Variable frequency drive technology has been used to control many mechanical tasks and automated robots, covering applications ranging from manufacturing and processing plants to warehouses and other logistics facilities.
Whether in material handling, machining, or pump and fan applications, frequency converters (FDs) are an economical choice that helps businesses optimize performance, reduce energy consumption, and permanently lower the lifecycle costs of machines and robots. FDs can be used in basic voltage modes, as well as for 230V, 480V, or 600V motors operating on three-phase power supplies. The selection of a frequency converter depends on the motor type, voltage, rated current, power supply, and input/output (I/O) requirements. Its size depends on a range of application-related factors, including the motor's full-load rated power and maximum voltage at full load.
In the most basic applications of frequency converters, operators can match the motor speed to the load requirements by adjusting the frequency and voltage of the power supply connected to the motor. For specific applications, this allows the motor to operate at its most efficient speed while reducing energy consumption.
Variable frequency drives (VFDs) offer a wealth of achievable efficiency potential for innovative OEMs and end-users. Newer approaches to VFD drive technology help address the challenges of specific motion control applications, making them more economical and profitable. Below are six real-world scenarios demonstrating how VFD solutions can handle advanced motion control applications.
1. Conveyor belt with varying load
Whether in airports or factories, conveyor belts carrying variable loads have always been a long-standing challenge and a significant limitation in terms of power consumption. An idle conveyor belt does not require full power, but it needs to respond after a certain period, when a load is applied, or after receiving instructions to adjust the motor.
Conveyors carrying variable loads can utilize frequency converters, which significantly reduces power consumption (see Figure 1). The frequency converter senses lighter loads and then adjusts the motor's power factor to make it operate more efficiently, even during low-load cycles. This mode minimizes power consumption when full load is not required, and allows the motor to increase power and operate at optimal performance when a larger load is applied.
Figure 1: Conveyors transporting variable loads can be operated using frequency converters, significantly reducing power consumption. Frequency converters sense lighter loads and then adjust the motor's power factor to make it operate more efficiently, even during low-load cycles. Image source: Lenze
For large factories or automated systems with a wide footprint, decentralized frequency converters eliminate the time and cost (including materials and labor) of laying cables to control cabinets. Furthermore, it is simpler and more cost-effective to connect power from a power bus located as close as possible to the motors.
2. Simplify the internal equipment combination
Variable frequency drives (VFDs) help optimize some systems using simpler solutions. Compared to VFDs with automatic speed control, newer VFDs with multiple fixed speed options can significantly reduce the number of different geared motor combinations used in internal logistics applications by changing the speed of the motor.
In a large warehouse, all conveyor belts are connected within a large network, requiring different locations to operate at different speeds. This means installing numerous gearboxes in different parts of the system, each with a unique power input-output ratio to ensure that each section of the conveyor belt operates at the correct speed. However, the result is the need to use many different gearbox input-output ratios to support the same power requirements.
Unlike deploying 20 gearboxes of varying sizes, the new solution requires only a combination of 4 to 5 inverters/motors/gearboxes. By adjusting the frequency to control the speed, operators can optimize each combination without relying on a single speed motor connector bridging the line.
3. Operating induction motors at higher frequencies
Conventional induction motors are designed to operate on a 60Hz power supply, but this is not necessarily the optimal design for the application. Using frequency converters, OEMs can design motors that can operate as low as 20Hz for applications such as wind power, or as high as 100 to 600Hz for applications with much higher power density.
Because power can be calculated by multiplying speed by torque, OEMs can design smaller motors that have the same power output as traditional induction motors. Generally, these higher-frequency motors are half the size of motors operating at 50/60Hz, but offer the same power. Furthermore, due to the reduced inertia, induction motors using frequency converters are capable of providing more dynamic system functionality.
4. Running the induction motor in servo mode
Servo control requires high-precision speed and position, demanding accuracy. Therefore, permanent magnet motors are the preferred choice for performing servo functions. However, because they rely on rare metals, they are relatively expensive.
If the feedback is satisfactory, an induction motor controlled by a frequency converter can also operate in servo mode. Compared to traditional permanent magnet servo motors, frequency converters offer a more cost-effective alternative. Although frequency converters are primarily used for open-loop speed control and are generally not considered to achieve particularly high precision, this technology is sufficient to control the rotor position of motors in many servo applications.
If the power density isn't ideal, the motor will need to be slightly larger, so careful consideration of system requirements, motor size, and functionality is essential. For example, a variable frequency drive (VFD) induction servo motor won't accelerate as quickly as a permanent magnet motor; however, you need to consider whether your application truly requires this functionality. While the solution may have slightly lower dynamism, the significant cost savings can provide a substantial competitive advantage for businesses in the market.
5. Running a permanent magnet motor without feedback
For general applications, permanent magnet motors are the most efficient type of motor, but they require feedback information to track electrode positions and perform proper motor rectification.
Currently, inverter technology can operate permanent magnet motors without feedback and achieve a position accuracy within 5 degrees. With an inverter, when the motor is at a stop position, the position of the electrodes is calculated, and then the motor can be rectified for better control.
Position control applications requiring no feedback eliminate the need for cables and more expensive servo inverters, replacing them with more economical and efficient inverters. Using inverter technology to power permanent magnet motors also means that if reducing power consumption is more critical for certain applications, these applications can operate in speed mode.
6. Reduce the floor space of the control panel and the length of the cables.
One of the simplest and most easily overlooked advantages of using frequency converters is their space-saving effect. Integrating the motor and drive together reduces the footprint of control panels and the length of motor cables in the factory. For applications where the motor has a large footprint, or where one set of moving parts shares a power supply track with other moving parts in a system, integrating the frequency converter drive with the motor offers even greater benefits (see Figure 2).
Figure 2: For applications where the motor occupies a large area, or where a set of moving parts and other moving parts in a system share a set of power supply rails, it makes sense to integrate the frequency converter with the motor.
Instead of laying all the cables from the equipment to the central control cabinet, system engineers could implement a distributed system that relies on independently driven motors, which only require control cables to be laid from the main control cabinet to the various components on the machine side.
