JP2016119779A - Control device for inverter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a control device for an inverter by which a motor is easily started.SOLUTION: A control device is configured to control an inverter that outputs an AC voltage to a motor including a field magnet and an armature. An inverter control part controls the inverter by using primary magnetic flux control in which the inverter is controlled over an initial excitation term T1, the armature generates a stop magnetic field for stopping the field magnet at a predetermined stop position relatively to the armature, and a primary magnetic flux λ0 that is a combination of a chain magnetic flux, generated by the field magnet, to the armature and a magnetic flux generated by a reaction of the armature is controlled on the basis of a primary magnetic flux command value λ0* that is a command value of the primary magnetic flux λ0, after the lapse of the initial excitation term T1. A primary magnetic flux command output part outputs the primary magnetic flux command value λ0* at a start time point of the primary magnetic flux control to the inverter control part after setting it at a value greater than the primary magnetic flux λ0 while the motor is not rotated, during the initial excitation term T1.SELECTED DRAWING: Figure 6

Description

  The present invention relates to an inverter control device.

  Patent Document 1 describes a control method for starting an electric motor. In Patent Document 1, an initial excitation period is provided in order to rotate the rotor of the electric motor to a predetermined initial position. In this initial excitation period, the switching element of the upper arm is turned off in the U phase, and the switching element of the upper arm is turned on in the V phase and the W phase. Note that the switching element of the lower arm of each phase is controlled opposite to the switching element of the upper arm. As a result, the rotor rotates to the initial position corresponding to the switch-on pattern.

  Non-Patent Document 1 describes a method for controlling an electric motor. Non-Patent Document 1 employs primary magnetic flux control for controlling the primary magnetic flux of an electric motor.

Japanese Patent No. 5001642

Kazunori Kaku, Naoki Yamamura, Joe Tsunehiro, “One Sensorless Control Method of DC Brushless Motor”, The Institute of Electrical Engineers of Japan D, 111, 8, 1991, p.639-644

  However, when the load torque of the mechanical load connected to the electric motor is large, the rotor may end the rotation at a position shifted from the initial position according to the switching pattern.

  When the primary magnetic flux control is performed in a state where the rotor is shifted from the initial position, there is a case where only a primary magnetic flux smaller than the primary magnetic flux command is generated and a necessary torque cannot be generated. In this case, the starting of the electric motor may fail.

  In view of the above, an object of the present invention is to provide an inverter control device that easily starts an electric motor.

  A first aspect of an inverter control device according to the present invention is a control device that controls an inverter (1) that outputs an AC voltage to an electric motor (2) having a field (21) and an armature (22). 3), controlling the inverter over an initial excitation period (T1), generating a magnetic field in the armature to stop the field at a predetermined rotational position with respect to the armature, After the initial excitation period, a primary magnetic flux command value that is a command value of the primary magnetic flux is a primary magnetic flux (λ0) that is a combination of the interlinkage magnetic flux (Λa) to the armature by the field and the magnetic flux by the armature reaction. Using the primary magnetic flux control controlled based on (λ0 *), the inverter control unit (31) for controlling the inverter, and the primary magnetic flux command value (λ0 *) at the start of the primary magnetic flux control The primary magnetic flux (λ0 when the motor is not rotating during the excitation period (T1). ) And a primary magnetic flux command output unit (32) that outputs a value set to the inverter control unit.

  A second aspect of the inverter control device according to the present invention is the inverter control device according to the first aspect, wherein the primary magnetic flux command output unit (32) is an initial period from the start of the primary magnetic flux control. At (T21), the primary magnetic flux command value is reduced with time and outputted to the inverter control unit.

  A third aspect of the inverter control device according to the present invention is the inverter control device according to the second aspect, wherein the primary magnetic flux command output unit (32) The primary magnetic flux command value (λ0 *) is set to a value that minimizes the amplitude of the alternating current output from the inverter (20).

  According to the first aspect of the control apparatus for an inverter according to the present invention, the primary magnetic flux command value at the start of the primary magnetic flux control is larger than the primary magnetic flux that stops the motor during the initial excitation period. It becomes easy.

