JP2016167899A - Motor control device and electrical equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a motor control system capable of obtaining position information from non-energization phases independently of a switching situation of energization phases.SOLUTION: A motor control device comprises: a power conversion circuit (4) connected with respective both ends of stator coils (33U, 33V, and 33W) of a plurality of phases provided on a motor (3); a voltage detection circuit (50) that detects an inter-terminal voltage of the stator coils (33U, 33V, and 33W) of each phase; and a position calculation part (5) that calculates a rotational angle (θ) of the motor (3) on the basis of the inter-terminal voltage of an open phase, detected by the voltage detection circuit (50).SELECTED DRAWING: Figure 1

Description

  The present invention relates to a motor control device and an electric device.

  As a background art of this technical field, the abstract of the following Patent Document 1 states that “the current flowing through the motor changes due to load torque fluctuation and the length of the commutation overlap period changes in the commutation overlap period. Prevents false detection of position information and realizes a sensorless drive system capable of high-efficiency drive from the extremely low speed range near zero speed, "" Ends the inverter commutation overlap period from the output value of the first-order lag filter " The position is estimated by determining whether or not the terminal voltage value of the non-energized phase of the permanent magnet motor 2 has exceeded the energization mode switching threshold after the commutation overlap period ends, and the inverter 1 is determined from the position estimation result. “De-energized phase is set”.

JP 2014-79031 A

In the technique disclosed in Patent Document 1, a commutation spike voltage is generated at a non-conduction phase terminal after the conduction phase is switched. And while this commutation spike voltage is generated (commutation overlap period), position information cannot be obtained from the open phase electromotive voltage of the non-conduction phase.
The present invention has been made in view of the above-described circumstances, and an object thereof is to provide a motor control device and an electric device that can obtain position information from a non-energized phase regardless of the switching state of the energized phase.

  In order to solve the above problems, in the present invention, a power conversion circuit connected to each end of a plurality of stator windings provided in a motor, and a voltage between terminals of the stator windings of each phase are obtained. It has a voltage detection circuit to detect, and a position calculation part which calculates the rotation angle of the motor based on the voltage between the terminals of the open phase detected by the voltage detection circuit.

  According to the present invention, position information can be obtained from a non-energized phase regardless of the switching status of the energized phase.

It is a schematic block diagram of the motor control system by one Embodiment of this invention. It is a figure which shows the characteristic of the back electromotive force of an open phase with respect to a rotation angle. It is a figure which shows the motor efficiency with respect to the rotational speed of a motor.

[Configuration of the embodiment]
Next, the configuration of a motor control system according to an embodiment of the present invention will be described with reference to the block diagram shown in FIG.
In FIG. 1, a motor 3 is a permanent magnet type synchronous motor, and has a rotor (not shown) and a stator core (not shown). This rotor has a permanent magnet embedded therein and is configured to be rotatable. The stator core has a substantially cylindrical back yoke surrounding the rotor and a plurality of teeth protruding from the back yoke toward the rotor. The U-phase, V-phase, and W-phase stator windings 33U, 33V, and 33W shown in FIG. 1 are wound around these teeth.

  The power conversion apparatus 1 performs PWM (pulse width modulation) modulation on the DC voltage Ed supplied from the DC power supply 2 and applies it to the motor 3, and controls the power conversion circuit 4 for PWM modulation. A pulse control unit 7 that supplies a signal, a position calculation unit 5 that calculates the rotation angle θ of the motor 3, and an inverter control unit 6 that outputs a speed command signal to the pulse control unit 7 are provided. In a three-phase bridge circuit 41 provided inside the power conversion circuit 4, MOSFETs (Metal-Oxide-Semiconductor Field-Effect Transistors) 11, 12 are connected in series. Similarly, the MOSFETs 13 and 14 and the MOSFETs 15 and 16 are connected in series, and a DC voltage Ed is applied to these series circuits by the DC power supply 2. The connection points of the MOSFETs 11 and 12, the connection points of the MOSFETs 13 and 14, and the connection point of the MOSFETs 15 and 16 are connected to one ends of the stator windings 33U, 33V, and 33W, respectively.

  The three-phase bridge circuit 43 includes MOSFETs 21 to 26, and these MOSFETs 21 to 26 are connected in the same manner as the MOSFETs 11 to 16 described above. The voltages at the connection points of the MOSFETs 21 and 22, the connection points of the MOSFETs 23 and 24, and the connection points of the MOSFETs 25 and 26 are respectively connected to the other ends of the stator windings 33U, 33V, and 33W. The gate drivers 42 and 44 apply gate voltages to the MOSFETs 11 to 16 in the three-phase bridge circuit 41 and the MOSFETs 21 to 26 in the three-phase bridge circuit 43, respectively.

