Research on Single-phase Bridge Rectifier Circuit Based on MATLAB1 Introduction Rectifiers, especially single-phase bridge-type controllable rectifiers, are important in power electronics technology and are also widely used in circuits. They are not only used in general industry, but also widely used in transportation, power systems, communication systems, Energy systems and other fields. Therefore, the comparative analysis and research on the relevant parameters of the single-phase bridge-type controllable rectifier circuit and the working conditions of different types of loads has strong practical significance. It is not only an important part of the theoretical study of power electronic circuits, but also the actual engineering practice. Application has a predictive and guiding role. 2 Single-phase bridge half-controlled rectifier circuit In Figure 1, VT1 and VT2 are thyristors with a 180° difference in phase of the trigger pulse, and VD1 and VD2 are rectifier diodes. These four devices form a single-phase bridge-type semi-controlled rectifier circuit. The resistance R and the inductance L are the load. If it is assumed that the inductance L is large enough, that is, ωL≥R, since the current in the inductance cannot change suddenly, it can be considered that the load current maintains a constant value during the entire steady-state operation. Due to the characteristics of the bridge structure, as long as the thyristor is turned on, the load always adds forward voltage, and the load current always flows in one direction. Therefore, the bridge half-controlled rectifier circuit can only work in the front quadrant, because ωL≥R, Therefore, regardless of the value of the control angle α, the change in the load current id is small.
Figure 1 Principle of single-phase bridge half-controlled rectifier circuit In the positive half cycle of u2, a trigger pulse is applied to the thyristor VT1 at the trigger angle α, and u2 supplies power to the load through VT1 and VD4. When u2 crosses zero and becomes negative, the current will no longer flow through the secondary winding of the transformer due to inductance, but will flow continuously by VT1 and VD2. At this stage, if the on-state voltage drop of the device is ignored, the load voltage drop ud will not appear negative. At the moment of the negative half-cycle firing angle α of u2, VT2 and VD3 are triggered to turn on, and at the same time, reverse voltage is applied to VT1 and turned off, and u2 supplies power to the load through VT2 and VD3. When u2 crosses zero and becomes positive, VD4 turns on and VD3 turns off. VT1 and VD4 continue to flow, and the load voltage drop ud becomes zero again. According to the above analysis, the average value of the output load voltage can be calculated as:
Fig. 2 Simulation model of single-phase bridge half-controlled rectifier circuit (1) With pure resistive load Corresponding parameter settings: ① AC voltage source parameters U=100V, f=50Hz; ② Thyristor parameters Rn=0.001Ω, Lon=0H, Vf=0.8V, Rs=10Ω, Cs=250e-6F; ③ Load parameter R= 10Ω, L=0H, C=inf; ④ The amplitude of the trigger signal 1 and 2 of the pulse generator is 5V, the period is 0.02s (that is, the frequency is 50Hz), and the pulse width is 2. Set the initial phase of trigger signal 1 to 0s (ie 0?), and the initial phase of trigger signal 2 to 0.01s (ie 180?). The simulation result at this time is shown in Figure 3(a); set the initial phase of trigger signal 1 The phase is 0.0025s (that is, 45?), and the initial phase of the trigger signal 2 is 0.0125s (that is, 225?). The simulation result at this time is shown in Figure 3(b).
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