ELECTRIC VEHICLE

An electric vehicle may include a battery; an inverter; a motor; a first and second terminal configured to connect to an external power supply; a first wire connecting the first terminal to a neutral point; a second wire connecting the second terminal to the battery, a first relay disposed on the first wire; a first and second voltage sensor configured to measure a potential difference; and a controller. The controller may be configured to: calculate permissible power of the battery; calculate a first voltage value obtained by adding a first margin to a detected value by the first voltage sensor; calculate a second voltage value obtained by adding a second margin to a detected value by the second voltage sensor; and calculate a current command value to the external power supply based on the permissible power and a smaller value of the first voltage value and the second voltage value.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to Japanese Patent Application No. 2023-061743 filed on Apr. 5, 2023. The entire content of the priority application is incorporated herein by reference.

BACKGROUND ART

The technology disclosed herein relates to electric vehicle comprising a battery, an inverter, and an electric motor.

Japanese Patent Application Publication No. 2021-175363 discloses a technology for boosting the power supplied from an external power source using a motor drive system and charging a battery therewith.

SUMMARY

When charging a battery, the power supplied from an external power source is required not to exceed the power the battery can accept. In case of using a required current as a power supply command to the external power source, the power supplied from the external power source needs to be calculated by measuring the supply voltage using a voltage sensor used in a voltage booster circuit. However, when the accuracy of the voltage sensor in the booster circuit is lower than the accuracy of a voltage sensor in the battery, it is necessary to provide a sufficient margin to the voltage value measured by the voltage sensor in the booster circuit, which may make the calculated supply power larger than the actual supply power. This makes a current command value lower than the one actually required and thus makes the charging time longer.

An electric vehicle disclosed herein may comprise a battery; an inverter comprising three arm circuits, wherein each of the three arm circuits comprises an upper switching element connected to a positive electrode of the battery and a lower switching element connected to a negative electrode of the battery, and the upper switching element and the lower switching element are connected in series; a motor comprising three coils, wherein in each of the three coils, one end thereof is connected to a neutral point and other end thereof is connected to a midpoint of corresponding one of the three arm circuits; a first terminal configured to connect to a positive electrode of an external power supply; a second terminal configured to connect to a negative electrode of the external power supply; a first wire connecting the first terminal to the neutral point; a second wire connecting the second terminal to the negative electrode of the battery, a first relay disposed on the first wire; a first voltage sensor configured to measure, between the first terminal and the first relay, a potential difference between the first wire and the second wire; a second voltage sensor configured to measure, between the first relay and the neutral point, a potential difference between the first wire and the second wire; and a controller configured to control the inverter to increase a voltage of power supplied from the external power supply and charge the battery. The controller may be configured to: calculate permissible power of the battery; calculate a first voltage value obtained by adding a first margin to a detected value by the first voltage sensor; calculate a second voltage value obtained by adding a second margin to a detected value by the second voltage sensor; and calculate a current command value to the external power supply based on the permissible power and a smaller value of the first voltage value and the second voltage value.

According to this configuration, the supply voltage from the external power source can be measured using the two voltage sensors. Further, the smaller voltage can be used to calculate a current command value. This allows the supply voltage to be measured more accurately than measuring the supply voltage using a single voltage sensor. Therefore, the current command value can be maximized while controlling the supply power from the external power source not to exceed the acceptable power of the battery. This prevents an unnecessarily extended charging time.

DETAILED DESCRIPTION OF DETAILED DESCRIPTION

In one embodiment of the technology disclosed herein, the electric vehicle may further comprise a second relay disposed on the first wire between the first relay and the neutral point. The second voltage sensor may be configured to measure, between the first relay and the second relay, a potential difference between the first wire and the second wire.

According to this configuration, a function of detecting whether the second relay have a trouble and a function of measuring the second voltage value can be realized by the second voltage sensor.

In one embodiment of the technology disclosed herein, the electric vehicle may further comprise a third wire connecting a connection path between the first relay and the second relay to the positive electrode of the battery; and a third relay disposed on the third wire.

