Converter system and control method thereof

Abstract

A converter system (100) is provided. The converter system (100) includes a first converter (10) having a first AC side (10A) with a first frequency (f1) and a second AC side (10B) with a second frequency (f2), the first converter (10) comprising a converter having a plurality of branches; a plurality of second converter units 21~2n) configurable to be coupled between the first converter (100) and a plurality of DC units 301~30n), each of the plurality of DC units 301~30n) being a DC load or a DC source; and a controller (30) configured to control at least one of the first converter (10) and at least one second converter unit (21) to control power supplied to or by at least one of the plurality of DC units 301~30n).

Description

CONVERTER SYSTEM AND CONTROL METHOD THEREOFTECHNICAL FILED

[0001] The present disclosure relates to a converter system and a control method for controlling the converter system.BACKGROUND

[0002] A converter can convert an alternating current (AC) into a direct current (DC) and vice versa. The converter can change the voltage or frequency of the current or do some combination of these. The converter includes a matrix converter, which is an AC -AC converter having an array of controlled power switches. The matrix converter has attractive features that have been investigated and brought closer to the industrial application.

[0003] In the last few years, cascading a matrix converter with a rectifier to form a converter system that can be applied to DC applications has become a hot spot in power electronics research. In the prior art, there i s still room for improvement in such a converter system . For example, problems such as complex structure, high cost and large footprint need to be solved.SUMMARY

[0004] According to one aspect of the invention, a converter system is provided. The converter system includes a first converter having a first AC side with a first frequency and a second AC side with a second frequency, the first converter comprising a converter having a plurality of branches; a plurality of second converter units configurable to be coupled between the first converter and a plurality of DC units, each of the plurality of DC units being a DC load or a DC source; and a controller configured to control atleast one of the first converter and at least one second converter unit to control power supplied to or by at least one of the plurality of DC units.

[0005] In an embodiment, the first frequency is at the power frequency, and the second frequency is greater than the first frequency and in the range of 100Hz~ 10kHz.

[0006] In an embodiment, the converter is a matrix converter and has a first terminal coupled to at least two phases. The plurality of branches comprise a first set of branches and a second set of branches, the first set of branches including branches that are coupled with one phase of the at least two phases, and the second set of branches including branches that are coupled with the other phase of the at least two phases . One branch of the first set of branches is configured to be combined phase wise or potential wi se to a corresponding branch comprised in the second set of branches.

[0007] In an embodiment, the converter is a matrix converter, and includes nine branches each comprising one or more modules and a branch inductor connected in series to the one or more modules, and each branch has a first end coupled to one of three phases a, b, c of a first terminal of the matrix converter and a second end coupled to one of three phases x, y, z of a second terminal of the matrix converter. The nine branches comprise first to ninth branches. First ends of the first, second and third branches are coupled to the phase a of the first terminal, and second ends of the first, fourth and seventh branches are coupled to the phase x of the second terminal . First ends of the fourth, fifth and sixth branches are coupled to the phase b of the first terminal, and second ends of the second, fifth and eighth branches are coupled to the phase y of the second terminal . First ends of the seventh, eighth and ninth branches are coupled to the phase c of the first terminal, and second ends of the third, sixth and ninth branches are coupled to the phase z of the second terminal .

[0008] In an embodiment, the matrix converter further includes nine branchswitches each of which is arranged in a corresponding one of the nine branches. The controller is configured to, in the case that a fault occurs in at least one of the nine branches, control one or more of the nine branch switches to clear the fault.

[0009] In an embodiment, the converter is a matrix converter, and includes six branches each including one or more modules and a branch inductor connected in series to the one or more modules . Each branch has a first end coupled to one of three phases a, b, c of a first terminal of the matrix converter and a second end coupled to one of three phases x, y, z of a second terminal of the matrix converter. The six branches comprise first to sixth branches. First ends of the first and sixth branches are coupled to the phase a of the first terminal, and second ends of the first and second branches are coupled to the phase x of the second terminal . First ends of the second and third branches are coupled to the phase b of the first terminal, and second ends of the third and fourth branches are coupled to the phase y of the second terminal . First ends of the fourth and fifth branches are coupled to the phase c of the first terminal, and second ends of the fifth and sixth branches are coupled to the phase z of the second terminal .

[0010] In an embodiment, the converter is a matrix converter, and includes twelve branches each comprising one or more modules and a branch inductor connected in series to the one or more modules . The twelve branches comprises first to sixth branches forming a first part and seventh to a twelfth branches forming a second part. Each branch of the first part has a first end coupled to one of three phases a, b, c of a first terminal of the matrix converter, and each branch of the second part has a first end coupled to one of three phases x, y, z of a second terminal of the matrix converter . First ends of the first and fourth branches are coupled to the phase a of the first terminal, first ends of the second and fifth branches are coupled to the phase b of the first terminal, and first ends of the third and sixth branches are coupled to thephase c of the first terminal . First ends of the seventh and tenth branches are coupled to the phase x of the second terminal, first ends of the eighth and eleventh branches are coupled to the phase y of the second terminal, and first ends of the ninth and twelfth branches are coupled to the phase z of the first terminal . Each of the first to the third branches has a second end coupled to a first connection point, and each of the seventh to the ninth branches has a second end coupled to the first connection point. Each of the fourth to the sixth branches has a second end coupled to a second connection point, and each of the tenth to the twelfth branches has a second end coupled to the second connection point.

[0011] In an embodiment, the converter is a matrix converter, and includes six branches each comprising one or more modules and a branch inductor connected in series to the one or more modules . The six branches comprise first to sixth branches each of which has a first end coupled to one of three phases a, b, c of a first terminal of the matrix converter. First ends of the first and fourth branches are coupled to the phase a of the first terminal . First ends of the second and fifth branches are coupled to the phase b of the first terminal, and first ends of the third and sixth branches are coupl ed to the phase c of the first terminal . Each of the first to third branches has a second end coupled to a first connection point, and each of the fourth to sixth branches has a second end coupled to a second connection point.

[0012] In an embodiment, the converter system further includes a plurality of filters each coupled between one of the plurality of second converter units and one of the plurality of DC units.

[0013] In an embodiment, the converter system further includes a transformer unit coupled between the first converter and the plurality of second converter units.

[0014] In an embodiment, the transformer unit comprises a plurality of transformers each coupled between the first converter and one of the pluralityof second converter units.

[0015] In an embodiment, the transformer unit includes one transformer having one primary winding and a plurality of secondary windings each coupled to one of the plurality of second converter units.

[0016] In an embodiment, the controller is configured to receive feedback information from at least one of the first converter, at least one of the plurality of second converter units and a DC unit coupled with the at least one second converter unit and to control at least one of the first converter and the at least one second converter unit based on the feedback information.

[0017] In an embodiment, the converter system is operable to operate in one of the following operation modes : a first operation mode where power is transferred from an AC source coupled with the first side of the first converter to one or more of the plurality of DC units; a second operation mode where power is transferred from one or more DC sources of the plurality of DC units to the first AC side; a third operation mode where at least one of the plurality of second converter units is configured to receive power from both the first converter and at least another one of the plurality of second converter units; and a fourth operation mode where at least one of the plurality of second converter units is configured to receive power from at least another one of the plurality of second converter units or from both the first converter operating by isolating at least one faulty branch from the plurality of the branches and said at least another second converter unit.

[0018] In an embodiment, the controller is comprised in the first converter.

[0019] In an embodiment, the plurality of second converters have a common local controller, and wherein the controller is comprised in the common local converter.

