Power grid

Abstract

The present disclosure relates to a power grid comprising a conversion stage comprising a plurality of DC / DC converters connected in parallel. At least one of the DC / DC converters is a single-stage isolated DC / DC converter that includes a voltage control configured to control a voltage of the respective DC / DC converter.

Description

[0001] This application is a divisional application of the invention patent application filed on October 16, 2020, with application number 202011108352.0 and title "Power Grid". Technical Field

[0002] This disclosure relates to power grids. Specifically, this disclosure proposes a power distribution and collection network or power redistribution network based on parallel-connected converters. Power distribution units for individual loads allow for efficient use of infrastructure and increased availability. The innovative power distribution and collection network achieves maximum efficiency and control over electricity costs through overall energy management. Background Technology

[0003] Energy sources and loads have changed in recent years, leading to different demands on the power grid. Typical new loads and sources in the power distribution network include heat pumps, data centers and communication infrastructure with primary AC connections, battery energy systems at the grid edge, DC chargers for electric vehicles, electric buses, and electric trains, and renewable energy sources such as photovoltaic (PV) solar systems.

[0004] According to existing technology, the distribution network is based on a high-voltage (HV) or medium-voltage (MV) network connection using one or more low-frequency (i.e., 50 Hz or 60 Hz) transformers. This allows for different power distribution concepts to be used at lower voltages. Figure 1 An exemplary configuration according to the prior art is shown. It employs a common HV or MV AC bus, transformer stages, parallel-connected AC / DC converters, and additional DC / DC converters depending on the connected load or source. The network can supply DC loads 1 to N via dynamic power distribution, battery energy storage devices (BESS), and PV solar energy.

[0005] like Figure 2 As shown, a single AC / DC converter is connected upstream of a series of parallel DC / DC converters, where the DC / DC converters share a common DC connection. The load and source can be similar to... Figure 1 Examples. Charging electric vehicles using AC / DC typically allows for unidirectional power flow, but it can also be bidirectional to support, for example, vehicle-to-grid operations. Figure 3 The given example has parallel AC / DC converters and one branch has a parallel DC / DC converter supplying the load. The load and source can be similar to those in the preceding figures. Additionally, in Figure 4 The image shows a traditional AC power distribution scheme for a large data center. DC power distribution schemes can offer substantially higher efficiency and lower costs. Summary of the Invention

[0006] This disclosure proposes a power distribution and harvesting network based on parallel-connected converters. To achieve individual voltage control for each connected load, SiC MOSFET-based power source converters and energy storage elements are preferably used. Power distribution units for individual loads allow for efficient use of the infrastructure and increase availability. The innovative power distribution and harvesting network's overall energy management achieves maximum efficiency and control over electricity costs.

[0007] The independent claims define this disclosure. The dependent claims describe preferred embodiments.

[0008] This disclosure relates to a power grid including a conversion stage comprising a plurality of DC / DC converters connected in parallel. At least one DC / DC converter is a single-stage isolated DC / DC converter including a voltage controller configured to control the voltage of the respective DC / DC converter.

[0009] Various embodiments may preferably achieve the following features.

[0010] The power grid may further include an additional conversion stage, which comprises at least one converter, wherein the additional conversion stage may be connected upstream of a parallel connection of the DC / DC converter. Preferably, the parallel connection is a DC bus.

[0011] Preferably, at least one of the converters in the other conversion stage is a unidirectional AC / DC converter and / or a bidirectional AC / DC converter, the unidirectional AC / DC converter including a diode or thyristor rectifier, and the bidirectional AC / DC converter based on a 2-level or 3-level topology or a modular multi-electrode converter (MMC) topology.

[0012] Preferably, at least one of the DC / DC converters in the conversion stage includes at least two DC / AC converters connected in parallel and an AC / DC converter configured to provide a DC output, wherein the at least two DC / AC converters and the AC / DC converter are configured to be connected to a transformer unit for coupling the parallel DC / AC converters to the AC / DC converter.

[0013] Preferably, at least one of the DC / DC converters includes a DC / AC converter and an AC / DC converter, the DC / AC converter including a series switch configured to convert a DC input to AC, and the AC / DC converter configured to provide a DC output. The DC / AC converter and the AC / DC converter are preferably configured to be connected to a transformer unit. Preferably, the transformer unit is configured to couple the DC / AC converter to the AC / DC converter.

