Implement circuit breaker opening at current zero crossing


Fundamental Blocks/Elements


The Breaker block implements a circuit breaker where the opening and closing times can be controlled either from an external Simulink® signal (external control mode), or from an internal control timer (internal control mode).

A series Rs-Cs snubber circuit is included in the model. It can be connected to the circuit breaker. If the Breaker block happens to be in series with an inductive circuit, an open circuit or a current source, you must use a snubber.

When the Breaker block is set in external control mode, a Simulink input appears on the block icon. The control signal connected to the Simulink input must be either 0, which opens the breaker, or any positive value, which closes the breaker. For clarity, a 1 signal is commonly used to close the breaker.

When the Breaker block is set in internal control mode, the switching times are specified in the dialog box of the block.

When the breaker is closed, it is represented by a resistance Ron. The Ron value can be set as small as necessary in order to be negligible compared with external components (a typical value is 10 mohms). When the breaker is open, it has an infinite resistance.

The arc extinction process is simulated by opening the breaker device when its current passes through 0 at the first current zero crossing following the transition of the Simulink control input from 1 to 0.



The Breaker closes when

Control signal goes to 1 (for discrete systems, control signal must stay at 1 for at least three times the sampling period)

The Breaker opens when

Control signal goes to 0

Breaker current passes through 0


The Breaker block may not be the appropriate switching device to use for DC circuits. For such applications, it is recommended that you use the Ideal Switch block as a switching device.


Initial status

The initial state of the breaker. A closed contact is displayed in the block icon when it is set to 1, and an open contact is displayed when it is set to 0. Default is 0.

If the breaker initial state is set to 1 (closed), the software automatically initializes all the states of the linear circuit and the Breaker block initial current, so that the simulation starts in steady state.

Switching times

Specifies the vector of switching times when using the Breaker block in internal control mode. At each switching time the Breaker block opens or closes depending on its initial status. For example, if the Initial status parameter is 0 (open), the breaker closes at the first switching time, opens at the second switching time, and so on. The Switching times parameter is not available if the External check box is selected. Default is [1/60 5/60].


If selected, adds a Simulink input to the Breaker block for external control of the switching times of the breaker. The switching times are defined by a logical signal (0 or 1) connected to the Simulink input. Default is selected.

Breaker resistance Ron

The internal breaker resistance, in ohms (Ω). The Breaker resistance Ron parameter cannot be set to 0. Default is 0.01.

Snubber resistance Rs

The snubber resistance, in ohms (Ω). Set this parameter to inf to eliminate the snubber from the model. Default is 1e6.

Snubber capacitance Cs

The snubber capacitance, in farads (F). Set this parameter to 0 to eliminate the snubber, or to inf to get a resistive snubber. Default is inf.


Select Branch voltage to measure the voltage across the Breaker block terminals.

Select Branch current to measure the current flowing through the Breaker block. If the snubber device is connected to the breaker model, the measured current is the one flowing through the breaker contacts only.

Select Branch voltage and current to measure the breaker voltage and the breaker current.

Default is None.

Place a Multimeter block in your model to display the selected measurements during the simulation.

In the Available Measurements list box of the Multimeter block, the measurement is identified by a label followed by the block name:



Branch voltage


Branch current



When the block is connected in series with an inductor or another current source, you must add the snubber circuit. In most applications, you can use a resistive snubber (Snubber capacitance parameter set to inf) with a large resistor value (Snubber resistance parameter set to 1e6 or so). Because of modeling constraints, the internal breaker inductance Ron cannot be set to 0.

Use a stiff integration algorithm to simulate circuits with the Breaker block. ode23tb with default parameters usually gives the best simulation speed.

For discretized models, the control signal must stay at 1 for a minimum of three sampling time periods to correctly close the Breaker block, otherwise the device stays open.


See the power_breaker example for a circuit using the Breaker block.

Introduced before R2006a

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