Determining Efficiency of Brushless Permanent Magnet DC Motor Using Magnetic Circuit Simulation

Abstract

This paper investigates the efficiency of two categories of the fourpole brushless permanent magnet (BLPM) DC motor based on the
position of the permanent magnet using magnetic circuit simulation.
Finite element analysis (FEA) of the two motors was presented to
determine the static and transient characteristics. The performance
characteristics of both motors were given in a comparative form.
Magnetic properties of the motor such as magnetic flux density, flux
lines, air gap flux density were studied. The maximum magnetic flux
density and flux lines in motor 1 (pole type 1) were 1.7811 T and
1.5476x10-2 Wb/m respectively. While that of motor 2 (pole type 2)
were 1.8294 T and 1.6925x10-2 Wb/m respectively. Also, efficiency
determination of the motors were performed in which pole type 2
attained maximum efficiency of 93.7% at a speed of 1302 rpm while
pole type 1 recorded an efficiency of 82.4% at the same speed.
Therefore, there was an efficiency improvement of 11.3% by pole
type 2. The maximum power output of pole type 1 and pole type 2
were recorded to be 2.21 kW and 2.47 kW respectively at
corresponding speeds of 600 rpm and 780 rpm. Again, it is clear that
more power output was given out by motor 2. In order to compare
the dynamic behaviors of the two types of the motor during
operation; the motor was monitored for a period of 20 ms with time
step of 5ms. Both the torque and current characteristics of the pole
type 2 recorded an improvement of 47.1% and 50.4% respectively.
From the results, the preference to use the motor with pole type 2 has
been highlighted. It shows that the motor can offer robust structure
with high mechanical strength. It is also suitable for the applications
demanding enhanced performance with relatively high speed.