CN117977682A - Photovoltaic power generation system and alternating current fault ride-through method and device - Google Patents
Photovoltaic power generation system and alternating current fault ride-through method and device Download PDFInfo
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Abstract
The invention relates to a photovoltaic power generation system and an alternating current fault ride-through method and device, which belong to the technical field of new energy power generation.
Description
Technical Field
The invention belongs to the technical field of new energy power generation, and particularly relates to a photovoltaic power generation system, an alternating current fault ride-through method and an alternating current fault ride-through device.
Background
The electric energy generated by the photovoltaic array is merged into an alternating current power grid through a photovoltaic inverter, but various faults are inevitably generated in the grid connection process, and influence is caused on a photovoltaic grid connection system. The power unbalance phenomenon of the alternating current side and the direct current side of the photovoltaic inverter when the voltage of the power grid drops is the root cause of the influence of the voltage drop on the photovoltaic grid-connected system, and under the unbalanced power grid condition, the key of the fault ride-through control of the photovoltaic power generation system is the control of grid-connected positive and negative sequence currents, so that the control of positive sequence currents and negative sequence currents is required to be respectively carried out for the suppression of power doubling fluctuation and grid-connected negative sequence currents. Under the normal working condition of a power grid, a proportional-integral (PI) controller is often used, but the proportional-integral (PI) controller cannot realize the no-static-difference tracking of positive and negative sequence currents at the same time, so that the controller needs to be improved to realize the no-static-difference tracking of the positive and negative sequence currents.
Disclosure of Invention
The invention aims to provide a photovoltaic power generation system, an alternating current fault ride through method and an alternating current fault ride through device, which are used for solving the problem that positive and negative sequence currents cannot be tracked without static difference at the same time.
In order to solve the technical problems, the invention provides an alternating current fault ride-through method of a photovoltaic power generation system, when voltage drop is caused by power grid faults, a photovoltaic inverter in the photovoltaic power generation system adopts a single closed-loop control strategy of a single current loop, and a current controller of the single current loop adopts a PI-R controller.
Further, in the single closed-loop control strategy, according to a voltage interval where the grid-connected point voltage is located, determining an active current parameter value and a reactive current reference value in a single current loop corresponding to the grid-connected point voltage; wherein, a voltage interval corresponds to a calculation mode of an active current parameter value and a reactive current reference value.
Further, the voltage intervals are 4 voltage intervals in total, which are (K1 x U N,+∞],(K2UN,K1*UN],(K3UN,K2*UN],(-∞,K3*UN ]; K1 is a first preset value, K2 is a second preset value, K3 is a third preset value, U N is a system rated voltage, K1 is more than K2 and more than K3, and an active current parameter value corresponding to a voltage interval (K1 is U N, ++ infinity)And reactive current reference value/>The calculation formulas of (a) are respectively as follows:
Wherein I N is rated current of the input side of the transformer, and a and b are set coefficients;
Reactive current reference value corresponding to voltage interval (K2U N,K1*UN) 0, Active current reference value flow/>The calculation formula of (2) is as follows:
Active current reference value flow corresponding to voltage interval (K3U N,K2*UN) And reactive current reference value/>The calculation formulas of (a) are respectively as follows:
Wherein K2 is a second preset value, and b is a set coefficient;
Active current reference value flow corresponding to voltage interval (- ≡, K3 ×U N) And reactive current reference value/>The calculation formulas of (a) are respectively as follows:
where c is a set coefficient.
Further, when the power grid works normally, a photovoltaic inverter in the photovoltaic power generation system adopts a double closed-loop control strategy of a voltage outer loop and a current inner loop, the voltage outer loop is a voltage outer loop for controlling direct-current voltage of a direct-current side of the photovoltaic inverter, and a current controller of the current inner loop adopts a PI controller.
In order to solve the technical problem, the invention also provides an alternating current fault ride-through device of the photovoltaic power generation system, which comprises a memory, a processor and computer program instructions stored in the memory and running on the processor, wherein the processor is used for executing the computer program instructions stored in the memory to realize the alternating current fault ride-through method of the photovoltaic power generation system.
