Using Inverter-Based Renewable Generators to Improve the Grid Power Quality-A Review

With the increasing penetration of renewable power in the grid,renewable generators are expected to play more important roles rather than merely working as active power sources.Considering the high controllability and considerable idle capacity of the inverter-based renewable generators,various auxiliary functions for them have been studied to benefit the grid.Among these auxiliary functions,the grid power quality improvement is very promising.This paper presents a review of the emerging control strategies for inverter-based renewable generators to improve grid power quality.The related papers are classified with different power quality issues and technical routes,and a comprehensive comparison is presented.The future trends of this research area are also discussed.

Optimal Trading Decision-Making of Power Supply Chain under Renewable Portfolio Standards

Under the background of implementing renewable portfolio standards and the ever-improving tradable green certificate scheme,the increasingly environmentally-friendly preference of power users is leading to changes in electricity demand,which,in turn,is driving changes in the decision-making behaviors of various actors in the power supply chain.Based on this,with the goal of pursuing maximum profit,consumer-power-demand functions have been introduced with some consideration of the factors of consumer preference to establish an optimal profit model for each trading subject in non-cooperative states of the power supply chain,under the constraints of meeting renewable energy portfolio standards.Here,the optimal strategy of each trading subject is presented by adopting the reverse induction method.Furthermore,examples are used to analyze factors such as the influence of environmental protection preferences,quota ratios,price substitutions,and market demand as well as the optimal profit of each trading subject in view of providing a reference for the decision-making in the power supply chain trading subjects.

An Assessment of Renewable Energy Options for Somalia Turkey Hospital

Somalia Mogadishu-Turkey Training and Research Hospital is only powered by diesel generator currently.In this paper,the energy demand of this hospital is supplied by determining the optimum hybrid power renewable generating system.Therefore,numerous hybrid renewable power generating systems including the components like diesel generator,wind turbine,photovoltaic(PV)and battery are considered in different configurations.Eventually,they are technically,environmentally and economically analyzed by using the well-known HOMER software.Furthermore,a sensitivity analysis is also performed considering variations in three important parameters,namely average wind speed,current diesel price and also solar radiation.According to the results,the optimal system is the standalone Wind/Diesel/Battery hybrid renewable energy system(HRES)with the configuration of 1,000 kW wind turbine,350 kW diesel generator,250 kW power converters and 750 batteries.Additionally,this system has the net present cost of$5,056,700 as well as the cost of energy as$0.191/kWh.Lastly,it is clearly occurred that the Wind/Diesel/Battery HRES is eco-friendlier than other HRESs.

Pilot Protection Based on Amplitude Comparison for Renewable Power Teed Lines

Fault behaviors of inverter-interfaced renewable energy generators(IIREGs)are quite diverse from those of synchronous generators(SGs).They show the variable system impedance,the limited current and low inertia,so the proportional brake differential protection installed on the transmission line has a high risk of failure for phase-phase failures.To cope with this adaptive problem,a new pilot protection is proposed considering the huge differences in both current amplitudes.Also,an improved criterion is presented for a scenario with a teed line.The existing protection principles focus excessively on the fault current characteristics of IIREGs,so they cannot operate correctly once IIREGs do not output their fault current.This happens when IIREGs produce no power or the circuit breakers exactly reclose on permanent failures.However,the proposed method has good performance for the above cases.The proposed method only requires current amplitude information,and in this case the strict synchronizing measurement is not necessary.Case studies are performed under different fault conditions,and they confirm the proposed method has good performance under different fault conditions.Furthermore,it is also verified using field-testing data.

Analysis and control of wind-driven self-excited induction generators connected to the grid through power converters

The analysis of the wind-driven self-excited induction generators （SEIGs） connected to the grid through power converters has been developed in this paper. For this analysis, a method of representing the grid power as equivalent load resistance in the steady-state equivalent circuit of SEIG has been formulated. The technique of genetic algorithm （GA） has been adopted for making the analysis of the proposed system simple and straightfor- ward. The control of SEIG is attempted by connecting an uncontrolled diode bridge rectifier （DBR） and a line commutated inverter （LCI） between the generator term- inals and three-phase utility grid. A simple control technique for maximum power point tracking （MPPT） in wind energy conversion systems （WECS）, in which the firing angle of the LCI alone needs to be controlled by sensing the rotor speed of the generator has been proposed. The effectiveness of the proposed method of MPPT and method of analysis of this wind-driven SEIG-converter system connected to the grid through power converters has been demonstrated by experiments and simulation. These experimental and simulated results confirm the usefulness and successful working of the proposed system and its analysis.

Two-stage Optimal Dispatching of AC/DC Hybrid Active Distribution Systems Considering Network Flexibility

The increasing flexibility of active distribution systems(ADSs)coupled with the high penetration of renewable distributed generators(RDGs)leads to the increase of the complexity.It is of practical significance to achieve the largest amount of RDG penetration in ADSs and maintain the optimal operation.This study establishes an alternating current(AC)/direct current(DC)hybrid ADS model that considers the dynamic thermal rating,soft open point,and distribution network reconfiguration(DNR).Moreover,it transforms the optimal dispatching into a second-order cone programming problem.Considering the different control time scales of dispatchable resources,the following two-stage dispatching framework is proposed.d dispatch uses hourly input data with the goal(1)The day-ahea of minimizing the grid loss and RDG dropout.It obtains the optimal 24-hour schedule to determine the dispatching plans for DNR and the energy storage system.(2)The intraday dispatch uses 15-min input data for 1-hour rolling-plan dispatch but only executes the first 15 min of dispatching.To eliminate error between the actual operation and dispatching plan,the first 15 min is divided into three 5-min step-by-step executions.The goal of each step is to trace the tie-line power of the intraday rolling-plan dispatch to the greatest extent at the minimum cost.The measured data are used as feedback input for the rolling-plan dispatch after each step is executed.A case study shows that the comprehensive cooperative ADS model can release the line capacity,reduce losses,and improve the penetration rate of RDGs.Further,the two-stage dispatching framework can handle source-load fluctuations and enhance system stability.