Three-level capacitance-inductance hybrid isolation type direct-current transformer and control method thereof

Abstract

The invention discloses a three-level capacitance-inductance hybrid isolation type direct-current transformer and a control method thereof, and belongs to the technical field of direct-current transformers. The three-level capacitance-inductance hybrid isolation type direct-current transformer comprises a primary side conversion module, a voltage transformation module and a secondary side conversion module; the primary side conversion module, the voltage transformation module and the secondary side conversion module are connected in sequence and then are connected between a first port voltage and a second port voltage; the primary side conversion module comprises a plurality of three-level units, first ports of the plurality of three-level units are connected with the first port voltage after being cascaded, and second ports of the plurality of three-level units are connected with the first port of the voltage transformation module after being connected in parallel. According to the three-level capacitance-inductance hybrid isolation type direct current transformer, direct current conversion with a high transmission ratio can be achieved, a capacitance-inductance hybrid isolation mode is adopted, higher power density is achieved, the power density of the direct current transformer is increased under medium-high voltage high-power transmission, and the size is reduced.

Description

Technical Field

[0001] This invention relates to the field of DC transformer technology, and in particular to a three-level capacitive-inductive hybrid isolation DC transformer and its control method. Background Technology

[0002] With the rapid development of new power systems based on new energy sources such as photovoltaics and wind power, the proportion of DC elements in power distribution networks is constantly increasing. As a key piece of equipment for constructing medium-voltage DC power distribution systems, DC solid-state transformers must take into account basic characteristics such as high gain, high power, bidirectional power flow, and electrical isolation.

[0003] In medium- and high-voltage, high-power applications, the voltage and current stress on devices is significantly increased, making traditional two-level DC transformer topologies unsuitable for engineering requirements. The Input-Series Output-Parallel (ISOP) structure shares the voltage and current stress by connecting inputs in series and outputs in parallel, enabling high-power transmission with low-voltage devices. Its modular design process and ease of expansion have led to widespread research and application in academia and industry. However, the power density of ISOP structures is relatively low and difficult to improve due to the limitations of transformer size and quantity. Furthermore, while using a hybrid isolation method combining capacitors and transformers can further increase power density, traditional two-level solutions require a large number of high-voltage film capacitors, significantly increasing the size of the DC transformer. Summary of the Invention

[0004] The purpose of this application is to overcome the shortcomings of the prior art and provide a three-level capacitive-inductive hybrid isolation DC transformer and its control method, so as to increase the power density of the DC transformer and reduce its volume under medium- and high-voltage high-power transmission.

[0005] In a first aspect, this application provides a three-level capacitive-inductive hybrid isolation DC transformer, including a primary-side conversion module, a transformer module, and a secondary-side conversion module, wherein the primary-side conversion module, the transformer module, and the secondary-side conversion module are sequentially connected and then connected between the first port voltage and the second port voltage; The primary-side conversion module includes multiple three-level units. The first ports of the multiple three-level units are cascaded and connected to the voltage of the first port. The second ports of the multiple three-level units are connected in parallel and connected to the first port of the transformer module.

[0006] Optionally, each of the three-level units includes a first switch, a second switch, a third switch, a fourth switch, a first capacitor, a second capacitor, a third capacitor, and a fourth capacitor. The first terminal of the first capacitor is connected to the first terminal of the first port voltage. The second terminal of the first capacitor is connected to the first terminal of the second capacitor. The second terminal of the second capacitor is connected to the first terminal of the second three-level unit. The first terminal of the first switch is connected to the first terminal of the first capacitor. The second terminal of the first switch is connected to the first terminal of the second switch. The second terminal of the second switch is connected to the second terminal of the first capacitor and the first terminal of the third switch. The second terminal of the third switch is connected to the first terminal of the fourth switch. The second terminal of the fourth switch is connected to the second terminal of the second capacitor. The first terminal of the third capacitor is connected to the second terminal of the first switch. The second terminal of the third capacitor is connected to the first terminal of the transformer module. The first terminal of the fourth capacitor is connected to the second terminal of the third switch. The second terminal of the fourth capacitor is connected to the second terminal of the transformer module.

[0007] Optionally, the transformer module includes a first transformer, a second transformer, a third transformer, or a fourth transformer.

[0008] Optionally, the first transformer, the second transformer, and the third transformer are multi-winding transformers; the fourth transformer is a high-frequency transformer.

[0009] Optionally, the transformer module further includes a leakage inductance or a series inductance, which is connected to the primary winding of the corresponding transformer.

[0010] Optionally, the secondary-side conversion module includes one or more rectifier units, the first ports of the plurality of rectifier units are connected to the corresponding secondary windings in the transformer module, and the second ports of the plurality of rectifier units are connected in parallel to the two ends of the voltage at the second port.

[0011] Optionally, each of the rectifier units includes a fifth switch, a sixth switch, a seventh switch, an eighth switch, and a fifth capacitor. The first terminal of the fifth switch is connected to the first terminal of the fifth capacitor, the second terminal of the fifth switch is connected to the first terminal of the sixth switch, the second terminal of the sixth switch is connected to the second terminal of the fifth capacitor, the first terminal of the seventh switch is connected to the first terminal of the fifth capacitor, the second terminal of the seventh switch is connected to the first terminal of the eighth switch, the second terminal of the eighth switch is connected to the second terminal of the fifth capacitor, the first terminal of the fifth capacitor is connected to the first terminal of the second port voltage, and the second terminal of the fifth capacitor is connected to the second terminal of the second port voltage.

[0012] Optionally, it also includes connecting the first ports of multiple rectifier units in parallel to the corresponding secondary windings in the transformer module, and connecting the second ports of multiple rectifier units in parallel to the two ends of the voltage at the second port.

