This application claims the priority to and the benefit of Chinese Patent Application No. 201310164929.3, filed May 7, 2013 and entitled “bi-directional DC-DC converter” which is incorporated herein by reference in its entirety.
The present disclosure relates generally to a converter, and particularly to a bidirectional DC-DC (direct current-direct current) converter.
Isolated bi-directional DC-DC converters have important applications in electronic devices with energy-storage batteries, and so on, and play a role of bridge in exchanging energy between the batteries and DC buses. There are some technical problems in the applications of a low-voltage side current-fed and high-voltage side voltage-fed isolated bi-directional DC-DC converter.
For example, in an application of using a battery as backup power, since the battery voltage is generally lower than a DC bus voltage, the bi-directional DC-DC converter functions as charging and discharging the battery. In comparison with a non-isolated bi-directional DC-DC converter, the isolated bi-directional DC-DC converter can achieve an electrical isolation, and also can achieve a higher transformation ratio. K. Wang, C. Y. Lin et al. disclosed a low-voltage side current-fed and high-voltage side voltage-fed bi-directional DC-DC converter with active clamp (see “Bidirectional DC to DC converters for fuel cell systems”, Power Electronics in Transportation, 1998, pp. 47-51), which achieves voltage clamping and soft switching of some switching components by the operation of the active-clamp switching components in corporation with the switching components in the bridge arms.
However, such switching components for achieving the soft-switching operation depend highly on the active-clamp switching components, and the active-clamp switching components per se are hard switching, which additionally increases current of switching components in the bridge arms. As an improvement, Tsai-Fu Wu, Yung-Chu Chen, et al. proposed an isolated bi-directional DC-DC converter (see “Isolated bidirectional full-bridge DC-DC converter with a flyback snubber”, Power Electronics, IEEE Transactions on, vol. 25, pp. 1915-1922, 2010), in which the converter achieves the soft switching by using a flyback snubber in corporation with leakage inductances in a transformer. Although this snubber is independent from a power circuit and the clamping voltage can be set, it is required to use leakage inductances in transformer to achieve the soft switching of the switching components in the bridge arms, which may affect transfer efficiency of the transformer to a certain extent.
To solve the above-mentioned problems, an object of the present disclosure is to provide a bi-directional DC-DC converter which, in part, may improve efficiency of the transformer while achieving soft switching of the switching components therein.
In one aspect, the bi-directional DC-DC converter of the present disclosure comprises: a primary-side inverting/rectifying module, two terminals of the primary-side inverting/rectifying module at a primary side being coupled to a first DC port, for receiving a DC power from the first DC port or outputting a DC power to the first DC port; an isolated transformer, comprising a primary winding and a secondary winding, two terminals of the primary winding being respectively coupled to two terminals of the primary-side inverting/rectifying module at a secondary side; a secondary-side rectifying/inverting module, comprising at least a switching component, wherein two terminals of the secondary-side rectifying/inverting module at the primary side are respectively coupled to two terminals of the secondary winding and two terminals of the secondary-side rectifying/inverting module at the secondary side are respectively coupled to a second DC port, and the secondary-side rectifying/inverting module rectifying energy from the isolated transformer and outputting the rectified current to the second DC port, or receiving a DC power from the second DC port; wherein the primary-side inverting/rectifying module comprises a first bridge arm composed of a first switching component and a second switching component connected in series and a clamping circuit comprising a resonant inductor and a clamping bridge arm composed of a first semiconductor component and a second semiconductor component connected in series, and two terminals of the resonant inductor are respectively coupled to a common node of the first switching component and the second switching component and a common node of the first semiconductor component and the second semiconductor component.
The topology with bi-directional energy transfer proposed by the present disclosure can achieve the soft switching of the switching components in the bridge arms by employing an additional resonant inductor and a clamping diode, and not relying on leakage inductances in the transformer, which enables the leakage inductances in transformer to be designed to a minimum and facilitates to improve efficiency of transformer. Furthermore, voltage in the bridge arms may be effectively clamped by using the clamping diode in the present disclosure, and voltage spikes may be confined.
These and other aspects of the present disclosure will become apparent from the following description of the preferred embodiment taken in conjunction with the following drawings, although variations and modifications therein may be effected without departing from the spirit and scope of the novel concepts of the disclosure.
