Method and device for controlling photovoltaic inverter, and feed water device

• US 20050116671A1
• Filed: 01/29/2003
• Published: 06/02/2005
• Est. Priority Date: 01/31/2002
• Status: Active Grant

• Current Assignee: Ebara Corporation, Fuji Electric Company Limited (Fuji Electric Systems Company Limited)
• Original Assignee: Fuji Electric Holdings Company Limited (Fuji Electric Systems Company Limited)
• Inventors: Minami, Masahiro, Ichikawa, Hiroaki, Nakajima, Kaoru, Murai, Yukio, Kawai, Masahito
• Granted Patent: US 7,126,294 B2
• Time in Patent Office: Days
• US Class Current: 318/275
• CPC Class Codes: G05F 1/67 to the maximum power available from a generator, e.g. from solar cell
• CPC Class Codes: H02J 7/35 with light sensitive cells
• CPC Class Codes: H02M 1/0022 the disturbance parameters being input voltage fluctuations
• CPC Class Codes: H02M 7/53875 with analogue control of three-phase output
• CPC Class Codes: H02P 27/06 using dc to ac converters or inverters H02P27/05 takes precedence
• CPC Class Codes: Y02E 10/56 Power conversion systems, e.g. maximum power point trackers
• CPC Class Codes: Y10S 323/906 Solar cell systems

Abstract

A photovoltaic inverter control method includes steps of monitoring a variation in output voltage of a solar battery by a power and voltage monitoring circuit (51) and, when the variation occurs, accelerating or decelerating an electric motor (3) to maximize the output voltage of the solar battery (1), whereby the electric motor for driving, for example, a pump and a fan by the solar battery as a power source can be driven by a photovoltaic inverter always at the maximum power point of the solar battery.

Claims

1. A method of controlling a photovoltaic inverter for variable-speed controlling a motor with solar cells as its power source comprising

a step of starting up the motor by supplying a start-up power through the photovoltaic inverter from said solar cells while monitoring the output power and voltage of said solar cells,

a step of storing the voltage value of the solar cells as a reference voltage V_BASE when the power of said solar cells reached the maximum power point in the process of accelerating the rotational speed of this motor for a given acceleration time,

a step of continuing accelerating until the voltage of the solar cells shifts from said reference voltage V_BASE to a voltage (V_BASE-V_OVER) lower by a previously set voltage range V_OVER,

a step of, after the voltage of the solar cells reached this voltage (V_BASE-V_OVER), decelerating the speed of said motor for a given deceleration time until the voltage of the solar cells shifts from this voltage to said reference voltage V_BASE, and

a step of, after this deceleration operation is over, when the voltage of the solar cells is within the given allowable voltage regulation range Hb with reference to said reference voltage V_BASE, controlling said photovoltaic inverter in such way that said motor may continue operating at the current speed.

2. The method of controlling a photovoltaic inverter according to claim 1 wherein, during said continuous operation, when the voltage of the solar cells rises beyond the given allowable voltage regulation range Hb with reference to said reference voltage V_BASE, the rotational speed of the motor is accelerated for a given acceleration time until the voltage of the solar cells shifts from said reference voltage V_BASE to a voltage V_BASE-V_OVERlower by said given voltage range V_OVER, and the voltage value of the solar cells prevailing at the time when the power of the solar cells reached the maximum power point in this acceleration process is stored as a new reference voltage V_BASE 2, and after the voltage of the solar cells reached said voltage V_BASE-V_OVER, said photovoltaic inverter is controlled in such a way that the rotational speed of said motor may be decelerated by a given deceleration time until the voltage of the motor shifts from this voltage to said new reference voltage V_BASE 2.

3. The controlling method of a photovoltaic inverter according to claim 1 wherein, during said continuous operation, when the voltage of said solar cells drops beyond said allowable voltage regulation range Hb with reference to said reference voltage V_BASE, the rotational speed of said motor is decelerated by a given deceleration time until said voltage of the solar cells reaches said reference voltage value V_BASE, the rotational speed of said motor is accelerated for a given acceleration time until the voltage of said solar cells shifts from the reference voltage V_BASE to the voltage V_BASE-V_OVER lower by the previously set voltage range V_OVER, and the voltage value of the solar cells prevailing at the time when the power of said solar cells reached the maximum power point in this acceleration process is stored as a new reference voltage V_BASE 3, and after the voltage of said solar cells reached said voltage V_BASE-V_OVER, said photovoltaic inverter is controlled in such a way that the rotational speed of said motor may be decelerated by a given deceleration time until the voltage of the motor shifts from this voltage to said new reference voltage V_BASE 3.

