Should You Consider a Bi-Directional Power Supply?

What does it mean when you hear about a bi-directional power supply? Simply put, it’s an instrument that is truly all in one: a DC power supply (a power source) and an electronic load (a power sink). A bi-directional power supply thus performs multiple instrument functions in one enclosure. 

If you have a need for both a DC power supply and a DC electronic load in your test system, or if you anticipate that you will need both functions in the future, you can cost-effectively choose a bi-directional power supply.

The bi-directional power supply operates in two quadrants, quadrant I and II.  See Figure 1. In quadrant I, the instrument acts as a power supply and sources power. In quadrant II, the instrument is an electronic load and absorbs or sinks power. If your test system requirements allow you to utilize the power supply and the load at different times, you can benefit from a bi-directional power supply. The bi-directional power supply:

• Simplifies test code by enabling control of a single instrument 
• Saves precious automated system rack space
• Reduces cooling requirements with one less instrument
• Reduces the inventory of different types of instruments
• Saves on capital test costs.

Example applications in which a bi-directional power supply is useful include:

• Testing re-chargeable batteries
  • The power supply can simulate a charger to test the battery’s re-charge cycle
  • The electronic load can test battery output under a wide range of conditions
• Testing DC-DC converter circuits
  • The power supply can test the DC-DC converter’s response to a wide range of input voltages
  • The electronic load can test the DC-DC converters regulation under different loads
• Testing electric vehicle (EV) circuits
  • The power supply can emulate the battery
  • The electronic load can test circuits such as motor drive circuits

These are just three examples of applications where a test system requires both a a bi-directional power supply and an electronic load. 

Why Select an EA Elektro-Automatik Bi-Directional Power Supply?

EA Elektro-Automatik bi-directional power supplies have a number of capabilities that make them excellent choices. They have an auto ranging output for the supply mode and for the load mode that enables the delivery or absorption of a wide range of voltage and current levels. With auto ranging, the bi-directional power supplies can output or absorb full power even when the voltage is 33% of its maximum value. The function generator allows the user to program an operational curve that mimics a battery. The additional Battery Simulator software can simulate the characteristics of lead-acid or lithium-ion batteries. EA Elektro-Automatik bi-directional power supplies have regenerative circuitry to return absorbed power to the grid. Furthermore, you have an extensive choice of interfaces to allow the instrument to easily interface into either an automated test system or an industrial process control system.

Auto Ranging Output

Compared with a conventional power supply that has a rectangular output characteristic and can deliver maximum power only at one point, Vmax and Imax, EA auto ranging power supplies deliver full power all along its constant power output characteristic (Figure 1). In addition, the auto ranging supplies can output higher voltage and deliver more current than a conventional, rectangular output power supply. In many cases, you can save capital costs by purchasing a lower wattage power supply than what you would need if you selected a conventional power supply. Auto ranging applies to the load operation of the bi-directional supply as well.

Figure 1. Auto ranging output of a 30 kW EA bi-directional power supply. Maximum voltage is 500 V and maximum current is ±180 A. The constant power curve shows all the points of maximum power output.

Built-In Function Generator

With a built-in function generator, both the power supply and the electronic load can more fully test the device-under test (DUT). The function generator can create I-V curves to emulate a battery, a fuel cell, and a solar cell. The electronic load can emulate dynamic load conditions. The power supply can emulate a noisy source to test how noise impacts a DUT. The electronic load can create step, ramp, or pulse-like load changes to test how a DUT responds to dynamic changes. 

The function generator is internal to the bi-directional power supply. This saves the complexity of designing a power supply of load connected to an external signal source. Connecting a low power signal source to a high-power supply is a major challenge as the signal source needs protection from the high output or input level of the source or load. The built-in function generator in EA bi-directional supplies avoids the external circuitry and avoids having to control an additional device.

Regenerative Energy Recovery

The bi-directional power supply uses an inverter to convert the energy absorbed when the instrument is acting as a load. The inverter returns this energy to the grid. In the load or sink mode, the instrument can operate at up to 96% efficiency. Avoiding having to dissipate the absorbed energy as heat reduces the instrument’s cooling requirements. Of most importance, the utility savings for a bi-directional supply when it is sinking high power are significant.

More ways to interface to a Controller 

EA Elektro-Automatik bi-directional power supplies interface both to a personal computer (PC) and a programmable logic controller (PLC) with numerous interface options. For PC-controlled automated test systems, PC interfaces include USB and Ethernet which are standard on all bi-directional power supplies. The RS-232 PC interface is an option. 

For process control applications in which a PLC is the controller, the bi-directional power supplies have numerous PLC-based interface options. Optional interfaces include CAN, CANopen, Profibus, EtherCAT, and Modbus. Not only do the bi-directional power supplies interface to a PLC, but they are also programmable with Modbus commands which allows easy control for PLC programmers. The supplies have the standard SCPI command language for PC-based control. You can select the programming command set on which you want the instrument to operate. You can choose among the many field-installable interface options. 

Applications For a Bi-directional Power Supply

If your project requires a power supply and an electronic load and if the two functions are used for separate automated tests or perform at different times in an industrial system, then a bi-directional supply can save capital cost, inventory, and test rack space. Or you may want the flexibility of a bi-directional supply for future test requirements. There is one less instrument to build up the heat load in an instrument rack and one less instrument that requires control code. 

EA Elektro-Automatik bi-directional power supplies offer significant benefits for automated testing and control. The auto ranging output and input maximizes the ability to source or sink maximum power at numerous points along the constant power output curve compared with the single maximum power point of a conventional rectangular output power supply. EA Elektro-Automatik bi-directional power supplies enable simplified sourcing or sinking of dynamic waveshapes with the built-in function generator. You can easily simulate a specific source or load. These supplies have regenerative power transfer to the AC line which saves utility costs and instrument heat buildup. EA supplies provide more interface options to accommodate both PC and PLC interfacing.