JPS6053531B2 - Inverter control method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an inverter device that is operated in synchronization with the frequency of another AC power source, and relates to an inverter control method that enables parallel operation of the inverter device and other AC power source. be.

When operating an inverter device in parallel with another AC power source having a low impedance such as a commercial power source, the following two points need to be taken into consideration as in a general parallel system of AC power sources.

One of them is that if the phase of the inverter and commercial power supply is shifted,
A cross current of active current flows from a power source with a leading phase to a power source with a phase lag.

Another reason is that when the output voltage of the inverter device differs from the commercial power supply voltage, a cross current of reactive current flows from the high voltage power supply to the low voltage power supply. The former problem can be easily solved by adopting a commercial synchronization method, which is a well-known technology, in which the inverter is operated by synchronizing its output frequency with the frequency of the commercial power supply, but the latter problem can be easily solved by using a commercial synchronization method, which is a known technique. There was no technology that could easily solve the problem. SUMMARY OF THE INVENTION An object of the present invention has been made in view of the above points, and the object of the present invention is to insert an impedance element between the output end of an inverter device and another AC power source to reduce reactive power deviation caused by voltage fluctuations of the other AC power source. is detected as a voltage deviation between the two power supplies, and the amount of deviation is added to the comparator of the inverter's voltage control system to control the inverter so that the inverter's output voltage immediately follows the AC power supply voltage, thereby reducing the flow of cross current of reactive current. The present invention provides an inverter control method that prevents this from occurring.

Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

In the inverter device 30a shown in FIG. 1, 3a is an inverter that converts the DC voltage supplied from the DC bus 2a into AC, and the output signal of this inverter 7a 3a is shaped into a sine wave by the subsequent AC filter 4a. Ru. lb is a commercial power supply, 4b is a reactor 6 as a load, and 35 is a common bus line formed by commonly connecting the output ends of both power supplies. 41a rectifies the output voltage E33a of the AC filter 4a and supplies it to the comparator 4.
Rectifiers 51a and 51b are used to rectify the output voltage E3la of the inverter 3a and the commercial power supply voltage E3lb, respectively, and provide the rectifiers 51a and 51b to the voltage deviation detection circuit 52.

43a is a reference voltage source, 44a is an error amplifier, and 45a is a phase shifter.

An oscillator 46 provides a frequency reference for the inverter 3a, and in the present invention is a known commercial synchronous oscillator that oscillates in synchronization with the commercial power supply 1b.

47a is a gate circuit for generating a signal for controlling firing of each thyristor of the inverter 3a in a predetermined order.

In the above control circuit configuration, except for the voltage deviation detection circuit 52, the voltage control system of the inverter 3a is well known, and therefore a description thereof will be omitted. FIG. 2 shows an example of the voltage deviation detection circuit 52.
E5la and e5lb are rectifiers 51a and 51 shown in FIG.
Output voltage b, 52a is a switch for setting the voltage deviation signal to zero when only the inverter device is operated without performing the parallel operation of the present invention (that is, when the switch contact is open, the voltage deviation signal is zero) , 52v is a variable resistor, and 52r is a fixed resistor.

Next, the inverter device 3 shown in FIG. 1 to which this method is applied
The operation of the control circuit of the present invention will be described in the case where the commercial power supply voltage E3lb fluctuates while the commercial power supply 0a and the commercial power supply 1b are operating in the same manner.

Now, as a result of fluctuations in the commercial power supply, if the output voltage E33a of the inverter device 30a is higher than the commercial power supply voltage E3lb, the control circuit system 40a changes to the comparator 42 which is a voltage control system.
a from the voltage deviation detection circuit 52; (E3lb-E3l
As a result of adding a negative amount proportional to a), inverter 3
The output voltage E3la of a is controlled to decrease. Here, the variable resistor 52v allows the output currents of the inverter device 30a and the commercial power source 1b to vary to a value commensurate with the capacity of each power source. Set the partial pressure ratio in advance so that the
When the commercial power supply voltage E3lb fluctuates under the above-determined conditions, causing an output voltage deviation and disrupting the balanced state, the control circuit/circuit system 40a of the inverter device 30a adjusts the output voltage deviation to maintain a predetermined current balance. Therefore, the balance between the inverter device 30a and the commercial power supply 1b is always maintained.

