Three-winding coupling inductor bipolar output high-gain DC-DC converter

Abstract

The invention relates to a three-winding coupling inductor bipolar output high-gain DC-DC converter, which is characterized in that a coupling inductor and switched capacitor boosting technology is introduced into a three-level Boost bipolar output converter, and bipolar output voltages Uo1 and Uo2 are controlled by adjusting the turn ratio of the coupling inductor and the duty ratio of a switch; and the input and output power is changed by adjusting the resistance value of the output load. The DC-DC converter is low in input current ripple, high in voltage gain and low in switching tube voltage stress, and bipolar output voltage can be flexibly adjusted through the duty ratio and the coupling inductor turn ratio.

Description

Technical Field

[0001] The present invention relates to the technical field of DC-DC converters, and particularly to a three-winding coupled inductor bipolar output high-gain DC-DC converter. Background Art

[0002] Since there is no power synchronization in a DC microgrid, the impacts brought by harmonics and reactive power are avoided, and control can be easily achieved. Moreover, with the wide application of renewable energy, DC microgrid technology has received great attention and research from researchers due to its reliability and high efficiency. A bipolar DC microgrid not only has the general advantages of a DC microgrid, but also facilitates the access of electrical equipment and distributed power sources and is used as a solution for connecting various renewable energy sources and emerging loads. Therefore, as a new type of power system architecture, a bipolar DC microgrid can effectively improve the flexibility and reliability of a DC power system.

[0003] In recent years, DC-DC converters with high voltage gain have received much attention in the field of power electronics and have become an important research direction. It has been found that a variety of technologies can convert the low voltage generated by photovoltaic modules into high voltage. In theory, a traditional boost converter can achieve high voltage gain through a large duty cycle close to 1, but this usually results in high conduction losses and ultimately leads to a decline in the overall performance of the converter. Generally, a traditional boost converter has obvious disadvantages in high-voltage applications. The switching tubes in the converter must withstand high voltages, and there are serious reverse recovery losses in the output diodes. The converter not only has to achieve a relatively high output voltage, but also be able to reduce the input current ripple and the voltage stress in the power switches, so as to effectively improve the stability of the power system. Moreover, a converter with low input current ripple can effectively extend the service life of renewable energy components.

[0004] Figure 1 Shown is a bipolar output DC-DC converter with continuous input current and no transformer structure. The topology of this converter can achieve low input current ripple and high voltage gain, and the converter can achieve high voltage output without adjusting to an extreme duty cycle, which is very suitable for processing power from low-voltage power sources such as renewable energy. However, its disadvantages will lead to unbalanced output voltages.

[0005] Figure 2Shown is a novel high-boost bipolar-output DC-DC converter based on an integrated boost-CUK topology. A dual-winding coupled inductor is added to the converter, enabling the converter to have a high voltage gain. And in this dual-switch converter, an active clamp circuit structure is adopted, which can effectively absorb the leakage energy of the coupled coil. Therefore, zero-voltage turn-on of the switch tube and zero-current turn-off of the diode can be achieved. However, the series coupling between the input and the coupled coil generates a high input current ripple, which limits its application in renewable energy. Summary of the Invention

[0006] The object of the present invention is to provide a three-winding coupled-inductor bipolar-output high-gain DC-DC converter, which has low input current ripple, high voltage gain, low voltage stress of the switch tube, and can flexibly adjust the bipolar output voltage by the duty cycle and the turn ratio of the coupled inductor.

[0007] To achieve the above object, the technical solution adopted by the present invention is: a three-winding coupled-inductor bipolar-output high-gain DC-DC converter, which introduces a coupled inductor and a switched-capacitor boost technology on a three-level Boost bipolar-output converter, and controls the bipolar output voltages U o1 and U o2 by adjusting the turn ratio of the coupled inductor and the duty cycle on the switch; and changes the input-output power by adjusting the resistance value of the output load.

