The Ascension of the Electric Motor

­1. Motor efficiency

Whatever power source is chosen for the future - be it a self-powered or occasionally plugged-in battery pack, a fuel cell that converts hydrogen or ammonia, or even a fossil fuel driven generator - the most efficient motor to provide motion power is an electric one.

The typical efficiency of a traditional gasoline engine ranges from 12 to 27%. In a typical road car today, a modern hybrid engine ranges from 25 to 35% efficiency. Large ship engines and gas turbines push that efficiency into the 40~45% range, and state-of-the-art Formula 1 engines touch on to the magical 50% barrier. And these last ones are certainly very specific use-cases under very particular conditions.

The most efficient use of burning fuel is in co-generation applications. This can be seen in large industrial gas co-generation units, where a gas generator provides electricity and the exhaust heat is re-used for heating a transfer liquid, the recuperated heat is then used to heat buildings, generate steam, provide heat to ovens etc. These installations can reach up to 70% efficiency, due to this recuperation of heat in the cooling water and most of all in the exhaust fumes, even by after-burning the large amounts of O₂ remaining in the gas exhaust.

Compared to electric motors, easily reaching efficiencies above 90%, up to 99% for the best topologies, there is no contest as to which is the most power-efficient solution.

2. Regulations

On the other hand, electric motors are one of the largest consumers of the worldwide electricity consumption. Optimally converting electrical to mechanical energy has a far-reaching impact on both the worldwide energy consumption and reducing operational costs of the equipment.

According to a report by the International Energy Agency (IEA), electric motor driven systems were already responsible for 53% of global electricity use in 2016. To mitigate the power loss in inefficient electric motors, international reference levels for minimum efficiency were set.

The International Electrotechnical Commission (IEC) has contributed to the definition of energy-efficient electric motor systems through the IEC 60034-2-1 test standard for electric motors and the IEC 60034-30-1 classification scheme, comprising four levels of motor efficiency. These International Efficiency (IE) levels of standards, colloquially called “IE Codes”, serve as a reference for governments to specify their Minimum Energy Performance Standards (MEPS). In EU Regulation 2019/1781 you can see the tables outlining according to motor power and number of poles, what the minimum efficiency for that motor needs to be.

This regulation covers a wide scope of electric motors, from 0.12 kW to 1000 kW output power, defining minimum efficiencies according to the number of motor poles (2-, 4-, 6- and 8-pole motors). As of 1st July 2021 motors between 0.75 kW and 1000 kW are required to meet a minimum efficiency class of IE3 (“Premium Efficiency”), the group of smaller motors from 0.12 kW to 0.75 kW minimum IE2 (“High Efficiency”). From the 1st July 2023, motors between 75 kW and 200 kW are required to meet the even higher efficiency class of IE4 (“Super Premium Efficiency”).

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The European Union has also included for the first time requirements for converters in the 2019/1781 regulation, based on IEC 61800-9-2, edition 1. From 1st July 2021, the minimum requirement is IE2 class of losses in converters with power ratings between 0.12 kW and 1000 kW. 

For example, the minimum required efficiency of a three phase 4 pole motor rated at 111kW needs to meet class IE4, exceeding 96.3%. Similarly, a Variable Speed Drive (VSD) orated at 110kW needs to exceed 95.34%.

By 2020, the point was reached where countries consuming 76% of the global electricity consumption by electric motor systems have set MEPS for motors at either IE2 or IE3 level.

3. Electromotor topologies

Different types of electric motors have their own natural limits on energy conversion, which makes motor design one of the most fundamental factors of system efficiency and power output. The efficiency of electric motors depends on how well a motor can convert current into mechanical energy. For all types of electric motors, this conversion comes down to the amount of heat they generate, which indicates how much electric power is lost and fails to convert to mechanical motion.

Generally, motor efficiency is expressed as a percentage of the electrical energy that becomes mechanical force (or torque), and the remainder is roughly equivalent to the amount of heat also produced. The main factors influencing this dynamic are steel magnetism, conductor materials, thermal management, aerodynamic design, manufacturing processes and quality controls. The goal is to achieve maximum motor output with as little heat generated as possible. Reducing energy loss in the form of heat not only improves motor efficiency but protects various motor components from unnecessary wear and malfunction.

Comparing the various types of motors and the efficiencies they can achieve, not many words need to be spent on brushed DC motors, as they are one of the most inefficient kinds of motor designs and require a high degree of maintenance. Aside from the most cost-conscious applications, they are going out of use, converting only 75–80% of electrical power to mechanical energy. Higher motor speeds translate to greater efficiency, but this is true of almost all types of electric motors.

A brushless DC motor (BLDC) uses electronic controllers to convert current to the motor winding via a magnetic field. The field itself rotates and moves a permanent magnet rotor with it. By omitting rotor windings, a permanent magnet rotor dramatically reduces slip between the rotor and stator. The result is much higher efficiency than brushed DC motors, with electromechanical conversion rates between 85% and 90%.

An AC induction motor, or asynchronous motor, drives rotor movement through electromagnetic induction originating in the stator winding's magnetic field. Induction involves some inherent slippage between the applied current and the magnetic field, resulting in an asynchronous lag between the rotor and the stator. Depending on speed variability and the number of stator poles, an induction motor can achieve 90–93% efficiency.

