New energy voltage source converter station equivalent impedance calculation method based on network following control

Abstract

The application discloses a new energy voltage source converter station equivalent impedance calculation method based on grid-following control and relates to the technical field of power electronics. The application includes the impedance equivalence of the control strategy and the converter model of the voltage source converter station of the grid-following control, is simple in logic and accurate in value. The method can effectively avoid the difficulty in impedance analysis caused by the mutual interference between the coupling quantities and the adoption of complex analysis methods such as small signal analysis by fully decoupling the converter itself and the coupling quantities in the grid-following control strategy through the conversion of the control coordinate system to the complex vector coordinate system, the equivalent process is simple, and the calculation amount is reduced. The new energy voltage source converter station equivalent impedance calculation method provided by the application is divided into control strategy equivalence and converter model equivalence, is finally integrated into a unified impedance expression, and the real-time equivalence of the new energy converter station impedance considering the new energy working condition is realized.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of power electronics, and particularly relates to a new energy voltage source converter station equivalent impedance calculation method based on grid-following control. BACKGROUND

[0002] Building a large-scale new energy grid-connected transmission system is a key link in China's energy transformation. With the continuous expansion of new energy base scale, the problems of large power fluctuation amplitude of new energy station, small system inertia, and power electronics characteristics are highlighted. By analyzing the grid-connected impedance of new energy base, the influence of new energy grid connection on the existing network can be judged from the electrical distance level, so the equivalent impedance analysis of new energy converter station becomes a new research direction. Unlike traditional generator impedance, the equivalent impedance of new energy converter station is related to the type of converter and the control strategy of converter, so the equivalent impedance of new energy converter station is a variable. Considering the large fluctuation amplitude and high fluctuation frequency of new energy output, it is necessary to combine the real-time working condition of new energy converter station for equivalent, and a simpler and faster calculation method is needed to calculate the equivalent impedance of new energy station.

[0003] When the new energy base power is stable, if the grid-connected line impedance of new energy is ignored, the electrical distance between the new energy base and the grid-connected point is mainly the equivalent impedance of the converter station; when the new energy output fluctuates, both the grid-connected voltage and current fluctuate, and the fluctuations of the two are affected by the type and control strategy of the new energy converter station. The influence of new energy output fluctuation on the grid-connected point can be measured by the electrical connection degree between the new energy base and the grid-connected point.

[0004] Currently, there is little research on the equivalent impedance calculation of new energy converter station. In view of the fact that the current wind power and photovoltaic power in China are mainly converted by grid-following control voltage source converter (VSC) and then connected to the AC network, the main research focus is to improve the control strategy or integrate supporting devices to reduce the impact of new energy grid connection on the stability of the network, and the focus is on improving the voltage strength of the new energy grid-connected point. There is still a gap in analyzing the connection between new energy station grid connection and power grid from the electrical distance level, i.e. using equivalent impedance.

[0005] In order to solve the above problems, the present application provides a new energy voltage source converter station equivalent impedance calculation method based on grid-following control. SUMMARY

[0006] The application aims to provide a new energy voltage source converter station equivalent impedance calculation method based on a grid-following control to solve the problem of measuring the connection degree of a new energy base and a system in the background art.

[0007] To achieve the above-mentioned purpose, the application adopts the following technical solutions:

[0008] The new energy voltage source converter station equivalent impedance calculation method based on the grid-following control is realized by a new energy voltage source converter station equivalent impedance calculation system based on the grid-following control, and the calculation system comprises:

[0009] The complex vector coordinate system is used to decouple the control link and the converter model in the new energy converter station, and realize independent reflection of the voltage-current relationship of different coordinate axes.

[0010] The controlled source equivalence is used to reflect the influence of the decoupled control quantity on the output voltage and current of the new energy converter station to the impedance, and realize the equivalence of the grid-following new energy voltage source converter station impedance.

[0011] The calculation method comprises the following steps:

[0012] First, the dq coordinate system is further converted into the complex vector coordinate system to ensure that the voltage-current relationship in the same coordinate axis is independent.

[0013] Then, the grid-following new energy voltage source converter station is equivalent to a controlled source, so that the control strategy is reflected to the control quantity of the controlled source.

[0014] Finally, the control quantity is reflected to the circuit impedance to realize the equivalent calculation of the impedance of the grid-following new energy voltage source converter station.

[0015] Preferably, the grid-following control comprises power control and current control.

[0016] Preferably, the equivalent impedance comprises the equivalent impedance of the new energy converter station control module and the converter module, i.e., the equivalent impedance based on the grid connection point.

