CN115366711A - Foreign matter detection system and method for wireless charging system of electric automobile based on thermal infrared image processing - Google Patents
Foreign matter detection system and method for wireless charging system of electric automobile based on thermal infrared image processing Download PDFInfo
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B60—VEHICLES IN GENERAL
- B60L—PROPULSION OF ELECTRICALLY-PROPELLED VEHICLES; SUPPLYING ELECTRIC POWER FOR AUXILIARY EQUIPMENT OF ELECTRICALLY-PROPELLED VEHICLES; ELECTRODYNAMIC BRAKE SYSTEMS FOR VEHICLES IN GENERAL; MAGNETIC SUSPENSION OR LEVITATION FOR VEHICLES; MONITORING OPERATING VARIABLES OF ELECTRICALLY-PROPELLED VEHICLES; ELECTRIC SAFETY DEVICES FOR ELECTRICALLY-PROPELLED VEHICLES
- B60L53/00—Methods of charging batteries, specially adapted for electric vehicles; Charging stations or on-board charging equipment therefor; Exchange of energy storage elements in electric vehicles
- B60L53/10—Methods of charging batteries, specially adapted for electric vehicles; Charging stations or on-board charging equipment therefor; Exchange of energy storage elements in electric vehicles characterised by the energy transfer between the charging station and the vehicle
- B60L53/12—Inductive energy transfer
- B60L53/124—Detection or removal of foreign bodies
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
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- H02J50/10—Circuit arrangements or systems for wireless supply or distribution of electric power using inductive coupling
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- H—ELECTRICITY
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- H—ELECTRICITY
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- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J50/00—Circuit arrangements or systems for wireless supply or distribution of electric power
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- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
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- Y02T10/00—Road transport of goods or passengers
- Y02T10/60—Other road transportation technologies with climate change mitigation effect
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- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
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- Y02T10/00—Road transport of goods or passengers
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Abstract
The invention provides a foreign matter detection system and method of an electric vehicle wireless charging system based on thermal infrared image processing, and relates to the technical field of wireless power transmission. The controller extracts the image characteristics of the foreign matters through the infrared detection module and an improved image processing algorithm, obtains the information of the temperature, the area, the perimeter, the position and the like of the foreign matters, sends the information to a mobile phone or a computer upper computer of a user by virtue of the communication module, and sends out an alarm signal. The user can input commands and modify parameters through the upper computer, the communication module and the interaction module, so that the system performance is improved; the modification result can be checked in real time through the display screen, and debugging work under different environments is facilitated. The invention utilizes the improved method of thermal infrared image processing to detect, the foreign matter detection system can stably work in the wireless charging process, and has strong environmental adaptability, simple structure and low cost. And the non-contact detection of foreign matters and positions thereof in the wireless charging system under any frequency can be realized, and the wireless charging system is hardly influenced.
Description
Technical Field
The invention relates to the technical field of wireless power transmission, in particular to a foreign matter detection system and method of an electric vehicle wireless charging system based on thermal infrared image processing.
Background
The background of the invention is Foreign Object Detection (FOD) for wireless power transmission system of electric vehicle. In the face of increasingly prominent energy crisis and environmental problems, the promotion of automobile electromotion has become a world consensus, and wireless charging gradually becomes a main mode of charging electric automobiles due to the advantages of convenience, safety, strong interoperability, suitability for severe weather and the like. In order to improve charging power and efficiency and meet the ground clearance requirement of various types of vehicle chassis, a magnetic coupling Resonant Wireless power transfer (MCR-WPT) mode is generally adopted in the Wireless charging system for the electric vehicle. However, in an actual application environment, foreign matters are easily generated in the energy transfer space, especially, the metal foreign matters can influence the wireless charging system, damage the resonance state, rapidly reduce the charging efficiency, even cause fire at high temperature, and have great harm. How to detect the foreign matters quickly, accurately and efficiently is a bottleneck for promoting the industrial development of the wireless charging of the automobile.
