JP2014023263A - Electric vehicle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric vehicle capable of preventing a power element in a voltage converter from being overheated.SOLUTION: The electric vehicle includes a voltage converter 3, a cooler 26 and a controller 9. The voltage converter 3 boosts an output voltage of a battery 12 and supplies the boosted voltage to an inverter 21. The voltage converter 3 includes a switching element and a diode in its circuit. The cooler 26 cools the voltage converter 3 by circulating refrigerant. The controller 9 determines a limit value of an electric current input into the voltage converter 3 (current limit value) on the basis of a duty ratio of a PWM signal applied to the switching element and a refrigerant temperature and limits an input current so that the current is not more than its current limit value.

Description

  The present invention relates to an electric vehicle. The “electric vehicle” in this specification includes a hybrid vehicle including both a motor and an engine, and a fuel cell vehicle.

  The electric vehicle includes an inverter that converts the DC power of the battery into AC power having a frequency suitable for driving the traveling motor. Further, when the motor drive voltage is higher than the output voltage of the battery, a voltage converter that boosts the voltage of the battery may be provided between the battery and the inverter. Generally, an inverter or a converter includes a switching element such as an IGBT and a diode in its circuit. The traveling motor consumes a large amount of power, and therefore a large current flows through the switching elements and diodes of the inverter and converter. Semiconductor elements such as switching elements and diodes that handle large currents are sometimes collectively referred to as power elements.

  The power element generates a large amount of current and generates a large amount of heat. Technologies for suppressing overheating of power elements are disclosed in, for example, Patent Documents 1 and 2. Both documents limit the input current to the voltage converter and prevent overheating of the power element. In the technique of Patent Document 1, the first current limit value for protecting the battery and the second current limit value for protecting the diode of the voltage converter are compared, and the smaller one of the input current to the voltage converter is compared. Set as a limit value. The second current limit value is determined based on the temperature of the refrigerant that cools the power element. The technique of Patent Document 2 determines the limit value of the input current according to the temperature change amount of the switching element of the voltage converter.

JP 2011-250511 A JP 2012-019587 A

  As disclosed in Patent Documents 1 and 2, overheating of the power element can be prevented by limiting the input current. However, if the limit value of the input current is excessively lowered, the output power of the voltage converter is reduced, which affects the running of the vehicle. Therefore, the limit value of the input current should be as high as possible. On the other hand, the techniques of Patent Documents 1 and 2 both determine the limit value of the input current based on the temperature of the refrigerant that cools the power element. This specification introduces another parameter in addition to the refrigerant temperature to determine an appropriate limit value for the input current.

  In addition to the refrigerant temperature, there are other factors that affect the temperature rise of the power element. As the current flowing through the power element increases, the power element generates heat. In general, switching elements and diodes are less susceptible to heat. Therefore, the technique disclosed in this specification focuses on the current flowing through the diode to determine the current limit value.

  In many cases, a voltage converter has a configuration in which a diode and a switching element are connected in series, and one end of a reactor is connected to an intermediate point thereof. In such a circuit configuration, the current flowing through the diode changes according to the switching operation of the switching element. The longer the OFF time of the switching element, the smaller the current flowing through the diode and the smaller the heat generation. The OFF time of the switching element is determined by the duty ratio of the PWM signal given to the switching element. Therefore, the technique disclosed in this specification determines the limit value of the input current based on the duty ratio of the PWM signal applied to the switching element in addition to the refrigerant temperature.

  An electric vehicle according to an aspect of the technology disclosed in this specification includes a voltage converter, a cooler, and a controller. The voltage converter boosts the output voltage of the battery and supplies it to the inverter. The voltage converter includes a switching element and a diode in its circuit. The cooler cools the voltage converter by circulating the refrigerant. The cooler specifically cools power elements such as switching elements and diodes. The controller determines a limit value (current limit value) of the current input to the voltage converter based on the duty ratio of the PWM signal applied to the switching element and the refrigerant temperature, and supplies the voltage converter so as to be equal to or less than the current limit value. Limit the input current.

