Battery-powered motor and motor drive system

Abstract

Provided are a battery-driven motor and a motor-driven system which achieve high output density without impairing the efficiency of the total system. This battery-driven motor is supplied with power from a battery via an inverter and drives a load. The battery-driven motor is supplied with a supply current of 3.0C or more from the battery when being driven at the maximum output and is provided with a stator core (12) using, as a core material, an electromagnetic steel sheet having a magnetic flux density of 1.65T or more at a magnetic field strength of 5000A / m and an iron loss of 40.0W / kg or less with a sine-wave excitation of 1kHz-1.0T.

Description

[Technical field]

[0001] The present disclosure relates to a battery-powered motor and a motor drive system, particularly to a battery-powered motor and a motor drive system that are operated at high speeds and are suitable for use in battery-powered cordless household appliances, electric vehicles (EVs), cutting equipment, drones, and the like. [Background technology]

[0002] Motors driven by power supply from a battery are required to be highly efficient and capable of long-term operation. On the other hand, there is a strong demand for reducing the size and weight of the entire device. These are often in a trade-off relationship, and it is technically difficult to achieve both at a high level. In other words, it is easy to obtain relatively high efficiency in a motor by, for example, increasing the size and decreasing the excitation magnetic flux density of the iron core, but the weight and size will increase. In addition, the maximum rotation speed may be increased to reduce the size of the motor, but since there are restrictions on the power supply voltage in motors driven by power supply from a battery as described above, measures on the power supply side are required. For example, a method of ensuring a high voltage for high-speed rotation is to provide a boost circuit, but this inevitably increases the size and weight of the entire device, which may offset the miniaturization achieved by increasing the motor speed.

[0003] Incidentally, it is known that the use of materials with high magnetic flux density and low core loss as core materials is effective for improving motor efficiency and output, not only for the motors described above. However, there is a limit to the improvement of core loss and magnetic flux density of core materials, and even for the same motor, the material properties required change depending on the operating conditions. In particular, the ideal core material properties under the power supply constraints of battery drive have not been clarified so far, and it has not been possible to select an optimal material for a battery-driven motor and optimize the efficiency, size, and weight of the entire device. In response to this situation, in some special applications such as automobile racing, iron core materials such as permendur (Fe-Co alloy), which has excellent saturation magnetic flux density characteristics, are sometimes used (for example, Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2018-174650 A Summary of the Invention [Problem to be solved by the invention]

[0005] Here, the cost of permendur is relatively high, and the supply of Co can be unstable. Therefore, there is a demand for technology that can optimize the efficiency, size, and weight of the entire equipment using readily available non-oriented electrical steel sheets.

[0006] An object of the present disclosure, made to solve the above problems, is to provide a battery-powered motor and a motor drive system that achieve high power density without compromising the efficiency of the entire system. [Means for solving the problem]

[0007] In light of the above-mentioned problems, the inventors of the present disclosure have conducted extensive research into iron core materials with electromagnetic properties suitable for high-speed motors. As a result, they have developed a motor iron core material with a magnetic flux density (B 50 ) is 1.65T or more, and the iron loss (W 10 / 1000 It was found that by using electrical steel sheets with a thermal conductivity of 40.0 W / kg or less, it is possible to effectively reduce losses in the entire system and achieve both power density and efficiency.

[0008] A battery-powered motor according to one embodiment of the present disclosure includes: A battery-driven motor that drives a load by receiving power from a battery via an inverter, When driven at maximum output, the supply current from the battery is 3.0C or more; The stator core is made of electromagnetic steel sheet as the iron core material, which has a magnetic flux density of 1.65 T or more at a magnetic field strength of 5000 A / m and an iron loss of 40.0 W / kg or less under sinusoidal excitation of 1 kHz-1.0 T.

[0009] Moreover, the motor drive system according to an embodiment of the present disclosure includes: Battery and An inverter; a battery-driven motor that receives power from the battery via the inverter to drive a load, The battery-powered motor is When driven at maximum output, the supply current from the battery is 3.0C or more; The stator core is made of electromagnetic steel sheet as the iron core material, which has a magnetic flux density of 1.65 T or more at a magnetic field strength of 5000 A / m and an iron loss of 40.0 W / kg or less under sinusoidal excitation of 1 kHz-1.0 T. Effect of the Invention

[0010] According to the present disclosure, it is possible to provide a battery-powered motor and a motor drive system that achieves high power density without compromising the efficiency of the overall system. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 is a diagram illustrating a schematic configuration of a battery-driven motor according to an embodiment of the present disclosure. [Diagram 2] FIG. 2 is a diagram for explaining the evaluation flow of the battery loss and the definition of the battery loss Wb. [Diagram 3] FIG. 3 is a diagram showing an example of an actual measurement evaluation result of battery loss in a battery-driven motor. [Figure 4] FIG. 4 is a diagram showing an example of the configuration of a battery-driven motor manufactured as an IPM (interior permanent magnet) motor. [Diagram 5] FIG. 5 is a diagram showing an example of the configuration of a battery-driven motor manufactured as an SPM (surface permanent magnet) motor. [Figure 6] FIG. 6 is a diagram showing the shape of the manufactured iron core. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Fig. 1 is a diagram showing a schematic configuration of a battery-driven motor 10 according to an embodiment of the present disclosure. The battery-driven motor 10 drives a load by receiving power from a battery via an inverter that converts DC power to AC power. The battery-driven motor 10, the battery, and the inverter constitute a motor drive system 1 as shown in Fig. 1.

[0013] The motor drive system 1 can be used in battery-driven devices such as electric vehicles, vacuum cleaners, drones, etc. The battery-driven motor 10 operates with a rotating shaft or the like of the battery-driven device as a load.

[0014] The requirements for the electromagnetic steel sheet, which is the core material of the battery-powered motor 10, and the reasons for the limitations will be explained below. There are no limitations on the type of battery-powered motor 10. Furthermore, there are no limitations on the components or manufacturing method of the electromagnetic steel sheet, so long as the specified magnetic properties are obtained. In the following explanation, the "%" simply used to refer to the amount of added components means "% by mass."

[0015] As the magnetic steel sheet used as the core material of the battery-powered motor 10, a steel sheet that satisfies the requirements described below should be selected.

[0016] (The battery current supply at maximum output is 3.0C or more) To increase the power density of a motor, it is advantageous to apply a power source capable of supplying large capacity, i.e., high voltage and large current. However, in a system driven by power supply from a battery, there is a voltage constraint, and providing a boost circuit leads to an increase in size and weight. Therefore, in this embodiment, a configuration is proposed in which lithium-ion battery cells are connected in series or parallel, or in a combination of series and parallel, depending on the voltage required to drive the motor, and a current is supplied at a relatively large discharge rate of 3.0C or more, in a system suitable for increasing the power density of a motor, in which losses in the entire system are reduced. Battery loss Wb, which will be described later, increases in proportion to the square of this discharge rate (C rate) (see FIG. 3). However, by applying the configuration of this embodiment, it is possible to reduce the current compared to the conventional technology and effectively reduce losses in the battery. Here, the C rate indicates the speed of discharge, and the magnitude of the current that completely discharges the nominal capacity of the battery in one hour is defined as 1C. For example, 2.0C is the magnitude of the current that completely discharges the nominal capacity of the battery in 0.5 hours. The higher the C-rate value of the maximum discharge condition of the battery, the greater the loss in the battery, but the higher this value, the higher the power density of the motor can be obtained, and the easier it is to obtain the effect of improving losses in the entire system by applying the technology of the present invention. Therefore, it is preferably 5.0C or higher, and more preferably 8.0C or higher. On the other hand, if the maximum C-rate is lower than 3.0C, it is difficult to obtain the effect.