Documents of the prior art:
in 2010 KaranthAvinash et al propose to add a plurality of heat sensitive pieces as temperature sensors on the transmitting end coil to detect the temperature change of each area of the transmitting end coil. When the metal foreign bodies exist in the working process of the charging system, the metal foreign bodies generate heat due to the eddy heat effect, so that the local temperature of the transmitting end is obviously increased, and the existence and the position of the metal foreign bodies can be detected through the temperature sensor.
Us Katherine l.hall, 2011, et al, propose to use infrared temperature sensors to detect temperature changes in the charging region. The infrared temperature sensor is arranged on the front wall of the automobile, and the temperature sensor only detects the temperature around the resonator. If the detected temperature is higher than the reference temperature, it is considered that the metallic foreign matter is present in the charging system.
In 2011, nishio Takeshi et al proposed a foreign object detection technique based on light intensity variation. A radiation light unit is additionally arranged near a receiving coil at the bottom of the automobile, and an optical fiber is laid on a coil at a transmitting end. If foreign matters exist in the primary and secondary charging areas, the light intensity detected by the optical sensor at the transmitting end coil is lower than that of the case without the foreign matters.
In Inoue Junji et al, japan in 2012 proposed measuring the distance between a transmitting coil and a receiving coil based on sonar or radar methods and comparing the measured distance with a reference distance. And if the measured distance is smaller than the reference distance, judging that foreign matters exist between the primary side and the secondary side.
In 2015, in the patents applied by Liuson, rohaotong, chenyonggui and the like, a single-turn circular detection coil array is provided, and sub-coils are closely arranged to realize full coverage of a transmitting coil of a wireless power transmission system.
In 2015, american scholars research a WPT foreign matter detection method based on real-time thermal imaging, and the method realizes the thermal infrared foreign matter detection of wireless charging of an electric automobile through a neural network, and needs a processor to have strong calculation power and high cost.
In 2018, by using a machine vision detection method, such as the Jindengfeng of Harbin Industrial university, a machine learning model is established, and a foreign matter recognition network based on an SVM is trained, so that foreign matter recognition can be realized, but the cost is high.
In 2019, the university of Tianjin in the Tianjin industry provides a multi-turn annular detection coil array, and the coil array is of a hollow square structure. Meanwhile, the author designs an optimal detection coil model according to the influence of the metal foreign matter on the eddy current loss of the wireless power transmission system.
In 2019, the korean kai st and GIST group designed a variable-turn-number symmetric rectangular coil assembly that better offset the differential coil induced voltage problem caused by unequal transmitter coil magnetic fields.
In 2020, the korean kast and GIST team designed a multi-turn number-symmetric rectangular coil assembly.
State of the art and problems (drawbacks) present:
1. at present, foreign matter detection methods of wireless charging systems mainly comprise an auxiliary coil method and a system parameter method. However, in the case of a high-power electromagnetic environment, the auxiliary coil is equivalent to a metal foreign body, which can shield energy transmission, reduce energy transmission efficiency of the system, and cause potential safety hazard due to high voltage induced by the auxiliary coil during operation.
2. According to the method for detecting the foreign matters based on the system parameters, although an additional auxiliary coil is not needed, when small-size foreign matters with great harmfulness invade, the system parameters change very weakly, the foreign matters are difficult to detect quickly, the foreign matters need to be calibrated again when the transceiving coils are staggered and the height of a chassis changes, and the universality of actual working conditions is not strong.
3. Although the precision of the foreign matter detection method based on machine vision is improved, the algorithm is complex, the cost of required equipment is high, and the applicability of a vision system is reduced in a scene with large change of ambient light.
4. The detection method based on ultrasonic waves and radar is long in detection distance and large in detection area, can detect non-metallic foreign bodies and living foreign bodies, cannot distinguish metal foreign bodies, is high in cost, and is greatly influenced by environmental factors.
