Multi-split air conditioner communication system

Abstract

According to the multi-split air conditioner communication system, any one of an outdoor unit and an indoor unit is a communication node and is a transmitting communication node and a receiving communication node; the communication chip is used for receiving a communication signal from the Homebus and transmitting the communication signal sent by the main controller to the Homebus; a receiving side AC coupling circuit; the reference circuit comprises a first reference branch and a second reference branch, the first reference branch and the second reference branch are respectively connected with the same reference ground, the first output end of the first reference branch is connected to the position where the first receiving end is connected with the receiving side alternating current coupling circuit, and the second output end of the second reference branch is connected with the second receiving side alternating current coupling circuit; the second output end of the second reference branch is connected to the position where the second receiving end is connected with the receiving side alternating current coupling circuit. According to the invention, the interference generated on the bus communication waveform can be filtered, and the communication quality is improved.

Description

Technical Field

[0001] This invention relates to the field of air conditioning communication technology, and in particular to a multi-split air conditioning communication system. Background Technology

[0002] Multi-split air conditioning systems consist of an indoor unit system with multiple indoor units and an outdoor unit system with multiple outdoor units. Communication between the indoor and outdoor units typically uses the HomeBus (i.e., home bus system) communication protocol. Currently, most multi-split air conditioning systems use the Sanmei Electric MM1192 communication chip or its similar HH1198 chip as the core, with various communication circuits, drive circuits, and protection circuits integrated in the periphery to form a HomeBus communication system.

[0003] Existing Homebus communication systems that rely on the MM1192 communication chip or its similar HH1198 chip typically use a communication frequency of 9.6KHz and match an RC terminal circuit at the end of the outdoor unit. However, due to the design limitations of the communication hardware circuit, they often cannot support higher communication frequencies. With the increasing demand for high-speed (e.g., 48KHz) communication, in addition to matching an RC terminal circuit on the outdoor unit side, an RC terminal circuit is also matched on the indoor unit side.

[0004] However, regardless of whether it is a low-speed communication scheme at 9.6KHz or a high-speed communication scheme at 48KHz, in practical applications, waveform distortion, attenuation and oscillation on the communication bus will still be encountered. Therefore, finding the key factors affecting the bus communication waveform is the key to improving communication quality. Summary of the Invention

[0005] In response to the problems pointed out in the background art, some embodiments of this application provide a multi-split air conditioning communication system that eliminates interference input to the communication chip by converting differential-mode interference introduced on the communication bus into a common-mode signal to the reference ground, thereby improving the bus communication quality.

[0006] To achieve the above-mentioned objectives, the present invention employs the following technical solution: Some embodiments of this application relate to a multi-split air conditioning communication system, including multiple indoor units and multiple outdoor units communicatively connected to a Homebus bus, wherein any of the outdoor unit and indoor unit is a communication node, and the communication node includes: The master controller is used to control the communication nodes; A communication chip, which is communicatively connected to the main controller, is used to receive communication signals from the Homebus bus and transmit the communication signals sent by the main controller to the Homebus bus; The receiving-side AC coupling circuit is connected to the receiving end of the communication chip and is used to receive communication signals from the Homebus bus. The reference circuit includes a first reference branch and a second reference branch, which are respectively connected to the same reference ground. The first output terminal of the first reference branch is connected to the location where the first receiving terminal is connected to the receiving-side AC coupling circuit in the receiving terminal, and the second output terminal of the second reference branch is connected to the location where the second receiving terminal is connected to the receiving-side AC coupling circuit in the receiving terminal. The resistance value between the first output terminal and the reference ground is equal to the resistance value between the second output terminal and the reference ground, and the resistance value is determined based on the resistance value of the built-in resistor of the communication chip.

[0007] Some embodiments of this application, by setting a reference circuit, analyze the causes of poor communication waveforms. These problems include overshoot, undershoot, noise superposition, and signal attenuation on the differential signals of the first and second receiving terminals of the communication chip due to the non-common grounding of the substrates in different communication nodes. This leads to erroneous switching of the output level signal of the communication chip, reducing communication quality. In order to improve communication quality, this application eliminates the differential-mode interference generated on the communication bus through the reference ground of the reference circuit, avoiding erroneous switching of the output level signal of the communication chip and improving communication quality.

