Converter output optimization method and device

Abstract

The invention provides a converter output optimization method and device, and belongs to the technical field of converters. The optimization method comprises the following steps: acquiring a first system parameter of a converter grid-connected system and a second system parameter of a power grid subsystem under a current working condition; substituting the first system parameter into a converter impedance model to obtain impedance of a power supply side; substituting the second system parameter into an impedance model of a power grid subsystem to obtain impedance of a power grid side; determining a value of a stability index based on the impedance of the power supply side and the impedance of the power grid side; the output of the converter is optimized according to the value of the stability index, and the converter impedance model comprises the coupling relation between the operation conditions of a phase-locked loop and a grid-connected point in the converter grid-connected system. The oscillation risk of the system can be reduced based on the output of the converter.

Description

Technical Field

[0001] The present disclosure belongs to the technical field of converters, and specifically relates to a method and device for optimizing converter output, electronic equipment, a computer-readable storage medium, and a computer program product. Background Art

[0002] At present, new energy generally adopts the development mode of "centralized development and long-distance power transmission". Large-scale new energy is connected to the system through weak power grids, and broadband oscillation problems often occur, seriously affecting the safe and stable operation of the system. A typical case is that in a certain year, a direct-drive wind turbine in a certain area interacted with a weak power grid and caused a 19 / 81Hz super-synchronous oscillation. This oscillation, as a forced disturbance source, triggered the torsional vibration protection action of the shaft system of a thermal power unit hundreds of kilometers away, which attracted widespread attention.

[0003] According to the small signal stability analysis, the oscillation occurs mainly because there is a characteristic root with weak damping in the corresponding frequency band. When the initial operating conditions change, the characteristic root changes from positive damping to negative damping, causing oscillation. The field oscillation data shows that the stability characteristics of the power grid system are significantly affected by the operating conditions. For example, the oscillation in Guyuan area mainly occurs at low power output levels at night, while the oscillation of the flexible direct current converter station mainly occurs at high power output levels.

[0004] At present, the oscillation research of power grid system is often analyzed under relatively ideal working conditions, that is, the active output of the converter is fully generated and the power factor is 1. However, there are few studies on the coupling between the operating conditions and the phase-locked loop, and the impact of the changes in the operating conditions of the grid connection point on the converter impedance is ignored. Summary of the invention

[0005] The present invention aims to solve at least one of the technical problems existing in the prior art, and provides a method for optimizing converter output, an optimization device, a computer-readable storage medium and a computer program product. The solution provided by the present disclosure can.

[0006] In order to achieve the above-mentioned object, in a first aspect, an embodiment of the present disclosure provides a method for optimizing converter output, comprising: obtaining a first system parameter of a converter grid-connected system and a second system parameter of a power grid subsystem under a current working condition;

[0007] Substitute the first system parameters into the converter impedance model to obtain the impedance on the power supply side, where:

[0008] The converter impedance model includes the coupling relationship between the operating conditions of the phase-locked loop and the grid connection point in the converter grid-connected system;

[0009] Substituting the second system parameter into the impedance model of the power grid subsystem to obtain the impedance of the power grid side;

[0010] Determining a value of a stability index based on the impedance of the power supply side and the impedance of the grid side;

[0011] The output of the converter is optimized according to the value of the stability index.

[0012] In some embodiments, the first parameter of the converter grid-connected system includes at least one of the following: a grid-connected point current, a phase-locked loop transfer function, a ratio of the current loop, an integral coefficient of the current loop, a q-axis component and a d-axis component of the grid-connected point current in the converter grid-connected system, a d-axis component and a q-axis component of the grid-connected point voltage in the converter grid-connected system, and a d-axis component and a q-axis component of the duty cycle of a pulse width modulation signal.

[0013] In some embodiments, the converter impedance model is:

[0014]

[0015] Among them, Y VSC (s) is the transformer impedance model, L VSC and R VSC are the filter inductance of the converter and the resistance of the converter respectively; V dc is the DC bus voltage of the converter, k pi and k ii are the ratio of the current loop and the integral coefficient of the current loop, I is the unit matrix, G PLL is the phase-locked loop transfer function, and are the q-axis component and d-axis component of the grid-connected point current in the converter grid-connected system, V d s and V q s are respectively the d-axis component and the q-axis component of the grid-connected point voltage in the converter grid-connected system, and s is the complex frequency variable in the Laplace transform.

[0016] In some embodiments, the converter impedance model is:

[0017]

[0018] Among them, Y VSC (s) is the target impedance model, L VSC and R VSC are the filter inductance of the converter and the resistance of the converter respectively; V dc is the DC bus voltage of the converter, k pi and k ii are the ratio of the current loop and the integral coefficient of the current loop respectively, I is the unit matrix, and are the q-axis component and d-axis component of the grid-connected point current, and are the q-axis component and d-axis component of the duty cycle of the pulse width modulation signal, G PLL is the phase-locked loop transfer function, ω is the fundamental frequency of the converter grid-connected system, and s is the complex frequency variable in the Laplace transform.

[0019] In some embodiments, the second system parameters include line inductance and line resistance in the power grid subsystem, and the impedance model of the power grid subsystem is:

[0020]

[0021] Among them, Z grid represents the impedance model of the power grid subsystem, Lg and Rg are the line inductance and resistance in the power grid subsystem respectively, ω is the fundamental frequency of the power grid subsystem, and s is the complex frequency variable in the Laplace transform.

