JP4591049B2 - AC / AC direct converter motor controller - Google Patents

Description

  The present invention belongs to the field of controlling an AC motor by a power converter, and in particular, an AC / AC for driving a motor that converts an AC input voltage into an AC voltage of an arbitrary size and frequency without a large energy buffer and outputs the AC voltage. In a direct converter, the present invention relates to a motor control device that suppresses torque pulsation and rotation unevenness of a motor by controlling the output voltage to be within a PWM controllable range of the input voltage and weakening the motor magnetic flux. It is.

As an example of this type of AC / AC direct converter, a known matrix converter is taken as an example, and the prior art will be described below.
FIG. 10 shows a schematic configuration of the matrix converter 2. The matrix converter 2 is bidirectional connected between each phase terminal of the three-phase AC power source 1 and the output terminals U, V, W. As shown in the figure, these AC switches S1 to S9 are composed of two anti-parallel connection circuits of semiconductor switching elements such as IGBTs and diodes in series. Or, only two semiconductor switching elements having reverse blocking capability are connected in antiparallel.

  As is well known, a matrix converter is an AC / AC direct converter that directly outputs an AC voltage of any size and frequency from an AC power supply voltage without using a large energy buffer such as a capacitor. It has a long life and space saving, and can control the input current so that it can regenerate power and suppress harmonics of the power supply.

  Next, FIG. 11 is a waveform diagram for explaining the output voltage possible range of the matrix converter. Since the matrix converter can generate positive and negative voltages for each phase of the input voltage and outputs the voltage by directly cutting the power supply voltage with an AC switch, the output voltage range is an envelope of 6-phase AC Within the line range.

When the magnitude of the voltage between the positive and negative peak values of the input voltage is 1.0, PWM control is possible when trying to output a voltage in the region (overmodulation region) exceeding 0.866 times (within the shaded range). Out of range, the output voltage is distorted as indicated by the line voltage V _uv , the motor torque of the motor driven by the matrix converter pulsates, and noise and vibration are generated due to uneven rotation, which is not preferable.
Therefore, the matrix converter needs to be designed so that the rated output voltage is 0.866 times or less of the input voltage (voltage utilization factor is 0.866 or less). Furthermore, when the system voltage decreases, it is necessary to design the rated output voltage in consideration of the system voltage decrease.

  By the way, when an electric motor is driven by an inverter that converts AC to DC once and converts it into AC, that is, an AC / DC / AC inverter, field weakening control that limits the output voltage by weakening the motor magnetic flux is known. ing. Here, field weakening control is a vector control in which the current of the motor is separated into a component parallel to the motor magnetic flux (flux current component) and an orthogonal component (torque current component), and the magnetic flux and torque are controlled independently. In this case, the speed control range is expanded by performing control so that the output current is constant by weakening the magnetic flux current component in the high speed region.

  The field weakening control in the inverter is disclosed in Patent Document 1 described later, and will be briefly described below. In the following, an axis parallel to the motor magnetic flux is called a d-axis, and an axis orthogonal to the d-axis is called a q-axis.

FIG. 12 is a block diagram of a drive system that drives an electric motor by an inverter that is subjected to field weakening control.
In FIG. 12, 200 is a DC power source obtained by converting AC power, 201 is an inverter, 202 is an electric motor such as a cylindrical permanent magnet synchronous motor, 203 is a rotor position detector, 204 is a speed detector, and 205 is Load 206, current detection means for detecting each phase output current (motor current) i _u , i _v , i _w of inverter 201, 210 performs adjustment calculation so that angular velocity detection value ω matches angular velocity command value ω ^* Speed adjusting means for performing and outputting torque command value T ^* , 211 for q-axis current command calculating means for calculating q-axis current command value i _q ^* based on torque command value T ^* , and 212 for q-axis current command value i _The d-axis current command calculation means 216 calculates the d-axis current command value i _d ^* based on _q ^* and the angular velocity detection value ω, and 216 calculates each phase current detection value i _u , i _v , i _w based on the phase angle information θ. on dq rotation coordinates Component (d-axis current detection value, q-axis current detection _value) i d, the coordinate conversion means for converting the _{i q,} 213 is _{i q} is computed q-axis voltage command value _v ^{q *} so as to coincide with _i ^{q *} q-axis current control means 214, _d- axis current control means 214 for calculating the d-axis voltage command value v _d ^* so that i _d coincides with i _d ^* , and 215 for v _d ^* and v _q ^* as phase angle information θ The coordinate conversion means for converting the voltage command values v _u ^* , v _v ^* , and v _w ^* of each phase based on the above, 217 performs a PWM operation according to the voltage command values v _u ^* , v _v ^* , and v _w ^* to perform inverter 201 PWM pulse generation means for generating drive pulses for the switching elements.