[0020] In an embodiment, the first converter comprises a local control unit, and each of the plurality of second converter units comprises a local controlunit. The controller is in communication with each local control unit for cooperative control of the first converter and the plurality of second converter units.

[0021] In an embodiment, the controller is configured to control at least one of the first converter and at least one second converter unit such that at least one of a voltage and a current for providing power to or receive power from at least one of the plurality of DC units is regulated based on a configured regulation value and operation mode for the converter system.

[0022] In an embodiment, the controller is configured to, in the case that the converter system is operated in the third operation mode, determine according to a preset configured value the amount of power to be received from the first converter and the amount of power to be received from said at least another second converter unit.

[0023] According to another aspect of the present invention, a control method for controlling a converter system is provided. The converter system includes a first converter and a plurality of second converter units, the first converter having a first AC side with a first frequency and a second AC side with a second frequency, the first converter comprising a converter having a plurality of branches, the plurality of second converter units being configurable to be coupled between the first converter and a plurality of DC units, each of the plurality of DC units being a DC load or a DC source. The method includes controlling at least one of the first converter and at least one second converter unit to control power supplied to or by at least one of the plurality of DC units.

[0024] According to yet another aspect of the present invention, a power supply system for powering an electrolyzer is provided. The powering system includes the converter system described above.BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The following description of figures of examples or embodiments may further illustrate and explain aspects of the converter system and the control method. Arrangements, devices, modules and blocks with the same structure and the same effect, respectively, appear with equivalent reference symbols. In so far as arrangements, devices, modules and blocks correspond to one another in terms of their function in different figures, the description thereof is not repeated for each of the following figures.

[0026] Figure 1 is schematic block diagram of a converter system according an embodiment of the present invention.

[0027] Figures 2~8 show examples of the converter system of Figure 1.

[0028] Figures 9~ 12 are exemplary circuits of the first converter of the converter system in Figure 1 .

[0029] Figures 13- 15 are exemplary circuits of the second convert unit of the converter system in Figure 1.

[0030] Figure 16 is schematic flowchart of a control method according to an embodiment of the present invention.

[0031] Figures 17-21 show examples of the main step of the control method illustrated in Figure 16.DETAILED DESCRIPTIONOverview

[0032] Examples of the present invention relate to a converter system and a control method for controlling the converter system. The converter system includes a first converter coupled with an AC source, a second converter coupled between the first converter and a plurality of DC units, and a controller for controlling at least one of the first converter and the secondconverter. Each of the plurality of DC units is a DC load or a DC source. The controller controls the converter system according to feedback information from at least one of the first converter, the second converter, and at least one DC unit, so that the converter system can provide the most suitable conversion for a DC application under the current scenario.

[0033] The converter system has four operation modes. The converter system is operable to operate in one of the four operation modes. The four operation modes include first to fourth operation modes. The first operation mode is where power is transferred from an AC source coupled with the first side of the first converter to one or more of the plurality of DC units. The second operation mode is where power is transferred from one or more DC sources of the plurality of DC units to the first AC side. The third operation mode is where at least one of the plurality of second converter units is configured to receive power from both the first converter and at least another one of the plurality of second converter units. The fourth operation mode is where at least one of the plurality of second converter units is configured to receive power from at least another one of the plurality of second converter units or from both the first converter operating by isolating at least one faulty branch from the plurality of the branches and said at least another second converter unit.

[0034] The first to third operation modes can be applied to a scenario where a grid coupled with the AC source is a normal operation state and thus the first to third operation modes can be seen as normal modes. The fourth operation can be applied to a scenario where the grid or at least one module comprised in a branch of the first converter is in a fault state and thus the fourth operation mode can be seen as a fault mode.

[0035] S uch a converter system has the advantages of compact structure, high intelligence and low cost.

[0036] In an example, the converter system is a transformer free system, which allows for flexibility in connection and handling fault conditions.

[0037] In an example, the first converter has a plurality of branches each ofwhich can be controlled to provide power transmission. In this way, by controlling one branch of the plurality of branches, excess power can be transferred to a DC unit coupled with said one branch. This is especially meaningful when the DC unit is an energy storage such as a storage battery.Example systems

[0038] Figure 1 schematically shows a converter system 100 according to an embodiment of the present invention. The converter system 100 is coupled between an AC source 200 and a plurality of DC units 301 ~30n.

[0039] Referring to Figure 1 , the AC source 200 is, for example, a medium voltage AC source (MVAC). As indicated by a block connected with the AC source 200 via a dashed line, the AC source 200 can be coupled to an AC grid via a transformer, a DC grid via a DC-AC converter, or a renewable energy via a DC-AC converter or an AC -AC converter.

[0040] The plurality of DC units can include one or more DC loads such as one more electrolyzers. In an example, one DC load can be implemented as including one electrolyzer (e.g., the DC load 301 ). One DC load can also be implemented as including a plurality of electrolyzers connected in series or in parallel or a combination thereof (e.g. , the DC load 30n) . The plurality of DC units can also include one or more DC sources which are used as energy storage components. The DC sources can include one or more of a PV, a battery, a fuel cell or a bi-directional electrolyzer.

[0041] The converter system 100 can convert an alternating current (AC) from the AC source 200 into a direct current (DC) which is suitable for powering DC loads. The converter system 100 can also convert a direct current (DC) from a DC source into an alternating current (AC) and transfer the AC to the AC source 200. The converter system 100 can al so be operated to provide energy stored in an energy storage device functioning as a DCsource to a DC load.

[0042] The converter system 100 has four operation modes (i . e., first to fourth operation modes) each of which is introduced in the below.

[0043] In the case where the converter system 100 operates in the first operation mode, an AC from the AC source 200 is converted into a DC to power a DC load. For example, in the first operation mode, the converter system 100 is operated to power an electrolyzer.

[0044] In the case where the converter system 100 operates in the second operation mode, energy stored in one or more DC sources is delivered to the AC source 200. In an application scenario of the second operation mode, energy stored in an EV (electric vehicle) or a battery energy storage system can be returned to the AC source 200 or other equipment. In another application scenario of the second operation mode, energy stored in a renewable energy source can be delivered to the AC source 200. In an example, in the second operation mode, the converter system 100 is operated as a distributed grid-connected inverter system.

[0045] In the case where the converter system 100 operates in the third operation mode, a DC load can be powered by both the AC source 200 and one or more DC sources. In this case, the third operation mode can be referred to as a mixture mode and is especially suitable for the one or more DC source being renewable sources. For example, in the third operation mode, an electrolyzer is powered as much as possible by a renewable source and also can be supplemented by the AC source 200.

[0046] In the case where the converter system 100 operates in the fourth operation mode, the DC load can be powered by one or more DC sources . This can be applied to a fault condition. Examples of applying the fourth operation mode to the fault condition are described below.

[0047] In an example, when the grid coupled with the AC source 200 i s in afault state or temporarily not available and therefore the AC source 200 cannot provide power supply to the DC load, in this case, the one or more DC sources can power the DC load and thus the powering of the DC load can be maintained for a period of time. For some DC loads, such as electrolyzers, if there is a sudden power failure or the power supplied is less than a certain percentage of the rated power, the DC loads need to be restarted. In this case, operating the converter system 100 in the fourth operation mode can solve this problem.

[0048] In another example, a fault happens in at least one branch of the first converter (e.g. , a fault where one or more branches is a faulty branch, or a fault where one or more modules of one branch are faulty modules and thus said one branch is a faulty branch). In this case, the first converter is operated to isolate the faulty branch. The DC load can receive power from the first converted isolating the faulty branch and one or more DC sources. This is to say, at least one of the plurality of second converter units receives power from both the first converter isolating the faulty branch and at least another one of the plurality of second converter units.

[0049] With continuing reference to Figure 1 , the converter system 100 includes a first converter 10, a second converter 20 cascaded with the first converter 10, and a controller 30 in communication with the first converter 10, the second converter 20 and the plurality of DC units.

[0050] The first converter 10 has a first AC side 10A and a second AC side 10B . The first AC side 10A provides a first AC with a first frequency (fl ) . The second AC side 10B provides a second AC with a second frequency (f2). The first converter 10 can convert the first AC with the first frequency into the second AC with the second frequency. The first converter 10 can also converter the second AC with the second frequency into the first AC with the first frequency. The first converter 10 is an AC -AC converter. The first converter 10 i s, for example, includes a matrix converter having a plurality ofbranches.

[0051] The second converter 20 is coupled between the first converter 10 and the plurality of DC units 301 ~30n. The second converter 20 includes a plurality of second converter units 21 ~2n. The plurality of second converter units can be implemented as individual converters, and also can be integrated as a modular converter. In an example, each second converter unit is implemented as a rectifier and performs AC -DC conversion (e.g., the converter system 100 operates in the first operation mode) . In another example, each second converter unit is implemented as an inverter and performs DC-AC conversion (e.g., the converter system 100 operates in the second operation mode) . In yet another example, the plurality of second converter units includes one or more rectifiers and one or more inverters (e.g., the converter system 100 operates in the third operation mode) .

[0052] Each of the plurality of second converter units is coupled between the first converter 10 and a DC load or a DC source. Each of the plurality of second converter units has a first end coupled with the first converter 10 and a second end coupled with a DC load or a DC source. For example, as shown in Figure 1 , the second converter unit 21 has a first end 21 A coupled with the first converter 10 and a second end 21B coupled with the DC load 301 ; the second converter unit 22 has a first end 22A coupled with the first converter 10 and a second end 22B coupled with the DC source 302 ... the second converter unit 2n has a first end 2nA coupled with the first converter 10 and a second end 2nB coupled with the DC load 30n. It is noted that each of the plurality of second converter units 21 ~2n can be coupled to the first convertor 10 via an AC bus or directly.

[0053] In an example, an on / off switch can be provided between a second converter unit and a DC unit coupled with the second converter unit so that the DC unit can be disconnected from the converter system 100 by operating the on / off switch.

[0054] Examples of a second converter unit are introduced below.

[0055] In an example, the second converter unit can be implemented as a thyristor-based rectifier which is a semi-controlled component. In this example, the second converter unit can supply an adjustable DC voltage to a DC load such as an electrolyzer.

[0056] In another example, the second converter unit can be implemented as a diode-based rectifier which is a non-controllable component. In this example, the second converter unit can supply a fixed DC voltage (i . e. , a non- adjustable DC voltage) to a DC load such as an electrolyzer.

[0057] In yet another example, the second converter unit is implemented as including a diode-based rectifier and a DC-DC converter coupled with the diode-based rectifier where the diode-based rectifier is a non-controllable component and the DC-DC converter is a controlled component. In this example, the second converter unit can supply an adjustable DC voltage to a DC load such as an electrolyzer.

[0058] In yet another example, the second converter unit is implemented as an active rectifier. In this example, the second converter unit is capable of providing both AC-DC conversion in one direction (i .e. act as a rectifier) and DC-AC conversion in the other direction (i . e. act as an inverter).

[0059] It is noted that the plurality of second converter units can include two or more types of converters as described above.

[0060] The controller 30 controls the first converter 10 and / or at least one second converter unit based on feedback information. The feedback information can include measurement information (e.g., a measured current and / or a measure voltage) measured by sensors (e.g., current sensors and / or voltage sensors) arranged in the converter system 100. For clarity, the sensors are shown in Figure 2 by gray hollow circles and gray solid circles . As shown in Figure 2, the sensors are arranged in the converter system 100and thus the feedback information can be generated inside the converter system 100. The feedback information can also include state information obtained by a state monitoring system (not shown) for monitoring a state of each of the plurality of DC units. The monitoring system can include a plurality of monitoring units each of which is coupled with one of the plurality of DC units and monitors a state of the coupled DC unit .

[0061] It is noted that the state of each DC unit can also be determined based on the measurement information (for example, a measured voltage and / or a measured current measured at a branch between each second converter unit and a corresponding DC unit) and thus the state of each DC unit can also be obtained inside the converter system 100.

[0062] In an example, the feedback information includes one or more of: 1 ) feedback information from the first side 10A of the first converter 10 (e.g., a measured current and / or a measure voltage measured at the first side 10A); 2) feedback information from each of the plurality of branches of the matrix converter (e.g., a measured current measured at each of the plurality of branches of the matrix converter); 3) feedback information from the second side 10B of the first converter 10 (e.g. , a measured current and / or a measure d voltage measured at the second side 10B); 4) feedback information from each branch connecting the first converter 10 and each of the plurality of second converter units (e.g. , a measured current and / or a measured voltage at each branch connecting the first converter 10 and each of the plurality of second converter units); 5) feedback information from each branch connecting each of the plurality of second converter units and a corresponding DC unit (e.g. , a measured current and / or a measured voltage measured at each branch connecting each of the plurality of second converter units and a corresponding DC unit); 6) feedback information from one or more of the plurality of DC units (e.g. , a state of each DC unit detected by a state monitoring system associated with the plurality of DC units). In the case thata DC load is an electrolyzer, a state of the electrolyzer can include an aging degree, an aging speed, a hydrogen production rate and an operating efficiency of the electrolyzer. The state of the electrolyzer can be determined by calculation of a current and a voltage of the electrolyzer.

[0063] The controller 30 can provide a first control signal C S_1 to the first converter 10 based on the received feedback information to control the conversion operation of the first converter 10. For example, under the control of the first control signal, the first converter 10 is operated to convert the first AC of the first side 10A to the second AC of the second side 10B or convert the second AC of the second side 10B to the first AC of the first side 10A.

[0064] The controller 30 can provide the second control signal C S_2 to the second converter 20 based on the received feedback information to control conversion operation of each of the purity of second converter units of the second converter 20. For example, under the control of the second control signal, each of the plurality of the second converter units is operated to perform a rectification operation or an inversion operation. In the case where a second converter unit is implemented as a controllable device, a DC voltage of output from the second converter unit can be adjusted under the control of the second control signal .

[0065] In an example, as shown in Figure 3 , the controller 30 is implemented as a high-level controller (for example, a central controller) , the first converter 10 includes a local control unit 1 1 , and each second converter unit includes a local control unit. For example, the second converter unit 21 includes a local control unit 21 1 , the second converter unit 22 includes a local control unit 221 ... the second converter unit 2n includes the control unit 2n l . In this example, the controller 30 is communicatively connected with the local control unit 1 1 of the first converter 10 to send the first control signal to the local control unit 1 1 and the local control unit 1 1 manipulatesthe first converter 10 according to the first control signal . The controller 30 is communicatively connected with the local control unit of each second converter unit to send the second control signal to the local control unit and the local control unit manipulates the second converter unit according to the second control signal . In this way, coordinated control of the first and second converters can be realized. Moreover, independent control of the powering of each DC load can also be realized. In thi s example, the controller 30 and the local control units can form a distributed control system.

[0066] In another example, the controller 30 is comprised in the first converter 10. For example, the controller 30 is integrated with the local control unit 1 1 of the first converter 10. In thi s way, the local control unit of the first converter can control the first converter 10 and can also control the plurality of second converter units 21 ~2n.

