TWI464994B - Distributed power generation system with seamlessly grid-connected transition and method for implementing grid-connected transition for distributed power generation system - Google Patents

Description

Decentralized power generation system with seamless grid-connected function and method for seamlessly integrating distributed power generation system

The present invention provides a distributed power generation system with seamless grid-connecting function and a method for seamlessly integrating a distributed power generation system.

Due to the rising awareness of international environmental protection, the construction of large-scale centralized power plants and transmission and distribution lines has become more and more difficult, and the investment cost has become higher and higher. In this case, in order to improve the efficiency of use of electric energy, the concept of a distributed power generation system has been proposed. Among them, the distributed power generation system greatly improves the power efficiency and power quality by reducing the power consumption of the load and reducing the loss of the power during transportation. Small-scale decentralized power generation systems, such as cogeneration systems, solar power systems, and wind power systems, will be the direction of future power liberalization.

The distributed power generation system mainly generates AC power from the inverter to supply the load. If the distributed power generation system wants to be connected in parallel with the mains system when the island is running, it must consider the problem of synchronous operation. Otherwise, the output voltage, frequency and phase of the inverter will be different from the mains system, resulting in excessive transient current. Therefore, when the distributed power generation system is connected in parallel with the mains system, the voltage information of the mains terminal must be fed back to the inverter for synchronous control, which not only increases the complexity of the signal acquisition but also reduces the flexibility of the parallel power grid.

Therefore, the development of a method or device that can solve the above-mentioned deficiencies is an urgent problem to be solved.

Accordingly, the present invention is to solve the above-mentioned shortcomings of the prior art, and aims to provide a distributed power generation system with seamless grid-connecting function and a method for seamlessly integrating a distributed power generation system to achieve a distributed power generation system and The distributed power generation system and the mains system can be operated in parallel without any communication connection between the utility systems.

To achieve the object of the present invention, a distributed power generation system with seamless grid connection function is provided for driving a load. The decentralized power generation system can be selectively connected to the mains system. The distributed power generation system includes: a current transformer, a filter circuit, a sensing circuit, and a control unit. The inverter is used to convert the DC voltage into a three-phase AC voltage and output a three-phase current. The filter circuit is electrically connected to the output end of the inverter for filtering the three-phase AC voltage and outputting the AC voltage of the node. The sensing circuit outputs a voltage signal and a current signal according to the node AC voltage and the three-phase current. The control unit is electrically connected to the sensing circuit and the inverter, and receives the voltage signal and the current signal and controls the inverter. When the current value of the three-phase current does not exceed the threshold current value, the inverter operates in the falling control mode. When the distributed power generation system is connected to the mains system and the current value of the three-phase current exceeds the threshold current value, the inverter is operated in the transition mode, and when the inverter is in the transition mode, the control unit controls the three-phase current. The current value is zero, and after a predetermined delay time, the inverter is switched from the transition mode to the falling control mode.

In order to achieve another object of the present invention, a method for seamlessly integrating distributed power generation is provided, comprising: operating a distributed power generation system in an island operation mode, wherein a flow reactor in a distributed power generation system operates at a lower limit. Control mode, and the inverter is used to convert the DC voltage into a three-phase AC voltage and output a three-phase current; output a voltage signal current signal according to the three-phase AC voltage and the three-phase current; by indicating a reference value of the threshold current value Continuously comparing the current signal with the reference value to indicate whether the current value of the three-phase current exceeds the threshold current value; and the distributed power generation system is connected to the mains system, and the current value of the three-phase current will exceed the threshold current value. , the control inverter is switched from the falling control mode to the transition mode; when the inverter operates in the transition mode, the current value of the three-phase current is controlled to be zero, and the phase-locked loop is started to update the phase of the three-phase alternating voltage. After the preset delay time, the inverter switches from the transition mode to the fall control mode.

Therefore, the present invention can make the distributed power generation system and the commercial power system do not need communication connection, and can arbitrarily make the distributed power generation system and the commercial power system can be operated in parallel to achieve the seamless grid connection function, and improve the circuit application. Degree of freedom.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In the following description, the same elements will be assigned the same reference numerals even in the different drawings. Further, in the following description of the present invention, the related functions and features are omitted to avoid confusion with the subject matter of the present invention.

