Apparatus and system for power conversion and method for operating the apparatus

Abstract

An apparatus and system for power conversion and a method for operating the apparatus are provided. The apparatus comprises: at least one first partial power converter (PPC) string connected in parallel with a DC bus, the at least one first partial power converter (PPC) string comprising at least one series connected PPC and at least one PPC group, where each PPC group comprises more than one parallel connected PPC, where in each PPC group, the at least one first partial power converter (PPC) string is connected in parallel with the DC bus, and the at least one first partial power converter (PPC) string is connected in parallel with the DC bus. The respective outputs of each of the more than one PPC connected in parallel are connected in parallel to form an output of the PPC group, and wherein, in the first PPC string, the at least one series-connected PPC and the respective outputs of each of the at least one PPC group are connected in series, and wherein, in the second PPC string, the at least one series-connected PPC and the respective outputs of each of the at least one PPC group are connected in series. For each PPC of the at least one series-connected PPC and more than one parallel-connected PPC of the at least one PPC group, an input of the PPC is connected to a corresponding power source, and the input of the PPC and an output of the PPC have one common terminal.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to the field of power conversion, and more specifically, to an apparatus and system for power conversion, and a method for operating the apparatus for power conversion. BACKGROUND

[0002] An energy storage system (ESS) is a system that contains, for example, batteries such as lithium batteries, lead batteries as energy storage carriers to store electrical energy to supply electrical energy for a certain period of time. ESS is widely used in power grids to regulate the peaks and frequencies of the power grid, thereby ensuring the safe operation of the power grid.

[0003] A conventional ESS typically includes multiple strings of batteries connected in parallel, which are further connected to a grid-connected AC / DC converter. This results in at least the following problems:

[0004] 1) Due to the manufacturing tolerance of the cells, there will be an unbalanced current between the strings of cells connected in parallel. Moreover, considering the aging of the cells, this unbalanced current problem will worsen over time. This problem will result in different aging speeds between the battery strings, and eventually some battery strings will reach the end of life earlier than the designed life; and

[0005] 2) In order to build a higher DC voltage for large-scale PCS systems, a larger number of cells are connected in series in one string. Due to the manufacturing tolerance of the cells, only some of the cells in one string can be fully charged or discharged even at the same discharge current. In other words, the state of charge (SOC) of each cell is different. The more cells connected in series, the greater the SOC deviation. This is a waste of cell capacity. Although the BMS has a certain cell balancing capability, it is quite limited. SUMMARY

[0006] The present disclosure provides an apparatus and system for power conversion, and a method for operating the apparatus.

[0007] According to one aspect of the disclosure, an apparatus for power conversion is disclosed. The apparatus comprises at least one first partial power converter (PPC) string connected in parallel to a DC bus, the first partial power converter (PPC) string comprising at least one series connected PPC and at least one PPC group, wherein each PPC group comprises more than one parallel connected PPC, wherein in each PPC group, a respective output of each of the more than one parallel connected PPCs is connected in parallel to form an output of the PPC group, and wherein in the first PPC string, a respective output of each of the at least one series connected PPC and the at least one PPC group is connected in series, and wherein for each of the at least one series connected PPC and the more than one parallel connected PPC in the at least one PPC group, an input of the PPC is connected to a corresponding power source, and the input of the PPC and an output of the PPC have one common terminal.

[0008] According to some embodiments, in each of the at least one series connected PPC (11i-11j) and the more than one parallel connected PPC (111 a -111l) in the at least one PPC group (111), a first PPC terminal of the PPC is connected to a first bus terminal of the DC bus or a third PPC terminal of a neighboring PPC closer to the first bus terminal than the PPC, a second PPC terminal of the PPC is connected to a first source terminal of a corresponding power source, and a third PPC terminal of the PPC is connected to a second source terminal of the corresponding power source and one of a second bus terminal of the DC bus and a first PPC terminal of a neighboring PPC closer to the second bus terminal than the PPC, and an input of the PPC is formed between the second PPC terminal of the PPC and the third PPC terminal of the PPC, and an output of the PPC is formed between the first PPC terminal of the PPC and the third PPC terminal of the PPC, and wherein in each of the at least one PPC group, the second PPC terminals of the more than one parallel connected PPCs are connected, and the third PPC terminals of the more than one parallel connected PPCs are connected.

[0009] According to some embodiments, the at least one first PPC string is further connected to a grid-tied AC / DC converter, wherein an input of the grid-tied AC / DC converter is connected to the DC bus, and an output of the grid-tied AC / DC converter is connected to a grid.

[0010] According to some embodiments, the apparatus for power conversion further comprises a second PPC string connected in parallel to the DC bus, wherein the second PPC string is a string of one PPC or a string of more than one series connected PPC.

[0011] According to some embodiments, in each of the at least one PPC group, a voltage difference connected to the corresponding power source of more than one parallel connected PPC is below a (predetermined) voltage threshold, and for at least one series connected PPC in the first PPC string, the corresponding source connected to the at least one series connected PPC is of the same type, wherein the corresponding source connected to the PPC is either of a bidirectional type source or of a unidirectional type source.

[0012] According to another aspect of the present disclosure, a method of operating the above-mentioned power conversion apparatus is provided. The method comprises: determining a state of the apparatus, wherein the state of the apparatus comprises a power source mode and a voltage source mode; obtaining, for each of at least one first PPC string, a respective control signal for the first PPC string according to the state of the apparatus; obtaining, for each PPC in the first PPC string, a respective control signal for the PPC according to the state of the apparatus; and controlling, for each PPC in the first PPC string, the PPC based on the respective control signal for the PPC according to the state of the apparatus.

[0013] According to some embodiments, obtaining, for each of the at least one first PPC string, a respective control signal for the first PPC string according to the state of the apparatus comprises: in response to the state of the apparatus being the power source mode, generating the respective control signal for the first PPC string based on a power reference for the apparatus, an output power of the apparatus, and a respective state parameter of each of the at least one first PPC string, wherein the control signal for the first PPC string comprises a current reference for the first PPC string, and wherein obtaining, for each PPC in the first PPC string, a respective control signal for the PPC according to the state of the apparatus comprises: in response to the state of the apparatus being the power source mode, generating the respective control signal for the PPC based on the respective current reference for the first PPC string, a current of the first PPC string, and a respective state parameter of each of the PPCs in the first PPC string, wherein the control signal for the PPC comprises at least one of an input voltage reference, an input current reference, and an input power reference for the PPC, and wherein controlling, for each PPC in the first PPC string, the PPC based on the respective control signal for the PPC according to the state of the apparatus comprises: in response to the state of the apparatus being the power source mode, controlling the PPC based at least in part on the respective control signal for the PPC and a feedback parameter corresponding to the respective control signal for the PPC.

[0014] According to some embodiments, the apparatus further comprises a second string of PPCs connected in parallel with the DC bus, wherein the second string of PPCs is one string of PPCs or more than one string of series connected PPCs, and wherein generating the respective control signals for the first string of PPCs based on the power reference for the apparatus, the output power of the apparatus, and the respective state parameters of the first string of PPCs comprises generating the respective control signals for each of the at least one first string of PPCs and the second string of PPCs based on the power reference for the apparatus, the output power of the apparatus, and the respective state parameters of each of the at least one first string of PPCs and the second string of PPCs, wherein the control signal for a string comprises a current reference for the string.

[0015] According to some embodiments, generating the respective control signals for the PPCs in the first string of PPCs based on the respective current reference for the first string of PPCs, the current of the first string of PPCs, and the respective state parameters of each of the PPCs in the first string of PPCs comprises generating the respective control signals for each of the at least one string of series connected PPCs and the at least one group of PPCs based on the respective current reference for the first string of PPCs, the current of the first string of PPCs, and the respective state parameters of each of the PPCs in the first string of PPCs; and for each of the at least one group of PPCs, generating the respective control signals for each of the more than one PPC connected in parallel in the group of PPCs based on the respective control signal for the group of PPCs.

[0016] According to some embodiments, the at least one first string of PPCs is further connected to a grid-tied AC / DC converter, wherein an input of the grid-tied AC / DC converter is connected to the DC bus, and an output of the grid-tied AC / DC converter is connected to a power grid, and wherein the grid-tied AC / DC converter controls the voltage of the DC bus based on the DC bus voltage and at least one of: a power efficiency of the PPCs in the apparatus; a power efficiency of the grid-tied AC / DC converter; a temperature of the battery; and a temperature of a cabinet of the PPCs in the apparatus.