In order to solve the technical problem, the invention also provides a photovoltaic power generation system which comprises a photovoltaic array and a photovoltaic inverter, wherein the photovoltaic array is connected with the direct current side of the photovoltaic inverter, the alternating current side of the photovoltaic inverter is used for being connected with a power grid, and the photovoltaic power generation system further comprises an alternating current fault ride-through device.
Further, the photovoltaic inverter is a three-phase full-bridge inverter.
Further, the photovoltaic power generation system further comprises a capacitor connected in parallel with the direct current side of the photovoltaic inverter for balancing the output power of the photovoltaic array and the photovoltaic inverter.
The beneficial effects of the technical scheme are as follows: when the power grid works normally, a photovoltaic inverter in the photovoltaic power generation system adopts a double closed-loop control strategy of a voltage outer loop and a current inner loop, a current controller of the current inner loop adopts a PI controller, and when the power grid generates fault voltage drop, the PI controller of the current controller of the inner loop of the photovoltaic power generation system is changed into a PI-R current controller, so that no static difference tracking of positive and negative sequence components is realized, and the stability of the control system is improved.
Drawings
FIG. 1 is a topological structure diagram of a photovoltaic grid-connected power generation system of an embodiment of the photovoltaic power generation system of the present invention;
FIG. 2 is a flow chart of an embodiment of a photovoltaic power generation system of the present invention;
FIG. 3 is a PI-R current controller of an embodiment of the photovoltaic power generation system of this invention;
Fig. 4 is a control block diagram of an embodiment of the photovoltaic power generation system of the present invention.
Detailed Description
The invention provides an alternating current fault ride-through method of a photovoltaic power generation system, wherein when a power grid generates fault voltage drop, an inner loop current controller of the photovoltaic power generation system adopts a PI-R current controller. And a PI-R current controller is adopted in the inner loop current control, a non-ideal resonance controller is introduced to be combined with the PI controller, so that a proportional-integral-resonance (PI-R) controller under a positive sequence synchronous rotation coordinate system is formed, no static difference tracking on positive and negative sequence components is realized, and the stability of a control system is improved.
The present invention will be described in further detail with reference to the drawings and examples, in order to make the objects, technical solutions and advantages of the present invention more apparent.
Photovoltaic power generation system embodiments:
The photovoltaic power generation system of the embodiment, as shown in fig. 1, includes a photovoltaic array, an inductance L, an anti-reflection diode, an IGBT, a capacitor C pr, a capacitor C dc, and a photovoltaic inverter. The photovoltaic array is connected with a capacitor C pr in parallel, an inductor L is connected with an IGBT in series and then connected with a capacitor C pr in parallel, an anti-reflection diode is connected with a capacitor C dc in series and then connected with the IGBT in parallel, a capacitor C dc is connected with the direct current side of the photovoltaic inverter in parallel, and the alternating current side of the photovoltaic inverter is used for being connected with a power grid. The photovoltaic inverter can be a three-phase full-bridge inverter; the capacitor C dc represents a capacitor device of the dc bus, the left half of the capacitor represents a front structure of the photovoltaic system, and the right half represents a rear structure of the photovoltaic system. The output power of the photovoltaic cell is larger than the output power of the photovoltaic inverter after passing through the boost circuit, in order to balance the power, the capacitor C dc needs to absorb redundant energy, and likewise, when the output power of the photovoltaic cell is smaller than the output power of the photovoltaic inverter, the capacitor C dc needs to release energy to compensate the system. The alternating current fault ride-through device for the photovoltaic power generation system comprises a memory and a processor connected with the memory through an internal bus, wherein the memory stores computer program instructions, and the processor executes the computer program instructions stored in the memory to realize the alternating current fault ride-through method for the photovoltaic power generation system. The alternating current fault ride-through device of the photovoltaic power generation system can be a controller of a photovoltaic inverter.
The photovoltaic inverter adopts a double closed-loop control strategy of a voltage outer loop and a current inner loop, and a current controller of the current inner loop adopts a PI controller when the power grid works normally.
When the voltage drops due to the power grid faults, a PI-R controller is adopted by a current controller of the current inner loop. As particularly shown in fig. 1.
And when the power grid fails to cause voltage drop, a voltage outer ring in the double closed-loop control strategy is disconnected, so that the photovoltaic inverter adopts a single closed-loop control strategy with a single current ring. The feedforward work of the power grid voltage starts, take the dropping depth of the voltage as the calculation basis, carry on the reference value of the active currentReference value of reactive current/>And then calculate the reference value/>, of the active currentReference value of reactive current/>And the PI-R current controller is used for controlling, reactive current is finally injected into the power system through the photovoltaic inverter, and grid-connected point voltage is improved to a certain extent to realize fault ride-through.
In a single closed-loop control strategy, determining an active current parameter value and a reactive current reference value in a single current loop corresponding to the grid-connected point voltage according to a voltage interval in which the grid-connected point voltage is located; wherein, a voltage interval corresponds to a calculation mode of an active current parameter value and a reactive current reference value.
In this embodiment, the total voltage intervals are 4 voltage intervals, which are respectively (K1×u N,+∞],(K2UN,K1*UN],(K3UN,K2*UN],(-∞,K3*UN), K1 is a first preset value, K2 is a second preset value, K3 is a third preset value, U N is a rated voltage of the system, the first preset value is greater than the second preset value, the second preset value is greater than the third preset value, in this embodiment, K1 is 1.1, K2 is 0.9, and K3 is 0.2.
The voltage interval (1.1 x u N, in +++ infinity' corresponding has power current parameter valueAnd reactive current reference value/>The calculation formulas of (a) are respectively as follows:
wherein I N is rated current of the input side of the transformer;
reactive current reference value corresponding to voltage interval (0.9U N,1.1*UN) 0, Active current reference value flow/>The calculation formula of (2) is as follows:
Active current reference value flow corresponding to voltage interval (0.2U N,0.9*UN) And reactive current reference value/>The calculation formulas of (a) are respectively as follows:
Active current reference value flow corresponding to voltage interval (- ≡,0.2×u N) And reactive current reference value/>The calculation formulas of (a) are respectively as follows:
Under the unbalanced power grid condition, the key of the fault ride-through control of the photovoltaic power generation system is the control of grid-connected positive and negative sequence currents, and positive sequence currents and negative sequence currents are required to be controlled respectively to inhibit power doubling fluctuation and grid-connected negative sequence currents.
Thus for active currentReactive current/>And performing control adjustment, wherein the negative sequence component is expressed as a double-frequency fluctuation component under a positive sequence rotation coordinate system, and no static difference tracking on positive and negative sequence currents cannot be realized at the same time by using a proportional-integral (PI) controller, so that a non-ideal resonance controller, namely a PI-R controller, is introduced to realize no static difference tracking on the positive and negative sequence components. The controller transfer function is as follows:
Wherein: k r is the resonance coefficient; omega c、ωr is cut-off frequency and resonance frequency respectively, and the controller bandwidth can be changed by changing the cut-off frequency, so that the stability of the control system is improved.
The above resonance controller and the PI controller are combined to form a proportional-integral-resonance (PI-R) controller in a positive sequence synchronous rotation coordinate system, and the PI-R controller is specifically shown in fig. 3. In fig. 3, i gd and i gq are the d-and q-axis components of the current, respectively, and i gq,ref is the reference value of i gd; e gd is the d-axis component of the voltage; k p is a proportionality coefficient; k i is an integral coefficient; v gd,ref is the reference value of the d-axis component of the inverter output voltage.
Active current pair through PI-R controllerReactive current/>And (3) performing control adjustment, and finally injecting reactive current into the power system through the photovoltaic inverter according to the adjusted result, so that grid-connected point voltage is improved to a certain extent to realize fault ride-through. As shown in particular in fig. 4.
An embodiment of an alternating current fault ride-through method of a photovoltaic power generation system comprises the following steps:
The invention also provides an alternating current fault ride-through method of the photovoltaic power generation system, wherein a photovoltaic inverter in the photovoltaic power generation system adopts a double closed-loop control strategy of a voltage outer loop and a current inner loop, and the voltage outer loop is a voltage outer loop for controlling direct current voltage of a direct current side of the photovoltaic inverter; when the voltage drops due to the power grid faults, the current controller of the current inner loop adopts a PI-R controller. The specific content of the ac fault ride-through method of the photovoltaic power generation system is described in detail in the photovoltaic power generation system embodiment, and will not be described here again.
