JP2668914B2 - Induction motor speed control device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a speed controller for controlling an input current of an induction motor, that is, a primary current to control a rotation speed of the motor.

[Prior Art] Conventionally, for example, as shown in FIG. 2, electric power supplied from a DC power supply 1 is converted into three-phase AC by an inverter circuit 3 via a smoothing capacitor 2 to convert the electric power into a three-phase AC. As a control device for driving the electric motor 4), there is a speed control device based on slip frequency control.

Generally, this speed control device determines the rotation speed fm of the motor 4 at that time and the rotation speed of the motor 4 from the speed command setting device 6 based on a detection signal detected by a speed detector 5 which detects the actual rotation speed of the motor 4. The speed command value fm * to be commanded is output to the subtractor 7. Then, the subtracter 7 subtracts by the speed command value fm * rotation speed fm to obtain a deviation Δfm (= fm * −fm), and outputs the deviation Δfm to the slip frequency setting device 8. The slip frequency setting unit 8 outputs a slip frequency fs uniquely determined with respect to the deviation Δfm prepared in advance to the adder 9 and the current amplitude calculation circuit 10. The adder 9 receives the rotation speed fm of the electric motor 4 detected by the speed detector 5 and adds the rotation speed fm and the slip frequency fs.
Is output to the current amplitude calculation circuit 10 and the command current calculator 11 as the primary frequency f (= fm + fs) of the input current (primary current). The current amplitude calculation circuit 10 calculates the amplitude value of the primary current of the motor 4 based on the primary frequency f and the slip frequency fs.
Calculates the I _1, and outputs to the next stage of the command current calculator 11. The command current calculator 11 calculates a speed command value fm commanded by the speed command setting device 6 based on the amplitude value I ₁ of the motor 4 and the primary frequency f.
In *, instantaneous value currents (hereinafter referred to as command currents) ia *, ib * for two phases for rotating the motor 4 are calculated. Then, the command currents ia *, ib * calculated by the command current calculator 11
Is output to the subtracters 12a and 12b.

The subtracters 12a and 12b input current detection values ia and ib at that time from current detectors 13a and 13b that detect instantaneous values of two-phase input currents among three-phase input currents input to the motor 4, respectively.
Deviation Δia (=) from the detected values ia, ib and command currents ia *, ib *
ia * -ia) and Δib (= ib * -ib) are obtained and output to the current control unit 14, respectively.

As shown in FIG. 3, the current control unit 14 includes a proportional integration circuit (hereinafter, referred to as a PI circuit) 16a, corresponding to each of the three phases composed of an operational amplifier 15, a capacitor C, and resistors R1, R2, and R3.
It is composed of 16b, 16c and one computing unit 17. Then, the PI circuits 16a and 16b proportionally integrate and amplify the deviations Δia and Δib, respectively, and output the proportionally integrated output signals Sa and Sb. Further, the PI circuit 16c also proportionally integrates and amplifies the deviation Δic (= − (Δia + Δib)) of the remaining one phase obtained by the calculator 17 for the deviations Δia and Δib, and outputs the proportionally integrated output signal.
Output Sc.

A pulse width modulation circuit (hereinafter referred to as a PWM circuit) 18 compares the output signals Sa, Sb, Sc of each phase with a carrier triangular wave to determine pulse width modulation, that is, a switching pattern of an inverter element in the inverter circuit 3. , And outputs a pulse train signal of each phase to the drive circuit 19.

The drive circuit 19 controls ON / OFF of each inverter element of the inverter circuit 3 based on the pulse train signal of each phase, and inputs the input current of each phase to the command current ia *, ib designated by the command current calculator 11. *, Ic * (=-(ia * + ib *))
Then, the rotation speed fm of the electric motor 4 is controlled to the speed command value fm * commanded by the speed command setter 6.

[Problems to be Solved by the Invention] However, each PI circuit constituting the current control unit 14
Since the values of the resistor R2 and the capacitor C in 16a to 16c are uniquely determined and fixed, the resistor R2 and the capacitor C are fixed.
The proportional integral constants (hereinafter referred to as PI constants) determined by are fixed, and it is difficult to obtain good motor control characteristics in a wide speed range. That is, for example, if the PI constant is set to ensure the motor control characteristics in the high rotation speed region, the gain increases in the low rotation speed region and the operational amplifier 15
There was a problem that the output balance of the PI circuits 16a to 16c was badly affected by the offset of the.

