Alternating current and direct current voltage robust control method for medium-voltage multi-terminal flexible direct current distribution network converter

Abstract

The invention relates to the technical field of power electronic converter control, in particular to an AC / DC voltage robust control method, medium and equipment for a medium-voltage flexible DC converter, and the control method comprises the steps: constructing the reference potential of the medium-voltage flexible DC converter under a rotating coordinate system dq0; cascading a voltage and current inner ring through the constructed reference potential; and driving the medium-voltage flexible DC converter through pulse width modulation (PWM). The invention provides an AC / DC voltage robust control method for a medium-voltage flexible DC converter, and the method gives consideration to AC-side network construction and DC voltage stability, can maintain the stability of AC-side frequency and voltage, can also guarantee the stability of DC-side voltage, and can better meet the actual control demands.

Description

Technical Field

[0001] The present invention relates to the technical field of power electronic converter control, and in particular to a method, medium and device for robustly controlling AC and DC voltages of a medium-voltage flexible DC converter. Background Art

[0002] The statements in this section merely provide background information related to the present invention and do not necessarily constitute prior art.

[0003] As an application form of DC technology, medium voltage multi-terminal DC system (MTDC) provides new solutions for large-scale access to renewable energy, flexible dispatching of power systems and inter-regional power exchange. The core medium voltage DC converter of the MTDC system can realize the conversion and reverse conversion from AC to DC. The MTDC converter requires a complex control and protection system to ensure the stable operation and safety of the system. The control system needs to realize functions such as voltage balance at each end and active and reactive power distribution. The AC side network control strategy has been applied to the MTDC system, aiming to improve the dynamic response performance and stability of the voltage and frequency on the AC side. However, the current network control focuses on the stability of the AC side and ignores the regulation of the DC side voltage. Especially in the flexible DC interconnection system, the stability of DC is crucial. While ensuring the stability of the voltage and frequency on the AC side, ensuring the stability of the DC voltage is a key technical issue.

[0004] The converters of multi-terminal flexible DC distribution networks currently adopt various control modes such as droop control and virtual synchronous machines. At present, the above control modes are difficult to take into account the active support of the voltage and frequency on the AC side and the stable control on the DC side. The DC side stable control is limited and the DC voltage is prone to instability under DC side disturbances. In addition, there are serious challenges to the frequency disturbance on the AC side through multi-terminal DC distribution networks. The frequency regulation capability mainly depends on the inertia and primary frequency regulation capability of the disturbed AC system. By increasing the DC side voltage control to enhance the robustness of the DC voltage, the overall stability of the power grid and its response to disturbances can be improved. Under the premise that the converter adopts grid control, it is necessary to balance the frequency regulation of the disturbed AC system and the voltage stability of the DC power grid.

[0005] Since the system consists of multiple converter stations in parallel, each converter station directly affects the DC bus voltage. Coordinating the control actions of each converter station to ensure the stability of the DC voltage requires not only efficient communication protocols, but also complex control algorithms to synchronize the actions of each port, which is particularly difficult under dynamically changing load and generation conditions, and the system's response to disturbances is poor. In the face of system disturbances such as sudden load changes or fluctuations in renewable energy, each converter station needs to quickly adjust the control amount to suppress the fluctuation of the DC voltage. When a fault occurs in the DC system, it is crucial to quickly and accurately detect and isolate the fault location to prevent the fault from spreading to the entire power grid. In addition, ensuring the normal operation of non-faulty converter stations places higher requirements on the design of control strategies, requiring more sophisticated control and protection strategies. The tuning complexity of controller parameters is high. Each control link in the multi-terminal flexible DC distribution network needs to be precisely tuned, involving multiple parameters and feedback loops. Advanced optimization algorithms are usually required to achieve the optimal configuration, which increases the complexity of system design and implementation.

[0006] Currently, there is no control strategy for medium voltage flexible DC converter that takes into account both AC side grid construction and DC voltage stability. In view of the above defects, the present invention makes improvements. Summary of the invention

[0007] In order to overcome the shortcomings of the background technology, the present invention provides a method, medium and equipment for robust AC and DC voltage control of a medium-voltage flexible DC converter. The method takes into account both AC side networking and DC voltage stability, can maintain the stability of the AC side frequency and voltage, and can ensure the voltage stability of the DC side, thereby better meeting actual control needs.

[0008] To achieve the above object, the present invention provides a method for robustly controlling AC and DC voltages of a medium voltage flexible DC converter, the control method comprising:

[0009] Constructing a reference potential of the medium voltage flexible DC converter in a rotating coordinate system dq0;

[0010] By constructing the reference potential cascade voltage-current inner loop;

[0011] The medium voltage flexible DC converter is driven by pulse width modulation (PWM).

