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.

In the block there is a possibility to choose the equation of the connection between the current through the capacitor and voltage when the capacity on port C is equal to .

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

  • .

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

    .

  • .

    Use the equation above if the capacitance 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 usage 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 bank with no series resistance.

Ports

Input

C — pass capacity:q[<br>] scalar

The input signal determining the capacitance value, F.

The capacity must be finite, greater than zero.

Undirected

+ — 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 (by 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 curve «charge-voltage» for a given voltage. This option is used by default.

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

Minimum capacity C>0 — minimum capacity
1e−9F (by 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 — serial resistance
1e−6 ohms (by default)

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

Initial value — initial voltage value v
0 (by default)

The initial value of the voltage, V.

Dependencies

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

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

The initial value of the charge, Kl.

Dependencies

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