Dimensioning the amplifier

The first consideration when designing a PHIL test setup is to specify the operating range of the devices that will be coupled. A common mistake is to select an amplifier solely on the basis of its power output without considering some important points. Should the amplifier be able to absorb power? What bandwidth do we need?

Furthermore, the design should be chosen to meet test requirements that may be exceeded by transients or inrush currents that may cause transient overloads.

The following aspects should be considered when choosing the amplifier:

Specifications specific to the application.

  1. The number of phases or channels needed.
  2. Rated power at rated frequency (kVA for AC, kW for DC)
  3. Power factor and actual power required in all 4 quadrants (bipolar setup).
  4. The rated DC and AC voltage required by the setup.
  5. The frequencies at which testing takes place.
  6. Determine the power and current range, taking into account any starting currents (motors).

Power peaks and amplifier operating specifications

In addition to these features, amplifier manufacturers specify the degree of configurability for overvoltage and overcurrent protection and limit setting. Users can take these into account when determining the operating range of the test setup. Most amplifier manufacturers can provide characteristic graphs of the amplifier’s dynamics to verify that the operating range is sufficient.

Some amplifiers can handle higher current and power than their advertised limit for a short period of time. Additional information on this can be provided by the manufacturer.

At TTMS, we have available, among others, Cinergia’s amplifiers that can deliver 200% of the specified power and current for 2 seconds.

In some cases, it may be necessary to add a step-up transformer to achieve the target voltage of the DUT. The power specifications of this transformer should be at least 10% to 20% higher than that of the amplifier for safety reasons. Also note that adding a transformer can change the frequency. In addition, transformers can easily saturate, depending on their saturation characteristics and operating conditions. High transformer saturation induced by DC voltages or transients can be perceived by the amplifier as a quasi short circuit, which can cause the amplifier to trip. Therefore, it is very important to know the needs of the application for which a PHIL configuration is being designed. Some transformer designs allow a wider range of linear operation, but the cost and weight can increase significantly. Ultimately, the design of a PHIL test setup always involves compromises with regard to cost and operating conditions.


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