[0012] Further,

[0013] The medium voltage flexible DC converter is a voltage source converter.

[0014] Further,

[0015] The step of constructing the reference potential of the medium voltage flexible DC converter in the rotating coordinate system dq0 comprises:

[0016] Construct active-frequency channel and reactive-voltage channel in rotating coordinate system dq0;

[0017] Calculating a reference voltage phase using the active power-frequency channel;

[0018] Calculating a reference voltage amplitude using the reactive-voltage channel;

[0019] The reference potential is calculated based on the reference voltage phase and the reference voltage magnitude.

[0020] Further,

[0021] The active power-frequency channel calculates the reference voltage phase by detecting the DC side voltage and instantaneous active power of the medium voltage flexible DC converter;

[0022] In the active power-frequency channel, the AC active power-phase relationship equation is:

[0023]

[0024] in, is the first-order differential of the phase, ω ref is the AC frequency reference value, k is the dynamic droop coefficient, P ref is the reference value of active power, P is the instantaneous active power, V ref is the AC output voltage amplitude reference, V is the instantaneous AC voltage amplitude, R d is the DC voltage droop coefficient, Δv dc It is the difference between the DC voltage reference value and the DC voltage sampling signal.

[0025] Further,

[0026] In the active power-frequency channel, the relationship equation between DC voltage and active power is:

[0027]

[0028] in is the DC voltage reference value, v dc is the DC voltage sampling signal, R d is the DC voltage droop coefficient, P ref is the reference value of active power, and P is the instantaneous active power.

[0029] Further,

[0030] In the active power-frequency channel, the active power deviation caused by the frequency disturbance is:

[0031]

[0032] Among them, ΔP and Δf are the changes of active power and frequency under perturbation, k is the dynamic droop coefficient, R dis the DC voltage droop coefficient, Δv dc It is the difference between the DC voltage reference value and the DC voltage sampling signal.

[0033] Further,

[0034] The reactive power-voltage channel calculates the reference voltage amplitude by detecting the instantaneous reactive power of the medium voltage flexible DC converter;

[0035] In the reactive power-voltage channel, the AC reactive power-voltage relationship equation is:

[0036]

[0037] in, is the first-order differential of the voltage, k is the dynamic droop coefficient, η is the convergence adjustment coefficient, which is used to adjust the speed at which the voltage converges to the reference value, V ref is the AC output voltage amplitude reference, V is the instantaneous AC voltage amplitude, Q ref is the reference value of reactive power, and Q is the instantaneous reactive power.

[0038] Further,

[0039] The calculating of the reference potential based on the reference voltage phase and the reference voltage amplitude comprises:

[0040] V ref =Ve jθ

[0041] Among them, V ref is the reference potential, V is the reference voltage amplitude, θ is the reference voltage phase, e is a natural constant, and j is an imaginary unit.

[0042] Based on the same inventive concept, the present invention also provides a computer-readable storage medium storing one or more programs, which, when executed, can implement the aforementioned AC and DC voltage robust control method of the medium voltage flexible DC converter.

[0043] Based on the same inventive concept, the present invention also provides an electronic device, including a processor, a communication interface, a computer-readable storage medium as described above, and a communication bus; wherein the processor, the communication interface, and the computer-readable storage medium communicate with each other via the communication bus; and the processor is used to execute the program stored in the computer-readable storage medium.

[0044] Compared with the prior art, the present invention has the following beneficial effects:

[0045] 1. It takes into account both AC side grid construction and DC voltage stability, which can not only maintain the stability of AC side frequency and voltage, but also ensure the voltage stability of DC side, which can better meet the actual control needs;

[0046] 2. The constructed medium voltage flexible DC converter reference potential combines the frequency stability of the AC side and the robustness of the DC side voltage in one control framework through the coupled DC voltage and active power channels (i.e., active-frequency channels); maintains the consistency of voltage, frequency and phase, and provides dynamic adaptive capability for the system;

[0047] 3. The voltage and current inner loop can be cascaded through the constructed reference potential. The role of the inner loop is to achieve fast dynamic response, while the outer loop (reference potential) provides steady-state reference and overall control target. The combination of the two ensures steady-state accuracy and transient response. The cascade of the voltage and current inner loop enables the system to achieve precise control of voltage and current on both the AC and DC sides at the same time, meeting the dual constraint requirements of the system under large disturbance conditions.

[0048] 4. The medium voltage flexible DC converter is driven by pulse width modulation (PWM). In the robust control method of AC and DC voltages, the reference potential provides a benchmark for the steady-state and transient control of the system. The function of PWM is to convert this reference signal into the actual output voltage of the medium voltage flexible DC converter. PWM generates a pulse signal that matches the reference potential by controlling the on and off time of the switching device (pulse area equivalence principle).

