Voltage cooperative control method based on AC small signal synchronization and local controller

Abstract

The voltage cooperative control method based on AC small signal synchronization provided by the invention is applied to a local controller of each converter device, and obtains a fundamental wave current component, an orthogonal component thereof and an AC small signal current component through obtaining a capacitor voltage and an output current and separating the fundamental wave current component and the orthogonal component. A fundamental wave voltage reference is synthesized based on the fundamental wave current and the capacitor voltage, virtual impedance voltage drop is calculated, target converter equipment node estimation voltage is determined, alternating current small signal active power is calculated through small signal current and a preset voltage reference, a node estimation voltage average value is further calculated, and a voltage compensation value is generated through PI adjustment. And the small signal synthesis module is used for determining an AC small signal frequency reference and synthesizing a target small signal voltage reference, finally synthesizing the fundamental wave reference, the virtual impedance voltage drop and the small signal reference into a total voltage reference, and generating a modulation wave through a voltage and current loop to control the converter equipment. Therefore, the node voltage amplitude deviation can be effectively eliminated.

Description

Technical Field

[0001] This application relates to the field of voltage collaborative control technology for high-proportion distributed power distribution areas, and in particular to a voltage collaborative control method and local controller based on AC small-signal synchronization. Background Technology

[0002] In distribution substations with a high proportion of distributed photovoltaic (PV) grid integration, distributed PV inverters and power electronic transformers are typically used as converters, connected in parallel via a common bus. These two types of converters supply power to the load at the common node, and each inverter and power electronic transformer is equipped with an independent local controller for its own operation. The common node plays a crucial role in supplying power to the load, and maintaining its voltage stability is essential for ensuring power supply reliability. Meanwhile, power electronic transformers are increasingly used in distribution substations due to their flexible operation and strong control capabilities. However, the parallel grid operation of power electronic transformers and PV inverters within the substation typically employs a droop control method, which can easily cause voltage amplitude deviations at the node. Especially when nonlinear or unbalanced loads are connected to the common node, this further exacerbates the distortion and imbalance of the three-phase voltage, severely impacting power quality.

[0003] Traditional control methods based on node voltage sampling typically transmit voltage signals collected at the nodes to the local controllers of each inverter via communication lines. Due to the geographically dispersed nature of distributed power sources, this approach is highly dependent on communication links, increasing system construction and maintenance costs. Furthermore, the signal transmission process is susceptible to line noise interference, resulting in poor engineering applicability. Another control method based on proportional-integral regulators (PI-SVC), while not relying on remote communication, still has significant limitations in node voltage estimation. Firstly, the asynchronous startup of PI-SVCs in parallel units leads to different voltage compensation values ​​in the integral stages of each regulator, affecting the voltage reference in droop control and deteriorating reactive power distribution performance. Secondly, when line impedance parameters are inaccurate, the estimation results of node voltages by each device deviate. Because PI regulators have zero steady-state error, their integral stages continuously accumulate compensation until the estimated voltage reaches the rated value. This estimation deviation causes divergence in the output voltage compensation and reactive power of each device, potentially even leading to system instability.

[0004] In summary, existing node voltage control methods are difficult to accurately adjust the voltage of common nodes under conditions of multi-source parallel connection and uncertain line impedance parameters, which easily leads to voltage amplitude deviation and thus affects reactive power distribution and system stability. Summary of the Invention

[0005] The purpose of this application is to address the aforementioned technical deficiencies, particularly the technical shortcomings of existing node voltage control methods, which struggle to accurately adjust the common node voltage and are prone to voltage amplitude deviations under conditions of multi-source parallel connection and uncertain line impedance parameters.

[0006] In a first aspect, this application provides a voltage collaborative control method based on AC small-signal synchronization, applied to the local controller of various converter equipment, the method comprising:

[0007] Obtain the capacitor voltage and output current of the connected target converter, and separate the AC small-signal current component, fundamental current component and its orthogonal component from the output current;

[0008] Based on the capacitor voltage and fundamental current component, after frequency and voltage modulation by droop control, a fundamental voltage reference is synthesized, and the virtual impedance voltage drop is calculated based on the fundamental current component and its orthogonal components.

[0009] Determine the estimated node voltage of the target converter, and calculate the AC small-signal active power using the AC small-signal current component and the preset AC small-signal voltage reference. Then, calculate the average value of the estimated node voltage based on the AC small-signal active power and the estimated node voltage.

[0010] The average estimated node voltage and the rated node voltage are PI-regulated to generate a voltage compensation value. The voltage compensation value is then used to determine the AC small-signal frequency reference. Based on the AC small-signal frequency reference and the AC small-signal voltage amplitude, the target AC small-signal voltage reference is synthesized.

[0011] After combining the fundamental voltage reference, virtual impedance voltage drop, and target AC small-signal voltage reference into a total voltage reference, a modulation wave is generated through a voltage-current loop. The modulation wave is used to control the target converter equipment.

[0012] In one embodiment, the step of separating the AC small-signal current component, the fundamental current component, and their quadrature components from the output current includes:

[0013] A quadrature signal generator (SOGI-QSG) based on second-order generalized integral is set in parallel with the output current input.

[0014] By using the first orthogonal signal generator to perform bandpass filtering on the output current at the fundamental angular frequency, the fundamental current component and its orthogonal component are obtained.

[0015] By using a second quadrature signal generator to perform bandpass filtering on the output current at the AC small-signal angular frequency reference, the AC small-signal current component is obtained.

[0016] In one embodiment, the step of calculating the virtual impedance voltage drop based on the fundamental current component and its orthogonal components includes:

[0017] The virtual impedance voltage drop is calculated using the following formula:

[0018]

[0019]

[0020] in, , and These represent the virtual impedance voltage drop. Axial components, Axial components and Axial components, Indicates virtual resistance. Represents virtual inductance. Indicates the rated frequency of the target converter equipment. , , and These represent the fundamental current. Axial components, Axial components, Axial components and Orthogonal components of the axes.

[0021] In one embodiment, the step of calculating AC small-signal active power using AC small-signal current components and a preset AC small-signal voltage reference includes:

[0022] The following formula is used to calculate the AC small-signal active power:

[0023]

[0024] in, Indicates the active power of the small-signal AC signal. and Representing the small-signal current component of AC Axial components and Axial components, and Indicates the preset AC small-signal voltage reference. Axial components and Axial components.

