Grid-connected control circuit, grid-connected control method and grid-connected system

Abstract

The application relates to a grid-connected control circuit, a grid-connected control method and a grid-connected system. The grid-connected control circuit comprises an auxiliary power supply unit, a surge sampling unit, a differential operation unit and a control unit. The auxiliary power supply unit comprises a pre-charging component. The surge sampling unit is connected to both ends of the pre-charging component and is used for acquiring a surge sampling signal at both ends of the pre-charging component. The differential operation unit is connected to the surge sampling unit and an inverter main circuit and is used for receiving a main current sampling signal of the inverter main circuit and performing differential operation on the main current sampling signal and the surge sampling signal to output a differential control signal. The control unit is connected to the differential operation unit and the inverter main circuit and is used for controlling the inverter main circuit based on the differential control signal to adjust a grid-connected output current, so that a surge compensation current is superimposed in the grid-connected output current, and the surge compensation current corresponds to power acquired by the auxiliary power supply unit. The application solves the THDI deterioration problem caused by power acquisition of an auxiliary power supply.

Description

Technical Field

[0001] This application relates to the field of grid-connected inverter control technology, and in particular to a grid-connected control circuit, a grid-connected control method, and a grid-connected system. Background Technology

[0002] With the rapid development of power electronics technology, grid-connected inverter systems such as photovoltaic power generation and energy storage systems have been widely used. Grid-connected inverter systems typically need to convert AC power from the grid or its own converted power into low-voltage DC power required by the system's internal control chips and drive circuits. In conventional grid-connected inverter systems, the auxiliary power supply system is often designed with two power supply points, allowing for power switching based on the system's operating status, thus preventing the auxiliary power supply from continuously drawing power from the grid after normal grid connection. However, in non-isolated grid-connected inverter systems, due to limitations in the internal electrical isolation architecture, a dual power supply design cannot be adopted, forcing the auxiliary power supply to continuously draw power from the grid system during grid-connected operation.

[0003] This continuous power extraction from the grid introduces periodic pulse currents during the power acquisition process. These currents, superimposed on the main circuit, cause waveform distortion in the grid-connected output current, worsening the total harmonic distortion (THDI) and making it difficult to meet increasingly stringent power quality requirements. To address the distortion problem caused by auxiliary power supply extraction, related technologies attempt to acquire the total current and perform software correction by adding high-power current sensors. However, because the power of the auxiliary power supply is significantly smaller than that of the main power circuit, the distorted current it introduces accounts for a very small proportion within the large dynamic range of the main current. This makes it difficult for conventional sampling devices to accurately capture this distortion component, rendering existing compensation schemes ineffective in achieving precise harmonic suppression. Summary of the Invention

[0004] Therefore, it is necessary to provide a grid-connected control circuit, grid-connected control method, and grid-connected system to solve the problem of THDI degradation in grid-connected current.

[0005] In a first aspect, this application provides a grid-connected control circuit applied to a grid-connected system, the grid-connected system including a grid access terminal and an inverter main circuit connected to the grid access terminal, the grid-connected control circuit including:

[0006] An auxiliary power supply unit is connected to the power grid access terminal to obtain electrical energy, and includes a pre-charging component;

[0007] A surge sampling unit is connected to both ends of the precharge component and is used to acquire surge sampling signals from both ends of the precharge component.

[0008] A differential operation unit, connected to the surge sampling unit and the inverter main circuit, is used to receive the main current sampling signal of the inverter main circuit, and perform differential operation on the main current sampling signal and the surge sampling signal to output a differential control signal; and,

[0009] The control unit, connected to the differential arithmetic unit and the inverter main circuit, is used to control the inverter main circuit based on the differential control signal to adjust the grid-connected output current, so that a surge compensation current is superimposed on the grid-connected output current, and the surge compensation current corresponds to the electrical energy obtained by the auxiliary power supply unit.

[0010] In some embodiments, the control unit is further configured to acquire a grid-connected current reference value, subtract the grid-connected current reference value from the differential control signal to obtain a current error value, and adjust the current error value to generate a pulse width modulation signal for driving the inverter main circuit.

[0011] In some embodiments, after the grid connection task is set in the grid-connected system, the control unit is further configured to control the inverter main circuit through the pulse width modulation signal, so that the inverter main circuit outputs an actual value of sinusoidal current superimposed with the surge compensation current based on the pulse width modulation signal; and after the actual value of sinusoidal current obtains power through the auxiliary power supply unit, it outputs a standard sinusoidal current signal at the grid access terminal.

[0012] In some embodiments, the differential operation unit is used to subtract the voltage signal corresponding to the main current sampling signal output by the inverter main circuit from the voltage signal corresponding to the surge sampling signal output by the surge sampling unit to generate the differential control signal, and output it to the control unit.

[0013] In some embodiments, the differential operation unit includes an operational amplifier; the non-inverting input and the inverting input of the operational amplifier respectively receive the voltage signal corresponding to the main current sampling signal and the voltage signal corresponding to the surge sampling signal; the output of the operational amplifier is connected to the control unit, and the operational amplifier is used to generate and output the differential control signal based on the voltage signal corresponding to the main current sampling signal and the voltage signal corresponding to the surge sampling signal.

