Zhenyu Tan

Advanced Distribution Management System

This paper proposes an advanced distribution management system (DMS) that a) monitors each component and performs protection functions using a dynamic state estimation, b) the estimated states are transmitted to the DMS where the real time model of the entire feeder is synthesized, c) uses the real time model to perform upper level optimization (operations planning) and lower level optimization (real time control) via a hierarchical optimization procedure; and d) applies proper controls to operate the system at optimal points. The proposed approach for protection, operations planning, and real time control of the system provides the infrastructure for additional important applications. As an example, the paper presents a novel application for monitoring available reserves from all resources in the system. We propose the concept of Reserve-O-Meter that monitors in real time the available reserves from all resources (utility and customer owned).

Setting-Less Protection: Feasibility Study

A new protection scheme is proposed that does not require settings or the settings are simple and the need to coordinate with other protective devices has been removed. The approach can be viewed as a generalization of differential protection and it is enabled with dynamic state estimation. Specifically, the proposed protection scheme is based on continuously monitoring terminal voltages and currents of the component and other possible quantities such as tap setting, temperature, etc. as appropriate for the component under protection. The monitored data are utilized in a dynamic state estimation that continuously provides the dynamic state of the component by fitting the data to the basic model equations of the device under protection. The dynamic state is then used to determine the health of the component. Tripping or no tripping is decided on the basis of the health of the component. The basic approach, the analytics and the requirements for successful implementation of this concept are presented. Numerical experiments are presented to validate the method as well as an example comparison with conventional protection. Finally an evaluation of feasibility is provided based on present day microprocessor capabilities and it is concluded that present day microprocessors do have the computational power required by the proposed approach.

Chance constrained unit commitment with wind generation and superconducting magnetic energy storages

System operation reserve requirement keeps going up in the past 3 years to compensate for the variation of wind power. This reduces the efficiency of thermal units by limiting their energy output. Superconducting magnetic energy storage (SMES) as a novel technology was proposed to provide up and down regulation reserve due to its fast response to charge and discharge. However, given the cost and utilization ratio of SMES, an optimal unit commitment (UC) with the integration of SMES is necessary. This paper modifies the traditional UC model into a chance-constrained stochastic problem to realize the optimal schedule objective. To solve this non-convex problem, a Branch/Bound (BB) Technique and Particle Swarm Optimization (PSO) algorithm is introduced, while the initialization of PSO is achieved by the simplex algorithms. Finally, a comparison between the deterministic UC and stochastic UC is given. The result indicates the model in this paper offers independent system operators (ISO) more freedom to balance the system dispatch cost and reliability and it can successfully reduce the SMES costs.

Dynamic State Estimation-Based Protection: Status and Promise

The introduction of the microprocessor-based numerical relay in the 1980s resulted in multifunctional, multidimensional, communications-enabled complex protection systems for zone and system protection. The increasing capabilities of this technology created new unintended challenges: 1) complexity has increased and selecting coordinated settings is a challenge leading to occasional miscoordination; 2) protection functions still rely on a small number of measurements (typically three voltages and three currents) limiting the ability of protection functions to dependably identify the type of fault conditions; and 3) present approaches are incapable of dealing with hidden failures in the protection system. Statistically, 10% of protection operations are misoperations. This paper presents a new approach to protection that promises to eliminate the majority of the problems that lead to misoperations. The approach is described, demonstrated in the laboratory, compared to traditional protection functions and its application to a substation coordinated protection system capable of detecting and dealing with hidden failures is described. This paper also discusses the planned field testing of the approach.

Methodology for monitoring, control and operation of power systems with wind farms

This paper presents an infrastructure and a monitoring and control approach for systems with wind farms that enables coordination of the operation of wind farms with the bulk power system and maximizes the utilization of the available wind energy at the wind farm locations. A hierarchical optimization scheme is proposed in this work. In particular, a system level optimization defines the optimal operating point for the wind farms, the thermal generating units and other controllable devices in the system. At each wind farm, a lower level optimization procedure is performed which defines the operating condition of each wind turbine at the wind farm. The proposed infrastructure is enabled by a distributed state estimation procedure that evaluates the real time model of the system and the wind farms, used by the hierarchical optimization scheme, continuously with speeds of 60 times per second.

