Question

Draw a schematic diagram and explain the operation of a C dump converter used for the control of SRM

Answer 1

Answer)

The 4-phase C-dump converter is shown in Figure with an energy recovery circuit. The stored magnetic energy is partially diverted to the capacitor Cd and recovered from it by the single quadrant chopper comprising of Z13, Lr, and Dr and sent to the dc source. Assume that T1 is turned on to energize phase A and when the A-phase current exceeds the reference,T1 is turned off.This enables the diode D1 to be forward biased, and the current path is closed through Cd which increases the voltage across it. This has the effect of reducing the A-phase current, and, when the current falls below the reference by Δi i.e., current window, T1 is turned on to maintain the current close to its reference. When current has to be turned off completely in phase A, T1 is turned off, and partially stored magnetic energy in phase A is transferred to energy dump capacitor, Cd . The remaining magnetic energy in the machine phase has been converted to mechanical energy .This converter has the advantage of minimum switches allowing independent phase current control.Speedy commutation of currents requires larger vo, which results in increasing the voltage rating of the power devices. Further, the energy circulating between Cd and the dc link results in additional losses in the machine, Z13,Lr, and
Dr, thereby decreasing the efficiency of the motor drive.The energy recovery circuit is activated only whenT1, T2, T3, orT4 switches are conducting to avoid freewheeling of the phase currents. The
control pulses to Z13, end with the turn-off of the phase switches. The control pulse is generated based on the reference and actual value of E with a window of hysteresis to minimize the switching of Z13. This circuit has gained in popularity since its introduction in the early stages of SRM drive research and development.