JP3027891B2 - Control method of variable speed inverter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a variable voltage variable frequency (VVVF) inverter (hereinafter referred to as "VVVF") suitable for driving a water pump driving motor at a variable speed using a solar cell as a power supply.
Solar inverter or variable speed inverter).

[0002]

2. Description of the Related Art Conventionally, in this type of solar inverter,
A control method called a maximum power tracking control method (Pmax control method) is generally adopted. This is a method of finding a point at which the maximum power Ph can be supplied while changing the load on the power characteristic curve of the solar cell as shown in FIG. If such a method is applied to a variable speed inverter that drives a pump motor as it is, the following will occur.

[0003] (1) First, the frequency (speed) of the motor is gradually increased. As the speed increases, the load capacity (power) also increases. (2) If the load capacity exceeds the power that can be supplied by the solar cell, power cannot be supplied from the solar cell, and the power decreases. Therefore, the speed of the motor is reduced to return to the maximum power point Ph that can be supplied by the solar cell. The procedure is as follows.

[0004]

However, in such a method, when the load capacity actually exceeds the power that can be supplied by the solar cell, the DC voltage of the solar cell rapidly decreases, and the power that can be supplied is also reduced. As a result, the balance between the load capacity and the power supplied from the solar cell is lost, and the inverter cannot continue to operate, resulting in a problem that the system goes down. FIG. 6 shows the state at this time. FIG. 6A shows a change in frequency (speed), and FIG.
Indicates a change in power, and shows an example in which the system goes down at time T1.

[0005] For this reason, a control method has been proposed in which when the power is reduced, the speed is rapidly reduced to avoid a system down. According to this method, when the power decreases as shown in FIG. 7B, the speed is rapidly reduced as shown in FIG. 7A, and the speed is gradually increased from there, as shown in FIG. Wait for the power to rise, and when the power drops, the same figure (a)
The control is performed such that the speed is rapidly reduced as shown in FIG. However, since this method constantly changes the speed, there is a problem that the solar cell cannot be used efficiently. Therefore, it is an object of the present invention to eliminate system down and to enable efficient use of solar cells.

[0006]

According to a first aspect of the present invention, there is provided a variable-speed inverter for driving a motor at a variable speed by using a solar cell as a power source, and monitoring the power of the solar cell. When the frequency decreases from the maximum value, the frequency command is rapidly reduced to a constant value, and the frequency at which the power decreases is stored, and as long as the power does not decrease, immediately before the stored frequency from the constant value. Until the value is reached, the frequency command is gradually increased.

According to a second aspect of the present invention, the voltage of the solar cell of the variable speed inverter that drives the motor at a variable speed using the solar cell as a power source is monitored, and when the voltage drops below a predetermined level, the frequency command is kept constant. While the voltage is rapidly lowered to a value, the frequency at which the voltage is reduced is stored, and as long as the voltage does not fall below a fixed value, the frequency is gradually increased from the fixed value to a value immediately before the stored frequency. It is characterized by increasing the order.

[0008]

The power or voltage of the solar cell is monitored, and a speed command slightly lower than the point at which the power balance is lost is given to control the inverter, so that the power supplied from the solar cell to the load is maximized.

[0009]

FIG. 1 is a schematic diagram showing a first embodiment of the present invention.
FIG. 2 is an explanatory diagram for explaining the operation. In addition,
In FIG. 1, 1 is a solar cell, 2 is a multiplier, and 3 is a RAM.
A processing unit (CPU unit) including a memory 31, a comparator 32, a speed command calculator 33, and the like, and 4 denotes a VVVF inverter, respectively. That is, the multiplier 2 obtains the electric power P by multiplying the voltage V and the current I of the solar cell 1 and supplies the electric power P to the CPU unit 3. The CPU unit 3 converts the signal into a digital signal by a converter (not shown) and stores it in the RAM memory 31.
2, the previous value (for VVVF inverter 4)
The speed (frequency) command value ω ^* is increased / decreased and output at regular time intervals, and is compared with the previous speed command value and the corresponding power value).

