CN115498708B - Grid-connected VSC and power grid interaction analysis method based on frequency response method - Google Patents
Grid-connected VSC and power grid interaction analysis method based on frequency response method Download PDFInfo
- Publication number
- CN115498708B CN115498708B CN202211119808.2A CN202211119808A CN115498708B CN 115498708 B CN115498708 B CN 115498708B CN 202211119808 A CN202211119808 A CN 202211119808A CN 115498708 B CN115498708 B CN 115498708B
- Authority
- CN
- China
- Prior art keywords
- grid
- current
- voltage
- power
- connected converter
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Active
Links
- 238000000034 method Methods 0.000 title claims abstract description 72
- 230000004044 response Effects 0.000 title claims abstract description 44
- 238000012482 interaction analysis Methods 0.000 title abstract description 7
- 230000003993 interaction Effects 0.000 claims abstract description 26
- 238000012546 transfer Methods 0.000 claims description 33
- 230000008569 process Effects 0.000 claims description 22
- 230000008859 change Effects 0.000 claims description 18
- 230000009471 action Effects 0.000 claims description 14
- 238000004458 analytical method Methods 0.000 claims description 14
- 239000003990 capacitor Substances 0.000 claims description 10
- 230000008846 dynamic interplay Effects 0.000 claims description 7
- 230000010355 oscillation Effects 0.000 abstract description 12
- 238000011217 control strategy Methods 0.000 abstract description 4
- 238000012423 maintenance Methods 0.000 abstract description 2
- 238000010586 diagram Methods 0.000 description 7
- 230000001360 synchronised effect Effects 0.000 description 6
- 238000010248 power generation Methods 0.000 description 4
- 238000011160 research Methods 0.000 description 4
- 238000006243 chemical reaction Methods 0.000 description 2
- 230000008878 coupling Effects 0.000 description 2
- 238000010168 coupling process Methods 0.000 description 2
- 238000005859 coupling reaction Methods 0.000 description 2
- 230000009286 beneficial effect Effects 0.000 description 1
- 238000004364 calculation method Methods 0.000 description 1
- 229910052799 carbon Inorganic materials 0.000 description 1
- 238000013461 design Methods 0.000 description 1
- 238000011161 development Methods 0.000 description 1
- 230000009977 dual effect Effects 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 230000007613 environmental effect Effects 0.000 description 1
- 230000002452 interceptive effect Effects 0.000 description 1
Classifications
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
- H02J3/46—Controlling of the sharing of output between the generators, converters, or transformers
- H02J3/48—Controlling the sharing of the in-phase component
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
- H02J3/46—Controlling of the sharing of output between the generators, converters, or transformers
- H02J3/50—Controlling the sharing of the out-of-phase component
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J2203/00—Indexing scheme relating to details of circuit arrangements for AC mains or AC distribution networks
- H02J2203/10—Power transmission or distribution systems management focussing at grid-level, e.g. load flow analysis, node profile computation, meshed network optimisation, active network management or spinning reserve management
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E10/00—Energy generation through renewable energy sources
- Y02E10/70—Wind energy
- Y02E10/76—Power conversion electric or electronic aspects
Landscapes
- Engineering & Computer Science (AREA)
- Power Engineering (AREA)
- Supply And Distribution Of Alternating Current (AREA)
Abstract
A grid-connected VSC and grid interaction analysis method based on a frequency response method belongs to the technical field of operation and maintenance of power systems. On the basis of determining a dynamic response model and a control strategy of the grid-connected converter, the invention deduces a linearization small signal model of active output and reactive output of the grid-connected converter under the condition of small disturbance on the power grid side, further analyzes the response characteristics of active power and reactive power of the grid-connected converter and the interaction between the grid-connected converter and an alternating current power grid under the electromechanical time scale by utilizing a frequency response method, and theoretically analyzes the influence on the electromechanical oscillation characteristics of the power grid after the permanent magnet wind turbine generator based on the grid-connected converter is integrated into the power grid, thereby having important significance for safe and stable operation of a power system with high-proportion access of new energy. Therefore, the invention has high practical application value.
Description
Technical Field
The invention belongs to the technical field of operation and maintenance of power systems, and particularly relates to a grid-connected VSC and grid interaction analysis method based on a frequency response method.
Background
Climate change has become one of the significant environmental and development challenges facing the human society at present, and electric power systems will play a vital leading and supporting role in energy low-carbon conversion. New energy power generation technology represented by wind power and photovoltaic is developed at high speed in all countries of the world, and the new energy power generation ratio in a power grid is continuously improved. Different from the traditional synchronous machine set, the new energy power supply is connected into a power grid through a grid-connected converter (Voltage Source Converter, VSC), and the grid-connected converter VSC enhances the controllability of the new energy power generation system and meanwhile, the dynamic process of the power system after disturbance is extremely complex due to multi-time scale cascade control. The dynamic characteristics of the grid-connected converter under the electromechanical time scale are further studied, and the interaction between the grid-connected converter and the alternating current power grid in the electromechanical dynamic process is analyzed, so that the method has important significance in ensuring the safe operation of the power system after large-scale new energy grid connection.
For the research of electromechanical oscillation of a system after the grid connection of a large-scale new energy unit, the method is mainly focused on the aspect of linear state space modeling of a new energy power generation system, and combines an established state space model with a small signal model of an alternating current system, and calculates electromechanical characteristic parameters of the system by using a traditional small interference analysis method, so that the electromechanical characteristic analysis of the whole system after the grid connection of the new energy is realized. However, the complex multi-time scale response characteristic of the grid-connected converter leads to obvious differences from the dynamic process of the synchronous machine. In the electromechanical oscillation process under the action of small disturbance at the network side, each synchronous unit can generate interaction through AC power grid coupling while oscillating. For a new energy unit connected with a power grid, the power of the new energy unit is interacted with a synchronous generator unit in the system through the grid-connected converter, so that the research on the dynamic characteristics of the grid-connected converter and the interaction between the grid-connected converter and the power grid in the electromechanical process is significant, however, the related research is less at present.
