Three-level inductance-capacitance hybrid isolated dc transformer and control method thereof

Abstract

The application 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 transformation module and a secondary side conversion module, wherein the primary side conversion module, the transformation module and the secondary side conversion module are sequentially connected between a first port voltage and a second port voltage; the primary side conversion module comprises a plurality of three-level units, the first ports of the plurality of three-level units are connected in cascade and connected to the first port voltage, and the second ports of the plurality of three-level units are connected in parallel and connected to the first port of the transformation module. The three-level capacitance-inductance hybrid isolation type direct-current transformer can realize high transmission ratio direct-current conversion, adopts a capacitance-inductance hybrid isolation mode, has higher power density, realizes the increase of the power density of the direct-current transformer under the transmission of medium-high voltage and high power, and reduces the volume.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of direct current transformer, and particularly relates to a three-level capacitor-inductor hybrid isolation type direct current transformer and a control method thereof. BACKGROUND

[0002] With the rapid development of new power systems mainly based on new energy such as photovoltaic and wind energy, the proportion of direct current elements in distribution networks is increasing. As a key equipment for building medium-voltage direct current distribution systems, direct current solid-state transformers need to consider basic characteristics such as high gain, high power, bidirectional power flow and electrical isolation.

[0003] Due to the significant increase in device voltage and current stress in medium and high voltage and high power applications, the traditional two-level direct current transformer topology cannot meet the engineering requirements. The input-series output-parallel (ISOP) structure shares voltage and current stress through input series connection and output parallel connection to realize high-power transmission with low-voltage devices. Due to the short design process and easy expansion of the modular design, the input-series output-parallel structure is widely studied and applied in academia and industry. However, due to the constraints of transformer volume and quantity, the power density of the input-series output-parallel structure is low and difficult to improve. Moreover, the use of capacitor and transformer hybrid isolation can further improve the power density, but the number of high-voltage thin film capacitors in the traditional two-level scheme is large, which significantly increases the volume of the direct current transformer. SUMMARY

[0004] The present application aims to overcome the defects of the prior art and provide a three-level capacitor-inductor hybrid isolation type direct current transformer and a control method thereof, which can increase the power density of the direct current transformer and reduce the volume under medium and high voltage and high power transmission.

[0005] In a first aspect, the present application provides a three-level capacitor-inductor hybrid isolation type direct current transformer, comprising 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 connected in sequence and connected between a first port voltage and a second port voltage.

[0006] The primary side conversion module comprises a plurality of three-level units, the first ports of the plurality of three-level units are connected in cascade and connected to the first port voltage, and the second ports of the plurality of three-level units are connected in parallel and connected to a first port of the transformer module.

[0007] Optionally, each of the three-level units comprises a first switch, a second switch, a third switch, a fourth switch, a first capacitor, a second capacitor, a third capacitor, a fourth capacitor, a first terminal of the first capacitor is connected to a first terminal of the first port voltage, a second terminal of the first capacitor is connected to a first terminal of the second capacitor, a second terminal of the second capacitor is connected to a first terminal of a second three-level unit, a first terminal of the first switch is connected to the first terminal of the first capacitor, a second terminal of the first switch is connected to a first terminal of the second switch, a second terminal of the second switch is connected to the second terminal of the first capacitor and a first terminal of the third switch, a second terminal of the third switch is connected to a first terminal of the fourth switch, a second terminal of the fourth switch is connected to a second terminal of the second capacitor, a first terminal of the third capacitor is connected to the second terminal of the first switch, a second terminal of the third capacitor is connected to a first terminal of the voltage conversion module, a first terminal of the fourth capacitor is connected to the second terminal of the third switch, and a second terminal of the fourth capacitor is connected to a second terminal of the voltage conversion module.

[0008] Optionally, the voltage conversion module comprises a first transformer or a second transformer or a third transformer or a fourth transformer.

[0009] Optionally, the first transformer, the second transformer, and the third transformer are multi-winding transformers, and the fourth transformer is a high-frequency transformer.

[0010] Optionally, the voltage conversion module further comprises a leakage inductance or a series inductance, and the leakage inductance or the series inductance is connected to a primary winding of a corresponding transformer.

[0011] Optionally, the secondary-side conversion module comprises one or more rectifier units, a first port of each of the rectifier units is connected to a corresponding secondary winding in the voltage conversion module, and second ports of the rectifier units are connected in parallel and then connected to both ends of the second port voltage.

[0012] Optionally, each of the rectifier units comprises a fifth switch, a sixth switch, a seventh switch, an eighth switch, and a fifth capacitor, a first terminal of the fifth switch is connected to a first terminal of the fifth capacitor, a second terminal of the fifth switch is connected to a first terminal of the sixth switch, a second terminal of the sixth switch is connected to a second terminal of the fifth capacitor, a first terminal of the seventh switch is connected to the first terminal of the fifth capacitor, a second terminal of the seventh switch is connected to a first terminal of the eighth switch, a 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 a first terminal of the second port voltage, and the second terminal of the fifth capacitor is connected to a second terminal of the second port voltage.

[0013] Optionally, the first ports of the plurality of rectifier units are connected in parallel to the corresponding secondary side windings of the transformer module, and the second ports of the plurality of rectifier units are connected in parallel to both ends of the second port voltage.