[0017] Furthermore, reducing losses in the battery directly contributes to suppressing the rise in battery temperature, and is therefore also effective in suppressing deterioration due to the charge / discharge cycles of the battery, which is one of the major advantages of the battery-driven motor 10 and motor drive system 1 according to this embodiment.

[0018] As described above, the number of lithium ion batteries connected in series may be adjusted according to the required voltage. Also, lithium ion batteries may be connected in parallel to increase the number of batteries according to the required dimensions and continuous drive time of the motor drive system 1. The type of battery is preferably a lithium ion battery in order to achieve high energy density and high power density. However, the type of battery is not limited.

[0019] (About battery loss Wb) FIG. 2 shows the evaluation flow of the battery loss Wb. First, the CC (constant current) discharge characteristics are evaluated using a charging and discharging device. In detail, a constant current discharge test is performed at 0.2C (current value that reaches the discharge end voltage in 5 hours) and a discharge rate when driving at the maximum motor output, using the method shown in "JIS C 8711". By integrating the curve of the obtained discharge capacity W (Ah) and the terminal voltage V (V), the electrical work (Wh) provided by the battery to the external system can be calculated. Then, the battery loss Wb (W) is calculated from the difference in the voltage drop curves at 0.2C and the C rate at the maximum output. Specifically, the difference (energy (Wh) shown in FIG. 2) is divided by the discharge time (h) to obtain the battery loss Wb (W) at the maximum output per unit time. Here, if the C rate at the maximum output (maximum C rate) is, for example, 3.0C, V (C max ) is V(3.0C). Also, 1 / C of the discharge time max is 1 / (3.0).

[0020] FIG. 3 shows an example of the measurement result of the battery loss Wb for a lithium-ion battery with a rated voltage of 21.6V and a rated capacity of 2.8Ah. For the measurement, a charge / discharge device PFX2512 manufactured by Kikusui Electronics Co., Ltd. was used. Any evaluation device may be used as long as a similar constant current discharge test can be performed according to the voltage / current capacity of the evaluation target. Since it is difficult to evaluate a large battery pack with many cells connected, such as an electric vehicle, a charge / discharge test may be performed by extracting a part or a single cell. As shown in FIG. 3, when the discharge rate increases, the battery loss Wb increases. Here, the effect of reducing the motor current proportional to the battery current is effectively produced in a form in which the above-mentioned battery loss Wb is Wm≦Wb with respect to the motor loss Wm (iron loss and copper loss). More preferably, Wm×2.0≦Wb. Therefore, it is preferable to select an iron core material so that such a relationship is satisfied.

[0021] (About electrical steel sheet properties) Magnetic flux density (B 50 The higher the magnetic flux density (B ) of the material, the higher the torque of the motor can be obtained, so the motor current can be reduced when comparing at the same torque. 50 ) is 1.65T or more. Here, the magnetic flux density (B 50 ) is the magnetic flux density at a magnetic field strength of 5000A / m. There is no particular upper limit to the range. Also, magnetic flux density (B 600 ) is preferably 1.95T or more, and more preferably 2.00T or more, because it effectively contributes to increasing torque (i.e., reducing current) when the iron core material is close to magnetic saturation, particularly when the motor is driven at maximum output. Here, the magnetic flux density (B 600 ) is the magnetic flux density at a magnetic field strength of 60,000 A / m. Also, iron loss (W 10 / 1000 ) is an effective indicator of the reduction in iron loss during motor operation. Therefore, the iron loss (W 10 / 1000 ) is 40.0 W / kg or less, and more preferably 30.0 W / kg or less. Here, iron loss (W 10 / 1000 ) is the iron loss under 1kHz-1.0T sinusoidal excitation.

[0022] There are no other restrictions on the magnetic steel sheet as long as it achieves the above magnetic properties. For example, differences in the components and manufacturing method of the magnetic steel sheet do not affect the effect. Also, there are no special restrictions on the insulating coating as long as it has a known insulating coating on at least one side. Here, Co-Fe alloys such as permendur, which are known as soft magnetic materials with high magnetic flux density (magnetic flux density B 50 The application of 2.3T or more is not anticipated due to the high material costs and poor availability.

