Although the probability of occurrence of station internal ac grounding faults in modular multilevel converter (MMC) based high-voltage direct-current systems is low, they may lead to severe consequences that should be considered when designing protection systems. This paper analyzes the characteristics of valve-side single-phase-to-ground (SPG) faults in three configurations of MMC systems. Fault responses for symmetrical monopolar MMCs are first studied. Upper arm overvoltages and ac side non-zero-crossing currents arising from SPG faults in asymmetrical and bipolar configurations are then investigated. DC grounding using an LR parallel circuit is employed to create current zero-crossings which will enable the operation of grid side ac circuit breakers. The theoretical analysis is verified through simulations performed in PSCAD/EMTDC, with simulation results and the theoretical analysis showing a good agreement. The studies in this paper will be valuable for the design of protection systems for station internal ac grounding faults.

The rapid response characteristics and high-speed growth of electric vehicles (EVs) demonstrate its potential to provide auxiliary frequency regulation services for independent system operators through vehicle-to-grid (V2G). However, due to the spatiotemporal random dynamics of travel behavior, it is challenging to evaluate the ability of EV cluster to provide ancillary services under the premise of reaching the expected state of charge (SOC) level. To address this issue, a novel calculation model of charge and discharge capacity of EV cluster based on trip chain with excellent parallel computing performance is presented in this work. Following the introduction of the characteristic variables of the proposed trip chain model, the user’s continuous travel behavior in a time scale of several weeks is simulated. In particular, a bidirectional V2G scheduling strategy based on the five-zone map is designed to guide the charging and discharging behavior of EVs, where the expected SOC levels are guaranteed. The results of a 3-week travel simulation verify the effectiveness of the presented model in coordinating the V2G scheme and calculating the charge and discharge capacity of the EV cluster.

One of the most critical faults affecting modular multilevel converter (MMC) based bipolar high-voltage direct-current (HVDC) transmission systems is the single-phase-to-ground (SPG) faults between the converter transformer and the valve. However, half-bridge (HB) and full-bridge (FB) based MMCs exhibit a different behavior following such a fault and, thus, converter protection should be addressed in a different manner for each configuration. For HB-MMCs, an SPG fault at the valve-side leads to a severe overvoltage on the submodule (SM) capacitors in the converter upper arms and to grid-side non-zero crossing currents. Although FB-MMCs only exhibit overvoltage, these are more severe than for their HB counterparts. To address this problem, this paper presents a protection strategy considering thyristor bypass branches placed in parallel with upper arms of FB-MMCs. By employing this configuration, the upper arm overvoltage in the faulted converter is mitigated and remote converters can be quickly blocked using their local protection schemes. For completeness, the effectiveness of the strategy is verified through time-domain simulations in PSCAD/ EMTDC. The studies in this paper demonstrate the effectiveness of the presented protection scheme for station internal faults occurring in FB-MMCs in bipolar HVDC systems.

This paper presents a novel approach to multi-type distributed generation (DG) planning based on the analysis of investment and income brought by grid-connected DG. Firstly, the timing characteristics of loads and DG outputs, as well as the environmental benefits of DG are analyzed. Then, on the basis of the classification of daily load sequences, the typical daily load sequence and the typical daily output sequence of DG per unit capacity can be computed. The proposed planning model takes the location, capacity and types of DG into account as optimization variables. An improved adaptive genetic algorithm is proposed to solve the model. Case studies have been carried out on the IEEE 14-node distribution system to verify the feasibility and effectiveness of the proposed method and model.

As the realization form of integrated energy system, integrated energy park is the key research object in the field of energy. Actual integrated energy parks are often partitioned internally. In order to take into account the interests of each zone in the optimal scheduling of integrated energy parks, a double-layer optimal scheduling model of integrated energy parks based on non-cooperative game theory is proposed. First, according to the operation of the integrated energy park, the output and cost model of the park is established. Second, with the minimum daily cost as the upper layer objective and the highest energy efficiency of the cogeneration system as the lower layer objective, a double-layer optimal scheduling model is established. Then based on non-cooperative game, the optimal operation strategy of each zone is obtained through the game among all the zones. An integrated energy park is taken as an example, the results show that the proposed model can make zones adjust their operation strategies more reasonably, thus helping to reduce the cost of the park and improve energy efficiency.

With the growing influence of fog and haze (F-H) weather and the rapid development of distributed energy resources (DERs) and smart grids, the concept of the virtual power plant (VPP) employed in this study would help to solve the dispatch problem caused by multiple DERs connected to the power grid. The effects of F-H weather on photovoltaic output forecast, load forecast and power system dispatch are discussed according to real case data. The wavelet neural network (WNN) model was employed to predict photovoltaic output and load, considering F-H weather, based on the idea of “similar days of F-H”. The multi-objective optimal dispatch model of a power system adopted in this paper contains several VPPs and conventional power plants, under F-H weather, and the mixed integer linear programming (MILP) and the Yalmip toolbox of MATLAB were adopted to solve the dispatch model. The analysis of the results from a case study proves the validity and feasibility of the model and the algorithms.