[0008] Furthermore, the resistance values ​​between the first output terminal and the reference ground, as well as the resistance values ​​between the second output terminal and the reference ground, are determined based on the resistance values ​​of the built-in resistors of the communication chip, without affecting the operation of the communication chip itself.

[0009] In some embodiments of this application, the first reference branch is a first pull-down resistor, one end of which is connected to the reference ground, and the other end forms the first output terminal; The second reference branch is a second pull-down resistor, one end of which is connected to the reference ground, and the other end forms the second output terminal.

[0010] In some embodiments of this application, a first pull-down resistor and a second pull-down resistor are used to introduce differential-mode interference on the communication bus into the reference ground when different communication nodes communicate.

[0011] In some embodiments of this application, the reference circuit is powered by a DC power supply of +5V; The first reference branch includes a first pull-up resistor and a first pull-down resistor connected in series. The connection point between the first pull-up resistor and the first pull-down resistor forms the first output terminal. The first pull-up resistor is connected between the first output terminal and the DC power supply, and the first pull-down resistor is connected between the first output terminal and the reference ground. The second reference branch includes a second pull-up resistor and a second pull-down resistor connected in series. The connection point between the second pull-up resistor and the second pull-down resistor forms the second output terminal. The second pull-up resistor is connected between the second output terminal and the DC power supply, and the second pull-down resistor is connected between the second output terminal and the reference ground. The resistance values ​​of the first pull-up resistor, the second pull-up resistor, the first pull-down resistor, and the second pull-up resistor are equal.

[0012] The reference circuit provided in this application not only provides a reference ground, but also clamps the voltage levels at the first and second receiving terminals of the communication chip to a strict 2.5V when idle, ensuring the accuracy of the communication signal transmission of the communication chip.

[0013] In some embodiments of this application, the receiving-side AC coupling circuit includes: The first RC circuit has one end connected to the first differential bus and the other end connected to the common connection point of the first output terminal and the first transceiver terminal. The second RC circuit has one end connected to the second differential bus and the other end connected to the common connection point of the second output terminal and the second transceiver terminal; The first RC circuit and the second RC circuit have the same structure.

[0014] By setting up the first RC circuit and the second RC circuit, interference on the communication bus is prevented from directly entering the communication chip, thus avoiding erroneous switching of the communication signal output level.

[0015] In some embodiments of this application, multiple outdoor units form a first transceiver system, and multiple indoor units form a second transceiver system. The multi-split air conditioning communication system includes: A common-mode inductor having a differential-mode component, the common-mode inductor having a first winding and a second winding, one end of the first winding being connected to a common connection point of the first differential bus, the first receiving terminal and the first transmitting terminal of the first transceiver system, and the other end of the first winding being connected to a common connection point of the first differential bus, the first receiving terminal and the first transmitting terminal of the second transceiver system, one end of the second winding being connected to a common connection point of the second differential bus, the second receiving terminal and the second transmitting terminal of the first transceiver system, and the other end of the second winding being connected to a common connection point of the second differential bus, the second receiving terminal and the second transmitting terminal of the second transceiver system; The common-mode inductor is used to suppress differential-mode interference and common-mode interference on the communication bus, and the cutoff frequency of the common-mode inductor is determined based on the length of the communication bus and the attenuation is 12dB or more.

[0016] Some embodiments of this application relate to a multi-split air conditioning communication system. By simplifying the communication model of the multi-split air conditioning system, the factors affecting the quality of the communication waveform are identified. By setting a common-mode inductor with differential-mode components on the communication bus, common-mode interference and differential-mode interference on the communication bus can be suppressed. At the same time, large current pulses generated on the communication waveform can also be suppressed, thereby improving the quality of the communication waveform.

[0017] The common-mode inductor involved in this application can be designed with an attenuation of 12dB or more, resulting in good communication performance and facilitating high-speed and long-distance transmission of communication signals.

