Frequency and phase detection method and device suitable for multi-harmonic frequency conversion power grid

Abstract

The invention discloses a frequency and phase detection method and device suitable for a multi-harmonic frequency conversion power grid. The method comprises the following steps: step 1, carrying out ADC sampling on three-phase voltage of the power grid; 2, performing coordinate transformation on the three-phase voltage to obtain a power grid voltage under a two-phase static coordinate system; step 3, performing cascade delay signal elimination on the voltage signal, eliminating all harmonic components except target harmonic for the multi-harmonic frequency conversion power grid through CDSC modules, and setting a plurality of CDSC modules to respectively obtain fundamental wave and each harmonic component in the multi-harmonic frequency conversion power grid; 4, constructing a parameter identification system with a power grid frequency and phase estimator; 5, feeding back the frequency parameter obtained by the estimator to a cascade delay signal elimination module, and updating the delay time of the cascade delay signal elimination module; and step 6, circularly executing the step 2 to the step 5 until the output is stable. When facing a multi-harmonic frequency conversion power grid, the system can stably and accurately obtain the parameters of the fundamental wave and each harmonic wave.

Description

A method and apparatus for frequency and phase detection suitable for multi-harmonic frequency conversion power grids Technical Field

[0001] This invention belongs to the field of measuring electrical variables, specifically relating to a method and device for frequency and phase detection suitable for multi-harmonic frequency conversion power grids. Background Technology

[0002] With the rapid development of modern power grids, large-scale grid connection of new energy sources (such as wind power and photovoltaics) is underway, and these new energy sources are being transmitted to various regions through a vast power grid. This smart grid, based on power transmission systems and framed by the internet, will inevitably become the mainstream in the future. At the same time, this will also make the operating conditions of the power grid increasingly complex. When generating electricity using new energy sources, the output power is often unstable, generating a large number of harmonic components, posing a significant challenge to power quality.

[0003] Traditional measurement methods face severe challenges in terms of dynamic response, anti-interference capability, and measurement accuracy. The Discrete Fourier Transform (DFT), the most widely used method in practice, often fails to achieve synchronous sampling when truncating infinitely long signals using an analog-to-digital converter (ADC). This leads to unavoidable spectral leakage and the picket-fence effect, ultimately affecting the identification accuracy of the fundamental frequency and harmonics. Some researchers have attempted to use multiple second-order generalized integrators (MSOGI-FLL) for fundamental and harmonic measurement, but due to the extremely high computational cost of this structure, the dynamic response and stability of the system are affected to some extent if there are many harmonics. Furthermore, the frequency-locked loop in this structure exhibits significant oscillations when faced with large frequency jumps, ultimately leading to system instability and failing to meet the requirements for detecting the frequency and phase of multi-harmonic power grids.

[0004] Accurate measurement of power grid frequency and phase is a crucial prerequisite for ensuring power system stability, improving power quality, and ensuring accurate power metering. Therefore, a robust method for measuring power grid frequency and phase is needed to enhance power system stability.

[0005] In summary, the current technology still has the following shortcomings: First, when there are a large number of harmonic components in the power grid, the system has a large amount of computation and cannot guarantee stability; second, if the power grid experiences a large frequency jump, the system's ability to track the frequency is obviously insufficient. Summary of the Invention

[0006] In order to overcome the shortcomings of the existing technology, the present invention aims to provide a frequency and phase detection method and device suitable for multi-harmonic frequency conversion power grids. When the power grid has multiple harmonics and large frequency jumps, the system can stably and accurately obtain the parameters of the fundamental wave and each harmonic.

[0007] To achieve the above objectives, the technical solution adopted by this invention is as follows: Step 1, the voltage of the three-phase power grid is sampled by an ADC; Step 2, the three-phase voltage sampled in Step 1 is subjected to a first coordinate transformation to obtain the power grid voltage in a two-phase stationary coordinate system; Step 3, the voltage signal after coordinate transformation in Step 2 is subjected to cascaded delay signal elimination. Multiple cascaded DSC operators are used to form a CDSC module to eliminate all harmonic components except the target harmonic in the multi-harmonic frequency converter power grid. Multiple CDSC modules are set up to obtain the fundamental frequency and each harmonic component in the multi-harmonic frequency converter power grid; Step 4, based on the fundamental frequency and each harmonic component obtained in Step 3, a parameter identification system with a power grid frequency and phase estimator is constructed. The system is suitable for frequency converter power grids; Step 5, the frequency parameters obtained by the estimator are fed back to the cascaded delay signal elimination module to update the delay time of the cascaded delay signal elimination module; Step 6, Steps 2 to 5 are executed repeatedly until the output is stable.

