A systematic method is proposed to generate 2-SiC and 4-SiC hybrid three-level active neutral-point-clamped (3L-ANPC) inverter topologies from two types of switching cells based on the arrangement of freewheeling paths. The 2-SiC hybrid 3L-APNC inverter and the 4-SiC hybrid 3L-ANPC inverter are analyzed in detail with switching states and modulation strategies given. The power losses are quantitative compared between the 2-SiC hybrid 3L-ANPC inverter and the 4-SiC hybrid 3L-ANPC inverter. The junction operating temperatures of active switches in different hybrid 3L-ANPC inverters are also calculated. A universal prototype for these different Si/SiC hybrid schemes is built to evaluate these topologies at conversion efficiency. Experimental results and analysis show that the 2-SiC hybrid 3L-ANPC inverter has the highest efficiency and the lowest cost. The efficiency of the 4-SiC hybrid 3L-ANPC inverter with modulation strategy I is a litter bit lower than that of 2-SiC hybrid 3L-ANPC inverter. However, it has better thermal balance characteristic. Therefore, with the same specifications and switching device parameters, the maximum output power of 4-SiC hybrid 3L-ANPC inverter with modulation strategy I is almost 1.26 times than that of 2-SiC hybrid 3L-ANPC inverter, which shows significant superiority in high power and high power density applications.

In this paper, a new systematic method is proposed to analyze the system frequency in power systems under uncertain variability (UV). UV gradually increases in power systems, which originates from the renewable energy generation, random loads, frequency measurement, and communication channels, exerting noteworthy impacts on dynamic system frequency. The UV is modeled as a stochastic process in this paper. Then, the stochastic differential equations are used to describe the dynamic system frequency response of a power system under UV, which is based on the classic system frequency response (SFR) model. To assess system frequency dynamics under UV, an index of intra-range probability is put forward. Based on stochastic analysis theory, an analytic method is proposed to analyze the system frequency under UV, by which the intra-range probability can be analytically solved. Compared with Monte Carlo simulation in a typical system frequency response case and the Iceland electricity transmission network, the proposed method shows almost the same results using much less computation resource. Finally, insights for improving the system frequency response under UV are provided. The proposed method can be used to quickly verify whether the system frequency could withstand the UV and keep system frequency in the security range.

Since wave fluctuates continuously, the forecast of the wave energy is very important for the operation of power systems integrated with large-scale wave energy generation. A combined model of day-ahead wave energy forecast based on improved grey BP neural network (BPNN) and modified ensemble empirical mode decomposition (MEEMD) -autoregressive integrated moving average (ARIMA) is proposed in this paper. Firstly, the wave is decomposed into wind waves and swells by wave theories. Secondly, the correlation between wind wave and wind speed is analyzed with improved grey BPNN, and the average height of wind waves can be forecasted based on the historical wind speed data. Thirdly, the MEEMD-ARIMA model is utilized to forecast the average wave height of swells. Thus, combining the wind wave and the swell, the average wave height of the integrated wave can be obtained. Finally, a conversion model from wave elements to wave energy for Archimedes wave swing (AWS) is introduced. A case study using the measured wind and wave data from a real ocean is illustrated, and the effectiveness of the proposed wave energy forecast model is validated.

Compared with full-SiC MOSFETs converters, the hybrid utilization of Si/SiC converters is an alternative approach to achieve the tradeoff between performance and cost. In this paper, a 2-SiC hybrid five-level active neutral-point-clamped (5L-ANPC) full-bridge inverter is proposed. The proposed inverter is constructed by combining a 2-SiC hybrid 3L-ANPC half-bridge inverter and a two-level half-bridge arm. The operation principle of the proposed inverter by using the conventional modulation scheme is analyzed in detail. Further, a dedicated modulation scheme is proposed to lower the conduction losses. The calculated power losses of the 2-SiC hybrid 5L-ANPC full-bridge inverter with the conventional modulation scheme and the proposed modulation scheme are addressed and compared. The proposed modulation scheme exhibits higher efficiencies under high power conditions. But the conventional modulation scheme shows efficiency superiority under low power conditions. Therefore, a hybrid modulation scheme is also proposed to achieve an overall high efficiency performance. A 4 kW prototype is built to evaluate the proposed topology and its modulation scheme at conversion efficiency. Experimental results and analysis show that comparing to the conventional modulation scheme, the hybrid modulation scheme can reduce power loss without increasing the hardware cost.

The wind speeds of each wind turbine generator (WTG) are the basis for establishing an aggregated model of a wind farm for power system transient simulation. However, the commonly obtained operation data of the wind farm do not include the wind speeds of each WTG. Thus, a modeling method for the wind speeds of the WTGs of same moment inside the wind farm was proposed. A wind speed combination model (WSCM) is established via K-means clustering from the sorted field-measured wind speed data, which can provide reasonable wind speeds for each WTG when aggregate modeling the wind farm. Subsequently, an improved two-step clustering method of the WTGs was proposed, by which the WTGs are initially clustered according to whether they enter low voltage ride through (LVRT) mode or not. An “N-1 VS One” aggregated model and the binary search algorithm were used to quickly and correctly predict whether a WTG in the wind farm enters LVRT mode under a grid fault. The case study demonstrates the satisfactory performance of the WSCM and the necessity of clustering the WTGs according to whether they enter or do not enter LVRT mode for obtaining an accurate aggregated model of the wind farm. All the data, models, and the programs used in this paper can be found at DOI: 10.21227/dqyk-t852.

Due to the coupling network constraints, the prosumers' trading strategies influence each other. This article analyzes the generalized Nash equilibrium (GNE) formulated by the prosumers and proposes a distribution locational marginal price (DLMP)-parametrized alternating direction method of multipliers (ADMM) algorithm to seek the GNE of peer-to-peer (P2P) transactive energy trading. We first present the prosumers' and distribution system operator's models in the P2P transactive energy market. To explicitly add the coupling network constraints to the prosumers' problems, we linearize the distribution network power flow model and project the linear constraints to the prosumers' feasible regions. We then analyze the GNE in the network-constrained P2P transactive energy market and reduce the original GNE to normalized Nash equilibrium (NNE). We relax the original model into a partial dual problem and employ DLMPs to depict the prosumers' heterogeneous influences on the distribution network operation. We modify the ADMM algorithm to decompose the prosumers' trading processes to protect their privacy. The algorithm convergence and market properties at NNE are finally listed and discussed. A four-bus toy model is introduced to illustrate the convergence and properties of our proposed method. We import a modified IEEE 69-bus system to further highlight the advantages of our model.