A grid-type control system for wind power and photovoltaic reuse

Abstract

To address the problem that conventional grid-connected renewable energy sources, when connected to the grid at a high rate, effectively reduce grid inertia and are prone to abnormal interactions with the grid, leading to problems such as low-frequency oscillations, subsynchronous oscillations, and harmonic oscillations, the present invention proposes a grid-connected control system for wind power and photovoltaic power generation, comprising: a wind turbine, a synchronous generator, a wind turbine-side converter, a capacitor, a grid-side converter, an LCL filter, a grid, a photovoltaic power generation unit, a photovoltaic converter, a control loop for the wind turbine-side converter, a control loop for the grid-side converter, and a control loop for the photovoltaic converter. This invention enables wind power and photovoltaic power generation to be connected to the grid through the same grid-side converter, reducing costs. It also presents a voltage source-like characteristic to the grid, similar to that of a synchronous generator, providing inertia and frequency support to the grid, while enhancing the stability of their interaction with the grid and suppressing oscillations.

Description

Technical Field

[0001] The present invention relates to the technical field of electrical control of new energy, and in particular to a grid-type control system for multiplexing wind power and photovoltaic power. Background Art

[0002] In recent years, renewable energy sources, represented by wind power and photovoltaics, have rapidly developed and are gradually becoming the primary power source after thermal power and hydropower. However, as the proportion of renewable energy connected to the grid continues to increase, the power system faces numerous challenges. First, because renewable energy sources like wind power and photovoltaics are connected to the grid via power electronic converters, conventional grid-following control methods lack inertia support for these converters. The high proportion of renewable energy connected to the grid effectively reduces the grid inertia, which can easily lead to frequency instability in the power system. Second, power electronic converters exhibit wideband dynamics. With the high proportion of renewable energy connected to the grid, abnormal interactions between the converters and the grid are increasing, leading to problems such as low-frequency oscillations, subsynchronous oscillations, and harmonic oscillations, jeopardizing the safe and stable operation of the grid.

[0003] Therefore, it is necessary to study the grid-type control strategy of new energy to enhance its inertia and frequency support capabilities for the power grid; in addition, it is also necessary to study the control strategy to enhance the operational stability of new energy to reduce the oscillation and instability problems caused by its abnormal interaction with the power grid. Summary of the Invention

[0004] The purpose of the present invention is to solve the above problems. For wind power and photovoltaic power sources, a grid-type control system for wind power and photovoltaic reuse is proposed, so that the new energy presents external characteristics similar to those of a synchronous generator to the power grid, and has the ability to provide inertia and frequency support to the power grid, while enhancing its interactive stability with the power grid and suppressing oscillation and other problems.

[0005] In order to achieve the above-mentioned purpose of the invention, the technical solutions adopted are as follows:

[0006] A grid-type control system for multiplexing wind power and photovoltaic power, comprising: a wind wheel, a synchronous generator, a wind turbine-side converter, a capacitor, a grid-side converter, an LCL filter, a grid, a photovoltaic power generation unit, a photovoltaic converter, a control loop of the wind turbine-side converter, a control loop of the grid-side converter, and a control loop of the photovoltaic converter. The wind wheel is connected to the rotor of the synchronous generator, and the stator of the synchronous generator outputs three-phase AC power, which is converted into DC power by the wind turbine-side converter. The DC side of the wind turbine-side converter is connected in parallel with the capacitor; the other side of the capacitor is connected to the DC side of the grid-side converter, and the AC side of the grid-side converter is filtered by the LCL filter and then connected to the grid; the current output by the photovoltaic power generation unit enters one side of the photovoltaic converter, and the other side of the photovoltaic converter is connected in parallel to the capacitor on the DC side of the wind turbine-side converter. The photovoltaic converter is a DC / DC converter; the trigger pulse S of the wind turbine-side converterm Provided by the control loop of the wind turbine side converter, the trigger pulse S of the grid side converter g Provided by the control loop of the grid-side converter, the trigger pulse S of the photovoltaic converter pv Provided by the control loop of the photovoltaic converter.

