Column: Electric Vehicles
Transforming high-voltage batteries into SELV systems
By Patrick Wadden, Global Vice President of Automotive Business, and Nicolas Richard, Director of Automotive Business, Vicor
T
he power architectures of pure electric and hybrid vehicles store and distribute power at a mix of voltages for a wide variety of sensing, control, safety and infotainment subsystems. Tis presents a cost, space and weight challenge for the power storage and power
delivery network, which hybrid vehicles solve with a 48V battery and 48V distribution system, and EVs solve with high-voltage batteries (800V, 400V) and a 48V distribution system. While a 48V battery can instantaneously supply the required power, any intermediate battery in EV architectures adversely affects weight, space and cost. To preserve the advantages of high-voltage energy storage
whilst removing the need for an intermediate battery in EV power architectures is to use a high-voltage battery with a DC-DC converter, to deliver power within a safety (or separated) extra low voltage (SELV) system range. A conventional converter can provide this voltage conversion but lacks the fast response time required to meet the power needs of all the subsystems. Te Vicor BCM offers low impedance and fast response time, transforming a high-voltage battery into what appears to the power delivery network as a 48V battery, eliminating the need for an intermediate battery.
Vicor’s BCM converter Te BCM converter performs fixed-ratio conversion, where the output (secondary side) voltage is a fixed fraction of the input (primary side) voltage. Tat fixed fraction, or the K factor, can be greater, equal or less than one. Te K factor is defined as the voltage at the input divided by the ). When the K factor is below one,
voltage at the output (VPRI / VSEC
input voltages scale down, but input currents scale up. Te opposite is true when it is above one; i.e., the input voltages scale up and input currents scale down. Te internal operation of the BCM converter has three main
stages: 1. A primary-side switching stage converts the DC input into a sinusoid;
2. An ideal transformer stage that converts AC to AC and scales the voltage by the ratio of the turns between the primary and
14 March 2023
www.electronicsworld.com Figure 1: Comparison of power distribution and energy storage methods secondary sides (the K factor);
3. A secondary-side switching stage that converts the sinusoid from the ideal transformer into a DC output. Te switching stages switch at the zero-current, zero-voltage crossings of the sine wave in the transformer, minimising switching losses and EMI. Due to the symmetry and with the appropriate sequencing and
control, it is possible to operate the BCM as either a step-down (high to low) or a step-up (low to high) conversion. Tis innate bidirectional capability enables the BCM to convert power with the same efficiency in both directions, which is highly suitable for rapid charging and discharging applications, such as in storage elements, for example. But, here we will focus on the high-to-low conversion direction.
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