A control method and system for harmonic self-compensation of a direct-current charging pile

Abstract

The application discloses a control method for harmonic self-compensation of a direct-current charging pile, which is applied to a Vienna type direct-current charging pile, comprises a first module and a second module, and both of the modules comprise one or more Vienna type topology rectifying units, and comprises the following steps: controlling the first module to output reactive power to the outside; sampling input current of the first module and extracting harmonics; generating a harmonic compensation reference voltage according to the harmonics generated by the first module; and controlling the second module to output harmonics of the same amplitude and opposite phase with the harmonics generated by the first module according to the harmonic compensation reference voltage. Through the two modules electrically connected and both comprising the Vienna type topology rectifying unit, one of the modules is controlled to output reactive power to the outside, and the other module is enabled to track and analyze the harmonic current generated when the one module outputs the reactive power and generate the harmonic of the same amplitude and opposite phase, so that the Vienna type direct-current charging pile can stably output the reactive power and absorb harmonic pollution.

Description

Technical Field

[0001] This invention relates to the field of circuits, and in particular to a control method and system for harmonic self-compensation of DC charging piles. Background Technology

[0002] In recent years, with the continuous increase of high-power nonlinear loads in power grid construction, the reactive power impact and harmonic pollution of the power grid have been rising. The power grid as a whole shows the phenomenon of insufficient reactive power compensation capacity or unreasonable configuration. In order to deal with reactive power impact and harmonic pollution, it is often necessary to install devices such as SVC (Static Var Compensator), STATCOM (Static Synchronous Compensator), and APF (Active Power Filter) in the power grid.

[0003] With the rise of the electric vehicle industry, electric vehicle charging stations have been built in various places. However, electric vehicle DC charging piles contain a large number of power electronic devices. When used only for charging, they become high-power nonlinear loads, which have a significant impact on the power distribution network. This not only increases the burden on the power distribution network but may also bring new harmonic pollution and reduce the power factor of the power distribution network.

[0004] Among them, the VIENNA rectifier has advantages such as high power factor, low THD (total harmonic distortion) of input current, fewer switching devices, low switching stress, no switching dead zone problem and high reliability. It is particularly suitable for medium and high power applications with unidirectional energy flow, and therefore it is widely used in the charging modules of DC charging piles for electric vehicles.

[0005] However, due to its unique topology, the VIENNA rectifier topology has significant limitations when used in circuit structures for conventional harmonic compensation and reactive power regulation in power distribution networks. Specifically, when providing reactive power support, the phase angle of the three-phase rectifier bridge input voltage lags behind the phase of the three-phase input current, resulting in errors in the modulated power switch pulse signals. This leads to severe distortion of the three-phase input current, making it difficult to effectively suppress harmonic pollution caused by the reactive power output of charging piles using conventional modulation methods alone. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a control method and system for harmonic self-compensation of DC charging piles, so as to control the VIENNA type DC charging piles to both stably output reactive power and absorb harmonic pollution.

[0007] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: A control method for harmonic self-compensation in a DC charging pile, applied to a Vienna-type DC charging pile, wherein the Vienna-type DC charging pile includes a first module and a second module, both the first module and the second module including one or more Vienna-type topology rectifier units, comprising the following steps: S1. Control the first module to output reactive power; S2. Sample the input current of the first module and extract the harmonics; S3. Generate a harmonic compensation reference voltage based on the harmonics generated by the first module; S4. Control the second module to output a harmonic that is equal in amplitude and opposite in phase to the harmonic generated by the first module according to the harmonic compensation reference voltage; Both the first module and the second module include one or more Vienna topology rectifier units.

[0008] To solve the above-mentioned technical problems, another technical solution adopted by the present invention is as follows: A control system for harmonic self-compensation of a DC charging pile includes a first module, a second module, and a processing module; The first module and the second module are electrically connected; Both the first module and the second module include one or more Vienna topology rectifier units; The processing module controls the first module and the second module to execute the steps in a control method for harmonic self-compensation of a DC charging pile.

[0009] The beneficial effects of this invention are as follows: It provides a control method and system for harmonic self-compensation of DC charging piles. Through two electrically connected modules, both of which contain Vienna-type topology rectifier units, one module is controlled to output reactive power, while the other module is activated to track and analyze the harmonic current generated when the first module outputs reactive power and generate harmonics of equal amplitude and opposite direction. Since both modules contain Vienna-type rectifier topology units, they are compatible when generating harmonic currents, which can avoid the phenomenon of incorrect modulation of power switching pulse signals due to phase difference. Thus, the VIENNA-type DC charging pile can stably output reactive power while absorbing harmonic pollution. Attached Figure Description

[0010] Figure 1 This is a flowchart of a control method for harmonic self-compensation of a DC charging pile according to an embodiment of the present invention; Figure 2 This is an architecture diagram of a harmonic self-compensation control system for a DC charging pile according to an embodiment of the present invention. Figure 3 This is a circuit topology diagram of the Vienna-type DC charging device in an embodiment of the present invention; Figure 4 This is a detailed architecture diagram of the dual closed-loop control unit and the harmonic compensation control unit of a DC charging pile harmonic self-compensation control system according to an embodiment of the present invention. Figure 5 This is a schematic diagram of the second module tracking the d-axis and q-axis components of the first module in an embodiment of the present invention.

[0011] Figure 6 The waveform diagram of the input current and input voltage of phase a after the first module outputs reactive power in an embodiment of the present invention is shown. Figure 7 This is the three-phase input current waveform of the charging pile without harmonic self-compensation in this embodiment of the invention; Figure 8 This is a schematic diagram of the harmonic content of the charging pile input current without harmonic self-compensation in an embodiment of the present invention (the vertical axis represents the percentage of each harmonic component relative to the fundamental wave). Figure 9 The diagram shows the three-phase input current waveforms of the charging pile after self-compensation for the 5th and 7th harmonics in an embodiment of the present invention. Figure 10 This is a schematic diagram of the harmonic content of the charging pile input current after self-compensation of the 5th and 7th harmonics in an embodiment of the present invention. Detailed Implementation

[0012] To explain in detail the technical content, objectives, and effects of the present invention, the following description is provided in conjunction with the embodiments and accompanying drawings.

[0013] Please refer to Figure 1 A control method for harmonic self-compensation in a DC charging pile, applied to a Vienna-type DC charging pile, wherein the Vienna-type DC charging pile includes a first module and a second module, both the first module and the second module including one or more Vienna-type topology rectifier units, comprising the following steps: S1. Control the first module to output reactive power; S2. Sample the input current of the first module and extract the harmonics; S3. Generate a harmonic compensation reference voltage based on the harmonics generated by the first module; S4. Control the second module to output a harmonic that is equal in amplitude and opposite in phase to the harmonic generated by the first module according to the harmonic compensation reference voltage.

[0014] As can be seen from the above description, the beneficial effects of the present invention are as follows: by controlling two modules, both of which contain Vienna-type topology rectifier units, to output reactive power, one module is controlled to output reactive power, while the other module is enabled to track and analyze the harmonic current generated when the first module outputs reactive power and generate harmonics of equal amplitude and opposite to it. Since both modules contain Vienna-type rectifier topology units, they are compatible when generating harmonic currents, which can avoid the phenomenon of incorrect modulation of power switching pulse signals due to phase difference. Thus, the VIENNA type DC charging pile can stably output reactive power while absorbing harmonic pollution.

[0015] Further, step S2 specifically includes: S21. When the current of the first module enters a steady state, the input current of the first module is sampled; S22. Harmonic feature vectors are extracted from the input current of the first module obtained by sampling using a harmonic extraction algorithm.

[0016] As described above, due to the phase difference in the reactive power output of the Vienna rectifier topology unit, sampling the input current of the first module requires waiting for the input current of the first module to reach a steady state. Simultaneously, a harmonic extraction algorithm is used to extract the harmonic feature vector of the input current of the first module. Specifically, Fourier series or least squares methods can be used as harmonic extraction algorithms to extract harmonic orders that have a significant impact on reactive power in practical applications.

[0017] Further, step S22 specifically includes: S221. Use a harmonic extraction algorithm to extract the harmonics of the input current of the first module obtained by sampling; S222. Based on the dq two-phase rotating coordinate system, the harmonics are subjected to phase-locking and coordinate transformation to obtain the characteristic vector of the harmonics of the first module; the characteristic vector includes the d-axis component, q-axis component and instantaneous phase angle of the harmonics.

[0018] As can be seen from the above description, in order to effectively extract the harmonics generated by the first module, a two-phase rotating coordinate system of dq is used to perform phase-locking and coordinate transformation on the harmonics, thereby obtaining the d-axis component, q-axis component and instantaneous phase angle of the extracted harmonics.

[0019] Further, step S3 specifically includes: S31. Take the opposite values ​​of the d-axis and q-axis components of the harmonics in the first module, and combine them with the instantaneous phase angle of the harmonics to synthesize the harmonic compensation input reference value. S32. Sample the input current of the second module and extract the feature vector of the harmonics of the second module after sampling; S33. Generate a harmonic compensation reference voltage by combining the harmonic compensation input reference value and the characteristic vector of the harmonics in the second module.

[0020] As described above, in order to self-compensate the harmonics generated by the first module, it is necessary to control the second module to generate equal-amplitude reverse harmonics. However, due to deviations in the harmonic current output by the second module during actual operation, it is necessary to combine the harmonic compensation input reference value obtained from the first module to eliminate the deviation. Specifically, a PI controller (linear controller) can be used to compare the harmonic compensation input reference value with the characteristic vector of the harmonics output by the second module, and the harmonic compensation reference voltage can be finally determined through coordinate transformation.

[0021] Further, step S32 specifically includes: S321. Sample and extract harmonics from the input current of the second module, and use a harmonic extraction algorithm to extract harmonics from the sampled input current of the second module. S322. Based on the dq two-phase rotating coordinate system, the harmonics are subjected to phase-locked loop and coordinate transformation to obtain the characteristic vector of the harmonics of the second module. As can be seen from the above description, in order to effectively extract the harmonics generated by the second module, the same dq two-phase rotating coordinate system is used to perform phase-locking and coordinate transformation on the harmonics, just like the first module, so as to obtain the d-axis component, q-axis component and instantaneous phase angle of the harmonics.

[0022] Further, step S4 specifically includes: S41. Obtain the fundamental three-phase reference voltage of the second module and superimpose it with the harmonic compensation reference voltage to obtain a pulse voltage; S42. Based on the pulse voltage, control the space voltage vector pulse width modulation unit to generate a pulse signal; S43. Control the second module to output a harmonic with the same amplitude but opposite phase as the harmonic generated by the first module according to the pulse signal.

[0023] As can be seen from the above description, since both the first module and the second module have the function of outputting power to the outside in the DC charging pile, it is also necessary to consider the weak three-phase reference voltage during the operation of the second module, and superimpose it with the harmonic compensation reference voltage in the above steps to generate the pulse voltage of the input space voltage vector pulse width modulation unit (SVPWM); finally, the SVPWM generates a pulse signal according to the pulse voltage, and the switching unit in the second module outputs a harmonic with the same amplitude and opposite to that of the first module according to the pulse signal.

[0024] Further, step S1 specifically includes: The fundamental frequency of the input current of the first module is controlled to generate an orthogonal component greater than 0.

[0025] As can be seen from the above description, in order to enable the first module to output reactive power, based on the Vienna topology rectifier unit, the fundamental wave of the input current of the first module is controlled to generate an orthogonal component greater than 0, and the phase of the three-phase input current is actively made to lead the three-phase input voltage, so that the first module outputs reactive power without affecting the charging function.

[0026] Please refer to Figure 2 and Figure 3 A control system for harmonic self-compensation of DC charging pile, comprising a first module, a second module and a processing module; The first module and the second module are electrically connected; Both the first module and the second module include one or more Vienna topology rectifier units; The processing module controls the first module and the second module to execute the steps in a control method for harmonic self-compensation of a DC charging pile.

[0027] As described above, the execution system of the control method for harmonic self-compensation of DC charging piles is provided. It controls one of the modules, which both contain Vienna topology rectifier units, to output reactive power through two electrically connected modules. At the same time, the other module is activated to track and analyze the harmonic current generated when the first module outputs reactive power and generate harmonics of equal amplitude and opposite to it. By utilizing the adaptiveness of the harmonic current generated by the two modules, harmonic self-compensation control is performed on the charging pile using the Vienna topology rectifier unit.

