time:2024-12-11 11:00:08Views:
Inverters are essential devices that control electrical energy by converting industrial frequency power into another frequency. They achieve this by using the on-off function of power semiconductor devices. The rapid advancements in power electronics and microelectronics have led to the maturation of high-voltage, high-power frequency conversion devices. These developments have successfully addressed many high-voltage challenges through series or unit connections of devices.
High-voltage inverters are generally classified into two types: voltage source and current source inverters. Voltage source inverters convert DC from a voltage source into AC, with a capacitor as the filter element in the DC circuit. They are typically used for frequency conversion and speed regulation applications, such as motor control.
Current source inverters, on the other hand, convert DC from a current source into AC. The filter element here is an inductor, providing better control over the current and stability in the load. Both inverter types serve different industrial needs and are crucial for modern motor control systems.
In an asynchronous motor, the torque is generated by the interaction between the motor's magnetic flux and the current flowing through the rotor. If the voltage remains constant and the frequency is reduced, the magnetic flux will increase, leading to motor saturation, which can cause damage. Therefore, the inverter adjusts both the frequency and voltage simultaneously to maintain a constant magnetic flux in the motor, preventing magnetic saturation. This is known as VVVF (Variable Voltage Variable Frequency) control, which ensures efficient motor operation at various speeds.
With an industrial frequency power supply, a reduction in voltage results in an increase in current. However, with an inverter, if the voltage decreases proportionally with the frequency, the current does not increase significantly. If the output power remains constant, the current will increase at low speeds, but when maintaining constant torque, the current remains almost unchanged. This makes inverters more energy-efficient and smoother in operation compared to traditional power supplies.
Inverter-driven motors start more smoothly than those powered by industrial frequency power supply. With the inverter, both frequency and voltage are gradually increased as the motor accelerates, which limits the starting current to less than 150% of the rated current. This is significantly lower than the 6-7 times rated current seen with direct industrial frequency startup, which can cause mechanical and electrical shocks.
The starting current with an inverter is typically 1.2 to 1.5 times the rated current, and the starting torque is between 70% and 120% of the rated torque. Inverters with automatic torque enhancement functions can provide full-load starting torque, improving motor reliability and performance.
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