JPS6118393A - Control circuit of inverter - Google Patents

Abstract

PURPOSE:To eliminate insufficient torque by judging whether it is power drive or a generative drive by a mode discriminator and automatically correcting the impedance drop in response to the operation mode when a current increases, thereby always maintaining an exciting magnetic flux constant. CONSTITUTION:A polarity adding circuit 15 produces the output of an absolute circuit 14 as positive polarity by the output of a mode discriminator 13 at power drive time and the absolute value output as negative polarity at regenerative drive time. A correcting voltage outputting circuit 12 outputs a voltage to be corrected. Thus, even if a current increases due to a load, since the output voltage is corrected to be added in the power drive mode and to be subtracted in the regenerative mode, insufficient torque due to the reduction in the exciting magnetic flux at power drive heavy load time can be eliminated, and an overexcitation phenomenon can be avoided at the regenerative heavy load time.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to an inverter control circuit that improves the torque characteristics of an induction motor during power running and during regeneration.

[Prior art]

A conventional device of this type is shown in FIG. In the figure, 1 is an AC power supply, 2 is an AC/DC conversion circuit that converts AC to DC, 3 is a smoothing capacitor, 4 is a DC/AC conversion circuit that converts DC to new AC, and 5 is an induction motor. Further, 6 is a frequency setting circuit, T is a cushion circuit for smoothly following the characteristic to the frequency set by the frequency setting circuit 6, 8 is a voltage frequency ratio circuit for commanding voltage to frequency, and 9 is the cushion circuit. Frequency command output from 7 and voltage frequency ratio circuit 8
This is a PWM generation circuit that determines the switching timing of the inverter output based on the voltage command output from the inverter. Reference numeral 10 denotes a current detector that detects the direct current of the DC bus and outputs a voltage proportional to the current. Reference numeral 11 denotes a current setting circuit that sets the current value during no-load. By subtracting it from the output value of the detector 10, the increase in current due to the load is detected. Reference numeral 12 denotes a correction voltage output circuit that outputs a voltage proportional to the increase in current, and its proportionality constant is made approximately equal to the primary resistance (rl in FIG. 2) of the induction machine. This correction voltage from the correction voltage output circuit 12 and the output of the voltage O frequency ratio circuit 8 are added, and the PWM
The signal is input to the generating circuit 9.

Next, the operation of the conventional circuit shown in FIG. 1 will be explained.

Before entering into a detailed explanation of the operation, the equivalent circuit of the induction motor shown in FIG. 2 will be explained. First, the terminal voltage E of the excitation winding at no load is equal to the current at no load of 1. Then, K = V4- (r1+ Ptt)to...
・・・・・・・・・・・・・・・・・・・・・(1) However, p= − t, where rl; − the resistance of the secondary winding, t1 the leakage inductance of the secondary winding. Become. Assuming that the load becomes heavy and the total 9S increases and the no-load current io changes to io+Δ1, the excitation winding voltage E' is expressed by equation (2).

E'='h - (r1+P4X1o+Δ1)=V1-(
rx+P4)to (r1+Pt1)Δs ・-・
-[21 Therefore, the excitation winding voltage E' is (rx+pz4)
It decreases by Δl. This voltage decrease is calculated as AC input voltage ■1
In the conventional example shown in FIG. 1, the excitation winding voltage E' is controlled to be constant.

That is, the current detector 10 first detects the peak value of the DC bus current. The waveform in Fig. 4(a) shows the DC bus current 1 dc and the 3-phase AC single-phase line current 1 on the same scale when the inverter output voltage is a square wave, i
The peak value ip of dc matches the peak value of the line current l. On the other hand, (peak value of line current i) = 1 fundamental wave effective value) 10 i (harmonic ripple component), and the harmonic ripple component is almost constant regardless of the fundamental wave effective value of line current i. . Therefore, by detecting the DC bus current peak value ip and subtracting the fixed harmonic ripple component, the fundamental wave effective value of the line current l can be obtained.

That is, the current detector 10 performs the above-mentioned circuit calculation and outputs a voltage corresponding to the fundamental wave effective value of the line current 1. Furthermore, the DC bus current can be detected by multiplying the inverter output frequency of one detector by six. Therefore, compared to detecting the inverter output current (line current i), this method is more effective in terms of responsiveness and economy.

Next, in the current setting circuit 11, a value corresponding to the no-load current IQ of equation (2) is set in advance and subtracted from the output of the current detector 10. Through this numerical calculation, the current increase amount Δl due to the load shown in equation (2) is obtained. The correction voltage output circuit 12 is a correction voltage output circuit that multiplies the current increase amount Δi by 11, and this output signal provides the voltage value to be corrected. More precisely, it should be multiplied by (rl+pt1) in the correction voltage output circuit 12, but since tl is smaller than rl, it is ignored. Further, the output of the corrected voltage output circuit 12 is added to the output of the voltage frequency ratio circuit 8 and input to the PWM generation circuit 9. Due to the above operation, the υ line current l is reduced due to the influence of the motor load.
Since the voltage E shown in FIG. 2 is kept constant even when E increases, it is possible to eliminate the torque shortage caused by a decrease in excitation magnetic flux during heavy loads.

