Non-feedback network photovoltaic air conditioning system and control method thereof

Abstract

The invention discloses a non-feed network photovoltaic air conditioning system and a control method thereof.The non-feed network photovoltaic air conditioning system comprises an air conditioning unit, a photovoltaic controller used for supplying power to the air conditioning unit and an alternating current mains supply, and the alternating current mains supply is connected to a direct current bus through a power factor correction circuit; the photovoltaic controller is connected to a direct current bus through a first conversion module, and the first conversion module and the power factor correction circuit can construct bus voltage of the direct current bus. Compared with the prior art, the non-stop operation of the air conditioning unit can be realized under the photovoltaic condition when the alternating current mains supply is powered off, and meanwhile, the smooth transition from the off-grid state to the grid-connected state is realized when the alternating current mains supply is powered on.

Description

Technical Field

[0001] This invention relates to the field of photovoltaic air conditioning technology, and in particular to a non-grid photovoltaic air conditioning system and its control method. Background Technology

[0002] Photovoltaic air conditioning systems mainly include two types: photovoltaic direct-drive grid-connected power generation systems and photovoltaic direct-drive off-grid systems. In the former, photovoltaic power directly drives the air conditioner, with excess electricity fed into the grid in real time; in the latter, while the photovoltaic power drives the air conditioner, it cannot feed excess electricity back into the grid. In practical applications, users often expect the photovoltaic system to both drive the load and achieve photovoltaic optimization when the grid is normal, and to independently drive the indoor and outdoor units of the air conditioner solely through photovoltaic power generation during abnormal grid outages.

[0003] However, existing photovoltaic (PV) air conditioning system solutions cannot simultaneously meet the above requirements. Traditional grid-connected PV air conditioning systems typically trigger islanding protection and shut down when AC mains power fails, making independent off-grid operation impossible. Meanwhile, ordinary off-grid PV air conditioning systems lack a smooth switching mechanism when AC mains power is connected, easily leading to bus voltage fluctuations or even system shutdown. Furthermore, existing solutions usually require complex DC conversion or integrated converters within the air conditioning unit, resulting in long development cycles, high costs, and difficulty in directly adapting to commercially available ordinary air conditioning outdoor units.

[0004] Therefore, how to achieve stable operation and smooth switching of photovoltaic air conditioning systems under conditions of mains power and no mains power (off-grid) is a technical problem that the industry urgently needs to solve. Summary of the Invention

[0005] In response to the problem that photovoltaic air conditioning systems are prone to abnormal shutdown when the power grid fails, this invention proposes a non-grid-fed photovoltaic air conditioning system and its control method.

[0006] The technical solution of the present invention is to propose a non-grid photovoltaic air conditioning system, including an air conditioning unit, a photovoltaic controller for supplying power to the air conditioning unit, and AC mains power. The AC mains power is connected to a DC bus through a power factor correction circuit, and the photovoltaic controller is connected to the DC bus through a first conversion module. Both the first conversion module and the power factor correction circuit can construct the bus voltage of the DC bus.

[0007] Furthermore, the photovoltaic controller is externally mounted on the air conditioning unit, and the photovoltaic controller is connected to the air conditioning unit via a DC port.

[0008] Furthermore, the first conversion module includes at least a power switch, an inductor and a diode connected to the source of the power switch, the inductor and the diode being used to construct the bus voltage of the DC bus.

[0009] Furthermore, the off-grid photovoltaic air conditioning system also includes an AC voltage sampling circuit for detecting whether the AC mains power is on;

[0010] The off-grid photovoltaic air conditioning system switches the bus voltage of the DC bus to be constructed by the first conversion module or the power factor correction circuit based on the detection results of the AC voltage sampling circuit.

[0011] This invention also proposes a control method for a non-grid photovoltaic air conditioning system, comprising:

[0012] When an off-grid state is detected where the AC mains power is lost, the photovoltaic controller is controlled to operate in a voltage stabilization mode to build up the bus voltage of the DC bus to drive the air conditioning unit to operate.

