INTEGRATED ACTIVE INSULATION MEASUREMENT

Abstract

An exemplary insulation test circuit includes a first switch that connects a first insulation resistor to a terminal of a measuring resistor, the first insulation resistor also being connected to a positive bus of a power distribution system. The insulation test circuit also includes a second switch that connects a second insulation resistor to the terminal of the measuring resistor, the second insulation resistor also being connected to a negative bus of the power distribution system. The insulation test circuit also includes a pulse generator that connects the measuring resistor to chassis ground.

Description

TECHNICAL AREA

[0001] The disclosure concerns the measurement of parameters for high-voltage battery systems. BACKGROUND

[0002] This disclosure relates to high-voltage insulation measurement for high-voltage power distribution systems. High-voltage insulation can be used in a wide variety of circuits and devices, such as high-voltage DC power distribution circuits. High-voltage insulation can include high-resistance components, such as power resistors, between a positive bus and ground and / or a negative bus and ground.

[0003] High-voltage insulation is frequently used when electrical safety is important. For example, high-voltage insulation can be used in electric vehicles, self-driving vehicles, or other installations where an electrical short circuit or fault could lead to safety hazards. SUMMARY

[0004] In general, the disclosure describes active insulation measurement techniques for verifying the insulation resistance between a high-voltage power distribution system and a reference, such as ground. For an electric vehicle, the high-voltage power distribution system should be completely isolated from the vehicle chassis, e.g., the reference. The insulation resistance should be measured periodically over the lifetime of the electric vehicle or over the lifetime of other systems using a high-voltage power distribution system to ensure that no fault has occurred that could compromise the electrical insulation, which protects the user, mechanic, or anyone who might touch the electric vehicle from an unwanted electric shock.

[0005] Active insulation measurement techniques can be used without the presence of high voltage and can therefore be employed on either side of relays that control the delivery of high voltage to the loads of the HV distribution system. For example, an active insulation measurement system can be used between the high-voltage (HV) battery and the HV relays, or between the HV relays and the loads supplied by the HV battery. Active insulation measurement can include circuitry that may comprise any or all of an insulation measurement circuit, an isolation island, and signal conditioning to convert the measurement into a signal that can be processed by circuitry designed to determine and control further action as needed.

[0006] In an example, this disclosure describes an insulation measurement circuit comprising: a first switch connecting a first insulation resistor to a terminal of a measuring resistor, the first insulation resistor also being connected to a positive bus of a power distribution system; a second switch connecting a second insulation resistor to the terminal of the measuring resistor, the second insulation resistor also being connected to a negative bus of the power distribution system; and a pulse generator connecting the measuring resistor to the chassis ground.

[0007] In another example, this disclosure describes a power distribution system comprising: a power supply configured to supply power to a load, wherein the power supply and the load are isolated from a chassis ground for the power distribution system; an isolation measurement circuit comprising: a first switch connecting a first insulation resistor to a first terminal of a sense resistor, the first insulation resistor also being connected to a positive bus of a power distribution system; a second switch connecting a second insulation resistor to a second terminal of the sense resistor, the second insulation resistor also being connected to a negative bus of the power distribution system; and a pulse generator connecting the sense resistor to the chassis ground.

[0008] In another example, this disclosure describes a method comprising: controlling a switch to connect a bus of a power distribution system to a first terminal of a sense resistor, wherein the bus is connected to the first terminal of the sense resistor via an insulation resistor; applying a pulse between a chassis ground and a second terminal of the sense resistor by a pulse generator of an insulation measurement circuit; measuring a value across the sense resistor, wherein the value measured across the sense resistor includes a specification of an insulation resistance between a chassis ground and the bus when the switch is conducting and the pulse generator includes the pulse.

[0009] Details of this and other examples are set forth in the accompanying drawings and the description below. Other features, functions, and advantages will become apparent from the description, the drawings, and the claims. BRIEF DESCRIPTION OF THE DRAWINGS Fig. Figure 1 is a block diagram illustrating an example power distribution system. Fig. Figure 2 is a schematic and block diagram illustrating an exemplary active insulation measurement circuit. Fig. Figure 3 is a schematic circuit diagram illustrating an exemplary active insulation measurement circuit. Fig. Figure 4 is a schematic diagram illustrating an example voltage follower for the signal conditioning circuit. Fig. Figure 5 is a schematic diagram illustrating an example differential amplifier for the signal conditioning circuit. Fig. Figure 6 is a schematic diagram illustrating an example circuit to provide a signal for evaluation by a processing circuit. Fig. Figure 7 is a flowchart illustrating an exemplary procedure for measuring insulation resistance. Fig. Figure 8 is a diagram of an exemplary voltage signal as a function of time, as produced by the exemplary active insulation measurement circuit of Fig. 2 or Fig. 3 is measured. DETAILED DESCRIPTION

[0010] This disclosure relates to active insulation measurement techniques for verifying the insulation resistance between a high-voltage power distribution system and a reference, such as ground. Road vehicles with a high-voltage (HV) system may have dedicated insulation resistance to ensure safe operation. Government regulations or industry standards may require specific resistance levels and Y-capacitance levels for electric or hybrid vehicles. For example, according to ISO 6469-3, road vehicles with a high-voltage (HV) system should have a dedicated insulation resistance of at least 100 ohms / V or 500 ohms / V if there is no specific protection in the AC environment, such as an inverter.Furthermore, according to ISO 17409, the maximum Y-capacitance between the fully floating HV power distribution network and the vehicle chassis should not exceed 4 microfarads (µF) at 400 V or 2 µF at 800 V. To ensure safe operation, these values ​​should be monitored within the vehicle. Currently, passive isolation networks are used, which require high voltage to be present within the system.

[0011] According to the techniques and apparatus disclosed herein, an insulation measurement circuit comprises switches (e.g., transistors formed in semiconductor materials) connecting insulation resistors between the positive and negative high-voltage buses of the power distribution system, and a measurement system comprising a sense resistor and a pulse generator connecting the sense resistor to a reference, e.g., ground, or a vehicle chassis ground. The insulation measurement circuit is an active insulation measurement circuit configured to measure the resistance and / or insulation of the power distribution system (e.g., the resistance of the insulation resistors or a voltage proportional to the resistance of the insulation resistors) without the presence of the high-voltage source, e.g., whether the high-voltage source is connected to or disconnected from a load.

[0012] The devices and techniques described herein offer several advantages. For example, they provide improved protection of the measurement components by eliminating the need for a high voltage to be present. If, for instance, the insulation resistances fail, the high voltage can wear out or degrade electrical components of the measurement system. Furthermore, they offer improved monitoring of the high-voltage system's insulation by increasing the time a measurement can be performed, thus enabling faster detection of a trend toward decreasing insulation resistance values.Furthermore, the devices and techniques can provide improved longevity of components of the high-voltage distribution system, for example by not requiring relatively large relays to open or close in order to obtain a measurement, thus saving wear on the relays that might otherwise need to be replaced after relatively few opening / closing cycles (e.g., less than ten opening / closing cycles).

