JPH0642798B2 - Flux control method for induction motor - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a magnetic flux control method for an induction motor using a variable voltage variable frequency (VVVF) inverter, and which region of a region where a magnetic flux vector divides the circumference into equal parts. The position of the bisector for dividing the area of the magnetic flux vector position detecting means for detecting whether the current vector exists in the area is variable, and the tangential component (torque component) and the normal component (magnetization or demagnetization) of the voltage vector in each region are set. By controlling the magnitude of the (component), it is possible to reduce the distortion of the Lissajous's flux vector when the induction motor is operating at low speed and light load.

As a result, the distortion of the current waveform is also reduced, and the control of the induction motor can be expected to improve the characteristics at low speeds and light loads.

[Conventional technology]

The basic operation of the magnetic flux control method for an induction motor according to the present invention is described in a paper entitled "New High-Speed Torque Control Method for Induction Motor Based on Instantaneous Slip Frequency Control" on page 9 of Vol. ing.

In this paper, the motor input voltage is detected and integrated in the control circuit to obtain the motor magnetic flux. That is,
This is a so-called magnetic flux calculation type control method, and selects an inverter output voltage that follows a magnetic flux command given the length of the magnetic flux vector and draws a circular locus.

Further, the motor generated torque is calculated as a vector product of the magnetic flux and the motor input current, and the inverter output voltage whose magnitude follows the given torque command is selected. The control is performed so that the instantaneous values of the magnetic flux and the torque are kept within a predetermined error, and the inverter output voltage is updated at high speed every moment.

FIG. 7 is a block diagram of a torque control system that employs the output voltage detection method of the PWM inverter proposed by the present applicant in Japanese Patent Application No. 61-99228 in the control method described in the above paper. Electric power is supplied from the voltage source 1 to the three-phase induction motor 6 via the three-phase PWM inverter 3 via the positive bus 1a and the negative bus 1b. The control circuit 7 processes the command and the detected current and voltage signals, and generates an energization signal for the switching element of the PWM inverter 3.

The PWM inverter 3 is composed of six arms each having a transistor and a diode connected in anti-parallel, but can be represented as three changeover switches Su, Sv, Sw as shown in the figure.

From each output terminal of the PWM inverter 3, current detectors 5u, 5v,
Power is supplied to the three-phase induction motor via 5w, and the voltage detector 2 is connected between the positive and negative buses on the DC side. Each phase current and each phase voltage can be detected from these detectors and switch state variables described later. There is.

The primary terminal voltage and current of the three-phase squirrel cage induction motor And the secondary current is Then, the voltage equation is However, the symbol Is a vector display of the amount converted on the straight axis, the horizontal axis, that is, the d and q2 axes. Let v _{1d be the} d-axis component and v _{1q be the} q-axis component Indicated by Is similarly defined. In the left side of the equation, both d and q axis components are 0, and in the case of the squirrel cage rotor, the secondary voltage is as follows.

The constant in the formula is R ₁ ; primary winding resistance L ₁₁ ; primary inductance R ₂ ; secondary winding resistance L _22, secondary inductance M; mutual inductance m is rotational angular velocity, p is differential operator, j is vector Represents the product.

On the other hand, as the definition of magnetic flux, the primary magnetic flux Is Expand the first line of the expression Substituting expressions and rearranging If you integrate both sides That is, the primary magnetic flux of the electric motor is obtained by the integral calculation of the equation.

The changeover switches S _u , S _v , and S _w may fall to the positive bus line 1a side or to the negative bus line 1b side, and do not take intermediate positions. When the former is the state 1 and the latter is the state 0, the output states of the inverter can all be represented by the switch state variable table shown below.

Here, k is a number indicating the state of the changeover switch, and there are only eight of these. Also, ▲ ▼ and ▲ ▼ are d and q
With the switch state variables expressed by two axis components, the actual d and q axis voltages v _1d and v _1q are the same as the voltage V of the DC voltage source 1. Multiply by Can be expressed as

The switch state variable table is shown in FIG.
The parentheses next to v ₁ indicate the states of the changeover switches S _u , S _v , and S _w , and represent the voltage vector that steps in 60 ° clockwise steps as k increases.

