skip to main content


Title: A Complete Design of a High Frequency Medium Voltage Multi-Port Transformer
In this paper, design of a compact high frequency four-port transformer for a Solid-State Transformer (SST) arrangement is presented. Unlike other SSTs, the four-port system integrates three active sources and a load port with galvanic isolation via a single transformer core. In addition to this feature, one of the three source ports is designed to operate at Medium Voltage (MV) 7.2kV for direct connection to 4.16kV AC grid, while other ports nominal voltages are rated at 400V. The transformer is designed to operate at 50kHz and to supply 25kW/port. Thus, the proposed system connects the MV grid, Energy Storage System (ESS), PV, and DC load to each other on a single common transformer core. Based on the system power demand and availability of renewable energy resources, utility and energy storage ports can either supply or draw power, while PV port can only supply power, maintaining the required demand for the load. This work focuses mainly on the High Frequency Transformer (HFT) design. An extensive study is carried out to obtain the optimal, compact, cost effective, and high efficiency model. Modeling, mathematical, and simulation results are derived and presented to demonstrate the viability of this design.  more » « less
Award ID(s):
1650470
NSF-PAR ID:
10223262
Author(s) / Creator(s):
; ; ; ;
Date Published:
Journal Name:
2019 8th International Conference on Renewable Energy Research and Applications (ICRERA)
Page Range / eLocation ID:
761 to 766
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. null (Ed.)
    With the growth in penetration number and power level of renewable energy resources, the need for a compact and high efficient solid state transformer becomes more important. The aim of this paper is to design a compact solid state transformer for microgrid application. The proposed transformer has four ports integrated on a single common core. Thus, it can integrate different renewable energy resources and energy storage systems. The transformer is operating at 50kHz switching frequency, and each port can handle 25kW rated power. In this paper, the ports are chosen to represent a realistic industrial microgrid model consisting of grid, energy storage system, photovoltaic system, and load. The grid port is designed to operate at 4160V AC, while the other three ports operate at 400V. Moreover, the grid, energy storage, and photovoltaic ports are active ports with dual active bridge topologies, while the load port is a passive port with full bridge rectifier one. In this paper, an extensive and complete design and modeling of the entire solid state transformer is presented. The proposed design is first validated with simulation results, and then the proposed transformer is implemented. Some preliminary experimental tests are also performed and the obtained results are reported. 
    more » « less
  2. This paper proposes a generalized Gallium Nitride (GaN) based modular multiport multilevel flying capacitor architecture. In other words, the attractive flying capacitor multilevel (FCML) design and the full-bridge unfolding circuit are employed to develop a multiport multilevel converter architecture that fits various applications. Each module can be designed to contain any combination of AC and DC ports connected through DC-to-DC and DC-to-AC power conversion paths. These conversion paths are FCML topologies that can be designed with any number of levels; the DC-to-AC paths incorporate the full-bridge unfolding circuit. Two example prototypes with open-loop control, three-port and four-port, have verified this generalized architecture. A single module 3 kW three-port four-level prototype with two DC ports and an AC port has achieved a compact size of 11.6 in 3 (4.8 in ×4.3 in × 0.56 in) and a high power density of 258.6 W/in 3 . The three ports are connected through DC-to-AC and DC-to-DC paths that have achieved peak efficiencies of 98.2% and 99.43%, respectively. The total harmonic distortion (THD) of the AC port's voltage and current are 1.26% and 1.23%, respectively. It operates at a high switching frequency of 120 kHz because of the GaN switches and has an actual frequency (inductor's ripple frequency) of 360 kHz thanks to the frequency multiplication effect of the FCML. The four-port prototype contains three DC ports and an AC port and achieved similar high figures of merit. These experimental results of the two prototypes of high efficiency, power density, and compact size are presented in this article and highlight this architecture's promising potential. The choice of the number of modules, ports, and levels depends on the application and its specification; therefore, this proposed generalized structure may serve as a reference design approach for various applications of interest. 
    more » « less
  3. In this study, a four-port solid-state transformer (SST) with decoupled control scheme to control the power flow and the output voltage is proposed. The proposed decoupled control scheme controls all of the four ports' powers independently. In addition, the design of the four-port transformer including core material selection and winding placement is investigated. The designed transformer is modeled in ANSYS-Maxwell and also co-simulated with ANSYS-Simplorer. The operating frequency of the system is designed for 100 kHz; therefore, a very compact size is obtained for the entire multi-port converter. The performance of the proposed system is validated throughout MATLAB/Simulink simulation and experimental studies carried out for a 10kW/port SST prototype. The obtained results show that the four-port SST provides an interface for four-different power supplies or loads. It is seen that the proposed decoupled control scheme can control the output voltage at the desired value and track the reference power signals for each port. It provides as well a good steady state and dynamic performance. 
    more » « less
  4. Solid State Transformers (SSTs) are being considered as a replacement to the classic transformers especially for renewable energy and energy storage systems mainly due to their much smaller size and controllability and regulation over the transferred power. Multi-Port SSTs share one high frequency core for the isolation between several devices and hence are even more compact and efficient but the system is complex and the control of such a system is a challenge. This paper considers a four-port, MPSST connected to a renewable source, battery, load, and the grid and discusses various scenarios and operating points. It is shown that several factors including the ratio of the renewable power to the load, battery SOC status and role of the battery in the system change the desired power flow in the system and there are several control structure needed for each mode of operation. These modes of operation and the boundary between them are recognized and eventually a MIMO control scheme is suggested that includes several switches to changes the structure of the controller to adjust the controller structure to the operating condition. Eventually, input-output linearization technique has been adopted to the system to linearize the model and achieve a better control performance. 
    more » « less
  5. Development of the new generation of high power and high frequency power electronic switches along with the need for compact controllable converters for utilization of distributed energy resources in the grid, have led to significant developments in the area of solid state transformers in the last years. The design process of a high frequency transformer as the main element in the solid state transformer is illustrated in this article. A multi winding transformer for multiport SST application is designed, studied and built in this research. In a MPSST several windings feed the core. As the result, coupling coefficient between each pair of windings, become an important factor which is studied in this study. Since the transformer is designed for high frequency applications, the power loss in the wire and core of the transformer increases as the result of higher skin effect and eddy current loss in high frequency. Three important factors in the design of HF transformer for MPSST are discussed in the paper. First, four different possible core materials are compared based on their flux density, frequency range, loss and price. Then the cable selection is illustrated and finally, different winding placement and distribution on the same core are suggested and the inductance and coupling coefficient matrices are calculated using ANSYS Maxwell 3D simulation. The transformer is built in the lab and the inductance values matches the expected values from the simulation. 
    more » « less