The foregoing summary is not intended to summarize each potential embodiment or every aspect of the present disclosure.
The accompanying drawings illustrate one or more embodiments of the disclosure and together with the written description, serve to explain the principles of the disclosure. Wherever possible, the same reference numbers are used throughout the drawings to refer to the same or like elements of an embodiment, and wherein:
Specific embodiments in this disclosure have been shown by way of example in the foregoing drawings and are hereinafter described in detail. The figures and written description are not intended to limit the scope of the inventive concepts in any manner. Rather, they are provided to illustrate the inventive concepts to a person skilled in the art by reference to particular embodiments.
Hereinafter, the embodiments of the present disclosure are described in detail. It should be noted that the embodiments are only illustrative, not limit the present disclosure.
The present disclosure will now be described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments of the disclosure are shown. This disclosure may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art. Like reference numerals refer to like elements throughout.
The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the disclosure. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” or “includes” and/or “including” or “has” and/or “having” when used herein, specify the presence of stated features, regions, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, regions, integers, steps, operations, elements, components, and/or groups thereof.
Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and the present disclosure, and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.
A bi-directional DC-DC converter provided by the present disclosure has a topology as shown in
Two terminals of the primary-side inverting/rectifying module 2 at the primary side are coupled to a first DC voltage source located at the primary-side DC port 1, and are used to receive a direct current (DC) power from the primary-side DC port 1 or output a DC power to the primary-side DC port 1.
The isolated transformer 3 includes a primary winding and a secondary winding, and two terminals of the primary winding are respectively coupled to two terminals of the primary-side inverting/rectifying module 2 at the secondary side.
The secondary-side rectifying/inverting module 4 includes at least a switching component. Two terminals of the secondary-side rectifying/inverting module 4 at the primary side are respectively coupled to two terminals of the secondary winding of the isolated transformer 3, and two terminals of the secondary-side rectifying/inverting module 4 at the secondary side are coupled to the secondary-side DC port 6. The secondary-side rectifying/inverting module 4 rectifies energy from the isolated transformer 3 and outputs the rectified current to a second DC voltage source located at the secondary-side DC port 6, or receives a DC power from the second DC voltage source at the secondary-side DC port 6. As shown in
In particularly, the primary-side inverting/rectifying module 2 includes a first bridge arm composed of two switching components connected in series and a clamping circuit. The clamping circuit includes a resonant inductor and a clamping bridge arm composed of two clamping switching components connected in series, wherein one terminal of the resonant inductor is connected to a midpoint of the clamping bridge arm, and the other terminal of the resonant inductor is connected to a midpoint of the first bridge arm.
The secondary-side rectifying/inverting module 4 includes a full-bridge bi-directional rectifier bridge including two bridge arms, each of which is composed of switching components connected in series. Those skilled in the art should understand that the secondary-side rectifying/inverting module may also include other types of bi-directional rectifier bridge structure, such as a bi-directional rectifier bridge with push-pull structure or full-wave structure, according to particular applications.
The bi-directional DC-DC converter of the present disclosure may operate in one of the following two states: in a first state, energy is transferred from the primary side to the secondary side; and in a second state, energy is transferred from the secondary side to the primary side.
When the bi-directional DC-DC converter operates in the first state, the primary side inverting/rectifying module 2 receives and inverts energy from the primary-side DC port 1 (i.e., DC-AC), then the isolated transformer 3 transfers the inverted energy from the primary side to the secondary side, and thereafter, the secondary-side rectifying/inverting module 4 rectifies and filters energy received from the isolated transformer 3 (AC-DC), so as to generate a DC output at the secondary-side DC port 6.
When the bi-directional DC-DC converter operates in the second state, energy from the secondary-side DC port 6 is transferred to the secondary-side rectifying/inverting module 4, the secondary-side rectifying/inverting module 4 inverts the received energy (i.e., DC-AC), and the inverted energy is then transferred from the secondary side to the primary side by the isolated transformer 3, and rectified by the primary-side inverting/rectifying module 2 so as to generate a DC output at the primary-side DC port 1.
