JPS5914372A - Inverter device - Google Patents

Abstract

PURPOSE:To stabilize an inverter device by providing an impedance in an inverter main circuit, and inserting an impedance in the main circuit only when an arm of the inverter is energized. CONSTITUTION:When the quantity of light emission is reduced at the time of driving a pulse at the normal time so the the voltage of a battery becomes a reference level of lower of a comparator 12, a relay 13 is deenergized, normal- open contacts B131, B132 are opened, an impedance 3 is inserted into a DC intermediate circuit of an inverter, and a voltage control system which includes a voltage control amplifier 14 immediately opens. An ON gate signal is applied to energize only specific arm of a power inverter 4 under the condition that the relay 13 is deenergized in a pulse width modulation controller 17 in a parallel with this operation. In this manner, an impedance 3 is connected as a load of a solar battery 1, and the power from a battery 1 is limited.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an inverter device using a solar cell as an input power source, and particularly relates to an unstable phenomenon when the inverter is started when the amount of light irradiation is small and the voltage of the solar cell is low. (such as stoppage phenomenon). The present invention aims to provide an improved inverter device.

An inverter device that operates using solar cells as an input power source is
It is being used as a variable frequency power source for driving pumps.

When using such a solar cell as an operating power source, as is well known, the voltage and power of the solar cell are dependent on the amount of light irradiation and the cell temperature. A diagram of current and output characteristics versus battery voltage (with battery voltage on the horizontal axis and output and current on the vertical axis, showing the voltage-current and output characteristics when the battery temperature is constant and the amount of light irradiation is used as a parameter) Then, the battery current is adjusted to perform predetermined speed control so that the inverter operates at the maximum power point of each characteristic indicated by the broken line. With such an inverter control method, the inverter is operated at the maximum power point shown by the broken line for each characteristic with the amount of light irradiation as a parameter, so battery power can always be used efficiently and effectively. . However, the problem is that
This is the state of the solar cell that is the input power source when starting the inverter. In other words, if you start the inverter when there is a certain amount of light irradiation and the battery voltage is lower than the voltage value corresponding to the maximum power point, the battery voltage will drop suddenly and the inverter will eventually stop. An unstable phenomenon is observed. As a method to solve this unstable phenomenon at startup, for example, a small simulated load (generally indicating impedance) such as the smallest load among the regular inverter loads is prepared, and the voltage value of the solar cell is set in advance. If the voltage is below the reference level, the inverter is disconnected, the simulated load is connected as a battery load, and the inverter is turned on again after waiting for the battery voltage to recover and reaches the reference level, after which the simulated load is cut off. A method is proposed. This method has the disadvantage that a new simulated load must be provided and the inverter itself becomes larger. More importantly, in the case of a pump load under steady state, as is well known, the pump output is
Since it is a characteristic that changes in proportion to the power of the inverter control system, the gain of the inverter control system during control is high in the high rotational speed region, and low gain in the low speed region, so it changes over the entire operating range. The gain changes greatly, making stable operation impossible.

The present invention was invented in view of this point, and in particular, the present invention provides an impedance as a simulated load in the inverter main circuit, and when the impedance is inserted, only one arm of the inverter is in a energized state, which further reduces the size of the inverter. The major feature of this system is that it achieves operational stability, and will be described in detail below based on the embodiment shown in FIG.

In the same embodiment, 1 is a solar cell formed by connecting an arbitrary number of cells in parallel, 2 is a DC reactor of the DC intermediate circuit, and 6 is inserted into the inverter main circuit only when the solar cell output is below a reference level. A simulated load as an impedance, the capacity of which is preselected in advance to be, for example, a value lower than the minimum value of the pump load of the inverter.

4 is an inverse conversion section, and this inverse conversion section includes thyristors 6, to 61.
+ and current suppression reactor 5□ ~ 56 Monbetsu - Sato Kirine confrontation -
≠≠ It consists of Toki 7-Machi, and the accelerator inserted in each arm is for suppressing the forward current "/dt", 7 is a rust conduction motor for driving the pump, 8 is the pump, 9 is a voltage setting device, 10 is a voltage detection circuit that detects the voltage between the terminals of the solar cell, 11 is a comparator that compares the voltage setting command signal and the voltage detection signal, and 12 is a comparator that compares the ON voltage of the inverter. The OFF! pressure has a hysteresis characteristic as shown in the figure. 13 is a relay that operates using the output of the comparator, and its normally open contact 13 is connected in parallel with the impedance. 14 is a voltage control 15 is an amplifier for upper-lower limits that limits the upper and lower limits of the voltage command value by +7 within the specified range.
16 is a function generator to keep the loop gain of the control system constant, and the characteristic of this function generator is that the pump output is 3 times the rotation speed.
Since the characteristic is proportional to the power, the input-output characteristic should have a function of Y as shown in the figure. Reference numeral 17 denotes a pulse width modulation control unit for controlling the switching element group of the inverse conversion unit in pulse width.As is well known, this control unit generates a signal based on a frequency command signal derived from a function generator. The sine wave signal of the signal wave and the triangular wave signal of the carrier wave are matched, and the signal obtained as a result of this comparison is used to gate drive the element group of the inverse conversion section.

