JP4702094B2 - Inverter synchronous control device - Google Patents

Description

  The present invention relates to an inverter synchronous control device for synchronously controlling an inverter output with a commercial AC power supply.

  This type of synchronous control is applied, for example, to an apparatus that synchronously inserts an AC electric motor driven at a variable speed by an inverter into a commercial AC power supply (see, for example, Patent Document 1). In this synchronous insertion, the AC motor is started and accelerated by the inverter, and the power source of the AC motor is switched from the inverter to the AC power source side while the output of the inverter is synchronized with the AC power source.

  When switching between the inverter and the AC power supply, synchronous control is required in which the output voltage / frequency and phase of the inverter are synchronized with the AC power supply.

In the inverter synchronous control, generally, the output frequency and voltage of the inverter are made to coincide with the AC power supply, and the phase is made to coincide with a proportional-integral (PI) operation, a PLL circuit, or the like (for example, Patent Documents). 1, see Patent Document 2).
Japanese Patent No. 3678781 JP 2001-197683 A

  In the conventional synchronous control method, the output frequency and voltage of the inverter are matched with the commercial frequency, and then the phase is adjusted. However, the phase adjustment takes time because the output frequency cannot be changed greatly during the phase adjustment.

  For example, if the difference between the commercial frequency and the inverter output frequency is adjusted at 0.1 Hz, the phase adjustment takes 5 seconds if there is a phase difference of 180 °. Also. At the time of switching, since the adjustment time varies greatly depending on the phase when the commercial frequency is reached, there also arises a problem that it is difficult to assemble a synchronous switching control sequence.

  FIG. 8 shows a case where the inverter output voltage vector (phase) is advanced with respect to the phase of the commercial power supply at the stage where the frequencies coincide with each other. Although the frequency is changed using the PI control circuit and the PLL circuit, a long phase adjustment period is essential. When a delay occurs in this phase adjustment, a steel plant or the like hinders sequence control that repeats operation / stop of the AC motor.

  An object of the present invention is to provide a synchronous control device for an inverter that can reduce the time required for synchronous control of a commercial AC power source and an inverter and can perform synchronous control excellent in ease and stability.

  In order to solve the above-described problems, the present invention has the following configuration.

(1) An inverter synchronous control device for synchronously controlling an inverter output to a commercial AC power source,
A frequency calculation unit that limits the value proportional to the deviation between the frequency command in accordance with the frequency of the AC power supply and the output frequency of the inverter with an acceleration rate limiter, and obtains the output frequency command of the inverter by proportional-integral calculation of this value;
In the frequency control of the inverter by the frequency calculation unit, a commercial phase calculation unit that calculates the phase of the AC power supply at the arrival point where the frequencies of the AC power supply and the inverter output match,
In the frequency control of the inverter by the frequency calculation unit, an output phase calculation unit that calculates the phase of the inverter output at the arrival point where the frequencies of the AC power supply and the inverter output match,
The arrival point phase that synchronizes the phase at the arrival point by adjusting the acceleration rate or frequency control amount of the output frequency of the frequency calculation unit according to the error between the phase of the AC power supply at the arrival point and the phase of the inverter output A regulator,
It is provided with.

  (2) A limiter is provided for limiting an excessive correction of the frequency acceleration rate or frequency control amount by the arrival point phase regulator.

  (3) The arrival point phase regulator converts a phase correction amount range in a direction to reduce an acceleration rate or a frequency control amount with respect to an error between the phase of the AC power source and the inverter output at the arrival point. It has the part.

  (4) A frequency arrival determination unit that determines whether or not a deviation between the frequency command of the frequency calculation unit and the output frequency exceeds a threshold value and switches the gain of the regulator based on the determination result is provided. To do.

  As described above, according to the present invention, the time required for synchronous control of a commercial AC power supply and an inverter can be shortened.

  Further, since the phase error at the frequency arrival point is controlled, the phase can be handled by the DC amount, and the synchronization control becomes easy.

  Also, stable synchronization control can be performed by limiting the correction of the frequency acceleration rate or the frequency control amount from being excessive, and switching the gain of the regulator.

  Further, stable synchronous control can be performed by converting the range of the phase correction amount in the direction of decreasing the acceleration rate or the frequency control amount.

(Embodiment 1)
FIG. 1 is a synchronous control block diagram showing an embodiment of the present invention. The frequency calculation unit 1 indicated by the broken line block limits the value proportional to the deviation between the frequency command matched to the frequency of the commercial AC power supply and the output frequency command of the inverter by the acceleration rate limiter 1A. To obtain an inverter output frequency control command. This output frequency command is used as an output frequency control signal for a control circuit such as a PWM control circuit for the inverter, and is used for output frequency / voltage control of the inverter together with the voltage control signal.