[0067] In yet another example, the plurality of second converter units 21 ~2n have a common local controller (not shown). In an embodiment of this example, the controller 30 is comprised in the common local controller. In this way, the common local controller can control the plurality of second converter units 21 ~2n and can also control the first converter 10.

[0068] According to various configurations of the controller, the local control units and the common local controller, corporative control of the converter system 100 can be realized by at least one control signal to operate the first converter and / or one or more of second converter units.

[0069] The controller 30 can be implemented by means of hardware or software or a combination of hardware and software, including code stored in a non-transitory computer-readable medium such as a memory and implemented as instructions executed by a processor. Regarding the part implemented by means of hardware, it may be implemented in an application specific integrated circuit (ASIC), a digital signal processor (DSP), a data signal processing device (DSPD), a programmable logic device (PLD), a fieldprogrammable gate array (FPGA), a processor, a controller, a microcontroller, a microprocessor, an electronic unit, or a combination thereof. The part implemented by software may include a microcode, a program code or code segments. The software may be stored in a machine-readable storage medium, such as a memory.

[0070] In an example, the controller 30 includes a memory and a processor. Instructions are stored in the memory. The instructions, when executed by the processor, cause the processor to execute control methods according to examples of the present invention.

[0071] Examples of the converter system 100 are shown in Figures 4~8.

[0072] According to examples of the present invention, as shown in Figures 4 and 5, the converter system 100 further includes a transformer unit 40 coupled between the first converter 10 and the second converter 20. Such a configuration of the converter system 100 is beneficial . For example, in the case where the first converter 10 is operated to convert the first AC of the first side 10A to the second AC of the second side 10B, the first side 10A is an input side and the second side 10B is an output side. The output voltage of the first converter 10 has an optimal voltage, that is, the first converter 10 has an optimal output voltage . Moreover, the output voltage of the first converter 10 needs to match an output voltage of the second converter 20 because the converter system 100 needs to provide a voltage that is suitable for powering DC loads. In the case that the converter system 100 includes the transformer unit 40 coupled between the first converter 10 and the second converter 20, the optimal output voltage of the first converter 10 can be realized because the optimal output voltage can used as an input voltage of the transformer unit 40 and the above-mentioned voltage matching can be realized with the help of the transformer unit 40.

[0073] Referring to Figure 4, in an example, the transformer unit 40 includes a plurality of transformers 41 ~4n. Each of the plurality oftransformers is coupled between the first converter 10 and one of the plurality of second converter units. For example, the transformer 41 is coupled between the first converter 10 and the second converter unit 21 ; the transformer 42 is coupled between the first converter 10 and the second converter unit 22 ... the transformer 4n is coupled between the first converter 10 and the second converter unit 2n. In this example, the number of transformers of the transformer unit 40 is equal to the number of second converter units of the second converter 20.

[0074] Referring to Figure 5, in another example, the transformer unit 40 includes a multi-winding transformer 401. The multi-winding transformer 401 includes a primary winding 4010 and a plurality of secondary windings 401 1 ~401 n. Each of the plurality of secondary windings is coupled to one of the plurality of second converter units. In this example, the number of the secondary windings of the multi -winding transformer is equal to the number of the second converter units.

[0075] It is noted that examples of Figures 4 and 5 can be combined. For example, the transformer unit 40 can include a plurality of transformers arranged as shown on Figure 4 and a multi-winding transformer arranged as shown in Figure 5 .

[0076] According to an example of the present invention, as shown in Figure 6, the converter system 100 further includes a filter unit 50. The filter unit 50 includes a plurality of filers 51 ~5n. Each of the plurality of filers 51 ~5n is coupled between one of the plurality of second converter units and a DC load or a DC source. For example, the filter 51 is coupled between the second converter unit 21 and the DC load 301 ; the filter 52 is coupled between the second converter unit 22 and the DC source 302 ... the filter 5n is coupled between the second converter 2n and the DC load 30n. Each filter filters the de ripple on a DC voltage supplied to a DC load or a DC source. In the case wherein a filter is connected to an electrolyzer, the filter isdesigned / selected according to a requirement regarding the DC ripple of the electrolyzer (e.g. , <5%).

[0077] According to examples of the invention, the converter system 100 further includes both a transformer unit and a filter unit.

[0078] In an example, as shown in Figure 7, the converter system 100 further includes both a transformer unit and a filter unit. In this example, the transformer unit can be implemented by means of the transformer unit 40 of Figure 4 and the filter unit can be implemented by means of the filter unit 50 of Figure 6. For thi s reason, various features describ ed above with reference to the transformer unit 40 of Figure 4 and the filter unit 50 of Figure 6 are also applicable in the exemplary converter system 100 of Figure 7.

[0079] In another example, as shown in Figure 8, the converter system 100 further includes both a transformer unit and a filter unit. In this example, the transformer unit can be implemented by means of the transformer unit 40 of Figure 5 and the filter unit can be implemented by means of the filter unit 50 of Figure 6. For this reason, various features described above with reference to the transformer unit 40 of Figure 5 and the filter unit 50 of Figure 6 are also applicable in the exemplary system 100 of Figure 8.

[0080] The first frequency fl and the second frequency f2 are described below.

[0081] The first frequency fl is at the power frequency, for example, 50Hz or 60Hz.

[0082] The second frequency f2 is greater than the first frequency fl . In an example, the second frequency i s predetermined to be in the range of 100Hz~ 10kHz based on an optimal design and with the purpose of minimizing the system cost. Experimental results and model calculation show that when the second frequency is within such a frequency range, the size of the transformer (e.g., each transformer or the multi -winding transformer of thetransformer unit) is greatly reduced, and the needs for filtering DC ripples can be reduced so that it is feasible to implement the converter syst em without providing the filter unit or providing the filter unit of low cost. Moreover, power loss caused by on and off operations of power switches of the first converter and the second converter will not be too much to reduce the system efficiency. The second frequency can be pre-determined by experiments and / or model calculation so that the system is cost effective and also applicable to the current DC application scenario .

[0083] Examples of the matrix converter are described below.

[0084] According to examples of the present invention, the matrix converter has a first terminal coupled with the first side 10A of the first converter 10 and a second terminal coupled with the second side 10B of the first converter 10. The matrix converter can convert a first AC into a second, single phase or multi-phase AC. The first terminal is coupled to a first phase system, for example, three phases (a, b, c). The second terminal is coupled to a second phase system, for example, three phases (x, y, z), or a two-phase AC or a single-phase AC .

[0085] In an example, the first terminal of the matrix converter is coupled to at least two phases. The matrix converter includes a plurality of branches. The plurality of branches include at least two sets of branches, namely, a first set of branches and a second set of branches. The first set of branches includes branches that are coupled with one phase of the at least two phases, and the second set of branches includes branches that are coupled with the other phase of the at least two phases. For example, the first set of branches includes branches that are coupled with one phase of the three phases (a, b, c), and the second set of branches includes branches that are coupled with any one of the remaining two phases of the three phases (a, b, c) . Moreover, one branch of the first set of branches is configured to be combined phase wise or potential wise to a corresponding branch comprised in the second set.

[0086] Figure 9 shows an exemplary circuit of the matrix converter according to an example of the invention.

