JPH0223087A - Control circuit for induction motor - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] This invention relates to a control circuit for an induction motor using a variable voltage variable frequency (vvvy) inverter.

[Conventional technology]

FIG. 3 is a block diagram showing a case in which a conventional variable voltage variable frequency (vvvF) inverter control circuit disclosed in Japanese Patent Publication No. 60-56362 is used to drive an induction motor for full operation of an electric vehicle. In the figure, (1) is a DC power supply, and (2) is a variable voltage variable frequency (hereinafter vv
v: abbreviated as p) inverter, [3] is an induction motor that receives the output of the vvvy inverter (2) and drives the electric vehicle;
(4) is a signal vM proportional to the rotation speed of the induction motor (3)
The finger speed generator that outputs (5) inputs the above-mentioned signal '7M and the external command value vsy for driving the electric car and generates an induction chamber! ! ! The frequency F of the vvvy inverter (2) is adjusted so that the slip frequency 78 of one machine (3) is set to a predetermined value.
The first control element (6) that controls the induction motor (3)
Input a plurality of notch command values for controlling the torque (rotational force) of the motor, and change the magnitude of the output voltage of the vvvyr inverter (2) applied to the induction motor (3) according to this input to the vvvy inverter (2). a second control element that outputs a signal for suppressing the frequency to a constant value when the frequency exceeds a predetermined value, (7) is an output signal of the second control element (6), the above signal VM, and the above external command value vsy and enter the above vv
The output voltage V of the vy inverter (2) is V/'1 according to the frequency 1 region! This is the third control element that controls so that V is constant and V is constant.

A conventional induction motor control circuit is configured as described above, and V
The output voltage V of the V'7F inverter (2) is controlled by the second and third control elements (a) a (7), and has the voltage vs. frequency characteristic as shown in FIG. Become. That is, for example, if the command is 2 notches, the frequency is 0-
Between FO2, voltage V increases in proportion to frequency IFK,
When the frequency is in the range of yg2 or higher, the output voltage is constant and has a magnitude of 702.

On the other hand, the output torque of the induction motor (3) becomes the torque TαIFs X (-) (1) in the range where the slip S is small, so it is affected by the first control element (5) and has a frequency of 9 and the number 1.
8 is controlled to a constant value, the torque versus frequency characteristic of the induction motor (3) becomes the characteristic shown in FIG. 5, corresponding to the voltage versus frequency characteristic shown in FIG. For example, if the command is 2 notches, the torque will be constant To in the frequency range up to FO2, and at higher frequencies, l/I
The torque decreases in proportion to F2.

Furthermore, it is considered that the following relational expression generally holds between the electric current V flowing through the induction motor (3) and the torque T.

? -K-! IM! , z 7 o Ma? ? 7S -K (-) ・? s (2
)? Here ni-ni-K 1? , , K is a constant, and
##3: ,, .

7 Therefore, when v (output voltage of inverter (2))/7 (frequency) is constant, the magnitude of current is proportional to torque T, and when V is constant, the magnitude of frequency 1 is 0 (all υ frequencies? When operating with S constant) From these relationships, the current flowing to the induction motor (3), 1vvvy, the output voltage V of the inverter (2), and its frequency 1 , the relationship in terms of torque is as shown in FIG. FIG. 6 shows a case where the command is two notches. Such torque versus frequency characteristics are the same as those of conventional DC motors for driving electric vehicles.

[Problem to be solved by the invention]

In the conventional induction motor control circuit as described above, when the induction motor (3) is operated at high speed, that is, when the vvvy inverter (2)
In the region where the frequency 7 is large, in order to maintain the output voltage of the vvvy inverter (2) at a constant value lower than the maximum output voltage (-to modulate the output voltage), the vvvy
rThe number of switching of inverter (2) increases,
The problem was that the power switching loss was large.

The present invention was made to solve this problem, and an object of the present invention is to obtain an induction motor control circuit in which the switching loss of the vvvyp inverter is small even when the induction motor is operated at high speed.

