Control device and method of photovoltaic air conditioning system and photovoltaic air conditioning system

Abstract

The invention discloses a control device and method of a photovoltaic air conditioning system and the photovoltaic air conditioning system, the photovoltaic air conditioning system is provided with a photovoltaic air conditioner and an external power supply of the photovoltaic air conditioner, and the external power supply comprises a power grid, a photovoltaic module and a photovoltaic storage battery; the control device of the photovoltaic air conditioning system comprises a control unit used for controlling the bidirectional AC-DC device to work in a charging mode or a discharging mode; the bidirectional AC-DC device is arranged between the power grid and the photovoltaic storage battery and is used for supplementing the electric energy of the power grid to the photovoltaic storage battery under the control of the control unit and under the condition of working in a charging mode; or under the condition of working in the discharging mode, the electric energy stored in the photovoltaic storage battery is fed back to the power grid. According to the scheme, the power grid supplements power automatically when the photovoltaic air conditioner uses power at high power, the electric energy stored in the photovoltaic storage battery is fed back to the power grid when the photovoltaic air conditioner is not used, and the energy utilization rate is increased.

Description

Technical Field

[0001] This invention belongs to the field of photovoltaic air conditioning system technology, specifically relating to a control device, method and system for a photovoltaic air conditioning system, and particularly to a grid-connected photovoltaic air conditioning system based on a bidirectional AC-DC (i.e., AC to DC conversion) circuit, its control method and system. Background Technology

[0002] With the widespread application of renewable energy, photovoltaic (PV) power generation technology is playing an increasingly important role in household and industrial electricity consumption. However, PV power generation technology is greatly affected by sunlight conditions, exhibiting intermittency and instability. Many related solutions employ unidirectional power supply methods for PV air conditioning systems, meaning that power is supplied to the load solely by the PV system or the grid, lacking a bidirectional energy flow mechanism, resulting in low energy utilization.

[0003] The above content is only used to help understand the technical solution of the present invention and does not represent an admission that the above content is prior art. Summary of the Invention

[0004] The purpose of this invention is to provide a control device, method, and system for a photovoltaic air conditioning system, in order to solve the problem that most photovoltaic air conditioning systems in related solutions adopt a unidirectional power supply method and lack a bidirectional energy flow mechanism, resulting in low energy utilization. The invention achieves the effect of automatically supplementing power from the grid when the photovoltaic air conditioner is using high power, and feeding back the electrical energy stored in the photovoltaic battery to the grid when the photovoltaic air conditioner is not in use, thereby improving energy utilization.

[0005] This invention provides a control device for a photovoltaic air conditioning system. The photovoltaic air conditioning system includes a photovoltaic air conditioner and an external power supply for the photovoltaic air conditioner. The external power supply for the photovoltaic air conditioner includes a power grid and a photovoltaic power source. The photovoltaic power source includes photovoltaic modules and a photovoltaic battery. The control device for the photovoltaic air conditioning system includes a bidirectional AC-DC device and a control unit. The bidirectional AC-DC device is disposed between the power grid and the photovoltaic battery. The control unit is used to control the bidirectional AC-DC device to operate in a charging mode or a discharging mode. Under the control of the control unit, when the bidirectional AC-DC device is operating in the charging mode, the bidirectional AC-DC device is used to replenish the photovoltaic battery with electrical energy from the power grid; or, when the bidirectional AC-DC device is operating in the discharging mode, it feeds the electrical energy stored in the photovoltaic battery back to the power grid.

[0006] In some embodiments, the control unit controls the bidirectional AC-DC device to operate in charging mode or discharging mode, including: detecting the power level of the photovoltaic battery and determining whether the photovoltaic battery power level is greater than a preset power threshold and the photovoltaic air conditioner is in an unused state; if it is determined that the photovoltaic battery power level is greater than the preset power threshold and the photovoltaic air conditioner is in an unused state, then a reminder message is initiated indicating that the photovoltaic battery power level can be fed back to the power grid, and upon receiving a user's consent message based on the reminder message, the control unit controls the bidirectional AC-DC device to operate in the discharging mode; if it is determined that the photovoltaic battery power level is less than or equal to the preset power threshold, and / or the photovoltaic air conditioner is in use, then the control unit controls the bidirectional AC-DC device to operate in the charging mode.

[0007] In some embodiments, the bidirectional AC-DC device includes: a filtering unit, a rectifier and inverter unit, and a DC-DC converter unit; wherein the filtering unit, the rectifier and inverter unit, and the DC-DC converter unit are sequentially disposed between the power grid and the photovoltaic battery; when the bidirectional AC-DC device operates in the charging mode, the rectifier and inverter unit operates in the rectification mode, and the DC-DC converter unit operates in the buck mode; when the bidirectional AC-DC device operates in the discharging mode, the rectifier and inverter unit operates in the inverter mode, and the DC-DC converter unit operates in the boost mode.

[0008] In some embodiments, the filtering unit includes a three-phase LC filter; the rectification and inverter unit includes a three-phase bridge rectifier and a bus capacitor; the DC-DC converter unit includes a bidirectional DC-DC converter; wherein the three-phase bridge rectifier uses a transistor with a freewheeling diode as a power switch; when the rectification and inverter unit operates in the rectification mode, the transistor in the power switch is not working and the freewheeling diode of the transistor is working; when the rectification and inverter unit operates in the inverter mode, the transistor in the power switch is working and controlled by the control unit.

[0009] In some implementations, when the rectifier and inverter units are operating in the inverter mode, the control unit uses the SVPWM algorithm to control the operation of the rectifier and inverter units.

[0010] In some embodiments, the DC-DC converter unit includes a dual active bridge circuit; when the DC-DC converter unit operates in the boost mode or the buck mode, the control unit uses a single-phase shift modulation algorithm to control the dual active bridge circuit to operate in the boost mode or the buck mode.

[0011] In some embodiments, the control unit uses a single-phase-shift modulation algorithm to control the dual active bridge circuit to operate in the boost mode or the buck mode, including: in the charging mode, when the DC-DC converter unit operates in the buck mode, using a single-phase-shift modulation algorithm to control the dual active bridge circuit to operate in the buck mode, thereby stepping down the high-voltage DC output from the rectifier and inverter unit to the required low-voltage DC; comparing the low-voltage DC output from the dual active bridge circuit with a preset first reference voltage to obtain a first comparison result; and adjusting the phase of the single-phase-shift modulation algorithm according to the first comparison result to adjust the low-voltage DC output from the dual active bridge circuit to a first target DC.

