TWI509935B - Decentralized power supply synchronous and network method - Google Patents

Description

Decentralized power supply synchronization method

The invention relates to a method for synchronizing grid connection of a distributed power source, in particular to a phase difference of a balanced or unbalanced state between a distributed power source and a utility power, so as to estimate a zero crossing point of the utility voltage. Synchronously parallel connection between the distributed power supply and the mains under zero conditions, so that the phase angle difference between the distributed power supply and the commercial power can be quickly and accurately detected, and the degree and time of disturbance to the commercial power when the distributed power supply and the commercial power are not synchronized are reduced. , and make the grid-connected operation of the distributed power supply achieve stable, robust and automatic grid connection.

According to the current era of micro-grid boom, because the grid architecture has the existence of decentralized power supplies, and distributed power supplies play the role of sharing the power supply of the mains in the grid, but most of the decentralized power supplies The generated power is not directly connected to the mains, because some distributed power supplies generate DC power and some are unstable.

Therefore, the power generated by the distributed power supply must be converted to a stable AC power source through the converter, which also highlights the increasing importance of the converter.

However, the distributed power supply of the parallel mains must operate in the form of frequency and phase angle synchronized with the mains. To meet such conditions, it must be achieved by means of the phase angle detection mechanism in the converter. Therefore, the converter The phase angle detection must exist in the parallel operation of the distributed power supply and the commercial power.

In the past, phase angle detection of converters was mostly achieved by phase-locked loops. However, if the imbalance of the mains is encountered, the previous mechanism cannot adjust the output phase angle of the converter to achieve zero phase angle with the mains. Poor, this will cause the output voltage of the converter to be disturbed by the mains. The time of this disturbance will depend on the magnitude of the phase angle difference.

In order to solve the various shortcomings of the application, the inventor of this case devoted himself to research and developed a "distributed power supply synchronous grid connection method" to effectively improve the shortcomings of the conventional use.

The main purpose of the present invention is to easily know the phase angle difference between the distributed power source and the mains balance or unbalance state, to estimate the zero crossing point of the mains voltage, so that the distributed power source and the mains are at zero difference. Under the condition of synchronous parallel connection, the phase angle difference between the distributed power supply and the commercial power can be quickly and accurately detected, and the degree and time of disturbance to the commercial power when the distributed power source and the commercial power are not synchronized are reduced, and the grid-connected operation of the distributed power source is achieved. Stable, robust and automatic grid connection.

In order to achieve the above purpose, the present invention is a method for synchronous power supply synchronous grid connection, which is connected to the three-phase voltage of the mains terminal and the converter AC terminal to synchronous control under the condition of three-phase load imbalance of the small micro grid. After the operation, conversion and comparison by the synchronous controller, a phase angle difference is obtained, and the phase angle difference is fed back to the converter to use the phase angle difference as the converter AC terminal to synchronize with the commercial terminal. The parallel reference angle allows the synchronous controller to control the converter for synchronization, allowing the converter to output a fixed voltage, frequency, phase, and current.

In an embodiment of the invention, the small microgrid is connected to a synchronous controller.

In an embodiment of the present invention, the synchronization controller includes a k/g computing unit, a root mean square unit connected to the k/g computing unit, and a root mean square unit. a phase angle calculation unit, a converter connected to the phase angle calculation unit, a phase lock loop connected to the converter, and a voltage/current controller connected to the converter.

In an embodiment of the invention, the k/g computing unit performs the required operations in conjunction with the three-phase voltages of the mains terminal and the AC terminal of the converter.

In an embodiment of the invention, the phase A voltage of the mains terminal is V _Ga =V _g cos(ω t), the phase B voltage is V _Gb =V _g cos(ω t-2/3 π), phase C The voltage is V _Gc =V _g cos(ω t-4/3 π), and the phase A voltage of the AC terminal of the converter is V _Ia =V ₁ cos(ω t-θ ), and the phase B voltage is V _Ib = V ₂ cos(ω t-2/3 π-θ), C phase voltage is V _Ic =V ₃ cos(ω t-4/3 π-θ), if k=V _Ia V _Ga +V _Ib V _Gb + V _Ic V _Gc , and the g=V _Ia V _Gb +V _Ib V _Gc +V _Ic V _Ga can be obtained by the k/g calculation unit with the rms unit and the phase angle calculation unit to obtain sin θ=2/ 3[(2V ₁ -V ₂ +2V ₃ )k+(4V ₁ +V ₂ +V ₃ )g]/√3(V ₁ V ₂ +V ₂ V ₃ +V ₁ V ₃ ).

