Company Profile
Shenzhen Sifang Electric Technology Co., Ltd. is a private high-tech enterprise in Shenzhen, recognized as a national high-tech enterprise and a software enterprise by the Shenzhen Science and Technology Bureau. Founded in 2004, the company specializes in the development, production, sales, and service of industrial automation products. Its main products include servo drives, frequency converters , permanent magnet synchronous motors , PLCs, and HMIs.
Sifang Electric's corporate vision is to become a "leading provider of automation products and solutions." To ensure the leading and innovative nature of its professional technologies, the company continuously improves its core competitiveness through sustained investment and optimized R&D layout. Relying on its proprietary technologies, the company closely collaborates with customers, continuously providing them with satisfactory products and solutions, as well as proactive value-added services, thus promoting industrial development and upgrading. Currently, the company's products are widely used in machine tools, plastics, lifting, construction, textiles, wire and cable, air compressors, water supply, HVAC, food, printing and packaging, and many other fields. Based in the field of industrial automation, Sifang Electric is committed to creating a respected and highly innovative industry-renowned brand.
Compared to asynchronous motors, synchronous motors have advantages such as high power factor, high efficiency, measurable rotor parameters, large air gap between stator and rotor, good control performance, small size, light weight, simple structure, and high torque-to-inertia ratio. They are increasingly widely used in petroleum, chemical, textile, mining, vehicle, CNC machine tool, robot, and aerospace industries, and are developing towards higher power (high speed, high torque), higher functionality, and miniaturization.
A permanent magnet synchronous motor consists of a stator and a rotor. The stator is similar to that of an asynchronous motor, consisting of three-phase windings and a stator core. The rotor is equipped with pre-magnetized permanent magnets, which can establish a magnetic field in the surrounding space without external energy input. This simplifies the motor structure and saves energy. This article starts with the characteristics of permanent magnet synchronous motors and, combined with practical applications, illustrates the comprehensive benefits of promoting permanent magnet synchronous motors.
1. Key advantages of permanent magnet synchronous motors
(1) Because the rotor is made of permanent magnets, the magnetic flux density is high, no excitation current is required, and excitation loss is eliminated. Compared with asynchronous motors, the excitation current of the stator winding and the copper and iron losses of the rotor are reduced, and the reactive current is greatly reduced. Since the stator and rotor magnetomotive forces are synchronized, the rotor core has no fundamental iron loss. Therefore, the efficiency (related to active power) and power factor (related to reactive power) are higher than those of asynchronous motors. Permanent magnet synchronous motors are generally designed to have high power factor and efficiency even when running under light load. Figure 1 shows the comparison curves of efficiency and power factor of a certain permanent magnet synchronous motor and an asynchronous motor of the same specification. From the perspective of motor load changes, rare earth permanent magnet synchronous motors can maintain high power factor and high efficiency in the range of 25% to 120% of rated power, while general three-phase asynchronous motors can usually only maintain a high performance operation in the range of 60% to 100% of rated power.
Figure 1 Comparison of efficiency and power factor of two types of motors
(2) The speed and frequency of a permanent magnet synchronous motor maintain a strictly constant fixed relationship. Unlike asynchronous motors, which have a large slip rate when operating under load, permanent magnet synchronous motors have a stiffer mechanical characteristic and a stronger ability to withstand torque disturbances caused by load changes. The rotor core of a permanent magnet synchronous motor can be made into a hollow structure to reduce rotor inertia. Moreover, the start-up and braking times of permanent magnet synchronous motors are much faster than those of asynchronous motors. The high torque/inertia ratio makes permanent magnet synchronous motors more suitable for operation under fast response conditions than asynchronous motors.
(3) The size of a permanent magnet synchronous motor is much smaller and its weight is also greatly reduced compared to an asynchronous motor. Under the same heat dissipation conditions and insulation materials, a permanent magnet synchronous motor has more than twice the power density of a three-phase asynchronous motor. In large cities where land is extremely valuable, users are increasingly aware of the impact of equipment footprint on cost.
(4) The rotor structure is greatly simplified, making maintenance easier and improving operational stability. In AC permanent magnet servo motors, the magnets on the rotor are typically bonded to the iron core using high-temperature adhesive. The adhesive curing time is generally long, increasing production cycle and cost. Furthermore, during motor operation, the magnets are subject to repeated temperature changes and impacts, posing a risk of deformation or even detachment. To solve this technical problem, our company's CM500 series heavy-duty permanent magnet synchronous motor replaces the adhesive bonding process with a mechanical fastening method using stainless steel sleeves, as shown in Figure 2, completely eliminating the risk of magnet detachment. This innovative application technology has been patented and represents a significant advancement in motor rotor technology.
Three-phase asynchronous motors require a very small air gap between the stator and rotor to achieve a high power factor. The uniformity of this air gap is also crucial for safe operation and noise reduction. Therefore, asynchronous motors have relatively strict requirements for the dimensional tolerances and concentricity of components, and less freedom in selecting bearing clearance. Larger-frame asynchronous motors typically use oil-lubricated bearings, requiring regular lubrication within specified operating intervals. Oil leakage or delayed lubrication accelerates bearing failure, making bearing maintenance a significant part of three-phase asynchronous motor repair. Furthermore, the presence of induced current in the rotor of three-phase asynchronous motors has led to increased research attention on bearing electro-corrosion in recent years. Permanent magnet synchronous motors (PMSMs) do not have this problem. Due to their larger air gap, the issues caused by the smaller air gap in asynchronous motors are less pronounced in PMSMs. Additionally, PMSM bearings are grease-lubricated bearings with dust covers, and are pre-lubricated with a suitable amount of high-quality grease at the factory, requiring no maintenance for their entire lifespan.