[0018] In some embodiments of this application, the multi-split air conditioning system further includes an impedance matching circuit for matching the impedance during communication signal transmission. The impedance matching circuit includes: The first terminating impedance has one end connected to the common connection point of one end of the first winding, the first receiving end and the first transmitting end of the first transceiver system, and the other end connected to the common connection point of one end of the second winding, the second receiving end and the second transmitting end of the first transceiver system. The second terminating impedance has one end connected to the common connection point of the other end of the first winding, the first receiving end and the first transmitting end of the second transceiver system, and the other end connected to the common connection point of the other end of the second winding, the second receiving end and the second transmitting end of the second transceiver system. Distributed capacitance, which is disposed on the communication bus, is used to eliminate the effect of distributed inductance on impedance matching on the communication bus; Wherein, the resistance values ​​of the first terminal impedance, the second terminal impedance, and the characteristic impedance of the cable used in the communication bus are all equal, and When the first terminating impedance and the second terminating impedance are set at different positions, the following condition must be met: The first terminal impedance is located on the transceiver side of the communication node between the two ends of the first transceiver system, and the second terminal impedance is located on the transceiver side of the communication node between the two ends of the second transceiver system.

[0019] Some embodiments of this application relate to a multi-split air conditioning communication system that, considering high-speed transmission, achieves impedance matching by setting a terminal impedance and a distributed capacitance between the first and second transceiver systems, wherein the resistance values ​​of the first and second terminal impedances are both equal to the characteristic impedance of the cable.

[0020] To avoid communication problems caused by waveform oscillations on the bus during long-distance communication with multiple communication nodes, the distributed parameters of the cable are considered. By setting the distributed capacitance, the influence of inductance on the wiring is eliminated, thereby improving the communication quality.

[0021] In some embodiments of this application, the first terminal impedance is set on the transceiver side of the communication node located at the end of the plurality of communication nodes in the first transceiver system. The second terminal impedance is set on the transceiver side of any one of the multiple communication nodes in the second transceiver system.

[0022] After testing and debugging, it was found that when the first terminal impedance is set on the transceiver side of the communication node located at the head or tail of the multiple communication nodes in the first transceiver system, and the second terminal impedance is set on the transceiver side of the second transceiver system, the communication waveform is good.

[0023] In some embodiments of this application, the second terminal impedance is set on the transceiver side of the communication node located at the end of the plurality of communication nodes in the second transceiver system; The first terminal impedance is set on the transceiver side of any one of the multiple communication nodes in the first transceiver system.

[0024] After testing and debugging, it was found that when the second terminal impedance is set on the transceiver side of the communication node located at the head or tail of the multiple communication nodes in the second transceiver system, while the first terminal impedance is set on the transceiver side of the first transceiver system, the communication waveform is good.

[0025] In some embodiments of this application, the first terminating impedance includes: The first terminal impedance is set on the transceiver side of the communication node located at one end of the multiple communication nodes in the first transceiver system. The second sub-terminal impedance is connected in parallel with the first sub-terminal impedance and is set on the transceiver side of the communication node located at the other end of the multiple communication nodes of the first transceiver system. The resistance values ​​of the first terminal impedance and the second terminal impedance are equal, and the resistance value of the two connected in parallel is equal to the resistance value of the first terminal impedance. The second terminating impedance is set at the transceiver side of the communication node at the free end of the multiple communication nodes in the second transceiver system.

[0026] In some embodiments of this application, the distributed capacitance is calculated based on the cable type, the longest distance, and the communication frequency used.

[0027] In some embodiments of this application, the common-mode inductor is a surface-mount inductor.

[0028] In some embodiments of this application, the surface mount inductor is also known as a power inductor, a high current inductor, and a surface mount high power inductor. It features miniaturization, high quality, high energy storage, and low resistance. Furthermore, its miniaturized design facilitates PCB layout and reduces costs. Attached Figure Description