[0017] According to some embodiments, obtaining the respective control signals for the first string of PPCs as a function of the state of the apparatus comprises, in response to the state of the apparatus being the voltage source mode, generating the respective control signals for the first string of PPCs based on a voltage reference for the apparatus, an output voltage of the apparatus, and a respective state parameter of each of the at least one first string of PPCs, wherein the control signals for the first string of PPCs comprise at least one droop characteristic parameter for the first string of PPCs, and wherein obtaining the respective control signals for the PPCs as a function of the state of the apparatus comprises, in response to the state of the apparatus being the voltage source mode, determining a voltage reference for the first string of PPCs based on the at least one droop characteristic for the first string of PPCs and a current of the first string of PPCs, and generating a respective output control signal for each of the PPCs of the first string of PPCs based on the voltage reference for the first string of PPCs and a respective state parameter of each of the PPCs in the first string of PPCs, and wherein controlling the PPCs based on the respective control signals for the PPCs as a function of the state of the apparatus comprises, in response to the state of the apparatus being the voltage source mode, controlling the PPCs based at least in part on the respective control signals for the PPCs and feedback parameters corresponding to the respective control signals for the PPCs.

[0018] According to some embodiments, the apparatus further comprises a second string of PPCs connected in parallel with the DC bus, wherein the second string of PPCs is a string of one PPC or a string of more than one series connected PPCs, and wherein generating the respective control signals for the first string of PPCs based on the voltage reference for the apparatus, the output voltage of the apparatus, and the respective state parameter of each of the at least one first string of PPCs and the second string of PPCs comprises generating the respective control signals for each of the at least one first string of PPCs and the second string of PPCs based on the voltage reference for the apparatus, the output voltage of the apparatus, and the respective state parameter of each of the at least one first string of PPCs and the second string of PPCs, wherein the control signals for the strings comprise at least one droop characteristic parameter for the strings.

[0019] According to some embodiments, generating, based on the voltage reference for the first string of PPCs and the respective state parameters of each of the PPCs in the first string of PPCs, respective output control signals for the PPCs of the first string of PPCs comprises generating, based on the voltage reference for the first string of PPCs and the respective state parameters of each of the PPCs in the first string of PPCs, respective output voltage references for each of the at least one series-connected PPCs and respective output current references for each PPC in the at least one group of PPCs, and wherein controlling the PPCs based at least in part on the respective control signals for the PPCs and feedback parameters corresponding to the respective control signals for the PPCs comprises, for each of the at least one series-connected PPCs, controlling the PPC based at least in part on the respective output voltage reference for the PPC and an output voltage of the PPC, and for each PPC in the at least one group of PPCs, controlling the PPC based at least in part on the respective output current reference for the PPC and an output current of the PPC.

[0020] According to some embodiments, the method further comprises, in response to the state of the apparatus being the voltage source mode, generating a voltage reference for the apparatus based on the DC bus voltage and at least one of the following parameters: power efficiency of the PPCs in the apparatus; power efficiency of the grid-tied AC / DC converter; temperature of the battery; and temperature of a cabinet of the PPCs in the apparatus.

[0021] According to yet another aspect of the disclosure, a system for power conversion is provided. The system comprises: the apparatus described above; a DC bus; and a plurality of power sources connected to the apparatus.

[0022] It is to be understood that the details set forth in this section are not intended to limit or otherwise restrict the scope of the embodiments of the disclosure. Other aspects of the disclosure will readily occur to those skilled in the art based on the disclosure contained herein. BRIEF DESCRIPTION OF DRAWINGS

[0023] The accompanying drawings, which are included to provide a further understanding of the application and are incorporated in

[0024] Figure 1 is a schematic illustration of a connection of a string of PPCs in an apparatus for power conversion according to an embodiment of the disclosure.

[0025] Figures 2A-2B is a schematic illustration of a connection of a string of PPCs in an apparatus for power conversion according to an embodiment of the disclosure. Figure 1

[0026] Figure 3 ​is a schematic illustration of a device showing power conversion according to an embodiment of the disclosure.

[0027] Figures 4A-4B is a schematic illustration of a device showing power conversion according to an embodiment of the disclosure. Figure 1

[0028] Figure 5 is a flowchart showing a method for operating a device for power conversion according to an embodiment of the disclosure.

[0029] Figure 6 is a schematic illustration of a control loop of a device showing power conversion according to an embodiment of the disclosure.

[0030] Figure 7 is a flowchart showing a method for operating a device for power conversion according to an embodiment of the disclosure. Figure 1

[0031] Figure 8A is a schematic illustration of a control loop of a device showing power conversion according to an embodiment of the disclosure. Figure 6

[0032] Figure 8B is a schematic illustration of a control loop of a device showing power conversion according to an embodiment of the disclosure. Figure 6

[0033] Figure 8C is a schematic illustration of a control loop of a device showing power conversion according to an embodiment of the disclosure. Figure 6

[0034] Figure 9 is a flowchart showing a method for operating a device for power conversion according to an embodiment of the disclosure. Figure 1

[0035] Figure 10A is a schematic illustration of a control loop of a device showing power conversion according to an embodiment of the disclosure. Figure 6

[0036] Figure 10B is a schematic illustration of a control loop of a device showing power conversion according to an embodiment of the disclosure. Figure 6

[0037] Figure 10C is a schematic illustration of a control loop of a device showing power conversion according to an embodiment of the disclosure. Figure 6 DETAILED DESCRIPTION

[0038] ​​​​​​​​​The present disclosure will be described in further detail below with reference to the accompanying drawings and embodiments. It is to be understood that the embodiments described herein are only for explaining the related disclosure and not to limit the disclosure. It should also be noted that, for ease of description, only parts related to the disclosure are shown in the drawings.

[0039] It should be noted that the embodiments in the present disclosure and the features in the embodiments can be combined with each other without conflict if possible. If the number of elements is not specifically limited, there can be one or more elements unless the context clearly indicates otherwise. In addition, the number of steps or functional modules used in the present disclosure is only for identifying the steps or functional modules, and not to limit the order of executing the steps or the connection relationship between the functional modules. As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items. The term "based on" should be interpreted as "based at least in part on".

[0040] According to embodiments of the present disclosure, an apparatus and system for power conversion and a method for operating the apparatus are provided.

[0041] According to embodiments of the present disclosure, an apparatus for power conversion is provided, the apparatus comprising at least one first PPC string connected in parallel to a DC bus, the first PPC string comprising at least one series connected PPC and at least one PPC group, wherein each PPC group comprises more than one parallel connected PPC, wherein in each PPC group, a respective output of each of the more than one parallel connected PPC is connected in parallel to form an output of the PPC group, and wherein in the first PPC string, a respective output of each of the at least one series connected PPC and the at least one PPC group is connected in series, and wherein for each of the at least one series connected PPC and the more than one parallel connected PPC in the at least one PPC group, an input of the PPC is connected to a corresponding power source, and the input of the PPC and the output of the PPC have one common terminal.

[0042] According to embodiments of the present disclosure, the apparatus for power conversion can provide at least the following advantages:

[0043] 1) The series connected PPC and the PPC group of the parallel connected PPC are connected in series to build a DC bus with high voltage for MV or HV applications, for example, power sources with high output current and low output voltage output characteristics (e.g. super capacitors) can be connected in series;

[0044] 2) The parallel connected PPC can improve the current capacity of the apparatus by using parallel connection, for example, power sources with high output voltage and low output current output characteristics (e.g. PV panels) can be connected in parallel;

[0045] 3) it can limit the unbalanced current between the strings of parallel connection of power sources (such as battery cells), thereby it can prolong the life of the power sources;

[0046] 4) it can provide more precise control for each power source, thereby it can fully utilize the energy of each power source even if multiple power sources in one string are in different states (e.g., in different SOC states);

[0047] 5) with PPC, it can improve power efficiency and reduce capital cost, thereby it provides a low-cost solution;

[0048] 6) the power sources can be decoupled from each other, so that power sources with different characteristics (e.g., from different suppliers) can be used together, and new power sources can be added to increase capacity or prolong the life of the device;

[0049] 7) the power electronics-based PPC can sense power source failure and eliminate the failure impact, so that the failure impact can be limited, thereby it provides fast failure diagnosis, location, and clearing; and

[0050] 8) the modularly designed PPC is easy to replace and has limited maintenance cost, thereby it reduces the maintenance cost of the entire device.

[0051] Figure 1 is a schematic illustration of a device 1000 showing power conversion according to an embodiment of the present disclosure.

[0052] As shown in Figure 1 , the device 1000 for power conversion includes at least one first PPC string 1010, …, 10j0 of PPCs connected in parallel with a DC bus 1100. For brevity, only the details of the configuration of the string 1010 are drawn, and the details of the configuration of the other strings are omitted. The first PPC string includes at least one series-connected PPC 1011 and at least one PPC group 1012, where each PPC group includes more than one parallel-connected PPCs, for example, the PPC group 1012 includes PPCs 1013 a , …, 101i a .

[0053] According to some embodiments, in each PPC group, the respective outputs of each of the more than one parallel-connected PPCs are connected in parallel to form an output of the PPC group. For example, the outputs of the PPCs 1013 a , …, 101i a are connected in parallel to form an output of the PPC group 1012. According to some embodiments, in the first PPC string 1100, the respective outputs of each of the at least one series-connected PPC 1011 and the at least one PPC group 1012 are connected in series.