[0017] Preferably, the transformation of the complex vector coordinate system is a further conversion based on the dq coordinate system, and all control quantities are subjected to coordinate transformation to decouple the control link and the converter model in the new energy converter station, so as to ensure that the voltage-current relationship in the same coordinate axis is independent.

[0018] Preferably, the controlled source equivalence further represents the equivalence of the grid-following type new energy voltage source converter station to a controlled source, reflects the control strategy into the control quantity, and then reflects the control quantity into the circuit impedance to achieve the equivalent calculation of the impedance of the grid-following type new energy voltage source converter station.

[0019] Preferably, the specific function of the calculation method is represented as follows:

[0020] The input / output model formula of the voltage source converter in the complex vector coordinate system is as formula (1):

[0021]

[0022] Wherein, L c , r c respectively represent the inductance and resistance of the AC side of the converter; ω represents the grid angle frequency; u sdq+ , u sdq- respectively represent the components of the forward vector and the backward vector of the grid-connected point voltage of the grid-following type new energy voltage source converter station; u dq+ , u dq- respectively represent the components of the forward vector and the backward vector of the outlet of the grid-following type new energy voltage source converter station; i dq+ , i dq- respectively represent the components of the forward vector and the backward vector of the current of the converter in the complex quantity form;

[0023] The control strategy of the voltage source converter in the complex vector coordinate system is as formula (2):

[0024]

[0025] Wherein, i dq+ref , i dq-ref respectively represent the forward vector and the backward vector components of the current setting value of the grid-following type new energy voltage source converter station;

[0026] The equivalence of the impedance of the grid-following type new energy voltage source converter station in the complex vector coordinate system is as formula (3):

[0027]

[0028] Z dq+ , Z dq- are calculated as formula (4) and formula (5)

[0029]

[0030]

[0031] Wherein, G I (s)=k pi +k ii / s represents a proportional integral element in current control, G V (s)=k pv +k iv / s represents a proportional integral element in voltage control; k pv , k iv respectively represent a proportional control constant and an integral control constant of voltage control.

[0032] Compared with the prior art, the application provides a new energy voltage source converter station equivalent impedance calculation method based on grid-following control, which has the following beneficial effects:

[0033] The application provides a new energy voltage source converter station equivalent impedance calculation method based on grid-following control, which decouples control elements and converter models in a new energy converter station in a complex vector coordinate system, reflects the influence of the decoupled control quantity on the output voltage and current of the new energy converter station into impedance based on a controlled source equivalent, realizes the equivalent of the impedance of the grid-following new energy voltage source converter station, and can evaluate the influence of the new energy converter station on the grid voltage after the new energy converter station is connected according to the equivalent impedance of the grid-following new energy voltage source converter station in combination with the new energy output, which has important significance for actual engineering application. BRIEF DESCRIPTION OF DRAWINGS

[0034] Figure 1 The application provides a new energy voltage source converter station equivalent impedance calculation method based on grid-following control, which has the following beneficial effects:

[0035] Figure 2 The application provides a new energy voltage source converter station equivalent impedance calculation method based on grid-following control, which has the following beneficial effects:

[0036] Figure 3 The application provides a new energy voltage source converter station equivalent impedance calculation method based on grid-following control, which has the following beneficial effects:

[0037] Figure 4 The application provides a new energy voltage source converter station equivalent impedance calculation method based on grid-following control, which has the following beneficial effects: DETAILED DESCRIPTION

[0038] The technical solutions in the embodiments of the application will be clearly and completely described below with reference to the drawings in the embodiments of the application. Obviously, the described embodiments are only part of the embodiments of the application, rather than all the embodiments of the application.

[0039] Embodiment 1:

[0040] The application provides a new energy voltage source converter station equivalent impedance calculation method based on grid-following control.

[0041] A complex vector coordinate system is used to decouple control links and converter models in the new energy converter station, and independent reflection of voltage and current relationships corresponding to different coordinate axes is realized.

[0042] A controlled source equivalent is used to reflect the influence of the decoupled control quantity on the output voltage and current of the new energy converter station to the impedance, and the equivalent of the grid-following new energy voltage source converter station impedance is realized.

[0043] Based on the above system, the calculation method is specifically as follows:

[0044] First, the dq coordinate system is further converted into a complex vector coordinate system to ensure that the voltage and current relationship under the same coordinate axis is independent, and then the grid-following new energy voltage source converter station is equivalent to a controlled source, so that the control strategy is reflected to the control quantity of the controlled source, and finally the control quantity is reflected to the circuit impedance, realizing the equivalent calculation of the grid-following new energy voltage source converter station impedance, which is simple in logic and convenient in calculation.

