A photovoltaic inverter circuit with both anti-current direct filling and soft start functions

Abstract

The present application belongs to the field of photovoltaic power generation power electronic conversion technology, and discloses a photovoltaic inverter circuit with the functions of preventing direct current filling and soft starting, which comprises a photovoltaic input terminal, a Boost voltage boosting unit, a BUS bus, a bus filter capacitor, and is further provided with a direct filling prevention soft starting branch and a controller connected in parallel between the cathode of the Boost freewheeling diode and the BUS bus; the branch comprises a single-pole relay RY1 and a soft starting switch tube Q1 connected in parallel. The controller collects the photovoltaic input voltage and the BUS bus voltage, and performs differential pressure segmented control: when the differential pressure is greater than the set threshold, RY1 is turned off, Q1 is turned on for current limiting soft starting, and the current is blocked from directly filling through the diode without control; when the differential pressure is less than the set threshold, RY1 is closed, and Q1 is turned off, and the current is supplied through the relay to reduce the loss. The present application integrates double functions, has few components and low cost, takes into account power-on safety and efficient operation, and is suitable for wide voltage input scenes.

Description

Technical Field

[0001] This invention belongs to the field of photovoltaic power generation power electronic conversion technology, and more specifically, it relates to a photovoltaic inverter circuit that has both anti-current direct injection and soft start functions. Background Technology

[0002] In photovoltaic (PV) power generation systems, the Boost converter circuit is the core topology for connecting the PV side to the DC bus and realizing voltage conversion and energy transmission. It is widely used in various inverter products, including off-grid, grid-connected, and integrated PV-storage systems. For models that support a wide range of PV input, especially off-grid PV systems that are compatible with 24V low-voltage battery input, have a nominal bus voltage of up to 396V after push-pull boost and transformer isolation, and a PV input range covering 100V to 450V, the traditional Boost circuit has an inherent design flaw: the cathode of the freewheeling diode in the Boost unit is directly connected to the DC bus. When the PV input voltage is higher than the bus voltage, even if the controller does not output a drive signal for the Boost switch, the PV current can still flow uncontrolled into the bus through the freewheeling diode, forming an uncontrolled conduction path. This defect poses serious risks under multiple operating conditions: During the power-on pre-charging phase, the bus is in a low-voltage state, and the instantaneous connection of the photovoltaic high voltage will generate a large current surge far exceeding the rated withstand value of the devices, which can easily lead to overcurrent damage or even failure of components such as switching transistors and diodes; During the low-voltage pre-charging phase of the bus, due to the lack of current limiting control, the uncontrollable pre-charging current will cause the bus voltage to overshoot, affecting the startup stability of the subsequent circuits; During the inverter's load operation phase, if there are sudden loads on the battery or bus voltage drops, the voltage difference exceeding the limit will cause the photovoltaic direct-feed current to be superimposed on the load current, causing the system operating power to exceed the design limit, and at the same time, it will disrupt the power distribution logic of photovoltaic charging and load operation, resulting in functional abnormalities. Existing solutions typically employ separate anti-reverse current control circuits and pre-charge soft-start circuits to address the two types of problems. This not only increases the number of components such as relays, power resistors, and dedicated control chips, raising hardware costs and board space requirements, but also presents issues such as relay arcing during path switching after pre-charging and additional losses due to the continuous conduction of the soft-start element. It is difficult to simultaneously meet the requirements of power-on safety, operating efficiency, and wide voltage compatibility. Therefore, there is an urgent need for an integrated, low-loss circuit solution that can simultaneously solve the two major technical challenges of direct current control and soft-start pre-charging.

[0003] Therefore, the present invention provides a photovoltaic inverter circuit that combines protection against direct current injection and soft start function. Summary of the Invention

[0004] In view of the above-mentioned problems of the existing technology, the purpose of the present invention is to provide a photovoltaic inverter circuit that combines the functions of preventing direct current injection and soft start. It integrates the functions of preventing direct current injection and soft start, and the differential voltage segmented control takes into account both power-on safety and low loss. It is compatible with wide voltage input and improves system reliability.