[0054] According to some embodiments, for each of the at least one series-connected PPC and the more than one parallel-connected PPC in the at least one PPC group, an input of the PPC is connected to a corresponding power source, e.g., the series-connected PPC 1011 a is connected to a corresponding power source 1011 b and the parallel-connected PPCs 1013 in the PPC group 1012 a are connected to a corresponding power source 1013 b and the input of the PPC and the output of the PPC have one common terminal.

[0055] Here, a partial power converter in the present disclosure refers to a converter with partial power handling characteristics, i.e., a portion of power flows directly from the source to the load, thus bypassing the converter, and the remaining power is handled by the converter, such that compared with a full power converter, the overall efficiency can be improved and the capital cost can be reduced.

[0056] It should be understood that, Figure 1 is for illustration only, and there can be more than one series-connected PPC and / or more than one PPC group in the first PPC string.

[0057] According to some embodiments, the number of parallel-connected PPCs can be different in different PPC groups. According to some embodiments, the apparatus can include more than one series-parallel-connected string, and the configuration (e.g., the number of series-connected PPCs, the number of PPC groups, and the number of parallel-connected PPCs in a PPC group) of the more than one series-parallel-connected string can be different.

[0058] According to some embodiments, “the respective outputs of each of the at least one series-connected PPC and the at least one PPC group are connected in series” means that for each PPC or PPC group, one output terminal of the PPC or PPC group is connected to the output terminal of the adjacent PPC or PPC group closer to the first terminal of the DC bus, and the other output terminal of the PPC or PPC group is connected to the output terminal of the other adjacent PPC or PPC group closer to the second terminal of the DC bus.

[0059] According to some embodiments, in each of the at least one series-connected PPC and the more than one parallel-connected PPC in the at least one group of PPCs, a first PPC terminal of the PPC is connected to a first bus terminal of the DC bus or a third PPC terminal of a neighboring PPC closer to the first bus terminal than the PPC, a second PPC terminal of the PPC is connected to a first source terminal of a corresponding power source, and a third PPC terminal of the PPC is connected to a second source terminal of the corresponding power source and one of: a second bus terminal of the DC bus and a first PPC terminal of a neighboring PPC closer to the second bus terminal than the PPC, and an input of the PPC is formed between the second PPC terminal of the PPC and the third PPC terminal of the PPC, and an output of the PPC is formed between the first PPC terminal of the PPC and the third PPC terminal of the PPC, and wherein in each of the at least one group of PPCs, the second PPC terminals of the more than one parallel-connected PPCs are connected, and the third PPC terminals of the more than one parallel-connected PPCs are connected. According to embodiments of the present disclosure, the outputs of the series-connected PPCs in the first PPC string and the groups of PPCs are connected in series in turn to form a relatively high DC bus voltage, which can make it easier to connect to the MV system, the outputs of the parallel-connected PPCs in the groups of PPCs are connected together to increase the current capacity of the device, and the inputs of each PPC in the first PPC string are connected to a corresponding power source (e.g., a battery module) to decouple the power sources from each other and provide more precise control for each power source.

[0060] According to some embodiments, when the PPC or the group of PPCs to which the PPC belongs is the PPC / group of PPCs closest to a first DC bus terminal of the PPCs and groups of PPCs in the first PPC string, a first PPC terminal of the PPC is connected to the first bus terminal of the DC bus; otherwise, the first PPC terminal of the PPC is connected to a third PPC terminal of a neighboring PPC closer to the first bus terminal than the PPC. According to some embodiments, when the PPC or the group of PPCs to which the PPC belongs is the PPC / group of PPCs closest to a second DC bus terminal of the PPCs and groups of PPCs in the first PPC string, a third PPC terminal of the PPC is connected to the second bus terminal of the DC bus; otherwise, the third PPC terminal of the PPC is connected to a first PPC terminal of a neighboring PPC closer to the second bus terminal than the PPC.

[0061] Some embodiments of the string 1010 in the device 1000 in Figure 2A and Figure 2B are described below. Figure 1

[0062] According to some embodiments, as Figure 2A and Figure 2B ​As shown, in each PPC, the input of the PPC is formed between the second PPC terminal and the third PPC terminal of the PPC, and the output of the PPC is formed between the first PPC terminal and the third PPC terminal of the PPC.

[0063] According to some embodiments, such as Figure 2A As shown, string 1010 includes the first PPC 1011 a and the first PPC group 1012, wherein, for the first PPC 1011 a The first PPC 1011 a The first PPC terminal is connected to the first bus terminal of DC bus 1100, the first PPC 1011 a The second PPC terminal is connected to the corresponding first power source 1011 b The first source terminal, the first PPC 1011 a The third PPC terminal is connected to the first power source 1011 b The second source terminal and PPC 1013 in PPC group 1012 a , ..., 101i a The first PPC terminal (i.e., compared to the first PPC 1011) a The adjacent PPC closer to the second bus terminal), and for the first PPC group 1012, PPC 1013 in the first PPC group 1012. a , ..., 101i a The first PPC terminal is connected and further connected to the first PPC 1011. a The third PPC terminal (i.e., compared to PPC 1013) a , ..., 101i a The adjacent PPC closer to the first bus terminal, and PPC 1013 a , ..., 101i a The third terminal is connected and further connected to the second bus terminal of DC bus 1100, and for PPC 1013 a , ..., 101i a In each of them, the second PPC terminal and the third PPC terminal of the PPC are respectively connected to the first source terminal and the second source terminal of the corresponding power source.

[0064] According to some embodiments, such as Figure 2B As shown, except for the first PPC 1011 a In addition to the first PPC group 1013, string 1010 also includes a second PPC 1012. a Among them, for the first PPC 1011 a The first PPC 1011a The first PPC terminal is connected to the first bus terminal of DC bus 1100, the first PPC 1011 a The second PPC terminal is connected to the corresponding first power source 1011 b The first source terminal, the first PPC 1011 a The third PPC terminal is connected to the first power source 1011 b The second source terminal and the second PPC 1012 a The first PPC terminal (i.e., compared to the first PPC 1011) a The adjacent PPC closer to the second bus terminal, for the second PPC 1012 a The first PPC 1011 a The first PPC terminal is connected to the first PPC 1011 a The third PPC terminal (i.e., compared to the second PPC 1012) a The adjacent PPC closer to the first bus terminal), the second PPC 1011 a The second PPC terminal is connected to the corresponding second power source 1012 b The first source terminal, the second PPC 1012 a The third PPC terminal is connected to the second power source 1012. b The second source terminal and PPC 1014 in PPC group 1013 a , ..., 101i a The first PPC terminal (i.e., compared to the second PPC 1012) a The adjacent PPC closer to the second bus terminal), and for the first PPC group 1013, PPC 1014 in the first PPC group 1013. a , ..., 101i a The first PPC terminal is connected and further connected to the second PPC 1012. a The third PPC terminal (i.e., compared to PPC 1013) a , ..., 101i a The adjacent PPC closer to the first bus terminal), and PPC 1014 a , ..., 101i a The third terminal is connected and further connected to the second bus terminal of DC bus 1100, and for PC 1014 a , ..., 101i a In each of them, the second PPC terminal and the third PPC terminal of the PPC are respectively connected to the first source terminal and the second source terminal of the corresponding power source.

[0065] Figure 3is a schematic illustration of a power conversion device according to embodiments of the present disclosure. Figure 3 The power conversion device 1000 and the DC bus 1100 in Figure 1 The power conversion device 1000 and the DC bus 1100 in

[0066] As shown in Figure 3 The first PPC string 1010 is further connected to a grid-tie AC / DC converter 1200. In this configuration, the input of the grid-tie AC / DC converter 1200 is connected to the DC bus 1100, and the output of the grid-tie AC / DC converter 1200 is connected to the grid 1300. According to embodiments of the present disclosure, by connecting to the grid via the grid-tie AC / DC converter, power from the device can be fed to the grid when the power source connected to the device is discharging, and power from the grid can be provided to the device when the power source connected to the device is charging.

[0067] According to some embodiments, the power conversion device 1000 can receive power from the grid 1300 or feed power to the grid 1300 through the grid-tie AC / DC converter 1200. According to some embodiments, the grid-tie AC / DC converter 1200 or the power conversion device 1000 can control the DC bus 1100, which will be described in detail below.

[0068] According to some embodiments, the power conversion device further comprises a second PPC string connected in parallel to the DC bus, wherein the second PPC string is one string of PPCs or more than one string of series-connected PPCs. According to embodiments of the present disclosure, by the combination of the first PPC string of series-connected PPCs and the second string of one PPC or series-connected PPCs, more possible configurations of the device can be provided, for example, power sources with high voltage characteristics can be connected to the PPCs in the second PPC string of one PPC, and power sources with relatively low voltage characteristics can be connected to the series-connected PPCs in the second PPC string of series-connected PPCs or the series-connected PPCs in the first PPC string, and power sources with relatively low current characteristics can be connected to the parallel-connected PPCs in the first PPC string.