[0023] Similarly, there is no restriction on the thickness of the electromagnetic steel sheet, but it may be appropriately selected to satisfy the above-mentioned iron loss. As the iron core material, one containing Si may be selected. In many cases, there is a trade-off between magnetic flux density and iron loss among the material grades of electromagnetic steel sheets. However, by having a distribution of Si concentration in the thickness direction, it is possible to reduce iron loss at high frequencies while minimizing the decrease in material magnetic flux density, so it is relatively easy to achieve both high magnetic flux density and low iron loss. In addition, there is no restriction on the processing and lamination method of the electromagnetic steel sheet, but a high space factor is preferable in order to effectively obtain an increase in motor torque (current reduction) due to the high magnetic flux density characteristics of the material. For example, it is preferable to cut the electromagnetic steel sheet into the desired motor core shape by laser processing, vacuum-impregnate it with an epoxy-based adhesive while applying pressure in the lamination direction, and process-harden it, which can obtain a space factor of 90% or more.

[0024] (Maximum motor speed) As described above, since high speed rotation is an effective means for increasing the output density of a motor, it is preferable that the maximum rotation speed is 10,000 rpm or more. Depending on the degree of demand for small size and high speed, or depending on the voltage value that can be supplied, the rotation speed may be further increased, and the maximum rotation speed is more preferably 20,000 rpm or more. The maximum rotation speed is further preferably 50,000 rpm or more.

[0025] In order to reduce the size and weight of the entire system, it is effective to reduce the size of the motor, which is a heavy object, especially the iron core. Therefore, it is preferable to select the iron core material so that the output (kW) per iron core weight (kg) of the motor exceeds 5kW / kg. More preferably, it is 7kW / kg. Even more preferably, it is 10kW / kg.

[0026] As described above, there is no limitation on the motor type of the battery-driven motor 10, and any type can be effective. However, in order to increase the output density of the motor and achieve high efficiency, an SPM (surface permanent magnet) motor or an IPM motor that uses magnets is preferable. EXAMPLES

[0027] Examples and comparative examples are shown below, but the present disclosure is not limited to the conditions used in the following examples.

[0028] Example 1 An IPM motor with the shape shown in Fig. 4 was manufactured using the electromagnetic steel sheets shown in Table 1 as the iron core material. The manufactured IPM motor includes rotor core 11, stator core 12, shaft 13, and magnets 14. The iron core was processed by punching with a die and laminating by crimping. Magnets 14 were inserted into the obtained rotor core 11, and windings were applied to stator core 12. These were assembled to manufacture the IPM motor. In addition, 200 lithium-ion battery cells (3.6V) were prepared to supply power to the IPM motor. 100 of these cells were connected in series, and two of these were connected in parallel to obtain a battery with a total voltage of 360V.

[0029] [Table 1]

[0030] The battery and motor were controlled by a motor drive system 1 including an inverter, and the current supplied from the battery at maximum motor output was set to 4.0 C. The lithium-ion battery cells used were evaluated according to Fig. 2, and the battery loss Wb at 4.0 C was found to be 10 W. In other words, the battery loss Wb for the entire battery (200 cells) was 2 kW.

[0031] Table 2 shows the results of evaluating the output and motor loss Wm of the manufactured IPM motor when it was operated at maximum output (18,000 rpm). The motor of the embodiment using iron core material A having magnetic properties within a specified range had a high maximum output and a high maximum motor output density (kW / kg) relative to the weight of the motor core. Here, the specified range refers to the magnetic flux density (B) at a magnetic field strength of 5,000 A / m. 50 ) is 1.65T or more and the iron loss (W 10 / 1000 ) is 40.0 W / kg or less.

[0032] [Table 2]

[0033] Meanwhile, Table 3 shows the results of measuring the time from a fully charged battery state until the motor stopped and the battery temperature immediately after stopping when the same motor was driven at a motor output of 12 kW (10,000 rpm).

