JPS61196795A - Inverter control system - Google Patents

Abstract

PURPOSE:To obtain a control system of an inexpensive inverter control configuration by driving an AC motor of free-running state without detecting the free- running speed of the motor in a voltage control type inverter. CONSTITUTION:A voltage control type inverter has an upper limit controller 12 for applying a variable upper limit to an output voltage reference signal (c), and a deceleration controller 14 for abruptly decelerating an acceleration limiter 7 when inputting the output signal of a current detector 13 for detecting the current of an AD motor 5 and detecting the current of the prescribed value or higher. When driving an AC motor of free-running state, the inverter output frequency is set to the free-running starting speed or higher of the motor while the inverter output voltage remains zero, the inverter output voltage is raised at the suitable time constant to reduce the inverter output frequency to the vicinity of the free-running frequency while suppressing the increase in the motor current.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a voltage controlled inverter device, which is particularly applicable to switching an AC motor driven by a commercial power supply to an inverter drive in the event of a momentary power outage (hereinafter referred to as "commercial inverter switching"). The present invention relates to an inverter control method for driving an AC motor in a free running state that occurs when the motor is in a free running state.

[Technical background of the invention and its problems] When driving an AC motor in a free-running state with a voltage-controlled inverter device, the free-running rotational speed and the moment of inertia that are used for normal low-frequency starting must be adjusted. An overcurrent may flow into the inverter device due to the regenerated power from the AC motor, or the DC circuit of the inverter device may become overvoltage, making it impossible to start up the inverter device.

In order to avoid such a situation, an inverter control method as shown in FIG. 3 has conventionally been adopted. In other words, when an AC motor that is in a free running state due to a momentary power outage or switching to a commercial inverter at time t1 is to be driven by an inverter device, the motor rotation frequency is changed to a speedometer generator (tachogenerator) or a residual voltage cycle detection circuit, etc. The inverter output frequency reference is increased from time t2 while being detected by , and the increase in the inverter output frequency reference is stopped at time t3 when it reaches the vicinity of the motor rotation frequency, and the inverter output voltage is increased from zero with an appropriate time constant. By doing so, the regenerative power from the motor is eliminated and the motor is started, and the predetermined output voltage and output frequency (hereinafter referred to as V/F
By accelerating the inverter output frequency to the set value of the inverter output frequency within a predetermined acceleration limit time at time t4 when the ratio is reached, the inverter device is driven without overcurrent or overvoltage.

However, in the conventional inverter control method 1,
Since it is necessary to detect the rotational speed of the AC motor during free running, a speedometer generator or a residual voltage synchronous detection circuit must be added, resulting in a very expensive inverter control configuration.

[Object of the Invention] The present invention has been made to solve the above-mentioned problems, and its purpose is to provide a voltage controlled inverter device with:
It is an object of the present invention to provide an inverter control system capable of driving an AC motor in a free run state without detecting the free run rotational speed of the AC motor and having an inexpensive inverter control configuration.

[Summary of the Invention] In order to achieve the above object, the present invention converts the inverter output frequency setting value into an output voltage/output frequency reference signal through an acceleration limiting circuit, and calculates the output voltage reference from this output voltage/output frequency reference signal. In a voltage controlled inverter device that obtains a signal and an output frequency reference signal and controls the output voltage/output frequency of an AC motor according to these output voltage reference signals and output frequency reference signals, a variable upper limit is set for the output voltage reference signal. When driving an AC motor in a free-running state by adding an upper limit control circuit that provides a maximum limit control circuit and a deceleration control circuit that suddenly decelerates the acceleration limiting circuit when the AC motor current exceeds a predetermined value, the inverter output voltage can be set to zero. By making the inverter output frequency equal to or higher than the AC motor free run start rotation frequency and increasing the inverter output voltage with an appropriate time constant, the inverter output frequency can be freed while suppressing the increase in AC motor current. It is characterized in that it is lowered to near the run rotation frequency.

[Embodiments of the invention] An embodiment of the present invention shown in the drawings will be described below.

FIG. 1 shows an example of the configuration of a voltage-controlled inverter device to which the inverter control method of the present invention is applied. In the figure, an inverter circuit 4 inputs DC voltage smoothed by a smoothing capacitor 3 from an AC power supply 1 via a rectifier circuit 2, and outputs m power of AC electric power of variable frequency variable voltage □ to drive an AC motor 5. The inverter main circuit configuration is such that

On the other hand, the control circuit converts the set value a of the inverter output frequency setter 6 into a V/'F reference signal through the acceleration limiting circuit 7, and supplies this signal to the output voltage reference circuit 8 and the output frequency reference circuit 9, respectively. Obtain an output voltage reference signal C and an output frequency reference signal d, and further convert these signals C9d into P
The basic configuration is a voltage-controlled inverter device that controls the V/F by inputting it to the WM control circuit 10 as a pulse signal that controls the inverter output voltage and output wave number to the base drive circuit 11. An upper limit control circuit 12 for giving a variable upper limit to the output voltage reference signal C and an output signal from a current detector 13 for detecting the current of the d-current 6-motor 5 are input, The configuration includes a deceleration control circuit 14 that rapidly decelerates the acceleration limiting circuit 7 when a current is detected.