[0012] In some embodiments, the control unit uses a single-phase-shift modulation algorithm to control the dual active bridge circuit to operate in the boost mode or the buck mode. The method further includes: in the discharge mode, when the DC-DC converter is operating in the boost mode, using a single-phase-shift modulation algorithm to control the dual active bridge circuit to operate in the boost mode, boosting the low-voltage DC output from the photovoltaic battery to the required high-voltage DC; comparing the high-voltage DC output from the dual active bridge circuit with a preset second reference voltage to obtain a second comparison result; and adjusting the phase of the single-phase-shift modulation algorithm according to the second comparison result to adjust the high-voltage DC output from the dual active bridge circuit to a second target DC.

[0013] In conjunction with the above-mentioned device, the present invention further provides a photovoltaic air conditioning system, including: the control device for the photovoltaic air conditioning system described above.

[0014] In conjunction with the aforementioned device, the present invention further provides a control method for a photovoltaic air conditioning system, comprising: controlling the bidirectional AC-DC device to operate in a charging mode or a discharging mode; supplementing the photovoltaic battery with electrical energy from the grid when the bidirectional AC-DC device is operating in the charging mode; or, feeding back the electrical energy stored in the photovoltaic battery to the grid when the bidirectional AC-DC device is operating in the discharging mode.

[0015] Therefore, the solution of the present invention, for photovoltaic air conditioners whose external power supply is the power grid (i.e., mains power) and photovoltaic power (photovoltaic power includes photovoltaic modules and photovoltaic batteries), sets up a bidirectional AC-DC circuit structure between the mains power and the photovoltaic battery. This bidirectional AC-DC circuit structure includes a filter unit (such as... Figure 3The circuit includes an LC filter, a three-phase bridge rectifier, and a bidirectional DC-DC converter. Utilizing this bidirectional AC-DC circuit structure, a bidirectional energy flow mechanism is employed to enable bidirectional power flow between the power grid and the photovoltaic battery. This allows for automatic grid-supplemented power supply during periods of high power consumption by the photovoltaic air conditioner, and the feeding back of stored energy from the photovoltaic battery to the grid during periods of non-use. Thus, by automatically supplementing power from the grid during periods of high power consumption by the photovoltaic air conditioner and feeding back stored energy from the photovoltaic battery to the grid during periods of non-use, energy utilization efficiency is improved.

[0016] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention.

[0017] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the structure of a control device for a photovoltaic air conditioning system according to an embodiment of the present invention;

[0019] Figure 2 This is a schematic diagram of a photovoltaic air conditioning grid-connected system based on a bidirectional AC-DC circuit.

[0020] Figure 3 This is a schematic diagram of the overall circuit topology of a photovoltaic air conditioning grid-connected system based on a bidirectional AC-DC circuit.

[0021] Figure 4 This is a schematic diagram of the topology of a three-phase bridge rectifier circuit.

[0022] Figure 5 This is a schematic diagram of the topology of a bidirectional AC-DC circuit;

[0023] Figure 6 This is a schematic diagram of the topology of a dual active bridge circuit;

[0024] Figure 7 This is a flowchart illustrating the SVPWM control algorithm.

[0025] Figure 8 This is a control block diagram of the circuit corresponding to a photovoltaic air conditioning grid-connected system based on a bidirectional AC-DC circuit;

[0026] Figure 9 This is a flowchart illustrating an embodiment of the control method for the photovoltaic air conditioning system of the present invention. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with specific embodiments and corresponding drawings. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0028] Considering that most photovoltaic air conditioning systems in relevant schemes adopt a unidirectional power supply method and lack a bidirectional energy flow mechanism, resulting in low energy utilization, especially when photovoltaic air conditioning is operating at high load, power supply shortages are likely to occur. Furthermore, when there is surplus photovoltaic power, it cannot effectively feed back to the grid, causing energy waste. The proposed bidirectional energy flow mechanism refers to: when photovoltaic air conditioning consumes a large amount of electricity and the photovoltaic battery supply is insufficient, dispatching the grid to provide power to the photovoltaic battery; when photovoltaic air conditioning consumes less electricity and the photovoltaic battery has surplus power, dispatching the photovoltaic battery's power to provide power to the grid.

[0029] In some schemes, while bidirectional converter systems are introduced, the primary methods employed are Maximum Power Point Tracking (MPPT) units and Sinusoidal Pulse Width Modulation (SPWM) algorithms. However, MPPT units are mainly used for large-scale photovoltaic power generation. For small-scale photovoltaic air conditioning power generation suitable for residential applications, MPPT units offer limited efficiency improvements in energy conversion and consume significant software computing resources, increasing circuit costs. SPWM algorithms, on the other hand, have a relatively simple control strategy, low energy conversion efficiency, and poor compatibility with the generated three-phase AC power grid.

[0030] Therefore, there is an urgent need for a method that can realize bidirectional energy flow between the power grid and photovoltaic (PV) air conditioning batteries, thereby improving system energy efficiency and grid connection quality control. Therefore, this invention proposes a control device for a PV air conditioning system, specifically a control device for a PV air conditioning grid-connected system based on a bidirectional AC-DC circuit. By introducing a bidirectional AC-DC circuit structure and adopting a bidirectional energy flow mechanism, bidirectional power flow is achieved between the power grid and the PV batteries. This allows for automatic supplemental power supply from the grid when the PV air conditioning is using high power, and the feeding back of stored energy from the PV batteries to the grid during periods when the PV air conditioning is not in use, thus improving energy utilization.

[0031] According to an embodiment of the present invention, a control device for a photovoltaic air conditioning system is provided. See also... Figure 1The diagram shows a structural schematic of an embodiment of the device of the present invention. The photovoltaic air conditioning system includes a photovoltaic air conditioner and an external power supply for the photovoltaic air conditioner. The external power supply for the photovoltaic air conditioner includes the power grid and a photovoltaic power source. The photovoltaic power source includes photovoltaic modules and a photovoltaic battery. In the solution of the present invention, as shown... Figure 1 As shown, the control device of the photovoltaic air conditioning system includes: a bidirectional AC-DC device and a control unit. The bidirectional AC-DC device is disposed between the power grid and the photovoltaic battery. The bidirectional AC-DC device has a bidirectional AC-DC circuit structure, and the control unit has a main control circuit structure.

[0032] The control unit is used to control the bidirectional AC-DC device to operate in charging mode or discharging mode.

[0033] The bidirectional AC-DC device is used, under the control of the control unit, to replenish the photovoltaic battery with electrical energy from the grid when the bidirectional AC-DC device is operating in the charging mode; or, when the bidirectional AC-DC device is operating in the discharging mode, to feed the electrical energy stored in the photovoltaic battery back to the grid.

[0034] Preferably, the control unit is configured to control the bidirectional AC-DC device to operate in charging mode during periods when the photovoltaic air conditioner is used at a power level above a preset value; and to control the bidirectional AC-DC device to operate in discharging mode during periods when the photovoltaic air conditioner is not used.

