JP2013034315A - Inverter control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve a motor driver system with wide variable speed range and low loss.SOLUTION: An inverter control device 100 comprises: a gate signal generation part 101 having an asynchronous PWM mode and a synchronous PWM mode; and an asynchronous/synchronous change part 102. When the gate signal generation part 101 is generating a gate signal to be given to an inverter 10 in the synchronous PWM mode, the asynchronous/synchronous change part 102 determines whether or not a d-axis current becomes positive among currents supplied to a motor 20 from the inverter 10, and changes a generation mode of the gate signal in the gate signal generation part to the asynchronous PWM mode when the determination result is affirmative.

Description

  The present invention relates to an inverter control apparatus that drives a motor at a variable speed, and in particular, has an asynchronous PWM (Pulse Width Modulation) mode and a synchronous PWM mode as a generation mode of a gate signal for driving the inverter. The present invention relates to a control device that generates a gate signal by switching modes.

  As is well known, a permanent magnet synchronous motor is a motor that generates a rotating magnetic field by applying a three-phase AC voltage to a three-phase stator winding and rotates a rotor provided with a permanent magnet by the rotating magnetic field. An inverter is generally used as a means for generating a three-phase AC voltage applied to the three-phase stator winding of the permanent magnet synchronous motor. This inverter is a device that generates an AC voltage by switching an input DC voltage using a switching element. The inverter control device applies a PWM pulse as a gate signal for ON / OFF control to the switching element of the inverter, controls the pulse width of the gate signal, and outputs the frequency of the AC voltage to be output to the inverter. Control the amplitude.

  As a gate signal generation mode in the inverter control device, there is an asynchronous PWM mode. In this asynchronous PWM mode, a gate signal, which is a PWM pulse, is generated by pulse width modulation using a voltage command indicating an AC voltage waveform to be supplied from the inverter to the motor and a carrier having a predetermined frequency asynchronous to the voltage command. It is a mode to do. In this asynchronous PWM mode, the inverter control device controls the motor torque by controlling the current flowing through the stator winding of the motor.

  When a permanent magnet synchronous motor is driven by an inverter, when the motor rotates at a high speed, the induced voltage generated in the stator winding of the motor increases, and the margin of the inverter output voltage with respect to the induced voltage decreases. As a result, the current that generates the torque cannot be supplied from the inverter to the motor, and the torque of the motor is reduced.

One means for solving this problem is field-weakening control described below. First, the current flowing through the stator windings of the motor, along the d-axis current i _d is a component along the d-axis oriented in the direction of the N pole of the rotor of the permanent magnets, the q-axis orthogonal to the d-axis It can be decomposed into q-axis current i _q which is a component. Here, the q-axis current i _q is a current that contributes to generation of magnet torque in the motor, and the d-axis current i _d is a current that contributes to generation of reluctance torque. Field weakening control reduces the induced voltage generated in the stator windings by the rotation of the rotor by flowing the negative d-axis current i _d to the motor stator windings, thereby increasing the q-axis current i _q, the motor This increases the torque.

  By performing this field weakening control, the problem of insufficient torque in a region where the rotational speed of the motor is high can be solved to some extent. However, there is a limit to field weakening control, and when the rotational speed of the motor exceeds a certain limit, there arises a problem that a desired motor cannot be obtained in the high speed rotation region even if field weakening control is performed in the asynchronous PWM mode.

  Therefore, there is a case where control is performed such that the gate signal generation mode in the control device is switched from the asynchronous PWM mode to, for example, the one-pulse synchronous PWM mode. Here, in the synchronous PWM mode, a gate signal that is a PWM pulse is generated by pulse width modulation using a voltage command instructing an AC voltage waveform to be supplied from the inverter to the motor and a carrier synchronized with the voltage command. It is a mode to do. The 1-pulse synchronous PWM mode is a mode in which one PWM pulse is generated during one cycle of the voltage command. By switching to the synchronous PWM mode such as one pulse, a high fundamental wave voltage can be supplied from the inverter to the motor, so that the problem of insufficient torque in the high-speed rotation region can be solved.

There is Patent Document 1 as a document disclosing a technology related to switching from the asynchronous PWM mode to the synchronous PWM mode. In Patent Document 1, there is an invention that reduces torque fluctuation in switching between an asynchronous PWM mode (referred to as sine wave control in Patent Document 1) and a one-pulse synchronous PWM mode (referred to as rectangular wave control in Patent Document 1). It is disclosed. The outline is as follows.
(1) The phase and amplitude of a sine wave voltage command for generating a torque required for the motor, and the phase of a rectangular wave voltage command are obtained.
(2) The phase and amplitude of the voltage command are changed simultaneously and continuously from a sine wave to a rectangular wave. At this time, the voltage command is trapezoidal (see FIG. 4 of Patent Document 1).
(3) The trapezoidal voltage command in (2) above is compared with the carrier, and a gate signal (PWM pulse) for the inverter is generated.

  Further, as shown in FIG. 13 (corresponding to FIG. 6 of Patent Document 1), the generation mode of the gate signal is switched to the 1-pulse synchronous PWM mode (rectangular wave control mode in Patent Document 1) in the high rotation and high torque regions. . Here, in the high rotation region ((a) of FIG. 13), the back electromotive force of the motor is high, exceeds the direct current intermediate voltage of the inverter, and torque is likely to decrease. Therefore, the 1-pulse synchronous PWM mode is applied in the range above the switching line.

JP-A-11-285288

“Basics and Applications of AC Motor Variable Speed Drive”, edited by the Institute of Electrical Engineers of Japan, Corona

  By the way, when only the inverter loss is considered, the synchronous PWM mode is more advantageous than the asynchronous PWM mode. This is because, in the synchronous PWM mode, the number of times the inverter is switched is small. For example, in the synchronous PWM mode of one pulse, the voltage polarity of the PWM pulse is once from positive to negative and from negative to positive once in one cycle of the voltage command. Only switching. Therefore, it is possible to minimize the switching loss of the inverter.

