Engee documentation

Variable Capacitor

Linear variable capacitor.

blockType: AcausalElectricPowerSystems.Passive.VariableCapacitor

variable capacitor

Path in the library:

/Physical Modeling/Electrical/Passive/Variable Capacitor

Description

Block Variable Capacitor It is a model of a linear capacitor with variable capacitance.

The unit has the possibility to select the equation of the connection between the current through a capacitor and voltage with a capacity on port C equal to .

The Equation parameter determines which of the following equations uses the block:

  • .

    Use the equation above if the capacitance is defined as the local gradient of the charge-voltage curve for a given voltage.:

    .

  • .

    Use the equation above if the capacity is defined as the charge ratio. to steady state voltage:

    .

The block simulates a resistor connected in series with a variable capacitor. A resistor can be used to represent the total ohmic resistance of a capacitor, including contact resistances. In addition, the use of a resistor may be required to prevent computational errors in some circuit topologies. For example, when the block Variable Capacitor connected in series with another capacitor unit without series resistance.

Ports

Entrance

C — pass capacity:q[<br>] scalar

The input signal determining the value of the capacitance, F.

The capacity must be finite, greater than zero.

Non-directional

+ — positive
electricity

The electrical port corresponds to the positive terminal of the capacitor.

− — negative
electricity

The electrical port corresponds to the negative terminal of the capacitor.

Parameters

Equation — equation for the current in the capacitor
I = C*dV/dt (default) | I = C*dV/dt + dC/dt*V

Select one of the following options to calculate the capacitor current:

  • I = C*dV/dt — if it is assumed that the capacity is a local gradient of the charge-voltage curve for a given voltage. This option is used by default.

  • I = C*dV/dt + dC/dt*V — if it is assumed that the capacity is the ratio of charge to steady-state voltage.

Minimum capacity C>0 — minimum pass capacity:q[<br>] 1e−9F (default)

The lower limit on the signal size on port C. This limitation prevents the signal from reaching a value that has no physical meaning.

Series resistance — sequential resistance
1e−6 ohms (default)

The value of the resistance connected in series with a variable capacitor.

Initial value — initial voltage value v
0 (default)

The initial voltage value, V.

Dependencies

This option is only used when selecting I = C*dV/dt for the Equation parameter.

Initial charge — initial charge value of q
0 (default)

Initial charge value, Kl.

Dependencies

This option is used only when selecting I = C*dV/dt + dC/dt*V for the Equation parameter.