|
Sensors and other Inputs/Outputs
Sensors for control feedback:
Boost current and h-bridge output current are measured with two hall effect sensors. Initially, only one current sensor was provisioned for, but another was added after a failure. Once in operation, the inverter operates within limits. However, during motor spool up and closing the compressor clutch, large transient currents can occur. The current sensors provide feedback to the controlling micro which can reduce output power or shutdown to save itself.
Boost-stage output voltage is measured with an isolated linear opamp. Designed for use with current shunts, this opamp also works with a very high ratio voltage divider on the input. Feed it 0-250mv on one side and get an isolated 2.5-5V signal on the other side. One potential issue is that this creates a little less than 2 ADC bits of resolution per volt, but the output voltage does not need to be tightly regulated - a little error in accuracy is ok.
Each IGBT module also has an internal thermistor to measure internal temperature. Initially, both module temperatures were planned to be measured, but I ended up using one of them as the input from the extra current sensor. Now, only the bridge temperature is monitored.
Other inputs/outputs
The control board has an opto isolated input signal to turn on or off the inverter. Additionally, there is an analog input from a thermistor in the a/c duct that could be used to cycle the clutch at low fan settings (though I haven't set this up yet) and there are two relay drivers - one is used for the condensor fans and clutch and the other is for the internal precharge circuit.
|