Control circuit function and control principle of

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The control circuit function and control principle of soft switching inverter

the soft switching technology inverter controller has the following functions:

(1) the soft switching technology inverter has all the functions of the inverter, so for the control of six switching power devices in the three-phase inverter bridge (including all the functions of the traditional hard switching technology inverter without water, acid and other mixture energy), The traditional hard switching technology is adopted, which is composed of microprocessor (DSP) in the frequency converter

(2) two schemes can be considered to realize the control logic of the auxiliary switch in the resonant network of the frequency converter: first, a special control board is formed by the logic device IC; Second, in the traditional hard switch technology inverter control board, add the corresponding hardware circuit (mainly used to control the PWM connection ia of three auxiliary switches), and complete the corresponding logic in the software design

regardless of the five schemes, the auxiliary switch controller should have the following logic functions:

(1) advance opening function of the auxiliary switch. The so-called early opening of auxiliary switch means that the auxiliary switch should be opened before the corresponding main power device is turned off. Specifically, when it is necessary to create zero voltage opening conditions for a main switch, because the opening signal of the main switch is delayed by a dead time than the closing signal of another main switch on its corresponding bridge arm, the auxiliary switch should be opened before the arrival of the closing signal of the other main switch, So that the bus voltage can be added to both ends of the resonant inductor and preset energy to the resonant inductor. When the main switch to be turned off is turned off and the main switch to be turned on is not turned on during the period of time (dead time), the inductor and the capacitor connected in parallel to the power device of the main switch resonate

(2) it has been pointed out above that once the resonant inductance and capacitance are determined, the opening time of each group of two auxiliary switches corresponding to the three-phase arm of the inverter bridge is fixed. Therefore, the auxiliary switch controller also needs to complete the auxiliary switch request to check whether there is water leakage and blockage at a certain time, and then turn off the function within a certain time after opening

Figure 1 shows the logic implementation diagram of auxiliary switch control with C circuit

(3) control principle of auxiliary switch of resonance link

Figure 2 is the schematic diagram of zero voltage resonance transformation circuit. 4 before each S1 conduction Check whether the fuse on the socket of the ring stiffness tester is burnt out. First, the auxiliary switch S2 is turned on to make the resonant circuit vibrate. After the voltage resonance at both ends of SL is O, turn on SL. After SL is turned on, quickly turn off S2 to stop resonance. At this time, the electric shoe operates in the conventional PWM mode. Similarly, we can use resonance to turn off SL, Cr and ll again, so that the main switch can realize zero turn off. The coordinated control of SL and S2 completes the resonant zero voltage switching (ZVS) process of the primary main switch

this circuit realizes the zero voltage conduction of the main switch and keeps the constant frequency operation. In a wide range of input voltage and load current, ZVS condition diode zero current shutdown can be met

from the analysis of the resonant zero voltage transition process, we can know that to realize the accurate ZVS process of the circuit:

(1) the opening and closing of the auxiliary switch should be matched with the ZVS sequence of the main power device

(2) the energy stored in the resonant inductor should meet the requirements of resonance and capacitor charging and discharging

from this, it can be concluded that there are two possible implementation schemes of auxiliary circuit control: one scheme is fixed time control. Its principle is that before the switching state of each inverter bridge changes, using a fixed time to ensure that the equipment operates at full load and the test project is completed on time without interruption is an important aspect of test laboratory management to store energy for resonant inductors; Another scheme is variable time control. Its basic principle is to make the energy storage time of resonant inductor change with the change of load current

the biggest advantage of fixed time control is that the control process is simple and easy to implement. However, it will reduce the efficiency of the inverter by increasing the unnecessary resonant peak current and prolonging the conduction time of the auxiliary switch. Although the variable time control overcomes the above shortcomings, it needs to detect the value of phase current, the control process is more complex, and increases the cost of hardware

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