[0007] Furthermore, the control loop of the grid-side converter adopts the following control structure:

[0008] AC side voltage of the grid-side converter , AC side current After the rotation coordinate transformation, the voltage in the rotating coordinate system is generated 、 and the current in the rotating coordinate system 、 , the phase used for the rotation coordinate transformation is θ; the DC voltage per unit value of the grid side converter is After passing through an integrator, the output of the integrator is the phase θ; the DC voltage u of the grid side converter dc Enter the reactive power side stabilizer, the output of the reactive power side stabilizer is the reactive power change ;

[0009] In the reactive power loop, the reference value of reactive power is Superimposed reactive power change , minus the reactive power feedback value After passing through the first PI regulator, the output of the first PI regulator is the reference value of the d-axis component of the AC side voltage , reference value of the q-axis component of the AC side voltage =0; in the grid-side AC voltage loop, the reference value 、 Respectively 、 Then, they pass through the second PI regulator respectively. The outputs of the two second PI regulators are the current values 、 Current value 、 Entering the current limiter, the output of the current limiter is the reference value of the d-axis component of the AC side current , AC side current q-axis component reference value , and AC current limit flag I LTEN ; In the grid-side AC current loop, 、 Respectively 、 The difference is made, and then passes through the third PI regulator respectively. The outputs of the two third PI regulators are the modulation voltage d-axis components , modulation voltage q-axis component ; 、 Generate three-phase modulated voltage through rotation coordinate transformation , After pulse width modulation, the trigger pulse S of the grid side converter is generated. g .

[0010] Furthermore, the output of the reactive power side stabilizer , enter u dc There is the following relationship between them,

[0011]

[0012] Where s is the Laplace operator, K is the reactive power side stability control gain, and T1 and T2 are the reactive power side stability control time constants, respectively.

[0013] Furthermore, the current limiter adopts the following control structure:

[0014] Current value 、 Generate amplitude through phase transformation and phase φ, amplitude Enter the limit comparator, the output of the limit comparator is the limit flag I LTEN , amplitude reference value , amplitude reference value The sum phase φ is transformed into the AC side current d-axis component reference value , AC side current q-axis component reference value ;

[0015] The output of the limit comparator I LTEN With input There is the following relationship between them,

[0016]

[0017] in is the output current limit amplitude.

[0018] Furthermore, the output of the limiting comparator With input There is the following relationship between them,

[0019] .

[0020] Furthermore, the control loop of the wind turbine side converter adopts the following control structure:

[0021] Detect the per-unit value of the DC voltage of the wind turbine side converter , Enter the inertia support and frequency adjustment module. The output of the inertia support and frequency adjustment module is the active power adjustment value. ; Detect the per-unit value of the wind wheel speed , Enter the maximum power tracking module. The output of the maximum power tracking module is the reference value of the active power on the wind turbine side. ; Overlay , minus the feedback value of the active power on the fan side After passing through the third PI regulator, the output of the third PI regulator is the reference value of the q-axis current on the fan side , reference value of d-axis current on the fan side is 0; 、 Entering the machine-side current loop, the output of the machine-side current loop undergoes rotational coordinate transformation and pulse width modulation to generate the trigger pulse S of the fan-side converter. m ;

[0022] Per unit value of wind rotor speed , Feedback value of active power on the wind turbine side , AC current limit flag I LTEN Enter the pitch angle control module; if I LTEN The value is 0, the pitch angle control module is based on 、 According to the conventional pitch angle adjustment method, the output pitch angle β is controlled; if I LTEN The value of is 1, increase the pitch angle β until I LTEN until the value becomes 0.

[0023] Furthermore, the inertia support and frequency adjustment module adopts the following control structure:

[0024] Detect the per-unit value of the DC voltage of the wind turbine side converter , After passing through a first-order low-pass filter with a gain of T, and then through a filter with a gain of -K in The output of the differential link is , Enter the inertia side stabilization controller, the output of the inertia side stabilization controller is ;

[0025] 1 minus After a gain of K d The output of the proportional link is , Enter the frequency regulation side stabilization controller, the output of the frequency regulation side stabilization controller is ; Overlay The output after is the active power regulation .

