An enhanced phase-locked loop applied to a converter system
By employing an enhanced phase-locked loop (PLL) closed-loop feedback control architecture and the concept of virtual power angle, the transient stability problem of traditional PLL converters in complex power grid environments is solved, achieving accurate tracking and rapid convergence of the power grid phase, thus improving the robustness and stability of the converter system.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- CHINA DATANG GRP TECH INNOVATION CO LTD
- Filing Date
- 2026-03-03
- Publication Date
- 2026-06-09
AI Technical Summary
Traditional phase-locked loop (PLL) converters exhibit insufficient transient stability when facing complex power grid environments, making it difficult to effectively improve their transient stability.
An enhanced phase-locked loop is adopted, and a closed-loop feedback control architecture is constructed through the coordinated work of the coordinate transformation module, the phase error construction module and the phase generation module, combined with a proportional-integral controller. The detection range of phase error is expanded by utilizing the polarity logic of voltage amplitude and d-axis component, and the concept of virtual power angle is introduced for accurate phase tracking.
It significantly enhances the robustness and transient stability of the converter system under complex grid disturbances, ensures rapid convergence of the synchronous phase angle, achieves real-time and accurate tracking of the grid phase, and improves the system's global convergence capability and dynamic stability.
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Figure CN122178903A_ABST
Abstract
Description
Technical Field
[0001] This application generally relates to the field of power electronic control technology. More specifically, this application relates to an enhanced phase-locked loop (PLL) for use in converter systems. Background Technology
[0002] With the rapid development of new energy technologies and the large-scale investment in power electronic equipment, the traditional power grid is gradually transforming into a new type of power system characterized by a high proportion of renewable energy and power electronic equipment. In this process, the proportion of synchronous generators, which can provide inertial support, is gradually decreasing, while the application of phase-locked loop converters is becoming increasingly widespread. While this facilitates the integration of new energy sources into the power grid, it also brings new challenges to the safe and stable operation of the grid.
[0003] In the analysis of transient stability of power systems, the analysis of traditional single-machine infinite bus systems usually relies on the equal area rule, using the deceleration and acceleration areas to reveal the physical mechanism. However, new power systems dominated by new energy sources are characterized by complex coordinate system transformations and nonlinear characteristics such as switching and limiting in the control loop, making it difficult to directly apply traditional theories for in-depth analysis.
[0004] Current technologies for transient analysis of converters during grid connection are often limited to certain simple scenarios. While traditional phase-locked loops (PLLs) used inside converters can achieve basic frequency and phase control, their transient stability is insufficient in complex grid environments and urgently needs improvement.
[0005] In view of this, there is an urgent need to provide an enhanced phase-locked loop (PLL) for use in converter systems to effectively improve the transient stability of PLL-type converters. Summary of the Invention
[0006] In order to at least address one or more of the technical problems mentioned above, this application proposes an enhanced phase-locked loop for use in converter systems.
[0007] This application provides an enhanced phase-locked loop (PLL) for a converter system, comprising: a coordinate transformation module for acquiring the three-phase voltage signal at the converter output and transforming the three-phase voltage signal to a rotating dq coordinate system based on an input feedback reference phase angle to obtain the d-axis voltage component and the q-axis voltage component at the converter output; a phase error construction module for calculating the voltage amplitude at the converter output based on the d-axis and q-axis voltage components, and constructing a phase error angle based on the polarity of the voltage amplitude and the d-axis voltage component; and a phase generation module for taking the phase error angle as an input signal, adjusting it through a proportional-integral controller, and performing integral calculations to output a synchronization phase angle, wherein the synchronization phase angle is fed back to the input of the coordinate transformation module as a feedback reference phase angle for the next moment.
[0008] In some embodiments, the expression for the phase error angle is:
[0009] ,in, The phase error angle, The voltage amplitude at the output terminal of the converter. , The d-axis voltage component at the converter output terminal. This represents the q-axis voltage component at the converter output.
[0010] In some embodiments, the converter system includes a converter and a cascaded control structure. The cascaded control structure includes: a power outer loop for outputting d-axis current reference values and q-axis current reference values based on active power reference values, reactive power reference values, and measured power; and a current inner loop for decoupling adjustment in a synchronously rotating dq coordinate system based on the d-axis current reference values, q-axis current reference values, and measured current feedback signals, to output d-axis voltage command signals and q-axis voltage command signals.
