A method and system for operating a photovoltaic inverter to participate in grid frequency regulation

Abstract

The application relates to a photovoltaic inverter operation control method and system involved in power grid frequency regulation, and comprises the following steps: determining a slope change amount in a power-voltage characteristic curve of a photovoltaic generator set according to a load reduction rate of the photovoltaic generator set; determining a direct-current side voltage reference value of a photovoltaic inverter by using an improved MPPT algorithm based on the slope change amount in the power-voltage characteristic curve of the photovoltaic generator set; and controlling on-off of IGBT in the photovoltaic inverter based on the direct-current side voltage reference value of the photovoltaic inverter. The application considers the influence of the load reduction rate of the photovoltaic generator set on the photovoltaic inverter control, and improves the accuracy of the photovoltaic inverter control.

Description

Technical Field

[0001] This invention relates to the field of power grid frequency regulation and control, and specifically to a photovoltaic inverter operation control method and system that participates in power grid frequency regulation. Background Technology

[0002] To prevent global warming and energy depletion, there is an urgent need to develop renewable energy sources such as solar and wind power. Among various renewable energy sources, solar energy has become one of the fastest-growing renewable energy sources due to its advantages such as cleanliness, safety, and inexhaustibility. The installed capacity of large-scale solar power plants worldwide is increasing year by year.

[0003] Photovoltaic inverters are an indispensable component in power systems. Precise control of photovoltaic inverters can effectively improve the power imbalance between supply and demand, thereby achieving the effect of regulating grid frequency.

[0004] Centralized photovoltaic inverters are a widely used type of photovoltaic inverter. They employ a single-stage DC-AC power electronic full-bridge inverter structure, such as... Figure 1 As shown, a centralized photovoltaic inverter converts the direct current (DC) generated by photovoltaic modules into alternating current (AC), then boosts the voltage before connecting it to the power grid. Therefore, the inverter has a relatively high power output.

[0005] Compared to string inverters, the capacity of a single string inverter is only tens of kW, while the minimum capacity of a single centralized inverter can reach 500 kW. It is more suitable for large ground-mounted power plants or large commercial rooftops with a capacity of MW or more, that is, it is more suitable for large-scale photovoltaic power grid application scenarios.

[0006] Large-scale photovoltaic (PV) integration into the power system inevitably leads to a reduction in system inertia and frequency regulation capabilities, affecting the system's power quality. As PV penetration continues to increase, modern power grids are increasingly requiring PV power plants to operate in off-load mode, reserving a certain amount of backup power for the power system and enabling it to have primary frequency regulation capabilities.

[0007] However, the control technology of traditional photovoltaic inverters is designed based on output power tracking of maximum output power. If photovoltaic power plants still use this technology when operating in load reduction mode, it will inevitably lead to unsatisfactory control performance of photovoltaic inverters.

[0008] Therefore, it is urgent to develop control technology for photovoltaic inverters when photovoltaic power plants are operating in unloaded mode. Summary of the Invention

[0009] To address the shortcomings of existing technologies, the present invention aims to provide a photovoltaic inverter operation control method and system that participates in grid frequency regulation. This method considers the impact of the photovoltaic generator set's load shedding rate on the photovoltaic inverter control, thereby improving the accuracy of photovoltaic inverter control.

[0010] The objective of this invention is achieved through the following technical solution:

[0011] This invention provides a photovoltaic inverter operation control method participating in grid frequency regulation, the improvement of which is that the method includes:

[0012] The slope change in the power-voltage characteristic curve of the photovoltaic generator set is determined based on the load reduction rate of the photovoltaic generator set.

[0013] Based on the slope change in the power-voltage characteristic curve of the photovoltaic generator set, the reference value of the DC side voltage of the photovoltaic inverter is determined by the improved MPPT algorithm.

[0014] The switching on and off of IGBTs in a photovoltaic inverter is controlled based on the DC-side voltage reference value of the photovoltaic inverter.

[0015] The improvement of the MPPT algorithm lies in the introduction of a power disturbance term on the DC side of the photovoltaic inverter into the calculation formula for the change in active power on the DC side of the photovoltaic inverter.

[0016] Preferably, determining the slope change in the power-voltage characteristic curve of the photovoltaic generator set based on the load shedding rate includes:

[0017] The change in slope of the power-voltage characteristic curve of a photovoltaic generator at the current time t is determined by the following formula.

[0018]

[0019] In the formula, a0(t) is the value of the first fitting coefficient at the current time t, a1(t) is the value of the second fitting coefficient at the current time t, and σ%(t) is the load reduction rate of the photovoltaic generator at the current time t.

[0020] Furthermore, a0(t) is determined by the following formula:

[0021] a0(t)=]0.2795T(t)-62.27]×[-0.054S(t)-0.4705]

[0022] The a1(t) is determined by the following formula:

[0023] a1(t)=[0.04873T(t)-13.02]×[-3.078e-8×S 3(t)+9.517e-5×S(t) 2 -0.07112S(t)-5.272]

[0024] In the above formula, T(t) is the temperature of the photovoltaic panel of the photovoltaic generator set at the current time t, and S(t) is the light intensity received by the photovoltaic panel of the photovoltaic generator set at the current time t.

[0025] Preferably, the determination of the DC-side voltage reference value of the photovoltaic inverter using the improved MPPT algorithm based on the slope change in the power-voltage characteristic curve of the photovoltaic generator set includes:

[0026] Based on the slope change in the power-voltage characteristic curve of the photovoltaic generator set, the improved MPPT algorithm is used to determine the DC side reference voltage of the photovoltaic inverter during the load shedding control of the photovoltaic generator set.

