Aiming at the testing difficulties of valve control equipment due to its large quantity of interface in VSC-HVDC transmission project, this paper designs a physical dynamic simulation testing system to realize the full access test of VSC-HVDC valve control equipment with large-scale nodes. An interface expansion device is developed, which can realize the full access and full function test for valve control equipment with large-scale nodes through a small amount of physical sub-modules. The software and hardware design scheme of the interface expansion device are introduced in detail. Full access and full function tests are carried out on the valve control equipment developed by Xuji Group for Yu-E project, which verifies the correctness of the proposed physical dynamic simulation testing system.

In order to solve DC voltage control problem of two-terminal VSC-HVDC system without communication, on the basis of detailed analysis of existing control modes, an improved DC voltage margin control strategy is proposed in this paper. The proposed controller realizes the exchange of different control modes before PI controller by constructing an error function and weigh coefficient of quadratic function. Compared with traditional DC voltage margin control priciple, the proposed strategy can simplify the controller structure, and meanwhile it can greatly reduce the limit level of DC voltage during fault-ride-through and power reversal. Simulation results prove the effectiveness of the proposed method.

VSC-HVDC has significant influence on LCC-HVDC in hybrid multi-infeed HVDC system. Based on a hybrid dual-infeed HVDC system, the multi-infeed effective short circuit ratio (MIESCR) is deduced which quantitates the improvement effect of infeed point and infeed current of VSC-HVDC to LCC-HVDC. Considering both the normal operation target of VSC-HVDC and the transient voltage compensation needed by LCC-HVDC, a control strategy of VSC-HVDC is proposed which can achieve maximum MIESCR, and its effectiveness is verified through digital simulation in PSCAD.

The no-load switching of transformer will result in sympathetic inrush current of the transformer connected in series or in parallel. The sympathetic inrush current of the two transformers exhibits different characteristics from the typical inrush current, and the harmonic characteristics also change. In the AC-DC hybrid power grid, the harmonic coupling characteristic of the converter makes the harmonics in the AC power grid coupled to the DC side which will cause the DC protection malfunction and lead to DC blocking, meanwhile threaten the safe operation of power grid. In this paper, based on the parameters of actual transformer core magnetization characteristic curve, the electromagnetic transient simulation software PSCAD is used to simulate the sympathetic inrush current. The second harmonic characteristics of the single transformer inrush and the sympathetic inrush current are simulated and analyzed. The conclusion is that for single transformer the inrush current is mainly positive-sequence second harmonic current, while the sympathetic inrush current has obvious negative sequence characteristics. This will provide an analytical basis for the practical problems of the negative sequence secondary harmonics that will affect the DC protection.

In order to study the mechanical properties of UHV solid composite post insulators, static lateral push test and dynamic property test are carried out. The strain at the bottom of composite post insulators, the force-displacement relationship, and fundamental frequencies before and after the failure are obtained by arranging strain gauges at the bottom of the post insulators, displacement transduces and accelerometers on the top of post insulators, respectively. It’s observed that the fractures on the metal flanges and the bond failure between the post insulator bar and the flange are the most common failure modes, and the fundamental frequency of the post insulators decreased significantly after its failure. The force-displacement relationship of the post insulator under lateral force can be divided into linear elasticity stage and elastic-plasticity stage. Except for the other parameters, the lateral load bearing capacity of the post insulators mainly depends on the height of flanges. Due to the higher bonding region and the better bonding effect, the insulator with a lager flange height will have a greater lateral load bearing capacity when other parameters of the post insulator bar are the same. For composite post insulator without reinforcement rib on the flange, the lateral bearing capacity of its components is different, and the bearing capacity of post insulator bar is higher than that of the flange and the bonding material.

