Abstract
The present invention provides a LLC resonant converter with magnetic-flux balance control circuit. The LLC resonant converter comprises a primary-side circuit and a secondary-side circuit, wherein the control loop of secondary-side circuit comprises a voltage control unit, a digital pulse-width-modulation generation unit, and the control loop of primary-side circuit comprises a DC detection unit, a balance control unit, a digital pulse-width-modulation generation unit.
Claims
1. A LLC resonant converter with magnetic-flux control circuit, comprising: a LLC resonant converter, which includes a primary-side circuit and a secondary-side circuit, wherein the primary-side circuit including a primary-side winding, a resonant inductor, a resonant capacitor, a first switch and a second switch, the secondary-side circuit includes a secondary-side winding, a first diode, a second diode, an output capacitor and an output resistor, the secondary-side winding includes a first secondary-side winding and a second secondary-side winding; a voltage control unit, which being connecting to the secondary-side circuit, the voltage control unit, which being receiving the output voltage, and outputting a control voltage; a digital pulse-width-modulation generation unit, which being connecting to the voltage control unit, the voltage control unit sends the control voltage to the digital pulse-width-modulation generation unit for adjusting and controlling the switching period of the first switch and the second switch; a DC detection unit, which is connecting the primary-side circuit, the DC detection unit detecting the sensed resonant inductor current signal of the primary-side circuit in accordance with the pulse signal generated by the digital pulse-width-modulation generation unit, and calculating the magnetizing inductor average current of a transformer in accordance with the sensed resonant inductor current signal; and a balance control unit, which being connecting to the DC detection unit, wherein, the balance control unit achieving to adjust the transformer magnetizing inductor average current to zero ampere, through adjusting the first switch duty-cycle ratio of the first switch and the second switch duty-cycle ratio of the second switch.
2. The LLC resonant converter with magnetic-flux control circuit according to claim 1, wherein, the LLC resonant converter includes a DC power source, a first switch, a second switch, a resonant inductor, a resonant capacitor, a magnetizing inductor, a first diode, a second diode, an output capacitor, an output resistor and an ideal center-tapped transformer; wherein, the first switch, the second switch, the resonant inductor, the resonant capacitor, the magnetizing inductor, and the output resistor having a first end and a second end, respectively; wherein, the DC power source, the first diode, the second diode, and the output capacitor having a positive end and a negative end, respectively; wherein, the secondary-side winding including a first secondary-side winding and a second secondary-side winding; the primary-side winding, the first secondary-side winding and the second secondary-side winding have a positive end and a negative end, respectively; wherein, the positive end of the DC power source connecting to the first end of the first switch, and the negative end of the DC power source connects to the second end of the second switch; wherein, the second end of the first switch and the first end of the second switch, and the first end of the resonant capacitor being all connected together; wherein, the second end of the resonant capacitor connecting to the first end of the resonant inductor; wherein, the second end of the resonant inductor connecting to the first end of the magnetizing inductor and the positive end of the primary-side winding; wherein, the second end of the magnetizing inductor and the negative end of the primary-side winding, and the second end of the second switch being all connected together; wherein, the positive end of the first secondary-side winding and the negative end of the second secondary-side winding, the positive end of the output capacitor, and the first end of the output resistor being all connected together; wherein, the negative end of the first secondary-side winding connecting the negative end of the first diode; wherein, the positive end of the second secondary-side winding connecting the negative end of the second diode; and wherein, the positive end of the first diode and the positive end of the second diode, the negative end of the output capacitor, and the second end of the output resistor being all connected together.
