A contact state monitoring and control method for a direct current contactor

Abstract

This invention relates to the field of digital circuit control technology, and more particularly to a method for monitoring and controlling the contact status of a DC contactor. The method includes the following steps: monitoring the contact status of the DC contactor and acquiring the drive encoding signal of the DC contactor; filtering and extracting the feature code; performing spiral hierarchical recognition on the feature code, parsing the hierarchical information to distinguish drive commands, and obtaining the feature code recognition result; allocating the feature code recognition result to the corresponding drive circuit; and outputting a rated drive voltage to the corresponding DC contactor coil according to the feature code recognition result, causing the drive coil to drive the armature to close, thus closing the DC contactor contacts. This invention achieves refined control and anomaly handling of the DC contactor through a combination of filtering and spiral hierarchical encoding recognition, improving the accuracy of command execution and the stability of the entire control process.

Description

Technical Field

[0001] This invention relates to the field of digital circuit control technology, and in particular to a method for monitoring and controlling the contact status of a DC contactor. Background Technology

[0002] DC contactors, as core components for controlling the on / off states of DC circuits, are widely used in new energy power, industrial automation, and other fields. Their control accuracy and operational stability directly affect the reliability of circuit equipment. Currently, the industry's control of DC contactors mostly adopts a single code recognition and fixed voltage drive technology. The code parsing stage relies solely on basic filtering and overall verification, lacking a refined design for disassembling the code signal at different levels. This makes it impossible to accurately distinguish the different drive circuits corresponding to multiple sets of codes, easily leading to command matching deviations and making it difficult to guarantee the accuracy of multi-circuit parallel control. This problem is further amplified in multi-contactor cluster control scenarios, directly affecting the overall control efficiency of the system. In the voltage drive stage, traditional solutions often directly output the rated voltage to maintain contact closure, without combining the contact engagement state with the coil operating parameters for dynamic adaptation and adjustment. This fails to balance engagement stability and energy consumption control, and also makes it difficult to avoid abnormal coil temperature rise. Summary of the Invention

[0003] Therefore, it is necessary to provide a method for monitoring and controlling the contact status of a DC contactor to solve at least one of the above-mentioned technical problems.

[0004] To achieve the above objectives, a method for monitoring and controlling the contact status of a DC contactor is provided, the method comprising the following steps:

[0005] Step S1: Monitor the contact status of the DC contactor and collect the drive code signal of the DC contactor. After filtering, extract the feature code; perform spiral hierarchical recognition on the feature code, parse the hierarchical information to distinguish the drive command, and obtain the feature code recognition result; allocate the feature code recognition result to the corresponding drive circuit. Step S2: Based on the feature code recognition result, output the rated drive voltage to the corresponding DC contactor coil, drive the coil to drive the armature to close, and close the DC contactor contacts; Step S3: After detecting that the DC contactor contacts are closed, perform a stepped voltage reduction switching on the coil drive voltage, adjust it to the PWM drive voltage range, and continuously output the PWM drive voltage to the coil; Step S4: Perform cross-checking on the contactor drive encoding signal in the feature code recognition result. When an encoding abnormality is detected, cut off the coil drive voltage and trigger the DC contactor mechanical lockout. Step S5: Reacquire the abnormal contactor drive encoding signal, and perform secondary verification using the linked spiral hierarchical identification and cross-verification; after the secondary verification is passed, release the mechanical lockout of the DC contactor and restore the coil drive voltage output.

[0006] The present invention also provides a contact state monitoring and control device for a DC contactor, including a control system for executing the above-described contact state monitoring and control method for a DC contactor, the control system comprising: The encoding acquisition and recognition module is used to acquire the drive encoding signal of the DC contactor, extract the feature code after filtering, perform spiral hierarchical recognition on the feature code, parse the hierarchical information to distinguish the drive command, and obtain the feature code recognition result; and allocate the feature code recognition result to the corresponding drive circuit. The drive voltage output module is used to output the rated drive voltage to the corresponding DC contactor coil according to the feature code recognition result. The drive coil drives the armature to attract and close the DC contactor contacts. The drive voltage switching module is used to perform a stepped voltage reduction switching on the coil drive voltage after detecting that the DC contactor contacts are closed, adjust it to the PWM drive voltage range, and continuously output PWM drive voltage to the coil. The cross-check interlocking module is used to perform cross-checking on the contactor drive encoding signal in the feature code recognition result. When an encoding abnormality is detected, the coil drive voltage is cut off, triggering the DC contactor mechanical interlocking. The abnormal signal verification module is used to re-acquire abnormal contactor drive encoding signals, and perform secondary verification in conjunction with spiral hierarchical identification and cross-verification; after the secondary verification is passed, the mechanical lockout of the DC contactor is released and the coil drive voltage output is restored.

[0007] The beneficial effects of the present invention are as follows: On the one hand, by relying on the hierarchical identification and multi-verification mechanism of the drive coding signal, the DC contactor can be precisely controlled; the combined operation of combined filtering and spiral hierarchical identification analyzes the drive coding signal layer by layer, verifies the hierarchical identifier bit and the corresponding instruction identifier bit bit by bit, realizes the precise matching of drive instructions and contactor circuit, so that each group of coding signals can correspond to a unique drive action, improves the accuracy of instruction execution, and ensures that the contactor completes the engagement and disengagement actions according to the preset logic.

[0008] On the other hand, a combination of stepped voltage reduction switching and PWM drive is adopted to adjust the coil drive voltage in stages, simultaneously collect coil temperature and contact resistance, dynamically optimize the PWM duty cycle based on the resistance difference, accurately adapt to the coil engagement state, ensure the smoothness of the armature engagement process, avoid the impact of voltage sudden changes on the coil, and maintain a stable contact state after the contactor contacts are closed. At the same time, a coordinated operation of differentiated cross-checking and secondary check is adopted to check the instruction flag bit and the level flag bit respectively. In abnormal conditions, mechanical interlocking is triggered, and secondary comparison and unlocking are completed in enhanced acquisition mode. This ensures that the contactor quickly enters a safe state when the encoded signal is abnormal, and accurately resumes normal operation after the abnormality is cleared, achieving full-process safety and stability of contactor control. Attached Figure Description

[0009] Figure 1 A flowchart illustrating the steps of a method for monitoring and controlling the contact status of a DC contactor; Figure 2 This is a schematic diagram of a DC contactor step-down switching process in one embodiment; Figure 3 A schematic diagram of the contact status monitoring and control device for a DC contactor; The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0010] The technical method of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0011] Furthermore, the accompanying drawings are merely illustrative of the invention and are not necessarily drawn to scale. The same reference numerals in the drawings denote the same or similar parts, and therefore repeated descriptions of them will be omitted. Some block diagrams shown in the drawings are functional entities and do not necessarily correspond to physically or logically independent entities. These functional entities can be implemented in software, in one or more hardware modules or integrated circuits, or in different network and / or processor methods and / or microcontroller methods.

