EP3942310A1

EP3942310A1 - Arc fault detection in a motor control unit of a vehicle and a method of operation thereof

Info

Publication number: EP3942310A1
Application number: EP20718397.1A
Authority: EP
Inventors: Surajit Das; Junia Sosa GEORGE; Banda Jambunath RAJENDRANATH
Original assignee: TVS Motor Co Ltd
Current assignee: TVS Motor Co Ltd
Priority date: 2019-03-21
Filing date: 2020-03-08
Publication date: 2022-01-26
Also published as: WO2020188592A1; CN113574400A

Abstract

The present subject matter described herein relates to a motor control unit (200) configured for arc fault detection in a vehicle. The motor control unit (200) as described herein is provided with a plurality of power terminals (201,202,203,204,205) for connection to a battery and a motor. Particularly, each power terminal of said plurality of power terminals (201,202,203,204,205) is provided with an arc fault detection element (210) each for detecting arc faults generated therein. More particularly, said arc fault detection elements provided are thermistors disposed within the motor control unit at said power terminals. The motor control unit (200) thus provided with said thermistors is configured to disable the vehicle based on detection of arc fault in said power terminals (201,202,203,204,205) by said thermistors. By providing said arc fault detection elements (210) within the motor control unit, compactness of the motor control unit and that of the vehicle is ensured.

Description

ARC FAULT DETECTION IN A MOTOR CONTROL UNIT OF A

VEHICLE AND A METHOD OF OPERATION THEREOF

TECHNICAL FIELD

[0001 ] The present subject matter described herein generally relates to arc fault detection in a vehicle.

BACKGROUND

[0002] In recent times there is an increased demand to enhance powertrain efficiency and to control emissions from automobiles. As a result, a number of hybrid and electric vehicles are seeing the light of the day in order to minimize the amount of emissions.

[0003] Typically, hybrid and electric vehicles make use of 400-500V battery packs and high voltage direct current throughout the vehicle. High voltage electric networks within the vehicles very often become susceptible to a phenomenon called arc fault which occurs when there is high power discharge of electricity between two or more conductors or between phase conductors and ground. The discharge often translates into heat which has the potential to damage the insulation of wires carrying high power current and trigger electrical fire which can be devastating. The arc faults can range in power from few amperes to up to few thousands of amperes and can be variable in terms of duration and strength. Development of such arc faults if left unchecked can lead to a potential fire / undesirable safety risk to the user of the vehicle. Common causes of arc faults include faulty connections due to faulty initial installation or due to corrosion. The resulting current sometimes may be lower than the trip current of the protection devices. In these cases, either the fault is temporarily cleared or not cleared at all. BRIEF DESCRIPTION OF DRAWINGS

[0004] The detailed description of the present subject matter is described with reference to an embodiment for a two-wheeled saddle-type vehicle with the accompanying figures. Same numbers are used throughout the drawings to reference like features and components.

[0005] Fig.l illustrates a saddle-type vehicle provided with a motor control unit configured for arc fault detection in accordance with an embodiment of the present invention.

[0006] Fig.2 illustrates a schematic representation of the motor control unit operatively connected to different electrical components of said vehicle in accordance with an embodiment of the present invention.

[0007] Fig.3 illustrates a front perspective view of the motor control unit configured for arc fault detection as per an embodiment of the present invention.

[0008] Fig.4 illustrates a flow chart depicting steps of a method of operation of the motor control unit configured for arc fault detection in accordance with an embodiment of the present invention.

DETAILED DESCRIPTION

[0009] Exemplary embodiments detailing features of the motor control unit configured for arc fault detection in accordance with the present invention will be described hereunder. The embodiments described herein apply to a vehicle having a battery pack and powered by either a motor alone or by both internal combustion engine, and the motor. Also, although the embodiments have been exemplified for a two-wheeled saddle-type vehicle, the present invention is applicable for all types of vehicles having a battery pack and powered by either a motor alone or by both the internal combustion engine, and the motor. The battery pack may be composed of lead acid cells or Li ion cells or fuel cells and the like.

