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The Benefits of Regenerative Loads & Sources

Utility Grid Testing - NH Research (NHR)

Intro to Regenerative Loads & Sources

Traditional loads, either air-cooled or water-cooled, convert the unit-under-test’s (UUT) output power into heat waste whereas regenerative loads recycle the UUT output power back onto the facility or UUT in the form of re-usable electricity. This allows the test system to lower the total electrical usage while significantly reducing waste heat. For example a regenerative load with > 90% efficiency would return more than 90% of the UUT’s output power back to the facility and convert less than 10% of the UUT power into heat.

Traditional Electronic Loads vs. Regenerative Loads

An electronic load converts 100% of the discharge power (P = V*I) directly into heat. Unlike resistors, electronic loads are able to provide more sophisticated loading profiles such as constant current, constant voltage, and constant power, in addition to constant resistance. The load profile can be changed dynamically without disconnecting the UUT. Air-cooled electronic loads dissipate the waste heat into the air and can be used anywhere in a laboratory or manufacturing space as long as there is sufficient space or air-chiller capacity. Water-cooled electronic loads dissipate the waste heat through a water connection, which limits where these loads can be used. Testing may also get halted when the water-chiller system is under maintenance.

Regenerative electronic loads convert discharge power (P = V*I) back into usable electricity for the facility, thereby increasing flexibility in two ways. First, the total power demand and associated electrical costs are reduced. Second, regeneration creates significantly less waste heat, which in turn reduces  the energy and equipment required for facility cooling. This allows maximum flexibility when planning, upgrading, or rearranging laboratory or manufacturing workspaces.

Regeneration Significantly Reduces the Cost of Heat

Using regenerative AC and DC loads and sources dramatically reduces the total amount of power required from the utility.  This is because the UUT can use the power from both the utility connection and the power returned by the regenerative load. This directly reduces the total amount of power used by the facility to conduct the required testing, the amount of waste heat, and the power to remove the heat. Additionally, the total cost of ownership of traditional loads often includes far more than just the initial purchase of the load. Traditional loads imply more electrical usage and higher electrical usage may require electrical system upgrades to support additional test stations. Each new station will generate significant amount of waste heat, which may require facility modifications such as new air-handlers or water-chiller connection points. All these costs can be associated with simply trying to remove waste heat.

NHR Regenerative Test Solutions

NH Research (NHR) provides regenerative AC and DC loads with expandable power to meet future higher test-power needs. This modular design allows for maximum flexibility in test by providing unmatched configuration options as well as future scalability. Both AC and DC products are bi-directional allowing them to reverse power flow using the same internal electronics.

Regenerative AC/DC Loads and Sources:

To learn more about potential cost savings , download our Regenerative Loads and Sources Application Note.

Download “Regenerative Loads & Sources” App Note

Electric Vehicle Market Drivers & Testing Requirements

Electric Vehicle Transportation - NH Research (NHR)

EV Batteries & Powertrains Increase in Power Levels

As the electric vehicle (EV) industry continues to accelerate, automotive engineers must address new testing challenges for designing higher performance batteries, electric powertrain systems, power electronic components and DC fast chargers. Power levels are increasing across e-mobility markets such as passenger electric vehicles, heavy duty electric trucks, and electric fleets. These market trends require test solutions that can test today’s technologies and tomorrow’s innovations.

Power and voltage levels are transitioning from a traditional 300/400VDC level toward 800/1000VDC. Higher voltages permit faster charging and increase power transfer while reducing vehicle weight. For example, in 2019 most available BEVs were similar to Tesla’s Model 3 and GM’s Chevy Bolt, with a nominal voltage of ~350VDC, whereas Porsche announced the Taycan architecture utilizing a higher 800VDC battery system. This higher voltage allows nearly three times (3x) the additional power to be transferred for the same wire size. Porsche demonstrated this with an IONITY system charging at 350kW, which is nearly 3x the 120kW available through other “fast” supercharging networks.

It is expected that both 800V and 350V vehicles will charge at an electric-only refueling station the same way gasoline and diesel cars do today. Engineers should keep this dual-voltage reality in mind when specifying the power requirements because many of the high-power test systems are only designed for a single range. Selecting a system that can provide both traditional and high-voltage levels ensures that the right equipment is available to meet current and future needs. It is equally important that a battery emulation system reacts with a quick voltage response to changes in current or power draw in order to accurately simulate the electrical storage system (battery).