[0012] It should be understood that although the terms "first," "second," etc., may be used herein to describe various units, these units should not be limited by these terms. These terms are used merely to distinguish one unit from another. For example, without departing from the scope of the exemplary embodiments, a first unit may be referred to as a second unit, and similarly, a second unit may be referred to as a first unit. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0013] To achieve the above objectives, please refer to Figures 1 to 3 A method for monitoring and controlling the contact status of a DC contactor, the method comprising the following steps: Preferably, step S1: monitor the contact status of the DC contactor and collect the drive code signal of the DC contactor, filter and extract the feature code; perform spiral hierarchical recognition on the feature code, analyze the hierarchical information to distinguish the drive command, and obtain the feature code recognition result; allocate the feature code recognition result to the corresponding drive circuit. Optionally, in step S1, spiral hierarchical recognition is performed on the feature code, and the hierarchical information is parsed to distinguish the driving instructions, resulting in the feature code recognition result including: Perform a low-pass filter operation on the driving encoding signal to filter out high-frequency interference signals, and perform a notch filter operation on the low-pass filtered signal to filter out specific frequency clutter signals; The filtered drive encoding signal is transmitted to the feature code extraction unit to extract the level identifier bit and instruction identifier bit from the feature code; The DC contactor grouping level is determined by spiral hierarchical identification and analysis of the hierarchical identifier bits, and the drive command is distinguished by analyzing the instruction identifier bits layer by layer based on the DC contactor grouping level. The feature code recognition results are distributed to the drive circuits of each DC contactor according to the group level.

[0014] In this embodiment, a low-pass filter is performed on the drive encoding signal of the DC contactor. The low-pass filter circuit adopts an RC passive filter architecture. The resistance and capacitance values ​​can be set to different values ​​according to the frequency characteristics of the actual drive encoding signal. The high-frequency interference signals higher than the cutoff frequency in the drive encoding signal are filtered out by the charging and discharging characteristics of the capacitor. A notch filter is then performed on the low-pass filtered drive encoding signal. The notch filter circuit adopts a double-T type RC filter architecture. The resistance and capacitance values ​​can be flexibly adjusted according to the carrier frequency of the drive encoding signal to accurately match the carrier frequency and filter out specific frequency noise signals in its vicinity. In this embodiment, a low-pass filter circuit with a cutoff frequency of 1kHz is selected with a resistance of 10kΩ and a capacitance of 15.9nF, and a notch filter circuit with a center frequency of 500Hz is selected with a resistance of 20kΩ and a capacitance of 159nF.

[0015] The filtered drive-encoded signal is transmitted to the feature code extraction circuit. This circuit converts the analog signal into a digital signal through a voltage comparator of model LM393. The comparator threshold voltage can be set to different values ​​according to the actual signal amplitude range. If the voltage is higher than the threshold voltage, it outputs a high level 1, and if the voltage is lower than the threshold voltage, it outputs a low level 0. Then, the binary data in the digital signal is read bit by bit through an 8-bit shift register 74HC165 to extract the 3-bit hierarchical identifier and the 5-bit instruction identifier from the feature code. The number of bits of the hierarchical identifier and the instruction identifier can be adjusted according to the number of DC contactor groups and the number of drive instructions to distinguish different DC contactor groups and drive instructions.

[0016] The extracted feature code is parsed using a spiral hierarchical recognition logic. The verification interval can be set to different values ​​according to the transmission rate of the encoded signal. First, the 3-bit hierarchical identifier is read, and the code is verified bit by bit from high to low. The integrity of the corresponding instruction identifier is verified synchronously for each bit. If a binary value is missing or the level is abnormal, the parsing of the current level is stopped immediately, and the code is returned to the previous level for re-verification. After the parsing is completed, the DC contactor grouping level is determined. Based on the grouping level, the 5-bit instruction identifier is parsed layer by layer to distinguish the drive instructions of different DC contactors and form the feature code recognition result.

[0017] The feature code recognition result is input to the drive circuit distribution circuit. The decoder converts the level identifier bit and the instruction identifier bit into the corresponding control signal. The remaining instruction identifier bit is used as an extended control signal. The multiplexer distributes the feature code recognition result to each DC contactor drive circuit according to the group level based on the high and low levels of the control signal. Each drive circuit corresponds to one DC contactor, thus completing the drive instruction distribution.

[0018] Optionally, the filtering operation in step S1 is as follows: Set the cutoff frequency of the low-pass filter to 0.8kHz-1.2kHz, and match the center frequency of the notch filter to the carrier frequency of the driving coded signal. The amplitude of the filtered signal is acquired in real time during the filtering process. When the signal amplitude fluctuates beyond 0.3V-0.7V, the feature code extraction operation is paused. Perform a combined low-pass and notch filter operation to adjust the low-pass filter cutoff frequency to 0.6kHz-0.9kHz.

[0019] In this embodiment, a combination of low-pass filtering and notch filtering is performed on the drive encoding signal of the DC contactor. The low-pass filter circuit adopts an RC passive filter architecture, and its cutoff frequency can be adjusted in the range of 0.8kHz-1.2kHz according to the actual characteristics of the drive encoding signal. The notch filter circuit adopts a double-T type RC filter architecture, and its center frequency is consistent with the carrier frequency of the drive encoding signal. In this embodiment, the cutoff frequency of the low-pass filter is set to 1kHz, and the center frequency of the notch filter matches the 500Hz carrier frequency of the drive encoding signal. The low-pass filter uses a combination of a 10kΩ resistor and a 15.9nF capacitor, and the notch filter uses a combination of a 20kΩ resistor and a 159nF capacitor to complete the construction of the basic filter circuit.

