Common Simulation Modules for Power Systems MATLAB/SIMULINK (1)

    The content of this paper is a reference to the MATLAB-based graphical simulation of electrical control systems.

When simulating a power system, it is important to first understand the components that make up the power system. This chapter describes the relevant power system modules in theMATLAB/SIMULINK inside the use. This includes:

1. Synchronous generator module 2. Power Transformer 3. Transmission lines 4. Load5. Circuit Breaker and Fault Module

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1. Synchronized generator module

1.1 Simplified synchronous motor module

simplifiedsynchronous motorThe module ignores the armature reactance inductance, excitation and leakage inductance of the damping windings, and consists only of an ideal voltage source in series with an RL line, where both R and L are the internal impedance of the motor.

The following two simplified synchronous motor modules are available in the library given by SimPowerSyestem.

The two modules for simplified synchronous motors are essentially the same, the only difference being that the parameters are selected in different units. pu is the Mississippi value and SI is the International System of Units.

The simplified synchronous motor module has two input terminals, one output terminal and three electrical connection terminals. The module'sFirst input terminal(Pm) the mechanical power of the input motor, which can be a constant, or the output of the prime mover; the module'sSecond input terminal(E) is the voltage of the motor's internal voltage source, which can be a constant or directly connected to the output of the voltage regulator; the module'sThree electrical connection terminals(A,B,C) is the stator output voltage.output side(m) Outputs a range of internal motor signals, consisting of a total of 12 signals:

Double clicking on the Simplified Motor module will bring up the parameter dialog box for the module

(1) Rated parameters text box: three-phase rated apparent power, rated line voltage RMS, rated frequency.

(2) Text box for mechanical parameters: moment of inertia J or inertia time constant H, damping coefficient Kd, polar logarithm p.

(3) Internal impedance text box: single-phase resistance R and inductance L. RL is the impedance of the internal motor, allowing R to be equal to 0 when setting, but L must be greater than 0

(4) Initial conditions text box: initial angular velocity offset, initial angular displacement of rotor, line current amplitude, phase angle. The initial conditions can be obtained automatically by the Powergui module.

1.2. Synchronous motor module

SimPowerSyestem provides three synchronous motor modules for dynamic modeling of three-phase implicit and convex pole synchronous motors. The diagrams are shown below:

The synchronous motor module has two inputs, one output and three electrical connection terminals.

        First input terminal(Pm) is the mechanical power of the motor. When the mechanical powerstatuteindicates that the synchronous motor is running in generator mode; when the mechanical powernegative (math.)When, it indicates that the synchronous motor is operating in motor mode. In generator mode, the input can be a positive number, a function or the output of the prime mover module; in motor module, the input is usually a negative number or a function.

        Second input(Vf) is the excitation voltage, which can be supplied by the excitation module in generator mode and is a constant in motor mode.

The three electrical connection terminals (A,B,C) are stator voltage outputs. The output terminal (m) outputs the internal signals of a series of motors, consisting of 22 signals.

(1) SI basic synchronous motor module

(1) Preset model drop-down box: after selecting the internal model set by the system, the synchronous motor automatically obtains various data, if you do not want to use the parameters given by the system, select "no".

2) Mechanical quantity input checkbox: you can browse and select the mechanical parameters of the motor

3) Winding type: Convex and hidden poles

(4) Rated parameters: three-phase rated apparent power, rated line voltage rms, rated frequency, rated excitation current

5) Stator parameters: stator resistance, leakage inductance, d-axis armature reaction inductance, q-axis armature reaction inductance

6) Excitation parameters: excitation resistance, excitation leakage inductance

7) Damping winding parameters: d-axis damping resistance, d-axis leakage inductance, q-axis damping resistance, q-axis inductance. For solid rotor also need to enter the damping resistance and leakage inductance that reacts to the eddy current loss of the rotor bar deep in the large motor.

8) Mechanical parameters: moment of inertia, coefficient of friction, pole pair number

9) Initial conditions: initial angular velocity offset, initial rotor angular displacement, line current magnitude, phase angle, initial excitation voltage

(10) Saturation Simulation checkbox: Set whether the stator and rotor are saturated. Check the checkbox if saturation needs to be considered.

(2) pu basic motor module

 

This dialog is similar to that of the SI Basic Synchronous Motor module, with one difference:

1) Rated parameters: In contrast to the SI basic synchronous motor module, the excitation current is not included in this item.

2) Stator parameter: In contrast to the SI basic synchronous motor module, this parameter is the standard value normalized to the stator side.

3) Excitation parameter: In contrast to the SI basic synchronous motor module, this parameter is the standard value normalized to the stator side.

4) Damping winding parameter: In contrast to the SI basic synchronous motor module, this parameter is the standard value normalized to the stator side.