[0035] The bidirectional AC-DC device is used, under the control of the control unit, to operate in the charging mode to replenish the photovoltaic battery with the power from the grid, so as to supply the photovoltaic air conditioner with electricity during periods of use above a preset power level; or, to operate in the discharging mode to feed the power stored in the photovoltaic battery back to the grid, so as to realize the utilization of photovoltaic energy by the photovoltaic air conditioner during periods of non-use.

[0036] This invention proposes a photovoltaic air conditioning grid-connected system and control scheme based on a bidirectional AC-DC circuit. By introducing a bidirectional AC-DC circuit structure and adopting a bidirectional energy flow mechanism, bidirectional power flow is achieved between the power grid and the photovoltaic battery. This allows for automatic grid supplementation of power when the photovoltaic air conditioner is using high power, ensuring stable system operation. During periods when the photovoltaic air conditioner is not in use, the electrical energy stored in the photovoltaic battery is fed back to the grid, improving energy utilization. This scheme enables the photovoltaic air conditioning grid-connected system to have higher energy dispatch flexibility and power supply stability, improving overall energy efficiency and optimizing energy allocation.

[0037] In some embodiments, the control unit controls the bidirectional AC-DC device to operate in charging mode or discharging mode, including:

[0038] The control unit is further configured to detect the power level of the photovoltaic battery and determine whether the photovoltaic battery power level is greater than a preset power threshold and the photovoltaic air conditioner is in an unused state; wherein the preset power threshold is the minimum power required for the photovoltaic air conditioner to operate normally.

[0039] The control unit is further configured to, if it is determined that the power of the photovoltaic battery is greater than a preset power threshold and the photovoltaic air conditioner is in an unused state, initiate a reminder message that the power of the photovoltaic battery can be fed back to the power grid, and, upon receiving a consent message from the user based on the reminder message, control the bidirectional AC-DC device to operate in the discharge mode.

[0040] The control unit is further configured to control the bidirectional AC-DC device to operate in the charging mode if it is determined that the power of the photovoltaic battery is less than or equal to a preset power threshold, and / or that the photovoltaic air conditioner is in use. Wherein, the photovoltaic air conditioner is in use, i.e., in the start-up and running phase; the photovoltaic air conditioner is in unused phase, i.e., in the standby phase.

[0041] This invention provides a photovoltaic air conditioning grid-connected system based on a bidirectional AC-DC circuit, enabling bidirectional energy flow between the power grid and the photovoltaic battery, thus overcoming the deficiency of related solutions where photovoltaic air conditioners cannot be connected to the grid. In this invention, the main control circuit detects the battery charge of the photovoltaic air conditioner. When the battery charge is insufficient, the main control circuit automatically mobilizes the power grid for power supply. When the battery is fully charged, the grid-connected system prompts the user, who can then decide whether to feed the battery power back to the grid for economic gain.

[0042] In some embodiments, the bidirectional AC-DC device includes: a filtering unit, a rectification and inverter unit, and a DC-DC converter unit, wherein the filtering unit is as follows: Figure 3 The LC filter shown has a rectifier and inverter unit as described above. Figure 3 The three-phase bridge rectifier shown has a DC-DC converter unit as follows: Figure 3 The bidirectional DC-DC converter shown.

[0043] The filtering unit, the rectifier and inverter unit, and the DC-DC converter unit are sequentially arranged between the power grid and the photovoltaic battery.

[0044] When the bidirectional AC-DC device is operating in the charging mode, the rectifier and inverter unit operates in the rectification mode, and the DC-DC converter unit operates in the buck mode.

[0045] When the bidirectional AC-DC device is operating in the discharge mode, the rectifier and inverter unit operates in the inverter mode, and the DC-DC converter unit operates in the boost mode.

[0046] The present invention provides a photovoltaic air conditioner grid-connected system based on a bidirectional AC-DC circuit. This photovoltaic air conditioner grid-connected system realizes the charging of the photovoltaic air conditioner battery by the grid and the discharging of the battery to the grid using a single circuit. Figure 2 This is a schematic diagram of a photovoltaic air conditioning grid-connected system based on a bidirectional AC-DC circuit. Figure 2 This demonstrates the energy flow process between the power grid and the photovoltaic battery in a photovoltaic air conditioning grid-connected system based on a bidirectional AC-DC circuit. For example... Figure 2 As shown, the photovoltaic air conditioning grid-connected system based on bidirectional AC-DC circuit includes: grid input terminal, filter, three-phase bridge rectifier, bidirectional DC-DC (i.e., DC to DC conversion) conversion circuit (such as bidirectional DC-DC converter) and photovoltaic battery module (i.e., equivalent module of photovoltaic battery).

[0047] See Figure 2 In the example shown, the direction from the grid input terminal, filter, three-phase bridge rectifier, bidirectional DC-DC converter circuit to the photovoltaic battery module is the direction of charging the photovoltaic battery from the grid; the direction from the photovoltaic battery module, bidirectional DC-DC converter circuit, three-phase bridge rectifier, filter to the grid input terminal is the direction of discharging the photovoltaic battery module to the grid.

[0048] See Figure 2 The example shown illustrates the following workflow for the power grid to charge the photovoltaic air conditioner's battery: The three-phase AC power from the grid is filtered and then enters a three-phase bridge rectifier, where it is rectified into high-voltage DC power. A bidirectional DC-DC circuit then steps down the rectified high-voltage DC power to supply the photovoltaic battery with low-voltage DC power. This operation converts the 380V three-phase AC power from the grid into high-voltage DC power (around 520V), and then converts it into low-voltage DC power (e.g., 24V) suitable for the battery.

[0049] See Figure 2As shown in the example, the discharge process of a photovoltaic air conditioner battery to the grid is as follows: The low-voltage DC power output from the photovoltaic air conditioner battery is boosted to high-voltage DC power by a bidirectional DC-DC circuit; a three-phase bridge rectifier circuit controlled by the SVPWM (Space Vector Pulse Width Modulation) algorithm then inverts the high-voltage DC power into three-phase AC power, which is then filtered and input into the grid. This operation converts the low-voltage DC power from the battery into high-voltage DC power, and then converts the high-voltage DC power into three-phase AC power to be connected to the grid.

[0050] This invention proposes a photovoltaic air conditioning grid-connected system and control scheme based on a bidirectional AC-DC circuit. The system mainly consists of a filter circuit, a three-phase rectifier circuit, a dual active bridge circuit, a photovoltaic air conditioning battery, and a control circuit (such as a main control circuit). This system achieves bidirectional energy flow between the grid and the photovoltaic battery (i.e., the photovoltaic air conditioning battery) through a single circuit, reducing circuit size and cost. Furthermore, it efficiently converts electrical energy and generates high-quality three-phase AC power for grid connection, improving energy utilization.

[0051] In some embodiments, the filtering unit includes a three-phase LC filter; the rectification and inverter unit includes a three-phase bridge rectifier and a bus capacitor; and the DC-DC converter unit includes a bidirectional DC-DC converter.