[0045] Based on the above content, the grid-following new energy voltage source converter station impedance equivalent calculation method specifically includes the following content:

[0046] The input / output model formula of the voltage source converter under the complex vector coordinate system is as formula (1):

[0047]

[0048] Wherein: L c , r c are the inductance and resistance of the AC side of the converter, ω is the grid angle frequency, u sdq+ , u sdq- are the components of the forward vector and backward vector of the grid-connected point voltage of the grid-following new energy voltage source converter station, u dq+ , u dq- are the components of the forward vector and backward vector of the outlet of the grid-following new energy voltage source converter station, i dq+ , i dq- are the components of the forward vector and backward vector of the converter current in the complex quantity form.

[0049] As can be seen from formula (1), the forward vector of the converter voltage is only related to the forward vector of the current, and the backward vector of the voltage is only related to the backward vector of the current, and the converter itself model is decoupled.

[0050] The voltage source converter control strategy under the complex vector coordinate system is as formula (2):

[0051]

[0052] Wherein: i dq+ref , i dq-ref Respectively, the forward vector and the backward vector component of the current setting value of the grid-following new energy voltage source converter station.

[0053] As can be seen from formula (2), the corresponding voltage forward vector of the converter control is only related to the current forward vector, and the voltage backward vector is only related to the current backward vector, and the converter control corresponding model realizes decoupling.

[0054] The equivalent impedance of the grid-following new energy voltage source converter station in the complex vector coordinate system is as formula (3):

[0055]

[0056] Z dq+ , Z dq- The calculation is as formula (4) and formula (5)

[0057]

[0058]

[0059] Wherein: G I (s) = k pi +k ii / s is the proportional integral element in the current control, G V (s) = k pv +k iv / s is the proportional integral element in the voltage control, k pv , k iv Respectively, the proportional control constant and the integral control constant of the voltage control, which can be adjusted in combination with the control parameters of the converter station.

[0060] The application will be further described in detail in combination with the drawings:

[0061] Figure 1 The application provides a grid-following new energy voltage source converter station equivalent impedance calculation method corresponding converter station control link and equivalent model schematic diagram. As Figure 1As shown, the grid-connected renewable energy voltage source converter station uses power control and current control to trigger the converter based on grid connection point voltage information collected by the phase-locked loop (PLL), combined with the power setting value and the actual voltage and current at the grid connection point. A coupling strategy exists between the current control link and the converter model, and this collaboration achieves decoupled control of the converter station's active and reactive power. However, this only achieves decoupled control of the converter station. Coupling still exists for calculating the converter station's equivalent impedance, hindering the reflection of the converter station's voltage and current relationships. Therefore, a complex quantity coordinate system is introduced to further transform the control coordinate system.

[0062] Figure 2 This diagram shows the voltage-current response relationship between the forward and backward vectors of the converter station current control and the converter model, after conversion to a complex coordinate system. The current control is decoupled from the forward and backward vector components of the converter model. The voltage circuit relationship of the current control model is primarily related to the proportional-integral control link and the system inductance, but the system inductance has opposite effects on the forward and backward vectors, which is consistent with the actual current control link. The converter station model, on the other hand, is primarily related to system parameters, and its output voltage-current relationship is affected by the system's own parameters. At this point, the voltage-current relationship corresponding to the converter station's forward and backward vectors is only affected by the control parameters of this control link and the system parameters, facilitating analysis of the system voltage-current relationship under the two vectors.

[0063] Figure 3 After the grid-following new energy converter is equivalent to a controlled source, the control quantity is decomposed by combining the converter station control strategy and the converter working model under the compound quantity coordinate, and reflected in the control of the circuit voltage and current. If there is a preprocessing of the corresponding variables in the circuit, such as the voltage feedforward gain corresponding to Fv in the figure, it can also be included in the control coefficient of the controlled source without introducing a new coupling quantity. According to the controlled source equivalent principle, the control coefficient corresponding to the current-controlled voltage source can be equivalent to the impedance connected in series to the controlled source circuit, and the control coefficient corresponding to the voltage-controlled current source can be equivalent to the admittance connected in parallel to the controlled source circuit. By combining the i in the forward vector and the backward vector dq+ 、i dq- The extraction and merging of different flow control and pressure control coefficients can be realized separately, providing a basis for converting the control coefficients into equivalent impedance.

