The most common operating mode for AC power sources is to provide controlled power to electrical products under test. In this mode, the power source simply replaces utility-supplied AC line power, whether 120V-60Hz “North American type” power, 220/230V-50Hz used in most of Asia, South America and Europe, or 100V-50/60Hz used in Japan.
The advantage of using an external power source is that it allows you to precisely control the voltage amplitude, and frequency of the supply voltage. A programmable power source also lets you simulate anomalous conditions such as distortion, dips, sags, interruptions, spikes, and other power quality problems. Using an external power supply, you can ensure that your product will continue to operate even if the supply has a high level of harmonic distortion or the voltage dips 10% or more. And, if your product does have problems operating correctly under worst case conditions, being able to simulate these conditions in a controlled way makes troubleshooting easier.
Regenerative Mode Operation
In addition to sourcing power, some power sources, such as the AMETEK RS Series and MX Series with the -SNK option, can also sink power from a device under test. This returned power can be a short-term event, such as a motor shutting down, or it may be a semi-permanent condition, such as a solar power or wind power-based inverter supplying power back to the source. An inverter may supply power continuously, intermittently, or even during only part of an AC cycle.
Not only can the AMETEK RS Series and MX Series sink this power, they can transfer this power back to the grid. This mode of operation is called regenerative mode. A regenerative power source that accepts power provided by an inverter is able to transfer this power back to the utility grid, as illustrated in Figure 1.
Generally, only switch-mode AC power sources are capable of transferring power back to the public supply. Linear power sources, whose output stage is typically a high-power amplifier, will simply dissipate the returned power in the output stage. In other words, a linear power source acts like a load and converts the returned power into heat.
When using a linear supply for an application like this, the losses are actually twice the amount of power that the inverter returns to the power source. You have power losses both coming and going. Very often, the power losses are so great, that you'll have to provide a cooling system to dissipate all of the heat. That can be very costly.
By using a regenerative, switch-mode power source, you can actually return the power to the utility grid with minimal loss. So, when a solar inverter is connected to the AC circuit, it supplies power to the load and also to the power source – an AMETEK RS or MX power source in this case – which in turn sends the excess power back into the public supply in a controlled fashion. The RS and MX Series power sources automatically switch between source and sink modes and can regenerate up to 100% of the rated output power back to the utility grid during sink mode operation.
For more information, refer to the application note, “AMETEK's MX Series Programmable Power Source Operating in Regenerative Mode (SNK Option).