Abstract : Low-voltage frequency converters are widely used in industrial production, and their energy-saving effect is well-known. However, very few users have adopted high-voltage frequency converters. But with the advancement of science and technology, the number of manufacturers producing high-voltage frequency converters in China is increasing, and more and more people are paying attention to, developing, and using them. Domestically produced high-voltage frequency converters will eventually gain user recognition due to their high efficiency and energy saving. Keywords : High-voltage high-power frequency converter; Energy saving; Speed ​​regulation principle 1 Overview Circulating fluidized bed boilers have attracted a large number of customers due to their low requirements for coal quality, energy saving, and environmental protection. After more than ten years of rapid development, small and medium-sized circulating fluidized bed technology has matured in China and is experiencing further development. To maximize its economic and social benefits, many manufacturers have equipped their auxiliary facilities, such as induced draft fans, primary air fans, and secondary air fans, with high-voltage high-power frequency converters, further improving the output efficiency of the entire boiler system. Currently, frequency conversion speed regulation is a globally recognized ideal energy-saving speed regulation technology. There are many users of low-voltage frequency converters, but very few users of high-voltage frequency converters. Previously, this was the biggest obstacle to the widespread application of high-voltage frequency converters. Traditional high-voltage frequency converters suffer from significant harmonic pollution. Harmonics not only waste reactive power, increase line losses, and affect the reliable operation of relay protection, but also generate additional torque and losses in motors, interfere with weak current systems, and cause severe voltage distortion in the power grid, potentially leading to power system safety accidents. Therefore, green high-voltage frequency converters have emerged. Many domestic high-voltage frequency converter manufacturers have overcome the aforementioned challenges and gradually solved the harmonic problem of high-voltage frequency converters. We conducted a survey on the high-voltage, high-power frequency converters used in the three fans of a 75t circulating fluidized bed boiler at the TEDA No. 5 heat source plant. Experiments showed an average power saving of 263.33kW per hour, equivalent to RMB 75,840 per month. These impressive figures demonstrate the bright future of domestically produced high-voltage frequency converters, which will gain the same recognition from enterprise users as low-voltage frequency converters. 2. Variable Frequency Drive (VFD) Control in Fluidized Bed Boilers We investigated only the circulating fluidized bed boiler at the TEDA No. 5 heat source plant. All three fans on the No. 1 boiler are equipped with VFDs manufactured by Chengdu Dongfang Kaiqi Co., Ltd.: the induced draft fan is 10kV, 560kW, using a DFCVERT-MV-710/10B VFD; the primary air fan is 10kV, 315kW, using a DFCVERT-MV-450/10B VFD; and the secondary air fan is 10kV, 250kW, using a DFCVERT-MV-355/10B VFD. 2.1 VFD Speed ​​Control Principle Variable frequency speed control aims to achieve smooth changes in motor voltage and frequency. A high-voltage, high-power VFD consists of multiple power units connected in series (as shown in Figure 1). Each power unit is powered by the secondary isolation coil of an isolation phase-shifting transformer, and the unit outputs a PWM waveform. The secondary coils supplying power to the power unit have a phase difference, achieving multi-stage series rectification to eliminate harmonic interference to the power grid. This avoids harmonic pollution of the system caused by harmonics generated during inverter operation, reducing motor heating, noise, torque pulsation, and excessive common-mode voltage caused by harmonics. It also enables satisfactory sinusoidal voltage and current across various speed ranges. [b][align=center]For more details, please click: A Look at Domestic High-Voltage Inverters Through Application in Circulating Fluidized Beds[/align][/b]