High-reliability bipolar output voltage self-balancing Cuk DC-DC converter

Abstract

The invention discloses a high-reliability bipolar output voltage self-balancing Cuk DC-DC converter. The converter comprises i direct current input sources, i Cuk converters and j positive polarity voltage expansion units. The positive polarity conversion unit is composed of an inductor, two capacitors and a diode. By adjusting the number of the positive polarity conversion units, the input and output gains of the converter and the voltage stress of the switching device can be adjusted. The whole converter has a wide voltage gain characteristic. The voltage self-balancing of the converter is realized through the clamping effect of an auxiliary capacitor in the positive polarity conversion unit. Different output capacitor parallel circuits can be formed in different modes, and the mean values of output voltages of the two poles are clamped to the voltage peak value and the voltage mean value of the auxiliary capacitor respectively. By increasing the capacitance value of the auxiliary capacitor and lowering the difference between the voltage peak value and the voltage mean value of the auxiliary capacitor, the deviation of the output voltage between the two electrodes is reduced.

Description

Technical Field

[0001] The invention relates to a Cuk DC-DC converter, in particular to a high-reliability bipolar output voltage self-balancing Cuk DC-DC converter. Background Art

[0002] In the application of bipolar DC power supply, there are mainly two types of DC distribution systems: pseudo bipolar bus and true bipolar bus. The true bipolar bus is composed of two converters with DC outputs in series and the midpoint grounded. The positive and negative voltages of the pseudo bipolar bus are generated by a single converter, using a split capacitor on the output side and the neutral point grounded, so it is also called a symmetrical monopole structure. The symmetrical monopole structure is currently widely used in low-voltage DC microgrids.

[0003] For example, the patent with application publication number CN111865079A discloses a pseudo-bipolar power supply circuit, which uses a board bridge structure to realize an inter-pole voltage balancing circuit with a single-input symmetrical bipolar output. Using bootstrap drive, both switches can achieve soft switching in the full range from no-load to full-load. However, the reliability of the bipolar circuit is not high, and when the switch tube fails, the entire converter cannot work properly. In addition, although the converter can achieve voltage balance when there is a slight imbalance in the positive and negative loads, when one of the poles has a short circuit or open circuit fault, the output of the other pole cannot work properly. Therefore, it is of great significance to study a non-isolated bipolar multi-output DC / DC converter that can achieve automatic balancing of bipolar voltage and has high reliability. Summary of the invention

[0004] In order to solve the problem of inter-pole voltage balance in the existing non-isolated bipolar multi-output DC-DC converter, the present invention proposes a high-reliability bipolar output voltage self-balancing Cuk DC-DC converter based on the traditional Cuk circuit. The converter consists of a Cuk converter and a plurality of positive polarity conversion units. By adjusting the number of positive polarity conversion units, the input and output voltage gain and the voltage stress of the switching device can be adjusted. When one of the switch tubes is damaged, the remaining circuits can work normally. The converter has simple control and drive circuits, self-balanced output voltage, low voltage stress of the switching device, wide input and output voltage adjustment range, and high reliability; it is more suitable for bipolar power supply occasions where the input and output voltage variation ranges are relatively large, multiple power supplies are required, and reliability requirements are high.

[0005] The technical solution adopted by the present invention is:

[0006] A high reliability bipolar output voltage self-balancing Cuk DC-DC converter,

[0007] The converter includes i Cuk converters and j positive polarity conversion units;

[0008] In the i Cuk converters:

[0009] The first Cuk converter consists of a DC input source u in1 , two inductors L 11 , L 12 , two capacitors C 11 , C 12 , a power switch S1, a diode D 11 ; Its connection form is as follows: DC input source u in1 The positive connection inductor L 11 One end of the inductor L 11 The other end is connected to the drain of power switch S1 and capacitor C 11 One end, capacitor C 11 The other end is connected to the diode D 11 Anode, inductor L 12 One end of the inductor L 12 The other end of the capacitor C 12 One end of the capacitor C 12 The other end is connected to the diode D 11 The cathode of the power switch S1, the source of the DC input source u in1 The negative pole of the power supply is connected to the ground;

[0010] The second Cuk converter consists of a DC input source u in2 , two inductors L 21 , L 22 , two capacitors C 21 , C 22 , a power switch S2, a diode D 21 ; Its connection form is as follows: DC input source u in2 The positive connection inductor L 21 One end of the inductor L 21 The other end is connected to the drain of power switch S2 and capacitor C 21 One end, capacitor C 21 The other end is connected to the diode D 21 Anode, inductor L 22 One end of the inductor L 22 The other end of the capacitor C 22 One end of the capacitor C 22 The other end is connected to the diode D 21 The cathode;

[0011] The third Cuk converter consists of a DC input source u in3 , two inductors L 31 , L 32 , two capacitors C31 , C 32 , a power switch S3, a diode D 31 ; Its connection form is as follows: DC input source u in3 The positive connection inductor L 31 One end of the inductor L 31 The other end is connected to the drain of power switch S3 and capacitor C 31 One end, capacitor C 31 The other end is connected to the diode D 31 Anode, inductor L 32 One end of the inductor L 32 The other end of the capacitor C 32 One end of the capacitor C 32 The other end of the diode D 31 The cathode;

[0012] ...and so on;

[0013] The i-th Cuk converter consists of a DC input source u ini , two inductors L i1 , L i2 , two capacitors C i1 , C i2 , a power switch S i , a diode D i1 ; Its connection form is as follows: DC input source u ini The positive connection inductor L i1 One end of the inductor L i1 The other end is connected to the power switch S i The drain capacitor C i1 One end, capacitor C i1 The other end is connected to the diode D i1 Anode, inductor L i2 One end of the inductor L i2 The other end of the capacitor C i2 One end of the capacitor C i2 The other end of the diode D i1 The cathode;

