Diversification of control schemes adopted by inverter-interfaced distributed generators (IIDGs) leads to difficulties in fault current estimation in a microgrid, which might make preexisting protection systems invalid and threaten the safety of power electronic devices. It is therefore important to study fault characteristics of IIDGs. This paper investigates characteristics of fault current of IIDGs caused by both symmetrical and asymmetrical faults. Two kinds of widely used control modes, current control (constant current control and PQ control) and voltage control (V/F control and droop control), are under investigation to provide an intuitive comparison on fault current. In particular, a novel algorithm is proposed to calculate fault current of droop-controlled IIDGs. It is found that different limiters have great impacts on fault response of IIDGs and detailed research works are carried out to identify the effects in this paper. Simulation results based on PSCAD/EMTDC and calculation results based on MATLAB/Simulink verify the correctness of the proposed fault models.

There has been an increasing interest in using model predictive control (MPC) for power electronic applications. However, the exponential increase in computational complexity and demand of computing resources hinders the practical adoption of this highly promising control technique. In this article, a new MPC approach using an artificial neural network (termed ANN-MPC) is proposed to overcome these barriers. A power converter with a virtual MPC controller is first designed and operated under a circuit simulation or power hardware-in-the-loop simulation environment. An artificial neural network (ANN) is then trained offline with the input and output data of the virtual MPC controller. Next, an actual FPGA-based MPC controller is designed using the trained ANN instead of relying on heavy-duty mathematical computation to control the actual operation of the power converter in real time. The ANN-MPC approach can significantly reduce the computing need and allow the use of more accurate high-order system models due to the simple mathematical expression of ANN. Furthermore, the ANN-MPC approach can retain the robustness for system parameter uncertainties by flexibly setting the input elements. The basic concept, ANN structure, offline training method, and online operation of ANN-MPC are described in detail. The computing resource requirement of the ANN-MPC and conventional MPC are analyzed and compared. The ANN-MPC concept is validated by both simulation and experimental results on two kW-class flying capacitor multilevel converters. It is demonstrated that the FPGA-based ANN-MPC controller can significantly reduce the FPGA resource requirement (e.g., 2.11 times fewer slice LUTs and 2.06 times fewer DSPs) while offering a control performance same as the conventional MPC.

Wide-bandgap (WBG) power semiconductors offer a higher switching frequency and lower switching loss than their silicon counterparts but suffer from a significantly higher component cost. In this article, we propose a new WBG and Si hybrid half-bridge (HHB) power processing approach, which combines the high-frequency performance of WBG and low cost of Si toward optimal tradeoff among efficiency, power quality, and cost. The HHB approach uses a low-frequency base-power Si half bridge in a typical power converter to achieve a full-power conversion at a low cost and a high-frequency fractional-power WBG half bridge in parallel to improve the efficiency and power quality at a reasonable cost penalty. A current ripple and a cost analysis model are developed in great detail to indicates that the HHB approach can achieve a 20%–50% device cost reduction in comparison to an all-WBG converter design while offering almost the same efficiency and power quality. A simple control strategy is developed to enable the unique operation of the proposed HHB approach in this article. The HHB approach combining with the proposed control strategy can be easily implemented in a wide range of power converters. A 3-kW bidirectional dc–dc converter is built using Si IGBTs and SiC mosfet s as a case study to validate the HHB concept. In comparison with the all-SiC design, the HHB-based converter achieves a comparable efficiency and two times higher current spectrum with at least 17% total cost reduction and 33% capacitor rms current reduction.

In this paper, two continuous control set model predictive control (CCS-MPC) methods with one-step prediction horizon for three-level flying capacitor boost converter (FCBC) that can provide constant switching frequency are presented. The first one is explicit model predictive control (EMPC), which can provide explicit solution. In order to further reduce the complexity and the computational burden of EMPC while meeting the control requirements, a simple model predictive control (SMPC) is proposed as the second CCS-MPC method. The proposed CCS-MPC will be used as the inner loop controller to control the inductor current and flying capacitor voltage. Besides, a suitable outer loop control strategy for the output voltage is proposed to provide a suitable inductor current reference to improve the dynamic response of the output voltage while avoiding overcurrent. Compared with the previous control method for three-level FCBC, the proposed control method has good dynamic performance and stronger ability to resist input voltage disturbance. The effectiveness of the proposed method is verified by simulation and experimental results.

A high-frequency dynamically coordinated Si/SiC hybrid continuous conduction mode (CCM) totem-pole bridgeless PFC (TPBPFC) converter is reported in this article. The proposed hybrid TPBPFC converter is interleaved with a low-current high-frequency SiC phase and a high-current low-frequency Si phase, in comparison to the prior-art design of two half-capacity SiC phases, resulting in a considerable cost reduction. A coordinated Si/SiC control strategy is proposed to address the un-compensable range issue in hybrid-frequency interleaving topologies, and to dynamically distribute power load between the Si and SiC phases for optimal efficiency and performance. An average current mode control (ACMC) based control algorithms and sequences are discussed in detail to enable the unique operation. A 3.3-kW hybrid TPBPFC prototype made of Si IGBTs and SiC MOSFETs is built and tested to validate the proposed design concept. Compared to the prior art two-phase all-SiC interleaved TPBPFC design, the proposed hybrid TPBPFC has demonstrated nearly identical power efficiency, THD, power factor, and effective frequency, while offering 33.5% device cost and 15.1% total cost reductions.

WBG power semiconductors offer lower switching loss and higher power density than silicon but suffer from significantly higher cost. In this paper, we introduce a design methodology which uses a low-frequency silicon base power processor to achieve high efficiency and low cost, and a high-frequency WBG fractional power active filter to reduce harmonics and achieve high power quality. The mixed use of WBG and Si delivers the same WBG benefits but at a reduced component cost. A boost PFC converter based on this design principle is reported that comprises two interleaved Si and GaN phases. We develop a new unified control strategy to allow the base power processed efficiently by the Si phase switching at a low frequency of 10 kHz and the harmonics to be minimized by the MHz-frequency GaN phase as an active filter. A 2.1kW Si/GaN interleaved PFC prototype exhibits a peak efficiency of 98.04% and a power factor of 0.998 even with a frontend diode bridge. The new interleaved PFC is validated by simulation and experimentally to achieve excellent efficiency, power density, and harmonics mitigation at a cost much lower than a full-scale WBG design.