In view of the foregoing, there is a need in the art for a method for effectively analyzing the dynamic interaction between a new energy grid-connected converter and an ac grid during the electromechanical oscillation process, so as to solve the above-mentioned problems.
Disclosure of Invention
The technical problems to be solved by the invention are as follows: the method is used for solving the technical problem that in the prior art, in order to analyze the electromechanical oscillation research of a new energy grid-connected power system, a small signal model is mainly built, characteristic values are adopted for analysis, and the influence of the dynamic characteristics of a grid-connected converter and the interaction between the grid-connected converter and the power grid on the electromechanical characteristics cannot be considered.
The interaction analysis method of the grid-connected VSC and the power grid based on the frequency response method comprises the following steps of:
step one, establishing a topological structure of connection of a grid-connected converter VSC and an alternating current power grid and a corresponding control system, and obtaining a system formed by connection of the grid-connected converter VSC and the alternating current power grid:
① The direct current power of the wind turbine generator after rectification by the rectifier is stabilized by the direct current capacitor and then fed into the alternating current power grid by the grid-connected converter VSC and the filter reactance to obtain a topological structure of the connection of the grid-connected converter VSC and the alternating current power grid;
② Establishing a control system corresponding to the topological structure, wherein the topological structure and the corresponding control system form a system formed by connecting a grid-connected converter VSC and an alternating current power grid, the control system realizes vector control of power grid voltage orientation by adopting a d-q decoupled double-closed-loop control structure combining a voltage outer ring and a current inner ring on the VSC at the alternating current power grid side, d-axis current is active current, q-axis current is reactive current, active power transmitted to the alternating current power grid is controlled by using d-axis current, and reactive power flowing to the alternating current power grid is controlled by using q-axis current;
The outer ring of the d-axis current is controlled by direct current voltage, and the output of the d-axis current is the reference value of the d-axis current and the actual current deviation value of the d-axis; the outer ring of the q-axis current is controlled by alternating voltage, and the output of the q-axis current is the deviation value of the reference value of the q-axis current and the q-axis actual current;
step two, obtaining a small signal model after linearization of active output and reactive output of the grid-connected converter VSC under small disturbance of an alternating current power grid side:
the analysis process of a system formed by connecting the grid-connected converter VSC with an alternating current power grid is simplified through three conditions of a, b and c,
A. The direct current side power is kept constant;
b. Neglecting internal loss of the grid-connected converter VSC;
c. the voltage of a public connection point of the grid-connected converter VSC connected with the alternating current power grid always coincides with the d axis in the electromechanical process;
according to the instantaneous power theory, under the condition that the q-axis voltage is 0, the outlet active power and reactive power of the grid-connected converter VSC satisfy the following conditions:
Wherein P is the active power of the VSC outlet of the grid-connected converter; q is reactive power of a grid-connected converter VSC outlet; v pcc is the ac voltage at the common connection point of the grid-connected converter VSC and the ac grid; i d is the d-axis current; i q is q-axis current;
Under the small disturbance of the AC power grid side, linearizing the formula (1) at a system steady-state operating point comprises the following steps:
Wherein Δp is the amount of change in active power P; Δq is the amount of change in reactive power Q; deltav pcc is the variation of the grid-connected point alternating current voltage v pcc; v pcc0 is the steady state value of the grid-connected point ac voltage V pcc; i d0 is the steady-state component of the d-axis current; i q0 is the steady-state component of the q-axis current; Δi d is the amount of change in d-axis current; Δi q is the amount of change in q-axis current;
Under the action of a control system, the interaction exists between the grid-connected converter VSC and the voltage at the public connection point of the alternating current grid, so that the characteristic is utilized to simplify the formula (2), and the conditions between the inner loop current of each controller in the control system and the corresponding reference value are satisfied:
Wherein G id(s) is a PI controller of the d-axis current inner loop; g iq(s) is a PI controller of the q-axis current inner loop; Δi dref is a reference value for Δi d; Δi qref is a reference value for Δi q; k p_id is the proportional gain of the d-axis current loop; k i_id is the integral gain of the d-axis current loop; k p_iq is the proportional gain of the q-axis current loop; k i_iq is the integral gain of the q-axis current loop; l is a Law transform operator; s is complex frequency;
Further, the relation between the d-axis and q-axis current reference value variation amounts and the outer ring corresponding control amounts satisfies:
Wherein G udc is the transfer function of the direct-current voltage outer loop PI controller; g upcc is the transfer function of the AC voltage outer loop PI controller; Δu dcref is a reference value of the dc voltage variation Δu dc; deltav pccref is a reference value of the variation Deltav pcc of the grid-connected point alternating voltage; k p_udc is the proportional gain of the DC voltage control loop; k i_udc is the integral gain of the dc voltage control loop; k p_vpcc is the proportional gain of the ac voltage control loop; k i_vpcc is the integral gain of the ac voltage control loop;
The direct current voltage variation quantity Deltau dc and the grid-connected point alternating current voltage variation quantity Deltav pcc are both outer ring voltage variation quantities, so that subsequent unfolding analysis is inconvenient, and therefore, in order to intuitively analyze the dynamic response characteristics of the grid-connected converter VSC under the small disturbance of the alternating current grid side, the direct current capacitance dynamic characteristics given by the formula (5) are further combined, and the direct current voltage component in the input component, namely the direct current voltage variation quantity Deltau dc, is eliminated:
-ΔP＝Udc0CsΔudc (5)
Wherein, delta P is the voltage variation of two ends of the direct current capacitor; u dc0 is the steady-state voltage value of the voltage; c is the capacitance value of the direct current capacitor;
The transfer function corresponding to the active control path is obtained as a small signal model corresponding to the active control path, wherein the transfer function is input by the variable quantity Deltav pcc of the grid-connected point alternating current voltage, and the variable quantity of the active power injected into the alternating current power grid is output; the transfer function corresponding to the reactive power control path is obtained as a small signal model corresponding to the reactive power control path, wherein the variable quantity Deltav pcc of the grid-connected point alternating current voltage is taken as input, and the variable quantity of the reactive power is taken as output;