[0025] In one embodiment, the step of calculating the average value of the node estimated voltage based on the AC small-signal active power and the node estimated voltage includes:

[0026] The average estimated voltage at nodes is calculated using the following formula:

[0027]

[0028] in, This represents the estimated average voltage at the node. Indicates the estimated voltage at the node. Indicates the active power of the small-signal AC signal. This represents the cutoff angular frequency of the low-pass filter used for voltage estimation. and Indicates the weighting coefficient. This represents a complex variable.

[0029] In one embodiment, the step of performing PI regulation on the estimated average node voltage and the rated node voltage to generate a voltage compensation value includes:

[0030] The voltage compensation value is generated using the following formula:

[0031]

[0032] in, Indicates the voltage compensation value. Indicates the rated node voltage. This represents the estimated average voltage at the node. and This represents the proportional gain and integral gain of the PI control. This represents a complex variable.

[0033] In one embodiment, the step of determining an AC small-signal frequency reference using a voltage compensation value includes:

[0034] The AC small-signal frequency reference is determined using the following formula:

[0035]

[0036] in, Indicates the AC small-signal frequency reference. Indicates the rated AC small-signal angular frequency. This represents the droop coefficient of the small-signal AC signal. This indicates the voltage compensation value.

[0037] In one embodiment, the step of synthesizing a target AC small-signal voltage reference based on an AC small-signal frequency reference and an AC small-signal voltage amplitude includes:

[0038] The target AC small-signal voltage reference is synthesized using the following formula:

[0039]

[0040]

[0041] in, , and These represent the target AC small-signal voltage references, respectively. Axial components, Axial components and Axial components, Indicates the amplitude of the small-signal AC voltage. This represents the frequency reference for small-signal AC signals.

[0042] In one embodiment, the step of generating a modulated wave via a voltage-current loop includes:

[0043] The total voltage reference is compared with the capacitor voltage of the target converter to obtain the voltage deviation signal, and a current reference command is generated based on the voltage deviation signal.

[0044] The current reference command is compared with the inductor current of the target converter to obtain the current deviation signal, and a voltage control signal is generated based on the current deviation signal.

[0045] The voltage control signal is pulse-width modulated to generate a modulated wave.

[0046] Secondly, this application provides a local controller, including: one or more processors, and memory;

[0047] The memory stores computer-readable instructions, which, when executed by one or more processors, perform the steps of any of the voltage cooperative control methods based on AC small-signal synchronization in the above embodiments.

[0048] As can be seen from the above technical solutions, the embodiments of this application have the following advantages:

[0049] This application provides a voltage collaborative control method and local controller based on AC small-signal synchronization. By introducing an AC small-signal synchronization mechanism into the local control layer of each converter device, it combines fundamental power regulation with small-signal voltage collaborative regulation, constructing a multi-stage collaborative control link of fundamental droop, virtual impedance, small-signal power synchronization, and voltage compensation. This transforms voltage regulation from traditional single-amplitude control to a comprehensive control method based on dynamic estimation and closed-loop correction of node states. Specifically, by separating the fundamental component and the AC small-signal component in the output current, droop control is used at the fundamental level to achieve adaptive power allocation in a multi-source parallel system, and virtual impedance voltage drop is calculated by combining orthogonal components to suppress voltage coupling effects from the perspective of equivalent impedance. At the small-signal level, power is calculated using AC small-signal current and small-signal voltage references, and quantifiable small-signal active power is used to compensate for the common node voltage deviation information reflected by each converter device. Then, the node voltage is combined with the estimated node voltage to form the node voltage average value, achieving distributed sensing of the common node voltage state. On this basis, a voltage compensation value is generated through PI regulation to eliminate the deviation between the node voltage average value and the rated value. By establishing a mapping relationship between voltage compensation values ​​and small-signal frequencies, and leveraging the frequency consistency of small signals within the system, the consistency of voltage compensation values ​​across different converter devices is ensured. This allows for coordinated correction of node voltage amplitudes without relying on precise line parameters or centralized communication. Therefore, even under conditions of multi-source parallel operation and uncertain line impedance parameters, this application can still establish an implicit voltage consistency adjustment channel through a small-signal frequency synchronization mechanism. This weakens the impact of inaccurate line impedance parameters on voltage estimates, suppresses common node voltage amplitude deviation, improves the steady-state accuracy of node voltages and the consistency of voltage regulation among multiple converter devices, while simultaneously considering system stability and scalability. This effectively solves the technical problems of inaccurate common node voltage adjustment and the tendency for amplitude deviations in existing technologies. Attached Figure Description

[0050] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0051] Figure 1 A typical three-phase four-wire distributed photovoltaic inverter and power electronic transformer parallel system structure diagram provided for embodiments of this application;

[0052] Figure 2 A schematic flowchart of a voltage cooperative control method based on AC small-signal synchronization provided in an embodiment of this application;

[0053] Figure 3 A general control block diagram of the local controller for the voltage cooperative control method based on AC small-signal synchronization provided in the embodiments of this application;

[0054] Figure 4 This is a diagram illustrating the current signal extraction structure provided in an embodiment of this application.

[0055] Figure 5 Example figures of experimental results provided for embodiments of this application;

[0056] Figure 6 This is a schematic diagram of the internal structure of the local controller provided in an embodiment of this application. Detailed Implementation

[0057] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0058] This application provides a voltage coordinated control method based on AC small-signal synchronization. The following embodiments illustrate the application of this method to a local controller. It can be understood that the local controller is a control unit set inside or connected to the power electronic converter equipment, used to collect electrical operating parameters and perform voltage and current closed-loop control and modulation control functions. It can be implemented using a digital signal processor (DSP), microcontroller (MCU), field-programmable gate array (FPGA) or a combination thereof. Figure 1 This is a block diagram of a parallel system of power electronic transformers and distributed photovoltaic inverters in a high-proportion distributed photovoltaic (PV) distribution area. Each inverter consists of a DC voltage source and a three-phase PV inverter, while the power electronic transformer consists of an AC source and the transformer body. The interface inverter, power electronic transformer, and load are connected to the same node. i and L i (i = 1,2,…,n) represents the line resistance and line inductance between the terminal bus of the i-th inverter or power electronic transformer and the distribution substation node. The local controller measures the capacitor voltage v. Cabc Inductor current i Labc and output current i oabc To generate the modulated wave v mabc This allows control of the inverter.