  According to the second aspect of the inverter control device of the present invention, the M axis along the primary magnetic flux and the T axis whose phase is advanced by 90 degrees from the M axis are set. If the primary magnetic flux is reduced, the M-axis component (M-axis current) of the current output from the inverter is reduced, so that power consumption can be reduced.

  According to the third aspect of the inverter control device of the present invention, it contributes to reduction of power consumption.

It is a figure which shows roughly an example of a structure of a power converter device. It is a figure which shows an example of a structure of an inverter roughly. It is a figure which shows an example of a vector diagram roughly. It is a figure which shows an example of a vector diagram roughly. It is a figure which shows an example of a vector diagram roughly. It is a figure which shows an example of a primary magnetic flux roughly. It is a figure which shows an example of an electric current schematically. It is a figure which shows roughly an example of the relationship between a primary magnetic flux and the amplitude of an electric current.

  FIG. 1 schematically shows an example of an electric motor drive device. The electric motor drive device includes an inverter 1 and a control device 3.

  A DC voltage is input to the inverter 1. The inverter 1 is controlled by the control unit 3, converts this DC voltage into an AC voltage, and outputs it to the synchronous motor 2.

  FIG. 2 is a diagram schematically showing an example of the internal configuration of the inverter 1. For example, the inverter 1 is a three-phase inverter, and outputs a three-phase AC voltage from the output terminals Pu, Pv, and Pw. These output terminals Pu, Pv, Pw are connected to the synchronous motor 2. The inverter 1 includes, for example, switching elements Sup and Sun, Svp, Svn, Swp, and Swn and diodes Dup, Dun, Dvp, Dvn, Dwp, and Dwn. Note that “u”, “v”, and “w” included in the reference numerals indicating the respective configurations indicate that the configurations belong to the U phase, the V phase, and the W phase, respectively. For example, the switching elements Sup, Sup, the diodes Dup, Dun, and the output terminal Pu belong to the U phase.

  The switching elements Sxp, Sxn (x represents u, v, w, hereinafter the same) are connected in series between the DC lines LH, LL to which a DC voltage is applied. The switching element Sxp is connected between the DC line LH and the output terminal Px, and controls whether or not a current flows from the DC line LH toward the output terminal Px by conduction / non-conduction. The switching element Sxn is connected between the DC line LL and the output terminal Px, and controls whether or not a current flows from the output terminal Px to the DC line LL due to conduction / non-conduction. The diodes Dxp and Dxn are connected in parallel to the switching elements Sxp and Sxn, respectively, and their forward directions are directions from the DC line LL to the DC line LH.

  When the switching elements Sxp and Sxn are appropriately controlled by the control device 3, the inverter 1 can convert a DC voltage into an AC voltage and output it.

  The synchronous motor 2 has a field 21 and an armature 22. The field magnet 21 has, for example, a permanent magnet, and supplies an interlinkage magnetic flux (hereinafter also referred to as a field magnetic flux) linked to the armature 22. The armature 22 has, for example, U-phase, V-phase, and W-phase armature windings 221 that are connected to the output terminals Pu, Pu, and Pw of the corresponding inverter 1, respectively. When the three-phase AC voltage from the inverter 1 is applied to the three-phase armature winding 221, the armature 22 applies a rotating magnetic field corresponding to the three-phase AC voltage to the field magnet 21. The field 21 rotates with respect to the armature 22 according to the rotating magnetic field.

  The control device 3 includes an inverter control unit 31 and a primary magnetic flux command output unit 32. The primary magnetic flux command output unit 32 generates a primary magnetic flux command value [λ *] for a primary magnetic flux (described later) generated in the synchronous motor 2, and outputs this to the inverter control unit 31. The inverter control unit 31 controls the inverter 1 by executing primary magnetic flux control for controlling the primary magnetic flux based on the primary magnetic flux command value [λ *].

  Here, the control device 3 includes a microcomputer and a storage device. The microcomputer executes each processing step (in other words, a procedure) described in the program. The storage device is composed of one or more of various storage devices such as a ROM (Read Only Memory), a RAM (Random Access Memory), a rewritable nonvolatile memory (EPROM (Erasable Programmable ROM), etc.), and a hard disk device, for example. Is possible. The storage device stores various information, data, and the like, stores a program executed by the microcomputer, and provides a work area for executing the program. It can be understood that the microcomputer functions as various means corresponding to each processing step described in the program, or can realize that various functions corresponding to each processing step are realized. Further, the control device 3 is not limited to this, and various procedures executed by the control device 3 or various means or various functions to be realized may be realized by hardware.