Here, the operation of the d-axis current command calculation means 212 in the above configuration will be described.
FIG. 13 is a phasor diagram of the output voltage of the cylindrical permanent magnet synchronous motor. In the permanent magnet synchronous motor, a speed electromotive force e ₀ is generated in proportion to the motor speed. Since the magnetic flux generated by the permanent magnet does not change, the d-axis voltage v _d is generated by the inverter 201 so as to cancel the speed electromotive force e _0, and the output voltage of the inverter 201 is limited.
From FIG. 13, the output voltage v _out of the inverter 201 is expressed by Equation 1. Ignore the armature winding.

Here, when Equation 1 is rewritten to limit the output voltage v _out of the inverter 201 to a desired voltage limit value v _lim ^* , Equation 2 is obtained.

The q-axis reactance X _q can be expressed by Equation 3 by the product of the q-axis inductance L _q and the rotational angular velocity ω.

Substituting Equation 3 into Equation 1 to obtain the d-axis voltage command value v _d ^* yields Equation 4.

Next, when the d-axis current command value i _d ^* is expressed by the d-axis voltage command value v _d ^* , Expression 5 is obtained.

By substituting Equation 4 into Equation 5 and converting the q-axis current i _q to the q-axis current command value i _q ^* , the d-axis current command value i _d ^* becomes Equation 6.

Therefore, if the inverter 201 is vector-controlled by the d-axis current command value i _d ^* obtained by Equation 6, the output voltage v _out of the inverter 201 can be suppressed to the limit value v _lim ^* .

As it is apparent from FIG. 13, because the d axis voltage value _v ^{d *} generates in a direction to cancel the _{e 0,} in the case of performing field-weakening _{control, e 0> √ {v lim} * 2 - (ωL q i q ^* ) ² }, the d-axis current command value i _d ^* is negative.

Japanese Patent Laid-Open No. 11-178399 (paragraphs [0006], [0007], FIGS. 1 to 4 etc.)

  When the output voltage rating value of the matrix converter is designed in consideration of the system voltage drop, the current capacity increases in order to obtain the same output as when not considering it. For example, if 15% is taken into account when the system voltage decreases and the rated voltage is decreased by 15%, the output current will increase by approximately 15%. An increase in current capacity causes an increase in apparatus capacity, resulting in an increase in cost and an increase in installation space.

Further, field weakening control in the conventional inverter often makes the output voltage limit value v _lim ^* coincide with the output voltage rated value, and if this is applied to the matrix converter as it is, depending on the magnitude of the input voltage, the output voltage May weaken the field even though the PWM controllable range. If field weakening is performed within the PWM controllable range, an unnecessary current increase is caused, resulting in a decrease in efficiency and overheating of the converter and the motor. Conversely, when the input voltage decreases, the output voltage limit value may fall outside the range in which PWM control is possible, causing problems such as causing torque pulsation of the motor due to distortion of the output voltage.

  Therefore, the problem to be solved by the present invention is to obtain an optimum output voltage limit value corresponding to the magnitude of the input voltage in real time in an AC / AC direct converter such as a matrix converter and to prevent the motor magnetic flux from exceeding the limit value. It is an object of the present invention to provide an inexpensive electric motor control apparatus that reduces distortion of the output voltage and prevents an unnecessary increase in current within a PWM controllable range.

