Drive unit for an electric lathe

Abstract

Drive device for an electric lathe (100) which drives and controls an electric AC lathe (MG), wherein the drive device for an electric lathe (100) comprises: an inverter (10) which is electrically connected between a DC power supply (11) and the electric lathe (MG), and switches an electrical energy between a DC current and an AC current; a smoothing capacitor (40) which is electrically connected between the DC power supply (11) and the inverter (10), and is connected between a positive pole and a negative pole of a DC side of the inverter (10); an inverter control unit (8) that controls the switching of a switching element of the inverter (10) according to a predetermined switching frequency (fc); and an inductance control unit (8, 50) which switches an inductance (Ld) on the DC side between a positive pole of the DC power supply (11) and a positive pole of the smoothing capacitor (40) according to the switching frequency (fc) between a predefined standard inductance (Ls) and a high inductance (Lh) which is higher than the standard inductance (Ls).

Description

TECHNICAL FIELD

[0001] The present invention relates to a drive device for an electric rotary machine or a rotary electric machine drive device that drives and controls an electric AC rotary machine. BACKGROUND

[0002] In recent years, hybrid vehicles and electric vehicles, each equipped with an electric rotary machine as a driving power source, have attracted attention from the perspectives of, for example, energy conservation and environmental pollution reduction. Such a vehicle includes a DC power supply, such as a battery, that supplies power when the electric rotary machine functions as a driving power source (motor), and stores generated power when the electric rotary machine serves as a power source (generator). When the electric rotary machine functions as the driving power source (motor), DC power supplied from the DC power supply is converted into AC power by an inverter to drive the electric rotary machine.When the electric rotary machine functions as the generator, AC energy generated by the electric rotary machine is converted into DC energy by the inverter to be stored as regenerated energy in the DC power supply.

[0003] A smoothing capacitor for smoothing the DC power is provided between the DC power supply and the inverter to reduce fluctuations such as pulsation in the DC power. Generally, the DC side of the inverter for driving the rotary electric machine as the driving power source of a hybrid vehicle or an electric vehicle operates at a high voltage of 200 [V] to 400 [V]. Therefore, the smoothing capacitor is required to have high withstand voltage performance against such high voltages, while also taking into account the fluctuation due to pulsation. In addition, when withstanding voltages of the switching elements constituting the inverter are considered, the smoothing capacitor must have sufficient capacitance to reduce the pulse component.These requirements generally increase the cost of the smoothing capacitor and increase its physical size, requiring a large installation space. Furthermore, the inverter and smoothing capacitor are often installed in an integrated manner or close to each other as parts of a drive device of a rotating electric machine. In particular, an on-board drive device for a rotating electric machine is required to be lightweight and small in size from the perspective of weight and installation space, so the inverter and smoothing capacitor are desirably lightweight and small.

[0004] For example, Japanese Patent Application Laid-Open No. 2009-106046 (Patent Document 1) describes a space-saving drive device for a rotary electric machine (power converter) with a cooling mechanism. In this drive device for a rotary electric machine, a power module with switching elements is arranged on a flat surface within a housing having a heat-radiating portion. A smoothing capacitor electrically connected to the power module is arranged adjacent to the power module on a flat surface formed one step lower than the flat surface on which the power module is arranged (see paragraphs 7 and 8, Fig. 1, etc.). The smoothing capacitor, which requires a high withstand voltage and large capacitance, tends to be large in size. In Patent Document 1, the heat dissipation section and the power module are arranged according to the height of the smoothing capacitor, thus reducing the overall height of the drive device for a rotary electric machine, thereby saving space.

[0005] In this way, space savings can be achieved to some extent by making improvements in the layout of, for example, the circuit section (power module), the cooling mechanism, and the smoothing capacitor of the inverter. However, reducing the weight and size of the entire device has not been achieved by reducing the physical size of the smoothing capacitor, which is determined by the withstand voltage and capacitance. Reducing the capacitance of the smoothing capacitor can reduce the size, but the pulse component described above cannot be sufficiently reduced, causing a possible weakening of the effects of reducing deterioration of the DC power supply and the switching elements.

[0006] Generally, the DC power supply includes a resistance component (R component) and an inductance component (L component). Consequently, an RLC circuit is formed in conjunction with the capacitance component (C component) of the smoothing capacitor. This results in the following: when a voltage gain on the DC side is obtained by dividing a system voltage, which is the voltage on the DC side of the inverter, by a system current as a current on the DC side of the inverter, and a current gain on the DC side is obtained by dividing a power supply current, which is a current flowing through the DC power supply, by the system current, the frequency characteristics of each of the voltage gain on the DC side and the current gain on the DC side have a resonance point.The value of each of the gains increases as the switching frequency increases from zero, reaches its maximum value (resonance point) at the resonant frequency, and decreases as the switching frequency increases from the resonance point, which serves as an inflection point. Pulsations in the system voltage and power supply current occur in conjunction with voltage and current fluctuations associated with the switching of the inverter's switching elements. Specifically, pulsations in the system voltage and power supply current occur according to the switching frequency of the switching elements. For example, pulsations with a frequency component twice the switching frequency are known to occur. In addition, these pulsations also have harmonic components.Harmonic components (especially sixth-order harmonic components and harmonic components of integer multiple orders thereof) are generated according to the rotational speed of the rotating electric machine, so both pulsations must be considered. The magnitudes (amplitudes) of the pulsations increase according to the value of the voltage gain on the DC side as one indicator and the value of the current gain on the DC side as another indicator. Thus, to keep the pulsations of the system voltage and power supply current low, it is preferable to prevent the values ​​of the voltage gain on the DC side and the current gain on the DC side from increasing excessively. In particular, when the capacitance of the smoothing capacitor is reduced to reduce its size, sharp resonance peaks occur.Consequently, it is preferable to prevent the switching frequency from approaching the resonant frequency in order to keep the values ​​of the corresponding gains at low levels. [Prior art documents][Patent documents]

[0007] Patent Document 1: Japanese Patent Application Laid-Open No. JP 2009-106046 A

[0008] The publications DE 10 2008 025 446 A1 and DE 10 2010 050 383 A1 disclose a DC link of a vehicle electrical system, with the inductances contained therein, including parasitic ones, which, together with the capacitances also contained therein, constitute oscillatory systems. The B6 pulse-controlled inverter operated on this vehicle electrical system is operated in such a way that the applied switching frequency avoids the resonant frequencies as much as possible. SUMMARY OF THE INVENTION

[0009] In view of the above-described background, a technique is desirable that can reduce the capacitance of a smoothing capacitor on the DC side of an inverter while reducing fluctuation such as pulsation of the voltage and current on the DC side of the inverter. [Means of solving the problem]

[0010] According to the present invention, which is made in view of the problem described above, a characteristic feature of a driving device of a rotating electric machine that drives and controls an alternating current rotating electric machine is that it comprises an inverter that is electrically connected between a direct current power supply and the rotating electric machine and converts an electric power between a direct current and an alternating current, that it has a smoothing capacitor that is electrically connected between the direct current power supply and the inverter and is connected between a positive pole and a negative pole on a direct current side of the inverter, that it has an inverter control unit that controls switching of the switching element of the inverter according to a predetermined switching frequency, and that it has an inductance control unit,which switches an inductance on the DC side between a positive pole of the DC power supply and a positive pole of the smoothing capacitor according to the switching frequency between a predefined standard inductance and a high inductance that is higher than the standard inductance.

