Wolfspeed Inverter 2L 25 kW Interface Rev03#

Rev03 is the first productive revision of the uz_per_wolfspeed_25kw_FM3 interface PCB. It interfaces the UltraZohm with the Wolfspeed CRD25DA12N-FMC inverter by replacing the original control card.

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Fig. 303 Functional areas of the Rev03 interface PCB#

Layout#

The PCB is structured by functional areas as shown in Functional areas of the Rev03 interface PCB.

  1. HFBR-1521Z/2521Z digital optical transmitters and receivers

  2. RJ45 port for analog signal transmission

  3. Driver stages for the optical links

  4. TI THS4561 fully differential amplifier stages

  5. Power section with TPS7A20 3.3 V LDO and REF35 voltage references

  6. Samtec HSEC8 120-pin edge-card connector mating with the Wolfspeed inverter

Analog Signals#

The inverter-side analog signals are single-ended and are converted to fully differential signals for noise-robust transmission to the UltraZohm ADC board. The interface scales the single-ended signals by a factor of 1.5038 (10 / 6.65) to match the inverter-side 3.3 V analog range to the 5 V input range of the UltraZohm ADC board.

The reported total sensing gain was measured experimentally and includes both the inverter-side measurement device and the interface board. The bandwidth was determined theoretically from LTSpice simulations.

Signal

Source

Total measurement gain

UltraZohm ADC channel

Phase current U

LEM LAH 50-P

0.02417 V/A, bandwidth about 50 kHz

I_U / Ch1

Phase current V

LEM LAH 50-P

0.02417 V/A, bandwidth about 50 kHz

I_V / Ch2

Phase current W

LEM LAH 50-P

0.02417 V/A, bandwidth about 50 kHz

I_W / Ch3

DC-link voltage

Non-isolated voltage divider

0.003744 Vsec/Vprim, bandwidth about 7 kHz

V_DC / Ch4

Digital Signals#

Rev03 uses optical receivers for the UltraZohm-to-inverter PWM and gate-disable signals. The inverter-to-UltraZohm overcurrent and temperature signals use optical transmitters.

The overcurrent detection signal is active low. When an overcurrent event is detected, the signal goes low and the transmitter LED is off. The default Wolfspeed overcurrent limits are set to approximately +/-79 A and can be adjusted with the reference resistors described in the Wolfspeed documentation.

Signal

Direction

Conditioning

Notes

U_HS_PWM, U_LS_PWM, V_HS_PWM, V_LS_PWM, W_HS_PWM, W_LS_PWM

UltraZohm to inverter

Optical receivers

High-side and low-side PWM for three phases; dead time is generated in the UltraZohm.

GD_DIS

UltraZohm to inverter

Optical receiver

Global gate-driver disable signal.

OC

Inverter to UltraZohm

SN74HCS08DR AND logic and optical transmitter

Consolidated overcurrent signal from six comparator outputs.

NTC_ISO

Inverter to UltraZohm

Optical transmitter

Inverter-side temperature signal forwarded as a digital optical signal.

Testing#

Rev03 was tested up to 10 kW with an RL load consisting of a 14 Ohm resistor and a 1 mH inductor.

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Fig. 304 Integrated testing setup with RL load#

Stable three-phase sinusoidal currents were measured using a Rohde & Schwarz MXO 5 series oscilloscope.

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Fig. 305 Oscilloscope measurement at 100 kHz switching frequency with a 999 V / 8.33 A DC-link input#

Mechanical Support#

A 3D-printed support stand was added to keep the board mechanically stable when plugged into the inverter. The step file of the stand is available in the PCB repository.

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Fig. 306 Interface board with 3D-printed stand for mechanical stability#

Software Used for Testing#

The inverter was tested with the feature/wolfspeed_inverter_adapterboard branch of the ultrazohm_sw repository. The branch comparison is available here.

Documents#