[0022] In some embodiments, determining the value of the stability index based on the impedance of the power supply side and the impedance of the grid side includes:

[0023] Calculating the eigenvalue of the power matrix of the power grid system based on the impedance of the power supply side and the impedance of the power grid side;

[0024] The value of the stability index is determined according to the eigenvalue of the return matrix.

[0025] In some embodiments, determining the value of the stability index according to the eigenvalue of the return matrix includes:

[0026] Determine a trajectory curve of the eigenvalues ​​of the rate matrix on a complex plane;

[0027] The value of the stability index is determined according to the intersection point of the trajectory curve and the leftmost side of the real axis in the complex plane.

[0028] In some embodiments, optimizing the output of the converter according to the value of the stability index includes:

[0029] When the value of the stability index is less than -1, there is a risk of instability in the system, and the converter is controlled to reduce reactive power and / or active power output to increase the stability of the power grid system.

[0030] In a second aspect, the present disclosure further provides a device for optimizing converter output, comprising:

[0031] An acquisition module, used to acquire a first system parameter of the converter grid-connected system and a second system parameter of the power grid subsystem under a current working condition;

[0032] A first calculation module, used for bringing the first system parameter into a converter impedance model to obtain an impedance on a power supply side, wherein the converter impedance model includes a coupling relationship between an operating condition of a phase-locked loop and a grid-connected point in the converter grid-connected system;

[0033] A second calculation module is used to bring the second system parameters into the impedance model of the power grid subsystem to obtain the impedance of the power grid side;

[0034] A determination module, configured to determine a value of a stability index based on the impedance of the power supply side and the impedance of the grid side;

[0035] An optimization module is used to optimize the output of the converter according to the value of the stability index.

[0036] In some embodiments, the first parameter of the converter grid-connected system includes at least one of the following: a grid-connected point current, a phase-locked loop transfer function, a ratio of the current loop, an integral coefficient of the current loop, a q-axis component and a d-axis component of the grid-connected point current in the converter grid-connected system, a d-axis component and a q-axis component of the grid-connected point voltage in the converter grid-connected system, and a d-axis component and a q-axis component of the duty cycle of a pulse width modulation signal.

[0037] In some embodiments, the converter impedance model is:

[0038]

[0039] Among them, Y VSC (s) is the transformer impedance model, L VSC and R VSC are the filter inductance of the converter and the resistance of the converter respectively; V dc is the DC bus voltage of the converter, k pi and k ii are the ratio of the current loop and the integral coefficient of the current loop, I is the unit matrix, G PLL is the phase-locked loop transfer function, and are respectively the q-axis component and the d-axis component of the grid-connected point current in the converter grid-connected system, and are respectively the d-axis component and the q-axis component of the grid-connected point voltage in the converter grid-connected system, and s is the complex frequency variable in the Laplace transform.

[0040] In some embodiments, the converter impedance model is:

[0041]

[0042] Among them, Y VSC(s) is the target impedance model, L VSC and R VSC are the filter inductance of the converter and the resistance of the converter respectively; V dc is the DC bus voltage of the converter, k pi and k ii are the ratio of the current loop and the integral coefficient of the current loop respectively, I is the unit matrix, and are the q-axis component and d-axis component of the grid-connected point current, and are the q-axis component and d-axis component of the duty cycle of the pulse width modulation signal, G PLL is the phase-locked loop transfer function, ω is the fundamental frequency of the converter grid-connected system, and s is the complex frequency variable in the Laplace transform.

[0043] In some embodiments, the determining module includes:

[0044] A third calculation module, used for calculating the eigenvalue of the rate matrix of the power grid system based on the impedance of the power supply side and the impedance of the power grid side;

[0045] The determination submodule is used to determine the value of the stability index according to the eigenvalue of the return rate matrix.

[0046] In some embodiments, the determining submodule includes:

[0047] A first determination submodule is used to determine a trajectory curve of the eigenvalue of the rate matrix on a complex plane;

[0048] The second determination submodule is used to determine the value of the stability index according to the intersection point of the trajectory curve and the leftmost side of the real axis in the complex plane.

[0049] In some embodiments, the optimization module is specifically used for: when the value of the stability index is less than -1, there is a risk of instability in the system, and the converter is controlled to reduce reactive output and / or active output to increase the stability of the power grid system.

[0050] In a third aspect, the present disclosure further provides an electronic device, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein when the processor executes the program, the computing method of the first aspect described above is implemented.

[0051] In a fourth aspect, the present disclosure further provides a computer-readable storage medium storing a computer program for executing the computing method of the first aspect.

[0052] In a fifth aspect, the present disclosure further provides a computer program product, including a computer program / instruction, which implements the steps of the computing method of the first aspect when the computer program / instruction is executed by a processor.