Further, in the description of the elements of the present invention, for example, the first, second, A, B, (a), (b) or other similar terms and labels are used. These terms are not intended to define the nature, order, or permutation of the corresponding elements, but only to distinguish them from other elements. Please note that throughout the description, a component is "coupled", "connected", "coupled" to another component, and the first component may directly "couple", "connect", or "join" to the second component. It is also indicated that there may be a third element "combined", "connected", "joined" between the first and second elements.

Please refer to Figure 1 and Figure 2. 1 is a circuit block diagram of a distributed power generation system having a seamless grid-connecting function in a first mode according to an embodiment of the present invention; and FIG. 2 is a diagram showing a seamless grid-connecting function according to an embodiment of the present invention. A block diagram of a circuit in which the distributed power generation system and the utility power system are connected to the second mode. As shown in FIG. 1, the distributed power generation system 100 having a seamless grid-connecting function includes a inverter 101, a filter circuit 102, a sensing circuit 103, and a control unit 104. The inverter 101 is for converting the DC voltage V _dc into a three-phase AC voltage V _ac1 and outputting a three-phase current I _ac1 to drive the load 200. When the distributed power generation system 100 supplies power to the load 200, the distributed power generation system 100 operates in an islanding operation, that is, the first mode. In this embodiment, the distributed power generation system 100 can pass through the switch 300. The grid is connected to the mains system 400, that is, the distributed power generation system 100 can be switched from the island operation mode to the mains grid-connected mode, that is, the second mode. In this embodiment, the switch 300 can be, but is not limited to, a solid state switch. The filter circuit 102 is configured to convert the three-phase AC voltage V _ac1 into a node AC voltage V _acn . The sensing circuit 103 receives the three-phase AC voltage V _ac1 and the three-phase current I _ac1 and outputs a voltage signal V _s and a current signal I _s . The sensing circuit 103 further outputs a DC voltage signal V _dcs according to the DC voltage V _dc .

The control unit 104 is electrically connected to the inverter 101 and the sensing circuit 103, and is used to control the inverter 101. In this embodiment, the control unit 104 receives the voltage signal V _s , the current signal I _{s ,} and the DC voltage signal V . _Dcs . In this embodiment, the control unit 104 includes a comparison unit 1041, a first controller 1042, a second controller 1043, a mode signal unit 1044, and a phase locked loop 1045. The comparison unit 1041 receives the voltage signal V _s and the current signal I _s . In this embodiment, the comparison unit 1041 has a reference value indicating a threshold current value, and continuously indicates whether the current value of the three-phase current I _ac1 exceeds the threshold current value by continuously comparing the current signal I _s with a reference value. The first controller 1042 and the second controller 1043 are used to control the working mode of the inverter group. In this embodiment, the first controller 1042 can be a down controller, and the second controller 1043 can be a transition controller. .

When the distributed power generation system 100 operates in the island operation mode, the current value of the three-phase current I _ac1 does not exceed the threshold current value, so the mode signal unit 1044 will control the first controller 1042 to output the falling control signal V ₁ to the opposite. The streamer 101 operates the inverter 101 in the down control mode. In the present embodiment, the purpose of the down control mode is mainly to coordinate the real and virtual power outputs of the parallel operation of the inverter 101 in the complex array distributed power generation system 100, and to make the reverse flow in each of the distributed power generation systems 100. There is no need for a communication link between the devices 101.

In this embodiment, the falling control formula of the inverter 101 in each group of the distributed power generation system 100 can be expressed as:

ω _i =ω _o -m _i (P _oi -P _i )

E _i =E _o -n _i (Q _oi -Q _i )

Wherein, the subscript i represents the number of the inverter 101 in each group of the distributed power generation system 100, m _i is the real power drop control coefficient, n _i is the virtual power drop control coefficient, P _oi is the rated output real work, Q _oi For the rated output virtual work, ω _o is the rated frequency, E _o is the rated voltage. Adjusting the output real power is achieved by adjusting the angular frequency. Adjusting the output virtual power is achieved by adjusting the voltage amplitude.

