The thesis describes an optimal selective harmonic elimination strategy suitable for singlephase
AC-DC converter-fed traction drives. The objective is to eliminate low-order supply
current harmonics, including those injected into the supply due to load-side current ripple.
Other advantages that the switching strategy has to offer over phase-control include
improved supply power factor, reduced VA consumption for a given demand speed and
load, reduced torque and speed ripple and smaller armature circuit smoothing inductance.
The effect of field current boost on the dynamic response of the drive is also described.
It is shown that field boost helps to reduce the speed rise-time by increasing the
electromagnetic torque available during acceleration periods.
Closed-loop control of a 4-quadrant DC drive is described and a comparison made between
the performance of PID-control and pseudo-derivative feedback control. It is shown that
pseudo-derivative feedback control has several advantages to offer, amongst which are ease
of tuning of the controller gains and a superior performance following load torque
A laboratory size drive system was designed and built, and used to validate simulation
predictions for both the switching strategy and pseudo-derivative feedback control. A
microcontroller based hardware implementation of both the switching strategy and a digital
pseudo-derivative feedback controller was adopted, with the switching strategy being
implemented using an off-line approach of precalculating the switching angles and storing
these in look-up tables.
The armature voltage controller comprises a dual-converter employing IGBTs as switching
devices. The use of IGBTs allows higher switching frequencies at significant power levels
than would be possible if GTOs were used. It also simplifies the gate drive circuit design
and minimises the need to use snubber circuits.
A Doctoral Thesis. Submitted in partial fulfillment of the requirements for the award of Doctor of Philosophy of Loughborough University.