Power conversion system and communication method thereof

Abstract

The present application discloses a power conversion system and a communication method thereof for transmitting common mode information. The communication method comprises the following steps: (a) providing at least two power conversion units, the first ends of which are electrically coupled, and each power conversion unit comprising a resonance control unit; (b) each power conversion unit generating an alternating harmonic wave according to a first electrical signal at the first end thereof, wherein the amplitude of each alternating harmonic wave represents the first information of the corresponding power conversion unit, and the frequencies of all alternating harmonic waves are the same; (c) injecting the corresponding generated alternating harmonic wave at the first end of each power conversion unit, and using the resonance control unit in the power conversion unit to carry out closed-loop suppression on the corresponding generated alternating harmonic wave, and controlling the resonance control unit to output a second electrical signal related to the first information, which comprises common mode information or is capable of further generating common mode information with the injected alternating harmonic wave. The present application can transmit common mode information without relying on additional communication lines.

Description

Technical Field

[0001] This invention relates to a power conversion technology, and more particularly to a power conversion system and its communication method. Background Technology

[0002] Connecting power electronic modules in series and parallel enables high-voltage, high-current applications, achieving purposes such as capacity expansion or redundant power supply to improve reliability. Such series-parallel systems are widely used. For example... Figure 1A The power electronic transformer system shown consists of multiple modules M1 per phase (each module M1 may include, for example, a front-end AC-DC sub-module and a back-end DC-DC sub-module) cascaded on the AC side to handle medium voltage, and connected in parallel on the DC side. The three-phase DC outputs are connected together to provide a suitable DC voltage to the load. It can convert medium-voltage AC power into low-voltage DC power, and has broad application prospects in data centers, charging stations, new energy power generation, and other fields.

[0003] For such modular systems, a distributed control approach is generally adopted, where the controller is installed locally on each module, giving the combined system excellent flexibility, scalability, and reliability. However, independent control of each module requires consideration of voltage, current, or power sharing issues, and traditional solutions typically employ droop control. To compensate for the steady-state error caused by droop control, average voltage, current, or power values ​​need to be transmitted. Existing transmission methods rely heavily on communication lines, and this additional communication reduces system reliability and modularity, causing difficulties in installation and debugging. Furthermore, as the number of modules increases, communication speed decreases, affecting the system's dynamic performance. Therefore, finding a way to achieve inter-module information transmission without relying on communication lines is of great significance.

[0004] Furthermore, for a three-phase Y-connected system, if simple, completely independent control of the three phases is used, the advantages of the three-phase combination cannot be fully utilized. For example... Figure 1B The three-phase Y-connected system shown includes multiple modules M2. Injecting a zero-sequence voltage component into the AC arm voltage of the three-phase Y-connected system can improve DC voltage utilization and reduce DC-Link frequency fluctuations by a factor of two. Traditional zero-sequence voltage injection is implemented based on a centralized controller, assuming the three-phase voltages (e.g., v) are known simultaneously. gA v gB v gC ) and three-phase current (e.g., i gA i gB i gC The zero-sequence voltage is calculated based on this. Traditional zero-sequence voltage injection relies on communication between the three phases, which requires the installation of communication loops between the three-phase controllers, making the commissioning and maintenance of the three-phase system more complex. Currently, there is no technology for distributed zero-sequence voltage injection into a three-phase system.

[0005] Therefore, how to provide common-mode information transmission without relying on communication lines in modular systems has become one of the urgent problems to be solved in the industry. Summary of the Invention

[0006] The purpose of this invention is to provide a power conversion system and its communication method, which can effectively solve at least one defect of the prior art and transmit common-mode information without relying on communication lines.

[0007] To achieve the above objective, the present invention provides a communication method for a power conversion system for transmitting common-mode information. The communication method includes the following steps: (a) providing at least two power conversion units, wherein the first terminals of the at least two power conversion units are electrically coupled, and each power conversion unit includes a resonant control unit; (b) each power conversion unit generates an AC harmonic according to a first electrical signal at its first terminal, wherein the amplitude of each AC harmonic characterizes the first information of the corresponding power conversion unit, and all the AC harmonics have the same frequency; (c) injecting the corresponding generated AC harmonic into the first terminal of each power conversion unit, and using the resonant control unit in the power conversion unit to perform closed-loop suppression on the corresponding generated AC harmonic, controlling the resonant control unit to output a second electrical signal related to the first information, wherein the second electrical signal contains the common-mode information or can further generate the common-mode information of the power conversion unit with the injected AC harmonic.

[0008] In one embodiment of the present invention, step (b) in which the power conversion unit generates an AC harmonic according to the first electrical signal at its first terminal includes: (b1) performing phase-locking on the first electrical signal at the first terminal of the power conversion unit and performing frequency multiplication to generate the phase of the AC harmonic; (b2) setting K times the first information of the power conversion unit as the amplitude of the AC harmonic, where K is a positive number.

[0009] In one embodiment of the present invention, the power conversion system is a single-phase system, and the first terminals of the at least two power conversion units are connected in series, and the first electrical signal is the current flowing through the first terminal.

[0010] In one embodiment of the present invention, the power conversion system is a single-phase system, and the first terminals of the at least two power conversion units are connected in parallel, and the first electrical signal is the voltage of the first terminal.

[0011] In one embodiment of the present invention, the power conversion system is a three-phase system and includes three power conversion units. Each power conversion unit has a first terminal including a positive input terminal and a negative input terminal. The positive input terminal of each power conversion unit is connected to a corresponding phase input source. The negative input terminals of all power conversion units are connected together. The first electrical signal is the voltage of the first terminal of the corresponding power conversion unit.

[0012] In one embodiment of the present invention, each piece of first information represents the variable value or integral value of the current, voltage, power, and temperature of the corresponding power conversion unit, and the common mode information is the average value of all the first information.

[0013] In one embodiment of the present invention, each power conversion unit includes an electrically coupled power conversion module and a controller. Each controller includes a voltage outer loop control unit and a current inner loop control unit. Each current inner loop control unit generates a voltage reference value for the first terminal of the power conversion unit based on the current at the first terminal of its corresponding power conversion unit, a reference value of the current at the first terminal, and the injected AC harmonics. Each voltage outer loop control unit generates a reference value of the current at the first terminal of the power conversion unit based on the voltage reference value at the first terminal of its corresponding power conversion unit, so that each power conversion unit performs dual-loop control.

[0014] In one embodiment of the present invention, each current inner loop control unit includes the resonant control unit and a first arithmetic unit, wherein each resonant control unit includes a first proportional controller and an M-order resonant controller, where M is a positive integer greater than 1, wherein: the first proportional controller performs proportional calculation on the current at the first terminal of the corresponding power conversion unit and the reference value of the current at the first terminal, and outputs a first output signal accordingly; the M-order resonant controller performs resonant control on the current at the first terminal of the corresponding power conversion unit and the reference value of the current at the first terminal, and outputs an M-order harmonic signal accordingly, wherein the M-order harmonic signal is a second electrical signal containing the common-mode information; the first arithmetic unit generates a voltage reference value at the first terminal of the power conversion unit according to the first output signal of the corresponding power conversion unit, the M-order harmonic signal and the injected AC harmonic; wherein, when the power conversion system is a three-phase system, M is not equal to a multiple of 3.

[0015] In one embodiment of the present invention, each of the controllers further includes an average value extraction unit for extracting the average value of all the first information in the Mth harmonic signal.

[0016] In one embodiment of the present invention, the first electrical signal is the voltage of the first terminal, the first information is K times the amplitude of the first electrical signal, where K is a positive number; the common-mode information is the zero-sequence component of the voltage of the first terminal.

[0017] In one embodiment of the present invention, each power conversion unit includes an electrically coupled power conversion module and a controller. Each controller includes a voltage outer loop control unit and a current inner loop control unit. Each current inner loop control unit generates a voltage reference value for the first terminal of the power conversion unit based on the current at the first terminal of its corresponding power conversion unit, a reference value of the current at the first terminal, and the AC harmonics. Each voltage outer loop control unit generates a reference value of the current at the first terminal of the power conversion unit based on the voltage reference value of its corresponding power conversion unit, so that each power conversion unit performs dual-loop control.

