JPS6159063B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for controlling the operation of an AC rotating machine, in which the AC rotating machine is accelerated by a variable frequency power source and then operated by switching to, for example, a commercial frequency power source.

Various methods have been put into practical use for starting large-capacity AC rotating machines, that is, induction motors or synchronous motors. Recently, a method of switching to commercial power after starting and accelerating a rotating machine has been widely applied.

Hereinafter, in FIG. 1, an AC rotating machine M is accelerated by a variable voltage variable frequency (hereinafter referred to as VVVF) inverter 1, and a commercial frequency power source 6
The process of switching to

That is, (i) Accelerate from time t ₀ to t ₁ and confirm completion of acceleration at t ₁ .

(ii) Between t ₁ and t ₂ , as shown in Figure 2, VVVF
The automatic synchronization circuit compares the output voltages of the first power supply 1 consisting of
SYN synchronizes the output voltage of the first power supply 1 to the second power supply 6 by fine-tuning the voltage controlled oscillator VCO.

(iii) From t ₂ to t ₃ , synchronization is confirmed by the synchronization confirmation circuit DET.

(iv) between t ₃ and t ₄ contactor 88L to 88
Switch to H.

(v) After t ₄ , operation is performed using the second power source 6.

When switching to commercial power after such a process, various transient phenomena occur, such as overcurrent due to sudden acceleration and overvoltage due to regenerated power due to sudden braking. This may cause inverter commutation failure or thyristor breakdown.

FIG. 3 explains the process of automatic synchronization. For simplicity, the acceleration process from 0Hz to 59Hz is omitted. First, at time t ₁ , let's assume that it is 59.0Hz.
It is assumed that the acceleration has been completed.

Originally, it should accelerate to 60Hz, or more precisely, to the commercial frequency at that time, but here we will consider a case where acceleration is completed at a slightly lower 59.0Hz due to circuit errors. After the acceleration is completed, there is a time limit of several seconds.
Automatic _{synchronization} control circuit (Phase locked loop,
Suppose we make use of the PLL (also called PLL for short) (in addition,
Although the above-mentioned time limit is not necessarily necessary, such a time limit often occurs even if it is not set intentionally. ). PLL
The phase difference Δψ between the first power source 1 and the second power source 6 at the moment when the first power source 1 and the second power source 6 are activated usually has some kind of phase difference, as shown at point P shown in FIG. 3b.
This value can have any value between -180° and +180°.

When Δψ is (-) value as shown in Figure 3b, the PLL
When the signal is utilized, a signal corresponding to Δψ at point P is input in a stepwise manner to the input of a control amplifier of a general PLL as shown in FIG. 6, which will be described later. Therefore, as is well known, the PLL control amplifier tries to increase the frequency of the voltage controlled oscillator (VCO) in the case of a (-) Δψ signal, so the frequency of t ₂ increases as shown in Figure 3a. From the point in time, the frequency f is suddenly increased and at t ₃
After reaching 60.0Hz, it goes through an overshoot process.
It settles down to 60.0Hz. Since the inverter frequency is lower than 60.0 Hz from t ₂ to t ₃ , Δψ continues to increase, and when it exceeds 60.0 Hz at t ₃ , Δψ starts to decrease and converges to Δψ→0.

Corresponding to the above, as a response to the output voltage of VVVF, for example, the DC circuit current IDC settles at a value corresponding to the load at the rotation speed between t ₁ and t ₂ , but at t ₂ At this point, the AC rotating machine M is rapidly accelerated, and the DC current increases while a current transient phenomenon as shown in FIG. 3c occurs, accelerating the AC rotating machine M. t ₄
When the frequency converges from overshoot to 60.0Hz at the point in time, a light braking state occurs, so the DC current temporarily decreases (in some cases, it decreases to zero) and then returns to 60.0Hz. settles on the corresponding value.

Next, let us consider a case where due to a circuit error or the like, the acceleration is completed after the acceleration reaches, for example, 61 Hz, as shown in FIG. 4a. Acceleration is completed at time t ₁ ,
Assuming that the PLL is turned on at time t ₂ , in this case Δψ is positive, corresponding to point P shown in Figure 4b, so the PLL lowers the frequency of the voltage controlled oscillator (VCO). The inverter frequency is 60.0Hz at t ₃ , but at t ₄
continues to decrease until starts to rise again from t ₄
Converges to 60.0Hz. As a result, the phase difference increases until t ₃ , and from t ₃ onwards, the inverter frequency becomes lower than the commercial frequency of 60.0Hz, so the phase difference Δψ increases until t ₃ .
decreases from and converges to 0.

