3.4 Rotor Speed Calculation

The rotor speed can be calculated by using the observed rotor position value. The incremental change in the rotor position angle is used to calculate the speed in a moving average filter.

${\displaystyle {\theta }_e\left(n\right)=\frac{1}{{NT}_s}[\mathrm{\Delta }{\theta }_e\left(n\right)+\mathrm{\Delta }{\theta }_e(n-1)+\mathrm{....}+\mathrm{\Delta }{\theta }_e(n-N+1)]}$

Where:

N is the number of samples in a moving average filter, T_s is the sampling time, and ΔΘ_e is the incremental change in the electrical rotor position.

The calculated rotor speed is further filtered using a Low Pass Filter (LPF) with a cut-off frequency Θ_c to avoid unwanted disturbances which could affect the result. The LPF can be implemented in discrete time with a sampling time T_s as follows:

${\displaystyle {\theta }_{eFilt}\left(n\right)=(1-{\theta }_c{T}_s){\theta }_{eFilt}(n-1)+{\theta }_c{T}_s{\theta }_e\left(n\right)}$