  One suitable method for determining the current limit value is that the controller stores a map of the current limit value with the duty ratio and the refrigerant temperature as parameters, and the map is based on the measured value of the refrigerant temperature and the actual duty ratio. It is to determine by reference. The relationship between the refrigerant temperature and the duty ratio and the current limit value for preventing overheating of the diode can be obtained in advance by experiments or simulations. In general, the current limit value decreases as the duty ratio increases, and the current limit value decreases as the refrigerant temperature increases. If the relationship is mapped and stored, the current limit value can be determined by a simple process.

  Many electric vehicles use a motor as a generator and charge a battery with the electric power generated by the motor. Specifically, the inverter converts the AC power generated by the motor into DC power, and the voltage converter steps down the voltage of the DC power to the battery voltage. Charging a battery by generating electricity with a motor is generally called “regeneration”. On the other hand, driving the motor with battery power is called “powering”. It is preferable to prevent overheating of the power element even during regeneration. Accordingly, one improvement of the electric vehicle disclosed in this specification has the following configuration. The voltage converter includes a step-down switching element and a step-down diode, and also functions to step down the voltage of regenerative power supplied from the inverter side and supply it to the battery. The controller limits the current of the regenerative power supplied from the inverter side to a current limit value or less determined based on the duty ratio applied to the step-down switching element and the refrigerant temperature. By providing the above configuration, overheating of the power element can be prevented not only during power running but also during regeneration.

  Since the diode is weaker to overheating than the switching element, overheating of the switching element can be prevented by the current limit value determined by paying attention to the diode.

  Details and further improvements of the technology disclosed in this specification will be described in the following “DETAILED DESCRIPTION”.

It is a block diagram of the electric power system of the electric vehicle of an Example. It is an example of the map of a current limiting value. It is a flowchart of an example of the current limiting process which a controller performs.

  An electric vehicle 2 according to an embodiment will be described with reference to the drawings. In FIG. 1, the block diagram of the electric power system of the electric vehicle 2 is shown. Note that FIG. 1 does not necessarily show all units included in the electric vehicle 2.

  The electric vehicle 2 according to the embodiment is an electric vehicle that travels by driving a traveling motor 22 with electric power of a battery 12. The battery 12 is connected to the voltage converter 3 via the system main relay 13. The voltage converter 3 has a boosting function that boosts the voltage of the battery 12 and supplies the boosted voltage to the inverter 21, and a step-down function that steps down the power generated by the motor 22 and supplies it to the battery 12. The AC power generated by the motor 22 is input to the voltage converter 3 after the inverter 21 converts it to DC power. Since the circuit configuration of the inverter 21 is well known, description thereof is omitted.

  The battery side of the voltage converter 3 is referred to as a low voltage end, and the inverter side is referred to as a high voltage end. In each of the low voltage end and the high voltage end, the higher potential side is referred to as a positive electrode.

  A current sensor 15 and a current limiter 14 are connected between the positive electrode of the battery 12 and the positive electrode at the low voltage end of the voltage converter 3. A current sensor 18 and a current limiter 19 are also connected between the positive electrode at the high voltage end of the voltage converter 3 and the positive electrode of the inverter 21. The current limiters 14 and 19 can limit the flowing current according to a command from the controller 9 described later. In addition, voltage sensors 16 and 17 for measuring voltage are connected to the low voltage end side and the high voltage end side of the voltage converter 3, respectively. Furthermore, a capacitor 20 for smoothing the current input to the inverter 21 is connected to the input terminal of the inverter 21.

