An AC / DC hybrid power electronic transformer

Abstract

This invention discloses a novel AC / DC hybrid power electronic transformer, comprising a transformer housing, a power module housing, and an auxiliary circuit housing. The transformer housing houses transformer windings, a current transformer, and a BCT terminal box. The auxiliary circuit housing includes a power distribution unit, a lightning protection unit, a bypass protection unit, and a maintenance component unit. The power module housing includes an AC / DC module and a DC / AC module. The transformer boasts a compact overall design, making it more suitable for dual-pole cross-arm installation in substations, reducing construction complexity. In AC / DC hybrid mode, it achieves flexible power coordination between the AC and DC grids, while meeting output voltage compliance requirements under varying input voltage conditions and enabling continuous online regulation.

Description

Technical Field

[0001] The present invention relates to the technical field of smart grids, and in particular to a novel AC / DC hybrid power electronic transformer. Background Art

[0002] Traditional power distribution substations typically include 10kV / 0.4kV distribution transformers and JP cabinets or branch boxes. Distribution transformers typically have taps to ensure low-voltage output voltages meet substation requirements under varying input voltage conditions. However, adjusting between taps requires a power outage, and the voltage compliance rate for each substation load type cannot be guaranteed across the board, impacting user experience. JP cabinets or branch boxes contain substation metering, branch switches, and reactive power compensation. These cabinets or branch boxes are installed separately from the distribution transformer, requiring significant installation space and making installation difficult.

[0003] Furthermore, traditional low-voltage AC distribution networks operate in a unidirectional manner, with power flowing from transformers in a radial fashion. This type of power transmission line is typically less than 2 km long, and line impedance is significant. Active and reactive power fluctuate constantly, affecting voltage amplitudes at various points along the line. Impedance is highest at the end of the distribution line, which can easily lead to low voltage limits when the end is heavily loaded during peak hours. The presence of a large number of distributed power sources (DGs) at the end of the line can also lead to high voltage limits. Furthermore, with the rise of the new energy industry, the coverage of distributed power sources is increasing year by year. This randomness in the generation of DGs can cause significant line voltage fluctuations, impacting the stability and reliability of the power supply system.

[0004] To address the above problems, the existing technical solutions generally include:

[0005] 1) Add a separate voltage regulator to the distribution substation (either at the headend or mid-to-back end of the line), either a traditional on-load voltage regulator or a power electronic voltage regulator, to address the problem of the existing distribution transformer being unable to adjust the gear under power. This solution may have installation space issues and be difficult at the headend of the substation, so it can only be used as a transitional solution;

[0006] 2) A cross-station flexible DC interconnection system is used. Bidirectional converters are installed on the transformer sides of the two substations, connecting their DC busbars. This allows for port interconnection and power control, while also enabling DC loads to be connected to the DC-LINK. This system features a full-power topology, resulting in high capacity and high losses.

[0007] Therefore, how to solve the above technical problems is the research direction that those skilled in the art are committed to. Summary of the Invention

[0008] The purpose of the present invention is to overcome the shortcomings of the existing technology and provide a new AC / DC hybrid power electronic transformer to solve the problem that the current distribution station area does not have online voltage regulation to meet the full-caliber voltage qualification rate and to meet the access of the DC microgrid system under the new power system, realize AC / DC power mutual assistance, and increase the utilization rate of new energy.

[0009] To achieve the above object, the technical solution adopted by the present invention is: a new AC / DC hybrid power electronic transformer, comprising a transformer box, a power module box and an auxiliary circuit box,

[0010] The transformer box is provided with a transformer winding, a current transformer and a BCT terminal box. The transformer winding is divided into a low-voltage winding and a high-voltage winding. The low-voltage winding includes a first winding and a second winding. The first winding interface is connected to the power supply line; the second winding is an adjustable winding and is connected to the auxiliary circuit box; the current transformer is used to sample the current of the low-voltage winding in real time and is connected to the outside through the BCT terminal box;

[0011] The auxiliary circuit box includes a power distribution unit, a lightning protection unit, a bypass protection unit and a maintenance component unit, wherein:

[0012] The power distribution unit includes a power module box input side circuit breaker QF1 and a DC side circuit breaker QF3. The power distribution unit is used to provide a DC port to the outside.