[0020] After the filtering operation is started, the amplitude of the filtered drive encoded signal is acquired in real time through the signal acquisition circuit. The acquisition frequency is set to 100Hz. The acquired signal amplitude is transmitted to the signal amplitude detection circuit. This circuit compares the real-time acquired signal amplitude with the preset fluctuation range through a voltage comparator. The preset fluctuation range of the signal amplitude is 0.3V-0.7V. In this embodiment, the preset fluctuation threshold is set to 0.5V. When the real-time acquired signal amplitude fluctuation is detected to exceed 0.5V, the signal amplitude detection circuit outputs a trigger signal to control the feature code extraction circuit to pause the feature code extraction operation.

[0021] After the feature extraction operation is paused, the combined low-pass and notch filtering operation is immediately re-executed. At this time, the cutoff frequency of the low-pass filter is adjusted and reset within the range of 0.6kHz-0.9kHz. In this embodiment, the adjusted low-pass filter cutoff frequency is set to 0.8kHz. Correspondingly, the resistance and capacitor parameters of the low-pass filter circuit are adjusted, selecting a combination of a 12.5kΩ resistor and a 20nF capacitor, while keeping the parameters of the notch filter circuit unchanged to ensure that the center frequency of the notch filter still matches the carrier frequency of the driving encoding signal.

[0022] After restarting the combined filtering operation, the signal acquisition circuit continuously acquires the amplitude of the filtered signal, and the signal amplitude detection circuit compares it synchronously until the signal amplitude fluctuation is detected to be within the range of 0.3V-0.7V and remains stable for 10ms. Then, the signal amplitude detection circuit outputs a recovery signal to control the feature code extraction circuit to restart the feature code extraction operation. The filtering operation continues until the driving encoded signal is filtered, providing a stable signal basis for subsequent feature code extraction.

[0023] Optionally, the spiral hierarchical identification in step S1 includes: When parsing the hierarchical identifier, a bit-by-bit verification operation is performed, and the integrity of the instruction identifier of the corresponding level is verified simultaneously when one hierarchical identifier is verified. If an error is detected during the verification, the current level of parsing is stopped, and the parsing operation is performed at the previous level's flag. After parsing, the feature code recognition result is matched with the drive circuit identification information. After the matching operation is completed, the drive instruction allocation operation is performed. After the instruction allocation operation is completed, the instruction is transmitted to the corresponding drive circuit.

[0024] In this embodiment, a spiral hierarchical recognition operation is performed on the filtered feature code. The feature code includes a level identifier bit and an instruction identifier bit. The level identifier bit is set to 3 binary bits, and the instruction identifier bit is set to 5 binary bits. The hierarchical recognition circuit is used to implement the parsing operation. This circuit consists of a shift register, a verification circuit, and a logic control circuit. The shift register is a 74HC165 model, the verification circuit is constructed using XOR gates, and the logic control circuit uses a microcontroller to implement timing control. The verification interval is set to 10μs.

[0025] When parsing the level identifier bit, the shift register outputs the binary data of the level identifier bit bit by bit, and transmits it to the verification circuit from the high bit to the low bit. For each level identifier bit bit transmitted, the verification circuit synchronously receives the instruction identifier bit data of the corresponding level and performs integrity verification on the binary bits of the instruction identifier bit to detect whether there are missing bits, abnormal levels, etc. The verification circuit outputs a high level to indicate that the verification is normal and outputs a low level to indicate that the verification is wrong.

[0026] If the verification circuit outputs a low level, the logic control circuit immediately sends a stop signal to cut off the parsing operation of the current level's identifier bit. At the same time, it sends a reset signal to control the shift register to return the binary data of the identifier bit of the previous level and restart the verification operation of the identifier bit of this level and the corresponding instruction identifier bit. This process continues until the verification of this level is normal, and then the parsing and verification of the identifier bit of the next level is performed. This cycle continues until the parsing of all level identifier bits is completed.

[0027] After all the hierarchical identifier bits are parsed, the logic control circuit transmits the complete feature code recognition result to the matching circuit. The matching circuit has a built-in drive circuit identification information table, which stores the unique identification code of each DC contactor drive circuit. The matching circuit compares the hierarchical identifier bits and command identifier bits in the feature code recognition result with the drive circuit identification information table bit by bit. After the comparison is completed, it outputs a matching signal. The logic control circuit controls the drive circuit distribution circuit according to the matching signal to transmit the drive command to the corresponding DC contactor drive circuit, thus completing the drive command distribution operation.

[0028] Preferably, in step S2: the rated driving voltage is output to the corresponding DC contactor coil according to the feature code recognition result, and the driving coil drives the armature to attract and close the DC contactor contacts. Optionally, step S2 includes the following steps: A portion of the rated drive voltage is output to the DC contactor coil, and after the voltage of this portion is output for a preset time, the real-time current value of the DC contactor coil is collected. The real-time current value is compared with the preset current threshold, and after the comparison is completed, the full rated drive voltage is output to the DC contactor coil. When the full rated drive voltage is output to the DC contactor coil, it drives the armature of the DC contactor coil to engage. After the armature engages, the voltage output is maintained until the contacts are fully closed.

[0029] In this embodiment, the DC contactor coil drive operation is initiated using a DC regulated power supply as the voltage output unit. The output voltage of this power supply is adjustable within the range of 0-36V. The rated drive voltage of the DC contactor coil is set to 24V. A portion of the rated drive voltage is initially output to the DC contactor coil; this portion can be flexibly adjusted according to the coil parameters. In this embodiment, it is set to 60% of the rated drive voltage, i.e., 14.4V. A current-limiting resistor with a resistance of 200Ω is connected in series in the voltage output circuit to limit the initial coil current. The duration of the 14.4V output is preset to 50ms to ensure slow coil preheating and prevent damage to the coil from instantaneous high voltage.

[0030] After continuously outputting 14.4V for 50ms, the real-time current value of the DC contactor coil is acquired by a current sensor connected in series in the coil circuit. The current sensor is a Hall current sensor with a sampling frequency set to 200Hz. The acquired real-time current value is transmitted to the current comparison circuit, which is composed of an operational amplifier. The preset current threshold is set to 0.3A. The current comparison circuit compares the real-time coil current value with the preset current threshold of 0.3A. During the comparison process, the voltage output remains stable and the current output amplitude is not changed.