[0018] In one embodiment of the present invention, each of the current inner loop control units includes the resonant control unit and a first arithmetic unit, wherein each of the resonant control units includes a first proportional controller and a third resonant controller, and each of the first arithmetic units includes a first arithmetic unit and a second arithmetic unit. The first proportional controller performs proportional calculations on the current at the first terminal of its corresponding power conversion unit and a reference value of the current at the first terminal, and outputs a first output signal accordingly. The third resonant controller performs resonant control on the current at the first terminal of its corresponding power conversion unit and a reference value of the current at the first terminal, and outputs a third harmonic signal accordingly. The third harmonic signal is a second electrical signal containing the common-mode information. The first arithmetic unit generates the common-mode information of its corresponding power conversion unit based on the third harmonic signal of its corresponding power conversion unit and the injected AC harmonics. The second arithmetic unit generates the voltage reference value at the first terminal of its corresponding power conversion unit based on the first output signal of its corresponding power conversion unit and the common-mode information.

[0019] To achieve the above objectives, the present invention further provides a power conversion system comprising: at least two power conversion units electrically coupled to their first terminals, each power conversion unit including a controller, and each controller including a resonant control unit; wherein the controller of each power conversion unit is configured to perform: generating an AC harmonic based on a first electrical signal at the first terminal of the power conversion unit, wherein the amplitude of each AC harmonic characterizes first information of the corresponding power conversion unit, and all AC harmonics have the same frequency; injecting the corresponding generated AC harmonic into the first terminal of the power conversion unit, and using the resonant control unit in the power conversion unit to perform closed-loop suppression of the corresponding generated AC harmonic; and controlling the resonant control unit to output a second electrical signal related to the first information, the second electrical signal containing the common-mode information or capable of further generating the common-mode information of the power conversion unit with the injected AC harmonic.

[0020] In another embodiment of the invention, the resonant control unit of the controller of each power conversion unit is configured to perform: phase-locking of the first electrical signal at the first terminal of the power conversion unit and frequency multiplication to generate the phase of the AC harmonic; setting K times the first information of the power conversion unit as the amplitude of the AC harmonic, where K is a positive number.

[0021] In another embodiment of the present invention, the power conversion system is a single-phase system, and the first terminals of the at least two power conversion units are connected in series, and the first electrical signal is the current flowing through the first terminal.

[0022] In another embodiment of the present invention, the power conversion system is a single-phase system, and the first terminals of the at least two power conversion units are connected in parallel, and the first electrical signal is the voltage of the first terminal.

[0023] In another embodiment of the present invention, the power conversion system is a three-phase system and includes three power conversion units, wherein the first terminal of each power conversion unit includes a positive input terminal and a negative input terminal, the positive input terminal of each power conversion unit is connected to a phase input source, the negative input terminals of all power conversion units are connected together, and the first electrical signal is the voltage of the first terminal of the corresponding power conversion unit.

[0024] In another embodiment of the present invention, each piece of the first information represents the variable value or integral value of the current, voltage, power, and temperature of the corresponding power conversion unit, and the common mode information is the average value of all the first information.

[0025] In another embodiment of the present invention, each power conversion unit includes an electrically coupled power conversion module and a controller. Each controller includes a voltage outer loop control unit and a current inner loop control unit, wherein: the current inner loop control unit is configured to generate a voltage reference value for the first terminal of the power conversion unit based on the current at the first terminal of its corresponding power conversion unit, a reference value of the first terminal current, and the injected AC harmonics; the voltage outer loop control unit is configured to generate a reference value of the current at the first terminal of the power conversion unit based on the voltage reference value at the first terminal of its corresponding power conversion unit, so that each power conversion unit performs dual-loop control respectively.

[0026] In another embodiment of the present invention, each of the current inner loop control units includes the resonant control unit and a first arithmetic unit, wherein each of the resonant control units includes a first proportional controller and an M-order resonant controller, where M is a positive integer greater than 1, wherein: the first proportional controller is configured to perform proportional calculation on the current at the first terminal of the corresponding power conversion unit and a reference value of the first terminal current, and output a first output signal accordingly; the M-order resonant controller is configured to perform resonant control on the current at the first terminal of the corresponding power conversion unit and a reference value of the first terminal current, and output an M-order harmonic signal accordingly, wherein the M-order harmonic signal is a second electrical signal containing the common-mode information; the first arithmetic unit is configured to generate a voltage reference value at the first terminal of the power conversion unit according to the first output signal of the corresponding power conversion unit, the M-order harmonic signal, and the injected AC harmonics; wherein, when the power conversion system is a three-phase system, M is not equal to a multiple of 3.

[0027] In another embodiment of the invention, each of the controllers further includes an average value extraction unit for extracting the average value of all the first information in the Mth harmonic signal.

[0028] In another embodiment of the present invention, the first electrical signal is the voltage of the first terminal, the first information is K times the amplitude of the first electrical signal, where K is a positive number; the common-mode information is the zero-sequence component of the voltage of the first terminal.

[0029] In another embodiment of the present invention, each power conversion unit includes an electrically coupled power conversion module and a controller. Each controller includes a voltage outer loop control unit and a current inner loop control unit, wherein: the current inner loop control unit is configured to generate a voltage reference value for the first terminal of the power conversion unit based on the current at the first terminal of the corresponding power conversion unit, a reference value of the first terminal current, and the injected AC harmonics; the voltage outer loop control unit is configured to generate a reference value for the first terminal current of the power conversion unit based on the voltage reference value of the corresponding power conversion unit, so that each power conversion unit performs dual-loop control.

[0030] In another embodiment of the present invention, each of the current inner loop control units includes the resonant control unit and a first arithmetic unit, wherein each of the resonant control units includes a first proportional controller and a third resonant controller, and each of the first arithmetic units includes a first arithmetic unit and a second arithmetic unit, wherein the first proportional controller is configured to perform proportional calculation on the current at the first terminal of the corresponding power conversion unit and a reference value of the first terminal current, and output a first output signal accordingly; the third resonant controller is configured to perform resonant control on the current at the first terminal of the corresponding power conversion unit and a reference value of the first terminal current, and output a third harmonic signal accordingly, wherein the third harmonic signal is a second electrical signal containing the common-mode information; the first arithmetic unit is configured to generate the common-mode information of the corresponding power conversion unit according to the third harmonic signal of the corresponding power conversion unit and the injected AC harmonics, and the second arithmetic unit generates the voltage reference value of the first terminal of the corresponding power conversion unit according to the first output signal of the corresponding power conversion unit and the common-mode information.

[0031] The present invention has the following technical advantages: (1) Common mode information can be transmitted without relying on additional communication lines; (2) AC harmonics at the connection port of the power conversion unit are suppressed, which does not cause harmonic pollution to the system and improves voltage quality; (3) AC harmonics of the same frequency are injected into each power conversion unit, which occupies a small frequency band and is simple to control.

[0032] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. Attached Figure Description

[0033] The above and other features and advantages of the present invention will become more apparent from a detailed description of exemplary embodiments thereof with reference to the accompanying drawings.

[0034] Figure 1A This is a schematic diagram of the composition of an existing power electronic transformer system;

[0035] Figure 1B This is a schematic diagram of the composition of an existing three-phase Y-connected system;

[0036] Figure 2 This is a flowchart illustrating the communication method of the power conversion system of the present invention;

[0037] Figure 3 The circuit of the power conversion system of the first embodiment of the present invention is a single-phase series system and a method for calculating the average value of all first information is shown, wherein the calculated average value is used as common-mode information.

[0038] Figure 4 It shows Figure 3 The effect of averaging all the first information in a single-phase series system;

[0039] Figure 5 The steps of the method for calculating the average of all first information in a single-phase series system of the present invention are shown.

[0040] Figure 6 This invention illustrates a method for phase-locking a first electrical signal at a first terminal in a series or parallel system.

[0041] Figure 7A The step response relationship between the gain and the average value of the resonant controller of the present invention is shown.

[0042] Figure 7B The relationship between the bandwidth of the resonant controller of the present invention and the step response obtained by averaging is shown.

[0043] Figure 8A The present invention illustrates the method for calculating the average value for, for example... Figure 1A The diagram shows the AC-DC control block diagram of each power conversion unit in the power electronic transformer system during simulation control.

[0044] Figure 8B The present invention illustrates the method for calculating the average value for, for example... Figure 1A The diagram shows the DC-DC control block diagram of each power conversion unit in the power electronic transformer system during simulation control.

[0045] Figure 9 The simulation results obtained after simulation control are shown.