[0005] The objective of this invention can be achieved through the following technical solutions: A photovoltaic inverter circuit with both anti-current direct-suction and soft-start functions includes photovoltaic input terminals PV+ and PV-, a boost unit, a BUS bus, and a bus filter capacitor EC1. The boost unit includes an energy storage inductor L1, a freewheeling diode D1, and a boost switching transistor Q2. The photovoltaic input terminal PV+ is connected to the anode of D1 via L1, and the cathode of D1 is connected to the BUS bus. The photovoltaic input terminal PV- is connected to the BUS reference ground. EC1 is connected in parallel between the BUS bus and the BUS reference ground. The photovoltaic inverter circuit also includes a direct-current-injection soft-start branch and a controller. The direct-current-injection soft-start branch is connected in parallel between the D1 cathode and the BUS bus. The direct-current-injection soft-start branch includes a single-pole relay RY1 and a soft-start switch Q1 connected in parallel. The controller collects the photovoltaic input voltage and the BUS bus voltage, and configures differential voltage segmented control logic: when the difference between the photovoltaic input voltage and the BUS bus voltage is greater than a set threshold, the RY1 contact is opened, the output drive signal is turned on to Q1, and the soft start pre-charging is achieved by limiting the current through Q1 to block the photovoltaic current from directly feeding the bus through D1; when the difference between the photovoltaic input voltage and the BUS bus voltage is less than a set threshold, the RY1 contact is closed and Q1 is turned off, and the current supplies power to the BUS bus through the RY1 contact.

[0006] As a further preferred technical solution of the present invention, the two ends of the switching contact of the single-pole relay RY1 are respectively connected to the cathode of D1 and the BUS bus, the drain of the soft starter switch Q1 is connected to the cathode of D1, the source of Q1 is connected to the BUS bus, and the RY1 contact and Q1 form a parallel dual power supply path.

[0007] As a further preferred technical solution of the present invention, the Boost switch Q2 is configured with a gate drive circuit and a drain-source RC snubber circuit. The gate drive circuit includes a current-limiting resistor R5, a pull-down resistor R6, and a filter capacitor C6. The RC snubber circuit consists of a resistor R2 and a capacitor C4 connected in series and then in parallel across the drain and source of Q2.

[0008] As a further preferred technical solution of the present invention, the photovoltaic inverter circuit also includes a BUS current sampling chip U1, which is connected in series in the BUS bus circuit. The current sampling signal output terminal of U1 is electrically connected to the controller, and the controller adjusts the duty cycle of the Q1 drive signal according to the bus current fed back by U1.

[0009] As a further preferred technical solution of the present invention, the electromagnetic coil of the single-pole relay RY1 is connected to the output terminal of the controller, and the coil is switched on and off by the output level of the controller to switch the contact opening and closing state. The model of the single-pole relay RY1 is 832A-1C-FC.

[0010] As a further preferred technical solution of the present invention, the Q1 drive signal output by the controller is connected to the gate of Q1 through the current limiting resistor R3, and the resistor R8 and the capacitor C1 are connected in parallel across the gate and source of Q1 to form a gate RC debouncing filter circuit.

[0011] As a further preferred technical solution of the present invention, when the photovoltaic input voltage is higher than the BUS bus voltage and the voltage difference between the two is greater than a set threshold, the controller keeps RY1 in the off state and forms a current-limiting charging path only through the conducting Q1 to suppress the power-on impact caused by the photovoltaic high current direct charging to the bus.

[0012] As a further preferred technical solution of the present invention, when the difference between the photovoltaic input voltage and the BUS bus voltage is reduced to less than a set threshold, the controller first closes the RY1 contact and then cuts off the Q1 drive signal, so that all the charging current flows through the RY1 contact to reduce conduction loss.

[0013] As a further preferred technical solution of the present invention, when the circuit is in any of the following operating conditions: photovoltaic high-power input, bus low-voltage pre-charging, and inverter load operation, the controller continuously executes the differential pressure judgment logic. If the differential pressure between the photovoltaic and the bus exceeds the set threshold, the working state of RY1 disconnected and Q1 current-limiting soft start is maintained.