[0013] Fig. Figure 1 is a block diagram illustrating an exemplary insulation system 10 comprising an HV power distribution system 100 and an active insulation measurement circuit 200. Although described here as part of an electric vehicle, the insulation system 10 represents any electrical system comprising an HV power distribution system 100. In the example shown, the insulation system 10 also includes insulation resistors 202 and 204 and chassis ground 120.

[0014] In the example shown, the HV power distribution system 100 comprises a power supply 102, electrical loads 104-110, a positive HV terminal 112 and a negative HV terminal 114, relays 116 and 118, and a positive HV bus 120 and a negative HV bus 122. The power supply 106 is electrically connected to the electrical loads 104-110 via electrical relays 116 and 118 and positive and negative HV buses 212 and 214, and is configured to provide the voltage for the electrical loads 104-110 to draw electrical current from the power supply 102. In the example shown, the electrical loads 104-110 include a motor 104, a DC-DC converter, a heater 108, and an air conditioning system 110. In other examples, the HV power distribution system 100 may include fewer or more electrical loads, e.g., one, two, three, or five or more electrical loads.In the example shown, the electrical loads 104-110 are connected in parallel, and in other examples, one or more of the electrical loads 104-110 can be connected in series or in any combination of series and / or parallel connections. The power supply 102 is configured to provide a relatively high voltage to the positive and negative HV buses 212, 214, e.g., ±400 V, ±800 V, or any suitable positive or negative voltage.

[0015] Relay 116 is connected to the positive HV terminal 112 and the positive HV bus 212, and relay 118 is connected to the negative HV terminal 114 and the negative HV bus 214. Relays 116 and 118 are configured to connect and disconnect the power supply 102 from loads 104–110, for example, in the event of a short circuit, overload, or overcurrent. Relays 116 and 118 may include electromechanical devices configured to switch high-voltage signals. In some examples, relays 116 and 118 may include semiconductor-based relay devices, such as power MOSFETs (metal-oxide-semiconductor field-effect transistors). The relays 116, 118 can be designed to be essentially robust against switching high voltages, high currents and / or high signal frequencies, e.g. for a large number of opening and closing cycles.In some examples, the relays 116, 118 are robust and also designed to be replaced after a relatively small number of opening / closing cycles, e.g., about 5 opening / closing cycles or about 10 opening / closing cycles, so that it may be desirable not to have to open / close the relays 116, 118 in order to obtain a measurement of the resistance and / or integrity of the insulation resistances 202, 204.

[0016] The insulation resistors 202 and 204 are connected between the HV power distribution system 100 and the chassis ground 120 and are designed to isolate the HV power distribution system, e.g., from surfaces with which a user might come into contact. In the example shown, the first insulation resistor 202 is connected to the positive HV bus 212 and also to the chassis ground 120 via the active insulation measurement circuit 200, and the second insulation resistor 204 is connected to the negative HV bus 214 and also to the chassis ground 120 via the active insulation measurement circuit 200. The insulation resistors 202 and 204 can each provide insulation between the positive and negative buses or the chassis ground, respectively, and can comprise one or more electrical components, e.g., any combination of resistors, power resistors, or the like.The insulation resistances 202, 204 can degrade over time or after relatively large currents have passed through them. In some examples, the insulation resistances 202, 204 can represent a variety of electrical components instead of individual resistors; for example, they can represent the insulation resistance of an electrical path between the positive bus 212 and the negative bus 214 of the HV power distribution system 100 and the chassis ground 120.

[0017] The active insulation measurement circuit 200 is connected between each of the insulation resistors 202, 204 and the chassis ground and is configured to measure the insulation resistance of each of the insulation resistors 202, 204, and in some examples, to measure the Y-capacitance of each of the positive and negative HV buses 212, 214 (e.g., between each bus and chassis ground 120) and / or the X-capacitance between the positive and negative HV buses 212, 214. The active insulation measurement circuit 200 can be configured to inject a pulse and / or a signal via a pulse generator and to measure the resulting voltage drop across a measuring resistor, as described below.

[0018] Fig. Figure 2 is a schematic and block diagram illustrating an exemplary active insulation measurement circuit 200. In the example shown, the active insulation measurement circuit 200 comprises switches 206 and 208, a control circuit 230, a measuring resistor 210, and an insulation island 216. The insulation island 216 includes a pulse generator 220 and a signal and measurement circuit 218. In the example shown, the active insulation measurement circuit 200 is connected between the insulation resistor 202 and chassis ground 120, as well as between the insulation resistor 204 and chassis ground 120, and is communicatively coupled to the processing circuit 222.

[0019] In the example shown, the first switch 206 connects the insulation resistor 202 to terminal 210A of the measuring resistor 210, and the second switch 208 connects the insulation resistor 204 to terminal 210A of the measuring resistor 210. The first and second switches 206, 208 can be relatively small switches, e.g., low-voltage switches, since the insulation resistors 202, 204 can be high-voltage resistors and the switches 206, 208 are connected to the lower voltage and current side of the insulation resistors 202, 204. In some examples, the switches 206, 208 can be transistors, e.g., low- or medium-voltage MOSFETs. In other examples, the switches 206, 208 can be any suitable switches, e.g., high-, medium-, or low-voltage switches.

[0020] The pulse generator 220 connects the measuring resistor 210 to the chassis ground, e.g., between terminal 210B of the measuring resistor 210 and the chassis ground. The pulse generator 220 is designed to generate and / or apply an electrical pulse (e.g., a voltage and / or current pulse with pulse characteristics such as pulse width, pulse frequency, pulse amplitude, and timing or timing delay) between the chassis ground 120 and the second terminal 210B of the measuring resistor 210.

[0021] The control circuit 230 is configured to control the opening / closing of switches 206 and 208 and the operation of pulse generator 220. The control circuit is connected to the gates of switches 206 and 208 and is communicatively linked to pulse generator 220. In some examples, control circuit 230 can optionally be communicatively linked to processing circuit 222 and / or the control circuit of a battery management system. For example, processing circuit 222 can determine when insulation resistance measurements are performed and communicate the measurement parameters (e.g., the pulse characteristics and the timing of when switches 206 and 208 are opened and closed) to control circuit 230, which then controls switches 206 and 208 and pulse generator 220 to perform the insulation measurements according to the parameters.