A driving signal can be separately applied to the primary side or the secondary side of the bi-directional DC-DC converter in order to achieve bi-directional transfer of energy. For example, when energy is transferred from the primary side to the secondary side, a control circuit may only output a driving signal to the switching components at the primary side; and when energy is transferred from the secondary side to the primary side, the control circuit may only output a driving signal to the switching components at the secondary side.
Additionally, when the bi-directional DC-DC converter switches between the two states, in order to quickly switch the transfer direction of energy in the converter, the driving signal may be applied to the switching components both at the primary side and at the secondary side simultaneously.
Therefore, the bi-directional DC-DC converter of the present disclosure further includes a control circuit for generating a driving signal to the switching components in the primary-side inverting/rectifying module and the secondary-side rectifying/inverting module. In one embodiment, the control circuit may output the driving signal in real time to the primary-side inverting/rectifying module and the secondary-side rectifying/inverting module according to the DC signal in the converter so that the converter outputs an appropriate DC power.
Hereafter, a first embodiment of the present disclosure will be described with reference to
In the first embodiment of the present disclosure, the bi-directional DC-DC converter includes a primary-side DC port 1, a primary-side inverting/rectifying module 2, an isolated transformer 3, a secondary-side rectifying/inverting module 4, and a secondary-side DC port 6.
As shown in
In this embodiment, although the semiconductor devices Dr1 and Dr2 connected in series are implemented by diodes, it should be understood that the present disclosure is not limited to this, and the semiconductor devices Dr1 and Dr2 may be other types of switching components, such as MOSFET and IGBT.
In addition, the primary-side inverting/rectifying module 2 further includes a second bridge arm composed of switching components S3 and S4 connected in series. The second bridge arm, the first bridge arm, and the clamping bridge arm are connected in parallel with the primary-side DC port 1, so as to achieve the inverting/rectifying function at the primary side.
The isolated transformer is a transformer T including a primary-side winding (that is, a primary winding) and a secondary-side winding (that is, a secondary winding), and the turn ratio of the primary winding to the secondary winding is Np:Ns, and may be determined according to a step-up ratio or a step-down ratio. Two terminals of the primary winding of the transformer T are respectively connected to a midpoint B (i.e. a common node B of the switching component S3 and S4) of the second bridge arm and the midpoint C of the clamping bridge arm. The secondary winding of the transformer T is connected to the secondary-side rectifying/inverting module 4.
In this embodiment, the secondary-side rectifying/inverting module 4 includes a bi-directional full-bridge rectifier bridge including two bridge arms connected in parallel, each of which is respectively composed of switching components S5, S6 connected in series and S7, S8 connected in series, and two terminals of the secondary winding in the transformer T are respectively connected to midpoints D and E of the two bridge arms. Those skilled in the art should understand that the secondary-side rectifying/inverting module may also include other types of bi-directional rectifier bridge structure, such as a bi-directional rectifier with a push-pull structure or a full-wave structure, according to particular applications.
Considering leakage inductances existing in an actual transformer (although the topology of the present disclosure may reduce the leakage inductances of the transformer as much as possible, there still exist relatively small leakage inductances), the secondary-side rectifying/inverting module further includes a voltage-clamping circuit which is connected in parallel with the secondary-side rectifying/inverting module to absorb voltage spike across the switching components in the secondary-side rectifying/inverting module. The voltage-clamping circuit at the secondary side may be implemented in various manners, for example, may employ a RCD clamping circuit with a simple structure.
Further, the bi-directional DC-DC converter of the present disclosure may also include a filtering inductor Lf at the secondary side which is connected in series with the secondary-side rectifying/inverting module and coupled to a DC capacitor CB at the secondary side so as to filter the current rectified by the secondary-side rectifying/inverting module.
In addition, taking magnetic bias into account, a blocking capacitor is serially connected to the transformer windings at the high-voltage side, for example, a blocking capacitor is serially connected at a connection between the transformer T and a node B or a node C. For ease of description, the magnetic bias and the leakage inductances of the transformer will not be considered in the analysis of the specific operating states described later.
Further, backward diodes (anti-parallel diodes) and capacitors are connected in parallel with the switching components as shown in
In the present disclosure, the primary-side DC port may be a high-voltage port or a low-voltage port with respect to the secondary-side DC port, that is, the bi-directional DC-DC converter of the present disclosure may be a boost converter or a buck converter. For example, in the case of a battery application where the battery voltage is relatively low and the battery has some limitation to a current ripple, if the battery is located at the secondary-side DC port, the primary-side DC port is a high-voltage port and the secondary-side DC port is a low-voltage port.