[0014] A photovoltaic inverter includes a battery-side boost unit and an inverter power unit. With the aforementioned photovoltaic inverter circuit that combines protection against direct current injection and soft start function, the photovoltaic input is connected to the BUS bus via the photovoltaic inverter circuit, and the BUS bus power is output as AC power through the inverter power unit.

[0015] As described above, the photovoltaic inverter circuit provided by the present invention, which combines protection against direct current injection and soft-start function, has the following beneficial effects: 1. The present invention utilizes the above-mentioned photovoltaic inverter circuit that combines anti-current direct charging and soft-start functions. Compared with the prior art, by connecting an anti-current direct charging soft-start branch composed of a single-pole relay and a soft-start switch in parallel between the Boost freewheeling diode and the BUS bus, only two additional components are needed to simultaneously achieve the two functions of anti-current direct charging and soft-start pre-charging. There is no need to set up separate anti-reverse charging circuits and pre-charging circuits, which reduces the number of components and the space occupied by the circuit board, and lowers the hardware cost.

[0016] 2. This invention utilizes a photovoltaic inverter circuit that combines anti-current direct injection and soft-start functions. Compared with existing technologies, the controller executes segmented logic based on the real-time voltage difference between the photovoltaic input voltage and the BUS bus voltage: when the voltage difference is greater than a set threshold, the relay is disconnected and the soft-start switch is turned on with current limiting. This not only blocks the uncontrolled direct injection path of photovoltaic current through the freewheeling diode, but also avoids overcurrent damage to devices caused by the large current surge at power-on. When the voltage difference is less than the set threshold, the relay is closed first and then the soft-start switch is turned off. When the relay contacts are closed, the voltage difference is extremely small and there is no risk of arcing. All subsequent current is conducted through the relay, eliminating the conduction loss of the switch being continuously turned on and improving the overall efficiency.

[0017] 3. This invention utilizes a photovoltaic inverter circuit that combines anti-current direct injection and soft-start functions. Compared with existing technologies, it continuously executes differential voltage judgment logic under all operating conditions, including high-power photovoltaic input, low-voltage bus pre-charging, and inverter operation under load. Once a differential voltage exceeding the limit is detected, it immediately switches to soft-start current limiting mode. This solves the problem that traditional Boost circuits cannot control direct injection current when the photovoltaic voltage is higher than the bus voltage, avoiding risks such as over-power operation and generator failure, and is suitable for a wide range of photovoltaic input voltage scenarios.

[0018] 4. The present invention utilizes a photovoltaic inverter circuit that combines anti-current direct injection and soft-start functions. Compared with the prior art, it achieves precise closed-loop control of the pre-charge current by using a BUS current sampling chip to provide real-time feedback of the bus current and dynamically adjusting the drive duty cycle of the soft-start switch transistor by the controller. This avoids bus voltage overshoot caused by excessive current fluctuations during the pre-charge process and improves the stability of system power-on and operating condition switching.

[0019] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the 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.

[0021] Figure 1 This is a schematic diagram of the circuit structure of a photovoltaic inverter circuit that combines protection against direct current injection and soft start function, as per this invention application. Detailed Implementation

[0022] The following specific embodiments illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification.

[0023] It should be understood that the structures, proportions, sizes, etc., depicted in the accompanying drawings of this specification are merely for illustrative purposes to aid those skilled in the art and are not intended to limit the scope of the invention. Therefore, they have no substantial technical significance. Any modifications to the structure, changes in proportions, or adjustments to size, without affecting the effectiveness and purpose of the invention, should still fall within the scope of the technical content disclosed in this invention. Furthermore, the terms such as "upper," "lower," "left," "right," "middle," and "one" used in this specification are merely for clarity and are not intended to limit the scope of the invention. Changes or adjustments to their relative relationships, without substantially altering the technical content, should also be considered within the scope of the invention. Specific structures can be described with reference to the accompanying drawings of the patent application.