[0008] Further, the winding coupled-inductor bipolar-output high-gain DC-DC converter includes an input voltage U in , an input inductor L1, an exciting inductor L m , two switch tubes S1 and S2, six diodes D1, D2, D3, D4, D o1 and D o2 , five energy storage capacitors C1, C2, C3, C o1 and C o2 and three coupled inductor windings N1, N2 and N3; wherein, N1 is the primary winding, N2 and N3 are the secondary windings, and the turn ratio of the three coupled inductor winding coils is 1:n1:n2, where n1 = N2 / N1 and n2 = N3 / N1; after the positive pole of the input voltage U in is connected to the input inductor L1, it is simultaneously connected to the positive poles of diodes D1 and D2. The negative pole of diode D1 is simultaneously connected to the same-named end of the primary winding N1 and the positive pole of the energy storage capacitor C1. The negative pole of diode D2 is simultaneously connected to the opposite-named end of the primary winding N1, the same-named end of the secondary winding N2, the positive pole of diode D3 and the D pole of the switch tube S1. Both ends of the primary winding N1 are connected in parallel with the exciting inductor L m, the opposite-named terminal of the secondary winding N2 is connected to the negative electrode of the energy storage capacitor C2, and the positive electrode of the energy storage capacitor C2 is simultaneously connected to the negative electrode of the diode D3 and the positive electrode of the diode D o1 ; the negative electrode of the diode D o1 is simultaneously connected to the positive electrode of the energy storage capacitor C o1 and one end of the first output load; the negative electrode of the input voltage U in is simultaneously connected to the negative electrode of the energy storage capacitor C1, the opposite-named terminal of the secondary winding N3, the negative electrode of the diode D4, and the S pole of the switching tube S2. The same-named terminal of the secondary winding N3 is connected to the positive electrode of the energy storage capacitor C3, and the negative electrode of the energy storage capacitor C3 is simultaneously connected to the positive electrode of the diode D4 and the negative electrode of the diode D o2 ; the positive electrode of the diode D o2 is simultaneously connected to the negative electrode of the energy storage capacitor C o2 and one end of the second output load; the S pole of the switching tube S1, the D pole of the switching tube S2, the negative electrode of the energy storage capacitor C o1 , the positive electrode of the energy storage capacitor C o2 , the other end of the first output load, and the other end of the second output load; the conduction or cut-off of the switching tubes S1 and S2 is realized through the single-polarity PWM control method, so as to switch different working modes of the circuit.

[0009] Further, an exciting inductor L m is connected in parallel at both ends of the primary winding N1.

[0010] Further, the three-winding coupled inductor bipolar output high-gain DC-DC converter has four working modes, among which the time occupied by mode 1 and mode 3 is extremely short and can be ignored in the steady-state analysis, and only mode 2 and mode 4 are considered;

[0011] In mode 2, the switching tubes S1 and S2 are both fully conducting during this time period; the diodes D2, D3, and D4 are fully conducting, while the diodes D1, D o1 and D o2 are in the off state; the input voltage U in transfers energy to the input inductor L1 through the switching tubes S1 and S2, and the current of the input inductor L1 increases linearly; at the same time, the energy storage capacitors C o1 and C o2 release the stored energy to the load through discharging, so as to keep the load voltage constant; the primary winding N1 transfers energy to the energy storage capacitor C1; the secondary windings N2 and N3 charge the energy storage capacitors C2 and C3 through the diodes D3 and D4 respectively;

[0012] In mode 4, the diodes D1, D o1 and D o2 are fully conducting, the diodes D2, D3, and D4 are fully off, and the switching tubes S1 and S2 are fully off; the input voltage Uin , the input inductor L1, the exciting inductor L m , the primary winding N1, the secondary winding N2 and the energy storage capacitor C2 supply energy to the load through the diodes D1 and D o1 . The energy of the input inductor L1 is transferred to the energy storage capacitor C1. At this time, the current of the input inductor L1 linearly decreases, and the exciting current i Lm also linearly decreases.

[0013] Compared with the prior art, the present invention has the following beneficial effects:

[0014] 1. The converter power supplies are concentrated on two DC buses, making the overall efficiency of the power system higher;

[0015] 2. Under the conditions of low input current ripple and small switching voltage spikes, a high voltage gain can be achieved;

[0016] 3. By introducing the coupled inductor and switched capacitor technologies on the basis of the three-level Boost topology, a high voltage gain can be obtained in a wide input voltage range;

[0017] 4. By introducing the three-winding coupled inductor structure, the overall circuit structure is optimized, effectively avoiding the overstress problem of the switching devices and avoiding the too long conduction time of the converter. Brief Description of the Drawings

[0018] Figure 1 is the circuit topology diagram of a bipolar output DC-DC converter with continuous input current and no transformer structure in the prior art;

[0019] Figure 2 is the circuit topology diagram of a novel high-boost bipolar output DC-DC converter based on the integrated boost-CUK topology in the prior art;

[0020] Figure 3 is the circuit topology diagram of a three-winding coupled inductor bipolar output high-gain DC-DC converter according to an embodiment of the present invention;

[0021] Figure 4 is the key waveform diagram of the main devices of a three-winding coupled inductor bipolar output high-gain DC-DC converter according to an embodiment of the present invention;

[0022] Figure 5 is the equivalent circuit diagram of the switching mode of a three-winding coupled inductor bipolar output high-gain DC-DC converter according to an embodiment of the present invention. Specific Embodiments

[0023] The present invention will be further described below with reference to the drawings and embodiments.

