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A new topological structure and working principle

Author: released in: 2015/3/13 12:44:04 hits:

A new topological structure and working principle

Every kind of switching power supply current applied in all kinds of electric equipments, most of them with indirect DC/DC converter. It has good isolation performance, easy for providing multiple output DC power supply etc.. Indirect DCPDC converter is usually divided into single side and double side circuit circuit. Switching power supply generally small capacity uses single ended forward or flyback DC/DC converter circuit, the high-frequency transformer core flux is the single direction fluctuation. The main disadvantages of the single end indirect DC transform circuit is high frequency transformer core flux in the work in the first quadrant of the magnetization curve, on one hand makes the iron core can not be fully utilized, on the other hand, the general need to solve the problem of magnetic reset. In contrast, switching power supply of double end indirect type DC/DC conversion circuit is suitable for large capacity, alternating between the symmetrical working flux high-frequency transformer core magnetization curves in the first, the 3 quadrant, iron utilization rate is higher, also need not worry about the problem of the flux reduction. And corresponding to the positive and the negative half cycle can transfer energy to the output, and the high frequency transformer core flux variation of wide linear range, is beneficial to reduce the transformer winding turns and the volume of the core of the switching power supply, improving the power density and efficiency. So the research and development of perfect, double forward DC/DC converter topology reliable scheme has been for the domestic and foreign related research and engineering and technical personnel concerned.

Based on the above considerations, we in the scientific research practice, put forward half bridge topology scheme of a new type of double ended forward DC/DC converter, particularly suitable for power electronic system in rectifier, inverter with high voltage DC link, use the ready-made HVDC link, provide multiple DC power system protection control, drive and detection. Compared with the double end forward type topological structure before, its characteristic is can effectively avoid the two upper and lower bridge arm is easy to appear in the process of high frequency PWM switch short-circuit problem, so that the reliability of the switching power supply is improved greatly, and the input voltage can be very high, the output DC power source capacity is big, many groups, especially suitable for medium and high power electronic system. At home and abroad at present there is no relevant literature reports similar topology.

In view of the double end forward DC/DC converter all half bridge topology, in high DC input voltage, high frequency transformer ratio under the condition of large flux, are not ideal to maintain the freewheeling stage, this paper presents a unique flux to maintain the continued flow control method. At the same time, in order to solve the problem from the start of the switching power supply, the paper also gives a bootstrap circuit.

The main circuit uses such as topological structure shown in Figure 1. Figure in the primary side of the transformer adopts the half bridge type double forward circuit, the main circuit can be directly using high voltage DC link power supply. The two primary winding L1 and L2 symmetry, opposite polarity, sharing the same core. This structure can be effectively avoided in the high frequency PWM switch function, because the MOS pipe under the bridge arm off not timely which may arise through phenomenon.

The upper right loop diagram represents a series of side edge with center tapped windings and the high-frequency rectifying filter link. It produces to the secondary winding ends are 2 zero 2 negative three level alternating high frequency pulse voltage, through two fast recovery diode to achieve full wave rectifier, and then L-C filter or direct capacitor filtering voltage stabilizing output. In addition, in order to stabilize the output voltage and improve the anti-interference ability, the circuit also choose one group vice side for the SG3525 chip PWM control provides a feedback voltage.

The following will each switching cycle is divided into three phases to analyze the working principle of the main circuit part. The first to assume the positive direction of current transformer primary side winding is the inflow of homonymous ends. In the main circuit of the switch tube M1, M2 duty ratio in the range of 0 ~ 50%, and the alternate conduction.

1) switch tube M1 is conducted, the forward voltage capacitor C1 is added in the primary winding L1. This voltage excitation, according to the U =Ld i/d T, can be deduced

Type U=Ud/2, i.e. input half side DC voltage, L of the high frequency transformer equivalent excitation inductance. When the circuit is working at steady state after each cycle of the switch, the excitation current initial tube corresponding to M1 just conduction when the values of the I0 should be negative, and the excitation current with the slope of UPL (constant) from negative to positive linear increase (it should be noted here is that the current through L1 is composed of the excitation current and the total load current synthesis thus, current L1 size also depends on the load), and both ends of each side of the winding induction generate a positive voltage pulse.

2) M2 switch tube conduction situation is similar to the M1, because the capacitor C2 terminal voltage U = Ud/2, relative to the L2 of the same name end into reverse polarity effect, its initial excitation current value I0 is positive, so during the excitation current is increased with slope of UPL from positive to negative reverse linear, because each the secondary winding ends generates negative voltage pulse.

3) when M1, M2 are not conducted, need the main magnetic flux excitation current is kept at the maximum value of I0 invariant, so that each winding flux to maintain constant value, according to Faraday's law of electromagnetic induction u = - D psi /d T, the terminal voltage of main circuit during this primary winding and the secondary winding of the inner keeps zero, so that the transformer secondary voltage of three level PWM pulse waveform, thereby ensuring the output DC voltage is controllable.

From the analysis above we see not hard excitation main circuit of the high frequency transformer potential is in accordance with the law

The linear increase (from negative to positive) = = maintain constant (in the excitation afterflow circuit) = (linear decreases from positive to negative)

Change, makes the main flux of symmetry in the first and 3 quadrant alternating, satisfy the double end forward type control requirements.




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