[0013] When AC mains power is detected, the photovoltaic controller is controlled to maintain the off-grid operation until the preset grid connection switching conditions are met;

[0014] When the grid connection switching conditions are met, the photovoltaic controller is controlled to exit the voltage regulation mode, and a control signal is sent to trigger the air conditioning unit to activate the power factor correction circuit to construct the bus voltage of the DC bus.

[0015] Furthermore, the grid connection switching condition is: from the moment the AC mains power is detected to be connected, the AC mains power is continuously connected for a preset duration;

[0016] The preset duration is set to a length of time sufficient to confirm that the AC mains power is stable.

[0017] Furthermore, it also includes: when the AC mains power is powered on and in grid-connected state, the AC mains power constructs the bus voltage of the DC bus through the power factor correction circuit;

[0018] When an AC mains power failure is detected, the system switches to off-grid mode powered by the photovoltaic controller and constructs the DC bus voltage through the first conversion module.

[0019] Furthermore, the photovoltaic controller may have at least two photovoltaic modules. In the off-grid state where the AC mains power is detected to be out of power, the photovoltaic controller is controlled to operate in a voltage regulation mode, including: controlling the photovoltaic control loop corresponding to one photovoltaic module to operate in the voltage regulation mode to build and maintain the bus voltage of the DC bus, and controlling the photovoltaic control loops corresponding to the remaining photovoltaic modules to operate in maximum power point tracking mode.

[0020] Furthermore, when the AC mains power is on and the system is in grid-connected state, the control actions of the photovoltaic controller include: if the output power of the photovoltaic modules in the photovoltaic controller is sufficient, then controlling the photovoltaic controller to provide only the energy required by the air conditioning unit;

[0021] If the output power of the photovoltaic modules in the photovoltaic controller is insufficient, the photovoltaic controller is controlled to output maximum power, and the AC mains power and the photovoltaic controller together provide energy for the air conditioning unit.

[0022] Furthermore, the specific method for detecting AC mains power failure is as follows: the effective value of the voltage at the mains terminal is detected by an AC voltage sampling circuit, and when the effective voltage value is lower than a set value, it is determined that the AC mains power has failed.

[0023] Compared with the prior art, the present invention has at least the following beneficial effects:

[0024] In this invention, both the photovoltaic controller and the AC mains power can construct the DC bus voltage. By establishing specific control logic among the photovoltaic controller, AC mains power, and air conditioner, intelligent switching and stable operation of the off-grid photovoltaic air conditioning system in off-grid and grid-connected states are achieved. In off-grid state, the photovoltaic controller actively operates in voltage stabilization mode, establishing and maintaining the DC bus voltage, ensuring the startup and operation capability of the off-grid air conditioning system under conditions of no AC mains power and only photovoltaic power, solving the problem that traditional photovoltaic air conditioning systems cannot work without AC mains power. Simultaneously, when the AC mains power is restored, a strategy of maintaining the off-grid logic for a period of time before transferring control is adopted, effectively avoiding repeated switching and oscillations between on-grid and off-grid due to grid voltage fluctuations, achieving a smooth transition from off-grid to grid-connected, and ensuring uninterrupted operation of the air conditioning unit. Furthermore, this invention utilizes the power factor correction circuit built into the air conditioning unit to take over bus control, eliminating the need for internal hardware modifications to the air conditioning unit. Direct photovoltaic drive can be achieved solely through an external photovoltaic controller, greatly reducing the cost and development difficulty of the off-grid air conditioning system and improving the utilization rate of photovoltaic energy. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of the present invention, 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.

[0026] Figure 1 This is a schematic diagram of the overall structure of a grid-connected photovoltaic air conditioning system in the prior art;

[0027] Figure 2This is a schematic diagram of the overall structure of the non-grid photovoltaic air conditioning system in this invention;

[0028] Figure 3 This is a schematic diagram of the overall structure of the first conversion module in this invention;

[0029] Figure 4 This is a schematic diagram of the overall structure of the second conversion module in this invention;

[0030] Figure 5 This is a schematic diagram of the overall structure of the AC voltage sampling circuit in this invention;

[0031] Figure 6 This is a flowchart illustrating the control method of the non-grid photovoltaic air conditioning system in this invention. Detailed Implementation

[0032] To make the technical problems to be solved, the technical solutions, and the beneficial effects of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present invention and are not intended to limit the present invention.