[0010] A known art provides an arc fault detection apparatus for an electric vehicle which includes a current transformer, a signal conversion circuit, an amplifying and a filtering circuit, a digital signal processor, a CAN communication transceiver and a serial port transceiver. The arc fault detection apparatus thus described is used for arc fault detection on a DC high voltage bus, and works by quickly detecting the occurrence and communicating the same to a remote controller, which finally operates to clear the arc fault. Thus, although several components are used in the arc fault detection apparatus, the components do not directly contribute to clearing the arc fault and the same is achieved by a remote controller. The cost entailed in such an arc fault detection apparatus is significantly high which is undesirable.

[0011] Another art describes an art fault detection equipment including an arc fault detection circuit comprising a current sensing circuit coupled to a line conductor carrying a current. The current sensing circuit operates to sense current and output data indicative of the sensed current. The equipment also includes a processing circuit which identifies an arc fault condition on the line conductor by identifying differences in said frequency data between at least two subsequent observation windows. Thus the art fault detection equipment as described above includes a complex and elaborate circuitry for detection of arc fault which is not economical.

[0012] Besides including several components, the arc fault detection equipments described in the background arts include a large sized controller for processing arc fault data and clearing arc fault. The size of the controller becomes a constraint especially in relatively small sized two-wheeled or three-wheeled saddle type electric vehicles, in which arc fault detection is to be performed.

[0013] There is therefore a need for a compact, and low cost and efficient arc fault detection apparatus/assembly with a compact size of the controller of the electric/hybrid vehicle. [0014] The present subject matter has been made in view of the above circumstances.

[0015] It is an object of the present subject matter to provide a vehicle having a motor control unit configured for arc fault detection, said motor control unit being compact in size.

[0016] It is another object of the present subject matter to provide a method of arc fault detection in a motor control unit, said method being simple, convenient to use and which is economical.

[0017] It is one more object of the present subject matter to provide a motor control unit configured to not only detect arc faults but also configured to disable a running vehicle in a condition where arc fault is detected.

[0018] With the above and other objects in view the present invention provides a vehicle comprising a motor control unit configured to detect arcing in high current paths connecting different components forming parts of different electric circuits provided in said vehicle. For example, typically high current cables connect a battery and a motor of said vehicle with a motor control unit. The phenomenon of arcing is most common when a loose connection is made while connecting components such as the battery or the motor with a motor control unit. The heat generated due to arcing has the potential to damage the insulation of wires/cables and trigger an electrical fire which can be devastating. All electric and hybrid vehicles employing a motor control unit for the operation of the vehicle are very susceptible to electric fire due to arcing. Different means and techniques are known for arc fault detection in vehicles. However, arc fault detection in two-wheeled and three-wheeled saddle-type electric and hybrid vehicles is significantly challenging due to layout and cost constraints involved in the manufacture of two-wheeled or three-wheeled saddle type electric and hybrid vehicles. Therefore, there is a need to employ a simple and economical means for arc fault detection without involving the use of complex arc fault detection circuits. [0019] The present subject matter seeks to provide a simple and cost effective means of performing arc fault detection by providing an arc fault detection system within a motor control unit of the vehicle. Particularly, as per an aspect of the present subject matter, said arc fault detection system is configured with temperature sensitive elements such as thermistors and a signal conditioning circuit connecting said temperature sensitive elements to a microcontroller of the motor control unit. Particularly, said elements are mounted on a top portion of power terminals of the motor control unit. More particularly, said elements are connected in parallel with one another. Further, the other ends of the power terminals of the motor control unit are connected to respective power terminals of the battery and the motor. For example, while terminals GND, and DC Link are operatively connected to corresponding terminals of the battery, phase terminals R, Y and B are operatively connected to corresponding terminals of the motor.

[0020] In a condition where a loose connection is made at any one of the five above mentioned power terminals, arcing occurs at the corresponding power terminal resulting in increased temperature at said power terminal. As the temperature of the affected power terminal increases, the resistance of the corresponding thermistor decreases. This results in the decrease in the effective resistance of the parallel thermistor circuit. Particularly, once the vehicle starts running, the temperature at the power terminals also increases normally and equivalent resistance starts decreasing correspondingly. Under normal running conditions, this temperature rise has a limit Tiimit and correspondingly the equivalent resistance fall of the thermistors also has an equivalent resistance limit (Reqjimit). If there is any loose contact in any of the power terminals resulting in arcing, the temperature at that point increases rapidly to a very high value. In that situation, the resistance of the corresponding thermistor decreases to a very low value resulting in the equivalent resistance (Req) of thermistors becoming much lower than the equivalent resistance limit (Reqjimit). Further, a voltage corresponding to said (Req) which is lower than a voltage corresponding to said equivalent resistance limit (Reqjimit) is communicated to a microcontroller of said motor control unit.

