Rotating speed measurement filtering method and system for static frequency converter
By combining a low-pass filter and an integral filter, and dynamically adjusting the filter frequency and integral period, the problems of high hardware cost and low measurement accuracy in speed measurement of static inverters are solved, and accurate speed measurement under all operating conditions is achieved.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-12-08
- Publication Date
- 2026-03-10
AI Technical Summary
Existing methods for measuring the speed of static inverters suffer from high hardware costs and low measurement accuracy in large-capacity motors. In particular, at low speeds, severe harmonic interference leads to large measurement errors. Traditional filters cannot adapt to all operating conditions of static inverters, resulting in inaccurate measurements.
A combination of low-pass and integral filters is used to acquire three-phase voltage waveforms through AC voltage transformers. The filters are automatically switched using a phase-locked loop and switching algorithm, and the filter frequency and integral period are dynamically adjusted to ensure that the harmonic content is within the threshold range, thereby achieving sinusoidal voltage waveform and accurate speed calculation.
It achieves accurate speed measurement under all operating conditions of the static inverter, with good filtering effect at low speeds and fast response at high speeds, ensuring measurement accuracy and stability.
Smart Images
Figure CN121633531A_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The present application relates to the field of pumped storage power station electric drive technology, in particular to a rotational speed measurement filtering method and system for a static frequency converter. BACKGROUND
[0002] At present, static frequency converters are widely used in high-power electric drive, such as phase modulators, pumped storage units, pump stations, fans, large ships and other occasions.
[0003] In these application occasions, the control algorithm of the frequency converter needs to collect and measure the rotational speed of the motor, which mainly includes two ways, one is to directly measure the rotational speed by using an optical encoder and a Hall sensor to directly measure and convert the measurement into a voltage signal to send to the controller; The other is to indirectly measure the rotational speed by using the motor terminal voltage signal to indirectly calculate the motor speed.
[0004] The direct measurement method of rotational speed is commonly used in small and medium power motor drive measurement, and is less used in measuring the rotational speed of large capacity motors, mainly for two reasons: First, the hardware cost of the sensor for directly measuring the rotational speed of large capacity motors is high; Second, it is easy to be disturbed by the environment, resulting in low measurement accuracy.
[0005] The indirect measurement method of direct current is to measure the terminal voltage by using a voltage transformer, and the static frequency converter is a power electronic device, mainly using thyristors as power electronic devices, which makes the voltage signal have harmonics during the dragging process, which makes the measurement have a large error, and even measurement error, resulting in control instability; Especially at low speed, the voltage distortion is very serious, which makes it impossible to measure; Therefore, the indirect measurement of direct current needs to add a filter, and the traditional filter mainly filters a certain fixed frequency, mainly 50Hz.
[0006] However, during the dragging process of the static frequency converter, the frequency continuously changes from 0 to 50Hz, which makes the traditional filter unable to adapt to the dragging of the static frequency converter in all working conditions, resulting in poor filtering effect at low frequency, and further inaccurate measurement of rotational speed at low speed; Although a filter with reasonable parameters can meet the filtering requirements at low frequency, the filter completely fails at high speed.
[0007] In summary, the existing indirect measurement of rotational speed cannot effectively and accurately measure the rotational speed of the static frequency converter. SUMMARY
[0008] The application aims to provide a rotating speed measurement filtering method and system for a static frequency converter.
[0009] The technical scheme of the application is as follows: The rotating speed measurement filtering method for the static frequency converter comprises the following steps: S1, determining an AC voltage collection point: determining a motor terminal AC voltage collection point position on the static frequency converter to be measured, and collecting real-time waveforms of three-phase voltages by using an AC voltage transformer; S2, transmitting the collected real-time waveforms of the three-phase voltages to a static frequency converter controller, filtering the three-phase voltage waveforms by using a low-pass filter, and obtaining a standard voltage sine wave; S3, calculating a harmonic content of the voltage sine wave, if the harmonic content is less than a threshold value, sending three-phase voltage signals into a phase-locked loop, and if the harmonic content is greater than the threshold value, adjusting a turning frequency of the low-pass filter until the harmonic content is less than the threshold value; S4, filter automatic switching: a switching algorithm is used to automatically switch the low-pass filter to an integral filter for filtering; S5, extracting phase angles of the three-phase voltages by using the phase-locked loop for the filtered voltage waveforms, calculating a frequency of the voltage by derivation of the phase angles, and obtaining a measured rotating speed of the unit.