[0028] Furthermore, such as Figure 4 As shown, the second module also includes a fundamental closed-loop control unit, a harmonic compensation unit, and a space voltage vector pulse width modulation unit; The fundamental closed-loop control unit is used to generate the fundamental three-phase reference voltage of the second module; The harmonic compensation unit is used to generate a harmonic compensation reference voltage. The space voltage vector pulse width modulation unit is used to generate pulse signals.

[0029] As can be seen from the above description, in order to enable the second module to self-compensate the harmonics generated by the first module, it is necessary to detect and control the fundamental wave of the second module, and at the same time, the first module needs to generate a harmonic compensation voltage. Therefore, a fundamental wave closed-loop control unit and a harmonic compensation unit are set in the second module. The two synthesize the final pulse voltage input to the space voltage vector pulse width modulation unit to generate a pulse signal, which is used to generate the corresponding harmonics.

[0030] Furthermore, the second module also includes a switching unit that generates a three-phase harmonic current based on the pulse signal.

[0031] As can be seen from the above description, in order to receive pulse signals and generate corresponding harmonics, the second module is also equipped with a switching unit to generate the required harmonics based on the input pulse signal.

[0032] This invention provides a control method and system for harmonic self-compensation in DC charging piles, mainly applied in DC charging piles based on Vienna topology rectification. The following is a detailed description with reference to embodiments: Example 1: Please refer to Figure 1 A control method for harmonic self-compensation in a DC charging pile, applied to a Vienna-type DC charging pile, wherein the Vienna-type DC charging pile includes a first module and a second module, both of which include one or more Vienna-type topology rectifier units, and includes the following steps: S1. Control the first module to output reactive power; S2. Sample the input current of the first module and extract harmonics; S3. Generate a harmonic compensation reference voltage based on the harmonics generated by the first module; S4. Control the second module to output harmonics with the same amplitude but opposite phase as the harmonics generated by the first module, based on the harmonic compensation reference voltage.

[0033] Both the first and second modules include one or more Vienna-type topology rectifier units. Since both modules contain Vienna-type rectifier topology units, they are compatible when generating harmonic currents. By controlling one module to output reactive power, the other module is enabled to track and analyze the harmonic current generated when the first module outputs reactive power and generate harmonics of equal amplitude and opposite to it. This avoids the phenomenon of incorrect modulation of power switch pulse signals due to phase difference. In this embodiment, the VIENNA DC charging pile can stably output reactive power while absorbing harmonic pollution.

[0034] Specifically, step S1 is as follows: The fundamental frequency of the input current of the first module is controlled to generate an orthogonal component greater than 0.

[0035] In order to enable the first module to output reactive power, based on the Vienna topology rectifier unit, the fundamental wave of the input current of the first module is controlled to generate a quadrature component greater than 0, and the phase of the three-phase input current is actively made to lead the three-phase input voltage, so that the first module outputs reactive power without affecting the charging function.

[0036] Example 2: Based on Example 1, step S2 specifically includes: S21. When the current of the first module enters a steady state, the input current of the first module is sampled. Since there is a phase difference when the Vienna rectifier topology unit outputs reactive power, the input current of the first module needs to be sampled after the input current of the first module enters a steady state. S22. Harmonic feature vectors are extracted from the input current of the first module obtained from sampling using a harmonic extraction algorithm. Specifically, Fourier series or least squares methods can be used as harmonic extraction algorithms to extract harmonics that have a significant impact on reactive power in practical applications.

[0037] Step S22 is as follows: S221. Use a harmonic extraction algorithm to extract the harmonics of the input current of the first module obtained from sampling; S222. Based on the dq two-phase rotating coordinate system, phase-locking and coordinate transformation are performed on the harmonics to obtain the characteristic vector of the harmonics of the first module; the characteristic vector includes the d-axis component, q-axis component, and instantaneous phase angle of the harmonics. That is, in this embodiment, in order to effectively extract the harmonics generated by the first module, the dq two-phase rotating coordinate system is used to perform phase-locking and coordinate transformation on the harmonics, thereby obtaining the d-axis component, q-axis component, and instantaneous phase angle of the extracted harmonics.