[0013] The lightning protection unit includes a miniature circuit breaker QF2 and a surge protector FB1. The lightning protection unit is used for input surge protection. One end of the surge protector FB1 is connected to one end of the miniature circuit breaker QF2, and the other end is grounded. The other end of the miniature circuit breaker QF2 is connected to one end of the circuit breaker QF1 on the input side of the power module box.

[0014] The bypass protection unit includes a miniature circuit breaker QF4, an anti-parallel thyristor assembly SCR, and an AC contactor KM1. The miniature circuit breaker QF4 and the anti-parallel thyristor assembly SCR are connected in series, and the miniature circuit breaker QF4 and the AC contactor KM1 are connected in parallel. The bypass protection unit is used for transient switching and protection when the main circuit in the power module box is operating and when the shutdown transformer is bypassing.

[0015] The maintenance component unit includes a double-cut isolating switch QS1, which is used to short-circuit the second winding and form a maintenance breakpoint when the power module box is repaired;

[0016] The power module box includes an AC / DC module and a DC / AC module;

[0017] The DC circuit breaker QF3 is a 2P circuit breaker. The positive and negative poles of the AC / DC module and the DC / AC module are connected to one end of the DC circuit breaker QF3. The other end of the DC circuit breaker QF3 provides an external DC interface. The DC interface is located on the auxiliary circuit box and is used to connect to external devices.

[0018] The input A / B / C / N terminals of the AC / DC module are connected to the circuit breaker QF1 on the input side of the power module box and then to the output side of the first winding;

[0019] The output A / B / C terminals of the DC / AC module are connected to one end of the second winding.

[0020] As a specific implementation, the second winding is a series coupled winding.

[0021] As a specific implementation manner, the power module box and the auxiliary circuit box are respectively arranged on the left and right sides of the transformer box.

[0022] As a specific implementation, the transformer has the following operating modes:

[0023] 1) AC / DC mutual assistance mode: The power module box input-side circuit breaker QF1, miniature circuit breaker QF2, DC-side circuit breaker QF3, miniature circuit breaker QF4, and double-cut disconnector QS1 are all in the closed state, and the AC contactor KM1 is in the open state. At this time, the power module box receives the dispatch instruction and operates, the AC / DC module operates normally for voltage regulation, and the DC / AC module outputs according to the received power instruction signal, adjusting the amplitude and phase of its output voltage to achieve continuous and precise power regulation. At this time, the DC-side circuit breaker QF3 is connected to the external DC port of the external device;

[0024] 2) Bypass operation mode: The circuit breaker QF1, miniature circuit breaker QF2, miniature circuit breaker QF4, double-cut disconnector QS1 and AC contactor KM1 on the input side of the power module box are all in the closed state, and the DC side circuit breaker QF3 is in the open state. At this time, the AC / DC module is operating normally, and the DC / AC module is in the shutdown state;

[0025] 3) Main circuit voltage regulation operation mode: The power module box input-side circuit breaker QF1, miniature circuit breaker QF2, miniature circuit breaker QF4, and double-cut disconnector QS1 are all in the closed state, and the AC contactor KM1 and DC-side circuit breaker QF3 are in the open state. At this time, the AC / DC module operates normally. The DC / AC module detects the grid voltage data and makes real-time judgments to adjust the overall port output voltage to meet the output voltage qualification rate under different input voltage conditions, achieving continuous online regulation.

[0026] 4) Maintenance mode: The circuit breaker QF1, miniature circuit breaker QF2, double-cut isolating switch QS1, and AC contactor KM1 on the input side of the power module box are all in the disconnected state, and the DC side circuit breaker QF3 and miniature circuit breaker QF4 are in the closed state. At this time, the power module box is powered off, and the AC / DC module, DC / AC module, AC contactor KM1 and anti-parallel thyristor assembly SCR are inspected and maintained.

[0027] As a specific implementation method, among multiple transformer areas, transformers in every two adjacent transformer areas are interconnected via a DC interface.

[0028] As a specific implementation method, among multiple transformer areas, the AC sides of transformers in every two adjacent transformer areas are interconnected.

[0029] Due to the application of the above technical solution, the present invention has the following advantages compared with the prior art:

[0030] 1) The transformer of the present invention is structured using a transformer box and power module boxes and auxiliary line boxes located on its left and right sides. The overall design is compact and more suitable for the double-pole cross-arm installation method in the substation area, reducing the difficulty of construction.