[0014] Preferably, the power grid further includes at least one DC current limiting and / or current interruption unit.

[0015] Preferably, at least one DC current limiting or interruption unit is located in at least one of the DC / DC converters in the conversion stage, or is located upstream of the conversion stage of the DC / DC conversion stage.

[0016] The power grid preferably further includes a power distribution unit configured to distribute power to at least one user load. The power distribution unit preferably includes at least one switch for each DC / DC converter in the conversion stage, the at least one switch being configured to connect or disconnect the outputs of at least two DC / DC converters in the conversion stage from the user load.

[0017] Preferably, the power distribution unit includes multiple switches for each converter, which are configured to connect or disconnect the output of the conversion stage, wherein the number of switches corresponds to the number of loads.

[0018] Preferably, the power distribution unit further includes a control unit configured to control at least one switch to distribute power according to loads and / or sources connected to the power grid. Preferably, the control unit is configured to manage the distribution of output voltages of multiple converters in the conversion stage according to loads and / or sources connected to the power grid.

[0019] Preferably, the power grid can be connected to at least one or any combination of a variable-speed heat pump system, a hyperscale data center, a distributed battery energy storage device, a physically distributed or configured DC charger, or a renewable energy source.

[0020] This disclosure also relates to a method for controlling a power grid, preferably as described herein. The method includes converting a DC input to a DC output using single-stage isolated DC / DC converters connected in parallel and including voltage control elements configured to control the voltage of the respective DC / DC converters.

[0021] This disclosure further relates to a DC / AC converter used in a power grid, preferably as described herein. The converter includes a plurality of switches connected in series, a DC input connection, and at least two capacitors. The switches are configured to convert a DC input voltage to an AC output voltage. Attached Figure Description

[0022] This disclosure is further described with reference to the accompanying drawings. The drawings are as follows: Figures 1 to 4 The configuration according to the prior art is shown; Figure 5 Examples according to this disclosure are shown; Figure 6 The connection of the series units according to the example is shown; Figure 7 The connection of the series switches according to the example is shown; Figure 8 The configuration shown is an example according to this disclosure; Figures 9 to 11 An example of a power distribution unit according to this disclosure is shown; and Figure 12 and Figure 13 An exemplary flowchart of the control unit is shown.

[0023] Unless otherwise indicated, elements with the same reference numerals or symbols in the various figures represent the same or similar elements. Detailed Implementation

[0024] The core idea of ​​this invention is to construct a flexible and efficient power distribution and collection network that can supply multiple applications, such as variable-speed heat pump systems, hyperscale data centers, distributed battery energy storage devices, and physically distributed or configured EV chargers. Furthermore, according to this disclosure, the integration of renewable energy sources is also feasible.

[0025] Specifically, this disclosure employs multiple isolated (and, according to embodiments, single-stage) DC / DC converters connected in parallel. This parallel connection can be achieved, for example, by connecting multiple isolated DC / DC converters to a single DC bus. Therefore, a flexible power grid capable of operating different loads and sources can be provided without affecting the stability of the grid.

[0026] Figure 5 The main structure of a power grid according to an example of this disclosure is shown. Figure 5 The power grid (also referred to as a power distribution and collection or power redistribution network) includes one or more medium-voltage or high-voltage (MV / HV) grid connection points connected to one or more transformers, with one or more AC / DC power conversion units following downstream of the transformers. One or more outputs of at least one AC / DC converter are connected to a local or distributed DC distribution network (also referred to as a (common) DC bus 4). Alternatively, HVDC or MVDC can be directly supplied to parallel connection elements, such as a DC bus. Additionally, other connection elements besides the DC bus can be used.

[0027] The following description is based on the DC bus and should not be construed as limiting. Any connector suitable for parallel connection of multiple DC / DC converters may be used and falls within the scope of this disclosure.

[0028] At DC bus 4, multiple distributed single-stage isolated DC / DC converters 1 are connected. Specifically, each isolated DC / DC converter 1 has individual voltage control capability. Additionally, each such isolated DC / DC converter 1 may have individual DC current limiting and / or current interruption functions. Some isolated DC / DC converters 1 may preferably supply DC loads (DC loads_1 to L), which will be described below in the power distribution unit 2. Optionally, one or more isolated DC / DC converters 1 supply one or more energy storage devices (DC storage devices_1 to M), and / or one or more isolated DC / DC converters 1 supply DC sources (DC sources_1 to N) or AC loads and sources (AC loads or sources_1 to P).

