Nobukazu Hoshi

Analysis of anti-directional-twin-rotary motor drive characteristics for electric vehicles

A new power train for electric vehicles is proposed using an anti-directional twin rotary (ADTR) motor. A stator in a conventional motor was reformed to be movable, and the stator (outer rotor) rotates in the opposite direction to the inner rotor. In this paper, several characteristics of an induction motor-type ADTR motor are reported. When an ADTR motor is used in electric vehicles, the direction of one of the rotors should be reversed and both rotors rotate in the same direction, propelling the two wheels of the electric vehicle. The torque of the wheels can be balanced without a differential gear. The fundamental torque-balancing characteristics of an ADTR motor are clarified, namely, the torque balance theory, the torque-speed characteristics, the rotor-speed transient characteristics and the transient torque response under speed sensorless torque control.

A novel six-phase inverter system with sixty-step output voltages for high-power motor drives

A novel six-phase voltage-fed inverter system is proposed. The system consists of two main three-phase inverters, coupling reactors, and an additional single-phase inverter. The ripple voltage injected into the DC link by the additional inverter results in 60-step load voltages with the help of the coupling reactors. The main inverters operate at the same frequency as the output and the additional inverter operates at a frequency six times higher. The advantages and disadvantages of the system are quantitatively discussed.

Small-scale hydropower

A novel harmonics-reducing system of cascaded-induction generators has been proposed, and its effectiveness has been confirmed by the simulation results. Comparing the characteristics of the cascaded generators with those of the single generator, we see that the power efficiency decreases by 1-3%, and the input power factor decreases by around 20%, but the power factor can be improved by controlling the reactive power of the power-recovery inverter. Since the proposed system has the advantages of a low-cost system, a brushless structure, and adjustable-speed characteristics, we anticipate that its use will be practical for small hydroelectric power plants.

Coupling rectifier systems with harmonic cancelling reactors

This paper shows that double-diode rectifiers can generate 12-step voltages by using well-designed line-side reactors, although with relatively large self-inductances. The usage of three-level rectifiers can alleviate this disadvantage. The double three-level rectifier system proposed features the following advantages over conventional transformer-coupled systems: small in size, light in weight, and more economical; control capabilities of output DC voltage in a limited range; low current and voltage ratings required for additional circuits; and highly reliable operation due to 12-step operation capability without additional circuits.

Voltage-phase shifting effect of three-phase harmonic canceling reactors and their applications to three-level diode rectifiers

For replacing a conventional transformer-coupled system, a novel double rectifier system with 24-step input voltages is proposed for mid-power applications. The system consists of double three-level voltage-type diode rectifiers coupled with three harmonic canceling reactors with a total power capacity of 13.4-18.2% of the DC output power. Additional switches of the unit rectifiers act as forced commutation circuits and the reactors absorb lower harmonics. The proposed system has the advantages over conventional transformer coupled systems of: economical design; small size; light weight; high-quality input currents; and highly reliable operation.

Novel inverter topologies for two-wheel drive electric vehicles with two permanent magnet synchronous motors

Novel topology of an inverter that can independently control two permanent magnet synchronous motors (PMSMs) is proposed. In conventional, 12 switching devices, i.e. two three-phase three-leg inverters, are required to control two PMSMs; thus, the equipment size becomes large. The proposed inverter requires the same number of switches as the conventional inverter, i.e. only 6 switching devices. In this paper, the circuit configuration and control principle of the proposed inverter are introduced; and a controller was constructed using an FPGA. Moreover, the basic characteristics of the inverter, which is connected with two Y-connected RL loads, are shown through computer simulations and experiments. As a result, it was verified through the simulations and the experiments that the proposed inverter could output different amplitude and frequency for each load.

A low-cost system of variable-speed cascaded induction generators for small-scale hydroelectricity

A novel variable-speed cascaded induction generator system is proposed for small-scale hydroelectric power plants, in which the second induction generator has double three-phase stator windings (or six-phase windings). The proposed low-cost system can provide a brushless, robust structure and less distorted currents without using an expensive PWM rectifier on the machine side and an expensive adjustable-blade water turbine. The simulated results showed that the system has sufficient capabilities for practical use.

Experimental Considerations on Adjustable Dead-Time Control Scheme for Resonant Snubber Inverter

This paper proposes adjustable dead-time control scheme, which avoid the failure of natural zero voltage switching (ZVS) turn-on in low output current in auxiliary resonant snubber inverters (RSIs). RSI achieves ZVS in the inverter main switches using auxiliary circuit; however, additional conduction loss is caused by using the auxiliary circuit simultaneously. The additional conduction loss can be suppressed by decrease of the operating frequency of the auxiliary circuit using natural ZVS, in which ZVS can be achieved without using the auxiliary circuit by using the output current. However, natural ZVS turn-on is failed near zero output current when the dead-time was constant. This paper describes the basic concept of the proposed control scheme and the developed controller using a FPGA (Field Programmable Gate Array). In addition, it was confirmed that the control scheme is effective for the natural ZVS failure problem by PSpice simulations and experiments in single-phase RSI.

A novel control method for single-phase slow switching multilevel rectifiers

A novel control method for single-phase multilevel rectifiers is proposed to meet harmonic current limiting standards with minimum input filter inductance. Since the proposed rectifier consists of a main power circuit of a diode bridge and two auxiliary semiconductor switches in parallel with the main circuit, it provides several features; high efficiencies, high input power factor, and low EMI. The simulation and the experimental results show that the proposed control method reduces the input filter inductance minimum.

Traction control of anti-directional-twin-rotary motor drive based on electric vehicle driving simulator

An anti-directional-twin-rotary motor (ADTR) was tested on the electric vehicle (EV) driving simulator, which behaves as if the ADTR-motor is installed in the EV, and was driven in the EV driving conditions. The ADTR-motor has novel motor structure suitable for EV drives, in which the stator in a conventional motor was reformed to be movable, and the stator (outer rotor) rotates in the anti-direction of a rotor in conventional motor (inner rotor). Several motor structures of ADTR-motor are possible; a permanent magnet (PM) type, an induction motor (IM) type and so on. In this paper, driving characteristics of a permanent magnet type ADTR-motor on the EV driving simulator were measured, and we proposed a traction control for the EV using ADTR-motor.