John Undrill

Load modeling in power system studies: WECC progress update

This paper provides an update on a composite load model development in Western Electricity Coordinating Council (WECC). A composite load model structure is described. The two salient features of the new load model are: (a) the model recognizes electrical distance between the transmission bus and the end-uses and (b) the model represents the diversity in composition and dynamic characteristics of various electrical end-uses. The load model data includes (a) data for a distribution equivalent model, (b) load component model data and (c) load component fractions. The paper presents tests and modeling of various electrical end-uses. The paper in particular focuses on modeling compressor motors in single-phase air-conditioners. Load composition methodology is also discussed. The model structure was implemented and tested in a production-level grid simulator.

PDCI damping control analysis for the western North American power system

Transmission capacity in the western North American power system (termed the wNAPS) is often limited by poorly-damped electromechanical oscillations. To date, the primary damping controllers applied in the wNAPS are via generator controls using localized feedback signals. Such controls have limited effectiveness for inter-area modes. Recent development of reliable real-time wide-area measurement systems (WAMS) has enabled the potential for large-scale damping control approaches. One such approach is feedback modulation of the Pacific DC Intertie (PDCI). This paper summarizes simulation results from a study to evaluate PDCI damping control in the wNAPS. This includes developing a safe and effective control strategy, quantifying potential improved damping, and conducting open-loop actual-system probing tests.

Phasor modeling approach for single phase A/C motors

In this paper we present results of a development of a single-phase induction motor model using dynamic phasors. This phasor model is intended to represent the compressor portion of the behavior of a typical residential air conditioner load. A review of the model is presented. This model is then used to validate data from laboratory tests of air conditioners at Bonneville Power Administration. The results show that the model accurately captures the relations between voltage, frequency, active power, and reactive power. Furthermore, the model reproduces motor stall conditions, both the onset and severity of the stall. We expect that the use of this load model will improve our ability to anticipate voltage and transient stability problems in the power grid.

Transient Model of Air-Conditioner Compressor Single Phase Induction Motor

This paper describes an air-conditioner (A/C) compressor single phase induction motor (SPIM) model for use in an electro-magnetic transients (EMTs) simulation. The system of differential equations representing the SPIM model is developed and formulated. The angular position of the rotor shaft is retained in the electrical and mechanical equations of the model so that position dependence of the driven-load torque can be explicitly recognized. The equivalent circuit of the proposed model is represented as an interface to the external electric network in the EMTs simulator. Motor dynamic response to voltage dip at different points on the voltage waveform has been studied. The rationale of motor stalling is explored. Multiple aggregate units of the proposed model have been implemented on a distribution feeder to test and verify the motor dynamics in an EMTs simulation.

Converter Model for Representing Converter Interfaced Generation in Large Scale Grid Simulations

This paper addresses the positive sequence modeling of converter-based sources in commercial transient stability analysis software. A simple and computationally economical model of the converter has been developed while ensuring a reliable representation of the detailed converter behavior. This model has been implemented as a user defined model in commercial positive sequence software such as PSLF. The behavior of the proposed model in positive sequence has the same form as the behavior obtained from detailed point on wave simulation. Tests have been carried out on a three-generator nine-bus equivalent system and the 18,205 bus Western Electricity Coordinating Council system to assess the impact and performance of the converters. The behavior of these converter interfaced generation sources for various system contingencies has been investigated.

Transient stability analysis of an all converter interfaced generation WECC system

In this paper, a transient stability analysis of an 18205 bus Western Electricity Coordinating Council (WECC) system has been carried out when all conventional sources have been replaced with converter interfaced generation (CIG). In this 100% CIG system, the only rotating machines directly connected to the network are wound rotor induction generator wind turbines and induction motor loads. The inertia contribution of these rotating devices is small. With close to zero inertia in the system, the dynamic performance of the system under different contingencies is examined and discussed. The analysis conducted demonstrates that while such a futuristic system can survive certain contingencies, well designed coordinated wide-area converter control action may have to be incorporated to enhance the reliability of the system.

Transient model of air-conditioner compressor single phase induction motor

Summary form only given. This paper describes an air-conditioner (A/C) compressor single phase induction motor (SPIM) model for use in an electro-magnetic transients (EMTs) simulation. The system of differential equations representing the SPIM model is developed and formulated. The angular position of the rotor shaft is retained in the electrical and mechanical equations of the model so that position dependence of the driven-load torque can be explicitly recognized. The equivalent circuit of the proposed model is represented as an interface to the external electric network in the EMTs simulator. Motor dynamic response to voltage dip at different points on the voltage waveform has been studied. The rationale of motor stalling is explored. Multiple aggregate units of the proposed model have been implemented on a distribution feeder to test and verify the motor dynamics in an EMTs simulation.

Development of a linearized model of a pressurized water reactor generating station for power system dynamic simulations

A pressurized water reactor (PWR) nuclear power plant (NPP) model is introduced into Positive Sequence Load Flow (PSLF) software in order to evaluate the load-following capability of NPPs. The nuclear steam supply system (NSSS) consists of a reactor core, hot and cold legs, plenums, and a U-tube steam generator. The physical systems listed above are represented by mathematical models utilizing a state variable lumped parameter approach. A steady-state control program for the reactor, and simple turbine and governor models are also developed. Subsequently, the NSSS representation is incorporated into PSLF and coupled with built-in excitation system and generator models. Different simulation cases are run when sudden loss of generation occurs in a power system which includes hydroelectric and natural gas power plants besides the developed PWR NPP. The effect of the load-following operational mode on the key variables of the NSSS is observed.

Performance-Based Linearization Approach for Modeling Induction Motor Drive Loads in Dynamic Simulation

This paper describes a technique to model a vector-controlled induction motor drive in large-scale phasor-level dynamic simulation programs. The performance-based load model is implemented by obtaining the linearized power-voltage and power-frequency transfer functions from test data or from detailed electro-magnetic transient simulation used as a surrogate for test data. Voltage and frequency modulations are performed to obtain the amplitude and phase responses of the detailed vector-controlled drive model for a range of discrete frequencies. The prediction error minimization technique is utilized to generate best-fit analytical transfer function expressions. The electrical interface of the performance-based drive load model is developed to interact with the external system in positive-sequence dynamic simulation programs. The drive model is used to investigate the relative damping effects of drive-connected and direct-connected motors on system voltage and frequency oscillations.

Power quality requirements for electric vehicle chargers: Bulk power system perspective

End-use load composition is rapidly changing, particularly towards electronically-coupled or inverter-based load. In particularly, the proliferation of electric vehicles (EV) is expected to continue as consumer prices decrease and charging capability expands. The electric power grid has experienced disruptive technologies since its inception, and it is imperative to study potential future impacts in order to prepare for them if they do occur. This paper highlights fundamental load response of EV chargers, and proposes a set of requirements that are deemed “grid-friendly” to the overall stability and control of the bulk power system at the interconnection-level. Loads exhibiting at least constant current characteristic (constant impedance are very much desirable if possible) with ride-through and reconnection capability will ensure long-term reliability of the grid. The goal is to outline these grid-level requirements in an effort to collaborate with the manufacturing community for sustained grid support from the end-use loads.