CN108631685B

CN108631685B - Rotational position estimation device and rotational position estimation method of synchronous motor

Info

Publication number: CN108631685B
Application number: CN201810233211.8A
Authority: CN
Inventors: 柴野勇介; 前川佐理; 久保田寿夫; 吴梦悦
Original assignee: Toshiba Corp; Meiji University
Current assignee: Toshiba Corp; Meiji University
Priority date: 2017-03-21
Filing date: 2018-03-21
Publication date: 2021-07-20
Anticipated expiration: 2038-03-21
Also published as: JP2018157717A; JP6810421B2; CN108631685A

Abstract

According to the rotational position estimation device and the rotational position estimation method of the synchronous motor of the embodiment, the rotational position estimation device includes: a phase failure generation unit that sets any one of three phases as a phase failure in an inverter connected to a three-phase synchronous motor and including a plurality of switching elements, the inverter being in a non-energized state; an open-phase determining unit that determines which phase is to be the open phase; an open-phase voltage detection unit that detects the open-phase voltage; an open-phase voltage storage unit that stores the voltage; a voltage zero point estimating unit that estimates a zero point of the voltage based on the open-phase voltage stored in the open-phase voltage storage unit; and a position estimating unit that estimates a rotational position of the motor based on the zero point.

Description

Device and method for estimating rotational position of synchronous motor

Technical Field

Embodiments of the present invention relate to a device and a method for estimating a rotational position of a synchronous motor.

Background

Conventionally, the rotational position is detected in order to appropriately control the motor. The detection of the rotational position is to detect an electrical angle phase as a position on an electrical angle coordinate of the motor. In some methods, a position sensor such as a rotary encoder (rotary encoder), a resolver (resolver), or a hall element is used to detect the rotational position. However, the position sensor may not be provided due to cost of the product, structural constraints, and the like.

Therefore, a method of inferring the rotational position from information of the current or voltage without using a position sensor is implemented. Examples of the method include an induced voltage utilization type and an inductance utilization type. The induced voltage utilization type is a method of calculating an induced voltage proportional to the speed of the motor by an input voltage and a current to the motor and estimating the induced voltage based on the calculated induced voltage. This is an estimation method using the characteristic that the induced voltage generated by the rotation of the motor changes according to the electrical angle of the motor as the rotational position.

In the case of the induced voltage utilization type, sufficient accuracy cannot be obtained in a region where the rotation speed of the motor is high. However, in a region where the rotation speed is low, the amplitude of the induced voltage is small or no amplitude of the induced voltage is generated, and therefore, accurate estimation cannot be performed at the time of stopping the motor or at the time of low speed by the induced voltage use type.

On the other hand, the inductance utilization type is a method of estimating a rotational position by calculating the inductance of the motor from a current or a voltage, and utilizes a characteristic that the inductance of the motor varies with a period of two times according to an electrical angle. As this estimation method, for example, there is proposed a method in which an ac signal for sensing irrespective of the driving frequency is applied to the motor, and the rotational position is estimated from the relationship between the voltage and the current.

The frequency of the ac signal applied to obtain the inductance is generally set to be lower than the carrier frequency of the PWM control, and is, for example, about several 100Hz to several kHz. However, in this case, the current ripple frequency of the motor enters the audible range of human beings, and thus, noise increases. Further, since it is necessary to detect the current at least within the carrier period, detection becomes difficult if the carrier frequency becomes high.

As a rotational position estimation method other than the above, a rotational position estimation method using an open-phase voltage is proposed in japanese patent application laid-open No. 2009-189176 of patent document 1. This method is a method of estimating the rotational position based on a voltage difference generated by an inductance difference of the other two phases generated according to the rotational position when any one of the three-phase inverters is in a non-energized state. According to the open-phase voltage utilization type, the rotational position can be estimated at a low speed in the same manner as the inductance utilization type estimation method, and the carrier frequency can be set high for detecting the voltage.

However, in patent document 1, since the 120-degree conduction method is assumed, it is basically impossible to apply the method to a 180-degree conduction method or the like of a phase in which a non-conduction state does not occur.

