Application of energy feedback of the hottest freq

2022-08-18
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Application of frequency converter + energy feedback in crane system (3)

(2) design of electric control system

A) selection of frequency converter

when the motor of the system is determined, the design of control system can be started. The first is the selection of frequency converter. At present, there are many domestic and foreign inverter brands in the market, and there are great differences in control level and reliability. Force deformation technology can sensitively capture market changes at the same time, which can be divided into v/f control, vector control and DTC direct torque control. For the lifting mechanism of tower crane, it is recommended to choose the frequency converter with vector control function or DTC direct torque control function. There are many brands of such frequency converters, and the designer can choose them according to his familiarity, technical support, the use of factories in other industries and other factors

because of the inverter product b: please check whether the settings of "force sensor" and "decoder" are correct. The overload capacity and rated current value of the downconverter with the same power are not completely consistent. Therefore, when selecting the capacity of the frequency converter, we should not only look at the rated power, but also check whether the rated working current is greater than or equal to the rated current of the motor. The general experience is that the power of the frequency converter is greater than the motor power by about 10 ~ 30%

b) selection of energy consumption resistance

as a lifting and reuse frequency conversion system, its design focus is on the system reliability when the motor is in the feedback braking state, because the failure of this system often occurs in the working conditions when the weight drops, such as hook slipping, overspeed, overvoltage, etc. In other words, the performance of the frequency conversion system will directly affect the safe operation of the whole lifting mechanism when the weight is lowered. This requires designers to clearly understand the feedback process of variable frequency drive system, so as to know it well

in the product descriptions of most frequency converters, there is no very clear description of how to select the resistance value and power of energy consumption resistance, and often the recommended standard configuration can not fully meet the requirements of lifting conditions. At the same time, there are few articles on this aspect, so the selection of resistance parameters in the design of frequency conversion lifting control system appears to be a little confused. But now a new type of energy feedback unit realizes the consumption problem caused by the energy generated by the motor during braking and lowering, and completely abolishes the original way of old-fashioned resistance energy consumption in the past. This paper will make a qualitative analysis of the working mechanism of the system when the motor works in the feedback braking state. Readers can further get relevant solutions to the energy feedback unit through these analyses

principle of feedback braking

realizing energy feedback braking requires the same frequency and phase control of voltage, feedback current control and other conditions. It uses the active inverter technology to invert the regenerative electric energy into AC with the same frequency and phase as the electricity, so as to realize braking, as shown in Figure 2

the advantage of feedback braking is that it can operate in four quadrants. As shown in Figure 3, electric energy feedback improves the efficiency of the system. Its disadvantages are: (1) this feedback braking method can be used only under the stable electric voltage that is not prone to failure (the electric voltage fluctuation is not greater than 10%). Because when the power generation braking is running, if the electric voltage fault time is greater than 2ms, the commutation failure may occur and the device may be damaged. (2) During feedback, there is certain harmonic pollution to electricity. (3) . complex control and high cost

selection of feedback unit

the selection of feedback unit depends on the actual current of energy feedback. You can refer to the selection method of the original resistance and replace the resistance with feedback unit:

① selection of resistance value

according to document No. 350

it can be basically determined according to the parameters given by the frequency converter sample. The basic principle is, Considering the voltage of the DC circuit (it will exceed 600vdc when the weight drops), the current on the resistance does not exceed the rated current of the frequency converter

② selection of resistance power

it is very important to accurately select the power of resistance. If the selection is too large, it will increase the system cost, and if it is too small, it will cause unreliable operation. However, to reasonably and accurately select the power of energy consumption resistance is a more cumbersome thing, and there are many factors that affect this parameter, such as the size of motor power, the reverse efficiency of reducer, the length of reduced operation time, the size of negative acceleration, the deceleration operation time, and the moment of inertia of transmission components, etc. Therefore, we must first analyze the working process of the system under the descending condition, so as to obtain the determination method of resistance power

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