Disclosure of Invention
The invention aims to detect foreign matters in wireless charging, and provides a system and a method for detecting foreign matters in a wireless charging system of an electric vehicle based on thermal infrared image processing, wherein the specific scheme is as follows:
a foreign matter detection system of an electric vehicle wireless charging system based on thermal infrared image processing, the system comprising: the device comprises a controller, an infrared detection module, a command input module and a signal output module;
the infrared detection module is connected with the controller through a communication bus, the infrared detection module collects infrared images of the wireless charging device, the controller processes the collected images and extracts foreign matter image characteristics, and the command input module is connected with the controller and inputs corresponding image processing commands to the controller; the other end of the controller is connected with a signal output module, and the signal output module outputs foreign matter detection information and alarm information.
Furthermore, the infrared detection module comprises an optical system, a photoelectric conversion module, a signal amplification circuit, a filter circuit and an analog-to-digital conversion module;
the optical system collects infrared radiation signals of a transmitting coil area in the wireless charging device, outputs the signals to the photoelectric conversion module, the photoelectric conversion module converts the radiation signals into electric signals, the electric signals are amplified through the signal amplification circuit, the amplified signals are filtered through the filter circuit, and the filtered signals are converted into digital signals through analog-to-digital conversion and transmitted to the controller.
Further, a plurality of infrared detection modules are employed to maximize the utilization of the detection space.
Further, the command input module comprises a key module and a WiFi module, and a user inputs commands and modifies parameters through the key module and the WiFi module so as to be suitable for a specific test environment.
Furthermore, the signal output module comprises a display module, a wireless sending module, an alarm output module and a power-off signal module;
the display screen displays an image processing result, the alarm output module is used for sending an alarm signal, the wireless sending module is used for sending foreign matter detection information to an upper computer, a mobile phone or a computer of a user, and the power-off module is used for carrying out power-off processing on the wireless charging device according to the foreign matter detection information.
A foreign matter detection method of an electric vehicle wireless charging system based on thermal infrared image processing of the improved Otsu method comprises the following steps:
step 1: the foreign matter detection system starts detection, the controller sequentially reads temperature data and image data information of the infrared detection modules at different positions, and the controller judges whether dead spots exist or not according to the read information and marks the existing dead spots;
step 2: loading system parameters stored in advance or receiving parameters input by a user, initializing the system, selecting an ROI according to preset parameters, and determining a transmitting coil area;
and 3, step 3: performing data enhancement on the received image by adopting a bilinear interpolation method, and filtering partial noise through Gaussian filtering to obtain a real image; binaryzation is carried out on the filtered image through an improved Otsu method, and image characteristics of foreign matters are preliminarily extracted;
and 4, step 4: filtering noise points through morphological operation, and extracting an accurate foreign body image; determining the temperature, perimeter, area and gravity center of the foreign matters through traversal of a connected domain algorithm so as to determine the size and position of the foreign matters;
and 5: displaying the foreign body on a display screen in real time, and sending the temperature, size and position information of the foreign body to an upper computer through Bluetooth; the type of the foreign matter is judged according to the temperature and the area information of the foreign matter, the influence degree of the foreign matter on the wireless charging system is determined, the foreign matter with the temperature higher than the background is identified, and emergency alarm and power-off signal output are achieved.
The invention has the following effects:
the detection system provided by the invention adopts the thermal infrared detection module combined with the microcontroller, has strong environmental adaptability, low cost, simple structure, high integration level and small volume, can be suitable for detecting foreign matters of vehicles of various models and other wireless charging equipment, and has wide application range.
The invention utilizes the thermal infrared image processing method for detection, can realize the non-contact detection of foreign matters and the determination of positions in the wireless power supply system under any frequency, has almost no influence on the wireless charging system, and can stably work in the wireless charging process.