As shown in
In one embodiment, the control circuit 7 may output a driving signal in real time to the primary-side inverting/rectifying module and the secondary-side rectifying/inverting module according to a DC signal in the converter, so as to perform energy transfer and conversion according to requirements. For example, the control circuit 7 controls transfer direction of energy, especially transfer direction of energy in a stable state, by controlling certain signals (e.g., current direction of a filtering inductor 5 shown in
In this embodiment, the sampling module samples a DC signal (a current signal or a voltage signal) in the converter circuit, and transmits the sampled signal to the control module. Then the control module processes the sampled signal to generate a corresponding control signal, and outputs the control signal to the driving module. Afterwards, the driving module outputs a corresponding driving signal to respective switching components at the primary side and the secondary side according to the control signal generated by the control module. For example, when energy is transferred from the primary side to the secondary side, the driving module may output a high-frequency driving signal to switching components at the primary side and output a constant low-level driving signal to switching components at the secondary side, according to the control signal generated by the control module. When energy is transferred from the secondary side to the primary side, the driving module may output a high-frequency driving signal to switching components at the secondary side and output a constant low-level driving signal to switching components at the primary side, according to the control signal generated by the control module. Of course, if the converter continues to switch between two states of energy transfer, in order to quicken this switching, the driving module may simultaneously output a high-frequency driving signal to the switching components both in the primary-side inverting/rectifying module and in the secondary-side rectifying/inverting module.
The control circuit 7 performs a control according to the desired control target. For example, when it is required to transfer energy to the secondary side, i.e., transfer the energy from the primary side to the secondary side, a signal (for example, an output voltage signal or current signal) at the secondary-side output port may be sampled so as to perform the control, typically according to energy transfer mode of a load connected at the secondary-side output port.
For example, if the load connected at the secondary side is a battery in a constant-current charging state, the current in the battery is used as the sampling target, which will be sampled by the sampling module and outputted to the control module. As shown in
Similarly, when it is required to transfer energy from the secondary side to the primary side, i.e., the energy flows from the secondary side to the primary side, the control to the transfer direction of energy is described by taking a battery connected to the secondary-side DC terminal as an example as well. When the battery at the secondary side operates in the constant-current state, the direction of energy transfer is controlled by setting current direction of the battery, for example, setting current direction of the filtering inductor Lf. When the battery operates in the constant-voltage state, the current direction of the battery may be determined by setting a desired battery voltage value. For example, when the desired battery voltage value is larger than the current voltage of the battery, the battery at the secondary side is in a charge state, which indicates that energy flows from the primary side to the secondary side. On the contrary, when the desired battery voltage value is smaller than the current voltage of the battery, the battery at the secondary side is in a discharge state, which indicates that energy flows from the secondary side to the primary side.
The operating states of the circuit shown in
(1) an Example of Applying a High-Frequency Switching Signal to a Single Side
Assuming that the primary side is a high-voltage side and the secondary side is a low-voltage side, operation states of the circuit will be described in the case of applying a high-frequency switching signal to a single side. When energy is transferred from the high-voltage side to the low-voltage side, a high-frequency switching signals is only applied to the switching components S1 to S4 at the primary side, and the switching components S5 to S8 at the secondary side are always in an off state due to the application of low-level switching signals. When energy is transferred from the low-voltage side to the high-voltage side, a high-frequency switching signal is only applied to the switching components S5 to S8 at the secondary side, and the switching components S1 to S4 are always in an off state due to the application of low-level switching signals. Hereafter, different switching states in the different transfer direction of energy will be analyzed in detail in the case of applying high-frequency switching signals to a single side.
