Tokuo Ohnishi

Three phase PWM converter/inverter by means of instantaneous active and reactive power control

A novel PWM (pulse-width-modulated) technique for the three-phase PWM converter/inverter is proposed. The instantaneous active and reactive power are used as the PWM control variables instead of the three-phase line currents. They are directly controlled by the PWM switching from the appropriate voltage vector selection. The features of the proposed PWM technique are simple construction, high efficiency, high response, and wide application. The principle of the PWM technique, the PWM control system, the control circuit, the control range, and the design indexes are described. Some simulation results and experimental results are shown.<<ETX>>

An improved voltage vector control method for Neutral-Point-Clamped inverters

A new PWM method for Neutral-Point-Clamped (NPC) inverters is introduced. The method is based on closed-loop control of the line-to-line voltage vectors. It uses independent hysteresis comparator controllers to regulate the direct and quadrature axis components of the three phase output voltages. The controllers select the appropriate inverter output voltage vectors through an EPROM table. The closed-loop control allows a high performance over the whole range of operation, even when low speed devices such as the GTO are used. A neutral-point potential control is described, which is capable of stabilizing the variations within fixed limits during steady and transient states. The principle of the method is discussed and the vector selection technique is presented. The effectiveness in the output-voltage-waveform generation and the balance of the DC-link capacitor voltages are verified by simulation and experiment.<<ETX>>

A new PWM inverter for photovoltaic power generation system

In this paper, the authors propose a novel multi-step PWM inverter for a solar power generation system. The circuit configuration is constructed by adding a bi-directional switch to the conventional bridge type inverter circuit using the isolated DC power supply for which the solar cell is very suitable. The new type of PWM inverter presented has many features such as good output waveform, small size of filter, low switching losses, and low acoustic noise. In this paper the authors describe the circuit configuration, control method and the characteristics of the system, and they also investigate the relation between the inverter and the solar cell characteristics. Finally, some simulation results and experimental results are shown.<<ETX>>

DC voltage sensorless single-phase PFC converter

We propose a simple DC voltage sensorless single phase PFC converter by detecting an AC line voltage waveform. Both DC voltage and AC current sensors used in the conventional PFC converter are not required to construct the control system. The conventional converter circuit with a boost chopper circuit in the DC side from a rectifier circuit is used as the main PFC converter circuit. In the control system, the circuit parameters such as a series inductance L and equivalent load resistance value R/sub d/ are used to generate the sinusoidal current waveform. The DC voltage is directly controlled by the command input signal k/sub d/(=E/sub d//E/sub a/) for the boost chopper circuit. The DC voltage regulation is small because of the feed forward control for the AC line voltage E/sub a/ and no dependence of the circuit parameters. The sinusoidal current waveform in phase with the AC line voltage can be obtained. The feasibility of the proposed control system is verified by some simulation and experimental results.

V/f control of permanent magnet synchronous motors suitable for home appliances by DC-link peak current control method

This paper presents a sensorless sinusoidal driving method of permanent magnet synchronous motors (PMSMs) for fans and pumps by V/f control. The proposed method is a simple method that controls DC-link peak currents by a single shunt resistor and a peak detector. Due to the damping factor from the square torque load characteristics of fans and pumps, the drives of PMSMs for fans and pumps by V/f control can be stabilized at starting and steady state. In general, pressure losses of the fluid pass of fan and pump systems are nearly constant; therefore, the flow rate and motor torque are determined by revolutions. Accordingly, high efficiency driving is possible by setting the reference currents corresponding to the q-axis currents at target revolutions. Because of the simple and low cost sensorless control, the proposed method is suitable for fan and pump motor driving systems of home appliances.

Single phase amplitude modulation inverter for utility interaction photovoltaic system

In this paper, a new inverter for a utility interactive photovoltaic system is proposed. This system consists of the DC converter that generates the single phase absolute value of sinusoidal current and a square wave voltage inverter which synchronizes with the AC power source. This DC converter consists of two switching devices and a capacitor for a nondissipative snubber circuit. The DC converter is applied to a pulse width modulation to obtain absolute value of sinusoidal current. It is not necessary to set the dead time of the switching devices in generating waveforms. Therefore, we can regard the dead time effects as small. The inverter is switched by the AC power source frequency so the line noise of voltage and current caused by the high frequency switching is very small. In this paper, it is confirmed by simulation that the proposed inverter for a new photovoltaic system has stable operation and good output characteristics are obtained by the experimental results.

Power compensation system for partially shaded PV array using electric double layer capacitors

In this paper, the power compensation and control system for the partially shaded photovoltaic (PV) array is presented. The proposed system utilizes electric double layer capacitors (EDLCs), which has some advantages, e.g. the high density of output power, the long lifetime, compared with other energy storage devices. This system is constructed by the simple combination of EDLCs-bank and a relay. Comparing with the prevalent measures, the proposed system can realize more efficient usage of generation power from PV array. The feasibility of the system is investigated and verified from some simulation results.

Observation of frequency oscillation in western Japan 60 Hz power system based on multiple synchronized phasor measurements

Western Japan 60 Hz power system is a longitudinal power system which consists of interconnected six major electric power companies. Though the power system has some interesting oscillation characteristics, there were few researches based on observation as a whole system. Authors have constructed an online global monitoring system of the power system dynamics, which is based on multiple synchronized phasor measurement technique using time stamp of the Global Positioning System (GPS) and Internet. This paper presents some results of observing system frequency oscillation and discussed the difference among the measured point. System dynamics due to the load frequency control (LFC) can be extracted from observed frequency oscillations by time-frequency analysis based on the Wavelet transform. Because variations of phase difference between the interconnected two areas are closely related with tie line power flow variations, relations between the frequency oscillations and the LFC are also investigated.

Line voltage sensorless three phase PWM converter by tracking control of operating frequency

Much research about a power line voltage sensorless PWM converter has been presented from the view points of the simplicity and the reliability of the control system. Most schemes need some calculations to estimate the power line voltage using circuit parameters. In this paper, we propose a novel control strategy of the three phase PWM converter by tracking control of the operating frequency based on the power balance of the converter. The system is composed of the direct PWM control loop of the instantaneous active and reactive current. The features of the proposed PWM control system are simplicity without sensing the line voltage, high reliability with poor dependence of the circuit parameters, high efficiency and fast response etc.

Simple structure and control method for a neutral-point-clamped PWM inverter

A new configuration for a neutral point clamped PWM inverter and its control strategy is proposed. The proposed configuration consists of an auxiliary circuit with four switching devices and a single full-bridge inverter. The control method is based on closed-loop regulation of the instantaneous line-to-line output voltages. The proposed scheme is simple, has fast response, and is effective for reducing the size of the DC-link capacitors. The performance of the system is verified by computer simulation and by experiment.<<ETX>>