JPH0619356Y2 - Inverter variable resistance setting device - Google Patents

Description

TECHNICAL FIELD The present invention relates to a voltage / frequency variable resistance setting device for an inverter used for speed control of an induction motor.

2. Description of the Related Art Generally, an inverter converts a commercial AC power source into a direct current, modulates this direct current into a pulse width to convert it into an alternating current, and drives an induction motor. However, the voltage V / frequency F supplied to the induction motor is used.
The characteristics must be supplied by selecting the V / F ratio according to the characteristics of the load. As shown in FIG. 4, in the left half 2 of the rotation angle of the variable resistor 1, the constant torque load H ₁ ~ shown in FIG.
So as to select the V / F characteristics of the H 8 _(H characteristics), P ₁ ~ the right half 3 in the third, as shown in FIG square lower limit torque load
The V / F characteristic of P ₈ (P characteristic) can be selected. In the selection of the V / F characteristic by this method, the H characteristic and the P characteristic may coexist in the vicinity 4 of the boundary point of the left and right rotation angles of the variable resistor 1. Therefore, the selection of the V / F characteristic of the variable resistor 1 is performed. Since the output of the variable resistor 1 is subjected to analog / digital conversion and digitally controlled, there are problems such as conversion error, resolution, and stability of the variable resistor 1 near the boundary point 4 of the variable resistor 1.
However, there is a drawback that the V / F characteristics cannot be properly selected in the above.

EXAMPLE A control circuit for an inverter that is generally used will be described with reference to FIG. _1. Reference numeral 10 is a bridge diode D _1.
A full-wave rectifier composed of D ₆ to forward-converts the three-phase power supplies R, S, and T into direct current, and 11 is an inverter that reverse-converts direct current to obtain alternating current output and is connected to the direct current side of the full-wave rectifier 10. And transistors D _{1 to} T ₆ are connected in antiparallel with diodes D _{7 to} D ₁₂ . 12 is an AC motor connected to the output of the inverter 11 , 13 is a voltage smoothing capacitor, 14 is an I / O port for expanding the arithmetic processing function, 1
Reference numeral 5 is a central processing unit to which the output of the I / O port 14 is applied, 16 is an analog / digital converter, and 17 is a V / F.
A + 5V DC power source is applied to the variable resistor that selects a pattern, the setting output of the variable resistor 17 is converted from analog to digital by the analog / digital converter 16, and 18 is a memory circuit for storing a plurality of V / F patterns. , 19 are driver units, and the pulse width modulation output obtained by the arithmetic processing by the central processing unit 15 is applied through the I / O port 14 and the timer 20. The output of the driver unit 19 is the inverter 1
The first transistor _T 1 through T ₆ and the pulse width control for a variable speed drive AC motor 12.

The V / F characteristic is selected according to the load characteristic of the AC electric motor 12 by the rotation of the variable resistor 17. Generally, the following is provided between the torque (T) and the voltage (V) frequency (F) of the AC electric motor 12. Have a relationship.

T = K (V / F) ² (1) (K is a constant) To keep the torque T constant from the equation (1), (V / F)
The ratio needs to be constant. When the frequency F is changed, the output voltage V is also changed to keep the V / F ratio constant. However, since the AC motor 12 has a loss such as copper loss, the voltage V is slightly increased in the low frequency region to increase the torque. T constant torque characteristics so that Keru not a near-constant characteristic (H characteristics) until H ₁ to H ₈ as an example V / F characteristic as shown in FIG. 2 8
As described above, the selection of the H _{1 to} H ₈ characteristics is performed in the left region 21 of the rotation angle of the variable resistor 17 shown in FIG.

Further, from the formula (1), in the case of the AC motor 17 used for the fan, the pump, etc., the squared reduction torque characteristic (P characteristic) is required, and the V / F characteristic is P ₁ as one embodiment shown in FIG. ~
The selection of the eight V / F characteristics of P ₈ is performed in the right side region 22 of the variable resistor 17.

Therefore, in the present application, when the V / F characteristic is selected by the variable resistor 17, as shown in FIG. 5, it belongs to any of the H characteristic and P characteristic between the left side region 21 and the right side region 22 of the variable resistor 17. In the region of the dead zone 23, H ₈ is provided.
The output is stopped without belonging to any of the characteristics and P ₁ characteristics, and H ₈
The characteristic and the P ₁ characteristic are prevented from being selected by mistake. The DC output of the variable resistor 17 is 0 to 5 V, and this DC output is analog / digital converted by the 8-bit analog / digital converter 16, and the digital value becomes 0 to FFH. To divide the digital value 0 to FFH into 17 equal parts, divide by 15 to obtain 0 to 11H, which is H ₁ shown in FIG.
Area is 0, H ₂ area is 1, and P ₈ area is 11H. When the dead zone 23 is 8, it becomes a dead zone where the output is zero.

Next, the operation of the variable resistor 17 for selecting the V / F characteristic will be described based on the flowchart of FIG. 6. In step, it is judged whether the set output frequency value FRQ of the variable resistor 17 is 0, and if it is 0, Step by step variable resistor 17
Analog / digital conversion value ADCVR of the voltage setting value of
The current value obtained by dividing 15 by 15 is Vf1, and when the variable resistor 17 is set to the dead zone 23 in step, Vf1 =
If 8 is judged and the answer is yes, the flag (vfFLAG) on the RAM is set to 1 in step, the release counter VfC is reset to 0 in step, and operation commands such as frequency setting and forward / reverse operation are set in step. Judge
In step, it is determined whether or not the flag VfFLAG is 0, and if it is not 0, in step the inverter stop processing is performed. If the current value Vf1 of (converted value ADCVR / 15) is other than 8 in step, the result is no, and if the release counter VfC has not reached the set number A in step, no.
Then, the release counter VfC + 1 is incremented in step,
The operation command is judged in the step, and the flag V is detected in the step.
When fFLAG is not 0, the inverter performs stop processing in step. When the release counter VfC reaches the set number A in step, the determination result becomes yes and in step the flag Vf
FLAG becomes 0 and resets, the operation command is judged in step, flag VfFLAG becomes 0 in step, and yes when the determined value Vf of (conversion value ADCVR / 15) is smaller than 8 and V in step
/ F ratio setting the V / F characteristics of the H ₁ to H ₈ corresponding performs arithmetic processing of the output voltage in step, to operate the inverter outputs a pulse width modulated voltage pattern at step. When the determined value Vf of (conversion value ADCVR / 15) is larger than 8 in step, it becomes no, and in step 41, the V / F characteristic of P _{1 to} P ₈ corresponding to the V / F ratio is set, and through step, Operate the inverter.
Although the present application has described the example of selecting the V / F characteristic of the inverter by the rotation of the variable resistor 17, anything that selects two different types of characteristics by the variable resistor can be applied, for example, a robot controller, It can be applied to temperature controllers.

Effect of the Invention As described above, in the present invention, in the inverter that selects the V / F characteristic by the variable resistor, when selecting two different V / F characteristics in the left and right regions of the rotation angle of the variable resistor, A dead zone is provided between them, and has the following effects.

(1) Two types of different V / F characteristics can be selected without error without considering the error and resolution accuracy of analog / digital conversion of the variable resistor and the stability of the variable resistor itself.

(2) Since a dead zone is provided at the boundary point of two different V / F characteristics, two kinds of V / F characteristics in the vicinity of the boundary point will not be erroneously selected. However, it is possible to provide a function that is not required for the P characteristic, and conversely, a function that is required for the P characteristic but not required for the H characteristic, and a separate function with one terminal. As an example, in the range of the H characteristic, the two-step speed switching function of the induction motor can be provided, and in the range of the P characteristic, the upper and lower limit setting function of the induction motor can be provided by one terminal.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of an inverter variable resistance setting device according to the present invention, and FIG. 1 is a basic circuit diagram of an inverter,
FIG. 2 is a V / F characteristic diagram of a constant torque characteristic, FIG. 3 is a V / F characteristic diagram of a square low limit torque characteristic, and FIG. 4 is a V / F of a conventional example.
Figure of variable resistor for selecting characteristics, Fig. 5 shows V /
FIG. 6 is a diagram of a variable resistor for selecting the F characteristic, and FIG. 6 is a flow chart for explaining the V / F characteristic selecting operation. 14 is an I / O port, 15 is a central processing unit 16 is an analog / digital converter, 17 is a variable resistor, 18 is a memory circuit, 19 is a driver unit, 20 is a timer, 21
Is a left side area, 22 is a right side area, and 23 is a dead zone.

Claims (1)

[Scope of utility model registration request] 1. An I / O port for applying an analog / digital conversion output of a variable resistor, a memory circuit storing a plurality of voltage / frequency patterns selected by the output of the I / O port, and a memory circuit of the memory circuit. In the central processing unit for processing the voltage / frequency pattern and the output of the I / O port, and the inverter for controlling the pulse width by the output of the central processing unit via the timer and the driver unit, the rotation region of the variable resistor And a different voltage / frequency pattern set by the digital converted value according to the DC output obtained in step 1) is set in the left / right rotation area of the variable resistor, and different voltage / frequency patterns are set at the boundary points of the left / right rotation area of the variable resistor. A variable resistance setting device for an inverter provided with a dead band of zero output that is not set in any of the frequency patterns.