COUPLING TRAFO IMPLEMENTATION VERSUS BOLAB 4 QUADRANT AMPLIFIER IN SERIES FOR HIGH VOLTAGE TESTS FOR ELECTRIC VEHICLES

The biggest challenges in testing according to:

DIFFERENCES BETWEEN LV 123, VW 80300 AND ISO 21498-2 FOR IMMUNITY TO VOLTAGE RIPPLE

	LV 123	VW 80300	ISO 21498-2
Robustness against Voltage Ripple	10.4.6	EHV-09	6.6
Frequency range	15 Hz … 20 kHz	10 Hz … 150 kHz	10 Hz … 150 kHz
Max. Amplitude	15 Vpk	16 Vpk	Must be agreed between customer and supplier
Robustness against Load Dump	10.4.9	EHV-10	6.11
Load dump all the way to HV voltage limit
HV-Slope ΔVHV/Δt:	250 V/ms	250 V/ms	250 V/ms
Load dump with rapid rate of change	No Test	EHV-10	No Test
HV Slope		3000 V/ms
Peak Voltage		Upk = UN,HV + 20 V
Resulting Speed		dU/dt pk= 20 V / 7µs

SETUP WITH COUPLING TRANSFORMERS AND RESULTING PROBLEMS

• Available for different frequency ranges and currents (50 A / 100 A)
• Setup must be changed to exchange coupling transformers
  → test must be interrupted to run full frequency range
• At low frequencies, as required in LV 123 for simple DUTs with low capacitive components and low currents, this solution can work well
• Coupling transformers go into saturation at the lowest frequencies through their high inductivity
  → Low-frequency range must be performed only with a power supply
• High frequencies up to 150 kHz are difficult or impossible (LV 80300, ISO 21498-2) under real DUT/load conditions
• Many OEMs and standards are required to run the entire frequency range without interruption, no stop or modification of setup
  

COUPLING TRANSFORMER CHARACTERISTICS FOR LOW-FREQUENCY RANGE AND ANOTHER FOR HIGH-FREQUENCY RANGE – WITH OHMIC LOADS

COUPLING TRANSFORMER CHARACTERISTICS WITH OHMIC LOADS

- TRANSFORMER FOR LOWER FREQUENCY RANGE TRANSFORMER WITH 100 A, EXAMPLE RIPPLE 20 V_PP

Result:

The low-frequency transformer characteristic shows that only for low current and low frequency can the transformer be used even with ohmic loads.

COUPLING TRANSFORMER CHARACTERISTICS WITH OHMIC LOADS

- TRANSFORMER FOR HIGHER FREQUENCY RANGE TRANSFORMER WITH 100 A, EXAMPLE RIPPLE 20 V_PP

Result:

The high-frequency transformer characteristic shows that only for low current can it be used even with ohmic loads.

 PROBLEMS WITH COUPLING TRANSFORMERS 

• What if a DUT consumes 200 A, 300A, or more ripple current?
  • Several coupling transformers (e.g. 100 A transformers) can be put in parallel or assembled in one housing
  • But: Each coupling transformer requires its own power amplifier
  • → This requires an enormous effort to implement coupling transformers with different frequency ranges at high current applications
  • → The quality result is not satisfactory despite the disproportionately large effort
• In most cases, DUTs have considerable input capacitance à Cannot be handled by a transformer, only ohmic loads
• Limits of technical feasibility are quickly reached
• Expensive bad investments are and were made because the physical and electro-technical limits were not conscious or one is not pointed out at all to these limitations.
• Only periodic sinusoidal signals can be coupled in
  • Transient pulses such as EHV-10 "Load Dump with a rapid rate of change" from the VW 80300 → impossible
• Many standards require closed-loop procedures, in which the voltage must be readjusted up to certain levels to maintain the voltage at the DUT
• The dramatic voltage losses from the coupled voltage to the applied ripple voltage at the DUT cannot be compensated as losses inside the transformers are too dramatic
• The reason is the insufficient output voltage of the amplifier at the required current demands, which results in a limited or often insufficient readjustment possibility in the amplifier

BOLAB‘S SOLUTION:

BOLAB AC AMPLIFIER IN SERIES TO THE HV-DC VOLTAGE SOURCE

• In this case, an AC 4-quadrant amplifier system is connected in series to the HV-DC power supply
• Solves the difficulties of the coupling transformer solution out of an ideal power waveform generation
• Full frequency range without changing any setup
• The identical current flows through both the HV-DC source and the 4-quadrant amplifier

WHY ARE SUCH SOLUTIONS LESS COMMON ON THE MARKET?