[0059] like Figure 2 As shown, the method may include the following steps:

[0060] S101: Obtain the capacitor voltage and output current of the connected target converter, and separate the AC small-signal current component, fundamental current component and its orthogonal component from the output current.

[0061] In this embodiment, capacitor voltage refers to the instantaneous voltage signal across the capacitor in the filter branch of the converter equipment, used to characterize the voltage regulation basis of the converter equipment; output current refers to the three-phase current signal output by the converter equipment to the AC side node, reflecting the power exchange between the equipment and the common node of the distribution area; AC small-signal current component refers to the small disturbance current component superimposed on the fundamental current, with a frequency located in a preset small-signal frequency band separated from the fundamental current, used to carry node state change information; fundamental current component refers to the main current component in the output current that is consistent with the system rated frequency, used to characterize the active and reactive power undertaken by the equipment; orthogonal component refers to the current component with the same frequency as the fundamental current but with a phase difference of 90°, used to construct the complete phase information of the current vector, thereby realizing the calculation of power and impedance related quantities.

[0062] In high-proportion distributed photovoltaic (PV) distribution area scenarios, inverters or power electronic transformers are connected to the common node via terminal buses. The control unit collects the instantaneous voltage across the capacitors using voltage sensors and the three-phase output current signals using current sensors. These analog signals are converted to digital values ​​and sent to the control program for real-time processing. The capacitor voltage signal reflects the AC voltage output by the converter equipment, while the output current signal serves as the basic input for subsequent power decomposition and small-signal extraction.

[0063] To obtain components with different physical meanings from the output current, the sampled three-phase currents are first transformed into a coordinate system that facilitates analysis. Then, digital filtering is used to extract the fundamental current component, which corresponds to the system's rated frequency. This fundamental component reflects the steady-state power output level of the equipment at the common node. After obtaining the fundamental component, orthogonal signal channels are constructed to generate orthogonal components with the same frequency but a 90° phase difference from the fundamental component, thus forming a complete current vector representation and providing a foundation for subsequent virtual impedance calculations.

[0064] After the fundamental current is separated, the original output current is compared with the extracted fundamental current. The high-frequency and low-amplitude components remaining after filtering out the main fundamental components are taken as the AC small-signal current component. This small-signal component reflects the dynamic coupling information caused by the interaction of injected small signals among multiple devices. Separation is achieved through orthogonal signal separation and filtering, ensuring that the small-signal channel is unaffected by the fundamental current, thereby establishing a consistent sharing of voltage compensation values. The entire separation process is completed within the same control cycle, ensuring temporal consistency among the current components and providing a synchronization basis for subsequent coordinated control.

[0065] By collecting the capacitor voltage and output current of the converter equipment, we can obtain basic electrical quantities that reflect the device's own output voltage state and external power exchange state, thus establishing a real and real-time local operating parameter basis for subsequent control. On the other hand, by further separating the output current into the fundamental current component, the AC small-signal current component, and the corresponding orthogonal component, the current signal can achieve frequency decoupling in a physical sense. The fundamental current component is used to characterize the main power output level undertaken by the equipment at the rated frequency, the orthogonal component supplements the phase dimension information to form a complete current vector, and the AC small-signal current component characterizes the power state at the small-signal frequency for voltage compensation. Thus, by simultaneously obtaining the fundamental and small-signal power under the same measurement system, we can provide independent, physically clear, and anti-coupling interference input quantities for subsequent control links, thereby improving the ability to finely perceive the node's operating state and the accuracy of voltage regulation-related control quantity calculations.

[0066] S102: Based on the capacitor voltage and fundamental current component, after frequency and voltage modulation by droop control, a fundamental voltage reference is synthesized, and the virtual impedance voltage drop is calculated based on the fundamental current component and its orthogonal components.

[0067] In this embodiment, droop control refers to a control method that adaptively adjusts the frequency and voltage amplitude based on changes in output power, enabling multiple power electronic devices in a parallel system to achieve power coordination without centralized communication; the fundamental voltage reference refers to the target fundamental voltage command quantity obtained after frequency and voltage modulation and used for voltage inner-loop control; the virtual impedance voltage drop refers to the equivalent voltage drop calculated based on the set equivalent virtual impedance parameters and current components, used to simulate the influence of line impedance on voltage distribution at the control level.

[0068] In high-proportion distributed photovoltaic (PV) distribution areas, multiple inverters and power electronic transformers are connected to the same common node via impedance lines. The line impedance creates a coupling relationship between the port voltages of each device and the node voltage. During operation, capacitor voltages are continuously collected to reflect the inverter output voltage status, while the separated fundamental current component characterizes the current output power level. The output power is compared with the rated power, and the frequency reference and voltage amplitude reference are adjusted according to a preset droop coefficient based on the power deviation, thereby obtaining a fundamental voltage reference value suitable for the current operating state. This reference value reflects the voltage support level that the equipment should bear in a parallel system.

[0069] After obtaining the fundamental voltage reference, a current vector expression is constructed using the fundamental current component and its orthogonal components. This vector expression is then combined with preset virtual resistance and inductance parameters to calculate the virtual impedance voltage drop corresponding to the current. This voltage drop, at the control level, equivalently simulates the impedance characteristics between the device port and the common node, ensuring that connected devices exhibit consistent external impedance characteristics during voltage regulation. This virtual impedance voltage drop is then coordinated with the aforementioned fundamental voltage reference, ensuring that the voltage command reflects both power distribution requirements and equivalent circuit characteristics, thus providing a physically meaningful reference quantity for subsequent voltage and current closed-loop control.