[0014] In a second aspect, the application further provides a control method of the three-level capacitance-inductance hybrid isolation type DC transformer, which is used to execute the three-level capacitance-inductance hybrid isolation type DC transformer according to any one of the first aspect, and includes the following steps:

[0015] The first switch and the second switch in each three-level unit are set to be complementary on, the third switch and the fourth switch are set to be complementary on, and the first switch and the fourth switch are set to be on together at a first duty ratio;

[0016] Each rectifier unit is set to be synchronous rectification, and the two switches of the same bridge arm are set to be complementary on;

[0017] The output voltage is adjusted by changing the switching frequency, so as to realize the control of the three-level capacitance-inductance hybrid isolation type DC transformer.

[0018] Optionally, the two switches of the same bridge arm in each rectifier unit are set to be complementary on, and the two switches of different bridge arms are set to be phase-shifted on; the power transmitted by the three-level capacitance-inductance hybrid isolation type DC transformer is adjusted by changing the phase-shift angle of the primary side voltage and the secondary side voltage of the transformer module.

[0019] The application provides a three-level capacitance-inductance hybrid isolation type DC transformer and a control method thereof. The three-level capacitance-inductance hybrid isolation type DC transformer is isolated by a capacitance and an inductance, the bias voltage of the high-voltage capacitor is greatly reduced, the insulation stress caused by the partial discharge of the three-level capacitance-inductance hybrid isolation type DC transformer is reduced, the number of high-frequency transformers is reduced, the insulation design difficulty of the high-frequency transformer is reduced, and thus the volume of the three-level capacitance-inductance hybrid isolation type DC transformer is reduced, the power density is improved, the modular design makes the input voltage of the transformer module be the voltage of each three-level unit, the high-dielectric problem of the transformer is reduced, the primary side conversion module adopts a three-level structure, the number of high-voltage capacitors is reduced, the number of switches can be greatly reduced, the cost is reduced, and the power density of the system is improved, the two switches of different bridge arms are phase-shifted on, the power transmitted by the three-level capacitance-inductance hybrid isolation type DC transformer is adjusted by changing the phase-shift angle of the primary side voltage and the secondary side voltage of the transformer module, the three-level capacitance-inductance hybrid isolation type DC transformer has the characteristics of a dual active bridge and can perform bidirectional power transmission.

[0020] In order to make the above features and advantages of the application more obvious and easy to understand, the following embodiments are described in detail below, and the accompanying drawings are described as follows. BRIEF DESCRIPTION OF DRAWINGS

[0021] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the related art, the following will briefly introduce the drawings needed to be used in the embodiments or the related art description. Obviously, the drawings in the following description only some embodiments of the present application, and for those skilled in the art, other drawings can also be obtained without creative labor on the basis of these drawings.

[0022] Figure 1 The topological structure diagram of the three-level inductance-capacitance hybrid isolation type DC transformer provided in an embodiment of the present application.

[0023] Figure 2 The specific structure diagram of the three-level inductance-capacitance hybrid isolation type DC transformer provided in an embodiment of the present application.

[0024] Figure 3 The topological structure diagram of the three-level inductance-capacitance hybrid isolation type DC transformer provided in another embodiment of the present application.

[0025] Figure 4 The topological structure diagram of the three-level inductance-capacitance hybrid isolation type DC transformer provided in another embodiment of the present application.

[0026] Figure 5 The topological structure diagram of the three-level inductance-capacitance hybrid isolation type DC transformer provided in another embodiment of the present application.

[0027] Figure 6 The flow chart of the control method of the three-level inductance-capacitance hybrid isolation type DC transformer provided in an embodiment of the present application.

[0028] Figure 7 The phase-shift control waveform diagram in the control method of the three-level inductance-capacitance hybrid isolation type DC transformer provided in an embodiment of the present application.

[0029] Figure 8 The simulation waveform diagram in the control method of the three-level inductance-capacitance hybrid isolation type DC transformer provided in an embodiment of the present application.

[0030] Figure 9 The coupling capacitor isolation voltage waveform diagram in the control method of the three-level inductance-capacitance hybrid isolation type DC transformer provided in an embodiment of the present application. DETAILED DESCRIPTION

[0031] In order to make the purpose and technical solutions of the embodiments of the present application clearer, the technical solutions of the embodiments of the present application will be described clearly and completely below in conjunction with the drawings of the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the described embodiments of the present application, all other embodiments obtained by a person of ordinary skill in the art without any inventive effort fall within the scope of protection of the present application.

[0032] In one embodiment, referring to Figure 1 , the present application provides a three-level inductance hybrid isolation type DC transformer, comprising a primary side conversion module 1, a transformation module 2, and a secondary side conversion module 3. The primary side conversion module 1, the transformation module 2, and the secondary side conversion module 3 are sequentially connected and then connected between a first port voltage and a second port voltage .

[0033] As an example, the first port voltage may be a high-voltage side; and the second port voltage may be a low-voltage side.

[0034] As an example, referring to Figure 2 , the primary side conversion module 1 comprises a plurality of three-level units. The first ports of the plurality of three-level units are connected in cascade and then connected to the first port voltage . The second ports of the plurality of three-level units are connected in parallel and then connected to the first port of the transformation module 2.

[0035] As an example, referring to Figure 2 , the primary side conversion module 1 can comprise N three-level units, specifically comprising a first three-level unit 11, a second three-level unit 12, …, and an Nth three-level unit 1N. The first terminal of the first three-level unit 11 is connected to the first terminal of the first port voltage . The second terminal of the first three-level unit 11 is connected to the first 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 second terminal of the first port voltage . The third terminals of the first three-level unit 11, the second three-level unit 12, …, and the Nth three-level unit 1N are all connected to the first terminal of the transformation module 2. The fourth terminals of the first three-level unit 11, the second three-level unit 12, …, and the Nth three-level unit 1N are all connected to the second terminal of the transformation module 2.

