TW201511441A - Method for synchronous grid-tying of distributed power - Google Patents

Abstract

A method for synchronous grid-tying of distributed power is disclosed. For three-phase unbalanced load of miniature micro-grid, the three-phase voltage of the current transformer at the AC end and the mains end is inputted to the synchronous controller for calculation, conversion and comparison to obtain a phase angle difference to be fed back to the current transformer as the reference angle for synchronous grid-tying at the current transformer AC end and the mains end, so as to allow the synchronous controller to control the synchronization of the current transformer, making the current transformer output a constant voltage, frequency, phase and current. Thus, the phase angle difference at the balanced or unbalanced state between the distributed power generation source and the mains can be obtained easily to estimate the zero-crossing point of the mains voltage, enabling synchronous grid-tying of the distributed power generation source and the mains at the condition of zero phase difference, thereby rapidly and accurately detecting the phase angle difference between the distributed power and mains, reducing the degree and time of mains interference due to asynchronous distributed power and mains, and allowing grid-tying of the distributed power to achieve the efficacy of stable, robust, and automatic grid-tying.

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 calculation unit, a root mean square unit connected to the k/g calculation unit, and a phase angle calculation unit connected to the root mean square unit. a converter coupled to the phase angle computing unit, a phase locked loop coupled to the converter, and a voltage/current controller coupled 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(ωt), the phase B voltage is V _Gb =V _g cos(ωt-2/3π), and the phase C voltage is V. _Gc = V _g cos(ωt-4/3π), and the phase A voltage of the AC terminal of the converter is V _Ia = V ₁ cos(ωt - θ), and the phase B voltage is V _Ib = V ₂ cos(ωt- 2/3π-θ), the phase C voltage is V _Ic =V ₃ cos(ωt-4/3π-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 , then the k/g calculation unit can be combined 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‧‧‧mains terminal 12‧‧•inverter 2‧‧‧synchronous controller 21‧‧‧k/g calculation unit 22‧‧‧ root mean square unit 23‧‧‧ phase angle Calculation unit 24‧‧‧Converter 25‧‧‧ phase-locked circuit 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 paralleling 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 derivation method at 250 MVA, and the 250 MVA Schematic diagram of the phase angle difference between the mains terminal and the AC terminal 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, and the synchronous parallel connection under the derivation method at 500 MVA Schematic diagram, schematic diagram of the phase angle difference between the mains terminal and the AC terminal of the converter at 500 MVA, the rms value of the three-phase voltage on the load at 500 MVA, the forced parallel diagram without the parallel method at 750 MVA, and the derivation at 750 MVA The synchronous parallel diagram under the method, the phase angle difference between the mains terminal and the AC terminal of the converter at 750 MVA and the rms value of the three-phase voltage on the load at 750 MVA. As shown in the figure: The present invention is a method for synchronous power grid synchronization and networking, which is described as follows:

When the three-phase load imbalance of the small microgrid 1 is input, the three-phase voltages of the commercial terminal 11 and the AC terminal of the converter 12 are input to the synchronous controller 2, and the synchronous controller 2 performs calculation, conversion and comparison. Obtaining a phase angle difference, and returning the phase angle difference to the current transformer 12, so as to use the phase angle difference as a reference angle of the synchronous connection between the AC terminal and the commercial terminal 11 of the converter 12, thereby allowing the synchronous controller 2 The converter 12 is controlled 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 voltages of the phases of the mains terminal 11 are as follows:

The phase A voltage is V _Ga =V _g cos(ωt);

The phase B voltage is V _Gb =V _g cos(ωt-2/3π);

The phase C voltage is V _Gc =V _g cos(ωt-4/3π).

The voltages of the AC terminals of the converter 12 are as follows:

The phase A voltage is V _Ia = V ₁ cos(ωt - θ);

The phase B voltage is V _Ib = V ₂ cos(ωt-2/3π-θ);

The phase C voltage is V _Ic =V ₃ cos(ωt-4/3π-θ).