According to this configuration, the positive electrode of the external power source can be directly connected to the positive electrode of the battery by the third relay. This allows the battery to be directly charged by the external power source.

In one embodiment of the technology disclosed herein, the controller may further be configured to: calculate a voltage drop value based on a resistance value of a connection path between the first voltage sensor and the second voltage sensor and the current command value; and correct the first voltage value or the second voltage value based on the voltage drop value.

According to this configuration, the effect of voltage drop occurring in the connection path between the first and second voltage sensors can be canceled. This allows for a more accurate determination on which of the first voltage value and the second voltage value is larger/smaller.

In one embodiment of the technology disclosed herein, the first margin may be different from the second margin.

EMBODIMENTS

Configuration of Electric Vehicle2

An electric vehicle2according to an embodiment is described with reference to the drawings.FIG.1shows a block diagram of the electric vehicle2. The electric vehicle2mainly includes a battery3, an inverter10, an electric traction motor20, and a controller30. The dashed arrow lines inFIG.1represent signal lines.

The battery3is connected to a DC-terminal of the inverter10. A positive electrode3pof the battery3is connected to a DC-terminal positive electrode10pand a negative electrode3nof the battery3is connected to a DC-terminal negative electrode10n. A main relay19is connected between the battery3and the inverter10. The main relay19is controlled by the controller30.

The inverter10includes three sets of arm circuits11a,11b, and11c. The arm circuit11aincludes an upper switching element12a, a lower switching element13a, a diode14aconnected in reverse parallel to the upper switching element12a, and a diode15aconnected to the lower switching element13a. The upper switching element12aand the lower switching element13aare connected in series. The upper switching element12ais connected to the positive electrode3pof the battery3via a high-potential wire29and the DC-terminal positive electrode10p. The lower switching element13ais connected to the negative electrode3nof the battery3via a second wire23nand the DC-terminal negative electrode10n. In other words, the upper switching element12aand the lower switching element13aare connected in series such that the upper switching element12ais located on the high potential side and the lower switching element13ais located on the low potential side.

The arm circuit11bincludes an upper switching element12b, a lower switching element13b, a diode14b, and a diode15b. The arm circuit11cincludes an upper switching element12c, a lower switching element13c, a diode14c, and a diode15c. The arm circuits11band11chave the same structure as the arm circuit11a, so their description is omitted. The three sets of arm circuits11a,11b, and11care connected in parallel between the DC-terminal positive electrode10pand the DC-terminal negative electrode10nof the inverter10. In other words, the three sets of arm circuits11a,11b,11care connected in parallel between the positive electrode3pand the negative electrode3nof the battery3.

A capacitor17is connected between the DC-terminal positive electrode10pand the DC-terminal negative electrode10nof the inverter10. The capacitor17is provided to suppress the pulsation of a current flowing in the DC terminal of the inverter10.

Upper switching elements12ato12cand lower switching elements13ato13cof the inverter10are controlled as appropriate by the controller30. When the upper and lower switching elements are turned on and off alternately, alternating currents are output from midpoints16a,16b, and16cof the three sets of arm circuits11a,11b, and11c, respectively.

The electric motor20is connected to the midpoints16a,16b, and16c. The electric motor20includes three coils21a,21b,21c. The three coils21a,21b,21care wound around a stator (not shown) of the electric motor20. One end of each coil21a,21b,21cis connected to corresponding one of the midpoints16a,16b,16c. The other ends of the three coils21a,21b, and21care coupled at a single point. The point where the other ends of the three coils21a,21b, and21care coupled to each other is called a neutral point22. The configuration in which the other ends of the coils of respective phases of the stator are connected at the neutral point22is called star connection and is a well-known circuit structure in three-phase AC motors.

The electric vehicle2further includes a first wire23p, second wire23n, third wire23B, charging relays24pand24n, a neutral point relay25, a bypass relay26, a temperature sensor27, a charging inlet28, a first voltage sensor31, and a second voltage sensor32. The charging inlet28is provided in the body of the electric vehicle2. The charging inlet28has a first terminal28pand a second terminal28n. A power cable41extending from an external DC power source40is connected to the charging inlet28. Each of the first terminal28pand the second terminal28nare thereby connected to a positive terminal40pand a negative terminal40nof the external DC power source40. The external DC power source40is, for example, a charging station.

