Decoupling control method for three-bridge single-phase voltage-type unified power quality conditioner

Abstract

The application discloses a decoupling control method of a three-bridge-arm single-phase voltage-type unified power quality conditioner. First, a mathematical model is established, the working compensation principle of the system is determined through steady-state analysis, and a control target is set according to the working compensation principle. According to the output of the control loop and the average model, it is found through analysis that there is a controllable freedom degree among the duty cycles corresponding to the three bridge arms. The specific values of the duty cycles of each bridge arm are obtained by optimizing and solving the freedom degree in combination with the interval constraint of the duty cycles of the three bridge arms and the inherent constraint condition of the circuit itself. The application effectively solves the coupling problem between the series and parallel converters of the three-bridge-arm UPQC, realizes the simultaneous compensation of the voltage-type and current-type power quality problems under the premise of not increasing the additional hardware cost, retains the advantages of the three-bridge-arm topology in the volume and cost, guarantees the stable operation and compensation accuracy of the system under complex working conditions, and has strong practicability.

Description

Technical Field

[0001] This invention relates to the field of power electronic converter control, and specifically to a decoupling control method for a three-arm single-phase voltage-type unified power quality regulator. Background Technology

[0002] With the increasing prevalence of distributed energy resources and the rise of sensitive loads, power quality issues such as voltage sags, harmonics, and low power factor are becoming increasingly prominent. Unified Power Quality Conditioners (UPQCs), by integrating series and parallel converters, can simultaneously compensate for voltage- and current-source power quality problems, making them one of the most effective solutions for improving power quality in distribution networks.

[0003] Traditional UPQCs typically employ a four-arm or full-bridge structure. While offering independent control, they involve a large number of switching devices, resulting in a bulky size and higher cost. To meet the stringent requirements of home users and offices in terms of space and system cost, three-arm single-phase UPQCs utilize arm multiplexing technology to reduce the number of fully controlled switching devices, offering significant advantages in cost and high power density.

[0004] However, the reuse of bridge arms introduces strong physical and electromagnetic coupling between the series and parallel converters. Under traditional control frameworks, this strong coupling makes it difficult for the system to simultaneously achieve multiple control objectives, such as load voltage regulation, constant DC bus voltage, and unity power factor operation on the grid side, increasing the complexity of the system's control scheme design. How to effectively achieve decoupled control of the three-arm UPQC without increasing hardware costs and ensuring compensation accuracy under complex operating conditions is currently a key technical challenge facing the widespread application of this topology. Summary of the Invention

[0005] The purpose of this invention is to provide a decoupling control method for a three-bridge-arm single-phase voltage-type unified power quality regulator to solve the above-mentioned technical problems.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A decoupling control method for a three-bridge-arm single-phase voltage-source unified power quality regulator includes the following steps:

[0008] S1. Establish an average model of a three-bridge-arm single-phase voltage-type unified power quality regulator, and clarify the working compensation principle of the system through steady-state analysis;

[0009] S2. Set the system control objectives based on the compensation requirements for voltage and current power quality;

[0010] S3. Based on the average model and the output of the control loop, analyze the relationship between the duty cycles of the three bridge arms, revealing that there is a control degree of freedom for the duty cycles of the three bridge arms. Using this control degree of freedom, combined with the inequality constraints of the duty cycles and the circuit's own constraints, solve for the duty cycle of each bridge arm, realize the decoupling control between the parallel converter and the series converter, and form the overall control scheme of the system.

[0011] As a preferred technical solution of the present invention, step S1 is specifically as follows:

[0012] The mathematical model of the S1 three-bridge single-phase voltage-type unified power quality regulator is as follows:

[0013] ;

[0014] in and These are the mains voltage and the output voltage, respectively. This is the DC bus voltage. For parallel side control voltage, For series-side control voltage, The duty cycles corresponding to bridge arms A, B, and C;

[0015] S12. Steady-state analysis is as follows:

[0016] System series-side converter voltage compensation principle:

[0017] ;

[0018] in, This is the load voltage;

[0019] System parallel-side converter current compensation principle:

[0020] .

[0021] As a preferred embodiment of the present invention, the system control objective set in step S2 is as follows:

[0022] By controlling the output voltage of the series-side converter, it is ensured that the load-side voltage is always maintained at the preset expected value;

[0023] The DC bus voltage is controlled in a closed loop to maintain it at a set constant operating voltage.

[0024] Input current The compensation current of the parallel-side converter is controlled by adjusting the compensation current of the parallel-side converter. This ensures that the grid-side current and voltage are in phase, enabling the grid side to operate at unity power factor.

[0025] As a preferred embodiment of the present invention, the control of the system's series side is as follows:

[0026] Voltage outer loop: Feedback value of DC bus voltage With a given value The difference calculation is performed, and the active component command of the current is generated through the PI controller. At the same time, the reactive current on the grid side is... The difference between the given value and the input value is calculated, and the reactive component command of the current is generated through the PI controller.

[0027] Inner current loop: Combine the above two commands to obtain the parallel-side compensation current reference signal. and the actual compensation current For comparison, the PI controller is adjusted.

[0028] Feedforward compensation: Introducing grid voltage As a feedforward compensation signal, the final output is the parallel-side control voltage. ;

[0029] The control details on the parallel side of the system are as follows:

[0030] Voltage outer loop: based on grid voltage With load voltage expectation The difference generates the load voltage command value. ;Will With actual output voltage For comparison, a PR controller is used to generate a reference signal for the series-side current. ,

[0031] Inner current loop: Feedback value of series branch current The difference is calculated and adjusted by a PI controller.

[0032] Feedforward compensation: Introducing output voltage As a feedforward, the final output series-side control voltage .

[0033] As a preferred technical solution of the present invention, the process of uniquely solving the duty cycle of each bridge arm in step S3 is as follows:

[0034] S31. Establish a duty cycle correlation model:

[0035] Based on the system average model, the duty cycles of the three bridge arms are established. Control voltage between bridge arms and DC bus voltage The constraints between them:

[0036] ;

[0037] ;

[0038] This confirms that the system has a duty cycle for arm A. The degree of freedom to control the impact;

[0039] S32. Construct a set of inequality constraints:

[0040] Combining the linear modulation constraint of the duty cycle itself Where x = A, B, C, we can construct a system of equations (1) to determine the degrees of freedom. The system of inequalities:

[0041] ;

[0042] ;

[0043] ;

[0044] S33. Solve for the range of degrees of freedom:

[0045] Solving the system of inequalities yields the baseline bridge arm duty cycle. The dynamic feasible domain range is:

[0046] ;

[0047] Any value of the above feasible region can be used as The final control command is given, and based on this, the duty cycle commands for the remaining arms can be determined:

[0048] ;

[0049] ;

[0050] By allocating and mapping this degree of freedom, the series converter and the parallel converter are decoupled on the common bridge arm A.

[0051] The decoupling control method for a three-arm single-phase voltage-type unified power quality regulator proposed in this invention first clarifies the compensation principle and sets the control target by establishing a mathematical model of the system. Then, based on the average model, it reveals a control degree of freedom between the duty cycles of the three arms. Combining this with constraints, the degree of freedom is optimized to obtain the specific value of the duty cycle for each arm, thus forming a complete decoupling scheme. This invention effectively eliminates the coupling interference between series and parallel converters caused by arm reuse without increasing additional hardware costs. It achieves simultaneous compensation for voltage-type and current-type power quality problems, retaining the core advantages of the three-arm topology in terms of size and cost, and significantly improving the system's operational stability and compensation accuracy under complex operating conditions, demonstrating strong practical value.

[0052] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0053] This invention effectively solves the strong coupling interference problem between series and parallel converters in bridge arm multiplexing topologies by exploring and utilizing the control degrees of freedom among the duty cycles of the three bridge arms. It achieves coordinated control of load voltage stabilization, DC bus voltage constantness, and grid-side unity power factor without increasing additional hardware costs. This invention not only fully retains the inherent advantages of the three-bridge arm topology in terms of size and cost, but its control logic can also fully utilize the constraints of the modulation range, significantly improving the dynamic compensation accuracy and operational stability of the system under complex operating conditions such as grid voltage swells or droops. Furthermore, this method is entirely implemented by the controller's internal algorithm, resulting in low computational overhead and ease of engineering application, providing effective technical support for low-cost, high-performance power quality management. Attached Figure Description

[0054] Figure 1 This is a circuit diagram of a three-bridge single-phase voltage-type unified power quality regulator in the prior art.

[0055] Figure 2 This is a control block diagram of the parallel side of the system in an embodiment of the present invention;

[0056] Figure 3 This is a block diagram of the system series-side control in an embodiment of the present invention;

[0057] Figure 4 This is a flowchart illustrating the steps of the decoupling control method for a three-arm single-phase voltage-type unified power quality regulator in an embodiment of the present invention.

[0058] Figure 5 The simulation waveform of load voltage compensation under grid voltage sag conditions using the decoupling control method of the present invention is shown.