[0014] The DC input source u of the first Cuk converter in1 The negative poles are connected to the DC input source u of the second Cuk converter in2 The negative pole of the third Cuk converter is the DC input source u in3 The negative pole of the ith Cuk converter, ..., the DC input source u ini The negative electrode;

[0015] The source of the power switch S1 of the first Cuk converter is connected to the source of the power switch S2 of the second Cuk converter, the source of the power switch S3 of the third Cuk converter, and so on. i The source of

[0016] In the j positive polarity conversion units:

[0017] The first positive polarity conversion unit includes an inductor L 13 , a diode D 12 , two capacitors C 13 , C 14 ; Among them, the capacitor C 13 The other end is connected to the diode D 12 Anode, inductor L 13 One end of the inductor L 13 The other end of the capacitor C 14 One end of the capacitor C 14 The other end of the diode D 12 The cathode;

[0018] The second positive polarity conversion unit includes an inductor L 23 , a diode D 22 , two capacitors C 23 , C 24 ; Among them, the capacitor C 23 The other end is connected to the diode D 22 Anode, inductor L 23 One end of the inductor L 23 The other end of the capacitor C 24 One end of the capacitor C 24 The other end of the diode D 22 The cathode;

[0019] The third positive polarity conversion unit includes an inductor L 33 , a diode D 32 , two capacitors C 33 , C 34 ; Among them, the capacitor C 33 The other end is connected to the diode D 32 Anode, inductor L 33 One end of the inductor L 33 The other end of the capacitor C 34 One end of the capacitor C 34 The other end of the diode D 32 The cathode;

[0020] ...and so on;

[0021] The jth positive polarity conversion unit includes an inductor L j3 , a diode D j2 , two capacitors C j3 , C j4 ; Among them, the capacitor C j3 The other end is connected to the diode D j2 Anode, inductor L j3 One end of the inductor L j3 The other end of the capacitor C j4 One end of the capacitor C j4 The other end of the diode D j2 The cathode;

[0022] The capacitor C in the first positive polarity conversion unit 13 One end of the inductor L in the first Cuk converter is connected 12 One end of the capacitor C in the second positive polarity conversion unit 23 One end of the inductor L in the second Cuk converter is connected 22 One end of the jth positive polarity conversion unit, ..... and so on, the capacitor C j3 One end of the inductor L in the i-th Cuk converter is connected to i2 one end of

[0023] Capacitor C in the first Cuk converter 12 The other end is connected to the capacitor C in the first positive polarity conversion unit. 14 One end of the capacitor C in the first positive polarity conversion unit 14 The other end is connected to the capacitor C in the second positive polarity conversion unit 24 One end of the capacitor C in the second positive polarity conversion unit 24 The other end is connected to the capacitor C in the third positive polarity conversion unit 34 One end of the capacitor C in the j-1th positive polarity conversion unit. (j-1)4 The other end is connected to the capacitor C in the jth positive polarity conversion unit j4 one end of

[0024] The capacitor C in the i-th Cuk converter i2 One end is connected to the negative load R N One end of the negative load R N The other end is connected to the capacitor C in the first Cuk converter 12 The other end, positive polarity load R P One end of the positive load R P The other end is connected to the capacitor C in the jth positive polarity conversion unit j4 the other end.

[0025] (1) The positive polarity conversion unit and the Cuk converter structure of the proposed high-reliability bipolar output voltage self-balanced Cuk converter structure can be continuously expanded until they include i Cuk converters and j positive polarity conversion units.

[0026] (2) Take the first Cuk converter and the first positive polarity conversion unit as an example. When the main switch tube S1 is turned off, the diode D in the positive polarity conversion unit 12 First, it is turned on. At this time, the auxiliary capacitor C 13 and capacitor C 12 Since the capacitor has a clamping effect, C 12 The voltage on C 13 After that, the diode D of the first Cuk converter 11 is turned on, forming an auxiliary capacitor C 13 and capacitor C 14 The parallel circuit, C 14 The voltage on C 13 The voltage across the two ends. Therefore, the positive and negative output capacitors C 12 , C 14 The voltage of the auxiliary capacitor C 13 voltage is near.

[0027] A high-reliability bipolar output voltage self-balancing Cuk DC-DC converter, the converter includes two Cuk converters and two positive polarity conversion units;

[0028] The first Cuk converter consists of a DC input source u in1 , two inductors L 11 , L 12 , two capacitors C 11 , C 12 , a power switch S1, a diode D 11 ; Its connection form is as follows: DC input source u in1 The positive connection inductor L 11 One end of the inductor L 11 The other end is connected to the drain of power switch S1 and capacitor C 11 One end, capacitor C 11 The other end is connected to the diode D 11 Anode, inductor L 12 One end of the inductor L 12 The other end of the capacitor C 12 One end of the capacitor C 12 The other end is connected to the diode D 11 The cathode of the power switch S1, the source of the DC input source uin1 The negative pole of the power supply is connected to the ground;

[0029] The second Cuk converter consists of a DC input source u in2 , two inductors L 21 , L 22 , two capacitors C 21 , C 22 , a power switch S2, a diode D 21 ; Its connection form is as follows: DC input source u in2 The positive connection inductor L 21 One end of the inductor L 21 The other end is connected to the drain of power switch S2 and capacitor C 21 One end, capacitor C 21 The other end is connected to the diode D 21 Anode, inductor L 22 One end of the inductor L 22 The other end of the capacitor C 22 One end of the capacitor C 22 The other end of the diode D 21 The cathode;

