Advantages of Brushless DC (BLDC) Motors in Robotics and Automation
Brushless DC (BLDC) motors offer numerous advantages over brushed motors, making them a preferred choice in robotics and automation applications. While BLDC motors require a control system for precise speed and torque regulation, their benefits outweigh the additional complexity. The key advantages of BLDC motors include:
- Enhanced Efficiency: BLDC motors deliver higher energy efficiency, a crucial factor considering the significant global electricity consumption attributed to electric motors.
- Accurate Control: BLDC motors enable precise speed and torque control, allowing for optimized performance under varying load conditions. This level of control is essential in robotics and automation, where precise movements and responses are required.
- Improved Durability: Unlike brushed motors that experience performance degradation due to brush wear and arcing, BLDC motors maintain their performance over time. This longevity contributes to the overall reliability and lifespan of robotic systems.
- Low Noise Operation: BLDC motors operate quietly, minimizing noise generation in robotic applications. This characteristic is particularly important in environments that require reduced noise levels for improved user experience or to meet regulatory standards.
- Reduced Electromagnetic Interference (EMI): BLDC motors produce lower levels of electromagnetic interference, ensuring minimal disruption to other electronic components or communication systems within robotic systems.
- Compact and Lightweight Design: BLDC motors are designed to be compact and lightweight, making them suitable for applications with limited space or weight restrictions. This advantage facilitates the integration of BLDC motors in various robotic systems, from small-scale devices to large industrial automation setups.
With their superior efficiency, precise control, durability, low noise operation, reduced EMI, and compact design, BLDC motors have become indispensable in a wide range of applications. From computer hard drives to electric vehicles and from small-scale robotics to large industrial automation, BLDC motors continue to drive advancements in efficiency and performance across the robotics and automation industry.
One drawback of BLDC motors is the intricate control circuit and the subsequent rise in expenses. Precisely timed electrical signals are necessary for the electronic switching technique, necessitating driver circuits that can generate them.
Nevertheless, modern designers now have the advantage of extensive commercial availability of power devices specifically designed for BLDC motor drivers. These devices come in standalone form or integrated with a microcontroller (the controller), making the design process simpler and decreasing the overall cost of the solution.
The controllers
Apart from regulating speed and torque, plays a crucial role in initiating, halting, and reversing the motor’s rotation. It can acquire rotor position information through two methods: sensor-type control, where the controller directly receives this data, or sensorless control, where the controller deduces the position using appropriate algorithms implemented at the firmware or hardware level. The electrical signals applied to the power MOSFETs, in terms of amplitude and duration, are determined based on the rotor’s position.
Sensored BLDC motors are commonly employed in applications where starting the motor under load is required since the exact position of the motor is immediately known. There are several methods for determining the position:
- Hall-effect magnetic sensors: These sensors are highly resilient and can operate effectively even in harsh conditions, such as automotive applications.
- Rotary encoders: These devices convert mechanical motion into electrical impulses and provide crucial data such as position, speed, and direction. Depending on the technology employed, encoders can be optical, capacitive, or magnetic.
- Variable reluctance sensors: These sensors generate an electrical signal that corresponds to the displacement of a magnetically conductive or permeable object in relation to a coil.
The sensorless controller employs a technique of estimating the back electromotive force (EMF) generated in the stator windings by the rotating armature to detect the current position of the rotor. By measuring the back EMF, the controller can determine the rotor’s position, with higher back EMF indicating a closer magnet.
The design or selection of the controller is a critical task that requires meticulous accuracy. The primary functions performed by a motor controller are as follows:
- Speed and direction regulation: The controller regulates the motor’s speed and controls its direction of rotation.
- Torque regulation: By monitoring the applied load, the controller determines the appropriate torque value to achieve optimal motor performance.
- Management of start and stop phases: The controller gradually initiates and stops the motor, following precise acceleration and deceleration profiles.
- Protection against overvoltage or overcurrent: The controller safeguards the motor by detecting and responding to excessive voltage or current levels.
