Direct current charging pile and direct current charging pile contactor contact adhesion detection method and device

Abstract

The invention belongs to the technical field of direct-current charging piles, and particularly relates to a direct-current charging pile and a direct-current charging pile contactor contact adhesion detection method and device. The method comprises the following steps: injecting a first frequency voltage signal coupled by a parallel voltage capacitor into a charging loop after detecting that charging is finished, determining the resistance value of the parallel voltage capacitor under the first frequency by the impedance of a resistor, and judging whether the contact adhesion of the double contactors occurs based on the voltage at the output ends of the positive and negative electrodes of the charging pile under the condition; when the double contactors are not adhered at the same time, a second frequency voltage signal coupled by the parallel voltage capacitors is injected into the charging loop, and the resistance value of the parallel voltage capacitors under the frequency is determined by the capacitive reactance of the capacitors; whether single contactor contact adhesion occurs is judged based on the voltage variation of the positive and negative output ends of the charging pile, and real detection of double contactor contact adhesion, single contactor contact adhesion or no adhesion after charging is completed is realized.

Description

Technical Field

[0001] The present invention belongs to the technical field of DC charging piles, and in particular relates to a DC charging pile, a method and a device for detecting contact adhesion of a DC charging pile contactor. Background Art

[0002] When charging electric vehicles using charging piles, the high charging voltage and current can cause contact sticking in the charging pile's contactor switches during the moment of connection or disconnection. GB 44263-2024, "Safety Requirements for Electric Vehicle Conductive Charging Systems," released on July 24, 2024, explicitly requires that both DC power supply equipment and electric vehicles be equipped with a sticking detection function for the high-voltage DC contactors in the DC power supply circuit. This mandatory national standard ensures the safety of the conductive charging process for electric vehicles and applies to AC and DC charging systems for electric vehicles with a rated voltage not exceeding 1000V AC or 1500V DC on the power grid side and a maximum rated voltage not exceeding 1000V AC or 1500V DC on the electric vehicle side. However, this standard only checks for an alarm function for sticking contactors in charging piles. The existing inspection method simulates either a normally closed or normally open contactor by shorting the DC output terminals or triggering the DC contactor's feedback signal before an insulation self-test. After charging is initiated, the DC power supply equipment's communication status, charging status, and alarm information are checked to determine whether the sticking alarm function is in place. And in the energy transmission stage, the DC output terminal is short-circuited or the DC contactor feedback signal is triggered to simulate any contactor in the normally closed state or the normally open state. By checking the communication status, charging status, and alarm information of the DC power supply equipment at the end of charging, it is determined whether the alarm function of contact adhesion is available. The above method is aimed at the alarm function detection under the contact adhesion simulation. It cannot detect whether the contactor of the charging pile has real contact adhesion, which poses a safety risk during charging. In particular, if the contactor contacts cannot be disconnected due to adhesion after charging is completed, and the contactor is in the normally closed state, then the charging pile is prone to high-voltage leakage, which seriously threatens personal and equipment safety. Summary of the Invention

[0003] The purpose of the present invention is to provide a method and device for detecting contact adhesion of a DC charging pile and a DC charging pile contactor, so as to solve the problem that the existing contact adhesion detection method only detects whether the alarm function of the contact adhesion is normal in an analog way, and is unable to detect whether the charging pile contactor contacts are actually adhered after charging is completed.

[0004] In order to solve the above technical problems, the present invention provides a method for detecting contact adhesion of a DC charging pile contactor, comprising:

[0005] After detecting that charging is completed, the frequency sweep unit injects a voltage signal of the first frequency into the charging circuit via the coupling unit, detects the voltage at the positive and negative output terminals of the charging pile and records it as the first voltage. If the first voltage is less than a first set value, it is determined that both contactors of the charging pile are adhered; otherwise, both contactors are not adhered.

[0006] If both contactor contacts are not stuck, the frequency sweep unit is controlled to input a voltage signal of the second frequency into the charging circuit via the coupling unit, and the voltage at the positive and negative output terminals of the charging pile is detected and recorded as the second voltage; then one of the poles of the frequency sweep unit is controlled to be connected to the ground wire of the charging pile, and the voltage at the positive and negative output terminals of the charging pile is detected and recorded as the third voltage. If the voltage difference between the third voltage and the second voltage is greater than a third set value, it is determined that a single contactor contact of the charging pile is stuck; otherwise, the contactor contact of the charging pile is not stuck;

[0007] The coupling unit includes a resistor and a capacitor connected in parallel. The parallel resistance of the coupling unit at the first frequency is determined by the impedance of the resistor, and the parallel resistance of the coupling unit at the second frequency is determined by the capacitive reactance of the capacitor.

