MMC grid-connected power control method

Abstract

The invention belongs to the technical field of grid-connected power control, and aims to provide an MMC grid-connected power control method. The passive current inner loop controller with linear damping is introduced into the current inner loop, so that energy dissipation is accelerated, the dynamic response performance and the adjusting speed of the system are improved, current harmonics can be effectively suppressed, and the stability of the system is enhanced; meanwhile, a self-adaptive power outer ring controller containing a self-adaptive rotational inertia compensation mechanism of an arctan function and a self-adaptive damping compensation mechanism is introduced into a power outer ring, so that the rotational inertia change rate in self-adaptive control is effectively suppressed, transient oscillation of the system is further suppressed, and the reliability of the system is improved. And the dynamic response performance and the transient stability of the MMC grid-connected system are further improved.

Description

Technical Field

[0001] The invention belongs to the technical field of grid-connected power control, and in particular relates to an MMC grid-connected power control method. Background Art

[0002] With the rapid development of new energy technologies, distributed power sources, energy storage components and AC and DC loads are connected to the power grid on a large scale, making the energy interaction of the power grid more frequent. In order to achieve the coordinated operation of "source-grid-load-storage" in the power grid system, the research and application of power electronic transformers (PET) are becoming more and more extensive. PET has flexible and changeable structure, flexible access to distributed power sources, can realize bidirectional energy transmission, and has the capabilities of voltage sag compensation, instantaneous voltage regulation and power factor correction. It is currently widely used in new power systems.

[0003] PET involves a lot of AC / DC conversion, and common converter topologies include two-level, three-level, cascaded H-bridge and modular multilevel converter (MMC). Among them, MMC does not require multiple switch devices in series in high-voltage applications, and has a certain redundancy mechanism; when the power and voltage on the grid side fluctuate, the number of sub-modules in operation is adjusted to achieve flexible switching of power and voltage levels, avoiding the problems of large circulating current, high heat generation and high cost caused by the introduction of multi-winding phase-shifting transformers in traditional converters to increase power and voltage levels.

[0004] However, in the process of using the prior art, the inventors found that the prior art has at least the following problems: Existing MMCs lack damping inertia in weak power grids and have poor dynamic performance. Specifically, a large number of distributed power sources, energy storage components, and AC and DC loads are connected to the grid in weak power grids, which can easily cause load and voltage fluctuations on the grid side. Traditional MMC control methods lack sufficient inertia support, resulting in reduced power quality and system stability. Domestic and foreign scholars have conducted a lot of research on the above issues.

[0005] In terms of current control, reference [1] introduces the principle of system energy balance from the perspective of nonlinear systems, and replaces the traditional PI (Proportional Integral) control with passive control, which improves the system's ability to cope with grid voltage mismatch, but it does not consider the power fluctuation and frequency oscillation caused by grid-side load mutation. Reference [2] combines feedback linearization control with sliding mode control to optimize the current inner loop control structure, so that the MMC has better dynamic performance and stability, but does not involve the optimization of primary frequency regulation performance. Reference [3] introduces a sliding mode controller with an improved exponential convergence law in the current inner loop of the MMC, making the selection of system inertia parameters more flexible, improving dynamic response performance, and reducing DC voltage deviation, but its calculation is more complicated and the control parameter setting is more difficult.

[0006] In terms of power control, Reference [4] introduced a VSG (Virtual Synchronous Generators) controller into the power outer loop controller of MMC, which provided voltage and frequency support for the stable operation of traditional MMC and enhanced the anti-interference ability of the system to a certain extent. Reference [5] introduced additional virtual impedance to reduce the damping coefficient of the system by analyzing the damping characteristics, thereby improving the damping characteristics of VSG. Reference [6] introduced a sliding mode controller based on internal model control into VSG control, which can suppress the current and power shocks generated by the system when a sudden load fault occurs in the system, thereby improving the robustness of the system. However, the damping coefficient and moment of inertia of the control system are constant, sacrificing certain dynamic response performance. Reference [7] introduced a VSG control strategy based on fuzzy control algorithm into MMC control, which optimized the frequency regulation and transmission power balance performance of the system. However, its control algorithm is relatively complex and difficult to be widely used in practice.

[0007] In summary, the above existing technologies have improved the dynamic response capability of the system by improving the control system, but lack research that simultaneously considers the current inner loop control and outer loop control. Both the inner and outer loop controls of the MMC will affect the dynamic performance of the MMC. Summary of the invention

[0008] The present invention aims to solve the above technical problem at least to a certain extent, and provides a MMC grid-connected power control method.

