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from the commutator, and overall reduction of electromagnetic interference (EMI). The maximum power that can be applied to a BLDC motor is exceptionally high, limited almost exclusively by heat, which can damage the magnets. BLDCs main disadvantage is higher cost, which arises from two issues. First, BLDC motors reąuire complex electronic speed controllers to run. Brushed DC motors can be regulated by a comparatively trivial variable resistor (potentiometer or rheostat), which is inefficient but also satisfactory for cost-sensitive applications. Second, many practical uses have not been well developed in the commercial sector

a)

b)

STATOR

(LAMINATED)

4-POLE PM ROTOR

Rotor

Permanent

magnets

Concentrating

winding

Fig.2.2. Crossection of the three phase BL DC motors. a) distributed winding construction. b) concentrating winding construction

BLDC motors are considered to be morę efficient than brushed DC motors. This means that for the same input power, a BLDC motor will convert morę electrical power into mechanical power than a brushed motor, mostly due to the absence of friction of brushes. The enhanced efficiency is greatest in the no-load and low-load region of the motor's performance curve. Under high mechanical loads, BLDC motors and high-quality brushed motors are comparable in efficiency.

2.1. IDEAŁ BRUSHLESS DC MOTOR WAYEFORMS

Let us suppose that the PM produces a rectangular air gap flux distribution over cą>m = % (180°) (figurę 2.3.a). Generally the surface PM extends over an angle apM less than 180° (which represent the pole pitch, Fig.2.2). The stator phase mmf is supposed to be rectangular, a case corresponding to q = 1 (three slots per pole). Consequently the PM flux linkage in the stator winding i#>m(0) varies linearly with rotor position (Fig.2.3b). Finally the phase emf E_a is rectangular with respect to rotor position (Fig.2.3c).

UNIA EUROPEJSKA

EUROPEJSKI FUNDUSZ SPOŁECZNY

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