JPS62286112A - Inverter controller - Google Patents

Abstract

PURPOSE:To reduce the loss of a DC circuit together with application of parts of low breakdown strength, etc. and to improve the economical properties with inverter controller, by using a circuit which uses a switch to perform the short circuit control in a partial period before and after the inverter is started. CONSTITUTION:A short circuit control circuit 5 performs the conduction control of the switching element of an inverter 2 based on the voltage detected by a voltage dividing circuit 4, that is, the short circuit control of a switch 6 based on the output frequency, the voltage control and a prescribed sequence. In other words, the circuit 5 closes the switch 6 before an inverter is started and the voltage applied to the inverter 2 is lowered less than the open voltage levels of full DC series circuit 1a and 1b of a solar battery 1. Thus high voltage is never applied to the inverter 2. Then the voltage less than said open voltage and decided by a load line is applied to the inverter 2 when the switch 6 is opened at an appropriate time point after the start of the inverter 2. Thus it is possible to reduce the loss of a DC circuit and to secure application of parts of low breakdown strength or a general-purpose inverter. Then the economical properties can be improved with an inverter controller.

Description

Detailed Description of the Invention 3. Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a control device for an inverter device driven by a power source formed by connecting a plurality of solar cells in series.

[Prior art]

An inverter that uses solar cells as a power source is disclosed in Japanese Patent Application Laid-Open No. 1983-132.
It is publicly known from Publication No. 174 and the like. This will be explained with reference to FIG. In the figure, a plurality of solar cells 1 are connected in series, and a voltage divider circuit 4 and VVVF (
(variable voltage, variable frequency) inverters 2 are connected in parallel, and the output of the inverter 2 drives the three induction motors.

Reference numeral 5 denotes a control circuit for setting the output voltage and output frequency of the inverter 2, which detects the power supply voltage, that is, the output voltage of the series circuit of the solar cells 1 via the voltage dividing circuit 4, and adjusts the output voltage 1 based on this. Determine the frequency. The details of control by the control circuit 5 will be explained below.

Fig. 2 is a graph showing the relationship between the output voltage, current, and power of a power supply consisting of a series circuit of solar cells 1 at a certain amount of light, where r, (solid line) is the voltage-current characteristic, and PI (dashed line) is the voltage. - Shows power characteristics. R8 is a load line viewed from the power supply side, and the maximum output P, may be obtained at the output voltage (1) at the intersection with the voltage-current characteristic I.

On the other hand, induction electric g9.3 human power P. is approximately 3 of the rotational speed N
Since it is proportional to the power of
By changing the output frequency of the power supply, it is possible to change the slope of the load line as seen from the power supply. Therefore, the control circuit 5
detects the power supply voltage using the voltage divider circuit 4, and controls the output frequency of the inverter so that this voltage matches the voltage (2) at the intersection point where the maximum output p,may is obtained. however,
In practice, constant torque operation is performed, so the voltage is also changed in accordance with the frequency, and the voltage/frequency ratio - window side '4In is calculated. Note that even if the amount of light received by the solar cell 1 changes, the voltage at which the solar cell 1 generates the maximum output is approximately constant, so the control of the control circuit 5 does not need to depend on changes in the amount of light received.

[Problem that the invention seeks to solve]

Now, in the conventional device as described above, the inverter is always started from point a (current O) of the open circuit voltage of the power supply, but the voltage at point a is the optimum operating voltage, that is, the voltage at point b It is 1.4 to 1.5 times. A switching element that constitutes the inverter 2.

Since it is necessary to use a filter capacitor on the DC side that can withstand this open circuit voltage, there are disadvantages in that component costs are high or a general-purpose VVVF inverter cannot be used. On the other hand, regarding the power supply side, it is desirable to increase the number of batteries connected in series in order to reduce loss in the DC circuit, but there is an inconvenience that there is an upper limit to the number of batteries connected in series due to the above-mentioned open-circuit voltage restriction (V).

The present invention was made to solve these problems, and by configuring the power supply to have a configuration that can increase the optimum operating voltage to the inverter's allowable input voltage or a value close to this, it is possible to reduce losses in the DC circuit. It is an object of the present invention to provide an inverter control device that is highly economical and can use low-voltage components or a general-purpose VVVF inverter.

[Means for solving problems]

The inverter control device according to the present invention is provided with a switch that can short-circuit a part of the series circuit of solar cells, and has a configuration in which the switch is closed for a part of the period before and after starting the inverter.

[Effect]

Before startup, some of the solar cells connected in series are short-circuited, so the voltage applied to the inverter is lower than the open-circuit voltage of the entire series circuit of solar cells. Therefore, high voltage is not applied to the inverter at startup as in the conventional case.

When the switch is opened at an appropriate time after startup, a voltage lower than the open circuit voltage and determined by the load line is applied to the inverter.

〔Example〕

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below based on drawings showing embodiments thereof.

