Abstract

Power hardware-in-the-loop (PHIL) is increasingly being recognized as an effective real time emulation technique to mimic electrical dynamics of machines with the help of real time digital systems using real time simulator like Opal-RT, RTDS, D-space etc. In PHIL machine emulation, a power electronic converter or a linear amplifier emulates the behavior of electrical machines which are used in several applications such as Transportation, Aerospace / Military, Automotive, e-vehicle, Grid and motor Applications. Using these emulation techniques, various complex control algorithms or different configurations of controllers/drives for electrical machines can be tested, and also allows the testing of complex control strategies of an ac microgrid with critical industrial machines.
The emulation techniques can be used to represent new machine prototypes thus reducing the time to market of the complete drive system significantly. That is prior to the installation of a physical machine, testing of an electric drive or micro grid can be done with the help of a real time machine emulator. Therefore, if the drive controller fails, it will not jeopardize the life of a costly machine. Different loading profiles can be tested. In addition, a PHIL based machine emulation can be particularly useful to emulate faulted machine behavior. A machine undergoes wear and tear and may develop faults such as winding faults, bearing faults, or rotor eccentricity etc. If such machines are being emulated, their corresponding impact on the driving inverter, controller and power system can be studied without implementing these faults on a healthy motor. In fact, these emulation related research areas explore the feasibility of employing a real machine under such atypical conditions. Furthermore, machine emulation also provides an idea of detecting specific faults in advance.
The main research areas focused on this research are development of machine models of high accuracy, development of an emulator controller to attain dynamic current/voltage tracking capability and research in emulator configuration. Several atypical conditions are considered including short circuit faults, open circuit faults and switching faults. The mathematical models are developed considering the machine steady state and transient behavior under starting and different fault operating conditions of the machine. The emulator chosen is a linear amplifier, because of its high bandwidth and performance. However, in comparison to a low bandwidth switched power amplifiers, it also possesses maximum current limitations. The emulator control strategies consider the abnormal conditions to which the machine is exposed. Hence, the emulator in this research work can replace the real machine effectively. Also, this method of emulation can be applied to any machine such as permanent magnet synchronous machine, synchronous reluctance machine, wound rotor induction machine etc. Especially, when the machine is rated in the MW power range, the developed emulator can be used with scaled down parameters.
In this PhD work, the main components in the emulator test bench include a real time system, back-to-back converters or linear amplifiers, link filters, required sensors and the grid. The developed IM emulator test bench can be used for studying the performance of the grid or drive control system for various grid faults, drive faults and other severe transient conditions. To validate the designed machine emulator system and its control philosophy, results are taken with a real 5 hp machine under same transient conditions.
On the other hand, this PHIL technology is also employed for grid emulation. An interface algorithm in the power hardware in the loop determines the accuracy and stability of emulation. Conventionally, this PHIL setup uses the ideal-transformer-method (ITM) as an interface algorithm between the device-under-test (DUT) and the real-time grid simulation model. The closed-loop PHIL interface with the DUT is usually stabilized using low-pass filters in the feedback path. Such filters stabilize the closed-loop PHIL interface, but with compromised accuracy. To improve the accuracy of the PHIL interface, this research work presents a method to design an optimal feedback compensator. This method depends on the type of physical filter topology used for the device under test.
To summarize, this research work represents 1) different induction machine emulators for different conditions of the grid and drive converters. This includes grid faults and test drive faults. 2) A grid emulator is designed with PHIL technology to test balanced and unbalanced resistive loads, islanding and grid connected modes of a distributed energy source (DER). The results obtained from the analysis and simulation for machine emulation and grid emulation are validated experimentally.