[0053] The embodiment of the present disclosure includes the coupling relationship between the operating conditions of the phase-locked loop and the grid connection point in the converter impedance model required for calculating the value of the stability index. When the power grid system is determined to be in an unstable state according to the value of the stability index, the current operating condition of the power grid system can be adjusted based on the converter impedance model to implement a strategy of limiting the converter output level based on the converter impedance, so that the power grid system is in a stable state, thereby reducing the risk of oscillation. The current operating condition refers to the active output, reactive output, and voltage and current related conditions in the power grid system (including the converter and / or the power grid subsystem). The embodiment provided by the present disclosure can suppress oscillations from the perspective of converter control. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] In order to more clearly illustrate the embodiments of the present disclosure or the technical solutions in the prior art, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present disclosure. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0055] Figure 1 A schematic diagram of the structure of a converter grid-connected system provided by an embodiment of the present disclosure;

[0056] Figure 2 A flowchart of a method for optimizing converter output provided by an embodiment of the present disclosure;

[0057] Figure 3 A method for Figure 1 Control block diagram of

[0058] Figure 4-Figure 6 They are respectively waveform diagrams of the converter impedance model provided by the embodiments of the present disclosure under different operating conditions;

[0059] Figure 7 A schematic diagram of a curve of a stability index and an operating condition provided in an embodiment of the present disclosure;

[0060] Figure 8 A structural diagram of a converter output optimization device provided in an embodiment of the present disclosure;

[0061] Fig. 9 A schematic diagram of the physical structure of an electronic device provided in an embodiment of the present disclosure. DETAILED DESCRIPTION

[0062] In order to enable those skilled in the art to better understand the technical solution of the present invention, the present invention is further described in detail and completely in conjunction with the accompanying drawings and specific implementation methods. Obviously, the described embodiments are only part of the embodiments of the present disclosure, rather than all the embodiments. Based on the embodiments in the present disclosure, all other embodiments obtained by ordinary technicians in the field without making creative work are within the scope of protection of the present disclosure.

[0063] In the first aspect, the embodiments of the present disclosure provide a method for optimizing converter output. The optimization method can be applied to a power grid system, wherein the power grid system includes a converter grid-connected system as a power supply side and a power grid subsystem as a power grid side, and the power supply side and the power grid side are closely coordinated to ensure the balance of power supply and demand.

[0064] Figure 1 A schematic diagram of the structure of a converter grid-connected system provided in an embodiment of the present disclosure. As shown in the figure, the converter grid-connected system includes a circuit part 1 and a control part 2, wherein the circuit part 1 can consider inductance filtering, and the control part 2 includes a phase-locked loop and a current loop. The phase-locked loop calculates the system phase angle of the converter grid-connected system according to the grid connection point voltage to achieve real-time following of the converter control dq coordinate system, thereby affecting the conversion and sampling of the duty cycle of the voltage, current and pulse width modulation signal between coordinate systems. Among them, unreasonable control of the converter and the interaction between the converter and the power grid subsystem will cause oscillation. Based on this, an embodiment of the present disclosure proposes a method for optimizing the converter output to suppress the oscillation of the power grid system from the perspective of converter control.

[0065] Figure 2 A flowchart of a method for optimizing converter output provided in an embodiment of the present disclosure.

[0066] like Figure 2 As shown, the method for optimizing the output of the converter specifically includes:

[0067] S1. Obtaining a first system parameter of a converter grid-connected system and a second system parameter of a power grid subsystem under a current working condition.

[0068] S2. Substitute the first system parameters into a converter impedance model to obtain the impedance on the power supply side, wherein the converter impedance model includes a coupling relationship between operating conditions of a phase-locked loop and a grid-connected point in the converter grid-connected system.

[0069] S3. Substitute the second system parameters into the impedance model of the power grid subsystem to obtain the impedance of the power grid side.

[0070] S4. Determine a value of a stability index based on the impedance of the power supply side and the impedance of the grid side.

[0071] S5. Optimizing the output of the converter according to the value of the stability index.

[0072] Specifically, the value of the stability index is used to identify the stability of the power grid system. The value of the stability index is related to the converter and the power grid subsystem. The embodiment of the present disclosure can adjust the output of the converter in real time by monitoring the value of the stability index so that the power grid system is in a stable state.

[0073] Among them, the phase-locked loop in the inverter grid-connected system will introduce negative damping. At the same time, the phase-locked loop is coupled with the operating conditions of the grid-connected point, affecting the impedance of the inverter, and then affecting the stability of the grid system after the inverter is connected to the grid system. Therefore, unreasonable phase-locked loop control is one of the main causes of broadband oscillation.

[0074] The embodiment of the present disclosure includes the coupling relationship between the operating conditions of the phase-locked loop and the grid connection point in the converter impedance model required for calculating the value of the stability index. When the power grid system is determined to be in an unstable state according to the value of the stability index, the current operating condition of the power grid system can be adjusted based on the converter impedance model to implement a strategy of limiting the converter output level based on the converter impedance, so that the power grid system is in a stable state, thereby reducing the risk of oscillation. The current operating condition refers to the active output, reactive output, and voltage and current related conditions in the power grid system (including the converter and / or the power grid subsystem). The embodiment provided by the present disclosure can suppress oscillations from the perspective of converter control.

[0075] In some embodiments, the first parameter of the converter grid-connected system includes at least one of the following: a grid-connected point current, a phase-locked loop transfer function, a ratio of the current loop, an integral coefficient of the current loop, a q-axis component and a d-axis component of the grid-connected point current in the converter grid-connected system, a d-axis component and a q-axis component of the grid-connected point voltage in the converter grid-connected system, and a d-axis component and a q-axis component of the duty cycle of a pulse width modulation signal.