As a result of controlling Δψ by the PLL as described above, the AC rotating machine M is braked from t ₂ to t ₄ .
After t ₄ , it becomes accelerated. Therefore, the DC input current of the inverter varies from approximately t ₂ to t ₄ as shown in Figure 4c.
Since the value between is negative, the DC power is regenerated to the inverter's DC power, so a double converter capable of regenerating the DC power is required.

As shown above, in the case of Fig. 3, there is a risk of overcurrent when the PLL is used to synchronize, and in the case of Fig. 4, when the PLL is used, a regeneration state will occur, so if the DC power If the converter is not a double converter, there is a risk of DC overvoltage.

It is assumed that the PLL is active when the difference and phase difference in both FIGS. 3 and 4 have the same polarity, but in the case of opposite polarity, a more complicated process will be followed. That is, (1) When the PLL is utilized when the inverter frequency is lower than the commercial frequency and the phase difference is positive.

This is the case when Δψ at point P in Figure 3 is positive, but if Δψ is positive, the PLL amplifier assumes that the inverter is advancing, and lowers the voltage controlled oscillator (VCO) once, causing Δψ to become negative. After that, the voltage controlled oscillator (VCO) is raised.

(2) When the PLL is used when the inverter frequency is higher than the commercial frequency and the phase difference is negative.

This is the case when Δψ at point P in Figure 4 is negative. If Δψ is negative, the phase of the PLL amplifier lags behind the inverter even though the inverter frequency is high, so the voltage controlled oscillator (VCO ) once in the upward direction.

After Δψ transitions from negative to positive, the voltage controlled oscillator (VCO) is controlled to lower, and Δψ converges to zero.

For the sake of simplicity, the above explanation assumes that the initial conditions for the phase difference and frequency difference are relatively good when the PLL is used, and that they do not cross +180° or -180° after the PLL is used. In reality, there are cases where the angles cross +180° or -180° not once, but twice or three times before synchronizing.

An example is shown in FIG. In the figure, when acceleration is completed at t=0, T= ₁ /Δ changes periodically between +180° and -180°, assuming that the frequency difference is Δ until t1. If we utilize the PLL at time t ₁ ,
-180 once at t ₂ due to weak synchronization power of PLL
It crosses the angle, reaches 180 degrees, and then converges to 0 degrees.

As mentioned above, depending on the magnitude relationship between the commercial frequency and the inverter frequency when acceleration is completed, and the positive/negative relationship of Δψ at the time when PLL is utilized, transient phenomena occur when synchronizing the inverter while operating an AC rotating machine with the commercial frequency. It can be seen that the values are different, and overcurrent due to harmful sudden acceleration and overvoltage due to regeneration occur.

This invention was made in order to eliminate the above-mentioned drawbacks, and after accelerating an AC rotating machine by a variable frequency first power source and accelerating it to a rotational speed that almost matches the frequency of the second power source, When the phase difference of the first power supply with respect to the second power supply matches a predetermined value,
The present invention provides an operation control method for an AC rotating machine that can prevent sudden acceleration and braking phenomena by starting adjustment of the frequency and phase angle of a first power source.

Based on the above-mentioned analysis of the problems in the process of accelerating an AC rotary machine using an inverter and then synchronizing it with the commercial frequency, the present invention has added the following features.
This allows for smooth synchronization.

(i) In the process of synchronizing the inverter to the commercial frequency using PLL, if a regenerative condition occurs, a single converter will experience DC overcurrent, so a double converter is required as a DC power source, which is uneconomical. In order to avoid this, the frequency of the inverter at the time when the PLL is used is always set to be slightly lower than the commercial frequency, so that the PLL operation is always accelerated.

(ii) Depending on the sign of the phase difference at the moment when PLL is utilized,
PLL amplifiers work by either lowering or raising the voltage-controlled oscillator (VCO) suddenly.

This is because the PLL amplifier always requires phase lead compensation as shown in Figure 6, so the resistor R ₁
A step-like signal R ₂ /R ₁ Δψ ₀ determined by R ₂ is generated corresponding to Δψ ₀ when the PLL is utilized. Therefore, in the present invention, a circuit is provided to detect the moment when Δψ=0, and by setting Δψ ₀ =0, the PLL amplifier is prevented from kicking at the moment when the PLL is active.