[0049] Other features and advantages of the present invention will be described in the following description, and partly become apparent from the description, or understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained by the structures pointed out in the description, claims and drawings.

[0050] The present invention will be further described below in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0052] Figure 1 A schematic flow chart of a method for robustly controlling AC and DC voltages of a flexible DC converter according to an embodiment of the present invention;

[0053] Figure 2 A schematic diagram of a process for constructing a reference potential of a high-voltage flexible DC converter in an embodiment of the present invention;

[0054] Figure 3 A schematic diagram of a control calculation principle of a method for robustly controlling AC and DC voltages of a flexible DC converter according to an embodiment of the present invention;

[0055] Figure 4 A schematic diagram comparing the AC output voltage, frequency and DC side voltage of the AC-DC voltage robust control method of the flexible DC converter according to the embodiment of the present invention and the conventional droop control method under a large load disturbance on the DC side;

[0056] Figure 5 The figure is a schematic diagram of the structure of an electronic device according to an embodiment of the present invention. DETAILED DESCRIPTION

[0057] In order to make the purpose, technical solution and advantages of the implementation of the present invention clearer, the technical solution in the embodiment of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiment of the present invention. Obviously, the described embodiment is only a part of the embodiment of the present invention, not all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0058] like Figures 1 to 5 As shown, an embodiment of the present invention provides a method for robustly controlling AC and DC voltages of a medium voltage flexible DC converter, the control method comprising:

[0059] Constructing a reference potential of the medium voltage flexible DC converter in a rotating coordinate system dq0;

[0060] By constructing the reference potential cascade voltage-current inner loop;

[0061] The medium voltage flexible DC converter is driven by pulse width modulation (PWM).

[0062] In the above technical scheme, the voltage and current inner loop can be cascaded through the constructed reference potential. The role of the inner loop is to achieve fast dynamic response, while the outer loop (reference potential) provides steady-state reference and overall control target. The combination of the two ensures steady-state accuracy and transient response. In the AC and DC voltage robust control method, it is necessary to maintain the stability of the frequency and voltage on the AC side and to ensure the voltage stability on the DC side. The cascade of the voltage and current inner loop enables the system to achieve precise control of voltage and current on both sides of the AC and DC, meeting the dual constraint requirements of the system under large disturbance conditions. The medium-voltage flexible DC converter is driven by pulse width modulation PWM. In the AC and DC voltage robust control method, the reference potential provides a reference for the steady-state and transient control of the system. The role of PWM is to convert this reference signal into the actual output voltage of the medium-voltage flexible DC converter (this embodiment is a voltage source converter). PWM generates a pulse signal consistent with the reference potential by controlling the on-off time of the switching device (pulse area equivalence principle). The above-mentioned AC / DC voltage robust control method takes into account both AC side networking and DC voltage stability, which can not only maintain the stability of AC side frequency and voltage, but also ensure the voltage stability of DC side, and can better meet the actual control requirements. The medium voltage flexible DC converter of this embodiment refers to a medium voltage multi-terminal flexible DC distribution converter, referred to as a medium voltage flexible DC converter.

[0063] As a preferred technical solution, the medium voltage flexible DC converter is a voltage source converter. In this embodiment, the medium voltage flexible DC converter adopts a voltage source converter. Accordingly, the AC and DC voltage robust control method of the medium voltage flexible DC converter in the embodiment of the present invention is applicable to the voltage source converter, because the voltage source converter has the supporting capability.

[0064] As a preferred technical solution, this embodiment constructs a reference potential of a medium-voltage flexible DC converter in a rotating coordinate system dq0. Specifically, an active-frequency channel and a reactive-voltage channel are constructed in the rotating coordinate system dq0, and after calculating the reference voltage phase using the active-frequency channel and calculating the reference voltage amplitude using the reactive-voltage channel, the reference potential is calculated based on the reference voltage phase and the reference voltage amplitude. Further, this embodiment uses the AC active power-phase relationship equation and the AC reactive power-voltage relationship equation to obtain the reference potential signal. In this embodiment, the reference potential combines the frequency stability of the AC side with the voltage robustness of the DC side in a control framework through the coupled DC voltage and active power channels (i.e., active-frequency channels); the consistency of voltage, frequency and phase is maintained, providing the system with dynamic adaptive capabilities. In a multi-terminal flexible DC distribution network, each converter station is connected in parallel to the DC bus, and the existence of the reference potential provides a stable DC voltage reference for all converter stations. The converter station makes real-time adjustments according to the reference potential during operation, so that even when the load on each port changes, the system can still achieve voltage consistency and synchronization. The AC / DC voltage robust control method of this embodiment is a medium-voltage flexible DC converter control calculation method based on AC / DC voltage stabilization, which is designed for medium-voltage flexible interconnected systems under new energy consumption; the pertinence here is reflected in the fact that the method of the embodiment of the present invention is a control method designed for the new energy consumption process, especially according to specific control requirements in the medium-voltage flexible DC distribution network.