[0031] 2) The transformer structure of the present invention can be connected to a DC load or a photovoltaic MMPT / energy storage device in AC / DC mutual assistance mode through the DC-side circuit breaker QF3, achieving flexible power mutual assistance between the AC and DC grids. In the main line operation mode, the DC / AC module makes real-time judgments based on the detected grid voltage data and adjusts the overall port output voltage to meet the output voltage qualification rate under different input voltage conditions, achieving continuous online adjustment.

[0032] 3) The transformer structure of the present invention is equipped with a DC port, realizing AC / DC mixed supply, meeting various application scenarios of current new energy microgrids, solving the problem of unstable DC side voltage during peak and valley periods of new energy power generation, and solving the problem of short-term power outages during line maintenance and supply transfer. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 This is a topological diagram of the novel AC / DC hybrid power electronic transformer described in the present invention;

[0034] Figure 2 This is a top view of the design of the new AC / DC hybrid power electronic transformer according to the present invention;

[0035] Figure 3 It is a topological diagram of AC-DC-AC power mutual assistance among multiple intervals;

[0036] Figure 4 It is a topological diagram of AC and DC power mutual assistance among multiple intervals;

[0037] Among them: 1. Transformer box; 2. Power module box; 3. Auxiliary line box. DETAILED DESCRIPTION

[0038] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0039] The present invention provides a new AC / DC hybrid power electronic transformer, including a transformer box, a power module box and an auxiliary circuit box. Figure 2 As shown, the transformer box is centered, and the power module box and the auxiliary line box are respectively arranged on the left and right sides of the transformer box. This arrangement makes the overall structural design of the transformer compact. At the same time, this design is more suitable for the double-pole cross-arm installation method in the substation area, reducing the construction difficulty.

[0040] See also Figure 1 As shown, the transformer housing houses transformer windings, a current transformer, and a BCT terminal box. The transformer windings are divided into low-voltage and high-voltage windings. The low-voltage winding comprises a first winding and a second winding. The first winding interface is connected to the power supply line, that is, the AC load. The second winding is an adjustable winding, specifically a series-coupled winding, connected to the auxiliary circuit box. The current transformer is used to sample the low-voltage winding's current in real time and is connected to the outside world via the BCT terminal box.

[0041] The auxiliary circuit box includes a power distribution unit, a lightning protection unit, a bypass protection unit, and a maintenance component unit. Specifically, the power distribution unit includes a circuit breaker QF1 on the input side of the power module box and a DC side circuit breaker QF3. The power distribution unit is used to provide a DC port to the outside.

[0042] The lightning protection unit includes a miniature circuit breaker QF2 and a surge protector FB1. The lightning protection unit is used for input surge protection. One end of the surge protector FB1 is connected to one end of the miniature circuit breaker QF2, and the other end is grounded; the other end of the miniature circuit breaker QF2 is connected to one end of the circuit breaker QF1 on the input side of the power module box.

[0043] The bypass protection unit includes a miniature circuit breaker QF4, an anti-parallel thyristor assembly SCR and an AC contactor KM1. The miniature circuit breaker QF4 is connected in series with the anti-parallel thyristor assembly SCR, and the miniature circuit breaker QF4 is connected in parallel with the AC contactor KM1. The bypass protection unit is used for transient switching and protection when the main circuit in the power module box is running and when the shutdown transformer is bypassing.

[0044] The maintenance component unit includes a double-cut isolating switch QS1, which is used to short-circuit the second winding and form a maintenance breakpoint when the power module box is repaired, so as to facilitate product maintenance.

[0045] The power module box includes AC / DC module and DC / AC module. The power module box mainly realizes the comprehensive management of the power quality at the outlet of the distribution transformer. The AC / DC module manages the current quality issues, and the DC / AC module manages the voltage quality issues to ensure the qualified rate of the outlet voltage of the substation.

[0046] Here, the DC side circuit breaker QF3 is a 2P circuit breaker. The positive and negative poles of the AC / DC module and the DC / AC module are connected respectively and then connected in parallel to one end of the DC side circuit breaker QF3. The other end of the DC side circuit breaker QF3 provides an external DC interface. The DC interface is set on the auxiliary circuit box for connecting to external devices; the input A / B / C / N terminals of the AC / DC module are connected to the circuit breaker QF1 on the input side of the power module box and then connected to the output side of the first winding; the output A / B / C terminals of the DC / AC module are connected to one end of the second winding.

