JPH02184285A - Limiting system of output voltage of instantaneous space vector controlling inverter - Google Patents

Abstract

PURPOSE:To limit an output voltage by a method wherein a flux commanding value is changed to a value whereat the counter electromotive force of an induction motor in that rotating speed becomes lower than the DC voltage of an inverter when a value, obtained by multiplying a predetermined flux commanding value by the rotating speed of the induction motor, is larger than another value, obtained by multiplying the DC voltage of the inverter by a given constant. CONSTITUTION:A multiplier 811 of a deciding part 81 multiplies the rotating speed Nm of an induction motor by a set flux commanding value phiSET* and the products are sent to an operator 812. The DC voltage E of an inverter is also inputted into the operator 812 and when the product of the rotating speed Nm by a set flux com manding value phiSET* is larger, '1' is outputted to a signal generating unit 82 but when the product is smaller, '0' is outputted to the signal generating unit 82. When a signal sent from the deciding part 81 is '0', an operating circuit 822 outputs '0' but, on the contrary, when it is '1', the operating circuit 822 operates a flux command ing value phi* and outputs it to an OR circuit 823. The input of either one of both input terminals of the OR circuit 823 is '0' at all times and the other input is outputted to a control circuit 7.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to voltage limitation in the instantaneous torque and primary flux control system of a three-phase induction motor using a variable voltage variable frequency inverter under instantaneous space vector control.

According to the present invention, it is possible to improve the control failure caused by the saturation of the output voltage when the power supply voltage drops, which has been a drawback in the past.

(Prior art) The basic operation of driving an induction motor by the instantaneous space vector control inverter according to the present invention is described in "Instantaneous The basic principle is that the primary current i+ and the primary magnetic flux φ of the induction motor are expressed as space vectors, and the vector product of the vectors is Calculate the instantaneous generated torque, select a pre-tabled inverter switching pattern according to the deviation between this and the torque command T9, and the deviation between the primary magnetic flux vector length φ1 and the magnetic flux command value φ1', and select the inverter switching pattern. The output voltage of the magnet is updated every moment to instantaneously control the instantaneous torque and primary magnetic flux.

FIG. 2 is a block diagram of an example to which the control method described in the paper is applied. The inverter 3 is composed of six arms each having a switching element such as a transistor and a diode connected in antiparallel, but is simplified in the figure by three changeover switches 5urSv, S, .

The three-phase voltage type inverter 3 is supplied with power from the DC voltage source 1 via the positive bus 1a and the negative bus 1b, and the control circuit 7 controls each changeover switch Su of the inverter 3.

The AC voltage converted by Sv, S being pushed to the positive and negative bus bars 1b, lb side is detected by the current detector 5ul 5v.
Power is supplied to each phase terminal u, v, and w of the three-phase dielectric motor 6 through +5 lines. The voltage of the DC voltage source 1 is detected by a voltage detector 2 inserted between the positive and negative buses.

In this control method, electromagnetic force is handled as an instantaneous vector expressed by two orthogonal d-q axes. That is 12=i2d
+ j jzQ φ1 = φId + jφ1q. Here, j represents a vector product.

From iv and iw, the primary voltage V and primary current i can be calculated using the following equations.

If the primary voltage is V, the current is primary current i, and the current induced on the rotor side of the motor is secondary current 12 + the primary magnetic flux on the stator side is φ, then V, = V, d j V, q L = ild + J 1 +Q where R+: Primary winding resistance LII: Primary inductance R2: Secondary winding resistance LB: Secondary inductance M: Mutual inductance, θ is each rotation speed , p represents a differential operator.

By definition, the primary magnetic flux φ1 is φ electric −L+ r L +Mtz
・・・・・・■L R11+=Pφ1
・Old...■ Integrate both sides and get φ+ = f (V+ R+i+) dt
-=■ That is, the primary magnetic flux φ1 of the induction motor is obtained by the integral calculation of 2〇.

On the other hand, the instantaneous torque T is determined by equation (2) as the vector product of the primary magnetic flux φ1 determined by 20 and the primary current 11.

T=φHX11=φ, dXi, q-φ, qxi, cl
t+t++■Each changeover switch S that makes up the inverter 3
u.