  In this embodiment, the phase at the frequency arrival point of the commercial power supply and the inverter output is calculated so that the phase can be synchronized simultaneously when the output frequency of the inverter controlled by the output frequency of the frequency calculation unit 1 matches the frequency of the commercial power supply. The acceleration rate of the output frequency or the frequency control amount is adjusted according to the phase error at the frequency arrival point. The phase synchronization control for this purpose is realized by the calculation elements 2 to 4, and will be described in detail below.

(1) Term Definition First, terms used in the present embodiment are defined. Commercial frequency Fs [Hz], current inverter output frequency Fi [Hz], output frequency Fe [Hz] at the arrival point, inverter acceleration time (time for inverter to accelerate from zero to commercial frequency) Ta [sec], inverter acceleration Rate Ka [Hz / sec] = Fs / Ta, time ΔT [sec] until the current frequency reaches the commercial frequency, current commercial power supply voltage phase θs [rad], current inverter output voltage phase θi [rad], The commercial power supply phase θse [rad] at a different point and the inverter output voltage phase θie [rad] at the arrival point.

  These relationships are illustrated in the figure as shown in FIG. However, the α-β axis is an arbitrary fixed coordinate axis.

(2) Time ΔT
The time ΔT required to reach the commercial frequency from the current frequency can be obtained from the acceleration rate of the inverter, the current frequency, and the arrival frequency (= commercial frequency). In other words, since output frequency = acceleration rate x time,

Can be obtained as

(3) Commercial power supply voltage phase θse at the wrong point
Next, the commercial power supply phase at the point A is obtained. Here, for convenience, the frequency of the commercial power source is assumed to be fixed. In this case, the phase that changes from the present time to the point of inconsistency is

It becomes. Therefore,

  Here, substituting equation (1),

It becomes. The relationship between ΔT, θs, and Ka is shown in FIGS.

(4) Inverter output voltage phase θie at the arrival point
Next, the inverter output voltage phase at the arrival point A is obtained. The phase that changes from the current point to the destination is

  From equation (1)

  Therefore,

And can.

(5) Matching control of commercial power supply voltage phase and inverter output voltage phase at the arrival point If control is performed so that θse and θie according to the above equations (4) and (7) are matched, The output voltage phases of the commercial power supply and the inverter can be matched. Therefore, when accelerating the output frequency of the inverter at a constant speed, the time at the above-mentioned difference can be estimated from the acceleration rate, so the commercial power supply phase and the inverter output voltage phase at the arrival point are calculated, and the error becomes zero. Thus, the phase is matched when the acceleration of the inverter is completed by controlling the acceleration rate or the frequency control amount of the output frequency during acceleration with a regulator.

  In order to realize this control, in FIG. 1, the phase calculation unit 2 obtains the current phase θi of the output voltage of the inverter controlled by the output frequency command of the frequency calculation unit 1.

  Further, the commercial phase calculation unit 3 is based on the above equation (4), from the current inverter output frequency Fi, the output frequency Fe at the arrival point, the inverter acceleration rate Ka, and the current commercial power supply voltage phase θs to the point A The commercial power supply phase θse at is obtained.

  Further, the output phase calculation unit 4 is based on the above equation (7), and the difference A from the inverter acceleration rate Ka, the current inverter output frequency Fi, the output frequency Fe at the arrival point, and the current inverter output voltage phase θi. The output voltage phase θie of the inverter at is obtained.

  The arrival point phase regulator 5 determines the correction amount at which the error between the commercial power supply phase θse output from both the arithmetic units 3 and 4 and the output voltage phase θie of the inverter reaches zero when reaching the acceleration / deceleration rate limiter of the frequency arithmetic unit 1. Addition / subtraction or multiplication by the correction amount.

  Therefore, according to the synchronous control of the present embodiment, the following operational effects can be obtained.

  -Since the phase at the arrival point A is obtained and controlled, the phase can be adjusted from the stage where the arrival point A has not been reached, and the synchronization time can be shortened by substantially synchronizing the phase when the frequencies coincide.

  -Since the phase at the point A is controlled, it can be handled with a stationary phase (a regulator can be assembled).

  ・ Because ΔT is expressed as (Fe−Fi) Ka, after reaching (Fe = Fi), the phase estimation coefficient automatically becomes zero, and the control to match the other phases operates continuously. It is possible. That is, there is no need to switch the control at the arrival point, and it is advantageous to be continuous in terms of sample timing.

(Embodiment 2)
FIG. 5 is a synchronous control block diagram showing an embodiment of the present invention. The difference from FIG. 1 is that the output of the arrival point phase regulator 5 is limited by the correction frequency limiter 6 and the acceleration rate or frequency control amount is shown. The point is to correct.

  When correcting the acceleration rate or the frequency control amount in the first embodiment, if the correction amount is excessive, the inverter may be stopped due to overcurrent, overload, or overvoltage. Therefore, in this embodiment, the limit of the frequency acceleration rate or frequency control amount correction range is limited by the limiter 6 so as to be within the expected change in the acceleration rate or frequency control amount, thereby preventing a failure stop.

