Three-phase Solid State Transformer Research Articles

Simulation of the Operation of a Three-Phase Solid-State Transformer under Variation of Load

Simulation of the Operation of a Three-Phase Solid-State Transformer under Variation of Load

Simulation of the operation of a three-phase solid-state transformer when the load changes

Simulation of the operation of a three-phase solid-state transformer when the load changes

A Gen-3 10-kV SiC MOSFET-Based Medium-Voltage Three-Phase Dual Active Bridge Converter Enabling a Mobile Utility Support Equipment Solid State Transformer

The emergence of medium-voltage silicon carbide (SiC) power semiconductor devices, in ranges of 10&#x2013;15 kV, has led to the development of simple two-level converter systems for medium-voltage applications. A medium-voltage mobile utility support equipment-based three-phase solid state transformer (MUSE-SST) system, based on Gen3 10 kV SiC MOSFETs, is developed to interconnect a three-phase 4160 V/60 Hz grid to a three-phase 480 V/60 Hz grid to provide a shore-to-ship power interface for naval vessels. The MUSE-SST system consists of three power conversion stages, namely, MVac/MVdc stage (MV: active front-end converter), MVdc/LVdc stage (dual active bridge converter), and LVdc/LVac stage (LV: active front-end converter). The galvanic isolation is introduced in the MVdc/LVdc stage using MV/LV high-frequency transformers (HFTs). This article demonstrates the operation of the three-phase Y&#x2013;<inline-formula> <tex-math notation="LaTeX">$\Delta $ </tex-math></inline-formula> connected dual active bridge converter used in the MVdc/LVdc stage of the MUSE-SST system. Equations for phase currents, power flow, and zero-voltage switching (ZVS) boundaries are derived for all possible modes for the three-phase Y&#x2013;<inline-formula> <tex-math notation="LaTeX">$\Delta $ </tex-math></inline-formula> configuration. A detailed parasitic simulation model is derived by measuring and experimentally verifying the parasitic elements of the HFT. A brief discussion regarding the design considerations required for the hardware development of the medium- and low-voltage sides of the three-phase dual active bridge converter is also provided. Successful tests demonstrating the operation and feasibility of the medium-voltage dual active bridge converter, at medium-voltage levels (7.2 kV dc-link voltage), are shown. The results indicate that these devices can accelerate the growth and deployment of the medium-voltage SiC-based converter for isolated and bidirectional medium- to low-voltage dc systems.

Control of Three-Phase Solid-State Transformer With Phase-Separated Configuration for Minimized Energy Storage Capacitors

This paper presents the control structure of a solid-state transformer for three-phase ac/ac, to reduce the required size of capacitors. The structure consists of an ac/dc converter based on cascaded H-bridge converters, isolated dc/dc converters, and a dc/ac inverter. The phase separated configuration requires a high capacitance for the smoothing capacitors owing to the instantaneous power oscillation at the double-line frequency. This paper reviews control methods of the dc/dc converter to achieve synchronous instantaneous power with the ac/dc converter, and thereby cancel the double-line frequency component applied to the capacitors between the ac/dc and dc/dc converters. This study also proposes incorporating a control method to cancel the oscillating instantaneous power caused by unbalanced load current. The overall control was demonstrated using a 6-kVA laboratory prototype. The required minimum capacitance, which is decided by the switching frequency, is discussed, and the demonstration of a design case study on a 300-kVA system is described. The likely increase in loss in the isolated dc/dc converter owing to the power oscillation controls was evaluated with a 10-kW loss evaluation-model of a dc/dc converter.

A frequency-based LCL filter design and control considerations for three-phase converters for solid-state transformer applications

This paper presents a design methodology of a LCL filter for its application on the interconnection with the grid of a three-phase solid-state transformer, which is based on a three-stage configuration. The filter operates without damping resistors, and the design methodology proposed is based on the direct location of resonance frequencies, taking into consideration the effect of the grid impedance. The developed methodology can be applied to different power levels. In addition, control tuning considerations are proposed in order to avoid resonance points, evaluating the overall performance through the current total harmonic distortion in the point of common coupling. Furthermore, the used dq0 reference control frame achieves the objectives without the need to increase the number of sensors, neither the use of observers. The design methodology is validated by testing the operating system at 10 kW, 100 kW and 1 MW. For 1 MW, it is also implemented on a real-time simulator.

Performance and Control Strategy of Real-Time Simulation of a Three-Phase Solid-State Transformer

This paper shows the real-time simulation of a three-stage three-phase solid-state transformer with an Opal OP5607 platform. The simulation model considers the complete electronic full-order circuit for the topology without the use of simplifications, such as average models or equivalent circuits for the coupling transformer and the input and output converters, which may neglect part of the dynamics of interest for the converter design. The simulation is made through an electronic hardware solver (eHS), which can achieve smaller solving times than the regular algorithms, allowing to reach the switching frequency rate for this converters. The simulation model takes the RTE-library which is used for DC-DC converters, with simple arrangements in order to operate with the topology.

Power and Voltage Balance Control of a Novel Three-Phase Solid-State Transformer Using Multilevel Cascaded H-Bridge Inverters for Microgrid Applications

This paper presents a new application of power and voltage balance control schemes for the cascaded H-bridge multilevel inverter (CHMI)-based solid-state transformer (SST) topology. To reduce load on the controller and simplify modulation algorithm, a master–slave control (MSC) strategy is designed for the dual active bridge (DAB) stage. The master controller executes all control and modulation calculations, and the slave controllers manage only device switching and protection. Due to the inherent power and dc-link voltage unbalance in cascaded H-bridge-based SST, this paper presents a compensation strategy based on three-phase dq decoupled current controller. An optimum zero-sequence component is injected in the modulation scheme so that the three-phase grid currents are balanced. Furthermore, to tightly regulate the output voltage of all the DAB modules to target value, a dynamic reference voltage method is also implemented. With this proposed control method, the three-phase grid currents and dc-link voltage in each module can be simultaneously balanced. Finally, simulation and experimental results are presented to validate the performance of the controller and its application to microgrid SST.

A 50 kVA Three-Phase Solid State Transformer Based on the Minimal Topology: Dyna-C

The Dynamic Current or Dyna-C is a minimal topology for implementing the bidirectional three-phase solid-state transformer (SST). While only two current-source power conversion stages are employed, the Dyna-C SST has features of voltage step up/down, arbitrary power factors, and frequencies between the input and output terminals. In this paper, a compact 50-kVA three-phase SST based on this minimal topology is designed. More specifically, design considerations and practical implementation techniques are presented. Results from experimental measurements are shown and discussed.

A Transformerless Intelligent Power Substation: A three-phase SST enabled by a 15-kV SiC IGBT

The solid-state transformer (SST) is a promising power electronics solution that provides voltage regulation, reactive power compensation, dc-sourced renewable integration, and communication capabilities, in addition to the traditional step-up/step-down functionality of a transformer. It is gaining widespread attention for medium-voltage (MV) grid interfacing to enable increases in renewable energy penetration, and, commercially, the SST is of interest for traction applications due to its light weight as a result of medium-frequency isolation. The recent advancements in silicon carbide (SiC) power semiconductor device technology are creating a new paradigm with the development of discrete power semiconductor devices in the range of 10-15 kV and even beyond-up to 22 kV, as recently reported. In contrast to silicon (Si) IGBTs, which are limited to 6.5-kV blocking, these high-voltage (HV) SiC devices are enabling much simpler converter topologies and increased efficiency and reliability, with dramatic reductions of the size and weight of the MV power-conversion systems.