Method of checking the reasonableness of insulation monitoring of a high-voltage system of an electric vehicle

Abstract

The invention relates to a method for checking the reasonableness of the insulation monitoring of a high-voltage system (100) of an electrically operated vehicle during charging of traction batteries of the electrically operated vehicle, wherein the electrical insulation of the high-voltage system (100) is monitored by means of an insulation monitoring device (101), wherein a check is carried out periodically as to whether a further insulation monitoring device is active on a high-voltage bus of the high-voltage system (100).

Description

Technical Field

[0001] This invention relates to a method for checking the rationality of insulation monitoring of the high-voltage system of an electric vehicle during the charging of a traction battery, wherein the electrical insulation of the high-voltage system is monitored by means of an insulation monitoring device. Background Technology

[0002] When charging the traction battery of an electric vehicle, especially when charging with DC current (DC charging), the electric vehicle is connected to the charging equipment, specifically the DC charging equipment, in a current-driven manner. The high-voltage system of an electric vehicle is typically designed as a so-called IT system, the abbreviation "IT" meaning "IsoléTerre" (French for "insulated ground"). "I" refers to the (PE) insulation network, and "T" refers to the grounding device. This IT system is maintained during charging to ensure current insulation from ground / ground.

[0003] Based on existing technology, the generally known protection mechanism involves continuously monitoring electrical insulation using insulation monitoring devices, specifically targeting extremely high insulation resistance to grounding. In some countries, specifically for DC charging, the electric vehicle itself is responsible for insulation monitoring during the charging process.

[0004] DE 102 12 493 A1 discloses an insulation monitoring of a DC network electrically insulated from the ground of a device, wherein two insulation monitoring devices monitor two different power supply units, wherein the insulation monitoring devices are alternately connected to and disconnected from the ground by means of a non-contact switch, so that measurement interference may not occur between the insulation monitoring devices.

[0005] DE 10 2019 109 260 A1, DE 10 2019 112 839 B3 and DE 10 2018 116 055 B3 disclose various embodiments of an insulation monitoring device for monitoring current insulation in electric vehicles.

[0006] Many insulation monitoring devices are based on the so-called three-voltmeter method, a passive measurement method used to alternately measure the potential difference between individual conductors. In the three-voltmeter method, three different potential differences are measured. Possible fault currents can be calculated based on the measured values ​​obtained during the process. For example, Kirchhoff's rule is used to measure and evaluate the potential differences between +HV and ground, -HV and ground, and +HV and -HV. Here, +HV is the potential applied to the positive terminal of the traction battery, and correspondingly, -HV is the potential applied to the negative terminal of the traction battery.

[0007] DE 10 2018 116 055 B3 proposes an improved method for active insulation monitoring of a high-voltage system, wherein the high-voltage system includes a first line having a first voltage value +HV and a second line having a second voltage value -HV, wherein a first potential difference is formed between +HV and ground, wherein a second potential difference is formed between -HV and ground, wherein a first series circuit having a first semiconductor switch with a first resistor is arranged between +HV and ground, and a second series circuit having a second semiconductor switch with a second resistor is arranged between -HV and ground, wherein a first pulse width modulation and a second pulse width modulation are applied to the two semiconductor switches, wherein a first pair of resistance values ​​and a second pair of resistance values ​​of the two series circuits are modulated by means of the corresponding pulse width modulation, wherein a first voltage measurement is performed for the first pair of resistance values ​​and thereby a first pair of values ​​is determined from the first potential difference and the second potential difference, wherein a second voltage measurement is performed for the second pair of resistance values ​​and thereby a second pair of values ​​is determined from the first potential difference and the second potential difference, and wherein a first insulation resistance of the first line and a second insulation resistance of the second line are calculated using the two pairs of values. Therefore, various system states are generated by directional use of switching elements (semiconductor switches) driven by pulse width modulation, and two insulation resistances are calculated. Similar to the passive voltmeter method described above, this active method, also referred to below as the active voltmeter method, calculates the insulation resistance based on voltage measurements. Various system states can also be generated, for example, by a defined current injection instead of switching elements.

[0008] When multiple electric vehicles are connected to charging equipment in a charging infrastructure, a problem arises where two or more insulation monitoring devices activated simultaneously may interfere with each other, potentially leading to false detections of insulation faults. Furthermore, grounding interference coupling can also affect the voltmeter, thus causing similarly incorrectly reported insulation faults. Incorrectly detected insulation faults can terminate the charging process, resulting in interoperability issues. Summary of the Invention

[0009] Therefore, the object of the present invention is to provide a method for checking the rationality of insulation monitoring of the high-voltage system of an electric vehicle during the charging of a traction battery, the method being able to easily and effectively prevent erroneous detection of insulation faults.

[0010] This objective is achieved through a general method for examining the suitability of insulation monitoring of the high-voltage system of an electric vehicle during the charging of its traction battery, using features according to the method described in the next paragraph. The following preferred and advantageous embodiments relate to an advantageous development of the invention.