[0011] In some embodiments, the converter is connected to the power grid via an LCL filter, and the state equation of the converter system is: ,in, The d-axis voltage component at the converter output terminal. This refers to the q-axis voltage component at the converter output. The d-axis voltage component of the power grid. The q-axis voltage component of the power grid. Let represent the d-axis component of the current flowing from the converter to the grid. Let represent the q-axis component of the current flowing from the converter to the grid. For grid-side line inductance, For the grid-side equivalent reactance, This refers to the line resistance on the grid side.
[0012] In some embodiments, the instantaneous phase difference between the converter output voltage vector and the grid voltage vector is defined as the virtual power angle; wherein, the expression for the relationship between the d-axis voltage component and the q-axis voltage component at the converter output and the virtual power angle is: , The d-axis voltage component at the converter output terminal. This refers to the q-axis voltage component at the converter output. The d-axis voltage component of the power grid. The q-axis voltage component of the power grid. For virtual power angle, Let represent the d-axis component of the current flowing from the converter to the grid. Let represent the q-axis component of the current flowing from the converter to the grid. For the grid-side equivalent reactance, This refers to the line resistance on the grid side.
[0013] In some embodiments, the expression for the relationship between the converter output voltage amplitude, determined by the d-axis voltage component and the q-axis voltage component, and the virtual power angle is: ,in, The voltage amplitude at the output terminal of the converter. , The d-axis voltage component at the converter output terminal. This refers to the q-axis voltage component at the converter output. , , Let represent the d-axis component of the current flowing from the converter to the grid. Let represent the q-axis component of the current flowing from the converter to the grid. For the grid-side equivalent reactance, For grid-side line resistance, The voltage amplitude of the power grid. This is a virtual power angle.
[0014] In some embodiments, the phase error construction module performs the following steps: constructing a discriminant variable representing the spatial position of the grid voltage vector based on the virtual power angle; real-time monitoring of the sign bit of the discriminant variable and the polarity of the d-axis voltage component at the converter output; determining whether the absolute value of the virtual power angle exceeds π / 2 based on the monitoring results; and, in response to the absolute value of the virtual power angle exceeding π / 2, adjusting the d-axis voltage component at the converter output. Under the condition of constructing the phase error angle; responding to the absolute value of the virtual power angle not exceeding π / 2, the d-axis voltage component at the converter output terminal. The phase error angle is constructed under the given conditions; where the expression for the discriminant variable is: ,in, , , Let represent the d-axis component of the current flowing from the converter to the grid. Let represent the q-axis component of the current flowing from the converter to the grid. For the grid-side equivalent reactance, For grid-side line resistance, This is a virtual power angle.
[0015] In some embodiments, the converter system further includes a drive actuator; the drive actuator includes a coordinate inverse transformation module, which is used to map the d-axis voltage command signal and q-axis voltage command signal output by the current inner loop from the synchronous rotating dq coordinate system to the three-phase stationary coordinate system based on the synchronous phase angle, so as to obtain the inversely transformed three-phase voltage command.
[0016] In some embodiments, the drive actuator further includes a PWM modulator, which generates drive pulses based on the inversely transformed three-phase voltage command to control the on and off of the power switching transistors in the converter.
[0017] In some embodiments, the LCL filter includes a converter-side inductor, a filter capacitor, and a grid-side line inductor; wherein the three-phase voltage signal is the instantaneous voltage across the filter capacitor.
[0018] By employing the enhanced phase-locked loop (PLL) for converter systems described above, this embodiment of the application constructs a closed-loop feedback control architecture and utilizes the synergy of coordinate transformation and phase error construction modules to achieve real-time and accurate tracking of the grid phase. By comprehensively utilizing voltage amplitude information and the polarity logic of the d-axis component, it overcomes the limitation of traditional PLLs that are prone to losing synchronization when the phase deviation is large, greatly expanding the effective detection range of the phase error and significantly enhancing the system's robustness and transient stability under complex grid disturbances. Through the coordination of a proportional-integral (PI) regulation mechanism, it ensures that the output synchronization phase angle converges rapidly.