[0046] Figure 10 This demonstrates the effect of the present invention on harmonic injection and cancellation when calculating the average value of all first information;

[0047] Figure 11The experimental results of the first embodiment of the present invention are shown;

[0048] Figure 12 The circuit of the power conversion system of the second embodiment of the present invention is a three-phase system and its zero-sequence component injection method without communication is shown, wherein the zero-sequence component is used as common-mode information.

[0049] Figure 13 The various steps of the three-phase system distributed zero-sequence component injection method of the present invention are shown;

[0050] Figure 14 The principle of zero-sequence component injection in a three-phase Y-connected system according to the present invention is illustrated;

[0051] Figure 15 The simulation waveform of the zero-sequence component injection method of the present invention in a three-phase Y-connected system when the three-phase power grid is balanced is shown.

[0052] Figure 16 The simulation waveform of the zero-sequence component injection method of the present invention is shown in a three-phase Y-connected system when the three-phase power grid is unbalanced.

[0053] Figure 17 Parts (A) and (B) show the suppression effect of the DC-Link voltage at twice the frequency of the present invention before and after the zero-sequence component is injected.

[0054] Figure 18 The circuit and its averaging method for a three-phase Y-connected power conversion system according to the third embodiment of the present invention are shown.

[0055] Figure 19 The principle of the method for calculating the average of all first information in a three-phase Y-connected system of the present invention is shown;

[0056] Figure 20 The experimental waveforms of the third embodiment of the present invention are shown. Detailed Implementation

[0057] Exemplary embodiments will now be described more fully with reference to the accompanying drawings. However, these exemplary embodiments can be implemented in many forms and should not be construed as limited to the embodiments set forth herein; rather, they are provided so that the invention will be thorough and complete, and the concept of the exemplary embodiments will be fully conveyed to those skilled in the art. The same reference numerals in the drawings denote the same or similar structures, and therefore their detailed description will be omitted.

[0058] In describing the elements / components / etc. described and / or illustrated herein, the terms “a,” “an,” “the,” “the,” and “at least one” are used to indicate the presence of one or more elements / components / etc. The terms “comprising,” “including,” and “having” are used to indicate an open-ended inclusion and to mean that additional elements / components / etc. may exist in addition to those listed. Furthermore, the terms “first,” “second,” etc., in the claims are used only as designations and are not intended to limit the number of objects to which they pertain.

[0059] like Figure 2 As shown, the present invention provides a communication method 200 for a power conversion system, used to transmit common-mode information. The communication method 200 mainly includes the following steps:

[0060] (a) Provide at least two power conversion units, the first terminals of the at least two power conversion units being electrically coupled, and each of the power conversion units including a resonant control unit;

[0061] (b) Each of the power conversion units generates an AC harmonic according to the first electrical signal at its first terminal, wherein the amplitude of each AC harmonic represents the first information of the corresponding power conversion unit, and all the AC harmonics have the same frequency.

[0062] (c) Inject the corresponding generated AC harmonic into the first terminal of each power conversion unit, and use the resonant control unit in the power conversion unit to perform closed-loop suppression of the corresponding generated AC harmonic, and control the resonant control unit to output a second electrical signal related to the first information, the second electrical signal containing common-mode information or capable of further generating common-mode information of the power conversion unit with the injected AC harmonic.

[0063] The present invention also provides a power conversion system 100-1, which includes at least two power conversion units, for example... Figure 3 The embodiment includes N power conversion units CELL1, CELL2, ..., CELLN, for example... Figure 12 The embodiment includes three power conversion units CELL1, CELL2, and CELL3. The first terminals of these power conversion units CELL1, CELL2, ..., CELLN are electrically coupled, and each power conversion unit (CELL1 / CELL2 / ... / CELLN) includes an electrically coupled power conversion module 10 and a controller 20, for example... Figure 3The power conversion units CELL1, CELL2, ..., CELLN in the invention respectively include controller 1, controller 2, ..., controller N. In particular, each controller 20 may include a resonant control unit 21. The controller 20 of each power conversion unit can be configured to perform:

[0064] (S1) An AC harmonic is generated based on the first electrical signal E1 at the first terminal of the power conversion unit (CELL1 / CELL2 / ... / CELLN). Figure 3 Harmonics v in bhM In this context, the amplitude of each AC harmonic can characterize the first information of its corresponding power conversion unit, and all AC harmonics have the same frequency.

[0065] (S2) The corresponding generated AC harmonics are injected into the first terminal of the power conversion unit (CELL1 / CELL2 / ... / CELLN), and the corresponding generated AC harmonics are suppressed by the resonant control unit 21 in the power conversion unit (CELL1 / CELL2 / ... / CELLN) in a closed loop. The resonant control unit 21 is controlled to output a second electrical signal related to the first information. The second electrical signal (e.g. Figure 3 R in M or Figure 12 R3 in the equation contains common-mode information or can further generate common-mode information of the power conversion unit with the injected AC harmonics.

[0066] Preferably, step (b) of each power conversion unit generating an AC harmonic according to the first electrical signal at its first terminal may further include, for example, (b1) phase-locking the first electrical signal E1 at the first terminal of the power conversion unit and multiplying the frequency to generate the phase of the AC harmonic; (b2) setting K times the first information of the power conversion unit as the amplitude of the AC harmonic, where K is a positive number, for example, it can be any positive number such as 1, 1.5, 3, etc.

[0067] exist Figure 3 In the illustrated embodiment, the power conversion system 100-1 can be, for example, a single-phase series system, wherein the first terminals of the N power conversion units CELL1, CELL2, ..., CELLN are connected in series and connected to a single-phase input source v. g The first electrical signal E1 can be, for example, the current i flowing through the first terminal. g (For example Figure 3 (Grid current). However, it is understood that in other embodiments, the power conversion system 100-1 may also be a single-phase parallel system, for example... Figure 6In part (C), the first terminals of the N power conversion units CELL1, CELL2, ..., CELLN can be connected in parallel, where the first electrical signal can be, for example, the voltage at the first terminal, i.e. Figure 6 The parallel port voltage V shown in section (C) pcc .

[0068] In the single-phase series system or single-phase parallel system of the present invention, each first piece of information is, for example, a variable value or integral value characterizing the current, voltage, power, and temperature of its corresponding power conversion unit, while the common-mode information is, for example, the average value of the first pieces of information of all power conversion units.

[0069] Continue to refer to Figure 3 Combined with reference Figure 8A In this invention, each controller 20 may include, for example, a current inner loop control unit 201 and a voltage outer loop control unit 202. Each current inner loop control unit 201 can adjust the current based on the current at the first terminal of its corresponding power conversion unit (e.g., i...). g ), the reference value of the current at the first terminal (e.g., i) gref ), and injected AC harmonics (e.g. Figure 3 v in bhM and Figure 8A v in bhMi This generates a voltage reference value (e.g., V) at the first terminal of the power conversion unit. bref Each voltage outer loop control unit 202 uses the voltage reference value (e.g., V) of the first terminal of its corresponding power conversion unit. bref The reference value (e.g., i) that generates the current at the first terminal of the power conversion unit. gref This allows each power conversion unit to perform dual closed-loop control.

[0070] Continue to refer to Figure 3 Combined with reference Figure 8A In some embodiments of the present invention, each current inner loop control unit 201 may include, for example, a resonant control unit 21 and a first arithmetic unit 22. Each resonant control unit 21 may include a first proportional controller 211 and an M-order resonant controller 212, where M may be a positive integer greater than 1. The resonant control unit 21 may, for example, be a PR controller, which includes a K... P The controller and an M-th harmonic controller, preferably where M is equal to, for example, 3 (i.e., a third harmonic controller), are used to resonate and control the current at the first terminal of the corresponding power conversion unit and a reference value of the first terminal current, and output a third harmonic signal accordingly. The first proportional controller 211 can be configured to control the current at the first terminal of the corresponding power conversion unit (e.g., i... g ), the reference value of the current at the first terminal (e.g., i) grefAfter performing proportional calculations, a first output signal (e.g., Out1) is output. The M-fold resonant controller 212 can be configured to control the current (e.g., i) at the first terminal of its corresponding power conversion unit. g ), the reference value of the current at the first terminal (e.g., i) gref After resonance control, the corresponding output is an Mth harmonic signal (e.g., R). M The first arithmetic unit 22 can be configured to output the first signal (e.g., Out1) and the Mth harmonic signal (e.g., R) of its corresponding power conversion unit. M ) and injected AC harmonics (e.g. Figure 3 v in bhM and Figure 8A v in bhMi This corresponds to generating the voltage reference value (e.g., v) at the first terminal of the power conversion unit. bref The Mth harmonic signal contains common-mode information (e.g., the average of the first information from all power conversion units, such as...). Figure 8A Int, the integral average value vdcmean The second electrical signal.

