Green motor control: Sustainable practices and energy-efficient motors

Electric motors are one of the world's biggest electricity consumers; according to the International Energy Agency (IEA), electric motor-driven systems are responsible for 53% of global electricity consumption. Suppose if we consider the distribution of environmental impacts in the lifecycle of e-motors; it is predicted that 1% to 5% of the effect comes from manufacturing them, 95% to 99% in their usage, and disposal or recycling. Since electric motors are essential components in industrial machinery, automobiles, HVAC systems, household appliances, and others, making them as sustainable as possible is essential. Thus, increasing motor efficiency while minimizing power consumption for a greener environment is necessary. Many industrial manufacturing practices also affect the green environment. This article explains energy-efficient motor designs, Variable Speed Drivers for altering the power consumption of motors depending on the workload, its configuration, and sustainable practices in industrial manufacturing for a green environment.

1. Energy-efficient motor designs

Manufacturers usually focus on minimizing rotor and stator losses for higher efficiency. The manufacturers have continuously tried to increase the motor's performance by altering their designs and using power-efficient materials like better lamination materials for assemblies and better electrical conductors, such as copper in cage rotors, instead of low-cost aluminum. However, such an arrangement alters the power consumption. Following are a few design constraints introduced in motors to reduce power consumption without affecting the performance for a green environment.

Copper rotor motors are standard induction motors. Figure 1 indicates the induction motor with the copper rotor. They have the same operating principle and structure but a different rotor material: the regular aluminum cage is substituted by a copper cage. Copper has lower resistance than aluminum, which reduces rotor losses. The motor slip is also reduced due to lower losses. This makes the nominal speed higher and, with it, the speed of the driven machine. Depending on the specific application, this may cause the driven machine to operate with higher efficiency.

Figure 1: Induction motor with copper rotor (Analog Devices)n

PM motors are classified as synchronous motors, implying there is no slip between the rotating fields of the rotor and stator as in three-phase induction motors. The types and designs of PM motors are shown in Figure 2. The permanent magnets offer the necessary rotor magnetization without any associated losses and increase motor efficiency. PM motors are distinctly more efficient than induction motors in reduced-speed operation and can operate with frequency converters without any problems.

Figure 2: Design of PM motorsn

A line-start PM motor is a hybrid combination of a three-phase induction motor and a PM motor. It has a cage rotor but with magnets buried underneath the cage. It has a significant advantage over standard PM motors: it can run directly from the mains without a controller. The cage winding is engaged in the starting phase. Once the motor accelerates to the speed determined by the mains frequency, it synchronizes and has the same high efficiency as a PM motor.

These motors utilize reluctance force, which results from changing the magnetic reluctance. New, specially designed rotor cutouts guide the magnetic field lines inside the rotor to produce reluctance torque with high energy efficiency.

There are many different types of EC motors in practice, such as small servo motors with power ratings of a few watts or motors in building automation systems. They have a reputation for being highly efficient, particularly for tiny drives, which are distinctly better than universal or split pole motors with approximately 30% more efficiency. EC motors built according to the original concept operate with a commutated DC voltage. This is why they are also called brushless DC motors (BLDC) or Electronically Commutated motors (ECM).

2. How do VSDs contribute to a green environment?

Traditional motors run at fixed speeds, resulting in constant energy consumption irrespective of the load requirements. However, VSDs allow motors to operate at varying speeds instead of running at full capacity continuously, depending on the workload, thus offering significant energy-saving potential. Along with speed control, VSDs provide a few distinct features, like a soft motor start and progressively ramp up the speed, avoiding the sudden energy spikes associated with motor starting methods. It manages the load, reduces energy consumption by avoiding peak demand, and controls motor acceleration during motor start. Due to inefficiencies in mechanical control mechanisms, dampers and throttle valves often result in energy losses. VSD, by electronically adjusting the speed of motors, minimizes energy wastage caused by throttling or mechanical losses. Thus, it reduces wear and tear on equipment and promotes its long lifespan.

Figure 3 provides signal chain solutions integrating superior precision feedback, current sensing, isolation, power management, and seamless connectivity to deliver deterministic motion solutions.

Figure 3: Signal chain solutions for advanced motion control using current and voltage feedback with variable speed drive(Source)

Current feedback is important for optimizing drive performance and determining motors' overall control bandwidth and response time. Using current sense amplifiers to improve the motor's performance ensures peak efficiency, low latency, and synchronized measurements. A better system also allows a faster response for low-voltage drives. For higher voltage systems, isolated sigma-delta ADC products offer low offset drift for reduced torque ripple. It also allows the use of low-value shunt resistors for improved system efficiency, accuracy, and reliability.

