A DLL/PLL based multi-phase interleaved DC-DC converter with digital off-time control and active series balancing for electric vehicles

In this paper, a Delay-Locked Loop (DLL) and Phase Locked Loop (PLL) interleaving control scheme is demonstrated for multi-phase dc-dc converters in a light electric vehicle (LEV) application. Three interleaved non-inverting buck-boost (NIBB) sub-converters operate in peak current mode control (PCMC), and a fully digital off-time generator (OTG) is used in lieu of slope compensation for more accurate battery current sensing and improved converter dynamics. A DLL adjusts the master sub-converter off-time to maintain quasi fixed-frequency operation, while a PLL adjusts the two slave sub-converter off-times to achieve inductor current interleaving. Active series balancing is achieved by adding a single switch to the NIBB that connects to the adjacent series battery. The modified topology reuses the NIBB inductor to reduce system cost, complexity and weight, while providing balancing capabilities. The series balancing scheme is validated in simulation, and the DLL/PLL interleaving control schemes are demonstrated experimentally on a 12 V, 270 W dc-dc converter running at 555 kHz. With the DLL and PLL based frequency control, multi-phase dc-dc converter interleaving is achieved within 150 μs, and stable QFF operation and interleaving are maintained through step-up and step-down transient events.