The invention adopts a self-adaptive infrared image processing algorithm, the accuracy and the applicable power level are far higher than the parameter detection of the coil and the system, and the detectable foreign body size is smaller. Compared with a machine vision method and a neural network algorithm, the method has the advantages that the operation speed is higher, and the method is suitable for being deployed on embedded equipment.
Drawings
FIG. 1 is a schematic diagram of the detailed construction of a foreign object detection system;
FIG. 2 is a flowchart of the operation of the infrared detection module;
FIG. 3 is a view showing an installation manner of an infrared receiving module;
FIG. 4 is a flow chart of foreign object detection;
FIG. 5 is a foreign object testing position;
FIG. 6 is a diagram of the OSTU binarization improvement effect under the condition of multiple foreign matters;
FIG. 7 is a diagram of the improvement effect of OSTU binarization under the condition of no foreign matter;
fig. 8 is a graph showing the result of image processing for different foreign objects at different positions.
Detailed Description
The technical solutions in the embodiments of the present invention will be described clearly and completely with reference to the accompanying drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be obtained by a person skilled in the art without making any creative effort based on the embodiments in the present invention, belong to the protection scope of the present invention.
With reference to fig. 1 to 8, the present invention provides a foreign object detection system for an electric vehicle wireless charging system based on thermal infrared image processing, the system includes: the device comprises an infrared detection module, a controller, a command input module and a signal output module;
the infrared detection module is connected with the controller through an IIC bus, the infrared detection module collects infrared images of the wireless charging device, the controller processes the collected images and extracts foreign body images, the command input module is connected with the controller in a control mode, and a user interactively controls the controller through the command input module; the data signal output end of the controller is connected with the signal output module, and the signal output module outputs foreign matter detection information and alarm information.
The infrared detection module comprises an optical system, a photoelectric conversion module, a signal amplification circuit, a filter circuit and an analog-to-digital conversion module;
the optical system collects infrared radiation signals of a transmitting coil area in the wireless charging device, outputs the signals to the photoelectric conversion module, the photoelectric conversion module converts the radiation signals into electric signals, the electric signals are amplified through the signal amplification circuit, the amplified signals are filtered through the filter circuit, and the filtered signals are converted into digital signals through the analog-to-digital conversion module and transmitted to the controller.
The command input module comprises a key module and a WiFi module, and a user inputs commands and modifies parameters through the key module and the WiFi module.
The signal output module comprises an LCD display module, an LED indicator light, a loudspeaker, a power-off signal module and a Bluetooth sending module;
the LCD display module shows the modification result, LED pilot lamp and speaker are used for sending alarm signal, bluetooth module is used for sending foreign matter detection information to user's cell-phone or computer host computer on, and the outage module is used for carrying out the outage according to foreign matter detection signal and handles wireless charging device.
The controller extracts the foreign body image through an image processing algorithm, and obtains information such as the temperature, the area, the perimeter, the position and the like of the foreign body. Then the Bluetooth is transmitted to a mobile phone of a user or a computer upper computer, and a loudspeaker, an LED lamp and the like send out alarm signals. The user can improve system performance through host computer, wiFi module and button interactive module command input and parameter modification, can look over the modification result in real time through the LCD screen simultaneously, the debugging under the different environment of convenience is worked.
The controller adopts an STM32 microcontroller, and the infrared detection module adopts an MLX90640 module. STM32 microcontroller cost is lower, simple structure, the integrated level is high, and is small, can be applicable to various vehicles and other wireless battery charging outfit's foreign matter detection, and application scope is wide.
The thermal infrared sensor adopts an MLX90640 module, and when the height is about 12cm, the detection range of the thermal infrared sensor is smaller than the range (850 mm multiplied by 750 mm) of an automobile wireless charging transmitting coil, so that four sensor modules are arranged at four corners of a receiving end (the size of a receiving coil is smaller than 450mm multiplied by 450 mm) in a mode shown in figure 3. The main control and man-machine interaction module is arranged above a receiving end shielding plate of the charging device to prevent the electromagnetic field of the charging device from influencing each other.