[0008] Furthermore, the first set value is determined based on a reference voltage, where the reference voltage is a voltage value output by the frequency sweeping unit via the coupling unit, measured when the frequency sweeping unit is disconnected from the charging pile ground wire and the frequency sweeping unit is not connected to the charging circuit.

[0009] Furthermore, the condition for judging the end of charging is: charging is judged to be ended when it is detected that the voltage at the positive and negative output terminals of the charging pile is less than a second set value.

[0010] The beneficial effects of the above technical solution are as follows: the present invention is a pioneering invention. After detecting that charging is completed, a first frequency voltage signal coupled through a parallel voltage capacitor is first injected into the charging circuit of the charging pile. The resistance of the parallel voltage capacitor at the first frequency is determined by the resistance impedance. Based on whether the voltage at the positive and negative output terminals of the charging pile collected after the injection of the first frequency voltage signal is less than a first set value, it is determined whether the charging pile is short-circuited, and further whether the dual contactor contacts are stuck. When the dual contactors are not stuck at the same time, a second frequency voltage signal coupled through a parallel voltage capacitor is further injected into the charging circuit of the charging pile. The resistance of the parallel voltage capacitor at this frequency is determined by the capacitive reactance. Then, after controlling either pole of the sweep unit to connect to the ground wire of the charging pile, it is determined whether the voltage at the positive and negative output terminals of the charging pile has changed significantly in combination with the ground capacitance to determine whether the single contactor contact is stuck. This achieves true detection of dual contactor contact sticking, single contactor contact sticking, or no sticking after charging is completed, thereby improving charging safety.

[0011] In order to solve the above technical problems, the present invention also provides a device for detecting contact adhesion of a DC charging pile contactor, comprising a processor, an acquisition unit, a frequency sweeping unit and a coupling unit; the processor is used to control the frequency sweeping unit to inject a voltage signal of a first frequency into the charging circuit via the coupling unit after detecting that charging is completed, and then judge whether the voltage at the positive and negative output terminals of the charging pile detected by the acquisition unit under this condition is less than a first set value. If it is less than the first set value, it is judged that both contactor contacts of the charging pile are adhered, otherwise, both contactor contacts are not adhered; if both contactor contacts are not adhered, the frequency sweeping unit is controlled to input a voltage signal of a second frequency into the charging circuit via the coupling unit. In the loop, the voltages at the positive and negative output terminals of the charging pile detected by the acquisition unit under this condition are obtained and recorded as the second voltage; then one of the poles of the frequency sweep unit is controlled to be connected to the ground wire of the charging pile, the voltages at the positive and negative output terminals of the charging pile detected by the acquisition unit under this condition are obtained and recorded as the third voltage, and it is determined whether the voltage change between the third voltage and the second voltage is greater than a third set value. If so, it is determined that a single contactor contact of the charging pile is adhered, otherwise, the contactor contact of the charging pile is not adhered; wherein, the coupling unit includes a resistor and a capacitor arranged in parallel, and the parallel resistance of the coupling unit at the first frequency is determined by the impedance of the resistor, and the parallel resistance of the coupling unit at the second frequency is determined by the capacitive reactance of the capacitor.

[0012] Furthermore, the first set value is determined based on a reference voltage, and the reference voltage is a voltage value output by the frequency sweeping unit through the coupling unit measured by the acquisition unit when the frequency sweeping unit is disconnected from the charging pile ground wire and the frequency sweeping unit is not connected to the charging circuit.

[0013] Furthermore, whether charging is completed is determined based on the voltage at the positive and negative output terminals of the charging pile detected by the acquisition unit. When the voltage at the positive and negative output terminals of the charging pile is less than a second set value, charging is determined to be completed.

[0014] Furthermore, a switch is provided between the positive and / or negative pole of the frequency sweep unit and the ground wire of the charging pile, and the switch controls the connection or disconnection between the positive or negative pole of the frequency sweep unit and the ground wire of the charging pile.

[0015] Furthermore, the frequency sweeping unit includes a frequency sweeping generator, a voltage power amplifier circuit and a booster, the output end of the booster is the output end of the frequency sweeping unit; the voltage power amplifier circuit is arranged between the frequency sweeping generator and the booster, and is used to power amplify the voltage signal output by the frequency sweeping generator; the booster is used to further amplify the signal output by the voltage power amplifier circuit.

[0016] Furthermore, the acquisition unit includes a voltage divider circuit, an acquisition circuit and a differential amplifier. The voltage divider circuit sampling is connected to the positive and negative bus bars of the charging circuit. The differential amplifier is used to perform impedance matching on the voltage signal detected by the voltage divider circuit. The acquisition circuit is used to perform digital-to-analog conversion on the voltage signal output by the differential amplifier.