When the distributed power generation system 100 is connected to the commercial power system 400, the falling control coefficient in the falling control mode of the inverter 101 in each of the distributed power generation systems 100 can be directly selected to be in the distributed power generation system 100. The output of the inverter 101 is inversely proportional to the rated actual work, as shown by the following formula:

-m ₁ P ₀₁ =-m ₂ P ₀₂ =...=-m _i P _0i

P ₁ /P _o1 =P ₂ /P _o2 =...=P _i /P _oi

In this way, the output power of the inverter 101 in each group of the distributed power generation system 100 is proportional to its rated output power, so that the inverter 101 in each group of the distributed power generation system 100 can achieve the purpose of coordinated output power. Therefore, the drop control mode can make the real and virtual power outputs in parallel operation in parallel without any communication connection between the inverters 101 in each group of distributed power generation systems 100.

However, since the distributed power generation system 100 is connected to the commercial power system 400, the phase of the three-phase AC voltage V _ac1 will be different from the commercial power voltage V _ac2 output by the commercial power system 400, and this error will cause the current of the three-phase current I _ac1 . If the value is too high, too high a current value will cause the circuit to malfunction or be damaged. When the comparison unit 1041 compares the current value of the three-phase current I _{ac1 to} exceed the threshold current value, the mode signal unit 1044 will control the second controller 1043 to output the transition signal V ₂ to the inverter 101, so that the inverter 101 Working in the transition mode, the load 200 is now driven by the utility system 400.

The control unit 104 will start the phase-locked loop 1045 when the inverter 101 is in the transition mode, and when the inverter 101 is operating in the transition mode, the control unit 104 will control the current value of the three-phase current I _{ac1 to} be zero due to The current value of the three-phase current I _ac1 is zero, so that there is no potential and phase difference between the node AC voltage V _acn and the mains voltage V _ac2 , that is, by controlling the current value of the three-phase current I _ac1 to zero, The node AC voltage V _acn is the same as the phase of the mains voltage V _ac2 . At this time, the sensing circuit 103 outputs the voltage signal V _s according to the node AC voltage V _acn having the same phase as the commercial voltage V _{ac2 , and} the phase locked loop 1045 updates the phase required by the first controller 1042 based on the voltage signal V _s . . After a predetermined delay time is set, the mode signal unit 1044 will control the first controller 1042 to output the falling control signal V ₁ to control the inverter 101 to switch from the transition mode to the falling control mode. At this time, the load 200 is dispersed. The power generation system 100 and the utility system 400 are driven together to complete seamless integration.

In this embodiment, the phase-locked loop 1045 is a method for adjusting the voltage phase. The calculation of the sync box conversion is used to convert the voltage to the synchronous reference frame to generate a real axis (q-axis) and a virtual axis (d-axis). Where the real axis represents the amount of in-phase, and the imaginary axis represents the amount of orthogonality. If the phase generated by the phase-locked loop 1045 is the same as the phase of the target voltage, the orthogonal quantity is zero (ie, the imaginary axis is zero), so When the amount of the imaginary axis under the synchronous reference frame is controlled to zero, the phase generated by the phase-locked loop 1045 is exactly the same as the phase of the target voltage.

In this embodiment, the control unit 104 further includes a inverter switch switching unit 1047. The inverter switch switching unit 1047 controls whether the inverter 101 is activated according to the DC voltage signal V _dcs to protect the inverter 101. In some embodiments, when the inverter 101 is switched from the transition mode to the falling control mode, the phase of the updated node AC voltage V _acn will still have a slight error with the phase of the mains voltage V _ac2 , and this error will result in The transient loop is generated, so the control unit 104 activates the virtual inductor 1046 by means of voltage control, so that the impedance in the circuit is increased to suppress the transient loop.

Therefore, by switching the inverter 101 to the transition mode and controlling the current value of the three-phase current I _{ac1 to} zero, and then updating the phase required by the first controller 1042 through the phase-locked loop 1045, the distributed power generation can be made. The system 100 and the commercial power system 400 do not need to be connected to each other, and the distributed power generation system 100 and the commercial power system 400 can be arbitrarily operated in parallel to achieve the seamless grid connection function, and the degree of freedom in circuit application is improved.