[0030] The DC input source u of the first Cuk converter in1 The negative pole is connected to the DC input source u of the second Cuk converter in2 The source of the power switch S1 of the first Cuk converter is connected to the source of the power switch S2 of the second Cuk converter;

[0031] The first positive polarity conversion unit includes an inductor L 13 , a diode D 12 , two capacitors C 13 , C 14 ; Among them, the capacitor C 13 The other end is connected to the diode D 12 Anode, inductor L 13 One end of the inductor L 13 The other end of the capacitor C 14 One end of the capacitor C 14 The other end of the diode D 12 The cathode;

[0032] The second positive polarity conversion unit includes an inductor L 23 , a diode D 22 , two capacitors C 23 , C 24 ; Among them, the capacitor C 23 The other end is connected to the diode D 22 Anode, inductor L23 One end of the inductor L 23 The other end of the capacitor C 24 One end of the capacitor C 24 The other end of the diode D 22 The cathode;

[0033] The capacitor C in the first positive polarity conversion unit 13 One end of the inductor L in the first Cuk converter is connected 12 One end of the capacitor C in the second positive polarity conversion unit 23 One end of the inductor L in the second Cuk converter is connected 22 one end of

[0034] Capacitor C in the first Cuk converter 12 The other end is connected to the capacitor C in the first positive polarity conversion unit. 14 One end of the capacitor C in the first positive polarity conversion unit 14 The other end is connected to the capacitor C in the second positive polarity conversion unit 24 one end of

[0035] The capacitor C in the second Cuk converter 22 One end is connected to the negative load R N One end of the negative load R N The other end is connected to the capacitor C in the first Cuk converter 12 The other end, positive polarity load R P One end of the positive load R P The other end is connected to the capacitor C in the second positive polarity conversion unit 24 the other end.

[0036] When the number of positive polarity conversion units j = 2, the number of Cuk converter units i = 2, and assuming that the inductor L 11 , L 12 , L 13 , L 21 , L 22 , L 23 The current is continuous, and the converter has 6 operating modes in the entire operation cycle:

[0037] Mode 1: At this moment, the switches S1 and S2 are turned on, and the diode D 11 , D 12 , D 21 , D 22 Withstands reverse voltage and remains off. The inductor L in the Cuk converter 11 , L 12 , L 21 , L 22 and capacitor C12 , C 22 Charging, capacitor C 11 , C 21 Discharge. The inductor L in the positive polarity conversion unit 13 , L 23 and capacitor C 13 , C 23 Charging, capacitor C 14 , C 24 Discharge. The voltage on each inductor can be expressed as:

[0038]

[0039] Mode 2: At this moment, the switch tube S1 enters the shutdown process, and S2 remains on. 11 , D 21 , D 22 Both continue to remain in the off state, D 12 At this time, the inductor L in the Cuk converter is turned on and a forward current flows through it. 21 , L 22 and capacitor C 11 , C 12 , C 22 Charging, inductance L 11 , L 12 and capacitor C 21 Discharge. The inductor L in the positive polarity conversion unit 23 and capacitor C 14 , C 23 Charging, inductance L 13 and capacitor C 13 , C 24 Discharge. The voltage on each inductor can be expressed as:

[0040]

[0041] Mode 3: At this moment, the switch tube S1 remains off, S2 remains on, and the diode D 21 , D 22 All off, D 11 , D 12 is turned on and a forward current flows through it. 21 , L 22 , L 23 and capacitor C 11 , C 12 , C 14 , C 22 , C 23 Charging, inductance L 11 , L 12 , L 13 and capacitor C 13 , C 21 , C24 Discharge, the voltage on the inductor can be expressed as:

[0042]

[0043] In the formula, u N Indicates the negative output voltage of the converter, u P Indicates the positive polarity output voltage of the converter, u in1 Indicates the input voltage of the first Cuk converter, u in2 represents the input voltage of the second Cuk converter. This is true for all six modes.

[0044] Mode 4: At this moment, the switches S1 and S2 are turned off, and the diode D 21 Shutdown, D 11 , D 12 , D 22 Capacitor C 11 , C 12 , C 14 , C 22 , C 23 Charging, inductance L 11 , L 12 , L 13 , L 21 , L 22 , L 23 and capacitor C 13 , C 21 , C 24 Discharge, the voltage on the inductor can be expressed as:

[0045]

[0046] Mode 5: At this moment, the switches S1 and S2 are turned off, and the diode D 12 Shutdown, D 11 , D 21 , D 22 Capacitor C 11 , C 13 , C 14 , C 21 , C 24 Charging, inductance L 11 , L 12 , L 13 , L 21 , L 22 , L 23 and capacitor C 12 , C 22 , C 23 Discharge, the voltage on the inductor can be expressed as:

[0047]

[0048] Mode 6: At this moment, switch tube S1 is turned on, S2 is turned off, and diode D 11 , D 12 Shutdown, D 21 , D 22 Conductive. Inductor L 11 , L 12 , L 13 and capacitor C 13 , C 21 , C 24 Charging, inductance L 21 , L 22 , L 23 and capacitor C 11 , C 12 , C 14 , C 22 , C 23 Discharge, the voltage on the inductor can be expressed as:

[0049]

[0050] By applying the volt-second balance principle to each inductor, the average voltage across the converter capacitors can be found as:

[0051]

[0052] The present invention provides a high-reliability bipolar output voltage self-balancing Cuk DC-DC converter, and the technical effects are as follows:

[0053] 1) Input and output gain is high, output capacitors are connected in series and voltage is balanced. 11 , L 12 , L 13 , L 21 , L 22 , L 23 When the current is continuously conducted, the details are as follows:

[0054] When i Cuk converters are used, j positive polarity units are used, and there are i input power sources in total, the maximum output voltages of the positive and negative polarities are respectively:

[0055] Where D1 represents the duty cycle of the switch S1 in the first Cuk converter, D i represents the switch tube S in the i-th Cuk converter i The duty cycle size, u in1 Indicates the input voltage of the first Cuk converter, u ini Represents the input voltage of the i-th Cuk converter.