  The electric vehicle 2 includes a controller 9 that controls the voltage converter 3, the inverter 21, the system main relay 13, and the current limiters 14 and 19. The controller 9 determines the output (target output) of the motor 22 based on the vehicle speed and the accelerator opening, and applies the PWM signal or inverter 21 to the switching elements 6a and 6b of the voltage converter 3 so as to realize the target output. PWM signal is generated and output. Normally, the electric vehicle 2 performs various processes in cooperation with a plurality of controllers. In FIG. 1, the plurality of controllers are represented by a single controller 9. The switching elements 6a and 6b are typically IGBTs.

  The voltage converter 3 includes a capacitor 4, a reactor 5, a step-up switching element 6b, a step-up diode 7a, a step-down switching element 6a, and a step-down diode 7b. The voltage converter 3 is provided with a cooler 26 for cooling the switching elements 6a and 6b, the diodes 7a and 7b, the reactor 5, and the capacitor 4. The cooler 26 circulates the refrigerant to cool components such as a diode. The cooler 26 is provided with a temperature sensor 25 that measures the temperature of the refrigerant.

  The capacitor 4 is connected in parallel to the low voltage end of the voltage converter 3. Reactor 5 has one end connected to the positive electrode side of capacitor 4 and the other end connected to an intermediate point between step-down switching element 6a and step-up switching element 6b. The step-up switching element 6b and the step-down switching element 6a are directly connected, and the step-down switching element 6a is located on the high potential side. The step-up diode 7a is connected in antiparallel with the step-down switching element 6a, and the step-down diode 7b is connected in antiparallel with the step-up switching element 6b.

  The circuit of the voltage converter 3 will be described by function as follows. The booster circuit includes a capacitor 4, a reactor 5, a boosting switching element 6b, and a boosting diode 7a. The step-up switching element 6b and the step-up diode 7a are connected in series, and one end of the reactor 5 is connected to an intermediate point thereof. The other end of the reactor is connected to the positive electrode at the low voltage end. The capacitor 4 is connected in parallel to the low voltage end. The step-down circuit includes a capacitor 4, a reactor 5, a step-down switching element 6a, and a step-down diode 7b. The step-down switching element 6a and the step-down diode 7b are connected in series, and one end of the reactor is connected to the middle point. The other end of the reactor is connected to the positive electrode at the low voltage end. The capacitor 4 is connected in parallel to the low voltage end.

  As is well known, the step-up operation of the voltage converter 3 shown in FIG. 1 is as follows. When the boosting switching element 6b is ON, electric energy is stored in the reactor 5, and when it is OFF, the electric energy is converted to a current and flows through the boosting diode 7a, so that the voltage at the high voltage end is higher than that at the low voltage end. Get higher. A desired boost ratio can be obtained by appropriately selecting a PWM (Pulse Width Modulation) signal to be supplied to the boost switching element 6b. The step-down operation is as follows. While the step-down switching element 6a is ON, electric energy is accumulated in the reactor 5 by the electric power from the high-voltage end. While the step-down switching element 6a is OFF, the current input from the high-voltage end is interrupted, but the reactor The electric energy stored in 5 circulates through the step-down diode 7b, and the voltage at the low voltage end is maintained.

  According to the above configuration, in the step-up operation, the higher the duty ratio of the step-up switching element 6b (the shorter the OFF time), the larger the current flowing through the step-up diode 7a. Similarly, in the step-down operation, the higher the duty ratio of the step-down switching element 6a (the shorter the OFF time), the more current flows through the step-down diode 7b. The more current that flows, the greater the amount of heat generated by the diode.

  As described above, the elements in the voltage converter 3 are cooled by the cooler 26. However, if a large current continues to flow, the cooler 26 cannot suppress the temperature rise, and the temperature of each element rises. When the element is overheated, the performance of the voltage converter 3 is degraded. Further overheating can damage the device. In particular, the diodes 7a and 7b are vulnerable to heat compared to other elements. Therefore, the electric vehicle 2 limits the input current in order to suppress overheating of the diodes 7a and 7b.

