JP2530854Y2 - Motor speed control device - Google Patents

Description

[Detailed description of the invention] [Industrial application field] This invention adjusts the speed of the motor driving the pump at short intervals to cope with fluctuations in the discharge pipe pressure of the pump as a load. Related to the device.

[Conventional technology]

As a device of this type, a control device that conventionally controls the operation of an electric motor having a pump as a load by an inverter device and is configured to input a detection voltage of a pressure switch attached to a discharge pipe of the pump to a filter circuit, It is known that the detected voltage is compared with a target value while leaving a certain amount of pulsation of the detected voltage, and the speed of the motor is controlled in accordance with the comparison output.

[Problems to be solved by the invention]

However, when using the above filter circuit, the pressure detection voltage becomes a delayed voltage to pass through the filter,
Therefore, when the pressure detection voltage greatly changes due to a sudden change in the load, the inverter device needs a considerable amount of time to cope with the change, resulting in a shortcoming in that a responsive control cannot be performed.

In a device that simply compares the pressure detection voltage with a target value and raises or lowers the output frequency of the inverter device according to the result, the output signal compared in response to a very small change in the pressure detection voltage is a fine positive or negative voltage. Therefore, even when the load is almost constant, there is a disadvantage that the inverter output frequency SC fluctuates sensitively as shown in FIG.

This invention keeps the operation of the inverter device stable when the load is almost constant and the fluctuation of the pressure detection voltage is small,
It is an object of the present invention to provide a motor speed control device that can obtain a quick response when a load suddenly changes.

[Means for solving the problem]

In order to achieve the above object, the motor speed control device of the present invention has a variable voltage to the motor driving the pump, an inverter main circuit outputting a variable frequency alternating current, and a discharge pipe pressure detection voltage of the pump. A control circuit for outputting a control signal to the inverter main circuit, in the motor speed control device, it is determined whether the comparison output voltage between the pressure detection voltage and the target value is only the same polarity voltage within a predetermined time If the comparison output voltage is not only the same polarity voltage, a control signal for operating the motor at a constant speed is output.If the comparison output voltage is only the same polarity voltage, the motor is decelerated when the comparison output voltage is a positive voltage. Means for outputting a control signal for accelerating the motor in the case of a negative voltage is provided in the control circuit.

[Action]

According to this invention, the comparison output voltage between the pressure detection voltage and the target value is determined at predetermined time intervals to determine whether or not only the same-polarity voltage is present,
As a result of this determination, if the comparison output voltage is the same polarity voltage, a control signal for accelerating and decelerating the motor is output, and if not, a control signal for operating the motor at a constant speed is output.
The output frequency of the inverter is adjusted based on this control signal, and the motor can be operated at a constant speed or accelerated / decelerated, so that the discharge pressure of the pump can be constantly maintained.

〔Example〕

FIG. 1 is a circuit diagram showing an embodiment of the present invention. In the figure, a rectifier 2 for rectifying an input from an AC power supply 1, a smoothing circuit 3 for smoothing a rectified output, and a variable voltage from DC power,
An inverter main circuit is configured by the inverter 4 that outputs an AC having a variable frequency. And inverter 4
The motor P is driven by the rotation of the motor M. Reference numeral 5 denotes a discharge pipe connected to the pump P, and a pressure detector 6 for detecting a pressure of a liquid or the like circulating in the discharge pipe 5 is attached to a part of the discharge pipe. Reference numeral 7 denotes a filter that receives the output voltage of the pressure detector 6, and reference numeral 8 denotes a comparator that determines whether the output signal of the filter 7 is a positive voltage or a negative voltage. Reference numeral 9 denotes a central processing unit (hereinafter referred to as a CPU) which receives the output of the comparator 8 and performs a calculation shown in the flow chart of FIG. 2 to output a signal for instructing acceleration / deceleration. Is a base drive circuit that outputs a firing signal of the PWM system or the PAM system.

In such a configuration, when the motor M is driven by receiving the output power of the inverter 4, the pressure detection voltage S 1 is input from the pressure detector 6 to the filter 7. The voltage waveform of the pressure detection voltage S1 shown in FIG. 3 is slightly flattened by the filter 7 and the filter output signal S2 is obtained. This signal
The comparator 8 that receives S2 outputs a positive voltage signal when the voltage is positive with respect to the target value, and outputs a negative voltage signal when the voltage is negative with respect to the target value and inputs the signal to the CPU. In the CPU, within a predetermined time determined by the value of the natural frequency, it is determined whether the input signal is only a positive voltage or a negative voltage as shown in the flowchart of FIG. When there is a case of a positive voltage and a case of a negative voltage within a predetermined time, a signal is output that causes the inverter 4 to operate at a constant speed. Next, if the voltage is the same, it is determined whether the voltage is a negative voltage.
The signal for increasing the operating frequency of the inverter 4 is output from the CPU, and in the case of NO, a signal for decreasing the operating frequency of the inverter 4 is output. The motor M is operated at a constant speed or an acceleration / deceleration according to the respective signals. The rotation of the pump P changes in conjunction with the rotation of the motor M. In FIG. 3, when the pressure detection voltage S1 increases, it is determined according to the flowchart shown in FIG. 2 and the inverter output frequency S3 decreases. It is shown. As described above, the inverter control signal is continuously obtained at short predetermined times by determining whether the comparison output voltage between the pressure detection voltage S1 and the target value is the same polarity voltage or more negative voltage at predetermined times.

In this embodiment, the determination is made based on whether the comparison output voltage is positive or negative as the target voltage for the determination. However, the determination can be similarly performed based on the level of the voltage.

[Effect of the invention]

According to the invention, it is determined whether or not the comparison output voltage between the pressure detection voltage and the target value is only the same polarity voltage within a predetermined time, and if the comparison output voltage is not only the same polarity voltage, the motor is operated at a constant speed. Means for outputting a control signal for decelerating the motor when the comparison output voltage is a positive voltage and for accelerating the motor when the comparison output voltage is a negative voltage. By providing it in the control circuit of the inverter, the load is almost constant and a control signal of the inverter constant speed can be obtained for minute fluctuations in the detected voltage, and stable operation can be performed. Alternatively, a control signal for deceleration is obtained, so that quick responsive operation can be performed.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, FIG. 2 is a flowchart showing the operation of the embodiment of the present invention, and FIG. 3 is a waveform diagram showing signals input to one member of the embodiment of the present invention. FIG. 4 is a waveform diagram showing signals input to one member of the conventional device. 4 ... Inverter, 5 ... Discharge pipe, 8 ... Comparator, 9 ...
... Central processing unit (CPU), M ... Electric motor, P ... Pump.

Claims (1)

(57) [Scope of request for utility model registration] An inverter main circuit for outputting a variable voltage and a variable frequency alternating current to a motor for driving a pump; and a control circuit for outputting a control signal to the inverter main circuit in accordance with a discharge pipe pressure detection voltage of the pump. In the speed control device of the electric motor composed of: determines whether the comparison output voltage of the pressure detection voltage and the target value is only the same polarity voltage within a predetermined time, if the comparison output voltage is not only the same polarity voltage Outputting a control signal for operating the motor at a constant speed, and controlling the motor to decelerate when the comparison output voltage is a positive voltage and to accelerate the motor when the comparison output voltage is a negative voltage if only the same polarity voltage is used. A speed control device for an electric motor, wherein a means for outputting a signal is provided in the control circuit.