[0070] By using both capacitor voltage and fundamental current component as adjustment criteria, the system leverages both the capacitor voltage (reflecting the device's output voltage state) and the fundamental current component (representing the actual power output level) to directly correspond the adjustment to the actual operating state of the equipment, thus avoiding a disconnect between voltage reference and power handling capacity. Furthermore, a drooping principle is employed to adjust frequency and voltage amplitude in tandem, enabling parallel devices to automatically develop consistent external characteristics during power changes. This achieves adaptive power allocation without centralized coordination, improving the coordination and stability of the parallel system. Simultaneously, a complete current vector is constructed using the fundamental current component and its orthogonal components, and a virtual impedance voltage drop is calculated. This introduces equivalent impedance characteristics at the control level, including compensation information for current magnitude and phase relationships in the voltage reference. This weakens the influence of line impedance on port voltage, suppresses circulating current and voltage coupling, and ensures consistent equivalent output characteristics for each device under different connection conditions. Therefore, the voltage reference reflects both power sharing requirements and equivalent impedance constraints, improving the consistency between voltage adjustment and actual electrical relationships, and enhancing the rationality and operational stability of voltage distribution in multi-source parallel systems.

[0071] S103: Determine the estimated node voltage of the target converter, and calculate the AC small-signal active power using the AC small-signal current component and the preset AC small-signal voltage reference. Based on the AC small-signal active power and the estimated node voltage, calculate the average value of the estimated node voltage.

[0072] In this embodiment, the node estimated voltage refers to the voltage value of the common connection node calculated based on the device port measurements and equivalent impedance relationship, which is used to reflect the voltage status on the external power grid side of the device; the preset AC small-signal voltage reference refers to the voltage reference quantity set in the small-signal control channel, which is used to construct the voltage reference basis for power calculation; the AC small-signal active power refers to the power quantity jointly determined by the AC small-signal voltage and the in-phase component of the AC small-signal current, which is used to characterize the direction and magnitude of energy exchange in the small-signal channel; the node estimated voltage average value refers to the more accurate voltage estimate obtained by processing the deviation of the node estimated voltage caused by inaccurate line impedance measurement and using small-signal active power compensation.

[0073] In the operation of a high-proportion distributed photovoltaic (PV) distribution network parallel system, each converter device is connected to the same common node via impedance lines. The directly measured port voltage is not entirely equivalent to the actual node voltage. By combining the obtained current information and equivalent impedance relationships, a correction calculation is performed on the port-side voltage to obtain the estimated node voltage corresponding to the common node. This expands the voltage quantity from a local quantity to a reflection of the state of the common connection point. This estimation process is continuously updated within each control cycle, ensuring that the voltage state information remains synchronized with changes in system operation.

[0074] While obtaining the estimated node voltage, the AC small-signal current component is introduced into the small-signal power calculation channel and subjected to synchronous calculation with a preset AC small-signal voltage reference. The in-phase components of the current and voltage are extracted to form the AC small-signal active power. This power reflects the direction and amplitude of energy transfer in the small-signal channel, enabling more accurate compensation of the estimated node voltage.

[0075] Furthermore, the AC small-signal active power and the estimated node voltage are jointly processed. By filtering the compensated estimated node voltage, the average value of the estimated node voltage is obtained, which weakens the impact of instantaneous fluctuations while preserving the overall trend. This average voltage, as a comprehensive representation of the node voltage state, includes both spatial information derived from electrical quantities and compensation information for small-signal power, making it closer to the actual node voltage.

[0076] By first constructing estimated node voltages, the voltage representation is expanded from a device port quantity to an equivalent voltage quantity reflecting the state of the point of common coupling (PCC). This compensates for the deviation between directly measured quantities and the actual node voltages caused by line impedance, thus providing a voltage basis closer to the actual node state for subsequent regulation. Simultaneously, the AC small-signal current component is combined with a preset AC small-signal voltage reference to calculate the AC small-signal active power. Based on this, the average value of the estimated node voltage is formed using the AC small-signal active power and the estimated node voltage. A filter is then used to make the node voltage representation more stable. This improves the accuracy of sensing the PCC voltage state without relying on additional communication, providing a more reliable, disturbance-resistant, and physically clear control basis for subsequent voltage regulation.

[0077] S104: Perform PI regulation on the estimated average node voltage and rated node voltage to generate voltage compensation value. Then, use the voltage compensation value to determine the AC small-signal frequency reference and synthesize the target AC small-signal voltage reference based on the AC small-signal frequency reference and AC small-signal voltage amplitude.

[0078] In this embodiment, the rated node voltage refers to the target voltage reference value of the distribution substation under design operating conditions; PI regulation refers to the regulation method that continuously corrects the voltage deviation based on proportional and integral actions; the voltage compensation value refers to the adjustment amount obtained after PI calculation to compensate the fundamental voltage; the AC small-signal frequency reference refers to the reference signal used to characterize the rated frequency of the small signal in the small-signal channel, which is used to reflect the frequency correction requirement caused by the voltage compensation value deviation; the AC small-signal voltage amplitude refers to the amplitude reference set in the small-signal voltage channel, which is used to limit the small-signal injection intensity; and the target AC small-signal voltage reference refers to the small-signal voltage command amount composed of frequency reference and amplitude information, which is used to superimpose it onto the fundamental control channel.

[0079] During the operation of a high-proportion distributed photovoltaic (PV) distribution area parallel system, the node voltage will deviate due to the combined effects of load and line impedance. Based on the average estimated node voltage obtained in the previous steps, it is compared with the rated node voltage to obtain the voltage error compensation value. Proportional and integral operations are used to process this error, ensuring that the compensation amount can both respond to the current deviation and eliminate the persistent steady-state error, thus forming an accurate voltage compensation value.

[0080] After obtaining the voltage compensation value, a mapping relationship is established between this compensation amount and the AC small-signal frequency reference. As the voltage compensation value changes, the small-signal frequency adjusts accordingly, making the small-signal frequency exhibit voltage state-dependent variation characteristics. Based on this, the AC small-signal frequency reference is combined with a preset AC small-signal voltage amplitude to generate a target AC small-signal voltage reference with definite frequency and amplitude characteristics. By using a small-signal frequency that is separate from the fundamental frequency, the small signal can be stably superimposed into the original voltage control channel without affecting the stability of the fundamental frequency main control.

