A Data-Driven Method for Suppressing DC Bus Voltage Ripple in a Three-Phase PWM Rectifier

Abstract

This invention relates to a data-driven method for suppressing DC bus voltage ripple in a three-phase PWM rectifier, belonging to the field of rectifier control technology in power electronics. In existing technologies, when there are errors in the sampling of the three-phase voltage in a three-phase PWM rectifier, the second-order ripple in the DC bus voltage and the third harmonic of the grid-side current cannot be effectively suppressed. The method described in this invention establishes a relationship between the grid-side negative-sequence current and the amplitude of the second-order ripple of the DC bus voltage based on the law of power conservation. By perturbing the negative-sequence current and observing the amplitude of the DC bus voltage ripple, effective information contained in the data is extracted to realize the calculation of the negative-sequence command current. Using the method described in this invention, the second-order ripple of the DC bus voltage and the harmonics of the grid-side current can be effectively suppressed, avoiding the use of the grid-side power model, thereby eliminating the influence of voltage sampling errors on ripple suppression performance and further improving the robustness of the method to voltage and inductance parameters.

Description

Technical Field

[0001] This invention belongs to the field of power electronics control technology, specifically relating to a data-driven method for suppressing DC bus voltage ripple in a three-phase PWM rectifier. Background Technology

[0002] Three-phase PWM rectifiers enable bidirectional power flow, high power factor, and low current harmonic rectification, exhibiting excellent performance under normal operating conditions. Therefore, they are widely used in motor drives, high-voltage direct current transmission, microgrid systems, and electric vehicle charging. However, due to the increasing proportion of renewable energy grid integration and grid load imbalance, grid asymmetry faults occur frequently. Asymmetrical grid voltages contain negative sequence components, preventing the complete cancellation of AC components in the three-phase output power. This results in an AC component at twice the grid fundamental frequency in the DC bus voltage, increasing the risk of power switch overvoltage. Furthermore, the secondary ripple of this DC bus voltage, through voltage negative feedback, introduces odd harmonics into the grid current, which is detrimental to the safe and green operation of the grid. Therefore, effectively suppressing DC bus voltage ripple and grid-side current harmonics is of great significance.

[0003] References to relevant patent applications:

[0004] Existing technologies include harmonic injection and the addition of active filter converters. [1] proposes a method for suppressing voltage ripple of MMC capacitor based on second harmonic injection, which reduces the ripple of bus voltage by injecting second harmonic circulating current. However, the voltage ripple is not completely suppressed. [2] proposes a strategy for suppressing DC bus voltage ripple when AC grid voltage is unbalanced, which transfers the voltage ripple on the DC bus of the three-phase rectifier to the thin film capacitor through a Buck / Boost converter, effectively suppressing the voltage ripple on the bus and the grid-side current harmonics. However, an additional converter is required, which increases the development cost of the system. [3] proposes a direct power control strategy for online identification of inductors, which improves the robustness of the control strategy to changes in inductor parameters. However, this method still depends on the sampling and estimation of grid-side voltage and rectifier AC voltage. When there is an error in voltage sampling, the ripple suppression performance of this method will decrease.

[0005] Therefore, among the current methods, one type requires additional devices to buffer the secondary ripple on the DC bus voltage, which increases the system development cost and difficulty; the other type improves the system robustness and ripple suppression performance by adding additional control methods, but does not fundamentally break away from the limitations of the rectifier grid-side power mathematical model, and the control performance is still constrained by parameters such as sampling and inductance.

[0006] [1] Sun Jianyu, Sun Shuangkui, Wang Peng, Li Shushan, Lü Junzhang, Liu Xiaobing, Ma Hongxia, Zhao Xiuwen, Lai Li, Chen Yongchao, Dong Zhaohui, Ma Hongxiang, Wang Ling, Zhang Qiang, Zhang Cunchao, Zhou Bingyan, Jiang Xiuting, Zhang Wei. A method for suppressing voltage ripple of MMC capacitor based on second harmonic injection [P]. Qinghai Province: CN114465465A, 2022-05-10.

