阅读说明：本技术 逆变装置和车辆控制装置 (Inverter device and vehicle control device ) 是由 中岛明生 于 2020-03-27 设计创作，主要内容包括：本发明的课题在于提供一种逆变装置和车辆控制设备,其中,可防止在车辆出发等的马达旋转的开始时,电流偏到一部分的相的开关元件以使该开关元件损伤的情况,或者通过该防止的控制,转矩不足的情况可改善。逆变装置包括逆变器(1)和控制部(9),该逆变器(1)通过各相的半导体开关元件(3)的开闭,将直流电流变换为与马达(10)的形式相对应的交流电流。控制部(9)在启动上述马达(10)后等时的马达(10)的转数小于阈值的场合,施加电流限制。另外,控制部(9)在表示开关元件(3)的使用状况的已确定的事项满足设定条件的场合,减缓上述电流限制。表示上述使用状况的已确定的事项比如,为开关元件(3)或其冷却用的冷却水的测定温度,此外,也可采用经历时间。(The present invention addresses the problem of providing an inverter device and a vehicle control device that can prevent a switching element of a phase whose current is partially biased to damage the switching element at the start of motor rotation such as when a vehicle starts, or can prevent torque shortage from being reduced by the control of the prevention. The inverter device is provided with an inverter (1) and a control unit (9), wherein the inverter (1) converts a direct current into an alternating current corresponding to the form of a motor (10) by opening and closing semiconductor switching elements (3) of each phase. The control unit (9) limits the current when the number of rotations of the motor (10) is less than a threshold value after the motor (10) is started or the like. The control unit (9) slows down the current limitation when a predetermined item indicating the use state of the switching element (3) satisfies a set condition. The predetermined items indicating the use state are, for example, the measured temperature of the switching element (3) or the cooling water for cooling the switching element, and the elapsed time.)

1. An inverter device including an inverter for converting a direct current into an alternating current corresponding to a form of a motor to be driven by opening and closing switching elements each including a semiconductor of each phase, and a control unit for controlling the inverter,

the control unit applies a current limit when the number of revolutions of the motor is smaller than a threshold value after the motor is started, and reduces the current limit when a predetermined item indicating the usage state of the switching element satisfies a set condition.

2. The inverter device according to claim 1, wherein the determined event indicating the use state of the switching element includes an event of a temperature directly or indirectly measured by the switching element.

3. The inverter device according to claim 2, wherein the current limit is reduced when a temperature of cooling water for cooling the inverter is lower than a set temperature.

4. The inverter according to claim 2, wherein the current limit is reduced when a measured temperature of a temperature sensor that measures a temperature of the switching element is lower than a set temperature.

5. The inverter device according to claim 1, wherein the determined event indicating the use condition of the switching element includes an elapsed time from the start of energization or from the time when a current value exceeds a set value.

6. The inverter device according to claim 1, wherein the case where the predetermined items indicating the use states of the switching elements satisfy the setting conditions includes: the temperature of the cooling water for cooling the inverter is less than a set temperature, the temperature of the temperature sensor for measuring the temperature of the switching element is less than the set temperature, and the elapsed time is set.

7. A vehicle control device, wherein the inverter device according to any one of claims 1 to 6 is mounted, and the motor is a motor for driving a vehicle.

Technical Field

The present invention relates to an inverter device for controlling a motor and a vehicle control apparatus equipped with the same.

Background

Fig. 1 shows a concept of a general in-wheel system electric vehicle. The specific structure thereof will be described in connection with the embodiment for carrying out the invention. A VCU (vehicle control unit) 14 reads an accelerator operation angle of a driver, converts the accelerator operation angle into a torque command, and executes the torque command in the inverter device 1A. The inverter device 1A converts electric power from the battery 2 into three-phase alternating current based on a torque command, and controls the corresponding motor 10. In this case, 2 inverter devices may be used, but the inverter device 1A of the present example is 2-shaft integrated, and can drive 2 motors 10. The present example is rear wheel drive, but front wheel drive and 4 wheel drive can be realized by the same structure.