  However, in the synchronous PWM mode, a current flows from the inverter to the motor even when the motor is unloaded, and a motor loss occurs. On the other hand, in the asynchronous PWM mode, when the motor is in a no-load state, almost no current flows from the inverter to the motor. Therefore, in order to realize a motor drive system having a wide variable speed range and a low loss as a whole, as disclosed in Patent Document 1, in the region where the rotational speed is lower than the threshold value, the asynchronous PWM mode is used. In a region where the gate signal for the inverter is generated and the rotation speed is higher than the threshold value, it is a good idea to generate the gate signal for the inverter in the synchronous PWM mode.

  However, even if the rotational speed is higher than the threshold value, it may not always be a good idea to switch to the synchronous PWM mode in view of the loss of the inverter and the motor as a whole. Further details are as follows.

  First, when switching from the asynchronous PWM mode to the synchronous PWM mode, when a negative d-axis current flows and field weakening control works (when the output voltage of the inverter is lower than the induced voltage), there is a problem of insufficient torque. Eliminate.

  However, in a situation where a positive d-axis current flows, the magnetic flux density in the motor increases and the motor loss (that is, the output of the inverter that does not contribute to the generation of torque) increases. Thus, when switching to the synchronous PWM mode in the region where the motor is rotating at high speed, the loss of the inverter and the motor as a whole may increase.

  The present invention has been made in view of the circumstances described above, and an object of the present invention is to provide an inverter control device that can realize a motor drive system with a wide variable speed range and a low loss.

  The present invention is a means for generating a gate signal for switching ON / OFF of a switching element constituting an inverter that drives a motor, and should be supplied from the inverter to the motor as a generation mode of the gate signal. Asynchronous PWM mode for generating the gate signal by pulse width modulation using a voltage command indicating an AC voltage waveform and a carrier having a predetermined frequency asynchronous to the voltage command, and synchronized with the voltage command and the voltage command A gate signal generating means having a synchronous PWM mode for generating the gate signal by pulse width modulation using a carrier, and the gate signal generating means is generating a gate signal to be supplied to the inverter in the synchronous PWM mode, Of the current supplied from the inverter to the motor, the rotor of the motor It is determined whether or not the d-axis current, which is a component corresponding to the direction of the north pole of the permanent magnet, has become positive, and when the determination result is affirmative, the gate signal generation mode of the gate signal generation means And an asynchronous / synchronous switching means for switching to the asynchronous PWM mode.

  According to the present invention, when the gate signal generating means generates a gate signal to be supplied to the inverter in the synchronous PWM mode, if the d-axis current out of the current supplied from the inverter to the motor becomes positive, the gate signal generating means The generation mode of the gate signal can be switched to the asynchronous PWM mode. Therefore, it is possible to prevent the synchronous PWM mode from being continued in a situation where the field weakening does not work, and to avoid an increase in motor loss.

  In a preferred aspect, the asynchronous / synchronous switching means temporarily sets the generation mode of the gate signal in the gate signal generation means when the gate signal generation means generates a gate signal to be supplied to the inverter in the asynchronous PWM mode. When switching to the synchronous PWM mode, it is determined whether or not the d-axis current supplied from the inverter to the motor is 0 or less. If the determination result is affirmative, the gate signal of the gate signal generating means Is switched to the synchronous PWM mode.

  According to this aspect, when the switching to the synchronous PWM mode is performed during the period when the gate signal generating means is generating the gate signal in the asynchronous PWM mode, the field weakening works and the motor loss does not increase. Only in this case, switching to the synchronous PWM mode is performed. Therefore, it is possible to realize a motor drive system capable of high-speed operation without increasing loss.

  In another preferable aspect, the asynchronous / synchronous switching unit is configured to generate a gate signal generation mode in the gate signal generation unit when the gate signal generation unit generates a gate signal to be supplied to the inverter in the asynchronous PWM mode. Is switched to the synchronous PWM mode, it is determined whether or not the d-axis current supplied from the inverter to the motor is less than a predetermined negative value. If the determination result is affirmative, the gate signal The generation mode of the gate signal of the generation means is switched to the synchronous PWM mode.

  In this aspect, hysteresis is provided between the switching from the synchronous PWM mode to the asynchronous PWM mode and the switching from the asynchronous PWM mode to the synchronous PWM mode. Therefore, frequent switching between the synchronous PWM mode and the asynchronous PWM mode can be prevented, and the operation of the motor drive system can be stabilized.

  Various modes can be considered for the means for determining whether or not the d-axis current is equal to or lower than a predetermined value when the gate signal generation mode in the gate signal generation means is switched to the synchronous PWM mode. In a preferred aspect, the control device is configured to detect the DC intermediate voltage input to the switching unit of the inverter, and based on the DC intermediate voltage detected by the DC voltage detecting means, the control PWM device in the synchronous PWM mode. Total voltage for calculating the total magnetic flux generated in the motor based on the output voltage calculation means for calculating the output voltage of the inverter, the output voltage of the inverter calculated by the output voltage calculation means, and the rotation speed of the motor The d-axis current of the motor when the gate signal generating means is operated in the synchronous PWM mode based on the calculating means, the back electromotive voltage at the base frequency of the motor and the total magnetic flux calculated by the total magnetic flux calculating means. Switching load angle calculating means for calculating a switching load angle that is a load angle at which becomes a predetermined value; A load angle calculating means for calculating a load angle for generating torque according to the current torque command in the synchronous PWM mode, a load angle calculated by the load angle calculating means, and a switching load angle calculating means Whether the asynchronous / synchronous switching means performs switching from the asynchronous PWM mode to the synchronous PWM mode based on the comparison result of the load angle comparing means. Determine whether or not.

