V. Ramanarayanan

Mutual Coupling and Its Effect on Steady-State Performance and Position Estimation of Even and Odd Number Phase Switched Reluctance Motor Drive

In this paper, we analyze mutual coupling of switched reluctance (SR) motors with even and odd numbers of phases. We illustrate that SR motors with an even number of phases produce asymmetric mutual flux in different phases. On the other hand, an SR motor with an odd number of phases produces symmetric mutual coupling in all the phases. Then, we explain a practical way of measuring the mutual flux in SR motors and present the test results for an 8/6 pole, four-phase 4 kW motor. We simulated the performance of the SR motor with and without mutual flux, thereby demonstrating the effect of mutual flux on phase current, flux, and average torque. We verified the effect of mutual flux on position estimation by simulation and experiment. We show that appropriate correction for mutual flux may improve the accuracy of estimated position by 3deg, which will give better performance of the drive while driven without any shaft sensors. We also show that an SR motor with an odd number of phases is a better choice than one with an even number of phases because of its symmetric mutual coupling, its ability to utilize short flux paths, and the fact that it does not require costly bipolar excitation.

Reduced Acoustic Noise Variable DC-Bus-Voltage-Based Sensorless Switched Reluctance Motor Drive for HVAC Applications

In this paper, a control strategy for reduced acoustic noise and sensorless operation of a switched reluctance (SR) motor is proposed for heating, ventilation, and air conditioning (HVAC) application, where the magnitude of the dc-bus voltage is controlled as a function of speed and the motor is operated in a single-pulse mode for all speed range. The dc-bus voltage is controlled by incorporating a dc chopper between the three-phase line rectifier and a split dc-link capacitor-type four-switch power converter. Such controller reduces the acoustic noise, provides more accurate position estimation for sensorless operation, and improves the life expectancy of the motor. The algorithm is first simulated through MATLAB/SIMULINK and then tested on a four-phase 8/6-pole 4-kW SR motor. The test results of achieved acoustic noise and improved sensorless operation are presented. Through the proposed method, the acoustic noise is reduced by almost 15 dB compared to the conventional scheme at low-speed regime. The proposed method is intended to drive a fan type of load in HVAC applications, where the dynamic performance requirement is not a stringent criterion.

A unified model for the ZVS DC-DC converters with active clamp

Active clamp DC-DC converters are recently introduced family of two switch pulse width modulated converters featuring zero-voltage switching. The topological structure of these converters in relation to their hard-switched PWM converters is highlighted. With proper designation of the circuit variables (throw voltage V and the pole current I), all these converters are seen to be governed by an identical set of equations. In this framework, these circuits exhibit 6 sub-periods per cycle with identical current waveform in the resonant inductor. With idealized switches, the steady-state performance is obtainable in an analytical form. This set of equations may be solved through a simple spreadsheet programme. The steady-state performance provides a design constraint on the normalized current. The conversion ratio of the converter is also readily available. A generalized equivalent circuit emerges for all these converters from this steady-state conversion ratio. It is interesting to note that this equivalent circuit provides a dynamic model as well. The circuit model proposed in this paper enables one to use the familiar state space averaged results of the standard PWM DC-to-DC converters (both steady-state and dynamic) for their ZVS active clamp counterparts.

Effect of mutual inductance on steady-state performance and position estimation of switched reluctance motor drive

In this paper, a practical way of measuring the mutual flux in a switched reluctance (SR) motor is explained and the test results for an 8/6 pole, 4 kW motor are presented. The performance of the drive is studied in simulation with and without mutual flux. The effect of mutual flux on phase current, flux and average torque is demonstrated with the simulation result. Further, the effect of the same on position estimation is verified in simulation and experiment. It is shown that appropriate correction for mutual flux may improve the accuracy of the estimated position by 3/spl deg/.

Sensorless control of switched reluctance motor drive with self-measured flux-linkage characteristics

In this paper, a novel discrete position estimation scheme for sensorless operation of switched reluctance (SR) motor drive is proposed. The classical flux-current approach is adopted for estimating the position. In the proposed method, the required flux-linkage characteristics measurement is automated and integrated as a part of the sensorless controller. The algorithm is tested on a real motor and the relevant test results are presented. The method is suitable for low-cost mass-produced applications.

Phase angle balance control for harmonic filtering of a three phase shunt active filter system

This paper proposes a new strategy for harmonic filtering of a three-phase shunt active filter system. The shunt harmonic filters control objective is defined as: balance the phase angle of the input current with the phase angle of the line frequency component of the load current. This objective is achieved in discreet implementation without sensing the input voltages. The controller uses a phase shifting method on the sensed input current and then applies the resistor emulator type input current shaping strategy on the phase-shifted current. In implementation Texas Instruments DSP based unit TMS320F240 EVM is used as the digital hardware platform. The control algorithm is computationally simple yet the harmonic filtering performance is high. The analysis, simulation and experimental results of a three-phase shunt active filter prototype on a 25A nonlinear load are presented.

A voltage sensorless control method to balance the input current of the boost rectifier under unbalanced input voltage condition

This paper proposes a control method that can balance the input current of the three phase, three wire, boost rectifier under unbalanced input voltage condition. The control objective is to operate the rectifier in the high power factor mode under normal operating condition but to give overriding priority to the current balance function in case of unbalance in the input voltages. The inner loop implements resistor emulator type input current shaping strategy. The outer control loop performs magnitude scaling and phase shifting operations on current of one axis to make it balanced with respect to the current on the other axis. The coefficients of scaling and shifting functions are determined by two closed loop PI controllers. The control method is input voltage sensorless. In implementation Texas Instruments DSP TMS320F240F is used as the digital controller.