The invention provides a foreign matter detection method of an electric vehicle wireless charging system based on improved Otsu method thermal infrared image processing, which comprises the following steps of:
step 1: the foreign matter detection system starts detection, the controller sequentially reads temperature data and image data information of the infrared detection modules at different positions, and the controller judges whether dead pixels exist or not according to the read information and marks the dead pixels;
step 2: loading system parameters stored in advance or receiving a parameter initialization system input by a user, selecting an ROI according to a preset parameter frame, and determining a transmitting coil area;
and step 3: performing data enhancement on the received image by adopting a bilinear interpolation method, and filtering partial noise information by Gaussian filtering to obtain a real image; binaryzation is carried out on the filtered image through an Otsu method, and an image of foreign matters is preliminarily extracted;
and 4, step 4: filtering noise points through morphological operation, and extracting an accurate foreign body image; determining the perimeter, the area and the gravity center of the foreign matter through traversal of a connected domain algorithm;
and 5: displaying the foreign body on an LCD display screen in real time, and sending the temperature, size and position information of the foreign body to an upper computer through Bluetooth; and judging the type of the foreign matter according to the temperature and the area information of the foreign matter, determining the influence degree of the foreign matter on the wireless charging system, and controlling whether to directly cut off the charging system.
Since the size of the transmitting coil is centrosymmetric, only one quarter of the detection condition of the whole system needs to be verified, and the test position for placing the foreign matters in the experimental test is shown in fig. 5.
In order to extract foreign matter information in the WPT energy transmission space image, the image needs to be binarized to distinguish foreign matter from background information. This requires selecting a suitable binarization method to obtain the global threshold. The maximum inter-class variance method (OSTU) is chosen here. The method is also called Otsu method, and is an algorithm capable of adaptively determining the image binary segmentation threshold. The algorithm assumes that image pixels can be divided into background and object portions according to a global threshold. The optimal threshold is then calculated to distinguish the two types of pixels such that the degree of distinction between the two types of pixels is maximized.
After the threshold value obtained by the method is subjected to binarization segmentation, the variance between the foreground and background classes of the image is maximum. The method is simple in calculation and is not influenced by the contrast and brightness of the image, so that the method is very suitable for being applied to a foreign matter detection system. Since variance is a measure of the uniformity of the gray level distribution of an image, the larger the between-class variance of the background and foreground, the larger the difference between the two parts constituting the image, since the difference between the two parts becomes smaller as soon as the two parts are erroneously distinguished. Therefore, a segmentation that maximizes the inter-class variance means that the probability of false scores is minimized.
The image binarization method through Otsu method comprises the following specific steps:
let m be the number of pixels with a gray level of i in the image i The overall gray scale value range is [0, N-1 ]]The total number of pixels of each gray level is expressed by:
determining the proportion of each gray value in the image as follows:
the threshold value of the image is T, and the image is divided into foregrounds C 1 And background C 2 Two parts, each of which is represented by the following formula:
let the average gray scale of the global image be μ and the average gray scales of the two regions be μ 1 、μ 2 Expressed as follows:
the average gray level of the global image is determined by:
the between-class variance of the two regions is represented by:
g＝P 1 (μ 1 -μ) 2 +P 2 (μ 2 -μ) 2 ＝P 1 P 2 (μ 1 -μ 2 ) 2 (8)
and traversing the segmentation gray threshold in the gray range of the whole image, so that the computed inter-class variance g is the optimal threshold of the global image when the inter-class variance g is maximum.
