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

Abstract

The invention discloses a new energy voltage source converter station equivalent impedance calculation method based on network tracking type control, and relates to the technical field of power electronics. According to the invention, impedance equivalence is carried out on the network-following controlled voltage source converter station including the control strategy and the converter model, the logic is simple, and the numerical value is accurate. According to the method, the control coordinate system is converted into the complex vector coordinate system, the converter and the coupling quantity in the converter and the network type control strategy are fully decoupled respectively, it can be effectively avoided that due to mutual interference between the coupling quantities, impedance analysis is difficult, and complex analysis methods such as small signal analysis are adopted, the equivalent process is simple, and the calculated amount is reduced; the method for calculating the equivalent impedance of the new energy voltage source converter station under network tracking type control is divided into control strategy equivalence and converter model equivalence, the control strategy equivalence and the converter model equivalence are finally integrated into a unified impedance expression, and real-time equivalence of the impedance of the new energy converter station considering the new energy working condition is achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of power electronics and in particular to a method for calculating equivalent impedance of a new energy voltage source converter station based on grid-following control. Background Art

[0002] Building a large-scale renewable energy grid-connected transmission system is a key link in my country's energy transformation. With the continuous expansion of the scale of new energy bases, the problems faced by new energy stations, such as large power fluctuations, small system inertia, and power electronic characteristics, have become prominent. By analyzing the grid-connected impedance of new energy bases, the impact of new energy grid connection on the existing grid can be judged from the electrical distance level. Therefore, the equivalent impedance analysis of new energy converter stations has become a new research direction. Unlike traditional generator impedance, the equivalent impedance of a new energy converter station is related to the converter type, converter control strategy, etc. Therefore, the equivalent impedance of a new energy converter station is a variable. Taking into account the large fluctuation amplitude and high fluctuation frequency of new energy output, this requires the need to be equivalent in combination with the real-time operating conditions of the new energy converter station. A simpler and faster calculation method is needed to calculate the equivalent impedance of the new energy station.

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

[0004] At present, there are few studies on the calculation of equivalent impedance of new energy converter stations. Given that my country's wind power and photovoltaic power are currently mainly converted into AC grids by grid-following control voltage source converters (VSC), the main research focus is on improving control strategies or incorporating supporting equipment to reduce the impact of new energy grid connection on grid stability, with a focus on improving the voltage intensity of new energy grid connection points. There is still a gap in analyzing the connection between new energy stations and the power grid from the electrical distance level, that is, using equivalent impedance.

[0005] In order to solve the above problems, the present invention proposes a method for calculating the equivalent impedance of a new energy voltage source converter station based on grid-following control. Summary of the invention

[0006] The purpose of the present invention is to propose a method for calculating the equivalent impedance of a new energy voltage source converter station based on grid-following control to solve the problem of measuring the degree of connection between a new energy base and a system proposed in the background technology. The present invention is based on complex vector coordinate transformation and controlled source equivalence, combined with control strategies and converter models to calculate the equivalent impedance of a new energy voltage source converter station.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions:

[0008] A method for calculating equivalent impedance of a new energy voltage source converter station based on grid-following control, wherein the method is implemented based on an equivalent impedance calculation system for a new energy voltage source converter station based on grid-following control, and the calculation system comprises:

[0009] Complex vector coordinate system: used to decouple the control link and converter model in the new energy converter station, and realize the independent reflection of the voltage and current relationship corresponding to different coordinate axes;

[0010] 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 equivalence of the impedance of the grid-type new energy voltage source converter station;

[0011] The calculation method comprises the following steps:

[0012] Firstly, 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;

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

[0014] Finally, the control quantity is reflected in 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 includes power control and current control.

[0016] Preferably, 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.

[0017] Preferably, the transformation of the complex vector coordinate system is a further conversion based on the dq coordinate system, and coordinate transformation is performed on all control quantities to decouple the control links and converter models in the new energy converter station to ensure that the voltage and current relationship under the same coordinate axis is independent.

[0018] Preferably, the controlled source equivalence further represents 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, so as to realize the equivalent calculation of the impedance of the grid-controlled new energy voltage source converter station.

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

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

[0021]

[0022] Among them, 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 forward vector and backward vector components of the grid-connected point voltage of the grid-connected new energy voltage source converter station respectively; u dq+ 、u dq- They represent the components of the forward vector and the 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 vector and the backward vector of the converter current in the compound quantity form respectively;

[0023] The control strategy of the voltage source converter in the complex vector coordinate system is as follows:

[0024]

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

[0026] The equivalent impedance of the grid-type new energy voltage source converter station in the complex vector coordinate system is as follows:

[0027]

[0028] Z dq+ , Z dq- The calculation of is as shown in formula (4) and formula (5)

[0029]

[0030]

[0031] Among them, 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.