High-Voltage Side→Low-Voltage Side:
In vertical axis of
Seen from
In addition, further seen from
With reference to
Switching state 1 [before t0] (referring to
As shown in
Switching state 2 [t0˜t1] (referring to
As shown in
Switching state 3 [t1˜t2] (referring to
As shown in
Switching state 4 [t2˜t3] (referring to
As shown in
Switching state 5 [t3˜t4] (referring to
As shown in
Switching state 6 [t4˜t5] (referring to
As shown in
Switching state 7 [t5˜t6] (referring to
As shown in
Switching state 8 [t6˜t7] (referring to
As shown in
Switching state 9 [t7˜t8] (referring to
As shown in
Switching state 10 [t8˜t9] (referring to
As shown in
Low-Voltage Side→High-Voltage Side:
Switching state 1 [before t0] (referring to
As shown in
Switching state 2 [t0˜t1] (referring to
As shown in
Switching state 3 [t1˜t2] (referring to
As shown in
Switching state 4 [t2˜t3] (referring to
As shown in
(2) an Example of Applying the Switching Signal to Two Sides
The situation where the high-frequency switching signal is simultaneously applied to two side of the converter, that is, the high-frequency switching signal is simultaneously applied to the switching components S1˜S8, will be described hereafter. The specific analysis of different switching states in a case of different transfer directions of energy will be given below.
High-Voltage Side→Low-Voltage Side:
Switching state 1 [before t0] (referring to
As shown in
Switching state 2 [t0˜t1] (referring to
As shown in
Switching state 3 [t1˜t2] (referring to
As shown in
Switching state 4 [t2˜t3] (referring to
As shown in
Switching state 5 [t3˜t4] (referring to
As shown in
Switching state 6 [t4˜t5] (referring to
As shown in
Switching state 7 [t5˜t6] (referring to
As shown in
Switching state 8 [t6˜t7] (referring to
As shown in
Switching state 9 [t7˜t8] (referring to
As shown in
Switching state 10 [t8˜t9] (referring to
Low-Voltage Side→High-Voltage Side:
Switching state 1 [before t0] (referring to
As shown in
Switching state 2 [t0˜t1] (referring to
As shown in
Switching state 3 [t1˜t2] (referring to
As shown in
Switching state 4 [t2˜t3] (referring to
As shown in
Switching state 5 [t3˜t4] (referring to
As shown in
Switching state 6 [t4˜t5] (referring to
As shown in
Switching state 7 [t5˜t6] (referring to
As shown in
From the above analysis of the operation states of the bi-directional DC-DC converter in the case of applying the high-frequency driving signal to a single side or two sides of the converter, the circuit topology of the present disclosure can achieve the soft switching (that is, zero-voltage or zero-current on and off) of the switching components, especially the switching components at the primary side, in the bidirectional DC-DC converter, thereby protecting the switching components and enables the leakage inductance of the transformer to be designed very small, which is conducive to improve transfer efficiency of the transformer and thus improve the total transfer efficiency of energy in the bi-directional DC-DC converter.
In the first embodiment, the operation states of the circuit topology in which two terminals of the isolated transformer at the primary side are connected to the lagging leg (that is, the first bridge arm composed of the switching components S1 and S2 in the primary-side inverting/rectifying module) has been described. In the second embodiment of the present disclosure, the isolated transformer may be connected to a leading leg, as shown in
High-Voltage Side→Low-Voltage Side:
Switching state 1 [before t0]
Before the time of t0, the switching components S1 and S3 are turned on, the current through the resonant inductor Lr flows through the diode D1 and the switching component S3, and the difference between the current through the resonant inductor Lr and the current through the transformer flows through the clamping diode Dr1.
Switching state 2 [t0˜t1]
At the time of t0, the switching component S3 is turned off, the resonant inductor Lr charges the capacitor C3, and the capacitor C4 is discharged.
Switching state 3 [t1˜t2]
At the time of t1, the capacitors C3 and C4 are completely charged and discharged respectively, the current through the resonant inductor Lr is transferred to the diode D4, the DC voltage at the high-voltage side is applied to two terminals of the resonant inductor Lr, and the current through the resonant inductor Lr declines linearly. During this period, the switching component S4 is zero-voltage turned on.
Switching state 4 [t2˜t3]
At the time of t2, the current through the resonant inductor Lr drops to zero, and then increases reversely and linearly.
Switching state 5 [t3˜t4]
At the time of t3, the current through the resonant inductor Lr increases to a current at high-voltage side commuted according to the current through the filtering inductor Lf, and the capacitors C6 and C7 are charged.