<Outline of primary magnetic flux control>
FIG. 3 is a vector diagram showing the relationship between the primary magnetic flux [λ0] (symbol [] represents a vector quantity; the same applies hereinafter) in the synchronous motor 2 and the field magnetic flux [Λa] in the synchronous motor 2. The field magnetic flux [Λa] is generated by, for example, the permanent magnet when the synchronous motor 2 has a permanent magnet, and the field winding when the synchronous motor 2 has a field winding. Occurs when current flows through the wire.

  In the illustration of FIG. 3, a dq rotating coordinate system, an MT rotating coordinate system, and an Mc-Tc rotating coordinate system are shown. The d-axis is set in phase with the field magnetic flux [Λa], and the q-axis advances 90 degrees with respect to the d-axis. Therefore, the rotational speed ωe of the dq rotational coordinate system can be grasped as the rotational speed of the synchronous motor 2 when viewed from a so-called electrical angle. The M axis is set in phase with the primary magnetic flux [λ0], and the phase of the T axis advances 90 degrees with respect to the M axis. The phase of the Tc axis advances by 90 degrees with respect to the Mc axis. The Mc-Tc rotating coordinate system is a control coordinate system used in the control device 3.

  The primary magnetic flux [λ0] is a combination of the magnetic flux [λi] due to the armature reaction generated by the current flowing through the armature winding 221 and the field magnetic flux [Λa]. As is well known, the magnetic flux [λi] due to the armature reaction is determined by the current flowing through the armature winding 221 and the inductance of the armature winding 221.

  The output torque Te output from the synchronous motor 2 includes the M-axis component (hereinafter also referred to as M-axis current) and the T-axis component (hereinafter also referred to as T-axis current) of the current flowing through the armature winding 221 as IT and IM, respectively. Assuming that the M-axis component and the T-axis component of the primary magnetic flux [λ0] are λT and λM, the following expression is used.

  Te = λM · IT−λT · IM (1)

  According to the definition of the MT rotating coordinate system, since the T-axis component λT of the primary magnetic flux [λ0] is zero, the output torque Te is expressed by the following equation.

  Te = λM · IT (2)

  As described above, the output torque Te is the product of the M-axis component λM of the primary magnetic flux [λ0] and the T-axis current IT. Since the T-axis component λT is zero, the magnitude of the primary magnetic flux [λ0] is represented by the M-axis component λM. Hereinafter, the magnitude of the primary magnetic flux [λ0] may be referred to as a primary magnetic flux λ0 (= λM).

  In the primary magnetic flux control, the primary magnetic flux [λ0] is controlled based on the primary magnetic flux command value [λ *]. More specifically, the Tc axis component of the primary magnetic flux command value [λ *] for the primary magnetic flux [λ0] is set to zero, and the Mc axis component is set to the command value λ0 *. Since the Tc-axis component of the primary magnetic flux command value [λ *] is zero, the command value λ0 * is hereinafter also referred to as a primary magnetic flux command value. Then, in order to control the primary magnetic flux [λ0] based on the primary magnetic flux command value λ0 *, the inverter control unit 31 generates a switching signal based on the primary magnetic flux command value λ0 *, and sends these to the switching elements Sxp and Sxn. Is output.

  Such primary magnetic flux control is well known, and for example, a technique such as Non-Patent Document 1 can be applied. Therefore, detailed description is omitted here, and only an outline of an example is described. For example, an alternating current flowing through the synchronous motor 2 (more specifically, the armature winding 221) is detected using a predetermined current detection unit, and this is coordinate-converted to a current value in the Tc-Mc axis rotation coordinate system. For this coordinate conversion, the rotation angle of the control coordinate system is used.