1 represents the case where SV and S each fall toward the positive genera la side.
If the case where it falls to the negative bus side is expressed as 0, there are 8 switch states from the combination of the three changeover switches S, , Sv, S, but the output voltage of the inverter 3 in these switch states is When the vector vl is calculated from equation (2), it is as shown in the following voltage vector table. However, the actual value of vldvIq is based on the value in the table, Q0000, and voltage detector 2.
This is the value multiplied by the voltage E of the DC voltage source 1 detected in .

Voltage vector table As shown in the voltage vector table above, when the switch state number for each combination of switch states is k, the output voltage νI(2) of the inverter 3 in each switch state is calculated as shown in the voltage vector diagram shown in FIG. Blocks 701 and 703b included in the control circuit 7 in FIG. This is a block that calculates V.

A block 702 is a block that calculates the primary current 11 from the three-phase currents iu, iv, i, .

A primary winding is applied to this primary current i1 in block 703a.

Block 705 is a block that performs an integral calculation of the magnetic flux according to 2〇, and both d and q axis components of the primary magnetic flux φ1 are obtained.

In block 710, the clockwise rotation angle θ of the primary magnetic flux φ with respect to the d-axis is 30° as a boundary line.

90°, 150°, 210', 270', 3
30' (7) A control flag fθ is generated as follows depending on which region partitioned by 60 degrees belongs to.

-30@≦θ<306: fθ=1 30″≦θ<908: fθ=2 90@≦θ<150°: fθ=3 150”≦θ<210': fθ=4210'≦θ
<270°: fθ-5 270'≦θ<330°: fθ-6 Block 706 is a block that calculates the magnetic flux vector length φ using the following equation.

φ+ = $+d" +$+ma...
. . . In block 708, the magnetic flux vector length φ is subtracted from the magnetic flux command value φI' given from the outside to calculate the magnetic flux deviation.

Block 711 is a hysteresis comparator, and when the deviation of the magnetic flux sent from block 708 is positive and exceeds a predetermined value, that is, when it is necessary to increase the magnetic flux, fφ = +1, and when the deviation of the magnetic flux is negative and exceeds a predetermined value. When it is necessary to reduce the magnetic flux, fφ=-
Set to 1.

Block 707 is a block that calculates the instantaneous torque T by calculating the vector product of the re-outputs of blocks 702 and 705 using equation (2).In block 709, the instantaneous torque T is subtracted from the torque command T0 given from the outside, and the torque Calculate the deviation.

Block 712 is a hysteresis comparator for instantaneous torque T, and has the structure of a multiple hysteresis comparator. When the torque deviation is within a predetermined error range, only the inner comparator operates, and when the torque deviation exceeds the predetermined error range, such as when the external torque command T0 changes suddenly, the outer comparator also operates. , when the torque deviation becomes small again, only the inner comparator starts operating. This inner hysteresis comparator controls a control flag f, which selects between the zero vector and other voltage vectors. The outer hysteresis comparator generates a control flag fTI that selects whether the power or regenerative torque should be generated, that is, in which direction the instantaneous slip frequency should be applied. Therefore, the voltage vector is the value of these two control flags f
a. It is selected by the combination of +fTI, and a voltage vector as shown in the following torque control flag table is output.

Torque control flag table block 713 is a block that determines the most suitable inverter output voltage for each combination of control flags fθ, fφ, f□+fT+1 output from blocks 710, 711, and 712, and selects the following voltage vector. From the table, switch state number k shown in the voltage vector table above according to control flag rθ, fφ + f'l'l + f7°
Knowing this, a switching signal is sent to the inverter 3, and instantaneous control of magnetic flux and torque is performed.

As explained above in detail, according to such a magnetic flux calculation type control method, the primary magnetic flux φ1 at each instant is calculated while hardly using the internal constants of the induction motor.
By keeping the magnetic flux vector length φ substantially constant, the Lissajous figure drawn by the magnetic flux vector component φId+φ, q can draw a substantially circular shape, and high-speed torque control can be performed.

(Problems to be Solved by the Invention) Generally, when an induction motor is driven at variable speed by a variable voltage variable frequency inverter, the voltage and frequency are usually in a proportional relationship.

The instantaneous space vector control inverter also attempts to control the magnetic flux command value φ9 by keeping it constant, but if the power supply voltage drops while the induction motor is taking a load near its rated rotation, the inverter output voltage will become saturated. The necessary rotational speed may not be obtained, leading to control malfunctions and accidents resulting therefrom.