[0081] By incorporating the deviation between the estimated average node voltage and the rated node voltage into PI regulation, the voltage error gains both rapid response to the current deviation and the ability to accumulate and correct persistent steady-state offsets over time, thereby generating continuous, smooth voltage compensation values ​​that correspond to long-term node voltage deviations. Based on this, the voltage compensation values ​​are mapped to an AC small-signal frequency reference, ensuring consistency of voltage compensation values ​​across all converter devices through frequency uniformity. Furthermore, a target AC small-signal voltage reference is synthesized by combining preset AC small-signal voltage amplitudes, ensuring that the small-signal injection has a clear regulatory direction while maintaining amplitude control. This allows for the introduction of voltage compensation correction information without significantly disturbing the fundamental main control, thus achieving gradual compensation for long-term node voltage deviations and improving the smoothness, stability, and steady-state accuracy of the voltage regulation process.

[0082] S105: After combining the fundamental voltage reference, virtual impedance voltage drop and target AC small-signal voltage reference into a total voltage reference, a modulation wave is generated through a voltage-current loop. The modulation wave is used to control the target converter equipment.

[0083] In this embodiment, the total voltage reference refers to the voltage command quantity formed by superimposing the fundamental voltage reference, the virtual impedance voltage drop, and the target AC small-signal voltage reference according to their amplitude and phase, which is used to guide the voltage generation at the output of the converter equipment; the modulated wave refers to the PWM signal generated by the total voltage reference through voltage-current closed-loop control calculation, which is used to drive the power switching elements of the inverter or power electronic converter, so that the output voltage and current follow the changes of the total voltage reference.

[0084] In high-proportion distributed photovoltaic (PV) distribution areas, multiple inverters and power electronic transformers are connected to a common node via impedance lines. Directly controlling the port voltage cannot fully reflect the node's coordinated regulation requirements. By superimposing the fundamental voltage reference with the virtual impedance voltage drop and the target AC small-signal voltage reference to form a total voltage reference, the voltage command simultaneously includes the fundamental power requirement, line impedance compensation information, and small-signal regulation, achieving comprehensive control of the port voltage. This allows each device to generate an output target locally that matches the node voltage state.

[0085] After obtaining the total voltage reference, it is sent to the voltage and current closed-loop control channel. By measuring the voltage and current in real time, a modulation wave adapted to the power switch of the converter equipment is generated, so that the output voltage and current change along the total voltage reference. This ensures that the output signal satisfies the fundamental power distribution and is also superimposed with a small signal voltage for fine adjustment of the deviation. At the same time, line difference compensation is introduced through virtual impedance voltage drop, thereby achieving closed-loop consistency between port voltage and node voltage.

[0086] Figure 3 The diagram shows the overall control block diagram of the local controller based on the voltage cooperative control method of AC small-signal synchronization. In this overall control block diagram, traditional droop control is first deployed. Specifically, the active power and reactive power are calculated as follows:

[0087]

[0088]

[0089] in, Active power Reactive power and These are the α-axis and β-axis components of the capacitor voltage, respectively. and These are the α-axis and β-axis components of the output current, respectively. It is the cutoff angular frequency of the low-pass filter used in power calculations. It is a complex variable.

[0090] Sagging control specifically refers to:

[0091]

[0092]

[0093] In the formula, and , respectively, represent the given frequency and given voltage amplitude of the inverter or power electronic transformer; m and n represent the reactive droop coefficient and active droop coefficient, respectively; Q and P represent the output reactive power and output active power of the inverter or power electronic transformer, respectively. and These are the rated reactive power and the rated active power, respectively. and For the rated frequency and rated port voltage.

[0094] Fundamental voltage reference Axis components are The calculation is as follows:

[0095]

[0096]

[0097] in, , and These are the fundamental voltage references. of Axial components, Axial components and Axial components.

[0098] In one embodiment, the step of separating the AC small-signal current component, the fundamental current component, and their quadrature components from the output current includes:

[0099] The output current is input to a parallel-connected quadrature signal generator based on a second-order generalized integral;

[0100] By using the first orthogonal signal generator to perform bandpass filtering on the output current at the fundamental angular frequency, the fundamental current component and its orthogonal component are obtained.

[0101] By using a second quadrature signal generator to perform bandpass filtering on the output current at the AC small-signal angular frequency reference, the AC small-signal current component is obtained.

[0102] Among them, the second-order generalized integral quadrature signal generator is a signal processing device that can decompose the input signal into in-phase and quadrature components. Its output can be filtered at different frequencies to obtain the current components at the fundamental frequency and AC small signal frequency, respectively.

[0103] In practical implementation, the output current first enters two parallel-operating orthogonal signal generators (SOGI-QSG) based on second-order generalized integrals. The first orthogonal signal generator performs bandpass filtering on the fundamental angular frequency to extract the fundamental current component and its orthogonal components. Accurate separation of the fundamental signal facilitates subsequent calculation of virtual impedance voltage drop and generation of the fundamental voltage reference, thereby ensuring power distribution and steady-state control of node voltages in multi-source parallel operation of various converter devices. Simultaneously, the second orthogonal signal generator performs bandpass filtering on the AC small-signal angular frequency reference to obtain the AC small-signal current component. This AC small-signal current component can be used to calculate the active power of small deviations in node voltage, providing accurate input for node voltage estimation, PI compensation, and the generation of the AC small-signal reference voltage.

[0104] The overall structure for current signal extraction is as follows: Figure 4 As shown in (a), the structure includes two dual SOGI quadrature signal generators (DSOGI-QSGs) operating in parallel to separate the fundamental output current. and small signal frequency output current And their components that lag by 90° and Each SOGI-QSG, such as Figure 4 As shown in (b), the transfer function from the input signal v to the output signals v' and qv' is expressed as:

[0105]

[0106] in, For SOGI-QSG direct channel transfer functions, The forward traffic transfer function of SOGI-QSG. The Laplace transform of the input signal for SOGI-QSG. This is the Laplace transform of the direct output signal of the SOGI-QSG. The Laplace transform of the quadrature output signal of SOGI-QSG. For complex variables, This is the damping coefficient (gain coefficient) of SOGI-QSG. This is the center angular frequency of the SOGI-QSG.