Fig. 7 shows a basic structure of a 1-axis inverter 1A. In the example of fig. 1, 2 sets of this basic structure are employed.

The inverter device 1A includes an inverter 1 constituting a strong electric circuit and a control unit 9 for controlling the inverter 1, and the inverter device 1A is mounted on a vehicle body. The inverter 1 is supplied with electric power from a battery 2, and the electric power is stabilized by a smoothing capacitor 5 therein, and a gate drive circuit 7 appropriately drives a switching element (for example, IGBT)3 made of a semiconductor so as to flow a current corresponding to a torque calculated by an arithmetic circuit unit 8 in a control unit 9.

The motor drive current is measured by the current sensor 4, and is determined by the current monitoring circuit 6 as to whether or not the current is an appropriate current, and is controlled by the arithmetic circuit unit 8. The arithmetic circuit unit 8 controls the motor current by: the command current is further increased if the metered current is less than the calculated current command value and the command current is further decreased if the metered current is greater than the calculated current command value.

In general, the 3-phase alternating currents Iu, Iv, Iw can be obtained, for example, as follows

Iu＝Acos(θ)

Iv＝Acos(θ+120°)

Iw＝Acos(θ－120°)

And is shown. A represents an effective value of the current, and θ represents a phase angle.

Disclosure of Invention

Problems to be solved by the invention

Fig. 8 shows a 3-phase alternating current waveform when the effective value a is 100 (Arms). For example, when a 4-pole motor is driven, the motor is rotated 1/4 turns at a phase angle of 0 to 360 ° which is an electromotive angle of 360 °. That is, the time of the electric angle of 360 ° corresponds to the time of 1/4 rotations of the motor. In addition, the wheel rotates only by the amount that imparts the reduction ratio of the reduction gear.

Here, in fig. 7, when a current of 100(Arms) Iu, for example, flows during the rotation of the motor, the switching element 3-up of the 6 switching elements 3 is responsible for carrying the current when the phase angle is in the range of 0 to 180 °, and the switching element 3-vn is responsible for carrying the current when the phase angle is in the range of 180 to 360 °. Then, for example, if a case where 1 of the switching elements 3 flows a current of an effective value 1/2, that is, 50(Arms) is considered, a loss can be calculated. All other switching elements may also pass a current of 50 (Arms).

Here, a case when the vehicle starts, that is, when the motor 10 starts to start from a stop is considered. For example, when the phase angle is 90 ° at this time, the number of revolutions of the motor is 0, and therefore, the U-phase flowsI.e., the current of 141(a) is concentrated only in the switching elements 3-up. In addition, for the V, W phases, in switching elements 3-vn and 3-wn, respectively, half of each flow,that is, a current of 70.5(a) does not flow through the other 3 switching elements. This is the worst condition for the load of the switching element 3-up. The corresponding switching element 3 is in the same worst condition as described above at a specific phase angle.

The loss of the switching element 3 is mainly divided into a switching loss and a conduction loss in the case of low rotation, but if the switching speed is constant, it is substantially proportional to the current. Since the temperature rise of the switching element 3 is determined by the loss and the cooling performance, the greater the loss, the greater the temperature rise. Since the junction temperature of the switching element 3 is usually about 150 ℃, which constitutes a limit, it is necessary to control the junction temperature to be equal to or lower than this temperature at ordinary times. The maximum value of the junction temperature is Tjmax. Normally, a temperature sensor is provided in the vicinity of the switching element 3 to estimate the junction temperature and control the junction temperature so as not to exceed Tjmax, but the junction temperature cannot be estimated solely from the temperature difference due to the thermal resistance between the switching element 3 and the temperature sensor, and thus the switching element 3 cannot be sufficiently protected solely by the temperature sensor.

Here, if the cooling performance is regarded as constant by simple calculation, the loss is 2.82 times under the worst condition, and therefore only 1/2.82, that is, 35% of the current for normal running can flow at the time of start-up. The torque of the motor 10 is substantially proportional to the current at the time of low rotation. Thus, the torque is also limited to 35%.

When such a situation is applied to a vehicle, for example, when the vehicle travels on a slope, the vehicle can be driven with sufficient torque, but when the vehicle starts traveling on a slope of the same angle, the torque is limited to 35% in consideration of the worst condition, and as a result, the vehicle cannot be driven. Alternatively, when the switching element 3 capable of flowing a large current is selected in consideration of the above-described worst condition, there is a disadvantage that the switching element exceeds the specification in the case of normal running, and the cost increases.

Therefore, it is necessary to establish an operation method capable of ensuring the climbing performance without selecting the switching element 3 whose output is more than necessary.

In the case of the technique described in patent document 1, an improvement of 8% is obtained by shifting the phase of the concentrated current. However, a slightly larger improvement is contemplated.

The present invention has been made to solve the above problems, and an object of the present invention is to provide an inverter device and a vehicle control device that can prevent a switching element of a phase in which a current is partially biased to damage the switching element at the start of motor rotation such as when a vehicle starts, or can improve a torque shortage by the prevention control.

Means for solving the problems

An inverter device 1A of the present invention includes an inverter 1 for converting a direct current into an alternating current corresponding to a form of a motor 10 to be driven by opening and closing switching elements made of semiconductors of respective phases, and a control unit 9 for controlling the inverter 1, wherein the control unit 9 imposes a current limit when a rotation number of the motor 10 after the motor 10 is started or the like is smaller than a threshold value, and relieves the current limit when a predetermined matter indicating a usage state of the switching elements 3 satisfies a set condition.

According to this configuration, the control unit 9 limits the current when the number of revolutions of the motor 10 is smaller than the threshold value, for example, after the motor 10 is started. Thus, even when the current is biased to the switching element 3 which is a part of the inverter 1 for extremely low speed rotation at the time of starting, the switching element 3 is prevented from being damaged by an overcurrent. If the current is strongly limited, the switching element 3 is hardly damaged, but a torque shortage of the motor 10 occurs. Further, the switching element 3 has a margin for a limited current depending on the usage situation at the time of its activation, the ambient temperature, the usage situation after the start of activation, and the like. Then, the control unit 9 determines items indicating the use state of the switching element 3 and setting conditions for alleviating the current limitation, and alleviates the current limitation when the setting conditions are satisfied. This prevents the current of the switching element 3 from being unnecessarily limited, and can improve the torque shortage.

In this way, when the number of revolutions of the motor 10 immediately after the start of the start is low, the current is basically limited, and the switching elements 3 of the phases in which the current is biased to a part to reduce the limitation only when the conditions are sufficient can be prevented from being damaged, and the torque shortage can be improved by the control of the prevention.

In the present invention, the specified items indicating the usage state of the switching element 3 may include items of a temperature directly or indirectly measured by the switching element 3.

Damage to the switching element 3 due to overcurrent occurs when the temperature of the element 3 rises to some extent due to heat generation. Thus, the current limitation is appropriately alleviated by using the temperature of the switching element 3 as the matter indicating the usage state of the switching element 3 for alleviating the determination of the current limitation. In addition, if it is temperature, the measurement is easy.

When the determined item is the temperature of the switching element 3, the current limit may be reduced when the temperature of the cooling water for cooling the inverter 1 is lower than a set temperature.

The switching element 3 is incorporated in the package, and it is difficult to directly measure the temperature thereof, but the temperature of the cooling water of the inverter 1 can be easily measured. Although the temperature of the cooling water does not represent the temperature of the switching element 3 with good accuracy, the correlation between the temperature of the cooling water and the temperature of the switching element 3 is strong, and also constitutes an index representing the ability to cool the switching element 3. Thus, when the temperature of the cooling water is low, the current limitation is reduced, and the reduction of the current limitation is controlled easily.

When the determined item is the temperature of the switching element 3, the current limit may be reduced when the measured temperature of the temperature sensor that measures the temperature of the switching element 3 is lower than a set temperature.

A temperature sensor for measuring the temperature of the switching element 3 can be provided by the configuration of the inverter 1. The temperature sensor may be provided with a temperature detection unit, for example, in a housing of each switching element 3. When the temperature of each switching element 3 can be measured by a temperature sensor, the temperature measured by the temperature sensor is used to control the current limitation to be alleviated with further high accuracy.

