A high-stability and low-ripple high-voltage DC converter

Abstract

The present invention discloses a high-stability, low-ripple high-voltage DC converter. The high-voltage DC converter includes a full-bridge inverter circuit, a resonant filter circuit, a transformer, and a voltage doubler rectifier circuit connected in sequence: wherein the voltage doubler rectifier circuit is formed by cascading a plurality of voltage doubler modules; the output ends of a plurality of the voltage doubler modules are connected in series to form a high-voltage DC output; each of the voltage doubler modules is formed by connecting a plurality of voltage doubler units in parallel and output in series and then connecting them in parallel with a bus capacitor; all bus capacitors are connected in series in sequence and then connected to the load. The voltage doubler rectifier circuit in the scheme of the present invention reduces the average current value and voltage variation on the capacitor and reduces the output ripple without increasing the device voltage level; at the same time, it reduces the total output voltage variation when the load changes, reduces the voltage regulation range of the resonant cavity, and improves the output voltage stability.

Description

Technical Field

[0001] The present invention relates to the technical field of switch converters, and in particular to a high-stability and low-ripple high-voltage direct current converter. Background Art

[0002] With the development of high-voltage electrical equipment, high-voltage DC converters have been widely used in various fields such as industrial production and rail transportation. As the requirements for power supply quality in application scenarios are increasing, how to achieve high-stability and low-ripple high-voltage DC power conversion has become a research hotspot today.

[0003] Traditional high-voltage converters that use industrial frequency transformers to step up voltage are bulky and have poor output voltage regulation capabilities. Switch-mode high-voltage DC conversion is mainly concentrated on phase-shifted full-bridge converters or LCC resonant converters, in which the output end of the transformer is connected to a voltage doubler rectifier circuit to reduce device stress. The phase-shifted full-bridge converter is difficult to achieve soft switching in the lagging bridge arm when adjusting voltage over a wide range or under light load, and the device shutdown current is large. The LCC resonant converter can integrate the parasitic parameters of the step-up transformer to achieve resonant cavity gain adjustment and inverter circuit soft switching. The traditional voltage doubler rectifier circuits mainly include Dickson and CW voltage doubler rectifier circuits, such as Figure 1 As shown in (a), in the Dickson voltage doubler rectifier circuit, the current flowing through the support capacitor and the bus capacitor is small, so it has the advantages of low output voltage drop and low ripple, but its last bus capacitor is directly connected in parallel to both ends of the load, and the capacitor voltage stress is high. Figure 1 As shown in (b), in the CW voltage doubler rectifier circuit, multiple bus capacitors are connected in series and then in parallel at both ends of the load. Although the device voltage stress is low, the current of the support capacitor and the bus capacitor is large, and the output voltage change and ripple are large.

[0004] Therefore, the existing voltage doubler rectifier circuit cannot meet the requirements of low device voltage stress and low output voltage drop and low ripple. Under the condition of limited device voltage level, the output voltage fluctuates greatly when the load changes, the output voltage stability is low, and a wide range of resonant cavity gain adjustment is required to maintain the total output voltage.

[0005] In summary, the current conventional high-voltage DC converters are difficult to achieve high-stability, low-ripple, and low-device voltage stress high-voltage DC power conversion, and cannot meet the increasingly stringent application requirements. How to achieve high-stability, low-ripple, and low-device voltage stress high-voltage DC conversion is a technical difficulty of the current high-voltage DC converters. Summary of the invention

[0006] In order to solve the technical problem that conventional high-voltage DC converters are difficult to achieve high-voltage DC power conversion with high stability, low ripple and low device voltage stress, an embodiment of the present invention provides a high-voltage DC converter with high stability and low ripple.

[0007] The technical solution of the embodiment of the present invention is achieved as follows:

[0008] An embodiment of the present invention provides a high-stability, low-ripple high-voltage DC converter, which includes a full-bridge inverter circuit, a resonant filter circuit, a transformer, and a voltage doubler rectifier circuit connected in sequence: wherein the voltage doubler rectifier circuit is formed by cascading a plurality of voltage doubler modules; the output ends of the plurality of voltage doubler modules are connected in series to form a high-voltage DC output; each of the voltage doubler modules is formed by a plurality of voltage doubler units having inputs connected in parallel and outputs connected in series and then connected in parallel with a bus capacitor; all bus capacitors are connected in series in sequence and then connected to a load.