[0069] According to some embodiments, the power conversion device further includes at least one of a second PPC string and more than one third PPC string connected in series, wherein at least one of the second and third PPC strings is connected in parallel with a DC bus. For the PPCs in the second PPC string, the PPC terminals of the PPCs are connected to the first bus terminals of the DC bus, the second PPC terminals of the PPCs are connected to the first source terminals of the corresponding power sources, and the third PPC terminals of the PPCs are connected to the second source terminals of the corresponding power sources and the second bus terminals of the DC bus. For the third string, more than one PPC includes at least a first PPC and a second PPC, wherein the first PPC terminal of the first PPC is connected to the first bus terminal of the DC bus, the second PPC terminal of the first PPC is connected to the first source terminal of the first power source, and the third PPC terminal of the first PPC is connected to the second source terminal of the first power source and the first PPC terminal of an adjacent PPC closer to the second bus terminal than the first PPC, and the first PPC terminal of the second PPC is connected to the third PPC terminal of an adjacent PPC closer to the first bus terminal than the second PPC, the second PPC terminal of the second PPC is connected to the first source terminal of the second power source, and the third PPC terminal of the second PPC is connected to the second source terminal of the second power source and the second bus terminal of the DC bus.

[0070] According to some embodiments, in each of at least one PPC group, the voltage difference between the corresponding power sources of the PPCs connected in parallel is below a (predetermined) voltage threshold. According to embodiments of this disclosure, by setting the voltage difference between the corresponding power sources of the PPCs connected in parallel to the PPCs below a (predetermined) voltage threshold, the ratio k of the output voltage to the input voltage of all those parallel-connected PPCs is... PPC It can be set at an ideal value. The closer the output voltages of the power sources connected to the parallel-connected PPC are to each other, the higher the ratio k of the output voltage to the input voltage of the parallel-connected PPC. PPC The closer the PPCs are to each other, and the more closely connected they are in parallel, the better. PPC The more uniform the power distribution, the lower the rated power of the power generation unit (PPC), and therefore the lower the total cost of the PPC. For example, for PPCs connected in parallel within a PPC group, if the corresponding power source is a battery stack, their output voltage difference can be kept within the maximum voltage drop due to cell aging, which serves as a (predetermined) voltage threshold. Alternatively, if the corresponding power source is, for example, a solar panel, their output voltage difference can be kept within the MPPT (Maximum Power Point Tracking) voltage regulation range, which serves as a (predetermined) voltage threshold.

[0071] According to some embodiments and for at least one series-connected PPC in the first PPC string, the corresponding source connected to the at least one series-connected PPC is of the same type, where the corresponding source connected to the PPC is either a bidirectional type source or a unidirectional type source. According to embodiments of the present disclosure, by setting the power sources connected to the series-connected PPCs to be of the same type, the capacity of the power sources can be fully utilized. For example, it is undesirable to have a PPC connected to a PV panel in series with a PPC connected to a battery. The output current of the series-connected PPCs is the same, and thus the direction of the input current of the series-connected PPCs is the same.

[0072] Figures 4A-4B is a schematic illustration showing a connection configuration of a PPC in Figure 1 according to embodiments of the present disclosure.

[0073] According to some embodiments, as shown in Figures 4A-4B , the PPC 1011 a comprises a first AC / DC converter 1011 a -1 and a second AC / DC converter 1011 a -2. Here, the term “AC / DC converter” is not intended to limit the conversion direction of AC and DC of the converter. The AC / DC converter can convert DC to AC or AC to DC. For example, either of the first AC / DC converter 1011 a -1 and the second AC / DC converter 1011 a -2 can have a circuit structure of H-bridge, IGBT, IGCT, MOSFET, GTO, or a single diode, etc.

[0074] According to some embodiments, as shown in Figures 4A-4B , the first AC / DC converter 1011 a -1 and the second AC / DC converter 1011 a -2 are coupled at AC ports of the first AC / DC converter 1011 a -1 and the second AC / DC converter 1011 a -2, and the DC port of the second AC / DC converter forms one of the input and output of the PPC 1011 a . The DC port of the first AC / DC converter 1011 a -1 and the DC port of the second AC / DC converter 1011 a -2 are connected in series to form the other of the input and output of the PPC 1011 a .

[0075] According to some embodiments, the second AC / DC converter 1011a -2 are connected in series to form an input of the PPC 1011 a The other of the input and the output of the PPC 1011

[0076] According to some embodiments, the first AC / DC converter 1011 a -1 and the second AC / DC converter 1011 a -2 are electromagnetically coupled or coupled through a capacitor on the AC side of the first AC / DC converter 1011 a -1 and the second AC / DC converter 1011 Figure 4A -3 (as shown in Fig. 1) or an inductor.

[0077] According to some embodiments, the first AC / DC converter 1011 Figure 4A -1 and the second AC / DC converter 1011 a -2 are coupled at the AC ports of the first AC / DC converter 1011 a -1 and the second AC / DC converter 1011 a -2, and the DC port of the second AC / DC converter forms an input of the PPC 1011 a -1 and the second AC / DC converter 1011 a -2 are connected in series to form an output of the PPC 1011 a -1 and the second AC / DC converter 1011 a -2 are connected in series to form an output of the PPC 1011 a -1 and the second AC / DC converter 1011

[0078] According to some embodiments, the DC side of the first AC / DC converter 1011 a -1 has a first DC terminal 1 and a second DC terminal 2, and the DC side of the second AC / DC converter 1011 a -2 has a third DC terminal 3 and a fourth DC terminal 4, wherein the first DC terminal 1 is connected to a first terminal 10 of the PPC 1011 a -1 and the second AC / DC converter 1011 a -2 are connected in series to form an output of the PPC 1011 a -1 and the second AC / DC converter 1011 a -1 and the second AC / DC converter 1011 a -2, a part of the power is bypassed from the power source 1011b directly to the output of the PPC 1011 a and the remaining power is handled by the first AC / DC converter 1011 a -1 and the second AC / DC converter 1011 a -2 and then passed to the output of the PPC 1011 a .

[0079] According to some embodiments, as shown in Figure 4B , the first AC / DC converter 1011 a -1 and the second AC / DC converter 1011 a -2 are coupled at the AC ports of the first AC / DC converter 1011 a -1 and the second AC / DC converter 1011 a -2 and the DC port of the second AC / DC converter forms the output of the PPC 1011 a . The DC port of the first AC / DC converter 1011 a -1 and the DC port of the second AC / DC converter 1011 a -2 are connected in series to form the input of the PPC 1011 a .

[0080] According to some embodiments, the DC side of the first AC / DC converter 1011 a -1 has a first DC terminal 1 and a second DC terminal 2 and the DC side of the second AC / DC converter 1011 a -2 has a third DC terminal 3 and a fourth DC terminal 4, wherein the first DC terminal 1 is connected to the second terminal 20 of the PPC 1011 a , the second DC terminal 2 and the third DC terminal 3 are connected to the first terminal 10 of the PPC 1011 a , and the fourth DC terminal 4 is connected to the third terminal 30 of the PPC 1011 a . In this case, by bypassing the first AC / DC converter 1011 a -1 and the second AC / DC converter 1011 a -2, a part of the power flows directly to the output of the PPC 1011 b from the power source 1011 a and the remaining power is handled by the first AC / DC converter 1011 a -1 and the second AC / DC converter 1011 a -2 and then passed to the output of the PPC 1011 a .

[0081] In some embodiments, at least one of the switching devices in each of the first AC / DC converter 1011 a -1 and the second AC / DC converter 1011 a -2 is a controllable switch. The controllable switch can include IGBT, IGCT, MOSFET, GTO, triode, etc. In some embodiments, when the AC / DC converter is in the controlled mode, at least one controllable switch in the AC / DC converter can be controlled to switch between the open state and the closed state (e.g., according to the PWM signal). In other embodiments, when the AC / DC converter is in the uncontrolled mode, all controllable switches in the AC / DC converter remain open or remain closed, where keeping the switching device open means that the switching device is always in the off state, and keeping the switching device closed means that the switching device is always in the on state. It should be understood that when the switching device is in the off state, current can still pass through the parallel diode in the device. In this way, unnecessary switching of the switching device can be avoided, thereby improving the efficiency of the converter and reducing power loss due to continuous switching.

[0082] In some embodiments, the rated power of each of the first AC / DC converter 1011 a -1 and the second AC / DC converter 1011 a -2 can be less than the rated power of the corresponding power source 1011 b , thereby further reducing the cost of the converter and improving power efficiency.

[0083] According to some embodiments, a method of operating the above-described power conversion device is provided. The method includes determining the state of the device, wherein the state of the device includes the power source mode and the voltage source mode; for each first PPC string in the at least one first PPC string, obtaining a corresponding control signal for the first PPC string according to the state of the device; for each PPC in the first PPC string, obtaining a corresponding control signal for the PPC according to the state of the device; and for each PPC in the first PPC string, controlling the PPC based on the corresponding control signal for the PPC according to the state of the device. According to embodiments of the present disclosure, more precise control can be provided for each string and each PPC and its corresponding power source.

