Motors are widely used in various industrial and consumer products, and are quite common and important electronic components. In addition, with the rapid development of electric vehicles (EVs), the market demand for motors is rising rapidly. How to improve the operating efficiency of motors has become a key element of related applications. This paper will introduce the types and selection factors of motors, as well as the functional characteristics of high-performance mixed-signal microcontroller units (MCU) introduced by ST (STMicroelectronics) which can be used for motor control.
Improve the efficiency of motor drives to prolong the service life of battery-powered systems
One frequently cited figure in addressing the topic of energy use is that more than half of the world' s electricity is used to drive motors. The industrial sector is the main cause of this phenomenon, but the impact of many consumer applications, such as air conditioners or household appliances, cannot be overlooked, especially in recent years, as a result of the rapid development of electric vehicles (EVs). It is very important to improve the efficiency of motor drives as much as possible to reduce the overall energy consumption and maximize the service time of battery-powered systems.
In order to improve the efficiency of motor drives, it is necessary to analyze the efficiency from the perspective of the system level to determine various factors causing loss, which may be loss caused by movement, liquid/gas flow, or thermal sources.
In order to improve the efficiency of the operation of electronic devices, priority must first be given to identifying the main causes of the reduction in the operating efficiency of the devices. For example, improved insulation of refrigerators will yield tangible results in terms of power savings. In addition, if the equipment has a drive system (gear or belt) that may reduce overall drive efficiency by up to 20 percent, it should be considered whether a direct drive is available. Only a detailed analysis can yield the desired results, and for some complex systems, such as electric vehicles, efficiency is also affected by driving habits and environmental conditions.
The next point to consider is motor drive optimization, starting with the choice of motor type. To date, brushless motors will be preferred, taking efficiency as a standard, be it three-phase AC induction (high efficiency type), switching reluctance, or better permanent magnet synchronous motors (PMSM). In the area of household appliances, they have increasingly replaced conventional DC brushed universal motors, whose disadvantage is that their brushes cause additional friction losses, which can easily lead to wear and whistling noises.
Different motor types have different operating efficiencies
In motors, mechanical torque is generated by the interaction between an inner magnetic field and an outer magnetic field. The efficiency difference between permanent magnet synchronous motors and asynchronous motors is mainly due to their different structures and working principles. Permanent magnet synchronous motors use the magnetic field provided by permanent magnets to achieve higher efficiency, while asynchronous motors consume energy to generate a magnetic field. This is the main cause of efficiency variances, which can be increased by up to 15% during low-load operations. For high rated power, the efficiency variation is lower, but permanent magnet (PM) motors are always several percentage points more efficient than AC induction motors (ACIM), reaching 95% or more.
Permanent magnet synchronous motors are also favored due to higher power density and high torque at start-up. They are more competitive in terms of prices, in part because they are less sensitive to copper price fluctuations and require less copper than AC induction motors, which are still the mainstream in the field of ultra-high power (over 100kW) motors, even though this demand needs to be balanced with their magnet demand for rare earth elements.
When selecting motors, some manufacturers recommend replacing induction motors with synchronous reluctance motors that are more efficient at some loads and do not use rare earth permanent magnets in the rotors. Recent research papers have presented the design of permanent magnet-assisted synchronous reluctance motors that combine reluctance torque with magnetic interaction torque for greater efficiency and further limiting the costs associated with the use of ferrite magnets, types of motors that may soon be available for industrial or consumer applications.
From the perspective of electronic controllers, the operation of brushed DC motors is simple, using a low-cost general-purpose MCU and a power transistor to modulate the current, and if you need to reverse the direction of rotation, up to four can be used. Similarly, universal motor control requires only one Triac module or automatic speed drive (ASD) switch to disconnect the 50/60Hz mains voltage. This motor is indeed a brushed DC motor commonly used in household appliances and can be powered by DC bus or AC power. Changes in flux polarity will not change the direction of rotation, as it is reversed in both stators and wound rotors.
Power factor correction is used to improve the quality of electrical energy
Improvements in electrical energy quality can be achieved by performing power factor correction (PFC), while efficient motor control can be achieved by using the sensorless magnetic Field-Oriented Control (FOC) technology.