  Next, a voltage command value for the output voltage of the inverter 1 is generated on the Tc-Mc axis rotation coordinates using the rotation speed command value, the primary magnetic flux command value λ0 *, and the current value according to a known voltage equation. To do. Then, this is coordinate-transformed to generate a three-phase voltage command value, and switching signals for the switching elements Sxp and Sxn are generated based on the three-phase voltage command value. Generation of a switching signal based on a three-phase voltage command value is also well known, and is performed based on, for example, a comparison between a three-phase voltage command value and a triangular wave.

  As a result, a primary magnetic flux [λ0] substantially equal to the primary magnetic flux command value λ0 * is generated, and a current for outputting a necessary output torque flows to the synchronous motor 2. And the synchronous motor 2 will rotate appropriately. Ideally, the Mc-Tc rotating coordinate system coincides with the MT rotating coordinate system.

<Outline of DC excitation control>
Now, when starting the synchronous motor 2, the inverter control part 31 performs direct current excitation control in the initial excitation period prior to primary magnetic flux control. This DC excitation control is a control for making the rotational position of the field 21 relative to the armature 22 coincide with a predetermined initial position. That is, the synchronous motor 2 is started by positioning the field magnet 21 at the initial position and performing the primary magnetic flux control based on the initial position. This initial position corresponds to the initial value of the rotation angle of the control coordinate system in the primary magnetic flux control.

  In such DC excitation control, the inverter control unit 31 controls the inverter 1 to cause the armature 22 to generate a stop magnetic field for stopping the field 21 at a predetermined initial position. As the control for generating such a stop magnetic field, for example, the technique of Patent Document 1 or Non-Patent Document 1 can be employed. An example is described below.

  For example, during the initial excitation period, one of the switching patterns that allows the switching elements Sxp and Sxn of each phase to conduct exclusively is adopted. Here, the term “zero switching pattern” is used to collectively refer to a switching pattern for conducting all the switching elements Sxp and a switching pattern for conducting all the switching elements Sxn. In these zero switching patterns, the output terminals Pu, Pv, and Pw are short-circuited with each other, and a voltage cannot be output to the armature 22. Therefore, switching patterns other than these zero switching patterns are employed in the initial excitation period. However, as described later, when a switching pattern other than the zero switching pattern is adopted, the zero switching pattern may be used in combination.

  In the direct current excitation control, for example, the switching elements Sup and Svp are made conductive and the switching element Swn is made conductive. As a result, currents Iu, Iv, and Iw flow through the armature windings 221 of the respective phases through current paths corresponding to the switching patterns. More specifically, currents Iu and Iv flow from the output ends Pu and Pv to the U-phase and V-phase armature windings 221, respectively, and they are joined together via the W-phase armature winding 221. A current Iw flows to the output terminal Pw.

  A magnetic field is generated in the armature winding 221 of each phase by the currents Iu, Iv, and Iw. A magnetic field obtained by synthesizing this magnetic field (hereinafter also referred to as an armature magnetic field) is generated in the entire armature 22. Since the magnetic field generated in each armature winding 221 is generated by currents Iu, Iv, and Iw corresponding to the switching pattern, the direction of the armature magnetic field of the armature 22 depends on the switching pattern. The stop magnetic field means a magnetic field in which the direction of the armature magnetic field is substantially maintained in one direction, and the rotating magnetic field means a magnetic field in which the armature magnetic field is substantially rotated over time.

  If one switching pattern is employed over the initial excitation period, an armature magnetic field (stop magnetic field) in a direction determined by one of the switching patterns is generated over the initial excitation period.

  4 and 5 schematically show examples of vector diagrams in the initial excitation period. 4 and 5 also show the current vector [I]. The current vector [I] is a vector of the current output from the inverter 1 (current flowing through the armature winding 221), and the direction thereof coincides with the direction of the armature magnetic field.

  When an armature magnetic field is applied to the field 21, the d-axis of the field 21 (permanent magnet) rotates along the direction of the armature magnetic field as shown in FIG. That is, the field 21 stops at the initial position indicated by the direction of the armature magnetic field (direction of the current vector [I]). At this time, since the current vector [I] coincides with the d-axis, the torque current (T-axis current IT) becomes zero, and the M-axis also follows the d-axis.

