Rectifier current loop control system based on fractional order phase-locked loop observer

Abstract

The application discloses a rectifier current loop control system based on a fractional order phase-locked loop observer, which comprises a rectification module, a phase-locked loop module, a coordinate transformation module, a fractional order phase-locked loop control module and a PWM modulation module; the input end of the rectification module is connected with a three-phase power grid voltage, and the output end outputs a direct current voltage; the input end of the phase-locked loop module is connected with the three-phase power grid voltage, and the output end outputs an electric angle and is connected with the input end of the coordinate transformation module and the input end of the PWM modulation module; the input end of the coordinate transformation module is connected with the output end current of the rectification module, and the output end is connected with the input end of the fractional order phase-locked loop control module; the fractional order phase-locked loop control module is connected with the PWM modulation module; and the PWM modulation module is connected with the rectification module. Compared with a traditional linear extended state observer, the fractional order phase-locked loop observer designed in the application has more obvious effects of suppressing resonance peaks and reducing current harmonic content, and has strong adaptability to parameter changes of the system.

Description

Technical Field

[0001] This invention relates to the field of rectifier control technology, and in particular to a rectifier current loop control system based on a fractional-order phase-locked loop observer. Background Technology

[0002] The complex coupling and inherent resonance of LCL rectifiers can affect system stability. Traditional methods use notch filters, active damping, and passive damping to eliminate inherent resonance and employ PI controllers for control. However, these methods suffer from limitations in practical applications due to reliance on system accuracy, excessive power consumption, and the need for additional sensors. Many researchers have proposed methods such as proportional resonance, repetitive control, model predictive control, and dead-time compensation to suppress current harmonics. Proportional resonance is effective at suppressing current harmonics at specific frequencies, but it cannot suppress harmonic disturbances at integer multiples of the AC side frequency. Repetitive control effectively suppresses periodic disturbances introduced by space vector pulse width modulation, but it suffers from inherent phase lag, poor frequency adaptability, and high computational complexity. Model predictive control offers fast dynamic response, but multiple sensors are required to ensure MPC control performance. Dead-time compensation improves the current sinusoidality, but it is easily affected by current and voltage sampling and cannot suppress current harmonics caused by AC side voltage disturbances or drive signals. Linear Extended State Observer (LESO) can observe and feed back disturbances in the system, such as parameter errors, grid fluctuations, complex coupling, and resonant spikes, thereby enhancing the system's robustness and stability. However, traditional LESO suffers from limitations in its observation capabilities due to insufficient bandwidth. While it performs well in observing large disturbances, it is less effective at suppressing low-frequency, small-amplitude harmonics. Summary of the Invention

[0003] In order to overcome the above-mentioned shortcomings and deficiencies of the prior art, the purpose of this invention is to provide a rectifier current loop control system based on a fractional-order phase-locked loop observer.

[0004] The objective of this invention is achieved through the following technical solution:

[0005] A rectifier current loop control system based on a fractional-order phase-locked loop observer includes: a rectifier module, a phase-locked loop module, a coordinate transformation module, a fractional-order phase-locked loop control module, and a PWM modulation module;

[0006] The rectifier module has its input terminal connected to the three-phase power grid voltage and its output terminal outputting DC voltage connected to the load.

[0007] The phase-locked loop module has its input terminal connected to the three-phase power grid voltage and its output terminal outputting the power grid electrical angle, which is connected to the coordinate transformation module and the PWM modulation module respectively.

[0008] The coordinate transformation module has its input terminals connected to the three-phase power grid electrical angle and the three-phase current on the rectifier side, respectively, and its output terminal outputs the d-axis and q-axis current components in the rotating coordinate system to the fractional-order phase-locked loop control module.

[0009] The fractional-order phase-locked loop control module has its output connected to the PWM modulation module, including a linear state feedback controller (LESF) and a fractional-order phase-locked loop observer (FOPLLO).

[0010] The PWM modulation module outputs a control signal to control the operation of the rectifier module.

[0011] Furthermore, the Linear State Feedback Controller (LESF) compensates for system disturbances and realizes current closed-loop control. The input terminal of the LESF receives the current setpoints of the d-axis and q-axis and the real-time current values ​​of the d-axis and q-axis output by the coordinate transformation module. The LESF observes the real-time disturbance values ​​of the d-axis and q-axis in real time and outputs the control signals of the d-axis and q-axis to the fractional-order phase-locked loop observer (FOPLLO) and the PWM modulation module.

[0012] Furthermore, the input terminal of the fractional phase-locked loop observer FOPLLO receives the real-time values ​​of the d-axis and q-axis currents output by the coordinate transformation module and the d-axis and q-axis control signals output by the linear state feedback controller LESF, and the output terminal receives the observed perturbation values ​​of the d-axis and q-axis.