[0033] Therefore, a feature pointed out in this specification is used to describe one feature of one embodiment of the invention, and does not imply that every embodiment of the invention must have the described feature. Furthermore, it should be noted that this specification describes many features. Although certain features may be combined to illustrate possible system designs, these features may also be used in other combinations not explicitly stated. Therefore, unless otherwise stated, the described combinations are not intended to be limiting.

[0034] The principles and structure of the present invention will be described in detail below with reference to the accompanying drawings and embodiments.

[0035] Traditional grid-connected photovoltaic air conditioning systems typically trigger islanding protection and shut down when AC mains power fails, making them unable to operate independently off-grid. Off-grid photovoltaic air conditioning systems, on the other hand, lack a smooth switching mechanism when AC mains power is connected, which can easily lead to bus voltage fluctuations or even system shutdown.

[0036] To address the above problems, this invention proposes a non-grid photovoltaic air conditioning system, which includes an air conditioning unit, a photovoltaic controller for supplying power to the air conditioning unit, and AC mains power.

[0037] The AC mains power is connected to the DC bus through a power factor correction circuit, and the photovoltaic controller is connected to the DC bus through a first conversion module. Both the first conversion module and the power factor correction circuit can construct the bus voltage of the DC bus.

[0038] like Figure 2 As shown, the photovoltaic controller (i.e., the attached) in this invention Figure 2 The photovoltaic DC / DC controller in the middle has multiple photovoltaic modules (each with attached) Figure 2 The photovoltaic module includes PV+ and PV-, a DC filter module connected to the photovoltaic module, and a first conversion module (i.e., an auxiliary module) connected to the DC filter module. Figure 2 (In the DC / DC converter), the first conversion module is connected to the DC bus;

[0039] The AC mains power is the AC input section connected to the AC EMI filter module, which passes through a power factor correction circuit (i.e., attached). Figure 2 The PFC circuit in the circuit is then connected to the DC bus;

[0040] This invention is configured so that both the first conversion module and the power factor correction circuit can independently construct the DC bus voltage. In this way, even in off-grid mode (i.e., when the AC mains power is off), the photovoltaic controller can still construct the DC bus voltage, thereby ensuring the stable operation of the air conditioning unit. At the same time, when switching to grid-connected mode (i.e., when the AC mains power is connected), this invention can maintain the off-grid logic for a period of time before handing over the construction of the DC bus voltage to the power factor correction circuit, thus achieving a smooth transition from off-grid to grid-connected mode and ensuring the uninterrupted operation of the air conditioning unit.

[0041] Please see Figure 1 Existing grid-connected photovoltaic air conditioning systems integrate the entire photovoltaic controller into the air conditioning unit, which requires adjustments to the internal space and wiring layout of the air conditioning unit, as well as a redesign of the thermal management of the entire air conditioning unit. This results in a long project development cycle. To address this issue, this invention places the photovoltaic controller externally within the air conditioning unit, and the photovoltaic controller is connected to the air conditioning unit via a DC port.

[0042] like Figure 2 As shown, this invention sets the photovoltaic controller as an external electrical box, which is connected to the air conditioning unit through a DC port. It communicates with the air conditioning unit and the AC mains power through a communication port. With this design, this invention can save costs and development time. In addition, by being external, it can be used with ordinary air conditioning units without modifying the internal layout and wiring of the air conditioning unit. Only one external interface needs to be reserved to achieve the effect of direct photovoltaic drive.

[0043] As mentioned above, both the first conversion module and the power factor correction circuit in this invention can independently construct the DC bus voltage. Here, the power factor correction circuit is a built-in circuit within the air conditioning unit, which can take over the control of the DC bus without requiring further hardware modifications to the air conditioning unit. Regarding the first conversion module, this invention includes a power switch transistor, an inductor connected to the source of the power switch transistor, and a diode. The inductor and diode are used to construct the DC bus voltage.

[0044] Please see Figure 3 The first conversion module has an inductor L, a diode D, and an IGBT as a power switch. By controlling the switching on and off of the IGBT, DC / DC conversion can be achieved. During this process, the inductor L and the diode D can construct the bus voltage of the DC bus.