[0107] In one embodiment, the step of calculating the virtual impedance voltage drop based on the fundamental current component and its orthogonal components includes:

[0108] The virtual impedance voltage drop is calculated using the following formula:

[0109]

[0110]

[0111] in, , and These represent the virtual impedance voltage drop. Axial components, Axial components and Axial components, Indicates virtual resistance. Represents virtual inductance. Indicates the rated frequency of the target converter equipment. , , and These represent the fundamental current. Axial components, Axial components, Axial components and Orthogonal components of the axes.

[0112] This formula calculates the virtual impedance voltage drop by combining the α, β, and γ axis components of the fundamental current and their orthogonal components with virtual resistance and virtual inductance, thereby generating a voltage reference value locally adapted to the load and line characteristics. The formula treats the virtual resistance as acting in phase with the current and the virtual inductance as acting orthogonally with the current, achieving active adjustment of voltage amplitude and phase, enabling the converter equipment to respond quickly to current changes.

[0113] This implementation allows for the simulation of line impedance effects by adjusting the voltage output without altering the physical wiring, effectively suppressing circulating currents in multi-source parallel systems and improving the uniformity of node voltage distribution. Simultaneously, calculating the virtual impedance voltage drop based on local current allows for real-time reflection of the load status of each converter and changes in network parameters, making node voltage regulation more precise and dynamic, reducing voltage deviations and transient disturbances, and improving overall system stability and power supply reliability.

[0114] In one embodiment, the step of calculating AC small-signal active power using AC small-signal current components and a preset AC small-signal voltage reference includes:

[0115] The following formula is used to calculate the AC small-signal active power:

[0116]

[0117] in, Indicates the active power of the small-signal AC signal. and Representing the small-signal current component of AC Axial components and Axial components, and Indicates the preset AC small-signal voltage reference. Axial components and Shaft component. This formula calculates the AC small-signal active power by combining the AC small-signal current component with a preset AC small-signal voltage reference in phase.

[0118] In one embodiment, the step of calculating the average value of the node estimated voltage based on the AC small-signal active power and the node estimated voltage includes:

[0119] The average estimated voltage at nodes is calculated using the following formula:

[0120]

[0121] in, This represents the estimated average voltage at the node. Indicates the estimated voltage at the node. Indicates the active power of the small-signal AC signal. This represents the cutoff angular frequency of the low-pass filter used for voltage estimation. and Indicates the weighting coefficient. This represents a complex variable.

[0122] It should be noted that, When selecting a frequency, it should be lower than the cutoff angular frequency of the low-pass filter used in power calculations. The calculation is as follows:

[0123]

[0124]

[0125] in, and The α-axis and β-axis components of the node voltage are estimated, respectively. and These are the α-axis and β-axis components of the capacitor voltage, respectively. and The measured line inductance and line resistance.

[0126] In one embodiment, the step of performing PI regulation on the estimated average node voltage and the rated node voltage to generate a voltage compensation value includes:

[0127] The voltage compensation value is generated using the following formula:

[0128]

[0129] in, Indicates the voltage compensation value. Indicates the rated node voltage. This represents the estimated average voltage at the node. and This represents the proportional gain and integral gain of the PI control. This represents a complex variable.

[0130] PI regulators use nodes to estimate the average voltage V. PCCEstAvg By generating a voltage compensation value δv and superimposing it on the fundamental droop reference voltage, we can obtain:

[0131]

[0132] The formula in this embodiment generates a voltage compensation value by inputting the deviation between the rated node voltage and the estimated average node voltage into a PI regulator, thereby achieving closed-loop regulation of the node voltage. In the formula, the proportional coefficient is used to respond to voltage deviations in real time, and the integral coefficient is used to eliminate steady-state errors, so that the compensation value can respond quickly to short-term fluctuations while ensuring long-term steady-state accuracy.

[0133] This implementation allows for the automatic calculation of voltage compensation based on node voltage deviations locally, superimposing the compensation value onto the fundamental droop reference voltage to precisely adjust the output voltage of the converter equipment. This effectively reduces voltage amplitude deviations in multi-source parallel systems caused by load variations or uncertain line parameters, improves the stability and consistency of common node voltages, enhances the system's adaptability to dynamic load disturbances, and ensures both rapid voltage regulation and steady-state accuracy, achieving high-precision coordinated control of node voltages.

[0134] In one embodiment, the step of determining an AC small-signal frequency reference using a voltage compensation value includes:

[0135] The AC small-signal frequency reference is determined using the following formula:

[0136]

[0137] in, Indicates the AC small-signal frequency reference. Indicates the rated AC small-signal angular frequency. This represents the droop coefficient of the small-signal AC signal. This indicates the voltage compensation value.

[0138] In one embodiment, the step of synthesizing a target AC small-signal voltage reference based on an AC small-signal frequency reference and an AC small-signal voltage amplitude includes:

[0139] The target AC small-signal voltage reference is synthesized using the following formula:

[0140]

[0141]

[0142] in, , and These represent the target AC small-signal voltage references, respectively. Axial components, Axial components and Axial components, Indicates the amplitude of the small-signal AC voltage. This represents the frequency reference for small-signal AC signals.

[0143] This formula combines the AC small-signal voltage amplitude with an AC small-signal frequency reference, generating the α-axis and β-axis components of the target AC small-signal voltage reference using sine and cosine functions, while setting the γ-axis component to zero, thus achieving precise injection of the AC small signal in a two-dimensional plane. The formula generates phase through integration with the frequency reference, ensuring the continuity and synchronization of the small-signal voltage in time, thereby enabling effective adjustment of minute deviations in node voltages.

[0144] In one embodiment, the step of generating a modulated wave via a voltage-current loop includes:

[0145] The total voltage reference is compared with the capacitor voltage of the target converter to obtain the voltage deviation signal, and a current reference command is generated based on the voltage deviation signal.

[0146] The current reference command is compared with the inductor current of the target converter to obtain the current deviation signal, and a voltage control signal is generated based on the current deviation signal.

[0147] The voltage control signal is pulse-width modulated to generate a modulated wave.