Switching state 6 [t4˜t5]
At the time of t4, the capacitors C6 and C7 are completely charged, the current ip is equal to a current commuted according to the current through the filtering inductor Lf, and the difference between the current through the resonant inductor Lr and the current through the transformer flows through the clamping diode Dr2.
Switching state 7 [t5˜t6]
At the time of t5, the current ip increases to be equal to the current through the resonant inductor Lr, and the clamping diode Dr2 is off.
Switching state 8 [t6˜t7]
At the time of t6, the switching component S1 is turned off, the capacitor C1 is charged, the capacitor C2 is discharged, the current ip drops, the clamping diode Dr2 is on, and the capacitors C6 and C7 are discharged.
Switching state 9 [t7˜t8]
At the time of t7, the capacitor C1 is completely charged, and the capacitors C2, C6, and C7 are completely discharged.
Low-Voltage Side→High-Voltage Side:
Switching state 1 [before t0]
Before the time of t0, the switching components S1 and S3 are turned on, and the current through the resonant inductor Lr flows through the diode D1 and the switching component S3.
Switching state 2 [t0˜t1]
At the time of t0, the switching components S6 and S7 are turned off, the capacitors C6 and C7 are charged, and the current through the resonant inductor Lr increases.
Switching state 3 [t1˜t2]
At the time of t1, the capacitors C6 and C7 are charged such that the voltage across the capacitors C6 and C7 are equivalent to the voltage across the DC port at high-voltage side, the clamping diode Dr2 is on, and the current through the transformer is equal to a current at the high-voltage side commuted according to the current through the filtering inductor Lf. The switching component S3 is turned off, the capacitor C3 is charged, and the capacitor C4 is discharged. The current through the clamping diode Dr2 is a difference between the current through the transformer and the current through the resonant inductor Lr.
Switching state 4 [t2˜t3]
At the time of t2, the capacitor C3 is completely charged and the capacitor C4 is completely discharged, and the current through the resonant inductor Lr flows into the diode D4. Thereafter, the switching component S4 may be zero-voltage turned on.
Switching state 5 [t3˜t4]
At the time of t3, the current ip through the transformer drops to be equal to the current through the resonant inductor Lr, and the clamping diode Dr2 is off. During this period, the switching component S1 can be zero-voltage turned off.
Switching state 6 [t4˜t5]
At the time of t4, the switching components S6 and S7 are turned on, the voltage of the transformer at the high-voltage side is applied to two terminals of the resonant inductor Lr, and the current through the resonant inductor Lr declines linearly.
Switching state 7 [t5˜t6]
At the time of t5, the current through the resonant inductor Lr drops to zero, the capacitor C1 is charged, and the capacitor C2 is discharged.
Switching state 8 [t6˜t7]
At the time of t6, the capacitor C1 is completely charged and C2 is completely discharged.
Since the main circuit topology in this embodiment is substantially the same as that in the first embodiment, the description in detail will be omitted. Likewise, in this embodiment, a separate resonant inductor is provided and used in conjunction with a clamping circuit, thereby protecting switching components and enabling the leakage inductor of the transformer to be designed to a minimum. Thus, the transfer efficiency of the transformer can be improved and the total transfer efficiency of energy in the bi-directional DC-DC converter can be further improved.
Similarly, since the main circuit topology in this embodiment is substantially the same as that in the first embodiment, the description in detail will be omitted. Likewise, in this embodiment, a separate resonant inductor is provided and used in conjunction with a clamping circuit, thereby protecting switching components and enabling the leakage inductor of the transformer to be designed to a minimum. Thus, the transfer efficiency of the transformer can be improved and the total transfer efficiency of energy in the bi-directional DC-DC converter can be further improved.
The embodiments were chosen and described in order to explain the principles of the disclosure and their practical applications so as to activate others skilled in the art to utilize the disclosure and various embodiments and with various modifications as are suited to the particular use contemplated. Alternative embodiments will become apparent to those skilled in the art to which the present disclosure pertains without departing from its spirit and scope. Accordingly, the scope of the present disclosure is defined by the appended claims rather than the foregoing description and the exemplary embodiments described therein.
Number | Date | Country | Kind |
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201310164929.3 | May 2013 | CN | national |