Teruo Kataoka

A new control strategy for voltage type PWM rectifiers to realise zero steady-state control error in input current

In this paper, a new simple control strategy for AC input current of voltage type PWM rectifiers which can eliminate the steady state control error completely is proposed. This control method requires neither the instantaneous value of the supply voltage nor any accurate circuit parameters on the AC side of the rectifier. Thus, a robust operation against the variation of the circuit parameters can be achieved. In the proposed control system, a digital resonant element implemented by a digital signal processor is introduced as a feedback controller. The digital resonant element exhibits a function similar to an integrator for the fundamental frequency components. Thus, it can eliminate the steady state control error of the input current completely. The principle of the proposed control method is discussed and its effectiveness is shown theoretically. The detailed method of the implementation of the loss-less digital resonant element is explained. The effects of the harmonics in the supply voltage on the AC input current waveform are clarified. To confirm the effectiveness of the proposed control method, some experimental results from two laboratory test systems are shown.

A Pulsewidth Controlled AC-to-DC Converter to Improve Power Factor and Waveform of AC Line Current

As a method for improving power factor and waveform of ac line current drawn by an ac-to-dc converter a new pulsewidth controlled converter is proposed, its commutation mechanism is described, and experimental results are given which show a good power factor, a good waveform of the line current, and a wide adjustable range of dc output voltage.

A current-type PWM rectifier with active damping function

A new control method for current-type pulse-width modulation (PWM) rectifiers which can provide active damping function is presented. This damping function is effective only on the harmonic components of AC input current selectively. Thus steady-state waveform distortion and transient oscillation of the input current are reduced by the active damping effects. The active damping function can be realized by feedback control of an LC filter connected to the AC side of the rectifier, and it does not require any additional components in the main circuits, permitting a simple circuit configuration. The control system of the proposed PWM rectifier is analyzed by using a simple block diagram developed in the present paper. From the analytical results, the influence of the circuit parameters and control delay on the active damping effects and the stability of the operation are clarified to establish the design method. To confirm the effectiveness of the active damping function, some results of basic experiments are included. As an example of application of the active damping function, the proposed rectifier is applied to reduce the harmonic currents generated by conventional rectifiers operating in parallel with the proposed rectifier. Some experimental results in this application are also included.

Damping of transient oscillations on the output LC filter of PWM inverters by using a virtual resistor

This paper presents a method to damp transient oscillations on the output LC filter of PWM inverters by using a virtual resistor. A virtual resistor is an additional control algorithm that simulates the roles of a resistor in the output LC filters. Because no real resistor is used, the oscillations can be damped effectively without sacrificing the power efficiency. The implementation of the virtual resistor is determined by how the resistor is connected to the LC filter. Experimental results are included to verify the proposed method.

State feedback control of current type PWM AC-to-DC converters

A control method of current type PWM AC-to-DC converters which realize sinusoidal AC input current and unity power factor is discussed. In such a type of converter, an LC filter required on the AC side may cause a resonant problem especially in the transient condition. To overcome this problem, state feedback control is introduced, and a control strategy which is suitable for the DC output current control as well as the AC side current control is proposed. Circuit parameters and feedback coefficients in the AC side current control system are optimized on the basis of an analysis in which the system is treated as a sampled data system. This system is applied to current pattern control of a reactor.<<ETX>>

A new state feedback based transient control of PWM AC to DC voltage type converters

This paper presents a new state feedback based control strategy for a PWM AC to DC voltage type converter with phase and amplitude control. In this control strategy the state variables of the LC filter connected to the AC side of the converter are fed back to the PWM pattern generator, thereby eliminating a DC offset of the AC input currents as well as oscillations of the DC output current during transients. Computer simulation of the converter system with the proposed control strategy shows that the transient waveforms of AC input and DC output currents are improved greatly even if the damping effect of the AC side resistance can not be expected. The DC voltage regulation with good dynamic response is also achieved even if DC capacitance is substantially reduced. Experimental results from a low power laboratory model are also included to confirm the simulated results and to demonstrate the effectiveness of the proposed control strategy. >

Analysis and minimization of ripple components of input current and voltage of PWM inverters

Analysis and minimization of the ripple components of the input current and voltage of three-phase voltage-source pulsewidth modulated (PWM) inverters are presented in this paper. The analytical expressions for the rms values of the input current and voltage ripples as a function of the shape of the PWM reference signal are derived. It is found that the reference signal which produces a minimum ripple in the input voltage varies as a function of the load power factor. It is also found that the rms value of the inverter input current ripple does not depend on the shape of the reference signal. In respect of the inverter input current and voltage ripples, the addition of harmonics other than the third into the sinusoidal reference is neither useful nor necessary. Experimental results are included to verify the derived expressions.

Application of an extended Kalman filter to parameter identification of an induction motor

An extended Kalman filter is used to identify the parameters of an induction motor using measurements of the stator voltages, currents, and rotor speed. A model of the induction motor in the state space and the Kalman filter algorithm are shown. This filter is applied to the parameter identification of an inverter-fed induction motor. A simple and practical method of setting the covariance matrices of the noises, which are important in the Kalman filter algorithm, is proposed. The starting values of the state and parameter vectors as well as the covariance matrix of the estimation error are then shown, and, finally, the results of parameter identification are shown. The results demonstrate that the filter is capable of identifying the parameters.<<ETX>>

Transient Performance Analysis of Self-Controlled Synchronous Motors

The transient performance of self-controlled synchronous motors which are used as variable speed motors in industries is analyzed considering two types of position sensor used in these motors. A set of equations valid for the transient state is first derived and represented in a block diagram. Based on these equations, mechanical and electrical transient responses of the motors in the case of a step change in input voltage are analyzed. It is shown that the transient responses differ remarkably depending on the type of position sensor used. The transient characteristics of margin angle of commutation of thyristors are then compared in detail with the steady-state ones. It is shown that the thyristors in the inverter are commutated more successfully in the transient state than in the steady state when compared at the same dc input current. Finally, the transient responses in the case of a step change in load torque are investigated.

Characteristics analysis of transformer type superconducting fault current limiter

The transformer type superconducting fault current limiter, which is made up of a series transformer and a superconducting current limiting device, has many advantages such as the design flexibility of the current limiting device. However, the design strategy for determining the superconducting current limiting device ratings and the transformer ratings is unclear because the relations between the current limiting characteristics and these ratings are not analyzed enough. In this paper, the relations between the current limiting characteristics and these ratings are analyzed theoretically. The experimental results of the transformer type superconducting fault current limiter are also shown.