[0009] In order to achieve the above object, the present invention adopts the following technical solutions: In a first aspect, the present invention provides a MMC grid-connected power control method, comprising: Collecting the grid-side voltage value and the grid-side current value of the grid-connected output terminal of the MMC module, and performing power calculation according to the grid-side voltage value and the grid-side current value to obtain the active power value and the reactive power value; Obtaining an active power reference value, a reactive power reference value, a grid angular velocity reference value, a voltage reference value, and a grid angular velocity of the MMC module, and using the active power value, the reactive power value, the grid-side voltage value, the active power reference value, the reactive power reference value, the grid angular velocity reference value, the voltage reference value, and the grid angular velocity as input values ​​of a power outer loop controller, so as to obtain a current reference value based on the power outer loop controller; wherein the power outer loop controller adopts a VSG control method, and the power outer loop controller introduces an adaptive moment of inertia compensation mechanism containing an arctan function and an adaptive damping compensation mechanism; The current reference value, the grid-side current value and the grid-side voltage value are used as input values ​​of a current inner-loop controller, so as to obtain the three-phase differential-mode voltage values ​​of the MMC module based on the current inner-loop controller; wherein the current inner-loop controller is injected with positive linear damping, and the current inner-loop controller adopts a PBC passive control method; The differential mode voltage value is used as an input value of the MMC modulator, so as to obtain an MMC control signal based on the MMC modulator, and the MMC module is controlled according to the MMC control signal.

[0010] In one possible design, the power outer loop controller includes a VSG active power controller, an integrator and a VSG reactive power controller; the current reference value includes a d-axis current reference value and a q-axis current reference value; correspondingly, obtaining the current reference value based on the power outer loop controller includes: The active power value, the active power reference value, the grid angular velocity reference value and the grid angular velocity are used as input values ​​of the VSG active power controller, so as to obtain a grid angular velocity differential value based on the VSG active power controller; Using the grid angular velocity differential value as the input value of the integrator to obtain the phase angle; Using the grid-side voltage value, the reactive power value, the reactive power reference value and the voltage reference value as input values ​​of the VSG reactive power controller, so as to obtain a virtual electromotive force based on the VSG reactive power controller; Obtaining a three-phase virtual electromotive force according to the phase angle and the virtual electromotive force, and inputting the three-phase virtual electromotive force into an excitation equation to obtain a three-phase current component; The three-phase current components are decomposed into a dq two-phase rotating coordinate system to obtain a d-axis current reference value and a q-axis current reference value.

[0011] In a possible design, the grid angular velocity differential value is obtained by the following formula: ; In the formula, is the differential value of the grid angular velocity; , P ref is the active power reference value, K p is the preset active power-frequency droop coefficient, is the grid angular velocity, 0 is the grid angular velocity reference value; P is the active power value; J is the preset moment of inertia; D is the preset damping coefficient.

[0012] In a possible design, the adaptive control strategy of the moment of inertia and the damping coefficient is: ; In the formula, J 0 is the preset moment of inertia setting value; D 0 is the preset damping coefficient setting value; K j is a preset adjustment coefficient of the moment of inertia; K d is a preset adjustment coefficient of the damping coefficient; T i is a preset first limiting threshold; T d is a preset second limiting threshold.

[0013] In one possible design, the virtual electromotive force is: ; In the formula, K q for Preset reactive power regulation factor ; K u for Preset voltage regulation factor ; represents an integrator in the VSG reactive power controller; Q ref is the reactive power reference value; Q is the reactive power value; U ref is the voltage reference value; U g is the grid-side voltage value; E n It is the preset MMC no-load electromotive force.

[0014] In a possible design, the differential mode voltage values ​​of the three phases of the MMC module include the d-axis differential mode voltage value and the q-axis differential mode voltage value after being decomposed into the dq two-phase rotating coordinate system; correspondingly, the differential mode voltage value of any phase of the MMC module is: ; In the formula, U diffd is the d-axis differential mode voltage of any phase of the MMC module; U diffq is the q-axis differential mode voltage of any phase of the MMC module; U sd The grid-side voltage value is decomposed into a d-axis grid-side voltage value after the grid-side voltage value is decomposed into a dq two-phase rotating coordinate system; U sq The grid-side voltage value is decomposed into a q-axis grid-side voltage value after the grid-side voltage value is decomposed into a dq two-phase rotating coordinate system; is the grid angular velocity; L=0.5L 0 +L g , L 0 is the bridge arm inductance of any phase of the MMC module, and is the grid-side inductance of any phase of the MMC module; I vd is the d-axis bridge arm current of any phase of the MMC module; I vq is the q-axis bridge arm current of any phase of the MMC module; R=0.5R 0, R 0 is the bridge arm resistance of any phase of the MMC module; To decompose the current reference value into the d-axis current reference value after the dq two-phase rotating coordinate system, is a q-axis current reference value after decomposing the current reference value into a dq two-phase rotating coordinate system; R n1 and R n2 is the positive linear damping injected into the current inner loop controller R n = The element value in .

[0015] In a possible design, the linear damping injected by the current inner loop controller is 60Ω.

