Multi-Phase Current Source Inverter
Overview
This model features a multi-phase current source inverter (CSI). The CSI is an inverter circuit which creates AC current and voltage from a DC current source. The multi-phase CSI is implemented with a configurable subsystem which showcases the 3-phase, 4-phase and 5-phase topology.
The circuit parameter is chosen with no specific reasons. The inverter is controlled in open-loop fashion. The highlight of this demo is to demonstrate the modeling of a generic modulation strategy for multi-phase CSI, proposed by the authors in [1].
Note
Model
The top-level schematics of the demo model is shown in Fig. 1. It consists of a “Modulator” subsystem and a “CSI” subsystem. PWM signals are connected between the two subsystems to form an open-loop control.
Fig. 1 The figure caption of the main schematic
Since the invention of the MOSFET, voltage source inverters (VSIs) have been far more widely used in various applications compared to CSIs. As a result, advancements in modulation and control techniques in power electronics have primarily focused on VSIs. One of the most well-known modulation techniques is Space Vector Modulation (SVM), introduced for three-phase VSIs.
VSIs used Pulse Width Modulation (PWM) on a per-phase basis, whereas CSIs do not operate on a per-phase basis; instead, the switches connected to the upper (positive) rail are treated as a unified entity, as the DC link current flow must always be maintained. Similarly, switches near the lower (negative) rail are also considered as a single entity.
Plant
The plant subsystem is a configurable subsystem which has 3 configurations: 3-phase, 4-phase and 5-phase CSI topology. It can be viewed by right-clicking on the “Multi-phase CSI” subsystem + Subsystem + Open subsystem. The parameter \(n\) is used in the model initialization commands to choose the number of phases, hence the corresponding topology configuration. These 3 configurations are depicted in Fig. 2, Fig. 3 and Fig. 4 respectively.
The inverter is powered by a fixed DC link current source \(I_\mathrm{dc}\). The inverter consists of \(2n\) unidirectional switches, implemented with upper switch \(\mathrm{S_u}_1\) to \(\mathrm{S_u}_n\) with upper diodes \(\mathrm{D_u}_1\) to \(\mathrm{D_u}_n\), and lower switches \(\mathrm{S_l}_1\) to \(\mathrm{S_l}_n\) with lower diodes \(\mathrm{D_l}_1\) to \(\mathrm{D_l}_n\).
Fig. 2 3-phase current source inverter schematic
Fig. 3 4-phase current source inverter schematic
Fig. 4 5-phase current source inverter schematic
Controller
More details about the modulator can be found in [1]. Fig. 5 shows the controller schematic. The PLECS schematic is built following that of Fig. 6 of [1]. A PWM method tailored specifically for CSIs without any requirements typical for SVM, such as sector identification, is used here.
The primary objective of the proposed modulation strategy in [1] is to use linear algebra to determine the average duty ratio values \(d_{\mathrm{u}k}\) for upper cells and \(d_{\mathrm{l}k}\) for lower cells (for \(k=1,... n\)). They are represented by the Signal Goto tag named “du” and “dl” respectively in the schematic presented in Fig. 5.
These values are then applied to the proposed multi-threshold modulator (MTM), which generates the PWM switching signals that control \(\mathrm{S_u}_k\) and \(\mathrm{S_l}_k\), ultimately ensuring the desired average values for the inverter output currents. As an example, Fig. 6 shows the schematic of the upper-cell MTM for the 3-phase CSI. Note that the MTM uses the identical algorithm for the upper and lower cells. Furthermore, its pattern is easily extendable from a 3-phase up to multi-phase CSI application.
Fig. 5 Control schematic of the multi-phase CSI
Fig. 6 Schematic of the upper-cell multi-threshold modulator in the 3-phase CSI
The control signals in Fig. 5 before the MTM subsystem are vectorized to fit the dimension of \(n\) (number of phases). The MTM is a configurable subsystem, whose configuration is selected automatically to match the definition of \(n\) in the model initialization commands.
Simulation
The main simulation results are depicted in Fig. 7, Fig. 8 and Fig. 9, respectively for the 3-phase, 4-phase and 5-phase CSI. They exhibit a good agreement with the results presented in Fig. 7 of [1].
Fig. 7 Simulation results for the 3-phase CSI
Fig. 8 Simulation results for the 4-phase CSI
Fig. 9 Simulation results for the 5-phase CSI
Conclusion
This demo aims at showcasing a novel modulation technique for current source inverters with an arbitrary number of phases.
Bibliography
[1]
Pejović, P., Ohno, T., Borović, U. and Mirić S., “Pulse width modulation for current source inverters with arbitrary number of phases,” in Scientific Reports 15, 8744 (2025). Available: https://doi.org/10.1038/s41598-025-92388-9. [Accessed: Aug. 28, 2025].