Assumption:

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 cooperate with the root mean square unit 22 and the phase angle calculation unit 24 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 Converting the obtained sin θ into Δθ, and matching with the phase-locked loop 25 to obtain the phase angles θ ^old and abc/dq of the AC terminal of the converter 12 for park conversion, and then controlling the voltage/current according to the data after the operation. The converter 26 controls the converter 12 so that the converter 12 can output a fixed voltage, frequency, phase and current, so that the distributed power source and the mains are synchronously connected in parallel under zero conditions.

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 700 V, the voltage of the mains terminal 11 is 22.8 kV, 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 mains is 250 MVA, which is connected in parallel with the mains terminal 11 at the AC side of the 1.5465 s converter. Figure 2 is the forced parallel connection without the parallel method, and Figure 3 is the synchronous parallel connection under the derivation method of the present invention. The phase angle difference between the commercial terminal 11 and the AC terminal of the converter 12, and Fig. 5 is the rms value of the three-phase voltage on the load.
2. The short-circuit capacity of the mains is 500 MVA, and the AC end of the 1.5465 s converter 12 is connected in parallel with the mains terminal 11. This Figure 6 shows the forced parallel connection without the parallel method, and the seventh figure shows the synchronous parallel connection under the derivation method. The figure shows the phase angle difference between the mains terminal 11 and the AC terminal of the converter 12, and the figure 9 shows the rms voltage of the three-phase voltage on the load.
3. The short-circuit capacity of the mains is 750 MVA, and the AC end of the 1.5547 s converter 12 is connected in parallel with the mains terminal 11. The tenth figure shows the forced parallel connection without the parallel method, and the eleventh figure is the synchronous parallel connection under the derivation method, the 12th The figure shows the phase angle difference between the mains terminal 11 and the AC terminal of the converter 12, and Fig. 13 shows the three-phase voltage rms value 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 is only the preferred embodiment of the present invention, and the scope of the present invention is not limited thereto; therefore, the simple equivalent changes and modifications made in accordance with the scope of the present invention and the contents of the invention are modified. All should remain within the scope of the invention patent.

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 (1)

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, allowing the converter to output a fixed voltage, frequency, phase, and current.

2. The method of synchronously connected to a distributed power source according to claim 1, wherein the small micro-grid is connected to a synchronous controller.

3. The method according to claim 2, wherein the synchronous controller comprises a k/g computing unit, a root mean square unit connected to the k/g computing unit, a phase angle calculation unit coupled to the root mean square unit, a converter coupled to the phase angle calculation unit, a phase lock loop coupled to the converter, and a voltage/current controller coupled to the converter.

4. The method according to claim 3, wherein 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.

5. The method according to claim 4, wherein the phase A voltage of the mains terminal is VGa=Vgcos(ωt), and the phase B voltage is VGb=Vgcos(ωt-2/ 3π), C phase voltage is VGc=Vgcos(ωt-4/3π), and the phase A voltage of the AC terminal of the converter is VIa=V1cos(ωt -θ), and the phase B voltage is VIb=V2cos(ωt-2 /3π-θ), the C-phase voltage is VIc=V3cos(ωt-4/3π-θ), and if k=VIaVGa+VIbVGb+VIcVGc, and the g=VIaVGb+VIbVGc+VIcVGa, the unit can be calculated by k/g With the rms unit and the phase angle calculation unit, sin θ=2/3[(2V1-V2+2V3)k+(4V1+V2+V3)g]/√3 (V1V2+V2V3+V1V3) is obtained.

6. The method according to claim 5, wherein the rms unit is used to calculate a root mean square value of a three-phase voltage of the AC terminal of the converter.

7. The method according to claim 5, wherein the phase angle calculation unit is configured to calculate sin θ.

8. The method according to claim 5, wherein the converter converts the obtained sin θ into Δθ, and cooperates with the phase-locked loop to obtain the phase of the AC end of the converter. The angles θold and abc/dq are for park conversion.

9. The method according to claim 3, wherein the voltage/current controller is used to control the converter so that the converter can output a fixed voltage, frequency, and phase. And current.