[0084] Figure 5 is a flow chart showing a method 500 of controlling the power conversion device 1000 in Figure 1 , according to embodiments of the present disclosure, wherein the power conversion device is substantially the same as the device described with reference to Figure 1 - Figure 4, and details regarding the same features are omitted for brevity. As shown in Figure 5 , the method 500 includes steps S501-S504.

[0085] In step S501, the state of the device is determined, wherein the state of the device includes power source mode and voltage source mode.

[0086] In step S502, for each of the at least one first PPC strings, a corresponding control signal for the first PPC string is obtained according to the state of the device.

[0087] In step S503, for each PPC in the first PPC string, a corresponding control signal for the PPC is obtained according to the state of the device.

[0088] In step S504, for each PPC in the first PPC string, the PPC is controlled based on the corresponding control signal for the PPC according to the state of the device.

[0089] The details of steps S501-S504 are described below.

[0090] According to some embodiments, when the power conversion device is in power source mode, it can be controlled to provide a fixed amount of power, and the DC bus voltage can be controlled by other devices (e.g., Figure 3 (such as grid-connected AC / DC converters). According to some embodiments, when the power conversion device is in voltage source mode, it can be controlled to construct a DC bus voltage.

[0091] Figure 6 This is an illustration based on embodiments of the present disclosure. Figure 1 A schematic diagram of the control loop 6000 of the power conversion device 1000 in the middle.

[0092] like Figure 6 As shown, the control loop 6000 includes: a system-level controller 6100, a device-level controller 6200, a cascade controller 6310, ..., 63j0, and a PPC-level controller 6411, ..., 641i, ..., 64j1, ..., 64jk.

[0093] According to some embodiments, the above method 500 can be implemented as a control loop 6000, wherein step S501 can be implemented as a system-level controller 6100, step S502 can be implemented as a device-level controller 6200, step S503 can be implemented as a cascade controller 6310, ..., 63j0, and step S504 can be implemented as a PPC-level controller 6411, ..., 641i, ..., 64j1, ..., 64jk.

[0094] According to some embodiments, the system-level controller 6100 generates control signals for the power-converted device 1000, e.g., the control signals for the power-converted device 1000 are output power references when the power-converted device 1000 is in the power source mode, and the control signals for the power-converted device 1000 are DC bus voltage references when the power-converted device 1000 is in the voltage source mode. According to some embodiments, the system-level controller 6100 also generates control signals for the grid-tied AC / DC converter, e.g., the system-level controller 6100 generates DC bus voltage references for the grid-tied AC / DC converter when the power-converted device 1000 is in the power source mode.

[0095] According to some embodiments, the device-level controller 6200 generates a respective control signal for each of the strings 1010,..., 10j0 in the device 1000. According to some embodiments, the device-level controller 6200 receives state parameters of the strings 1010,..., 10j0 in the device and generates respective control signals for the strings 1010,..., 10j0 in the device based on the state parameters of the strings 1010,..., 10j0 in the device, thereby providing more accurate control for each string based on the individual state of each string.

[0096] According to some embodiments, for each of the string-level controllers 6310,..., 63j0, the string-level controller generates a respective control signal for each of the PPCs in the string. According to some embodiments, for each of the string-level controllers 6310,..., 63j0, the string-level controller receives state parameters of the PPCs in the string and generates respective control signals for the PPCs in the string based on the state parameters of the PPCs in the string, thereby providing more accurate control for each PPC based on the individual state of each PPC.

[0097] According to some embodiments, obtaining the respective control signals for the first PPC strings according to the state of the apparatus comprises, in response to the state of the apparatus being the power source mode, generating the respective control signals for the first PPC strings based on a power reference for the apparatus, an output power of the apparatus, and a respective state parameter of each of the at least one first PPC string, wherein the control signals for the first PPC strings comprise a current reference for the first PPC strings, and wherein obtaining the respective control signals for the PPCs according to the state of the apparatus comprises, in response to the state of the apparatus being the power source mode, generating the respective control signals for the PPCs based on the respective current reference for the first PPC strings, a current of the first PPC strings, and a respective state parameter of each of the PPCs in the first PPC strings, wherein the control signals for the PPCs comprise at least one of an input voltage reference, an input current reference, and an input power reference for the PPCs, and wherein controlling the PPCs according to the state of the apparatus based on the respective control signals for the PPCs comprises, in response to the state of the apparatus being the power source mode, controlling the PPCs based at least in part on the respective control signals for the PPCs and feedback parameters corresponding to the respective control signals for the PPCs. According to embodiments of the present disclosure, when the apparatus is in the power source mode, the respective control signals for each of the first PPC strings in the apparatus are generated based on the respective state parameters of the strings, so that the first PPC strings can be controlled based on the respective state parameters of the strings, which provides differentiated control for the PPC strings; and the respective control signals for each of the PPCs are generated based on the respective state parameters of the PPCs, so that the PPCs can be controlled based on the respective state parameters of the PPCs, which provides differentiated control for the PPCs.

[0098] Figure 7 is a method 700 of operating an apparatus 1000 for power conversion in Figure 1 according to embodiments of the present disclosure, wherein the apparatus for power conversion is substantially the same as the apparatus described with reference to Figure 1 - Figure 4, and thus details regarding identical features are omitted for brevity. As shown in Figure 7 the method 700 comprises steps S701-S704.

[0099] In step S701, a state of the apparatus is determined, wherein the state of the apparatus is a power source mode.

[0100] In step S702, in response to the state of the apparatus being the power source mode, the respective control signals for the first PPC strings are generated based on a power reference for the apparatus, an output power of the apparatus, and a respective state parameter of each of the at least one first PPC string, wherein the control signals for the first PPC strings comprise a current reference for the first PPC strings.

[0101] According to some embodiments, step S702 can be implemented asFigure 8A The device-level controller 6200 in the middle, of which, Figure 8A The device-level controller 6200 in the middle corresponds to Figure 6 The device-level controller 6200 in the middle. According to some embodiments, such as Figure 8A As shown, the difference between the power reference for the device and the output power of the device is first calculated, and then the sub-controller (e.g., a PI controller) generates a current reference for the string in the device based on the difference between the power reference for the device and the output power of the device, as well as the state parameters of the string in the device.

[0102] According to some embodiments, the device further includes a second PPC string connected in parallel with the DC bus, wherein the second PPC string is a string of one PPC or more strings of PPCs connected in series, and wherein generating a corresponding control signal for the first PPC string based on a power reference for the device, the output power of the device, and corresponding state parameters of the first PPC string includes: generating a corresponding control signal for each of at least one first PPC string and the second PPC string based on a power reference for the device, the output power of the device, and corresponding state parameters of each of at least one first PPC string and the second PPC string, wherein the control signal for the string includes a current reference for the string. According to embodiments of this disclosure, when the device is in power source mode, in addition to the first PPC string, corresponding control signals for the second PPC string in the device are generated based on the corresponding state parameters of the strings, so that the second PPC string can also be controlled based on the corresponding state parameters of the strings, which also provides differentiated control for the second PPC string.

[0103] In step S703, in response to the device being in power source mode, a corresponding control signal for the PPC is generated based on a corresponding current reference for the first PPC string, the current of the first PPC string, and a corresponding state parameter of each PPC in the first PPC string. The control signal for the PPC includes at least one of an input voltage reference, an input current reference, and an input power reference for the PPC.

[0104] According to some embodiments, generating the respective control signals for the PPCs based on the respective current reference for the first string of PPCs, the current of the first string of PPCs, and the respective state parameters of each of the PPCs in the first string of PPCs comprises generating the respective control signals for each of the at least one series-connected string of PPCs and the at least one group of PPCs based on the respective current reference for the first string of PPCs, the current of the first string of PPCs, and the respective state parameters of each of the PPCs in the first string of PPCs; and for each of the at least one group of PPCs, generating the respective control signals for each of the more than one parallel-connected PPCs in the group of PPCs based on the respective control signals for the group of PPCs. According to embodiments of the present disclosure, the control signals for each of the series-connected strings of PPCs and the groups of PPCs in the string are determined first, and then the control signals for each of the parallel-connected PPCs in the groups of PPCs are determined.

[0105] According to some embodiments, step S703 can be implemented as Figure 8B the string-level controller 6300 in FIG. 6B, wherein, Figure 8B the string-level controller 6300 in FIG. 6B corresponds to Figure 6 the string-level controller 6310, …, 63j0 in FIG. 6B.

[0106] According to some embodiments, as shown in Figure 8B , the difference between the current reference for the string and the output power of the string is first calculated, and then the sub-controller generates the control signals for the series-connected PPCs and the groups of PPCs in the string based on the difference between the current reference for the string and the output power of the string and the state parameters of the PPCs in the string, and then the reference divider generates the control signals for the parallel-connected PPCs in the groups of PPCs in the string based on the control signals for the groups of PPCs.

