The present disclosure relates to a power grid. In particular, the present disclosure proposes a power distribution and collection grid or power redistribution grid based on parallel connected converters. Power distribution units for the individual loads allow efficient use of the infrastructure and increased availability. Overall energy management of the innovative power distribution and collection grid enable highest efficiency and control of the electrical energy costs.
The energy sources as well as the loads have changed in recent years, leading to different requirements of a power grid. Typical new loads and sources in the distribution grid are e.g. heat pumps, mainly alternating current (AC) connected, data centers and communication infrastructure, battery energy systems at the grid edge and electric vehicle DC chargers for electric vehicles, E-buses, E-trucks and E-trains and renewables like photovoltaic (PV) solar systems.
According to the state of the art, distribution grids are based on a high voltage (HV) or medium voltage (MV) grid connection using one or multiple low frequency transformers, i.e. 50 or 60 Hz. This allows different power distribution concepts at lower voltage.
As shown in
This disclosure proposes a power distribution and collection grid based on parallel connected converters. To achieve individual voltage control of the connected loads, energy storage elements and energy sources converters based on SiC MOSFETs may be used. Power distribution units for the individual loads allow efficient use of the infrastructure and increased availability. Overall energy management of the innovative power distribution and collection grid enable highest efficiency and control of the electrical energy costs.
The present disclosure is defined in the independent claims. Dependent claims describe example embodiments.
The present disclosure relates to a power grid comprising a converting 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 comprising a voltage control configured to control a voltage of the respective DC/DC converter.
Various embodiments may implement the following features.
The power grid may further comprise another converting stage comprising at least one converter, wherein the other converting stage may be connected upstream of the parallel connection of the DC/DC converters. The parallel connection may be a DC bus.
At least one of the at least one converter of the other converting stage may be a unidirectional AC/DC converter comprising a diode or thyristor rectifier, and/or a bidirectional AC/DC converter based on a 2-level or 3-level topology or a Modular Multi-Level Converter, MMC, topology.
At least one of the DC/DC converters of the converting stage may comprise 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.
At least one of the DC/DC converters may comprise a DC/AC converter comprising series switches configured to convert a DC input into AC and an AC/DC converter configured to provide a DC output. The DC/AC converter and the AC/DC converter may be configured to be connected to a transformer unit. The transformer unit may be configured to couple the DC/AC converter to the AC/DC converter.
The power grid may further comprise at least one DC current limiting and/or breaking unit.
The at least one DC current limiting or breaking unit may be positioned in at least one of the DC/DC converters of the converting stage, or may be positioned upstream of the converting stage of the DC/DC converting stage.
The power grid may further comprise a power distribution unit configured to distribute the power to at least one consumer load. The power distribution unit may comprise at least one switch per DC/DC converter of the converting stage configured to connect or disconnect outputs of at least two DC/DC converters of the converting stage to the consumer load.
The power distribution unit may comprise a plurality of switches per converter configured to connect or disconnect outputs of the converting stage, wherein the number of switches corresponds to the number of loads.
The power distribution unit may further comprise a control unit configured to control the at least one switch to distribute power according to loads and/or sources connected to the power grid. The control unit may be configured to manage assignment of the output voltages of the plurality of converters of the converting stage according to loads and/or sources connected to the power grid.
The power grid may be connectable to at least one of variable speed heat pump systems, hyperscale data centers, distributed battery energy storage, physically distributed or collocated DC chargers, or renewable energy sources or any combination thereof.
The disclosure further relates to a method for controlling a power grid, such as are described herein. The method comprises converting a DC input to a DC output using single-stage isolated DC/DC converters connected in parallel and comprising a voltage control configured to control a voltage of the respective DC/DC converter.
The disclosure further relates to a DC/AC converter for use in a power grid, such as are described herein. The converter comprises a DC input connection, at least two capacitors, and a plurality of switches connected in series. The switches are configured to convert a DC input voltage into an AC output voltage.
The present disclosure is further defined by the following items.
Further embodiments may implement the following features.
The present disclosure is further described with reference to the attached drawings. Therein,
In case not indicated otherwise, elements with the same reference signs or symbols denote the same or similar elements in the respective figures.
