TWI556461B - Method for controlling output electrical energy of power system - Google Patents

Description

Power output control method of power system

The present invention relates to a method of power output, and more particularly to a method of power output applied to a photovoltaic power system.

Solar cells are a kind of renewable energy that is quite popular at present. In general, the output of the solar array can be connected to a photovoltaic inverter to convert the DC power generated by the battery array to AC power.

In a conventional power system with a solar cell array and a photovoltaic inverter, a virtual power compensation circuit is often provided to eliminate the virtual power generated by the power system during operation, thereby improving the overall power factor of the power system.

The virtual power compensation circuit also causes the input voltage of the power system to rise, which causes an overvoltage problem. In order to overcome the overvoltage problem, an electric energy recovery device must be additionally provided to recover electric energy; however, the arrangement of the virtual work compensation circuit and the electric energy recovery device increases the volume and circuit complexity of the power supply system.

The invention provides a power output control method for a power system to improve the overall efficiency of the power system.

According to the present invention, a power output control method for a power supply system is provided for use in an AC power grid. The power output control method of the power supply system of the present invention comprises the following steps. First, the control unit detects a phase change of the alternating current power output by the power conversion unit of the power system, wherein the control unit has a first power factor, a second power factor, and an average power factor. Thereafter, when entering the energy storage period, the control unit causes the power conversion unit to output AC power according to the first power factor, and when the control unit detects the AC power as the virtual power zone, the control unit controls the power conversion unit to convert part of the power of the AC power grid. Stored in the energy storage unit; when entering the energy release period, the control unit causes the power conversion unit to output the AC power according to the second power factor, and drives the power conversion unit to release the energy stored by the energy storage unit into the AC power and output it to the AC. Grid. The power factor average of the energy storage period and the energy release period is equal to the average power factor.

In the power output control method of the power supply system of the present invention, the virtual power zone is a current waveform of the alternating current energy and a section of the voltage waveform in different directions, the first power factor is less than the average power factor, and the second power factor is greater than the average power factor.

Furthermore, the control unit may enter the energy release period when the energy stored in the energy storage unit is greater than the first predetermined value, and enter the energy storage period when the energy stored in the energy storage unit is not greater than the second predetermined value. The length of time may be different from the length of the energy release period.

The power output control method of the power system of the present invention controls the power conversion unit when the power supply system enters the energy storage period to output the alternating current power having the first power factor, and when the alternating current power is the virtual power area, the control unit controls the power conversion unit. The part of the electrical energy of the alternating current grid is stored in the energy storage unit; after the power supply system enters the energy release period, the control unit causes the power supply system to output the alternating current energy having the second power factor, and the control unit simultaneously drives the power conversion unit to release the energy storage unit. The electrical energy, the current released by the energy storage unit and the AC energy output by the power system are output to the AC grid.

Please refer to FIG. 1, which is a circuit block diagram of a power supply system of the present invention. The power supply system 1 is disposed between the DC supply device 2 and the AC power grid 3. The DC power supply device 2 can be, for example, a solar battery module for providing DC power (including DC voltage VDC and DC current IDC) to the power system 1. The power system 1 is used to convert DC power into AC power (including AC voltage VAC and AC current IAC) and feed it into the AC grid 3. The power supply system 1 includes a power conversion unit 10, an energy storage unit 12, and a control unit 14.

The power conversion unit 10 can be implemented by a photovoltaic inverter. The energy storage unit 12 is disposed between the DC supply device 2 and the power conversion unit 10, and is electrically connected to the DC supply device 2 and the power conversion unit 10; wherein the energy storage unit 12 is connected in parallel with the DC supply device 2.

The control unit 14 is electrically connected to the power conversion unit 10 and the energy storage unit 12. The control unit 14 is pre-configured with a first power factor, a second power factor, and an average power factor. The first power factor is less than the average power factor, and the second power is The factor is greater than the average power factor.