[0022] The measuring resistor 210 is connected between the pulse generator 220 and each of the switches 206 and 208. The measuring resistor 210 can be any suitable resistor and / or any electrical component designed to cause a voltage drop across the resistor to be measured, for example, by the measuring circuit 218. For example, the measuring resistor 210 can be a carbon composition resistor, a carbon pile resistor, a printed carbon resistor, a thick or thin film resistor, an axial resistor, a metal film resistor, a metal oxide resistor, a wire-wound resistor, a metal foil resistor, an adjustable resistor, a potentiometer, or any other suitable resistor.

[0023] The measuring circuit 218 is connected across the measuring resistor 210, for example, to terminals 210A and 210B. Terminals 210A and 210B can be measuring nodes of the measuring resistor 210. The measuring circuit 218 is configured to measure a voltage drop across the measuring resistor 210 and / or an electric current through the measuring resistor 210. In some examples, the measuring circuit 218 includes a voltmeter and / or an ammeter, or any suitable electrical component configured to measure voltage and / or current. In some examples, the measuring circuit 218 may include a differential amplifier. For example, the measuring circuit 218 may measure a negative voltage drop across the measuring resistor 210. The processing circuit 222 cannot tolerate negative voltages, and a differential amplifier of the measuring circuit 218 may be configured to condition the measured voltage, for example, by...The measured negative voltage is converted into a positive voltage and the voltage is amplified to increase or decrease it within a range that can be used by the processing circuit 222. In some examples, a series of two diodes can be used to supply only a single signal to the processing circuit 222, for example, to a monitoring device, a battery management system (BMS) microcontroller, or the like. In some examples, the measuring circuit 218 measures a voltage signal, such as a voltage drop signal as a function of time, and can condition the signal and supply the conditioned signal to the processing circuit 222.In some examples, the measuring circuit 222 may include a memory and may be configured to store one or more voltage measurements, one or more voltage signal measurements and / or one or more values ​​derived from voltage or voltage signal measurements, e.g., one or more insulation resistances of the insulation resistances 206, 208.

[0024] The processing circuit 222 is communicatively coupled to the measuring circuit 218 and is configured to receive measurements, e.g., voltages, voltage signals, currents, current signals, or derived quantities, e.g., resistances and / or measurement and signal conditioning parameters, from the measuring circuit 218. The processing circuit 222 can also be communicatively coupled to the control circuit 230 and can be configured to supply switching and pulse generation parameters to the control circuit 230 and measurement timing control to both the measuring circuit 218 and the control circuit 230.

[0025] In the example shown, the pulse generator 220 and the measuring circuit 218 are contained within the isolation island 216. The isolation island 216 and electrical components within the isolation island 216 can be galvanically isolated from voltages and currents in the active isolation measuring circuit 200. For example, the pulse generator 220 and the measuring circuit 218 can be a circuit and / or components with a relatively low voltage, e.g., 12 V, 24 V, or the like. In some examples, the isolation island 216 can include a coreless transformer; for example, electrical components such as the pulse generator 220 and the measuring circuit 218 can be electrically connected to the rest of the active isolation measuring circuit 200 but galvanically isolated from it. B. the switches 206, 208, the measuring resistor 210, the chassis ground 120 and electrical wires, conductors or conductor tracks that couple the switches 206, 208, the measuring resistor 210 and the chassis ground 120.In some examples, the isolation island 216 includes a first coreless transformer that couples the pulse generator 220 and the measuring circuit 218 to the rest of the active isolation measuring circuit 200, e.g., the pulse generator to the control circuit 230, the measuring resistor terminal 210A, and the chassis ground 120, and the measuring circuit to terminals 210A and 210B of the measuring resistor 210. The isolation island 216 can then also include a second coreless transformer that couples the active isolation measuring circuit 200 to the processing circuit 222, e.g., the measuring circuit 218 and the processing circuit 222.

[0026] The active insulation measurement circuit 200 can be configured to determine values ​​that, for example, the processing circuit 222 uses to determine whether an insulation-to-ground fault is present. For instance, the control circuit 230 can be configured to open the switch 208 to disconnect the measuring resistor 210 from the insulation resistor 204, and to close the switch 206 to connect the measuring resistor 210 and the insulation resistor 202 together (e.g., such that the switch 206 is essentially conducting) in order to measure a value that indicates the insulation resistance between chassis ground 120 and the positive HV bus 212. In some examples, the value can be a voltage drop across the measuring resistor 210. For example, with switch 204 open and switch 202 closed, the pulse generator 220 can apply a pulse between chassis ground 120 and terminal 210B of the measuring resistor 210.If the insulation resistor 202 is robust and exhibits a substantially high resistance, e.g., an insulation resistance of 1 / 2, then the voltage drop across the sense resistor 210 due to the pulse is very small. If the insulation resistor 202 is degraded and exhibits a resistance less than a threshold value, e.g., 100 Ω / V or 500 Ω / V, then current can flow through the sense resistor 210, and the voltage drop across the sense resistor 210 for the pulse can be relatively larger, e.g., greater than a predetermined voltage drop. The measuring circuit 218 can measure the resulting voltage drop across the sense resistor 210 for the pulse, which can be a value indicating the insulation resistance between chassis ground 120 and the positive HV bus 212 provided by the insulation resistor 202.

[0027] The control circuit 230 can be configured to close switch 208 to connect the sense resistor 210 and the insulation resistor 204 together, and to open switch 206 to disconnect the sense resistor 210 from the insulation resistor 202 in order to measure a value indicating the insulation resistance between chassis ground 120 and the negative HV bus 214. In some examples, the value can be a voltage drop across the sense resistor 210. For example, with switch 204 closed and switch 202 open, the pulse generator 220 can apply a pulse between chassis ground 120 and terminal 210B of the sense resistor 210. If the insulation resistor 204 is robust and has a substantially high resistance, such as insulation resistance, then the voltage drop across the sense resistor 210 for the pulse will be very small.If the insulation resistor 204 is degraded and exhibits a resistance less than a threshold value, e.g., 100 Ω / V or 500 Ω / V, then current can flow through the sense resistor 210, and the voltage drop across the sense resistor 210 for the pulse can be relatively larger, e.g., greater than a predetermined voltage drop. The measuring circuit 218 can measure the resulting voltage drop across the sense resistor 210 for the pulse, which can be a value indicating the insulation resistance between chassis ground 120 and the negative HV bus 24 provided by the insulation resistor 204.

[0028] In some examples, the active insulation measurement circuit 200 is configured to determine and store initial values ​​that specify the insulation resistance for the insulation resistors 202 and 204. For example, an initial active insulation measurement circuit 200 is used at an initial time, such as the initial time when the HV power distribution system 100 is used, or at another time when, for example, the insulation resistance of the insulation resistors 202 and 204 is known and / or is known to provide insulation for the HV power distribution system 100, or periodically, for example, annually, monthly, weekly, daily, or at any other time. The active insulation measurement circuit 200 can then be configured to determine an insulation resistance and / or to determine whether an insulation ground fault exists by comparing current measurements with the initial values.For example, the active insulation measurement circuit 200 can take repeated values ​​measured across the measuring resistor 210 over time and compare them with the initial measured values ​​using the active insulation measurement circuit 200 and / or the processing circuit 222.