In an embodiment of the invention, the root mean square unit is used to calculate the root mean square value of the three-phase voltage of the AC terminal of the converter.

In an embodiment of the invention, the phase angle calculation unit is configured to calculate sin θ.

In an embodiment of the present invention, the converter converts the obtained sin θ into Δθ, and cooperates with the phase-locked loop to obtain the phase angles θ ^old and abc/dq of the AC end of the converter for park conversion.

In an embodiment of the invention, the voltage/current controller is configured to control the converter such that the converter can output a fixed voltage, frequency, phase, and current.

1‧‧‧Small microgrid

11‧‧‧ City terminal

12‧‧‧Converter

2‧‧‧Synchronous controller

21‧‧‧k/g calculation unit

22‧‧‧ root mean square unit

23‧‧‧phase angle calculation unit

24‧‧‧ converter

25‧‧‧ phase-locked loop

26‧‧‧Voltage/current controller

Figure 1 is a schematic diagram of the block flow of the present invention.

Figure 2 is a schematic diagram of forced paralleling without a parallel method at 250 MVA.

Figure 3 is a schematic diagram of synchronous parallelization under the derivation method at 250 MVA.

Figure 4 is a schematic diagram showing the phase angle difference between the mains terminal and the AC terminal of the converter at 250 MVA.

Figure 5 is a schematic diagram of the rms voltage of the three-phase voltage on the load at 250 MVA.

Figure 6 is a schematic diagram of forced paralleling without a parallel method at 500 MVA.

Figure 7 is a schematic diagram of synchronous parallelization under the derivation method at 500 MVA.

Figure 8 is a schematic diagram showing the phase angle difference between the mains terminal and the AC terminal of the converter at 500 MVA.

Figure 9, is a schematic diagram of the rms voltage of the three-phase voltage on the load at 500 MVA.

Figure 10 is a schematic diagram of forced paralleling without a parallel method at 750 MVA.

Figure 11 is a schematic diagram of synchronous parallelization under the derivation method at 750 MVA.

Figure 12 is a schematic diagram showing the phase angle difference between the mains terminal and the AC terminal of the converter at 750 MVA.

Figure 13, is a schematic diagram of the rms voltage of the three-phase voltage on the load at 750 MVA.

Please refer to the "Figure 1 to Figure 13" for the block flow diagram of the present invention, the forced parallel diagram under the parallel method at 250 MVA, the synchronous parallel diagram under the 250 MVA derivation method, and the commercial terminal at 250 MVA. Schematic diagram of the phase angle difference at the AC end of the converter, the rms value of the three-phase voltage on the load at 250 MVA, the forced parallel diagram under the parallel method at 500 MVA, the synchronous parallel diagram under the derivation method at 500 MVA, and the mains terminal at 500 MVA Schematic diagram of the phase angle difference with the AC terminal of the converter, the rms value of the three-phase voltage on the load at 500 MVA, the forced parallel diagram under the parallel method at 750 MVA, the synchronous parallel diagram under the derivation method at 750 MVA, and the mains supply at 750 MVA Schematic diagram of the phase angle difference between the terminal and the AC terminal of the converter and the rms value of the three-phase voltage on the load at 750 MVA. As shown The invention is a method for synchronous grid-connected power supply synchronization, which is described as follows: in the case of three-phase load imbalance of the small microgrid 1, the three-phase input of the commercial terminal 11 and the AC terminal of the converter 12 are input. The voltage is applied to the synchronous controller 2, and after the operation, conversion and comparison by the synchronous controller 2, a phase angle difference is obtained, and the phase angle difference is fed back to the converter 12 to utilize the phase angle difference as the variable current. The AC terminal of the device 12 is synchronized with the commercial terminal 11 in parallel with the reference angle, so that the synchronous controller 2 controls the converter 12 to synchronize, so that the converter 12 can output a fixed voltage, frequency, phase and current.

