Diode (SimPowerSystems)

Implement a diode model

Library

Power Electronics

Description

A diode is a semiconductor device that is controlled by its own voltage Vak and current Iak. When a diode is forward biased (Vak>0), it starts to conduct with a small forward voltage Vf across it. It turns off when the current flow into the device becomes 0. When the diode is reverse biased (Vak<0), it stays in the off state.

The Diode block is simulated as a resistor, an inductor, and a DC voltage source connected in series with a switch. The switch is controlled by the voltage Vak and current Iak.

The Diode block also contains a series Rs-Cs snubber circuit that can be connected in parallel with the diode device (between nodes A and K).

The static VI characteristic of this model is shown in the following figure.

Dialog Box and Parameters

Resistance Ron: The diode internal resistance Ron, in ohms (). The Resistance Ron parameter cannot be set to 0 when the Inductance Lon parameter is set to 0.
Inductance Lon: The diode internal inductance Lon, in henries (H). The Inductance Lon parameter cannot be set to 0 when the Resistance Ron parameter is set to 0.
Forward voltage Vf: The forward voltage of the diode device, in volts (V).
Initial current Ic: Specifies an initial current flowing in the diode device. It is usually set to 0 in order to start the simulation with the diode device blocked. If the Initial Current IC parameter is set to a value greater than 0, the steady state calculation of Power System Blockset considers the initial status of the diode as closed.; Initializing all states of a power electronic converter is a complex task. Therefore, this option is useful only with simple circuits.
Snubber resistance Rs: The snubber resistance, in ohms (). 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.
Show measurement port: If selected, adds a Simulink output to the block returning the diode current and voltage.

Inputs and Outputs

The anode of the diode is identified with the letter a and the cathode is identified by the letter k. The Simulink output is a measurement output vector [Iak Vak] returning the diode current and voltage.

Assumptions and Limitations

The Diode block implements a macromodel of a diode device. It does not take into account either the geometry of the device or the complex physical processes underlying the state change [1]. The leakage current in the blocking state and the reverse-recovery (negative) current are not considered. In most circuits, the reverse current does not affect converter or other device characteristics.

Depending on the value of the inductance Lon, the diode is modeled either as a current source (Lon > 0) or as a variable topology circuit (Lon = 0). The Diode block cannot be connected in series with an inductor, a current source, or an open circuit, unless its snubber circuit is in use. See the Advanced Topics chapter for more details on this topic.

You must use a stiff integrator algorithm to simulate circuits containing diodes. ode23tb or ode15s with default parameters usually gives the best simulation speed.

The inductance Lon is forced to 0 if you choose to discretize your circuit.

Example

The psbdiode.mdl demo illustrates a single pulse rectifier consisting of a Diode block, an RL load, and an AC Voltage source block, with the following parameters.

Simulation produces the following results.

References

[1] Rajagopalan, V., Computer-Aided Analysis of Power Electronic Systems, Marcel Dekker, Inc., New York, 1987.

[2] Mohan, N., T.M. Undeland, and W.P. Robbins, Power Electronics: Converters, Applications, and Design, John Wiley & Sons, Inc., New York, 1995.

See Also
Thyristor, Universal Bridge

DC Voltage Source Discrete System