UM1036
Board description
Doc ID 18293 Rev 1
17/48
3.3.2 Inrush
limitation
The input stage of the demonstration board is provided with an NTC resistor to eliminate
input inrush current peak during the charging of the bulk capacitors. To achieve a higher
efficiency of the inverter it is possible to bypass the NTC after the start-up phase. The NTC
bypass signal is provided from the MCU board through the J2 connector. The yellow D10
LED diode “Current limiter” is turned off when the inrush NTC is bypassed.
A basic EMI filter based on X2 and Y2 capacitors was implemented on the board. The EMI
filter is not able to absorb EMI distortion coming from the inverter for all ranges of the
applications. The final EMI filter must be designed according to the motor and the design of
the related EMI filter is up to the user according to the chosen motor and final target
application. The heatsink itself is connected to the earth pin in the J1 connector. It is
recommended to connect the heatsink to a negative voltage potential - common ground
when a DC voltage is used to supply the demonstration board.
3.3.3
Power block based on IGBT module
The IGBT module STGIPS20K60 consists of high, rugged IGBT power switches and three
smart drivers. STGIPS20K60 is provided with advanced gate smart drivers, many features
are available, such as integrated comparators for overcurrent or short-circuit protection, and
the “SMART SHUTDOWN” function. Please refer to the STGIPS20K60 datasheet for more
information.
3.3.4 Brake
function
A hardware brake feature is implemented on the STEVAL-IHM028V1 demonstration board.
This feature connects the external resistive load, applied to the J7 connector, to the main
supply bus to eliminate overvoltage generated while the motor acts as a generator. This
connected load must be able to dissipate all motor generated energy. Almost any kind of
high power resistor which may be used as dissipative load also has relative high parasitic
inductance. Due to such inductance it is important to take care not to damage the brake Q8
IGBT switch with a freewheeling diode applied directly to the terminals of the dissipative
power resistor used.
Voltage on the bus is sensed through a voltage divider net, with resistors R40, R41, and
R48, and is compared to the precise voltage reference U5. The brake dummy load is
switched on when the voltage on the bus reaches approximately 435 VDC and is switched
off when the voltage falls bellows 415 VDC. This voltage level has been chosen to be fully
compliant with the possible use of front-end PFC stage. The brake function can also be
activated by the microcontroller through the J2 motor-control connector (PWM_Brake
signal). For this configuration, the user should set the W2 jumper to position “A”. The brake
threshold levels can be modified by calculating R49 and R51 new values. D13 red LED
diode “Brake” indicates the acting brake switch.
3.3.5 Overcurrent
protection
Hardware overcurrent protection (OCP) is implemented on the board. This feature takes
advantage of STGIPS20K60 intelligent module where an internal comparator is
implemented. Thanks to the internal connection between the comparator output and
shutdown block of the IPM, the intervention time of overcurrent protection is extremely low,
ranging slightly above 200 ns. Please see
Figure 10
for details.
