Background technology
Three-level resonant transformer comprises former limit circuit, transformer, secondary circuit, and former limit circuit comprises bleeder circuit, switching circuit, resonant circuit, freewheeling circuit, and secondary circuit comprises current rectifying and wave filtering circuit.It is open-minded that the main switch of three-level resonant transformer is operated in no-voltage, and rectifier is operated in zero-current switching; When higher direct current input, high power applications, can adopt low withstand voltage switching device.
Shown in Figure 1 is existing a kind of three-level resonant transformer, this three-level resonant transformer comprises former limit circuit, transformer, secondary circuit, former limit circuit comprises two dividing potential drop capacitor C 1, C2, is used for input voltage is divided equally, and producing two only is half voltage source of input voltage; Switching circuit is in series by four switch Q1, Q2, Q3, Q4, is used for direct voltage is reverse into a square wave or staircase voltage; Freewheeling circuit is made up of two diode D5, D6, wherein the first diode D5 is connected between the contact of the mid point of dividing potential drop electric capacity and the first switch Q1 source electrode and second switch Q2 drain electrode, the second diode D6 connect with the mid point of dividing potential drop electric capacity and the 4th switch Q4 drains and the contact of the 3rd switch Q3 source electrode between; Resonant circuit comprises capacitor C r, inductance L r, inductance L m, and capacitor C r connects with inductance L r, and Lm can show as the magnetizing inductance of transformer, also can be outer coilloading and equivalent inductance after magnetizing inductance is in parallel.The former limit of transformer is connected on the resonant circuit.This resonant circuit is connected between the output of the mid point of dividing potential drop electric capacity and switching circuit, series capacitance Cr and series inductance Lr resonance constitute first eigenfrequency of controlled resonant converter of the present invention, represent with fs, series capacitance Cr and series inductance Lr and shunt inductance Lm resonance constitute second eigenfrequency of controlled resonant converter, represent with fm; Transformer links to each other with the rectification circuit of being made up of D7, D8, and the filter circuit of being made up of capacitor C that butts up against rectification circuit output end provides a unidirectional pulse current; Rectification circuit, filter circuit, being used for that pulse current is changed into a direct current electric current provides energy to output loading circuit R.
Above-mentioned converter makes less frequency range just can realize bigger input and output voltage adjustable range by the LLC resonant circuit with dual intrinsic resonance frequency, simultaneously, making each switching voltage stress by a pair of fly-wheel diode is half of input voltage, and gamut realizes voltage switch) and need not add any circuit, rectifier diode is operated in ZCS (Zero Current Switch).This converter efficient when the input of high terminal voltage is higher, is applied in high input voltage and advantageous particularly on the power supply product that the outage retention time requires is arranged.
But because the transformer of present three-level resonant transformer is one, secondary need flow through whole load currents, although switching loss lower (ZCS), on-state loss is higher.Therefore the transformer thermal stress is concentrated, and when high power applications, causes thermal stress to be difficult to satisfy the derate requirement.And existing output current ripple bigger, noise index difficulty satisfies actual requirement; Large ripple current reduces the output filter capacitor weak point in useful life simultaneously.
Summary of the invention
Thereby technical problem to be solved by this invention provides a kind of transformer thermal stress of can disperseing makes thermal stress can satisfy the three-level resonant transformer that derate requires easily.
Three-level resonant transformer of the present invention comprises: transformer, with the resonant circuit of the former limit of transformer windings in series, make the former limit of described transformer produce the switching circuit of alternating current; It is characterized in that: described transformer is at least two, and the former limit winding of each transformer is connected with resonant circuit, the secondary output-parallel of each transformer; The former limit winding of each transformer is in series, and the former limit windings in series of the transformer after the series connection is on same resonant circuit.Because the former limit windings in series of transformer, the maximum functional magnetic flux density of transformer is lower, and magnetic loss reduces, and can disperse the main transformer thermal stress better like this, but can not realize making the output current ripple to reduce.
The number of described transformer is two.This is a kind of comparatively simple design.
The number of described resonant circuit is consistent with the number of transformer, and the former limit winding of each transformer is series at a resonant circuit respectively; The number of switching circuit is consistent with the number of resonant circuit, and each switching circuit connects a resonant circuit respectively, has phase difference between the resonant circuit.This design can make the ripple superimposed of output current, thereby fluctuation is reduced.And can effectively reduce the ripple current that flows through output filter capacitor, improve the useful life of filter capacitor.
Having phase difference between the described resonant circuit is 180 °/N, and wherein N is the number of resonant circuit.She Ji three-level resonant transformer is best a kind of scheme like this, can make the ripple superimposed better effects if of output current.
The number of described resonant circuit is 2, and phase difference is 90 ° between the resonant circuit.This design can make the converter output current realize frequency multiplication, and fluctuation reduces.
