JPH06351292A - Controller for induction motor - Google Patents

Abstract

PURPOSE:To allow control of a plurality of types of induction motor having different V/F patterns using a limited control data by determining the switching pattern of a switching element based on the voltage vector amounts operated sequentially in response to the operational frequency. CONSTITUTION:An operational frequency command circuit 51 commands the operational frequency of a motor compressor based on a control signal delivered from an indoor control section 7. A V/F pattern memory means 52 stores a plurality of V/F patterns for various motor compressors 3. A V/F pattern selecting section 8 selects a V/F pattern corresponding to a motor compressor 3 being used from the V/F pattern memory means 52. A voltage vector operating means 53 operates a required output voltage based on the operational frequency command and a V/F pattern selected at the V/F pattern selecting section 8 thus determining a voltage vector amount. A PWM signal output means 54 determines a switching pattern at a reverse converting section 4 from the voltage vector amount and delivers the switching pattern to a drive circuit 6.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control device for an induction motor using an inverter device for controlling the voltage applied to the induction motor and its frequency to variably control the rotation speed of the induction motor.

[0002]

2. Description of the Related Art In general, variable voltage / variable frequency control, that is, VVVF control, using an inverter device as a speed changing means of an induction motor is performed. In this VVVF control, the ratio V of the output voltage V to the output frequency F shown in FIG.
By controlling / F constant, even if the output frequency of the inverter device changes, the magnetic flux of the induction motor becomes constant,
The output torque is controlled to be constant.

In an induction motor controller used in an air conditioner or the like, the output voltage V and the output frequency F of the inverter device are controlled by a pulse width modulation control method in order to realize the VVVF control with a constant V / F. It is variable.

Among the pulse width modulation control methods, the most representative sine wave / triangle wave comparison pulse width modulation control method (hereinafter,
The PWM control method will be described). FIG. 3 shows a typical voltage waveform of this PWM control type inverter device and its waveform generation method. However, in this example, 3
Waveforms relating to the w phase among the phases are omitted, and the PWM control method in the case where the number of pulses in one cycle of a triangular wave that is a carrier wave is 9 is illustrated.

First, the waveform generation method will be explained. ST is a triangular wave signal which is a carrier wave, and SA and SB are two sine wave signals having a phase difference of 120 °. In one cycle of the sine wave signal, ST There are nine triangular wave signals.
The u-phase terminal voltage VU depends on the sine wave signal SA and the triangular wave signal ST.
VU becomes “H” when the sine wave signal SA is larger than the triangular wave signal ST, and VU becomes “U” when the sine wave signal SA is smaller than the triangular wave signal ST.
Becomes'L 'and a u-phase terminal voltage waveform is generated. Similarly, the v-phase terminal voltage VV is obtained by comparing the voltages of the sine wave signal SB and the triangular wave signal ST whose phase is delayed by 120 ° with respect to the sine wave signal SA. The voltage actually applied to the induction motor is the line voltage VUV of the pulse wave obtained by the output difference between the u-phase terminal voltage VU and the v-phase terminal voltage VV, and the fundamental wave effective value of this pulse wave is that of the inverter device. The output voltage becomes V.

Here, in order to vary the output voltage V of the inverter device, the amplitude of the triangular wave signal ST may be kept constant and the amplitudes of the sine wave signals SA and SB may be varied. For example, the output voltage V of the inverter device may be changed. To raise it, the fundamental wave effective value of the pulse wave is increased by making the amplitudes of the sine wave signals SA and SB larger than the amplitude of the triangular wave signal ST.

In the conventional control of the inverter device, based on the V / F pattern according to the specific specifications of the induction motor,
The fundamental wave effective value of the pulse wave, that is, the output voltage V is calculated for each output frequency F by Fourier transform or the like, and the amplitude difference between the sine wave signal and the triangular wave signal is determined so that V / F becomes constant. Then, the obtained terminal voltage signals (V
U, VV, VW) data strings, such as (HHL), (HLL),
(HLH), ... Is compressed for one cycle or data to reduce the amount of data and stored in the ROM of the control circuit or the storage unit of the microcomputer. If the output frequency has 10 levels, 10 kinds of data strings are required for each, and it is necessary to store all the data strings in the ROM or the like.

