A High-Performance, Integrated Powertrain Solution: the Key to EV Adoption

A High-Performance, Integrated Powertrain Solution: The Key to EV Adoption

Nagarajan Sridhar Marketing Manager High-Voltage Power, High-Power Drivers Texas Instruments This paper examines the benefits of using an integrated powertrain solution to speed adoption of electric vehicles through power electronics. Implementation of wide band-gap semiconductor switches and isolated gate drivers are highlighted to illustrate the value of powertrain integration.

by regulations across the globe to curb carbon-dioxide At a glance emissions, sales are increasing annually at 20% to 25% [1] and are projected to represent 20% to 25% of vehicles sold Powertrain integration is crucial to enabling by 2030 [2]. In addition, an increase in consumer acceptance mass market adoption of electric vehicles. for HEV/EVs has led to greater demand for energy-efficient, robust and compact systems with improved performance Performance improvements: and longer driving ranges. 1 increasing power density One of the biggest concerns in this space is how to make Isolated gate drivers with advanced HEVs/EVs more affordable, in order to facilitate mass-market diagnostics and protection features adoption and address the current lack of profitability for enable integration and lower cost. automakers. Today, the average price of a small- to mid- size EV is around $12,000 higher than a similar internal combustion engine vehicle [3]. Wide band-gap semiconductor 2 devices: a disruptive technology At first, the price difference was thought to be solely in the automotive market attributable to battery costs. It is true that battery costs

Using silicon carbide (SiC) and gallium may drop significantly in the future. However, detailed nitride (GaN) for power switches business models recently indicated other options that can enables higher efficiencies in electric reduce costs [3] and accelerate the time in which original vehicles. equipment manufacturers (OEMs) can make profitable HEV/ EV sales. One option is design to cost (DTC), which focuses An integrated powertrain on powertrain integration where the power electronics solution at a system level 3 components are positioned closer together, reducing the Lower costs and maximize board space number of components and integrating them into fewer with the powertrain system in one unit. boxes.

In this white paper, I’ll examine how applying DTC to power

Automotive manufacturers are increasing the electrification electronics can enable OEMs to achieve mass-market of vehicle powertrains as more hybrid electric vehicles adoption. I’ll begin by explaining why advances in power (HEVs) and electric vehicles (EVs) make their debut. Driven electronics were able to alleviate consumer “range anxiety” while striving for lower DTC in the powertrain system, and

A High-Performance, Integrated Powertrain Solution: The Key to EV Adoption 2 April 2021 describe an integrated powertrain solution at a system level Performance improvements: increasing designed to approach DTC, with a particular emphasis on power density optimizing semiconductor integrated circuit (IC) and power The power efficiency and size of the powertrain system device content. determines the performance of an HEV or EV. The ratio Resolving range anxiety of power efficiency to overall size – also known as power density – is a key figure of merit in the power-management Range anxiety has been the No. 1 concern of consumers world. The goal is to achieve the highest level of power when shopping for HEVs and EVs. In 2020, several EVs density. The EV industry is extending this goal to powertrain are expected to be released with ranges beyond 200 miles systems through integration – to achieve the highest [4]. What these EV models have in common, even among efficiency in the most compact space. “Compact space” in different OEMs, is a from-the-ground-up powertrain platform this context implies smaller printed circuit board (PCB) space design that optimizes battery stacking and packaging and casing material, also positively impacting DTC. for high ranges. Higher battery stacks translate to higher At the power electronics level, there have been significant voltages and higher horsepower. changes in topologies/architectures, integrated IC Modern EVs typically have battery voltages around 400 V, solutions and semiconductor power switches in powertrain but achieving greater horsepower requires increasing the subsystems, including the onboard charger (OBC), DC/DC battery voltage to 800 V, particularly in high-end EVs. Higher converter (high voltage to low voltage) and traction inverter. voltages translate to higher horsepower for the same amount Figure 1 shows a typical block diagram of a powertrain of current. Optimization of the battery stacking and packaging system in an HEV/EV. enables compact spacing and lower DTC. Let’s discuss the impact of changes to semiconductor Also, higher voltages increase efficiency for the same power switches and how to integrate the functionality amount of power because the lack of high current lowers required for an efficient power electronics architecture into thermal dissipation. Lower cabling diameters and lower an IC. This is the basis for an integrated powertrain solution weight in turn lowers DTC. at a system level.