[Means to solve the problem]

An induction motor control circuit according to the present invention includes a variable voltage variable wave number inverter that drives an induction motor, a current pattern generation circuit that outputs a first current pattern according to an external command value, and an output of this current pattern generation circuit. a multiplication circuit that outputs a second current pattern obtained by multiplying the output frequency by one-square of the output frequency of the inverter; and controlling the output current and output voltage of the inverter based on the first or second current pattern. control elements.

[Effect]

In this invention, the control element outputs the output based on the first current pattern when the frequency is below the predetermined range, and based on the second current pattern when the frequency is within the predetermined range. In addition to controlling the current, when the frequency is below the predetermined range or within the predetermined range, the output voltage is made proportional to the output frequency, and when the frequency is above the predetermined range, the output voltage is set to a constant maximum. The control element controls the inverter to maintain the value.

〔Example〕

FIG. 1 is a block diagram showing an embodiment of driving an electric vehicle (not shown) using an induction motor control circuit according to the present invention, and includes a DC power supply (1), a 7771 inverter (
2), induction motor 1i11 (3), and finger speed generator (4) are the same as conventional ones. (5A) is the first control element (
5A) e ()A) is the third control element 0 The above third control element (7 people) is the conventional second control element (6)
The input from is gone, and a new input to the river (Δ
Engineers) will be added. This human power Δ1 is also input to the first control element (5mm). (8) is the r first value according to the first external command value S such as the variable load for driving the electric vehicle.
Current pattern generation circuit that outputs an OT flow pattern (9
) inputs the output of the current pattern generation circuit (8) and the output of the first control element (5A), that is, the output frequency (1 in FIG. 1) instruction signal of the Vma v1 inverter (2), '777 on the output of the current pattern generation circuit (8)? A multiplication circuit (9) that outputs a second current pattern multiplied by the square of the output frequency of the inverter (2), α0 is the output of the current pattern generation circuit (8) and the first control element (5 A multiplier circuit that inputs the output of a person) and outputs a third current pattern obtained by multiplying the output of the current pattern generation circuit (8) by the reciprocal of the output frequency of the VVY inverter (2). When receiving a notch (N) command to operate the notch (N), the frequency corresponding to the notch (N) value? OII value and vvv
a command device such as a notch (6) that outputs a value of frequency 70 corresponding to the fixed maximum value Vo of the output voltage of the y-inverter (2);
are a current pattern generation circuit (8), a multiplication circuit (9),
(1 (1, Notsuchi etc. command unit■, first control element (5 people)
input the output of vvvy inverter (2), frequency 7
When is below the frequency FON corresponding to the notch command, the input from the current pattern generation circuit (8) is output, and when the frequency 1 is within the range from the frequency 1'ON to FQ, the input from the multiplier circuit (9) is output. Output the input and set the above frequency 1
When the value is 0 or more, the current selector outputs the input from the multiplier circuit α0, and its output current is 1'. The magnitude of this current 1′ and the current flow M flowing through the induction motor (3) are compared, and the difference ΔΔM between the two is determined by the first control element (5A
) and the third control element (i). In addition, the output voltage V and output frequency F of the vvvy inverter (2) are controlled by the above-mentioned notch command I, flow selector (2), first control element (5A), and third control element (A). and output current (
This constitutes a control element 0 that controls the electrical current (corresponding to the electrical current V).

In the induction motor control circuit configured as described above, the first control element (5A) of the control elements 0 responds to the rotation speed of the induction motor (3) which is the output signal of the finger speed generator (4). Input the proportional signal VM, the second external command value vsp for operating the induction motor (3) with the Spe9 frequency XIB at a predetermined value, and the above difference Δengine M,
A signal indicating the value of the output frequency 7 of the inverter (2) is output. On the other hand, the third control element (
'l'A) inputs the same input signal vM + vs, #ΔEngineer as the first control element (5 people), and
A signal indicating the value of the output voltage V of the inverter (2) is output. When the value of the above output frequency 1 is smaller than the above frequency 1PoO value, the value of this output voltage V is
is made proportional to the value of output frequency 1, and when the value of output frequency 1 is equal to or higher than frequency 70, an instruction is given to hold it at a constant maximum value vO. Current selector (2) among control elements (to)
inputs the output signals of the notch etc. command unit 0 and the first control element (5), and when the value of the output frequency 1 of the vvvy inverter (2) is below the frequency I'ON, the output signal of the first control element (5) is input.
When the value of output frequency 1 is between the frequency FON and the frequency 70, the second current pattern is selected.
Select the current pattern of , and the value of output frequency 7 is the first half frequency F. In the above cases, select the above third current pattern,
Output as current value KMI. In the control element 0, this current value 1' and the current value M flowing through the induction motor (3) are compared, and the value of the difference Δ1 is calculated from the above-mentioned first control element (5A) and third It is output to the control element ()A).