[0017] In order to solve the above technical problems, the present invention further provides a DC charging pile, which adopts the above-mentioned DC charging pile contactor contact adhesion detection method to perform contactor contact adhesion detection.

[0018] The beneficial effects of the above technical solution are as follows: the present invention is a pioneering invention. After detecting that charging is completed, a first frequency voltage signal coupled through a parallel voltage capacitor is first injected into the charging circuit of the charging pile. The resistance of the parallel voltage capacitor at the first frequency is determined by the resistance impedance. Based on whether the voltage at the positive and negative output terminals of the charging pile collected after the injection of the first frequency voltage signal is less than a first set value, it is determined whether the charging pile is short-circuited, and further whether the dual contactor contacts are stuck. When the dual contactors are not stuck at the same time, a second frequency voltage signal coupled through a parallel voltage capacitor is further injected into the charging circuit of the charging pile. The resistance of the parallel voltage capacitor at this frequency is determined by the capacitive reactance. Then, after controlling either pole of the sweep unit to connect to the ground wire of the charging pile, it is determined whether the voltage at the positive and negative output terminals of the charging pile has changed significantly in combination with the ground capacitance to determine whether a single contactor contact is stuck. This achieves true detection of dual contactor contact sticking, single contactor contact sticking, or no sticking after charging is completed, thereby improving the charging safety of the charging pile. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 Schematic diagram of a device for detecting contact adhesion of a DC charging pile contactor according to an embodiment of the present invention;

[0020] Figure 2 This is a schematic diagram of the principle of the collection unit of an embodiment of the device of the present invention;

[0021] Figure 3 This is a schematic diagram of the principle of a frequency sweep unit of an embodiment of the device of the present invention;

[0022] Figure 4 This is a wiring diagram of a sweep frequency generator according to an embodiment of the present invention;

[0023] Figure 5 is a schematic diagram of a voltage power amplifier circuit of an embodiment of the device of the present invention;

[0024] Figure 6 This is a flow chart of contact adhesion detection for a DC charging pile contactor according to an embodiment of the present invention;

[0025] Figure 7 1 is an equivalent circuit diagram of an embodiment of the device of the present invention. DETAILED DESCRIPTION

[0026] In order to make the objectives, technical solutions and advantages of the present invention more clear, the specific embodiments of the present invention are further described below with reference to the accompanying drawings.

[0027] The inventive concept of the present invention is as follows: after charging is completed, a first frequency voltage signal is injected into the charging circuit so that the parallel resistance of the coupling unit is determined by the impedance of the resistor to test whether the double contactor contacts are sticking. When the double contactor contacts are not sticking, a second frequency voltage signal is injected into the charging circuit so that the parallel resistance of the coupling unit is determined by the capacitive reactance of the capacitor. The capacitance to ground of the DC charging pile is used in combination with the change in voltage to test whether the single contactor contact is sticking, thereby realizing the detection of double contactor sticking, single contactor sticking or no sticking.

[0028] Device embodiment

[0029] The present invention provides a device for detecting contact adhesion of a DC charging pile contactor, such as Figure 1 As shown, it includes: a processor, an acquisition unit, a frequency sweeping unit and a coupling unit. The acquisition unit is used to collect the voltage at the positive and negative output terminals of the charging pile, and its sampling terminal is connected to the positive and negative busbars of the charging circuit, that is, connected to the positive and negative busbars between the positive and negative output terminals of the charging pile and the positive and negative poles of the electric vehicle battery, and the output is connected to the processor. The frequency sweeping unit injects the voltage signal of the first frequency or the second frequency into the positive and negative busbars of the charging circuit through the coupling unit. The processor connects the acquisition unit and the frequency sweeping unit to complete the core algorithm, task scheduling and input of the present invention, etc., to realize a method for detecting contact adhesion of a DC charging pile contactor. The following is a detailed description of a contact adhesion detection device for a DC charging pile contactor.

[0030] Collection unit such as Figure 2 As shown, the device includes a voltage divider circuit and a data acquisition circuit. The voltage divider circuit is composed of resistors R1 and R2. The voltage divider circuit is connected to the positive and negative busbars of the charging circuit to sample the voltage and convert the sampled value proportionally. In this embodiment, the resistance of resistor R1 is 998kΩ and the resistance of resistor R2 is 2kΩ. Resistors R1 and R2 are precision resistors with a stability of 1 part per million and an accuracy of 0.01%. The voltage divider circuit converts the collected voltage to 500:1.

[0031] The acquisition circuit includes an analog-to-digital conversion unit, which converts the sampled analog value into a digital voltage value. This unit can use the AD7380 chip, which has an input voltage range of 0 to +2.5V and a built-in 2.5V reference voltage. This chip can perform 16-bit A / D conversion on analog inputs, achieving a 16-bit quantization error and significantly improving voltage resolution.

