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Phase Current Sensor and Short Circuit Protection Based on PCB-Embedded Rogowski Coils Integrated in the Gate Driver of a 1.2 kV 300 A SiC MOSFET Module

Image of Phase current reconstruction principle
Fig. 1. Phase current reconstruction principle.
The market and technology trends in applications such as electric and hybrid electric vehicles are striving towards high-density and high-efficiency conversion. Silicon-carbide (SiC) power metal-oxide semiconductor field-effect transistors (MOSFETs) have become attractive solutions for these applications due to their high breakdown electric field, high working temperature, fast switching speed, and low on-state resistance, as well as recent packaging advancements and decreased cost. The necessity of new, fast, and reliable short circuit protection methods, and high-density, high-efficiency trends, has led to a gate driver (GD) with an integrated Rogowski switch current sensor (RSCS). In the newly designed GD, switch currents are measured and used for protection, while the same information is used for obtaining the phase current with simple manipulation of the GD itself (principle shown in Fig. 1.). By understanding the switch currents in the complete switching cycle, outputting the phase current from the GD is possible by subtracting these two currents. The phase current information from the GD for a continuous pulse width modulated inverter can then be sent back to main controller for control purposes.

Architecture for this gate driver includes an RSCS for the top and bottom devices on the controller (common) ground and digital reconstruction of the phase current. In order to subtract two-current information in some sort of digital signal processor, two analog-to-digital converters are required. A field-programmable gate array is employed for digital subtraction and turning off the RSCS when the corresponding switch is not conducting. A digital-to-analog converter is necessary to convert phase current information back to analog in order to emulate commercial current measurement, perform a comparison, and send information to the controller for control purposes.

Fig. 2 shows the reconstructed sinusoidal current from one of the phases of the inverter, together with the switches current of the corresponding phase. It is clear that the reconstructed phase current waveform (yellow) is the result of subtracting the top switch current (cyan) from the bottom switch current (purple). Comparison with the commercial measurement (green) can also be seen in Fig. 2. The reconstructed phase current appropriately follows the commercial measurement in both amplitude and phase with a consistent delay of 1.6 µ. Tests are performed with the low gate source external resistance in order to push transient speed and reduce switching losses. dV/dt was 15 V/ns. In this severe noise environment and from switch currents illustrated in Fig. 2., it is shown that there are no shoot-through events caused by the Miller effect or induced signal malfunction. Furthermore, chosen components that participate in phase current reconstruction cope well with the common mode noise created by the dV/dt, and successfully reconstruct the current.

Image of Reconstructed phase current in inverter
Fig. 2. Reconstructed phase current in inverter.