Position Compensation

Compensate for position offset due to different types of delays

Since R2022b

• 

Libraries:
Motor Control Blockset / Signal Management

Description

The Position Compensation block compensates for position offset due to different types of delays in a system.

Motor control algorithms can introduce offsets in the computed position because of different algorithmic entities such as delays and filters. These offsets affect accuracy in motor control algorithms such as the field-oriented control (FOC) and direct-torque control (DTC). You can use this block to compensate for the offsets in the motor control algorithms.

The block uses the following computations for a sample delay compensation.

$$\text{Offset introduced by delay }=\text{ Applied compensation }=\left(-\text{ Sample time}\right)\times \left(\text{Number of delay}\right)\times \left(\text{angular velocity}\right)\text{ radians}$$

The block uses the following computations for a first-order Butterworth highpass and lowpass filter compensation.

• For a highpass filter:

  $$Phaseoffset=\frac{\pi }{2}-\arctan \left(\frac{{\omega }_{speed}}{{\omega }_{cutoff}}\right)=\arctan \left(\frac{{\omega }_{cutoff}}{{\omega }_{speed}}\right)$$

  $$Phasecompensation=-\arctan \left(\frac{{\omega }_{cutoff}}{{\omega }_{speed}}\right)$$

• For lowpass filter:

  $$Phaseoffset=-\arctan \left(\frac{{\omega }_{speed}}{{\omega }_{cutoff}}\right)$$

  $$Phasecompensation=\arctan \left(\frac{{\omega }_{speed}}{{\omega }_{cutoff}}\right)$$

Ports

Input

θ_in — Position input value

scalar

Position input value that needs offset correction. This port supports the following range of values:

• -2π to +2π radians

• 0 to 1 per-unit

• -360 to +360 degrees

Data Types: single | double | fixed point

ϕ — Position offset

scalar

Externally computed position offset value. This value must have same unit as that of θ_in input. This port supports the following range of values:

• -2π to +2π radians

• 0 to 1 per-unit

• -360 to +360 degrees

Dependencies

To enable this port, set Nature of offset parameter to External delay.

Data Types: single | double | fixed point

ω — Angular velocity

scalar

Externally computed angular velocity. This value represents the change in the θ_in input.

Dependencies

To enable this port, set Nature of offset parameter to Sample delay, High-pass filter delay, or Low-pass filter delay.

Data Types: single | double | fixed point

Output

θ_out — Position output value

scalar

Position output value that is corrected for offset.

Data Types: single | double | fixed point

Parameters

Nature of offset — Type of offset

Sample delay (default) | Constant delay | External delay | High-pass filter delay | Low-pass filter delay

Type of delay or offset in the system that you want to compensate for. Select one of the following values:

• Constant delay — Compensate for a fixed delay or offset.

• External delay — Compensate for a constant delay using an externally computed position offset value.

• Sample delay — Compensate for the delay based on a discrete step size or block execution time.

• High-pass filter delay — Compensate for delay from first-order Butterworth highpass filter using a cutoff frequency value.

• Low-pass filter delay — Compensate for delay from first-order Butterworth lowpass filter using a cutoff frequency value.

Offset value — Position offset value

0.1 (default) | scalar

Position offset for constant delay in a system.

Dependencies

To enable this parameter, set Nature of offset to Constant delay.

Number of sample delay — Number of block execution time samples

1 (default) | scalar

Number of block execution time samples that the block uses for position offset compensation.

Dependencies

To enable this parameter, set Nature of offset to Sample delay.

Discrete step size (s) — Sample time after which block executes again

50e-6 (default) | scalar

The fixed time interval (in seconds) between consecutive instances of block execution.

Dependencies

To enable this parameter, set Nature of offset to Sample delay.

Cut-off frequency (Hz) — Filter cutoff frequency

9.578 (default) | scalar

Cutoff frequency of the first-order Butterworth highpass or lowpass filter.

Dependencies

To enable this parameter, set Nature of offset to High-pass filter delay or Low-pass filter delay.

Position unit — Unit of position input

Radians (default) | Degrees | Per unit

Unit of the position input θ_in.

Speed unit — Unit of angular velocity input

RPM (default) | Degrees/Sec | Radians/Sec | Per unit

Unit of the angular velocity input ω.

Dependencies

To enable this parameter, set Nature of offset to Sample delay, High-pass filter delay, or Low-pass filter delay.

Maximum application speed (RPM) — Upper limit of angular velocity

4000 (default) | scalar

Upper limit or the maximum possible value for the angular velocity input ω, in RPM.

Dependencies

To enable this parameter, set Nature of offset to Sample delay, High-pass filter delay, or Low-pass filter delay.

Extended Capabilities

C/C++ Code Generation
Generate C and C++ code using Simulink® Coder™.

Fixed-Point Conversion
Design and simulate fixed-point systems using Fixed-Point Designer™.

Version History

Introduced in R2022b