Yasuo Notohara

A stable field-weakening control using voltage phase operations in the high-power region

A field-weakening control is required in order to achieve high power output and stable control in the voltage saturation region. In this paper, a voltage phase-operated field-weakening control and a frequency-compensation control are presented. The voltage phase operation control adjusts the voltage phase command with the voltage maintained at the maximum value. Therefore the proposed control can provide higher output power. The frequency compensation control decreases motor speed command in the motor torque limit region, and the motor speed overshoot is thus suppressed. Experimental results show that the proposed controls are effective in suppressing motor speed overshoot and allowing high power output.

Sensorless Control and PMSM Drive System for Compressor Applications

Sensorless control strategies and a PMSM drive system for compressor applications are presented. The drive system consists of a boost PFC rectifier and a three-phase inverter controlled by one micro-controller-unit (MCU: SH7046, Renesas Tech.). To realize low-cost, high performance, and high reliability, sensorless (current and position) control and a novel vector control strategy are proposed to satisfy the requirements of different compressors. The effectiveness and validity of the proposed control strategies are confirmed by experimental results

Inductance measurement method for permanent magnet synchronous motors using AC with DC bias

We have developed a method that uses AC with a DC bias to measure the inductances (Ld, Lq) of permanent magnet synchronous motors (PMSMs). Such motors are widely used in electrical equipment because they are highly efficient. Our method can be used to measure nonlinear characteristics of a PMSM, such as magnetic flux and inductance with cross-magnetization. We have compared our method with a conventional method and the results of a finite-element method analysis. The comparisons with the finite-element method analysis revealed that our method can be used to accurately determine the inductances of PMSMs, which is necessary in some vector control strategies.

Controlling power factor correction converter for single-phase AC power source without line voltage sensor

As various kinds of domestic electrical goods and office automation equipment have become more widely used, interference from harmonic currents, which are generated from home appliances, has become a problem. Therefore, A power factor correction, PFC, converter has been developed to reduce harmonic currents. In this paper, suitable for a single-phase sinusoidal current input converter. This method provides a sinusoidal input current without using an input current having a standard sinusoidal wave-form. Experiments showed that the method worked effectively. Therefore, we found that it is possible to control harmonic currents and thus improve the efficiency of a PFC converter.

Beatless control in over-modulation range for permanent magnet synchronous motor drives

In an AC-DC-AC motor drive system, a beat phenomenon of the motor current occurs, especially in the over-modulation range with DC-link voltage ripple and low frequency carrier. We analyze this beat phenomenon and propose two beatless control methods. One modifies the carrier frequency in accordance with the motor speed within a narrow range, and as a result, the beat frequency can be shifted to a high range, and the beat currents can be reduced. The other shifts the modulation waves by using a feedback loop to cancel the influence of DC-link voltage ripple. Both methods do not need the output frequency of an inverter to be modified, so a motor can be driven at any speed. With these proposed methods, the beat currents can be suppressed greatly, and the torque ripple of a motor becomes smaller. Simulation and experimental results verified the effectiveness of the proposed control methods.

Sensorless vector control suitable for position-dependent load torque applications

An applicative sensorless vector control with an additional current loop has been developed. The proposed method is suitable for applications such as compressors and pumps that have position-dependent load torque properties because the basic concepts of the proposed method keep motor phase current constant. That is to say, the proposed controller reduces peak current and suppresses rotor speed fluctuation simultaneously by keeping the motor torque constant over one rotation. The additional current loop consists of a periodic component extraction function applying a simplified Fourier transform algorithm and controls the extracted fundamental component of a periodic load torque using the q-axis current controller. Simulation results show detailed behaviors of additional current loop and their effectiveness. Moreover, the effects of the proposed method were clarified by results of an experiment in which a refrigerator equipped with a reciprocating compressor was used as an actual verification application.

Embedded-friendly online dead-time compensation using PWM timer

An applicative and embedded-friendly improved dead-time compensation method has been developed. Basic concepts of the proposed method are based on the error time between phase voltage commands and each phase actual output voltage. The error time can be obtained by applying an external pulse width measuring timer which is synchronized with a PWM timer of a micro-controller unit (MCU). This means that key components for the proposed method have already been implemented into most controllers. Also, because of the high frequency of the MCU base clock, the proposed method precisely compensated for dead time errors even in the tricky time period caused by switching ripple zero-crossing. Various experimental results show that the proposed method is effective and robust. Moreover, curious results are investigated in which the compensation time for the error time has transition periods through the current zero-crossing. Finally, the relationships between the current zero-crossing period and the voltage compensation values are experimentally verified.

A digital automatic current control system based on an optimum assumed model

In this paper, a new ACR (automatic current regulator) scheme is introduced for brushless DC motors. It consists of a model closely resembling the motor and PWM inverter, an assumed rising pattern of the current, and a parameter estimation. Using the control scheme, the mean value of the motor current is kept at the reference current, and the transient current of the motor is kept equal to the rising pattern. For the disturbance, because of DC-line voltage change, the proportional path from the error to the duty cycle of the PWM signal stabilizes the ACR. This ACR scheme can be realized with a microcomputer. >

Low-cost high-power-factor three-phase rectifier with turn-on current suppression circuit

We propose a low-cost high-power-factor three-phase rectifier with a turn-on current suppression circuit. With the proposed suppression circuit, standard rectifier diodes can be used instead of fast-recovery diodes in the main diode bridge even with a pulse-width-modulation (PWM) frequency above 10 kHz of the bidirectional switches. We also propose a detection method of the ac source phase using only resistors and a table-based PWM control method, with which the harmonic currents can be limited under the IEC61000-3-2 standard over an extended output range. We present the simulation and experimental results to verify the effectiveness of the proposed suppression circuit and the control methods.

Sensorless control for a three-phase PWM rectifier-inverter system with single-chip micro-controller

A three-phase PWM rectifier-inverter system for a PMSM drive with a single-chip micro-controller is presented. To reduce the cost of the system, the input/output currents and dc-link voltage are detected only using resistors. With the proposed sensorless control, neither an ac voltage/phase sensor nor a rotor speed/position sensor is needed in the system. All of the proposed control schemes can be realized by a single-chip micro-controller (SH7149, Renesas Tech.). The experimental results from a 5-kW prototype confirmed that the proposed system worked well.