Resonant DC link converters and their use in rail traction applications

Ellams, P

Abstract

Conventional 'hard switching' converters suffer from significant switching loss due to the
simultaneous imposition of high values of current and voltage on the devices during commutation.
Resonant converters offer a solution to this problem. A review of resonant circuit topologies is
presented, which includes a summary of the interference problems which may occur when using
power converters in the rail traction environment. Particular attention is given to the Resonant
DC Link Inverter (RDCLI) which shows a great deal of pronuse using currently available
devices.
The frequency domain simulation of RDCLIs is discussed as a means of rapidly evaluating
circuit behaviour, especially in relation to modulation strategies. A novel modulation strategy is
proposed for Resonant DC Link Inverters, based on a procedure known as Simulated Annealing
which allows complex harmonic manipulations such as han-nonic minimisation, to be performed.
This is despite the fact that RDCLIs are constrained to use Discrete Pulse Modulation whereby
switch commutations are restricted to specific moments in time. The modulation algorithms were
verified by use of a low-power test rig and the results obtained are compared against theoretical
values. Details of the hardware implementation are also included.
A single-phase pulse-converter input stage is described which may be incorporated into the
Resonant DC Link Inverter topology. This input stage also benefits from soft-sVVItching and
allows four-quadrant operation at any desired power factor. A modulation scheme based on
SiMulated Annealing is proposed for the pulse-converter, to achieve hannomc control whilst also
synchronising with the supply wavefon-n. Practical results are presented and compared with those
obtained by simulation and calculation.
Finally the design of Resonant DC Link Converters is discussed and reconunendations made for
the choice of resonant components based on the minimisation of overall losses. Comparisons are
made between hard-switching and soft-switching converters in terms of loss and harmonic
performance, in an attempt to quantify the benefits which may be obtained by the application of
soft-switching.

Citation

Ellams, P. Resonant DC link converters and their use in rail traction applications. (Thesis). University of Salford

• Thesis Type: Thesis
• Deposit Date: Sep 23, 2011
• Publicly Available Date: Sep 23, 2011
• Award Date: Jan 1, 1994