Asymmetric two-way transmission DC transformer topology system and control method

Abstract

The invention discloses an asymmetric two-way transmission direct-current transformer topological system and a control method, and belongs to the technical field of direct-current converters. The asymmetric two-way transmission direct-current transformer topological system comprises a low-voltage side filter capacitor, a three-phase bridge circuit, a first isolation transformer bank, a second isolation transformer bank, a hybrid bridge circuit, a first medium-voltage side filter capacitor and a second medium-voltage side filter capacitor, the low-voltage-side filter capacitor and the three-phase bridge circuit are connected in parallel to form a low-voltage direct-current port, the first medium-voltage-side filter capacitor and the second medium-voltage-side filter capacitor are connected in series and then connected with the hybrid bridge circuit in parallel to form a high-voltage direct-current port, the voltage stress of all switching devices is half of the input voltage, and the current waveform is approximate to a trapezoidal wave in a modulation mode. Compared with a triangular waveform, the current peak value is reduced, the current stress of the device is reduced, the cost and the conduction loss of the device are reduced, the secondary side rectifier diode can also realize ZCS switching on and switching off, the reliability of the direct current converter is improved, the working frequency of the transformer is intermediate frequency, and the capacity is easy to increase.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of direct current converter, in particular to an asymmetric bidirectional transmission direct current transformer topology system and a control method. BACKGROUND

[0002] The direct current converter is one of the key parts of the new energy medium voltage direct current collection system, can realize the interconnection of direct current transmission and distribution networks of different voltage levels, and improve the flexibility of direct current transmission and distribution.

[0003] Especially for the offshore wind power scene, if a unidirectional direct current converter is used to realize offshore wind power direct current collection, due to the unidirectionality of power transmission, the wind turbine generator needs to be additionally configured with an energy storage unit or an auxiliary converter to realize black start, which increases the complexity of the system. If a bidirectional direct current converter is used, the power required for starting the wind turbine generator is less than the power generated by the collection and sending out, the utilization rate of the power device is low, and the investment cost of the system is increased. SUMMARY

[0004] In view of the above problems, the present application is proposed.

[0005] Therefore, the technical problem solved by the present application is: for the offshore wind power scene, if a unidirectional direct current converter is used to realize offshore wind power direct current collection, due to the unidirectionality of power transmission, the wind turbine generator needs to be additionally configured with an energy storage unit or an auxiliary converter to realize black start, which increases the complexity of the system. If a bidirectional direct current converter is used, the power required for starting the wind turbine generator is less than the power generated by the collection and sending out, the utilization rate of the power device is low, and the investment cost of the system is increased.

[0006] To solve the above technical problems, the present application provides the following technical scheme: an asymmetric bidirectional transmission direct current transformer topology system, comprising, a low-voltage side filter capacitor, a three-phase bridge circuit, a first isolation transformer group, a second isolation transformer group, a hybrid bridge circuit, a first medium-voltage side filter capacitor and a second medium-voltage side filter capacitor; The low-voltage side filter capacitor and the three-phase bridge circuit are connected in parallel to form a low-voltage direct current port. The first medium-voltage side filter capacitor and the second medium-voltage side filter capacitor are connected in series and connected in parallel with the hybrid bridge circuit to form a high-voltage direct current port.

[0007] As a preferred scheme of the asymmetric bidirectional transmission DC transformer topology system, in the three-phase bridge circuit, the middle point of the bridge arm formed by the series connection of the first low-voltage side switch tube and the second low-voltage side switch tube is connected to the same name end of the low-voltage side winding of the main transformer through the first leakage inductor, the middle point of the bridge arm formed by the series connection of the third low-voltage side switch tube and the fourth low-voltage side switch tube is connected to the different name end of the low-voltage side winding of the main transformer and the different name end of the low-voltage side winding of the auxiliary transformer through the second leakage inductor, and the middle point of the bridge arm formed by the series connection of the fifth low-voltage side switch tube and the sixth low-voltage side switch tube is connected to the same name end of the low-voltage side winding of the auxiliary transformer through the third leakage inductor.

[0008] As a preferred scheme of the asymmetric bidirectional transmission DC transformer topology system, in the mixed bridge circuit, the middle point of the rectifier circuit formed by the series connection of the first medium-voltage side rectifier diode and the second medium-voltage side rectifier diode is connected to the same name end of the high-voltage side winding of the main transformer through the first filter inductor; the middle point of the bridge arm formed by the series connection of the first medium-voltage side switch tube and the second medium-voltage side switch tube is connected to the same name end of the high-voltage side winding of the main transformer through the second filter inductor; the different name end of the high-voltage side winding of the main transformer is connected to the same name end of the high-voltage side winding of the auxiliary transformer; the different name end of the high-voltage side winding of the auxiliary transformer is connected to the middle point of the first medium-voltage side filter capacitor and the second medium-voltage side filter capacitor.