[0029] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0030] Figure 1 This refers to the connection method of existing multi-split air conditioning systems; Figure 2 A block diagram illustrating the principle of communication between communication nodes in an existing multi-split air conditioning system; Figure 3 This is a communication block diagram between the outdoor and indoor units in an existing multi-split air conditioning system. Figure 4 The waveform diagram shows the actual communication signals of the indoor unit bus, outdoor unit bus, and RXD terminal. Figure 5 This is a circuit layout diagram for the first and second receiving terminals of the communication chip in the indoor unit, where the communication nodes are located. Figure 6 The waveforms of the signal transmitter TXD of the transmitting communication node, the first receiving end IN(2) / second receiving end IN(1) of the receiving communication node, and the signal receiver RXD under ideal conditions are shown. Figure 7 The waveforms of the signal transmitter TXD of the transmitting communication node, the first receiving end IN(2) / second receiving end IN(1) of the receiving communication node, and the signal receiver RXD are shown in the actual situation. Figure 8 The waveforms of the first receiving terminal IN(2) (pin 15 of the MM1192 chip, denoted as 1192-15) / the second receiving terminal IN(1) (pin 16 of the MM1192 chip, denoted as 1192-16), the signal receiving terminal RXD, and the differential signal waveforms of the bus are shown in the diagrams. Figure 9 The waveforms of the first receiving terminal IN(2) / second receiving terminal IN(1) and the bus differential signal of the receiving communication node under non-communication conditions are shown. Figure 10This is a communication schematic diagram of the reference circuit in the communication node of the multi-split air conditioning communication system embodiment proposed in this application; Figure 11 When the communication node is the indoor unit, the circuit connecting the communication chip in the indoor unit to the reference circuit is... Figure 1 ; Figure 12 When the communication node is the indoor unit, the circuit connecting the communication chip in the indoor unit to the reference circuit is... Figure 2 ; Figure 13 Showing the use of Figure 12 The actual waveforms tested are shown when using the reference circuit. Figure 14 Showing the use of Figure 12 The reference circuit shown is used to test the waveforms of pins 15 and 16 of the communication chip separately. Figure 15 Simplified diagram of communication nodes in a multi-split air conditioning communication system Figure 1 ; Figure 16 Waveforms of bus voltage and bus current in a multi-split air conditioning communication system when the outdoor unit is transmitting signals and the indoor unit is silent; Figure 17 The outdoor unit bus communication waveform diagram is a test result of the actual communication line at 0m when the outdoor unit sends a signal and the indoor unit is silent in a multi-split air conditioning communication system. Figure 18 A graph showing the inductance and attenuation relationship of the common mode inductor selected in a multi-split air conditioning communication system; Figure 19 Simulated bus communication waveforms after adding a common-mode inductor to a multi-split air conditioning communication system; Figure 20 This is a schematic diagram of the impedance matching circuit in an embodiment of a multi-split air conditioning communication system according to this application.

[0031] Figure label: 100. Communication nodes; 200 Indoor unit; 210 Indoor main controller; 220 Indoor communication chip; 230 Receiving side AC coupling circuit; 240 Bus drive circuit; 250 Sending side AC coupling circuit; 260 First reference circuit; 300 Outdoor unit; 310 Outdoor main controller; 320 Outdoor communication chip; 330 Second reference circuit; 400 Communication line; 410 Common mode inductor; 1000, First transceiver system; 2000, Second transceiver system. Detailed Implementation

[0032] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0033] In the description of this application, it should be understood that the terms "center", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.

[0034] The terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, unless otherwise stated, "a plurality of" means two or more.

[0035] In the description of this application, it should be noted that, unless otherwise expressly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection between two components. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0036] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can include direct contact between the first and second features, or contact between the first and second features through another feature between them. Furthermore, "above," "over," and "on top" of the second feature includes the first feature directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature includes the first feature directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0037] The following disclosure provides many different embodiments or examples for implementing various structures of the invention. To simplify the disclosure, specific examples of components and arrangements are described below. These are merely examples and are not intended to limit the invention. Furthermore, reference numerals and / or letters may be repeated in different examples; such repetition is for simplification and clarity and does not in itself indicate a relationship between the various embodiments and / or arrangements discussed. In addition, examples of various specific processes and materials are provided in this invention, but those skilled in the art will recognize the application of other processes and / or the use of other materials.

[0038] Basic working principle of air conditioners Air conditioners execute a refrigeration cycle using a compressor, condenser, expansion valve, and evaporator. The refrigeration cycle involves a series of processes, including compression, condensation, expansion, and evaporation, to cool or heat an indoor space.

[0039] Low-temperature, low-pressure refrigerant enters the compressor, which compresses it into a high-temperature, high-pressure refrigerant gas and discharges the compressed refrigerant gas. The discharged refrigerant gas flows into the condenser. The condenser condenses the compressed refrigerant into a liquid phase, and the heat is released to the surrounding environment through the condensation process.

[0040] The expansion valve expands the high-temperature, high-pressure liquid refrigerant that condenses in the condenser into a low-pressure liquid refrigerant. The evaporator evaporates the expanded refrigerant in the expansion valve and returns the low-temperature, low-pressure refrigerant gas to the compressor. The evaporator achieves its cooling effect by utilizing the latent heat of refrigerant evaporation to exchange heat with the material being cooled. Throughout the cycle, the air conditioner regulates the temperature of the indoor space.