Referring to FIG. 3 and FIG. 1 and FIG. 2, FIG. 3 is a diagram showing voltage phase waveforms when a commercial power system and a distributed power generation system are connected to each other according to an embodiment of the present invention. In this embodiment, the waveform of the three-phase AC voltage V _ac1 output by the inverter 101 is a square wave and has noise, and the filter circuit 102 mainly filters the three-phase AC voltage V _ac1 to obtain a waveform as a sine wave. non-alternating voltage node V _acn of noise, the three-phase AC voltage of the AC voltage V _{ac1 line} V _acn node of the same amplitude and waveform. Further, in the three phase system, the control component Ruoyu three-phase system, each phase must be individually controlled, and therefore, only the alternating voltage V _ACN node of the first phase voltage and the mains voltage V _acnA V in the present description The first phase voltage V _{ac2a of ac2} is represented. As shown in FIG. 3, at initial time t _0, a first phase of the AC voltage _V acna voltage node V _acn different from the first phase voltage _V ac2a voltage V _ac2 of the city, and the distributed power generation system 100 to the mains The system 400 is connected to the grid at a first time t ₁ , but due to the difference in phase, the current value of the three-phase current I _ac1 exceeds the threshold current value.

When the current value of the three-phase current I _ac1 exceeds the threshold current value, the control unit 104 controls the inverter 101 to enter the transition mode, and causes the current value of the three-phase current I _ac1 output by the inverter 101 to be zero. The phase of the three-phase AC voltage V _{ac1 is} updated by the phase-locked loop 1045, and the first phase V _{acna of the} new node AC voltage V _{acn is} output by the filter circuit 102, after a predetermined delay time, that is, the second time t _{At 2} o'clock, the control unit 104 switches the control inverter 101 to the down control mode, and the inverter 101 will restart the output of the three-phase current I _ac1 . At the same time, the control unit 104 will activate the virtual inductor 1046 to suppress the communication due to the node. The phase of the voltage V _acn and the mains voltage V _ac2 phase still have a slight phase difference caused by the transient current. At this time, the load 200 is commonly driven by the distributed power generation system 100 and the commercial power system 400. The other two phase voltages of the three-phase AC voltage V _{ac1 are} adjusted as described above, and therefore will not be described again.

Referring to FIG. 4 and FIG. 1 and FIG. 2, FIG. 4 is a flow chart showing a method for seamlessly connecting a distributed power generation system according to an embodiment of the present invention. As shown in FIG. 3, the method of seamlessly integrating the distributed power generation includes steps 301 to 306.

In step 301, the distributed power generation system 100 is operated in an islanding operation mode. At this time, the inverter 101 in the distributed power generation system 100 is controlled by the first controller 1042 in the control unit 104 to operate in the descending control mode. It is used to convert the DC voltage V _dc into a three-phase AC voltage V _ac1 and output a three-phase current I _ac1 . At this time, the load 200 is driven by the distributed power generation system 100.

In step 302, the sensing circuit 103 in the distributed power generation system 100 receives the three-phase AC voltage V _ac1 and the three-phase current I _ac1 to output the voltage signal V _s and the current signal I _s .

In step 303, the comparison unit 1041 in the control unit 104 of the distributed power generation system 100 receives the voltage signal V _s and the current signal I _s , wherein the comparison unit 1041 has a reference value indicating the threshold current value, by continuing The ground is compared and based on the current signal I _s and the reference value to indicate whether the current value of the three-phase current I _ac1 exceeds the threshold current value.

In step 304, the distributed power generation system 100 is connected to the mains system 400. At this time, the current value of the three-phase current I _ac1 will exceed the threshold current value, and the mode signal unit 1044 in the control unit 104 will output the transition signal. V ₂ to the second controller 1043 causes the second controller 1043 to control the inverter 101 to switch from the falling control mode to the transition mode. At this time, the load 200 is driven by the commercial power system 400.