  Currents supplied from the three-phase bridge circuit 41 to the first input terminal of each phase of the motor 3 are referred to as Iu, Iv, and Iw. These may be collectively referred to as a current Iuvw as shown in FIG. The measured value of the current Iuvw is supplied to the position calculation unit 5. The terminal voltages of the stator windings 33U, 33V, and 33W are referred to as Vu, Vv, and Vw. The voltage detection circuit 50 includes differential amplifiers 51, 52, and 53, which detect voltages Vu, Vv, and Vw. The position calculation unit 5 calculates the rotor position of the motor 3, that is, the rotation angle θ based on the voltages Vu, Vv, Vw and the currents Iu, Iv, Iw, and sends the calculated rotation angle θ to the inverter control unit 6. Supply.

  In the inverter control unit 6, the rotation speed is calculated by differentiating the rotation angle θ. Further, when the inverter control unit 6 receives a command on the target rotation speed of the motor 3 from a host device (not shown) or the like, it outputs a speed command signal that brings the current rotation speed close to the target rotation speed and matches it. . The pulse controller 7 determines the on / off timing of each of the MOSFETs 11 to 16 and 21 to 26 based on the speed command signal, and sends a control signal for commanding the on / off of these MOSFETs to the gate drivers 42 and 44. Supply. Based on these control signals, the gate drivers 42 and 44 apply gate voltages to the MOSFETs 11 to 16 and 21 to 26, respectively.

[Operation of Position Calculation Unit 5]
Next, the position detection operation in the position calculation unit 5 will be described.
When the rotational speed of the motor 3 reaches a certain speed, the rotational angle θ of the motor 3 can be detected by the counter electromotive force in the non-conducting phase, that is, the voltages Vu, Vv, Vw. However, since the magnitude of the back electromotive force is proportional to the rotation speed, the detection accuracy decreases due to the influence of noise or the like when the rotation speed becomes extremely low. Therefore, the position calculation unit 5 of the present embodiment detects the rotation angle θ based on a change in inductance due to magnetic saturation.

First, a period in which the U phase is an open phase (a phase in which no PWM modulation wave is applied) is assumed. When the inductance of the U-phase stator winding 33U is Lu, the U-phase voltage Vu and the current Iu are
Vu = Lu (dIu / dt) (1)
There is a relationship. Here, the inductance Lu changes with the rotation angle θ. That is, when the permanent magnet embedded in the rotor is at a position where the magnetic flux in the stator winding 33U is strengthened, the influence of magnetic saturation becomes strong, so the inductance Lu becomes small. On the other hand, when the permanent magnet is at a position where the magnetic flux in the stator winding 33U is weakened, the influence of magnetic saturation is weakened, and the inductance Lu is increased.

  Therefore, when the inductance Lu is obtained based on the differential value (dIu / dt) of the voltage Vu and the current Iu, the rotation angle θ can be obtained. The PWM modulated wave applied to the stator winding 33U is kept off in the vicinity of the zero cross point of the current Iu (at least in the range of 60 ° of zero cross point ± 30 °). Accordingly, the position calculation unit 5 uses the “60 ° range” as the U-phase measurement period, continuously detects the voltage Vu and the current Iu without interruption every predetermined sampling period, and calculates the rotation angle θ. To do. In addition, for the V phase and the W phase, the position calculator 5 continuously detects the voltage and current of each phase without interruption in the 60 ° range in the vicinity of each zero cross point, and the rotation angle θ. Is calculated.

  Thus, the position calculation unit 5 assigns 60 ° measurement periods in the order of the U phase, the V phase, and the W phase, and calculates the rotation angle θ based on the voltage and current of the assigned phase. As a result, the position calculation unit 5 continues to calculate the rotation angle θ continuously without interruption at every predetermined sampling period in the entire range (0 ° to 360 °) of the rotation angle θ.

[Effect of the embodiment]
Next, the effect of this embodiment will be described with reference to FIG. FIG. 2 is a graph showing the characteristics of the open-circuit back electromotive voltage with respect to the rotation angle θ.
An example of a voltage waveform in the open phase measurement period according to the present embodiment is shown as V1 in FIG. In the present embodiment, the stator windings 33U, 33V, and 33W are independent from each other and are hardly affected by the voltage applied to the other phase, and therefore the voltage waveform V1 is substantially linear with respect to the rotation angle θ. The value changes to.

