Mehrdad Chapariha

Constant-Parameter

Transient simulation programs, either nodal analysis-based electromagnetic transient program (EMTP-like) or state-variable-based, are used very extensively for modeling and simulation of various power and energy systems with electrical machines. It has been shown in the literature that the method of interfacing machine models with the external electrical network plays an important role in numerical accuracy and computational performance of the overall simulation. This paper considers the state-variable-based simulation packages, and provides a constant-parameter decoupled RL-branch equivalent circuit for interfacing the ac induction and synchronous machine models with the external electrical network. The proposed interfacing circuit is based on the voltage-behind-reactance formulation which has been shown to have advantageous properties. For the synchronous machines, this paper describes both implicit and explicit (approximate) interfacing methods. The presented case studies demonstrate the advantages of using the proposed interfacing method over the traditional -models that are conventionally used in many simulation packages.

RL

Interfacing of ac electrical machine models in power system transient simulation programs is receiving increasing attention in the literature. Models based on the voltage-behind-reactance (VBR) formulation have been recently proposed to achieve a direct interface with external power networks. However, the rotor-position-dependent interfacing inductances due to dynamic saliency in synchronous machine models increase the computational cost of the overall system solution and limit the application of most VBR formulations. This paper presents new methods for elimination of dynamic saliency using continuous- and discrete-time approximation techniques to achieve explicit formulations. The proposed models have simple interfacing circuit consisting of decoupled constant-parameter RL branches. The new models are implemented in MATLAB/Simulink and the PLECS toolbox, and are shown to offer simple and easy-to-use interface, high accuracy, and numerical efficiency as compared to the existing models. The proposed models can find wide application in common state-variable-based transient simulation programs.

-Branch Equivalent Circuit for Interfacing AC Machine Models in State-Variable-Based Simulation Packages

Interfacing of electrical machine models with ac power networks has a significant impact on numerical accuracy and efficiency in state-variable-based transient simulation programs. This paper continues the recent work in this area by proposing a new explicit constant-parameter voltage-behind-reactance (VBR) induction machine model that includes main flux saturation and allows a direct interface to any external network. The proposed model uses numerical approximations to achieve a decoupled interfacing circuit with constant RL branches that is easy to use in many simulation programs. Computer studies demonstrate that the proposed model provides high numerical accuracy for machines with a diverse range of parameters, even at fairly large integration step sizes.

Explicit Formulations for Constant-Parameter Voltage-Behind-Reactance Interfacing of Synchronous Machine Models

Brushless permanent magnet (BLPM) motor drives based on Hall sensors have received extensive attention in the literature and are widely used in many applications. However, most of the available and published controllers assume that the Hall signals are always available, which is not true if any of the sensors are faulted. In this paper, several fault-tolerant control schemes for BLPM motor drives are proposed. The methodology is based on fault diagnosis and its classification, and subsequent signal reconstruction. Simulation and experimental results demonstrate the effectiveness and advantages of the proposed fault-tolerant schemes in restoring the motor operation when failures occur in up to two Hall sensors. The proposed fault-tolerant schemes can be easily and flexibly realized for conventional drive systems, either by adding the code in the existing driver or by adding a simple auxiliary circuit between the Hall sensors and the driver.

Constant-Parameter Voltage-Behind-Reactance Induction Machine Model Including Main Flux Saturation

The stability of vehicles under certain driving conditions is improved by forcing the wheels to turn at the same speed regardless of the available traction under individual wheels. For conventional vehicles this can be achieved by locking the mechanical differential system. This paper proposes an innovative approach for locking the electrical differential system (EDS) of electric vehicles (EV) with independent brushless DC (BLDC) machine-based wheel drives. The proposed method locks the active wheels of the vehicle as if they were operating on a common shaft. The locking algorithm is implemented by processing the Hall sensor signals of the considered motors and driving them with a single set of “averaged” Hall signals, thereby operating the motors at the same speed and angle. A detailed switch-level model of the EDS embedded with the proposed sync-lock control (SLC) along with the BLDC propulsion motors has been developed and compared against the measurements for the considered BLDC propulsion motors. The proposed technique is shown to achieve better results compared to a conventional speed control loop as the considered motors are locked directly through the corresponding magnetic fields.