[0013] Furthermore, the specific working process of the coordinate transformation module is as follows:

[0014] The current in a three-phase stationary coordinate system is transformed into the current in a two-phase stationary coordinate system using the constant amplitude Clark transformation. The transformation formula is as follows:

[0015]

[0016] Among them, i a i b i c It is the three-phase current on the rectifier side, i α i β It is the AC component in a two-phase stationary coordinate system;

[0017] to i α i β Perform the Park transformation, the transformation formula is as follows:

[0018]

[0019] Where θ is the electrical angle of the three-phase power grid output by the phase-locked loop module, and i d i qIt consists of the DC current components of the d-axis and q-axis in a synchronous rotating coordinate system. The three-phase AC quantity is converted into a two-phase DC quantity through the coordinate transformation module.

[0020] Furthermore, the fractional-order phase-locked loop control module includes a d-axis fractional-order phase-locked loop controller and a q-axis phase-locked loop controller with identical structures.

[0021] Furthermore, the control process of the d-axis fractional-order phase-locked loop controller is as follows:

[0022] Based on the differential equation of the d-axis rectifier side current, an extended state-space expression for the controlled object is established.

[0023] Design a phase-locked loop observer based on the extended state-space expression, and obtain the observation error expression;

[0024] The fractional-order calculus stage yields a fractional-order phase-locked loop observer, which is used to obtain the estimated system disturbance.

[0025] Furthermore, the phase-locked loop observer is a second-order observer established based on the rectifier-side current feedback.

[0026] Furthermore, a one-beat hysteresis is added to the input of the fractional-order phase-locked loop observer.

[0027] Furthermore, the PWM modulation module adopts a dual-sampling single-update mode.

[0028] Furthermore, the dual sampling refers to sampling and calculation at both the carrier peak and trough, updating the control parameters only at the peak or trough.

[0029] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0030] (1) The present invention designs a fractional-order phase-locked loop observer, which has a more significant effect on suppressing resonance peaks and reducing current harmonic content compared with the traditional LESO, and has strong applicability to system parameter changes.

[0031] (2) The rectifier-side current feedback modeling used in this invention reduces the relative order, thereby reducing the order of the observer and simplifying the parameter tuning process.

[0032] (3) The present invention introduces a one-beat lag in the input stage of the observer to offset the time delay caused by sampling and SVPWM modulation, thereby enhancing the stability of the system.

[0033] (4) The present invention uses a dual sampling single update mode, that is, sampling calculation is performed at the peak and trough of the carrier wave, and the control parameters are updated only at the peak or trough, which reduces the calculation delay, increases the system control bandwidth, and improves the system control performance. Attached Figure Description

[0034] Figure 1 This is a system structure block diagram of the present invention;

[0035] Figure 2 yes Figure 1 Block diagram of a fractional-order phase-locked loop controller. Detailed Implementation

[0036] The present invention will be further described in detail below with reference to the embodiments, but the implementation of the present invention is not limited thereto.

[0037] like Figure 1 and Figure 2 As shown, a rectifier current loop control system based on a fractional-order phase-locked loop observer includes a rectifier module, a phase-locked loop module, a coordinate transformation module, a fractional-order phase-locked loop control module, and a PWM modulation module.

[0038] The rectifier module includes an LCL filter and a three-phase full-bridge rectifier, which takes single and three-phase current and voltage as input and outputs DC voltage to the load.

[0039] The phase-locked loop module has its input terminal connected to the three-phase power grid voltage and its output terminal outputting the power grid electrical angle, which is connected to the coordinate transformation module and the PWM modulation module respectively.

[0040] The coordinate transformation module has its input terminals connected to the three-phase power grid electrical angle and the three-phase current on the rectifier side, respectively, and its output terminal outputs the d-axis and q-axis current components in the rotating coordinate system to the fractional-order phase-locked loop control module.

[0041] The fractional-order phase-locked loop control module has its output connected to the PWM modulation module, including a linear state feedback controller (LESF) and a fractional-order phase-locked loop observer (FOPLLO).

[0042] Furthermore, the fractional-order phase-locked loop (PLL) control module includes a structurally identical d-axis PLL controller and a q-axis PLL controller. The two PLL controllers comprise a linear state feedback controller (LESF) and a fractional-order PLL observer (FOPLLO).

[0043] The Linear State Feedback Controller (LESF) compensates for system disturbances and achieves closed-loop current control. The input terminals of the LESF are the current setpoints for the d-axis and q-axis, as well as the real-time current values ​​for the d-axis and q-axis output by the coordinate transformation module. The LESF monitors the real-time disturbance values ​​of the d-axis and q-axis in real time, and outputs the control signals for the d-axis and q-axis, which are then sent to the fractional-order phase-locked loop (FOPLLO) observer and the PWM modulation module.