[0016] The beneficial effects of the present invention are: The present invention discloses a MMC grid-connected power control method based on VSG and PBC passive control, which can realize MMC grid-connected power control, and simultaneously considers current inner loop control and outer loop control, which is beneficial to improving the dynamic performance of the MMC grid-connected system. Specifically, this embodiment accelerates energy dissipation, improves the dynamic response performance and regulation speed of the system by introducing a passive current inner loop controller with linear damping in the current inner loop, can effectively suppress current harmonics, and enhance the stability of the system; at the same time, this embodiment also introduces an adaptive power outer loop controller with an adaptive moment of inertia compensation mechanism containing an arctan function and an adaptive damping compensation mechanism in the power outer loop, thereby effectively suppressing the moment of inertia change rate in the adaptive control, thereby suppressing the transient oscillation of the system, and further improving the dynamic response performance and transient stability of the MMC grid-connected system.

[0017] Other beneficial effects of the present invention will be further described in the specific embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 is a topological diagram of the MMC grid-connected system including the MMC module in Example 1; Figure 2 is a schematic diagram of the structure of the power outer loop controller and the current inner loop controller in Example 1; Figure 3 It is a schematic diagram of a power angle curve and an angular power oscillation curve of a power outer loop controller system when the active power changes from P1→P2→P3→P2→P1 in Example 1; wherein (a) is a schematic diagram of a power angle curve of a power outer loop controller system when the active power changes from P1→P2→P3→P2→P1, and (b) is a schematic diagram of an angular power oscillation curve of a power outer loop controller system when the active power changes from P1→P2→P3→P2→P1; Figure 4 is a simplified diagram of the MMC module in Example 1; Figure 5 Schematic diagram of the amplitude-frequency characteristic curve of the relationship between the passive control current of the inner loop of the conventional MMC module and its reference value in Embodiment 1; Figure 6 It is a frequency-time relationship diagram of an MMC grid-connected system corresponding to the conventional VSG control method using Example 1 when a given power mutation is used as an example; Figure 7 It is an example of the active power-time relationship diagram of the MMC grid-connected system corresponding to the embodiment 1 and the traditional VSG control method when a given power mutation is applied. DETAILED DESCRIPTION

[0019] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the present invention will be briefly introduced below in combination with the drawings and the description of the embodiments or the prior art. Obviously, the following description of the structure of the drawings is only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work. It should be noted that the description of these embodiments is used to help understand the present invention, but does not constitute a limitation of the present invention.

[0020] Embodiment 1: This embodiment discloses an MMC grid-connected power control method, which can be executed by, but is not limited to, a computer device or a virtual machine with certain computing resources, such as a personal computer, a smart phone, a personal digital assistant, or a wearable device, or by a virtual machine.

[0021] A method for controlling the grid-connected power of an MMC may include, but is not limited to, the following steps: S1. Collect the grid-side voltage value and grid-side current value of the grid-connected output end of the MMC module in the MMC grid-connected system, and perform power calculation based on the grid-side voltage value and the grid-side current value to obtain active power value and reactive power value; it should be noted that, in this embodiment, the MMC module is used as an inverter in the MMC grid-connected system, one side of which is connected to the DC source stage, and the other side is used as the grid-connected output end for grid connection.

[0022] Specifically, in this embodiment, the topology diagram of the MMC grid-connected system is as follows: Figure 1 In addition, in this embodiment, the bridge arm submodule of the MMC module adopts a widely used half-bridge submodule (Half-Bridge Sub Module, HBSM).

[0023] S2. Obtain an active power reference value, a reactive power reference value, a grid angular velocity reference value, a voltage reference value and a grid angular velocity of the MMC module, and use the active power value, the reactive power value, the grid-side voltage value, the active power reference value, the reactive power reference value, the grid angular velocity reference value, the voltage reference value and the grid angular velocity as input values ​​of a power outer loop controller, so as to obtain a current reference value based on the power outer loop controller; wherein, the power outer loop controller adopts a VSG (Virtual Synchronous Generators) control method, and the power outer loop controller introduces an adaptive moment of inertia compensation mechanism containing an arctan function and an adaptive damping compensation mechanism; it should be understood that the active power reference value, the reactive power reference value, the grid angular velocity reference value and the voltage reference value are all system preset values.

[0024] Specifically, in this embodiment, the specific structure diagram of the power outer loop controller and the current inner loop controller is as follows: Figure 2 shown.

