A photovoltaic grid-connected maximum power point tracking system and method

Abstract

The application discloses a photovoltaic grid-connected maximum power point tracking system and method, and relates to the technical field of photovoltaic grid-connected power generation.The system comprises a feeding disturbance circuit, a discharging disturbance circuit and a controller, the feeding disturbance circuit is used for being connected with a photovoltaic module and a direct-current conversion circuit, the discharging disturbance circuit is used for being connected with the direct-current conversion circuit and an inverter circuit, and the controller is configured to acquire an actual output power of the photovoltaic module, judge whether the absolute value of a power change value of the actual output power of the photovoltaic module is greater than a preset first threshold value or whether a working period of the photovoltaic module reaches a preset period, if yes, control the discharging disturbance circuit and the feeding disturbance circuit to respectively perform coarse adjustment and fine adjustment on the power change value, so that the absolute value of the power change value of the actual output power of the photovoltaic module is less than a preset third threshold value.The application can realize fast tracking of the maximum power point, and can reduce photovoltaic module output power loss caused by frequent use of the disturbance circuit.

Description

Technical Field

[0001] This invention relates to the field of photovoltaic grid-connected power generation technology, and in particular to a photovoltaic grid-connected maximum power point tracking system and method. Background Technology

[0002] Driven by industrial policies and technological development, distributed photovoltaic (PV) power has experienced rapid growth in recent years. How to fully utilize rooftop resources and effectively harness solar energy has become a current research focus and hot topic. However, the output characteristics of PV modules exhibit severe nonlinearity due to factors such as light intensity and ambient temperature, resulting in low and unstable output efficiency. Therefore, maximizing the output power of PV modules and improving their energy utilization efficiency has become a key issue in system optimization within the PV power generation field.

[0003] Maximum Power Point Tracking (MPPT) technology is an effective means to improve the output power of photovoltaic (PV) modules. Currently, commonly used tracking methods include CVT, perturbation-observation, and conductivity methods. However, existing tracking methods are constantly in a perturbation state during practical applications. Frequent perturbations cause significant power loss in the PV module output, affecting the energy utilization efficiency of the PV module. Summary of the Invention

[0004] This invention provides a photovoltaic grid-connected maximum power point tracking system and method to solve the technical problem that existing maximum power point tracking systems require frequent disturbances, resulting in significant power loss in photovoltaic modules.

[0005] Firstly, a photovoltaic grid-connected maximum power point tracking system is provided, comprising:

[0006] A power supply disturbance circuit, which is used to connect to photovoltaic modules and DC-DC conversion circuits;

[0007] Discharge disturbance circuit, which is used to connect to DC-DC converter circuits and inverter circuits;

[0008] The controller, which is used to connect to the photovoltaic module, the discharge disturbance circuit, and the feed disturbance circuit, is configured to:

[0009] Obtain the actual output power of the photovoltaic module;

[0010] Determine whether the absolute value of the power change in the actual output power of the photovoltaic module is greater than a preset first threshold or whether the working cycle of the photovoltaic module has reached a preset cycle;

[0011] If so, control the operation of the discharge disturbance circuit and the power supply disturbance circuit to coarsely and finely adjust the power change value of the actual output power of the photovoltaic module, so that the absolute value of the power change value of the actual output power of the photovoltaic module is less than the preset third threshold.

[0012] In some embodiments, the photovoltaic grid-connected maximum power point tracking system further includes:

[0013] An energy recovery circuit is connected to the discharge disturbance circuit and the power supply disturbance circuit. The energy recovery circuit is used to recover the energy discharged by the discharge disturbance circuit and provide it to the power supply disturbance circuit.

[0014] In some embodiments, the power supply disturbance circuit is a DC / DC circuit, the discharge disturbance circuit includes a first resistor and a first MOSFET, and the energy recovery circuit includes a first transformer, a first capacitor, and a first diode;

[0015] The DC / DC circuit is connected to the positive and negative terminals of the photovoltaic module and the controller;

[0016] The first end of the first resistor is connected to the positive terminal of the DC-DC converter circuit, the second end of the first resistor is connected to the first end of the first current transformer, the second end of the first current transformer is connected to the drain of the first MOSFET, the gate of the first MOSFET is connected to the controller, and the source of the first MOSFET is connected to the negative terminal of the DC-DC converter circuit.

[0017] The third terminal of the first current transformer is connected to the anode of the first diode, the cathode of the first diode is connected to the DC / DC circuit, the first terminal of the first capacitor is connected to the cathode of the first diode, and the second terminal of the first capacitor is connected to the negative terminal of the DC-DC converter circuit.

[0018] In some embodiments, the discharge disturbance circuit further includes a second resistor, a second capacitor, and a transient voltage suppression diode;

[0019] The first end of the second resistor is connected to the controller, and the second end of the second resistor is connected to the gate of the first MOS transistor.

[0020] The first terminal of the second capacitor is connected to the gate of the first MOS transistor, and the second terminal of the second capacitor is connected to the negative terminal of the DC-DC converter circuit.

[0021] The cathode of the transient voltage suppressor diode is connected to the first terminal of the second resistor, and the anode of the transient voltage suppressor diode is connected to the negative terminal of the DC-DC converter circuit.

