JP2874321B2 - Inverter control device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a control device for an inverter for driving an induction motor.

2. Description of the Related Art In recent years, inverters have rapidly spread, and accordingly, the frequency of power supply voltage fluctuations has increased, and the frequency of use of inverters under various power supply voltages has increased. However, there is an increasing demand for making the output characteristics of the inverter constant.

Conventionally, as a method of detecting the power supply voltage and correcting the output voltage in response to this kind of request, for example, as shown in the paper “60-B61” of IEEJ Transactions on Volume 105, No. 6,
The configuration shown in the figure was common.

Hereinafter, the configuration will be described with reference to FIG.

FIG. 3 is a block diagram of a conventional inverter device and its control device, wherein 1 is an AC power supply, 2 is a forward converter for converting the output of the AC power supply 1 to DC, and 3 is an output of the forward converter 2 for smoothing. Capacitor 4 is an inverter for converting DC to AC, 5 is an induction motor driven by the output of inverter 4, 6
Is frequency setting means for setting the output frequency of the inverter 4,
Reference numeral 7 denotes acceleration / deceleration control means for setting an output frequency every moment based on the output of the frequency setting means 6, reference numeral 10 denotes a DC voltage detection means for detecting a DC voltage smoothed by the capacitor 3, and reference numeral 12
Is an output voltage setting means for setting the output voltage of the inverter 4 based on the output of the acceleration / deceleration control means 7, and 13 is a correction coefficient setting means for calculating a correction coefficient for the output voltage based on the output of the DC voltage detecting means 10. , 14 are output voltage correcting means for correcting the output of the output voltage setting means 12 based on the output of the correction coefficient setting means 13, and 15 is a switching element constituting the inverter 4 based on the output of the output voltage correcting means 14. A waveform generating means 16 for generating an on / off signal to be controlled is a signal amplifying circuit for providing an output of the waveform generating means 15 to the inverter 4.

In the above configuration, the output converted to DC by the forward converter 2 connected to the AC power supply 1 is smoothed by the capacitor 3, converted to AC of a predetermined frequency and voltage by the inverter 4, and then converted to AC by the induction motor 5. It is supplied as electric power. Further, the frequency set by the frequency setting means 6 is converted into an output frequency setting every 1 ms, for example, every 1 ms through the acceleration / deceleration control means 7 and is input to the output voltage setting means 12. In response to this, the output voltage setting means 12 calculates output voltages for three phases for each switching cycle of the switching element of the inverter 4.
At this time, the voltage of the AC power supply 1 is calculated assuming that the voltage is normal. On the other hand, the DC voltage detecting means 10 detects the voltage smoothed by the capacitor 3, and the correction coefficient setting means 13 calculates the ratio to the case where the voltage of the AC power supply 1 is a normal voltage as a correction coefficient. It is input to the correction means 14. The product of the output of the output voltage setting means 12 and the output of the correction coefficient setting means 13 is calculated by the output voltage correction means 14, and is input to the waveform generation means 15 as a final voltage setting. On the basis of this, the on / off time is determined from the switching cycle in the waveform generating means 15 and is supplied to the inverter 4 via the signal amplifier circuit 16 as a signal for controlling the switching element.

By the operation described above, the voltage supplied to the induction motor 5 can be kept substantially constant even if the power supply of the AC power supply 1 fluctuates. However, unless the output waveform of the inverter 4 approaches a trapezoidal wave or a rectangular wave, it is impossible to output a voltage higher than the voltage of the AC power supply 1, and it goes without saying that there is a limit to the correction. .

However, in the above configuration, when the detection processing time delay of the DC voltage detection unit 10 cannot be ignored, for example, A /
If the delay is several milliseconds due to the method of D conversion or giving priority to the processing by the waveform generating means 15, there has been an inconvenience in that the output voltage may become unstable due to the correction.
In particular, in the case of rapid acceleration, the load current flowing through the induction motor 5 temporarily increases, the smoothing ability of the capacitor 3 becomes insufficient, the ripple increases, and the correction is adversely affected.
In the case of sudden deceleration when the voltage of the AC power supply 1 is higher than normal, the regenerative voltage sometimes becomes higher than when no correction is performed, which is inconvenient.

An object of the present invention is to solve the above-described problems, and an object of the present invention is to provide an inverter control device which can provide a good correction effect even when a time delay of detection of a power supply voltage and correction coefficient setting is somewhat large.

