Compensation of Supply Voltage Ripple in a Reversible PWM Converter
Abstract Generated abstract
This paper addresses the influence of rectified supply voltage ripple in DC electric drives using an uncontrolled rectifier, reversible pulse-width converter, and motor. It argues that filtering is often impractical at higher motor powers, and proposes compensating the ripple by additionally modulating the converter output voltage according to the instantaneous rectified supply voltage. A reversible pulse-width modulator circuit is described in which comparison elements and amplifiers vary the relative duration of output voltage pulses as a function of both control voltage polarity and supply voltage, thereby reducing ripple effects without large filtering components.
Full Text
COMPENSATION OF RShIP SUPPLY-VOLTAGE RIPPLE
V. A. Beinarovich, L. S. Udut, V. S. Fadeev
(Presented by the scientific and technical seminar of the Scientific Research Institute of Nuclear Power Engineering)
In DC electric drives using the system uncontrolled rectifier — reversible pulse-width converter (RShIP) — motor, it is advisable to eliminate the influence of ripple in the RShIP supply voltage. This makes it possible to reduce the number of phases of the uncontrolled rectifier under whose action the amplitude of the output voltage and current of the RShIP pulsates, which has a harmful effect on the properties of electric drives, especially with low-inertia motors having a smooth or printed armature. Eliminating the influence of the pulsating rectified voltage by means of a filter is of low effectiveness at considerable motor powers, since the dimensions of the filter increase to an almost unacceptable size.
Fig. 1
The simplest way to eliminate the influence of supply-voltage ripple is additional modulation of the RShIP output voltage as a function of the magnitude of the rectified supply voltage, since the switching frequency of the RShIP is much higher than the frequency of the supply-voltage ripple.
In this case, the relative duration of the output-voltage pulses of the RShIP must depend on the control and supply voltages. Such modulation can be carried out by means of a reversible pulse-width modulator, whose circuit is shown in Fig. 1.
The pulse-width modulator contains two comparison elements, implemented on transistors of opposite conductivity in a common-base circuit, T1 and T2, and two amplifiers on transistors of direct conductivity in a common-emitter circuit.
The bias voltage \(U1(U2)\) is obtained by dividing the voltage of rectifier B1, made according to the same circuit as the rectifier supplying the RShIP, by means of the divider \(R1, R2, (R3, R4)\). In the absence of a control voltage \((U_y = 0)\), transistors T1, T2 are cut off by the negative bias voltage. By changing the value of the control voltage \(U_y\), it is possible to regulate the relative duration of the voltage pulses obtained at one of outputs 1 or 2 (Fig. 1), depending on the polarity of \(U_y\).