[0076] In some embodiments, the converter impedance model is:

[0077]

[0078] Among them, Y VSC (s) is the target impedance model, L VSC and R VSC are the filter inductance of the converter and the resistance of the converter respectively; V dc is the DC bus voltage of the converter, k pi and k ii are the ratio of the current loop and the integral coefficient of the current loop respectively, I is the unit matrix, and are the q-axis component and d-axis component of the grid-connected point current, and are the q-axis component and d-axis component of the duty cycle of the pulse width modulation signal, G PLL is the phase-locked loop transfer function, ω is the base frequency, and s is the complex frequency variable in the Laplace transform.

[0079] Specifically, Figure 3 A method for Figure 1 The control block diagram of Figure 3 As shown, the circuit part 1 of the inverter grid-connected system includes an open-loop transfer function Z from voltage to current. out and the open-loop transfer function G from the duty cycle of the pulse width modulation signal to the current id , as shown in the following formulas (1) and (2).

[0080]

[0081] Where ω is the fundamental frequency, V dc is the converter DC bus voltage, L VSC and R VSC are the converter filter inductance and resistance respectively, and s is the complex frequency variable in the Laplace transform.

[0082] The current loop of the converter includes proportional-integral control G ci and decoupling control G dei , as shown in the following formulas (3) and (4).

[0083]

[0084] Among them, k pi and k ii They are the proportion of the current loop and the integral coefficient of the current loop respectively.

[0085] The phase-locked loop of the converter calculates the phase angle θ according to the q-axis voltage at the grid connection point, and the phase-locked loop transfer function is shown in the following formula (5). The conversion of the duty cycle of the current and pulse width modulation signal between the dq coordinate system of the control and system is shown in the following formulas (6) and (7).

[0086]

[0087]

[0088] Among them, G PLL is the phase-locked loop transfer function, and are respectively the current component of the phase-locked loop transfer function and the duty cycle component of the pulse width modulation signal of the phase-locked loop transfer function, tfpll is the open-loop transfer function of the phase-locked loop, k ppll and k ipll are the ratio of the phase-locked loop and the integral coefficient of the phase-locked loop, I d s and I q s are the dq axis components of the grid-connected point current, V d s and V q s are the dq axis components of the grid connection point voltage, D d s and D q s They are the dq axis components of the duty cycle of the pulse width modulation signal, respectively. The superscript s represents the component in the system coordinate system, the superscript c represents the component in the control coordinate system, and the upper wavy line ~ represents the small disturbance component of the corresponding variable.

[0089] Therefore, the converter admittance (i.e., converter impedance model) can be obtained according to the following formula (8):

[0090]

[0091] According to formula (8), the transformer impedance model Y VSC (s) is divided into two parts, among which only the converter impedance model Y VSC The second term of (s) (i.e., the term on the right side of “*” in formula (1)) contains the grid-connected current and phase-locked loop related parameters, i.e., only the converter impedance model Y VSC The second term of (s) is related to the coupling between the phase-locked loop control and the grid-connected point operating conditions.

[0092] Furthermore, since the grid connection point voltage can be maintained between 0.95 pu and 1.05 pu, and its variation range is relatively small, therefore, in the embodiment of the present disclosure, it can be considered that V d s =1p.u.,V q s =0p.u.

[0093] In some embodiments, there is a relationship between the duty cycle of the pulse width modulation signal and the voltage and current as shown in the following formula (9):

[0094]

[0095] In some embodiments, based on the relationship between the duty cycle of the pulse width modulation signal and the voltage and current, the converter impedance model may also be:

[0096] That is:

[0097]

[0098] It can be seen from the above converter impedance model provided by the embodiment of the present disclosure that the coupling between the phase-locked loop of the converter grid-connected system and the grid-connected point operating conditions will affect the converter impedance, and thus affect the converter output. In this way, the embodiment of the present disclosure can adjust the current operating conditions and adjust the converter output, thereby adjusting the stability of the power grid system after the converter is connected to the power grid subsystem.

[0099] Furthermore, in the converter impedance model provided by the embodiment of the present disclosure, formula (10) is simpler than formula (8) based on the relationship between the duty cycle of the pulse width modulation signal and the voltage and current, and the relationship between the converter impedance model in formula (10) and the operating conditions is more intuitive, making it more convenient to optimize the output of the converter based on the operating conditions so that the power grid system is in a stable state.

[0100] Figure 4-Figure 6 The waveform diagrams of the converter impedance model provided by the embodiment of the present disclosure under different operating conditions are shown respectively. The operating condition includes the active output and reactive output of the converter. The active output of the converter can be expressed by the d-axis component I of the grid-connected point current. d s The reactive output of the converter can be expressed as the q-axis component I of the grid-connected current. q s express.

[0101] See also Figure 4 , L1, L2 and L3 represent the waveforms corresponding to the converter impedance model when the reactive output of the converter impedance model is 0 and the active output is different. d s They are -190A, -95A, and -47.5A respectively (the current direction is positive when it flows in). First, the influence of active output is analyzed. When the reactive output is not considered, the above formula (10) shows that the converter admittance decoupling is obtained. The active output mainly affects Y VSCqq , that is like Figure 4 As shown in Figure 2, when the active output increases, Y VSCqq The amplitude increases.

