Today, conventional power systems are evolving to smart grids, which encompass clusters of AC/DC microgrids, interfaced through power electronics converters. In such systems, increasing penetration of the power electronics-based distributed generations, energy storages, and modern loads provide a great opportunity for power quality control. In this paper, an overview of the power quality control of smart hybrid AC/DC microgrids is presented. Different types of power quality issues are studied first, with consideration of real-world hybrid microgrid examples, including data centers, electric railway systems, and electric vehicles charging stations. It shows that compared to traditional centralized power quality compensations, smart interfacing power converters from distributed generations, energy storages, and loads, and the AC and DC subgrids interfacing converters are promising candidates for power quality control. To realize the smart interfacing converters' power quality control, both primary converters control and secondary system coordination are required. In this paper, a thorough review of the primary control of interfacing converters to integrate the power quality compensation are presented, with a focus on the hybrid AC/DC microgrid harmonics compensation and unbalance compensation. For multiple interfacing converters, the secondary control with system-level coordination and optimization for harmonics and unbalance compensation (considering both unbalance and harmonics in single-phase and three-phase systems) are also presented. Challenges like low switching frequency of interfacing converters, parallel interfacing converters operation, and interfacing converters communications are discussed, and typical solutions for primary and secondary controls to deal with them are presented. The paper also includes rich case study results.

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Power Quality Control of Smart Hybrid AC/DC Microgrids: An Overview

The invention discloses a charging pile scheduling method. The method includes: after an electric automobile is connected with charging piles, the electric automobile sends storage battery residual capacity information to the charging piles; the charging piles send charging request information to a scheduling device, wherein the charging request information carries the received storage battery residual capacity information of the electric automobile; the scheduling device determines the charging priority of the charging piles according to the current power grid power supply redundancy amount and the storage battery residual capacity of the electric automobile; and the scheduling device ranks and controls the charging piles according to the charging priority of the charging piles. Besides, the invention also discloses a charging pile scheduling system and scheduling apparatus. By employing the method, system and apparatus, the cost is reduced, and the utilization rate of electric energy is increased.

Charging pile scheduling method, system and apparatus

Power grids will benefit when electric vehicle (EV) charging stations provide more services in addition to charging. This paper presents a new configuration of the unified power quality conditioner (UPQC) that uses a microgrid in an EV charging station. A double-layer direct current structure is used in the microgrid to connect EVs in parallel and restrain direct current voltage variations in the UPQC. Control of the UPQC is modified to address the charging of EVs by using power from the grid directly while compensating for power quality issues. Recommended control parameters for the UPQC are derived from small signal analysis. An equal time ratio discharging control for EVs is proposed when a charging station UPQC acts as an emergency power supply to compensate for power interruptions. The performance of the proposed system was analyzed through simulations. Results show that the proposed system can compensate for harmonics, voltage sag and swell, voltage unbalance, and voltage interruption while ensuring EV charging.

Electric vehicle charging station microgrid providing unified power quality conditioner support to local power distribution networks

With the increasing uptake of new technologies such as electric vehicles (EVs), photovoltaic (PV) and wind generation, and LED lighting, there is a need to study their effect on the Power Quality (PQ) of the low voltage (LV) distribution network. These new technologies use power electronic converters which result in harmonics being injected into the AC network. In this paper the impact of EV chargers in terms of harmonic distortion is assessed. The complete LV (400V) network of a distribution company comprising 10,558 11kV to 415V transformers and their associated low voltage distribution feeders, is modelled; and the impact on harmonic levels is determined. The predicted harmonic levels are also considered in a case with photovoltaics and background harmonic distortion, and the levels are compared to the relevant PQ standards and guidelines. Finally, some guidance regarding the practical implications of this work is given.

Impact of electric vehicle chargers on harmonic levels in New Zealand

Electric vehicles (EVs) are emerging as the future of transportation systems aimed at reducing greenhouse gas emissions and fossil fuel dependence in the transportation sector. The deepening penetration of Plug-in EVs (PEVs) forecasted for the incoming years could cause significant strain on distribution networks (DNs), as well as the need to address the growing energy demand. In order to limit the negative drawbacks associated with PEVs energy demand and to properly address related issues, in the paper we consider an energy-packet based (EPB) scheduling approach for PEVs charging, comparing its performance with a conventional charging approach. We formulate an optimization framework in order to reduce the overall peak power demand and to maximize fully charged PEVs during their declared parking time. We compare the performance among the scheduling approaches by running simulations on a real DN and using real vehicle parking data.