[0008]

As described above, in the method of storing the data string of the terminal voltage signal of each phase for the PWM control in the storage element such as the ROM, the operating frequency of the induction motor is set in multiple stages. In order to perform the control in accordance with each operating frequency, it is necessary to store various kinds of data strings corresponding to each operating frequency in the ROM, and there is a drawback that the ROM capacity becomes large. Further, since the ROM capacity is also limited, the output voltage V cannot be continuously varied according to the operating frequency F, and the operating frequency control of the induction motor becomes more discrete and the control characteristics deteriorate. was there.

Further, if the specifications of the induction motor change, it is necessary to calculate the data string so that the V / F becomes constant according to the specifications, and one ROM or a microcomputer has a plurality of specifications of V. It was also difficult to store the / F pattern. This has also been a factor in hindering the common use of ROMs and microcomputers and increasing costs.

Further, the output voltage V output from the inverse converter
Is calculated based on the DC voltage E obtained by rectifying the AC power supply by the rectification unit and is uniquely determined for each operating frequency F. Therefore, it should be used as a reference when the voltage of the AC power supply fluctuates. The DC voltage E may change and the relationship of constant V / F may be broken, and the induction motor may operate with low efficiency.
In particular, when the AC power supply voltage dropped, the induction motor sometimes broke down due to insufficient torque.

Even when the load of the induction motor fluctuates, the relationship of constant V / F may be broken, and if the V / F pattern is uniquely determined, torque shortage or excessive torque may occur. .

Depending on these voltage fluctuations and load fluctuations, V /
In order to maintain the constant F relationship, a data string of the terminal voltage signal corresponding to the variation is required, but it was difficult to store all these data strings due to the limitation of the ROM capacity.

Therefore, an object of the present invention is to control different V / F patterns of a plurality of types of induction motors with a small amount of control data, and to easily control fluctuations in power supply voltage and fluctuations in load. It is an object of the present invention to provide a control device for an induction motor that can follow.

[0014]

According to the present invention, V / F pattern control is performed on an induction motor by a PWM control method, and it is possible to store all data strings of terminal voltage signals in a storage element such as a ROM. According to the specifications of the induction motor, voltage vector calculation means for calculating the voltage vector from the operating frequency at that time to obtain the optimum output voltage, and the V / F pattern corresponding to a plurality of types of induction motors are approximated by the gradient. A V / F pattern storage means for storing as a coefficient and a selection means for selecting a coefficient of a specific V / F pattern for the induction motor to be controlled from the V / F pattern storage means are provided. In order to expand, an AC voltage detector that detects fluctuations in the AC power supply and load detection means that indirectly or directly detect load fluctuations in the induction motor are provided. It is provided with a V / F pattern correcting means for controlling and correcting the V / F pattern by detection value.

[0015]

Operation: If the induction motor to be controlled is decided, V /
The F pattern selection means selects the coefficient k of the V / F pattern corresponding to the induction motor from the V / F pattern storage means. The voltage vector calculation means calculates a voltage vector according to the operating frequency of the induction motor based on the selected coefficient k, thereby determining the switching pattern of the switching element of the inverse converter and outputting the output voltage.
Further, fluctuations of the AC power supply during operation are detected by an AC voltage detector, and the V / F pattern correction means reduces the voltage vector amount to decrease the output voltage when the AC voltage decreases, and when the AC voltage increases. The output voltage is increased by increasing the amount of the voltage vector, and the V / F is controlled to be constant.

The load detecting means detects the load fluctuation during operation, and similarly the V / F pattern correcting means calculates a voltage vector amount corresponding to the fluctuation amount for the induction motor, and V / F becomes Control so that it becomes constant.

[0017]

Embodiments of the present invention will be described in detail with reference to the drawings.

First, according to the specifications of the induction motor, a voltage vector is calculated from the operating frequency at that time so as to obtain an efficient and optimum output voltage, and a magnetic flux control type pulse that determines the switching time of the switching element of the inverse conversion section is calculated. The width modulation control method (hereinafter, abbreviated as magnetic flux control method) is
A method applied to the operation control of the constant F induction motor will be described.

