Independent double-bridge-arm variable-frequency soft starter and control method thereof

Abstract

The invention discloses an independent double-bridge-arm variable-frequency soft starter and a control method thereof. The independent double-bridge-arm variable-frequency soft starter comprises a rectifying circuit, an inverter circuit, capacitors C, a bidirectional silicon controlled rectifier and a switching S and K switch, wherein the wire outlet end of the rectifying circuit is connected withthe wire inlet end of the inverter circuit through a direct-current bus; the two-phase inversion output of three-phase alternating current respectively corresponds to a U phase and a V phase of the motor, and the midpoint of each capacitor C corresponds to a W phase of the motor; the two capacitors C are connected in series and then connected in parallel to the DC bus end, and the midpoints of the two capacitors C are used as reference points to be connected with the A phase of the power supply and the W phase of variable-frequency output through the bidirectional silicon controlled rectifier. According to the independent double-bridge-arm variable-frequency soft starter, the difference between the frequency converter and the soft starter is reduced, power switching devices in a traditional AC-DC-AC variable-frequency circuit are reduced, the independent double-bridge-arm variable-frequency soft starter is adopted, high-efficiency soft starting of a motor is achieved, the switching can be achieved, the reliability is high, the size is small, and the cost is low.

Description

technical field [0001] The invention belongs to the technical field of AC-DC-AC inverters, in particular to an independent double-bridge-arm frequency-variable soft starter and a control method for a three-phase asynchronous motor. Background technique [0002] For medium-to-high power motors with no speed regulation requirements, soft starters are usually required to start them due to their large direct starting current to prevent the motor from impacting the power grid. The widely used thyristor voltage regulating soft starter has the advantages of low cost, flexible control and controllable starting current, and is one of the most commonly used soft starters at present. However, because it adopts the principle of voltage regulation and speed regulation, there is a defect in principle that the starting torque is too small to achieve on-load starting, while the AC-DC-AC frequency conversion technology can achieve rated torque starting and the current is limited within the r...

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Problems solved by technology

[0004] In order to solve the problems that the traditional AC-DC-AC frequency converter is used for soft starting, there are many power switching devices in the circuit and it is difficult to switch bypasses, etc., the present invention provides an independent double-bridge arm frequency conversion soft starter and a control method, using the number of power switching devices It saves one-third of the traditional frequency conversion circuit, reduces the volume of the frequency converter, reduces the cost, and increases the switching circuit to realize multi-machine soft starting. The control method first converts the frequency and then adjusts the voltage to achieve high efficiency and high starting torque of the frequency conversion circuit. Control of low starting current

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