Recently, Voltage Source Converter (VSC) basedHigh Voltage Direct Current (HVDC) transmission systems have gained more attention. In this paper, a control method for a modular VSC based HVDC transmission system with high frequency isolation referred to as high frequency isolated modular converter is proposed. In the high frequency isolated modular converter configuration, several floating DC capacitors in all three phases are connected in series, and voltage balancing control of these floating dc capacitors is required. In this paper, an appropriate control structure with the capacitor voltage balancing controller is proposed. The proposed control scheme consists of three layers to control terminal DC bus voltage and balance DC capacitor voltages of each building block. Detailed PSCAD simulation results are presented to evaluate the performance of high frequency isolated modular converter. Controller hardware-in-the-loop simulation of the high frequency isolated modular converter is also performed by Real Time Digital Simulator (RTDS), and RTDS results are presented to verify the control structure. Finally, lab-scale experimental results are presented to validate the proposed control method. Index Terms-Voltage Source Converter (VSC), HVDC transmission systems, Capacitor Voltage Balancing Controller, High Frequency Isolated Modular Converter.0093-9994 (c) , respectively. His recent research interests are PV/battery power electronic systems, high frequency power converters and high bandwidth current sensing schemes.

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We propose a Convertible Static Transmission Controller (CSTC) concept that enables coordinated power flow control with emphasis on large penetration of renewable energy resources based transmission in a meshed network. CSTS can be connected across the substation power transformer and reconfigured for different modes of operation to perform as a versatile transmission controller with several functions including: power flow control for transmission of renewable resources, and as a transformer back-up for disaster management and/or life extension purposes. Different connecting configuration options, i.e. shunt-shunt, series-shunt, and series-series can be obtained. In this paper, we demonstrated the viability of the proposed concept using Typhoon HIL400 ultra-high fidelity Hardware-in-the-Loop (HIL) system in three different modes of operation. HIL simulations are used to verify the validity of the proposed control architecture for CSTC operation during both normal and unbalanced power system conditions for different connecting configurations.

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In order to synchronize the distributed control systems (DCS) in modular converters such as Advanced ModularMulti-level Converters (AMMC) and Modular Transformer Converter (MTC) to the supervisory controller, a network layer must be established, and appropriate control architecture must be designed. In this paper, different control architectures for DCS with application in AMMC and MTC including series (daisy chain), parallel, and parallel-daisy (using both serial and parallel setup) are explored. There are practical issues in synchronization of modules in modular converters that have been addressed by and given solution to in the paper. The laboratory experimental test beds for MTC and AMMC configurations with distributed control systems (series (daisy chain), and parallel) architectures are implemented and experimental results are presented to validate the distributed control configurations.