[0008] In step one: the voltage of the three-phase power grid is sampled by ADC. The voltage of phases A, B and C of the power grid is sampled by voltage sensors and converted from digital to analog, and the voltage data of the three-phase power grid is collected.

[0009] In step two: the three-phase voltage sampled in step one undergoes a first coordinate transformation, and the calculation formula is as follows: In the formula, , , It is the three-phase voltage of the power grid. , It is the grid voltage in a two-phase stationary coordinate system after Clarke transformation.

[0010] In step three: the voltage signal after coordinate transformation in step two is subjected to cascaded delay signal elimination, and the time-domain signal form of a DSC module is represented as: in, The grid voltage is represented in a two-phase stationary coordinate system, T / n represents the delay time, and the rotation matrix is ​​used. , angle is ; It is the target harmonic order; for example, the fundamental frequency is +1. It is the delay factor; after the voltage signal passes through the DSC operator, in It achieves unity gain and zero phase shift at one harmonic component, while at other harmonic components... The gain is zero at this point; if there are too many harmonics in the power grid, a single DSC operator cannot eliminate all harmonic components except the target harmonic. In this case, multiple DSC operators can be cascaded to achieve the same result, thus forming a CDSC module.

[0011] Using the fundamental frequency and each harmonic component as the target harmonic, corresponding CDSC modules are set up to eliminate all harmonic components except the target components, thus obtaining the fundamental frequency and each harmonic component of the multi-harmonic frequency converter grid.

[0012] In step four: based on the fundamental wave and harmonic components obtained in step three, a parameter identification system with a power grid frequency and phase estimator is constructed; let the single fundamental wave component obtained after passing through the CDSC module be... and After the Park transformation, we get: In the formula, and It is the fundamental voltage of the power grid in a two-phase rotating coordinate system obtained after Park transformation. This is the estimated fundamental phase value of the power grid, obtained by a subsequent phase estimator. The initial value is 0 by default; this step converts the quadrature signal to a DC signal; and After the following mathematical transformation: Construct a parameter identification system with grid frequency and phase estimators. Grid frequency and phase estimators: in, It is the compensated angular frequency, set as the standard angular frequency of the power grid; the amplitude and phase of the fundamental and nth harmonics are determined by... and get: The frequency of the nth harmonic can be obtained by multiplying it by the corresponding factor using a frequency estimator.

[0013] In step five: the frequency parameters obtained by the estimator are fed back to the cascaded delay signal cancellation module to update the delay time of the cascaded delay signal cancellation module. In the design of the digital signal processor (DSP), the frequency estimate obtained by the estimator is... The signal is fed back in real time to the cascaded delay signal cancellation module, and closed-loop control is achieved through software interrupt procedures.

[0014] The formula for updating the delay time is: The cascaded delay signal cancellation module cancels the signal based on this new delay time.

[0015] In step six, steps two through five are executed repeatedly until the output stabilizes. The criterion for stability is... and If the error between two consecutive outputs is less than a specified threshold, the output is the estimated power grid amplitude, frequency, and phase.

[0016] A frequency and phase detection device suitable for multi-harmonic frequency conversion power grids includes a voltage sampling module, a CDSC module, a frequency and phase estimator module, and a parameter identification module.

[0017] The voltage sampling module uses a voltage sensor to acquire three-phase voltage signals; the CDSC module is responsible for separating harmonic components in the multi-harmonic power grid. It first converts the three-phase voltage signals into voltage signals in a two-phase stationary coordinate system using Clark transformation, and then extracts the harmonic signals through signal delay, rotation, and summation operations; the frequency and phase estimator module is a half-tangent phase-locked loop (PLL) responsible for locking the frequency and phase of the power grid and outputting real-time frequency estimates. and phase estimate The parameter identification module is responsible for outputting the amplitude, frequency, and phase parameters of the harmonic components.