the transfer functions corresponding to the active control path and the reactive control path are respectively as follows:
Wherein: g p(s) is a transfer function corresponding to the active control path; g q(s) is a transfer function corresponding to the reactive control path;
Analyzing active output and reactive output characteristics of the grid-connected converter VSC and dynamic interaction between the active output and reactive output characteristics and an alternating current power grid under an electromechanical time scale by using a frequency response method:
And (3) selecting parameters of a grid-connected converter VSC designated controller, namely a direct-current voltage control outer loop PI controller parameter k p_udc,ki_udc, an alternating-current voltage control outer loop PI controller parameter k p_vpcc,ki_vpcc, d-axis and q-axis PI controller parameters k p_id、kp_iq,ki_id、ki_iq of a current control inner loop, a direct-current capacitance value C, a filter reactance X f and a system reactance X s by utilizing a small signal model corresponding to an active control path and a small signal model corresponding to a reactive control path obtained in the step (6), qualitatively analyzing the characteristics of the active control path transfer function G p(s) and the reactive control path transfer function G q(s) of the alternating-current power grid under the small disturbance action of the alternating-current power grid by utilizing a frequency response method, and qualitatively analyzing the dynamic characteristics of the active output and the reactive output of the grid-connected converter VSC to the alternating-current power grid according to the magnitude in the characteristics of the logarithmic amplitude frequencies, analyzing the dynamic characteristics of the active output and the reactive output, and obtaining the characteristics of the alternating-current power grid under the small disturbance action of the alternating-current power grid under the condition of the small disturbance action of the alternating-current power grid, and completing the interaction of the alternating-current power grid by utilizing the frequency response method of the VSC under the condition of the frequency response method.
Through the design scheme, the invention has the following beneficial effects:
On the basis of determining a dynamic response model and a control strategy of the grid-connected converter, the invention deduces a linearization small signal model of active output and reactive output of the grid-connected converter under the condition of small disturbance on the power grid side, further analyzes the response characteristics of active power and reactive power of the grid-connected converter and the interaction between the grid-connected converter and an alternating current power grid under the electromechanical time scale by utilizing a frequency response method, and theoretically analyzes the influence on the electromechanical oscillation characteristics of the power grid after the permanent magnet wind turbine generator based on the grid-connected converter is integrated into the power grid, thereby having important significance for safe and stable operation of a power system with high-proportion access of new energy. Therefore, the invention has high practical application value.
Compared with the prior art, the invention has the following characteristics:
The method is based on analysis of a dynamic response model of the grid-connected converter VSC and a control strategy thereof, derives a linearization small signal model of active and reactive output of the grid-connected converter VSC, namely a small signal model corresponding to an active control path and a small signal model corresponding to a reactive control path under the condition that small disturbance occurs at a power grid side, analyzes active characteristics and reactive characteristics of the grid-connected converter VSC in the electromechanical oscillation process by utilizing a frequency response method, and analyzes interaction characteristics between the active and reactive output of the grid-connected converter VSC and the power grid; compared with the previous study for analyzing the influence of the access of the new energy unit to the power grid on the electromechanical dynamic behavior of the power grid, the invention can account for the interaction between the new energy unit and the alternating current power grid, effectively analyze the influence of the dynamic response characteristic of the system of the interactive coupling of the power electronic equipment and the power grid on the electromechanical oscillation characteristic of the system, and has higher practical application value.
Drawings
The invention is further described with reference to the drawings and detailed description which follow:
Fig. 1 is a topology of a grid-connected converter and a control system structure diagram thereof in an embodiment of a method for analyzing interaction between a grid-connected VSC and a power grid based on a frequency response method.
Fig. 2 is a small signal model diagram of the grid-connected converter VSC with common connection point voltage and direct current voltage as inputs in the embodiment of the interaction analysis method of the grid-connected VSC and the grid based on the frequency response method.
Fig. 3 is a diagram of a small signal model of the grid-connected converter VSC with the voltage at the common connection point as a single input in an embodiment of the method for analyzing interaction between the grid-connected VSC and the grid based on the frequency response method.
Fig. 4 is a diagram of a small signal model of the grid-connected converter VSC with the voltage of the common connection point as a single input in an embodiment of the method for analyzing interaction between the grid-connected VSC and the grid based on the frequency response method.
Fig. 5 is a graph of logarithmic magnitude-frequency characteristics of Gp(s) and Gq(s) in an embodiment of the method for analyzing interactions between grid-connected VSCs and a grid based on a frequency response method of the present invention.
Detailed Description
The invention relates to a method for analyzing interaction between grid-connected VSC and a power grid based on a frequency response method, which is characterized in that a linearization model of active and reactive output of a grid-connected converter is deduced under the condition that small disturbance occurs at the power grid side, and then the active and reactive characteristics of the grid-connected converter and interaction between the grid-connected converter and the power grid under the electromechanical time scale are analyzed by using the frequency response method. The calculation process comprises the following steps:
step one, determining a topological structure of a power system containing a grid-connected converter VSC and a corresponding control system:
Firstly, a topological structure diagram of connection of the converter VSC and an alternating current power grid is provided, namely, direct current power of a wind turbine generator after passing through a machine side rectifier is stabilized by a direct current capacitor C and fed into the alternating current power grid through a grid-connected converter VSC and a filter reactance.
