Jianguo Li

Capacitor voltage balancing control based on CPS-PWM of Modular Multilevel Converter

As a new generation of high-capacity Voltage Source Converter (VSC), Modular Multilevel Converter (MMC) is a potential topology of VSC based High Voltage Direct Current Transmission System (VSC-HVDC). This paper focuses on the voltage balancing control of floating dc capacitors based on CPS-PWM. The imbalance mechanics of capacitor voltage between and within arms are theoretically revealed. A new balancing control strategy called Capacitor Voltage Balancing Control Loop (CVBC Loop) is proposed, which can directly and accurately regulate the active power injected into the MMC module to guarantee dc voltage balance of capacitors within the same arm. A 10kVA laboratory prototype has been built. The experiment results verify the validity of the proposed control strategy under both steady and dynamic state.

FPGA-based universal multilevel space vector modulator

This paper presents a new circuit design of multilevel space vector modulation (SVM) strategy. This strategy is based on the decomposition of the reference voltage, and it is utilized at any number of levels. The proposed algorithm has been realized using field programmable gate array (FPGA) technology. A FPGA XILINX XC2S100 was used for the implementation of the SVM IC. The designed SVM IC was incorporated with a digital signal processor (DSP) to provide a solution for a three-phase five-level inverter. Experimental results are provided to verify the implemented SVM control IC

Minimum Voltage Tracking Balance Control Based on Switched Resistor for Modular Cascaded Converter in MVDC Distribution Grid

This paper provides a characterizationr analysis for the voltage balance of modular cascaded converter in a medium-voltage direct-current distribution grid. Specifically, voltage stability and traditional auxiliary resistor solution are analyzed from the theoretical level. On this basis, a minimum voltage tracking balance (MVTB) control based on a switched resistor is proposed. The voltage balance during startup and normal locked processes can be adjusted effectively by MVTB control. Moreover, the resistor does not need to absorb power continuously; instead, it is just switched into operation for a while when a difference occurs, and the power loss can be decreased after the system recovers to a steady state. Finally, experimental results verify the effectiveness of the MVTB control.

Comparative Analysis of Multilevel-High-Frequency-Link and Multilevel-DC-Link DC–DC Transformers Based on MMC and Dual-Active Bridge for MVDC Application

This paper gives a comprehensive comparison of multilevel high-frequency-link (HFL) dc transformer (abbreviated MDCT) based on modular multilevel converter (MMC) and multilevel-dc-link dc transformer (abbreviated ADCT) based on dual-active-bridge (DAB) for medium-voltage dc (MVDC) application. The topology, operation, HFL voltage and current, active and circulating power, characteristic currents, switching behaviors, and power loss are analyzed in detail. Both MDCT and ADCT have fault treatment ability for MVDC application. However, the installation and commissioning of ADCT are more flexible and simpler. In addition, the MDCT needs more switches and high-frequency (HF) inductors than ADCT in the MVDC side with the same voltage level, but the number of HF transformer can be reduced. Compared with MDCT, the ADCT has higher power transfer ability and lower circulating power, lower HFL voltage, and RMS current and peak values with the same transmission power in the MVDC side. However, the arm RMS and average currents of MDCT are lower than those of ADCT in the MVDC side. The switching performance of MDCT deteriorates when the MVDC voltage fluctuates, but the switching behaviors of half bridges are added to ADCT. The loss of ADCT almost keep the same when the MVDC voltage fluctuates, but the loss of MDCT changes a lot. Finally, a small-scale prototype platform with 1 kW/450 V/150 V is built and experimental results verify the correctness and effectiveness of the theoretical analysis.

An Improved DC Solid State Transformer Based on Switched Capacitor and Multiple-Phase-Shift Shoot-Through Modulation for Integration of LVDC Energy Storage System and MVDC Distribution Grid

This paper proposes an improved dc transformer (NDCT hereinafter) based on switched capacitor with reduced switches for the integration of low-voltage dc energy storage systems and medium-voltage dc power distribution grid. The topology, phase-shift (PS) shoot-through and multiple PS modulations, and voltage, current, and power characterizations, as well as commutation characterization and control strategy, are proposed and analyzed comprehensively. Compared with the traditional schemes, the proposed NDCT not only can enhance reliability and flexibility but can increase voltage adjustment and power transfer capabilities as well. Moreover, the current ripple performance and soft-switching performance are improved, and the number and capacity of switches are reduced, thereby increasing the efficiency and cost of the system. Finally, an NDCT prototype is built. Experimental results verify the correctness and effectively of the proposed solution.