Documentation

Machine Mechanical Power (SI)

Machine mechanical power defined in SI units

Library

Machines

Description

The Machine Mechanical Power (SI) 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 Pm defines the mechanical power in SI units that is input to the machine. In motor mode, it defines the mechanical power output from the machine. The Pm input must always be positive.

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

Electrical Defining Equations

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=2HSrated(2πFrated/N)2,

where:

  • J is inertia in kg⋅m2.

  • H is the inertia constant in sW/VA.

  • Srated is the rated apparent power of the connected machine in VA.

  • Frated is the rated electrical frequency of the connected machine in Hz.

  • N is the number of pole pairs in the connected machine.

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:

ωbase=2πFratedN,

Tbase=Sratedωbase,

Dbase=Tbaseωbase,

and

D=DpuDbase,

where:

  • ωbase is the base mechanical speed in rad/s.

  • Tbase is the base damping torque in Nm.

  • Dbase is the base damping coefficient in Nm/(rad/s).

  • Dpu is the damping coefficient in per-unit.

  • D is the damping coefficient in SI units of Nm/(rad/s).

Parameters

Main Tab

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.

Inertia Tab

Specify inertia parameterization by

Inertia specification. The choices are 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⋅m2.

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).

Initial Conditions Tab

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.

Ports

The block has the following ports:

Pm

Physical signal input port associated with mechanical power, W

R

Mechanical rotational conserving port associated with the machine rotor

C

Mechanical rotational conserving port associated with the machine case

Introduced in R2014b

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