[0027] The sum of the DC-side reference voltage of the photovoltaic inverter during the photovoltaic generator load shedding control and the DC-side reference voltage of the photovoltaic inverter during the photovoltaic generator droop control is used as the DC-side voltage reference value of the photovoltaic inverter.

[0028] Furthermore, the method for determining the DC-side reference voltage of the photovoltaic inverter during load shedding control using an improved MPPT algorithm based on the slope change in the power-voltage characteristic curve of the photovoltaic generator set includes:

[0029] Based on the change in slope of the power-voltage characteristic curve of the photovoltaic generator set at the current time t, the change in active power on the DC side of the photovoltaic inverter, ΔP(t), which introduces the power disturbance term on the DC side of the photovoltaic inverter at the current time t, is obtained by the following formula.

[0030] If ΔP(t) is not equal to 0 and ΔU(t) is not greater than 0, then

[0031] If ΔP(t) is not equal to 0 and ΔU(t) is greater than 0, then

[0032] otherwise,

[0033] Among them, ΔU(t)=u(t)-u(t-1), P(t)=I(t)·u(t), P(t-1)=I(t-1)·u(t-1), Let ΔU(t) be the DC-side power disturbance term of the photovoltaic inverter at the current time t, and let ΔU(t) be the change in DC-side voltage of the photovoltaic inverter at the current time t. Let u(t) be the DC-side reference voltage of the photovoltaic inverter when the photovoltaic generator set is under load shedding control at the current time t, u(t) be the measured value of the DC-side voltage of the photovoltaic inverter at the current time t, Δd be the disturbance step size, P(t) be the DC-side active power of the photovoltaic inverter at the current time t, I(t) be the measured value of the DC-side current of the photovoltaic inverter at the current time t, P(t-1) be the DC-side active power of the photovoltaic inverter at time t-1, I(t-1) be the measured value of the DC-side current of the photovoltaic inverter at time t-1, and u(t-1) be the measured value of the DC-side voltage of the photovoltaic inverter at time t-1.

[0034] Furthermore, the process of obtaining the DC-side reference voltage of the photovoltaic inverter during the droop control of the photovoltaic generator set includes:

[0035] The primary frequency regulation active power deviation of the photovoltaic generator set is calculated based on the grid frequency deviation and the droop coefficient of the photovoltaic generator set.

[0036] Substituting the primary frequency regulation active power deviation of the photovoltaic generator set into the first PI controller, the DC side reference voltage of the photovoltaic inverter corresponding to the droop control is obtained.

[0037] Among them, the power grid frequency deviation is the difference between the measured value of the power grid frequency and the reference value of the power grid frequency.

[0038] Furthermore, the calculation of the primary frequency regulation active power deviation of the photovoltaic generator set based on the grid frequency deviation and the droop coefficient of the photovoltaic generator set includes:

[0039] The primary frequency regulation active power deviation ΔP of the photovoltaic generator at the current time t is determined by the following formula. x (t):

[0040] ΔP x (t)=k d (t)·Δf(t)

[0041] In the formula, k d (t) represents the value of the droop coefficient at the current time t, and Δf(t) represents the power grid frequency deviation at the current time t.

[0042] Wherein, k is determined by the following formula. d (t):

[0043]

[0044] In the formula, P c (t) represents the actual output power of the photovoltaic generator at the current time t, σ% represents the load shedding rate of the photovoltaic generator, and P n k is the rated output power of the photovoltaic generator set. dmax k represents the maximum value of the droop coefficient. dminThis is the minimum value of the droop coefficient.

[0045] Preferably, the control of the on / off state of the IGBTs in the photovoltaic inverter based on the DC-side voltage reference value of the photovoltaic inverter includes:

[0046] The d-axis modulation voltage of the photovoltaic inverter on the grid side is determined based on the DC-side voltage reference value of the photovoltaic inverter.

[0047] The q-axis modulation voltage on the grid side of the photovoltaic inverter is determined based on the reactive power reference value of the photovoltaic inverter.

[0048] The d-axis modulation voltage and q-axis modulation voltage on the grid side of the photovoltaic inverter are PWM modulated to obtain the switching control pulse of the IGBT in the photovoltaic inverter.

[0049] The switching control pulses of the IGBTs in the photovoltaic inverter are used to control the on and off states of the IGBTs.

[0050] Furthermore, determining the d-axis modulation voltage of the photovoltaic inverter on the grid side based on the DC-side voltage reference value of the photovoltaic inverter includes:

[0051] Based on the measured DC-side voltage of the photovoltaic inverter, the reference DC-side voltage of the photovoltaic inverter, the grid-side d-axis current component, the grid-side q-axis current component, and the grid-side d-axis voltage component of the photovoltaic inverter, the d-axis modulation voltage of the photovoltaic inverter on the grid side is determined using the constant DC voltage control technology of the photovoltaic inverter DC side.

[0052] Furthermore, determining the q-axis modulation voltage on the grid side of the photovoltaic inverter based on the reactive power reference value output by the photovoltaic inverter includes:

[0053] Based on the measured reactive power of the photovoltaic inverter, the reference value of the reactive power output of the photovoltaic inverter, the grid-side q-axis current component, the grid-side d-axis current component, and the grid-side q-axis voltage component of the photovoltaic inverter, the DC-side constant reactive power control technology of the photovoltaic inverter is used to determine the q-axis modulation voltage of the photovoltaic inverter on the grid side.

