Load Flow Analyzer

(To be removed) Perform positive-sequence load flow or unbalanced load flow and initialize models containing load flow blocks

Since R2021a

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The Specialized Power Systems library will be removed in R2026a. Use the Simscape™ Electrical™ blocks and functions instead. For more information on updating your models, see Upgrade Specialized Power System Models to use Simscape Electrical Blocks.

Description

The Load Flow Analyzer app uses the power_loadflow function and relies on the Newton-Raphson method to provide a robust and fast convergence solution.

The Load Flow Analyzer app allows you to perform two types of load flows:

  • Positive-sequence load flow applied to a three-phase system. Positive-sequence voltages and active power (P) and reactive power (Q) flows are computed at each three-phase bus.

  • Unbalanced load flow applied to a mix of three-phase, two-phase, and single-phase systems. Individual phase voltage and PQ flow are computed for each phase.

To solve a load flow, you need to determine these four quantities at each bus:

  • The net active power P and reactive power Q injected into the bus

  • The voltage magnitude V and angle Vangle of bus positive-sequence voltage (positive-sequence voltage or phase voltage)

Before solving the load flow, two of the above quantities are known at every bus and the other two are to be determined. Therefore, the following bus types are used:

  • PV bus — For this type of bus, specify P and V. This is a generation bus where a generator, such as a voltage source or three-phase synchronous machine, is connected. The active power P is generated and the generator terminal voltage V is imposed. The load flow solution returns the machine reactive power Q that is required to maintain the reference voltage magnitude V, and the reference voltage angle Vangle.

  • PQ bus — At this bus, the specified active power P and reactive power Q are either injected into the bus (generation PQ bus) or absorbed by a load connected at that bus. The load flow solution returns the bus voltage magnitude V and angle Vangle.

  • Swing bus — This bus imposes the voltage magnitude V and angle Vangle. The load flow solution returns the active power P and reactive power Q that is generated or absorbed at that bus in order to balance generated power, loads, and losses. At least one bus in the model must be defined as a swing bus, but usually a single swing bus is required unless you have isolated networks. For a positive-sequence load flow, you typically select one synchronous machine or voltage source as a swing bus. For an unbalanced load flow, you can select the three phases of a Three-Phase Voltage Source block or single-phase AC Voltage Source blocks as swing buses.

Use the Load Flow Bus block to define the buses in your model.

If you perform a positive-sequence load flow, you connect a Load Flow Bus block with the Connectors parameter specified as single to any phase (A, B, or C) of every load flow block in the model. When several load flow blocks are connected together at the same nodes, only one Load Flow Bus block is required to identify the bus.

If you perform an unbalanced load flow, you connect a Load Flow Bus block to all phases of every load flow block in the model. Depending on the number of phases, you need to specify the Connectors parameter by selecting either three connectors (ABC), two connectors (AB, AC, or BC) or a single connector (A, B, or C). When several load flow blocks are connected together at the same nodes, only one Load Flow Bus block is required to identify the bus. In the load flow report, each bus is identified by its Bus identification parameter followed by _a, _b, or _c.

Load Flow Blocks for Positive-Sequence Load Flow

Load flow blocks are Simscape Electrical Specialized Power Systems blocks in which you can specify active power (P) and reactive power (Q) to solve the positive-sequence load flow. They are:

  • Asynchronous Machine

  • Simplified Synchronous Machine

  • Synchronous Machine

  • Three-Phase Dynamic Load

  • Three-Phase Parallel RLC Load

  • Three-Phase Series RLC Load

  • Three-Phase Programmable Voltage Source

  • Three-Phase Source

You specify P and Q in the Load Flow tab of the block dialog boxes.

Load Flow Parameters of Three-Phase Sources and Synchronous Machines

The Three-Phase Source and Synchronous Machine blocks allow you to control the generated or absorbed powers P and Q and the positive-sequence terminal voltage. You can set Generator type to swing, PV, or PQ.

Load Flow Parameters of Asynchronous Machine Blocks

The Asynchronous Machine blocks require you to specify the mechanical power Pmec at the machine shaft.