  In another preferred embodiment, the DC intermediate voltage is not detected but stored in advance in the DC voltage storage means.

  The switching load angle may not be calculated each time, but may be stored in advance as a table calculated by assuming various rotation speeds of the motor, and this table may be referred to.

  Many inverter control devices include a processor and a memory that stores a program to be executed by the processor. Therefore, assuming various motors, a program for causing a computer to function as the control device may be created and distributed to users of inverter control devices.

It is a block diagram which shows the structure of the motor drive system containing the control apparatus which is 1st Embodiment of this invention. It is a figure which shows the relationship between the load angle and torque in the same embodiment. It is a vector diagram which shows the magnetic flux in a motor when a motor is a no-load state in the same embodiment. It is a vector diagram which shows the magnetic flux in a motor when a motor is in a light load state in the embodiment. It is a vector diagram which shows the magnetic flux in a motor when the d-axis current of a motor becomes 0 in the same embodiment. It is a vector diagram which shows the magnetic flux in a motor when the d-axis current of a motor becomes negative in the embodiment. It is a figure which shows the switching method of the asynchronous PWM mode and synchronous PWM mode in the embodiment. It is a figure which shows the effect of the same embodiment. It is a block diagram which shows the structure of the motor drive system containing the control apparatus which is 2nd Embodiment of this invention. It is a block diagram which shows the structure of the motor drive system containing the control apparatus which is 3rd Embodiment of this invention. It is a block diagram which shows the structure of the motor drive system containing the control apparatus which is 4th Embodiment of this invention. It is a figure which illustrates the contents of the change load angle table used in the embodiment. It is a figure which shows the control method of the conventional inverter.

  Embodiments of the present invention will be described below with reference to the drawings.

<First embodiment (basic form)>
FIG. 1 is a block diagram showing a configuration of a motor drive system including a control device according to a first embodiment of the present invention. This motor drive system includes an inverter 10, a motor 20, and a control device 100 according to the present embodiment. In this example, the motor 20 is a permanent magnet synchronous motor. The inverter 10 is a device that generates AC power for driving the motor 20. The inverter 10 has a three-phase structure including a DC power supply 11, a capacitor 12 charged by the DC power supply 11, and an inverter DC intermediate voltage that is a charging voltage of the capacitor 12. It is comprised by the switching part 13 converted into an alternating voltage. Similar to the known inverter, the switching unit 13 of the inverter 10 is a bridge circuit configured by using six sets of IGBTs (Insulated Gate Bipolar Transistors) and flywheel diodes.

  The control device 100 includes a gate signal generation unit 101 and an asynchronous / synchronous switching unit 102. The gate signal generation unit 101 is a device that generates a gate signal for performing ON / OFF switching of each IGBT of the switching unit 13. Similar to a known inverter, the gate signal generation unit 101 of the control device 100 performs pulse width modulation using a voltage command and a carrier for instructing an AC voltage waveform to be supplied to the motor 20, and obtains the pulse width modulation. The supplied PWM pulse is supplied to each IGBT of the switching unit 13 as a gate signal.

  The gate signal generation unit 101 has an asynchronous PWM mode and a one-pulse synchronous PWM mode as generation modes of the gate signal. As described above, the asynchronous PWM mode is a generation mode in which a PWM pulse is generated by pulse width modulation using a voltage command and a carrier having a predetermined frequency asynchronous to the voltage command, and is output as a gate signal. The synchronous PWM mode is a generation mode in which a PWM pulse is generated by pulse width modulation using a voltage command and a carrier synchronized with the voltage command, and is output as a gate signal. The outline of the operation of the gate signal generation unit 101 in each of these modes will be described below.

First, the asynchronous PWM mode will be described. The torque T generated in the rotor of the motor 20 which is a permanent magnet synchronous motor is given by the equation (1).

In this equation (1), P _n is the number of pole pairs, Ψ _m is a magnetic flux generated by a permanent magnet of the rotor and interlinks with the stator winding, i _d is a d-axis current, i _q is a q-axis current, L _d Is a d-axis inductance, and L _q is a q-axis inductance. In the formula (1), the first term is torque generated by the magnetic flux generated by the permanent magnet, and the second term is reluctance torque.

In the asynchronous PWM mode, the gate signal generation unit 101 controls the gate signal supplied to the inverter 10 so that a current that provides a desired torque is supplied from the inverter 10 to the motor 20. At that time, when the output voltage of the inverter 10 has a margin with respect to the terminal voltage of the motor 20, the d-axis current _id and the q-axis current _iq are controlled so that the current value becomes the minimum. When the output voltage of the inverter 10 is lower than the voltage, field weakening control is performed.

  Next, the synchronous PWM mode will be described. Here, a one-pulse synchronous PWM mode will be described as an example.

上記式（２）および（３）において、Ｒａはモータ２０の固定子巻線の巻線抵抗、ωはモータ２０の回転速度により決まる電気角速度である。 When the AC voltage applied to the stator winding of the motor 20 is decomposed into a d-axis voltage v _d that is a component in the d-axis direction and a q-axis voltage v _q that is a component in the q-axis direction in a steady state, these d-axes The voltage v _d and the q-axis voltage v _q are given by the equations (2) and (3).

In the above formulas (2) and (3), Ra is the winding resistance of the stator winding of the motor 20, and ω is the electrical angular velocity determined by the rotational speed of the motor 20.

The relationship between the terminal voltage v _mt of the motor 20, the d-axis voltage v _d, and the q-axis voltage v _q is expressed by the following equation.