[0013] Secondly, this application also provides a control method for a three-level capacitive-inductor hybrid isolation DC transformer, used to execute the three-level capacitive-inductor hybrid isolation DC transformer as described in any one of the first aspects, comprising the following steps: In each three-level unit, the first switch and the second switch are complementary in conduction, the third switch and the fourth switch are complementary in conduction, and the first switch and the fourth switch are turned on together with a first duty cycle. Each rectifier unit is configured to perform synchronous rectification, and the two switches on the same bridge arm are complementary in conduction. By adjusting the switching frequency to regulate the output voltage, the control of a three-level capacitive-inductive hybrid isolation DC transformer can be achieved.

[0014] Optionally, it also includes setting two switches on the same bridge arm in each rectifier unit to conduct complementaryly, and phase-shifting conduction between different bridge arms; adjusting the power transmitted by the three-level capacitive-inductive hybrid isolation DC transformer by the phase shift angle of the primary and secondary voltages of the transformer module.

[0015] This application provides a three-level capacitive-inductive hybrid isolation DC transformer and its control method. By using a hybrid isolation method of capacitors and inductors, the bias voltage of the high-voltage capacitor significantly reduces the insulation stress caused by partial discharge in the three-level capacitive-inductive hybrid isolation DC transformer, reduces the number of high-frequency transformers, lowers the insulation design difficulty of high-frequency transformers, and thus reduces the size of the three-level capacitive-inductive hybrid isolation DC transformer, thereby improving power density. The modular design ensures that the input voltage of the transformer module is the voltage of each three-level unit, reducing the high dielectric problem of the transformer. The primary-side conversion module adopts a three-level structure, reducing the number of high-voltage capacitors and the number of switches, thereby reducing costs and improving the power density of the system. Phase-shifted conduction between different bridge arms, the power transmitted by the three-level capacitive-inductive hybrid isolation DC transformer is adjusted by the phase shift angle of the primary and secondary voltages of the transformer module, exhibiting the characteristics of a dual active bridge and enabling bidirectional power transmission.

[0016] To make the above-mentioned features and advantages of the invention more apparent and understandable, specific embodiments are described below, and detailed descriptions are provided in conjunction with the accompanying drawings. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments or related technologies of this application, the accompanying drawings used in the description of the embodiments or related technologies will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a schematic diagram of the topology of a three-level capacitive-inductance hybrid isolation DC transformer provided in one embodiment of this application.

[0019] Figure 2 This is a schematic diagram of the specific structure of a three-level capacitive-inductance hybrid isolation DC transformer provided in one embodiment of this application.

[0020] Figure 3 This is a schematic diagram of the topology of a three-level capacitive-inductance hybrid isolation DC transformer provided in another embodiment of this application.

[0021] Figure 4 This is a schematic diagram of the topology of a three-level capacitive-inductance hybrid isolation DC transformer provided in another embodiment of this application.

[0022] Figure 5 This is a schematic diagram of the topology of a three-level capacitive-inductance hybrid isolation DC transformer provided in another embodiment of this application.

[0023] Figure 6 This is a flowchart of a control method for a three-level capacitive-inductive hybrid isolation DC transformer provided in one embodiment of this application.

[0024] Figure 7 This is a phase-shift control waveform diagram in the control method of a three-level capacitive-inductance hybrid isolation DC transformer provided in one embodiment of this application.

[0025] Figure 8 This is a simulation waveform diagram of the control method for a three-level capacitive-inductance hybrid isolation DC transformer provided in one embodiment of this application.

[0026] Figure 9 This is a waveform diagram of the coupling capacitor isolation voltage in the control method of a three-level capacitive-inductive hybrid isolation DC transformer provided in one embodiment of this application. Detailed Implementation

[0027] To make the objectives and technical solutions of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this application. All other embodiments obtained by those skilled in the art based on the described embodiments of this application without creative effort are within the scope of protection of this application.

[0028] In one embodiment, see Figure 1 This application provides a three-level capacitive-inductive hybrid isolation DC transformer, including a primary-side transformation module 1, a transformer module 2, and a secondary-side transformation module 3. The primary-side transformation module 1, transformer module 2, and secondary-side transformation module 3 are sequentially connected and then connected to the first port voltage. With the second port voltage between.

[0029] As an example, the voltage at the first port It can be the high-voltage side; the second port voltage It can be the low-pressure side.

[0030] For example, please refer to Figure 2 The primary-side conversion module 1 includes multiple three-level units, and the first ports of the multiple three-level units are cascaded and connected to the first port voltage. The second ports of multiple three-level units are connected in parallel and then connected to the first port of transformer module 2.

[0031] For example, please refer to Figure 2 The primary-side conversion module 1 may include N three-level units, specifically including a first three-level unit 11, a second three-level unit 12, ..., an Nth three-level unit 1N. The first terminal of the first three-level unit 11 is connected to the first port voltage. The first terminal of the first three-level unit 11 is connected to the second terminal of the second three-level unit 12, the second terminal of the second three-level unit 12 is connected to the first terminal of the third three-level unit 13, ..., the second terminal of the Nth three-level unit 1N is connected to the first port voltage. The second terminal of the transformer module 2 is connected to the first terminal of the transformer module 2, and the third terminals of the first three-level unit 11, the second three-level unit 12, ..., the Nth three-level unit 1N are all connected to the second terminal of the transformer module 2.

[0032] As an example, the voltage at the first port The first terminal can be a positive terminal, and the voltage at the first port is... The second terminal can be a negative terminal.

[0033] The structures of the N three-level units are identical. The specific structure is described below using the first three-level unit 11 as an example.

[0034] For example, please refer to Figure 2 The first three-level unit 11 includes switches S1, S2, S3, and S4, and capacitors C1, C2, and C3. r1 Capacitor C r2 The first terminal of capacitor C1 is connected to the voltage of the first port. The first terminal of capacitor C1 is connected to the second terminal of capacitor C2. The second terminal of capacitor C2 is connected to the first terminal of the second three-level unit 12. The first terminal of switch S1 is connected to the first terminal of capacitor C1. The second terminal of switch S1 is connected to the first terminal of switch S2. The second terminal of switch S2 is connected to the second terminal of capacitor C1 and the first terminal of switch S3. The second terminal of switch S3 is connected to the first terminal of switch S4. The second terminal of switch S4 is connected to the second terminal of capacitor C2. r1 The first terminal is connected to the second terminal of switch S1, and capacitor C r1 The second terminal is connected to the first terminal of transformer module 2, and capacitor C r2 The first terminal is connected to the second terminal of switch S3, and capacitor C r2 The second terminal is connected to the second terminal of transformer module 2.

