JPH0832200B2 - Induction motor controller - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to a control device for an induction motor using a PAM inverter.

B. SUMMARY OF THE INVENTION The present invention, the primary voltage e _{l [alpha]} in the alpha-beta coordinate system of the induction motor, although by combining e _{l [beta]} controls the voltage of the converter unit, position of the inverter unit voltage vector voltage e _{l [beta]} modulated in accordance with the phase difference by adjusting the modulation area phase voltage e _{l [beta]} according to the average value ratio of the voltage e _{l [alpha]} with respect to the voltage e _{l [beta],} to suppress the torque pulsation to high slip control, regardless of further operating conditions Instead, it enables stable control.

C. Conventional technology To achieve high-performance slip frequency control for induction motors, PW
M-type inverters and cycloconverters have been used. These converters are designed to obtain the desired AC output by switching the power semiconductor elements, but there is a problem that electromagnetic noise is generated by the switching of the elements. In particular, PWM inverters generate a lot of noise because the voltage contains many high-order harmonics. This problem includes
It can be solved by raising the carrier frequency to several tens of KHz or more that is inaudible to the human ear, but the elements that can be switched at this carrier frequency are limited to those with a small controllable current capacity, Make realization difficult.

From these problems, there is a PAM type inverter as a converter which is advantageous for reducing noise and increasing capacity. In this PAM type inverter, basically the converter controls the voltage,
The voltage source inverter is configured to control the frequency, and the PW
Compared with the M inverter, the higher harmonic current is reduced and the switching frequency of the inverter is also lowered, which is suitable for noise reduction and variable speed of large capacity motors. However, on the other hand, it has a drawback that torque pulsation, especially rotation fluctuation at low speed due to the torque pulsation becomes large.

D. Problems to be Solved by the Invention In the PAM type inverter, the voltage source inverter unit is a control in which six switching elements are bridge-connected and sequentially turned on according to the output frequency. Therefore, as shown in FIG. 2, the vector phase of the output voltage of the inverter unit has six fixed phases V _{1 to} V ₆ on the coordinate system (dq coordinate system) fixed on the primary side of the induction machine. I can only take it. On the other hand, in the high-performance slip frequency control, the output voltage vector of the inverter unit rotates at the output frequency ω ₀ as shown in FIG. 3 to become an ideal three-phase sinusoidal voltage that draws a circular locus. However, in reality, there is a problem that the induction machine causes a sixth-order torque pulsation when the inverter is driven by a voltage vector having a fixed phase. This will be described in detail below.

Rotate the induction motor in synchronization with the primary voltage vector α
The voltage equation represented by the −β axis becomes the following expression (1), and the generated torque T becomes the expression (2).

Here, each symbol is a quantity shown below.

e ₁ ; primary voltage (α, β components) e ₂ ; secondary voltage (α, β components) i ₁ ; primary current (α, β components) λ ₂ ; secondary magnetic flux (α, β components) r ₁ ; primary Resistance r ₂ ; Secondary resistance M; Excitation inductance L ₂ ; Secondary inductance L ₁ ; primary inductance ω ₀ ; power source angular frequency ω _r ; rotor angular frequency i ₂ ; secondary current (α, β components) The above equations (1) and (2) are
As shown in the figure. Here, in the high-performance slip frequency control, for example, as proposed in JP-A-59-165981, in order to match the phase of the magnetic flux with the α axis and the phase of the torque current with the β axis, By giving such conditions, non-interference control is performed to compensate mutual interference due to the magnetic flux current and the torque current.

According to such conditions, λ _2β = 0 and i _2α = 0, and the torque T becomes the following formula (5) from the formula (2), and T = −λ _2α i _2β (5) Secondary current It can be uniquely controlled by the β axis component i _2β of.