[0107] According to some embodiments, the sub-controller generates the control signals for the series-connected PPCs and the groups of PPCs in the string based on the difference between the current reference for the string and the output power of the string and the state parameters of the series-connected PPCs and the groups of PPCs in the string, wherein the state parameters for the groups of PPCs are determined based on the state parameters of the PPCs in the groups of PPCs.

[0108] According to some embodiments, for each group of PPCs, the reference divider generates the control signals for the PPCs in the group of PPCs based on the control signals for the group of PPCs and the state parameters of the PPCs in the group of PPCs.

[0109] According to some embodiments, the type of control signal for the PPC (i.e., input voltage reference, input current reference, and input power reference for the PPC) is determined based on the mode of the power source connected to the PPC. For example, when the power source is in constant current mode, the control signal for the PPC is the input current reference.

[0110] In step S704, in response to the state of the apparatus being the power source mode, the PPC is controlled based at least in part on the respective control signal for the PPC and the feedback parameter corresponding to the respective control signal for the PPC.

[0111] According to some embodiments, controlling the PPC based at least in part on the respective control signal for the PPC and the feedback parameter corresponding to the respective control signal for the PPC includes controlling the PPC based on the respective control signal for the PPC, the feedback parameter corresponding to the respective control signal for the PPC, and at least one of: a change in the state parameter for the PPC; and a difference between the input voltage and the output voltage of the PPC.

[0112] According to some embodiments, the feedback parameter corresponds to the respective control signal for the PPC, for example, when the control signal for the PPC is the power reference for the PPC, the feedback parameter is the output power of the PPC.

[0113] According to some embodiments, step S704 can be implemented as Figure 8C the PPC-level controller 6400 in Figure 8C the PPC-level controller 6400 in corresponds to Figure 6 the PPC-level controller 6411, …, 641i, …, 64j1, …, 64jk in According to some embodiments, as shown in Figure 8C first, a first difference between the control signal for the PPC and the change in the state parameter for the PPC is calculated, then a second difference between the first difference and the feedback parameter for the PPC is calculated, then the sub-controller 1 generates an internal control signal for the PPC based on the second difference, then a third difference between the internal control signal for the PPC and the difference between the input voltage and the output voltage of the PPC is calculated, and finally the sub-controller 2 generates a control signal (e.g., a PWM signal) for the switch in the PPC based on the third difference.

[0114] According to some embodiments, Figure 8COption 1 for the change of the state parameter of the PPC and Option 2 for the difference between the input voltage and the output voltage of the PPC shown in FIG. 6 can be omitted, i.e., there can be only one of Option 1-2 in the controller 6400, or there can be none of Option 1-2 in the controller 6400. According to some embodiments, when Option 1 for the change of the state parameter of the PPC is omitted, the difference between the control signal for the PPC and the feedback parameter for the PPC is calculated and then input into the sub-controller. According to some embodiments, when Option 2 for the difference between the input voltage and the output voltage of the PPC is omitted, the output of the sub-controller 1 is directly output as the control signal for the switch in the PPC.

[0115] According to some embodiments, obtaining the respective control signals for the first PPC strings according to the state of the apparatus comprises, in response to the state of the apparatus being the voltage source mode, generating the respective control signals for the first PPC strings based on a voltage reference for the apparatus, an output voltage of the apparatus, and a respective state parameter of each of the at least one first PPC string, wherein the control signals for the first PPC strings comprise at least one droop characteristic parameter for the first PPC strings, and wherein obtaining the respective control signals for the PPC according to the state of the apparatus comprises, in response to the state of the apparatus being the voltage source mode, determining a voltage reference for the first PPC strings based on the at least one droop characteristic for the first PPC strings and a current of the first PPC strings; and generating a respective output control signal for each of the PPCs in the first PPC strings based on the voltage reference for the first PPC strings and a respective state parameter of each of the PPCs in the first PPC strings, and wherein controlling the PPC based on the respective control signals for the PPC according to the state of the apparatus comprises, in response to the state of the apparatus being the voltage source mode, controlling the PPC based at least in part on the respective output control signals for the PPC and a feedback parameter corresponding to the respective control signals for the PPC. According to embodiments of the present disclosure, similar to the power source mode, when the apparatus is in the voltage source mode, the respective control signals for each of the first PPC strings in the apparatus are generated based on the respective state parameters of the strings, so that the first PPC strings can be controlled based on the respective state parameters of the strings, which provides differentiated control for the PPC strings; and the respective control signals for each of the PPCs are generated based on the respective state parameters of the PPCs, so that the PPCs can be controlled based on the respective state parameters of the PPCs, which provides differentiated control for the PPCs.

[0116] Figure 9 is a flowchart showing a method 900 for operating the apparatus 1000 for power conversion in Figure 1 FIG. 6, wherein the output of the sub-controller 1 is directly output as the control signal for the switch in the PPC. Figure 1- the apparatus described in Figure 4 is substantially the same, therefore details about the same features are omitted for brevity. As shown in Figure 9, the method 900 comprises steps S901-S904. Figure 9

[0117] In step S901, a state of the apparatus is determined, wherein the state of the apparatus is the voltage source mode.

[0118] In step S902, in response to the state of the apparatus being the voltage source mode, respective control signals for the first PPC strings are generated based on a voltage reference for the apparatus, an output voltage of the apparatus, and a respective state parameter of each of the at least one first PPC string, wherein the control signals for the first PPC strings comprise at least one droop characteristic parameter for the first PPC strings.

[0119] According to some embodiments, step S902 can be implemented as the apparatus-level controller 6200 in Figure 10A Figure 10A According to some embodiments, the apparatus-level controller 6200 in Figure 6 corresponds to the apparatus-level controller 6200 in Figure 10A According to some embodiments, as shown in Figure 9, first, a difference between the DC bus voltage reference and the DC bus voltage is calculated, then the sub-controllers generate internal control signals for the apparatus based on the difference between the DC bus voltage reference and the DC bus voltage, then the droop characteristic definition block generates droop characteristic parameters for the strings in the apparatus based on the internal control signals for the apparatus and the state parameters of the strings in the apparatus.

[0120] According to some embodiments, the droop characteristic parameters for each string comprise at least one of a rate of the droop characteristic and a node increment.

[0121] According to some embodiments, the apparatus further comprises a second PPC string connected in parallel with the DC bus, wherein the second PPC string is one string of a PPC or more than one string of a PPC connected in series, and wherein generating respective control signals for the first PPC strings based on a voltage reference for the apparatus, an output voltage of the apparatus, and a respective state parameter of the first PPC strings comprises generating respective control signals for each of the at least one first PPC string and the second PPC string based on the voltage reference for the apparatus, the output voltage of the apparatus, and the respective state parameter of each of the at least one first PPC string and the second PPC string, wherein the control signals for the strings comprise at least one droop characteristic parameter for the strings. According to embodiments of the present disclosure, similar to the power source mode, when the apparatus is in the voltage source mode, in addition to the first PPC strings, respective control signals for the second PPC strings in the apparatus are generated based on the respective state parameters of the strings, so that the second PPC strings can also be controlled based on the respective state parameters of the strings, which also provides differentiated control for the second PPC strings.​​

[0122] In step S903, in response to the state of the apparatus being the voltage source mode, a voltage reference for the first string of PPCs is determined based on the at least one droop characteristic for the first string of PPCs and a current of the first string of PPCs, and respective output control signals for each of the PPCs in the first string of PPCs are generated based on the voltage reference for the first string of PPCs and respective state parameters of each of the PPCs in the first string of PPCs.

[0123] According to some embodiments, generating the respective output control signals for each of the PPCs in the first string of PPCs based on the voltage reference for the first string of PPCs and the respective state parameters of each of the PPCs in the first string of PPCs comprises generating respective output voltage references for each of the at least one series connected PPCs and respective output current references for each of the PPCs in the at least one group of PPCs based on the voltage reference for the first string of PPCs and the respective state parameters of each of the PPCs in the first string of PPCs. According to embodiments of the present disclosure, the series connected PPCs are controlled in the voltage source mode to facilitate the building up of the DC bus voltage, while the parallel connected PPCs are controlled in the current source mode as it is difficult to control the output voltage of the parallel connected PPCs due to the parallel connection of the outputs of the PPCs.

[0124] According to some embodiments, step S903 can be implemented as the string level controller 6300 in Figure 10B wherein the string level controller 6300 corresponds to Figure 10B the string level controller 6310, …, 63j0 in Figure 6 According to some embodiments, as shown in Figure 10B the droop characteristic of the droop controller is determined based on the droop characteristic parameters of the string and the droop controller determines a voltage reference for the string based on the droop characteristic parameters of the string and a current of the string, then calculates a difference between the voltage reference for the string and the DC bus voltage, then the sub-controller generates output voltage references for the series connected PPCs in the string and output current references for the parallel connected PPCs in the group of PPCs in the string based on the difference between the voltage reference for the string and the DC bus voltage and the state parameters of the PPCs in the string.

[0125] In step S904, in response to the state of the apparatus being the voltage source mode, the PPCs are controlled based at least in part on the respective output control signals for the PPCs and feedback parameters corresponding to the respective control signals for the PPCs.