The control system corresponding to the topology is described as follows: in order to ensure the stability of the voltage of a direct current bus of the VSC and the voltage quality of a power grid, the voltage of the power grid is generally controlled by adopting vector control of the voltage orientation of the power grid for the VSC at the power grid side, namely, the VSC at the power grid side commonly adopts a d-q decoupling double closed loop control structure with a voltage outer ring and a current inner ring combined, wherein d-axis current and q-axis current are respectively active current and reactive current, the d-axis current is controlled so as to control the active power transmitted to the power grid, and the reactive power flowing to the power grid is controlled by the q-axis current. The topological structure and the corresponding control system form a system formed by connecting a grid-connected converter VSC with an alternating current power grid, and in order to ensure the stable operation of the system and consider the reactive support requirement of the machine side converter on the system, for d-axis current, the outer ring of the d-axis current is controlled by direct current voltage, and the output of the d-axis current is a reference value of the d-axis current; for q-axis current, its outer loop is controlled by an ac voltage, which is output as a reference value for q-axis current.
Deducing a small signal model after linearization of active output and reactive output of the grid-connected converter VSC under small disturbance of the alternating current power grid side:
the dynamic characteristics of the system formed by connecting the grid-connected converter VSC with an alternating current power grid are mainly determined by a multi-scale cascade control system of the system, and the dynamic characteristics are complex. To simplify the analysis process, the following three-point assumption is first made:
a. the dc side power remains constant.
B. the internal losses of the grid-connected converter VSC are ignored.
C. the voltage of the common connection point of the grid-connected converter VSC and the power grid is always coincident with the d axis in the electromechanical process.
According to the instantaneous power theory, under the condition that the q-axis voltage is 0, the outlet active power and reactive power of the grid-connected converter VSC satisfy the following conditions:
Wherein P is the active power of the VSC outlet of the grid-connected converter; q is reactive power of a grid-connected converter VSC outlet; v pcc is the ac voltage at the common connection point of the grid-connected converter VSC and the ac grid; i d is the d-axis current; i q is q-axis current;
Under the small disturbance of the AC power grid side, linearizing the formula (1) at a system steady-state operating point comprises the following steps:
Wherein Δp is the amount of change in active power P; Δq is the amount of change in reactive power Q; deltav pcc is the variation of the grid-connected point alternating current voltage v pcc; v pcc0 is the steady state value of the grid-connected point ac voltage V pcc; i d0 is the steady-state component of the d-axis current; i q0 is the steady-state component of the q-axis current; Δi d is the amount of change in d-axis current; Δi q is the amount of change in q-axis current;
under the control system, the interaction exists between the grid-connected current and the voltage at the grid public connection point, so that the characteristic can be utilized to simplify the formula (2). The inner loop current of the controller and the reference value thereof satisfy the following conditions:
Wherein G id(s) is a PI controller of the d-axis current inner loop; g iq(s) is a PI controller of the q-axis current inner loop; Δi dref is a reference value for Δi d; Δi qref is a reference value for Δi q; k p_id is the proportional gain of the d-axis current loop; k i_id is the integral gain of the d-axis current loop; k p_iq is the proportional gain of the q-axis current loop; k i_iq is the integral gain of the q-axis current loop; l is a Law transform operator; s is complex frequency;
Further, the relation between the d-axis and q-axis current reference value variation amounts and the outer ring corresponding control amounts satisfies:
Wherein G udc is the transfer function of the direct-current voltage outer loop PI controller; g upcc is the transfer function of the AC voltage outer loop PI controller; Δu dcref is a reference value of the dc voltage variation Δu dc; deltav pccref is a reference value of the variation Deltav pcc of the grid-connected point alternating voltage; k p_udc is the proportional gain of the DC voltage control loop; k i_udc is the integral gain of the dc voltage control loop; k p_vpcc is the proportional gain of the ac voltage control loop; k i_vpcc is the integral gain of the ac voltage control loop;
The direct current voltage variation quantity Deltau dc and the grid-connected point alternating current voltage variation quantity Deltav pcc are both outer ring voltage variation quantities, so that subsequent unfolding analysis is inconvenient, and therefore, in order to intuitively analyze the dynamic response characteristics of the grid-connected converter VSC under the small disturbance of the alternating current grid side, the direct current capacitance dynamic characteristics given by the formula (5) are further combined, and the direct current voltage component in the input component, namely the direct current voltage variation quantity Deltau dc, is eliminated:
-ΔP＝Udc0CsΔudc(5)
Wherein, delta P is the voltage variation of two ends of the direct current capacitor; u dc0 is the steady-state voltage value of the voltage; c is the capacitance value of the direct current capacitor;
furthermore, a single-input small-signal model is deduced, which takes Δv pcc as input and takes the change amounts of active power and reactive power injected into the power grid as output, namely the transfer functions of an active control loop and a reactive control loop are respectively as follows:
wherein G p(s) is a transfer function corresponding to the active control path; g q(s) is a transfer function corresponding to the reactive control path;
Analyzing active output and reactive output characteristics of the grid-connected converter VSC and dynamic interaction between the active output and reactive output characteristics and an alternating current power grid under an electromechanical time scale by using a frequency response method:
And (3) selecting parameters of a grid-connected converter VSC designated controller, namely a direct-current voltage control outer loop PI controller parameter k p_udc,ki_udc, an alternating-current voltage control outer loop PI controller parameter k p_vpcc,ki_vpcc, d-axis and q-axis PI controller parameters k p_id、kp_iq,ki_id、ki_iq of a current control inner loop, a direct-current capacitance value C, a filter reactance X f and a system reactance X s by utilizing a small signal model corresponding to an active control path and a small signal model corresponding to a reactive control path obtained in the step (6), qualitatively analyzing the characteristics of the active control path transfer function G p(s) and the reactive control path transfer function G q(s) of the alternating-current power grid under the small disturbance action of the alternating-current power grid by utilizing a frequency response method, and qualitatively analyzing the dynamic characteristics of the active output and the reactive output of the grid-connected converter VSC to the alternating-current power grid according to the magnitude in the characteristics of the logarithmic amplitude frequencies, analyzing the dynamic characteristics of the active output and the reactive output, and obtaining the characteristics of the alternating-current power grid under the small disturbance action of the alternating-current power grid under the condition of the small disturbance action of the alternating-current power grid, and completing the interaction of the alternating-current power grid by utilizing the frequency response method of the VSC under the condition of the frequency response method.
