Patent Application
20190267901
Conventional LLC resonant converters are so named because they are made up of two inductors (e.g., one resonant inductor and the primary winding of an isolation transformer) and one capacitor. An exemplary LLC resonant converter 100 is illustrated in
LLC resonant converters are sometimes used to convert a fixed/constant high DC input voltage into low DC output voltage. However, there are known drawbacks to this type of converter. For example, in applications where the input voltage (e.g., VDCin) may vary widely, large input voltage ranges can result in corresponding large operating frequency ranges for the switches Qmain and Qaux. This may prove problematic when a very low switching frequency may be required to achieve a high voltage conversion gain when the DC input voltage is low. This reduced switching frequency can cause high magnetizing current, which can substantially increase circulating currents and the associated conduction losses. Additionally, circuit complexity and cost may be increased because of the need for full bridge output rectification, e.g., a center-tapped transformer secondary and two synchronous rectifier switches QSR1 and QSR2 (as shown) or a single secondary winding with a four switch synchronous rectifier (not shown).
Another resonant converter topology is the primary resonant (PR) flyback converter, such as that illustrated in
PR flyback converters may be used in applications requiring a medium power converter with galvanic isolation between the input and output. However, the physical size of the transformer/coupled windings, which is dictated by the energy transfer requirements, may be a drawback in some applications, particularly those in which galvanic isolation between input and output is not required
Thus, there is a need in the art for a power converter that can provide power for medium to high power loads, from a widely varying input voltage, having reduced circuit complexity, cost, size, and component count.
Disclosed herein is a power converter having a resonant circuit, which itself has an input terminal and an output terminal. A main switch may couple the input of the resonant circuit to a DC input voltage of the converter. An auxiliary switch may couple the input of the resonant circuit to ground. The power converter may further have a rectifying component coupled between an output of the resonant circuit and an output of the power converter. The main switch and auxiliary switch may be operated to alternately couple the input of the resonant circuit to the DC input voltage and ground, thereby converting the DC input voltage to an output voltage of the converter. Resonance of the resonant circuit may allow for the main switch and the auxiliary switch to be closed under zero voltage switching conditions.
The resonant circuit may be a series resonant circuit comprising a resonant capacitor, a resonant inductor, and a magnetizing inductor. A first terminal of the resonant capacitor may be the input of the resonant circuit. A junction of the resonant inductor and the magnetizing inductor may be the output of the resonant circuit. The rectifying component may be a diode or a synchronous rectifier. The inductance of the resonant inductor may be much less than the inductance of the magnetizing inductor. The power main switch and the auxiliary switch may be operated at a fixed switching frequency. A duty cycle of the main switch may be increased in response to increased load on the converter.
Also disclosed herein is a wireless power transfer (WPT) circuit having a rectifier configured to receive an AC voltage and convert the received AC voltage to a first DC voltage. The WPT circuit may also include a power converter coupled to the rectifier and configured to convert the first DC voltage to a second DC voltage. The power converter may include a resonant circuit, a main switch configured to selectively couple an input of the resonant circuit and the first DC voltage, an auxiliary switch configured to selectively couple the input of the resonant circuit to ground; and a rectifying component coupled between an output of the resonant circuit and an output of the power converter. The main switch and auxiliary switch may be alternately operated, under zero voltage switching conditions facilitated by resonance of the resonant circuit, to convert the first DC voltage to the second DC voltage. The WPT circuit may also include an inverter coupled to receive the second DC voltage and generate an alternating current voltage delivered to one or more transmitter coils.
Also disclosed herein is a method of operating a power converter having a resonant circuit alternately coupled to a DC input voltage by a main switch and ground by an auxiliary switch. The method can include closing a main switch under zero voltage switching caused by resonance of the resonant circuit, thereby coupling an input of the resonant circuit to the DC input voltage; opening the main switch, thereby allowing the resonant circuit to begin resonating; closing an auxiliary switch under zero voltage switching caused by resonating of the resonant circuit, thereby coupling the resonant circuit to ground; and opening the auxiliary switch, thereby allowing the resonant circuit to continue resonating.
In the following description, for purposes of explanation, numerous specific details are set forth to provide a thorough understanding of the disclosed concepts. As part of this description, some of this disclosure's drawings represent structures and devices in block diagram form for sake of simplicity. In the interest of clarity, not all features of an actual implementation are described in this disclosure. Moreover, the language used in this disclosure has been selected for readability and instructional purposes, has not been selected to delineate or circumscribe the disclosed subject matter. Rather the appended claims are intended for such purpose.