[0014] In some embodiments, the surge sampling unit includes a sampling amplifier, the two detection terminals of which are respectively connected to the two ends of the precharge component, and are used to collect the voltage drop generated by the current flowing through the precharge component, and amplify the voltage drop to generate a voltage signal corresponding to the surge sampling signal.

[0015] In some embodiments, the pre-charge component includes a pre-charge resistor; the auxiliary power supply unit includes a rectifier component, the pre-charge resistor is connected in series between the grid access terminal and the rectifier component; the surge sampling unit is used to acquire the voltage formed on the pre-charge resistor by the pulse surge current generated by the rectifier component, as the surge sampling signal.

[0016] In some embodiments, the grid-connected control circuit further includes an inverter current sampling circuit, which is used to collect the current of the inverter main circuit so as to output the main current sampling signal to the differential operation unit.

[0017] Secondly, this application also provides a grid-connected control method, applied to the grid-connected control circuit described in any of the above embodiments, the grid-connected control method comprising:

[0018] A differential control signal is acquired, which is determined by differential operation between the main current sampling signal and the surge sampling signal; and,

[0019] The grid-connected output current is adjusted based on the differential control signal, so that the grid-connected output current is superimposed with the surge compensation current corresponding to the system surge.

[0020] In some embodiments, adjusting the grid-connected output current based on the differential control signal includes:

[0021] Obtain the grid-connected current reference value;

[0022] The current error value is obtained by subtracting the grid-connected current reference value from the differential control signal.

[0023] The current error value is adjusted to generate a pulse width modulation signal;

[0024] After setting the grid connection task, the actual value of the sinusoidal current, which is superimposed on the surge compensation current, is output based on the pulse width modulation signal. This is so that the surge compensation current superimposed on the actual value of the sinusoidal current cancels out the surge current obtained by the system, thus forming a standard sinusoidal grid-connected output current.

[0025] In some embodiments, obtaining the grid-connected current reference value includes:

[0026] Obtain the effective value of the target current and convert the effective value of the target current into the target peak value;

[0027] The target peak value is synchronously calculated with the phase angle information output by the phase-locked loop algorithm to determine the grid-connected current reference value.

[0028] Thirdly, this application also provides a grid-connected system, including:

[0029] Grid connection end;

[0030] The grid-connected switch assembly is connected to the grid access terminal;

[0031] The inverter main circuit is connected to the grid connection terminal via the grid-connected switch assembly; and...

[0032] The grid-connected control circuit as described in any of the above embodiments is connected to both the grid access terminal and the inverter main circuit; wherein...

[0033] The grid-connected system is a non-isolated grid-connected inverter system; when the inverter main circuit is in grid-connected operation, the auxiliary power supply unit in the grid-connected control circuit obtains power through the grid access terminal.

[0034] The aforementioned grid-connected control circuit, by setting up an auxiliary power supply unit connected to the grid access terminal to obtain electrical energy and including a pre-charging component, works with a surge sampling unit to acquire surge sampling signals from both ends of the pre-charging component in real time. These signals are then differentially processed in a differential operation unit along with the main current sampling signal of the inverter main circuit. The control unit, based on the output differential control signal, controls the inverter main circuit to adjust the grid-connected output current, thereby precisely superimposing the surge compensation current corresponding to the electrical energy obtained by the auxiliary power supply unit into the grid-connected output current. This setup enables online compensation for current distortion caused by the auxiliary power supply unit obtaining electrical energy, avoiding the degradation of the grid-connected current THDI caused by pulse surges introduced by the auxiliary power supply in non-isolated grid-connected systems, and ensuring accurate grid-connected current output. Attached Figure Description

[0035] To more clearly illustrate the technical solutions in the embodiments of this application or the conventional technology, the drawings used in the description of the embodiments or the conventional technology will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0036] Figure 1 This is a schematic diagram of a grid-connected system according to one embodiment.

[0037] Figure 2 This is a circuit diagram of a grid-connected control circuit according to one embodiment.

[0038] Figure 3 The inverter output current waveform diagram is shown in one embodiment, which is a superimposed auxiliary power supply surge current.

[0039] Figure 4 This is a flowchart of a grid connection control method according to one embodiment. Detailed Implementation

[0040] To facilitate understanding of this application, a more complete description will be provided below with reference to the accompanying drawings. Embodiments of this application are illustrated in the drawings. This application can be implemented in many different forms and is not limited to the embodiments described herein. These embodiments are provided so that the disclosure of this application will be more thorough and complete.

[0041] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application.

[0042] It is understood that the terms "first," "second," etc., used herein may be used to describe various elements, but these elements are not limited by these terms. These terms are only used to distinguish one element from another. For example, without departing from the scope of this application, a first resistor may be referred to as a second resistor, and similarly, a second resistor may be referred to as a first resistor. Both the first resistor and the second resistor are resistors, but they are not the same resistor.

