This three-level Neutral-Point Clamped (NPC) converter is a switching function model of a Voltage Source Converter. The NPC topology is often used for its harmonic and switching loss reduction and smaller output current ripple. The switching function offers a good compromise between the real-time performance of an average model and the accuracy of using detailed switches by preserving the harmonic content of a switching device.

NOTE: In order to obtain accurate results, the options Activate iterative method and Solve control inputs before solving power in Simulation Settings must be selected when using this component.

Mask and Parameters

Parameter Name	Description	Unit	Variable = {Possible Values}
Description	Use this field to add all kinds of information about the component		Description = {'string'}
Diode on-state resistance	Internal resistance of diodes	Ohm	Rclose = { [1e-12, 1e12] }
Diode snubber resistance	Snubber resistance of the diodes	Ohm	Rsnubber = { [1e-12, 1e12] }

Ports, Inputs, Outputs and Signals Available for Monitoring

Ports

Name	Description
net_1	Network connector on the AC side (supports only 3-phase connections)
DCplus	Network connector on the DC side. The symbol + shows that this is the positive end (supports only 1-phase connections)
DCminus	Network connector on the DC side. The symbol - shows that this is the negative end (supports only 1-phase connections)
DCneutral	Neutral network connector (supports only 1-phase connections)

Inputs

Name	Description
P	Vectorized signal containing twelve firing pulses to control the converter

Outputs

Name	Description
V	Vectorized voltage signal containing the phase-to-ground voltages on the AC side (Va, Vb, and Vc) and the DC link (Vdc).
I	Vectorized current signal containing phase currents on the AC side (Ia, Ib and Ic) and the current of the DC link (Idc).

Sensors

Name	Description	Unit
P[P1]	Gating signal controlling Q1.
P[P2]	Gating signal controlling Q2.
P[P3]	Gating signal controlling Q3.
P[P4]	Gating signal controlling Q4.
P[P5]	Gating signal controlling Q5.
P[P6]	Gating signal controlling Q6.
P[P7]	Gating signal controlling Q7.
P[P8]	Gating signal controlling Q8.
P[P9]	Gating signal controlling Q9.
P[P10]	Gating signal controlling Q10.
P[P11]	Gating signal controlling Q11.
P[P12]	Gating signal controlling Q12.
V[Va]	Voltage signal of phase A on the AC side of the converter.	V
V[Vb]	Voltage signal of phase B on the AC side of the converter.
V[Vc]	Voltage signal of phase C on the AC side of the converter.
V[Vdc]	Converter DC link voltage signal.
I[Ia]	Phase A current signal on the AC side.	A
I[Ib]	Phase B current signal on the AC side.
I[Ic]	Phase C current signal on the AC side.
I[Idc]	Current signal of the DC link.

Additional Information

The converter is modeled by a switching function. The switches are replaced by two voltage sources and two diodes per phase on the AC side and two current sources on the DC side.

The figure below shows the internal circuit of the converter that can be accessed by opening the subcircuit. Although its topology is similar to the 2-Level Converter (Switching Function), it is important to note that the amplitude control equations for voltage and current sources are different.

The converter is controlled by firing pulses produced by a PWM generator or by firing pulses averaged over a time step of the simulation (1 / Ts), providing signals between 0 and 1 (see PWM Average Generator for 3-Level Converter (Switching Function)). Both operating modes accurately produce harmonics. In addition, this converter model correctly simulates the operation as a rectifier as well as the blanking time.

The PWM average generator outputs a vectorized gating signal to control the converter. The gating signal contains 12 firing pulses. The first four pulses control the Q1 to Q4 switching devices (phase A of the converter), pulses five to eight control the Q5 to Q8 switching devices (phase B of the converter), and the last four pulses control the Q9 to Q12 switching devices (phase C of the converter).

Limitations

This model is to be used with the PWM Average Generator for 3-Level Converter (Switching Function) component available in the Control Sources library of HYPERSIM or with an input FPGA module (contact our technical support for an example).

This model does not participate in the load flow solution.

References

MathWorks, Three-Level NPC Converter https://www.mathworks.com/help/physmod/sps/powersys/ref/threelevelnpcconverter.html

M. H. Rashid, Power electronics handbook, 4^th ed. Butterworth-Heinemann, 2017

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