[0029] In other examples, the active insulation measurement circuit 200 can be configured to determine an insulation resistance and / or to determine whether an insulation-to-ground fault exists by comparing current measured values ​​with a threshold value, e.g., a threshold voltage drop across the measuring resistor 210. For example, the active insulation measurement circuit 200 can take repeated values ​​measured across the measuring resistor 210 over time for comparison by the active insulation measurement circuit 200 and / or the processing circuit 222 with a threshold value. In other examples, the active insulation measurement circuit 200 can be configured to determine an insulation resistance and / or to determine whether an insulation-to-ground fault exists by comparing measured values ​​over time, e.g., with previous measured values.For example, the active insulation measurement circuit 200 can take repeated values ​​measured across the measuring resistor 210 over time. The active insulation measurement system 200 or the processing circuit 222 can then determine a trend that can indicate whether and / or when the insulation resistance of one or both insulation resistors 202, 204 is or will be less than a threshold insulation resistance, or whether a measured value deviates by a threshold amount relative to repeated value measurements, e.g., one or more previously measured values.

[0030] In some examples, the active insulation measurement circuit 200 can include a capacitance measurement circuit configured to measure or make measurable a capacitance between the chassis ground and the positive HV bus 212, or between the chassis ground 120 and the negative HV bus 214 (e.g., Y capacitances), or between the positive HV bus 212 and the negative HV bus 214 (e.g., an X capacitance). For example, the active insulation measurement circuit 200 can include an RC circuit (in Fig. (2 not shown) which is connected across the measuring resistor 210, e.g., to terminals 210A and 210B. A pulse from the pulse generator 220 can be measured across the measuring resistor 210 by the measuring circuit 218 with a modified pulse shape, e.g., with a rise time and a fall time related to the charging of the capacitor of the RC circuit. In some examples, the RC circuit can have known resistance and capacitance values, and the rise time and / or fall time of the measured value, e.g.,The voltage signal resulting from a pulse from the pulse generator 220 can vary depending on the capacitance between the positive HV bus 212 and chassis ground 120 when switch 204 is open and switch 202 is closed, or the capacitance between the negative HV bus 214 and chassis ground 120 when switch 202 is open and switch 204 is closed, or the capacitance between the positive HV bus 212 and the negative HV bus 214 when both switches 202 and 204 are closed. In other examples, the active insulation measurement circuit 200 may not include separate components forming an RC circuit, and the active insulation measurement circuit 200 may include an intrinsic RC circuit via its resistance and the capacitance between the positive / negative buses 212, 214 and chassis ground, or between each other, e.g.The measured rise time and / or fall time of the measured value can indicate a capacitance between the positive HV bus 212 and chassis ground 120 when switch 204 is open and switch 202 is closed, or a capacitance between the negative HV bus 214 and chassis ground 120 when switch 202 is open and switch 204 is closed, or a capacitance between the positive HV bus 212 and the negative HV bus 214 when both switches 202 and 204 are closed (e.g., specify directly).

[0031] Fig. Figure 3 is a schematic circuit diagram illustrating an exemplary active insulation measurement circuit 300. In the example shown, the active insulation measurement circuit 300 comprises switches 306, 308, voltage drivers 330, 332, a measuring resistor 310, a pulse generator 320, and an RC circuit 318. In the example shown, the active insulation measurement circuit 300 is connected both between the insulation resistor 202 and chassis ground 120, and between the insulation resistor 204 and chassis ground 120 and terminals 210A and 210B, which can be nodes at which the measuring circuit 218 ( Fig. 2) can be connected to measure a voltage or voltage signal across the measuring resistor 210, e.g. connected to terminals 210A, 210B.

[0032] Switches 306 and 308 can be essentially similar to switches 206 and 208 described above, and voltage drivers 330 and 332 can form part of the control circuit 230 ( Fig. 2) represent a circuit configured to control the opening and closing of switches 306 and 308, e.g., a voltage applied to the gates of switches 306 and 308. The pulse generator 320 may be substantially similar to the pulse generator 220 and may include a voltage driver 334 and a resistor 336. The voltage driver 334 and the resistor 336 may form part of the pulse generator 320 configured to provide a pulse to terminal 210B.

[0033] In the example shown, the pulse generator 320 is configured to provide a pulse to a high-voltage network on the positive and negative buses 212 and 214. Switches 306 and 308 can be triggered such that both switches 306 and 308 connect the measuring resistor 210 and the chassis ground 120 to buses 212 and 214 via the insulation resistors 202 and 204, respectively. Alternatively, only a single switch 306 or 308 can connect the measuring resistor 210 and the chassis ground 120 to bus 212 or 214 via the insulation resistor 202 or 204, respectively. For a simultaneous drop in the insulation resistance of both insulation resistors 202 or 204, only one of switches 306 or 308 can be closed / connected. When a pulse is triggered / generated by the voltage driver 334 of the pulse generator 320, the response of the system can be measured at the measuring resistor 210 at the terminals / nodes 210A, 210B.

[0034] The differential voltage at terminals 210A, 210B (e.g., the voltage drop across measuring resistor 210) of the active insulation measuring circuit 200 or the active insulation measuring circuit 300 can be negative. The processing circuit, e.g., the processing circuit 222 ( Fig. 2), can be configured to receive positive voltages, and the measuring circuit 218 can include a differential amplifier ( Fig. 5), which is configured to convert a measured negative voltage into a positive voltage. Additionally, the measuring circuit 218 can be configured to filter (e.g., to low-pass filters) and provide a single measured value and / or a single measured value signal to the processing circuit 222, which can be configured to store the conditioned, measured value and / or signal, e.g., within memory. Subsequent measurements can then be compared with stored measurements, and the processing circuit 222 can initiate a system response (e.g., removing a high voltage from the positive and negative buses 212, 214 and issuing instructions to a user interface) based on deviations of a current measurement from the stored measurements that are not within an expected tolerance (e.g., within an expected range of values ​​or above or below a threshold).In some examples, the processing circuit 222 can determine an insulation resistance value based on the gain of the differential amplifier.

[0035] Fig. Figures 4-6 are schematic diagrams illustrating circuits that can be used to condition a signal passed through the active isolation measurement circuit 300 (e.g., circuits that include the measurement circuit 218 ( Fig. 2) may include) or is measured by the active insulation measuring circuit 300. Fig. Figure 4 is a schematic diagram illustrating an exemplary voltage follower circuit 400. Fig. Figure 5 is a schematic diagram illustrating an exemplary differential amplifier circuit 500, and Fig. Figure 6 is a schematic diagram illustrating an exemplary single output circuit 600.