[0035] As an example, switches S1, S2, S3, and S4 are connected in series in the same direction.

[0036] As an example, the two terminals of capacitors C1 and C2 connected in series form the first port of the first three-level unit 11. r1 The second terminal and capacitor C r2 The second terminal is the second port of the first three-level unit 11.

[0037] As an example, capacitor C r1 Capacitor C r2 It can be a high-voltage capacitor. The bias voltage of the high-voltage capacitor can greatly reduce the insulation stress caused by partial discharge of the transformer, which can reduce the size of the three-level capacitive-inductive hybrid isolation DC transformer and improve the power density.

[0038] As an example, capacitor C r1 The first terminal can be connected to the midpoint of the series connection between switch S1 and switch S2, and capacitor C r2 The first terminal can be connected to the midpoint of the series connection between switch S3 and switch S4.

[0039] As an example, switches S1 and S2 are complementary in conduction, switches S3 and S4 are complementary in conduction, and switches S1 and S4 are both conducting together with a 50% duty cycle.

[0040] As an example, transformer module 2 may include a first transformer, a second transformer, a third transformer, or a fourth transformer.

[0041] As an example, transformer module 2 may also include leakage inductance or series inductance, which is connected to the primary winding of the corresponding transformer.

[0042] As an example, the first transformer, the second transformer, and the third transformer can be multi-winding transformers.

[0043] As an example, the first transformer, the second transformer, and the third transformer each share a common magnetic core.

[0044] As an example, the fourth transformer can be a high-frequency transformer.

[0045] As an example, the secondary-side conversion module 3 may include one or more rectifier units, with the output sides of multiple rectifier units connected in parallel or the input and output sides of multiple rectifier units connected in parallel.

[0046] For example, please refer to Figure 2 The secondary-side conversion module 3 includes M rectifier units, specifically: a first rectifier unit 31, a second rectifier unit 32, ..., an Mth rectifier unit 3M. The first terminal of the first rectifier unit 31 is connected to the third terminal of the transformer module 2, the second terminal of the first rectifier unit 31 is connected to the fourth terminal of the transformer module 2, the first terminal of the second rectifier unit 32 is connected to the fifth terminal of the transformer module 2, the second terminal of the second rectifier unit 32 is connected to the sixth terminal of the transformer module 2, ..., the first terminal of the Mth rectifier unit 3M is connected to the (M+2)th terminal of the transformer module 2, the second terminal of the Mth rectifier unit 3M is connected to the (M+3)th terminal of the transformer module 2, and the third terminals of the first rectifier unit 31, the second rectifier unit 32, ..., the Mth rectifier unit 3M are all connected to the second port voltage. The first terminal, and the fourth terminal of the first rectifier unit 31, the second rectifier unit 32, ..., the Mth rectifier unit 3M are all connected to the second port voltage. The second terminal.

[0047] As an example, the voltage at the second port The first terminal can be a positive terminal, and the voltage at the second port can be... The second terminal can be a negative terminal.

[0048] As an example, the number of rectifier units M is less than or equal to the number of three-level units N, that is... .

[0049] Each rectifier unit has the same structure. The specific structure is described below using the second rectifier unit 32 as an example.

[0050] For example, please refer to Figure 2 The second rectifier unit 32 includes switches Q1, Q2, Q3, and Q4, and capacitor C0. The first terminal of switch Q1 is connected to the first terminal of capacitor C0. The second terminal of switch Q1 is connected to the first terminal of switch Q2. The second terminal of switch Q2 is connected to the second terminal of capacitor C0. The first terminal of switch Q3 is connected to the first terminal of capacitor C0. The second terminal of switch Q3 is connected to the first terminal of switch Q4. The second terminal of switch Q4 is connected to the second terminal of capacitor C0. The first terminal of capacitor C0 is connected to the second port voltage. The first terminal of capacitor C0 is connected to the second port voltage. The second terminal. Switches Q1 and Q2 are connected in series in phase to form the first bridge arm, and switches Q3 and Q4 are connected in series in phase to form the second bridge arm. The first bridge arm and the second bridge arm are connected in parallel. The midpoint of the first bridge arm is connected to the first terminal of the secondary winding of the transformer in transformer module 2, and the midpoint of the second bridge arm is connected to the second terminal of the secondary winding of the transformer in transformer module 2.

[0051] In one example, switches Q1, Q2, Q3, and Q4 can be power switches. Switches Q1 and Q2 in the first bridge arm can be configured to conduct complementaryly, and switches Q3 and Q4 in the second bridge arm can conduct complementaryly, thus adjusting the output voltage by changing the switching frequency.

[0052] As an example, the secondary-side transformation module 3 implements synchronous rectification.

[0053] In another example, the switches Q1 and Q2 of the first bridge arm can be set to conduct complementaryly, and the switches Q3 and Q4 of the second bridge arm can be set to conduct complementaryly. The phase shift between different bridge arms can be adjusted by adjusting the phase shift angle of the primary and secondary voltages of the transformer in the transformer module 2.

[0054] As an example, switches S1, S2, S3, S4, Q1, Q2, Q3, and Q4 all include corresponding parasitic capacitances and parasitic diodes.

[0055] As an example, switches S1, S2, S3, S4, Q1, Q2, Q3, and Q4 can be semiconductor devices that can be used as switching transistors, such as IGBTs, MOSFETs, and transistors, but this invention is not limited thereto.