[0019] Furthermore, in some embodiments, a precise phase observation model covering the entire plane is constructed by introducing piecewise inverse trigonometric function calculation logic based on the polarity of the d-axis voltage component at the converter output. First, the phase error signal is linearized through voltage amplitude normalization and arcsin operation, eliminating the defect of nonlinear gain variation with operating point in traditional phase-locked loops. Second, the sign of the d-axis voltage component at the converter output is crucially used as the quadrant criterion, and the monotonic intervals of the arcsine function are spliced and corrected, successfully breaking through the mathematical limitation that conventional algorithms are only effective in the range of [-π / 2, π / 2], and extending the accurate detection range of phase error to the entire cycle of [-π, π]. This means that even if the power grid experiences a large phase jump of more than 90 degrees or an extreme phase reversal fault, the system can still obtain a monotonic, continuous, and correct error feedback signal, thereby ensuring that the converter has extremely strong global convergence capability and transient stability.
[0020] Furthermore, in some embodiments, a power-current cascaded decoupled control architecture based on a synchronously rotating dq coordinate system is established, defining the control benchmark for independent regulation of active and reactive power. First, by introducing an accurate state equation for the CL filter, incorporating grid-side resistance and reactance, high-fidelity modeling of the physical system characteristics is achieved. Second, the concept of virtual power angle is creatively defined, and its analytical relationship with voltage components, current, and line impedance voltage drop is derived, mathematically quantifying the impact of line impedance on terminal voltage observation. This not only provides a rigorous theoretical basis for subsequently eliminating phase detection errors caused by line voltage drop but also reveals the deep coupling mechanism between the converter output voltage amplitude and the power angle and load current. This ensures that even in non-ideal grid environments (such as weak grids or long lines), the phase-locked loop can still clearly see the true grid voltage vector through line impedance, achieving high-precision control orientation.
[0021] Furthermore, in some embodiments, by introducing a physical parameter compensation unit, an adaptive phase tracking logic based on discriminant variables is constructed, effectively solving the stability problem of the phase-locked loop (PLL) under large disturbances. Utilizing discriminant variables including line impedance parameters, the system can accurately identify whether the virtual power angle crosses the critical instability boundary of π / 2, thereby achieving accurate situational awareness of the grid voltage vector spatial position. Based on this awareness result, the system can intelligently and seamlessly switch phase calculation paths between normal and extended modes. This mechanism eliminates the calculation blind spot of traditional PLLs when the voltage vector jumps at large angles, ensuring that even under extremely harsh grid conditions (such as deep voltage drops or phase reversals), the PLL can still maintain the monotonicity and continuity of phase detection, greatly improving the global dynamic stability of the converter system. Attached Figure Description
[0022] The above and other objects, features, and advantages of exemplary embodiments of this application will become readily understood by reading the following detailed description with reference to the accompanying drawings. In the drawings, several embodiments of this application are illustrated by way of example and not limitation, and the same or corresponding reference numerals denote the same or corresponding parts, wherein:
[0023] Figure 1 An exemplary structural block diagram of an enhanced phase-locked loop applied to a converter system according to an embodiment of this application is shown;
[0024] Figure 2 An exemplary structural block diagram of a converter system 200 according to an embodiment of this application is shown;
[0025] Figure 3 An exemplary flowchart illustrating the operation of the phase error construction module according to an embodiment of this application is shown;
[0026] Figure 4 This paper illustrates a schematic diagram of the variation curve of the discriminant variable with the virtual work angle in an embodiment of this application.
[0027] Figure 5 The transient response diagrams of the enhanced phase-locked loop and the ordinary phase-locked loop converter according to embodiments of this application are shown.
[0028] Figure 6 The transient simulation waveforms of a conventional phase-locked loop converter, as shown in this application, are illustrated.
[0029] Figure 7 The transient simulation waveforms of the enhanced phase-locked loop (PLL) of this application are shown. Detailed Implementation
[0030] 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, not all, of the embodiments of this application. 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.
[0031] It should be understood that the terms "comprising" and "including" used in the specification and claims of this application indicate the presence of the described features, integrals, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components and / or collections thereof.
[0032] It should also be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application. As used in this specification and claims, the singular forms “a,” “an,” and “the” are intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the term “and / or” as used in this specification and claims refers to any combination and all possible combinations of one or more of the associated listed items, and includes such combinations.
[0033] Figure 1 An exemplary structural block diagram of an enhanced phase-locked loop 100 applied to a converter system according to an embodiment of this application is shown.
[0034] like Figure 1 As shown, the enhanced phase-locked loop 100 includes a coordinate transformation module 110, a phase error construction module 120, and a phase generation module 130.
[0035] Specifically, the coordinate transformation module 110 is used to acquire the three-phase voltage signal at the output of the converter, and convert the three-phase voltage signal to the step-rotating dq coordinate system based on the input feedback reference phase angle to obtain the d-axis voltage component and the q-axis voltage component at the output of the converter.