FIG. 1 is an insulator circuit diagram showing an embodiment of an inverter control device according to the present invention. In the figure, numeral 1 denotes solar cells, many of which are connected in series. A series circuit of a switch 6 and a voltage divider circuit 4 made up of transistors, and a VVVF inverter 2 are connected in parallel between the positive and negative electrodes of a power supply made of such a solar battery series circuit.
The inverter output is given to the induction motor 3.

The connection point between the switch 6 and the voltage divider circuit 4 is connected to the middle of the series circuit of the solar cell 1, so the series circuit 1a divided into two is connected to the voltage divider circuit 4, and the other series circuit 1b is connected to the switch. 6 are connected in parallel.

The control circuit 5 controls the switching elements of the inverter 2 based on the voltage detected from the voltage dividing circuit 4, that is, controls the output frequency 'eJ, number, and voltage, and also controls the short circuit of the switch 6 based on a predetermined sequence. conduct.

Next, the control contents of this control circuit 5 will be explained. The control circuit 5 closes the switch 6 before starting the inverter 2. Since the solar cell 1 has drooping characteristics, the switch 6
Even if a short circuit occurs, an excessive short circuit current will not flow through the switch 6 and the series circuit 1b.

In Fig. 2, the voltage-current characteristics at the same light intensity as in I, P, of the series circuit 1a of the solar cell 1 are 2 (actual vA), and the voltage-power characteristics are P! (dashed line). If the inverter 2 is driven with the switch 6 short-circuited, the voltage at point e becomes the open voltage at startup. By appropriately selecting the number of solar cells 1 in the series circuit 1a, it is possible to set the voltage at point e to the optimum operating voltage 1. Next, the control circuit 5 increases the output frequency of the inverter 2 using the output of the voltage dividing circuit 4 in the same manner as described above to increase the rotational speed of the induction motor 3.
Control is performed to set the voltage at point d, which provides the maximum output P2max under this condition. R2 is the load line at this time.

When this state is reached, the control circuit 5 opens the switch 6. Now, assuming that the total number of solar cells in the series open circuits 1a and lb is equal to the number of solar cells in FIG. 4, by closing the switch 6,
The operating point of the circuit of FIG. 1 shifts to the intersection C of R2 and I. Next, under the condition in which the series circuits 1a and lb supply power, the maximum output is obtained, and control is performed to shift to point &b.

In this way, from the time of startup until the maximum output P is reached, the transition is made to points e, f, d, c, and b.

On the other hand, when stopping, first the switch 6 is closed.

As a result, the operating point moves from b to [, so it is only necessary to stop the inverter 2 next, and thereby the operating point moves from f to e.

Therefore, as described above, by appropriately selecting the number of solar cells in the series circuits 1a and 1b, the input terminal of the inverter 2 can always be kept at the optimum operating voltage V1 or lower.

In the above embodiment, the switch 6 is turned off at the voltage 2 at point d in FIG. 2, which is the optimum operating voltage of the series circuit 1a of the solar cell 1.
Although the circuit is open, the point C then shifts to b. Such a transition causes a large change in output voltage, so the induction motor 3
The change in the generated torque (proportional to the square of the input terminal) is large, therefore the change in rotational speed is also large, and the rotation is unstable. Therefore, as shown in Figure 3, the voltage dividing circuit is
If it is possible to detect the voltage of the series circuit of , and decide the timing to open the switch 6 based on this detected voltage value, it is also possible to perform control to directly shift from the point f to the point f.

〔effect〕

In the case of the device of the present invention as described above, it is possible to increase the proper operating voltage (1) of the power source using solar cells to the allowable input voltage of the inverter, and therefore it is possible to reduce loss in the DC circuit as well as to reduce the inverter's power consumption. Is there an inverter or its system that is economical because it can use pressure-resistant parts or a general-purpose inverter? An IO device can be realized.

[Brief explanation of drawings]

Fig. 1 is an implicit circuit diagram of the device of the present invention, Fig. 2 is an inverter voltage, current, and output characteristic diagram, Fig. 3 is an implicit circuit diagram of another embodiment of the present invention, and Fig. 4 is an implicit circuit of a conventional device. It is a diagram. 1...Solar cell 1a, Lb...Series circuit 2...
・Impark 4...Voltage dividing circuit 5...Control circuit
6... Switch In the drawings, the same reference numerals indicate the same or corresponding parts. (nee, -two (nee, -12 Shimi 2nd generation v2 self a -ichigaden 7th child 2nd figure 3rd figure

Claims (1)

[Claims] 1. In a control device for an inverter driven by a plurality of solar cells connected in series, a switch provided to short-circuit some of the plurality of solar cells; An inverter control device comprising: a short-circuit control circuit that is short-circuited for a period before startup and for a part of the period after startup. 2. The short-circuit control circuit is configured to open the switch when the voltage of the series circuit can reach a voltage determined in relation to the optimal operating voltage of the series circuit of all solar cells when the series circuit is not short-circuited. A control device for an inverter according to item 1.