The control unit 14 can detect not only the electric energy stored in the energy storage unit 12 but also the phase change of the alternating current voltage VAC and the alternating current IAC in the alternating current electric energy output by the electric energy conversion unit 10. The control unit 14 can include, for example, a controller 140 and a phase detector 144 that is electrically coupled to the power conversion unit 10, the energy storage unit 12, and the phase detector 144. The phase detector 144 is configured to detect a phase change of the AC voltage VAC and the AC current IAC in the AC power output by the power conversion unit 10. In actual implementation, the controller 140 may perform the phase detection function without passing through the phase detector 144. For example, the controller 140 may perform an operation to obtain an AC voltage VAC and an AC after detecting the AC voltage VAC and the AC current IAC. The phase of the current IAC changes.

Referring to FIG. 2, a circuit diagram of an energy storage unit and an electrical energy conversion unit according to a first embodiment of the present invention is shown. For convenience of description, the DC supply device 2, the AC grid 3, and the controller 140 are further illustrated in FIG. The power conversion unit 10 includes switching elements M1, M2, an energy storage element 100, diodes D1, D2, and an output filter 102. The switching elements M1, M2 are connected in series and are connected in parallel with the DC supply device 2, and the energy storage element 100 is electrically connected between the switching elements M1, M2 (ie, end point a). In the present embodiment, each of the switching elements M1 and M2 is a metal oxide semiconductor field effect transistor, and the energy storage element 100 is an inductor. The source of the switching element M1 is connected to the drain of the switching element M2, and the drain of the switching element M1 and the source of the switching element M2 are respectively connected to the ends of the energy storage unit 12. The gates of the switching elements M1, M2 are connected to the controller 140, respectively. The diodes D1 and D2 are respectively connected between the drain and the source of the switching elements M1 and M2. The cathodes of the diodes D1 and D2 are respectively connected to the drains of the switching elements M1 and M2, and the diode D1. The anodes of D2 are respectively connected to the sources of the switching elements M1 and M2. The output filter 102 is electrically connected between the energy storage element 100 and the AC grid 3.

The energy storage unit 12 includes capacitors C1 and C2. The capacitors C1 and C2 are connected in series, and the series branch formed by the capacitors C1 and C2 is connected in parallel to the series branch formed by the switching elements M1 and M2.

Please refer to FIG. 1 and FIG. 2 at the same time. When power is output, the controller 140 of the control unit 14 controls the duty cycle of the switching elements M1, M2 according to a first power factor or a second power factor.

In addition, the phase detector 144 of the control unit 14 detects the AC voltage VAC of the AC power and the phase of the AC current IAC, and the controller 140 detects the energy stored in the energy storage unit 12; wherein, the power system 1 can be in the energy When the energy stored in the storage unit 12 is greater than the first predetermined value, the energy release period is entered, and when the energy stored in the energy storage unit 12 is not greater than the first predetermined value, the energy storage period is entered; or the power system 1 is available in the energy storage unit. When the stored energy is less than the second predetermined value, the energy storage period is entered, and when the energy stored in the energy storage unit 12 is greater than the second predetermined value, the energy release period is entered, and the first predetermined value is greater than the second predetermined value.

During the energy storage period (such as the t1 segment shown in FIG. 3 and FIG. 4), the control unit 14 causes the power conversion unit 10 to output AC power according to the first power factor, and the AC current waveform and the AC voltage waveform of the AC power are different. The virtual power zone defined by the direction section (such as the A1 zone shown in FIG. 3 and FIG. 4) controls the duty cycle of the switching elements M1 and M2 so that the voltage of the terminal a is continuously smaller than the instantaneous voltage of the AC grid 3, Part of the electrical energy of the AC grid 3 is entered into the power system 1 and stored in the energy storage unit 12. Wherein, the voltage of the terminal a can be expressed by the following formula: Wherein: D1 is the duty cycle of the switching element M1; D2 is the switching period of the switching element M2; V _C1 is the voltage of the capacitor C1; and V _C2 is the voltage of the capacitor C2.

During the energy release period (such as the t2 section shown in FIG. 3 and FIG. 4), the control unit 14 causes the power conversion unit 10 to output the alternating current power according to the second power factor, and controls the duty cycle of the switching elements M1, M2 of the power conversion unit 10. The voltage of the terminal a is continuously greater than the instantaneous voltage of the AC grid 3, so that the stored electrical energy of the energy storage unit 12 is incorporated into the AC power and output to the AC grid 3 together with the aforementioned AC power.