[0025] In step S2, the power outer loop controller includes a VSG active power controller, an integrator and a VSG reactive power controller; the current reference value includes a d-axis current reference value and a q-axis current reference value; correspondingly, the current reference value is obtained based on the power outer loop controller, including: S201. Using the active power value, the active power reference value, the grid angular velocity reference value and the grid angular velocity as input values ​​of the VSG active power controller, so as to obtain a grid angular velocity differential value based on the VSG active power controller; In step S201, in order to obtain strong inertia support, the operating characteristics of the synchronous generator are used to build the electrical equivalent relationship of the MMC based on VSG control, and the DC source level is regarded as the prime mover and the MMC module is regarded as the synchronous generator. At this time, from the perspective of power and angular velocity, it can be seen that the operation of the MMC simulated synchronous generator must satisfy the rotor motion equation of the synchronous generator, which is also the equation for obtaining the differential value of the grid angular velocity, as shown below: ; In the formula, is the differential value of the grid angular velocity; , P ref is the active power reference value, K p is the preset active power-frequency droop coefficient, is the grid angular velocity, 0 is the grid angular velocity reference value; P is the active power value; J is the preset moment of inertia; D is the preset damping coefficient.

[0026] During the implementation, in order to simulate the frequency regulation characteristics of the synchronous generator, a speed regulator with active power-frequency droop characteristics is introduced into the VSG control: ; In the formula, P ref is the active power reference value; K p is the preset active power-frequency droop coefficient; P m According to the active power reference value P ref , Active power-frequency droop coefficient Kp , grid angular velocity and grid angular velocity reference value 0 is the mechanical power value obtained.

[0027] because , the rotor motion equation and the speed regulator equation with active power-frequency droop characteristics are combined to obtain: ; Based on this, a VSG active power controller can be constructed.

[0028] S202. Use the grid angular velocity differential value as the input value of the integrator to obtain a phase angle; in this embodiment, the integrator is expressed as 1 / s, and the obtained phase angle is θ.

[0029] S203. Using the grid-side voltage value, the reactive power value, the reactive power reference value and the voltage reference value as input values ​​of the VSG reactive power controller, so as to obtain a virtual electromotive force based on the VSG reactive power controller; In step S203, the virtual electromotive force is: ; In the formula, K q is the preset reactive power regulation coefficient; K u is the preset voltage regulation coefficient; represents an integrator in the VSG reactive power controller; Q ref is the reactive power reference value; Q is the reactive power value; U ref is the voltage reference value; U g is the grid-side voltage value; E n is the preset MMC no-load electromotive force. It should be noted that The VSG reactive power regulation part in the virtual electromotive force ; The VSG terminal voltage regulation part in the virtual electromotive force is constituted .

[0030] S204. Obtain a three-phase virtual electromotive force according to the phase angle and the virtual electromotive force, and input the three-phase virtual electromotive force into an excitation equation to obtain a three-phase current component; Specifically, in this embodiment, the three-phase virtual electromotive force includes the A-phase virtual electromotive force Esinθ 、B phase virtual electromotive force Esin(θ-2π / 3)and C phase virtual electromotive force Esin(θ+2π / 3) .

[0031] S205. Decompose the three-phase current components into a dq two-phase rotating coordinate system to obtain a d-axis current reference value and a q-axis current reference value.

[0032] Specifically, in this embodiment, the d-axis current reference value is expressed as , the q-axis current reference value is expressed as .

[0033] It should be noted that the system is prone to power disturbances under weak power grids. When power disturbances occur under VSG control under grid-connected conditions, the power and frequency in the system will oscillate with attenuation. Figure 3 The power angle curve and angular power oscillation curve of the power outer loop controller system when the active power changes from P1→P2→P3→P2→P1. As shown in the figure, the time period of the angular power oscillation curve corresponding to the active power change of the power outer loop controller system P1→P2→P3→P2→P1 is T1→T2→T3→T4→T5. Let the difference between the angular velocity and the reference angular velocity be ∆ω The rate of change of angular velocity is dω / dt .

[0034] because J Affects the response speed of the system. D Affects the amplitude change of the system. In the T1-T2 time period, ∆ω >0, d ω / dt >0, to ensure the stability of the system angular velocity, the angular frequency change needs to be reduced. At this time, the J and D ; During the T2-T3 period, ∆ω >0, dω / dt <0, in order to make the angular velocity reach the grid angular velocity as quickly as possible, the J and D ; During the T3-T4 period, ∆ω <0, dω / dt <0, so in order to reduce the angular velocity conversion rate and overshoot, the inertia should be increased J and D ; In the time period T4-T5, ∆ω<0, dω / dt >0, in order to make the system angular velocity quickly reach the rated angular velocity. The inertia needs to be reduced J , increase D .

[0035] Combined with the above analysis, considering the moment of inertia J To solve the problem of too fast or too large changes, this paper introduces the arctan function in the adaptive control strategy, that is, the adaptive control strategy of the moment of inertia and the damping coefficient is: ; In the above formula, since the range of arctan(x) function is -π / 2 to π / 2, the moment of inertia is J The value range is limited to J 0 ±K j Between, can effectively suppress the moment of inertia J Problems with changes that are too fast or too large. J 0 is the preset moment of inertia setting value when the VSG is in steady-state operation; D 0 is the preset damping coefficient setting value when the VSG is in steady-state operation; K j is a preset adjustment coefficient of the moment of inertia; K d The damping coefficient is preset D The adjustment coefficient of T i is a preset first limiting threshold; T d is a preset second limiting threshold.