In order to solve the above-mentioned problem, the invention described in claim 1 is an AC / AC direct converter for driving an electric motor by converting an AC voltage into an AC voltage of an arbitrary magnitude and frequency by a bidirectional semiconductor switch.
Means for detecting the magnitude of the input voltage of the direct converter;
Means for calculating an output voltage limit value for limiting the output voltage of the direct converter within a range in which the input voltage can be PWM controlled according to the magnitude of the input voltage detected by the means;
Means for calculating an output voltage command value of the direct converter so as to reduce the motor magnetic flux based on the output voltage limit value.

The invention described in claim 2 is an AC / AC direct converter for driving an electric motor by converting an AC voltage into an AC voltage having an arbitrary size and frequency by a bidirectional semiconductor switch.
Means for detecting the magnitude of the input voltage of the direct converter;
Means for calculating an output voltage limit value for limiting the output voltage of the direct converter within a range in which the input voltage can be PWM controlled according to the magnitude of the input voltage detected by the means;
Coordinate conversion means for converting the motor current detection value into a parallel component and an orthogonal component with respect to the motor magnetic flux,
Means for calculating the parallel component of the current command value based on the output voltage limit value;
Means for calculating an output voltage command value of the direct converter so that a parallel component of the electric motor current detection value coincides with a parallel component of the current command value.

The invention described in claim 3 is as described in claim 1 or 2,
The means for calculating the output voltage command value of the direct converter calculates the output voltage command value for the virtual inverter assumed in the matrix converter as the direct converter.

According to the invention of claim 1, the output voltage limit value is calculated in real time according to the magnitude of the input voltage of the AC / AC direct converter so that the output voltage of the AC / AC direct converter is within the limit value. An output voltage command value (d-axis voltage command value) is generated to weaken the motor magnetic flux. As a result, the output voltage of the direct converter can be limited to a range in which the PWM control of the input voltage is possible, and torque pulsation and rotation unevenness of the motor due to distortion of the output voltage do not occur.
According to the invention of claim 2, when vector control is performed, the d-axis current command value is generated so as to be within the output voltage limit value calculated according to the magnitude of the input voltage of the AC / AC direct converter. By weakening the motor magnetic flux, it is possible to limit the output voltage of the direct converter and prevent the occurrence of torque pulsation and rotation unevenness of the motor.
In any of the first and second aspects, when the output voltage can be controlled within a range in which PWM control is possible, the motor magnetic flux is not weakened, and an unnecessary current increase is not generated to reduce efficiency and overheat. To prevent.
In addition, according to the present invention, the calculation of the voltage command value and the current command value can be realized by simple four arithmetic operations, so that an expensive arithmetic device is unnecessary, and torque pulsation of the motor caused by saturation of the output voltage An inexpensive control device that does not cause an unnecessary increase in current can be realized.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a block diagram showing a first embodiment of the present invention. In FIG. 1, 1 is a three-phase AC power source, 2 is a matrix converter as an AC / AC direct converter, 3 is an electric motor such as a cylindrical permanent magnet synchronous motor, 4 is a load, and 5 is an input voltage v of each phase of the matrix converter 2. Voltage detecting means for detecting _{r 1} , v _s , v _t , 6 is a magnitude detecting means for detecting the magnitude | V _i | of the input voltage (input voltage vector), 7 is | V _i | and the angular velocity command value ω ^*. And a d-axis voltage command value v _d ^* based on the q-axis voltage command value v _q ^* and a d-axis voltage command calculation means 8 for calculating the q-axis voltage command value v _q ^* based on the angular velocity command value ω ^*. Q-axis voltage command calculating means for calculating, 9 a virtual rectifier command calculating means for calculating a command to the virtual rectifier (input current command of the matrix converter 2) from the input voltages v _r , v _s and v _t , 10 is a d-axis, q-axis voltage command value _v ^d *, _q ^* and phase angle information θ virtual inverter command calculating means for calculating a command (output voltage command of the matrix converter 2) for the virtual inverter on the basis of (calculated by integrating the angular speed command value omega ^*), 11 is the virtual rectifier Directive Virtual rectifier PWM generating means for generating PWM pulses based on the above, 12 is a virtual inverter PWM generating means for generating PWM pulses based on the virtual inverter command, and 13 is a PWM pulse combining for synthesizing output pulses of these generating means 11 and 12 The 18 semiconductor switching elements of the matrix converter 2 are driven by the PWM pulse output from the synthesizing means 13.