Note that k = 0 and k = 7 are called zero vectors and coincide with the origin in the figure. k = 0 and k = 7 are the output of the inverter, respectively, and the changeover switches _Su and S in FIG.
_v, or S _w collapses all positive line 1a side, or of differences fall into negative bus 1b side, but which also zero either the line voltage of the induction motor 6 is a three-phase short circuit mode. Also, u,
The reference axes of the v and w phases are respectively k
= 1, k = 3, k = 5.

The instantaneous torque T is the primary magnetic flux of the formula And primary current It is calculated by the formula as the vector product of.

Here, φ _1d , φ _1q and i _1d , i _1q are the primary magnetic flux, respectively. And primary current Is each component when is decomposed into d and q2 axes.

Block 701 and 703b are changeover switch S _u, and a S _v, the voltage V of the DC voltage source that is detected in the state of S _w and the voltage detector 2 1
This is a block for calculating the next terminal voltage _v1, and is calculated from the switch state variable table and the formula.

Block 702 is 3 detected by current detectors 5 _u , 5 _v , 5 _w
This is a block for converting the phase currents i _u , i _v , and i _w into the d and q biaxial components by the following equation.

This primary current Is multiplied by the primary winding resistance R ₁ in block 703a, and the product of the primary winding resistance R ₁ and the primary current i ₁ is subtracted from the primary terminal voltage v ₁ in block 704.

The block 705 is a block for integrating the magnetic flux according to the formula D and q biaxial components φ _1d and φ _1q of
At 710, the magnetic flux vector length φ ₁ is calculated by the following equation.

Further, in block 710, as shown in the magnetic flux state diagram of FIG. The clockwise rotation angle θ with respect to the d axis of the vector is 30 °, 90 °, 150 °, 210 °, 270 °, 330 ° as the boundary line.
The control flag fθ is generated as follows depending on which region is divided at every 60 °.

-30 ° ≦ θ <30 °; fθ = I 30 ° ≦ θ <90 °; fθ = II 90 ° ≦ θ <150 °; fθ = III 150 ° ≦ θ <210 °; fθ = IV 210 ° ≦ θ < 270 °; fθ = V 270 ° ≦ θ <330 °; fθ = VI FIG. 10 is a state control diagram of the hysteresis comparator.
The magnetic flux vector length φ ₁ is used for the magnetic flux command value ▲ φ ^* ₁ ▼ by using the error limit Δφ. A control flag fφ for controlling so that That is, the magnetic flux vector length φ ₁ increases and is the upper limit. Control flag fφ = 0 is generated when the magnetic flux vector reaches φ, and the magnetic flux vector length φ ₁ decreases to the lower limit. Control flag fφ = 1 for instructing the magnetization is generated.

Thus, the magnetic flux vector length φ ₁ is controlled so as to draw a limit cycle in the direction of the arrow shown in FIG. 10, but in reality, the magnetic flux vector length φ ₁ calculated by the equation in block 706. Is subtracted from the magnetic flux command value ▲ φ ^* ₁ ▼ in block 708, and control flag fφ = 1, in block 711 according to the state control diagram of FIG.
Generates 0.

The limit cycle of the magnetic flux shown in FIG. 10 is the primary magnetic flux with respect to FIG. This corresponds to the fact that the head of the vector is controlled to always exist in the illustrated torus part.

The control flag fφ according to FIG. 10 and the control flag fθ described with reference to FIG. 9 are combined, and for example, fφ = 1, fθ =
If the I control flag is set, the area is −30 ° ≦
Since it means the magnetization mode at θ <30 °, the primary magnetic flux Primary voltage to be integrated into vector The vector has an outward component of a circle, and it is possible that only k = 1, 2, or 6 is selected from FIG.

Block 707 is a block for calculating the instantaneous torque T computed the vector product between the output of the block 702, 705 by the equation, by subtracting the instantaneous torque T from the torque command T ^* at block 709, determined by the torque command T ^* and the formula In order to suppress the difference from the instantaneous torque T within a predetermined error limit, a control flag fτ is generated in block 712 according to the state control diagram of FIG.

