JPH0328915B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a control method for an inverter device whose load is an induction motor.

[Prior art]

Figure 1 shows the conventional slip frequency control method PWM.
1 is a schematic block diagram of a voltage controlled inverter device. In the figure, 1 is a three-phase AC commercial power supply, 2 is a converter circuit composed of a diode or thyristor, etc. that obtains a DC output from this three-phase AC commercial power supply,
3 is a DC voltage smoothing filter; 4 is an inverter main circuit composed of switching elements such as transistors; 5 is a load induction motor; 6 is a speed detector; 7 is a speed command circuit that provides a speed reference for the load motor 5; 8 is a speed detection circuit that detects the output signal of the speed detector 6; 9 is a slip frequency calculator that calculates the deviation between the output ω _ref of the speed command circuit 7 and the output ω of the speed detection circuit 8; 10 is a slip frequency calculator A voltage/frequency (V/F) converter that outputs a pulse train with a frequency proportional to the sum ω ₀ (=frequency command) of the output ω _s of the speed detection circuit 9 and the output ω of the speed detection circuit 8; 11 is a frequency command ω ₀ a voltage command circuit for outputting a voltage level commensurate with the V/F characteristics of the load motor 5 based on the received voltage;
1 is a reference voltage waveform forming circuit that receives the outputs of the voltage command circuit 11 and the V/F converter 10 and outputs a reference voltage waveform; 13 is a voltage detection circuit that detects the output voltage of the inverter main circuit 4; This is a PWM control circuit that outputs a signal that turns on/off the switching elements of the inverter main circuit 4 in accordance with the deviation between the voltage detection circuit 13 and the output of the voltage detection circuit 13.

FIG. 2 shows a rotational speed (ω)-output (P) characteristic diagram of the induction motor. In the figure, N ₀ is the base speed of the induction motor, which has constant torque characteristics in the region of 0<ω<N ₀ and constant output characteristics in the region of N ₀ ≦ω≦3N ₀ .

FIG. 3 shows the rotational speed (ω)-voltage (V) characteristics of the induction motor. This ω-V characteristic is a voltage characteristic necessary for a predetermined rated current to flow and to ensure a predetermined rated voltage.

Now, when an induction motor is driven by the inverter device shown in FIG. 1, the slip frequency calculator 9 controls the slip frequency ω _s by giving a limit value.
The conventional method was as shown in Figure 6. In the figure, 15 to 19 are resistors, and 20 is an operational amplifier. Here, by making the values of the resistors 17 and 18 equal, the output ω _s is limited to not exceed 1/2 of the output voltage of the operational amplifier 20.
As shown in FIG. 5, this limit value takes a constant value regardless of whether the rotation speed or the steady state is acceleration/deceleration, and this value is taken as the slip saturation value. Slip saturation value is 120% at maximum speed
It is set to the value required to generate torque.

By the way, in a constant output region, in order to generate the same torque for the same amount of change in slip, V ² /
ω needs to be constant at each rotation speed. However, since the induction motor exhibits the ω-V characteristic shown in FIG. 3, V ² /ω is not constant in the constant output region of N ₀ ≦ω≦3N ₀ . That is, ω=N ₀ and ω
=3N ₀ , the torque T for the same slip frequency ω _s changes as shown in FIG. As can be seen from the relationship: torque (T) ∝ current (I), this causes an overcurrent in the vicinity of the base speed of ω=N ₀ , which has the disadvantage of lowering reliability.

[Summary of the invention]

The present invention has been made to eliminate the above-mentioned drawbacks of the conventional inverter, and its object is to provide an inverter device that is stable and highly responsive without any transient current spikes even during severe sudden changes in speed. Therefore, the present invention makes the saturation value of the slip frequency ω _s variable during steady state and during acceleration/deceleration depending on the rotational speed.
Furthermore, since the present invention employs a digitally controlled inverter equipped with a microcomputer, variable control of slip saturation values for each rotational speed, which was extremely difficult in terms of hardware with conventional analog controlled inverters, can be easily performed. It also has the feature of being able to be realized.

