Fani S. Gunawan

Optimum torque control of permanent magnet AC machines in the field-weakened region

This paper presents a novel current regulation algorithm for permanent-magnet ac (PMAC) machines that provides maximum torque-per-ampere capability in the entire field-weakened region. The algorithm provides robust current regulation with maximum efficiency and torque capability for PMAC machines despite significant changes in the voltage source and machine parameters. The algorithm identifies when the current regulator starts to saturate and determines the optimum d-axis current command for the machine. The q-axis current command is determined from the torque command and d-axis current feedback. When the voltage angle reaches the maximum angle, the current magnitude is decreased to provide maximum torque per ampere. Experimental results from a machine prototype show that the algorithm provides good overall dynamic response and smooth transitions into the field-weakened region with maximum torque-per-ampere capability in all four quadrants of operation.

Current Control of Induction Machines in the Field-Weakened Region

This paper presents a novel current regulation algorithm for induction machines that enables smooth operation and maximum torque-per-ampere capability over the entire field-weakened region. The algorithm enables robust current regulation with maximum torque capability despite significant variation in voltage source and machine parameters. The algorithm identifies when the current regulator begins to saturate and determines the optimum d-axis current command for the machine. The q-axis current command is determined as a function of the torque command and the d-axis current feedback. In the field-weakened region, the q-axis current is monitored not to exceed the maximum q-axis current. The maximum q-axis current is calculated based on the maximum slip frequency, which is a function of rotor frequency, q-axis current ges maximum q-axis current (in motoring mode) indicates that the machine entered field-weakened region II, and the q-axis current is limited to its maximum value. Experimental results from a machine prototype show that the algorithm provides good overall dynamic response and smooth transitions into the field-weakened region with maximum torque-per-ampere capability in all four quadrants of operation

Linear control of PWM inverter by avoiding the pulse dropping

In PWM inverter fed ac machine drives, at higher modulation indices, the output pulse-width becomes very narrow. These short pulses do not contribute to produce torque in the machine but introduce additional losses and stress in the power switching devices. This is especially true in large drive systems, where the sine triangle based PWM strategies are being widely used. In this paper, a technique to eliminate these narrow pulses is proposed. This is based on injecting an optimized amount of third harmonic signal to the reference waveform. This optimized amount of the third harmonic is defined off-line for different modulation indices and minimum pulse-width required by the power electronics devices used in the inverter. Finally, use of this method in vector-controlled drives is explained and improvement of the efficiency is demonstrated by experiment.

Optimum torque control of induction machines in the field-weakened region

This paper presents a novel current regulation algorithm for induction machines that enables maximum torque-per-ampere capability over the entire field-weakened region. The algorithm enables robust current regulation with maximum efficiency and torque capability despite significant variation in voltage source and machine parameters. The algorithm identifies when the current regulator begins to saturate and determines the optimum d-axis current command for the machine. The q-axis current command is determined as a function of the torque command and the d-axis current feedback. When the voltage angle reaches the maximum allowable angle, the output of the q-axis and the d-axis current regulators are clamped, and the slip frequency that provides maximum torque is maintained. Experimental results from a machine prototype show that the algorithm provides good overall dynamic response and smooth transitions into the field-weakened region with maximum torque-per-ampere capability in all four quadrants of operation