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This paper presents the design and development of a three-phase 10-kV/400-V 500-kVA electronic power transformer (EPT). The power circuit is designed in a modular fashion, i.e., the main circuit consists of many identical ac–dc–dc–ac modules (abbreviated as power modules). Each power module consists of a high-voltage power cell, a low-voltage power cell (LVPC), a medium-frequency isolation transformer, and a filter. The corresponding control and protection system is developed. A special three-stage startup strategy is designed to shorten the startup time and reduce the startup inrush current. The negative-sequence current compensation is introduced in the input stage to handle the unbalanced loads. To keep the dc-link voltages balanced, an individual dc voltage balancing controller based on regulating the output power of each parallel LVPC is proposed. The detailed control hardware design and software implementation are discussed. The functions of this 10-kV EPT prototype are verified through the laboratory and field tests. The results are shown in this paper. Currently, the prototype is operating in the industrial power grid. [ABSTRACT FROM AUTHOR]

A lot of large-scale industrial critical loads suffer from voltage interruptions and sags which can cause a significant financial loss. The thyristor-based solid-state transfer switch (STS) and mechanical-based automatic transfer switch (ATS) are used to protect loads against these power quality problems. However, the STS has a great deal of loss consumption because of the forward voltage drop of the thyristors, and ATS can hardly satisfy the voltage-sensitive load due to the long transfer time. This paper proposes a 400 V/1000 kVA hybrid ATS (thyristor switch in parallel with mechanical switch) (HATS) to realize low power consumption under normal situation and transfer fast when required. The proposed HATS has four transfer strategies which can be chosen according to different applications, it realizes the overlapping transfer of the neutral wire, and it can make a decision to transfer or not according to the different fault locations (transfer on the source side and not transfer on the load side). The design details of the prototype are presented, and laboratory tests and field experiments show the prototype good performance. [ABSTRACT FROM PUBLISHER]

Abstract: An auto-balancing transformer based on power electronics is designed and proposed to prevent voltage or/and current unbalances arising on the primary side system from infecting the secondary side system, or in reverse. The multilevel converters and interleaving parallel connection technology are adopted in the transformer design to match the demand of power automatically balancing and high-voltage and high-power application. The operating principle is analyzed in detail and an effective control scheme is developed. To verify the new features of the proposed design, a detailed computer simulation model is established using Matlab\Simulink and typical simulations are carried out. And the experimental verification is also presented. All show satisfactory results. [Copyright &y& Elsevier]

Abstract: This paper presents the design of a linear-quadratic-regulator (LQR) with integral action to improve dynamic performance of an electronic power transformer for distribution systems (DEPT). The integral action is added to cancel the steady-state errors knowing that the standard LQR provides only proportional gains. This controller is designed to achieve the following four control objectives: (1) to keep the input currents sinusoidal and in phase with the input voltages to achieve unity input power factor, (2) to maintain the dc-link voltage at a reference value, (3) to maintain the output voltages at a constant value and (4) to keep the output voltages sinusoidal and symmetric. The DEPT model which includes the integral action in the d–q rotating frame is built and linearized around a set point. The system is tested for dc-link reference voltage, load and input voltages variations, respectively. The validity of the built model and the proposed control strategy is demonstrated by simulation results based on MATLAB/SIMULINK. [Copyright &y& Elsevier]