1 Introduction
rectifier circuit Especially the single-phase bridge controlled rectifier circuit is an important and widely used circuit in power electronics technology. It is not only used in general industry, but also widely used in transportation, power system, communication system, energy system and other fields. Therefore, the relevant parameters of the single-phase bridge controlled rectifier circuit and the working conditions of different loads are analyzed Comparative analysis and research has strong practical significance. It is not only an important part of power electronic circuit theory learning, but also plays a role in predicting and guiding the practical application of engineering practice.
2 single phase bridge half controlled rectifier circuit
In Figure 1, VT1 and vt2 are trigger pulse phase differences of 180? VD1 and VD2 are rectifier diodes, which form a single-phase bridge semi controlled rectifier circuit. Resistance R and inductance L are loads. If inductance L is assumed to be large enough, i.e ω L ≥ R, since the current in the inductance cannot change suddenly, it can be considered that the load current remains constant during the whole steady-state working process. Due to the characteristics of the bridge structure, as long as the thyristor is on, the load always adds the forward voltage, and the load current always flows in one direction. Therefore, the bridge semi controlled rectifier circuit can only work in the front quadrant because ω L ≥ R, so regardless of the control angle α The change of load current ID is very small.
Fig. 1 principle of single-phase bridge semi controlled rectifier circuit
In U2 positive half cycle, trigger angle α A trigger pulse is applied to the thyristor VT1, and U2 supplies power to the load through VT1 and VD4. When U2 changes from zero crossing to negative, the current no longer flows through the secondary winding of the transformer due to inductance, but freewheeling by VT1 and VD2. If the on state voltage drop of the device is ignored at this stage, the load voltage drop UD will not be negative. Trigger angle in U2 negative half cycle α At the same time, vt2 and VD3 trigger on, apply reverse voltage to VT1 and turn it off, and U2 supplies power to the load through vt2 and VD3. When U2 crosses zero and becomes positive, VD4 is on and VD3 is off. VT1 and VD4 freewheeling, load drop UD becomes zero again.
According to the above analysis, the average value of output load voltage can be calculated as:
（1）
α The phase shift range of the angle is 180 °. The average value of output current is:
（2）
The average value of current flowing through thyristor is only half of the average value of output DC, that is:
（3）
Effective value of current flowing through thyristor:
（4）
The simulation model of single-phase bridge half controlled rectifier circuit is shown in Figure 2.
Fig. 2 simulation model of single-phase bridge semi controlled rectifier circuit
(1) With pure resistive load
Corresponding parameter settings: ① AC voltage source parameters u = 100V, f = 50Hz; ② Thyristor parameters RN = 0.001 Ω, lon = 0h, VF = 0.8V, rs = 10 Ω, CS = 250e-6f; ③ Load parameters R = 10 Ω, l = 0h, C = inf; ④ The amplitude of trigger signals 1 and 2 of pulse generator is 5V, the period is 0.02s (i.e. the frequency is 50Hz), and the pulse width is 2.
Set the initial phase of trigger signal 1 as 0s (i.e. 0?), and the initial phase of trigger signal 2 as 0.01s (i.e. 180?), and the simulation results are shown in Fig. 3 (a); set the initial phase of trigger signal 1 as 0.0025s (i.e. 45?), and the initial phase of trigger signal 2 as 0.0125s (i.e. 225?), and the simulation results are shown in Fig. 3 (b).