[0056] The switch tube S in the i-th Cuk converter i The voltage stress is: Capacitor C i1 The voltage stress on is: Where k is a variable; capacitance C i2 The voltage stress on is:

[0057] The capacitor C in the jth positive polarity conversion unit j3 The voltage stress on is:

[0058] Where k is a variable; capacitance C j4 The voltage stress on is:

[0059] Where D1 represents the duty cycle of the switch S1 in the first Cuk converter, D (k-1) represents the switch tube S in the k-1th Cuk converter (k-1) The duty cycle of D k represents the switch tube S in the kth Cuk converter k The duty cycle size, and k∈[1,j]; u in1 Indicates the input voltage of the first Cuk converter, u in(k-1) represents the input voltage of the k-1th Cuk converter. Similarly, u ink Represents the input voltage of the kth Cuk converter, and k∈[1,j]. 2) The voltage balance of the converter is achieved by the clamping effect of the auxiliary capacitor in the positive polarity conversion unit. Through the sequential conduction of the diodes, different output capacitor parallel circuits are formed in different modes, and the mean values ​​of the output voltages of the two poles are clamped at the voltage peak and voltage mean of the auxiliary capacitors respectively. By increasing the capacitance of the auxiliary capacitors, the difference between the voltage peak and voltage mean of the auxiliary capacitors is lowered, thereby reducing the deviation of the output voltage between the two poles. Therefore, the converter has highly symmetrical and common-ground positive and negative output voltages, without the need for complex voltage or power balancing control circuits. BRIEF DESCRIPTION OF THE DRAWINGS

[0060] The present invention will be further described below in conjunction with the accompanying drawings and examples:

[0061] Figure 1 This is a circuit topology diagram of the DC-DC converter of the present invention when the number of positive polarity conversion units is 2 and the number of Cuk converters is 2.

[0062] Figure 2 The circuit topology diagram of the DC-DC converter of the present invention contains i Cuk converters and j positive polarity conversion units.

[0063] Figure 3 The figure is a comparison diagram of the voltage gain of the DC-DC converter of the present invention and the voltage gain of the Cuk converter.

[0064] Figure 4 It is a simulation voltage waveform diagram of the DC-DC converter of the present invention when the input voltage is 48V, D1=D2=0.6, and the loads are equal.

[0065] Figure 5 The simulated voltage waveform of the DC-DC converter of the present invention is shown when the input voltage is 48V, D1=D2=0.6, and the loads are unequal.

[0066] Figure 6 The figure shows the connection diagram between the bipolar DC bus and the bipolar converter.

[0067] Figure 7 Schematic diagram of the deviation between the converter output voltage and the bipolar DC bus voltage.

[0068] Figure 8 Schematic diagram of the unbalanced power processed by the converter and the bipolar DC bus voltage deviation. DETAILED DESCRIPTION

[0069] like Figure 1 As shown, the structure of the high reliability bipolar output voltage self-balancing Cuk converter of the present invention, wherein: the first Cuk converter includes a DC input source u in1 , two inductors L 11 , L 12 , two capacitors C 11 , C 12 , a power switch S1, a diode D 11 The connection form is as follows: the drain of the power switch S1 is connected to the inductor L 11 One end and capacitor C 11 The intersection of one end and the source of S1 is directly grounded. 11 The other end is connected to the diode D 11 Anode and inductor L 12 The intersection of one end. Inductance L 12 The other end of the capacitor C 12 Capacitor C 12 The other end of the diode D 11 The cathode of the DC input source u in1 The negative terminal is connected to the common ground.

[0070] The second Cuk converter consists of a DC input source u in2 , two inductors L 21 , L 22, two capacitors C 21 , C 22 , a power switch S2, a diode D 21 The connection form is as follows: the drain of power switch S2 is connected to the inductor L 21 One end and capacitor C 21 The intersection of one end and the source of S2 is directly grounded. 21 The other end is connected to the diode D 21 Anode and inductor L 22 The intersection of one end. Inductance L 22 The other end of the capacitor C 22 Capacitor C 22 The other end is connected to the diode D 21 cathode.

[0071] The input terminals of the two Cuk converters are connected in parallel, and the output terminals are connected in series. The detailed connection method is as follows: The parallel connection of the input ports is mainly reflected in the connection of the sources of the two power switches S1 and S2 and the common ground. At the same time, there are two DC input sources u in1 ,u in2 The output port series connection is mainly reflected in the superposition of the Cuk converter output loop. 21 , capacitor C 22 With inductance L 22 The output port of the second Cuk converter is superimposed on the diode D 11 , capacitor C 12 With inductance L 12 Above the output port of the first Cuk converter.

[0072] Since the negative output load is connected across the common point and the inductor L 22 and capacitor C 22 At the connected intersection, the negative polarity output voltage of the converter is twice the output voltage of the Cuk converter.

[0073] ... and so on, the i-th Cuk converter can still be superimposed on the i-1-th Cuk converter. Therefore, the negative output voltage of this converter is i times that of the Cuk converter. This makes the topology have a wider voltage gain range, which is more advantageous than the traditional voltage self-balancing converter.