[0018] The beneficial effects of this invention are as follows: This invention provides a frequency and phase detection method and apparatus suitable for multi-harmonic frequency conversion power grids, comprising a power grid voltage sampling module, a CDSC module, a frequency and phase estimator module, and a parameter identification module. Compared with traditional synchronous reference system phase-locked loops (PLLs), the half-tangent PLL used in this invention has a unique stable point, enabling timely locking of the power grid's frequency and phase when the power grid experiences significant frequency jumps, thus improving the accuracy of frequency and phase estimation. When the power grid voltage contains a large number of harmonics, the MSOGI-FLL method is structurally very complex. The CDSC module used in this invention performs delay and rotation operations on the input signal, and then sums it with the original input signal to eliminate specific harmonics. This module can extract harmonic components more quickly, reducing the computational load of the system. By combining CDSC and the half-tangent PLL, rapid extraction of single or multiple harmonic signals can be achieved, and system stability can be ensured in scenarios with significant frequency jumps, making it highly suitable for multi-harmonic frequency conversion power grids. Attached Figure Description

[0019] Figure 1 is a flowchart of the method for estimating the phase and frequency of multi-harmonic power grids implemented and provided by the present invention.

[0020] Figure 2 is a schematic diagram of the power grid phase and frequency estimation device provided by the present invention.

[0021] Figure 3 is a schematic diagram of the phase-locked loop phase estimation.

[0022] Figure 4 is a schematic diagram of the fundamental wave identification results.

[0023] Figure 5 is a schematic diagram of the third harmonic identification results.

[0024] Figure 6 is a schematic diagram of the 5th harmonic identification results. Detailed Implementation

[0025] The present invention will now be described in further detail with reference to the accompanying drawings.

[0026] As shown in Figure 1, a frequency and phase detection method suitable for multi-harmonic frequency conversion power grids includes the following steps: Step 1, sampling the voltage of the three-phase power grid using an ADC; sampling the A-phase, B-phase, and C-phase of the power grid using voltage sensors and converting the data from digital to analog, thereby collecting the voltage data of the three-phase power grid.

[0027] Step two: Perform a coordinate transformation on the three-phase voltages sampled in step one; then perform a Clarke transform on the sampled three-phase voltages, as shown in the following equation: In the formula, , , It is the three-phase voltage of the power grid. , This is the grid voltage in a two-phase stationary coordinate system after Clarke transformation. The purpose of this step is to convert the three-phase voltage signal into an orthogonal signal.

[0028] Step 3: Perform cascaded delay signal cancellation on the voltage signal after coordinate transformation in Step 2; the time-domain signal form of the delayed signal cancellation is as follows: in, The grid voltage is represented in a two-phase stationary coordinate system, T / n represents the delay time, and the rotation matrix is ​​used. , angle is ; It is the target harmonic order; for example, the fundamental frequency is +1. It is the delay factor; after the voltage signal passes through the DSC operator, in It achieves unity gain and zero phase shift at one harmonic component, while at other harmonic components... The gain is zero at this point; if there are too many harmonics in the power grid, a single DSC operator cannot eliminate all harmonic components except the target harmonic. Therefore, multiple DSC operators can be cascaded to achieve this, thus forming a CDSC module. Using the fundamental frequency and each harmonic component as the target harmonic, corresponding CDSC modules are established to eliminate all harmonic components except the target component, thus obtaining the fundamental frequency and each harmonic component of the multi-harmonic frequency converter power grid; rotation matrix The trigonometric function calculations are performed during the design phase, but during the actual execution of the system, no trigonometric function calculations are required; only simple multiplication, division, and addition operations are performed. Therefore, the CDSC algorithm is significantly more efficient than the MSOGI-FLL algorithm.

[0029] Step four: Based on the fundamental frequency and harmonic components obtained in step three, construct a parameter identification system with grid frequency and phase estimators; let the single fundamental frequency component obtained after passing through the CDSC module be... and After the Park transformation, we get: In the formula, and It is the fundamental voltage of the power grid in a two-phase rotating coordinate system obtained after Park transformation. This is the estimated fundamental phase value of the power grid, obtained by a subsequent phase estimator. The initial value is 0 by default; this step converts the quadrature signal to a DC signal; and After the following mathematical transformation: Construct a parameter identification system with grid frequency and phase estimators. Grid frequency and phase estimators: in, It is the compensated angular frequency, set as the standard angular frequency of the power grid; the amplitude and phase of the fundamental and nth harmonics are determined by... and get: The frequency of the nth harmonic can be obtained by multiplying it by the corresponding factor using a frequency estimator.

[0030] Thus, we can obtain estimates of the amplitude, phase, and frequency of the fundamental and all harmonic components of the multi-harmonic power grid voltage.