FIG. 11 is a state control diagram of the three-value hysteresis comparator, in which the torque deviation T ^* -T is the upper limit value ΔT ₁ when the motor is running.
When (ΔT ₁ > 0) is reached, the acceleration mode control flag f
Generate τ = 1. When the electric motor is accelerated and the torque deviation reaches the lower limit value −ΔT ₂ (ΔT ₂ > 0), a zero vector mode control flag fτ = 0 is generated, the torque is gradually decreased, and the deviation is increased again, and the upper limit value ΔT ₁ When it reaches, the mode shifts to the acceleration mode, and a limit cycle in which the hysteresis loop in the upper half of FIG.

If this is expressed in the time domain, the instantaneous torque T fluctuates as shown in the torque waveform diagram of FIG. 12, and the instantaneous torque T reciprocates within the band of the upper / lower deviation amount ΔT ₁ + ΔT ₂ across the torque command T ^* .

Next, when the electric motor is performing regenerative braking, a hysteresis loop in the lower half of FIG. 11 is drawn, and when the torque deviation reaches the negative lower limit value ΔT ₁ (ΔT ₁ > 0), the deceleration mode A control flag fτ = -1 is generated. After that, the limit cycle in the direction of the arrow is repeated at the same time as the power line. Thus, block 712 outputs the control flag fτ = 1, 0, −1.

A block 713 is a block for determining the most suitable inverter output voltage for each combination of the three control flags fθ, fφ, fτ output from the blocks 710, 711, 712, and the primary magnetic flux described in FIG. Of the vector length and rotation direction of these three control flags f
θ, fφ, fτ are controlled.

For example, when the control flags fφ = 1 and fθ = I as described above, the voltage vector is set according to k in the switch state variable table. If k = 1, 2, or 6 may be selected as the voltage vector, if the control flag fτ = 1 at this time, a vector k having a component that rotates in the clockwise direction is used. = 2, that is, the output voltage vector Is selected. If fτ = -1, When fτ = 0, it is a zero vector, Or Is selected.

The following switching table shows three control flags f
The value of the number k of the output voltage vector is shown for all combinations of φ, fθ, and fτ, and by referring to this switching table in block 713 for each operation cycle, the switching signal is sent to the inverter 3 and the magnetic flux And instantaneous control of torque is performed.

The inverter frequency is the primary magnetic flux in Fig. 9. It can be considered as the rotational speed of the vector, but this is not given from the outside but occurs as a result of integrating the voltage vector by the formula.

[Problems to be solved by the invention]

In the above technique, the torque control system has priority over the magnetic flux control system. This means that, for example, the control flag fφ =
When 1 is generated and the torque hysteresis comparator generates the control flag fτ = 0 in the zero vector mode, fφ = 1 and fτ = 0 in the switching table.
From k to 0 or 7 output voltage vectors are selected.

This allows Is output, and the control flag fφ = 1 that commands the magnetic flux hysteresis comparator to be magnetized is ignored,
It is known that the demand for magnetization is not satisfied.

In particular, when the induction motor has a low speed and a light load, and the torque hysteresis comparator frequently generates the zero vector mode control flag fτ = 0, the magnetic flux command is overridden by the torque control flag and the magnetic flux is completely ignored. As a result, the magnetic flux vector length φ ₁ is contracted, and the Lissajous waveform of the magnetic flux vector is distorted as shown in FIG. The primary magnetic flux is generated by the output voltage of the zero vector output by the torque control flag fτ = 0. Since the rotation of the vector is stopped and is attenuated toward the origin, if the magnetization is insufficient, a hexagonal side has a Lissajous waveform inwardly recessed.

When the Lissajous waveform of the magnetic flux vector is distorted in this way, the current waveform is also distorted, and the magnetizing current component increases to compensate for the shortage of the magnetic flux, and eventually the primary current of the induction motor. Increases and is not preferable for control.

That is, the conventional method described with reference to FIG. 7 has the drawback that the distortion of the magnetic flux and the current becomes large at the time of low speed operation, which makes the low speed operation of the induction motor difficult.

[Means for solving problems]

The present invention provides a magnetic flux control method for mitigating the adverse effect that the magnetic flux command is ignored and only the torque command is respected because the torque control system has priority over the magnetic flux control system as described above. .

