Photovoltaic grid-connected system with additional damping control and control method

Abstract

The present invention discloses a photovoltaic grid-connected control system and control method with additional damping control, wherein the control system comprises a photovoltaic panel, a boost circuit, an inverter, an output circuit, and a three-phase power grid connected in sequence, and further comprises a maximum power point tracking control circuit and a grid-connected inverter damping control module, wherein the grid-connected inverter damping control module receives the angular frequency deviation of the grid-connected system side, and outputs a signal to control the connected inverter through an SPWM drive circuit. The control system of the present invention has a simple structure, can effectively coordinate new disturbances brought to the power grid by various electronic devices, and ensure the safety and stability of the system; the control method of the present invention not only ensures the stable operation of the photovoltaic grid-connected system, but also improves the damping level of the AC system and enhances the dynamic stability of the AC system.

Description

Technical Field

[0001] The invention belongs to the field of photovoltaic power generation and grid connection, and relates to a photovoltaic grid connection inverter, specifically a photovoltaic grid connection system with additional damping control. The invention also provides a control method for the photovoltaic grid connection system with additional damping control. Background Art

[0002] With the continuous consumption of energy, the exploration of new energy sources has been continuously strengthened, especially electric energy, which has developed from the original traditional coal-fired power generation to a model where coal-fired power generation, wind power generation, photovoltaic power generation and other methods coexist. Among them, energy generation represented by photovoltaic power generation uses green energy existing in nature, and has therefore been highly praised in recent years. Since my country's current power system is mature, if the power output of the photovoltaic power generation system is to be incorporated into the existing power grid, it is necessary to design a grid-connected system to process the power output of the photovoltaic power generation system before incorporating it into the power system to ensure the stability of the power system after grid connection.

[0003] At present, photovoltaic power generation processes the direct current generated by photovoltaic panels through the grid-connected system, and finally forms three alternating currents that are synchronized with the power grid and input into the power grid. However, a large number of power electronic devices are used in the grid-connected system, and the coordinated control of the complex electronic devices brings new disturbance factors and safety and stability problems to the power grid. Therefore, it is necessary to design a reliable grid-connected system to ensure the stability of the power system. Summary of the invention

[0004] The purpose of the present invention is to provide a photovoltaic grid-connected system with additional damping control, so as to achieve stable operation of the photovoltaic grid-connected system and improve the damping level of the AC system.

[0005] Another object of the present invention is to provide a control method for a photovoltaic grid-connected system with additional damping control, which method can enhance the stability characteristics of an AC system.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0007] A photovoltaic grid-connected control system with additional damping control, comprising a photovoltaic panel, a boost circuit, a maximum power point tracking control circuit for controlling the photovoltaic panel to generate electricity at a maximum power point, an inverter, and an output circuit, wherein the output signal of the photovoltaic panel is connected to a three-phase power grid through the boost circuit, the inverter, and the output circuit in sequence, the input end of the maximum power point tracking control circuit is connected to the output end of the photovoltaic panel, and the output end thereof is controlled to be connected to the inverter, characterized in that it also comprises a grid-connected inverter damping control module, and the grid-connected inverter damping control module comprises an FPD controller, a decoupling capacitor, a PI controller, a current inner loop controller, and an SPWM drive. The decoupling capacitor is connected in parallel to the input end of the inverter. The signal input end of the FPD controller receives the angular frequency deviation of the grid-connected system side, outputs the current inner loop reactive current compensation value to the current inner loop controller, and outputs the inverter DC voltage compensation value to the PI controller at the same time; the input end of the PI controller also inputs the inverter DC voltage actual value and the inverter DC voltage reference value, and the output signal of the PI controller is transmitted to the current inner loop controller; the voltage and current on the AC side of the grid-connected system are both transmitted to the current inner loop controller as the current inner loop active and reactive decoupling; the output signal of the current inner loop controller is connected to the inverter through the SPWM drive circuit control.

[0008] As a limitation of the present invention: the boost circuit includes a boost inductor and a storage capacitor connected in series, the storage capacitor is connected in parallel to both ends of the photovoltaic panel output signal, and one end of the storage capacitor is connected to the positive output end of the photovoltaic panel and is connected in series with the boost inductor.