3. The LLC resonant converter with magnetic-flux control circuit according to claim 1, wherein, the control unit includes a voltage control unit, a balance control unit, a DC detection unit, and a digital pulse-width-modulation generation unit; wherein, the voltage control unit and balance control unit having an input end and an output end, respectively; wherein, the DC detection unit having a first input end, second input end, third input end and one output end; wherein, the digital pulse-width-modulation generation unit having a first input end, a second input end, a first output end, a second output end, a third output end, and a fourth output end; wherein, the first input end of digital pulse-width-modulation generation unit connecting to the output end of the voltage control unit; wherein, the input end of the voltage control unit connecting to the positive end of the output capacitor in the secondary-side circuit of the LLC resonant converter; wherein, the second input end of the digital pulse-width-modulation generation unit connecting to the output end of the balance control unit; wherein, the input end of the balance control unit connecting to the output end of the DC detection unit; wherein, the first output end and second output end of the digital pulse-width-modulation generation unit being the driven signal of the first switch and the second switch, respectively; wherein, the third output end of the digital pulse-width-modulation generation unit being the first pulse signal, which being also the second input end of the DC detection unit; wherein, the fourth output end of the digital pulse-width-modulation generation unit being the second pulse signal, which being also the third inputting end of the DC detection unit; and wherein, the first input end of the DC detection unit being the signal of the sensed resonant inductor current.
4. The LLC resonant converter with magnetic-flux control circuit according to claim 3, wherein, when the LLC resonant converter lying at the region 1 of voltage gain, and when the first switch being conducted, the digital pulse-width-modulation generation unit sending out a first pulse signal without the delay time, in order to obtain a minimum value of the magnetizing inductor current; wherein, when the second switch being conducted, the digital pulse-width-modulation generation unit sending out a second pulse signal without the delay time, in order to obtain a maximum value of the magnetizing inductor current.
5. The LLC resonant converter with magnetic-flux control circuit according to claim 4, wherein, when the LLC resonant converter lying at region 2 of the voltage gain, and when the first switch being conducted, the digital pulse-width-modulation generation unit sending out a first pulse signal with the delay time, in order to obtain a minimum value of the magnetizing inductor current; wherein, when the second switch being conducted, the digital pulse-width-modulation generation unit sending out a second pulse signal with the delay time, in order to obtain a maximum value of the magnetizing inductor current.
6. The LLC resonant converter with magnetic-flux control circuit according to claim 4, wherein, the DC detection unit adding the minimum value of the magnetizing inductor current and the maximum value of the magnetizing inductor current to obtain the average current value, and after adjusted by the balance control unit, the average current value being zero ampere.
7. The LLC resonant converter with magnetic-flux control circuit according to claim 6, wherein, when LLC resonant converter lying at the region 1 of the voltage gain, the digital pulse-width-modulation generation unit sending out a first pulse signal without the delay time, and a second pulse signal without the delay time.
8. The LLC resonant converter with magnetic-flux control circuit according to claim 6, wherein, when LLC resonant converter lying at region 2 of the voltage gain, the digital pulse-width-modulation generation unit sending out a first pulse signal with the delay time, and a second pulse signal with the delay time.
9. The LLC resonant converter with magnetic-flux control circuit according to claim 1, wherein, the sum of the first switch duty-cycle ratio and the second switch duty-cycle ratio is 100%.
10. The LLC resonant converter with magnetic-flux control circuit according to claim 9, wherein, under the balance condition of the LLC resonant converter circuit, wherein the first switch duty-cycle ratio being 50%, and the second switch duty-cycle ratio being also 50%.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
(1) The foregoing aspects and many of the attendant advantages of this invention will become more readily appreciated as the same becomes better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein:
(2) FIG. 1 illustrates the conventional half-bridge LLC resonant converter.
(3) FIG. 2A illustrates the conventional push pull converter.
(4) FIG. 2B illustrates the conventional half-bridge converter.
(5) FIG. 2C illustrates the conventional full-bridge converter.
(6) FIG. 3 illustrates a schematic diagram of the LLC resonant converter with magnetic-flux control circuit for an embodiment of the present invention.
(7) FIG. 4 illustrates an input/output voltage gain characteristic diagram of the LLC resonant converter for an embodiment of the present invention.