However, in the PAM type inverter, as described above, the voltage vector is limited to 6 ways, so (3)
The output voltage that obtains the primary voltages e _1α and e _1β in the formula cannot be an ideal sine wave, and the primary currents i _1α and i _1β fluctuate. The fluctuation of the current i _1β fluctuates as shown in FIG. 5, and the magnetic flux does not change abruptly. Therefore, the torque T expressed by the equation (5) causes torque pulsation as in the case of FIG.

E. Means for Solving Problems The present invention has been made in view of the above problems, and is an α-phase primary current setting value i _1α for setting a magnetic flux component of an induction motor and a β-phase for setting a secondary current component. An induction motor using a PAM inverter that synthesizes primary voltages e _1α and e _1β obtained by non-interference calculation from the primary current setting value i _1β to control the voltage of the converter unit and control the frequency of the inverter unit from the slip frequency of the induction motor. In the control device of
A coefficient calculation circuit for _obtaining a ratio k between the average value of _1α and the voltage e _1β and a region δ that rotates in synchronization with the α-β coordinate system of the induction motor and includes the positive β-axis and keeps the ratio k constant. A circuit to be sought, a voltage vector included in the region δ, a voltage vector generation circuit that uses the selected voltage vector as a reference phase signal of the inverter unit, the selected voltage vector and the α-β coordinates An arithmetic circuit for obtaining a phase difference γ with respect to the β axis of the system; an arithmetic circuit for _obtaining a primary voltage command e ₁ which is modulated according to the phase difference γ so that the primary voltage e _1β becomes substantially constant; And a voltage control circuit that controls the voltage of the converter unit according to the command e ₁ .

F. Action In the induction machine control by the PAM type inverter, the voltage vector is limited to 6 types as described above, and the decoupling voltage e
It is not possible to obtain an inverter voltage that simultaneously satisfies _1α and e _1β . Here, in order to eliminate the torque pulsation from FIG. 5, the current i _1β may be controlled so as not to change.

On the other hand, in the block diagram of FIG. 4, when λ _2β = 0, the block diagram is as shown in FIG. 6. From FIG. 4, in order to control the current i _1β constant, the voltage e _1β can be set to be constant. I understand that it is good. There are a plurality of voltage vectors having the voltage e _1β as a β-phase component, and the simplest example is the seventh
As shown in the figure, 60
Select a phase that exists within °. Here, when the α-β coordinate system rotates counterclockwise with respect to the dq coordinate system, the phase of the voltage vector (V _{1 to} V _{6 in} FIG. 2) of the inverter unit is as shown in FIG. Rotate clockwise with respect to the α-β coordinate system. Now, when attention is paid to the vector V ₁ is located in the region near the β-axis component obtained by projecting the β axis of e ₁ is constant to a constant magnitude of the voltage e ₁ of the β-phase component e _{l [beta]} Like e ₁
You can adjust the size of. Then, when the voltage vector V ₁ tends to deviate from the region, the next voltage vector V ₂ enters the region, and the voltage vector V ₂ may be adjusted to the same constant e _1β . That is, the voltage e ₁ (DC voltage of the converter) is controlled so that the β-phase component of the output voltage becomes constant in the ignition pattern switching cycle of the inverter. This suppresses torque ripple.

In the modulation of the voltage e _{l [beta]} to above, the voltage e _{l [beta]} is a constant in a cycle of each voltage vector, also has an area for switching the voltage vector constant ([delta] = constant). Therefore, the average value of the voltage e _1α fluctuates depending on the magnitude of the voltage e _1β . This is because the voltage e _1β changes depending on the control rotation speed and the load, so that the voltage e _1α changes depending on the rotation speed, the load, and the like.
That is, there is a change in the amount of the magnetic flux, and the desired torque may not be obtained depending on the operating conditions, for example, the magnetic flux becomes small at low speeds and the desired torque cannot be obtained.

Therefore, a phase adjusting means for adjusting a control region phase voltage e _{l [beta]} according to the average value ratio of the voltage e _{l [alpha]} with respect to the voltage e _{l [beta]} in the present invention, the rotational speed, the voltage e _{l [beta]} vary depending on the size of the load The average value ratio of the voltage e _1α is made constant, and the desired magnetic flux is obtained regardless of the operating conditions to obtain stable operation.