[0009] In one embodiment, each of the voltage doubling units is composed of two groups of two diodes connected in reverse series and two supporting capacitors; the midpoints of the two diodes connected in reverse series are connected to the output end, and the endpoints of the two diodes connected in reverse series are respectively connected to the endpoints of the reverse diodes in the other group and then connected to the input end through a supporting capacitor; the supporting capacitor of the last voltage doubling unit of the first voltage doubling module is short-circuited.

[0010] In one embodiment, the number of voltage doubling units included in the previous voltage doubling module is greater than or equal to the number of voltage doubling units included in the next voltage doubling module.

[0011] In one embodiment, the resonant filter circuit includes a series resonant inductor, a series resonant capacitor, and a parallel resonant capacitor equivalently connected in parallel at both ends of the secondary winding of the transformer; the parallel resonant capacitor includes the parasitic capacitance of the transformer winding, the equivalent parasitic capacitance of the voltage doubler rectifier circuit diode, and the external parallel resonant capacitor.

[0012] In one embodiment, the full-bridge inverter circuit is composed of four metal-oxide-semiconductor field-effect transistors.

[0013] In one embodiment, the voltage stress of the bus capacitor of each voltage doubler module in the voltage doubler rectifier circuit is less than or equal to the number of voltage doubler units in the voltage doubler module divided by the total number of voltage doubler units multiplied by the total output voltage in a no-load state; the primary winding and secondary winding voltages of the transformer are both lower than the total output voltage; at the same time, when the load is grounded at one end close to the first-stage voltage doubler module, the voltage between the primary and secondary sides of the transformer is lower than the total output voltage.

[0014] In one embodiment, when outputting rated voltage, the switching frequency of the full-bridge inverter circuit is greater than the resonant frequency of the resonant inductor and the resonant capacitor in the resonant filter circuit, and the converter implements soft switching.

[0015] In one embodiment, there are multiple voltage doubling modules.

[0016] In one embodiment, each voltage doubling module includes a plurality of voltage doubling units.

[0017] This embodiment has the following beneficial effects:

[0018] Compared with the traditional CW type voltage doubler rectifier circuit with low device voltage stress, the voltage doubler rectifier circuit of this embodiment has a small number of capacitors flowing through during the charging and discharging process of the support capacitor, and the current flowing through each level of the support capacitor is small, so the voltage change of the support capacitor is small. At the same time, since only the support capacitor charging and discharging current of the last level of the voltage doubler unit flows through the bus capacitor, and the bus capacitor is charged every half switching cycle, the ripple of the bus capacitor is low, and the total output voltage ripple is low.

[0019] Compared with the Dickson voltage doubler rectifier circuit, the voltage stress of the device of the voltage doubler rectifier circuit in this embodiment is low. The voltage stress of the capacitor of each voltage doubler module in the voltage doubler rectifier circuit is less than or equal to the number of voltage doubler units in the voltage doubler module divided by the total number of voltage doubler units multiplied by the total output voltage under no-load condition. The voltage stress of the diode is less than or equal to the output voltage of the transformer. The voltage of the primary winding and the secondary winding of the transformer are much lower than the total output voltage. At the same time, when the load is grounded near one end of the first-stage voltage doubler module, the voltage between the primary and secondary sides of the transformer is much lower than the total output voltage.