[0010] In the aforementioned rotating speed measurement filtering method for the static frequency converter, the turning frequency of the low-pass filter is set according to a highest frequency ±0.5 Hz in a pulse commutation stage in a static frequency converter control mode.
[0011] In the aforementioned rotating speed measurement filtering method for the static frequency converter, the harmonic content threshold value in S3 is dynamically adjusted according to actual conditions, and is set according to actual sine wave requirements; the harmonic content threshold value is initially set as 4%.
[0012] In the aforementioned rotating speed measurement filtering method for the static frequency converter, the switching algorithm can synchronously switch the filter according to a switching flag in a working mode of the static frequency converter from a pulse commutation mode to a load commutation mode, ensure smooth switching of the filter, and keep consistent with switching of the working mode of the static frequency converter.
[0013] A rotating speed measurement filtering system for a static frequency converter comprises a data collection module, a data processing module, a data control module, a filter algorithm switching module and a rotating speed calculation module which are connected with each other. The data collection module is used to collect real-time waveforms of three-phase voltages. The data processing module is used to filter the three-phase voltage waveforms to obtain a standard voltage sine wave. The data control module is used to calculate the harmonic content of the voltage sine wave and adjust the corner frequency of the low-pass filter; The filtering algorithm switching module is used to automatically switch the low-pass filter to an integral filter for filtering using a switching algorithm; The speed calculation module is used to calculate the voltage frequency to obtain the unit speed.
[0014] In the aforementioned speed measurement and filtering system for a static inverter, the static inverter includes a current-source load converter inverter comprising a 6-pulse device, a 12-pulse device, a multi-pulse device, and a DC reactor.
[0015] In the aforementioned speed measurement filtering system for a static frequency converter, the corner frequency of the low-pass filter can be dynamically adjusted.
[0016] The aforementioned speed measurement and filtering system for static frequency converters also includes a harmonic measurement module for real-time detection of voltage waveforms before and after switching. The integration period T of the integral filter is adjusted according to the real-time monitored frequency.
[0017] In the aforementioned speed measurement and filtering system for static frequency converters, the voltage waveforms after passing the harmonic measurement module before and after switching are synthesized to form the voltage detection waveform of the static frequency converter throughout the entire process.
[0018] In the aforementioned speed measurement and filtering system for static frequency converters, the harmonic measurement module can be used to detect harmonic content in real time, determine the filtering effect, and form a closed-loop dynamic adjustment until the low-frequency filtering effect meets the target threshold.
[0019] In the aforementioned speed measurement and filtering system for a static frequency converter, the 6-pulse device includes a 6-pulse rectifier-inverter circuit, and the AC voltage acquisition point of the 6-pulse rectifier-inverter circuit is located at the AC power supply.
[0020] Compared with the prior art, the present invention has the following beneficial effects: 1) The AC voltage waveform is acquired by the AC voltage transformer, and different types of filters are switched by the flag bit, so that the voltage waveform of the entire driving process can be filtered to obtain the waveform of the motor terminal sine wave. 2) The cutoff frequency of the low-pass filter is dynamically adjusted according to the harmonic content of the voltage waveform, and the integration period of the integral filter can also be dynamically adjusted according to the real-time rotation speed frequency to ensure that the harmonic content is within the threshold range and to ensure that the voltage waveform is sinusoidal throughout the process. 3) Compared with other types of filters, integral filters have a significant advantage in response speed. Furthermore, as the rotational speed changes, the integral period T is dynamically adjusted, resulting in a faster response speed, which is more adaptable to the high-frequency characteristics of power electronic devices. 4) This invention employs two types of filters: a low-pass filter and an integral filter. The low-pass filter is set with a dynamic cutoff frequency, providing good filtering performance at low speeds. At high speeds, it switches to the integral filter based on the working flag of the static inverter, providing a fast and effective filtering response at high speeds. This ensures accurate filtering throughout the entire motor startup process, guaranteeing the accuracy of speed measurement.
