JP6087802B2 - AC motor drive control device - Google Patents

Description

  The present invention relates to a drive control device for an AC motor.

  An AC motor drive control device is known. In Patent Document 1 (Japanese Patent Laid-Open No. 2000-50689), the voltage phase is controlled by torque feedback control. A rectangular voltage is applied to the motor in accordance with this voltage phase to improve motor output during high-speed rotation. In Patent Document 2 (Japanese Patent Laid-Open No. 2010-148331), in addition to the conventional torque feedback control, feedforward correction that is changed based on the torque command value is introduced to improve the torque tracking performance.

JP 2000-50689 A JP 2010-148331 A

In the conventional rectangular wave control method (for example, Japanese Patent Laid-Open No. 2000-50689, Japanese Patent Laid-Open No. 2010-148331), for example, when Ld = Lq, the relationship between the motor torque and the voltage phase is considered to be an ideal sine waveform relationship. It was. This is shown in FIG. (The graph in this figure corresponds to FIG. 3 in Japanese Patent Laid-Open No. 2000-50689.)
However, the present inventors have intensively researched and found that the relationship between torque and voltage phase in rectangular wave control is actually as shown in FIG. 2, and not the ideal sine wave of FIG. In FIG. 2, there are offsets and phase differences. FIG. 1 is only one special case of the ideal condition of FIG.

Therefore, the present inventors have found that the conventional rectangular wave control method based on the ideal sine wave as shown in FIG. 1 has the following problems.
(1) In order to maintain the stability of the torque feedback control, it is necessary to limit the voltage phase within a range in which the torque monotonously increases (for example, between −90 degrees and +90 degrees in FIG. 1). However, since the curve of FIG. 1 is not accurate, there is a possibility that the stable range is set conservatively or excessively. In fact, in the past, setting the control stability range has relied on conformance. Of course, fitting takes a lot of work.

(2) The torque followability can be improved to some extent by adding a feed forward function based on the waveform of FIG. However, since the waveform of FIG. 1 is not accurate, there is a limit to the calculation accuracy of the feedforward calculation. Therefore, even if the feedforward function is added while assuming the waveform of FIG.

(3) In the waveform shown in FIG. However, actually, as shown in FIG. 2, there is a non-zero torque at the zero phase. Compensation for this non-zero torque is an actual issue and is considered to be one of the causes of torque unevenness in torque feedback control.

(4) If the voltage phase upper limit value for suppressing the maximum torque is set based on the curve of FIG. 1, this is not accurate. In the end, we have to rely on the matching method, but there is no matching standard and it takes time.

(5) Since there is no standard for setting the upper limit value of the voltage phase for suppressing the maximum current, it depends on the adaptation, but the adaptation man-hours are required.

  Therefore, an object of the present invention is to provide a drive control device for an AC motor that can further improve the control stability of the AC motor by performing control based on accurate knowledge.

The AC motor drive control device of the present invention is
An inverter that converts a DC voltage into an AC voltage for rotationally driving an AC motor;
A rectangular wave voltage control unit that controls the voltage phase of the rectangular wave voltage applied to the AC motor so as to correspond to the torque command value, and
The rectangular wave voltage control unit
A phase guard unit for setting a voltage phase upper limit φv3 for limiting the relationship between torque and voltage phase within a monotonically increasing range;
The phase guard unit is
Calculate the phase difference α using the electrical angular velocity ωe of the AC motor in the operating state,
The voltage phase upper limit value φv3 is set to π / 2− | α | in the powering state of the AC motor, and is set to π / 2 + | α | in the regeneration state of the AC motor.

In the present invention,
The phase difference α is preferably calculated by the following equation.
α = tan ⁻¹ {R / (ωe · Lq)}

In the present invention,
It is preferable that the phase guard unit further sets the voltage phase upper limit value φvmax so that the current and torque do not exceed the respective maximum values.
That is, the voltage phase upper limit value φv2 corresponding to the maximum current value is obtained by an equation using the phase difference α and the electric angular velocity ωe of the AC motor in the operating state.
Further, the voltage phase upper limit value φv1 corresponding to the maximum torque is obtained by an equation using the phase difference α and the electric angular velocity ωe of the AC motor in the operating state.
The minimum value of φv1, φv2, and φv3 is set as a voltage phase upper limit value φvmax.

According to the present invention, the upper limit value of the voltage phase is set in consideration of the phase difference based on the actual operating state of the AC motor, so that the control stability is improved.
Since the phase difference α is derived using an arithmetic expression when setting the voltage phase control stability range, man-hours such as adaptation can be reduced.

