Feedback unit suppliers remind you that in daily use, the bridge rectifier circuit of general frequency converters is three-phase uncontrollable, so it is impossible to achieve bidirectional energy transfer between the DC circuit and the power supply. The most effective way to solve this problem is to use active inverter technology, which converts regenerated electrical energy into AC power of the same frequency and phase as the grid and feeds it back to the grid. The current tracking PWM rectifier is adopted, which makes it easy to achieve bidirectional power flow and has a fast dynamic response speed. The same topology structure allows us to fully control the exchange of reactive and active power between the AC and DC sides, with an efficiency of up to 97% and significant economic benefits. The heat loss is 1% of the energy consumption braking, while not polluting the power grid. So, feedback braking is particularly suitable for situations that require frequent braking, and the power of the electric motor is also high. At this time, the energy-saving effect is significant, with an average of about 20% energy-saving effect depending on the operating conditions.
Inverter feedback braking conditions
(1) During the deceleration process of the electric motor from high speed (fH) to low speed (fL), the frequency suddenly decreases. Due to the mechanical inertia of the electric motor, the slip s<0, and the electric motor is in a generating state. At this time, the back electromotive force E>U (terminal voltage).
(2) The electric motor is running at a certain fN, and when it stops, fN=0. During this process, the electric motor enters a generating operation state, and the back electromotive force E>U (terminal voltage).
(3) For potential energy (or potential energy) loads, such as when a crane is lifting heavy objects and descending, if the actual speed n is greater than the synchronous speed n0, the electric motor will also be in a power generation operation state, where E>U.
Characteristics of frequency converter feedback braking
(1) It can be widely used for energy-saving operation in energy feedback braking scenarios of PWM AC transmission.
(2) High feedback efficiency, reaching over 97.5%; Low heat loss, only 1% of energy consumption.
(3) The power factor is approximately equal to 1.
(4) The harmonic current is small, causing minimal pollution to the power grid and possessing the characteristics of green environmental protection.
(5) Save investment and easily control harmonic and reactive components on the power supply side.
(6) In multi motor transmission, the regenerative energy of each individual machine can be fully utilized.
(7) Has a significant energy-saving effect (related to the power level and operating conditions of the motor).
(8) When the workshop is powered by a shared DC bus for multiple devices, the energy from feedback braking can be directly returned to the DC bus for use by other devices. After calculation, it can save the capacity of feedback inverters, and even eliminate the need for feedback inverters.
Application scenarios of frequency converter feedback braking
(1) High speed separator used for glucose crystallization in pharmaceutical factories.
(2) High speed separator for crystallization of civilian sugar (granulated sugar).
(3) Paint mixers and mixers used in washing plants.
(4) Dyeing machines, batching machines, and mixers used in plastic factories.
(5) Medium to large-sized cleaning machines, dehydrators, and spin dryers used in washing plants.
(6) Washing machines, bed sheet cleaning machines, etc. used in hotels, guesthouses, and laundry shops.
(7) High speed centrifuges and separators in various specialized centrifugal machinery factories.
(8) Various dumping equipment such as converters, steel ladles, etc.
(9) Lifting machinery such as bridge, tower, and main lifting hooks that can be lifted (operating state when heavy objects are lowered).
(10) Cut the conveyor belt with high load-bearing capacity.
(11) Hanging cages (for loading or unloading) and inclined mine cars in mines.
(12) Various gate activation devices.
(13) Paper roller motors used in papermaking and stretching machines in chemical fiber machinery.