Reliability evaluation with cost analysis of alternate wind energy farms and interconnections

The increasing wind penetration into power systems has brought about the problem to have accurate planning and suitable connection of wind farms. Reliability and cost issues become more of concern for evaluating an interconnected wind farm. In this paper, AC systems, HVDC transmission systems, and low frequency AC transmission systems, typically at 20/16.7 Hz, is considered as alternative technologies for interconnection of remote wind farms to the power grid. Eight alternative configurations are discussed. Reliability analysis and cost analysis are performed on each of the eight configurations. Case studies with 30 wind turbines for each configuration are given and the results are compared.

Dynamic State Estimation Based Protection on Series Compensated Transmission Lines

Series compensated transmission lines challenge legacy protection schemes. In this paper, a dynamic state estimation based protection (EBP) method is proposed to address these challenges. The method requires GPS synchronized measurements at both ends of the line and a high-fidelity model of the protection zone. The paper presents the dynamic model of the protection zone and its impact on the performance of the protection scheme. Numerical simulations show that the method can correctly identify faults, independently of position and type. The paper also compares the proposed method versus legacy protection functions such as distance protection and line differential protection. The comparison shows faster detection of internal faults, immunity to current inversion caused by series capacitors (SCs) and improved detection sensitivity for high-impedance faults.

Microgrid black-start after natural disaster with load restoration using spanning tree search

One solution towards a resilient electric distribution system during extreme weather conditions and other natural disasters is microgrid with distribution automation. This low voltage bottom-up black start capability and feeder reconfiguration capability allow true realization of the full potentialities of distributed generation. This paper exploits the black start of a low voltage network supported by automatic sectionalization of microgrids. The loads are restored based on their criticality. The islanded or unserved critical loads are then picked up by the microgrids using spanning tree search that accommodates multiple faults. Unbalanced three phase power flow is performed to ensure all operational constraints have been satisfied. The simulation result is based on a modified IEEE 37-node system with dispersed distributed generation. The study validates the feasibility of the proposed approach.

Transient response improvement of doubly-fed induction machine during unbalanced network

This paper proposes an integral control scheme for doubly-fed induction machine (DFIM) based wind generation system. A positive and negative dq sequence model is presented which is used to analyze the transient response under both balanced and unbalanced network disturbances. The integral control optimizes the input signals (machine and converter currents) to the reference values with full state feedback so that no vague controller parameter (such as PI controller parameters) is needed. The reference values are calculated from the control targets, i.e. constant power and results in no oscillation, limited overshooting, avoidance of overcurrent and so on. Algebraic Riccati Equation is introduced to give the solutions for the controller parameters. Experiment studies verify the effectiveness of the control strategy in improving the transient response for a DFIM system under unbalanced conditions.

Linear quadratic control of SSSC to increase power oscillations damping of HVDC-AC power system

The HVDC-AC transmission system is becoming more and more popular for its numerous benefits, such as low cost, low losses for long distance transmission, etc. However, the power oscillation of this hybrid system has become a major obstacle for its further application. Tons of methods have been tried to damp the power oscillation and static series synchronous compensator (SSSC) is proved to be one of the most effective way for its excellent inherent characteristics. The SSSC offers many advantages as a FACTS device, but it is challenging to design a perfect controller for its application in a nonlinear system. In this paper, a linear-quadratic regulator (LQR) for SSSC is designed to increase power oscillations damping (POD) of an HVDC-AC power system. The LQR optimizes the system input (injected voltage of SSSC) to the reference value with full state feedback so that no vague controller parameter (such as PI controller parameters) is needed. The Algebraic Riccati Equation is introduced as well to provide the solutions for the controller parameters. Simulation results validate the feasibility of proposed modeling and control approach.