Inverters are advanced energy-saving devices that have gained popularity in recent years. They combine power electronics with computer technology, offering high-speed regulation, ease of use, and energy efficiency—especially when the output frequency is below 50Hz. These systems are widely used across industries such as machinery, chemical, metallurgy, and light manufacturing. Depending on application requirements, there are various methods for setting the inverter's frequency. This text will take the Mitsubishi FR-500 series inverter as an example to explain different frequency-setting techniques.
There are two main approaches to frequency setting: one using the inverter’s built-in control panel, and the other utilizing the control terminals. The first method involves adjusting the frequency directly through the operation panel. This is a simple process where users can press up and down buttons to change the frequency. It doesn’t require external wiring, offers high precision, and is ideal for single-unit applications. However, it is limited to local control and lacks flexibility for remote operations.
The second approach uses the inverter’s control terminals for frequency adjustment. This includes two common methods: using an external potentiometer or leveraging the inverter’s internal functions to simulate a potentiometer. For instance, the FR-500 series provides a 10V DC supply at terminal 10, an input terminal at 2, and a common terminal at 5. By connecting an external potentiometer between these points, the voltage applied to terminal 2 can be adjusted, allowing for precise frequency control. This method is straightforward, easy to operate, and allows for flexible placement of the potentiometer.
However, this method also has some drawbacks. First, temperature changes can affect the resistance of the potentiometer, causing drift in the frequency setting. Second, electromagnetic interference may induce unwanted voltages in the connecting cables, leading to instability in the frequency output. Third, if the potentiometer is placed too far from the inverter, voltage drop in the cable may prevent the full 10V from reaching the inverter, limiting the maximum frequency. As a result, this method is best suited for environments with low interference, stable temperatures, and less demanding speed control needs.
The second method, which uses the inverter’s internal settings to simulate a potentiometer via control terminals like RH and RM, offers several advantages over the external potentiometer approach. With this method, you can adjust the frequency by simply toggling switches connected to the inverter’s terminals. This results in higher accuracy—up to ±0.01% of the maximum frequency—and better resistance to external interference. Additionally, since no analog components are involved, there is no temperature drift, and installation becomes more flexible. You can even synchronize multiple inverters to adjust their frequencies simultaneously.
Ultimately, the choice of frequency-setting method depends on specific application needs. Whether you need high precision, remote control, or robust performance in harsh environments, selecting the right technique ensures optimal system performance and reliability. Understanding these options helps engineers and technicians make informed decisions for efficient and effective inverter operation.
The auxiliary Transformer for SPS (Switched Power Supply) is a device that converts high voltage AC power from the main transformer into low voltage AC power that is used to power the control circuits and other auxiliary devices in the SPS.
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