[0065] In order to more intuitively demonstrate the construction of the reference potential of the medium voltage flexible DC converter in the rotating coordinate system dq0, the embodiment of the present invention further provides a flow chart of the construction of the reference potential of the medium voltage flexible DC converter, as shown in FIG. Figure 2 As shown. Figure 2 In the calculation, active channel calculation refers to the calculation of active-frequency channel, and reactive channel calculation refers to the calculation of reactive-voltage channel. Figure 2 The process is further explained.

[0066] System initialization includes the setting of initialization voltage, frequency and the initial value of controller integration.

[0067] Regarding parameter setting, the key parameters closely related to the embodiments of the present invention are: DC voltage reference value, DC voltage droop coefficient, dynamic droop coefficient, AC side frequency reference value, convergence adjustment coefficient, and reference values ​​of active and reactive power.

[0068] DC side voltage tracking refers to making the DC side voltage close to its reference value through PI control, using the active response calculated by the active channel as feedback.

[0069] The AC frequency reference is a constant value that ensures the stability of the system frequency setting. Its connection with the DC side voltage tracking in the previous step is that they both rely on the frequency regulation of the active channel and work together on active power regulation.

[0070] The AC voltage reference represents the target amplitude of the AC side voltage. The instantaneous reactive power change result obtained by the reactive channel calculation is used to adjust the voltage amplitude and ensure voltage stability.

[0071] The embodiment of the present invention cascades these reference quantities to the voltage and current inner loops through a constructed dq0 rotating coordinate system based on the AC frequency reference and the AC voltage reference, thereby achieving stable control of the output of the medium voltage flexible DC converter.

[0072] Meeting the stable tracking of the AC and DC sides specifically means that the AC and DC voltages and frequencies of the system are close to the set reference values. The criterion for meeting the stable tracking of the AC and DC sides is that the voltage and frequency deviations are within the allowable range. If this is not met, only the active channel is calculated because the reactive channel depends on the AC voltage.

[0073] When the AC and DC side stability is met (i.e., the AC and DC side stable tracking is met), feedback regulation is performed, including fault isolation and voltage recovery, to ensure continuous and stable operation of the non-fault area.

[0074] Here, “reference” refers to preset target values, such as voltage or frequency set points, and “tracking” refers to the system’s dynamic response to approach these reference values ​​to ensure a stable output.

[0075] The control method proposed in the embodiment of the present invention is based on an AC inductive line, and mainly includes an active-frequency channel and a reactive-voltage channel. Here, based on an AC inductive line means that the control method draws on the power control theory of an AC inductive line, especially in the processing of the coupling relationship between power and frequency and voltage; because the AC side inductive line has known frequency-power and voltage-power characteristics.

[0076] As a preferred technical solution, the active-frequency channel calculates the reference voltage phase by detecting the DC side voltage and instantaneous active power of the medium voltage flexible DC converter; in this embodiment, the calculation of the active-frequency channel involves utilizing the relationship between the DC side voltage and the instantaneous active power.

[0077] In the active power-frequency channel, this embodiment combines the DC side voltage control rate to design the AC active power-phase relationship equation as follows:

[0078]

[0079] in, is the first-order differential of the phase, ω ref is the AC frequency reference value, and ω in this embodimentref is 100πrad / s, k is the dynamic droop coefficient, P ref is the reference value of active power, P is the instantaneous active power, V ref is the AC output voltage amplitude reference, V is the instantaneous AC voltage amplitude, which can be obtained by calculating the reactive-voltage channel, and R d is the DC voltage droop coefficient, Δv dc is the difference between the DC voltage reference value and the DC voltage sampling signal. In this embodiment, the DC side voltage control rate refers to how to adjust the DC side voltage so that it remains stable under load changes or system disturbances; Δv dc Indicates the DC voltage reference value With the DC voltage sampling signal v dc The difference.

[0080] As a preferred technical solution, in the active power-frequency channel, for DC side voltage control, the relationship equation between DC voltage and active power in this embodiment is:

[0081]

[0082] in, is the DC voltage reference value, v dc is the DC voltage sampling signal, R d is the DC voltage droop coefficient, which is set based on the multi-port DC voltage equalization ratio, P ref is the reference value of active power, and P is the instantaneous active power.