[0043] It is understood that the term "connection" in the following embodiments should be understood as "electrical connection," "communication connection," etc., if the connected circuits, modules, units, etc., have electrical signal or data transmission with each other.

[0044] It is understandable that "at least one" refers to one or more, and "multiple" refers to two or more. "At least a part of an element" refers to part or all of an element.

[0045] When used herein, the singular forms of “a,” “an,” and “the” may also include the plural forms unless the context clearly indicates otherwise. It should also be understood that the terms “comprising / including” or “having,” etc., specify the presence of the stated features, wholes, steps, operations, components, parts, or combinations thereof, but do not preclude the possibility of the presence or addition of one or more other features, wholes, steps, operations, components, parts, or combinations thereof. Meanwhile, the term “and / or” as used in this specification includes any and all combinations of the associated listed items.

[0046] Grid-connected systems are widely used in photovoltaic power generation, energy storage converters, and various new energy power generation scenarios. They are primarily responsible for converting various types of DC power or unconventional AC power into AC power that conforms to grid standards, and for ensuring safe transmission and energy exchange to the public grid. With the rapid evolution of power electronics technology, the power quality (such as total harmonic distortion (THDI)), the simplicity of the system topology, and the reliability of auxiliary energy supply have become key indicators for evaluating the performance of grid-connected equipment.

[0047] like Figure 1 As shown, this application also provides a grid-connected system 1, including a grid connection terminal 11, a grid-connected switch assembly 12, an inverter main circuit 13, and a grid-connected control circuit 20. The grid-connected switch assembly 12 is connected to the grid connection terminal 11. The grid-connected switch assembly 12 is connected between the grid connection terminal 11 and the inverter main circuit 13. The inverter main circuit 13 is connected to the grid connection terminal 11 through the grid-connected switch assembly 12. The grid-connected control circuit 20 is connected to both the grid connection terminal 11 and the inverter main circuit 13. Specifically, the grid-connected system 1 is a non-isolated grid-connected inverter system. The grid connection terminal 11 is used to connect the system to the external power grid 3 and to exchange electrical energy. The inverter main circuit 13 is used to perform power conversion to output grid-connected current to the grid. The grid-connected switch assembly 12 is used to control the on / off connection between the inverter main circuit 13 and the grid connection terminal 11. The grid-connected control circuit 20, as the core control hub, is used to collect system signals and control the inverter main circuit 13 to adjust the grid-connected output current. In this non-isolated grid-connected inverter system, when the inverter main circuit 13 is in grid-connected operation, the auxiliary power supply unit in the grid-connected control circuit 20 obtains power through the grid access terminal. The architecture of the aforementioned grid-connected system 1 provides a solid operational foundation for subsequent coordinated control and compensation, ensuring reliable coordination between energy acquisition and main circuit power conversion under the non-isolated architecture.

[0048] In order to accurately compensate for the distortion in the grid-connected output current, the specific structure, components and working principle of the grid-connected control circuit 20 will be described in detail below.

[0049] like Figure 1As shown, the grid-connected control circuit 20 includes an auxiliary power supply unit 21, a surge sampling unit 22, a differential operation unit 23, and a control unit 24. The auxiliary power supply unit 21 is connected to the grid access terminal 11 to obtain electrical energy and includes a pre-charge component 211. The surge sampling unit 22 is connected to both ends of the pre-charge component 211 to obtain surge sampling signals from both ends of the pre-charge component 211. The differential operation unit 23 is connected to the surge sampling unit 22 and the inverter main circuit 13, and is used to receive the main current sampling signal of the inverter main circuit 13, and perform differential operation on the main current sampling signal and the surge sampling signal to output a differential control signal. The control unit 24 is connected to the differential operation unit 23 and the inverter main circuit 13, and is used to control the inverter main circuit 13 based on the differential control signal to adjust the grid-connected output current, so that a surge compensation current is superimposed on the grid-connected output current, and the surge compensation current corresponds to the electrical energy obtained by the auxiliary power supply unit 21. Specifically, the auxiliary power supply unit 21 obtains electrical energy from the grid access terminal 11 to supply the system operation, and generates pulse surge current through the pre-charge component 211 during the energy acquisition process. A surge sampling unit 22 is connected across the two ends of the pre-charge component 211 to acquire the surge sampling signal formed by the pulse surge current flowing through the two ends of the pre-charge component 211 in real time. The differential operation unit 23 receives the main current sampling signal of the inverter main circuit 13 and the surge sampling signal output by the surge sampling unit 22, performs differential operation on them, and thus obtains and outputs a differential control signal reflecting the surge characteristics. Further, the control unit 24 performs closed-loop regulation of the inverter main circuit 13 according to the differential control signal, so that the grid-connected output current is superimposed with the surge compensation current corresponding to the electrical energy obtained by the auxiliary power supply unit 21. Through the interaction and collaborative work of the above units, online active compensation for current distortion caused by the auxiliary power supply unit 21 obtaining power is realized. This effectively solves the problem of THDI deterioration of grid-connected current caused by the continuous power supply from the grid side in non-isolated grid-connected systems, and ensures the accuracy and quality of grid-connected output current.