[0009] As a further limitation of the present invention: the maximum power point tracking control circuit includes a solar controller, a seventh modem, and a seventh switch tube. The signal input end of the solar controller is connected to the negative output of the photovoltaic panel, and its output end is connected to the emitter of the seventh switch tube through the seventh modem. The collector of the seventh switch tube is connected to one end of the boost inductor that is not connected to the energy storage capacitor.

[0010] As a further limitation of the present invention: the series circuit of the decoupling capacitor and the diode is connected in parallel to the two ends of the boost circuit, wherein one end of the decoupling capacitor is connected to the cathode of the diode, the anode of the diode is connected to the positive output end of the boost circuit, the other end of the decoupling capacitor is connected to the negative output end of the boost circuit, and the end of the decoupling capacitor outputs the actual value of the DC side voltage;

[0011] The output circuit includes an inverter-side inductor and a grid-side inductor. The output end of the inverter is sequentially connected in series with the inverter-side inductor and the grid-side inductor to connect to a three-phase grid.

[0012] The present invention also provides a control method for controlling the above-mentioned photovoltaic grid-connected system with additional damping control. The method uses the angular frequency deviation on the grid-connected system side as the input of the FPD controller to obtain the inverter DC voltage compensation value and the current inner loop reactive current compensation value respectively; then the inverter DC voltage compensation value, the inverter DC voltage actual value and the inverter DC voltage reference value are input to the PI controller as the outer loop, and the PI controller outputs the current inner loop command value used to maintain the DC side voltage constant. At the same time, the PI controller identifies and uses the AC side voltage and current of the grid-connected system as the active and reactive decoupling control input values ​​of the current inner loop controller; finally, the inverter triggers the SPWM drive circuit to perform damping adjustment and grid-connected control under the additional PDK control mode.

[0013] As a limitation of the above method: the inverter DC voltage reference value is obtained by the following formula:

[0014] U dcref =U m (1-0.00288△T)·ln(e+0.5△s) (1)

[0015] Among them, S is the light intensity, Um is the voltage value corresponding to the maximum photovoltaic power output, △T is the temperature difference, and △s is the light difference.

[0016] As a further limitation of the above method: the current inner loop command value output by the PI controller for maintaining the DC side voltage constant includes the d-axis reference current I dref , d-axis reference voltage U dref , Q-axis reference current I qref , Q axis reference voltage U qref , where the d-axis reference current I dref Calculated by the following formula:

[0017] I dref = kp1(U dcref -U dc +△p)+ki1·y1 (2);

[0018] d-axis reference voltage U dref Calculated by the following formula:

[0019] U dref =kp2(I dref -I d )+ki2·y2-ωL I Q +U d (3)

[0020] In formula (2) and (3), U dcis the actual value of the inverter DC voltage, p1 is the d-axis proportional coefficient, △p is the inverter DC voltage compensation value, k is the gain, i1 is the d-axis integral coefficient, I d is the AC side output current of the grid-connected system, IQ is the d-axis current of the AC side of the grid-connected system, U d is the AC side output voltage of the grid-connected system, i2 is the q-axis integral coefficient, y1 and y2 are variables, and the y1 and y2 variables satisfy the following formula:

[0021]

[0022] Q-axis reference current I qref Calculated by the following formula:

[0023] I qref = kp3(Q ref -Q+△Q)+ki3·y3 (5);

[0024] Q-axis reference voltage U qref Calculated by the following formula:

[0025] U qref =kp4(I qref -I q )+ki4·y4-ωL I d +U Q (6)

[0026] In formula (5) and (6), Q ref is the reactive reference value, Q is the reactive output value, △Q is the current inner loop reactive current compensation value, i3 is the inner loop integral coefficient, p4 is the inner loop proportional coefficient, i4 is the inner loop integral coefficient, ω is the angular frequency, L is the inductance I d , U Q is the d-axis output current of the AC side of the grid-connected system, y3 and y4 are variables, and the y3 and y4 variables satisfy the following formula:

[0027]

[0028] The ω is obtained by the setting formula of the phase α to be compensated:

[0029]

[0030] Where T1 is the time constant in the PDK control system, T2 is the hysteresis coefficient, and θ is the phase angle.