[0036] Referring to Fig. The voltage follower circuit 400 comprises a first voltage follower 402, configured to be connected to terminal 210A (e.g., the high-voltage side of the measuring resistor 210), and a second voltage follower 404, configured to be connected to terminal 210B (e.g., the low-voltage side of the measuring resistor 210). The voltage follower circuit 400 can be configured to function as a buffer for the measured values ​​and to provide a high impedance for supplying the measured values ​​and / or the signal (e.g., the voltages and / or the voltage signal) to the processing circuit 222 with a relatively low impedance, e.g., via the differential amplifier circuit 500 and the single output circuit 600.In the example shown, the first voltage follower 402 can be configured to output a positive measured voltage at terminal 410A, and the second voltage follower 404 can be configured to output an inverted measured voltage at terminal 410B.

[0037] Referring to Fig. Figure 5 includes the exemplary differential amplifier circuit 500 comprising a first operational amplifier 522 and a second operational amplifier 524. In the example shown, the non-inverting input of operational amplifier 522 is configured to be connected to terminal 410A (e.g., to obtain the positive measured voltage), and the inverting input of operational amplifier 522 is configured to be connected to terminal 410B (e.g., to obtain the inverted measured voltage). Additionally, the non-inverting input of operational amplifier 524 is configured to be connected to terminal 410B (e.g., to obtain the inverted measured voltage), and the inverting input of operational amplifier 524 is configured to be connected to terminal 410A (e.g., to obtain the positive measured voltage).In the example shown, the operational amplifier 522 can be configured to output a positive differential voltage at terminal 510A, e.g., the voltage drop across the measuring resistor 210 as a positive, non-inverted value, and the operational amplifier 524 can be configured to output an inverted differential voltage at terminal 510B, e.g., the voltage drop across the measuring resistor 210 also as a positive value, since the circuit inverts the inverted (e.g., negative) measured voltage.In some examples, the differential amplifier circuit 500 is configured to output a positive differential voltage at terminal 510A, indicating an insulation resistance and / or capacitance between the positive bus 212 and chassis ground 120 and / or a capacitance between the positive bus 212 and the negative bus 214. The differential amplifier circuit 500 is also configured to output an inverted differential voltage at terminal 510B (which can now be a positive value), indicating an insulation resistance and / or capacitance between the negative bus 212 and chassis ground 120 and / or a capacitance between the positive bus 212 and the negative bus 214. For example, the positive differential voltage can indicate the resistance and / or integrity of the insulation resistor 202, and the inverted differential voltage can indicate the resistance and / or integrity of the insulation resistor 204.

[0038] Referring to Fig. The single output circuit 600 comprises a first diode 602 configured to be connected to terminal 510A (e.g., to receive a positive differential voltage as an input) and a second diode 604 configured to be connected to terminal 510B (e.g., to receive an inverted differential voltage as an input). The outputs of diodes 602 and 604 can be connected together, and diodes 602 and 604 are configured to output a positive differential voltage and / or an inverted differential voltage to terminal 610, e.g., the terminal to which the processing circuit 222 can be connected. Whether a positive differential voltage and / or an inverted differential voltage is output to terminal 610 can be determined from the time of opening and closing of switches 206 and 208 ( Fig. 2) or switch 306, 308 ( Fig. 3) depend. The individual output circuit 600 can be configured to low-pass filter a positive differential voltage and / or an inverted differential voltage, and can also be configured to convert a positive differential voltage and / or an inverted differential voltage into a digital signal, e.g. the individual output circuit 600 can also be configured to function as an analog-to-digital converter.

[0039] Fig. Figure 7 is a flowchart illustrating an exemplary procedure for measuring insulation resistance. Although the exemplary procedure of Fig. 7 in relation to the active insulation measuring circuits 200 and 300 of Fig. 1- Fig. 3 and the signal conditioning circuits 400, 500 and 600 of Fig. 4- Fig. As described in section 6, the exemplary technique of Fig. 7. performed using any device comprising a pulse generator, switch and measuring resistor. Fig. 7 is referred to Fig. 8 described. Fig. Figure 8 comprises a variety of diagrams 802-808 of exemplary measured voltage signals as a function of time for a variety of insulation resistance-202 resistance values, as obtained by the exemplary active insulation measurement circuit of Fig. 2 or Fig. 3 can be measured.

[0040] The processing circuit 222 or the control circuit 230 can control the switch 202 to connect the positive bus 212 of the HV power distribution system 100 to a first terminal 210A of the measuring resistor 210 (702). In some examples, the processing circuit 222 or the control circuit 230 can simultaneously control the switch 204 to disconnect the negative bus 212 from the first terminal 210A of the measuring resistor 210.

[0041] In the Fig. In example 8, the processing circuit 222 or the control circuit 230 controls the switch 202 to close (e.g., connect) at time Son during step (702) and to open (e.g., disconnect) at time Soff. Fig. In Figure 8, each of the diagrams 802-808 is a diagram of one or more measured values, e.g., voltage signals, measured across the measuring resistor 210 for a variety of possible resistances of the insulation resistance 202. In the example shown, the HV power distribution system 100 can be an 800 V HV power distribution system 100. Diagram 802 is the measured voltage signal for a 5-megaohm insulation resistance 202, which can be a fault-free, e.g., fail-safe, resistor.For example, for the 800 V HV power distribution system 100, the insulation resistance should be at least 80 kilohms to meet an insulation resistance threshold of 100 ohms / V, or at least 400 kilohms to meet an insulation resistance threshold of 500 ohms / V. Graph 804 is the measured voltage signal for a 500 kilohm insulation resistance 202, graph 806 is the measured voltage signal for a 100 kilohm insulation resistance 202, and graph 808 is the measured voltage signal for a 1 ohm insulation resistance 202. Each of graphs 804-808 can represent an inadequate or fail-safe insulation resistance 202.

[0042] The pulse generator 220 can apply a pulse between chassis ground 120 and a second terminal 210B of the measuring resistor 210 (704). For example, the control circuit 230, simultaneously with the closing of switch 202 and the opening of switch 204, can cause the pulse generator 230 to output one or more pulses and / or a pulse signal. In the Fig. In the example shown, pulse generator 220 applies pulses 850, 852, and 854 at times T2, T3, and T5, respectively, with pulse widths of T2-T1, T4-T3, and T6-T5. In the example shown, pulses 850, 852, and 854 have the same pulse amplitudes (which, however, cannot be on the same scale as the diagram scale shown and are merely illustrative), but in other examples, pulses 850, 852, and 854 may have different amplitudes.