Generally, when a rotating magnetic field is generated in the induction motor, the rotor rotates at the angular velocity of the rotating magnetic field. In the magnetic flux control method, the fact that the magnetic flux vector that forms this rotating magnetic field is expressed by the time integration of the voltage vector is used to select the voltage pattern so that the trajectory of the magnetic flux vector of the output of the inverse conversion unit becomes a circle. This is a method, and the relationship between the magnetic flux vector Φ and the voltage vector V is expressed by equation (1).

DΦ (t) / dt = V (t) ... (1) When this is expressed by a differential expression using the sample period TS, it becomes an expression (2).

Φ (n) −Φ (n−1) = ΔΦ (n) = TS · V (n) (2) Further, for the phase angle θ and the angular velocity ω, F is the operating frequency. Then, there is a relation of Expression (3).

Δθ (n) = ω · TS = 2πf · TS (3) FIG. 4 shows the relationship between the state of each phase u, v, w of the three-phase inverter device and the voltage vector V. . The possible states of u, v, and w of the three-phase inverter device are (011) (01
0) (110) (100) (101) (001) (00
0) (111), and the voltage vector in each state can be represented by six space vectors v1 to v6 divided by 60 ° intervals and two zero vectors v0 and v7. By combining these eight types of switching modes, that is, eight voltage vectors, it is possible to generate an arbitrary magnetic flux vector, that is, a rotating magnetic field in the induction motor.

The magnitude of the magnetic flux vector Φ is the voltage vector V
Adjust with zero vector of. At this time, the magnetic flux vector Φ is represented by the two voltage vectors vi and vj and the zero vector vz determined in each region and is expressed by the equation (4).

ΔΦ (n) = viTi + vjTj + vzTz (where TS =
Ti + Tj + Tz) (4) Here, for the zero vector vz, one of v0 and v7 in each region is selected so as to reduce the number of switching times.

As shown in FIG. 5, for example, the magnetic flux vector Φ in the case of the region 0 is combined with the voltage vectors v1, v2 and v7. The zero vector v7 determines the magnitude of the voltage vectors v1 and v2.

The switching patterns of the u, v, and w phases at this time are as shown in FIG. 6, and when the horizontal axis is the time axis, v1
Is Ti, v2 is Tj, and v7 is Tz.

The magnitude of this voltage vector is related to the output voltage V of the inverse converter, and is output by the number of voltage vectors during one rotation of the rotating magnetic field and the sampling period Ts which is the time until the next vector is output. The frequency F is determined.

As described above, the switching pattern of the switching element can be controlled by calculating the magnetic flux vector without storing the data strings of all the switching patterns in the ROM, and the output voltage V and the output frequency F can be arbitrarily set. Can be set to.

According to the present invention, the voltage vector calculating means for calculating and outputting the voltage vector as described above and the V / F for storing the plurality of V / F patterns according to the specifications of the plurality of electric motors by the coefficients approximated by the gradients thereof. A pattern storage means and a V / F pattern selection means capable of selecting the stored V / F pattern according to a specific induction motor used in an air conditioner or the like are provided, and further, V / F constant control is performed. In order to expand the control range, an AC voltage detector that detects fluctuations in the AC power supply voltage and a load detection unit that indirectly or directly detects load fluctuations in the induction motor are provided, and the V / F pattern is detected based on the detected values. V / F pattern correction means for correcting and controlling

Hereinafter, an electric compressor used in an air conditioner or the like will be described as an embodiment of a control device for an induction motor according to the present invention.

FIG. 1 is a block diagram showing a first embodiment of the present invention. In this control device, a rectification unit 2 that rectifies and smoothes an input from an AC power supply 1, and outputs the same, and an inverse conversion unit 4 that converts a DC voltage from the rectification unit 2 into a three-phase AC and outputs the three-phase AC to the electric compressor 3. A control unit 5 for controlling the output voltage and the output frequency of the inverse conversion unit 4; and an indoor control unit 7 for transmitting a control signal such as the rotation speed of the electric compressor to the control unit 5 based on the room temperature and the set temperature. Shown.

The control unit 5 outputs a switching signal for controlling the frequency and voltage of the voltage applied to the electric compressor 3 via the inverse conversion unit 4 from the output terminals S1 to S6, whereby the drive unit 6 outputs the power transistor. The semiconductor switching elements Q1 to Q6 are driven to control the rotation speed of the electric compressor 3 to vary the cooling capacity and the heating capacity of the air conditioner.

The control section 5 is realized by a microcomputer having a ROM, a RAM, etc., and an operating frequency command means 51 for instructing an operating frequency of the electric compressor by a control signal from the indoor side control section 7, A plurality of V / F patterns uniquely determined by various specifications of the electric compressor 3 are stored so that the V / F pattern selection unit 8 can select the V / F pattern according to the electric compressor 3 used. V / F
In addition to the pattern storage means 52, the voltage vector calculation means 53 calculates the required output voltage based on the V / F pattern from the command value of the operating frequency to determine the voltage vector amount. The PWM signal output means 54 determines the switching pattern of the switching element of the inverse converter 4 from the voltage vector amount and outputs it to the drive circuit 6.

Next, the V / F pattern selection unit 8 will be described. It is assumed that the V / F pattern of the specification of a certain electric compressor is approximated to the gradient and V / F = k0. Further, the V / F pattern of another electric compressor is stored in advance in the V / F pattern storage means 52 such that V / F = k1.

When an electric compressor having a V / F coefficient k0 is used, it is selected by the V / F pattern selection unit 8,
This selection method includes a method in which a specific input port of the microcomputer of the control unit 5 is set to "H" or "L" to select a coefficient inside the microcomputer, or a signal of a plurality of input ports is combined and selected. . Further, it is also possible to input the analog voltage directly using the A / D port without selecting and set it by A / D conversion by the microcomputer.

In the control unit 5, when the operating frequency commanding unit 51 gives an instruction of the operating frequency F, the voltage vector calculating unit 53
The selected V / F coefficient k0 is read from the V / F pattern storage means 52 and the equation (5) is calculated to determine the voltage vector amount V0.

V0 = k0 · F (5) When another electric compressor is used and V / F = k1, the equation (6) is similarly calculated to determine the voltage vector amount V1. .

V1 = k1 · F (6) Then, the PWM signal output means calculates the magnitude of the zero vector on the basis of the calculated voltage vector amount, and the value of the voltage vector currently output is calculated. The region of the vector and the phase angle within the region are determined from the angular velocity of the vector determined by the position and the operating frequency F. A switching pattern for driving the switching element of the inverse conversion unit 4 is determined from these data and output to the driving unit 6. Further, for a complicated V / F pattern as shown in FIG. 7, it suffices to store the coefficients approximated to the gradient of the number of inflection points + 1.

With respect to the V / F pattern selection section 8, if the analog voltage value is directly input using the A / D port without selection, or the shift amount of the V / F pattern is input as the analog voltage value. It is also possible to respond to changes in the specifications of electric compressors during mass production.

Next, the second embodiment will be described. FIG. 8 is a block diagram showing a second embodiment, but since the basic configuration is the same as that of the first embodiment of FIG. 1, only different parts will be described, and 9 detects the voltage of a commercial AC power supply. The reference numeral 55 designates an AC voltage detector, and 55 designates a V / F pattern correcting means for shifting the V / F pattern due to the voltage fluctuation of the AC power source.

In general, the voltage E of the AC power supply and the fundamental wave effective voltage V output from the inverse converter have a direct proportional relationship.
If the operating frequency F is the same, the output voltage V increases as the AC voltage E increases. However, conventionally, the V / F pattern was uniquely determined by the electric compressor, so that the fluctuation of the AC voltage E directly affected the output voltage V and the V / F constant relationship was broken. Therefore, the present invention also detects the fluctuation of the AC voltage E by the AC voltage detector 9,
The V pattern is corrected by the F pattern correcting means 55 so as to be corrected and controlled.

When the AC voltage E is the rated voltage E0, it is assumed that the output voltage V is V0 and the V / F coefficient is V0 / F = k0. The relationship between the magnetic flux vector Φ when the output voltage is V0, the voltage vectors v1 and v2, and the zero vector v0 is as shown in FIG. 9A. The switching pattern of each switching element for outputting this voltage vector is as shown in FIG. 9 (b).