As a result, if the power value has increased from the previous time, the speed command value ω ^* is also increased, and if the power value has decreased, the speed command value ω ^* (frequency f0 in FIG. 2) at that time is stored. , The speed command value ω ^* is set to a constant value (in FIG.
b) drop rapidly. Thereafter, the speed command value ω ^* is gradually increased until immediately before the stored value. In FIG. 2, the immediately preceding value is indicated by the frequency ft. And, but for a certain period of time driving to increase again the speed command value ω ^* After a certain period of time to drive at that speed command value ω ^*, and stores the speed command value ω ^* at that time if the power value is lower than the previous value At the same time, the speed command value ω ^* is rapidly reduced to a constant value, and thereafter, the speed command value ω ^* is gradually increased until immediately before the stored value.
As a result, as shown in FIG. 2B, the load is supplied with power substantially equal to the maximum power Ph.

FIG. 3 is a block diagram showing another embodiment of the present invention, and FIG. 4 is an explanatory diagram for explaining its operation.
1 and 2 monitors the electric power P of the solar cell 1, whereas here, a comparator 5 and a setting unit 6 are provided as shown in FIG. The voltage V is monitored, and when the voltage V falls below a certain level Va as shown in FIG. 4B, the speed command value ω ^* at that time (in FIG. 4, the frequency f
0 ′) is stored, and the speed command value ω ^* is rapidly reduced to a constant value (frequency fb ′ in FIG. 2). Thereafter, the speed command value ω ^* is gradually increased to just before the stored value. In FIG. 2, the immediately preceding value is indicated by the frequency ft ′. And, although operating a certain period of time to increase the ^* again speed command value ω After a certain period of time to drive at that speed command value ω ^*, the voltage value to store the speed command value ω ^* at that time if it falls below the previous value At the same time, the speed command value ω ^* is rapidly reduced to a constant value, and thereafter, the speed command value ω ^* is gradually increased until immediately before the stored value. As a result, a substantially constant voltage Vc is supplied to the load as shown in FIG.

The above description has been made mainly on the case where the water pump is driven. However, the present invention is not limited to this, and can be generally applied to loads using a solar cell as a power source.

[0013]

According to the present invention, the power or voltage of the solar cell is monitored, and the inverter is controlled by giving a speed command slightly below the point at which the power balance is lost. There is an advantage that a substantially constant voltage can be efficiently supplied from the solar cell to the load.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a first embodiment of the present invention.

FIG. 2 is an explanatory diagram for explaining the operation of FIG. 1;

FIG. 3 is a block diagram showing a second embodiment of the present invention.

FIG. 4 is an explanatory diagram for explaining the operation of FIG. 3;

FIG. 5 is a graph showing voltage-power characteristics of a solar cell.

FIG. 6 is an explanatory diagram for explaining a system down.

FIG. 7 is an explanatory diagram for explaining an example of a conventional control method.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Solar cell, 2 ... Multiplier, 3 ... Processing part (CPU part),
4 VVVF inverter, 5, 32 comparator, 6 setter, 31 RAM memory, 33 speed command calculator.

Claims (2)

(57) [Claims] 1. A variable speed inverter that drives a motor at a variable speed using a solar battery as a power supply monitors the power of the solar battery, and when the power drops from a maximum value, rapidly reduces a frequency command to a constant value. The frequency at which the power decreases is stored, and as long as the power does not decrease, the frequency command is gradually increased from the constant value to a value immediately before the stored frequency. Control method of variable speed inverter. 2. A variable speed inverter that drives a motor at a variable speed by using a solar battery as a power supply monitors a voltage of the solar battery, and when the voltage drops below a predetermined level, rapidly reduces a frequency command to a certain value. At the same time, the frequency at which the voltage decreases is stored, and as long as the voltage does not fall below a certain value, the frequency command is gradually increased from the constant value to a value immediately before the stored frequency. A method for controlling a variable-speed inverter, comprising: