Converter background harmonic suppression and positive active damping area expansion control method

Abstract

The invention discloses a control method for background harmonic suppression and positive active damping area expansion of a converter, and belongs to the technical field of grid-connected inverters, and the method comprises the steps: calculating a current preset value according to an obtained phase angle of a power grid voltage value; inputting a difference value between the current preset value and a power grid side current value obtained in advance into a current regulator to generate a current regulation output quantity; inputting the obtained capacitor voltage value into a feedback branch containing a proportional term function, a primary differential term function and a secondary differential term function to generate a feedback quantity; superposing the current regulation output quantity and the feedback quantity, and generating a modulation signal through a preset delay link and the ratio of the direct current side voltage of the inverter to the triangular carrier amplitude; comparing the modulation signal with a pre-obtained triangular carrier wave, and generating a control signal of an inverter bridge switch tube through sine pulse width modulation; according to the invention, the time delay problem in capacitor voltage full-feedback control is solved by expanding the range of the positive active damping region and suppressing harmonic waves.

Description

Technical Field

[0001] The present invention relates to a control method for suppressing background harmonics of a converter and expanding the positive active damping region, belonging to the technical field of grid-connected inverters. Background Art

[0002] With the rapid development of new energy power generation technologies such as wind energy and photovoltaic energy, grid-connected inverters in the power system, as important connection devices between new energy distributed generation and the power grid, play a crucial role in the power quality of the power grid and the stability of the system. Especially in the case of a high-penetration power grid and a weak power grid, the background harmonics in the power grid have a more significant impact on the output current of the grid-connected inverter, which may threaten the power quality and system stability.

[0003] To weaken the influence of grid voltage background harmonics on the output current of the grid-connected inverter, scholars have proposed grid voltage feed-forward control. In a grid-connected inverter system, the voltage at the point of common coupling (PCC) is usually used to replace the grid voltage. In practical engineering applications, the grid-connected inverter needs to be connected to a step-up transformer to be connected to the grid, and the leakage inductance of the step-up transformer can be used as the grid-side inductance. At this time, the voltage at the PCC is actually the voltage of the filter capacitor. Research shows that adopting a full feed-forward control strategy of capacitor voltage can effectively eliminate the influence of grid voltage on the grid-connected current and provide active damping for the grid-connected inverter, thereby suppressing harmonic resonance and improving the stability of the LCL grid-connected inverter.

[0004] Based on the full feed-forward of grid voltage, scholars have also proposed full feedback of capacitor voltage. However, different from the grid voltage feed-forward scheme, capacitor voltage feedback will change the loop gain of the system, thereby affecting the stability of the system. Inevitable control delay has an impact on the stability of the grid-connected inverter. The control delay makes the active damping no longer appear as a constant resistance but becomes a virtual resistance that changes with frequency. When its equivalent resistance is positive, it can damp the resonance peak, and when it is negative, it will introduce a right-half plane pole, causing the system to be unstable. This greatly affects the stability of the system, especially in the case of high-frequency harmonics. Based on this, aiming at the delay problem in the full feedback control of capacitor voltage, there is an urgent need for a control method that can expand the range of the positive active damping region and suppress harmonics. Summary of the Invention

[0005] The purpose of the present invention is to overcome the deficiencies in the prior art and provide a control method for suppressing background harmonics of a converter and expanding the positive active damping region, so as to solve the delay problem in the full feedback control of capacitor voltage by expanding the range of the positive active damping region and suppressing harmonics.

[0006] To achieve the above purpose, the present invention is implemented by adopting the following technical solutions:

[0007] In a first aspect, the present invention provides a control method for converter background harmonic suppression and positive active damping region expansion, including:

[0008] Calculating a preset current value according to the phase angle of the acquired grid voltage value;

[0009] Inputting the difference between the preset current value and the previously acquired grid-side current value into a current regulator to generate a current regulation output quantity;

[0010] Inputting the acquired capacitor voltage value into a feedback branch including a proportional term, a first-order differential term, and a second-order differential term function to generate a feedback quantity;

[0011] Superposing the current regulation output quantity and the feedback quantity, and generating a modulation signal through a preset delay link and the ratio of the DC-side voltage of the inverter to the amplitude of the triangular carrier wave;

[0012] Comparing the modulation signal with the previously acquired triangular carrier wave, and generating a control signal for the inverter bridge switching tubes through sinusoidal pulse width modulation.

[0013] Further, the formula for calculating the preset current value according to the phase angle of the acquired grid voltage value is as follows: ; Wherein, is the preset current value, I* is the amplitude of the preset current value, and θ is the phase angle of the grid voltage value.

[0014] Further, the expression of the current regulator is: ; Wherein, k p is the proportionality coefficient, k i is the integral coefficient, and s is the Laplace operator.

[0015] Further, the expression of the current regulation output quantity is: ; In the formula, V PI is the current regulation output quantity, i ref is the preset current value, and i g is the grid-side current value.

[0016] Further, the expression of the feedback quantity is: ; In the formula, V c_fd is the feedback quantity of the capacitor voltage V c , and G ff (s) is the feedback coefficient; The feedback coefficient G ffThe expression of (s) is as follows: ; Where: K PWM is the ratio of the DC - side voltage of the inverter to the amplitude of the triangular carrier wave, G LPF (s) is a first - order low - pass filter, Q is the coefficient of the first - order differential term, T s is the system sampling time, L1 is the inductance value of the inverter machine side, C is the capacitance value of the inverter, and s is the Laplace operator.

[0017] Furthermore, the expression of the modulation signal is:

[0018] ;

[0019] Where: V M is the modulation signal, G d (s) is a delay link.

[0020] Furthermore, the value range of the coefficient Q of the first - order differential term is as follows:

[0021] ;

[0022] Where: Q is the parameter of the first - order differential term, f c_LPF is the cut - off frequency of the low - pass filter, f is the frequency, L1 is the inductance value of the inverter machine side, and C is the capacitance value of the inverter.

[0023] In a second aspect, the present invention provides a control device for suppressing background harmonics and expanding the positive active damping region of a converter, including:

[0024] A memory for storing computer programs / instructions;

[0025] A processor for executing the computer programs / instructions to implement the steps of the method described in any one of the foregoing.

[0026] In a third aspect, the present invention provides a computer - readable storage medium, on which a computer program is stored, and when the program is executed by a processor, it implements the steps of the method described in any one of the foregoing.

[0027] In a fourth aspect, the present invention provides a computer program product, including computer programs / instructions, and when the computer programs / instructions are executed by a processor, they implement the steps of the method described in any one of the foregoing.

[0028] Compared with the prior art, the beneficial effects achieved by the present invention:

[0029] The present invention provides a control method for suppressing background harmonics and expanding the positive active damping region of a converter. Based on the traditional capacitor voltage feedback, by introducing a primary differential feedback branch, the suppression effect on grid harmonics is further enhanced. In addition, by adjusting the control parameters, it is ensured that the equivalent resistance of the LCL converter is all positive resistance within the Nyquist frequency, improving the working performance and stability of the system. Brief Description of the Drawings

[0030] Figure 1 is a flowchart of a control method for suppressing background harmonics and expanding the positive active damping region of a converter provided by an embodiment of the present invention;

[0031] Figure 2 is a control block diagram of full feedback of capacitor voltage provided by an embodiment of the present invention;

[0032] Figure 3 is a total impedance - frequency curve diagram provided by an embodiment of the present invention;

[0033] Figure 4 is a Q - value frequency curve diagram provided by an embodiment of the present invention;

[0034] Figure 5 is a schematic diagram of an algorithm verification model built in Simulink provided by an embodiment of the present invention;

[0035] Figure 6 is a schematic diagram of the waveform change when the model provided by an embodiment of the present invention switches from having capacitor voltage feedback to without capacitor voltage feedback. Detailed Embodiment

[0036] The present invention will be further described below with reference to the drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention and cannot be used to limit the protection scope of the present invention.