If the AC voltage E remains unchanged at E0, the locus of the magnetic flux vector Φ which becomes the rotating magnetic field is the locus of the circle drawn by the broken line shown in FIG. 9A.

Next, when the voltage E of the AC power supply fluctuates, if the AC voltage E is detected by the AC voltage detector 9 as the power supply voltage detection means and becomes high, the output voltage of the inverter is increased in direct proportion. Nari V1 (V1> V
0). Therefore, the V / F value becomes as shown in the equation (7), and the constant V / F relationship is broken.

V1 / F = k1> k0 ... (7) Then, the output voltage V1 of the inverter is set so that k1 = k0.
The V / F pattern correcting means 55 determines the correction amount of the voltage vector based on the stored V / F coefficient k0 and the V / F coefficient k1 from the detected AC voltage. That is, the output voltage V1 may be set to V0, and the calculation is performed according to the equation (8).

V1 × (k0 / k1) = V0 ... (8) The loci of the magnetic flux vector and the voltage vector at this time are
As shown in FIG. 10A, the zero vector increases and the circular locus of the rotating magnetic field also decreases. The switching pattern of the switching element when outputting this voltage vector is PWM
It is determined by the signal output means 54 and becomes as shown in FIG. From this figure, it can be seen that the ON time is reduced as a whole as compared with FIG. 9 (b). Then, the switching pattern determined here is output to the drive unit 6 to drive the switching element of the inverse conversion unit 4.

As described above, the V / F is maintained constant by deciding the switching pattern so that the voltage vector becomes smaller as the AC voltage becomes higher, and lowering the output voltage V, and conversely, if the AC voltage becomes lower. The output voltage is increased by increasing the voltage vector.

Next, as shown in FIG. 11, a current detector 10 as a load detecting means for detecting a current flowing into the inverse converter.
In the third embodiment, the load vector of the inverse converter is indirectly detected and the voltage vector amount is controlled so that the electric compressor 3 can always be operated at a high efficiency point regardless of the size of the load. is there.

Similarly, the discharge pressure detector 11 for detecting the discharge pressure of the electric compressor 3 directly detects the load fluctuation of the electric compressor, and the voltage vector quantity is set so that the electric compressor 3 can be operated at a high efficiency point. It is the fourth embodiment shown in FIG.

In the fifth embodiment, as shown in FIG. 13, a line current detector 12 for detecting the line current flowing into the electric compressor.
Is provided to detect the load fluctuation during one rotation of the rotor of the electric compressor, and to control the voltage vector amount so that the electric compressor 3 can be operated at a high efficiency point.

Up to now, the electric compressor mainly used in the air conditioner has been described as an embodiment, but the present invention is not limited to this, and the present invention is applied to a refrigerator, a washing machine, a vacuum cleaner or the like using an induction motor. The control device of the invention may be used.

[0052]

As is apparent from the above description, the present invention successively calculates the voltage vector amount corresponding to the operating frequency,
Since the switching pattern of the switching element is determined thereby, it is not necessary to have the PWM control signal for determining the output voltage and the output frequency of the inverter device as all the data strings for each of the plurality of frequencies, and the ROM capacity of the control device is reduced. be able to. In addition, V / F patterns corresponding to the specifications of multiple induction motors
By storing a plurality of pattern coefficients and selecting and using the coefficient according to the induction motor to be used, a microcomputer or RO
This has the advantage that M can be shared, and changes in the specifications of the induction motor can be dealt with quickly and easily.

Conventionally, a more discrete control of the operating frequency has been forced due to the limitation of the ROM capacity.
The present invention enables continuous control and improves control characteristics.

Further, according to the correcting means of the present invention, it becomes possible to operate the induction motor with high efficiency in spite of the voltage fluctuation of the AC power supply, the breakdown of the induction motor does not occur, and the semiconductor of the inverse conversion unit etc. The switching element composed of will not burn out.

Further, the induction motor can always be operated with high efficiency even when the load on the electric compressor changes due to factors such as the outside air temperature and the state of refrigerant in the air conditioner, and the discharge pressure of the electric motor increases. Since the output voltage of the inverter can be increased to cope with this, the air conditioner can be continuously operated without stopping the compressor.
Similarly, other induction motor control devices can always be operated with high efficiency by detecting load fluctuations and load torques.