[0059] Figure 6The simulation waveforms show the grid-side unity power factor operation during the reactive power switching process using the decoupling control method of this invention. Detailed Implementation

[0060] The present invention will be further illustrated below with reference to the accompanying drawings and specific embodiments. It should be understood that the following specific embodiments are for illustrative purposes only and are not intended to limit the scope of the invention.

[0061] like Figure 1 As shown, the existing three-arm single-phase voltage-type unified power quality conditioner includes a DC bus capacitor C. d Fully controlled switching transistors Q1, Q2, Q3, Q4, Q5, Q6; filter inductors L1, L2; output filter capacitor C. o And single-phase AC power supply,

[0062] The switching transistors Q1 and Q2 form the first power bridge arm, the switching transistors Q3 and Q4 form the second power bridge arm, and the switching transistors Q5 and Q6 form the third power bridge arm.

[0063] One end of the filter inductor L1 is connected to the positive terminal of the single-phase AC power supply, and the other end is connected to point C, the midpoint between switching transistors Q1 and Q2. The midpoint between switching transistors Q3 and Q4 is point A. One end of a wire is connected to point A, and the other end is connected to the negative terminal of the single-phase AC power supply and the output filter capacitor C. o Between the negative terminals, one end of the filter inductor L2 is connected to point B, the midpoint between switching transistors Q5 and Q6, and the other end is connected to the output filter capacitor C. o The positive electrode,

[0064] The DC bus capacitor C d They are connected in parallel between the second power bridge arm composed of switching transistors Q3 and Q4 and the third power bridge arm composed of switching transistors Q5 and Q6.

[0065] The input current through the filter inductor L1 at the midpoint C of the first power bridge arm is i. C The output current at point A, the midpoint of the second power bridge arm, is i. A The output current at the midpoint B of the third power bridge arm is i B .

[0066] Six fully controlled switching transistors form three power bridge arms, integrating series and parallel converters through bridge arm multiplexing technology, and connected via the aforementioned filter inductor. With output capacitor To achieve comprehensive compensation for power quality problems.

[0067] like Figure 4As shown, the present invention proposes a decoupling control method for a three-arm single-phase voltage-source unified power quality regulator, comprising the following steps:

[0068] S1. Establish an average model of a three-bridge-arm single-phase voltage-type unified power quality regulator, and clarify the working compensation principle of the system through steady-state analysis;

[0069] The mathematical model for the three-bridge single-phase voltage-source unified power quality regulator is as follows:

[0070] ;

[0071] in and These are the mains voltage and the output voltage, respectively. This is the DC bus voltage. For parallel side control voltage, For series-side control voltage, The duty cycles corresponding to bridge arms A, B, and C;

[0072] The steady-state analysis is as follows:

[0073] System series-side converter voltage compensation principle:

[0074] ;

[0075] in, This is the load voltage;

[0076] System parallel-side converter current compensation principle:

[0077] .

[0078] S2. Set the system control objectives based on the compensation requirements for voltage and current power quality;

[0079] The system control objectives are set as follows:

[0080] By controlling the output voltage of the series-side converter, it is ensured that the load-side voltage is always maintained at the preset expected value;

[0081] The DC bus voltage is controlled in a closed loop to maintain it at a set constant operating voltage.

[0082] Input current The compensation current of the parallel-side converter is controlled by adjusting the compensation current of the parallel-side converter. This ensures that the grid-side current and voltage are in phase, enabling the grid side to operate at unity power factor.

[0083] like Figure 2 The diagram shows the control method on the parallel side of the system. Its main objective is to maintain the DC bus voltage stability and achieve unity power factor operation on the grid side.

[0084] Voltage outer loop: Feedback value of DC bus voltage With a given value The difference calculation is performed, and the active component command of the current is generated through the PI controller. Simultaneously, the reactive current on the grid side is... The reactive component of the current is generated by performing a difference operation with a given value (usually 0) through a PI controller.

[0085] Inner current loop: Combine the above two commands to obtain the parallel-side compensation current reference signal. and the actual compensation current The results are compared and adjusted by a PI controller.

[0086] Feedforward compensation: Introducing grid voltage As a feedforward compensation signal, the final output is the parallel-side control voltage. This voltage will serve as one of the key inputs for determining the bridge arm duty cycle in the subsequent step S3.

[0087] like Figure 3 The diagram shows the control method on the series side of the system. Its main objective is to compensate for temporary rises or falls in the grid voltage and ensure the stability of the load-side voltage.