[0036] S3. Using the current reference value, the grid-side current value and the grid-side voltage value as input values ​​of the current inner-loop controller, so as to obtain the three-phase differential-mode voltage value of the MMC module based on the current inner-loop controller; wherein the current inner-loop controller is injected with positive linear damping, and the current inner-loop controller adopts a PBC (Passivity-Based Control) passive control method; Specifically, in step S3, the differential mode voltage values ​​of the three phases of the MMC module include the d-axis differential mode voltage value and the q-axis differential mode voltage value after being decomposed into the dq two-phase rotating coordinate system; correspondingly, the differential mode voltage value of any phase of the MMC module is: ; In the formula, U diffd is the d-axis differential mode voltage of any phase of the MMC module; U diffq is the q-axis differential mode voltage of any phase of the MMC module; U sd The grid-side voltage value is decomposed into a d-axis grid-side voltage value after the grid-side voltage value is decomposed into a dq two-phase rotating coordinate system; U sq The grid-side voltage value is decomposed into a q-axis grid-side voltage value after the grid-side voltage value is decomposed into a dq two-phase rotating coordinate system; is the grid angular velocity; L=0.5L 0 +L g ,L 0 is the bridge arm inductance of any phase of the MMC module, and is the grid-side inductance of any phase of the MMC module; I vd is the d-axis bridge arm current of any phase of the MMC module; I vq is the q-axis bridge arm current of any phase of the MMC module; R=0.5R 0, R 0 is the bridge arm resistance of any phase of the MMC module; To decompose the current reference value into the d-axis current reference value after the dq two-phase rotating coordinate system, is a q-axis current reference value after decomposing the current reference value into a dq two-phase rotating coordinate system; R n1 and R n2 is the positive linear damping injected into the current inner loop controller R n = The element value in .

[0037] Specifically, in this embodiment, in order to increase the response speed of the MMC grid-connected system and suppress current harmonics, the PBC passive control method is selected as the control method of the current inner loop controller. In this embodiment, any phase of the MMC module is taken as phase A for specific analysis, and the corresponding simplified diagram is as follows: Figure 4 As shown. Among them, U dc The DC side voltage of phase A is input to the DC source stage; U p is the voltage sum of the upper bridge arm HBSM of phase A; U n is the voltage sum of the lower bridge arm HBSM; L 0 and R 0 are the inductance and resistance on the bridge arm of phase A respectively; U s is the grid-side voltage value of phase A; L g is the grid-side inductance of phase A; I p , I n and I v They are the upper bridge arm current, lower bridge arm current and grid-side current values ​​of phase A respectively; U NM It is the potential difference between point N on the DC side of phase A and point M on the grid side.

[0038] Using Kirchhoff's current-voltage law, the equations for the upper and lower bridge arms of phase A are as follows: ; Adding the upper and lower bridge arm equations together yields the following equation: ; Let the differential mode voltage be , R =0.5 R 0, L =0.5 L0 + L g , then the above formula can be converted to: ; Decomposing it into the dq two-phase rotating coordinate system, the following formula can be obtained: ; In the formula, I vd is the d-axis bridge arm current of phase A; I vq is the q-axis bridge arm current of phase A; U sd The grid-side voltage value is decomposed into a d-axis grid-side voltage value after the grid-side voltage value is decomposed into a dq two-phase rotating coordinate system; U sq The grid-side voltage value is decomposed into a q-axis grid-side voltage value after the grid-side voltage value is decomposed into a dq two-phase rotating coordinate system; is the grid angular velocity; s is a differential operator; Write the above formula in EL form, that is: ; Where U is the input vector ; x is the state variable ; J is the interconnection matrix (antisymmetric) ; R is a semi-positive definite dissipation matrix ; M is a positive definite energy storage matrix .

[0039] Let the energy storage function of the MMC module be , for MMC grid-connected system , the energy storage function can be derived as follows: ; because , J is the interconnection matrix (antisymmetric), so , , the EL form of the expression We can get: ; make , can be obtained satisfy Therefore, it can be seen that the MMC module in this embodiment meets the passivity requirement and a passive-related control strategy can be used.

[0040] The d-axis current reference value and the q-axis current reference value are taken as the desired stable equilibrium point , then the state error of the MMC module is: ; In the above formula, x e It is the status error of the MMC module; U e is the output error of the MMC module.

[0041] Combined With , the error EL model of the MMC module is obtained as follows: ; In the above formula, V e is the error energy storage function of the MMC grid-connected system.