[0031] After the comparison is completed, if the real-time current value is within the preset current threshold range, the DC regulated power supply adjusts the output voltage to output the complete rated drive voltage of 24V to the DC contactor coil. At the same time, the current limiting resistor is switched to 100Ω to adapt to the coil current requirement under the rated voltage. After the complete rated drive voltage is applied to the coil, the coil generates electromagnetic attraction, which drives the armature inside the DC contactor to start to engage. During the armature engagement process, the coil current gradually increases to a stable value of 0.24A.

[0032] The armature engagement status is detected in real time by a position sensor installed at the corresponding position of the DC contactor armature with a detection accuracy of 0.1mm. When the armature is detected to be engaged, the rated 24V drive voltage is continuously output until the position sensor detects that the DC contactor contacts are fully closed. The contact closure detection uses a contact feedback switch. After the feedback switch is closed, a signal is sent to the voltage control circuit. The voltage control circuit maintains the current voltage output state until the subsequent voltage reduction operation is started, completing the entire coil drive and contact closure operation.

[0033] Preferably, in step S3: after detecting that the DC contactor contacts are closed, the coil drive voltage is switched by step reduction to adjust to the PWM drive voltage range and continuously outputs the PWM drive voltage to the coil; Optionally, after detecting the closure of the DC contactor contacts in step S3, performing a stepped voltage reduction switch on the coil drive voltage includes: When the driving voltage of the DC contactor coil drops from the rated driving voltage to 65%-75% of the rated driving voltage, the DC contactor coil engagement feedback signal is collected simultaneously and the engagement stability is determined. After the stability is determined, the voltage reduction operation is performed. When the driving voltage drops to 45%-55% of the rated driving voltage, the real-time temperature of the coil is collected synchronously and compared with the preset safe temperature range. After determining that the temperature is within the safe range, the voltage reduction operation is performed. When the driving voltage drops to the PWM driving voltage range of 30%-40% of the rated driving voltage, the coil engagement status is monitored in real time during the voltage reduction process. If the armature engagement status is detected to be loose, the voltage reduction operation is paused to maintain the current driving voltage range.

[0034] In this embodiment, after detecting that the DC contactor contacts are fully closed, a stepped voltage reduction switching operation of the coil drive voltage is initiated. A DC regulated power supply is used to provide the voltage output, and the rated drive voltage of the coil is set to 24V as the initial voltage reference for the voltage reduction switching. The voltage reduction operation is executed step by step in three stages. In the first stage, the drive voltage is reduced from 24V to 70% of the rated drive voltage, i.e., 16.8V. At the same time, the coil engagement feedback signal is collected by an electromagnetic induction sensor. Engagement status data is collected every 100ms for 5 consecutive times. After determining that the coil engagement is stable, the next stage of voltage reduction is executed.

[0035] The second stage reduces the drive voltage to 50% of the rated drive voltage, i.e., 12V. During the voltage reduction process, the coil temperature is monitored in real time by a temperature sensor at a frequency of once every 30 seconds. The preset safe temperature range is 0-60℃. Once the coil temperature is detected to be within the safe range, the voltage reduction operation continues. If the coil temperature is detected to exceed 60℃, the voltage reduction is immediately paused, and the current 12V voltage output is maintained until the temperature drops back to the safe range before continuing the voltage reduction.

[0036] In the third stage, the driving voltage is reduced to 35% of the rated driving voltage, i.e., 8.4V, and the PWM driving mode is switched to. The PWM driving frequency is set to 1kHz, and the duty cycle is initially set to 50%. During the voltage reduction process, the armature position is detected in real time by a displacement sensor with a detection accuracy of 0.1mm. If the detected armature displacement exceeds 0.5mm, it is determined that the engagement is loose, and the voltage reduction operation is immediately paused. The current 8.4V voltage output is maintained until the armature returns to a stable engagement state, and then the voltage reduction operation is completed. The voltage output is maintained continuously throughout the process to ensure that the coil is always in a stable working state.

[0037] Throughout the buck process, the voltage adjustment rate is controlled at 0.5V / 100ms. After each buck stage is completed, the voltage output accuracy is confirmed by the voltage detection module to ensure that the buck process is stable and without voltage sudden changes. At the same time, the coil current is collected in real time, and the current fluctuation is controlled within ±0.02A to ensure that the entire buck process meets the preset operating specifications and completes the stepped buck and PWM drive switching.

[0038] Please see Figure 2 This diagram illustrates the stepped voltage reduction switching process of the DC contactor according to the present invention. It shows the four-stage stepped voltage reduction control logic of the DC contactor coil drive voltage, fully presenting the gradual switching process from the rated drive voltage to the PWM drive voltage range. The first step reduces the drive voltage to 80%-90% of the rated drive voltage, completing the initial voltage reduction transition. The second step reduces the drive voltage to 65%-75% of the rated drive voltage, simultaneously verifying the armature engagement stability. The third step reduces the drive voltage to 45%-55% of the rated drive voltage, combining coil temperature monitoring to determine the safety of the voltage reduction. The fourth step reduces the drive voltage to 30%-40% of the rated drive voltage, entering the PWM drive voltage range, achieving low-power stable drive of the coil.

[0039] Optionally, the stepped voltage reduction switching in step S3 specifically involves: After completing the first-stage voltage reduction operation, the real-time temperature value of the coil is collected, and the collected temperature value is compared with the preset temperature threshold. If the temperature exceeds the preset temperature threshold, adjust the duration range of the next level of pressure reduction; if the temperature is within the safe range, maintain the original pressure reduction duration. The coil temperature is checked every preset time interval during the continuous output of PWM drive voltage; The detected temperature value is transmitted to the duty cycle adjustment unit, which dynamically adjusts the duty cycle range of the PWM drive voltage according to the temperature value.

[0040] In this embodiment, a low-pass filter is performed on the drive encoding signal of the DC contactor. The filter circuit adopts an RC passive filter architecture, with the cutoff frequency of the low-pass filter set to 1kHz. A combination of a 10kΩ resistor and a 10μF capacitor is selected in the filter circuit to ensure the stability of the filtered signal. After the filtering operation is initiated, the drive encoding signal is acquired in real time through the signal acquisition circuit at a frequency of 100Hz. Low-pass filtering and notch filtering operations are performed simultaneously. The cutoff frequency of the low-pass filter is set to 1kHz, and the center frequency of the notch filter matches the carrier frequency of the drive encoding signal. The signal acquisition circuit acquires the amplitude of the filtered signal in real time. When the signal amplitude fluctuation exceeds 0.3V, the feature code extraction operation is paused, and the drive loop matching operation is initiated.

