SWAY033A december 2020 – december 2020 F29H850TU , F29H859TU-Q1 , LMG3410R050 , TMS320F280025 , TMS320F280025-Q1 , TMS320F280049 , TMS320F280049-Q1 , TMS320F28377D , TMS320F28377D-Q1 , TMS320F28377S , TMS320F28377S-Q1 , TMS320F28384D-Q1 , TMS320F28384S-Q1 , TMS320F28386D-Q1 , TMS320F28386S-Q1 , TMS320F28388D , TMS320F28P650DH , TMS320F28P650DK , TMS320F28P650SH , TMS320F28P650SK , TMS320F28P659DH-Q1 , TMS320F28P659DK-Q1 , TMS320F28P659SH-Q1
The electric vehicle (EV) market has been growing rapidly since 2010, with original equipment manufacturers (OEMs) announcing EV models through 2025. This evolution toward more pure EVs rather than hybrids is a reaction to government environmental policies mandating a transition away from internal combustion engines.
Higher-capacity battery packs, while reducing consumer anxiety related to limited driving ranges, place increasing demands on an EV’s power electronics – specifically the onboard charger (OBC), which not only needs to accommodate higher power ratings to accommodate higher power capacities, but must also possess higher power density and higher efficiency to reduce weight of the vehicle and reduce cost per charge.
The emergence of gallium nitride (GaN) and silicon carbide (SiC) wide-bandgap power semiconductors has provided an opportunity to massively shrink the size and weight of the power electronics in EVs given their ability to operate efficiently at much higher switching frequencies than silicon.
The challenge for OEMs and Tier-1s is to provide OBC solutions that can support multiple geographic regions with different power-grid infrastructures. For example, higher power EV chargers in China need to support connections to a three-phase power line, while EVs in the U.S. need to connect to a single-phase power line. OEMs want to supply variants with power ratings ranging from 3.3 kW to 22 kW typically – and as high as 44 kW in some cases.
The most critical systems in an EV powertrain are the OBC that is used to charge the high-voltage battery, the high-voltage to low-voltage DC/DC converter which charges the 12-V/48-V battery, and the traction inverter that controls the EV motor, shown in Figure 1.
Efficient control and management of the power flow in these systems can be achieved using one or more real-time microcontrollers (MCUs). To save mechanical costs and reduce the size of power electronics, one popular trend is to integrate OBC equipment with the high-voltage to low-voltage DC/DC converter, which can save as much as 10%-20% of board space. However, this adds additional requirements for the real-time MCU, as it need to support more pulse-width modulators (PWMs), more ADCs and allow for multicore processing to manage multiple power stages.
Further, OBCs need to support bidirectional operation for vehicle-to-grid, which result in more complex topology choices that necessitate even greater care when selecting an MCU for an OBC. The MCU must include features that:
The MCU should also be part of a scalable portfolio to support the variety of options when integrating OBCs with the high-voltage to low-voltage DC/DC converter. In this white paper, we will review the typical topologies and challenges for each stage and highlight some of the features of C2000 real-time MCUs to help you solve those challenges.
Manish Bhardwaj,
This paper discusses common control challenges of onboard chargers and high-voltage to low-voltage DC/DC converters, and the benefits of C2000™ real-time MCUs in these subsystems.
1 Totem-pole PFC and CLLLC topology for onboard chargers | A totem-pole bridgeless PFC
improves efficiency by lowering the number of power devices in the current
path, while enabling bidirectional operation. The CLLLC isolated DC/DC
converter provides a soft-switching capability to enable a higher switching
frequency and smaller magnetics size. |
2 Peak current mode control for high-voltage to low-voltage DC/DC converters | The analog integration on a
C2000 real-time microcontroller enables peak current mode with control loops
fully in hardware. |
3 Scalable portfolio of real-time MCUs for onboard chargers | C2000 real-time MCUs offer a
scalable portfolio to address the variety of integration needs and discrete
options in on-board charger systems. |
Figure 2 shows a 3.3-kW OBC with a totem-pole PFC stage for the OBC PFC and a capacitor-inductor-inductor-inductor-capacitor (CLLLC) stage for the OBC DC/DC converter. A totem-pole bridgeless PFC improves efficiency by lowering the number of power devices in the current path, while enabling bidirectional operation (compared to a conventional bridge-based PFC). Implementations of totem-pole bridgeless PFC were previously limited to lower power levels only because the inherent body diode in silicon power metal-oxide semiconductor field-effect transistors was susceptible to high reverse-recovery losses under hard switching. With no such body diode within its structure, GaN power switches such as the LMG3410R050 from Texas Instruments have now made it practically feasible to implement multikilowatt totem-pole bridgeless PFC power supplies. Since GaN devices feature low output capacitance (Coss), they can be operated at high frequencies (100 to 200 kHz), which further allows using smaller inductor and thus shrinks the size of the passive components required in the totem-pole PFC converter.
During dead time, however, third-quadrant operation in GaN switches results in additional losses that a real-time MCU needs to optimize by regulating the dead time precisely. C2000 real-time MCU type 4 PWMs enable features such as high-resolution dead time, which can regulate the deadband to 150 ps of resolution. As an example, for a 100-kHz totem-pole PFC, the loss savings with dead-time optimization is 1 W. As the designers reduce the inductor size further by increasing the switching frequency to 1MHz and employing control techniques such as Critical Mode PFC, the power loss savings can be as high as 10W, thus making optimization of third quadrant losses a critical feature, for which precise and accurate control of the dead time if required.