[0087] Referring to Figure 9, the matrix converter includes nine branches each including one or more modules (B l l ~B l n) and a branch inductor (i . e., branch reactor) connected in series to the one or more modules (B l l ~B l n) . Each of the one or more modules can be implemented as a full bridge circuit. Each branch has a first end coupled to one of three phases a, b, c of the first terminal of the matrix converter and a second end coupled to one of three phases x, y, z of the second terminal of the matrix converter. The nine branches includes first to ninth branches (Branches 1~9). First ends of the first, second and third branches are coupled to the phase a of the first terminal . Second ends of the first, fourth and seventh branches are coupled to the phase x of the second terminal . First ends of the fourth, fifth and sixth branches are coupled to the phase b of the first terminal . Second ends of the second, fifth and eighth branches are coupled to the phase y of the second terminal . First ends of the seventh, eighth and ninth branches are coupled to the phase c of the first terminal . Second ends of the third, sixth and ninth branches are coupled to the phase z of the second terminal .

[0088] In this example, the matrix converter can further includes nine branch switches each of which is arranged in one of the nine branches . The branch switches can be operated for protection in a fault condition . For example, it can be implemented with the fourth operation mode of the converter system that is described elsewhere in this invention .

[0089] For example, in the case where a fault occurs in at least one of the first, fifth and ninth branches, branch switches in the first, fifth and ninth branches are operated to open by the controller or manually. In this way, the matrix converter can still work under the fault condition. Similarly, in the case that a fault occurs in at least one of the second, sixth and seventh branches, branch switches in the second, sixth and seventh branches areoperated to open by the controller or manually . In this way, the matrix converter can still work under the fault condition. Similarly, in the case that a fault occurs in at least one of the third, fourth and eighth branches, branch switches in the third, fourth and eighth branches are operated to open by the controller or manually. In this way, the matrix converter can still work under the fault condition. Though, in this example the fault condition is described in a specific branch, a person skilled in the art will be able to appreciate that when a fault is sensed in any of the module in a branch, the controller can operate the first converter to isolate the faulty branch and operate the first converter through the other phase wise or voltage wise related branches.

[0090] Figure 10 shows an exemplary circuit of the matrix converter according to another example of the invention.

[0091] Referring to Figure 10, the matrix converter includes six branches each including one or more modules (B l l ~B l n) and a branch inductor connected in series to the one or more modules. Each of the one or more modules can be implemented as a full bridge circuit. Each branch has a first end coupled to one of three phases a, b, c of the first terminal of the matrix converter and a second end coupled to one of three phases x, y, z of the second terminal of the matrix converter. The six branches include first to sixth branches (Branches 1~6). First ends of the first and sixth branches are coupled to the phase a of the first terminal . Second ends of the first and second branches are coupled to the phase x of the second terminal . First ends of the second and third branches are coupled to the phase b of the first terminal . Second ends of the third and fourth branches are coupled to the phase y of the second terminal . First ends of the fourth and fifth branches are coupled to the phase c of the first terminal . Second ends of the fifth and sixth branches are coupled to the phase z of the second terminal .

[0092] Figure 1 1 shows an exemplary circuit of the matrix converter according to yet another example of the invention.

[0093] Referring to Figure 1 1 , the matrix converter includes twelve branches each including one or more modules (B l l ~B l n) and a branch inductor connected in series to the one or more modules . Each of the one or more modules can be implemented as a half bridge circuit. The twelve branches includes first to sixth branches (Branches 1~6) forming a first part and seventh to a twelfth branches (Branches 7~ 12) forming a second part. Each branch of the first part has a first end coupled to one of three phases a, b, c of the first terminal of the matrix converter. Each branch of the second part has a first end coupled to one of three phases x, y, z of the second terminal of the matrix converter. First ends of the first and fourth branches are coupled to the phase a of the first terminal . First ends of the second and fifth branches are coupled to the phase b of the first terminal . First ends of the third and sixth branches are coupled to the phase c of the first terminal . First ends of the seventh and tenth branches are coupl ed to the phase x of the second terminal . First ends of the eighth and eleventh branches are coupled to the phase y of the second terminal . First ends of the ninth and twelfth branches are coupled to the phase z of the first terminal . Each of the first to the third branches has a second end coupled to a first connection point (which are at a same potential, and thereby the branches are said to be combined together based on potential at the connection point) . Each of the seventh to the ninth branches has a second end coupled to the first connection point . Each of the fourth to the sixth branches has a second end coupled to a second connection point. Each of the tenth to the twelfth branches has a second end coupled to the second connection point. In this example, the first connection point can be a positive terminal of a DC bus and the second connection point can be a negative terminal of the DC bus. In general terms, it can be said that one branch of the first set of branches is configured to be combined potential wise to a corresponding branch comprised in the second set at the first and second connection points.

[0094] Figure 12 shows an exemplary circuit of the matrix converteraccording to yet another example of the invention.

[0095] Referring to Figure 12, the matrix converter includes six branches each including one or more modules (B l l ~B l n) and a branch inductor connected in series to the one or more modules. Each of the one or more modules can be implemented as a full bridge circuit. The six branches includes first to sixth branches (Branches 1~6) each of which has a first end coupled to one of three phases a, b, c of a first terminal of the matrix converter. First ends of the first and fourth branches are coupled to the phase a of the first terminal . First ends of the second and fifth branches are coupled to the phase b of the first terminal . First ends of the third and sixth branches are coupled to the phase c of the first terminal . Each of the first to third branches has a second end coupled to a first connection point. Each of the fourth to sixth branches has a second end coupled to a second connection point. In this example, the first connection point can be a positive terminal of a DC bus and the second connection point can be a negative terminal of the DC bus. The first connection point and the second connection point configure a single phase of the second AC.

[0096] Exemplary circuits of a second converter unit are described below. For clarity, the exemplary circuits are described taking the second converter unit 21 as an example. Other second converter units can be implemented in a similar way.

[0097] Figure 13 show an exemplary circuit of the second converter unit 21 according to an example of the present invention. As shown in Figure 13 , the second converter unit 21 is implemented as a three-phase thyristor rectifier. In this example, the second converter unit 21 is coupled with the filter 51 which is a DC filter. The filter 5 1 includes an inductor and / or one or more capacitors. The filter 51 is coupled between the second converter unit 21 and the DC load 301 to filter out DC ripples.

[0098] Figure 14 show an exemplary circuit of the second converter unit 21according to another example of the present invention. As shown in Figure14, the second converter unit 21 i s implemented as a three-phase IGBT-based voltage source converter (VSC) . In this example, the second converter unit 21 is coupled with the filter 51 which is a DC filter. The filter 51 includes one or more capacitors. The filter 51 is coupled between the second converter unit 21 and the DC load 301 to filter out DC ripples.

[0099] Figure 15 show an exemplary circuit of the second converter unit 21 according to another example of the present invention. As shown in Figure15, the second converter unit 21 is implemented as a three-phase diode rectifier in combination with a buck converter. In an example, the diode rectifier performs the AC / DC conversion and the buck converter is operated to adjust an output voltage or current based on requirements of powering of the DC load 3 1 . The filter 51 is a DC filter 51 and includes one or more capacitor. The filter 51 is coupled between the second converter unit 21 and the DC load 301 to filter out DC ripples.Example methods

[0100] Further to example systems described above, example methods are now described. Such methods can be performed using the controller 30 described above. It should be understood that the operations involved in the following methods do not need to be performed in the precise order described. Rather, various operations may be performed in a different order or simultaneously, and operations may be added or omitted.

[0101] Figure 16 shows a control method 1600 for controlling the converter system 100 according to an embodiment of the present invention .

[0102] In block 1610, the controller 30 receives feedback information from at least one of the first converter, at least one of the plurality of second converter units and a DC unit coupled with the at least one second converterunit. In an example, the feedback information include s measurement information obtained by current sensors and / or voltage sensors arranged in the converter system 100. It is noted that the various features described above with reference to the feedback information are also applicable here.