Various embodiments of the disclosed concepts are illustrated by way of example and not by way of limitation in the accompanying drawings in which like references indicate similar elements. For simplicity and clarity of illustration, where appropriate, reference numerals have been repeated among the different figures to indicate corresponding or analogous elements. In addition, numerous specific details are set forth in order to provide a thorough understanding of the implementations described herein. In other instances, methods, procedures and components have not been described in detail so as not to obscure the related relevant function being described. References to “an,” “one,” or “another” embodiment in this disclosure are not necessarily to the same or different embodiment, and they mean at least one. A given figure may be used to illustrate the features of more than one embodiment, or more than one species of the disclosure, and not all elements in the figure may be required for a given embodiment or species. A reference number, when provided in a given drawing, refers to the same element throughout the several drawings, though it may not be repeated in every drawing. The drawings are not to scale unless otherwise indicated, and the proportions of certain parts may be exaggerated to better illustrate details and features of the present disclosure.
Disclosed herein is a forward mode, soft switching, resonant converter. The converter may be operated with a fixed switching frequency to directly convert a high voltage DC input to a low voltage DC output with high efficiency. The disclosed forward mode, soft-switching, resonant converter is a new topology, which incorporates zero voltage switching (ZVS) (for both the primary side control switches and the output side rectification switches) to reduce (i.e., substantially eliminate) switching losses. As a result of the resonant operation and ZVS, high efficiency and high power density can be a achieved in a relatively small form factor. This non-isolated converter may be used in a variety of applications in which it is desirable to get a low DC output voltage from a high DC input voltage with very high efficiency from a simple, low cost circuit. Furthermore, because the disclosed converter's output current is sinusoidal, electromagnetic interference (EMI) may also be substantially reduced.
With respect to the switching operations,
In some embodiments, resonant inductor Lr may be selected to have an inductance value that much less than the inductance of the magnetizing inductance Lm (i.e., Lr<<Lm). For example, in some embodiments the resonant inductor may have an inductance that is between 1/10th and 1/100th the value of the magnetizing inductance, although other ratios could also be used. As a result, the resonant frequency of the Lr/Cr portion of the circuit may be much higher than the Cr/(Lr+Lm) circuit. This allows for a high resonating current, with a sinusoidal waveform, to be delivered to the load through output diode D1, while a relatively lower resonant current flows through the magnetizing inductor. This magnetizing inductance current iLm (discussed below with respect to
Once main switch Qmain is opened, the resonant current 504 follows the current path illustrated in
Once auxiliary switch Qaux is turned on, the resonant operation allows the current through the resonant circuit to reverse, as illustrated by current 505 in
Turning to
In the switching operations described above, because both high voltage switches (i.e., main switch Qmain and auxiliary switch Qaux) are turned on under a zero voltage switching condition, the switching losses for the converter are negligible. Moreover, because output diode D1 operates with zero current switching and has a sinusoidal current waveform, its capacitive losses are also minimal. As a result, the converter described above can operate with a very high efficiency. Additionally, although the high voltage side of the converter described above uses a series resonant circuit, the two primary side switches have their potential voltage stress effectively clamped by DC input voltage.
Current waveform 606 illustrates resonant inductor current iLr, i.e., the current flowing through resonant inductor Lr. As can be seen, beginning at time 603, when main switch Qmain is switched on, the resonant inductor current increases sinusoidally and then begins to decrease. Once resonant inductor current iLr decreases sufficiently that output diode D1 becomes reverse biased, terminating current flow to the load, the current again increases slightly until main switch Qmain is turned off at time 604. Once main switch Qmain is turned off, the current continues to resonate sinusoidally, now with a somewhat lower frequency (as described above). This continues until time 605, when main switch Qmain is turned on again.
Current waveform 607 illustrates the magnetizing current iLm through magnetizing inductor Lm. As can be seen, beginning at time 603, when main switch is turned on, the magnetizing current iLm increase linearly until time 604. At time 604, when main switch Qmain is turned off, magnetizing current iLm, then resonates. As a result of this resonance, the magnetizing current decays sinusoidally (although nearly linearly) until time 605. At time 605, main switch Qmain is turned on again, and magnetizing current iLm then again increases linearly.
Current waveform 608 illustrates the load current iout that flows through output diode D1 to the load. At time 603, load current iout begins increasing sinusoidally from zero. For output diode D1, this is a zero current switching (ZCS), soft start operation. As noted above, resonant operation of the circuit causes the load current iout to rise and then fall back to zero as a result of output diode D1 being reverse biased, resulting in a second zero current switching event for output diode D1. Load current remains at zero until main switch Qmain is turned on again at time 605.
Voltage waveform 609 illustrates the voltage Vx at the junction of main switch Qmain, auxiliary switch Qaux, and the input terminal of resonant capacitor Cr. This voltage goes from approximately zero volts to VDCin at time 603 when main switch Qmain is closed. This voltage remains at approximately VDCin until main switch Qmain is turned off at time 604 and auxiliary switch Qaux is turned on (after a short dead time to prevent shorting the input power source). Voltage Vx then remains at approximately zero volts until main switch Qmain is turned on again at time 605.
