Variable Capacitor
Linear variable capacitor.
Description
The Variable Capacitor unit is a model of a linear capacitor with variable capacitance.
The block has the option of selecting the equation for the relationship between the current through the capacitor and the voltage with the capacitance on the C port 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 charge-voltage curve for a given voltage:
-
Use the equation above if capacitance is defined as the ratio of charge to steady-state voltage:
The block models a resistor in series with a variable capacitor. The resistor can be used to represent the total ohmic resistance of the 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 a Variable Capacitor block is connected in series with another capacitor block with no series resistance.
Ports
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 current in the capacitor:
-
I = C*dV/dt- if it is assumed that the capacitance is the 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 capacitance is the ratio of charge to steady-state voltage.
Minimum capacitance C>0 - minimum capacitance
1e-9 F (By default).
Lower limit on the signal value on the C port. This limitation prevents the signal from reaching a value that makes no physical sense.
Series resistance - series resistance
1e-6 ohms (by default).
The value of the resistance included in series with the variable capacitor.
Initial value - initial value of voltage v
0 (By default)
Initial value of voltage, V.
Dependencies
This parameter is only used when I = C*dV/dt is selected for the Equation parameter.
Initial charge - initial value of charge q
0 (By default)
Initial charge value, Cl.
Dependencies
This parameter is only used when I = C*dV/dt + dC/dt*V is selected for the Equation parameter.