[0034] [Table 3]

[0035] The example using iron core material A has a continuous operating time that is more than 10% longer than the comparative examples using iron core material B and iron core material C, demonstrating that it is extremely excellent as a motor for battery-powered equipment. Furthermore, the battery temperature after the motor in the example is stopped is reduced by more than 10°C. This is due to a reduction in battery loss, and is expected to have a positive effect not only on reducing the risk of failure due to thermal runaway of the battery, but also on the cycle characteristics of repeated use.

[0036] (Examples 2 to 5) Next, an SPM motor with the shape shown in Figure 5 was manufactured using the electromagnetic steel sheets shown in Table 4 as the iron core materials. Core materials A to C are the same as above. A new electromagnetic steel sheet different from core materials A to C was used as iron core material D. The iron core was processed by punching with a die and laminating by crimping.

[0037] [Table 4]

[0038] The resulting rotor core was made up of a shaft and magnets, and the stator core was wound. These were then assembled to create the SPM motor. In addition, lithium-ion battery cells (3.6V) were prepared to supply power to the SPM motor. Seven of these cells were connected in series (7 series) or seven in series in two parallel connections (7 series x 2 parallel), resulting in a battery with a total voltage of 25.2V.

[0039] The battery and motor are controlled by a motor drive system 1 including an inverter, and the supply current from the battery at maximum motor output is 6.0C for 7 cells in series, and 3.0C for 2 cells in parallel. The lithium-ion battery cells used here were evaluated according to Figure 2, and the battery loss Wb at 6.0C was 20W. In other words, the battery loss Wb for the entire battery (7 cells) was 140W. On the other hand, the battery loss at 3.0C was 5W. In other words, the battery loss Wb for the entire battery (14 cells) was 70W.

[0040] Table 5 shows the results of evaluating the output and motor loss Wm of the manufactured SPM motor when it was operated at maximum output (100,000 rpm). The motors of the embodiment using iron core materials A and D, which have magnetic properties falling within a predetermined range, had high maximum output and a high maximum motor output density relative to the weight of the motor iron core. Here, the predetermined range refers to the magnetic flux density (B) at a magnetic field strength of 5,000 A / m. 50 ) is 1.65T or more and the iron loss (W 10 / 1000 ) is 40.0 W / kg or less.

[0041] [Table 5]

[0042] Meanwhile, Table 6 shows the results of measuring the time from a fully charged battery state until the motor stops and the battery temperature immediately after stopping when the same motor is driven at a motor output of 0.4 kW (90,000 rpm).

[0043] [Table 6]

[0044] It can be seen that the examples using iron core materials A and D have a longer continuous operating time than the comparative examples using iron core materials B and C, and are extremely excellent as motors for battery-powered devices. In addition, the battery temperature after the motor of the examples is also reduced. This is due to a reduction in battery loss, and it is expected that it will not only reduce the risk of failure due to thermal runaway of the battery, but also have a positive effect on the cycle characteristics due to repeated use. Furthermore, among the above examples, when the battery configuration is 7 in series and used under conditions of a higher C rate (Examples 2 and 3), the continuous operating time is nearly 10% longer than in the comparative examples (Comparative Examples 3 and 4), and the battery temperature after the motor is stopped is nearly 10°C lower, and it can be seen that this is a significantly superior motor for battery-powered devices.

[0045] Next, using the core materials E and F shown in Table 7, an iron core with the shape shown in Figure 6 was manufactured. Here, the motor type is a 14-pole outer rotor SPM. The iron core weighs 35g. The iron core was processed by punching and then laminating to a height of 10.5mm using adhesive lamination to create the motor core. The obtained motor core was coated with an insulating paint and wound, and assembled into a motor. In addition, to supply power to this motor, four lithium-ion battery cells (3.7V) were connected in series to obtain a battery with a total voltage of 14.8V.

[0046] [Table 7]

[0047] Table 7 also shows the results of evaluating the time until the motor drive system can no longer maintain the motor drive when the motor is continuously driven at 10,000 rpm-0.31 Nm (325 W). Both iron core materials E and F are examples of the invention and have almost the same magnetic properties. However, iron core materials E and F differ in the presence or absence of a gradient of the Si component in the plate thickness direction. And while the magnetic properties are almost the same, iron core material F has an improved motor drive time of about 15%, and it can be seen that an excellent motor system can be constructed when there is a Si gradient in the plate thickness direction. This result is considered to be due to the effect of suppressing deterioration when the iron core material is processed into an iron core by having a Si gradient. Alternatively, it is considered that the material having a Si gradient suppresses the adverse effect on the magnetic properties due to the stress applied to the motor core by the insulating coating and winding. From the above, in the battery-driven motor of the present disclosure, having a Si gradient not only makes it easier to satisfy the magnetic properties required of the material, but also effectively acts to improve the performance of the entire system when assembled into a motor.

[0048] As described above, the battery motor 10 and motor drive system 1 according to this embodiment are configured as described above to effectively reduce losses in the entire system and achieve both high power density and efficiency. In other words, the battery motor 10 and motor drive system 1 according to this embodiment can achieve high power density without compromising the efficiency of the entire system. Furthermore, by applying the battery motor 10 and motor drive system 1 according to this embodiment, it is possible to realize small, highly efficient battery-driven devices such as electric vehicles, vacuum cleaners, and drones.

[0049] Although the embodiments of the present disclosure have been described based on the drawings and examples, it should be noted that those skilled in the art can easily make various modifications or corrections based on the present disclosure. Therefore, it should be noted that these modifications and corrections are included in the scope of the present disclosure. [Explanation of symbols]

[0050] 1 Motor drive system 10 Battery-powered motor 11 Rotor core 12 Stator core 13 Shaft 14. Magnets

Claims

1. A battery-driven motor that drives a load by receiving power from a battery via an inverter, When driven at maximum output, the supply current from the battery is 3.0 C or more; The stator core is made of an electromagnetic steel sheet having a magnetic flux density of 1.65 T or more at a magnetic field strength of 5000 A / m and an iron loss of 40.0 W / kg or less at a sinusoidal excitation of 1 kHz-1.0 T as an iron core material, The stator core is formed by punching the electromagnetic steel sheets and then laminating them, and has a Si gradient in the sheet thickness direction, The battery-driven motor has a motor loss Wm of the battery-driven motor, and a battery loss Wb of the battery-driven motor when the battery is driven at maximum output, such that Wm≦Wb.

2. 2. The battery-powered motor of claim 1, wherein the battery is a lithium-ion battery.

3. 3. The battery-driven motor according to claim 1 or 2, wherein the maximum rotation speed is 10,000 rpm or more, and the output (kW) relative to the iron core weight (kg) exceeds 5 kW / kg.

4. 4. A battery-driven motor according to claim 1, wherein the electromagnetic steel sheet has a magnetic flux density of 1.95 T or more at a magnetic field strength of 60,000 A / m and an iron loss of 30.0 W / kg or less under sinusoidal excitation of 1 kHz-1.0 T.

5. 5. The battery-driven motor according to claim 1, wherein the iron core material has a distribution of Si concentration in the thickness direction.

6. Battery and An inverter; a battery-driven motor that receives power from the battery via the inverter to drive a load, The battery-powered motor is When driven at maximum output, the supply current from the battery is 3.0 C or more; The stator core is made of an electromagnetic steel sheet having a magnetic flux density of 1.65 T or more at a magnetic field strength of 5000 A / m and an iron loss of 40.0 W / kg or less at a sinusoidal excitation of 1 kHz-1.0 T as an iron core material, The stator core is formed by punching the electromagnetic steel sheets and then laminating them, and has a Si gradient in the sheet thickness direction, A motor drive system in which, when the battery is driven at maximum output, a battery loss Wb satisfies Wm≦Wb with respect to a motor loss Wm of the battery-driven motor.

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