Electric Vehicles (EVs)have an overall powertrain efficiency of 80%, compared to 17% for a gasoline-powered internal combustion engine. By far, the largest amount of energy in EVs is consumed by the powertrain (77%-82%), followed by the Heating, Ventilating, and Air Conditioning (HVAC) system, followed by other car accessories such as mirrors, infotainment, and lights.[1],[2] The challenge today is in getting the most out of the limited power offered by on-board batteries. For EVs, around 16% inefficiency alone stems from charging and discharging the batteries (see Figure 1).

Figure 1: Energy for EVs is lost through braking, charging the batteries, and powering auxiliary accessories. (Image: U.S. Department of Energy)

Charging and discharging the batteries becomes a thermal management problem. Efficiency is lost through resistance and friction, both of which produce heat. Components can create significant heat, affecting system performance if it’s not managed.

Selecting components for EVs

Efficiency losses and heat from multiple components can add up; therefore, selecting the best components makes a difference. Some of the component losses to heat include:

  • Equivalent Series Resistance (ESR), which is the resistance of the capacitor’s terminals and electrodes. ESR contributes to heat rising from the component when ripple current is applied. ESR depends on the construction materials of the component. ESR is not a pure resistance, and it decreases with increasing frequency. A low ESR contributes less to component self-heating. ESR produces a non-ideal parasitic loss to heat from current flow.
  • An inductor’s DC Resistance (DCR) should be as low as possible to reduce self-heating of the inductor. Where possible, choose the inductor with the lowest DCR value to minimize power loss.

Inductors can generate heat and lose efficiency through core losses. Core loss occurs in a magnetic core due to alternating magnetization, which is the sum of the hysteresis loss and the eddy current loss. The core loss can be used to calculate the total power dissipation and subsequent temperature rise. Kemet’s Engineering Center has an Inductor Core Loss Calculator that can help you determine trade-offs.

Figure 2: Inductor core losses occur in a magnetic core due to alternating magnetization, which is the sum of the hysteresis loss and the eddy current loss. (Source: KEMET Capacitor and Inductor Fundamentals, PDF

Component properties that lead to lower self-heating equate to improved efficiency. Less heat generation also contributes to better performance and a longer life for electronics in the system in general.

New products provide choices by leveraging innovative technology enabling efficient topologies.  A resonant converter is a new switching topology that reduces energy dissipation in a switching transistor as it turns on and turns off. Resonant converters combine the switching transistor with an LC circuit. The combination changes the current from a square waveform to a sinusoidal waveform. The transistor is timed such that the on and off switching occurs at the zero-crossing of the current’s sine wave. The result removes any overlap at turn-on as the current rises and the voltage falls. Likewise, when the switching transistor turns off, there’s no overlap of falling current and rising voltage.

Wide Band-Gap (WBG) materials replacing traditional silicon materials have made significant headway into improving efficiency over the past decade. KEMET’s KC-LINK ™ capacitors are ideal for fast-switching applications like EV powertrains and charging systems, and operate at higher voltages, temperatures, and frequencies than similar non-WBG components. KC-LINK capacitors are AEC-Q200 qualified for automotive applications, with operating temperatures of 150°C. KC-LINK capacitors can be mounted near fast switching transistors in high power density applications.

Figure 3: With extremely low effective series resistance (ESR) and very low thermal resistance, KC-LINK capacitors can operate at very high ripple currents with no change in capacitance versus DC voltage, and negligible change in capacitance versus temperature. (Source: KEMET KC-LINK Datasheet – PDF)

KEMET also offers automotive-grade T598 Polymer Electrolytic Organic Capacitors with a rated voltage range from 2.5 – 50.0 VDC and ultra-low ESR. The new T598 capacitors not only demonstrate very stable ESR under harsh conditions, but they also provide extra robustness for use in applications where polymer capacitors were previously vulnerable.

Figure 4: The existing full AEC-Q200 qualified series T598 (125ºC) and T599 (150ºC) from KEMET can help to provide better capacitance stability, better capacitance retention, lower ESR, higher ripple handling, and long life. (Source: KEMET T598/T599 datasheet, PDF)

Another automotive-grade component meant for EV powertrain and battery bank charging is KEMET Electronics’ METCOM MPX1 Metal Composite Power Inductors, with an operating temperature up to +155°C. METCOM metal composite power inductors exceed traditional ferrite inductors due to the core’s high saturation flux density, which enables a stronger magnetic field. Low magnetic flux leakage and high saturation characteristics are ideal for designs requiring stable inductance across temperature and current.

AEC-Q200 Automotive qualified film capacitors are another option, with capacitor values ranging from 47 pF to 600 µF and voltage ratings from 16 to 3,000 VDC. The A50 automotive-grade series of capacitors are ideal for typical applications that include blocking, coupling, decoupling, bypassing, and interference suppression in low voltage automotive applications.

KEMET has several families of aluminum-electrolytic film capacitors that are well-suited for automotive applications. Aluminum-electrolytic capacitors tolerate demanding applications requiring a very long life, high vibration resistance, and high ripple current. Operating temperatures up to 150°C and a broad range of voltage ratings are available.

Visit a wide range of AEC-Q200 qualified capacitors at KEMET.com to browse KEMET Electronics’ extensive offering of automotive-grade components.

References

[1] Hayes, J. and Goodarzi, G. (2018). Electric Powertrain, pp. 34. 1st ed. Wiley.

[2] Mebarki, B., Draoui, B., Allaou, B., Rahmani, L., & Benachour, E. (2013). Impact of the Air-Conditioning System on the Power Consumption of an Electric Vehicle Powered by Lithium-Ion Battery. Modelling and Simulation in Engineering, 2013, 1-6. doi:10.1155/2013/935784