Disclosure of Invention

Therefore, a rotational position estimating device for a synchronous motor and a rotational position estimating method for a synchronous motor are provided which can cope with a wider range of energization modes.

According to one embodiment, a rotational position estimation device for a synchronous motor includes: an open-phase generation unit that sets any one of three phases as an open phase in an inverter connected to a three-phase synchronous motor and configured by a plurality of switching elements, the inverter being in a non-energized state; an open-phase determining section for determining which phase is the open phase; an open-phase voltage storage unit for detecting the open-phase voltage; an open-phase voltage storage unit for storing the voltage; a voltage zero point pushing unit for estimating a zero point of the voltage based on the open-phase voltage stored in the open-phase voltage storage unit; and a position estimating unit that estimates a rotational position of the motor based on the zero point.

Drawings

Fig. 1 is a functional block diagram showing a configuration of a motor drive control device including a rotational position estimating device according to an embodiment.

Fig. 2 is (one of) a diagram showing a part of the configuration of the open-phase voltage detection unit.

Fig. 3 is a diagram (two) showing a part of the structure of the open-phase voltage detection unit.

Fig. 4 is a flowchart showing the estimation process of the rotational position.

Fig. 5 is a graph showing an approximation function of the open-phase voltage.

Fig. 6 is a diagram illustrating a process of specifying a zero point of an open-phase voltage to estimate a rotational position.

Fig. 7 is a diagram showing the estimation result of the rotational position.

Fig. 8 is a diagram showing three-phase PWM signals obtained by the 180-degree energization system.

Fig. 9 is a diagram showing three-phase PWM signals in a case where a phase-open section is provided in the 180-degree conduction mode.

Fig. 10 is a diagram illustrating an open-phase voltage.

Fig. 11 is a diagram showing a relationship between the open-phase voltage and the rotational position.

Detailed Description

Hereinafter, an embodiment will be described with reference to the drawings. Fig. 1 is a functional block diagram showing a configuration of a motor control device including a rotational position estimating device. The dc power supply 1 generates dc power and supplies the generated dc power to an inverter unit 2. The dc power supply 1 also includes a part generated by rectifying an ac power supply. Each phase output terminal of the inverter unit 2 is connected to one end of a corresponding phase winding of the synchronous motor 3. The inverter unit 2 and the motor 3 are each configured with three phases. The dc voltage detection unit 4 detects the voltage Vdc of the dc power supply 1, and inputs the detection result to the PWM generation unit 5.

Each phase output terminal of the inverter unit 2 is connected to each phase input terminal of the phase current detection unit 6. The respective phase currents detected by the phase current detecting unit 6 are input to the three-phase/dq converting unit 7 and converted into d-axis currents Id and q-axis currents 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 the 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 from the difference between each of the current commands Id _ ref and Iq _ ref and each of the currents Id and Iq.

The d-axis voltage Vd and the q-axis voltage Vq are input to the dq/three-phase conversion unit 10 and converted into three-phase voltages Vu ', Vv ', Vw '. The three-phase voltages Vu ', Vv ', Vw ' are input to the open-phase determining unit 11, become three-phase voltages Vu, Vv, Vw including an open-phase section, and are input to the PWM generating unit 5. That is, the open-phase determining unit 11 also includes a function as an open-phase generating unit. The PWM generator 5 generates PWM signals Vu ±, Vv ±, Vw ± for driving the switching elements of each phase arm (arm) constituting the inverter 2, based on the three-phase voltages Vu, Vv, Vw, and inputs the PWM signals to the inverter 2.

Further, 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 detection unit 12 detects the open-phase voltage of each phase, and inputs the detection result to the rotational position estimation unit 13. The rotational position estimating unit 13 estimates the rotational position θ est of the motor 3 based on the input open-phase voltage, and inputs the estimated rotational position θ est to the three-phase/dq converting unit 7, the dq/three-phase converting unit 10, the open-phase determining unit 11, and the open-phase voltage detecting unit 12. The rotational position estimating unit 13 also functions as an open-phase voltage storage unit and a voltage zero point estimating unit.

