Three-Phase Full-Wave Rectifier

This ability of a bi-directional power transfer makes the controlled ac-dc converter suitable for a use between a synchronous machine driven by the combustion engine and the battery-bus in hybrid vehicles [36]. 

Due to the fixed conductance causality of the switches the causality at junctions Oa, Ob, and Oc remains undetermined. Therefore, C-elements in integral causality have been attached. Their constitutive ODE is formulated so that the capacitance can be set to zero. 

Let Vs denote the knee voltage of the diodes. The transformer modulus in the piecewise linear model Sw Di of diode Dj, i = 1. 6, then reads 

Furthermore, let gi () denote the piecewise linear approximation of the nonlinear flow versus effort relation of the t-tti diode according to Shockley s equation implemented by the switch model Sw Z),. 

Then the following equations can be deduced from the bond graph of Fig. 8.38 by summing efforts and flows respectively at the designated junctions. 

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Another popular rectifier circuit is the full-controlled three-phase full wave rectifier. This circuit is more expensive because six thyristors are used. However, the form factor is much better, about 1.01, and the ripple current is 360 Hz. The higher frequency makes it easier to filter the ripple current. The half-controlled three-phase bridge rectifier circuit may require armature current smoothing reactors to reduce the ripple current. Another problem associated with the non-uniform DC input to the motor is the commutation. The motor must commutate under a relatively high degree of leakage reactance. 

The exciter is an AC generator with a stator-mounted field. Direct cur rent for the exciter field is provided from an external source, typically u small variable voltage rectifier mounted at the motor starter. Exciter oui put is converted to DC through a three-phase, full-wave, silicon-diode bridge rectifier. Thyristors (silicon-controlled rectifiers) switch the cur rent to the motor field and the motor-starting, field-discharge resistors These semiconductor elements are mounted on heat sinks and assembled on a drum bolted to the rotor or shaft. 

The DC voltage from the solid-state power supply generally has a rather poor form factor. The magnitude of the form factor is dependent on the configuration of the rectifier circuitry. The poorer the form factor, the higher the ripple current in the DC motor. This increases motor heating and reduces the power efficiency. Several three-phase rectifier circuits are available for the AC line power into DC. Most drives over 5 hp use three-phase full wave circuitry. Figure 3.5 shows a three-phase half-controlled full wave rectifier. 

Figure 3.5 Three-phase half-controlled full wave rectifier...

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