- Optimization of motor efficiency: The controller manages various engine parameters to maximize overall efficiency.
In the past, controllers were built using discrete components along with a microcontroller that executed the firmware with the control algorithms. However, the current trend favors highly integrated solutions that combine power and control functions into a single chip.
BLDC (Brushless DC) motors find extensive application
BLDC (Brushless DC) motors find extensive application in various industries and systems due to their advantageous construction characteristics. The benefits derived from electronic commutation, such as enhanced current management, increased torque, precise speed control, and overall motor performance improvement, contribute to their widespread use. Some of the notable applications of BLDC motors include:
- Industrial applications: BLDC motors are utilized in industrial machinery and equipment, such as pumps, compressors, conveyors, and machine tools, to provide efficient and reliable operation.
- Electric vehicles (EVs) and e-mobility: BLDC motors are an integral part of electric vehicles, including cars, motorcycles, scooters, and bicycles, due to their high efficiency, power density, and improved range.
- Unmanned aerial vehicles (UAVs) and drones: BLDC motors are commonly employed in UAVs and drones for their lightweight design, high efficiency, and precise control, enabling stable flight and maneuverability.
- Hard drives: BLDC motors are used in hard disk drives to achieve precise and reliable spindle motor control, ensuring accurate data read/write operations.
- Consumer electronics: BLDC motors are found in various consumer electronic devices such as fans, air conditioners, refrigerators, and washing machines, offering energy efficiency, quiet operation, and extended lifespan.
- Robotics and industrial automation: BLDC motors are extensively utilized in robotic systems and automation equipment for their precise motion control, high torque, and durability. They enable safer and more efficient processes, enhancing productivity in industries.
Industrial robotic arms, in particular, are revolutionizing manufacturing processes by improving worker safety, accelerating production, and boosting productivity. These versatile and programmable robotic arms are utilized in factories, warehouses, and even agricultural settings. BLDC motors play a vital role in robotic arms by providing accurate speed and torque regulation, alongside reliability, durability, and immunity to electromagnetic radiation.
In summary, the ability of BLDC motors to offer precise speed control, high torque, durability, and immunity to electromagnetic interference makes them well-suited for various applications, ranging from industrial machinery to electric vehicles and robotics.
Designing
Designing a BLDC controller requires expertise in both hardware and software aspects. While commercially available integrated solutions can fulfill the requirements of most applications, there are cases where a customized solution may be necessary.
Driver: To facilitate electronic commutation, power transistors capable of withstanding high voltages and currents are typically employed. Examples of such transistors include silicon (Si) MOSFETs, IGBTs, silicon carbide (SiC) MOSFETs, and gallium nitride (GaN) HEMTs.
The conventional approach for a BLDC controller involves a half-bridge topology. This topology utilizes two switches, with one Transistor on the high side and one on the low side, as opposed to a full H-bridge solution. Since Three-Phase BLDC motors are commonly used in robotics and industrial automation applications due to their superior performance and efficiency compared to single- or dual-phase variants, a typical controller scheme consists of three half-bridges. Figure 3 illustrates the diagram of a Three-Phase driver employing a highly integrated gate driver.
The control of a three-phase BLDC motor involves six steps, which make up a complete commutation cycle, to energize all three stator windings. This is achieved by sequentially switching the high-side and low-side transistors on and off.
The high-side switches are commonly controlled using the pulse-width modulation (PWM) technique. PWM converts the DC input voltage into a modulated drive voltage, allowing for more efficient management, particularly during motor startup, and enabling precise control of speed and torque.
The selection of the PWM frequency is a critical consideration. Designers often aim for a balance between switching losses, which are more pronounced at high frequencies, and ripple currents, which are mainly generated at low frequencies. The use of GaN (gallium nitride) devices can significantly reduce switching losses, even at high frequencies.
By carefully optimizing the PWM frequency and taking advantage of GaN technology, designers can achieve improved efficiency and performance in controlling the three-phase BLDC motor.