Therefore, it is necessary to limit the output voltage of the inverter according to fluctuations in the power supply voltage, but it is simply necessary to limit the rotational speed N of the induction motor.
1 or control based only on the DC voltage of the inverter, that is, the voltage E of the DC voltage source 1, this will have an effect even during normal operation.

The output voltage limiting method of the instantaneous vector control inverter according to the present invention aims to suitably limit the output voltage by changing the magnetic flux command value by the necessary amount only when it is truly necessary.

(Means for Solving the Problems) The output voltage limiting method of the instantaneous vector control inverter according to the present invention provides an instantaneous space for controlling the instantaneous torque and instantaneous primary magnetic flux of a three-phase induction motor to drive the induction motor at variable speed. In a vector control inverter, if the value obtained by multiplying the predetermined magnetic flux command value by the rotational speed of the induction motor is larger than the value obtained by multiplying the DC voltage of the inverter by a constant, the magnetic flux command value is It is characterized in that the electromotive force is changed to a value that is less than or equal to the DC voltage of the inverter.

(Function) In an instantaneous space vector control inverter that controls instantaneous torque and instantaneous primary magnetic flux to drive an induction motor at variable speed, the magnetic flux command value φ9 and the back electromotive force of the induction motor are determined by El and the inverter frequency r. The following relational expression holds true between them.

φ"×f5-kE0f (k is a proportional constant) Since the back electromotive force E0 of the induction motor cannot exceed the DC voltage of the inverter, that is, the voltage E of the DC voltage source 1, φ1×f, ≦kE.

Now, the magnetic flux command values set to keep the ratio of the inverter's output voltage and frequency constant for variable speed drive are φ and E.
? ′, the frequency output frequency f of the inverter and the rotational speed of the dielectric motor are in a proportional relationship, so φ, a′ × N, ≦′ E (k′ is a constant of proportionality)...
It can be expressed as ■.

That is, if the product of the set magnetic flux command value φSET' and the rotation speed N7 of the induction motor exceeds a value obtained by multiplying the voltage E of the DC voltage source 1 by a constant constant, it is necessary to lower the magnetic flux command value.

The magnetic flux command value, rotational speed of the induction motor, and voltage of the DC voltage source at the maximum rated operation are each φSET*N s r
If a f and E r a f, φSET ”X
N,,,,=k'Eraf''...(
m holds true.

Therefore, during actual operation, between the magnetic flux command value φ0, the rotational speed N1 of the induction motor, and the voltage E of the DC voltage source, φ"XN, ≦ 'E......■
In order to hold, it must be from the equation [phase] and ■. When the magnetic flux command value φ1 is given using this equal sign, the induction motor can be operated with the maximum realizable magnetic flux.

The voltage control method of the present invention uses both the DC voltage of the inverter, that is, the voltage E of the DC voltage source 1, and the rotational speed N1 of the induction motor as parameters, so even if the power supply voltage decreases, it can be used at startup or at low speeds. There are no restrictions and there is no effect on driving.

Furthermore, if the power supply voltage is normal even when the rotational speed is around the rated speed, there is no restriction, and the voltage can be restricted only when necessary.

Moreover, since the limit is given by the magnetic flux command value φ9, it can be realized without affecting the vector control loop such as increasing the calculation time.

(Example) Hereinafter, an example of the output voltage limiting method of the instantaneous space vector control inverter of the present invention will be described with reference to the drawings. 1st
The figure is a block diagram of an instantaneous torque and magnetic flux control system of an induction motor using the output voltage control method according to the present invention, and is the same as the block diagram of FIG. 2 except that a magnetic flux limiting section 8 is added.

Conventionally, the control circuit 7 has the previously explained set magnetic flux command value φ, 7.
' was directly input as the magnetic flux command value φ0. In this embodiment, the magnetic flux control unit 8 is connected to the input portion of the control circuit 7 for the magnetic flux command value φ9, and the set magnetic flux command value φ30. . is input to the magnetic flux limiting section 8, processed according to the present invention, converted into a magnetic flux command value φ'', and sent to the post-control circuit 7.

