Emerging large-scale modular power converters are pursuing high-performance distributed control systems. As opposed to the centralized control architecture, the distributed control architecture features shared computational burdens, pulse-width modulation (PWM) latency compensation, simplified fiber-optic cable connection, redundant data routes, and greatly enhanced local control capabilities. Modular multilevel converters (MMCs) with conventional control are subjected to large capacitor voltage ripples, especially at low-line frequencies. It is proved that with appropriate arm current shaping in the timescale of a switching period, referred as the switching-cycle control (SCC), such line-frequency dependence can be eliminated and MMCs are enabled to work even in dc-dc mode. Yet the SCC demands multiple times of arm current alternations in one switching period. To achieve the high-bandwidth current regulation, hybrid modulation approach incorporating both the carrier-based modulation and the peak-current-mode (PCM) modulation is adopted. The combined digital and analog control and the extreme time-sensitive nature together pose great challenges on the practical implementation that the existing distributed control systems cannot cope with. This dissertation aims to develop an optimized distributed control system for SCC implementation. The critical analog PCM modulation is enabled by the intelligent gate driver with integrated rogowski coil and field programmable gate array (FPGA). A novel distributed control architecture is proposed accordingly for SCC applications where the hybrid modulation function is shifted to the gate driver. The proposed distributed control solution is verified in the SCC-based converter operations. Accompanied by the growing availability of medium-voltage silicon carbide (SiC) devices, fast-switching-enabled novel control schemes raise a high synchronization requirement for the communication network. Power electronics system network (PESNet) 3.0 is a proposed next-generation communication network designed and optimized for a distributed control system. This dissertation presents the development of PESNet 3.0 with a sub-nanosecond synchronization error (SE) and a gigabits-per-second data rate dedicated for large-scale high-frequency modular power converters. The White Rabbit Network technology, originally developed for the Large Hadron Collider accelerator chain at the European Organization for Nuclear Research (CERN), has been embedded in PESNet 3.0 and tailored to be suited for distributed power conversion systems. A simplified inter-node phase-locked loop (N2N-PLL) has been developed. Subsequently, stability analysis of the N2N-PLL is carried out with closed-loop transfer function measurement using a digital perturbation injection method. The experimental validation of the PESNet 3.0 is demonstrated at the controller level and converter level, respectively. The latter is on a 10 kV SiC-MOSFET-based modular converter prototype, verifying ±0.5 ns SE at 5 Gbps data rate for a new control scheme. The communication network has an impact on the converter control and operation. The synchronicity of the controllers has an influence on the converter harmonics and safe operation. A large synchronization error can lead to the malfunction of the converter operation. The communication latency poses a challenge to the converter control frequency and bandwidth. With the increased scale of the modular converter and control frequency, the low-latency requirement of communication network becomes more stringent. / Doctor of Philosophy / Emerging silicon carbide (SiC) power devices with 10 times higher switching frequencies than conventional Si devices have enabled high-frequency high-density medium-voltage converters. In the meantime, the power electronics building block (PEBB) concept has continually benefited the manufacturing and maintenance of modular power converters. This philosophy can be further extended from power stages to control systems, and the latter become more distributed with greatly enhanced local control capabilities. In the distributed control and communication system, each PEBB is equipped with a digital controller. In this dissertation, a real-time distributed control architecture is designed to take the advantage of the powerful processing capability from all digital control units, achieving a minimized digital delay for the control system. In addition, pulse-width modulation (PWM) signals are modulated in each PEBB controller based on its own clock. Due to the uncontrollable latency among different PEBB controllers, the synchronicity becomes a critical issue. It is necessary to ensure the synchronous operation to follow the desired modulation scheme. This dissertation presents a synchronized communication network design with sub-ns synchronization error and gigabits-per-second data rate. Finally, the impact of the communication network on the converter operation is analyzed in terms of the synchronicity, the communication latency and fault redundancy.

Numerous power electronics building blocks (PEBB) based power conversion systems have been developed to explore modular design, scalable voltage and current ratings, low-cost operations, etc. This paper further extends the modular concept from the power stage to the control system. The communication network in SiC-based modular power converters is becoming significant for distributed control architecture, with the requirements of tight synchronization and low latency. The influence of the synchronization accuracy on harmonics under the phase-shifted carrier pulse width modulation (PSC-PWM) is evaluated. When the synchronization is accurate, the influence of an increase in harmonics can be ignored. Thus, a synchronous distributed control and communication protocol with well-performed synchronization of 25 ns accuracy is proposed and verified for a 120 kHz SiC-based impedance measurement unit (IMU) with cascaded H-bridge PEBBs. An improved synchronization method with additional analog circuits is further implemented and verified with sub-ns synchronization accuracy. / The power electronics building block (PEBB) concept is proposed for medium-voltage converter applications in order to realize the modular design of the power stage. Traditionally, the central control architecture is popular in converter systems. The voltage and current are sensed and then processed in one central controller. The control hardware interfaces and software have to be customized for a specified number of power cells, and the scalability of controller is lost. In stead, in the distributed control architecture, a local controller in each PEBB can communicate with the sensors, gate drivers, etc. A high-level controller collects the information from each PEBB and conducts the control algorithm. In this way, the design can be more modular, and the local controller can share the computation burden with the high-level controller, which is good for scalability. In such distributed control architecture, a synchronous communication system is required to transmit data and command between the high-level controller and local controllers. A power converter always requires a highly synchronized operation to turn on or turn off the devices. In this work, a synchronous communication protocol is proposed and experimentally validated on a SiC-based modular power converter.