[0036] As an example, the first terminal of the first port voltage may be a positive terminal, and the second terminal of the first port voltage may be a negative terminal.

[0037] The structures of the N three-level units are the same, and the specific structure of the first three-level unit 11 is introduced below as an example.

[0038] As an example, refer to Figure 2 , the first three-level unit 11 includes switches S1, S2, S3, S4, capacitors C1, C2, and C r1 . r2 The first terminal of the capacitor C1 is connected to the first terminal of the voltage , the second terminal of the capacitor C1 is connected to the first terminal of the capacitor C2, the second terminal of the capacitor C2 is connected to the first terminal of the second three-level unit 12, the first terminal of the switch S1 is connected to the first terminal of the capacitor C1, the second terminal of the switch S1 is connected to the first terminal of the switch S2, the second terminal of the switch S2 is connected to the second terminal of the capacitor C1 and the first terminal of the switch S3, the second terminal of the switch S3 is connected to the first terminal of the switch S4, the second terminal of the switch S4 is connected to the second terminal of the capacitor C2, the first terminal of the capacitor C r1 is connected to the second terminal of the switch S1, the second terminal of the capacitor C r1 is connected to the first terminal of the transformer module 2, the first terminal of the capacitor C r2 is connected to the second terminal of the switch S3, and the second terminal of the capacitor C r2 is connected to the second terminal of the transformer module 2.

[0039] As an example, the switches S1, S2, S3, and S4 are connected in series in the same direction.

[0040] As an example, the two terminals of the series connection of the capacitors C1 and C2 are the first port of the first three-level unit 11, and the second terminal of the capacitor C r1 and the second terminal of the capacitor C r2 are the second port of the first three-level unit 11.

[0041] As an example, the capacitors C r1 and C r2 can be high-voltage capacitors. The bias voltage of the high-voltage capacitors greatly reduces the insulation stress caused by partial discharge of the transformer, and can reduce the volume of the three-level inductance-capacitance hybrid isolation type DC transformer and improve the power density.

[0042] As an example, the first terminal of the capacitor C r1 can be connected to the midpoint of the series connection of the switches S1 and S2, and the first terminal of the capacitor C r2 can be connected to the midpoint of the series connection of the switches S3 and S4.

[0043] As an example, the switches S1 and S2 are complementary on, the switches S3 and S4 are complementary on, and the switches S1 and S4 are on together with a 50% duty cycle.

[0044] As an example, the transformer module 2 can include a first transformer or a second transformer or a third transformer or a fourth transformer.

[0045] As an example, the transformer module 2 can further include a leakage inductance or a series inductance connected with the primary winding of the corresponding transformer.

[0046] As an example, the first transformer, the second transformer and the third transformer can be multi-winding transformers.

[0047] As an example, the first transformer, the second transformer and the third transformer share a magnetic core respectively.

[0048] As an example, the fourth transformer can be a high-frequency transformer.

[0049] As an example, the secondary side conversion module 3 can include one or more rectifier units, and the output sides of the plurality of rectifier units are connected in parallel or the input and output sides of the plurality of rectifier units are connected in parallel.

[0050] As an example, referring to Figure 2 , the secondary side conversion module 3 includes M rectifier units, specifically including a first rectifier unit 31, a second rectifier unit 32, …, and 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, and 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, and 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+2th terminal of the transformer module 2, and the second terminal of the Mth rectifier unit 3M is connected to the M+3th terminal of the transformer module 2. The third terminals of the first rectifier unit 31, the second rectifier unit 32, …, and the Mth rectifier unit 3M are all connected to the first terminal of the second port voltage , and the fourth terminals of the first rectifier unit 31, the second rectifier unit 32, …, and the Mth rectifier unit 3M are all connected to the second terminal of the second port voltage .

[0051] As an example, the first terminal of the second port voltage may be a positive terminal, and the second terminal of the second port voltage may be a negative terminal.

[0052] As an example, the number M of the rectifier units is less than or equal to the number N of the three-level units, i.e. .

[0053] Each rectifier unit has the same structure, and the specific structure will be described below taking the second rectifier unit 32 as an example.

[0054] As an example, please refer to Figure 2 , the second rectifying unit 32 comprises switches Q1, Q2, Q3, Q4, and a capacitor C0, the first terminal of the switch Q1 is connected to the first terminal of the capacitor C0, the second terminal of the switch Q1 is connected to the first terminal of the switch Q2, the second terminal of the switch Q2 is connected to the second terminal of the capacitor C0, the first terminal of the switch Q3 is connected to the first terminal of the capacitor C0, the second terminal of the switch Q3 is connected to the first terminal of the switch Q4, the second terminal of the switch Q4 is connected to the second terminal of the capacitor C0, the first terminal of the capacitor C0 is connected to the first terminal of the second port voltage , and the second terminal of the capacitor C0 is connected to the second terminal of the second port voltage . The switches Q1 and Q2 are connected in series in phase to form a first bridge arm, the switches Q3 and Q4 are connected in series in phase to form a 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 the 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 the transformer module 2.