[0011] A method according to the invention for checking the adequacy of insulation monitoring of the high-voltage system of an electric vehicle during charging of a traction battery is characterized by periodically checking whether another insulation monitoring device is operating on the high-voltage bus of the high-voltage system. Therefore, it is very simple to determine whether the cause of an insulation fault detected by the insulation monitoring device is another insulation monitoring device also operating on the high-voltage bus of the high-voltage system. Therefore, the method according to the invention makes it easy and effective to prevent false detections of insulation faults. Therefore, charging interruptions can be avoided, thereby achieving overall improved charging availability.

[0012] In a preferred embodiment, a reasonable check time is provided during each check cycle to disable the active portion of the insulation monitoring device formed by a switching element (specifically a semiconductor switch) or a current injection member, during which a check is performed regarding whether another insulation monitoring device is operating on the high-voltage bus of the high-voltage system.

[0013] In a particularly preferred embodiment, the insulation monitoring device may be configured such that the following condition applies: (Insulation monitoring device startup time - Reasonableness check time) > Insulation resistance determination time.

[0014] Preferably, the duration of the start-up time can be selected from 30 seconds to 150 seconds, and more preferably from 60 seconds to 120 seconds.

[0015] In an advantageous embodiment, the method involves measuring three different potential differences using a 3-voltmeter with the aid of an insulation monitoring device, and thereby calculating the insulation resistance of the high-voltage system. Therefore, insulation monitoring can be performed in a very simple manner.

[0016] In a particularly advantageous embodiment, it is proposed that after the active portion of the insulation monitoring device is deactivated, three potential differences continue to be measured. By measuring the three potential differences and evaluating the measured data obtained in the process, it can be appropriately determined whether another insulation monitoring device is operating on the high-voltage bus of the relevant high-voltage system. During this process, it is preferable to check whether the three measured potential differences exhibit a low-frequency cyclic pattern. If such a pattern is present, it indicates that another insulation monitoring device is operating on the high-voltage bus of the relevant high-voltage system. Attached Figure Description

[0017] Further features and advantages of the invention will become apparent from the following description of preferred exemplary embodiments with reference to the accompanying drawings. In the drawings:

[0018] Figure 1 A schematic representation of the circuit diagram of a high-voltage system with an insulation monitoring device is shown.

[0019] Figure 2A schematic representation of the time series of insulation monitoring for a high-voltage system is shown. Detailed Implementation

[0020] refer to Figure 1 The diagram shows a circuit diagram of a high-voltage system 100 of an electric vehicle connected to a DC voltage charging device 200, which allows the traction battery of the electric vehicle to be charged. The DC voltage charging device 200 is part of a charging infrastructure that includes multiple corresponding DC voltage charging devices, enabling the traction batteries of multiple electric vehicles to be charged simultaneously.

[0021] During charging, there is a current insulation between the electric vehicle and the ground. This insulation is monitored by means of an insulation monitoring device 101 of the high-voltage system 100, which is described in further detail below. The basic structure and operating mode of the insulation monitoring device 101 are known from DE 10 2018 116 055 B3.

[0022] After the traction battery of the electric vehicle has been connected to the DC voltage charging device 200, the terminal voltage 104 (U1 = U HV A voltage is applied to each terminal of the traction battery. The first terminal of the traction battery has a first voltage value of 110 (+HV). The second terminal of the traction battery has a second voltage value of 120 (-HV). A first potential difference 118 is generated by the difference between the first voltage value 110 (+HV) and the ground potential. A second potential difference 128 is generated by the difference between the ground potential and the second voltage value 120 (-HV).

[0023] Insulation monitoring device 101 is designed to perform active insulation monitoring of high-voltage system 100 and includes: a first voltage measuring device 112; a second voltage measuring device 122; a first series circuit having a first resistor 116 and a first semiconductor switch driven by a first pulse width modulation signal 114; and a second series circuit having a second resistor 126 and a second semiconductor switch driven by a second pulse width modulation signal 124. By modulating the corresponding pulse width modulation signals 114 and 124, an active asymmetric function ensures that the two potential differences 118 and 128 are matched, and the following condition applies to the voltage value: U2 = U HV / 2 and U3 = U HV / 2. Then, the potential curve is also applicable. Figure 1 Part 102 of the high-voltage system 100 shown on the right.

[0024] Pulse width modulation modulates the duty cycle of a corresponding rectangular pulse at a constant frequency. Using this corresponding rectangular pulse (pulse width modulation signals 114, 124), a corresponding semiconductor switch is opened or closed according to its type during the pulse's duration, thus generating various states of the high-voltage system 100. Therefore, changes in the corresponding duty cycle cause changes in the corresponding resistance value of the corresponding series circuit, and consequently, changes in the corresponding potential difference determined by the corresponding voltage measurement. Similar to the voltmeter method, the insulation resistance is then calculated based on the voltage measurement.