Examples
The interaction analysis method of the grid-connected VSC and the power grid based on the frequency response method comprises the following steps:
step one, determining a topological structure of a power system containing a grid-connected converter VSC and a corresponding control strategy:
The topological structure diagram of the connection of the grid-connected converter VSC and the alternating current power grid is determined, as shown in fig. 1, namely, the direct current power of the wind turbine generator after passing through the side rectifier is fed into the alternating current power grid through the grid-connected converter VSC and the filter reactance after being stabilized by the direct current capacitor C. The PLL is a phase-locked loop and provides a reference phase for d-q conversion so as to ensure that the grid-connected converter VSC and the alternating current power grid keep synchronous; q vsc is the reactive power injected into the system by the grid-connected converter VSC; x f is the filter reactance.
In addition, in order to ensure the stability of the voltage of the direct current bus of the VSC of the grid-connected inverter and the voltage quality of the power grid, vector control of the voltage orientation of the power grid is generally adopted for the VSC of the grid-connected inverter, that is, a d-q decoupled dual closed loop control structure with a voltage outer loop and a current inner loop combined is generally adopted for the VSC of the grid-connected inverter, wherein d-axis current and q-axis current are respectively active current and reactive current, d-axis current is controlled to control active power transmitted to the power grid, and q-axis current is utilized to control reactive power flowing to the power grid. The topological structure and the corresponding control system form a system formed by connecting a grid-connected converter VSC with an alternating current power grid, and in order to ensure the stable operation of the system and consider the reactive support requirement of the machine side converter on the system, for d-axis current, the outer ring of the system is controlled by direct current voltage, and the output of the system is a reference value of the d-axis current; for q-axis current, its outer loop is ac voltage controlled, and its output is a reference value for q-axis current.
Deducing a linearization small signal model of active output and reactive output of the grid-connected converter VSC under small disturbance of the power grid side:
the dynamic characteristics of the system formed by connecting the grid-connected converter VSC with an alternating current power grid are mainly determined by a multi-scale cascade control system of the system, and the dynamic characteristics are complex. To simplify the analysis process, the following three-point assumption is first made:
a. the dc side power remains constant.
B. the internal losses of the grid-connected converter VSC are ignored.
C. the voltage of the common connection point of the grid-connected converter VSC and the power grid is always coincident with the d axis in the electromechanical process.
According to the instantaneous power theory, under the condition that the q-axis voltage is 0, the outlet active power and reactive power of the grid-connected converter VSC satisfy the following conditions:
wherein P is the active power of the VSC outlet of the grid-connected converter; q is reactive power of a grid-connected converter VSC outlet; v pcc is the ac voltage at the common connection point of the grid-connected converter VSC and the ac grid; i d is the d-axis current; i q is q-axis current.
Under the small disturbance of the AC power grid side, linearizing the formula (1) at a system steady-state operating point comprises the following steps:
Wherein Δp is the amount of change in active power P; Δq is the amount of change in reactive power Q; deltav pcc is the variation of the grid-connected point alternating current voltage v pcc; v pcc0 is the steady state value of the grid-connected point ac voltage V pcc; i d0 is the steady-state component of the d-axis current; i q0 is the steady-state component of the q-axis current; Δi d is the amount of change in d-axis current; Δi q is the amount of change in q-axis current.
Under the control system, the interaction exists between the grid-connected current and the voltage at the grid public connection point, so that the characteristic can be utilized to simplify the formula (2). The inner loop current of the controller and the reference value thereof satisfy the following conditions:
Wherein G id(s) is a PI controller of the d-axis current inner loop; g iq(s) is a PI controller of the q-axis current inner loop; Δi dref is a reference value for Δi d; Δi qref is a reference value for Δi q; k p_id is the proportional gain of the d-axis current loop; k i_id is the integral gain of the d-axis current loop; k p_iq is the proportional gain of the q-axis current loop; k i_iq is the integral gain of the q-axis current loop; l is a Law transform operator; s is the complex frequency.
Further, the relation between the d-axis and q-axis current reference value variation amounts and the outer ring corresponding control amounts satisfies:
Wherein G udc is the transfer function of the direct-current voltage outer loop PI controller; g upcc is the transfer function of the AC voltage outer loop PI controller; Δu dcref is a reference value of the dc voltage variation Δu dc; deltav pccref is a reference value of the variation Deltav pcc of the grid-connected point alternating voltage; k p_udc is the proportional gain of the DC voltage control loop; k i_udc is the integral gain of the dc voltage control loop; k p_vpcc is the proportional gain of the ac voltage control loop; k i_vpcc is the integral gain of the ac voltage control loop;
By combining the formulas (2) to (4), a small signal model with the outer ring voltage variation (including the direct current voltage variation deltau dc and the grid-connected point alternating current voltage variation deltav pcc) as input and the active power and reactive power variation of the grid injected by the grid-connected converter VSC as output can be deduced, as shown in fig. 2. As is clear from fig. 2, in the case of the determination of the external ring reference value and the controller parameter, the common connection point voltage v pcc acts on the reactive power of the grid-connected converter outlet via two paths: wherein one part changes its outlet reactive power through the current path and the other part affects the reactive power output dynamic process through the ac voltage path. Unlike reactive power, grid-connected converter outlet active power is simultaneously affected by the combined action of direct voltage u dc and common junction voltage v pcc, namely, one part is affected by common junction voltage v pcc through steady-state current I d0 with d axis, and the other part is affected by direct voltage and direct voltage control loop.