[0037] Embodiment 1. This embodiment introduces a control method for suppressing background harmonics and expanding the positive active damping region of a converter, including:

[0038] Calculating a preset current value according to the phase angle of the obtained grid voltage value;

[0039] Inputting the difference between the preset current value and the previously obtained grid - side current value into a current regulator to generate a current regulation output;

[0040] Inputting the obtained capacitor voltage value into a feedback branch including proportional term, primary differential term, and secondary differential term functions to generate a feedback quantity;

[0041] Superposing the current regulation output and the feedback quantity, and generating a modulation signal through a preset delay link and the ratio of the DC - side voltage of the inverter to the amplitude of the triangular carrier wave;

[0042] Compare the modulation signal with the pre-acquired triangular carrier wave, and generate the control signal of the inverter bridge switch tube through sinusoidal pulse width modulation.

[0043] As Figure 1 shown, the control method for background harmonic suppression and positive active damping region expansion of the converter provided in this embodiment specifically involves the following steps in its application process:

[0044] Step 1: Obtain the phase angle θ of the grid voltage value V g from the phase-locked loop, input θ, multiply it by the trigonometric function and coefficient, and output the preset current value i ref ;

[0045] For the understanding of the content of this application, as Figure 2 shown, the inverter structure of this application is briefly introduced through a control block diagram. The control system includes: a phase-locked loop PLL, a current loop, and a PWM modulation sampling module. The grid-connected inverter single-machine system obtains the actual grid-connected current value and the phase angle of the capacitor voltage grid connection point from the current controller PI, compares the grid-connected current transformed based on the phase angle of the capacitor voltage grid connection point with the reference value of the controller circuit, and then outputs a voltage control signal after passing through the current controller PI, and obtains the inverter bridge arm control signal after PWM modulation.

[0046] Step 2: Obtain the grid-side current value i g , subtract the grid-side current value i ref from the preset current value i g , input the difference into the current regulator G i (s), and its final output value is V PI ;

[0047] The expression of the current regulator G i (s) is:

[0048] ;

[0049] Among them, k p is the proportional coefficient, and k i is the integral coefficient.

[0050] The current regulator G i (s) eliminates the error between the preset current value i ref and the grid-side current value i g through the proportional and integral links, and finally makes the two equal. The setting of the parameters of the current regulator G i (s) will affect the anti-interference ability and stability of the system.

[0051] The expression of the V PI is:

[0052] ;

[0053] In the formula: i ref is the preset current value, and i g is the actual grid-side current value, and G i (s) is the current regulator.

[0054] Step 3: Send the capacitor voltage value V c to the feedback branch, and use the generated output as the feedback quantity V c of the capacitor voltage V c_fd , and feedback it to the front of the delay link G d (s).

[0055] The expression of the feedback coefficient G ff (s) is:

[0056] ;

[0057] Among them, K PWM is the transfer function of the inverter, G LPF (s) is a first-order low-pass filter, Q is the coefficient of the first-order differential term, T s is the system sampling time, L1 is the inductor value on the machine side of the inverter, with the unit of mH, G d (s) is a 1.5-beat delay link, that is, e -1.5sTs , and s is the Laplace operator.

[0058] The total resistance equivalent formula of the feedback coefficient G ff (s) is:

[0059] ;

[0060] In the formula: Q is the first-order differential term parameter. The total resistance-frequency curve of the feedback coefficient is as shown in Figure 3 .

[0061] According to the resistance parallel formula, to ensure that the total resistance is all positive within the Nyquist frequency, the formula for finding the Q range is:

[0062] ;

[0063] The Q value-frequency curve is as shown in Figure 4 .

[0064] The feedback quantity V c of the capacitor voltage V c_fd has the following expression:

[0065] ;

[0066] In the formula: G ff (s) is for Vc_fd Feedback coefficient, V c is the capacitor voltage value.

