The effectiveness of an active power filter depends basically on three characteristics: (a) the modulation method used; (b) the design characteristics of the PWM modulator; and (c) the method implemented to generate the reference template. For the last characteristic there are many methods, most of them complicated and hence difficult to implement and adjust. In this paper, a new method, which has simplicity at its main characteristic, is presented. The method is based on "sample and hold" circuits, synchronized with the peak value of the phase-to-neutral mains voltage. This method is useful for shunt active power filters and is capable to eliminate harmonics, compensate power factor, and correct unbalance problems simultaneously. It also has the ability to slow-down sudden transient changes in the load. Experimental results, with the reference template obtained with the method, are presented in the paper.

Control system for three-phase active power filter which simultaneously compensates power factor and unbalanced loads

In this paper, a new power line conditioning system is proposed. This system is constructed by a flying capacitor multilevel VSC (voltage source converter) and two reactors. The phase-shift SPWM (sinusoidal pulse width modulation) switching scheme is applied to control the switching devices of this converter. Due to this multilevel VSC and the switching scheme applied to this converter, the system is applicable to distribution systems or industrial applications. The reactive power compensation, harmonic suppression and load balancing functions of the power line conditioner are analyzed. A novel and effective startup procedure is proposed to start up the system. System simulation is carried out to verify the theoretical analysis results.

A power line conditioner based on flying capacitor multilevel voltage source converter with phase shift SPWM

A full compensating system for distribution networks, able to eliminate harmonics, correct unbalanced loads, and generate or absorb reactive power, is presented. The system is based on a combination of a thyristor binary compensator (TBC), and a pulsewidth-modulation insulated gate bipolar transistor active power filter (APF) connected in cascade. The TBC compensates the fundamental reactive power and balances the load connected to the system. The APF eliminates the harmonics and compensates the small amounts of load unbalances or power factor that the TBC cannot eliminate due to its binary condition. The TBC is based on a chain of binary-scaled capacitors and one inductor per phase. This topology allows, with an adequate number of capacitors, a soft variation of reactive power compensation and a negligible generation of harmonics. The capacitors are switched on when the line voltage reaches its peak value, avoiding inrush currents generation. The inductor helps to balance the load, and absorbs reactive power when required. The APF works measuring the source currents, forcing them to be sinusoidal. The two converters (TBC and APF) work independently, making the control of the system simpler and more reliable. Simulations show that the system is able to respond to many kinds of transient perturbations in no more than a couple of cycles. The paper analyzes the circuit proposed, the way it works and shows some experimental results obtained under operation.

A full compensating system for general loads, based on a combination of thyristor binary compensator, and a PWM-IGBT active power filter

In this paper, a novel method for the voltage-controlled grid-connected inverter with the function of islanding detection is proposed for the distribution power generation system. The salient features of the proposed voltage-controlled grid-connected inverter are simple control circuit and fast transient response. Besides, an islanding detection method is proposed and incorporated into the controller of a voltage-controlled grid-connected inverter. The proposed islanding detection method will cause variation in amplitude and frequency of the load voltage when the utility is interrupted so as to immediately detect the islanding operation. A prototype is developed and tested to demonstrate the performance of the proposed voltage-controlled grid-connected inverter. The experimental results show that the performance of the proposed voltage-controlled grid-connected inverter is as expected.

A Simplified Control Method for the Grid-Connected Inverter With the Function of Islanding Detection

This paper presents a critical analysis of various topologies for power circuits used in power line conditioners designed to attenuate or remove disturbances in the electric power system. By defining a series of merit figures, it becomes possible to appraise the desirable qualities shown by the technical and economical aspects in each configuration. There is also a description of the basic lines for designing practical equipment. Finally, experimental results of a novel topology which reconfigures to UPS operation in the case of a power line failure are shown to confirm the validity of the prospective method.

Active power filters for line conditioning: a critical evaluation

The performance and dynamic characteristics of a solid-state line conditioning system which simultaneously eliminates line current harmonics and compensates load power factor is presented and analysed. The line conditioning system is implemented with a pulsewidth modulated voltage-source inverter. Power factor compensation is achieved by controlling the magnitude and the phase angle (delta) of the transistorised PWM inverter output voltage. Fast response times are obtained by adjusting the amplitude of the PWM inverter output voltage through a modulation index control. The principal advantage of this scheme is that it can maintain a near unity mains overall power factor without sensing and computing the associated reactive power component. It can also substantially reduce the harmonic content of the line current when the load is nonlinear. A time domain model is derived and used to accurately predict dynamic behaviour, the stability region and to adjust system controllers. The transfer function of the line conditioning system for open-loop and closed-loop operation is derived. Experimental results confirm the operation characteristics obtained by computer simulation and mathematical analyses.

Line conditioning system with simple control strategy and fast dynamic response

The performance and dynamic characteristics of a solid-state power factor compensator which simultaneously eliminates line current harmonics are presented and analyzed. Power factor compensation is achieved by controlling the magnitude and the phase angle (delta) of the transistorized PWM inverter output voltage. Fast response times are obtained by adjusting the amplitude of the PWM inverter output voltage through a modulation index control. The principal advantage of this scheme is that it can maintain a near unity mains overall power factor without sensing and computing the associated reactive components. It can also substantially reduce the harmonic content of the line current when the load is nonlinear. A time domain model is derived and used to accurately predict dynamic behavior and stability region, and to adjust system controllers. The transfer function of the power factor compensator is obtained. Experimental results confirm the operation characteristics obtained by computer simulation and analyses. >

E. Mora

Papers

Line conditioning system with simple control strategy and fast dynamic response

Performance analysis of a power factor compensator which simultaneously eliminates line current harmonics