[0021] Therefore, the present invention has the advantage of being able to accurately measure the speed of a static inverter. Attached Figure Description
[0022] Figure 1 This is a typical device structure diagram of the static frequency converter in the embodiments of the present invention; Figure 2 This is a schematic diagram of the filtering process of the present invention; Figure 3 shows the measured waveform of the static inverter in an embodiment of the present invention; where 3a is before AC side filtering and 3b is after filtering using the present invention. Figure 4 is a comparison of the measured frequency results after filtering with the single filter of the present invention and the measured frequency after filtering with the present invention; where 4a is a single low-pass filter, 4b is a single integral filter, and 4c is the filter combination of the present invention. Figure 5 This is a schematic diagram of the process of this invention; Figure 6 This is a schematic diagram of the system framework structure of the present invention. Detailed Implementation
[0023] The present invention will be further described below with reference to the accompanying drawings and embodiments, but this should not be construed as limiting the present invention.
[0024] Example. A speed measurement filtering method for a static frequency converter, such as... Figure 5 As shown, it includes the following steps: S1. Determine the AC voltage acquisition point: Determine the location of the AC voltage acquisition point at the motor terminal on the static inverter under test, and use an AC voltage transformer to acquire the real-time waveform of the three-phase voltage. S2. The collected real-time three-phase voltage waveform is transmitted to the static inverter controller, and a low-pass filter is used to filter the three-phase voltage waveform to obtain a standard voltage sine wave. S3. Calculate the harmonic content of the voltage sine wave. If the harmonic content is less than the threshold, send the three-phase voltage signal into the phase-locked loop. If the harmonic content is greater than the threshold, adjust the cutoff frequency of the low-pass filter until the harmonic content is less than the threshold. S4. Automatic Filter Switching: The filter algorithm controller uses a switching algorithm to automatically switch the low-pass filter to an integral filter for filtering. S5. Extract the phase angle of the three-phase voltage from the filtered voltage waveform using a phase-locked loop. Calculate the voltage frequency by differentiating the phase angle, which is the measured unit speed.
[0025] The cutoff frequency of the low-pass filter is set to ±0.5Hz of the highest frequency of the pulse commutation stage of the static inverter to ensure good filtering effect at low speed; the highest frequency is usually 5Hz.
[0026] The harmonic content threshold mentioned in S3 is dynamically adjusted according to the actual situation and set according to the actual sine wave requirements; the initial harmonic content threshold is set to 4%.
[0027] The switching algorithm can synchronously switch the filter according to the switching flag bit in the static inverter's operating mode when switching from pulse commutation mode to load commutation mode, ensuring smooth filter switching and consistency with the static inverter's operating mode switching.
[0028] A speed measurement and filtering system for a static frequency converter, such as Figure 6 As shown, it includes interconnected data acquisition modules, data processing modules, data control modules, filter algorithm switching modules, and speed calculation modules; The data acquisition module is used to acquire real-time waveforms of three-phase voltage. The data processing module is used to filter the three-phase voltage waveform to obtain a standard voltage sine wave; The data control module is used to calculate the harmonic content of the voltage sine wave and adjust the corner frequency of the low-pass filter; The filtering algorithm switching module is used to automatically switch the low-pass filter to an integral filter for filtering using a switching algorithm; The speed calculation module is used to calculate the voltage frequency to obtain the unit speed.
[0029] The static inverter includes a current source type load converter inverter comprising a 6-pulse device, a 12-pulse device, a multi-pulse device, and a DC reactor.
[0030] The 6-pulse device includes a 6-pulse rectifier-inverter circuit, and the AC voltage acquisition point of the 6-pulse rectifier-inverter circuit is located at the AC power supply.
[0031] The 12-pulse device includes a 12-pulse rectifier-inverter circuit, and the multi-pulse device includes a multi-pulse rectifier-inverter circuit; the AC current acquisition point of the 12-pulse rectifier-inverter circuit and the multi-pulse rectifier-inverter circuit is located at any one of the AC power sources of the multiple series-connected rectifier-inverter circuits.
[0032] The cutoff frequency of the low-pass filter can be dynamically adjusted; The integral filter is used for filtering in 6-pulse and 12-pulse rectifier-inverter circuits.
[0033] It is also equipped with a harmonic measurement module for real-time detection of voltage waveforms before and after switching. The integration period T of the integral filter is adjusted according to the real-time monitored frequency, and the integration period T is dynamically adjusted as the rotation speed changes, resulting in a faster response speed and better adaptability to the high-frequency characteristics of power electronic devices.
[0034] The voltage waveforms after passing the harmonic measurement module before and after switching are synthesized to form the voltage detection waveform of the static inverter throughout the entire process.
