A direct current voltage transformation subunit and a direct current voltage transformer comprising the direct current voltage transformation subunit

Abstract

The application provides a DC voltage transformation subunit and a DC voltage transformer comprising the DC voltage transformation subunit, the DC voltage transformation subunit comprising a fault isolation voltage balancing module and a DC / DC converter; the high-voltage side of the fault isolation voltage balancing module is connected with a high-voltage DC bus, and the low-voltage side of the DC / DC converter is connected with a low-voltage DC bus, and the DC voltage transformation subunit has small mass and floor area and low cost; the DC voltage transformer comprising a plurality of DC voltage transformation subunits; the high-voltage sides of the plurality of DC voltage transformation subunits are connected in series to meet the withstand voltage grade requirement, and the low-voltage sides of the plurality of DC voltage transformation subunits are connected in parallel to meet the high-power requirement, thereby greatly reducing the number of layers of the DC voltage transformation subunits, reducing the floor area, saving the cost, meeting different application scenarios of one-way power flow and two-way power flow, and realizing automatic isolation and crossing of high-voltage side faults.

Description

Technical Field

[0001] This invention relates to the field of DC power transmission and distribution technology, specifically to a DC transformer subunit and a DC transformer including the DC transformer subunit. Background Technology

[0002] In AC power grids, voltage transformation and energy transfer can be achieved solely through power frequency transformers. However, DC power grids must rely on power electronic equipment to achieve voltage matching and energy exchange between different grids.

[0003] The main topologies of DC transformers include MMC type, ultra-high voltage device type, and ISOP type. Among them, the ISOP type is the most widely used. The ISOP type uses multiple high-frequency transformers to achieve electrical isolation and voltage matching between different power grids. The series structure on the medium-voltage side resolves the contradiction between the low withstand voltage of power semiconductor devices and the high voltage of the power grid, while the output side is connected in parallel to the low-voltage DC bus to achieve high current output.

[0004] In DC transformers, each layer of DC / DC sub-units can adopt a dual active bridge converter (DAB) structure, a CLLC structure, an LLC structure, etc. The ISOP topology DC / DC sub-unit cannot achieve high-voltage side fault isolation. Typically, an SC module is added to the high-voltage side of the DC / DC module to achieve high-voltage side fault isolation. However, this results in a large number of cascaded layers in the DC transformer, leading to significant weight, footprint, and cost. Summary of the Invention

[0005] To overcome the shortcomings of existing DC transformers, such as large size, large footprint, and high cost, this invention provides a DC transformer subunit and a DC transformer including the DC transformer subunit. The DC transformer subunit includes a fault isolation voltage equalization module and a DC / DC converter connected in series. The high-voltage side of the fault isolation voltage equalization module is connected to the high-voltage DC bus, and the low-voltage side of the DC / DC converter is connected to the low-voltage DC bus. The fault isolation voltage equalization module is used to isolate faults from the high-voltage DC bus / low-voltage DC bus and achieve voltage equalization. It has a small size, small footprint, and low cost.

[0006] To achieve the above-mentioned objectives, the present invention adopts the following technical solution:

[0007] The present invention provides a DC transformer subunit, including a fault isolation voltage equalization module and a DC / DC converter connected in series;

[0008] The high-voltage side of the fault isolation voltage equalization module is connected to the high-voltage DC bus, and the low-voltage side of the DC / DC converter is connected to the low-voltage DC bus.

[0009] The fault isolation voltage equalization module is used to isolate faults from the high-voltage DC bus / low-voltage DC bus and achieve voltage equalization.

[0010] The fault isolation voltage equalization module includes a bypass switch K, a first IGBT module, a second IGBT module, a voltage equalization branch, and a DC support capacitor branch.

[0011] The bypass switch K, voltage balancing branch, and DC support capacitor branch are all connected between the positive high-voltage DC bus and the negative high-voltage DC bus. The first IGBT module is connected in series on the positive high-voltage DC bus and is located between the bypass switch K and the voltage balancing branch. The second IGBT module is connected in series on the negative high-voltage DC bus and is located between the bypass switch K and the voltage balancing branch.

[0012] The voltage balancing branch includes an IGBT branch and an LC branch;

[0013] The IGBT branch includes multiple IGBT modules connected end to end, and each IGBT module includes two upper IGBTs and a lower IGBT connected end to end.

[0014] The LC branch includes one less LC resonant module than the IGBT module, multiple LC resonant modules are connected in series, and each LC resonant module includes a resonant inductor and a resonant capacitor connected in series with the resonant inductor.