• It’s too difficult to operate two completely different sources in series which actually do not fit together.
• This table shows the differences between the two supply components:

COMPARISON SETUP

Coupling Network Transformers (CDN)	DC power supply + 4-Quadrant Amplifier in series
LOW FREQUENCY, NO CAPACITOR IN DUT
→ Both the coupling transformer and the AC + DC solution full fill this task well.
LOW FREQUENCY, SMALL CAPACITOR IN DUT
◊Voltage drop to approx. 9 Vpk ◊The voltage difference can be readjusted by increasing the transformer control voltage.	◊ Voltage stays on 12 Vpk with DUT capacitor of 7,5 µF
LOW FREQUENCY, HIGH CAPACITOR IN DUT
	◊ Missing measurement, See below measurements for high frequency
◊Voltage of 12 Vpk drops to 500 mVpk ◊The amplifier that is responsible for the transformer voltage thus does not have sufficient resources to compensate for these drastic voltage drops → Test fails!	◊ No Drop in Voltage, Voltage stays on 12 Vpk
HIGH FREQUENCY, NO CAPACITOR IN DUT
	◊ Missing measurement, See below measurements for more difficult conditions
◊ Voltage drop to approx. 11 Vpk ◊ The voltage difference can be readjusted by increasing the transformer control voltage.	◊ Voltage stays on 12 Vpk
HIGH FREQUENCY, SMALL CAPACITOR IN DUT
◊ Voltage drops to approx. 1,5 Vpk ◊ Amplifier, that is responsible for the transformer voltage thus does not have sufficient resources to compensate for these drastic voltage drops → Test fails!	◊ Voltage stays at 12 Vpk with DUT capacitor of 7,5 µF at 150 kHz
HIGH FREQUENCY, HIGH CAPACITOR IN DUT
◊ Voltage drops to approx. 1,5 Vpk ◊ Amplifier, that is responsible for the transformer voltage thus does not have sufficient resources to compensate for these drastic voltage drops → Test fails!	◊ Voltage stays on 12 Vpk even with DUT capacitor of 8000 µF at 150 kHz
HIGHEST FREQUENCY, SMALL CAPACITOR IN DUT
only signal not seen at 250kHz → Test fails!
	◊ Example test choosen from a requirement from an automobile manufacturer:      ◊ 8 Vpk at 250 kHz → this system concept also provides sufficient reserves for even higher requirements with future perspectives

SUMMARY OF COUPLING TRANSFORMER SOLUTIONS

• Datasheets in most cases, only provide information about technical data and tests under no-load operating conditions
• High frequencies are specified, but without specification of load, respectively in reference to impedance conditions

→ Neither reliable statements about resistive loads nor reactive loads are available

CONCLUSION

• The advantages of the BOLAB system solution with an HV-DC source in series with BOLAB´s amplifier systems show impressive results
• Tests according to standards can now be realized that were impossible before
• By using a powerful amplifier, both high-voltage standards such as LV 123, VW 80300, ISO 21498-2, etc. and the low-voltage standards for the 12 V, 24 V, and 48 V electrical systems such as LV 124, VW 80000, VDA 320, etc., can be carried out with the same amplifier system
• Only a few components have to be procured
  • low purchase price
  • low complexity of the system design
• Standards and norms appearing in the future with even higher requirements can also be implemented and carried out with this solution approach.
• Not only superimposed AC voltages can be performed with this approach, but also load dump tests can be performed.
• A modular BOLAB 4-quadrant amplifier system also has the advantage that a simple upgrade with further power amplifier modules is possible at any time and thus also expands future perspectives.
• For the high voltage DC power supply part, most of all high voltage sources and manufacturers can be used; high-performance high voltage DC power supplies are part of BOLAB solutions as well.