(8) FIG. 5A illustrates the waveform diagram under magnetic-flux balance at region 1.
(9) FIG. 5B illustrates the waveform diagram under magnetic-flux unbalance at region 1.
(10) FIG. 6A illustrates the waveform diagram under magnetic-flux balance at region 2.
(11) FIG. 6B illustrates the waveform diagram under magnetic-flux unbalance at region 2.
(12) FIG. 7A illustrates the current waveform time sequence diagram at region 1.
(13) FIG. 7B illustrates the current waveform time sequence diagram at region 2.
(14) FIG. 8A illustrates the full-bridge LLC resonant converter.
(15) FIG. 8B illustrates half-bridge LLC resonant converter with the split capacitor at the input end.
DESCRIPTION OF THE PREFERRED EMBODIMENT
(16) Please refer to FIG. 3, FIG. 3 illustrates a schematic diagram of the LLC resonant converter with magnetic-flux control circuit for an embodiment of the present invention.
(17) Please refer to FIG. 3 again, which illustrates the LLC resonant converter with magnetic-flux control circuit 300, including a LLC resonant converter 302, and a control unit 320. The LLC resonant converter 302 includes a primary-side circuit 3022 and a secondary-side circuit 3024, wherein the primary-side circuit 3022 includes a primary-side winding N.sub.p, a resonant capacitor C.sub.r, a resonant inductor L.sub.r, a magnetizing inductor L.sub.m, a first switch Q.sub.1, a second switch Q.sub.2, and a DC power source V.sub.i. The secondary-side circuit 3024 includes a secondary-side winding N.sub.s, a first diode D.sub.1, a second diode D.sub.2, an output capacitor C.sub.o, and an output resistor R.sub.o. The secondary-side winding N.sub.s includes a first secondary-side winding N.sub.s1 and a second secondary-side winding N.sub.s2. The control unit 320 includes a voltage control unit 304, a digital pulse-width-modulation generation unit 306, a DC detection unit 308, and a balance control unit 310.
(18) Refer to the schematic diagram of the LLC resonant converter with magnetic-flux control circuit for an embodiment of the present invention illustrated in FIG. 3, in the primary-side circuit 3022 of the LLC resonant converter 302, the first switch Q.sub.1, the second switch Q.sub.2, the resonant inductor L.sub.r, the resonant capacitor C.sub.r, and the magnetizing inductor Lm have a first end and a second end, respectively, the primary-side winding N.sub.p and the DC power source V.sub.i have a positive end and a negative end, respectively. The positive end of the DC power source V.sub.i connects to the first end of the first switch Q.sub.1. The negative end of the DC power source V.sub.i connects to the second end of the second switch Q.sub.2. The second end of the first switch Q.sub.1 and the first end of the second switch Q.sub.2, and the first end of the resonant capacitor C.sub.r are all connected together. The second end of the resonant capacitor C.sub.r connects to the first end of the resonant inductor L.sub.r. The second end of the resonant inductor L.sub.r connects to the first end of the magnetizing inductor L.sub.m and the positive end of the primary-side winding N.sub.p. The second end of the magnetizing inductor L.sub.m and the negative end of the primary-side winding N.sub.p and the second end of the second switch Q.sub.2 are all connected together.
(19) Refer to the schematic diagram of the LLC resonant converter with magnetic-flux control circuit for an embodiment of the present invention illustrated in FIG. 3, in the secondary-side circuit 3024 of the LLC resonant converter 302, the output resistor R.sub.o has a first end and a second end. The first secondary-side winding N.sub.s1, the second secondary-side winding N.sub.s2, the first diode D.sub.1, the second diode D.sub.2, and the output capacitor C.sub.o have a positive end and a negative end, respectively. The positive end of the transformer first secondary-side winding N.sub.s1 and the negative end of the second secondary-side winding N.sub.s2, the positive end of the output capacitor C.sub.o, and the first end of the output resistor R.sub.o are all connected together. The negative end of the transformer first secondary-side winding N.sub.s1 connects to the negative end of the first diode D.sub.1. The positive end of the transformer second secondary-side winding N.sub.s2 connects to the negative end of the second diode D.sub.2, the positive end of the first diode D.sub.1 and the positive end of the second diode D.sub.2, the negative end of the output capacitor C.sub.o, and the second end of the output resistor R.sub.o are all connected together.