  In this embodiment, a virtual rectifier and a virtual inverter are assumed in the matrix converter 2 and the matrix converter 2 is controlled by a “virtual AC / DC / AC system” that controls them independently. Here, the virtual AC / DC / AC system is a non-patent literature, for example, “Improvement method of input / output waveform of matrix converter by virtual AC / DC / AC conversion system” by Shinichi Ito, Ikuya Sato and Shigeo Konishi. Semiconductor power conversion study group SPC02-90 / IEA-02-31,2002).

  In the virtual AC / DC / AC system, it is necessary to prevent a power supply short circuit and to prevent the load end from being opened in order to secure a current circulation path for the load reactor. On the virtual rectifier side, the same restrictions as the current-type PWM rectifier are required. On the other hand, it is necessary to determine a switching pattern that does not short-circuit the DC link voltage on the virtual inverter side under the same constraint conditions as the voltage source inverter.

According to the non-patent document, the three-phase output voltage of the matrix converter is expressed as follows: a switching matrix (a determinant of a switching function (logic 1 is on, logic 0 is off) of the switching elements constituting the matrix converter) and a three-phase input voltage. Can be represented by the product of
In order to obtain the same output voltage and input voltage as this matrix converter, the switching voltage of the matrix converter (referred to as SM1 for convenience), the input voltage and the direct current in the PWM rectifier / inverter (AC / DC / AC) system The product of the switching matrix (referred to as SM2) of the PWM rectifier that shows the relationship with the link voltage and the switching matrix (referred to as SM3) of the PWM inverter that also shows the relationship between the DC link voltage and the output voltage are made equal. (That is, SM1 = SM2 · SM3).

Therefore, assuming a virtual rectifier and a virtual inverter in the matrix converter, a virtual AC / DC / AC is obtained by synthesizing the PWM pulse for the virtual rectifier and the PWM pulse for the virtual inverter and applying them to each switching element of the matrix converter. An AC / AC direct converter of the type can be realized.
The virtual rectifier command generation means 9, virtual inverter command generation means 10, virtual rectifier PWM pulse generation means 11, virtual inverter PWM pulse generation means 12 and PWM pulse synthesis means 13 in FIG. 1 are for realizing the above operating principle. It is.

Based on such a virtual AC / DC / AC system, the main part of the present embodiment will be described below.
In FIG. 1, the voltage detection means 5 detects the input voltages v _r , v _s and v _t of the matrix converter 2, and the magnitude calculation means 6 calculates the magnitude | V _i | of the input voltage vector. FIG. 2 is a block diagram of the size calculation means 6. The square root of the square sum of the AC biaxial components v _α and v _β obtained by three-phase / two-phase conversion of v _r , v _s and v _t is shown. Then, the magnitude | V _i | is calculated.
Here, v _α and v _β are expressed by Equation 7, and the magnitude | V _i | of the input voltage vector is expressed by Equation 8.

The magnitude | V _i | of the input voltage obtained by Expression 8 is input to the d-axis voltage command calculation means 7. In addition to the above calculation, the input voltage magnitude calculation means 6 may be realized by full-wave rectifying the three-phase input voltage and obtaining an average value thereof.

Next, FIG. 3 is a block diagram of the d-axis voltage command calculation means 7. The output voltage limit value v _lim ^* is set by Equation 9 based on the magnitude | V _i | of the input voltage vector.

  Here, the constant K may be set to 0.866, or may be set with a margin in consideration of an error in the output voltage accompanying the dead time.

Substituting the output voltage limit value v _lim ^* obtained from Equation 9 into Equation 4 and expressing the speed electromotive force e ₀ by the angular velocity command value ω ^* and the no-load induced voltage E ₀ , the d-axis voltage command value v _d ^* Is represented by Equation 10.

In Expression 10, when the d-axis voltage command value v _d ^* is expressed as ω ^* L _q i _q = v _q ^* , Expression 11 is obtained.

