# Switched Reluctance Machine (Multi-Phase)

Four, five, or six-phase switched reluctance machine (SRM)

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• Simscape / Electrical / Electromechanical / Reluctance & Stepper

## Description

The Switched Reluctance Machine (Multi-Phase) block represents a four-phase, five-phase, or six-phase switched reluctance machine (SRM).

The diagram shows the motor construction for the four-phase machine.

The diagram shows the motor construction for the five-phase machine.

### Equations

The rotor stroke angle for a multiphase machine is

`${\theta }_{st}=\frac{2\pi }{{N}_{s}{N}_{r}}$`

where:

• θst is the stoke angle.

• Ns is the number of phases.

• Nr is the number of rotor poles.

The torque production capability, β, of one rotor pole is

`$\beta =\frac{2\pi }{{N}_{r}}.$`

The mathematical model for a switched reluctance machine (SRM) is highly nonlinear due to influence of the magnetic saturation on the flux linkage-to-angle curve, λ(θph). The phase voltage equation for an SRM is

`${v}_{ph}={R}_{s}{i}_{ph}+\frac{d{\lambda }_{ph}\left({i}_{ph},{\theta }_{ph}\right)}{dt}$`

where:

• vph is the voltage per phase.

• Rs is the stator resistance per phase.

• iph is the current per phase.

• λph is the flux linkage per phase.

• θph is the angle per phase.

Rewriting the phase voltage equation in terms of partial derivatives yields this equation:

`${v}_{ph}={R}_{s}{i}_{ph}+\frac{\partial {\lambda }_{ph}}{\partial {i}_{ph}}\frac{d{i}_{ph}}{dt}+\frac{\partial {\lambda }_{ph}}{\partial {\theta }_{ph}}\frac{d{\theta }_{ph}}{dt}.$`

Transient inductance is defined as

`${L}_{t}\left({i}_{ph},{\theta }_{ph}\right)=\frac{\partial {\lambda }_{ph}\left({i}_{ph},{\theta }_{ph}\right)}{\partial {i}_{ph}},$`

or more simply as

`$\frac{\partial {\lambda }_{ph}}{\partial {i}_{ph}}.$`

Back electromotive force is defined as

`${E}_{ph}=\frac{\partial {\lambda }_{ph}}{\partial {\theta }_{ph}}{\omega }_{r}.$`

Substituting these terms into the rewritten voltage equation yields this voltage equation:

`${v}_{ph}={R}_{s}{i}_{ph}+{L}_{t}\left({i}_{ph},{\theta }_{ph}\right)\frac{d{i}_{ph}}{dt}+{E}_{ph}.$`

Applying the co-energy formula to equations for torque,

`${T}_{ph}=\frac{\partial W\left({\theta }_{ph}\right)}{\partial {\theta }_{r}},$`

and energy,

`$W\left({i}_{ph},{\theta }_{ph}\right)=\underset{0}{\overset{{i}_{ph}}{\int }}{\lambda }_{ph}\left({i}_{ph},{\theta }_{ph}\right)d{i}_{ph}$`

yields an integral equation that defines the instantaneous torque per phase, that is,

Integrating over the phases gives this equation, which defines the total instantaneous torque as

`$T=\sum _{j=1}^{{N}_{s}}{T}_{ph}\left(j\right).$`

The equation for motion is

`$J\frac{d\omega }{dt}=T-{T}_{L}-{B}_{m}\omega$`

where:

• J is the rotor inertia.

• ω is the mechanical rotational speed.

• T is the rotor torque. For the Switched Reluctance Machine block, torque flows from the machine case (block conserving port C) to the machine rotor (block conserving port R).

• TL is the load torque.

• J is the rotor inertia.

• Bm is the rotor damping.

For high-fidelity modeling and control development, use empirical data and finite element calculation to determine the flux linkage curve in terms of current and angle, that is,

`${\lambda }_{ph}\left({i}_{ph},{\theta }_{ph}\right).$`

For low-fidelity modeling, you can also approximate the curve using analytical techniques. One such technique [2] uses this exponential function:

`${\lambda }_{ph}\left({i}_{ph},{\theta }_{ph}\right)={\lambda }_{sat}\left(1-{e}^{-{i}_{ph}f\left({\theta }_{ph}\right)}\right),$`

where:

• λsat is the saturated flux linkage.

• f(θr) is obtained by Fourier expansion.

For the Fourier expansion, use the first two even terms of this equation:

`$f\left({\theta }_{ph}\right)=a+b\mathrm{cos}\left({N}_{r}{\theta }_{ph}\right)$`

where a > b,

and

### Calculating Iron Losses

The Switched Reluctance Machine (Multi-Phase) block implements the iron losses as a reduction in the electrical torque.

If you set the Stator parameterization parameter to `Specify parametric data`, specify the Magnetizing resistance parameter to model iron losses.

If you set the Stator parameterization parameter to `Specify tabulated flux data`, the block tabulates the losses as the power lost in each stator phase. The losses for each stator only depends on the stator current in that phase, the rotor angle (geometrically shifted to that phase), and the rotor speed. The iron loss power of the rotor is computed as a percentage of the total iron loss power, as specified in the Percentage of total iron losses associated with the rotor parameter.