Onboard charger DC/DC converter Traction inverter Onboard charger DC/DC converter Traction inverter

Amplifier / hall Amplifier / hall Analog / digital Temp sensor Temp sensor sensor sensor Galvanic isolation temp sensors Controlled AC power Primary current Primary temp Secondary temp Secondary current sense DC to HV Isolated Reverse PFC temp sense sense sense sense 5V or Isolated Temp Temp from grid battery LV amplifier bias To Buck / LDO 5V or Amplifier / hall To polarity DC/DC DC/DC DC/DC High voltage others amplifier / hall sensor sensor rail supply MCU others sensor MCU protection sensor Non-isolated DC/DC Redundant power supply Primary current Primary Secondary Secondary Input power sensing bias power supply (backup) Primary current temperature temperature current sensing Secondary current protection DC/DC PFC power Shunt / DC/DC primary Shunt / supply sense sense sense bias supply secondary sense stage magnetic power stage magnetic power stage Isolated Loads amplifier Amplifier 12 DC/DC DC/DC Primary Secondary Circuit voltage sense voltage sense breaker Isolated bias supply HV Shunt / QC QG QA QE Shunt / 12V battery magnetic Voltage magnetic battery Isolated Isolated gate System Amplifier Isolated Half Bridge / Isolated supervisor & DC/DC amplifier driver gate driver watchdog monitors gate driver Voltage PFC voltage PFC current DC/DC primary gate MCU monitoring & HS diagnosis sense L sense PFC gate driver sense driver DC/DC secondary gate driver driver To Diagnostics LDOs D I O Isolated Half amplifier MCU I S G Voltage sense QB QD QF QH bridge Voltage sense G O I M Digital Isolator / I/O LS Current sense Primary MCU communication MCU Current Sense C voltage sense SPI WDT driver Temp sense Temp Sense Pos. PFC controller PFC to DC/DC comm DC/DC controller System basis chip (SBC) / I SENSE

QD V QA QB QC QE QF QG QH Power stage 12V Reverse Non- To non-iso Isolated Isolated Isolated battery isolated driver Digital Comm / Buck / LDO battery Isolated gate Half bridge / DC/DC Buck / LDO DC/DC DC/DC isolator diagnostics protection DC/DC driver isolated gate CAN PWM supply supply supply driver Reverse battery Redundant Safety & glue logic PFC PFC bias PFC power Primary bias DC/DC Secondary bias Secondary protection power supply Isolated gate driver CAN/LIN A communication supplies supply supplies communication supplies power supply Half bridge driver GPIOs ISO M AMP CAN P PWM MCU core Gate driver bias CAN Charger interface HEV CAN 12V supply Voltage PFC supply ADC DC / Non- reference Current & voltage sense Reverse/ transient HV CAN Isolated isolated protection battery PWM Voltage reference Wired interface Digital processing CAN PLC Wireless DC/DC DC/DC Gate driver bias supply MCU OBC CAN Input protection Communication Sensors EVSE communication High side switches DC/DC LDO/PMIC ADC Microcontroller PMIC Low side switches / diagnostics D I (V,T,I %..) Major auxiliary Minor auxiliary SBC Contactor control Position sensing I S power supply power supply PMIC Microcontroller Digital isolation G O Motor Temp Connector LED VREF AFE river sensor handshake driver Interlock/ Rotor position Valve control / isolation motor control sensing leakage Signal isolation Self-diagnostics/monitoring Connector control & diagnosis Indicators OBC controller HEV/EV safety Thermal management

Figure 1. Block diagram of a powertrain system in an HEV/EV.

A High-Performance, Integrated Powertrain Solution: The Key to EV Adoption 3 April 2021 Wide band-gap semiconductor devices: a thermal management and size-reduction benefits. Even disruptive technology in the automotive market though wide band-gap switches are expensive today, the cost will decline over time. At a system level, eliminating or Power electronics play a critical role in attempting to minimizing the mechanical blocks for cooling and the amount meet demanding power-density requirements. Power of material for passive elements and casing realizes the lower semiconductor devices inside power electronics must have DTC. these attributes: • Lower power losses. Isolated gate-driver ICs to operate the power • High-frequency operation. switches

