Energy storage converter and direct current component suppression method and device thereof
By superimposing a DC suppression controller in the dual closed-loop control of the energy storage converter, the d-axis and q-axis components of the three-phase AC current are processed. The PR controller is used to adjust the current reference value, which solves the complex problem of DC component suppression, achieves fast response and stable DC component suppression effect, reduces hardware cost and improves power quality.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-08-28
- Publication Date
- 2026-03-13
AI Technical Summary
Existing energy storage converters generate DC components at their AC output ports, leading to increased power grid equipment losses and safety and stability issues. Existing hardware and software suppression methods are complex and costly.
A DC suppression controller is superimposed in the dual closed-loop control of the converter. By acquiring and processing the d-axis and q-axis components of the three-phase AC current, the PR controller is used to adjust the current reference value to suppress the DC component, thereby achieving fast response and real-time control.
It effectively suppresses DC components, reduces hardware costs, improves power quality, enhances the reliability and performance of converters, and adapts to stable operation under different working conditions.
Smart Images
Figure CN121663517A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of converter control technology, specifically relating to an energy storage converter and its DC component suppression method and device. Background Technology
[0002] Most existing industrial and commercial energy storage converters employ PWM modulation. However, due to factors such as asymmetrical capacitor distribution, control logic errors, and the non-ideal nature of switching elements, a DC component is generated at the AC output port during actual operation. Injecting this DC component into the power grid can cause significant damage to grid equipment. For example, DC injection into a transformer can cause DC bias, leading to severe distortion of the excitation current, increased harmonic content, and increased losses, ultimately resulting in a voltage drop in the power grid system and affecting its safe and stable operation. The "Technical Requirements for Energy Storage Converters in Electrochemical Energy Storage Systems" clearly stipulates that under grid-connected operation conditions and at rated power, the DC current component in the AC port current should not exceed 0.5% of the rated AC port current.
[0003] To address the issue of excessive DC component, existing technologies typically involve connecting filters or series capacitor couplers to the AC output ports of commercial and industrial energy storage converters. However, this requires adding or modifying components, and the AC fundamental voltage flowing through the capacitors and filters can cause significant voltage drops, affecting the size, efficiency, structural layout, and hardware cost of the energy storage converter.
[0004] The added hardware significantly increases the cost of energy storage converters, and the structural layout of energy storage converters needs to be redesigned, which is also costly. Therefore, methods using software-level control algorithms have emerged. However, existing DC component suppression methods usually involve mathematical calculations and injecting reverse harmonic components of a specific frequency into the output AC current, which is quite complex. Summary of the Invention
[0005] The purpose of this invention is to provide an energy storage converter and its DC component suppression method and apparatus to solve the technical problem of complex calculations in existing DC component suppression methods.
[0006] To solve the above-mentioned technical problems, the present invention provides a method for suppressing the DC component of an energy storage converter. The method includes: obtaining the d-axis and q-axis components of the DC offset in the three-phase AC current at the AC output port of the energy storage converter; subtracting the d-axis and q-axis components of the DC offset from the d-axis and q-axis reference DC components respectively to obtain the d-axis and q-axis DC component deviations; inputting the d-axis and q-axis DC component deviations into corresponding DC suppression controllers, wherein the output of the DC suppression controller is superimposed on the current reference value of the inner current loop control in the dual closed-loop control of the energy storage converter.
[0007] The beneficial effects of the above technical solution are as follows: The technical solution of the DC component suppression method for energy storage converters of the present invention belongs to an improved invention. Based on the existing dual-closed-loop control of converters, the present invention superimposes a current reference value (i.e., the output of the DC suppression controller) required to eliminate the DC component onto the reference value of the inner current loop control. Only one control variable is added to the original control algorithm, which does not significantly burden the original control, and enables real-time control and rapid response. The present invention solves the technical problem of complex calculations in existing DC component suppression methods.
[0008] Furthermore, the d-axis and q-axis components of the DC offset are obtained as follows: the DC offset is obtained by subtracting the three-phase AC current at the AC output port of the energy storage converter from the theoretical three-phase current; the d-axis and q-axis components of the DC offset are obtained by performing a dq coordinate transformation on the DC offset.
