System Implementation has been broken into several stages to manage project complexity. The system implementation consists of a set of commercially available instrumentation attached to a custom built hardware system under the control of an agile software framework developed in LabVIEW.
Figure 1: Overview of the electrical system.
The industrial hardware consists of a 300MHz Agilent DSO5034A oscilloscope with a 1ns sample rate and 1Mpts memory for large transient acquisition, a 20 MHz Agilent 33220A function generator for gate signal control, a National Instruments PCI-6229 data acquisition card with a SCC-68 breakout containing three SCC-TC02 thermocouple measurement modules and one SCC-RTD01 resistance temperature detector, a DCS2050A analog programmable power supply capable of sourcing 20V and 50A, three thermocouple modules, a Raytek RACI3A infrared sensor, a Tenney T5STR environmental chamber capable of temperature, humidity and pressure control, and a computer running LabVIEW and Matlab.
Custom hardware was developed to compliment the commercial instrumentation and serve as the physical test bed for the transistor under test. This hardware includes a primary test board with a built in 200KHz current sensor with a 100A maximum current, an infrared temperature sensor port, BNC transient output ports connected to the DSO5024A oscilloscope, and a bank of 30Hz low-pass filtered output ports connected to the PCI-6229 data acquisition card. An onboard gate driver switching network allows for the in-situ swapping of two separate gate signal sources. A gate isolation switching network is also implemented to remove unnecessary instrumentation when performing current leakage measurements or tests involving high voltage.
A power conditioner and load board was also constructed. It includes a power conditioning stage with three parallel capacitors with staggered capacitance values of 120mF, 4700uF and 47uF. This filtering system removes cable inductance and power supply interference from most transient measurements. The board also provides a two port swappable load network, allowing three parallel loads across node 1 and two parallel loads across node 2. A freewheeling diode port is also provided. Board voltages are low pass filtered and acquired by the PCI-6229.
Figure 2: Schematic for the linear gate driver with only one of three capacitively coupled operational amplifiers displayed.
The gate driver board consists of four parallel LM7171 linear voltage feedback operational amplifiers (op-amps) operating in a non-inverting configuration with input coupled to an Agilent 33220A waveform generator. The gate driver board has an approximate bandwidth of 100MHz, rail to rail voltages from -2V to 23V and can achieve slew rates of 0.5V/ns into a 50Ω load. The design of the driver, shown in Figure 2, consists of a single op-amp directly connected to the driver board output for DC operation and three additional op-amps capacitively coupled to the driver board output to assist in driving the largely capacitive loads associated with power transistor gates. The capacitive coupling prevents damage to op-amps in the event of gain mismatch during steady-state operation. The driver board additionally contains adjustable feedback resistors used in gain calibration to ensure stable operation.
Figure 3: Large signal step response of the gate driver into the IGBT gate.
Figure 3 show a 23V step through a 50Ω resistor across the gate of an IGBT. Rise time is 40ns. Figure 4 shows an impedance test of an IGBT gate. A 0.25V RMS sine wave is coupled with a 5V DC bias. Voltage is measured with an ac coupled oscilloscope across a 50Ω resistor connected in series with the gate.
Figure 4: Small Signal response of the IGBT gate used for impedance characterization.
A custom thermal control unit is also under development to attach thermocouples to fixed positions on the transistor package and utilize a Peltier unit capable of 60°C temperature swings in both negative and positive directions for use in rapid thermal cycling. The Peltier unit is driven by a 15A linear amplifier and attached to a large heat sink for that acts as a reservoir for heat dissipation. An infrared sensor is also included for applications requiring contactless measurements, though infrared sensors have exhibited large temperature errors in our applications due to emissivity and beam localization considerations.
Figure 5: Overview of the thermal test system.