Here, assuming that the winding resistance is sufficiently small (Ra≈0), substituting v _d = −Va · sin δ and v _q = Va · cos δ into the equations (2) and (3), the equation (2 ), Equation (3) is solved for i _d and i _q and substituted into Equation (1), Equation (5) is obtained. However, Va is an inverter output voltage, δ is a load angle, that is, an angle formed by the direction of the total magnetic flux Ψ ₀ generated in the motor 20 and the direction of the magnetic flux Ψ _m of the permanent magnet of the rotor.

In the 1-pulse synchronous PWM mode, the gate signal generation unit 101 causes the inverter 10 to output a constant voltage Va having the same frequency as the voltage command. Assuming that the inverter DC voltage charged in the capacitor 12 is _edc , the output voltage Va of the inverter 10 is given by equation (6).

In the 1-pulse synchronous PWM mode, the voltage Va in the above equation (5) is constant, so the torque T generated in the motor 20 depends on the load angle δ. FIG. 2 shows the relationship between the load angle δ and the torque in equation (5). The region where the load angle δ is positive is a region where power running (operation as a motor) is performed in the motor 20. The region where the load angle δ is negative is a region where regeneration (operation as a generator) is performed in the motor 20.
The above is the outline of the operations in the asynchronous PWM mode and the one-pulse synchronous PWM mode.

  The asynchronous / synchronous switching unit 102 is a device that performs switching control of whether the gate signal generation mode of the gate signal generation unit 101 is the asynchronous PWM mode or the synchronous PWM mode. The feature of this embodiment resides in this asynchronous / synchronous switching unit 102.

  Under the prior art, based on the rotational speed of the motor 20, switching control was performed to determine whether the generation mode of the gate signal is the asynchronous PWM mode or the synchronous PWM mode. However, if such uniform switching control based only on the rotational speed is performed, the overall loss of the inverter 10 and the motor 20 may increase when switching to the synchronous PWM mode is performed in the high-speed rotation region. . Therefore, the asynchronous / synchronous switching unit 102 in this embodiment synchronizes the gate signal generation unit 101 on the condition that field weakening control works and there is no disadvantage that the loss of the inverter 10 and the motor 20 as a whole increases. Operate in PWM mode. Hereinafter, the principle of switching control between the asynchronous PWM mode and the synchronous PWM mode performed by the asynchronous / synchronous switching unit 102 will be described.

The loss generated in the inverter 10 and the motor 20 depends on the current supplied from the inverter 10 to the motor 20. Therefore, first, a gate signal was generated in the one-pulse synchronous PWM mode in a state where the counter electromotive voltage generated in the stator winding of the motor 20 was lower than the DC intermediate voltage e _dc charged in the capacitor 12. In this case, the current flowing in the stator winding of the motor 20 is examined.

FIG. 3 shows a vector diagram of magnetic flux in the motor 20 at zero load, that is, at a load angle δ = 0. Here, the total magnetic flux Ψ ₀ generated in the motor 20 can be obtained by Expression (7).

As seen from FIG. 3, d-axis current i _d under the output voltage Va is constant conditions of the inverter 10 even no load flowing through the motor 20. Since further d-axis current i _d is positive, the d-axis current id is strengthen the magnetic flux in the motor 20. Here, in the asynchronous PWM mode, if the torque is zero, almost no current is supplied from the inverter 10 to the motor 20, so that almost no loss occurs in the inverter 10. However, in the synchronous PWM mode, since the output voltage Va of the inverter 10 constant, as shown in FIG. 3, the inverter 10 for the load of the motor 20 flows through the d-axis current i _d from the inverter 10 to the motor 20 at zero Loss. Further, paying attention to the motor 20, even no load d-axis current i _d copper loss is generated in the stator windings of the motor 20 if flows through. When the strengthened flows d-axis current i _d to the magnetic flux direction (i.e., a positive d-axis current i _d is the flow), since the increased magnetic flux density of the iron core of the motor 20, a problem iron loss is increased to generate .

FIG. 4 shows a vector diagram of magnetic flux in the motor 20 at a light load. When the load angle δ increases, the q-axis current i _q begins to flow. However, the d-axis current i _d remains positive. Focusing on the iron loss of the motor 20, also iron loss because the flowing d-axis current i _d to the magnetic flux direction intensified increases.

Load Yuki increases, the load angle δ increases, d-axis current i _d, as shown in FIG. 6 the next i _{d =} 0, as shown in FIG. 5, further load increase is negative. As described above, in the synchronous PWM mode, in the region where the d-axis current id flowing through the motor 20 is 0 or negative, the iron loss in the motor 20 does not increase. Further, when the d-axis current _id is negative, the magnetic flux in the motor 20 is weakened, and the counter electromotive voltage induced in the stator winding of the motor 20 is reduced. Therefore, the q-axis current i _q is increased, and the motor The torque generated at 20 can be increased.

Therefore, asynchronous / synchronous switching unit 102 in this embodiment, whether the period of the gate signal generator 101 is generating a gate signal in the synchronous PWM mode, d-axis current i _d flowing through the motor 20 becomes positive When the determination result is affirmative, the gate signal generation mode of the gate signal generation unit 101 is switched to the asynchronous PWM mode. Further, the asynchronous / synchronous switching unit 102, when the gate signal generation unit 101 generates the gate signal in the asynchronous PWM mode, temporarily switches to the synchronous PWM mode, and the d-axis current i flowing in the motor 20 _It is determined whether _d is 0 or negative, and when the determination result is affirmative, the gate signal generation mode of the gate signal generation unit 101 is switched to the synchronous PWM mode. That is, in this embodiment, as shown in FIG. 7, when the output voltage Va of the inverter 10 is constant, the synchronous PWM mode is adopted in the region where the d-axis current _id is 0 or negative, Asynchronous PWM mode is adopted in the area.

