Hysteretic Current Mode Control of a Wide Output Voltage Three-Level Converter

Multilevel dc-dc converters can offer very high efficiency but have been generally limited to voltage mode control schemes for wide output voltage applications due to difficulties with current mode control near certain duty-cycles. For applications that require current mode control, this article proposes a hysteretic current mode control scheme which allows cycle-by-cycle control of multilevel converters over a wide duty-cycle range while also allowing operation at the critical duty-cycles found in multilevel converters. This enables high-efficiency solutions for applications that require a wide range of tightly regulated outputs, such as capacitor and battery charging, direct laser diode driving, and motor control. This is achieved using a multimode control scheme with ramped current references, a maximum interval timer, and reference offsetting for flying capacitor balancing. This control scheme is verified in Simulink modeling and implemented on a prototype three-level buck converter using a combination of a low-cost field programmable gate array and discrete analog circuitry. Alternative implementations are also described.