TW201406026A - DC to DC converter and a voltage converter capable of selecting coupling ratios - Google Patents

Abstract

The present invention is a DC to DC converter and voltage converter capable of selecting coupling ratios comprising a full-bridge circuit, a transformer and a rectifying unit. The full-bridge circuit is connected to a DC voltage source. A primary side of the transformer is connected to the full-bridge circuit to receive the DC voltage source, wherein its secondary side has a frequently connected winding and at least a switching winding. If the DC voltage source is lower than a threshold, the switch of the switching winding turns into conducting closed to command the secondary winding and the switching winding to form a series connection so as to enhance the coupling ratio of the transformer. Accordingly, the transformer may convert a DC voltage source into an output DC voltage having desired levels.

Description

Selectable coupling ratio DC/DC converter and voltage converter

The present invention relates to a DC/DC converter, and more particularly to a DC/DC converter that can change the coupling ratio to generate a DC voltage of a desired level, and appropriately select a rectifier for rectification operation.

As shown in FIG. 5, a conventional power converter for converting an input DC voltage into an output AC voltage includes a three-stage circuit, that is, a boosting unit 50, a DC/DC converter 60, and a DC/AC. Converter 70. The DC/DC converter 60 mainly includes a transformer T1 and a bridge rectifier composed of four diodes D2~D5.

The three-stage circuit structure of the existing converter is complicated and has high power consumption. When the input DC voltage on capacitor C1 is relatively low, the boost unit 50 must boost the voltage across capacitor C1. Therefore, when the input DC voltage is relatively low, more power consumption is caused because the circuit of the boosting unit 50 operates.

The main object of the present invention is to provide a DC/DC converter capable of changing the coupling ratio, which has a relatively simple circuit structure, and can generate a DC voltage of a desired magnitude by changing the coupling ratio of a transformer, and appropriately switch and select A rectifier rectifies the DC voltage.

In order to achieve the aforementioned purpose, the DC/DC conversion of the coupling ratio can be changed. The converter includes: a full bridge circuit comprising four power transistors to form two input terminals and two output terminals, wherein the two input terminals are connected to a DC voltage source; and a transformer includes a primary side And a secondary side, wherein the primary side has a primary side winding connected to the two output ends of the full bridge circuit; on the secondary side, there is a normally connected winding and at least one switching winding, the normally connected winding and the switching winding can be Switching to form a series; a rectifying unit is composed of a plurality of diodes, each of which is connected in series at a series node to form a single branch, and all the branches are connected in parallel with each other, the common winding and Portions of the branches are connected and the switching windings are connected to other corresponding branches via respective switches.

According to the size of the DC voltage source, one of the switches is selected to be turned on and closed, thereby changing the coupling ratio of the transformer. As the coupling ratio of the transformer is increased, the secondary side of the transformer can generate a DC voltage of a desired magnitude. And as the switch is turned on, the corresponding diode in the rectifying unit can constitute a complete rectifier, and rectify the generated DC voltage.

Referring to the preferred embodiment shown in FIG. 1, the DC/DC converter 10 of the present invention is applied to a power inverter. In addition to the DC/DC converter 10, the converter 1 further includes a DC/AC converter 20, wherein the converter 1 converts a _DC- generated _DC voltage source V _DC into a desired AC voltage.

The DC/DC converter 10 includes a full bridge circuit 11 and a transformer The unit T1 and a rectifying unit 13.

The full-bridge circuit 11 includes four power transistors Q1 - Q4 formed with two input terminals and two output terminals, wherein the two input terminals are connected to the DC voltage source V _DC .

The rectifying unit 13 is composed of P diodes, where P = 2M + 2, and M is the number of secondary windings of the transformer T1. In the present embodiment, the transformer T1 has two secondary windings, M=2, so the rectifying unit 13 is composed of six diodes D1 to D6. Each of the two diodes is connected in series to form a branch. The tandem nodes of the diodes D1 to D6 are a1~a3, and the plurality of branches are connected in parallel with each other; for example, the diodes D1 and D4 are The nodes a1 are connected in series, the other two diodes D2 and D5 are connected in series by the node a2, and the remaining diodes D3 and D6 are connected in series by the node a3. A DC capacitor C1 is connected to the output end of the rectifying unit 13

The transformer T1 has a primary side and a secondary side, and has a primary side winding N1 at the primary side portion, which is connected to the output end of the full bridge circuit 11. The secondary side portion has M secondary windings, including a normally connected winding N2 and at least one controllable switching winding N3, wherein M≧2, the normally connected winding N2 and the switching winding N3 may have the same or different coils. number. In the first embodiment, a normal winding N2 and a switching winding N3 are taken as an example.