Load Flow Parameters of the RLC Load Blocks

For the Three Phase RLC Load block, you can specify Load type as constant Z (impedance), constant PQ (power), or constant I (current).

Load Flow Parameters of Dynamic Load Blocks

The Three-Phase Dynamic Load block dialog box does not have a Load Flow tab. The load is always considered as a constant PQ load. P and Q are the initial active and reactive power Po, Qo that you specify by using the Active and reactive power at initial voltage [Po(W) Qo(var)] parameter. The Initial positive-sequence voltage Vo [Mag(pu) Phase (deg.)] parameter (Mag and Phase) updates according to the load flow solution.

Load Flow Blocks for Unbalanced Load Flow

Load flow blocks are Simscape Electrical Specialized Power Systems blocks in which you can specify active power (P) and reactive power (Q) to solve the load flow at each phase of every bus. They are:

  • AC Voltage Source

  • Asynchronous Machine

  • Parallel RLC Load

  • Series RLC Load

  • Synchronous Machine

  • Three-Phase Dynamic Load

  • Three-Phase Parallel RLC Load

  • Three-Phase Series RLC Load

  • Three-Phase Source

You specify P and Q in the Load Flow tab of the block dialog boxes.

Load Flow Parameters of Single-Phase and Three-Phase Sources

The single-phase AC Voltage Source block allows you to control the generated or absorbed powers P and Q and the terminal voltage. The Three-Phase Source block allows you to control the generated or absorbed powers P and Q and the terminal voltages for each phase (A, B, and C). For these two blocks, you can set Generator type to swing, PV, or PQ.

Load Flow Parameters of Synchronous Machine

The Three-Phase Synchronous Machine block allows you to control generated or absorbed powers P and Q (total of phases A, B, and C) and its positive-sequence terminal voltage. You can set Generator type to PV or PQ.

Load Flow Parameters of Asynchronous Machine Blocks

The Asynchronous Machine blocks require you to specify the mechanical power Pmec developed in positive-sequence at the machine shaft.

Load Flow Parameters of the RLC Load Blocks

You can specify the Load type parameter for the single-phase and three-phase RLC Load blocks as constant Z (impedance), constant PQ (power), or constant I (current). You can connect single-phase loads phase-to-ground or phase-to-phase. You can connect three-phase loads connected in Wye (grounded or floating) or delta.

Load Flow Parameters of Dynamic Load Blocks

The Three-Phase Dynamic Load block dialog box does not have a Load Flow tab. The load is always considered as a constant PQ load. P and Q are the initial active and reactive power Po, Qo that you specify by using the Active and reactive power at initial voltage [Po(W) Qo(var)] parameter. The Initial positive-sequence voltage Vo [Mag(pu) Phase (deg.)] parameter (Mag and Phase) updates according to the load flow solution.

Load Flow Analyzer app

Open the Load Flow Analyzer App

  • MATLAB® command prompt: Enter powerLoadFlow

  • powergui Block Parameters dialog box: On the Tools tab, click Load Flow Analyzer.

  • To perform a load flow analysis and initialize your model so that it starts in steady state:

    1. Define the model buses using Load Flow Bus blocks.

    2. Specify the load flow parameters of all blocks that have load flow parameters. These blocks are referred to as load flow blocks.

    3. Solve the load flow and interactively modify the load flow parameters until a satisfactory solution is obtained.

    4. Save the load flow parameters and machine initial conditions in the model.

Parameters

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Name of model to perform load flow analysis on.

Click to get the latest changes in the model. Any previous load flow solution is cleared from the table.

Click to solve the load flow. The solution is displayed in the V_LF, Vangle_LF, P_LF, and Q_LF columns of the table. The load flow is performed at the frequency, base power, PQ tolerance, and max iterations specified in the Preferences tab of the powergui block.

Click to apply the load flow solution to the model.

Click to add Load Flow Bus blocks to the model. The Load Flow Analyzer app determines the load flow bus required for your model and adds Load Flow Bus blocks only in places where there is no Load Flow Bus block already connected.

Click to save a load flow report that shows the power flowing toward each bus. You can save the report in either Excel®or MATLAB format.

Version History

Introduced in R2021a

See Also

Functions