A development of single cycle control low level voltage grid connected inverter
Thesis DisciplineElectrical Engineering
Degree GrantorUniversity of Canterbury
Degree NameMaster of Engineering
The thesis describes a development of simple and low engineering cost Single Cycle Controlled grid connected inverter. The voltage source current controlled inverter aims to support low voltage grid from small scale distributed power sources.
Single Cycle Controller uses real time current to control PWM switching of the inverter. The controller forces output current to have the same phase as an ordered AC signal. The inverter supports the grid at unity power factor if the AC signal is taken directly from the grid. Use of a generated AC signal is proposed, which allows control over active and reactive current injection or absorption by the inverter. A new synchronized waveform generation method implementable in a microcontroller is proposed in the thesis.
A number of Single Cycle Control switching strategies for the H-bridge converter are tested. A hybrid pulse width modulation switching strategy is used as it switches only one switch at high frequency at any time, which reduces switching losses in the bridge and allows easier implementation in hardware. The controller limitation near voltage zero crossing in boost mode is illustrated.
Single Cycle Control faces results in current distortion near voltage zero crossings. Strategies to manage this are presented.
The inverter is simulated in PSCAD and hardware prototype is built. The prototype results are presented for current injection into the grid at unity power factor.