The paper proposes several concepts of integrators for sinusoidal signals. Parallel and series associations of the basic PI units using the stationary frame generalized integrators are used for current control of active power filters. Zero steady state error for the concerned current harmonics are realized, with reduced computation, under unbalanced utility or load conditions. Designing of the PI constants, digital realization of the generalized integrators, as well as compensation of the computation delay etc. are studied. Extensive test results from a 10 kW active power filter prototype are demonstrated.

Stationary-frame generalized integrators for current control of active power filters with zero steady-state error for current harmonics of concern under unbalanced and distorted operating conditions

Use of multilevel inverters is becoming popular in recent years for high power applications. Various topologies and modulation strategies have been investigated for utility and drive applications in literature. Trends in power semiconductor technology indicate a trade-off in the selection of power devices in terms of switching frequency and voltage sustaining capability. New power converter topologies permit modular realization of multilevel inverters using a hybrid approach involving integrated gate commutated thyristors (IGCT) and insulated gate bipolar transistors (IGBT) operating in synergism. This paper is devoted to the investigation of a hybrid multilevel power conversion system typically suitable for high performance, high power applications. This system designed for 4.16 kV, /spl ges/100 hp load comprises of a hybrid seven-level inverter, a diode bridge rectifier and an IGBT rectifier per phase. The IGBT rectifier is used on the utility side as a real power flow regulator to the low voltage converter and as a harmonic compensator for the high voltage converter. The hybrid seven-level inverter on the load side consists of a high voltage, slow switching IGCT inverter and a low voltage, fast switching IGBT inverter. By employing different devices under different operating conditions, it is shown that one can optimize the power conversion capability of entire system. A detailed analysis of a novel hybrid modulation technique for the inverter, which incorporates stepped synthesis in conjunction with variable pulse width of the consecutive steps is included. In addition, performance of a multilevel current regulated delta modulator as applied to the single phase full bridge IGBT rectifier is discussed. Detailed computer simulations accompanied with experimental verification are presented in the paper.

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Hybrid multilevel power conversion system: a competitive solution for high power applications

This paper presents the comparative evaluation of the performance of three state-of-the-art current control techniques for active filters. The linear rotating frame current controller, the fixed-frequency hysteresis controller, and the digital deadbeat controller are considered. The main control innovations, determined by industrial applications, are presented, suitable criteria for the comparison are identified, and the differences in the performance of the three controllers in a typical parallel active filter setup are investigated by simulations.

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Comparison of current control techniques for active filter applications

This paper proposes a control algorithm for parallel active power filters, based on current-controlled pulsewidth-modulated converters, which allows precise compensation of selected harmonic currents produced by distorting loads. The approach is based on the measurement of line currents and performs the compensation of the selected harmonics using closed-loop synchronous frame controllers. Thanks to the closed-loop operation, full compensation of the desired harmonics is achieved even in the presence of a significant delay in the current control. Thanks to the selective approach, active filter interactions with possible dynamic components of the load are minimized. Moreover, the complexity of the synchronous frame controllers is overcome using equivalent stationary frame controllers. Experimental results confirm the theoretical expectations.

A closed-loop selective harmonic compensation for active filters

This article gives a survey of the commonly used methods for harmonic detection in active power filters (APFs). The work proposes a simulation setup that decouples the harmonic detection method from the active filter model and its controllers. In this way, the selected methods can be equally analyzed and compared with respect to their performance, which helps in anticipating possible implementation issues. A comparison is given that may be used to decide the future hardware setup implementation. The comparison shows that the choice of numerical filtering is a key factor for obtaining a good accuracy and dynamic performance of an active power filter.

Detection is key - Harmonic detection methods for active power filter applications

Adjustable speed AC drives with low input current THD are becoming increasingly important in industry. This article has detailed the implementation of a parallel active filter, which is integrated within a 450 kW adjustable speed drive to provide an overall system which conforms to IEEE 519, and which provides significant benefits on a system level. The design of the active filter is seen to be driven by overall system specifications which include input current THD, efficiency, displacement power factor, a high level of integration with the load converter, and cost targets. Active filter operation and control has been analyzed at a detailed level, and fundamental issues relating to current regulator topology and operation, limits on compensation capability, DC bus control, switching frequency ripple suppression, etc., have all been addressed, and have all been shown to be very important in terms of helping the system meet its performance objectives. The overall drive system including the active filter, meets IEEE 519 by reducing the supply current THD from 26.8% without the active filter to 4.1% with the active filter operating. This is achieved in presence of supply voltage THD of 2.3% and filter terminal voltage V/sub f/ unbalance of 1.3% and, includes an ASD load induced subharmonic component at 33 Hz. Further, individual harmonic limits are met up to the 35th harmonic.

Active filter system implementation

This paper presents a parallel active filter system implementation for utility interface of an an adjustable speed drive air-conditioner chiller application to meet IEEE 519 recommended harmonic standards. Specifications of displacement power factor, efficiency, cost, size and packaging requirements with the rectifier front-end topology are used to determine the optimal active filter solution. Design issues and interaction of parallel active filter inverter switching ripple filter, rectifier front-end and supply are addressed. A synchronous reference frame based controller and a predictive charge error based current regulator and their hardware implementation has been developed for the parallel active filter. Experimental results of the parallel active filter system are presented for a 'stiff' utility system interface of a 450 kW adjustable speed drive air-conditioner chiller application to meet IEEE 519 harmonic limits in the supply current.

T.M. Frank

Papers

Active filter system implementation

Parallel active filter system implementation and design issues for utility interface of adjustable speed drive systems