[0015] Each LC resonant module has its two ends connected to the middle lead-out points of the two adjacent IGBT modules, respectively.

[0016] The DC support capacitor branch includes the same number of DC support capacitors as the IGBT modules;

[0017] All DC support capacitors are connected end-to-end with their positive and negative terminals connected in parallel. Each DC support capacitor is connected in parallel with the corresponding IGBT module, and the positive terminal of each DC support capacitor is connected to the collector of the upper IGBT, while its negative terminal is connected to the emitter of the lower IGBT.

[0018] The first IGBT module includes a first IGBT and a diode D1 connected in anti-parallel to the first IGBT;

[0019] The second IGBT module includes a second IGBT and a diode D2 connected in antiparallel to the second IGBT.

[0020] The DC / DC converter is an LLC type converter, a DAB type converter, or a CLLC type converter, which includes a high-voltage side converter, a high-frequency transformer, and a low-voltage side converter connected in series.

[0021] Both the high-voltage side converter and the low-voltage side converter are H-bridge converters, and each bridge arm includes an IGBT and a diode connected in anti-parallel to the IGBT.

[0022] On the other hand, the present invention also provides a DC transformer located between a high-voltage DC bus and a low-voltage DC bus, which includes multiple DC transformer sub-units;

[0023] The high-voltage side of the multiple DC transformer subunits is connected in series and connected to the high-voltage DC bus;

[0024] The low-voltage sides of the multiple DC transformer subunits are connected in parallel and connected to the low-voltage DC bus.

[0025] Compared with the closest existing technology, the technical solution provided by the present invention has the following beneficial effects:

[0026] The DC transformer subunit provided by this invention includes a fault isolation voltage equalization module and a DC / DC converter connected in series; the high-voltage side of the fault isolation voltage equalization module is connected to the high-voltage DC bus, and the low-voltage side of the DC / DC converter is connected to the low-voltage DC bus; the fault isolation voltage equalization module is used to isolate faults from the high-voltage DC bus / low-voltage DC bus and achieve voltage equalization, with small size and footprint, and low cost.

[0027] The DC transformer provided by the present invention includes multiple DC transformer sub-units; the high-voltage side of the multiple DC transformer sub-units is connected in series to meet the withstand voltage level requirements, and the low-voltage side of the multiple DC transformer sub-units is connected in parallel to meet the high power requirements, which greatly reduces the number of layers of DC transformer sub-units, reduces the footprint, and lowers the cost.

[0028] The DC transformer subunit provided by this invention can meet different application scenarios of unidirectional power flow and bidirectional power flow;

[0029] The DC transformer provided by this invention can achieve automatic isolation and ride-through of high-voltage side faults, while also avoiding short-circuit impact on capacitor discharge caused by bypass switch closure;

[0030] In the event of a high-voltage side fault in the DC transformer provided by this invention, the anti-parallel diodes inside the IGBT module automatically block the internal capacitors of the DC transformer subunit from discharging to the high-voltage fault point, and can maintain the normal operation of the DC transformer subunit, thereby achieving high-voltage fault ride-through of the DC transformer.

[0031] When the bypass switch K in this invention is closed, since the first IGBT module and the second IGBT module are operating in anti-parallel diode mode, it can be ensured that no overcurrent will occur during the closing process of the bypass switch K.

[0032] The number of layers of the DC transformer subunit in the DC transformer provided by this invention can be adjusted according to the change of the rated power of the DC transformer, and is no longer a fixed number of layers, which further reduces the size and cost of the equipment. Attached Figure Description

[0033] Figure 1 This is a structural diagram of the DC transformer subunit in an embodiment of the present invention;

[0034] Figure 2 This is a structural diagram of a DC transformer in an embodiment of the present invention. Detailed Implementation

[0035] The present invention will now be described in further detail with reference to the accompanying drawings.

[0036] Example 1

[0037] Embodiment 1 of the present invention provides a DC transformer subunit, such as Figure 1 As shown, it includes a series-connected fault isolation voltage equalization module and a DC / DC converter;

[0038] The high-voltage side of the fault isolation voltage equalization module is connected to the high-voltage DC bus, and the low-voltage side of the DC / DC converter is connected to the low-voltage DC bus.

[0039] The fault isolation voltage equalization module is used to isolate faults originating from the high-voltage DC bus / low-voltage DC bus and to achieve voltage equalization.