[0036] Specifically, the phase error construction module 120 is used to calculate the voltage amplitude at the output terminal of the converter based on the d-axis voltage component and the q-axis voltage component at the output terminal of the converter, and to construct the phase error angle based on the polarity of the voltage amplitude and the d-axis voltage component at the output terminal of the converter.
[0037] Specifically, the phase generation module 130 is used to take the phase error angle as an input signal, and after adjustment and integration by the proportional-integral controller, output a synchronous phase angle. The synchronous phase angle is fed back to the input of the coordinate transformation module as a feedback reference phase angle for the next moment.
[0038] In the embodiments of this application, the expression for the phase error angle is:
[0039] ,in, The phase error angle, The voltage amplitude at the output terminal of the converter. , The d-axis voltage component at the converter output terminal. This represents the q-axis voltage component at the converter output.
[0040] In the embodiments of this application, the enhanced phase-locked loop 100 is applied in the converter system 200, and the specific composition of the converter system 200 can be found in [reference needed]. Figure 2 .
[0041] Figure 2 An exemplary structural block diagram of a converter system 200 according to an embodiment of this application is shown.
[0042] like Figure 2 As shown, the converter system 200 includes an enhanced phase-locked loop 100, a converter 210, an LCL filter 220, a cascaded control structure 230, and a drive actuator 240.
[0043] Specifically, converter 210 is connected to grid 250 via LCL filter 220. LCL filter 220 feeds back the three-phase voltage signal of converter 210 to enhanced phase-locked loop 100 and returns the current signal flowing from converter 210 to grid 250 to cascaded control structure 230. Enhanced phase-locked loop 100 outputs the synchronization phase angle to drive actuator 240. Cascaded control structure 230 completes the step-by-step decoupling regulation of power and current, and transmits the generated voltage command signal to drive actuator 240. Drive actuator 240, combined with the synchronization phase angle provided by enhanced phase-locked loop 100, generates drive pulses through coordinate inverse transformation and PWM modulation, which are applied to the power transistors of converter 210, thereby achieving precise power injection into the grid through LCL filter 220.
[0044] In the embodiments of this application, the converter 210 is a three-phase converter composed of power switching transistors (such as IGBTs), one end of which is connected to the DC voltage bus V. DC It inverts direct current into pulse-width modulated (PWM) alternating current. Its other end is connected to an LCL filter 220.
[0045] In embodiments of this application, the LCL filter 220 includes a converter-side inductor L. F Filter capacitor C F And the inductance L of the grid side line g Inductor-side inductor L F The first terminal is connected to converter 210, and filter capacitor C F The first terminal is connected to the converter-side inductor L F The second terminal, the filter capacitor C F The second end is connected to ground, and the grid-side line inductance L g The first terminal is connected to the filter capacitor C. F The first end, the grid-side line inductance L g The second end is connected to the grid-side line resistor. Connect to the power grid 250.
[0046] The high-frequency switching harmonics generated by the converter 210 are suppressed by the LCL filter 220. The filter capacitor C... F The three-phase voltage signal V at both ends abcFeedback is sent to the enhanced phase-locked loop 100, flowing through the grid-side line inductance L. g Current signal I abc The sampled data is then fed into the cascaded control structure 230.
[0047] In the embodiments of this application, the aforementioned acquisition of the three-phase voltage signal at the output of the converter is achieved by the filter capacitor C. F The instantaneous voltage at both ends.
[0048] In the embodiments of this application, the cascaded control structure 230 includes a power outer loop 231 and a current inner loop 232.
[0049] Specifically, the power outer loop 231 is used to output d-axis current reference values and q-axis current reference values based on the active power reference value, reactive power reference value and measured power.
[0050] Specifically, the inner current loop 232 is used to perform decoupling adjustment in the synchronously rotating dq coordinate system based on the d-axis current reference value, the q-axis current reference value, and the measured current feedback signal, so as to output the d-axis voltage command signal and the q-axis voltage command signal to the drive actuator 240.
[0051] In the embodiments of this application, the drive actuator 240 includes a coordinate inverse transformation module 241 and a PWM modulator 242.
[0052] Specifically, the coordinate inverse transformation module 241 is used to map the d-axis voltage command signal and q-axis voltage command signal output by the current inner loop from the synchronous rotating dq coordinate system to the three-phase stationary coordinate system based on the synchronous phase angle, so as to obtain the inversely transformed three-phase voltage command, which is synchronized with the power grid.
