Abstract:As a new generation of direct current (DC)transmission technology, voltage sourced converter (VSC)based high voltage direct current (HVDC) has been widely developed and applied all over the world. China has also carried out a deep technical research and engineering application in this area, and at present, it has been stepped into a fast growing period. This paper gives a general review over China's VSC based HVDC in terms of engineering technology,application and future development. It comprehensively analyzes the technical difficulties and future development orientation on the aspects of the main configurations of VSC based HVDC system, topological structures of converters,control and protection technologies, flexible DC cables, convertervalve tests, etc. It introduces the applicable fields and current status of China's VSC based HVDC projects, and analyzes the application trends of VSC based HVDC projects both in China and all over the world according to the development characteristics and demands of future power grids.

Abstract:In this paper, a robust design method for current control is proposed to improve the performance of a three phase voltage source converter (VSC) with an inductor-capacitor-inductor (LCL) filter. The presence of the LCLfilter complicates the dynamics of the control system and limits the achievable control bandwidth (and the over all performance), particularly when the uncertainty of the parameters is considered. To solve this problem, the advanced control theory is employed to design a robust current controller in stationary coordinates. Both control ofthe fundamental frequency current and suppression of thepotential LC resonance are considered. The design procedure and the selection of the weight functions are presented in detail. A conventional proportional-resonant PR controller is also designed for comparison. Analysis showed that the proposed current controller achieved a good frequency response with explicit robustness. The conclu-sion was verified on a 5 kW VSC that had a LCL filter.

Abstract:This paper presents the power hardware in the loop (PHIL) validation of a feed forward DC voltage control scheme for the fault ride through (FRT) of voltage source converter (VSC) high voltage DC (HVDC) connected offshore wind power plants (WPPs). In the proposed FRT scheme, the WPP collector network AC voltage is actively controlled by considering both the DC voltage error and the AC current from the WPP AC collector system which ensures fast and robust FRT of the VSC HVDC connected offshore WPPs. The PHIL tests were carried out in order to verify the efficacy of the proposed feed forward DC voltage control scheme for enhancing the FRT capability of the VSC HVDC connected WPPs. The PHIL test results have demonstrated the proper control coordination between the offshore WPP and the WPP side VSC and the efficient FRT of the VSC HVDC connected WPPs.

Abstract:The DC fault characteristics of voltage source converter based high voltage direct current (VSC-HVDC)systems are analyzed in this paper. The phenomenon whereby the capacitor on DC side discharges quickly during a DC fault contributes to a large short-circuit faultcurrent. Neither traditional DC breakers nor DC switches can cut off the fault current under this condition. A fast solid state DC breaker design method is proposed in thispaper. This method is based on the fault current charac-teristics of the inverter in multi-terminal HVDC systems(MTDC), where a fault current appears at the natural zero-crossing point near the inverter. At this point, by coordi-nating the AC breakers near the rectifier, the DC breakercould reliably cut off the DC fault current and protect thesystem. A detailed model for this fast solid state DCbreaker and its operation sequence are studied, based on this design method. Simulations modeling a five-terminalmeshed DC grid and a fast DC breaker were carried outwith PSCAD/EMTDC using this design method. There sults from the simulations confirmed the validity of thedesign method.

Abstract:Primary energy has the potential to bring challenges to the reliability, economic, and eco-friendlinessof global electric power systems. The concept of electric power security are proposed, including many factors thatare not considered in power system reliability analysis,such as coal supply for power system, fuel price for electricity power market, carbon emissions of power generation, and so on. It is broader than power system reliability and security, which means that providing energy in the form of reliable, economical, and ecofriendly electric power. Following an account of existing blackout defence methods and systems, the processes of transforming various kinds of primary energy into electric power and the interactions between them are described, particularly with regard to flows of energy, capital, and information. Factorsthat limit the liquidity of these flows are defined as '"gen-eralized congestion", and the challenges presented byprimary energy are named "primary energy congestion".China's dilemma on coal supply for power generation is presented in some detail as an example of primary energy congestion. To cope with impacts of the primary energy on electric power systems, an idea is introduced to extend the scope of existing coordinated black out defence systems toan integrated tool to provide decision support to power system operators accounting for primary energy congestion.