As shown in fig. 2 and 3, one end of the open-phase voltage detection unit 12 is connected to each phase output terminal of the inverter unit 2, and the open-phase voltage detection unit 12 includes

series circuits

21U and 22U, 21V and 22V, 21W and 22W of voltage detection resistors corresponding to each phase. 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 detects a difference voltage between a common connection point a of the phase resistors 21 and 22 and a common connection point B of the phase series circuits in the open-phase section as an open-phase voltage.

Here, the principle of the rotational position estimation method according to the present embodiment will be described with reference to fig. 10 and 11. The open-phase voltage is a voltage generated when a voltage is applied to the remaining two phases while one phase of the three-phase motor is in a non-energized state, and the open-phase voltage is generated in the non-energized state.

Assume a case where, when the rotor is stopped and the induced voltage is 0V, a pulse voltage is applied between the phases VW with the U-phase set as an open phase as shown in fig. 10. At this time, since the same current flows in the V-phase and the W-phase, the voltages of the V, W-phase are equal and the voltage at the point O, that is, the voltage of the U-phase does not change when the inductance of the V, W-phase is unchanged. However, in reality, since the magnetic flux changes according to the rotational position of the rotor, the inductance of the V, W phase changes.

V, W, the closer the phase is to the rotational position, the larger the magnetic flux, and therefore the inductance is smaller, and V, W phase causes a difference in inductance. Then, since the phase currents iv and iw flow as the same current i in the V-phase and the W-phase, respectively, the change in inductance appears as a voltage in the U-phase, which is an open phase. As shown in fig. 11, since this voltage has a position dependency, the position of the rotor can be detected by detecting the voltage of the open phase.

In order to detect the open-phase voltage as described above, it is necessary to set any phase of the motor to an open phase in a non-energized state. For example, as shown in fig. 8, since the PWM signal waveform does not cause phase interruption when the motor is sine-wave-driven by two-phase modulation using the 180-degree conduction method, the phase interruption voltage cannot be detected.

Therefore, in the present embodiment, in the sine wave drive shown in fig. 9, the open phase occurs in the vicinity of the zero point of the open phase voltage of a certain phase. During this period, the open-phase voltage is detected, and the timing of becoming the zero point is determined based on the detected voltage. Then, the rotational position is estimated from the determined timing, and the speed of the motor is calculated from the estimated rotational position and used for the control of the motor.

Here, the longer the period in which the open-phase voltage can be detected, the longer the period in which the open-phase voltage is generated, but since the driving state is close to the rectangular wave driving, noise and torque ripple are likely to be generated. That is, in order to maintain the sine wave driving state as much as possible, it is necessary to shorten the period of occurrence of the phase failure as much as possible. Hereinafter, the phase failure generation period is referred to as a phase failure interval. The operation of bringing a certain phase into a non-energized state may be referred to as "off". On the other hand, if the phase-open section is shortened too much, the zero point may not appear in this section or the zero point cannot be detected with high accuracy, and the accuracy of estimating the rotational position may deteriorate.

Therefore, in the present embodiment, in order to shorten the open-phase section, the zero point of the open-phase voltage is obtained by an approximate function of the voltage. Thus, even if the phase-loss section is shortened, the rotational position can be estimated with high accuracy.

Here, as shown in fig. 5, when a certain phase of the motor is turned off during the entire period before and after the zero point at which the open-phase voltage is estimated to occur, the open-phase voltage is set on the horizontal axis, the nth detection is set on the vertical axis, and the first order approximation function is obtained by using the least square method, equation (1) is obtained. a is the slope of the approximation function and b is the intercept.

n × (phase-loss voltage) + b … (1)

Fig. 5 shows, as an example, a slope a of-4.43 and an intercept b of 4.56. Note that, each node (plot) of the open-phase voltage shown in fig. 5 is graphically illustrated, and an example of the slope and the intercept is determined based on actual measurement.

A series of flows of the process of estimating the rotational position will be described below with reference to fig. 6. The rotational position of the zero point of the phase failure obtained first is represented by θ 1. 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 is n 01.