[0021 ] As per an aspect of the present subject matter, said motor control unit is configured to disable the vehicle based on communication of voltage corresponding to said (Req) which is lower than a voltage corresponding to said equivalent resistance limit (Reqjimit) to the microcontroller. In other words, said motor control unit is configured to disable the vehicle based on detection of arc fault in any one of the power terminals thereof. A first step in the method of operation of said control unit involves detection of vehicle speed (Vrpm), followed by checking if said vehicle speed (Vrpm) is greater than a threshold vehicle speed (Vrpm h). Further, if said vehicle speed (Vrpm) is greater than said threshold speed (Vrpmjh), said control unit checks if equivalent resistance (Req) of the thermistor circuit is lesser than said equivalent resistance limit (Reqjimit) of said circuit which is stored in memory of the microcontroller. If it is found that said equivalent resistance (Req) of the thermistor circuit is lesser than said (Reqjimit) when vehicle speed (Vrpm) is greater than said threshold speed (Vrpmjh), then said control unit disables the vehicle, thereby ensuring that arcing in any one or more of the high current paths does not cause damage either to the vehicle or to the rider of the vehicle.

[0022] Summary provided above explains the basic features of the invention and does not limit the scope of the invention.

[0023] With reference to Fig.l a description is made of a vehicle 100 which is a hybrid two-wheeled saddle-type vehicle in accordance with an embodiment of the present invention. FIG.l is a side view the vehicle 100. The vehicle 100 illustrated, has a step-through type frame assembly. The step-through type frame assembly includes a head tube 101, a main tube 102 and a pair of side tubes 103. Particularly, the main tube 102 extends downwards from a rear portion of the head tube 101 and then extends rearwards in an inclined manner. Further, the pair of side tubes 103 extends inclinedly upwardly from the main tube 102. Thus, the frame assembly extends from a front portion to a rear portion of the vehicle.

[0024] The vehicle 100 further includes a plurality of body panels for covering said frame assembly, and is mounted thereto. In the present embodiment said plurality of panels includes a front panel 104, a leg shield 105, an under-seat cover 106, and a left and a right side panel 107. Further, a glove box may be mounted to said leg shield

105

[0025] In a step through space formed between said leg shield 105 and said under seat cover 106, a floorboard 108 is provided. Further, a seat assembly 110 is disposed above said under-seat cover 106, and is mounted to the pair of side tubes 103. A utility box (not shown) is disposed below the seat assembly 110. A fuel tank (not shown) is positioned at one end of the utility box. A rear fender 111 for covering at least a portion of a rear wheel 112 is positioned below the utility box.

[0026] One or more suspension(s)/shock absorbers 120 are provided in a rear portion of said vehicle 100 for comfortable ride. Further said vehicle 100 comprises of plurality of electrical and electronic components including a headlight 115, a taillight (not shown), a transistor controlled ignition (TCI) unit (not shown), a starter motor (not shown) and the like. A touch screen LCD unit (not shown) is provided on a handle bar 109 to display various operating modes, power flow pattern and warning signals. Rear view mirrors 113 are mounted on the right and left sides of the handle bar 109. Said vehicle 100 is also provided with hazard lamps (not shown). Further said vehicle also includes an arc fault detection indicator (not shown) near the touch screen of the instrument cluster. The indicator glows on detection of any arc fault in the vehicle indicating that the vehicle would be disabled shortly.

[0027] An internal combustion engine 135, hereinafter“engine”, is arranged behind said floorboard 108 and supported between the pair of side tubes 103. Particularly, said internal combustion engine 135 is supported by a swing arm 136. The swing arm 136 is attached to a lower portion of the main tube 102 by means of a toggle link (not shown). The other end of the swing arm 136 holds the rear wheel 112. The rear wheel 112 and the swing arm 136 are connected to the pair of side tubes 103 by means of one or more shock absorbers 120 provided on either side of said vehicle 100.