[0031] As a final limitation to the above method: the reactive current compensation value of the current inner loop is obtained by the following formula:

[0032] ΔQ=K Q Δω=K Q pΔδ (9);

[0033] Where K Q is the reactive power compensation gain, p is the differential operator, and △δ is the power angle difference.

[0034] Due to the adoption of the above technical solution, the present invention has the following technical advances compared with the prior art:

[0035] (1) The present invention is provided with a grid-connected inverter damping control module, which adds damping to the inverter voltage outer loop and current inner loop as a reference input for reactive current, thereby ensuring the stable operation of the photovoltaic grid-connected system while improving the damping level of the AC system and enhancing the stability of the system.

[0036] (2) The present invention is provided with a maximum power point tracking control circuit, which obtains an SPWM signal according to the DC voltage and DC current emitted by the photovoltaic panel. The combustion control uses the SPWM signal to control the on and off of the switch tube, thereby controlling the photovoltaic panel to generate electricity at the maximum power point.

[0037] (3) The control method of the present invention uses the angular frequency deviation of the grid-connected system as the input of the FPD controller, and obtains the inverter DC voltage compensation value and the current inner loop reactive current compensation value respectively. Then, the inverter DC voltage compensation value, the inverter DC voltage actual value, and the inverter DC voltage reference value are transmitted as input values ​​to the PI controller for processing and then outputting the d-axis current reference value, and the above-mentioned d-axis current reference value is used as the current inner loop instruction to maintain the constant voltage on the DC side of the inverter; at the same time, the PI controller identifies and uses the voltage and current on the AC side of the grid-connected system as the active and reactive decoupling control input values ​​of the current inner loop controller; finally, the inverter triggers the SPWM drive circuit to perform damping adjustment and grid-connected control under the additional PDK control mode. The above-mentioned control method by adding damping to the inverter voltage outer loop and the current inner loop as the reference input of reactive current not only ensures the stable operation of the photovoltaic grid-connected system, but also improves the damping level of the AC system and enhances the dynamic stability of the AC system.

[0038] In summary, the control system of the present invention has a simple structure and can effectively coordinate the new disturbances brought to the power grid by various electronic devices to ensure the safety and stability of the system; the control method of the present invention not only ensures the stable operation of the photovoltaic grid-connected system, but also improves the damping level of the AC system and enhances the dynamic stability of the AC system. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 is a circuit schematic diagram of embodiment 1 of the present invention;

[0040] Figure 2 This is a simplified model diagram of the photovoltaic inverter additional damping control strategy in Example 1;

[0041] Figure 3 It is a principle block diagram of the PDK control link of the present invention;

[0042] Figure 4 An equivalent circuit diagram for incorporating the control system of Example 1 into a system power grid;

[0043] Figure 5 This is a simulation equivalent circuit diagram of a 2-area 4-machine system constructed in Example 3 of the present invention;

[0044] Figure 6 This is a waveform diagram of active power of the line under additional control of the photovoltaic power station in Example 3 of the present invention;

[0045] Figure 7 is an active power waveform diagram of the generator G2′ in Embodiment 3 of the present invention;

[0046] Figure 8 This is a grid-connected power waveform diagram of the photovoltaic panel under additional PDK damping control in Example 3 of the present invention;

[0047] Fig. 9 This is a waveform diagram of the sudden change in irradiance of the photovoltaic panel in Example 3 of the present invention;

[0048] Fig.10 This is a waveform diagram of active power of synchronous units in photovoltaic power station with sudden illumination change in embodiment 3 of the present invention;

[0049] Fig.11 This is a waveform diagram of the grid-connected bus voltage response to a sudden change in illumination intensity in a photovoltaic power station in Example 3 of the present invention. DETAILED DESCRIPTION

[0050] In order to better explain the present invention and facilitate understanding, the present invention is described in detail below through specific implementation modes in conjunction with the accompanying drawings.

[0051] Example 1 Photovoltaic grid-connected system with additional damping control

[0052] The “front”, “rear”, “left” and “right” described in this embodiment are defined for the convenience of description and do not constitute a limitation on the protection scope of the present invention.

[0053] This embodiment provides a photovoltaic grid-connected system with additional resistance control. Figure 1 As shown, including:

[0054] 1. Photovoltaic panel PV, the photovoltaic panel PV is a photovoltaic power generation panel in the prior art, and the two ends of the photovoltaic panel PV are respectively a positive output end and a negative output end.

[0055] 2. Boost circuit is used to convert the DC voltage U generated by the photovoltaic panel PV v The boost circuit in this embodiment consists of a boost inductor Lv and energy storage capacitor C v The energy storage capacitor C v Connected in parallel to both ends of the photovoltaic panel PV output signal, the energy storage capacitor C v One end connected to the positive output end of the photovoltaic panel PV is connected in series with the boost inductor L v .

[0056] 3. Inverter, used to convert the input DC power into three-phase AC power. The inverter in this embodiment adopts the inverter in the prior art, that is, Figure 1 As shown, it includes a first switch tube V1 to a sixth switch tube V6, and a diode is connected in series between the collector and the emitter of each switch tube.

[0057] 4. Output circuit, used to process the three-phase AC power converted by the inverter and then connect it to the three-phase power grid. The output circuit in this embodiment includes an inverter side inductor L p , grid-side inductance L m The output end of the inverter is connected to the three-phase grid after being connected to the inverter side inductor and the grid side inductor in series. To ensure that the output voltage is not interfered, the output circuit also includes a filter, and the signal output end of the filter is connected to the inverter side inductor L p and the grid-side inductance L m On the connected line.

[0058] 5. Maximum power point tracking control circuit, used to control the photovoltaic panel PV power generation to work at the maximum power point. The maximum power point tracking control circuit in this embodiment includes a solar controller MPPT, a seventh modem SPWM7, and a seventh switch tube V7, wherein the signal input end of the solar controller MPPT is connected to the negative output of the photovoltaic panel PV, and its output end is connected to the emitter of the seventh switch tube V7 through the seventh modem SPWM7, and the collector of the seventh switch tube V7 is connected to the boost inductor L v Energy storage capacitor C is not connected v one end.

[0059] 6. Grid-connected inverter damping control module, including FPD controller, decoupling capacitor C connected to the inverter input terminal dc , PI controller, current inner loop controller, and SPWM drive circuit, the decoupling capacitor C dc One end is connected to the negative output end of the photovoltaic panel PV, and the other end is connected to the negative output end of the photovoltaic panel PV through the first diode VD1. dc The signal input end of the FPD controller is connected in parallel to the input end of the inverter; the signal input end of the FPD controller is connected to the decoupling capacitor C dcReceive the angular frequency deviation △ω on the grid-connected system side, output the current inner loop reactive current compensation value △Q to the current inner loop controller, and output the inverter DC voltage compensation value △P to the PI controller; the input end of the PI controller also inputs the actual DC side voltage value U dc and the inverter DC voltage reference value U dcref The inverter DC voltage reference value U dcref It is obtained by the following formula:

[0060] U dcref =U m (1-0.00288△T)·ln(e+0.5△s) (1)

[0061] Among them, S is the light intensity, Um is the voltage value corresponding to the maximum photovoltaic power output, △T is the temperature difference, and △s is the light difference.

[0062] The current inner loop command value output by the PI controller to maintain the DC side voltage constant is referenced to Figure 2 As shown, including the d-axis reference current I dref , d-axis reference voltage U dref , Q-axis reference current I qref , Q axis reference voltage U qref , where the d-axis reference current I dref Calculated by the following formula:

[0063] I dref = kp1(U dcref -U dc +△p)+ki1·y1 (2);

[0064] d-axis reference voltage U dref Calculated by the following formula:

[0065] U dref =kp2(I dref -I d )+ki2·y2-ωL I Q +U d (3)

[0066] In formula (2) and (3), U dc is the actual value of the inverter DC voltage, p1 is the d-axis proportional coefficient, △p is the inverter DC voltage compensation value, k is the gain, i1 is the d-axis integral coefficient, I d is the AC side output current of the grid-connected system, IQ is the d-axis current of the AC side of the grid-connected system, U d is the AC side output voltage of the grid-connected system, i2 is the q-axis integral coefficient, y1 and y2 are variables, and the y1 and y2 variables satisfy the following formula:

[0067]