In step 305, when the inverter 101 operates in the transition mode, the control unit 104 controls the current value of the three-phase current I _{ac1 to} be zero, and the control unit 104 also activates the phase-locked loop 1045, and the phase-locked loop 1045 is based on the voltage signal. V _s to update the phase of the three-phase AC voltage V _ac1 , so that the filter circuit 102 filters the updated three-phase AC voltage V _ac1 and outputs a new node AC voltage V _acn , after a predetermined delay time, The streamer 101 is switched from the transition mode to the down control mode. In some embodiments, at this time, the control unit 104 will activate the virtual inductor 1046 to suppress the transient current caused by the phase of the node AC voltage V _acn still having a slight phase difference from the phase of the mains voltage V _ac2 .

Therefore, by switching the inverter 101 to the transition mode and controlling the current value of the three-phase current I _{ac1 to} zero, and then updating the phase required by the first controller 1042 through the phase-locked loop 1045, the distributed power generation can be made. The system 100 and the commercial power system 400 do not need to be connected to each other, and the distributed power generation system 100 and the commercial power system 400 can be arbitrarily operated in parallel to achieve the seamless grid connection function, and the degree of freedom in circuit application is improved.

In summary, the distributed power generation with seamless grid-connecting function of the present invention can coordinate the flow reactors in parallel operation by reducing the control mode so that there is no need for communication connection between the inverter and the inverter. Real and virtual power. In addition, when the distributed power generation system and the mains system are connected to the grid, the zero current control in the transition mode suppresses the excessive transient current caused by the phase difference, and the voltage phase is updated by the phase locked loop, and the distributed power generation system The virtual inductor is set to improve the transient circulation caused by the control mode switching instant, so that the distributed power generation can be connected to or disconnected from the mains system at any time, increasing the degree of freedom of circuit application.

In addition, the terms "including", "comprising" and "having" as used throughout the specification and subsequent claims are an open term and should be interpreted as "including but not limited to". Many technical and scientific terms cited herein refer to specific components that should be understood by those of ordinary skill in the art. If the terms are not clearly defined in the specification, the definitions of terms that are commonly used may be interpreted according to the meaning of the dictionary, constructed and equivalent to the relevant description in the context, and should not be limited by the meaning of the model or over-standardization in the dictionary.

The above description is only a preferred embodiment of the present invention, and it should be noted that those skilled in the art can also make several improvements and retouchings without departing from the principles of the present invention. These improvements and retouchings should also be considered. It is the scope of protection of the present invention.

100. . . Decentralized power generation system

101. . . Reflux

102. . . Filter circuit

103. . . Sense circuit

104. . . control unit

1041. . . Alignment unit

1042. . . First controller

1043. . . Second controller

1044. . . Mode signal unit

1045. . . Phase-locked loop

1046. . . Virtual inductance

1047. . . Reflux switch unit

200. . . load

300. . . switch

400. . . Mains system

V _dc . . . DC voltage

I _ac1 . . . Three-phase current

V _ac1 . . . Three-phase AC voltage

V _ac2 . . . Mains voltage

V _acn . . . Node AC voltage

V _dcs . . . DC voltage signal

V _s . . . Voltage signal

I _s . . . Current signal

V ₁ . . . Falling control signal

V ₂ . . . Transition signal

V _acna . . . First phase voltage of the node AC voltage

V _ac2a . . . First phase voltage of mains voltage

Step 301 to step 305

In order to clearly explain the foregoing objects, features and advantages of the present invention, the embodiments of the present invention are described in detail with reference to the accompanying drawings.

1 is a circuit block diagram of a distributed power generation system with seamless grid-connecting function in a first mode according to an embodiment of the present invention;

2 is a block diagram showing a circuit of a distributed power generation system with a seamless grid-connecting function and a utility system in a second mode according to an embodiment of the present invention;

3 is a voltage phase waveform diagram of a commercial power system and a distributed power generation system connected to each other according to an embodiment of the present invention;

4 is a flow chart showing a method for seamlessly integrating a distributed power generation system according to an embodiment of the present invention.