[0055] In one example, the switches Q1, Q2, Q3, and Q4 can be power switches. The switches Q1 and Q2 of the first bridge arm can be set to be complementary to be turned on, the switches Q3 and Q4 of the second bridge arm can be set to be complementary to be turned on, and the output voltage can be adjusted by changing the switching frequency.

[0056] As an example, the secondary side conversion module 3 realizes synchronous rectification.

[0057] In another example, the switches Q1 and Q2 of the first bridge arm can be set to be complementary to be turned on, the switches Q3 and Q4 of the second bridge arm can be set to be complementary to be turned on, and the power transferred by the transformer can be adjusted by phase-shifting the primary and secondary voltages of the transformer in the transformer module 2.

[0058] As an example, the switches S1, S2, S3, S4, Q1, Q2, Q3, and Q4 each comprise a corresponding parasitic capacitor and parasitic diode.

[0059] As an example, the switches S1, S2, S3, S4, Q1, Q2, Q3, and Q4 can be IGBTs, MOSFETs, transistors, or other semiconductor devices that can be used as switches, and the present application is not limited thereto.

[0060] In one embodiment, please refer to Figure 1 , the transformer module 2 can comprise an inductor L r1 and a first transformer T1, the first terminal of the inductor L r1 is connected to the first terminal of the second port of the primary side conversion module 1, the second terminal of the inductor L r1the second terminal of the first transformer T1 primary winding n 11 the first terminal of the first transformer T1 primary winding n 11 the second terminal of the first transformer T1 primary winding n 21 the first terminal of the first transformer T1 primary winding n 21 the second terminal of the first transformer T1 primary winding n 22 the first terminal of the first transformer T1 primary winding n 22 the second terminal of the first transformer T1 primary winding n 2M the first terminal of the first transformer T1 primary winding n 2M the second terminal of the first transformer T1 primary winding n

[0061] As an example, the first transformer T1 can be a multi-winding transformer. By designing different turns of the secondary winding, multiple sets of different amplitude voltages can be obtained at the same time to meet the differentiated demand of voltage levels of multiple loads in the system, which can not only isolate the high voltage or interference signal of the primary side to improve the safety of the system, but also effectively suppress electromagnetic interference to enhance the stability of the circuit; through the multi-winding transformer, the energy of the primary side can be distributed to multiple secondary branches through the magnetic circuit, and the impedance transformation characteristics of the multi-winding transformer are used to optimize the power transmission efficiency to adapt to the power distribution demand of multiple loads.

[0062] As an example, the inductor L r1 may be leakage inductance or series inductance.

[0063] As an example, please refer to Figure 1 , the secondary side conversion module 3 can include M rectifier units, the first port of the M rectifier units is connected to the corresponding secondary winding in the transformer module 2, and the second port of the M rectifier units is connected to the two ends of the second port voltage .

[0064] In yet another embodiment, please refer to Figure 3 , the transformer module 2 can include an inductor L r2 and a second transformer T2, the first terminal of the inductor L r2 is connected to the first terminal of the second port of the primary side conversion module 1, the second terminal of the inductor L r2 is connected to the first winding n 31 of the primary side of the second transformer T2, the first terminal of the first winding n 31 of the primary side of the second transformer T2 is connected to the first winding n 31 of the primary side of the second transformer T2.the second terminal of the second transformer T2 primary side second winding n 32 the first terminal of the second transformer T2 primary side second winding n 32 the second terminal of the second transformer T2 primary side third winding n 33 the first terminal of the second transformer T2 primary side Mth winding n 3M the second terminal of the second transformer T2 secondary side first winding n 41 the first terminal of the second transformer T2 secondary side first winding n 41 the second terminal of the second transformer T2 secondary side second winding n 42 the first terminal of the second transformer T2 secondary side second winding n 42 the second terminal of the second transformer T2 secondary side Mth winding n 4M the first terminal of the second transformer T2 secondary side Mth winding n 4M the second terminal of the second transformer T2 secondary side Mth winding n.

[0065] As an example, the inductance L r2 may be leakage inductance or series inductance.

[0066] As an example, the primary side windings of the second transformer T2 are connected in series, and the alternating current generated by the primary side conversion module 1 is passed through the series-connected primary side windings. The magnetic motive force generated by each primary side winding is superimposed, and the alternating magnetic flux is excited in the shared magnetic core. The current of the series-connected primary side windings is the same, and the magnetic motive force of each winding can be superimposed or compensated according to requirements, thereby optimizing the magnetic flux utilization rate of the magnetic core and improving the overall energy transmission efficiency in a multi-output scenario. Each primary side winding can be matched with an independent secondary side winding, which can be designed individually according to the voltage level and power requirement of different loads to achieve precise multi-supply customization.

[0067] As an example, the multiple windings of the second transformer T2 share one magnetic core.

[0068] As an example, please continue to refer to Figure 3 The secondary side conversion module 3 can include M rectifier units, and the first ports of the M rectifier units are connected to the corresponding secondary side windings in the transformer module 2. The second ports of the M rectifier units are connected in parallel to the two ends of the second port voltage .

[0069] In yet another embodiment, please refer to Figure 4The first terminal of each of the M inductances is connected in series to a first terminal of a first winding n1 of a third transformer T3.

[0070] As an example, the M inductances can be leakage inductances or series inductances.