A PFC is a circuit that improves the power factor at the AC power end and is one of the common circuits in switched mode power supplies. Common PFC requirements include continuous conduction mode (CCM) interleaved PFCs supporting two channels, interleaved 180° phase shifts, and digital control of voltage loops, current loops, load balance, as well as overvoltage protection (OVP)/undervoltage protection (UVP)/overcurrent protection (OCP) input, OVP/UVP and overtemperature protection (OTP) output protection, and soft starts with digital inrush current limiter.
Digital PFCs offer greater flexibility, have the advantage of software-programmable digital PFCs, distinguish between control performance while maintaining the same hardware, support algorithm upgrades and painless customization, and can add/remove features at any time, reducing the cost of their solutions as the number of components decreases and saving PCB and validation time.
ST introduces platform-wide control based on the STM32G491 to support dual-motor FOC and combined high-frequency interleaved digital power factor correction (dPFC). It can support the inverse transformer power supply of SLLIMM® IPMs (intelligent power modules). Compressor IPMs have 𝜂>97% performance, adopt ST-proprietary trench gate field stop IGBT technology, the PFC has the characteristics of 𝜂>96%, iTHD<2%, PF>0.99 at 40kHz, and a VIPER31 auxiliary power supply section. They can support the maximum input power of 4kW, have a high degree of integration, and can be applied to commercial air conditioning, data centers, energy storage, heat pumps, and other fields.
STM32 supports digital PFCs and dual motor controls on the same MCU, PFCs can be turned on only when needed, and allows the compressor can enter flux-weakening region at higher speeds for higher motor efficiency, bus voltage can be adjusted based on AC input and motor speed, better bus voltage regulation, faster motor dynamic response, and other performance improvements.
STM32G4 series mixed-signal MCU with DSP and FPU instructions
The STM32G4 series has high performance, integrating the 32-bit Arm® Cortex®-M4 kernel running at 170 MHz (supporting FPU and DSP instructions) combined with three different hardware accelerators: ART Accelerator®, CCM-SRAM routine booster, and mathematical accelerators.
The STM32G4 series also features seven comparators with a propagation delay as low as 19ns, five 12-bit and 16-bit analog-to-digital converters (ADCs) with hardware oversampling supporting 4MSPS (0.25µs), and seven 12-bit 15-MSPS digital-to-analog converters (DACs) with motor-controlled timer and high-resolution timer with a resolution, the resolution up to 184 ps, and provided other rich advanced analog peripherals.
The STM32G4 series supports power supply units and power factor correction, USB Type-C interface with power delivery including a physical layer (PHY), high robustness, high immunization against fast transients, robust IOs resistance to negative injections, hardware checksum and dual-bank flash memory with error-correcting code (ECC)(supporting in-field firmware upgrade), securable memory area, parity check on RAM, and security features such as FuSa software library (SIL) and AES hardware encryption. It supports FD CAN where the bit rate of a maximum of 3 instances and a payload is 8 times that of a standard CAN. Flexible internal interconnect matrix enable autonomous communication between peripherals, save CPU resources, and reduce power consumption.
The STM32G4 series is highly compatible with the STM32F3 series to ensure excellent efficiency in designing derivative applications at different performance levels. The STM32G4 series mixed-signal microcontrollers consist of STM32G4×1 basic-type series equipped with an entry-level analog peripheral general-purpose microcontroller, the STM32G4x3 enhanced series with a maximum number of analog peripheral general-purpose microcontrollers, and the STM32G4x4 high-resolution series with high-resolution timer, complex waveform builder and event handler (HRTIM) for digital power conversion applications such as power, lighting, welding, solar energy, and wireless charging in digital switch mode.
The package options for the STM32G4 series are LQPF32/48/64/80/100/128, UFBGA 64/100/121, WLCSP48/64/81, UQFN32/48, and are suitable for devices with a fast-flash memory size of 32-512 KB that can operate at temperatures of -40-85°C or -40-125°C.
Conclusion
With the widening application of motors in electronic products, how to improve the operating efficiency of motors and the operation time of battery-powered devices is becoming an important subject in product development. In addition to supporting DSP and FPU instructions, STM32G4 series mixed-signal MCUs, the brand-new series of microcontrollers developed by ST, integrate new mathematical arithmetic logic units and a large number of analog peripherals, making them suitable MCUs for motor control and an ideal choice for developing motor related applications.