3-Phase Current Source Inverter

Purpose

3-phase 2-level current source inverter module

Library

Electrical / Power Modules

Description

This power module implements a 3-phase 2-level current source inverter. It offers two configurations:

Switched

All power semiconductors inside the module are modeled with ideal switches. The individual switches are controlled with logical gate signals. A switch is on if the corresponding gate signal is not zero. For compatibility with the averaged configuration it is recommended to use the value \(1\) for non-zero gate signals.

Sub-cycle average

The module as a whole is modeled with controlled voltage and current sources. The DC side of the inverter has voltage source behavior and must be connected to positively biased inductors or current sources. The AC side is typically connected to filter capacitors. Only delta-connected filter capacitors are allowed since no neutral point is considered in the model. The six control inputs are the relative on-times of switches with values between \(0\) and \(1\).

In the average configuration the 3-phase 2-level current source inverter can be operated in two ways:

• The control signals are instantaneous logical gate signals having the values \(0\) and \(1\).

• The control signals are the duty cycles of the individual switches. They are either computed directly from the modulation index or by periodically averaging the digital gate signals over a fixed period of time, e.g. using the Periodic Average block. The averaging period does not need to be synchronized with the PWM and can be as large as the inverse of the switching frequency.

In both use cases, the average implementation correctly accounts for live times, i.e. when during commutation at least one of the upper switches and one of the lower switches are both turned on to sustain the dc-side externally connected current source.

It also supports rectifier operation mode, when power is flowing from AC side to DC side. In rectifier mode, both cases of free-wheeling diode on dc-side and no free-wheeling diode are included. It has to be specified correctly under Parameters of the mask dialogue window.

Since the duty cycle is simulated accurately even with relatively large time steps, the average configuration is particularly well suited for real-time simulations with high switching frequencies.

Note

The sub-cycle average implementation cannot model an open circuit of the DC side. Therefore for inverter mode, the sum of the control signals for the upper three switches and the lower three switches must larger than \(1\) at any point in time. The block will flag an error if this condition is not met. For rectifier mode, please see the description of the Free-wheeling diode on DC side parameter below. Also, the applied DC currents must never become negative.

Parameters

Configuration

Switched or averaged circuit model.

Free-wheeling diode on DC side

This parameter is only applicable for rectifier mode. The option no means no extra free-wheeling diode on the DC side is modeled and that the sum of the control signals for the upper three switches and the lower three switches must be larger than \(1\) at any point in time. Otherwise the block will flag an error. The option yes means an extra DC-side free-wheeling diode is included. In this case no flag error will be triggered when the sum of the control signals for the upper three switches and the lower three switches is smaller than \(1\), because the DC current can flow through this extra free-wheeling diode.