[0071] In particular, the first terminal of the inductance ML r31 is connected to a first terminal of a second port of the primary conversion module 1, the second terminal of the inductance ML r31 is connected to a first terminal of a first winding n1 of a primary side of the third transformer T3, the second terminal of the first winding n1 of the primary side of the third transformer T3 is connected to a second terminal of the second port of the primary conversion module 1; the first terminal of the inductance ML 51 is connected to a first terminal of a second port of the primary conversion module 1, the second terminal of the inductance ML 51 is connected to a first terminal of a second winding n2 of the primary side of the third transformer T3, the second terminal of the second winding n2 of the primary side of the third transformer T3 is connected to a second terminal of the second port of the primary conversion module 1; the first terminal of the inductance ML r32 is connected to a first terminal of a second port of the primary conversion module 1, the second terminal of the inductance ML r32 is connected to a first terminal of a third winding n3 of the primary side of the third transformer T3, the second terminal of the third winding n3 of the primary side of the third transformer T3 is connected to a second terminal of the second port of the primary conversion module 1; the first terminal of the inductance ML 52 is connected to a first terminal of a second port of the primary conversion module 1, the second terminal of the inductance ML 52 is connected to a first terminal of an M winding nM of the primary side of the third transformer T3, the second terminal of the M winding nM of the primary side of the third transformer T3 is connected to a second terminal of the second port of the primary conversion module 1; the first terminal of a first winding n1 of a secondary side of the third transformer T3 is connected to a first terminal of a first rectifying unit 31, the second terminal of the first winding n1 of the secondary side of the third transformer T3 is connected to a second terminal of the first rectifying unit 31; the first terminal of a second winding n2 of the secondary side of the third transformer T3 is connected to a first terminal of a second rectifying unit 32, the second terminal of the second winding n2 of the secondary side of the third transformer T3 is connected to a second terminal of the second rectifying unit 32; the first terminal of an M winding nM of the secondary side of the third transformer T3 is connected to a first terminal of an M rectifying unit 3M, the second terminal of the M winding nM of the secondary side of the third transformer T3 is connected to a second terminal of the M rectifying unit 3M. r3M r3M 5M 5M 61 61 62 62 6M 6M

[0072] ​​​​​​​​​​As an example, the primary winding of the third transformer T3 is connected in series with the corresponding inductor in parallel at the second port of the primary conversion module 1. After the primary conversion module 1 outputs alternating electric energy, multiple branches are connected in parallel, each branch being connected in series by an inductor and the corresponding primary winding of the third transformer T3. The current of each branch flows in the series circuit of the inductor and the primary winding, and an alternating voltage proportional to the number of turns is generated in the secondary winding of the third transformer T3 through electromagnetic induction. The alternating voltage is sent to the corresponding rectifier unit, and after rectification, multiple independent direct current voltages are output to meet the power supply needs of different loads. The inductor in series can form a resonant circuit with the primary switch and the primary winding to help achieve zero-voltage switching or zero-current switching, greatly reducing switching loss. 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, and can simultaneously meet the differentiated needs of sensitive small current loads, large current power loads, etc., with wider adaptability.

[0073] As an example, the multiple windings of the third transformer T3 share one magnetic core.

[0074] As an example, please refer to Figure 4 , the secondary conversion module 3 can include M rectifier units, the first port of the M rectifier units being connected to the corresponding secondary winding in the transformation module 2, and the second port of the M rectifier units being connected in parallel to the two ends of the second port voltage .

[0075] In yet another embodiment, please refer to Figure 5 , the transformation module 2 can include an inductor L r4 and a fourth transformer T4, the first terminal of the inductor L r4 being connected to the first terminal of the second port of the primary conversion module 1, the second terminal of the inductor L r1 being connected to the first terminal of the primary winding n 71 of the fourth transformer T4, the second terminal of the primary winding n 71 of the fourth transformer T4 being connected to the second terminal of the second port of the primary conversion module 1; the first terminal and the second terminal of the secondary winding n 81 of the fourth transformer T4 being connected to the first port of the secondary conversion module 3.

[0076] As an example, the fourth transformer T4 can be a high-frequency transformer, and the primary winding n n 71 of the fourth transformer T4 is matched with the primary conversion module 1 and the inductor L L r4 to generate alternating magnetic flux at high frequency. Under high-frequency operation, the magnetic flux density of the fourth transformer T4 changes at a high rate, which can greatly reduce the volume of the magnetic core and the number of turns of the winding, significantly reducing the overall size of the transformer, and meeting the design requirements of miniaturization and integration of electronic devices.

[0077] As an example, the inductance L r4 may be a leakage inductance or a series inductance.

[0078] As an example, please continue to refer to Figure 5 The secondary side conversion module 3 can include M rectifier units, the first port of the M rectifier units is connected in parallel to the two ends of the secondary side winding in the transformer module 2, and the second port of the M rectifier units is connected in parallel to the two ends of the second port voltage The first port and the second port of the M rectifier units are connected in parallel, that is, the input and output sides of the M rectifier units are connected in parallel, and the total output power is the sum of the powers of each unit, which can easily meet the power demand of large loads and is suitable for high-power power supply scenarios; the characteristics of each rectifier unit are consistent, and the uniform distribution of output current can be realized after parallel connection, avoiding damage to a single rectifier unit due to overload, while optimizing the load efficiency of each rectifier unit.

[0079] It should be understood that the three-level capacitive and inductive hybrid isolated DC transformer of the present application can realize bidirectional power transmission, that is, it can convert the first port voltage V H into the second port voltage V L , and can also convert the second port voltage V L into the first port voltage V H .