[0032] The acquisition unit also includes a differential amplifier, located between the voltage divider circuit and the acquisition circuit. This amplifier performs impedance matching on the voltage signal detected by the voltage divider circuit. The acquisition circuit then performs digital-to-analog conversion on the voltage signal output by the differential amplifier. Impedance matching effectively prevents signal loss and interference, improving the efficiency and stability of signal transmission. The differential amplifier can utilize the AD620 programmable gain amplifier.

[0033] like Figure 3 As shown, the sweep frequency unit includes a sweep frequency generator. Figure 4 As shown, it includes a direct digital frequency synthesizer DDS (such as AD9833 chip), capacitors C3 and C4, and a crystal. Capacitor C3 is 10nF, capacitor C4 is 100nF, and the crystal is a 10M active crystal. The output frequency of the sweep generator is:

[0034]

[0035] Among them, f is the output frequency of the sweep generator, D is the program setting value, f MCLK is the crystal frequency (10M).

[0036] The processor connects to the AD9833's FSYNC (SPI synchronization clock), SCLK (SPI clock), and SDATA interfaces via the SPI interface to set the D value, controlling the frequency sweep generator to output a voltage signal of the set frequency. For example, if a 10kHz voltage signal is required, the D value is set to:

[0037]

[0038] Since the voltage signal output by the sweep generator has an amplitude of 1V, to further improve detection accuracy, the present invention also amplifies the voltage signal output by the sweep generator. Specifically, the sweep unit also includes a voltage amplifier circuit and a voltage booster. The voltage amplifier circuit is disposed between the sweep generator and the voltage booster to isolate and amplify the voltage signal output by the sweep generator; the voltage booster is used to further amplify the signal output by the voltage amplifier circuit.

[0039] like Figure 5As shown, the voltage power amplifier circuit includes a power amplifier chip, a feedback resistor Ra, and a feedback resistor Rb. In this embodiment, the power amplifier chip uses OPA548, whose maximum output current is 3A. The resistance values of the feedback resistors Ra and Rb are both 100Ω, which can amplify the input voltage by 2 times before outputting it. The booster is used to further amplify the output voltage of the voltage power amplifier circuit and output it to the positive output terminal Vs+ and the negative output terminal Vs- of the frequency sweeping unit. For example, the output voltage of the voltage power amplifier circuit is amplified 100 times. That is, for a 1V electrical signal output by the frequency sweeping transmitter, the output voltage of the voltage power amplifier circuit is approximately 2V and the output current is maximum 3A, while the output voltage of the booster is 200V and the output current is maximum 30mA. The voltage power amplifier circuit is arranged between the frequency sweeping generator and the booster to perform power amplification.

[0040] The coupling unit is composed of a capacitor and a resistor connected in parallel. The resistance of the resistor and the capacitance of the capacitor in the coupling unit can be customized. The setting principle is: the parallel resistance of the coupling unit at the first frequency is determined by the impedance of the resistor; the parallel resistance of the coupling unit at the second frequency is determined by the capacitive reactance of the capacitor. The coupling unit includes a first coupling unit and a second coupling unit. Figure 1 As shown, the first coupling unit includes a resistor RL1 and a capacitor C21 arranged in parallel, and the second coupling unit includes a resistor RL2 and a capacitor C22 arranged in parallel. The positive output of the frequency sweep unit is connected to the positive output of the charging pile through the first coupling unit, and the negative output of the frequency sweep unit is connected to the negative output of the charging pile through the second coupling unit. The positive output of the frequency sweep unit is connected to the ground line of the charging pile through the first switch K3, and / or the negative output of the frequency sweep unit is connected to the ground line of the charging pile through the second switch K4.

[0041] In one embodiment, resistors RL1 and RL2 are 1W metal film resistors with a resistance of 100kΩ and an accuracy of 1%. Capacitors C21 and C22 are 1500V capacitors with a capacitance of 1nF and an accuracy of 1%. The coupling unit provides mutual protection between the DC charging pile and the device for detecting contact adhesion of a DC charging pile contactor of the present invention, ensuring safe operation of the DC charging pile and the device for detecting contact adhesion of a DC charging pile contactor of the present invention.

[0042] The processor can use the BF533 motherboard, which is composed of the BF533 chip of ADI and its peripherals. The chip has a large number of built-in peripherals, including 1 SPI interface, two SPORT interfaces, 3 external timers, 16 general IO ports, AMC interface (asynchronous memory interface), etc. The IO port of the BF533 motherboard is connected to the keyboard for input control. The keyboard of the present invention adopts a simple keyboard, and 6 keyboards are connected to the 6 IO ports of the processor. Figure 1As shown, the BF533 chip is connected to the acquisition unit through the SPORT1 interface and is connected to the frequency sweep circuit through the SPORT2 interface and the SPI interface.

