JPH05103485A - Inverter - Google Patents

Abstract

PURPOSE:To enhance a decelerating capacity by calculating a switching output according to a function wherein a DC voltage is a rated value for a DC voltage of a smoothing capacitor at the time of decelerating and outputting it to an inverter circuit. CONSTITUTION:A switching output calculator 14 calculates a switching output according to a function wherein a DC voltage is a rated value for a DC voltage of a smoothing capacitor 2 at the time of decelerating, and thus calculated switching output is delivered to an inverter circuit 3. Thus, even if the DC voltage of the capacitor 2 is raised by the regenerative power of an induction motor 8, the circuit 3 is driven by the switching output calculated according to the function of the rated value, and the output voltage of the circuit 3 is raised corresponding to an output frequency raised in proportion to the function of the rated value. Thus, an exciting current to the motor 8 is increased, and a loss of a winding is increased. In this manner, a regenerative current to the circuit 3 is reduced as compared with that of prior art to enhance a decelerating capacity.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inverter device for controlling the speed of an AC motor, and more particularly to regenerative electric power to the inverter device.

[0002]

2. Description of the Related Art FIG. 4 is a block diagram showing a conventional inverter device, and FIG. 5 is a graph showing a relationship between an output frequency and an output voltage of the inverter device. In the figure, 1 is a converter circuit that is a rectifier circuit that converts an AC voltage of an AC power supply 7 into a DC voltage, 2 is a smoothing capacitor that smoothes the DC voltage of the converter circuit 1, and 3 is a switching element that is turned on at a predetermined timing. An inverter circuit, which is an inverse conversion circuit that converts the DC voltage of the smoothing capacitor 2 into an AC voltage of a predetermined frequency when turned off, 4 is a microcomputer for PWM controlling the inverter circuit 3, and 5 is a switching element of the inverter circuit 3. A reference numeral 6 is a base amplifier for outputting the PWM signal, a reference numeral 6 is a direct current voltage detection circuit for detecting the direct current voltage of the smoothing capacitor 2, and a reference numeral 150 is an inverter device composed of the converter circuit 1 to the direct current voltage detection circuit 6. Reference numeral 8 is an induction motor driven by the AC voltage of the inverter circuit 3, and 200 is a driving command device that gives a driving command to the inverter device 150. The driving command device is a microcomputer 21, a key sheet 22, and a display 2.
3, the inverter device 150 can be set with forward, reverse, and stop operation commands and output frequency operation commands.

The operation when the induction motor 8 is operated by the conventional inverter device 150 configured as described above will be described with reference to the operation flowchart of FIG. First, for example, a normal rotation operation command is input from the operation command device 200, and then an operation command for the output frequency is input to start the operation (step S1). Next, it is determined whether or not the microcomputer 4 is stopped by checking whether or not a stop flag is set in the microcomputer 21 of the operation command device 200 (step S2). Then, when it is determined that the operation is not stopped, the microcomputer 4 reads the operation command of the output frequency set to the predetermined frequency (step S3), and when it is determined that the operation is stopped, the microcomputer 4 outputs the output frequency of 0 Hz. The command is read (step S4). Thereafter, the microcomputer 4 reads the DC voltage detected by the DC voltage detection circuit 6 (step S5), and calculates the switching output by a function such that the output frequency of the DC voltage is always the commanded value ( In step S6), the switching output is output to the bearer amplifier 5, the switching element of the inverter circuit 3 is driven by the PWM signal, and the AC voltage of the output frequency set by the inverter circuit 3 is output (step S7).

The calculation of the switching output in step S6 described above is such that the output voltage is uniquely determined for an arbitrary output frequency as shown in FIG. 5, and even if the DC voltage of the smoothing capacitor 2 changes, the output at the same frequency is output. The voltages are calculated to be the same. That is, even if the DC voltage changes, the output voltage is always calculated to have the value shown in FIG. Next, a case where the induction motor 8 is decelerated will be described. The speed of the induction motor 8 is reduced by reducing (decreasing) the output frequency of the inverter device 150. At this time, the induction motor 8 serves as a generator to supply or regenerate the electric power to the inverter device 150. As a result, the smoothing capacitor 2 is charged by the regenerative power and the DC voltage rises, but the output voltage becomes a constant value with respect to the output frequency as shown in FIG. 5 as described above. When the rise of the DC voltage of the smoothing capacitor 2 exceeds a predetermined protection level value, the output is shut off to protect the inverter device 150 from overvoltage, but the protection operation works and the inverter device 150 operates.
To prevent as much as possible from tripping, when the DC voltage reaches a specified value below the protection level value, the frequency is stopped once to suppress the increase of the DC voltage, and when the DC voltage becomes smaller than the specified value, Decelerates by repeating the operation of decelerating.