In the inverter device of the present invention, the predetermined items indicating the use state of the switching element 3 may include an elapsed time from the start of energization or from when the current value exceeds a set value.

In general, if the current is a short-time current such as a momentary current, the switching element 3 and other electronic elements can flow a somewhat large current. In addition, the measurement of time is easily performed. Thus, by setting the elapsed time to a condition for alleviating the restriction, the appropriate alleviation of the current restriction can be easily achieved.

In the inverter device of the present invention, the predetermined conditions indicating the usage state of the switching element 3 include a plurality of conditions among a condition in which the temperature of the cooling water for cooling the inverter 1 is lower than a predetermined temperature, a condition in which the measured temperature of the temperature sensor for measuring the temperature of the switching element 3 is lower than a predetermined temperature, and a condition in which the predetermined conditions of the elapsed time are satisfied.

By determining a plurality of items that affect the damage of the switching element 3, the current limitation can be reduced in many cases while preventing the damage with certainty, thereby improving the torque shortage improvement effect. Further, if the improvement degree of the torque shortage is the same, more reliable damage prevention is required.

The vehicle control device according to the present invention may be equipped with the inverter device 1A according to any one of the aspects of the present invention described above, and the motor 10 may be a motor 10 for driving the vehicle.

The inverter device 1A of the present invention for controlling the motor 10 for driving the vehicle can prevent the switching elements 3 from being damaged by a current bias in the switching elements 3 of a part of the phases of the present invention, and effectively improve the torque shortage by the prevention control.

In addition, any combination of at least 2 structures disclosed in the claims and/or the specification and/or the drawings is included in the present invention. In particular, any combination of 2 or more of the claims in the claims is also included in the present invention.

Drawings

The invention will be more clearly understood from the following description of preferred embodiments with reference to the accompanying drawings. However, the embodiments and the drawings are for illustrative and descriptive purposes only and are not intended to determine the scope of the present invention. The scope of the invention is determined by the claims. In the drawings, the same reference numerals in the drawings denote the same parts.

Fig. 1 is a conceptual diagram of an example of an electric vehicle equipped with an in-wheel system;

fig. 2 is an explanatory view showing a conceptual configuration of an inner wheel device according to an embodiment of the present invention;

FIG. 3 is a schematic diagram of a water-cooled switching element module;

FIG. 4 is a graph showing an example of current limitation of the number of revolutions;

fig. 5 is a graph showing an example of current limitation with the lapse of time;

fig. 6 is a perspective view of an example of a switching element module;

fig. 7 is a block diagram of a conceptual scheme of an inverter apparatus in the past;

fig. 8 is a graph of a current waveform of 3-phase alternating current.

Detailed Description

(basic structure of vehicle)

An embodiment of the present invention will be described with reference to fig. 1 to 6.

Fig. 1 is a conceptual diagram of an example of an electric vehicle equipped with an inner wheel system. The inverter device 1A of the electric vehicle is the inverter device of the present embodiment. The electric vehicle is a rear-wheel two-wheel drive vehicle in which left and right wheels 22 constituting rear wheels are drive wheels driven by the motor 10, respectively, and wheels 21 constituting front wheels are driven wheels steered by a steering device 23. The motor 10 is a motor constituting an in-wheel motor device. The motor 10 may be a motor provided on the vehicle body 20. Each motor 10 is an ac motor, and a three-phase synchronous motor is used. The steering device 23 is operated by a steering operation mechanism 24 such as a steering wheel. Each of the wheels 21 and 22 is provided with a brake 25, and braking is performed by a stepping operation or the like of a brake operating mechanism 16 constituted by a brake pedal.

