F. Fleming

Synchronization of three-phase converters and virtual microgrid implementation utilizing the Power-Hardware-in-the-Loop concept

This paper addresses the timely issues of synchronization and application of three-phase power converters connected in parallel utilizing the Power-Hardware-in-the-Loop concept. Without proper synchronization, distinguishing the currents circulating between the converters are unclear. The paper centers on control methodology for achieving precise phase synchronization for equal load sharing, with minimum current circulation between the paralleled power converter modules, and robust dynamic system control under different transient conditions. One of the possible applications for the configuration presented in this paper is the conceptual virtual microgrid, which utilizes the reactive power compensation ability of the Static Synchronous Compensator (STATCOM). The microgrid behavior and load dynamics are simulated with a real-time digital simulator which generates appropriate control commands to a power electronics based voltage amplifier interfaced via a cascaded LC-LC type filter to a variable speed drive (VSD). This is necessary as reactive power control is a critical consideration in improving the power quality of power systems. To compensate for reactive power, the STATCOM controller will be developed and integrated into the proposed virtual microgrid system. This concept provides a solution for de-risking these costs as it utilizes the PHIL concept in conjunction with high-fidelity microgrid model and detailed load dynamics. Selected experimental results on two, 25-kVA and 15-kVA, converters in parallel are presented.

An Induction Machine Emulator for High-Power Applications Utilizing Advanced Simulation Tools With Graphical User Interfaces

In this paper, a method is presented for removing the risk associated with the testing and development of novel drive system topologies, prototype electrical machines, advanced control system strategies, or a combination of the aforementioned without using any real motors/generators. The test platforms for low-power machines are relatively inexpensive and accessible; however, as power levels increase into the upper kilowatt and megawatt range, validation of prototype machines and drives becomes costly. The proposed induction machine emulator (IME) platform utilizes the power hardware-in-the-loop concept in conjunction with a high-fidelity machine model and load dynamics. The electrical machine and its load dynamics are simulated with a real-time digital simulator, which generates appropriate control commands to a power electronics-based voltage amplifier that interfaces to a variable speed drive (VSD). Specifically, the current draw is recreated by altering the phase and magnitude of a voltage amplifier connected to a VSD under test via a unique transformer-based LCL-type coupling network. Based on the proposed concept, the use of a multiwinding, tap-changing transformer establishes a truly versatile and universal test platform for a wide range of power levels. In addition, this paper presents a control strategy in the synchronously rotating reference frame in dq coordinates for the power electronic converters in IME operation. Experimental results at the 25-kVA power level validate the feasibility and highly dynamic performance of the proposed test platform.

Power semiconductor loss evaluation in voltage source IGBT converters for three-phase Induction Motor drives

This paper addresses the timely issues of power loss calculation methods in the most common voltage source three phase PWM converters (VSC). There are mainly two kinds of power semiconductor losses to be considered, the conduction losses and the switching losses. A reconfigurable Induction Motor (IM) drive is controlled by the conventional PWM and space vector PWM based methods. The power losses will be evaluated with the different control strategies and verified based on the test-bed using a control system rapid prototyping environment such as dSPACE.

Real-Time Emulation of Switched Reluctance Machines via Magnetic Equivalent Circuits

This work proposes to develop a novel real-time (RT) magnetic equivalent-circuit machine model, for providing accurate electromagnetic (EM) device characteristics in a time frame acceptable for RT applications. Utilizing this model with the Hardware-in-the-Loop (HIL) concept enables a wide variety of useful applications. HIL concept requires accurate, RT models to emulate the characteristics of the modeled system, thus the proposed method provides a larger range of observable dynamics for large-scale simulations, controller tests, or hardware emulations. The proposed model is implemented for a switched reluctance machine (SRM) on a field-programmable gate array (FPGA). Finite-element analysis (FEA), lumped parameter modeling, and an experimental test bed serve to benchmark the modeling accuracy and RT applicability under static, dynamic, and controlled test conditions.

Application of a maximum torque per ampere control strategy for DSRM drives

Discrete-switched reluctance machine (DSRM) drives represent a new class of reluctance machine in which stator phases are magnetically independent of each other. This machine type is very suitable for in-wheel propulsion applications such as those in the automotive area. Due to the absence of mutual coupling between windings there are many possible control strategies that may be employed for control, and that furthermore may be simplified in nature with respect of conventional machine topologies. This work presents a maximum torque per ampere control strategy that seeks to minimize the rms phase current at all angles for a given torque, thus providing the basis for an efficient machine. This work will be specifically applied to a 5-phase DSRM.