Subsequently, the motor is rotated to cause phase interruption similarly before and after the zero point of the open-phase voltage of the other phase, and the timing n02 is obtained. The rotational position of the phase-failure zero point at this time is θ 2. When Δ T is a sampling period of the open-phase voltage, a time T12 between a timing n01 of the first open-phase voltage zero point and a timing n02 of the second open-phase voltage zero point is expressed by equation (2).

T12＝(n02－n01)×△t…(2)

The motor rotation speed ω 21 between T12 can be obtained by equation (3).

ω21＝(θ2－θ1)/360/(T12)…(3)

That is, at the timing N02 when the second detection of the open-phase voltage is completed, the rotation speed based on the open-phase voltage can be calculated by equations (2) and (3).

Further, the rotational position θ 02' of the timing N02 is obtained using equation (4).

θ02’＝θ2+ω21×(N02－n02)…(4)

The conventional rotational position θ 02 at which the second open-phase section ends is obtained by equation (5) from the zero point of the 0 th open-phase voltage detected by the same method as the method for detecting the zero point of the first open-phase voltage.

θ02＝θ1+ω10×(N02－n01)…(5)

Then, at the timing of N02, the rotational position is updated from θ 02 to θ 02', and then the rotational position is calculated based on θ 2 and ω 21.

The third open-phase section calculates the rotational position based on ω 12 and θ 2, and determines the start timing of the next open-phase section. The rotational position θ 03 at which the next phase-open period ends is obtained by equation (6).

θ03＝θ2+ω21×(N03－n02)…(6)

At timing N03, ω 32 is obtained by equation (7) and θ 03' is obtained by equation (8).

ω32＝(θ3－θ2)/360/(T32)…(7)

θ03’＝θ3+ω32×(N03－n03)…(8)

After that, by repeating the processing as described above, the rotational position and speed estimated based on the open-phase voltage are sequentially updated to control the motor. That is, the next phase failure and phase failure section are determined based on the information up to the previous time, and the speed is calculated by obtaining the zero point of the phase failure by the approximation function at the timing when the phase failure ends. The rotational position at the phase interruption completion timing is recalculated based on the speed and the rotational position of the phase interruption zero point, and then the rotational position estimated based on the recalculated rotational position and speed is updated to control the motor and determine the next phase interruption interval.

Fig. 4 is a flowchart showing the estimation processing of the rotational position based on the above principle. First, which phase is to be turned off is determined, and the start rotational position θ An and the end rotational position θ Bn of the phase-off section are determined (S1). If the rotational position θ est under estimation does not reach the start rotational position θ An (no), the rotational position θ est is updated by the equation (9) (S13). Further, ω_nn－1The rotation speed in n steps is shown, and delta t is a control period.

θest＝θest+ω_nn－1×Δt…(9)

Then, the motor control is performed based on the updated rotational position θ est (S14), and the process returns to step S2.

If the rotational position θ est reaches the start rotational position θ An (yes at S2) and the rotational position θ est does not reach the end rotational position θ Bn (no at S3), the phase-open voltage is detected with the selected phase as the phase-open (S4) (S5). The detected voltage is stored in a storage unit built in the rotational position estimating unit 13. Then, the process proceeds to step S13. When the rotation position θ est reaches the end rotation position θ Bn (yes in S3), the phase-open period is ended (S6), and the approximation function is calculated from the phase-open voltage obtained in the period (S7).

Then, the time t when the open-phase voltage reaches zero is deduced according to the approximate function_0n(S8), based on this time t_0nDetermining the rotational position theta corresponding to the zero point_0n(S9). Then, the time t corresponding to the zero point obtained previously is used_0n－1And a rotational position theta_0n－1To find the rotation speed omega_nn－1(S10), the rotational position θ est is estimated by the equation (10) (S11).

θest＝θ_0n+ω_nn－1×t_0n…(10)

Then, the step number n is incremented (increment) (S12) and the process proceeds to step S1.