[0029] To realize a physically distributed system, the voltage level of the common DC bus can be changed according to the required power transmission. This can be a low-voltage DC (LVDC) or medium-voltage DC (MVDC) type. The structure of the isolated single-stage DC / DC converter 1 connected in parallel to DC bus 4 achieves a stable and flexible power grid, allowing for the connection of various loads and sources without affecting the stability of the power grid.

[0030] Depending on the type of voltage input, i.e., AC or DC, at least one AC / DC conversion unit 5 may be provided, or no AC / DC conversion unit 5 may be provided. Additionally, the AC / DC power conversion may allow unidirectional or bidirectional current. Specifically, the unidirectional AC / DC power conversion unit 5 may be a parallel or series multi-pulse diode or thyristor rectifier. Alternatively, the bidirectional AC / DC power conversion unit 5 may be a switch-based converter (i.e., NPC) or a battery-based converter (i.e., MMC). Optionally, the AC / DC power conversion unit 5 may have current limiting and / or current interruption functions, such as... Figure 5 The cross symbol is shown in the image.

[0031] The isolated DC / DC converter 1 can be based on a series resonant converter or a dual active bridge topology. Current limiting or interruption functions can be added to or replaced upstream of the DC bus 4; each DC / DC converter 1 can have individual DC current limiting and / or interruption functions.

[0032] DC / DC converter 1 can be based on a series cell (e.g., half-bridge or full-bridge) on the common DC bus 4 side. According to the example, the series cell is connected to DC bus 4 and as follows: Figure 6The diagram shows two DC / AC converters 11 connected in parallel. An AC / DC converter 13 provides a DC output to the load. The DC / AC converters 11 and 13 are configured to be connected to a transformer 12, which couples the DC / AC converters 11 and 13. A capacitor between the DC / AC converters 11 and the transformer 12 can act as a DC block. Multiple DC / AC converters 11 or AC / DC converters 13 can be provided on either side. Multiple converters can be provided, for example, via a DC bus 4 and connected in parallel. Figure 6 The structure.

[0033] Figure 7 A further example of a DC / DC converter 1 based on series switches 16 is shown. As shown above, the DC / DC converter 1 is connected to DC bus 4 and includes at least one DC / AC converter 11 based on the series switches 16 and at least one AC / DC converter 13, wherein converters 11 and 13 are configured to be connected to transformer 12 for coupling the respective converters 11 and 13. Each series switch 16 may be connected in parallel to a diode, such as... Figure 7 As shown. Optionally, capacitors can be connected in parallel to each diode. An additional capacitor between the output of DC / AC converter 11 and transformer 12 can act as a DC blocker.

[0034] In other words, the converter includes a DC input connector that can be connected, for example, to a DC bus 4, at least two capacitors, and a plurality of switches 16 connected in series. The switches 16 are configured to convert the DC input voltage to an AC output voltage, thus forming a DC / AC converter 11.

[0035] According to the embodiments, the DC / DC converter 1 and, in particular, at least one DC / AC converter 11 are based on SiC MOSFET or Si IGBT technology and use an intermediate frequency transformer to achieve current isolation on the load, storage device, or source side.

[0036] An energy management system can be provided to control groups of loads and sources connected to and from the common DC bus via DC / DC converters to the AC network. The energy management system can further optimize load flow to minimize the electricity bill for the AC network connections. The energy management system may be related to the power distribution unit described below.

[0037] Figure 8An example of a current-limiting or DC circuit breaker circuit according to this disclosure is shown. The circuit breaker circuit may be part of the DC / DC converter 1 or may be located external to the DC / DC converter 1. The exemplary circuit breaker circuit 6 includes at least one switch, a diode connected in parallel to each of the at least one switch, and a variable resistor connected in parallel to each diode. Depending on its location in the network, the DC circuit breaker circuit 6 may disconnect at least one DC / DC converter 1 and / or a load and / or a source. If an overload is detected or the network becomes unstable, the circuit breaker circuit 6 may in particular disconnect at least one DC / DC converter 1 and / or a load and / or a source.