  However, when the mechanical load of the synchronous motor 2 is heavy (the load torque is large), the d-axis can deviate from the armature magnetic field. For example, the field 21 can be stopped in the state of FIG. At this time, although the synchronous motor 2 is stopped, an output torque slightly smaller than the load torque of the mechanical load is output. Therefore, in FIG. 4, the T-axis current IT, which is the T-axis component of the current indicating the torque current, is not zero.

  The initial excitation period is a sufficient time required until the field magnet 21 is stopped.

<Initial primary magnetic flux control>
If the primary magnetic flux control is started in a state where the field 21 (d-axis) is deviated from the initial position as shown in FIG. 4, only the primary magnetic flux λ0 smaller than the primary magnetic flux command value λ0 * may be generated. The reason will be briefly described. The magnetic flux [λi] of the armature reaction for generating the primary magnetic flux λ0 equal to the primary magnetic flux command value λ0 * is shifted from the M-axis and the d-axis as compared with the state where the M-axis and the d-axis coincide (FIG. 5) The state (Fig. 4) is larger. That is, the necessary current is larger in the state of FIG. 4 than in the state of FIG. Therefore, if the primary magnetic flux control is performed on the assumption that the d-axis and the M-axis coincide with each other, a necessary amount of current does not flow, and the primary magnetic flux λ0 decreases.

  If the primary magnetic flux λ0 becomes small in this way, sufficient output torque Te cannot be output, and the synchronous motor 2 may not be started properly.

  Therefore, the primary magnetic flux command output unit 32 outputs a primary magnetic flux command value λ0 * larger than the primary magnetic flux λ0 at the end of the initial excitation period to the inverter control device 31. At the end of the initial excitation period, the synchronous motor 2 is considered to be stopped. Therefore, the primary magnetic flux at the end of the initial excitation period can also be described as the primary magnetic flux when the synchronous motor 2 is not rotating during the initial excitation period.

  FIG. 6 schematically shows an example of the primary magnetic flux λ0. In FIG. 6, the primary magnetic flux λ0 is indicated by a broken line in the DC excitation period T1, and the primary magnetic flux command value λ * is indicated as the primary magnetic flux in the primary magnetic flux control period T2 in which the primary magnetic flux control is performed thereafter. Has been. This is because in the ideal primary magnetic flux control, the primary magnetic flux λ0 matches the primary magnetic flux command value λ *. FIG. 6 shows a part of the initial excitation period T1, for example, the initial excitation period T1 from the state where the synchronous motor 2 is stopped according to the stop magnetic field. In the primary magnetic flux period T2 after the initial excitation period T1, primary magnetic flux control is performed. In the illustration of FIG. 6, the primary magnetic flux command value λ0 * at the start time t1 of the primary magnetic flux control is set to be larger than the primary magnetic flux λ0 at the end of the initial excitation period T1.

  The primary magnetic flux in the initial excitation period T1 can be obtained by simulation or experiment taking into account the mechanical load of the synchronous motor 2.

  Thereby, in the initial stage of the primary magnetic flux period T2, the synchronous motor 2 can output a high output torque Te. Therefore, it is easy to start the synchronous motor 2.

  By the way, the load torque (or the average value of the load torque in one rotation of the synchronous motor 2) is high at the start, and when it decreases with the passage of time, the output torque Te to be output by the synchronous motor 2 also decreases with the passage of time. To do. Therefore, as illustrated in FIG. 6, in the initial period T21 in the primary magnetic flux period T2, the primary magnetic flux command output unit 32 may reduce the primary magnetic flux command value λ0 * with the passage of time. In the illustration of FIG. 6, the primary magnetic flux command value λ0 * is reduced in proportion to time.

  FIG. 7 schematically illustrates a waveform of a current flowing through one armature winding 221. By reducing the primary magnetic flux command value λ0 * in the initial period T21, the current amplitude in the initial period T21 decreases with the passage of time. This is because reducing the primary magnetic flux command value λ0 * mainly reduces the M-axis current IM. Thereby, reduction of the power consumption which arises with the synchronous motor 2 in the initial period T21 can be aimed at.

  In addition, if the reduction rate with respect to time of primary magnetic flux command value (lambda) 0 * is enlarged, primary magnetic flux (lambda) 0 will reduce rapidly. For example, when the reduction rate of the primary magnetic flux λ0 is larger than the reduction rate with respect to time of the load torque, that is, when the primary magnetic flux λ0 decreases more rapidly than the load torque, the T-axis current IT increases by the primary magnetic flux control. (See equation (2)).