[0067] Step 4: Add the output of the current regulator to the capacitor voltage V c Feedback quantity V c_fd , pass through the delay link G d (s) and the transfer function K of the inverter PWM , output the modulation signal V M , compare it with the triangular carrier wave, and through sinusoidal pulse width modulation, obtain the control signals of each switch tube of the inverter bridge to control the entire system.

[0068] The modulation signal V M The expression is:

[0069] ;

[0070] In the formula: V PI is the output value of the current regulator, V c_fd is the feedback quantity of the capacitor voltage V c , G d (s) is a 1.5-beat delay link, that is, e -1.5sTs , s is the Laplace operator, T s is the system sampling time, K PWM is the ratio of the DC side voltage of the inverter to the amplitude of the triangular carrier wave.

[0071] The introduction of the current loop enhances the dynamic response speed of the system, and the introduction of the capacitor voltage feedback branch improves the harmonic suppression ability and the stability of the system. The hybrid control of the two enables the system to respond faster to input changes.

[0072] Experimental verification stage:

[0073] In this embodiment, a single-phase LCL-type grid-connected inverter system is built in MATLAB / Simulink. The system model is as Figure 5 shown. To verify the effectiveness of the capacitor voltage feedback control strategy of the present invention, Figure 6 is a schematic diagram of the waveform change of the model provided by the embodiment of the present invention when switching from having capacitor voltage feedback to no capacitor voltage feedback;

[0074] As can be Figure 6 seen, under the control strategy of capacitor voltage feedback, even if the grid harmonics are large, the grid current still maintains a good sine wave and the system is stable. When the system switches to the control strategy without capacitor voltage feedback, the system becomes unstable, finally proving the effectiveness of the capacitor voltage feedback control strategy of the present invention.

[0075] In summary, in the above embodiments, based on the traditional capacitor voltage feedback, the present invention further strengthens the suppression effect on power grid harmonics by introducing a primary differential feedback branch. In addition, by adjusting the control parameters, it is ensured that the equivalent resistance of the LCL converter is all positive resistance within the Nyquist frequency, improving the working performance and stability of the system.

[0076] Embodiment 2. This embodiment provides a control device for suppressing background harmonics and expanding the positive active damping region of a converter, including:

[0077] A memory for storing computer programs / instructions;

[0078] A processor for executing the computer programs / instructions to implement the steps of the method described in any one of Embodiment 1.

[0079] Embodiment 3. This embodiment provides a computer-readable storage medium with a computer program stored thereon, and when the program is executed by a processor, it implements the steps of the method described in any one of Embodiment 1.

[0080] Embodiment 4. This embodiment provides a computer program product including computer programs / instructions, and when the computer programs / instructions are executed by a processor, they implement the steps of the method described in any one of Embodiment 1.

[0081] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the technical principle of the present invention, several improvements and deformations can be made, and these improvements and deformations should also be regarded as the protection scope of the present invention.

[0082] Those skilled in the art should understand that the embodiments of the present disclosure can be provided as methods, systems, or computer program products. Therefore, the present disclosure can take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware aspects. Moreover, the present disclosure can take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0083] The present disclosure is described with reference to the flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to the embodiments of the present disclosure. It should be understood that each flow and / or block in the flowcharts and / or block diagrams, as well as the combination of flows and / or blocks in the flowcharts and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to the processors of general-purpose computers, special-purpose computers, embedded processors, or other programmable data processing devices to generate a machine, so that the instructions executed by the processors of the computer or other programmable data processing devices generate for implementing in the process Figure 1one process or multiple processes and / or blocks Figure 1 a device for the functions specified in one block or multiple blocks.

[0084] These computer program instructions can also be stored in a computer-readable memory that can direct a computer or other programmable data processing device to work in a specific manner, so that the instructions stored in the computer-readable memory produce a manufactured article including an instruction device, and the instruction device implements the processes Figure 1 one process or multiple processes and / or blocks Figure 1 the functions specified in one block or multiple blocks.