  The current limitation when the voltage converter 3 boosts the voltage of the battery 12 and supplies it to the inverter 21 (during power running) will be described. The current limitation when the motor 22 generates power and the voltage converter 3 steps down the output DC voltage of the inverter 21 and supplies it to the battery 12 (during regeneration) will be described later.

  In the case of power running, the low voltage end of the voltage converter 3 is the input side. In the case of powering, a current flows through the boosting diode 7a. More specifically, during the step-up operation of the voltage converter 3, a current flows through the step-up diode 7a corresponding to the ON / OFF operation of the step-up switching element 6b. Therefore, the current flowing through the boosting diode 7a is determined by the duty ratio of the PWM signal applied to the boosting switching element 6b. The amount of heat generated by the boosting diode 7a depends on temperature and flowing current. Therefore, the controller 9 determines a limit value (current limit value Ib_Lmt) for limiting the input current to the voltage converter 3 using the temperature and the duty ratio as parameters. Here, the temperature is the refrigerant temperature Tw of the cooler that cools the voltage converter 3 including the boosting diode 7a. As described above, the cooler 26 includes the temperature sensor 25 that measures the refrigerant temperature Tw. The controller 9 acquires the refrigerant temperature Tw from the temperature sensor 25. Further, the duty ratio Dt of the PWM signal applied to the boosting switching element 6b is determined according to the accelerator opening and the vehicle speed in another process executed by the controller 9.

  The upper limit value of the input current (that is, the current limit value Ib_Lmt) for preventing the boosting diode 7a from being damaged at the specific duty ratio Dt and the specific refrigerant temperature Tw can be specified in advance by experiments or simulations. it can. Therefore, the controller 9 stores a map of the current limit value Ib_Lmt using the duty ratio Dt and the refrigerant temperature Tw as parameters. Reference numeral 10 in FIG. 1 indicates a map of the current limit value Ib_Lmt. The controller 9 refers to the map 10 and specifies the current limit value Ib_Lmt from the measurement data of the temperature sensor 25 and the duty ratio determined by itself, and the current input from the battery 12 to the voltage converter 3 is equal to or less than the current limit value Ib_Lmt. The current limiter 14 is controlled so that

  FIG. 2 shows an example of a map of the current limit value Ib_Lmt. In the graph of FIG. 2, the horizontal axis indicates the duty ratio Dt (%), and the vertical axis indicates the current limit value Ib_Lmt (A). The solid line is a graph of the current limit value Ib_Lmt when the refrigerant temperature Tw is equal to or lower than the threshold temperature Tw_h, and the broken line is a graph of the current limit value Ib_Lmt when the refrigerant temperature Tw is larger than the threshold temperature Tw_h. As shown in FIG. 2, the current limit value Ib_Lmt decreases as the duty ratio Dt increases. Moreover, the current limit value Ib_Lmt decreases as the refrigerant temperature Tw increases. Here, the threshold temperature Tw_h is a temperature determined in advance by experiment or simulation. Note that “duty ratio” indicates the ratio of the ON time to the period of the PWM signal. Therefore, as the duty ratio Dt increases, the ON time of the switching element becomes longer and the OFF time becomes relatively shorter. When the duty ratio Dt is increased, the OFF time of the boosting switching element 6b is shortened, and as a result, the current flowing through the boosting diode 7a is increased. Therefore, the current limit value Ib_Lmt is decreased as the duty ratio Dt is increased, and the heat generation of the boosting diode 7a is suppressed. Further, the higher the refrigerant temperature Tw, the more easily the boosting diode 7a is damaged. Thus, the higher the refrigerant temperature Tw, the smaller the current limit value Ib_Lmt, thereby preventing the boost diode 7a from generating heat. In the example of FIG. 2, the refrigerant temperature range is classified into two ranges, a range exceeding the threshold temperature Tw_h and a range below Tw_h, but the range above the threshold temperature Tw_h (Tw ≧ Tw_h) and the threshold temperature Tw_h. You may classify | categorize into the range below (Tw <Tw_h). In the example of FIG. 2, the refrigerant temperature is classified into only two types, a range exceeding the threshold temperature Tw_h and a range below Tw_h. However, it is also preferable to classify the refrigerant temperature Tw into three or more ranges. is there. The controller 9 stores, as a map, the relationship between the duty ratio Dt and the current limit value Ib_Lmt with respect to the refrigerant temperature Tw illustrated in FIG.