[0050] In some embodiments, the control unit 24 is further configured to acquire a grid-connected current reference value, subtract the grid-connected current reference value from the differential control signal to obtain a current error value, and adjust the current error value to generate a pulse width modulation signal for driving the inverter main circuit 13. In this embodiment, firstly, the effective value of the target current is acquired and converted into a target peak value. Then, the target peak value is synchronously calculated with the phase angle information output based on the phase-locked loop algorithm, and finally determined as the grid-connected current reference value. With this configuration, by the control unit 24 subtracting the grid-connected current reference value from the differential control signal to obtain the current error value, and adjusting the current error value to generate a pulse width modulation signal for driving the inverter main circuit 13, closed-loop feedback regulation can be achieved, enabling the drive signal of the inverter main circuit 13 to incorporate the surge differential compensation amount in real time, thereby improving the adjustment accuracy and response speed of the grid-connected control system under dynamic operating conditions.

[0051] In some embodiments, after the grid connection task is set in the grid-connected system, the control unit 24 is further configured to control the inverter main circuit 13 via a pulse width modulation signal, so that the inverter main circuit 13 outputs an actual sinusoidal current value superimposed with surge compensation current based on the pulse width modulation signal, and after the actual sinusoidal current value obtains power from the auxiliary power supply unit 21, it outputs a standard sinusoidal current signal at the grid access terminal 11. When the inverter main circuit 13 is in an inactive state, the amplitude of the main current sampling signal is zero, and the control unit 24 does not perform grid connection current control on the differential control signal. In this embodiment, after setting the grid connection task, the inverter main circuit 13 is controlled by a pulse width modulation signal to output an actual sinusoidal current value superimposed with surge compensation current, and after the current obtains power from the auxiliary power supply unit 21, it outputs a standard sinusoidal current signal at the grid access terminal 11. This process realizes the energy balance interaction between dynamic compensation and power acquisition, ensuring that the current waveform flowing into the grid is smooth and distortion-free.

[0052] In some embodiments, the differential operation unit 23 is used to subtract the voltage signal corresponding to the main current sampling signal output by the inverter main circuit 13 from the voltage signal corresponding to the surge sampling signal output by the surge sampling unit 22 to generate a differential control signal, which is then output to the control unit 24. In this embodiment, the differential operation unit 23 generates the differential control signal by subtracting the voltage signal corresponding to the main current sampling signal from the voltage signal corresponding to the surge sampling signal. This subtraction operation simplifies the signal processing chain and ensures real-time cancellation of the analog current between the main circuit current and the surge current.

[0053] To further clarify the specific circuits and component connections of the above units, a detailed explanation is provided below with reference to specific circuit diagrams.

[0054] In some embodiments, the precharge component 211 includes a precharge resistor RE. The rectifier component 212 includes a rectifier bridge DB1. The precharge resistor RE is connected in series between the grid connection terminal 11 and the rectifier component 212. The surge sampling unit 22 is used to acquire the voltage formed on the precharge resistor by the pulse surge current generated by the rectifier component 212, as a surge sampling signal. Specifically, as shown... Figure 2 As shown, the AC input terminal of the auxiliary power supply unit 21 is connected to the grid access terminal 11, such as the live wire Grid_L and the neutral wire Grid_N. The pre-charge resistor RE, acting as a pre-charge component 211, is connected in series between the neutral wire Grid_N and one AC input terminal of the rectifier bridge DB1. The rectifier bridge DB1, acting as a rectifier component 212, has its DC output terminals DC+ and DC- connected to the subsequent DC-DC auxiliary power supply module 213. During system operation, the rectifier bridge DB1 performs uncontrolled rectification, generating a pulse surge current. This current flows through the pre-charge resistor RE, creating a transient voltage drop across it. In this embodiment, by using the pre-charge component 211 as a pre-charge resistor, connected in series between the grid access terminal 11 and the rectifier component 212 of the auxiliary power supply unit 21, the surge sampling unit 22 acquires the voltage formed on the pre-charge resistor RE by the pulse surge current generated by the rectifier component 212. In this structure, the pre-charge resistor RE serves as a sampling reference, achieving accurate capture of the rectified pulse surge.

[0055] In some embodiments, the surge sampling unit 22 includes a sampling amplifier U1, whose two detection terminals are respectively connected to the two ends of the pre-charge component 211, and is used to collect the voltage drop generated by the current flowing through the pre-charge component 211, and amplify the voltage drop to generate a voltage signal corresponding to the surge sampling signal. Specifically, as shown in the figure... Figure 2 As shown, the surge sampling unit 22 includes a sampling amplifier U1. The non-inverting and inverting input terminals of the sampling amplifier U1 serve as two detection terminals, connected across the pre-charge resistor RE via a first current-limiting filter resistor R1 and a second current-limiting filter resistor R2, respectively. A first matching resistor R3 and a first filter capacitor C1 are connected between the non-inverting input terminal and the ground terminal GND. A first feedback resistor R4 and a second filter capacitor C2 are connected between the output terminal and the inverting input terminal of the sampling amplifier U1. The sampling amplifier U1 is used to acquire and amplify the transient voltage drop across the pre-charge resistor RE, converting it into a conditioned surge voltage signal I_AUX at its output terminal, which is the voltage signal corresponding to the surge sampling signal. In this embodiment, the sampling amplifier U1 in the surge sampling unit 22 is connected across the pre-charge resistor RE to acquire and amplify the voltage drop across the pre-charge resistor RE, converting it into the voltage signal corresponding to the surge sampling signal. This configuration improves the signal-to-noise ratio and sampling accuracy of the weak surge voltage drop signal.

[0056] In some embodiments, the grid-connected control circuit 20 further includes an inverter current sampling circuit 25, which is used to collect the current of the inverter main circuit 13 to output a main current sampling signal to the differential operation unit 23. Specifically, as Figure 2 As shown, the inverter current sampling circuit 25 includes a current transformer L and a sampling amplifier U2. The current transformer L is coupled to the AC output line of the inverter main circuit 13 and is used to sense the main circuit current. The input terminal of the sampling amplifier U2 is connected to the secondary side of the current transformer L through the third filter resistor R6, the fourth filter resistor R7, and the bias resistor R8. Its non-inverting input terminal is connected to a grounded RC network R9 and C3, and the inverting input terminal is connected to the output terminal by a second feedback resistor R10 and a third filter capacitor C4. After sampling and linearly amplifying the induced current, the sampling amplifier U2 generates and outputs a main current voltage signal I_INV0, which reflects the actual current of the inverter main circuit 13, i.e., the main current sampling signal, at its output terminal. By setting up the inverter current sampling circuit 25 to collect the current of the inverter main circuit 13 and outputting the main current sampling signal I_INV0 to the differential operation unit 23, a reliable basic data source is provided for differential operation.

[0057] In some embodiments, the differential operation unit 23 includes an operational amplifier U3. The non-inverting and inverting inputs of the operational amplifier U3 respectively receive the voltage signal corresponding to the main current sampling signal and the voltage signal corresponding to the surge sampling signal. The output of the operational amplifier U3 is connected to the control unit 24, and the operational amplifier U3 is used to generate and output a differential control signal based on the voltage signal corresponding to the main current sampling signal and the voltage signal corresponding to the surge sampling signal. Specifically, as shown... Figure 2 As shown, the differential operation unit 23 includes a differential operational amplifier U3. The inverting input of operational amplifier U3 receives the main current voltage signal I_INV0 through a fifth filter resistor R11, and the non-inverting input receives the surge voltage signal I_AUX through a sixth filter resistor R12. A second bias resistor R13 and a fourth filter capacitor C5 are connected between the non-inverting input and the ground terminal GND, and a third feedback resistor R14 and a fifth filter capacitor C6 are connected between the inverting input and the output terminal. Operational amplifier U3 uses analog hardware circuitry to perform real-time subtraction and proportional amplification of the voltage signals at the non-inverting and inverting inputs, and outputs a differential control signal I_INV that eliminates or integrates surge characteristics in real time, which is then sent to the sampling pin of control unit 24. By setting the non-inverting and inverting inputs of operational amplifier U3 to receive the main voltage signal and the surge voltage signal respectively, and utilizing the operational amplifier characteristics to complete the subtraction and output of the two voltage signals, a low-cost and stable differential control signal can be provided.

[0058] In addition, the inverter main circuit 13 also includes a DC bus section, which includes the positive DC bus (BUS+), the negative DC bus (BUS-), and a DC bus capacitor CE1 connected between the positive and negative DC bus terminals, providing stable DC voltage support for the full-bridge inverter circuit. The inverter main circuit 13 includes full-bridge switches Q1-Q4, a filter inductor LDE1, and a filter capacitor CE2, forming the inverter circuit. The grid-connected switch assembly 12 includes AC relays RLY1 and RLY2, used to achieve safe isolation and switching of the AC main circuit.

[0059] To achieve precise differential and online active compensation at the hardware level, the surge sampling unit 22 and the inverter current sampling circuit 25 are designed with sensitivity matching. The sampling amplifier U1's sampling and amplification coefficient for the voltage across the pre-charge resistor RE is proportionally matched to the current sensitivity of the sampling amplifier U2 for sampling the inverter main circuit current, i.e., the amplitude of the output voltage signal corresponding to each ampere of current. This ensures that the output surge voltage signal I_AUX and the main current voltage signal I_INV0 have the same level sensitivity range, guaranteeing that the differential operational amplifier U3 can perform proportional subtraction.

[0060] Based on this, the resistance value of the pre-charge resistor RE has been optimized: On the one hand, since the power consumption of the auxiliary power supply unit 21 is relatively small (e.g., 5W to 8W), if the resistance value of the pre-charge resistor RE is too small, the resulting voltage drop will be extremely weak. In this embodiment, by selecting a pre-charge resistor RE with a slightly larger resistance value within the allowable operating voltage range of the auxiliary power supply unit 21, a voltage signal in the millivolt to volt range can be generated when the pulse surge current flows through the pre-charge resistor RE. The surge voltage signal I_AUX formed after the voltage drop signal is amplified by the sampling amplifier U1 has a high signal-to-noise ratio. Compared with the weak distortion component sampled by the large-range Hall sensor on the traditional grid side, this embodiment improves the reliability and accuracy of the sampling process. On the other hand, the upper limit of the resistance value of the pre-charge resistor RE is limited to the threshold range that meets the normal start-up and operation of the subsequent DC-DC auxiliary power supply module 213 under low-voltage grid conditions, avoiding the problem of excessively low DC+ voltage due to excessively large resistance value.

[0061] To further illustrate the dynamic control principle and current waveform cancellation derivation process of the grid-connected control circuit 20 at different operating stages, the following section combines... Figure 2 and Figure 3 To elaborate further.

[0062] Combination Figure 2 and Figure 3As shown, when the inverter main circuit 13 is in the off-start (not grid-connected) state, the actual current in the inverter main circuit 13 is zero, and the amplitude of the main current voltage signal I_INV0 output by the inverter current sampling circuit 25 is 0V. At this time, the current on the grid connection terminal 11 side is only the pulse surge current generated when the auxiliary power supply unit 21 obtains power through the pre-charge resistor RE and the rectifier bridge DB1. During this stage, the system has no grid-connected THDI control requirements, and the control unit 24 does not perform grid-connected current closed-loop control on the differential control signal I_INV.

[0063] After the system is set to perform grid connection, the control unit 24 initiates the grid connection control process: The control unit 24 first obtains the target current effective value Irms_Ref, and multiplies the target current effective value Irms_Ref by... The target current peak value Ipeak_Ref is converted into the target current peak value. Subsequently, the control unit 24 performs synchronous multiplication operation on the target current peak value Ipeak_Ref and the phase angle cosine value Cos (Angle PLL) output based on the phase-locked loop algorithm (such as SPLL) to calculate and determine the grid-connected sinusoidal current target reference value Igrid_ref.

[0064] During grid-connected operation, the inverter main circuit 13 starts according to the control command. The operational amplifier U3 in the differential operation unit 23 performs hardware subtraction on the main current voltage signal I_INV0 and the surge voltage signal I_AUX in real time to generate a differential control signal I_INV, which is then input to the ADC sampling port of the control unit 24. The control unit 24 calculates the difference between the received differential control signal I_INV and the grid-connected sinusoidal current target reference value Igrid_ref to obtain the current error signal, and sends this current error signal to the PI controller in the control unit 24 for closed-loop regulation. The output of the PI controller is superimposed with the grid voltage feedforward signal to generate the pulse width modulation signal (PWM duty cycle) used to drive the full-bridge switching transistors Q1-Q4 in the inverter main circuit 13.

[0065] like Figure 3 As shown, under the above closed-loop control, the inverter main circuit 13 outputs the actual inverter sinusoidal current (e.g., based on the pulse width modulation signal) according to the pulse width modulation signal. Figure 3 The I_INV0 waveform in the diagram has a surge compensation waveform that is equal in magnitude and opposite in direction to the pulse surge current of the auxiliary power supply unit 21, which is actively superimposed on its sinusoidal fundamental waveform. When the actual inverter sinusoidal current with the superimposed surge compensation current flows through the grid access terminal 11, the superimposed surge compensation amount is the same as the pulse surge current extracted by the auxiliary power supply unit 21 when it obtains power online (such as the pulse surge current extracted by the auxiliary power supply unit 21 when it obtains power online). Figure 3 The I_AUX waveforms in the signal cancel each other out spatially, thus the grid-connected output current flowing into the external power grid 3 forms a smooth, harmonic-free standard sinusoidal current signal (such as...). Figure 3 The I_INV waveform in the diagram solves the problem of THDI degradation caused by auxiliary power supply in non-isolated systems.

[0066] Through the grid-connected control circuit 20 described above, this embodiment eliminates the need for complex information such as the phase and amplitude of the auxiliary power supply surge current to be sampled at high frequency in the software control strategy as a software compensation quantity, which is required in related technologies. The acquisition of the distortion signal can be completed in the hardware circuit without adding a complex software control algorithm, which simplifies the system control logic and improves the real-time response and operational reliability of the compensation control.

[0067] Based on the same concept, this application embodiment, in addition to providing the above-described grid-connected system 1 and grid-connected control circuit 20, also provides a corresponding grid-connected control method applied to the grid-connected control circuit 20, especially the control unit 24 therein. The following is in conjunction with... Figure 4 The specific process of this control method will be described in detail.

[0068] like Figure 4 As shown, this application also provides a grid connection control method, which includes steps S1 and S2. Wherein,

[0069] Step S1: Obtain the differential control signal. The differential control signal is determined by differential operation between the main current sampling signal and the surge sampling signal.