• Higher junction temperatures. Powertrain system architectures require an isolated gate driver to drive the power switches efficiently. Isolated gate • High-voltage operation. drivers convert pulse-width modulation signals from the • Increased heat dissipation. controller into gate pulses for the power switches to turn The incorporation of advanced high-voltage devices such on or off. Because of the high voltages associated with the as wide band-gap semiconductors using SiC and GaN battery, galvanic isolation is necessary between the controller for power switches makes it possible for HEVs/EVs to (the primary side) and the power switch (the secondary side). achieve higher efficiencies compared to traditional silicon- Galvanic isolation is a technique to isolate functional based power switches such as power silicon metal-oxide sections of electrical systems to prevent direct current semiconductor field-effect transistors (MOSFETs) and or uncontrolled transient current from flowing in between insulated gate bipolar transistors (IGBTs). them. Data and energy does need to pass through this As power levels rise, power silicon MOSFET or IGBT thermal galvanic isolation barrier, however. Capacitive isolation is a management becomes challenging, due to the limitation in key isolation technology that has digital circuits for encoding their maximum operating temperature, known as allowable and decoding incoming signals to pass through the isolation junction temperature. This limitation requires the addition of barrier [5, 6]. cooling components, such as large copper blocks with water Capacitive isolation is the preferred choice for implementing jackets, in the powertrain system – especially in a traction an isolation barrier in isolated gate drivers due to its high inverter where the power levels can rise higher than 100 kW. data rate and high noise immunity (also called common- Adding cooling components impacts vehicle size, weight and mode transient immunity [CMTI] above 150 V/ns) and can cost. Conversely, SiC has a much higher allowable junction help realize the potential switching capability of wide band- temperature. Additionally, the thermal conductivity of SiC is gap solutions. Powertrains experience high levels of noise two to three times higher than silicon [4]. The combination of and vibration. Therefore, having a gate driver with CMTI is the high junction temperature and high thermal conductivity in preferable. In addition, isolated gate drivers reduce PCB SiC makes it an attractive candidate for powertrain systems, space, vehicle cost and weight through the elimination of as it eliminates the need for big copper blocks and water pulse transformers or external discrete isolators. jackets. Using GaN in OBCs and DC/DC converters can also enable a significant reduction in passive elements, such as Isolated gate-driver integration: a key aspect of magnetics and capacitors, because of its ability to switch in system-level functional safety and lower DTC the hundreds of kilohertz to megahertz range. At a system level, when viewed as a black box, there are Several automakers are already incorporating wide band- three semiconductor components for powertrain systems: gap solutions into their HEV/EV powertrain designs to the digital controller (microcontroller), isolated gate driver and achieve higher horsepower and higher efficiency, along power semiconductor. with increased battery voltages. In addition, it is possible to Besides requiring key functionalities for high-efficiency lower DTC from wide band-gap solutions through improved systems, isolated gate drivers have recently become a

A High-Performance, Integrated Powertrain Solution: The Key to EV Adoption 4 April 2021 primary component because of the increasing need for Power stage using a simple isolated gate driver powertrain system diagnostics and protection developed at the highest functional safety levels. Monitoring and protection needs to occur intelligently, and integrating these features in the gate driver is becoming a popular solution.

The failure-in-time (FIT) rate is considered a key metric toward achieving the highest levels of automotive safety integrity. For example, the FIT rate should be lower than 10 in order to achieve an ASIL D-compliant system; such an ASIL level is very common in traction inverters. A traction inverter spins the motor, which in turn moves the wheels of the vehicle. Similar ASIL requirements (typically ASIL B or Power stage using a smart isolated gate driver ASIL C) are now becoming a requirement for OBCs and DC/DC converters as well.

In order to achieve the lowest possible FIT rates, all of the features for diagnostics and protection that would traditionally be positioned discretely in the system are now being integrated into the isolated gate driver, as shown in Figure 2. This directly enables a lower DTC, as it significantly reduces the number of components and PCB space. TI has recently introduced the UCC5870-Q1, which offers an advanced level Integrated features of smart isolated gate drivers enable: of diagnostics and protection. The device provides a dramatic • Significant system cost reduction benefit in component reduction, enabling lower DTC and the • 2 times PCB area reduction ability to achieve the desired ASIL level, as shown in Figure 3 for the traction inverter system.

Figure 2. Benefits of integration.

VB 5v Vcore DC+ VB 3.3v 1.8v VIO VIO PMIC UCC5870-Q1 VCC2 CANWU RES To MCU 1 36 WD Digital ports GND1 DESAT IGN 2 35 U err NC VCC2 IGBT/SiC temp sensing 3 34 VB NC VCECLP DRVOFF 4 33 NC BST U 5 32 VBAT OUTH 6 31 VDDIO OUTL U 7 30 2 U GPIO nFLT1 VEE2 E E

GPIO 8 29 V nFLT2 CLAMP GPIO 9 28 EN GND2 10 27 U ASC trigger from LV side ASC VREF Real time PWM 11 26 U IN- AI1 PWM 12 25 AI2 U SPI 13 IN+ 24 control CLK AI3 SPI 14 23 nCS AI4 SPI 15 22 SDI AI5 U 16 21 MCU SPI SDO AI6 17 20 GPIO VREG2 18 DOUT 19 Redundant phase Phase U VEE2U Vref U GND1 VEE2 U current sensing U U UCC5870-Q1 Phase V