[0148] In this embodiment, the voltage deviation signal is the difference between the total voltage reference and the capacitor voltage, representing the degree to which the output voltage deviates from the desired value. The current reference command is the target current command calculated under the action of the voltage deviation signal, used to drive the inductor current to approach the desired current. The current deviation signal is the difference between the current reference command and the actual inductor current, used to generate a precise voltage control signal. The modulation wave is a PWM signal obtained by pulse width modulation of the voltage control signal, used to directly drive the inverter switching devices to generate the target output voltage.

[0149] In practice, the total voltage reference is first compared with the capacitor voltage to obtain a voltage deviation signal. Then, a current reference command is calculated based on the voltage deviation signal, causing the inductor current output by the target converter to gradually approach the command value. Next, the current reference command is compared with the actual inductor current to obtain a current deviation signal. This signal is then processed through proportional or multi-harmonic compensation to generate a voltage control signal. Finally, the voltage control signal is pulse-width modulated to form a high-frequency modulated wave, which is directly used to control the switching of the inverter or power electronic transformer, thereby enabling the output voltage to accurately track the total voltage reference.

[0150] Before pulse-width modulation (PWM) of the voltage control signal to generate the modulated wave, the voltage-current inner loop employs a combination of voltage outer loop multi-proportion-resonant (PR) control and current inner loop proportional control to ensure accurate output voltage tracking of the fundamental frequency and small-signal reference, while simultaneously achieving SACS injection. The multi-PR controller in the voltage outer loop tracks the voltage reference at the fundamental and SACS frequencies; its transfer function can be expressed as:

[0151]

[0152] In the formula, k pv The proportional gain of the voltage controller; k rf and k rss The gains of the fundamental resonant controller and the SACS resonant controller are ω, respectively. c This is the cutoff angular frequency of the resonant controller. This is the reference angular frequency generated by SACS. This control structure enables precise tracking of both the fundamental voltage and the small-signal voltage simultaneously, providing a high-precision control signal for subsequent pulse width modulation. This control strategy allows for local management of both the fundamental and AC small-signal injections, achieving fine-tuning of node voltages in multi-source parallel systems. By using multiple PR controllers to resonate and amplify specific frequencies, the system's response to both the fundamental and small-signal frequencies is significantly enhanced, thereby reducing node voltage deviations, improving the stability and consistency of the common node voltage, and ensuring the rapid dynamic response and steady-state accuracy of the output voltage. This also enhances the system's robustness under complex loads and parameter uncertainties.

[0153] In this embodiment, the voltage deviation signal is obtained by comparing the total voltage reference with the capacitor voltage. This is to reflect the deviation between the output voltage of the target converter and the desired voltage in real time, thus providing a precise basis for adjustment. This voltage deviation signal is used to generate a current reference command, enabling the output inductor current to be dynamically adjusted to approximate the desired value. The current deviation signal is obtained by comparing the current reference command with the actual inductor current, and is used to further calculate the voltage control signal, achieving closed-loop linkage control of voltage and current. Finally, the voltage control signal is pulse-width modulated to generate a modulated wave, which directly drives the inverter or power electronic transformer switch, making the output voltage track the total voltage reference. This closed-loop control method enables precise dual-loop adjustment of output voltage and current, allowing the target converter to quickly respond and automatically correct deviations when facing load fluctuations, line disturbances, or multi-source parallel conditions. This significantly suppresses node voltage deviations, improves the stability and balance of common node voltage, reduces circulating current and transient fluctuations, and enhances the steady-state accuracy, dynamic response capability, and overall operational reliability of the multi-source parallel system under complex operating conditions.

[0154] This invention proposes a voltage cooperative control method based on AC small-signal synchronization. This section presents the experimental results of the invention, as shown in the table below:

[0155]

[0156] To test this invention, a parallel experimental platform was built, and the system parameters are shown in the table. To demonstrate the effectiveness and superiority of this invention, it is necessary to compare the node voltage waveforms using the proposed method and droop control under this operating condition, as shown... Figure 5 As shown. Figure 5 In (a), only the node voltage V estimated by measuring the line impedance is used. PCCEst Waveform, Figure 5 (b) The average value of the node voltage estimates V before and after adopting the proposed voltage collaborative control method. PCCEstAvg Waveform, Figure 5 (c) Node voltage V before and after applying the proposed voltage collaborative control method PCC Waveform, Figure 5 (d) The reactive power Q waveform before and after adopting the proposed voltage collaborative control method.

[0157] Initially, only traditional droop control and virtual impedance control were used, and the proposed control method was activated at t=2s. Figure 5 As can be seen in (a), due to inaccurate line impedance, the estimated node voltage V of the two converter devices is... PCCEst They are slightly different from each other. Figure 5 (b)V PCCEst The difference between them was P ss The difference is compensated to ensure that V, used as the input signal of the PI regulator, is...PCCEstAvg This applies to both inverters and power electronic transformers. Therefore, the effects of inaccurate line impedance in traditional PI-SVCs can be eliminated. Figure 5 From (c), we can obtain the node voltage V. PCC After using the proposed method, the voltage was gradually adjusted from deviating from the rated value to being within range, thus restoring the node voltage to its rated value. Simultaneously, from Figure 5 As can be seen from (d), using the proposed method will not affect the reactive power distribution performance.

[0158] In one embodiment, this application also provides a local controller storing computer-readable instructions that, when executed by one or more processors, cause the one or more processors to perform the steps of the voltage cooperative control method based on AC small-signal synchronization as described in any of the above embodiments.

[0159] Indicatively, such as Figure 6 As shown, Figure 6 This is a schematic diagram of the internal structure of a local controller provided in an embodiment of this application. The local controller 200 can be provided as a server. (Refer to...) Figure 6 The local controller 200 includes a processing component 202, which further includes one or more processors, and memory resources represented by memory 201 for storing instructions, such as application programs, that can be executed by the processing component 202. The application programs stored in memory 201 may include one or more modules, each corresponding to a set of instructions. Furthermore, the processing component 202 is configured to execute instructions to perform the voltage cooperative control method based on AC small-signal synchronization of any of the above embodiments.

[0160] The local controller 200 may also include a power supply component 203 configured to perform power management of the local controller 200, a wired or wireless network interface 204 configured to connect the local controller 200 to a network, and an input / output (I / O) interface 205. The local controller 200 may operate on an operating system stored in memory 201, such as Windows Server™, Mac OS X™, Unix™, Linux™, Free BSD™, or similar.