  With reference to FIG. 3, an example of the voltage limiting process which the controller 9 performs is demonstrated. The process of FIG. 3 shows the current limiting process during powering. In summary, the controller 9 determines the limit value Ib_Lmt of the current Ib input to the voltage converter 3 from the temperature Tw of the refrigerant that cools the voltage converter 3 and the duty ratio Dt of the step-up switching element 6b, and becomes equal to or less than the IB_Lmt. Thus, the input current to the voltage converter 3 is limited.

  First, the controller 9 measures the refrigerant temperature Tw using the temperature sensor 25 (S2). Next, the controller 9 acquires the duty ratio Dt determined by itself (S3). As described above, the duty ratio Dt is determined by the controller 9 based on the vehicle speed, the accelerator opening, and the like in a routine different from the process shown in FIG. Next, the controller 9 determines a current limit value Ib_Lmt corresponding to the measured refrigerant temperature Tw and the acquired duty ratio Dt with reference to the map 10 shown as an example in FIG. 2 (S4).

  Next, the controller 9 measures the input current Ib using the current sensor 15 (S5). Next, the controller 9 measures the input voltage VL to the voltage converter 3 using the voltage sensor 16 (S6). The voltage VL corresponds to the voltage at the low voltage end of the voltage converter 3. Next, the controller 9 calculates a power difference dW = (Ib_Lmt−Ib) × VL (S7). Here, the power difference dW is obtained by multiplying the difference between the current limit value Ib_Lmt and the current actual input current Ib by the current input voltage VL. In other words, this power difference is the difference between the maximum power that can be received in the range where the boosting diode 7a does not overheat under the conditions of the current refrigerant temperature Tw and the duty ratio Dt and the actual power that is currently received. It is. If Ib_Lmt> Ib, the power difference dW is a positive value, and if Ib_Lmt <Ib, the power difference dW is a negative value. The former still has a margin up to the current limit value, and the current input to the voltage converter 3 can be increased. The latter has already exceeded the current limit value, and in this case, it is necessary to reduce the current Ib input to the voltage converter 3.

  Next, the controller 9 updates the target power Wt of the voltage converter 3 by adding dW (S8). Finally, the controller 9 controls the current limiter 14 so that the input power to the voltage converter 3 becomes the updated target power Wt (S9). Thus, the controller 9 limits the current Ib input to the voltage converter 3 so as to be equal to or less than the current limit value Ib_Lmt determined based on the duty ratio Dt of the PWM signal applied to the switching element and the refrigerant temperature Tw.

  In the process of the flowchart of FIG. 3, a parameter called power difference dW is introduced. However, the power difference dW is based on the difference between the current limit value Ib_Lmt and the measured input current Ib, and the current limiter 14 directly controls the input current Ib. The input current is controlled to be equal to or less than the limit value Ib_Lmt.

  In the above description, the current limiting process during powering that drives the motor 22 with the power of the battery 12 has been described. At the time of regeneration, that is, when charging the battery 12 with the power generated by the motor 22, the voltage converter 3 steps down the voltage VH applied to the high voltage end and outputs it to the low voltage end. The controller 9 executes the same current limiting process as in the flowchart of FIG. 3 during regeneration. In the process in that case, the duty ratio Dt acquired in step S3 is the duty ratio of the PWM signal for the step-down switching element 6a. Also, “input current Ib” in step S5 is replaced with “current measured by current sensor 18”, and “low voltage VL” in step S5 is replaced with “high voltage VH”. The high-voltage side voltage VH is measured by the voltage sensor 17 (see FIG. 1). Further, step S9 is changed to “limit the current input to the high voltage end by the current limiter 19 so that the target power Wt is obtained”. In addition to the map illustrated in FIG. 2, the controller 9 stores a correspondence map of the duty ratio Dt of the step-down switching element 6a and the current limit value Ib_Lmt for the step-down diode 7b with respect to the refrigerant temperature Tw. In time, refer to the map. The controller 9 stops the current limiter 19 during power running and limits the input current to the low-voltage end side by the current limiter 14, and stops the current limiter 14 during regeneration and stops the current limiter 19 by the current limiter 19. Limit the input current to.