[0043] The detection device also includes a power supply unit for providing working power to the processor, acquisition unit, and frequency sweep unit. The power supply unit includes a power supply module, such as a small switching power supply that converts 5V to +15V, -15V, and 5V outputs, with a current output of 0.5A.

[0044] The power supply unit also includes a charging module. The power module is connected to the charging module and supports "charging and discharging at the same time" and "stopping when fully charged". The charging module can be a power bank, such as Xiaomi's PLM09ZM power bank, which supports "charging and discharging at the same time" and "stopping when fully charged". Its capacity is 10,000 mA and the output voltage is 5V.

[0045] The power supply unit also includes a power converter, which converts the power supply voltage of the power module into the operating voltage of the analog-to-digital conversion unit and the sweep generator. In this embodiment, the power converter is a 5V to 3.3V linear voltage regulator module, which converts the 5V power supply to 3.3V for the BF533 motherboard and AD7380 chip. The fixed voltage output chip REG1117F-3.3V can be used.

[0046] The DC charging pile contactor adhesion detection device also includes a display module for displaying the charging pile output voltage, the electrical signal sent to the charging pile, and the contactor adhesion detection results. The display module can be a liquid crystal display (LCD), directly driven by the BF533 motherboard through the AMC interface.

[0047] Based on the above detection device, the present invention can realize a method for detecting contact adhesion of a DC charging pile contactor, such as Figure 6 As shown, the following steps are included:

[0048] 1) Control the frequency sweep unit to disconnect from the charging pile ground wire, detect whether charging is completed, and determine whether the contactor contacts are stuck after detecting that charging is completed.

[0049] The equivalent circuit of the detection device of the present invention after being connected to the charging pile charging system is as follows: Figure 7 As shown, C1 is the equivalent capacitance between the positive and negative output wires of the charging pile, K1 and K2 are charging pile contactors, C11 is the safety capacitance of the DC charging pile to the ground, and C12 is the coupling capacitance of the DC charging pile to the ground. C11 and C12 are generally tens of nF, and C1 is generally a maximum of 1nF.

[0050] When the positive output of the frequency sweep unit is connected to the ground wire of the charging pile through the first switch K3 and the negative output of the frequency sweep unit is connected to the ground wire of the charging pile through the second switch K4, K3 and K4 are turned on. During the entire charging process, the processor determines whether charging is completed based on the voltage at the positive and negative output terminals of the charging pile detected by the acquisition unit. The judgment method is as follows:

[0051] After connecting the charging pile and the electric vehicle, the charging pile waits for its DC signal output. After the user successfully swipes their card for verification, charging starts and the DC charging pile outputs DC power. Because the charging pile's output internal resistance is very small (<1Ω), the DC internal resistance output by the frequency sweep circuit is approximately equal to RL1+RL2=200kΩ. The coupling unit acts as a shield, shielding the DC charging pile from the frequency sweep unit. At this point, the voltage signal output by the charging pile's positive and negative output terminals should be a DC signal. When the voltage at the charging pile's positive and negative output terminals collected by the acquisition unit is greater than a fourth set value, the contactor is judged to be closed and connected normally. When the voltage at the charging pile's positive and negative output terminals is detected to be less than a second set value, charging is judged to be complete and the DC signal essentially disappears. The second and fourth set values are set based on the charging pile's output voltage. For example, if the charging pile output power is 300V, the fourth set value can be set to 100V, 150V, or 200V, etc. The second set value can be set to 5V, 10V, or 12V, etc.

[0052] 2) Control the frequency sweep unit to output a voltage signal of the first frequency through the keyboard.

[0053] The frequency sweep unit is used to input the voltage signal of the first frequency into the charging circuit through the coupling unit. Under this condition, the voltage V1Hz_2 at the positive and negative output terminals of the charging pile is collected and recorded as the first voltage. If V1Hz_2 is less than the first set value, it is determined that both contactors of the charging pile are stuck.