[0064] Figure 4 It is the final equivalent circuit diagram considering power control, current control and converter model in the complex quantity coordinate system. Figure 3The controlled quantity of the controlled source is extracted and combined, the control coefficients corresponding to different control quantities are impedance equivalent, the conversion relationship of the voltage source and the current source is combined, and the equivalent impedance is connected into the circuit; then power control is added, and the controlled quantity and the control coefficient of the controlled source are repeatedly impedance equivalent and connected into the circuit, wherein, * represents the conjugate of complex power. Finally, the equivalent impedance of the grid-connected new energy voltage source converter station is calculated through coordinate inverse transformation.

[0065] The above is only the preferred specific embodiment of the present application, but the protection scope of the present application is not limited thereto, any person skilled in the art can make equivalent replacement or change according to the technical scheme and the inventive concept of the present application within the technical range disclosed by the present application, which should be covered within the protection scope of the present application.

Claims

1. A method for calculating equivalent impedance of a new energy voltage source converter station based on grid-following control, characterized in that: The calculation method is implemented based on an equivalent impedance calculation system for a new energy voltage source converter station with grid-following control, and the calculation system includes: Complex vector coordinate system: used to decouple the control links and converter models in the new energy converter station, and realize the independent reflection of the voltage and current relationship corresponding to different coordinate axes; Controlled source equivalence: used to reflect the influence of the decoupled control quantity on the output voltage and current of the new energy converter station into the impedance, so as to achieve the impedance equivalence of the grid-connected new energy voltage source converter station; The calculation method comprises the following steps: First, the dq coordinate system is further converted into a complex vector coordinate system to ensure that the voltage and current relationships on the same coordinate axis are independent. Then, the grid-connected new energy voltage source converter station is equivalent to the controlled source, so that the control strategy is reflected in the controlled quantity of the controlled source; Finally, the control quantity is reflected in the circuit impedance to achieve equivalent calculation of the impedance of the grid-following new energy voltage source converter station; The specific function of the calculation method is expressed as follows: The input / output model formula of the voltage source converter in the complex vector coordinate system is as follows: (1) in, L c 、 r c Respectively represent the inductance and resistance of the AC side of the converter; ω represents the grid angular frequency; u sdq+ 、 u sdq- They represent the components of the forward vector and backward vector of the grid connection point voltage of the grid-following new energy voltage source converter station respectively; u dq+ 、 u dq- They represent the components of the forward vector and backward vector at the outlet of the grid-connected new energy voltage source converter station respectively; i dq+ 、 i dq- They represent the components of the forward and backward vectors of the converter current in compound quantity form respectively; The control strategy of the voltage source converter in the complex vector coordinate system is as follows: (2) in, i dq+ref 、 i dq-ref They represent the forward vector and backward vector components of the current setting value of the grid-following new energy voltage source converter station respectively; The equivalent impedance of the grid-type new energy voltage source converter station in the complex vector coordinate system is as follows: (3) Z dq+ 、 Z dq- The calculation of is as shown in formula (4) and formula (5) (4) (5) in, G I (s)= k pi + k ii / s Represents the proportional integral link in current control, G V (s)= k pv + k iv / s Represents the proportional integral link in voltage control; k pv 、 k iv They represent the proportional control constant and integral control constant of voltage control respectively.

2. The method for calculating equivalent impedance of a new energy voltage source converter station based on grid-following control according to claim 1 is characterized in that: The grid-following control includes power control and current control.

3. The method for calculating equivalent impedance of a new energy voltage source converter station based on grid-following control according to claim 1 is characterized in that: The equivalent impedance includes the equivalent impedance of the new energy converter station control module and the converter module, that is, the equivalent impedance based on the grid connection point.

4. The method for calculating equivalent impedance of a new energy voltage source converter station based on grid-following control according to claim 1 is characterized in that: The transformation of the complex vector coordinate system is a further conversion based on the dq coordinate system. The coordinates of all control variables are transformed to decouple the control links and converter models in the new energy converter station to ensure the independence of the voltage and current relationship under the same coordinate axis.

5. The method for calculating equivalent impedance of a new energy voltage source converter station based on grid-following control according to claim 1 is characterized in that: The controlled source equivalence further indicates that the grid-controlled new energy voltage source converter station is equivalent to a controlled source, the control strategy is reflected in the control quantity, and the control quantity is then reflected in the circuit impedance, thereby realizing the equivalent calculation of the impedance of the grid-controlled new energy voltage source converter station.

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