FIG. 4 is a flowchart showing the operation of the d-axis voltage command calculation means 7.
The d-axis voltage command value v _d ^* is calculated based on the above-described formulas 9 and 11 (steps S1 and S2), and v _d ^* is output only when v _d ^* <0 (S3 No). From FIG. 13, when v _d ^* is generated in the state of v _d ^* > 0, the d-axis voltage command value v _d ^* has the same sign as the speed electromotive force e _0, and a current flows in the direction of increasing the motor magnetic flux. Therefore, when v _d ^* ≧ 0, v _d ^* = 0 is set (S3 Yes, S4) to prevent an unnecessary increase in current.

1 outputs a three-phase sine wave voltage command from the d-axis voltage command value v _d ^* , the q-axis voltage command value v _q ^* and the phase angle information θ. The phase angle information is obtained by integrating the angular velocity command value ω ^* . However, the phase angle information may be obtained from the detected speed value of the electric motor 3, or the estimated speed value may be used.

As described above, in this embodiment, the output voltage limit value v _lim ^* is calculated according to the magnitude of the input voltage, and the d-axis is calculated using the limit value v _lim ^* and the q-axis voltage command value v _q ^*. The voltage command value v _d ^* is obtained, and a d-axis voltage command value v _d ^* that weakens the motor magnetic flux according to the positive / negative is generated and given to the virtual inverter command calculation means 10, thereby outputting the output voltage of the matrix converter 2. Can be controlled within the range in which the input voltage can be PWM controlled to suppress distortion of the output voltage, and the occurrence of torque pulsation and rotation unevenness of the electric motor 3 can be prevented.

Next, FIG. 5 is a block diagram showing a second embodiment of the present invention. In this embodiment, vector control is applied to virtual inverter control.
In FIG. 5, the same components as those in FIG. 1 are denoted by the same reference numerals, and the description thereof is omitted. Hereinafter, different portions will be mainly described.

In FIG. 5, 14 is a position detector for obtaining phase angle information θ, 15 is a speed detector, 16 is a speed adjusting means for adjusting the angular speed detected value ω so as to coincide with the angular speed command value ω ^* , and 17 is Q-axis current command calculation means for calculating the q-axis current command value i _q ^* from the output of the speed adjustment means 16, 18 is the magnitude of the output voltage vector | V _i |, the q-axis current command value i _q ^*, and the angular velocity detection value d-axis current command calculation means for calculating a d-axis current command value i _d ^* from ω, 19 is a current detection means for detecting the output current of the matrix converter 2 (current of the motor 3), and 20 is a current detection value i for each phase. _{r, i} s, d-axis of the _{i t} three-phase / two-phase conversion to biaxial components, q-axis current detection value _i d, coordinate transformation means for obtaining a _{i q,} 21 its a q-axis current detection value _{i q} Starring the q-axis voltage command value _v ^{q *} so as to coincide with the command value _i ^{q *} Q-axis current control means for, 22 d-axis current control unit which calculates a d axis voltage value v _d ^* to match the d-axis current detection value i _d to the command value i _d ^*, 23 is the d-axis voltage The coordinate conversion means obtains a three-phase voltage command value for the virtual inverter by performing two-phase / three-phase conversion on the command value v _d ^* and the q-axis voltage command value v _q ^*. ) Is input to the virtual inverter PWM generation means 12.
Other configurations are the same as those in FIG.

In this embodiment, since the vector control technique is known except for the d-axis current command calculation means 18 for calculating the d-axis current command value i _d ^* , only the operation of the d-axis current command calculation means 18 will be described here.

FIG. 6 is a block diagram of the d-axis current command calculation means 18.
Similarly to the first embodiment, when the output voltage limit value v _lim ^* set by Expression 9 is substituted into Expression 4, and the speed electromotive force e ₀ is expressed by the angular speed detection value ω and the no-load induced voltage E ₀ , the d axis The voltage command value v _d ^* is expressed by Equation 12.

When the d-axis current command value i _d ^* is obtained from Equation 12, Equation 13 is obtained.

FIG. 7 is a flowchart showing the operation of the d-axis current command calculation means 18. Based on the equations 9, 12, 13 described above calculates the d-axis current command value _i ^{d *} (S11 to S13), by the same principle as the first _embodiment, the _i ^{d *} only if the ^{i d} * <0 Output (S14 No), and if i _d ^* ≧ 0, i _d ^* = 0 is set (S14 Yes, S15) to prevent an unnecessary increase in current.
In Equation 13, the d-axis current command value i _d ^* is calculated using the q-axis current command value i _q ^* , but the calculation is performed using the q-axis current detection value i _q and the torque command value T ^*. Also good.