[0024] It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present application belongs.

[0025] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0026] This embodiment provides a three-winding coupled-inductor bipolar-output high-gain DC-DC converter. By introducing a coupled inductor and a switched-capacitor boost technique into a three-level Boost bipolar-output converter, the bipolar output voltages U o1 and U o2 are effectively controlled by flexibly adjusting the turns ratio of the coupled inductor and the duty cycle of the switches; and by adjusting the resistance value of the output load to change the input-output power, the optimal performance can be found.

[0027] Figure 3 is the topological structure diagram of the three-winding coupled-inductor bipolar-output high-gain DC-DC converter proposed in this embodiment. As Figure 3 shown, the three-winding coupled-inductor bipolar-output high-gain DC-DC converter includes an input voltage U in , an input inductor L1, an exciting inductor L m , two switching transistors S1 and S2, six diodes D1, D2, D3, D4, D o1 and D o2 , five energy storage capacitors C1, C2, C3, C o1 and C o2 and three coupled inductor windings N1, N2 and N3; wherein, N1 is the primary winding, N2 and N3 are the secondary windings, and the turns ratio of the three coupled inductor winding coils is 1:n1:n2, where n1 = N2 / N1 and n2 = N3 / N1; after the positive pole of the input voltage U in is connected to the input inductor L1, it is simultaneously connected to the positive poles of diodes D1 and D2. The negative pole of diode D1 is simultaneously connected to the same-named end of the primary winding N1 and the positive pole of the energy storage capacitor C1. The negative pole of diode D2 is simultaneously connected to the opposite-named end of the primary winding N1, the same-named end of the secondary winding N2, the positive pole of diode D3, and the D pole of the switching transistor S1. The two ends of the primary winding N1 are connected in parallel with the exciting inductor L m, the opposite-named terminal of the secondary winding N2 is connected to the negative electrode of the energy storage capacitor C2, and the positive electrode of the energy storage capacitor C2 is simultaneously connected to the negative electrode of the diode D3 and the diode D o1 's positive electrode, the diode D o1 's negative electrode is simultaneously connected to the positive electrode of the energy storage capacitor C o1 and one end of the first output load; the negative electrode of the input voltage U in is simultaneously connected to the negative electrode of the energy storage capacitor C1, the opposite-named terminal of the secondary winding N3, the negative electrode of the diode D4, and the S pole of the switching tube S2. The same-named terminal of the secondary winding N3 is connected to the positive electrode of the energy storage capacitor C3, and the negative electrode of the energy storage capacitor C3 is simultaneously connected to the positive electrode of the diode D4 and the diode D o2 's negative electrode, the diode D o2 's positive electrode is simultaneously connected to the negative electrode of the energy storage capacitor C o2 and one end of the second output load; the S pole of the switching tube S1, the D pole of the switching tube S2, the negative electrode of the energy storage capacitor C o1 , the negative electrode of the energy storage capacitor C o2 , the positive electrode of the energy storage capacitor C in , the other end of the first output load, and the other end of the second output load. The conduction or cut-off of the switching tubes S1 and S2 is realized by the unipolar PWM control method, so as to switch different working modes of the circuit. Generally, the input current ripple (ΔI in ) is about 20% of the average value of the input current.

[0028] To simplify the circuit analysis, it is assumed that all devices of the converter work under ideal conditions, there is no influence of non-ideal factors on the performance of the converter circuit, and it is stipulated that the voltage across the capacitor remains unchanged within a working cycle. The turn ratio of the three-winding coupled coil is 1:n1:n2, where n1 = N2 / N1 and n2 = N3 / N1. Figure 4 is the waveform diagram of the theoretical analysis of the main devices in the converter proposed in this embodiment. Considering the four working modes of the converter, it has four working modes. Through Figure 4 's time axis and theoretical principle, it can be seen that the time occupied by Mode 1 and Mode 3 is extremely short and can be ignored in the steady-state analysis. Only Mode 2 and Mode 4 are considered. The equivalent circuits of Mode 2 and Mode 4 of the converter proposed in this embodiment are as Figure 5 shown.

