Bipolar full-bridge inverter control

full bridge inverter is a full bridge (Full Bridge) PWM DC / DC converter's main part, its main circuit is shown in Figure 1, it is the tube by four switches V1 to V2, and its Anti-parallel diodes D1 ~ D4, and the output transformer Tr, and other components. The input DC power supply voltage Ui, the output AC voltage U. The primary winding of the transformer Tr, two midpoint of the bridge arm connected to the A and B two turns of the primary winding of the transformer is W1, the secondary winding turns W2,Grid tie inverter, and a variable ratio Κ = W1/W2 is. The full bridge inverter may be used bipolar control, finite bipolar control and phase shifting control mode.
1. Bipolar control mode
bipolar control
full-bridge inverter waveform shown in Figure 1 (b), (c). The switch tube V1 to V2 is used in the PWM control mode. V1 and V4 lead in the first half of a switching period TS weeks, switch to pass on-time TON, DU is the duty cycle, the latter half cycle switch V2 and V3 conduction, conduction time TOn. Switch V1 and V4 conduction Excluding switch-state voltage drop, the voltage on the primary winding of the transformer for UAB =-Ui; switch V2 and V3 conduction, the voltage on the primary winding uAB =-Ui; switch tube V1 and V4, and V2 and V3 are off,power inverter, the voltage on the primary winding UAB = 0, and the open circuit of the transformer secondary, the primary winding of the transformer on the waveform of the voltage UAB Fig 1 (b) shown is a square wave voltage. Adjusting the conduction time of the switch tube, i.e., to adjust the duty ratio DU, can be adjusted voltage UAB pulse width, so as to achieve the purpose of adjusting the voltage UAB RMS size. The secondary voltage U2. UAB same waveform amplitude Ui / K. / p>
the secondary access resistive load RLd, flowing through the load current is isO. Current is, waveform voltage UO, UAB, the same amplitude. IP waveform of the transformer primary current and secondary current is the same, and its amplitude. This equation also can be written in R1, converted to the primary value of the secondary load resistance RLd; Found that, if the transformer is an ideal transformer, which is connected to the transformer secondary the load resistor RLd with without transformer directly connected to the resistor R1, while at both ends of the A, B the effect is the same. Therefore, when the switch tube V1 and V4 conduction, flowing through the current of the V1 and V4, V2 and V3 conduction switch tubes, flowing through the current V2 and V3, the switch tube V1 ~ V4 antiparallel diode D1 ~ D4, there is no current flow.

Figure 3-29 bipolar control mode
If the inductive load L is connected in the secondary of the transformer, when the switch tube V1 and V4 conduction, the transformer primary voltage UAB = Ui, of secondary voltages UO = K0 - the role of the voltage UO, the load current from zero began to increase, the rate of increase, http://www.gridtieinverter.de. This current, i.e. switch tube V1 and V4 will be off reaches a maximum when the switch tube V1 and V4 off, this current can not be a sudden change occurs, and will continue in accordance with the direction of the original flow. It will make the diode D3 and D2 conduction, so the voltage UAB =-Ui, Uo polarity reverse. Under the action of a reverse voltage, the load inductor current will be reduced to the same, the rate of increase of the reduced speed with the switch tube V1 and V4 opened. In this case, the primary and secondary transformer voltage waveform, and resistive loads, there is a great difference, the emergence of a shaded area. UAB: pure inductive load area of the shadow, and the resistive load when the area of the same size. Therefore, the waveform of the output voltage Uo is determined not only by the conduction state of the switch tube v1 and v4, but also related to the nature of the load. When the duty ratio DU ≥, i.e., the conduction time of the switch tube V1 and v4 Ton ≥ Ts / 4,power inverter, the waveform of the voltage UAB becomes a square wave pulse width of 180 ° in electrical angle. I.e., when DU in the range of ~ 1 changes,Grid tie inverter, the voltage UAB and Uo is always 180 ° pulse width of a square wave, from the duty cycle affect Du changes. From the above analysis, the full-bridge inverter should not be used in the inductive load such a pulse width control mode.