[0041] A bit-by-bit verification operation is performed on the feature code, with the verification frequency set to 100Hz. Signal amplitude comparison is achieved through a voltage comparator. When a signal amplitude fluctuation exceeding 0.5V is detected, the feature code extraction operation is paused, and the system switches to combined filtering mode. The drive voltage is adjusted to 0.8kHz to maintain the center frequency of the notch filter matching the carrier frequency of the drive encoded signal, ensuring stable transmission of the drive encoded signal. When a signal amplitude fluctuation exceeding 0.3V is detected, the combined filtering operation is immediately initiated, adjusting the cutoff frequency of the low-pass filter to 0.8kHz, while simultaneously controlling the signal transmission of the drive circuit.

[0042] After completing the drive command allocation, a matching operation is performed to compare the feature code recognition result with the drive circuit identification information, ensuring that the parameters of each step are consistent. When a signal amplitude fluctuation exceeding 0.5V is detected, the feature code extraction operation is paused, and the low-pass filter parameter settings are readjusted to maintain stable transmission of the drive encoded signal. Real-time monitoring of the signal amplitude is achieved through a voltage comparator. When a signal amplitude fluctuation exceeding 0.7V is detected, the PWM drive mode is activated to ensure the normal operation of the drive circuit.

[0043] Optionally, the adjustment to the PWM drive voltage region in step S3 specifically involves: During the duty cycle adjustment process, the contact resistance value of the contact point is collected in real time, and the difference between the contact resistance value and the preset resistance threshold is calculated to obtain the resistance difference. If the resistance difference is positive and exceeds the preset difference threshold, the duty cycle of the PWM drive voltage is increased according to the preset gradient, and the duty cycle value is recorded once for each increase. If the resistance difference is negative or within a preset difference threshold, the current PWM duty cycle will remain unchanged.

[0044] In this embodiment, the DC contactor coil drive voltage is adjusted, PWM drive mode is activated, and a voltage comparator is used to collect the contact resistance value in real time. The contact resistance value collection frequency is set to 10Hz, with each collection interval of 0.5 seconds. The collected contact resistance value is accurate to 0.1Ω, the preset contact resistance threshold is 5Ω, the preset difference threshold is 0.5Ω, and the preset duty cycle adjustment gradient is 5%. The collected contact resistance value is transmitted to the signal processing circuit, which calculates the difference between the contact resistance value and the preset resistance threshold using a subtraction operation: subtracting the preset resistance threshold from the contact resistance value to obtain the resistance difference. The signal processing circuit has a built-in difference comparison module that performs real-time judgment on the resistance difference to ensure accurate difference calculation. When the resistance difference is positive and exceeds the preset threshold of 0.5Ω, the signal processing circuit outputs an adjustment signal to control the PWM drive circuit to increase the duty cycle by 5% each time. After each increase, the current duty cycle value is immediately recorded with an accuracy of 0.1%. After each increase, the adjustment is paused for 0.3 seconds before proceeding to the next adjustment, until the duty cycle stabilizes. When the resistance difference is negative or within the preset threshold of 0.5Ω, the signal processing circuit does not output an adjustment signal, maintaining the current duty cycle of the PWM drive voltage unchanged. It continuously acquires the contact resistance value and monitors the resistance difference in real time to ensure stable output of the PWM drive voltage. All the values ​​set above can be adjusted according to the actual usage scenario and requirements.

[0045] Of particular importance, the continuous output of PWM drive voltage to the coil in step S3 includes: The contact resistance value of the contact point is collected in real time. When the contact resistance value exceeds the preset resistance threshold after multiple consecutive sampling results, the PWM drive voltage output operation is paused. The rated drive voltage is output to the DC contactor coil. After the DC contactor coil drives the armature to engage, a stepped voltage reduction switching operation is performed. After the buck switching operation is completed, the PWM drive voltage output is restored. After the output is restored, the contact resistance value is continuously collected. Real-time sampling stops when the contact resistance value stabilizes.

[0046] In this embodiment, the PWM drive voltage output by the DC contactor coil is continuously controlled. A voltage sensor is used to collect the coil drive voltage in real time, with a sampling frequency of 10Hz and a sampling interval of 100ms to ensure stable voltage output. Contact resistance detection adopts a series detection method, with a detection frequency of 50Hz, to collect the contact resistance value in real time. When the contact resistance value exceeds 50Ω, the PWM drive voltage output is immediately paused, and the contact resistance abnormality handling process is initiated.

[0047] A temperature sensor is used to collect the coil temperature in real time at a frequency of 20Hz. The temperature detection accuracy is controlled within ±0.5℃. When the detected coil temperature exceeds 70℃, the duty cycle of the PWM drive voltage is automatically adjusted to reduce the output power until the coil temperature drops below 60℃, and then the normal output power is restored.

[0048] The contact resistance value is collected in real time. A series detection circuit is used with a detection frequency of 30Hz. When the contact resistance value exceeds 50Ω and the duration reaches 500ms, the contact resistance abnormality handling is immediately triggered, the PWM drive voltage output is paused, and the contact resistance calibration process is started until the contact resistance value is restored to within 50Ω.

[0049] A voltage comparator is used to monitor the output voltage in real time at a frequency of 100Hz. When the output voltage fluctuation exceeds 0.5V, the voltage output module parameters are automatically adjusted to maintain the output voltage within the range of 24V±0.5V, ensuring a continuous and stable output of the drive voltage and completing the entire PWM drive voltage control process.

[0050] Preferably, step S4: perform cross-checking on the contactor drive encoding signal in the feature code recognition result; when an encoding abnormality is detected, cut off the coil drive voltage and trigger the DC contactor mechanical lockout. Optionally, step S4 includes the following steps: Perform parity check on the instruction flag bit in the feature code recognition result, and perform cyclic redundancy check on the hierarchy flag bit in the feature code recognition result; The parity check operation and the cyclic redundancy check operation are synchronously transmitted to the check result integration unit. When either the parity check operation or the cyclic redundancy check operation detects an encoding abnormality, an abnormal signal is output and transmitted to the drive control unit. The drive control unit cuts off the drive voltage of the DC contactor coil and locks the drive circuit, while simultaneously triggering the mechanical lockout of the DC contactor.