From the first diagram, the small microgrid 11 is connected to the synchronous controller 2, and the synchronous controller 2 includes a k/g computing unit 21 and a rms connected to the k/g computing unit 21. The unit 22, a phase angle calculating unit 23 connected to the root mean square unit 22, a converter 24 connected to the phase angle calculating unit 23, a phase locked loop 25 connected to the converter 24, and a converter 24 are connected. The voltage/current controller 26, and the k/g computing unit 21 performs the required operations in conjunction with the three-phase voltages of the mains terminal 11 and the AC terminal of the converter 12, in the case of an unbalanced load: the mains The voltages of the phases of terminal 11 are as follows: phase A voltage is V _Ga =V _g cos(ω t); phase B voltage is V _Gb =V _g cos(ω t-2/3 π); phase C voltage is V _Gc = V _g cos(ω t-4/3 π).

The voltages of the AC terminals of the converter 12 are as follows: the phase A voltage is V _Ia = V ₁ cos (ω t - θ); the phase B voltage is V _Ib = V ₂ cos (ω t-2 / 3 π - θ); The phase C voltage is V _Ic =V ₃ cos(ω t-4/3 π-θ).

Assume that k=V _Ia V _Ga +V _Ib V _Gb +V _Ic V _Gc ;g=V _Ia V _Gb +V _Ib V _Gc +V _Ic V _Ga , then the k/g calculation unit 21 can be matched with the root mean square unit 22 and the phase angle calculation unit 24 are operated to obtain the following expression: sin θ=2/3[(2V ₁ -V ₂ +2V ₃ )k+(4V ₁ +V ₂ +V ₃ )g]/√3(V ₁ V ₂ + V ₂ V ₃ + V ₁ V ₃ ).

In this way, the root mean square unit 22 can be used to calculate the root mean square value of the three-phase voltage of the AC terminal of the converter 12, and the phase angle calculating unit 23 calculates the sin θ, and then the converter 24 The sin θ obtained is converted into Δθ, and the phase angles θ ^old and abc/dq of the AC terminal of the converter 12 are obtained by the phase-locked loop 25 for park conversion, and then the voltage is used according to the calculated data. The current controller 26 controls the converter 12 such that the converter 12 can output a fixed voltage, frequency, phase, and current to synchronize the distributed power supply and the commercial power in a synchronous phase.

The following is a comparison of the invention and its use:

Assume that the starting phase angle of the mains terminal 11 and the AC terminal of the converter 12 is 180°, the DC terminal voltage of the converter 12 is 700V, the voltage of the commercial terminal 11 is 22.8kV, and the load is 10kW+j2.01kVar, 20kW+j4. 02kVar and 1kW+j0.201kVar, the following simulates different mains short-circuit capacities for comparison:

1. The short-circuit capacity of the commercial power is 250MVA, and the AC end of the 1.5465s converter 12 is connected in parallel with the mains terminal 11. The second figure shows the forced parallel connection without the parallel method, and the third figure is the synchronous parallel connection under the derivation method of the present invention. The picture shows The phase angle difference between the mains terminal 11 and the AC terminal of the converter 12, and the fifth figure is the three-phase voltage rms value on the load.

2. The short-circuit capacity of the mains is 500MVA, and the AC end of the 1.5465s converter 12 is connected in parallel with the mains terminal 11. The sixth figure shows the forced parallel connection without the parallel method, and the seventh figure shows the synchronous parallel under the derivation method. Figure 8 shows the phase angle difference between the mains terminal 11 and the AC terminal of the converter 12, and Figure 9 shows the three-phase voltage rms value on the load.

3. The short-circuit capacity of the mains is 750MVA, and the AC end of the 1.5547s converter 12 is connected in parallel with the mains terminal 11. The tenth figure shows the forced parallel under the parallel method, and the eleventh figure is the synchronous parallel under the derivation method. Figure 12 shows the phase angle difference between the mains terminal 11 and the AC terminal of the converter 12. Figure 13 shows the rms voltage of the three-phase voltage on the load.

