Control method and system for limiting high potential of fuel cell

Abstract

The application provides a control method and device for limiting high potential of a fuel cell, and belongs to the technical field of fuel cells, and solves the problem that the prior art cannot effectively and safely avoid high potential during the operation of a fuel cell. The method comprises the following steps: when the fuel cell is in an operating state, the output current of the fuel cell is acquired in real time, and it is determined whether the fuel cell has a high potential risk; if the fuel cell has a high potential risk, the average single-piece voltage of the fuel cell is acquired, and it is determined whether the average single-piece voltage exceeds a high potential judgment threshold V cell If yes, the air flow into the stack is reduced, and then the average single-piece voltage is identified again; otherwise, the duration for which the average single-piece voltage of the fuel cell maintains the voltage at the time when the identification is finished is identified, and after the duration reaches a calibration stable time T1, control information that the high potential risk of the fuel cell has been eliminated is output. The method can safely and effectively realize the function of clamping the potential, and can effectively protect the safety of the battery.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of fuel cell technology, and in particular to a control method and system for limiting high potential of a fuel cell. BACKGROUND

[0002] Under the dual pressure of energy and environment, fuel cell vehicles have become an important industrial development direction for future vehicles. High potential can cause the degradation of cathode catalyst, which is considered to be the main factor causing the performance degradation of the stack. When the stack is at high potential, the carbon material in the carrier is easily oxidized, thereby weakening the binding force between the platinum particles (pt) and the carbon carrier, causing the platinum particles to fall off, ultimately leading to the dissolution of platinum particles in the electrolyte, affecting the catalytic performance of the stack. More seriously, the platinum particles after falling off combine with the electrolyte or the binder, causing the resistance of the electrolyte to increase.

[0003] The prior art generally avoids the operation of the fuel cell under open circuit conditions, or increases the discharge resistance to suppress the occurrence of high potential during the operation of the fuel cell, which is limited in use, requires additional hardware devices, and cannot avoid the gradual decline in performance of the fuel cell over time. SUMMARY

[0004] In view of the above analysis, the embodiments of the present application aim to provide a control method for limiting the high potential of a fuel cell to solve the problem that the prior art cannot effectively and safely avoid the occurrence of high potential during the operation of the fuel cell.

[0005] In one aspect, the embodiments of the present application provide a control method for limiting the high potential of a fuel cell, comprising the following steps:

[0006] When the fuel cell is in an operating state, the output current of the fuel cell is obtained in real time, and it is determined whether the fuel cell has a high potential risk; if so, the next step is performed;

[0007] The average single piece voltage of the fuel cell is obtained;

[0008] It is determined whether the average single piece voltage of the fuel cell exceeds a high potential judgment threshold V cell If so, the air flow into the stack is reduced and then identified again, otherwise, the next step is directly performed;

[0009] The duration for which the average single piece voltage of the fuel cell maintains the voltage at the end of the identification of the previous step is identified, and after the duration reaches a calibration stable time T1, control information that the high potential risk of the fuel cell has been eliminated is output.

[0010] The beneficial effects of the above technical solutions are as follows: a scheme for limiting high potential of a fuel cell by controlling air flow into the stack is proposed for the first time. When the fuel cell engine is working, once there is a high potential risk of the fuel cell, and any single cell of the fuel cell stack is monitored by a fuel cell single piece voltage inspection device to be at a high potential point, the oxygen amount participating in the electrochemical reaction per unit time is reduced by a low air metering ratio (closed loop control) to reduce the single piece voltage, avoid damage caused by the single piece of the fuel cell stack working at a high potential point, and realize the clamping potential function. While solving the high potential, no additional hardware devices are needed, and the performance of the engine will not be reduced, and the adaptability is better than that of the existing technology.

[0011] Based on the further improvement of the above method, the control method further comprises the following steps:

[0012] The air flow at the moment when the high potential risk is eliminated is obtained as the initial value of the air flow into the stack when the output current of the fuel cell reaches the output current.