[0026] Furthermore, the output of the inertia side stabilization controller Between input Has the following relationship,

[0027]

[0028] Where s is the Laplace operator, T in is the time constant of the inertia side stabilization control.

[0029] Furthermore, the output of the frequency regulation side stabilization controller With input There is the following relationship between them,

[0030]

[0031] Where s is the Laplace operator, T d It is the time constant of stable control on the frequency regulation side.

[0032] Furthermore, the control loop of the photovoltaic converter adopts the following control structure:

[0033] The output of the photovoltaic maximum power tracking control module is the photovoltaic power reference value , detect the actual active power output of the photovoltaic converter , and The difference between the two passes through the fourth PI regulator, and the output of the fourth PI regulator is pulse-width modulated to generate a trigger pulse S for the photovoltaic converter. pv .

[0034] The wind power and photovoltaic multiplexing grid-type control system of the present invention adopts the above technical solution and has the following technical effects compared with the existing technology:

[0035] The wind power and photovoltaic power grid-connected control system of the present invention enables wind power and photovoltaic power to be connected to the power grid through the same grid-side converter, reducing costs and presenting voltage source external characteristics similar to those of a synchronous generator to the power grid. The proposed inertia support and frequency regulation module can enhance the support capability of renewable energy for the power grid and improve frequency stability. The proposed inertia-side and frequency regulation-side stabilization controllers can achieve phase correction, enhance the operational stability of renewable energy, and suppress oscillations. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 This is a schematic structural diagram of a wind power and photovoltaic multiplexing grid-type control system according to the present invention;

[0037] Figure 2 A circuit block diagram of a control loop of a grid-side converter according to the present invention;

[0038] Figure 3 This is a control block diagram of the current limiter of the present invention;

[0039] Figure 4 A circuit block diagram of a control loop of a fan-side converter according to the present invention;

[0040] Figure 5 This is a control block diagram of the inertia support and frequency adjustment module of the present invention;

[0041] Figure 6 A circuit block diagram of a control loop of a photovoltaic converter according to the present invention;

[0042] Figure 7 This is a simulation embodiment of the present invention - the frequency adjustment module gain K d Simulation waveform when increasing;

[0043] Figure 8 This is a simulation waveform diagram of a grid-type control system that multiplexes wind power and photovoltaic power when there is a sudden load increase, a simulation embodiment of the present invention. DETAILED DESCRIPTION

[0044] In order to make the technical problems, technical solutions and advantages to be solved by the present invention clearer, a detailed description will be given below with reference to the accompanying drawings and specific embodiments.

[0045] like Figure 1 As shown, an embodiment of the present invention provides a grid-type control system for multiplexing wind power and photovoltaic power, including: a wind wheel, a synchronous generator, a wind turbine side converter, a capacitor, a grid side converter, an LCL filter, a grid, a photovoltaic power generation unit, a photovoltaic converter, a control loop of the wind turbine side converter, a control loop of the grid side converter and a control loop of the photovoltaic converter. The wind wheel is connected to the rotor of the synchronous generator, and the stator of the synchronous generator outputs three-phase AC power, which is converted into DC power by the wind turbine side converter. The DC side of the wind turbine side converter is connected in parallel with the capacitor; the other side of the capacitor is connected to the DC side of the grid side converter, and the AC side of the grid side converter is connected to the grid after filtering by the LCL filter; the current output by the photovoltaic power generation unit enters one side of the photovoltaic converter, and the other side of the photovoltaic converter is connected in parallel to the capacitor on the DC side of the wind turbine side converter. The photovoltaic converter is a DC / DC converter; the trigger pulse S of the wind turbine side converter m Provided by the control loop of the wind turbine side converter, the trigger pulse S of the grid side converter g Provided by the control loop of the grid-side converter, the trigger pulse S of the photovoltaic converter pv Provided by the control loop of the photovoltaic converter.