[0031] Step 5: Feedback the frequency parameters obtained by the estimator to the cascaded delay signal cancellation module; in the design of the digital signal processor (DSP), the frequency estimate obtained by the estimator is used... Real-time feedback is sent to the cascaded delay signal cancellation module to update its delay time. Closed-loop control is achieved through a software interrupt routine. The formula for updating the delay time is: The cascaded delay signal cancellation module cancels the signal based on this new delay time.

[0032] Step six: Repeat steps two through five until the output stabilizes. The criterion for stability is... and The error between two consecutive outputs is less than a specified threshold. The output is the estimated power grid amplitude, frequency, and phase.

[0033] To obtain the fundamental frequency and each harmonic component, we need to design the system structure diagram shown in Figure 2.

[0034] First, the three-phase grid voltage is sampled by a voltage sensor and then input to the subsequent modules after passing through a digital-to-analog converter.

[0035] The sampled voltage signal is then subjected to Clark transformation and input to multiple CDSC modules, ultimately outputting a voltage signal containing only a single component. In the diagram, CDSC1 is responsible for extracting the fundamental component, CDSC3 is responsible for extracting the third harmonic component, and so on, with CDSCn responsible for extracting the nth harmonic component.

[0036] Then, the fundamental component output by CDSC1 is transformed using Park and input to the frequency and phase estimation module, which uses a half-tangent phase-locked loop (PLL). The output frequency estimate is used to update the delay time of the CDSC module.

[0037] Finally, the voltage signal output by each CDSC module is input into the parameter identification module, which can then output the amplitude, frequency, and phase information of each harmonic component.

[0038] Simulation Application: In the simulation, it is considered that in addition to the fundamental component, the grid voltage also contains the 3rd and 5th harmonics. These harmonic components are relatively common in actual power grids and account for a high proportion. The fundamental amplitude is 311V, the 3rd harmonic amplitude is 40V, and the 5th harmonic amplitude is 20V.

[0039] At t=1s, the fundamental frequency jumps from 50Hz to 52Hz, while other parameters remain unchanged.

[0040] The simulation results are shown in Figures 3-6. Figure 3 shows the estimated phase value of the fundamental voltage obtained by the estimator. It can be clearly seen that the frequency jump causes the voltage waveform period to shorten to less than 20ms.

[0041] Figure 4 shows the fundamental frequency estimate obtained by the estimator and the fundamental amplitude calculated by the identification module. Under the influence of frequency jump, the estimator can accurately track the fundamental frequency in about half a cycle. The amplitude fluctuates slightly and tends to stabilize after several decaying oscillations. The steady-state error of both the fundamental frequency and amplitude is zero.

[0042] Figure 5 shows the third harmonic frequency and amplitude calculated by the identification module. Under the influence of frequency jump, the stabilization time of the third harmonic frequency and amplitude is about 10ms. The amplitude tends to stabilize after several decaying oscillations. Finally, the steady-state error of the third harmonic frequency and amplitude is zero.

[0043] Figure 6 shows the 5th harmonic frequency and amplitude calculated by the identification module. Under the influence of frequency jump, the 5th harmonic frequency and amplitude stabilize in about 10ms. The amplitude tends to stabilize after several decaying oscillations. Finally, the steady-state error of the 5th harmonic frequency and amplitude is zero.

Claims

1. A frequency and phase detection method suitable for multi-harmonic frequency conversion power grids, characterized in that, The process includes the following steps: Step 1, sampling the three-phase voltage of the power grid using an ADC; Step 2, performing a first coordinate transformation on the three-phase voltage sampled in Step 1 to obtain the power grid voltage in a two-phase stationary coordinate system; Step 3, performing cascaded delay signal cancellation on the voltage signal after the coordinate transformation in Step 2, constructing a CDSC module by cascading multiple DSC operators to eliminate all harmonic components except the target harmonic in the multi-harmonic frequency converter power grid, and establishing multiple CDSC modules to obtain the fundamental frequency and each harmonic component in the multi-harmonic frequency converter power grid; Step 4, constructing a parameter identification system with a power grid frequency and phase estimator based on the fundamental frequency and each harmonic component obtained in Step 3, the system being applicable to frequency converter power grids; Step 5, feeding back the frequency parameters obtained by the estimator to the cascaded delay signal cancellation module to update the delay time of the cascaded delay signal cancellation module; Step 6, repeating Steps 2 to 5 until the output stabilizes.

