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    • 专利摘要:
    System and procedure for controlling the alternating current of a multilevel modular converter by voltage proportional to the current error. 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 {image-01} And. Obtain the alternating current references iabc on axes {image-02} F. Obtain the alternating current references {image-03} G. Calculate the number of modules in the on state in each branch. (Machine-translation by Google Translate, not legally binding)
    公开号:ES2600757A1
    申请号:ES201500590
    申请日:2015-07-30
    公开日:2017-02-10
    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:

    MULTI-LEVEL CONVERTER WITH ADAPTA TIV TENSION A
    SECTOR OF THE TECHNIQUE
    5 First sector: POWER ELECTRONICS Second sector: ELECTRONIC CONVERTERS FOR HIGH VOLTAGE APPLICATIONS
    STATE OF THE TECHNIQUE
    1 O The converters used in high-voltage direct current (HVDC) transmission are essentially of two types, while a third type can be found more at the level of research and is beginning to be used in some facilities. The two types of commonly used converters are the line switched converter (LCC) and the voltage source converter (VSC). VSC converters can be two levels or 15 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 HVDC transmission:
    20 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.
    25 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.
    30 To control the output voltage of the converter, the state of the art offers several possibilities:
    1) Multilevel PWM control. It takes the reference of the output voltage as a starting point, calculates the average value of the reference voltage in each PWM period, and determines how long the modules have to be ON for the average value of
    output be the same.

    2) PWM control with carrier phase shift. It is based on the comparison of the reference of the output voltage with a number of triangular carriers 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 state 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, G.D. Demetriades, VSC-based HVDC power transmission systems: an overview, IEEE Trans Power Electron. 2009; 24 (3): 592-602.
    M. Montilla-DJesus, D. Santos-Martin, S. Amaltes, E.D. Castronuovo Optimal reactive power allocation in an offshore wind farms with LCC-HVdc link connection. Renew Energy 20 12; 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. Bemet, M. Hiller, R. Sommer, Modulation, losses, and semiconductor requirements ofmodular 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 CPS-PWMbased 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 dc voltage control for chopper-cell-based modular multilevel converters in D-STATCOM application, IEEE Trans Power Deliver. 2013; 28 (4): 2030-8.
    H. Moharnmadi P., M. Tavakoli Bina, A transformerless medium-voltage STATCOM topology based on extended modular multilevel converters, IEEE Trans Power Electron. 2011; 26 (5): 1534
    Four. Five.
    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 nI, respectively. The sum of both must be equal to the number of modules n per branch, n = nu + nl 'Therefore, the voltage of each module must be regulated to a value equal to ve = Voc / n.
    The output voltage of each Voabe branch can only take one of n + 1 discrete values. For example, if n = 5 (Table 1), the number of Voabc values is 6: {-V ~ c + OVe; ... -V ~ c + 5ve}. Table 1 shows the number of modules of the upper and lower branch nI of each phase that
    you have to connect ON in each case.
    The system and method of controlling the alternating current of a modular multilevel converter (MMC) by voltage proportional to the current error comprises:
    one) Means for measuring the voltage Voc in the direct current zone.
    2) Means for measuring the voltage of the Vabe 'grid
    3) Means for measuring the output voltage of the MMC Voabe 'converter
    4) Measuring means of the iabe 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 e of the vector of the network voltage Vabe '
    b. Get the components a and ~ of the mains voltage Vabe (goes Yv ~) and of the current
    of the iabe converter (ia and i ~)
    C. Obtain the d and q components of the mains voltage (Vd Y vq) and the current
    of the iabe converter (id and iq).
    d. Generate the current references of the iabe converter on the d and q axes (id · and iq *).
    and. Obtain the current references of the iabe converter on the axes a and ~ (ia · and ip ").
    F. Obtain the references of the current of the iabe · 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 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 it is inside, the number of modules in the ON state of each branch (called nu if it is an upper branch, and even if it is a lower branch) remains the same as in the previous iteration. If it is outside the current band, the voltage of the converter is increased or reduced by an amount proportional to the distance between the current and the edge of the band. In this way, the farther the band current is, the more voltage is applied to the mating coil with the network to get the current back into the band.