Means for Solving the Problems To achieve the above object, the present invention provides a frequency comparison unit, a DC voltage storage unit that stores an output of a DC voltage detection unit when a state of the frequency comparison unit changes, A timer for measuring a predetermined time after the output of the frequency comparing means detects a constant speed state is provided, and a coefficient for correcting the output voltage can be selectively used from among a plurality.

Effect of the Invention With the above configuration, the present invention normally calculates a correction coefficient with reference to the output of the DC voltage detecting means, accelerates or decelerates, thereby increasing the DC voltage ripple or suddenly changing the DC voltage due to the regenerative voltage. If it is predicted that the correction will be performed, the correction coefficient can be calculated by referring to the output of the DC voltage storage means stored immediately before the fluctuation, or the correction can be interrupted to reduce the adverse effect of the correction. It is.

Also, especially during rapid acceleration, the rotation speed of the rotor of the induction motor becomes constant later than the output frequency of the inverter becomes constant. It is possible to delay the shift to the calculation of the coefficient and obtain a more effective correction effect without directly detecting the rotation speed of the rotor.

Embodiment An embodiment of the present invention will be described below with reference to FIGS. 1 and 2.

FIG. 1 is a block diagram of an inverter device and a control device according to the present invention. The third described in the section of the prior art
The difference from the configuration of the figure is that a frequency comparing means 8 for comparing a set frequency output from the frequency setting means 6 with an output frequency output from the acceleration / deceleration control means 7 is provided, and the state of the frequency comparing means 8 changes. The point is that the DC voltage storage means 11 for storing the output of the DC voltage detection means 10 at the time is provided, and the output is input to the correction coefficient setting means 13. Further, a timer 9 started when the frequency comparing means 8 detects the constant speed state.
Is provided, and the output is input to the correction coefficient setting means 13 together with the output of the frequency comparison means 8.

FIG. 2 is a flowchart showing the contents of a program when the control section having the above configuration is realized by a microcomputer.

Hereinafter, the operation of the present invention will be described with reference to the flowchart of FIG.

First, the main program will be described with reference to FIG. When the program starts, first, the microcomputer performs initialization processing such as setting a stack pointer, clearing a RAM, and setting and permitting an interrupt for a reference timer (step 1). Next, it is determined whether there is an operation command (step 2). If there is an operation command, the set frequency is read (step 3). If not, the set frequency is set to zero (step 4). Next, a DC voltage is read (step 5).

Next, the acceleration / deceleration state of the output frequency of the inverter is determined (steps 6 and 8). If the speed is constant and the timer 9 has expired, it is determined that the induction motor 5 is also in the steady state, and the DC voltage is detected. On the basis of the output of the means 10, the ratio of the power supply of the AC power supply 1 to the normal power supply (for example,
When the phase is 200 V, 283 is used as a denominator, and the output of the DC voltage detection means 10 is used as a numerator (Step 7).
During deceleration, the correction coefficient is set to "1" (correction is interrupted) in order to avoid the influence of the regenerative voltage (step 9). The ratio to the case where the power supply of the AC power supply 1 is normal is calculated as a correction coefficient (step 10). As described above, in steps 6 to 10, the correction coefficient of the output voltage can be selectively prepared according to the states of the frequency comparing means 8 and the timer 9.

Steps 2 to 10 described above are repeatedly executed as an infinite loop together with other processes (not shown) related to the sequence control of the inverter.

Next, an interrupt process for realizing the acceleration / deceleration control means will be described with reference to FIG.

This interrupt processing is started periodically, for example, every 1 ms. The set frequency output from the frequency setting means 6 is compared with the output frequency output from the acceleration / deceleration control means 7 (steps 100 and 101). Steps
If the output frequency is low in 101, acceleration processing is performed until the output frequency matches the set frequency. Before that, in order to detect an edge of the acceleration processing, it is determined whether or not acceleration has been performed (step 102). If the acceleration is not being performed, the value of the DC voltage storage means 11 is updated with the output of the DC voltage detection means 10 (step 103), and the DC voltage at the start of acceleration is stored. Next, the output frequency is added and updated according to a predetermined acceleration rate (step 104). If the output frequency is equal to or higher than the set frequency (step 105), the output frequency is set equal to the set frequency (step 106). The timer 9 is started to measure a predetermined time (for example, 100 mS) for waiting until the rotation speed of the motor reaches a steady state (step 107), and the process returns from the interrupt process.