[0009] Furthermore, the reference DC components for both the d-axis and q-axis are 0.
[0010] Furthermore, the DC suppression controllers corresponding to the DC component deviations of the d-axis and q-axis are both PR controllers.
[0011] Furthermore, the three-phase AC current at the AC output port of the energy storage converter is obtained by processing the original measured value through a low-pass filter.
[0012] Furthermore, the method also includes an averaging process: the DC component deviations of the d-axis and q-axis are averaged before being input into the corresponding DC suppression controller.
[0013] The present invention also provides a technical solution for a DC component suppression device for an energy storage converter: a DC component suppression device for an energy storage converter includes a processor, the processor being used to execute a computer program to implement the steps of the DC suppression method for the energy storage converter as described above.
[0014] The present invention also provides a technical solution for an energy storage converter: an energy storage converter including an energy storage converter controller, wherein the energy storage converter controller is used to execute a computer program to implement the steps of the DC component suppression method of the energy storage converter as described above. Attached Figure Description
[0015] Figure 1 This is a flowchart of the control loop in an embodiment of the DC suppression method for the energy storage converter of the present invention;
[0016] Figure 2 This is a control block diagram of an embodiment of the DC suppression method for the energy storage converter of the present invention. Detailed Implementation
[0017] This invention, based on existing dual-loop control for converters, superimposes a current reference value (i.e., the output of the DC suppression controller) needed to eliminate the DC component onto the reference value of the inner current loop control. It adds only one control variable to the original control algorithm, without significantly burdening the original control, and achieves real-time control and rapid response. This invention solves the technical problem of complex calculations in existing DC component suppression methods.
[0018] Example of DC component suppression method for energy storage converter:
[0019] A method for suppressing the DC component of an energy storage converter includes: acquiring the d-axis and q-axis components of the DC offset in the three-phase AC current at the AC output port of the energy storage converter; subtracting the d-axis and q-axis components of the DC offset from the d-axis and q-axis reference DC components, respectively, to obtain the d-axis and q-axis DC component deviations; inputting the d-axis and q-axis DC component deviations into corresponding DC suppression controllers, wherein the output of the DC suppression controller is superimposed on the current reference value of the inner current loop control in the dual closed-loop control of the energy storage converter.
[0020] like Figure 1 As shown, the method includes sampling, low-pass filtering, DC component extraction, error calculation, averaging, and controller circuitry. Finally, the current waveform is fed into the control inner loop and comprehensively adjusted by the core control unit of the industrial and commercial energy storage converter.
[0021] The sampling stage collects the AC current at the output port of the energy storage converter and the reference AC voltage on the grid side. The sampling stage uses three current sensors and three voltage sensors to collect the three-phase output AC current and three-phase grid voltage of the industrial and commercial energy storage converter. The low-pass filtering stage filters out high-frequency components mixed in the collected current signal to prevent high-frequency noise or stray components in the feedback signal from amplifying errors and causing instability in the closed-loop control. The DC component extraction stage calculates the DC offset by subtracting the collected three-phase current from the theoretical three-phase current. The error calculation stage sets the target value of the reference DC component to zero. (Or close to 0), and calculate the DC component deviation of the three-phase output current of the industrial and commercial energy storage converter; the averaging process averages the DC component deviation over a specified period to prevent overshoot caused by output current fluctuations; the controller inputs the average deviation value of the input DC component into the PR (proportional resonance) controller (i.e., DC suppression controller) to obtain the reference adjustment value of the control inner loop current; the control inner loop integrates the current reference values obtained from the various outer loop controls of the industrial and commercial energy storage converter, including DC component suppression, and finally adjusts the output waveform to achieve effective suppression of the DC component.
