Unity Power Factor Control Research Articles

Line-voltage-sensorless active power filter for reactive power compensation

A line-voltage-sensorless three-phase active power filter is presented, and a current controller with fast dynamics for an active power filter is described, along with line synchronisation for an active power filter, which does not require any additional hardware. The line synchronisation can be properly operated under line-voltage distortion or notching and line-frequency variation. Reactive power compensation is achieved without computing the reactive current of the load. Current compensation is done in the time domain allowing a fast time response. The DC voltage-control loop keeps the voltage across the DC capacitor constant. Unity power-factor control by an active power filter is described. All control functions are implemented in software using a single-chip microcontroller, thus simplifying the control circuit. It is shown, via experimental results, that the proposed controller gives a good performance in the line-voltage-sensorless active power filter.

Unity power factor and efficiency control of a voltage source inverter-fed variable-speed induction motor drive

Variable speed AC drives with inverters contribute to the distortion of line side current waveforms and to poor power factors. They have inherent switching losses, and they also de-rate the motors due to harmonic losses. The scheme proposed here maintains the linearity of the modulation index throughout the speed range of the operation and the total losses within the permissible limit, and hence improves the de-rating of the motor. This is achieved by incorporating a boost converter in the conventional inverter-fed induction motor drives. This simple boost converter with a diode bridge rectifier enables unity-power-factor operation and improves the input current waveform. The magnitude of the DC bus voltage and proper selection of the switching pattern in the speed range, where the total loss exceeds the permissible loss-limit, is obtained by the control circuit. This unity-power-factor, efficiency- optimal control (UPFEOC) is achieved by using a personal computer. In this scheme, minimisation of the control hardware and application of a simple algorithm are implemented. The simulation results are validated with a prototype of an IGBT-based voltage-source inverter drive.

Control of a PWM Convertor for Linear Generator as a Variable Impedance

We are developing a linear generator system as an onboard power source for Maglev vehicles. This linear generator system mainly consists of power collecting coils and has a Pulse Width Modulated convertor that functions as an impedance to compensate for reactive power in the generator circuit. The PWM convertor detects only instantaneous currents and realizes unity power factor control with excellent performance. Nevertheless, the measured impedance of the circuit differs from that estimated from the parameters of PWM convertor. The system becomes unstable when we set certain impedance values for the PWM convertor.We analyzed the control system as a closed loop digital control system and we derived impedance realized in the circuit We also obtained stable areas of impedance and currents from the conditions of stability of digital control system. The analyzed results of stability were in agreement with simulation results.

A line-voltage-sensorless synchronous rectifier

A line-voltage-sensorless control for three-phase pulsewidth-modulated (PWM) synchronous rectifiers is presented. A line synchronization and unity power factor control are described. Indirect synchronization without sensing the line voltage allows a standard vector-controlled inverter to be used as a synchronous rectifier without requiring any additional hardware. Furthermore, the line synchronization can be properly operated under line voltage distortion or notching and line frequency variation. All control functions are implemented with a single-chip microcontroller. It is shown via experimental results that the proposed controller gives good performance for the synchronous rectifier.

Three-phase PWM synchronous rectifiers without line-voltage sensors

A line-voltage-sensorless control for three-phase pulse-width-modulated (PWM) synchronous rectifiers is presented. A line synchronisation and unity power factor control are described. Indirect synchronisation without sensing the line voltage allows a standard vector-controlled inverter to be used as a synchronous rectifier without requiring any additional hardware. Furthermore, the line synchronisation can be operated properly under line-voltage distortion or notching and line-frequency variation. It is shown via experimental results that the proposed controller gives good performance for the synchronous rectifier.

A power-factor controller for single-phase PWM rectifiers

A novel power-factor controller for single-phase pulsewidth modulated rectifiers is proposed. The unity power-factor controller for a sinusoidal input current is derived using the feedback linearization concept. Two active switches and two diodes are utilized for AC-to-DC power conversion. Experimental results obtained on a 4 kW prototype are discussed.

Linear Drive Systems and their Related Technologies. PWM Converter Using Instantaneous Current Detection for Linear Generator of Maglev Vehicle.

For power supply on-borad of Maglev vehicle using EDS (electrodynamic suspension) Maglev system and super-conducting magnets (SCM), an inductive power collection method is proposed, which gets electric power from induced voltage of the on-board power collection coils using magnetic field harmonics of ground coils. As for EDS, adoption of null-flux levitation and guidance is proposed because of less ground coil current being obtained than in the case of normal-flux levitation. In this case, a smaller magnetic field harmonics of ground coils and eddy currents of the outer vessel of the SCM result in a smaller electromotive force per one turn so that we need current collection coils with more turns, which means high source impedance. A normal full-wave rectifier can not give the needed electric power. So a PWM converter with a unity power factor control, which can cancel the power supply side impedance, is proposed. We have developed a PWM converter, which functions just like the active capacitor, using IGBT and instantaneous current control. We achieved a power factor × efficiency value of 0.97 in a stationary experiment of the system. Here are described the working principle, the simulation and the result of the stationary experiment.

Compensation strategies for shunt active-filter control

Compensation strategies for control of shunt active filters are compared in the paper. It is shown that the strategy based on unity-power factor control is appropriate when the supply voltage waveform of the plant where the active filter is connected shows significant distortion. As voltage distortion increases, this strategy provides compensated line current having lower harmonic distortion and RMS value with respect to the strategy generally used. This contributes to diminish the current and voltage distortion in networks. The unity-power factor compensation strategy conditions the current flowing in the plant where compensation is realized to fit the voltage waveform, thus reaching a unity power factor. Hence, the line current RMS value is minimum. The comparison of the strategies is performed by both Monte Carlo and ATP simulation. >