In FIG. 3, the length of the energy storage period is the same as the length of the energy release period; in FIG. 4, the length of the energy storage period is different from the length of the energy release period. However, regardless of whether the length of the energy storage period is the same as the length of the energy release period, the power factor period of the energy storage period and the energy release period must be equal to the average power factor.

Referring to FIG. 5, a circuit diagram of an energy storage unit and an electrical energy conversion unit according to a second embodiment of the present invention is shown. For convenience of description, the DC supply device 2, the AC grid 3, and the controller 140 are further illustrated in FIG. The energy storage unit 12 includes a capacitor C3 that is connected in parallel to the DC supply 2. The power conversion unit 10 includes switching elements M3 and M4, diodes D3 and D4, an output filter 102, an energy storage element 104, and a commutator 106. The output filter 102 is connected in parallel with the inverter 106.

In the present embodiment, the switching elements M3 and M4 are metal oxide semiconductor field effect transistors, and the energy storage element 104 is an isolated transformer including a primary winding 1040 and a secondary winding 1042. One end of the primary winding 1040 is connected to the energy storage unit 12, and the other end is connected to the drain of the switching element M3 and the cathode of the diode D3. The gate of the switching element M3 is electrically connected to the controller 140, and the source of the switching element M3 is electrically connected to the energy storage unit 12 and the anode of the diode D3. One end of the secondary winding 1042 is connected to the output filter 102, the other end of the secondary winding 1042 is connected to the drain of the switching element M4 and the cathode of the diode D4, and the gate of the switching element M4 is electrically connected to the controller 140, the switch The source of component M4 is electrically coupled to output filter 102.

Referring to FIG. 1 and FIG. 5 simultaneously, when performing power output, the control unit 14 controls the switching states of the switching elements M3, M4 according to the first power factor or the second power factor.

The phase detector 144 of the control unit 14 detects the AC voltage VAC of the AC power and the phase of the AC current IAC, and the controller 140 detects the energy stored in the energy storage unit 12; wherein the power system 1 can be in the energy storage unit When the stored energy is greater than the first predetermined value, the energy release period is entered, and when the energy stored in the energy storage unit 12 is not greater than the first predetermined value, the energy storage period is entered; or the power system 1 is available in the energy storage unit 12 The stored energy enters the energy storage period when the stored energy is not greater than the second predetermined value, and enters the energy release period when the energy stored in the energy storage unit 12 is greater than the second predetermined value.

During the energy storage period (such as the t1 segment shown in FIGS. 3 and 4), the control unit 14 causes the power conversion unit 10 to output the alternating current energy according to the first power factor. The control unit 14 first turns on the switching element M4 in the virtual current region defined by the alternating current electric wave type of the alternating current electric energy and the section in the different direction of the alternating current voltage waveform (the A1 area shown in FIG. 3 and FIG. 4), and the switching element M3 is turned on first. The cutoff is to allow part of the electrical energy of the AC grid 3 to be stored in the secondary winding 1042; the switching element M3 is turned on, and the switching element M4 is turned off to couple the electrical energy stored in the secondary winding 1042 to the primary winding 1040 and stored in the energy storage. Unit 12.

During the energy release period (such as the t2 section shown in FIGS. 3 and 4), the control unit 14 causes the power conversion unit 10 to output AC power according to the second power factor. The control unit 14 first turns on the switching element M3, the switching element M4 is turned off, and the electric energy stored in the energy storage unit 12 is stored in the primary winding 1040; the switching element M4 is turned on, and the switching element M3 is turned off, so that the energy storage unit 12 is released. The electric energy is incorporated into the aforementioned alternating current electric energy and output to the alternating current electric network 3 together with the aforementioned alternating electric energy. The energy factor average of the energy storage period and the energy release period must be equal to the average power factor.