Three-level resonant transformer comprises: transformer, with the resonant circuit of the former limit of transformer windings in series, make the former limit of described transformer produce the switching circuit of alternating current; Described transformer is at least two, and the former limit winding of each transformer is connected with resonant circuit, the secondary output-parallel of each transformer; Described resonant circuit is at least more than two, the number of switching circuit is consistent with the number of resonant circuit, each switching circuit connects a resonant circuit respectively, all be in series with one group of transformer on each resonant circuit, there is phase difference in the former limit windings in series of the transformer in a group between the resonant circuit.Such scheme can be applied in disperse the transformer thermal stress need be than higher circuit design, promptly design for sort circuit, transformer of series connection does not satisfy the requirement that disperses the transformer thermal stress on the resonant circuit, thereby need connect one group of transformer on a resonant circuit.
The number of described resonant circuit, switching circuit is 2, and phase difference is 90 ° between the resonant circuit, and the number of transformer is 2 in described one group of transformer.The output current of this three-level resonant transformer is realized frequency multiplication; And since transformer add up to 4, so the effect of thermal stress of disperseing transformer is than the better effects if of two transformers.
Described resonant circuit also comprises limit that add an and former inductance inductance in parallel.Like this can be easily change some parameters of former limit inductance by adjustment to the magnetizing inductance that adds.
The present invention is owing to adopt plural transformer, and secondary flows through the electric current sum and equals load current, and on-state loss significantly reduces.Thereby can effectively reduce the wastage, disperse thermal stress.When high power applications, make thermal stress can satisfy the derate requirement.
Embodiment
Referring to Fig. 1, Fig. 2, Fig. 7, Fig. 8-16, introduce the operation principle of showing existing a kind of three-level resonant transformer among Fig. 1 earlier.
A switch periods of this converter can be divided into 8 mode of operations, and operation principle is as follows:
(1) pattern 1:t0<t<t1.At t=t0 constantly, Q1, Q2 are open-minded simultaneously.The transformer primary current flows through Q1 and Q2, the conducting of secondary diode D7 positively biased, and Cr and Lr produce series resonance, and inductance L r electric current is increased to maximum with sinusoidal rule forward and reduces then, flows through linear the increasing of electric current of inductance L m.
(2) pattern 2:t1<t<t2.At t1 constantly, the electric current of resonant inductance Lr equates that with the electric current of inductance L m the transformer primary current drops to zero, and secondary current also drops to zero, and diode D7 realizes that ZCS turn-offs naturally.Lm voltage becomes free inductance and Lr series connection and Cr resonance not by clamp.Big more many than Lr because of Lm, harmonic period is long, in t1~t2, can be similar to and think that resonance current is constant.
(3) mode 3: t2<t<t3.At t=t2 constantly, send the Q1 cut-off signals, Q2 is conducting still.Resonance current is to the charging of the output junction capacitance of Q1, when Vds1 rises to incoming level one half, and diode D5 conducting, Vds1 is clamped on 1/2 incoming level, and Q1 turn-offs.
(4) pattern 4:t3<t<t4.T3 sends the Q2 cut-off signals constantly, and Vds2 rises.When rising to input voltage one half, D3, D4 are biased to zero.For Q3, Q4 no-voltage are opened and are created conditions.
(5) pattern 5:t4<t<t5.At t4 constantly, send Q3 simultaneously, Q4 opens signal, is added in the voltage reversal of Cr, Lr, Lm, diode D8 conducting, Cr and Lr generation resonance, resonance current oppositely increases to maximum by sinusoidal rule and reduces then.Inductance L m goes up the electric current reverse linear to be increased.
(6) pattern 6:t5<t<t6, in the t5 moment, resonant inductance Lr electric current equates that with inductance L m electric current the transformer primary current drops to zero, and secondary current also will arrive zero, and diode D8 realizes that ZCS turn-offs naturally.
(7) pattern seven:: t6<t<t7, t6 sends the Q4 cut-off signals constantly, and Q3 is conducting still.Resonance current is to the charging of the output junction capacitance of Q4, when Vds4 rises to incoming level one half, and diode D6 conducting, Vds4 is clamped on 1/2 incoming level, and Q4 turn-offs.
(8) pattern seven:: t7<t<t8, t7 constantly send the Q3 cut-off signals, and resonance current is to the output junction capacitance charging of Q3, when Vds3 rises to incoming level one half, diode D1, D2 zero partially, for Q1, Q2 no-voltage are opened and are created conditions.Enter next cycle period.
Transverse axis is time t among Fig. 2, and the longitudinal axis is I
0, represented is the sinusoidal waveform of output current.