[0022] Secondly, a method for maximum power point tracking (MPPT) of grid-connected photovoltaic systems is provided, including the following steps:

[0023] Obtain the actual output power of the photovoltaic module;

[0024] Determine whether the absolute value of the power change in the actual output power of the photovoltaic module is greater than a preset first threshold or whether the working cycle of the photovoltaic module has reached a preset cycle;

[0025] If so, control the operation of the discharge disturbance circuit and the power supply disturbance circuit to coarsely and finely adjust the power change value of the actual output power of the photovoltaic module, so that the absolute value of the power change value of the actual output power of the photovoltaic module is less than the preset third threshold.

[0026] In some embodiments, if so, controlling the operation of the discharge disturbance circuit and the feed disturbance circuit to coarsely and finely adjust the power change value of the actual output power of the photovoltaic module, so that the absolute value of the power change value of the actual output power of the photovoltaic module is less than a preset third threshold, including:

[0027] Control the operation of the discharge disturbance circuit;

[0028] Determine whether the absolute value of the power change in the actual output power of the photovoltaic module is greater than a preset first threshold:

[0029] If so, the disturbance direction of the discharge disturbance circuit is determined based on the voltage change value and amplitude of the actual output voltage of the photovoltaic module, and the discharge disturbance circuit is coarsely adjusted to the power change value by the determined disturbance direction and the preset first disturbance step size.

[0030] If not, determine whether the absolute value of the power change of the actual output power of the photovoltaic module is greater than the preset second threshold. If yes, determine the disturbance direction of the discharge disturbance circuit based on the power change of the actual output power of the photovoltaic module, and control the discharge disturbance circuit to coarsely adjust the power change value according to the determined disturbance direction and the preset first disturbance step size. If not, control the power supply disturbance circuit to work so that the absolute value of the power change of the actual output power of the photovoltaic module is less than the preset third threshold.

[0031] In some embodiments, if so, the disturbance direction of the discharge disturbance circuit is determined based on the voltage change value and amplitude of the actual output voltage of the photovoltaic module, and the discharge disturbance circuit is controlled to coarsely adjust the power change value according to the determined disturbance direction and the preset first disturbance step size, including:

[0032] Determine if the voltage change of the actual output voltage of the photovoltaic module is less than zero:

[0033] If so, the discharge disturbance circuit is controlled to coarsely adjust the power change value based on the current disturbance direction and the preset first disturbance step size;

[0034] If not, determine whether the amplitude of the actual output voltage of the photovoltaic module is greater than the preset amplitude: if yes, control the discharge disturbance circuit to coarsely adjust the power change value with the current disturbance direction and the preset first disturbance step size; if not, control the discharge disturbance circuit to coarsely adjust the power change value with the opposite direction of the current disturbance direction and the preset first disturbance step size.

[0035] In some embodiments, if so, the disturbance direction of the discharge disturbance circuit is determined based on the power change value of the actual output power of the photovoltaic module, and the determined disturbance direction and a preset first disturbance step size are used to control the discharge disturbance circuit to coarsely adjust the power change value, including:

[0036] If the actual output power of the photovoltaic module changes more than the preset second threshold, the discharge disturbance circuit is controlled to coarsely adjust the power change value with the current disturbance direction and the preset first disturbance step size.

[0037] If the actual output power change of the photovoltaic module is not greater than zero and the absolute value is greater than the preset second threshold, the discharge disturbance circuit is controlled to coarsely adjust the power change value in the opposite direction of the current disturbance direction and the preset first disturbance step size.

[0038] In some embodiments, if not, controlling the power supply disturbance circuit to operate so that the absolute value of the power change in the actual output power of the photovoltaic module is less than a preset third threshold includes:

[0039] Control the operation of the power supply disturbance circuit;

[0040] Determine whether the absolute value of the power change in the actual output power of the photovoltaic module is greater than a preset first threshold:

[0041] If so, the control discharge disturbance circuit will perform a coarse adjustment on the power change value again;

[0042] If not, determine whether the absolute value of the actual output power change of the photovoltaic module is greater than the preset third threshold. If yes, determine the disturbance direction of the feed disturbance circuit based on the actual output power change of the photovoltaic module, and control the feed disturbance circuit to fine-tune the power change value according to the determined disturbance direction and the preset second disturbance step size. If not, control the feed disturbance circuit to stop working.

[0043] In some embodiments, if so, the disturbance direction of the feed disturbance circuit is determined based on the power change value of the actual output power of the photovoltaic module, and the feed disturbance circuit is finely adjusted to finely adjust the power change value based on the determined disturbance direction and a preset second disturbance step size, including:

[0044] If the actual output power of the photovoltaic module changes more than the preset third threshold, the control power supply disturbance circuit finely adjusts the power change value with the current disturbance direction and the preset second disturbance step size.

[0045] If the actual output power change of the photovoltaic module is not greater than zero and the absolute value is greater than the preset third threshold, the control power supply disturbance circuit finely adjusts the power change value in the opposite direction of the current disturbance direction and the preset second disturbance step size.