Modular multilevel converter (MMC) converter is widely used in the application of high voltage large power scenarios, but the shoot-through problem in bridge topology places MMC converter at a serious risk of capacitor short-circuit. A novel MMC converter based on dual buck circuit is designed, where the base cell of the MMC converter is not bridge circuit but dual buck circuit. MMC converter based on dual buck circuit eliminates the risk of shoot-through and reverse-recovery of body diode. The details of working principle and operating modes are analyzed. Control method based on switching of capacitor with maximum (minimum) capacitance sequence is given to realize the balancing control of capacitance voltage. Simulation results on Saber are identical with the theory, which verifies the stability of the system can be improved.

Partial discharge(PD) is the main insulation defect of gas insulated switchgear (GIS),when it occurs in GIS, the insulation will be deteriorated and breakdown will finally happen, so it is very important to detect and localize internal PD as early as possible, and then carry out defect inspection and repair work. This paper proposes a PD recognition and localization method based on data driven, which means threshold and correlation statistics analysis of time series by multiple sensors. In this paper, sensor’s location is coded firstly, then the spatial and electric position of sensors can be identified by machine, and cumulative discharge amplitude of chracteristic is constructed to distinguish stable PD. According to the correlation analysis of monitoring values of sensors, the propagation way of PD is judged, and whether or not it being an internal PD can be identified. For an internal PD, its position can be located by comparing the cumulative discharge amplitude. Verification by online monitoring data of Qianfan station also proves that the discharge phenomenon can be recognized effectively and the method is feasible.

By 2018, China will carry out the national carbon trading policy. In the carbon trading market, the power suppliers are facing with the risk of uncertainty in the carbon trading price. Considering the risks of carbon trading, the low carbon dispatch problem of power suppliers is worth studying. Drawing on the theory of risk management in financial field, this paper uses conditional value at risk (CVaR) as a risk measurement index, and proposes a low carbon dispatch optimization model for power suppliers considering the risks of carbon trading. The model is used to calculate the carbon trading portfolio optimization of power suppliers. At the same time, the impacts of power suppliers risk preference confidence, changes in carbon trading prices and carbon emission limits on the carbon trading risks of power suppliers are analyzed. The effectiveness of the proposed model is verified by examples. The power suppliers can optimize the power generation, balance profits and risks by using the model, and the model has a certain reference value and guiding role for the power suppliers business decisions.

In recent years, peak load has been growing yearly and peak-valley difference of load has been increasing, which brings great pressure on grid operation. Two typical thermostatic controlled loads (TCLs) ie, water heater and air conditioning are selected as controlled objects. The phenomenon of payback effect is taken into consideration and a linear planning mathematical model of load regulation is put forward to maximize the amount of peak load reduction orderly through full-time and split-time control strategies. Through the load regulation of typical summer day in Nanjing, the amount of peak load reduction under different conditions are analyzed. The results verify the validity of the proposed linear planning mathematical model.

Distributed feeder automation can significantly improve the self-healing speed of distribution network. However, it relies on real-time communication network, which becomes the key factor restricting the application of distributed feeder automation. This paper presents a method to adjust feeder automation(FA) strategy based on real-time quality of communication network. Through the real-time detection of communication quality, the feeder automation is realized in the most reliable way when communication is in good condition. When communication is unstable, the number of interactions is reduced to improve the self-healing speed; When communication does not meet the distributed FA conditions, local control method is adopted to ensure the reliability of distributed system application. This method overcomes the over-reliance of FA system on communication, extends the adaptability of FA in different communication quality and enhances the ability to cope with communication network failure.

Large consumers direct power purchase plays a crucial role in supporting the national industry, facilitating the real economy development, and promoting local economy prosperity. Combined the current situation of large consumers direct power purchase in our country nowadays, this paper summarizes the relevant transaction principal members, types of transactions, transaction process and the settlement methods associated with large consumers direct power purchase in southern region, and analyzes the advantages and disadvantages of the related transaction types and settlement modes. Finally, the paper discusses the challenges and problems to be solved for large consumers direct power purchase, and reviews the possible applications of applying block chain technology.