[0040] The fault isolation voltage equalization module includes a bypass switch K, a first IGBT module, a second IGBT module, a voltage equalization branch, and a DC support capacitor branch;

[0041] The bypass switch K, the voltage balancing branch, and the DC support capacitor branch are all connected between the positive high-voltage DC bus and the negative high-voltage DC bus. The first IGBT module is connected in series on the positive high-voltage DC bus and is located between the bypass switch K and the voltage balancing branch. The second IGBT module is connected in series on the negative high-voltage DC bus and is located between the bypass switch K and the voltage balancing branch.

[0042] The voltage balancing branch includes the IGBT branch and the LC branch;

[0043] The IGBT branch includes multiple IGBT modules connected end to end, and each IGBT module includes two IGBT1 and IGBT2 connected end to end.

[0044] The LC branch includes one less LC resonant module than the IGBT module. Multiple LC resonant modules are connected in series, and each LC resonant module includes a resonant inductor and a resonant capacitor connected in series with the resonant inductor.

[0045] Each LC resonant module has its two ends connected to the middle lead-out points of the two adjacent IGBT modules, respectively.

[0046] The DC support capacitor branch includes the same number of DC support capacitors as the IGBT modules;

[0047] All DC support capacitors are connected end-to-end with their positive and negative terminals connected in parallel. Each DC support capacitor is connected in parallel with the corresponding IGBT module, and the positive terminal of each DC support capacitor is connected to the collector of IGBT1, while its negative terminal is connected to the emitter of IGBT2.

[0048] like Figure 1 As shown, in Embodiment 1 of the present invention, the left side of the fault isolation voltage equalization module is used as the input terminal, and the right side of the DC / DC converter is used as the output terminal to realize the conversion from high voltage to low voltage. Vin is the input voltage of the fault isolation voltage equalization module, Vm is the input voltage of the high-voltage side converter, VL is the output voltage of the low-voltage side converter, K is the bypass switch, C4 is the first IGBT module, C5 is the second IGBT module, and C... i1 C i2 ... C in Let C be the n DC supporting capacitors in the DC supporting capacitor branch. r1 L is the resonant capacitance of the first LC resonant module in the LC branch. r1 Let C be the resonant inductance of the first LC resonant module in the LC branch. The number of resonant capacitors and resonant inductors in the LC branch is the same, let's say m; 1a C 1b C is the first IGBT module in the IGBT branch. 1a The upper IGBT, referred to as the first IGBT module, C 1b The lower IGBT of the first IGBT module is called C, and so on. na C nb This is the nth IGBT module in the IGBT branch, i.e., the last IGBT module. All IGBT modules in the IGBT branch are connected sequentially, meaning the emitter of the upper IGBT of the first IGBT module is connected to the collector of the lower IGBT of the first IGBT module, the emitter of the lower IGBT of the first IGBT module is connected to the collector of the upper IGBT of the second IGBT module, and so on. The emitter of the upper IGBT of the nth IGBT module is connected to the collector of the lower IGBT of the nth IGBT module, and the collector of the lower IGBT of the nth IGBT module is connected to the emitter of C5. The nth DC support capacitor is also connected. The number of LC resonant modules is one less than the number of IGBT modules, i.e., m = n - 1.

[0049] The first IGBT module includes a first IGBT and a diode D1 connected in anti-parallel to the first IGBT;

[0050] The second IGBT module includes a second IGBT and a diode D2 connected in anti-parallel to the second IGBT.

[0051] DC / DC converters can be LLC, DAB, or CLLC type converters, which include a high-voltage side converter, a high-frequency transformer, and a low-voltage side converter connected in series.

[0052] Both the high-voltage and low-voltage converters are H-bridge converters, with each bridge arm consisting of an IGBT and a diode connected in anti-parallel to the IGBT.

[0053] In Embodiment 1 of this invention, both the high-voltage side converter and the low-voltage side converter are LLC type converters. Figure 1 A1a, A2a, A1b, and A2b in the text refer to IGBTs in the high-voltage side converter. ii C r B1a, B2a, B1b, and B2b are capacitors in the high-voltage side converter, and B1a, B2a, B1b, and B2b are IGBTs in the low-voltage side converter. o For the capacitor in the low-voltage side converter, L r and L m This refers to the inductance in a high-frequency transformer.

