Shengchun Yang

An Efficient Decomposition Method for the Integrated Dispatch of Generation and Load

In response to the computational challenges produced by the integrated dispatch of generation and load (IDGL), this paper proposes a novel and efficient decomposition method. The IDGL is formulated using the mixed-integer quadratic constrained programming (MIQCP) method. To efficiently solve this complex optimization problem, the nodal equivalent load shifting bidding curve (NELSBC) is proposed to represent the aggregated response characteristics of customers at a node. The IDGL is subsequently decomposed into a two-level optimization problem. At the upper level, grid operators optimize load shifting schedules based on the NELSBC of each node. Transmission losses are explicitly incorporated into the model to coordinate them with generating costs and load shifting costs. At the bottom level, customer load adjustments are optimized at individual nodes given the nodal load shifting requirement imposed by the grid operators. The key advantage of the proposed method is that the load shifting among different nodes can be coordinated via NELSBCs without iterations. The proposed decomposition method significantly improves the efficiency of the IDGL. Parallel computing techniques are utilized to accelerate the computations. Using numerical studies of IEEE 30-bus, 118-bus, and practically sized 300-bus systems, this study demonstrates that accurate and efficient IDGL scheduling results, which consider the nonlinear impact of transmission losses, can be achieved.

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.

Load Following of Multiple Heterogeneous TCL Aggregators by Centralized Control

Aggregate thermostatically controlled loads (TCLs) are good candidates for providing load following services in power systems. This paper is concerned with the modeling, evaluation, and control problems of a population of heterogeneous TCLs. Specifically, the heterogeneous population is divided into multiple homogeneous clusters and each cluster, i.e., TCL aggregator, is modeled by an approximated three-input single-output state space model. Here, the aggregators serve as a bridge connecting the load utility and the terminal TCLs, which have their own decision makers and are responsible for aggregate estimation and command issuing. And aggregate evaluation is carried out for the aggregator so as to provide the aggregate regulation capacities and ramping rates, which is useful for setting of the reference power trajectory. Based on the established control model, we furthermore propose a hierarchical centralized control algorithm for a bus load utility to regulate all TCLs inside it so as to provide load following service, while not affecting the customers’ comfort levels. Finally, simulation results with respect to a common bus load are provided to demonstrate the effectiveness of the proposed aggregate modeling and the centralized load following 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.

A Decentralized Approach for Frequency Control and Economic Dispatch in Smart Grids

This paper proposes a decentralized approach for frequency control and economic dispatch in smart grids with distributed energy resources and responsive demands. The approach is implemented based on a distributed multi-agent system, in which each agent works in a collaborative manner via local computation and peer to peer communication. The approach is comprised of two strategies. A consensus-based strategy is implemented at the supply side to regulate system frequency economically. Self-adaptive updating rules are proposed for the key parameters to improve the accuracy and robustness of the consensus-based strategy. A threshold-based strategy is implemented at the demand side to provide ancillary services for frequency regulation. Simulation results are presented to demonstrate the effectiveness and robustness of the approach.

An efficient decomposition method for integrated dispatch of generation and load

Summary form only given: In response to the computational challenges produced by the integrated dispatch of generation and load (IDGL), this paper proposes a novel and efficient decomposition method. The IDGL is formulated using the mixed-integer quadratic constrained programming (MIQCP) method. To efficiently solve this complex optimization problem, the nodal equivalent load shifting bidding curve (NELSBC) is proposed to represent the aggregated response characteristics of customers at a node. The IDGL is subsequently decomposed into a two-level optimization problem. At the upper level, grid operators optimize load shifting schedules based on the NELSBC of each node. Transmission losses are explicitly incorporated into the model to coordinate them with generating costs and load shifting costs. At the bottom level, customer load adjustments are optimized at individual nodes given the nodal load shifting requirement imposed by the grid operators. The key advantage of the proposed method is that the load shifting among different nodes can be coordinated via NELSBCs without iterations. The proposed decomposition method significantly improves the efficiency of the IDGL. Parallel computing techniques are utilized to accelerate the computations. Using numerical studies of IEEE 30-bus, 118-bus, and practically sized 300-bus systems, this study demonstrates that accurate and efficient IDGL scheduling results, which consider the nonlinear impact of transmission losses, can be achieved.

A contingency selection approach considering uncertainty based on interval theory

The Static Security Assessment of power system is affected by the uncertainty of the power flow distribution introduced by renewable resources. In this paper, a fast contingency selection approach considering load and generation uncertainties is proposed. Firstly, a linearized interval power flow algorithm is developed for post-contingency simulation. Then, an interval number comparison method based on Bayesian Theory is applied in interval contingency index comparison. Finally, an approximately consistent ranking method is introduced to contingency ranking. The effectiveness of the proposed approach is demonstrated by applying it to contingency selection for several IEEE standard test systems and two practical provincial power grids in China. Simulation results indicate that the proposed approach is computationally light and highly accurate under uncertainties.

A distributed strategy for flexible load as Spinning Reserves in power system

Flexible loads with fast response ability can be used as Spinning Reserves in power systems. However, due to the numerous quantity and decentralized distribution, the control center cannot accurately perceive and control these flexible loads, which results in the existing centralized control mode cannot be used any more. Based on the theories of multi-agent system and the consensus control, a distributed control strategy is proposed for massive flexible loads to participate in the Spinning Reserve of the system. Specifically, an optimal control strategy to allocate unbalanced active power among generators and load aggregators and a consensus control strategy for massive load agents within an aggregator are also designed. Simulation of IEEE9 bus system is utilized to show the effectiveness of the proposed strategy.