[Embodiments of the invention]

FIG. 7 shows a block diagram of a PWM voltage controlled inverter device equipped with a microcomputer, which is an embodiment of the present invention. In the figure, the same reference numerals as in FIG. 1 indicate the same or equivalent parts, 21 is a current/voltage detection circuit that detects the current/voltage of the converter circuit 2 and the inverter main circuit 4, and 22 is a digital output of the analog output of the current/voltage detection circuit. A/D converter that converts into a value,
23 is a processing unit CPU, 24 is an input/output interface consisting of a dip switch/switchbox and an LED, and 25 is a converter firing angle command which receives a converter voltage command from the CPU 23 and a converter voltage feedback output from the A/D converter 22. 26 is a speed input interface that receives the speed command input from the input/output interface 24 and the speed feedback output from the speed detector 8 and issues a frequency command; 27 is the output of the speed input interface 26; Based on the reference voltage for PWM control
This is a reference sine wave generation circuit that generates frequencies.

The operation of the speed input interface 26 and its surroundings in FIG. 7 will be explained with reference to FIG. 8. A slip frequency ω _s is output according to the deviation between the speed command signal ω _ref from the input/output interface 24 and the speed feedback signal ω from the speed detector 8, but the saturation value of ω _s varies during steady state or during acceleration/deceleration. An appropriate pattern is selected depending on the speed ω. This slip saturation value pattern is
Read-on memory ROM built into 23
The data is stored in the memory, and is addressed and read out as appropriate by instructions from the CPU. That is, the CPU monitors the speed and switches from the acceleration/deceleration pattern to the steady state pattern as appropriate. This is the same as the conventional method in that the speed feedback signal ω is added to the slip frequency ω _s to obtain the frequency command ω ₀ . Steady state slip saturation value pattern is 120% at each rotation speed
This is a pattern necessary for generating torque. On the other hand, the slip saturation pattern during acceleration/deceleration is an appropriate pattern that does not affect acceleration/deceleration time. FIG. 9 shows a specific example of a pattern of slip saturation values. In the figure, the solid line is the slip saturation value pattern during steady state, and the broken line is the slip saturation value pattern during acceleration/deceleration. The slip saturation value during acceleration and deceleration is variable depending on the rotational speed, and is further made different from the slip saturation value during steady state.

〔Effect of the invention〕

As explained above, the present invention includes a memory that stores slip saturation value patterns corresponding to the steady state and acceleration/deceleration of the induction motor for each rotational speed of the induction motor, and monitors the speed of the induction motor during each operation. By easily controlling the slip saturation value during steady state and acceleration/deceleration depending on the rotational speed, it is easy to prevent excessive current overflow even during severe sudden changes in speed. Since it is possible to suppress the torque and generate a predetermined torque, it is possible to provide a stable and highly reliable inverter device.

[Brief explanation of the drawing]

Figure 1 is a schematic block diagram of a conventional slip frequency control type PWM voltage control type inverter device, Figure 2
Figure 3 shows the ω-P characteristic diagram of the induction motor, Figure 3 shows the ω-V characteristic diagram of the induction motor, and Figure 4 shows the ω _s characteristic diagram of the induction motor.
-T characteristic diagram, Fig. 5 is a conventional slip saturation value characteristic diagram, Fig. 6 is a block diagram of a conventional slip saturation value control method, and Fig. 7 is a block diagram of a microcomputer-equipped PWM voltage-controlled inverter device of the present invention. , FIG. 8 is a block diagram of the slip saturation value variable control system of the present invention, and FIG. 9 is an explanatory diagram of the slip saturation value pattern. 1...Three-phase AC commercial power supply, 4...Inverter main circuit, 5...Induction motor, 8...Speed detector, 2
4...I/O (input/output) interface, 23...
...CPU, 26...Speed input interface.

Claims (1)

[Claims] 1. In a slip frequency control type inverter device that uses an induction motor as a load and is equipped with a slip saturation value setting means, a memory that stores slip saturation value patterns corresponding to the steady state and acceleration/deceleration of the induction motor for each rotational speed of the induction motor. and pattern switching means for monitoring the speed of the induction motor and switching to a slip saturation value pattern during each operation, and controlling the slip saturation value at the time of deceleration of the induction motor according to the rotational speed of the induction motor. A slip frequency controlled inverter device characterized in that the slip frequency is variable and the slip saturation value is set to a value different from the steady state slip saturation value.