[0088] Voltage outer loop: based on grid voltage With load voltage expectation The difference generates the load voltage command value. ;Will With actual output voltage For comparison, a PR (proportional resonant) controller (utilizing its characteristic of zero steady-state error tracking of AC signals) is used to generate a reference signal for the series-side current. .

[0089] Inner current loop: Feedback value of series branch current The difference is calculated and adjusted by a PI controller.

[0090] Feedforward compensation: Introducing output voltage As a feedforward, the final output series-side control voltage This voltage also serves as the core input for the duty cycle decoupling calculation in subsequent step S3.

[0091] S3. Based on the average model and the output of the control loop, analyze the relationship between the duty cycles of the three bridge arms, revealing that there is a control degree of freedom for the duty cycles of the three bridge arms. Using this control degree of freedom, combined with the inequality constraints of the duty cycles and the circuit's own constraints, solve for the duty cycle of each bridge arm, realize the decoupling control between the parallel converter and the series converter, and form the overall control scheme of the system.

[0092] By Figure 2 and Figure 3 The calculated control voltage is mapped to the physical duty cycle signal, and the specific execution process is as follows:

[0093] Establish a duty cycle correlation model:

[0094] First, control the voltage on the parallel side. Series side control voltage and real-time monitoring of DC bus voltage Input algorithm module. Based on the average model of the three-arm topology, establish the duty cycles of the three arms. Algebraic relationships between them:

[0095] ;

[0096] ;

[0097] This confirms that the system has a duty cycle for arm A. The degree of freedom to control the impact.

[0098] Construct a set of inequality constraints:

[0099] Combining the linear modulation constraints that switching devices must physically satisfy (x=A,B,C), construct the duty cycle of the reference bridge arm A as follows. The system of inequalities:

[0100] ;

[0101] ;

[0102] ;

[0103] Solve for the range of degrees of freedom:

[0104] By solving the above system of inequalities simultaneously, we can obtain the solution. The feasible region that satisfies all physical constraints within the current control cycle. The lower bound of this region is determined by the maximum value of the negative values ​​of each control voltage and 0, and the upper bound is determined by the minimum value of the margin between the ratio of each control voltage to the bus voltage and 1. Specifically, it is expressed as follows:

[0105] ;

[0106] To achieve optimal dynamic response performance and maximum modulation margin, this invention employs a median allocation principle, which can be determined in specific implementations. The specific instruction values ​​are used to synchronously map and calculate the duty cycle instructions for bridge arm B and bridge arm C:

[0107] ;

[0108] ;

[0109] By allocating and mapping this degree of freedom, the series converter and the parallel converter are decoupled on the common bridge arm A.

[0110] Through the above process, the present invention transforms the original spatially physically coupled series and parallel control requirements into mutually independent bridge arm drive signals, thereby achieving fully decoupled control of the system without increasing hardware costs.

[0111] like Figure 5 The figure shows the simulated waveforms of load voltage compensation under grid voltage sag conditions using the decoupling control method proposed in this invention. The upper waveform compares the load voltage and the grid voltage, while the lower waveform represents the output voltage on the series side. The simulation results show that the grid voltage experiences a 20% sag at 0.1 seconds. Under the proposed method, the series converter responds quickly and outputs the corresponding compensation voltage, ensuring that the load voltage remains at the preset desired constant value during and after the sag, almost unaffected by sudden changes on the grid side. This demonstrates that the proposed modulation method exhibits excellent dynamic voltage compensation performance.

[0112] like Figure 6The figure shows the simulation results of grid-side unity power factor operation during reactive power switching using the decoupling control method proposed in this invention. The figure displays the operating waveforms of the grid voltage and grid input current. As can be seen from the figure, the system performed reactive load switching operation at 0.2s. Whether in the steady-state phase before reactive load switching or during the dynamic switching process, the grid current accurately tracks the grid voltage phase, maintaining in-phase operation, and the current waveform is smooth without significant distortion. This not only proves that the system successfully achieved unity power factor operation on the grid side, but also demonstrates that the proposed algorithm effectively suppresses coupling interference caused by bridge arm reuse.

[0113] The method of this invention first clarifies the compensation principle and sets the control objective by establishing a mathematical model of the system. Then, based on the average model, it reveals a control degree of freedom among the duty cycles of the three bridge arms. Combining this with constraints, it optimizes and solves this degree of freedom to obtain the specific value of the duty cycle for each bridge arm, thus forming a complete decoupling scheme. This invention effectively eliminates the coupling interference caused by the reuse of three bridge arms without increasing additional hardware costs, achieving simultaneous compensation for voltage-type and current-type power quality problems. It not only retains the core advantages of the three-bridge-arm topology in terms of size and cost but also significantly improves the system's operational stability and compensation accuracy under complex operating conditions, demonstrating strong practical value.

