Kazuo Oka

Characteristic Comparison between Five-Leg Inverter and Nine-Switch Inverter

This paper presents a characteristic comparison between a five-leg inverter and a nine-switch inverter. The five-leg inverter and the nine-switch inverter is a single inverter that can drive two AC motors independently. Concretely, we show a circuit architecture of both inverters, a modulation method for an independent drives and a division of voltage utility factor. Moreover, investigate about the inverter losses and a switching device capacity in driving two AC motors independently and adapting a control method to decrease the inverter losses.

Performance for Position Control of Two Permanent Magnet Synchronous Motors with the Five-Leg Inverter

Recently, the five-leg inverter, with which we are able to control two AC motors independently, is suggested. This inverter has five legs, so we make space for one leg compared with using two three-leg inverters. In this paper, the method of independent vector control of driving two permanent magnet synchronous motors (PMSMs) is described. Although it is difficult to drive two PMSMs in parallel with a single three-leg inverter, that is achieved by using the five-leg inverter. However, the five-leg inverter has two failings. Applying the proposed method, voltage utility factor (VUF) is 50%, and the amplitude of the peak current flowed common leg is twice as others. In order to improve the second problem, this paper presents that the method of reducing loss at the common leg under the driving in parallel

Characteristics of independent two induction motor drives fed by a four-leg inverter

This paper presents the experimental results of the independent drive characteristics of two three-phase induction motors (IMs) fed by a four-leg inverter (FLI). The FLI is a single inverter that can drive two three-phase AC motors independently. The inverter consists of four legs and two capacitors connected in a series. The U and V phases of both motors are connected in each leg respectively whereas the W phase of both motors is connected in the neutral point of two-sprit capacitors. The PWM technique in three-phase voltage source inverter (three-VSI) is not directly applicable for the FLI because only two phases must be modulated. Then, the paper also analyzes about potential in the neutral point of two-sprit capacitors and inverter output voltage. Next, modulation technique in the FLI is also shown. The PWM strategy may apply carrier-based PWM. Experimental results demonstrate the characteristics of two IM independent drives and the validity of those analytic results.

Characteristic of Independent Two AC Motor Drives Fed by a Five-Leg Inverter

This paper presents the experimental test results of the independent vector control characteristics of two three- phase induction motors (IMs) and two three-phase permanent magnet synchronous motors (PMSMs) fed by a five-leg inverter (FLI). To drive two motors (IMs or PMSMs) independently, the system connected one motor to one three-phase voltage source inverter (three-VSI) is generally used and is required two three- VSIs. Therefore, twelve and ten-switching devices are necessary in the three-VSIs and FLI respectively. Finally, the FLI can decrease two-switches and will be expected for saving space and reduction of inverter losses. Experimental results are verified for the independent driving characteristics in two motors with the FLI.

Analysis and compensation method of voltage error by dead-time with five-leg inverter for two-AC motor independent drives

This paper presents the analysis and compensation method of the voltage error by a dead-time with a five-leg inverter (FLI). The FLI is the single inverter to drive two three-phase AC motors independently. For the reason that the inverter connects one phase of each motor to a common leg, the voltage error caused by the dead-time will be different in case of a three-phase voltage source inverter (VSI). In case of motor drive with low-speed or using high speed switching devices such as insulated gate bipolar transistor (IGBT), considering about the dead-time voltage error is especially important for reduction of torque ripple. Firstly, the difference of the dead-time voltage error between the three-phase VSI and FLI is theoretically analyzed and discussed in this paper. Second, the dead-time compensation method is introduced. Moreover, the validity of these analyses and compensation method is shown by experimental results.

Independent Position Controls of Two Permanent Magnet Synchronous Motors Fed by a Five-Leg Inverter

This paper presents the experimental test results of the independent vector control characteristics of two three-phase permanent magnet synchronous motors (PMSMs) fed by a five-leg inverter (FLI). Recently, the use of PMSM is more and more spreading in industrial field. It has the features of saving-weight and high-efficiency compared with DC motor and induction motor. The maximum feature of the PMSMs is the realization of high performance position control. The independent position control validates for the factory automation (FA) apparatus as machine tool. If the independent position control of two motors with the FLI may be realized, the belt conveyer used at the FA apparatus will become possible not only one dimension but also two dimensions without double three-phase voltage source inverters. In this paper, experimental results are verified for the independent position control of two PMSMs fed by the FLI with the vector control. In addition, two PMSMs independent characteristics on condition that one motor operates at speed control and the other PMSM at position control also investigated.

