JPH03253291A - Driving device for motor - Google Patents

Abstract

PURPOSE:To conduct a lagging power factor operation in a low speed region of a motor and to make a power factor be 1 substantially when a speed reaches a prescribed region by providing a power factor correcting means which corrects an output signal from a power factor computing means in accordance with a reference value, and a means which calculates an output voltage. CONSTITUTION:A current flowing through a direct-current link unit is detected by a current sensor 31 and inputted to a current detecting means 33 and waveform shaping is conducted therein. In a power factor computing means 34, a difference in the DC current is computed as a power factor. A value thus obtained is inputted to a power factor correcting means 40. A speed command value W* is inputted also thereto and the value of the aforesaid power factor is corrected therein in accordance with a speed. In a voltage frequency computing means 35, the value of the aforesaid power factor is incorporated in a control element for a voltage value determined by the command value W*, and computed, and thus a voltage determined by the command value W* and the power factor is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention (Industrial Application Field) The present invention relates to a motor drive device that drives an electric motor at variable speed, and in particular to a motor drive device equipped with means for preventing step-out. Regarding.

(Prior Art) As a conventional drive device of this type, one that drives a brushless motor at variable speed will be described.

In brushless motor drive devices, this method detects the relative position of the stator coil and permanent magnet rotor by using terminal voltage, including the induced voltage generated in the stator coil, without using a position detection element such as a Hall element. are increasingly being adopted.

This conventional example is shown in FIG. That is, 1 is a DC power supply, 2 is a stator coil 3U, 3V, and 3 of a brushless motor 3.
4, 5, and 6 are filter circuits for phase-shifting the terminal voltages UV, VV, and WV containing induced voltages generated in the stator coils 3U, 3V, and 3W by 909; 7 is a filter circuit for these filter circuits 4; Detection circuit for obtaining neutral point voltage NV from output signals of 8.9 and 10
1 is a comparator that compares the output signals of filter circuits 4.5 and 6, which are first-order delay elements, with the neutral point voltage NV, and 11 is a control circuit. FIG. 4 is a time chart showing the operation of the conventional example, and now, referring to this chart, let us consider the U phase. The terminal voltage UV generated in the stator coil 3U (see FIG. 4(a)) includes a spike-like voltage component that is generated due to conduction of the paired arm freewheeling diode during commutation in the inverter circuit 2. In order to eliminate the influence of the voltage component, the phase of the terminal voltage UV is shifted by 90° by the filter circuit 4 to obtain a phase-shifted voltage DUV as shown in Fig. 4(b).
The comparator 8 compares the neutral point voltage NV shown in FIG. 4(b) and outputs the position detection signal PS as shown in FIG. 4(c).
Get U.

The same applies to the other V and W phases, and position detection signals PSV and PSW are obtained from comparators 9 and 10 as shown in FIGS. 4(d) and (e) based on terminal voltages VV and Wv. These position detection signals PSU, PSV and PSW
are 180" energized and 120@signals with different phases, and when these are given to the control circuit 11, the control circuit 11 outputs six drive signals and applies them to the bases of the transistors that are the switching elements of the inverter circuit 2. become.

However, in the above configuration, filter circuits 4 to 6 having a 90@lag phase characteristic are provided in order to remove spike-like voltage components included in the terminal voltages UV, VV, and Wv. Since the constant is large, there is a problem that it cannot follow rapid acceleration/deceleration, and there is also a problem that position detection in a low speed region is difficult. Furthermore, since the magnitude of the spike-like voltage components included in the terminal voltages UV, VV, and Wv changes depending on the current of the stator coils 3U, 3V, and 3W, that is, the magnitude of the load, if the load fluctuation is large, the filter circuit 4 or This will cause a phase error in the signal waveforms after 6, which poses a stability problem.

Therefore, in order to solve this problem, a driving device that performs control based on the current flowing through the stator coil without using the terminal voltage of the stator coil may be considered.

The drive device will be explained.

