Vahe Caliskan

Multifrequency averaging of DC/DC converters

This paper presents some of the issues involved in applying frequency-selective averaging to modeling the dynamic behavior of pulsewidth-modulated (PWM) DC-DC converters. We use the boost converter as an example to show the details involved in deriving some novel extended averaged models, and we use simulations to highlight the accuracy of the models even when traditional small-ripple conditions are not satisfied.

Automotive power generation and control

This paper describes some new developments in the application of power electronics to automotive power generation and control. A new load-matching technique is introduced that uses a simple switched-mode rectifier to achieve dramatic increases in peak and average power output from a conventional Lundell alternator, along with substantial improvements in efficiency. Experimental results demonstrate these capability improvements. Additional performance and functionality improvements of particular value for high-voltage (e.g., 42 V) alternators are also demonstrated. Tight load-dump transient suppression can be achieved using this new architecture. It is also shown that the alternator system can be used to implement jump charging (the charging of the high-voltage system battery from a low-voltage source). Dual-output extensions of the technique (e.g., 42/14 V) are also introduced. The new technology preserves the simplicity and low cost of conventional alternator designs, and can be implemented within the existing manufacturing infrastructure.

Uncontrolled generator operation of interior PM synchronous machines following high-speed inverter shutdown

Interior permanent magnet (IPM) synchronous machine drives are vulnerable to a special fault mode when gating is suddenly removed from the inverter switches during high-speed operation. The resulting IPM machine operation as a generator in combination with an uncontrolled rectifier must be properly understood and accounted for in the machine design to avoid damage to either the machine or inverter. An approximate closed-form solution is derived in this paper which relates the resulting machine phase current (and torque) to the IPM machine parameters, the DC link voltage, and the rotor speed. The resulting operating characteristics are particularly interesting for IPM machines that have been designed with inductance saliency ratios greater than 2. The validity of the approximate solution is confirmed using dynamic simulation results, and the implications of these results for the machine designer seeking to minimize or eliminate the impact of this undesired operating mode are thoroughly discussed.

Analysis of three-phase rectifiers with constant-voltage loads

This work presents a quantitative analysis of the operating characteristics of three-phase diode bridge rectifiers with AC-side reactance and constant-voltage loads. We focus on the case where the AC-side currents vary continuously (continuous AC-side conduction mode). This operating mode is of particular importance in alternators and generators, for example. Simple approximate expressions are derived for the line and output current characteristics as well as the input power factor. Expressions describing the necessary operating conditions for continuous AC-side conduction are also developed. The derived analytical expressions are applied to practical examples and both simulations and experimental results are utilized to validate the analytical results. It is shown that the derived expressions are far more accurate than calculations based on traditional constant-current models.

Multi-frequency averaging of DC/DC converters

This paper presents some of the issues involved in applying frequency-selective averaging to modeling the dynamic behavior of PWM DC-DC converters. We use the boost converter as an example to show the details involved in deriving some novel averaged models and use simplifications to highlight the accuracy of the models even when traditional small-ripple conditions are not satisfied.

Modeling and analysis of FACTS devices with dynamic phasors

The paper reviews the use of dynamic phasors in modeling and analysis of FACTS, and illustrates the capabilities of the methodology on thyristor-controlled series capacitors (TCSCs) and on unified power flow controllers (UPFCs), the large signal phasor models of these subsystems are expressed in continuous time, making them directly compatible with the conventional models used for the other system components.

Maximum power tracking in parallel connected converters

A control scheme for parallel connected converter systems that will transfer the maximum available power from a nonideal voltage source is presented. Monitoring the rates of change in both the average input current and average input power from the source in each switching period, the proposed control method can dynamically regulate the DC-DC converter system to track the peak power of the source. The amplitude and frequency of the oscillation due to a limit-cycle around the system peak power point is analyzed. In addition, the central-limit current distribution control for the system is incorporated in this control scheme to improve the system efficiency and reliability by uniformly distributing the total peak power among the converters connected in parallel. >

Design and evaluation of Feedforward Active ripple filters

An active ripple filter is an electronic circuit that cancels or suppresses the ripple current and electromagnetic interference generated by the power stage of a power converter, thus reducing the passive filtration requirements. This paper explores the design of feedforward active ripple filters for current ripple cancellation, including the design tradeoffs, advantages, and limitations of different implementation methods. The design and performance of an active filter using a novel Rogowski-coil current sensor is discussed in detail. Experimental results from a prototype converter system using this approach are presented, and quantitative comparisons are made between a hybrid passive/active filter and a purely passive filter. It is demonstrated that substantial improvements in filter mass and converter transient performance are achievable using this active ripple filtering method.

Peak power tracking in parallel connected converters

A control scheme for parallel-connected converter systems that will transfer the maximum available power from a nonideal voltage source is presented. Monitoring the rates of change in both the average input current and the average input power from the source, the proposed control scheme can dynamically regulate the DC-DC converter system to track the peak power point of the source. The amplitude and the frequency of oscillation due to a limit cycle around the system peak power point are analyzed.<<ETX>>

Design and evaluation of an active ripple filter with Rogowski-coil current sensing

An active ripple filter is an electronic circuit which cancels or suppresses the ripple current and EMI generated by the power stage of a power converter, thus reducing the passive filtration requirements. This paper presents the design and evaluation of a feedforward active ripple filter which employs a Rogowski coil for ripple current sensing. The design of the active filter is discussed in detail, including the advantages, tradeoffs, and limitations of the approach. Experimental results from a prototype converter system using this approach are presented, and quantitative comparisons are made between a hybrid passive/active filter and a purely passive filter. It is demonstrated that substantial improvements in filter mass and converter transient performance can be achieved using the proposed active ripple filtering method.