[0056] In one implementation, please refer to Figure 1 Transformer module 2 may include inductor L r1 And a first transformer T1, inductor L r1 The first terminal is connected to the first terminal of the second port of the primary-side conversion module 1, and the inductor L r1The second terminal is connected to the primary winding n of the first transformer T1. 11 The first terminal, the primary winding n of the first transformer T1 11 The second terminal is connected to the second terminal of the second port of the primary-side transformation module 1, and the first winding n of the secondary side of the first transformer T1 21 The first terminal is connected to the first terminal of the first rectifier unit 31, and the first winding n of the secondary side of the first transformer T1 21 The second terminal is connected to the second terminal of the first rectifier unit 31, and the second winding n of the secondary side of the first transformer T1 22 The first terminal is connected to the first terminal of the second rectifier unit 32, and the second winding n of the secondary side of the first transformer T1 22 The second terminal is connected to the second terminal of the second rectifier unit 32, ..., the Mth winding n of the secondary side of the first transformer T1 2M The first terminal is connected to the first terminal of the Mth rectifier unit 3M, and the Mth winding n of the secondary side of the first transformer T1 2M The second terminal is connected to the second terminal of the Mth rectifier unit 3M.

[0057] As an example, the first transformer T1 can be a multi-winding transformer. By designing secondary windings with different numbers of turns, multiple sets of voltages with different amplitudes can be obtained simultaneously, meeting the differentiated voltage level requirements of multiple loads in the system. This not only isolates high voltage or interference signals on the primary side, improving system safety, but also effectively suppresses electromagnetic interference, enhancing circuit stability. The multi-winding transformer can distribute the energy of the primary side to multiple secondary branches through a magnetic circuit, while utilizing the impedance transformation characteristics of the multi-winding transformer to optimize power transmission efficiency, thus adapting to the power distribution requirements of multiple loads.

[0058] As an example, inductor L r1 It can be a leakage inductance or a series inductance.

[0059] As an example, please continue reading Figure 1 The secondary-side transformer module 3 may include M rectifier units. The first ports of the M rectifier units are connected to the corresponding secondary windings in the transformer module 2. The second ports of the M rectifier units are connected in parallel and then connected to the second port voltage. The two ends.

[0060] In yet another implementation, please refer to Figure 3 Transformer module 2 may include inductor L r2 And a second transformer T2, inductor L r2 The first terminal is connected to the first terminal of the second port of the primary-side conversion module 1, and the inductor L r2 The second terminal is connected to the first winding n of the primary side of the second transformer T2. 31 The first terminal, the first winding n of the primary side of the second transformer T2 31The second terminal is connected to the second winding n of the primary side of the second transformer T2. 32 The first terminal, the second winding n of the primary side of the second transformer T2 32 The second terminal is connected to the third winding n of the primary side of the second transformer T2. 33 The first terminal, ..., the Mth winding n of the primary side of the second transformer T2 3M The second terminal is connected to the second terminal of the second port of the primary-side transformer module 1; the first winding n of the secondary side of the second transformer T2 41 The first terminal is connected to the first terminal of the first rectifier unit 31, and the second winding n of the secondary side of the second transformer T2 41 The second terminal is connected to the second terminal of the first rectifier unit 31, and the second winding n of the secondary side of the second transformer T2 42 The first terminal is connected to the first terminal of the second rectifier unit 32, and the second winding n of the secondary side of the second transformer T2 42 The second terminal is connected to the second terminal of the second rectifier unit 32, ..., the Mth winding n of the secondary side of the second transformer T2. 4M The first terminal is connected to the first terminal of the Mth rectifier unit 3M, and the second transformer T2 secondary winding n is connected to the Mth winding. 4M The second terminal is connected to the second terminal of the Mth rectifier unit 3M.

[0061] As an example, inductor L r2 It can be a leakage inductance or a series inductance.

[0062] As an example, the primary windings of the second transformer T2 are connected in series. When the alternating current generated by the primary-side transformation module 1 passes through the series-connected primary windings, the magnetomotive force generated by each primary winding is superimposed, which excites alternating magnetic flux in the shared magnetic core. The current of the series-connected primary windings is the same, and the magnetomotive force of each winding can be superimposed or compensated as needed to optimize the magnetic flux utilization rate of the magnetic core and improve the overall energy transmission efficiency in multi-output scenarios. Each primary winding can be paired with an independent secondary winding, which can be designed separately according to the voltage level and power requirements of different loads to achieve precise multi-power supply customization.

[0063] As an example, the multiple windings of the second transformer T2 share a single magnetic core.

[0064] As an example, please continue reading Figure 3 The secondary-side transformer module 3 may include M rectifier units. The first ports of the M rectifier units are connected to the corresponding secondary windings in the transformer module 2. The second ports of the M rectifier units are connected in parallel and then connected to the second port voltage. The two ends.

[0065] In yet another implementation, please refer to Figure 4The transformer module 2 may include M inductors and a third transformer T3, with each inductor connected in series with the first terminal of the primary winding of the third transformer T3.

[0066] As an example, the M inductors can be leakage inductors or series inductors.

[0067] Specifically, inductor ML r31 The first terminal is connected to the first terminal of the second port of the primary-side conversion module 1, and the inductor ML r31 The second terminal is connected to the first winding n of the primary side of the third transformer T3. 51 The first terminal, the first winding n of the primary side of the third transformer T3 51 The second terminal is connected to the second terminal of the second port of the primary-side conversion module 1; inductor ML r32 The first terminal is connected to the first terminal of the second port of the primary-side conversion module 1, and the inductor ML r32 The second terminal is connected to the second winding n of the primary side of the third transformer T3. 52 The first terminal, the second winding of the primary side of the third transformer T3 n 52 The second terminal is connected to the second terminal of the second port of the primary-side conversion module 1, ..., inductor ML r3M The first terminal is connected to the first terminal of the second port of the primary-side conversion module 1, and the inductor ML r3M The second terminal is connected to the primary winding of the third transformer T3, specifically the M-th winding n. 5M The first terminal, the Mth winding of the primary side of the third transformer T3 5M The second terminal is connected to the second terminal of the second port of the primary-side transformer module 1; the first winding n of the secondary side of the third transformer T3 61 The first terminal is connected to the first terminal of the first rectifier unit 31, and the first winding n of the secondary side of the third transformer T3 61 The second terminal is connected to the second terminal of the first rectifier unit 31; the second winding n of the secondary side of the third transformer T3 62 The first terminal is connected to the first terminal of the second rectifier unit 32, and the second winding n of the secondary side of the third transformer T3 62 The second terminal is connected to the second terminal of the second rectifier unit 32, ..., the Mth winding n of the secondary side of the third transformer T3 6M The first terminal is connected to the first terminal of the Mth rectifier unit 3M, and the Mth winding n of the secondary side of the third transformer T3. 6M The second terminal is connected to the second terminal of the Mth rectifier unit 3M.