[0022] The control block diagram of the DC component suppression method for the energy storage converter in this implementation is as follows: Figure 2 As shown in the figure, V ac V is the mains voltage; ac_dq I represents the d / q-axis components of the grid voltage. out I represents the three-phase AC current at the AC output port of the energy storage converter. dc DC component deviation; I ref To control the inner loop current reference value (i.e., the output of the PR controller); I ac_ref This represents the theoretical three-phase current.
[0023] Specifically, the theoretical three-phase current consists of three sinusoidal signals with a phase difference of 120°.
[0024] First, the sampling process uses three current sensors and a voltage sensor to sample the average value of the three-phase output current and three-phase grid voltage of the industrial and commercial energy storage converter over two power frequency cycles. The collected output current I of the energy storage converter is then converted into the average value of the average value of the three-phase output current and the average value of the three-phase grid voltage. out and grid voltage V ac The signal is transmitted to the main control chip DSP (Digital Signal Processor) for subsequent calculations. This method has relatively lower accuracy requirements for the current sensor compared to DC suppression methods such as mathematical operations and injecting reverse specific frequency harmonic components into the output AC current.
[0025] Then, the three-phase output current I of the energy storage converter sampled in the previous stage is filtered out by a low-pass filter stage. outThe inclusion of high-frequency components and noise prevents current signal fluctuations or jitters caused by high-frequency components from intermittently increasing errors. Low-pass filtering can ensure smooth changes in the three-phase current acquisition signal and improve the stability of current feedback closed-loop control.
[0026] In other implementations, other filters or filtering algorithms with the same function can be used, such as mean filtering.
[0027] The next step is the DC component extraction stage, which extracts the three-phase current I after it has been processed by a low-pass filter. out Compared with the theoretical three-phase current I ac_ref The DC offset is obtained by subtracting the values.
[0028] The next step is error calculation, which consists of two steps. Step 1: Perform Clarke / Park transformation (i.e., dq coordinate transformation) on the DC offset to obtain the d-axis and q-axis components of the DC offset. Then, use a phase-locked loop (PLL in the diagram) to control the phase difference between the input and output of the dq coordinate transformation. The reference phase of the PLL is obtained from the three-phase voltage of the power grid, ensuring that the transformed DC offset can stably track the grid frequency and phase, guaranteeing that the industrial and commercial energy storage converter can operate synchronously with the grid. Step 2: Calculate the error between the d-axis and q-axis components of the DC offset and the reference DC components for the d-axis and q-axis, respectively, as the DC component deviation I. dc .
[0029] In this embodiment, the d-axis and q-axis components of the DC offset are obtained as follows: the DC offset is obtained by subtracting the three-phase AC current at the AC output port of the energy storage converter from the theoretical three-phase current; the d-axis and q-axis components of the DC offset are obtained by performing a dq coordinate transformation on the DC offset.
[0030] In other embodiments, the d-axis and q-axis components of the DC offset can also be obtained as follows: the three-phase AC current and the theoretical three-phase current at the AC output port of the energy storage converter are first transformed into dq coordinates, and the d-axis and q-axis components of the obtained converter output current are subtracted from the d-axis and q-axis components of the theoretical three-phase current to obtain the d-axis and q-axis components of the DC offset.
[0031] Next is the averaging process, which takes the average value of the DC component deviation of 3 to 5 adjacent sampling periods and performs averaging to obtain the average feedback value of the DC component, which can effectively prevent overshoot problems caused by output current fluctuations.
[0032] In other implementations, other algorithms such as Gaussian filtering may be used to prevent overshoot problems, or no processing may be performed.
[0033] Next, the averaged DC component deviation is input into the PR controller, and the calculated value is the current reference value I required to eliminate the DC component. ref .
[0034] In this embodiment, the DC suppression controller is a PR (proportional-resonant) controller to utilize the better AC current tracking capability of the PR controller. In other embodiments, the DC suppression controller may also employ other closed-loop control algorithms such as PI (proportional-integral) controller, PID (proportional-integral-derivative) controller, and PIR (proportional-integral-resonant) controller.
[0035] Finally, the output of the PR controller is superimposed on the current reference value of the current control inner loop. After the control inner loop integrates the reference values given by the outer loop control, such as PQ (constant active and reactive power) control and DC component suppression control, the output current waveform of the industrial and commercial energy storage converter is adjusted, and DC component suppression control is finally achieved.