[0013] Further, the step of obtaining the output current of the fuel cell in real time when the fuel cell is in a running state and determining whether the fuel cell has a high potential risk further comprises:

[0014] Obtain the real-time state information of the fuel cell to identify whether the fuel cell is in a running state; if yes, execute the next step, otherwise, continue to identify the running state at the next moment;

[0015] Obtain the output current of the fuel cell at the current moment;

[0016] Identify whether the output current of the fuel cell is greater than or equal to the target current; if yes, determine that the fuel cell has a high potential risk, otherwise, determine that the fuel cell does not have a high potential risk.

[0017] Further, the step of reducing the air flow into the stack further comprises:

[0018] Obtain the average single piece voltage of the fuel cell at the current moment;

[0019] According to the average single piece voltage of the fuel cell, the target air flow F2 into the stack at the next moment is determined by the following formula,

[0020]

[0021] In the formula, V avg is the average single piece voltage of the fuel cell at the current moment, V cell is a high potential judgment threshold, K is a single piece voltage conversion flow coefficient, T is a controller scheduling time, and F1 is an initial value of the air flow into the stack;

[0022] The control of the air flow into the stack is reduced to the target air flow F2.

[0023] Further, the high potential determination threshold V cell is 0.82-0.85V.

[0024] Compared with the prior art, the control method for limiting the high potential of the fuel cell has the following beneficial effects:

[0025] 1. When the single-cell voltage of the fuel cell meets the set potential requirement, the high potential risk elimination controller records the current air flow into the stack as the target air flow initial value for the next regulation, thereby solving the adaptive problem of the clamped potential.

[0026] 2. The method is suitable for the prediction and correction of the high potential after the current is stabilized when the fuel cell engine is working.

[0027] 3. The method is simple, the control effect is good, and it is beneficial to improve the service life of the fuel cell stack and the user experience.

[0028] On the other hand, the embodiment of the present application provides a control system for limiting the high potential of the fuel cell using the above method, comprising a fuel cell stack, an air flow regulation device, a DC-DC converter, a current monitoring device, a fuel cell single-cell voltage inspection device and a controller; wherein,

[0029] The air inlet of the fuel cell stack is connected to the output end of the air flow regulation device, the total power output end is connected to the external power consumption device through the DC-DC converter and the current monitoring device, and the power supply output end of the single-cell battery is connected to the fuel cell single-cell voltage inspection device;

[0030] The controller is used to acquire the output current of the fuel cell in real time when the fuel cell is in the running state, determine whether there is a high potential risk of the fuel cell, acquire the average single-cell voltage of the fuel cell when there is a high potential risk, reduce the air flow into the stack until the average single-cell voltage is less than the high potential determination threshold V cell when the average single-cell voltage exceeds the high potential determination threshold V cell , identify the duration that the average single-cell voltage of the fuel cell maintains the current time voltage, and output the control information that the high potential risk of the fuel cell has been eliminated after the duration reaches the calibration stable time T1.

[0031] The input end one of the controller is connected to the current monitoring device, the input end two is connected to the fuel cell single-cell voltage inspection device, and the output end is connected to the control end of the air flow regulation device.

[0032] Preferably, the air flow regulation device further comprises an air compressor and a flow control valve connected in sequence; and,

[0033] The air inlet of the fuel cell stack is connected to the output end of the air compressor through a flow control valve.

[0034] Preferably, the controller has a display module; and the display screen of the display module respectively displays the control information of whether the fuel cell has high potential risk and the high potential risk of the fuel cell has been eliminated.

[0035] Preferably, the DC-DC converter is a bidirectional DC-DC converter with voltage clamping function.

[0036] Preferably, the control system further comprises a discharge relay and a discharge resistor; wherein,

[0037] One end of the discharge relay is connected to the positive pole of the power supply output end of the fuel cell, the other end is connected to the discharge resistor, and the control end is connected to the output end of the controller;

[0038] One end of the discharge resistor is connected to the negative pole of the power supply output end of the fuel cell and grounded, and the other end is connected to the discharge relay. BRIEF DESCRIPTION OF DRAWINGS

[0039] The above and other objects, features and advantages of the present disclosure will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings, in which like reference characters refer to like parts throughout the figures, and in which:

[0040] Figure 1 The control method steps for limiting the high potential of the fuel cell in Example 1 are shown in the schematic diagram;

[0041] Figure 2 The control method flow chart for limiting the high potential of the fuel cell in Example 2 is shown in the schematic diagram;

[0042] Figure 3 The control system composition for limiting the high potential of the fuel cell in Example 3 is shown in the schematic diagram. DETAILED DESCRIPTION

[0043] Embodiments of the present disclosure will be described in more detail by referring to the drawings. Although the embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided to make the present disclosure more thorough and complete, and to fully convey the scope of the present disclosure to those skilled in the art.