The control system includes: a VCU 14, the VCU 14 performing overall integrated control and cooperative control of the vehicle; and an inverter device 1A, wherein the inverter device 1A controls the motor 10 in accordance with a command output from the VCU 14. The VCU 14 is constituted by a microcomputer, an electronic circuit, and the like. The VCU 14 reads an acceleration input such as an operation angle of the acceleration operation mechanism 15 of the driver and a brake input such as an operation angle of the brake operation mechanism 16, converts them into a torque command, and executes the command to the inverter device 1A. The inverter device 1A converts electric power from the battery 2 into three-phase alternating current based on a torque command, and controls the corresponding motor 10. In this case, 2 inverter devices may be used, but the inverter device 1A in the example of the figure is 2-shaft integrated, and can drive 2 motors 10. Although the present example is a rear wheel drive, the inverter device and the vehicle control device of the present embodiment can be applied to all wheel drive vehicles and 4-wheel drive vehicles.

(basic structure of inverter)

Fig. 2 shows a basic structure of an inverter device 1A having 1 axis, and the inverter device 1A shown in fig. 1 includes 2 sets of this basic structure.

In fig. 2, inverter device 1A includes inverter 1 and control unit 9 for controlling inverter 1.

The inverter 1 is a bridge circuit including upper and lower switching elements 3(Up, Un, Vp, Vn, Wp, and Wn) for each phase U, V, W, and converts the dc current of the battery 2 into a 3-phase ac current having a pseudo sinusoidal wavelength by turning off the switching elements 3. In addition, when the switching elements 3 are distinguished, the reference numerals are denoted by the above-mentioned Un, Vp, Vn, Wp and Wn after "3" and are shown as "3-up". The switching element 3 is a semiconductor switching element such as an IGBT or a MOS-FET. Smoothing capacitor 5 is connected in parallel with battery 2. The output terminals of the respective phases of the inverter 1 are connected to the input terminals of the respective phases of the motor 10.

(basic structure of control section)

The control unit 9 includes an arithmetic circuit unit 8, a gate drive circuit 7, and a current monitoring circuit 6. The arithmetic circuit unit 8 supplies a command to the gate drive circuit 7 through the basic control unit 31 so that a current corresponding to a torque command supplied from the high-level VCU 14 (fig. 1) flows. The gate drive circuit 7 opens and closes the switching element 3. The motor driving current outputted from the inverter 1 and flowing through the motor 10 is measured by the current sensor 4, and is determined by the current monitoring circuit 6 as to whether or not it is an appropriate current, and is controlled by the arithmetic circuit unit 8. The basic control unit 31 of the arithmetic circuit unit 8 controls the motor current by current feedback control in which the command current is further increased when the measured current is smaller than the calculated current command value and the command current is further decreased when the measured current is larger than the calculated current command value.

(Current limiter)

In the inverter device 1 having such a basic configuration, the current limiting unit 32 is provided in the arithmetic circuit unit 8 of the control unit 9. The current limiting unit 32 limits the current when the number of revolutions of the motor 10 immediately after the start of the motor 10 is smaller than a threshold value, and reduces the current limit when a predetermined item indicating the usage state of the switching element 3 satisfies a design condition. The current limit condition is set in the limit condition setting unit 33, and the slow condition is set in the slow condition setting unit 34. The conditions for alleviating the trouble are items indicating the use state of the switching element 3 and the setting conditions related to the items.

The specified items indicating the usage state of the switching element 3 include items of the temperature of the switching element 3 measured directly or indirectly. Specifically, the term "temperature" refers to, for example, the temperature of the cooling water for cooling the inverter 1, and when the temperature is lower than a set temperature, the current limit is reduced.

The temperature-related item may be a measured temperature of a temperature sensor that measures a temperature of the switching element, and the current limit may be reduced when the measured temperature is lower than a set temperature for the element.

(Cooling water temperature restriction alleviation)

Fig. 3 is a simplified schematic diagram of a water-cooled switching element 3. The switching element 3 is provided in a radiator 11 made of metal or the like. The radiator 11 is provided with a cooling water jacket 13 covering the inner surface thereof, and the cooling water 12 in the cooling water jacket 13 is impregnated with the heat radiating fins 11a of the radiator 11. The heat lost by the switching element 3 is conducted to the radiator 11 and cooled by the cooling water 12. The cooling water 12 is circulated through a circulation line by a circulation mechanism not shown in the figure, and is cooled by a radiator (not shown in the figure) in the circulation line.