[0045] When supplying power to the air conditioning unit, there are voltage differences. Therefore, this invention also includes a second conversion module (i.e., an auxiliary module). Figure 2 The AC / DC converter (often referred to as AC / DC) converts alternating current to direct current and performs voltage conversion to supply power to the air conditioning unit. Please refer to [link to relevant documentation]. Figure 4 This refers to the configuration of the second conversion module mentioned above. In this configuration, the second conversion circuit has multiple power switching transistors, namely switching transistor S1, switching transistor S2, switching transistor S3, and switching transistor S4. By controlling the on / off state of switching transistors S1, S2, S3, and S4, the function of converting AC power into DC power and performing voltage conversion can be realized. Here, the power switching transistors in the second conversion circuit can be either IGBTs or MOSFETs.

[0046] Based on the above settings, the off-grid photovoltaic air conditioning system proposed in this invention should have four operating states: grid-connected operation (when the AC mains power is on and controls the bus voltage, and the photovoltaic controller can supply power to the air conditioning unit), off-grid operation (when the AC mains power is off, the photovoltaic controller controls the bus voltage and supplies power to the air conditioning unit), AC mains power off in grid-connected operation, and AC mains power on in off-grid operation.

[0047] For the two scenarios of AC mains power failure in grid-connected operation and AC mains power on in off-grid operation, it is necessary to monitor the power on and power failure of AC mains. Therefore, this invention also includes an AC voltage sampling circuit, which is used to detect whether AC mains is powered on.

[0048] If, during grid-connected operation, a sudden AC mains power failure is detected (i.e., the system is no longer powered on), it can be determined that the system has entered grid-connected operation and an AC mains power failure has occurred, requiring the execution of relevant switching strategies.

[0049] If AC mains power is suddenly detected while the system is in off-grid operation, it can be determined that the system has entered off-grid operation mode and AC mains power has been activated, and relevant switching strategies need to be implemented.

[0050] Implementing the above switching strategy actually involves switching the control of the bus voltage. The DC bus voltage is constructed through the first conversion module and the power factor correction circuit. That is, as mentioned above, the off-grid photovoltaic air conditioning system switches the DC bus voltage constructed by the first conversion module or the power factor correction circuit based on the detection results of the AC voltage sampling circuit.

[0051] Please see Figure 5 In this invention, the AC voltage sampling circuit is composed of multiple resistors connected in series to a voltage follower. The current signal is converted into a voltage signal through the resistors, and the voltage follower outputs a corresponding voltage signal, so as to obtain the power-on status of the AC mains. When the AC mains power is off, the output of the voltage follower will become zero, which can be used to determine whether the AC mains power is off.

[0052] By setting up this AC voltage sampling circuit, the present invention can accurately detect whether the AC mains power is lost, providing a basis for bus voltage switching control.

[0053] The main drawback of the existing technology is that it is only applicable to two situations: AC mains power failure in grid-connected operation and AC mains power supply in off-grid operation. In the case of AC mains power failure in grid-connected operation, the existing technology cannot independently build bus voltage through photovoltaic controller, which will cause the air conditioning unit to shut down after the AC mains power failure.

[0054] In the case of AC mains power supply in off-grid operation, the existing technology causes fluctuations in bus voltage when switching from off-grid to grid-connected operation, which can easily lead to the shutdown of the air conditioning unit.

[0055] To this end, the present invention also proposes a control method for a grid-fed photovoltaic air conditioning system, which aims to achieve intelligent switching and stable operation of the off-grid photovoltaic air conditioning system in off-grid and grid-connected states through specific control logic.

[0056] For the situation where AC mains power is supplied during off-grid operation, the control method for the off-grid photovoltaic air conditioning system proposed in this invention includes:

[0057] When an AC mains power failure is detected in the off-grid state, the photovoltaic controller is controlled to operate in a voltage stabilization mode to build up the DC bus voltage to drive the air conditioning unit.

[0058] When AC mains power is detected, the photovoltaic controller is controlled to maintain off-grid operation until the preset grid-connection switching conditions are met.

[0059] When the grid connection switching conditions are met, the photovoltaic controller exits the voltage regulation mode and sends a control signal to trigger the air conditioning unit to activate the power factor correction circuit to build the bus voltage of the DC bus.

[0060] The above control method is divided into three stages: first, the off-grid voltage stabilization operation stage; second, the grid-connected switching transition stage; and finally, the grid-connected MPPT operation stage.

[0061] During the off-grid voltage stabilization operation phase, in the off-grid state, since there is no AC mains power support, the starting energy of the air conditioning unit comes entirely from the photovoltaic controller. The DC bus voltage is constructed through the first conversion module to drive the operation of the air conditioning unit. At this time, the photovoltaic controller operates in voltage stabilization mode to stabilize the DC bus voltage.

[0062] During the grid connection transition phase, when AC mains power is connected, it is necessary to avoid grid oscillations caused by grid voltage fluctuations or unstable connections. At this time, the first conversion module does not immediately transfer control of the DC bus voltage to the power factor correction circuit. Instead, it transfers control only after the grid connection switching conditions are met. Here, the grid connection switching conditions are: from the moment AC mains connection is detected, the AC mains connection must be continuously connected for a preset duration, which is set to a length sufficient to confirm the stability of the AC mains state.

[0063] Only after the grid-connected switching regulation is met will the controller of the DC bus voltage be handed over to the power factor correction circuit. This ensures that the grid voltage is stable when the power factor correction circuit controls the DC bus voltage, achieving a smooth transition from off-grid to grid-connected state and avoiding the problem of air conditioning unit shutdown.

[0064] During the grid-connected MPPT operation phase, the first conversion circuit transfers the control of the DC bus voltage to the power factor correction circuit. At this time, the photovoltaic controller follows the principle of non-grid feeding to manage energy and performs MPPT optimization control to achieve maximum power point tracking.

[0065] Based on the above control method, the present invention can achieve a smooth transition from off-grid to on-grid state, ensuring the uninterrupted operation of the air conditioning unit.

[0066] To address the issue of AC mains power failure during grid-connected operation, this invention proposes a control method for a non-grid-fed photovoltaic air conditioning system, comprising:

[0067] When the AC mains is powered on and in grid-connected state, the AC mains constructs the bus voltage of the DC bus through the power factor correction circuit;

[0068] When an AC mains power failure is detected, the system switches to off-grid mode powered by the photovoltaic controller and constructs the DC bus voltage through the first conversion module.

[0069] In the event of a sudden AC mains power failure, the power factor correction circuit cannot control the bus voltage. At this time, the power supply will switch to the photovoltaic controller. The DC bus voltage is constructed through the first conversion module. In this process, after the AC mains power fails, the DC bus voltage can be constructed through the first conversion module. Compared with the grid-connected photovoltaic air conditioning system, which will trigger islanding protection and shut down when the AC mains power fails, this invention can maintain the operation of the air conditioning unit independently through the photovoltaic controller, thus avoiding the above-mentioned problems.

[0070] For off-grid operation when AC mains power is lost, the system supplies power to the air conditioning unit separately through a photovoltaic controller. Depending on the number of photovoltaic modules in the controller, there are two power supply scenarios:

[0071] In the first case, when there is only one photovoltaic module, the first conversion circuit controls the DSP to be powered on and perform power-on initialization. After the initialization is completed, the first conversion circuit controls the DC bus voltage. At this time, the inductor L and diode D in the first conversion circuit establish the bus voltage. In this case, if the output power of the photovoltaic module in the photovoltaic controller is sufficient, the photovoltaic controller is controlled to provide only the energy required by the air conditioning unit.

[0072] The second scenario involves at least two photovoltaic modules. In this case, the photovoltaic control loop corresponding to one photovoltaic module is controlled to operate in a voltage stabilization mode to build and maintain the bus voltage of the DC bus. The photovoltaic control loops corresponding to the remaining photovoltaic modules are controlled to operate in maximum power point tracking mode, thereby ensuring that the air conditioning unit operates at the maximum power point.

[0073] Based on this control method, the present invention can achieve normal operation of the air conditioning unit in the absence of AC mains power, while maintaining the operating power of the air conditioning unit and ensuring the normal operation of the air conditioning unit.