The magnetic flux limiting section 8 is composed of a determination section 81 and a signal generation section 82, and the determination section 81 and the signal generation section 82 each contain set magnetic flux command values φ, T', inverter DC voltage E, and the induction motor. Rotational speed N.

is input. The inverter DC voltage E is the voltage of the DC voltage source 1 detected by the voltage detector 2, but the rotation speed N of the induction motor is determined by a speed sensor connected to the three-phase induction motor 6, as well as by various methods. The detected value may be used.

The determination section 81 is composed of a multiplier 811 and a calculation unit 812. send to The inverter DC voltage E is also input to the arithmetic unit 812, and in order to perform the comparison according to
Compare it with the value sent from 11, and if the product of the rotational speed N of this induction motor and the set magnetic flux command value φ, A1 is larger, output “1”, and if smaller, output “0”. and sends it to the signal generation section 82.

The signal generation section 82 has an inverted input terminal AND circuit 821. The signal sent from the determination section 81 is input to the inverted input terminal of the 0 inverted input terminal AND circuit 821, which is composed of an arithmetic circuit 822 and an OR circuit 823. The set magnetic flux command values φ, * are input to the non-inverting input terminal.

Therefore, this inverting input terminal material AND circuit 821 outputs "0" when the signal sent from the determination section 81 is "1", and conversely, when the signal sent from the determination section 81 is "0", the set magnetic flux command value φ, ? is output and sent to the OR circuit 823.The arithmetic circuit 822 receives the output signal of the determination section 81, the inverter DC voltage E, and the rotational speed N of the induction motor, and the signal sent from the determination section 81 is " 0”, it outputs “0”, and conversely, when it is “1”, it calculates and outputs the magnetic flux command value φ8 according to the equal sign in the formula @, and sends it to the OR circuit 823. The input of one of the input terminals is always 0'', and the input of the other is sent to the control circuit 7 as an output.

That is, the signal generating section 82 determines that the output of the determining section 81 is "
0'', the set magnetic flux command value φ, A'' is used as the magnetic flux command value φ1, and conversely, when it is '1'', the value calculated by 2@ is sent to the control circuit 7 as the magnetic flux command value φ9. As a result, the magnetic flux control unit 8 uses the set magnetic flux command value φ8.' as is when the formula ■ holds true, and uses the value calculated by the formula @ when the formula 2 does not hold as the magnetic flux command value φ. " is sent to the control circuit 7 as ".

In addition, the rated rotational speed of the induction motor in the formula @ is
The ratio between m f and the rated DC voltage E rsf of the inverter may be stored in the arithmetic circuit 822 without being input each time.

In addition, in this embodiment, the magnetic flux command value φ1 is
has been calculated, but it is possible to modify this formula as long as it satisfies a certain calculation style.

(Effects of the Invention) As mentioned above, the voltage limiting method of the present invention does not apply the limitation at startup or at low speeds even if the power supply voltage drops, and when the rotational speed of the induction motor is close to the rated value, that is, the output voltage of the inverter Even if the power supply voltage drops in a region where is close to the input voltage, the output voltage is suppressed in proportion to the input voltage, so the magnetic flux of instantaneous space vector control normally follows a circular locus, and control is performed normally.

Furthermore, since the calculation for this restriction is calculated outside the vector control loop and the target is the magnetic flux command value φ9, it is possible to perform the restriction without prolonging the calculation time of vector control.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of an example of an instantaneous torque and magnetic flux control system of an induction motor using the output voltage control method according to the present invention. Fig. 2 is a block diagram of an example of an instantaneous torque and magnetic flux control system of a conventional induction motor. Figure 3 is an inverter output voltage vector diagram. 1... DC voltage source 1a... Positive bus 1b...
・Negative bus 2... Voltage detector 3... Inverter 5u, 5v, 5-... Current detector 6.
...Three-phase induction motor 7...Control circuit 8...Magnetic flux limiting section 82...Signal generation section 81...Judgment section

Claims (1)

[Claims] In an instantaneous space vector control inverter that controls the instantaneous torque and instantaneous primary magnetic flux of a 1- and 3-phase induction motor to drive the induction motor at variable speed, the rotational speed of the induction motor is adjusted to a predetermined magnetic flux command value. If the value multiplied by Features an output voltage limiting method for instantaneous space vector control inverters.