GB2558010A

GB2558010A - Method and device for surge protection of electric vehicle during charging

Info

Publication number: GB2558010A
Application number: GB1701554.6A
Authority: GB
Inventors: Rao Narendar; Gowrisankar Gowrisankar; Patil Anand; Naikodi Allabaksh
Original assignee: Mahindra Electric Mobility Ltd
Current assignee: Mahindra Electric Mobility Ltd
Priority date: 2016-12-16
Filing date: 2017-01-31
Publication date: 2018-07-04
Anticipated expiration: 2037-01-31
Also published as: GB2558010B; GB201701554D0; CN108206505A

Abstract

An input surge voltage protection circuit for an on-board charging system in an electric vehicle EV, when the EV is plugged-in for charging from the utility grid, comprises first and second thermal fuses 201, 202 and first, second, third and fourth Surge Protection Devices (SPD) 203-206. The first thermal fuse is connected in series in an L line; the second thermal fuse connected in series in a N (neutral) line; the first Surge Protection Device connected between the L line and the N line; the second SPD connected to the L line; the third SPD connected to the N line; and the fourth SPD connected to a midpoint of the second SPD and the third SPD and an E (earth) line. The first, second and third SPDs may be Metal Oxide Varistors (MOV). The fourth SPD may be a Gas Discharge Tube (GDT).

Description

(54) Title of the Invention: Method and device for surge protection of electric vehicle during charging Abstract Title: Surge protection of electric vehicle during charging (57) An input surge voltage protection circuit for an on-board charging system in an electric vehicle EV, when the EV is plugged-in for charging from the utility grid, comprises first and second thermal fuses 201,202 and first, second, third and fourth Surge Protection Devices (SPD) 203-206. The first thermal fuse is connected in series in an L line; the second thermal fuse connected in series in a N (neutral) line; the first Surge Protection Device connected between the L line and the N line; the second SPD connected to the L line; the third SPD connected to the N line; and the fourth SPD connected to a midpoint of the second SPD and the third SPD and an E (earth) line. The first, second and third SPDs may be Metal Oxide Varistors (MOV). The fourth SPD may be a Gas Discharge Tube (GDT).

EV 104

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EV104

FIG.l

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TF1201

FIG. 2

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FIG. 3

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FIG.4

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FIG. 5

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FIG. 6 “Method and device for surge protection of electric vehicle during charging”

TECHNICAL FIELD [001] Embodiments disclosed herein relate to protection of electrical circuits and more particularly to protection of electrical circuits from input surge voltages.

BACKGROUND [002] Typically an electric vehicle (EV) needs to be charged from the electrical grid. However, the utility grid is not always pure because of reasons such as lightening and also due to the highly non-linear loads, which are running in parallel and may inject high voltage or current surges into the charging system when the EV is plugged in for charging. The large surges in the grid power results in the failure of the input section of the EV charger. To prevent the aforementioned issues, the on-board charging system is equipped with a surge protection circuit, which is capable of absorbing the high voltage or current surges irrespective of occurrences between or through any power lines including the earth terminal.

[003] Currently available surge protection circuits have a short life, as the number of over voltage and current pulses defines the life of the protection circuit. Currently available surge protection circuits cannot operate for continuous supply imbalances, especially in areas where the distribution system is having undesired voltage/current levels. Currently available surge protection circuits are having lesser response times so that chances of protecting the onboard charging system are lower.

[004] Also, existing solutions are having more number of protection devices. This increases the leakage current during normal operation of the charging system and also it increases the size and cost of the protection system.

OBJECT [005] The principal object of embodiments disclosed herein is to disclose a surge protection circuit for an on-board charging system in an EV, when the EV is plugged-in for charging from the utility grid.

BRIEF DESCRIPTION OF FIGURES [006] Embodiments disclosed herein are illustrated in the accompanying drawings, through out which like reference letters indicate corresponding parts in the various figures.

The embodiments herein will be better understood from the following description with reference to the drawings, in which:

[007] FIG. 1 depicts a surge protection circuit connected between an AC power supply and a charging system of an EV, according to embodiments as disclosed herein;

[008] FIG. 2 depicts the surge protection circuit, according to embodiments as disclosed herein;

[009] FIG. 3 depicts an example of a surge protection circuit, according to embodiments as disclosed herein.

[0010] FIG. 4 depicts the characteristics of a MOV, according to embodiments as 10 disclosed herein.

[0011] FIG. 5 depicts the characteristics of a GDT, according to embodiments as disclosed herein.

[0012] FIG. 6 depicts the characteristics of a MOV and GDT series combination, according to embodiments as disclosed herein.

