How to use high voltage inverter - Solutions - Huaqiang Electronic Network

Probe high frequency needle JTK-50L-Q has 5 needles in the high frequency needle

Crystal oscillator

Photocoupler

1: The disadvantage of choosing an over-voltage level is to choose an excessively high voltage level, resulting in an excessive investment and a long payback period. As the voltage level increases, the insulation of the motor must be increased to increase the price of the motor. The increase in the voltage level increases the number of series connection of power semiconductor devices in the inverter, and the cost increases.
It can be seen that it is extremely uneconomical and unreasonable to use a 6kV, 10kV voltage level for a motor system of 200 to 2000 kW.
2: The relationship between the inverter capacity and the phase number of the rectifier device The inverter device must be in compliance with the national regulations on harmonic suppression when it is put into the 6kV grid. This is related to the grid capacity and the rated power of the unit.
The short-circuit capacity is less than 1000MVA, and the 1000-kW device 12-phase (transformer secondary-side double winding) can be used. If the 24-phase power is up to 2000 kW, the 12-phase basically eliminates the 5th and 7th harmonics with large amplitude.
After the number of rectified phases exceeds 36, the harmonic current amplitude is not significantly reduced, and the manufacturing cost is too high. If the grid short-circuit capacity is 2000 MVA, the device allows for a larger capacity.
3: Lowering the maximum voltage below 3kV can save a lot of investment. It is necessary to consider the voltage level from the characteristics and safety factor of power electronics. Due to the voltage of the power electronics and the dv/dt limit allowed by the motor, the 6kV inverter must adopt multi-level. Or multiple devices connected in series, resulting in complicated lines, high price, and poor reliability. For the 6kV inverter, if the 1700V IGBT is used, the American Robincon PERFECTHARMONY series 6kV high-voltage inverter is taken as an example. Each phase consists of five power units with a rated voltage of 690V connected in series, and three phases have a total of 60 devices. If you use 3300V devices, you need 3 strings of 30 devices, which is huge. On the other hand, the device current is small, and the current capability of the device is not fully utilized. Taking 560kW as an example, the 6kV motor current is only about 60A, while the 1700V IGBT current has reached 2400A, and the 3300V device current is 1600A. It is extremely unreasonable to use a large number of small devices in series. Even if the motor power is 2000kW, the current is only about 140A, which is still small.
Foreign medium voltage inverters have multiple voltage levels: 1.1kV, 2.3kV, 3kV, 4.2kV, 6kV, which are mainly determined by the voltage level of power electronics.
For inverters that output the same power, the cost of using a higher voltage or more units in series is greater than the cost of using a lower voltage, a smaller number, and a larger current unit. That is, the device current should be selected as much as possible. Low voltage level.