Performance comparison between scheduling strategies for PEVs charging in smart grids

The invention relates to an orderly charging system and method for an electric taxi charging station, and belongs to the field of intelligent power grid control. The system is composed of a battery management system, a batter charger, a charging point, an SCADA (supervisor control and data acquisition) system/a PQ (performance quality) monitoring system, an orderly charging control center and a batter charging information database. According to the background load of a to-be-predicted power grid and the demand on the charging power of an electric taxi, the optimal charging start time and the optimal charging phase plan are formulated for each electric taxi, and the electric power of the power grid at a valley period is fully utilized for charging a power battery of the electric taxi, so that the load of a superior transformer substation can be adjusted, the difference between the peak and the valley can be relieved, the load fluctuation of the power grid can be restrained, and the economy and the efficiency of the power grid are improved. Meanwhile, according to the single phase charging manner of the taxi, the optimal charging phase can be selected via the system, so the unbalance of the three-phase load can be reduced.

Orderly charging system and method for electric taxi charging station

Electric vehicle (EV) charging may lead to power quality problems for chargers work as electric-electronic converters. It is necessary to get to know the influence to the power system caused by chargers before EVs operating in scale. Based on monitoring data, power quality problems in EV charging stations are presented and analyzed in this paper. Harmonic current emissions of different kinds of chargers are investigated first. Then harmonic current saturation is detected and discussed. In the next section, power quality of bus voltage and the influencing factors are analyzed . At the end of this paper, suggestions and recommendations are given to improve the power quality of EV charging stations.

Monitoring and analysis of power quality in electric vehicle charging stations

The invention discloses an ordered electric automobile charging method orientated to an active intelligent distribution network in the technical field of intelligent power grids. The method comprises the following steps of: predicting the conventional load power, the generated energy of a distributed power supply and the charge capacity, so as to obtain a power reference value of total load power in a set time period; obtaining the charging load power reference value of the electric automobile through the actual conventional load power and the actual generated power of the distributed power supply; and adjusting the charging power of the electric automobile through the actual value of the charging load power of the electric automobile. The charging load power of the electric automobile is controlled, so that the fluctuation of the conventional power load and new energy load is suppressed, and the operating economical efficiency and controllability of the distribution network and the new energy consumption capacity are improved.

Ordered electric automobile charging method orientated to active intelligent distribution network

Scale-of electric vehicle (EV) charging will bring great impacts to the operation of the power grid. Coordinated charging can guide these effects to the beneficial aspects. This paper firstly derived a steady mathematical model of single charge load as the basis of coordinated charging scheduling. Secondly, based on the schedulability of the EV charging load in time domain, a new kind of coordinated charging control method is put forward. An optimal model is proposed with the objective of minimum total load energy, concerning capacity of transformer and distributing lines and demands of charging time. By changing the charging time of each EV, minimum fluctuation of the total load curve be achieved. This method is verified the effectiveness by the simulation results. At last, the application design scheme in actual EV charging station is introduced for engineering application.

Coordinated EV charging and its application in distribution networks

The invention discloses a method for computing an allocation ratio of electric vehicle fast/slow charging facilities, which belongs to the technical field of modern transportation. The method comprises the steps of: 1) using whether electric energy complemented by one-time charging in a slow charging way by an electric vehicle user can meet the electric energy needed by the next traveling distance of the user or not as a basis for judging whether a fast charging requirement exists or not according to the statistics of traveling and charging laws of the user in a target area; 2) computing the probability of the fast charging requirement; 3) computing the allocation ratio of the fast/slow charging facilities in a to-be-researched area. According to the method for computing the allocation ratio of the electric vehicle fast/slow charging facilities, disclosed by the invention, the requirements of the electric vehicle user on different types of charging modes can be fully met by the construction of charging facilities, the construction and investment economic performance of the charging facilities can be ensured, and the waste of resources caused as the fast charging facilities are constructed in large quantities is avoided.

Shun Tao

Papers

Orderly charging system and method for electric taxi charging station

Monitoring and analysis of power quality in electric vehicle charging stations

Ordered electric automobile charging method orientated to active intelligent distribution network

Coordinated EV charging and its application in distribution networks

Method for computing allocation ratio of electric vehicle fast/slow charging facilities