Referring to the second embodiment shown in FIG. 2, the secondary side of the transformer T1 has a normally connected winding N2 and two switching windings N3, N4. The rectifying unit 13 has four branches. Each of the windings N2 to N4 on the secondary side has a first end and a second end, and the windings N2 to N4 are connected in series. The two ends of the common winding N2 are connected to the series connection nodes a3 and a4 of the two branches of the rectifying unit 13; the first ends of the remaining switching windings N3 and N4 are respectively connected via a switch S1. S2 is connected to the corresponding other series nodes a1, a2.

The DC/AC converter 20 is connected to the output of the DC/DC converter 10, receives the DC voltage generated by the DC/DC converter 10, and converts it into an AC output voltage Vac.

Referring to FIG. 3 further, when the DC voltage source V _{DC is} greater than a threshold value, the energy generated by the solar energy is sufficient, and the switch S1 connected to the switching winding N3 is maintained in a non-conducting state, so the switching winding N3 is in a starting state. No effect. The transformer T1 couples energy from the primary side winding N1 to the secondary side normal winding N2. The four diodes D2, D3, D5, and D6 in the rectifying unit 13 constitute a rectifier. The two diodes D2 and D6 and the other two diodes D3 and D5 belonging to different branches will be alternately turned on, thereby transferring energy to the DC/AC converter 20. The DC/AC converter 20 further converts the DC bus voltage V _C1 to the desired AC voltage Vac so that the AC current can be fed to the power system.

When the generated DC voltage source V _{DC is} relatively low and less than the threshold, the switch S1 will turn into conduction closing, so that the two windings N2, N3 on the secondary side form a complete series. As the number of windings N2, N3 on the secondary side increases, the transformer T1 naturally has a higher coupling ratio, so that a higher voltage can be generated on the secondary side. In this case, the four diodes D1, D3, D4, D6 in the rectifying unit 13 will constitute a rectifier, wherein the two diodes D1, D6 and the other two diodes D3, D4 belonging to different branches will It is alternately turned on, thereby transferring energy to the DC/AC converter 20. Therefore, even if the DC voltage V _DC generated by the solar energy is relatively low, the DC bus voltage V _C1 on the capacitor _C1 can still be converted into the required AC voltage Vac by means of a higher coupling ratio. The voltage Vac can still be greater than the peak voltage of the power system to ensure that the AC current can be fed into the power system.

As shown in FIG. 2, the number of windings on the secondary side of the transformer T1 can be more than two sets according to actual needs, so that a higher output voltage can be provided on the secondary side. Therefore, in the second embodiment, two threshold values V _TH1 , V _{TH2 are set} and compared with the DC voltage source V _DC to determine whether the switches S1 and S2 should be turned on or off.

As shown in FIG. 2 and FIG. 4, when the generated DC voltage source V _{DC is} greater than the two threshold values V _TH1 and V _TH2 , the energy generated by the solar energy is sufficient, and both switches S1 and S2 are maintained in a non-conducting state. The transformer T1 couples the energy of the primary side to the normally connected winding N2. When V _TH2 ≧V _DC ≧V _TH1 , only the first switch S1 is controlled to be turned on. If the DC voltage source V _{DC is} further less than V _TH1 , only the second switch S2 is controlled to be turned on. In the state where the second switch S2 is turned on, the transformer T1 has the highest coupling ratio. The diodes D3, D6, D7, and D8 form a rectifier, wherein the two diodes D7 and D6 and the other two diodes D3 and D8 are alternately turned on, and the energy of the secondary side is transmitted to the DC/AC conversion. 20.

In summary, when the DC/DC converter of the present invention is applied to a power converter, the power converter is composed of only two stages of circuits, that is, a DC/DC converter and a DC/AC converter. In this way, it is not necessary to use the primary boost circuit alone, which naturally simplifies the circuit architecture. And even if the input DC voltage source is low, the DC/DC converter can provide a higher conversion ratio to provide the desired level of output voltage.

1‧‧‧converter

10‧‧‧DC/DC Converter

11‧‧‧Full bridge circuit

13‧‧‧Rectifier unit

20‧‧‧DC/AC converter

50‧‧‧Boost unit

60‧‧‧DC/DC Converter

70‧‧‧DC/AC converter

Figure 1 is a circuit diagram of a first embodiment of a DC/DC converter of the present invention applied to a converter.

Figure 2 is a circuit diagram of a second embodiment of the DC/DC converter of the present invention applied to a current transformer.