[0053] In the embodiments of this application, the formula used by the coordinate inverse transformation module 241 during the inverse transformation process is:
[0054] ,in, This refers to the a-axis voltage in the three-phase voltage command. This refers to the b-axis voltage in the three-phase voltage command. This refers to the c-axis voltage in the three-phase voltage command. This is the d-axis voltage command output by the inner current loop. θ is the q-axis voltage command output by the inner current loop, and θ is the synchronization phase angle.
[0055] Specifically, the PWM modulator 242 is used to generate drive pulses based on the inverse-converted three-phase voltage command generated by the enhanced phase-locked loop 100, so as to control the turn-on and turn-off of the power switching transistors in the converter 210, and finally enable the converter to output the required AC voltage.
[0056] By employing a coordinate inverse transformation module and utilizing the synchronous phase angle, the abstract DC command output from the inner current loop is seamlessly mapped into a three-phase AC sinusoidal command that is strictly synchronized with the power grid. Furthermore, combined with a PWM modulator, these analog commands are converted into discrete drive pulses that control the on / off switching of power devices. This design not only ensures high-precision tracking of the converter output voltage with the power grid in terms of frequency, phase, and amplitude, achieving grid synchronization, but also seamlessly transforms complex decoupling control strategies into actual power conversion actions, guaranteeing the final execution efficiency of the control system.
[0057] In the embodiments of this application, the state equation of the converter system is:
[0058] ,in, The d-axis voltage component at the converter output terminal. This refers to the q-axis voltage component at the converter output. The d-axis voltage component of the power grid. The q-axis voltage component of the power grid. Let represent the d-axis component of the current flowing from the converter to the grid. Let represent the q-axis component of the current flowing from the converter to the grid. For grid-side line inductance, For the grid-side equivalent reactance, This refers to the line resistance on the grid side.
[0059] By establishing the state equations of the converter system, a clear mathematical model foundation is provided for the entire converter system, clarifying the dynamic coupling relationship between the converter output voltage and the grid voltage in the dq rotating coordinate system. This modeling method not only quantitatively describes the specific impact of grid-side line inductance, resistance, and equivalent reactance (Xg) on the dynamic current process, but also directly reveals the decoupling requirements within the system. This provides the necessary theoretical basis for the subsequent design of precise current inner-loop control strategies and the realization of independent regulation of active and reactive power, thereby helping to improve the dynamic response performance and control accuracy of the converter under complex operating conditions.
[0060] In the embodiments of this application, the instantaneous phase difference between the converter output voltage vector and the grid voltage vector is defined as the virtual power angle.
[0061] In the embodiments of this application, the expression for the relationship between the d-axis voltage component and the q-axis voltage component at the converter output terminal and the virtual power angle is as follows: , The d-axis voltage component at the converter output terminal. This refers to the q-axis voltage component at the converter output. The d-axis voltage component of the power grid. The q-axis voltage component of the power grid. For virtual power angle, Let represent the d-axis component of the current flowing from the converter to the grid. Let represent the q-axis component of the current flowing from the converter to the grid. For the grid-side equivalent reactance, This refers to the line resistance on the grid side.
[0062] By introducing a virtual power angle and establishing a mathematical model analyzing its relationship with the converter output voltage, and defining the virtual power angle as the instantaneous phase difference between the converter output voltage vector and the grid voltage vector, this model can intuitively quantify the synchronization state of the system. Further derivation... , The expression reveals that the converter output voltage depends not only on the current and line impedance, but also on a clear trigonometric function (sine / cosine) coupling relationship with the virtual power angle. This mechanism provides a theoretical basis for subsequently using voltage components to infer the system stability boundary (such as whether the virtual power angle exceeds π / 2), enabling the system to indirectly sense the power angle state by monitoring voltage changes. This lays a solid foundation for achieving enhanced transient stability control without directly measuring the power angle.
[0063] In the embodiments of this application, the expression for the relationship between the voltage amplitude at the converter output terminal, determined by the d-axis voltage component and the q-axis voltage component at the converter output terminal, and the virtual power angle is as follows:
[0064] ,in, The voltage amplitude at the output terminal of the converter. , The d-axis voltage component at the converter output terminal. This refers to the q-axis voltage component at the converter output. , , Let represent the d-axis component of the current flowing from the converter to the grid. Let represent the q-axis component of the current flowing from the converter to the grid. For the grid-side equivalent reactance, For grid-side line resistance, The voltage amplitude of the power grid. This is a virtual power angle.
