This control technique is one of the most important inverter technique, the pulse-width modulation techniques are the major part of the power inverter techniques, which have been the major subject of intensive research during the last few decades. A large variety of methods, different in concept and performance, have been recently developed and described. Their implementation in the design of the voltage source inverters depends on the load types, the power levels, and the semiconductor devices used in the power converter. The performance and cost criteria determines the choice of a PWM method in a specified application. 15,16,24
A new nonlinear control technique one-cycle control is proposed to control the duty-cycle of the switch such that in each cycle the average value of the switched variable of the switching converter is exactly equal to or proportional to the control reference in the steady-state or in a transient. The conventional one cycle control (OCC) technique needs that the integrator is reset instantaneously as shown the fig 3. The integration value is
Where, switching frequency is fs, 1/ fs=Ts, and Ts, is switching cycle. In each cycle, the switch is on for a time duration Ton and is off for a time duration Toff, and Ton + Toff =Ts. The duty-ratio D=Ton/Ts is modulated by an analog control reference Vref. When Vint reaches the control reference Vref, a reset pulse is generated at the output of the comparator that resets the RS flip-flop (Q=O), starting another switching state, switch M1 is turned on and switch M2 is turned off as a consequence as shown the fig. 3. The falling edge of the pulse at the Q terminal triggers the narrow-pulse generator to produce a very narrow pulse to reset the integrator. The integrator restarts integration from zero voltage after the reset. During this switching state, therefore, Vint keeps decreasing until the arrival of the next clock pulse, which starts a new switching cycle. In total switching cycle, the integrator value is
D is the duty-ratio of a cycle. The duty-ratio of the switch is modulated such that the integration of the switched variable at the output is exactly equal to the integration of the control reference in each cycle
If the cycle is tiny enough, the output will follow the reference signal with high accuracy no matter whether the reference is constant or variable. Therefore, the dynamic response is very fast. It can improve the output waveform quality, and also can eliminate the undesired harmonic contents.
Most often, the pulse-width modulation (PWM) schemes are compared with the harmonic distortion produced by different schemes when operating with the same effective switching frequency. However, the one-cycle control technique has shown excellent improvement compared with conventional sinusoidal pulse width modulation (SPWM).
In OCC unipolar, the gating logic is unchanged from the PWM case. However, OCC contains an integrator, with a switch utilized for resetting (across the capacitor). During each individual switching period,
The integrating time constant ? should be close to, but a bit shorter than the switching period TS. Since
An acceptable integration time constant (T=40 µs) is given by
R= 100k? and C= 400 pF