To describe the operation of this embodiment configured as described above, if the level of the solar cell detection signal derived from the voltage detection circuit 10 is equal to or higher than the reference level of the voltage setting device 90, the output of the comparator 12 is The relay 16 is energized and its normally open contacts 13+ and 13x are closed, and the battery output of the solar cell is transferred from the DC reactor 2 to the normally open contacts 13. →The upper-lower limit IJ transmitter amplifier 15-function Generator 1
A predetermined gate signal is generated in the path of the 6-pulse width modulation control section 17, and the element group 6.6 of the inverse conversion section 4 is generated. For example, when the battery output is high and the pump 8 is driven in a high speed region, the characteristic of the function generator 16 is the cube root characteristic (Y) shown in the figure, so the pulse width of the function generator 16 is controlled by pulse width. During the period when the highest level signal limited by the lower limiter amplifier 15 is input, the output signal level of the function generator 16 is limited so that the gain change is approximately equal to the low speed to medium speed region, and this signal is Accordingly, a predetermined speed control is performed to regulate the inverter frequency and prevent the pump speed from increasing rapidly. In such a state, when the amount of light irradiation decreases and the battery output drops, the output signal level of the voltage control amplifier 14 that amplifies the error voltage also decreases, and the frequency command output from the function generator 16 gradually decreases. The pump speed is controlled in the direction of deceleration. If the battery output of the solar cell is at the same level as the reference level, the upper-lower limit IJ
The signal output from the transmitter amplifier 15 is held at the lower limit level, and using this signal, the function generator 16 outputs a required frequency command and the pump speed is driven in a low speed region. As described above, according to this embodiment, the pump rotation speed is controlled according to the output level of the solar cell, and during such control, as shown in the characteristic diagram of FIG. It goes without saying that the battery current taken into the inverter is adjusted so that the inverter operates at the maximum output point that intersects with the broken line in order to constantly improve efficiency during operation and effectively utilize the battery.

When the light irradiation amount suddenly decreases and the battery voltage falls below the reference level of the comparator 12 during pump driving in such a steady state, the relay 16 is turned off and 13. - i 3
．． Each normally open contact is opened, an impedance 6 is inserted into the DC intermediate circuit of the inverter, and the voltage control system including the voltage control amplifier 14 is immediately opened. In parallel with this operation, the pulse width modulation control unit 17 is configured to energize only specific arms of the inverse conversion unit 4 on the condition that the relay 16 is turned off. If so, the U-arm element 6. An ON gate signal is applied to the element 64 of the X arm, and gate signals to other element groups are immediately blocked. By performing such a predetermined operation, diimpedance 3 is connected as a load to solar cell 1, and solar cell 1→DC reactor 2→impedance 3→reactor 51→element 6. A current shown by the arrow flows through the path → element 64 → reactor 54, and the power from the battery is transferred to the impedance 6 and the reactor 2-5. -5. will be limited by. In addition, even during such operation, the total impedance of the impedance 6 and each reactor is set in advance so that the battery current corresponding to the maximum power point of the characteristic is taken into the above path in accordance with the battery voltage. It is specified that the inverter will not become inoperable when the battery is recovered due to a sudden drop in battery output.

As described above, in the present invention, an impedance is provided in the inverter main circuit, and the impedance is inserted into the main circuit only when the inverter is energized at one time, and waits for the battery voltage to recover. This provides various effects as shown below.

■The impedance inserted into the main circuit of the inverter is a resistor, and this resistor and the main circuit reactor constitute a simulated load, so the inverter itself can be miniaturized.

■If the battery voltage is below the reference level, the simulated load is connected as a battery load and the inverter is restarted after waiting for the battery to recover. Unstable phenomena such as operation stoppage can be resolved all at once.

■Since there is a level difference between the ON operating voltage and OFF operating voltage of the inverter to create a hysteresis characteristic, the inverter will turn ON and OFF when the battery voltage is near the operating point.
It is possible to completely prevent operational hunting such as that caused by F, and to realize a highly stable inverter device.

(2) Since the loop gain of the control system is kept constant over the entire operating range, it is possible to realize a device with even higher operational stability based on the advantage of item (2) above.

[Brief explanation of the drawing]

FIG. 1 is a specific circuit configuration diagram of an inverter device showing one embodiment of the present invention, and FIG. 2 is a characteristic diagram showing the general voltage-current and output correspondence of a solar cell. . 1 is a solar cell, 2 is a DC reactor, 6 is an impedance, 4 is an inverse conversion unit, 51 to 56 are di/at suppression reactors, 61 to 66 are thyristors, 9 are voltage setting devices, 1
0 is a battery voltage detection circuit, 12 is a comparator, 16 is a relay, 14 is a voltage control amplifier, 15 is a lower limit IJ
16 is a function generation circuit, and 17 is a pulse width modulation control section. %￥ [Applicant

Claims (3)

[Claims] (1) In a device that uses the output of a solar cell as a DC power source to drive a load at variable speed, an impedance is provided that is inserted into the inverter main circuit only when the output voltage level of the solar cell is below the inverter operating level. An inverter device characterized in that when this impedance is inserted, only one arm of the inverter is energized and the other arm is de-energized. (2) The inverter device according to claim 1, wherein the impedance is a resistance. (3) The total impedance of the impedance and the inverter main circuit is 1. The inverter device according to claim 1 or 2, wherein the inverter load is set to a value lower than the minimum load of the inverter.