The first wire23pconnects the first terminal28pto the neutral point22. The second wire23nconnects the second terminal28nto the negative electrode3nof the battery3. The second wire23nis also called a ground wire. The third wire23B connects a connection path between the charging relay24pand the neutral point relay25to the positive electrode3pof the battery3.

The charging relay24pis disposed on the first wire23p. The charging relay24nis disposed on the second wire23n. The neutral point relay25is disposed on the first wire23pbetween the charging relay24pand the neutral point22. The bypass relay26is disposed on the third wire23b. The bypass relay26directly connects the positive electrode40pof the external DC power source40to the positive electrode3pof the battery3.

The first voltage sensor31is disposed between connection paths between the charging inlet28and the charging relays24pand24n. In other words, the first voltage sensor31is configured to measure, between the first terminal28pand the charging relay24p, a potential difference between the first wire23pand the second wire23n. By the first voltage sensor31, whether a trouble, such as welding, is occurring in the charging relays24pand24ncan be detected. As described below, the first voltage sensor31can also measure a first voltage value V1.

The second voltage sensor32is disposed on the connection path between the charging relay24pand the neutral point relay25. In other words, the second voltage sensor32is configured to measure, between the charging relay24pand the neutral point relay25, a potential difference between the first wire23pand the second wire23n. By the second voltage sensor32, whether a trouble, such as welding, is occurring in the neutral point relay25can be detected. As described below, the second voltage sensor32can also measure a second voltage value V2.

The temperature sensor27is a sensor that measures the temperature of the battery3. The measured value by the temperature sensor27is sent to the controller30.

The electric vehicle2further includes three current sensors18a,18b, and18cthat measure the currents flowing in the three coils21ato21c, respectively. The measured values by the three current sensors18ato18care sent to the controller30. The controller30uses the measured values from the three current sensors18ato18cto feedback control the upper switching elements12ato12cand the lower switching elements13ato13c. Specifically, it performs current-controlled PWM control. This allows the currents flowing through the respective three coils21ato21cto follow target current values. The current sensors18may be positioned at other locations than those shown inFIG.1. Further, instead of the current sensors18, each switching element may include a function to measure a current.

Booster Circuit using Electric Motor20

From a different viewpoint, it can be said that the lower switching element13aand the diode14aof the inverter10and the coil21aconstitute a booster circuit. The neutral point22corresponds to the input terminal, and the DC-terminal positive electrode10pof the inverter10corresponds to the output terminal. The positive electrode40pof the external DC power source40is connected to the neutral point22(input terminal) and the positive electrode3pof the battery3is connected to the DC-terminal positive electrode10p(output terminal). The negative electrode3nof the battery3is connected to the DC-terminal negative electrode40nof the external DC power source40via the second wire23n.

When the lower switching element13ais turned on for a predetermined short period of time, one end of the coil21ais connected to the second wire23nand a current flows through the coil21a. At this time, electrical energy is stored in the coil21a. When the lower switching element13ais switched from on to off, the current stops flowing from the coil21ato the second wire23n. An induced electromotive force is generated in the coil21a. Due to the induced electromotive force in the coil21a, a current flows from the coil21ato the DC-terminal positive electrode10pthrough the diode14a. In other words, the voltage at the DC-terminal positive electrode10pbecomes higher than the voltage at the neutral point22. When the voltage at the DC-terminal positive electrode10pbecomes higher than the voltage at the positive electrode3pof battery3, a current flows from the external DC power source40to the battery3, and the battery3is charged.

The lower switching element13b, the coil21b, and the diode14balso constitute a booster circuit. The lower switching element13c, the coil21c, and the diode14calso constitute a booster circuit. In other words, from a different viewpoint, the inverter10and the electric motor20can be regarded as three booster circuits connected in parallel.