[0080] In the above-mentioned three-level capacitive and inductive hybrid isolated DC transformer, the primary side conversion module 1 adopts a structure combining cascading and parallel connection of multiple three-level units, cooperates with the complementary and synchronous conduction strategy of the switch, can reduce the switch loss and optimize the voltage output waveform, greatly reduces the insulation stress caused by partial discharge of the transformer by using the bias voltage of the high-voltage capacitor, can reduce the volume of the transformer and improve the power density; the transformer module 2 adopts diversified design, can realize precise conversion and electrical isolation of multiple voltage, meets the voltage level demand of different loads, and at the same time realizes soft switching by using the resonance characteristics of the inductance and the winding, improves the energy transmission efficiency; the secondary side conversion module 3 has input and output in parallel through multiple rectifier units, which not only integrates multiple power outputs to adapt to large load demand, but also optimizes the output voltage ripple and dynamic response; bidirectional power transmission can flexibly realize energy conversion between high and low voltage sides. In summary, the three-level capacitive and inductive hybrid isolated DC transformer of the present application has the characteristics of high voltage adaptability, high power capacity, high reliability and high efficiency, and is suitable for power supply demand in multiple scenarios.

[0081] In another embodiment, please refer to Figure 6The application further provides a control method of the three-level capacitance-inductance hybrid isolation type DC transformer, which can include the following steps: steps S1-S3.

[0082] Step S1: The first switch and the second switch in each three-level unit are set to be complementarily turned on, the third switch and the fourth switch are set to be complementarily turned on, and the first switch and the fourth switch are set to be turned on together at a first duty ratio.

[0083] Step S2: Each rectification unit is set to be synchronously rectified, and the two switches of the same bridge arm are set to be complementarily turned on.

[0084] Step S3: The output voltage is adjusted by changing the switching frequency, so as to realize the control of the three-level capacitance-inductance hybrid isolation type DC transformer.

[0085] In the control method of the three-level capacitance-inductance hybrid isolation type DC transformer, the first switch and the second switch and the third switch and the fourth switch in each three-level unit are set to be complementarily turned on, and the first switch and the fourth switch are set to be synchronously turned on at a first duty ratio, so that the three-level module can output stable intermediate voltage, provide high-quality voltage excitation for the primary energy transmission, and effectively reduce the interference of voltage fluctuation on the subsequent resonant circuit; each rectification unit is set to be synchronously rectified, and the two switches of the same bridge arm are set to be complementarily turned on, so that the conduction loss of the secondary rectification process can be greatly reduced, the energy conversion efficiency can be improved, the risk of short circuit caused by simultaneous conduction of the switches can be avoided, and the safe and reliable operation of the secondary circuit can be ensured; the output voltage can be flexibly and accurately adjusted by changing the switching frequency, the stable control of the output voltage can be realized, the working state can be optimized, the reactive loss can be reduced, and the energy transmission efficiency can be further improved.

[0086] In step S1, refer to step S1 in Figure 6 , the first switch and the second switch in each three-level unit are set to be complementarily turned on, the third switch and the fourth switch are set to be complementarily turned on, and the first switch and the fourth switch are set to be turned on together at a first duty ratio.

[0087] Specifically, the switch S1 and the switch S2 in each three-level unit can be set to be complementarily turned on, the switch S3 and the switch S4 can be set to be complementarily turned on, and the switch S1 and the switch S4 can be set to be turned on together at a first duty ratio.

[0088] For example, the first duty ratio can be set to 50%.

[0089] In step S2, refer to step S2 in Figure 6 , each rectification unit is set to be synchronously rectified, and the two switches of the same bridge arm are set to be complementarily turned on.

[0090] 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.

[0091] 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.

[0092] 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.

[0093] As an example, the target voltage on the low-voltage side V Lref It can be set according to actual needs.

[0094] 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.

[0095] Specifically, the switch S1 and the switch S2 in each three-level unit can be set to be complementary on, the switch S3 and the switch S4 can be set to be complementary on, and the switch S1 and the switch S4 can be set to be on together at a second duty ratio; each rectifier unit can be set to be synchronous rectification, the switch Q1 and the switch Q2 in the first bridge arm can be set to be complementary on, the switch Q3 and the switch Q4 in the second bridge arm can be set to be complementary on, and the first bridge arm and the second bridge arm can be set to be phase-shifted on.

[0096] As an example, the first bridge arm and the second bridge arm can be set to be phase-shifted on, the driving signal of the switch Q1 and the switch Q4 can be set to be different by , and the driving signal of the switch Q2 and the switch Q3 can also be set to be different by , wherein, is an inner phase-shift angle of each rectifier unit. The power transferred by the three-level inductive-capacitive hybrid isolation type DC transformer can be adjusted by the phase-shift angle of the primary and secondary voltages of the transformer.

[0097] As an example, the second duty ratio can be set to be 50%.

[0098] In one example, please refer to Figure 7 , Figure 7 is a phase-shift control waveform diagram in a three-level inductive-capacitive hybrid isolation type DC transformer. The working principle of the three-level inductive-capacitive hybrid isolation type DC transformer will be introduced below by taking the phase-shift control and the power transmission from high voltage to low voltage as an example.

