Current sensor If a power module is equipped with a current sensor, the signal is primarily used for output current control (e.g., in transmission applications) and can also act as a protective device. The requirements of motor control determine the characteristics of the current sensor. In many cases, faults (including temperature drifts) must be below 1... 2%.
The requirements for temperature (-40 ° C to 125 ° C) and low current loss are set by the power module itself. Device PROTECTION function SETS overcurrent capacity (maximum short-circuit current is 5 times of rated current), upper cut-off frequency (> 100kHz). For low and medium power devices, the use of current diverters is an accurate and cost-effective solution. The current limit is about 30A to 40A. The disadvantages are additional power losses, loss of isolation and interference in the IGBT gate signal if the shunt is used to measure emitter currents.
For high performance and high power semiconductor modules, electrically isolated sensors are generally used. The pure Hall effect sensor without compensating current has poor performance in terms of error and temperature stability. Sensors are available in user-specified modules because the requirements in these modules are clearly defined. A sensor with high linearity and low temperature drift operates with a compensation current. The current counteracts the magnetic field in the core of the sensor where the current is measured.
The control signal of the compensated current amplifier is provided by the Hall effect, magnetic field or reluctance probe. For intelligent power modules (IPM) such as the Semicomic SKiiP system, the use of high-precision sensors is most appropriate due to the high performance requirements of the final application. In the final application, the sensor is directly integrated in the enclosure of the module, which wraps around the main terminal to save space, and the evaluation circuit for signal monitoring and conversion is part of the driver circuit.
Specially designed ASIC chips ensure high integration and reliability, which is difficult to achieve in a solution using external sensors. Inside the IPM, the current monitoring circuit is directly connected to the driver circuit. It can detect the external short circuit in the shortest time, and can turn off the power semiconductor in 2-3 μs. In the future, this feature will become increasingly important because the new generation of IGBTs allows only 6 μs short circuit time compared to the 10μs short circuit time allowed by the past IGBTs.
The current sensor at the AC terminal of the voltage source inverter cannot detect the short circuit in the inverter bridge. Here, the slope resistor of the semiconductor in the open state is used for protection purposes by monitoring the VCE(SAT). This method is sufficient for short circuit protection, but it is not suitable for current measurement.