[0025] In the following text, the first resistance value of the first series circuit is referred to as R. S1 The second resistance value of the second series circuit is called R. S2 The first insulation resistance is called R. i1 The second insulation resistance is called R. i2 The first potential difference is called V1, and the second potential difference is called V2.

[0026] The following relationship stems from the application of Kirchhoff's rule: V1 / R s1 +V1 / R i1 =V2 / R s2 +V2 / R i2 The insulation resistance R can be obtained from the above equation by measuring the voltage difference between the two potentials. i1 and R i2 Among them, the various resistance values ​​{R} caused by pulse width modulation are respectively S1 (1),R S2 (1)} and {R} S1 (2),R S2 (2)} Measure each pair of values ​​{V1(1),V2(1)} and {V1(2),V2(2)}. Before implementing the method, determine the corresponding resistance value of the corresponding series circuit generated during the corresponding PWM of the corresponding semiconductor switch.

[0027] When multiple electric vehicles are connected to the charging equipment of a charging infrastructure, a problem arises where two or more insulation monitoring devices 101 activated simultaneously may interfere with each other, potentially leading to false detections of insulation faults. Furthermore, grounding interference coupling may also affect the methods described above for determining insulation resistance R. i1 and R i2 The active 3V voltmeter method, and therefore also leads to incorrectly reported insulation faults. Incorrectly detected insulation faults will cause the charging process to terminate, and thus cause interoperability problems.

[0028] To remedy this problem, periodic checks are performed to determine whether another insulation monitoring device, besides insulation monitoring device 101, is operating on the high-voltage bus of the high-voltage system 100. Therefore, it is very simple to determine whether the cause of an insulation fault detected by insulation monitoring device 101 is another insulation monitoring device operating on the high-voltage bus of the high-voltage system 100. During this process, the active portion of insulation monitoring device 101, which is formed by a semiconductor switch in this invention, is deactivated for a defined reasonable check time within each check cycle, during which checks are performed to determine whether the other insulation monitoring device is operating on the high-voltage bus of the high-voltage system 100. Figure 2 The corresponding time series is shown in the figure. This leads to the conclusion that: (Insulation monitoring device startup time t0 - Reasonableness check time t1) > Insulation resistance determination time t2. Figure 2 In this context, t3 indicates the response time to insulation monitoring. Preferably, the duration of the start-up time t0 can be selected from 30 seconds to 150 seconds, and more preferably from 60 seconds to 120 seconds.

[0029] After the active portion of insulation monitoring device 101 is deactivated, three potential differences are measured. By evaluating the measured data obtained during this process, it can be appropriately determined whether another insulation monitoring device is operating on the high-voltage bus of the relevant high-voltage system 100. During this process, it is preferable to check whether the three measured potential differences exhibit a low-frequency cyclic pattern. If such a pattern is present, it indicates that another insulation monitoring device is operating on the high-voltage bus of the relevant high-voltage system 100.

[0030] Therefore, the method presented in this paper enables easy and effective prevention of false detections of insulation faults. This avoids charging interruptions and thus improves overall charging availability.

Claims

1. A method for checking the suitability of insulation monitoring of a high-voltage system (100) of an electric vehicle during charging of a traction battery, wherein the electrical insulation of the high-voltage system (100) is monitored by means of an insulation monitoring device (101), characterized in that, Periodically check whether another insulation monitoring device is operating on the high-voltage bus of the high-voltage system (100) to determine whether the cause of an insulation fault detected by the insulation monitoring device is the other insulation monitoring device operating on the high-voltage bus of the high-voltage system. During each inspection cycle, the active portion of the insulation monitoring device (101) formed by the switching element or current injection member is deactivated for a reasonable inspection time that is continuously limited, during which an inspection is performed to check whether another insulation monitoring device is working on the high-voltage bus of the high-voltage system (100). Among these methods, three different potential differences are measured using a voltmeter method with the aid of the insulation monitoring device (101); and After the active portion of the insulation monitoring device (101) is deactivated, three potential differences are measured, and by evaluating the three measured potential differences, it is determined whether another insulation monitoring device is operating on the high-voltage bus of the high-voltage system (100).

2. The method according to claim 1, characterized in that, The switching element is a semiconductor switch.

3. The method according to claim 1 or 2, characterized in that, The insulation monitoring device (101) is configured such that the following condition applies: (Insulation monitoring device start-up time - Reasonableness check time) > Insulation resistance determination time.

4. The method according to claim 3, characterized in that, The duration of the startup time is selected to be between 30 and 150 seconds.

5. The method according to claim 4, characterized in that, The duration of the startup time is selected to be between 60 and 120 seconds.

6. The method according to any one of claims 1, 2, 4 and 5, characterized in that, The insulation resistance of the high-voltage system (100) is calculated from the three different potential differences.

7. The method according to claim 3, characterized in that, The insulation resistance of the high-voltage system (100) is calculated from the three different potential differences.

8. The method according to claim 1, characterized in that, An inspection was conducted to determine whether the three measured potential differences exhibited a low-frequency cyclic pattern.

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