[0074] For grid-connected operation with AC mains power, a power factor correction circuit is used to construct the DC bus voltage, and a photovoltaic controller provides auxiliary power. The control actions of the photovoltaic controller include:

[0075] If the output power of the photovoltaic modules in the photovoltaic controller is sufficient, the photovoltaic controller will only provide the energy required by the air conditioning unit.

[0076] If the output power of the photovoltaic modules in the photovoltaic controller is insufficient, the photovoltaic controller will be controlled to output the maximum power, and the AC mains power and the photovoltaic controller will work together to provide energy for the air conditioning unit.

[0077] Furthermore, in the grid-connected state with AC mains power, if it is raining or at night and photovoltaic power supply is unavailable, the air conditioning unit needs to be powered by AC mains. On sunny days, when the output power of the photovoltaic modules in the photovoltaic controller is sufficient, since this invention is a non-grid-feed structure, the energy generated by the photovoltaic controller will not be supplied to the grid. In this case, the photovoltaic controller can be controlled to only provide the energy required by the air conditioning unit. If the output power of the photovoltaic modules in the photovoltaic controller is insufficient, the air conditioning unit needs to be powered by both AC mains and the photovoltaic controller.

[0078] Based on this part of the solution, the present invention can ensure the stable operation of the air conditioning unit, and since the power supply is given priority by the photovoltaic controller, it can also avoid the problem of the air conditioning unit stopping when the AC mains power suddenly fails.

[0079] As mentioned above, when performing bus voltage switching control of the DC bus, this invention needs to determine whether the AC mains power is off. The specific method is as follows: the effective value of the AC mains voltage at the grid terminal is detected by the AC voltage sampling circuit. When the effective value of the voltage is lower than the set value, it is determined that the AC mains power is off.

[0080] Based on this part of the solution, the present invention can accurately detect the moment of AC mains power failure and simultaneously switch the control of DC bus voltage in a timely manner, ensuring a smooth switch between off-grid and grid-connected states and avoiding air conditioning unit shutdown.

[0081] Figure 6 The overall control logic of this invention first determines whether there is mains power (that is, whether AC mains power is on).

[0082] If the determination is yes, then the system enters the grid-connected state. The power factor correction circuit controls the DC bus voltage, and the air conditioning unit operates in grid-connected mode. Then, it continuously monitors whether the AC mains power is available. If the determination is no, it means that the AC mains power is lost in the grid-connected state. At this time, it is necessary to switch to the photovoltaic controller to maintain the DC bus voltage through the first conversion circuit, and the air conditioning unit operates in off-grid mode.

[0083] During this process, it is necessary to detect whether AC mains power is present. If it is found to be present, the AC mains power is supplied in the off-grid mode. At this time, it is necessary to run in off-grid mode for one minute, which is the preset time mentioned above. After the AC mains power is connected and stabilized, the power factor correction circuit is switched to control the DC bus voltage.

[0084] Based on the above solution, the present invention has at least the following beneficial effects:

[0085] In this invention, both the photovoltaic controller and the AC mains power can construct the DC bus voltage. By establishing specific control logic among the photovoltaic controller, AC mains power, and air conditioner, intelligent switching and stable operation of the off-grid photovoltaic air conditioning system in off-grid and grid-connected states are achieved. In off-grid state, the photovoltaic controller actively operates in voltage stabilization mode, establishing and maintaining the DC bus voltage, ensuring the startup and operation capability of the off-grid air conditioning system under conditions of no AC mains power and only photovoltaic power, solving the problem that traditional photovoltaic air conditioning systems cannot work without AC mains power. Simultaneously, when the AC mains power is restored, a strategy of maintaining the off-grid logic for a period of time before transferring control is adopted, effectively avoiding repeated switching and oscillations between on-grid and off-grid due to grid voltage fluctuations, achieving a smooth transition from off-grid to grid-connected, and ensuring uninterrupted operation of the air conditioning unit. Furthermore, this invention utilizes the power factor correction circuit built into the air conditioning unit to take over bus control, eliminating the need for internal hardware modifications to the air conditioning unit. Direct photovoltaic drive can be achieved solely through an external photovoltaic controller, greatly reducing the cost and development difficulty of the off-grid air conditioning system and improving the utilization rate of photovoltaic energy.