[0011] A value of each of the DC-side voltage gain obtained by dividing a system voltage (a voltage on the DC side of the inverter) by a system current (a current on the DC side of the inverter), and a DC-side current gain obtained by dividing a power supply current (a current flowing through the DC power supply) by the system current, increases as the frequency increases from zero, reaches a maximum value (resonance point) at a resonant frequency, and decreases as the frequency increases from the resonance point, which serves as an inflection point. A frequency characteristic of each of the DC-side voltage gain and the DC-side current gain gives a frequency characteristic corresponding to a level of inductance on the DC side.The frequency (resonance frequency) that yields the maximum value of each gain shifts to a lower frequency as the inductance on the DC side increases. Therefore, the resonance frequencies of the corresponding gains corresponding to the standard inductance and the high inductance are separated into different frequency ranges. As a result, for example, when the switching frequency increases, both resonance points can be avoided by switching the inductance on the DC side from the standard inductance to the high inductance after the frequency passes the resonance point corresponding to the high inductance before the frequency reaches the resonance point corresponding to the standard inductance.Conversely, when the switching frequency decreases, both of the resonance points can be avoided by switching the inductance on the DC side from the high inductance to the standard inductance after the frequency passes the resonance point corresponding to the standard inductance before the frequency reaches the resonance point corresponding to the high inductance.

[0012] With this characteristic feature, when the switching frequency changes, the inductance on the DC side switches between the standard inductance and the high inductance according to the switching frequency. Therefore, the frequency characteristics of each of the voltage gain on the DC side and the current gain on the DC side can be switched between the frequency characteristics corresponding to the standard inductance and the frequency characteristics corresponding to the high inductance according to the switching frequency. Accordingly, the inductance on the DC side can be appropriately switched, preventing the switching frequency from approaching both of the two resonant frequencies corresponding to the respective inductances, thereby keeping the values ​​of the respective gains low.As a result, the frequency component twice the switching frequency and the harmonic components generated according to the rotational speed of the rotary electric machine can be prevented from increasing as a whole, and thus the pulsations of the system voltage and power supply current can be prevented from increasing. As a result, the capacitance of the smoothing capacitor can be reduced, while fluctuations such as voltage and current pulsations on the DC side of the inverter are reduced.

[0013] In a frequency characteristic of the voltage gain on the DC side obtained by dividing a system voltage, which is a voltage on the DC side of the inverter, by a system current, which is a current on the DC side of the inverter, a first frequency is a frequency at which a value of the voltage gain on the DC side corresponding to the standard inductance is equal to a value of the voltage gain on the DC side corresponding to the high inductance.In a frequency characteristic of the DC-side current gain obtained by dividing a power supply current, which is a current flowing through the DC power supply, by the system current, a second frequency is a frequency at which a value of the DC-side current gain corresponding to the standard inductance is equal to a value of the DC-side current gain corresponding to the high inductance. Preferably, the inductance control unit switches the DC-side inductance to the standard inductance when the switching frequency is lower than a frequency of a switching point set in a frequency range between the first frequency and the second frequency, and to the high inductance when the switching frequency is higher than the frequency of the switching point.

[0014] With this configuration, when the switching frequency changes, the inductance on the DC side switches between the standard inductance and the high inductance at the switching point set in the frequency range between the first frequency and the second frequency. Accordingly, the frequency characteristics of each of the DC-side voltage gain and the DC-side current gain can be switched between the frequency characteristics corresponding to the standard inductance and the frequency characteristics corresponding to the high inductance before and after the switching frequency reaches the switching point frequency.In this case, the resonant frequencies of the respective gains corresponding to the standard inductor and the high inductor are separated in a range of frequencies higher than the switching point frequency and a range of frequencies lower than the switching point frequency. Consequently, when the switching frequency changes, the inductance on the DC side can be appropriately switched according to the switching frequency, thus preventing the switching frequency from approaching both of the resonant frequencies corresponding to the respective inductors. As a result, the values ​​of the respective gains can be kept low.As a result, the frequency component twice the switching frequency and the harmonic components generated according to the rotational speed of the rotary electric machine can be prevented from increasing as a whole, and thus the pulsations of the system voltage and power supply current can be prevented from increasing. As a result, the capacitance of the smoothing capacitor can be reduced, while fluctuations such as voltage and current pulsations on the DC side of the inverter are reduced.

[0015] For each of the frequency characteristics of the DC-side voltage gain and the DC-side current gain, the two resonant frequencies are separated according to the corresponding inductances on both sides of the frequency range where the switching point is set. The width of the frequency range where the switching point can be set is determined according to the difference between the first and second frequencies. Accordingly, when the difference between the first and second frequencies is larger, the switching point frequency is easier to set farther from the two resonant frequencies. When the difference between the first and second frequencies is larger, the switching point frequency can be set with a greater degree of freedom.Appropriately adjusting the first and second frequencies and the switching point frequency can effectively reduce the pulsation of at least one of the system voltage and the power supply current, which is preferable. The first and second frequencies are determined based on the respective gains corresponding to the standard inductance and the high inductance. Therefore, it is equally important to appropriately adjust each of the two switchable inductance levels on the DC side. As one aspect of the present invention, the standard inductance, the high inductance, and the switching point frequency are preferably adjusted so that a pulsation amplitude of the system voltage is within a predefined allowable range.As one aspect of the present invention, the standard inductance, the high inductance, and the frequency of the switching point are preferably adjusted so that a pulsation amplitude of the power supply current is within a predefined allowable range.

[0016] To set the switching point in the frequency range between the first and second frequencies, it is preferable to consider margins of the pulsation amplitudes of the system voltage and the power supply current corresponding to the switching point frequency with respect to the allowable ranges for the corresponding pulsation amplitudes. In this case, considering that the first frequency is determined based on the frequency characteristics of the voltage gain on the DC side, the pulsation amplitude of the power supply current at the first frequency is preferably within the allowable range thereof with a certain amount of margin.In contrast, considering that the second frequency is determined based on the frequency characteristics of the current gain on the DC side, the pulsation amplitude of the system voltage at the second frequency is preferably within the allowable range of this with a certain amount of margin. If the pulsation amplitudes of the power supply current and the system voltage are within the allowable ranges for the respective pulsation amplitudes, the switching point is preferably set at a frequency corresponding to the larger of the margins.

[0017] As one aspect of the present invention, in a case where a margin of the pulsation amplitude of the power supply current with respect to the predefined allowable range for the power supply current when the switching frequency is the first frequency is larger than a margin of a pulsation amplitude of the system voltage with respect to the predefined allowable range for the system voltage when the switching frequency is the second frequency, the frequency of the switching point is preferably set closer to the first frequency than a median value of the first frequency and the second frequency, and in a case where the margin of the pulsation amplitude of the power supply current with respect to the allowable range thereof when the switching frequency is the first frequency is smaller than the margin of the pulsation amplitude of the system voltage with respect to the allowable range thereof when the switching frequency is the second frequency,the frequency of the switching point is preferably set closer to the second frequency than the median value. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a block diagram schematically showing an example of a system structure of a driving device for a rotary electric machine. Fig. Figure 2 is a block diagram showing a control model of a DC power supply unit. Fig. Figure 3 shows a frequency characteristic of a gain (Vdc / Idc) when only a resistance component is considered. Fig. Figure 4 shows the frequency characteristic of the gain (Vdc / Idc) when the resistance component and an inductance component are taken into account. Fig. Figure 5 shows a frequency characteristic of a gain (Ib / Idc) when only the resistance component is considered. Fig. Figure 6 shows the frequency characteristic of the gain (Ib / Idc) when the resistance component and the inductance component are taken into account. Fig. Figure 7 is a waveform diagram showing variations in the frequency characteristic of the gain (Vdc / Idc) corresponding to variations in the inductance component. Fig. Figure 8 is a waveform diagram showing variations in the frequency characteristic of the gain (Ib / Idc) corresponding to variations in the inductance component. Fig. 9 is a diagram showing a condition for determining a frequency of a switching point in the frequency characteristic. Fig. 10 is a diagram showing the condition for determining the frequency of the switching point in the frequency characteristic. Fig. Figure 11 is a graph showing a change in the frequency characteristic of the gain (Vdc / Idc) associated with switching an inductor on the DC side. Fig. Figure 12 is a graph showing a change in the frequency characteristic of the gain (Ib / Idc) associated with the switching of the inductance on the DC side. Fig. 13 is a partial block diagram showing another embodiment of a switching unit of the inductance on the DC side. Fig. 14 is a partial block diagram showing another embodiment of the DC side inductance switching unit. Fig. 15 is a partial block diagram showing another embodiment of the DC side inductance switching unit. Fig. 16 is a partial block diagram showing another embodiment of the switching unit of the inductor on the DC side. Fig. 17 is a diagram showing a correspondence map of the switching frequency according to a rotational speed of an electric rotary machine. Fig. Figure 18 is a diagram showing another correspondence map of the switching frequency according to the rotational speed of the electric rotary machine. MODES OF OPERATION FOR CARRYING OUT THE INVENTION

[0018] Based on the drawings, an embodiment of the present invention will be described using an example of a rotary electric machine driving device that controls a rotary electric machine MG serving as a source of driving power of a hybrid vehicle, an electric vehicle, and the like. A block diagram of Fig. 1 schematically shows a system structure of a drive device for a rotary electric machine 100. The rotary electric machine MG as the source of the driving power of the vehicle is a rotary electric machine that operates with an alternating current having a plurality of phases (here, a three-phase alternating current) and can serve as both an electric motor and an electric generator.