[0071] Reference Figure 3 In some embodiments of the present invention, each first arithmetic unit 22 may include, for example, a first arithmetic unit 221 and a second arithmetic unit 222. The first arithmetic unit 221 may, for example, be configured to operate according to the Mth harmonic signal (e.g., R) of its corresponding power conversion unit. M ) and injected AC harmonics (e.g., v bhM This generates a third electrical signal (e.g., E2) for the power conversion unit. The signal contains AC harmonics (e.g., V). bhM For example, it can be injected into unit 23 via Mth AC harmonics (see...). Figure 8A The second arithmetic unit 222 may be configured, for example, to generate a voltage reference value (e.g., v) at the first terminal of the power conversion unit based on the first output signal (e.g., Out1) and the third electrical signal (e.g., E2) of its corresponding power conversion unit. bref In some embodiments, the first arithmetic unit 22 may further include a third arithmetic unit 223, which is configured to operate on the feedforward voltage v of its corresponding power conversion unit. b (For example, the x-axis component of the grid voltage or bridge arm voltage after phase-locking, such as v) bref x-axis component v brefx The first output signal (e.g., Out1) is added to the second output signal (e.g., v) to produce a second output signal. bref1 The second arithmetic unit 222 is configured to output a second output signal (e.g., v) based on the output of the third arithmetic unit 223. bref1The third electrical signal (e.g., E2) generates a voltage reference value (e.g., v) at the first terminal of the power conversion unit. bref ).

[0072] Reference Figure 3 In some embodiments, the resonant control unit 21 may further include a fourth arithmetic unit 213, which may be configured to reference a current (e.g., i) at the first terminal of its corresponding power conversion unit. gref ) and the current at the first terminal (e.g., i) g The subtraction operation is performed and a corresponding operation result is output. The operation result is transmitted to the first proportional controller 211 and the Mth resonant controller 212 respectively to perform the above-mentioned proportional operation and resonant control.

[0073] In some embodiments of the present invention, such as Figure 8A As shown, each controller 20 may further include an average value extraction unit 24, used to extract the average value of the first information of all power conversion units in the Mth harmonic signal (i.e., common mode information, such as...). Figure 8A Int, the integral average value vdcmean ).

[0074] The following will combine Figures 3-11 The method for calculating the average value of first information of all power conversion units in the first embodiment of the present invention, for example, a single-phase series system or a single-phase parallel system, is described in detail, wherein each power conversion unit performs:

[0075] Step 1: Perform phase-locked loop (PLL) on the first electrical signal at the first terminal of the power conversion unit to obtain the PLL results sinθ and cosθ of the power conversion unit, such as... Figure 5 As shown in step one. In this series system, the first electrical signal at the first terminal of each power conversion unit is the current flowing through all power conversion units, such as... Figure 6 The series port current i shown in section (B) g In a parallel system, the first electrical signal at the first terminal of each power conversion unit is the parallel port voltage, such as... Figure 6 The parallel port voltage V shown in section (C) pcc The specific phase-locked loop (PLL) methods are as follows: Figure 6 As shown in section (A), for a series system, it is based on a reference value of the current at the first terminal of the power conversion unit (e.g., i). gref ) and the current at the first terminal (e.g., i) g Obtain the bridge arm voltage reference value v b1ref Then the bridge arm voltage reference value v b1ref After fundamental component extraction (e.g., extracting component v) b1x v b1yAfter operations such as normalization, the phase-locked loop results sinθ and cosθ are obtained. For parallel systems, the voltage V at the parallel connection point of the power conversion unit is... pcc Perform fundamental component extraction (e.g., extract component v) b1x v b1y After operations such as normalization, the phase-locked loop results sinθ and cosθ are obtained.

[0076] Step 2: The sinθ and cosθ values ​​of the phase-locked loop results from the power conversion unit are multiplied by frequency doubling to generate the phase of the Mth AC harmonic of the power conversion unit, such as... Figure 5 Step two is shown. The harmonic formula, for example, can be cos2θ = 2cos... 2 θ-1, sin2θ=2 sinθcosθ, etc.

[0077] Step 3: Set the first information d for the power conversion unit to calculate the average value. i (or first information d) i Multiplying by a predetermined coefficient K (where K is a positive number, such as 1, 1.5, 3, etc.) gives the amplitude of the Mth AC harmonic of the power conversion unit. Figure 5 As shown in step three. Where, d i The variable value represents the first information of the i-th (n=1,2,3…) power conversion unit. The first information can be, for example, the value of an actual physical quantity such as voltage, current, temperature, or power of the corresponding power conversion unit, or it can be the integral value of any physical quantity obtained by the controller of the corresponding power conversion unit (as shown in Figure 8, the integral value Int of the voltage at the first terminal of the corresponding power conversion unit). vdci The values ​​of virtual physical quantities, such as the state of the battery, are not intended to limit the invention.

[0078] exist Figure 3 In the illustrated embodiment, the controller 20 of each power conversion unit CELL1, CELL2, ..., CELLN generates M-order AC harmonics of the same frequency through the first electrical signal (e.g., the current at the series port) of each power conversion unit CELL1, CELL2, ..., CELLN. These M-order AC harmonics have the same phase (which can be determined by adjusting the current i at the series port of the power conversion unit). g (When phase-locked loop is reached), the amplitudes of these M-order AC harmonics can be different, and the amplitudes of these M-order AC harmonics characterize the variable values ​​of the first information of the corresponding power conversion unit.

[0079] Step 4: Inject the Mth AC harmonic generated by the power conversion unit into the connection port (i.e., the first end of the power conversion unit) in an open loop, and use a harmonic control unit to suppress the injected Mth AC harmonic in a closed loop, such as... Figure 5Step four is shown in the diagram. Step four is executed in the current inner loop control unit 201. The output R of the harmonic control unit... M It can cancel the Mth AC harmonics injected in the open loop.

[0080] The harmonic control unit of the present invention (e.g.) Figure 3 The PR controller in the middle includes a first proportional controller 211 (i.e., K). p The controller 212 and the Mth resonant controller 212 are based on the traditional proportional controller, with the addition of the Mth resonant controller 212. Wherein, K... p Given the parameters of the first proportional controller 211, the expression for the Mth resonant controller is: K r Characterizing the magnitude of gain, Characterize the bandwidth. Set the input of the Mth resonant controller to the current i at the first terminal of its corresponding power conversion unit. g and the reference value i of the current at the first terminal gref R Mx and R My For the two mutually orthogonal outputs of the Mth resonant controller, i gref It does not contain the Mth harmonic component. The output R of the Mth harmonic controller Mx Multiply by (1+K) p / K r The total output of the PR controller is equal to the Mth AC harmonic injected in the open loop, v. bhM Superposition cancellation, that is, the output R of the Mth resonant controller Mx It can cancel the corresponding open-loop injected Mth AC harmonic v bhM Since the inputs to the Mth harmonic controllers of each power conversion unit are the same, and the parameters of the resonant control units of each power conversion unit are also set in the same way, the outputs of the Mth harmonic controllers of each power conversion unit are also the same. Therefore, the outputs of each Mth harmonic controller (e.g., R...) can be... M The average value of the first information of all power conversion units (i.e., common mode information) is extracted.

[0081] Step 5: At the output (sine wave) R of the Mth resonant controller M The average value of the first information of all power conversion units is extracted, such as... Figure 5 As shown in step five. Specifically, R can be... M Rotate to the Mth AC harmonic v injected in an open-loop manner bhM In an oriented coordinate system, the d-axis component represents R. M Amplitude, Let be the average of the first information of all power conversion units. The calculation formula is:

[0082]

[0083] in, , Each power conversion unit can draw power from the output R of its corresponding Mth resonant controller. M Extract the average value of the first information (i.e., common-mode information) of all power conversion units. At this time, R M It is a second electrical signal that contains common-mode information.

[0084] The method for calculating the average value of the first information of all power conversion units in a single-phase series system or a single-phase parallel system proposed in this invention has the following technical advantages:

[0085] (1) The controllers of each power conversion unit CELL1, CELL2, ..., CELLN can suppress the Mth AC harmonics injected by each unit simultaneously. Therefore, the average value of the first information of all power conversion units (i.e., common mode information) is obtained quickly and is independent of the number of power conversion units connected in series and parallel, making it easy to expand the system capacity.