Synchronous motors completely eliminate the need for current to flow into the rotor. This is possible due to the synchronization of current frequency and the magnetic field generated by the winding. The shaft and magnetic field rotate in lockstep with current oscillation, driven by the stator's sophisticated electromagnet geometry. This reduces internal rotor resistance, regardless of its position, increasing flux availability for maximum conversion. It also breaks the dependency on fast rotor speeds to attain higher efficiency. Synchronous motors can produce a near-perfect conversion of electrical to mechanical energy, making up to 99% efficiency rates possible. Synchronous motors can also provide higher power with more compact designs, as well as superior torque at lower speeds.

4. Auxiliary power supply

Aside from the main traction drive supplying the motion, a vehicle has many auxiliary power needs, like harvesting equipment, a trash compactor, street-cleaning brushes and so on. Traditionally, this equipment is powered through a mechanical coupling, directly on the combustion engine output or transferred by an axle.

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Setting the auxiliaries up with their own electric motor and drive unit has several benefits. The mechanical link can be omitted, reducing weight and removing a potential source of breakdown while reducing the maintenance cost. The efficiency of the overall solution also becomes much higher. In for example an electric Power-Take-Off (ePTO) unit, providing hydraulic pressure to auxiliary equipment, the system energy savings can reach up to 12% improvement in efficiency.

By replacing mechanical couplings and shafts, notorious for wear and tear, the maintenance and replacement costs can be reduced drastically.

5. Electric power conversion

Inverter technology has been a cornerstone of power electronics, enabling efficient conversion between voltage domains, be it AC-to-DC, DC-to-DC or DC-to-AC. The choice of semiconductor materials in inverters significantly impacts their performance, efficiency, and suitability for various applications. Inverters have been used for decades, in a wide range of applications, with Silicon Carbide (SiC) MOSFET based inverters gradually taking over the higher power applications. Since SiC can operate at higher voltages, temperatures, and frequencies compared to traditional silicon Insulated Gate Bipolar Transistors (IGBTs), SiC inverters offer low switching losses and high thermal conductivity, making them ideal for applications that require high power density, efficiency, and compact design.

At CISSOID, we realized that the most significant value that can be added to power semiconductors, is making the life of the engineers as easy as possible, reducing the development time for an electric drive train as much as possible. With the new EVK-PLA1060 series of on-board inverter reference designs, the developer can take an existing and proven solution to get their electric motor running and calibrated within days, and mounted into a proof-of-concept or prototype within a very short time, drastically increasing the speed-to-market.

These reference designs are based on CISSOID’s own 3-phase 1200V/340A-550A SiC Inverter Control Modules (ICMs), covering a power range from 100 to 350kW on 100~850V bus voltages. The EVK-PLA1060 reference designs contains a bespoke low inductance DC link capacitor, the necessary current sensors, a DC bus EMC filter, together with the necessary power and comms+control connectors. All in a less than 7 litre volume housing, achieving over 50kW/litre of power density and efficiencies reaching 99.6%.

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The processor at the heart of the Inverter Control Module is Silicon Mobility’s OLEA® T222 Field Programmable Control Unit (FPCU). This highly flexible processor was developed specifically to drive electric motors in a safe and efficient manner. Using a dual ARM®️ Cortex-R5F core running in lockstep, the T222 FPCU takes real-time and critical safety processing to the next level. Real-time processing and control of sensors and actuators are significantly accelerated due to the on-board programmable logic in the Flexible Logic Unit. The flexible programable logic off-loads precious core processing cycles to the Advanced Motor Event Control (AMEC^®️) block, enabling rapid detection of faults and executing corrective actions. All this results in dazzlingly fast response times, reducing system-level fault detection, correction and containment to within tens of nanoseconds.

Likewise, Silicon Mobility’s OLEA® INVERTER software brings multiple benefits to the overall solution. Features such as Optimized Pulse Patterns (OPP) and Dead Time Compensation reduce distortion of the motor current significantly, thereby reducing stray fields and the resultant additional heat as well as interference in the motor. Making the overall solution very efficient both in low power and torque requirements as in high-speed conditions.

All these features enable reliable and fast execution of safety-critical applications in real-time. Both the OLEA® T222 processor and inverter software are ISO26262 ASIL-D and AUTOSAR 4.3 certified for functional safety, whereas CISSOID’s Inverter Control Module is designed for ISO-26262 compliance, currently undergoing certification.

The unique position of CISSOID’s solution is that a developer can start from a ready-made, off-the-shelf solution to get up and running very quickly, and then offers the capability to start customizing both the software and hardware to the degree needed by the application. This provides a degree of freedom that is only paralleled by assembling all the various parts from separate suppliers, but alleviates all the headaches of making the differing components play well together into a coherent and efficiently performing system.

6. Electrification does not necessarily equal battery-powered

A common misconception is that electrification of vehicles means they need to be battery powered. There will certainly be a battery involved for buffering standby and start-up power requirements, and for example to temporarily store braking energy, but the battery pack does not need to be the main power source. There are better alternatives already on the horizon. But regardless of power source, the “engine” driving the vehicle will be an electric motor.

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