[0024] The circuit in this embodiment is applicable to off-grid photovoltaic inverter systems with a 24V battery input: the battery side is boosted via push-pull and transformer isolation before being connected to the high-voltage bus of the BUS; the photovoltaic side is connected to the same BUS bus via a Boost circuit. The nominal voltage of the BUS bus is 396V, and the photovoltaic input voltage range is 100V to 450V. The system can operate in three conditions: ① photovoltaic power supply pre-charging bus operation; ② photovoltaic + battery joint load operation; ③ photovoltaic simultaneous load and battery charging operation.

[0025] like Figure 1 As shown, the photovoltaic inverter circuit disclosed in this embodiment includes: photovoltaic input terminals PV+, PV-, Boost boost unit, BUS bus, bus filter capacitor EC1, anti-direct-charge soft start branch, and controller.

[0026] The Boost converter unit uses a conventional topology: the energy storage inductor L1 is connected in series between PV+ and the anode of the freewheeling diode D1, the cathode of D1 is connected to the positive terminal of the BUS bus, the drain of the Boost switch Q2 is connected to the anode of D1 and the source is connected to the BUS reference ground, and PV- is directly connected to the BUS reference ground; the bus filter capacitor EC1 is connected in parallel between the positive and negative terminals of the BUS bus.

[0027] The anti-direct-current soft-start branch is connected in parallel between the D1 cathode and the BUS bus. It consists of a dual power supply path formed by the parallel single-pole relay RY1 and the soft-start switch Q1: the two ends of the switch contacts of RY1 are connected to the D1 cathode and the BUS bus respectively; Q1 is an N-channel MOSFET, with its drain connected to the D1 cathode and its source connected to the BUS bus.

[0028] The controller serves as the core of the control system. Its input terminals are connected to the photovoltaic input voltage sampling terminal, the BUS bus voltage sampling terminal, and the output terminal of the BUS current sampling chip U1, respectively. Its output terminals are connected to the RY1 electromagnetic coil, the Q1 gate drive circuit, and the Q2 gate drive circuit, respectively.

[0029] The gate drive circuit configuration of the Boost switch Q2 is as follows: the current-limiting resistor R5 is connected in series between the controller drive output and the gate of Q2, and the pull-down resistor R6 and the filter capacitor C6 are connected in parallel between the gate and the source of Q2 to suppress drive signal interference and provide a reliable turn-off circuit for Q2; the drain-source parallel RC snubber circuit is as follows: the resistor R2 and the capacitor C4 are connected in series and then in parallel across the drain and source of Q2 to absorb voltage spikes during the switching process of Q2 and reduce EMI interference.

[0030] The Q1 drive signal output by the controller is connected to the gate of Q1 through the current limiting resistor R3. The resistor R8 and the capacitor C1 are connected in parallel between the gate and the source of Q1 to form a gate RC debouncing filter circuit to prevent Q1 from being falsely triggered by interference.

[0031] The single-pole relay RY1 is model 832A-1C-FC. Its electromagnetic coil is connected to the output terminal of the controller. The controller's level signal controls the coil's on / off state, switching the contact opening and closing state. This model of relay has a rated current carrying capacity that meets the system's maximum operating current requirements, and the contact resistance is less than 10mΩ, which can effectively reduce conduction losses.

[0032] The BUS current sampling chip U1 is connected in series in the positive circuit of the BUS bus to collect the bus current in real time and feed it back to the controller, forming a pre-charge current closed-loop control loop.

[0033] The controller has built-in differential pressure segmented control logic, which uses the difference between the photovoltaic input voltage Vpv and the BUS bus voltage Vbus as the judgment basis. The first threshold ΔV1=20V and the second threshold ΔV2=5V are set, and differential pressure detection is continuously performed under all operating conditions. The specific workflow is as follows: Phase 1 – Power-on Pre-charge / Differential Voltage Exceedance Phase: Vpv-Vbus>ΔV1=20V When the system is first connected to the photovoltaic system, the BUS bus is in a low-voltage state, or the battery voltage drops during operation under load, causing Vbus to be low, if Vpv is detected to be more than 20V higher than Vbus, the controller will execute the following steps: ① Keep the RY1 electromagnetic coil de-energized, the contacts open, and cut off the relay's direct path; ② Turn off the drive signal of Boost switch Q2 to prevent Boost circuit from malfunctioning; ③ Output PWM drive signal to turn on Q1. By adjusting the PWM duty cycle, control the on-resistance of Q1 so that the photovoltaic current is limited and pre-charged through the paths of L1, D1, Q1 and BUS bus in sequence.