[0047] Here, the transformer has the following working modes:

[0048] 1) AC / DC mutual assistance mode: The power module box input-side circuit breaker QF1, miniature circuit breaker QF2, DC-side circuit breaker QF3, miniature circuit breaker QF4, and double-cut disconnector QS1 are all in the closed state, and the AC contactor KM1 is in the open state. At this time, the power module box receives the dispatch instruction and operates, the AC / DC module operates normally for voltage regulation, and the DC / AC module outputs according to the received power instruction signal, adjusting the amplitude and phase of its output voltage to achieve continuous and precise power regulation. At this time, the external DC port of the DC-side circuit breaker QF3 is connected to a DC load or photovoltaic MMPT / energy storage device, achieving flexible power mutual assistance between the AC and DC grids;

[0049] 2) Bypass operation mode: The power module box input-side circuit breaker QF1, miniature circuit breaker QF2, miniature circuit breaker QF4, double-cut disconnector QS1, and AC contactor KM1 are all in the closed state, and the DC-side circuit breaker QF3 is in the open state. At this time, the AC / DC module operates normally and the grid current quality problem is being addressed. The DC / AC module is in the shutdown state.

[0050] 3) Main circuit voltage regulation operation mode: The power module box input-side circuit breaker QF1, miniature circuit breaker QF2, miniature circuit breaker QF4, and double-cut disconnector QS1 are all in the closed state, and the AC contactor KM1 and DC-side circuit breaker QF3 are in the open state. At this time, the AC / DC module operates normally. The DC / AC module detects the grid voltage data and makes real-time judgments to adjust the overall port output voltage to meet the output voltage qualification rate under different input voltage conditions, achieving continuous online regulation.

[0051] 4) Maintenance mode: The circuit breaker QF1, miniature circuit breaker QF2, double-cut isolating switch QS1, and AC contactor KM1 on the input side of the power module box are all in the disconnected state, and the DC side circuit breaker QF3 and miniature circuit breaker QF4 are in the closed state. At this time, the power module box is powered off, and the AC / DC module, DC / AC module, AC contactor KM1 and anti-parallel thyristor assembly SCR are inspected and maintained.

[0052] When multiple stations simultaneously apply this new AC / DC hybrid power electronic transformer, see Figure 3 As shown, the transformers in two adjacent substations can be interconnected through a DC interface, achieving two-way power mutual assistance in the AC-DC-AC mode, flexibly mobilizing the distribution resources of adjacent substations, and combining them with DC-side photovoltaic and energy storage devices to maximize economic benefits. This technical solution solves the problem that traditional distribution substations cannot continuously adjust the voltage online. At the same time, it integrates the solution of comprehensive voltage and current management of multiple devices in traditional substations, realizing a truly integrated design of distribution transformers. It has intelligent and multifunctional characteristics, is equipped with a DC port, and realizes AC / DC mixed supply, meeting the various application scenarios of current new energy microgrids, solving the problem of unstable DC side voltage during the peak and valley periods of new energy power generation, and solving the problem of short-term power outages during line maintenance and supply.

[0053] When the second winding is added to the transformer box as a series coupled winding, it can be realized that the power part capacity is only the adjustment power during the regulation process, that is, the system high power is mobilized with a small power. Based on this feature, the AC side can also be interconnected, such as Figure 4 The block diagram shown can realize direct resource sharing between adjacent substations on the AC side, and resource sharing between the DC side and the AC sides on both sides, forming a hand-in-hand ring power grid, increasing the reliability of power grid operation. Based on this solution, uninterrupted power supply can also be achieved between multiple substations, improving users' electricity experience.

[0054] The above embodiments are intended only to illustrate the technical concepts and features of the present invention. Their purpose is to enable those skilled in the art to understand the contents of the present invention and implement them accordingly. They are not intended to limit the scope of protection of the present invention. Any equivalent changes or modifications made in accordance with the spirit of the present invention are intended to be covered by the scope of protection of the present invention.

