Self-Commissioning of AC Motor Drives

In modern motion control and power conversion applications, the use of inverter-fed electrical machines is fast growing with continuous development in the field of power electronics and drives. The Variable Voltage Variable Frequency (VVVF) supply for electrical machines gives superior performance in terms of speed control, efficiency and dynamics compared to the machines operated directly from the mains. In one of the most basic configurations, a drive system consists of a closed loop speed control that has a current controller inside the loop. For effective and stable current control, the controller gains need to be set according to the parameters of the machine at hand. Besides, accurate parameter information is helpful in ensuring better machine exploitation as well as maintaining higher efficiency in various operating modes and conditions. The traditional methods of determining machine parameters consist of extensive machine testing under prescribed supply and ambient conditions. These methods become impracticable when the machine cannot be isolated from its load or the test equipment cannot be made available. Under such conditions, the alternatives are needed that use only the available hardware included in a standard drive to completely define the machine parameters. Self-commissioning thus comes into play in such situations. The automatic determination of machine electrical parameters before the drive is put in continuous operation is called self-commissioning of the drive system. In this thesis, self-commissioning of AC electric motors is studied, analyzed and results are presented for the implementation of different self-commissioning methods either proposed in the literature or developed in the course of this research. By far the commonest control strategy of AC machines is the vector control that allows dc machine like decoupled control of machine flux and torque. The separation of flux and torque producing current components depends heavily on the parameters of the machine at hand. In case the parameters fed to the controller do not match the actual machine parameters, the control performance deteriorates both in terms of accuracy and efficiency. For synchronous machines using permanent magnets, the magnetic model of the machine is important both for flux estimation accuracy at low speeds and for deriving maximum torque out of machine per ampere of input stator current. The identification of the magnetic model of permanent magnet synchronous machines requires special tests in a laboratory environment by loading the machine. A number of machine parameter identification methods have been studied in the past and proposed in the literature. As the power amplifier implied is almost always an inverter, the estimation of machine parameters at start-up by generating special test signals through the inverter have been researched in depth and are investigated in this thesis. These techniques are termed as offline parameter identification strategies. Other methods that focus on parameter updating during routine machine operation are called online parameter estimation methods. In this thesis, only the offline identification schemes are studied and explored further. With continuous improvements in power semiconductor devices' switching speeds and more powerful microprocessors being used for the control of electric drives, generating a host of test signals has been made possible. Analysing the machine response to the injected test signals using enhanced computational power onboard is relatively easier. These conditions favour the use of even more complex test strategies and algorithms for self-commissioning and to reduce the time required for conducting these tests. Moreover, the universal design of electric drives renders the self commissioning algorithms easily adaptable for different machine types used in industry. Among a number of AC machines available on the market, the most widely used in industrial drives are considered for study here. These include AC induction and permanent magnet synchronous machines. Induction machines still play a major part in industrial processes due, largely, to their ruggedness and maintenance-freeness; however, the permanent magnet machines are fast replacing them as competitive alternatives because of their low volume-to-power, weight-to-power ratios and higher efficiency. Their relatively light weight makes these machines a preferred choice in traction and propeller applications over their asynchronous counterpart

High dynamic performance power quality conditioner for AC microgrids

This paper deals with power quality problems encountered in weak AC microgrids and solutions for mitigation. A power electronic converter can be used as an effective power quality conditioner to compensate non-idealities in currents drawn from the grid. A power quality conditioner consisting of three power converters connected to a common DC link is analysed. One of these converters acts as an active power filter for removing unwanted harmonics in grid currents feeding a non-linear load. The other two converters instead remove the harmonics from the voltage at the terminals of a sensitive load. The control of the shunt converter is designed to be fast enough for power quality servicing but also has a fast disturbance rejection capability. Simulation and experimental results validating the concept are provided along with obtained total harmonic distortion improvements

A New Position and Speed Estimation Scheme for Position Control of PMSM Drives Using Low-Resolution Position Sensors

A new position control method for permanent magnet synchronous motor (PMSM) drive with a low-resolution encoder is proposed in this paper. Three binary Hall position sensors are utilized to realize a moderate-performance position control system for the consideration of economy and simplicity in servo application. Compared with sensorless control, the usage of binary Hall position sensors is a guarantee of both control performance and low cost. However, the low resolution of the Hall sensor will heavily deteriorate the accuracy of the position and speed calculation. Such drawback can be effectively minimized by using appropriate position and speed estimation schemes. With the help of polynomial fitting and state observer techniques, a solution is provided to realize semi-closed loop control by treating the position and speed estimators as separate systems. The performance can be improved (1) by proposing a polynomial fitting scheme with least squares method, high-resolution rotor-position predictor can be derived by fitting the predefined position data from binary Hall position sensors in a linear or quadratic manner; (2) by adopting the dual-sampling-rate observer, instantaneous speed can be estimated at each control cycle and the estimation error is corrected once a new measurement form the Hall arrives. Furthermore, a nonlinear position control algorithm is introduced to increase standstill stability. Extensive experimental results are given to demonstrate the feasibility of the proposed method and its superiority over conventional methods

