Method of duty cycle generation for extending the linear modulation range in a pulse width modulated voltage source inverter

A control system for a multi-phase electric machine for controlling the flow of electrical current between a voltage source and the multi-phase electric machine to operate the electric machine as a motor, the control system comprising:

• wherein, between each phase of the multi-phase electric machine and the voltage source, the control system includes:
• a high side diode and a high side switch positioned in parallel between a positive terminal of the voltage source and the electric machine with the high side diode being reverse biased with regard to the positive terminal;
• and
• a low side diode and a low side switch positioned in parallel between a negative terminal of the voltage source and the electric machine with the low side diode being reverse biased with regard to the electric machine;
• wherein the control system is a pulse width modulated control system with a pulse cycle duration and wherein the physical components of the control system define a minimum duty cycle (Dmin), the control system further defining a deadtime duty cycle (Ddead) and being operable to define a variable duty cycle (D*) from zero to one:
• wherein Dmin is the minimum non-zero duty cycle defined by the control system during operation of the electric machine as a motor;
• and
• wherein the maximum non-unity duty cycle (Dmax) defined by the control system during operation of the electric machine is equivalent to (1−Dmin).