Fault Diagnosis and Signal Reconstruction of Hall Sensors in Brushless Permanent Magnet Motor Drives

Recently, the concepts of dynamic phasors and shifted-frequency analysis (SFA) have received renewed attention as a possible solution framework for the modeling of power system components and transients, as opposed to using instantaneous time-domain variables or conventional phasors. In this paper, a new voltage-behind-reactance (VBR) synchronous machine model based on SFA is presented. Using dynamic phasors, the proposed model permits the use of a much larger range of step sizes to efficiently simulate electromagnetic and electromechanical transients. Moreover, the proposed model has a constant-parameter (CP) stator interface, which is simple to implement and numerically more efficient compared with the prior state-of-the-art models with rotor-position-dependent stator inductance matrices. Rigorous transient case studies demonstrate that the new model requires significantly fewer time steps than the conventional time-domain models, and is more efficient than the previously established variable-parameter SFA model.

Locking electric differential for brushless DC machine-based electric vehicle with independent wheel drives

A new state-space constant-parameter voltage-behind-reactance synchronous machine model has recently been proposed. Several efficient explicit formulations were derived using continuous- and discrete-time approximations. This letter complements the previous publication and presents a simple and flexible procedure for selecting the parameters of the continuous-time filters. A case study is included to demonstrate the proposed procedure.

A Constant-Parameter Voltage-Behind-Reactance Synchronous Machine Model Based on Shifted-Frequency Analysis

This paper presents a hardware implementation of the previously introduced locking Electric Differential System (EDS) of Electric Vehicle (EV) with two independent Brushless DC (BLDC) machine-based drives. The proposed method locks the active wheels of the vehicle as if they were operating on a common shaft. The locking algorithm is realized by processing the Hall sensor signals of the considered motors and driving them with a single set of “averaged” Hall signals. The proposed Sync-Lock Controller (SLC) is implemented digitally using a programmable integrated circuit microcontroller. First, the Hall signals undergo a layer of filtering to mitigate the errors due to hall sensor misalignment. Then, the locking algorithm is implemented by averaging the filtered Hall sensor signals. The proposed technique locks the motors directly through their corresponding magnetic fields and is shown to achieve better results as compared to a conventional speed control loop. The SLC prototype is implemented in the form of a standalone dongle-circuit that can be easily placed between the original Hall-sensors and the BLDC motor driver.

Pole Selection Procedure for Explicit Constant-Parameter Synchronous Machine Models

Representation of synchronous machines using constant-parameter voltage-behind-reactance (VBR) formulations improves accuracy and numerical efficiency of power systems transient simulation programs. This paper extends the VBR representation to the rotor circuit and presents two new formulations that achieve direct constant-parameter interfacing of the rotor and stator terminals with arbitrary external networks. In the first model, the entire machine is represented by constant RL branches that have algebraic coupling among the circuit variables. In the second model, all damper windings are implemented in state-space form to increase the numerical efficiency, while the stator and field windings are provided as constant-parameter circuits. The proposed models are validated against the commonly used and some state-of-the-art alternative models using a single machine with a simplified ac excitation system. Computer studies demonstrate the improved accuracy and efficiency of the proposed models when external rotor circuitry is considered.

Hall sensor-based Locking Electric Differential System for BLDC motor driven electric vehicles

This paper presents the implementation of a constant-parameter voltage-behind-reactance (CP-VBR) synchronous machines model that can be directly interfaced in most state-variable-based transient simulation programs. The stator is interfaced using constant and decoupled RL branches, and the rotor equations are expressed in state-space form to facilitate their implementation. The proposed model accommodates salient or round rotor machines, and its implementation is shown in three popular MATLAB/Simulink toolboxes: SimPowerSystems, ASMG, and PLECS. The presented studies compare the efficiency and accuracy of the CP-VBR models with the classical qd0 model. It is demonstrated that the CP-VBR models are faster, have higher accuracy, and are easy to implement. Additionally, the limitations of each toolbox for the simulation of different scenarios are discussed. It is also noted that the built-in toolbox models do not include zero-sequence, which may limit their application and make them invalid for some studies.