[0046] like Figure 2 As shown, the control loop of the grid-side converter adopts the following control structure:

[0047] AC side voltage of the grid-side converter , AC side current After the rotation coordinate transformation, the voltage in the rotating coordinate system is generated 、 and the current in the rotating coordinate system 、 , the phase used for the rotation coordinate transformation is θ; the DC voltage per unit value of the grid side converter is After passing through an integrator, the output of the integrator is the phase θ; the DC voltage u of the grid side converter dc Enter the reactive power side stabilizer, the output of the reactive power side stabilizer is the reactive power change ;

[0048] In the reactive power loop, the reference value of reactive power is Superimposed reactive power change , minus the reactive power feedback value After passing through the first PI regulator, the output of the first PI regulator is the reference value of the d-axis component of the AC side voltage , reference value of the q-axis component of the AC side voltage =0; in the grid-side AC voltage loop, the reference value 、 Respectively 、 Then, they pass through the second PI regulator respectively. The outputs of the two second PI regulators are the current values 、 Current value 、 Entering the current limiter, the output of the current limiter is the reference value of the d-axis component of the AC side current , AC side current q-axis component reference value , and AC current limit flag I LTEN ; In the grid-side AC current loop, 、 Respectively 、 The difference is made, and then passes through the third PI regulator respectively. The outputs of the two third PI regulators are the modulation voltage d-axis components , modulation voltage q-axis component ; 、 Generate three-phase modulated voltage through rotation coordinate transformation , After pulse width modulation, the trigger pulse S of the grid side converter is generated. g .

[0049] Among them, the output of the reactive power side stabilizer , enter u dc There is the following relationship between them,

[0050]

[0051] Where s is the Laplace operator, K is the reactive power side stability control gain, and T1 and T2 are the reactive power side stability control time constants, respectively.

[0052] like Figure 3 As shown, the current limiter adopts the following control structure:

[0053] Current value 、 Generate amplitude through phase transformation and phase φ, amplitude Enter the limit comparator, the output of the limit comparator is the limit flag I LTEN , amplitude reference value , amplitude reference value The sum phase φ is transformed into the AC side current d-axis component reference value , AC side current q-axis component reference value .

[0054] The output of the limiting comparator I LTEN With input There is the following relationship between them,

[0055]

[0056] in is the output current limit amplitude.

[0057] The output of the limit comparator With input There is the following relationship between them,

[0058] .

[0059] like Figure 4 As shown, the control loop of the fan side converter adopts the following control structure:

[0060] Detect the per-unit value of the DC voltage of the wind turbine side converter , Enter the inertia support and frequency adjustment module. The output of the inertia support and frequency adjustment module is the active power adjustment value. ; Detect the per-unit value of the wind wheel speed , Enter the maximum power tracking module. The output of the maximum power tracking module is the reference value of the active power on the wind turbine side. ; Overlay , minus the feedback value of the active power on the fan side After passing through the third PI regulator, the output of the third PI regulator is the reference value of the q-axis current on the fan side , reference value of d-axis current on the fan side is 0; 、 Entering the machine-side current loop, the output of the machine-side current loop undergoes rotational coordinate transformation and pulse width modulation to generate the trigger pulse S of the fan-side converter. m ;

[0061] Per unit value of wind rotor speed , Feedback value of active power on the wind turbine side , AC current limit flag I LTEN Enter the pitch angle control module; if I LTEN The value is 0, the pitch angle control module is based on 、 According to the conventional pitch angle adjustment method, the output pitch angle β is controlled; if I LTEN The value of is 1, increase the pitch angle β until I LTEN until the value becomes 0.

[0062] like Figure 5 As shown, the inertia support and frequency adjustment module adopts the following control structure:

[0063] Detect the per-unit value of the DC voltage of the wind turbine side converter , After passing through a first-order low-pass filter with a gain of T, and then through a filter with a gain of -K in The output of the differential link is , Enter the inertia side stabilization controller, the output of the inertia side stabilization controller is ;

[0064] 1 minus After a gain of K d The output of the proportional link is , Enter the frequency regulation side stabilization controller, the output of the frequency regulation side stabilization controller is ; Overlay The output after is the active power regulation .