Figure 3 is a schematic diagram showing a comparison of a DC source voltage V _DC with a threshold value in the present invention.

Fig. 4 is a view showing a comparison of a direct current source voltage V _DC and a second critical value in the present invention.

Figure 5: Circuit diagram of an existing power converter.

1‧‧‧converter

10‧‧‧DC/DC Converter

11‧‧‧Full bridge circuit

13‧‧‧Rectifier unit

20‧‧‧DC/AC converter

Claims (8)

A DC/DC converter with selectable coupling ratio, comprising: a full bridge circuit comprising four power transistors to form two input terminals and two output terminals, wherein the two input terminals are connected to the DC current a voltage source; a transformer comprising a primary side and a secondary side, wherein the primary side has a primary side winding connected to the two output ends of the full bridge circuit; and the secondary side has M secondary side windings, The secondary winding comprises a common winding and a plurality of switching windings, wherein M ≧ 2, each secondary winding has a first end and a second end; and a rectifying unit is composed of P diodes, wherein P=2M+2, each two diodes are connected in series on a series node to form a single branch, and all the branches are connected to each other in parallel; the first end and the second end of the normally connected winding are respectively connected to the foregoing two a series node of different branches; a first end of each switching winding is connected to a series node of another branch via a corresponding switch, and is not connected to a branch to which the normally connected winding is connected; wherein, according to the size of the DC voltage source From Selecting one of the plurality of switches turned on and allowed to close, thereby changing the coupling ratio of the transformer, the secondary side of the transformer capable of producing a DC voltage of desired size. The DC/DC converter of the coupling ratio can be selected as described in claim 1, wherein when the selected switch is turned on, the normally-connected winding is connected in series with one or more switching windings to increase the coupling ratio of the transformer. DC/DC conversion with selectable coupling ratio as described in claim 1 The transformer has a M-1 switches connected to the secondary side, and the DC source voltage is compared with M-1 thresholds to select a switch to be turned on according to the comparison result. A DC/DC converter with selectable coupling ratio, comprising: a full bridge circuit comprising four power transistors to form two input terminals and two output terminals, wherein the two input terminals are connected to the DC current a voltage source; a transformer comprising a primary side and a secondary side, wherein the primary side has a primary side winding connected to the two output ends of the full bridge circuit; and the secondary side has a common winding and a switching winding, One end of the switching winding is connected with a switch, and the other end is connected to one end of the normally connected winding and connected in series; a rectifying unit is composed of six diodes, and each two diodes are connected in series on a series node. Thereby forming a first branch, a second branch and a third branch, all branches being parallel to each other; the other end of the switch is connected to the series node on the first branch; the two ends of the normally connected winding are respectively connected to the second branch And a series connection node of the third branch; wherein, when the DC voltage source is less than a threshold, the switch is turned into a conduction closure, so that the normally-connected winding is connected in series with the switching winding, thereby increasing the transformation The coupling ratio of the device enables the secondary side of the transformer to generate a DC voltage of the required magnitude. A DC/DC converter of a coupling ratio may be selected as described in claim 4, wherein the switch is open when the DC voltage source is greater than the threshold. A DC/DC converter of a coupling ratio may be selected as described in claim 4, wherein the normally connected winding has the same number of turns of the coil as the switching winding. A DC/DC converter of a coupling ratio can be selected as described in claim 4, wherein the normally connected winding has a different number of coil turns than the switching winding. A voltage converter comprising: a full bridge circuit comprising four power transistors to form two input terminals and two output terminals, wherein the two input terminals are connected to a DC voltage source; a transformer, The primary side and the secondary side are included, wherein the primary side has a primary side winding connected to the two output ends of the full bridge circuit; on the secondary side, there are M secondary side windings, and the secondary side windings include a winding and a plurality of switching windings, wherein M≧2, each secondary winding has a first end and a second end; and a rectifying unit is composed of P diodes, wherein P=2M+2, Each of the two diodes is connected in series on a series node to form a single branch, and all the branches are connected to each other in parallel; the first end and the second end of the normally connected winding are respectively connected to the series node of the two different branches; a first end of each switching winding is connected to a series node of one of the other branches via a corresponding switch, and is not connected to a branch to which the normally connected winding is connected; wherein, from the plurality of switches, according to the magnitude of the DC voltage source Choose which One of them is turned on and closed, thereby changing the coupling ratio of the transformer so that the secondary side of the transformer can generate a DC voltage of a desired magnitude; a DC/AC converter connected to the rectifying unit to rectify The DC voltage is converted to an AC voltage.