Dylan Liu, Geehy Semiconductor
Nacho Facerías, Eurotronix
Industrial fans require high efficiency, fluid motion, and low noise. Advanced algorithms such as field-oriented control (FOC) can effectively achieve these goals, albeit at significant computational and economic cost. However, dedicated motor control microcontrollers with integrated FOC mitigate costs and computational issues, and some designs can also address other issues such as position sensing and fluid bidirectional starting.
In this article, we will examine industrial fan microcontrollers and FOC concepts, as well as discuss the challenges engineers face when implementing control of such motors. We will also explore how Geehy Semiconductors’ APM32F035 microcontroller addresses the specific challenges of industrial fans.
Industrial Fan Controllers
A fan controller regulates the speed of the fan motor, controlling the air movement produced. However, adjusting the fan speed has other benefits: it allows you to control the noise level and energy consumption.
Figure 1 shows a block diagram of a control system for a three-phase brushless interior permanent magnet (IPM) DC motor. In this example, space vector pulse width modulation (SVPWM) is used to modulate the three-phase voltage required by the motor.
It is worth noting that comparators, operational amplifiers and ADCs are integrated into this system, providing an all-in-one solution for the entire control system. This high degree of integration helps improve system performance and simplify implementation tasks for engineers.
Figure 1. Block diagram of the Motor Control System. Image courtesy of Geehy
A vital aspect of a motor controller is the control algorithm used. The type of algorithm can be based on the type of motor (e.g. trapezoidal or sinusoidal), whether position sensors are used, and what the speed and current control requirements are.
Critical issues for industrial fan performance
Over the years, many advances have been made in BLDC motor controllers, especially with the increase in data processing power and the use of dedicated MCUs. However, engineers still face challenges when it comes to industrial fan motor control, including efficient power usage, noise control, and optimal performance. FOC can mitigate these issues, but its typical implementation remains debatable as it requires additional components such as external sensors that increase cost and generate an extensive bill of materials (BOM).
Another issue for industrial fan performance is home position detection, which is essential as it affects initial start-up and running fan performance, along with the possibility of unintended direction changes. The conventional start-up sequence for standard motors comprises three distinct stages: positioning, acceleration and circuit closure. During the positioning phase, the possibility of such unintended direction changes may arise.
In addition, high-speed bi-directional starting remains a challenge: if there is strong wind, the fan may already be moving before activation. It must be determined whether the motor is already moving before activating fan operation. For example, a gradual deceleration must occur when the motor is about to reverse due to headwind. While solutions exist, they must provide the performance engineers are looking for.
Optimum fan performance with special MCU features
As we’ve discussed so far, improving the performance of industrial fans can be a challenging task. Implementing FOC and other features can be tricky for system designers. Fortunately, today’s advanced CPUs offer sophisticated technology that meets these needs. One example is Geehy’s APM32F035 MCU.
The chip is a dedicated 32-bit FOC motor control MCU and is based on the Arm Cortex-M0+ core running at 72 MHz. An M0CP coprocessor including a shift unit, 32-bit/32-bit divider, multiply and add operation, square root, trigonometric functions, and SVPWM further improves performance. The block diagram in Figure 2 summarizes several features of the APM32F035.
Figure 2. Block diagram of the Geehy APM32F035. Image courtesy of Geehy
This MCU also integrates a motor-specific PWM for complementary and brake modes linked with M0CP. Figure 3 shows the high-voltage evaluation board for motor control. A low-voltage evaluation board is also available.
Figure 3. High voltage motor control evaluation board for the APM32F035. Image courtesy of Geehy
FOC – Field-Oriented Integrated Control
The APM32F035 includes an integrated vector computer with dedicated math accelerators that comprehensively support computationally intensive FOC control algorithms. This integration eliminates the need for external sensors, improves efficiency, and provides efficient open-loop startup. It also reduces overall design costs, and reduces the bill of materials.
As microcontrollers have increased in capability, the motor control industry has begun to look to more complex, high-end control algorithms such as FOC. The motor control system presented in Figure 1 uses FOC, also known as vector control. Vector control is for three-phase AC electric motors, including two-phase stepper motors and brushless DC (BLDC) motors (the type used in Figure 1).
FOC aims to achieve maximum torque at a given speed, and achieves this by ensuring that the rotor field is 90 degrees behind the stator. To achieve this, the control system must:
- Measure motor currents.
- Measure rotor position (either using speed and position sensors or by inferring it indirectly)
- Transform the motor currents into a coordinate system that rotates with the rotor.
- Calculate the rotor flow angle.
- Control the currents in the stator windings to achieve 90 degree rotor lag.
FOC enables smooth acceleration and deceleration over the entire speed range and generates full torque upon start-up. It has proven to be ideal when high-precision control is required in high-performance motion applications, including industrial fans.
Home Position Detection
Conventional starting methods struggle to achieve effective home position sensing (IPD), but the APM32F035, with its innovative home position sensing feature, helps overcome this limitation. While saturated or variable inductance is typically the industry standard, the APM32F035 amplifies the current we see in the red box, injecting six pulses to achieve a precise and discernible signal, as illustrated in Figure 4.
Figure 4. IPD implementation with GEEHY. Image courtesy of Geehy
High speed bi-directional start
To deal with the motion problems due to strong wind, Geehy adopts the solution illustrated in Figure 5, which shows the motor phase current. The APMF32F035 uses forward/reverse wind detection logic to trigger the starting process by detecting the motor operation. The graph demonstrates the forward wind starting.
Figure 5. Illustration of the wind detection logic. Image courtesy of Geehy
Troubleshooting for industrial fan systems
The APM32F035 solves problems for various industrial fan applications. For powerful exhaust fans, it supports constant power control, perfect protection control, and an optimized starting algorithm. High-speed fans benefit from ultra-high-speed operation, field weakening control, and upwind/downwind starting. Industrial exhaust fans experience a 100% successful starting rate in both downwind and downwind conditions, along with perfect protection control.
The APM32F035 offers numerous advantages as a choice for industrial motor control applications. Other uses include large and small household appliances, electric bicycles, high-pressure water pumps and garden tools. It offers a motor control solution with integrated FOC, highly efficient algorithms and a powerful CPU.
