N.R. Zargari

A two switch high performance current regulated DC/AC converter module

A high-performance current-regulated single-phase DC/AC converter module is proposed. Its features include a two-switch topology with no short-through paths, high output to input voltage gain, low and constant switching frequencies, and practically instantaneous recovery from input or output transients. By utilizing an inner filter capacitor current control loop, the module can maintain nearly perfect sinusoidal output voltages, even with highly nonlinear loads. Three-phase operation can be obtained by using three of these modules. The analysis and design of the converter power and control circuits and the experimental confirmation of key predicted results are presented.<<ETX>>

Input Filter Design for PWM Current-Source Rectifiers

Pulse-width modulated (PWM) rectifiers are increasingly used because they allow the elimination of low-order harmonics, and therefore a reduction in input filter components. Filtering requirements for PWM current-source rectifiers are usually satisfied through the use of low-pass LC input filters. This paper offers a systematic and user-friendly approach to choosing the filter components. Design of LC filters involves the positioning of the resonant frequency to meet the harmonic attenuation requirements (THD), and introducing damping at the resonant frequency to avoid amplification of residual harmonics. The problem is further complicated by considerations related to cost, power factor, voltage attenuation, system efficiency, and filter parameter variation. The systematic approach proposed in this paper focuses on PWM rectifiers, but can easily be extended to other classes of converters. Practical design considerations are detailed and design equations derived. Simulated results are presented to validate the design approach

Input filter design for PWM current-source rectifiers

Pulse width modulated (PWM) rectifiers allow the elimination of low order harmonics. Filtering requirements for PWM current-source rectifiers are usually satisfied through the use of low-pass LC input filters. The design of LC filters involves the positioning of the resonant frequency to meet the harmonic attenuation requirements (THD), and the introduction of damping at the resonant frequency to avoid amplification of residual harmonics. The systematic approach proposed is focused on PWM rectifiers but can be extended to other classes of converters. Practical design considerations are detailed and design equations are derived. Simulated results are presented to validate the design approach.<<ETX>>

A three-phase current-source type PWM rectifier with feed-forward compensation of input displacement factor

Three-phase current-source type PWM rectifiers are often used as the front-end power converter unit in utility-interfaced systems. Due to the input filter (needed for current harmonic suppression), the input displacement factor is less than unity. It varies with the rectifier operating point and may result in unacceptable low values. In this paper, a new control method is proposed to achieve unity displacement factor independent of the load conditions. The proposed method controls the phase shift of the input currents in a feedforward fashion. The modulating signals are phase shifted according to the rectifier operating point to always result in near unity input displacement factor. The compensation scheme makes use of a DC current loop and the standard DC voltage regulation loop to produce the modulating signals with the required phase shift. As a result, the control circuitry does not require additional sensors. The PWM pattern is generated online, which results in fast response to transients. The rectifier is analyzed and design equations are derived. A design example is given and theoretical considerations are verified through simulation and by experimental results obtained on a 1 kVA laboratory prototype.<<ETX>>

A near unity power factor input stage with minimum control requirements for AC drive applications

Conventional AC induction motor drives use a PWM voltage source inverter (VSI) fed from a diode rectifier. In retrofit applications, due to voltage drops and the inverter voltage gain, six-step operation of the inverter is required at rated speed, resulting in large low order harmonic current and torque components. To allow the inverter to operate in the PWM mode at rated speed, a synchronous rectifier is proposed in this paper to slightly boost the DC bus voltage. The resulting converter system presents all the advantages associated with active front-end rectifiers. However, since the DC bus control requirements are not stringent, a simple control structure is used, the main purpose being to ensure unity power factor operation. Furthermore, optimized PWM patterns and pattern synchronization can be used to reduce the switching frequency of the rectifier. The paper presents a complete analysis and design guidelines for the DC bus supply and inverter systems. Simulation and experimental results confirm the feasibility and advantages of the proposed structure. >

Online mechanical fault diagnosis of induction motor by wavelet artificial neural network using stator current

A novel online fault diagnostic method for the mechanical faults of induction motors is proposed. The method is based on artificial neural networks and Wavelet Packet Decomposition. New feature for mechanical fault detection is defined through the signature analysis of the wavelet packet decomposition coefficients of induction motor stater current. The theoretical background and description of the detection algorithm using artificial neural network is presented. Simulation results prove that the proposed method accurately detects the faults for a wide range of load conditions.

Modeling and simulation of induction motor with mechanical fault based on winding function method

A practical and accurate model for three-phase induction motors with various mechanical faults is presented in this paper. From the motor dimensions, the parameters of inductance and resistance of the motor can be determined by the winding function method. The model also takes into account the effect of magnetic saturation and non-linearity of the induction motor magnetic core. Simulation results for an induction motor with broken rotor bar are presented.

A neural network controlled unity power factor three phase PWM rectifier

The simplest method of operating three-phase PWM rectifiers is based on the use of offline PWM patterns. However, in this scheme the input power factor is less than unity and varies with the rectifier operating point due to the presence of the input LC filter. Furthermore, the response to transient conditions is slow and large current oscillations may occur due to the resonance of the filter. In this paper an online neural network (NN) controller, proposed to waveshape the input line currents, forces unity power factor operation and damps the low frequency resonance of the input filter. The proposed controller is insensitive to load/parameter variations thus resulting in a robust system. The performance of the proposed NN controller is verified by simulation.<<ETX>>

A performance comparison of PWM rectifiers and synchronous link converters

The authors present a systematic comparison of the current source topology (pulse width modulation, or PWM rectifier) and the voltage source topology (synchronous link power converter) from the point of view of power converter and switch kilovolt ampere ratings. PWM patterns and input and output filtering requirements, power factor, operating regions, and control aspects. Experimental results obtained on laboratory prototypes are used to validate the theoretical considerations. In general, it is concluded that the synchronous link power converter gives a higher performance but is more complicated to operate. Unity power factor and regenerative operation are achieved with closed-loop control. The PWM rectifier provides good performance with simple control strategies. It requires a larger filter to suppress the input line harmonics, but is simple to operate since open-loop operation is possible.<<ETX>>

An on-line operated unity power factor PWM rectifier for AC drive applications

In order to minimize their impact on the AC supply, AC drives often require an input rectifier stage with low input current harmonics and high input power factor. High efficiency is also desirable. Drawbacks of the conventional off-line operated PWM rectifiers include slow transient response, load dependent input power factor and the need for damping resistors to avoid harmonic amplification and current oscillations, particularly under transient conditions. In this paper, an on-line operated PWM rectifier with inherent damping and pattern synchronization with the AC mains is proposed. Since the modulation scheme uses the voltages across the input filter capacitors as templates, faster transient response is achieved under normal and starting conditions and the need of the damping resistors is eliminated. Moreover, an additional phase-shifting circuit is used in the control scheme to achieve unity power factor, independently of the DC link current variations. The paper includes analysis and design guidelines for the rectifier control circuit. Experimental results on a 1 kVA laboratory prototype confirm the feasibility of the proposed control structure.<<ETX>>