JPS58108975A - Current controller - Google Patents

Abstract

PURPOSE:To enable to operate a stable AC machine by controlling in weak- field even if the frequency of an inverter becomes high and controlling the integration while comparing the DC current reference with the mean current of a load even if an AC current reference value is reduced. CONSTITUTION:A rectifier 23 converts load currents iu, iv, iw, into direct currents. An amplifier 22 compares and amplifies the DC current reference with the mean value of the current as the output of the rectifier 23, and proportionally integrates the error between the reference and the mean value. On the other hand, a level detector 24 discriminates at the level the output of a tachometer generator 7, thereby operating a switch 25, and applies the output of the amplifier 22 to an addition amplifier 26 which inputs a DC current reference when the frequency of an induction motor becomes high. In this structure, the DC current reference as the output of a function generator 10 is corrected by the amplifier 26 in response to the frequency of the motor, is converted into the mean current reference, and is inputted to D/A converters 13-15.

Description

DETAILED DESCRIPTION OF THE INVENTION The technical field of the invention is a current control device, and more particularly, a current control device suitable for precisely controlling the AC output current of a power converter at a high frequency.

Technical Background of the Invention Recently, control of alternating current machines using inverters and cycloconverters has been widely adopted. In particular, slip frequency control and vector control of induction motors are being used to provide control performance comparable to that of direct current even in the control of alternating current machines, and the scope of their applications is expanding.

FIG. 1 is a schematic configuration diagram showing an example of a current control device applied to a control device for such an alternating current machine. In the configuration shown in the figure, a transistor bridge 2 connected to a DC power supply 1 constitutes an inverter bridge that converts DC to AC. The transistor bridge 2 controls the inverter output voltage through PWM control (pulse width modulation), and the current detectors 3, 4 .
AC power is supplied to the one-conductor motor 6 via the motor 5. The speed of the induction motor is detected by a tachometer generator.

The speed reference set in the speed setter 8 and the output of the tacho generator turf are compared, and the difference is amplified by the amplifier 9 and outputted as a torque reference T'. The torque reference T4 is input to a function generator 10 and converted into a DC current reference 11.

On the other hand, the output of the tacho generator turf and the torque reference T" are added together and input to a V/F converter (voltage-frequency converter) IHC, where it is converted into a frequency signal proportional to the inverter frequency. This frequency signal is stored in the ROM ( The ROM circuit 12 shifts the phase by 12σ in electrical angle according to the frequency signal, and converts the sine wave pattern into a D/A converter (digital-to-analog converter) 1.
3, 14, 154 outputs. As a result, the D/A converters 13, 14, and 15 each output a DC reference h
A sinusoidal alternating current reference t, , it , proportional to
it is output.

~The alternating current reference 11 generated by the converter 13 is compared with the load current 11I detected by the current detector 3,
The signal is amplified by the amplifier 16 and input to the PWM control circuit. The output of the amplifier 16 is the triangular wave oscillator 1 for the modulation frequency.
The signal is compared with the output of the transistor bridge 2 and converted into a logic level signal by the PWM control circuit, which drives the transistor of the transistor bridge 2 via the drive circuit 21. As a result, the load current 1. is controlled to match the alternating current reference i, -. on the other hand.

AC current reference 1. , ,i, in the same way, the load current lv.

11, amplified by amplifiers 17 and 18, and applied to a PWM control circuit, compared with the output of a triangular wave oscillator 19, and converted into a logic level signal. This signal is supplied to the transistors of the transistor bridge 2 via the drive circuit 21, and the load current it,
it is an alternating current reference i, 1. Control is performed to match the .

Since such a current control loop is configured in an analog manner, the amplifiers 16, 17, and 18 use PI (proportional integral)
Control is often adopted, and it is common to insert a series circuit of a resistor and a capacitor in the feedback circuit of the operational amplifier as shown in the figure in the block of the amplifier 16.

Problems with the Background Art For the reasons stated above, as the frequency of the inverter increases, the gain of the current control loop decreases. For this reason,
When the inverter frequency increases, the AC current reference 1□i,,
i, and load current 1. ．． 1. ,i, no longer match.

That is, the input of the amplifier 16 is the AC current reference 1. and alternating current 1. The output of the amplifier 16 is the difference between the two currents multiplied by the gain of the amplifier 16. In the case of the PWM method in which the current of the induction motor 6 is made into a sine wave, the output of the amplifier 16 becomes a sine wave voltage. When the input frequency of the amplifier 16 is low, the gain of the amplifier 16 is high and the AC current reference 1. and load current 1. Although the difference in is a very small amount, as the input frequency increases, the impedance of the capacitor in the feedback circuit of the amplifier 16 decreases,
The gain of amplifier 16 becomes lower. For this reason, the amplifier 16
An input for making the output of the oscillator wave as a sinusoidal voltage, that is, an alternating current reference 1. and load current 1. As a result, the difference between the alternating current reference in and the amount of current that actually flows becomes large. This thing.

The same holds true for the loops including amplifications @17 and 18.

However, when considering the amplifier 16 based on the theory of automatic control, it is an integral amplifier, and the input error is close to zero for the DC component, but for the AC input number ζ, it is considered as a proportional amplifier. It is necessary to be careful that the input error becomes large and small because of the operation.

However, when performing vector control, if the current reference and the load current do not match, accurate vector control cannot be achieved and stable operation cannot be achieved, which poses a major problem. Such problems become more noticeable as the inverter frequency increases, and the field weakening further increases the current reference i.

In view of the problems of the prior art, this is a particular problem when the size of the inverter frequency is increased.