[0038] Example 3: Based on Example 2, step S3 specifically includes: S31. Take the opposite values ​​of the d-axis and q-axis components of the harmonics in the first module, and combine them with the instantaneous phase angle of the harmonics to synthesize the harmonic compensation input reference value. S32. Sample the input current of the second module and extract the characteristic vector of the harmonics of the second module after sampling. Since there is a deviation when the second module outputs harmonic current during actual operation, it is necessary to combine the harmonic compensation input reference value obtained from the first module to eliminate the deviation.

[0039] S33. Generate a harmonic compensation reference voltage by combining the harmonic compensation input reference value and the characteristic vector of the harmonics from the second module. Specifically, the harmonic compensation reference voltage can be determined by comparing the harmonic compensation input reference value with the characteristic vector of the harmonics output by the second module through a PI controller (linear controller) and by coordinate transformation.

[0040] Step S32 is as follows: S321. Sample and extract harmonics from the input current of the second module, and use the harmonic extraction algorithm to extract harmonics from the sampled input current of the second module. S322. Based on the dq two-phase rotating coordinate system, phase-locked loop and coordinate transformation are performed on the harmonics to obtain the characteristic vector of the harmonics in the second module. In this embodiment, in order to effectively extract the harmonics generated by the second module, the same dq two-phase rotating coordinate system is used to perform phase-locking and coordinate transformation on the harmonics, just like the first module, so as to obtain the d-axis component, q-axis component and instantaneous phase angle of the harmonics.

[0041] Example 4: Based on Example 3, step S4 specifically includes: S41. Obtain the fundamental three-phase reference voltage of the second module and superimpose it with the harmonic compensation reference voltage to obtain the pulse voltage. Since both the first and second modules have the function of outputting power to the outside in the DC charging pile, the weak three-phase reference voltage of the second module during operation also needs to be considered. S42. Based on the pulse voltage, control the space voltage vector pulse width modulation unit to generate a pulse signal; that is, superimpose it with the harmonic compensation reference voltage in the above steps to generate the pulse voltage of the input space voltage vector pulse width modulation unit (SVPWM); S43. Control the second module to output a harmonic that is equal in amplitude and opposite in phase to the harmonic generated by the first module according to the pulse signal.

[0042] Example 5: Please refer to Figure 2 and Figure 3 A harmonic self-compensation control system for DC charging piles includes a first module, a second module, and a processing module. The first and second modules are electrically connected. Both the first and second modules include one or more Vienna-type topology rectifier units. The processing module controls the first and second modules to execute the steps of any one of the harmonic self-compensation control methods for DC charging piles in Embodiments 1 to 4. Specifically, utilizing the adaptive nature of the harmonic current generated by the two modules, one module is controlled to output reactive power, while the other module tracks and analyzes the harmonic current generated when the first module outputs reactive power and generates harmonics of equal amplitude and opposite direction, thus performing harmonic self-compensation control on the charging pile using the Vienna-type topology rectifier unit.

[0043] Specifically, such as Figure 4 The second module also includes a fundamental closed-loop control unit, a harmonic compensation unit, a space voltage vector pulse width modulation unit, and a switching unit; the fundamental closed-loop control unit is used to generate the fundamental three-phase reference voltage of the second module; the harmonic compensation unit is used to generate the harmonic compensation reference voltage; and the space voltage vector pulse width modulation unit is used to generate pulse signals.

[0044] In this embodiment, to enable the second module to self-compensate for the harmonics generated by the first module, it is necessary to detect and control the fundamental frequency of the second module, and simultaneously generate a harmonic compensation voltage corresponding to the first module. Therefore, a fundamental frequency closed-loop control unit and a harmonic compensation unit are set in the second module. The two synthesize the final pulse voltage input to the space voltage vector pulse width modulation unit to generate a pulse signal, which is used to generate the corresponding harmonics. In order to receive the pulse signal and generate the corresponding harmonics, the second module also includes a switching unit to generate the required harmonics based on the input pulse signal.