[0065] Among them, the output of the inertia side stabilization controller Between input Has the following relationship,

[0066]

[0067] Where s is the Laplace operator, T in is the time constant of the inertia side stabilization control.

[0068] Among them, the output of the frequency regulation side stabilization controller With input There is the following relationship between them,

[0069]

[0070] Where s is the Laplace operator, T d It is the time constant of stable control on the frequency regulation side.

[0071] like Figure 6 As shown, the control loop of the photovoltaic converter adopts the following control structure:

[0072] The output of the photovoltaic maximum power tracking control module is the photovoltaic power reference value , detect the actual active power output of the photovoltaic converter , and The difference between the two passes through the fourth PI regulator, and the output of the fourth PI regulator is pulse-width modulated to generate a trigger pulse S for the photovoltaic converter. pv .

[0073] like Figure 7 As shown, a simulation embodiment of the present invention - the frequency adjustment module gain K d The simulation waveform when the power grid short-circuit ratio is 2. Figure 7 In (a), the frequency regulation side stabilization controller is not added. The frequency regulation module gain K at 40 seconds d When the value increases from 5.2 to 5.28, the DC voltage and the grid-side converter output power show oscillation divergence, and the system becomes unstable. Figure 7 In (b), the frequency regulation side stabilization controller is not added. The frequency regulation module gain K at 40 seconds d When the gain of the frequency regulation module is increased from 50 to 50.2, the DC voltage and the grid-side converter output power oscillate slightly and then recover, indicating that the proposed frequency regulation side stabilization controller can keep the system stable even when the gain of the frequency regulation module is large, effectively enhancing the stability of the grid-type control system with wind power and photovoltaic power reuse.

[0074] like Figure 8As shown in FIG. 1 , a simulation waveform of a grid-type control system for wind power and photovoltaic power multiplexing during a sudden load increase is shown in FIG. 1 , wherein the grid short-circuit ratio is 2. Figure 8 In (a), inertia support and frequency regulation control are not added. It can be seen that when the load suddenly increases, the grid frequency drops rapidly, and the lowest frequency point is 49.675Hz. Figure 8 In (b), inertia support and frequency regulation control are added. It can be seen that when the load suddenly increases, the grid frequency drops rapidly, and the lowest frequency point is 49.72Hz. Figure 8 In (a) and (b), it is not difficult to find that the added inertia support and frequency regulation control can increase the lowest point of the grid frequency when the load suddenly increases, effectively realize the active support of the grid, and enhance the frequency stability of the grid.

[0075] In summary, the grid-connected control system for wind power and photovoltaic power reuse proposed in the present invention enables wind power and photovoltaic power to be connected to the power grid through the same grid-side converter, reducing costs and presenting voltage source external characteristics similar to those of a synchronous generator to the power grid; the proposed inertia support and frequency regulation module can enhance the support capability of renewable energy for the power grid and enhance frequency stability; the proposed inertia-side and frequency regulation-side stabilization controllers can achieve phase correction, enhance the operational stability of renewable energy, and suppress oscillations.

