2.6. Adjustment of the active and reactive power

With the help of power converters, it is possible to adjust the phase displacement φ between the voltage and the current (Figure 2.65), in addition to the frequency and the amplitude of the alternative waves.

Figure 2.65. Phase displacement φ between the voltage and current

ch2-fig2.65.gif

Active and reactive powers depend on this phase displacement. It is thus possible to adjust them by controlling the latter. Their expressions in single-phase are as follows:

[2.15a] images

[2.15b] images

In three-phase: they take the following forms depending on whether we are considering the phase to ground voltages V (of the phase) or the phase-to-phase (of the line) voltages U:

[2.16a] images

[2.16b] images

A third power, called the apparent power, is defined by the relationship:

[2.17] images

We thus define the power triangle, linking P, Q, S and φ (Figure 2.66).

Figure 2.66. Power triangle

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