[0068] As an example, the primary winding of the third transformer T3 is connected in series with the corresponding inductor and then in parallel to the second port of the primary-side conversion module 1. After the primary-side conversion module 1 outputs alternating power, multiple branches are connected in parallel. Each branch is connected in series with the inductor and the corresponding primary winding of the third transformer T3. The current in each branch flows in the series circuit of the inductor and the primary winding, generating an alternating voltage proportional to the number of turns in the secondary winding of the third transformer T3 through electromagnetic induction. The alternating voltages are fed into the corresponding rectifier units, and after rectification, multiple independent DC voltages are output to meet the power supply requirements of different loads. The series-connected inductor can form a resonant circuit with the primary-side switch and the primary winding, helping to achieve zero-voltage switching or zero-current switching, significantly reducing switching losses. The filtering effect of the inductor can reduce current ripple and improve power transmission stability. Under the parallel structure, the load changes of each branch do not interfere with each other, which can simultaneously meet the differentiated needs of sensitive small-current loads and large-current dynamic loads, making it more adaptable.

[0069] As an example, the multiple windings of the third transformer T3 share a single magnetic core.

[0070] As an example, please continue reading Figure 4 The secondary-side transformer module 3 may include M rectifier units. The first ports of the M rectifier units are connected to the corresponding secondary windings in the transformer module 2. The second ports of the M rectifier units are connected in parallel and then connected to the second port voltage. The two ends.

[0071] In yet another implementation, please refer to Figure 5 Transformer module 2 may include inductor L r4 And a fourth transformer T4, inductor L r4 The first terminal is connected to the first terminal of the second port of the primary-side conversion module 1, and the inductor L r1 The second terminal is connected to the primary winding n of the fourth transformer T4. 71 The first terminal, the primary winding n of the fourth transformer T4 71 The second terminal is connected to the second terminal of the second port of the primary-side transformer module 1; the secondary winding n of the fourth transformer T4 81 The first and second terminals are connected to the first port of the secondary-side conversion module 3.

[0072] As an example, the fourth transformer T4 can be a high-frequency transformer, and the primary winding of the fourth transformer T4... n 71 With primary-side transformation module 1, inductor L r4 In conjunction with the high frequency, alternating magnetic flux is generated. Under high frequency operation, the magnetic flux density change rate of the fourth transformer T4 is high, which can significantly reduce the core volume and the number of winding turns, and significantly reduce the overall size of the transformer, thus meeting the design requirements of miniaturization and integration of electronic equipment.

[0073] As an example, inductor L r4 It can be a leakage inductance or a series inductance.

[0074] As an example, please continue reading Figure 5 The secondary-side transformer module 3 may include M rectifier units. The first ports of the M rectifier units are connected in parallel and then connected to the two ends of the secondary winding in the transformer module 2. The second ports of the M rectifier units are connected in parallel and then connected to the second port voltage. The first and second ports of the M rectifier units are connected in parallel, meaning that the input and output sides of the M rectifier units are connected in parallel. The total output power is the sum of the power of each unit, which can easily meet the power requirements of large loads and is suitable for high-power power supply scenarios. Each rectifier unit has the same characteristics, and after being connected in parallel, the output current can be evenly distributed, avoiding damage to a single rectifier unit due to overload, while optimizing the load efficiency of each rectifier unit.

[0075] It should be understood that the three-level capacitive-inductive hybrid isolation DC transformer of this application can achieve bidirectional power transmission, that is, it can convert the voltage at the first port... V H Transformed into the second port voltage V L It can also convert the voltage at the second port. V L Transformed into the first port voltage V H .

[0076] In the aforementioned three-level capacitive-inductor hybrid isolation DC transformer, the primary-side conversion module 1 adopts a structure combining multiple cascaded and parallel three-level units. Combined with complementary and synchronous switching strategies, it reduces switching losses and optimizes the voltage output waveform. The bias voltage of the high-voltage capacitor significantly reduces the insulation stress caused by partial discharge in the transformer, thus reducing the transformer's size and increasing power density. The transformer module 2 employs a diversified design, enabling precise multi-channel voltage conversion and electrical isolation to meet the voltage level requirements of different loads. Simultaneously, it utilizes the resonant characteristics of the inductor and windings to achieve soft switching, improving energy transmission efficiency. The secondary-side conversion module 3 uses multiple rectifier units with parallel input and output, integrating multiple power outputs to adapt to large load demands while optimizing output voltage ripple and dynamic response. Bidirectional power transmission allows for flexible energy conversion between high and low voltage sides. In summary, this three-level capacitive-inductor hybrid isolation DC transformer possesses high-voltage adaptability, high power capacity, high reliability, and high efficiency, making it suitable for various power supply scenarios.

[0077] In another embodiment, please refer to Figure 6This application also provides a control method for a three-level capacitive-inductor hybrid isolation DC transformer. The control method for the three-level capacitive-inductor hybrid isolation DC transformer may include the following steps: steps S1 to S3.

[0078] Step S1: Set the first switch and the second switch in each three-level unit to be complementary to conduct, the third switch and the fourth switch to be complementary to conduct, and the first switch and the fourth switch to conduct together with the first duty cycle.

[0079] Step S2: Set each rectifier unit to perform synchronous rectification, and the two switches on the same bridge arm are complementary to conduct.

[0080] Step S3: Adjust the output voltage by changing the switching frequency to achieve control of the three-level capacitive-inductive hybrid isolation DC transformer.

