Power Electronics in Automobile and Traction
29/05/2021
Over the last few years, electrical loads into an auto-motive system have grown from lighting and battery-charging towards infotainment, sensors and safety. This has made people to drive the car with more fun. Figure 1 contains the detail diagram of electric drive system. With the trend of electronics in infotainment systems continues, a future trend is electronics which is in power train systems which can provide better engine propulsion, like the engine blocks, transmission and controls. The efficiency can be improved in power trains if we replace conventional mechanical and hydraulic load with electrical loads. This trend is seen with focus on electric vehicle concepts — hybrid (HEV) and pure (EV). By using electric loads we can lower C02 emission requirements. The increasing in demand of electric loads makes the conventional 12V power system more challenging. It is critical task to have higher voltages in order to handle power train loads more efficiently and with flexibility. Switched-mode power supplies (SMPS) can provide the above requirement. This can be possible because of huge advancement in power electronics is made. The very way to accomplish this is to have different power-conditioning systems between the batteries and loads. As we know that power electronics systems makes use of silicon-based power management with power semiconductor switches. These switches are usually power metal-semiconductor field-effect transistors (MOSFETs), insulated gate bipolar transistors (IGBTs), and a variety of diodes that have made significant improvements in their performances.
The SMPS Switched-mode power supply (SMPS) is completely based on semiconductor devices that operate in ON and OFF states. It has no power loss at each of these two states. Theoretically, it has 100% efficiency. The technique known as Pulse Width Modulation is used to turn ON and OFF the switch. Also, under high frequencies we can use this switches, which makes the power converters less bulky and smaller in size. Based on this information, there are three types of power conditioners in automotive power train systems which are: AC/DC (rectifier); DC/DC (converter); and AC/DC (inverter).
SMPS applications in the power train system
Electric vehicles, HEVs and ICE primarily need the following SMPS conditioners in their power train systems:
• Regenerative braking (AC/DC)
• Onboard charger (AC/DC)
• Dual-battery system (DC/DC)
o Battery management for Lithium-Ion (Li-Ion) batteries
o 48V-12V bi-directional power supply
• 400V Battery (for pure EV only)o Bi-directional 400V-12V power supply (DC/DC)
o Traction motor (DC/AC)
DC/DC converters
There are several basic topologies which are available for these power-conditioning systems based on the electrical load safety requirements which are classified as isolated and non-isolated topologies. Both types of topologies are used in power train systems as shown in fig. 2. These topologies are depending on the loads and standards requirements. Irrespective of type, market adoption is growing towards a soft-switching concept using an LLC or resonant mode. Soft switching means switches which are used are subjected to lower stress, which implies a longer life and higher reliability of these converters, very vital for automotive markets.
Traction inverter (DC/AC)
In order to run vehicles, motors are required to convert to convert electrical to mechanical energy. Previously, DC motors were used because of their simplicity and ease of control. However, DC motors has low efficiency compare to AC motors. Over the last decades, tremendous progress is been done in building controllers for AC motors. AC motors are small in size with fewer parts that significantly improve its reliability. Therefore, the power stored in the battery (EV, HEV or ICE) must be converted from DC to AC in order to run AC motors. These inverters, called traction inverters, and it usually transfers power in the tens of kW range. Hence, the switches used in these topologies (full bridge) are IGBTs (individual or intelligent power modules, depending on the current requirement).
Regardless of power conditioning system type (DC/DC, AC/DC or DC/AC), all require controllers and gate drivers. Currently, the choice of analog or digital controllers is highly dependent on the vehicle or power supply manufacturer’s requirements. This includes cost, flexibility, integration, reliability and availability to write firmware (for digital controllers). Likewise, the choice of gate drivers is dependent on the drive current that in turn is dependent on several factors. This includes the semiconductor switch it needs to operate, reduced component count (single channel versus bridge drivers), features such as dead-time control, and adaptive delay to avoid shoot-through between high-side and low-side switches and isolation, to name a few. Texas Instruments has several automotive grade analog and digital controllers and gate drivers to turn the power electronic switches on and off.
References
Schoener, Hans-Peter & Hille, Peter. (2000). Automotive power electronics — New challenges for power electronics. PESC Record — IEEE Annual Power Electronics Specialists Conference. 1. 6–11 vol.1. 10.1109/PESC.2000.878789.
Omar Hegazy, Ricardo Barrero, Joeri Van Mierlo, Philippe Lataire, Noshin Omar, Thierry Coosemans, “An Advanced Power Electronics Interface for Electric Vehicles Applications”, IEEE Transactions on Power Electronics ( Volume: 28, Issue: 12, Dec. 2013)