In order to obtain such balance, the voltage deviation detection circuit 52 shown in FIG. 2 performs the following operation. That is, the voltage E5l converted into direct current by the rectifiers 51a and 51b
When the voltage deviation from a and e5lb is ★E5la=E5lb, the variable resistor 5 is set so that a predetermined current balance is obtained.
If you set the partial pressure ratio n of 2v, for example ★E5la
>E5ld, in the direction of the arrow shown (Me
When 5la<E5lb, a current flows in the opposite direction of the arrow), and as a result, a voltage of 1 (Ine5la-E5lb) appears across the fixed resistor 52r of the voltage deviation detection circuit 52. The voltage 53a extracted in this way is applied to the comparator 42a of the voltage control system, and the voltage difference with the reference voltage source 43a is applied to the phase shifter 45a. This phase shifter 45a receives pulses from the commercial synchronous oscillator. Depending on the level of the differential voltage,
In addition to the pulse width control gate circuit 47a, the inverter 3a
Controls the firing of the thyristor.

Note that in the above embodiment, parallel operation of one inverter device and a commercial power source was explained, but parallel operation of a parallel system consisting of two or more inverter devices and a commercial power source,
It goes without saying that the present invention can also be applied to other uncontrollable AC power sources instead of commercial power sources.

It goes without saying that the present invention is limited to the above-mentioned embodiments and may be modified in various ways.

For example, the detection point for the voltage deviation between the inverter device 30a and the commercial power source is on the input side of the AC filter 4a1 impedance element 4b, but the inverter device may be taken out from a predetermined location of the AC filter 4a, or the point of detection of the voltage deviation between the inverter device 30a and the commercial power supply If the voltage across the reactor is a commercial power supply, the voltage across the impedance element may be used. As described above, according to the present invention, an impedance element having a predetermined impedance is inserted between the output side of the inverter device and the output side of another AC power source, and the inverter is simply connected to the comparator of the inverter output voltage control system. Since it is only necessary to add a voltage deviation signal between the input side of the AC filter of the device and the input side of the impedance element, parallel operation of the inverter device and another AC power source can be easily realized.

In addition, the impedance element can be replaced by a transformer that is normally installed for the purpose of insulation, voltage step-up, voltage step-down, etc., which is economically advantageous. Therefore, if an uninterruptible power supply system is configured using a device to which the control method according to the present invention is applied, the cost of the entire system can be reduced and high reliability can be expected.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention, and FIG. 2 is a schematic configuration diagram showing an example of a voltage deviation detection circuit of the device shown in FIG. 30a... Inverter device, 3a... Inverter,
4b...AC filter, 40a...control circuit system, 4
1a... Rectifier, 42a... Comparator, 43a...
Reference voltage source, 44a...Error amplifier, 45a...Phase shifter, 46a...Commercial synchronous oscillator, 47a...Gate circuit, 52...Voltage deviation detection circuit, 1b...Commercial power supply, 4b... Impedance element, 6... Load.

Claims (1)

[Claims] 1. The output of an inverter device that includes an inverter and an AC filter, compares the output of the AC filter with a reference voltage using a comparator, controls the pulse width using the difference voltage, and controls the firing of the thyristor of the inverter; In a device in which the output of a commercial AC power source is operated in parallel with the output of a commercial AC power source via an impedance element, the output frequency of the inverter is controlled so that the output of the inverter device is synchronized with the output of the commercial AC power source, and a predetermined frequency of the AC filter is controlled. The deviation between the voltage taken out from the position and the voltage obtained from the input side of the impedance element provided on the output side of the commercial AC power source is detected, and this deviation amount is added to the comparator, and the output voltage of the AC filter is adjusted to the output voltage of the AC filter. An inverter control method, characterized in that the inverter is controlled so as to match the output voltage of an impedance element.