Next, the inverter control method of the present invention based on this configuration will be described using FIG. 2. In FIG. 2, when the electric motor 5 is being driven by an inverter or a commercial power supply until time t1, and at time t1 the AC motor 5 enters a free-run state due to a momentary power outage or a commercial inverter switching operation, AC motor 5 with inverter device
When driving, the gate is blocked so that the inverter output voltage becomes zero, and the upper limit control circuit 12 sets the limit value of the output voltage reference signal to zero, and from time t2, the V/F reference signal is increased to make it free. The gate block is released at time t3 when the value exceeds the run start time t1, and then the limit 1 value of the output voltage reference signal is set to a time constant that is less than the response of the deceleration control circuit 14 and faster than the acceleration limit time. By increasing the V/F reference signal, the motor current increases rapidly because the inverter output frequency is higher than the AC motor rotation speed, but at time t4 when the inverter output frequency is about to flow over a predetermined value, the deceleration control circuit 14 changes the V/F reference signal to the inverter. Since rapid deceleration is performed with a faster response than the time constant for the output voltage to rise, the inverter output frequency is lowered to near the AC motor free-run rotation frequency while suppressing an increase in the AC motor current. Thereafter, when a predetermined V/F reference signal is reached, the AC motor current naturally decreases and the deceleration control is stopped. In addition, since the output voltage reference signal value increases regardless of the V/F reference signal, the inverter output voltage is no longer limited by the upper limit.
The AC motor 5 can be accelerated to the inverter output frequency setting value within a predetermined acceleration time limit while outputting a value commensurate with the V/F reference signal together with the inverter output frequency.

As described above, the inverter control method according to the present invention includes an upper limit control circuit 12 that gives a variable upper limit to the output voltage reference signal C to a voltage controlled inverter device;
When adding a deceleration control circuit 14 that suddenly decelerates the acceleration limiting circuit 7 when the AC motor current detected by the current detector 13 exceeds a predetermined value, and driving the AC motor 5 in a free running state, the inverter output frequency is set to be higher than the AC motor 5 free run start rotation frequency, and the inverter output voltage is raised from zero slower than the deceleration control response and faster than the acceleration limit time, so the AC motor 5 free run rotation speed is detected. It is possible to drive the AC motor 5 in a free running state without any problems, and it becomes unnecessary to newly provide conventional means for detecting the rotational speed, making it possible to provide an inexpensive inverter control configuration.

Further, since the current detector 13 of the AC electric motor Ia5 is essential for the original protection of the inverter device, there is no need to newly provide it for the inverter control method of the present invention, and the above effects are further improved. become remarkable.

[Effects of the Invention] As explained above, according to the present invention, in a voltage controlled inverter device, an AC motor in a free run state can be driven without detecting the free run rotational speed of the AC motor, and an inexpensive inverter control can be achieved. An inverter control method that can be configured can be provided.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram showing an embodiment of a voltage-controlled inverter device to which the inverter control method of the present invention is applied, FIG. 2 is a diagram for explaining the inverter control method of the present invention, and FIG.
The figure is a diagram for explaining a conventional inverter control method. 4... Inverter circuit, 5... AC motor, 6...
- Inverter output frequency setter, 7... Acceleration limit circuit, 8... Output voltage reference circuit, 9... Output frequency reference circuit, 12... Upper limit control circuit, 13... Current detector, 14...Deceleration control circuit. Applicant's agent Patent attorney Takehiko Suzue Figure 1 JP-A-6L-196795 (4) Figure 2'□

Claims (1)

[Claims] The inverter output frequency setting value is used as an output voltage/output frequency reference signal through an acceleration limiting circuit, an output voltage reference signal and an output frequency reference signal are obtained from this output voltage/output frequency reference signal, and these output voltage reference signals and output The output voltage of the AC motor depends on the frequency reference signal.
In a voltage-controlled inverter device that controls an output frequency, an upper limit control circuit provides a variable upper limit to the output voltage reference reference signal, and a deceleration circuit rapidly decelerates the acceleration limiting circuit when the AC motor current is equal to or higher than a predetermined value. When driving an AC motor in a free run state, the inverter output voltage is set to a gate block state so that it becomes zero, and the limit value of the upper limit control circuit is set to zero, and the inverter output frequency starts free run. Set the output voltage/output frequency reference signal to be equal to or higher than the rotation frequency, then release the gate block to increase the inverter output voltage, and set the limit value below the response in the deceleration control circuit and also below the acceleration limit time. The inverter output frequency is lowered to near the AC motor free-run rotational frequency while suppressing the increase in AC motor current by increasing it with a fast time constant, and then the inverter output frequency is reduced to a predetermined output voltage/output frequency reference signal and acceleration limit time. An inverter control method characterized by accelerating an AC motor to a set value.