One key idea of the innovation is to build a flexible and highly efficient power distribution and collection grid, which can serve multiple applications like variable speed heat pump systems, hyperscale data centres, distributed battery energy storage and physically distributed or collocated EV chargers. Furthermore, an integration of renewable energy sources is also feasible according to the present disclosure.
In particular, the disclosure employs a plurality of isolated, and according to an embodiment single-stage, DC/DC converters which are connected in parallel. The parallel connection may e.g. be realised by connecting a plurality of isolated DC/DC converters to a DC bus. Thereby, a flexible power grid may be provided which is capable of handling different loads and sources without affecting stability of the grid.
The following description will be based on a DC bus but is not to be understood in a restrictive manner Any connection suitable for connecting a plurality of DC/DC converters in parallel may be used with and fall under the scope of the present disclosure.
At the DC bus 4, multiple distributed single-stage isolated DC/DC 1 converters are connected. In particular, each of the isolated DC/DC converters 1 has an individual voltage control capability. Furthermore, each such isolated DC/DC converter 1 may have an individual DC current limiting and/or breaking functionality. Some of the isolated DC/DC converters 1 may serve DC loads (DC loads_1_to_L), optionally by means of a power distribution unit 2 which will be described below. Optionally, one or some of the isolated DC/DC converters 1 are serving one or more electrical energy storage systems (DC storage_1_M) and/or one or some of the isolated DC/DC converters 1 are serving DC sources (DC sources_1_to_N) or AC loads and sources (AC loads or sources_1_to_P).
To achieve physically distributed systems, the common DC bus voltage level can be varied according to the needed power transfer. It may be of the low voltage DC (LVDC) or medium voltage DC (MVDC) type. The structure of isolated single-stage DC/DC converters 1 connected in parallel to a DC bus 4 ensure a stable and flexible grid which allows the connection of various loads and sources without affecting grid stability.
Depending on the type of voltage input, i.e. AC or DC, no or at least one AC/DC conversion unit 5 may be provided. Moreover, the AC/DC power conversion may allow unidirectional or bidirectional flow. In particular, a unidirectional AC/DC power conversion unit 5 can be a parallel or series multi-pulse diode or thyristor rectifier. Alternatively, a bidirectional AC/DC power conversion unit 5 can be a switch based converter, i.e. NPC or a cell based converter, i.e. MMC. The AC/DC power conversion units 5 may optionally have a current limiting and/or breaking functionality, indicated by crosses in
The isolated DC/DC converters 1 may be based on the series resonant converter or dual active bridge topology. In addition or alternatively to a current limiting or breaking functionality upstream of the DC bus 4, each DC/DC converter 1 may have an individual DC current limiting and/or breaking functionality.
The DC/DC converters 1 may be based at the common DC bus 4 side on series cells (e.g. half bridge or full bridge). According to an example, a series cell is connected to the DC bus 4 and comprises two DC/AC converters 11 connected in parallel as shown of
In other words, the converter comprises a DC input connection, which may e.g. be connected 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 a DC input voltage into an AC output voltage and thus form a DC/AC converter 11.
According to an embodiment, the DC/DC converter 1 and in particular the at least one DC/AC converter 11 is based on a SiC MOSFET or Si IGBT technology and uses a medium frequency transformer to achieve galvanic isolation at the load, storage or source side.
An energy management system may be provided to control a cluster of load and sources connected by the DC/DC converter to the common DC bus and from there to the AC grid. The energy management system may further optimise the load flow to minimise the electrical energy bill of the AC grid connection. Said energy management system may be related to the power distribution unit to be described below.