[0007] [2] Wang Jinhao, Chang Xiao, Ren Yuan, Gao Le, Zhang Min, Li Rui, Wen Yu, Fan Rui, Zhao Jun, Zhang Tao, Wang Tengxin, Zhi Huiqiang, Guo Xiangyu, Meng Runquan. A strategy for suppressing DC bus voltage ripple under AC grid voltage imbalance [P]. Shanxi Province: CN114123203A, 2022-03-01.

[0008] [3]Y.Zhang, J.Jiao and J.Liu, "Direct power control of PWM rectifiers with online inductance identification under unbalanced and distorted network conditions," IEEE Trans.Power Electron., vol.34, no.12, pp.12524-12537, Dec.2019. Summary of the Invention

[0009] To address the shortcomings of existing technologies, the purpose of this invention is to provide a method for suppressing DC bus voltage ripple in PWM rectifiers under three-phase unbalanced operating conditions. This method can effectively suppress DC bus voltage ripple by extracting effective information from historical data without needing to accurately know the grid-side inductance and voltage parameters, and has strong robustness.

[0010] To achieve the above objectives, the technical solution adopted in this invention is: a data-driven method for suppressing DC bus voltage ripple in a three-phase PWM rectifier, wherein the input of the three-phase PWM rectifier is a three-phase power supply, the three-phase power supply is connected to one end of a three-phase inductor, the other end of the three-phase inductor is connected to the midpoint of the bridge arm of a three-phase full-bridge rectifier, and the upper and lower ends of the three-phase full-bridge rectifier are the positive and negative terminals of the DC bus output, which are respectively connected to the positive and negative terminals of a DC bus capacitor, and the voltage between the two terminals is the DC bus voltage. The method includes the following steps:

[0011] (1) Calculation of negative sequence active current disturbance value: Calculate the disturbance value of the two disturbances of negative sequence active current based on the positive sequence active current.

[0012] (2) Observation of DC bus voltage ripple amplitude under undisturbed conditions: The DC bus voltage ripple is extracted by a bandpass filter, and then the DC bus voltage ripple amplitude is observed under undisturbed conditions.

[0013] (3) Negative sequence active current first disturbance: The negative sequence active current first disturbance value calculated in step (1) is used as the command current to control the DC bus voltage ripple to change, and the corresponding DC bus voltage ripple amplitude is observed.

[0014] (4) Secondary disturbance of negative sequence active current: The second disturbance value of negative sequence active current calculated in step (1) is used as the command current to control the change of DC bus voltage ripple, and the amplitude of the corresponding DC bus voltage ripple is observed.

[0015] (5) Calculation and injection of negative sequence active current command value: Based on the aforementioned negative sequence active current disturbance value and the corresponding DC bus voltage ripple amplitude, calculate the negative sequence active current command value that can suppress DC bus voltage ripple, and inject it as the current command to the grid side current.

[0016] (6) Change the negative sequence active current in the above steps to negative sequence reactive current, and repeat step (1).

[0017] Up to (5).

[0018] Furthermore, in step (1), while ensuring system stability, the DC bus voltage ripple amplitude is changed by perturbing the negative sequence current. The two perturbation values ​​of the negative sequence current are determined according to the following formula.

[0019]

[0020] in, These are the two disturbance values ​​of the negative sequence current, λ. d0 , λ d1 The disturbance coefficient is... This is the positive sequence active current.

[0021] Furthermore, in steps (2), (3), and (4), the DC bus voltage ripple amplitude is calculated according to the following formula.

[0022]

[0023] Among them, U dc_ac U represents the DC bus voltage ripple amplitude, N represents the number of voltage samples per power frequency cycle, and u represents the voltage amplitude. dc_BPF (i) represents the i-th output value of the bandpass filter.

[0024] Furthermore, in step (5), let the i-th observed value of the secondary ripple amplitude of the DC bus voltage be u. di Negative sequence active current command value The i-th observation value is i di Given a total of n observations, calculate a from the sample using the following formula. d bd c d The estimated value

[0025]

[0026] Where d is determined by the fundamental angular frequency ω of the grid voltage. f DC component U in DC bus voltage dc_dc The capacitance constant C of the DC bus capacitor is determined, and its expression is as follows:

[0027]

[0028] Furthermore, in step (5), the negative sequence command current is calculated according to the following formula.