[0043] The measuring circuit 218 can measure a value across the measuring resistor 210 (706). For example, a voltmeter of the measuring circuit 218 can measure a voltage across the measuring resistor 210 at a single point in time during a pulse from the pulse generator 230, or it can measure a variety of voltages as a function of time, e.g., a voltage signal. The value(s) measured across the measuring resistor 210 can include a specification of an insulation resistance between chassis ground 120 and the positive bus 212 when the switch 202 is conducting (e.g., closed) and the pulse generator 230 is emitting the pulse. In the Fig. In the example shown, the measuring circuit 218 can measure voltage signals corresponding to diagrams 802-808, each of which can indicate an insulation resistance, e.g., via the voltage level of the respective signals / diagrams. For example, diagram 802 exhibits a very low voltage, corresponding, for example, to the relatively low voltages of pulses 850, 852, and 854. In contrast, diagrams 804-808 exhibit higher voltages, corresponding, for example, to the relatively low voltages of 850, 852, and 854 plus the additional DC voltage from the positive bus 212 due to the insufficient insulation resistance of the insulation resistor 202 for these respective diagrams.

[0044] In some examples, the processing circuit 222 or the control circuit 230 can control the switch 202 to disconnect the positive bus 212 of the HV power distribution system 100 from the first terminal 210A of the sense resistor 210, and can control the switch 204 to connect the negative bus 214 of the HV power distribution system 100 to the first terminal 210A of the sense resistor 210. The pulse generator 220 can apply a pulse between the chassis ground 120 and the second terminal 210B of the sense resistor 210, e.g., simultaneously with the opening of the switch 202 and the closing of the switch 204, causing the pulse generator 230 to output one or more pulses and / or a pulse signal. The measuring circuit 218 can measure a second value across the sense resistor 210, e.g.,A voltmeter of the measuring circuit 218 can measure a voltage across the measuring resistor 210 at a single point in time during the pulse from the pulse generator 230, or can measure a variety of voltages as a function of time, e.g. a voltage signal, and the value(s) can include a specification of an insulation resistance between the chassis ground 120 and the negative bus 214 when the switch 204 is conducting (e.g. closed) and the pulse generator 230 is emitting the pulse.

[0045] In some examples, the processing circuit 222 or the measuring circuit 218 can determine whether an isolation-to-ground failure is present, based on performing repeated value measurements across the measuring resistor 210 and determining whether a previously measured value or signal deviates from the repeated value or signal measurements by a threshold amount. In the Fig. In the example shown, the processing circuit 222 or the measuring circuit 218 can determine whether an insulation-to-ground fault exists based on whether the measured voltage signals 802-808 are less than or equal to the threshold voltage value 810. In other examples, graphs similar to graphs 802-808 may not be at a constant value over time; for example, a graph may "float up" or increase in voltage, such as when the insulation resistance 202 begins to degrade. Instead of a global voltage threshold, the processing circuit 222 or the measuring circuit 218 can determine whether an insulation-to-ground fault exists based on a subsequent voltage measurement or signal that differs from a previous voltage measurement or signal by a threshold amount.

[0046] In some examples, the measuring circuit 218 can receive the insulation resistance value (e.g., the voltage and / or voltage signal) and condition the signal for use by other circuits, e.g., the processing circuit 222. For example, the measuring circuit can buffer, differentially amplify, digitize, and / or output the signal to the processing circuit 222 via a single output terminal.

[0047] In some examples, the measuring circuit 218 and / or the processing circuit 222 can determine a capacitance between the positive bus 212 and chassis ground 120 (e.g., a first Y capacitance), a capacitance between the negative bus 214 and chassis ground 120 (e.g., a second Y capacitance), or a capacitance between the positive bus 212 and the negative bus 214 (e.g., an X capacitance) based on the measured value(s) and / or the signal. In some examples, the measuring circuit 218 and / or the processing circuit 222 can determine a capacitance based on the rise time and / or fall time of the value (e.g., the voltage) across the measuring resistor 210.

[0048] In the Fig.In the example shown, a Y-capacitor between the positive bus 212 and chassis ground 120 and the resistors of the active insulation measurement circuit 200 or 300 can function as an RC circuit that modifies the shape of the measured voltage signals relative to the shape of the pulses (e.g., low-pass filtering). In the example shown, pulses 850, 852, and 854 are essentially square-wave pulses, and graphs 802–806 of the measured signals are essentially sawtooth-shaped measured responses of the active insulation measurement circuit 200 or 300 to the input square-wave pulses (however, graph 808 of the measured signal for the 1-ohm insulation resistance is dominated by the high-voltage DC from the positive bus 212). For example, each of the measured impulse responses 820, 822 and 824 of diagram 802 exhibits rise times between T1 and T2, T3 and T4 or T5 and T6 respectively, and fall times between T2 and T3, T4 and T5 or T6 and T7 respectively.The rise and fall times of the measured impulse responses 820, 822, and 824 (e.g., due to charging and discharging of the Y-capacitance) are characteristic of the RC circuit of the measuring system and indicate the Y-capacitance between the positive bus 212 and chassis ground 120. Similarly, the active insulation measurement circuit 200 or 300 can measure voltage signals similar to diagrams 802-808, with switch 202 open and switch 204 closed to measure values ​​indicating the resistance of the insulation resistor 204 and the Y-capacitance between the negative bus 214 and chassis ground 120, and with both switches 202 and 204 closed to measure values ​​indicating an X-capacitance between the positive bus 212 and the negative bus 214.

[0049] The techniques described in this disclosure may be implemented, at least partially, in hardware, software, firmware, or any combination thereof. For example, various aspects of the described techniques may be implemented within one or more processors or processing circuitry comprising one or more microcontrollers (e.g., the Microcontrollers 102, 502, and / or 602), microprocessors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or any other equivalent integrated or discrete logic circuitry, as well as any combination of such components. The terms "processor" or "processing circuitry" may generally refer to any of the foregoing logic circuitry alone or in combination with other logic circuitry or any other equivalent circuitry.A control unit comprising hardware may also perform one or more of the techniques of this disclosure.

[0050] Such hardware, software, and firmware may be implemented within the same device or within separate devices to support the various operations and functions described in this disclosure. Additionally, any of the described units, circuits, or components may be implemented together or separately as discrete but interoperable logic devices. The representation of various features as circuits or units is intended to highlight different functional aspects and does not necessarily imply that such circuits or units must be implemented by separate hardware or software components. Rather, the functionality associated with one or more circuits or units may be performed by separate hardware or software components or integrated into common or separate hardware or software components.