[0045] Example 6: An example of a harmonic self-compensation control method for DC charging piles based on VIENNA rectification is as follows: A dual closed-loop control method for voltage and current in a two-phase rotating coordinate system (dq) is adopted. The VIENNA-type DC charging pile includes two charging modules: a first module and a second module. Each module consists of two VIENNA-type charging modules connected in parallel. The first module outputs reactive power, while the second module compensates for the 5th and 7th harmonics generated by the first module (these harmonics have a significant impact on the distribution network in practical applications; the 5th harmonic is a negative-sequence harmonic, and the 7th harmonic is a positive-sequence harmonic). The specific implementation steps are as follows: (1) When charging two electric vehicle power batteries at the same time using a charging pile, after the circuit enters a steady state and the charging current is stable, the q-axis reference current value Iq* of the two VIENNA type rectifier units in the first module is changed from 0 to a positive value (step S1), so that the phase of the three-phase input current of the first module of the charging pile leads the three-phase input voltage, and the charging pile outputs reactive power. At this time, the first module outputs harmonic current. The harmonic order is mainly 5, 7, 11, 13 and other 6k±1 harmonics. Among them, the 5th and 11th harmonics are negative sequence harmonics, and the 7th and 13th harmonics are positive sequence harmonics. In this example, the 5th and 7th harmonics are selected as the main influencing harmonics for adjustment.

[0046] (2) When the circuit re-enters steady state, the three-phase input current of the first module is sampled (step S21), and the 5th and 7th harmonic currents are extracted using harmonic extraction algorithms such as Fourier series or least squares. (3) The harmonic signals extracted in step (2) are subjected to phase-locked loop and coordinate transformation to obtain the d-axis component, q-axis component and instantaneous phase angle of the 5th and 7th harmonics respectively (step S22). (4) Take the opposite of the d-axis and q-axis components of the 5th and 7th harmonics and divide them by the number of Vienna topology rectifier units in the second module (2 in this example). Use them together with the instantaneous phase angle of the 5th and 7th harmonics as the harmonic compensation input reference value of the sub-module B (step S31). (5) Sample the three-phase input current of each sub-unit of the B group module (step S32), perform coordinate transformation on the instantaneous phase angle of the 5th and 7th harmonics to be compensated obtained in step (3), obtain the d and q axis components of the three-phase input current of each sub-unit in the B group, compare with the reference value obtained in step (3), and finally obtain the 5th and 7th harmonic reference voltage through PI control and coordinate transformation; (6) Add the 5th and 7th harmonic reference voltages obtained in step (5) to obtain the total harmonic compensation reference voltage (step S33). (7) The harmonic compensation reference voltage obtained in step (6) is added to the fundamental three-phase reference voltage obtained by the fundamental dual closed-loop unit control (step S41) and then sent to the SVPWM unit to obtain the pulse signal of the power switching unit (step S42). (8) The pulse signal controls the switching device in the second module to generate the required 5th and 7th harmonic currents. The harmonic currents are equal in magnitude and opposite in phase to the 5th and 7th harmonics generated by the first module. The two phases cancel each other out, and the charging pile does not emit 5th and 7th harmonics to the outside (step S43).

[0047] Following the steps above, a DC charging pile model based on VIENNA rectification was built in Matlab / Simulink. The simulation results of the example are analyzed below: In the simulation, the charging power is about 120kW (60kW for the first module and 60kW for the second module). The first module outputs about 10kvar of reactive power. The difference is that the first module outputs reactive power, while the second module compensates for the harmonics generated when the first module outputs reactive power. like Figure 5 As shown, the first module is set to start outputting reactive power at 0.1s, and the second module is activated at 0.4s to perform harmonic compensation control. The 5th and 7th harmonic components of the second module track the reference value of the first module.

[0048] like Figure 6 As shown, Ia_MA is the three-phase input current after the first module outputs reactive power. As can be seen from the waveform, the current is severely distorted at this time. like Figure 7 As shown, the three-phase input current of the charging pile is distorted at this time; like Figure 8 As shown, FFT (Fast Fourier Transform) analysis was performed at this time, and the total harmonic distortion (THD) of the charging pile input current reached 3.76%, of which the 5th and 7th harmonics contained 2.84% and 2.30%, respectively.

[0049] like Figure 9As shown, after using the second module to compensate for the 5th and 7th harmonics generated by the first module, the distortion of the three-phase input current waveform of the charging pile is significantly reduced.

[0050] like Figure 10 As shown, after compensation in the second module, FFT analysis was performed on the total harmonic distortion (THD) of the charging pile. The THD decreased from 3.76% to 1.10%, with the 5th and 7th harmonic content decreasing to 0.027% and 0.038%, respectively. This demonstrates that the DC charging pile harmonic self-compensation control method and system adopted in this invention achieves the effect of both stable reactive power output and harmonic pollution absorption in the VIENNA type DC charging pile.