[0035] The harmonic measurement module can be used to detect harmonic content in real time, determine the filtering effect, and form a closed-loop dynamic adjustment until the low-frequency filtering effect meets the target threshold.
[0036] like Figure 1 As shown, a typical static inverter consists of a 12-pulse rectifier bridge and a 6-pulse inverter bridge DC reactor. The three-phase AC voltage on the AC side of the static inverter device is collected in real time through an AC current transformer; the AC voltage transformer is installed on the generator (motor) side.
[0037] The waveform collected by the voltage transformer is input to the data acquisition module in real time. The data acquisition module conditions the waveform to ensure that the waveform signal is not distorted and filters out external electromagnetic interference before inputting it according to the voltage level required by the control module.
[0038] like Figure 2 As shown, the data processing module transmits the real-time waveform of the three-phase voltage to the static inverter controller, and uses a low-pass filter to filter the three-phase voltage waveform to obtain a standard voltage sine wave. The initial cutoff frequency of the low-pass filter is set according to the pulse commutation mode switching frequency of the static inverter. The harmonic measurement module detects in real time. If the harmonic threshold of 4% is not met, the cutoff frequency is dynamically adjusted until the voltage harmonics meet the threshold.
[0039] When the static inverter switches operating modes, the synchronous switching filter is switched to the integral filter to ensure good filtering effect at high speeds.
[0040] The switching flag bit in the static inverter's operating mode, which switches from pulse commutation mode to load commutation mode, is used to synchronously switch the filter, ensuring smooth filter switching and consistency with the static inverter's operating mode switching.
[0041] As shown in Figures 3a and 3b, due to the fact that static frequency converters are power electronic devices and use thyristors as power electronic components, the phase-controlled rectification and inversion methods cause severe harmonic distortion of the motor terminal voltage, especially at low speeds. If the speed measurement module measures this unprocessed voltage waveform, the speed measurement will be severely distorted. The actual operating frequency is around 3Hz, but the measured frequency is 85Hz, leading to a series of consequences such as over-frequency protection activation.
[0042] After being filtered, the voltage waveform becomes distinctly sinusoidal. The voltage waveform is then processed by the speed calculation module. The phase angle of the three-phase voltage is extracted by a phase-locked loop. By differentiating the phase angle, the frequency of the voltage is calculated, which is the measured unit speed.
[0043] As shown in Figure 4a and 4b, these are the unit frequencies measured after filtering with a single low-pass filter and an integral filter during the process of the motor being driven to the rated speed. As can be seen from 4a, the frequency measurement of the low-pass filter is normal at low speed, but it is completely distorted at high speed. The reason is that the low-pass filter has a fixed cutoff frequency at this time, and it is only effective in filtering out harmonics near the cutoff frequency, while it is completely ineffective at other frequencies. The integral filter is exactly the opposite. As can be seen from 4b, it is completely distorted at low speeds, but the measurement is normal at high speeds. This is because the integral period T is set to the power frequency period, which results in poor filtering of low-frequency harmonics. As shown in 4c, this invention uses a low-pass filter at low speeds and switches to an integral filter at 5Hz, resulting in a waveform that is normal and undistorted overall.
[0044] like Figure 5 As shown, the data sampling module initializes the three-phase voltage parameters, and initializes the parameters at the beginning of each scan cycle of the program to ensure that the program can continuously refresh the sampling.
[0045] The data processing module transmits the collected real-time waveforms of the three-phase voltage to the static inverter controller. It uses a low-pass filter to filter the three-phase voltage waveforms, assigns values to the filtered data, and sends it to the harmonic detection module for detection. If the harmonic threshold is met, it proceeds to the next step. If not, it automatically performs dynamic adjustment of the cutoff frequency until the harmonics meet the harmonic threshold.
[0046] The filter switching frequency is a preset value. The initial frequency parameter is set according to the pulse commutation switching load commutation frequency of the static inverter. The setting is based on the inverter model with different parameters. After setting, it remains unchanged. The parameter setting is in the form of a permanent variable.
[0047] When the program flow reaches the frequency switching stage, the filter switching program switches according to the flag S1. After the switching is completed, the integral filter immediately performs filtering operations. At the same time, the integral period of the integral filter is dynamically adjusted according to the detection value of the harmonic detection module. The adjustment of the integral period T can form a closed loop in the sequential process, ensuring that the filtering effect of the integral filter is optimal and the response speed is the fastest.
