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A three-phase, sinusoidal, active rectifier is presented, based on the classical inverter topology. The switches are governed by a fixed pulse width modulation (PWM) pattern, and the control strategy is extremely simplified as compared with many active rectifiers. General equations describing the steady-state operation of fixed pattern rectifiers are given. A dynamic model of the simplified control rectifier is presented, based on the nonlinear equations describing the system. Based on the analytical model, the classical PI-controller yields poor dynamic results, especially at low load conditions. However, the dynamic performance of the prototype is much better, due to the effects of commutation dead time of the rectifier switches. It is shown that a small modification to the classical PI-controller yields a remarkable increase in amplitude and phase margin, without slowing down the response. The obtained dynamics show a clear improvement over the classical PI-controller and are adequate for most applications. All proposed controls are verified on a 380 V, 15 kW prototype. Index Terms--AC-DC, control system synthesis, power converters, power factor correction.

When a "classical" current control scheme is applied, the line current of a boost power-factor-correction (PFC) converter leads the line voltage, resulting in a nonunity fundamental displacement power factor and in important zero-crossing distortion in applications with a high line frequency (e.g., 400-Hz power systems on commercial aircraft). To resolve this problem, a current- control scheme is proposed using duty-ratio feedforward. In this paper, the input impedance of the boost PFC converter for both the classical current-loop controller and the controller using duty-ratio feedforward are derived theoretically. A comparison reveals the advantages of the proposed control scheme: a low total harmonic distortion of the line current, a resistive input impedance, virtually no zero-crossing distortion, and a fundamental displacement power factor close to unity. The theoretical results obtained are verified using an experimental setup of a digitally controlled boost PFC converter. [ABSTRACT FROM AUTHOR]

Whereas power-factor-correction (PFC) converters for low-power ranges (less than 250 W) are commonly designed for operation in the discontinuous conduction mode, converters for higher power levels are operated in the continuous conduction mode. Nevertheless, when these converters are operated at reduced power, discontinuous conduction mode will appear during parts of the line period, yielding input current distortion. This distortion can be eliminated by employing a dedicated control algorithm, consisting of sample correction and duty-ratio feedforward. The reduction of the harmonic distortion of the input current and the increase of the power factor are demonstrated by experiments on a 1-kW boost PFC converter. [ABSTRACT FROM AUTHOR]

In this letter, it is shown that the positive- and negative-sequence components of a three-phase, sinusoidal and unbalanced voltage system can be calculated exactly without the application of the Fortescue transformations in the complex plane, while only the root mean square (RMS) line-to-line voltages are required, and without having to measure the phase relationships between these voltages. This results in a convenient procedure to assess voltage unbalance in the field. The phase relation- ships between the sequence and line components can also be calculated. Moreover, if the RMS values of the line-to-neutral voltages are known, the zero-sequence component can he calculated exactly as well, again, without the application of complex mathematics. [ABSTRACT FROM AUTHOR]