Conventional inverter control devices are configured as described above, so they detect the positive polarity current peak value of the DC bus current and add and correct the output voltage without determining whether the motor operation mode is power running mode or regeneration mode. Therefore, in the regeneration mode, the flow of current io in the equivalent circuit shown in Figure 2 is reversed, so the E voltage increases even without output voltage correction, resulting in overexcitation operation. Since the conventional correction method performs additive correction, there are also drawbacks such as overexcitation operation.

[Summary of the invention]

This invention was made in order to eliminate the drawbacks of the conventional ones as described above, and includes a mode discriminator that automatically determines whether the motor operation mode is power running mode or regeneration mode. It is an object of the present invention to provide an inverter control device that performs additive correction on the output voltage according to the load current level and subtractive correction on the output voltage during regeneration according to the load current level to avoid overexcitation operation.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to the drawings. In the figure, the same parts as in Figure 1 are designated by the same reference numerals.
In the figure, 101 is an instantaneous current detector that detects the instantaneous value of the DC bus current, 13 is a mode discriminator that determines the power running mode if the average value of the instantaneous current detector 101 is positive, and the regeneration mode if it is negative, and 14 is the instantaneous current Absolute value circuit that obtains a positive polarity output proportional to the current from the current detection output value of the detector 101, 1
5 is a polarity adding circuit which receives the output of the mode discriminator 13 and adds a positive sign to the absolute value output in the power running mode, and adds a negative sign to the absolute value output in the regeneration mode.

Next, the operation will be explained. First, the mode is determined from the relationship between the DC bus current and output current during power running and regeneration, and the DC bus current using Fig. 4, and the absolute value of the output proportional to the output current is obtained using the absolute value circuit 14. Explain the principle. However, in order to simplify the explanation, FIG. 4 shows the current waveform at the time of a rectangular wave output voltage, and ignores the influence of PWM.

Furthermore, although the current waveform when performing sine wave approximation PWM becomes a sine wave, the basic relationship remains the same in PWM.

First, in Fig. 4, (a) to (d) are power running mode, (
e) to (h) are diagrams for explaining the operation in regeneration mode. Therefore, (a) is the power running mode, (e) is the regeneration mode, the output current (line current for one AC phase) i and the DC bus current 1dc
The waveform of is shown. In power running mode, DC bus current 1d
The maximum positive value (peak value) of c and the peak value of output current 1 match. In addition, in the regeneration mode, the DC bus current 1
The maximum negative value of dc and the peak value of the output current l match.

If it can be determined from these phenomena whether it is the power running mode or the regeneration mode, the peak value of the output current l can be determined from the DC bus current idc. Alternatively, since the peak value of the absolute value of the DC bus current 1dc matches the peak value of the output current l, the peak value of the multi-output current i, that is, the effective value level, can be determined by observing the DC bus current idc. become.

Next, we will show how to determine whether the mode is power running mode or regeneration mode. First, during power running, the inverter supplies power to the motor, the output power of the DC section is positive, and the average value of the DC bus current 1dc is positive. The waveform at this time is shown in (b). During regeneration, power is supplied from the motor to the inverter in reverse, and the average value of the DC bus current idc becomes negative as shown in (f). Therefore, depending on the polarity of the average value of the DC bus current 1 dc, it is determined that if it is positive, it is power running, and if it is negative, it is regeneration. (C) and (g) in FIG. 4 are the absolute value of the DC bus current 1 da and its peak value ip. In addition, (d) and (h) are the peak value of (c) 1. (b).

The state of the waveform obtained in (f) with added polarity is shown.

Subsequently, the operation shown in FIG. 3 will be explained.

First, the DC bus current ide is detected by the instantaneous DC detector 101.
Detect. As shown in FIG. 5, if the average value of 1 dc is determined by the mode discriminator 13 and is positive, it is determined that it is a power running mode, and if it is negative, it is determined that it is a regeneration mode. Next, in the absolute value circuit 14, the DC bus current 1 is
Take the absolute value of dc and hold its peak value. This detected value coincides with the peak value of the output current 1 as shown in FIG. That is, as mentioned above, the output current i is (
1 peak value) = (1 fundamental wave effective value) + L (harmonic ripple current), and the harmonic ripple component remains almost constant regardless of the fundamental wave effective value of the output current l. Therefore, by detecting the peak value 1p of the DC bus current idc and subtracting the fixed harmonic ripple, the effective value of the fundamental wave of the output current i can be obtained.

