JP2018157717A - Rotation position estimation device of synchronous motor and rotation position estimation method of synchronous motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rotation position estimation device of a synchronous motor capable of coping even with a wider energization system.SOLUTION: According to a rotation position estimation device of a synchronous motor of an embodiment, an inverter which is connected with a three-phase synchronous motor, and constituted of a plurality of switching elements is provided with: an opening phase generation part which makes any one phase of three phases into a non-conductive state to be made into an opening phase; an opening phase determination part which determines what phase is made into the opening phase; an opening phase voltage detection part which detects voltage of the opening phase; an opening phase voltage storage part which stores the voltage; a voltage zero point estimation part which estimates a zero point of the voltage from the opening phase voltage stored by the opening phase voltage storage part; and a position estimation part which estimates a rotation position of the motor on the basis of the zero point.SELECTED DRAWING: Figure 1

Description

  Embodiments described herein relate generally to an apparatus and a method for estimating a rotational position of a synchronous motor.

  Conventionally, the rotation position is detected in order to appropriately control the electric motor. The detection of the rotational position is to detect an electrical angle phase that is a position on the electrical angle coordinate of the electric motor. For detecting the rotational position, there is a method using a position sensor such as a rotary encoder, a resolver, or a Hall element. However, there are cases where a position sensor cannot be provided due to product cost, structural limitations, and the like.

  Therefore, a method for estimating the rotational position from current and voltage information without using a position sensor has been implemented. Examples of such methods include an induced voltage utilization type and an inductance utilization type. The induced voltage utilization type is a method in which an induced voltage proportional to the speed of the electric motor is calculated from the input voltage and current to the electric motor, and is estimated based on this induced voltage. This is an estimation method using the fact that the induced voltage generated by the rotation of the electric motor changes according to the electric angle of the electric motor at the rotational position.

  In the case of using the induced voltage, sufficient accuracy can be obtained in a region where the rotational speed of the motor is high. However, since the amplitude of the induced voltage becomes small or does not occur in the region where the rotational speed is low, the induced voltage utilization type cannot accurately estimate when the motor is stopped or at a low speed.

  On the other hand, the inductance utilization type is a method of estimating the rotational position by calculating the inductance of the motor from current and voltage information, and utilizes the fact that the inductance of the motor changes at a cycle twice according to the electrical angle. is there. As this estimation method, for example, several methods have been proposed in which an AC signal for sensing not related to the drive frequency is applied to the motor, and the rotational position is estimated from the relationship between the voltage and current.

  In this way, the frequency of the AC signal applied for obtaining the inductance is generally set lower than the carrier frequency in the PWM control, and is, for example, about several hundred Hz to several kHz. However, in this case, since the current ripple frequency of the motor enters the human audible range, noise increases. In addition, since the current needs to be detected at least within the carrier cycle, detection becomes difficult when the carrier frequency increases.

  As a rotational position estimation method other than the above, Patent Document 1 proposes a rotational position estimation method using an open phase voltage. This method is a method for estimating the rotational position based on the voltage difference generated by the inductance difference between the other two phases generated according to the rotational position when any one of the three-phase inverters is in a non-energized state. is there. According to this open phase voltage utilization type, the rotational position can be estimated even at a low speed as in the inductance utilization type estimation method, and the carrier frequency can be set high to detect the voltage.

JP 2009-189176 A

However, since Patent Document 1 is premised on the 120-degree energization method, it cannot be applied to a 180-degree energization method in which a non-energized phase is basically not generated.
Therefore, a rotational position estimation device for a synchronous motor and a rotational position estimation method for a synchronous motor that can support a wider range of energization methods are provided.