[0103] In block 1620, the controller 30 controls at least one of the first converter 10 and at least one second converter unit based on the feedback information to control power supplied to or by the DC unit. For example, the controller 30 controls at least one of the first converter and at least one second converter unit such that at least one of a voltage and a current for providing power to or receive power from at least one of the plurality of DC units is regulated based on a configured regulation value and operation mode of the converter system. In this way, regulating at least one of the voltage and current supplied to a DC unit to cope with changes in the demand at the load side, i . e. , loading the DC unit can be realized by controlling at least one of the first converter and at least one second converter unit. Moreover, the configured regulation value is the value used to configure the controller for the above-mentioned regulation, and coordinated controlling the first converter and at least one second converter unit by the techniques provide in the invention can also help to improve the precision of the regulation.

[0104] Examples of the controlling in block 1620 are described below.

[0105] Fi gure 17 shows an example (method 1700) of block 1620. In this example, the converter system 100 is operated in the first operation mode. For clarity, this example will be described by taking powering the DC load 301 with the first converter 10 and the second converter unit 21 as an example. In this example, the DC load 301 is powered by the AC source 200.

[0106] Referring to Figure 17, in block 1710, the controller 30 control s the first converter 10 to convert the first AC of the first side 10A to the second AC of the second side 10B, and control s the second converter unit 21 to work as a rectifier (i .e., perform AC-DC conversion).

[0107] In block 1720, the controller 30 determines an amount of voltage regulation for a voltage supplied to the DC load 301 and / or an amount of current regulation for a current supplied the DC load 301 based on the feedback information. For example, according to the demand of the current application to which the converter system is applied, the voltage supplied to the load 301 needs to be increased by 10%, and this demand can be included in the feedback information. In this case, the controller 30 determines to increase the voltage supplied to the DC load 301 by 10% based on the feedback information.

[0108] In block 1730, the controller 30 judges whether the determined amount of voltage regulation and / or the determined amount of current regulation can be achieved by the first converter 10 to achieve a configured regulation value for the first converter 10. In an example, the configured regulation value (predetermined regulation value) of the first converter 10 can include the above-mentioned the amount of voltage regulation and / or the amount of current regulation, and may also include a calibration value for realizing the amount of voltage regulation and / or the amount of current regulation (e.g. line regulation). There is a situation where the configured regulation value of the first converter 10 may be equal to the minimum regulation value that is achievable by the first converter 10 (i .e., the configured regulation value is the achievable limit value of the regulation accuracy of the first converter). In this situation, the controller 30 judges whether the first converter is able to achieve the configured regulation value. For example, the controller 30 can determine whether the accuracy value of voltage regulation of the first converter satisfies the determined amount of voltage regulation or a line regulation value of the first converter 10. Similarly, the controller 30 can determine whether the accuracy value of current regulation of the first converter satisfies the determined amount of current regulation or a line regulation value of the first converter 10.

[0109] It is noted that the minimum regulation value that is achievable by the first converter 10 corresponds to the regulation accuracy of the first converter. The minimum regulation value can be preset. For example, the minimum regulation value is set equal to the sum of a minimum regulation value determined based on the device performance of the first converter and an offset, which can be predetermined according to the current application scenario.

[0110] If the judgement in block 1730 is negative (“NO”), that i s, it is judged that determined amount of voltage regulation and / or the determined amount of current regulation cannot be achieved by the first converter 10, the method 1700 proceeds to block 1740. In block 1740, the controller 30 controls the second converter unit 21 to adjust an output current and / or an output voltage of the second converter unit 21 by the amount of voltage regulation and / or the determined amount of current regulation.

[0111] If the judgement in block 1730 is positive (“YES”), that i s, it is judged that determined amount of voltage regulation and / or the determined amount of current regulation can be achieved by the first converter 10 , the method 1700 proceeds to block 1750. In block 1750, the controller 30 controls the first converter 10 to adjust an output current and / or an output voltage of the first convert 10 by the determined amount of voltage regulation and / or the determined amount of current regulation .

[0112] In block 1760, the controller 30 controls the second converter unit 21 to compensate a difference between the determined regulation and the regulation achieved by the first converter 10 such that the accuracy of the voltage regulation and / or the current regulation is improved.

[0113] For example, it i s determined to increase the voltage supplied to the DC load 301 by 100V. The controller 30 compares the determined amount of voltage regulation (e.g., 100V) with the amount of voltage regulation (e.g., 90V) achieved by the first converter 10 to obtain a difference (e.g., 10V)between them. Then, the controller 30 controls the second converter unit 21 to increase an output voltage of the second converter unit by 10V such that the difference is compensated. In thi s way, the voltage regulation and / or the current regulation can be realized with higher accuracy.

[0114] It is noted that the control of the first converter can be seen as a first level control to fairly accurate the required regulation. The regulation achieved by the second converter unit can be seen as a fine-tuning to improve the accuracy.

[0115] Alternatively, the first converter and at least one second converter can be controlled simultaneously based on a configured regulation value. The regulation value is configured based on the amount of voltage regulation and / or the amount of current regulation and further based on a preset reference value for improving the accuracy.

[0116] In this way, the cooperative control of the converter system 100 is realized. This is beneficial because there are situations where the first converter cannot be relied on to achieve the determined regulation due to the limitation of the minimum regulation ability of the first converter 10. Moreover, the fine-tuning function of the second converter unit can be utilized. According to the control strategy of method 1700, various regulation situations can be dealt with, and the accuracy of regulation under various regulation situations can be improved.

[0117] Fi gure 18 shows another example (method 1800) of block 1620. In thi s example, the converter system 100 i s operated in the first operation mode and used to power a plurality of electrolyzers. For clarity, this example is described for powering electrolyzers 301 and 30n with the first converter 10, the second converter unit 21 and the second converter unit 2n as an example. The distributed control system described above in conjunction with Figure 3 is especially suitable for the implementation of method 1800.

[0118] Referring to Figure 18, in block 1810, the controller 30 controls thefirst converter 10 to convert the first AC of the first side 10A to the second AC of the second side 10B, control s the second converter unit 21 to work as a rectifier (i .e., perform AC-DC conversion), and control s the second converter unit 2n to also work as a rectifier (i .e., perform AC -DC conversion).

[0119] In block 1820, the controller 30 determines a total regulation amount of voltages and / or currents supplied to the electrolyzers 301 and 30n based on the feedback information. In an example of an industrial application, the feedback information can include a change in the demand of a hydrogen production rate, and the total regulation amount of voltages and / or currents supplied to the electrolyzers 301 and 30n can be determined based on the change in the demand of the hydrogen production rate .

[0120] In block 1830, the controller 30 determines configured regulation value ( preset values ) for the first converter 10, the second converter unit 21 and the second converter unit 2n based on the determined total regulation amount and further based on an operation state of each of the plurality of electrolyzers 301 and 30n.

[0121] The operation state of each of the plurality of electrolyzers 301 and 30n can be determined based on the feedback information. In the case of a voltage regulation, the preset values include a regulation amount of the output voltage of the first converter 10, a regulation amount of the output voltage of the second converter unit 21 , and a regulation amount of the output voltage of the second converter unit 2n. In the case of a current regulation or of both a current regulation and a voltage regulation, the preset values can be implemented in a similar manner.

[0122] In an example, a hydrogen production rate of each electrolyzer can be fine-tuned (individually adjusted) by controlling a corresponding second converter unit. For example, it is expected that the electrolyzer with a high degree of aging will work in a light-load state to delay its aging speed . It is also expected that the electrolyzer with a low degree of aging will work in ahigher loading state to improve the overall hydrogen production efficiency. In this way, the determined hydrogen production rate can be realized . Moreover, the aging speed of each electrolyzer tends to be the same, thereby reducing the maintenance cost of the electrolyzers.