[0052] The three-phase bridge rectifier uses a transistor with a freewheeling diode as a power switch. When the rectification and inverter unit is operating in the rectification mode, the transistor in the power switch is not working and the freewheeling diode of the transistor is working. When the rectification and inverter unit is operating in the inverter mode, the transistor in the power switch is working and is controlled by the control unit.

[0053] In the solution of this invention, the topology of the circuit corresponding to the photovoltaic air conditioning grid-connected system based on the bidirectional AC-DC circuit is as follows: Figure 3 As shown. Figure 3 This is a schematic diagram of the overall circuit topology of a photovoltaic air conditioning grid-connected system based on a bidirectional AC-DC circuit. Figure 3 The circuit hardware topology of a photovoltaic air conditioning grid-connected system based on a bidirectional AC-DC circuit is demonstrated.

[0054] like Figure 3As shown, the power grid input includes three-phase AC input terminals, such as the input terminals of three-phase AC Ua, Ub, and Uc. The filter includes an LC filter composed of three-phase inductors Ls and three-phase capacitors, such as inductors Lsa, Lsb, and Lsc, and three-phase capacitors Csa, Csb, and Csc. The three-phase bridge rectifier includes: transistors S1, S2, S3, S4, S5, and S6; freewheeling diodes D1 and D2 for transistors S1, D3 and D4 for S3, D6 and D6 for S5, and a bus capacitor C. The bidirectional DC-DC converter includes: transistors S7 and S8, a freewheeling diode D7 for transistor S7, a freewheeling diode D8 for transistor S8, and an inductor L. The photovoltaic battery module includes a resistor r and a capacitor c1.

[0055] The input terminal of AC current Ua is connected to the first terminal of capacitor Csa via inductor Lsa, and the second terminal of capacitor Csa is grounded. The input terminal of AC current Ub is connected to the first terminal of capacitor Csb via inductor Lsb, and the second terminal of capacitor Csb is connected to the second terminal of capacitor Csa. The input terminal of AC current Uc is connected to the first terminal of capacitor Csc via inductor Lsc, and the second terminal of capacitor Csc is connected to the second terminal of capacitor Csa. The first terminal of capacitor Csa is connected to the emitter of transistor S1, the anode of diode D1, the collector of transistor S2, and the cathode of diode D2, respectively. The collector of transistor S1, the cathode of diode D1, the collector of transistor S3, the cathode of diode D3, the collector of transistor S5, the cathode of diode D5, and the first terminal of bus capacitor C are also connected. The first terminal of capacitor Csb is connected to the emitter of transistor S3, the anode of diode D3, the collector of transistor S4, and the cathode of diode D4, respectively. The first terminal of capacitor Csc is connected to the emitter of transistor S5, the cathode of diode D5, the collector of transistor S6, and the cathode of diode D6, respectively. The emitter of transistor S2, the anode of diode D2, the emitter of transistor S4, the anode of diode D4, the emitter of transistor S6, the anode of diode D6, and the second terminal of bus capacitor C are connected. The first terminal of bus capacitor C is connected to the collector of transistor S7 and the cathode of diode D7, respectively. The emitter of transistor S7, the anode of diode D7, the collector of transistor S8, the cathode of diode D8, and the first terminal of inductor L are connected. The second terminal of bus capacitor C is connected to the emitter of transistor S8 and the anode of diode D8, respectively. The second terminal of inductor L is connected to the emitter of transistor S8 via resistor r and capacitor c1.

[0056] In the solution of this invention, the three-phase bridge rectifier rectifies three-phase AC power into high-voltage DC power in the following manner: Figure 3 Transistors S1, S2, S3, S4, S5, and S6 are turned off. In the embodiment of this invention, the topology of the three-phase bridge rectifier is simplified as follows: Figure 4 .

[0057] Figure 4 This is a schematic diagram of the topology of a three-phase bridge rectifier circuit. Figure 4 This paper demonstrates the hardware topology of a three-phase rectifier circuit in a photovoltaic air conditioning grid-connected system based on a bidirectional AC-DC circuit. By controlling this three-phase bridge rectifier circuit using a three-phase SVPWM algorithm, efficient conversion between three-phase AC and high-voltage DC power can be achieved. Figure 4 As shown, this three-phase bridge rectifier circuit consists of a bridge structure composed of six diodes (such as diodes D1, D2, D3, D4, D5, and D6), with R being the load resistance. When a pair of diodes (a pair of diodes refers to two diodes on different arms of the bridge) is conducting, the output DC voltage is equal to the largest of the AC line voltages. Taking the moment when a pair of diodes, such as diodes D1 and D4, are simultaneously conducting as the zero point, the zero-crossing angle of phase a voltage is δ, and the output voltage Udc is the voltage difference between phases a and b (i.e., the difference between phase a voltage Ua and phase b voltage Ub):

[0058] (1).

[0059] Where U2 is the input phase voltage of the three-phase AC power grid, and the effective value of U2 in the Chinese standard industrial power grid is 220V; δ is the zero-crossing angle of the phase voltage of phase a; ω is the angular frequency of AC power, ω=2πf, where f is the AC voltage frequency, and f is 50Hz in household electricity; t is time, and in this formula, Udc is a function of time t.

[0060] See Figure 4 In the example shown, the conduction sequence of the six diodes in the three-phase bridge rectifier circuit is D1, D4→D1, D6→D3, D6→D3, D2→D5, D2→D5, D4. Commutation occurs once every 60°, completing six commutations within one cycle (360°), resulting in a six-pulse DC voltage output. This six-pulse DC voltage is smoothed by a large capacitor (such as the bus capacitor C), resulting in a DC voltage Udc with relatively small ripple. The output voltage of the three-phase bridge rectifier circuit under no-load conditions is... As the load R increases, the output voltage Udc of the three-phase bridge rectifier circuit decreases, and the output voltage of the three-phase bridge rectifier circuit... (That is, the output DC voltage is between 514.8V and 539V).

[0061] In the solution of this invention, in the photovoltaic air conditioning grid-connected system based on bidirectional AC-DC circuit, the filtering unit includes a three-phase LC filter, the rectification and inverter unit includes a three-phase bridge rectifier and a bus capacitor, and the DC-DC conversion unit includes a bidirectional DC-DC converter, which can efficiently realize the conversion of electrical energy and generate high-quality three-phase AC power to be connected to the grid, thereby improving energy utilization.

[0062] In some implementations, when the rectifier and inverter units are operating in the inverter mode, the control unit uses the SVPWM algorithm to control the operation of the rectifier and inverter units.

[0063] In the scheme of this invention, the SVPWM control algorithm is as follows: Figure 7 As shown. Figure 7 This is a flowchart illustrating the SVPWM control algorithm. Figure 7 The flow of the SVPWM algorithm is demonstrated. For example... Figure 7 As shown, the flow of the SVPWM control algorithm includes:

[0064] Step 1: Combine the three-phase voltages into the target vector V_ref, and then proceed to Step 2.

