Kiyoaki Sasagawa

Voltage-balancing method for IGBTs connected in series

This paper presents a new method for balancing voltages of series-connected insulated gate bipolar transistors (IGBTs). This method can be implemented only by adding simple circuits to the gate drive system of the IGBTs, and its effect of balancing the IGBTs collector-emitter voltages during the switching transients is remarkable. This principal strategy and experimental results with series-connected IGBTs are first described. After that, further experimental results are shown from the switching tests of four 2.5-kV flat-packaged IGBTs connected in series. Through the switching tests, superior characteristics of the proposed method have been confirmed.

Fundamental characteristics of five-level double converters with adjustable dc voltages for induction motor drives

In this paper, two kinds of control strategies for a three-phase five-level double converter are described on the assumption that the converter is applied to an induction motor drive system. The purposes of the proposed control strategies are to correct voltage imbalance of the DC-bus capacitors, to keep the input power factor at near unity, and to achieve an adjustable-speed drive. Characteristics of the converter operated by each of the two control strategies are examined and the validity is verified by experiments using a 3.7-kW induction motor.

Voltage balancing method for IGBTs connected in series

This paper presents a new method to balance the voltages of the series connected IGBTs. This method can be realized only by adding simple circuits to the gate drive system of the IGBTs, and its effect of balancing the IGBTs collector-Emitter voltages during the switching transients is remarkable. Principal of this strategy and experimental results with series connected two IGBTs are described firstly. After that, further experimental results are set forth, which are switching tests with four 2.5 kV flat-packaged IGBTs connected in series. Through the switching tests, superior characteristics of the proposed method have been confirmed.

A Novel Commutation Method of Matrix Converter Fed Induction Motor Drive Using RB-IGBT

A 3-phase to 3-phase matrix converter is developed based on 600 V/100 A RB-IGBT (Reverse Blocking IGBT). This RB-IGBT is newly developed based on ultra-thin wafer technology and one important feature of it is reverse leakage current is mostly affected by Vge. Under the same temperature condition, when Vce is negative, a positively biased Vge leads to the great reduction of the reverse leakage current therefore, a novel commutation method is proposed for reducing the losses caused by this reverse leakage current. The realization of this method is based on output current direction and certain voltage polarities of bi-directional switches and it is featured as a 2-step commutation. A simple circuit in the designed RB-IGBT drive circuit is used to obtain the required signals by sensing Vce of RB-IGBT. Then the constant Volts/Hz method is employed for controlling the matrix converter induction motor drive. Finally, detail experimental results and analysis are presented.

A novel driving and protection circuit for reverse blocking IGBT used in matrix converter

Reverse blocking IGBT (RB-IGBT), with the capability of blocking both forward and reverse voltage, is now receiving widely attention in power converter applications. In this paper, by introducing two dynamical current sources, a three-stage driving circuit is designed for RB-IGBT to reduce the switching transition while limiting the turn-on di/dt and the turn-off dv/dt within the safe area. Furthermore, a novel v/sub ce/ sensing method is proposed. Using the detected v/sub ce/, over-current and short-circuit protection schemes are implemented respectively. The v/sub ce/ is also used as a sign of current direction, which is helpful for commutation between bidirectional switches.

Sensorless control of direct-field-oriented induction motor operating at high efficiency using adaptive rotor flux observer

The speed sensorless control of direct-field-oriented induction motors using an adaptive rotor flux observer was developed recently. This method drives the induction motor using a constant-rated rotor flux in order to estimate rotor speed without loss of accuracy and to prevent degeneration of dynamic response. However, the driving efficiency of the field-oriented induction motor must be maximized for applications such as electric vehicles which have a limited power supply. The authors apply rotor flux control which enables high-efficiency sensorless direct-field-oriented induction motor systems to be developed. Using experimental and simulation results, this paper shows the advantages of sensorless direct-field-oriented induction motor control using an adaptive rotor flux observer.

A novel method for loss reduction in high-voltage inverters

This paper presents a high-voltage inverter configuration employing series connections of 1.2 kV rated standard IGBTs instead of high-voltage rated IGBTs, which allows the losses of switching devices to considerably decrease. Voltage balancing across all of the IGBTs connected in series, which is one of the most critical issues especially during the transient phases, is realized by magnetically coupling of all the gate wires with a two-winding transformer without any snubber components or active gate controls. Moreover, influence of stray capacitance associated with insulators in IGBT modules on the voltage sharing is investigated, and an optimized configuration including these heat sinks is proposed to achieve a more accurate voltage equalization. To validate the performance on the series connection of the standard IGBTs with respect to the voltage sharing and the device losses in practical uses, a prototype 170 kVA rated inverter based on three series connection of 1.2 kV rated IGBTs are implemented and tested. The experimental results are shown.

Analysis of Dynamic Variation on a Combined Control Strategy for a Five-Level Double Converter

We have studied a three-phased five-level double converter for high power induction motors, which consist of a three-phase five-level rectifier and three-phase five-level inverter. In this paper, a novel control strategy with a combination of the pulse amplitude modulation (PAM) in the high-speed area and pulse width modulation (PWM) in the low-speed is proposed. The strategy can reduce the loss of switching devices in the inverter circuit and the harmonic distortion of the inverter output current waveform, and allows high power induction motors to achieve higher efficiency and smooth drive. These high performances are confirmed by simulation results

Performance of IGBTs Series Connection Technologies for Auxiliary Power Supply System

This paper presents a novel auxiliary power supply (APS) system for the commuter trains with 1.5kVdc employing series-connected 1.2-kV general purpose IGBTs as a switching device, substituted for high-voltage IGBTs over 3kV. The carrier frequency of 5kHz in the APS is realized due to considerable low switching loss of the IGBTs. Voltage balance across the series connected IGBTs are achieved by magnetically coupling all the gate lines using a simple two-winding transformer without snubber circuits. To ensure that such the high carrier frequency is effective on APS performance, sound level from filter and output voltage stability with a sudden changed load are evaluated using a single-phase inverter, and then compared with that of a conventional carrier frequency. On the basis of the series connection technique with the 1.2kV IGBTs, a prototype of the APS system is designed and built for the actual uses, and then its performance is evaluated at its rating specifications. From the results, it is confirmed that the APS system features smaller volume and lower sound level rather than conventional ones with the high-voltage IGBTs.

Control strategy of a three-phase five-level double converter with adjustable DC voltage for induction motor drives

This paper describes a control strategy for a five-level double converter that consists of the five-level rectifier, the DC link, and the five-level inverter. The purposes of the proposed control strategy are to correct voltage imbalance of the DC link capacitors, to keep the input power factor at near unity, and to achieve adjustable-speed drive. The five-level rectifier is controlled by the instantaneous-value-compared current control method using multi-band hysteresis comparators. On the other hand, the five-level inverter is controlled by the space vector pulse-width modulation method. The validity of the control strategy is verified by experiments using a 3.7 kW induction motor.