  Here, for comparison, an example of a voltage waveform obtained by the technique of Patent Document 1 described above is shown as V2 in FIG. In the technique of Patent Document 1, since the stator windings of each phase are connected to the neutral point in the motor, it is not possible to directly measure the voltage of the stator windings of each phase. . Therefore, a pseudo neutral point is created outside the motor and the voltage waveform V2 is measured. In the technique of Patent Document 1, since the stator winding of each phase is connected to the neutral point, as shown in FIG. 2, the voltage waveform V2 of the open phase is obtained when a voltage is applied to the other phase. Disturbed.

  If the voltage waveform V2 is disturbed in a certain sampling period, the rotation angle θ cannot be calculated based on the sampling value of the voltage waveform V2 or the like at that time, so a method of “estimating” the current rotation angle θ based on the past sampling value Must be taken. However, when an unexpected disturbance occurs, the rotation angle θ obtained by the “estimation” deviates greatly from the actual value, which may hinder the control. On the other hand, according to the present embodiment, the rotation angle θ is calculated without interruption based on the voltage waveform V1 in the sampling period for each sampling period, so even when an unexpected disturbance occurs. Thus, the accurate rotation angle θ can be continuously calculated, and the motor 3 can be controlled with high accuracy.

  Further, in the technique of Patent Document 1, since the output voltage of the DC power source cannot be applied to each stator winding, the voltage applied to each stator winding is lower than the output voltage of the DC power source. . In contrast, in the present embodiment, the DC voltage Ed output from the DC power source 2 can be directly applied to the stator windings 33U, 33V, and 33W. In other words, even if the same power source is used, according to this embodiment, a voltage about twice that of the technique according to Patent Document 1 can be applied to the stator windings 33U, 33V, and 33W. Therefore, if the same stator iron core is used and the number of turns of the stator winding is the same, this embodiment can operate the motor 3 at a higher speed than that of Patent Document 1.

  Depending on the application of the motor 3, it may be more important to realize an expansion of the operation range and higher efficiency during low-speed operation than to realize high-speed operation. In such a case, the motor 3 is selected so as to be suitable for low-speed operation, such as selecting a material that is likely to cause magnetic saturation as the stator core or increasing the number of windings of the stator windings 33U, 33V, 33W. It is good to design. If the motor 3 is designed to be suitable for low-speed operation, performance degradation during high-speed operation occurs, for example, the maximum speed decreases. However, this embodiment is more advantageous than that of Patent Document 1 in that the DC voltage Ed can be directly applied to the stator windings 33U, 33V, and 33W, and this compensates for the performance degradation during high-speed operation. It becomes possible.

  Next, a specific example of this effect will be described with reference to FIG. FIG. 3 is a diagram showing the motor efficiency with respect to the rotational speed N of the motor. A characteristic G2 in FIG. 3 is an example of the characteristic according to the technique of Patent Document 1, and the operating range of the motor is a range of rotational speeds N1 to N2. A characteristic G1 is an example of the characteristic according to the present embodiment. According to this embodiment (characteristic G1), the minimum speed of the motor operating range extends to a rotational speed N3 lower than N1. Furthermore, the motor efficiency near the rotational speed N1 is higher than that of Patent Document 1 (characteristic G2). This is because the motor 3 is designed to be suitable for low speed operation. On the other hand, the maximum speed in the operating range is maintained at the rotational speed N2. This is because the DC voltage Ed can be directly applied to the stator windings 33U, 33V, 33W.

[Modification]
The present invention is not limited to the above-described embodiments, and various modifications can be made. The above-described embodiments are illustrated for easy understanding of the present invention, and are not necessarily limited to those having all the configurations described. Further, a part of the configuration of an embodiment can be replaced with the configuration of another embodiment, and the configuration of another embodiment can be added to the configuration of an embodiment. Further, it is possible to delete a part of the configuration of each embodiment, or to add or replace another configuration. Examples of possible modifications to the above embodiment are as follows.

(1) In the above embodiment, the change in inductance based on magnetic saturation is detected by detecting both the voltage and current of the open phase, and the rotation angle θ is calculated. However, the open phase current need not necessarily be detected. In other words, the rotational angle θ may be calculated only from the open-phase counter electromotive voltage, as long as practically sufficient accuracy can be obtained only by the counter electromotive voltage without performing extremely low speed operation control. Even in this case, as described in FIG. 2, the voltage waveform V1 of the counter electromotive voltage is hardly affected by the voltage applied to the other phase, so that the rotation angle θ can be continuously calculated without interruption. The same effect as the above embodiment can be obtained.