[0019] A vehicle such as an automobile that cannot be supplied with electric power from an overhead line as in the case of a railway is equipped with a direct current power supply as a power source for driving the rotating electric machine MG, including secondary cells (battery) such as nickel-hydrogen cells or lithium-ion cells or electric double-layer capacitors. In the present embodiment, a battery 11 (high-voltage direct current power supply) with a power supply voltage of approximately 200 [V] to 400 [V] is provided as the large-capacity high-voltage direct current power supply for supplying power to the rotating electric machine MG. A direct current flowing through the battery 11 will be referred to as "battery current (power supply current)" where appropriate in the following description.The rotating electric machine MG is an AC rotating electric machine, so an inverter 10 for performing power conversion between direct current and alternating current is provided between the battery 11 and the rotating electric machine MG. A direct current voltage between a positive power supply line P (positive high-voltage direct current line) and a negative power supply line N (negative high-voltage direct current line) on the DC side of the inverter 10 is called "system voltage Vdc" when appropriate in the following description. The battery 11 can supply power to the rotating electric machine MG via the inverter 10 and can store power generated by and received from the rotating electric machine MG. A smoothing capacitor 40 (DC link capacitor) is provided.A DC link capacitor (DC link capacitor) for smoothing the DC voltage (system voltage Vdc) is provided between the inverter 10 and the battery 11. The smoothing capacitor 40 stabilizes the DC voltage, which fluctuates in response to a fluctuation in the power consumption of the rotary electric machine MG.

[0020] The battery 11 is formed by a plurality of battery cells and has an internal impedance including an internal resistance (resistance component) and an internal inductance (induction component). In the present embodiment, these are referred to as battery resistance Rb and battery inductance Lb. The battery 11 is connected to the inverter 10 using, for example, metal wiring elements called bus bars. Such bus bars also have a line impedance including a line resistance (resistance component) and a line inductance (induction component). That is, the wiring connecting the battery 11, the smoothing capacitor 40, and the inverter 10 has a wiring impedance including a wiring resistance and a wiring inductance. In the present embodiment, these are referred to as wiring resistance Rw and wiring inductance Lw.

[0021] An inductance switching unit 50 capable of switching the amount of inductance (induction component) is provided between a positive terminal of the battery 11 and a positive terminal of the smoothing capacitor 40. In the present embodiment, the inductance switching unit 50 includes a switch (mechanical switch) 51 interposed in a wiring connecting the positive terminal of the battery 11 to the positive terminal of the smoothing capacitor 40, and an auxiliary coil 52 connected in parallel to the switch 51. The auxiliary coil 52 has an impedance including an inductance (induction component). In the present embodiment, this is referred to as an auxiliary inductance La.The switch 51 is controlled on-off and off based on a control signal from a controller 8, which will be described later, to electrically interpose the auxiliary coil 52 between the battery 11 and the smoothing capacitor 40. The switch 51 is turned on to electrically connect the battery 11 to the smoothing capacitor 40 without interposing the auxiliary coil 52. In the present embodiment, the controller 8 cooperates with the inductance switching unit 50 to serve as an "inductance control unit" in the present invention.

[0022] When viewed from the battery 11 side of the inverter 10, the internal resistance of the DC power supply unit including wiring elements such as bus bars (internal power supply resistance Rps) is the sum of the battery resistance Rb and the wiring resistance Rw. The internal inductance of the DC power supply unit (internal power supply inductance Lps) is the sum of the battery inductance Lb and the wiring inductance Lw when the switch 51 is on, and the internal inductance of the DC power supply unit is obtained by further adding the additional inductance La to the sum when the switch 51 is off. However, in many cases, the battery resistance Rb is much larger than the wiring resistance Rw, and the battery inductance Lb and the additional inductance La are much larger than the wiring inductance Lw.Consequently, in the following description, the battery resistance Rb is used as the internal power supply resistance Rps and the battery inductance Lb (plus the additional inductance La depending on the state of the switch 51) is used as the internal power supply inductance Lps.

[0023] The internal power supply resistance Rps is a resistance on the battery 11 side of the inverter 10 and can be referred to as the "DC-side resistance" or "DC-side resistance." The internal power supply inductance Lps is an inductance on the battery 11 side of the inverter 10 and can be referred to as the "DC-side inductance Ld" or "DC-side inductance Ld." In the present embodiment, the inductance Ld on the DC side when the switch 51 is on (battery inductance Lb) is referred to as the "standard inductance Ls," and the inductance Ld on the DC side when the switch 51 is off (the sum of the battery inductance Lb and the additional inductance La) is referred to as the "high inductance Lh." The high inductance Lh is significantly higher than the standard inductance Ls. A block diagram of Fig. 2 shows a control model representing a relationship between the voltage between terminals (battery voltage VB) of the battery 11 as the DC power supply unit and the system voltage Vdc.

[0024] The inverter 10 converts the DC power at the system voltage Vdc into AC power with a plurality of phases (n phases, where n is a natural number; here, three phases) and supplies the AC power to the rotating electric machine MG. The inverter 10 also converts the AC power generated by the rotating electric machine MG into DC power and supplies the DC power to the DC power supply. The inverter 10 includes a plurality of switching elements. A power semiconductor device such as an insulated gate bipolar transistor (IGBT) or a power metal oxide semiconductor field-effect transistor (MOSFET) is preferably used as the switching elements.Instead of such a silicon (Si) device, a silicon carbide (SiC) device such as a SiC MOSFET or a SiC static induction transistor (SiC SIT), or a complex compound power device such as a gallium nitride MOSFET (GaN MOSFET) operating at high frequencies may preferably be used as the switching element. In the present embodiment, an IGBT 3 is used as each of the switching elements, as shown in FIG. Fig. 1 is shown.

[0025] The inverter 10 for performing the energy conversion between direct current and alternating current with a plurality of phases (here, three-phase alternating current) is formed by a bridge circuit having a number of arms corresponding to the number of phases (here, three phases), which is known. Specifically, as shown in Fig. As shown in Figure 1, two of the IGBTs 3 are connected in series between the positive DC side (positive power supply line P on the positive side of the DC power supply) of the inverter 10 and the negative DC side (negative power supply line N on the negative side of the DC power supply) of the inverter 10 to form an arm 10A. The IGBT 3 connected to the positive power supply line P is called an upper-stage IGBT (upper-stage switching element or high-side switching element), and the IGBT 3 connected to the negative power supply line N is called a lower-stage IGBT (negative-side switching element or low-side switch).