1 GND1 DESAT 36

2 Motor 2 35 L NC VCC2 C 3 34 C V Redundant DC NC VCECLP 4 33 Shunt / Magnetic

NC BST L 5 32 VBAT OUTH bus sensing 6 31 L

VDDIO OUTL 2

7 30 E L

nFLT1 VEE2 E Phase W

8 29 V nFLT2 CLAMP 9 28 EN GND2 10 27 ASC VREF L 11 26 IN- AI1 12 25 AI2 13 IN+ 24 CLK AI3 L L 14 AI4 23 Phase voltage 15 nCS 22 SDI AI5 16 21 SDO AI6 sensing 17 20 L DOUT VREG2 18 19 GND1 VEE2 VEE2L Vref

L L DC-

Safety VCC1B VCC2L 1 Vcc1 Vcc2 36 ASC trigger from HV side ASC command 2 35 MCU IN1 Out1 3 34 IN2 Out2 4 33 GND GND VEE L

Figure 3 Benefits of the UCC5870-Q1.

A High-Performance, Integrated Powertrain Solution: The Key to EV Adoption 5 April 2021 Another idea involves the development of an integrated The DTC model includes efforts to reduce cost in the power transformer bias supply IC that can further significantly lower electronics of powertrain subsystems. In addition to wide DTC, which are applicable to traction inverters, OBCs and band-gap power switches such as SiC and GaN, isolated DC/DC converters. gate drivers have emerged as a key component that enables OEMs to reduce costs through component integration and An integrated powertrain solution at a system achieve high functional safety levels. The UCC5870-Q1, TI’s level newly released gate driver, provides such a solution.

The focus over the years has centered on integration, DTC Taking this integration concept to the next level is the reduction and power-density improvements of individual emerging trend that combines OBCs, DC/DC converters subsystems in powertrains. OEMs are taking this to the and traction inverters into one solution, which both reduces next level to further lower costs by integrating the whole costs and benefits the power-to-weight ratio. powertrain system into one unit, similar to the system-on- chip concept in the IC industry. To date, the first step has Additional resources been combining either the OBC and DC/DC subsystems into 1. Anwar, Asif. HEV-EV Semiconductor Technology one box, and the traction inverter and DC/DC subsystems Outlook: What Role will SiC and GaN Play? Strategy into one box. New platforms combine all three subsystems Analytics forecast and outlook, July 17, 2019. into one box. Regardless of the configuration, the integrated 2. Erriquez, Mauro; Morel, Thomas; Mouliere, Pierre- powertrain concept can significantly reduce the overall Yves; Schafer, Philip. Trends in electric-vehicle design. weight of the powertrain system, increase the power-to- McKinsey & Co., McKinsey Center for Future Mobility, weight ratio, eliminate cabling among the subsystems, and October 25, 2017. achieve DTC goals. Studies and prototypes have reduced costs by as much as 15% [7]. In addition to gate-driver 3. Baik, Yeon; Hensley, Russell; Hertzke, Patrick; Knupfer, integration at the semiconductor component level, sharing Stefan. Making electric vehicles profitable. McKinsey & MCUs among these subsystems further lowers the total cost Co., McKinsey Center for Future Mobility, March 8, 2019. of the powertrain system. 4. Sridhar, Nagarajan. Silicon carbide gate drivers – a Powertrain integration reduces the assembly cost and disruptive technology in power electronics, Texas build as well as the time to validate, thereby lowering the Instruments white paper SLYY139A, 2019. overall cost of ownership and time to market for OEMs. One 5. Bonifield, Tom.Enabling high voltage signal isolation trade-off, however, is the lack of flexibility of original design quality and reliability. Texas Instruments white paper manufacturing sourcing. SSZY028, 2017.

Conclusion 6. Sridhar, Nagarajan. Impact of an isolated gate driver. Texas Instruments white paper SLYY140A, 2019. The HEV and EV market is growing rapidly, and appears to be recovering from initial customer skepticism by achieving 7. Muhlberg, Gunter, Dr. Hackmann, Wilhelm, Buzziol Kai. longer driving ranges and high performance. The future Highly Integrated Electric Powertrain, ATZ elektronik growth of this market hinges on cost reduction in order to worldwide, April 2017. make HEVs and EVs affordable for consumers and profitable for OEMs.

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