[0085] These computer program instructions can also be loaded onto a computer or other programmable data processing device, so that a series of operation steps are executed on the computer or other programmable device to generate a computer-implemented process. Therefore, the instructions executed on the computer or other programmable device provide steps for implementing the functions specified in Figure 1 one process or multiple processes and / or blocks Figure 1 one block or multiple blocks.

[0086] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present disclosure rather than limit the scope of its protection. Although the present disclosure has been described in detail with reference to the above embodiments, those of ordinary skill in the art should understand that: after reading the present disclosure, those skilled in the art can still make various changes, modifications or equivalent replacements to the specific implementation manners of the invention. However, these changes, modifications or equivalent replacements are all within the protection scope of the pending claims of the disclosure.

Claims

1. A control method for suppressing background harmonics and expanding the positive active damping region of a converter, characterized in that, Including: Calculating a preset current value according to the phase angle of the acquired grid voltage value; Inputting the difference between the preset current value and the previously acquired grid-side current value into a current regulator to generate a current regulation output quantity; Inputting the acquired capacitor voltage value into a feedback branch including proportional term, first-order differential term and second-order differential term functions to generate a feedback quantity; Superimposing the current regulation output quantity and the feedback quantity, and generating a modulation signal through a preset delay link and the ratio of the DC-side voltage of the inverter to the amplitude of the triangular carrier wave; Comparing the modulation signal with the previously acquired triangular carrier wave, and generating a control signal for the inverter bridge switching tubes through sinusoidal pulse width modulation.

2. The control method for background harmonic suppression and positive active damping region extension of the converter according to claim 1, characterized in that The formula for calculating the preset current value according to the phase angle of the acquired grid voltage value is as follows: ； Among them, is the preset current value, I* is the amplitude of the preset current value, and θ is the phase angle of the grid voltage value.

3. The control method for background harmonic suppression and positive active damping region expansion of the converter according to claim 2, characterized in that, The expression of the current regulator is: ； where k p is the proportionality coefficient, k i is the integral coefficient, and s is the Laplace operator.

4. The control method for background harmonic suppression and positive active damping region expansion of the converter according to claim 3, characterized in that The expression of the current regulation output quantity is: ； Wherein, V PI is the current regulation output, i ref is the preset current value, and i g is the grid-side current value.

5. The control method for background harmonic suppression and positive active damping region expansion of the converter according to claim 4, characterized in that, The expression of the feedback quantity is: ； where, V c_fd is the feedback quantity of the capacitor voltage V c , and G ff (s) is the feedback coefficient; The feedback coefficient G ff (s) is expressed as: ； Where: K PWM is the ratio of the DC - side voltage of the inverter to the amplitude of the triangular carrier wave, G LPF (s) is a first - order low - pass filter, Q is the coefficient of the first - order differential term, T s is the system sampling time, L1 is the inductance value of the inverter machine side, C is the capacitance value of the inverter, and s is the Laplace operator.

6. The control method for background harmonic suppression and positive active damping region extension of the converter according to claim 5, characterized in that The expression of the modulation signal is: ； Where: V M is the modulation signal, and G d (s) is the delay element.

7. The control method for background harmonic suppression and positive active damping region extension of the converter according to claim 5, characterized in that The value range of the first-order differential term coefficient Q is as follows: ； Where: Q is the parameter of the first derivative term, f c_LPF is the cut-off frequency of the low-pass filter, f is the frequency, L1 is the inductance value of the inverter machine side, and C is the capacitance value of the inverter.

8. A control device for suppressing background harmonics and expanding the positive active damping region of a converter, characterized in that, Including: A memory for storing computer programs / instructions; A processor for executing the computer programs / instructions to implement the steps of the method according to any one of claims 1-7.

9. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the program is executed by the processor, the steps of the method according to any one of claims 1-7 are implemented.

10. A computer program product, comprising a computer program / instructions, characterized in that, When the computer programs / instructions are executed by the processor, the steps of the method according to any one of claims 1-7 are implemented.

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