[0054] The parallel resistance of the coupling unit at the first frequency is mainly determined by the impedance of the resistors. For example, when the resistance of resistors RL1 and RL2 is 100kΩ and the capacitance of capacitors C21 and C22 is 1nF, the first frequency is a low-frequency signal, which can be 1Hz, 2Hz, or 5Hz. When the first frequency is 1Hz, the capacitive reactance of capacitors C21 and C22 is 1590kΩ, which is 15.9 times larger than the resistance of resistors RL1 and RL2 of 100kΩ. At this time, the parallel resistance of the coupling unit is mainly determined by the impedance of the resistors. When both contactor contacts of the charging pile are adhered, that is, K1 and K2 are closed, the DC charging pile is equivalent to a short circuit, the output voltage of the DC charging pile is 0, and the voltage at the positive and negative output terminals of the charging pile collected by the collection unit is an AC voltage, and the AC voltage is close to 0. In one embodiment, the first set value is a voltage value less than or equal to 0.1V, which can be set to 0.05V or 0.1V, etc.

[0055] As a preferred embodiment, in order to make a more accurate judgment, the first set value is determined based on the reference voltage. The reference voltage is the voltage value output by the sweeping unit through the coupling unit when the sweeping unit is disconnected from the ground wire of the charging pile and the sweeping unit is not connected to the charging circuit. Specifically, before the detection device is connected to the charging system (K3 and K4 are disconnected), that is, when the sweeping unit is not connected to the charging circuit, the sampling end of the acquisition unit is connected to the output end of the sweeping unit through the coupling unit, and the voltage value V1Hz_1 output at this time is measured and used as the reference voltage. If the first voltage is less than the first set value, it is judged that the two contactor contacts of the charging pile are both adhered, otherwise the two contactor contacts are not both adhered. For example, the first set value is set to 0.01*reference voltage, that is, when the following formula is satisfied, it is judged that the two contactor contacts of the charging pile are both adhered:

[0056]

[0057] 3) If the two contactor contacts of the charging pile are not both adhered, the frequency sweep unit is controlled by the keyboard to output a voltage signal of the second frequency.

[0058] The frequency sweep unit uses the coupling unit to input the second frequency voltage signal into the charging circuit. Under this condition, the voltage V10Hz_1 at the positive and negative output terminals of the charging pile is collected and recorded as the second voltage. The parallel resistance of the coupling unit at the second frequency is determined by the capacitive reactance of the capacitor. For example, when the resistance values of resistors RL1 and RL2 are 100kΩ and the capacitance values of capacitors C21 and C22 are 1nF, the second frequency is a high-frequency signal, which can be 10kHz, 12kHz, or 15kHz. When the second frequency is 10kHz, the capacitive reactance of capacitors C21 and C22 is 15.90kΩ, which is 6.2 times smaller than the resistance value of resistors RL1 and RL2 of 100kΩ. At this time, the parallel resistance of the coupling unit is mainly determined by the capacitive reactance of the capacitor. When the equivalent capacitor C1 is at most 1nF, the voltage divider ratio between the voltage of C1 and the second frequency voltage signal output by the frequency sweep unit is approximately 1 / 3.

[0059] When switch K3 or K4 is closed, the acquisition unit collects the voltage at the positive and negative output terminals of the charging pile and records it as the third voltage, which is an AC voltage. If the difference between the third voltage and the second voltage is greater than a third set value, the voltage change is considered excessive, indicating that a single contactor of the charging pile is sticking. Otherwise, the charging pile contactor is not sticking. The third set value is set based on actual conditions.

[0060] For example, after closing switch K3, if a single contactor contact of the charging pile is stuck, the DC charging pile's safety capacitor C11 to ground and the coupling capacitor C12 to ground are connected in parallel and superimposed on C21, which reduces the capacitive reactance of the second coupling unit. Compared with when K3 is disconnected, the voltage distributed by the second coupling unit becomes smaller, resulting in a significant increase in the third voltage collected by the collection unit. When the following formula is met, it is determined that a single contactor contact is stuck:

[0061]

[0062] Wherein, V10kHz_2 is the third voltage measured after closing K3.

[0063] Similarly, after closing switch K4, if the charging pile has a single contactor contact stuck, the DC charging pile's safety capacitor C11 to ground and the coupling capacitor C12 to ground are connected in parallel and superimposed on C22, making the capacitive reactance of the first coupling unit smaller. Compared with when K4 is disconnected, the voltage distributed by the first coupling unit becomes smaller, resulting in a significant increase in the third voltage collected by the collection unit. When the following formula is met, it is determined that the single contactor contact is stuck:

[0064]

[0065] Wherein, V10kHz_3 is the third voltage measured after closing K4.

[0066] Method Example

[0067] A method for detecting contact adhesion of a DC charging pile contactor of the present invention comprises the following steps:

[0068] S1: Determine whether charging is completed.