2 Typical Applications of Permanent Magnet Synchronous Motors
2.1 Application Solution of Electro-hydraulic Servo Injection Molding Machine
Traditional injection molding machines use three-phase asynchronous motors to drive quantitative pumps, requiring the motors to run continuously for extended periods during operation. Through energy-saving modifications to the servo oil pump drive system, the rapid response and high starting torque of the permanent magnet synchronous motor allow the pump to generate pressure only when the injection molding process is complete. During material feeding and mold closing, the main oil pump motor remains off, achieving intermittent zero power consumption. Comparative studies show energy savings of up to 85%.
Thanks to superior servo motor algorithm control, the noise level is significantly lower than that of ordinary injection molding machines. Under ideal conditions with a low-noise screw pump, the overall noise level of the injection molding machine is below 70 decibels, achieving quiet operation and improving the working environment.
2.2 Energy-saving applications in iron ore dry separators
The equipment was used at a mining site in Northwest China, a dusty environment. It uses 125 electric motors. The winch requires a large starting torque, but during normal operation, the motors run at 30%–50% of their rated power under light load. The original three-phase asynchronous motors had an efficiency of only about 65% and a power factor of about 0.4–0.6, resulting in significant energy waste. The replacement with permanent magnet synchronous motors resulted in a very significant energy saving. Energy-saving test statistics are shown in Table 1. Figure 4 shows on-site photos before and after the replacement.
Table 1. Comparison of energy-saving parameters between 1125 permanent magnet synchronous motors and high-efficiency three-phase asynchronous motors.
3. Several questions that users are most concerned about
3.1 Motor lifespan
The CM500 series motors utilize robust and durable rotary transformers or absolute magnetic encoders as angle measurement devices, meeting the high-precision control requirements of motors while offering higher reliability than optical encoders. For applications with slightly lower control precision and no overload requirements, sensorless vector control can be employed, saving on the cost of angle measurement devices. The overall lifespan of the motor depends on the bearing lifespan. The motor housing has an IP54 protection rating, which can be increased to IP65 in special environments, meeting the requirements of most dusty and humid environments. With good coaxiality of the motor shaft extension and appropriate radial load on the shaft, the minimum bearing lifespan is over 20,000 hours. Secondly, the cooling fan's lifespan is also significant. The fan uses a single-phase 220V shaded-pole motor, which has a longer lifespan than capacitor-run motors. During long-term operation in dusty and humid environments, it is necessary to regularly remove sticky substances adhering to the fan to prevent it from burning out due to overload.
3.2 Failure and Protection of Permanent Magnet Materials
The development of permanent magnet motors is closely related to the development of permanent magnet materials. Since the beginning of the 21st century, with the continuous improvement and perfection of the performance of permanent magnet materials, excellent magnetic materials with high remanence, high coercivity, high energy product and linear demagnetization curve are particularly suitable for manufacturing motors. In particular, the improvement of the thermal stability and corrosion resistance of neodymium iron boron permanent magnets and the gradual reduction in price have enabled the research and application of permanent magnet motors to develop rapidly.
The importance of permanent magnet materials to permanent magnet motors is self-evident, accounting for nearly a quarter of the total material cost of the motor. Our company has specifically formulated enterprise standards for permanent magnet materials, focusing on corrosion resistance, consistency, high-temperature demagnetization testing, and linear demagnetization curve testing. Current permanent magnet materials can operate for extended periods within the allowable temperature rise limits of motor windings, with a demagnetization rate of less than 2%. Conventional permanent magnet materials require the surface coating to withstand salt spray testing for more than 24 hours. For environments with severe oxidation and corrosion, users should contact the manufacturer to select permanent magnet materials with higher protection technologies.
3.3 Coil burnt out
Traditional asynchronous motors have a coil burnout failure rate exceeding 8%, primarily due to issues with thermal protection and the quality of electrical materials. Traditional asynchronous motors often lack thermal protection components, and manufacturers prioritizing production volume often compromise on insulation, resulting in even weaker insulation after repairs. Our CM500 series permanent magnet synchronous motors, however, incorporate thermally sensitive elements within the coils. When the coil temperature rises to the F-class insulation limit of 105K, the driver uses the temperature signal collected by the thermally sensitive element to implement overheat protection, ensuring safe operation. Furthermore, the motor stator undergoes a double vacuum impregnation process, significantly improving the stator qualification rate.
4 Conclusion
From an economic perspective, permanent magnet synchronous motors are particularly suitable for applications requiring heavy starting and light operation. Promoting their use yields significant economic and social benefits and is crucial for energy conservation and emission reduction. Furthermore, permanent magnet synchronous motors offer valuable advantages in reliability and stability. Therefore, selecting a high-efficiency permanent magnet synchronous motor is a one-time investment with long-term benefits.
