 Hi, I'm John Johnson, Automotive Systems Marketing at ST Microelectronics. Our topic this time is motor control as it applies to electric vehicles. We'll discuss the traction drive in a separate session. For today, we'll focus on other motors present in an electric vehicle and how they're driven and controlled. We'll use electric power steering as our example use case. So hop in and let's go! Engine that is creating motion with an electric motor instead of an internal combustion engine has a profound impact on the electrical system of the vehicle. This is not just because of the presence of a high voltage bus, the battery and the traction inverter. At first, one might think that replacing hydraulic systems, for example, braking and steering with electric motors is a consequence of not having an internal combustion engine present with its ability to drive fans and pumps with pulleys and belts. However, energy efficiency is hyper-emphasized as a key performance indicator in a battery electric vehicle, and powering systems with electric motors is significantly more efficient. This is because the motor provides work only when it's needed. That is, the motor does not introduce a constant load to the system. Let's examine one such electrified system in more detail. Electric power steering. First, here are some definitions to help clarify what I'm talking about. Electric power steering is where electric motors boost torque applied to the steering mechanism. That is, the motor replaces the role of hydraulics employed in traditional steering systems. This is in prevalent use today. Electro-hydraulic power steering employs an electric motor to pressurize hydraulic fluid. This was prevalent prior to mass deployment of electric power steering systems. This is employed on very large commercial vehicles, and then they're steer-by-wire. There's no physical linkage between the steering wheel and the steering mechanism. Position and torque applied to the steering wheel are transferred electronically to actuators and motors that directly control the steering mechanism. This has been deployed on a very limited basis. However, it's a key technology for autonomous vehicles. EPS boosts the torque applied to the steering mechanism via an electric motor. Heavier vehicles require that the torque is boosted via the steering rack or pinion, while lighter passenger cars have EPS systems that apply torque boost via the steering column. Here is a simplified block diagram of the EPS system. A conventional system receives control input via the sensors on the steering wheel. Systems that incorporate ADAS can receive inputs via the vehicle communication bus as well. That is lane departure features that offer correction. As mentioned previously, one of the keys to EPS system design is efficiency, and this is not only because the motor only presents a load when motor is to be boosted. If the motor is controlled inefficiently, then to some extent electrification could not have an optimal efficiency benefit. To ensure that the motor is controlled efficiently, field or vector-oriented control is used. Let's examine FOC more closely. It may or may not be intuitive, but if we consider the fundamental operating principles of a motor, then the method of optimizing efficiency and torque ripple will become apparent. A motor rotates due to the interaction of magnetic fields. For a PMSM or a BLDC motor, the rotor field is provided by a permanent magnet. The stator field is the vector sum of the magnetic fields produced by the stator poles. This vector summed field is electronically rotated causing the motor to spin. Torque is maximized when the stator field and rotor field are orthogonal. The effectiveness of generating this field and maintaining orthogonality is determined by the ability of the control 2, 1, precisely sense rotor position relative to the stator, 2, precisely control the phase of each stator pole, 3, respond to changes in control settings and changes in load, and 4, deliver sufficient control bandwidth to support the operational range desired. Field-oriented control goes beyond simply ensuring orthogonality of the rotor in the stator fields. This relationship can be achieved without FOC by employing sinusoidal control and to some extent trapezoidal control, which is adequate for slow speeds, but problematic as speed increases beyond the point at which the bandwidth of the PI current controller is exceeded. At this point, without employing FOC, motor efficiency and torque jitter increase significantly. Let's explore how FOC accomplishes this. Field-oriented control is employed to ensure that a motor is operating at peak efficiency, that is, energy in gives you torque out. The key is to simplify the controls by changing the frame of reference from a stationary, that is, stator, to a rotational, that is, rotor frame of reference, and then back again. By controlling the current space vector directly in the stationary DQ reference frame of the rotor, torque and efficiency can be optimized over a wide range of operational modes. FOC VOC employs a few mathematical transforms that changes the system from a complex one where multiple differential equations must be solved in real time to a simple one in which linear algebra is all that is required. In essence, this changes the commutation problem from a three-phase AC motor into a single-phase DC motor. Here is a control diagram that illustrates the partitioning between hardware and software for the EPS system. It includes the L9907, which we'll discuss in more detail a little later. The 32-bit microcontroller must be ASL-D rated and have an adequate throughput to compute the torque control loops and transforms discussed on the previous slide. Sometimes microcontrollers include hardware accelerators for motor control as well. Now let's re-examine the block diagram of the EPS system to gain some insight into solutions offered by ST. Several ST part numbers are shown here as ST has enjoyed considerable success providing solutions to the EPS market. EPS includes a power supply as well as certain communications channels. Of course, it's always good practice to use transient protection devices on both. The microcontroller must provide enough throughput to compute the torque control loops discussed earlier. Newer systems must also sometimes include hardware security, and this will become more common place as the industry draws closer to autonomous operation. Let's look at the motor driver portion more closely. The L9907 is a three-phase FET pre-driver ideal for 48-volt EPS applications. It includes three half-bridge pre-drivers with full diagnostics as well as floating current-sense amplifiers used as sense motor current. The L9907 serves as a bridge between the microcontroller and the power stages, which we'll talk about next. ST Microelectronics' STRIP FET offering provides the power stage companion devices to the L9907, L9908 discussed earlier. The F7 series provides an ideal choice for EPS systems that operate from 12 volts or a 48-volt bus. The bottom line is that ST Microelectronics provides solutions to difficult mission-critical motor control problems. So give your local sales team a call or contact us at www.st.com. I'm John Johnson for ST Microelectronics.