[0074] The first positive polarity conversion unit includes an inductor L 13 , a diode D 12 , two capacitors C 13 , C 14 Among them, the capacitor C 13 The lower end is connected to the diode D 12 The anode and inductance L 13The inductance L 13 The other end of the capacitor C 14 One end of the capacitor C 14 The other end of the diode D 12 cathode connection.

[0075] The second positive polarity conversion unit includes an inductor L 23 , a diode D 22 , two capacitors C 23 , C 24 Among them, the capacitor C 23 The lower end is connected to the diode D 22 The anode and inductance L 23 The inductance L 23 The other end of the capacitor C 24 One end of the capacitor C 24 The other end of the diode D 22 cathode connection.

[0076] The connection form of the first positive polarity conversion unit and the second positive polarity conversion unit is as follows:

[0077] From the output side, the output loops of multiple positive polarity conversion units are superimposed: the diode D 22 , capacitor C 24 With inductance L 23 The output port of the second positive polarity conversion unit is superimposed on the diode D 12 , capacitor C 14 With inductance L 13 On the output port of the first positive polarity conversion unit.

[0078] ...and so on, the j-th positive polarity transformation unit can still be superimposed on the j-1-th positive polarity transformation unit.

[0079] From the above analysis, it can be known that the positive polarity conversion unit and Cuk converter unit contained in the converter can be expanded to increase or decrease to different voltage levels, which is well adapted to the needs of the bipolar power supply bus.

[0080] The connection relationship between the first positive polarity conversion unit and the first Cuk converter is as follows:

[0081] The capacitor C of the first positive polarity conversion unit 13 The upper end is connected to the capacitor C in the first Cuk converter 11 、Diode D 11 Anode, inductor L 12 Connect the capacitor C in the first positive polarity conversion unit. 14 With inductance L13 The intersection point is connected to the common point of the first Cuk converter.

[0082] The connection relationship between the second positive polarity conversion unit and the second Cuk converter is as follows:

[0083] The capacitor C of the second positive polarity conversion unit 23 The upper end is connected to the capacitor C in the second Cuk converter 21 、Diode D 21 Anode, inductor L 22 At the connected intersection of .

[0084] Negative load R N One end of the capacitor C in the second Cuk converter 22 and inductor L 22 The intersection of the negative load R N The other end is connected to the common point in the first Cuk converter.

[0085] Positive load R P One end of the capacitor C in the second positive polarity conversion unit 24 and diode D 22 The cathode intersection is connected to the positive polarity load R P The other end is connected to the negative load R N connected to the public places.

[0086] When the number of positive polarity conversion units j = 2, the number of Cuk converter units i = 2, and assuming that the inductor L 11 , L 12 , L 13 , L 21 , L 22 , L 23 The current is continuous, and the converter has 6 operating modes in the entire operation cycle:

[0087] Mode 1: At this moment, the switches S1 and S2 are turned on, and the diode D 11 , D 12 , D 21 , D 22 Withstands reverse voltage and remains off. The inductor L in the Cuk converter 11 , L 12 , L 21 , L 22 and capacitor C 12 , C 22 Charging, capacitor C 11 , C 21 Discharge. The inductor L in the positive polarity conversion unit 13 , L 23 and capacitor C 13 , C23 Charging, capacitor C 14 , C 24 Discharge. The voltage on each inductor can be expressed as:

[0088]

[0089] Mode 2: At this moment, the switch tube S1 enters the shutdown process, and S2 remains on. 11 , D 21 , D 22 Both continue to remain in the off state, D 12 At this time, the inductor L in the Cuk converter is turned on and a forward current flows through it. 21 , L 22 and capacitor C 11 , C 12 , C 22 Charging, inductance L 11 , L 12 and capacitor C 21 Discharge. The inductor L in the positive polarity conversion unit 23 and capacitor C 14 , C 23 Charging, inductance L 13 and capacitor C 13 , C 24 Discharge. The voltage on each inductor can be expressed as:

[0090]

[0091] Mode 3: At this moment, the switch tube S1 remains off, S2 remains on, and the diode D 21 , D 22 All off, D 11 , D 12 is turned on and a forward current flows through it. 21 , L 22 , L 23 and capacitor C 11 , C 12 , C 14 , C 22 , C 23 Charging, inductance L 11 , L 12 , L 13 and capacitor C 13 , C 21 , C 24 Discharge, the voltage on the inductor can be expressed as:

[0092]

[0093] Mode 4: At this moment, the switches S1 and S2 are turned off, and the diode D 21Shutdown, D 11 , D 12 , D 22 Capacitor C 11 , C 12 , C 14 , C 22 , C 23 Charging, inductance L 11 , L 12 , L 13 , L 21 , L 22 , L 23 and capacitor C 13 , C 21 , C 24 Discharge, the voltage on the inductor can be expressed as:

[0094]

[0095] Mode 5: At this moment, the switches S1 and S2 are turned off, and the diode D 12 Shutdown, D 11 , D 21 , D 22 Capacitor C 11 , C 13 , C 14 , C 21 , C 24 Charging, inductance L 11 , L 12 , L 13 , L 21 , L 22 , L 23 and capacitor C 12 , C 22 , C 23 Discharge, the voltage on the inductor can be expressed as:

[0096]

[0097] Mode 6: At this moment, switch tube S1 is turned on, S2 is turned off, and diode D 11 , D 12 Shutdown, D 21 , D 22 Conductive. Inductor L 11 , L 12 , L 13 and capacitor C 13 , C 21 , C 24 Charging, inductance L 21 , L 22 , L 23 and capacitor C 11 , C 12 , C14 , C 22 , C 23 Discharge, the voltage on the inductor can be expressed as:

[0098]

[0099] By applying the volt-second balance principle to each inductor, the average voltage across the converter capacitors can be found as:

[0100]

[0101] Figure 4 The simulated voltage waveform of the converter of the present invention is shown when the input voltage is 48V, D1=D2=0.6, and the loads are equal.