[0042] Lian Li With an expression of EL form We can get: ; The derivative of the error energy storage function in the error EL model is: ; In order to quickly converge to the desired point, even if The fast value is 0, and damping can be injected into it to accelerate energy dissipation. Suppose the injected damping dissipation is: ,in R n is the injected positive definite linear damping, R n = , combined with the above formula have to: ; To eliminate the steady-state error, decoupling is achieved, namely: ; Substituting the above formula into You can get: ; At this time, the above formula realizes decoupling, and , indicating that the selected input vector U can make the energy error function converge quickly.

[0043] Will Substitution , the design formula of the current inner loop controller can be obtained, namely: .

[0044] It should be understood that injection damping R n1 and R n2 and voltage coupling , The state equation of the system is linearized to achieve decoupling of the nonlinear system. In this embodiment, the current inner loop controller is constructed based on the design formula of the current inner loop controller.

[0045] Furthermore, in order to verify the effect of the current inner loop controller, the design formula of the current inner loop controller is substituted into the above formula: In the equation, the relationship between the passive control current of the inner loop of the MMC module and its reference value is: ; The relationship between the inner loop PI control current of the traditional MMC module and its reference value is: ; The amplitude-frequency characteristic curves of the above two relations are as follows: Figure 5 As shown in the figure, it can be seen that the PBC passive control of the current inner loop controller in this embodiment has a larger cutoff frequency than the traditional PI control, the bandwidth of the current loop is larger, the signal tracking ability of the system is stronger, the response speed of the system is faster, and as the injection resistance increases, the cutoff frequency of the system becomes larger and larger, but the system's ability to suppress high-frequency interference is poor.

[0046] In addition, since the injected damping in the PBC control has a great influence on the stability of the system, considering the rapidity and stability of the system comprehensively, in this embodiment, the linear damping injected by the current inner loop controller is selected to be 60Ω.

[0047] S4. Using the differential mode voltage value as an input value of the MMC modulator, so as to obtain an MMC control signal based on the MMC modulator, and controlling the MMC module according to the MMC control signal.

[0048] This embodiment discloses a MMC grid-connected power control method based on VSG and PBC passive control, which can realize MMC grid-connected power control, and takes into account the current inner loop control and outer loop control at the same time, which is conducive to improving the dynamic performance of the MMC grid-connected system. Specifically, this embodiment accelerates energy dissipation, improves the dynamic response performance and adjustment speed of the system by introducing a passive current inner loop controller with linear damping in the current inner loop, can effectively suppress current harmonics, and enhance the stability of the system; at the same time, this embodiment also introduces an adaptive moment of inertia compensation mechanism containing arctan function and an adaptive power outer loop controller with adaptive damping compensation mechanism in the power outer loop, thereby effectively suppressing the moment of inertia change rate in adaptive control, thereby suppressing the transient oscillation of the system, and further improving the dynamic response performance and transient stability of the MMC grid-connected system.

[0049] In order to verify the feasibility and effectiveness of the method in this embodiment, this embodiment built an MMC grid-connected system model based on VSG-PBC parameter adaptive control based on MATLAB / Simulink, and set the MMC grid-connected system under the conditions of given power, grid voltage amplitude and grid-side load mutation, and simulated and compared the adaptive VSG-PBC control of this embodiment with the VSG-PBC control without adaptation and the traditional VSG control. Specifically, the experimental conditions are as follows: at 0~1s, the given power is set to 6MW, at 1~1.7s, the given power suddenly changes to 8MW, and at 1.7~2.5s, the given power suddenly changes to 6MW; the comparison diagrams of the results of using this embodiment and the traditional MMC grid-connected power control method are shown as follows. Figure 6 and Figure 7 As shown, Figure 6 is the frequency-time relationship diagram, Figure 7 It is an active power-time relationship diagram. The results show that, when the MMC grid-connected system of the present application has a given power mutation, the frequency and power amplitude overshoot of the adaptive VSG-PBC control of this embodiment is lower, the system stable adjustment time is faster, and the dynamic performance is better; the system current THD value is lower, and the steady-state performance is better; in addition, when the voltage amplitude of the grid side changes, compared with the traditional VSG control, the frequency and power fluctuations of the MMC under the adaptive VSG-PBC control are smaller, the system stable recovery time is shorter, and the dynamic performance is better; the system current THD value is lower, and the steady-state performance is better; finally, when the system load mutates, the frequency and power amplitude overshoot of the MMC under the adaptive VSG-PBC control of this embodiment is smaller, the system stable recovery time is shorter, the dynamic performance is better, and the stability is stronger; the MMC output current THD value is lower, and the steady-state performance is better.