However, fig. 2 shows a multiple-input model composed of a dc voltage u dc and a common-node voltage v pcc, which makes it difficult to intuitively analyze the dynamic response characteristics of the grid-connected converter under system disturbance. For this purpose, the dc voltage component, that is, the dc voltage variation Δu dc is eliminated by means of the dc capacitance dynamic characteristic model in equation (5).
-ΔP＝Udc0CsΔudc(5)
Wherein: Δp is the voltage variation across the capacitor; u dc0 is the steady-state voltage value of the voltage; c is the capacitance.
Furthermore, a single-input small-signal model (as shown in fig. 3) with Δv pcc as input and with the active power variation of the injected power grid as output, and a single-input small-signal model (as shown in fig. 4) with Δv pcc as input and with the reactive power variation of the injected power grid as output are derived, wherein the two small-signal models are respectively a transfer function corresponding to the active control path and a transfer function corresponding to the reactive control path:
Step three: analyzing the active output and reactive output characteristics of the grid-connected converter VSC under the electromechanical time scale by utilizing a frequency response method and the dynamic interaction between the active output and reactive output characteristics and a power grid:
and (3) selecting parameters of a grid-connected VSC typical controller by using the small signal model corresponding to the active control path and the small signal model corresponding to the reactive control path obtained in the step (II) under the electromechanical time scale, substituting the parameters into the grid (6) as shown in a table 1, and qualitatively analyzing the dynamic characteristics of active output and reactive output of the grid-connected converter under the action of small disturbance of the grid, thereby analyzing the power interaction characteristics between the grid-connected converter and the alternating current grid in the small disturbance electromechanical process. The logarithmic amplitude-frequency characteristic diagrams of Gp(s) and Gq(s) obtained by the frequency response method are shown in fig. 5. As can be seen from an analysis of fig. 5, the amplitude of the transfer function Gp(s) corresponding to the active control path is small in the electromechanical frequency band range (frequency range of 0.1 to 2.5 Hz), and the frequency response amplitude is small, less than-10 dB, even at the upper limit of 2.5Hz of the electromechanical frequency band. From this, it can be seen that during the electromechanical oscillation process, the interaction process of the grid-connected inverter and the ac grid active power is weaker. Meanwhile, the amplitude of the transfer function Gq(s) corresponding to the reactive power control path is constantly greater than zero in the electromechanical oscillation frequency band, which indicates that the reactive interaction between the permanent magnet direct-drive wind turbine generator and the power grid is greater than active power in the electromechanical oscillation process, and the reactive power response is a main form of interaction between the grid-connected converter and the alternating-current power grid.
Table 1 grid-connected inverter control link parameters
The invention provides an effective method for analyzing dynamic interaction of grid-connected VSC and an alternating current power grid under an electromechanical time scale, which can qualitatively analyze dynamic interaction of a permanent magnet synchronous wind turbine generator set based on a converter and the alternating current power grid in the electromechanical oscillation process, and provides an effective analysis method for electromechanical dynamic behavior analysis of high-proportion access of new energy into the power grid.
Claims (1)
1. A method for analyzing interaction between a grid-connected converter VSC and a power grid based on a frequency response method is characterized by comprising the following steps: comprising the following steps, and the following steps are carried out in sequence,
Step one, establishing a topological structure of connection of a grid-connected converter VSC and an alternating current power grid and a corresponding control system, and obtaining a system formed by connection of the grid-connected converter VSC and the alternating current power grid:
① The direct current power of the wind turbine generator after rectification by the rectifier is stabilized by the direct current capacitor and then fed into the alternating current power grid by the grid-connected converter VSC and the filter reactance to obtain a topological structure of the connection of the grid-connected converter VSC and the alternating current power grid;
② Establishing a control system corresponding to the topological structure, wherein the topological structure and the corresponding control system form a system formed by connecting a grid-connected converter VSC and an alternating current power grid, the control system realizes vector control of power grid voltage orientation by adopting a d-q decoupled double-closed-loop control structure combining a voltage outer ring and a current inner ring on the VSC at the alternating current power grid side, d-axis current is active current, q-axis current is reactive current, active power transmitted to the alternating current power grid is controlled by using d-axis current, and reactive power flowing to the alternating current power grid is controlled by using q-axis current;
The outer ring of the d-axis current is controlled by direct current voltage, and the output of the d-axis current is the reference value of the d-axis current and the actual current deviation value of the d-axis; the outer ring of the q-axis current is controlled by alternating voltage, and the output of the q-axis current is the deviation value of the reference value of the q-axis current and the q-axis actual current;
step two, obtaining a small signal model after linearization of active output and reactive output of the grid-connected converter VSC under small disturbance of an alternating current power grid side:
the analysis process of a system formed by connecting the grid-connected converter VSC with an alternating current power grid is simplified through three conditions of a, b and c,
A. The direct current side power is kept constant;
b. Neglecting internal loss of the grid-connected converter VSC;
c. the voltage of a public connection point of the grid-connected converter VSC connected with the alternating current power grid always coincides with the d axis in the electromechanical process;
according to the instantaneous power theory, under the condition that the q-axis voltage is 0, the outlet active power and reactive power of the grid-connected converter VSC satisfy the following conditions:
Wherein P is the active power of the VSC outlet of the grid-connected converter; q is reactive power of a grid-connected converter VSC outlet; v pcc is the ac voltage at the common connection point of the grid-connected converter VSC and the ac grid; i d is the d-axis current; i q is q-axis current;
Under the small disturbance of the AC power grid side, linearizing the formula (1) at a system steady-state operating point comprises the following steps:
Wherein Δp is the amount of change in active power P; Δq is the amount of change in reactive power Q; deltav pcc is the variation of the grid-connected point alternating current voltage v pcc; v pcc0 is the steady state value of the grid-connected point ac voltage V pcc; i d0 is the steady-state component of the d-axis current; i q0 is the steady-state component of the q-axis current; Δi d is the amount of change in d-axis current; Δi q is the amount of change in q-axis current;
Under the action of a control system, the interaction exists between the grid-connected converter VSC and the voltage at the public connection point of the alternating current grid, so that the characteristic is utilized to simplify the formula (2), and the conditions between the inner loop current of each controller in the control system and the corresponding reference value are satisfied:
Wherein G id(s) is a PI controller of the d-axis current inner loop; g iq(s) is a PI controller of the q-axis current inner loop; Δi dref is a reference value for Δi d; Δi qref is a reference value for Δi q; k p_id is the proportional gain of the d-axis current loop; k i_id is the integral gain of the d-axis current loop; k p_iq is the proportional gain of the q-axis current loop; k i_iq is the integral gain of the q-axis current loop; l is a Law transform operator; s is complex frequency;
Further, the relation between the d-axis and q-axis current reference value variation amounts and the outer ring corresponding control amounts satisfies:
Wherein G udc is the transfer function of the direct-current voltage outer loop PI controller; g upcc is the transfer function of the AC voltage outer loop PI controller; Δu dcref is a reference value of the dc voltage variation Δu dc; deltav pccref is a reference value of the variation Deltav pcc of the grid-connected point alternating voltage; k p_udc is the proportional gain of the DC voltage control loop; k i_udc is the integral gain of the dc voltage control loop; k p_vpcc is the proportional gain of the ac voltage control loop; k i_vpcc is the integral gain of the ac voltage control loop;
The direct current voltage variation quantity Deltau dc and the grid-connected point alternating current voltage variation quantity Deltav pcc are both outer ring voltage variation quantities, so that subsequent unfolding analysis is inconvenient, and therefore, in order to intuitively analyze the dynamic response characteristics of the grid-connected converter VSC under the small disturbance of the alternating current grid side, the direct current capacitance dynamic characteristics given by the formula (5) are further combined, and the direct current voltage component in the input component, namely the direct current voltage variation quantity Deltau dc, is eliminated:
-ΔP＝Udc0CΔudcs (5)
wherein U dc0 is a voltage steady-state voltage value; c is the capacitance value of the direct current capacitor;
The transfer function corresponding to the active control path is obtained as a small signal model corresponding to the active control path, wherein the transfer function is input by the variable quantity Deltav pcc of the grid-connected point alternating current voltage, and the variable quantity of the active power injected into the alternating current power grid is output; the transfer function corresponding to the reactive power control path is obtained as a small signal model corresponding to the reactive power control path, wherein the variable quantity Deltav pcc of the grid-connected point alternating current voltage is taken as input, and the variable quantity of the reactive power is taken as output;
the transfer functions corresponding to the active control path and the reactive control path are respectively as follows:
wherein G p(s) is a transfer function corresponding to the active control path; g q(s) is a transfer function corresponding to the reactive control path;
Analyzing active output and reactive output characteristics of the grid-connected converter VSC and dynamic interaction between the active output and reactive output characteristics and an alternating current power grid under an electromechanical time scale by using a frequency response method:
And (3) selecting parameters of a grid-connected converter VSC designated controller, namely a direct-current voltage control outer loop PI controller parameter k p_udc,ki_udc, an alternating-current voltage control outer loop PI controller parameter k p_vpcc,ki_vpcc, d-axis and q-axis PI controller parameters k p_id、kp_iq,ki_id、ki_iq of a current control inner loop, a direct-current capacitance value C, a filter reactance X f and a system reactance X s by utilizing a small signal model corresponding to an active control path and a small signal model corresponding to a reactive control path obtained in the step (6), qualitatively analyzing the characteristics of the active control path transfer function G p(s) and the reactive control path transfer function G q(s) of the alternating-current power grid under the small disturbance action of the alternating-current power grid by utilizing a frequency response method, and qualitatively analyzing the dynamic characteristics of the active output and the reactive output of the grid-connected converter VSC to the alternating-current power grid according to the magnitude in the characteristics of the logarithmic amplitude frequencies, analyzing the dynamic characteristics of the active output and the reactive output, and obtaining the characteristics of the alternating-current power grid under the small disturbance action of the alternating-current power grid under the condition of the small disturbance action of the alternating-current power grid, and completing the interaction of the alternating-current power grid by utilizing the frequency response method of the VSC under the condition of the frequency response method.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202211119808.2A CN115498708B (en) | 2022-09-15 | 2022-09-15 | Grid-connected VSC and power grid interaction analysis method based on frequency response method |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202211119808.2A CN115498708B (en) | 2022-09-15 | 2022-09-15 | Grid-connected VSC and power grid interaction analysis method based on frequency response method |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CN115498708A CN115498708A (en) | 2022-12-20 |
| CN115498708B true CN115498708B (en) | 2024-06-07 |
