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    • 专利摘要:
    Voltage control method for a system comprising a converter (3) connected to a limited power source (1), and a capacitor (2) connected in parallel to a converter (3), with which a reference power is calculated to control the power to be injected by the system. To calculate said reference power, the method comprises the steps of measuring the output voltage (v) of the power source (1) and calculating the square of said output voltage (v), calculating a voltage error as the difference between said square and the square of a reference voltage, apply the voltage error as input for a controller, which outputs a required power, calculate a virtual power in a virtual impedance (Zv) arranged in parallel to the capacitor (2), and add the required power and the virtual power. (Machine-translation by Google Translate, not legally binding)
    公开号:ES2805174A1
    申请号:ES201930742
    申请日:2019-08-09
    公开日:2021-02-10
    发明作者:Senosiain Roberto Gonzalez；Malumbres Juan Luis Agorreta；Erburu Andoni Urtasun；Gurpide Pablo Sanchis；Palomo Luis Marroyo
    申请人:Ingeteam Power Technology SA；
    IPC主号:
    专利说明:

    [0002] Voltage control method for an electrical power system
    [0004] TECHNICAL SECTOR
    [0006] The present invention relates to a voltage control method for an electrical power system comprising a converter connected to a limited power source.
    [0008] PRIOR STATE OF THE TECHNIQUE
    [0010] Usually, the power sources need to be connected to an electronic converter to adapt the voltage and current levels, as well as their characteristics (direct or alternating), to those required by the load or system to which they are connected. In the case of voltage converters, a capacitor is placed in parallel between it and the power source, allowing the voltage to be set and harmonics reduced. For correct operation, it is normally necessary to carry out a voltage control of the power source, which is carried out by the converter.
    [0012] Thus, for example, the power sources that supply direct current are connected to the electrical network by means of an electronic converter called an inverter, and between the source and the converter a capacitor is placed to fix the voltage and reduce harmonics (normally physically included in the converter).
    [0014] The type of power source used greatly affects voltage control. Some power sources, called limited power sources, supply a power whose value varies with the operating point of the source itself and which is limited to a maximum value. This operating characteristic is typical for most renewable energy sources, such as photovoltaic or wind generators.
    [0016] Limited power sources have a power-voltage curve whose slope varies according to the operating voltage, as shown by way of example in the Figure 1, according to the following pattern:
    [0017] • If the voltage is greater than the maximum power voltage V mpp , the slope is negative.
    [0018] Therefore, in this operating zone, an increase in voltage causes a reduction in the power supplied.
    [0019] • If the voltage is equal to the maximum power voltage V mpp , the slope is equal to zero and small voltage variations do not cause power variations.
    [0020] • If the voltage is less than the maximum power voltage V mpp , the slope is positive.
    [0021] In other words, in this operating zone, an increase in voltage causes an increase in the power supplied.
    [0023] When designing the required tension control for these systems, it is imperative to maintain stability throughout the operating range. However, when the output voltage of the source is less than the maximum power voltage V mpp , the limited power source behaves as a negative resistance to the voltage control and tends to destabilize it. This influence is more important the greater the slope of the power-voltage curve (for the same power, it affects to a greater extent in systems with low voltage and high current), and the smaller the capacitor. For this reason, it is common to oversize the capacitor, which reduces the influence of the limited power source and stabilizes the control throughout the operating range, at the expense of increasing the cost of the system.
    [0025] For a photovoltaic application, a comprehensive analysis of the factors causing instability can be found in the document T Messo, J. Jokipii, J. Puukko, and T. Suntio. Determining the Value of DC-Link Capacitance to Ensure Stable Operation of a Three-Phase Photovoltaic Inverter. IEEE Transactions on Power Electronics, vol. 29, no. 2, pp. 665-673, Feb.
    [0026] 2014". The authors of this article calculate the minimum value of the capacitor necessary to be able to make the control stable over the entire operating range, showing that it is necessary to oversize it.
    [0028] EXHIBITION OF THE INVENTION
    [0030] The object of the invention is to provide a voltage control method for an electrical power system comprising a converter connected to a limited power source and a capacitor connected in parallel between the converter and the source, as described in the claims.
    [0032] The output power of the converter is controlled by an active power control. The proposed method determines a reference or command power to be used as an input for said active power control. The active power control employed can be any known and conventional such control.
