Fast electromagnetic transient simulation methods and prospects of high-frequency isolated power electronics transformers

With the increasing uptake of distributed renewable energy and low-carbon technologies (e.g. energy storage and electric vehicle), the conventional AC distribution network is transferring to hybrid AC/DC or pure DC. Power electronics transformers (PETs), also known as solid-state transformers, are multifunctional of integrating distributed generation, regulating bidirectional power flow, and achieving grid interconnection, reactive power compensation, harmonic control, etc. Therefore, PETs can serve as key interfaces for energy conversion in future distribution networks. At present, a number of medium- and low-voltage distribution networks using PETs have commissioned in China, such as the Xiaoertai substation in Zhangbei and Tangjia Bay three-terminal DC distribution network in Zhuhai. The off-line and real-time electromagnetic transient (EMT) simulation studies are of great significance for system-level analysis and prototype development of PETs, which should be investigated timely

Fast electromagnetic transient simulation methods and prospects of high-frequency isolated power electronics transformers

With the increasing uptake of distributed renewable energy and low-carbon technologies (e.g. energy storage and electric vehicle), the conventional AC distribution network is transferring to hybrid AC/DC or pure DC. Power electronics transformers (PETs), also known as solid-state transformers, are multifunctional of integrating distributed generation, regulating bidirectional power flow, and achieving grid interconnection, reactive power compensation, harmonic control, etc. Therefore, PETs can serve as key interfaces for energy conversion in future distribution networks. At present, a number of medium- and low-voltage distribution networks using PETs have commissioned in China, such as the Xiaoertai substation in Zhangbei and Tangjia Bay three-terminal DC distribution network in Zhuhai. The off-line and real-time electromagnetic transient (EMT) simulation studies are of great significance for system-level analysis and prototype development of PETs, which should be investigated timely

Modeling for complex modular power electronic transformers using parallel computing

The modular power electronic transformer (PET) faces difficulty carrying out microsecond-level electromagnetic transient (EMT) simulations. This paper provides a high-speed and high-precision simulation method capable of eliminating the internal nodes and reducing the order of the nodal admittance matrix. Meanwhile, the parallel computing is integrated into the whole solution process, which achieves a significant simulation speedup. A physical prototype is established to prove that the detailed model is sufficient to reflect the dynamics of physical devices. Moreover, simulations in PSCAD/EMTDC are carried out to compare the proposed method with the detailed model in terms of accuracy and time efficiency. Simulation results show that the proposed method is accurate to simulate the external and internal dynamics of PET with hundreds of times simulation speed acceleration

Dual harmonic injection for reducing the sub-module capacitor voltage ripples of hybrid MMC

Reducing the capacitor voltage ripples of the half-bridge sub-modules (HBSM) and full-bridge sub-modules (FBSM) in a hybrid modular multilevel converter (MMC) is expected to reduce the capacitance, volume and costs. To address this issue, this paper proposes a dual harmonic injection method which injects the second harmonic circulating current and third order harmonic voltage into the conventional MMC control. Firstly, the mathematical model of the proposed control is established and analyzed. Then, the general strategy of determining the amplitude and phase angle of each injection component is proposed to suppress the fluctuations of the fundamental and double frequency instantaneous power. The proposed strategy can achieve the optimal power fluctuation suppression under various operating conditions, which also has the advantage of reducing the voltage fluctuation difference between HB and FB SMs. The correctness and effectiveness of the proposed strategy are verified in simulations in PSCAD/EMTDC

Accelerated electromagnetic transient (EMT) equivalent model of solid-state transformer

Accurate and efficient electromagnetic transient (EMT) simulation of various types of solid-state transformers (SST) is extremely time-consuming due to the complex module structure, flexible topology connections, large number of electrical nodes and simulation time-steps limited in the range of micro-seconds. Therefore, it is urgent to develop the EMT equivalent modelling and fast simulation of SSTs for system level studies. Taking the modular multilevel converter (MMC) based SST as an example, this paper proposes an accelerated EMT model which focuses on the equivalence of the dual active bridge (DAB) based high-frequency link (HFL) in the SST. Compared with the existing algorithms, two critical factors of the proposed method that contribute the most to the efficiency improvement are the preprocessing of the nodal admittance equation and the conversion of the short-circuit admittance parameters. The proposed model is verified in PSCAD/EMTDC by comparing it with the detailed EMT model. The results show that the accelerated model is one to two orders of magnitude faster than the detailed model without sacrificing the accuracy. The experiment validation also confirms the validity of the proposed model

A Novel Decoupled EMT Approach and Parallel Simulation Framework for Modularized Solid-state Transformers

Electromagnetic transient (EMT) modeling for the modularized solid-state transformer (MSST) faces critical difficulties because the dynamics of the complex-structured submodules, which contain dual active bridges (DAB) and multiple active bridges (MAB), are hard to be described in analytical formulas. Existing models have problems of a narrow dynamic frequency band, insufficient simulation accuracy, or are unable to operate under fast transients. This paper proposes a parallel simulation framework for MSST that preserves the original model’s broadband characteristics and remarkably improves the simulation efficiency. The main novelty towards previous work is the detailed modeling of the multi-winding transformer, the decoupled modeling of the submodules, and the parallel design of simulation processes. Finally, the proposed framework is verified through the accuracy and efficiency analysis carried out in PSCAD/EMTDC. The simulation results verify that the proposed framework has excellent accuracy and time efficiency