[0005]

In the conventional inverter device 150, even if the DC voltage of the smoothing capacitor 2 changes, the switching output is calculated by a function such that the output frequency always has a commanded value with respect to the DC voltage. However, since the inverter circuit 3 driven by the switching output outputs a predetermined output voltage corresponding to the set output frequency, when the output frequency is reduced to decelerate the induction motor 8, The DC voltage of the smoothing capacitor 2 rises due to the regenerative electric power from the induction motor 8, which may damage the inverter device 150. Therefore, in order to repeat the operation of once stopping the deceleration of the induction motor 8, that is, lowering the output frequency when the DC voltage rises above a predetermined value, and decelerating again when the DC voltage becomes smaller than the predetermined value, There was a problem that the deceleration of the induction motor 8 took longer than a desired time, or the overvoltage protection operation of the inverter device 150 worked.

Further, as shown in Japanese Utility Model Laid-Open No. 62-11396, when the capacitor voltage rises to a predetermined value, the lowering of the frequency of the inverter is interrupted, and the frequency until the capacitor voltage drops to a predetermined value is maintained. , JP-A-1
The rate of increase in the DC voltage is calculated by a differentiating circuit or the like as disclosed in Japanese Patent No. 152967, and the speed command is corrected so as to suppress the deceleration gradient when the specified value is reached, and the output frequency is sequentially decreased. Some of them have been made to stop, but the problem that it takes time to decelerate the AC motor still cannot be solved.

As a measure for solving such a problem, a DC power consumption type braking method, that is, an inverter, as shown in JP-A-63-48176, JP-A-1-143296 and JP-A-3-60389. When the voltage rise of the DC circuit in the equipment is detected and when this voltage rises above a certain value, a current is passed through a resistor connected in parallel with the capacitor and the braking energy is consumed as Joule heat. However, there are new problems such as increased cost and larger inverter unit. The present invention has been made to solve the above problems, and an object thereof is to obtain an inverter device which is inexpensive and has an improved deceleration capability.

[0008]

An inverter device according to the present invention comprises a converter circuit for converting an AC power supply into a DC power supply,
An inverter circuit that converts the output voltage of the converter circuit into an AC voltage of a predetermined frequency via a smoothing capacitor, and a DC voltage detection circuit that detects the DC voltage of the smoothing capacitor,
During operation other than deceleration, the switching output is calculated by a function that always has the same output frequency with respect to the DC voltage of the smoothing capacitor, and during deceleration operation, when the DC voltage is the rated value with respect to the DC voltage of the smoothing capacitor. A switching output calculation circuit that calculates a switching output by a function and outputs it to the inverter circuit is configured.

[0009]

In the present invention, the switching output arithmetic circuit performs switching output with a function that always has the same output frequency with respect to the DC voltage of the smoothing capacitor detected by the DC voltage detection circuit during the acceleration and constant speed operations other than deceleration. Is calculated and output to the inverter circuit, the output voltage output from the inverter circuit 3 is uniquely determined by the output frequency even if the power supply voltage of the AC power supply 7 changes and the DC voltage of the smoothing capacitor 2 changes. And a predetermined output voltage. Further, during deceleration operation, the switching output calculation circuit 4 calculates the switching output by a function when the DC voltage is the rated value with respect to the DC voltage of the smoothing capacitor 2 and outputs it to the inverter circuit. Even if the DC voltage of the smoothing capacitor 2 rises due to the power, the inverter circuit 3 is driven by the switching output calculated by the function of the rated value, and the output voltage of the inverter circuit 3 becomes equal to the DC voltage of the smoothing capacitor 2. As a result of the increase, the output frequency increases in proportion to the function of the rated value. When the output voltage rises in this way, the exciting current to the induction motor 8 increases, and the loss in the winding of the induction motor 8 increases.

[0010]

1 is a book diagram showing an embodiment of the present invention, and FIG. 2 is a block diagram showing the relationship between the output frequency and the output voltage of the embodiment. In the figure, the same configurations as those of the conventional example of FIG.
Reference numeral 14 is a microcomputer for PWM controlling the inverter circuit 3, and a normal rotation set by a switching output calculation circuit 15 for calculating a switching output signal at the time of operation commands other than deceleration and at the time of operation commands for deceleration and the operation command device 200. R to store operation commands for reverse rotation, stop and output frequency
The AM 16 is included in the configuration.

Next, the operation in the case of operating the induction motor according to the above embodiment will be described with reference to the operation flowchart of FIG. First, for example, a normal rotation driving command is input from the driving command device 200, and then a driving command of the output frequency is input to start the driving (step S1).
1). Next, it is determined whether or not the microcomputer 14 is stopped by checking whether a stop flag is set in the microcomputer 21 of the operation command device 200 (step S1).
2). When it is determined that the operation is not stopped, the microcomputer 14 reads the operation command of the output frequency set to the predetermined frequency (step S13), and when it is determined that the operation is stopped, the microcomputer 14 reads the output frequency command of 0 Hz. (Step S14). Then, it is determined whether the microcomputer 14 is decelerating or not by checking whether the deceleration flag is set in the microcomputer 21 of the operation command device 200 (step S15). When it is determined that the deceleration is not performed, the microcomputer 14 reads the DC voltage detected by the DC voltage detection circuit 6 (step S16), and the output frequency is always a set value for the DC voltage. The switching output is calculated by (step S18), the switching output is output to the base amplifier 5, and the switching element of the inverter circuit 3 is driven by the PWM signal to output the AC voltage of the output frequency set by the inverter circuit 3. (Step S19).

