JPH11220812A - Electric vehicle electric system - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To prevent reduction in traction characteristics and maximum driving speed of a vehicle, and to maintain high vehicle driving performance and system efficiency. An electric system of an electric vehicle that supplies electric power of a DC power supply to a wheel driving motor through a wheel driving semiconductor power converter such as an inverter and drives the vehicle by driving the motor at a variable speed, or The present invention relates to an electric system of an electric vehicle using both an engine and a DC power supply as power sources. Power storage device 1 or power storage device 4 as the DC power supply
A step-up / step-down chopper 200 is connected between the inverter 0 and the inverter 2 or the semiconductor power converter 100, and the chopper 200 is controlled so that the DC input voltage of the inverter 2 or the like becomes substantially constant.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention is applied to an electric vehicle powered only by a DC power source or a hybrid electric vehicle powered by an engine and a DC power source.
The present invention relates to an electric system of an electric vehicle.

[0002]

2. Description of the Related Art FIG. 6 shows an electric system (drive system) of a typical electric vehicle running using a power storage device as a DC power supply. In the figure, 1 denotes a power storage device, 2 denotes an inverter as a wheel driving semiconductor power converter, 3 denotes a wheel driving AC motor, 4 denotes a speed reducer, 5 denotes a differential gear, and 6 denotes wheels. 7 is an auxiliary battery, 8 is a power storage device 1
A DC / DC converter as a charging semiconductor power converter for charging the auxiliary battery 7 from the power supply, and 9 is an auxiliary device such as a lighting device and a pump.

In the system shown in FIG. 6, a secondary battery, which is a chemical battery, is used as the power storage device 1. The DC power of the power storage device 1 is converted into a variable voltage and a variable frequency AC voltage by an inverter 2 by an electric motor 3. And drives the motor 3 at a variable speed to drive the vehicle. Here, an electric system using a solar cell, a fuel cell, or the like as a DC power supply is also well known. Also in this case, the configuration of the electric system is basically the same as that of FIG.

FIG. 7 shows an electric system of a typical series hybrid electric vehicle. 6, the same components as those in FIG. 6 are denoted by the same reference numerals. 7, 10 is an engine, 20 is a generator, and 30 is AC / D.
C converter and 40 indicate a power storage device, respectively. In the system of FIG. 7, the mechanical energy of the engine 10 is converted into electric energy by the generator 20, and the electric energy is supplied to the electric motor 3 via the AC / DC converter 30 and the inverter 2 to be converted into mechanical energy again. And drive the vehicle. The generator 20 outputs substantially constant power, and the difference between the generated power and the power required by the motor 3 is covered by charging and discharging from the power storage device 40. The system of FIG. 7 is called a series type because the flow of energy for driving the vehicle is serial.

FIG. 8 shows an electric system of a typical parallel hybrid electric vehicle. 6, the same components as those in FIGS. 6 and 7 are denoted by the same reference numerals.
8, reference numeral 60 denotes a clutch; 70, a generator motor having both functions of a generator and a motor; 80, a transmission; 100, a DC power of the power storage device 40 which is converted into a variable voltage and a variable frequency AC voltage to generate power. It is a semiconductor power converter supplied to the motive 70.

In the system shown in FIG. 8, it is possible to drive wheels only by the engine 10, drive wheels only by the electric motor (generator 70), and drive wheels by the power of both the engine 10 and the electric motor. The power storage device 40 is charged by the power generation motive 7
0 is operated as a generator and is performed via the semiconductor power converter 100. Note that the present invention does not mainly provide a drive system for a parallel hybrid electric vehicle, and thus a detailed description of the present system will be omitted.

[0007]

For example, in the system shown in FIG. 6, when a secondary battery is used as a power storage device and the AC motor is driven at a variable speed via an inverter using the power of the secondary battery, the first problem is that Another problem is that the traction characteristics of an electric vehicle in the middle / high-speed range are greatly affected by the battery voltage value. FIG. 9 shows speed-torque (traction force) characteristics of the AC motor using the battery voltage as a parameter. In the figure, a is the tractive force characteristic when the battery is almost fully charged, b is the tractive force characteristic when the battery is almost in the discharge end state (state immediately before discharge end), and c is the running resistance characteristic. From this figure, it can be seen that the torque characteristics in the middle / high speed range greatly change according to the level of the DC input voltage (battery voltage) of the inverter.

Since the difference between the characteristic a or b and the characteristic c in FIG. 9 determines the acceleration performance of the vehicle, the acceleration performance of the vehicle is greatly affected by the level of the battery voltage. Also, since the intersection of the characteristic a or b and the characteristic c indicates the maximum operating speed, it is apparent from FIG. 3 that the maximum operating speed decreases as the battery voltage decreases. If the output of the inverter or the motor is further increased, the target characteristics can be ensured even if the battery voltage decreases, but problems such as an increase in the size, weight, and cost of the device occur.

A second problem in the case where a secondary battery is used as a power storage device and the AC motor is driven at a variable speed via the inverter by the use of the power is the second problem that the voltage of the secondary battery greatly fluctuates. That is, the operating voltage of the motor fluctuates greatly. FIG. 10 shows a typical example of the current-voltage characteristics of a secondary battery as a chemical battery in a charge mode and a discharge mode in each of a substantially fully charged state and a substantially terminated state. In the drawing, a is a characteristic in a substantially fully charged state, b is a characteristic in a substantially discharge terminated state,
c is the rated voltage of the secondary battery, d is the maximum allowable voltage during charging,
e indicates the maximum power limit line of the inverter during discharging, and f indicates the maximum power limit line of the inverter during charging. The inverter operates inside both limit lines e and f.

As is apparent from FIG. 1, even when the battery is fully charged during powering (discharging when viewed from the battery), the DC input voltage (battery voltage) of the inverter is constant according to the battery characteristics. The operating point B is lower than the operating point A on c, and further decreases to the operating point C as the battery is discharged.
Further, during regenerative braking (when charging as viewed from the battery), the operating point shifts from D to E, and operation is performed at a voltage limited by the allowable maximum voltage d of the battery. When this is viewed from the inverter, the input voltage greatly fluctuates from the maximum voltage operating point E to the minimum voltage operating point C. In the illustrated example,
It varies between + 20% and -30% with respect to the rated voltage c of the secondary battery.

The inverter must operate even at the maximum voltage at the time of charging, and must be capable of exhibiting predetermined vehicle characteristics even at a voltage (operating point C in the illustrated example) which has been reduced to almost the discharge end state. In order to ensure good vehicle performance even at the battery voltage immediately before the end of discharge, in the example shown in the figure, the output is about 1.7 as compared with the case where the battery is operated at a constant voltage.
Equipment that is twice as large is required. For this reason, there is a disadvantage that the size, weight, and cost of the device are increased as in the first problem.

FIG. 11 shows the combined efficiency of the inverter and the motor with respect to the DC input voltage of the inverter when the efficiency is designed to be maximum at the rated voltage. It can be seen from the figure that when the DC input voltage of the inverter fluctuates significantly, the efficiency also drops significantly. Since the reduction in efficiency is a very serious problem for electric vehicles, the third problem is that the efficiency is reduced due to the fluctuation of the battery voltage. Each of the above-mentioned problems has been described using an example in which a secondary battery that is a chemical battery is used as a power storage device of an electric vehicle.However, a physical battery such as an electric double layer capacitor or another secondary battery is used as a power storage device. A similar problem arises when the battery is used or when various DC power sources such as a solar cell and a fuel cell are used, since the DC voltage greatly fluctuates.

[0013] Therefore, the present invention is to maintain a substantially constant DC input voltage of a semiconductor power converter such as an inverter,
An object of the present invention is to provide an electric system of an electric vehicle that can prevent a decrease in traction characteristics and a maximum driving speed of a vehicle and maintain high vehicle driving performance and system efficiency.

[0014]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a vehicle-mounted DC power source (generically referring to a secondary battery, an electric double layer capacitor, a solar battery, a fuel cell, etc.) and a wheel drive such as an inverter. By inserting a step-up / step-down chopper between the semiconductor power converter and the semiconductor power converter, the DC input voltage of the semiconductor power converter is maintained at a substantially constant value. As a result, it is possible to prevent the traction characteristics and the maximum driving speed of the vehicle in the middle / high speed range of the electric vehicle from being reduced and the efficiency of the device from being reduced.

That is, according to the first aspect of the present invention, an electric vehicle which supplies a power of a DC power supply to a motor for driving a wheel via a semiconductor power converter for driving a wheel and drives the motor at a variable speed to drive a vehicle. In the above electric system, a step-up / step-down chopper is connected between the DC power source and the wheel driving semiconductor power converter.

According to a second aspect of the present invention, the power of a generator connected to an engine is supplied to a DC power supply via a charging semiconductor power converter, and the power of the DC power supply is supplied to a wheel driving semiconductor power supply. In an electric system of an electric vehicle, which supplies a power to a wheel driving motor via a converter and drives a vehicle with the power of the generator and the DC power supply, the electric power system moves up and down between the DC power supply and the wheel driving semiconductor power converter. A pressure chopper is connected.