Embodiment 1 is referring to Fig. 3, three-level resonant transformer in the present embodiment comprises former limit circuit, transformer, secondary circuit, former limit circuit comprises two resonant circuits, two switching circuits, transformer comprises transformer TI, T2, first resonant circuit comprises capacitor C r1, inductance L r1, magnetizing inductance Lm1, connects with inductance L r1, capacitor C r1 after the former limit among the transformer TI and the magnetizing inductance Lm1 parallel connection; Second resonant circuit comprises capacitor C r2, inductance L r2, magnetizing inductance Lm2, connects with inductance L r2, capacitor C s2 after the former limit among the transformer T2 and the magnetizing inductance Lm2 parallel connection; First switching circuit is in series by four switch Q1, Q2, Q3, Q4, second switching circuit is in series by four switch Q5, Q6, Q7, Q8, the input of first, second switching circuit connects different drive circuits respectively, and drive circuit is connected with control circuit; Bleeder circuit comprises dividing potential drop capacitor C 1, the C2 of two series connection, first resonant circuit is connected between the output of the mid point of dividing potential drop electric capacity and first switching circuit, and second resonant circuit is connected between the output of the mid point of dividing potential drop electric capacity and second switching circuit.Secondary circuit comprises the center-tap rectifier circuit be made up of D7, D8, D15, D16, by the filter circuit of capacitor C.The phase difference of described two resonant circuits is 90 °.
Fig. 4 is the sinusoidal waveform figure of the output current of present embodiment.As can be seen from the figure, the converter output current has been realized frequency multiplication, and fluctuation reduces.Can effectively reduce the ripple current that flows through output filter capacitor, improve the useful life of filter capacitor.And, because two transformers are set, thus disperseed the main transformer thermal stress, thus when high power applications, make thermal stress can satisfy the derate requirement.
Embodiment 2
Referring to Fig. 5, the three-level resonant transformer in the present embodiment comprises former limit circuit, and former limit circuit comprises a resonant circuit, a switching circuit, and transformer comprises transformer TI, T2.Resonant circuit comprises capacitor C r1, inductance L r1, magnetizing inductance Lm1, Lm2, former limit among the transformer TI is in parallel with magnetizing inductance Lm1, the former limit among the transformer T2 is in parallel with magnetizing inductance Lm2, connects with two above-mentioned parallel circuitss in inductance L r1, capacitor C r1 series connection back; Switching circuit is in series by four switch Q1, Q2, Q3, Q4, the input drive circuit of switching circuit, and drive circuit is connected with control module; Bleeder circuit comprises dividing potential drop capacitor C 1, the C2 of two series connection, and resonant circuit is connected between the output of the mid point of dividing potential drop electric capacity and switching circuit.The circuit structure of secondary circuit is with embodiment 1.
Present embodiment is owing to be provided with two transformers, thus disperseed the main transformer thermal stress, thus when high power applications, make thermal stress can satisfy the derate requirement.But the described three-level resonant transformer of present embodiment can not be realized the purpose that the output current ripple reduces.
Embodiment 3
Referring to Fig. 6, the three-level resonant transformer in the present embodiment comprises former limit circuit, and former limit circuit comprises two resonant circuits, two switching circuits; Transformer comprises transformer TI, T2, T3, T4.First resonant circuit comprises capacitor C r1, inductance L r1, magnetizing inductance Lm1, Lm2, former limit among the transformer TI is in parallel with magnetizing inductance Lm1, the former limit among the transformer T2 is in parallel with magnetizing inductance Lm2, connects with two above-mentioned parallel circuitss in inductance L r1, capacitor C r1 series connection back; Second resonant circuit comprises capacitor C r2, inductance L r2, magnetizing inductance Lm3, Lm4, former limit among the transformer T3 is in parallel with magnetizing inductance Lm3, the former limit among the transformer T4 is in parallel with magnetizing inductance Lm4, connects with two above-mentioned parallel circuitss in inductance L r2, capacitor C r2 series connection back.First switching circuit is in series by four switch Q1, Q2, Q3, Q4, second switching circuit is in series by four switch Q5, Q6, Q7, Q8, the input of first, second switching circuit connects different drive circuits respectively, and drive circuit is connected with control module; Bleeder circuit comprises dividing potential drop capacitor C 1, the C2 of two series connection, first resonant circuit is connected between the output of the mid point of dividing potential drop electric capacity and first switching circuit, and second resonant circuit is connected between the output of the mid point of dividing potential drop electric capacity and second switching circuit.The rectification circuit that secondary circuit comprises secondary inductance among transformer TI, T2, T3, the T4, be made up of D7, D8, D9, D10, D17, D18, D19, D20, the filter circuit of forming by capacitor C, inductance R.The phase difference of described two resonant circuits is 90 °.
In the present embodiment because four transformers are set, therefore more obvious than among the embodiment 1,2 on the effect of having disperseed the main transformer thermal stress, owing to also be that the phase difference of two resonant circuits is set to 90 °, therefore on flowing through the effect of ripple current of output filter capacitor, reduction is equivalent to embodiment 1.
Above content be in conjunction with concrete preferred implementation to further describing that the present invention did, can not assert that concrete enforcement of the present invention is confined to these explanations.For the general technical staff of the technical field of the invention, without departing from the inventive concept of the premise, can also make some simple deduction or replace, as: resonant circuit can be set to more than two, the rectification circuit of secondary can adopt full-wave rectifying circuit etc.