Patent Application
20110249474
1. Field of the Invention
Embodiments of the present invention generally relate to power conversion and, more particularly, to a method and apparatus for performing power conversion using an interleaved flyback converter with alternating master and slave branches.
2. Description of the Related Art
A number of pulse width modulated DC-to-DC converter topologies are available in the power electronics for performing DC-to-DC conversion. Such converters employ a flyback converter topology which is used in instances that require electrical isolation, voltage boost-up, and high efficiency. A flyback converter topology consists of a transformer, a switch (usually a MOSFET transistor) and a diode. Typically, the switch is in series with the primary winding of the transformer and the secondary winding the transformer is serially coupled through the diode to a load. By switching a current through the primary coil, the DC voltage applied across the primary coil and switch is “boosted” to a higher voltage level at the load.
In order to double the output power available from a typical DC-to-DC converter, two flyback converters may be connected in parallel and operated in an interleaved fashion. Each of the flyback converters forms a “branch” of the overall DC-to-DC conversion process. Each branch is activated independently and in an interleaved manner. To facilitate a balanced operation such that the power is accurately converted from the input DC to the DC applied to the load, each branch must be “matched”.
However, with the activation of 2 branches, the power consumption increases and degrades the efficiency. One method to reduce power consumption is using the 2 branches as master and slave branch. The master branch is always on, while the slave branch is off when the power is below a threshold level. However, this method may cause the different operation in master and slave branch. This difference causes the mismatch and related issues, such as temperature difference, different device degradation, etc. Also as the master branch is always on, reliability and lifetime of the converter is constricted by the master branch.
Therefore, there is a need in the art for a method and apparatus to improve power conversion efficiency and reliability for interleaved flyback converter.
Embodiments of the present invention generally relate to a method and apparatus for converting DC input power to DC output power, specifically to an interleaved flyback converter with alternating master and slave branches. The apparatus comprises a plurality of parallel connected flyback circuits. A controller is coupled to the switches within the flyback circuits to turn-on and turn-off the plurality of flyback circuits, so that slave circuit only turn-on when the power is higher than a threshold value, while the master circuit is on at any power value. Meanwhile, the master and slave circuit are alternating to even the usage of the circuits, so that the performance and reliability of the converter is improved.
So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.
The topology provided by the subject invention solves many of the problems associated with, and has many advantages over, the prior art topologies. The present invention device is unique when compared with other known devices and solutions because the present invention provides: an interleaved flyback converter with alternating master and slave branches. The apparatus comprises a plurality of parallel connected flyback circuits; a controller is coupled to the switches within the flyback circuits to turn-on and turn-off the plurality of flyback circuits; a current monitor element at the output connected to the controller; a voltage monitor element connected to the controller; based on monitored current and voltage the controller controls the operation of flyback circuit; slave circuit only turn-on when the power is higher than a threshold value; the master and slave circuits are alternating to even the usage of the circuits.
While the present invention is hereafter described in terms of an interleaved flyback converter, one skilled in the art will recognize that the power element can possess multiple functionalities without departing from the spirit of the invention. Specific embodiments of the present invention are hereafter described in detail with reference to the accompanying Figures. Like elements in the various Figures are identified by like reference numerals for consistency. Although the invention has been described and illustrated with a certain degree of particularity, it is understood that the present disclosure has been made only by way of example and that numerous changes in the combination and arrangement of parts can be resorted to by those skilled in the art without departing from the spirit and scope of the invention.
The DC-to-DC converter 100 converts DC voltage from a DC source 101 to a DC voltage at output 102. The DC source 101 may be photo voltaic (PV) panels or some other source of DC power. The output 102 may be connected to a device that uses the DC power, including a DC-to-AC converter. The DC-to-DC converter 100 (an interleaved flyback converter) comprises an input capacitor 103 that is used for storing energy to facilitate an accurate DC-to-DC conversion process and a plurality of flyback circuits, such as first flyback circuit 105 and a second flyback circuit 106. The flyback circuits are arranged in a parallel manner with respect to the input DC source 101 and output 102.
