Pulse Width Modulated Voltage Waveforms Research Articles

永久磁石モータのインピーダンスを用いたキャリア高調波による回転子渦電流損の計算手法

In this paper, an analytical method using the impedance for calculating rotor eddy-current losses caused by inverter carrier harmonics in a permanent magnet motor is investigated. With respect to different types of motors, the accuracy of the proposed method is compared with direct calculation by finite element analysis (FEA) using pulse width modulation (PWM) voltage waveforms. First, the two-phase and three-phase current circuits are investigated for calculation of the impedance. Next, impedance and eddy-current losses of six types of motor are calculated in order to investigate the influences of the motor structure and stator magnetomotive force (MMF) on the rotor eddy-current losses. Because the magnetic saturation of the motor core decreases the accuracy of the calculation, an estimation method is proposed that takes the magnetic saturation into account in order to improve the accuracy. The validity of the proposed method is verified by a comparison with the results of direct calculation by FEA using PWM voltage waveforms. Moreover, the effect of the calculation time reduction obtained by the proposed method is also compared with the case where it is calculated directly by FEA.

Dynamic Finite Element Hysteresis Model for Iron Loss Calculation in Non-Oriented Grain Iron Laminations Under PWM Excitation

This paper introduces a dynamic finite element model for calculating iron loss in ferromagnetic non-oriented grain laminations under pulse-width modulation (PWM) excitation. The proposed methodology accounts for static hysteresis, classical eddy currents and anomalous losses and has been validated by measurements in Epstein device in different cases of PWM voltage waveforms. The model is based on a particular 2-D finite-element technique by using standard static iron lamination characteristics and offers sufficient accuracy in all studied cases.

A New Space-Vector PWM With Optimal Switching Selection for Multilevel Coupled Inductor Inverters

Multilevel space vector pulsewidth modulation (SVPWM) control is shown to be a very useful tool for coupled inductor inverters as six independent pulsewidth modulation (PWM) signals are required, and there is additional complexity of meeting the performance requirements for the coupled inductor while balancing the winding common-mode dc current and generating high-quality multilevel PWM output voltages. A new multilevel SVPWM technique with a five-segment switching sequence is described, where half-wave symmetrical PWM voltage waveforms are used to balance the inductor common-mode dc voltages and also to avoid all possible switching states with a high winding current ripple. The proposed SVPWM is shown to have better inverter performance, compared with traditional carrier-based and the original multilevel SVPWM schemes at low modulation depths. Inverter operation with the proposed SVPWM is validated through simulation and experimental results.

PWM Inverters Using Split-Wound Coupled Inductors

The number of output-voltage levels available in pulsewidth-modulated (PWM) voltage-source inverters can be increased by inserting a split-wound coupled inductor between the upper and lower switches in each inverter leg. Interleaved PWM control of both inverter-leg switches produces three-level PWM voltage waveforms at the center tap of the coupled inductor winding, representing the inverter-leg output terminal, with a PWM frequency twice the switching frequency. The winding leakage inductance is in series with the output terminal, with the main magnetizing inductance filtering the instantaneous PWM-cycle voltage differences between the upper and lower switches. Since PWM dead-time signal delays can be removed, higher device switching frequencies and higher fundamental output voltages are made possible. The proposed inverter topologies produce five-level PWM voltage waveforms between two inverter-leg terminals with a PWM frequency up to four times higher than the inverter switching frequency. This is achieved with half the number of switches used in alternative schemes. This paper uses simulated and experimental results to illustrate the operation of the proposed inverter structures.

Mechanical Resonance in Nonoriented Electrical Steels Induced by Magnetostriction Under PWM Voltage Excitation

Acoustic noise in inverter-fed motors can increase if resonance induced by magnetostriction occurs. This paper presents results of measurements of magnetostriction-induced mechanical resonance in nonoriented (NO) steels, commonly used in motor cores, under pulse width modulation (PWM) excitation. The resonant frequency of a strip of NO steels was determined and it was magnetized by PWM voltage waveforms. The PWM switching frequency was chosen to be the same as the sample resonant frequency. The peak-to-peak magnetostriction under PWM excitation was up to 28% higher than that under sinusoidal excitation when an integer multiple of the switching frequency matched the resonant frequency of the sample.

An extended Kalman filter approach to rotor time constant measurement in PWM induction motor drives

A rotor time constant estimation technique for the purpose of updating the control gains of an induction motor field-oriented controller is described. An extended Kalman filter is employed to estimate the inverse rotor time constant online only using measurements of the stator voltages and currents and rotor speed of an induction motor. The motor is driven by a pulsewidth modulated (PWM) inverter with or without current feedback loops. By utilizing the wideband harmonic contents inherent in conventional PWM voltage waveforms, no external random test signal is required for parameter estimation. Both computer simulation and experimental results show that the filter is capable of estimating the rotor time constant while the rotor speed is either constant or time varying. >

Induction motor speed control using a microprocessor-based PWM inverter

An MC68000, 16-bit microprocessor system was used to generate pulse-width modulation (PWM) voltage waveforms for a three-phase inverter. An MC6840 programmable timer module (PTM) was used to give real-time PWM voltage waveforms at its three outputs. The MC68000 calculates the width of the pulses for only the first quarter cycle and sorts these into a table. The remaining pulses for the complete cycle are generated using the values of the first quarter because there are conditions of quarter and half-wave symmetry. This results in a considerable saving of microprocessing time. The well-known expressions that define the width of regular sampled PWM pulses were modified to be compatible with the timing system. A real-time method of setting the 120 degrees phase shift between the three phases of the pulses using the PTM was developed and showed a good level of accuracy. The PWM inverter was tested with passive impedance and motor loads. With an induction motor load, harmonics of the stator current and voltage of an order lower than the nineteenth and twenty-third were found to be virtually eliminated. The nineteenth and twenty-third harmonics had the value of 0.09 pu of the current, compared with 0.3 for the voltage, at a depth of modulation of unity. >