Machine mechanical power defined in the per-unit system

Machines

The Machine Mechanical Power (pu) block supplies specified power to, or draws specified power from, the machine that it connects to. It includes a representation of machine inertia and a mechanical rotational reference. In generator mode, the physical signal input pu defines the per-unit mechanical power that is input to the machine. In motor mode, it defines the mechanical power output from the machine. The pu input must always be positive.

The figure shows an equivalent configuration to the Machine Mechanical Power (pu) block using Simscape™ mechanical rotational components.

To calculate the torque that it applies to the inertia, the
block divides the power demand by the present speed. To set the peak
torque limit, specify a value for the **Peak torque to rated
torque ratio** parameter. Use the **Specify inertia
parameterization by** parameter to specify inertia, *J*,
directly or indirectly, with the inertia constant for the machine, *H*.

If you specify the inertia constant for the machine, the block calculates inertia as

$$J=\frac{2H{S}_{rated}}{{(2\pi {F}_{rated}/N)}^{2}},$$

*J*is inertia in kg⋅m^{2}.*H*is the inertia constant in sW/VA.*S*is the rated apparent power of the connected machine in VA._{rated}*F*is the rated electrical frequency of the connected machine in Hz._{rated}*N*is the number of machine pole pairs.

Damping represents viscous friction between the machine
rotor and mechanical rotational reference. Based on the value you
select for the **Specify damper parameterization by** parameter,
you specify a damping coefficient in per-unit or in SI units. If you
specify the damping coefficient in per-unit, the block calculates
the damping coefficient in SI units using these equations:

$${\omega}_{base}=\frac{2\pi {F}_{rated}}{N},$$

$${T}_{base}=\frac{{S}_{rated}}{{\omega}_{base}},$$

$${D}_{base}=\frac{{T}_{base}}{{\omega}_{base}},$$

$$D={D}_{pu}{D}_{base},$$

*ω*is the base mechanical speed in rad/s._{base}*T*is the base damping torque in Nm._{base}*D*is the base damping coefficient in Nm/(rad/s)._{base}*D*is the damping coefficient in per-unit._{pu}*D*is the damping coefficient in SI units of Nm/(rad/s).

**Input power sign convention**Machine type specification. The choices are

`Generator`

and`Motor`

. The default value is`Generator`

.**Rated apparent power**Rated apparent power of the connected machine. The default value is

`555e6`

`V*A`

.**Rated electrical frequency**Nominal electrical frequency corresponding to the rated apparent power of the connected machine. The default value is

`60`

`Hz`

.**Number of pole pairs**Number of pole pairs of the connected machine. The default value is

`1`

.**Peak torque to rated torque ratio**Ratio that the block multiplies by the base torque to provide the upper limit for the torque that accelerates the inertia. The default value is

`2`

.

**Specify inertia parameterization by**Inertia specification. The choices are between

`Actual Inertia, J`

and`Inertia constant, H`

. The default value is`Inertia constant, H`

.**Inertia constant, H**Inertia constant. This parameter is visible only if you set

**Specify inertia parameterization by**to`Inertia constant, H`

. The default value is`3.525`

`s*W/VA`

.**Actual inertia, J**Inertia. This parameter is visible only if you set

**Specify inertia parameterization by**to`Actual Inertia, J`

. The default value is`27548`

kg⋅m^{2}.**Specify damper parameterization by**Damping specification. The choices are

`Per-unit damping coefficient, pu_D`

and`SI damping coefficient, D`

. The default value is`Per-unit damping coefficient, pu_D`

.**Per-unit damping coefficient**Damping coefficient in per-unit. This parameter is visible only if you set

**Specify damper parameterization by**to`Per-unit damping coefficient, pu_D`

. The default value is`0.01`

.**SI damping coefficient**Damping coefficient in SI units. This parameter is visible only if you set

**Specify damper parameterization by**to`SI damping coefficient, D`

. The default value is`39.0509`

Nm/(rad/s).

**Specify initialization by**Frequency initialization. The choices are

`Initial electrical frequency`

and`Initial mechanical frequency`

. The default value is`Initial electrical frequency`

.**Initial electrical frequency**Initial electrical frequency. This parameter is visible only if you set

**Specify initialization by**to`Initial electrical frequency`

. The default value is`60`

`Hz`

.**Initial mechanical frequency**Initial mechanical frequency. This parameter is visible only if you set

**Specify initialization by**to`Initial mechanical frequency`

. The default value is`60`

`Hz`

.

The block has the following ports:

`pu`

Physical signal input port associated with mechanical power, per-unit

`R`

Mechanical rotational conserving port associated with the machine rotor

`C`

Mechanical rotational conserving port associated with the machine case

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