JPH0564029B2 - - Google Patents

Description

Detailed Description of the Invention [Technical Field of the Invention] The present invention relates to an AC load driven by a variable frequency power converter and an AC power supply independent of the variable frequency power converter. The present invention relates to a variable frequency power converter having an improved operating method for use in switching power sources.

[Technical background of the invention and its problems] The configuration shown in FIG. 1 is a power source for an AC load 3 that is switched by a variable frequency power converter 2 and an AC power source 1 and a switching device 4 that are independent of the power converter. It is a figure showing a case. In the conventional example in the same figure, although the sequence is not shown, the AC load is once disconnected from the power converter 2, and after a predetermined time, the AC power source 1
This was done by switching to However, this method has the problem of overcurrent flowing through the AC load 3 and sudden load fluctuations during switching. Another method is to switch the power supply by matching the output phase of the power converter and the power supply phase of the AC power source.

In this conventional example, as shown in FIG. 2, in an AC load 3 having a variable frequency power converter 2 and an AC power source 1 having an independent AC power source 1 for the power converter 2, the power converter 2 and the AC load 3.
1. Consists of a second switch 42 provided between the AC power supply 1 and the AC load 3. Only the frequency control of the power conversion device 2 is performed by the second
As shown in the figure, generally a speed setter 11, an input limiting circuit 12 that sets acceleration/deceleration time, an oscillator 13 that converts a frequency reference into a pulse signal, and the oscillator 13
a frequency divider circuit 14 that divides the output signal of, for example, 1/6;
A phase coincidence detection circuit 15 that detects that the output AC phase of the power converter 2 and the phase of the commercial power supply 12 have a predetermined phase difference, a PLL circuit 16 that detects the phase of the AC power supply 1, and a power supply switching circuit. It is constituted by a power supply switching circuit 17 that issues a command.

In this configuration, when switching from the power conversion device 2 to the AC power source 1, the speed setting device 1
1 is set as the AC power supply frequency, and the power converter 2 is accelerated to the AC power supply frequency according to the acceleration/deceleration time determined by the input limiting circuit 12. After completing acceleration,
The frequency reference is subtly changed so that the phase of the AC power supply 1 detected by the PLL circuit 16 and the output AC phase of the power converter 2 fall within a predetermined phase difference, and the output AC phase of the power converter 2 is adjusted to the AC power supply. 1
The phase matching detection circuit 15 confirms that the phase difference is within a predetermined value, and the power switching circuit 17 outputs a power switching signal to the second switch 42. The second switch 42 is turned on by this power supply switching signal, and the power converter 2 and the AC power supply 1 are connected in parallel, resulting in a parallel running period. It is opened and power switching is completed.

The above-described power supply switching has the following disadvantages.

Stable power supply switching was not possible since it took time for the first switch 41 or the second switch 42 to be turned on after the output phase of the variable frequency power converter 2 and the AC power supply phase were synchronized.
In order to switch within a fixed time, it is necessary to supply a certain amount of transfer difference, and an excessive current flows through the AC load 3 and the power converter 2.

If the AC power frequency is f ₀ , the output frequency of the power converter is f ₁ , and the difference between the AC power frequency and the output frequency of the power converter is fc, then the relationship is fc = f ₀ − f ₁ ...(1). . In this case, the maximum time T required to detect that the phase with the AC power supply frequency is in phase can be determined from the relationship T=1/fc (2). As can be seen from equation (2), the smaller the difference fc between the two power supply frequencies, the longer the phase matching detection time becomes. Therefore, in conventional power converters, the output frequency of the power converter is increased to the AC power supply frequency and then the frequency is slightly changed to detect phase matching, so the difference fc between the two frequencies becomes minimal and phase matching is detected. It takes a very long time.

[Object of the Invention] Therefore, the object of the present invention is to improve the reliability of switching between two independent AC power sources by being able to complete the switching within a predetermined time without passing an excessive current to the AC load, etc. An object of the present invention is to provide a power conversion device.

[Summary of the Invention] The present invention detects that the output frequency of a power conversion device deviates from the AC power supply frequency by a certain frequency, maintains the output frequency, and maintains the output frequency by a certain phase difference with respect to the AC power supply phase at that frequency. It is detected that there is a relationship between After that, by accelerating and decelerating at a rate of change determined by the maintained frequency and phase difference, when the frequency becomes the same as the AC power supply frequency, the phase also matches, which allows switching in a very short time. This is what I decided to do.