[0123] Examples for achieving a 30% increase in hydrogen production rate (i . e. , the target regulation amount of the hydrogen production rate is +30%) are illustrated in Table 1 below. In Table 1 , the first column represents the number of each of the example, the second column represents a regulation amount of the hydrogen production rate realized by the first converter 10, the third column represents a regulation amount of the hydrogen production rate realized by the second converter unit 21 , the fourth column represents a regulation amount of the hydrogen production rate realized by the second converter unit 2n, and the fifth column represents the target regulation amount of the hydrogen production rate. In Table 1 , the symbol “+” represents increasing and the symbol “ represents decreasing.Table 1

[0124] The controller 30 can determine the preset values for the cooperative control of the first converter 10 and the second converter units 21 and 2n based on the fine-tuning of the hydrogen production rate of each electrolyzer. For example, referring to Ex 1 illustrated in Table 1 , the preset values are determined such that the output voltage of the first converter 10 is increased by 28%, the output voltage of the second unit 21 is increased by 1 %, and the output voltage of the second converter unit 2n is increased by 1 %.

[0125] In block 1840, the controller 30 sends the preset values to the local control unit 1 1 of the first converter 10, the local control unit 21 1 of the second converter unit 21 , and the local control unit 2n l of the second converter unit 2n, such that the local control units control the first converter 10 and the second converter units 21 and 2n according to the preset values. In this way, the cooperative control of the converter system 100 is achieved.

[0126] It is noted that preset values can be dynamically adjusted according to the feedback information. For example, when a relative aging speed between two electrolyzers changes, the preset values will be changed accordingly.

[0127] Figure 19 shows yet another example (method 1900) of block 1620. In this example, the converter system 100 is operated in the second operation mode and used to transfer energy stored in one or more DC sources to the AC source 200. For clarity, thi s example is described taking energy stored in the DC source 302 being transferred to the AC source 200 as an example.

[0128] Referring to Figure 19, in block 1910, the controller 30 controls the first converter 10 to convert the second AC of the second side 10B to the first AC of the first side 10A, and control s the second converter unit 22 to work as an inverter (i .e., perform DC-AC conversion).

[0129] In block 1920, the controller 30 determines an energy transmission mode based on the property characteristics of the DC source 302 and controls the first converter 10 and the second converter unit 22 based on the determined energy transmission mode. In an example, the energy transmission mode is one of a continuous transmission mode and an intermittent transmission mode. For example, when the DC source 302 is a solar source, the transmission mode is determined by considering the intensity of light and can be the intermittent transmission mode . When the DC source 302 is associated with wind energy, the transmission mode is determined by considering the seasonality and can be the intermittent transmission mode .When the DC source 302 is a fuel cell (the fuel cell can generate electricity from H2 and O2), the transmission mode can be determined to be the continuous transmission mode.

[0130] F igure 20 shows yet another example (method 2000) of block 1620. In this example, the converter system 100 is operated in the third operation mode and used to power a DC load with the first converter 10 and one or more DC sources. That is to say, the DC load i s power by both the AC source 200 and one or more DC sources. For clarity, this example is described for powering the DC load 301 with the fist converter 10 and the second convert units 21 -22 as an example. The distributed control system described above in conjunction with Figure 3 is especially suitable for the implementation of method 2000.

[0131] Referring to Figure 20, in block 2010, the controller 30 controls the first converter 10 to convert the first AC of the first side 10A to the second AC of the second side 10B, control s the second converter unit 21 to work as a rectifier (i .e., perform AC-DC conversion), and control s the second converter unit 22 to work as an inverter (i . e. , perform DC -AC conversion).

[0132] In block 2020, the controller 30 determines a preset configured value for a distribution between the amount of power to be received from the first converter and the amount of power to be received from the second converter unit 22. For example, the configured preset value can be a ratio of the amount of power received from the first converter (i .e., power provided by the AC source 200) to the amount of power received from the second converter unit 22 (i . e., power provided by the DC source 22). In an example, the DC source 302 is a renewable energy source and thus can provide green energy. In this example, the green energy could be utilized as much as possible. Therefore, the maximum amount of energy that the DC source 302 can provide will be used first. When the maximum amount of energy that the DC source 302 can provide is not enough to power to the DC load 301 , theenergy from the AC source 200 will be used as a supplement.

[0133] In block 2030, the controller 30 sends the preset value to the local control unit 1 1 of the first converter 10 and the local control unit 221 of the second converter unit 22 such that the local control units control the first converter 10 and the second converter unit 22 according to the preset value.

[0134] F igure 21 shows yet another example (method 2100) of block 1620. In this example, the converter system 100 is operated in the fourth operation mode and used to power a DC load with one or more DC sources. This example is especially suitable for a fault condition where the AC source 200 cannot provide power to the DC load either due to unavailability of power from grid due to grid fault or due to a fault in a module of a branch of the first converter. For clarity, this example is described for powering the DC load 301 with the second convert units 21 and 22 as an example. That is to say, the DC load 301 is powered only by the DC source 302 to ride-through the fault condition. Alternatively, in the cause of a fault in a branch of the first converter, the first converter is operated through the other branches that can be phase wise combined from the sets of branches.

[0135] In block 21 10, the controller 30 controls the second converter unit 21 to work as a rectifier (i .e., perform AC-DC conversion) and control s the second converter unit 22 to work as an inverter (i .e., perform DC -AC conversion).

[0136] In block 2120, the controller 30 controls the second converter units 21 and 22 so that energy flows from the DC source 302 to the DC load 301 through the second converter unit 22 and the second converter unit 21 in sequence.

[0137] S uch a control strategy is advantageous because it can ensure that the DC load can be powered continuously and thus it does not need to be shut down during the troubleshooting period. This is especially useful for the case where the power grid coupled to the AC source 200 experience s transientfailures. In this case, according to the control strategy of method 2100, the DC load can continue to work without being affected.

Claims

WHAT IS CLAIMED IS:

1. A converter system (100) comprising: a first converter (10) having a first AC side (10A) with a first frequency (fl) and a second AC side (10B) with a second frequency (f2), the first converter (10) comprising a converter having a plurality of branches; a plurality of second converter units (21 ~2n) configurable to be coupled between the first converter (10) and a plurality of DC units (300 ~ 3 On), each of the plurality of DC units (300 ~ 3 On) being a DC load or a DC source; and a controller (30) configured to control at least one of the first converter (10) and at least one second converter unit (21) to control power supplied to or by at least one of the plurality of DC units (300 ~ 3 On) .

2. The converter system (100) of claim 1, wherein the first frequency (fl) is at the power frequency; and the second frequency (f2) is greater than the first frequency (fl) and in the range of 100Hz~10kHz.

3. The converter system (100) of any one of claims 1-2, wherein the converter (100) is a matrix converter and has a first terminal coupled to at least two phases; the plurality of branches comprise a first set of branches and a second set of branches, the first set of branches comprising branches that are coupled with one phase of the at least two phases, the second set of branches comprising branches that are coupled with the other phase of the at least two phases; and one branch of the first set of branches is configured to be combined phase wise or potential wise to a corresponding branch comprised in the second set of branches.