[0086] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A non-grid-fed photovoltaic air conditioning system, comprising an air conditioning unit, a photovoltaic controller for supplying power to the air conditioning unit, and AC mains power, characterized in that, The AC mains power is connected to the DC bus through a power factor correction circuit, and the photovoltaic controller is connected to the DC bus through a first conversion module. Both the first conversion module and the power factor correction circuit can construct the bus voltage of the DC bus.

2. The non-grid photovoltaic air conditioning system according to claim 1, characterized in that, The photovoltaic controller is externally mounted on the air conditioning unit and is connected to the air conditioning unit via a DC port.

3. The non-grid photovoltaic air conditioning system according to claim 1, characterized in that, The first conversion module includes at least one power switch, an inductor and a diode connected to the source of the power switch, the inductor and the diode being used to construct the bus voltage of the DC bus.

4. The non-grid photovoltaic air conditioning system according to claim 1, characterized in that, The off-grid photovoltaic air conditioning system also includes an AC voltage sampling circuit for detecting whether the AC mains power is on; The off-grid photovoltaic air conditioning system switches the bus voltage of the DC bus to be constructed by the first conversion module or the power factor correction circuit based on the detection results of the AC voltage sampling circuit.

5. A control method for a non-grid-fed photovoltaic air conditioning system as described in any one of claims 1 to 4, characterized in that, include: When an off-grid state is detected where the AC mains power is lost, the photovoltaic controller is controlled to operate in a voltage stabilization mode to build up the bus voltage of the DC bus to drive the air conditioning unit to operate. When AC mains power is detected, the photovoltaic controller is controlled to maintain the off-grid operation until the preset grid connection switching conditions are met; When the grid connection switching conditions are met, the photovoltaic controller is controlled to exit the voltage regulation mode, and a control signal is sent to trigger the air conditioning unit to activate the power factor correction circuit to construct the bus voltage of the DC bus.

6. The control method for a non-grid photovoltaic air conditioning system according to claim 5, characterized in that, The grid connection switching condition is: from the moment the AC mains power is detected to be connected, the AC mains power is continuously connected for a preset duration; The preset duration is set to a length of time sufficient to confirm that the AC mains power is stable.

7. The control method for a non-grid photovoltaic air conditioning system according to claim 5, characterized in that, Also includes: When the AC mains power is powered on and in grid-connected state, the AC mains power constructs the bus voltage of the DC bus through the power factor correction circuit; When an AC mains power failure is detected, the system switches to off-grid mode powered by the photovoltaic controller and constructs the DC bus voltage through the first conversion module.

8. The control method for a non-grid photovoltaic air conditioning system according to claim 5, characterized in that, The photovoltaic controller may have at least two photovoltaic modules. When an off-grid state with a detected AC mains power failure is detected, the photovoltaic controller is controlled to operate in a voltage regulation mode, including: controlling the photovoltaic control loop corresponding to one photovoltaic module to operate in the voltage regulation mode to build and maintain the bus voltage of the DC bus, and controlling the photovoltaic control loops corresponding to the remaining photovoltaic modules to operate in maximum power point tracking mode.

9. The control method for a non-grid photovoltaic air conditioning system according to claim 5, characterized in that, When the AC mains power is on and the system is in grid-connected state, the control actions of the photovoltaic controller include: if the output power of the photovoltaic modules in the photovoltaic controller is sufficient, then controlling the photovoltaic controller to provide only the energy required by the air conditioning unit; If the output power of the photovoltaic modules in the photovoltaic controller is insufficient, the photovoltaic controller is controlled to output maximum power, and the AC mains power and the photovoltaic controller together provide energy for the air conditioning unit.

10. The control method for a non-grid photovoltaic air conditioning system according to claim 5, characterized in that, The specific method for detecting AC mains power failure is as follows: the effective value of the AC mains voltage at the grid terminal is detected by an AC voltage sampling circuit. When the effective value of the voltage is lower than a set value, it is determined that the AC mains power has failed.

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