    [0034] To calculate said reference power, the method comprises the steps of:
    [0035] - measure the output voltage of the power source,
    [0036] - calculate the square of the output voltage of the measured power source,
    [0037] - calculating a voltage error as the difference between the square of the output voltage of the measured power source and the square of a given reference voltage, said reference voltage being the required output voltage for said power source,
    [0038] - apply the voltage error as an input for a controller that outputs a required power necessary to bring the system to operate at the determined reference voltage (and thus control the output voltage based on this condition),
    [0039] - emulating the presence of a virtual impedance arranged in parallel to the power source and the capacitor, and calculating a virtual power in said virtual impedance, from the square of the measured output voltage, and
    [0040] - add together the reference power and the virtual power.
    [0042] The reference power is the result of this sum.
    [0044] The present invention focuses on modifying the voltage control to reduce the influence of the limited power source, and for this the concept of virtual impedance emulation is used. With the method of the invention it is achieved that the voltage loop is stable throughout the operating range of the power source, without the need to oversize the capacitor, in such a way that said method is adapted to stabilize the voltage control. Thus, since it is possible to use a condenser of a smaller size than that achieved in the state of the art, the method of the invention allows reducing the costs of the system and increase its reliability, with a change in the control of the converter that has low computational cost and that can be easily implemented even in systems that are already in the field.
    [0046] This and other advantages and characteristics of the invention will become apparent in view of the figures and the detailed description of the invention.
    [0048] DESCRIPTION OF THE DRAWINGS
    [0050] Figure 1 shows a power-voltage curve for a photovoltaic generator.
    [0052] Figure 2 shows a system adapted to support an embodiment of the method of the invention, composed of a limited power source, a capacitor and a converter.
    [0054] Figure 3 shows a block diagram that generically represents a voltage control loop, which includes an embodiment of the control method of the invention, an internal power control and the plant of the system of Figure 2.
    [0056] Figure 4 shows a block diagram in the Laplace domain, representing a voltage loop of an embodiment of the control method of the invention.
    [0058] Figure 5 shows a block diagram in the Laplace domain, representing the voltage loop of Figure 4, together with an internal power control and the system plan of Figure 2.
    [0060] Figure 6 shows a block diagram in the Laplace domain, representing a voltage loop of another embodiment of the control method of the invention that comprises an analog filter, together with an internal power control and the plant of the system of the figure 2.
    [0062] Figure 7 shows a block diagram in the Laplace domain, representing a voltage loop of another embodiment of the control method of the invention comprising an analog filter and a digital filter, together with an internal power and plant control. of the system figure 2.
    [0064] Figure 8a shows the result of the simulation of a control method without virtual impedance emulation, against steps in the reference voltage, with voltages close to and lower than the maximum power point voltage.
    [0066] Figure 8b shows the result of the simulation with the preferred embodiment of the control method of the invention, against steps in the reference voltage, with voltages close to and lower than the voltage of the maximum power point.
    [0068] DETAILED EXHIBITION OF THE INVENTION
    [0070] The method of the invention is adapted to control the voltage of a limited power source 1 of an electrical power system 100 as shown in Figure 2, and is preferably performed dynamically. Preferably the power source 1 is a renewable energy source such as photovoltaic or wind. The system 100 also comprises a capacitor 2 connected in parallel to the power source 1. In turn, this set is connected to the destination to which it is desired to inject power generated in the power source 1, such as a converter, a battery , a DC network or the electrical network, for example, by means of a converter 3 of the system 100 itself. The converter 3 can be a DC / DC converter, a DC / AC converter or a DC / DC DC / AC converter, for example, depending on where you want to connect the assembly. Alternatively the capacitor 2 could be integrated in the converter 3 itself, for example.
    [0072] Such a system 100 is shown in Figure 2, where P source is the power supplied by power source 1 and P out is the output power of converter 3, which is equal to the power injected by system 100 to the destination. correspondent.
    [0074] The method of the invention proposes a new voltage control method to reduce the influence of the limited power source 1 in said control, more specifically in eliminating or reducing the effect of the variability of the power source 1. In systems 100 As described, it is common to perform an active power control to control the output power P out to be injected by system 100, by means of an LP power control. The method of the invention is configured to calculate a reference power Pref that is used as input of the LP power control, as it is represented in a generic way in the example of figure 3, by means of the implementation of a voltage loop 9 Said reference power Pref is the power required to be injected at the output.
    [0076] Starting from the reference power Pref, there are various ways to control this power (to implement the LP power control), which is outside the scope of the present invention, being able to use any known or conventional power control applicable to said system 100. Thanks to this LP power control, the output power P out injected by the system 100 will follow the reference power Pref calculated with the method of the invention, with certain dynamic characteristics that depend on the LP power control. employee.