The electric vehicle2allow the battery3to be charged using the external DC power source40, which has a lower output voltage than the battery3, by using the inverter10and the electric motor20as booster circuits.

Operation Flowchart of Charging Process

FIG.2shows a flowchart of a charging process. With reference toFIG.2, the charging process by the controller30is explained. When the power cable41of the external DC power source40is connected to the charging inlet28of the electric vehicle2and the user turns on a charging switch (not shown), the process shown inFIG.2starts. The controller30first closes the main relay19to connect the inverter10to the battery3(step S10). At this stage, the charging relays24pand24nremain open.

In step S15, the controller30obtains permissible power Win of the battery3. The permissible power Win can be calculated, for example, based on the temperature of the battery3. The permissible power Win of the battery3is lower with the lower temperature of the battery3. In order to prevent performance degradation of the battery3due to lithium precipitation, the battery needs to be charged with power that is equal to or lower than the permissible power Win. In other words, the permissible power Win is the upper limit of charging power.

In step S20, the controller30determines whether the voltage of the battery3is higher than the voltage of the external DC power source40. If the voltage of the external DC power source40is higher (520: NO), it is determined that a voltage boost is not required for charging. Therefore, the flow proceeds to step S25, where the controller30closes the charging relays24p,24n, and the bypass relay26. As a result, the battery3is directly charged by the external DC power source40. The flow then proceeds to step S90.

If the voltage of the battery3is higher (520: YES), it is determined that a voltage boost is required for charging. Therefore, the charging relays24p,24n, and the neutral point relay25are closed. Then, the flow proceeds to step S30to perform the above-described charging operation using the booster circuits with the electric motor20.

In step S30, the controller30calculates a first voltage value V1. As shown in (A) ofFIG.3, the first voltage value V1is obtained by adding a first margin M1to a detected value D1by the first voltage sensor31. The first voltage sensor31has the first margin M1on + side and − side with respect to the detected value D1. The first margin M1is determined by the design value of the first voltage sensor31and can be known in advance. The more precisely designed the first voltage sensor31is, the smaller the first margin M1is. The value obtained by adding the first margin M1to the detected value D1is the first voltage value V1. The value obtained by subtracting the first margin M1from the detected value D1is a lower limit voltage value V1L. An actual voltage Va, which is the actual voltage, always falls within the range from the lower limit voltage value V1L to the first voltage value V1. The first voltage value V1, which is the upper limit value, is used as a value for calculating supply power as described below. Thus, the first voltage value V1does not exceed the actual voltage Va even with the largest measurement error.

In step S40, the controller30calculates a second voltage value V2. As shown in (B) ofFIG.3, the second voltage value V2is obtained by adding a second margin M2to a detected value D2by the second voltage sensor32. The value of the first margin M1and the value of the second margin M2may be different from each other. In other words, the accuracy of the first voltage sensor31and the accuracy of the second voltage sensor32may be different from each other. The value obtained by subtracting the second margin M2from the detected value D2is a lower limit voltage value V2L. Since the second voltage value V2is the same as the first voltage value V1described above, its detailed explanation is omitted.

In step S50, the controller30determines which of the first voltage value V1and the second voltage value V2is smaller. If it is determined that the first voltage value V1is smaller (S50: V1), the flow proceeds to step S60. In the example inFIG.3, the first voltage value V1is smaller than the second voltage value V2, so the flow proceeds to step S60(seeFIG.3, arrow A1).

In step S60, the controller30calculates a current command value CC. The current command value CC is information for conveying a current value to be supplied from the external DC power source40to the electric vehicle2to the external DC power source40. The current command value CC is calculated based on the permissible power Win and the first voltage value V1. Specifically, the calculation “CC=Win/V1” is performed. Then, the flow proceeds to S80.

If it is determined in step S50that the second voltage value V2is smaller (S50: V2), the flow proceeds to step S70. In step S70, the controller30calculates the current command value CC based on the permissible power Win and the second voltage value V2. Specifically, the calculation “CC=Win/V2” is performed. Then, the flow proceeds to S80.

