Abstract: This paper describes a two-level power unit composed of IGCT power devices, combined with a phase-shifting frequency converter, to realize a high-voltage frequency converter of 10000kW and above, and its test method. Keywords: IGCT, high-power frequency converter, test method. Currently, high-voltage high-power frequency converters are a very important application field. However, the maximum power level of frequency converters based on IGBTs is mostly around 5000kW, and it is difficult to realize high-voltage frequency converters of 10000kW and above using IGBTs. At present, international companies such as ABB have launched three-level frequency converters based on IGCTs. However, under the conditions of high-voltage high-power applications, the reliability of three-level technology still needs to be improved in China. In addition, the performance test of high-voltage high-power frequency converters is also a challenge. This paper mainly introduces a high-power frequency converter composed of IGCTs and its test method, for reference only. 1. Construction Principle 1.1 6KV Frequency Converter Figure 1 shows the construction principle diagram of a 6KV frequency converter. The specific working process is as follows: Taking a 6kV frequency converter as an example, as shown in Figure 1, the grid voltage is reduced to 1750V by a phase-shifting transformer, rectified by rectifier bridge D, and then enters a buffer circuit composed of capacitors Cc and Cd, inductor Lc, resistor Rc, and diode Ds. Then, the electrical signal is input to a two-level power unit composed of an IGCT inverter bridge. Each phase consists of two IGCT power units connected in series to form an AC voltage, which is then output to the motor at high voltage. Each two-level power unit consists of a rectifier bridge, a voltage regulator circuit, and an IGCT inverter bridge. The voltage regulator circuit is connected to the input terminal of the IGCT inverter bridge. Resistor Rc and diode Ds are connected in series, and their two ends are connected in parallel with inductor Lc. A capacitor Cc is connected between resistor Rc and diode Ds, and the other end of capacitor Cc is connected to capacitor Cd. The other end of capacitor Cd is connected to the input terminal of inductor Lc and resistor Rc. The IGCT inverter bridge consists of four anti-parallel units composed of IGCT devices and diodes (Dr). For a 6kV inverter, the secondary voltage of the phase-shifting transformer is 1750V, and the DC voltage of the power unit is 2500V. Two power units are connected in series per phase, requiring only six power units in the power section. The phase-shifting transformer has six secondary windings. Thus, the maximum output voltage of each power unit is 1750V, and two power units connected in series can output 3500V, which corresponds exactly to the phase voltage of the 6kV system. For a 4500V/4000A IGCT, its long-term operating current RMS value can reach 1500A. Therefore, the inverter capacity is S = 1.732 × 6000 × 1500 = 15000kVA. Considering the motor's power factor, this type of inverter can easily drive a 12000kW motor. 1.2 The 10kV frequency converter is shown in Figure 2. For a 10kV frequency converter, the secondary voltage of the phase-shifting transformer is 1900V, and the DC voltage of the power unit is 2700V. Three power units are connected in series per phase, requiring only nine power units in the power section. The phase-shifting transformer has nine secondary windings. Thus, the maximum output voltage of each power unit is 1900V, and three power units connected in series can output 5700V, which corresponds exactly to the phase voltage of the 10kV system. In applications requiring high reliability, four IGCT power units can also be connected in series per phase. For a 4500V/4000A IGCT, its long-term operating current RMS value can reach 1500A. Therefore, the capacity of the frequency converter is S = 1.732 × 10000 × 1500 = 26000kVA. Considering the power factor of the motor, this type of frequency converter can easily drive a 22000kW motor. Figure 2. Schematic diagram of a 10kV frequency converter. 1.3 3kV frequency converter (see Figure 3). For a 3kV frequency converter, each phase of the transformer uses one power unit, requiring only three power units for the power section. Figure 3. Schematic diagram of a 3kV frequency converter. 2. Performance Testing of High-Voltage High-Power Frequency Converters Pre-shipment testing of high-voltage high-power frequency converters is a crucial step in product quality inspection, especially the full-load (i.e., full rated load) test. Rongxin Power Electronics Co., Ltd. has established a full-load testing system for "motor-generator sets," which can conduct frequency converter characteristic tests under various loads, especially full load, ensuring the authenticity of product performance. All performance defects can be resolved before shipment. The above-mentioned high-voltage frequency converters have all undergone full-load multi-directional performance testing and have met design requirements through field application. References: [1] Wu Jingchang, Sun Shuqin, Song Wennan, et al. Power System Harmonics [M]. Beijing: Water Resources and Electric Power Press, 1988. [2] Wang Zhaoan, Yang Jun, Liu Jinjun, Wang Yue. Harmonic Suppression and Reactive Power Compensation [M]. Second Edition. Beijing: Machinery Industry Press, 2005. [3] Chinese National Standard GB12326-2000: Permissible Voltage Fluctuation and Flicker in Power Quality [S]. Beijing: China Standards Press, 2000. [4] Zhuo Fang, Hu Junfei, Wang Zhaoan. 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