In summary, the power supply system 1 of the present invention uses the control unit 140 to cause the power supply system 1 to enter an energy storage period to output AC power having a first power factor, and when the AC power is a virtual power zone, the control unit 140 The electric energy conversion unit 10 is controlled to store part of the electric energy of the alternating current grid 3 in the energy storage unit 12; after that, when the power supply system 1 enters the energy release period, the control unit 140 causes the power supply system 1 to output the alternating current electric energy having the second power factor, and controls The unit 140 drives the power conversion unit 10 to release the energy stored in the energy storage unit 12, and the power released by the energy storage unit 12 and the AC power output from the power system 1 are output to the AC grid 3.

6 and 7 are flow charts respectively showing a method of controlling the power output of the power supply system according to the first embodiment and the second embodiment of the present invention. The difference between FIG. 6 and FIG. 7 lies in the judgment basis of the power system operating in the energy storage period and the energy release period.

In FIG. 6, the control unit 14 first detects the phase change of the AC power and the AC voltage of the AC power output from the power system 1 and the energy stored in the energy storage unit 12 (step S100). Determining whether the energy stored in the energy storage unit 12 is greater than a first predetermined value (step S102), and entering an energy storage period when the energy stored in the energy storage unit 12 is not greater than a first predetermined value, the power conversion unit 10 is first The power factor outputs AC power (step S104). Next, it is determined whether the AC power output by the power conversion unit 10 is a virtual power zone (step S106), and when the AC power output by the power conversion unit 10 is a virtual power zone, the control unit 14 causes the power conversion unit 10 to connect the AC power grid 3. Part of the electrical energy is stored in the energy storage unit 12 (step S108). Thereafter, the process returns to step S100 to re-detect the phase change of the AC power and the AC voltage of the AC power output by the power system 1 and the energy stored in the energy storage unit 12, and the energy stored in the energy storage unit 12 is greater than the first predetermined value. At this time, the energy release period is entered, and the power conversion unit 10 outputs the AC power with the second power factor (step S110).

In FIG. 7, the control unit 14 first detects the phase change of the AC power and the AC voltage of the AC power output from the power system 1 and the energy stored in the energy storage unit 12 (step S200). Determining whether the energy stored in the energy storage unit 12 is not greater than a second predetermined value (step S202), and entering an energy storage period when the energy stored in the energy storage unit 12 is not greater than a second predetermined value, the power conversion unit 10 A power factor outputs AC power (step S204). Next, it is determined whether the AC power output by the power conversion unit 10 is a virtual power zone (step S206), and when the AC power output by the power conversion unit 10 is a virtual power zone, the control unit 14 causes the power conversion unit 10 to connect the AC power grid 3. Part of the electrical energy is stored in the energy storage unit 12 (step S208). Thereafter, the process returns to step S200 to re-detect the phase change of the AC power and the AC voltage of the AC power output by the power system 1 and the energy stored in the energy storage unit 12, and the energy stored in the energy storage unit 12 is greater than the second predetermined value. At this time, the energy release period is entered, and the power conversion unit 10 outputs the AC power with the second power factor (step S210).

Please refer to FIG. 8 , which is a circuit block diagram of a power supply system according to a second embodiment of the present invention. In FIG. 8, the power supply system 1 is disposed between the DC supply device 2 and the AC power grid 3, and is electrically connected to the DC power supply device 2 and the AC power grid 3 for outputting AC power having an average power factor. The difference between the power supply system 1 shown in FIG. 8 and the power supply system shown in FIG. 1 is that the controller 14 shown in FIG. 8 does not detect the voltage level of the energy storage unit 12, and provides a fixed power to the open circuit command. Factor disturbance period.

The power system 1 includes a power conversion unit 10, an energy storage unit 12, and a control unit 14, and the power conversion unit 10 is electrically connected to the AC grid 3 for outputting AC power having a first power factor or a second power factor. The energy storage unit 12 is disposed between the DC supply device 2 and the power conversion unit 10, and is electrically connected to the DC supply device 2 and the power conversion unit 10.

The control unit 14 is electrically coupled to the electrical energy conversion unit 10, the control unit 14 having a first power factor, a second power factor, and an average power factor; wherein the first power factor is less than the average power factor and the second power factor is greater than the average power factor.

