Satoshi Sumita

Evaluation of increasing rates in eddy-current loss of the motor due to carrier frequency

This paper describes that a theoretical formula for evaluating loss ratio in eddy current of a permanent magnet (PM) motor fed by a PWM inverter is proposed. A formula for evaluating the increasing rates of eddy-current loss in iron core due to carrier frequency corresponding to inverter output parameters (i.e., DC-bus-voltage, modulation index and modulation methods) are derived. Calculated and measured increasing rates of eddy-current loss in iron core were compared. According to the results of this comparison, the difference between the calculated and measured results is within 10 % when the modulation index is less than 0.7. The increasing tendencies of the calculated and measured increasing rates of eddy current loss agree well. The proposed theoretical formula can be applied for improving the efficiency of motor-inverter drive systems.

A simplified sensorless vector control based on the average of the DC bus current

This paper describes a simplified sensorless vector control for permanent magnet synchronous motors (PMSM) using the average of the DC bus current. This method sets up the drive control system at relatively inexpensive because the micro controller does not need to have a precise timer and the calculation load is slight. The proposed method effectively changes two different current estimation methods in accordance with the operation mode. First, the controller estimates d-axis current and identifies back-EMF parameter in synchronous operation mode at the low speed region. The identification error of back-EMF parameter affects efficiency of the proposed system, so it needs to be zero. Second, the controller estimates q-axis current in vector control mode. The identified parameter and q-axis current define voltage reference to realize high efficiency drive. Experimental results confirm the effectiveness of proposed method.

A 3.7-kW axial-gap switched-reluctance motor robustly designed by using a mathematical model

An axial-gap switched-reluctance motor (SRM) was designed with high power density by using a mathematical model. To shorten the analysis time by 3D finite element analysis (3D-FEA) to calculate the torque characteristics of the axial-gap SRM, an analytical method was proposed and used for designing the SRM. The key feature of the method is expressing the mutual flux with a mathematical model by employing transient analysis using pre-processed inductance tables. A 3.7-kW prototype axial-gap SRM designed was designed by this method and tested. According to the test results, output density of the prototype SRM is 16% higher than that of conventional induction motors.

Sensorless control method using differentiation circuit for switched reluctance motor

A method is introduced for estimating the rotor phase of a switched reluctance motor (SRM) accurately. The rotor phase is estimated by substituting a differential current into the motor model. The differential current is measured by sampling the current twice and dividing the difference in the two values by the sampling period. The division error increases in high carrier frequency because the sampling period is short. First-order analog circuit is utilized to reduce the error in the proposed method. The circuit is a stable feedback system which has a first-order integrator element. When current is input to the circuit, the output signal of the integrator is convergence to the current and the input signal of the integrator is measured as a differential current. Therefore, the differential current is directly measured without division. The experimental results confirm the effectiveness of the proposed method at a carrier frequency of 20 kHz.