[0051] The techniques described in this disclosure may also be embodied or encoded in a computer-readable medium, such as a computer-readable storage medium containing instructions that can be described as non-transitory media. Instructions embedded or encoded in a computer-readable storage medium may cause a programmable processor or other processor to perform the procedure, for example, when the instructions are executed. Computer-readable storage media may include random-access memory (RAM), read-only memory (ROM), programmable read-only memory (PROM), erasable programmable read-only memory (EPROM), electronically erasable programmable read-only memory (EEPROM), flash memory, a hard disk, a CD-ROM, a floppy disk, a cassette, magnetic media, optical media, or other computer-readable media.

[0052] Various aspects of the techniques can be enabled by the following examples.

[0053] Example 1: An insulation measurement circuit comprises: a first switch connecting a first insulation resistor to a terminal of a measuring resistor, the first insulation resistor also being connected to a positive bus of a power distribution system; a second switch connecting a second insulation resistor to the terminal of the measuring resistor, the second insulation resistor also being connected to a negative bus of the power distribution system; and a pulse generator connecting the measuring resistor to chassis ground.

[0054] Example 2: Insulation measurement circuit according to Example 1, wherein the insulation measurement circuit is configured to determine a first value and a second value: wherein the first value is measured across the measuring resistor and includes a specification of the insulation resistance between the chassis ground and the positive bus when the first switch is conducting and the pulse generator outputs a pulse, wherein the second value is measured across the measuring resistor and includes a specification of the insulation resistance between the chassis ground and the negative bus when the second switch is conducting and the pulse generator outputs a pulse.

[0055] Example 3: Insulation measuring circuit according to Example 2, wherein the insulation measuring circuit is configured to determine whether an insulation ground fault is present by: taking repeated values ​​measured across the measuring resistor over time; and determining whether a measured value deviates from the repeated value measurements by a threshold amount.

[0056] Example 4: Insulation measurement circuit according to Example 2 or 3, which further comprises a signal conditioning circuit, wherein the signal conditioning circuit is configured to obtain the indication of the insulation resistance and to condition the signal for use by other circuits.

[0057] Example 5: Insulation measurement circuit according to Example 4, wherein the signal conditioning circuit includes a differential amplifier.

[0058] Example 6: Insulation measurement circuit according to one of Examples 1-5, which further comprises a capacitance measurement circuit designed to measure a capacitance between the chassis ground and the positive bus and / or the negative bus.

[0059] Example 7: Insulation measurement circuit according to one of Examples 1-6, which further comprises a capacitance measurement circuit designed to measure a capacitance between the positive bus and the negative bus.

[0060] Example 8: A power distribution system comprises: a power supply configured to supply power to a load, wherein the power supply and the load are isolated from a chassis ground for the power distribution system; an insulation measurement circuit comprises: a first switch connecting a first insulation resistor to a first terminal of a measuring resistor, wherein the first insulation resistor is also connected to a positive bus of a power distribution system; a second switch connecting a second insulation resistor to a second terminal of the measuring resistor, wherein the second insulation resistor is also connected to a negative bus of the power distribution system; and a pulse generator connecting the measuring resistor to the chassis ground.

[0061] Example 9: Power distribution system according to Example 8, wherein the insulation measurement circuit is configured to determine a first value and a second value: wherein the first value is measured across the measuring resistor and includes a specification of an insulation resistance between the chassis ground and the positive bus when the first switch is conducting and the pulse generator emits a pulse, wherein the second value is measured across the measuring resistor and includes a specification of the insulation resistance between the chassis ground and the negative bus when the second switch is conducting and the pulse generator emits a pulse.

[0062] Example 10: Power distribution system according to Example 8 or 9, wherein the insulation measurement circuit is configured to determine whether an insulation ground fault is present by: repeated values ​​measured across the measuring resistor over time; determining whether a measured value deviates from the repeated value measurements by a threshold amount.

[0063] Example 11: Power distribution system according to one of Examples 8-10, further comprising a signal conditioning circuit, wherein the signal conditioning circuit is configured to obtain the insulation resistance specification and to condition the signal for use by downstream circuits.

[0064] Example 12: Power distribution system according to Example 10 or 11, wherein the signal conditioning circuit includes a differential amplifier.

[0065] Example 13: Power distribution system according to one of Examples 8-10, which further includes a capacitance measurement circuit designed to measure a capacitance between the chassis ground and the positive bus.

[0066] Example 14: A method comprises: controlling a switch to connect a bus of a power distribution system to a first terminal of a sense resistor, wherein the bus is connected to the first terminal of the sense resistor via an insulation resistor; applying a pulse between a chassis ground and a second terminal of the sense resistor by a pulse generator of an insulation measurement circuit; measuring a value across the sense resistor, wherein the value measured across the sense resistor includes a specification of an insulation resistance between a chassis ground and the bus when the switch is conducting and the pulse generator is emitting the pulse.

[0067] Example 15: Method according to Example 14, wherein the switch is a first switch, the bus is a first bus, and the insulation resistance is a first insulation resistance, wherein the value is a first value, the method further comprising: controlling the first switch to disconnect the first bus from the first terminal of the sense resistor; controlling a second switch to connect a second bus of the power distribution system to the first terminal of the sense resistor, the second bus being connected to the first terminal of the sense resistor via a second insulation resistor; applying a pulse between the chassis ground and the second terminal of the sense resistor by the pulse generator of the insulation measurement circuit;and measuring a second value across the measuring resistor, wherein the second value measured across the measuring resistor is an indication of the insulation resistance between chassis ground and the second bus when the second switch is conducting and the pulse generator is emitting the pulse.

[0068] Example 16: Method according to Example 15, wherein the first switch is conductive when the second switch is not conductive.

[0069] Example 17: Procedure according to Example 16, further comprising: performing repeated measurements across the measuring resistor; and determining whether a measured value deviates from the repeated measurements by a threshold amount.

[0070] Example 18: Method according to Example 16 or 17, further comprising: obtaining the indication of the insulation resistance by a signal conditioning circuit; and conditioning the signal for use by other circuits.

[0071] Example 19: Method according to Example 18, wherein the signal conditioning circuit includes a differential amplifier.

[0072] Example 20: Method according to one of Examples 14-18, further comprising: measuring a rise time of the value across the measuring resistor, wherein the rise time is a specification of a capacitance between the chassis mass and the bus.

[0073] Example 21: Method according to any of Examples 15-20, further comprising: controlling the first switch to connect the first bus to the first terminal of the measuring resistor; applying a pulse between the chassis ground and the second terminal of the measuring resistor by the pulse generator of the insulation measurement circuit; and measuring a rise time of a third value across the measuring resistor, wherein the rise time of the third value measured across the measuring resistor is an indication of a capacitance between the first bus and the second bus.

[0074] Several examples have been described. These and other examples fall within the scope of protection of the following claims.