First, the overall configuration will be described according to FIG. 2
1 is a three-phase AC power supply, and the three-phase AC voltage is passed through a full-wave rectifier circuit 2, which is made up of six diodes connected in a three-phase bridge.
It is designed to be applied to the second AC input terminal. The DC output voltage of the full-wave rectifier circuit 22 is applied to the DC buses 25 and 26 via a smoothing capacitor 24 constituting a DC power supply 23. 27 is 6
This is an inverter circuit formed by connecting transistors, which are switching elements, in a three-phase bridge, and its input terminal is set to 1 so that the DC voltage between DC buses 25 and 26 is applied. 28 is a 3-phase 4-pole brushless motor,
This includes a stator 29 having U, V and W phase stator windings 29U, 29V and 29W, and a permanent magnet rotor 3.
0. And stator winding 29U, 29V
and 29W are star-connected, and the AC output voltage from the output terminal of the inverter circuit 27 is supplied to these. Reference numeral 31 denotes a current detector consisting of a Hall CT, which is provided on the DC bus 25, which is the DC side portion of the inverter circuit 27. 32 is a DC amplification circuit, which includes a current detector 31 and a current detection means 33.
It constitutes. The DC current signal 1dc detected by the current detector 31 is applied via a DC amplifier circuit 32 to an input terminal of a power factor calculation circuit 34 serving as power factor calculation means. This power factor calculation circuit 34 calculates a power factor signal ΔIdc and a current change amount ΔIdc− based on a DC current signal 1dc, and the power factor signal ΔIdc and current change amount ΔIdc− are outputted as signals from an output terminal. V is the voltage frequency (V/F) calculation means.
The signal is applied to the input terminal of the /F calculation circuit 35. This V/F calculation circuit 35 has a power factor signal Δ1dC9
The voltage signal V and frequency signal F are calculated based on the current change amount ΔIdc= and the speed command ω8 given from a setting device (not shown), and these are outputted from the output terminal and given to the input terminal of the drive circuit 36. It has become. The drive circuit 36 outputs six drive signals PWM-controlled based on the voltage signal V and the frequency signal F from the output terminal and applies them to the bases of the six transistors of the inverter circuit 27. Thereby, the rotor 30 of the brushless motor 28 is rotated at the rotational speed indicated by the speed command value ω1.

Next, an explanation will be given with reference to FIG. 6 showing its effect.

FIG. 6 shows the waveform of the DC current signal 1dc of the current detection means 33 with respect to power factor changes when power factor control is not performed by the inverter circuit 27. That is, when the power factor is delayed, the waveform changes every 1/6 period (60' in electrical angle) of the output frequency, and the change is upward-sloping, as shown in FIG. On the other hand, when the power factor advances, the waveform changes every cycle, as shown in Figure (C).
The change is downward to the right. When the power factor becomes approximately 1, the waveform becomes almost unchanged, as shown in FIG. 3(b). Therefore, since the waveform of the DC current signal Idc repeatedly changes every 60 degrees of electrical angle, the time point of every 60 degrees of electrical angle (0 degrees 60'120' 18
0'...360'), and calculate the difference (
Ib-1a) is detected, and this difference is zero, that is, the current value 1a, I
By controlling b so that they are equal, the brushless motor 28 is controlled so that the power factor becomes approximately 1 as shown in FIG. 6(b).
can be driven. In other words, it is possible to perform the same operation as the conventional brushless motor method in which the magnetic pole position is detected from the terminal voltage of the stator winding.

(Problem to be Solved by the Invention) However, even in the motor drive device configured as described above, when controlling a motor such as a synchronous motor, the low speed region lags behind the voltage due to the motor characteristics. Even though the advance range is narrower, it is detected at a predetermined electrical angle even in the low speed range, so if the load suddenly changes, for example, control may be delayed and a step-out state may occur, so the motor cannot be driven stably. This was a major obstacle at the top.

Therefore, in view of the above problems, the present invention performs delayed power factor operation in the low speed region of the electric motor, and when the speed reaches a predetermined speed region, it is possible to start operation such that the power factor becomes approximately 1. The purpose of the present invention is to provide an electric motor drive device.

[Structure of the Invention] (Means for Solving the Problems) In order to achieve the above object, the present invention provides a converter means for converting AC power supplied from a power source into DC power, and a converter means for converting AC power supplied from a power source into DC power. An electric motor drive device that includes an inverter means for converting AC power having an arbitrary frequency and controls a motor at variable speed using the AC power from the inverter means, a current detection means for detecting a DC current of the inverter means; A power factor calculation means for calculating the power factor based on the detection signal from the current detection means; and a power factor correction means for correcting the output signal from the power factor calculation means according to a preset reference value. The present invention provides an electric motor driving device characterized in that it comprises a calculation means for calculating an output voltage based on the output signal from the power factor correction means and the preset reference value.

(Function) According to the motor drive device configured in this way, the frequency of the voltage applied to the motor is adjusted by a predetermined electrical angle (for example, 60 m
) is obtained as the power factor, and a correction value according to the speed standard is added to this DC current difference to control the voltage and frequency applied to the motor. Even if, for example, the load suddenly changes in the area, step-out can be prevented and reliable control can be achieved.

(Example) An embodiment of the present invention will be described below with reference to the drawings.

In addition, the same reference numerals are attached to the same constituent elements as in the conventional art, and the explanation thereof will be omitted.

As shown in FIG. 1, the motor drive device of this embodiment is an example for driving a synchronous motor.

First, a current flowing through a DC link section that converts DC to AC is detected by a current sensor 31, and is input to a current detection means 33, where waveform shaping is performed by amplification, sampling, holding, and the like. As mentioned above, the difference in power factor results in a current waveform as shown in Figure 6, so in order to operate with a power factor of approximately 1, the difference in DC current (IB-IA) must be zero. As such, it needs to be controlled. Therefore, the power factor calculation means circuit 34 calculates this current difference as a power factor.

This value is then input to the power factor correction means 40.

Here, the speed command value ω7 is also manually input, and the power factor value calculated in the previous stage is corrected according to the speed. The operation will be described using FIG.