[0020] That is, this embodiment can achieve a high-voltage DC output with low device stress, high stability and low ripple. Without increasing the device voltage level, the voltage doubler rectifier circuit in this embodiment can reduce the average current value and voltage variation on the capacitor, and reduce the output ripple; at the same time, when the load changes, the total output voltage variation is reduced, the voltage regulation range of the resonant cavity is reduced, and the output voltage stability is improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 Schematic diagram of a traditional voltage doubler rectifier circuit; (a) is a schematic diagram of a Dickson voltage doubler rectifier circuit; (b) is a schematic diagram of a CW voltage doubler rectifier circuit;

[0022] Figure 2 A schematic diagram of a high-stability and low-ripple high-voltage DC converter according to an embodiment of the present invention;

[0023] Figure 3 The main circuit diagram of the high-stability and low-ripple high-voltage DC converter according to an embodiment of the present invention is shown in FIG. 1 , wherein (a) is a circuit diagram of the full-bridge inverter part, the resonant filter circuit, and the transformer part of the main circuit; (b) is a circuit diagram of the voltage doubler rectifier circuit part of the main circuit;

[0024] Figure 4 Schematic diagram of typical waveforms of a high voltage DC converter according to an embodiment of the present invention;

[0025] Figure 5 Schematic diagram of the working mode of the high voltage DC converter according to the embodiment of the present invention; wherein (a) is when the voltagev Ts near U Ts Schematic diagram of the conduction current path of the diode when the voltage v Ts near- U Ts Schematic diagram of the conduction current path of the diode when the voltage v Ts Schematic diagram of the diode's conduction current path when the amplitude is less than the sum of the capacitor voltages of all current paths. DETAILED DESCRIPTION

[0026] The present invention will be described in further detail below with reference to the accompanying drawings and embodiments.

[0027] The embodiment of the present invention provides a high-stability and low-ripple high-voltage DC converter, such as Figure 2 As shown, the high-voltage DC converter includes a full-bridge inverter part 10, a resonant filter circuit and transformer part 20, and a high-stability and low-ripple voltage doubler rectifier circuit part 30. The three parts are connected in sequence to convert the input low-voltage DC into high-voltage DC. Among them, the full-bridge inverter part 10 includes a full-bridge inverter circuit 101; the resonant filter circuit and transformer part 20 includes a resonant filter circuit 201 and a transformer 202; the high-stability and low-ripple voltage doubler rectifier circuit part 30 is formed by cascading a voltage doubler module 301 and a voltage doubler module 302; the output ends of the voltage doubler module 301 and the voltage doubler module 302 are connected in series to form a high-voltage DC output; the voltage doubler module 301 is formed by the voltage doubler unit 3011, the voltage doubler unit 3012, and the voltage doubler unit 3013 input in parallel and output in series and then connected in parallel with the bus capacitor 3014; the voltage doubler module 302 is formed by the voltage doubler unit 3021, the voltage doubler unit 3022, and the voltage doubler unit 3023 input in parallel and output in series and then connected in parallel with the bus capacitor 3024; the bus capacitor 3014 and the bus capacitor 3024 are connected in series and connected to the load R L connect.

[0028] The number of voltage doubling modules in this embodiment is 2, and the number of voltage doubling units in each voltage doubling module is 3. In practical applications, the number of voltage doubling modules can be multiple, and the number of voltage doubling units in each voltage doubling module can also be multiple, which can be set according to actual needs.

[0029] The voltage doubler rectifier circuit in this embodiment is formed by cascading multiple voltage doubler modules; the output ends of multiple voltage doubler modules are connected in series to form a high-voltage DC output; each voltage doubler module is formed by connecting multiple voltage doubler units in parallel and output in series and then connecting them in parallel with a bus capacitor; all bus capacitors are connected in series in sequence and then connected to the load. The voltage doubler rectifier circuit using the above structure can provide a high-voltage DC output with low device stress, high stability and low ripple; without increasing the device voltage level, the average current value and voltage change on the capacitor can be reduced, and the output ripple can be reduced; at the same time, the total output voltage change is reduced when the load changes, the voltage regulation range of the resonant cavity is reduced, and the output voltage stability is improved.

[0030] In addition, each voltage doubling unit in the present embodiment can be composed of two groups of two diodes connected in reverse series and two supporting capacitors; the midpoints of the two diodes connected in reverse series are connected to the output end, and the endpoints of the two diodes connected in reverse series are respectively connected to the endpoints of the reverse diodes in the other group and then connected to the input end through a supporting capacitor; the supporting capacitor of the last voltage doubling unit of the first voltage doubling module is short-circuited.