Claims

[1] Insulation measuring circuit (200) comprising: a first switch (206) which connects a first insulation resistor (202) to a terminal of a measuring resistor (210), wherein the first insulation resistor (202) is also connected to a positive bus (212) of a power distribution system; a second switch (208) which connects a second insulation resistor (204) to the terminal of the measuring resistor (210), the second insulation resistor (204) also being connected to a negative bus (214) of the power distribution system; and a pulse generator (220; 320) which connects the measuring resistor (210) to chassis ground (120). [2] Insulation measuring circuit (200) according to claim 1, wherein the insulation measuring circuit (200) is configured to determine a first value and a second value: wherein the first value is measured across the measuring resistor (210) and includes a specification of the insulation resistance between chassis ground (120) and the positive bus (212) when the first switch (206) is conducting and the pulse generator (220; 320) emits a pulse, wherein the second value is measured across the measuring resistor (210) and includes a specification of the insulation resistance between chassis ground (120) and the negative bus (214) when the second switch (208) is conducting and the pulse generator (220; 320) emits a pulse. [3] Insulation measuring circuit (200) according to claim 1 or 2, wherein the insulation measuring circuit (200) is configured to determine whether an insulation ground fault is present, by: Taking repeated values ​​measured across the measuring resistor (210) over time; and Determine whether a measured value deviates from repeated measurements by a threshold amount. [4] Insulation measuring circuit (200) according to claim 2 or 3, which further comprises a signal conditioning circuit, wherein the signal conditioning circuit is configured to obtain the indication of the insulation resistance and to condition the signal for use by other circuits. [5] Insulation measuring circuit (200) according to claim 4, wherein the signal conditioning circuit comprises a differential amplifier. [6] Insulation measuring circuit (200) according to one of claims 1 to 5, which further comprises a capacitance measuring circuit configured to measure a capacitance between the chassis ground (120) and the positive bus (212) and / or the negative bus (214). [7] Insulation measuring circuit (200) according to one of claims 1 to 6, which further comprises a capacitance measuring circuit configured to measure a capacitance between the positive bus (212) and the negative bus (214). [8] A power distribution system that features: a power supply designed to supply power to a load, wherein the power supply and the load are isolated from a chassis mass (120) for the power distribution system; an insulation measuring circuit (200) which features: a first switch (206) which connects a first insulation resistor (202) to a first terminal (210A) of a measuring resistor (210), wherein the first insulation resistor (202) is also connected to a positive bus (212) of a power distribution system; a second switch (208) which connects a second insulation resistor (204) to a second terminal (210B) of the measuring resistor (210), wherein the second insulation resistor (204) is also connected to a negative bus (214) of the power distribution system; and a pulse generator (220; 320) which connects the measuring resistor (210) to the chassis ground (120). [9] Power distribution system according to claim 8, wherein the insulation measuring circuit (200) is configured to determine a first value and a second value: wherein the first value is measured across the measuring resistor (210) and includes a specification of an insulation resistance between chassis ground (120) and the positive bus (212) when the first switch (206) is conducting and the pulse generator (220; 320) emits a pulse, wherein the second value is measured across the measuring resistor (210) and includes a specification of the insulation resistance between chassis ground (120) and the negative bus (214) when the second switch (208) is conducting and the pulse generator (220; 320) emits a pulse. [10] Power distribution system according to claim 8 or 9, wherein the insulation measuring circuit (200) is configured to determine whether an insulation ground fault is present, by: repeated values ​​measured across the measuring resistor (210) over time; Determine whether a measured value deviates from repeated measurements by a threshold amount. [11] Power distribution system according to one of claims 9 to 10, further comprising a signal conditioning circuit, wherein the signal conditioning circuit is configured to obtain the insulation resistance value and to condition the signal for use by downstream circuits. [12] Power distribution system according to claim 11, wherein the signal conditioning circuit comprises a differential amplifier. [13] Power distribution system according to one of claims 8 to 12, which further comprises a capacitance measurement circuit configured to measure a capacitance between the chassis ground (120) and the positive bus (212). [14] Method which features: Controlling a switch (206) to connect a bus of a power distribution system to a first terminal (210A) of a measuring resistor (210), wherein the bus is connected to the first terminal (210A) of the measuring resistor (210) via an insulation resistor; Applying a pulse between a chassis ground (120) and a second terminal (210B) of the measuring resistor (210) by a pulse generator (220; 320) of an insulation measuring circuit (200), Measuring a value across the measuring resistor (210), wherein the value measured across the measuring resistor (210) includes a specification of an insulation resistance between a chassis ground (120) and the bus when the switch is conducting and the pulse generator (220; 320) is emitting the pulse. [15] Method according to claim 14, wherein the switch is a first switch (206), the bus is a first bus and the insulation resistance is a first insulation resistance (202), wherein the value is a first value, wherein the method further comprises: Controlling the first switch (206) to disconnect the first bus from the first terminal (210A) of the measuring resistor (210); Controlling a second switch (208) to connect a second bus of the power distribution system to the first terminal (210A) of the measuring resistor (210), wherein the second bus is connected to the first terminal (210A) of the measuring resistor (210) via a second insulation resistor (204); Applying a pulse between the chassis ground (120) and the second terminal (210B) of the measuring resistor (210) by the pulse generator (220; 320) of the insulation measuring circuit (200); and Measuring a second value across the measuring resistor (210), where the second value measured across the measuring resistor (210) is an indication of the insulation resistance between chassis ground (120) and the second bus when the second switch (208) is conducting and the pulse generator (220; 320) is emitting the pulse. [16] Method according to claim 15, wherein the first switch (206) is conductive when the second switch (208) is non-conductive. [17] Method according to claim 15 or 16, further comprising determining whether an insulation mass fault exists, based on: Performing repeated measurements across the measuring resistor (210); and Determine whether a measured value deviates from repeated measurements by a threshold amount. [18] Method according to any one of claims 15 to 17, further comprising: Obtaining the insulation resistance value through a signal conditioning circuit; and Conditioning the signal for use by other circuits. [19] Method according to claim 18, wherein the signal conditioning circuit comprises a differential amplifier. [20] Method according to any one of claims 14 to 19, further comprising: Measuring the rise time of the value across the measuring resistor (210), where the rise time is a specification of a capacitance between the chassis mass (120) and the bus. [21] The method of claim 15, further comprising: Controlling the first switch (206) to connect the first bus to the first terminal (210A) of the measuring resistor (210); Applying a pulse between the chassis ground (120) and the second terminal (210B) of the measuring resistor (210) by the pulse generator (220; 320) of the insulation measuring circuit (200); and Measuring the rise time of a third value across the measuring resistance (210), where the rise time of the third value, measured across the measuring resistor (210), is an indication of a capacitance between the first bus and the second bus.

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