[0046] The beneficial effects of the technical solution provided by this invention include:

[0047] This invention provides a photovoltaic grid-connected maximum power point tracking (MPPT) system and method. The tracking system includes a feed disturbance circuit, a discharge disturbance circuit, and a controller. When the absolute value of the power change in the actual output power of the photovoltaic module exceeds a preset first threshold at a preset interval, the controller uses the discharge disturbance circuit and the feed disturbance circuit to adjust the power change value. A composite control strategy combining a fixed period and abrupt changes is employed. This ensures rapid tracking of the maximum power point by the photovoltaic module during sudden changes in light intensity or ambient temperature. Furthermore, when the light intensity or ambient temperature is stable, it reduces power loss caused by frequent use of the disturbance circuit, thereby improving the energy efficiency of the photovoltaic module. In addition, this invention employs dual load disturbances (discharge and feed), which not only increases the adjustment range but also improves impedance change resolution to accommodate more types of photovoltaic modules. The combination of coarse and fine adjustments significantly improves the speed and stability of the adjustment. Attached Figure Description

[0048] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0049] Figure 1 A schematic diagram of a photovoltaic grid-connected maximum power point tracking system provided in an embodiment of the present invention;

[0050] Figure 2 A circuit diagram of a photovoltaic grid-connected maximum power point tracking system provided in an embodiment of the present invention;

[0051] Figure 3 A flowchart of a photovoltaic grid-connected maximum power point tracking method provided in an embodiment of the present invention;

[0052] Figure 4A schematic diagram of a photovoltaic grid-connected maximum power point tracking process provided in an embodiment of the present invention;

[0053] Figure 5 The simulation waveform diagram of maximum power point tracking for photovoltaic grid connection is provided for an embodiment of the present invention. Detailed Implementation

[0054] 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.

[0055] This invention provides a photovoltaic grid-connected maximum power point tracking system, which can solve the technical problem that existing maximum power point tracking systems require frequent disturbances, resulting in significant power loss in photovoltaic module output.

[0056] See Figure 1 As shown, this embodiment of the invention provides a photovoltaic grid-connected maximum power point tracking system, including: a power supply disturbance circuit, a discharge disturbance circuit, and a controller.

[0057] The power supply disturbance circuit is used to connect to the photovoltaic module and the DC-DC converter circuit, and the discharge disturbance circuit is used to connect to the DC-DC converter circuit and the inverter circuit. The controller is used to connect to the photovoltaic module, the discharge disturbance circuit, and the power supply disturbance circuit, and is configured to:

[0058] The actual output power of the photovoltaic module is obtained. Specifically, the controller can collect the actual output voltage and actual output current of the photovoltaic module, and calculate the actual output power of the photovoltaic module based on the actual output voltage and actual output current.

[0059] Determine whether the absolute value of the power change in the actual output power of the photovoltaic module is greater than a preset first threshold or whether the working cycle of the photovoltaic module has reached a preset cycle.

[0060] If so, the control discharge disturbance circuit and the power supply disturbance circuit will perform coarse and fine adjustments to the power change value respectively, so that the absolute value of the power change value of the actual output power of the photovoltaic module is less than the preset third threshold.

[0061] Specifically, see Figure 3As shown, the preset first threshold can be set to 2Γ. If the absolute value of the power change value of the actual output power of the photovoltaic module is |ΔP|>2Γ, then the discharge disturbance circuit and the feed disturbance circuit are controlled to perform coarse and fine adjustments on the power change value respectively, so that the absolute value of the power change value of the actual output power of the photovoltaic module is less than the preset third threshold.

[0062] Alternatively, the preset period can be set to T. If the working cycle of the photovoltaic module reaches the preset period T, the discharge disturbance circuit and the feed disturbance circuit will be controlled to perform coarse and fine adjustments on the power change value, respectively, so that the absolute value of the power change value of the actual output power of the photovoltaic module is less than the preset third threshold. The preset third threshold can be ξ, which is a very small value.

[0063] The photovoltaic grid-connected maximum power point tracking system in this embodiment of the invention includes a feed disturbance circuit, a discharge disturbance circuit, and a controller. When the absolute value of the power change in the actual output power of the photovoltaic module exceeds a preset first threshold at a preset interval, the controller uses the discharge disturbance circuit and the feed disturbance circuit to adjust the power change value. This employs a composite control strategy combining a fixed period and sudden changes in load. On the one hand, it ensures rapid tracking of the maximum power point by the photovoltaic module when there are sudden changes in light intensity or ambient temperature. On the other hand, when the light intensity or ambient temperature is stable, it reduces the output power loss of the photovoltaic module caused by frequent use of the disturbance circuit, thereby improving the energy utilization efficiency of the photovoltaic module. Furthermore, this embodiment of the invention uses dual load disturbances—discharge and feed—which not only increases the adjustment range but also improves the impedance change resolution to adapt to more types of photovoltaic modules. By combining coarse and fine adjustments, it greatly improves the speed and stability of the adjustment.

[0064] As an optional implementation, in one embodiment of the invention, see [link to relevant documentation]. Figure 1 As shown, the photovoltaic grid-connected maximum power point tracking system further includes an energy recovery circuit, which is connected to the discharge disturbance circuit and the feed disturbance circuit. The energy recovery circuit recovers the energy discharged by the discharge disturbance circuit and supplies it to the feed disturbance circuit. When the feed disturbance circuit is finely adjusted, the disturbance energy of the feed disturbance circuit comes from the recovered energy discharged by the discharge disturbance circuit, thus eliminating the need for additional energy consumption. This significantly reduces the impact of load discharge on energy utilization, reduces power loss at the photovoltaic array output, and further improves the energy utilization efficiency of the photovoltaic modules.