[0076] The above is a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A grid-type control system for wind power and photovoltaic multiplexing, characterized in that: include: A wind wheel, a synchronous generator, a wind turbine side converter, a capacitor, a grid side converter, an LCL filter, a grid, a photovoltaic power generation unit, a photovoltaic converter, a control loop of the wind turbine side converter, a control loop of the grid side converter, and a control loop of the photovoltaic converter. The wind wheel is connected to the rotor of the synchronous generator. The stator of the synchronous generator outputs three-phase AC power, which is converted into DC power by the wind turbine side converter. The DC side of the wind turbine side converter is connected in parallel with the capacitor; the other side of the capacitor is connected to the DC side of the grid side converter, and the AC side of the grid side converter is filtered by the LCL filter and then connected to the grid; the current output by the photovoltaic power generation unit enters one side of the photovoltaic converter, and the other side of the photovoltaic converter is connected in parallel to the capacitor on the DC side of the wind turbine side converter. The photovoltaic converter is a DC / DC converter; the trigger pulse S of the wind turbine side converter m Provided by the control loop of the wind turbine side converter, the trigger pulse S of the grid side converter g Provided by the control loop of the grid-side converter, the trigger pulse S of the photovoltaic converter pv Provided by the control loop of the photovoltaic converter; The control loop of the grid-side converter adopts the following control structure: DC voltage u of the grid-side converter dc Enter the reactive power side stabilizer, the output of the reactive power side stabilizer is the reactive power change ; In the reactive power loop, the reference value of reactive power is Superimposed reactive power change , minus the reactive power feedback value After passing through the first PI regulator, the output of the first PI regulator is the reference value of the d-axis component of the AC side voltage , reference value of the q-axis component of the AC side voltage =0; in the grid-side AC voltage loop, the reference value 、 Respectively 、 Then, they pass through the second PI regulator respectively. The outputs of the two second PI regulators are the current values 、 Current value 、 Entering the current limiter, the output of the current limiter is the reference value of the d-axis component of the AC side current , AC side current q-axis component reference value , and AC current limit flag I LTEN ; The output of the reactive power side stabilizer , enter u dc There is the following relationship between them, ； Where s is the Laplace operator, K is the reactive power side stability control gain, T1 and T2 are the reactive power side stability control time constants respectively; The control loop of the fan side converter adopts the following control structure: Detect the per-unit value of the DC voltage of the wind turbine side converter , Enter the inertia support and frequency adjustment module. The output of the inertia support and frequency adjustment module is the active power adjustment value. ; Per unit value of wind rotor speed , Feedback value of active power on the wind turbine side , AC current limit flag I LTEN Enter the pitch angle control module; if I LTEN The value is 0, the pitch angle control module is based on 、 According to the conventional pitch angle adjustment method, the output pitch angle β is controlled; if I LTEN The value of is 1, increase the pitch angle β until I LTEN until the value becomes 0.

2. A wind power and photovoltaic multiplexing grid-type control system according to claim 1, characterized in that: The current limiter adopts the following control structure: Current value 、 Generate amplitude through phase transformation and phase φ, amplitude Enter the limit comparator, the output of the limit comparator is the limit flag I LTEN , amplitude reference value , amplitude reference value The sum phase φ is transformed into the AC side current d-axis component reference value , AC side current q-axis component reference value ; The output of the limit comparator I LTEN With input There is the following relationship between them, ； in is the output current limit amplitude.

3. A wind power and photovoltaic multiplexing grid-type control system according to claim 1, characterized in that: The inertia support and frequency adjustment module adopts the following control structure: Detect the per-unit value of the DC voltage of the wind turbine side converter , After passing through a first-order low-pass filter with a gain of T, and then through a filter with a gain of -K in The output of the differential link is , Enter the inertia side stabilization controller, the output of the inertia side stabilization controller is ; 1 minus After a gain of K d The output of the proportional link is , Enter the frequency regulation side stabilization controller, the output of the frequency regulation side stabilization controller is ; Overlay The output after is the active power regulation .

4. A wind power and photovoltaic multiplexing grid-type control system according to claim 2, characterized in that: The output of the clipping comparator With input There is the following relationship between them, 。 5. A wind power and photovoltaic multiplexing grid-type control system according to claim 3, characterized in that: The output of the inertia side stabilization controller Between input Has the following relationship, ； Where s is the Laplace operator, T in is the time constant of the inertia side stabilization control.

6. A wind power and photovoltaic multiplexing grid-type control system according to claim 3, characterized in that: The frequency regulation side stabilizes the output of the controller With input There is the following relationship between them, ； Where s is the Laplace operator, T d It is the time constant of stable control on the frequency regulation side.

7. A wind power and photovoltaic multiplexing grid-type control system according to claim 1, characterized in that: The control loop of the photovoltaic converter adopts the following control structure: The output of the photovoltaic maximum power tracking control module is the photovoltaic power reference value , detect the actual active power output of the photovoltaic converter , and The difference between the two passes through the fourth PI regulator, and the output of the fourth PI regulator is pulse-width modulated to generate a trigger pulse S for the photovoltaic converter. pv .

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