METHOD FOR CONTROLLING OUTPUT ENERGY OF A POWER SYSTEM
A method for controlling output energy of a power system includes following steps: Using a controlling unit to detect a phase offset between voltage and current of an AC power outputted from the power system. When the power system enters an energy-storage cycle, the controlling unit makes a power conversion unit output the AC power having a first preset power factor and store a partial energy of an AC grid in an energy-storage unit when the AC power is in a reactive power area. When the power system enters an energy-release cycle, the controlling unit makes the power conversion unit output the AC power having a second preset power factor and release the energy stored in the energy-storage unit, wherein an average value of the power factor in the energy-storage cycle and the energy-release cycle is the same as a preset average power factor.
Field of the Invention
The present invention relates to a method for controlling output energy of a power system, and in particular to a method for controlling output energy of a photovoltaic power system.
Description of Related Art
Sunlight is a well-known renewable energy source, and solar cells, as widely known, are designed to absorb sunlight and generate electric power. Typically, a solar energy system includes a plurality of solar cells disposed in an array or panel and a photovoltaic (PV) inverter connected to the solar cells to invert direct current (DC) power derived from the solar cells into alternative current (AC) power for connection to the utility.
In general, the solar energy system including solar cells and PV inverter mentioned above further includes a reactive power compensation device for improving power quality by controlling the reactive power and keeping the power factor as close to unity as possible.
However, the reactive power compensation device cause an overvoltage condition since the voltage inputted to the solar energy system is raised. Therefore it is desirable to use an energy recycle device to suppress overvoltage condition. The solar energy system includes the reactive power compensation device and energy recycle device, however, is bulky and the circuit thereof is complex.
SUMMARY OF THE INVENTIONAccording to one aspect of the present disclosure is to provide a method for controlling output energy of a power system that can improve overall efficiency of the power system.
Accordingly, the method for controlling output energy of a power system is applied to feed an alternative current (AC) power to an AC grid. The method comprises following steps. First, a phase offset between an AC voltage and an AC current of the AC power outputted from a power conversion unit of the power system is detected by a controlling unit, wherein the controlling unit has a first preset power factor, a second preset power factor, and a preset average power factor. After that, the controlling unit makes the power conversion unit output the AC power having the first preset power factor to the AC grid when the power system enters an energy-storage cycle. The controlling unit further makes the power conversion unit store a partial energy of the AC grid in the energy-storage unit when in a reactive power area of the AC power having the first preset power factor. Besides, the controlling unit makes the power conversion unit output the AC power having the second preset power factor and release the energy stored in the energy-storage unit when the power system enters the energy-release cycle, wherein the released energy and AC power outputted from the power conversion unit are fed to the AC grid. In particular, an average value of a power factor in the energy-storage cycle and the energy-release cycle is the same as the average power factor.
In the present disclosure, the reactive power area where the AC voltage and the AC current are out of phase, the first preset power factor is lower than the preset average power factor, and the second preset power factor is higher than the preset average power factor.
Besides, the controlling unit may make the power system enter the energy-release cycle when the energy stored in the energy-storage unit and detected thereby is higher than a first preset value, and the controlling unit may makes the power system enters the energy-storage cycle when the energy stored in the energy-storage unit and detected thereby is not higher than a second preset value, wherein the period of the energy-storage cycle is different from that of the energy-release cycle.
The method of the present invention employed controlling unit to make the power conversion unit output the AC power having the first preset power factor when entering the energy-storage cycle. The controlling unit 140 further makes a partial energy of the AC grid feed to the power system when the AC power having the first power factor is in the reactive power area of the energy-storage cycle. The controlling unit 140 further makes the power system 1 output the AC power having the second preset power factor and release the energy stored in the energy-storage unit 12 when entering the energy-release cycle, wherein the energy released by the energy-storage unit is inverted into AC power and feed to the AC grid.
The features of the invention believed to be novel are set forth with particularity in the appended claims. The invention itself, however, may be best understood by reference to the following detailed description of the invention, which describes an exemplary embodiment of the invention, taken in conjunction with the accompanying drawings, in which:
Reference is made to
The power conversion unit 10 is, for example, a photovoltaic inverter. The energy-storage unit 12 is arranged between the DC power supply 2 and the power conversion unit 10, and is electrically connected to the DC power supply 2 and the power conversion unit 10. In particular, the energy-storage unit 12 is electrically connected to the DC power supply 2 in parallel.