4. The converter system (100) of any one of claims 1-2, wherein the converter is a matrix converter, and comprises nine branches each comprising one or more modules (B l 1 -B l n) and a branch inductor connected in series to the one or more modules (B 1 1 ~B 1 n), and eachbranch has a first end coupled to one of three phases a, b, c of a first terminal of the matrix converter and a second end coupled to one of three phases x, y, z of a second terminal of the matrix converter; and wherein the nine branches comprise first to ninth branches (Branches 1 -9); first ends of the first, second and third branches are coupled to the phase a of the first terminal, and second ends of the first, fourth and seventh branches are coupled to the phase x of the second terminal; first ends of the fourth, fifth and sixth branches are coupled to the phase b of the first terminal, and second ends of the second, fifth and eighth branches are coupled to the phase y of the second terminal; and first ends of the seventh, eighth and ninth branches are coupled to the phase c of the first terminal, and second ends of the third, sixth and ninth branches are coupled to the phase z of the second terminal.

5. The converter system (100) of claim 4, wherein the matrix converter further comprises nine branch switches each of which is arranged in a corresponding one of the nine branches; and wherein the controller (30) is configured to, in the case that a fault occurs in at least one of the nine branches, control one or more of the nine branch switches to clear the fault.

6. The converter system (100) of any one of claims 1-2, wherein the converter is a matrix converter, and comprises six branches each comprising one or more modules (B 1 1 -B l n) and a branch inductor connected in series to the one or more modules, and each branch has a first end coupled to one of three phases a, b, c of a first terminal of the matrix converter and a second end coupled to one of three phases x, y, z of a second terminal of the matrix converter; and wherein the six branches comprise first to sixth branches (Branches 1 -6); first ends of the first and sixth branches are coupled to the phase a of the first terminal, and second ends of the first and second branches are coupled to the phase x of the second terminal; first ends of the second and third branches are coupled to the phase b of the first terminal, and second ends of the third and fourth branches are coupled to the phase y of thesecond terminal; and first ends of the fourth and fifth branches are coupled to the phase c of the first terminal, and second ends of the fifth and sixth branches are coupled to the phase z of the second terminal.

7. The converter system of any one of claims 1-2, wherein the converter is a matrix converter, and comprises twelve branches each comprising one or more modules (B 1 1 -B l n) and a branch inductor connected in series to the one or more modules (B 1 1 ~B 1 n); the twelve branches comprises first to sixth branches (Branches 1 -6) forming a first part and seventh to a twelfth branches (Branches 7- 12) forming a second part; and each branch of the first part has a first end coupled to one of three phases a, b, c of a first terminal of the matrix converter, and each branch of the second part has a first end coupled to one of three phases x, y, z of a second terminal of the matrix converter, first ends of the first and fourth branches are coupled to the phase a of the first terminal, first ends of the second and fifth branches are coupled to the phase b of the first terminal, and first ends of the third and sixth branches are coupled to the phase c of the first terminal; first ends of the seventh and tenth branches are coupled to the phase x of the second terminal, first ends of the eighth and eleventh branches are coupled to the phase y of the second terminal, and first ends of the ninth and twelfth branches are coupled to the phase z of the first terminal; each of the first to the third branches has a second end coupled to a first connection point, and each of the seventh to the ninth branches has a second end coupled to the first connection point; and each of the fourth to the sixth branches has a second end coupled to a second connection point, and each of the tenth to the twelfth branches has a second end coupled to the second connection point.

8. The converter system of any one of claims 1-2, wherein the converter is a matrix converter, and comprises six branches each comprising one or more modules (B 1 l -B I n) and a branch inductor connected in series to the one or more modules;the six branches comprise first to sixth branches (Branches 1~6) each of which has a first end coupled to one of three phases a, b, c of a first terminal of the matrix converter; first ends of the first and fourth branches are coupled to the phase a of the first terminal, first ends of the second and fifth branches are coupled to the phase b of the first terminal, and first ends of the third and sixth branches are coupled to the phase c of the first terminal; and each of the first to third branches has a second end coupled to a first connection point, and each of the fourth to sixth branches has a second end coupled to a second connection point.

9. The converter system (100) of any one of claims 1-8, further comprising a plurality of filters (51 ~5n) each coupled between one of the plurality of second converter units (21 ~2n) and one of the plurality of DC units (301 ~30n).

10. The converter system (100) of any one of claims 1-9, further comprising a transformer unit (40) coupled between the first converter (10) and the plurality of second converter units (21~2n).

11. The converter system (100) of claim 10, wherein the transformer unit (40) comprises a plurality of transformers (41 ~4n) each coupled between the first converter (10) and one of the plurality of second converter units (21 ~2n).

12. The converter system (100) of claim 10, wherein the transformer unit (40) comprises one transformer having one primary winding and a plurality of secondary windings each coupled to one of the plurality of second converter units (21 ~2n) .

13. The converter system (100) of any one of claims 1-12, wherein the controller is configured to receive feedback information from at least one of the first converter (10), at least one of the plurality of second converter units (21 ~2n) and a DC unit coupled with the at least one second converter unit (21) and to control at least one of the first converter (10) and the at least one second converter unit (21) based on the feedback information.

14. The converter system (100) of any one of claims 1-13, wherein the converter system is operable to operate in one of the following operation modes: a first operation mode where power is transferred from an AC source coupled with the first side of the first converter (10) to one or more of the plurality of DC units (301 -3 On); a second operation mode where power is transferred from one or more DC sources of the plurality of DC units (301 -3 On) to the first AC side; a third operation mode where at least one of the plurality of second converter units (21 ~2n) is configured to receive power from both the first converter (10) and at least another one of the plurality of second converter units (21 ~2n); and a fourth operation mode where at least one of the plurality of second converter units (21 ~2n) is configured to receive power from at least another one of the plurality of second converter units (21 ~2n) or from both the first converter (10) operating by isolating at least one faulty branch from the plurality of the branches and said at least another second converter unit (21).

15. The converter system (100) of any one of claims 1-14, wherein the controller (300) is comprised in the first converter (10).

16. The converter system (100) of any one of claims 1-14, wherein the plurality of second converters have a common local controller, and wherein the controller (100) is comprised in the common local converter.

17. The converter system (100) of any one of claims 1-14, wherein the first converter (10) comprises a local control unit (11), and each of the plurality of second converter units (21 ~2n) comprises a local control unit (221); and the controller is in communication with each local control unit for cooperative control of the first converter (10) and the plurality of second converter units (21 ~2n) .

18. The converter system (100) of any one of claims 1-17, wherein the controller isconfigured to: control at least one of the first converter (10) and at least one second converter unit (21) such that at least one of a voltage and a current for providing power to or receive power from at least one of the plurality of DC units (301 -3 On) is regulated based on a configured regulation value and operation mode for the converter system (100).

19. The converter system (100) of claim 14, wherein the controller is configured to: in the case that the converter system (100) is operated in the third operation mode, determine according to a preset configured value the amount of power to be received from the first converter (10) and the amount of power to be received from said at least another second converter unit (2n).

20. A control method (1600) for controlling a converter system (100), the converter system (100) comprising a first converter (10) and a plurality of second converter units (21 ~2n), the first converter (10) having a first AC side (10A) with a first frequency (fl) and a second AC side (10B) with a second frequency (f2), the first converter (10) comprising a converter having a plurality of branches, the plurality of second converter units (21 ~2n) being configurable to be coupled between the first converter (10) and a plurality of DC units (301 -3 On), each of the plurality of DC units (301 -3 On) being a DC load or a DC source, the method comprising: controlling at least one of the first converter (10) and at least one second converter unit (21) to control power supplied to or by at least one of the plurality of DC units (301 -3 On) .

21. A power supply system for powering an electrolyzer, the powering system comprising the converter system (100) of any one of claims 1-19.

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