[0102] See also Figure 5 , L4 and L5 represent the waveforms of the converter impedance model with the same active output and opposite reactive output. Figure 5 As shown in the figure, when the reactive power output remains unchanged but the direction changes, the corresponding impedance phase changes by 180°. That is, the q-axis component Iq s The direction affects the phase angle of the impedance.

[0103] See also Figure 6 , L4, L5 and L6 represent the waveforms of the converter impedance model with the same active output but different reactive output. Figure 6 As shown in the figure, the active output is the same, the direction of the reactive output is consistent, but the magnitude of the reactive output is different, and the corresponding impedance changes. That is, the q-axis component I of the grid-connected point current corresponding to the reactive output q s The larger the impedance is, the stronger the coupling between the phase-locked loop and the grid-connected point operation condition is. VSCdq That is to say It represents the coupling term between the phase-locked loop and the grid-connected point operating conditions.

[0104] See also Figure 5-Figure 6 Analyze the influence of reactive power output. From equation (10), it can be obtained that the diagonal element of the converter admittance remains unchanged, and the reactive power output mainly affects the coupling term Y VSCdq When the reactive power is inductive or capacitive, Y VSCdq The phase of Y is opposite; when the reactive power output increases, VSCdq The amplitude increases.

[0105] Based on the above Figure 4-Figure 6 From the analysis, it can be seen that the negative resistance frequency band of the converter admittance is mainly determined by the phase-locked loop bandwidth, the active output will affect the amplitude of the negative resistance, and the reactive output will affect the coupling degree of the converter admittance.

[0106] Since active output and reactive output affect converter impedance, after the converter grid-connected system is connected to the grid subsystem to form a grid system, the stability of the grid system can be controlled by controlling the output of the converter.

[0107] In some embodiments, the second system parameters include line inductance and line resistance in the power grid subsystem, and the impedance model of the power grid subsystem is:

[0108]

[0109] Among them, Z grid represents the impedance model of the power grid subsystem, Lg and Rg are the line inductance and resistance in the power grid subsystem respectively, ω is the fundamental frequency, and s is the complex frequency variable in Laplace transform.

[0110] In some embodiments, the impedance model of the power grid subsystem may also be:

[0111]

[0112] Among them, C loadand R load are the load capacitance and resistance respectively.

[0113] In some embodiments, step S4, determining the value of the stability index based on the impedance of the power supply side and the impedance of the grid side, includes:

[0114] S41. Calculate the eigenvalue of the power matrix of the power grid system based on the impedance of the power supply side and the impedance of the power grid side.

[0115] S42: Determine the value of the stability index according to the eigenvalue of the return rate matrix.

[0116] Specifically, according to the generalized Nyquist criterion (Nyquist stability criterion), the impedance of the source (converter in the present disclosure) and the load subsystem (grid subsystem in the present disclosure) is used to calculate the eigenvalue of the system return matrix, and the value of the stability index GM is determined according to the calculated eigenvalue. GNC Among them, when GM GNC <-1, the system is unstable; when GM GNC >-1, the system is stable and GM GNC The further away from -1, the greater the system stability margin.

[0117] In the embodiment of the present disclosure, the product / ratio of the impedance on the power supply side and the impedance on the power grid side is calculated to obtain the power matrix of the power grid system and calculate the eigenvalue of the matrix. That is, the power matrix of the power grid system is obtained by multiplying the above formula (10) by the above formula (11), and the eigenvalue of the matrix is ​​calculated, or the power matrix of the power grid system is obtained by dividing the calculation formula (10) by the above formula (12), and its eigenvalue is calculated.

[0118] The impedance on the power supply side required for calculating the characteristic value in the embodiment of the present disclosure (i.e., the converter impedance model) includes the coupling relationship between the operating conditions of the phase-locked loop and the grid-connected point in the converter grid-connected system. Therefore, the value of the stability index determined by the characteristic value is also related to the coupling between the operating conditions of the phase-locked loop and the grid-connected point. Furthermore, the stability of the power grid system can be adjusted by optimizing the output of the converter.

[0119] In some embodiments, S42, determining the value of the stability index according to the eigenvalue of the return matrix includes:

[0120] S421. Determine a trajectory curve of the eigenvalues ​​of the rate matrix on a complex plane.

[0121] S422. Determine the value of the stability index according to the intersection point of the trajectory curve and the leftmost side of the real axis in the complex plane.

[0122] Specifically, according to the generalized Nyquist criterion, when the eigenvalue trajectory surrounds the point (-1, 0), the system is unstable, and when the eigenvalue trajectory does not surround the point (-1, 0), the system is stable. In the embodiment of the present disclosure, the intersection of the trajectory curve and the leftmost point of the real axis in the complex plane is determined as the value GM of the stability index. GNC， So, if GM GNC <-1, the eigenvalue trajectory surrounds (-1,0), and the system becomes unstable; when GM GNC >-1, the eigenvalue trajectory will not surround (-1,0), the system is stable, and GM GNC The further away from -1, the greater the system stability margin.

[0123] The embodiment of the present disclosure determines the intersection point of the characteristic value trajectory curve and the leftmost side of the real axis in the complex plane as the value of the stability index, thereby making it simpler, more convenient and more accurate to judge the stability of the power grid system.

[0124] In some embodiments, step S5, optimizing the output of the converter according to the value of the stability index, includes: when the value of the stability index is less than -1, controlling the converter to reduce reactive output and / or active output to increase the stability of the power grid system.

