A New SVPWM Technique for DC Negative Rail Current Sensing at Low Speeds

Negative rail current sensing with the conventional space vector pulsewidth modulation (SVPWM) scheme imposes several challenges, particularly at low speeds and sector boundaries, where the pulsewidths of active vectors become narrow while the dc negative rail current becomes zero in null vectors (111) or (000). This paper presents a new SVPWM scheme by replacing null vectors with complementary active vectors such that the added vectors effectively cancel out each other, and the applied resultant voltage remains the same as in the conventional SVPWM. Hence, the pulsewidths of active vectors can be increased at low speeds without introducing additional switching losses, adding switching complexity, or introducing low frequency noise to the waveforms. Moreover, the proposed scheme reduces the system error caused by the deadtime of the switches with enlarged pulsewidths, enabling low-speed drive. The proposed technique is experimentally verified using a TMS320F28035 (Piccolo) microcontroller.