[0034] At this time, since RY1 is disconnected, the photovoltaic current cannot be directly and uncontrolled into the BUS bus through D1, completely blocking the direct injection path; at the same time, the controller dynamically adjusts the duty cycle of Q1 drive according to the bus current fed back by U1, limiting the pre-charge current to a safe range, for example: setting the maximum pre-charge current to 30% of the rated current to avoid bus voltage overshoot and device overcurrent.

[0035] This stage is suitable for a wide range of photovoltaic high-voltage input scenarios. Even if Vpv reaches the upper limit of 450V and Vbus is only 300V, it can avoid large current surges through Q1 current limiting, thus solving the problem of "uncontrollable current when photovoltaic voltage is higher than bus voltage" in traditional Boost circuits.

[0036] Phase 2 – Threshold Switching Phase: ΔV2 = 5V ≤ Vpv - Vbus ≤ ΔV1 = 20V As pre-charging proceeds, Vbus gradually increases. When the voltage difference between the two voltages narrows to the 5V to 20V range, the controller maintains the current-limited conduction state of Q1 and continues to raise the bus voltage with a small current until the voltage difference is less than 5V, at which point the switching process begins. ① First, output a high level to drive the RY1 electromagnetic coil and close the RY1 contact: At this time, the voltage difference across the contact is less than 5V, and no arcing will occur at the moment of closing, thus extending the service life of the relay; ② After a 10ms delay to confirm that the contacts are fully engaged, stop outputting the drive signal for Q1 and turn off Q1.

[0037] After the switch is completed, all photovoltaic current flows through the RY1 contact to supply power to the BUS bus, Q1 is turned off with zero current and there is no additional conduction loss.

[0038] Phase 3: Normal operation phase: Vpv - Vbus < ΔV2 = 5V When the voltage difference between the two stabilizes within 5V, the controller maintains the state of RY1 contact closed and Q1 closed. At this time: If the system is in photovoltaic stand-alone power supply mode: the controller normally outputs the drive signal of the Boost switch Q2, the Boost circuit starts to boost the voltage, the photovoltaic energy is regulated by the Boost and then supplied to the BUS bus. The relay contacts carry the bus current and the loss is extremely low. If the system is in load operation mode: the power energy of the BUS bus is converted into AC power by the inverter power unit and output to the outside. The excess photovoltaic power can flow back to the battery side through the Boost circuit to charge the battery. There is no risk of direct charging throughout the process. If the differential pressure exceeds 20V again during operation, for example, if the battery suddenly increases its load and causes Vbus to drop, the controller will immediately disconnect RY1 and turn on Q1, switching back to the current-limiting soft-start mode to achieve dynamic protection under all operating conditions.

[0039] In this embodiment, an N-channel MOSFET is selected as the soft start switch. In other embodiments, IGBTs or other fully controlled switching devices can also be used. The differential voltage threshold can be adjusted according to the actual voltage level of the system. For example, in a high-voltage grid-connected system, the first threshold can be set to 50V and the second threshold can be set to 10V. The relay can also be replaced by a combination topology of electronic switch and mechanical switch, all of which are within the protection scope of this invention.

[0040] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

Claims

1. A photovoltaic inverter circuit with both anti-current direct-current and soft-start functions, comprising photovoltaic input terminals PV+ and PV-, a Boost converter, a BUS bus, and a bus filter capacitor EC1, wherein the Boost converter includes an energy storage inductor L1, a freewheeling diode D1, and a Boost switch Q2; the photovoltaic input terminal PV+ is connected to the anode of D1 via L1, the cathode of D1 is connected to the BUS bus, the photovoltaic input terminal PV- is connected to the BUS reference ground, and EC1 is connected in parallel between the BUS bus and the BUS reference ground, characterized in that... It also includes a direct-injection soft-start branch and a controller. The direct-injection soft-start branch is set in parallel between the D1 cathode and the BUS bus. The direct-injection soft-start branch includes a single-pole relay RY1 and a soft-start switch Q1 connected in parallel. The controller collects the photovoltaic input voltage and the BUS bus voltage, and configures differential voltage segmented control logic: when the difference between the photovoltaic input voltage and the BUS bus voltage is greater than a set threshold, the RY1 contact is opened, the output drive signal is turned on to Q1, and the soft start pre-charging is achieved by limiting the current through Q1 to block the photovoltaic current from directly feeding the bus through D1; when the difference between the photovoltaic input voltage and the BUS bus voltage is less than a set threshold, the RY1 contact is closed and Q1 is turned off, and the current supplies power to the BUS bus through the RY1 contact.