[0050] Embodiment 2: This embodiment discloses an MMC grid-connected power control system, which is used to implement the MMC grid-connected power control method in Embodiment 1; the MMC grid-connected power control system includes: A signal acquisition module, used to collect the grid-side voltage value and the grid-side current value of the grid-connected output terminal of the MMC module, and perform power calculation according to the grid-side voltage value and the grid-side current value to obtain the active power value and the reactive power value; An outer loop control module is connected to the signal acquisition module, and is used to obtain an active power reference value, a reactive power reference value, a grid angular velocity reference value, a voltage reference value, and a grid angular velocity of the MMC module, and use the active power value, the reactive power value, the grid-side voltage value, the active power reference value, the reactive power reference value, the grid angular velocity reference value, the voltage reference value, and the grid angular velocity as input values ​​of a power outer loop controller, so as to obtain a current reference value based on the power outer loop controller; wherein the power outer loop controller adopts a VSG control method, and the power outer loop controller introduces an adaptive moment of inertia compensation mechanism containing an arctan function and an adaptive damping compensation mechanism; An inner loop control module is connected to the signal acquisition module and the inner loop control module, and is used to use the current reference value, the grid-side current value and the grid-side voltage value as input values ​​of the current inner loop controller, so as to obtain the three-phase differential mode voltage value of the MMC module based on the current inner loop controller; wherein the current inner loop controller is injected with positive linear damping, and the current inner loop controller adopts the PBC passive control method The control module is connected to the inner loop control module and is used to use the differential mode voltage value as an input value of the MMC modulator so as to obtain an MMC control signal based on the MMC modulator and control the MMC module according to the MMC control signal.

[0051] It should be noted that the working process, working details and technical effects of the MMC grid-connected power control system provided in this embodiment 2 can be found in embodiment 1 and will not be described in detail here.

[0052] Embodiment 3: Based on Embodiment 1 or 2, this embodiment discloses an electronic device, which may be a smart phone, a tablet computer, a laptop computer, or a desktop computer, etc. The electronic device may be called a user terminal, a portable terminal, a desktop terminal, etc. The electronic device includes: a memory for storing computer program instructions; and, The processor is used to execute the computer program instructions to complete the operation of the MMC grid-connected power control method as described in any one of Embodiment 1.

[0053] Embodiment 4: Based on any one of Embodiments 1 to 3, this embodiment discloses a computer program product, including a computer program or an instruction, wherein when the computer program or the instruction is executed by a computer, the MMC grid-connected power control method as described in any one of Embodiments 1 is implemented. The computer may be a general-purpose computer, a special-purpose computer, a computer network, or other programmable devices.

[0054] Obviously, those skilled in the art should understand that the above modules or steps of the present invention can be implemented by a general computing device, they can be concentrated on a single computing device, or distributed on a network composed of multiple computing devices, and optionally, they can be implemented by a program code executable by a computing device, so that they can be stored in a storage device and executed by the computing device, or they can be made into individual integrated circuit modules, or multiple modules or steps therein can be made into a single integrated circuit module for implementation. Thus, the present invention is not limited to any specific combination of hardware and software.

[0055] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention has been described in detail with reference to the above embodiments, a person skilled in the art should understand that the technical solutions described in the above embodiments can still be modified, or some of the technical features can be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

[0056] References in the background technology are as follows: References [1] Xue Hua, Tian Guangping, Hu Zenghui, et al. Passive consistency control method of modular multilevel converter under unbalanced power grid [J]. Automation of Electric Power Systems, 2022, 46(03): 85-95. Reference [2] Cheng Qiming, Sun Yinghao, Cheng Yinman. MMC-PET nonlinear composite control strategy under non-ideal conditions [J]. China Southern Power Grid Technology, 2023, 17(10): 1-12. Literature[3]Zhou J, Zhou J, Yang H, et al. Passive Super-TwistingSecond-Order Sliding Mode Control Strategy for Input Stage of MMC-PET[J]. Energies, 2024, 17(9). Literature [4] Li H, Xia Y, Chen Y, et al. Research on the Power Control ofMMC-PET System Based on VSG and PBC[C] / / 2024 IEEE 7th International Electrical and Energy Conference (CIEEC). IEEE, 2024: 4595-4601. Literature [5]HUANG LB, XIN HH, YUAN H, et al. Damping effect of virtual synchronous machines provided by a dynamical virtual impedance [J]. IEEETransactions on Energy Conversion, 2021, 36(1): 570-573. Reference [6] Wang Xiquan, He Shan, Yan Xueqin, et al. Research on MMC control strategy based on VSG and internal model-sliding mode [J]. Renewable Energy, 2023, 41(07): 942-948. Reference [7] Hou Shiwei, Du Changshun, Geng Zhiqiang, et al. MMC-HVDC control method based on fuzzy adaptive PI control and model predictive control [J]. Journal of Beijing University of Chemical Technology (Natural Science Edition), 2023, 50(06): 55-65.