[0083] As a preferred technical solution, in the active power-frequency channel, the active power deviation caused by the frequency disturbance is:

[0084]

[0085] Among them, ΔP and Δf are the changes of active power and frequency under perturbation, k is the dynamic droop coefficient, R d is the DC voltage droop coefficient, which is set based on the multi-port DC voltage equalization ratio, Δv dc The difference between the DC voltage reference value and the DC voltage sampling signal, that is, the DC voltage reference value With the DC voltage sampling signal v dc Formula (3) relates the active power change caused by frequency disturbance to the deviation of DC voltage.

[0086] As a preferred technical solution, the reactive-voltage channel calculates the reference voltage amplitude by detecting the instantaneous reactive power of the medium voltage flexible DC converter; the calculation of the reactive-voltage channel in this embodiment determines the AC output voltage amplitude by detecting the instantaneous reactive power, and is based on the designed AC reactive power-voltage relationship equation.

[0087] In order to maintain the robustness of the AC side voltage, in the reactive power-voltage channel, this embodiment introduces a square term (i.e., the first term on the right side of the equation) to design the AC reactive power-voltage relationship equation as follows:

[0088]

[0089] in, is the first-order differential of the voltage, k is the dynamic droop coefficient, η is the convergence adjustment coefficient, which is used to adjust the speed at which the voltage converges to the reference value, V ref is the AC output voltage amplitude reference, V is the instantaneous AC voltage amplitude, Q ref is the reference value of reactive power, and Q is the instantaneous reactive power.

[0090] In this embodiment, the first and second terms on the right side of the AC reactive power-voltage relationship equation correspond to the elimination of voltage and reactive static errors, thereby achieving dual-degree-of-freedom tracking performance; wherein, the first term ensures that the system adjusts the amplitude according to the set voltage reference value, and the second term introduces the reactive static error elimination term to quickly compensate for the instantaneous fluctuation of reactive power, ensuring that the voltage can be stabilized near the target value under disturbance conditions, and reactive power tracking is achieved through the second term. This embodiment achieves dual-degree-of-freedom tracking performance through independent active-frequency and reactive-voltage control decoupling and separation, and can adjust the AC frequency and voltage amplitude respectively; this feature gives the system flexibility in dynamic response and steady-state accuracy, enabling it to track the reference set point separately on the frequency and voltage dual channels, ensuring that frequency stability and voltage steady state are maintained simultaneously in complex power grid disturbances. The dual-degree-of-freedom control structure achieves precise decoupling and independent regulation of AC side power through independent active-frequency and reactive-voltage control channels. In the regulation of reactive power, the dual-degree-of-freedom structure ensures that the change of reactive power is not disturbed by the active power regulation, realizing precise control of the voltage amplitude. At the same time, it enables the system to maintain voltage stability and recover quickly in the event of grid disturbances, load fluctuations, etc.

[0091] This embodiment introduces a square term in the first term on the right side of the AC reactive power-voltage relationship equation to maintain the robustness of the AC side voltage; in control theory, nonlinear terms can respond by strengthening deviations, and the square term introduces higher-order feedback in the control. This design enables the system to have high-gain fine-tuning capabilities in a small range, and has tolerance and strong recovery capabilities in a large range, reducing the system's sensitivity to disturbances of varying degrees, thereby improving robustness. The stability of the AC voltage amplitude is usually affected by load fluctuations and system dynamic changes. This embodiment introduces a square term (i.e., the first term on the right side of the AC reactive power-voltage relationship equation). The adjustment of the voltage amplitude not only depends on the linear response of the reactive power, but also produces a stronger feedback effect on small-amplitude voltage deviations through the square term, so that the voltage can recover quickly in the initial stage.

[0092] The controller designed based on the AC / DC voltage robust control method of the medium voltage flexible DC converter in the embodiment of the present invention can adjust the power output through the preset power set point and ensure the global asymptotic stability of the AC / DC voltage and power set points. For the preset power set point, the power electronics system must determine the ideal power value (i.e., the preset power set point) based on the optimization algorithm and steady-state analysis according to factors such as the stability requirements of the power grid, load characteristics and system capacity; as a grid-forming source, it must track the power set point. In this embodiment, the medium voltage flexible DC converter compares the actual power output with the target power (i.e., the preset power set point) to generate an error signal; then, the control system corrects the power output by adjusting the voltage amplitude and phase (active power-frequency channel) or the reactive power-voltage relationship (reactive power-voltage channel). This embodiment adjusts the coupling relationship between active power and frequency, and reactive power and voltage, and at the same time optimizes the convergence adjustment coefficient η and the droop coefficient k, R d , ensuring real-time tracking and steady-state convergence of voltage and power.