[0009] To solve the above technical problems, the present application provides the following technical scheme: an asymmetric bidirectional transmission DC transformer topology control method, comprising: using a pulse width modulation mode, including a forward power transmission mode and a reverse power transmission mode; in the forward power transmission mode, energy is transmitted from the low-voltage DC port to the high-voltage DC port, the three-phase bridge circuit on the low-voltage side works in an active inverter state, and the switch tubes in the mixed bridge circuit on the medium-voltage side are locked, and the rectifier circuit works in a passive rectifier state; in the reverse power transmission mode, energy is transmitted from the high-voltage DC port to the low-voltage DC port, part of the switch tubes in the mixed bridge circuit on the medium-voltage side and part of the switch tubes in the three-phase bridge circuit on the low-voltage side work in an active modulation state.

[0010] As a preferred scheme of the asymmetric bidirectional transmission DC transformer topology control method, in the forward power transmission operation mode, the first low-voltage side switch tube, the fourth low-voltage side switch tube and the fifth low-voltage side switch tube are simultaneously turned on, the second low-voltage side switch tube, the third low-voltage side switch tube and the sixth low-voltage side switch tube are simultaneously turned on with a half switching period lag, and the first medium-voltage side switch tube and the second medium-voltage side switch tube are locked.

[0011] As a preferred scheme of the asymmetric bidirectional transmission DC transformer topology control method, in the forward power transmission operation mode, at the beginning of each positive half cycle, the first low-voltage side switch, the fourth low-voltage side switch and the fifth low-voltage side switch are turned on to make the transformer current rise; at the end of each positive half cycle, the fifth low-voltage side switch is turned off in advance to make the transformer current quickly drop to zero before the end of the positive half cycle.

[0012] As a preferred scheme of the asymmetric bidirectional transmission DC transformer topology control method, in the reverse power transmission operation mode, the sixth low-voltage side switch and the first medium-voltage side switch are turned on at the same time, the fifth low-voltage side switch and the second medium-voltage side switch are turned on at the same time with a half switch cycle lag, and the first low-voltage side switch, the second low-voltage side switch, the third low-voltage side switch and the fourth low-voltage side switch are locked.

[0013] As a preferred scheme of the asymmetric bidirectional transmission DC transformer topology control method, at the beginning of each positive half cycle, the first high-voltage side switch and the sixth low-voltage side switch are turned on to make the transformer current rise; at the end of each positive half cycle, the sixth low-voltage side switch is turned off in advance to make the transformer current quickly drop to zero before the end of the positive half cycle.

[0014] As a preferred scheme of the asymmetric bidirectional transmission DC transformer topology control method, the transmission power in the forward power transmission operation mode is adjusted by controlling the conduction duty cycle of the fifth low-voltage side switch.

[0015] As a preferred scheme of the asymmetric bidirectional transmission DC transformer topology control method, the transmission power in the reverse power transmission operation mode is adjusted by controlling the conduction duty cycle of the sixth low-voltage side switch.

[0016] The application provides a computer device, including a memory and a processor, and the memory stores a computer program.

[0017] The application provides a computer readable storage medium, which stores a computer program.

[0018] The application makes the medium-voltage side hybrid bridge circuit only consist of non-controlled rectification path of rectifier diode in forward power transmission, reduces the conduction loss and switching loss of power devices; in reverse power transmission, the medium-voltage side switch tube and the low-voltage side partial switch tube are used to realize the active control transmission of small power, which avoids the problems of power device capacity redundancy and low utilization caused by the completely symmetrical bidirectional converter, thereby effectively reducing the complexity and investment cost of the overall system on the basis of ensuring the integrity of the system function. BRIEF DESCRIPTION OF DRAWINGS

[0019] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings needed in the embodiment description will be briefly introduced as follows. Obviously, the drawings in the following description are only some embodiments of the present application, and all other drawings obtained by those skilled in the art without creative labor should be within the protection scope of the present application.