[0026] When the alternating current with multiple phases is three-phase alternating current, three lines (10U, 10V, and 10W for three phases) of such series circuits (10A for one arm) are connected in parallel. Specifically, a bridge circuit is formed in which one set of series circuits (10A arm) corresponds to each of the U phase, V phase, and W phase of the rotary electric machine MG. In the upper-stage IGBT in each phase, the collector terminal is connected to the positive power supply line P, and the emitter terminal is connected to the collector terminal of the lower-stage IGBT in the same phase. The emitter terminal of the lower-stage IGBT in each phase is connected to the negative power supply line N.A midpoint of the series circuit (arm 10A) formed by a pair of IGBTs 3 in each phase, that is, a connection point between the upper-stage IGBT and the lower-stage IGBT in each phase, is connected to the corresponding stator coil of the rotary electric machine MG. A freewheeling diode 39 (regenerative diode) is connected in parallel to each of the IGBTs 3. The freewheeling diode 39 is connected in parallel to each of the IGBTs 3 in such a manner that the cathode terminal of the freewheeling diode 39 is connected to the collector terminal of the IGBT 3, and the anode terminal of the freewheeling diode 39 is connected to the emitter terminal of the IGBT 3.

[0027] As in Fig. 1, the inverter 10 is controlled by a controller 8. The controller 8 includes an electronic control unit (ECU) constructed using a logic circuit such as a microcomputer as a core element. In the present embodiment, the ECU controls the rotating electric machine MG through the inverter 10 by performing current control using a vector control method based on a target torque TM of the rotating electric machine MG, which is provided to the controller 8 as a request signal from, for example, another controller such as an in-vehicle ECU (not shown). The ECU of the controller 8 includes various functional units for current control, and the functional units are implemented through cooperation of hardware such as the microcomputer and software (programs).It should be noted that although the present embodiment assumes an example in which the inverter 10 and the inductance switching unit 50 are controlled by the same control device 8, both components may of course be controlled by different control devices.

[0028] An actual current flowing through the stator coil in each phase of the rotating electric machine MG is detected by a current sensor 12, and the controller 8 acquires the detection result. A rotation sensor 13 detects a magnetic pole position of a rotor of the rotating electric machine MG at any time, and the controller 8 acquires the detection result. The rotation sensor 13 is configured, for example, by a resolver. The magnetic pole position represents a rotation angle of the rotor in terms of an electrical angle. The ECU of the controller 8 performs feedback control of the rotating electric machine MG based on the detection results of the current sensor 12 and the rotation sensor 13.

[0029] The vehicle is equipped with a low-voltage battery (low-voltage DC power supply) (not shown) serving as a lower-voltage power supply than the battery 11, in addition to the battery 11 as the high-voltage DC power supply. The low-voltage battery has a power supply voltage of, for example, 12 V to 24 V and supplies power to the control device 8 (ECU), electrical components such as an audio system, lighting equipment, interior lighting equipment, instrument lighting devices, power windows, and control devices for controlling these electrical components. The control device 8 includes, for example, a control circuit and generates a power source suitable for operating the microcomputer and the like based on the power supplied from the low-voltage battery.

[0030] The gate terminal, which serves as the control terminal, of each of the IGBTs 3 constituting the inverter 10 is connected to the control unit 8 (ECU) via a drive circuit 7 and is individually controlled to be switched. The high-voltage circuits for driving the rotary electric machine MG differ significantly in operating voltage (power supply voltage of the circuits) from the low-power circuits such as the ECU having the microcomputer and the like as a core. For this reason, a control signal (switching control signal) for each of the IGBTs 3, generated by the control unit 8 (ECU) serving as a low-voltage circuit, is supplied to the corresponding IGBT 3 through the drive circuit 7 as a gate drive signal of the high-voltage circuit.The drive circuit 7 often includes an insulating element such as a photocoupler or a transformer.

[0031] As described above, the control device 8 is configured by the logic circuit such as the microcomputer serving as a core. In the present embodiment, the control device 8 is configured by the microcomputer serving as a core, which executes a drive program for a rotary electric machine. The microcomputer includes a CPU core, a program memory, a parameter memory, a working memory, a timer, and terminals. The CPU core is a core of the microcomputer and includes an instruction register, an instruction decoder, an arithmetic logic unit (ALU) serving as the main execution body of various operations, tag registers, general-purpose registers, and an interrupt controller.In the present embodiment, while a configuration in which the microcomputer is configured by a semiconductor chip is illustrated, a configuration in which a microcomputer is configured by a combination of a plurality of components may obviously be employed.

[0032] The program memory is a non-volatile memory that stores the control program for an electric lathe. The parameter memory is a non-volatile memory that stores various parameters that are referenced when the program is executed. The parameter memory can be configured in a manner that is not different from the program memory. The program memory and the parameter memory are preferably configured using, for example, a flash memory. The random access memory is a memory for temporarily storing temporary data while the program is running. The random access memory can be volatile and is formed of a dynamic random access memory (DRAM) or a static random access memory (SRAM), which enables fast data reading and writing.

[0033] The timer measures time using a clock cycle of the microcomputer as the minimum resolution. The timer monitors, for example, the execution period of the program. The timer also measures the effective time of the switching control signal for driving the IGBT 3 of the inverter 10 and generates the switching control signal. The timer also manages control periods predefined by the program or parameters, such as the period (basic control period) of executing a current control loop and the output period (switching period Tc) of the switching control signal. The terminals serve as a terminal control unit that outputs, for example, the switching control signal for the IGBT 3 of the inverter 10 through a terminal of the microcomputer and receives the rotation detection signal supplied from the rotation sensor 13 and input to the microcomputer, and the current detection signal from the current sensor 12.

[0034] As in Fig. As shown in Figure 2, the transfer function for the control model of the battery 11, which serves as the DC power supply unit, includes the inductance Ld on the DC side and the capacitance (DC link capacitance Cd) of the smoothing capacitor 40 as impedance components depending on the frequency. As a result, the system voltage Vdc is a function of the frequency. Each of the Fig. 3 and Fig. Figure 4 shows a frequency characteristic of a gain (voltage gain on the DC side) defined by the system voltage Vdc and a system current Idc flowing through the inverter 10. When the inductance Ld on the DC side is not considered, the gain (voltage gain on the DC side) of the system voltage Vdc relative to the system current Idc is defined by formula (1) and has the Fig. 3. When the inductance Ld on the DC side is taken into account, the voltage gain on the DC side is defined by formula (2) and has the Fig. 4 shows the frequency characteristic. [Formula 1] Gain(DC link voltage)=Vdcldc=Rb1+ω2⋅Cd2⋅Rb2 [Formula 2] Gain(DC link voltage)=Vdcldc=Rb2+(ω⋅Ld)2(1−ω2⋅Cd⋅Ld)2+(ω⋅Rb⋅Cd)2

[0035] As can be seen from formulas (1) and (2) and Fig. 3 and Fig. 4, the voltage gain on the DC side becomes smaller as the capacitance (capacitance Cd of the DC link) of the smoothing capacitor 40 increases. In other words, reducing the capacitance of the smoothing capacitor 40 to reduce the size of the smoothing capacitor 40 increases the voltage gain on the DC side and thus reduces the effect of suppressing pulsation of the system voltage Vdc. In addition, as can be seen from the comparison between Fig. 3 and Fig. As can be seen in Figure 4, when the inductance Ld on the DC side, which is the impedance of the DC power supply unit, is taken into account, resonance occurs between the inductance Ld on the DC side and the capacitance Cd of the DC link. This resonance must also be taken into account. In other words, if the inductance Ld on the DC side is not taken into account, simply reducing the capacitance of the smoothing capacitor 40 simply results in a higher voltage gain on the DC side. In contrast, if the inductance Ld on the DC side is taken into account, the resonance greatly increases the voltage gain on the DC side at a certain frequency (resonance frequency). As shown in Fig. As shown in Figure 4, the value of the gain at a resonance point (Q2) when the capacitance Cd of the DC link is equal to C1 [µF] is much larger than the value of the gain at a resonance point (Q1) when the capacitance Cd of the DC link is equal to C2 [µF], which is ten times as large as C1 (=10·C1).