[0070] Step S2: Adjust the grid-connected output current based on the differential control signal so that the grid-connected output current is superimposed with the surge compensation current corresponding to the system surge.

[0071] This grid connection control method is applied to the above. Figures 2 to 3 The grid-connected control circuit 20 is shown. Combined with... Figures 2 to 4 As shown, during the closed-loop operation of the system, the control unit 24 reads the differential control signal I_INV output by the differential operation unit 23 in real time through the built-in analog-to-digital conversion interface. This differential control signal I_INV has undergone real-time subtraction of the main current sampling signal I_INV0 and the surge sampling signal I_AUX at the front end, thus carrying reverse surge characteristics. The control unit 24 uses this signal, which incorporates surge characteristics, to participate in control calculations, thereby controlling the inverter main circuit 13 to actively inject a dynamic compensation amount into the grid-connected current with the opposite direction and equivalent amplitude to the power pulse drawn from the auxiliary power supply unit 21 while outputting the main current. By executing the differential control signal determined by the differential operation of the main current sampling signal and the surge sampling signal, and adjusting the grid-connected output current based on this signal to superimpose the surge compensation current corresponding to the system surge, the circuit signal cancellation concept of the grid-connected control circuit 20 is transformed into corresponding control commands, enabling the system to actively suppress the power distortion caused by the auxiliary power supply in the control flow, thereby solving the THDI degradation problem caused by the auxiliary power supply in non-isolated systems.

[0072] In some embodiments, step S2, adjusting the grid-connected output current based on the differential control signal, includes: obtaining a grid-connected current reference value; subtracting the grid-connected current reference value from the differential control signal to obtain a current error value; adjusting the current error value; generating a pulse width modulation signal; and, after setting the grid-connected task, outputting a sinusoidal current actual value superimposed with surge compensation current based on the pulse width modulation signal, so that the surge compensation current superimposed on the sinusoidal current actual value cancels out the surge current obtained by the system, thus forming a standard sinusoidal grid-connected output current. Specifically, in conjunction with... Figures 2 to 3 As shown, the control unit 24 uses the grid-connected current reference value Igrid_ref calculated by the previous stage as the tracking target, and performs a digital subtraction operation with the sampled differential control signal I_INV to determine the real-time current deviation. Subsequently, the control unit 24 sends the deviation to the proportional-integral (PI) controller for feedforward filtering and dynamic adjustment, calculates the PWM duty cycle required for the full-bridge switches Q1-Q4 in the main inverter circuit 13, and outputs the corresponding pulse width modulation signal. When the system is in grid-connected operation, the main inverter circuit 13 outputs a sine wave pre-mixed with surge compensation components under the drive of the PWM signal. After the waveform is obtained by the uncontrolled rectification of the auxiliary power supply at the grid connection terminal 11, the residual current forms a pure standard sine wave. By sequentially executing the closed-loop control of target reference value acquisition, error calculation, digital adjustment, and PWM drive generation, the drive pulse output by the control unit 24 can counteract or cancel pulse surges. This closed-loop control strategy eliminates the THDI degradation problem caused by auxiliary power supply, and enhances the steady-state response performance and waveform quality of the system during grid voltage fluctuations and load switching.

[0073] In some embodiments, obtaining a grid-connected current reference value includes: obtaining a target current RMS value, converting the target current RMS value into a target peak value, and performing synchronous calculations with the target peak value and phase angle information output based on a phase-locked loop algorithm to determine the grid-connected current reference value. Specifically, in conjunction with... Figures 2 to 3 As shown, the control unit 24 first obtains the target current RMS value Irms_Ref according to the power command, and then multiplies it by the amplitude coefficient. The target peak current Ipeak_Ref is calculated. Simultaneously, the control unit 24 runs a software phase-locked loop (SPLL) algorithm to track the voltage phase of the external power grid 3 in real time, outputting the real-time phase angle cosine value Cos(Angle PLL) of the grid voltage. Finally, the control unit 24 performs a multiplication dot product operation on the target peak current Ipeak_Ref and the phase angle cosine value Cos(Angle PLL) to generate a sinusoidal grid-connected current reference value Igrid_ref that is strictly in phase and frequency synchronized with the grid voltage. By converting the target effective value into a peak value and combining it with the real-time phase output of the PLL for phase angle synchronization calculation, the generated current control reference has high phase and frequency tracking accuracy, enabling the system to maintain a high power factor while eliminating surge distortion, further ensuring the quality and stability of the power flowing into the grid.

[0074] In the description of this specification, references to terms such as "some embodiments," "other embodiments," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of this application. In this specification, the illustrative descriptions of the above terms do not necessarily refer to the same embodiments or examples.

[0075] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0076] The embodiments described above illustrate several implementation methods of this application, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of this application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, all of which fall within the protection scope of this application. Therefore, the protection scope of this application should be determined by the appended claims.