[0069] After connecting the charging pile and the electric vehicle, the charging pile waits for its DC signal output. After the user successfully swipes their card for verification, charging starts and the DC charging pile outputs DC power. Because the charging pile's output internal resistance is very small (<1Ω), the DC internal resistance output by the frequency sweep circuit is approximately equal to RL1+RL2=200kΩ. The coupling unit acts as a shield, shielding the DC charging pile from the frequency sweep unit. At this point, the voltage signal output by the charging pile's positive and negative output terminals should be a DC signal. When the voltage at the charging pile's positive and negative output terminals collected by the acquisition unit is greater than a fourth set value, the contactor is judged to be closed and connected normally. When the voltage at the charging pile's positive and negative output terminals is detected to be less than a second set value, charging is judged to be complete and the DC signal essentially disappears. The second and fourth set values are set based on the charging pile's output voltage. For example, if the charging pile output power is 300V, the fourth set value can be set to 100V, 150V, or 200V, etc. The second set value can be set to 5V, 10V, or 12V, etc.

[0070] S2: After charging is complete, the frequency sweep unit injects a voltage signal of the first frequency into the charging circuit via the coupling unit. The voltage at the positive and negative output terminals of the charging pile is detected and recorded as a first voltage. If the first voltage is less than a first set value, it is determined that both contactors of the charging pile are stuck. The coupling unit includes a resistor and a capacitor connected in parallel. The parallel resistance of the coupling unit at the first frequency is determined by the impedance of the resistor.

[0071] The first set value is a voltage value less than or equal to 0.1V, which can be set to 0.05V or 0.1V, etc. As a preferred embodiment, in order to make a more accurate judgment, the first set value is determined based on a reference voltage. The reference voltage is the voltage value output by the frequency sweeping unit through the coupling unit when the frequency sweeping unit is disconnected from the ground wire of the charging pile and the frequency sweeping unit is not connected to the charging circuit. For example, the first set value is set to 0.01*reference voltage. Specifically, before the detection device is not connected to the charging system (K3 and K4 are disconnected), that is, when the frequency sweeping unit is not connected to the charging circuit, the sampling end of the acquisition unit is connected to the output end of the frequency sweeping unit through the coupling unit, and the voltage value V1Hz_1 output at this time is measured and used as the reference voltage. If the first voltage is less than the first set value, it is determined that the two contactor contacts of the charging pile are both adhered, otherwise the two contactor contacts are not both adhered.

[0072] S3: If both contactor contacts are not stuck, the frequency sweep unit is controlled to input a voltage signal of the second frequency into the charging circuit via the coupling unit, detecting the voltage at the positive and negative output terminals of the charging pile and recording it as the second voltage. The frequency sweep unit is then controlled to connect one terminal to the charging pile ground wire, detecting the voltage at the positive and negative output terminals of the charging pile and recording it as the third voltage. If the voltage difference between the third voltage and the second voltage is greater than a third set value, it is determined that a single contactor contact of the charging pile is stuck. Otherwise, the contactor contacts of the charging pile are not stuck. The parallel resistance of the coupling unit at the second frequency is determined by the capacitive reactance of the capacitor.

[0073] DC charging pile embodiment

[0074] A DC charging pile of the present invention, based on the original configuration, further includes a DC charging pile contactor contact adhesion detection device. The detection device has been described in detail in the device embodiment and will not be repeated here.

[0075] The present invention adopts a high-resistance coupling unit, a sweep signal output and a grounding switch to perform adhesion detection. Compared with the existing device that adopts short circuit or changes the internal contactor and can only test the adhesion alarm function, the present invention can truly measure the contactor adhesion condition of the DC charging pile on site without unpacking, and can determine whether it is a single contactor adhesion or two contactors adhesion state when adhesion occurs. The test is safer, simple to operate, and lower in cost. Moreover, whether the adhesion detection device is used as a load or as a signal source, its current does not exceed 30mA, which does not affect the normal charging of the charging pile. The adhesion detection device can be set inside the DC charging pile, or it can be set independently. When it is set independently, the device as a whole is also smaller and convenient to carry on site.

Claims

1. A method for detecting contact adhesion of a DC charging pile contactor, characterized in that: include: After detecting that charging is completed, the frequency sweep unit injects a voltage signal of the first frequency into the charging circuit via the coupling unit, detects the voltage at the positive and negative output terminals of the charging pile and records it as the first voltage. If the first voltage is less than a first set value, it is determined that both contactors of the charging pile are adhered; otherwise, both contactors are not adhered. If both contactor contacts are not stuck, the frequency sweep unit is controlled to input a voltage signal of the second frequency into the charging circuit via the coupling unit, and the voltage at the positive and negative output terminals of the charging pile is detected and recorded as the second voltage; then one of the poles of the frequency sweep unit is controlled to be connected to the ground wire of the charging pile, and the voltage at the positive and negative output terminals of the charging pile is detected and recorded as the third voltage. If the voltage difference between the third voltage and the second voltage is greater than a third set value, it is determined that a single contactor contact of the charging pile is stuck; otherwise, the contactor contact of the charging pile is not stuck; The coupling unit includes a resistor and a capacitor connected in parallel. The parallel resistance of the coupling unit at the first frequency is determined by the impedance of the resistor, and the parallel resistance of the coupling unit at the second frequency is determined by the capacitive reactance of the capacitor.