[0086] (2) The present invention does not rely on additional communication lines to obtain the average value of the first information of all power conversion units, thus reducing production costs;

[0087] (3) The AC harmonics injected into the connection port (i.e. the first end) of the power conversion unit are suppressed, which basically does not cause harmonic pollution to the power conversion system, improves the voltage quality, and injects AC harmonics of the same frequency into each power conversion unit, which occupies a small frequency band and is simple to control.

[0088] Next, taking a single-phase series system as an example, the basic principle of the above method for obtaining the average value of the first information will be explained. Figure 3 In the illustrated embodiment, each power conversion unit CELL1, CELL2, ..., CELLN injects an Mth AC harmonic with the same phase into the open-loop series port. The amplitude of the Mth AC harmonic represents the variable value of the first information to be averaged in each power conversion unit CELL1, CELL2, ..., CELLN. Therefore, the amplitudes of the Mth AC harmonics injected by each power conversion unit CELL1, CELL2, ..., CELLN are not necessarily the same. Figure 4 As shown, because Figure 3 The power conversion system in the diagram is a series system, so the Mth AC harmonic injected at the final port is injected by each power conversion unit CELL1, CELL2, ..., CELLN (e.g., ...). , ... The sum of ) is denoted as Each resonant control unit (e.g., a PR controller) can control the first electrical signal (e.g., grid current i) at the series port of its corresponding power conversion unit. g Suppress AC harmonics in the power conversion unit (CELL1, CELL2, ..., CELLN). Set KN for all power conversion units (CELL1, CELL2, ..., CELLN). p If the values ​​are the same and the parameters of the Mth resonant controller are also the same, then the outputs of the Mth resonant controllers in each power conversion unit CELL1, CELL2, ..., CELLN will be the same, i.e. The sum of the AC harmonic suppression outputs of the PR controllers of each power conversion unit CELL1, CELL2, ..., CELLN is denoted as... ,in K r Characterizing the magnitude of gain, K p These are the parameters of the proportional controller. When the circuit reaches steady state, the grid current i g The Mth alternating harmonic in the signal is suppressed to almost zero. ,but This reflects the average value of the injected M-th AC harmonic amplitude. Because each power conversion unit CELL1, CELL2, ..., CELLN simultaneously injects M-th AC harmonics into its series port, and simultaneously uses a PR controller with the same control parameters for harmonic suppression, the average value obtained by this method, i.e., the transmission of common-mode information, is not affected by the number of power conversion units n.

[0089] Furthermore, the speed of averaging in this method mainly depends on the speed of harmonic extraction, i.e., it is affected by the parameters of the Mth resonant controller. The transfer function of the Mth resonant controller is... The step response obtained by averaging is as follows: Figure 7A and Figure 7B As shown, in the grid-side filter inductor L f =15mH, control frequency is 10k, K p With a gain of 50, by modifying the parameters of the Mth resonant controller, we can see that the gain K of the Mth resonant controller... r The larger the size, the faster the response, such as Figure 7A As shown; the larger the bandwidth r of the Mth resonant controller, the faster the response, such as Figure 7B As shown. By Figure 7A and Figure 7B It is evident that a reasonable design of K r The average value of r can be calculated in 2ms.

[0090] Simulation of the effect of the first embodiment:

[0091] The averaging method of the present invention is used in, for example... Figure 1AIn the control of the power electronic transformer system shown (e.g., the SST system), only a single phase is taken in the SST system. This phase consists of two cascaded power conversion units (CELLs). Each power conversion unit includes two stages: AC-DC and DC-DC. The two stages need to be controlled separately. Figure 1A The Vdc voltage in this simulation is also called the DC-LINK voltage. A simulation is built in Matlab, and the control block diagram for each power conversion unit (CELL) is shown below. Figure 8A and Figure 8B As shown. Figure 8A As shown, the AC-DC control employs a bridge arm voltage droop loop 25 to reduce the bridge arm voltage. This droop causes a steady-state error in the Vdc voltage control. Therefore, a distributed secondary regulation loop 26 is used for integration to eliminate the Vdc steady-state error. To avoid inconsistencies in integration among different power conversion units, the integral values ​​need to be averaged to ensure consistency across all power conversion units. The communication method of this invention can be used, for example, to calculate the average integral output of the secondary regulation loop. For instance, this invention can extract the average integral value Int of the Vdc voltage through the average value extraction unit 24. vdcmean The average value of this integral is Int vdcmean The integral value Int is output through the secondary adjustment loop 26. vdci .like Figure 8B As shown, the DC-DC stage is an LLC, which performs closed-loop frequency modulation control of the output voltage, and uses a Vdc voltage droop loop for Vdc voltage droop control.

[0092] Assume that the Vdc voltage is set to a fixed 780V and the output voltage Vo is set to 350V.

[0093] Figure 9 The simulation results show that the grid voltage drops to 90% of its rated value at 0.1s. At this time, the droop setpoint of the AC-DC bridge arm voltage deviates from the set value. Due to the bridge arm voltage droop control, the DC-LINK voltage, Vdc, drops. Since the DC-DC converter uses Vdc droop control, the output voltage Vo also drops. Because Vdc is adjusted twice and the integral average value is obtained using the method of this invention, the output voltage Vo begins to recover, and after stabilization, the output voltage has no steady-state error. This demonstrates the effectiveness of the method of this invention in eliminating steady-state error caused by droop control through averaging.

[0094] Figure 10 This invention clearly demonstrates the process of AC harmonic injection and cancellation during the averaging process. Here, Vb is the total bridge arm voltage, VbMi is the Mth AC harmonic injected in the open loop, and Vbh2x is the output of the PR controller to cancel the open-loop injected Vbh2.

[0095] The experimental results of the first embodiment are as follows: Figure 11As shown, the experiment involved cascading three single-phase power conversion units (CELL1, CELL2, and CELL3). The AC-DC converter in each unit used a Totem-Pole PFC module, and the DC-DC converter was an LLC. The outputs were connected in parallel to power an electronic load. The effective value of the grid voltage was 880V, and the grid-side filter inductor L... f =15mH. The control frequency is 12K, and the relevant parameter values ​​extracted by averaging are: K p = 30, K r = 50, α = 0.01. The DCLINK voltage setting is 700V, the output voltage setting is 468V, and the mains voltage amplitude setting is 410V. When the mains voltage is adjusted to 105% of the setting, Vdc will drop because the droop setpoint of the AC-DC bridge arm voltage amplitude Vbm deviates from the setting. The secondary regulation loop will then integrate the Vdc error and output the result. The steady-state waveform experiment is as follows: Figure 11 As shown, the method of the present invention can successfully obtain the integral average value, which is then used for secondary adjustment to ensure that Vdc has no steady-state error, the output voltage has no steady-state error, and does not pollute the grid current.

[0096] The second embodiment of the present invention is a distributed zero-sequence component injection method applied to a three-phase Y-connected system.

[0097] like Figure 12 As shown, the power conversion system 100-2 of this second embodiment is, for example, a three-phase Y-connected system, which may include three Y-connected power conversion units CELLA, CELLB, and CELLC. The first terminal of each power conversion unit CELLA / CELLB / CELLC respectively includes an input positive terminal and an input negative terminal. The input positive terminal of each power conversion unit CELLA / CELLB / CELLC is connected to a phase input source (e.g., V). gA v gB v gC All power conversion units CELLA, CELLB, and CELLC share a common negative input terminal (e.g., connected to node N1). Each power conversion unit CELLA, CELLB, and CELLC includes a controller 20, which contains a harmonic control unit 21.

