How to make innovative MCUs achieve energy efficient motor control
The contribution of electric motors to energy consumption is close to 50% in the United States, so reducing motor energy consumption can effectively improve energy efficiency, and using advanced microcontroller (MCU) technology to achieve motor control is an effective method. This paper introduces the latest developments in motor control MCU technology and its applications.
One of the main targets for reducing energy consumption is the motor, which consumes about 50% of the total US energy consumption. More than 50 motors can be found in the home, usually 70 to 80. In the industrial field, the automatic control of the factory is also widely used.
Today, recent developments in MCU technology allow motors to operate more efficiently at lower cost. In some markets, this accelerates the transition from electromechanical to electronic control, enabling variable speed motor control to optimize motor efficiency and reduce the cost of all applications at the device level.
Low cost brushless DC motor control MCU
Compared to brushed motors that are often used in motor control, MCU-controlled brushless DC (BLDC) motors eliminate brush wear and arcing mechanisms, so the life of the motor is essentially limited by the life of the bearing. In addition, the advantages of MCU-based BLDC motor systems include high efficiency, high torque-inertia ratio, higher speed performance, low noise, better thermal efficiency, and lower EMI characteristics.
The use of 8-bit MCUs specifically designed for mass production of motor control is a very low cost method for solving digital motor control problems. With up to 10 MIPS of performance and motion control-specific hardware (including center-aligned 14-bit PWM, a motion feedback module, and a high-speed ADC), applications that previously required expensive processors can now be addressed with low-cost 8-bit MCUs.
The 8-bit microcontroller drives a three-phase ACIM variable frequency drive.
Three-phase PWM control in some MCUs, such as the PIC18F4431, can provide all three of the BLDC controls in hardware, minimizing the software that must be developed and debugged. Up to 8 available PWM channels, usually only need 6 to drive a three-phase motor. Therefore, the remaining two channels can be used for other functions without the need for additional components. The motion feedback module with integral encoder interface as the main part of the MCU reduces the number of components and system cost.
An MCU with an ADC with a sampling rate of 200K per second provides the speed necessary for closed loop control. Simultaneous use of two different channels makes it possible to simultaneously sample voltage and current. Such a fast transition is required when measuring the back end electromotive force (EMF) in closed loop motor control, and the ability to synchronize the ADC with the PWM on the rising or falling edge minimizes switching noise. Together, these modules eliminate the need for external motor control components such as high speed ADCs and position encoders.
In many motor control applications, fail-safe operation is very important. An MCU with a fail-safe clock monitor (an internal RC oscillator that can be used as a backup clock in the event of a crystal failure) allows designers to use digital control that provides high reliability. Programmable deadtime delays on the PWM minimize switching noise, reduce development time by weeks, and meet critical program deadlines to bring new products to market. In all cases, MCUs with reliable flash memory offer the potential for rapid time-to-market and flexibility to adjust to changes in demand before installation or during use.