According to the rotational position estimation device for a synchronous motor of an embodiment, for an inverter connected to a three-phase synchronous motor and configured by a plurality of switching elements, any one of the three phases is deenergized and the open phase is set. An open phase generator to
An open phase determination unit for determining which phase is the open phase;
An open phase voltage detector for detecting the voltage of the open phase;
An open phase voltage storage unit for storing the voltage;
From the open phase voltage stored by the open phase voltage storage unit, a voltage zero point estimation unit for estimating the zero point of the voltage,
A position estimation unit that estimates a rotational position of the electric motor based on the zero point.

1 is a functional block diagram showing the configuration of an electric motor drive control device including a rotational position estimation device according to an embodiment The figure which shows a part of structure of an open phase voltage detection part (the 1) A figure showing a part of composition of an open phase voltage detection part (the 2) Flowchart showing rotation position estimation processing Diagram showing approximate function of open phase voltage The figure explaining the process which estimates the zero point of an open phase voltage, and estimates a rotation position The figure which shows the estimation result of the rotation position The figure which shows the three-phase PWM signal by a 180 degree energization system The figure which shows the three-phase PWM signal at the time of providing an open phase area in a 180 degree energization system Diagram explaining open phase voltage Diagram showing the relationship between open phase voltage and rotational position

  Hereinafter, an embodiment will be described with reference to the drawings. FIG. 1 is a functional block diagram showing a configuration of an electric motor control device including a rotational position estimation device. The DC power source 1 generates a DC power source and supplies it to the inverter unit 2. The DC power supply 1 includes one that rectifies and generates an AC power supply. Each phase output terminal of the inverter unit 2 is connected to one end of each corresponding phase winding of the synchronous motor 3. Both the inverter unit 2 and the electric motor 3 have a three-phase configuration. The DC voltage detector 4 detects the voltage Vdc of the DC power supply 1 and outputs the detection result to the PWM generator 5.

  Each phase output terminal of the inverter unit 2 is connected to each phase input terminal of the phase current detection unit 6. Each phase current detected by the phase current detector 6 is input to the three-phase / dq converter 7 and converted into a d-axis current Id and a q-axis current Iq. The converted d-axis current Id and q-axis current Iq are input to the current control unit 8. The d-axis current command Id_ref and q-axis current command Iq_ref generated by the current command unit 9 are input to the current control unit 8. The current control unit 8 generates a d-axis voltage Vd and a q-axis voltage Vq according to the difference between each current command Id_ref, Iq_ref and each current Id, Iq.

  The d-axis voltage Vd and the q-axis voltage Vq are input to the dq / 3-phase converter 10 and converted into three-phase voltages Vu ′, Vv ′, and Vw ′. The three-phase voltages Vu ′, Vv ′, and Vw ′ are input to the open phase determination unit 11 to become the three-phase voltages Vu, Vv, and Vw including the open phase period, and are input to the PWM generation unit 5. That is, the open phase determination unit 11 includes a function as an open phase generation unit. The PWM generation unit 5 generates PWM signals Vu ±, Vv ±, Vw ± for driving the switching elements of the respective phase arms constituting the inverter unit 2 based on the three-phase voltages Vu, Vv, Vw. Input to part 2.

  In addition, each phase output terminal of the inverter unit 2 is connected to each phase input terminal of the open phase voltage detection unit 12. The open phase voltage detector 12 detects the open phase voltage of each phase and inputs the detection result to the rotational position estimator 13. The rotational position estimation unit 13 estimates the rotational position θest of the electric motor 3 based on the input open phase voltage, the three-phase / dq conversion unit 7, the dq / 3-phase conversion unit 10, the open phase determination unit 11, and the open phase. Input to the voltage detector 12. The rotational position estimation unit 13 also has functions as an open phase voltage storage unit and a voltage zero point estimation unit.

  As shown in FIGS. 2 and 3, the open-phase voltage detection unit 12 includes one end connected to each phase output terminal of the inverter unit 2, and voltage detection resistor series circuits 21 U and 22 U and 21 V corresponding to each phase. 22V, 21W and 22W are provided. The other ends of these series circuits are connected in common. The open phase voltage detection unit 12 includes a detection circuit including voltage buffers 23 and 24 and a differential amplifier circuit 25 for each phase, and a common connection point A of each phase resistance 21 and 22 and each phase series circuit in the open phase section. The difference voltage from the common connection point B is detected as an open phase voltage.