[0044] The term "includes" and its variants are meant to cover non-exclusive inclusions, i.e., that the listed items are among a list of items but not excluding others. Unless otherwise specified, the term "or" means "and / or." The term "based on" means "based, at least in part, on." The term "one example embodiment" and "an embodiment" means "at least one example embodiment." The term "another embodiment" means "at least one additional embodiment." The terms "a first," "a second," etc. do not require that there be only one of each, but rather that there are at least one of each. Other explicit and implicit definitions can be found below.

[0045] Embodiment 1

[0046] One embodiment of the present application discloses a control method for limiting high potential of fuel cell, as shown in the formula (1), comprising the following steps: Figure 1

[0047] S1. When the fuel cell is in operation, real-time acquisition of the output current of the fuel cell, to determine whether the fuel cell has high potential risk; if yes, execute the next step;

[0048] Specifically, one or more combinations of variables such as amplitude, phase, rate of change, acceleration of change, etc. of the output current can be used to identify whether the fuel cell has high potential risk. Embodiment 2 only provides the simplest identification method;

[0049] S2. Acquisition of the average single piece voltage of the fuel cell;

[0050] Specifically, the average single piece voltage of the fuel cell is generally obtained by a fuel cell single piece voltage inspection device, and then the average single piece voltage of the fuel cell is obtained;

[0051] S3. Identification of whether the average single piece voltage of the fuel cell exceeds the high potential judgment threshold V cell , if yes, reduce the air flow into the stack and identify again, otherwise, directly execute the next step;

[0052] Specifically, the high potential judgment threshold V cell of the fuel cell (average single piece) can be obtained by laboratory calibration; the air flow into the stack can be adjusted by controlling the speed of the air compressor or the opening of the flow control valve in the existing fuel cell system;

[0053] S4. Identification of the duration that the average single piece voltage of the fuel cell maintains the voltage at the end of the previous step, until the duration reaches the calibration stable time T1, outputting the control information that the high potential risk of the fuel cell has been eliminated.

[0054] Specifically, the first time the average single piece voltage of the fuel cell is identified to be less than the high potential judgment threshold V cell ​at the moment, keep the air flow into the stack unchanged until the duration reaches the calibration stable time T1, and the elimination of high potential risk of the fuel cell is realized.

[0055] Compared with the prior art, the insulation detection device provided by the embodiment first proposes a scheme for limiting high potential of the fuel cell by controlling the air flow into the stack. In the scheme, when the fuel cell engine is working and the current is stable, once there is a high potential risk of the fuel cell, when any single cell of the fuel cell stack is monitored to be at a high potential point by the fuel cell single piece voltage inspection device, the amount of oxygen participating in the electrochemical reaction per unit time is reduced by the low air metering ratio (closed loop control), so as to reduce the single piece voltage and avoid damage caused by the single piece of the fuel cell stack working at the high potential point, and the clamping potential function is realized. While solving the high potential, no additional hardware device needs to be added, and the performance of the engine will not be reduced, and the adaptability is better than that of the discharge resistor of the prior art.

[0056] Embodiment 2

[0057] On the basis of embodiment 1, the method further comprises the following steps:

[0058] S5. Obtain the air flow at the moment when the high potential risk is eliminated, as the initial value of the air flow into the stack when the output current of the fuel cell reaches the output current next time.

[0059] Preferably, step S1 further comprises:

[0060] S11. Obtain the real-time state information of the fuel cell, and identify whether the fuel cell is in a running state; if yes, execute the next step, otherwise, continue to identify the running state at the next moment;

[0061] S12. Obtain the output current of the fuel cell at the current moment;

[0062] S13. Identify whether the output current of the fuel cell is greater than or equal to the target current, if yes, determine that there is a high potential risk of the fuel cell, otherwise, determine that there is no high potential risk of the fuel cell.

