Three phase inverter in current control mode interfaced to a three phase inverter in voltage control mode

The circuit files for this case are in these two links:

This is the first multi-inverter case successfully simulated with this circuit simulator. One of the three phase inverters is controlled in voltage control mode and forms the voltage source. The other three phase inverter is controlled in current control mode and injects current into the source. Typically, there would also be other load which in this case is modeled as a passive R-L load. The dc bus of the inverter in voltage control mode is a constant dc source while the dc bus of the inverter in current control mode is formed by a dc capacitor charged by a diode rectifier fed by another three phase ac source. The inverter in voltage control mode is designated as VSI1 and the inverter in current control mode is designated as VSI2. The sequence of operation is as follows.

  1. Until 0.05s, the inverter VSI1 in voltage control mode alone operates. The gate signals to VSI2 are blocked.
  2. At 0.05s, VSI2 connects to the grid formed by VSI1. However, the current injected by VSI 2 is zero until 0.1s.
  3. At 0.1s, the inverter VSI2 begins to inject 30A into the grid. This 30A is an in-phase component causing active power to be injected into the grid.

The first result is the voltages produced by VSI1 in the d and q domain. The objective of voltage control applied on VSI1 is to regulate the d component of the output voltage to 150V and the q component to 0. The waveforms have oscillations as VSI2 is turned on at 0.05s and at 0.1s injects current into the grid.

The three phase voltage produced by VSI2 are as shown below.

The next figure shows the tracking performance of the current controller of VSI 2 in the d and q domain. The d component of current becomes -20A after 0.1s while the q component remains 0.

The actual three phase currents are shown below.

The next figure shows currents supplied by the diode rectifier charger for VSI2 and the dc bus voltage of VSI2. The active power supplied by VSI2 to the grid causes its dc bus voltage to drop which is then charged by the diode rectifier fed by a separate three phase source. Typically, this diode rectifier will be energized by a transformer connected to the output of VSI1. This will be simulated later.

This simulation was executed at a simulation time step of 100 nanoseconds. Improvements in the solver could allow the simulation to be run at larger time steps. However, up to four simulations were executed simultaneously on an eight year old laptop. This is promising for the proposed simulation of multi-inverter microgrids at a later stage.