In step S80, the controller30causes the external DC power source40to supply a current based on the calculated current command value CC. Thus, the battery can be charged such that the power supplied from the external DC power source40does not exceed the permissible power Win of the battery3.

In step S90, the controller30determines whether the amount of power in the battery3has reached a predetermined threshold amount of power. If not (S90: NO), the flow returns to S15and the charging continues. On the other hand, if yes (S90: YES), the controller30opens the charging relays24pand24nand terminates the charging process.

Effects

Here, the problem to be solved is described. In case of using the current command value CC to convey a power supply command to the external DC power source40, the supply voltage of the external DC power source40needs to be measured by using a voltage sensor (e.g., the first voltage sensor31, the second voltage sensor32) in the booster circuits with the electric motor20. This is because the power to be supplied from the external DC power source40needs to be calculated by multiplying the current command value CC by the supply voltage and the power to be supplied from the external DC power source40needs to be controlled not to exceed the permissible power Win of the battery3. However, when the accuracy of the voltage sensor of the booster circuits is lower than that of a voltage sensor (not shown) of the battery3, a sufficient margin needs to be given to the voltage value measured by the voltage sensor of the booster circuits, which may make the calculated supply power larger than the actual supply power. As a result, the current command value CC may be made lower than actually required and thus the charging time may be extended.

In view of the above, in the technology disclosed herein, the supply voltage from the external DC power source40can be measured using the two voltage sensors, namely the first voltage sensor31and the second voltage sensor32. Further, the current command value CC can be calculated using the smaller one of the first voltage value V1with the first margin M1added and the second voltage value V2with the second margin M2added. This allows for a more accurate measurement of the supply voltage than measuring it using a single voltage sensor. Therefore, the current command value CC can be maximized without allowing the supply power from the external DC power source40to exceed the permissible power Win. This suppresses the unnecessarily extended charging time.

While specific examples of the present disclosure have been described above in detail, these examples are merely illustrative and place no limitation on the scope of the patent claims. The technology described in the patent claims also encompasses various changes and modifications to the specific examples described above. The technical elements explained in the present description or drawings provide technical utility either independently or through various combinations. The present disclosure is not limited to the combinations described at the time the claims are filed. Further, the purpose of the examples illustrated by the present description or drawings is to satisfy multiple objectives simultaneously, and satisfying any one of those objectives gives technical utility to the present disclosure.

Variants

The method of calculating the first voltage value V1(S30) and the method of calculating the second voltage value V2(S40) may be varied. For example, a voltage drop value of a connection path between the first voltage sensor31and the second voltage sensor32may be calculated. The voltage drop value can be calculated based on a resistance value of the connection path between the first voltage sensor31and the second voltage sensor32and the current command value CC. The resistance value of the connection path can be obtained in advance, for example, by adding up resistance values of the charging relays24pand24nand resistance values of various circuits, which are not shown (e.g., shutdown circuit). The first voltage value V1or the second voltage value V2may be corrected based on the calculated voltage drop value. For example, the voltage drop value may be subtracted from the first voltage value V1or the voltage drop value may be added to the second voltage value V2. This cancels the effect of the voltage drop occurring in the connection path between the first voltage sensor31and the second voltage sensor32. Thus, it is possible to determine more accurately which of the first voltage value V1and the second voltage value V2is larger/smaller.

The number of voltage sensors that measure the supply voltage of the external DC power source40is not limited to two. N (N is a natural number greater than or equal to 3) voltage sensors can be used. In this case, a margin may be added to each of the detected values by the N voltage sensors to calculate N voltage values. The current command value CC then may be calculated by using the minimum voltage value among the N voltage values.

The margins may be added to the detected values by the voltage sensors in various manners. For example, the margins may be added in a percentage of the detected values.

The term “electric vehicle” used herein can also include a hybrid vehicle including an engine as well as a battery, a n inverter, and an electric motor. In other words, the technology according to the embodiment is also suitably applied to hybrid vehicles.

The charging relay24pis an example of the first relay. The neutral point relay25is an example of the second relay. The bypass relay26is an example of the third relay.