Alexander L. Julian

Elimination of common mode voltage in three phase sinusoidal power converters

The paper describes the addition of a fourth leg to the bridge of a three-phase inverter for the purpose of eliminating the common mode voltage to ground. An appropriate four-phase filter is used to eliminate common mode currents due to modulation. With a suitable modulation strategy and a three-phase LC filter on three legs of the inverter, sinusoidal output line-to-line voltages are obtained. A simple modification of the modulation strategy is implemented for the four-phase inverter to achieve a three-phase star output neutral to ground voltage which is equal to zero at all times. The modulation strategy thereby completely eliminates the common mode potential produced by traditional modulation techniques with traditional inverter topologies.

A new space vector modulation strategy for common mode voltage reduction [in PWM invertors]

In this paper, the impact of the inverter modulation strategy on common mode conducted emissions is addressed. Whereas typically passive filter designs are used to mitigate the common mode current produced by the inverter, active filtering is proven to greatly reduce common mode conducted emissions due to the modulation of the power converter. A new space vector modulation strategy is presented for common mode EMI reduction in three- and four-phase DC/AC power converters.

Mitigating Circulating Common-Mode Currents Between Parallel Soft-Switched Drive Systems

A mathematical model that Is developed for a generalized drive system, including common-mode passive and active elements, is used to explore the issues of paralleling soft-switched resonant dc-link drive systems. Differences between the modulation pattern for each drive system cause common voltage disturbances, which lead to significant circulating currents between the drive systems. Control methods for actively compensating for common-mode circulating currents or reducing the common- mode voltage disturbances are investigated. Practical modifications to the drive system controls are implemented to reduce the circulating currents between paralleled systems.

Active filtering for common mode conducted EMI reduction in voltage source inverters

As solid-state power converters become more numerous, the unwanted EMI effects created by these converters increase. To address this issue, more attention has recently been given to the reduction of electromagnetic emissions created by power electronics. The proliferation of solid-state inverters brings the cost of semiconductors down, making active filtering an attractive alternative to passive filter topologies. Active filtering may also realize higher efficiency than passive filtering. This paper focuses on an active filter topology that significantly reduces the common mode voltage created by voltage source inverters. The reduction of common mode voltage is achieved by introducing a novel inverter topology and a new hysteresis modulation strategy to control this inverter topology.

Three-Phase VSI with FPGA-Based Multisampled Space Vector Modulation

This paper demonstrates improved performance of a three-phase voltage source inverter (VSI) when digital multisampled space vector modulation is used. The modulator and the inverter controller are implemented entirely using a field-programmable gate array platform, thus achieving increased bandwidth with respect to a typical digital signal processor or microprocessor-based controller. Increased controller bandwidth results in lower output voltage harmonic distortion in the frequency range above the fundamental and below the switching frequency. Experimental validation is presented together with the analysis carried out using a state space model of a VSI with an output LC filter.

Induction motor modeling for common mode and differential mode emission evaluation

The paper deals with the development of a detailed model of a three-phase induction motor useful for evaluating separately common mode and differential mode currents. The proposed approach simplifies the decoupling of the common mode and differential mode current spectra, using the dq0 stationary reference frame transformation, and allowing a separate analysis of the phenomena, which is useful for EMI filter design. The proposed model can also be used to evaluate new inverter modulation techniques in terms of current harmonic generation.

Multi-speed control of single-phase induction motors for blower applications

A simple electronic scheme is studied for multi-speed operation of a permanent split capacitor single phase induction motor used to run fractional horsepower blowers and pumps. Computer simulations predict efficiency, harmonic distortion, and pulsating torque when the motor is fed at 60 Hz, 40 Hz or 30 and by means of a four-triac bridge circuit. Results of simulations and laboratory tests are compared, showing close agreement. This scheme may be a cost effective alternative to tapped-winding or pole-changing motors. >

Power-Electronics-Based Energy Management System With Storage

This paper demonstrates the functionality of a power-electronics-based energy management system (EMS). The EMS includes batteries and a digitally controlled single-phase voltage source inverter (VSI), which can be controlled as a current source or a voltage source depending on the status of the ac grid and the users preference. The EMS guarantees that the critical loads are powered when the ac grid fails; in which case, the VSI is controlled as a voltage source. It also accomplishes peak power control by supplying battery power to the local loads while they are powered by the ac grid if the loads get large. The electricity cost savings accomplished by peak shaving are estimated. The EMS functionality is demonstrated by experimental measurements on a laboratory prototype. The control architecture and logic embedded in the EMS are discussed in detail.

Sensorless synchronous motor drive for use on commercial transport airplanes

This paper describes a sensorless synchronous machine drive to be used for starting an auxillary power unit (APU) on commercial transport airplanes. The proposed method utilizes the synchronous generator mounted on the APU, and presently only used as a source of electrical power, as a synchronous motor for starting the APU. The developed sensorless synchronous motor drive starting function involves measurement of machine terminal voltage and current, from which the desired current command is then calculated and implemented by the drive power converter. Power into the machine is determined by a power control loop, while the system voltage is limited to a desired value by a field weakening loop in the controller.<<ETX>>

Application of the transmission line theory to the frequency domain analysis of the motor voltage stress caused by PWM inverters

The innovative contribution of this paper is the application of a frequency domain model based on the transmission line modeling techniques for a four conductor cable bundle without the assumption of lossless lines. A thorough documentation of the mathematical model is included. Laboratory measurements validate the model which predicts the peak motor terminal voltage caused by: 1) different motor cable sizes and geometry 2) variations of the inverter dv/dt 3) variations of the voltage step size applied to the cable 4) termination networks inserted at the motor terminals to control the dv/dt.