[0102] Figure 5 The simulated voltage waveform of the converter of the present invention is shown when the input voltage is 48V, D1=D2=0.6, and the loads are unequal.

[0103] When the bus voltage deviation becomes larger and larger, the converter's ability to support the bus voltage deviation is achieved by differentially outputting the converter's own input power to the pole with lower bus voltage.

[0104] refer to Figure 6 The specific analysis is as follows:

[0105] (1). When the bus voltage u NZ ,u ZP As a known external factor, the converter voltage u' o1 ,u' o2 When the voltage u' at the output port of the converter is unknown and is affected by unbalanced power as the dependent variable, the voltage u' at the output port of the converter can be listed according to the law of conservation of loop power. o1 ,u' o2 , and the uncertain bus current i' P ,i' N ,i' Z The formula is:

[0106]

[0107] Where r N , r P , r Z Represent the line resistance on N, P, and Z respectively.

[0108] (2). When the bus voltage u' NZ ,u' ZP As a dependent variable, its size is affected by the converter output port voltage and power, and the converter u' is listedo1 ,u' o2 The expression of output voltage is:

[0109]

[0110] In the formula, u in Indicates the input voltage of the Cuk converter, i in represents the input current of the Cuk converter; D1 represents the duty cycle of the switch S1 in the Cuk converter; P in It represents the total input power of the proposed converter, P N It represents the negative output power of the proposed converter, P P Indicates the magnitude of the positive output power of the proposed converter; u C11 ,u C14 Represents the output side capacitance C 11 , C 14 The voltage size.

[0111] Combining the above formulas, we can get the exact function expression of the converter output voltage:

[0112]

[0113] The above expression clearly shows the functional relationship between known quantities such as converter output side voltage, converter input side power, duty cycle, bus voltage deviation, etc.

[0114] The specific simulation results can be obtained:

[0115] a: When there is a power deviation between the positive and negative poles of the bus, resulting in a low voltage at one pole, the output voltage of the converter at that pole will increase to support the lower voltage of the bus at that pole.

[0116] b: When there is a 5% deviation in the voltage between the two poles of the bus, all the input power of the converter will be output to the lower side of the bus voltage, and the ability to support the voltage between the two poles of the bus will reach its limit.

[0117] Figure 7 The deviation between the converter output voltage and the bipolar DC bus voltage is shown. It can be seen that the deviation of the converter output voltage is smaller than the deviation of the bipolar DC bus voltage.

[0118] Figure 8 The relationship between the unbalanced power handled by the converter and the voltage deviation of the bipolar DC bus is shown. It can be seen that when there is a 5% deviation between the two polar voltages of the bus, the entire input power of the converter, 300W, is output to the lower voltage side, which is the limit of the unbalanced power that the converter can handle.

[0119] The present invention discloses a high-reliability bipolar output voltage self-balancing Cuk DC-DC converter, which includes i DC input sources, i Cuk converters, and j positive polarity voltage expansion units. The positive polarity conversion unit is composed of an inductor, two capacitors and a diode. By adjusting the number of positive polarity conversion units, the input and output gain of the converter and the voltage stress of the switching device can be adjusted. The voltage self-balancing of the converter is achieved by the clamping effect of the auxiliary capacitor in the positive polarity conversion unit. Different output capacitor parallel circuits can be formed in different modes, and the mean values ​​of the output voltages of the two poles are clamped at the voltage peak value and the voltage mean value of the auxiliary capacitor respectively. By increasing the capacitance of the auxiliary capacitor, the difference between the voltage peak value and the voltage mean value of the auxiliary capacitor is lowered, thereby reducing the deviation of the output voltage between the two poles, without the need for a complex voltage or power balancing control circuit. By decoupling the mutual influence relationship between the converter voltage and the bus voltage, it can be obtained that the output power of the two poles of the converter will correspondingly supplement the deviation of the power consumption of the two poles of the bus, so as to achieve the ability to support the voltage of the two poles of the bus.

