Takaharu Takeshita

Current waveform control of PWM converter system for harmonic suppression on distribution system

The voltage waveform on the electric power distribution system is distorted by harmonic-producing loads. Regardless of the terminal voltage waveform with or without harmonics, the conventional current waveform of the pulsewidth-modulated converter systems connected to the power distribution system is always controlled to be sinusoidal. For harmonic suppression of the voltage and current on the distribution system, the authors propose the distorted current waveform whose harmonic components are in phase with the terminal voltage harmonics. The effectiveness of the proposed current waveform has been verified by experiments.

A new sensorless drive of brushless DC motor

A position and speed sensorless drive of a brushless DC motor is presented which provides high-quality torque control. Motor position and speed information is obtained by using the current difference between a model and an actual motor. The current difference is decomposed into two components. One is used for estimation of position while the other is used for estimation of speed. Therefore, independent estimation is possible. Experimental results based on the proposed algorithm are presented which demonstrate desired control characteristics both in steady state and starting conditions.<<ETX>>

PWM control and input characteristics of three-phase multi-level AC/DC converter

The authors discuss the current control and pulse width modulation (PWM) pattern generation of a multilevel power converter which is capable of producing three levels of phase voltage. In the proposed current control, fast response is realized by introducing a converter model in the control algorithm and the effect of parameter difference between the model and an actual system is compensated for through proportional-plus-integral control of current difference. In PWM pattern generation, the balance of two capacitor voltages is taken into account. For the same sampling period, the current distortion factor of the proposed system can be approximately reduced to 60% of that of a conventional two-level power converter. The prototype was made using a digital signal processor, and simulation and experimental results were compared.<<ETX>>

A single to three phase matrix converter with a power decoupling capability

This paper deals with a new approach for single to three phase matrix converters. In almost all of these converters, three-phase voltages and currents are distorted because of the inherent fluctuation of single-phase instantaneous power. On the contrary, in our proposed matrix converter, that fluctuation is compensated for and three phase voltages and currents can be controlled to be pure sine wave. Our circuit is composed of the conventional single to three-phase matrix converter circuit, an AC reactor and three bi-directional switches. By using the single-phase instantaneous active and reactive power theory (ps-qs theory), the ripple component of the single-phase instantaneous power is detected and is sorted in the AC reactor. Some significant characteristics are verified by means of a simulation with a 200 V/3.7 kW PM motor.

Sensorless control and initial position estimation of salient-pole brushless DC motor

This paper presents a position sensorless drive and an initial rotor position estimation for a salient-pole brushless DC motor with a sinusoidal flux distribution. To estimate the position and back EMF, the controller calculates the motor current by using the estimated position and back EMF of the motor model. The difference between the actual and the calculated currents is used to estimate the position and back EMF. The initial rotor position at standstill should be estimated for stable starting without temporary reverse revolution. The principle of the initial position estimation relies on the saliency of the motor and uses the current response difference due to the rotor position. To confirm the effectiveness of the proposed algorithm, experimental results using a 6-pole 200 W test motor are shown.

All Nodes Voltage Regulation and Line Loss Minimization in Loop Distribution Systems Using UPFC

Voltage regulation and line loss minimization in distribution networks are challenging problems, particularly when it is not economic to upgrade the entire feeder system. This paper presents a new method for achieving line loss minimization and all nodes voltage regulation in the loop distribution systems, simultaneously, by using unified power flow controller (UPFC), one of the most important FACTS devices. First, the line loss minimum conditions in the loop system are presented. Then, load voltage regulation is applied under line loss minimum conditions. Reference voltage of the controlled node is determined based on the assumption that this voltage can subsequently improve all node voltages to be within the permissible range. Also, the proposed control scheme of the UPFC series converter, to regulate all node voltages under line loss minimization, is presented. The effectiveness of the proposed control scheme has been experimentally verified.

Matrix converter control using direct ac/ac conversion method for reducing output voltage harmonics

This paper presents a control scheme of matrix converters for reducing the output voltage harmonics. The proposed control scheme is based on the direct AC/AC conversion approach and the carrier-based PWM control to obtain the constant switching frequency. The proposed scheme can realize the simultaneous control of both the output voltage and the input power factor. The feature of the proposed control scheme is the reduction of both the output voltage harmonics and the number of the commutations. The effectiveness of the proposed control algorithm of the matrix converters has been verified by experiments.

Modeling and harmonic suppression for power distribution systems

Expansion of voltage distortions along power distribution systems, which is referred to as the harmonic propagation, is pointed out. This is caused by the LC resonances between the distribution line inductances and the power capacitors. This paper presents a modeling and harmonic suppression procedure for power distribution systems. In our proposal, the power distribution system is analyzed based on the modal analysis and it is represented by a reduced-order model. For the harmonic suppression, a series active filter is used and its controller is designed based on the reduced-order model so as to cancel the dominant LC resonances in the power distribution system. Some significant characteristics are verified by experiments using a single-phase power distribution system.

Stator-flux-oriented sensorless induction motor drive for optimum low-speed performance

For high-performance AC drives, the speed-sensorless vector control of induction motors has received increasing attention from the standpoints of cost, size, noise immunity, and reliability. This paper presents the speed- and voltage-sensorless drive of vector-controlled induction motors for general-purpose drive applications. The rotor speed is determined by the difference between the synchronous angular frequency and the estimated slip angular frequency, which is estimated by the detected stator current and the stator-flux reference. To improve the low-speed drive characteristics, accurate applied-voltage calculation is proposed under considerations of the compensations for the quantization error in the digital controller, the forward voltage drop of switching devices, and the dead time of the inverter. The experimental studies show the improved drive characteristics.

Line Loss Minimization in Isolated Substations and Multiple Loop Distribution Systems Using the UPFC

This paper presents the line loss minimum condition in isolated substations and same substation multiple loop distribution systems by using the unified power flow controller (UPFC). In each case, the mathematical model is presented and the line loss minimum conditions are obtained based on the line parameters of the distribution feeders. Since multiple loop distribution system is fed from same substation, the line loss minimization can be achieved by compensating the summation of the line reactance voltage drop. In an isolated substation loop distribution system, the line loss minimization can be achieved by compensating the summation of the line reactance voltage drop in addition to the voltage difference of the substations. Realization of both cases can be achieved if the loop current is eliminated from the loop system. The series compensation technique applied by the UPFC is used to eliminate the loop current from the loop distribution system and hence minimize the total line loss. The effectiveness of the proposed control schemes of the UPFC have been verified experimentally.