The DC breaker circuit 6 may be provided in the DC/DC converter 1 or upstream of the DC/DC converter 1. The DC breaker circuit 6 may be provided for at least one DC/DC converter 1 or may be provided in a plurality. In particular, the DC breaker circuit 6 may be positioned at or in a DC/DC converter(s) 1 and/or upstream of the DC/DC converter(s) 1 and/or upstream of the parallel connection of the DC/DC converters 1, e.g. the DC bus 4. The DC/DC converter 1 according to the example of
Each of the examples described with reference to
The power distribution unit is described with reference to an exemplary vehicle charging system using charging poles as loads 22 that can be connected to a vehicle to be charged. In case each charging pole 22 gets its own bus and each DC converter 1 can be connected to each of these busses, there would be nine switches (3×3) necessary for three poles and three outputs, and one hundred switches for ten outputs and ten poles. I.e., there is a quadratic growth for the number of switches related to the number of outputs. An alternative solution in order to save switches could be a ring structure, with each DC-output connectable by disconnectors or switches 21 to two neighboured outputs and with each charging pole 22 directly connectable via a disconnector 21 to one of the DC outputs. This is shown in
In other words and referring to the examples described above, the system may be based on a SST topology, wherein the key components in the topology are several isolated DC/DC converters 1 and switching groups. The isolated DC/DC converters 1 are connected input terminals in series. The two outermost terminals of the in-series input terminals are connected to an MV DC bus. The output terminals of each isolated DC/DC converter 1 connect all the electric vehicle (EV) chargers via a switching group. The switching groups control their DC/DC converters 1 to join into one appointed EV charger. The MV DC bus is supported by a controllable DC source.
Optionally, the grid may further comprise a control unit 22 and/or a bypass breaker circuit 23. The control unit 24 may also be referred to as (coordination) controller. This controller 24 is proposed for smoothing operation of the proposed SST topology. The controller 24 generates the system operation references and switching orders, including current reference Idcref for the DC source, DC/DC converter 1 voltage references UPMjref, and switching group control order SPMj_EVi.
A flow chart is depicted in
Consequently, the selected power modules and their voltage references can be calculated, e.g. utilising the formulae (F2) and (F3) shown below. In particular, (F2) is used to calculate the power reference PPMj of the power module j, i.e. the respective DC/DC converter 1. Using (F3), a voltage reference UPMj of the power module j, i.e. the respective DC/DC converter 1, is calculated, wherein N is the number of loads and UPM_nom denotes the nominal voltage. In addition, a switching group action can be confirmed. The MVDC bus current reference can be also calculated. The calculation may exemplarily be performed with formula (F4) shown below.
As mentioned above, the system may also comprise an optional bypass breaker circuit 23. The bypass breaker circuit 23 is exemplarily laid out in the input terminal of each isolated DC/DC converter 1 as shown in
Furthermore, the controller 24, or station control, may be provided for handling assignment of loads such as charging poles 22 (in case of a DC charger for electric vehicles). Taking an example with four poles (cf.
The power distribution unit may also be combined with other power distribution grids and other loads or sources as presented in the examples above.
According to the present disclosure, an improved power redistribution grid is provided capable of handling a plurality of inputs and outputs with an optimum efficiency.
The present disclosure also encompasses a corresponding method.
The present disclosure thus provides a flexible and highly 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 of the connected loads, energy storage elements and energy sources converters based on SiC MOSFETs are used according to an embodiment. Power distribution units for the individual loads allow efficient use of the infrastructure and increased availability. Overall energy management of the innovative power distribution and collection grid enable highest efficiency and control of the electrical energy costs. The grid can thus be maintained in a stable state irrespective of the connected sources and loads, and particularly asymmetrical loads.
Other aspects, features, and advantages will be apparent from the summary above, as well as from the description that follows, including the figures and the claims.
While the disclosure has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive. It will be understood that changes and modifications may be made by those of ordinary skill within the scope of the following claims. In particular, the present disclosure covers further embodiments with any combination of features from different embodiments described above and below.
Furthermore, in the claims the word “comprising” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude a plurality. A single unit may fulfil the functions of several features recited in the claims. The terms “essentially”, “about”, “approximately” and the like in connection with an attribute or a value particularly also define exactly the attribute or exactly the value, respectively. Any reference signs in the claims should not be construed as limiting the scope.
Number | Date | Country | Kind |
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202011108352.0 | Oct 2020 | CN | national |
20203160.5 | Oct 2020 | EP | regional |
This application is a 35 U.S.C. § 371 national stage application of PCT International Application No. PCT/EP2021/078695 filed on Oct. 15, 2021, which in turn claims foreign priority to European Patent Application No. 20203160.5 filed on Oct. 21, 2020, and to Chinese Patent Application No. 202011108352.0 filed on Oct. 16, 2020, the disclosures and content of which are incorporated by reference herein in their entirety.
Filing Document | Filing Date | Country | Kind |
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PCT/EP2021/078695 | 10/15/2021 | WO |