(20) Refer to the schematic diagram of the LLC resonant converter with magnetic-flux control circuit for an embodiment of the present invention illustrated in FIG. 3 continuously, in the control unit 320, the voltage control unit 304 and the balance control unit 310 have an input end and an output end, respectively. The DC detection unit 308 has a first input end, a second input end, a third input ends and one output end. The digital pulse-width-modulation generation unit 306 has a first input end, a second input end, a first output end, a second output end, a third output end, and a fourth output end. The first input end t.sub.sw of the digital pulse-width-modulation generation unit 306 connects to the output end V.sub.conv of the voltage control unit 304. The input end of the voltage control unit 304 connects to the positive end of the output capacitor C.sub.o in the secondary-side circuit 3024 of the LLC resonant converter 302. The second input end d.sub.Q1(d.sub.Q2) of the digital pulse-width-modulation generation unit 306 connects to the output end V.sub.conb of the balance control unit 310. The first output end V.sub.gs,Q1 and the second output end V.sub.gs,Q2 of the digital pulse-width-modulation generation unit 306 are the driven signal of the first switch Q.sub.1 and the second switch Q.sub.2, respectively. The third output end SOC.sub.i,nd of the digital pulse-width-modulation generation unit 306 is the first pulse signal. The fourth output end SOC.sub.i,pd of the digital pulse-width-modulation generation unit 306 is the second pulse signal. The input end of the balance control unit 310 connects to the output end i.sub.Lm,DC of the DC detection unit 308. The first input end i.sub.Lr,sen of the DC detection unit 308 is the signal of the sensed resonant inductor current i.sub.Lr. The second input end SOC.sub.i,nd of the DC detection unit 308 connects to the third output end of the digital pulse-width-modulation generation unit 306. The third input end SOC.sub.i,pd of the DC detection unit 308 connects to the fourth output end of the digital pulse-width-modulation generation unit 306.
(21) As shown in FIG. 3, the DC detection unit 308 calculates an average magnetizing current value i.sub.Lm,DC through the sensed resonant inductor current signal i.sub.Lr,sen according to the first pulse signal SOC.sub.i,nd and the second pulse signal SOC.sub.i,pd, and adjusted by the balance control unit 310, in order to achieve zero ampere of the DC magnetizing current. The balance control unit 310 achieves to adjust the average magnetizing current value i.sub.Lm,DC to zero ampere, through controlling the first switch duty-cycle ratio d.sub.Q1 of the first switch Q.sub.1 and the second switch duty-cycle ratio d.sub.Q2 of the second switch Q.sub.2. The LLC resonant converter 302 is a half-bridge LLC resonant converter. The sum of the first switch duty-cycle ratio d.sub.Q1 and the second switch duty-cycle ratio d.sub.Q2 is 100%.
(22) As shown in FIG. 4, the input/output voltage gain characteristic diagram of the LLC resonant converter for an embodiment of the present invention is illustrated. The output voltage gain characteristic diagram includes a region 1 and a region 2.
(23) As shown in FIG. 5A, the waveform diagram under the magnetic-flux balance at region 1 is illustrated, the driven waveform V.sub.gs1 of the primary-side first switch Q.sub.1, the driven waveform V.sub.gs2 of the primary-side second switch Q.sub.2, the resonant inductor current i.sub.Lr, the magnetizing inductor current i.sub.Lm, and the current i.sub.D1 of the secondary-side first diode, the current i.sub.D2 of the secondary-side second diode, and the output voltage V.sub.o waveform of serial equivalent resistor of the output capacitor C.sub.o under steady-state balance of region 1 are shown sequentially.