[0038] A DC circuit breaker circuit 6 may be provided in or upstream of the DC / DC converter 1. A DC circuit breaker circuit 6 may be provided for at least one DC / DC converter 1, or multiple DC circuit breaker circuits 6 may be provided. Specifically, the DC circuit breaker circuit 6 may be located at or upstream of the DC / DC converter 1 and / or upstream of its parallel connections (e.g., DC bus 4). Figure 8 The example DC / DC converter 1 includes a DC / AC converter 11, a transformer 12, and an AC / DC converter 13 to provide the functions described above. Figure 8 The circuit breaker can be applied to any of the embodiments described herein.

[0039] refer to Figures 5 to 8 Each example described can be combined with a power distribution unit 2 configured to connect the DC output to or disconnect it from the load.

[0040] The power distribution unit is described with reference to an exemplary vehicle charging system using charging piles that can be connected to the vehicle to be charged as loads 22. With each charging pile 22 having its own bus and each DC converter 1 connectable to each of these buses, nine switches (3 x 3) are required for three charging piles and three outputs, and one hundred switches are required for ten outputs and ten charging piles. That is, the number of switches increases quadratically with the number of outputs. An alternative to save switches could be a ring structure, where each DC output can be connected to two adjacent outputs via an isolating switch or switch 21, and each charging pile 22 can be directly connected to one of the DC outputs via the isolating switch 21. This is in... Figure 9As shown, reference numeral 1 denotes the DC / DC converter and the corresponding DC output, and reference numeral 22 denotes the load or charging station according to the example above. This arrangement allows for the use of only 2 x n switches 21, where n is the number of outputs. To utilize available power most efficiently, intelligent management of the sequence in which vehicles are connected to the free charging stations 22 can be employed. The goal of this management is to always provide a high probability that at least one charging station 22 is available for dual-power fast charging, which can be achieved by connecting adjacent DC outputs via switches 21 and uniformly loading all DC outputs on the other hand.

[0041] Figure 10 Further exemplary configurations of a power distribution and collection network including or connected to power distribution unit 2 are shown. In this example, switch 21 also forms a ring configuration.

[0042] Figure 11 An alternative configuration, which can be described as a matrix configuration, is depicted. In each corresponding output terminal of each DC / DC converter 1, there are N switches 21 connected to N DC loads respectively. The total number of switches is N*n, where N is the number of loads 22, which in this case is the number of charging piles, and n is the number of DC / DC converters 1. Matrix switch arrays can be used in applications where open-circuit and short-circuit currents are not required. If the switches only need to be open for the current of normal operation, the matrix switch current is only 1 / N of the loop current.

[0043] In other words, referring to the example above, the system can be based on an SST topology, where the key components are multiple isolated DC / DC converters 1 and a switch group. The isolated DC / DC converters 1 are connected in series with their input terminals. The two outermost terminals of the series input terminals are connected to the MV DC bus. The output terminals of each isolated DC / DC converter 1 are connected to all electric vehicle (EV) chargers via the switch group. The switch group controls their DC / DC converters 1 to connect to a designated EV charger. The MV DC bus is powered by a controllable DC source.

[0044] Optionally, the network may further include a control unit 22 and / or a bypass circuit breaker circuit 23. The control unit 24 may also be referred to as a (coordination) controller. This controller 24 is proposed for smoothing the operation of the proposed SST topology. Controller 24 generates system operating references and switching commands, including a current reference for the DC source. DC / DC converter 1 voltage reference and switch group control commands .

[0045] Figure 11This is a schematic diagram of a power grid and distribution unit according to an exemplary embodiment, showing the basic structure and optional features such as a matrix configuration of switch 21, control unit 24, and bypass circuit breaker circuit 23.