[0125] Specifically, Figure 7 A schematic diagram of a stability index and operating conditions curve provided by an embodiment of the present disclosure. Figure 7 As shown, reference Figure 7 In (a), first, gradually reduce the active output (i.e., I d s ), the value of the stability index GM GNC When the active output is reduced to about 20, the value of the stability index is further away from -1, and when the active output is further reduced, the value of the stability index tends to be stable. Figure 7 (b) in the figure shows the gradual change of reactive output (i.e. I q s ), when the reactive power output is large, GM GNC The closer it is to -1, the smaller the system stability margin is. Therefore, the optimal method for converter output can be obtained. In order to improve the system stability margin under weak power grid, the converter should try not to generate reactive power, and can appropriately reduce the active power output when necessary. GNC If it is less than -1, the system is at risk of instability. The adjustment methods for active and reactive power are similar and will not be repeated here.

[0126] In the embodiment of the present disclosure, the intersection point of the characteristic value trajectory and the leftmost point of the real axis is taken as the value GM of the stability index. GNC, which can more simply and accurately judge the stability of the power grid system after the converter is connected to the power grid subsystem. At the same time, the coupling between the phase-locked loop and the grid connection point operating conditions is considered when constructing the converter impedance model. Based on this, the converter output is optimized to reduce the oscillation risk of the converter connected to the weak power grid system.

[0127] In a second aspect, based on the same inventive concept, the disclosed embodiment also provides a device for optimizing the output of a converter.

[0128] Figure 8 FIG. 7 is a structural diagram of a converter output optimization device 700 provided in an embodiment of the present disclosure. Figure 8 As shown, the optimization device 700 includes: an acquisition module 701, a first calculation module 702, a second calculation module 703, a determination module 704 and an optimization module 705.

[0129] Among them, the acquisition module 701 is used to obtain the first system parameter of the converter grid-connected system and the second system parameter of the grid subsystem under the current working condition. The first calculation module 702 is used to bring the first system parameter into the converter impedance model to obtain the impedance on the power supply side. The second calculation module 703 is used to bring the second system parameter into the impedance model of the grid subsystem to obtain the impedance on the grid side. The determination module 704 is used to determine the value of the stability index based on the impedance on the power supply side and the impedance on the grid side. The optimization module 705 is used to optimize the output of the converter according to the value of the stability index, wherein the converter impedance model includes the coupling relationship between the operating conditions of the phase-locked loop and the grid connection point in the converter grid-connected system.

[0130] The first calculation module 702 in the embodiment of the present disclosure calculates the impedance of the power supply side by using the converter impedance model including the coupling relationship between the operating conditions of the phase-locked loop and the grid connection point in the converter grid-connected system, so that the value of the stability index determined by the determination module 704 is also related to the coupling of the operating conditions of the phase-locked loop and the grid connection point. The optimization module 705 can adjust the current operating conditions of the power grid system based on the converter impedance model when it is determined that the power grid system is in an unstable state according to the value of the stability index, so as to implement a strategy of limiting the output level of the converter based on the converter impedance, so that the power grid system is in a stable state, thereby reducing the risk of oscillation. Among them, the current operating conditions refer to the active output, reactive output, and voltage and current related conditions in the power grid system (including the converter and / or the grid subsystem). The optimization device 700 provided in the present disclosure can suppress oscillations from the perspective of converter control.

[0131] In some embodiments, the first parameter of the converter grid-connected system includes at least one of the following: a grid-connected point current, a phase-locked loop transfer function, a ratio of the current loop, an integral coefficient of the current loop, a q-axis component and a d-axis component of the grid-connected point current in the converter grid-connected system, a d-axis component and a q-axis component of the grid-connected point voltage in the converter grid-connected system, and a d-axis component and a q-axis component of the duty cycle of a pulse width modulation signal.

[0132] In some embodiments, the converter impedance model is:

[0133]

[0134] Among them, Y VSC (s) is the transformer impedance model, L VSC and R VSC are the filter inductance of the converter and the resistance of the converter respectively; V dc is the DC bus voltage of the converter, k pi and k ii are the ratio of the current loop and the integral coefficient of the current loop, I is the unit matrix, G PLL is the phase-locked loop transfer function, and are the q-axis component and d-axis component of the grid-connected point current in the converter grid-connected system, V d s and V q s are respectively the d-axis component and the q-axis component of the grid-connected point voltage in the converter grid-connected system, and s is the complex frequency variable in the Laplace transform.

[0135] In some embodiments, the converter impedance model is:

[0136]

[0137] Among them, Y VSC (s) is the target impedance model, L VSC and R VSC are the filter inductance of the converter and the resistance of the converter respectively; V dc is the DC bus voltage of the converter, k pi and k ii are the ratio of the current loop and the integral coefficient of the current loop respectively, I is the unit matrix, and are the q-axis component and d-axis component of the grid-connected point current, and are the q-axis component and d-axis component of the duty cycle of the pulse width modulation signal, G PLLis the phase-locked loop transfer function, ω is the fundamental frequency of the converter grid-connected system, and s is the complex frequency variable in the Laplace transform.