If you tabulate the losses with current, speed, and angle, the iron loss torque reduces the electrical torque of a generic "A" phase:

`${\tau }_{elecA}=\tau \left({i}_{A},{\theta }_{A}\right)-{\tau }_{loss}\left({i}_{A},w,{\theta }_{A}\right)$`

where ${\tau }_{loss}\left({i}_{A},w,{\theta }_{A}\right)=sign\left(w\right)\frac{{P}_{loss}\left(abs\left({i}_{A}\right),abs\left(w\right),{\theta }_{A}\right)}{abs\left(w\right)+{w}_{min}}$ is the torque loss computed as the mechanical power loss divided by the rotor speed. wmin is the minimum rotor speed and it is equal to `1` `rad/s`. This value prevents a division by zero when the rotor speed is equal to `0`.

If you tabulate the losses in function of only current and speed, the iron loss torque reduces the electrical torque of a generic "A" phase:

`${\tau }_{loss}\left({i}_{A},w\right)=sign\left(w\right)\frac{{P}_{loss}\left(abs\left({i}_{A}\right),abs\left(w\right)\right)}{abs\left(w\right)+{w}_{min}}.$`

The iron losses are applied to the mechanical side as a reduction in torque. If you create the iron loss table, Ploss, from FEM results, the FEM tool might express the power lost as electrical power instead of mechanical power.

The total electrical torque is equal to the sum of the electrical torque of each phase:

`${\tau }_{elec}={\tau }_{elecA}+{\tau }_{elecB}+{\tau }_{elecC}.$`

The total power dissipated is equal to the sum of the iron losses and the copper losses:

`${P}_{dissipated}=\left({\tau }_{lossA}+{\tau }_{lossB}+{\tau }_{lossC}\right)w+{R}_{a}{i}_{a}^{2}+{R}_{b}{i}_{b}^{2}+{R}_{c}{i}_{c}^{2}.$`

Iron losses with thermal ports

If you expose the thermal ports of the block, the power dissipated in each phase act as heat sources in the motor and in the rotor:

`$\begin{array}{l}{P}_{dissA}={R}_{a}{i}_{a}^{2}+{P}_{ironA}\\ {P}_{dissB}={R}_{b}{i}_{b}^{2}+{P}_{ironB}\\ {P}_{dissC}={R}_{c}{i}_{c}^{2}+{P}_{ironC}\\ {P}_{dissR}={P}_{ironR}\end{array}$`

The iron loss in the rotor is equal to a percentage of the total iron losses. This loss remains constant and does not depend on other states:

`${P}_{ironR}=\frac{percen{t}_{rotor}}{100}\left({\tau }_{lossA}+{\tau }_{lossB}+{\tau }_{lossC}\right)w.$`

Then the remaining iron loss is distributed among the different stator phases:

`$\begin{array}{l}{P}_{ironA}=\left(1-\frac{percen{t}_{rotor}}{100}\right){\tau }_{lossA}\text{\hspace{0.17em}}w\\ {P}_{ironB}=\left(1-\frac{percen{t}_{rotor}}{100}\right){\tau }_{lossB}\text{\hspace{0.17em}}w\\ {P}_{ironC}=\left(1-\frac{percen{t}_{rotor}}{100}\right){\tau }_{lossC}\text{\hspace{0.17em}}w\end{array}$`

### Model Thermal Effects

You can expose thermal ports to model the effects of losses that convert power to heat. To expose the thermal ports, set the Modeling option parameter to either:

• `No thermal port` — The block does not contain thermal ports.

• `Show thermal port` — The block contains multiple thermal conserving ports.

For more information about using thermal ports in actuator blocks, see Simulating Thermal Effects in Rotational and Translational Actuators.

### Assumptions

A zero rotor angle corresponds to a rotor pole that is aligned perfectly with the a-phase, that is, peak flux.

### Variables

Use the Variables settings to specify the priority and initial target values for the block variables before simulation. For more information, see Set Priority and Initial Target for Block Variables.

## Ports

### Conserving

expand all

Mechanical rotational conserving port associated with the machine rotor.

Data Types: `double`

Mechanical rotational conserving port associated with the machine case.

Data Types: `double`

Electrical positive supply for phase-a.

Data Types: `double`

Electrical positive supply for phase-b.

Data Types: `double`

Electrical positive supply for phase-c.

Data Types: `double`

Electrical positive supply for phase-d.

Data Types: `double`

Electrical positive supply for phase-e.

This port is visible if you select `Five-phase` for the Number of stator phases parameter.

Data Types: `double`

Electrical positive supply for phase-f.

This port is visible if you select `Six-phase` for the Number of stator phases parameter.

Data Types: `double`

Electrical negative supply for phase-a.

Data Types: `double`

Electrical negative supply for phase-b.

Data Types: `double`

Electrical negative supply for phase-c.