[0046] Figure 12 A flowchart is provided. During a control period, controller 24 first calculates the appropriate number of power modules (DC / DC converter 1) for each EV charger 22 based on the principle of minimum voltage difference and the most recent average power of all chargers. This principle can be explained as follows: the number of power modules to be switched to the i-th charger is calculated using the rounded result of dividing the power requirement of the i-th charger by the average power of all chargers. This calculation is performed exemplarily using the following formula (F1): (F1) Therefore, the selected power modules and their voltage references can be calculated, for example, using formulas (F2) and (F3) listed below. Specifically, (F2) is used to calculate the power reference for power module j (i.e., the corresponding DC / DC converter 1). Using (F3), calculate the voltage reference for power module j (i.e., the corresponding DC / DC converter 1). Where N is the number of loads. This indicates the rated voltage. Additionally, the operation of the switchgear can be verified. The MVDC bus current reference can also be calculated. This calculation can be performed using the following formula (F4) as an example.

[0047] (F2) (F3) (F4) As mentioned above, the system may also include an optional bypass circuit breaker circuit 23. The bypass circuit breaker circuit 23 is exemplarily disposed in the input terminals of each isolated DC / DC converter 1, such as... Figure 11 As shown. The bypass circuit breaker 23 of each isolated DC / DC converter 1 is used to temporarily disable the converter to prevent excessively low input DC voltage and thus ensure efficient operation. In some operating conditions, the power differential of the isolated DC / DC converters 1 is very large. Therefore, some converters operate with low input DC voltage and thus have low operating efficiency. To avoid this, these DC / DC converters 1 are disabled by closing the bypass circuit breaker 23 of some of them. The operating DC / DC converters 1 will then have more uniform power requirements and input DC voltage. However, the bypass circuit breaker 23 is optional in this topology. The bypass circuit breaker 23 can also be controlled by the coordination controller 24.

[0048] Figure 13 A corresponding flowchart with the function of bypass circuit breaker 23 is shown. The various formulas (F1) to (F4) are described above. This is based on the difference between the voltage of the maximum power module and the voltage of the minimum power module. No more than the threshold voltage ,according to Figure 12 Normal operation is then performed. However, if the threshold voltage is exceeded... Then the bypass circuit breaker 23 is activated to bypass the corresponding power module (i.e., DC / DC converter), and the number of loads N is reduced.

[0049] Additionally, a controller 24 or station controller can be provided to manage the distribution of loads to charging piles 22, such as (in the case of DC chargers for electric vehicles). For example, consider four charging piles (see...). Figure 10 (Pile 22), station control 24 attempts to keep two adjacent DC terminals (DC / DC converter 1) idle. That is, after pile 1 is connected to the DC 1 output, the next vehicle will be connected to pile 2 or pile 4 (e.g., indicated by traffic lights, where a red light on pile 3 indicates that pile 3 is occupied or not connected, and green lights on piles 2 and 4 indicate that they are available). If this is done, the two adjacent DC terminals will be available for fast charging after the second vehicle is connected. No DC output needs to be idle. When not all chargers are being used, the interconnecting switch can be connected to adjacent DC outputs, and the load can be shared. In the four-pile system above, when charging piles 1 and 2 are working, the interconnecting switch from DC 1 to DC 4 can be closed, and the interconnecting switch between DC 2 and DC 3 can also be closed. Thus, all DC outputs are loaded. Even when piles 1 and 3 are active and a new vehicle (which can then only utilize the power of one DC output for charging) arrives, the load of the higher-loaded pile 1 or 3 can be shared with the idle remaining DC outputs by closing the relevant interconnecting switch.

[0050] The power distribution unit can also be combined with other power distribution networks and other loads or sources as shown in the example above.

[0051] According to this disclosure, an improved power redistribution network is provided that can operate multiple inputs and outputs with optimal efficiency.

[0052] This disclosure also covers the corresponding methods.

[0053] Therefore, this disclosure provides a flexible and efficient power grid based on parallel-connected converters. According to an embodiment, the parallel-connected converters are single-stage isolated DC / DC converters. To achieve individual voltage control for the connected loads, SiC MOSFET-based energy source converters and energy storage elements are used according to the embodiment. Power distribution units for individual loads allow for efficient use of the infrastructure and increased availability. The overall energy management of the innovative power distribution and collection network achieves maximum efficiency and controls electricity costs. Therefore, the grid can be kept in a stable state regardless of the connected sources and loads, especially asymmetrical loads.

[0054] Other aspects, features, and advantages will become apparent from the above overview and the following description (including the accompanying drawings and claims).

