A Hierarchical Digital Control System for Medium-Voltage Modular Converters Enabling Peak Current Mode Control for Parallel Operation

One of the key characteristics of modular converters is scalability; therefore, precise parallel operation of multiple modular converters with current mode control is desired. Furthermore, a well-structured digital control scheme allows for the programmability of the modular converter to achieve different functions, and thus needs to be carefully defined. This paper introduces a hierarchical digital control system for medium-voltage modular converters which uses gate drivers for pulse width modulations (PWMs). The gate driver, which features a PCB-embedded Rogowski current sensor and a local FPGA with peripherals, is capable of directly sensing the switching currents of SiC devices and locally implementing PWM. As an application example in this paper, a modular converter system is constructed and operated as paralleled-synchronous buck converters with peak current mode control. Each modular converter employs a hierarchical control structure where the local controller is responsible for the arithmetic calculation of control schemes, and the gate drivers conduct peak current mode modulation. Data transmission between the local controller and the gate drivers occurs digitally through fiber optic cables, which further increase the noise immunity of the modular converter. Good load current sharing between the paralleled modular converters is achieved, and test results are demonstrated in this paper.