JPH0619355Y2 - Current source inverter for induction motor drive - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention relates to a constant current type inverter for driving an induction motor.

(Prior Art) Generally, when an induction motor is driven by a constant current type inverter, constant V / f control is performed to make the motor voltage proportional to the frequency. That is, the output voltage command of the inverter is automatically determined corresponding to the frequency command, and the difference between this voltage command and the voltage feedback signal is taken and converted into a current command via the amplifier / regulator, and further with the current feedback signal. A deviation is taken between the two and converted into a gate signal of the forward converter thyristor via a phase shifter.

This voltage control system is a normal control system with a current minor loop, and in a constant speed operation state without acceleration / deceleration, the motor current is supplied with a value commensurate with the load torque, resulting in stable operation.
During acceleration or deceleration, the transfer function of the motor changes and the motor torque and the motor current are not in a proportional relationship. That is, the current according to the electric motor torque is not fed back, the required torque cannot be generated, and smooth acceleration / deceleration cannot be performed, resulting in erratic tuning.

Therefore, conventionally, a method has been adopted in which the PI time constant of the voltage control system adjuster is set to be in a stable state during acceleration / deceleration, and the transient response during constant speed rotation is sacrificed.

(Problems to be solved by the invention) It is to solve problems such as disturbances during acceleration / deceleration without affecting control performance during constant speed operation.

(Means for Solving Problems) A ramp function generator that compares and amplifies inputs and outputs to form an integrator input, and that the acceleration / deceleration occurs when the comparative amplification output of the ramp function generator is a certain value or more. An acceleration / deceleration detection circuit for judging and a resistance / capacitor switching means for switching the PI time constant of the voltage regulator according to the output of the detection circuit are provided.

(Operation) Acceleration / deceleration is detected by comparing the input / output voltage of the ramp function that converts the frequency command to the ramp voltage command, and the detection output activates the relay circuit to switch the constant of the voltage regulator to accelerate / decelerate. The RC time constant at time is made short and the damping constant is made large, and the output of the regulator, which is a current command, is enhanced so as to generate the torque necessary and sufficient for acceleration / deceleration.

(Embodiment) FIG. 1 is a block diagram of an embodiment, and FIG.
The figure shows the acceleration / deceleration detection circuit, and FIG. 3 shows the main circuit. In the control system block diagram of FIG. 1, (1) is a ramp function generator that converts a frequency command into a ramp voltage command,
(2) is a voltage regulator, (3) is a current regulator, (4) is a phase shifter,
The difference between this voltage command and the voltage feedback signal is converted to the current command of the current minor loop via the voltage regulator (2), and compared with the current feedback signal, and after the comparison result is amplified by the current regulator (3), It becomes the gate signal of the forward converter thyristor through the phase shifter (4), and controls the inverter output voltage to the command voltage determined by the V / f constant control. Further, (5) is a V / f converter, and (6) is a gate distributor, which converts the ramp-shaped voltage command into a pulse signal of frequency command, the inverse converter determines the firing cycle of each thyristor, and determines the inverter output frequency. To match the command frequency.

In this way, the control system is divided into two systems, a forward converter that controls the output voltage of the inverter and an inverse converter that controls the output frequency. The ramp function generator (1) is used, and if the integrator input of the comparison amplification is a certain value or more, the acceleration / deceleration detection circuit (7) that determines whether acceleration or deceleration is in progress and the relay element (8 ) Is operated to switch the PI time constant of the voltage regulator (2), the resistance / capacitor switching means (9) is provided. That is, the voltage regulator (2) is composed of the feedback constant of the capacitor C and the resistor VR during constant speed operation without acceleration / deceleration, but the output is generated in the acceleration / deceleration detection circuit (7) during acceleration / deceleration. When the element operates, the feedback constants of the capacitor C ₁ and the resistors R ₁ and VR ₁ are newly connected in parallel.
As a result, the PI time constant is short, the damping constant is large, the output current command is increased, and the output torque is increased.

In FIG. 2, (7) is an acceleration / deceleration detection circuit, which includes a diode OR DOR, a comparator CP, and a relay element X. (1) is a ramp function generator, which includes an operational amplifier OP ₁ for input / output comparison amplification, input resistances R ₂ , R ₃ , a sign converter T, anti-parallel diodes D ₁ , D ₂ for acceleration / deceleration, and an adjustment resistance VR. ₂ , VR ₃ , input resistors R ₄ , R ₅ , feedback capacitor C ₂ , and operational amplifier OP ₂ . That is, when the frequency command U ₁ and the voltage command U ₂ of the lamp output are used as the input signal of the operational amplifier OP ₁ , and there is a difference between these U ₁ and U ₂ , the difference is taken out as the output of the operational amplifier OP _{1 and is} output to the comparator. The presence / absence of acceleration / deceleration is discriminated via CP to determine whether or not the biasing of the relay element X is possible. The frequency command U ₁ is newly set and the output lamp voltage command U ₂ is increasing and U ₁
When> U _2, the output of the operational amplifier OP ₁ has reached saturation, the output of the comparator CP is H, the relay element X is energized, and the series path of the capacitor C ₁ resistor R ₁ of the voltage regulator (2) is grounded. From the state, it is connected to the adjustment resistor VR ₁ on the input side. That is, the damping constants of C ₁ , R ₁ , and VR ₁ are newly connected, the time constant becomes short, the output becomes large, and the current command increases. Similarly, during deceleration, the frequency command U ₁ and the voltage command ramp output U ₂ do not match, and the operational amplifier O
Although the P ₁ output is saturated, it has a negative saturation because of the relationship of U ₁ <U ₂ , and is converted to a positive saturation value via the sign converter T.
It is input to the comparator CP via the diode OR DOR and energizes the relay element X.

The damping constant of this voltage regulator (2), C ₁ R ₁
Is connected between the output of the operational amplifier OP ₁ and the ground during constant speed operation, and is connected to the input side during acceleration / deceleration.
The inrush current of ₁ does not have to be taken into consideration, and switching of the damping constant does not have a bad effect on the control system such as a shock, and smooth switching can always be performed.

The current source inverter main circuit is shown in FIG. 3, which is composed of a forward converter (10) for controlling the output voltage, a DC reactor (11), and an inverse converter (12) for frequency control. The voltage control system controls the gate phase of the forward converter thyristor, and the frequency control system controls the firing period of the inverse converter thyristor.

(Effect of the Invention) In this invention, in a constant current type inverter provided with a ramp function generator that gives each command of voltage and frequency by a ramp function, the input / output voltage of the ramp function generator is compared through an operational amplifier. Acceleration / deceleration is determined with a simple configuration, and the PI time constant of the voltage regulator is switched via a relay element according to the determination signal.
It is not necessary to set the voltage controller PI time constant to a value commensurate with the acceleration / deceleration operation to sacrifice the transient response in the constant speed operation, regardless of whether the acceleration / deceleration or the constant speed is performed. The optimum control response characteristic can always be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of an embodiment, FIG. 1 shows the entire control system, FIG. 2 shows an acceleration / deceleration detection circuit, and FIG. 3 shows a main circuit. (1) ...... Ramp function generator (7) ...... Acceleration / deceleration detection circuit (8) ...... Relay element (9) ...... Resistance capacitor switching means

Claims (1)

[Scope of utility model registration request] A ramp function generator for converting a frequency command into a lamp output is provided, and the ramp output is used as a voltage command and a frequency command to control each thyristor of a forward converter and an inverse converter to drive an induction motor. In the induction motor driving current source inverter, the ramp function generator is composed of an operational amplifier that compares the frequency command and the ramp output and amplifies the difference, and an integrator that integrates the output of the operational amplifier, If the output of the operational amplifier is a certain value or more, it is judged as acceleration / deceleration, and an acceleration / deceleration detection circuit for outputting the output, and a relay element is operated by the output of the acceleration / deceleration detection circuit, and the output terminal of the voltage regulator and the ground An induction current characterized by comprising a resistor / capacitor switching means for switching a series path of a resistor / capacitor inserted between the ground side and the input side of the voltage regulator. Machine driving current source inverter.