[0065] By deriving an analytical expression for the relationship between the converter output voltage amplitude and the virtual power angle, a direct mapping relationship was established between the observable physical quantity of the system (voltage amplitude) and the core stability indicator (virtual power angle), which is difficult to measure directly. This formula synthesizes the complex dq-axis components, clarifying that the voltage amplitude V is a function of the virtual power angle. This means that the control system does not need to rely on a complex power angle observer; it can infer the transient synchronous stability state of the system simply by monitoring the changing trend of the output voltage amplitude in real time. This intuitive mathematical correlation provides solid theoretical support for the subsequent design of stability criteria based on voltage amplitude feedback, greatly simplifies the detection logic of system instability risk, and enhances the converter's situational awareness capability under grid disturbances.
[0066] The specific working process of the aforementioned phase error construction module 120 in the embodiments of this application can be found in [reference needed]. Figure 3 .
[0067] Figure 3 An exemplary flowchart illustrating the operation of the phase error construction module according to an embodiment of this application is shown.
[0068] like Figure 3 As shown, in step S310, a discriminant variable representing the spatial location of the grid voltage vector is constructed based on the virtual power angle. In step S320, the sign bit of the discriminant variable and the polarity of the d-axis voltage component at the converter output are monitored in real time. In step S330, based on the monitoring results, it is determined whether the absolute value of the virtual power angle exceeds π / 2. In response to the absolute value of the virtual power angle exceeding π / 2, in step S340, the d-axis voltage component at the converter output is... Under the condition that the phase error angle is constructed. In response to the absolute value of the virtual power angle not exceeding π / 2, in step S350, the d-axis voltage component at the converter output is... The phase error angle is constructed under the condition of [condition].
[0069] In the embodiments of this application, the expression for the discriminant variable is: ,in, , , Let represent the d-axis component of the current flowing from the converter to the grid. Let represent the q-axis component of the current flowing from the converter to the grid. For the grid-side equivalent reactance, For grid-side line resistance, This is a virtual power angle.
[0070] In the embodiments of this application, considering the control strategy after a 50% voltage drop, then... And there are in the power grid Therefore, the resistance is ignored, and we have Differentiation shows that exist Since time is an increasing function, therefore exist Time is also an increasing function. Simultaneously, plotting... exist Follow The change curve can be referred to Figure 4 .according to Figure 4 , exist It started to decrease, but remained in the deceleration range. All are less than the acceleration range .thereby, The value in the deceleration range is always less than The value in the acceleration range, i.e. The value in the deceleration range is always less than The value within the acceleration range. Therefore, Compared to When a large disturbance occurs, its acceleration area will decrease, while its deceleration area will increase. and exist arrive They are positively correlated, therefore exist The acceleration area will decrease, while the deceleration area will increase. (See reference...) Figure 5 .
[0071] Based on the above, the K value and the virtual power angle A monotonic correspondence exists within the critical interval, thus verifying the ability to characterize the spatial location of the grid voltage vector by monitoring K (i.e., determining...). Is it feasible to exceed π / 2? That is, by introducing a variable V (whose trend is consistent with K) to affect V. q Normalization can reduce the acceleration area and increase the deceleration area of the system under large disturbances, thereby improving the transient stability of the enhanced phase-locked loop.
[0072] In the comparative examples of this application, the transient simulation waveforms of a conventional phase-locked loop converter and the transient simulation waveforms of the enhanced phase-locked loop of the embodiments of this application are compared. Figure 6 The transient response waveform of a conventional phase-locked loop (PLL) converter is shown when the grid voltage drops to 0.055 pu under a large disturbance. Due to the lack of sufficient deceleration area, the virtual power angle of the conventional PLL converter further decreases under this condition, exceeding the virtual power angle corresponding to the unstable equilibrium point, reaching the unstable region, and then continuously increasing, causing the system to lose stability. According to... Figure 7The transient response waveform of the enhanced phase-locked loop converter is shown when the grid voltage drops to 0.055 pu under a large disturbance. Even at very low residual voltage, the converter system using the enhanced phase-locked loop can still maintain the virtual power angle in the stable region, while simultaneously enabling the system to enter a new operating point and maintain stable operation.
[0073] In summary, through the enhanced phase-locked loop (PLL) for converter systems provided above, this embodiment of the application constructs a closed-loop feedback control architecture and utilizes the synergy of coordinate transformation and phase error construction modules to achieve real-time and accurate tracking of the grid phase. By comprehensively utilizing voltage amplitude information and the polarity logic of the d-axis component, it overcomes the limitation of traditional PLLs being prone to loss of synchronization when the phase deviation is large, greatly expanding the effective detection range of phase error and significantly enhancing the robustness and transient stability of the system under complex grid disturbances. Combined with a proportional-integral (PI) regulation mechanism, it ensures that the output synchronization phase angle converges rapidly.
[0074] Furthermore, in some embodiments, a precise phase observation model covering the entire plane is constructed by introducing piecewise inverse trigonometric function calculation logic based on the polarity of the d-axis voltage component at the converter output. First, the phase error signal is linearized through voltage amplitude normalization and arcsin operation, eliminating the defect of nonlinear gain variation with operating point in traditional phase-locked loops. Second, the sign of the d-axis voltage component at the converter output is crucially used as the quadrant criterion, and the monotonic intervals of the arcsine function are spliced and corrected, successfully breaking through the mathematical limitation that conventional algorithms are only effective in the range of [-π / 2, π / 2], and extending the accurate detection range of phase error to the entire cycle of [-π, π]. This means that even if the power grid experiences a large phase jump of more than 90 degrees or an extreme phase reversal fault, the system can still obtain a monotonic, continuous, and correct error feedback signal, thereby ensuring that the converter has extremely strong global convergence capability and transient stability.
[0075] Furthermore, in some embodiments, a power-current cascaded decoupled control architecture based on a synchronously rotating dq coordinate system is established, defining the control benchmark for independent regulation of active and reactive power. First, by introducing an accurate state equation for the CL filter, incorporating grid-side resistance and reactance, high-fidelity modeling of the physical system characteristics is achieved. Second, the concept of virtual power angle is creatively defined, and its analytical relationship with voltage components, current, and line impedance voltage drop is derived, mathematically quantifying the impact of line impedance on terminal voltage observation. This not only provides a rigorous theoretical basis for subsequently eliminating phase detection errors caused by line voltage drop but also reveals the deep coupling mechanism between the converter output voltage amplitude and the power angle and load current. This ensures that even in non-ideal grid environments (such as weak grids or long lines), the phase-locked loop can still clearly see the true grid voltage vector through line impedance, achieving high-precision control orientation.
[0076] Furthermore, in some embodiments, by introducing a physical parameter compensation unit, an adaptive phase tracking logic based on discriminant variables is constructed, effectively solving the stability problem of the phase-locked loop (PLL) under large disturbances. Utilizing discriminant variables including line impedance parameters, the system can accurately identify whether the virtual power angle crosses the critical instability boundary of π / 2, thereby achieving accurate situational awareness of the grid voltage vector spatial position. Based on this awareness result, the system can intelligently and seamlessly switch phase calculation paths between normal and extended modes. This mechanism eliminates the calculation blind spot of traditional PLLs when the voltage vector jumps at large angles, ensuring that even under extremely harsh grid conditions (such as deep voltage drops or phase reversals), the PLL can still maintain the monotonicity and continuity of phase detection, greatly improving the global dynamic stability of the converter system.
[0077] While numerous embodiments of this application have been shown and described herein, it will be apparent to those skilled in the art that such embodiments are provided by way of example only. Many modifications, alterations, and alternatives will arise for those skilled in the art without departing from the spirit and intent of this application. It should be understood that various alternatives to the embodiments of this application described herein may be employed in the practice of this application. The appended claims are intended to define the scope of protection of this application and therefore cover equivalents or alternatives within the scope of these claims.
Claims
1. An enhanced phase-locked loop (PLL) for use in converter systems, characterized in that, include: The coordinate transformation module is used to acquire the three-phase voltage signal at the output of the converter, and convert the three-phase voltage signal to the step-rotation dq coordinate system based on the input feedback reference phase angle to obtain the d-axis voltage component and the q-axis voltage component at the output of the converter. The phase error construction module is used to calculate the voltage amplitude at the output terminal of the converter based on the d-axis voltage component and the q-axis voltage component at the output terminal of the converter, and to construct the phase error angle based on the voltage amplitude and the polarity of the d-axis voltage component at the output terminal of the converter. The phase generation module is used to take the phase error angle as an input signal, and after adjustment and integration by the proportional-integral controller, output a synchronous phase angle. The synchronous phase angle is fed back to the input of the coordinate transformation module as a feedback reference phase angle for the next moment.