[0029]

[0030] Compared with the prior art, the beneficial effects of the present invention are:

[0031] 1. The proposed method can effectively suppress DC bus voltage ripple and grid-side current harmonics without changing the system stability margin and dynamic response speed.

[0032] 2. The proposed method upgrades the solution of negative sequence command current from the traditional model-driven to data-driven, thereby effectively avoiding problems such as deteriorated ripple suppression performance caused by voltage sampling error and inaccurate grid-side inductance parameters.

[0033] 3. The proposed method does not require an additional power converter, thereby reducing system development costs and expanding the application scenarios of the proposed method. Attached Figure Description

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

[0035] Figure 2 This is a flowchart of the data-driven adaptive current disturbance controller workflow;

[0036] Figure 3 The present invention provides the method for suppressing the dynamic process waveform of DC bus voltage, including (a) three-phase voltage, DC bus voltage and DC bus voltage ripple amplitude, and (b) three-phase current and negative sequence command current in the dq coordinate system.

[0037] The main symbol name in the figure above is: e a e b e c i a i b i c These represent the three-phase voltage and current in a three-phase stationary coordinate system, eα e β i α i β and represent voltage and current in a two-phase stationary coordinate system, respectively. These are the command currents in the two-phase stationary coordinate system, respectively. These are the positive and negative sequence command currents in a two-phase stationary coordinate system, respectively. These are the positive-sequence and negative-sequence command currents in a two-phase rotating coordinate system, respectively. These are the command voltages in the two-phase stationary coordinate system, L a L b L c R a R b R c These are the three-phase inductors and their equivalent series resistances, U. ref U is the command value for the DC bus voltage. dc This is the DC bus voltage. Detailed Implementation

[0038] A specific embodiment of the present invention will now be described in conjunction with the accompanying drawings, and the technical principles and effects of the present invention will be further explained.

[0039] A data-driven method for suppressing DC bus voltage ripple in a three-phase PWM rectifier, the control block diagram of which is shown below. Figure 1 As shown, the data-driven adaptive disturbance current controller consists of three parts: a bandpass filter, an online calculator for the second-order ripple peak of the DC bus voltage, and an adaptive disturbance current generator. The bandpass filter extracts the AC component of the DC bus voltage; the online calculator for the second-order ripple peak of the DC bus voltage provides ripple amplitude data for calculating the negative-sequence command current; and the data-driven adaptive disturbance current controller generates the disturbance current and calculates the final required negative-sequence current based on the corresponding voltage ripple amplitude data. Its workflow diagram is shown below. Figure 2 As shown.

[0040] The following is combined with Figure 1 The control block diagram shown is similar to Figure 2 The flowchart shown below illustrates the workflow of the data-driven adaptive current disturbance controller, providing a detailed explanation of the steps in this embodiment of the invention.

[0041] According to step (1), assuming the rated power of the three-phase PWM rectifier is 3kW, the positive sequence active current is [data missing] under the condition that the three-phase voltage is symmetrical and the effective value is 110V. The value is approximately 16A. According to equation (1), the two disturbance values ​​of the negative sequence active current are calculated as follows:

[0042]

[0043] The principle of step (1) is as follows:

[0044] DC bus voltage ripple amplitude U dc_ac With negative sequence active current The relation is

[0045]

[0046] From equation (7), it can be seen that the DC bus voltage and the negative sequence active current have a parabolic relationship. Under the condition that the negative sequence reactive current is constant, when the negative sequence active current is -b d / (2a d The DC bus voltage ripple is minimized when the negative sequence active current is far from -b. d / (2a d When ), the DC bus voltage ripple amplitude increases. And because of a d b d With parameters unknown, the negative-sequence active current disturbance value can be estimated based on the positive-sequence active current. However, if the disturbance factor is too large, it will increase the DC bus voltage ripple and exacerbate grid-side current distortion; if the disturbance factor is too small, the change in the DC bus voltage ripple amplitude will be difficult to observe, hindering the determination of the final command current. Therefore, λ is chosen here. d0 =15%, λ d1 =7.5%.