[0098] In the second embodiment, the controller 20 also includes a current inner loop control unit 201 and a voltage outer loop control unit 202. Each current inner loop control unit 201 also includes a resonant control unit 21 and a first arithmetic unit 22. The resonant control unit 21 also includes a first proportional controller 211 and an M-order resonant controller 212. The composition and operation of the current inner loop control unit 201, the voltage outer loop control unit 202, the resonant control unit 21, and the first arithmetic unit 22 are basically the same as in the first embodiment, and will not be repeated here. Unlike the first embodiment, in the second embodiment, the M-order resonant controller 212 is a tertiary resonant controller. The tertiary resonant controller is configured to control the current (e.g., i) at the first terminal of its corresponding power conversion unit. g ), the reference value of the current at the first terminal (e.g., i) gref After resonance control, the corresponding output is a first and third harmonic signal (e.g., R3). This third harmonic signal is a second electrical signal related to the first information, which can be further combined with the injected AC harmonics (e.g., V). bh3 The first arithmetic unit 22 is configured to generate common-mode information (e.g., zero-sequence component) of the corresponding power conversion unit based on the first output signal (e.g., Out1), the third harmonic signal (e.g., R3), and the injected AC harmonic (e.g., v) of its corresponding power conversion unit. bh3 This corresponds to generating the voltage reference value (e.g., v) at the first terminal of the power conversion unit. bref Furthermore, the first arithmetic unit 221 in the first arithmetic unit 22 is configured to operate according to the third harmonic signal (e.g., R3) of its corresponding power conversion unit and the injected AC harmonic (e.g., v). bh3 This generates the zero-sequence component (e.g., v) of the power conversion unit. bh30 This zero-sequence component is the common-mode information. The second arithmetic unit 222 in the first arithmetic unit 22 is configured to, based on the first output signal (e.g., Out1) of its corresponding power conversion unit and the zero-sequence component (e.g., v) of that power conversion unit,... bh30 This generates a voltage reference value (e.g., V) at the first terminal of the power conversion unit. bref ).

[0099] The distributed zero-sequence component injection method for the three-phase Y-connected system in the second embodiment is basically the same as the method for calculating the average value of the first information of all power conversion units applied to a single-phase series system or a single-phase parallel system in the first embodiment, and will not be described again here. The difference from the first embodiment is that, as... Figure 12 As shown, in step one, the first electrical signal at the first terminal of each power conversion unit is, for example, the bridge arm voltage v of the corresponding power conversion unit. bA v bB v bCIn step three, each power conversion unit uses K times the amplitude of its bridge arm voltage (i.e., the voltage at the first port of the power conversion unit) as the amplitude of the third AC harmonic, where K is a positive number, preferably K=1 / 3, meaning that the first information of each power conversion unit is 1 / 3 times the amplitude of its first electrical signal; in step five, the first arithmetic unit 221 is configured to calculate the amplitude of the third harmonic signal (e.g., R3) of its corresponding power conversion unit and the injected third AC harmonic (e.g., v) based on the third harmonic signal (e.g., R3) of its corresponding power conversion unit. bh3 ) generates the zero-sequence component of the power conversion unit (e.g. Figure 12 v in bh30 (i.e., common mode information), the specific steps are as follows: Figure 13 Steps one through five are shown in the diagram and will not be repeated here.

[0100] In the second embodiment, the controller 20 of each single-phase power conversion unit CELLA / CELLB / CELLC injects a third AC harmonic (preferably with an amplitude of 1 / 3 of the fundamental wave) in an open-loop manner into the bridge arm voltage of its respective phase, synchronized with the fundamental wave of its respective bridge arm voltage. The PR controller of the resonant control unit (including K...) P The controller and the third resonant controller perform closed-loop suppression of the third AC harmonic. Their output cancels out the positive or negative sequence components of the third AC harmonic injected into the open loop, ultimately yielding the zero-sequence component of the third AC harmonic, thus realizing the zero-sequence component (e.g., ...). Figure 12 v in bh30 Injection (i.e., the transmission of common mode information).

[0101] Because the current in a three-phase Y-connected system reflects the positive or negative sequence components of the bridge arm voltage, but not the zero-sequence component, when the resonant control reaches steady state, the output of the resonant controller cancels out the positive or negative sequence components of the third AC harmonic injected in the open loop, leaving only the zero-sequence component in the bridge arm voltage of each power conversion unit. In this second embodiment, the first electrical signal is the voltage at the first terminal of the power conversion unit (i.e., the bridge arm voltage), and the first information is K times the amplitude of the first electrical signal, where K is a positive number. The common-mode information is the zero-sequence component of the voltage at the first terminal of the power conversion unit.

[0102] Furthermore, the function of the triple resonant controller can be used as follows: Figure 14 The superposition theorem explanation shown assumes that only the third AC harmonic v is injected in the open-loop voltage of phase A bridge arm. bh3A When the resonant control reaches steady state, there is almost no third harmonic current in the circuit. Therefore, the final third harmonic of each bridge arm voltage should satisfy the following relationship: , where R 3A R 3B R 3C These are the outputs of the phase A triple resonant controller, the phase B triple resonant controller, and the phase C triple resonant controller, respectively.

[0103] Furthermore, since the output of the resonant controller is proportional to the third AC harmonic in the current, and according to the current distribution relationship of the circuit, it can be known that... Combining the two equations above, we can obtain , , .

[0104] When a third AC harmonic is injected into each phase in open loop, the output of each resonant controller can be obtained according to the superposition theorem. , , .

[0105] in The zero-sequence component of the third AC harmonic is injected into the open loop. Therefore, the output of the third resonant controller consists of positive and negative sequence components, while the total bridge arm voltage of the power conversion unit ultimately only contains the zero-sequence component.

[0106] This second embodiment has the following technical advantages:

[0107] (1) The zero-sequence component injection method of the third AC harmonic proposed in this second embodiment does not require the installation of communication lines between the three phases. Each phase controller samples the voltage information of its own phase bridge arm locally, without sampling the voltage or current information of other phase grids.

[0108] (2) The zero-sequence component injection method of the third AC harmonic proposed in this second embodiment can improve DC utilization (15%) and reduce the second harmonic fluctuation of DC-Link.

[0109] (3) When the grid voltage is asymmetrical, the zero-sequence component injection method for the third AC harmonic proposed in this second embodiment can still be implemented without causing harmonic pollution to the system. Specifically, if the three-phase grid voltage is asymmetrical, the amplitudes and phases of the third AC harmonics generated by each phase are not equal and are not the same (containing not only zero-sequence components but also positive and negative sequence components). This will cause third harmonic current. By adding the third AC harmonic closed-loop suppression algorithm, the third harmonic current is basically eliminated, and finally, the harmonics of each phase only contain the zero-sequence component v. bh30 .

[0110] Simulation of the effect of the second embodiment:

[0111] Create such a structure in Matlab Figure 1B The diagram shows a three-phase Y-connected system. The mains voltage is set to 1000V, and the three phases are balanced. For simplicity, the DC-link voltage is set to a fixed 1500V. A single current loop control is used, with a current Idref = 40A. The zero-sequence injection coefficient K3 = 0.3. The simulation waveform is shown below. Figure 15 As shown. Figure 15The diagram also shows that when the three-phase grid voltage is balanced, after zero-sequence injection, the three-phase bridge arm voltages form a saddle-shaped wave (see v for the corresponding information). brefABC This improves DC voltage utilization and ensures distortion-free three-phase current (see i for details). gABC The third harmonic injected into the three-phase bridge arm voltage through the open loop is basically equal to the total third harmonic, indicating that the output of the third resonant controller is basically zero.

[0112] Figure 16 When the three-phase power grid voltage is unbalanced, after injecting zero sequence, the three-phase bridge arm voltages form a saddle-shaped wave (see v for corresponding information). brefABC This improves DC voltage utilization and ensures no distortion in the three-phase current (see i for details). gABC The third AC harmonics injected into the three-phase bridge arm voltage open loop are different. The phase with higher grid voltage has a larger amplitude of the third AC harmonic injected into the open loop. However, the total third AC harmonics are basically the same in all phases. This indicates that the third resonant controller enables the total third AC harmonics to automatically synchronize and achieve the zero-sequence effect.

[0113] Figure 17 Parts (A) and (B) respectively illustrate the suppression effect of the DC-Link voltage at twice the frequency of the circuit before and after the zero-sequence component is injected according to the present invention. Figure 17 It can be seen that the injection of the third harmonic makes the waveform of the bridge arm voltage closer to a square wave. The power fluctuation of the power obtained by multiplying the bridge arm voltage and current by 2 times is reduced. The peak value of the Vdc voltage fluctuation peak in the figure is reduced from 80V to 50V, a reduction of more than 30%.

[0114] The third embodiment of the present invention is a method for calculating the average value of all first information applied to a three-phase Y-connected system.

