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    • 专利摘要:
    System and procedure of control of a multilevel modular converter as a current source. The system comprises: 1) measuring means of the dc voltage vdc and alternating voabc of the converter. 2) means of measuring the network voltage vabc. 3) measuring means of alternating current iabc. 4) means of measuring the voltage vsm in the modules. 5) control means responsible for: To. Get the angle θ of the network voltage vector vabc. B. Get the components α β of the network voltage vabc (v{al} and v{be}) and of the alternating current iabc (i{al} and i{be}). C. Obtain the dq components of the network voltage vabc (vd and vq) and the alternating current iabc (id eiq) D. Generate alternating current references iabc on axes dq (id * and iq *). And. Obtain the alternating current references iabc in axes α β (i{al} * and i{be} *). F. Obtain the alternating current references iabc *. G. Calculate the number of modules in the on state in each branch. (Machine-translation by Google Translate, not legally binding)
    公开号:ES2598809A1
    申请号:ES201500591
    申请日:2015-07-30
    公开日:2017-01-30
    发明作者:Fernando MARTÍNEZ RODRIGO；Santiago DE PABLO GÓMEZ；Luis Carlos Herrero De Lucas；Dionisio Ramírez Prieto
    申请人:Universidad Politecnica de Madrid；Universidad de Valladolid；
    IPC主号:
    专利说明:

    Multilevel converter current source. Technical sector
    First sector: POWER ELECTRONICS
    Second sector: ELECTRONIC CONVERTERS FOR ALTATENSION APPLICATIONS State of the art
    The converters used in high-voltage direct current (HVDC) transmission are fundamentally of two types, while a third type can be found more at the research level and is beginning to be used in some installations. The two types of commonly used are the line switched converter (LCC) and the voltage source converter (VSC). VSC converters can be two levels or multilevel. At the research and experimentation level is the multi-level modular converter (MMC), first introduced for HVDC applications by Marquardt. MMC converters have the following advantages over other topologies used in the
    1) Capacitive energy storage is distributed.
    2) It is a modular topology, so it is easily scalable.
    3) Due to the large number of levels, filters and transformer may not be necessary.
    4) The resulting switching frequency is high.
    The disadvantage is the large number of semiconductors and drivers that are needed. In addition, the energy stored in the capacitors is greater than in the VSC converters of two or three conventional levels. It is a very interesting topology, not only for HVDC transmission, but also for other applications, such as: motor drive, STATCOM, back-to-back converters, solar and wind generation, matrix converters and more.
    To control the output voltage of the converter, the state of the art offers several possibilities:
    1) Multilevel PWM control. Take the reference of the output voltage as a starting point, calculate the average value of the reference voltage in each PWM period, and determine how long the modules have to be ON for the average output value to be the same .
    2) PWM control with carrier phase shift. Is based on the
    comparison of the reference of the output voltage with a number of carriers
    triangular equal to the number of modules per branch.
    3) Predictive control. Calculate, each switching period, a cost function for
    each of the module status combinations, and select the status
    With the lowest cost function.
    The converter's output voltage control systems have the inconvenience of complexity and the need for high computing power. Each of the three output voltage control systems requires a large number of operations in a very small time. In addition, the system has the complexity of needing an external current control loop to control the voltage and a decoupling block of the equations for connection to the network on the d and q axes.
    N. Flourentzou, V.G. Agelidis, GD. Demetriades, VSC-based HVDC power transmission systems: an overview, IEEE Trans Power Electron. 2009; 24 (3): 592-602.
    M. Montilla-DJesus, D. Santos-Martín, S. Arnaltes, E.D. Castronuovo Optimal reactive power allocation in an offshore wind farms with LCC-HVdc link connection. Renew Energy 2012; 40 (1): 157-66.
    A. Lesnicar, R. Marquardt, An innovative modular multilevel converter topology suitable for a wide power range. Proc. Power Tech Conference; 23-26 Jun. 2003. Bologna-Italy.
