Single Shunt Current Reconstruction

Single-Shunt current reconstruction is the use of one current shunt resistor on the DC bus to take precisely timed current measurements. Since we know the state of the gates in our inverter circuit, we can determine the current in each phase. Figure 1 shows an example state below.

Figure 1. Positive A Switching State (Source)

As we can see, all of the dc current measured in this state flows in the positive direction through phase A, so we know the phase A current! The current then splits through phases B and C on the low side, so no information for those phases is gained. For another example, let's take a look at Figure 2.

Figure 2. Negative C Switching State (Source)

From this image, we see that the current splits on the high side (through phases A and B) this time. On the low side, however, all of the current flows through phase C. This means that our dc current is equal to the negative of the phase C current. See below for a full list of switching states and the phase current that's measured in them.

Figure 3. Single Shunt State Table (Source)

There are timing considerations that become important when using this method, but we'll get to those later.