[0054] The DC transformer subunit provided by this invention can meet different application scenarios of unidirectional and bidirectional power flow, as detailed below:

[0055] 1) The power flow direction is from the high-voltage side to the low-voltage side:

[0056] a) Both C4 and C5 are locked, allowing the anti-parallel diodes inside C4 and C5 to carry current. When a high-voltage side fault occurs, the anti-parallel diodes inside C4 and C5 automatically block the internal capacitors of the DC transformer subunit from discharging to the high-voltage fault point, thus realizing the high-voltage fault ride-through function of the DC transformer.

[0057] b) The resonant capacitors (Cr1~Crm) and resonant inductors (Lr1~Lrm) are configured as an LC branch that matches the switching frequency of the IGBT series. The IGBT branch (C1a / b~Crm) is controlled according to a certain duty cycle. n The switching on and off of a / b) enables voltage equalization of the DC support capacitors (Ci1~Cin);

[0058] c) When any component inside a DC transformer subunit fails, the current layer can be bypassed by controlling the bypass switch K to ensure that the remaining DC transformer subunits can still operate normally. When the bypass switch K is closed, since C4 and C5 operate in anti-parallel diode mode, overcurrent can be prevented during the bypass switch closing process.

[0059] 2) The power flow direction is from the low-voltage side to the high-voltage side:

[0060] a) When C4 and C5 are continuously triggered, the anti-parallel diodes inside C4 and C5 naturally turn off, allowing the IGBTs in C4 and C5 to flow in reverse. When a high-voltage side fault occurs, the IGBTs in C4 and C5 are blocked, and the anti-parallel diodes in C4 and C5 automatically prevent the capacitors inside the DC transformer subunit from discharging to the high-voltage fault point, thus realizing the high-voltage fault ride-through function of the DC transformer;

[0061] b) Resonant capacitors (Cr1~Crm) and resonant inductors (Lr1~Lrm) are configured as an LC branch matching the switching frequency of the IGBT series. The IGBT branch (C1a / b~C...) is controlled according to a certain duty cycle. n The switching on and off of a / b) enables voltage equalization of the DC support capacitors (Ci1~Cin);

[0062] c) When any component inside the DC transformer subunit fails, the IGBT trigger pulse is first blocked, and the bypass switch K is controlled to bypass this layer to ensure that the remaining subunits can still operate normally. When the bypass switch K is closed, since the trigger pulses of the IGBTs in C4 and C5 have been blocked, the anti-parallel diodes inside C4 and C5 can ensure that no overcurrent occurs during the bypass switch closing process.

[0063] The input voltage Vin of the fault isolation voltage equalization module and the input voltage Vm of the high-voltage side converter satisfy a certain proportional relationship. When the capacitance values ​​of all series capacitors are equal, this proportional relationship is the same as the number of DC support capacitors.

[0064] The maximum transmission power of the DC transformer subunit is limited by the manufacturing process and heat dissipation level of the high-frequency transformer. Assuming the maximum transmission power of the high-frequency transformer is P0 and the total power of the DC transformer is P, the required number of series and parallel layers is X = P / P0. When the calculated value is not an integer, round up to the nearest integer.

[0065] When the high-voltage side voltage of the DC transformer is VH, without considering the redundancy layer, the input voltage Vin of each sub-DC transformer unit is VH / X.

[0066] Based on the input voltage Vin of each DC subunit and the voltage rating of the selected IGBT device (1700V, 3300V, 4500V, etc.), the number of DC support capacitors in the fault isolation voltage equalization module can be calculated: n = Vin / (permissible DC voltage of IGBT).

[0067] Based on the number of DC support capacitors in the fault isolation voltage equalization module, design the number of resonant capacitors and resonant inductors required for voltage equalization.

[0068] The number of layers of the DC transformer subunit in the DC transformer provided by this invention can be adjusted according to the change of the rated power of the DC transformer, and is no longer a fixed number of layers, which further reduces the size and cost of the equipment.

[0069] Example 2

[0070] Embodiment 2 of the present invention provides a DC transformer, such as Figure 2 As shown, Figure 2 In the middle, V H V is the voltage of the high-voltage DC bus. L The voltage of the low-voltage DC bus is the DC transformer located between the high-voltage DC bus and the low-voltage DC bus. It includes multiple DC transformer sub-units. Embodiment 2 of the present invention includes k DC transformer sub-units.

[0071] The high-voltage side of the k DC transformer subunits is connected in series and connected to the high-voltage DC bus to meet the withstand voltage requirements.