  Here, the principle of the rotational position estimation method in the present embodiment will be described with reference to FIGS. The open phase voltage is a voltage generated in the open phase that is in the non-energized state when one phase of the three-phase motor is in a non-energized state and voltage is applied to the remaining two phases.

  When the rotor is stopped and the induced voltage is 0 V, consider a case where the U phase is an open phase and a pulse voltage is applied between the V and W phases as shown in FIG. At this time, since the same current flows in the V phase and the W phase, when the inductance of the V and W phases does not change, the voltages of the V and W phases are equal, and the voltage at the point O, that is, the U phase voltage does not change. However, in practice, the amount of magnetic flux changes according to the rotational position of the rotor, so that the V and W phase inductances change.

  Of the V and W phases, the closer to the rotational position, the larger the amount of magnetic flux, the smaller the inductance and the difference between the V and W phase inductances. Then, since the phase currents iv and iw flow as the same current i in the V phase and the W phase, the change in inductance appears as a voltage in the U phase that is an open phase. Since this voltage has position dependency as shown in FIG. 11, the position of the rotor can be detected by detecting the open-phase voltage.

  As described above, in order to detect the open phase voltage, any one phase of the motor needs to be an open phase in a non-energized state. For example, as shown in FIG. 8, an open phase voltage cannot be detected because an open phase does not occur in the PWM signal waveform when the motor is driven in a sinusoidal wave with two-phase modulation by the 180-degree conduction method.

  Therefore, in the present embodiment, as shown in FIG. 9, during the sine wave drive, an open phase is generated in the vicinity where the open phase voltage of a certain phase becomes a zero point. The open phase voltage is detected during that period, and the timing at which the zero point is reached is determined from the detected voltage. Then, the rotational position is estimated from the determined timing, and the speed of the motor is also calculated from the estimated rotational position and used for controlling the motor.

  Here, the longer the open phase generation period, the longer the period during which the open phase voltage can be detected. However, since the drive state approaches rectangular wave drive, noise and torque ripple are likely to occur. That is, in order to maintain the sine wave drive state as much as possible, it is necessary to shorten the generation period of the open phase as much as possible. Hereinafter, the generation period of the open phase is referred to as an open phase section. Moreover, putting a certain phase into a non-energized state may be referred to as “open”. On the other hand, if the open phase section is too short, the zero point may not appear in the section, or the zero point may not be detected with high accuracy, and the estimation accuracy of the rotational position may be deteriorated.

  Therefore, in the present embodiment, in order to shorten the open phase interval, the zero point of the voltage is obtained from the approximate function of the open phase voltage. Thereby, even if the open phase section is shortened, the rotational position can be accurately estimated.

Here, as shown in FIG. 5, a certain phase of the motor is opened over the period before and after the zero point of the open phase voltage is estimated to occur, the horizontal axis is the open phase voltage, and the vertical axis is the nth detection. As a first-order approximation function is obtained using the least square method, Equation (1) is obtained. a is the slope of the approximate function, and b is the intercept.
n = a × (open phase voltage) + b (1)
FIG. 5 shows an inclination a = −4.43 and an intercept b = 4.56 as an example. In addition, although each plot of the open phase voltage shown in FIG. 5 is illustrated in an image, an example of the slope and intercept is determined based on actual measurement.

  Hereinafter, a series of processes for estimating the rotational position will be described with reference to FIG. The rotation position of the zero point of the open phase obtained first is defined as θ1. In order to obtain the timing n01 of the zero point of the open phase voltage, 0 may be substituted into the open phase voltage, and b = n01.