[Embodiment of the Invention] FIG. 3 is a block diagram showing an embodiment of the present invention. In the figure, a circuit that supplies current to an AC load 3 includes a power converter 2 that generates a variable frequency, and a power converter 2 that generates a variable frequency. 2, an AC power supply 1 independent of the power converter 2 or an AC load 3 driven by the AC power supply 1, and a first switch 41 provided between the power converter 2 and the AC load 3. ,
It consists of a second switch 42 provided between the AC power supply 1 and the AC load 3. The control circuit also includes a speed setter 11 that provides a speed reference to the power converter 2, an input limiting circuit 12 that gives a certain slope to the speed reference provided by the speed setting device 11, and an output signal of the input limiting circuit 12. an oscillator 13 that converts the output of the oscillator 13 into a pulse signal, a frequency dividing circuit 14 that divides the output of the oscillator 13 into 1/6, and an output AC phase of the power conversion device 2 and a power supply phase of the AC power source 1 within a predetermined phase difference. A phase coincidence detection circuit 15 detects the phase of the AC power supply 1, a PLL circuit 16 detects the phase of the AC power supply 1, and the output signal of the phase coincidence detection circuit 15 causes the first switch 41 and the second
a power supply switching circuit 17 which outputs an opening/closing signal to the switch 42; a switch 22 which is opened and closed by the output signal of the phase coincidence detection circuit 15; an acceleration rate circuit 21 having a predetermined slope independent of the input limiting circuit 12; The frequency detection circuit 24 detects that the output signal of the input control circuit 12 has reached a predetermined value and makes the output signal value of the oscillator 13 constant, and the switch 23 is opened and closed by this signal.

In this way, this embodiment includes a frequency detection circuit 24 that detects the output frequency of the power converter 2 at a point lower than the AC power supply frequency by a predetermined value and keeps the output frequency of the power converter 2 constant. A switch 23 that cuts off the output signal of the speed setting device 11 according to the signal and the output frequency of the power converter 2 are made constant and the AC power supply phase and the output phase of the power converter 2 fall within predetermined values. When switching the power supply in the power converter 2 characterized in that it is equipped with a phase coincidence detection circuit 15 that detects a phase coincidence detection circuit 15, a switch 22 that operates an acceleration rate circuit 21 by this output signal, and an acceleration rate circuit 21, Paying attention to the points described later, the power supply is switched within a predetermined period of time.

In giving a detailed explanation of the present invention, it is assumed, for example, that the AC power frequency f ₀ is 50 Hz, the output frequency f ₁ of the power converter is 49 Hz, and the difference between the two frequencies fc is 1 Hz. After the frequency detection circuit 24 detects f ₁ =49Hz, the time required for the phase coincidence detection circuit 15 to detect that the two phases are within a predetermined value is 1 second at the most according to the above (Formula 2). In addition, after phase detection at f ₁ = 49Hz, the acceleration rate circuit 2 is used to accelerate the output frequency of the power converter 2 to the AC power frequency.
1 has a rate of change of 1 Hz/1 second. This acceleration change rate of 1 Hz/1 second is the AC power frequency f ₀ = 50
Hz, and only when the output frequency f ₁ of the power conversion device 2 is 49 Hz, and varies depending on the conditions of f ₀ and f ₁ . The acceleration rate circuit 21 adjusts the output frequency of the power converter.
When accelerating f ₁ from 49Hz to 50Hz, the phase coincidence detection circuit 15 detects that the output phase of the power conversion device 2 and the AC power supply phase reach a predetermined value at f ₁ = 49Hz. The output frequency f ₁ of the power converter 2 increases by 1 Hz, and it takes 2 seconds until the output phase of the power converter 2 and the AC power phase are synchronized to the point where the AC power frequency f ₀ =50 Hz. It can be completed in seconds. At this time, the phase coincidence detection circuit 15 outputs a phase coincidence detection signal to the power supply switching circuit 17, so that the power conversion device 2
Also, the power supply can be switched within a predetermined time without causing an overcurrent to flow through the AC load 3 or the like.