  Therefore, it is desirable to set the reduction rate of the primary magnetic flux command value λ0 * so that the magnitude of the current vector [I] does not increase. As a specific example, it is desirable to set the reduction rate of the primary magnetic flux command value λ0 * so that the T-axis current IT does not increase. For example, if the reduction rate of the primary magnetic flux λ0 is smaller than the reduction rate with respect to time of the load torque, the T-axis current IT does not increase. Therefore, the reduction rate of the primary magnetic flux command value λ0 * is smaller than the reduction rate with respect to time of the load torque. It is desirable.

  Such a reduction rate of load torque with respect to time can be known in advance by simulation or experiment.

  Next, the primary magnetic flux command value λ0 * in the period T22 after the initial period T21 will be described. In this period T22, the primary magnetic flux command value λ0 * may be set so that the amplitudes of the currents (alternating currents) Iu, Iv, Iw output from the inverter 1 are minimized. FIG. 8 is a diagram illustrating the relationship between the primary magnetic flux λ0 (that is, the M-axis component λM) and the amplitude ia of the alternating current output from the inverter 1 when the output torque Te is constant. FIG. 8 shows that the amplitude ia has a minimum value with respect to the primary magnetic flux λ0. The above relationship with respect to various output torques Te can be obtained in advance by simulation or experiment.

  The primary magnetic flux command output unit 32 generates a primary magnetic flux command value [λ *] that minimizes the amplitude ia based on the above relationship, and outputs this to the inverter control unit 31.

  Thereby, the primary magnetic flux [λ0] is controlled so that the amplitude ia is minimized, and the synchronous motor 2 can be controlled with higher efficiency. In other words, power consumption can be reduced.

  In the above example, one of the switching patterns is adopted over the initial excitation period T1. However, there are only a few types of this switching pattern. This is because, in this switching pattern, the switching elements Sxp and Sxn of each phase are made to conduct exclusively to each other, and the zero switching pattern is not adopted. Therefore, if only one of the switching patterns is employed in the initial excitation period T1, the initial position is selected from the rotational positions corresponding to several types.

  However, the present embodiment is not limited to this. By adopting a plurality of switching patterns at a predetermined duty ratio in the initial excitation period T1, an arbitrary rotational position can be adopted as the initial position. In this case, a zero switching pattern may also be adopted.

  In the present invention, the above-described various embodiments can be appropriately modified and omitted within the scope of the present invention as long as they do not contradict each other.

DESCRIPTION OF SYMBOLS 1 Inverter 2 Synchronous motor 3 Control apparatus 31 Inverter control part 32 Primary magnetic flux command output part

Claims (3)

A control device (3) for controlling an inverter (1) that outputs an AC voltage to an electric motor (2) having a field (21) and an armature (22),
Controlling the inverter over an initial excitation period (T1), generating a magnetic field in the armature to stop the field at a predetermined rotational position with respect to the armature, after the initial excitation period, Based on a primary magnetic flux command value (λ0 *) that is a command value of the primary magnetic flux, a primary magnetic flux (λ0) that is a combination of the interlinkage magnetic flux (Λa) to the armature by the field and the magnetic flux by the armature reaction. Using the primary magnetic flux control to control the inverter, the inverter control unit (31) for controlling the inverter,
The primary magnetic flux command value (λ0 *) at the start of the primary magnetic flux control is set to a value larger than the primary magnetic flux (λ0) when the motor is not rotating in the initial excitation period (T1). An inverter control device comprising: a primary magnetic flux command output unit (32) that outputs to the inverter control unit.   The primary magnetic flux command output unit (32) reduces the primary magnetic flux command value over time and outputs it to the inverter control unit in an initial period (T21) from the start of the primary magnetic flux control. The inverter control device described in 1.   The primary magnetic flux command output unit (32) sets the primary magnetic flux command value (λ0 *) to a value that minimizes the amplitude of the alternating current output by the inverter (20) after the initial period (T21). The inverter control device according to claim 2.

Images