The figure which showed the relationship between a motor torque and a voltage phase with the ideal sine waveform. The figure which showed the relationship between a motor torque and a voltage phase based on exact knowledge. The figure which shows q phase reference | standard voltage phase (phi) v. The figure which shows the relationship between the magnitude | size of a current vector, and a voltage phase when a driving | running state (Vh, (omega) e) is constant. The figure which shows the voltage phase characteristic when the inverter input voltage Vh is constant. The functional block diagram which shows the control apparatus of the alternating current motor which concerns on this embodiment. The figure which shows the operation | movement flow of the rectangular wave voltage control part 300.

An embodiment of the present invention will be illustrated and described with reference to symbols in each element in the drawings.
The present embodiment is realized by using some basic formulas found by the present inventors.
Therefore, in describing the embodiment of the present invention, the derivation process of the basic expressions used in the present embodiment and their meaning will be described in principle first.

(Derive of basic formula)
The output torque characteristic reflecting the motor operating state is grasped by a torque calculation formula described below.
As is generally known, voltage equations and torque equations on the d-axis and q-axis in a permanent magnet type synchronous motor are shown below.

R represents an armature winding resistance.
Ke represents the armature counter electromotive force constant of the permanent magnet.
ωe represents the electrical angular velocity of the AC motor.
Ld and Lq are inductances.

  In a steady state, since the rate of change of Id and Iq is small, the current transient term can be ignored. For this reason, said formula is shown by a following formula.

  Further, during rectangular wave voltage control, the fundamental wave component of the motor applied voltage (line voltage) indicated by the d-axis voltage and the q-axis voltage is 0.78 times the system voltage Vh. That is, the following equation is obtained.

  φv is a voltage phase based on the q-axis (see FIG. 3). Vh is an inverter input voltage.

  From (Equation 3), by using (Equation 4), the relationship of Iq-φv and the relationship of Id-φv in rectangular wave control can be obtained. When Ld = Lq of the motor, Iq and Id can be expressed by the following equations.

A (Vh, ωe) is the amplitude of the sine wave and is a function of Vh and ωe.
b _Iq (ωe) is an offset of Iq and is a function of ωe.
b _Id (ωe) is an offset of Id and is a function of ωe.

  As can be seen from the equations (5) and (6), Iq and Id have a sinusoidal relationship with φv. However, the amplitude of the sine wave varies depending on fluctuations in the operation state (inverter input voltage Vh, electrical angular velocity ωe). Alternatively, there are a phase difference α and an offset term (two items on the right side), and the magnitude changes as the electrical angular velocity varies.

  As described above, the torque calculation expression indicating the relationship between the voltage phase φv of the rectangular wave voltage and the output torque Te of the AC motor can be obtained.

  Kt is a torque constant.

(Equation 8) has the following characteristics.
(1) The amplitude of the sine function is determined by the inverter input voltage Vh and the motor electrical angular velocity ωe.
On the other hand, since Vh and ωe vary depending on the operation state, the sine function amplitude as a result of this calculation is not constant and varies depending on the operation state.

(2) There is a phase difference α. Due to the presence of the phase difference α, the monotonically increasing range of torque and voltage phase, that is, the phase control range is shifted by α from between −90 degrees and +90 degrees. This is shown in FIG. That is, the phase range of the stable control is [−π / 2−α] to [π / 2−α].

(3) There are two offset terms on the right side of (Equation 8). It can be seen that due to the presence of the offset term, the torque may not match the sign of the voltage phase. This means that the motor torque does not become zero even when the voltage phase φv is zero.

  On the other hand, for the control of the AC motor, either a PWM control mode by sine wave PWM control or overmodulation PWM control or a rectangular wave voltage control mode is selectively applied according to the operating state. Although the rectangular wave control is generally used in the high speed region of the motor, as can be seen from (Equation 8), the phase difference α and the offset term are almost zero during extremely high speed rotation.

  When the motor rotation speed is extremely high, the influence of the resistance R in (Equation 8) can be ignored. At that time, (Equation 8) can be approximately expressed as follows.

  (Expression 9) is a basic expression used in the conventional rectangular wave control. Examples thereof include Japanese Patent Application Laid-Open Nos. 2000-50689 and 2010-148331. The torque characteristics obtained from (Equation 9) are shown in FIG.

  In general, the use range of the rectangular wave control is limited to a high speed range, but in fact, the deviation between (Equation 9) and (Equation 8) increases depending on the maximum operating speed of the motor or closer to the medium speed range. growing. That is, there is a possibility that the magnitude of the phase difference α and the magnitude of the offset term in (Equation 8) cannot be ignored. Therefore, it is necessary to perform feedback control and feedforward control based on (Equation 8).

  In the conventional rectangular wave control method, for example, Japanese Patent Laid-Open No. 2000-50689 obtains the same expression as (Equation 9) assuming that Id = 0. However, in reality, there is almost no situation where Id = 0 in the rectangular wave control. Conversely, the value of Id in rectangular wave control can be quite large. Thereby, the magnitude of the phase current vector is also increased. The magnitude of the phase current vector can be calculated as follows.