2. The frequency and phase detection method for multi-harmonic frequency conversion power grids according to claim 1, characterized in that, In step one: the voltage of the three-phase power grid is sampled by ADC. The voltage of phases A, B and C of the power grid is sampled by voltage sensors and converted from digital to analog, and the voltage data of the three-phase power grid is collected.

3. The frequency and phase detection method for multi-harmonic frequency conversion power grids according to claim 2, characterized in that, In step two: the three-phase voltage sampled in step one undergoes a first coordinate transformation, and the calculation formula is as follows: In the formula, ， ， It is the three-phase voltage of the power grid. , It is the grid voltage in a two-phase stationary coordinate system after Clarke transformation.

4. The frequency and phase detection method for multi-harmonic frequency conversion power grids according to claim 3, characterized in that, In step three: the voltage signal after coordinate transformation in step two is subjected to cascaded delay signal elimination, and the time-domain signal form is: in, The grid voltage is represented in a two-phase stationary coordinate system, T / n represents the delay time, and the rotation matrix is ​​used. , angle is ； It is the target harmonic order. It is the delay factor; after the voltage signal passes through the DSC operator, in It achieves unity gain and zero phase shift at one harmonic component, while at other harmonic components... The gain is zero at the point; if there are too many harmonics in the power grid, multiple DSC operators are cascaded to form a CDSC module; the fundamental frequency and each harmonic component are used as target harmonics, and corresponding CDSC modules are set up to eliminate all harmonic components except the target components, so as to obtain the fundamental frequency and each harmonic component of the multi-harmonic frequency conversion power grid.

5. The frequency and phase detection method for multi-harmonic frequency conversion power grids according to claim 4, characterized in that, In step four: based on the fundamental wave and harmonic components obtained in step three, a parameter identification system with a power grid frequency and phase estimator is constructed; let the single fundamental wave component obtained after passing through the CDSC module be... and After the Park transformation, we get: In the formula, and It is the fundamental voltage of the power grid in a two-phase rotating coordinate system obtained after Park transformation. This is the estimated fundamental phase value of the power grid, obtained by a subsequent phase estimator. The initial value is 0 by default; this step converts the quadrature signal to a DC signal; and After the following mathematical transformation: Construct a parameter identification system with grid frequency and phase estimators. Grid frequency and phase estimators: in, It is the compensated angular frequency, set as the standard angular frequency of the power grid.

6. The frequency and phase detection method for multi-harmonic frequency conversion power grids according to claim 5, characterized in that, The amplitude and phase of the fundamental and nth harmonic waves are determined by... and get: The frequency of the nth harmonic can be obtained by multiplying it by the corresponding factor using a frequency estimator.

7. The frequency and phase detection method for multi-harmonic frequency conversion power grids according to claim 6, characterized in that, In step five: the frequency parameters obtained by the estimator are fed back to the cascaded delay signal cancellation module to update the delay time of the cascaded delay signal cancellation module. In the design of the digital signal processor (DSP), the frequency estimate obtained by the estimator is... The signal is fed back in real time to the cascaded delay signal cancellation module, and closed-loop control is achieved through software interrupt procedures.

8. The frequency and phase detection method for multi-harmonic frequency conversion power grids according to claim 7, characterized in that, The formula for updating the delay time is: The cascaded delay signal cancellation module cancels the signal based on the new delay time.

9. A frequency and phase detection method for multi-harmonic frequency conversion power grids according to claim 8, characterized in that, Step six specifically involves: repeatedly executing steps two through five until the output stabilizes. The criterion for stability is... and If the error between two consecutive outputs is less than a specified threshold, the output is the estimated power grid amplitude, frequency, and phase.

10. A frequency and phase detection device suitable for multi-harmonic frequency conversion power grids for implementing the method according to any one of claims 1-9, characterized in that, It includes a voltage sampling module, a CDSC module, a frequency and phase estimator module, and a parameter identification module. The voltage sampling module acquires three-phase voltage signals using voltage sensors. The CDSC module is responsible for separating harmonic components in the multi-harmonic power grid. It first converts the three-phase voltage signals into voltage signals in a two-phase stationary coordinate system through Clark transformation, and then extracts the harmonic signals after signal delay, rotation, and summation operations. The frequency and phase estimator module is a half-tangent phase-locked loop (PLL) responsible for locking the frequency and phase of the power grid and outputting real-time frequency estimates. and phase estimate The parameter identification module is responsible for outputting the amplitude, frequency, and phase parameters of the harmonic components.

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