SUMMARY OF THE INVENTION An object of the present invention is to provide a speed control device for an induction motor capable of obtaining good control characteristics in a wide speed range from a low rotation speed to a high rotation speed in order to solve the above problems.

Means for Solving the Problems In order to achieve the above object, the present invention provides a speed detector for detecting the rotational speed of an induction motor whose drive is controlled by turning on and off each inverter element in an inverter circuit. And the input current of the induction motor is detected by the current detector, and the speed command is set based on the speed command value set by the speed command setter and the actual rotation speed detected by the speed detector. Calculate the command current value of each phase of the induction motor to obtain the rotation speed of the value, calculate the deviation between the command current value and the actual input current detected by the current detector, and proportionally calculate the deviation by the proportional integration circuit. After the integration, the output signal proportionally integrated by the pulse width modulation circuit is compared with a predetermined reference wave, the output signal is pulse width modulated, and the pulse width modulation signal is output to the drive circuit to drive the induction motor. Times In a speed control device for an induction motor configured to perform rotation control, a detection signal from a speed detector is input to the proportional-integral circuit, and the rotation speed of the induction motor is classified into three or more stages. A discriminating circuit for discriminating whether the motor belongs to the rotation speed region, a proportional integration constant setting circuit provided for each of the divided rotation speed regions, and a proportional integration constant for the rotation speed region being set; And a selection circuit for selecting a proportional integration constant circuit corresponding to the rotation speed region from among the respective proportional integration constant setting circuits.

[Operation] Based on the rotation speed region of the induction motor determined by the determination circuit at that time, the selection circuit selects a proportional integration constant circuit corresponding to the rotation speed region from the respective proportional integration constant setting circuits. Here, the rotational speed region of the induction motor is divided into three or more stages, and an optimum proportional integral constant is assigned to each region. As a result, the proportional integration circuit is changed to an optimum proportional integration constant corresponding to the rotation speed region by the selection, and the deviation between the command current value and the actual input current is proportionally integrated by the constant to perform the pulse width modulation circuit. Output to

[Embodiment] An embodiment of the present invention will be described below.
In this embodiment, for the sake of convenience of explanation, the configuration is the same as that of the conventional configuration except for the current control unit 14, and only the current control unit 14 having the features will be described. Further, since the PI circuits 16a to 16c of each phase of the current control unit 14 described below are substantially the same, the command current value ia * obtained by the subtractor 12a and the current detection value ia at that time are described for convenience of description. Only the PI circuit 16a that inputs the deviation Δia from and will be described.

In FIG. 1, an operational amplifier OP constituting a PI circuit 16a
The inverting input terminal of is input with the deviation Δia via the resistor Ra, and the non-inverting input terminal is grounded via the resistor Rc. Further, between the inverting input terminal and the output terminal of the operational amplifier OP, three types of PI constant setting circuits K1 to K3 for low, middle, and high rotation speed regions are connected in parallel with each other. Each setting circuit
K1 to K3 are resistors Rb1, Rb2, Rb3 and capacitors C1, C2, C, respectively.
3 and analog switches Sw1, Sw2, Sw3. Resistance Rb1, Rb2, Rb3 of each PI constant setting circuit K1 to K3
Resistance and the capacitance of capacitors C1, C2, C3 are operational amplifier OP
The PI constant is determined, and different values are set in advance.

In this embodiment, the resistance of the first PI constant setting circuit K1
The values of Rb1 and the capacitor C1 are suitable for controlling the rotation of the motor 4 in a low rotation speed region (0 <fm ≦ fm1) described later.
The resistance Rb2 of the second PI constant setting circuit K2 is set so that it becomes the I constant.
And the value of the capacitor C2 are set so that the electric motor 4
It is set in advance so that the PI constant is suitable for rotation control when 1 <fm ≦ fm2). Also, the third PI constant setting circuit
The values of the resistor Rb3 and the capacitor C3 of K3 are set to be PI constants suitable for controlling the rotation of the motor 4 in a high rotation speed region (fm2 <fm). That is, each PI constant is low,
The amplification rate of the operational amplifier OP is increased in the order of the middle and high rotational speed regions.