[0093] Adjusting power output is an essential function of a medium voltage flexible DC converter. This embodiment can ensure the stability of frequency and voltage on the AC side based on power tracking adjustment. For the embodiments of the present invention, the main goal of robust control of AC and DC voltages is to ensure that the power grid maintains a stable voltage level under load fluctuations, frequency disturbances or other system disturbances, and adjusting power output is a key means to achieve this goal. In robust control of AC and DC voltages, power output adjustment is a direct response to changes in voltage levels, ensuring that voltage stability is maintained by adjusting power output in real time when disturbances occur in the power grid. When the voltage on the AC side deviates from the target value, the system quickly restores the voltage by adjusting reactive power output (such as adjusting the reference voltage amplitude).

[0094] As a preferred technical solution, the calculation of the reference potential based on the reference voltage phase and the reference voltage amplitude includes:

[0095] V ref =Ve jθ (5)

[0096] Among them, V ref is the reference potential, V is the reference voltage amplitude, θ is the reference voltage phase, e is a natural constant, and j is an imaginary unit.

[0097] It should be noted that: 1. Reference potential V ref The characters are in bold, which indicates a vector, which is different from the AC output voltage amplitude reference V ref , the character is not bold. 2. The instantaneous AC voltage amplitude is the output voltage reference, and the reference voltage amplitude is the input voltage reference. Therefore, in this embodiment, the instantaneous AC voltage amplitude and the reference voltage amplitude are both represented by the same letter V; the dynamic instantaneous value of the output will track the input voltage reference.

[0098] In this embodiment, the reference potential is calculated by calculating the reference voltage phase and reference voltage amplitude as the basic calculation, which is specifically calculated by formula (5). Among them, the reference voltage amplitude is the voltage that the medium voltage flexible DC converter needs to reach when outputting; the reference voltage phase is the phase setting of the AC voltage, which is used to synchronize the frequency of the medium voltage flexible DC converter with the grid; the reference potential combines the reference voltage amplitude and the reference voltage phase to form a complex target voltage vector, which is used to generate the actual output signal of the medium voltage flexible DC converter.

[0099] In order to better demonstrate the control calculation principle of the AC / DC voltage robust control method of the flexible DC converter in the embodiment of the present invention, a control calculation principle schematic diagram is also provided, as shown in FIG. Figure 3 shown.

[0100] Depend on Figure 3 It can be seen that the key control parameters of the flexible DC converter in the embodiment of the present invention include: dynamic droop coefficient k, DC voltage droop coefficient R d , convergence adjustment coefficient η. The embodiment of the present invention is applicable to a typical medium voltage flexible DC topology, which is a prior art and will not be described in detail here.

[0101] exist Figure 3 In the figure, the upper part represents the calculation of the active-frequency channel, and the lower part represents the calculation of the reactive-voltage channel; the PI on the left represents the proportional-integral controller, which is used to adjust the error between the active power and the AC frequency of the system; the 1 / s on the right represents the integral operator in the Laplace transform, which is the cumulative response to the change in active power, ensuring that the system can adjust according to the continuous change of the frequency error to maintain a stable grid frequency. In the reactive-voltage channel, the box u 2 Indicates a square operation, which is a basic expression of the control block diagram. The left box u2 It represents the square of the AC voltage amplitude, that is, the square value of the amplitude of the system output voltage. Its function is to enhance the system's response ability to changes in voltage amplitude by introducing a square term.

[0102] The AC / DC voltage robust control method of the flexible DC converter in the embodiment of the present invention takes into account both AC side grid construction and DC voltage stability, which is mainly reflected in the following aspects:

[0103] 1. This is achieved through multi-level parameter adjustment and electrical quantity coupling to ensure effective response to dynamic fluctuations in AC frequency and voltage in multi-terminal flexible DC networks.

[0104] 2. Through the dynamic droop coefficient k and the DC side droop coefficient R d By setting the active power and frequency, the system realizes flexible adjustment between active power and frequency, so that the AC and DC voltages can track their respective set reference values ​​respectively, and has the control capability of dual degrees of freedom; by decoupling the frequency response and active power control, the robustness of the DC side voltage is improved, ensuring that the system maintains stable voltage control under load fluctuations or frequency disturbances.

[0105] 3. The square term is introduced into the AC reactive power-voltage relationship equation. The coupling design of reactive power and voltage ensures rapid recovery when the voltage amplitude fluctuates greatly, and achieves AC voltage amplitude tracking with high dynamic performance by eliminating reactive static errors (i.e., steady-state error adjustment of voltage-reactive).