[0031] Further, see Figure 3 , DC is the input DC source, V i is the input DC source voltage, C i is the DC bus capacitor. Metal-oxide-semiconductor field effect transistors (MOSFETs) Q1~Q4 constitute the full-bridge inverter part 10, and its output voltage is v r The resonant filter circuit and the transformer part 20 are composed of a resonant inductor L r With the resonant capacitor C r , transformer T1, parallel resonant capacitor C p The two ends of the secondary winding of T1 are connected in parallel. S1 and T S2 C p It includes the winding parasitic capacitance of transformer T1, the equivalent parasitic capacitance of the voltage doubler rectifier circuit diode, and the external parallel resonant capacitor. S1 and T S2 Connected to the input terminal of the voltage doubler rectifier circuit 30, the voltage is v Ts .

[0032] The number of voltage doubling modules included in the voltage doubling rectifier circuit may be n, and the number of voltage doubling units included in each voltage doubling module may be m1, m2, ..., m n For example, the voltage doubling unit 3011 is used as an example to illustrate the voltage doubling unit structure. A voltage doubling unit consists of four diodes D 11 , D 12 , D 11' and D 12'With two capacitors C 11 , C 11' Composition. 11 With D 11' Reverse series connection, D 12 With D 12' The midpoint of the two sets of diodes connected in reverse series is connected to the output terminal. 11 The anode is connected to D 12 The cathode of the 11 Connect to input 1, D 11' and D 12' , C 11' The connection is similar. The input terminals of the voltage doubler units 3011, 3012, and 3013 are connected in parallel and the output terminals are connected in series to the bus capacitor C b1 The first voltage doubling module 301 is formed by connecting them in parallel. Similarly, the input terminals of the voltage doubling units 3021, 3022, and 3023 are connected in parallel and the output terminals are connected in series to the bus capacitor C bn The bus capacitor C b1 -C bn Directly with load R L connected, called bus capacitance, and the capacitance C 11 , C 11' , ... not directly connected to the load R L The busbar capacitors of all voltage doubler modules are connected in series and then connected to the load resistor. R L The supporting capacitor of the last voltage doubling unit of the first-stage voltage doubling module is short-circuited.

[0033] Here, it should also be noted that, in this embodiment, the number of voltage doubling units included in the previous stage voltage doubling module must be greater than or equal to the number of voltage doubling units included in the next stage voltage doubling module.

[0034] Since the input current of the rear-stage voltage doubler module flows through the support capacitor of the last voltage doubler unit in the previous voltage doubler modules, it will cause a large change in capacitor voltage, which will affect the input voltage of the rear-stage voltage doubler module. Therefore, under the condition of limited device voltage level, increasing the number of units in the front-stage voltage doubler module and reducing the number of units in the rear-stage voltage doubler module can reduce the total output voltage change and improve the output voltage stability.

[0035] In addition, this embodiment takes a high-voltage DC converter including three voltage doubling modules, each of which includes three voltage doubling units, as an example, that is, m1=m2=m3=3, and its typical waveform is as follows: Figure 4 The positive direction of all electrical quantities is shown as Figure 3 Voltage vr is the output voltage of the full-bridge inverter circuit, and its amplitude is ± V i , the square wave voltage frequency is equal to the switching frequency, and the inverse of the switching frequency is its switching period T s . Current i r is the current of the resonant filter circuit. Under reasonable switching frequency and resonant component design, the current i r Lag behind inverter voltage v r , the full-bridge inverter circuit can achieve zero voltage turn-on, greatly reducing the switching loss of the MOSFET tube. v Ts is the output winding voltage of the transformer, which is also the terminal voltage of the parallel resonant capacitor and the input voltage of the voltage doubler rectifier circuit. Its amplitude is U Ts . Current i s1 is the input current of the voltage doubler rectifier circuit, marked in the figure i CDp , i D31 - i D33' , i D21 - i D23' and i D11 - i D13' The shaded areas represent the current in this time period. i s1 The parasitic capacitance C that mainly flows into the voltage doubler rectifier diode Dp 、Diode D 31 -D 33' , D 21 -D 23' With D 11 -D 13' .Voltage v C23 , v C23' , v C22 , v C22' , v C21 and v C21' Respectively represent the capacitance C 23 , C 23' , C 22 , C 22' , C 21 and C 21'The voltage at both ends is shown in the figure. The capacitor voltage waveform in the second voltage doubler module is used as an example. The capacitor voltages at other levels are similar. v b1 , v b2 and v b3 Represents bus capacitance C b1 , C b2 and C b3 terminal voltage.