If it is determined in step 101 that the output frequency is higher than the set frequency, the output frequency is subtracted and updated according to a predetermined deceleration rate (step 110), and if the output frequency becomes lower than the set frequency (step 111), the output frequency is made equal to the set frequency. Every other time (step 112), the process returns from the interrupt processing.

Next, an interrupt process for realizing the output voltage setting means and the output voltage correction means will be described with reference to FIG. This interrupt processing is started periodically, for example, every carrier cycle. First, output voltages for three phases when the voltage of the AC power supply 1 is normal are calculated (step 20).
0). Next, the results are multiplied by the correction coefficients calculated in steps 7, 9 and 10 in FIG. 2A to obtain final output voltages for three phases (step 201).

As described above, according to the inverter control apparatus of the embodiment of the present invention, the correction is performed by selectively referring to the DC voltage detecting means 10 and the DC voltage storing means 11 according to the states of the frequency comparing means 8 and the timer 9. Since the coefficient is obtained, it is possible to reduce the adverse effect of the correction due to the fluctuation of the DC voltage due to the acceleration / deceleration operation.

In the above embodiment, the output frequency and the carrier frequency are described as being asynchronous, but the same applies to a synchronous inverter control device. In the above-described embodiment, the case where the output voltage is kept constant has been described. For example, in step 7 of FIG. It is clear from the above description that the output voltage can sometimes be reduced intentionally.

Effects of the Invention As is clear from the above embodiments, according to the present invention,
The state of the DC voltage detecting means and the state of the frequency comparing means according to the state of the frequency comparing means for comparing the output frequency with the set frequency, and the state of the timer for measuring a predetermined time after the output of the frequency comparing means detects the constant speed state Since the correction coefficient is obtained by selectively referring to the DC voltage storage means for storing the output of the DC voltage detection means at the time of the change, the adverse effect of the correction accompanying the fluctuation of the DC voltage due to the acceleration / deceleration operation is reduced. Therefore, it is possible to provide an inverter control device which can provide a good correction effect even if the time delay of the detection of the power supply voltage and the setting of the correction coefficient is somewhat large.

[Brief description of the drawings]

FIG. 1 is a block diagram of an inverter control device according to one embodiment of the present invention, and FIGS. 2 (a), (b) and (c) show the contents of a program when the control portion of the device is realized by a microcomputer. FIG. 3 is a block diagram of a conventional inverter control device. 6 ... frequency setting means, 7 ... acceleration / deceleration control means, 8 ...
Frequency comparison means, 9 timer, 10 DC voltage detection means, 11 DC voltage storage means, 12 output voltage setting means, 13 correction coefficient setting means, 14 output voltage correction means.

────────────────────────────────────────────────── ─── Continued from the front page (72) Yoshiko Nakagawa, Inventor 1006 Kazuma, Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (58) Field surveyed (Int.Cl. ⁶ , DB name) H02P 5/408- 5/412 H02P 7/628-7/632 H02P 21/00

Claims (1)

(57) [Claims] A frequency setting means for setting an output frequency of the inverter; an acceleration / deceleration control means for setting an instantaneous output frequency based on an output of the frequency setting means; an output of the frequency setting means and the acceleration / deceleration control Frequency comparing means for comparing the outputs of the means to determine whether the acceleration / deceleration state is an acceleration state, a deceleration state, or a constant speed state, and a predetermined time from when the frequency comparison means detects the constant speed state. A timer for measuring time, a DC voltage detecting means for detecting a voltage of a DC part of the inverter, and a DC voltage storing means for storing an output of the DC voltage detecting means when a state of the frequency comparing means changes, Output voltage setting means for setting the output voltage of the inverter based on the output of the acceleration / deceleration control means; and The correction coefficient is calculated from a correction coefficient calculated with reference to the output of the voltage detection means, a correction coefficient calculated with reference to the output of the DC voltage storage means, and "1" as a coefficient when no correction is performed. A control device for an inverter, comprising: a correction coefficient setting means for selectively setting a coefficient; and an output voltage correction means for correcting a result of the output voltage setting means based on the correction coefficient set by the correction coefficient setting means. .