SimPowerSystems

3-Phase Dynamic Load

Implements a three-phase dynamic load with programmable active power and reactive power

Library

Elements

Description

The 3-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:

where

• V_o is the initial positive sequence voltage.
• P_o 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.

Dialog Box

Nominal L-L voltage and frequency

Specifies the nominal phase to phase voltage and nominal frequency of the load.

Active and reactive power at initial voltage

Specifies the initial active power and initial reactive power at the initial voltage.

Initial positive-sequence voltage Vo

Specifies the magnitude and phase of the initial positive-sequence voltage of the load.

External control of PQ

If, selected, the active power and reactive power of the load are defined by an external simulink signal.

Parameters [np nq]

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

Time constants [Tp1 Tp2 Tq1 Tq2]

Specifies the time constants controlling the dynamics of the active power and the reactive power.

minimum voltage Vmin

Specifies the minimum voltage where the load dynamics enter in action. The load impedance is constant below this value.

Example

The psbdynamicload.mdl model uses a 3-Phase Dynamic Load block connected on a 500 kV, 60 Hz power network. The network is simulated by its Thevenin equivalent (voltage source behind a R-L impedance corresponding to a three-phase short-circuit level of 2000 MVA). The source internal voltage is modulated in order to simulate voltage variation during a power swing. As the dynamic load is a nonlinear model simulated by current sources, it cannot be connected to an inductive network (R-L in series). Therefore, a small resistive load (1 MW) has been added in parallel with the dynamic load.

3-Phase Breaker

3-Phase Fault