G.M. Huang

A new bifurcation analysis for power system dynamic voltage stability studies

The dynamic of a large class of power systems can be represented by parameter dependent differential-algebraic models of the form x/spl dot/ = f (x, y, p) and 0 = g(x, y, p). When the parameter p of the system (such as load of the system) changes, the stable equilibrium points may lose their dynamic stability at local bifurcation points. The systems will lose its stability at the feasibility boundary, which is caused by one of three different local bifurcations: the singularity induced bifurcation, saddle-node and Hopf bifurcation. In this paper, the dynamic voltage stability of a power system is introduced and analyzed. Both the reduced and unreduced Jacobian matrix of the system are studied and compared. It is shown that the unreduced Jacobian matrix, whose eigenstructure matches well with the reduced one; and thus can be used for bifurcation analysis. In addition, the analysis avoids the singularity induced infinity problem, which may happen at reduced Jacobian matrix analysis, and is more computationally attractive.

Voltage stability constrained load curtailment procedure to evaluate power system reliability measures

This paper reports a method to evaluate composite power system reliability indices incorporating the voltage stability margin criteria. To compute the load curtailment evaluation, an optimal power flow (OPF) computation algorithm, considering the steady state voltage stability margin constraint is developed. A steady state voltage stability indicator is first discussed for its applicability as a suitable indicator for representing stability margin from the collapse point. The load curtailment formulation is then evolved and described in the OPFs objective function. A criterion based on the voltage stability indicator is then incorporated as an additional constraint into the OPF. A numerical example has been used to illustrate the effect of the algorithm on the composite system reliability evaluation. The expected energy not served (EENS) and down time is computed, both analytically and by the Monte Carlo Simulation.

Transmission loss allocations and pricing via bilateral energy transactions

A new method to allocate transmission losses for simultaneous bilateral transactions under a deregulated environment is proposed in this paper. Instead of conventional single slack bus concept, the proposed approach utilizes pairs (sending and receiving) from specific bilateral transactions to calculate associated loss contributions in an interconnected transmission network. Distinguishing from other existing approaches, our method distributes losses to all sending buses according to the incurred losses along the paths. Real and associated reactive support can be calculated and allocated. It is proven that the derived operating point from our method is independent of the slack bus selection. A composite pricing strategy is proposed to allocate loss cost for each transaction. The IEEE 30 buses RTS system is used to demonstrate the effectiveness of our method.

HVDC controls for power system stability

This paper discusses the impact of HVDC on Power System Stability and proposes a control mechanism to augment the system angle stability. At first, the authors discuss the HVDC model used in transient studies. Basically, it is the same as used in power flow studies, details of which have been given in Section II of the paper. The model considers the limits of HVDC lines, which consists of many control modes. A case has been studied where the HVDC tends to make the system unstable if the setting of the line is not changed during and after a fault. They then propose a control mechanism to strengthen the system stability. Two types of controllers, namely proportional control and proportional-integral control have been studied and compared. Also they have shown their effects on the system stability.

Transaction based power flow analysis for transmission utilization allocation

This paper proposes a framework of transaction based power flow analysis (TBPF) for transmission utilization allocation. The TBPF utilizes distributed purchase-sale pairs to replace the role of a single slack bus on energy imbalance during power flow calculation iterations. To compare with conventional power flow analysis, accurate allocation of use-of-transmission is part of a TBPF solution. In particular, the TBPF is able to identify interaction components among transactions as well as the effect of reactive power on transmission losses and active power flows. Two allocation rules for cross terms are proposed to hedge firm or existing transactions against market risk. The standard WSCC 9 bus system is used to demonstrate the performance of the TBPF.

The impacts of TCSC and SVC on power system load curtailments

This paper investigates the effect of thyristor controlled series capacitor (TCSC) and static VAr compensator (SVC) on power system load curtailments. The research on TCSC and SVC is abundant, but most of them are on power system stability improvement. This paper proposes a new use of TCSC and SVC to reduce load curtailments. An algorithm of optimal power flow (OPF) to reduce the load curtailment for installing TCSC/SVC in the system is proposed in this paper. Several examples are used to demonstrate the effect on load curtailment. The test results show that the effect of TCSC/SVC is significant. This paper also suggests some potential future research.

Detection of dynamic voltage collapse

This paper investigates how to detect a dynamic voltage collapse situation. The generator and governor dynamics are considered in the simulation process. An index proposed earlier has been investigated for its applicability to indicate the collapse situation. Time domain simulations, using a commercial software EUROSTAG, has been carried out in this work. The test result reflects the applicability of the index during the line loss, slow increasing loading and step loading situations. The paper also brings out the details of the simulation setup used, which would help others in carrying out further simulations and investigation.

Dynamic voltage stability reserve studies for deregulated environment

This paper first analyzes why voltage instability occurs in mature yet competitive power systems, and then investigates diverse voltage stability issues in deregulated power markets using the EUROSTAG commercial transient simulation program. Dynamic behaviors of major power system components, i.e., speed governor, excitation element, inductive motor, ULTC and mechanically switched shunt capacitor etc., are thoroughly examined by a small yet typical equivalent system. The presented simulation results help better understand the mechanism of the voltage collapse phenomena, and highlight the importance of dynamic reactive reserves, like generators, in dynamic voltage stability enhancement.

A heuristic approach for power system measurement placement design

Measurement placement design of electric power system is formulated as an optimization problem, whose objective is to minimize the installation cost under the constraint that the system remains observable for pre-selected single branch outage or any single measurement loss. The contribution of this paper is as follows: we consider both costs on remote terminal units (RTUs) and measurement devices. Furthermore, a two-step heuristic approach based on topological analysis is proposed to solve the problem. In the first step a measurement configuration with minimum number of measurements that satisfies the observability constraints is determined. In the second step the measurement configuration is further optimized to reduce the number of RTUs. Tests on the IEEE 30-Bus system are used to demonstrate the validity and efficiency of the proposed approach.

Incorporating TCSC into the voltage stability constrained OPF formulation

This paper investigates the effect of thyristor controlled series capacitor (TCSC) on the voltage stability constrained optimal power flow (OPF) formulation where the objective function is to minimize power system load curtailment. Incorporating TCSC affects the topology and hence the power flow distribution. Some numerical cases are presented to discuss the effects of TCSC that is expected when it is incorporated into the load curtailment formulation. The test result reflects the impacts TCSC has in reducing load curtailment during a line congestion situation. The paper also discusses the applicability of the approach in security based reliability studies for systems having control components like TCSC.