FIG. 2 shows a voltage (V)-frequency (F) characteristic with the horizontal axis representing the output frequency and the vertical axis representing the output voltage.

The dotted line shows the characteristics when operating on power factor path 1, above the dotted line is the lagging power factor region, and below the dotted line is the leading power factor region.In addition, in this example, an arbitrary frequency f1 is selected and the frequency range from 0Hz to flHz is In between, the power factor is corrected.

When a command value ω3 is given from the outside, a value inversely proportional to the speed, for example, the correction amount (ΔP) - GI X (fl - f), where Δ
P is the correction amount, Gl is the gain, and f is the frequency given by the command value ω8.

However, when f>fl, ΔP-0 is set.

A correction method is used in which the faster the speed, the smaller the correction amount is proportionally.

In the case of a lagging power factor, the power factor calculation means 34 at the front stage calculates Ib-
Ia has a negative value, and the control phase must be in the direction of lowering the voltage. Conversely, in the case of a leading power factor, Ib-Ia takes a positive value and must be controlled in the direction of increasing the voltage. Therefore, in the power factor correction means 40, by adding the above-mentioned correction amount ΔP to this Ib-1a, for example, Ib-1a
-0, that is, when the power factor is approximately 1, the value is positive by ΔP, so
In the direction of increasing the voltage, that is, in the power factor path 1, the value becomes positive by ΔP, so that the voltage shifts from the point in the direction of increasing the voltage, that is, in the power factor path 1 to a lagging power factor. In the lagging power factor, ΔP is added to the negative value of Ib-Ia, so the negative value becomes smaller and the degree of voltage reduction becomes smaller, and ΔP remains in the lagging power factor region as it is. Furthermore, in the leading power factor, ΔP is added to the positive value of Ib-1a, so the degree of voltage increase increases, and the transition to the lagging power factor region occurs.

Note that, as described above, since the amount of low speed side correction increases, the degree of transition to the low speed side lag power factor increases.

Further, in this power factor correction means 40, the output frequency is Q-f
, Hz, the power factor is corrected and output to the V/F calculation means 35. In the V/F calculating means 35, the above-mentioned power factor value is incorporated into the control element into the voltage value determined by the command value ω1, and is calculated, thereby obtaining the voltage determined by the command value ω1 and the power factor.

Then, the drive circuit 36 is controlled by the voltage value determined as the command value ω5, and the motor 28 is driven.

The characteristics at this time are shown by the solid line in FIG. 2, and in the range of 0 to f1Hz, the power factor operation is delayed.

In the present embodiment, the correction method of the power factor correction means 40 sets the arbitrary frequency to one point f, but the correction range is not limited to this, and the correction range may be divided into several parts. Further, the correction constant and correction formula may be changed in each range. (speed:
Various modifications are possible, not limited to the formula inversely proportional to . )Furthermore, although the power factor is made to be related only to the speed, there is no problem in adding correction to the power factor using parameters other than the speed. Furthermore, in addition to adding ΔP to Ib-Ia, (Ib-Ia) may be multiplied by a gain proportional to speed, etc., to improve controllability.

[Effects of the Invention] As described above, according to the present invention, the power factor obtained from the detection of the DC current of the inverter means by the power factor correction means,
Since an arbitrary correction amount is added in an arbitrary speed range, operation with different power factors can be performed, and even if the load suddenly changes, tax adjustment can be prevented.

Therefore, an excellent effect is achieved in that the electric motor can be driven stably.

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram showing one embodiment of the present invention, FIG. 2 is a graph showing voltage (V)-frequency (F) characteristics of the embodiment shown in FIG. 1, and FIGS. The figure shows a schematic configuration diagram of a conventional electric motor drive device, FIG. 4 is a signal waveform diagram of each part of the device shown in FIG. 3, and FIG. 6 shows the device shown in FIG. 5 with different power factors. FIG. 3 is a waveform diagram of a direct current signal of FIG. DESCRIPTION OF SYMBOLS 1... Three-phase AC power supply, 2... Full-wave rectifier circuit (converter means), 7... Inverter circuit (inverter means), 1... Current detection circuit, 32... DC amplifier circuit, 3 ... current detection means, 34 ... power factor calculation means, 5 ... V/F calculation means (
Calculation means), 0...Power factor correction means Fig. 2

Claims (1)

[Claims] It has converter means for converting AC power supplied from a power source into DC power, and inverter means for converting the DC power from the converter means into AC power having an arbitrary frequency, and the AC power from the inverter means can be used to drive a motor. In an electric motor drive device for variable speed control of the inverter, a current detecting means for detecting the direct current of the inverter means, a power factor calculating means for calculating a power factor based on a detection signal from the current detecting means, and a power factor calculating means for calculating a power factor based on a detection signal from the current detecting means; power factor correction means for correcting the output signal from the calculation means according to a preset reference value; and calculating an output voltage based on the output signal from the power factor correction means and the preset reference value. An electric motor drive device characterized by comprising calculation means for calculating.