The major advantages of BLDC motor includes the following:
• High efficiency: BLDC motors are the most efficient of all electric motors. This is due to the use of PMs for the excitation, which consume no power. The absence of mechanical commutator and brushes means low mechanical friction losses and therefore higher efficiency.
high operation efficiency. These prominent advantages are quite attractive for
their application in EVs and HEVs. Of the family of PM motors, the BLDC motor drive is the most promising candidate for EV and HEV applications.4
Electric Propulsion Systems
201
a
b
c Va Vb
Vc ia, i*a
ib, i*b
ic, ic*
0
1/2p
p
3/2p
2p
FIGURE 6.41 Current-controlled voltage source inverter (5% tolerance bandwidth).
• Low maintenance, great longevity, and reliability: The absence of brushes and mechanical commutators suppresses the need for associated regular maintenance and suppresses the risk of failure associated with these elements. The longevity is therefore only a function of the winding insulation, bearings, and magnet life-length.
6.3 Permanent Magnetic BLDC Motor Drives
By using high-energy PMs as the field excitation mechanism, a PM motor drive can be potentially designed with high power density, high speed, and
• Ease of control: The BLDC motor can be controlled as easily as a DC motor because the control variables are easily accessible and constant throughout the operation of the motor.
• Ease of cooling: There is no current circulation in the rotor. Therefore, the rotor of a BLDC motor does not heat up. The only heat production is on the stator, which is easier to cool than the rotor because it is static and on the periphery of the motor.
200
Modern Electric, Hybrid Electric, and Fuel Cell Vehicles
a 1–
0
Dia
–h/2
h/2
FIGURE 6.39 Input–output characteristics of a hysteresis current controller.
• Compactness: The recent introduction of high-energy density magnets (rare-earth magnets) has allowed achieving very high flux densities in the BLDC motor. This allows achieving accordingly high torques, which in turns allows making the motor small and light.
a
b
c Va
Vb
Vc ia, i*a
ib, i*b
ic, i*c
0
1/2p
p
3/2p
2p
FIGURE 6.40 Current-controlled voltage source inverter (10% tolerance bandwidth).
6.40 and 6.41, in which the switching variables, line-to-neutral voltages, and currents for an inverter supplying a resistive-plus-inductive load are at values of h = 10 and 5% of the amplitude of the reference current, respectively. In practice, the tolerance bandwidth should be set to a value that represents an optimal trade-off between the quality of the currents and the efficiency of the inverter.