As described in the magnetic flux state diagram of FIG. 9, the primary magnetic flux The position of the equidistant line for region division to detect in which region the vector exists in the region that divides the circumference equally,
Conventionally, the rotation angle θ in the clockwise direction with reference to the d axis is 30 °, 90
Partitions were made every 60 ° of °, 150 °, 210 °, 270 °, and 330 °.

Consider a new region in which the position of the bisector for this region division is shifted by α ° in the forward direction of the rotation angle θ. As shown in FIG. 9, the conventional switching table shows the primary magnetic flux when the shift angle α ° = 0. The position where the vector exists is divided into regions I, II, III, IV, V, and VI, and the voltage vector ▲ ▼ (k) having the largest tangential component, that is, the torque component in that region is selected.

In the region of the new bisectors shifted by α ° in the forward direction of the rotation angle θ, the primary magnetic flux The control flag fθ is generated as follows depending on which region the vector belongs to.

−30 ° + α ≦ θ <30 ° + α; fθ = I 30 ° + α ≦ θ <90 ° + α; fθ = II 90 ° + α ≦ θ <150 ° + α; fθ = III 150 ° + α ≦ θ <210 ° + α; fθ = IV 210 ° + α ≦ θ <270 ° + α; fθ = V 270 ° + α ≦ θ <330 ° + α; fθ = VI It is possible to increase the normal component, that is, the magnetizing component.

FIG. 1 (a) is a vector diagram when the position of the bisector for area division is shifted by α ° in the forward direction, and FIG. 1 (b)
Is the voltage vector shown in Fig. 8 for easier understanding. It is a deep-fried version of the figure.

A new dashed line is shown by a chain line at a position shifted by α ° in the forward direction from the position of the conventional dashed line shown by the broken line.

Now, as shown in FIG. 1 (a), for example, the primary magnetic flux Considering a case where the position of the vector is larger than 330 ° and smaller than 330 ° + α, the control flag fθ = I is output in the case of the conventional area division shown by the broken line, whereas the new area shown by the one-dot chain line is output. Control flag f in case of division
θ = VI is output.

Accordingly, when the control flag fφ = 1 and the acceleration mode control flag fτ = 1 for instructing the magnetization increase are generated, according to the switching table, in the case of the conventional area division, the voltage vector Was generated, but if a new domain division shifted by α ° is used, the voltage vector Will occur.

That is, by adopting a new area division shifted by α °, the tangential component, that is, the torque component is reduced, and the normal component, that is, the magnetizing component is increased. As can be seen from the above description, the position of the bisector for dividing the region for selecting the control flag fθ is shifted by α ° in the forward direction, and the shift angle α
Is variable in the range 0 ≦ α <60 °, Each component of the torque and magnetic flux of can be made variable.

[Action]

Let L ₁ , L ₂ and L ₃ be the _three equal dividing lines for dividing the region for selecting the control flag fθ. FIG. 2 is a diagram of bisectors for dividing a region. Fθ = VI, fθ = I and fθ = III
And fθ = IV are bounded by L ₁ , fθ = I and fθ = II and fθ = IV and fθ = V are bounded by L ₂ , fθ = II and fθ =
Let L _{3 be} the boundary line between III and fθ = V and fθ = VI, and the gradients of the straight lines L ₁ , L ₂ and L ₃ with respect to the d-axis to m ₁ and m, respectively.
₂ and m ₃ .

When the straight line representing the d-axis is Ld, the straight lines L ₁ , L ₂ and L ₃ are respectively expressed as follows.

L ₁ = m ₁ Ld L ₂ = m ₂ Ld L ₃ = m ₃ Ld where the gradients m ₁ , m ₂ and m ₃ are m ₁ = −tan (−30 ° + α) m ₂ = −tan (+ 30 ° + α ) M ₃ = −tan (−90 ° + α). Therefore, if the shift angle α is specified, the three equal dividing lines for area division can be determined.

If the magnitude of the shift angle α is given as a function of the rate of change of the phase of the magnetic flux vector and the torque command T ^* , then 1
Secondary magnetic flux It may be controlled by the rotation frequency of the vector, that is, both the drive frequency and the torque of the inverter. For example, the shift angle α, the phase change rate of the magnetic flux vector, and the torque command T ^*
Let α = f (, T ^* ) be the relational expression with, and set α to 0 when T ^* exceeds a predetermined value. Primary magnetic flux If the phase change rate of the vector is a low speed that falls below a predetermined value, α → large is set, and if the absolute value of the torque command T ^{* is} a low torque command that falls below a predetermined value, α → large.