[0065] Step 2: Determine the sector where the target vector V_ref is located, and then proceed to Step 3.

[0066] Step 3: Decompose the target vector V_ref into vector V1 and vector V2, and then proceed to step 4.

[0067] Step 4: Calculate the control time t1 and control time t2 corresponding to vectors V1 and V2, and then execute step 5.

[0068] Step 5: Allocate time t0 corresponding to the zero vector, and generate PWM signals using the time t0 corresponding to the zero vector, the control time t1 corresponding to vector V1 and the control time t2 corresponding to vector V2.

[0069] like Figure 7 The SVPWM algorithm shown generates PWM signals by synthesizing and decomposing voltage vectors, thereby achieving efficient and dynamic control of DC to three-phase AC power and improving the power quality of the grid.

[0070] Three-phase SVPWM modulation can invert DC voltage into three-phase AC voltage. Essentially, it maps the three-phase sinusoidal voltage into a voltage vector in a two-dimensional plane through mathematical transformation, and dynamically synthesizes the target vector using six basic voltage vectors (covering a period of 0° to 360°), thereby generating a low THD (Total Harmonic Distortion) three-phase sinusoidal output. The control flow of three-phase SVPWM modulation is as follows:

[0071] In a three-phase bridge rectifier, the upper and lower transistors of each phase arm are complementary in conduction. The switching function Sk of the bridge arm is defined as follows:

[0072] (3).

[0073] The AC side reference voltages u, v, and w can then be expressed as functions of the DC side voltage and the on / off state, such as:

[0074] ;

[0075] Among them, L s C is the AC-side inductance, and C is the DC-side capacitance. a u b u c V, U, and W voltages, respectively, i a i b i c V, U, and W are the AC currents, respectively, and R is the equivalent DC resistance. dc For DC voltage, S x =(S a +S b +S c ) / 3.

[0076] The reference voltage is synthesized using space vectors, then the voltage sector in which the reference voltage falls is determined, and the duration of the voltage vector's action is calculated. Finally, a PWM signal is generated. The three-phase SVPWM algorithm essentially converts direct current (DC) into three-phase sinusoidal alternating current (AC) by controlling the on / off state of six switching transistors. By synthesizing and decomposing voltage vectors, the three-phase SVPWM algorithm generates PWM signals to control the switching transistors, achieving efficient and dynamic control of the DC-to-AC conversion and improving the power quality of the grid.

[0077] In the present invention, the three-phase rectifier circuit controlled by the two-level space vector modulation (SVPWM) algorithm realizes the mutual conversion between three-phase AC power and high-voltage DC power; the superior algorithm adopted by the photovoltaic air conditioning grid-connected system based on the bidirectional AC-DC circuit can realize the conversion of electrical energy with high efficiency and generate high-quality three-phase AC power to be connected to the grid.

[0078] In some embodiments, the DC-DC converter unit includes a dual active bridge circuit.

[0079] When the DC-DC converter operates in either boost mode or buck mode, the control unit uses a single-phase-shift modulation algorithm to control the dual active bridge circuit to operate in either boost mode or buck mode.

[0080] In the solution of this invention, see Figure 2 The example shown illustrates the operation of a bidirectional DC-DC circuit (such as a bidirectional DC / DC converter): The bidirectional DC / DC converter can operate in both boost and buck modes. The switching between these two states is controlled by switches S7 and S8 (e.g., transistors S7 and S8). The circuit topology of the bidirectional DC / DC converter is shown below. Figure 5 As shown.

[0081] Figure 5 This is a schematic diagram of the topology of a bidirectional AC-DC circuit. Figure 5 The hardware topology of a bidirectional DC-DC circuit is shown, which enables the conversion between high-voltage DC and low-voltage DC. For example... Figure 5 As shown, when the grid supplies power to the photovoltaic air conditioner battery, the bidirectional DC-DC circuit is in Buck mode, converting the high-voltage DC output from the three-phase bridge rectifier into low-voltage DC power for the photovoltaic battery. At this time, switch S8 is open, and switch S7 is controlled by high-frequency pulse width modulation (PWM). When the photovoltaic air conditioner battery discharges to the grid, the circuit is in Boost mode, converting the low-voltage DC output from the photovoltaic battery into high-voltage DC power. At this time, switch S7 is open, and switch S8 is controlled by high-frequency PWM. The bidirectional DC-DC circuit has a high-voltage high-voltage side and a low-voltage low-voltage low-voltage side; electrical isolation between the high and low voltage sides is required to meet safety standards. In practical circuits, a dual active bridge (DAB) circuit topology is used (e.g., ...). Figure 6 (As shown) This achieves DC voltage conversion and provides electrical isolation between strong and weak currents through a transformer.

[0082] Figure 6 This is a schematic diagram of the topology of a dual active bridge circuit. Figure 6 The hardware topology of a dual active bridge circuit is demonstrated, showing how a single-phase-shift modulation (SPS) algorithm enables efficient switching between high-voltage and low-voltage DC power. The SPS modulation method, described below, achieves bidirectional energy flow by controlling the phase difference φ between the H-bridges on both sides of the DAB circuit, realizing efficient high-to-low DC voltage conversion with a simple single circuit. Figure 6As shown, the dual active bridge circuit includes: transistors M1, M2, M3, and M4; transistors M5, M6, M7, and M8; an inductor Lk; a transformer with a primary-to-secondary winding turns ratio of n:1; and input capacitors (such as bus capacitor C) and output capacitors. The positive terminal of the bus voltage Udc is connected to the first terminal of the input capacitor, and the negative terminal of Udc is connected to the second terminal of the input capacitor. The first terminal of the output capacitor is connected to the positive terminal of the output voltage U1, and the second terminal of the output capacitor is connected to the negative terminal of the output voltage U1. The positive terminal of the bus voltage Udc is also connected to the collectors of transistors M1 and M3, respectively; the emitter of transistor M1 is connected to the collector of transistor M2, and the emitter of transistor M1 is also connected to the first terminal of the primary winding of the transformer via inductor Lk; the emitter of transistor M3 is connected to the collector of transistor M4, and the emitter of transistor M3 is also connected to the second terminal of the primary winding of the transformer; the negative terminal of the bus voltage Udc is also connected to the emitters of transistors M2 and M4, respectively. The first connection terminal of the transformer's secondary winding is connected to the emitter of transistor M5 and the collector of transistor M6, respectively; the collectors of transistors M5 and M7 are both connected to the positive terminal of the output voltage U1; the second connection terminal of the transformer's secondary winding is connected to the emitter of transistor M7 and the collector of transistor M8, respectively; the emitters of transistors M6 and M8 are both connected to the negative terminal of the output voltage U1.