[0051] In summary, this invention provides a control method and system for harmonic self-compensation of DC charging piles. It uses two electrically connected modules, each containing a Vienna-type topology rectifier unit. One module outputs reactive power, while the other module tracks and analyzes the harmonic current generated when the first module outputs reactive power, generating harmonics of equal amplitude and opposite direction. Since both modules contain Vienna-type rectifier topologies, their harmonic current generation is compatible, avoiding errors in the modulated power switch pulse signal due to phase difference. This ensures that the VIENNA-type DC charging pile can stably output reactive power while absorbing harmonic pollution.

[0052] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent modifications made based on the content of the present invention specification and drawings, or direct or indirect applications in related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A control method for harmonic self-compensation of a DC charging pile, applied to a Vienna-type DC charging pile, characterized in that: The Vienna-type DC charging pile includes a first module and a second module, both of which include one or more Vienna-type topology rectifier units, and includes the following steps: S1. Control the first module to output reactive power; S2. Sample the input current of the first module and extract the harmonics; S3. Generate a harmonic compensation reference voltage based on the harmonics generated by the first module; S4. Control the second module to output a harmonic that is equal in amplitude and opposite in phase to the harmonic generated by the first module according to the harmonic compensation reference voltage; Step S2 specifically involves: S21. When the current of the first module enters a steady state, the input current of the first module is sampled; S22. Harmonic feature vectors are extracted from the sampled input current of the first module using a harmonic extraction algorithm. Step S22 specifically involves: S221. Use a harmonic extraction algorithm to extract the harmonics of the input current of the first module obtained by sampling; S222. Based on the dq two-phase rotating coordinate system, phase-locked loop and coordinate transformation are performed on the harmonics to obtain the characteristic vector of the harmonics of the first module; the characteristic vector includes the d-axis component, q-axis component and instantaneous phase angle of the harmonics; Step S3 specifically involves: S31. Take the opposite values ​​of the d-axis and q-axis components of the harmonics in the first module, and combine them with the instantaneous phase angle of the harmonics to synthesize the harmonic compensation input reference value. S32. Sample the input current of the second module and extract the feature vector of the harmonics of the second module after sampling; S33. Generate a harmonic compensation reference voltage by combining the harmonic compensation input reference value and the characteristic vector of the harmonics in the second module; Step S32 specifically involves: S321. Sample and extract harmonics from the input current of the second module, and use a harmonic extraction algorithm to extract harmonics from the sampled input current of the second module. S322. Based on the dq two-phase rotating coordinate system, the harmonics are subjected to phase-locking and coordinate transformation to obtain the characteristic vector of the harmonics of the second module; Step S4 specifically involves: S41. Obtain the fundamental three-phase reference voltage of the second module and superimpose it with the harmonic compensation reference voltage to obtain a pulse voltage; S42. Based on the pulse voltage, control the space voltage vector pulse width modulation unit to generate a pulse signal; S43. Control the second module to output a harmonic with the same amplitude but opposite phase as the harmonic generated by the first module according to the pulse signal; Step S1 specifically involves: The fundamental frequency of the input current of the first module is controlled to generate an orthogonal component greater than 0.

2. A control system for harmonic self-compensation of a DC charging pile, characterized in that: It includes a first module, a second module, and a processing module; The first module and the second module are electrically connected; Both the first module and the second module include one or more Vienna topology rectifier units; The processing module controls the first module and the second module to execute the steps in the control method for harmonic self-compensation of a DC charging pile as described in claim 1.

3. The control system for harmonic self-compensation of a DC charging pile according to claim 2, characterized in that: The second module also includes a fundamental closed-loop control unit, a harmonic compensation unit, and a space voltage vector pulse width modulation unit; The fundamental closed-loop control unit is used to generate the fundamental three-phase reference voltage of the second module; The harmonic compensation unit is used to generate a harmonic compensation reference voltage. The space voltage vector pulse width modulation unit is used to generate pulse signals.

4. The control system for harmonic self-compensation of a DC charging pile according to claim 3, characterized in that: The second module also includes a switching unit that generates three-phase harmonic current based on the pulse signal.

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