As described above, by shifting the three equal dividing lines for dividing the region by the required angle α, the voltage vector The torque component of is decreased and the magnetized component is increased.

FIG. 3 is a vector diagram for explaining the torque component and the magnetizing component of the voltage vector. For example, control flag fθ = I
Primary magnetic flux that generates Conventionally, the area of the vector angle θ is -30 ° ≤ θ <30 °, but if the bisectors for region division are each shifted forward by α °, then -30 ° + α ≤ θ <30. ° + α
Becomes

Now, when the control flag fφ = 1 and the acceleration mode control flag fτ = 1 for instructing the magnetization increase are generated, the voltage vector in the above region , The ratio of the torque component v _T (tangential component) between them becomes cos (α) to cos (60 ° + α), which decreases in the range of 0 <α <60 ° compared to the conventional one, but the increasing component vφ The ratio of (normal component) is sin (α) to sin (60 ° + α), and increases from the conventional value in the range of 0 <α <60 °.

The above description has been made only for the area where the control flag fθ = I is generated, but for any other area, 0 is set.
By shifting the bisector for area division in the range of <α <60 ° in the forward direction by α °, the voltage vector It is possible to reduce the torque component of and increase the magnetizing component.

〔Example〕

The angle α for shifting the bisector for discriminating the control flag fθ, the phase change rate of the magnetic flux vector, and the torque command T
^* The relationship α = f (, T ^*) as it is believed that various ones, illustrating an embodiment below.

The shift angle α is a function of the rate of change of the magnetic flux vector, k
It is defined by the following equation by ₁ and k ₂ which is a function of the torque command T ^* .

α = 30k ₁ k ₂ Figure 4 is a graph showing the relationship between k ₁ and, k ₁ in the range of 0 ≦ k ₁ ≦ 1 by the rate of change of the magnetic flux vector is changed. Here, ₁ is about 1/10 of the rated speed. That is, k ₁ is an evaluation coefficient of speed, and at low speeds, the shift angle α approaches 1 and a large value is obtained, and when the rate of change of the magnetic flux vector becomes about 1/10 or more of the rated speed, the shift angle α is increased. Becomes 0.

FIG. 5 is a graph showing the relationship between the T ^* and k _2, in the range of 0 ≦ k ₂ ≦ 1 by the torque command T ^* size k ₂ is changed. Here, ▲ T ^* ₁ ▼ is about 1/10 of the rated torque.
That is, k ₂ is an evaluation coefficient of the torque command, and when the torque command is small, it approaches 1 and the shift angle α can take a large value, and when the torque becomes about 1/10 or more of the rated torque, k ₂ becomes The shift angle α becomes 0 and the shift angle α becomes 0.

By the evaluation function α = 30k ₁ k ₂ using such functions k ₁ and k ₂ , the magnetic flux and the torque are correctly evaluated and controlled in the entire operating range, and the induction motor control at low speed, which has been a problem in the past, is controlled. It is possible to greatly reduce the difficulty.

FIG. 6 is a block diagram of a control device based on this evaluation function.
The portion shown by the bold line in FIG. 6 may be added to the control circuit 7 shown in the block diagram of FIG.

Block 800 is the primary magnetic flux output from block 705 Receiving the d and q biaxial components φ _1d and φ _1q of It is a block that calculates the rate of change of the phase of the vector,
The block 801 which receives the output calculates the function k ₁ from the graph shown in FIG.

The torque command T ^* sent to the block 709 is also blocked at the same time.
Also sent to 802, block 802 calculates the function k ₂ from the graph shown in FIG. The functions k ₁ and k ₂ are sent to the block 803, and the evaluation function α = 30k ₁ k ₂ is calculated and sent to the block 804.

In block 804, α as an evaluation function is used as a shift angle, and 3 for area division for selecting the control flag fθ.
The gradients m ₁ , m ₂ , m ₃ of the book bisectors L ₁ , L ₂ , L ₃ are calculated from the function table of tan and sent to block 710. Block 710
Then, the control flags fθ = I, II, II, IV, V and VI are transmitted according to the areas divided into these three straight lines.

