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Optimum performance of industrial fans with advanced Microcontroller features

Dylan Liu, Geehy Semiconductor
Nacho Facerías, Eurotronix 

Industrial fans require high efficiency, fluid movement and low noise. Advanced algorithms such as field-oriented control (FOC) can effectively achieve these goals, albeit at significant computational and economic cost. However, microcontrollers dedicated to motor control with integrated FOC mitigate costs and calculation issues, and some designs can also address other issues, such as position sensing and smooth bidirectional starting.

In this article, we will examine industrial fan microcontrollers and FOC concepts, as well as discuss the problems engineers face when implementing control of these types of motors. We'll also explore how Geehy Semiconductor's 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 advantages: it allows you to control the noise level and power consumption.

Figure 1 shows a block diagram of a control system for a three-phase brushless internal 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.

Notably, comparators, op-amps 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 Engine Control System.

A vital aspect of a motor controller is the control algorithm used, which can be based on the type of motor (e.g. trapezoidal or sine), whether position sensors are used, and what the speed and current control requirements are.

Critical Performance Issues for Industrial Fans

Over the years, many advances have been made in controllers for BLDC motors, especially with the increase in data processing power and the use of dedicated MCUs. However, engineers still face challenges when it comes to controlling industrial fan motors, including efficient energy use, 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 problem for the performance of industrial fans is the detection of the initial position, which is essential as it affects the initial start-up and running performance of the fan, along with the possibility of unwanted direction changes. The conventional starting sequence for standard motors encompasses three distinct stages: positioning, acceleration, and circuit closure. During the positioning phase, the possibility of such unwanted reversals may arise.

Additionally, high-speed bidirectional start-up remains a challenge: if there is strong wind, the fan may already be moving before activation. It must be determined if the motor is already moving before activating the fan operation. For example, gradual deceleration should occur when the engine is about to reverse due to headwind. While solutions exist, they must provide the performance engineers are looking for.

Optimal fan performance with special MCU features

As we have discussed so far, improving the performance of industrial fans can be a challenging task. Implementing FOC and other features can be complicated for system designers. Fortunately, today's advanced CPUs offer sophisticated technology that meets these needs. An example is the Geehy APM32F035 MCU.

The chip is an MCU dedicated to 32-bit FOC motor control and is based on the Arm Cortex-M0+ core running at 72 MHz. An M0CP coprocessor that includes a shift unit, 32-bit/32-bit divider, multiplication and addition, 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.

This MCU also integrates a motor-specific PWM for complementary and brake modes linked to M0CP. Figure 3 shows the high voltage evaluation board for motor control. Low voltage evaluation board is also available.

Figure 3. High voltage motor control evaluation board for the APM32F035.

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 effective open-loop starting. 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 at 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 lagged 90 degrees relative to the stator. To achieve this, the control system must:

• Measure the 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 throughout the speed range and generates full torque at start-up. It has proven to be ideal when high-precision control is needed in high-performance motion applications, including industrial fans.

Initial Position Detection

Conventional starting methods struggle to achieve Home Position Detection (IPD) effectively, but the APM32F035, with its innovative Home Position Detection function, 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. Implementation of the IPD with GEEHY.

High speed bi-directional start

To deal with motion problems due to strong wind, Geehy adopts the solution illustrated in Figure 5, which shows the phase current of the motor. The APMF32F035 uses forward/reverse wind detection logic to activate the starting process by detecting engine operation. The graph shows the start of the forward wind.

Figure 5. Illustration of the wind detection logic.

Conclusion: Troubleshooting for Industrial Fan Systems

The APM32F035 solves problems for various industrial fan applications. For powerful gas extractors, it supports constant power control, perfect protection control and optimized starting algorithm. High-speed fans benefit from ultra-high-speed operation, field weakening control, and upwind/downwind start. Industrial exhaust fans experience a 100% startup and success rate both upwind and downwind, along with perfect shielding control.

The APM32F035 has numerous advantages as an option for industrial motor control applications. Other uses include large and small appliances, electric bicycles, high-pressure water pumps and gardening tools. It offers a motor control solution with integrated FOC, highly efficient algorithms and a powerful CPU.