[0099] As an example, before the time point of t 0, the switch S2 and the switch S3 are off, the resonant current i r charges the parasitic capacitances of the switch S2 and the switch S3, and the voltage rises to V H / N / 2. The parasitic capacitances of the switch S1 and the switch S4 are discharged, the voltage drops to 0, and the parasitic diode of the switch S1 and the parasitic diode of the switch S4 are turned on.

[0100] Further, at the time point of t 0 to t 1, the switch S1 and the switch S4 are turned on, the switch Q2 and the switch Q4 are turned on, the resonant current i r rises, the resonant current i r changes polarity, the parasitic diode of the switch S1 and the parasitic diode of the switch S4 are turned off, and the resonant current i r flows through the switch S1 and the switch S4. The primary voltage of the three-level inductive-capacitive hybrid isolation type DC transformer is v p V H ​​ / N / 2, three-level inductive-capacitive hybrid isolated DC transformer secondary voltage v s is 0.

[0101] Further, at t 1 to t 2, switch Q2 is turned off, the resonance current i r flows through switch S1 and switch S4, the parasitic capacitance of switch Q1 begins to discharge, and the secondary current flows through switch Q1 and switch Q4. Three-level inductive-capacitive hybrid isolated DC transformer primary voltage v p is V H / N / 2, three-level inductive-capacitive hybrid isolated DC transformer secondary voltage v s is V L .

[0102] Further, at t 2 to t 3, switch Q1 is turned on, at this time the resonance current i r flows through switch S1 and switch S4, and the secondary current flows through the parasitic diode of switch Q1 and switch Q4. Three-level inductive-capacitive hybrid isolated DC transformer primary voltage v p is V H / N / 2, three-level inductive-capacitive hybrid isolated DC transformer secondary voltage v s is V L .

[0103] Further, at t 3 to t 4, switch Q4 is turned off, the resonance current i r flows through switch S1 and switch S4, the parasitic capacitance of switch Q3 begins to discharge, the parasitic capacitance of switch Q4 begins to charge, and the secondary current flows through the parasitic diode of switch Q3 and switch Q4. Three-level inductive-capacitive hybrid isolated DC transformer primary voltage v p is V H / N / 2, three-level inductive-capacitive hybrid isolated DC transformer secondary voltage v s is 0.

[0104] Further, at t 4 to t 5, switch Q3 is turned on, at this time the resonance currenti 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 .

[0105] 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.

[0106] 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.

[0107] 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.

[0108] 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.

[0109] 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 The resonant current flowing through the inductor L r1 The resonant current flowing through the inductor Figure 8 It can be seen that the primary voltage of the three-level capacitive-inductive hybrid isolated DC transformer v p presents a square wave with a duty cycle close to 50%, stable amplitude and consistent period. The primary conversion module 1 operates at a stable switching frequency, and the switching timing is accurate. The periodicity and amplitude consistency of the output voltage are good. The secondary voltage of the three-level capacitive-inductive hybrid isolated DC transformer v s presents a multi-phase square wave. The working state of the secondary conversion module 3 is stable, and it can respond to the periodic changes of the primary voltage synchronously, realizing efficient energy transfer and conversion. The resonant current i r has no obvious spikes or distortion, indicating that the control strategy (such as switching timing and phase shift angle) is well optimized, reducing the current stress of the device and benefiting the long-term reliable operation of the system. Figure 9 is the coupling capacitor isolation voltage waveform of the three-level capacitive-inductive hybrid isolated DC transformer when it is working stably. The curve in the figure represents the bias voltage of the high-voltage capacitor in different modules. From 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 of partial discharge of the high-frequency transformer and the insulation volume of the transformer; and reducing the ground potential of the three-level capacitive-inductive hybrid isolated DC transformer, thereby reducing the insulation stress caused by the partial discharge of the three-level capacitive-inductive hybrid isolated DC transformer.

[0110] In the control method of the three-level inductance-capacitance hybrid isolation type DC transformer, by setting the first switch and the second switch, the third switch and the fourth switch in each three-level unit to be complementary conduction respectively, and the first switch and the fourth switch to be synchronous conduction with a fixed duty ratio, the three-level module can output stable intermediate voltage, providing high-quality voltage excitation for the primary energy transmission, effectively weakening the interference of voltage fluctuation on the subsequent resonant circuit, avoiding the disorder of resonant state, and ensuring the stability of energy transmission foundation; by setting each rectifier unit to perform synchronous rectification and the two switches in the same bridge arm to be complementary conduction, compared with the traditional diode rectification, the conduction loss of the secondary side rectification process can be greatly reduced, the energy conversion efficiency is improved, and the risk of short circuit caused by the simultaneous conduction of the two switches in the same bridge arm is eliminated, which ensures the safe operation of the secondary circuit; by changing the switching frequency to adjust the output voltage, the voltage deviation on the low-voltage side can be flexibly responded, and the output voltage can be accurately stabilized at the target value; and the frequency regulation can optimize the working state of the circuit, reduce the reactive loss, and further improve the energy transmission efficiency; by adding phase-shift conduction between different bridge arms in the rectifier unit, and combining with the phase-shift angle regulation power of the primary and secondary voltages of the transformer module, the smooth transition of the secondary current can be realized, the device stress caused by current mutation can be avoided, the power transmission size can be accurately controlled, different load working conditions can be adapted, and the working condition adaptability, operation reliability and comprehensive energy utilization efficiency of the three-level inductance-capacitance hybrid isolation type DC transformer are significantly improved.

