Parallel current sharing technology of dry-type transformer
Writer： Hengfeng you electric Time：2023-04-14 views：times
In practice, the output parameters （such as voltage, current and power） of a DC stabilized dry-type transformer often can not meet the requirements, but the DC stabilized dry-type transformer satisfying the requirements of this parameter has the problem of redevelopment? Design? The process of production is bound to increase the cost? Therefore, the modular construction method is often selected in the useful, and the modular dry-type transformer of a certain specification series is selected to reach the output voltage according to a certain series or parallel method? Output current? Intention of output power expansion?
1. Measures to improve the reliability of dry-type transformer system
In the process of parallel current expansion of dry-type transformer, in order to improve the operation stability of the system, the method of N + m redundancy of transformer manufacturer can be selected? M represents the number of redundant copies. The greater the value of M, the higher the reliability of the system operation, and the system cost is added accordingly
In the parallel expansion of dry-type transformer, the widely used method is active current sharing? Is it through sampling? Electronically control the conditioning loop to ensure that the output current of the whole system is shared equally according to the output capacity of each unit, so as to achieve the intention of giving full play to the output capacity of each unit and ensuring the reliable operation of each unit?
Current sharing skills shall meet the following conditions:
① All dry-type transformer module units shall adopt common bus;
② The whole system should have good current sharing transient response characteristics;
③ Does the whole parallel output diffuser system have a common control?
Several common parallel current sharing skills are as follows:
① Changing the unit output internal resistance method （slope control method）； ② Master / slave control method;
③ External control method;
④ Uniform current type active load current sharing method;
⑤ Maximum current active current sharing method （active master / slave method? Democratic current sharing method）；
⑥ Forced current sharing method?
2. Change the operation principle of unit output internal resistance method
The completion methods of changing the unit output internal resistance method （slope control method, voltage droop method, output characteristic slope control method） are: u? Fixed, change slope; If the slope is fixed, change the structure and characteristic curve of the output voltage, as shown in Figure 2-23 （a）？ （b） As shown in, during which △ im = △ u? Im / △ u, internal resistance R= △U? △I? When the unit output current is I? During addition, the voltage drop of IA on the current detection dry-type transformer RS is added, resulting in the addition of A1 output voltage, which is superimposed with the unit voltage response signal U and sent to the A2 inverting input terminal. After being amplified by A2, it outputs u and becomes negative. Use this ur voltage to control the unit output current, and then complete the current sharing? It can be seen from figure 2-23 （b）： when the typical value △ u= 0.1%? When △ u, = ± 2%, then △ LMX = 0.05imx, that is, the adjustment accuracy is 5%? This conditioning accuracy is tolerable for most conditioning systems? The characteristic of the modified unit output internal resistance method （slope method） is that the current sharing effect is poor at low current, which can be seen from the formula △ imux0.05iax? Good current sharing at high current? For the voltage source, the internal resistance R? （slope） should be as small as possible? However, this current sharing method uses R? To complete current sharing and reduce the load characteristics of dry-type transformer output, that is, to complete current sharing at the expense of skill indicators?
With the development of microprocessor skills, this method is very simple to complete program control, and then complete ideal current sharing control.
3. Master / slave control method
Under this operation method, N units are used, among which one unit （main control unit） operates in the voltage source （CV） method and the other N-1 units operate in the current source （CC） method. The error voltage △ u from the output current is used to complete the current sharing operation. The operation block diagram is shown in Figure 2-24. In practice, it is a current controlled double loop control composed of voltage loop （outer loop） and current loop （inner loop）， or a voltage controlled current source
The main features of this approach are as follows:
① Once the main control unit fails, the whole system will collapse;
② Because the operating frequency band of voltage loop is wide, it is easy to be disturbed by noise;
③ It is necessary to have communication between master / slave units, so the whole system is messy;
④ The reliability depends on the main module, which can only share the current and cannot form a redundant system;
⑤ A system suitable for n power units.
4. External control method
The working principle of this method is: each unit adds an output current detection to detect its current, the generated response signal regulates the current of each unit, and then reaches the intention of output current sharing among units. In this case, there shall be a common bus between each unit. It is characterized by: this control method has good current sharing effect, but each unit needs to add a current control to become a part of the control loop, which needs to meet the overall requirements of the loop. Otherwise, the skill index and job stability of the unit will be reduced, and the dynamic response characteristics of the system will be reduced. Because each unit needs a control, there are many connections in the whole diffuser system.
The above is the explanation of parallel current sharing technology of dry-type transformer. If you don't understand it, you can contact our Qingdao hengfengyou oil immersed transformer manufacturer at any time: hfy@hengfengyou.com , we will provide you with the best solution.