Claims

1. A MMC grid-connected power control method, characterized in that: include: Collecting the grid-side voltage value and the grid-side current value of the grid-connected output terminal of the MMC module, and performing power calculation according to the grid-side voltage value and the grid-side current value to obtain the active power value and the reactive power value; Obtaining an active power reference value, a reactive power reference value, a grid angular velocity reference value, a voltage reference value, and a grid angular velocity of the MMC module, and using the active power value, the reactive power value, the grid-side voltage value, the active power reference value, the reactive power reference value, the grid angular velocity reference value, the voltage reference value, and the grid angular velocity as input values ​​of a power outer loop controller, so as to obtain a current reference value based on the power outer loop controller; wherein the power outer loop controller adopts a VSG control method, and the power outer loop controller introduces an adaptive moment of inertia compensation mechanism containing an arctan function and an adaptive damping compensation mechanism; The current reference value, the grid-side current value and the grid-side voltage value are used as input values ​​of a current inner-loop controller, so as to obtain the three-phase differential-mode voltage values ​​of the MMC module based on the current inner-loop controller; wherein the current inner-loop controller is injected with positive linear damping, and the current inner-loop controller adopts a PBC passive control method; The differential mode voltage value is used as an input value of an MMC modulator, so as to obtain an MMC control signal based on the MMC modulator, and the MMC module is controlled according to the MMC control signal.

2. A MMC grid-connected power control method according to claim 1, characterized in that: The power outer loop controller includes a VSG active power controller, an integrator and a VSG reactive power controller; the current reference value includes a d-axis current reference value and a q-axis current reference value; correspondingly, the current reference value is obtained based on the power outer loop controller, including: The active power value, the active power reference value, the grid angular velocity reference value and the grid angular velocity are used as input values ​​of the VSG active power controller, so as to obtain a grid angular velocity differential value based on the VSG active power controller; Using the grid angular velocity differential value as the input value of the integrator to obtain the phase angle; Using the grid-side voltage value, the reactive power value, the reactive power reference value and the voltage reference value as input values ​​of the VSG reactive power controller, so as to obtain a virtual electromotive force based on the VSG reactive power controller; Obtaining a three-phase virtual electromotive force according to the phase angle and the virtual electromotive force, and inputting the three-phase virtual electromotive force into an excitation equation to obtain a three-phase current component; The three-phase current components are decomposed into a dq two-phase rotating coordinate system to obtain a d-axis current reference value and a q-axis current reference value.

3. A MMC grid-connected power control method according to claim 2, characterized in that: The grid angular velocity differential value is obtained by the following formula: ； In the formula, is the differential value of the grid angular velocity; , P ref is the active power reference value, K p is the preset active power-frequency droop coefficient, is the grid angular velocity, 0 is the grid angular velocity reference value; P is the active power value; J is the preset moment of inertia; D is the preset damping coefficient.

4. A MMC grid-connected power control method according to claim 3, characterized in that: The adaptive control strategy of the moment of inertia and the damping coefficient is: ； In the formula, J 0 is the preset moment of inertia setting value; D 0 is the preset damping coefficient setting value; K j is a preset adjustment coefficient of the moment of inertia; K d is a preset adjustment coefficient of the damping coefficient; T i is a preset first limiting threshold; T d is a preset second limiting threshold.

5. The MMC grid-connected power control method according to claim 2, characterized in that: The virtual electromotive force is: ； In the formula, K q for Preset reactive power regulation factor ; K u for Preset voltage regulation factor ; represents an integrator in the VSG reactive power controller; Q ref is the reactive power reference value; Q is the reactive power value; U ref is the voltage reference value; U g is the grid-side voltage value; E n It is the preset MMC no-load electromotive force.

6. The MMC grid-connected power control method according to claim 1, characterized in that: The differential mode voltage values ​​of the three phases of the MMC module include the d-axis differential mode voltage value and the q-axis differential mode voltage value after being decomposed into the dq two-phase rotating coordinate system; correspondingly, the differential mode voltage value of any phase of the MMC module is: ； In the formula, U diffd is the d-axis differential mode voltage of any phase of the MMC module; U diffq is the q-axis differential mode voltage of any phase of the MMC module; U sd The grid-side voltage value is decomposed into a d-axis grid-side voltage value after the dq two-phase rotating coordinate system; U sq The grid-side voltage value is decomposed into a q-axis grid-side voltage value after the grid-side voltage value is decomposed into a dq two-phase rotating coordinate system; is the grid angular velocity; L= 0.5L 0 +L g , L 0 is the bridge arm inductance of any phase of the MMC module, and is the grid-side inductance of any phase of the MMC module; I vd is the d-axis bridge arm current of any phase of the MMC module; I vq is the q-axis bridge arm current of any phase of the MMC module; R= 0.5R 0, R 0 is the bridge arm resistance of any phase of the MMC module; To decompose the current reference value into the d-axis current reference value after the dq two-phase rotating coordinate system, is a q-axis current reference value after decomposing the current reference value into a dq two-phase rotating coordinate system; R n1 and R n2 is the positive linear damping injected into the current inner loop controller R n = The element value in .

7. The MMC grid-connected power control method according to claim 1, characterized in that: The linear damping injected by the current inner loop controller is 60Ω.

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