[0041] The outdoor unit of an air conditioner refers to the part of the refrigeration cycle that includes the compressor and the outdoor heat exchanger. The indoor unit of an air conditioner includes the indoor heat exchanger, and an expansion valve can be provided in either the indoor or outdoor unit.

[0042] The indoor and outdoor heat exchangers function as either condensers or evaporators. When the indoor heat exchanger is used as a condenser, the air conditioner functions as a heater in heating mode; when the indoor heat exchanger is used as an evaporator, the air conditioner functions as a cooler in cooling mode.

[0043] This application relates to a communication system for multi-split air conditioning systems. The basic working principle of a multi-split air conditioning system is described above in the section on the basic working principle of an air conditioner.

[0044] In some embodiments of this application, the multi-split air conditioning system includes multiple indoor units and multiple outdoor units that are sequentially connected to a communication bus (e.g., a Homebus bus). The indoor units and outdoor units communicate using differential signals on the Homebus bus.

[0045] See Figure 1 It shows multiple indoor units (IDU, In Door Unit) and multiple outdoor units (ODU, Out Door Unit) connected to the communication bus.

[0046] In the existing solution, the maximum number of outdoor units installed is 40, and the maximum number of indoor units installed is 160, for a total of 200 nodes.

[0047] Multiple outdoor units and multiple indoor units are connected sequentially to a communication bus. Each indoor and outdoor unit is a communication node and is used to send and receive communication signals transmitted through the communication bus.

[0048] Both indoor and outdoor units can serve as transmitting communication nodes, and both can serve as receiving communication nodes that communicate with transmitting communication nodes. The terms "transmitting" and "receiving" are relative.

[0049] In some embodiments of this application, for ease of description, the entire system formed by multiple indoor units is referred to as an indoor unit system, and the entire system formed by multiple outdoor units is referred to as an outdoor unit system.

[0050] In use, communication signals can be sent from the indoor unit in the indoor unit system to the outdoor unit in the outdoor unit system, and vice versa. Therefore, both the indoor unit system and the outdoor unit system can be used as transmitting systems, and both can be used as receiving and transmitting systems.

[0051] In some embodiments of this application, the indoor unit system is referred to as the first transceiver system 1000, and the outdoor unit system is referred to as the second transceiver system 2000.

[0052] For ease of description, any communication node (an indoor unit or an outdoor unit) is denoted as communication node 100.

[0053] In some embodiments of this application, in order to achieve communication between communication nodes, see [link to relevant documentation]. Figure 2 The communication node 100 includes a main controller and a communication chip.

[0054] In some embodiments of this application, the communication chip is typically the MM1192 communication chip, which receives signals that have undergone Alternate Mark Inversion (AMI) (referred to as AMI signals).

[0055] All communication chips have a Homebus interface for connecting to the Homebus bus.

[0056] The Homebus includes a first differential bus (i.e., bus A) and a second differential bus (i.e., bus B), on which the bus AMI signal is transmitted.

[0057] In some embodiments of this application, in order to ensure the transmission of AMI signals, corresponding peripheral circuits are also provided for the communication chip.

[0058] See Figure 2 Let's take a communication node 100 as an example for explanation.

[0059] The peripheral circuits described above include: signal coupling circuit, bus drive circuit, demodulation circuit, and modulation circuit.

[0060] Signal coupling circuit Signal coupling circuits are used to send and receive communication commands for communication chips.

[0061] The signal coupling circuit includes a receiving-side AC coupling circuit and a transmitting-side AC coupling circuit.

[0062] The receiving-side AC coupling circuit is used to receive communication signals sent from the transmitting end of the transmitting communication node on the Homebus bus and send them to the receiving end of the communication chip of the receiving communication node.

[0063] The AC coupling circuit on the receiving side is implemented by selecting appropriate resistors and capacitors to ensure that the signal received from the Homebus bus is filtered out of noise such as DC signals.

[0064] See Figure 3 This shows the communication between the indoor unit 200 and the outdoor unit 300.

[0065] exist Figure 3 The diagram shows that the AC coupling circuit 230 of the indoor unit 200, which serves as the receiving communication node, uses a resistor and a capacitor connected in series, or a resistor and a capacitor connected in parallel, etc.

[0066] See Figure 3 A first resistor R10 and a first capacitor C9 are connected in series between the second receiving terminal IN (1) of the communication chip in the first differential bus and the indoor unit 200.