The switching element modules 3A are configured such that the switching elements 3 are wound around the switching elements 3, respectively, and are accommodated in a package (not shown) together with the heat radiator 11. The cooling water jacket 13 may also be part of the skin of the package.

The relationship between the loss of the switching element 3 and the temperature will be described. If the temperature of the switching element 3 is Td (° c) and the temperature of the cooling water 12 is Tw (° c), Δ T becomes Td-Tw with respect to the temperature difference Δ T (° c).

Here, to be precise, thermal resistance from the switching elements 3 in the switching element 3A with a packing (packing) to the package, thermal resistance between the package and the radiator 11, thermal resistance between the radiator 11 and the cooling water 12, temperature distribution, flow rate of the cooling water 12, heat conduction inside the radiator 11, and the like are often considered, but for simplification of description and calculation, the heat lost by the switching elements 3 is entirely cooled by the cooling water 12, and the thermal resistance of the cooling water 12 is collected from 1 switching element 3 to obtain θ s (° c/w).

The loss of the switching element 3 is mainly divided into a switching loss and a conduction loss, and if the switching speed is constant, it is substantially proportional to the current in the case of low rotation. In practice, a Diode (FRD) in the reverse direction (not shown) is incorporated in the switching element 3, and the loss is also considered.

When the loss of the switching elements 3 to up exceeds the loss calculated from the actual effective value by the U-phase current, 1/2 indicating the exceeding of the actual effective value and 1/3 indicating the phase angle is 120 ° of 20 ° to 160 ° in all cycles are compared with the above description and fig. 8.

When the rotation of the motor 10 is at least a certain number of revolutions and the current is constant and in a thermally parallel state, the temperature of the switching element 3-up rises during the phase angle of 20 ° to 160 °, and the temperature of the switching element 3-up falls at other times.

If the rotation of the motor 10 is decreased, the temperature of the switching element 3-up having the phase angle of 20 ° to 160 ° is increased, but there is a possibility that the maximum value Tjmax of the junction temperature is exceeded. Therefore, in this case, it is necessary to reduce the maximum current by the number of revolutions of the motor. Fig. 4 shows an example of such a limitation.

In the example shown in fig. 4, when the rotation number of the motor 10, that is, the frequency of the 3-phase alternating current exceeds fn (hz), a current of 1max can be applied. The frequency of the 3-phase current is equal to or less than Fn (Hz), and is reduced to 1res along with the frequency.

In this way, the operation not exceeding the maximum value TImax of the junction temperature of the switching element 3 can be realized, and the inverter can be prevented from malfunctioning.

However, if the limit rate of the rotation speed is Rres, which is Imax/Ires, there is a possibility that Rres becomes 2.82 as described above and the torque at the time of starting becomes insufficient.

For simplification, Imax is determined by the losses Pa, Tw, Td, θ s of 1 switching element 3.

Td＝Tjmax

If Pa is substantially proportional to phase current I, with a proportionality factor Kp, then:

Pa＝Kp·I

pa is Δ T/θ s, so

Td－Tw＝Kp·I·θs

I＝(Td－Tw)/(Kp·θs)。

As an example, in a motor of 35kW driven by sampling at 10kHz, if

Td is 150, Tw is 60, Kp is 1, and θ s is 0.3, then:

Imax＝I＝300(Arms)

Ires＝I＝106(Arms)

the cooling water temperature Tw is, for example, 60 ℃ as described above, in consideration of the temperature rise at the time of continuous maximum output.

Here, if it is assumed that the cooling water temperature does not rise at the time of vehicle departure, which is, for example, 30 ℃, then:

Imax＝I＝400(Arms)

Ires＝I＝142(Arms)

in the case of Imax, it is necessary to request Tw of 60 for any increase in water temperature,

Imax＝I＝300(Arms)

Ires＝I＝142(Arms)

R_res2.11, 2.82/2.11, in this example, a slight improvement to 134%.

Alternatively, Tw can be measured with a water temperature meter to determine Ires.