[0138] In some embodiments, the second system parameter includes line inductance and line resistance in the power grid subsystem, and the impedance model of the power grid subsystem is:

[0139]

[0140] Among them, Z grid represents the impedance model of the power grid subsystem, Lg and Rg are the line inductance and resistance in the power grid subsystem respectively, ω is the fundamental frequency of the power grid subsystem, and s is the complex frequency variable in the Laplace transform.

[0141] In some embodiments, the determination module 704 includes a third calculation module 714 and a determination submodule 724.

[0142] The third calculation module 714 is used to calculate the eigenvalue of the rate matrix of the power grid system based on the impedance of the power supply side and the impedance of the power grid side. The determination submodule 724 is used to determine the value of the stability index according to the eigenvalue of the rate matrix.

[0143] In some embodiments, the determination submodule 724 includes a first determination submodule 7241 and a second determination submodule 7242 .

[0144] The first determination submodule 7241 is used to determine the trajectory curve of the eigenvalue of the return matrix on the complex plane. The second determination submodule 7242 is used to determine the value of the stability index according to the intersection of the trajectory curve and the leftmost point of the real axis in the complex plane.

[0145] In some embodiments, the optimization module 705 is specifically used to: when the value of the stability index is less than -1, control the converter to reduce reactive output and / or active output to increase the stability of the power grid system.

[0146] It can be understood that the specific details and corresponding technical effects of the optimization device provided in the embodiment of the present disclosure can refer to the specific details of the optimization method embodiment of the first aspect mentioned above, and will not be repeated here.

[0147] In a third aspect, an embodiment of the present disclosure further provides an electronic device, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein when the processor executes the computer program, the method described in any one of the first aspects is implemented.

[0148] Specifically, Fig. 9 A schematic diagram of the physical structure of an electronic device provided in an embodiment of the present disclosure, such as Fig. 9As shown, the electronic device 003 includes a processor 301, a memory 302 and a bus 303. The processor 301 and the memory 302 communicate with each other via the bus 303.

[0149] The processor 301 is used to call the program instructions in the memory 302 to execute the methods provided by the above method embodiments.

[0150] In a fourth aspect, an embodiment of the present disclosure further provides a computer-readable storage medium, wherein the computer-readable storage medium stores a computer program of the method described in any one of the first aspects above.

[0151] In a fifth aspect, an embodiment of the present disclosure further provides a computer program product, comprising a computer program / instructions, which, when executed by a processor, implement the steps of any one of the methods described in the first aspect above.

[0152] Those skilled in the art will appreciate that the embodiments of the present disclosure may be provided as methods, systems, or computer program products. Therefore, the present disclosure may take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware. Moreover, the present disclosure may take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0153] The present disclosure is described with reference to the flowcharts and / or block diagrams of the methods, devices (systems), and computer program products according to the embodiments of the present disclosure. It should be understood that each process and / or box in the flowchart and / or block diagram, as well as the combination of the processes and / or boxes in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to generate a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0154] These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0155] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process in the computer or other programmable device. Figure 1 A process or multiple processes and / or boxes Figure 1 The steps for the functions specified in one or more boxes.

[0156] Specific embodiments are used in the present disclosure to illustrate the principles and implementation methods of the present disclosure. The description of the above embodiments is only used to help understand the method of the present disclosure and its core idea. At the same time, for those skilled in the art, according to the idea of ​​the present disclosure, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as a limitation on the present disclosure.

Claims

1. A method for optimizing converter output, characterized in that: The method comprises: Obtaining a first system parameter of the converter grid-connected system and a second system parameter of the power grid subsystem under current working conditions; Substituting the first system parameter into a converter impedance model to obtain an impedance on the power supply side, wherein the converter impedance model includes a coupling relationship between an operating condition of a phase-locked loop and a grid-connected point in the converter grid-connected system; Substituting the second system parameter into the impedance model of the power grid subsystem to obtain the impedance of the power grid side; Determining a value of a stability index based on the impedance of the power supply side and the impedance of the grid side; The output of the converter is optimized according to the value of the stability index.

2. The method according to claim 1, characterized in that The first parameter of the inverter grid-connected system includes at least one of the following: grid-connected point current, phase-locked loop transfer function, ratio of the current loop, integral coefficient of the current loop, q-axis component and d-axis component of the grid-connected point current in the inverter grid-connected system, d-axis component and q-axis component of the grid-connected point voltage in the inverter grid-connected system, and d-axis component and q-axis component of the duty cycle of the pulse width modulation signal.

3. The method according to claim 2, characterized in that The transformer impedance model is: Among them, Y VSC (s) is the transformer impedance model, L VSC and R VSC are the filter inductance of the converter and the resistance of the converter respectively; V dc is the DC bus voltage of the converter, k pi and k ii are the ratio of the current loop and the integral coefficient of the current loop, I is the unit matrix, G PLL is the phase-locked loop transfer function, and are respectively the q-axis component and the d-axis component of the grid-connected point current in the converter grid-connected system, and V q s are respectively the d-axis component and the q-axis component of the grid-connected point voltage in the converter grid-connected system, and s is a complex frequency variable in Laplace transform.