Claims

1. A grid-connected control circuit, applied to a grid-connected system, the grid-connected system comprising a grid access terminal and an inverter main circuit connected to the grid access terminal, characterized in that, The grid-connected control circuit includes: An auxiliary power supply unit is connected to the power grid access terminal to obtain electrical energy, and includes a pre-charging component; A surge sampling unit is connected to both ends of the precharge component and is used to acquire surge sampling signals from both ends of the precharge component. A differential operation unit, connected to the surge sampling unit and the inverter main circuit, is used to receive the main current sampling signal of the inverter main circuit, and perform differential operation on the main current sampling signal and the surge sampling signal to output a differential control signal; and, The control unit, connected to the differential arithmetic unit and the inverter main circuit, is used to control the inverter main circuit based on the differential control signal to adjust the grid-connected output current, so that a surge compensation current is superimposed on the grid-connected output current, and the surge compensation current corresponds to the electrical energy obtained by the auxiliary power supply unit.

2. The grid-connected control circuit according to claim 1, characterized in that, The control unit is also used to acquire a grid-connected current reference value, subtract the grid-connected current reference value from the differential control signal to obtain a current error value, and adjust the current error value to generate a pulse width modulation signal for driving the inverter main circuit.

3. The grid-connected control circuit according to claim 2, characterized in that, After the grid-connected system is set to perform a grid-connected task, the control unit is also used to control the inverter main circuit through the pulse width modulation signal, so that the inverter main circuit outputs the actual value of a sinusoidal current superimposed with the surge compensation current based on the pulse width modulation signal. The actual value of the sinusoidal current is then powered by the auxiliary power supply unit and output as a standard sinusoidal current signal at the grid connection terminal.

4. The grid-connected control circuit according to claim 1, characterized in that, The differential operation unit is used to subtract the voltage signal corresponding to the main current sampling signal output by the inverter main circuit from the voltage signal corresponding to the surge sampling signal output by the surge sampling unit to generate the differential control signal, and output it to the control unit.

5. The grid-connected control circuit according to claim 1 or 4, characterized in that, The differential operation unit includes an operational amplifier; the non-inverting input and the inverting input of the operational amplifier respectively receive the voltage signal corresponding to the main current sampling signal and the voltage signal corresponding to the surge sampling signal; the output of the operational amplifier is connected to the control unit, and the operational amplifier is used to generate and output the differential control signal based on the voltage signal corresponding to the main current sampling signal and the voltage signal corresponding to the surge sampling signal.

6. The grid-connected control circuit according to claim 1, characterized in that, The surge sampling unit includes a sampling amplifier. The two detection terminals of the sampling amplifier are respectively connected to the two ends of the pre-charge component and are used to collect the voltage drop generated by the current flowing through the pre-charge component, and amplify the voltage drop to generate the voltage signal corresponding to the surge sampling signal.

7. The grid-connected control circuit according to claim 1, characterized in that, The pre-charge component includes a pre-charge resistor; the auxiliary power supply unit includes a rectifier component, and the pre-charge resistor is connected in series between the grid access terminal and the rectifier component; the surge sampling unit is used to acquire the voltage formed on the pre-charge resistor by the pulse surge current generated by the rectifier component, as the surge sampling signal.

8. The grid-connected control circuit according to claim 1, characterized in that, The grid-connected control circuit further includes an inverter current sampling circuit, which is used to collect the current of the inverter main circuit so as to output the main current sampling signal to the differential operation unit.

9. A grid-connected control method, characterized in that, The grid-connected control circuit applied to any one of claims 1 to 8, the grid-connected control method comprising: A differential control signal is acquired, which is determined by differential operation between the main current sampling signal and the surge sampling signal; and, The grid-connected output current is adjusted based on the differential control signal, so that the grid-connected output current is superimposed with the surge compensation current corresponding to the system surge.

10. The grid-connected control method according to claim 9, characterized in that, The adjustment of the grid-connected output current based on the differential control signal includes: Obtain the grid-connected current reference value; The current error value is obtained by subtracting the grid-connected current reference value from the differential control signal. The current error value is adjusted to generate a pulse width modulation signal; After setting the grid connection task, the actual value of the sinusoidal current, which is superimposed on the surge compensation current, is output based on the pulse width modulation signal. This is so that the surge compensation current superimposed on the actual value of the sinusoidal current cancels out the surge current obtained by the system, thus forming a standard sinusoidal grid-connected output current.

11. The grid-connected control method according to claim 10, characterized in that, The acquisition of the grid-connected current reference value includes: Obtain the effective value of the target current and convert the effective value of the target current into the target peak value; The target peak value is synchronously calculated with the phase angle information output by the phase-locked loop algorithm to determine the grid-connected current reference value.

12. A grid-connected system, characterized in that, include: Grid connection end; The grid-connected switch assembly is connected to the grid access terminal; The inverter main circuit is connected to the grid access terminal through the grid-connected switch assembly; as well as, The grid-connected control circuit as described in any one of claims 1 to 8 is connected to both the grid access terminal and the inverter main circuit; wherein, The grid-connected system is a non-isolated grid-connected inverter system; when the inverter main circuit is in grid-connected operation, the auxiliary power supply unit in the grid-connected control circuit obtains power through the grid access terminal.

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