[0081] In the control method of the three-level capacitive-inductive hybrid isolation DC transformer of this application, by setting the first and second switches, and the third and fourth switches in each three-level unit to conduct complementaryly, and the first and fourth switches to conduct synchronously with a first duty cycle, the three-level module can output a stable intermediate voltage, providing high-quality voltage excitation for primary-side energy transmission and effectively reducing the interference of voltage fluctuations on the subsequent resonant circuit. By setting each rectifier unit to perform synchronous rectification and the two switches on the same bridge arm to conduct complementaryly, the conduction loss of the secondary-side rectification process can be significantly reduced, the energy conversion efficiency can be improved, and the short-circuit risk caused by simultaneous switching can be avoided, ensuring the safe and reliable operation of the secondary circuit. By changing the switching frequency to adjust the output voltage, the adjustment requirements of the output voltage can be flexibly and accurately responded to, the stable control of the output voltage can be achieved, the working state can be optimized, reactive power loss can be reduced, and energy transmission efficiency can be further improved.

[0082] In step S1, please refer to Figure 6 In step S1, the first switch and the second switch in each three-level unit are set to be complementary to conduct, the third switch and the fourth switch are set to be complementary to conduct, and the first switch and the fourth switch are set to conduct together with a first duty cycle.

[0083] Specifically, in each three-level unit, switches S1 and S2 can be configured to conduct complementaryly, switches S3 and S4 can be configured to conduct complementaryly, and switches S1 and S4 can be configured to conduct together with a first duty cycle.

[0084] As an example, the first duty cycle can be set to 50%.

[0085] In step S2, please refer to Figure 6 In step S2, each rectifier unit is set to perform synchronous rectification, and the two switches on the same bridge arm are complementary to conduct.

[0086] Specifically, each rectifier unit can be configured to perform synchronous rectification, with the switches Q1 and Q2 of the first bridge arm conducting complementaryly, and the switches Q3 and Q4 of the second bridge arm conducting complementaryly.

[0087] In step S3, please refer to Figure 6 In step S3, the output voltage is adjusted by changing the switching frequency to achieve control of the three-level capacitive-inductive hybrid isolation DC transformer.

[0088] As an example, the low-voltage side voltage can be monitored in real time using a voltage sensor. V L The low-voltage side output voltage will be monitored in real time. V L With low-voltage side target voltage V Lref Comparison, when monitoring the low-voltage side output voltage in real time The switching frequency needs to be increased. As the switching frequency approaches the natural frequency, the amplitude of the resonant current increases, and more energy is transferred from the primary side of transformer module 2 to the secondary side. The secondary-side conversion module 3 converts this increased energy into DC voltage, thus increasing the voltage on the low-voltage side. V L Increase until the low-voltage side output voltage is monitored in real time. Stop increasing the switching frequency; when monitoring the low-voltage side output voltage in real time. The switching frequency needs to be reduced. As the switching frequency deviates from the natural frequency, the amplitude of the resonant current decreases, the energy transferred from the primary side of transformer module 2 to the secondary side decreases, and the DC voltage converted by the secondary-side conversion module 3 decreases accordingly, until the low-voltage side output voltage is monitored in real time. Stop adjusting the switching frequency.

[0089] As an example, the target voltage on the low-voltage side V Lref It can be set according to actual needs.

[0090] In another embodiment, the control method of the three-level capacitive-inductor hybrid isolation DC transformer of this application may further include: setting the first switch and the second switch in each three-level unit to be complementaryly connected, the third switch and the fourth switch to be complementaryly connected, and the first switch and the fourth switch to be connected together with a second duty cycle; setting the two switches of the same bridge arm in each rectifier unit to be complementaryly connected, and the phase shifting connection between different bridge arms; and adjusting the power transmitted by the three-level capacitive-inductor hybrid isolation DC transformer by the phase shifting angle of the primary and secondary voltages of the transformer module.

[0091] Specifically, in each three-level unit, switches S1 and S2 can be configured to conduct complementaryly, switches S3 and S4 can be configured to conduct complementaryly, and switches S1 and S4 can be configured to conduct together with a second duty cycle; each rectifier unit can be configured to perform synchronous rectification, with switches Q1 and Q2 of the first bridge arm conducting complementaryly, switches Q3 and Q4 of the second bridge arm conducting complementaryly, and phase-shifting conduction between the first bridge arm and the second bridge arm.

[0092] As an example, phase shifting can be used to enable conduction between the first and second bridge arms, which allows setting the phase difference between the drive signals of switch Q1 and switch Q4. The drive signals for switches Q2 and Q3 also differ. ,in, This refers to the internal phase shift angle for each rectifier unit. It is the phase shift angle of the voltage across the primary and secondary sides of the transformer. To adjust the power transmitted by the three-level capacitive-inductive hybrid isolation DC transformer.

[0093] As an example, the second duty cycle can be set to 50%.

[0094] In one example, see Figure 7 , Figure 7 This is a waveform diagram of phase-shift control in a three-level capacitive-inductive hybrid isolation DC transformer. The following section uses phase-shift control and power transfer from high voltage to low voltage as an example to introduce the working principle of the three-level capacitive-inductive hybrid isolation DC transformer of this application.

[0095] As an example, in t Before time 0, switches S2 and S3 are turned off, and the resonant current... i r The parasitic capacitances of switches S2 and S3 are charged, and the voltage rises to... V H At / N / 2, the parasitic capacitances of switches S1 and S4 discharge, the voltage drops to 0, and the parasitic diodes of switches S1 and S4 conduct.

[0096] Furthermore, in t 0 to t At time 1, switches S1 and S4 are turned on, and switches Q2 and Q4 are turned on, causing the resonant current to... i r Rising, resonant current i r When the polarity changes, the parasitic diodes of switch S1 and switch S4 turn off, and the resonant current... i r The current flows through switches S1 and S4. The primary voltage of the three-level capacitive-inductive hybrid isolation DC transformer... v p for V H / N / 2, Secondary voltage of a three-level capacitive-inductive hybrid isolation DC transformer v s It is 0.