[0083] Single-phase shift modulation (SPS) can control the direction of power flow in a dual active bridge circuit, enabling the mutual conversion between high-voltage DC U1 and low-voltage DC Udc. The single-phase shift (SPS) modulation method of the DAB converts the diagonal switches of the H-bridge into a pair (e.g., ...). Figure 6 The transformer uses transistors M1 and M4, M2 and M3, M5 and M8, and M6 and M7. Two pairs of switches on the same side of the transformer conduct alternately with a duty cycle of 50%. The phase difference between transistors M5, M6, M7, and M8, and ultimately M1, M2, M3, and M4, is φ. When φ > 0, energy flows from Udc to U1, meaning the grid charges the photovoltaic air conditioner battery; when φ < 0, energy flows from U1 to Udc, meaning the photovoltaic air conditioner battery discharges to the grid. The relationship between the output voltage U1 and the input voltage Udc is as follows:

[0084] (2).

[0085] Where R is the equivalent internal resistance of the photovoltaic air conditioner battery. From the above relationship, it can be seen that, given a fixed transformer turns ratio n, the output voltage U1 can be adjusted by adjusting the phase φ. w = 2πf, where f is the switching frequency of the H-bridge diagonal transistor; L is the equivalent inductance (transformer leakage inductance + parasitic inductance).

[0086] In the present invention, the dual active bridge circuit controlled by the single-phase shift modulation algorithm can realize the conversion of high and low DC voltages; the superior algorithm adopted by the photovoltaic air conditioning grid-connected system based on the bidirectional AC-DC circuit can realize the conversion of electrical energy with high efficiency and generate high-quality three-phase AC power to be connected to the grid.

[0087] The solution of this invention employs a three-phase rectifier circuit controlled by the SVPWM algorithm and a dual active bridge circuit controlled by the single-phase shift modulation algorithm, which can realize efficient power conversion between the power grid and photovoltaic batteries, and improve the power quality of the power connected to the power grid.

[0088] In some embodiments, the control unit employs a single-phase-shift modulation algorithm to control the dual active bridge circuit to operate in either the boost mode or the buck mode, including:

[0089] The control unit is further configured to, in the charging mode, when the DC-DC converter is operating in the buck mode, use a single-phase shift modulation algorithm to control the dual active bridge circuit to operate in the buck mode, thereby reducing the high-voltage DC output from the rectifier and inverter units to the required low-voltage DC.

[0090] The control unit is further configured to compare the low-voltage DC output from the dual active bridge circuit with a preset first reference voltage to obtain a first comparison result.

[0091] The control unit is further configured to adjust the phase of the single-phase shift modulation algorithm according to the first comparison result, so as to adjust the low-voltage DC output of the dual active bridge circuit to the first target DC.

[0092] In the solution of this invention, a three-phase SVPWM rectifier circuit and a dual active bridge circuit are used to improve the power conversion efficiency and enhance the power quality supplied to the power grid.

[0093] In some embodiments, the control unit uses a single-phase-shift modulation algorithm to control the dual active bridge circuit to operate in the boost mode or the buck mode, and further includes:

[0094] The control unit is further configured to, in the discharge mode, when the DC-DC converter is operating in the boost mode, use a single-phase shift modulation algorithm to control the dual active bridge circuit to operate in the boost mode, thereby boosting the low-voltage DC output from the photovoltaic battery to the required high-voltage DC.

[0095] The control unit is further configured to compare the high-voltage DC output from the dual active bridge circuit with a preset second reference voltage to obtain a second comparison result.

[0096] The control unit is further configured to adjust the phase of the single-phase shift modulation algorithm according to the second comparison result, so as to adjust the high-voltage DC output of the dual active bridge circuit to the second target DC.

[0097] In the solution of this invention, the overall control block diagram of the photovoltaic air conditioning grid-connected system based on a bidirectional AC-DC circuit is as follows: Figure 8 As shown. Figure 8 This is the control block diagram of the photovoltaic air conditioning grid-connected system based on a bidirectional AC-DC circuit. Figure 8 The circuit controlled by the main control MCU (i.e., the main control circuit) is shown. The main control MCU can monitor the voltage and current of each key point in the photovoltaic air conditioning grid-connected system based on bidirectional AC-DC circuit. By adjusting the algorithm, high-efficiency and high-quality power conversion is achieved. When the grid supplies power to the photovoltaic cell, it can be seen from formula (2) that the output voltage Udc can be adjusted by the switching frequency f of the controller H bridge. If the voltage across the photovoltaic cell is too high or too low, or if the grid voltage is unstable, the resulting ripple will damage the photovoltaic cell. The purpose of this adjustment is to stabilize the voltage supplied to the photovoltaic battery. When the photovoltaic cell supplies power to the grid, the single-phase shift algorithm controls φ to make energy flow to the grid and stabilizes the voltage of U1 by controlling the switching frequency f. The SVPWM algorithm generates stable and high-quality three-phase AC power by controlling the PWM wave to act on different bridge arms for a certain period of time. The main control MCU monitors the power of the photovoltaic battery. When the photovoltaic battery is insufficient, the grid is dispatched to provide power to the photovoltaic battery. When the photovoltaic battery has surplus power, the power of the photovoltaic battery is dispatched to provide power to the grid.

[0098] When the grid charges the photovoltaic air conditioner battery, the main control MCU controls the transistors S1 to S6 of the three-phase rectifier circuit to turn off and controls the bidirectional DC-DC circuit to charging mode, using a single-phase shift modulation method to generate low-voltage DC power. After sampling the generated low-voltage DC power, it is compared with the reference voltage. According to the relationship between U1 and Udc in formula (2), the phase of the single-phase shift modulation is adjusted to affect the output voltage. According to the relationship between U1 and Udc in formula (2), the single-phase shift modulation method mainly controls the output DC voltage Udc by adjusting the switching frequency f; the phase difference φ controls the direction of power flow.

[0099] When the photovoltaic battery discharges to the grid, the main control MCU controls the bidirectional DC-DC circuit to be in discharge mode. The DC bus of the bidirectional DC-DC circuit is sampled and compared with the reference bus voltage. The phase of the single-phase shift modulation is adjusted according to the comparison result. According to the relationship between U1 and Udc in formula (2), the single-phase shift modulation method mainly controls the output bus voltage U1 by adjusting the switching frequency f. A stable bus voltage U1 helps the SVPWM algorithm generate a stable three-phase AC power. When in discharge mode, the main control MCU will sample the voltage and current of the three-phase power output and adjust the conduction time of the bridge arm through the SVPWM algorithm to generate a high-quality three-phase sinusoidal waveform. The power of the photovoltaic battery is monitored by the MCU in real time. When the photovoltaic air conditioner is in peak power consumption, the main control MCU will switch the charging mode to supplement the power supply from the grid. When the photovoltaic battery is fully charged, the main control MCU will prompt the user, who can decide whether to feed the power back to the grid to obtain economic benefits.