Further, according to the present invention, the wheels are driven by the power of the engine, or the power of the DC power supply is supplied to the motor for driving the wheels via the semiconductor power converter to drive the motor at a variable speed. An electric system of an electric vehicle that drives the vehicle by this and charges the DC power by a generator connected to an engine, wherein a buck-boost chopper is connected between the DC power and the semiconductor power converter. is there.

As described in claims 4 and 5, a secondary battery or an electric double layer capacitor can be used as the DC power supply in the invention described in claim 1, 2 or 3. Further, as described in claims 6 and 7, a solar cell or a fuel cell may be used as the DC power supply in the invention described in claim 1.

Further, as described in claim 8, in the inventions described in claims 1 to 7, the switching operation of the step-up / step-down chopper causes the DC input voltage of the semiconductor power converter connected to the output side to be increased. The control is performed so as to be substantially constant.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows a first embodiment of the present invention, and corresponds to the first, fourth, and eighth aspects of the present invention.
The same components as those in FIG. 6 are denoted by the same reference numerals.
In FIG. 1, reference numeral 200 denotes a step-up / step-down chopper (polarity inversion chopper) connected between a power storage device 1 and a DC input side of an inverter 2 serving as a wheel driving semiconductor power converter. Show. In FIG.
Reference numeral 02 denotes a filter capacitor provided on the input side and the output side of the chopper 200, and the polarities of the voltages are opposite to each other as shown in the figure. One of the filter capacitors 201 is connected to the power storage device 1, and the other filter capacitor 202 is connected to the DC input side of the inverter 2.

Switching transistors 203 and 204 are connected in series between the positive electrode of the filter capacitor 201 and the negative electrode of the filter capacitor 202, and a diode 205 and a switching transistor 203 are connected to these transistors 203 and 204.
Reference numerals 206 are connected in anti-parallel. Further, the connection point between the transistors 203 and 204 and the capacitor 2
The reactor 207 is connected between the negative electrode 01 (the positive electrode of the capacitor 202). In addition, the power storage device 1
For example, it is constituted by a secondary battery as a chemical battery.

Since the control operation of the step-up / step-down chopper 200 is already known, its outline will be described here. During power running, only the transistor 203 is subjected to switching control, and the transistor 204 is turned off. The accumulation and release of energy in the reactor 207 are repeated by turning on and off the transistor 203, and at the time of release, DC power whose polarity is inverted to that of the output of the power storage device 1 is supplied to the inverter 2. During regenerative braking, on the contrary, the transistor 20
Only the switching control of the inverter 4 is performed to turn off the transistor 203, the polarity of the DC output of the inverter 2 is inverted, and the power storage device 1 is regenerated.

FIG. 3 shows an example of operating characteristics of the step-up / step-down chopper 200 during power running. When the input voltage and the output voltage of the chopper 200 are equal, the conduction ratio α of the transistor 203 is 0.5, and when the input voltage becomes higher than the output voltage, the conduction ratio α becomes smaller than 0.5, Becomes lower than the output voltage, the conduction ratio α becomes larger than 0.5. That is, a constant output voltage can be obtained by adjusting the conduction ratio α according to the input voltage. Here, the maximum value of the input voltage corresponds to the maximum voltage d (or operating point E) in FIG. 10, the minimum value of the input voltage corresponds to the operating point C in FIG. 10, and the output voltage is the rated voltage in FIG. c (or operating point A). That is, the switching operation of the buck-boost chopper 200 according to the power running operation and the regenerative braking operation causes the DC input voltage of the buck-boost chopper 200 (the power storage device 1).
) Fluctuates, the output voltage can be kept constant and the DC input voltage of the inverter 2 can be kept constant.

FIG. 4 shows a second embodiment of the present invention, and corresponds to the second embodiment of the present invention. In this embodiment, the present invention is applied to the series hybrid electric vehicle shown in FIG.
Step-up / step-down chopper 2 between the DC input side of
The configuration is the same as that of FIG. 7 except that 00 is connected.
The operation of the chopper 200 in this embodiment is similar to that of the first embodiment, and the DC input voltage of the inverter 2 can be kept constant regardless of the voltage fluctuation of the power storage device 40.

FIG. 5 shows a third embodiment of the present invention, and corresponds to the third embodiment of the present invention. This embodiment is an application of the present invention to the above-described parallel hybrid electric vehicle shown in FIG. 8, except that a buck-boost chopper 200 is connected between the DC side of the semiconductor power converter 100 and the power storage device 40. , And FIG. The operation of the chopper 200 is the same as in the first and second embodiments, and the DC input voltage of the semiconductor power converter 100 can be kept constant regardless of the voltage fluctuation of the power storage device 40.