[0115] like Figure 18 As shown, in the third embodiment of the present invention, the power conversion system is, for example, a three-phase Y-connected system, which may include three Y-connected power conversion units CELLA, CELLB, and CELLC. The first terminal of each power conversion unit CELLA / CELLB / CELLC includes a positive input terminal and a negative input terminal, respectively. The positive input terminal of each power conversion unit CELLA / CELLB / CELLC is connected to a phase input source (e.g., V). gA v gB v gC The negative input terminals of all power conversion units CELLA, CELLB, and CELLC are shared (e.g., shared at node N). Each power conversion unit CELLA, CELLB, and CELLC includes a controller 20, which includes a harmonic control unit 21. In some embodiments, each phase power conversion unit CELLA, CELLB, and CELLC may also be replaced with... Figure 3The circuit shown consists of N power conversion units connected in series, where N is an integer greater than 1.

[0116] In this third embodiment, the controller 20 also includes a current inner loop control unit 201 and a voltage outer loop control unit 202. Each current inner loop control unit 201 also includes a resonant control unit 21 and a first arithmetic unit 22. The composition and operation of the current inner loop control unit 201, the voltage outer loop control unit 202, the resonant control unit 21, and the first arithmetic unit 22 are basically the same as in the first embodiment, and will not be repeated here. Furthermore, the method for calculating the average value of the first information of all power conversion units in this third embodiment for a three-phase Y-connected system is basically the same as the method for calculating the average value of the first information of all power conversion systems in a single-phase series system or a single-phase parallel system in the first embodiment, and will not be repeated here either. Unlike the first embodiment, in this third embodiment, the value of M in the three-phase Y-connected system cannot be a multiple of 3; preferably, M=2. The first electrical signal at the first terminal of each power conversion unit is, for example, the bridge arm voltage v of the corresponding power conversion unit. bA v bB v bC .

[0117] Next, the principle of calculating the average value of the first information of all power conversion units in the three-phase Y-connected system of this third embodiment will be further explained. When M=2, the Mth AC harmonic injected into the open-loop controller 20 of each power conversion unit CELLA, CELLB, and CELLC is a negative sequence component, while the output R of the PR controller is... M This exactly suppresses the negative order component. Assume R MA The output of the A-phase PR controller, as described in the principle of the second embodiment, is... .like Figure 19 As shown, taking phase A as an example, V MA V MB V MC The two harmonics injected into the three-phase open-loop circuit have different amplitudes. Assuming the three-phase power grid is balanced, then V MA V MB V MC Phase difference 120 o R MA Rotate to V MA In an oriented coordinate system (i.e., step five in the first embodiment), R is obtained. MAd ,have V MAm V MBm V MCm V represents MA V MB V MC The amplitude, thus R MAdThis reflects the weighted average of the open-loop injected harmonic amplitudes of each phase. Similarly, we have... , .

[0118] Therefore, the method for calculating the average value of the first information of all power conversion units in a single-phase system can be directly applied to a three-phase Y-connected system. The result is a three-phase weighted average value, which is also the common-mode information.

[0119] Furthermore, to obtain the arithmetic mean of the first information in a three-phase Y-connected system, the following transformation can be performed:

[0120]

[0121]

[0122]

[0123] At this time there is .

[0124] Simulation of the effect of the third embodiment:

[0125] The averaging method of this third embodiment is used in... Figure 1A In the three-phase SST system shown, each phase contains one power conversion unit. The control block diagram and parameters of each power conversion unit are exactly the same as those of the power conversion unit in the first embodiment. This third embodiment is used to calculate the integral output average value of the Vdc voltage secondary regulation loop.

[0126] A simulation model was built in Matlab, with the Vdc voltage set to a fixed 780V and the output voltage set to 350V. The AC-DC converter in the power conversion unit uses a Totem-Pole PFC module, the DC-DC converter is an LLC, and the output is connected in parallel with an electronic load. The grid voltage is 880V, and the grid-side filter inductor L... f =15mH. The control frequency is 12K, and the relevant parameter values ​​extracted by averaging are: K p =30, K r = 50, α = 0.01. The Vdc voltage setting is 700V, the output voltage setting is 468V, and the mains voltage amplitude setting is 410V. When the mains voltage is adjusted to 95% of the set value, Vdc will drop because the droop setpoint of the AC-DC bridge arm voltage amplitude Vbm deviates from the set value. Subsequently, the secondary regulation loop will integrate the Vdc error and output it. The steady-state waveform experimental results are as follows: Figure 20 As shown, from Figure 20 It is evident that, in steady state, the secondary regulation loops of all three power conversion units have outputs, injecting the second harmonic VbM2 into the system, and the amplitudes of the injected values ​​differ across the three phases. avgThe average value is the result of the three-phase extraction. Because it is a weighted average of the integral values, the three phases are not exactly the same, but the sum is equal to the sum of the injected harmonic amplitudes. The final average Vdc voltage is 700V, and the average output voltage Vo is also 468V, the same as the set value. This experiment proves that the averaging method of this invention can be successfully applied to a three-phase Y-connected system and can eliminate the steady-state error caused by droop control.

[0127] In summary, the present invention has the following technical advantages: (1) it can transmit common mode information without relying on additional communication lines; (2) it suppresses the AC harmonics of the connection port of the power conversion unit, which does not cause harmonic pollution to the system and improves the voltage quality; (3) it injects AC harmonics of the same frequency into each power conversion unit, which occupies a small frequency band and is simple to control.

[0128] Exemplary embodiments of the present invention have been specifically illustrated and described above. It should be understood that the present invention is not limited to the disclosed embodiments; rather, the present invention is intended to cover various modifications and equivalent arrangements contained within the spirit and scope of the appended claims.

Claims

1. A communication method for a power conversion system, used to transmit common-mode information, characterized in that, The communication method includes the following steps: (a) Provide at least two power conversion units, the first terminals of the at least two power conversion units being electrically coupled, and each of the power conversion units including a resonant control unit; (b) Each of the power conversion units generates an AC harmonic according to the first electrical signal at its first terminal, wherein the amplitude of each AC harmonic represents the first information of the corresponding power conversion unit, and all the AC harmonics have the same frequency. (c) Inject the corresponding AC harmonic at the first terminal of each power conversion unit, and use the resonant control unit in the power conversion unit to perform closed-loop suppression of the corresponding AC harmonic, and control the resonant control unit to output a second electrical signal related to the first information, the second electrical signal containing the common-mode information or being able to further generate the common-mode information of the power conversion unit with the injected AC harmonic.

2. The communication method of the power conversion system according to claim 1, characterized in that, In step (b), the power conversion unit generates an AC harmonic based on the first electrical signal at its first terminal, including: (b1) The first electrical signal at the first terminal of the power conversion unit is phase-locked and frequency-multiplied to generate the phase of the AC harmonic; (b2) Set K times the first information of the power conversion unit to the amplitude of the AC harmonic, where K is a positive number.

3. The communication method of the power conversion system according to claim 1, characterized in that, The power conversion system is a single-phase system, and the first terminals of the at least two power conversion units are connected in series, and the first electrical signal is the current flowing through the first terminal.

4. The communication method of the power conversion system according to claim 1, characterized in that, The power conversion system is a single-phase system, and the first terminals of the at least two power conversion units are connected in parallel, and the first electrical signal is the voltage of the first terminal.

5. The communication method of the power conversion system according to claim 1, characterized in that, The power conversion system is a three-phase system and includes three power conversion units. Each power conversion unit has a positive input terminal and a negative input terminal at its first terminal. The positive input terminal of each power conversion unit is connected to a corresponding phase input source. All the negative input terminals of the power conversion units are connected together. The first electrical signal is the voltage at the first terminal of the corresponding power conversion unit.

6. The communication method of the power conversion system according to any one of claims 3-5, characterized in that, Each piece of the first information represents the variable value or integral value of the current, voltage, power, and temperature of the corresponding power conversion unit, and the common mode information is the average value of all the first information.

7. The communication method of the power conversion system according to claim 6, characterized in that, Each power conversion unit includes an electrically coupled power conversion module and a controller. Each controller includes a voltage outer loop control unit and a current inner loop control unit. Each current inner loop control unit generates a voltage reference value for the first terminal of the power conversion unit based on the current at the first terminal of its corresponding power conversion unit, a reference value of the current at the first terminal, and the injected AC harmonics. Each voltage outer loop control unit generates a reference value of the current at the first terminal of the power conversion unit based on the voltage reference value at the first terminal of its corresponding power conversion unit, so that each power conversion unit performs dual-loop control.