[0068] Q-axis reference current I qref Calculated by the following formula:

[0069] I qref = kp3(Q ref -Q+△Q)+ki3·y3 (5);

[0070] Q-axis reference voltage U qref Calculated by the following formula:

[0071] U qref =kp4(I qref -I q )+ki4·y4-ωL I d +U Q (6)

[0072] In formula (5) and (6), Q ref is the reactive reference value, Q is the reactive output value, △Q is the current inner loop reactive current compensation value, i3 is the inner loop integral coefficient, p4 is the inner loop proportional coefficient, i4 is the inner loop integral coefficient, ω is the angular frequency, L is the inductance I d , U Q is the d-axis output current of the AC side of the grid-connected system, y3 and y4 are variables, and the y3 and y4 variables satisfy the following formula:

[0073]

[0074] The ω is obtained by the setting formula of the phase α to be compensated:

[0075]

[0076] Where T1 is the time constant in the PDK control system, T2 is the hysteresis coefficient, and θ is the phase angle.

[0077] The data in the above formula (8) is obtained by PDK control. The specific PDK control link is as follows: Figure 3 The measurement process is shown in the figure. T1 is the time constant, the DC component isolation module, T w The value is 4 to 8s. The phase compensation module is fast. The pole of the imaginary axis of the coordinate axis is obtained through phase angle compensation to increase the stability of the system, and the proportional amplification K controls the damping strength.

[0078] And transmit it to the current inner loop controller; the AC side voltage and current U d , U Q ,I d ,I QThey are all transmitted to the current inner loop controller as active and reactive decoupling of the current inner loop; the output signal of the current inner loop controller is connected to the inverter through the SPWM drive circuit control.

[0079] The SPWM driving circuit in this embodiment includes a first modem SPWM1 to a sixth modem SPWM6, and each modem controls a switch tube in the inverter.

[0080] The reactive current compensation value △Q of the current inner loop described in this embodiment is obtained by the following formula:

[0081] ΔQ=K Q Δω=K Q pΔδ (9);

[0082] Where K Q is the reactive power compensation gain, p is the differential operator, and △δ is the power angle difference.

[0083] From the above formula (9), it can be seen that the damping characteristics of the system can be increased by adjusting the relevant parameters of the controller.

[0084] The control principle of this embodiment is: take the angular frequency deviation △ω of the grid-connected system side as the input of the FPD controller, and obtain the inverter DC voltage compensation value △P and the current inner loop reactive current compensation value △Q respectively; then convert the inverter DC voltage compensation value △P and the inverter DC voltage actual value U dc and the inverter DC voltage reference value U dcref As the outer loop input to the PI controller, the PI controller outputs the current inner loop command value used to maintain the DC side voltage constant. At the same time, the PI controller identifies and sets the AC side voltage and current U d , U q ,I d ,I q As the active and reactive decoupling control input value of the current inner loop controller; finally, the inverter triggers the SPWM drive circuit for damping adjustment and grid-connected control under the additional PDK control mode.

[0085] Embodiment 2 Grid-connected circuit of photovoltaic grid-connected system with additional damping control

[0086] In this embodiment, the photovoltaic grid-connected system with additional damping control provided in Embodiment 1 is connected to the power grid. The specific grid-connected circuit is as follows: Figure 4 As shown, the DC signal obtained by the photovoltaic panel PV is converted by the inverter and then connected to the grid through the step-up transformer. In the figure, G1 is a synchronous generator set; G2 is an infinite system; U g is the voltage at the grid connection point of the photovoltaic power station; E′ is the transient potential of G1; U is the voltage at the G2 terminal; θ is the difference between E′ and U gδ is the phase difference between E′ and U; x1 and x2 are the line reactances.

[0087] In the above circuit, the photovoltaic power station connected to the grid through the DC / AC inverter changes the system power flow distribution, reactive voltage and active frequency characteristics after being connected to the grid. However, through reasonable control of photovoltaic power, the damping characteristics of the connected synchronous generator system can be enhanced and the transient stability capability of the large power grid can be strengthened.