[0054] This invention provides a photovoltaic inverter operation control system that participates in grid frequency regulation, the improvement of which is that the system includes:

[0055] The first determining module is used to determine the slope change in the power-voltage characteristic curve of the photovoltaic generator set based on the load shedding rate of the photovoltaic generator set.

[0056] The second determination module is used to determine the DC-side voltage reference value of the photovoltaic inverter based on the slope change in the power-voltage characteristic curve of the photovoltaic generator set using an improved MPPT algorithm.

[0057] The control module is used to control the on / off state of the IGBTs in the photovoltaic inverter based on the DC-side voltage reference value of the photovoltaic inverter.

[0058] The improvement of the MPPT algorithm lies in the introduction of a power disturbance term on the DC side of the photovoltaic inverter into the calculation formula for the change in active power on the DC side of the photovoltaic inverter.

[0059] Compared with the closest existing technology, the present invention has the following advantages:

[0060] The technical solution provided by this invention determines the slope change in the power-voltage characteristic curve of a photovoltaic (PV) generator based on its load shedding rate; based on this slope change, an improved MPPT algorithm is used to determine the DC-side voltage reference value of the PV inverter; and the switching on and off of the IGBTs in the PV inverter is controlled based on this DC-side voltage reference value. This solution considers the impact of the PV generator's load shedding rate on the PV inverter control, thus improving the accuracy of PV inverter control. Attached Figure Description

[0061] Figure 1 This is a structural diagram of a centralized photovoltaic inverter grid-connected system;

[0062] Figure 2 This is a flowchart of a photovoltaic inverter operation control method that participates in grid frequency regulation;

[0063] Figure 3 This is a control block diagram of the constant DC voltage control and constant reactive power control on the DC side of the photovoltaic inverter in this embodiment of the invention;

[0064] Figure 4 This is a structural diagram of a photovoltaic inverter operation and control system that participates in grid frequency regulation. Detailed Implementation

[0065] The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.

[0066] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0067] Example 1:

[0068] This invention provides a photovoltaic inverter operation control method for participating in grid frequency regulation, such as... Figure 2 As shown, the method includes:

[0069] Step 101: Determine the slope change in the power-voltage characteristic curve of the photovoltaic generator set based on the load shedding rate of the photovoltaic generator set;

[0070] Step 102: Based on the slope change in the power-voltage characteristic curve of the photovoltaic generator set, the reference value of the DC side voltage of the photovoltaic inverter is determined using the improved MPPT algorithm.

[0071] Step 103: Control the switching on and off of the IGBTs in the photovoltaic inverter based on the DC-side voltage reference value of the photovoltaic inverter;

[0072] The improvement of the MPPT algorithm lies in the introduction of a power disturbance term on the DC side of the photovoltaic inverter into the calculation formula for the change in active power on the DC side of the photovoltaic inverter.

[0073] In the preferred embodiment of the present invention, since the photovoltaic generator set has no rotating equipment, it simulates the inertial response of a conventional generator set by changing the DC-side voltage, thus enabling the photovoltaic generator set to have frequency regulation performance similar to that of a synchronous generator. The photovoltaic inverter is a device directly connected to the photovoltaic generator set; precise control of the photovoltaic inverter can achieve a balance between supply and demand, maintaining the stability of the grid frequency.

[0074] The DC-side voltage reference value of the photovoltaic inverter is determined by the DC-side reference voltage of the photovoltaic inverter during the load shedding control of the photovoltaic generator set. When controlling the droop of a photovoltaic generator, the DC-side reference voltage ΔU of the photovoltaic inverter f Adding them together, we get:

[0075] By fitting the curves of load shedding rate versus temperature and irradiance, the slope change in the power-voltage characteristic curve of the photovoltaic generator set is obtained. Based on this slope change and the improved MPPT algorithm, the DC-side reference voltage of the photovoltaic inverter under load shedding control of the photovoltaic generator set under time-varying irradiance and temperature conditions is obtained. Then, the DC-side reference voltage ΔU of the photovoltaic inverter under droop control of the photovoltaic generator set is obtained. f To match the regulation capability of droop control under different light and temperature conditions, the droop coefficient is proportional to the actual power of the photovoltaic system. The combined regulation of load shedding control and droop control enables the photovoltaic system to actively participate in grid frequency regulation, improving grid stability.

[0076] Specifically, step 101 includes:

[0077] The change in slope of the power-voltage characteristic curve of a photovoltaic generator at the current time t is determined by the following formula.

[0078]

[0079] In the formula, a0(t) is the value of the first fitting coefficient at the current time t, a1(t) is the value of the second fitting coefficient at the current time t, and σ%(t) is the load reduction rate of the photovoltaic generator at the current time t.

[0080] Furthermore, a0(t) is determined by the following formula:

[0081] a0(t)=[0.2795T(t)-62.27]×[-0.054S(t)-0.4705]

[0082] The a1(t) is determined by the following formula:

[0083] a1(t)=[0.04873T(t)-13.02]×[-3.078e-8×S 3 (t)+9.517e-5×S(t) 2 -0.07112S(t)-5.272]

[0084] In the above formula, T(t) is the temperature of the photovoltaic panel of the photovoltaic generator set at the current time t, and S(t) is the light intensity received by the photovoltaic panel of the photovoltaic generator set at the current time t.

[0085] Specifically, step 102 includes:

[0086] Step 102-1: Based on the slope change in the power-voltage characteristic curve of the photovoltaic generator set, the improved MPPT algorithm is used to determine the DC side reference voltage of the photovoltaic inverter during the load shedding control of the photovoltaic generator set.

[0087] Step 102-2: The sum of the DC-side reference voltage of the photovoltaic inverter during the photovoltaic generator load reduction control and the DC-side reference voltage of the photovoltaic inverter during the photovoltaic generator droop control is used as the DC-side voltage reference value of the photovoltaic inverter.

[0088] Furthermore, step 102-1 includes:

[0089] Step 102-1-1: Based on the slope change in the power-voltage characteristic curve of the photovoltaic generator set at the current time t, the change in active power on the DC side of the photovoltaic inverter, ΔP(t), which introduces the power disturbance term on the DC side of the photovoltaic inverter at the current time t, is obtained by the following formula.

[0090] Step 102-1-2, if ΔP(t) is not equal to 0 and ΔU(t) is not greater than 0, then

[0091] If ΔP(t) is not equal to 0 and ΔU(t) is greater than 0, then

[0092] otherwise, Among them, ΔU(t)=u(t)-u(t-1), P(t)=I(t)·u(t), P(t-1)=I(t-1)·u(t-1), Let ΔU(t) be the DC-side power disturbance term of the photovoltaic inverter at the current time t, and let ΔU(t) be the change in DC-side voltage of the photovoltaic inverter at the current time t. Let u(t) be the DC-side reference voltage of the photovoltaic inverter when the photovoltaic generator set is under load shedding control at the current time t, u(t) be the measured value of the DC-side voltage of the photovoltaic inverter at the current time t, Δd be the disturbance step size, P(t) be the active power of the photovoltaic inverter on the DC side at the current time t, I(t) be the measured value of the DC-side current of the photovoltaic inverter at the current time t, P(t-1) be the active power of the photovoltaic inverter on the DC side at time t-1, I(t-1) be the measured value of the DC-side current of the photovoltaic inverter at time t-1, and u(t-1) be the measured value of the DC-side voltage of the photovoltaic inverter at time t-1.

[0093] Wherein, ΔU(t) is the difference between the measured value of the DC side voltage of the photovoltaic inverter at time t-1 and the measured value of the DC side voltage of the photovoltaic inverter at the current time t;

[0094] Furthermore, the process of obtaining the DC-side reference voltage of the photovoltaic inverter during the droop control of the photovoltaic generator set includes:

[0095] The primary frequency regulation active power deviation of the photovoltaic generator set is calculated based on the grid frequency deviation and the droop coefficient of the photovoltaic generator set.

[0096] Substituting the primary frequency regulation active power deviation of the photovoltaic generator set into the first PI controller, the DC side reference voltage of the photovoltaic inverter corresponding to the droop control is obtained.

[0097] Among them, the power grid frequency deviation is the difference between the measured value of the power grid frequency and the reference value of the power grid frequency.

[0098] Furthermore, the calculation of the primary frequency regulation active power deviation of the photovoltaic generator set based on the grid frequency deviation and the droop coefficient of the photovoltaic generator set includes:

[0099] The primary frequency regulation active power deviation ΔP of the photovoltaic generator at the current time t is determined by the following formula. x (t):

[0100] ΔP x (t)=k d (t)·Δf(t)

[0101] In the formula, k d (t) represents the value of the droop coefficient at the current time t, Δf(t) represents the power grid frequency deviation at the current time t, and Δf(t) represents the difference between the measured power grid frequency and the reference power grid frequency at the current time t.

[0102] Wherein, k is determined by the following formula. d (t):

[0103]

[0104] In the formula, P c (t) represents the actual output power of the photovoltaic generator at the current time t, σ% represents the load shedding rate of the photovoltaic generator, and P n k is the rated output power of the photovoltaic generator set. dmax k represents the maximum value of the droop coefficient. dmin This is the minimum value of the droop coefficient.

[0105] Specifically, step 103 includes:

[0106] Step 103-1: Determine the d-axis modulation voltage of the photovoltaic inverter on the grid side based on the DC side voltage reference value of the photovoltaic inverter;

[0107] Step 103-2: Determine the q-axis modulation voltage on the grid side of the photovoltaic inverter based on the reactive power reference value of the photovoltaic inverter;

[0108] Step 103-3: PWM modulation is performed on the d-axis modulation voltage and the q-axis modulation voltage of the photovoltaic inverter grid side to obtain the switching control pulse of the IGBT in the photovoltaic inverter.

[0109] Step 103-4: Use the switching control pulse of the IGBT in the photovoltaic inverter to control the on / off state of the IGBT in the photovoltaic inverter.

[0110] The reactive power reference value of the photovoltaic inverter is preset.

[0111] Furthermore, step 103-1 is used for:

[0112] Based on the measured DC-side voltage of the photovoltaic inverter, the reference DC-side voltage of the photovoltaic inverter, the grid-side d-axis current component, the grid-side q-axis current component, and the grid-side d-axis voltage component of the photovoltaic inverter, the d-axis modulation voltage of the photovoltaic inverter on the grid side is determined using the constant DC voltage control technology of the photovoltaic inverter DC side.

[0113] Furthermore, step 103-2 is used for:

[0114] Based on the measured reactive power of the photovoltaic inverter, the reference value of the reactive power output of the photovoltaic inverter, the grid-side q-axis current component, the grid-side d-axis current component, and the grid-side q-axis voltage component of the photovoltaic inverter, the DC-side constant reactive power control technology of the photovoltaic inverter is used to determine the q-axis modulation voltage of the photovoltaic inverter on the grid side.