FIG. 8 shows a loss analysis result of the inverter 10 when the back electromotive voltage of the motor 20 is lower than the DC intermediate voltage e _dc of the inverter 10. However, in the asynchronous PWM mode, the flux weakening control is performed at a current phase of 40 degrees, and in the 1-pulse synchronous PWM mode, the condition is i _d = 0 shown in FIG. As shown in FIG. 8, in the 1-pulse synchronous PWM mode, the IGBT turn-on and turn-off losses and the reverse recovery loss of the flywheel diode FWD are greatly reduced in comparison with the asynchronous PWM mode. Reduced by 50%. As described above, according to the present embodiment, when the gate signal generation unit 101 generates the gate signal to be supplied to the inverter 20 in the synchronous PWM mode, the d-axis current among the currents supplied from the inverter 10 to the motor 20. When the signal becomes positive, the gate signal generation mode of the gate signal generation unit 101 can be switched to the asynchronous PWM mode, so that the synchronous PWM mode is avoided in a situation where the field weakening does not work, and the motor loss increases. Can be avoided. Further, according to the present embodiment, when switching to the synchronous PWM mode is performed while the gate signal generation unit 101 is generating the gate signal in the asynchronous PWM mode, the field weakening works and the motor loss occurs. Only when the value does not increase, switching to the synchronous PWM mode is performed. Therefore, it is possible to realize a motor drive system capable of high-speed operation without increasing loss.

Second Embodiment
FIG. 9 is a block diagram showing a configuration of a motor drive system including a control device 100A according to the second embodiment of the present invention. The configurations of the inverter 10 and the motor 20 are the same as those in the first embodiment (FIG. 1). Hereinafter, the configuration of the control device 100A will be described.

Current detecting section 111, U-phase from the inverter 10 motor 20, detects the U-phase current i _u, V-phase current i _v, and W-phase current iw, which are respectively supplied to the respective stator windings of the V-phase and W-phase Means. The three-phase to two-phase conversion unit 112 converts the U-phase current i _u , the V-phase current _iv, and the W-phase current i _w detected by the current detection unit 111 into two in a predetermined stationary orthogonal coordinate system including the α axis and the β axis. It is a means for converting into phase currents i _α and i _β . The two-phase currents i _α and i _β are an α-axis component and a β-axis component of a current vector that rotates in a stationary orthogonal coordinate system. Then, the coordinate conversion unit 113 converts the currents i _α and i _β into a rotation orthogonal coordinate system including a d-axis facing the direction of the N pole provided in the rotor of the motor 20 and a q-axis orthogonal to the d-axis. Is a means for _performing coordinate conversion into a d-axis current _id and a q-axis current _iq . Since the three-phase / two-phase conversion unit 112 and the coordinate conversion unit 113 are well-known techniques, detailed description thereof is omitted, but is described in Non-Patent Document 1, for example.

ここで、モータ２０の回転速度ｎは、回転数検出部１２１により検出される。また、Ｐはモータ２０におけるロータの磁極数であり、極数記憶部１２５に予め記憶されている。 The rotation speed detection unit 121 detects the rotation speed n of the rotor of the motor 20. The DC voltage detection unit 122 detects the DC intermediate voltage e _dc charged in the capacitor 12 and outputs the detected voltage value e _dc to the output voltage calculation unit 123. The output voltage calculation unit 123 calculates the output voltage Va in the synchronous PWM mode according to the above equation (6), and outputs it to the total magnetic flux calculation unit 124. The total magnetic flux calculator 124 calculates the total magnetic flux Ψ ₀ as follows. First, the total magnetic flux calculation unit 124 calculates an electrical angular velocity ω corresponding to the rotational speed of the motor 20 according to Equation (8).

Here, the rotational speed n of the motor 20 is detected by the rotational speed detector 121. P is the number of magnetic poles of the rotor in the motor 20 and is stored in advance in the pole number storage unit 125.

Next, the total magnetic flux calculation unit calculates the total magnetic flux Ψ ₀ according to the above equation (7) based on the electrical angular velocity ω and the output voltage Va calculated by the output voltage calculation unit 123.

The counter electromotive voltage storage unit 126 stores the base frequency f _base and the counter electromotive voltage v _emf of the motor 20 at the base frequency. Here, the base frequency f _base is obtained by converting the maximum value of the rotational speed of the motor 20 at which the motor 20 can operate without reducing the maximum torque into the frequency of the counter electromotive voltage of the motor 20. The switching load angle calculation unit 127 is a means for calculating a switching load angle δ1 that is a load angle δ at which the d-axis current id becomes zero. The switching load angle calculation unit 127 first calculates the magnet magnetic flux Ψ _m according to the equation (9) based on the base frequency f _base and the back electromotive voltage v _emf stored in the back electromotive voltage storage unit 126.

Next, the switching load angle calculation unit 127 calculates the switching load angle δ ₁ according to the equation (10) based on the total magnetic flux Ψ ₀ and the magnet magnetic flux Ψ _m (see FIG. 7).

When the load angle calculation unit 131 switches to the synchronous PWM mode, the load angle δ necessary for generating the torque T according to the current torque command is calculated backward from the above equation (5). At that time, the total magnetic flux Ψ ₀ calculated by the total magnetic flux calculation unit 124 and the d-axis inductance Ld and the q-axis inductance Lq stored in advance in the Ld, Lq storage unit 132 are used.

The load angle comparison unit 141 compares the load angle δ with the switching load angle δ ₁ at which the d-axis current _id becomes zero. If δ <δ ₁ , the mode flag FLG is set to “0”, and if δ ≧ δ ₁ The mode flag FLG is set to “1”.