[0051] In this embodiment, a parity check is performed on the instruction flag bit in the feature code recognition result. A parity check circuit is used, with the check frequency set to 100Hz and the check voltage set to 5V. When an abnormal high-low level jump is detected in the level of the instruction flag bit, the check action is immediately triggered. The binary data of the instruction flag bit is compared bit by bit to ensure that the level of each binary number meets the preset standard. If a binary number does not meet the preset standard, it is determined to be an encoding abnormality, and the specific location and abnormality type of the abnormal code are recorded.

[0052] Cyclic redundancy check (CRC) is performed on the hierarchical identifier bits in the feature code recognition result. A CRC circuit is used, the check polynomial is set to CRC-16, the check clock frequency is set to 100Hz, and the check duration is 10ms. Cyclic redundancy calculation is performed on each binary data of the hierarchical identifier bits, and the result is compared with the preset check value. If the calculation result is inconsistent with the preset check value, the hierarchical identifier bit encoding is determined to be abnormal.

[0053] The results of parity check and cyclic redundancy check operations are synchronously transmitted to the check result integration unit. The transmission rate is set to 9600bps, and the transmission delay is controlled within 5ms to ensure that the two check results are summarized synchronously and to avoid the loss or delay of check signals. The check result integration unit performs logical judgment on the two check signals. If either check detects an encoding abnormality, an abnormal signal is immediately output. The abnormal signal transmission rate is 100Hz.

[0054] After receiving the abnormal signal transmitted by the verification result integration unit, the drive control unit immediately cuts off the drive voltage of the DC contactor coil, with the cut-off response time controlled within 10ms. At the same time, it locks the drive circuit, prohibits the output of drive signals, and triggers the internal mechanical locking structure of the DC contactor, keeping the contactor contacts in an open state until the verification abnormality is eliminated.

[0055] Preferably, in step S5: re-acquire the abnormal contactor drive encoding signal, and perform secondary verification by linking the spiral hierarchical identification and cross-verification; after the secondary verification is passed, release the mechanical lockout of the DC contactor and restore the coil drive voltage output.

[0056] Optionally, step S5, which involves re-acquiring the abnormal contactor drive encoding signal and performing secondary verification in conjunction with the spiral hierarchical identification and cross-checking, includes: The enhanced acquisition mode is used to acquire the contactor drive coded signal. During the acquisition process, low-pass filtering and notch filtering are performed simultaneously to filter out high-frequency interference and specific frequency noise in the acquired signal. The filtered signal is subjected to feature code extraction, and the hierarchical identifier and instruction identifier are extracted from it; The signal with extracted feature codes is subjected to spiral hierarchical recognition, and the grouping information corresponding to the hierarchical identifier bits and the driving content corresponding to the instruction identifier bits are analyzed layer by layer. Cross-validation is performed on the results obtained after hierarchical identification, and verification operations are performed on the hierarchical identifier bit and the instruction identifier bit respectively to complete the secondary identification and verification process of abnormal signals.

[0057] In this embodiment, a secondary verification process for the abnormal encoded signal is initiated, switching to enhanced acquisition mode to acquire the contactor drive encoded signal. The acquisition frequency is set to 100Hz, the acquisition voltage is set to 5V, and the acquisition accuracy is controlled within ±0.01V. During the acquisition process, a combination of low-pass filtering and notch filtering is simultaneously initiated. The low-pass filter adopts an RC passive filter architecture, selecting a 12kΩ resistor and a 13.3nF capacitor to form a filter circuit with a cutoff frequency of 1kHz, filtering out high-frequency interference signals above 1kHz. The notch filter adopts a double-T RC filter architecture, selecting an 18kΩ resistor and a 177nF capacitor to form a filter circuit with a center frequency of 500Hz, accurately filtering out specific frequency noise near the carrier frequency of the drive encoded signal.

[0058] After the filtering operation is completed, the filtered drive encoding signal is transmitted to the feature code extraction circuit. This circuit converts the analog signal into a digital signal through a voltage comparator. The comparator threshold voltage is set to 2.5V. If the voltage is higher than the threshold voltage, it outputs a high level 1, and if the voltage is lower than the threshold voltage, it outputs a low level 0. Then, the digital signal is read bit by bit through the shift register to extract the 3-bit hierarchical identifier and the 5-bit instruction identifier from the feature code. The extraction rate is 50bit / s to ensure that the identifier is extracted completely without any missing bits.

[0059] A spiral hierarchical recognition operation is performed on the extracted feature code. A hierarchical recognition circuit is used, and the verification interval is set to 8μs. The hierarchical identifier is parsed bit by bit from the high bit to the low bit. For each hierarchical identifier bit parsed, the integrity of the corresponding instruction identifier bit is checked simultaneously. If a missing identifier bit or abnormal level is detected, the process immediately returns to the previous level to re-parse until all hierarchical identifier bits and instruction identifier bits are parsed, and the grouping information corresponding to the hierarchical identifier bits and the driving content corresponding to the instruction identifier bits are clarified.

[0060] After parsing, a cross-check operation is performed on the recognition results. A cross-check circuit is used to perform cyclic redundancy check on the level identifier bits, with the check polynomial being CRC-16 and the check clock frequency being 100Hz. Parity check is performed on the instruction identifier bits, with a check frequency of 100Hz. The two check operations are performed simultaneously, and the check results are transmitted to the check unit in real time. The check unit compares the check results with the preset standard to complete the secondary recognition and check process of abnormal signals. All the parameters set above can be adjusted according to the actual situation.

[0061] Most importantly, after the secondary verification in step S5 passes, the mechanical lockout of the DC contactor is released, and the coil drive voltage output is restored as follows: Set the sampling frequency of the enhanced acquisition mode to 80Hz-120Hz; Perform a bit-by-bit comparison operation between the hierarchical identifier bits parsed from the spiral hierarchical identification and the hierarchical identifier bits obtained from the first identification; When the hierarchical identifier bits match, only the instruction identifier bits are cross-checked. When the hierarchical identifier bits do not match, a second cross-check is performed on both the hierarchical identifier bits and the instruction identifier bits. If the secondary cross-check passes, an unlock signal is output, and the mechanical lock of the DC contactor is released according to the unlock signal; Once the mechanical lockout of the DC contactor is released, the coil drive voltage output is restored.