[0100] In this invention, a three-phase rectifier circuit controlled by the SVPWM algorithm and a dual active bridge circuit controlled by the unidirectional shift modulation algorithm are introduced into the residential photovoltaic grid-connected system. The aforementioned control algorithm and circuit are mainly used for the charging and discharging control of electric vehicles in V2G (Vehicle-to-Grid) technology. Since the scenarios of residential photovoltaic air conditioning grid-connected systems and electric vehicle V2G are similar, when the grid charges the battery, it converts three-phase AC to DC; when the battery feeds back to the grid, it converts DC to three-phase AC. Both scenarios use a single circuit to achieve bidirectional flow of electrical energy. Unlike V2G technology, because electric vehicle batteries have a higher voltage while photovoltaic cells have a lower voltage, the dual active bridge circuit in this patent employs a high-low voltage isolation design to isolate the low-voltage circuit from the high-voltage circuit, ensuring circuit safety.

[0101] In the circuit controller section, an IoT module is added to communicate with the user's device APP. Figure 8With the addition of an IoT module, this app can replace the air conditioner remote control for solar-powered air conditioners. Furthermore, the IoT module can send the following information to the user, which can be viewed through the app: real-time solar cell power level, cumulative solar system power generation, cumulative solar power revenue, real-time electricity price, and estimated solar power revenue based on the real-time electricity price. When the solar cell power is surplus, the app will prompt the user, who can then choose whether to feed the solar-powered air conditioner's power back to the grid, and the amount fed back. When the user selects the amount of power to feed back, the following scenarios apply: 1. During seasons when air conditioning is not frequently used, the app will control and reserve 20% of the power, and the user can feed back a maximum of 80% of the power to the grid; 2. During hot summers and cold winters, when air conditioning is frequently used, the app will control and reserve 50% of the power, and the user can feed back a maximum of 50% of the power to the grid.

[0102] For grid-connected photovoltaic (PV) air conditioning systems, the industry primarily uses MPPT (Maximum Power Point Tracking) units, with some systems employing SPWM (Sinusoidal Pulse Width Modulation) algorithms. Compared to SPWM, SVPWM (Sinusoidal Pulse Width Modulation) utilizes the entire voltage space, resulting in higher energy conversion efficiency. SPWM's energy conversion efficiency is approximately 92%, while SVPWM can reach over 95%. Regarding power quality, SVPWM-modulated three-phase AC power exhibits a total harmonic distortion (THD) of less than 3%, while SPWM-modulated three-phase AC power has a THD exceeding 5%, exceeding the national standard requirement. Therefore, systems using SPWM require additional filtering units to meet this standard. The core function of the MPPT unit is to optimize the solar panel's output power in real time, ensuring it always operates at its maximum power point. MPPT units exhibit economies of scale; the larger the PV panel area, the more significant the improvement in MPPT unit efficiency. However, for residential PV air conditioning power generation, the smaller the PV panel area, the limited improvement in system efficiency. The SVPWM algorithm is controlled solely by the main MCU, while the MPPT unit requires an additional hardware control unit and consumes significant software computing resources during control, substantially increasing system costs. Therefore, a bidirectional AC-DC circuit controlled by the SVPWM algorithm is the optimal solution for grid-connected residential photovoltaic air conditioners.

[0103] In the solution of this invention, a photovoltaic air conditioner, a photovoltaic grid connection, a bidirectional AC-DC circuit, a dual active bridge, and an SVPWM three-phase rectifier are used. By introducing a bidirectional AC-DC circuit structure and adopting a bidirectional energy flow mechanism, bidirectional power flow is achieved between the power grid and the photovoltaic battery. When the photovoltaic air conditioner consumes high power, the power grid can automatically supplement the power supply. When the photovoltaic air conditioner is not in use, the electrical energy stored in the photovoltaic battery is fed back to the power grid, thereby improving energy utilization.

[0104] By employing the technical solution of this invention, a bidirectional AC-DC circuit structure is set between the mains power and the photovoltaic battery for photovoltaic air conditioners whose external power supply is the grid (i.e., AC power) and photovoltaic power (photovoltaic power includes photovoltaic modules and photovoltaic batteries). This bidirectional AC-DC circuit structure includes a filter unit (such as...). Figure 3 The circuit includes an LC filter, a three-phase bridge rectifier, and a bidirectional DC-DC converter. Utilizing this bidirectional AC-DC circuit structure, a bidirectional energy flow mechanism is employed to enable bidirectional power flow between the power grid and the photovoltaic battery. This allows for automatic grid-supplemented power supply during periods of high power consumption by the photovoltaic air conditioner, and the feeding back of stored energy from the photovoltaic battery to the grid during periods of non-use. Thus, by automatically supplementing power from the grid during periods of high power consumption by the photovoltaic air conditioner and feeding back stored energy from the photovoltaic battery to the grid during periods of non-use, energy utilization efficiency is improved.

[0105] According to an embodiment of the present invention, a photovoltaic air conditioning system corresponding to a control device for a photovoltaic air conditioning system is also provided. This photovoltaic air conditioning system may include the control device for the photovoltaic air conditioning system described above.

[0106] Since the processing and functions implemented by the photovoltaic air conditioning system in this embodiment are basically the same as those in the embodiments, principles and examples of the device, any details not covered in this embodiment can be found in the relevant descriptions in the foregoing embodiments, and will not be repeated here.

[0107] According to embodiments of the present invention, a control method for a photovoltaic air conditioning system corresponding to a photovoltaic air conditioning system is also provided, such as... Figure 9 The diagram shows a flowchart of an embodiment of the method of the present invention. The control method of the photovoltaic air conditioning system may include steps S110 to S120.

[0108] In step S110, the bidirectional AC-DC device is controlled to operate in charging mode or discharging mode.

[0109] In step S120, the bidirectional AC-DC device replenishes the photovoltaic battery with electrical energy from the grid when the device is operating in the charging mode; or, when the device is operating in the discharging mode, the electrical energy stored in the photovoltaic battery is fed back to the grid.

[0110] Preferably, the control unit controls the bidirectional AC-DC device to operate in charging mode during periods when the photovoltaic air conditioner is used at a power level above a preset value; and controls the bidirectional AC-DC device to operate in discharging mode during periods when the photovoltaic air conditioner is not used.

[0111] Under the control of the control unit, the bidirectional AC-DC device operates in the charging mode to replenish the photovoltaic battery with the power from the grid, so as to supply the photovoltaic air conditioner with electricity during periods when the power is above the preset level; or, it operates in the discharging mode to feed the power stored in the photovoltaic battery back to the grid, so as to realize the utilization of photovoltaic energy by the photovoltaic air conditioner during periods when it is not in use.