    [0078] The proposed voltage loop 9 has a reference voltage vref as a reference voltage, said reference voltage vref being the voltage v required for power source 1. The reference voltage vref depends on the application or use that is to be given to it. the power source 1, and may be that necessary for the power source 1 to give the maximum possible power, for example, or any other if it is required to limit the capacity of said power source 1.
    [0080] As shown in figure 3, the output power P out of the converter 3 is related to the output voltage v in the set formed by the power source 1 and the capacitor 2, whose relation is determined by the plant of the system 100.
    [0082] In the method, instead of directly using the measured output voltage v, the output voltage v squared is used since it is naturally related to the power, which facilitates the calculations since the objective is to calculate a power Pref reference that serves as an input for LP power control.
    [0084] In the method, an output voltage v of the power source 1 is measured, using said output voltage v measured as an input for the voltage loop 9, in addition to the reference voltage vref previously described (see Figures 3 and 4 for example). In the method, implemented in the voltage loop 9, the square of said output voltage v and the square of the reference voltage vref, and a voltage error is calculated which is the result of the subtraction between said square of the measured output voltage v and said square of the reference voltage Vref. The voltage error is used as an input to a controller 8, which outputs a required power Pv necessary to control the measured output voltage v. The controller 8 can be, for example, of the integral, proportional integral (PI) or proportional integral derivative (PID) type.
    [0086] It is known that the impedance of the power source 1 can be variable as a function of its operating point (which depends on the output voltage v), as previously described. Therefore, in the method of the invention it is proposed to emulate a virtual impedance Zv arranged in parallel to the power source 1, as shown in dashed lines in the example of figure 2, controlling the voltage of the assembly formed by the limited power source 1 and virtual impedance Zv in parallel. The virtual impedance Zv parallel to the power source 1 and, therefore, to the impedance of said power source 1, reduces the effect of the impedance of the power source 1. Thanks to the proposed method and in particular to the emulation of the virtual impedance Zv, the controller 8 sees an equivalent impedance different from the original one (without virtual impedance Zv), and, in this way, with this emulation it is possible to eliminate the effect of the variability of the impedance of the power source 1 , without it being necessary to oversize capacitor 2. Preferably a virtual impedance Zv is emulated with constant parameters, and a virtual impedance Zv is chosen so that the poles in the right half plane of the original system 100 are eliminated, which, as is known, facilitates stable control design.
    [0088] Thus, in the method (implemented in voltage loop 9), a virtual power P zv associated with said virtual impedance Zv emulated is calculated, from the output voltage v measured, and to said virtual power Pzv the output of the controller 8 (the required power Pv). The result of this sum is the reference power Pref that serves as input for the LP power control and that represents the output power P out to be supplied by the system 100. Thus, this output power P out has been obtained considering the virtual impedance Zv, which in turn cancels the variability of the impedance of power source 1, thereby obtaining an output power P out to supply suitable for different operating points and without the need for physical modifications such as the case of the state of the art, where capacitor 2 is dimensioned to be able to operate in all cases. Figure 4 shows an embodiment of the tension loop 9 in the Laplace domain, where Yv (s) represents the transfer function of the virtual admittance relative to the virtual impedance Zv, and Zv (s) represents the transfer function of the virtual impedance Zv itself.
    [0090] Figure 5 represents the example of Figure 3 in the Laplace domain, where LP (s) represents the transfer function of power control.
    [0092] The calculations required to calculate the reference power Pref can be performed in analog or digital form.
    [0094] The system 100 can further comprise an analog filter not represented in the figures and arranged at the output of the power source 1, to filter the noises and / or high-frequency components of the output voltage v. In this case, the method of the invention would take into account said filter, as represented by way of example in Figure 6.
    [0096] In some embodiments, at least one digital filter can be implemented in the control loop 9, with the purpose of eliminating or reducing the harmonics of a given frequency (as many digital filters as frequencies are to be eliminated or reduced), and this digital filter is it can be combined with an analog filter or it can be used without the need for an analog filter. Figure 7 represents the example of figure 3, further including a digital filter in the control loop 9 and the system 100 including an analog filter (which is also considered in the voltage loop 9). Figure 7 represents the transfer functions Hdig (s) and Han (s) of the digital and analog filters respectively.
    [0098] Although in Figures 6 and 7 the calculation of the square has been contemplated before filtering the output voltage v, such calculations could also be performed after filtering.