2. The method for detecting contact adhesion of a DC charging pile contactor according to claim 1, wherein: The first set value is determined based on a reference voltage, where the reference voltage is a voltage value output by the frequency sweeping unit via the coupling unit, measured when the frequency sweeping unit is disconnected from a ground wire of the charging pile and the frequency sweeping unit is not connected to a charging circuit.

3. The method for detecting contact adhesion of a DC charging pile contactor according to claim 1 or 2, characterized in that: The charging end judgment condition is: charging is judged to be ended when it is detected that the voltage at the positive and negative output terminals of the charging pile is less than a second set value.

4. A device for detecting contact adhesion of a DC charging pile contactor, characterized in that: The system comprises a processor, an acquisition unit, a frequency sweeping unit, and a coupling unit; the processor is configured to control the frequency sweeping unit to inject a voltage signal of a first frequency into the charging circuit via the coupling unit after detecting that charging is completed, and then determine whether the voltage at the positive and negative output terminals of the charging pile detected by the acquisition unit under this condition is less than a first set value. If the voltage is less than the first set value, it is determined that both contactor contacts of the charging pile are adhered; otherwise, both contactor contacts are not adhered; If the two contactor contacts are not both stuck, the frequency sweep unit is controlled to input the voltage signal of the second frequency into the charging circuit through the coupling unit, and the voltage of the positive and negative output terminals of the charging pile detected by the acquisition unit under this condition is obtained and recorded as the second voltage; then one pole of the frequency sweep unit is controlled to be connected to the charging pile ground wire, and the voltage of the positive and negative output terminals of the charging pile detected by the acquisition unit under this condition is obtained and recorded as the third voltage, and it is judged whether the voltage change of the third voltage compared with the second voltage is greater than the third set value. If it is greater, it is judged that a single contactor contact of the charging pile is stuck, otherwise the contactor contact of the charging pile is not stuck; wherein, the coupling unit includes a resistor and a capacitor arranged in parallel, and the parallel resistance value of the coupling unit at the first frequency is determined by the impedance of the resistor, and the parallel resistance value of the coupling unit at the second frequency is determined by the capacitive reactance of the capacitor.

5. The device for detecting contact adhesion of a DC charging pile contactor according to claim 4, characterized in that: The first set value is determined based on a reference voltage, where the reference voltage is a voltage value output by the frequency sweeping unit via the coupling unit and measured by the acquisition unit when the frequency sweeping unit is disconnected from the charging pile ground wire and the frequency sweeping unit is not connected to the charging circuit.

6. The device for detecting contact adhesion of a DC charging pile contactor according to claim 4 or 5, characterized in that: Whether charging is completed is determined based on the voltage at the positive and negative output terminals of the charging pile detected by the acquisition unit. When the voltage at the positive and negative output terminals of the charging pile is less than a second set value, charging is determined to be completed.

7. The device for detecting contact adhesion of a DC charging pile contactor according to claim 4, characterized in that: A switch is provided between the positive electrode and / or negative electrode of the frequency sweep unit and the ground wire of the charging pile, and the switch controls the connection or disconnection between the positive electrode or negative electrode of the frequency sweep unit and the ground wire of the charging pile.

8. The device for detecting contact adhesion of a DC charging pile contactor according to claim 4 or 7, characterized in that: The frequency sweeping unit includes a frequency sweeping generator, a voltage power amplifier circuit and a booster. The output end of the booster is the output end of the frequency sweeping unit. The voltage power amplifier circuit is arranged between the frequency sweeping generator and the booster, and is used to power amplify the voltage signal output by the frequency sweeping generator. The booster is used to further amplify the signal output by the voltage power amplifier circuit.

9. The device for detecting contact adhesion of a DC charging pile contactor according to claim 4, characterized in that: The acquisition unit includes a voltage divider circuit, an acquisition circuit and a differential amplifier. The voltage divider circuit sampling is connected to the positive and negative busbars of the charging circuit. The differential amplifier is used to perform impedance matching on the voltage signal detected by the voltage divider circuit. The acquisition circuit is used to perform digital-to-analog conversion on the voltage signal output by the differential amplifier.

10. A DC charging pile, characterized in that: The DC charging pile adopts the DC charging pile contactor contact adhesion detection method according to any one of claims 1 to 3 to perform contactor contact adhesion detection.

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