[0029] Mode 2 (as shown in (a) of Figure 5 ): The switching tubes S1 and S2 in the converter are both fully conductive during this period. The diodes D2, D3, and D4 are fully conductive, while the diodes D1, D o1 and D o2 are in the off state. The input voltage U in transfers energy to the input inductor L1 through the switching tubes S1 and S2. Since the inductor current cannot change suddenly, the current of the input inductor L1 in the converter increases linearly. At the same time, the capacitor Co1 and C o2 The stored energy is released to the load through discharging, so as to keep the load voltage constant. The primary winding N1 of the coupled inductor transfers the energy to the energy storage capacitor C1. The secondary windings N2 and N3 charge the energy storage capacitors C2 and C3 through the diodes D3 and D4 respectively. The voltage relationship in this state is as follows:

[0030]

[0031] Where, U L1_ON 、U NX_ON and U CX represent the voltages on the input inductor L1, the coupled inductor winding N X and the energy storage capacitor C X when the switching transistors S1 and S2 are turned on, respectively, where X = 1, 2, 3.

[0032] When the switching transistors S1 and S2 are turned on, the input source charges the exciting inductor and stores energy in the magnetic core.

[0033] Mode 4 (as shown in (b) of Figure 5 ): The diodes D1, D o1 and D o2 are fully turned on, the diodes D2, D3 and D4 are fully turned off, and the switching transistors S1 and S2 are fully turned off. The input voltage U in , the input inductor L1, the exciting inductor L m , the primary winding N1, the secondary winding N2 and the capacitor C2 supply energy to the load through the diodes D1 and D o1 . The energy of the input inductor L1 is transferred to the energy storage capacitor C1. At this time, the current of the input inductor L1 decreases linearly, and the exciting current i Lm also decreases linearly. The voltage relationship in this state is as follows:

[0034]

[0035] Where, U L1_OFF 、U NX_OFF and U CoY represent the voltages on the input inductor L1, the coupled inductor winding N X and the energy storage capacitor C oY when the switching transistors S1 and S2 are turned off, respectively, where Y = 1, 2, and U o represents the output voltage of the converter. According to the volt-second balance theory of inductive elements, it can be obtained that:

[0036]

[0037] Wherein, DT represents the actual duration when the switching transistors S1 and S2 are in the on state, and T represents the switching period required for the converter to complete four working modes.

[0038] When the switching transistors S1 and S2 are turned off, the stored energy is transferred to the secondary side through the turns ratio of the coupled windings (n1 = N2 / N1, n2 = N3 / N1) and superimposed on the output voltage, significantly increasing the voltage gain.

[0039] By combining equations (1)-(3), we can obtain:

[0040]

[0041] Then, the bipolar output voltage gain of the three-winding coupled-inductor bipolar-output high-gain DC-DC converter can be expressed as:

[0042]

[0043] In the design of the capacitor in the converter, its voltage stress is mainly considered. The voltage fluctuation of the capacitor needs to be controlled within a certain range. Generally, it is required that the capacitor voltage ripple (ΔU C ) is about 2% of the average value of the voltage across the capacitor.

[0044] The three-winding coupled-inductor bipolar-output high-gain DC-DC converter proposed by the present invention can adjust the bipolar output voltage by selecting appropriate turns ratios of the coupled coils and duty cycles according to different application scenarios. Appropriate sizes of inductors and capacitors are selected according to the requirements for the input inductor current ripple and capacitor voltage ripple.

[0045] The above are only the preferred embodiments of the present invention, and do not limit the present invention in other forms. Any person skilled in the art may use the disclosed technical content to make changes or modifications into equivalent embodiments with equivalent changes. However, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the technical solution content of the present invention still fall within the protection scope of the technical solution of the present invention.

Claims

1. A three-winding coupled inductor bipolar output high gain DC-DC converter, characterized in that: The coupled inductor and switched capacitor boost technology is introduced into the three-level Boost bipolar output converter. The bipolar output voltage U is controlled by adjusting the turns ratio of the coupled inductor and the duty cycle of the switch. o1 and U o2 ; and change the input and output power by adjusting the resistance value of the output load.

