Dan Zeng

Research on PI controller tuning for VSC-HVDC system

Dual closed loop structure is often adopted in VSC-HVDC control system, and the PI controller design and parameters tuning can be regarded as the core content in the control system design. This paper first designs the inner current loop follow three methods: typical I-type, typical II-type and second-order system, designs outer voltage loop under the low-frequency model, and then the step response and dynamic performance under different methods is analyzed through simulation. In order to improve the system stability, a novel strategy is also proposed for the outer voltage loop based on cutoff frequency and phase margin. Simulation is carried out to testify the feasibility of this strategy and shows that the PI parameters tuned by this method can drop into the actual value range, and the systems performance can be satisfied, which proves the correctness of this novel strategy.

A generalized power control strategy with droop feedback for VSC-HVDC

Based on the novel and controllable characteristics of VSC-HVDC, an improved double close-loop decoupling control system is proposed in this paper to utilize the supporting capability of VSC-HVDC for frequency and voltage of weak ac systems. A generalized power outer-loop with ac frequency and voltage additional control functions is designed to help the fast recovery of ac frequency and voltage after disturbances. Then, an adaptive droop control with power deviation feedback is adopted to improve stable operation range of VSC-HVDC. As an example, a typical weak ac system fed by a VSC-HVDC link, including a synchronous generator with an exciter, a governor and a turbine is simulated in PSCAD/EMTDC. The time-domain simulation results demonstrate that the proposed control strategy can seamlessly handle transitions between different control modes and effectively enlarge the stability operation extent of VSC-HVDC systems.

An interval-based contingency selection approach considering uncertainty

Static security assessment is affected by uncertainties of load flow distributions introduced by renewable sources. A fast contingency selection approach based on interval theory is proposed in this paper. Firstly, an interval line active flow calculation algorithm is developed to reduce conservation in application of interval mathematics in line flow calculation. Then a novel interval comparison method based on Bayesian probability theory is applied in interval index comparison to give the relative severity information of contingencies. Finally, an approximately consistent ranking method is utilized in contingency ranking to rank screened contingencies. Numerical studies on several IEEE standard test systems and two practical provincial power grids in China under different load and generation conditions have proved that the proposed approach is computationally light and highly accurate under different uncertainties.

Exploration of AGC Control Mode for North China-Central China-East China UHV Synchronous Power Grid

With the continuous construction of ultra high voltage (UHV) power grid, East China-Central China North China will be interconnected via UHV lines to be a UHV synchronous grid in the future. Further expansion of the grid scale, the existing active power and frequency control mode has been unable to adapt to the new features. Based on the future structure of North China-Central China-East China synchronized power grid, the article built the whole network of the AGC control model using PSD-FDS full dynamic simulation program. By the simulation of examples, the problems of AGC control mode for UHV synchronous power grid has been pointed out visually. Finally, the paper presented an ideal AGC control mode called centralized control mode to deal with the new challenge.

Coordinated Optimization and Control Technology between Active and Reactive Power

As the coupling between active and reactive power is enhanced along with the expansion of the grid scale and the AC-DC hybrid operation, voltage stability is not only closely related to reactive power, but also related to active power. By the constraints of generator power circle and its operating limits, the mechanism of interaction between the active and reactive power is clarified. Also, the hierarchy structure of coordinated optimization and control technology between them is established, and an improved AGC control strategy consideration to static voltage stability is proposed. By optimizing the active power output of the AGC unit, the dynamic reactive power reserve capacity of each unit is improved and the system voltage is supported. The strategy is verified through a variety of experiments on the IEEE-39 bus system.