[0088] The photovoltaic inverter based on active and reactive decoupling can adjust the power exchanged with the system and the grid-connected voltage level through additional control while ensuring the stability of the DC side voltage. In view of this, it is inferred that the photovoltaic power station based on the PDK additional control strategy can enhance the damping level of the grid-connected system with the synchronous generator set through the inverter dual-loop damping control, improve the ability to optimize the damping characteristics, and improve the stable operation level and reliable power supply capability of the photovoltaic grid-connected system.

[0089] Among them, the power output of the synchronous generator set G1 is expressed as:

[0090]

[0091] Ignoring the excitation and speed regulation factors of the synchronous generator set, the small disturbance equation of the synchronous generator set of the second-order classical model is:

[0092] H G p 2 Δδ+DpΔδ+Δp g =0 (11)

[0093] Where H G is the inertia coefficient, p is the differential operator, D is the damping coefficient, △δ is the power angle difference, △p g is the active power difference.

[0094] The power balance relationship between synchronous generator sets, photovoltaic panels and large power grid is as follows:

[0095]

[0096] The dynamic reactive power increment under the additional PDK control of the inverter device is △Q g , the △Q g It is obtained by the following formula:

[0097] ΔQ g =ΔQ=-k Q Δω (13)

[0098] In the above formula, -k Q is the reactive loop damping controller value, △ω is the photovoltaic additional damping controller input and the system angular frequency change.

[0099] The input of the photovoltaic additional damping controller is the system angular frequency change △ω. The angular frequency change range measured at the grid collection point (PCC) is regarded as the change of the generator angular frequency. The active power damping increment output by the controller is as follows:

[0100] Where: k is the active damping control coefficient, △ω is the angular frequency change value at PCC, that is, the angular frequency change of the photovoltaic additional damping controller input system. Then the small disturbance quantity is obtained for equation (12):

[0101]

[0102] Δθ=kΔδ+a1ΔU g +a2kk Q pΔδ (16)

[0103] In this embodiment, the pole configuration is -1.42+j6.21, the damping ratio is 18.02%, and the controller parameters are adjusted according to the formula:

[0104]

[0105] The small perturbation equation is obtained by combining

[0106]

[0107] Where a1 and a2 have the following relationship:

[0108]

[0109] In formula (18) and (19), H G is the inertia coefficient, p is the differential operator, Δδ is the power angle difference, D is the damping coefficient, Ug0 is the grid-connected point voltage of the photovoltaic power station, and δ0 and θ0 are the initial values ​​of the corresponding angles.

[0110] From formula (18), it can be seen that the value of the adjustment controller K is in a reasonable range; the photovoltaic power station additional damping controller significantly enhances the system damping characteristics through power regulation control efficiency. Q >0, the system characteristic root continues to shift leftward, further improving the damping capacity and ensuring the strong and stable operation of the grid-connected system.

[0111] Example 3 Simulation Analysis

[0112] This embodiment relies on the Digsilent platform to complete the construction of the additional damping control photovoltaic grid-connected system in Example 1 into a 4-machine 2-region system. The constructed model is as follows: Figure 5 As shown, Figure 5The MPPT algorithm is adopted in the middle. After the photovoltaic power station with additional damping control is inverted, it is connected to the grid through bus 6 with the synchronous unit G2′. The input signal of the damping controller is the system angular velocity deviation Δω S The maximum active power of the photovoltaic power station in normal mode is 250MW. The initial value of the irradiation intensity of the power station is set to 800W / m 2 The synchronous generator set is not equipped with PSS, the unit capacity is 900MW, and the active power output is 600MW under normal operation. The normal transmission power from area 1 to area 2 is 220MW.

[0113] 1. Normal operation mode photovoltaic additional control simulation

[0114] Assuming that the light intensity and temperature of the photovoltaic power station do not change suddenly, the first tie line of node 7 and node 8 has a three-phase short circuit fault at 1.8s, and the fault is removed after 0.05s; the active power of the tie line is shown in the simulation of photovoltaic inverter without additional damping control PV-NPD and additional feedforward power damping control PV-PD. Figure 6 , the active power of generator G2′ is Figure 7 , and the output power and grid-connected power waveforms under the photovoltaic panel additional damping control mode are as follows Figure 8 As shown. Figure 6 , Figure 7 It can be seen that under constant light and normal operation, the additional feedforward damping control of the photovoltaic power station inverter device effectively enhances and optimizes the damping of the grid-connected system. After the small disturbance begins, the interconnection line power and the same-year unit are smoothed within 8 seconds, which greatly shortens the duration of power oscillation. Figure 8 It can be seen that the output power of the photovoltaic panel is 248.6MW and the grid-connected power is 246.5MW, which shows that the additional damping inverter can provide a higher power factor while improving the damping characteristic capability, ensuring the reliable and high-quality operation of the grid-connected system.

