Abstract:
The work is aimed at proposing a phase modulated PWM scheme for two-phase voltage source
inverter optimizing the pattern for minimum third harmonic content. The proposed two phase
PWM controller is implemented with a Digital Signal Processor (DSP, TMS320C50). The
experimental waveforms is compared with the simulated ones for different characteristic
parameters like distortion factors. This work results in an improved controller for two phase
motor drives and position controllers employing DSP.
Both three level and two level PWM schemes are adopted for the generation of PWM signals
for the inverter. For implementation of the scheme two different programs are written in C by
using ANSI C compiler supplied with the TI's TMS320C50. For compiling and running the
program an INTEL Pentium IV microcomputer is used. After running the program the code is
uploaded to the TMS320C50 DSP kit. After that the DSP kit supplies the calculated switching
points through its VO ports to the external hardware interfacing circuit using EPROMs. The byte
patterns for PWM signals generated using MATLAB are stored in two EPROMs (27C256) as
data. The DSP kit sends calculated duty cycles to the EPROMs and then according to the
calculated duty cycles required patterns are obtained at the output of the EPROMs. For
controlling the whole process a 12-bit counter, a high frequency clock circuit, a monostable
timer and buffers are used.
To test the performance of the scheme these signals are then applied to a two phase halfbridge
inverter using MOSFETs. To drive the inverter properly an electronic controller circuit is also
developed. The supplied DC voltage to the inverter is 90V. The output of the inverter is fed to a
prototype 0.5 hp two phase induction motor. Phase currents of the motor are obtained using two
current transformers and resistors.
Finally the system performance IS evaluated from the MATLAB simulation results and
experimental waveforms. Upon completion of the work it is found that the two level scheme
gives the better system performance especially the distortion factors of output current is much
lower in this scheme than that in the three level scheme. The experimental result shows good
agreement with the simulated one.