[0115] The features of this invention are: load shedding control based on time-varying irradiance and temperature, and active power-frequency droop control with variable droop coefficient. The photovoltaic inverter control employs constant DC-side voltage and constant reactive power control; the load shedding control involves introducing an intermediate variable, fitting the curves of irradiance S and temperature T with the load shedding rate, and then obtaining the DC-side voltage through an improved MPPT algorithm; the droop control includes a proportional controller and a PI controller, which calculate the change in active power when the grid frequency changes.

[0116] Example 2:

[0117] This invention provides a photovoltaic inverter operation control system that participates in grid frequency regulation, such as... Figure 4 As shown, the system includes:

[0118] The first determining module is used to determine the slope change in the power-voltage characteristic curve of the photovoltaic generator set based on the load shedding rate of the photovoltaic generator set.

[0119] The second determination module is used to determine the DC-side voltage reference value of the photovoltaic inverter based on the slope change in the power-voltage characteristic curve of the photovoltaic generator set using an improved MPPT algorithm.

[0120] The control module is used to control the on / off state of the IGBTs in the photovoltaic inverter based on the DC-side voltage reference value of the photovoltaic inverter.

[0121] The improvement of the MPPT algorithm lies in the introduction of a power disturbance term on the DC side of the photovoltaic inverter into the calculation formula for the change in active power on the DC side of the photovoltaic inverter.

[0122] Specifically, the first determining module is used for:

[0123] The change in slope of the power-voltage characteristic curve of a photovoltaic generator at the current time t is determined by the following formula.

[0124]

[0125] In the formula, a0(t) is the value of the first fitting coefficient at the current time t, a1(t) is the value of the second fitting coefficient at the current time t, and σ%(t) is the load reduction rate of the photovoltaic generator at the current time t.

[0126] Furthermore, a0(t) is determined by the following formula:

[0127] a0(t)=]0.2795T(t)-62.27]×[-0.054S(t)-0.4705]

[0128] The a1(t) is determined by the following formula:

[0129] a1(t)=[0.04873T(t)-13.02]×[-3.078e-8×S 3 (t)+9.517e-5×S(t) 2 -0.07112S(t)-5.272]

[0130] In the above formula, T(t) is the temperature of the photovoltaic panel of the photovoltaic generator set at the current time t, and S(t) is the light intensity received by the photovoltaic panel of the photovoltaic generator set at the current time t.

[0131] Specifically, the second determining module includes:

[0132] The first determining unit is used to determine the DC side reference voltage of the photovoltaic inverter during the load shedding control of the photovoltaic generator set based on the slope change in the power-voltage characteristic curve of the photovoltaic generator set using an improved MPPT algorithm.

[0133] The setting unit is used to use the sum of the DC-side reference voltage of the photovoltaic inverter during the photovoltaic generator load reduction control and the DC-side reference voltage of the photovoltaic inverter during the photovoltaic generator droop control as the DC-side voltage reference value of the photovoltaic inverter.

[0134] Furthermore, the first determining unit includes:

[0135] The first calculation subunit is used to obtain the change in active power on the DC side of the photovoltaic inverter, ΔP(t), which is introduced into the DC side power disturbance term of the photovoltaic inverter at the current time t, based on the change in the slope of the power-voltage characteristic curve of the photovoltaic generator set at the current time t, using the following formula.

[0136] The conditional sub-unit is used if ΔP(t) is not equal to 0 and ΔU(t) is not greater than 0.

[0137] If ΔP(t) is not equal to 0 and ΔU(t) is greater than 0, then

[0138] otherwise,

[0139] Among them, ΔU(t)=u(t)-u(t-1), P(t)=I(t)·u(t), P(t-1)=I(t-1)·u(t-1), Let ΔU(t) be the DC-side power disturbance term of the photovoltaic inverter at the current time t, and let ΔU(t) be the change in DC-side voltage of the photovoltaic inverter at the current time t. Let u(t) be the DC-side reference voltage of the photovoltaic inverter when the photovoltaic generator set is under load shedding control at the current time t, u(t) be the measured value of the DC-side voltage of the photovoltaic inverter at the current time t, Δd be the disturbance step size, P(t) be the active power of the photovoltaic inverter on the DC side at the current time t, I(t) be the measured value of the DC-side current of the photovoltaic inverter at the current time t, P(t-1) be the active power of the photovoltaic inverter on the DC side at time t-1, I(t-1) be the measured value of the DC-side current of the photovoltaic inverter at time t-1, and u(t-1) be the measured value of the DC-side voltage of the photovoltaic inverter at time t-1.

[0140] Specifically, the second determining module includes an acquisition unit for acquiring the DC-side reference voltage of the photovoltaic inverter during droop control of the photovoltaic generator set. The acquisition unit includes:

[0141] The second calculation subunit is used to calculate the primary frequency regulation active power deviation of the photovoltaic generator set based on the grid frequency deviation and the droop coefficient of the photovoltaic generator set.

[0142] Substitute the value into the sub-unit to input the primary frequency regulation active power deviation of the photovoltaic generator into the first PI controller to obtain the DC side reference voltage of the photovoltaic inverter corresponding to the droop control.

[0143] Among them, the power grid frequency deviation is the difference between the measured value of the power grid frequency and the reference value of the power grid frequency.