[0115] 2. Simulation of Additional Control of Photovoltaic Power Station with Sudden Light Intensity Change

[0116] The photovoltaic power station is set at a constant temperature of 25°C, and the irradiance increases from 1500W / m 2 Sudden change to 800W / m 2 , study the dynamic response effect of additional control; Fig. 9 is the irradiance variation curve at 25℃. The active power of generator G2′ under photovoltaic mutation mode is as follows: Fig.10 As shown, the grid connection point voltage is shown in Fig.11 .

[0117] Depend on Fig.10 and Fig.11It can be seen that when the irradiance of the photovoltaic panel changes, compared with the voltage outer loop and current inner loop control of the traditional photovoltaic inverter, the additional damping control can respond well to the dynamic adjustment response of the system. The damping controller forms a significant mechanism to cope with external environmental interference by adding active power and reactive power compensation to the inverter decoupling double loop, and enhances the ability of the grid-connected synchronous unit to smooth power fluctuations. At the same time, the damping controller effectively suppresses the voltage fluctuation of the grid-connected system through the reactive voltage regulation capability, providing high-quality and reliable dynamic stability support capabilities for the large power grid.

[0118] The above simulation experiment inferred the mechanism of the additional control of the inverter to increase the damping torque of the system through the photovoltaic-synchronous machine grid-connected system, and adjusted the control parameters in combination with the damping torque analysis. The simulation of the additional damping control strategy of the photovoltaic inverter improves the damping level of the grid-connected system. Setting disturbance factors such as sudden changes in light further shows that the proposed control strategy has strong robust performance, can effectively stabilize the grid-connected busbar power grid, and greatly improves the stable operation capability and performance of the photovoltaic grid-connected system. The above description is only the best description of this embodiment and does not constitute a limitation on the scope of protection of the present invention.

Claims

1. A photovoltaic grid-connected system with additional damping control, comprising a photovoltaic panel, a boost circuit, a maximum power point tracking control circuit for controlling the photovoltaic panel to generate electricity at a maximum power point, an inverter, and an output circuit, wherein the output signal of the photovoltaic panel is connected to a three-phase power grid through the boost circuit, the inverter, and the output circuit in sequence, the input end of the maximum power point tracking control circuit is connected to the output end of the photovoltaic panel, and the output end thereof is controlled to be connected to the inverter, characterized in that: It also includes a grid-connected inverter damping control module, which includes an FPD controller, a decoupling capacitor, a PI controller, a current inner loop controller, and an SPWM drive circuit. The decoupling capacitor is connected in parallel to the input end of the inverter, the signal input end of the FPD controller receives the angular frequency deviation of the grid-connected system side, outputs the current inner loop reactive current compensation value to the current inner loop controller, and simultaneously outputs the inverter DC voltage compensation value to the PI controller; the input end of the PI controller also inputs the inverter DC voltage actual value and the inverter DC voltage reference value, and the output signal of the PI controller is transmitted to the current inner loop controller; the voltage and current on the AC side of the grid-connected system are both transmitted to the current inner loop controller as the current inner loop active and reactive decoupling; the output signal of the current inner loop controller is connected to the inverter through the SPWM drive circuit control.

2. The photovoltaic grid-connected system with additional damping control according to claim 1, characterized in that: The boost circuit includes a boost inductor and an energy storage capacitor connected in series. The energy storage capacitor is connected in parallel to both ends of the photovoltaic panel output signal. One end of the energy storage capacitor connected to the positive output end of the photovoltaic panel is connected in series with the boost inductor.