2. The enhanced phase-locked loop for converter systems according to claim 1, characterized in that, The expression for the phase error angle is: ,in, The phase error angle, The voltage amplitude at the output terminal of the converter. , The d-axis voltage component at the converter output terminal. This represents the q-axis voltage component at the converter output.
3. The enhanced phase-locked loop for converter systems according to claim 1, characterized in that, The converter system includes a converter and a cascaded control structure, wherein the cascaded control structure includes: The power outer loop is used to output d-axis current reference values and q-axis current reference values based on the active power reference value, reactive power reference value, and measured power. The inner current loop is used to decouple and adjust the synchronously rotating dq coordinate system based on the d-axis current reference value, the q-axis current reference value, and the measured current feedback signal, so as to output the d-axis voltage command signal and the q-axis voltage command signal.
4. The enhanced phase-locked loop for converter systems according to claim 3, characterized in that, The converter is connected to the power grid via an LCL filter, and the state equation of the converter system is: ,in, The d-axis voltage component at the converter output terminal. This refers to the q-axis voltage component at the converter output. The d-axis voltage component of the power grid. The q-axis voltage component of the power grid. Let represent the d-axis component of the current flowing from the converter to the grid. Let represent the q-axis component of the current flowing from the converter to the grid. For grid-side line inductance, For the grid-side equivalent reactance, This refers to the line resistance on the grid side.
5. The enhanced phase-locked loop for converter systems according to claim 4, characterized in that, Define the instantaneous phase difference between the converter output voltage vector and the grid voltage vector as the virtual power angle; The expression for the relationship between the d-axis voltage component and the q-axis voltage component at the converter output and the virtual power angle is as follows: , The d-axis voltage component at the converter output terminal. This refers to the q-axis voltage component at the converter output. For virtual power angle, Let represent the d-axis component of the current flowing from the converter to the grid. Let represent the q-axis component of the current flowing from the converter to the grid. For the grid-side equivalent reactance, This refers to the line resistance on the grid side.
6. The enhanced phase-locked loop for converter systems according to claim 5, characterized in that, The expression for the relationship between the converter output voltage amplitude, determined by the d-axis voltage component and the q-axis voltage component, and the virtual power angle is as follows: ,in, The voltage amplitude at the output terminal of the converter. , The d-axis voltage component at the converter output terminal. This refers to the q-axis voltage component at the converter output. , , Let represent the d-axis component of the current flowing from the converter to the grid. Let represent the q-axis component of the current flowing from the converter to the grid. For the grid-side equivalent reactance, For grid-side line resistance, The voltage amplitude of the power grid. This is a virtual power angle.
7. The enhanced phase-locked loop for converter systems according to claim 5 or 6, characterized in that, The phase error construction module performs the following steps: A discriminant variable representing the spatial location of the grid voltage vector is constructed based on the virtual power angle; The sign bit of the discriminant variable and the polarity of the d-axis voltage component at the converter output terminal are monitored in real time. Based on the monitoring results, determine whether the absolute value of the virtual power angle exceeds π / 2; In response to the absolute value of the virtual power angle exceeding π / 2, the d-axis voltage component at the converter output... Construct the phase error angle under the given conditions; In response to the absolute value of the virtual power angle not exceeding π / 2, the d-axis voltage component at the converter output... Construct the phase error angle under the given conditions; The expression for the discriminant variable is: ,in, , , Let represent the d-axis component of the current flowing from the converter to the grid. Let represent the q-axis component of the current flowing from the converter to the grid. For the grid-side equivalent reactance, For grid-side line resistance, This is a virtual power angle.
8. The enhanced phase-locked loop for converter systems according to claim 3, characterized in that, The converter system also includes a drive actuator; The drive actuator includes a coordinate inverse transformation module, which is used to map the d-axis voltage command signal and q-axis voltage command signal output by the current inner loop from the synchronous rotating dq coordinate system to the three-phase stationary coordinate system based on the synchronous phase angle, so as to obtain the inversely transformed three-phase voltage command.
9. The enhanced phase-locked loop for converter systems according to claim 8, characterized in that, The drive actuator further includes a PWM modulator, which is used to generate drive pulses based on the inversely transformed three-phase voltage command to control the on and off of the power switching transistors in the converter.
10. The enhanced phase-locked loop for converter systems according to claim 4, characterized in that, The LCL filter includes a converter-side inductor, a filter capacitor, and a grid-side line inductor. The three-phase voltage signal is the instantaneous voltage across the filter capacitor.