4.3.2.1. Improvement additional resistance voltage feeding

One way to improve engine response with fixed voltage feed is to increase the supply voltage, which causes the current establishment to occur more quickly. But it has to provide an external resistor to limit the current flowing through the motor windings to the rated current value.

Figure 4.29. Unipolar constant voltage control with additional resistance.

Analytically, the value of the external resistance Re has a proportional relationship to the supply voltage.

(4.6)

Now the time of establishment and cutting will be affected by the expression:

(4.7)

Although you get an improvement in engine response working at high speed, a better flow of current to these relations of steps. The drawbacks are obvious, the incorporation of resistance to the current working face, causing a loss of power in this, especially at rest or in a regime of low passes. Which leads to a significant decline in performance on the circuit.

For example, if the winding resistance of a 4-phase motor is 1.5Ω, the rated current is 4A and the set voltage is 24V. The resistance must be added to achieve the maximum current is 4.5Ω for each phase. The power dissipated is approximately 4.5 * 42 = 72W in the activation sequence of an active phase. This power is doubled when the activation sequence is two active phases.