4. The controlling method of a photovoltaic inverter according to claim 1 wherein, during said continuous operation, when the voltage of said solar cells drops beyond the minimum voltage value V_LOW tolerated by solar cells, the rotational speed of said motor is rapidly decelerated by a deceleration time shorter than the given deceleration time until the voltage of said solar cells reaches said minimum voltage value V_LOW, then the rotational speed of said motor is decelerated by said given deceleration time until the voltage of said solar cells reaches said reference voltage V_BASE, and after the voltage of said solar cells reached said reference voltage V_BASE, the rotational speed of said motor is accelerated by a given acceleration time until the voltage of said solar cells shifts from this voltage to the voltage V_BASE-V_OVER lower by the previously set voltage range V_OVER from said reference voltage V_BASE, and the voltage value of said solar cells prevailing at the time when the power of said solar cells reached the maximum power point in this acceleration process is stored as a new reference voltage V_BASE 4, and after the voltage of said solar cells reached said voltage V_BASE-V_OVER, said photovoltaic inverter is controlled in such a way that the speed of said motor may be decelerated by the given deceleration time until the voltage of the motor shifts from this voltage to said new reference voltage V_BASE 4.

5. The controlling method of a photovoltaic inverter according to claim 1, wherein said motor is a motor for driving a pump or a fan.

6. The controlling method of a photovoltaic inverter according to claim 5 wherein the acceleration time and the deceleration time of the motor for driving said pump or fan is set at a value equivalent to the cube of the ratio (n/N_MAX)³ of the present rotational speed instructing value (n) to the maximum set value (N_MAX) of the rotational speed of this motor.

9. The controlling method of a photovoltaic inverter according to claim 2, wherein said motor is a motor for driving a pump or a fan.

10. The controlling method of a photovoltaic inverter according to claim 3, wherein said motor is a motor for driving a pump or a fan.

11. The controlling method of a photovoltaic inverter according to claim 4, wherein said motor is a motor for driving a pump or a fan.

7. A controlling device of a photovoltaic inverter for variable-speed controlling a motor fed with power from solar cells comprising power and voltage monitoring means for monitoring respectively the power and voltage of said solar cells, an instructing value operation means for outputting acceleration or deceleration instructions based on this power and voltage monitoring means, a gradient coefficient operation means for outputting acceleration time or deceleration time, an adjustable speed controlling means for outputting frequency instructions based on the outputs of the instructing value operation means and the gradient coefficient operation means, wherein the voltage value of said solar cells prevailing at a time when the power of said solar cells reached the maximum point in the process of accelerating said motor is stored as a reference value V_BASE, at the same time the motor is accelerated until the voltage of said solar cells shifts from said reference voltage V_BASE to the voltage V_BASE-V_OVER lower by the previously set voltage range V_OVER, and after the voltage of said solar cells reached said voltage V_BASE-V_OVER the motor is decelerated until the voltage of said solar cells reaches said reference voltage V_BASE, and after this deceleration operation, when the voltage of said solar cells is within the given allowable voltage regulation range Hb with reference to said reference voltage V_BASE, the photovoltaic inverter is controlled in such a way that said motor may continue operating at the present rotational speed.

8. A water feeding device for feeding water by driving a pump variable-speed controlled by a photovoltaic inverter fed with power from solar cells wherein, in the process of starting up said motor and accelerating said motor by a given acceleration time while monitoring respectively the power and voltage of said motor, the voltage value of said solar cells prevailing at a time when the power of said solar cells has reached the maximum power point is stored as a reference voltage V_BASE, and the motor is accelerated until the voltage Vo of said solar cells shifts from said reference voltage V_BASE to the voltage V_BASE-V_OVER lower by the previously set voltage range V_OVER, and after the voltage of said solar cells has reached said V_BASE-V_OVER, the motor is decelerated until the voltage of said solar cells shifts from this voltage to said reference voltage V_BASE, and after this deceleration operation is over, when the voltage of said solar cells is within the given allowable voltage regulation range Hb with reference to said reference voltage V_BASE, said motor is kept operating at the present rotational speed to drive the pump and to feed water.