2018-09-30

1 the introduction

As an important and widely used circuit in power electronics technology, Rectifier circuit (especially single-phase bridge controllable Rectifier) is widely used in other fields such as transportation, power system, communication system and energy system, as well as general industry. Therefore, it is of great practical significance to compare and study the related parameters of single-phase bridge controllable rectifier circuit and the working conditions of different loads. It is not only an important part of the theoretical study of power electronic circuits, but also a prediction and guidance to the practical application of engineering practice.

Single - phase bridge half - control rectifier circuit

In figure 1, VT1 and VT2 are the phase differences of trigger pulses 180? The thyristor, VD1 and VD2 are rectifier diodes, and the single phase bridge semi-control rectifier circuit is composed of these four devices. Resistance R and inductance L are load. If it is assumed that inductance L is large enough, that is, the voltage L is greater than or equal to R. Since the current in inductance cannot be mutated, it can be assumed that the load current remains constant throughout the steady-state operation process. Due to the characteristics of the bridge structure, as long as the thyristor is switched on, the load is always plus the forward voltage, while the load current is always flowing in one direction. Therefore, the bridge semi-controlled rectifier circuit can only work in the front quadrant. Since the phase L is greater than or equal to R, the variation of load current id is very small regardless of the control Angle (s).

Figure 1. Principle of single-phase bridge semi-control rectifier circuit

In the positive half cycle of u2, the trigger Angle pulses are applied to the thyristor VT1, and u2 is fed to the load via VT1 and VD4. When u2 becomes negative, the inductance current no longer flows through the secondary windings of the transformer, but is continued by VT1 and VD2. At this stage, if the on-state pressure drop of the device is ignored, the load pressure drop ud will not be negative. When u2's negative half-week trigger Angle comes on, VT2 and VD3 trigger conduction, and at the same time, reverse voltage is applied to VT1 to turn it off. U2 supplies power to the load through VT2 and VD3. When u2 crosses zero, VD4 turns on and VD3 turns off. After VT1 and VD4 are continued, the load pressure drop ud becomes zero again.

According to the above analysis, the average value of output load voltage can be calculated as:

（1）

α Angle of phase shift in the range of 180 °. The average value of output current is:

（2）

The average current flowing through the thyristor is only half of the average output dc value, i.e.

（3）

Effective current through the thyristor :

（4）

The simulation model of single-phase bridge semi-control rectifier circuit is shown in figure 2.

Figure 2. Simulation model of single-phase bridge semi-control rectifier circuit

(1) load with pure resistance

Parameters: U=100V, f=50Hz; (2) the thyristor parameters Rn = 0.001 Ω, Lon = 0 h, Vf = 0.8 V, the Rs = 10 Ω, Cs = 250 e - 6 f; (3) R = 10 Ω load parameters, L = 0 h, C = inf. The amplitude of trigger signal 1 and 2 of the busy 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 be 0. , the initial phase of the trigger signal 2 is 0.01s (i.e. 180?). , the simulation results at this time are shown in figure 3 (a); Set the initial phase of the trigger signal 1 to be 0.0025s (i.e. 45?). , the initial phase of the trigger signal 2 is 0.0125s (i.e. 225?). , the simulation results at this time are shown in figure 3 (b).