Compute positive-sequence active and reactive powers

Simscape / Electrical / Specialized Power Systems / Control & Measurements / Measurements

Simscape / Electrical / Specialized Power Systems / Fundamental Blocks / Measurements / Additional Measurements

The Power (PLL-Driven, Positive-Sequence) block computes the positive-sequence active power P (in watts) and reactive power Q (in vars) of a periodic set of three-phase voltages and currents. To perform this computation, the block first computes the positive sequence of the input voltages and currents with a running window over one cycle of the fundamental frequency given by input 1. The reference frame required for the computation is given by the input 2. The first two inputs are normally connected to the outputs of a PLL block.

These formulas are then evaluated:

$$\begin{array}{c}P=3\times \frac{\left|{V}_{1}\right|}{\sqrt{2}}\times \frac{\left|{I}_{1}\right|}{\sqrt{2}}\times \mathrm{cos}(\phi )\\ Q=3\times \frac{\left|{V}_{1}\right|}{\sqrt{2}}\times \frac{\left|{I}_{1}\right|}{\sqrt{2}}\times \mathrm{sin}(\phi )\\ \phi =\angle {V}_{1}-\angle {I}_{1}\end{array}$$

V_{1} is the positive-sequence component
of input Vabc. I_{1} is the positive-sequence
component of input Iabc.

With these formulas, a current flowing into an RL circuit produces a positive P and a positive Q.

As this block uses a running average window, one cycle of simulation
must complete before the outputs give the correct value. For the first
cycle of simulation, the output is held constant using the values
specified by the **Voltage initial input** and **Current
initial input** parameters.

**Initial frequency (Hz)**Specify the frequency of the first cycle of simulation. Default is

`60`

.**Minimum frequency (Hz)**Specify the minimum frequency value to determine the buffer size of the Variable Time Delay block used by the block to compute the phasors. Default is

`45`

.**Voltage initial input [ Mag, Phase (degrees) ]**Specify the initial positive-sequence magnitude and phase (relative to the PLL phase), in degrees, of the voltage signals. Default is

`[1, 0]`

.**Current initial input [ Mag, Phase (degrees) ]**Specify the initial positive-sequence magnitude and phase (relative to the PLL phase), in degrees, of the current signals. Default is

`[1, 0]`

.**Sample time**Specify the sample time of the block, in seconds. Set to

`0`

to implement a continuous block. Default is`0`

.

`Freq`

Fundamental frequency (Hz) required by the computation. This input is normally connected to the output Freq of a PLL block.

`wt`

Angle of the reference frame (rad/s) required for the computation. This input is normally connected to the output wt of a PLL block.

`Vabc`

The vectorized signal of the three [a b c ] voltage sinusoidal signals. Typical input signals are voltages measured by the Three-Phase V-I Measurement block.

`Iabc`

The vectorized signal of the three [a b c ] current sinusoidal signals. Typical input signals are currents measured by the Three-Phase V-I Measurement block.

`P`

Positive-sequence active power (watts)

`Q`

Positive-sequence reactive power (vars)

Sample Time | Specified in the Sample Time parameterContinuous if Sample Time = 0 |

Scalar Expansion | No |

Dimensionalized | No |

The `power_PowerPLLDrivenPositiveSequence`

model
shows how the block evaluates the positive-sequence active and reactive
powers of a voltage source connected to a three-phase load. It shows
that the block outputs accurate values for P and Q even if the fundamental
frequency of the voltage supply (containing harmonics) varies during
the simulation.

The model sample time is parameterized by the Ts variable set
to a default value of 50e-6 s. Set Ts to 0 in the command window and
change the **Simulation type** parameter of the Powergui
block to `Continuous`

to simulate the model
in continuous mode.