JPH05284752A - Controlling method for voltage type inverter - Google Patents

Abstract

PURPOSE:To use in common with a system for suppressing an unstable output voltage due to an LC resonance and to operate without impairing features of both by inputting a predetermined delay time in a method for constantly controlling an output voltage due to a variation in an input power source voltage of an inverter. CONSTITUTION:A detected amount of a DC voltage detector 6 is once input to an integrator 14, and applied to a voltage operation corrector 11 for the variation in a power source voltage of a three-phase AC power source 1 through a delay of a set time constant. A voltage signal of a frequency setter 8 is converted to a frequency signal by a converter 9, and input to a voltage calculator 10. The corrector 11 corrects an output signal from the integrator 14 for a voltage signal to be output of the calculator 10, and outputs its output signal to an adder 13 as a voltage calculation correction amount. On the other hand, a DC component of an output of a variation of an intermediate DC voltage is cut at its DC component, and applied to the adder 13. It is added by the adder 13, its added result output is input to a PWM unit 12, and an induction motor 5 is PWM-controlled.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a voltage type inverter control method of a pulse width modulation (PWM) control method used in a voltage type inverter device.

[0002]

2. Description of the Related Art A conventional voltage source inverter incorporating an output voltage stabilizing circuit will be described with reference to FIGS. 3 and 4, the three-phase AC power supply 1 is converted into a DC voltage by the rectifier 2 and the filter capacitor 3, and is converted into the three-phase AC power supply by the inverter unit 4 including, for example, a transistor to drive the induction motor 5. Further, the voltage signal 103 of the frequency setter 8 is converted into the frequency signal 104 by the (frequency / voltage) converter 9, and becomes the voltage signal 105 of the (voltage / frequency) ratio in the voltage calculator 10.

By the way, generally, in a voltage source inverter having a capacitor in an intermediate DC portion as shown in FIGS. 3 and 4, the inverter output voltage changes proportionally when the input power supply voltage changes. The original output voltage-to-output frequency ratio control is not constant, but the constant output voltage control method shown in FIG. 3 is performed.

In such a case, the value of the voltage signal 101 by the DC voltage detector 6 for detecting the intermediate DC voltage is V _DC ,
When the value of the voltage signal 105 of the voltage calculation unit 10 is M and the reference setting value of the intermediate DC voltage is _VDC *, the output 106 of the voltage calculation correction circuit 11 is expressed by the following equation (1).

M · (V _DC * · V _DC ) ────────── (1) Then, the pulse width modulation unit (PWM
Part) 12 to modulate the pulse width to stabilize the inverter output voltage.

Further, unstable operation may occur during no-load operation when the induction motor is connected to the load or during light-load operation. This is due to the inductance of the induction motor (hereinafter referred to as L) and the capacitance of the above-mentioned capacitor of the inverter body (hereinafter referred to as C).
It is well known that resonance causes the output voltage of the inverter to become unstable.

In this case, the change amount ΔV of the voltage of the intermediate DC part
_DC is detected, and for sample time ΔT and correction gain K,
The voltage signal 102 output from the voltage fluctuation detection circuit 7 shown in FIG.
The voltage correction component is expressed by the equation (2).

(ΔV _DC / ΔT) · K ─────────── (2) Then, this detection result is calculated by the adder 13 as the voltage signal 105 output from the voltage calculation unit 10, and The output section 108 modulates the pulse width by the PWM section 12 to achieve stability. Furthermore, these two control methods as shown in FIGS. 3 and 4 have been used individually.

[0009]

Since both of the conventional systems detect the same point and control the voltage pulse width in the same manner, it has been difficult to use both in a PWM inverter. The reason is that LC of the capacitor of the inverter and the inductance of the induction motor of the load
When suppressing the fluctuation of the inverter output voltage due to resonance,
When the intermediate DC voltage rises, the voltage pulse width is widened, and when the intermediate DC voltage falls, the voltage pulse width is narrowed, thereby performing control for suppressing instability of the output voltage.

On the other hand, in the constant control of the output voltage with respect to the fluctuation of the input power supply voltage, the voltage pulse width is narrowed if the intermediate DC voltage rises, and the voltage pulse width is widened if the intermediate DC voltage falls to perform the constant output voltage control. To work. Therefore, although these two control methods are controlled by the same information, they act so as to cancel each other. That is, when they are used together, the original functions of both do not work, and conversely promote instability.

[0011]

As described above, a control method for detecting an intermediate DC voltage in order to stabilize the output voltage due to LC resonance and stabilizing the output voltage by voltage pulse width control, and an input power supply. In order to control the instability of the output voltage that occurs due to voltage fluctuations, the intermediate DC voltage is detected, and the detection result is suppressed by the voltage pulse width control. With the control method, the fluctuation of the intermediate DC voltage is detected. The time constant for the former control method is related to the resonance frequency due to LC resonance, and the time constant of the latter control method is related to the fluctuation of the input power supply voltage. The time constant of the former control method is fast. The present invention pays attention to the above points, realizes the combined use of both control methods, and makes the time constant of the latter control method sufficiently slower than that of the former control method. By having them, they can act without damaging the characteristics of both.