[0047] According to step (2), under the conditions of three-phase voltages of 50V, 110V, and 110V respectively, when the sampling frequency is 5kHz, the number of sampling points N per power frequency cycle is 100. Substituting the output value of the bandpass filter into equation (2), the DC bus voltage ripple amplitude under the condition of no disturbance is calculated to be

[0048]

[0049] According to step (3), let the negative sequence active current command value be... The first disturbance value of 2.4A, calculated in step (1), is equal to the value obtained in step (1). At this time, the DC bus voltage ripple amplitude changes. According to equation (2), U is calculated. dc_acd1 It is 11.38V.

[0050] According to step (4), set the negative sequence active current command value. The second disturbance value is 1.2A. At this time, the DC bus voltage ripple amplitude changes. U is calculated according to equation (2). dc_acd2 It is 12.89V.

[0051] According to step (5), substitute the above data into formula (3), where i d1 =0A, u d1 =Udc_acd0 =17.17V, u d2 =U dc_acd1 =11.38V, u d3 =U dc_acd2 =12.89V, calculated as follows For 20104, The value is -91521. Therefore, the negative-sequence active power command current that minimizes the secondary ripple amplitude of the DC bus voltage, calculated using equation (5), is...

[0052]

[0053] It is injected into the grid-side current as a negative sequence active current to suppress DC bus voltage ripple of the negative sequence active current.

[0054] The principle of step (5) is as follows:

[0055] From equation (7), it can be seen that the sum of squared observation errors can be calculated as follows:

[0056]

[0057] Due to the error sum of squares function L(a) d ,b d ,c d )≥0, when it is relative to a d b d c d The partial derivative reaches its minimum value when it is 0. A system of three linear equations in three variables can be established based on the following formula:

[0058]

[0059] By rearranging and simplifying equation (11), we can obtain equation (3).

[0060] According to step (6), replace the negative sequence active current with the negative sequence reactive current, repeat step (1), and calculate the two disturbance values ​​of the negative sequence reactive current as follows:

[0061]

[0062] According to step (6), repeat step (2), and under the condition that the negative sequence reactive current is 0, calculate and record the secondary ripple amplitude U of the DC bus voltage according to equation (2). dc_acq0 It is 11.51V.

[0063] According to step (6), repeat step (3) and set the negative sequence reactive current command value. The first disturbance value, 1.6A, obtained in step (1), is equal to the value calculated in step (1). At this time, the DC bus voltage ripple amplitude changes. U is calculated according to equation (2). dc_acq1 It is 1.78V.

[0064] According to step (6), repeat step (4) and set the negative sequence reactive current command value. The second disturbance value is equal to 0.8A. At this time, the DC bus voltage ripple amplitude changes. U is calculated according to equation (2). dc_acq2 It is 6.71V.

[0065] According to step (6), repeat step (5), where i q1 =0A, u q1 =U dc_acq0 =11.51V, u q2 =U dc_acq1 =1.78V, u q3 =U dc_acq2 =6.71V, calculated It is 22363. The value is -86731. Calculate the negative-sequence reactive power command current that minimizes the secondary ripple of the DC bus voltage.

[0066]

[0067] By injecting it as a negative-sequence reactive current into the grid-side current, DC bus voltage ripple suppression can be achieved.

[0068] This embodiment provides a detailed process for calculating the negative sequence command current using a data-driven method. When the rated power and current change, this process can be followed.

[0069] To demonstrate the significant effects of the present invention, this embodiment provides some experimental results obtained using the embodiments. Figure 3 The waveform of the DC bus voltage dynamic process suppressed by the method of this invention is presented. Within 0-1s, without the control method proposed in this invention, the peak-to-peak value of the DC bus voltage ripple is 17.17V, exhibiting significant ripple fluctuations at twice the power frequency; the effective values ​​of the three-phase voltages are 50V, 110V, and 110V, respectively, and the DC component of the DC bus voltage is 300V. The effective values ​​of the grid-side three-phase currents are 11.6A, 10.8A, and 11.4A, respectively, with total harmonic distortion rates of 4.6%, 4.5%, and 4.5%, indicating severe current distortion. After 1.1s, the negative sequence command current calculation of this method is completed. Thereafter, the peak-to-peak value of the DC bus voltage ripple is 0.8V, and the ripple fluctuations at twice the power frequency are effectively suppressed; the amplitudes of the third harmonic currents in the three-phase currents are 0.017A, 0.016A, and 0.016A, respectively, and the three-phase current THDs are 1.0%, 1.0%, and 1.1%, respectively, showing a significant reduction in current harmonics.