The controlling unit 14 is electrically connected to the power conversion unit 10 and the energy-storage unit 12. The controlling unit 14 includes a first preset power factor, a second preset power factor, and a preset average power factor, the first preset power factor is lower than the preset average power factor, and the second preset power factor is higher than the preset average power factor.
The controlling unit 14 is not only configured to detect the energy stored in the energy-storage unit 12, but also detect the phase offset between the AC voltage VAC and AC current IAC of the AC power outputted from the power conversion unit 10. The controlling unit 14 includes a controller 140 and a phase detector 144. The controller 140 is electrically connected to the power conversion unit 10, an energy-storage unit 12, and the phase detector 144. The phase detector 144 is configured to detect the phase offset between the AC voltage VAC and AC current IAC of the AC power outputted from the power conversion unit 10. In the practical application, however, the phase detector 144 can be omitted, and the controller 140 is configured to detect the AC voltage VAC and the AC current IAC and then calculate the phase offset between the AC voltage VAC and the AC current IAC of the AC power outputted from the power conversion unit 10.
Reference is made to
The energy-storage unit 12 includes capacitors C1 and C2 electrically connected in series, and the capacitors C1 and C2 in series connection is electrically connected to the switches M1 and M2 in series connection in parallel.
Referred is made to
The controller 140 of the controlling unit 14 further detects the energy stored in the energy-storage unit 12, and the phase detector 140 of the controlling unit 14 detects the phase offset between the AC voltage VAC and the AC current IAC. The power system 1 can be designed to enter an energy-release cycle while the energy stored in the energy-storage unit 12 is higher than a first preset value, and to enter an energy-storage cycle while the energy stored in the energy-storage unit 12 is not higher than the first preset value. The power system 1 can also be designed to enter the energy-storage cycle while the energy stored in the energy-storage unit 12 is not higher than a second preset value, and to enter the energy-release cycle while the energy stored in the energy-storage unit 12 is higher than the second preset value, and the first preset value can be higher than the second preset value.
In the energy-storage cycle (as the t1 period shown in the
Va=D1×VC1+D2×VC2
-
- ; where
- D1 is the duty cycle of the switch M1;
- D2 is the duty cycle of the switch M2;
- VC1 is the voltage of the capacitor C1; and
- VC2 is the voltage of the capacitor C2.
In the energy-release cycle (as the t2 period shown in the
In
Reference is made to
The switches M3 and M4 are MOSFETs, and the energy-storage component 104 is an isolating transistor including a primary winding 1040 and a secondary winding 1042 coupled to each other. One terminal of the primary winding 1040 is connected to the energy-storage unit 12, and the other terminal thereof is electrically connected to the drain of the switch M3 and the cathode of the diode D3. The gate of the switch M3 is electrically connected to the controller 140, and the source thereof is electrically connected to the energy-storage unit 12 and the anode of the diode D3. One terminal of the secondary winding 1042 is electrically connected to the output filter 102, and the other terminal thereof is electrically connected to the drain of the switch M4 and the cathode of the diode D4. The gate of the switch M4 is electrically connected to the controller 140, and the source thereof is electrically connected to the output filter 102.
Referred is made to
The controller 140 of the controlling unit 14 further detects the energy stored in the energy-storage unit 12, and the phase detector 144 of the controlling unit 14 detects the phase offset between the AC voltage VAC and the AC current IAC. The power system 1 can be designed to enter an energy-release cycle while the energy stored in the energy-storage unit 12 is higher than a first preset value, and to enter an energy-storage cycle while the energy stored in the energy-storage unit 12 is not higher than the first preset value. The power system 1 can also be designed to enter the energy-storage cycle while the energy stored in the energy-storage unit 12 is not higher than a second preset value, and to enter the energy-release cycle while the energy stored in the energy-storage unit 12 is higher than the second preset value, wherein the first preset value can be higher than the second preset value.