〔The invention's effect〕

The instantaneous values of magnetic flux and torque are calculated from the voltage and current signals of the induction motor, and the magnetic flux and torque are adjusted to follow the command values within a predetermined tolerance, so that the magnetization, demagnetization and power running,
In an induction motor control system using an inverter that selects a 6-step voltage vector that causes elliptical and regenerative conditions, by shifting the existence region of the primary magnetic flux vector for selecting this voltage vector, The ratio of the torque component and the magnetic flux component can be made variable.

Conventionally, since torque is not required at low speed and light load, the magnetic flux is attenuated by preferentially selecting the zero vector,
The trajectory of the magnetic flux vector is distorted and becomes a problem in control,
In particular, it was said that control was difficult at extremely low speeds.

By shifting the primary magnetic flux vector area determination angle by the magnetic flux control method for an induction motor according to the present invention, the distortion of the magnetic flux locus at low speed is reduced and asymptotically approximates to a perfect circle, and the distortion of the current waveform is also reduced. The efficiency of the electric motor is also improved.

[Brief description of drawings]

Fig. 1 (a) is a vector diagram when the position of the bisector for area division is shifted by α ° in the forward direction, and Fig. 1 (b) is the voltage vector. Fig. 2, Fig. 2 is a diagram of bisectors for area division, Fig. 3 is a vector diagram for explaining the torque component and the magnetization component of the voltage vector, and Fig. 4 is the magnetic flux of the function k ₁ . FIG. 5 is a graph showing the relationship with the change rate of the vector, FIG. 5 is a graph showing the relationship with the torque command T ^* of the function k ₂ , FIG. 6 is a block diagram of the control device according to the present invention, and FIG. Block diagram of torque control system, Fig. 8 is voltage vector diagram based on switch state variable table, Fig. 9 is magnetic flux state diagram, Fig. 10 is state control diagram of magnetic flux hysteresis comparator, and Fig. 11 is three-value torque hysteresis. State control diagram of comparator,
FIG. 12 is a torque waveform diagram, and FIG. 13 is a Lissajous waveform diagram of the magnetic flux vector. 1 ... DC voltage source, 2 ... voltage detector, 3 ... PWM inverter, 5 _u , 5 _v , 5 _w ... current detector, 6 ... induction motor, 7 ... control circuit.

Claims (2)

[Claims] 1. An instantaneous value of magnetic flux and torque is calculated from a voltage and current signal, and a magnetizing and demagnetizing signal is generated so that the length of the calculated magnetic flux vector follows a magnetic flux command given within a predetermined tolerance. The plane is divided into six regions by the first comparison means for generating the above and three division lines whose angles with the six output voltage vectors determined by the switching state of the inverter are all (π / 6). A magnetic flux vector position detecting means for detecting where the magnetic flux vector exists in these six areas, and a torque increase / decrease signal so that the instantaneous value of the torque follows a given torque command within a predetermined tolerance. Switching which includes a second comparing means for generating and optimizes a predetermined evaluation function prepared in advance from a combination of the output results of the first and second comparing means and the magnetic flux position detecting means. In a control method of performing a circular approximation control of a rotating magnetic flux by a variable voltage variable frequency inverter that executes a turn, a signal for variably controlling the positions of the three area dividing lines for detecting the magnetic flux vector position is a velocity feedback signal or As a function of the magnetic flux vector phase angle change rate signal,
The induction function is characterized in that the function is set so that the position angle of the region dividing line is limited to 30 ° and the signal is shifted in the rotational direction according to the decrease in the signal when the electric motor is operating at a low speed smaller than a predetermined value. Magnetic flux control method for electric motors. 2. A signal for variably controlling the position of the area dividing line of the magnetic flux vector position detecting means is a velocity feedback signal or a magnetic flux vector phase angle change rate signal and a torque command signal.
When the speed feedback signal or the magnetic flux vector phase angle change rate signal is lower than a predetermined value and the torque command value is smaller than the predetermined value as a variable function, the position angle of the area dividing line is limited to 30 °. The magnetic flux control method for an induction motor according to claim (1), wherein the function is set so as to shift in the rotational direction in response to a decrease in the magnetic flux phase change rate and a decrease in the torque command.