# Three-Phase Dynamic Load

Implement three-phase dynamic load with active power and reactive power as function of voltage or controlled from external input

Libraries:
Simscape / Electrical / Specialized Power Systems / Passives

## Description

The Three-Phase Dynamic Load block implements a three-phase, three-wire dynamic load whose active power P and reactive power Q vary as function of positive-sequence voltage. Negative- and zero-sequence currents are not simulated. The three load currents are therefore balanced, even under unbalanced load voltage conditions.

The load impedance is kept constant if the terminal voltage V of the load is lower than a specified value Vmin. When the terminal voltage is greater than the Vmin value, the active power P and reactive power Q of the load vary as follows:

`$\begin{array}{c}P\left(s\right)={P}_{0}{\left(\frac{V}{{V}_{0}}\right)}^{{n}_{p}}\frac{1+{T}_{p1}s}{1+{T}_{p2}s}\\ Q\left(s\right)={Q}_{0}{\left(\frac{V}{{V}_{0}}\right)}^{{n}_{q}}\frac{1+{T}_{q1}s}{1+{T}_{q2}s},\end{array}$`

where

• V0 is the initial positive sequence voltage.

• P0 and Qo are the initial active and reactive powers at the initial voltage Vo.

• V is the positive-sequence voltage.

• np and nq are exponents (usually between 1 and 3) controlling the nature of the load.

• Tp1 and Tp2 are time constants controlling the dynamics of the active power P.

• Tq1 and Tq2 are time constants controlling the dynamics of the reactive power Q.

For a constant current load, for example, you set np to 1 and nq to 1, and for constant impedance load you set np to 2 and nq to 2.

### Examples

The `power_dynamicload` model uses a Three-Phase Dynamic Load block connected on a 500 kV, 60 Hz power network.

## Ports

### Input

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Control for the active and reactive powers of the load, specified as a vector of two signals [P, Q].

#### Dependencies

To enable this port, select the External control of PQ parameter.

### Output

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Vector that contains these three signals:

• Positive-sequence voltage (pu)

• Active power P (W)

• Reactive power Q (vars)

### Conserving

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Specialized electrical conserving port associated with the terminal of phase A.

Specialized electrical conserving port associated with the terminal of phase B.

Specialized electrical conserving port associated with the terminal of phase C.

## Parameters

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To edit block parameters interactively, use the Property Inspector. From the Simulink® Toolstrip, on the Simulation tab, in the Prepare gallery, select .

Nominal phase-to-phase voltage, in volts RMS, and nominal frequency, in hertz, of the load.

Initial active power, Po, in watts, and initial reactive power, Qo, in vars, at the initial voltage, Vo.

When you use the Machine Initialization tool of the powergui block to initialize the dynamic load and start simulation in steady state, these parameters are automatically updated according to the P and Q points specified for the load.

When you use the Load Flow tool of the powergui block to initialize the dynamic load, these parameters represent the P and Q reference powers used by the load flow.

Magnitude and phase of the initial positive-sequence voltage of the load.

When you use the Load Flow tool or the Machine Initialization tool of the powergui block to initialize the dynamic load and start simulation in steady state, this parameter is automatically updated using the values computed by the load flow.

Option to define the active power and reactive power of the load by using an external Simulink vector of two signals.

np and nq parameters that define the nature of the load.

#### Dependencies

To enable this parameter, clear the External control of PQ parameter.

Time constants that control the dynamics of the active power and the reactive power.

#### Dependencies

To enable this parameter, clear the External control of PQ parameter.

Minimum voltage at which the load dynamics commences. The load impedance is constant below this value.

#### Dependencies

To enable this parameter, clear the External control of PQ parameter.

Time constant, in seconds, of the current filter of the Three-Phase Dynamic Load block.

## Version History

Introduced before R2006a