The forward mode, soft switching, resonant converter described above may be used in a variety of power conversion applications. One application that may be particularly suitable for use of such converters is wireless power transfer (WPT) circuits. WPT circuits are increasingly adopted for charging of portable electronic devices such as smartphones, tablet computers, laptop computers, etc. WPT implementations may have a variety of operating constraints that may lend themselves to use of converters like that described herein. For example, WPT circuits are beginning to be used in moderate to high power applications, for example, ranging from 60 to 70 watts. Additionally, WPT circuits may be used in applications in which the input voltage can vary widely, e.g., from 90V to 265V. This may correspond to DC voltage variations from 90V to 375V. It is desirable for such circuits to operate as efficiently as possible, which may be achieved by achieving soft switching across the entire range of operating voltages as described above. Additionally, because a WPT circuit relies on inductive coupling between the transmitter coil and receiver coil, such circuits may be constructed without their own source of galvanic isolation.
An exemplary wireless power transfer circuit 700 incorporating a forward mode soft switching resonant converter is illustrated in
More specifically, the output voltage sensed by output voltage sensor 804 acts as a feedback signal, which is compared to a reference voltage 805 by summer 806. The resulting error signal (i.e., the reference voltage minus the output voltage) is input into a control loop 807, which may be, for example, a proportional-integral-derivative control loop, although other control methodologies could also be used. The output of control loop 807 is input into comparator 808, which also receives a current signal from current sensor 803. Once the current through resonant inductor (sensed by current sensor 803) reaches a predetermined value, or once the output voltage (sensed by output voltage sensor 804) exceeds the reference 805, the output of comparator 808 transitions high. The output of comparator 808 is fed into OR gate 809 and a high output results in a reset of flip flop 812. This triggers gate drive 802 to open main switch Qmain.
Concurrently, the current through series inductor Lr, sensed by current sensor 803 is input into comparator 811. Comparator 811 compares the sensed current to an overcurrent protection reference value 810. The output of comparator 811 is coupled to OR gate 809, discussed above with respect to the voltage control loop. If the current through series inductor Lr exceeds the overcurrent protection threshold, then the output of comparator 811 transitions high. This triggers a reset of flip flop 812, which, in turn, causes gate drive 802 to open main switch Qmain.
Flip flop 812 may be an S-R type flip flop, which has its S or “set” input coupled to a clock 813 that determines the switching frequency of the converter. A high input from clock 813 on the S terminal of flip flop 812 will cause flip flop output Q to transition high, closing main switch Qmain, as described further below. The R or “reset” input of flip flop 812 may receive the signal from OR gate 809 discussed above, which triggers opening of the main switch Qmain. As described above, a high input at the R terminal (from OR gate 809) will reset the flip flop, causing flip flop output Q to transition low, opening main switch Qmain, as described further below. The Q or “output” terminal of flip flop 812 may be coupled to gate drive 802. Gate drive 802 may be configured to close main switch Qmain (and open auxiliary switch Qaux) when it receives a high input and to open main switch Qmain (and close auxiliary switch Qaux) when it receives a low input. In both cases, gate drive circuit 802 may implement a suitable short delay between opening one switch and closing the other to prevent cross, conduction, which would short out the input power source.
Then, the output voltage may be compared to the reference voltage (902, 904). If the output voltage is greater than the reference voltage, the main switch duty cycle may be reduced (903). If the output voltage is less than the reference voltage, the main switch duty cycle may be increased (905). Otherwise, the main switch duty cycle may be kept constant (906).
After a suitable delay time (907) to prevent cross conduction of the main and auxiliary switches, the auxiliary switch control cycle (908) may be commenced. Closing and opening of the auxiliary switch may be as described above with respect to
Described above are various features and embodiments relating to forward mode, soft switching, resonant converters. Such converters may be used in a variety of applications, but may be particular advantageous when used in conjunction with wireless power transmission systems and/or other power adapter solutions for use in conjunction with portable electronic devices such as mobile telephones, smart phones, tablet computers, laptop computers, media players, and the like, as well as the peripherals associated therewith. Such associated peripherals can include input devices (such as keyboards, mice, touchpads, tablets, microphones and the like), output devices (such as headphones or speakers), combination input/output devices (such as combined headphones and microphones), storage devices, or any other peripheral.
Additionally, although numerous specific features and various embodiments have been described, it is to be understood that, unless otherwise noted as being mutually exclusive, the various features and embodiments may be combined in any of the various permutations in a particular implementation. Thus, the various embodiments described above are provided by way of illustration only and should not be constructed to limit the scope of the disclosure. Various modifications and changes can be made to the principles and embodiments herein without departing from the scope of the disclosure and without departing from the scope of the claims.
| Number | Date | Country | |
|---|---|---|---|
| 62635853 | Feb 2018 | US |