The above-mentioned phase adjusting means will be described. In FIG. 7, the average value e _1α (A) of the voltage e _1α is given by the following equation.

When is calculated, it becomes as shown in FIG. Therefore, Was calculated, from this coefficient value k (7) determine the angle δ by an equation by the angle δ between the voltage e _{l [beta]} in the modulation area phase, voltage e _{l [beta]} to the average value e _{l [alpha]} of the voltage _e 1α (A)
Obtain stable control that eliminates the influence of changes in.

G. Embodiment FIG. 1 is a block diagram showing an embodiment of the present invention.
The rectifier 1 and the chopper transistor 2 form a converter circuit main circuit, and the direct current voltage E ₁ is controlled by the conductivity of the transistor 2. The transistor 2 is subjected to feedback control of the output voltage E ₁ with respect to the voltage command e ₁ by the voltage control amplifier 3 and the gate circuit 4. The inverter unit 5 has a transistor bridge connection as a main circuit, obtains a gate pulse of each phase from a reference phase signal from the voltage vector generation circuit 6, obtains a three-phase voltage output of a frequency according to the reference phase, and induces this. It is supplied as the primary voltage of the electric motor 7.

The speed detector 8 detects the rotor angular frequency ω _r of the induction motor 7, and the speed control amplifier 9 obtains the torque current command by PI calculation from the deviation between the speed command ω _n * and the detected value ω _r of the speed detector 8. Obtain the β-phase primary current command i _{1 β} *. The slip frequency calculation circuit 10 can calculate the slip frequency ω _s from the above equation (4).
Then, the adder 11 obtains the power source angular frequency ω _o by adding the rotor angular frequency ω _r and the slip frequency ω _s . The integrating circuit 12 obtains the rotational phase angle θ of the α-β coordinate system by integrating the frequency ω _o .

The coordinate conversion circuit 13 obtains the α-phase primary current i _1α and β-phase primary current i _1β from the primary currents i _a and i _b of the electric motor 7 and the rotation phase angle θ, and the conversion circuit 14 converts the current i _1α to the α-phase secondary magnetic flux. λ _2α
Ask for. The arithmetic circuits 15 and 16 obtain the primary voltage commands e _1β * and e _1α * of the α and β phases according to the above equation (3),
The arithmetic circuit 17 determines the magnitude of the primary voltage.

Here, the calculation by the calculation circuit 17 obtains the primary voltage e ₁ while keeping the β-phase component constant from the phase difference between the output voltage vector of the inverter and the α-β coordinate system. That is, as shown in FIG. 7, the rotation of the alpha-beta coordinate system, given the voltage e _{l [beta]} * a beta axis and the voltage vector V ₁ of the within that region so as to be constant in the hatched area shown against The voltage e ₁ is adjusted by the calculation of e ₁ = e _1β * / cos γ according to the phase difference γ. For this adjustment, the phase difference γ with the voltage vector is calculated by the arithmetic circuit.
18 is obtained by comparing the reference phase signal given to the inverter unit 5 by the voltage vector generation circuit 6 with the phase angle θ of the integration circuit 12. When the voltage vector V ₁ is out of the range, the voltage e ₁ is adjusted by the phase difference γ with the next voltage vector V ₂ .

Here, the angle δ for specifying the area is calculated by the coefficient calculation circuit 19 according to the above equation (8) and the angle k is calculated from the coefficient k by the above equation (7) or It is obtained by calculating the angle δ according to the table data of FIG. The reference phase signal from the voltage vector generation circuit 6 is referred to for the calculation of the angle δ, and synchronization with the voltage vector is performed. Then, the angle conversion circuit 21 _obtains the start point of the modulation region of the voltage e _{1β as} the angle U (see FIG. 7) with respect to the β axis from the angle δ, and sets the modulation region of the voltage e _1β * with respect to the voltage vector. . The γ calculation circuit 18 to which this angle U is given selects the voltage vector that has reached the phase of the starting point angle U and obtains the phase difference γ. Arithmetic circuit
17 determines the primary voltage e ₁ by the constant modulation of the voltage e _1β * in the region of 60 ° from the time when the voltage vector becomes the phase of the starting point angle U.