Fig. 7 shows the estimation result of the rotational position obtained by the method of the present embodiment. The processing shown in fig. 4 and 6 can accurately estimate the rotational position based on the zero point of the open-phase voltage detected with a resolution of 60 degrees. According to this estimation method, even if the zero point of the open-phase voltage cannot be accurately detected, it can be determined by the approximation function, and therefore, the open-phase section can be shortened. As a result, even when applied to the 180-degree conduction method, the sinusoidal drive state can be maintained as much as possible, and thus 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 to be an open phase, and sets the determined phase to a non-energized state. The rotational position estimating unit 13 stores the open-phase voltage detected by the open-phase voltage detecting unit 12, estimates a zero point of the voltage using an approximation function from the open-phase voltage, and estimates the rotational position of the motor 3 based on the zero point

θest。

Thus, the motor 3 can be driven in an extremely low speed range from a stopped state by a configuration substantially similar to that of a conventional sensorless control device that performs sinusoidal wave driving. Therefore, smooth acceleration of the motor 3 can be obtained without applying a special position detection voltage. Further, the voltage of the motor 3 may be detected, which is easier than detecting a current change according to the carrier frequency, and the carrier frequency can be set higher. This is particularly effective in inferring the rotational position of a small motor having very small inductance.

Then, the rotational position estimating unit 13 determines the timing at which the open-phase voltage reaches the zero point by using the first order approximation function calculated from the stored open-phase voltage, and therefore, the timing can be determined by using a simple approximation function. Further, the open-phase determination unit 11 can easily determine which phase is an open phase based on the rotational position θ est.

(other embodiments)

The approximation function is not limited to the first order approximation, and a curve may be obtained by the second order approximation, for example.

The open-phase determining unit does not necessarily need to determine the open-phase based on the rotational position.

The present invention can also be applied to an energization system other than the 180-degree energization system.

Several embodiments of the present invention have been described, but these embodiments are disclosed as examples and are not intended to limit the scope of the invention. These novel embodiments may be implemented in other various ways, and various omissions, substitutions, and changes may be made without departing from the spirit of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention shown in the claims and the scope of equivalents thereof.

Claims

1. A device for estimating a rotational position of a synchronous motor, comprising:

A phase failure generating unit for setting any one of the three phases in a non-conducting state to become a phase failure for the inverter connected to the three-phase synchronous motor and composed of a plurality of switching elements;

The phase failure determination part determines which phase is to be regarded as the above-mentioned phase failure;

The phase-opening voltage detection part detects the above-mentioned open-phase voltage;

an open-phase voltage storage unit for storing the above-mentioned voltage;

a voltage zero point estimating unit for estimating the zero point of the voltage based on the phase-off voltage stored by the phase-off voltage storage unit; and

a position estimating unit for estimating the rotational position of the electric motor based on the zero point,

The phase failure determination unit determines the phase failure based on the rotational position,

The above-mentioned synchronous motor is a synchronous motor driven by a sine wave by a 180-degree energization method.

2. The apparatus for estimating the rotational position of a synchronous motor according to claim 1, characterized in that:

The voltage zero point estimation unit estimates the zero point of the voltage using an approximate function obtained from the phase-off voltage.

3. The rotational position estimation device of a synchronous motor according to claim 2, characterized in that:

A first-order approximation function is used as the above approximation function.

4. A method for estimating a rotational position of a synchronous motor, characterized in that,

For an inverter connected to a three-phase synchronous motor and composed of a plurality of switching elements, when it is determined which phase of the three phases is to be the off-phase, the determined phase is set to the non-energized state,

Detect and store the voltage of the above-mentioned open phase,

From the stored open-phase voltage, infer the zero point of this voltage,

Based on the above zero point, infer the rotational position of the above motor,

The above-mentioned phase failure is determined based on the above-mentioned estimated rotational position,

5. The method for estimating the rotational position of a synchronous motor according to claim 4, characterized in that,

The zero point of the above-mentioned voltage is estimated using the approximate function obtained from the above-mentioned open-phase voltage.

6. The method for estimating the rotational position of a synchronous motor according to claim 5, wherein,