Auto manufacturers have dramatically increased the relative capacity of the battery packs in their vehicles to reduce “range anxiety”. For example, the 2019 Nissan Leaf has a 50% larger battery compared to older 40kW models, and Tesla’s Model S offers a 100kW battery, that is 66% larger than the original standard-sized battery. Battery capacity and battery performance are always improving, suggesting that engineers must consider flexibility and programmability in selecting a battery test or battery emulation solution.

EV Testing Requires Modular, Scalable Test Solutions

NHR Provides Modular, High Voltage Bi-Directional Power up to 2.4 MW

NHR’s ev test equipment is designed for fully independent operation and can be paralleled, increasing the maximum power and current capability to the level required. This modular expansion through paralleling ensures that you can start testing to today’s application levels, knowing that additional power is available if needed in the future. Higher-power models provide dual ranges, allowing the equipment to test and emulate today’s batteries and provide the right tool that can scale to address increases in battery voltage and power.

The 9300 High Voltage Battery Test System has a dual power range that covers both lower (up to 600 V) and higher power (up to 1200 V) applications using a single product. This modular system can be scaled up to 2.4 MW in 100 kW building blocks, offering a wide operating envelope. With NHR’s battery emulation mode, customers are able to simulate a wide range of battery power levels without having to change test equipment. Alternatively, the 9200 Battery Test System has a multi-channel capability with the possibility to mix and match voltage and current levels at lower power ranges. This battery cycler and battery emulator is expandable in 12kW block sizes and has voltage options from 40V to 600VDC. This series uses the same drivers, touch panel controls, and software options, making NHR your ideal solution partner for both high-power and low-power EV architectures.

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How is a Battery Emulator Different from Power Supplies & Electronic Loads?

Battery Emulator vs. Power Supplies and Loads - NH Research (NHR)

Battery Emulators VS. Power Supplies & Electronic Loads

Battery emulators are bi-directional, whereas power supplies and loads are unidirectional devices. A power supply regulates voltage and expects some amount of current to be drawn. Electronic loads regulate current and expect voltage to be provided. Being uni-directional, these devices are unable to accept or supply power in the reverse direction.

An approach engineers often take is to build their own test setup using sources and loads. This can be challenging, and time consuming, and has many of the disadvantages of the common DC bus architecture described above. Typically, DC sources have a programmed response time of 10 to 100 ms, which is far too slow for today’s EV applications such as electric powertrains. For example, using a DC load to modulate power or provide a return path for back-EMF requires complicated software development, considerable integration and test time, and does not provide an accurate simulation of the battery’s internal resistance. Additionally, the load must consume power at all times, and since it is not regenerative, all of the power is dissipated as heat waste, increasing operating costs and creating uncomfortable work conditions.

Battery emulators maintain a positive DC voltage and can immediately accept or deliver current, allowing power to flow in either direction. More advanced battery emulators, like NHR’s 9300 Battery Emulator, allow further real- world simulation of battery characteristics by modeling the battery packs series-resistance (RINT).

The RINT Model: Accurately Simulating Battery Characteristics

The Internal Resistance (RINT) model provides a simulation of the battery’s internal chemical resistance, along with additional pack resistances created by internal connections, contactors, and safety components. The RINT model can be implemented with a true bi-directional source (Vocv) and a programmable series-resistance (Rs). This model is sufficient for understanding the major characteristics of battery-based resistances and pack resistances. While the number of mathematical models has increased, these more complicated models are used to understand the electro-chemical characteristics of batteries, the nuances of  which have little impact on the overall system when compared with the total resistance of the pack.

NHR’s battery emulators feature this equivalent RINT Model providing an electronically programmable “Battery Emulation” mode. As in a real battery, NHR’s battery emulators adjust the output voltage depending on the direction and amplitude of current flow.  This automatic adjustment of output voltage better simulates real-world battery pack characteristics especially when compared with common DC-bus and source/load simulation systems.

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Battery emulation is ideal for applications such as electric powertrain, fuel cell emulation, energy storage systems emulation, Solar PV inverter testing, DC Bus emulation, and more. For more information about key differentiators and technology considerations for battery emulation, please contact us.

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