The asynchronous / synchronous switching unit 142 is configured to generate a gate signal generation mode of the gate signal generation unit 101 when the mode flag FLG is “1” during the period in which the gate signal generation unit 101 generates the gate signal in the asynchronous PWM mode. Is switched to the synchronous PWM mode, and when the mode flag FLG is “0”, the asynchronous PWM mode is maintained. Further, the asynchronous / synchronous switching unit 142 within the time gate signal generator 101 is generating a gate signal in synchronization PWM mode, if the d-axis current i _d calculated by the coordinate conversion unit 113 becomes positive The gate signal generation mode of the gate signal generation unit 101 is switched to the asynchronous PWM mode.

According to this embodiment, the same effect as the first embodiment can be obtained. In the present embodiment, since the calculation of the load angle δ when switching to the synchronous PWM mode is advanced in parallel with the control in the asynchronous PWM mode, the load angle δ is changed to the switching load angle δ ₁ in the control device 100A. It is possible to grasp the approaching situation. Therefore, when switching from the asynchronous PWM mode becomes [delta] ≧ [delta] ₁ to the synchronous PWM mode, it is possible to advance the control for the switching smoothly.

<Third Embodiment>
FIG. 10 is a block diagram showing a configuration of a motor drive system including a control device 100B according to the third embodiment of the present invention. The configurations of the inverter 10 and the motor 20 are the same as those in the first embodiment (FIG. 1). In the control device 100B in the present embodiment, the DC voltage detection unit 122 in the second embodiment (FIG. 9) is replaced with a DC voltage storage unit 128. The DC voltage storage unit 128 is a means for previously storing the inverter DC intermediate voltage e _dc charged in the capacitor 12. When the value of the inverter DC intermediate voltage e _dc hardly fluctuates, the inverter DC intermediate voltage e _dc stored in advance in the DC voltage storage unit 128 is used to perform switching control from the asynchronous PWM mode to the synchronous PWM mode. Also good. Since the contents of this switching control are the same as in the second embodiment, description thereof is omitted.

<Fourth embodiment>
FIG. 11 is a block diagram showing a configuration of a motor drive system including a control device 100C according to the fourth embodiment of the present invention. The configurations of the inverter 10 and the motor 20 are the same as those in the first embodiment (FIG. 1).

  In the control device 100C, the gate signal generation unit 101, the current detection unit 111, the three-phase two-phase conversion unit 112, the coordinate conversion unit 113, the rotation speed detection unit 121, and the Ld, Lq storage unit 132 are the same as those in the second embodiment (FIG. It is the same as 9).

The switching load angle storage unit 129 stores a table that associates the frequency f of the back electromotive voltage generated in the motor 20 with the switching load angle δ ₁ . Hereinafter, a method for creating the table of the switching load angle δ ₁ will be described with specific motor 20 specifications. As an example, it is assumed that the effective value of the counter electromotive voltage at a frequency of 400 Hz of the motor 20 is 380 V and the q-axis inductance Lq is 2.2 mH. Further, it is assumed that the inverter DC intermediate voltage e _dc is 565.7V. Further, it is assumed that the base frequency f _base of the motor 20 is 400 Hz, and the back electromotive voltage v _emf of the motor 20 at the base frequency is 380V. In this case, by substituting f _base = 400 Hz and v _emf = 380 V into equation (9), the magnet magnetic flux Ψm becomes 0.151 Wb.

The inverter output voltage Va is Va = 441.1V when e _dc = 565.7V is substituted into the equation (6). In this case, the switching load angle δ _{1 at} the frequency f is obtained as (Equation 16).

Substituting ψ _m , Va and the frequency f from 350 Hz to 400 Hz into the above equation (11), the switching load angle δ _{1 at} the frequency f = 350 Hz to 400 Hz is obtained. FIG. 12 shows the result. The switching load angle storage unit 129 stores a table of the switching load angle δ ₁ obtained in this way.

When the load angle calculation unit 133 is switched to the synchronous PWM mode, the load angle δ necessary for generating the torque T according to the current torque command is calculated backward from the above equation (5). At that time, the load angle calculation unit 133 obtains the frequency f = nP / 120 of the induced voltage of the motor 20 from the rotation speed n detected by the rotation number detection unit 121, and the total magnetic flux Ψ ₀ = Va determined by this frequency f. The load angle δ corresponding to the torque T is obtained by using / f and the d-axis inductance Ld and the q-axis inductance Lq stored in advance in the Ld, Lq storage unit 132.

The load angle comparison unit 143 reads the switching load angle δ ₁ corresponding to the frequency f of the induced voltage of the motor 20 from the table in the switching load angle storage unit 129, and the read switching load angle δ ₁ and the load angle calculation unit 133. The load angle δ calculated by the above is compared. If δ <δ ₁ , the mode flag FLG is set to “0”, and if δ ≧ δ ₁ , the mode flag FLG is set to “1”.

  The function of the asynchronous / synchronous switching unit 142 is the same as that of the second embodiment. Also in this embodiment, the same effect as the second embodiment can be obtained. Further, according to the present embodiment, since the calculation process of the switching load angle δ1 is replaced with the table reference process, there is an advantage that the calculation load of the control device 100C is less than that of the second embodiment.

<Other embodiments>
Although the first to fourth embodiments of the present invention have been described above, other embodiments are conceivable for the present invention. For example:

(1) The power source of the inverter may be a DC power source as shown, or may be obtained by converting AC to DC with a diode rectifier or the like.

(2) Although a torque command is given as an input to the gate signal generation unit, a method may be used in which a speed command is given and the torque command is obtained from the deviation between the speed command value and the actual speed.

(3) The current detector does not necessarily need to detect a three-phase current, but may detect two phases and obtain the remaining one phase by calculation.