The flyback circuits 105 and 106 are identical and termed “branch”. The flyback circuit 105 comprises a transformer T1 and a switch Q1 and a diode D1. The primary coil of the transformer T1 is coupled in series to the switch Q1. The secondary coil of the transformer T is coupled through diode D1 to output 102. In one embodiment, the switch Q1 uses a field effect transistor (FET). The drain of the transistor Q1 is coupled to ground as well as to one terminal of the DC source 101, and the source of the transistor Q1 is coupled to the primary coil of the transformer T1. The capacitor 103 is coupled across the input to the flyback circuit 105 such that one terminal of the capacitor 103 is coupled to one terminal of the primary coil of the transistor T1, and the second terminal of the capacitor 103 is coupled to the drain of the transistor Q1. The gate of the transistor is coupled to the controller 110 at the output of G1. The flyback circuit 106 comprises a transformer T2 and a switch Q2 and a diode. The input of the flyback circuit 106 is coupled in parallel with the input of the flyback circuit 105. The output of the flyback circuit 106 is coupled in parallel with the output of the flyback circuit 105.
At the output 102, there is a current monitoring element 111 and a voltage monitoring element 112. The current and voltage monitored is coupled to the controller 110 at Io and Vo to control the turn-on and turn-off of each branches (circuits 105, 106) of the DC-to-DC converter and to achieve the alternating of master and slave branches.
One embodiment of the present invention is to assign branches into different levels, such as master and slave when there are 2 branches. The master branch is always operating, but the slave would be off (termed “sleep”) when the power is below a threshold level. When the output power is below the threshold value, only the master branch is operating. Compared with the situation that both branches are operating with even power, this invention has less power consumption as less devices are operating.
Another embodiment of the invention is the alternating of branches. When the master branch is a fixed branch, as the master branch is always operating, while the slave branch sleeps in some time, the 2 branches have mismatches, such as operating temperature, device stress, etc. Different operation in master and slave branch results in different performance and device degradation, which causes all mismatch related problems. Also the lifetime of the converter would be limited by the master branch as it had more stress. With the alternating of the branches, meaning the 2 branches work as the master branch alternatively, the 2 branches have same operating period. Each branch has less operating time than the case of fixed master branch. As shown in
In the example above, the alternating period is the period of output power. In another embodiment, the period can be any other time settings, such as multiple periods, 1 second, 1 minute, 1 hour, 1 day, 1 week, 1 month, or likes.
An example of converter with 2 flyback circuits (branches) operating in parallel is discussed above. The invention can be expanded to any number (termed N) of flyback circuits coupled in parallel in the similar way. For peak output power at Pm, the peak output power of each ranch is Pm/N. The threshold voltage for alternating control may be set as Pth=Pm/(N*N). The number of the turn-on branches is the value of 1 plus the divide integer between Po and Pth. When Po is between 0 and Pth, 1 branch is turn-on, which is termed as master branch. When Po is between Pth and 2Pth, 2 branches are turn-on, which is termed as master and 1st slave 1 branch. When Po is between i*Pth and (i+1)*Pth, master branch and 1st to ith slave branches are turn-on. When Po is between (N−1)*Pth to Pm, all branches are turn-on, with master branch and 1st to N−1th slave branches.
Similar to the example above, the master and slave branches are alternating. For example, one embodiment can be s following: the master becomes slave 1, slave 1 becomes slave 2, slave i becomes slave i+1, and slave N−1 becomes the master.
In example above, the output power Po is used to control branches. As output voltage Vo is a constant DC voltage, another embodiment is only using monitored output current Io to control branches.
This patent application claims priority to U.S. Provisional Patent Application No. 61/342,293 to Luo filed on Apr. 12, 2010, which is herein incorporated by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 61342293 | Apr 2010 | US |