[0097] Furthermore, in t 1 to t At time 2, switch Q2 is turned off, and the resonant current... i r Current flows through switches S1 and S4, causing the parasitic capacitance of switch Q1 to discharge, and secondary current flows through switches Q1 and Q4. The primary voltage of the three-level capacitive-inductive hybrid isolation DC transformer... v p for V H / N / 2, Secondary voltage of a three-level capacitive-inductive hybrid isolation DC transformer v s for V L .

[0098] Furthermore, in t 2 to t At time 3, switch Q1 is turned on, and the resonant current is... i r The secondary current flows through switches S1 and S4, and through the parasitic diode of switch Q1 and switch Q4. The primary voltage of the three-level capacitive-inductive hybrid isolation DC transformer... v p for V H / N / 2, Secondary voltage of a three-level capacitive-inductive hybrid isolation DC transformer v s for V L .

[0099] Furthermore, in t 3 to t At time 4, switch Q4 is turned off, and the resonant current... i r Current flows through switches S1 and S4. The parasitic capacitance of switch Q3 begins to discharge, while the parasitic capacitance of switch Q4 begins to charge. Secondary current flows through the parasitic diode of switch Q3 and switch Q4. The primary voltage of the three-level capacitive-inductive hybrid isolation DC transformer... v p for V H / N / 2, Secondary voltage of a three-level capacitive-inductive hybrid isolation DC transformer v s It is 0.

[0100] Furthermore, in t 4 to t At time 5, switch Q3 is turned on, and the resonant current is...i r The primary current flows through switches S1 and S4, and the secondary current flows through switches Q1 and Q3. The primary voltage of the three-level capacitive-inductive hybrid isolation DC transformer is... v p for V H / N / 2, Secondary voltage of a three-level capacitive-inductive hybrid isolation DC transformer v s for V L .

[0101] Furthermore, in t At time 5, the primary-side switch is turned off, ending the first half of the cycle. The second half of the cycle operates on a similar principle, which can be referred to in the context of the first half of the cycle; therefore, it will not be elaborated upon here.

[0102] As an example, the primary voltage of a three-level capacitive-inductance hybrid isolation DC transformer. v p The voltage across the primary winding of the transformer in transformer module 2 is the voltage across the secondary winding of the three-level capacitive-inductive hybrid isolation DC transformer. v s The voltage across the secondary winding of the transformer in transformer module 2, and the resonant current. i r For flow through the inductor L r1 The current.

[0103] As an example, simulation verification was performed on a simulation platform to verify the feasibility of the three-level capacitive-inductance hybrid isolation DC transformer proposed in this application.

[0104] The following is based on Figure 1 Taking the three-level capacitive-inductance hybrid isolation DC transformer with the topology shown as an example, the simulation verification is introduced.

[0105] As an example, the voltage of the first port can be set. ±10kV, second port voltage The voltage is ±375V. The rated power can be set to 1MW, the switching frequency to 50kHz, the turns ratio of the first transformer to 1:1, the coupling capacitor to 0.47μF, and the inductor to... L r1 It is 6.2 μH. Figure 8 The simulation waveform diagram shows the stable operation of a three-level capacitive-inductive hybrid isolation DC transformer. v p This refers to the primary voltage of a three-level capacitive-inductive hybrid isolation DC transformer. v s This refers to the secondary voltage of a three-level capacitive-inductive hybrid isolation DC transformer. ir For flow through the inductor L r1 The resonant current. From Figure 8 It can be seen that the primary voltage of the three-level capacitive-inductive hybrid isolation DC transformer v p The output voltage exhibits a square wave with a duty cycle close to 50%, stable amplitude, and consistent period. The primary-side conversion module 1 operates at a stable switching frequency with precise switching timing, resulting in good periodicity and amplitude consistency of the output voltage. The secondary voltage of the three-level capacitive-inductor hybrid isolation DC transformer... v s Presenting a multi-level square wave, the secondary-side conversion module 3 operates stably and can synchronously respond to the periodic changes in the primary-side voltage, achieving efficient energy transfer and conversion; resonant current. i r The absence of obvious spikes or distortions indicates that the control strategy (such as switching timing and phase shift angle) is well optimized, reducing the current stress on the devices and facilitating long-term reliable operation of the system. Figure 9 This is a waveform diagram of the coupling capacitor isolation voltage when a three-level capacitive-inductive hybrid isolation DC transformer is operating stably. The curves in the diagram represent the bias voltage of the high-voltage capacitor in different modules. Figure 9 It can be seen that the high-voltage capacitor isolates the bias common-mode voltage of different modules, thereby reducing the difficulty of insulation design for partial discharge of the high-frequency transformer and reducing the insulation volume of the transformer; it also reduces the ground potential of the three-level capacitive-inductive hybrid isolation DC transformer, thereby reducing the insulation stress caused by partial discharge of the three-level capacitive-inductive hybrid isolation DC transformer.

[0106] In the control method of the three-level capacitive-inductive hybrid isolation DC transformer of this application, by setting the first and second switches, and the third and fourth switches in each three-level unit to conduct complementaryly, and the first and fourth switches to conduct synchronously with a fixed duty cycle, the three-level module can output a stable intermediate voltage, providing a high-quality voltage excitation for primary-side energy transmission, effectively reducing the interference of voltage fluctuations on subsequent resonant circuits, avoiding resonant state disorder, and ensuring the basic stability of energy transmission; by setting each rectifier unit to perform synchronous rectification and the two switches on the same bridge arm to conduct complementaryly, compared with traditional diode rectification, the conduction loss of the secondary-side rectification process can be significantly reduced, the energy conversion efficiency can be improved, and the same switching timing can be eliminated. The short-circuit risk of simultaneous conduction of two bridge arm switches provides a guarantee for the safe operation of the secondary circuit. By changing the switching frequency to adjust the output voltage, it can flexibly respond to the low-voltage side voltage deviation, accurately stabilize the output voltage at the target value, and the frequency adjustment can optimize the circuit operation state, reduce reactive power loss, and further improve energy transmission efficiency. By adding phase shift conduction between different bridge arms in the rectifier unit and adjusting the power in combination with the phase shift angle of the primary and secondary voltages of the transformer module, it can achieve smooth transition of secondary current, avoid device stress caused by current abrupt changes, and accurately control the power transmission magnitude to adapt to different load conditions. Overall, it significantly improves the operating condition adaptability, operational reliability, and comprehensive energy utilization efficiency of the three-level capacitive-inductive hybrid isolation DC transformer.