8. The communication method of the power conversion system according to claim 7, characterized in that, Each of the aforementioned current inner loop control units includes the resonant control unit and a first arithmetic unit, wherein each of the aforementioned resonant control units includes a first proportional controller and an Mth resonant controller, where M is a positive integer greater than 1, wherein: The first proportional controller performs proportional calculations on the current at the first terminal of the corresponding power conversion unit and the reference value of the current at the first terminal, and then outputs a first output signal accordingly. The Mth harmonic controller performs resonance control on the current at the first terminal of the corresponding power conversion unit and the reference value of the current at the first terminal, and outputs an Mth harmonic signal accordingly. The Mth harmonic signal is the second electrical signal containing the common mode information. The first arithmetic unit generates a voltage reference value for the first terminal of the power conversion unit based on the first output signal of the corresponding power conversion unit, the Mth harmonic signal, and the injected AC harmonic. Wherein, when the power conversion system is a three-phase system, M is not equal to a multiple of 3.

9. The communication method of the power conversion system according to claim 8, characterized in that, Each of the controllers further includes an average value extraction unit for extracting the average value of all the first information in the Mth harmonic signal.

10. The communication method of the power conversion system according to claim 5, characterized in that, The first information is K times the amplitude of the first electrical signal, where K is a positive number; the common-mode information is the zero-sequence component of the voltage at the first terminal.

11. The communication method of the power conversion system according to claim 10, characterized in that, Each power conversion unit includes an electrically coupled power conversion module and a controller. Each controller includes a voltage outer loop control unit and a current inner loop control unit. Each current inner loop control unit generates a voltage reference value for the first terminal of the power conversion unit based on the current at the first terminal of its corresponding power conversion unit, a reference value of the current at the first terminal, and the AC harmonics. Each voltage outer loop control unit generates a reference value for the current at the first terminal of the power conversion unit based on the voltage reference value of its corresponding power conversion unit, so that each power conversion unit performs dual-loop control.

12. The communication method for the power conversion system according to claim 11, characterized in that, Each of the aforementioned current inner loop control units includes the resonant control unit and a first arithmetic unit, wherein each of the resonant control units includes a first proportional controller and a third resonant controller, and each of the first arithmetic units includes a first arithmetic unit and a second arithmetic unit, wherein... The first proportional controller performs proportional calculations on the current at the first terminal of the corresponding power conversion unit and the reference value of the current at the first terminal, and then outputs a first output signal accordingly. The third harmonic controller performs resonance control on the current at the first terminal of the corresponding power conversion unit and the reference value of the current at the first terminal, and outputs a third harmonic signal accordingly. The first arithmetic unit generates the common-mode information of its corresponding power conversion unit based on the third harmonic signal of its corresponding power conversion unit and the injected AC harmonics. The second arithmetic unit generates the voltage reference value of the first terminal of its corresponding power conversion unit based on the first output signal of its corresponding power conversion unit and the common-mode information.

13. A power conversion system, characterized in that, The power conversion system includes: At least two power conversion units, the first terminals of the at least two power conversion units are electrically coupled, each power conversion unit includes a controller, and each controller includes a resonant control unit; The controller of each power conversion unit is configured to perform: An AC harmonic is generated based on the first electrical signal at the first terminal of the power conversion unit, wherein the amplitude of the AC harmonic represents the first information of the corresponding power conversion unit, and all the AC harmonics have the same frequency. The corresponding AC harmonics generated are injected into the first terminal of the power conversion unit, and the corresponding AC harmonics are suppressed by the resonant control unit in the power conversion unit. The resonant control unit is controlled to output a second electrical signal related to the first information. The second electrical signal contains common-mode information or can further generate common-mode information of the power conversion unit with the injected AC harmonics.

14. The power conversion system according to claim 13, characterized in that, The resonant control unit of the controller in each of the power conversion units is configured to perform: The first electrical signal at the first terminal of the power conversion unit is phase-locked and frequency-multiplied to generate the phase of the AC harmonic; The amplitude of the AC harmonic is set to K times the first information of the power conversion unit, where K is a positive number.

15. The power conversion system according to claim 13, characterized in that, The power conversion system is a single-phase system, and the first terminals of the at least two power conversion units are connected in series, and the first electrical signal is the current flowing through the first terminal.

16. The power conversion system according to claim 13, characterized in that, The power conversion system is a single-phase system, and the first terminals of the at least two power conversion units are connected in parallel, and the first electrical signal is the voltage of the first terminal.

17. The power conversion system according to claim 13, characterized in that, The power conversion system is a three-phase system and includes three power conversion units. Each power conversion unit has a positive input terminal and a negative input terminal at its first terminal. The positive input terminal of each power conversion unit is connected to a corresponding phase input source. All the negative input terminals of the power conversion units are connected together. The first electrical signal is the voltage at the first terminal of the corresponding power conversion unit.

18. The power conversion system according to claims 15-17, characterized in that, Each piece of the first information represents the variable value or integral value of the current, voltage, power, and temperature of the corresponding power conversion unit, and the common mode information is the average value of all the first information.

19. The power conversion system according to claim 18, characterized in that, Each of the power conversion units includes an electrically coupled power conversion module and a controller, each controller comprising a voltage outer loop control unit and a current inner loop control unit, wherein: The current inner loop control unit is configured to generate a voltage reference value for the first terminal of the power conversion unit based on the current at the first terminal of the corresponding power conversion unit, a reference value of the first terminal current, and the injected AC harmonics. The voltage outer loop control unit is configured to generate a reference value for the current at the first terminal of the corresponding power conversion unit based on the voltage reference value at the first terminal of the power conversion unit, so that each power conversion unit performs dual-loop control.

20. The power conversion system according to claim 19, characterized in that, Each of the aforementioned current inner loop control units includes the resonant control unit and a first arithmetic unit, wherein each of the aforementioned resonant control units includes a first proportional controller and an Mth resonant controller, where M is a positive integer greater than 1, wherein: The first proportional controller is configured to perform proportional calculations on the current at the first terminal of the corresponding power conversion unit and a reference value of the first terminal current, and then output a first output signal accordingly. The Mth harmonic controller is configured to resonate and control the current at the first terminal of the corresponding power conversion unit and the reference value of the first terminal current, and then output an Mth harmonic signal. The Mth harmonic signal is the second electrical signal containing the common mode information. The first arithmetic unit is configured to generate a voltage reference value for the first terminal of the power conversion unit based on the first output signal of the corresponding power conversion unit, the Mth harmonic signal, and the injected AC harmonic. Wherein, when the power conversion system is a three-phase system, M is not equal to a multiple of 3.

21. The power conversion system according to claim 20, characterized in that, Each of the controllers further includes an average value extraction unit for extracting the average value of all the first information in the Mth harmonic signal.

22. The power conversion system according to claim 17, characterized in that, The first information is K times the amplitude of the first electrical signal, where K is a positive number; the common-mode information is the zero-sequence component of the voltage at the first terminal.

23. The power conversion system according to claim 22, characterized in that, Each of the power conversion units includes an electrically coupled power conversion module and a controller, each controller comprising a voltage outer loop control unit and a current inner loop control unit, wherein: The current inner loop control unit is configured to generate a voltage reference value for the first terminal of the power conversion unit based on the current at the first terminal of the corresponding power conversion unit, a reference value of the first terminal current, and the injected AC harmonics. The voltage outer loop control unit is configured to generate a reference value for the first terminal current of the power conversion unit based on the voltage reference value of the corresponding power conversion unit, so that each power conversion unit performs dual-loop control.

24. The power conversion system according to claim 23, characterized in that, Each of the aforementioned current inner loop control units includes the resonant control unit and a first arithmetic unit, wherein each of the resonant control units includes a first proportional controller and a third resonant controller, and each of the first arithmetic units includes a first arithmetic unit and a second arithmetic unit, wherein... The first proportional controller is configured to perform proportional calculations on the current at the first terminal of the corresponding power conversion unit and a reference value of the first terminal current, and then output a first output signal accordingly. The third harmonic controller is configured to output a third harmonic signal after performing resonance control on the current at the first terminal of the corresponding power conversion unit and the reference value of the first terminal current. The first arithmetic unit is configured to generate common-mode information of the corresponding power conversion unit based on the third harmonic signal of the corresponding power conversion unit and the injected AC harmonics, and the second arithmetic unit generates a voltage reference value of the first terminal of the corresponding power conversion unit based on the first output signal of the corresponding power conversion unit and the common-mode information.

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