Of course, the robustness of the foreign object detection system cannot be guaranteed by using only the OSTU, because OSTU binarization is that the default image has a global threshold, that is, there is a foreign object in the visual field, and it selects the foreign object and the background which have the largest difference. However, in actual conditions, the foreign matter is not always present in the field of view, and may not be one. Therefore, it is necessary to appropriately adjust the binarization processing of the foreign object image based on the OSTU. For the condition of multiple foreign matters, the first two thresholds with larger inter-class variance are selected, and then the final threshold with smaller numerical value and smaller difference with other thresholds is selected, so that the selected information under the state of multiple foreign matters is more comprehensive. The effect pairs before and after the improvement are shown in fig. 6, it can be seen that the traditional OSTU algorithm can only extract the most obvious foreign matters, while the improved algorithm has a better effect on the treatment of the condition of multiple foreign matters and can extract smaller foreign matters.
For the case where there is no foreign object, it is necessary to set a minimum threshold limit to prevent erroneous recognition. The method can be manually calibrated under the condition of no foreign matters, the maximum value of the image pixel is used as the lowest threshold value, the lowest threshold value can also be manually input, and a program is automatically stored as the lowest threshold value for starting the computer next time. For example, as shown in fig. 7, the effect before and after improvement is that in the conventional OSTU algorithm, a default image can be segmented, so that misrecognition occurs, and the improved OSTU algorithm can process an image without the existence of foreign objects, so that the method is more suitable for a foreign object detection scene.
Fig. 8 is an image processing result of an experiment performed on a 30kW wireless charging device with two types of foreign objects (5-corner coin, M4 nut) respectively located at the corner point, the side line, and the center of the transmitting end. Each column in the figure, from left to right, is still the interpolated filtered result for display and the result after the binarization and switching operations.
As can be seen from the image processing results, as the size of the foreign object decreases, the extracted contour of the foreign object image also decreases. The approximate position of the foreign object in the transmitter coil can be determined by the position of the extracted foreign object contour in the image. The magnetic induction intensity at the corner point is higher, so that the temperature rise of the foreign matters at the corner point is relatively obvious, the processing result is more ideal, the side magnetic field intensity is inferior to the corner point, the contour of the foreign matters is slightly smaller, the central magnetic field intensity is lowest, and the contour is also smallest. By comparing image processing results, the system can accurately detect the foreign matter with the minimum size at the lowest point of the magnetic field by using the M4 nut, the detection success rate can reach more than 90%, and more accurate positioning can be realized.
The foreign matter detection system and the method of the wireless charging system of the electric vehicle based on the thermal infrared image processing are introduced in detail, the principle and the implementation mode of the invention are explained by applying a specific example, and the description of the embodiment is only used for helping to understand the method and the core idea of the invention; meanwhile, for a person skilled in the art, according to the idea of the present invention, there may be variations in the specific embodiments and the application scope, and in summary, the content of the present specification should not be construed as a limitation to the present invention.
Claims (9)
1. The utility model provides a wireless charging system foreign matter detection system of electric automobile based on thermal infrared image processing which characterized in that, the system includes: the device comprises a controller, an infrared detection module, a command input module and a signal output module;
the infrared detection module is connected with the controller through a communication bus, the infrared detection module collects infrared images of the wireless charging device, the controller processes the collected images and extracts foreign matter image characteristics, and the command input module is connected with the controller and inputs corresponding image processing instructions to the controller; the other end of the controller is connected with a signal output module, and the signal output module outputs foreign matter detection information and alarm information.
2. The foreign matter detection system of the electric vehicle wireless charging system based on the thermal infrared image processing as claimed in claim 1, wherein the infrared detection module comprises an optical system, a photoelectric conversion module, a signal amplification circuit, a filter circuit and an analog-to-digital conversion module;
the optical system collects infrared radiation signals of a transmitting coil area in the wireless charging device, outputs the signals to the photoelectric conversion module, the photoelectric conversion module converts the radiation signals into electric signals, the electric signals are amplified through the signal amplification circuit, the amplified signals are filtered through the filter circuit, and the filtered signals are converted into digital signals through analog-to-digital conversion and transmitted to the controller.
