In high-voltage frequency conversion systems, we recognize that the signals in the control unit cabinet are primarily low-voltage, but the entire system operates in a harsh environment with uncertain (long) transmission distances and various high-voltage signals. If pure copper wires are used for transmission, various problems arise, including interference, voltage boosting and bucking, high losses, and susceptibility to corrosion, leading to low reliability, limited practicality, and resource waste. Industrial optical fiber effectively solves these problems, making optical fiber communication an inevitable future primary communication method.
With the increasing intelligence of terminal blocks, the use of high-voltage frequency converters for speed control of pump loads not only benefits process improvement and product quality enhancement, but also meets the requirements for energy conservation and economical equipment operation, representing an inevitable trend for sustainable development. The benefits of speed control for pump loads are numerous. Application examples show that most have achieved good results (some achieving energy savings of up to 30%-40%), significantly reducing water treatment costs in waterworks, improving automation levels, facilitating pressure reduction in pumps and pipe networks, reducing leakage and pipe bursts, and extending equipment lifespan.
In high-voltage frequency converters, to solve the problems of strong and weak current isolation between the main control system and the power unit in the wiring terminals of the unit series multilevel high-voltage frequency converter, as well as electromagnetic interference between power units, a fiber optic connection method is proposed to realize long-distance transmission of power drive PWM signals.
Pumps, widely used in industries such as metallurgy, chemical engineering, power generation, municipal water supply, and mining, account for about 40% of the total energy consumption of electrical equipment, and electricity costs can even account for 50% of the water production cost in water treatment plants. This is because: on the one hand, equipment is usually designed with a certain margin; on the other hand, due to changes in operating conditions, pumps need to output different flow rates.
This unit-series multi-level PWM voltage source inverter uses several low-voltage PWM power units connected in series to achieve direct high-voltage output. This inverter has low harmonic pollution to the power grid, very low harmonic input current, and a high input power factor, eliminating the need for input harmonic filters and power factor compensation devices. Taking a 6kV output voltage level as an example, the grid voltage is stepped down by a multiplexed isolation transformer on the secondary side before supplying power to the power units. Each power unit is a three-phase input, single-phase output AC-DC-AC PWM power supply inverter structure. Connecting the outputs of adjacent power units in series forms a Y-connection structure, enabling direct high-voltage output through voltage and frequency conversion to power high-voltage motors.