[0062] In this embodiment, after the secondary verification is started, the frequency of the enhanced acquisition mode of the driving encoding signal is set in the range of 80Hz-120Hz. In this embodiment, the acquisition frequency is selected as 100Hz, the acquisition voltage is set to 5V, and the acquisition accuracy is controlled within ±0.01V. The driving encoding signal is continuously acquired through the signal acquisition circuit to provide a stable data source for subsequent comparison operations.

[0063] The hierarchical identifier data obtained from the spiral hierarchical identification is transmitted to the comparison circuit. This circuit has built-in the reference data of the hierarchical identifier obtained from the first identification. The comparison circuit performs a bit-by-bit comparison operation at 10μs intervals, comparing the binary values ​​of the two sets of hierarchical identifiers from the high bit to the low bit. During the comparison process, the high and low level states of each value are confirmed by the level detection module, and the consistency information of the comparison results is recorded.

[0064] If the comparison circuit outputs a signal indicating that the hierarchical identifier bits are consistent, the control verification circuit performs a double cross-check only on the instruction identifier bit, with the verification frequency set to 100Hz, and verifies the integrity of the instruction identifier bit bit by bit using a parity check method. If the comparison circuit outputs a signal indicating that the hierarchical identifier bits are inconsistent, the control verification circuit performs a double cross-check on both the hierarchical identifier bit and the instruction identifier bit. The hierarchical identifier bit uses a cyclic redundancy check method, with the check polynomial set to CRC-16, while the instruction identifier bit still uses a parity check method. The two checks are performed synchronously, and the check time is controlled within 20ms.

[0065] After all two cross-checks pass, the check circuit outputs a high-level unlock signal. This unlock signal is transmitted to the mechanical interlock control unit at a rate set to 9600bps. Upon receiving the signal, the control unit triggers the electromagnetic unlocking mechanism. The drive current of the electromagnetic unlocking mechanism is set to 0.5A, and the drive voltage is set to 24V, causing the interlocking pin to exit the locked position and releasing the mechanical interlock of the DC contactor. After the mechanical interlock is released, the control unit sends a voltage recovery signal to the power module. The power module outputs the coil drive voltage according to a preset program, with the voltage amplitude gradually increasing from 14.4V to 24V at a rate controlled at 0.5V / 100ms, completing the coil drive voltage recovery operation. All the parameters set above can be adjusted according to actual conditions.

[0066] The present invention also provides a contact state monitoring and control device for a DC contactor, including a control system for executing the above-described contact state monitoring and control method for a DC contactor, the control system comprising: The encoding acquisition and recognition module is used to acquire the drive encoding signal of the DC contactor, extract the feature code after filtering, perform spiral hierarchical recognition on the feature code, parse the hierarchical information to distinguish the drive command, and obtain the feature code recognition result; and allocate the feature code recognition result to the corresponding drive circuit. The drive voltage output module is used to output the rated drive voltage to the corresponding DC contactor coil according to the feature code recognition result. The drive coil drives the armature to attract and close the DC contactor contacts. The drive voltage switching module is used to perform a stepped voltage reduction switching on the coil drive voltage after detecting that the DC contactor contacts are closed, adjust it to the PWM drive voltage range, and continuously output PWM drive voltage to the coil. The cross-check interlocking module is used to perform cross-checking on the contactor drive encoding signal in the feature code recognition result. When an encoding abnormality is detected, the coil drive voltage is cut off, triggering the DC contactor mechanical interlocking. The abnormal signal verification module is used to re-acquire abnormal contactor drive encoding signals, and perform secondary verification in conjunction with spiral hierarchical identification and cross-verification; after the secondary verification is passed, the mechanical lockout of the DC contactor is released and the coil drive voltage output is restored.

[0067] Please see Figure 3 This is a schematic diagram of the contact status monitoring and control device for the DC contactor of the present invention. It illustrates the linkage control logic between the control system and the DC contactor. After the external drive encoding signal source inputs the encoded signal, the encoding acquisition and recognition module within the control system completes filtering, feature code extraction, spiral hierarchical recognition, and loop allocation, outputting the recognition result to the drive voltage output module. The drive coil then drives the armature to engage, closing the main contacts. The contact closure signal is transmitted to the drive voltage switching module, which performs a stepped voltage reduction switching and adjusts to the PWM drive range. The cross-checking and interlocking module performs parity and cyclic redundancy checks on the encoded signal. In case of an anomaly, the voltage is cut off and mechanical interlocking is triggered. The anomaly signal verification module re-acquires the signal and performs a secondary verification. After successful verification, the interlocking is released, the drive is restored, and the main contact status is fed back to the control system, forming a closed loop.

[0068] Therefore, the embodiments should be considered as exemplary and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of the equivalents of the application are intended to be included within the invention.

[0069] The above description is merely a specific embodiment of the present invention, enabling those skilled in the art to understand or implement the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the present invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features of the invention herein.

Claims

1. A method for monitoring and controlling the contact status of a DC contactor, characterized in that, Includes the following steps: Step S1: Monitor the contact status of the DC contactor and collect the drive coding signal of the DC contactor, then filter and extract the feature code; The feature code is subjected to spiral hierarchical recognition, the hierarchical information is parsed to distinguish the driving instructions, and the feature code recognition result is obtained; the feature code recognition result is then assigned to the corresponding driving loop. Step S2: Based on the feature code recognition result, output the rated drive voltage to the corresponding DC contactor coil, drive the coil to drive the armature to close, and close the DC contactor contacts; Step S3: After detecting that the DC contactor contacts are closed, perform a stepped voltage reduction switching on the coil drive voltage, adjust it to the PWM drive voltage range, and continuously output the PWM drive voltage to the coil; Step S4: Perform cross-checking on the contactor drive encoding signal in the feature code recognition result. When an encoding abnormality is detected, cut off the coil drive voltage and trigger the DC contactor mechanical lockout. Step S5: Reacquire the abnormal contactor drive encoding signal, and perform secondary verification using the linked spiral hierarchical identification and cross-verification; after the secondary verification is passed, release the mechanical lockout of the DC contactor and restore the coil drive voltage output.