3. The system for detecting the foreign matters in the wireless charging system of the electric automobile based on the thermal infrared image processing as claimed in claim 2, wherein a plurality of infrared detection modules are adopted to maximize the utilization of the detection space.
4. The system for detecting the foreign matters in the wireless charging system for the electric vehicle based on the thermal infrared image processing as claimed in claim 1, wherein the command input module comprises a key module and a WiFi module, and a user can input commands and modify parameters through the key module and the WiFi module so as to be suitable for a specific test environment.
5. The system for detecting the foreign matter in the wireless charging system of the electric automobile based on the thermal infrared image processing as claimed in claim 1, wherein the signal output module comprises a display module, a wireless transmission module, an alarm module and a power-off signal output.
6. The method for detecting the foreign matter in the wireless charging system of the electric automobile based on the thermal infrared image processing as claimed in claim 1, wherein the method for detecting the foreign matter in the non-contact wireless charging system using the thermal infrared sensor senses the existence of the foreign matter based on the thermal infrared image processing and the temperature change.
7. The method for detecting the foreign matters in the wireless charging system of the electric automobile based on the thermal infrared image processing as claimed in claim 6, characterized by comprising the following steps:
step 1: the foreign matter detection system starts detection, and the controller judges whether dead pixels exist and marks the dead pixels by reading temperature data and image data information of the infrared detection modules at different positions in sequence;
step 2: loading system parameters stored in advance or receiving parameters input by a user, carrying out system initialization, selecting an ROI according to preset parameters, and determining a transmitting coil area;
and step 3: performing data enhancement on the received image by adopting a bilinear interpolation method, and filtering partial noise through Gaussian filtering to obtain a real image; binaryzation is carried out on the filtered image through an improved Otsu method, and image characteristics of foreign matters are preliminarily extracted;
and 4, step 4: filtering noise points through morphological operation, and extracting an accurate foreign body image; determining the perimeter, the area and the gravity center of the foreign matter through traversal of a connected domain algorithm so as to determine the size and the position of the foreign matter;
and 5: displaying the processing result on a display screen in real time, and wirelessly sending the temperature, the size and the position information of the foreign matters to an upper computer; and judging the type of the foreign matter according to the temperature and the area information of the foreign matter, determining the influence degree of the foreign matter on the wireless charging system, and controlling whether to directly cut off the charging system.
8. The method for detecting the foreign matter in the wireless charging system of the electric vehicle based on the thermal infrared image processing as claimed in claim 7, wherein the image binarization by the improved Otsu method comprises the following specific steps:
let m be the number of pixels with a gray level of i in the image i The overall gray scale value range is [0, N-1 ]]The total number of pixels of each gray level is expressed by:
determining the proportion of each gray value in the image as follows:
the threshold value of the image is T, and the image is divided into foregrounds C 1 And background C 2 Two parts, each of which is represented by the following formula:
let the average gray scale of the global image be μThe average grayscales of the two regions are μ 1 、μ 2 Expressed as follows:
the average gray level of the global image is determined by:
the between-class variance of two regions is represented by:
g＝P 1 (μ 1 -μ) 2 +P 2 (μ 2 -μ) 2 ＝P 1 P 2 (μ 1 -μ 2 ) 2 (8)
and traversing the segmentation gray threshold in the gray range of the whole image, so that the computed inter-class variance g is the optimal threshold of the global image when the inter-class variance g is maximum.
9. The foreign matter detection method of the wireless charging system of the electric vehicle based on the thermal infrared image processing as claimed in claim 8, wherein for the case of multiple foreign matters, the first two thresholds with larger inter-class variance are selected, and then the final threshold with smaller numerical value and smaller difference with other thresholds is selected, so that the selected information is more comprehensive under the state of multiple foreign matters; for the case of no foreign object, a minimum threshold limit is set to prevent false recognition.
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