2. A three-winding coupled inductor bipolar output high-gain DC-DC converter according to claim 1, characterized in that: Including input voltage U in , input inductance L1, excitation inductance L m , two switch tubes S1 and S2, six diodes D1, D2, D3, D4, D o1 and D o2 , five energy storage capacitors C1, C2, C3, C o1 and C o2 And three coupled inductor windings N1, N2 and N3; where N1 is the primary winding, N2 and N3 are the secondary windings, and the turns ratio of the three coupled inductor winding coils is 1:n1:n2, where n1=N2 / N1, n2=N3 / N1; input voltage U in After the positive electrode of the input inductor L1 is connected, the positive electrodes of the diodes D1 and D2 are connected at the same time. The negative electrode of the diode D1 is connected to the same-name end of the primary winding N1 and the positive electrode of the energy storage capacitor C1 at the same time. The negative electrode of the diode D2 is connected to the opposite-name end of the primary winding N1, the same-name end of the secondary winding N2, the positive electrode of the diode D3 and the D pole of the switch tube S1 at the same time. The two ends of the primary winding N1 are connected in parallel with the excitation inductor L m The opposite end of the secondary winding N2 is connected to the negative electrode of the energy storage capacitor C2, and the positive electrode of the energy storage capacitor C2 is connected to the negative electrode of the diode D3 and the diode D o1 The positive pole of diode D o1 The negative electrode is connected to the energy storage capacitor C o1 The positive pole and the first output load end; input voltage U in The negative electrode of the energy storage capacitor C1 is connected to the negative electrode, the opposite end of the secondary winding N3, the negative electrode of the diode D4 and the S pole of the switch tube S2. The same end of the secondary winding N3 is connected to the positive electrode of the energy storage capacitor C3. The negative electrode of the energy storage capacitor C3 is connected to the positive electrode of the diode D4 and the S pole of the diode D o2 The cathode of diode D o2 The positive electrode is connected to the energy storage capacitor C o2 The negative electrode of the switch tube S1 and the second output load end; the S pole of the switch tube S1, the D pole of the switch tube S2, the energy storage capacitor C o1 The negative electrode, energy storage capacitor C o2 The positive electrode, the other end of the first output load and the other end of the second output load; the switching tubes S1 and S2 are turned on or off by a unipolar PWM control method to switch different working modes of the circuit.

3. The three-winding coupled inductor bipolar output high-gain DC-DC converter according to claim 2, characterized in that: The three-winding coupled inductor bipolar output high-gain DC-DC converter has four operating modes, among which mode 1 and mode 3 occupy a very short time and are ignored in the steady-state analysis, and only mode 2 and mode 4 are considered; In mode 2, the switches S1 and S2 are fully turned on during this period; the diodes D2, D3 and D4 are fully turned on, while the diodes D1, D o1 and D o2 It is in the off state; input voltage U in The energy is transferred to the input inductor L1 through the switch tubes S1 and S2, and the current of the input inductor L1 increases linearly; at the same time, the energy storage capacitor C o1 and C o2 The stored energy is released to the load by discharging, thereby keeping the load voltage constant; the primary winding N1 transfers energy to the energy storage capacitor C1; the secondary windings N2 and N3 charge the energy storage capacitors C2 and C3 through diodes D3 and D4 respectively; In mode 4, diodes D1, D o1 and D o2 The diodes D2, D3 and D4 are completely turned off, and the switch tubes S1 and S2 are completely turned off; the input voltage U in , input inductance L1, excitation inductance L m , primary winding N1, secondary winding N2 and energy storage capacitor C2, through diodes D1 and D o1 Provide energy to the load; the energy of the input inductor L1 is transferred to the energy storage capacitor C1, at which time the current of the input inductor L1 decreases linearly, and the excitation current i Lm It also decreases linearly.

4. The three-winding coupled inductor bipolar output high-gain DC-DC converter according to claim 3, characterized in that: The voltage relationship in mode 2 is as follows: Among them, U L1_ON , U NX_ON and U CX They represent the input inductor L1 and the coupled inductor winding N respectively when the switch tubes S1 and S2 are turned on. X and energy storage capacitor C X Voltage on, X = 1, 2, 3; The voltage relationship in mode 4 is as follows: Among them, U L1_OFF , U NX_OFF and U CoY They represent the input inductance L1 and the coupled inductance winding N when the switch tubes S1 and S2 are turned off. X and energy storage capacitor C oY Voltage on, Y=1,2,U o Indicates the output voltage of the converter; According to the volt-second balance theory of inductor components: Among them, DT represents the actual time that the switches S1 and S2 are in the on state, and T represents the switching cycle required for the converter to complete the four working modes; Combining equations (1)-(3), we can obtain: Then the bipolar output voltage gain of the three-winding coupled inductor bipolar output high-gain DC-DC converter is:

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