Novel Permanent Magnet Synchronous Motor with Integrated Filter Inductor Using Motor's Inherent Magnetics

A close functional and structural integration of passive elements is required to improve the power density of motor drives. Such power dense motor drives are prerequisite in aerospace and automotive applications. This paper presents a permanent magnet motor with integrated filter inductor, which not only eliminates inductor losses but also removes its associated weight and volume. The motor with integrated filter uses motor's inherent magnetics in order to use it as a filter inductance instead of adopting an external inductor option, which is traditionally placed outside the motor. A vector-controlled model, taking modulation and switching effect into account, has been developed by using MATLAB/Simulink tool. To experimentally validate the concept of the motor with integrated filter inductor, the winding connections of an existing motor are modified. The comparative analysis, between the traditional and integrated motor drive systems, is carried out in terms of magnitude of switching component, total system losses, weight and volume. The total losses in the motor with integrated filter are reduced by 34.2% at 2100rpm and 3Nm load, when compared to the motor with traditional filter inductor, whereas, its weight and volume in the motor with integrated filter inductor is eliminated completely

Theoretical analysis of the synchronous reactance influence on the speed regulation of PM motors

The paper summarizes the basic theoretical aspects concerning the speed regulation of surface mounted permanent magnet synchronous motors. In particular, the influence of the synchronous inductance is articulated considering the limitations imposed by the supply (maximum voltage and current) and the constraints for a specific variable-speed application. The study is conventionally approached, using the well-known single-phase equivalent circuit and the related steady-state vector diagrams. The involved key machine parameters are then discussed in term of sizing equations in order to predict the speed regulation capability since the initial el ectromagnetic design stage

Novel Motor-Shaped Rotational Inductor for Motor Drive Applications

This paper presents a validation of the novel motor-shaped rotational inductor. To validate the concept, 12 slots 2 poles rotational inductor is tested at different supply frequencies and rotor speeds. Experimental results have shown that the iron losses reduce as the rotor speed increases to the synchronous speed of the stator supply. The performance of the integrated rotational inductor is also compared with traditional EE core inductor in terms of total losses, synchronous inductance, copper resistance, and total harmonic distortion (THD). The total loss-to inductance ratio of the rotational inductor is reduced by 22.5% when rotor is rotating at 18 kRPM and supply frequency is held at 300 Hz. A significant reduction in copper resistance-to-inductance is also noticed when supply frequency is varied from 0 Hz to 20 kHz. Furthermore, the synchronous inductance and voltage and current's %THD of rotational inductor is found to be superior to EE core inductor

Parameter identification and self-commissioning of AC permanent magnet machines - A review

Parameter identification of permanent magnet synchronous machines is a topic of utmost interest these days. The growing effort and investment in this field of research is largely due to the ever-expanding market share of these machines. The high-performance and efficient control of the drive depends on the accuracy with which the information about the machine connected to its terminals is available. The available identification methods are surveyed here and they are classified into offline and online strategies. Self-commissioning, in principle, is a subset of offline methods, yet it is treated separately for its importance in modern adjustable speed drives that tend to minimize the user intervention. Fully exploiting the power electronic converter and the computational power on-board a modern drive, the self-commissioning feature can be embedded in the start-up routine of the drive to estimate the parameters of the machine at hand. This paper presents a review of the parameter identification techniques and schemes investigated over the past few decade

Induction Motor Magnetizing Characteristic Identification at Standstill with Single-Phase Tests Conducted Through the Inverter

In this paper, a magnetizing characteristic identification method for an induction machine at standstill is proposed. The technique is based on machine testing with a single-phase ac supply generated through a standard inverter. This type of test strategy is available in the literature, however, it has been used for parameter identification at a single current level thus ignoring the effects of magnetic saturation. To reproduce accurately the magnetizing curve, the test current level must be varied in order to trace the entire curve. The method presented here takes care of the magnetic saturation and estimates the magnetizing curve for complete current range of the machine. The proposed scheme does not require any external supply, measurement or data acquisition system and works at standstill thus avoiding the need to isolate the machine from its load or to block the rotor. This strategy is suitable for self-commissioning of induction motor drives and for sensorless control applications as well

Self-commissioning of interior permanent magnet synchronous motor drives with high-frequency current injection

The knowledge of electrical and mechanical parameters of high-performance electromechanical drive systems is of paramount importance for designing high-performance controllers and/or developing accurate simulation models. By high-performance control is meant least torque (position) ripple for torque (position) control. Machine parameters are typically load and temperature dependent. This makes their estimation a challenging task. In this paper, a simple and robust method for parameter estimation at rotor standstill is presented. The estimated parameters are stator resistance through dc test, dq inductances using high-frequency injection and permanent magnet flux by means of a closed-loop speed control maintaining rotor stationary. The proposed method does not require either locking the rotor or additional/special power supplies. The validity of the suggested method has been verified by implementation on Interior Permanent Magnet Synchronous Motors (IPMSMs). Finally, the estimated parameters have been compared against results obtained through finite element simulations and with machine magnetic characterization, separately performed, to validate the method's effectiveness. Saturation and cross-saturation effects are taken care of through amplitude modulation and cross-axis current application, respectivel