(2) The motor control system of the present embodiment can be applied to various electric devices having a motor, such as an air conditioner, a refrigerator, an automobile, a machine tool, and a construction machine. In these electrical devices, as described in the above embodiment, since the highly accurate position detection of the motor and the expansion of the operating range of the motor are realized, the performance of these electrical devices can be improved. it can.

(3) Since the functions of the components such as the position calculation unit 5, the inverter control unit 6, and the pulse control unit 7 can be realized by a computer and a program, the programs and the like that realize the functions of these components are stored in a storage medium. Alternatively, it may be distributed through a transmission line. Conversely, some or all of the functions of these components are performed by hardware processing using ASIC (Application Specific Integrated Circuit) or FPGA (field-programmable gate array). It may be realized.

[Overview of composition and effect]
As described above, the motor control device according to the embodiment includes the power conversion circuit (4) connected to both ends of the multi-phase stator windings (33U, 33V, 33W) provided in the motor (3). The voltage detection circuit (50) for detecting the voltage between the terminals of the stator windings (33U, 33V, 33W) of each phase, and the voltage between the terminals of the open phase detected by the voltage detection circuit (50) And a position calculation unit (5) for calculating the rotation angle (θ) of the motor (3). Thereby, since the voltage between terminals of each stator winding (33U, 33V, 33W) can be measured independently, the influence on the open phase due to the voltage of the energized phase can be reduced, and the accuracy is high. Position detection becomes possible. Furthermore, since the output voltage (Ed) of the power conversion circuit (4) can be directly applied to each stator winding (33U, 33V, 33W), the operating range of the motor (3) can be expanded.

  Further, the voltage detection circuit (50) includes a differential amplifier (51, 52, 53) for detecting a voltage between terminals of the stator windings (33U, 33V, 33W) of each phase. . Thereby, even if the voltage between terminals is very small, this can be detected accurately.

  Further, the voltage detection circuit (50) detects the voltage between the terminals in an open phase every predetermined sampling period, and the position calculation unit (5) detects the terminal in the sampling period for each sampling period. The rotation angle (θ) is calculated based on the inter-voltage. As a result, the rotation angle (θ) can be calculated based on the inter-terminal voltage detected in each sampling period, and high-precision motor control is possible.

  Furthermore, the position calculation unit (5) assigns a measurement period to the stator windings (33U, 33V, 33W) of each phase for each predetermined rotation angle (60 °), and assigns the measurement period. Based on the voltage between the terminals of the stator windings (33U, 33V, 33W), the rotation angle (θ without interruption) in the entire rotation angle range (0 ° to 360 °) every sampling period. ) Is continuously calculated. As a result, the rotation angle (θ) of the sampling period can be calculated based on the voltage between terminals detected in each sampling period in the entire range of rotation angles (0 ° to 360 °), and detected in the past sampling period. Since it is not necessary to predict the rotation angle (θ) based on the voltage between the terminals, motor control with higher accuracy is possible.

  Further, the electric device of the modified example (2) includes the motor control device of the above-described embodiment and the motor (3). Accordingly, in these electric devices, highly accurate position detection of the motor and expansion of the operation range of the motor are realized, so that the performance of these electric devices can be improved.

DESCRIPTION OF SYMBOLS 1 Power converter 2 DC power supply 3 Motor 4 Power conversion circuit 5 Position calculation part 6 Inverter control part 7 Pulse control parts 11-16, 21-26 MOSFET
33U, 33V, 33W Stator winding 41, 43 Three-phase bridge circuit 42, 44 Gate driver 50 Voltage detection circuit 51, 52, 53 Differential amplifier

Claims (5)

A power conversion circuit connected to each end of a plurality of stator windings provided in the motor;
A voltage detection circuit for detecting a voltage between terminals of the stator winding of each phase;
And a position calculation unit that calculates a rotation angle of the motor based on the voltage between the terminals in the open phase detected by the voltage detection circuit. The motor control device according to claim 1, wherein the voltage detection circuit includes a differential amplifier that detects a voltage between terminals of the stator winding of each phase. The voltage detection circuit detects the voltage between the terminals in an open phase for each predetermined sampling period, and the position calculation unit performs the rotation based on the voltage between the terminals in the sampling period for each sampling period. The motor control device according to claim 1, wherein an angle is calculated. The position calculation unit allocates a measurement period for each predetermined rotation angle to the stator winding of each phase, and the rotation based on the voltage between the terminals of the stator winding to which the measurement period is allocated. The motor control device according to claim 3, wherein the rotation angle is continuously calculated without interruption for each sampling period in the entire range of angles. A motor control device according to claim 1;
An electric device comprising the motor.

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