Characteristic of independent two induction motor drives fed by a five-leg inverter

This paper presents the experimental test results of the independent drive characteristics of two three-phase induction motors (IMs) fed by a five-leg inverter (FLI). To drive two motors independently, the system connected one motor to one three-phase voltage source inverter (three-VSI) is generally used and is required two three-VSIs. Therefore, twelve and ten-switching devices are necessary in the three-VSIs and FLI respectively. Finally, the FLI can decrease two-switches and will be expected for saving space and reduction of inverter losses. Experimental results are verified for the independent driving characteristics in two motors with the FLI.

Dual high frequency quasi-resonant inverter circuit by using power MOSFET for induction heating

This paper presents the dual high frequency quasi-resonant single inverter circuit that can output the frequency of 100kHz or more by Power Metal Oxide Semiconductor Field Effect Transistor (MOSFET) for induction heating. The induction heating is often used for the heat-treatment of a metal work-piece. In hardening of a gear, since the bottom or tips are heated at lower frequency fL or higher frequency fH respectively, the heating at two different frequencies for uniform heat-treatment is required. Therefore, two inverters are necessary to output different resonant frequency each other. To solve this problem, a single adjustable frequency quasi-resonant inverter circuits which have the short-circuit switch across a capacitor have been reported [1]. This inverter circuit includes the first resonant capacitor and that of the second with a one-way short-circuit switch. Synthetic series capacitance is varied by manipulating the on-time of the switch and then the resonant frequency can be adjusted. Insulated Gate Bipolar Transistor (IGBT) is used as the switching device of the circuit in [1]. The proposed circuit cannot realize with the IGBT to output the high frequency of 100kHz or more. The circuit uses the Power MOSFET instead of the IGBT. Otherwise, the device has the disadvantages of withstand voltage and current. However, this problem can be solved by the methods of connecting switching devices to series and using step down transformer. As an example, we could obtain the dual frequencies of 400kHz and 160kHz with the proposed single inverter composed of the Power MOSFETs.

A novel PWM technique with switching-loss reduction in five-leg inverter for independent drives of two three-phase AC motors

This paper presents the novel Pulse Width Modulation (PWM) technique with switching-loss reduction for a five-leg inverter (FLI). As the PWM strategy for the FLI, the PWM technique that available maximum voltage for two motors adds up to a DC-bus voltage has been proposed. Therefore, the DC-bus voltage can be fully available in this PWM strategy. However, this conventional PWM technique requires the frequency, phase and amplitude of phase voltage commands in the motor to make zero sequence voltages (ZSVs) with PWM. The novel PWM strategy has some effective features. Those features will introduce at this paper. The validity of the novel PWM technique will be shown by experimental results.

Improved high frequency quasi-resonant inverter for induction heating using power MOSFET

This paper describes the work heating power efficiency characteristics of a high frequency quasi-resonant inverter (QR-INV) and a normal resonant inverter (NR-INV) using power Metal Oxide Semiconductor Field Effect Transistor (MOSFETs), and also introduces a full-bridge type of QR-INV. The output frequency of NR-INV depends on resonant frequency in inverter load and cannot operate with variable frequency. Otherwise, the QR-INV circuit includes the first resonant capacitor and that of the second with a one-way short-circuit switch. Synthetic series capacitance is varied by manipulating the switch and then the resonant frequency can be adjusted. For the sake of the heating in metal stick that the inside diameter is about 2 mm, we are now developing a QR-INV that can vary the output frequency from 160 kHz to 400 kHz [1-5]. Therefore, the power MOSFETs are used as switching devices. The induction heating is often used for the heat-treatment of a metal work-piece. In hardening of a gear, since the bottom or tips are heated at lower frequency fL or higher frequency fH respectively, the heating at two different frequencies for uniform heat-treatment is required. Therefore, two NR-INVs are necessary to output different resonant frequency each other. To achieve saving space and the simplicity in the control circuit, a single adjustable frequency half-bridge QR-INV (HB-QR-INV) circuit has been proposed [6-7]. In this paper, power conversion efficiency from inverter input power to work heating power in HB-QR-INV and half-bridge type NR-INV (HB-NR-INV) are investigated in the experimental results. Moreover, we will propose the full-bridge type QR-INV (FB-QR-INV). This type will be able to expect the improvement of the increase of output power compared with HB-QR-INV of the same capacity.