5) Mechanical parameters: time constant of inertia, coefficient of friction, pole pair number

(6) saturation simulation: the excitation current and stator output voltage are standardized values; the reference value of the voltage is the rated line voltage rms; the reference value of the current is the rated excitation current.

(3) Standard synchronous motor module

 

Comparison of the various modules:

The simplified synchronous motor module is a second-order model that takes into account only the rotor dynamics, which is characterized by the simplicity of the model and is widely used in the analysis of large-scale power systems.

In the basic synchronous motor module, the stator winding transients are neglected, but the dynamic characteristics of the excitation winding and damping winding are considered. It is often used for the analysis of problems where the rotor super-transient process can be neglected but the rotor winding passing process is considered.

In the standard synchronous motor module, the stator winding transients are ignored, but the transients of the excitation winding, the damping winding, and the dynamic characteristics of the rotor winding are taken into account, as well as the convex pole effect of the motor. It is commonly used in cases where the accuracy of power system transient stability analysis is required to be high.

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2. Power transformer module

Transformers byMagnetic Circuit CharacteristicsThey can be categorized into linear and saturated transformers; byNumber of windingsIt can be categorized into double-winding and triple-winding transformers; according to thephase (math.)They can be categorized into single-phase and three-phase transformers.

2.1 Single-phase transformer module

 

The figure above shows a three-phase, three-winding transformer and its parameter setting dialog box. There are two unit systems, SI and.

1) Rated power and frequency: The rated frequency is selected to be consistent with the frequency of the selected excitation source.

2) Parameters of winding 1: It includes rated voltage V1, resistance and leakage inductance of the winding.

3) Parameters of winding 2: It includes the rated voltage V2, which is a step-down transformer if its value is less than V1 and a step-up transformer if it is greater than V1. Resistance and leakage inductance of winding 2.

(4) Three-phase winding transformer check box: selected this check box will be a single-phase three-winding transformer, at this point is also equivalent to two double-winding transformer; otherwise it is a single-phase double-winding transformer.

5) Parameters of winding 3: Similar function to that of V2.

6) Excitation resistance and inductance: The excitation resistance and inductance simulate the active and reactive losses of the core.

7) Measured option:

Selecting Winding Voltage measures the terminal voltage of each winding of the linear transformer module; selecting Winding Current measures the winding current flowing through the linear transformer; selecting Magnetizing Current measures the magnetizing current of the linear transformer module; the ALL option measures all of the above options.

8) If simulating an ideal transformer model just set the resistance and inductance of each winding to 0 and the excitation winding and inductance to inf.

2.2 Three-phase transformer module

A three-phase transformer can be made from three single-phase transformers. Three-phase transformers are connected to each other in the circuit and independent of each other in the magnetic circuit.

There are two types of linear and core-saturated three-phase transformers in the library.

There are 5 types of connections.

1) Rated power and frequency: rated power, rated frequency

2) Primary winding parameters: rated line voltage rms, resistance, leakage inductance

3) Secondary winding parameters: rated line voltage rms, resistance, leakage inductance

(4) excitation resistance: reaction transformer core loss, if the core to take 2%, then Rm = 500

(5) Excitation inductance: this text box appears only when the (Saturated core) checkbox is unchecked, unit

6) Saturation characteristics: Specify the current-flux characteristic curve from the coordinate origin (0,0).

(7) Hysteresis check box: to realize the simulation of transformer hysteresis phenomenon

(8) Flux Initialization check box: where the initial flux of each phase of the transformer are standardized.

9) Parameter Measurement drop-down box:

a. Winding voltage: Measurement of terminal voltage of three-phase transformer

b. Winding current: Measurement of the current flowing through the three-phase transformer

c. flux and excitation current:

d. Flux and magnetizing current: Measurement of flux and excitation current at transformer saturation

e. Measurement of all

The three-phase, three-winding transformer module functions similarly to the above.

2.3 Mutual inductive winding module

A mutual inductance winding is also a simple transformer module that consists of two or three coupled windings that have mutual inductance.

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3. Transmission line module

3.1 Principle analysis

Assuming that the parameters R,L,C of the transmission line are uniformly distributed along the line in the case of a balanced three-phase, a balanced three-phase transmission line can be simulated by using a π-shaped centralized parametric equivalent circuit. When the line is long, several identical π-shaped equivalent circuits can be utilized in series for simulation.

3.2 Modules for transmission lines

3.2.1. π-equivalent circuit module

The π-equivalent circuits of transmission lines include single-phase π-circuits and three-phase π-equivalent modules. In power systems, for overhead lines with lengths greater than 100km and longer cable lines, the effect of capacitance is generally not negligible. Therefore, the beat-shaped circuit module is often used in the calculation of tidal current, transient stability analysis and other calculations.