[0012]

With such a solution, the latter makes the output of the voltage detector sufficiently slow through, for example, an integrator, and the former allows the signal sent to the PWM section to be directly output and the latter function. It can operate faster than it can move, so there is no interference between the two. Hereinafter, the present invention will be described in detail with reference to the drawings.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows the essential structure of a position embodiment of the present invention shown in FIGS. 3 and 4, and 14 is an integrator.
2 shows a specific example of the voltage fluctuation detection circuit 7 of FIG. 1, in which 71 is a capacitor for cutting a direct current component, 72 is a regulator, and 73 is an amplifier. That is, L in FIG.
In the voltage fluctuation detection circuit 7 for instability correction due to C resonance, the amount of change in the intermediate DC voltage is detected by the capacitor 71, amplified by the amplifier 73 via the adjustment regulator 72, and output as the voltage signal 102.

Now, the detected amount by the DC voltage detector 6 is once inputted to the integrator 14 as the voltage signal 101 in the voltage calculation correction circuit 11 due to the fluctuation of the power supply voltage of the three-phase AC power supply 1, and the amount of the set time constant is added. Given via delay. Further, the voltage signal 103 commanded by the frequency setting device 8 is converted by the converter 9 into a frequency signal 104 having a proportional output frequency, and is input to the voltage calculation unit 10.

The voltage calculation correction circuit 11 corrects the signal 110 output from the integrator 14 with respect to the voltage signal 105 output from the voltage calculation unit 10, and the output 106 is added as a voltage calculation correction value to the adder.
Output to 13. On the other hand, the outputs 100 and 109, which are the original fluctuations of the intermediate DC voltage, have the DC signal cut and the voltage signal 10
It is given to the adder 13 as 2.

Therefore, the adder 13 adds the output of the voltage fluctuation detection circuit 7 to the output of the voltage calculation correction circuit 11, and the addition result is given to the PWM unit 12 as the output 108, and the PWM
The pulse width modulation is performed by the output 107 of the section 12, and the induction motor 5 is stably driven by the output voltage of the output of the inverter section 4. Of course, the correction for the power supply fluctuation of the intermediate DC voltage is corrected slowly for the integrator 14, and is controlled with a delay without any problem. The output voltage stabilizing means by LC resonance shown in FIG. 2 is implemented by hardware, but it goes without saying that it can be easily implemented by software.

[0017]

As described above, according to the present invention, L
In order to suppress the fluctuation of the output voltage due to the C resonance, the control method of detecting the intermediate DC voltage and stabilizing the output voltage by the voltage pulse width control unit, and the constant output voltage control caused by the fluctuation of the input power supply voltage are provided. In order to do this, the control method that detects the intermediate DC voltage and suppresses the fluctuation of the output voltage by the voltage pulse width control is used as the control method. Instead of speeding up the response to increase
It is possible to provide a method capable of realizing an extraordinary voltage source inverter that can use both functions in combination without promoting instability by sufficiently slowing down and can stably drive the induction motor.

[Brief description of drawings]

[0018]

FIG. 1 is a circuit diagram showing a voltage type inverter according to an embodiment of the present invention.

FIG. 2 is a configuration diagram showing an example of the voltage fluctuation detection circuit of FIG.

FIG. 3 is a circuit diagram showing a voltage type inverter in which a conventional output voltage change countermeasure means due to an input voltage change is incorporated.

FIG. 4 is a circuit diagram showing a voltage source inverter incorporating another conventional output resonance instability countermeasure means due to LC resonance.

[0019]

[Explanation of symbols]

 1 Three-phase AC power supply 2 Rectifier 3 Filter capacitor 4 Inverter unit 5 Induction motor 6 DC voltage detector 7 Voltage fluctuation detection circuit 10 Voltage calculation unit 11 Voltage calculation correction circuit 12 Pulse width modulation unit (PWM unit) 13 Adder 14 Integrator 71 Capacitor 72 Characteristic regulator 73 Amplifier

Claims (2)

[Claims] 1. A control method for stabilizing the inverter output voltage by detecting a change in the intermediate DC voltage of the inverter, and a method for detecting the intermediate DC voltage and controlling the output voltage to be constant with respect to the inverter input power supply voltage. A voltage source inverter control method characterized in that it is used together with a control method. 2. The voltage type inverter control method according to claim 1, wherein a predetermined delay time is set by a constant output voltage control method based on a change in the inverter input power supply voltage.