[0036] Example of a DC component suppression device for an energy storage converter:
[0037] A DC component suppression device for an energy storage converter includes a processor for executing a computer program to implement the steps of the DC component suppression method for the energy storage converter as described above. The specific DC component suppression method for the energy storage converter has been described in sufficient detail in the above-described embodiments and will not be repeated here.
[0038] Energy storage converter example:
[0039] An energy storage converter includes an energy storage converter controller, which executes a computer program to implement the steps of the DC component suppression method for the energy storage converter as described above. The specific DC component suppression method for the energy storage converter has been described in sufficient detail in the above-described embodiments and will not be repeated here.
[0040] This invention has the following characteristics:
[0041] The advantages of this invention lie in its use of current feedback closed-loop control technology, taking the output current as a variable for real-time tracking control and dynamic adjustment. DC components are suppressed in the control stage without requiring further hardware adjustments, achieving a balance between size and reduced hardware costs associated with suppressing DC components. This improves the power quality of the output current of the commercial and industrial energy storage converter and effectively reduces the DC components carried by the output of each stage at the converter's front end in the energy storage system. The proposed method adds a control variable to the existing control algorithm without significantly burdening the original control. It enables real-time control and rapid response, automatically adapting to different operating conditions based on real-time load changes and environmental conditions. It is unaffected by harmonic pollution or power factor changes caused by external conditions. This suppression method maintains efficient and stable operation under various operating conditions, significantly improving the reliability and performance of commercial and industrial energy storage converters. It has advantages such as low cost, good effect, and easy adjustment, and possesses high engineering application value and economic benefits. It also boasts the advantages of simple algorithm and high versatility.
[0042] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still make modifications to the technical solutions described in the foregoing embodiments without creative effort, or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.
Claims
1. A method for suppressing the DC component of an energy storage converter, characterized in that, The method includes: acquiring the d-axis and q-axis components of the DC offset in the three-phase AC current at the AC output port of the energy storage converter; subtracting the d-axis and q-axis components of the DC offset from the d-axis and q-axis reference DC components respectively to obtain the d-axis and q-axis DC component deviations; inputting the d-axis and q-axis DC component deviations into the corresponding DC suppression controllers, wherein the output of the DC suppression controllers is superimposed on the current reference value of the inner current loop control in the dual closed-loop control of the energy storage converter.
2. The DC component suppression method for the energy storage converter according to claim 1, characterized in that, The d-axis and q-axis components of the DC offset are obtained as follows: the DC offset is obtained by subtracting the three-phase AC current from the theoretical three-phase current at the AC output port of the energy storage converter; the d-axis and q-axis components of the DC offset are obtained by performing a dq coordinate transformation on the DC offset.
3. The DC component suppression method for the energy storage converter according to claim 1, characterized in that, The reference DC components for both the d-axis and q-axis are 0.
4. The DC component suppression method for an energy storage converter according to claim 1, 2, or 3, characterized in that, The DC suppression controllers corresponding to the DC component deviations of the d-axis and q-axis are both PR controllers.
5. The DC component suppression method for an energy storage converter according to claim 1, 2, or 3, characterized in that, The three-phase AC current at the AC output port of the energy storage converter is obtained by processing the original measured value through a low-pass filter.
6. The DC component suppression method for an energy storage converter according to claim 1, 2, or 3, characterized in that, The method also includes an averaging process: the DC component deviations of the d-axis and q-axis are averaged before being input into the corresponding DC suppression controller.
7. A DC component suppression device for an energy storage converter, comprising a processor, characterized in that, The processor is used to execute a computer program to implement the steps of the DC component suppression method for the energy storage converter as described in any one of claims 1 to 6.
8. An energy storage converter, comprising an energy storage converter controller, characterized in that, The energy storage converter controller is used to execute a computer program to implement the steps of the DC component suppression method for the energy storage converter as described in any one of claims 1 to 6.