  In the electric vehicle 2 of the embodiment, the input current Ib to the voltage converter 3 is determined based on the temperature Tw of the refrigerant that cools the power elements (switching elements and diodes) of the voltage converter 3 and the duty ratio Dt of the switching elements. It limits so that it may become below current limiting value Ib_Lmt. The electric vehicle 2 determines the current limit value depending not only on the refrigerant temperature but also on the duty ratio. Since the current limit value is determined by the two parameters, the value becomes a more appropriate value. Therefore, the performance of the vehicle can be sufficiently extracted without excessively limiting the input current to the voltage converter.

  Points to be noted for the technology described in the embodiments will be described. The flowchart of FIG. 3 is an example of a current limiting process. Steps S6, S7, and S8 may be skipped, and the process of step S9 may be “control the current limiter 14 so that the input current Ib is equal to or less than the current limit value Ib_Lmt”.

  In the electric vehicle 2 of the embodiment, the current input to the voltage converter 3 is limited by the current limiters 14 and 19. Instead of the current limiter, the input current may be lowered by lowering the duty ratio of the voltage converter 3. In this case, the duty ratio Dt acquired in step S3 and the duty ratio after step S9 are changed. However, the duty ratio Dt converges so that the input current Ib becomes equal to or less than the current limit value Ib_Lm while the current limit process is repeatedly executed in a specific cycle. Here, the specific cycle is a control cycle of the controller 9, for example. During regeneration, the input current to the voltage converter 3 may be limited by reducing the output current of the inverter 21.

  Specific examples of the present invention have been described in detail above, but these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and changes of the specific examples illustrated above. The technical elements described in this specification or the drawings exhibit technical usefulness alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing. In addition, the technology exemplified in this specification or the drawings can achieve a plurality of objects at the same time, and has technical usefulness by achieving one of the objects.

2: Electric vehicle 3: Voltage converter 4: Capacitor 5: Reactor 6a, 6b: Switching element 7a, 7b: Diode 9: Controller 10: Map 12: Battery 13: System main relay 14, 19: Current limiter 15, 18: Current sensors 16, 17: Voltage sensor 20: Capacitor 21: Inverter 22: Motor 25: Temperature sensor 26: Cooler

Claims (4)

A voltage converter that includes a switching element and a diode, boosts the output voltage of the battery, and supplies the boosted voltage to the inverter;
A cooler that cools the voltage converter with a refrigerant;
A controller that limits the input current to the voltage converter below a current limit value determined based on the duty ratio of the PWM signal applied to the switching element and the refrigerant temperature;
An electric vehicle characterized by comprising:   The electric vehicle according to claim 1, wherein the controller stores a map of current limit values using the duty ratio and the refrigerant temperature as parameters.   The electric vehicle according to claim 1, wherein the controller decreases the current limit value as the duty ratio increases, and decreases the current limit value as the refrigerant temperature increases. The voltage converter further includes a step-down switching element and a step-down diode, and has a function of stepping down the voltage of regenerative power supplied from the inverter side and supplying the voltage to the battery,
The controller limits the current of regenerative power supplied from the inverter side to a current limit value or less determined based on a duty ratio applied to the step-down switching element and the refrigerant temperature. The electric vehicle according to any one of the above.

Images