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Conditions and characteristics of inverter feedback braking

2020-12-03

In daily use, the bridge rectifier circuit of general purpose inverter is three-phase uncontrollable, so it is impossible to realize bidirectional energy transfer between DC circuit and power supply. The most effective way to solve this problem is to adopt active inverter technology, that is, the regenerated electric energy is converted into the AC power grid with the same frequency and phase as the power grid. It is easy to realize the bidirectional flow of power and has fast dynamic response speed. The same topology structure enables us to completely control the exchange of reactive power and active power between AC side and DC side, and the efficiency can be as high as 97%. The economic benefit is great. The heat loss is 1% of energy consumption braking, and does not pollute the power grid. Therefore, feedback braking is especially suitable for frequent braking occasions, and the motor power is also large, so the power saving effect is obvious. According to the operating conditions, the average power saving effect is about 20%.


Feedback braking condition of inverter


(1) When the motor decelerates from high speed (FH) to low speed (FL), the frequency suddenly decreases. Due to the mechanical inertia of the motor, the slip s < 0, and the motor is in the state of power generation. At this time, the back EMF E > U (terminal voltage).


(2) When the motor runs at a certain FN, FN = 0 when it stops. In this process, the motor will be in the state of generating operation, and the back EMF E > U (terminal voltage).


(3) For potential energy (or potential energy) load, if the actual speed n is greater than the synchronous speed N0 when the lifting weight of the crane is lowered, the motor will also be in the state of power generation operation, at this time, E > U.


Characteristics of inverter feedback braking


(1) It can be widely used in energy-saving operation of PWM AC drive with energy feedback braking.


(2) The feedback efficiency is higher than 97.5%, and the heat loss is only 1% of the energy consumption.


(3) The power factor is about 1.


(4) The harmonic current is small, the pollution to the power grid is very small, with the characteristics of green environmental protection.


(5) It can save investment and control harmonic and reactive power components easily.


(6) In the multi motor drive, the regenerative energy of each single machine can be fully utilized.


(7) It has great power saving effect (related to motor power and operating conditions).


(8) When the workshop is powered by a common DC bus, the regenerative braking energy can be directly returned to the DC bus for other equipment. After calculation, the capacity of feedback inverter can be saved, even without feedback inverter.


Application of inverter feedback braking


(1) High speed separator for glucose crystallization in pharmaceutical plants.


(2) A high speed separator for crystallization of sugar (granulated sugar) for civil use.


(3) Paint mixer and mixer used in washing plant.


(4) Dyeing machine, batching machine and mixer used in plastic plant.


(5) Large and medium-sized washing machines, dehydrators and dryers are used in washing plants.


(6) Washing machines and bed sheet washing machines for hotels, hotels and laundries.


(7) High speed centrifuges and separators in various professional centrifugal machinery factories.


(8) Various dumping equipment such as converter, ladle, etc.


(9) Hoisting machinery such as bridge type, tower type and main lifting hook that can be hoisted (running state when the weight is falling).


(10) - cut high loaded conveyor belt.


(11) The hanging cage (loading or charging) in the mine and the inclined mine car.


(12) Start up devices for various gates.


(13) Paper roller motor for paper making and drafting machine in chemical fiber machinery.


General purpose frequency converter


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