[0126] According to some embodiments, controlling a PPC at least in part based on a corresponding control signal for the PPC and a feedback parameter corresponding to the corresponding control signal for the PPC includes: for each of at least one series-connected PPCs, controlling the PPC at least in part based on a corresponding output voltage reference for the PPC and the output voltage of the PPC; and for each PPC in at least one group of PPCs, controlling the PPC at least in part based on a corresponding output current reference for the PPC and the output current of the PPC.

[0127] According to some embodiments, step S904 can be implemented as follows: Figure 10C The PPC-level controller 6400, among which, Figure 10C The PPC-level controller 6400 in the middle corresponds to Figure 6 The PPC-level controllers are 6411, ..., 641i, ..., 64j1, ..., 64jk. According to some embodiments, such as... Figure 10C As shown, a first difference is calculated between the output control reference for the PPC and the output feedback parameter of the PPC. Then, sub-controller 1 generates an internal control signal for the PPC based on the first difference and the state parameters of the PPC. Then, a second difference is calculated between the internal control signal for the PPC and the difference between the input voltage and the output voltage of the PPC. Finally, sub-controller 2 generates a control signal (e.g., a PWM signal) for the switches in the PPC based on the second difference.

[0128] According to some embodiments, this can be omitted. Figure 10C Option 1 shows the difference between the input and output voltages of the PPC. According to some embodiments, when option 1, which specifies the difference between the input and output voltages of the PPC, is omitted, the output of the sub-controller 1 is directly output as a control signal for the switches in the PPC.

[0129] In a PPC, the smaller ratio k of the output voltage to the input voltage PPC This reduces the cost of the PPC, which is related to its smaller rated power. When the voltage of the power source (i.e., the input voltage of the PPC) fluctuates within a certain range, a ratio k with a wide range should be designed. PPC The PPC is designed to provide constant DC bus voltage control, which increases the PPC's power capacity and cost. To address this issue, a floating DC bus voltage control is provided.

[0130] According to some embodiments, when the apparatus is in the power source mode, the grid-tied AC / DC converter controls the DC bus voltage. According to some embodiments, the at least one first PPC string is further connected to the grid-tied AC / DC converter, wherein an input of the grid-tied AC / DC converter is connected to the DC bus, and an output of the grid-tied AC / DC converter is connected to the grid, and wherein the grid-tied AC / DC converter controls the voltage of the DC bus based on the DC bus voltage and at least one of: power efficiency of the PPCs in the apparatus; power efficiency of the grid-tied AC / DC converter; temperature of the battery; and temperature of the cabinet of the PPCs in the apparatus. According to embodiments of the present disclosure, when the apparatus is in the power source mode, the grid-tied AC / DC converter controls the DC bus voltage based on current parameters of the apparatus and / or the grid-tied AC / DC converter, thereby providing a floating DC bus voltage control, rather than controlling the DC bus voltage at a fixed value. Thus, the floating DC bus voltage control provided based on embodiments of the present disclosure, the ratio k PPC may be limited in a small range, and the PPCs can be designed to have a smaller rated power capacity, and the total cost can be reduced and the efficiency of the PPCs can be improved.

[0131] According to some embodiments, when the apparatus is in the voltage source mode, the apparatus controls the DC bus voltage. According to some embodiments, in response to the state of the apparatus being the voltage source mode, a voltage reference for the apparatus is generated based on the DC bus voltage and at least one of the following parameters: power efficiency of the PPCs in the apparatus; power efficiency of the grid-tied AC / DC converter; temperature of the battery; and temperature of the cabinet of the PPCs in the apparatus. According to embodiments of the present disclosure, when the apparatus is in the voltage source mode, the voltage reference of the apparatus is a floating value determined based on current parameters of the apparatus and / or the grid-tied AC / DC converter, rather than a fixed value. Thus, the floating DC bus voltage control provided based on embodiments of the present disclosure, the ratio k PPC may be limited in a small range, and the PPCs can be designed to have a smaller rated power capacity, and the total cost can be reduced and the efficiency of the PPCs can be improved.

[0132] According to embodiments of the present disclosure, based on the floating DC bus voltage control, the ratio k PPC may be limited in a small range, and the PPCs can be designed to have a smaller rated power capacity, and the total cost can be reduced and the efficiency of the PPCs can be improved.

[0133] According to some embodiments, the PPC in the apparatus comprises a first AC / DC converter and a second AC / DC converter, the first AC / DC converter and the second AC / DC converter are coupled at AC ports of the first AC / DC converter and the second AC / DC converter, and a DC port of the second AC / DC converter forms one of the input and the output of the PPC, and a DC port of the first AC / DC converter and the DC port of the second AC / DC converter are connected in series to form the other of the input and the output of the PPC, and controlling the PPC based on the respective control signals for the PPC according to the state of the apparatus comprises: in response to the DC port of the second AC / DC converter forming the input of the PPC, and the DC port of the first AC / DC converter and the DC port of the second AC / DC converter being connected in series to form the output of the PPC, when the PPC is in the charging mode, controlling the first AC / DC converter of the PPC based on the respective control signals for the PPC according to the state of the apparatus, and setting the second AC / DC converter to the uncontrolled mode, and when the PPC is in the discharging mode, controlling the second AC / DC converter of the PPC based on the respective control signals for the PPC according to the state of the apparatus, and setting the first AC / DC converter to the uncontrolled mode; and in response to the DC port of the second AC / DC converter forming the output of the PPC, and the DC port of the first AC / DC converter and the DC port of the second AC / DC converter being connected in series to form the input of the PPC, when the PPC is in the discharging mode, controlling the first AC / DC converter of the PPC based on the respective control signals for the PPC according to the state of the apparatus, and setting the second AC / DC converter to the uncontrolled mode, and when the PPC is in the charging mode, controlling the second AC / DC converter of the PPC based on the respective control signals for the PPC according to the state of the apparatus, and setting the first AC / DC converter to the uncontrolled mode, wherein in the uncontrolled mode, all controllable switches in the AC / DC converter remain open or remain closed.

[0134] According to embodiments of the present disclosure, by setting one corresponding AC / DC converter in the PPC to the uncontrolled mode, in which all controllable switches in the AC / DC converter remain open or remain closed to avoid unnecessary switching loss, the efficiency of the apparatus can be improved, and the PPC-level controller for generating the control signals for the switches in the PPC can be simplified.

[0135] According to embodiments of the present disclosure, a system for power conversion is provided, which comprises: an apparatus for power conversion as described above (e.g., the apparatus 1000 in Figure 1 , the DC bus 1200 in Figure 1 ); and a plurality of power sources connected to the apparatus (e.g., the power sources 1011 b , …, 101i b).

[0136] The flow and block diagrams in the drawings represent possible architectural, functional, and operational scenarios of systems, methods, and computer program products according to various embodiments of the present disclosure. In this regard, each block in the flow and block diagrams can represent a module, a segment, or a portion of code, which comprises one or more executable instructions for implementing the specified logical function. It should also be noted that in some alternative implementations, the functions noted in the blocks can occur out of the order noted in the figures. For example, two blocks shown in succession may, in fact, be executed substantially concurrently, or the blocks can sometimes be executed in the reverse order, depending on the functionality involved. Such functionality can be executed in response to one or more events, may, in some instances, be executed continuously, and may, in some other instances, be executed in response to one or more inputs.

[0137] The foregoing merely illustrates the principles of the disclosure. Various modifications and adaptations will occur to those skilled in the art in view of the foregoing and detailed description of the embodiments. Thus, the foregoing and accompanying drawings are intended to be illustrative only and are not limiting of the scope of the disclosure. For example, the above-described features can be combined in any suitable manner in various embodiments of the disclosure. One skilled in the relevant art will recognize that the embodiments of the present disclosure can readily be modified to employ the techniques described herein without departing from the scope of the present disclosure, that the "preferred" elements of the present disclosure can actually be preferred when dependent on some technologies but not others, and that, therefore, all such "preferred" elements are meant to be an abstraction retaining the essence of the various embodiments of the present disclosure while allowing for the more detailed description herein.

Claims

1. An apparatus for power conversion, the apparatus comprising: at least one first partial power converter (PPC) string connected in parallel to a DC bus, the first partial power converter (PPC) string comprising at least one series connected PPC and at least one PPC group, wherein each PPC group comprises more than one parallel connected PPC, wherein in each PPC group, a respective output of each of the more than one parallel connected PPCs is connected in parallel to form an output of the PPC group, and wherein in the first PPC string, a respective output of each of the at least one series connected PPC and the at least one PPC group is connected in series, and wherein for each of the at least one series connected PPC and the more than one parallel connected PPCs in the at least one PPC group, an input of the PPC is connected to a corresponding power source, and the input of the PPC and the output of the PPC have one common terminal.