[0063] Preferably, the step of reducing the air flow into the stack in step S3 further comprises:

[0064] S31. Obtain the average single piece voltage of the fuel cell at the current moment;

[0065] S32. According to the average single piece voltage of the fuel cell, determine the target air flow into the stack F2 at the next moment by the following formula,

[0066]

[0067] In the formula, V avgV is the average single piece voltage of the fuel cell at the current moment, V cell K is a single piece voltage conversion flow coefficient, which can be determined through laboratory calibration, T is a controller scheduling time, and F1 is a control initial value of the air flow into the stack.

[0068] S33. The air flow into the stack is controlled to decrease to the target air flow F2 into the stack.

[0069] Preferably, the high potential judgment threshold V cell is 0.82-0.85V. The clamping potential air flow stabilization time T1 is different for different types of fuel cells and can be determined according to laboratory calibration.

[0070] The control process is described in Figure 2 , but is not limited to Figure 2 the content described.

[0071] Compared with the prior art, the control method for limiting the high potential of the fuel cell has the following beneficial effects:

[0072] 1. When the single piece voltage of the fuel cell meets the set potential requirement, the high potential risk elimination controller records the current air flow into the stack as the target air flow for next control, solving the clamping potential self-adaption problem.

[0073] 2. It is suitable for high potential prediction and correction after current stabilization when the fuel cell engine is working.

[0074] 3. The method is simple, the control effect is good, and it is conducive to improving the life of the fuel cell stack and user experience.

[0075] Embodiment 3

[0076] The application also provides a control system for limiting the high potential of the fuel cell corresponding to the method of embodiment 1 or 2, which comprises a fuel cell stack, an air flow control device, a DC-DC converter, a current monitoring device, a fuel cell single piece voltage inspection device and a controller, as shown in Figure 3 .

[0077] The air inlet of the fuel cell stack is connected to the output end of the air flow control device, the total power output end is connected to the external power device through the DC-DC converter and the current monitoring device, and the power supply output end of the single piece battery is connected to the fuel cell single piece voltage inspection device.

[0078] The controller is used to acquire the output current of the fuel cell in real time when the fuel cell is in a running state, determine whether the fuel cell has a high potential risk, and acquire the average single piece voltage of the fuel cell when the high potential risk exists, and the average single piece voltage exceeds the high potential judgment threshold V cellThe air flow into the stack is reduced until the average single-cell voltage is less than the high-voltage determination threshold V cell The duration for which the average single-cell voltage of the fuel cell maintains the current time voltage is identified, and after the duration reaches the calibrated stable time T1, control information indicating that the high-voltage risk of the fuel cell has been eliminated is output.

[0079] The program executed by the controller is described in the methods of embodiments 1 and 2.

[0080] The input end of the controller is connected to the current monitoring device, the input end two is connected to the fuel cell single-cell voltage inspection device, and the output end is connected to the control end of the air flow control device.

[0081] The fuel cell single-cell voltage inspection device is used to obtain and display all single-cell voltages of the fuel cell as a monitoring device for high-voltage of the fuel cell. Specifically, if the voltage of a single-cell battery exceeds the high-voltage determination threshold V cell , it indicates that a high voltage appears in the fuel cell. The specific structure of the fuel cell single-cell voltage inspection device is described in the existing patents CN202022989695.4, CN202121428683.2, etc.

[0082] The controller is built-in with a program for identifying the high-voltage risk of the fuel cell according to the data collected by the current monitoring device and a program for controlling the opening of the flow control valve according to the data collected by the fuel cell single-cell voltage inspection device when the fuel cell has a high risk.

[0083] The air flow control device is provided with a control key that can automatically or manually reduce the air flow into the stack, which is used as a control device to eliminate the current high-voltage of the fuel cell. Specifically, when it is monitored that any single-cell in the fuel cell has a high voltage, the air flow into the stack is reduced to reduce the amount of oxygen participating in the reaction per unit time through low air metering ratio (closed loop control), thereby reducing the single-cell voltage.

[0084] Compared with the prior art, the control system provided by the embodiment first proposes a scheme for limiting the high voltage of the fuel cell by controlling the air flow into the stack. When the fuel cell engine is working and there is a high-voltage risk of the fuel cell, when any single-cell of the fuel cell stack is monitored to be at a high-voltage point by the fuel cell single-cell voltage inspection device, the amount of oxygen participating in the electrochemical reaction per unit time is reduced through low air metering ratio (closed loop control), thereby reducing the single-cell voltage, avoiding damage caused by the single-cell of the fuel cell stack working at a high-voltage point, and achieving the function of clamping the voltage.