Further, according to the present invention, the effective voltage of the inverse converter can be controlled even with respect to the torque fluctuation during one rotation of the rotor of the induction motor, so that the vibration generated in the electric compressor can be suppressed and the noise can be reduced. It will be possible.

[Brief description of drawings]

FIG. 1 is a block diagram showing a first embodiment of the present invention.

FIG. 2 is F / V showing the relationship between output voltage V and output frequency F.
FIG.

FIG. 3 is a diagram showing a waveform creation method by a sine wave / triangle wave comparison PWM control method.

FIG. 4 is a voltage vector diagram of a magnetic flux control type PWM control system.

FIG. 5 is a vector diagram in a region 0 of the magnetic flux control method.

FIG. 6 is a switching waveform diagram of each phase in region 0 of the magnetic flux control method.

FIG. 7 is a complex V / F pattern diagram.

FIG. 8 is a block diagram showing a second embodiment of the present invention.

FIG. 9 is a vector when the AC voltage is rated and a switching waveform diagram at that time.

FIG. 10 is a vector when the AC voltage is high and a switching waveform diagram at that time.

FIG. 11 is a block diagram showing a third embodiment of the present invention.

FIG. 12 is a block diagram showing a fourth embodiment of the present invention.

FIG. 13 is a block diagram showing a fifth embodiment of the present invention.

[Explanation of symbols]

 2 Rectification unit 4 Inverse conversion unit 5 Control unit 6 Driving unit 8 V / F pattern selection unit 9 AC voltage detector 10 Current detector 11 Discharge pressure detector 12 Line current detector 51 Operating frequency command means 52 V / F pattern storage Means 53 Voltage vector calculation means 54 PWM signal output means 55 V / F pattern correction means

Claims (5)

[Claims] 1. A rectification unit for converting AC power of an AC power supply into DC power, an inverse conversion unit for converting DC power of the rectification unit into AC power to drive an induction motor, and an output voltage and output of the inverse conversion unit. In an induction motor control device equipped with a control unit that controls the frequency, calculate an arbitrary voltage vector that is determined by the combination of the ignition signals of the switching elements of the reverse conversion unit so that the output voltage can be varied even at the same operating frequency. V / F pattern storing means for storing a plurality of V / F patterns, which are ratios of output voltage and output frequency of the inverse conversion unit
An induction motor control device comprising: an F pattern storage means; and a V / F pattern selection means capable of selecting a stored V / F pattern according to the specifications of a specific induction motor. 2. A voltage detector for detecting the voltage of the AC power supply, and V / F pattern correction means for correcting the coefficient of the V / F pattern based on the voltage value detected by the voltage detector. 2. The control device for an induction motor according to claim 1, wherein the V / F pattern correction means corrects the magnitude of the voltage vector to control the output voltage of the inverse converter. 3. A current detector for detecting a direct current flowing from the rectifier to the inverse converter, and a load state of the induction motor based on the current value detected by the current detector, and the current value thereof. Is large, the voltage vector amount is increased, and when the current value is small, the voltage vector amount is reduced to correct the V / F pattern.
The control device for an induction motor according to claim 1, further comprising: a pattern correction unit for controlling an output voltage of the inverse conversion unit. 4. A means for directly detecting the load torque of the induction motor, and based on the detected load torque of the induction motor, when the load torque drops below a set value, the voltage vector amount is reduced to reduce the load vector. The V / F pattern correction means for correcting the V / F pattern by increasing the voltage vector amount when the torque rises above the set value, and controlling the output voltage of the inverse conversion section. Induction motor controller. 5. A line current detector that detects a line current output from the inverse conversion unit and flowing into the induction motor, and a current value obtained from the line current detector based on a current value obtained from the line current detector. By detecting a load change and decreasing the voltage vector amount when the current value decreases, and increasing the voltage vector amount when the current value increases, V
The control device for an induction motor according to claim 1, further comprising: a V / F pattern correction unit that corrects the / F pattern to control the output voltage of the inverse conversion unit.