[0112] In this invention, by introducing a bidirectional AC-DC device, such as a bidirectional AC-DC circuit structure, and employing a bidirectional energy flow mechanism, bidirectional power flow is achieved between the power grid and the photovoltaic battery. This allows for automatic supplemental power supply from the grid during periods of high power consumption by the photovoltaic air conditioner, ensuring stable system operation. During periods when the photovoltaic air conditioner is not in use, the stored energy in the photovoltaic battery is fed back to the grid, improving energy utilization. This solution enables the photovoltaic air conditioner grid-connected system to possess greater energy dispatch flexibility and power supply stability, improving overall energy efficiency and optimizing energy allocation.

[0113] Since the processing and functions implemented by the method in this embodiment are basically the same as the embodiments, principles and examples of the control device of the aforementioned photovoltaic air conditioning system, any details not covered in this embodiment can be found in the relevant descriptions in the aforementioned embodiments, and will not be repeated here.

[0114] In summary, it is readily understood by those skilled in the art that, without conflict, the aforementioned advantageous methods can be freely combined and superimposed.

[0115] The above description is merely an embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of the claims of the present invention.

Claims

1. A control device for a photovoltaic air conditioning system, characterized in that, The photovoltaic air conditioning system includes a photovoltaic air conditioner and an external power supply for the photovoltaic air conditioner. The external power supply for the photovoltaic air conditioner includes the power grid and a photovoltaic power source, and the photovoltaic power source includes photovoltaic modules and a photovoltaic battery. The control device of the photovoltaic air conditioning system includes a bidirectional AC-DC device and a control unit, wherein the bidirectional AC-DC device is disposed between the power grid and the photovoltaic battery. The control unit is used to control the bidirectional AC-DC device to operate in charging mode or discharging mode. The bidirectional AC-DC device is used, under the control of the control unit, to replenish the photovoltaic battery with electrical energy from the grid when the bidirectional AC-DC device is operating in the charging mode; or, when the bidirectional AC-DC device is operating in the discharging mode, to feed the electrical energy stored in the photovoltaic battery back to the grid.

2. The control device for the photovoltaic air conditioning system according to claim 1, characterized in that, The control unit controls the bidirectional AC-DC device to operate in charging mode or discharging mode, including: The power level of the photovoltaic battery is detected, and it is determined whether the power level of the photovoltaic battery is greater than a preset power threshold and the photovoltaic air conditioner is in an unused state. If it is determined that the power of the photovoltaic battery is greater than the preset power threshold and the photovoltaic air conditioner is in an unused state, then a reminder message is initiated that the power of the photovoltaic battery can be fed back to the power grid. Upon receiving a consent message from the user based on the reminder message, the bidirectional AC-DC device is controlled to operate in the discharge mode. If it is determined that the power of the photovoltaic battery is less than or equal to a preset power threshold, and / or it is determined that the photovoltaic air conditioner is in use, then the bidirectional AC-DC device is controlled to operate in the charging mode.

3. The control device for the photovoltaic air conditioning system according to claim 1, characterized in that, The bidirectional AC-DC device includes: a filtering unit, a rectification and inverter unit, and a DC-DC converter unit; wherein, The filtering unit, the rectifier and inverter unit, and the DC-DC converter unit are sequentially arranged between the power grid and the photovoltaic battery. When the bidirectional AC-DC device is operating in the charging mode, the rectifier and inverter unit operates in the rectification mode, and the DC-DC converter unit operates in the buck mode. When the bidirectional AC-DC device is operating in the discharge mode, the rectifier and inverter unit operates in the inverter mode, and the DC-DC converter unit operates in the boost mode.

4. The control device for the photovoltaic air conditioning system according to claim 3, characterized in that, The filtering unit includes a three-phase LC filter; the rectification and inverting unit includes a three-phase bridge rectifier and a bus capacitor; the DC-DC converter includes a bidirectional DC-DC converter. The three-phase bridge rectifier uses a transistor with a freewheeling diode as a power switch. When the rectification and inverter unit is operating in the rectification mode, the transistor in the power switch is not working and the freewheeling diode of the transistor is working. When the rectification and inverter unit is operating in the inverter mode, the transistor in the power switch is working and is controlled by the control unit.

5. The control device for the photovoltaic air conditioning system according to claim 3, characterized in that, When the rectifier and inverter units are operating in the inverter mode, the control unit uses the SVPWM algorithm to control the operation of the rectifier and inverter units.

6. The control device for the photovoltaic air conditioning system according to any one of claims 3 to 5, characterized in that, The DC-DC converter unit includes: a dual active bridge circuit; When the DC-DC converter operates in either boost mode or buck mode, the control unit uses a single-phase-shift modulation algorithm to control the dual active bridge circuit to operate in either boost mode or buck mode.

7. The control device for the photovoltaic air conditioning system according to claim 6, characterized in that, The control unit uses a single-phase-shift modulation algorithm to control the dual active bridge circuit to operate in either the boost mode or the buck mode, including: In the charging mode, when the DC-DC converter unit is operating in the buck mode, a single-phase shift modulation algorithm is used to control the dual active bridge circuit to operate in the buck mode, thereby reducing the high-voltage DC output from the rectifier and inverter unit to the required low-voltage DC. The low-voltage DC output from the dual active bridge circuit is compared with a preset first reference voltage to obtain a first comparison result; The phase of the single-phase shift modulation algorithm is adjusted according to the first comparison result to adjust the low-voltage DC output of the dual active bridge circuit to the first target DC.

8. The control device for the photovoltaic air conditioning system according to claim 6, characterized in that, The control unit uses a single-phase-shift modulation algorithm to control the dual active bridge circuit to operate in the boost mode or the buck mode, and also includes: In the discharge mode, when the DC-DC converter is operating in the boost mode, a single-phase shift modulation algorithm is used to control the dual active bridge circuit to operate in the boost mode, thereby boosting the low-voltage DC output from the photovoltaic battery to the required high-voltage DC. The high-voltage DC output from the dual active bridge circuit is compared with a preset second reference voltage to obtain a second comparison result; The phase of the single-phase shift modulation algorithm is adjusted according to the second comparison result to adjust the high-voltage DC output of the dual active bridge circuit to the second target DC.

9. A photovoltaic air conditioning system, characterized in that, include: The control device for the photovoltaic air conditioning system as described in any one of claims 1 to 8.

10. A control method for a photovoltaic air conditioning system that uses the control device of a photovoltaic air conditioning system as described in any one of claims 1 to 8 to achieve control of the photovoltaic air conditioning system, characterized in that, include: Control the bidirectional AC-DC device to operate in charging mode or discharging mode; The bidirectional AC-DC device, when operating in the charging mode, replenishes the photovoltaic battery with electrical energy from the grid; or, when operating in the discharging mode, feeds the electrical energy stored in the photovoltaic battery back to the grid.

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