When it is determined that the deceleration has occurred, the DC voltage value of the smoothing capacitor 2 is 200 × 2 ^{1 /} if the DC voltage value at the rated power supply voltage, for example, the rated AC power supply voltage is 200V. ² = 283V is set as the DC voltage value (step S17), the switching output is calculated by the function (step S18), the switching output is output to the base amplifier 5, and the switching element of the inverter circuit 3 is driven by the PWM signal. An AC voltage is output from the inverter circuit 3 (step S19). As a result, the output voltage of the inverter circuit 3 at the time of deceleration becomes the pattern A of FIG. 2 when the DC voltage is the rated value, but when the DC voltage increases due to the regenerative power of the induction motor 8, the output voltage is proportional to this. As shown in FIG. 2B, it rises. That is, during deceleration, for example, during acceleration and constant speed operation, even if the power supply voltage of the AC power supply 7 fluctuates, the output voltage of the inverter circuit 3 becomes a predetermined output voltage as shown in FIG. In the meantime, even if the DC voltage rises due to the regenerative power, the DC output voltage value is lower than the actual value, and the switching output signal is calculated by the function of the rated value 283V. As a result, since the switching elements of the inverter circuit 3 are driven in the same manner as a function of the rated value of the DC voltage regardless of the change of the DC voltage,
The output voltage rises in proportion to the rise of the DC voltage.

As described above, as the output voltage of the inverter circuit 3 increases during deceleration, the exciting current to the induction motor 8 increases and the loss in the winding of the induction motor 8 increases. This means that the regenerative power to the inverter circuit 3 is consumed by the induction motor 8 due to the increase of the exciting current to the induction motor 8, and the regenerative power to the inverter circuit 3 is reduced as compared with the conventional one, and the DC voltage is reduced. The rise of is also small. Therefore, it is possible to enhance the deceleration capability without interrupting the deceleration operation and without involving a circuit that consumes regenerative power by a resistor or the like. Further, the deceleration torque is also improved due to the increase in the exciting current.

[0014]

As described above, according to the present invention, during deceleration operation, the switching output calculation circuit calculates the switching output by a function when the DC voltage is the rated value with respect to the DC voltage of the smoothing capacitor, and outputs it to the inverter circuit. By doing so, the output voltage output from the inverter circuit rises corresponding to the output frequency that rises in proportion to the function of the rated value due to the rise in the DC voltage. Therefore,
During deceleration operation, when the DC voltage of the smoothing capacitor rises due to the regenerative power of the induction motor and the output voltage rises, the exciting current to the induction motor increases, the loss in the winding increases, and the regenerative power is transferred to the induction motor. In order to consume, the regenerative power to the inverter circuit is reduced compared to the conventional one, the rise of DC voltage is also small, and the circuit that consumes the regenerative power by the resistor etc. without interrupting the deceleration operation is provided. Even if it does not have, there is an effect that the deceleration ability can be enhanced.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is a graph showing a relationship between an output frequency and an output voltage in the same example.

FIG. 3 is a flowchart during operation of the same embodiment.

FIG. 4 is a block diagram showing a conventional inverter device.

FIG. 5 is a graph showing a relationship between an output frequency and an output voltage of the same inverter device.

FIG. 6 is a flowchart when the inverter device is in operation.

[Explanation of symbols]

 1 Converter Circuit 2 Smoothing Capacitor 3 Inverter Circuit 6 DC Voltage Detection Circuit 7 AC Power Supply 8 Induction Motor 14 Switching Output Calculation Circuit 150 Inverter Device

Claims (1)

[Claims] 1. A converter circuit for converting an AC power supply into a direct current, a smoothing capacitor for smoothing an output voltage of the converter circuit, and an inverter for converting a DC voltage of the smoothing capacitor into an AC voltage of a predetermined frequency by turning on / off a switching element. The circuit, the DC voltage detection circuit that detects the DC voltage of the smoothing capacitor, and the switching output is calculated by a function that always has the same output frequency with respect to the DC voltage detected by the DC voltage detection circuit during operation other than deceleration. During deceleration operation, a switching output operation circuit is provided that calculates a switching output by a function when the DC voltage is a rated value with respect to the DC voltage detected by the DC voltage detection circuit and outputs the calculated switching output to the inverter circuit. Inverter device.