(24) As shown in FIG. 5B, the waveform diagram under magnetic-flux unbalance at region 1 is illustrated. It shows the operation waveform at region 1 under steady-state unbalance. Its unbalance condition is the current i.sub.D1 of the first diode is smaller than the current i.sub.D2 of the second diode. After the current i.sub.D1 of the first diode and the current i.sub.D2 of the second diode are reflected to the primary-side winding N.sub.p through the transformer, which become the positive half cycle and the negative half cycle of the primary-side winding current i.sub.Np, respectively (refer to the LLC resonant converter 302 illustrated in FIG. 3). Because the resonant inductor current i.sub.Lr is distributed to the transformer primary-side winding current i.sub.Np and the magnetizing inductor current i.sub.Lm simultaneously, and because the resonant inductor is connected to the resonant capacitor, the average value of the resonant inductor current i.sub.Lr can be maintained at zero ampere in accordance with the balance characteristics of the capacitor charge, that is the positive half cycle area equals to the negative half cycle area. However, because the positive half cycle and the negative half cycle of transformer primary-side winding current i.sub.Np do not equal, that is the positive half cycle area is smaller than the negative half cycle area (i.sub.D1<i.sub.D2), so that the negative average value is generated. According to the principle of shunting, the direct flow part of the transformer primary-side winding current will flow to the magnetizing inductor L.sub.m, so that the magnetizing current i.sub.Lm will generate the positive average value (i.sub.Lm,DC), which causes the transformer to generate the magnetic-flux shift phenomenon finally, and may cause the generation of saturation phenomenon under serious condition.
(25) As shown in FIG. 6A, the waveform diagram under magnetic-flux balance at region 2 is illustrated. FIG. 6B illustrates the waveform diagram under magnetic-flux unbalance at region 2. As those shown in FIG. 5A and FIG. 5B, the driven waveform V.sub.gs1 of the primary-side first switch Q.sub.1, the driven waveform V.sub.gs2 of the primary-side second switch Q.sub.2, the resonant inductor current i.sub.Lr, the magnetizing inductor current i.sub.Lm, and the current i.sub.D1 of the secondary-side first diode, the current i.sub.D2 of the second diode, and the output voltage V.sub.o waveform of serial equivalent resistor of the output capacitor C.sub.o under steady-state balance of region 2 are shown sequentially. In FIG. 6B, when the unbalance is occurred, assume its unbalance condition is the current i.sub.D1 of the first diode is smaller than the current i.sub.D2 of the second diode. After the current i.sub.D1 of the first diode and the current i.sub.D2 of the second diode are reflected to the primary-side winding N.sub.p through the transformer, which become the positive half cycle and the negative half cycle of the primary-side winding current i.sub.Np, respectively (refer to the LLC resonant converter 302 illustrated in FIG. 3). Because the resonant inductor current i.sub.Lr is distributed to the transformer primary-side winding current i.sub.Np and the magnetizing inductor current i.sub.Lm simultaneously, and because the resonant inductor is connected to the resonant capacitor, the average value of the resonant inductor current i.sub.Lr can be maintained at zero ampere in accordance with the balance characteristics of the capacitor charge, that is the positive half cycle area equals to the negative half cycle area. But because the positive half cycle and the negative half cycle of transformer primary-side winding current i.sub.Np do not equal, that is the positive half cycle area is smaller than the negative half cycle area (i.sub.D1<i.sub.D2), so the negative average value is generated. According to the principle of shunting, the direct flow part of the transformer primary-side winding current will flow to the magnetizing inductor L.sub.m, so that the magnetizing current i.sub.Lm will generate the positive average value (i.sub.Lm,DC), which causes the transformer to generate the magnetic-flux shift phenomenon finally, and may cause the generation of saturation phenomenon under serious condition.