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

[0033] The present invention proposes a method for calculating the equivalent impedance of a new energy voltage source converter station based on grid-following control, decouples the control link and converter model in the new energy converter station in a complex vector coordinate system, and based on the controlled source equivalence, reflects the influence of the decoupled control quantity on the output voltage and current of the new energy converter station into the impedance, thereby realizing the equivalence of the impedance of the grid-following new energy voltage source converter station. At the same time, according to the equivalent impedance of the grid-following new energy voltage source converter station, the influence of the new energy converter station on the grid voltage after access can be evaluated in combination with the new energy output situation, which is of great significance to practical engineering applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 A schematic diagram of a converter station control link and an equivalent model corresponding to the equivalent impedance calculation method of a new energy voltage source converter station based on grid-following control proposed in Embodiment 1 of the present invention;

[0035] Figure 2 It is a schematic diagram of a decoupling model of current control and converter model after complex vector coordinate system conversion proposed in Embodiment 1 of the present invention;

[0036] Figure 3 It is a circuit diagram of controlling the voltage and current of a converter station based on the control strategy of the forward vector and the backward vector after the complex vector coordinate system conversion proposed in Embodiment 1 of the present invention;

[0037] Figure 4 This is a circuit diagram of converting the controlled coefficients based on the forward vector and the backward vector into equivalent resistance after adopting the controlled source equivalent proposed in Embodiment 1 of the present invention. DETAILED DESCRIPTION

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

[0039] Embodiment 1:

[0040] The present invention proposes a method for calculating equivalent impedance of a new energy voltage source converter station based on grid-following control. The method is implemented based on an equivalent impedance calculation system of a new energy voltage source converter station based on grid-following control, and includes:

[0041] The complex vector coordinate system is used to decouple the control link and converter model in the new energy converter station, and realize the independent reflection of the voltage and current relationship corresponding to different coordinate axes;

[0042] 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 into the impedance, so as to achieve the equivalence of the impedance of the grid-type new energy voltage source converter station;

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

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

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

[0046] The input / output model formula of the voltage source converter in the complex vector coordinate system is as follows:

[0047]

[0048] Where: L c 、r c is the inductance and resistance of the AC side of the converter, ω is the grid angular 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 the backward vector at the outlet of the grid-following new energy voltage source converter station, i dq+ 、i dq- The components of the forward vector and backward vector of the converter current in complex quantity form respectively.

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

[0050] The control strategy of the voltage source converter in the complex vector coordinate system is as follows:

[0051]

[0052] Where: i dq+ref 、i dq-ref They are respectively the forward vector and backward vector components of the current setting value of the grid-following new energy voltage source converter station.

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

[0054] The equivalent impedance of the grid-type new energy voltage source converter station in the complex vector coordinate system is as follows:

[0055]

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

[0057]

[0058]

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

[0060] The present invention is further described in detail below in conjunction with the accompanying drawings:

[0061] Figure 1 The figure is a schematic diagram of the converter station control link and equivalent model corresponding to the equivalent impedance calculation method of the grid-type new energy voltage source converter station provided by the present invention. Figure 1As shown in the figure, the grid-following new energy voltage source converter station realizes the triggering control of the converter through the power control and current control links according to the grid connection point voltage information collected by the phase-locked loop, combined with the power setting value and the actual voltage and current of the grid connection point. There is a coupling strategy between the current control link and the converter model, and the decoupling control of the active power and reactive power of the converter station is realized through the cooperation of the two. However, this is only to realize the decoupling control of the converter station. For the calculation of the equivalent impedance of the converter station, there is still coupling, which is not conducive to the reflection of the voltage and current relationship of the converter station. For this reason, the compound quantity coordinate system is introduced to further transform the control coordinate system.

[0062] Figure 2 This is the voltage-current response relationship diagram of the forward vector and backward vector corresponding to the converter station current control and converter model after conversion through the compound quantity coordinate system. The forward and backward vector components corresponding to the current control and converter model are decoupled, where the voltage circuit relationship of the current control model is mainly related to the proportional integral control link and the system inductance, but the system inductance has the opposite effect on the forward and backward vectors, which is also consistent with the actual current control link; while the converter station model is mainly related to the system parameters, and its output voltage-current relationship is affected by the system parameters itself. At this time, the voltage-current relationship corresponding to the forward vector and backward vector of the converter station is only affected by the control parameters of this control link and the system parameters, which is convenient for analyzing the relationship between the system voltage and current 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 enter 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 replacing 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 coefficient 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 3Extract and merge the control quantity of the controlled source, perform impedance equivalence on the control coefficients corresponding to different control quantities, and connect the equivalent impedance to the circuit by combining the conversion relationship between the voltage source and the current source; then add power control, repeat the impedance equivalence of the controlled source control quantity and the control coefficient and connect them to the circuit, where: * represents the conjugate of complex power. Finally, the calculation of the equivalent impedance of the grid-type new energy voltage source converter station is realized through inverse coordinate transformation.

[0065] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

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 of a new energy voltage source converter station controlled by a grid-following type, and the calculation system includes: Complex vector coordinate system: used to decouple the control link and converter model 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 equivalence of the impedance of the grid-type new energy voltage source converter station; The calculation method comprises the following steps: Firstly, 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; Then, the grid-connected new energy voltage source converter station is equivalent to a controlled source, so that the control strategy is reflected in the control quantity of the controlled source; Finally, the control quantity is reflected in the circuit impedance to realize the equivalent calculation of the impedance of the grid-following new energy voltage source converter station.

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 quantities are transformed, the control links and converter models in the new energy converter station are decoupled, and the voltage and current relationship under the same coordinate axis is ensured to be independent.

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.

6. 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 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: Among them, 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 forward vector and backward vector components of the grid-connected point voltage of the grid-connected new energy voltage source converter station respectively; u dq+ 、u dq- They represent the components of the forward vector and the 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 vector and the backward vector of the converter current in the compound quantity form respectively; The control strategy of the voltage source converter in the complex vector coordinate system is as follows: Among them, i dq+ref 、i dq-ref They respectively represent the forward vector and backward vector components of the current setting value of the grid-following new energy voltage source converter station; The equivalent impedance of the grid-type new energy voltage source converter station in the complex vector coordinate system is as follows: Z dq+ , Z dq- The calculation of is as shown in formula (4) and formula (5) Among them, 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.

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