Therefore, the absolute value circuit 14 performs the above circuit calculations and outputs a signal that corresponds to the effective value of the fundamental wave of the output current 1.

Next, in the polarity adding circuit 15, according to the output of the mode discriminator 13, the output of the absolute value circuit 14 is output as positive polarity during power running, and the absolute value output is output as negative polarity during regeneration.

Next, in the current setting circuit 11, the no-load current i(H
A value corresponding to is set in advance and subtracted from the output of the polarity adding circuit 15. Through this calculation, the current increase amount Δi due to the load in equation (2) is obtained. Correction voltage output circuit 12
is a correction voltage output circuit which multiplies Δi by 11, and this output provides the voltage to be corrected. To be exact, the correction voltage output circuit 12 should multiply it by (r1+Pt1), but since tl is small, it is ignored. Therefore, the output of the corrected voltage output circuit 12 is added to the output of the voltage frequency ratio circuit 8 and input to the PWM generation circuit 9.

As a result of the above operation, even if the current increases due to the load, the output voltage is added and corrected in the power running mode, and the paper power voltage is subtracted and corrected in the regeneration mode, so the voltage E in Figure 2 is kept constant and the power running load is It is possible to eliminate the torque shortage caused by the decrease in the excitation magnetic flux, and it is also possible to avoid the overexcitation phenomenon under regenerative heavy loads.

FIG. 5 is a configuration diagram of an inverter control circuit showing another embodiment of the present invention, in which a positive side peak hold circuit 16 and a negative side peak hold circuit 16 are used instead of the absolute value circuit 14 and polarity addition circuit 15 in FIG. The peak hold circuit 17 is designed to select a positive peak hold output during power running mode and a negative peak hold output during regeneration. The output of the selection circuit 18 is as shown in FIGS. 4(d) and (h). In addition, the example is PWM
Although an inverter method is shown, other methods such as a PAM modulation method may be used, and a microprocessor may also be used to calculate the corrected voltage value from the current detector output.

〔Effect of the invention〕

As described above, according to the present invention, the input current of the motor is detected from the DC bus current of the inverter and the average value thereof is determined to determine whether it is a power running mode or a regeneration mode, and when the current increases, the primary impedance decreases. Since the minutes are automatically corrected according to the operating mode, responsiveness is also good.
This has the effect of always keeping the excitation magnetic flux constant, eliminating torque shortages, and eliminating overexcitation operation.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a conventional control device of this type, FIG. 2 is an equivalent circuit diagram of an induction motor, and FIG. 3 is a control diagram of a conventional control device of this type. A circuit configuration diagram, FIG. 4 is a waveform diagram of the main part showing the relationship between the output current and the DC bus current, which is used to explain the operation of one embodiment of the present invention, and FIG. 5 shows another embodiment of the present invention. It is a circuit configuration diagram of an inverter control device. 1... AC power supply, 2... AC/DC conversion circuit, 3...
・Smoothing capacitor, 4...DC/AC conversion circuit, 5.
...Induction motor, 6...Speed setter, 7...Cushion circuit, 8...Voltage frequency ratio circuit, 9...PW
M generation circuit, 10.101...Current detector, 11...
・No-load current setting device, 12...Correction voltage output circuit, 1
3...Mote degree discriminator, 14...Absolute value circuit, 15
. . . polarity addition circuit, 16 . . . positive side peak hold circuit, 17 . . . negative side peak hold circuit, 18 . Figure 1 Figure 2 Vr Figure 3 Figure 5

Claims (2)

[Claims] (1) a frequency setter that sets the output frequency of the inverter circuit, and a command for output voltage at a preset voltage frequency ratio according to the output from the frequency setter;
In a voltage frequency ratio circuit and an inverter control circuit that outputs variable voltage and variable frequency from a PWM generation circuit in response to the output of the frequency setter, the load current of the inverter circuit is set to a current level equivalent to no load. A current setting circuit, a subtraction circuit that detects a current input to an induction motor driven by the inverter circuit, and subtracts a setting value of the current setting circuit from the detected current value, and a subtraction circuit that detects whether the inverter circuit is power or regeneration. and a mode discriminator for discriminating, and outputs an output command to the PWM generation circuit to add a voltage command approximately proportional to the output of the subtraction circuit to the output of the voltage frequency ratio circuit during power running, and to subtract it during regeneration. An inverter control circuit characterized by: (2) an absolute value circuit that detects the maximum and minimum values of the DC bus current of the inverter circuit; an instantaneous current detector that obtains the average value of the DC bus; and an absolute value circuit that detects the average value of the DC bus current; 2. The inverter control circuit according to claim 1, further comprising a mode discriminator that selects a maximum value when the value is negative, and a mode discriminator that selects the minimum value when the value is negative.