An embodiment of an alternating current fault ride-through device of a photovoltaic power generation system:
The invention also provides a photovoltaic power generation system alternating current fault ride through device, which comprises a memory, a processor and a computer program stored in the memory and running on the processor, wherein the processor is used for executing the computer program instructions stored in the memory to realize the photovoltaic power generation system alternating current fault ride through method. The specific content of the ac fault ride-through method of the photovoltaic power generation system is described in detail in the photovoltaic power generation system embodiment, and will not be described here again. The processor can select a processing device such as a microprocessor MCU, a programmable logic device FPGA and the like, and the memory can select a storage device such as a mobile hard disk, a read-only memory (ROM), a Random Access Memory (RAM) and the like.
Specific embodiments are given above, but the invention is not limited to the described embodiments. The basic idea of the invention is that the above basic scheme, it is not necessary for a person skilled in the art to design various modified models, formulas, parameters according to the teaching of the invention to take creative effort. Variations, modifications, substitutions and alterations are also possible in the embodiments without departing from the principles and spirit of the present invention.
Claims (8)
1. The alternating current fault ride through method of the photovoltaic power generation system is characterized in that when voltage drop is caused by power grid faults, a photovoltaic inverter in the photovoltaic power generation system adopts a single closed-loop control strategy of a single current loop, and a current controller of the single current loop adopts a PI-R controller.
2. The alternating current fault ride-through method of a photovoltaic power generation system according to claim 1, wherein in the single closed-loop control strategy, an active current parameter value and a reactive current reference value in a single current loop corresponding to the grid-connected point voltage are determined according to a voltage interval in which the grid-connected point voltage is located; wherein, a voltage interval corresponds to a calculation mode of an active current parameter value and a reactive current reference value.
3. The method of claim 2, wherein the voltage intervals are 4 voltage intervals in total, and are (K1. Times.U N,+∞],(K2UN,K1*UN],(K3UN,K2*UN],(-∞,K3*UN), K1 is a first preset value, K2 is a second preset value, K3 is a third preset value, U N is a rated voltage of the system, K1 > K2 > K3, and the voltage intervals (K1. Times.U N, +. Times.infinity) correspond to active current parameter valuesAnd reactive current reference value/>The calculation formulas of (a) are respectively as follows:
Wherein I N is rated current of the input side of the transformer, and a and b are set coefficients;
Reactive current reference value corresponding to voltage interval (K2U N,K1*UN) 0, Active current reference value flow/>The calculation formula of (2) is as follows:
Active current reference value flow corresponding to voltage interval (K3U N,K2*UN) And reactive current reference value/>The calculation formulas of (a) are respectively as follows:
Wherein K2 is a second preset value;
Active current reference value flow corresponding to voltage interval (- ≡, K3 ×U N) And reactive current reference value/>The calculation formulas of (a) are respectively as follows:
where c is a set coefficient.
4. The alternating current fault ride through method of a photovoltaic power generation system according to claim 1, wherein a photovoltaic inverter in the photovoltaic power generation system adopts a double closed loop control strategy of a voltage outer loop and a current inner loop when a power grid works normally, the voltage outer loop is a voltage outer loop for controlling direct current voltage of a direct current side of the photovoltaic inverter, and a current controller of the current inner loop adopts a PI controller.
5. A photovoltaic power generation system ac fault ride-through apparatus comprising a memory and a processor, and computer program instructions stored on the memory and running on the processor, the processor being operable to execute the computer program instructions stored in the memory to implement the photovoltaic power generation system ac fault ride-through method of any one of claims 1 to 4.
6. A photovoltaic power generation system comprising a photovoltaic array and a photovoltaic inverter, wherein the photovoltaic array is connected to the dc side of the photovoltaic inverter, and the ac side of the photovoltaic inverter is used to connect to a power grid, and the photovoltaic power generation system ac fault ride-through device according to claim 5 is further included.
7. The photovoltaic power generation system of claim 6, wherein the photovoltaic inverter is a three-phase full-bridge inverter.
8. The photovoltaic power generation system of claim 6, further comprising a capacitor connected in parallel with the dc side of the photovoltaic inverter for balancing the output power of the photovoltaic array and the photovoltaic inverter.
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