Family
ID=84468100
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CN202211119808.2A Active CN115498708B (en) | 2022-09-15 | 2022-09-15 | Grid-connected VSC and power grid interaction analysis method based on frequency response method |
Country Status (1)
| Country | Link |
|---|---|
| CN (1) | CN115498708B (en) |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN116595699B (en) * | 2023-07-18 | 2023-10-03 | 华北电力科学研究院有限责任公司 | Interactive processing method and device for power quality of converter and power distribution network |
Citations (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN108011390A (en) * | 2017-12-11 | 2018-05-08 | 华中科技大学 | A kind of flexible direct current power transmission system and bicyclic additional frequency control method back-to-back |
| CN110518600A (en) * | 2019-05-22 | 2019-11-29 | 国网辽宁省电力有限公司电力科学研究院 | A kind of grid-connected active support and control structure of PMSG of the modified multi-machine parallel connection based on VSG |
| CN110807168A (en) * | 2019-10-18 | 2020-02-18 | 广西电网有限责任公司 | Method and device for estimating sub-synchronous oscillation mode of grid-connected converter |
| CN113708399A (en) * | 2021-07-13 | 2021-11-26 | 南方电网科学研究院有限责任公司 | Method and equipment for analyzing dynamic stability of direct-current voltage control time scale |
| CN113872189A (en) * | 2021-09-17 | 2021-12-31 | 天津大学 | Equivalent PLL (phase locked loop) analysis method for low-frequency oscillation characteristics when VSC (Voltage Source converter) is connected into weak power grid |
-
2022
- 2022-09-15 CN CN202211119808.2A patent/CN115498708B/en active Active
Patent Citations (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN108011390A (en) * | 2017-12-11 | 2018-05-08 | 华中科技大学 | A kind of flexible direct current power transmission system and bicyclic additional frequency control method back-to-back |
| CN110518600A (en) * | 2019-05-22 | 2019-11-29 | 国网辽宁省电力有限公司电力科学研究院 | A kind of grid-connected active support and control structure of PMSG of the modified multi-machine parallel connection based on VSG |
| CN110807168A (en) * | 2019-10-18 | 2020-02-18 | 广西电网有限责任公司 | Method and device for estimating sub-synchronous oscillation mode of grid-connected converter |
| CN113708399A (en) * | 2021-07-13 | 2021-11-26 | 南方电网科学研究院有限责任公司 | Method and equipment for analyzing dynamic stability of direct-current voltage control time scale |
| CN113872189A (en) * | 2021-09-17 | 2021-12-31 | 天津大学 | Equivalent PLL (phase locked loop) analysis method for low-frequency oscillation characteristics when VSC (Voltage Source converter) is connected into weak power grid |
Non-Patent Citations (2)
| Title |
|---|
| Frequency Couplings and Response Characteristics of Grid-Tied VSC System;Ruiqing Fu等;《2021 IEEE Power & Energy Society General Meeting (PESGM)》;20211231;第1-5页 * |
| Investigation on Dynamic Response of Grid-Tied VSC During Electromechanical Oscillations of Power Systems;Guowei Cai等;《Energies》;20191223;第1-16页 * |
Also Published As
| Publication number | Publication date |
|---|---|
| CN115498708A (en) | 2022-12-20 |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| Xue et al. | A complete impedance model of a PMSG-based wind energy conversion system and its effect on the stability analysis of MMC-HVDC connected offshore wind farms | |
| CN110829421B (en) | System impedance modeling method for VSC cascaded LLC | |
| CN109586337B (en) | Frequency domain modeling-based VSC grid-connected system subsynchronous oscillation risk assessment method | |
| CN112217239A (en) | Energy storage electromechanical transient modeling method based on virtual synchronous generator technology | |
| CN109103903A (en) | A kind of judgment method causing sub-synchronous oscillation for straight drive blower | |
| CN110676874B (en) | Direct-drive fan subsynchronous oscillation electrical quantity analysis method considering frequency coupling effect | |
| CN105914778A (en) | Microgrid inverter multi-loop control method based on virtual synchronous generator | |
| CN110429611B (en) | Static var compensator sequence impedance modeling and control parameter adjusting method | |
| CN102623992A (en) | Method for islanding microgrid control and optimization based on rotating coordinate virtual impedance | |
| CN108880300B (en) | Double-fed fan rectifier impedance calculation method based on double closed-loop control | |
| CN110601268A (en) | Doubly-fed fan grid-connected port output impedance modeling and stability analysis method | |
| CN115498708B (en) | Grid-connected VSC and power grid interaction analysis method based on frequency response method | |
| CN115133578B (en) | Power self-synchronous control method for voltage source grid-connected converter without grid voltage sensor | |
| Feng et al. | Influences of DC bus voltage dynamics in modulation algorithm on power oscillations in PMSG-based wind farms | |
| CN114156946A (en) | Parallel inverter power balance control method based on common-mode voltage injection | |
| Yu et al. | Study on Small Disturbance Stability of Photovoltaic Grid-Connected Power Generation System | |
| Liu et al. | Analysis of Sub-synchronous Interaction Mechanism Between D-PMSG-based Wind Farm and LCC-HVDC | |
| Wang et al. | DQ impedance modeling and stability analysis of virtual synchronous generator considering voltage current loop | |
| CN114006400A (en) | Doubly-fed wind turbine impedance model considering power outer loop control and derivation method | |
| CN114899877B (en) | Modeling and parameter optimization method and device for virtual synchronous machine of combined heat and power system | |
| Jiang et al. | Configuration Analysis of Grid-forming Converter Under 100% Renewable Electricity Systems | |
| He et al. | Analysis of Subsynchronous Oscillation Mechanism and Its Influencing Factors in Large-scale Photovoltaic Series Compensation System | |
| Lu et al. | Virtual synchronous generator control strategy based on improved inner loop applied to power storage converter | |
| Li et al. | Impedance-based Stability Analysis of AD-DC Hybrid System Considering Grid Impedance | |
| Huang et al. | Subsynchronous Oscillation Suppression of Grid-Forming Converter Connected to Low-Impedance Grid |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PB01 | Publication | ||
| PB01 | Publication | ||
| SE01 | Entry into force of request for substantive examination | ||
| SE01 | Entry into force of request for substantive examination | ||
| CB03 | Change of inventor or designer information |
Inventor after: Wang Lixin Inventor after: Yang Deyou Inventor after: Jiang Chao Inventor after: Cao Zhichong Inventor after: Jia Songyue Inventor after: Cai Guowei Inventor before: Yang Deyou Inventor before: Wang Lixin Inventor before: Jiang Chao Inventor before: Cao Zhichong Inventor before: Jia Songyue Inventor before: Cai Guowei |
|
| CB03 | Change of inventor or designer information | ||
| GR01 | Patent grant |