2. The apparatus of claim 1, wherein, in each of the at least one series connected PPC and the more than one parallel connected PPCs in the at least one PPC group, a first PPC terminal of the PPC is connected to a first bus terminal of the DC bus or a third PPC terminal of an adjacent PPC closer to the first bus terminal than the PPC, a second PPC terminal of the PPC is connected to a first source terminal of the corresponding power source, and a third PPC terminal of the PPC is connected to a second source terminal of the corresponding power source and one of: a second bus terminal of the DC bus and a first PPC terminal of an adjacent PPC closer to the second bus terminal than the PPC, and the input of the PPC is formed between the second PPC terminal of the PPC and the third PPC terminal of the PPC, and the output of the PPC is formed between the first PPC terminal of the PPC and the third PPC terminal of the PPC, and wherein in each of the at least one PPC group, the second PPC terminals of the more than one parallel connected PPCs are connected, and the third PPC terminals of the more than one parallel connected PPCs are connected.

3. The apparatus of claim 1 or 2, wherein, the at least one first PPC string is further connected to a grid-tied AC / DC converter, wherein an input of the grid-tied AC / DC converter is connected to the DC bus, and an output of the grid-tied AC / DC converter is connected to the grid.

4. The apparatus of claim 1 or 2, further comprising a second PPC string connected in parallel with the DC bus, wherein, the second PPC string is a string of one PPC or a string of more than one series connected PPC.

5. The apparatus of claim 1 or 2, wherein, in each of the at least one PPC group, a voltage difference of the corresponding power sources connected to the more than one parallel connected PPCs is below a predetermined voltage threshold, and for the at least one series-connected PPC in the first PPC string, the corresponding source connected to the at least one series-connected PPC is of the same type, wherein the corresponding source connected to the PPC is either a bi-directional type source or a unidirectional type source, wherein, preferably, the predetermined voltage threshold is defined as a maximum voltage drop due to cell aging or a maximum power point tracking (MPPT) voltage regulation range.

6. A method of operating a power conversion apparatus according to claim 1, the method comprising: determining a state of the apparatus, wherein the state of the apparatus comprises a power source mode and a voltage source mode; for each first PPC string of the at least one first PPC string, obtaining a respective control signal for the first PPC string according to the state of the apparatus; for each PPC in the first PPC string, obtaining a respective control signal for the PPC according to the state of the apparatus; and for each PPC in the first PPC string, controlling the PPC based on the respective control signal for the PPC according to the state of the apparatus.

7. The method of claim 6, wherein, the obtaining a respective control signal for the first PPC string according to the state of the apparatus comprises: in response to the state of the apparatus being the power source mode, generating the respective control signal for the first PPC string based on a power reference for the apparatus, an output power of the apparatus, and a respective state parameter of each of the at least one first PPC string, wherein the control signal for the first PPC string comprises a current reference for the first PPC string, and wherein the obtaining a respective control signal for the PPC according to the state of the apparatus comprises: in response to the state of the apparatus being the power source mode, generating the respective control signal for the PPC based on a respective current reference for the first PPC string, the current of the first PPC string, and a respective state parameter of each of the PPCs in the first PPC string, wherein the control signal for the PPC comprises at least one of the input voltage reference, the input current reference, and an input power reference for the PPC, and wherein the controlling the PPC based on the respective control signal for the PPC according to the state of the apparatus comprises: in response to the state of the apparatus being the power source mode, controlling the PPC based at least in part on the respective control signal for the PPC and a feedback parameter corresponding to the respective control signal for the PPC.

8. The method of claim 7, wherein, the apparatus further comprises a second PPC string connected in parallel to the DC bus, wherein the second PPC string is a string of one PPC or a string of more than one series-connected PPC, and wherein the generating the respective control signal for the first PPC string based on the power reference for the apparatus, the output power of the apparatus, and the respective state parameter of the first PPC string comprises: generating, based on a power reference for the apparatus, an output power of the apparatus, and a respective state parameter of each of the at least one first string of PPCs and the second string of PPCs, a respective control signal for each of the at least one first string of PPCs and the second string of PPCs, wherein the control signal for the string comprises a current reference for the string.

9. The method of claim 7, wherein, the generating, based on a respective current reference for the first string of PPCs, the current of the first string of PPCs, and a respective state parameter of each of the PPCs in the first string of PPCs, a respective control signal for the PPCs comprises: generating, based on a respective current reference for the first string of PPCs, the current of the first string of PPCs, and a respective state parameter of each of the PPCs in the first string of PPCs, a respective control signal for each of the at least one series-connected string of PPCs and the at least one group of PPCs; and for each group of PPCs in the at least one group of PPCs, generating, based on a respective control signal for the group of PPCs, a respective control signal for each of the more than one parallel-connected string of PPCs in the group of PPCs.

10. The method of any one of claims 6-9, wherein, the at least one first string of PPCs is further connected to a grid-tied AC / DC converter, wherein the input of the grid-tied AC / DC converter is connected to the DC bus and the output of the grid-tied AC / DC converter is connected to the grid, and wherein the grid-tied AC / DC converter controls the voltage of the DC bus based on a DC bus voltage and at least one of: a power efficiency of the PPCs in the apparatus; a power efficiency of the grid-tied AC / DC converter; a temperature of the battery; and a temperature of a cabinet of the PPCs in the apparatus.

11. The method of claim 6, wherein, the obtaining, from a state of the apparatus, a respective control signal for the first string of PPCs comprises: in response to the state of the apparatus being the voltage source mode, generating, based on a voltage reference for the apparatus, an output voltage of the apparatus, and a respective state parameter of each of the at least one first string of PPCs, a respective control signal for the first string of PPCs, wherein the control signal for the first string of PPCs comprises at least one droop characteristic parameter for the first string of PPCs, and wherein the obtaining, from a state of the apparatus, a respective control signal for the PPCs comprises: in response to the state of the apparatus being the voltage source mode, determining a voltage reference for the first string of PPCs based on the at least one droop characteristic for the first string of PPCs and a current of the first string of PPCs; and generating, based on a voltage reference for the first string of PPCs and a respective state parameter of each of the PPCs in the first string of PPCs, a respective output control signal for each of the PPCs in the first string of PPCs, and wherein the controlling, based on a respective control signal for the PPCs, the PPCs from a state of the apparatus comprises: in response to the state of the apparatus being the voltage source mode, determining a voltage reference for the first string of PPCs based on the at least one droop characteristic for the first string of PPCs and a current of the first string of PPCs; and generating, based on a voltage reference for the first string of PPCs and a respective state parameter of each of the PPCs in the first string of PPCs, a respective output control signal for each of the PPCs in the first string of PPCs, and wherein the controlling, based on a respective control signal for the PPCs, the PPCs from a state of the apparatus comprises: in response to the state of the apparatus being the voltage source mode, controlling the PPCs based at least in part on respective output control signals for the PPCs and feedback parameters corresponding to the respective control signals for the PPCs.

12. The method of claim 11, wherein, The apparatus further comprises a second string of PPCs connected in parallel to the DC bus, wherein the second string of PPCs is a string of one PPC or a string of more than one series connected PPCs, and wherein the generating of respective control signals for the first string of PPCs based on a voltage reference for the apparatus, an output voltage of the apparatus, and respective state parameters of the first string of PPCs comprises: generating respective control signals for each of the at least one first string of PPCs and the second string of PPCs based on a voltage reference for the apparatus, an output voltage of the apparatus, and respective state parameters of each of the at least one first string of PPCs and the second string of PPCs, wherein the control signals for the strings comprise at least one droop characteristic parameter for the strings.

13. The method of claim 11, wherein, the generating of respective output control signals for each of the PPCs in the first string of PPCs based on the voltage reference for the first string of PPCs and respective state parameters of each of the PPCs in the first string of PPCs comprises: generating, for each of the at least one series connected PPC, a respective output voltage reference for the PPC and a respective output current reference for each PPC in the at least one group of PPCs based on the voltage reference for the first string of PPCs and respective state parameters of each of the PPCs in the first string of PPCs, and wherein the controlling of the PPCs based at least in part on respective control signals for the PPCs and feedback parameters corresponding to the respective control signals for the PPCs comprises: for each of the at least one series connected PPC, controlling the PPC based at least in part on a respective output voltage reference for the PPC and the output voltage of the PPC; and for each PPC in the at least one group of PPCs, controlling the PPC based at least in part on a respective output current reference for the PPC and the output current of the PPC.

14. The method of any one of claims 11-13, wherein, The at least one first string of PPCs is further connected to a grid-tied AC / DC converter, wherein the input of the grid-tied AC / DC converter is connected to the DC bus and the output of the grid-tied AC / DC converter is connected to the grid, and The method further comprises: in response to the state of the apparatus being the voltage source mode, generating the voltage reference for the apparatus based on a DC bus voltage and at least one of the following parameters: power efficiency of the PPCs in the apparatus; power efficiency of the grid-tied AC / DC converter; temperature of the battery; temperature of a cabinet of the PPCs in the apparatus.

15. A system for power conversion, the system comprising: an apparatus according to any one of claims 1-5; a DC bus; and a plurality of power sources connected to the apparatus. ​

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