    EXPLANATION OF 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 Voc, and a PI regulator for reactive power Q. It uses, according to the state of the art, modules for the transformation between components abc , (l ~ and dq. The invention is included in the "Comparator with excitation proportional to current error" block.
    Figure 4 shows: (a) the discrete values that the Vodel MMC output voltage can take, and that the values of the network voltage Vr are sinusoidal in shape and fall within the range of Vo values; (b) the network connection of each phase; (c) the control of the current of the MMC go within a band E of current around the reference value i /.
    Figure 5 shows the procedure for controlling the alternating current of a modular multilevel converter (MMC) by voltage proportional to the current error: (a) discrete Vo levels that can be applied depending on the current error; (b) when the ir current leaves the current band a magnitude equal to ir (i / + E) or (i / -E) -ir, a voltage Vo is applied proportional to the magnitude of the error; (c) procedure diagram.
    Figure 6 refers to the application example and shows the Voabe output voltages of the MMC, the voltages of the Vabe grid, the output currents of the iabe converter and the reference values of the output currents of the iabe * 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 Voabe as a function of the number of SM in ON of the upper branch nu and of the lower branch or of each phase, where ve = Voc / 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-intergral PI regulators (Figure 3). Another option is to replace the active power regulator P with a direct current voltage regulator VDC. • From the PI regulators the references of the currents in the direct axes id 'and in quadrature iq' are obtained with respect to the network voltage vector Vabe . From these currents, the references of the currents of the three iabe · phases are obtained. The angle e for the Park transformation is obtained from the tensions of the Vabe network, usually by means of a PLL. The values of P and Q are obtained from the iabe currents and the Vabe voltages of the network.
    The output voltage of each Voabe branch can take n + 1 different values (Figure 4a), depending on the number of modules in ON in the upper branches nu and lower nI (nu + n1 = n):
    Voe
    Vo = -2+ n¡ve
    5 In this invention, the if phase current (Figure 4b) is maintained in a band c around the reference current ir "(Figure 4c) by controlling the output voltage of each Vo phase (Figure 4b).
    The increase in the inductance current if depends on the voltage at its ends, Llif =
    1 O: c f (vo-vf) dt. The inductance current if increases or decreases depending on whether the voltage in the inductance is positive or negative, respectively. When the number of modules n of each branch is high, the voltage of each module may be insufficient to direct the inductance current to go effectively towards its reference value ir. "Therefore, in this invention a new one has been included procedure in which the output voltage of the MMC Voabe
    15 can take values distant from the value of the voltage of the Vabe network to direct the current go very effectively towards its reference value go ".
    The control procedure of this invention is as follows. When the current ir distances itself from the reference value ir "a magnitude greater than the band c, the necessary Voabe voltage is calculated,
    20 which will have a distance from the Vabe network voltage proportional to the distance between if and the current band (Figure 5b). A constant of proportionality k¡ is used between the distance of the Voabe and Vabe voltages, and the distance of the current to go with respect to the current band. The Voabe tension responds to the following formulas:
    Voe ((Cif * -c) -if))
    Vo = -2 + k + 1 + ent k¡ c ve
    Y
    Voe ((if - (if · + c)))
    Vo = -2 + k -ent k¡ c ve
    which are used, respectively, when the current going has gone below and above the 30 c band around going '. The expression "ent" means rounding to the nearest integer tending
    Voc + kve
    towards less infinite. The constant k is calculated so that the values -Y _ Voc +
    2 2
    (k + l) see the levels adjacent to the network voltage vf (Figure 5a).
    The procedure diagram can be seen in Figure 5c. At the beginning, the value of ni is calculated when the if current exceeds the band at the top. Then, the value of ni is calculated when the if current leaves the band at the bottom. When the if current is within the band, the value of ni is not changed from the previous iteration. The final part is a limitation of the value of nI, which must be in the range O to n, and the calculation of nu as a function of ni.
