Three-phase series-connected VSCs are composed of three single-phase VSCs connected in series at the DC side. Compared with conventional three-phase parallel-connected VSCs, this topology reduces the number of swithing devices offectively to withstand the same DC voltage and therefore reduces the investment. Firstly, the basic principle of three-phase series- connected VSCs riding though AC faults by mean of AC power regulation are analyzed, and then considering the connections of transformer windings, the corresponding current control schemes are proposed to achieve four various control objectives under AC faults, i.e., balancing AC current, suppressing ripples of instantaneous active power, suppressing ripples of instantaneous reactive power and suppressing zero-sequence current. The approach to derive the reference currents is presented and the expressions of current references corresponding to four different control schemes are also derived. Finally, simulations are performed in PSCAD/EMTDC and the results validate the proposed control strategies.

Based on analysis of the dynamic process of the arm capacitors during start-up and DC fault of a MMC, an improved equivalent electro-magnetic simulation model of MMC is proposed in this paper, and according to the dynamic characteristics of the total capacitor voltage of an arm, an averaged value model of MMC for its operating condition simulaton is proposed. Then detailed switching, equivalent and averaged value electro-magnetic models of a 21-level MMC are built on PSCAD/EMTDC. By taking simulations during start-up, current step, AC fault and DC fault, the proposd equivalent model and average value model are proved to be suitable to replace the detailed simulation model of MMC in the converter-level study and power system level study with significantly increased simulation speed.

VIENNA three level rectifier is widely used in wind turbine systems, UPS systems,etc. To improve its power quality, the mathmatical model and multi-loop control structure are built under d-q synchronous coordinate system, based on the important requirment for grid side currents and rectifier side voltage in unit power factor operation condition, the reason for currents distortion at zero-crossing point by using multi-loop control and conventional carrier-based PWM method under d-q rotating coordinate system is deeply studied To reduce the total harmonic distortion rate of grid side currents, the way to add compensation component to three-phase reference modulation voltage to eliminate the area that disobey the important limiting condition is applied, the currents distortion around zero-crossing point is inhibitted and the power quality is improved. The rectifier model is built in Saber simulation system, the correctness of theory analysis is proved by comparing the value of currents total harmonic distortion before and after compensation component is added in carrier-based PWM method.

There are a lot of problems such as bad environment adaptability, low degree of intelligence, multidisciplinary cross and more difficulty for power line inspection with large unmanned helicopter, at present unmanned helicopter patrol relies mainly on artificial ground operation, in order to improve inspection efficiency and safety, it is of great significance to study automatic inspection technology with large unmanned helicopter. This paper puts forward the concept of full automatic inspection, gives analysis on necessity of automatic inspection, discusses the key technologies on safety inspection of over low altitude and beyond visual range, including real-time differential positioning, communication relay, autonomous obstacle avoidance, high precision measurement of position and attitude, automatic photoelectric tracking, flight plan and path planning, task planning and control. Automatic inspection technology is used in transmission line inspection of power grid in China for the first time, inspection results show that this technology is advanced and effective. Automatic inspection technology represents an efficient, intelligent, and new power inspection mode, the development and progress of the technology has a significant role in promoting intelligent operation and maintenance level of power grid in China.

As there are large number of phase conductors of multi-circuit transmission line on the same tower, the parallel gaps configuration for the line is complicated and different configuration mode exhibits different lightning performance. Combined with double-circuit and triple-circuit transmission line on the same tower of Guangzhou Power Supply Bureau,optimal parallel gap configuration scheme for lightning performance of multi-circuit transmission line on the same tower is proposed based on analysis of lightning impulse characteristics of insulator strings and lightning protection performance, meanwhile, the lightning protection validity of parallel gaps is also studied. The results show that the lightning impulse 50% flashover voltage of long insulator with parallel gaps is about 80% of that without parallel gaps, and the voltage-time characteristic curve of long insulator with parallel gaps is under that without parallel gaps. The two aspects both indicate good insulation coordination between parallel gaps and insulator. The lightning impulse flashover arc can be led to the air formed by parallel gaps till extinction which proves effective protection of parallel gaps for insulator against lightning. It can be concluded as well that unbalanced insulation configuration between circuits formed by parallel gaps plays an effective role in reducing the lighting simultaneously trip-out rate of multi-circuit transmission line on the same tower.