    S. Rohner, S. Bernet, M. Hiller, R. Sommer, Modulation, Josses, and semiconductor requirements of modular multilevel converters, IEEE Trans Ind Electron. 2010; 57 (8): 2633-42.
    M. Zhang, L. Huang, W. Yao, Z. Lu, Circulating harmonic current elimination of a CPSPWM-based modular multilevel converter with a plug-in repetitive controller, IEEE Trans Power Electron. 2014; 29 (4): 2083-97.
    S. Du, J. Liu, A study on of voltage control for chopper-cell-based modular multilevel converters in D-STATCOM application, IEEE Trans Power Deliver. 2013; 28 (4): 2030-8.
    H. Mohammadi P., M. Tavakoli Bina, A transforrnerless medium-voltage STATCOM topology based on extended modular multilevel converters, IEEE Trans Power Electron. 2011; 26 (5): 1534-45.
    IN. Abildgaard, M. Molinas, Modeling and control of the modular multilevel converter (MMC), Energy Procedia. 2012; 20: 227-36. Description of the invention
    The present invention solves the aforementioned problems of the output voltage generation systems (complexity and need for high computing power). Replace the current control loop, plus the decoupling block of the voltage equations, plus the voltage modulator, with a single current control block.
    The system that has been invented allows the direct control of the output current of the converter, by means of the appropriate actuation of the modules of the different branches.
    The structure of the MMC can be seen in Figure 1. It has 6 branches, formed by the serial connection of several modules and an inductance. Each module consists of two IGBTs, two diodes and a capacitor. The number of modules in the ON state in the upper and lower branches are called nu and n1 respectively. The sum of both must be equal to the number of modules n per branch, n = nu + n1. Therefore, the voltage of each module must be regulated to a value equal to vc = VDC / n.
    The output voltage of each voabc branch can only take one of n + 1 the number of voabc values is. Table 1 shows the number of modules of the upper and lower branch n1 of each phase that must be switched ON in each case.
    The control system and procedure of a multi-level modular converter (MMC) as a current source comprises:
    1) Means of measurement of the voltage vDC in the DC zone.
    2) Means for measuring the voltage of the vabc power grid.
    3) Means for measuring the output voltage of the MMC voabc converter.
    4) Measuring means of the iabc current in the alternating current zone.
    5) Measuring means of the vSM voltage in the converter modules.
    6) Control means responsible for:
    to. Obtain the angle θ of the vector of the grid voltage vabc ·
    b. Obtain the components α and β of the mains voltage vabc (vα and vβ) and of the current of the iabc converter (iα and iβ).
    C. Obtain the components d and q of the mains voltage vabc (vd and vq) and the current of the iabc converter (id and iq).
    d. Generate the current references of the iabc converter on the d and q axes (id ● and iq ●).
    and. Obtain the current references of the iabc converter on the α and β axes (iα ● and iβ ●).
    F. Obtain the current references of the iabc ● converter.
    g. Calculate the number of modules that have to be in the ON state in each branch of the MMC. Brief Description of the Invention
    It is a system and procedure to control MMC converters as current sources. The control system consists of measuring elements of various voltages and currents, and calculation elements that can be digital processors or FPGA.
    The control procedure is an iterative system that in each cycle takes the values of the measurement elements and generates the number of ON / OFF modules β in each branch of the MMC.
    In each iteration, it is measured whether the current of each phase is within or outside a defined current band around the reference current of said phase. If inside, the number of modules in the ON state of each branch (called nu if it is an upper branch, and n1 if it is a lower branch) remains the same as in the previous iteration. If it is outside the current band, the output voltage (part of the alternating current) of the MMC is varied (increased or decreased) to get the value of the alternating current back into the band If the alternating current has exceeded In the band, the MMC output is chosen to be the one immediately below the mains voltage, while if the alternating current is lower than the band, an MMC output voltage immediately exceeds the mains voltage is imposed. Explanation of the figures and tables
    Figure 1 shows, according to the state of the art, a three-phase MMC with 5 modules (SM) per branch. The structure of each SM appears in the upper right.