By adjusting the voltage e _1β * by the arithmetic circuit 17 described above,
The voltage e ₁ (E ₁ ) is the voltage vector V _{1 to} V _{6 as} shown in FIG.
The waveform becomes a waveform modulated with a period (60 °) of which the phase with respect to the voltage vector is changed by the average value ratio of the voltage e _1β and the voltage e _1α . As a result, the current i
It is possible to obtain a stable rotation speed and torque output by suppressing the fluctuation of the average value e _1α (A) regardless of the magnitude of e _1β while suppressing the torque pulsation of the electric motor 7 by making _1β constant.

H. Effects of the Invention As described above, according to the present invention, in the induction motor control device using the PAM inverter, the position of each phase of the voltage vector of the inverter unit and the β-phase voltage of the α-β coordinate system of the induction machine. the voltage e _{l [beta]} modulates the voltage converter section so as to be constant in accordance with the phase difference, the voltage for the voltage e _{l [beta]} e
_Since the modulation area phase of the voltage e _1β is adjusted according to the average value ratio of _1α , the high-performance slip frequency control in which the induction machine is made non-interfering suppresses the torque pulsation while stabilizing the magnetic flux to affect the operating conditions. There is an effect that stable control can be obtained without being performed.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a voltage vector diagram of an inverter, FIG. 3 is a vector diagram of an ideal output voltage of an inverter, and FIG. 4 is an α-β of an induction machine.
An equivalent block diagram in the coordinate system, FIG. 5 is a β-phase current waveform diagram in non-interfering slip frequency control, FIG. 6 is a block diagram when λ _2β = 0 in FIG. 4, and FIG. FIG. 8 is a vector diagram showing the relationship of the α-β coordinate system, FIG. 8 is a characteristic diagram showing the relationship between the coefficient k and the region phase δ in the present invention, and FIG. 9 is a voltage waveform diagram of the converter section in the embodiment. 5 ... Inverter section, 7 ... Induction motor, 9 ... Speed control amplifier, 10 ... Slip operation circuit, 15, 16 ... Operation circuit, 17 ... Operation circuit, 18 ... γ operation circuit, 19 ... Coefficient operation circuit, 20 ... Angle operation Circuit, 21 ... Angle conversion circuit.

Claims (1)

[Claims] 1. A primary voltage e obtained by non-interference calculation from an α-phase primary current setting value i _1α for setting a magnetic flux component of an induction motor and a β-phase primary current setting value i _{1β for} setting a secondary current component.
_In an induction motor controller using a PAM inverter that synthesizes _1α and e _1β to control the voltage of the converter unit and controls the frequency of the inverter unit from the slip frequency of the induction motor, the average value of the voltage e _1α and the voltage A circuit (19) for calculating the ratio k of e _{1β and} a circuit (20) for rotating in synchronization with the α-β coordinate system of the induction motor and for obtaining a region δ that includes the β axis in the positive direction and keeps the ratio k constant. , 21), a voltage vector included in the region δ, and a voltage vector generation circuit (6) that uses the selected voltage vector as a reference phase signal of the inverter unit, the selected voltage vector and the An arithmetic circuit (18) for obtaining a phase difference γ from the β axis of the α-β coordinate system, and a primary voltage command e ₁ which is modulated according to the phase difference γ so that the primary voltage e _1β becomes substantially constant. With arithmetic circuit (17) A voltage control circuit (3, 4) for controlling the voltage of the converter unit according to the primary voltage command e ₁ , and a control device for an induction motor.