[0036] The gain of a battery current Ib relative to the system current Idc (battery current gain) is also a function of frequency. Each of the Fig. 5 and Fig. Figure 6 shows a frequency characteristic of the gain (battery current gain) defined by the battery current Ib and the system current Idc flowing through the inverter 10. If the inductance Ld on the DC side is not considered, the battery current gain is defined by formula (3) and has the Fig. 5. When the inductance Ld on the DC side is taken into account, the battery current gain is defined by formula (4) and has the Fig. 6. The battery current Ib corresponds to a power supply current flowing through the DC power supply of the present invention, and the battery current gain corresponds to a current gain on the DC side of the present invention. [Formula 3] Gain(battery current)=lbldc=11+ω2⋅Cd2⋅Rb2 [Formula 4] Gain(battery current)=lbldc=1(1−ω2⋅Cd⋅Ld)2+(ω⋅Rb⋅Cd)2

[0037] As can be seen from formulas (3) and (4) and Fig. 5 and Fig. 6, the battery current gain becomes smaller as the capacitance (capacitance Cd of the DC link) of the smoothing capacitor 40 increases. In other words, reducing the capacitance of the smoothing capacitor 40 to reduce the size of the smoothing capacitor 40 increases the gain and thus reduces an effect of suppressing pulsation generated in the battery current Ib. In addition, as can be seen from the comparison between Fig. 5 and Fig. As can be seen in Figure 6, when the inductance Ld on the DC side, which is the impedance of the DC power supply unit, is taken into account, resonance occurs between the inductance Ld on the DC side and the capacitance Cd of the DC intermediate circuit. This resonance must also be taken into account. In other words, if the inductance Ld on the DC side is not taken into account, simply reducing the capacitance of the smoothing capacitor 40 simply results in a higher battery current gain. In contrast, if the inductance Ld on the DC side is taken into account, the resonance greatly increases the battery current gain at a certain frequency (resonance frequency). As shown in Fig. 6, the value of the gain at the resonance point (Q2) when the capacitance Cd of the DC link is equal to C1 [µF] is much larger than the value of the gain at the resonance point (Q1) when the capacitance Cd of the DC link is equal to C2 [µF], which is ten times as large as C1.

[0038] Of the resistance component (R component) and the inductance component (L component) of the battery 11 and the capacitance component (C component) of the smoothing capacitor, the impedance components that depend on frequency are the L component and the C component. Consequently, the value of each of the DC-side voltage gain and the battery current gain increases as the frequency increases from zero, reaches the maximum value (resonance point) at the resonant frequency, and decreases as the frequency increases from the resonance point, which serves as an inflection point. For example, when analyzing at a switching frequency of 100 [Hz] or higher, the resonant frequency can be calculated based on only the resistance component (R component) and the inductance component (L component) of the battery 11.

[0039] Fig. Figure 7 shows simulation results of the voltage gain on the DC side obtained by varying the inductance Ld on the DC side while keeping the battery resistance Rb and the capacitance Cd of the DC link constant. In the present embodiment, Fig. 7 shows the voltage gains on the DC side that are obtained when an inductance Ld on the DC side is equal to L1 [µH], L2 (=2·L1) [µH], which is twice L1 [µH], L3 (≈3.3·L2) [µH], which is approximately 3.3 times L2 [µH], and L4 (=2.5·L3) [µH], which is approximately 2.5 times L3 [µH]. As can be seen from Fig. As can be understood from Figure 7, it is found that the resonance frequency of each of the voltage boosters on the DC side shifts toward a lower frequency as the inductance Ld on the DC side increases. When the smoothing capacitor 40 with a small capacitance is used, as in the case of the present embodiment, the resonance peak of each of the voltage boosters on the DC side becomes sharper depending on the capacitance of the smoothing capacitor 40 as the inductance Ld on the DC side increases.

[0040] Fig. Figure 8 shows simulation results of the battery current gain obtained by varying the inductance Ld on the DC side while keeping the battery resistance Rb and the capacitance of the DC link Cd constant. In the present embodiment, in the same manner as in Fig. 7, shows Fig. 8 shows the battery current gains obtained when the inductance Ld on the DC side is equal to L1 [µH], L2 [µH], L3 [µH] and L4 [µH]. As can be seen from Fig. As can be seen from Figure 8, it is found that the resonance frequency of each of the battery current gains shifts toward a lower frequency as the DC-side inductance Ld increases. When the smoothing capacitor 40 with a low capacitance is used, as in the case of the present embodiment, the resonance peak of each of the battery current gains becomes sharper as the DC-side inductance Ld increases, depending on the capacitance of the smoothing capacitor 40.

[0041] The pulsations of the system voltage Vdc and the battery current Ib occur in association with a fluctuation in the current and voltage associated with the switching of the IGBT 3 of the inverter 10. In other words, the pulsations of the system voltage Vdc and the battery current Ib occur according to a switching frequency fc (inverse of the switching period Tc) of the IGBT 3. For example, it is known that pulsations occur with a frequency component twice the switching frequency fc. In addition, the pulsations also have harmonic components (specifically, sixth-order harmonics and harmonics of an integer multiple of these) generated according to the rotational speed of the rotary electric machine MG.

[0042] In the present embodiment, the switching frequency fc of the IGBT 3 is set to a value that changes according to the rotational speed of the rotating electric machine MG. As an embodiment, a configuration may be adopted in which the switching frequency fc is set proportionally to the rotational speed of the rotating electric machine MG. For example, if the rotational speed of the rotating electric machine MG is designated as "N," the switching frequency fc may be set based on Formula (5). [Formula 5] fc=12π⋅N

[0043] Other embodiments can obviously be employed, provided that the switching frequency fc is set to a value that changes according to the rotational speed of the rotary electric machine MG. As an embodiment, it is also preferable to set a plurality of operating ranges according to the rotational speed of the rotary electric machine MG and to set the switching frequency fc to one of the values ​​that change between the operating ranges (see Fig. 17). Specifically, the switching frequency fc may preferably be set so that it increases gradually (fc1 < fc2 < ...) as the rotational speed of the electric lathe MG increases. In this case, both the rotational speed and the torque of the electric lathe MG may preferably be considered for setting the plurality of operating ranges (see Fig. 18).

[0044] When the switching frequency fc is closer to the resonance frequency between the capacitance Cd of the DC link and the inductance Ld on the DC side, the values ​​of the corresponding gains are larger, so the pulsations are greater. The resonance frequency is determined by the hardware structure of the drive device of the rotary electric machine 100. Therefore, to keep the pulsations of the system voltage Vdc and the battery current Ib low, it is preferable to prevent the values ​​of the DC side voltage gain and the battery current gain from increasing excessively. In particular, when the capacitance of the smoothing capacitor 40 is reduced to reduce its size, sharp resonance peaks occur.Consequently, it is preferable to keep the switching frequency fc, corresponding to the rotational speed of the electric rotary machine MG, from approaching the resonance frequency in order to keep the corresponding gain values ​​low. The following describes a configuration to keep the gains low.

[0045] As described above, the inductance switching unit 50 is provided between the positive pole of the battery 11 and the positive pole of the smoothing capacitor 40, and the controller 8 performs the on-off control of the switch 51 of the inductance switching unit 50. The inductance Ld on the DC side is set to the standard inductance Ls (battery inductance Lb) when the switch 51 is on, and the inductance Ld on the DC side is set to the high inductance Lh (battery inductance Lb + additional inductance La) when the switch 51 is off. Switching the inductance Ld on the DC side in a stepwise manner between the standard inductance Ls and the high inductance La changes the frequency characteristics of the voltage gain on the DC side and the battery current gain according to the level of the inductance Ld on the DC side (see Fig. 9 and Fig. 10). In these examples, the high inductance Lh is set to approximately seven times the standard inductance Ls (Lh ≈ 7-Ls), so that the frequency characteristics of the corresponding gains change greatly according to the switching of the inductance Ld on the DC side.

