FEATURE Electric Vehicles
Are batteries best for electric vehicles?
Pat Kowalyk, Field Application Engineer at Vicor, explains why eliminating the 12V battery will increase EV performance
Y
ou may be surprised to fi nd a conventional 12V lead-acid battery in electric vehicles (EVs); Why does an EV need a
conventional battery when there’s a 400V or 800V battery already in it to power the motors? Today, 12V and 48V batteries power all the other systems in the vehicle, but they add cost and weight in addition to using valuable space. So, removing the 12V battery and using the 400-800V one instead should be enough to power all the systems in the car, right?
The simple answer is that many automotive systems, especially safety systems, must respond quickly to sudden changes in power, and, typically, batteries have much better response times than DC- DC power converters – until recently.
A fresh look
New EVs consume up to twenty times more power (from 3kW to over 50kW) than combustion engines. To date, “progress” has meant adding more and higher-powered batteries to cars, but it is time for a fresh look. A typical load in a vehicle will have two types of current draw: one for starting up and another for steady-state operation. This could either be raw or existing power from which a signal can be derived. The loads that use raw power will draw
large amounts of current, either to charge a capacitor or turn an armature. After being energised (start-up), the current drops and the load operates continuously (steady state). This initial current draw is what makes the battery a good option for legacy ICE vehicles but not EVs, where weight dramatically impacts range and performance. Thus, it makes sense to eliminate the heavy lead-acid or lithium 12V battery and replace it with a lighter,
36 November 2022 | Automation
Vicor power modules bundled with EMI filtering, minimal components and an enclosure could replace a 12V lead-acid or lithium-ion battery, reducing weight by 15-40lbs
compact, high-performance DC-DC converter.
High-performance power modules Replacing the 12V vehicle battery with a traditional converter may cause the load voltage to drop so low that the load turns off , causing a reboot. A key parameter to look at is the load voltage deviation during a change in current over time, also known as transient response. The lower the voltage deviation, the higher the system performance. A modular power approach, combined with topologies such as Vicor’s Sine Amplitude Converter (SAC), enables a much higher slew rate of a 12V lead- acid battery. Using a SAC can provide thousands of amperes from the high- voltage battery to the load, eliminating dips or loss of regulation. Automobile manufacturers typically
require 250A/ms for their fastest loads, which 12V batteries can achieve (75A/30µs). The Vicor modular approach provides transient response of 75A/10µs, thus creating a “virtual battery” that responds three times faster than 12V. The SAC’s turns ratio, called the K
factor, is the primary to secondary turns ratio. A key advantage to SAC is that any primary-side capacitance is multiplied by the K factor squared. For a 12V-to-48V conversion, the K factor is ¼, which means the eff ective secondary capacitance is 42, or 16 times the primary capacitance. The Vicor NBM is an ideal converter to transfer the energy load from a mechanical
source, which is on all the time, to an electrical source of energy that cycles on and off , allowing better effi ciency and control. The NBM in conjunction with the SAC replicates the essential properties of a physical battery. With this modular approach, the power
source can be split into zones, with an NBM placed anywhere around the car – behind the dashboard, in the trunk or by each wheel. Having the power source closer to the load reduces parasitic inductances and series resistances, for a higher-performing power system. The same approach also applies to HV-to-48V conversion, creating a 48V virtual battery; see Figure 3. The largest source of energy in the vehicle is the traction motor battery, so it makes sense to use that to down-convert voltages. In an EV this is typically either 400V or 800V, soon to be replaced with 1,200VDC or 1,400VDC. A modular approach can easily process 700,000A/s, and can be paralleled in an array to create a large power-processing system, with isolation from any primary bus voltages of 60V or higher. In theory, the NBM’s power capability only suff ers due to thermal eff ects; but, if properly cooled, it can process very large amounts of power, providing the added benefi t of bidirectional operation.
CONTACT:
Vicor
www.vicorpower.com
automationmagazine.co.uk
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50
