A high-voltage frequency converter consists of several parts.
The main circuit primarily consists of components such as a three-phase or single-phase rectifier bridge, smoothing capacitors, filter capacitors, an IPM inverter bridge, current-limiting resistors, and contactors. Many common faults are caused by electrolytic capacitors. The lifespan of an electrolytic capacitor is mainly determined by the DC voltage applied across its terminals and its internal temperature. Since the capacitor model is selected during circuit design, the internal temperature plays a decisive role in its lifespan. Electrolytic capacitors directly affect the lifespan of the frequency converter; generally, for every 10°C increase in temperature, the lifespan is halved. Therefore, on the one hand, appropriate ambient temperature should be considered during installation; on the other hand, measures can be taken to reduce pulsating current. Using AC or DC reactors that improve the power factor can reduce pulsating current, thereby extending the lifespan of electrolytic capacitors.
When maintaining capacitors, the electrolytic capacitor's deterioration is usually judged by its relatively easy-to-measure capacitance. When the capacitance is lower than 80% of the rated value and the insulation resistance is below 5 MΩ, the electrolytic capacitor should be replaced.
Working principle of high voltage frequency converter
According to the basic principles of electrical machinery, the speed of a motor satisfies the following relationship: n = (1 - s) / 60f / p = n₀ × (1 - s) (p: number of pole pairs; f: motor operating frequency; s: slip). From this formula, we can see that the synchronous speed n₀ is proportional to the motor's operating frequency (n₀ = 60fp). Since the slip s is generally small (0-0.05), the actual speed n of the motor is approximately equal to the synchronous speed n₀. Therefore, adjusting the power supply frequency f of the motor can change the actual speed of the motor. The slip s of the motor is related to the load; the larger the load, the greater the slip. Therefore, the actual speed of the motor will decrease slightly as the load increases.
Single-phase or three-phase AC power is first converted into DC power by a rectifier circuit. The rectified DC power is then applied to a high-frequency switching circuit. The switching time of the switching circuit is controlled by a control circuit. As the switching circuit changes, AC power with a variable frequency is generated at the output terminal.