DETAILED DESCRIPTION [0013] The embodiments herein and the various features and advantageous details thereof are explained more fully with reference to the non-limiting embodiments that are illustrated in the accompanying drawings and detailed in the following description. Descriptions of well-known components and processing techniques are omitted so as to not unnecessarily obscure the embodiments herein. The examples used herein are intended merely to facilitate an understanding of ways in which the embodiments herein may be practiced and to further enable those of skill in the art to practice the embodiments herein. Accordingly, the examples should not be construed as limiting the scope of the embodiments herein.

[0014] The embodiments herein disclose a surge protection circuit for an on-board charging system in an EV, when the EV is plugged-in for charging from the utility grid. Referring now to the drawings, and more particularly to FIGS. 1 through 6, where similar reference characters denote corresponding features consistently throughout the figures, there are shown preferred embodiments.

[0015] Electric Vehicles (EVs) as defined herein is a vehicle that uses at least one or more electric motors for propulsion. In an embodiment herein, the EV can comprise of one or more different motors and/or engines, which can be used for propulsion.

[0016] Embodiments herein disclose a surge protection circuit for an on-board charging system in an EV, when the EV is plugged-in for charging from the utility grid; wherein the circuit comprises of transient absorbers such as MOV’s (Metal Oxide Varistor), GDT’s (Gas Discharge Tube), TVS (Transient Voltage Suppression) and thermal fuse devices.

[0017] FIG. 1 depicts an on-board charging system of an EV 104 when it is plugged in to the grid 102 through in-line control box 101. The AC power supply from grid 102 enters into in-line control box 101, which is used for making the connection between AC supply 102 and on-board charger 103 after the verification of safety functionalities. The controlled AC output from the in-line control box 101 is supplied to the on-board charger 103, which is placed inside the EV 104. The on-board charger 103 is generally an AC-DC converter 107, which converts the controlled AC output of in-line control box 101 into a DC power for the purpose of charging the battery system 105. In an embodiment herein, the surge protection circuit 106 can be located in the on-board charger 103, which is part of an EV 104. In an embodiment herein, the surge protection circuit 106 can be located in in-line control box, which is outside the EV 104.

[0018] FIG. 2 depicts the surge protection circuit 106. The surge protection circuit 106 can be placed in the on-board charger 103. The surge protection circuit 106 can be placed in the in-line control box 101. The surge protection circuit 106 can be placed in both the onboard charger 103 and the in-line control box 101.

[0019] Two thermal fuses TF1 201 and TF2 202 are connected in series in both line (L) and neutral (N) power lines. The thermal fuses have recovery characteristics after current through the surge protection circuit 106 falls below onetime current rating. A SPD1 (Surge Protection Device) 203 is connected between the L and N power lines. SPD2 204 and SPD3 205 are connected between two power lines with the midpoint connected to the earth (E) line through SPD4 206. As soon as SPD2 204 and SPD3 205 conducts, the surge current is passed to the earth (E) line through the SPD4 206.

[0020] The selection of SPD1 203, SPD2 204 and SPD3 205 can be based on parameters such as varistor voltage, clamping voltage and onetime current rating. For example, if the on-board charging system is designed to operate up to maximum AC input voltage of 270V (rms), then the values of SPD1 203, SPD2 204 and SPD3 205 should be chosen such that the allowable working AC voltage of MOV should be higher than the maximum AC input voltage. So that for the input voltages below 270V (rms), SPD1 203, SPD2 204 and SPD3 205 exhibit very high impedance (in Giga ohms) and the current flow through SPD1 203, SPD2 204 and SPD3 205 is negligible. The working voltage of SPD1 203, SPD2 204 and SPD3 205 can be calculated as 110% of maximum AC input voltage or above and which will allow the input AC voltages up to 320V (rms). The conduction of SPD1 203, SPD2 204 and SPD3 205 start from the varistor voltage (510V) where the current through the device increases non-linearly with the increase in the surge voltage above 510V. From the datasheet, the clamping voltage of SPD1 203, SPD2 204 and SPD3 205 is 840V at 150A, but as the current through SPD1 203, SPD2 204 and SPD3 205 increase above 150A the clamping voltage gradually increases. SPD1 203, SPD2 204 and SPD3 205 have a onetime current rating of 20kA, such that if the current through the MOV reaches above 20kA, the SPD1 203, SPD2 204 and SPD3 205 can fail. Consider an example wherein a surge voltage of 6kV is applied as per IEC 61000-4-5 (1.2/50us voltage waveform) across a S25K320 with 2Ω impedance, the maximum current through the S25K320 will be 3kA and correspondingly from the datasheet, the clamping voltage is observed as close to 1000V. This clamping voltage will appear across SPD1 203, SPD2 204 and SPD3 205 for a short duration and thereby the AC-DC converter 107 after the SPD1 203, SPD2 204 and SPD3 205 is protected from 6kV surge voltage. The clamping voltage of SPD1 203, SPD2 204 and SPD3

205 should not fail the AC-DC converter 107 and it is chosen from the maximum withstanding voltage of the circuit, which is to be protected. The selection also depends on the additional parameters such as energy dissipation of the SPD1 203, SPD2 204 and SPD3 205.