    EXAMPLE OF EMBODIMENT OF THE INVENTION
    An exemplary embodiment is presented with 10 modules per branch (n = 10), and the graphs of the variables obtained by simulation using the parameters in Table 2. The meaning of the parameters that have not previously appeared is:
    General Simulation Step
    Simulation step of the current regulator TPQr Simulation step of the regulators of P and Q kp, p; k¡, p Proportional and integral constants of the regulator of P kp, Q; k¡, Q Proportional and integral constants of the Q regulator
    The voltages and currents can be seen in Figure 6. The voltages have 11 levels that are not only the values immediately above and below the grid voltage, but are proportional to the current error, with a constant of proportionality k¡ chosen to minimize the harmonics of current injected into the network. 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 (1)
    [1]
    1) Alternating current control system of a modular multilevel converter (MMC) by voltage proportional to the current error characterized by comprising
    to. Means for measuring the voltage Voc in the direct current zone.
    b. Means for measuring the Vabe voltage in the alternating current zone.
    C. Measuring means of the iabe current in the alternating current zone.
    d. Means for measuring the voltage Vuabe and Vlabe in the upper and lower branches,
    respectively, of the converter.
    and. Control means
    2) Control system according to claim 1, characterized in that the control means is a digital signal processor. 3) Control system according to claim 1, characterized in that the control means is an FPGA. 4) Procedure for controlling the alternating current 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:
    a) Obtain the angle e of the vector of the network voltage Vabe.b) Obtain the components a and ~ of the mains voltage Vabe (va Y v ~) Y of the current of theiabe converter (ia and i ~).c) Obtain the components d and q of the mains voltage (Vd and vq) and the current of theiabe converter (id and iq).d) Generate the current references of the iabe converter on the d and q axes (id · e iq "), afrom two proportional-integral regulators that act on either the active powerP and reactive Q, or the DC voltage VDC AND reactive power Q.e) Obtain the current references of the iabe converter on the axes a and ~ (ia · and i ~ *).f) Obtain the references of the iabe converter current ".g) Calculate the number of modules that have to be in the ON state in each branch.
    5) Control procedure of a multilevel modular 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 if distance from the reference value goes "a magnitude greater than the band s, the necessary Voabe voltage is calculated, which will have a distance from the Vabe mains voltage
    proportional to the distance between going and the current band (Figure 5b). A constant of proportionality k¡ is used between the distance of the Voabc voltages YVabc, and the distance of the current to go with respect to the current band. The Voabc tension responds to the following formulas:
    Voc
    Vo = -2 + (k + 1 + ent (k¡ (if * -EE) -if)) Ve 5
    Y
    which are used, respectively, when the if current has gone below and above 10 the E band around go. "The expression" ent "means rounding to the nearest integer tending towards less infinity. The constant k is calculated so that the values -V ~ c + kvc Y
    - vDC + (k + l) vc are the levels adjacent to the network voltage vr
    PI
     Figure 3
    n = 5
    /
     one:;: /
    saw
    _._-; c + Ov ('+ (e) -, (a)
     Figure 4
    "---- ,,
    , ni = k + l + in (k, (- '. go _ * _-: _ J-_I ,, - /),
    t, - ~~ '+ - ~ n (k; ~ - ~ Y;~))} ~ _____ J
    Figure 5
    labe.labe ·
    Time
     Figure 6
    Fundamental (50Hz) = 197.6. THD = 1.67%
    Figure 7
    wildebeest neitherVoabc
    5 ORVDC - + Ovc 2
    4 oneVDC - + lvc 2
    3 2VDC -2 + 2vc
    2 3VDC - + 3vc 2
    one 4VDC - + 4vc 2
    OR 5VDC - + Svc 2
    Table 1
    n 10
    Ts 5J.lS
    Ter 15J.lS
    TPQr 120J.lS
    VOC 4kV
    and 60rnF
    L 375J.lH
    Vf, nns 1250V
    € 3A
    You 3rnH
    p * 370kW
    Q * -370kVAR
    kp, p OR
    ki p 0.1
    kp, Q OR
    k¡, Q -0.1
    k¡ 0.5
    Table 2
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    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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