  Using (Equation 5) and (Equation 6), the magnitude of the phase current vector becomes a nonlinear function of (Vh, ωe, φv), which can be expressed as follows.

  From (Equation 11), for example, when the voltage phase is a constant value, the magnitude of the phase current vector varies with the variation of the operating state (inverter input voltage Vh, electrical angular velocity ωe). Alternatively, for example, when the operation state (Vh, ωe) is constant, the relationship between the magnitude of the current vector and the voltage phase is as shown in FIG.

(Equation 11) has the following characteristics.
(1) The magnitude of the phase current vector is a function of the voltage phase and the operating state (inverter input voltage Vh, electrical angular velocity ωe). That is, for a constant phase φv, the magnitude of the phase current vector | I |
(2) The voltage phase φv corresponding to the maximum value Imax of the phase current vector changes depending on the change in the operating state.

  From (Equation 11), the voltage phase corresponding to the maximum value Imax of the phase current vector can be calculated from the equation, and the upper limit value φv2 can be expressed by the following nonlinear function.

From (Equation 12), it can be seen that, for example, when the inverter input voltage Vh is constant, the voltage phase corresponding to the maximum value Imax of the phase current vector changes depending on the fluctuation of the electrical angular velocity ωe.
The voltage phase characteristic is shown in FIG.

(Formula 12) has the following characteristics.
The voltage phase upper limit value φv2 corresponding to the maximum value Imax of the phase current vector varies depending on the change in the operating state, but can be calculated from (Equation 12) without using a map.

Based on the above principle, a control device 200 of the AC motor (motor) 100 according to the present embodiment is shown in FIG. The operation flow of the rectangular wave voltage control unit 300 is shown in the flowchart of FIG.
The present control device 200 includes a rectangular wave voltage control unit 300 and an inverter 400.

The rectangular wave voltage control unit 300 controls the phase of the rectangular wave voltage applied to the motor 100 via the inverter 400. That is, the rectangular wave voltage control unit 300 causes the motor torque to follow the torque command value by phase control of the rectangular wave voltage.
The rectangular wave voltage control unit 300 includes a feedback control unit 310, a feedforward control unit 320, a phase guard unit 330, and a rectangular wave generator 340.

A torque command is input to feedback control section 310 (ST101), and a torque detection value of motor 100 is input from torque detector 110 (ST103). The feedback control unit 310 calculates the deviation of the motor output torque with respect to the torque command value (311, ST104), and performs compensation for torque and voltage phase in the compensator 312 (ST105), and then performs PI control (313, ST106). ) To control the phase.
The compensator 312 will be described.
The relationship between torque and voltage phase (Equation 8) is affected by the operating state (inverter DC side voltage Vh and electrical angular velocity ωe). Due to the strong nonlinearity of the sine wave amplitude and the offset term, the gain setting of the PI calculator 313 becomes difficult. Therefore, compensating the torque by the compensator 312 eliminates the influence of fluctuations in the operating state. As a result of torque compensation, the compensated torque and voltage phase have a sinusoidal function relationship in which the amplitude is 1 and the offset term is zero. However, the phase of the sine wave is a combination of the voltage phase and the phase difference α depending on the operation state. This facilitates the gain setting of the PI calculator 313.

In order to improve the accuracy of feedback control section 310, feedback control section 310 is provided with FB phase calculator 314 (ST107). The motor torque is a sine wave function of the sum of the voltage phase φv and the phase difference α (Equation 8). Therefore, the result obtained from the torque feedback control is actually the sum of the voltage phase φv and the phase difference α. Therefore, the voltage phase component obtained from the torque feedback control is only the amount obtained by subtracting the phase difference α from the PI calculation result of torque feedback.
Therefore, the FB phase calculator 314 performs the following calculation.
φvfb = torque PI control result−α
However, (alpha) is calculated by (Formula 7).
Thereby, the motor torque unevenness phenomenon by torque feedback control can be reduced, and the improvement of the torque tracking performance can be expected.

  Feedforward control unit 320 calculates a voltage phase corresponding to the torque command value based on the relational expression (formula 8) between the torque and the phase (ST130). In addition, the acquired motor variable is input to the feedforward control unit 320 together with the torque command (ST101) (ST102). Here, the torque characteristic (tangent) used for feedforward control is generated based on (Equation 8). Thereby, the accuracy of the compensation amount of the phase calculated from the feedforward control can be improved, and an improvement in torque response can be expected.

  The voltage phase (feedback term φfb) by feedback control and the voltage phase (feedforward term φff) by feedforward control are added (ST108) to set a voltage phase φv corresponding to the phase command of the rectangular wave voltage.