2. The method for monitoring and controlling the contact status of a DC contactor according to claim 1, characterized in that, Step S1 involves performing spiral hierarchical recognition on the feature code, parsing the hierarchical information to distinguish driving instructions, and obtaining the feature code recognition result, including: Perform a low-pass filter operation on the driving encoding signal to filter out high-frequency interference signals, and perform a notch filter operation on the low-pass filtered signal to filter out specific frequency clutter signals; The filtered drive encoding signal is transmitted to the feature code extraction unit to extract the level identifier bit and instruction identifier bit from the feature code; The DC contactor grouping level is determined by spiral hierarchical identification and analysis of the hierarchical identifier bits, and the drive command is distinguished by analyzing the instruction identifier bits layer by layer based on the DC contactor grouping level. The feature code recognition results are distributed to the drive circuits of each DC contactor according to the group level.

3. The method for monitoring and controlling the contact status of a DC contactor according to claim 2, characterized in that, The filtering operation in step S1 is as follows: Set the cutoff frequency of the low-pass filter to 0.8kHz-1.2kHz, and match the center frequency of the notch filter to the carrier frequency of the driving coded signal. The amplitude of the filtered signal is acquired in real time during the filtering process. When the signal amplitude fluctuates beyond 0.3V-0.7V, the feature code extraction operation is paused. Perform a combined low-pass and notch filter operation to adjust the low-pass filter cutoff frequency to 0.6kHz-0.9kHz.

4. The method for monitoring and controlling the contact status of a DC contactor according to claim 2, characterized in that, The spiral hierarchical identification in step S1 includes: When parsing the hierarchical identifier, a bit-by-bit verification operation is performed, and the integrity of the instruction identifier of the corresponding level is verified simultaneously when one hierarchical identifier is verified. If an error is detected during the verification, the current level of parsing is stopped, and the parsing operation is performed at the previous level's flag. After parsing, the feature code recognition result is matched with the drive circuit identification information. After the matching operation is completed, the drive instruction allocation operation is performed. After the instruction allocation operation is completed, the instruction is transmitted to the corresponding drive circuit.

5. The method for monitoring and controlling the contact status of a DC contactor according to claim 1, characterized in that, Step S2 includes the following steps: A portion of the rated drive voltage is output to the DC contactor coil, and after the voltage of this portion is output for a preset time, the real-time current value of the DC contactor coil is collected. The real-time current value is compared with the preset current threshold, and after the comparison is completed, the full rated drive voltage is output to the DC contactor coil. When the full rated drive voltage is output to the DC contactor coil, it drives the armature of the DC contactor coil to engage. After the armature engages, the voltage output is maintained until the contacts are fully closed.

6. The method for monitoring and controlling the contact status of a DC contactor according to claim 1, characterized in that, After detecting the closure of the DC contactor contacts in step S3, the step-down switching of the coil drive voltage includes: When the driving voltage of the DC contactor coil drops from the rated driving voltage to 65%-75% of the rated driving voltage, the DC contactor coil engagement feedback signal is collected simultaneously and the engagement stability is determined. After the stability is determined, the voltage reduction operation is performed. When the driving voltage drops to 45%-55% of the rated driving voltage, the real-time temperature of the coil is collected synchronously and compared with the preset safe temperature range. After determining that the temperature is within the safe range, the voltage reduction operation is performed. When the driving voltage drops to the PWM driving voltage range of 30%-40% of the rated driving voltage, the coil engagement status is monitored in real time during the voltage reduction process. If the armature engagement status is detected to be loose, the voltage reduction operation is paused to maintain the current driving voltage range.

7. The method for monitoring and controlling the contact status of a DC contactor according to claim 6, characterized in that, The step-down switching in step S3 is specifically as follows: After completing the first-stage voltage reduction operation, the real-time temperature value of the coil is collected, and the collected temperature value is compared with the preset temperature threshold. If the temperature exceeds the preset temperature threshold, adjust the duration range of the next level of pressure reduction; if the temperature is within the safe range, maintain the original pressure reduction duration. The coil temperature is checked every preset time interval during the continuous output of PWM drive voltage; The detected temperature value is transmitted to the duty cycle adjustment unit, which dynamically adjusts the duty cycle range of the PWM drive voltage according to the temperature value.

8. The method for monitoring and controlling the contact status of a DC contactor according to claim 7, characterized in that, The adjustment to the PWM drive voltage region in step S3 specifically involves: During the duty cycle adjustment process, the contact resistance value of the contact point is collected in real time, and the difference between the contact resistance value and the preset resistance threshold is calculated to obtain the resistance difference. If the resistance difference is positive and exceeds the preset difference threshold, the duty cycle of the PWM drive voltage is increased according to the preset gradient, and the duty cycle value is recorded once for each increase. If the resistance difference is negative or within the preset difference threshold, the current PWM duty cycle will remain unchanged.

9. The method for monitoring and controlling the contact status of a DC contactor according to claim 8, characterized in that, The continuous output of PWM drive voltage to the coil in step S3 includes: The contact resistance value of the contact point is collected in real time. When the contact resistance value exceeds the preset resistance threshold after multiple consecutive sampling results, the PWM drive voltage output operation is paused. The rated drive voltage is output to the DC contactor coil. After the DC contactor coil drives the armature to engage, a stepped voltage reduction switching operation is performed. After the buck switching operation is completed, the PWM drive voltage output is restored. After the output is restored, the contact resistance value is continuously collected. Real-time sampling stops when the contact resistance value stabilizes.

10. The method for monitoring and controlling the contact status of a DC contactor according to claim 1, characterized in that, Step S4 includes the following steps: Perform parity check on the instruction flag bit in the feature code recognition result, and perform cyclic redundancy check on the hierarchy flag bit in the feature code recognition result; The parity check operation and the cyclic redundancy check operation are synchronously transmitted to the check result integration unit. When either the parity check operation or the cyclic redundancy check operation detects an encoding abnormality, an abnormal signal is output and transmitted to the drive control unit. The drive control unit cuts off the drive voltage of the DC contactor coil and locks the drive circuit, while simultaneously triggering the mechanical lockout of the DC contactor.

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