3. The photovoltaic grid-connected system with additional damping control according to claim 2, characterized in that: The maximum power point tracking control circuit includes a solar controller, a seventh modem, and a seventh switch tube. The signal input end of the solar controller is connected to the negative output of the photovoltaic panel, and its output end is connected to the emitter of the seventh switch tube through the seventh modem. The collector of the seventh switch tube is connected to one end of the boost inductor that is not connected to the energy storage capacitor.

4. The photovoltaic grid-connected system with additional damping control according to claim 3, characterized in that: The series circuit of the decoupling capacitor and the diode is connected in parallel to the two ends of the boost circuit, wherein one end of the decoupling capacitor is connected to the cathode of the diode, the anode of the diode is connected to the positive output end of the boost circuit, the other end of the decoupling capacitor is connected to the negative output end of the boost circuit, and the power supply end of the decoupling capacitor outputs the actual value of the DC side voltage; The output circuit includes an inverter-side inductor and a grid-side inductor. The output end of the inverter is sequentially connected in series with the inverter-side inductor and the grid-side inductor to connect to a three-phase grid.

5. A control method for a photovoltaic grid-connected system with additional damping control according to any one of claims 1 to 4, characterized in that: The angular frequency deviation on the grid-connected system side is used as the input of the FPD controller to obtain the inverter DC voltage compensation value and the current inner loop reactive current compensation value respectively; then the inverter DC voltage compensation value, the inverter DC voltage actual value and the inverter DC voltage reference value are input to the PI controller as the outer loop, and the PI controller outputs the current inner loop command value used to maintain the DC side voltage constant. At the same time, the PI controller identifies and uses the AC side voltage and current of the grid-connected system as the active and reactive decoupling control input values ​​of the current inner loop controller; finally, the inverter triggers the SPWM drive circuit for damping adjustment and grid-connected control under the additional PDK control mode.

6. The control method according to claim 5, characterized in that: The inverter DC voltage reference value is obtained by the following formula: U dcref =U m (1-0.00288△T)·ln(e+0.5△s) (1) Among them, S is the light intensity, Um is the voltage value corresponding to the maximum photovoltaic power output, △T is the temperature difference, and △s is the light difference.

7. The control method according to claim 6, characterized in that: The current inner loop command value output by the PI controller to maintain the DC side voltage constant includes the d-axis reference current I dref , d-axis reference voltage U dref , Q-axis reference current I qref , Q axis reference voltage U qref , where the d-axis reference current I dref Calculated by the following formula: AND dref =kp1(U dcref -IN dc +△p)+ki1·y1 (2); d-axis reference voltage U dref Calculated by the following formula: U dref =kp2(I dref -I d )+ki2·y2-ωL I Q +U d (3) In formula (2) and (3), U dc is the actual value of the inverter DC voltage, p1 is the d-axis proportional coefficient, △p is the inverter DC voltage compensation value, k is the gain, i1 is the d-axis integral coefficient, I d is the AC side output current of the grid-connected system, IQ is the d-axis current of the AC side of the grid-connected system, U d is the AC side output voltage of the grid-connected system, i2 is the q-axis integral coefficient, y1 and y2 are variables, and the y1 and y2 variables satisfy the following formula: Q-axis reference current I qref Calculated by the following formula: I qref =kp3(Q ref -Q+△Q)+ki3·y3 (5); Q-axis reference voltage U Qref Calculated by the following formula: IN qref =kp4(I qref -AND q )+ki4·y4-ωL I d +U Q (6) In formula (5) and (6), Q ref is the reactive reference value, Q is the reactive output value, △Q is the current inner loop reactive current compensation value, i3 is the inner loop integral coefficient, p4 is the inner loop proportional coefficient, i4 is the inner loop integral coefficient, ω is the angular frequency, L is the inductance I d , U Q is the d-axis output current and output voltage of the AC side of the grid-connected system, y3 and y4 are variables, and the y3 and y4 variables satisfy the following formula: The ω is obtained by the setting formula of the phase α to be compensated: Where T1 is the time constant in the PDK control system, T2 is the hysteresis coefficient, and θ is the phase angle.

8. The control method according to claim 6, characterized in that: The reactive current compensation value of the current inner loop is obtained by the following formula: ΔQ=K Q Give=K Q pΔδ (9); Where K Q is the reactive power compensation gain, p is the differential operator, and △δ is the power angle difference.

Images