[0114] It should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention in any other way. Any modifications or equivalent changes made based on the technical essence of the present invention shall still fall within the scope of protection claimed by the present invention.

Claims

1. A decoupling control method for a three-bridge-arm single-phase voltage-type unified power quality regulator, characterized in that, Includes the following steps: S1. Establish an average model of a three-bridge-arm single-phase voltage-type unified power quality regulator, and clarify the working compensation principle of the system through steady-state analysis; S2. Set the system control objectives based on the compensation requirements for voltage and current power quality; S3. Based on the average model and the output of the control loop, analyze the relationship between the duty cycles of the three bridge arms, revealing that there is a control degree of freedom for the duty cycles of the three bridge arms. Using this control degree of freedom, combined with the inequality constraints of the duty cycles and the circuit's own constraints, solve for the duty cycle of each bridge arm, realize the decoupling control between the parallel converter and the series converter, and form the overall control scheme of the system.

2. The decoupling control method for a three-bridge-arm single-phase voltage-type unified power quality regulator according to claim 1, characterized in that: Step S1 is as follows: S1. The mathematical model of the three-bridge single-phase voltage-type unified power quality regulator is as follows: ； in and These are the mains voltage and the output voltage, respectively. This is the DC bus voltage. For parallel side control voltage, For series-side control voltage, The duty cycles corresponding to bridge arms A, B, and C; S12. Steady-state analysis is as follows: System series-side converter voltage compensation principle: ； in, This is the load voltage; System parallel-side converter current compensation principle: 。 3. The decoupling control method for a three-bridge-arm single-phase voltage-type unified power quality regulator according to claim 1, characterized in that: The system control objective set in step S2 is as follows: By controlling the output voltage of the series-side converter, it is ensured that the load-side voltage is always maintained at the preset expected value; The DC bus voltage is controlled in a closed loop to maintain it at a set constant operating voltage. Input current The compensation current of the parallel-side converter is controlled by adjusting the compensation current of the parallel-side converter. This ensures that the grid-side current and voltage are in phase, enabling the grid side to operate at unity power factor.

4. The decoupling control method for a three-bridge-arm single-phase voltage-type unified power quality regulator according to claim 3, characterized in that: The control details on the parallel side of the system are as follows: Voltage outer loop: Feedback value of DC bus voltage With a given value The difference calculation is performed, and the active component command of the current is generated through the PI controller. At the same time, the reactive current on the grid side is... The difference between the given value and the input value is calculated, and the reactive component command of the current is generated through the PI controller. Inner current loop: Combine the above two commands to obtain the parallel-side compensation current reference signal. and the actual compensation current For comparison, the PI controller is adjusted. Feedforward compensation: Introducing grid voltage As a feedforward compensation signal, the final output is the parallel-side control voltage. ; The control details on the series side of the system are as follows: Voltage outer loop: based on grid voltage With load voltage expectation The difference generates the load voltage command value. ;Will With actual output voltage For comparison, a PR controller is used to generate a reference signal for the series-side current. , Inner current loop: Feedback value of series branch current The difference is calculated and adjusted by a PI controller. Feedforward compensation: Introducing output voltage As a feedforward, the final output series-side control voltage .

5. The decoupling control method for a three-bridge-arm single-phase voltage-type unified power quality regulator according to claim 1, characterized in that: The process of uniquely solving the duty cycle of each bridge arm in step S3 is as follows: S31. Establish a duty cycle correlation model: Based on the system average model, the duty cycles of the three bridge arms are established. Control voltage between bridge arms and DC bus voltage The constraints between them: ； ； This confirms that the system has a duty cycle for arm A. The degree of freedom to control the impact; S32. Construct a set of inequality constraints: Combined with the linear modulation constraint of the duty cycle itself Where x = A, B, C, we can construct a system of equations (1) to determine the degrees of freedom. The system of inequalities: ； ； ； S33. Solve for the range of degrees of freedom: Solving the system of inequalities yields the baseline bridge arm duty cycle. The dynamic feasible domain range is: ； Any value of the above feasible region can be used as The final control command is given, and based on this, the duty cycle commands for the remaining arms can be determined: ； ； By allocating and mapping this degree of freedom, the series converter and the parallel converter are decoupled on the common bridge arm A.

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