In the energy-storage cycle (as the t1 period shown in
In the energy-release cycle (as the t2 period shown in
In sum, when the power system 1 of the present invention enters the energy-storage cycle, the controlling unit 14 makes the power conversion unit 10 output the AC power having the first preset power factor. The controlling unit 140 further makes a partial energy of the AC grid 3 feed to the power system 1 when the AC power having the first power factor is in the reactive power area. When the power system 1 enters the energy-release cycle, the controlling unit 140 makes the power system 1 output the AC power having the second preset power factor, the controlling unit 14 further makes the power conversion unit 10 to release the energy stored in the energy-storage unit 12, hence the energy released by the energy-storage unit 12 and the DC power provided by the DC power supply 2 are inverted into AC power and fed to the AC grid 3 together, wherein the AC power fed to the AC grid 3 has the second preset power factor.
Reference is made to
In
In
Reference is made to
The power system 1 includes a power conversion unit 10, an energy-storage unit 12, and a controlling unit 14. The power conversion unit 10 is electrically connected to the AC grid 3 for outputting an AC power having a first preset power factor or a second preset power factor. The energy-storage unit 12 is arranged between the DC power supply 2 and the power conversion unit 10 and electrically connected thereto.
The controlling unit 14 is electrically connected to the power conversion unit 10 and has the first preset power factor, the second preset power factor, and an preset average power factor, wherein the first preset power factor is lower than the preset average power factor, and the second preset power factor is higher than the preset average power factor.
The power conversion unit 10 can be managed between an energy-storage cycle and an energy-release cycle, and an average value of the power factor in the energy-storage cycle and the energy-release cycle is the same as the preset average power factor.
When the power system 1 enters the energy-storage cycle, the controlling unit 14 makes the power system 1 output the AC power having the first preset power factor. Besides, when the AC power is in a reactive power area, the controlling unit 14 makes a partial energy of the AC grid 3 enter the power system 1 and store in the energy-storage unit 12.
When the power system 1 enters the energy-release cycle, the controlling unit 14 makes the power conversion unit 10 output the AC power having the second preset power factor. The controlling unit 14 further makes the energy-storage unit 12 release the energy stored in the energy-storage cycle mentioned above, and the released energy is then converted by the power conversion unit 10 and fed to the AC grid (3) with the AC power converted by the DC power provided by the DC power supply 2. As such, the AC power outputted from the power system 1 in the energy-release cycle is provided not only by the DC power supply, but also the energy released by energy-storage unit 12.
Although the present invention has been described with reference to the foregoing preferred embodiment, it will be understood that the invention is not limited to the details thereof. Various equivalent variations and modifications can still occur to those skilled in this art in view of the teachings of the present invention. Thus, all such variations and equivalent modifications are also embraced within the scope of the invention as defined in the appended claims.
Claims
1. A method for controlling power output energy of a power system (1) applied to feed an alternative current (AC) power to an AC grid (3), the method comprising:
- detecting a phase offset between an AC voltage and an AC current of the AC power outputted from a power conversion unit (10) of the power system (1) by a controlling unit (14), wherein the controlling unit (14) has a first preset power factor, a second preset power factor, and a preset average power factor;
- when entering an energy-storage cycle, the controlling unit (14) making the power conversion unit (10) output the AC power having the first preset power factor to the AC grid (3) and store a partial energy of the AC grid (3) in the energy-storage unit (12) when in a reactive power area of the AC power having the first preset power factor;
- when entering energy-release cycle, the controlling unit (14) making the power conversion unit (10) output the AC power having the second preset power factor and release the energy stored in the energy-storage unit (12), wherein the released energy and the AC power outputted from the power conversion unit (12) are fed to the AC grid (3);
- wherein an average value of a power factor in the energy-storage cycle and the energy-release cycle is the same as the average power factor.
2. The method of claim 1, further comprising:
- entering the energy-release cycle when the energy stored in the energy-storage unit (12) and detected by the controlling unit (14) is higher than a first preset value.
3. The method of claim 1, further comprising:
- entering the energy-storage cycle when the energy stored in the energy-storage unit (12) and detected by the controlling unit (14) is not higher than a second preset value.
4. The method of claim 1, wherein the reactive power area is an area where the AC voltage and the AC current are out of phase.
5. The method of claim 1, wherein the period of the energy-storage cycle is different from the period of the energy-release cycle.
6. The method of claim 1, wherein the first preset power factor is lower than the preset average power factor, and the second preset power factor is higher than the preset average power factor.
Type: Application
Filed: Oct 15, 2015
Publication Date: Apr 20, 2017
Inventors: Chu-Chen YANG (New Taipei City), Chao-Jui HUANG (New Taipei City)
Application Number: 14/884,006