[0144] Specifically, the second calculation subunit is used for:

[0145] The primary frequency regulation active power deviation ΔP of the photovoltaic generator at the current time t is determined by the following formula. x (t):

[0146] ΔP x (t)=k d (t)·Δf(t)

[0147] In the formula, k d (t) represents the value of the droop coefficient at the current time t, and Δf(t) represents the power grid frequency deviation at the current time t.

[0148] Wherein, k is determined by the following formula. d (t):

[0149]

[0150] In the formula, P c (t) represents the actual output power of the photovoltaic generator at the current time t, σ% represents the load shedding rate of the photovoltaic generator, and P n k is the rated output power of the photovoltaic generator set. dmax k represents the maximum value of the droop coefficient. dmin This is the minimum value of the droop coefficient.

[0151] Specifically, the control module includes:

[0152] The second determining unit is used to determine the d-axis modulation voltage of the photovoltaic inverter on the grid side based on the DC side voltage reference value of the photovoltaic inverter;

[0153] The third determining unit is used to determine the q-axis modulation voltage on the grid side of the photovoltaic inverter based on the reactive power reference value of the photovoltaic inverter;

[0154] The modulation unit is used to perform PWM modulation on the d-axis modulation voltage and the q-axis modulation voltage of the photovoltaic inverter grid side to obtain the switching control pulse of the IGBT in the photovoltaic inverter.

[0155] The control unit is used to control the on / off state of the IGBTs in the photovoltaic inverter using the switching control pulses of the IGBTs in the photovoltaic inverter.

[0156] Furthermore, the second determining unit is used for:

[0157] Based on the measured DC-side voltage of the photovoltaic inverter, the reference DC-side voltage of the photovoltaic inverter, the d-axis current component of the grid side of the photovoltaic inverter, the q-axis current component of the grid side of the photovoltaic inverter, and the d-axis voltage component of the grid side of the photovoltaic inverter, the constant DC voltage control technology of the DC side of the photovoltaic inverter is adopted to determine the d-axis modulation voltage of the grid side of the photovoltaic inverter.

[0158] Furthermore, the third determining unit is used for:

[0159] Based on the measured reactive power of the photovoltaic inverter, the reference value of the reactive power output of the photovoltaic inverter, the grid-side q-axis current component, the grid-side d-axis current component, and the grid-side q-axis voltage component of the photovoltaic inverter, the DC-side constant reactive power control technology of the photovoltaic inverter is used to determine the q-axis modulation voltage of the photovoltaic inverter on the grid side.

[0160] Example 3:

[0161] Step A: Measure the grid-side voltage V a,b,c and grid-side current I a,b,c V a,b,c The grid-side frequency f is obtained by phase-locked loop (PLL) measurement. reqand phase ω t ;

[0162] V a,b,c and I a,b,c The d-axis and q-axis components U of the voltage are obtained after Park transformation. td U tq and the d-axis and q-axis components of the current i d i q ;

[0163] Step B: Based on the PV single-peak characteristic curve of the photovoltaic cell, when At that time, the system operates to the right of the maximum power point. The output power is monotonically related to the power; as the load reduction rate σ% decreases, the DC-side voltage decreases, and the output power should be appropriately increased. That is the point of maximum power, as long as A value no greater than 0 ensures that the curve provides the correct frequency response.

[0164] The standard deviations of the second-order, third-order, and fourth-order fitting functions are 1.138, 0.8614, and 0.5868, respectively. The standard deviation of the fitting function shown in the following formula is smaller, only 0.5012. Therefore, this curve is chosen for fitting, where a0 and a1 are the corresponding fitting coefficients.

[0165]

[0166] Through experiments, Substituting the coefficients a0 and a1 into the above fitting function yields the result. The expression with σ%.

[0167] Step C: To convert the load shedding rate σ% into the DC-side reference voltage of the photovoltaic inverter during photovoltaic generator load shedding control. Improvements are needed on the existing MPPT algorithm.

[0168] First, the voltage and current U of the photovoltaic cell were measured. k U k-1 I k I k-1 Calculate P k and P k-1 P k =U k ×I k P k-1 =U k-1 ×I k-1 k is the current sampling time, and k-1 is the previous sampling time;

[0169] Based on the original criterion ΔP=P k -P k-1Subtract a new perturbation term from the base Obtain the judgment Where ΔU=U k -U k-1 By improving the MPPT algorithm, the DC-side reference voltage of the photovoltaic inverter during the load shedding control of the photovoltaic generator can be obtained.

[0170] Among them, the DC-side reference voltage of the photovoltaic inverter during the load shedding control of the photovoltaic generator can be obtained by improving the MPPT algorithm. The specific process is as follows:

[0171] If ΔP(t) is not equal to 0 and ΔU(t) is not greater than 0, then

[0172] If ΔP(t) is not equal to 0 and ΔU(t) is greater than 0, then

[0173] otherwise,

[0174] Step D: Introduce droop control ΔP = k on the DC side d Δf, k d The droop factor is an important indicator for evaluating the frequency regulation capability of a power grid. To match the regulation capability of droop control under different illumination and temperature conditions, the value of the droop factor is proportional to the actual power of the photovoltaic system. The measured grid frequency deviation Δf is used to calculate the frequency deviation ΔP through droop control, and the droop factor is set to [value missing]. Where P k P represents the actual output power of the photovoltaic array. n k is the rated power of the photovoltaic array. dmax and k dmin These represent the maximum and minimum values ​​of the droop coefficient, respectively. Analogous to conventional units, the reciprocal of the droop coefficient is the descent coefficient, which is typically taken as 2% to 5%. Therefore, in this invention, the maximum and minimum values ​​of the droop coefficient are respectively taken as k. dmax =50,k dmin =20.