2. A photovoltaic inverter circuit with both anti-current direct-current and soft-start functions as described in claim 1, characterized in that, The two ends of the switch contacts of the single-pole relay RY1 are connected to the cathode of D1 and the BUS bus respectively. The drain of the soft starter switch Q1 is connected to the cathode of D1, and the source of Q1 is connected to the BUS bus. The RY1 contacts and Q1 form a parallel dual power supply path.

3. A photovoltaic inverter circuit with both anti-direct current injection and soft-start functions as described in claim 1, characterized in that, The Boost switch Q2 is configured with a gate drive circuit and a drain-source RC snubber circuit. The gate drive circuit includes a current-limiting resistor R5, a pull-down resistor R6, and a filter capacitor C6. The RC snubber circuit consists of a resistor R2 and a capacitor C4 connected in series and then in parallel across the drain and source of Q2.

4. A photovoltaic inverter circuit with both anti-current direct-current and soft-start functions as described in claim 1, characterized in that, It also includes a BUS current sampling chip U1, which is connected in series in the BUS bus circuit. The current sampling signal output terminal of U1 is electrically connected to the controller, and the controller adjusts the duty cycle of the Q1 drive signal based on the bus current fed back by U1.

5. A photovoltaic inverter circuit with both anti-current direct-current and soft-start functions according to claim 2, characterized in that, The electromagnetic coil of the single-pole relay RY1 is connected to the output terminal of the controller. The controller output level controls the coil to switch the contact opening and closing state. The model of the single-pole relay RY1 is 832A-1C-FC.

6. A photovoltaic inverter circuit with both anti-current direct-current and soft-start functions as described in claim 1, characterized in that, The Q1 drive signal output by the controller is connected to the gate of Q1 through the current limiting resistor R3. The resistor R8 and the capacitor C1 are connected in parallel across the gate and source of Q1 to form a gate RC debouncing filter circuit.

7. A photovoltaic inverter circuit with both anti-current direct-feedback and soft-start functions as described in claim 1, characterized in that, When the photovoltaic input voltage is higher than the BUS bus voltage and the voltage difference between the two is greater than the set threshold, the controller keeps RY1 in the off state and forms a current-limiting charging path only through the conducting Q1 to suppress the power-on impact caused by the photovoltaic high current direct injection into the bus.

8. A photovoltaic inverter circuit with both anti-current direct-current and soft-start functions according to claim 1, characterized in that, When the difference between the photovoltaic input voltage and the BUS bus voltage narrows to less than the set threshold, the controller first closes the RY1 contact and then cuts off the Q1 drive signal, so that all the charging current flows through the RY1 contact to reduce conduction loss.

9. A photovoltaic inverter circuit with both anti-current direct-current and soft-start functions according to claim 1, characterized in that, When the circuit is in any of the following operating conditions: high power input of photovoltaic, low voltage pre-charging of bus, or inverter operation under load, the controller continuously executes the differential pressure judgment logic. If the differential pressure between photovoltaic and bus exceeds the set threshold, the controller maintains the working state of RY1 disconnected and Q1 current limiting soft start.

10. A photovoltaic inverter, characterized in that, It includes a battery-side boost unit, an inverter power unit, and a photovoltaic inverter circuit with both anti-current direct injection and soft-start functions as described in any one of claims 1 to 9; the photovoltaic input is connected to the BUS bus via the photovoltaic inverter circuit, and the BUS bus power is output as AC power through the inverter power unit.

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