    Figure 2 shows, according to the state of the art, the connection diagram of the MMC to the power grid by means of an inductance.
    Figure 3 shows the general control scheme. It includes, according to the state of the art, a PI regulator for active power P or for direct current voltage VDC, and a PI regulator for reactive power Q. It uses, according to the state of the art, modules for the transformation between components abc , αβ and dq. The invention is included in the "Comparator in current source" block.
    Figure 4 shows: (a) the discrete values that the output voltage v0 of the MMC can take, and that the values of the mains voltage vf are sinusoidal in shape and fall within the range of the vo values; (b) the network connection of each phase;
    (c) the control of the current of the MMC if within a band ε of current around the reference value if ●.
    Figure 5 shows the control procedure of a multilevel modular converter (MMC) as a current source: (a) the discrete levels of vo that can be applied are those immediately above and below the mains voltage vf; (b) when the current ir exceeds the current band, a voltage v immediately below the mains voltage vf is applied, while when the current if leaves the current band at the bottom, the MMC voltage is applied immediately higher than the mains voltage vf; (c) procedure diagram.
    Figure 6 refers to the application example and shows the voabc output voltages of the MMC, the voltages of the vabc power grid, the output currents of the iabc converter and the reference values of the output currents of the iabc ● converter.
    Figure 7 refers to the application example and shows the harmonics of the current ia of the first phase.
    Table 1 shows, according to the state of the art, the levels of the output voltage of the MMC voabc as a function of the number of SM in ON of the upper branch nu and of the lower branch n1 of each phase, where vc = vDC / n .
    Table 2 shows the simulation parameters used in the embodiment example of the invention. Detailed description of the invention
    The invention relates to the control of an MMC converter connected to the power grid by means of a coupling inductance (Figure 2) and controlled at a current source. The active powers P and reactive Q are controlled by two proportional integral PI regulators (Figure 3). Another option is to replace the active power regulator P with a DC voltage regulator VDC. The references of the currents in the direct axes id ● and quadrature iq ● are obtained from the PI regulators with respect to the network voltage vector vabc. From these currents the references of the currents of the three phases iabc ● are obtained. The angle θ for the Park transformation is obtained from the tensions of the vabc network, usually by means of a PLL. The values of P and Q are obtained from the iabc currents and the vabc voltages of the network.
    The output voltage of each voabc branch can take n + 1 different values (Figure 4a), depending on the number of modules in ON in the upper branches nu and lower n1 (nu + n1 = n):
    In this invention, the ir phase current (Figure 4b) is maintained in a bands around the reference current if ● (Figure 4c) by controlling the output voltage of each phase vo (Figure 4b).
    The increase in the inductance current ir depends on the voltage at its ends,
    ∆if = ∫ (vo - vf) dt. The inductance current ir increases or decreases depending on
    that the voltage in the inductance is positive or negative, respectively. When the number of modules n of each branch is reduced, the voltage of each module is normally sufficient to direct the current of the inductance if effectively towards its reference value if ●. Therefore, a new method has been included in this invention in which the output voltage of the voabc MMC takes the adjacent values
    (Figure 5a). To obtain these values of vo voltage, a number of modules (SM) equal to n1 = k must be switched ON. The reason for choosing these vo values is to reduce the value of the coupling inductance with the Lc network, taking advantage of the fact that the vo voltage can vary in small steps due to the use of a multilevel converter.
    The control procedure of this invention is as follows. When the if current is separated from the reference value if ● a magnitude greater than the ε band, the necessary voabc voltage is calculated, which will have a distance with respect to the network voltage vabc as small as possible (Figure 5b). Voabc voltage responds to the following formulas:
    Y
    which are used, respectively, when the current flow has gone below and above the band ε around if ●. The constant k is calculated so that the values kvC and
    (k + 1) vC are the levels adjacent to the network voltage vf
    (Figures 5a and 5b):
    The expression "ent" means rounding to the nearest integer tending towards less infinity.