In each of the above embodiments, a case has been described in which a power storage device composed of a chemical secondary battery is used as a DC power supply. However, the present invention is not limited to a physical battery such as an electric double layer capacitor. Of course, the present invention can be applied to a system using a DC power supply having a voltage fluctuation such as a power storage device, a solar cell, and a fuel cell.

[0027]

As described above, the present invention provides a chemical secondary battery,
In an electric vehicle powered by a DC power supply consisting of an electric double layer capacitor, a solar cell, a fuel cell, or the like, or a hybrid electric vehicle using both the DC power supply and an engine, a DC power supply and a semiconductor power converter for driving wheels. The DC input voltage of the semiconductor power converter is kept almost constant by the operation of the step-up / step-down chopper connected between the converter and the converter.

Therefore, the following effects can be obtained. (1) Since the operating voltages of devices such as inverters and electric motors can be kept substantially constant, an optimal design at these operating points becomes possible, and the size, weight and cost of the devices can be reduced. Further, even if the operating points of these devices change, high system efficiency can be obtained without lowering the traction force characteristics, the maximum operation speed, the efficiency, and the like. (2) Since it can be applied to various DC power sources such as a chemical secondary battery having a large voltage fluctuation, an electric double layer capacitor, a solar cell, and a fuel cell, it can contribute to the spread and development of electric vehicles.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing a first embodiment of the present invention.

FIG. 2 is a circuit diagram showing a configuration of a step-up / step-down chopper in FIG. 1;

FIG. 3 is an operation explanatory diagram of the step-up / step-down chopper in FIG. 1 during power running.

FIG. 4 is a configuration diagram showing a second embodiment of the present invention.

FIG. 5 is a configuration diagram showing a third embodiment of the present invention.

FIG. 6 is a diagram showing an electric system of an electric vehicle using a conventional secondary battery as a power source.

FIG. 7 is a diagram showing an electric system of a series hybrid electric vehicle.

FIG. 8 is a diagram showing an electric system of a parallel hybrid electric vehicle.

9 is a speed-torque characteristic diagram of an electric motor in the system of FIG.

FIG. 10 is a voltage-current characteristic diagram of the secondary battery in the system of FIG.

FIG. 11 is a diagram showing the efficiency of the device in the system of FIG. 6;

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 power storage device 2 inverter 3 wheel drive AC motor 4 reduction gear 5 differential gear 6 wheels 7 auxiliary battery 8 DC / DC converter 9 auxiliary device 10 engine 20 generator 30 AC / DC converter 40 power storage device 60 clutch 70 generator motor 80 transmission Reference Signs List 100 semiconductor power converter 200 step-up / step-down chopper 201, 202 filter capacitor 203, 204 switching transistor 205, 206 diode 207 reactor

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Yoshiaki Yamada Nissan Diesel Industry Co., Ltd. Inside the corporation

Claims (8)

[Claims] An electric system for an electric vehicle that supplies power of a DC power supply to a wheel driving motor via a wheel driving semiconductor power converter and drives the motor at a variable speed to drive a vehicle. An electric system for an electric vehicle, wherein a step-up / step-down chopper is connected between the power converter and the wheel driving semiconductor power converter. 2. The power supply of a generator connected to an engine is supplied to a DC power supply via a semiconductor power converter for charging, and the power of the DC power supply is supplied to the DC power supply via a semiconductor power converter for driving wheels. An electric system for an electric vehicle that supplies a motor and drives a vehicle with the power of the generator and the DC power supply, wherein a step-up / step-down chopper is connected between the DC power supply and the wheel driving semiconductor power converter. And the electric system of the electric vehicle. 3. The vehicle is driven by driving the wheels by the power of an engine or by supplying the power of a DC power supply to a motor for driving the wheels via a semiconductor power converter to drive the motor at a variable speed. An electric system for an electric vehicle that charges the DC power supply with a generator connected to an engine, wherein a buck-boost chopper is connected between the DC power supply and the semiconductor power converter. . 4. The electric system for an electric vehicle according to claim 1, wherein the DC power supply is a secondary battery as a chemical battery. 5. The electric system for an electric vehicle according to claim 1, wherein the DC power supply is an electric double layer capacitor. 6. The electric system for an electric vehicle according to claim 1, wherein the DC power supply is a solar cell. 7. The electric system for an electric vehicle according to claim 1, wherein the DC power supply is a fuel cell. 8. The method of claim 1, 2, 3, 4, 5, 6, or 7.
The electric system for an electric vehicle according to claim 1, wherein the switching operation of the step-up / step-down chopper controls the DC input voltage of the semiconductor power converter connected to the output side to be substantially constant. system.