(iii) As a further consideration, after completion of acceleration Δψ=
There is a problem with the time it takes to detect 0. Above (i)
As mentioned in the section above, the inverter is accelerated to a frequency slightly lower than the commercial frequency, but if the commercial frequency is 60.0 Hz, it is accelerated to 59.9 Hz. If the phase difference when the acceleration completion signal is output is just after passing 0 degrees, the phase will move 360 degrees through the process of 0 degrees → -180 degrees → +180 degrees → 0 degrees before reaching 0 degrees. Since the frequency difference is 0.1Hz, it will take 10 seconds.

Therefore, in order to shorten such extra time, it is necessary to intentionally adjust the inverter frequency at the time of completion of acceleration to be lower than the commercial frequency to some extent. This frequency difference is practically 0.6
~1.0Hz is considered a standard. In this case, the above waiting time will be 3.3 to 1 second or less.

The principle and operation of this invention will be explained below with reference to the configuration diagram shown in FIG. 6 and the operation waveforms shown in FIG. 7.

In the figure, an AC rotating machine M such as an induction motor or a synchronous motor is accelerated by a first power source 1 consisting of a VVVF inverter. 88L and 88H are contactors that switch to commercial operation after completion of acceleration. Acceleration is achieved by increasing the output frequency of the voltage controlled oscillator 3 at a frequency proportional to the increase in the output signal of the ramp signal generator 2. During acceleration, relay _K1 is closed, so the output of PLL amplifier 4 is zero.

The phase difference detection circuit 5 generates a signal proportional to the phase difference between the output voltages of the commercial frequency second power supply 6 and the first power supply 1 based on the signals of the voltage detectors PT1 and PT2, and outputs a signal to the PLL amplifier 4. tell to.

Reference numeral 7 denotes a holding circuit which holds the internal memory at the moment when the output of the phase difference detection circuit 5 becomes zero after the slope signal generation circuit 2 completes acceleration, and thereafter holds the relay K1. Therefore, as shown in FIG. 7b, the moment Δψ=0, the PLL operates and the first power source 1 synchronizes with the second power source 6. Figure 7b
In the case of , unlike the case in Figure 3, the moment Δψ ₀ = 0 at which the PLL lives, so the PLL amplifier does not generate the above-mentioned kick voltage of R ₂ /R ₁ Δψ ₀ , as shown in Figure 7 a. The frequency is smoothly accelerated from 59.5 Hz to 60.0 Hz, and as a result, the DC current of the inverter exhibits a sharp acceleration state from t ₂ to t ₄ as shown in FIG. 7c. Naturally the fourth
There is no braking condition as shown in the figure.

After synchronizing with the commercial frequency as described above, the voltage of the first power source 1 is adjusted to the voltage of the second power source 6, the contactor 88H is turned on, and the contactor 88L is turned off. It can be delivered to the second power supply 6 from there.

How to match the voltages of the first power supply 1 is not the subject of this invention, so a description thereof will be omitted.

In the above embodiment, after acceleration is performed using the variable frequency first power source, synchronous switching is performed with the commercial frequency second power source. Similar effects are expected.

According to this invention, after accelerating the alternating current rotating machine by the variable frequency first power source and accelerating it to a rotational speed that almost matches the frequency of the second power source, the position of the first power source with respect to the second power source is changed. By starting to adjust the frequency and phase angle of the first power supply when the phase difference matches a predetermined value, the PLL amplifier does not generate a kick voltage, so the frequency changes smoothly up to the predetermined value. Therefore, sudden acceleration and braking phenomena can be prevented.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram showing the acceleration state of an AC rotating machine;
Figure 2 is a block diagram of the synchronous switching device, Figures 3 and 4.
Figure 5 is an explanatory diagram of the operation of a conventional automatic synchronizer, Figure 5 is an explanatory diagram showing the synchronizing state, Figure 6 is a block diagram showing the configuration of an embodiment of the present invention, and Figure 7 is the operation of Figure 6. It is an explanatory diagram. In the figure, M is an AC rotating machine, 1 is a first power source, and 6 is a second power source. Note that the same reference numerals in each figure indicate the same or equivalent parts.

Claims (1)

[Claims] 1. After accelerating the alternating current rotating machine with a variable frequency first power source, and then adjusting the frequency and phase angle of the first power source to synchronize it with the second power source, the alternating current rotating machine In the operation control method of an AC rotating machine, the frequency of the first power source is increased by a predetermined value lower than the frequency of the second power source. The AC rotating machine is accelerated, and in this state, from the time when the phase difference between the first power source and the second power source becomes zero or near zero, the first power source
An automatic synchronization adjustment circuit for adjusting the frequency and phase of the power source is operated to increase the frequency of the first power source and match the phase difference between the first power source and the second power source. A method for controlling the operation of an AC rotating machine, characterized by: