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Three-Level Bridge

Implement three-level neutral point clamped (NPC) power converter with selectable topologies and power switching devices


Fundamental Blocks/Power Electronics


The Three-Level Bridge block implements a three-level power converter that consists of one, two, or three arms of power switching devices. Each arm consists of four switching devices along with their antiparallel diodes and two neutral clamping diodes as shown in the figure below.

The type of power switching device (IGBT, GTO, MOSFET, or ideal switch) and the number of arms (one, two, or three) are selectable from the dialog box. When the ideal switch is used as the switching device, the Three-Level Bridge block implements an ideal switch bridge having a three-level topology as shown in the following figure.


Number of bridge arms

Determine the bridge topology: one, two, or three arms. Default is 3.

Snubber resistance Rs

The snubber resistance, in ohms (Ω). Default is 1e5. Set the Snubber resistance Rs parameter to inf to eliminate the snubbers from the model.

Snubber capacitance Cs

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

To eliminate snubbers in all power electronic devices when using a continuous solver, select the Disable snubbers in switching devices option in the Powergui Preferences tab.

When your system is discretized, you can simulate power electronic devices with virtually no snubbers by specifying purely resistive snubbers with a very large resistance, thus producing negligible leakage currents. The bridge operates satisfactorily with purely resistive snubbers.

Power electronic device

Select the type of power electronic device to use in the bridge. Default is GTO/Diodes.

Internal resistance Ron

Internal resistance of the selected devices and diodes, in ohms (Ω). Default is 1e-3.

Forward voltages [Device Vf, Diode Vfd]

The forward voltage of the selected devices (for GTO or IGBT only) and of the antiparallel and clamping diodes, in volts. Default is [ 0 0 ].


Default is None.

Select All device currents to measure the current flowing through all the components (switching devices and diodes). If the snubber devices are defined, the measured currents are those flowing through the power electronic devices only.

Select Phase-to-Neutral and DC voltages to measure the terminal voltages (AC and DC) of the Three-Level Bridge block.

Select All voltages and currents to measure all voltages and currents defined for the Three-Level Bridge block.

Place a Multimeter block in your model to display the selected measurements during the simulation. In the Available Measurement list box of the Multimeter block, the measurement is identified by a label followed by the block name.


Label (for GTO, IGBT, MOSFET Devices)

Device currents

IQ1a, IQ2a, IQ3a, IQ4a,

IQ1b, IQ2b, IQ3b, IQ4b,

IQ1c, IQ2c, IQ3c, IQ4c,

ID1a, ID2a, ID3a, ID4a, ID5a, ID6a,

ID1b, ID2b, ID3b, ID4b, ID5b, ID6b,

ID1c, ID2c, ID3c, ID4c, ID5c, ID6c

Terminal voltages

Uan:, Ubn:, Ucn:, Udc+:, Udc-:


Label (for Ideal Switch Device)

Device currents

Isw1a, Isw2a, Isw3a, Isw1b, Isw2b, Isw3b,
Isw1c, Isw2c, Isw3c

Terminal voltages

Uan:, Ubn:, Ucn:, Udc+:, Udc-:

Inputs and Outputs

The input g is a vectorized gating signal containing pulses to control the power electronic devices of the bridge. The length of the input vector depends on the number of arm you specified for the bridge topology.


Pulse Vector of Input g

One arm


Two arms


Three arms


    Note   In the case of the ideal switch converter, the Q1 pulse is sent to Sw1, the Q4 pulse to Sw2, and a logical AND operation is performed on the Q2 and Q3 pulses and the result sent to Sw3.

Assumptions and Limitations

Turn-on and turn-off times (Fall time, Tail time) of power switching devices are not modeled in the Three-Level Bridge block.


The power_3levelVSC example illustrates the use of the Three-Level Bridge block.

Introduced before R2006a

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