Claims

1. An AC / DC hybrid power electronic transformer, characterized in that: Including transformer box, power module box and auxiliary line box, The transformer box is provided with a transformer winding, a current transformer and a BCT terminal box. The transformer winding is divided into a low-voltage winding and a high-voltage winding. The low-voltage winding includes a first winding and a second winding. The first winding interface is connected to the power supply line. The second winding is an adjustable winding and is connected to the auxiliary circuit box. The current transformer is used to sample the current of the low-voltage winding in real time and is connected to the outside through the BCT terminal box. The auxiliary circuit box includes a power distribution unit, a lightning protection unit, a bypass protection unit and a maintenance component unit, wherein: The power distribution unit includes a power module box input side circuit breaker QF1 and a DC side circuit breaker QF3. The power distribution unit is used to provide a DC port to the outside. The lightning protection unit includes a miniature circuit breaker QF2 and a surge protector FB1. The lightning protection unit is used for input surge protection. One end of the surge protector FB1 is connected to one end of the miniature circuit breaker QF2, and the other end is grounded. The other end of the miniature circuit breaker QF2 is connected to one end of the circuit breaker QF1 on the input side of the power module box. The bypass protection unit includes a miniature circuit breaker QF4, an anti-parallel thyristor assembly SCR, and an AC contactor KM1. The miniature circuit breaker QF4 and the anti-parallel thyristor assembly SCR are connected in series, and the miniature circuit breaker QF4 and the AC contactor KM1 are connected in parallel. The bypass protection unit is used for transient switching and protection when the main circuit in the power module box is operating and when the shutdown transformer is bypassing. The maintenance component unit includes a double-cut isolating switch QS1, which is used to short-circuit the second winding and form a maintenance breakpoint when the power module box is repaired; The power module box includes an AC / DC module and a DC / AC module; The DC circuit breaker QF3 is a 2P circuit breaker. The positive and negative poles of the AC / DC module and the DC / AC module are connected to one end of the DC circuit breaker QF3. The other end of the DC circuit breaker QF3 provides an external DC interface. The DC interface is located on the auxiliary circuit box and is used to connect to external devices. The input A / B / C / N terminals of the AC / DC module are connected to the circuit breaker QF1 on the input side of the power module box and then to the output side of the first winding; The output A / B / C terminals of the DC / AC module are connected to one end of the second winding.

2. The AC / DC hybrid power electronic transformer according to claim 1, characterized in that: The second winding is a series coupled winding.

3. The AC / DC hybrid power electronic transformer according to claim 1, characterized in that: The power module box and the auxiliary circuit box are respectively arranged on the left and right sides of the transformer box.

4. The AC / DC hybrid power electronic transformer according to any one of claims 1 to 3, characterized in that: The transformer has the following working modes: 1) AC / DC mutual assistance mode: The power module box input-side circuit breaker QF1, miniature circuit breaker QF2, DC-side circuit breaker QF3, miniature circuit breaker QF4, and double-cut disconnector QS1 are all in the closed state, and the AC contactor KM1 is in the open state. At this time, the power module box receives the dispatch instruction and operates, the AC / DC module operates normally for voltage regulation, and the DC / AC module outputs according to the received power instruction signal, adjusting the amplitude and phase of its output voltage to achieve continuous and precise power regulation. At this time, the DC-side circuit breaker QF3 is connected to the external DC port of the external device; 2) Bypass operation mode: The circuit breaker QF1, miniature circuit breaker QF2, miniature circuit breaker QF4, double-cut disconnector QS1 and AC contactor KM1 on the input side of the power module box are all in the closed state, and the DC side circuit breaker QF3 is in the open state. At this time, the AC / DC module is operating normally, and the DC / AC module is in the shutdown state; 3) Main circuit voltage regulation operation mode: The power module box input-side circuit breaker QF1, miniature circuit breaker QF2, miniature circuit breaker QF4, and double-cut disconnector QS1 are all in the closed state, and the AC contactor KM1 and DC-side circuit breaker QF3 are in the open state. At this time, the AC / DC module operates normally. The DC / AC module detects the grid voltage data and makes real-time judgments to adjust the overall port output voltage to meet the output voltage qualification rate under different input voltage conditions, achieving continuous online regulation. 4) Maintenance mode: The circuit breaker QF1, miniature circuit breaker QF2, double-cut isolating switch QS1, and AC contactor KM1 on the input side of the power module box are all in the disconnected state, and the DC side circuit breaker QF3 and miniature circuit breaker QF4 are in the closed state. At this time, the power module box is powered off, and the AC / DC module, DC / AC module, AC contactor KM1 and anti-parallel thyristor assembly SCR are inspected and maintained.

5. The AC / DC hybrid power electronic transformer according to claim 4, characterized in that: In a multi-station area, the transformers in each two adjacent stations are interconnected through a DC interface.

6. The AC / DC hybrid power electronic transformer according to claim 5, characterized in that: In multiple sections, the AC sides of the transformers in every two adjacent sections are interconnected.

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