(26) As shown in FIG. 7A, the current waveform time sequence diagram at region 1 is illustrated. When LLC resonant converter 302 lies at the region 1 of voltage gain, input the gate source voltage V.sub.gs1 of the first switch to the first switch Q.sub.1. When the first switch Q.sub.1 is conducted, the digital pulse-width-modulation generation unit 306 sends out a first pulse signal SOC.sub.i,nd, to obtain a minimum value i.sub.Lm,n (that is minimum value of the negative half cycle) of the magnetizing inductor current.
(27) Refer to FIG. 7A, the current waveform time sequence diagram at region 1 is illustrated. Upon inputting the gate source voltage V.sub.gs2 of the second switch to the second switch Q.sub.2, when the second switch Q.sub.2 is conducted, the digital pulse-width-modulation generation unit 306 sends out a second pulse signal SOC.sub.i,pd, to obtain a maximum value i.sub.Lm,p (that is maximum value of the positive half cycle) of the magnetizing inductor current.
(28) As shown in FIG. 7A, in the current waveform time sequence diagram at region 1, the DC detection unit 308 adds the minimum value i.sub.Lm,n of the magnetizing inductor current and the maximum value i.sub.Lm,p of the magnetizing inductor current, in order to obtain an average current value i.sub.Lm,DC of the magnetizing inductor. It is necessary to address that after the average current value i.sub.Lm,DC of the inductor described in this embodiment is controlled, it will become zero ampere.
(29) As shown in FIG. 7B, the current waveform time sequence diagram at region 2 is illustrated. When LLC resonant converter 302 lies at the region 2 of voltage gain, and the first switch Q.sub.1 is conducted, the digital pulse-width-modulation generation unit 306 will delay to send out the first pulse signal SOC.sub.i,nd at t.sub.d,soc of delay time, to obtain a minimum value i.sub.Lm,n of the magnetizing inductor current. When the second switch Q.sub.2 is conducted, the digital pulse-width-modulation generation unit 306 will delay to send out the second pulse signal SOC.sub.i,pd at t.sub.d,soc of delay time, to obtain a maximum value i.sub.Lm,p of the magnetizing inductor current.
(30) As shown in FIG. 7B, in the current waveform time sequence diagram at region 2, the DC detection unit 308 adds the minimum value i.sub.Lm,n of the magnetizing inductor current and the maximum value i.sub.Lm,p of the magnetizing inductor current, in order to obtain an average current value i.sub.Lm,DC of the magnetizing inductor. It is necessary to address that after the average current value i.sub.Lm,DC of the inductor described in this embodiment is controlled, it will become zero ampere.
(31) In addition, the abovementioned embodiment of the present invention except can be applied to the half-bridge LLC resonant converter shown in FIG. 1, it can also be applied to the full-bridge LLC resonant converter shown in FIG. 8A, and the half-bridge LLC resonant converter with the split capacitor at the input end shown in FIG. 8B, and further more can be applied to the LLC resonant converters with other different structures.
(32) The embodiment disclosed in the present invention provides a LLC resonant converter with magnetic-flux control circuit. The LLC resonant converter has the control and estimate mechanism for the transformer magnetic-flux balance. Through lesser sensing elements, cooperate with the estimate method provided by the present invention to detect the DC level of the magnetic-flux and control method, adjust the conduction time of switch, further to improve the magnetic-flux balance effect.
(33) It is understood that various other modifications will be apparent to and can be readily made by those skilled in the art without departing from the scope and spirit of this invention. Accordingly, it is not intended that the scope of the claims appended hereto be limited to the description as set forth herein, but rather that the claims be construed as encompassing all the features of patentable novelty that reside in the present invention, including all features that would be treated as equivalents thereof by those skilled in the art to which this invention pertains.