Power Hardware-in-the-Loop Testing of an Air Coil Superconducting Fault Current Limiter Demonstrator

This paper discusses power hardware-in-the-loop (PHIL) tests performed at the Center for Advanced Power Systems (CAPS) with a 60-kVA, 400-V, z= 6

Impact of modifying the stator tooth tip on electromagnetic torque production for an 8/6 switched reluctance machine

% air coil (AC) superconducting fault current limiter (AC-SFCL) demonstrator. The demonstrator was designed, built, and successfully tested for fault current limitation at Karlsruhe Institute of Technology (KIT) . Initial PHIL testing at CAPS focused on a single-phase setup to verify the results obtained at KIT. Subsequent PHIL testing in a three-phase system was accomplished by interfacing the physical AC-SFCL to the simulated system in phase A and simulating the effect of AC-SFCL devices in the other two phases. This was done by estimating the resistance and inductance of the AC-SFCL through instantaneous voltage and current measurements and inserting this impedance in phases B and C for cases in which these phases were part of the short-circuit path. For these PHIL experiments, the modified damping impedance (DIM) interface algorithm was employed. It was possible to reproduce earlier reference measurements using the modified DIM PHIL interface algorithm. The PHIL system was then used to create a three-phase power system consisting of a generator, a load, and a short-circuit path. Symmetrical and unsymmetrical short circuits have been performed with and without ground connection. The PHIL system maintained stability throughout the experiments, and the results show suitable current limitation for all performed types of short circuits.

Implementation of a virtual induction machine test bed utilizing the power hardware-in-the-loop concept

Switched reluctance machines (SRM) offer unique operational characteristics when compared to other electrical machines. For instance, SRMs tend to have higher fault tolerance when compared to the industrial standard, pulse width modulation driven induction machines, due to their phase winding isolation. Furthermore, they may remain in a locked rotor position safely without concern of faulting and have higher speeds than many other electrical machines. SRM still only have niche applications due to requiring higher currents, producing more acoustic noise and torque ripple, and needing for more advanced controls for effective operation. Such constraints contribute to the reduced commercial and industrial popularity when compared to other electrical machines and have limited the full potential of SRM from being exploited. This paper describes the impact on the electromagnetic torque production of an 8/6 switched reluctance machine when increasing and decreasing the stator pole arc at the tip. Such a technique of increasing the stator pole arc can provide torque shaping, furthermore, there is a significant improvement in the torque ripple of the machine. We focus on the qualitative analysis of the results from magnetic equivalent circuit of the SRM with modification of stator pole arc without pole tapering. Finite element analysis (FEA) with commercially available software is utilized to support our results.

Development and implementation of a 25 kW virtual induction machine test bed utilizing the power-hardware-in-the-loop concept

In this paper, a method for removing the risk associated with the testing and development of novel drive system topologies, prototype electric machines, advanced control system strategies, or a combination of the aforementioned without using any real motors/generators is presented. For low power machines, the test platforms are relatively inexpensive and accessible, however, as power levels increase into the upper kilowatt and megawatt range, validation of prototype machines and drives becomes costly. The proposed virtual machine (VM) test platform utilizes the power hardware-in-the-loop concept in conjunction with high-fidelity machine model and load dynamics. The electric machine and load dynamics are simulated with a real-time digital simulator, which generates appropriate control commands to a power electronics-based voltage amplifier that interfaces to a variable speed drive (VSD). Specifically, the current draw is recreated via altering the phase and magnitude of a voltage amplifier parallel connected to a VSD under test via a unique transformer-based LCL-type coupling network. Based on the proposed concept, use of a multi-winding, tap-changing transformer establishes a truly versatile and universal test bed in a wide range of power levels. In addition, this paper presents a novel control strategy in the synchronously rotating reference frame in dq-coordinates for parallel connected power electronic converters in VM operation. Experimental results at the kVA-power level validate the feasibility and highly dynamic performance of the proposed test platform.

Influence of DC-link fluctuations on three-phase induction motor drives

Experimental validation of motor drives to ensure appropriate efficiency and performance is essential to such sectors as: industrial; aerospace, naval and land propulsion devices; and utilities. For low power machines, this is typically a non-issue since test beds are relatively inexpensive and accessible. However, as power levels increase into the upper kilowatt and megawatt range, validation of prototype machines and drives becomes costly. These costs are primarily: materials, transportation, and test site development and operation. The Virtual Machine (VM) concept provides a solution for de-risking these costs by utilizing the power-hardware-in-the-loop (PHIL) concept in conjunction with high-fidelity machine models and detailed load dynamics. The VM and load dynamics are simulated with a real-time digital simulator which generates appropriate control commands to a power electronics based voltage amplifier that interfaces via a cascaded LC-LC type filter to a variable speed drive (VSD). The controlled voltage amplifier, in conjunction with the LC-LC type filter, acts as a current sink to the VSD. Provided the voltage amplifier has sufficient bandwidth, the VM will closely represent the terminal characteristics of a real machine and load, with respect to the VSD. This paper addresses the establishment of a 25 kW virtual machine test bed and associated issues.