In summary, the method for synchronous grid-connected power supply synchronization can effectively improve various shortcomings of the conventional use, and can easily know the phase angle difference between the distributed power source and the mains balance or unbalance state to estimate the commercial voltage. The zero crossing point makes the distributed power supply and the mains synchronously parallel under the condition of zero phase difference, which can quickly and accurately detect the phase angle difference between the distributed power supply and the mains, and reduce the mains caused when the distributed power supply and the mains are not synchronized. The degree of disturbance and time, so that the grid-connected operation of the distributed power supply achieves stable, robust and automatic grid-connected functions; thus, the invention can be made more progressive, more practical, and more suitable for consumer use. The requirements for the invention patent application, and the patent application is filed according to law.

However, the above description is only the preferred embodiment of the present invention, and the scope of the present invention cannot be limited thereto; The simple equivalent changes and modifications made to the content are still within the scope of the invention.

1‧‧‧Small microgrid

11‧‧‧ City terminal

12‧‧‧Converter

2‧‧‧Synchronous controller

21‧‧‧k/g calculation unit

22‧‧‧ root mean square unit

23‧‧‧phase angle calculation unit

24‧‧‧ converter

25‧‧‧ phase-locked loop

26‧‧‧Voltage/current controller

Claims (7)

A method for synchronous grid-connected power supply is connected to a three-phase voltage of a small-scale micro-grid with a three-phase load imbalance, and inputs a three-phase voltage of a mains terminal and a converter terminal to a synchronous controller, and the synchronous controller performs the operation. After conversion and comparison, a phase angle difference is obtained, and the phase angle difference is fed back to the converter to utilize the phase angle difference as a reference angle of the synchronous connection between the AC end of the converter and the mains terminal, thereby allowing synchronous control. The converter controls the converter to synchronize, and the converter can output a fixed voltage, frequency, phase and current; wherein the small micro-grid is connected to the synchronous controller, and the synchronous controller includes a k/g calculation a unit, a root mean square unit connected to the k/g computing unit, a phase angle calculating unit connected to the root mean square unit, a converter connected to the phase angle calculating unit, a phase locked loop connected to the converter, And a voltage/current controller connected to the converter. According to the method of claim 1, the decentralized power supply synchronous grid connection method, wherein the k/g calculation unit cooperates with each three-phase voltage of the main power terminal and the converter AC terminal to perform required operations. According to the method of the distributed power supply synchronous grid connection described in claim 2, wherein the phase A voltage of the mains terminal is V _Ga = V _g cos (ω t), and the phase B voltage is V _Gb = V _g cos (ω t-2/3 π), the phase C voltage is V _Gc =V _g cos(ω t-4/3 π), and the phase A voltage of the AC terminal of the converter is V _Ia =V ₁ cos(ω T-θ), phase B voltage is V _Ib =V ₂ cos(ω t-2/3 π-θ), and phase C voltage is V _Ic =V ₃ cos(ω t-4/3 π-θ), if The k=V _Ia V _Ga +V _Ib V _Gb +V _Ic V _Gc , and the g=V _Ia V _Gb +V _Ib V _Gc +V _Ic V _Ga can be matched by the k/g calculation unit with the rms unit The phase angle calculation unit is obtained by operation: sin θ=2/3[(2V ₁ -V ₂ +2V ₃ )k+(4V ₁ +V ₂ +V ₃ )g]/√3(V ₁ V ₂ +V ₂ V ₃ + V ₁ V ₃ ). According to the method of claim 3, the distributed root power synchronous grid connection method, wherein the root mean square unit is used to calculate the root mean square value of the three-phase voltage of the AC end of the converter. The method for synchronizing grid-connected power sources according to claim 3, wherein the phase angle calculating unit is configured to calculate sin θ. According to the method of claim 3, the distributed power supply synchronous grid connection method, wherein the converter converts the obtained sin θ into Δθ, and cooperates with the phase-locked loop to obtain the phase of the converter AC terminal. The angles θ ^old and abc/dq are for park conversion. The method for synchronizing grid-connected power supply according to claim 1, wherein the voltage/current controller is used to control the converter so that the converter can output a fixed voltage, frequency, phase and current. .