(Embodiment 3)
In the first or second embodiment, whether the correction is performed in the direction of increasing the frequency or the correction is determined depending on how the phase range of the input of the regulator is defined. Since the phase has a periodicity of 360 °, the input range of the regulator can be 0 ° to 360 ° or −180 ° to + 180 °. In general, when performing commercial synchronous switching, since the inertia is large, if it is corrected in the direction of increasing the frequency, it acts in the direction of tripping due to overcurrent or overload.

  Therefore, synchronous control can be obtained only in the direction of decreasing the frequency correction amount so that the difference calculation result in the regulator at the initial stage (at the start of control) becomes negative (in the direction of decreasing the acceleration rate or frequency control amount).

  For example, it is assumed that the commercial arrival phase at the start of control is 270 ° and the inverter arrival phase is 120 °. Then, the phase difference becomes positive at 270 ° −120 ° = 150 ° and tends to increase the frequency. Therefore, when the commercial arrival phase is changed from 270 ° to −90 °, it becomes negative at (−90 °) −120 ° = −210 °, and correction can be made in the direction of decreasing the frequency. In this example, the input of the regulator is in the range of 0 to -360 °. However, in reality, the target is 0 °, so that it does not converge at 0 to -360 °. Actually, it is necessary to correct within a range including the plus side, such as +10 to −350 °.

  From the above, in the present embodiment, by controlling the input phase of the phase control, the acceleration rate or the frequency control amount is corrected in a direction to reduce the correction amount, and overcurrent or overload is prevented. A synchronization control block diagram for this purpose is shown in FIG. 6, and a phase correction range conversion unit 7 is provided for converting the phase correction amount based on the error calculation result of θse and θie in the regulator 5 into a range of +10 to −350 °.

(Embodiment 4)
In Embodiments 1 to 3 described above, since the commercial frequency and the inverter frequency are different before the frequency reaches, the phase synchronization response becomes faster. On the other hand, in the phase correction after the inverter frequency reaches, the phase synchronization response is delayed because the frequencies match.

  Therefore, in the present embodiment, by changing the gain of the regulator depending on whether or not the frequency is close to the arrival point, it is possible to perform synchronous control that is stable over the entire area and has uniform response characteristics.

  A synchronization control block diagram for this purpose is shown in FIG. 7. The frequency arrival determination unit 8 determines whether or not the deviation between the frequency command and the output frequency exceeds a threshold value, and switches the gain of the regulator 5 based on the determination result. .

  Note that the gain switching by the frequency arrival determination unit 8 and the regulator 5 is not limited to one-stage switching, but can be a plurality of stages.

The synchronous control block diagram which shows Embodiment 1 of this invention. The term related figure of synchronous control in an embodiment. Explanatory drawing of the commercial phase in the arrival point in embodiment. Explanatory drawing of the inverter output phase in the arrival point in embodiment. The synchronous control block diagram which shows Embodiment 2 of this invention. The synchronous control block diagram which shows Embodiment 3 of this invention. The synchronous control block diagram which shows Embodiment 4 of this invention. Explanatory drawing of the acceleration of an inverter output frequency and phase adjustment in synchronous control.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Frequency calculation part 2 Output phase calculation part 3 Commercial phase calculation part 4 Inverter output phase calculation part 5 Arrival point phase regulator 6 Correction frequency limiter 7 Phase correction range conversion part 8 Frequency arrival determination part

Claims (4)

A synchronous control device for an inverter that synchronously controls an inverter output to a commercial AC power source,
A frequency calculation unit that limits the value proportional to the deviation between the frequency command in accordance with the frequency of the AC power supply and the output frequency of the inverter with an acceleration rate limiter, and obtains the output frequency command of the inverter by proportional-integral calculation of this value;
In the frequency control of the inverter by the frequency calculation unit, a commercial phase calculation unit that calculates the phase of the AC power supply at the arrival point where the frequencies of the AC power supply and the inverter output match,
In the frequency control of the inverter by the frequency calculation unit, an output phase calculation unit that calculates the phase of the inverter output at the arrival point where the frequencies of the AC power supply and the inverter output match,
The arrival point phase that synchronizes the phase at the arrival point by adjusting the acceleration rate or frequency control amount of the output frequency of the frequency calculation unit according to the error between the phase of the AC power supply at the arrival point and the phase of the inverter output A regulator,
An inverter synchronous control device comprising:   The inverter synchronous control device according to claim 1, further comprising a limiter that limits an excessive correction of a frequency acceleration rate or a frequency control amount by the arrival point phase regulator.   The arrival point phase regulator includes a phase correction range conversion unit that converts the range of the phase correction amount in a direction to reduce the acceleration rate or the frequency control amount with respect to the error between the phase of the AC power supply at the arrival point and the phase of the inverter output. The inverter synchronous control device according to claim 1, wherein the inverter synchronous control device is provided. 2. A frequency arrival determination unit that determines whether or not a deviation between a frequency command of the frequency calculation unit and an output frequency exceeds a threshold value, and switches a gain of the regulator based on the determination result. The inverter synchronous control apparatus of any one of 1-3.

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