[0085] Embodiment 4

[0086] On the basis of the system of embodiment 3, the air flow control device further includes an air compressor and a flow control valve connected in sequence.

[0087] An air compressor, whose output end is connected to the air inlet of the fuel cell stack, and the air flow into the stack can be adjusted by adjusting the rotating speed of the air compressor.

[0088] A flow control valve, whose input end is connected to the output end of the air compressor, whose output end is connected to the air inlet of the fuel cell stack, and whose control end is connected to the control key of the air flow regulating device. The air flow into the stack can also be adjusted by adjusting the opening of the flow control valve.

[0089] Preferably, the controller further comprises a high potential risk identification unit and a high potential risk elimination control unit.

[0090] The high potential risk identification unit is configured to predict whether there is a high potential risk at the current time according to the real-time data collected by the current monitoring device, and output a high potential risk warning information when there is a high potential risk. The input end of the high potential risk identification unit is connected to the current monitoring device, and the output end is connected to the high potential risk elimination control unit.

[0091] Specifically, if the real-time data collected by the current monitoring device is greater than or equal to the target current, there is a high potential risk. Otherwise, real-time identification is performed by the fuel cell single piece voltage inspection device.

[0092] The high potential risk elimination control unit is configured to, after receiving the high potential risk warning information, acquire the average single piece voltage (the mean value of all single piece voltages) of the fuel cell through the fuel cell single piece voltage inspection device data, and identify that the average single piece voltage exceeds the high potential judgment threshold V cell , start the control key of the air flow regulating device to reduce the air flow into the stack until the average single piece voltage of the fuel cell does not exceed the high potential judgment threshold V cell , output a high potential risk elimination information of the fuel cell, and record the current air flow into the stack as the air flow into the stack regulating initial value (target air flow initial value) of the air flow regulating device for next regulation.

[0093] The input end of the high potential risk elimination controller is respectively connected to the output end of the fuel cell single piece voltage inspection device and the high potential risk identification device, and the output end is connected to the control key of the air flow regulating device.

[0094] Preferably, the controller has a display module. And the display screen of the display module respectively displays the output current of the fuel cell, the average single piece voltage of the fuel cell, whether there is a high potential risk of the fuel cell (only displayed when there is a high potential risk), and the control information of the high potential risk elimination of the fuel cell (only displayed when there is a high potential risk).

[0095] Preferably, the DC-DC converter is a bidirectional DC-DC converter with voltage clamping function. The specific structure of the DC-DC converter can refer to the existing patent CN202020367848.9 and the like.

[0096] Preferably, the control system further comprises a discharge relay and a discharge resistor.

[0097] One end of the discharge relay is connected to the positive electrode of the power supply output end of the fuel cell, the other end is connected to the discharge resistor, and the control end is connected to the output end of the controller. One end of the discharge resistor is connected to the negative electrode of the power supply output end of the fuel cell and grounded, and the other end is connected to the discharge relay.

[0098] Compared with the prior art, the control system for limiting the high potential of the fuel cell has the following beneficial effects:

[0099] 1. When the single-piece voltage of the fuel cell meets the set potential requirement, the high potential risk elimination controller records the current air flow into the stack as the target air flow for the next regulation, solving the clamping potential adaptive problem.

[0100] 2. It is suitable for high potential prediction and correction after current stabilization when the fuel cell engine is working.

[0101] 3. The structure is simpler, the control effect is better, and it is conducive to improving the service life of the fuel cell stack and user experience.

[0102] The above has described the embodiments of the present disclosure, and the above description is exemplary, not exhaustive, and is not limited to the disclosed embodiments. Many modifications and changes are obvious to those skilled in the art without departing from the scope and spirit of the described embodiments. The selection of the terms used herein is intended to best explain the principles, practical application or improvement of the prior art of the embodiments, or to enable other ordinary skilled in the art to understand the embodiments disclosed herein.