4. The method according to claim 2, characterized in that: The transformer impedance model is: Among them, Y VSC (s) is the target impedance model, L VSC and R VSC are the filter inductance of the converter and the resistance of the converter respectively; V dc is the DC bus voltage of the converter, k pi and k ii are the ratio of the current loop and the integral coefficient of the current loop respectively, I is the unit matrix, and are the q-axis component and d-axis component of the grid-connected point current, and are the q-axis component and d-axis component of the duty cycle of the pulse width modulation signal, G PLL is the phase-locked loop transfer function, ω is the fundamental frequency of the converter grid-connected system, and s is the complex frequency variable in the Laplace transform.

5. The method according to claim 1, characterized in that The second system parameters include line inductance and line resistance in the power grid subsystem, and the impedance model of the power grid subsystem is: Among them, Z grid represents the impedance model of the power grid subsystem, Lg and Rg are the line inductance and resistance in the power grid subsystem respectively, ω is the fundamental frequency of the power grid subsystem, and s is the complex frequency variable in the Laplace transform.

6. The method according to claim 1, characterized in that The determining the value of the stability index based on the impedance of the power supply side and the impedance of the grid side includes: Calculating the eigenvalue of the power matrix of the power grid system based on the impedance of the power supply side and the impedance of the power grid side; The value of the stability index is determined according to the eigenvalue of the return matrix.

7. The method according to claim 6, characterized in that Determining the value of the stability index according to the eigenvalue of the return rate matrix includes: Determine a trajectory curve of the eigenvalues ​​of the rate matrix on a complex plane; The value of the stability index is determined according to the intersection point of the trajectory curve and the leftmost side of the real axis in the complex plane.

8. The method according to claim 1, characterized in that Optimizing the output of the converter according to the value of the stability index includes: When the value of the stability index is less than -1, there is a risk of instability in the system, and the converter is controlled to reduce reactive output and / or active output to increase the stability of the power grid system.

9. A device for optimizing converter output, characterized in that: The device comprises: An acquisition module, used to acquire a first system parameter of the converter grid-connected system and a second system parameter of the power grid subsystem under a current working condition; A first calculation module, used for bringing the first system parameter into a converter impedance model to obtain an impedance on a power supply side, wherein the converter impedance model includes a coupling relationship between an operating condition of a phase-locked loop and a grid-connected point in the converter grid-connected system; A second calculation module is used to bring the second system parameters into the impedance model of the power grid subsystem to obtain the impedance of the power grid side; A determination module, configured to determine a value of a stability index based on the impedance of the power supply side and the impedance of the grid side; An optimization module is used to optimize the output of the converter according to the value of the stability index.

10. The device according to claim 9, characterized in that The first parameter of the inverter grid-connected system includes at least one of the following: grid-connected point current, phase-locked loop transfer function, ratio of the current loop, integral coefficient of the current loop, q-axis component and d-axis component of the grid-connected point current in the inverter grid-connected system, d-axis component and q-axis component of the grid-connected point voltage in the inverter grid-connected system, and d-axis component and q-axis component of the duty cycle of the pulse width modulation signal.

11. The device according to claim 10, characterized in that The transformer impedance model is: Among them, Y VSC (s) is the transformer impedance model, L VSC and R VSC are the filter inductance of the converter and the resistance of the converter respectively; V dc is the DC bus voltage of the converter, k pi and k ii are the ratio of the current loop and the integral coefficient of the current loop, I is the unit matrix, G PLL is the phase-locked loop transfer function, and are respectively the q-axis component and the d-axis component of the grid-connected point current in the converter grid-connected system, and V q s are respectively the d-axis component and the q-axis component of the grid-connected point voltage in the converter grid-connected system, and s is the complex frequency variable in the Laplace transform.

12. The device according to claim 10, characterized in that The transformer impedance model is: Among them, Y VSC (s) is the target impedance model, L VSC and R VSC are the filter inductance of the converter and the resistance of the converter respectively; V dc is the DC bus voltage of the converter, k pi and k ii are the ratio of the current loop and the integral coefficient of the current loop respectively, I is the unit matrix, and are the q-axis component and d-axis component of the grid-connected point current, and are the q-axis component and d-axis component of the duty cycle of the pulse width modulation signal, G PLL is the phase-locked loop transfer function, W is the fundamental frequency of the converter grid-connected system, and s is the complex frequency variable in the Laplace transform.

13. The device according to claim 9, characterized in that The determination module comprises: A third calculation module, used for calculating the eigenvalue of the rate matrix of the power grid system based on the impedance of the power supply side and the impedance of the power grid side; The determination submodule is used to determine the value of the stability index according to the eigenvalue of the return rate matrix.

14. The device according to claim 13, characterized in that The determination submodule comprises: A first determination submodule is used to determine a trajectory curve of the eigenvalue of the rate matrix on a complex plane; The second determination submodule is used to determine the value of the stability index according to the intersection point of the trajectory curve and the leftmost side of the real axis in the complex plane.

15. The device according to claim 9, characterized in that The optimization module is specifically used for: when the value of the stability index is less than -1, there is a risk of instability in the system, and the converter is controlled to reduce reactive power and / or active power output to increase the stability of the power grid system.

16. An electronic device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that: When the processor executes the computer program, the method according to any one of claims 1 to 8 is implemented.

17. A computer-readable storage medium, characterized in that: The computer-readable storage medium stores a computer program for executing the method according to any one of claims 1 to 8.

18. A computer program product comprising a computer program / instructions, characterized in that When the computer program / instructions are executed by a processor, the steps of the method according to any one of claims 1 to 8 are implemented.

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