[0046] In the present embodiment, the switching frequency fc of the IGBT 3 is set proportional to the rotational speed of the rotating electric machine MG. Therefore, the frequency characteristics of the DC-side voltage gain and the battery current gain can be assumed to represent the values ​​of the respective gains corresponding to the rotational speed of the rotating electric machine MG. Therefore, by switching the DC-side inductance Ld between the standard inductance Ls and the high inductance Lh according to the switching frequency fc (in other words, the rotational speed of the rotating electric machine MG), the values ​​of the respective gains can be kept low.In this case, the inductance Ld on the DC side is switched when the switching frequency fc reaches a certain value (in other words, when the rotational speed of the rotary electric machine MG reaches a certain value), so the values ​​of the corresponding gains are kept low. In order to keep the pulsations of both the system voltage Vdc and the battery current Ib low, in this operation, the values ​​of both the voltage gain on the DC side and the battery current gain, each of which is a function of the switching frequency fc, must be kept low in a balanced manner. This can be achieved by appropriately adjusting the rotational speed of the rotary electric machine MG or the switching frequency fc, which determines the timing (switching point) of switching the inductance Ld on the DC side (a frequency fs of the switching point; see, for example, . Fig. 11).

[0047] In the present embodiment, in order to adjust the frequency fs of the switching point of the inductance Ld on the DC side, relationships of this with two specific frequencies (a first frequency f1 and a second frequency f2) are considered as shown in Fig. 9 and Fig. 10. The first frequency f1 is a frequency (other than zero) at which the value of the voltage gain on the DC side corresponding to the standard inductance Ls is equal to the value of the voltage gain on the DC side corresponding to the high inductance Lh in the frequency characteristic of the voltage gain on the DC side shown in Fig. 9. In other words, the first frequency f1 is a frequency in a frequency range between a resonance frequency frp1 corresponding to the standard inductance Ls and a resonance frequency frp2 corresponding to the high inductance Lh, at which the two values ​​of the voltage gains on the DC side corresponding to the inductances Ls and Lh are equal. The second frequency f2 is a frequency (other than zero) at which the value of the battery current gain corresponding to the standard inductance Ls is equal to the value of the battery current gain corresponding to the high inductance Lh in the frequency characteristics of the battery current gain shown in Fig. 10. In other words, the second frequency f2 is a frequency in the frequency range between the resonance frequency frp1 corresponding to the standard inductance L2 and the resonance frequency frp2 corresponding to the high inductance Lh, at which the two values ​​of the battery current gains corresponding to the inductances Ls and Lh are equal.

[0048] As from Fig. 9 and Fig. As can be seen from Fig. 10, the frequency range between the first and second frequencies f1 and f2 is located away from both of the two resonance frequencies frp1 and frp1. This is found to keep the values ​​of the DC-side voltage gain and the battery current gain in the frequency range between the first and second frequencies f1 and f2 lower than those at the resonance frequencies frp1 and frp2. Therefore, the switching frequency fc corresponding to the rotational speed of the rotary electric machine MG, which is set as the switching point (i.e., the frequency fs of the switching point), is preferably set in the frequency range between the first and second frequencies f1 and f2.

[0049] However, the first frequency f1 is only determined by the frequency characteristic of the voltage gain on the DC side, so that the battery current gain at the first frequency f1 can be relatively high in some cases, as in Fig. 10. If the value of the battery current gain increases, the pulsation amplitude of the battery current Ib may exceed its allowable range. In contrast, the second frequency f2 is determined only by the frequency characteristics of the battery current gain, so the voltage gain on the DC side at the second frequency f2 may be relatively high in some cases, as shown in Fig. 9. If the value of the voltage gain on the DC side increases, the pulsation amplitude of the system voltage Vdc may exceed its allowable range. The pulsation amplitude of the battery current Ib is a pulsation amplitude obtained by considering both a fundamental wave generated according to the switching frequency fc and harmonic components (specifically, a sixth-order harmonic component and harmonic components (6f, 12f, 18f, ...) of integer multiple orders thereof) generated according to the rotational speed of the rotary electric machine MG. The same applies to the pulsation amplitude of the system voltage Vdc.Accordingly, as one embodiment, the frequency fs of the switching point is preferably set so that the pulsation amplitude of the system voltage Vdc and the pulsation amplitude of the battery current Ib are within the limits of the allowable ranges for the respective pulsation amplitudes.

[0050] The frequency fs of the switching point described above is preferably determined by considering margins of the pulsation amplitudes of the system voltage Vdc and the battery current Ib with respect to the respective allowable ranges thereof. As one embodiment, the frequency fs of the switching point is preferably set to a frequency corresponding to the relatively larger of the margins of the pulsation amplitude of the battery current Ib when the switching frequency fc is the first frequency f1 and the pulsation amplitude of the system voltage Vdc when the switching frequency fc is the second frequency f2, with respect to the allowable ranges for the respective pulsation amplitudes.Specifically, when the margin of the pulsation amplitude of the battery current Ib with respect to the allowable range thereof when the switching frequency fc is the first frequency f1 is larger than the margin of the pulsation amplitude of the system voltage Vdc with respect to the allowable range thereof when the switching frequency fc is the second frequency f2, the frequency fs of the switching point is preferably set closer to the first frequency f1 than to an average value fm of the first and second frequencies f1 and f2.Instead, when the margin of the pulsation amplitude of the battery current Ib with respect to the allowable range thereof when the switching frequency fc is the first frequency f1 is smaller than the margin of the pulsation amplitude of the system voltage Vdc with respect to the allowable range thereof when the switching frequency fc is the second frequency f2, the frequency fs of the switching point is preferably set closer to the second frequency f2 than to the mean value fm.

[0051] Fig. 11 and Fig. 12 shows an example in which the margin regarding the pulsation amplitude of the battery current Ib at the first frequency f1 is smaller than the margin regarding the pulsation amplitude of the system voltage Vdc at the second frequency f2. In this example, the frequency fs of the switching point is set in the frequency range between the mean value fm and the second frequency f2.

[0052] Fig. 11 and Fig. 12 shows states of fluctuations in the DC-side voltage gain and the battery current gain associated with the switching of the DC-side inductance Ld according to the switching frequency fc (i.e., according to the rotational speed of the rotary electric machine MG). When the rotational speed of the rotary electric machine MG is relatively low and the switching frequency fc is lower than the switching point frequency fs, the DC-side inductance Ld is maintained at the standard inductance Ls by the inductance switching unit 50. As a result, at and around the time when the switching frequency fc coincides with the resonance frequency frp2 corresponding to the high inductance Lh, the DC-side inductance Ld is maintained at the standard inductance Ls, and truly dominant values ​​of the DC-side voltage gain and the battery current gain are kept low.

[0053] When the rotational speed of the rotary electric machine MG is comparatively high and the switching frequency fc is equal to or higher than the switching point frequency fs, the inductance Ld on the DC side is maintained at the high inductance Lh by the inductance switching unit 50. As a result, at and around the time when the switching frequency fc coincides with the resonance frequency frp1 corresponding to the standard inductance Ls, the inductance Ld on the DC side is maintained at the high inductance Lh, and the truly dominant values ​​of the DC side voltage gain and the battery current gain are kept low.

[0054] When the rotational speed of the rotary electric machine MG gradually increases from a comparatively low speed and the switching frequency fc reaches the switching point frequency fs, the inductance Ld on the DC side is gradually switched from the standard inductance Ls to the high inductance Lh. This switching instantly switches the frequency characteristics of the voltage gain on the DC side and the battery current gain from those corresponding to the standard inductance Ls to those corresponding to the high inductance Lh, between before and after the switching frequency fc reaches the switching point frequency fs. Although the actual dominant voltage gain on the DC side gradually increases at this time (see Fig. 11), the pulsation amplitude of the system voltage Vdc is within the allowable range of this (not shown). The actual dominant battery current gain decreases gradually (see Fig. 12) and the pulsation amplitude of the battery current Ib becomes further smaller (not shown).