[0021] The SPD4 206 can be a GDT and it can be selected based on the response times and derating curves of the SPD2 204 and SPD3 205. The GDT can have higher impedance, when compared to the SPD1 203, SPD2 204 and SPD3 205 and the characteristics of these devices are different from each other. The conduction of SPD4 206 from high impedance to very low impedance can be determined by the rate of voltage and thereby the current flows through the device. For example, consider an example where an EPCOS A230X GDT is used, wherein the EPCOS A230X GDT has a spark over voltage of 500V with lOOV/us rate and impulse spark over voltage of 650V for lkV/us rate. If the surge voltage is having lOOV/us rate, the SPD4 206 enters into low impedance state if the surge level crosses 500V. When a surge voltage of 6kV with 1.2/50us (as per IEC 61000-4-5) is applied across the series combination of the SPDs, high voltage appears across the SPD4 206 because of its impedance. During this period, the impedance of the SPD4 206 will fall gradually along with the rise in surge voltage and simultaneously the voltage across SPD1 203, SPD2 204 and SPD3 205 starts increasing because of its impedance. When the voltage across SPD1 203, SPD2 204 and SPD3 205 starts increasing beyond the varistor voltage, current through SPD1 203, SPD2 204 and SPD3 205 will begin to flow and thereby it bypasses the surge current to the earth through SPD4 206.

[0022] When the voltage between the L and N power lines exceeds the Varistor voltage of the SPD1 203, the current through the SPD1 203 increases and it limits the surge voltage to a protected voltage level. The TF1 201 opens when the current between the L and N lines exceeds the one-time current rating of the SPD1 203 and hence completely disconnects the AC-DC converter 107, which is to be protected. During the surge voltage between line to earth or neutral to earth, the SPD4 206 starts breaking down (as it has a higher impedance) and the impedance will decrease non-linearly and the voltages across SPD2 204 or SPD3 205 will increase respectively. For line to earth surge TF1 201 opens and for neutral to earth TF2 202 opens after the currents through the thermal fuse devices reaches above the one-time current ratings and hence the AC-DC converter 107 is protected from surge voltages and currents.

[0023] For SPD4 206, the transition between the high and low impedance states depend on the rate of surge voltage. The spark over voltage should be greater than the normal input operating voltage of the charging system 103 and the impulse spark should be lower than the maximum voltage that the surge protection circuit 101 can be allowed. In an embodiment herein, the spark over voltage can be defined at lOOV/us. In an embodiment herein, the impulse spark over voltage can be defined at lkV/ps. After the break down, the SPD4 206 enters into a low impedance state in which it maintains a voltage called arc voltage. During this state, a very high current will flow through SPD4 206 and if the current exceeds the single impulse current rating, the SPD4 206 will fail.

[0024] In an example embodiment depicted in FIG. 3, the SPD1 203, SPD2 204 and SPD3 205 are MOV’s and the SPD4 206 is a GDT.

[0025] The surge voltages on power lines are defined by the standard IEC 61000-4-5 and embodiments disclosed herein have been designed as per the standard surge voltage cycle with 1.2/50ps and surge current cycle with 8/20ps.

[0026] Embodiments herein disclose a surge protection system with the lesser number of components for EV on-board charging system so that it can charge from any wall mount socket. Embodiments disclosed herein can suppress multiple 6kV/ 3kA voltage & current pulses.

[0027] Embodiments disclosed herein uses independent thermal fuses and MOV devices to increase the life of protection circuit over TMOV devices.

[0028] The derating characteristics of the embodiments as disclosed herein are lesser compared to the existing configurations, so that the life of the circuit will be higher. The life of the protection devices majorly depends on the amount of surge current and its time duration. FIG. 4 depicts example characteristics of a MOV, which is having a clamping voltage of 500V. When the surge voltage of 6kV with 2Ω source impedance is applied to the MOV, initially the MOV is in high impedance state and the current through the device slowly increases until the surge voltage reaches to 500V. When the surge voltage is above the clamping voltage, the MOV enters into a low impedance state and current through the device increases non-linearly by maintaining the clamping voltage. The peak surge current is 3kA, which is defined by the source impedance (6kV/2 = 3kA) because the MOV is having very low impedance (in milliohms). The duration of the surge current for a single MOV is high which decreases the life.

[0029] FIG. 5 is an example depicting the characteristics of a GDT, which is having an impulse spark over voltage of 700V. When the input surge voltage of 6kV with 2Ω impedance is applied across a GDT, the GDT is in high impedance state and the current will not flow through the device until the surge voltage reaches to 700V. When the surge voltage reaches beyond 700V, the device enters into low impedance state and the voltage across the device will be the arcing voltage 12V. Due to this low arcing voltage, the GDT is not recommended between line & neutral because it virtually shorts the power lines.