[0161] Those skilled in the art will understand that Figure 6 The structure shown is merely a block diagram of a portion of the structure related to the present application and does not constitute a limitation on the local controller to which the present application is applied. A specific local controller may include more or fewer components than those shown in the figure, or combine certain components, or have different component arrangements.

[0162] Finally, it should be noted that in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element. In this document, "a," "an," "the," "the," and "its" may also include plural forms unless the context clearly indicates otherwise. "Multiple" refers to at least two, such as 2, 3, 5, or 8, etc. "And / or" includes any and all combinations of the related listed items.

[0163] The various embodiments in this specification are described in a progressive manner. Each embodiment focuses on the differences from other embodiments. The various embodiments can be combined as needed, and the same or similar parts can be referred to each other.

[0164] The above description of the disclosed embodiments enables those skilled in the art to make or use this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A voltage cooperative control method based on AC small-signal synchronization, characterized in that, The method, applied to local controllers of various converter devices, includes: Obtain the capacitor voltage and output current of the connected target converter, and separate the AC small-signal current component, fundamental current component and its orthogonal component from the output current; Based on the capacitor voltage and the fundamental current component, after frequency and voltage modulation by droop control, a fundamental voltage reference is synthesized, and based on the fundamental current component and its orthogonal components, the virtual impedance voltage drop is calculated. Determine the node estimated voltage of the target converter, and calculate the AC small-signal active power using the AC small-signal current component and a preset AC small-signal voltage reference. Calculate the average node estimated voltage based on the AC small-signal active power and the node estimated voltage. After PI regulation is applied to the estimated average voltage and rated node voltage of the node to generate a voltage compensation value, the AC small signal frequency reference is determined using the voltage compensation value, and the target AC small signal voltage reference is synthesized based on the AC small signal frequency reference and the AC small signal voltage amplitude. After combining the fundamental voltage reference, the virtual impedance voltage drop, and the target AC small-signal voltage reference into a total voltage reference, a modulation wave is generated through a voltage-current loop. The modulation wave is used to control the target converter equipment.

2. The voltage cooperative control method based on AC small-signal synchronization according to claim 1, characterized in that, The step of separating the AC small-signal current component, the fundamental current component, and their quadrature components from the output current includes: The output current is input into a quadrature signal generator based on a second-order generalized integral connected in parallel; The output current is bandpass filtered at the fundamental angular frequency using a first orthogonal signal generator to obtain the fundamental current component and its orthogonal component. The output current is bandpass filtered at the AC small-signal angular frequency reference using a second quadrature signal generator to obtain the AC small-signal current component.

3. The voltage cooperative control method based on AC small-signal synchronization according to claim 1, characterized in that, The step of calculating the virtual impedance voltage drop based on the fundamental current component and its orthogonal components includes: The virtual impedance voltage drop is calculated using the following formula: in, , and These respectively represent the virtual impedance voltage drop. Axial components, Axial components and Axial components, Indicates virtual resistance. Represents virtual inductance. This indicates the rated frequency of the target converter. , , and These respectively represent the fundamental current. Axial components, Axial components, Axial components and Orthogonal components of the axes.

4. The voltage cooperative control method based on AC small-signal synchronization according to claim 1, characterized in that, The step of calculating the AC small-signal active power using the AC small-signal current component and a preset AC small-signal voltage reference includes: The AC small-signal active power is calculated using the following formula: in, This indicates the active power of the AC small signal. and Representing the small-signal current component of the AC circuit Axial components and Axial components, and This indicates the preset AC small-signal voltage reference. Axial components and Axial components.

5. The voltage cooperative control method based on AC small-signal synchronization according to claim 1, characterized in that, The step of calculating the average value of the node estimated voltage based on the AC small-signal active power and the node estimated voltage includes: The estimated average voltage of the node is calculated using the following formula: in, This indicates the estimated average voltage of the node. This indicates that the node's estimated voltage is... This indicates the active power of the AC small signal. This represents the cutoff angular frequency of the low-pass filter used for voltage estimation. and Indicates the weighting coefficient. This represents a complex variable.

6. The voltage cooperative control method based on AC small-signal synchronization according to claim 1, characterized in that, The step of performing PI regulation on the estimated average voltage of the node and the rated node voltage to generate a voltage compensation value includes: The voltage compensation value is generated using the following formula: in, This represents the voltage compensation value. This indicates the rated node voltage. This indicates the estimated average voltage of the node. and This represents the proportional gain and integral gain of the PI control. This represents a complex variable.

7. The voltage cooperative control method based on AC small-signal synchronization according to claim 1, characterized in that, The step of determining the AC small-signal frequency reference using the voltage compensation value includes: The AC small-signal frequency reference is determined using the following formula: in, This refers to the AC small-signal frequency reference. Indicates the rated AC small-signal angular frequency. This represents the droop coefficient of the small-signal AC signal. This represents the voltage compensation value.

8. The voltage cooperative control method based on AC small-signal synchronization according to claim 1, characterized in that, The step of synthesizing a target AC small-signal voltage reference based on the AC small-signal frequency reference and the AC small-signal voltage amplitude includes: The target AC small-signal voltage reference is synthesized using the following formula: in, , and These respectively represent the target AC small-signal voltage reference. Axial components, Axial components and Axial components, This indicates the amplitude of the AC small-signal voltage. This refers to the AC small-signal frequency reference.

9. The voltage cooperative control method based on AC small-signal synchronization according to claim 1, characterized in that, The step of generating a modulated wave through a voltage-current loop includes: The total voltage reference is compared with the capacitor voltage of the target converter to obtain a voltage deviation signal, and a current reference command is generated based on the voltage deviation signal. The current reference command is compared with the inductor current of the target converter to obtain a current deviation signal, and a voltage control signal is generated based on the current deviation signal. The voltage control signal is subjected to pulse width modulation processing to generate the modulated wave.

10. A local controller, characterized in that, include: One or more processors, and memory; The memory stores computer-readable instructions, which, when executed by the one or more processors, perform the steps of the voltage cooperative control method based on AC small-signal synchronization as described in any one of claims 1 to 9.

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