    [0100] In a preferred embodiment, the method is applied to a photovoltaic generator (as power source 1) in parallel with a capacitor 2, both connected by means of a converter 3 to the electrical network. Preferably the converter 3 is therefore an inverter.
    [0102] In some embodiments, the voltage measurement is filtered before considering it for the various calculations, in analog and / or digital form as described above, to eliminate any specific frequency and / or high frequency noise. In the preferred embodiment, just an analog filter.
    [0104] In the same system 100, a control method has been simulated without virtual impedance emulation (figure 8a) and the preferred embodiment of the proposed control method (figure 8b), in both cases power source 1 being the same photovoltaic generator and the same capacitor 2. The results are shown in said figures 8a and 8b respectively, for the same reference voltage steps Vref in the most unfavorable operating zone, that is, with a voltage equal to or less than that of maximum power. It can be seen that the control method without virtual impedance emulation becomes unstable, approximately at 4s, being necessary to increase the size (capacity) of capacitor 2 to stabilize it. However, the proposed control method is stable over the entire operating range.
    1
    权利要求:
    Claims (1)
    [0001]
    Voltage control method for an electrical power system (100) comprising a converter (3) connected to a limited power source (1), and a capacitor (2) connected in parallel between the converter (3) and the source (1), characterized in that the method is adapted to calculate a reference power (Pref) for a power control (LP) with which the output power (P out ) of the converter (3) is controlled, and to calculating said reference power (Pref), the method comprises the steps of:
    - measure the output voltage (v) of the power source (1),
    - calculate the square of the output voltage (v) of the measured power source (1), - calculate a voltage error as the difference between the square of the output voltage (v) of the power source (1) and the square of a given reference voltage (vref), said reference voltage (vref) being the output voltage (v) required for said power source (1),
    - apply the voltage error as input for a controller (8), which outputs a required power (Pv) necessary to bring the system (100) to operate at the determined reference voltage (vref),
    - emulate the presence of a virtual impedance (Zv) arranged in parallel to the power source (1) and the capacitor (2), and calculate a virtual power (P zv ) in said virtual impedance (Zv), from the square of the measured output voltage (v), and - add together the reference power (Pv) and the virtual power (Pzv),
    the result of said sum being the reference power (Pref).
    Control method according to claim 1, wherein the controller (8) is of the integral, proportional integral (PI) or proportional integral derivative (PID) type.
    Control method according to any of the preceding claims, wherein the measured output voltage (v) is filtered before considering them for the different calculations or after calculating the square of said output voltage (v), the filter used being a filter low pass, high pass, band pass, band rejection, or a combination of these.
    Control method according to claim 3, wherein to filter the output voltage (v) measured, at least one analog filter is used.
    Control method according to claim 3 or 4, wherein to filter the measured output voltage (v), at least one digital filter is used.
    Control method according to claim 5, wherein the digital filter is configured to filter the components of the output voltage (v) of a given frequency.
    Control method according to claim 5 or 6, wherein a plurality of digital filters are used to filter the measured output voltage (v), each digital filter being configured to filter the components of the output voltage (v) of a determined frequency and said determined frequencies being different from each other.
    8. Control method according to any of the preceding claims, wherein the reference voltage (vref) is the voltage necessary for the power source (1) to supply the maximum possible power.
    Control method according to any one of claims 1 to 7, wherein the reference voltage (vref) is a voltage different from the voltage necessary for the power source (1) to supply the maximum possible power, in such a way that the capacity of said power source (1) is limited.
    Control method according to any of the preceding claims, wherein the calculation of the reference power (Pref) is carried out in an analog or digital way.
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    同族专利:
    公开号 | 公开日
    DE102020209797A1|2021-02-11|
    ES2805174B2|2021-10-27|
    引用文献:
    公开号 | 申请日 | 公开日 | 申请人 | 专利标题
    ES2641304A1|2016-05-06|2017-11-08|Ingeteam Power Technology, S.A|Method and control system to control the voltage of an electronic converter connected to a power source or storage system |
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    申请号 | 申请日 | 专利标题
    ES201930742A|ES2805174B2|2019-08-09|2019-08-09|Voltage control method for an electrical power system|ES201930742A| ES2805174B2|2019-08-09|2019-08-09|Voltage control method for an electrical power system|
    DE102020209797.6A| DE102020209797A1|2019-08-09|2020-08-04|Voltage control method for an electrical power supply system|
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