Claims

1. A high reliability bipolar output voltage self-balancing Cuk DC-DC converter, characterized in that: The converter includes i Cuk converters and j positive polarity conversion units; In the i Cuk converters: The first Cuk converter consists of a DC input source u in1 , two inductors L 11 , L 12 , two capacitors C 11 , C 12 , a power switch S1, a diode D 11 ; Its connection form is as follows: DC input source u in1 The positive connection inductor L 11 One end of the inductor L 11 The other end is connected to the drain of power switch S1 and capacitor C 11 One end, capacitor C 11 The other end is connected to the diode D 11 Anode, inductor L 12 One end of the inductor L 12 The other end of the capacitor C 12 One end of the capacitor C 12 The other end is connected to the diode D 11 The cathode of the power switch S1, the source of the DC input source u in1 The negative pole of the power supply is connected to the ground; The second Cuk converter consists of a DC input source u in2 , two inductors L 21 , L 22 , two capacitors C 21 , C 22 , a power switch S2, a diode D 21 ; Its connection form is as follows: DC input source u in2 The positive connection inductor L 21 One end of the inductor L 21 The other end is connected to the drain of power switch S2 and capacitor C 21 One end, capacitor C 21 The other end is connected to the diode D 21 Anode, inductor L 22 One end of the inductor L 22 The other end of the capacitor C 22 One end of the capacitor C 22 The other end of the diode D 21 The cathode; The third Cuk converter consists of a DC input source u in3 , two inductors L 31 , L 32 , two capacitors C 31 , C 32 , a power switch S3, a diode D 31 ; Its connection form is as follows: DC input source u in3 The positive connection inductor L 31 One end of the inductor L 31 The other end is connected to the drain of power switch S3 and capacitor C 31 One end, capacitor C 31 The other end is connected to the diode D 31 Anode, inductor L 32 One end of the inductor L 32 The other end of the capacitor C 32 One end of the capacitor C 32 The other end of the diode D 31 The cathode; ...and so on; The i-th Cuk converter consists of a DC input source u ini , two inductors L i1 , L i2 , two capacitors C i1 , C i2 , a power switch S i , a diode D i1 ; Its connection form is as follows: DC input source u ini The positive connection inductor L i1 One end of the inductor L i1 The other end is connected to the power switch S i The drain, capacitance C i1 One end, capacitor C i1 The other end is connected to the diode D i1 Anode, inductor L i2 One end of the inductor L i2 The other end of the capacitor C i2 One end of the capacitor C i2 The other end of the diode D i1 The cathode; The DC input source u of the first Cuk converter in1 The negative poles are connected to the DC input source u of the second Cuk converter in2 The negative pole of the third Cuk converter is the DC input source u in3 The negative pole of the ith Cuk converter, ..., the DC input source u ini The negative electrode; The source of the power switch S1 of the first Cuk converter is connected to the source of the power switch S2 of the second Cuk converter, the source of the power switch S3 of the third Cuk converter, and so on. i The source of In the j positive polarity conversion units: The first positive polarity conversion unit includes an inductor L 13 , a diode D 12 , two capacitors C 13 , C 14 ; Among them, the capacitor C 13 The other end is connected to the diode D 12 Anode, inductor L 13 One end of the inductor L 13 The other end of the capacitor C 14 One end of the capacitor C 14 The other end of the diode D 12 The cathode; The second positive polarity conversion unit includes an inductor L 23 , a diode D 22 , two capacitors C 23 , C 24 ; Among them, the capacitor C 23 The other end is connected to the diode D 22 Anode, inductor L 23 One end of the inductor L 23 The other end of the capacitor C 24 One end of the capacitor C 24 The other end of the diode D 22 The cathode; The third positive polarity conversion unit includes an inductor L 33 , a diode D 32 , two capacitors C 33 , C 34 ; Among them, the capacitor C 33 The other end is connected to the diode D 32 Anode, inductor L 33 One end of the inductor L 33 The other end of the capacitor C 34 One end of the capacitor C 34 The other end of the diode D 32 The cathode; ...and so on; The jth positive polarity conversion unit includes an inductor L j3 , a diode D j2 , two capacitors C j3 , C j4 ; Among them, the capacitor C j3 The other end is connected to the diode D j2 Anode, inductor L j3 One end of the inductor L j3 The other end of the capacitor C j4 One end of the capacitor C j4 The other end of the diode D j2 The cathode; The capacitor C in the first positive polarity conversion unit 13 One end of the inductor L in the first Cuk converter is connected 12 One end of the capacitor C in the second positive polarity conversion unit 23 One end of the inductor L in the second Cuk converter is connected 22 One end of the jth positive polarity conversion unit, ..... and so on, the capacitor C j3 One end of the inductor L in the i-th Cuk converter is connected to i2 one end of Capacitor C in the first Cuk converter 12 The other end is connected to the capacitor C in the first positive polarity conversion unit. 14 One end of the capacitor C in the first positive polarity conversion unit 14 The other end is connected to the capacitor C in the second positive polarity conversion unit 24 One end of the capacitor C in the second positive polarity conversion unit 24 The other end is connected to the capacitor C in the third positive polarity conversion unit 34 One end of the capacitor C in the j-1th positive polarity conversion unit. (j -1 )4 The other end is connected to the capacitor C in the jth positive polarity conversion unit j4 one end of The capacitor C in the i-th Cuk converter i2 One end is connected to the negative load R N One end of the negative load R N The other end is connected to the capacitor C in the first Cuk converter 12 The other end, positive polarity load R P One end of the positive load R P The other end is connected to the capacitor C in the jth positive polarity conversion unit j4 the other end.

2. A high reliability bipolar output voltage self-balancing Cuk DC-DC converter according to claim 1, characterized in that: When the converter includes the first Cuk converter and the first positive polarity conversion unit, when the main switch tube S1 is turned off, the diode D 12 First, it is turned on; at this time, the auxiliary capacitor C 13 and capacitor C 12 The parallel circuit of the capacitor has a clamping effect, so C 12 The voltage on C 13 The voltage across the two ends; then, the diode D of the first Cuk converter 11 is turned on, forming an auxiliary capacitor C 13 and capacitor C 14 The parallel circuit, C 14 The voltage on C 13 The voltage across the two ends; therefore, the positive and negative output capacitors C 12 , C 14 The voltage of the auxiliary capacitor C 13 voltage is near.

