ENHANCING THE PERFORMANCE OF PERMANENT MAGNET SYNCHRONOUS MOTOR WITH DAMPER WINDINGS

                                                                    

                                                                                       

 

Permanent magnet synchronous motor (PMSM) can be defined as a type of alternating current synchronous motor with a sinusoidal back EMF waveform and whose field excitation is produced by permanent magnets. However, it gets increasing importance in low cost drives applications such as pumps, fans and lots more applications in the range up to a few kilowatts. Also, PMSM are widely used in low and mid power applications such as computer peripheral equipments, robotics, adjustable speed drives and electric vehicles (Jaswant, et al 2001). The ever growing demand and wide application of PMSM drives has necessitated the development of simulation tools capable of analyzing the behavior of motor drive. The role of simulations in the development of cost effective and efficient motor drives cannot be overemphasized. These simulation tools can perform dynamic simulations of motor drives in a visual environment so as to give more detailed information on the motor performance, particularly before construction or development stage. Most (PMSMs) are designed to have permanent magnets mounted on the surface of the rotor. This makes the motor appear magnetically ‘‘round’’ and the motor torque is the result of the reactive force between the magnets on the rotor and the electromagnets of the stator (Nisha and Parvathi, 2016). Nevertheless, the PMSM are strongly non-linear systems (Rahman, et al., 1984). On the other hand, some PMSMs have magnets buried inside of the rotor frame. These motors are known as Interior Permanent Magnet (IPM) motors. Sequel to this, the radial flux generated is more concentrated at specific spatial angle than it is at others. This gives rise to an additional torque component known as reluctance torque which is affected by the change of motor inductance along the more concentrated and non-concentrated flux paths (Nisha and Parvathi, 2016).

The steady state modeling of PMSM has received considerable attention from several authors (Hosinger, 1980; Binns, et al., 1976). Compared to DC and induction motors, the PMSM has a lot of merits, especially high efficiency, high torque per volume and low moment of inertia (Okoro, 2004). The transient performance of PMSM has received less attention from researchers (Hosinger, 1980; Binns et al., 1976). This is mainly because of the non-linearity involved in the motor equations. 

It has been observed that PMSM usually have difficulties dealing with unstable loads, in worst case the load torque can go from 100% to 20% within seconds, stay at 20% for two seconds, and then back up to 100%. This load fluctuation can make PMSM to step out of the synchronous speed. Because PMSM are not intended to work outside synchronous speed, it may fail after the load variation.  

This effect has resulted to increase in cost and inefficiency in most PMSM. In this thesis, we will enhance the performance of this motor by adding damper windings to the rotor. Also, we will implement a simulation that includes all realistic components of a PMSM. However, this circuit will enable easy calculation of currents, voltages and losses in different parts of the motor under transient and steady state conditions. 

More so, a damper winding consists of several conducting bars on the field poles of synchronous motor, short circuited by conducting rings or plates at their ends, which is used in preventing pulsating variations of the position or magnitude of the magnetic field linking the poles. For every variation in load, the damper winding produces a torque to amend the effect of the load variation. Also, damper windings are capable of providing starting torque needed in self starting of synchronous motors. By adding damper windings in the rotor of a PMSM, "Hunting of motor" can be suppressed. Once there is a variation in load, excitation or variation of the motor, the rotor of the PMSM will oscillate to and fro about an equilibrium position. 

Often times, these oscillations may become too violent and causes loss of synchronism. The motor will then come to a halt

The two major problems of a Permanent Magnet Synchronous Motors are:

In this thesis, we will solve the above problems by introducing damper windings at the rotor of the Permanent Magnet Synchronous Motor. 

The main aim of the proposed research is to enhance the performance of PMSM with damper winding.

The objectives include:

In this research, we intend to show how damper windings help to enhance the performance of PMSM in dynamic state. The effect of damper winding on PMSM will be studied. The dynamic behaviors of the motor with and without damper windings, the dynamic behavior of the motor under different machine parameters and the effect of varying the saliency factor for PMSM without damper windings will also be studied.

Chapter Two presents a comprehensive survey of previous work on the study on the simulation of transient performance of PMSM with and without damper windings. The proposed Electrical and Mechanical simulation using a two-mass mechanical model is presented in Chapter Three. The determination of the dynamic behavior of the motor under varying parameters, the effect of varying the saliency factor for PMSM without damper windings and discussion of results of the proposed model are shown in Chapter Four. Conclusion and recommendations are summarized in Chapter Five.