[0020] Figure 1 A schematic diagram of an asymmetric bidirectional transmission DC transformer topology system provided by an embodiment of the present application. DETAILED DESCRIPTION

[0021] In order to make the above-mentioned purposes, features and advantages of the present application more obvious and easy to understand, the specific embodiments of the present application will be described in detail below with reference to the drawings of the specification. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor should be within the protection scope of the present application.

[0022] Embodiment 1, refer to Figure 1 For an embodiment of the present application, the embodiment provides an asymmetric bidirectional transmission DC transformer topology system, which comprises: In order to solve the problem that for the offshore wind power scene, if a unidirectional DC converter is used to realize the offshore wind power DC collection, due to the unidirectionality of power transmission, the wind turbine needs to be additionally configured with an energy storage unit or an auxiliary converter to realize black start, which increases the complexity of the system. If a bidirectional DC converter is used, due to the fact that the power required for starting the wind turbine is less than the power for generating and collecting and sending out, the utilization rate of the power device is low, which increases the investment cost of the system, the present application provides an asymmetric bidirectional transmission DC transformer topology system and method.

[0023] Among them, the low-voltage side filter capacitor is C LV , the first isolation transformer group and the second isolation transformer group are T1 and T2 respectively, and the first medium-voltage side filter capacitor and the second medium-voltage side filter capacitor are C HV1and C HV2 , the first low-voltage side switch tube, the second low-voltage side switch tube, the third low-voltage side switch tube, the fourth low-voltage side switch tube, the fifth low-voltage side switch tube and the sixth low-voltage side switch tube are S1, S2, S3, S4, S5, S6 respectively, the first leakage inductance, the second leakage inductance, the third leakage inductance are L T1 , L T2 , L T3 , the main transformer and the auxiliary transformer are T1, T2 respectively, the first medium-voltage side rectifier diode and the second medium-voltage side rectifier diode are D1 and D2 respectively, the first medium-voltage side switch tube and the second medium-voltage side switch tube are Q1 and Q2 respectively, the first filter inductance and the second filter inductance are L K1 and L K2 ; The low-voltage side filter capacitor C LV , the three-phase bridge circuit, the isolation transformer set T1 and T2, the hybrid bridge circuit and the medium-voltage side filter capacitor C HV1 and C HV2 ; The low-voltage side filter capacitor C LV is connected in parallel with the three-phase bridge circuit to form a low-voltage direct current port; The medium-voltage side filter capacitor C HV1 and C HV2 are connected in series and are connected in parallel with the hybrid bridge circuit to form a high-voltage direct current port.

[0024] Further, in the three-phase bridge circuit, the low-voltage side switch tubes S1 and S2 are connected in series, the middle point of the bridge arm passes through the first leakage inductance L T1 is connected to the same name end of the low-voltage side winding of the main transformer T1, the low-voltage side switch tubes S3 and S4 are connected in series, the middle point of the bridge arm passes through the second leakage inductance L T2 is connected to the different name end of the low-voltage side winding of the main transformer T1 and the different name end of the low-voltage side winding of the auxiliary transformer T2, the low-voltage side switch tubes S5 and S6 are connected in series, the middle point of the bridge arm passes through the third leakage inductance L T3 is connected to the same name end of the low-voltage side winding of the auxiliary transformer T2.

[0025] Further, in the hybrid bridge circuit, the medium-voltage side rectifier diodes D1 and D2 are connected in series, the middle point of the rectifier circuit passes through the first filter inductance L K1 is connected to the same name end of the high-voltage side winding of the main transformer T1; The medium-voltage side switch tubes Q1 and Q2 are connected in series, the middle point of the bridge arm passes through the second filter inductance L K2 is connected to the same name end of the high-voltage side winding of the main transformer T1; The different name end of the high-voltage side winding of the main transformer T1 is connected to the same name end of the high-voltage side winding of the auxiliary transformer T2; The different name end of the high-voltage side winding of the auxiliary transformer T2 is connected to the medium-voltage side filter capacitor CHV1 and C HV2 the midpoint of the line segment connecting the points A and B.

[0026] Embodiment 2, which is an embodiment of the present application, provides a control method of an asymmetric bidirectional transmission DC transformer topology based on the previous embodiment, comprising: using a pulse width modulation mode, including a forward power transmission mode and a reverse power transmission mode; In the forward power transmission mode, energy is transmitted from the low-voltage DC port to the high-voltage DC port, and the three-phase bridge circuit on the low-voltage side works in an active inverter state, while the switch tube in the hybrid bridge circuit on the medium-voltage side is locked, and the rectifier circuit works in a passive rectification state. In the reverse power transmission mode, energy is transmitted from the high-voltage DC port to the low-voltage DC port, and part of the switch tubes in the hybrid bridge circuit on the medium-voltage side work in an active modulation state in cooperation with part of the switch tubes in the three-phase bridge circuit on the low-voltage side.