[0028] Said 100 further includes a traction motor 150 mounted on a hub of the rear wheel 112. Said traction motor 150 is powered by a battery (shown in Fig.2) disposed in a rear portion of the vehicle. However, in another embodiment, the battery may be disposed in a front portion of the vehicle. A motor control unit (MCU) 200 (shown in FIG.2) is also provided to control various vehicle operative modes.

[0029] Said vehicle 100 is configured to be propelled either by the engine 135 alone or by the traction motor 150 alone or by both engine 135 and traction motor 150 simultaneously. At zero vehicle speed, a rider can select any of the following four operating drive modes with the help of a mode switch. The four operating drive modes of said vehicle 100 are: (a) a sole engine mode where engine 135 alone powers the vehicle (b) a sole motor mode where the traction motor 150 alone powers the vehicle (c) a hybrid power mode wherein the engine 135 and the traction motor 150 together power the vehicle 100 (d) a hybrid economy mode wherein only the engine 135 or only the traction motor 150 or both power the vehicle depending on the vehicle operating conditions.

[0030] In other words, the rear wheel 112 of the vehicle is driven by either the engine 135 alone or by the motor 150 alone or by both the engine 135 and the motor 150 simultaneously. Particularly, power from the engine 135 to the rear wheel 112 is transmitted by a transmission assembly including a drive system (not shown) as per an embodiment of the present invention. However, when the traction motor 150 drives, power from the motor 150 is directly transmitted to the rear wheel 112. In the present embodiment, said traction motor 150 is covered by a motor shroud (not shown) from at least one side.

[0031 ] Referring to Fig.2, description is made of a schematic representation of the motor control unit 200 of the vehicle 100 as per an embodiment of the present invention. The motor control unit 200 is configured to be communicatively connected with various components of the vehicle such as a powertrain integrated with hall sensor, an instrument cluster 125, an energy source like battery 160, and to a plurality of vehicle sensors such as throttle position sensor 161, and vehicle switches including ignition switch 151, a brake switch 152, and the like, in order to receive various inputs relating to vehicle operating conditions. In one embodiment the powertrain may be the traction motor 150.

[0032] Further the instrument cluster is configured with an arc detection indicator & a drive mode selection for the user to interact with.

[0033] As per an aspect of the present subject matter, the motor control unit

200 communicates with the above mentioned components, sensors and switches via controller area network (CAN) communication. Some of the above mentioned components such as the battery 160, and the instrument cluster 125 may include their own controllers. For example, the battery 160 may have a battery control module (BCM) (not shown) or a battery management system (BMS) (not shown) that sends and receives signals to and from the battery 160 and the motor control unit 200. In the present embodiment, said instrument cluster 125 includes a digital signal processor (not shown) for communication with the motor control unit 200. Further, the traction motor 150 is integrated with one or more hall sensors for communication with the motor control unit 200. Further, the motor control unit 200 is operatively connected to the battery 160 and the traction motor 150. While the battery 160 powers the motor control unit 50, power delivered to the traction motor 150 from the battery 160 is controlled by the motor control unit 200.

[0034] For example, Fig.3 illustrates the motor control unit 200 as per an embodiment of the present invention. As may be seen, the motor control unit 200 comprises a plurality of power terminals (201,202,203,204,205) for connection with the battery 160 (shown in Fig.2) and the motor 150 (shown in Fig.2). For example, while two extreme terminals GND 201 and DC Link 202 are connected to corresponding power terminals of the battery, three central power terminals R 203, Y 204 and B 205 of the motor control unit 200 are operatively connected to the corresponding power terminals of the motor 150. The above mentioned power terminals form part of the high current path between the motor control unit 200 and the battery 160 and that of the high current path between the motor control unit 200 and the motor 150. Thus, since high current passes through said power terminals (201,202,203,204,205), there are high chances of an arc being generated in the high current paths, which may result in potential fire in the vehicle resulting in safety risk for the user.

[0035] In order to detect arcing in the above mentioned power terminals (201,

202, 203, 204, 205), the motor control unit 200 is configured with an arc fault detection system comprising a plurality of arc fault detecting elements 210 at said power terminals (201, 202, 203, 204, 205) connected in parallel as may be seen in Fig.3. Further, said detection system comprises a corresponding signal conditioning circuit (not shown) connecting said elements 210 to a microcontroller (not shown) of said control unit 200. Particularly, as per an embodiment of the present subject matter said arc fault detecting elements 210 are temperature sensitive elements such as thermistors. More particularly, as per an embodiment of the present subject matter, said thermistors are negative coefficient thermistors. Further, at each power terminal one or more thermistors may be provided. As per an embodiment of the present subject matter and as may be seen in Fig.3, said arc fault detecting elements are connected in a top portion of each of said power terminals (201, 202, 203, 204, 205). Whereas one end of each thermistor is connected to each power terminal, other end of each terminal is connected to a connector 213 provided in a top signal board portion 214 of said motor control unit 200. Thus, the arc fault detecting elements 210 are secured within the motor control unit 200. Provision of said arc fault detecting elements 210 within the motor control unit 200 ensures compactness of the motor control unit 200. Having a compact motor control unit 200 further aids in having a compact vehicle layout as the motor control unit 200 may be easily accommodated in the vehicle.

[0036] In a condition when a loose connection is made at any one of the five above mentioned power terminals while connecting the motor control unit 200 to the battery 160 and the motor 150, arcing occurs at the corresponding power terminal resulting in increased temperature at said power terminal. As the temperature of the affected power terminal increases, the resistance of the corresponding thermistor decreases. This results in the decrease in the effective resistance of the parallel thermistor circuit. Particularly, once the vehicle starts running, the temperature at the power terminals also increases normally and equivalent resistance starts decreasing correspondingly. Under normal running conditions, this temperature rise has a predetermined limit Tiimit and correspondingly the equivalent resistance fall of said arc fault detecting elements 210 i.e. the thermistors also have an equivalent resistance limit (Reqjimit). If there is any loose contact in any of the power terminals resulting in arcing, the temperature at that point increases rapidly to a very high value. In that situation, the resistance of the corresponding thermistor decreases to a very low value resulting in the equivalent resistance (Req) of thermistors becoming much lower than the equivalent resistance limit (Reqjimit). Further, a voltage corresponding to said Req which is lower than said equivalent resistance limit (Reqjimit) is communicated to a microcontroller (not shown) of said motor control unit 200. The signal conditioning circuit (not shown) gives voltage corresponding to temperature variations measured by said thermistors. Further, the motor control unit 200 is configured to operate as per a steps of a method outlined below to eliminate arcing.

[0037] The method involving the steps of operation of the motor control unit and particularly that of the microcontroller in detecting arc fault in the high current paths connected to the motor control unit 200 through the power terminals (201, 202, 203, 204, 205) are described with reference to a flowchart 300 depicted in Fig.4. [0038] In a first step of its operation at block 301, the motor control unit 200 detects vehicle speed (Vrpm), followed by checking at block 302 if the vehicle speed at a particular instant is greater than a threshold vehicle speed (V_rpm ih). Further, if the vehicle speed (Vrpm) is greater than said threshold vehicle speed (V_rpm iΐ_u stored in the memory of said control unit, then at block 303 said control unit 200 checks if equivalent resistance (Req) of the parallel thermistor circuit is lesser than said equivalent resistance limit (Req iimit) of said thermistor circuit, a value of which is stored in memory of said control unit. If said equivalent resistance (Req) is less than said equivalent resistance limit (Req iimit), then at block 304 said control unit 200 disables the vehicle 100. In other words, when the equivalent resistance of the parallel thermistor circuit falls below the equivalent resistance limit due to rise in temperature at any one or more or all the power terminals (201,202, 203, 204, 205) of the motor control unit, thereby indicating presence of an arc fault in said thermistor circuit, said motor control unit disables the vehicle at block 304. This step is particularly performed when the vehicle speed is above a certain threshold, for e.g. above lOkmph. Further, if the limit conditions of vehicle speed or the resistance are not met, the control unit continues to operate normally.

[0039] Thus, the motor control unit as per the present subject matter is not only configured to detect arc faults, but is also configured to perform a vehicle disabling function on instantaneous detection of the arc fault. Thus, the motor control unit serves to be a compact multi-functional unit. Particularly, as per an embodiment of the present subject matter, said control unit disables the vehicle by switching OFF MOSFETS (not shown) in order to stop functioning of the motor 150. More particularly, said MOSFETS are switched OFF by controlling the PWM (pulse width modulation) pulses to the MOSFETS. As per one embodiment, said MOSFETS are disposed behind a heat sink bar 212 (shown in Fig.3) of the motor control unit 200.

[0040] The present invention described herein thus seeks to provide a compact motor control unit which is not only capable of performing arc fault detection but is also capable of disabling the vehicle in a condition where arc fault is detected. The motor control unit operates in a simple and efficient manner. Thus, the method of operation of said control unit not only ensures protection of the control unit but also that of the vehicle under arcing conditions. Moreover, since the arc fault elements in the form of thermistors are disposed within said control unit, compactness of said control unit is ensured. Also, no other components other than the thermistors are required for arc fault detection. Thus, compactness and simplicity of not only the arc fault detection system but that of the entire vehicle is ensured. Further, since the motor control unit is configured to operate with simple thermistors for arc fault detection, cost effectiveness for manufacture of the control unit and that of the vehicle is ensured.

Claims

We Claim:

1. A motor control unit (200) for a vehicle, said vehicle comprising a battery (160) and a motor (150) operatively connected to said motor control unit (200); said motor control unit (200) is configured for arc fault detection in high current paths connecting the battery (160) and the motor (150) to said control unit (200), said motor control unit (200) configured with an arc fault detection system having a plurality of arc fault detection elements (210) therein.

2. The motor control unit (200) as claimed in claim 1 , wherein said motor control unit (200) comprises a plurality of power terminals (201,202, 203, 204, 205) for operatively connecting said motor control unit (200) to the battery (160) and to the motor (150), and wherein one or more arc fault detection elements of said plurality of arc fault detection elements (210) is disposed in a top portion of each power terminal of said plurality of power terminals (201,202, 203, 204, 205).

3. The motor control unit (200) as claimed in claim 1, wherein said arc fault detection elements (210) are temperature sensitive elements.

4. The motor control unit (200) as claimed in claim 3, wherein said arc fault detection elements (210) are thermistors.

5. The motor control unit (200) as claimed in claim 4, wherein said thermistors are negative coefficient thermistors.

6. The motor control unit (200) as claimed in claim 4, wherein said thermistors are connected in parallel with one another.

7. The motor control unit (200) as claimed in claim 1, wherein said motor control unit (200) is configured to disable the vehicle (100) on detection of an arc fault in connections to either the battery (160) or the motor (150) or both the battery and the motor (150).

8. A method of operation of a motor control unit (200) configured for arc fault detection in a vehicle (100), wherein said motor control unit (200) comprises a plurality of power terminals (201,202,203, 204,205) operatively connected to a battery (160) and a motor (150) of said vehicle, each power terminal being provided with one or more arc fault detection elements (210) including thermistors, said method of operation of the motor control unit (200) in responding to detection of an arc fault comprising steps of:

measuring vehicle speed (Vrpm);

checking if vehicle speed (Vrpm) is greater than a threshold vehicle speed

(Vrpmjh);

if said threshold vehicle speed (V_rpm ih) is greater than said vehicle speed (Vrpm) then check if an equivalent resistance (Req) of a thermistor circuit is lesser than an equivalent resistance limit (Reqjimit) of said thermistor circuit;

if said equivalent resistance (Req) of said thermistor circuit is lesser than said equivalent resistance limit (Reqjimit) of said thermistor circuit, then disable the vehicle (100).

9. The method of operation of the motor control unit (200) as claimed in claim 8, wherein said thermistors connected at said power terminals (201,202, 203,204, 205) are negative coefficient thermistors.

10. The method of operation of the motor control unit (200) as claimed in claim 8, wherein said thermistors at said power terminals (201,202, 203,204, 205) are connected in parallel with one another forming the thermistor circuit.

11. The method of operation of the motor control unit (200) as claimed in claim 8, wherein said motor control unit (200) disables said vehicle (100) by controlling pulse width modulation pulses to the motor (150).

12. The method of operation of the motor control unit (200) as claimed in claim 11 , wherein controlling pulse width modulation pulses to the motor (150) results in the motor (150) getting turned OFF.