100. . . Decentralized power generation system

101. . . Reflux

102. . . Filter circuit

103. . . Sense circuit

104. . . control unit

1041. . . Alignment unit

1042. . . First controller

1043. . . Second controller

1044. . . Mode signal unit

1045. . . Phase-locked loop

1046. . . Virtual inductance

1047. . . Reflux switch unit

200. . . load

300. . . switch

400. . . Mains system

V _dc . . . DC voltage

I _ac1 . . . Three-phase current

V _ac1 . . . Three-phase AC voltage

V _ac2 . . . Mains voltage

V _acn . . . Node AC voltage

V _dcs . . . DC voltage signal

V _s . . . Voltage signal

I _s . . . Current signal

V ₁ . . . Falling control signal

V ₂ . . . Transition signal

Claims (8)

A distributed power generation system with seamless grid-connecting function for driving a load, the distributed power generation system can be selectively connected to a mains system, wherein the system comprises: a reflux device for The DC voltage is converted into a three-phase AC voltage, and a three-phase current is output; a filter circuit is electrically connected to the output end of the inverter for filtering the three-phase AC voltage and outputting a node AC voltage; a sensing circuit, which outputs a voltage signal and a current signal according to the AC voltage of the node and the three-phase current; and a control unit electrically connected to the sensing circuit and the inverter to receive the voltage signal and the current signal And controlling the inverter, when the current value of the three-phase current does not exceed a threshold current value, the inverter is operated in a falling control mode, and when the distributed power generation system is connected to the utility system, When the current value of the three-phase current exceeds the threshold current value, the inverter operates in a transition mode, and when the inverter is in the transition mode, the control unit controls the current value of the three-phase current. , And after one of a predetermined delay time, so that the reflux is switched by a mode transition pattern for the droop control. A distributed power generation system with a seamless grid-connecting function as described in claim 1, wherein the distributed power generation system further includes a solid state switch for selectively connecting to the utility system. The distributed power generation system with seamless grid-connecting function as described in claim 1, wherein the control unit comprises: a comparison unit having a reference value indicating the threshold current value, continuously comparing the current a signal and the reference value to indicate whether the current value of the three-phase current exceeds the threshold current value; a first controller and a second controller are configured to control an operating mode of the inverter; a mode signal unit is configured to control the first controller and the second controller when the three-phase current When the current value does not exceed the threshold current value, the mode signal unit controls the first controller to output a falling control signal to the inverter, so that the inverter operates in a falling control mode, and when the distributed power generation When the system is connected to the mains system, and the comparison unit indicates that the current value of the three-phase current exceeds the threshold current value, the mode signal unit controls the second controller to output a transition signal to the inverter, so that the system The inverter operates in a transition mode; and a phase locked loop updates the phase of the first controller based on the voltage signal. The distributed power generation system with seamless networking function according to claim 1, wherein the control unit further activates a virtual inductor when the inverter is switched from the transition mode to the falling mode. Suppresses one of the transient loops generated between mode switches. The distributed power generation system with seamless networking function as described in claim 1, wherein the sensing circuit outputs a DC voltage signal according to the DC voltage. The distributed power generation system with a seamless grid-connecting function as described in claim 5, wherein the control unit further includes a inverter switch switching unit, and the inverter switch switching unit is controlled according to the DC voltage signal. Whether the reflux is activated. A method for seamlessly integrating distributed power generation includes: operating the distributed power generation system in an island operation mode, wherein one of the distributed power generation systems operates in a falling control mode, and the reverse Streamer The system is configured to convert a DC voltage into a three-phase AC voltage and output a three-phase current; output a voltage signal and a current signal according to the three-phase AC voltage and the three-phase current; and represent one of the threshold current values a reference value continuously comparing the current signal with the reference value to indicate whether the current value of the three-phase current exceeds the threshold current value; and the distributed power generation system is connected to a mains system, and the three-phase current The current value will exceed the threshold current value, then the inverter is controlled to switch from the falling control mode to a transition mode; and when the inverter operates in the transition mode, the current value of the three-phase current is controlled Zero, and a phase-locked loop is started to update the phase of the three-phase AC voltage. After a predetermined delay time, the inverter switches from the transition mode to the falling control mode. A method for seamlessly integrating a distributed power generation device according to the seventh aspect of the invention, wherein when the inverter is switched from the falling control mode to the transition mode, a virtual inductor is further activated to suppress mode switching. One of the transient circulations generated.