As another embodiment of the present invention, as shown in FIG. 3, the internal circuits of the power conversion device 2, particularly the PLL circuit 16, the phase coincidence detection circuit 15, etc., are digitized. This eliminates amplifier offset, which is a problem with analog circuits, improves phase detection and frequency accuracy, and minimizes deviations between the power converter 2 output phase and the AC power supply phase, which can be a problem when switching power supplies. Therefore, shortening of switching time and stable power supply switching can be realized.

Further, FIG. 4 shows an operation diagram of another embodiment. f ₁
When the acceleration rate circuit 21 accelerates at a predetermined acceleration rate (1 Hz 1/1 sec) after phase matching is detected at =49Hz, f ₁ =49Hz is first detected by the frequency detection circuit 2.
Assume that there is an error in detection according to 4 and an error in phase coincidence detection. It is conceivable that after 1 SEC, f ₁ = f ₀ and the output phase of the power conversion device 2 and the AC power supply phase cannot match due to the above-mentioned error. This is the above (Equation 1) phase coincidence detection time T = 1/fc
When the error is -0.1Hz up to 49Hz due to [SEC]
f ₁ after 1SEC is 49.9Hz, and phase matching detection time T
This is because the smaller the error is, T=1/(50-49.9)=10 [SEC], the more difficult it becomes, and the phase matching will not work and the signal will pass through. Acceleration rate circuit 2
The power supply switching time can be shortened by changing the acceleration rate of the output signal 1 (1Hz/1SEC) to the same deceleration rate after a predetermined time, and by changing the acceleration rate to the same rate after a predetermined time and repeating this process. It becomes possible.

[Effects of the Invention] As described above, in the power converter according to the present invention, it is possible to switch the power supply with an independent AC power supply to the power converter in the shortest possible time, and to cause an excessive current to flow through the AC load and the power converter. Stable switching is achieved without any problems. This makes it possible to switch between the power converter and the AC power supply even in a load such as a boiler where fluctuations in air volume have a large effect on the machine, allowing the power converter to be used most effectively. Therefore, it is possible to provide a power conversion device that can be applied to an energy-saving variable speed drive system that is highly reliable and economical.

[Brief explanation of the drawing]

FIG. 1 is a system diagram using a power conversion device to which the present invention is applied, FIG. 2 is a block diagram of a conventional device, FIG. 3 is a block diagram showing an embodiment of the present invention, and FIG.
The figure is an operation explanatory diagram for explaining the operation of another embodiment of the present invention. 1... AC power supply, 2... Power converter, 3...
AC load, 4...Switching device, 11...Speed setter, 12...Input limiting circuit, 13...Oscillator, 1
4... Frequency dividing circuit, 15... Phase coincidence detection circuit, 1
6...PLL circuit, 17...Power switching circuit, 21
... Acceleration rate circuit, 22 ... Switch A, 23
...Switch B, 24...Frequency detection circuit, 41
...First switch, 42...Second switch.

Claims (1)

[Claims] 1. A power converter that generates variable frequency alternating current as an output, an AC power supply independent of the power converter, an AC load driven by the power converter or the AC power supply, and the power converter and the AC load. a first switch provided between the AC power source and the AC load; and a second switch provided between the AC power source and the AC load, for switching from the power conversion device to the AC power source as a power source for the AC load; a first means for detecting the phase of the alternating current power supply; a second means for detecting that the frequency of the power conversion device differs by a predetermined first frequency from the frequency of the alternating current power supply; a third means for instructing maintenance of the output frequency of the power converter according to the detection signal of the second means; while the third means is in operation, the output AC phase of the power converter is fourth means for detecting that the phase is a predetermined first phase difference from the phase of the power supply, and according to the detection signal of the fourth means, the frequency of the power converter is adjusted by the first frequency and fifth means for instructing the frequency of the AC power supply to approach the frequency of the AC power supply at a rate of change determined by the first phase difference; during operation, the fifth means commands the output AC phase of the power conversion device and the AC power supply to approach the frequency of the AC power supply at a rate of change determined by the first phase difference; detecting that the phases of the two match within a second phase difference that can be considered to be substantially in phase, and instructing switching of the power source from the power converter to the alternating current power source;
A power conversion device characterized by comprising the following means.