[0030] Fig. 6 depicts the characteristics of MOV and GDT, which are in series combination. It combines the advantages of both MOV and GDT from Figs. 4 and 5 respectively. The voltage across the combination during the surge is 512V, which is close to the clamping voltage (500V) of MOV. The surge current duration is reduced because of the GDT and there by the combination derates very slowly. Due to this, the life of the protection circuit is improved for a same number of input voltage surges, which are applied to a single MOV.

[0031] The leakage currents during the normal operation are almost negligible in embodiments as disclosed herein, as number of protection devices are reduced. From FIG. 4, the surge current through the MOV increases slowly with the surge voltage. As the number of MOV’s are increased in a parallel combination to share the surge current, the leakage current will also increases because of inherent characteristics of MOV. The leakage current is also completely reduced in the series combination as shown in FIG. 6 when compared to a single MOV as shown in FIG. 4.

[0032] Embodiments disclosed herein have a high response time as it is having the combination of GDT, MOV and thermal fuses. All these devices are having different operating characteristics and combining them in a protection circuit will provide the best protection for any voltage surges between any power lines. From FIG. 2, when a surge voltage occurs between the line and the neutral, the MO Vs and thermal fuses protect the system and similarly for line to earth and neutral to earth the combination of MOVs, GDT and thermal fuses protect the system.

[0033] The foregoing description of the specific embodiments will so fully reveal the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the embodiments as described herein.

STATEMENT OF CLAIMS

Claims

We claim:

1. A surge protection circuit for an Electric Vehicle (EV) comprising a first thermal fuse (201) connected in series in an L (line) line;

a second thermal fuse (202) connected in series in an N (neutral) line; a first Surge Protection Device (SPD) (203) connected between the L line and the N line; a second SPD (204) connected to the L line;

a third SPD (205) connected to the N line; and a fourth SPD (206) connected to a midpoint of the second SPD (204) and the third SPD (205) and an E (earth) line.

2. The surge protection circuit, as claimed in claim 1, wherein the first SPD (203), the second SPD (204) and the third SPD (205) are Metal Oxide Varistors (MOV).

3. The surge protection circuit, as claimed in claim 2, wherein values of the MOVs depend on at least one Varistor voltage, clamping voltage, one-time current rating, and energy dissipation.

4. The surge protection circuit, as claimed in claim 1, wherein the fourth SPD (206) is a Gas Discharge Tube (GDT).

5. The surge protection circuit, as claimed in claim 4, wherein values of the GDT depends on response times of the second SPD (204) and the third SPD (205) and derating curves.

6. The surge protection circuit, as claimed in claim 1, wherein the first thermal fuse (201) opens, on current between the L and N lines or between L and E lines exceeding the one-time current rating of the same fuse (202).

7. The surge protection circuit, as claimed in claim 1, wherein the second thermal fuse (202) opens, on current between N and E lines exceeding the one-time current rating of the same fuse (202).

8. The surge protection circuit, as claimed in claim 1, wherein spark over voltage is greater than normal input operating voltage of an on-board charger (103) connected to the surge protection circuit (106).

9. The surge protection circuit, as claimed in claim 1, wherein impulse spark is lower than a maximum voltage that the surge protection circuit (106) is allowed.

10. The surge protection circuit, as claimed in claim 1, wherein the surge protection circuit (106) is further configured for decreasing impedance of the fourth SPD (206) non-linearly, on detecting a surge voltage between at least one of L to E lines; and N to E lines;

increasing voltages across the second SPD (204) and the third SPD (205); and entering by the second SPD (204), the third SPD (205) and the fourth SPD (206) into a low impedance state.

11. The surge protection circuit, as claimed in claim 1, can be located inside at least one of an on-board charger; and an in-line control box.

12. A method for surge protection using a surge protection circuit comprising a first thermal fuse (201) connected in series in a L (line) line;

a second thermal fuse (202) connected in series in a N (neutral) line; a first Surge Protection Device (SPD) (203) connected between the L line and the N line; a second SPD (204) connected to the L line;

a third SPD (205) connected to the N line; and a fourth SPD (206) connected to a midpoint of the second SPD (204) and the third SPD (205) and an E (earth) line; the method comprising opening the first thermal fuse (201), on current between the L and N lines exceeding one time current rating of the same fuse (201); and opening the second thermal fuse (202), on current between the E and N lines exceeding one time current rating of the same fuse (202)

13. The method, as claimed in claim 12, wherein the method further comprises of decreasing impedance of the fourth SPD (206) non-linearly, on detecting a surge voltage between at least one of L to E lines; and N to E lines;

Intellectual

Property

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