Next, the electric motor rotates, and the open phase is similarly generated before and after the zero point of the open phase voltage of the other phase to obtain the timing n02. The rotational position of the open phase zero point at this time is θ2. Assuming that the open-phase voltage sampling period is Δt, the time T12 between the first open-phase voltage zero point timing n01 and the second open-phase voltage zero point timing n02 is expressed by Equation (2).
T12 = (n02−n01) × Δt (2)
The motor rotation speed ω21 during T12 can be obtained by Expression (3). Ω21 = (θ2−θ1) / 360 / (T12) (3)
That is, at the timing N02 when the detection of the second open-phase voltage is completed, the number of revolutions based on the open-phase voltage can be calculated by the equations (2) and (3).

Further, the rotational position θ02 ′ at the timing N02 is obtained using Expression (4).
θ02 ′ = θ2 + ω21 × (N02−n02) (4)
Note that the conventional rotational position θ02 for ending the second open phase interval is expressed by the equation (5) from the zero point of the zero open phase voltage detected in the same manner as the zero point of the first open phase voltage described above. )
θ02 = θ1 + ω10 × (N02−n01) (5)
Then, the rotational position is updated from θ02 to θ02 ′ at the timing of N02, and thereafter the rotational position is calculated based on θ2 and ω21.

Similarly, in the third open phase section, the rotational position is calculated based on ω12 and θ2, and the start timing of the next open phase section is determined. The rotational position θ03 for ending the next open phase section is obtained by Expression (6).
θ03 = θ2 + ω21 × (N03−n02) (6)
Then, at timing N03, ω32 is obtained from equation (7), and θ03 ′ is obtained from equation (8).
ω32 = (θ3-θ2) / 360 / (T32) (7)
θ03 ′ = θ3 + ω32 × (N03−n03) (8)

  Thereafter, by repeating the process as described above, the rotational position and speed estimated based on the open phase voltage are sequentially updated to control the electric motor. That is, the next open phase and the open phase section are determined from the information up to the previous time, and the zero point of the open phase is obtained from the approximate function at the timing when the open phase is completed, thereby calculating the speed. Recalculate the rotational position at the timing when the open phase ends from the rotational position of the speed and the open phase zero point, and then update the estimated rotational position based on the recalculated rotational position and speed, and control the motor Determine the next open phase interval.

FIG. 4 is a flowchart showing a rotational position estimation process based on the above principle. First, which phase is to be opened is determined, and the start rotation position θAn and the end rotation position θBn of the open phase section are determined (S1). If the currently estimated rotational position θest has not reached the starting rotational position θAn (NO), the rotational position θest is updated by equation (9) (S13). Note that ω _nn-1 is the number of rotations at n steps, and Δt is a control period.
θest = θest + ω _nn−1 × Δt (9)
Then, motor control is performed based on the updated rotational position θest (S14), and the process returns to step S2.

  When the rotational position θest reaches the start rotational position θAn (S2; YES), if the rotational position θest does not reach the end rotational position θBn (S3; NO), the selected phase is set as the open phase (S4) and the open phase voltage is set. Detect (S5). The detected voltage is stored in a storage unit built in the rotational position estimation unit 13. Then, the process proceeds to step S13. When the rotational position θest reaches the final rotational position θBn (S3; YES), the open phase section is terminated (S6), and an approximate function is calculated from the open phase voltage obtained in the section (S7).

Next, a time t _0n when the open phase voltage reaches the zero point is estimated from the approximate function (S8), and the rotational position θ _0n corresponding to the zero point is specified based on the time t _0n (S9). Then, the rotational speed ω _nn-1 is obtained using the time t _0n-1 and the rotational position θ _0n-1 corresponding to the zero point obtained last time (S10), and the rotational position θest is estimated by the equation (10) (S11). .
θest = θ _0n + ω _nn−1 × t _0n (10)
Thereafter, after the step number n is incremented (S12), the process proceeds to step S1.