(4) Instead of providing the rotation speed detection unit, a rotation speed prediction unit may be provided.

(5) synchronous transition from PWM mode to the asynchronous PWM mode switching at a load angle [delta] ₁ of d-axis current _{i d} is zero, the transition from the asynchronous PWM mode to the synchronous PWM mode conversely d-axis current id negative The load angle δ ₁ + Δδ (for example, Δδ = 5 degrees) may be started. In this case, hysteresis is provided between the switching from the synchronous PWM mode to the asynchronous PWM mode and the switching from the asynchronous PWM mode to the synchronous PWM mode. Therefore, frequent switching between the synchronous PWM mode and the asynchronous PWM mode can be prevented, and the operation of the motor drive system can be stabilized.

(6) In each of the above embodiments, the single-pulse synchronous PWM mode is adopted as the synchronous PWM mode. However, when the torque control is performed by controlling the load angle under a constant inverter output voltage, the synchronous PWM such as three pulses is used. Applicable to modes.

(7) In the fourth embodiment, the switching load angle storage unit 129 stores the switching load angle table that associates the frequency f of the back electromotive voltage proportional to the rotational speed n of the motor 20 with the switching load angle δ ₁ . However, instead of doing so, the switching load angle storage unit 129 stores another parameter proportional to the rotational speed n of the motor 20 or a switching load angle table that associates the rotational speed n of the motor 20 with the switching load angle δ _1. The switching load angle δ ₁ corresponding to the current rotational speed n may be obtained by referring to this switching load angle table.

(7) In each of the above embodiments, the asynchronous / synchronous switching unit performs the following two switching controls.
Switching control A: When the gate signal generation unit is generating a gate signal in the synchronous PWM mode, it is determined whether or not the d-axis current is positive, and if the determination result is affirmative, the gate signal generation unit The generation mode of the gate signal is switched to the asynchronous PWM mode.
Switching control B: Whether or not the d-axis current becomes 0 or less when the gate signal generation unit generates the gate signal in the asynchronous PWM mode and the gate signal generation mode is switched to the synchronous PWM mode. When the determination result is affirmative, the gate signal generation mode is switched to the synchronous PWM mode.
However, for the switching control B, for example, switching to the synchronous PWM mode may be performed by another method such as switching to the synchronous PWM mode when the rotational speed of the motor exceeds a threshold value. As a result, when the d-axis current becomes positive in the synchronous PWM mode, the switching control A works, so that it is possible to prevent the loss of the inverter and the motor as a whole.

(8) Many inverter control devices include a processor and a memory that stores a program to be executed by the processor. Therefore, assuming various motors, a program for causing a computer to function as a control device according to the present invention may be created, and this program may be distributed to users of inverter control devices. For example, in the second embodiment (FIG. 9), the gate signal generation unit 101, the three-phase two-phase conversion unit 112, the coordinate conversion unit 113, the output voltage calculation unit 123, the total magnetic flux calculation unit 124, the switching load angle calculation unit 127, The entities of the load angle comparison unit 141 and the asynchronous / synchronous switching unit 142 are arithmetic processing executed by the processor according to a program. Therefore, this program is created assuming various motors 20 and installed in the memory of the control device. At this time, parameters stored in various storage units such as the Ld and Lq storage units 132 may be included in the program itself, or may be stored in a non-volatile memory or the like. . The same applies when each embodiment other than the second embodiment is implemented as a program.

DESCRIPTION OF SYMBOLS 10 ... Inverter, 20 ... Motor, 100, 100A, 100B, 100C ... Control device, 101 ... Gate signal generation part, 102, 142 ... Asynchronous / synchronous switching part, 111 ... Current detection part, 112 ... ... three-phase to two-phase conversion section, 113 ... coordinate conversion section, 132 ... Ld, Lq storage section, 131 ... load angle calculation section, 121 ... rotation speed detection section, 122 ... DC voltage detection section, 123 ... ... Output voltage calculation unit, 124 ... Total magnetic flux calculation unit, 125 ... Pole number storage unit, 126 ... Back electromotive voltage storage unit, 127 ... Switching load angle calculation unit, 128 ... DC voltage storage unit, 141, 143... Load angle comparison unit, 129... Switching load angle storage unit.

Claims (8)

