Satoshi Ogasawara

Modeling and damping of high-frequency leakage currents in PWM inverter-fed AC motor drive systems

This paper presents an equivalent circuit for high-frequency leakage currents in PWM inverter-fed AC motors, which forms a series resonant circuit. The analysis based on the equivalent circuit leads to such a conclusion that the connection of a conventional common-mode choke or reactor in series between the AC terminals of a PWM inverter and those of an AC motor is not effective to reduce the RMS and average values of the leakage current, but effective to reduce the peak value. Furthermore, this paper proposes a common-mode transformer which is different in damping principle from the conventional common-mode choke. It is shown theoretically and experimentally that the common-mode transformer is able to reduce the RMS value of the leakage current to 25%, where the core used in the common-mode transformer is smaller than that of the conventional common-mode choke.

Analysis of variation of neutral point potential in neutral-point-clamped voltage source PWM inverters

The authors present the analysis of the neutral-point potential variation of the neutral-point-clamped voltage source PWM (pulse-width-modulation) inverter (NPC-VSI) for AC motor drives and static VAr compensators (SVC). The potential variation is analyzed with the focus on the current flowing out of or into the neutral point of the DC link. The theoretical minimum capacity of the DC link capacitors is discussed for its application to both a vector-controlled induction motor system of 2.2 kW and a SVC system of 10 MVA, 6.6 kV, 60 Hz. It is shown that the proposed control scheme makes it possible to suppress the neutral-point potential variation within a few percent, so that the total capacity of the DC link capacitors in the NPC-VSI is almost the same as that in the conventional voltage source inverter.<<ETX>>

Implementation and performance of cooperative control of shunt active filters for harmonic damping throughout a power distribution system

This paper proposes the cooperative control of multiple active filters based on voltage detection for harmonic damping throughout a power distribution system. The arrangement of a real distribution system would be changed according to system operation, and/or fault conditions. In addition, shunt capacitors and loads are individually connected to, or disconnected from, the distribution system. Independent control might make multiple active filters produce unbalanced compensating currents. This paper presents hardware and software implementations of cooperative control for two active filters. Experimental results verify the effectiveness of the cooperative control with the help of a communication system.

Implementation and position control performance of a position-sensorless IPM motor drive system based on magnetic saliency

This paper describes position-sensorless control of an interior permanent magnet synchronous motor (IPM motor), which is characterized by real-time position estimation based on magnetic saliency. The real-time estimation algorithm detects motor current harmonics and determines the inductance matrix including rotor position information. An experimental system consisting of an IPM motor and a voltage-source PWM inverter has been implemented and tested to confirm the effectiveness and versatility of the approach. Some experimental results show that the experimental system has the function of electrically locking the loaded motor, along with a position response of 20 rad/s and a settling time of 300 ms.

Circuit configurations and performance of the active common-noise canceler for reduction of common-mode voltage generated by voltage-source PWM inverters

This paper discusses two different circuit configurations of the active common-noise canceler (ACC) which has been proposed by the authors. One is characterized by its DC power supply isolated from the DC link of a PWM inverter. The configuration makes it possible to integrate the ACC with a medium-voltage PWM inverter. The other compensates a partial frequency component of the common-mode voltage. The purpose is not to achieve complete cancellation, but to restrict only a slope in a change of the common-mode voltage applied to an AC motor. As a result, the core size of the common-mode transformer used in the ACC becomes considerably small. Experimental results show good effects of the proposed active circuits on both ground current and conducted EMI.

Analysis and reduction of EMI conducted by a PWM inverter-fed AC motor drive system having long power cables

This paper analyzes conducted EMI generated by a PWM inverter-fed induction motor drive system. It is shown experimentally and analytically that resonant phenomena in a high-frequency range beyond a dominant resonant frequency are originated from the behavior of power cables as a distributed-constant circuit. Spectra of common-mode and differential-mode currents are simulated by means of introducing a distributed-constant model of the power cables, which consists of a 20-step ladder circuit. As a result, it is also shown that these resonances can be damped out by a single common-mode transformer (CMT) and three differential-mode filters (DMFs), both of which have been proposed by the authors.

Measurement and reduction of EMI radiated by a PWM inverter-fed AC motor drive system

This paper presents theoretical and experimental relationships in between radiated electromagnetic noises and common-mode and normal-mode currents, paying attention to an induction motor drive system fed by a voltage-source PWM inverter. A method of reducing both the currents is proposed, based on an equivalent model taking parasitic stray capacitors inside an induction motor into account. Electromagnetic interference (EMI) radiated by a 3.7 kW induction motor drive system is actually measured, complying with the VDE 0871 Class A [3m]. Experimental results verify that the combination of the already proposed common-mode transformer and the normal-mode filters being proposed in this paper is a practically viable and effective way to reduce the EMI resulting from both the common-mode and normal-mode currents.

Suppression of common-mode voltage in a PWM rectifier/inverter system

This paper proposes a PWM rectifier/inverter system capable of suppressing not only supply harmonic currents but also electromagnetic interference (EMI). An active common-noise canceler (ACC) developed for this system is characterized by sophisticated connection of a common-mode transformer which can compensate for common-mode voltages produced by both PWM rectifier and inverter. As a result, the size of the common-mode transformer can be reduced to 1/3, compared with the previously proposed ACC. A prototype PWM rectifier/inverter system (2.2 kW) has been implemented and tested. Some experimental results show reduction characteristics of the supply harmonic current and EMI.

An approach to real-time position estimation at zero and low speed for a PM motor based on saliency

This paper presents a magnetic saliency based position estimation approach for a PM motor fed by a voltage-source PWM inverter. The proposed real-time estimation algorithm detects the motor current harmonics and calculates the inductance matrix including the rotor position information. The position estimation can be performed every period of pulse-width-modulation or carrier cycle. An experimental system using an interior permanent magnet (IPM) synchronous motor has been constructed. Experimental results verify that the position estimation within 10 degrees in electrical angle is obtained at standstill and such an extremely low-speed as 1 r/min by the proposed approach.

An approach to a broad range of power control in voltage-source series-resonant inverters for corona discharge treatment-pulse-density-modulation

This paper implements a wide range of power control with pulse-density-modulation (PDM) in a voltage source series-resonant inverter which realizes a corona discharge for the surface treatment of films. The use of the PDM inverter enables the employment of a three-phase diode bridge rectifier as an electric utility interface. The PDM inverter produces either a square-wave AC voltage state or a zero voltage state at its AC terminals to control the discharge power of a corona surface treater. Moreover, it can achieve zero-current-switching (ZCS) and zero-voltage-switching (ZVS) under all the operating conditions, thus leading to a significant reduction of switching losses and electromagnetic noise. A 80 kHz, 6 kW surface treatment system consisting of a voltage-source PDM inverter, a step-up transformer and a corona discharge treater shows the establishment of a stable corona discharge in an extremely wide range of power control from 0.5 to 100 %, and therefore succeeds in performing both strong and weak surface treatment processes for films.