[0107] It should be understood that although the steps in the flowcharts of the accompanying drawings are shown sequentially according to the arrows, these steps are not necessarily executed in the order indicated by the arrows. Unless explicitly stated herein, there is no strict order restriction on the execution of these steps, and they can be executed in other orders. Moreover, at least some of the steps in the accompanying drawings may include multiple sub-steps or multiple stages. These sub-steps or stages are not necessarily completed at the same time, but can be executed at different times. The execution order of these sub-steps or stages is not necessarily sequential, but can be performed alternately or in turn with other steps or at least some of the sub-steps or stages of other steps.

[0108] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0109] Although this application has been disclosed above with reference to embodiments, it is not intended to limit this application. Anyone skilled in the art can make some modifications and refinements without departing from the spirit and scope of this application.

Claims

1. A three-level capacitive-inductive hybrid isolation DC transformer, characterized in that, include: The primary-side conversion module, the transformer module, and the secondary-side conversion module are sequentially connected and then connected between the first port voltage and the second port voltage. The primary-side conversion module includes multiple three-level units. The first ports of the multiple three-level units are cascaded and connected to the voltage of the first port. The second ports of the multiple three-level units are connected in parallel and connected to the first port of the transformer module.

2. The three-level capacitive-inductive hybrid isolation DC transformer according to claim 1, characterized in that, Each of the three-level units includes a first switch, a second switch, a third switch, a fourth switch, a first capacitor, a second capacitor, a third capacitor, and a fourth capacitor. The first terminal of the first capacitor is connected to the first terminal of the first port voltage. The second terminal of the first capacitor is connected to the first terminal of the second capacitor. The second terminal of the second capacitor is connected to the first terminal of the second three-level unit. The first terminal of the first switch is connected to the first terminal of the first capacitor. The second terminal of the first switch is connected to the first terminal of the second switch. The second terminal of the second switch is connected to the second terminal of the first capacitor and the first terminal of the third switch. The second terminal of the third switch is connected to the first terminal of the fourth switch. The second terminal of the fourth switch is connected to the second terminal of the second capacitor. The first terminal of the third capacitor is connected to the second terminal of the first switch. The second terminal of the third capacitor is connected to the first terminal of the transformer module. The first terminal of the fourth capacitor is connected to the second terminal of the third switch. The second terminal of the fourth capacitor is connected to the second terminal of the transformer module.

3. The three-level capacitive-inductive hybrid isolation DC transformer according to claim 2, characterized in that, The transformer module includes a first transformer, a second transformer, a third transformer, or a fourth transformer.

4. The three-level capacitive-inductive hybrid isolation DC transformer according to claim 3, characterized in that, The first, second, and third transformers are multi-winding transformers; the fourth transformer is a high-frequency transformer.

5. The three-level capacitive-inductive hybrid isolation DC transformer according to claim 3, characterized in that, The transformer module also includes a leakage inductance or a series inductance, which is connected to the primary winding of the corresponding transformer.

6. The three-level capacitive-inductive hybrid isolation DC transformer according to claim 1, characterized in that, The secondary-side conversion module includes one or more rectifier units. The first ports of the multiple rectifier units are connected to the corresponding secondary windings in the transformer module, and the second ports of the multiple rectifier units are connected in parallel to the two ends of the voltage at the second port.

7. The three-level capacitive-inductive hybrid isolation DC transformer according to claim 6, characterized in that, Each rectifier unit includes a fifth switch, a sixth switch, a seventh switch, an eighth switch, and a fifth capacitor. The first terminal of the fifth switch is connected to the first terminal of the fifth capacitor. The second terminal of the fifth switch is connected to the first terminal of the sixth switch. The second terminal of the sixth switch is connected to the second terminal of the fifth capacitor. The first terminal of the seventh switch is connected to the first terminal of the fifth capacitor. The second terminal of the seventh switch is connected to the first terminal of the eighth switch. The second terminal of the eighth switch is connected to the second terminal of the fifth capacitor. The first terminal of the fifth capacitor is connected to the first terminal of the second port voltage. The second terminal of the fifth capacitor is connected to the second terminal of the second port voltage.

8. The three-level capacitive-inductive hybrid isolation DC transformer according to claim 7, characterized in that, It also includes connecting the first ports of multiple rectifier units in parallel to the corresponding secondary windings in the transformer module, and connecting the second ports of multiple rectifier units in parallel to the two ends of the voltage at the second port.

9. A control method for a three-level capacitive-inductive hybrid isolation DC transformer, characterized in that, A three-level capacitive-inductive hybrid isolation DC transformer for performing any one of claims 1 to 8 includes the following steps: In each three-level unit, the first switch and the second switch are complementary in conduction, the third switch and the fourth switch are complementary in conduction, and the first switch and the fourth switch are turned on together with a first duty cycle. Each rectifier unit is configured to perform synchronous rectification, and the two switches on the same bridge arm are complementary in conduction. By adjusting the switching frequency to regulate the output voltage, the control of a three-level capacitive-inductive hybrid isolation DC transformer can be achieved.

10. The control method for a three-level capacitive-inductive hybrid isolation DC transformer according to claim 9, characterized in that, It also includes setting two switches in the same bridge arm of each rectifier unit to conduct complementaryly, and phase-shifting conduction between different bridge arms; adjusting the power transmitted by the three-level capacitive-inductive hybrid isolation DC transformer by adjusting the phase shift angle of the primary and secondary voltages of the transformer module.

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