  The phase guard unit 330 includes a guard value setting unit 331 and a guard processing unit 332. The guard value setting unit 331 sets the upper limit value of the voltage phase (ST111 to ST120). The voltage phase upper limit value is set so that the current and torque do not exceed their respective maximum values (ST111, ST112), and the relationship between torque and voltage phase is within a monotonically increasing range (ST113).

A method for setting the voltage phase upper limit value by the guard value setting unit 331 will be described.
The voltage phase upper limit value φv2 for suppressing the maximum value of the phase current vector is calculated based on the operating state by the mathematical relational expression (formula 12) of the current and the voltage phase (ST112). Further, the voltage phase for suppressing the maximum value of the torque is calculated based on the operating state by the mathematical relational expression (Equation 8) of the torque and the voltage phase, and the absolute value of the calculation result is set as the voltage phase upper limit value φv1 ST111). Furthermore, for feedback control stability, as shown in FIG. 3, the phase range is limited to a monotonically increasing range of torque and phase (ST113). In this case, the calculation is performed based on the operating state by a mathematical relational expression (Equation 8) of torque and voltage phase.
Specifically, first, the phase difference α is calculated using the electrical angular velocity from (Equation 7). As can be seen from (Equation 8), the phase upper limit value φv3 in the power running state of the motor is π / 2− | α |, and the phase upper limit value in the regenerative state is π / 2 + | α |. The maximum value φv3 is obtained. The minimum value of the calculated voltage phase upper limit values (voltage phase upper limit value φv2 corresponding to the maximum current value, voltage phase upper limit value φv1 corresponding to the maximum torque, and upper limit value φv3 of the phase control stable range) is obtained (ST114 to ST120). . The determined minimum value is the upper limit value of the voltage phase guard unit (ST120).

The effects of such voltage phase setting are as follows.
According to the upper limit value of the voltage phase guard unit 330 set as described above, the maximum value of the current and the maximum value of the torque are not exceeded, and the upper limit value of the voltage phase guard unit 330 increases monotonously in the torque-phase relationship. Since it is within the range, control stability can be guaranteed. Further, since the above voltage phase upper limit value can be calculated from a mathematical formula, it is more efficient than the fitting method. The calculation result of the voltage phase can be stored as a map. Further, even when the adaptation is necessary depending on the actual situation, the density of the adaptation data can be reduced based on the result obtained from the mathematical formula.

  The guard processing unit 332 executes guard processing for limiting the absolute value of the voltage phase φv so as not to exceed the phase upper limit value φmax set by the guard value setting unit 331 (ST141 to ST144). When the absolute value of voltage phase φv exceeds the phase upper limit value (ST141: YES), guard processing unit 332 sets output voltage phase φv = φmax or φv = −φmax depending on the sign of the voltage phase ( ST143). On the other hand, if phase command | φv | <φmax (ST141: NO), output voltage phase φv = phase command φv is set (ST142).

  Inverter 400 applies an AC voltage according to voltage phase φv determined in this way to motor 100.

  As described above, according to the present embodiment, the control stability of the AC motor can be further improved by performing control based on accurate knowledge.

Note that the present invention is not limited to the above-described embodiment, and can be changed as appropriate without departing from the spirit of the present invention.
The calculation result of the voltage phase may be stored as a map and may be adapted according to the actual situation. Even in this case, the density of the matching data can be reduced based on the result obtained from the mathematical formula.

DESCRIPTION OF SYMBOLS 100 ... Motor, 110 ... Torque detector, 200 ... Control apparatus, 300 ... Rectangular wave voltage control part, 310 ... Feedback control part, 312 ... Compensator, 313 ... PI calculator, 314 ... FB phase calculator, 320 ... Feed Forward control section, 330 ... phase guard section, 331 ... guard value setting section, 332 ... guard processing section, 340 ... rectangular wave generator, 400 ... inverter.

Claims (1)

An inverter that converts a DC voltage into an AC voltage for rotationally driving an AC motor;
A rectangular wave voltage control unit that controls the voltage phase of the rectangular wave voltage applied to the AC motor so as to correspond to the torque command value, and
The rectangular wave voltage control unit
Having a phase guard for setting a voltage phase upper limit for limiting the relationship between torque and voltage phase within a monotonically increasing range;
The phase guard unit is
Calculate the phase difference α using the electrical angular velocity ωe of the AC motor in the operating state,
The upper limit value of the voltage phase for limiting the relationship between the torque and the voltage phase within a monotonically increasing range is set to π / 2− | α | in the power running state of the AC motor, and in the regenerative state of the AC motor. Is set to π / 2 + | α |. A drive control device for an AC electric motor.

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