Ira J. Pitel

A new approach to improve power factor and reduce harmonics in a three phase diode rectifier type utility interface

A novel approach to improving power factor and reducing harmonics generated by a three-phase diode-rectifier-type utility interface is proposed. This approach is passive and consists of a novel interconnection of a star/delta power transformer between the AC and DC sides of the diode rectifier topology. This interconnection, in combination with the 120 degrees conduction intervals of each diode, is shown to generate a circulating third-harmonic current between the AC and DC side of the rectifier bridge. This current is shown to drastically improve the performance of the diode-rectifier-type interface. The resulting input current is near-sinusoidal, with significant reduction in line current harmonics. The proposed system can be viewed as a cost-effective retrofit to the existing diode rectifier utility interface applications. A design example illustrates the sizing of the necessary passive components. Selected results were verified experimentally on a laboratory prototype system.<<ETX>>

Polyphase transformer arrangements with reduced kVA capacities for harmonic current reduction in rectifier type utility interface

In this paper, polyphase transformer arrangements with reduced kVA capacities are presented for harmonic current reduction in high power rectifier utility interface systems. Based on the concept of an autotransformer, a proposed twelve-pulse rectifier system is realized with a resultant kVA rating of 0.18P/sub 0/ (pu). In this arrangement, the rectifier diodes each conduct for 120 degrees per cycle and the fifth and seventh harmonics are absent from the utility input line current. In the second scheme, an eighteen-pulse rectifier is realized with a kVA rating of 0.16P/sub 0/ (pu), rectifier diode conduction of 120 degrees per cycle and fifth, seventh, eleventh and thirteenth harmonic cancellation in the utility line currents. Additional applications for the proposed polyphase transformer arrangements include twelve and eighteen-pulse systems feeding multiple six-pulse nonlinear loads, such as AC motor drives, with an appropriate phase shift, and this arrangement substantially reduces the utility line current harmonics. For example, it is shown that the fifth and seventh harmonics generated by two separate six-pulse nonlinear loads are subtracted and this contributes to reduced harmonic distortion. Simulation results verifying the proposed concept are presented. >

White-noise modulation of high-frequency high-intensity discharge lamp ballasts

In this paper, a new method is proposed to avoid acoustic resonance related instabilities in metal halide lamps when operated with a high-frequency electronic ballast. Angle modulation of the inverter switching pattern has been used as a vehicle to randomize lamp driving frequency and to limit lamp power spectrum below the instability threshold. The optimal modulating pattern is obtained by studying the angle modulated spectra by periodic and random signals. Analysis is supported by simulations and verified experimentally with the ballasting of 250 watt lamps. >

Analysis and design of a new active power filter to cancel neutral current harmonics in three phase four wire electric distribution systems

An active power filter for cancelling harmonic currents in the neutral of a three-phase four-wire system is proposed. This approach employs a star/delta transformer along with a two-switch PWM (pulse-width-modulated) controlled active filter. The closed-loop control of the active power filter guarantees cancellation of neutral current harmonics under varying load conditions. The proposed system greatly improves the overall system performance and virtually eliminates transformer overheating due to harmonics. Experimental results from a prototype active power filter confirm the suitability of the proposed approach.<<ETX>>

Phase-Modulated Resonant Power Conversion Techniques for High-Frequency Link Inverters

Resonant power conversion techniques are examined and applied to high-frequency link inverters. A novel control principle using two high-frequency inverters modulated in phase to produce a dc isolated carrier containing wanted output on its sidebands is discussed. This power signal, when rectified, filtered, and inverted, results in sinusoidal outputs at utility frequencies. The method is analyzed for both dc and ac outputs and is demonstrated with a 3-kW high-frequency link inverter feeding both resistive and utility interactive loads. Typical waveforms are illustrated and performance is discussed.

A new active interphase reactor for 12-pulse rectifiers provides clean power utility interface

In this paper, a new active interphase reactor for twelve-pulse diode rectifiers is proposed. The proposed system draws near sinusoidal currents from the utility. In this scheme, a low kVA [0.02 P/sub o/ (PU)] active current source injects a triangular current into an interphase reactor of a twelve-pulse diode rectifier. This modification results in near sinusoidal utility line currents with less than 1% THD. It is further shown that a low kVA, 12-pulse system with an autotransformer arrangement [kVA rating of 0.18 P/sub o/ (PU)] can be implemented with the proposed active interphase reactor. The resulting system draws clean power from the utility and is suitable for powering larger kVA AC motor drive systems. Detailed analysis of the proposed scheme along with design equations is illustrated. Simulation results verify the concept. Experimental results are provided from a 208 V, 10 kVA rectifier system.

Characterization of Programmed-Waveform Pulsewidth Modulation

Programmed-waveform pulsewidth modulated (PWM) waveforms, applicable to ac-dc/dc-ac converters, are synthesized and analyzed in terms of several structural parameters. By invoking sensitivity studies and heuristics, optimal PWM structures are identified and contrasted. The results show total harmonic performance as a function of switching levels, waveform types, commutations per cycle, and filter bandpass.

Next generation distribution transformer: to address power quality for critical loads

A new single phase distribution transformer concept is proposed to improve power quality for critical loads. The secondary of the proposed transformer is composed of two windings, one of them equipped with a power electronic ac-ac converter. With the choice of proper turns ratio and the design of the PWM ac-ac converter, the proposed transformer has the following capabilities: (a) can compensate for 50% voltage sag and swells (b) can continuously shape the output voltage to be sinusoidal (low THD) even when the input voltage is distorted (c) can disconnect the load rapidly under fault conditions. The proposed approach does not employ any energy storage devices, such as large capacitors or inductors. The PWM ac-ac converter consists of four switching devices (IGBT) and is controlled with a four-step switching technique to achieve snubber-less operation. A design example is presented for a 480V/120V, 5 kVA transformer. Simulation results are discussed and experimental results on a 2kVA unit are presented.

Evaluation of acoustic resonance in metal halide (MH) lamps and an approach to detect its occurrence

A method to detect the occurrence of the acoustic resonance based on lamp electrical parameters has been proposed. Extensive experiments are conducted on 70 W metal halide lamps from different manufacturers and a lamp acoustic resonance detection method based on /spl Delta/R/R variation is developed. A new topology for a smart ballast which selects the operating frequency for stable operation based on real time measurements is proposed.

An advanced fuel cell simulator

Fuel cells are an emerging technology in the field of power generation. Fuel cell simulators would greatly aid in providing a convenient and economic alternative for testing various subsystems such as converters and inverters. This paper proposes a low-cost, easy-to-use fuel cell simulator to reproduce the electrical characteristics of a 5 kW solid oxide fuel cell. The simulator provides an advanced test bench for development and testing of power conditioning equipment.