[0070] The experimental results obtained in this embodiment demonstrate that the method described in this invention can not only effectively suppress DC bus voltage ripple, but also effectively eliminate grid-side current harmonics. Moreover, the process does not require parameters such as grid-side voltage and inductance, and has strong robustness.

[0071] This invention may be embodied in other specific forms without departing from its spirit or essential characteristics. The described embodiments are to be considered in all respects as illustrative rather than restrictive, for example:

[0072] 1) The application topologies include various types of three-phase rectifiers;

[0073] 2) Rated operating power of the rectifier;

[0074] 3) Design of the negative sequence disturbance current disturbance coefficient;

[0075] 4) Selection of various parameters, etc.

[0076] Therefore, the scope of this invention is indicated by the appended claims rather than the foregoing description. All variations falling within the meaning and scope of equivalent technical solutions of the claims are included within its scope.

Claims

1. A data-driven method for suppressing DC bus voltage ripple in a three-phase PWM rectifier, wherein the input of the three-phase PWM rectifier is a three-phase power supply, the three-phase power supply is connected to one end of a three-phase inductor, the other end of the three-phase inductor is connected to the midpoint of the bridge arm of a three-phase full-bridge rectifier, the upper and lower ends of the three-phase full-bridge rectifier are the positive and negative terminals of the DC bus output, which are respectively connected to the positive and negative terminals of a DC bus capacitor, and the voltage between the two terminals is the DC bus voltage, comprising the following steps: (1) Calculation of negative sequence active current disturbance value: Calculate the disturbance value of the negative sequence active current under two disturbances based on the positive sequence active current; (2) Observation of DC bus voltage ripple amplitude under undisturbed conditions: The DC bus voltage ripple is extracted by a bandpass filter, and then the DC bus voltage ripple amplitude is observed under undisturbed conditions; (3) First disturbance of negative sequence active current: The first disturbance value of negative sequence active current calculated in step (1) is used as the command current to control the change of DC bus voltage ripple, and the amplitude of the corresponding DC bus voltage ripple is observed. (4) Secondary disturbance of negative sequence active current: The second disturbance value of negative sequence active current calculated in step (1) is used as the command current to control the change of DC bus voltage ripple, and the amplitude of the corresponding DC bus voltage ripple is observed. (5) Calculation and injection of negative sequence active current command value: Based on the aforementioned negative sequence active current disturbance value and the corresponding DC bus voltage ripple amplitude, calculate the negative sequence active current command value that can suppress DC bus voltage ripple, and inject it as the current command to the grid side current. (6) Change the negative sequence active current in the above steps to negative sequence reactive current, and repeat steps (1) to (5). In step (1), while ensuring system stability, the DC bus voltage ripple amplitude is changed by perturbing the negative sequence current. The two perturbation values ​​of the negative sequence current are determined according to the following formula. in, , These are the two disturbance values ​​of the negative sequence current, respectively. , The disturbance coefficient is... This is the positive sequence active current; In steps (2), (3), and (4), the DC bus voltage ripple amplitude is calculated according to the following formula. U d c _ a c = ∑ i = 1 N u d c _ B P F i 2 N in, This represents the DC bus voltage ripple amplitude. N The number of voltage samples per power frequency cycle. For the bandpass filter i One output value; In step (5), let the second ripple amplitude of the DC bus voltage be... i The observed values ​​are Negative sequence active current command value No. i The observed values ​​are The total number of observations is n The data obtained from the sample is calculated according to the following formula. , , The estimated value , , , in, d The fundamental angular frequency of the grid voltage DC component in DC bus voltage DC bus capacitance constant C The decision, its expression is, In step (5), the negative sequence command current is calculated according to the following formula. 。

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