[0044] The input terminal of the fractional phase-locked loop observer FOPLLO receives the real-time values ​​of the d-axis and q-axis currents output by the coordinate transformation module and the d-axis and q-axis control signals output by the linear state feedback controller LESF. The output terminal is the observed disturbance values ​​of the d-axis and q-axis.

[0045] The PWM modulation module outputs a control signal to control the operation of the rectifier module.

[0046] Furthermore, the coordinate transformation module specifically comprises:

[0047] The current in a three-phase stationary coordinate system is transformed into the current in a two-phase stationary coordinate system using the constant amplitude Clark transformation. The transformation formula is as follows:

[0048]

[0049] Among them, i a i b i c It is the three-phase current on the rectifier side, i α i β It is the AC component in a two-phase stationary coordinate system;

[0050] to i α i β Perform the Park transformation, the transformation formula is as follows:

[0051]

[0052] Where θ is the electrical angle of the three-phase power grid output by the phase-locked loop module, and i d i q It is the DC component in the synchronous rotating coordinate system; through the coordinate transformation module, the three-phase AC quantity can be converted into a two-phase DC quantity.

[0053] Furthermore, the fractional-order phase-locked loop control module controls the current based on the given current value and the feedback real-time current value to obtain an output control signal. The control signal of the fractional-order phase-locked loop control module is output to the PWM modulation module. The fractional-order phase-locked loop consists of the same d-axis fractional-order phase-locked loop controller and q-axis fractional-order phase-locked loop controller.

[0054] Taking the d-axis as an example:

[0055] The differential equation for the d-axis rectifier side current is shown below.

[0056]

[0057] The above formula can be equivalent to:

[0058]

[0059] Among them, wg Let i be the angular velocity of the composite vector of the three-phase grid voltages. id i iq These are the d-axis and q-axis currents output by the coordinate transformation module, L i R is the rectifier-side inductance. i u is the parasitic resistance of the rectifier-side inductor. cd The voltage of the filter capacitor is u. id f is the voltage on the d-axis rectifier side. d The total disturbance is unknown.

[0060] Let x1 = i id x2 = f d Establish the extended state-space expression of the controlled object:

[0061]

[0062] in, C = [1 0].

[0063] Design a phase-locked loop observer:

[0064]

[0065] Where A z =A,B z =B, C z =C,L z =[0 β1] T L = [0 β2] T Matrix L and L z Let L be the error gain matrix of the phase-locked loop observer, and let L be the matrix L2. z The parameters directly affect the performance of the phase-locked loop observer, thereby affecting the disturbance rejection performance of the entire system.

[0066] Let e ​​= xz, then we can obtain the expression for the observation error matrix:

[0067]

[0068] in,

[0069] The poles of the characteristic polynomial are configured using the bandwidth method, namely:

[0070]

[0071] in, w o This represents the observer bandwidth.

[0072] Using the Caputo definition for fractional calculus, the resulting state equation for the fractional phase-locked loop state observer is:

[0073]

[0074] in, The error gain matrix of the fractional-order calculus unit. For non-negative real numbers, α is a fractional calculus operator, and α is the calculus constant.

[0075] z2 is the system disturbance estimate, and the system feedforward compensation structure is designed as follows: We can obtain:

[0076]

[0077] Where u′ is the equivalent closed-loop control quantity. After using a state observer for disturbance feedforward compensation, the controlled object is approximately a series integral system. A proportional controller is designed for the control quantity u′:

[0078] u′=k p (r id -y) (11)

[0079] Where, r id k is the given value for the d-axis current. p It is the controller gain.

[0080] Furthermore, the PWM modulation module outputs a control signal to control the operation of the rectifier module.

[0081] Furthermore, the phase-locked loop observer is a second-order observer established based on the rectifier-side current feedback.

[0082] A one-cycle hysteresis is added to the input of the fractional-order phase-locked loop observer. The one-cycle hysteresis refers to the delay of one control cycle, which can offset the time delay caused by current sampling and SVPWM modulation, and further improve the stability of the system.

[0083] In this embodiment, the PWM modulation module uses a dual-sampling single-update mode, that is, sampling and calculation are performed at the peak and trough of the carrier wave, and the control parameters are updated only at the peak or trough, which reduces the calculation delay, increases the system control bandwidth, and improves the system control performance.