At present, domestic operating companies judge partial discharge conditions of high voltage switchgear by foreign experience, and are lacking in localized switchgear status judging methods. According to the partial discharge data of 30 773 running high voltage switchgears in Guangzhou, a series of novel empirical cumulative distribution functions (ECDFs) based on on-site transient earth voltage (TEV) data of high voltage switchgears are proposed. Differences of typical features between local and foreign ECDFs of on-site TEV data are compared. According to the distribution criteria of 25%, 10% and 5%, the foreign thresholds are 19 dB·mV, 29 dB·mV and 35 dB·mV, whereas the local empirical thresholds are 13 dB·mV, 23 dB·mV and 32 dB·mV. The result illustrates that the foreign experience on the thresholds may not be suitable for local judgment. Based on the ECDFs, the suitable local on-site TEV tests criteria and maintenance strategy considering the risk of failure probability and the maintenance cost are concluded, which is more flexible and reliable.

Data of helicopter inspection and human inspection on power transmission lines during 2012-2014 years are compared and analyzed from viewpoints of visible inspecting method, infrared inspecting method, major and urgent defects, and typical defects. The effect of helicopter inspection and human inspection on power transmission lines as well as the characteristics of these two inspection methods are summarized. Suggestions on collaborative inspection for power transmission lines are proposed.

Aiming at the characteristics of multi-source panoramic information and highly complex heterogeneous of power Internet of Things devices, this paper proposes a multi-source heterogeneous data aggregation method. Through the data access process of Restful Web service and the quick service bus, the problem of distributed-environment data being difficult to effectively operate is solved with the method, and thus the service process arrangement, management and monitoring can be facilitated. By setting up the heterogeneous source data to RDF data via the RDF interface, and constructing the mapping between the local ontology and the global ontology via combination of the OWL ontology and SWRL rule, the key problem of semantic heterogeneity in the aggregation process can be solved. This method can shield the difference of the physics and logic of the underlying data source, and have good maintainability and expansibility.

The levelized cost of electricity (LCOE) is the main economic index for evaluating various power generation technologies. By introducing the LCOE to the optimal configuration of microgrid, an LCOE based evaluation method for islanded microgrid power supply is proposed, and an optimal allocation model for standalone microgrid power supply based on the minimum LCOE is established. The power output and reliability of the system are simulated based on Monte Carlo method. The genetic algorithm is used to solve the model. The simulation results verify the validity and rationality of the model, and the influences of the initial cost, fuel cost and reliability on the LCOE are analyzed. The established model can accurately evaluate the unit cost of each power supply, reasonably configure the capacity of the power supply and provides a new method for the power supply planning.

Carbon price and electricity price are bound together under the influence of external factors. Thus, the price randomness of carbon and electricity along with their correlation should be taken into consideration to form the bidding model for generation companies. The difference between actual profit and the expectation is defined as the risk and measured by multi-stochastic conditional risk method in this paper. Then, a CVaR-based bidding model which considers the price randomness of electricity and carbon along with their correlation is proposed. The Linear method is used to sample of the random variables concerning the correlation and to solve the conditional value at risk. Cases considering the correlation between electricity price and carbon price, carbon price cost, carbon price randomness and other risk measurement methods are tested respectively to evaluate their influences on the investment decision risk of generation companies. The results show that considering the price randomness of both electricity and carbon as well as their correlation is more in accordance with the generation companies’ requirement of increasing revenue and reducing risk, and conditional risk method is able to describe the risk more accurately.

Deep analysis of the characteristics of bus load is of great significance for bus load forecasting accuracy inprovement, power network safety and stability evaluation, and demand response potential identification. A data-driven based analytical framework of bus load characteristic is proposed in this paper, which is different from traditional load ratio and peak time. On the basis of data cleaning and normalization, the analysis of the daily bus load curve is carried out by clustering algorithm based on the Mahalanobis distance. Then, based on the clustering results, four indexes, including pattern switch entropy, relative volatility, daily average load, and temperature sensitivity are put forward to describe bus load characteristics. Simulation results of 130 bus load data in Guangzhou show that the proposed indexes can better describe the bus load characteristics, and can achieve better classification results.

A novel incremental network loss algorithm based on the dynamic power flow is proposed. The unbalance component of active power is taken into the power flow model in order to take full consideration of the regulation characteristics of generators in real power grids. Then the inversion of the transposed Jacobian matrix is performed to obtain all the generators’ nodal incremental network loss accurately, which can handle the unsolvable problem in the transposed jacobian matrix method because there is no active power constraints in the slack buses. Numerical results for several test systems demonstrate the effectiveness of the proposed algorithm and the advantage in economic dispatch for active power.