JPS5972996A - Control system for inverter - 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] This invention relates to a control method for variable speed control of a fossil motive machine using an inverter device.In general, wind and hydraulic equipment such as fans and pumps are There is a lot of demand for it because it allows for significant power savings, and in that case, the electric motor for driving hydraulic equipment is
Squirrel-cage induction tunnel engines are commonly used. An inverter device is known as a controller that can control the speed of this squirrel cage induction motor in the most ideal manner.In such an inverter device, the ratio of the output pressure to the frequency (V/
A constant V/F control method is adopted in which the F ratio is kept constant. By the way, if the capacity of the inverter device is sufficiently large compared to the total capacity of the AC motors connected thereto, no particular technical problem will occur with the drive system as a whole. However, if the rotation speed of wind and water power equipment is controlled to save electricity, the power required for the electric motor will be less, so from an economical point of view, it is possible to use a relatively small capacity motor that is commensurate with this power. An inverter device will be used. On the other hand, the rotation speed vs. torque characteristic of wind and hydraulic equipment has a square-law reduction torque characteristic (a characteristic in which the required torque decreases as the square of the speed as the rotation speed decreases), so the rotation speed slightly exceeds a predetermined value. Even so, relatively large driving power is required, so there is a risk that the inverter device will immediately become overloaded and stop. Of course, if slip control or vector control technology is applied to control the illumination of the n1 inverter device, an ideal inverter device will be created and the problem will be solved, but there is a drawback that the device will become complicated and expensive.

The present invention has been made in view of the above, and an object of the present invention is to provide a control system that can control an AC motor having the above-described reduced torque characteristic with high precision using a simple configuration.

Its feature is that when an AC motor with reduced torque is driven by an inverter, by adding an electric current compensation loop to the inverter's V/F-water control loop,
The point is that the control characteristics are improved.

Hereinafter, embodiments of this invention will be explained with reference to the drawings.

Fig. 1 is a block diagram showing an embodiment of the present invention, and Fig. 2 is a characteristic diagram showing rotational speed vs. torque or current characteristics.
In FIG. 1, 1 is an AC power supply, a 2-digit inverter (inverse converter), 3 is a control section of the inverter, 4 is a voltage detector,
5 is in the air? i! 1'1 detector, 6 is an AC motor, and the inverter control unit 3 further includes a speed setting device 31 and a current setting device 3.
2, adder 33, acceleration/deceleration calculator 34, % flow control pottery (AC
R) 35, an output side unit 36, a frequency control system 37, and a voltage control system 38. Inverter 2 is general 3! Any converter that can be supplied with AC power 1 and convert it to another voltage 1 frequency is sufficient, so-called voltage type I'7
Converters such as cycloconverters as well as Harter and current source inverters can be used.

*The speed signal N set by the speed setter 31 is given to the frequency control system 37 and the voltage control system 38 through the acceleration/deceleration calculator 34, so the frequency control system 37 adjusts the output frequency of the inverter while controlling the voltage. The controller 38 automatically adjusts the actual output voltage value of the inverter (detected voltage value obtained via the voltage detector 4) to a value that corresponds to its speed setting, thereby increasing the ratio of the output voltage of the inverter device to its frequency. Although the V/F ratio is controlled to be constant, the acceleration/deceleration calculator 34 performs a predetermined calculation based on the input signal, and calculates the characteristic as shown in block 34 in FIG. 1, for example. It is also called a pattern generator or soft start circuit. Up to this point, it can be said that the configuration and functions are necessary for a normal inverter device, but in this embodiment, the following is further implemented by a current detector 5, a current setter 32, a current 'tHtIrI regulator 35, and an output limiter 36. The following control is performed.

That is, the output current of the inverter 2 is determined by the current detector 5.
The current is detected by the rtL flow regulator 35, compared with the current setting value I* from the current setting device 32, and amplified. Output limiter 36 limits the output of current regulator 35 to only one polarity. That is, the current W4 node output is given to the adder 33 only when the detected output current value of the inverter 2 is larger than the set value I set by the current setter 32*.

* Note that the current setting II is selected to be the allowable output current value of the inverter 2. Therefore, in the adder 33, the Ni17! The output of the regulator 35 and the speed * setting signal N are added and given to the acceleration/deceleration wave n unit 34. Note that the output of the current n unit 35 is given as a negative signal, so a predetermined amount is subtracted from the setting signal N and given to the acceleration/deceleration calculator 34, and the V/F-water control is performed based on the output. will be carried out.

Assume now that the load characteristics of the AC motor 6 are as shown in FIG. In the same figure, ■ indicates torque characteristics, and ◎
respectively indicate the current characteristics. Here, when the rotational speed of the AC electric motor It'A6 increases and reaches the speed N, and then increases further, the output current of the inverter circuit 2 also increases with the rapid increase in the rotational torque TM, and its allowable output The current value will be exceeded. Therefore, in this embodiment, the current detector 5, the current setter 32, the current PJ'1f
A motor current compensation loop consisting of an inverter 35 and an output limiter 36 is provided, and when the output current exceeds the allowable value, the speed setting value N is reduced, that is, the rotational speed of the AC motor 6 is lowered. This is to suppress the output current value within the permissible value. Therefore, the inverter device is protected from overload, and unnecessary stoppage of the AC movable machine.
Furthermore, it is possible to avoid stopping the entire system including the inverter device, and it is also possible to widen the speed side glIIin. In general, v
Since there are many cases where reduced torque characteristics are required for the load characteristics of UBTS, the scope of application of the present invention can be said to be wide-ranging. In other words, the present invention is effective when applied to inverter devices that drive wind and hydraulic equipment such as fans and pumps, and is particularly effective for energy-saving devices such as fans and pumps.
The effect is fully exhibited in cases where the inverter device is applied for operation.

As described above, according to the present invention, when an AC motor with reduced torque characteristics is driven by an inverter, the motor is added to the V/F constant control loop! Highly accurate control is possible by simply providing a μ flow compensation loop.

Since it is a simple type that does not use a speed detector or speed regulator, it also has the advantage that it can be easily applied to existing systems.

[Brief explanation of the drawing]

Figure 941 is a block diagram showing an embodiment of this invention. $2
The figure is a characteristic diagram showing speed vs. torque or current characteristics. Description of symbols 1...AC power supply, 2...Inverter (inverse converter), 3...Inverter control unit, 4...
・Voltage detector, 5... Current detector, 6... Song alternating current masticator, 31... Song speed setting device, 32......m
Facility determiner, 33... Song comparison unit, 34... Acceleration/deceleration calculator, 35... Song/current 1 node (80R), 36... Song output limiter, 37... ...Frequency control system, 38...
...Voltage control system agent Patent attorney Akio Namiki Patent attorney Kiyoshi Matsuzaki

Claims (1)

[Claims] The specified AC power is converted to one of nine other voltages and frequencies to supply power to the load, and the output voltage to output frequency ratio (V/F
), and an acceleration/deceleration calculator that calculates the voltage and frequency settings from the speed settings. , the inverter device includes a detection means for detecting its output current, a current rA pre-means for performing a key 1Ir1 calculation to make the detected value coincide with a predetermined current setting value, and the detection F! output limiting means for validating the output of the current regulating means only when the current value exceeds the set value;
An inverter control method characterized in that the speed setting value is changed by an adjustment output to control the voltage and frequency of the inverter.