The power conversion unit 10 can operate during an energy storage period or an energy release period, and the average of the power factors of the energy storage period and the energy release period is equal to the average power factor.

When operating in the energy storage cycle, the control unit 14 causes the power conversion unit 10 to output AC power in accordance with the first power factor. In addition, when the alternating current power is the virtual power zone, the control unit 14 controls the power conversion unit 10 to enter part of the power of the alternating current grid 3 into the power system 1 and store it in the energy storage unit 12.

When entering the energy release period, the control unit 14 causes the power conversion unit 10 to output AC power according to the second power factor. At the same time, the energy storage unit 12 releases the stored electrical energy; wherein the energy storage unit 12 releases the electrical energy into the AC electrical energy and outputs it to the AC power grid 3.

While the present invention has been disclosed in the above embodiments, it is not intended to limit the invention, and the invention may be modified and modified in various ways without departing from the spirit and scope of the invention. The scope is subject to the definition of the scope of the patent application.

1‧‧‧Power System

10‧‧‧Power Conversion Unit

100, 104‧‧‧ energy storage components

102‧‧‧Output filter

1040‧‧‧Primary winding

1042‧‧‧Secondary winding

106‧‧‧Commutator

12‧‧‧ Energy storage unit

14‧‧‧Control unit

140‧‧‧ Controller

144‧‧‧ phase detector

2‧‧‧DC supply unit

3‧‧‧AC grid

A1‧‧‧ virtual area

C1, C2, C3‧‧‧ capacitors

D1, D2, D3, D4‧‧‧ diodes

IAC‧‧‧AC current

M1, M2, M3, M4‧‧‧ switching components

S100~S210‧‧‧ Power system power output control steps

VAC‧‧‧AC voltage

1 is a circuit block diagram of a power supply system in accordance with a first embodiment of the present invention;

2 is a circuit diagram of an energy storage unit and an electrical energy conversion unit according to a first embodiment of the present invention;

3 is a waveform diagram of AC power output by the power system of the present invention;

4 is another waveform diagram of AC power output by the power system of the present invention;

5 is a circuit diagram of an energy storage unit and an electrical energy conversion unit according to a second embodiment of the present invention;

6 is a flow chart showing a method of converting electric energy according to a first embodiment of the present invention;

7 is a flow chart showing a method of converting electric energy according to a second embodiment of the present invention;

8 is a circuit block diagram of a power supply system in accordance with a second embodiment of the present invention.

S100~S110‧‧‧Power system power output control steps

Claims (6)

A power output control method for a power system is applied to an AC power grid, and the power output control method of the power system includes the following steps: detecting, by a control unit, an AC power phase change outputted by an power conversion unit of the power system, the control The unit has a first power factor, a second power factor, and an average power factor; when entering an energy storage period, the control unit causes the power conversion unit to output the AC power according to the first power factor, and when the control unit When detecting the AC power as a virtual power zone, the control unit controls the power conversion unit to store a part of the power of the AC power grid in an energy storage unit; and when entering an energy release period, the control unit is configured according to the second power The factor causes the electrical energy conversion unit to output the alternating current electrical energy, and drives the electrical energy conversion unit to release the electrical energy stored by the energy storage unit to be integrated into the alternating current electrical energy and output to the alternating current power grid; wherein the energy storage period and the energy release period The power factor average is equal to the average power factor. The power output control method of the power system of claim 1, further comprising the step of: entering the energy release period when the control unit detects that the energy stored by the energy storage unit is greater than a first predetermined value. The power output control method of the power system of claim 1, further comprising the step of: entering the energy storage period when the control unit detects that the energy stored by the energy storage unit is not greater than a second predetermined value. The power output control method of the power system of claim 1, wherein the virtual power zone is a current waveform of the alternating current energy and a section of the voltage waveform in different directions. The power output control method of the power supply system of claim 1, wherein the length of time of the energy storage period is different from the length of time of the energy release period. The power output control method of the power supply system of claim 1, wherein the first power factor is less than the average power factor, and the second power factor is greater than the average power factor.