A means for generating a gate signal for ON / OFF switching of a switching element constituting an inverter that drives a motor, wherein an AC voltage waveform to be supplied from the inverter to the motor is generated as the generation mode of the gate signal. Asynchronous PWM mode in which the gate signal is generated by pulse width modulation using a voltage command to be instructed and a carrier having a predetermined frequency asynchronous to the voltage command, and a carrier synchronized with the voltage command and the voltage command is used. A gate signal generating means having a synchronous PWM mode for generating the gate signal by pulse width modulation;
When the gate signal generating means generates a gate signal to be supplied to the inverter in the synchronous PWM mode, out of the current supplied from the inverter to the motor, the N pole of the permanent magnet provided in the rotor of the motor It is determined whether or not the d-axis current, which is a component corresponding to the direction, has become positive, and when the determination result is affirmative, the gate signal generation mode of the gate signal generation unit is switched to the asynchronous PWM mode. And an inverter control device.   The asynchronous / synchronous switching means temporarily changes the generation mode of the gate signal in the gate signal generation means to the synchronous PWM mode when the gate signal generation means generates a gate signal to be supplied to the inverter in the asynchronous PWM mode. In the case of switching, it is determined whether or not the d-axis current supplied from the inverter to the motor is 0 or less. If the determination result is affirmative, the gate signal generation mode of the gate signal generation means is set. The control device according to claim 1, wherein the control device is switched to the synchronous PWM mode.   The asynchronous / synchronous switching means temporarily changes the generation mode of the gate signal in the gate signal generation means to the synchronous PWM mode when the gate signal generation means generates a gate signal to be supplied to the inverter in the asynchronous PWM mode. When switching, it is determined whether or not the d-axis current supplied from the inverter to the motor is equal to or less than a predetermined negative value. If the determination result is affirmative, the gate signal of the gate signal generating means The control device according to claim 1, wherein the generation mode is switched to the synchronous PWM mode. DC voltage detecting means for detecting a DC intermediate voltage input to the switching unit of the inverter;
Output voltage calculation means for calculating the output voltage of the inverter in the synchronous PWM mode based on the DC intermediate voltage detected by the DC voltage detection means;
Based on the output voltage of the inverter calculated by the output voltage calculation means and the rotational speed of the motor, total magnetic flux calculation means for calculating the total magnetic flux generated in the motor;
Based on the back electromotive voltage at the base frequency of the motor and the total magnetic flux calculated by the total magnetic flux calculating means, the d-axis current of the motor is a predetermined value when the gate signal generating means is operated in the synchronous PWM mode. A switching load angle calculating means for calculating a switching load angle that is a load angle of
A load angle calculation means for calculating a load angle for generating torque in accordance with the current torque command in the synchronous PWM mode;
Load angle comparison means for comparing the load angle calculated by the load angle calculation means and the switching load angle calculated by the switching load angle calculation means,
4. The asynchronous / synchronous switching unit determines whether or not to switch from the asynchronous PWM mode to the synchronous PWM mode based on a comparison result of the load angle comparing unit. The control device described. DC voltage storage means for storing a DC intermediate voltage input to the switching unit of the inverter;
An output voltage calculation means for calculating an output voltage of the inverter in the synchronous PWM mode based on a DC intermediate voltage stored in the DC voltage storage means;
Based on the output voltage of the inverter calculated by the output voltage calculation means and the rotational speed of the motor, total magnetic flux calculation means for calculating the total magnetic flux generated in the motor;
Based on the back electromotive voltage at the base frequency of the motor and the total magnetic flux calculated by the total magnetic flux calculating means, the d-axis current of the motor is a predetermined value when the gate signal generating means is operated in the synchronous PWM mode. A switching load angle calculating means for calculating a switching load angle that is a load angle of
A load angle calculation means for calculating a load angle for generating torque in accordance with the current torque command in the synchronous PWM mode;
Load angle comparison means for comparing the load angle calculated by the load angle calculation means and the switching load angle calculated by the switching load angle calculation means,
4. The asynchronous / synchronous switching unit determines whether or not to switch from the asynchronous PWM mode to the synchronous PWM mode based on a comparison result of the load angle comparing unit. The control device described. When the gate signal generating means is operated in the synchronous PWM mode, a switching load angle, which is a load angle at which the d-axis current of the motor becomes a predetermined value, and a rotation speed of the motor or a parameter proportional to the rotation speed Switching load angle storage means for storing a table to be associated;
A load angle calculation means for calculating a load angle for generating torque in accordance with the current torque command in the synchronous PWM mode;
Load angle comparison means for comparing the load angle calculated by the load angle calculation means and the switching load angle corresponding to the current motor rotation speed stored in the switching load angle storage means,
4. The asynchronous / synchronous switching unit determines whether or not to switch from the asynchronous PWM mode to the synchronous PWM mode based on a comparison result of the load angle comparing unit. The control device described. Computer
A means for generating a gate signal for ON / OFF switching of a switching element constituting an inverter that drives a motor, wherein an AC voltage waveform to be supplied from the inverter to the motor is generated as the generation mode of the gate signal. Asynchronous PWM mode in which the gate signal is generated by pulse width modulation using a voltage command to be instructed and a carrier having a predetermined frequency asynchronous to the voltage command, and a carrier synchronized with the voltage command and the voltage command is used. A gate signal generating means having a synchronous PWM mode for generating the gate signal by pulse width modulation;
When the gate signal generating means generates a gate signal to be supplied to the inverter in the synchronous PWM mode, out of the current supplied from the inverter to the motor, the N pole of the permanent magnet provided in the rotor of the motor It is determined whether or not the d-axis current, which is a component corresponding to the direction, has become positive, and when the determination result is affirmative, the gate signal generation mode of the gate signal generation unit is switched to the asynchronous PWM mode. A program that functions as a synchronization switching means. Computer
A means for generating a gate signal for ON / OFF switching of a switching element constituting an inverter that drives a motor, wherein an AC voltage waveform to be supplied from the inverter to the motor is generated as the generation mode of the gate signal. Asynchronous PWM mode in which the gate signal is generated by pulse width modulation using a voltage command to be instructed and a carrier having a predetermined frequency asynchronous to the voltage command, and a carrier synchronized with the voltage command and the voltage command is used. A gate signal generating means having a synchronous PWM mode for generating the gate signal by pulse width modulation;
When the gate signal generating means generates a gate signal to be supplied to the inverter in the synchronous PWM mode, out of the current supplied from the inverter to the motor, the N pole of the permanent magnet provided in the rotor of the motor It is determined whether or not the d-axis current that is a component corresponding to the direction has become positive, and when the determination result is affirmative, the gate signal generation mode of the gate signal generation means is switched to the asynchronous PWM mode, When the gate signal generation unit generates a gate signal to be supplied to the inverter in the asynchronous PWM mode, if the gate signal generation mode in the gate signal generation unit is switched to the synchronous PWM mode, the inverter When the d-axis current supplied to the motor is determined to be 0 or less and the determination result is affirmative Program for causing to function as an asynchronous / synchronous switching means for switching the mode for generating a gate signal of the gate signal generating means to the synchronous PWM mode.

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