Therefore, if the electric motor 4 appropriately selects and turns on the analog switches Sw1 to Sw3 according to the rotational speed fm, the operational amplifier OP is set to an optimum PI constant, and the PI circuit 16a affects the rotational speed of the electric motor 4. It is difficult to carry out proportional integration, and the output signal Sa is output to the PWM circuit 18 in the next stage.

First and second hysteresis comparators (hereinafter, simply referred to as first and second comparators) 21 and 22 detect signals from the speed detector 5 (that is, the rotational speed of the motor 4).
fm), the first comparator 21 inputs a first speed reference value fm1 preset by the first speed region setting unit 23, and the second comparator 22 inputs the second speed region The first speed reference value preset by the setter 24
A second speed reference value fm2 (> fm1) larger than fm1 is input. The first speed reference value fm1 is a rotation speed that separates the low rotation speed region and the middle rotation speed region of the electric motor 4, and the second speed reference value fm2 separates the middle rotation speed region and the high rotation speed region of the electric motor 4. It is the rotation speed, and its value is appropriately selected according to the electric motor 4 to be controlled.

Then, the first comparator 21 compares the rotation speed fm with the first speed reference value fm1, and when the rotation speed fm of the electric motor 4 at that time is less than or equal to the first speed reference value fm1 (0 <fm ≦ fm1) ,
A signal having a logical value “L” (zero volt in this embodiment) is output. On the contrary, when the rotation speed fm is larger than the reference speed value fm1 (fm> fm1), the logical value “H” (5 volt in this embodiment) is output. )) Is output.

On the other hand, the second comparator 22 compares the rotation speed fm with the second speed reference value fm2, and when the rotation speed fm is equal to or less than the second speed reference value fm2 (0 <fm ≦ fm2), the logical value “L” is set. And outputs a signal of logical value "H" when the rotation speed fm is greater than the reference speed value fm2 (fm2 <fm).

In the present embodiment, the comparator 21 and 22 and the speed region setters 23 and 24 constitute a discrimination circuit, and the electric motor 4
Is rotating in the low rotation speed region (0 <fm ≦ fm1), both comparators 21 and 22 output a signal of “L”, and when the electric motor 4 is rotating in the high rotation speed region (fm2 <fm). Both comparators 21 and 22 will output the signal of "H". In addition, the electric motor 4 has a medium rotation speed range (fm1 <fm ≦ f
When rotating at m2) the first and second comparators
21 outputs an "H" signal, and the second comparator 22 outputs an "L" signal.

As a selection circuit, the decoder 25 has two input terminals x1, x
2 is connected to the output terminals of the comparators 21 and 22, and three output terminals Y1, Y2 and Y3 are connected to the analog switches Sw1, Sw2 and Sw.
Connected to 3. The decoder 25 determines the rotation speed region of the electric motor 4 at that time based on the logical values of the comparators 21 and 22 input from the input terminals x1 and x2, and turns on a corresponding one of the analog switches Sw1, Sw2 and Sw3. . That is, when both the comparators 21 and 22 are "L" and the motor 4 is rotating in the low rotation speed region (0 <fm≤fm1), the analog switch of the first PI constant setting circuit K1
Sw1 is turned on, the comparator 21 is “H”, the comparator 22 is “L”, and the motor 4 is in the middle rotation speed region (fm1
When rotating at <fm ≦ fm2), the analog switch Sw2 of the second PI constant setting circuit K2 is turned on. or,
When both the comparators 21 and 22 are at "H" and the motor 4 is rotating in the high rotation speed region (fm2 <fm), the analog switch Sw3 of the third PI constant setting circuit K3 is turned on.

The output terminals Y1, Y2, and Y3 of the decoder 25 are connected to the other two-phase PIs.
It is connected to each analog switch of the constant setting circuit and controls these analog switches in the same manner.

As described above, in this embodiment, the operational amplifier OP has the deviation Δ
When ia is input, proportional integration is performed, and the output signal Sa is output to the PWM circuit 18 of the next stage, the rotation speed of the motor 4 at that time is output.
The PI constant of the operational amplifier OP is selected and set to a PI constant most suitable for the rotational speed fm depending on which of the low, medium, and high rotational speed regions the fm is in. Δia is proportionally integrated while the output balance is well maintained, and output to the PWM circuit 18. As a result, good motor control characteristics can be obtained in a wide rotation speed range without changing the motor control characteristics at individual rotation speeds fm.

In the above embodiment, the reference values fm1 and fm2 for determining the low, middle and high rotational speed regions and the respective resistors R of the PI constant setting circuits K1 to K3 are used.
The values of b1 to Rb3 and the capacitors C1 to C3 are not particularly limited, but may be determined experimentally or theoretically according to the type of the electric motor 4, the control range, and the like.

Further, although three speed regions are set in the above embodiment, the number may be changed to four or more. In that case, the PI constant circuit is also changed according to the number. Then, better motor control characteristics can be obtained as the number is increased.

[Effects of the Invention] As described above in detail, according to the present invention, an induction motor can be favorably controlled in a wide speed range from a low rotation speed to a high rotation speed.

[Brief description of the drawings]

FIG. 1 is an electric block circuit diagram showing an electric configuration of a proportional integration circuit embodying the present invention, FIG. 2 is an electric block circuit diagram of a speed control device of an induction motor, and FIG. It is an electric block circuit diagram which shows an electric constitution. 1 is a DC power supply, 3 is an inverter circuit, 4 is a three-phase induction motor as an induction motor, 5 is a speed detector, 6 is a speed command setting device, 10 is a current amplitude calculation circuit, 11 is a command current calculation device,
13a and 13b are current detectors, 14 is a current control unit, 16a to 16c are proportional integration circuits (PI circuits), 17 is a calculator, 18 is a PWM circuit, 19
Is a drive circuit, 21 is a first hysteresis comparator forming a discrimination circuit, 22 is also a second hysteresis comparator, 23 is also a first speed region setting device, 24 is a second speed region setting device, and 25 is A decoder as a selection circuit, K1 to K3 are first to third proportional integral (PI) constant setters, Rb1 to Rb3 are resistors, C1 to C3 are capacitors, Sw1 to Sw3 are analog switches, OP is an operational amplifier, and fm is Rotation speed, fm
* Is speed command value, Δia, Δib, Δic is deviation, fs is slip frequency, f is primary frequency, ia *, ib *, ic * is instantaneous value current (command current), ia, ib is current detection value, fm1 , fm2 are first and second speed reference values.

Claims (1)

(57) [Claims] A drive circuit detects the rotation speed of an induction motor whose drive is controlled by turning on and off each inverter element in the inverter circuit by a speed detector, and detects an input current of the induction motor by a current detector. Detected by the detector
Based on the speed command value set by the speed command setting device and the actual rotation speed detected by the speed detector, a command current value of each phase of the induction motor for obtaining the rotation speed of the speed command value is determined. A deviation between the command current value and the actual input current detected by the current detector is obtained, the deviation is proportionally integrated by a proportional integration circuit, and the proportionally integrated output signal is output by a pulse width modulation circuit. In the speed control device for an induction motor, the output signal is pulse width modulated in comparison with a predetermined reference wave, and a pulse width modulation signal is output to the drive circuit to control the rotation of the induction motor. A discriminating circuit for inputting a detection signal from the speed detector to a proportional-integral circuit and discriminating to which of a plurality of rotation speed regions the rotation speed of the induction motor belongs in advance; A proportional integral constant setting circuit provided for each of the divided rotational speed regions, and a proportional integral constant for the rotational speed region is set; and a proportional integral constant circuit corresponding to the rotational speed region at the time determined by the determination circuit. And a selection circuit that selects from among the proportional-integral-constant setting circuits, and the speed control of the induction motor is such that the proportional-integral constant of the proportional-integral circuit is changed in three or more stages in accordance with the current speed of the induction motor. apparatus.