  FIG. 7 shows the estimation result of the rotational position by the method of this embodiment. The rotational position can be accurately estimated based on the zero point of the open-phase voltage detected with a resolution of 60 degrees by the processing shown in FIGS. According to this estimation method, even if the zero point of the open phase voltage cannot be accurately detected, the open phase interval can be shortened because it can be obtained by an approximation function. As a result, the sine wave drive state can be maintained as much as possible even when applied to the 180-degree energization method, so that noise and torque ripple are reduced.

  As described above, according to the present embodiment, the open phase determination unit 11 determines which of the three phases is the open phase, and sets the determined phase in a non-energized state. The rotational position estimation unit 13 stores the open-phase voltage detected by the open-phase voltage detection unit 12 and estimates the zero point of the voltage from the open-phase voltage using an approximation function. Based on the zero point The rotational position θest of the electric motor 3 is estimated.

  As a result, the motor 3 can be driven from a stopped state to a very low speed region with a configuration substantially similar to a control device that performs a conventional sinusoidal drive sensorless system. Therefore, smooth acceleration of the electric motor 3 can be obtained without applying a special position detection voltage. In addition, the voltage of the electric motor 3 may be detected, detection is easier than detecting a change in current according to the carrier frequency, and the carrier frequency can be set high. This is particularly effective when estimating the rotational position of a small motor having a very small inductance.

  Then, the rotational position estimation unit 13 determines the timing at which the open-phase voltage reaches the zero point using the primary approximation function calculated from the stored open-phase voltage, so the timing is determined using a simple approximate function. it can. Further, the open phase determination unit 11 can easily determine which phase is the open phase based on the rotational position θest.

(Other embodiments)
The approximation function is not limited to linear approximation, and for example, a curve may be obtained by secondary approximation.
The open phase determination unit does not necessarily have to determine the open phase based on the rotational position.
The present invention may be applied to energization methods other than the 180-degree energization method.
Although several embodiments of the present invention have been described, these embodiments have been presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

  In the drawings, 2 is an inverter unit, 3 is a synchronous motor, 5 is a PWM generation unit, 6 is a phase current detection unit, 11 is an open phase determination unit, 12 is an open phase voltage detection unit, and 13 is a rotational position estimation unit.

Claims (8)

An open phase generation unit that is connected to a three-phase synchronous motor and includes a plurality of switching elements, and makes any one of the three phases non-energized to be an open phase;
An open phase determination unit for determining which phase is the open phase;
An open phase voltage detector for detecting the voltage of the open phase;
An open phase voltage storage unit for storing the voltage;
From the open phase voltage stored by the open phase voltage storage unit, a voltage zero point estimation unit for estimating the zero point of the voltage,
A rotational position estimation device for a synchronous motor, comprising: a position estimation unit that estimates a rotational position of the electric motor based on the zero point.   The synchronous motor rotational position estimating device according to claim 1, wherein the voltage zero point estimating unit estimates a zero point of the voltage using an approximation function obtained from the open phase voltage.   3. The synchronous motor rotational position estimating apparatus according to claim 2, wherein a linear approximate function is used as the approximate function.   The rotational position estimation device for a synchronous motor according to any one of claims 1 to 3, wherein the open phase determination unit determines the open phase based on the rotational position. For an inverter that is connected to a three-phase synchronous motor and is configured by a plurality of switching elements, when determining whether one of the three phases is an open phase, the determined phase is set to a non-energized state,
Detecting and storing the voltage of the open phase;
From the stored open phase voltage, estimate the zero point of the voltage,
A synchronous motor rotational position estimating method for estimating the rotational position of the electric motor based on the zero point.   6. The method for estimating a rotational position of a synchronous motor according to claim 5, wherein a zero point of the voltage is estimated using an approximation function obtained from the open phase voltage.   The method for estimating a rotational position of a synchronous motor according to claim 6, wherein a linear approximation function is used as the approximation function.   The synchronous motor rotational position estimation method according to any one of claims 5 to 7, wherein the open phase is determined based on the estimated rotational position.

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