An object of the present invention is to provide a current control device capable of accurately matching a current reference and a load current value even if the field weakening current reference becomes small.

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a current control device, a power conversion means controlled based on an alternating current reference generated in proportion to the direct current reference, and an output alternating current of the power conversion means. It is composed of a correction signal generating means for generating a correction signal by comparing the average value with a DC current reference, and a correction means for applying the correction signal to the DC current reference.

Examples of the invention The present invention will be described in detail below with reference to drawing number ζ.

FIG. 2 is a partial block diagram of a current control device according to an embodiment of the present invention, illustrating a case where the control device number ζ of a special alternating current machine is applied. In the configuration of FIG. 2, the rectifier circuit converts the load current 1m,i,,i, into direct current. Amplifier n compares and amplifies the DC current reference 11 and the average value of the current output from rectifier circuit n.

Proportional integration of both errors. On the other hand, the level detector Sae determines the level of the output of the tacho generator to operate the switch 6, and when the frequency of the induction motor 6 becomes too high, the output of the amplifier n is transferred to the summing amplifier which receives the DC current reference II. Apply No. 26.

In this configuration, the DC current reference 11, which is the output of the function generator 1o, is corrected by addition of an summing amplifier within the frequency of the induction motor 6, and converted into an average current reference 1-#.
It is used as an input to /A converters 13, 14, and 15. That is, the load current i,,i,,1. is rectifier circuit 23#
This converts it to direct current and outputs it in the form of the average value of the load current. This average value is compared with a DC current reference 1:, and the error is proportionally integrated by amplifier 22. On the other hand, the output of the tacho generator 7 is determined by a level detector 244, and when it is detected that the frequency of the induction motor 6 has increased, the switch 3 is closed by the output of the level detector. As a result, the output of the amplifier ρ and the DC current reference 11
are summed by the summing amplifier pressure, and an average current reference l- is output. Therefore, the alternating current reference i,
i,,i.

The size of is proportional to the average current reference 1 m K O ,・1 Through the above adding operation, now the DC current reference 51! As a result of the comparison of the average values of the load currents, if the average value of the load currents is small, the amplifier n amplifies this and produces an output obtained by adding the output of the amplifier l4 to the DC current reference l-, that is, the average current reference 1.
Output. Here, by making the amplifier n an integral type, the steady-state DC current reference voltage and the load current i, ,
Average current reference 1 until the magnitudes of it and iv are equal.
m will increase. As a result, the inverter frequency increases and the current control amplifiers 16, 17, 18
Even if the gain decreases and the current control accuracy decreases, since integral control is performed by the operation of the average current control loop, the average current reference value is corrected, and as a result, the current control accuracy can be improved.

Note that in the range of very low inverter frequencies, there is a ripple in the output of the rectifier circuit (for example, a 6-phase full-wave rectified waveform), so there is also a ripple in the output of amplifier n, so switch b is closed at this time. Then the average current reference 1
．． Ripple enters.

As a result, the waveforms of the current references l, , i, tw become different from sine waves, causing torque ripples to occur with the induction motor No. 6. Amplification lI2 against vengeance
If the integral constant is increased in order to reduce the ripple of the output of the second embodiment, a problem arises in that the response of the average current control loop becomes slow. On the other hand, in the low range of the inverter frequency, the gain of the AC minor loop is sufficient and the current control accuracy is high.In this embodiment, when the inverter frequency is low, the switch 6 is The average current control loop is separated, and only when the inverter frequency becomes high, the output of the tachometer generator is determined by the level detector, and the average current control loop is utilized.

In the above embodiment, the case where the switch b is inserted at the position where the output of the amplifier n is switched on and off is exemplified, but the implementation of the present invention is not limited to this.
Like switching the gain.

For example, if the inverter is operated at low frequency.

A configuration may be adopted in which a switch inserted in the feedback circuit of amplifier n is closed to make the gain zero.

Further, in the above embodiment, an example was given in which the induction motor was operated with an inverter.

It goes without saying that the present invention can be applied regardless of the type of load or the type of converter.

Effects of the Invention As described above, according to the present invention, even if the inverter frequency increases, the field weakens by 1, and even if the AC current reference value decreases, integral control is performed while comparing the DC current reference and the average current of the load. By doing this, it is possible to control the magnitude of the load current so that it always matches the target value regardless of the frequency, enabling stable operation of the AC machine, and even at low frequencies, the AC machine can be operated with good response without increasing torque ripple. A current control device that can control current can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram of a conventional current control device, and FIG. 2 is a partial block diagram of the current control device according to an embodiment of the present invention. 1...DC power supply, 2...Transistor bridge. 3.4.5...Current detector, 6...Induction motor, 7
...6 tacho generator, 8...speed regulator, 9...
·amplifier. 10... Numerical number generator, 11... V/F converter, 12
...ROM circuit, 13,14.15...D/A circuit, 16, 17, 18...amplifier, 19...triangle wave oscillator, 20...PWM llll11 circuit. 21...drive circuit, ρ...amplifier, ku...rectifier circuit, 24...level detector, 5...switch, ah...
...Summing amplifier. Applicant's agent Kiyoshi Inomata Figure 1 Figure 2 Figure 3

Claims (1)

[Claims] 1. Power conversion means controlled based on standardization of alternating current generated in proportion to a direct current reference, and correction by comparing the average value of the output alternating current of the power conversion means with the direct current reference. A current control device characterized by comprising a correction signal generation means for generating a signal, and a correction means for applying the correction signal to a DC current reference. 2. The current control device according to claim 1, comprising a circuit that disables a system that applies a DC current reference.