Claims

1. A control method for limiting high potential of a fuel cell, characterized by, The method comprises the following steps: When the fuel cell is in operation, the output current of the fuel cell is obtained in real time, and it is determined whether the fuel cell has high potential risk; If yes, the next step is performed; The average single piece voltage of the fuel cell is obtained; identifying whether the average single sheet voltage of the fuel cell exceeds a high potential determination threshold value V cell If yes, the stack air flow rate is reduced and the identification is performed again, otherwise, the next step is directly performed. The duration for which the average single piece voltage of the fuel cell maintains the voltage at the end of the previous step is identified, and after the duration reaches a specified stable time T1, control information that the high potential risk of the fuel cell has been eliminated is outputted; The step of obtaining the output current of the fuel cell in real time when the fuel cell is in operation and determining whether the fuel cell has high potential risk further comprises the following steps: Real-time state information of the fuel cell is obtained, and it is determined whether the fuel cell is in operation; if yes, the next step is performed, otherwise, the operation state identification at the next moment is continued; The output current of the fuel cell at the current moment is obtained; It is determined whether the output current of the fuel cell is greater than or equal to a target current; if yes, it is determined that the fuel cell has high potential risk; The step of reducing the air flow further comprises the following steps: The average single piece voltage of the fuel cell at the current moment is obtained; The target air flow F2 at the next moment is determined according to the average single piece voltage of the fuel cell by the following formula, In the formula, V avg V is the average single piece voltage of the fuel cell at the current time cell K is the single piece voltage conversion flow coefficient, T is the controller scheduling time, F1 is the initial value of the control of the air flow into the stack The air flow is controlled to reduce to the target air flow F2.

2. The control method for limiting high potential of a fuel cell according to claim 1, characterized by, The method further comprises the following steps: The air flow at the moment when the high potential risk has been eliminated is obtained as the initial value of the air flow control when the output current of the fuel cell reaches the target current next time.

3. The control method for limiting high potential of a fuel cell according to claim 1, characterized by, The high-potential determination threshold value V cell is 0.82 to 0.85 V.

4. A control system for limiting high potential of a fuel cell for implementing the method as claimed in claim 1, characterized by The method comprises a fuel cell stack, an air flow control device, a DC-DC converter, a current monitoring device, a fuel cell single piece voltage inspection device and a controller; wherein, The air inlet of the fuel cell stack is connected to the output end of the air flow control device, the total power supply output end is connected to the external power consumption device through the DC-DC converter and the current monitoring device, and the single piece battery power supply output end is connected to the fuel cell single piece voltage inspection device; The controller is configured to, when the fuel cell is in an operating state, acquire an output current of the fuel cell in real time, determine whether the fuel cell has a high potential risk, and when the fuel cell has the high potential risk, acquire an average single piece voltage of the fuel cell, reduce an air flow into the stack when the average single piece voltage exceeds a high potential judgment threshold V cell , until the average single piece voltage is less than the high potential judgment threshold V cell , identify a duration that the average single piece voltage of the fuel cell maintains a current time voltage, and output control information that the high potential risk of the fuel cell has been eliminated when the duration reaches a calibration stable time T1. The input end one of the controller is connected to the current monitoring device, the input end two is connected to the fuel cell single piece voltage inspection device, and the output end is connected to the control end of the air flow control device.

5. The control system for limiting high potential of a fuel cell according to claim 4, characterized by, The air flow control device further comprises an air compressor and a flow control valve connected in sequence; and The air inlet of the fuel cell stack is connected to the output end of the air compressor through the flow control valve.

6. The control system for limiting high potential of a fuel cell according to claim 4 or 5, characterized by, The controller has a display module; and the display screen of the display module displays whether the fuel cell has high potential risk and the control information that the high potential risk of the fuel cell has been eliminated.

7. The control system for limiting high potential of a fuel cell according to claim 4 or 5, characterized by, The DC-DC converter is a bidirectional DC-DC converter with voltage clamping function.

8. The control system for limiting high potential of a fuel cell according to claim 4 or 5, characterized by, The method further comprises a discharge relay and a discharge resistor; wherein, One end of the discharge relay is connected to the positive electrode of the fuel cell power supply output end, the other end is connected to the discharge resistor, and the control end is connected to the output end of the controller; One end of the discharge resistor is connected to the negative electrode of the fuel cell power supply output end and grounded, and the other end is connected to the discharge relay.

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