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DC-to-AC Converters LAB 2 - 6. Three-phase Two-level Inverter

In this section, the three-phase two-level inverter and its functional operation are discussed.
Figure 17 shows the simulated circuit for the study of the three-phase two-level inverter.
The power flows from the DC side to the AC side.
The load is a combination in series of resistance, inductance, and a three-phase AC-source.
Notice that the AC-source can be interpreted as a back-electromotive force (BEMF) for motor applications or an electric generator for power grid applications.

There are two possible configurations for the voltage inverter: with or without neutral connected, as shown in figure 17.
For the inverter with neutral connected: it consists in connecting the neutral load to the neutral created in a midpoint of the inverter DC bus.
This connection allows the flow of homopolar currents and can separately control load voltages as three single-phase systems.
So, this configuration is used in applications with compensation of homopolar sequence components.

Additionally, a three-phase delta-connected set of capacitors can be inserted at the output of the inverter, preceded by three-line inductances, leading thus to an LC-filter.
The student can control (i) the amplitude of the DC source, (ii) the inverter parameters, namely, the PWM frequency and the reference amplitude, (iii) the AC-source parameters, namely, the amplitude, the frequency, and the phase-shift. 

     Figure 17: Simulated Circuit for the Study of the Three-Phase Two-Level Inverter

The rest of this laboratory is organized as follows:

  • Section 7 describes the circuit block by block, namely, (i) the converter topology, (ii) the control of the switches and the PWM generation (iii) the load and filter (iv) the circuit parameters and (v) the measurement stations.
  • Section 8 is dedicated to the description of the panel.
    The two tabs associated with the two scenarios, namely, (i) Inverter Mode and (ii) LC Filter are covered in detail.
    The goal of this section is to explain to the students the functionalities of the control parameters, the control buttons, the scopes, the displays, and the help menu, making them capable of monitoring the panels and solving the exercises.
  • Section 9 comprises all the exercises associated with the inverter mode, as well as the LC filtering.
    It is worth noticing that, for this level-one courseware, most of the exercises will consist of changing the control parameters/buttons and observing/interpreting results.
    Consequently, advanced material such as spectral analysis, dead-time insertion, d-q representation and analysis, synthesis and design of closed-loop controller, integration of external controller will be the major components of the level-two courseware.

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