[0072] The low-voltage sides of the k DC transformer subunits are connected in parallel and connected to the low-voltage DC bus to meet the high power requirements.

[0073] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Those skilled in the art can still make modifications or equivalent substitutions to the specific implementation of the present invention by referring to the above embodiments. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention are within the protection scope of the claims of the present invention pending approval.

Claims

1. A DC transformer subunit, characterized in that, This includes a series-connected fault isolation voltage equalization module and a DC / DC converter; The high-voltage side of the fault isolation voltage equalization module is connected to the high-voltage DC bus, and the low-voltage side of the DC / DC converter is connected to the low-voltage DC bus. The fault isolation voltage equalization module is used to isolate faults from the high-voltage DC bus / low-voltage DC bus and to achieve voltage equalization. The fault isolation voltage equalization module includes a bypass switch K, a first IGBT module, a second IGBT module, a voltage equalization branch, and a DC support capacitor branch. The bypass switch K, voltage balancing branch, and DC support capacitor branch are all connected between the positive high-voltage DC bus and the negative high-voltage DC bus. The first IGBT module is connected in series on the positive high-voltage DC bus and is located between the bypass switch K and the voltage balancing branch. The second IGBT module is connected in series on the negative high-voltage DC bus and is located between the bypass switch K and the voltage balancing branch. The first IGBT module includes a first IGBT and a diode D1 connected in antiparallel to the first IGBT. The second IGBT module includes a second IGBT and a diode D2 connected in antiparallel to the second IGBT. When the bypass switch K is closed, the first IGBT module and the second IGBT module operate in antiparallel diode mode. When the power flow direction is from the high-voltage side to the low-voltage side, both the first IGBT module and the second IGBT module are locked, allowing the anti-parallel diodes inside the first IGBT module and the second IGBT module to carry current. When a high-voltage side fault occurs, the anti-parallel diodes inside the first IGBT module and the second IGBT module automatically block the capacitor inside the DC transformer subunit from discharging to the high-voltage fault point, thus realizing the high-voltage fault ride-through function of the DC transformer. When the power flow direction is from the low-voltage side to the high-voltage side, the first and second IGBT modules are always triggered. The anti-parallel diodes inside the first and second IGBT modules are naturally turned off, allowing the IGBTs in the first and second IGBT modules to conduct current in reverse. When a high-voltage side fault occurs, the IGBTs in the first and second IGBT modules are blocked. The anti-parallel diodes in the first and second IGBT modules automatically block the capacitors inside the DC transformer subunit from discharging to the high-voltage fault point, thus realizing the high-voltage fault ride-through function of the DC transformer.

2. The DC transformer subunit according to claim 1, characterized in that, The voltage balancing branch includes an IGBT branch and an LC branch; The IGBT branch includes multiple IGBT modules connected end to end, and each IGBT module includes two upper IGBTs and a lower IGBT connected end to end. The LC branch includes one less LC resonant module than the IGBT module, multiple LC resonant modules are connected in series, and each LC resonant module includes a resonant inductor and a resonant capacitor connected in series with the resonant inductor. Each LC resonant module has its two ends connected to the middle lead-out points of the two adjacent IGBT modules, respectively.

3. The DC transformer subunit according to claim 2, characterized in that, The DC support capacitor branch includes the same number of DC support capacitors as the IGBT modules; All DC support capacitors are connected end-to-end with their positive and negative terminals connected in parallel. Each DC support capacitor is connected in parallel with the corresponding IGBT module, and the positive terminal of each DC support capacitor is connected to the collector of the upper IGBT, while its negative terminal is connected to the emitter of the lower IGBT.

4. The DC transformer subunit according to claim 1, characterized in that, The DC / DC converter is an LLC type converter, a DAB type converter, or a CLLC type converter, which includes a high-voltage side converter, a high-frequency transformer, and a low-voltage side converter connected in series.

5. The DC transformer subunit according to claim 4, characterized in that, Both the high-voltage side converter and the low-voltage side converter are H-bridge converters, and each bridge arm includes an IGBT and a diode connected in anti-parallel to the IGBT.

6. A DC transformer, characterized in that, Located between the high-voltage DC bus and the low-voltage DC bus, it includes a plurality of DC transformer sub-units as described in any one of claims 1-5; The high-voltage side of the multiple DC transformer subunits is connected in series and connected to the high-voltage DC bus; The low-voltage sides of the multiple DC transformer subunits are connected in parallel and connected to the low-voltage DC bus.

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