[0175] Step E: Adjust the DC-side reference voltage of the photovoltaic inverter during photovoltaic generator load shedding control. When controlling the droop of a photovoltaic generator, the DC-side reference voltage ΔU of the photovoltaic inverter f The DC-side voltage reference value U of the photovoltaic inverter is obtained by adding them together. dcref :

[0176]

[0177] Step F: Referring to the control block diagram using constant DC side voltage and constant reactive power, the obtained Ud U q ;

[0178] The DC-side voltage control specifically involves: setting the measured DC-side voltage U of the photovoltaic inverter as the DC-side voltage value. dc DC side voltage reference value U of photovoltaic inverter dcref Substituting the values ​​into the PI controller, we obtain the d-axis current reference value i of the photovoltaic inverter. dref The grid-side d-axis current reference value i of the photovoltaic inverter dref and the grid-side d-axis current component i of the photovoltaic inverter d Substituting the values ​​into the PI controller, we obtain the grid-side d-axis voltage reference value U of the photovoltaic inverter. dref Based on U dref The grid-side q-axis current component i of the photovoltaic inverter q d-axis voltage component U on the grid side of the photovoltaic inverter td The inductance value and frequency of the photovoltaic inverter determine the d-axis modulation voltage U on the grid side of the photovoltaic inverter. d ;

[0179] The specific reactive power control involves: using the measured reactive power value Q of the photovoltaic inverter and the reference reactive power value Q of the photovoltaic inverter output. ref Substituting into the PI controller, we obtain the q-axis current reference value i of the photovoltaic inverter. qref The q-axis current reference value i of the photovoltaic inverter qref and the grid-side q-axis current component i of the photovoltaic inverter q Substituting the values ​​into the PI controller, we obtain the grid-side q-axis voltage reference value U of the photovoltaic inverter. qref Based on U qref The grid-side d-axis current component i of the photovoltaic inverter d The grid-side q-axis voltage component U of the photovoltaic inverter tq The inductance value and frequency of the photovoltaic inverter determine the q-axis modulation voltage U on the grid side of the photovoltaic inverter. q ;

[0180] U obtained under this control d U q The pulses are input to the PWM controller to control the operation of the inverter IGBT.

[0181] This invention considers the impact of load shedding control and droop control of photovoltaic generator sets on the reference value of DC-side voltage of photovoltaic inverters. By controlling the DC-side voltage, it adapts to the inertial response working state of photovoltaic generator sets simulating conventional units, so that the photovoltaic grid-connected structure has frequency regulation capability similar to that of synchronous generators and can actively participate in grid frequency regulation.

[0182] This invention fits a function of light intensity and temperature with intermediate quantities. The function enables load shedding control to be implemented under time-varying temperature and light intensity. Then, by improving the MPPT algorithm, the load shedding rate is converted into a DC-side voltage output reference value of the photovoltaic inverter. This DC-side voltage is added to the DC-side voltage reference value obtained by droop control to obtain a new DC-side voltage reference value. The inverter operation is controlled by the inverter's dual-loop voltage control.

[0183] The control strategy of this invention can maintain the stability of the system frequency when the grid load changes. It has the advantages of being reasonable and scientific, highly practical, and effective.

[0184] Those skilled in the art will understand that embodiments of this application can be provided as methods, systems, or computer program products. Therefore, this application can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, this application can take the form of a computer program product embodied on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0185] This application is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of this application. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart... Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0186] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0187] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0188] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A photovoltaic inverter operation control method participating in grid frequency regulation, characterized in that, The method includes: The slope change in the power-voltage characteristic curve of the photovoltaic generator set is determined based on the load reduction rate of the photovoltaic generator set. Based on the slope change in the power-voltage characteristic curve of photovoltaic generator sets, the reference value of DC side voltage of photovoltaic inverter is determined using an improved MPPT algorithm. The switching on and off of IGBTs in a photovoltaic inverter is controlled based on the DC-side voltage reference value of the photovoltaic inverter. The improvement of the MPPT algorithm lies in the introduction of a power disturbance term on the DC side of the photovoltaic inverter into the calculation formula for the change in active power on the DC side of the photovoltaic inverter in the MPPT algorithm. The determination of the slope change in the power-voltage characteristic curve of the photovoltaic generator set based on the load shedding rate includes: The power-voltage characteristic curve of the photovoltaic generator set at the current moment is determined by the following formula. slope change : In the formula, The first fitting coefficient at the current time The value of , The second fitting coefficient at the current time The value of , For the photovoltaic power generation unit at the current moment The load reduction rate; The method for determining the DC-side voltage reference value of the photovoltaic inverter using the improved MPPT algorithm, based on the slope change in the power-voltage characteristic curve of the photovoltaic generator set, includes: Based on the slope change in the power-voltage characteristic curve of the photovoltaic generator set, the improved MPPT algorithm is used to determine the DC side reference voltage of the photovoltaic inverter during the load shedding control of the photovoltaic generator set. The sum of the DC-side reference voltage of the photovoltaic inverter during the load shedding control of the photovoltaic generator set and the DC-side reference voltage of the photovoltaic inverter during the droop control of the photovoltaic generator set is used as the DC-side voltage reference value of the photovoltaic inverter. The method for determining the DC-side reference voltage of the photovoltaic inverter during load shedding control, based on the slope change in the power-voltage characteristic curve of the photovoltaic generator set, using an improved MPPT algorithm, includes: Based on the change in slope of the power-voltage characteristic curve of the photovoltaic generator set at current time t, the change in active power on the DC side of the photovoltaic inverter introduced into the DC side power disturbance term at current time t is obtained by the following formula. , ; like Not equal to 0 and If not greater than 0, then ; like Not equal to 0 and If greater than 0, then ; otherwise, ; in, , , , This is the DC-side power disturbance term of the photovoltaic inverter at the current time t. For the current moment The change in DC-side voltage of the photovoltaic inverter. For the current moment The DC-side reference voltage of the photovoltaic inverter during load shedding control of the photovoltaic generator set. For the current moment The measured value of the DC side voltage of the photovoltaic inverter. For the perturbation step size, For the current moment The active power of the DC side of the photovoltaic inverter For the current moment The measured value of the DC side current of the photovoltaic inverter. for The active power of the DC side of the photovoltaic inverter at any given time. for Measured DC-side current of the photovoltaic inverter at any given time. for Measured DC-side voltage of the photovoltaic inverter at a given time. The time is the current time. The moment before.

