Breaker - Implement circuit breaker opening at current zero crossing

Library

Elements

Description

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 or 1 (0 to open the breaker, 1 to close it).

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.

Operation	Conditions
The Breaker closes when	Control signal goes to 1 (for discrete systems, control signal must stay at 1 for at least 3 times the sampling period)
The Breaker opens when	Control signal goes to 0 Breaker current passes through 0

Operation

Conditions

The Breaker closes when

Control signal goes to 1 (for discrete systems, control signal must stay at 1 for at least 3 times the sampling period)

The Breaker opens when

Control signal goes to 0

Breaker current passes through 0

Note 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.

Dialog Box and Parameters

Breaker resistance Ron

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

Initial state

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

Snubber resistance Rs

The snubber resistance, in ohms (Ω). Set the Snubber resistance Rs parameter to inf to eliminate the snubber from the model.

Snubber capacitance Cs

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

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 state. For example, if the Initial state 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 visible in the dialog box if the External control of switching times parameter is selected.

External control of switching times

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.

Measurements

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.

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:

Measurement	Label
Branch voltage	`Ub:`
Branch current	`Ib:`

Limitations

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.

You must 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 3 sampling time periods to correctly close the Breaker block, otherwise the device stays open.

Example

The power_breaker demo illustrates a circuit breaker connected in series with a series RL circuit on a 60 Hz voltage source. The switching times of the Breaker block are controlled by a Simulink signal. The breaker device is initially closed and an opening order is given at t = 1.5 cycles, when current reaches a maximum. The current stops at the next zero crossing, then the breaker is reclosed at a zero crossing of voltage at t = 3 cycles.

Simulation produces the following results.

Note that the breaker device opens only when the load current has reached zero, after the opening order.