[0027] In the forward power transmission operation mode, the low-voltage side switch tubes S1, S4 and S5 are turned on at the same time, the low-voltage side switch tubes S2, S3 and S6 are turned on with a half switch period lag, and the medium-voltage side switch tubes Q1 and Q2 are locked.

[0028] At the beginning of each positive half cycle in the forward power transmission operation mode, the low-voltage side switch tubes S1, S4 and S5 are turned on to make the transformer current rise; at the end of each positive half cycle, the low-voltage side switch tube S5 is turned off in advance to make the transformer current drop rapidly to zero before the end of the positive half cycle.

[0029] In the reverse power transmission operation mode, the low-voltage side switch tube S6 and the medium-voltage side switch tube Q1 are turned on at the same time, the low-voltage side switch tube S5 and the medium-voltage side switch tube Q2 are turned on with a half switch period lag, and the low-voltage side switch tubes S1, S2, S3 and S4 are locked.

[0030] At the beginning of each positive half cycle, the high-voltage side switch tube Q1 and the low-voltage side switch tube S6 are turned on to make the transformer current rise; at the end of each positive half cycle, the low-voltage side switch tube S6 is turned off in advance to make the transformer current drop rapidly to zero before the end of the positive half cycle.

[0031] The transmission power in the forward power transmission operation mode is adjusted by controlling the conduction duty ratio of the low-voltage side switch tube S5.

[0032] The transmission power in the reverse power transmission operation mode is adjusted by controlling the conduction duty ratio of the low-voltage side switch tube S6.

[0033] This invention employs an asymmetric bidirectional topology and its corresponding modulation method to optimize device utilization and system economy while meeting the requirements for reverse low-power transmission during black start of offshore wind power. During high-power forward transmission, the medium-voltage side operates solely through a diode rectification path, avoiding switching losses and reducing costs. During low-power reverse transmission, only a portion of the medium-voltage side switches are activated in conjunction with a few switches on the low-voltage side for coordinated modulation, achieving precise control of the lower power output. This eliminates the need for a fully controlled device with the same capacity as the forward converter for the reverse channel, solving the problem of wasted device capacity caused by power level mismatch in traditional bidirectional converters.

[0034] This embodiment also provides an electronic device applicable to an asymmetric bidirectional transmission DC transformer topology system, comprising: a memory and a processor; the memory is used to store computer-executable instructions, and the processor is used to execute the computer-executable instructions to implement the asymmetric bidirectional transmission DC transformer topology system as proposed in the above embodiment.

[0035] This embodiment also provides a storage medium storing a computer program that, when executed by a processor, implements an asymmetric bidirectional transmission DC transformer topology system as described in the above embodiments.

[0036] The storage medium proposed in this embodiment and the implementation of an asymmetric bidirectional transmission DC transformer topology system proposed in the above embodiments belong to the same inventive concept. Technical details not described in detail in this embodiment can be found in the above embodiments, and this embodiment has the same beneficial effects as the above embodiments.

[0037] Based on the above description of the implementation methods, those skilled in the art can clearly understand that the present invention can be implemented using software and necessary general-purpose hardware, and of course, it can also be implemented using hardware, but in many cases the former is a better implementation method. Based on this understanding, the technical solution of the present invention, or the part that contributes to the prior art, can be embodied in the form of a software product. This computer software product can be stored in a computer-readable storage medium, such as a computer floppy disk, read-only memory (ROM), random access memory (RAM), flash memory, hard disk, or optical disk, etc., including several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute the methods of the various embodiments of the present invention.

[0038] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. An asymmetric bidirectional transmission DC transformer topology system, characterized in that: include, Low-voltage side filter capacitor, three-phase bridge circuit, first isolation transformer group, second isolation transformer group, hybrid bridge circuit, first medium-voltage side filter capacitor and second medium-voltage side filter capacitor; The low-voltage side filter capacitor is connected in parallel with the three-phase bridge circuit to form a low-voltage DC port; The first and second medium-voltage side filter capacitors are connected in series and then connected in parallel with the hybrid bridge circuit to form a high-voltage DC port.

