Liangyi Sun

Dynamic State Estimation based protection of microgrid circuits

Microgrid protection presents challenges because of the presence of inverter interfaced resources which results in insufficient separation between fault and load currents. This paper uses the Dynamic State Estimation (DSE) based protection (EBP) method for the protection of microgrid components. The paper demonstrates that this method provides a reliable protection system as opposed to traditional methods. Specifically, we verify that traditional protection functions such as overcurrent, distance etc. fail to provide selectivity in protection of microgrids. The EBP method can be viewed as an evolution of current differential protection and requires GPS synchronization if measurements come from different metering devices. The method mainly determines whether the measurements are consistent with the model of the protection zone by use of the chi-square test. Numerical simulations prove that the method can correctly respond to different fault types and locations. The method works equally well for three-phase balanced or unbalanced systems, two-phase or single-phase systems, and radial or networked microGrids.

Dynamic state estimation-based protection of power transformers

Power transformers are expensive and critical power system components. Reliable and secure protection schemes for transformers are extremely important. While transformer protection has evolved to a high degree of sophistication they cannot ensure 100% reliable and secure protection. A new transformer protection scheme based on dynamic state estimation is proposed. The dynamic transformer state is continuously estimated from measurements and the protective decision is based on the transformer state only (operating condition or health status). This scheme requires very few and simple settings, such as maximum permissible hot spot temperature. The protection algorithm is object-oriented. Specifically, the transformer model is expressed in a standard format, named the algebraic quadratic companion form (AQCF) and the dynamic state estimation operates directly on this object model. The method has been demonstrated in the laboratory. The paper describes the laboratory hardware. An example transformer protection is presented for a 115/25 kV three-phase transformer. Results verify the advantages of this scheme over traditional methods.

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.

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.

Command authentication via faster than real time simulation

This paper presents the use of a distributed dynamic state estimation, executed each cycle, to enable simultaneous cyber security and operational security. The basis of the method is: (a) data verification that detects bad data or byzantine type attacks and (b) command interception and fast authentication from the cyber security point of view (reliable detection of cyber intrusions) and from the operational reliability point of view. To ensure speed, the command authentication is done at the relay level and relay controls. Since all controls in a modern substation are exercised through a relay, this approach provides 100% coverage. The command authentication is performed by capturing each command, performing a simulation of the effects of the command via a faster than real time simulation using the real time model, and if there are no adverse effects, the command is authenticated and is allowed to proceed. This paper focuses on the approach that enables the faster than real time simulation and provides performance metrics of the method. The simulation results demonstrate the high speed-up of distributed DSE and validate the effectiveness of the command authentication and intrusion detection method based on the proposed equivalencing method.

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.

Cost analysis and optimal kV level selection of alternate wind farms

With the emerging of various transmission technologies, alternate wind farm configurations have been proposed to integrate different combinations of AC, HVDC and Low-frequency AC for in-farm and out-of-farm transmission. The problems of cost evaluation and kV level selection are raised for the alternate wind farm configurations. This paper presents the cost analysis method and the optimal kV level selection approach for the alternate configurations discussed. The analyzed cost consists of operational cost, acquisition cost and maintenance cost. The optimal kV level is selected based on the minimization of the total annualized cost of the wind farm. One of the proposed alternate configurations is used as a case study to demonstrate the cost analysis and optimal kV level selection methods. The kV level selection results and the minimum cost of all the eight alternate configurations proposed are also provided.

Data Attack Detection and Command Authentication via Cyber-Physical Comodeling

In this article, the authors study the problem of efficient authenticated encryption algorithms for use in embedded devices. In particular, they describe the ongoing Competition for Authenticated Encryption: Security, Applicability, and Robustness (CAESAR), and compare the different candidates of the competition with respect to a variety of metrics of relevance to constrained systems, including their memory footprints. —Alvaro Cardenas, University of Texas at Dallas

Dynamic state estimation based protection of mutually coupled transmission lines

Mutually coupled lines create challenges for 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 protected line. The paper presents the dynamic model of the protected line and its impact on the performance of the protection scheme. Numerical simulations prove that the method can correctly identify faults, independent of position and type. The work also demonstrates the advantages of the proposed method versus legacy protection functions such as distance protection and line differential. These advantages include reliable and faster detection of internal low impedance faults, inter-circuit faults, and high impedance faults, even in cases of 1) partially coupled lines and 2) lack of measurements in adjacent lines.