Abstract:This paper proposes a new method for power transmission risk assessment considering historical failure statistics of transmission systems and operation failure risks of system components. Component failure risks are integrated into the new method based on operational con-dition assessment of components using the support vectordata description (SVDD) approach. The traditional outage probability model of transmission lines has been modified to build a new framework for power transmission system risk assessment. The proposed SVDD approach can provide a suitable mechanism to map component assessment grades to failure risks based on probabilistic behaviors of power system failures. Under the new method, both up-to-date component failure risks and traditional system risk indices can be processed with the proposed outage model.As a result, component failure probabilities are not only related to historical statistic data but also operational data of components, and derived risk indices can reflect current operational conditions of components. In simulation studies, the SVDD approach is employed to evaluate component conditions and link such conditions to failure ratesusing up-to-date component operational data, including both on-line and off-line data of components. The IEEE24-bus RTS-1979 system is used to demonstrate that component operational conditions can greatly affect the over all transmission system failure risks.

Abstract:With the increased integration of photovoltaic(PV) power generation into active distribution networks, the operational challenges and their complexities are increased.Such networks need detailed characterization PV system sunder multiple operating conditions to understand true impacts. This paper presents a new mathematical model for a PV system to capture detailed effects of PV systems. The proposed model incorporates state transitions of componentsin a PV system and captures effects of insolation variations.The paper performs a reliability assessment incorporating PV systems at resource locations. The results suggest that there liability performance of an active distribution network atstressed operating conditions might be influenced by the high penetration of PV system. Reliability performance of distribution networks that are high penetrated with PV systemscan be affected by cloudy effects resulting from insolation variations. The proposed model can be used to quantify the level of reduction in reliability, resulting with cloudy effects.

Abstract:This paper describes the research on a large-scale dispatchable grid-connected photovoltaic (PV) systemfor supplying power to the grid for dispatch instead of supplying the electricity to a local load. In order to maximise the value of the solar energy, a hybrid electricity storage consisting of batteries and super capacitors is used with the PV system. This paper proposes a control strategy focusing onthe DC power at the DC link rather than at the grid-connected inverter. Two typical sets of real data, collected from existingsites, are used to demonstrate the practicality of the system.Finally, the simulation results are used to demonstrate the good performance and feasibility of the proposed system together with the proposed control strategy.

Abstract:The promotion of recent critical load securing of power system research has been directed towards centralized commands and control functions. This paper presents amultiagent based critical load securing in a PV based microgrid. For the trust worthy operation of critical buildings,the reliability, efficiency and security of the power system should be guaranteed. At present, to increase the security and reliability of electricity supply there is a need to design adistributed and autonomous subset of a larger grid or a microgrid. This work also clearly discusses the modelling and simulation of specialized microgrid called an Intelligent Distributed Autonomous Power Systems (IDAPS). The ID-APS microgrid plays a crucial role in constructing power grid that facilitate use of renewable energy technologies. IDAPS microgrid comprising of solar photovoltaic as distributed energy resources, different loads and their control algo-rithms, has been developed. Several case studies have been simulated to evaluate the operation of the IDAPS microgrid during parallel, islanded mode operation and securing criti-cal loads during emergency.

Abstract:A maloperation case of busbar protection caused by a dead-zone protection abnormality in the Bra-zilian Midwest Grid on September 19th, 2012, is briefly described. The operation process of pilot distance, automatic reclosure, busbar differential and dead-zone pro-tection, and the emphasis on the logic scheme of dead-zone protection are analyzed. The time delay between thebreaker's main pole and auxiliary contact during reclosurewas the main cause in this case, and a defect in the logicallowed it to occur. The differences in deadzone protection logic between Brazil and China are discussed. A test platform was constructed in the laboratory, and a site simulated experiment was also performed. Possible causes are suggested and test activities are carried out to verifythem. Results show the values of practical engineering approaches to the solution. Experience also contributed to avoiding future mal-operations and streng thening the reliability of the protection system, and thus of the power supply in Brazil.