[0036] The typical working mode of the voltage doubler rectifier circuit in the embodiment of the present invention is as follows: Figure 5 When the voltage v Ts near U Ts or- U Ts When the diode conduction current path is Figure 5 (a) Figure 5 As shown in (b), the dashed line with an arrow. v Ts When the amplitude is less than the sum of the capacitor voltages of all current paths, such as Figure 5 As shown in (c), all diodes bear the reverse voltage and turn off, and the current i s1 The parasitic capacitance of the diode in the voltage doubler rectifier circuit C Dp Charging, the current direction is v Ts The voltage change is related to the current direction, so the dotted line in the figure does not have an arrow. v Ts When the amplitude reaches the sum of the voltages of a certain current path, the diode on the path is turned on, and the capacitor is charged or discharged. Since the conduction and shutdown of the diode will change the current path of the capacitor, there will be a voltage difference between the capacitor voltage far away from the input end and the capacitor close to the input end. Therefore, the diode of the rear stage will be turned on first, and the diode of the front stage will be turned on later. It can be seen from the working mode that since each voltage doubler module has only one current path flowing through the bus capacitor, the ripple of the bus capacitor voltage and the total output voltage is small. At the same time, since the current of the rear-stage voltage doubler module will also flow through the last set of supporting capacitors of the previous-stage voltage doubler module, it is generally necessary to set m1≥m2>m n .

[0037] The total output voltage amplitude, output voltage ripple and device voltage stress of the embodiment of the present invention are analyzed as follows:

[0038] To simplify the analysis, it is assumed that in the positive half switching cycle ( t 2, t 4) and the negative half switching cycle [(t 0, t 1), ( t 5, t 6)], the voltage v Ts Equal to U Ts and- U Ts ; Ignore the bus capacitor voltage difference of each voltage doubler module, that is, v b1 = v b2 = v b3 = V o / 3; Assume that the values ​​of all supporting capacitors and busbar capacitors are C s and C b .

[0039] According to Kirchhoff's theorem, the current paths in the first and second voltage doubler modules satisfy equation (1), where the subscripts "Pend" and "Nend" represent the positive and negative half-switching cycles, respectively. Figure 5 (a) and Figure 5 (b) as shown:

[0040] (1)

[0041] At the same time, the voltage change caused by the charging and discharging process of the support capacitor can be written as formula (2):

[0042] (2)

[0043] Combining (1) and (2), we can get the voltage of the capacitor of the first and second voltage doubler modules as shown in formula (3):

[0044] (3)

[0045] Furthermore, the output voltage of the third-stage voltage doubler module and the total output voltage can be written as:

[0046] (4)

[0047] (5)

[0048] Since the two groups of diodes in the voltage doubler rectifier circuit are turned on alternately, the total output voltage ripple is twice the switching frequency. Assuming that the charging process is completed in an instant, the total output voltage ripple is v or It can be expressed as formula (6):

[0049] (6)

[0050] According to the voltage expression (3) of each capacitor and the analysis of the working mode, the voltage stress of each device is related to the output current at this time. When the input voltage amplitude is U Ts When the voltage stress of each device is the largest under no-load condition, the voltage stress of each diode is approximately equal to U Ts , and the voltage stress of each capacitor is summarized in Table 1:

[0051]

[0052] The high-stability and low-ripple high-voltage DC converter proposed in this embodiment can achieve the following beneficial effects:

[0053] 1. Highly stable high-voltage DC power conversion: By designing the parameters of the resonant filter circuit, transformer and voltage doubler rectifier circuit, when the load changes, the output voltage of the voltage doubler rectifier circuit changes little, which can achieve highly stable high-voltage DC power conversion and reduce the voltage regulation range requirements of the full-bridge inverter circuit and the resonant filter circuit.