[0055] Although this disclosure has been shown and described in detail in the accompanying drawings and the foregoing description, these illustrations and descriptions are to be considered illustrative or exemplary rather than limiting. It will be understood that changes and modifications falling within the scope of the appended claims can be made by those skilled in the art. Specifically, this disclosure covers further embodiments incorporating various combinations of features from the different embodiments described above and below.

[0056] Furthermore, in the claims, the term "comprising" does not exclude other elements or steps, and the indefinite articles "a" or "an" do not exclude multiple. A single unit can perform the function of multiple features listed in the claims. Terms such as "substantially," "about," "probably," etc., associated with a certain attribute or value also precisely define that attribute or value. Any reference numerals in the claims should not be construed as limiting the scope.

Claims

1. A power grid, comprising: a conversion stage, the conversion stage comprising a plurality of DC / DC converters (1) connected in parallel, wherein at least one of the DC / DC converters (1) is a single-stage isolated DC / DC converter (1) comprising a voltage control configured to control a voltage of the respective DC / DC converter (1), wherein at least one of the DC / DC converters (1) of the conversion stage comprises at least two DC / AC converters (11) connected in parallel and an AC / DC converter (13) configured to provide a DC output, wherein the at least two DC / AC converters (11) and the AC / DC converter (13) are configured to be connected to a transformer unit (12) for coupling the DC / AC converters (11) in parallel to the AC / DC converter (13), wherein the power grid further comprises a power distribution unit (2) configured to distribute power to at least one user load, wherein the power distribution unit (2) comprises a plurality of switches (21) of each DC / DC converter (1) of the conversion stage, the plurality of switches being configured to connect or disconnect outputs of at least two DC / DC converters (1) of the conversion stage to or from the user load, wherein the number of switches corresponds to the number of loads.

2. The power grid of claim 1, wherein, The power grid further comprises a further conversion stage, the further conversion stage comprising at least one converter (5), wherein the further conversion stage is connected upstream of the parallel connection of the DC / DC converters (1), wherein, preferably, the parallel connection is a DC bus (4).

3. The power grid according to claim 2, wherein at least one of the at least one converter (5) of the further conversion stage is a unidirectional AC / DC converter (5) comprising a diode or thyristor rectifier, and / or at least one of the at least one converter (5) of the further conversion stage is a bidirectional AC / DC converter (5) based on a 2-level or 3-level topology or a modular multilevel converter, MMC, topology.

4. The power grid of any one of claims 1-3, wherein, at least one of the DC / DC converters (1) comprises a DC / AC converter (11) comprising a series switch (16) configured to convert a DC input to an AC, and an AC / DC converter (13) configured to provide a DC output, wherein the DC / AC converter (11) and the AC / DC converter (13) are configured to be connected to a transformer unit (12), and wherein the transformer unit (12) is configured to couple the DC / AC converter (11) to the AC / DC converter (13).

5. The power grid of any one of claims 1-3, wherein, The power grid further comprises at least one DC current limiting and / or current breaking unit (6).

6. The power grid of claim 5, wherein, The at least one DC current limiting or blocking unit (6) is located in at least one of the DC / DC converters (1) of the conversion stage, or The at least one DC current limiting or blocking unit (6) is located upstream of the conversion stage of the DC / DC conversion stage (1).

7. The power grid of any one of claims 1-3, wherein, The power distribution unit further comprises a control unit configured to control the at least one switch (21) to distribute power depending on loads and / or sources connected to the power grid, wherein preferably the control unit is configured to manage the distribution of the output voltages of the plurality of converters of the conversion stage depending on loads and / or sources connected to the power grid.

8. The power grid of any one of claims 1-3, wherein, The power grid can be connected to at least one of a variable speed heat pump system, an ultra-large scale data center, a distributed battery energy storage, a physically distributed or configured charger, or a renewable energy source or any combination thereof.

9. A method for controlling a power grid, the power grid being according to any one of claims 1-8, the method comprising: - converting a DC input to a DC output using single stage isolated DC / DC converters (1) connected in parallel and comprising voltage controls configured to control the voltage of the respective DC / DC converter (1).

10. A DC / AC converter for use in a power grid according to any one of claims 1 to 8, the converter comprising a DC input connection, at least two capacitors, and a plurality of switches connected in series, wherein, The switch is configured to convert a DC input voltage to an AC output voltage.

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