[0048] The program combines a low-pass filter with dynamically adjusted corner frequency and an integral filter with dynamically adjusted integral period T in a sequential flow to obtain the fundamental waveform of the speed voltage at the start of the entire process.
[0049] The speed calculation module extracts the phase angle of the three-phase voltage from the filtered voltage waveform using a phase-locked loop. By differentiating the phase angle or performing differential operations, the frequency of the voltage is calculated, which is the measured unit speed.
Claims
1. A rotational speed measurement filtering method for a static frequency converter, characterized in that, The method comprises the following steps: S1, determining an AC voltage collection point: determining a motor terminal AC voltage collection point position on a to-be-measured static frequency converter, and collecting three-phase voltage real-time waveforms by using an AC voltage transformer; S2, transmitting the collected three-phase voltage real-time waveforms to a static frequency converter controller, and filtering the three-phase voltage waveforms by using a low-pass filter to obtain a standard voltage sine wave; S3, calculating a harmonic content of the voltage sine wave, if the harmonic content is less than a threshold value, then sending the three-phase voltage signal into a phase-locked loop; if the harmonic content is greater than the threshold value, then adjusting a turning frequency of the low-pass filter until the harmonic content is less than the threshold value; S4, filter automatic switching: a filter algorithm controller automatically switches the low-pass filter to an integral filter for filtering by using a switching algorithm; S5, extracting a phase angle of the three-phase voltage by using the phase-locked loop for the filtered voltage waveforms, and calculating a frequency of the voltage by deriving the phase angle, which is a measured unit speed.
2. The rotational speed measurement filtering method for a static frequency converter according to claim 1, characterized in that: The turning frequency of the low-pass filter is set according to a highest frequency ±0.5 Hz in a pulse commutation stage of a static frequency converter control mode.
3. The rotational speed measurement filtering method for a static frequency converter according to claim 1, characterized in that: The harmonic content threshold value in S3 is dynamically adjusted according to actual conditions and set according to actual sine wave requirements; the harmonic content threshold value is initially set as 4%.
4. The rotational speed measurement filtering method for a static frequency converter according to claim 1, characterized in that: The switching algorithm can synchronously switch the filter according to a switching flag in a working mode of the static frequency converter from a pulse commutation mode to a load commutation mode, ensure smooth switching of the filter, and keep consistent with switching of the working mode of the static frequency converter.
5. A speed measurement filtering system for a static frequency converter, which is used in the speed measurement filtering method for the static frequency converter according to any one of claims 1-4, and characterized in that: The system comprises a data collection module, a data processing module, a data control module, a filter algorithm switching module and a speed calculation module which are interconnected; The data collection module is used for collecting three-phase voltage real-time waveforms; The data processing module is used for filtering the three-phase voltage waveforms to obtain a standard voltage sine wave; The data control module is used for calculating a harmonic content of the voltage sine wave and adjusting a turning frequency of the low-pass filter; The filter algorithm switching module is used for automatically switching the low-pass filter to an integral filter for filtering by using a switching algorithm; The speed calculation module is used for calculating a voltage frequency to obtain a unit speed.
6. A rotational speed measurement filtering system for a static frequency converter according to claim 5, characterized in that: The static frequency converter comprises a 6-pulse device, a 12-pulse device, a multi-pulse device and a current source type load commutation frequency converter including a DC reactor.
7. A rotational speed measurement filtering system for a static frequency converter according to claim 5, characterized in that: The turning frequency of the low-pass filter can be dynamically adjusted.
8. A rotational speed measurement filtering system for a static frequency converter according to claim 5, characterized in that: A harmonic measurement module is further provided and used for detecting voltage waveforms before and after switching in real time, and an integral period T of the integral filter is adjusted according to a real-time monitored frequency.
9. A rotational speed measurement filtering system for a static frequency converter according to claim 8, characterized in that: The voltage waveforms detected by the harmonic measurement module before and after switching are synthesized to form a static frequency converter whole-process voltage detection waveform.
10. A rotational speed measurement filtering system for a static frequency converter according to claim 8, characterized in that: The harmonic measurement module can be used for detecting a harmonic content in real time, determining a filtering effect, forming a closed-loop dynamic adjustment, and satisfying a target threshold value until a low-frequency filtering effect meets the target threshold value.