    The procedure diagram can be seen in Figure 5c. At first, it is analyzed whether the current ir exceeds the band at the top, if> (if * + ε), and, if so, the number of modules in the lower branch n1 is changed to the value k, so that the tension of
    Vo output is equal to kvC. Afterwards, it is verified if the current flow goes through the part
    lower of the band, if <(if * -ε), and, if so, the number of modules in the lower branch n is changed, to the value (k + 1), so that the output voltage vo is equal to
    (k +
    1) vC. When the ir current is within the band, the value of n1 is not changed from the previous iteration. The final part is the calculation of nu as a function of n1. Example of embodiment of the invention
    An example of embodiment is presented with 5 modules per branch (n = 5), and the graphs of the variables obtained by simulation using the parameters in Table 2. The meaning of the parameters that have not appeared previously is:
    TS General Simulation Step
    Tcr Simulation step of the current regulator
    TPQr Simulation step of the P and Q regulators
    Kp, P; Ki, P Proportional and integral constants of the P regulator
    Kp, Q; ki, Q Proportional and integral constants of the Q regulator
    The voltages and currents can be seen in Figure 6. The voltages have 6 levels that are always the values immediately above and below the grid voltage. It is observed that the currents perfectly follow the values of their references. The harmonics of the phase currents (Figure 7) are lower than the limit values established by the regulations, both in total harmonic distortion and in magnitude of the individual harmonics.
    权利要求:
    Claims (5)
    [1]
    1. Control system of a multi-level modular converter (MMC) as a current source, characterized in that it comprises:
    to. Means for measuring the VDC voltage in the DC area.
    b. Means for measuring the vabc voltage in the alternating current zone.
    C. Measuring means of the iabc current in the alternating current zone.
    d. Means for measuring the voltage vuabc and v1abc in the upper and lower branches, respectively, of the converter.
    and. Control means
    [2]
    2.  Control system according to claim 1, characterized in that the control means is a digital signal processor.
    [3]
    3.  Control system according to claim 1, characterized in that the control means is an FPGA.
    [4]
    Four.  Control procedure of a modular multilevel converter (MMC) as a current source characterized in that the control means, according to claims 1, 2 and 3, is responsible for performing the following actions:
    to. Obtain the angle θ of the vector of the grid voltage vabc.
    b. Obtain the components αβ of the mains voltage vabc (vα and vβ) and the alternating current iabc (iα and iβ).
    C. Obtain the components dq of the mains voltage vabc (vd and vq) and the alternating current iabc (id and iq).
    d. Generate the alternating current references iabc on dq axes (id ● and iq ●).
    and. Obtain the references of alternating current iabc in axes αβ (iα ● and iβ ●).
    F. Get the references of alternating current iabc ●.
    g. Calculate the number of modules in ON state in each branch.
    [5]
    5. Control procedure of a modular multilevel converter (MMC) as a current source characterized in that the control means, according to claims 1 to 4, is responsible for calculating the number of modules in the ON state in each branch according to the procedure described below. :
    When the current ir distances itself from the reference value if ● a magnitude greater than the ε band, the voabc voltage is calculated using the following formulas:
    Y
    which are used, respectively, when the current flow has gone below and above the band ε around if ●. The constant k is calculated so that the values kvC and
    (k + 1) vC are the levels adjacent to the network voltage vf 10 using the following equation:
    The expression "ent" means rounding to the nearest integer tending towards at least 15 infinity.
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    同族专利:
    公开号 | 公开日
    ES2598809B1|2017-12-27|
    引用文献:
    公开号 | 申请日 | 公开日 | 申请人 | 专利标题
    ES2616274A1|2017-03-22|2017-06-12|Universidad Politécnica de Madrid|Method and control system of a multilevel modular converter of high voltage direct current |
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