The value of ΔE is a control amount corresponding to the minute change ΔJ5 in the slip frequency of the induction motor (3).

The vvvp inverter (2) is controlled as described above by the control element (to), and its output voltage V, output frequency 1. The relationship between the current 1 flowing through the induction motor (3) and its torque T is as shown in FIG. That is, in the region (■) shown in FIG. 6, the magnitude of the current flow M is constant, in the region H the magnitude is zMαl/IF2, and in the region (■) the magnitude of the current flow M is constant.
/F becomes. Further, in regions I and II, the output voltage V is proportional to the output frequency 1, and in the region ■, the output voltage is a constant maximum value v□. Such current and voltage characteristics and the above (2)
From the relationship with the equation, the torque has a constant magnitude in the region (2), and decreases in proportion to the value of 1/12 in the regions (2) and (2). This torque versus frequency characteristic is the same as in the conventional case. Further, in the positive high frequency region, the output voltage V is maintained at a constant maximum value, and voltage modulation is not performed to maintain it at a low constant value as in the conventional output voltage V shown in FIG.

By the way, in the above description, the case where the induction motor control circuit according to the present invention is applied to the operation of an electric vehicle has been described.
It may be applied to things other than electric cars.

〔Effect of the invention〕

The induction motor control circuit according to the present invention includes a variable voltage variable frequency inverter that drives the induction motor, a current pattern generation circuit that outputs a first current pattern, and an output frequency of the current pattern generated by the square of the output frequency of the inverter. a multiplication circuit that outputs a second current pattern multiplied by a value of 1/2, and controlling the output current of the inverter based on the first current pattern or the second current pattern according to the predetermined frequency range; and a control element that controls the output voltage of the inverter according to the frequency range, and the output voltage is maintained at a constant maximum value in the high frequency range, so that when the induction motor is operated at high speed, the There is no need to modulate the output voltage of the inverter, and therefore the switching power of the inverter can be reduced.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing an embodiment of the induction motor control circuit according to the present invention, Fig. 2 is an output characteristic diagram of the induction motor and inverter driven by the invention, and Fig. 3 is a diagram of the conventional induction motor control circuit. Block diagram, Figure 4 is a voltage vs. frequency characteristic diagram of one of the components in Figure 3, Figure 5 is a torque vs. frequency characteristic diagram of a conventional induction motor, and Figure 6 is an output characteristic diagram of a conventional induction motor and inverter. It is. In the figure, (2) is a variable voltage variable frequency inverter,
(3) is an induction motor, (8) is a current pattern generation circuit,
(9) is a multiplication circuit, and (to) is a control element. In each figure, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] A variable voltage variable frequency inverter that inputs DC power and converts it into AC power to drive an induction motor, a current pattern generation circuit that outputs a first current pattern in accordance with a first external command value, and this current pattern. A second value obtained by multiplying the output of the generating circuit by the value of one-square of the output frequency of the inverter.
a multiplier circuit that outputs a current pattern of the inverter; when the frequency is below a predetermined range, the output current of the inverter is controlled based on the first current pattern, and when the frequency is within the predetermined range, the The output current of the inverter is controlled based on a second current pattern, and when the frequency is below the predetermined range and within the predetermined range, the output voltage of the inverter is proportional to the frequency, A control circuit for an induction motor, comprising: a control element that controls the inverter to maintain the output voltage at a constant maximum value when the output voltage exceeds a predetermined range.