In the water supply frequency converter industry, there is a type of frequency converter with a single-input and three-output power supply. Because many users lack relevant professional knowledge, they often mistakenly believe that the output voltage of a single-input and three-output machine is 380V, or that a single-phase input frequency converter can be used on a single-phase water pump. Is this really the case ? After consulting with experts, we would like to share our findings with you.
1. Three-input, three-output inverter main circuit diagram
Figure 1 shows the main circuit diagram of a conventional three-phase input/output frequency converter, which mainly includes four parts: rectification, smoothing, braking, and inversion. The three-phase 380V power frequency is rectified into DC power by the rectifier, filtered, and finally inverted into a three-phase variable frequency AC output under the control of the CPU. It can be seen that there is no boost module in the main circuit, so the output voltage can only be equal to or less than 380V. Users often use a multimeter to measure the output voltage, which shows over 500 volts, and worry that it will burn out the motor. This is actually because the waveform of the frequency converter output is a sine wave, which interferes with the multimeter, leading to incorrect test data.
2. Single-input, three-output inverter main circuit diagram
Figure 2 shows the standard main circuit diagram of a single-phase input and three-phase output inverter. It is based on Figure 1, but one rectifier bridge is removed. The input terminal is directly connected to a 220V power supply, but the output terminal is also inverted to a three-phase output, with a maximum output voltage of 220V. Therefore, the maximum output of the single-phase input and three-phase output inverter is only 220V instead of 380V.
Users might ask, "Can a two-phase output drive a single-phase water pump?" The answer is definitely no! Because the starting method of a single-phase motor is different and the drive algorithm of the frequency converter is different, a single-input three-output frequency converter can only use a three-phase water pump, not a single-phase water pump.
Using installation wiring to show you a single input and three outputs:
The above-mentioned single-input, three-output frequency converter outputs three-phase 220V, and the maximum power of the product is usually only 2.2KW . However, there are no three-phase 220V water pumps sold in the domestic market. What to do? Don't worry, I'll answer your questions.
Currently, the main units of conventional motor products on the market are divided into two voltage specifications: three-phase 380V and single-phase 220V. Three-phase motors below 3KW generally have two operating voltages and wiring methods marked on their nameplates, as shown in Figure 3. They are manufactured with a star connection for 380V power supply and a delta connection for 220V power supply. Therefore, when using a single-input three-output frequency converter, it is necessary to purchase a three-phase 380V water pump of the same power and modify the water pump's wiring method to a delta connection for normal use. Wiring instructions are usually provided on the motor junction box, as shown in Figure 4.
Figure 3 Motor nameplate
Figure 4 Three-phase 220V delta connection
The single-input, three-output inverter is designed for applications where a three-phase power supply is unavailable but an inverter is still required. Its control algorithm and conversion efficiency are comparable to those of a 380V power supply. It has a wide range of applications; for example, in the case of a common household constant pressure water supply, a regular three-phase water pump can be used simply by modifying it to a delta connection, making it convenient and practical.