[0055] In this way, when the switching frequency fc increases according to the increase in the rotational speed of the rotary electric machine MG, the inductance Ld on the DC side is switched to the high inductance Lh before the switching frequency fc approaches the resonant frequency frp1 corresponding to the standard inductance Ls. In other words, the inductance Ld on the DC side is switched from the standard inductance Ls to the high inductance Lh before the switching frequency fc approaches the resonant frequency frp1, increasing the corresponding gains to excessively high levels. After switching, the switching frequency is already on the high-frequency side of the resonant frequency frp2 corresponding to the high inductance Lh, so the corresponding gains gradually decrease with a further increase in the switching frequency fc.

[0056] In contrast, when the rotational speed of the rotary electric machine MG gradually decreases from a comparatively high speed and the switching frequency fc reaches the switching point frequency fs, the inductance Ld on the DC side is gradually switched from the high inductance Ls to the standard inductance Lh. This switching switches the frequency characteristics of the voltage gain on the DC side and the battery current gain from those corresponding to the high inductance Lh to those corresponding to the standard inductance Ls between before and after the switching frequency fc reaches the switching point frequency fs. Although the actual dominant battery current gain gradually increases at this time (see Fig. 12), the pulsation amplitude of the battery current Ib is within the allowable range of this (not shown). The actual dominant voltage gain on the DC side decreases gradually (see Fig. 11) and the pulsation amplitude of the system voltage Vdc becomes further smaller (not shown).

[0057] In this way, when the switching frequency fc decreases according to the reduction in the rotational speed of the rotary electric machine MG, the inductance Ld on the DC side is switched to the standard inductance Ls before the switching frequency fc approaches the resonance frequency frp2 corresponding to the high inductance Lh. In other words, the inductance Ld on the DC side is switched from the high inductance Lh to the standard inductance Ls before the switching frequency fc approaches the resonance frequency frp2, increasing the corresponding gains to excessively high levels. After switching, the switching frequency fc is already on the low-frequency side compared to the resonance frequency frp1 corresponding to the standard inductance Ls, so the corresponding gains gradually decrease with a further reduction in the switching frequency fc.

[0058] As described above, the inductance Ld on the DC side is switched when the switching frequency fc changes according to the rotational speed of the rotary electric machine MG, so that the switching frequency fc can be prevented from approaching both of the two resonance frequencies frp1 and frp2 corresponding to the inductances Ls and Lh. As a result, the values ​​of the corresponding gains can be kept low over a wide frequency range (see Fig. 11 and Fig. 12), so that the pulsations of the system voltage Vdc and the battery current Ib can be prevented from increasing.

[0059] Generally, in order to reduce the ripple generated according to the switching frequency fc, in some cases, an inductance component (L component) such as a fixed inductor may be provided between the battery 11 and the inverter 10. However, such a configuration is only adopted when the capacitance of the smoothing capacitor 40 is large to a certain extent. In this case, if the capacitance of the smoothing capacitor 40 is reduced, the voltage gain on the DC side and the battery current gain may increase, and thus, the pulsations based on the harmonic components (especially the sixth-order harmonic and the harmonics of integer multiple orders thereof) may increase in the situation where the rotary electric machine MG is driven at a high speed.However, according to the present invention, the inductance Ld on the DC side is switched according to the rotational speed of the rotary electric machine MG, so that fluctuations such as pulsations of the system voltage Vdc and the battery current Ib can be reduced even when a smoothing capacitor 40 with a small capacity is used. Specifically, even when one of the frequency components twice the switching frequency fc and the harmonic components increases according to the rotational speed of the rotary electric machine MG, the inductance Ld on the DC side is switched so that the other component is reduced, whereby the pulsations as a whole can be reduced to a low level. As a result, fluctuations such as pulsations of the system voltage Vdc and the battery current Ib can be effectively reduced.

[0060] The present invention can be broadly applied to drive devices for rotary electric machines designed based on the concept described above. Those skilled in the art will readily understand that appropriate modifications can be made based on the specific embodiment described above without departing from the object of the present invention. Accordingly, the present invention obviously also encompasses other embodiments modified within the scope without departing from the object of the invention.

[0061] For example, the values ​​of the standard inductance Ls and the high inductance Lh, which are switchable as the inductance Ld on the DC side, can be appropriately changed. When the frequency fs of the switching point of the inductance Ld on the DC side is set in the frequency range between the first and second frequencies f1 and f2, as in the described configuration in the present embodiment, the width of the frequency range in which the switching point can be set is determined according to the difference between the first and second frequencies f1 and f2. Accordingly, when the difference between the first and second frequencies f1 and f2 is larger, the frequency fs of the switching point is more easily effectively located away from both resonance frequencies frp1 and frp2, which is preferable.As the difference between the first and second frequencies f1 and f2 increases, the switching point frequency fs can be adjusted with a higher degree of freedom, which is equally desirable. The first and second frequencies f1 and f2 are determined based on the corresponding gains corresponding to the standard inductance Ls and the high inductance Lh. Consequently, it is equally important to appropriately adjust two adjustable levels of the inductance Ld on the DC side. Appropriately adjusting these values ​​can effectively reduce the pulsation amplitude of the system voltage Vdc and the pulsation amplitude of the battery current Ib to low levels.As one embodiment, the standard inductance Ls and the high inductance Lh are preferably set so that the pulsation amplitude of the system voltage Vdc and the pulsation amplitude of the battery current Ib are within the allowable ranges for the respective pulsation amplitudes. While the above-described embodiment shows the example in which the high inductance Lh is set to be approximately seven times the standard inductance Ls, the high inductance Lh may be set higher (for example, ten or more times the standard inductance Ls). This does not preclude cases in which the high inductance Lh is set lower (for example, three to six times the standard inductance Ls).

[0062] As one embodiment, the frequency fs of the switching point may be set to one of the first frequency f1 and the second frequency f2. In this case, the frequency fs of the switching point may be set to the frequency corresponding to the relatively larger of the margins of the pulsation amplitudes of the battery current Ib when the switching frequency fc is the first frequency f1 and the pulsation amplitude of the system voltage Vdc when the switching frequency fc is the second frequency f2, with respect to the allowable ranges of the respective pulsation amplitudes.Specifically, in a case where the margin of the pulsation amplitude of the battery current Ib with respect to the allowable range thereof when the switching frequency fc is the first frequency f1 is larger than the margin of the pulsation amplitude of the system voltage Vdc with respect to the allowable range thereof when the switching frequency fc is the second frequency f2, the frequency fs of the switching point is set to the frequency f1. Instead, if the margin of the pulsation amplitude of the battery current Ib with respect to the allowable range thereof when the switching frequency fc is the first frequency f1 is smaller than the margin of the pulsation amplitude of the system voltage Vdc with respect to the allowable range thereof when the switching frequency fc is the second frequency f2, the frequency fs of the switching point may be set to the second frequency f2.

[0063] In the above-described embodiment, as an example, the frequency fs of the switching point for switching the inductance Ld on the DC side between the standard inductance Ls and the high inductance Lh is set in the frequency range between the first and second frequencies f1 and f2. However, the embodiment of the present invention is not limited to this example. The frequency fs of the switching point can be set outside the frequency range between the first and second frequencies f1 and f2.As an embodiment, the frequency fs of the switching point may be set in a frequency range that is higher than the higher one of the resonance frequency frp2 corresponding to the high inductance Lh in the frequency characteristic of the voltage boost on the DC side and the resonance frequency frp2 corresponding to the high inductance Lh in the frequency characteristic of the battery current boost, and that is lower than the lower one of the first frequency f1 and the second frequency f2.Alternatively, the switching point frequency fs can be set in a frequency range that is lower than the lower of the resonant frequency frp1 corresponding to the standard inductance Ls and the frequency characteristic of the DC-side voltage gain and the resonant frequency frp1 corresponding to the standard inductance Ls in the frequency characteristic of the battery current gain, and higher than the higher of the first frequency f1 and the second frequency f2. In both cases, the switching point frequency fs is preferably set away from the resonant frequencies frp1 and fpr2 so that the values ​​of the DC-side voltage gain and the battery current gain become smaller.

[0064] In the above-described embodiment, only one switching point frequency fs is set, and the DC-side inductance Ld is switched only once within the frequency range between the first and second frequencies f1 and f2. However, the embodiment of the present invention is not limited to this configuration, and a plurality of switching points may be set. As one embodiment, for example, a second switching point may be set in addition to the switching point (first switching point) between the first and second frequencies f1 and f2.In this case, the frequency of the second switching point can be set to a frequency higher than the higher of the resonance frequency frp1 corresponding to the standard inductance Ls in the frequency characteristic of the voltage boost on the DC side and the resonance frequency frp1 corresponding to the standard inductance Ls in the frequency characteristic of the battery current boost, and the inductance Ld on the DC side can be switched to the standard inductance Ls when the switching frequency is lower than that of the first switching point fs, to the high inductance Lh when the switching frequency is higher than that of the first switching point fs and lower than that of the second switching point, and back to the standard inductance Ls when the switching frequency is higher than that of the second switching point.Also in this case, the frequency of the second switching point is preferably set away from the resonance frequency frp1 so that the values ​​of the voltage gain on the DC side and the battery current gain become smaller.

[0065] As one embodiment, the frequency fs of the switching point is set with hysteresis. Specifically, when the switching frequency fc increases according to the increase in the rotational speed of the electric rotary machine MG, the frequency of the switching point can be set on the high-frequency side of the frequency of the switching point when the switching frequency fc decreases according to the decrease in the rotational speed of the electric rotary machine MG.

[0066] Any configuration may be employed as the specific configuration of the inductance switching unit 50, provided that at least switching of the inductance Ld on the DC side between the standard inductance Ls and the high inductance Lh is allowed. Fig. 13 to 16 show other embodiments of the inductance switching unit 50. Fig. 13 shows an example of using a semiconductor switch 53 with semiconductor devices such as thyristors as the switch connected in parallel with the additional coil 52. Fig. 14 shows an example of using a variable reactor 54 that can freely switch the amount of inductance. Fig. 15 shows an example of using a transformer 55, which includes a primary coil connected to a switching power supply (not shown) and a second coil connected between the positive terminal of the battery 11 and the positive terminal of the smoothing capacitor 40. In this example, the secondary coil is saturated with a magnetic field generated by AC power supplied to the primary coil, thereby changing the amount of inductance. Fig.16 shows an example of providing a switching element 5 formed by a semiconductor device (such as a MOSFET or an IGBT) connected in series with the auxiliary coil 52. In this example, on-off control of the switching element 56 saturates the auxiliary coil 52, thereby changing the amount of inductance. Selection from these examples can be made by comprehensively considering, for example, the required installation area, the need for an auxiliary power supply, and the need for a cooling mechanism.

[0067] As one embodiment, a resistor may be interposed between the inductance switching unit 50 and the positive terminal of the smoothing capacitor 40. Adding such a resistor may reduce the peak of the resonance point (reduce the values ​​of the corresponding gains at the resonance point). Based on such a configuration, the inductance switching unit 50 may be configured to switch the inductance Ld on the DC side, as described above.

[0068] In the embodiment described above, the IGBTs 3 are used as the switching elements as an example. However, the configuration of the present invention is also highly suitable for a case where SiC devices such as SiC MOSFETs or SiC SITs are used as the switching elements. That is, the SiC devices have characteristics of smaller switching loss, which can be operated more stably at higher temperatures than the Si devices. Therefore, the SiC devices are characterized by being stably operated with reduced loss even when the switching frequency is comparatively high. For this reason, the configuration of the present invention is particularly preferable when such SiC devices are used as the switching elements and a wide range of frequencies are used as the switching frequencies. INDUSTRIAL APPLICABILITY

[0069] The present invention can be applied to a driving device for an electric rotary machine that drives and controls an AC electric rotary machine. [Description of reference symbols] 8 Control device 10 inverters 11 Battery (DC power supply) 40 smoothing capacitor 50 Inductance switching unit 100 Drive device for an electric lathe Ib battery current (power supply current) IDC system current Ld inductance on the DC side Lh high inductance Ls standard inductance MG electric lathe Vdc system voltage f1 first frequency f2 second frequency fc switching frequency fm mean fs Frequency of the switching point

Claims

[1] A drive device for an electric lathe (100) which drives and controls an AC electric lathe (MG), the drive device for an electric lathe (100) comprising: an inverter (10) electrically connected between a direct current power supply (11) and the rotary electric machine (MG) and switching an electrical power between a direct current and an alternating current; a smoothing capacitor (40) electrically connected between the DC power supply (11) and the inverter (10), and connected between a positive pole and a negative pole of a DC side of the inverter (10); an inverter control unit (8) which controls switching of a switching element of the inverter (10) according to a predetermined switching frequency (fc); and an inductance control unit (8, 50) that switches an inductance (Ld) on the DC side between a positive pole of the DC power supply (11) and a positive pole of the smoothing capacitor (40) according to the switching frequency (fc) between a predefined standard inductance (Ls) and a high inductance (Lh) higher than the standard inductance (Ls). [2] Drive device for an electric rotary machine (100) according to claim 1, wherein, in a frequency characteristic of a voltage gain on a DC side obtained by dividing a system voltage (Vdc), which is a voltage on the DC side of the inverter (10), by a system current (Idc), which is a current on the DC side of the inverter (10), a first frequency (f1) is a frequency at which a value of a voltage gain on the DC side corresponding to the standard inductance (Ls) is equal to a value of the voltage gain on the DC side corresponding to the high inductance (Lh), in a frequency characteristic of the current gain on the DC side obtained by dividing a power supply current (Ib), which is a current flowing through the DC power supply, by the system current (Idc), a second frequency (f2) is a frequency at which a value of the current gain on the DC side corresponding to the standard inductance (Ls) is equal to a value of the current gain on the DC side corresponding to the high inductance (Lh), and the inductance control unit (8, 50) switches the inductance (Ld) on the DC side to the standard inductance (Ls) when the switching frequency (fc) is lower than a frequency of a switching point set in a frequency range between the first frequency (f1) and the second frequency (f2), and to the high inductance (Lh) when the switching frequency (fc) is higher than the frequency of the switching point. [3] A drive device for a rotary electric machine (100) according to claim 2, wherein the standard inductance (Ls), the high inductance (Lh) and the frequency of the switching point are adjusted so that a pulsation amplitude of the system voltage (Vdc) is within a predefined allowable range. [4] A driving device for a rotary electric machine (100) according to claim 2 or 3, wherein the standard inductance (Ls), the high inductance (Lh) and the frequency of the switching point are adjusted so that a pulsation amplitude of the power supply current (Ib) is within a predefined allowable range. [5] The drive device for a rotary electric machine (100) according to any one of claims 2 to 4, wherein, in a case where a margin of a pulsation amplitude of the power supply current (Ib) with respect to the predefined allowable range for the power supply current (Ib) when the switching frequency (fc) is the first frequency (f1) is larger than a margin of the pulsation amplitude of the system voltage (Vdc) with respect to the predefined allowable range for the system voltage (Vdc) when the switching frequency (fc) is the second frequency (f2), the frequency of the switching point is set closer to the first frequency (f1) than to a mean value (fm) of the first frequency (f1) and the second frequency (f2), and in a case where the margin of the pulsation amplitude of the power supply current (Ib) with respect to the allowable range thereof when the switching frequency (fc) is the first frequency (f1),is smaller than the margin of the pulsation amplitude of the system voltage (Vdc) with respect to the permissible range thereof, when the switching frequency (fc) is the second frequency (f2), the frequency of the switching point is set closer to the second frequency (f2) than to the mean value (fm).,

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