[0054] 2. Low-ripple high-voltage DC output: In the voltage doubler rectifier circuit of this embodiment, the bus capacitor of each voltage doubler module only flows through the charging current of the last voltage doubler unit in the module, and the bus capacitor is charged every half switching cycle. Therefore, the ripple of the bus capacitor is low and the total output voltage ripple is low.

[0055] 3. The voltage stress of the device is low and the application range is wide: Since the voltage doubler rectifier circuit of this embodiment is flexible in configuration and each device is much smaller than the total output high voltage, the applicable step-up ratio range is wide and the converter has a wide application range.

[0056] It should also be noted that the terms "include", "comprises" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, commodity or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, commodity or device. In the absence of more restrictions, the elements defined by the sentence "comprises a ..." do not exclude the existence of other identical elements in the process, method, commodity or device including the elements.

[0057] The above are only embodiments of the present application and are not intended to limit the present application. For those skilled in the art, the present application may have various changes and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application should be included within the scope of the claims of the present application.

Claims

1. A high-stability, low-ripple high-voltage DC converter, characterized in that: The high-voltage DC converter includes a full-bridge inverter circuit, a resonant filter circuit, a transformer and a voltage doubler rectifier circuit connected in sequence: The voltage doubler rectifier circuit is formed by cascading multiple voltage doubler modules; the output ends of multiple voltage doubler modules are connected in series to form a high-voltage DC output; each voltage doubler module is formed by connecting multiple voltage doubler units in parallel and then connecting them in series with a bus capacitor; all bus capacitors are connected in series in sequence and then connected to the load; Among them, each of the voltage doubling units is composed of two groups of two diodes connected in reverse series and two supporting capacitors; the midpoints of the two diodes connected in reverse series are connected to the output end, and the endpoints of the two diodes connected in reverse series are respectively connected to the endpoints of the reverse diodes in the other group and then connected to the input end through a supporting capacitor; the supporting capacitor of the last voltage doubling unit of the first voltage doubling module is short-circuited.

2. The high-stability, low-ripple high-voltage DC converter according to claim 1, characterized in that: The number of voltage doubling units included in the previous stage voltage doubling module is greater than or equal to the number of voltage doubling units included in the next stage voltage doubling module.

3. The high-stability, low-ripple high-voltage DC converter according to claim 1, characterized in that: The resonant filter circuit includes a series resonant inductor, a series resonant capacitor, and a parallel resonant capacitor equivalently connected in parallel at both ends of the secondary winding of the transformer; the parallel resonant capacitor includes the transformer winding parasitic capacitance, the equivalent parasitic capacitance of the voltage doubler rectifier circuit diode, and an external parallel resonant capacitor.

4. The high-stability, low-ripple high-voltage DC converter according to claim 1, characterized in that: The full-bridge inverter circuit is composed of four metal-oxide-semiconductor field effect transistors.

5. The high-stability, low-ripple high-voltage DC converter according to claim 1, characterized in that: The voltage stress of the bus capacitor of each voltage doubler module in the voltage doubler rectifier circuit is less than or equal to the number of voltage doubler units in the voltage doubler module divided by the total number of voltage doubler units multiplied by the total output voltage in a no-load state, and the voltage stress of the diode is less than or equal to the output voltage amplitude of the transformer; the primary winding and secondary winding voltages of the transformer are both lower than the total output voltage; at the same time, when the load is grounded at one end close to the first-stage voltage doubler module, the voltage between the primary and secondary sides of the transformer is lower than the total output voltage.

6. The high-stability, low-ripple high-voltage DC converter according to claim 1, characterized in that: When outputting the rated voltage, the switching frequency of the full-bridge inverter circuit is greater than the resonant frequency of the resonant inductor and the resonant capacitor in the resonant filter circuit, and the converter realizes soft switching.

7. The high-stability, low-ripple high-voltage DC converter according to claim 1, characterized in that: There are multiple voltage doubling modules.

8. The high-stability, low-ripple high-voltage DC converter according to claim 1, characterized in that: Each voltage doubling module includes a plurality of voltage doubling units.

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