[0065] Further, see Figure 2As shown, the power supply disturbance circuit is a DC / DC circuit, the discharge disturbance circuit includes a first resistor R1 and a first MOSFET Q1, and the energy recovery circuit includes a first transformer T1, a first capacitor C1, and a first diode D1. The DC / DC circuit is connected to the positive and negative terminals of the photovoltaic module and the controller. The first terminal of the first resistor R1 is connected to the positive terminal of the DC-DC converter circuit, the second terminal of the first resistor R1 is connected to the first terminal of the first transformer T1, the second terminal of the first transformer T1 is connected to the drain of the first MOSFET Q1, the gate of the first MOSFET Q2 is connected to the controller, and the source of the first MOSFET Q2 is connected to the negative terminal of the DC-DC converter circuit.

[0066] The third terminal of the first current transformer T1 is connected to the anode of the first diode D1, the cathode of the first diode D1 is connected to the DC / DC circuit, the first terminal of the first capacitor C1 is connected to the cathode of the first diode D1, and the second terminal of the first capacitor C1 is connected to the negative terminal of the DC-DC converter circuit.

[0067] Specifically, when the discharge disturbance circuit is working, it generates a discharge pulse current. When the pulse current flows through the first transformer T1, it causes a change in the magnetic field. The first transformer T1 uses the change in the magnetic field generated by the pulse current to induce a pulse current in the secondary coil. The generated pulse current charges the first capacitor C1 and stores it. The reverse leakage current of the first diode D1 is extremely small, which can prevent the loss of the charging energy stored in the first capacitor C1. The stored energy is used as the disturbance energy source of the power supply disturbance circuit.

[0068] Furthermore, see Figure 2 As shown, the discharge disturbance circuit further includes a second resistor, a second capacitor, and a transient voltage suppressor diode. The first terminal of the second resistor is connected to the controller, and the second terminal of the second resistor is connected to the gate of the first MOSFET. The first terminal of the second capacitor is connected to the gate of the first MOSFET, and the second terminal of the second capacitor is connected to the negative terminal of the DC-DC converter circuit. The cathode of the transient voltage suppressor diode is connected to the first terminal of the second resistor, and the anode of the transient voltage suppressor diode is connected to the negative terminal of the DC-DC converter circuit. The second resistor, the second capacitor, and the transient voltage suppressor diode ensure the normal operation of the first MOSFET Q1.

[0069] See Figure 3 As shown, this embodiment of the invention provides a photovoltaic grid-connected maximum power point tracking method, including the following steps:

[0070] Obtain the actual output power of the photovoltaic module;

[0071] Determine whether the absolute value of the actual output power change of the photovoltaic module is greater than a preset first threshold or whether the photovoltaic module's operating cycle has reached a preset cycle:

[0072] If so, the discharge disturbance circuit and the power supply disturbance circuit are controlled to perform coarse and fine adjustments on the actual output power change of the photovoltaic module, respectively, so that the absolute value of the actual output power change of the photovoltaic module is less than a preset third threshold. The preset third threshold can be ξ, which is a very small value.

[0073] Specifically, in combination Figure 3 The flowchart shown below illustrates the maximum power point tracking method for grid-connected photovoltaic systems:

[0074] In step S100, the processing flow is started.

[0075] In step S101, the actual output power of the photovoltaic module is obtained.

[0076] In step S102, it is determined whether the absolute value of the power change in the actual output power of the photovoltaic module is greater than a preset first threshold. If the determination result is "yes", then step S104 is executed, controlling the discharge disturbance circuit to operate, coarsely adjusting the power change in the actual output power of the photovoltaic module, and executing subsequent steps to make the absolute value of the power change in the actual output power of the photovoltaic module less than a preset third threshold; if the determination result is "no", then step S103 is executed. For example, the preset first threshold can be set to 2Γ. If the absolute value of the power change in the actual output power of the photovoltaic module |ΔP|>2Γ, then step S104 is executed; if the absolute value of the power change in the actual output power of the photovoltaic module |ΔP|≤2Γ, then step S103 is executed.

[0077] In step S103, it is determined whether the working cycle of the photovoltaic module has reached a preset cycle. If the determination result is "yes", then step S104 is executed; if the determination result is "no", then return to step S101 and continue to execute subsequent steps. For example, the preset cycle can be set to T. If the working cycle of the photovoltaic module reaches the preset cycle T, then step S104 is executed; if the working cycle of the photovoltaic module has not reached the preset cycle T, then step S101 is executed.

[0078] The photovoltaic grid-connected maximum power point tracking method in this embodiment of the invention adjusts the power change value using a discharge perturbation circuit and a feed perturbation circuit when the absolute value of the power change value of the actual output power of the photovoltaic module exceeds a preset first threshold at a preset interval or period. It employs a composite control strategy combining a fixed period and a sudden change in power, ensuring rapid tracking of the maximum power point by the photovoltaic module when there are sudden changes in light intensity or ambient temperature. Furthermore, when the light intensity or ambient temperature is stable, it reduces the output power loss of the photovoltaic module caused by frequent use of the perturbation circuit, thereby improving the energy utilization efficiency of the photovoltaic module. In addition, this embodiment of the invention uses dual load perturbation of discharge and feed, which not only increases the adjustment range but also improves the impedance change resolution to adapt to more types of photovoltaic modules. By combining coarse and fine adjustments, it greatly improves the speed and stability of the adjustment.

[0079] As an optional implementation, in one embodiment of the invention, see [link to relevant documentation]. Figure 3 As shown, if so, the operation of the control discharge disturbance circuit and the feed disturbance circuit is performed to coarsely and finely adjust the power change value of the actual output power of the photovoltaic module, so that the absolute value of the power change value of the actual output power of the photovoltaic module is less than a preset third threshold, including:

[0080] Control the operation of the discharge disturbance circuit;

[0081] Determine whether the absolute value of the power change in the actual output power of the photovoltaic module is greater than a preset first threshold:

[0082] If so, the disturbance direction of the discharge disturbance circuit is determined based on the voltage change value and amplitude of the actual output voltage of the photovoltaic module, and the discharge disturbance circuit is coarsely adjusted to the power change value by the determined disturbance direction and the preset first disturbance step size.

[0083] If not, determine whether the absolute value of the power change of the actual output power of the photovoltaic module is greater than the preset second threshold. If yes, determine the disturbance direction of the discharge disturbance circuit based on the power change of the actual output power of the photovoltaic module, and control the discharge disturbance circuit to coarsely adjust the power change value according to the determined disturbance direction and the preset first disturbance step size. If not, control the power supply disturbance circuit to work so that the absolute value of the power change of the actual output power of the photovoltaic module is less than the preset third threshold.

[0084] If so, the disturbance direction of the discharge disturbance circuit is determined based on the voltage change value and amplitude of the actual output voltage of the photovoltaic module. The determined disturbance direction and a preset first disturbance step size are used to control the discharge disturbance circuit to coarsely adjust the power change value, including:

[0085] Determine if the voltage change of the actual output voltage of the photovoltaic module is less than zero:

[0086] If so, the discharge disturbance circuit is controlled to coarsely adjust the power change value based on the current disturbance direction and the preset first disturbance step size;

[0087] If not, determine whether the amplitude of the actual output voltage of the photovoltaic module is greater than the preset amplitude: if yes, control the discharge disturbance circuit to coarsely adjust the power change value with the current disturbance direction and the preset first disturbance step size; if not, control the discharge disturbance circuit to coarsely adjust the power change value with the opposite direction of the current disturbance direction and the preset first disturbance step size.

[0088] If so, the disturbance direction of the discharge disturbance circuit is determined based on the power change value of the actual output power of the photovoltaic module, and the determined disturbance direction and the preset first disturbance step size are used to control the discharge disturbance circuit to coarsely adjust the power change value, including:

[0089] If the actual output power of the photovoltaic module changes more than the preset second threshold, the discharge disturbance circuit is controlled to coarsely adjust the power change value with the current disturbance direction and the preset first disturbance step size.

[0090] If the actual output power change of the photovoltaic module is not greater than zero and the absolute value is greater than the preset second threshold, the discharge disturbance circuit is controlled to coarsely adjust the power change value in the opposite direction of the current disturbance direction and the preset first disturbance step size.

[0091] Specifically, in combination Figure 3 The flowchart shown is explained below:

[0092] In step S104, the discharge disturbance circuit is controlled to operate.

[0093] In step S105, it is determined whether the absolute value of the power change in the actual output power of the photovoltaic module is greater than a preset first threshold. If the determination result is "yes", then step S106 is executed; if the determination result is "no", then step S107 is executed. Figure 3 In this context, the actual power change in output power is ΔP.

[0094] In step S106, it is determined whether the voltage change value of the actual output voltage of the photovoltaic module is less than zero. If the determination result is "yes", then step S108 is executed; if the determination result is "no", then step S109 is executed. Figure 3 In this context, the actual output voltage change is ΔU.

[0095] In step S107, it is determined whether the power change value of the actual output power of the photovoltaic module is greater than zero. If the determination result is "yes", then step S110 is executed; if the determination result is "no", then step S111 is executed.

[0096] In step S108, it is determined that the discharge disturbance circuit maintains the disturbance direction, and the process returns to step 104 to continue with subsequent steps.

[0097] In step S109, it is determined whether the amplitude of the actual output voltage of the photovoltaic module is greater than a preset amplitude. If the determination result is "yes", then step S112 is executed; if the determination result is "no", then step S108 is executed. Figure 3 In the process, the amplitude of the actual output voltage of the photovoltaic module is U. K The preset amplitude is U m .

[0098] In step S110, it is determined whether the power change value of the actual output power of the photovoltaic module is greater than a preset second threshold. If the determination result is "yes", then step S108 is executed; if the determination result is "no", then step S113 is executed, controlling the power supply disturbance circuit to operate, fine-tuning the power change value of the actual output power of the photovoltaic module, and executing subsequent steps to make the absolute value of the power change value of the actual output power of the photovoltaic module less than a preset third threshold. The preset second threshold is smaller than the preset first threshold, and the preset second threshold can typically be set to half of the preset first threshold, with a value of Γ.

[0099] In step S111, it is determined whether the absolute value of the power change in the actual output power of the photovoltaic module is greater than a preset second threshold. If the determination result is "yes", then step S112 is executed; if the determination result is "no", then step S113 is executed, controlling the power supply disturbance circuit to operate, fine-tuning the power change in the actual output power of the photovoltaic module, and executing subsequent steps to make the absolute value of the power change in the actual output power of the photovoltaic module less than a preset third threshold.

[0100] In step S112, it is determined that the discharge disturbance circuit has changed the disturbance direction. The process returns to step 104 and continues with subsequent steps.

[0101] See Figure 4 As shown, Figure 4 This is a schematic diagram of a photovoltaic grid-connected maximum power point tracking process provided by an embodiment of the present invention. When the actual output power of the photovoltaic module is adjusting to point P1 on the right, if the light intensity suddenly decreases, the PV (power-voltage) curve of the photovoltaic module shifts downward, and the actual output power falls to point P2, ΔP < 0 (for ease of explanation, it is assumed that the decrease in light intensity is large, and the change in actual output power is large, satisfying |ΔP| > 2Γ). According to the tracking logic of the prior art, the existing tracking system will not recognize that the decrease in actual output power is caused by a sudden decrease in light intensity based on the sign of the ΔP value, and will mistakenly believe that the actual output power has fallen to the maximum power point due to excessive adjustment. Figure 4The maximum power point is located to the right of the highest point of the upper PV curve, and the actual output power is adjusted to the left in the opposite direction to the power point P1'. However, the actual maximum power point is still on the right side; only the PV curve shifts downwards overall. Therefore, this embodiment of the invention makes a further determination: if ΔU < 0, the original adjustment direction remains unchanged; if ΔU ≥ 0 and the amplitude of the actual output voltage of the photovoltaic module is U... K Not greater than the preset amplitude value U m The original adjustment direction remains unchanged; if ΔU≥0 and the amplitude of the actual output voltage of the photovoltaic module is U K The amplitude is greater than the preset value U m The original adjustment direction is changed. Based on the above judgment process, this embodiment of the invention can avoid misjudgment of the tracking direction and accelerate the tracking speed.

[0102] Similarly, when the actual output power of a photovoltaic module is adjusting to point P3 on the left, if the light intensity suddenly decreases, the PV curve of the photovoltaic module will shift downward, and the actual output power will fall to point P4, ΔP < 0 (again assuming the power change in the actual output power is large, satisfying |ΔP| > 2Γ). According to the tracking logic of existing technology, the existing tracking system will not recognize that the decrease in actual output power is caused by a sudden decrease in light intensity based on the sign of the ΔP value, and will mistakenly believe that the actual output power has fallen to the maximum power point due to excessive adjustment. Figure 4 The maximum power point is located to the left of the highest point of the upper PV curve, and the adjustment will then move in the opposite direction to the right. However, the maximum power point is still on the left, only the PV curve shifts downwards overall. Therefore, this embodiment of the invention makes a further determination: if ΔU < 0, the original adjustment direction remains unchanged; if ΔU ≥ 0 and the amplitude of the actual output voltage of the photovoltaic module is U... K Not greater than the preset amplitude value U m The original adjustment direction remains unchanged; if ΔU≥0 and the amplitude of the actual output voltage of the photovoltaic module is U K The amplitude is greater than the preset value U m This changes the original adjustment direction.

[0103] See Figure 2 As shown, during actual tracking, the controller first pre-applies a reference pulse signal with a fixed period and a 50% duty cycle to the gate of the first MOSFET. Once the disturbance direction is determined, the pulse duty cycle is appropriately increased or decreased (adjusting the effective pulse width) to maintain or change the disturbance direction. The disturbance step size can be determined by adjusting the duty cycle ratio, i.e., the ratio of the reference pulse period, such as 1%T or 10%T, with an upper limit of less than 50%T. Generally, the smaller the fixed frequency of the pre-applied reference pulse, the higher the accuracy of the step size adjustment.

[0104] In summary, when the absolute value of the actual output power change is large, the embodiments of the present invention accurately determine the coarse adjustment disturbance direction based on the actual output voltage change and the amplitude of the actual output voltage, or when the absolute value of the actual output power change is slightly large, to avoid misjudgment of the tracking direction and guide the actual output power to quickly approach the maximum output power point.

[0105] As an optional implementation, in one embodiment of the invention, the step of controlling the power supply disturbance circuit to operate so that the absolute value of the power change in the actual output power of the photovoltaic module is less than a preset third threshold includes:

[0106] Control the operation of the power supply disturbance circuit;

[0107] Determine whether the absolute value of the power change in the actual output power of the photovoltaic module is greater than a preset first threshold:

[0108] If so, the control discharge disturbance circuit will perform a coarse adjustment on the power change value again;

[0109] If not, determine whether the absolute value of the actual output power change of the photovoltaic module is greater than a preset third threshold. If yes, determine the disturbance direction of the feeder disturbance circuit based on the actual output power change of the photovoltaic module, and use the determined disturbance direction and preset second disturbance step size to control the feeder disturbance circuit to fine-tune the power change value. If not, control the feeder disturbance circuit to stop working. The preset third threshold ξ is less than the preset second threshold Γ. The preset second disturbance step size is less than the preset first disturbance step size.

[0110] If so, the disturbance direction of the feed disturbance circuit is determined based on the power change value of the actual output power of the photovoltaic module, and the feed disturbance circuit is finely adjusted to finely adjust the power change value based on the determined disturbance direction and the preset second disturbance step size, including:

[0111] If the actual output power of the photovoltaic module changes more than the preset third threshold, the control power supply disturbance circuit will finely adjust the power change value with the current disturbance direction and the preset second disturbance step size.

[0112] If the actual output power change of the photovoltaic module is not greater than zero and the absolute value is greater than the preset third threshold, the control power supply disturbance circuit finely adjusts the power change value in the opposite direction of the current disturbance direction and the preset second disturbance step size.

[0113] Specifically, in combination Figure 3 The flowchart shown is explained below:

[0114] In step S113, the power supply disturbance circuit is controlled to operate.