3. The high reliability bipolar output voltage self-balancing Cuk DC-DC converter according to claim 1, characterized in that: When the number of positive polarity conversion units j = 2, the number of Cuk converter units i = 2, and assuming that the inductor L 11 , L 12 , L 13 , L 21 , L 22 , L 23 The current is continuous, and the converter has 6 operating modes in the entire operation cycle: Mode 1: At this moment, the switches S1 and S2 are turned on, and the diode D 11 , D 12 , D 21 , D 22 Withstand reverse voltage and remain off; the inductor L in the Cuk converter 11 , L 12 , L 21 , L 22 and capacitor C 12 , C 22 Charging, capacitor C 11 , C 21 Discharge; inductor L in the positive polarity conversion unit 13 , L 23 And capacitor C 13 , C 23 Charging, capacitor C 14 , C 24 discharge; the voltage on each inductor can be expressed as: Mode 2: At this moment, switch tube S1 enters the shutdown process, and S2 remains on; diode D 11 , D 21 , D 22 Both continue to remain in the off state, D 12 At this time, it is turned on and a forward current flows through it; the inductor L in the Cuk converter 21 , L 22 And capacitor C 11 , C 12 , C 22 Charging, inductance L 11 , L 12 And capacitor C 21 Discharge; inductor L in the positive polarity conversion unit 23 And capacitor C 14 , C 23 Charging, inductance L 13 And capacitor C 13 , C 24 discharge; the voltage on each inductor can be expressed as: Mode 3: At this moment, the switch tube S1 remains off, S2 remains on, and the diode D 21 , D 22 All off, D 11 , D 12 is turned on and a forward current flows through it; the inductor L 21 , L 22 , L 23 And capacitor C 11 , C 12 , C 14 , C 22 , C 23 Charging, inductance L 11 , L 12 , L 13 And capacitor C 13 , C 21 , C 24 Discharge, the voltage on the inductor can be expressed as: In the formula, u N Indicates the negative output voltage of the converter, u P Indicates the positive polarity output voltage of the converter, u in1 Indicates the input voltage of the first Cuk converter, u in2 Indicates the input voltage of the second Cuk converter; Mode 4: At this moment, the switches S1 and S2 are turned off, and the diode D 21 Shutdown, D 11 , D 12 , D 22 Conductivity; Capacitor C 11 , C 12 , C 14 , C 22 , C 23 Charging, inductance L 11 , L 12 , L 13 , L 21 , L 22 , L 23 And capacitor C 13 , C 21 , C 24 Discharge, the voltage on the inductor can be expressed as: Mode 5: At this moment, the switches S1 and S2 are turned off, and the diode D 12 Shutdown, D 11 , D 21 , D 22 Conductivity; Capacitor C 11 , C 13 , C 14 , C 21 , C 24 Charging, inductance L 11 , L 12 , L 13 , L 21 , L 22 , L 23 And capacitor C 12 , C 22 , C 23 Discharge, the voltage on the inductor can be expressed as: Mode 6: At this moment, switch tube S1 is turned on, S2 is turned off, and diode D 11 , D 12 Shutdown, D 21 , D 22 Conductivity; Inductance L 11 , L 12 , L 13 And capacitor C 13 , C 21 , C 24 Charging, inductance L 21 , L 22 , L 23 and capacitor C 11 , C 12 , C 14 , C 22 , C 23 Discharge, the voltage on the inductor can be expressed as: By applying the volt-second balance principle to each inductor, the average voltage across the converter capacitors can be found as:

4. A high reliability bipolar output voltage self-balancing Cuk DC-DC converter, characterized in that: The converter includes two Cuk converters and two positive polarity conversion units; The first Cuk converter consists of a DC input source u in1 , two inductors L 11 , L 12 , two capacitors C 11 , C 12 , a power switch S1, a diode D 11 ; Its connection form is as follows: DC input source u in1 The positive connection inductor L 11 One end of the inductor L 11 The other end is connected to the drain of power switch S1 and capacitor C 11 One end, capacitor C 11 The other end is connected to the diode D 11 Anode, inductor L 12 One end of the inductor L 12 The other end of the capacitor C 12 One end of the capacitor C 12 The other end is connected to the diode D 11 The cathode of the power switch S1, the source of the DC input source u in1 The negative pole of the power supply is connected to the ground; The second Cuk converter consists of a DC input source u in2 , two inductors L 21 , L 22 , two capacitors C 21 , C 22 , a power switch S2, a diode D 21 ; Its connection form is as follows: DC input source u in2 The positive connection inductor L 21 One end of the inductor L 21 The other end is connected to the drain of power switch S2 and capacitor C 21 One end, capacitor C 21 The other end is connected to the diode D 21 Anode, inductor L 22 One end of the inductor L 22 The other end of the capacitor C 22 One end of the capacitor C 22 The other end is connected to the diode D 21 The cathode; The DC input source u of the first Cuk converter in1 The negative pole is connected to the DC input source u of the second Cuk converter in2 The source of the power switch S1 of the first Cuk converter is connected to the source of the power switch S2 of the second Cuk converter; The first positive polarity conversion unit includes an inductor L 13 , a diode D 12 , two capacitors C 13 , C 14 ; Among them, the capacitor C 13 The other end is connected to the diode D 12 Anode, inductor L 13 One end of the inductor L 13 The other end of the capacitor C 14 One end of the capacitor C 14 The other end of the diode D 12 The cathode; The second positive polarity conversion unit includes an inductor L 23 , a diode D 22 , two capacitors C 23 , C 24 ; Among them, the capacitor C 23 The other end is connected to the diode D 22 Anode, inductor L 23 One end of the inductor L 23 The other end of the capacitor C 24 One end of the capacitor C 24 The other end of the diode D 22 The cathode; The capacitor C in the first positive polarity conversion unit 13 One end of the inductor L in the first Cuk converter is connected 12 One end of the capacitor C in the second positive polarity conversion unit 23 One end of the inductor L in the second Cuk converter is connected 22 one end of Capacitor C in the first Cuk converter 12 The other end is connected to the capacitor C in the first positive polarity conversion unit. 14 One end of the capacitor C in the first positive polarity conversion unit 14 The other end is connected to the capacitor C in the second positive polarity conversion unit 24 one end of The capacitor C in the second Cuk converter 22 One end is connected to the negative load R N One end of the negative load R N The other end is connected to the capacitor C in the first Cuk converter 12 The other end, positive polarity load R P One end of the positive load R P The other end is connected to the capacitor C in the second positive polarity conversion unit 24 the other end.

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