2. The asymmetric bidirectional transmission DC transformer topology system as described in claim 1, characterized in that: In the three-phase bridge circuit, the midpoint of the bridge arm formed by the first and second low-voltage side switches connected in series is connected to the same-name terminal of the low-voltage side winding of the main transformer through the first leakage inductance. The midpoint of the bridge arm formed by the third and fourth low-voltage side switches connected in series is connected to the opposite-name terminal of the low-voltage side winding of the main transformer and the opposite-name terminal of the low-voltage side winding of the auxiliary transformer through the second leakage inductance. The midpoint of the bridge arm formed by the fifth and sixth low-voltage side switches connected in series is connected to the same-name terminal of the low-voltage side winding of the auxiliary transformer through the third leakage inductance.

3. The asymmetric bidirectional transmission DC transformer topology system as described in claim 2, characterized in that: In the hybrid bridge circuit, the midpoint of the rectifier circuit formed by the first medium-voltage side rectifier diode and the second medium-voltage side rectifier diode connected in series is connected to the same terminal of the high-voltage side winding of the main transformer through the first filter inductor. The midpoint of the bridge arm formed by the first and second medium-voltage side switching transistors connected in series is connected to the same-name terminal of the high-voltage side winding of the main transformer through the second filter inductor. The opposite-named terminal of the high-voltage side winding of the main transformer is connected to the same-named terminal of the high-voltage side winding of the auxiliary transformer. The opposite-named terminal of the high-voltage winding of the auxiliary transformer is connected to the midpoint of the first medium-voltage side filter capacitor and the second medium-voltage side filter capacitor.

4. A method for controlling the topology of an asymmetric bidirectional transmission DC transformer, characterized in that, The method is applied to the topology system as described in any one of claims 1-3, characterized in that it includes: It employs pulse width modulation, including forward power transfer mode and reverse power transfer mode; In the forward power transmission mode, energy is transmitted from the low-voltage DC port to the high-voltage DC port. The three-phase bridge circuit on the low-voltage side operates in active inverter mode, while the switching transistors in the hybrid bridge circuit on the medium-voltage side are locked out, and the rectifier circuit operates in passive rectification mode. In the reverse power transmission mode, energy is transmitted from the high-voltage DC port to the low-voltage DC port, and some of the switching transistors in the hybrid bridge circuit on the medium-voltage side and some of the switching transistors in the three-phase bridge circuit on the low-voltage side work together in an active modulation state.

5. The asymmetric bidirectional transmission DC transformer topology system as described in claim 4, characterized in that: In the forward power transmission operation mode, the first low-voltage side switch, the fourth low-voltage side switch, and the fifth low-voltage side switch are turned on simultaneously, while the second low-voltage side switch, the third low-voltage side switch, and the sixth low-voltage side switch are turned on simultaneously with a delay of half a switching cycle, and the first medium-voltage side switch and the second medium-voltage side switch are locked.

6. The asymmetric bidirectional transmission DC transformer topology system as described in claim 5, characterized in that: At the beginning of each positive half-cycle in the forward power transmission operation mode, the first low-voltage side switch, the fourth low-voltage side switch, and the fifth low-voltage side switch are turned on to increase the transformer current. When each positive half-cycle is about to end, the fifth low-voltage side switch is turned off in advance to make the transformer current drop rapidly to zero before the end of the positive half-cycle.

7. The asymmetric bidirectional transmission DC transformer topology system as described in claim 6, characterized in that: In the reverse power transmission operation mode, the sixth low-voltage side switch and the first medium-voltage side switch are turned on simultaneously, the fifth low-voltage side switch and the second medium-voltage side switch are turned on simultaneously with a delay of half a switching cycle, and the first low-voltage side switch, the second low-voltage side switch, the third low-voltage side switch and the fourth low-voltage side switch are locked.

8. The asymmetric bidirectional transmission DC transformer topology system as described in claim 7, characterized in that: At the beginning of each positive half-cycle, the first high-voltage side switch and the sixth low-voltage side switch are turned on, causing the transformer current to rise; just before the end of each positive half-cycle, the sixth low-voltage side switch is turned off in advance, causing the transformer current to drop rapidly to zero before the end of the positive half-cycle.

9. The asymmetric bidirectional transmission DC transformer topology system as described in claim 8, characterized in that: The transmission power in the forward power transmission operation mode is adjusted by controlling the duty cycle of the fifth low-voltage side switch.

10. The asymmetric bidirectional transmission DC transformer topology system as described in claim 9, characterized in that: The transmission power in the reverse power transmission operation mode is adjusted by controlling the duty cycle of the sixth low-voltage side switch.

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