Alternatively, when there is no water temperature meter, Ires is determined using as Tw the measured value of a temperature sensor (not shown) attached to the switching element 3 at the time of stop. In this case, the measurement value of the temperature sensor attached to the switching element 3 rapidly increases with the temperature increase of the switching element 3, but the value of the initial cooling water temperature Tw is used even in a short time. The short time refers to, for example, a time during which the cooling water 12 circulates in the circulation line for 1 week. In other words, the time is the time obtained by dividing the total amount of cooling water by the flow rate.

Next, the thermal resistance was considered to be θ s in the case of only the switching element 3-up in the worst case, 141(a), 70.5(a) in the case of the switching element 3-vn and the switching element 3-wn, and 0 (a).

Fig. 6 shows an example of the switching element module 3A. The 6 switching elements 3 each emit heat in the region 1/6 of the radiator 11. In the worst case, since no current flows in the switching element 3-un and the switching element 3-vp, the switching element 3-un can use 2 radiator regions. Among them, since the heat resistance is not located directly below the switching elements 3-up, the heat radiator 11 cannot be used effectively in its entirety at 3/6. Here, assuming that the thermal resistance is 2 times, the same effect as that in the case where the 2/6 region of the radiator 11 is available is obtained, and θ s is 1/2.

In this case, compared to the case where Imax is 300(Arms), Ires is 106(Arms), Ires is 204(Arms), Rres is 1.47, 2.82/1.47, and the improvement is 192% in this example.

If the above are combined, in this example, a 134 × 192 ═ 257% improvement is achieved.

Rres＝1.10

Ires＝273(Arms)

In this case, the current limit can be further reduced by reducing the current limit in the next time.

An example of the mitigation of the current limit with time is explained.

Even in the worst case, if the time is short, the current can be made to flow up to Imax. That is, even when the initial value of Rres is 1, it is irrelevant. When the vehicle starts, the motor rotation speed gradually increases, and the frequency of the 3-phase alternating current reaches Fn in a short time.

In the case where the vehicle cannot move forward on a steep slope, a height difference, or the like, the motor 10 is in a locked state, the current is Imax, and the switching element 3 fails when the junction temperature exceeds Tjmax in a short time.

Therefore, it is effective to limit the current at a time from the start of energization or a time when a certain current value is exceeded.

The function of the current limitation can be performed in a sinusoidal waveform or by a straight line indicated by a dashed line, by way of example of the current limitation of time in fig. 5. In the case where Imax is 100(Arms), the waveform of the period Tlim is the frequency Fn and is the same as that in the case where the phase angle of the U phase is in the range of 90 ° to 160 ° in fig. 5. If the waveform is used, at least no problem should be caused because it is a waveform used on the high rotation side.

Alternatively, the restriction may be performed by a function such as a broken line.

In the current limiting method, for example, when the motor 10 is started, a time function is set with a time of 50% or more of the maximum current as a starting point, and the motor is combined with the limitation of the number of revolutions, and the larger current of the two is used for operation.

The above calculations are simplified for explaining the principle of the present invention, but in actual practice, rigorous calculations and simulation calculations may be added to change the numerical values.

While the embodiments for carrying out the present invention have been described above based on the embodiments, the embodiments disclosed herein are illustrative in all respects and not restrictive. The scope of the present invention is defined not by the above description but by the claims, and all changes that come within the meaning and range of equivalency of the claims are intended to be embraced therein.

Description of reference numerals:

reference numeral 1 denotes an inverter;

reference numeral 1A denotes an inverter device;

reference numeral 2 denotes a battery;

reference numeral 3 denotes a switching element;

reference numeral 5 denotes a capacitor;

reference numeral 6 denotes a current monitoring circuit;

reference numeral 7 denotes a gate drive circuit;

reference numeral 8 denotes an arithmetic circuit unit;

reference numeral 9 denotes a control section;

reference numeral 10 denotes a motor;

reference numeral 14 denotes a VCU;

reference numeral 20 denotes a vehicle body;

reference numeral 31 denotes a basic control section;

reference numeral 32 denotes a current limiting portion;

reference numeral 33 denotes a constraint condition setting unit;

reference numeral 34 denotes a mitigation condition setting section.