[0111] It should be understood that, although each step in the flowchart of the accompanying drawings is shown in sequence according to the direction of the arrow, these steps are not necessarily executed in sequence according to the direction of the arrow. Unless otherwise specified herein, the execution of these steps is not strictly limited in sequence, and these steps can be executed in other sequences. Moreover, at least part of the steps in the accompanying drawings can include multiple sub-steps or multiple stages, which are not necessarily executed at the same time, but can be executed at different times, and the execution sequence of these sub-steps or stages is not necessarily sequential, but can be executed alternately or alternately with at least part of other steps or sub-steps or stages of other steps.

[0112] The technical features of the above embodiments can be combined in any manner. In order to make the description concise, not all possible combinations of the technical features in the above embodiments are described, but as long as the combinations of the technical features do not exist contradictory, they should be considered as the scope of the present disclosure.

[0113] Although the present application has been disclosed as above with examples, it is not intended to limit the present application, and anyone with ordinary knowledge in the art can make some changes and modifications without departing from the spirit and scope of the present application.

Claims

1. A three-level capacitive-inductive hybrid isolated DC transformer, the three-level capacitive-inductive hybrid isolated DC transformer is bidirectional power transmission; characterized in that, The application relates to a three-port converter, which comprises a primary-side conversion module, a voltage transformation module and a secondary-side conversion module. The primary-side conversion module comprises a plurality of three-level units, the first ports of the three-level units are connected in series and then connected to the first port voltage, and the second ports of the three-level units are connected in parallel and then connected to the first port of the voltage transformation module. The voltage transformation module comprises a transformer with a plurality of windings sharing one magnetic core, the transformer comprises one primary winding and a plurality of secondary windings, or the transformer comprises a plurality of primary windings and a plurality of secondary windings, the number of the primary windings and the secondary windings is the same as the number of the plurality of rectifier units of the secondary-side conversion module. Each three-level unit comprises 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 of the uppermost first three-level unit is connected to the first terminal of the first port voltage, the second terminal of the second capacitor of the first three-level unit is connected to the first terminal of the first capacitor of the second three-level unit, and the second terminal of the second capacitor of the last three-level unit is connected to the second terminal of the first port voltage. For each three-level unit, the first terminal of the first capacitor is connected to the first terminal of the first switch, the second terminal of the first capacitor is connected to the first terminal of the second switch, the second terminal of the second capacitor, the first terminal of the third switch and the second terminal of the second switch, the second terminal of the second capacitor is connected to the second terminal of the fourth switch, the second terminal of the first switch is connected to the first terminal of the second switch, the first terminal of the third switch and the first terminal of the third capacitor, the second terminal of the third switch is connected to the first terminal of the fourth switch and the first terminal of the fourth capacitor, the second terminal of the third capacitor is connected to the first terminal of the first port of the voltage transformation module, and the second terminal of the fourth capacitor is connected to the second terminal of the first port of the voltage transformation module. The third capacitor and the fourth capacitor are high-voltage capacitors, and the bias voltage of the high-voltage capacitors reduces the insulation stress caused by partial discharge of the transformer. When the transformer comprises one primary winding and a plurality of secondary windings, the second terminal of the third capacitor of each three-level unit is connected to one end of the primary winding through leakage inductance or series inductance, and the second terminal of the fourth capacitor of each three-level unit is connected to the other end of the primary winding. When the transformer comprises a plurality of primary windings and a plurality of secondary windings, the plurality of primary windings are connected in series or in parallel. The first ports of the plurality of rectifier units of the secondary-side conversion module are respectively connected to the corresponding secondary windings in the voltage transformation module, the second ports of the plurality of rectifier units are connected in parallel and then connected to the two terminals of the second port voltage, the total output power is the sum of the powers of the units, and the uniform distribution of the output current is realized. ​ 2. The three-level inductive hybrid isolated DC-DC converter of claim 1, wherein, Each of the rectifier units comprises a fifth switch, a sixth switch, a seventh switch, an eighth switch, and a fifth capacitor, a first terminal of the fifth switch is connected to a first terminal of the fifth capacitor, a second terminal of the fifth switch is connected to a first terminal of the sixth switch, a second terminal of the sixth switch is connected to a second terminal of the fifth capacitor, a first terminal of the seventh switch is connected to the first terminal of the fifth capacitor, a second terminal of the seventh switch is connected to a first terminal of the eighth switch, a 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 a first terminal of a second port voltage, and the second terminal of the fifth capacitor is connected to a second terminal of the second port voltage.

3. A control method of a three-level inductive hybrid isolated DC transformer, characterized by, The three-level inductive-capacitive hybrid isolation type DC transformer for performing the method according to any one of claims 1 to 2 comprises the following steps: The first switch and the second switch in each three-level unit are set to be complementary on, the third switch and the fourth switch are set to be complementary on, and the first switch and the fourth switch are set to be on together at a first duty ratio; The two switches in each rectifier unit are set to be synchronous rectification, and the two switches in the same bridge arm are set to be complementary on; The output voltage is adjusted by changing the switching frequency, and the control of the three-level inductive-capacitive hybrid isolation type DC transformer is realized.

4. The control method of the three-level inductive hybrid isolated DC-DC converter according to claim 3, characterized in that, The two switches in each rectifier unit are set to be complementary on, and the two switches in different bridge arms are set to be phase-shifted on; the power transmitted by the three-level inductive-capacitive hybrid isolation type DC transformer is adjusted by changing the phase-shift angle of the primary and secondary side voltages of the transformer module.

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