With the development of virtual synchronous generator (VSG) techniques, parallel operations of synchronous generators (SGs) and VSGs become increasingly common in a microgrid. The differences between paralleled systems will affect transient stability of the system, which probably threatens stable operation of the system, especially under fault conditions. In this paper, transient angle stability of a paralleled synchronous and virtual synchronous generators (SG-VSG) system is investigated by compared with that of paralleled VSGs system. It is observed that the paralleled SG-VSG system is more prone to transient instability due to the differences between their speed governors. Then, a control method is proposed to improve the transient stability of paralleled SG-VSG system. Furthermore, a Lyapunov method is employed to establish the nonlinear model of islanded microgrid, by which the attraction domain of paralleled system is quantified. The hardware-in-loop experiment is performed to validate the theoretical analysis.

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.

Active power oscillation is observed when two or more parallel synchronverters undergo load fluctuations, potentially impacting the safe operation of the synchronverters. This paper provides a fundamental analysis for the power oscillation mechanisms, and proposes a new control strategy for suppressing power oscillation especially the oscillation excitation is proposed. It is found that power oscillation is inherently caused by weak damping and large inertia of the synchronverters under the condition of undesirable instantaneous active power sharing. Then the conditions for reducing the oscillation excitation of synchronverters which is caused by undesirable instantaneous active power sharing is deduced. The new control strategy effectively suppresses the power oscillation by adding a virtual damping element for enhancing the system damping and a virtual reactance for reducing the oscillation excitation to the conventional control scheme without changing the basic dynamic and steady characteristics of the synchronverters. The theoretical analysis and the proposed oscillation suppression control techniques are validated with an extensive hardware-in-loop simulation study.

With development of power electronic technology, the paralleled current-controlled voltage source converters (CCSs) and virtual synchronous generators (VSGs) system has advantages in providing power and voltage/frequency regulation at the same time in rural area or remote island. However, the paralleled system faces great challenges in safe and stable operation due to their limited thermal capacity and weak anti-disturbance ability, especially during fault periods. This paper focuses on transient stability and stability-oriented control design of the paralleled CCS-VSG system. First, mathematical model of the paralleled system is established and then the effect of two kinds of CCSs’ current injection angle (active current and reactive current) on VSG’s transient stability has been revealed through extended equal area criterion. Based on the theoretical analysis results, transient stability improvement control is put forward by controlling the CCS to track the VSG’s frame. Compared with the conditions that only active-or reactive current is provided by the CCS, the system can achieve the best transient performance when the proposed control is adopted. Moreover, the effect of CCS’s capacity on transient stability of the VSG has also been discussed. Finally, both Lyapunov’s method and simulation/experimental results are provided to validate the correctness of theoretical analysis.

The parasitic inductances of silicon carbide (SiC) power MOSFETs have a major influence on their operation and circuit performance. They incur negative effects such as switching oscillations, power losses and electromagnetic interference (EMI) noise. This paper introduces a new technique to accurately characterize the parasitic inductances of SiC power MOSFETs in both discrete packages and power modules based on two-port S-parameters measurement. By treating a power MOSFET as a two-port network, we obtain the scattering (S) and impedance (Z) parameters from network analyzer measurement. These parameters, through detailed network analysis, provide more accurate values of the internal parasitic inductances than the commonly used single-port impedance measurement technique. The new approach is first verified with high frequency circuit simulation and then applied in the case study of SiC power MOSFETs in a TO-247 discrete package and a half-bridge power module. In addition, a number of silicon power MOSFETs and IGBTs in TO-247, TO-220, D2PAK, DPAK, SO-8 packages are also characterized for comparison. A comparison between the characterization results from the new two-port and the prior art one-port methods reveals a significant difference ranging from 12.6% to 93.9%.

This paper presents an impedance-based method for stability analysis of multi-converter power systems based on the Generalized Nyquist Stability Criterion. The return-ratio matrix of the system is formulated on the basis of the nodal admittance matrix as well as output admittance of the converters, which can be applicable for the large-scale systems with complicated structure. A modified IEEE 13-bus system is used as the testing system, which shows that the proposed method can be easily implemented for location optimization of the converters. And the participation factors of return-ratio matrix’s critical eigenvalues (which encircle the critical point (-1, 0j)) at the instability frequencies are used to identify which converters have significant contributions to the instability, and then guidance for the design of system parameters can be provided. Simulations in PSCAD/EMTDC validate the effectiveness of the proposed stability analysis method.