions and unbalanced conditions as may be caused by a solid single-phase-to-ground fault.

VSC transmission operating under unbalanced AC conditions - analysis and control design

This paper proposes an advanced control strategy to enhance performance of shunt active power filter (APF). The proposed control scheme requires only two current sensors at the supply side and does not need a harmonic detector. In order to make the supply currents sinusoidal, an effective harmonic compensation method is developed with the aid of a conventional proportional-integral (PI) and vector PI controllers. The absence of the harmonic detector not only simplifies the control scheme but also significantly improves the accuracy of the APF, since the control performance is no longer affected by the performance of the harmonic tracking process. Furthermore, the total cost to implement the proposed APF becomes lower, owing to the minimized current sensors and the use of a four-switch three-phase inverter. Despite the simplified hardware, the performance of the APF is improved significantly compared to the traditional control scheme, thanks to the effectiveness of the proposed compensation scheme. The proposed control scheme is theoretically analyzed, and a 1.5-kVA APF is built in the laboratory to validate the feasibility of the proposed control strategy.

An Advanced Current Control Strategy for Three-Phase Shunt Active Power Filters

This paper presents a nonlinear control technique for a three-phase shunt hybrid power filter (SHPF) to enhance its dynamic response when it is used to compensate for harmonic currents and reactive power. The dynamic model of the SHPF system is first elaborated in the stationary ldquoabcrdquo reference frame and then transformed into the synchronous orthogonal ldquodqrdquo reference frame. The ldquodqrdquo frame model is divided into two separate loops, namely, the two current dynamic inner loops and the dc-voltage dynamic outer loop. Proportional-integral (PI) controllers are utilized to control the SHPF input currents and dc-bus voltage. The currents track closely their references so that the SHPF behaves as a quasi-ideal current source connected in parallel with the load. It provides the reactive power and harmonic currents required by the nonlinear load, thereby achieving sinusoidal supply currents in phase with supply voltages under dynamic and steady-state conditions. The SHPF consists of a small-rating voltage-source inverter (VSI) in series with a fifth-harmonic tuned LC passive filter. The rating of the VSI in the SHPF system is much smaller than that in the conventional shunt active power filter because the passive filter takes care of the major burden of compensation. The effectiveness of the control technique is demonstrated through simulation and experimentation under steady-state and dynamic operating conditions.

A New Control Technique for Three-Phase Shunt Hybrid Power Filter

This paper presents a modeling and a nonlinear control of three-phase voltage source shunt active filter. The modeling is based on the abc/dq transformation of the AC system variables. The currents injected by the active filter are controlled in the synchronous orthogonal dq frame using a decoupled nonlinear control strategy. The reference harmonic components are extracted from the sensed nonlinear load currents by applying the synchronous reference frame method, where a three-phase thyristor bridge rectifier with R-L load is taken as the nonlinear load. The voltage level of the DC side is regulated using a linearizing feedback control. The reference current needed to maintain a regulated DC voltage is added to the current loop reference. The transfer functions of the two loops are developed and synthesized to obtain the desired stability and dynamic response. Simulation results confirm the performances considered theoretically for the shunt active filter topology.

Modeling and nonlinear control of shunt active power filter in the synchronous reference frame

The modelling of, and a nonlinear control strategy for, a three-phase voltage source shunt active power filter is presented. The dynamic model is at first elaborated in the system 'abc' and then transformed into the synchronous orthogonal 'dq' frame. The 'dq' frame model is divided into two separate loops, namely the two current dynamics inner loop and the DC voltage dynamics outer loop. The exact feedback linearisation theory is applied in the design of the controller. Then, the pole placement strategy is used to synthesise the closed loop error dynamics of current tracking and DC bus voltage regulation. The adopted control strategy allows the decoupling of the currents and improves their tracking behaviour and enhances DC voltage regulation. Simulation results validate the expected active filter performance in both steady state and transient operation, and also show that the controller is capable of compensation under severe load current imbalances.

Nonlinear control technique to enhance dynamic performance of a shunt active power filter

This paper presents a new nonlinear decoupling control method of a three-phase three-wire voltage source shunt active filter. The currents injected by the active filter are controlled in the synchronous orthogonal dq frame using a decoupled feedback linearization control method. The reference currents are extracted from the sensed nonlinear load currents by applying the synchronous reference frame method. The voltage level of the DC side is regulated using an output feedback linearization control. Integral compensators are added in both current and voltage loops in order to eliminate the steady state errors due to system parameters uncertainty. Simulation results confirm the performance considered theoretically for the shunt active filter.

N. Mendalek

Papers

Correction to “Experimental Design of a Nonlinear Control Technique for Three-Phase Shunt Active Power Filter”

A New Control Technique for Three-Phase Shunt Hybrid Power Filter

Modeling and nonlinear control of shunt active power filter in the synchronous reference frame

Nonlinear control technique to enhance dynamic performance of a shunt active power filter

Nonlinear control strategy applied to a shunt active power filter