[0084] This embodiment of the rectifier current loop control method based on a fractional-order phase-locked loop observer, proposed by Haiyitong, includes the following steps:

[0085] Step 1: Input the three-phase grid voltage into the phase-locked loop module, and output the grid voltage angle to the coordinate transformation module and the PWM modulation module;

[0086] Step 2: Input the three-phase current from the rectifier side into the coordinate transformation module, and output the d-axis current component and q-axis current component to the fractional-order phase-locked loop control module;

[0087] Step 3: The fractional-order phase-locked loop control module controls the current based on the given current value and the feedback real-time current value to obtain the output control signal. The control signal of the fractional-order phase-locked loop control module is output to the PWM modulation module. The fractional-order phase-locked loop is composed of the same d-axis control module and q-axis control module.

[0088] Step 4: The PWM modulation module outputs a control signal to control the operation of the rectifier module.

[0089] This invention improves upon traditional LESO and incorporates fractional-order calculus to design a current closed-loop control for a fractional-order phase-locked loop observer. Compared to traditional LESO, it significantly suppresses resonance peaks and reduces current harmonic content, while also exhibiting strong adaptability to system parameter variations. Modeling the rectifier-side current feedback reduces the relative order, thereby lowering the observer's order and simplifying parameter tuning. A one-beat lag is introduced at the observer's input stage to offset the time delay caused by sampling and SVPWM modulation, enhancing system stability. A dual-sampling, single-update mode is used, where sampling and calculation are performed at carrier peaks and troughs, and control parameters are updated only at these peaks or troughs, reducing calculation delay, increasing system control bandwidth, and improving system control performance.

[0090] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the embodiments described above. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A rectifier current loop control system based on a fractional-order phase-locked loop observer, characterized in that, include: Rectifier module, phase-locked loop module, coordinate transformation module, fractional-order phase-locked loop control module, and PWM modulation module; The rectifier module has its input terminal connected to the three-phase power grid voltage and its output terminal outputting DC voltage connected to the load. The phase-locked loop module has its input terminal connected to the three-phase power grid voltage and its output terminal outputting the power grid electrical angle, which is connected to the coordinate transformation module and the PWM modulation module respectively. The coordinate transformation module has its input terminals connected to the three-phase power grid electrical angle and the three-phase current on the rectifier side, respectively, and its output terminal outputs the d-axis and q-axis current components in the rotating coordinate system to the fractional-order phase-locked loop control module. The fractional-order phase-locked loop control module has its output connected to the PWM modulation module, including a linear state feedback controller (LESF) and a fractional-order phase-locked loop observer (FOPLLO). The PWM modulation module outputs a control signal to control the operation of the rectifier module; The Linear State Feedback Controller (LESF) compensates for system disturbances and realizes current closed-loop control. The input terminal of the LESF receives the current setpoints of the d-axis and q-axis and the real-time current values ​​of the d-axis and q-axis output by the coordinate transformation module. The LESF observes the real-time disturbance values ​​of the d-axis and q-axis in real time and outputs the control signals of the d-axis and q-axis to the fractional phase-locked loop observer (FOPLLO) and the PWM modulation module. The input terminal of the fractional phase-locked loop observer FOPLLO is the real-time values ​​of the d-axis and q-axis currents output by the coordinate transformation module and the d-axis and q-axis control signals output by the linear state feedback controller LESF. The output terminal is the observed disturbance values ​​of the d-axis and q-axis. The specific working process of the coordinate transformation module is as follows: The current in a three-phase stationary coordinate system is transformed into the current in a two-phase stationary coordinate system using the constant amplitude Clark transformation. The transformation formula is as follows: in, , , It is the three-phase current on the rectifier side. , It is the AC component in a two-phase stationary coordinate system; right , Perform the Park transformation, the transformation formula is as follows: in, It is the electrical angle of the three-phase power grid output by the phase-locked loop module. , It consists of the DC current components of the d-axis and q-axis in a synchronous rotating coordinate system. The coordinate transformation module converts the three-phase AC quantity into a two-phase DC quantity. The fractional-order phase-locked loop control module includes a d-axis fractional-order phase-locked loop controller and a q-axis phase-locked loop controller with identical structures. The control process of the d-axis fractional-order phase-locked loop controller is as follows: Based on the differential equation of the d-axis rectifier side current, an extended state-space expression for the controlled object is established. Design a phase-locked loop observer based on the extended state-space expression, and obtain the observation error expression; The fractional-order calculus stage yields a fractional-order phase-locked loop observer, which is used to obtain the estimated system disturbance. The phase-locked loop observer is a second-order observer established based on the rectifier-side current feedback; A one-beat hysteresis is added to the input of the fractional-order phase-locked loop observer; The PWM modulation module adopts a dual-sampling single-update mode; The dual sampling refers to sampling and calculation at both the carrier peak and trough, updating control parameters only at the peak or trough.

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