[0106] 4. The above dual-degree-of-freedom design allows independent regulation of AC voltage and reactive power under complex dynamic conditions, improving the overall stability of the medium voltage system under large disturbances.

[0107] Figure 4 It is a transient response diagram of the AC output voltage, AC output frequency and DC side effective value of an embodiment of the present invention, which compares the AC output voltage, frequency and DC side voltage of the AC / DC voltage robust control method of the high-voltage flexible DC converter in an embodiment of the present invention with that of the traditional droop control method under large load disturbance on the DC side. Figure 4 The setting scenario is that the AC side load suddenly increases by 0.5pu in 10s to verify the anti-interference performance of the scheme of the present invention under large load disturbances. The AC side voltage of the medium-voltage flexible direct-current distribution network converter remains stable under large load disturbances. By comparing with the frequency deviation of 0.005Hz of traditional droop control, the frequency deviation of the AC side of this scheme is 0.015Hz; the DC side voltage of this scheme drops by 0.0057pu, and the traditional droop control voltage drops by 0.0152pu. The DC voltage drop of this scheme is significantly reduced, achieving stable operation of the AC and DC side voltages. In this embodiment, a sudden increase in the load on the AC side will cause a large frequency disturbance. Among them, the large frequency disturbance and the large load disturbance are consistent, and the frequency of load increase and decrease will change.

[0108] In summary, the AC / DC voltage robust control method of the medium voltage flexible DC converter in the embodiment of the present invention effectively improves the robustness of the AC / DC voltage to grid disturbances, can ensure the stability of the control strategy under disturbances such as grid voltage fluctuations, frequency deviations and load changes, and simultaneously realizes effective synchronization and coordinated control between multiple converters to maintain the AC / DC side voltage stability of the medium voltage flexible DC converter.

[0109] The first control channel (i.e., the active-frequency channel) of the embodiment of the present invention includes DC side voltage tracking calculation, calculates the active power reference deviation through PI control, and calculates the reference voltage phase through active power synchronization control; the second control channel (i.e., the reactive-voltage channel) includes reactive power tracking, establishes a square term to improve the stability of the AC voltage amplitude, and calculates the AC amplitude voltage reference.

[0110] By adopting the technical solution proposed in the embodiment of the present invention, by adjusting the control parameters (mainly including the dynamic droop coefficient k and the DC side droop coefficient R d ), the same performance as the existing method can be achieved. The AC / DC voltage robust control method of the flexible DC converter in the embodiment of the present invention adopts a control strategy based on AC / DC voltage regulation, combining a dual-degree-of-freedom control structure, nonlinear square term regulation and precise DC voltage-power coupling regulation. Its performance in steady-state stability, frequency regulation, reactive power compensation, etc. is equivalent to the control effect of the existing commonly used control technology (such as droop control or virtual synchronous machine), and has the same response accuracy in improving the system robustness and anti-disturbance capability. Among them, DC voltage-power coupling regulation refers to the coordination of the mutual coupling between voltage and power through the control algorithm of this embodiment, and adjusting the power of the system when the voltage or power changes; the embodiment of the present invention does not adopt the virtual synchronous machine strategy in terms of power, but adopts DC voltage-power coupling regulation, which is different from the existing scheme. The DC voltage-power coupling regulation in the embodiment of the present invention is realized by calculating the active-frequency channel. The change of DC voltage reflects the deviation of active power, so it can only be realized by calculating the active-frequency channel.

[0111] Compared with the existing medium voltage flexible DC control calculation, the AC and DC voltage robust control method of the medium voltage flexible DC converter in the embodiment of the present invention has the following advantages:

[0112] 1. Rapid and accurate tracking of active and reactive power on the AC side improves the stability and response performance of the medium voltage flexible DC converter control system. The tracking here refers to tracking reactive power instructions. The medium voltage flexible DC converter of the embodiment of the present invention has the function of tracking active and reactive power.

[0113] 2. Take into account the DC side voltage stability control. While ensuring frequency stability, give priority to the stability of DC voltage to avoid large fluctuations in DC voltage.

[0114] 3. Without the need for additional phase-locked loops and voltage and current inner loop calculations, adaptive synchronization of the AC side and anti-disturbance control of the DC side voltage of the medium voltage flexible DC converter can be achieved.

[0115] 4. Less sensitive to control parameters, enabling simple controller design. The solution of the embodiment of the present invention is less sensitive to control parameters, indicating that the robustness of the control system can adapt to parameter changes within a certain range without the need for frequent re-debugging or precise parameter matching.

[0116] Based on the same inventive concept, the present invention also provides a computer-readable storage medium storing one or more programs, which, when executed, can implement the aforementioned AC and DC voltage robust control method of the medium voltage flexible DC converter.