Data Types: `double`

Electrical negative supply for phase-d.

Data Types: `double`

Electrical negative supply for phase-e.

This port is visible if you select `Five-phase` for the Number of stator phases parameter.

Data Types: `double`

Electrical negative supply for phase-f.

This port is visible if you select `Six-phase` for the Number of stator phases parameter.

Data Types: `double`

Thermal conserving port associated with stator winding a.

#### Dependencies

To enable this port, set Modeling option to `Show thermal port`.

Thermal conserving port associated with stator winding b.

#### Dependencies

To enable this port, set Modeling option to `Show thermal port`.

Thermal conserving port associated with stator winding c.

#### Dependencies

To enable this port, set Modeling option to `Show thermal port`.

Thermal conserving port associated with stator winding d.

#### Dependencies

To enable this port, set Modeling option to `Show thermal port`.

Thermal conserving port associated with stator winding e.

#### Dependencies

To enable this port, set Modeling option to ```Show thermal port``` and Number of stator phases to `Five-phase`.

Thermal conserving port associated with stator winding f.

#### Dependencies

To enable this port, set Modeling option to `Show thermal port` and Number of stator phases to `Six-phase`.

Thermal conserving port associated with the rotor.

#### Dependencies

To enable this port, set Modeling option to `Show thermal port`.

## Parameters

expand all

Whether to enable the thermal ports of the block and model the effects of losses that convert power to heat.

### Main

Type of multiphase SRM in terms of the number of stator phases.

Number of pole pairs on the rotor.

Per-phase resistance of each of the stator windings.

Method for parameterizing the stator.

#### Dependencies

Selecting ```Specify saturated flux linkage``` enables these parameters:

• Aligned inductance

• Unaligned inductance

Selecting `Specify flux characteristic` enables these parameters:

• Current vector, i

• Angle vector, theta

#### Dependencies

To enable this parameter, set Stator parameterization to ```Specify saturated flux linkage```.

Inductance when the axis of the rotor pole is identical to the axis of the excited stator pole. The value of this parameter must be greater than the value of the Unaligned inductance parameter.

#### Dependencies

To enable this parameter, set Stator parameterization to ```Specify saturated flux linkage```.

Inductance when the axis between two rotor poles is identical to the axis of the excited stator pole. The value of this parameter must be less than the value of the Aligned inductance parameter.

#### Dependencies

To enable this parameter, set Stator parameterization to ```Specify saturated flux linkage```.

Current vector used to identify the flux linkage curve family.

#### Dependencies

To enable this parameter, set Stator parameterization to ```Specify flux characteristic```.

Angle vector used to identify the flux linkage curve family.

#### Dependencies

To enable this parameter, set Stator parameterization to ```Specify flux characteristic```.

#### Dependencies

To enable this parameter, set Stator parameterization to ```Specify flux characteristic```.

### Iron Losses

Whether to enable iron losses modeling.

#### Dependencies

To enable this parameter, set Stator parameterization to ```Specify tabulated flux data```.

Magnetizing resistance. The value must be greater than zero. The default value is `inf`, which implies that there are no iron losses.

#### Dependencies

To enable this parameter, set Stator parameterization to ```Specify parametric data```.

Vector of rotor speed at which the iron loss is tabulated.

#### Dependencies

To enable this parameter, set Model to either ```Tabulate losses from current and speed``` or ```Tabulate losses from current, speed, and angle```.

Mechanical power lost in the shaft due to iron losses in a particular phase, tabulated as a function of the instantaneous phase current and the rotor speed.

#### Dependencies

To enable this parameter, set Model to ```Tabulate losses from current and speed```.

Mechanical power lost in the shaft due to iron losses in a particular phase, tabulated as a function of the instantaneous phase current, the rotor speed, and the rotor angle.

#### Dependencies

To enable this parameter, set Model to ```Tabulate losses from current, speed, and angle```.

### Mechanical

Inertia of the rotor attached to mechanical translational port R.

Rotary damping.

### Thermal

To enable these parameters, set Modeling option to `Show thermal port`.

Temperature for which motor parameters are quoted.

Coefficient α in the equation relating resistance to temperature for all three windings, as described in Thermal Model for Actuator Blocks. The default value, `3.93e-3` 1/K, is for copper.

Thermal mass value for each stator winding. The thermal mass is the energy required to raise the temperature by one degree.

Thermal mass of the rotor. The thermal mass is the energy required to raise the temperature of the rotor by one degree.

Percentage of total iron losses associated with the rotor.

#### Dependencies

To enable this parameter, set Model to either ```Tabulate losses from current and speed``` or ```Tabulate losses from current, speed, and angle```.

## References

[1] Boldea, I. and S. A. Nasar. Electric Drives. 2nd Ed. New York: CRC Press, 2005.

[2] Iliĉ-Spong, M., R. Marino, S. Peresada, and D. Taylor. “Feedback linearizing control of switched reluctance motors.” IEEE Transactions on Automatic Control. Vol. 32, Number 5, 1987, pp. 371–379.

## Version History

Introduced in R2018b