Data isolators deliver digital isolation technology for protocols ranging from SPI, I2 C, USB, and CAN to gigabit LVDS. Isolators protect people and assets from high voltage and disruptive electric interference, and robust isolated gate drivers protect power devices from faults and electromagnetic transients.

Figure 4: Circuit representing digital isolation using data isolators

As motor drives become decentralized and are placed closer to the motor, there is a need for efficient power management in smaller enclosures. Flyback converters enable isolated and high-density power solutions while multi-output buck regulators regulate the output voltages for powering digital loads (e.g., FPGA / processor). Power limiters offer voltage and current protection for enhanced drive reliability.

Transceivers are designed with added noise immunity and robustness for reliable operation in harsh industrial environments. As connectivity increases, a need for higher security at the device level arises. Secure authenticator technology is necessary for protecting production assets from malware attacks and untrusted commands. Transceivers optimized for full duplex communication include integrated surge protection.

The essential three requirements of functional safety

• The use of reliable components. This means ICs with a sufficiently low Failures In Time (FIT) rate. FIT rates are often calculated as per standards such as IEC 62380 in C-Type VSDs
• Implement a set of measures shown in the past to design products with high safety. This is referred to as systematic integrity in the standards.
• Be fault-tolerant and accept faults due to random hardware failures or systematic faults will occur no matter how reliable the components are or how good the development process followed. Faults can be managed with two strategies: diagnostics and redundancy.

In Figures 5a and 5b, safety subfunctions such as STO (safe torque off) and SLS (safely limited speed) are defined, and a functional safety life cycle is outlined.

Figure 5a: STO Safety Function

5b. Safely Limited Speed

With the STO safety subfunction, the motor can achieve a safe state if the motor is cut off from power and can thus not produce force. Typically, this is done using pulse blocking or power removal at the gate driver when a guard is open.

You can monitor the speed of the motor with the SLS safety subfunction, and the drive takes the motor to a safe state if the motor speed exceeds a set level. A typical use of this safety subfunction occurs when a roller is cleaned in conjunction with a three-position grip switch. Figure 2 shows SLS engaging at t1 and disengaging at t2. The red block indicates a speed region that (if entered) will cause the drive to go to a safe state.

3. Practices for Green Manufacturing in Industries- A step towards sustainability

Green manufacturing is an approach that aims to minimize the impact of industries on the environment in manufacturing processes and products. Apart from introducing new product designs for energy efficiency, its main target is to opt for renewable energy sources, reduced water consumption, and better waste management as integral parts of innovative production processes.

Increasing the performance of HVAC systems and reducing its waste in industries is a practical method to enhance energy efficiency and assure sustainability. They can be made more efficient using purely electric heat pumps that don't generate greenhouse gases. This quality is significantly better than that of traditional gas-powered heating systems producing emissions. Installing photovoltaic cells to power HVAC systems can also help utilize renewable energy sources. It is necessary to consider factors like application requirements, energy efficiency rating, and green features that would boost its performance.

Eco-friendly material options: Automotive manufacturers can reduce their carbon footprint and contribute to a more sustainable environment. This is possible by choosing materials like thermoplastics derived from natural sources like recycled plastics and polymers made from cornstarch and soybeans. They form alternatives to traditional petroleum-based materials, though their application space may be limited.

Prototyping: Prototyping and testing in additive manufacturing help designers and engineers create prototypes for error detection and design correction before production. Prototyping saves time, resources, and money, as the produced parts match the final prototype and are immediately usable.

Lean Manufacturing Principles: Adopting lean manufacturing methodologies helps streamline production processes, reduce inefficiencies, and minimize waste generation. This includes practices like Just-In-Time (JIT) inventory management and reducing excess inventory, which ultimately leads to resource conservation.

Predictive maintenance (PdM): Data analysis helps identify potential equipment defects and operational anomalies, enabling timely repairs before failures occur. Manufacturers can use PdM to be more sustainable by reducing carbon emissions, waste, and energy consumption. With the help of IoT and predictive maintenance, manufacturers can alter their production processes, reduce costs, and achieve their sustainability initiatives.

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Conclusion

Various approaches, like altering motor designs, using loss-less materials in the rotor, and integrating variable speed drivers, can be combined and optimized to reduce the motor's energy consumption. It is one of the most effective ways to promote sustainability. Additionally, it also saves on operating costs. Variable-frequency drive can control speed and torque based on application demand and minimize motor energy consumption by greater extent. The importance of speed drives in sustainability is energy savings, motor reliability, and longevity. Using motors with higher efficiency adds another new aspect to using frequency converters. Implementing eco-friendly manufacturing principles like lean manufacturing methodologies and predictive maintenance by reducing carbon emissions and low energy consumption can contribute to a greener environment.