[0117] Based on the same inventive concept, the present invention also provides an electronic device, such as Figure 5 As shown, it includes a processor, a communication interface, a computer-readable storage medium as described above, and a communication bus; wherein the processor, the communication interface, and the computer-readable storage medium communicate with each other via the communication bus; and the processor is used to execute the program stored in the computer-readable storage medium.

[0118] In the above embodiments, the description of each embodiment has its own emphasis. For the part not described in detail in one embodiment, please refer to the relevant description of other embodiments. The parts not involved in the above embodiments are the same as the prior art or can be implemented by the prior art, and no further description is given here.

[0119] Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent substitutions for some of the technical features therein; and these modifications or substitutions do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for robust control of AC and DC voltages of a medium voltage flexible DC converter, characterized in that: The control method comprises: Constructing a reference potential of the medium voltage flexible DC converter in a rotating coordinate system dq0; By constructing the reference potential cascade voltage-current inner loop; The medium voltage flexible DC converter is driven by pulse width modulation (PWM).

2. The method for robust AC and DC voltage control of a medium voltage flexible DC converter according to claim 1, characterized in that: The medium voltage flexible DC converter is a voltage source converter.

3. The method for robust AC and DC voltage control of a medium voltage flexible DC converter according to claim 1 or 2, characterized in that: The step of constructing the reference potential of the medium voltage flexible DC converter in the rotating coordinate system dq0 comprises: Construct active-frequency channel and reactive-voltage channel in rotating coordinate system dq0; Calculating a reference voltage phase using the active power-frequency channel; Calculating a reference voltage amplitude using the reactive-voltage channel; The reference potential is calculated based on the reference voltage phase and the reference voltage magnitude.

4. The method for robust AC and DC voltage control of a medium voltage flexible DC converter according to claim 3, characterized in that: The active power-frequency channel calculates the reference voltage phase by detecting the DC side voltage and instantaneous active power of the medium voltage flexible DC converter; In the active power-frequency channel, the AC active power-phase relationship equation is: in, is the first-order differential of the phase, ω ref is the AC frequency reference value, k is the dynamic droop coefficient, P ref is the reference value of active power, P is the instantaneous active power, V ref is the AC output voltage amplitude reference, V is the instantaneous AC voltage amplitude, R d is the DC voltage droop coefficient, Δv dc It is the difference between the DC voltage reference value and the DC voltage sampling signal.

5. The method for robust AC and DC voltage control of a medium voltage flexible DC converter according to claim 3, characterized in that: In the active power-frequency channel, the relationship equation between DC voltage and active power is: in is the DC voltage reference value, v dc is the DC voltage sampling signal, R d is the DC voltage droop coefficient, P ref is the reference value of active power, and P is the instantaneous active power.

6. The method for robust AC and DC voltage control of a medium voltage flexible DC converter according to claim 3, characterized in that: In the active power-frequency channel, the active power deviation caused by the frequency disturbance is: Among them, ΔP and Δf are the changes of active power and frequency under perturbation, k is the dynamic droop coefficient, R d is the DC voltage droop coefficient, Δv dc It is the difference between the DC voltage reference value and the DC voltage sampling signal.

7. The method for robust AC and DC voltage control of a medium voltage flexible DC converter according to claim 3, characterized in that: The reactive power-voltage channel calculates the reference voltage amplitude by detecting the instantaneous reactive power of the medium voltage flexible DC converter; In the reactive power-voltage channel, the AC reactive power-voltage relationship equation is: in, is the first-order differential of the voltage, k is the dynamic droop coefficient, η is the convergence adjustment coefficient, which is used to adjust the speed at which the voltage converges to the reference value, V ref is the AC output voltage amplitude reference, V is the instantaneous AC voltage amplitude, Q ref is the reference value of reactive power, and Q is the instantaneous reactive power.

8. The method for robust AC and DC voltage control of a medium voltage flexible DC converter according to claim 3, characterized in that: The calculating of the reference potential based on the reference voltage phase and the reference voltage amplitude comprises: V ref =And jθ Among them, V ref is the reference potential, V is the reference voltage amplitude, θ is the reference voltage phase, e is a natural constant, and j is an imaginary unit.

9. A computer-readable storage medium storing one or more programs, characterized in that: When the one or more programs are executed, the AC and DC voltage robust control method of the medium voltage flexible DC converter as described in any one of claims 1 to 8 can be implemented.

10. An electronic device comprising a processor, a communication interface, the computer-readable storage medium of claim 9, and a communication bus; wherein: The processor, the communication interface, and the computer-readable storage medium communicate with each other via a communication bus; It is characterized in that The processor is configured to execute a program stored in a computer-readable storage medium.

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