FIG. 8 shows an input current waveform i _r (upper side) when the input voltage of the matrix converter is 180 [V] and 166 [V] which is 0.866 times or more is output when the present invention is not applied. And the output current waveform i _u (lower side).
In this example, the output voltage exceeds the range in which PWM control is possible, so the output voltage is distorted, and as a result, the output current is distorted.
On the other hand, FIG. 9 shows input / output current waveforms when the second embodiment of the present invention is applied. By performing field-weakening control according to the present embodiment, distortion of the input / output current waveform is considerably reduced as compared with FIG. 8, and generation of torque pulsation and rotation unevenness of the motor due to output voltage distortion can be prevented. .

1 is a block diagram showing a first embodiment of the present invention. It is a block diagram of the magnitude | size calculating means of the input voltage in FIG. It is a block diagram of the d-axis voltage command calculation means in FIG. It is a flowchart which shows operation | movement of the d-axis voltage command calculating means in FIG. It is a block diagram which shows 2nd Embodiment of this invention. FIG. 6 is a block diagram of d-axis current command calculation means in FIG. 5. It is a flowchart which shows operation | movement of the d-axis current command calculating means in FIG. It is an input / output current waveform of the matrix converter when the present invention is not applied. It is an input-output current waveform of the matrix converter at the time of applying 2nd Embodiment of this invention. It is a schematic block diagram of a matrix converter. It is a wave form diagram for demonstrating the voltage which a matrix converter can output. It is a block diagram of the electric motor drive system by the inverter by which field weakening control is carried out. It is a phasor figure of the output voltage of a cylindrical permanent magnet synchronous motor.

Explanation of symbols

1: AC power supply 2: Matrix converter 3: Motor 4: Load 5: Voltage detection means 6: Input voltage magnitude detection means 7: d-axis voltage command calculation means 8: q-axis voltage command calculation means 9: virtual rectifier command calculation Means 10: Virtual inverter command calculation means 11: Virtual rectifier PWM generation means 12: Virtual inverter PWM generation means 13: PWM pulse synthesis means 14: Position detector 15: Speed detector 16: Speed adjustment means 17: q-axis current command calculation Means 18: d-axis current command calculation means 19: current detection means 20: coordinate conversion means 21: q-axis current control means 22: d-axis current control means 23: coordinate conversion means

Claims (3)

In an AC / AC direct converter for driving an electric motor by converting an AC voltage into an AC voltage of an arbitrary size and frequency by a bidirectional semiconductor switch,
Means for detecting the magnitude of the input voltage of the direct converter;
Means for calculating an output voltage limit value for limiting the output voltage of the direct converter within a range in which the input voltage can be PWM controlled according to the magnitude of the input voltage detected by the means;
Means for calculating an output voltage command value of the direct converter based on the output voltage limit value so as to reduce the motor magnetic flux;
A motor control device for an AC / AC direct converter characterized by comprising: In an AC / AC direct converter for driving an electric motor by converting an AC voltage into an AC voltage of an arbitrary size and frequency by a bidirectional semiconductor switch,
Means for detecting the magnitude of the input voltage of the direct converter;
Means for calculating an output voltage limit value for limiting the output voltage of the direct converter within a range in which the input voltage can be PWM controlled according to the magnitude of the input voltage detected by the means;
Coordinate conversion means for converting the motor current detection value into a parallel component and an orthogonal component with respect to the motor magnetic flux,
Means for calculating the parallel component of the current command value based on the output voltage limit value;
Means for calculating an output voltage command value of the direct converter so that a parallel component of the motor current detection value matches a parallel component of the current command value;
A motor control device for an AC / AC direct converter characterized by comprising: In the motor control device for an AC / AC direct converter according to claim 1 or 2,
The means for calculating the output voltage command value of the direct converter calculates an output voltage command value for a virtual inverter assumed in a matrix converter as a direct converter, and the motor control device for an AC / AC direct converter .

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