Y. Takeda

Expansion of operating limits for permanent magnet motor by current vector control considering inverter capacity

The current vector control method of PM (permanent magnet) motors is examined to expand the operating limits associated with inverter capacity. This control method is optimum in the sense of deriving maximum output torque within the voltage and current constraints. The effects of motor parameters are examined by computer simulation. The operating limits are greatly expanded by controlling the d- and q-axis components of the armature current according to the rotor speed. The operating limits are examined considering the demagnetization of the permanent magnet. If the permanent magnet has a straight demagnetization curve, like a rare-earth permanent magnet, the PM motor can be safely operated until the demagnetizing coefficient becomes 1.0. If wide speed range or constant power operation is desirable, a permanent magnetic with a high coercivity and a linear demagnetization curve must be used for the PM motor. >

Current phase control methods for permanent magnet synchronous motors

Three types of current phase control methods are examined for the interior magnet motor and the surface magnet motor: (1) the i/sub d/=0 control method, (2) the cos phi =1 control method, and (3) the constant-flux-linkage control method. The control circuits for realizing these control methods were investigated and a drive test carried out. The most suitable current phase control method for the rotor geometry was examined by computer simulation and experimentation. It was found that in the i/sub d/=0 control method, high-performance torque control can be obtained as the torque is proportional to the armature current. In the cos phi =1 control method, the torque per armature current is small and the torque characteristic is nonlinear. Therefore, high-performance torque control cannot be expected. The constant-flux-linkage control method is desirable for interior magnet motors as the torque characteristic is almost linear and the required inverter capacity is comparatively small. >

Sinusoidal current drive system of permanent magnet synchronous motor with low resolution position sensor

The high performance drives of the sinusoidal back-EMF type permanent magnet synchronous motor can be achieved by the current vector control, where the sinusoidal currents flow according to the rotor position and the current phase is suitably controlled according to the operating condition. In such a high performance drive system, a high resolution position sensor is desired. In this paper, a sinusoidal current drive system with a low resolution position sensor is proposed. The high resolution position information is obtained by the position estimating circuit from the signal of a low resolution position sensor. The steady-state and transient characteristics are examined by several experiments, then it is confirmed that the sinusoidal current drive and the high performance current vector control can be achieved by the proposed drive system.

Effects and compensation of magnetic saturation in permanent magnet synchronous motor drives

The effects of magnetic saturation are examined, and the compensation of magnetic saturation is proposed for the PM (permanent magnet) motor drives. A speed control system is established based on a DSP, and drive tests were carried out on a prototype IPM (interior permanent magnet) motor. The q-axis inductance of a IPM motor is found to vary depending on the q-axis current because of the magnetic saturation. The terminal voltage exceeds the maximum value in the flux-weakening region and, as a result, the transient responses sometimes become unstable because of saturation of the current regulator. The q-axis inductance is simply modeled as a function of the q-axis current and this compensated value of L/sub q/ is used in the control algorithm. The control performances are greatly improved by the compensation of magnetic saturation.<<ETX>>

Design and control system of inverter-driven permanent magnet synchronous motors for high torque operation

This work describes a current vector control method for permanent magnet (PM) synchronous motors suitable for high-torque operation. The current phase angle is controlled according to load conditions in order to use the reluctance torque effectively. Characteristics such as torque, efficiency, power capability and so on are greatly improved by this control method in comparison with the conventional control method. The performance characteristics are greatly affected by the motor parameters, which depend on the rotor configurations and permanent magnet geometries. The available maximum torque and power capability are also examined for the several types of PM motor, taking into consideration the inverter capacity. The tendency toward magnetic saturation and demagnetization of the permanent magnet is also examined. >

A PWM strategy for reducing torque-ripple in inverter-fed induction motor

A novel pulse-width modulation (PWM) strategy suitable for an inverter-fed induction motor is described. The torque ripple of the induction motor can be reduced by this PWM technique. The output waveforms is the proposed PWM inverter are investigated both theoretically and experimentally. A modulating signal for the three-phase PWM inverter is obtained by superposing a rectangular wave on the specific trapezoidal wave whose flat portion is 120 degrees . By using the proposed modulating signal, the amplitude of the fundamental component is about 18% more than that of a conventional sine-wave inverter.<<ETX>>

Analyses for sensorless linear compressor using linear pulse motor

A reciprocating compressor with a rotary motor which is used in a refrigerator has low efficiency, since it has large mechanical losses due to the crank mechanism. In a free piston linear compressor with linear motors, the mechanical losses of the crank mechanism can be decreased and system efficiency improved. However, the compressor will fail and the system efficiency will be reduced if the piston position is not controlled successfully. A linear pulse motor (LPM) generally has precise positioning ability in open-loop control without a position sensor. Therefore, the authors expect that a sensorless linear compressor system with an LPM can be realized. In this paper, they examine the piston positioning accuracy and the efficiency of a sensorless linear compressor system with an LPM for various compressor sizes and operating conditions by using analytical and experimental approaches. As a result, the efficiency of the linear compressor system is higher than that of a conventional reciprocating compressor using an induction motor. The system efficiency is significantly improved in the linear compressor with LPM.