[0115] In step S114, it is determined whether the absolute value of the power change of the actual output power of the photovoltaic module is greater than a preset first threshold. If the determination result is "yes", then return to step 106 and continue to execute the subsequent steps; if the determination result is "no", then execute step S115.

[0116] In step S115, it is determined whether the power change value of the actual output power of the photovoltaic module is greater than zero. If the determination result is "yes", then step S116 is executed; if the determination result is "no", then step S117 is executed.

[0117] In step S116, it is determined whether the power change value of the actual output power of the photovoltaic module is greater than or equal to a preset third threshold. If the determination result is "yes", then step S118 is executed; if the determination result is "no", then step 101 is returned and subsequent steps are executed.

[0118] In step S117, it is determined whether the absolute value of the power change of the actual output power of the photovoltaic module is less than a preset third threshold. If the determination result is "yes", then return to step 101 and continue to execute the subsequent steps; if the determination result is "no", then execute step S119.

[0119] In step S118, it is determined that the power supply disturbance circuit maintains the disturbance direction, and the process returns to step 113 to continue with subsequent steps.

[0120] In step S119, it is determined that the power supply disturbance circuit has changed the disturbance direction. The process returns to step 113 and continues with subsequent steps.

[0121] Similarly, see Figure 2 As shown, the controller first pre-applies a reference pulse signal with a fixed period and a 50% duty cycle to the DC-DC converter. After determining the disturbance direction, it increases or decreases the pulse duty cycle (adjusting the effective pulse width) to maintain or change the disturbance direction. The disturbance step size can be determined by adjusting the duty cycle ratio. Of course, in this application, the preset second disturbance step size is smaller than the preset first disturbance step size.

[0122] In this embodiment of the invention, when the absolute value of the actual output power change is small, the direction of fine-tuning perturbation is accurately determined based on the actual output power change, guiding the actual output power very close to the maximum output power point. At this point, the maximum power point tracking process ends, and the photovoltaic module outputs almost at its maximum output power normally. Furthermore, to address the situation where the power change suddenly increases during the fine-tuning process, this embodiment of the invention introduces a discharge perturbation circuit again to coarsely adjust the power change value when the power change suddenly increases, thus improving the tracking accuracy.

[0123] Figure 5The simulation waveform diagram of maximum power point tracking for grid-connected photovoltaics provided in this embodiment of the invention shows that, under the influence of different disturbance loads, the actual output voltage U0 and actual output current I0 of the photovoltaic module can quickly stabilize without significant oscillation, that is, the actual output power of the photovoltaic module can quickly reach the maximum power point without significant oscillation.

[0124] In the description of this invention, it should be noted that the terms "upper," "lower," etc., indicating the orientation or positional relationship are based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. Unless otherwise expressly specified and limited, the terms "installed," "connected," and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication between two elements. For those skilled in the art, the specific meaning of the above terms in this invention can be understood according to the specific circumstances.

[0125] It should be noted that in this invention, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0126] The above description is merely a specific embodiment of the present invention, enabling those skilled in the art to understand or implement the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the present invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features of the invention herein.

Claims

1. A photovoltaic grid-connected maximum power point tracking system, characterized in that, include: A power supply disturbance circuit, which is used to connect to photovoltaic modules and DC-DC conversion circuits; Discharge disturbance circuit, which is used to connect to DC-DC converter circuits and inverter circuits; An energy recovery circuit is connected to the discharge disturbance circuit and the power supply disturbance circuit. The energy recovery circuit is used to recover the energy discharged by the discharge disturbance circuit and provide it to the power supply disturbance circuit. The controller, which is used to connect to the photovoltaic module, the discharge disturbance circuit, and the feed disturbance circuit, is configured to: Obtain the actual output power of the photovoltaic module; Determine whether the absolute value of the power change in the actual output power of the photovoltaic module is greater than a preset first threshold or whether the working cycle of the photovoltaic module has reached a preset cycle; If so, control the operation of the discharge disturbance circuit and the power supply disturbance circuit to coarsely and finely adjust the power change value of the actual output power of the photovoltaic module, so that the absolute value of the power change value of the actual output power of the photovoltaic module is less than the preset third threshold. The power supply disturbance circuit is a DC / DC circuit, the discharge disturbance circuit includes a first resistor and a first MOSFET, and the energy recovery circuit includes a first transformer, a first capacitor, and a first diode. The DC / DC circuit is connected to the positive and negative terminals of the photovoltaic module and the controller; the first terminal of the first resistor is connected to the positive terminal of the DC-DC converter circuit, the second terminal of the first resistor is connected to the first terminal of the first current transformer, the second terminal of the first current transformer is connected to the drain of the first MOSFET, the gate of the first MOSFET is connected to the controller, and the source of the first MOSFET is connected to the negative terminal of the DC-DC converter circuit; the third terminal of the first current transformer is connected to the anode of the first diode, the cathode of the first diode is connected to the DC / DC circuit, the first terminal of the first capacitor is connected to the cathode of the first diode, and the second terminal of the first capacitor is connected to the negative terminal of the DC-DC converter circuit.

2. The photovoltaic grid-connected maximum power point tracking system according to claim 1, characterized in that: The discharge disturbance circuit further includes a second resistor, a second capacitor, and a transient voltage suppression diode; The first end of the second resistor is connected to the controller, and the second end of the second resistor is connected to the gate of the first MOS transistor. The first terminal of the second capacitor is connected to the gate of the first MOS transistor, and the second terminal of the second capacitor is connected to the negative terminal of the DC-DC converter circuit. The cathode of the transient voltage suppressor diode is connected to the first terminal of the second resistor, and the anode of the transient voltage suppressor diode is connected to the negative terminal of the DC-DC converter circuit.

3. A photovoltaic grid-connected maximum power point tracking method, using the photovoltaic grid-connected maximum power point tracking system as described in claim 1, characterized in that, Includes the following steps: Obtain the actual output power of the photovoltaic module; Determine whether the absolute value of the power change in the actual output power of the photovoltaic module is greater than a preset first threshold or whether the working cycle of the photovoltaic module has reached a preset cycle; If so, control the operation of the discharge disturbance circuit and the power supply disturbance circuit to coarsely and finely adjust the power change value of the actual output power of the photovoltaic module, so that the absolute value of the power change value of the actual output power of the photovoltaic module is less than the preset third threshold.

4. The photovoltaic grid-connected maximum power point tracking method according to claim 3, characterized in that, If so, the operation of the control discharge disturbance circuit and the feed disturbance circuit is performed to coarsely and finely adjust the power change value of the actual output power of the photovoltaic module, so that the absolute value of the power change value of the actual output power of the photovoltaic module is less than a preset third threshold, including: Control the operation of the discharge disturbance circuit; Determine whether the absolute value of the power change in the actual output power of the photovoltaic module is greater than a preset first threshold: If so, the disturbance direction of the discharge disturbance circuit is determined based on the voltage change value and amplitude of the actual output voltage of the photovoltaic module, and the discharge disturbance circuit is coarsely adjusted to the power change value by the determined disturbance direction and the preset first disturbance step size. If not, determine whether the absolute value of the power change of the actual output power of the photovoltaic module is greater than the preset second threshold. If yes, determine the disturbance direction of the discharge disturbance circuit based on the power change of the actual output power of the photovoltaic module, and control the discharge disturbance circuit to coarsely adjust the power change value according to the determined disturbance direction and the preset first disturbance step size. If not, control the power supply disturbance circuit to work so that the absolute value of the power change of the actual output power of the photovoltaic module is less than the preset third threshold.

5. The photovoltaic grid-connected maximum power point tracking method according to claim 4, characterized in that, If so, the disturbance direction of the discharge disturbance circuit is determined based on the voltage change value and amplitude of the actual output voltage of the photovoltaic module. The determined disturbance direction and a preset first disturbance step size are used to control the discharge disturbance circuit to coarsely adjust the power change value, including: Determine if the voltage change of the actual output voltage of the photovoltaic module is less than zero: If so, the discharge disturbance circuit is controlled to coarsely adjust the power change value based on the current disturbance direction and the preset first disturbance step size; If not, determine whether the amplitude of the actual output voltage of the photovoltaic module is greater than the preset amplitude: if yes, control the discharge disturbance circuit to coarsely adjust the power change value with the current disturbance direction and the preset first disturbance step size; if not, control the discharge disturbance circuit to coarsely adjust the power change value with the opposite direction of the current disturbance direction and the preset first disturbance step size.

6. The photovoltaic grid-connected maximum power point tracking method according to claim 4, characterized in that, If so, the disturbance direction of the discharge disturbance circuit is determined based on the power change value of the actual output power of the photovoltaic module, and the determined disturbance direction and the preset first disturbance step size are used to control the discharge disturbance circuit to coarsely adjust the power change value, including: If the actual output power of the photovoltaic module changes more than the preset second threshold, the discharge disturbance circuit is controlled to coarsely adjust the power change value with the current disturbance direction and the preset first disturbance step size. If the actual output power change of the photovoltaic module is not greater than zero and the absolute value is greater than the preset second threshold, the discharge disturbance circuit is controlled to coarsely adjust the power change value in the opposite direction of the current disturbance direction and the preset first disturbance step size.

7. The photovoltaic grid-connected maximum power point tracking method according to claim 4, characterized in that, If not, the control of the power supply disturbance circuit to ensure that the absolute value of the power change in the actual output power of the photovoltaic module is less than a preset third threshold includes: Control the operation of the power supply disturbance circuit; Determine whether the absolute value of the power change in the actual output power of the photovoltaic module is greater than a preset first threshold: If so, the control discharge disturbance circuit will perform a coarse adjustment on the power change value again; If not, determine whether the absolute value of the actual output power change of the photovoltaic module is greater than the preset third threshold. If yes, determine the disturbance direction of the feed disturbance circuit based on the actual output power change of the photovoltaic module, and control the feed disturbance circuit to fine-tune the power change value according to the determined disturbance direction and the preset second disturbance step size. If not, control the feed disturbance circuit to stop working.

8. The photovoltaic grid-connected maximum power point tracking method according to claim 7, characterized in that, If so, the disturbance direction of the feed disturbance circuit is determined based on the power change value of the actual output power of the photovoltaic module, and the feed disturbance circuit is finely adjusted to finely adjust the power change value based on the determined disturbance direction and the preset second disturbance step size, including: If the actual output power of the photovoltaic module changes more than the preset third threshold, the control power supply disturbance circuit finely adjusts the power change value with the current disturbance direction and the preset second disturbance step size. If the actual output power change of the photovoltaic module is not greater than zero and the absolute value is greater than the preset third threshold, the control power supply disturbance circuit finely adjusts the power change value in the opposite direction of the current disturbance direction and the preset second disturbance step size.

Images