Three-Phase Dynamic Load

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

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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:

$$\begin{array}{c}P(s)=P_0{\left(\frac{V}{V_0}\right)}^{n_p}\frac{1+T_{p1}s}{1+T_{p2}s}\\ Q(s)=Q_0{\left(\frac{V}{V_0}\right)}^{n_q}\frac{1+T_{q1}s}{1+T_{q2}s},\end{array}$$

where

• V₀ is the initial positive sequence voltage.

• P₀ and Q_o are the initial active and reactive powers at the initial voltage V_o.

• V is the positive-sequence voltage.

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

• T_p1 and T_p2 are time constants controlling the dynamics of the active power P.

• T_q1 and T_q2 are time constants controlling the dynamics of the reactive power Q.

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

Examples

Dynamic Load and Programmable Voltage Source

The use of the 3-Phase Dynamic Load and 3-Phase Programmable Voltage Source blocks

• Open Model

Ports

Input

PQ — Control for active and reactive power

vector of two elements

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

m — Load output

vector of three elements

Vector that contains these three signals:

• Positive-sequence voltage (pu)

• Active power P (W)

• Reactive power Q (vars)

Conserving

A — Phase A terminal

specialized electrical

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

B — Phase B terminal

specialized electrical

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

C — Phase C terminal

specialized electrical

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

Parameters

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

Nominal L-L voltage and frequency [Vn(Vrms) fn(Hz)] — Nominal phase-to-phase voltage and frequency of load

[ 500e3 60 ] (default) | vector of two elements

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

Active and reactive power at initial voltage [Po(W) Qo(var)] — Initial active and reactive power

[50e6 25e6] (default) | vector of two elements

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.

Initial positive-sequence voltage Vo [Mag(pu) Phase (deg.)] — Magnitude and phase of initial positive-sequence voltage of load

[0.994 -11.8] (default) | vector of two elements

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.

External control of PQ — Option to define active and reactive power of load

off (default) | on

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

[np nq] — Nature of the load

[1.3 2] (default) | vector of two elements

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 [Tp1 Tp2 Tq1 Tq2] (s) — Time constants controlling dynamics of active and reactive power

[0 0 0 0] (default) | vector of four nonnegative elements

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 Vmin (pu) — Minimum voltage

0.7 (default) | nonnegative scalar

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.

Filtering time constant (s) — Time constant of current filter

1e-4 (default) | nonnegative scalar

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

Extended Capabilities

C/C++ Code Generation
Generate C and C++ code using Simulink® Coder™.

Version History

Introduced before R2006a