Power converters in the system-level real-time simulation are usually emulated by L/C-based associated discrete circuit (L/C-ADC). However, the L/C-ADC approaches may suffer from two issues: how to mitigate the unacceptable virtual power loss especially in high-frequency applications, and how to tune LC parameters setting which is affected by the external circuit. This paper proposes a novel generalized associated discrete circuit (G-ADC) model with parameterized history current sources. By utilizing the stability region of the feasible parameter space, the optimized G-ADC models with the best damping characteristic are developed for both two-level and three-level converters. The analytical results also guarantee that the parameters of the optimized G-ADC model are independent of the external circuit for most power grid applications. Furthermore, an FPGA-based real-time simulation platform is built to verify the feasibility of the proposed scheme. Extensive simulation and hardware-in-loop (HIL) experiment results demonstrate the effectiveness and superiority of best-damped models as well as the modeling flexibility corresponding to insensitivity to operating conditions and external system parameters.

The real-time simulation based on the field programmable gate array (FPGA) is receiving more and more attention. However, up to now, the simulation scale for the power electronic system is not so satisfactory due to the real-time requirement and the FPGA resource limitation. This paper proposes a sub-microsecond level real-time simulation method for microgrids. The power converters are modeled with fixed-admittance models and simulated with a compact electromagnetic transients program (EMTP) algorithm. In the meanwhile, the distribution lines/cables are modeled with π-circuit models and simulated with a distributed circuit solution method, called the latency insertion method (LIM). As a result, the distribution generation (DG) systems are decoupled with each other and can be simulated in parallel. The case study shows that the proposed simulation method consumes much fewer FPGA resources compared with the traditional one. Besides, the time step can be much smaller and doesn't need to increase with the simulation scale. With these advantages, the real-time simulation of a microgrid consisting of 3 three-phase converters, 3 boost circuits and 21 three-phase lines can be achieved on the Xilinx Kintex-7 410T FPGA with a minimum time-step of 380ns.

This paper presents the design of a filtered tracking error (FTE)-based robust current controller for three-phase grid- tied inverters interfacing distributed renewable resources (DERs) into the grid. An uncertainty and disturbance modeling based control law is developed for achieving the robustness against non- ideal grid conditions including the grid impedance variations, grid voltage harmonics and fluctuations in grid voltage magnitude (symmetrical/ asymmetrical), frequency and phase. The proposed controller is shown to have superior current tracking performance to directly control the current injected into the grid being pure sinusoidal and three-phase balanced. In addition, high dynamic and tracking performance can be further ensured since all the phase locked loops (PLLs) and multi-loop controllers are eliminated, which also delivers the advantage of a simple implementation. Especially, the system stability is proven by using the Lyapunov function. Both simulation and hardware in the loop (HIL) experimental results of the proposed robust controller, as well as the proportional-integral (PI) controller and the parallel proportional-resonant (PR) controller, are given and compared, which validates the performance and effectiveness of the proposed control strategy.

Globally abundant wave energy for power generation attracts ever increasing attention. Because of non-linear dynamics and potential uncertainties in ocean energy conversion systems, generation productivity needs to be increased by applying robust control algorithms. This paper focuses on control strategies for a small ocean energy conversion system based on a direct driven permanent magnet synchronous generator (PMSG). It evaluates the performance of two kinds of control strategies, i.e., traditional field-oriented control (FOC) and robust adaptive control. The proposed adaptive control successfully achieves maximum velocity and stable power production, with reduced speed tracking error and system response time. The adaptive control also guarantees global system stability and its superiority over FOC by using a non-linear back-stepping control technique offering a better optimization solution. The robustness of the ocean energy conversion system is further enhanced by investigating the Lyapunov method and the use of a DC-DC boost converter. To overcome system complexity, turbine-generator based power take-off (PTO) is considered. A Matlab/Simulink study verifies the advantages of a non-linear control strategy for an Oscillating Water Column (OWC) based power generation system.

Parallel operation of inverter modules is the solution to increase the reliability, efficiency, and redundancy of inverters in microgrids. Load sharing among inverters in distributed generators (DGs) is a key issue. This study investigates the feasibility of power-sharing among parallel DGs using a dual control strategy in islanded mode of a microgrid. PQ control and droop control techniques are established to control the microgrid operation. P-f and Q-E droop control is used to attain real and reactive power sharing. The frequency variation caused by load change is an issue in droop control strategy whereas the tracking error of inverter power in PQ control is also a challenge. To address these issues, two DGs are interfaced with two parallel inverters in an islanded AC microgrid. PQ control is investigated for controlling the output real and reactive power of the DGs by assigning their references. The inverter under enhanced droop control implements power reallocation to restore the frequency among the distributed generators with predefined droop characteristics. A dual control strategy is proposed for the AC microgrid under islanded operation without communication link. Simulation studies are carried out using MATLAB/SIMULINK and the results show the validity and effective power-sharing performance of the system while maintaining a stable operation when the microgrid is in islanding mode.

The electric vehicle (EV) charging station is a critical part of the infrastructure for the wide adoption of EVs. Real-time simulation of an EV station plays an essential role in testing its operation under different operating modes. However, the large numbers of high-frequency power electronic switches contained in EV chargers pose great challenges for real-time simulation. This paper proposes a compact electromagnetic transient program (C-EMTP) algorithm for FPGA-based real-time simulation of an EV station with multiple high-frequency chargers. The C-EMTP algorithm transforms the traditional EMTP algorithm into two parallel sub-tasks only consisting of simple matrix operations, to fully utilize the high parallelism of FPGA. The simulation time step can be greatly reduced compared with that of the traditional EMTP algorithm, and so the simulation accuracy for high-frequency power electronics is improved. The EV chargers can be decoupled with each other and simulated in parallel. A CPU-FPGA-based real-time simulation platform is developed and the proposed simulation of the EV station is implemented. The control strategy is simulated in a CPU with 100 μs time-step, while the EV station circuit topology is simulated in a single FPGA with a 250 ns time-step. In the case studies, the EV station consists of a two-level rectifier and five dual-active bridge (DAB) EV chargers. It is tested under different scenarios, and the real-time simulation results are validated using PSCAD/EMTDC.