Documentation

Current Controller (Brushless DC)

Implement current/torque controller model for brushless DC machine

Library

Electric Drives/Fundamental Drives

Description

The Current Controller (Brushless DC) block represents a hysteresis current controller for use with a brushless DC machine. It has two operating modes to represent a detailed or an average-value inverter.

Detailed Model

In detailed mode, the Current Controller (Brushless DC) block contains four main blocks:

The T to I block performs the conversion from the reference torque to the peak reference current. The relation that converts torque to current assumes pure rectangular current waveforms. In practice, due to the motor inductance, you cannot obtain these currents. Therefore the electromagnetic torque might be lower than the reference torque, especially at high speed.

The Hall decoder block extracts the BEMF information from the Hall Effect sensor signals. It represents the normalized ideal phase currents to be injected in the motor phases. The figure shows the BEMF of phase A and the output of the Hall decoder for the phase A.

The Current regulator block is a bang-bang current controller with adjustable hysteresis bandwidth. The Switching control block limits the inverter commutation frequency to a maximum value that you specify. In a detailed model, the Current Controller (Brushless DC) block outputs the actual pulses for the inverter switches.

Average Model

In average mode, the Current Controller (Brushless DC) block does not model the high-frequency switching actions of the power switches. The output of the block is the three-phase motor current references of the machine controlled by the average-value inverter.

Parameters

Model detail level

Specify the model detail level to use:

  • Detailed (default)

  • Average

Motor pairs of poles

The number of pole pairs of the machine controlled by the current controller. The default value is 4.

Specify

Select the machine constant that you want to specify for block parameterization. Choices are Flux linkage established by magnets (V.s) (default), Voltage Constant (V_peak L-L / krpm), and Torque Constant (N.m / A_peak).

Flux linkage

The constant flux, in weber, per pole pairs induced in the stator windings by the magnets of the machine controlled by the current controller. The default value is 0.175.

Voltage constant (V_peak L-L / krpm)

The peak line to line voltage per 1000 rpm of the machine controlled by the current controller. This voltage represents the peak open circuit voltage when the machine is driven as a generator at 1000 rpm. The default value is 146.6077.

Torque Constant (N.m / A_peak)

The torque per ampere constant of the machine controlled by the current controller. The default value is 1.4.

Back EMF flat area (degrees)

The width of the flat top for a half period of the electromotive force Φ' (degrees) of the machine controlled by the current controller. The default value is 120.

Maximum switching frequency (Hz)

The maximum inverter switching frequency, in hertz. This parameter is available only when the Model detail level parameter is set to Detailed. The default value is 20e3.

Sample time (s)

The current controller sampling time, in seconds. The sampling time must be a multiple of the simulation time step. The default value is 20e-6.

Current hysteresis bandwidth (A)

The current regulator hysteresis bandwidth, in ampere. This parameter is enabled only when the Model detail level parameter is set to Detailed. This value corresponds to the total hysteresis bandwidth distributed symmetrically around the current set point.

The default value is 0.01.

Inputs and Outputs

Torque*

Torque reference, typically provided by a speed controller.

Hall

Hall Effect sensor signals for phase A, B, and C.

I_abc

The three line currents of the brushless DC machine.

Sig

The three reference currents (iabc*) required by the average-value inverter. This output is visible only when the Model detail level parameter is set to Average.

Gates

Pulses for the six inverter switches. This output is visible only when the Model detail level parameter is set to Detailed.

Examples

The Current Controller (Brushless DC) block is used in the AC7 block in the Electric Drives library.

References

[1] Bose, B. K. Modern Power Electronics and AC Drives, NJ: Prentice-Hall, 2002.

Introduced in R2015b

Was this topic helpful?