Single-phase π-equivalent circuit

 

Three-phase π-circuit

1) Base frequency: the base frequency of the simulated system is used to calculate the RLC

2) Unit length resistance: positive and zero sequence resistance

3) Inductance per unit length: positive-order and zero-order inductance

4) Unit length capacitance: positive and zero sequence capacitance

5) Line length

For lines up to 300km in length a single π-circuit can be used instead, and for longer lines multiple stages can be simulated in series. π-circuits limit the voltage and current in the linefrequency changerange, for studying power systems at fundamental frequencies and the relationship between power systems and control systems, π-shaped circuits can achieve adequateaccuracyHowever, for the study of the switch opening and closingcis-variable processand other high-frequency transient components of the problem, it is necessary to take into account the properties of the distribution parameters and use theDistribution parameter linesModule.

3.2.2 Distributed Parameter Equivalent Circuit Module

1) Number of phases: change the number of phases of the distribution parameter line

2) Fundamental Frequency: The fundamental frequency is used to calculate the parameter values of R,L,C.

(3) unit length resistance: the unit length resistance expressed in a matrix, for two-phase and three-phase continuous commutation lines, you can enter the positive sequence and zero-sequence resistance r1,r0, for the symmetrical six-phase line, you can enter the positive-sequence, zero-sequence and coupling resistances [r0,r1,r0m]; for the N-phase asymmetric circuits, you must enter the expression and the interrelationships between each line and the lines of the N * N order of the matrix of resistances

4) Inductance per unit length: same as above

5) Unit length capacitance: same as described above

6) Line length:

7) Measurement parameters: Measurement of phase voltages at the sending and receiving ends of the line

3.3 RLC Series Branch Module

In power systems, for short lines with low voltage levels (overhead lines up to 100km in length), the effect of line capacitance is usually ignored and equated with RLC series branches.

The SimPowerSystems library provides two of the above RLC series branch circuit module icons inside. One is single-phase and the other is three-phase.

 

1) Resistance

2) Inductance

3) Capacitance

4) Measurement parameters

a. None

b. Branch circuit voltage

c. Branch current

d. All variables

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4. Load module

The usual load models are divided intostatic modelcap (a poem)dynamic modelThe static model represents the relationship between load power and voltage and frequency in steady state; the dynamic model responds to the change of load power with time when voltage and frequency change drastically. Commonly used load equivalent circuits include source-containing equivalent impedance branches, constant branch circuits and asynchronous motor equivalent circuits.

4.1 Static load module

Four static load modules are provided in the SimPowerSystems library. They are single-phase series RLC load; single-phase parallel RLC load; three-phase series RLC load; and three-phase parallel RLC load.

1) Connection of three-phase loads

2) Rated line voltage of the load

3) Rated frequency

4) Active power of the load

5) Inductive reactive power of three-phase loads

6) Capacitive reactive power for three-phase loads

7) Measurement: measure the voltage across the load and the current through the load

4.2 Dynamic load module

 

1) Rated line voltage and frequency of the loads

2) Active and reactive power at initial voltage

(3) Positive sequence voltage initialization: Specify the amplitude and phase angle of the positive sequence voltage.

(4) PQ external control: the active and reactive power of the load when selected can be controlled by these two external signals of thesimulinkVectors are defined.

5) Parameter np,nq: Specify the parameter np,nq that defines the load characteristics.

6) Time Constant: Specifies the time constant for controlling the active and reactive dynamic characteristics of the load.

(7) Minimum voltage: Specify the minimum voltage for the initial state of the dynamic load.

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5. Circuit breakers and fault modules

During the transient simulation of the power system, the opening and closing of the circuit breaker module or the three-phase fault module realizes the equipmentautomatic switching control。

5.1 Circuit breaker module

It can be controlled by internal and external signals, external control (0 cut off, 1 on) internal control (specified by parameters in the module dialog)

5.1.1 Single-phase circuit breaker module

1

1) Initial state of the circuit breaker: 1 closed, 0 open

2) Switch action time: 5/60 time points switch action once as shown in the figure.

3) External control

4) The equivalent resistance value of the circuit breaker after closing, which is generally very small.

5) Buffer Resistor: the value of the resistor in the parallel circuit, which is canceled when inf is selected.

6) Buffer capacitance: When the buffer capacitance is set to 0, the buffer capacitance will be canceled; when the buffer capacitance is set to inf, the buffer circuit is a purely resistive circuit.

7) Measurement parameters:

a. None

b. Circuit breaker voltage

c. Circuit breaker current

d. All

5.1.2 Three-phase circuit breaker module

1) Initial state

2) Checked to indicate which circuit breaker is allowed to operate

5.2 Three-phase fault module

The three-phase fault control module is composed of three separate circuit breakers capable of simulating phase-to-phase and phase-to-ground faults.

1) Ground Fault: Indicates that ground faults are allowed; when unchecked, the earth resistance is automatically set to the 6th power of 10.

2) Fault resistance: cannot be 0

(3) Earth resistance: the grounding resistance in case of a ground fault.