2. The method as described in claim 1, characterized in that, Determine the following formula : Determine the following formula : In the above formula, For the photovoltaic panels of the photovoltaic generator set at the current moment temperature, For the photovoltaic panels of the photovoltaic generator set at the current moment The intensity of light received.

3. The method as described in claim 1, characterized in that, The process of obtaining the DC-side reference voltage of the photovoltaic inverter during the droop control of the photovoltaic generator set includes: The primary frequency regulation active power deviation of the photovoltaic generator set is calculated based on the grid frequency deviation and the droop coefficient of the photovoltaic generator set. Substituting the primary frequency regulation active power deviation of the photovoltaic generator set into the first PI controller, the DC side reference voltage of the photovoltaic inverter corresponding to the droop control is obtained. Among them, the power grid frequency deviation is the difference between the measured value of the power grid frequency and the reference value of the power grid frequency.

4. The method as described in claim 3, characterized in that, The calculation of the primary frequency regulation active power deviation of the photovoltaic generator set based on the grid frequency deviation and the droop coefficient of the photovoltaic generator set includes: The photovoltaic generator set at the current moment is determined by the following formula. Primary frequency regulation active power deviation : In the formula, The droop coefficient at the current time The value of , For the current moment The power grid frequency deviation; Wherein, the following formula is used to determine the : In the formula, For the photovoltaic power generation unit at the current moment Actual output power The load reduction rate of the photovoltaic generator set. This refers to the rated output power of the photovoltaic generator set. This represents the maximum value of the droop coefficient. This is the minimum value of the droop coefficient.

5. The method as described in claim 1, characterized in that, The control of the on / off state of the IGBTs in the photovoltaic inverter based on the DC-side voltage reference value of the photovoltaic inverter includes: The d-axis modulation voltage of the photovoltaic inverter on the grid side is determined based on the DC-side voltage reference value of the photovoltaic inverter. The q-axis modulation voltage on the grid side of the photovoltaic inverter is determined based on the reactive power reference value of the photovoltaic inverter. The d-axis modulation voltage and q-axis modulation voltage on the grid side of the photovoltaic inverter are PWM modulated to obtain the switching control pulse of the IGBT in the photovoltaic inverter. The switching control pulses of the IGBTs in the photovoltaic inverter are used to control the on and off states of the IGBTs.

6. The method as described in claim 5, characterized in that, The determination of the d-axis modulation voltage on the grid side of the photovoltaic inverter based on the DC-side voltage reference value of the photovoltaic inverter includes: Based on the measured DC-side voltage of the photovoltaic inverter, the reference DC-side voltage of the photovoltaic inverter, the grid-side d-axis current component, the grid-side q-axis current component, and the grid-side d-axis voltage component of the photovoltaic inverter, the d-axis modulation voltage of the photovoltaic inverter on the grid side is determined using the constant DC voltage control technology of the photovoltaic inverter DC side.

7. The method as described in claim 5, characterized in that, The determination of the q-axis modulation voltage on the grid side of the photovoltaic inverter based on the reactive power reference value output by the photovoltaic inverter includes: Based on the measured reactive power of the photovoltaic inverter, the reference value of the reactive power output of the photovoltaic inverter, the grid-side q-axis current component, the grid-side d-axis current component, and the grid-side q-axis voltage component of the photovoltaic inverter, the DC-side constant reactive power control technology of the photovoltaic inverter is used to determine the q-axis modulation voltage of the photovoltaic inverter on the grid side.

8. A photovoltaic inverter operation control system participating in grid frequency regulation, used to implement the method as described in claim 1, characterized in that, The system includes: The first determining module is used to determine the slope change in the power-voltage characteristic curve of the photovoltaic generator set based on the load shedding rate of the photovoltaic generator set. The second determination module is used to determine the DC-side voltage reference value of the photovoltaic inverter based on the slope change in the power-voltage characteristic curve of the photovoltaic generator set using an improved MPPT algorithm. The control module is used to control the on / off state of the IGBTs in the photovoltaic inverter based on the DC-side voltage reference value of the photovoltaic inverter. The improvement of the MPPT algorithm lies in the introduction of a power disturbance term on the DC side of the photovoltaic inverter into the calculation formula for the change in active power on the DC side of the photovoltaic inverter.

Images