[0067] The AC coupling circuit on the transmitting side is used to receive the communication signals output by the communication chip of the transmitting communication node at the transmitting end and send them to the Homebus bus.

[0068] The AC coupling circuit on the transmitting side is implemented by selecting appropriate resistors and capacitors to ensure that the signal sent to the Homebus bus is filtered out of noise such as DC signals.

[0069] exist Figure 3 The diagram shows that the AC coupling circuit 250 on the transmitting side of the indoor unit 200, which serves as the transmitting communication node, is implemented using a series capacitor (e.g., capacitor C6).

[0070] Bus drive loop Due to the technical requirements of the MM1192 communication chip, see [link / reference]. Figure 2 A bus drive circuit is also connected between bus A and bus B of the Homebus bus to drive the signal output by the amplification communication chip at the transmitting end.

[0071] See Figure 3 The bus drive circuit 240 includes an NPN transistor Q6 connected to the output pins OUT(a) and OUT(A) of the MM1192 communication chip and an NPN transistor Q7 connected to the output pins OUT(b) and OUT(B) of the MM1192 communication chip, which are used to drive the amplified output signal.

[0072] Among them, OUT(A) and OUT(B) are the communication chip at the transmitting end.

[0073] The AMI signal from the Homebus (i.e., the signal shown at IV) is received by the Homebus bus interface on the receiving side of the communication chip and is shown at its output terminal DataOut at V.

[0074] The signal shown at output VI is converted by the demodulation circuit and received at the receiving end RXD of the master controller, which is the receiving node.

[0075] During transmission, after processing by the main controller, the signal shown at point I is output at the main controller's signal transmission terminal TXD and sent to the modulation circuit.

[0076] The signal shown at point III after conversion by the modulation circuit is input to the DataIn input terminal of the communication chip.

[0077] Figure 4 The waveforms of the signals received by the outdoor unit bus, indoor unit bus, and RXD terminal shown in the figure indicate a communication failure (see [reference]). Figure 4 (As shown in the red circle).

[0078] Interference on the communication bus is ever-changing. When the communication waveform on the bus is good, communication may still be poor; of course, when the communication waveform is bad, communication will definitely be poor.

[0079] In some embodiments of this application, in order to identify situations where communication waveforms are good but communication is poor, it is necessary to conduct in-depth analysis of the communication chip.

[0080] See Figure 5 It provides a block diagram of the peripheral principle of the communication chip.

[0081] Figure 5 BUS-A and BUS-B are Homebus buses. They are filtered by the AC coupling circuit 230 on the receiving side as described above, and finally differential operation is performed on pin 15 (i.e. the first receiving terminal IN (2)) and pin 16 (i.e. the second receiving terminal IN (1)) of the communication chip.

[0082] Signal conversion is performed by comparing the difference between the differential signals with the voltage comparison sensitivity limit Vrs. When the difference between pins 15 and 16 exceeds the voltage comparison sensitivity limit Vrs, the output terminal DataOut (i.e., pin 1) of the communication chip outputs a low level. When the difference between pins 15 and 16 is lower than Vrs, pin 1 of the communication chip outputs a high level.

[0083] It should be noted that Vrs is a parameter provided by the MM1192 chip and is set to 0.75V / 2.

[0084] See Figure 5 The receiving sensitivity has two indicators: one is the receiving sensitivity VRS of the communication chip; the other is the voltage comparison sensitivity limit Vrs.

[0085] VRS and Vrs are defined as follows: VRS = VIN1 - VIN2; Vrs = V1 - V2.

[0086] See Figure 5 , VIN1=V1*(R9+Rin1) / Rin1, VIN2=V2*(R10+Rin2) / Rin2.

[0087] Generally, Rin1=Rin2=33KΩ (integrated within the chip), R9=R10. Therefore, for ease of description, we denote Rin1=Rin2=Rin, R9=R10=R.

[0088] VRS=VIN1-VIN2=V1*(R9+Rin1) / Rin1-V2*(R10+Rin2) / Rin2=(V1-V2)*(Rin+R) / Rin=Vrs*(Rin+R) / Rin.

[0089] When R = Rin = 33KΩ, VRS = 2Vrs.

[0090] In practice, the VRS setting should be greater than the amplitude of the interference signal on the bus, but less than the difference between the differential signals on the bus, |VIN1-VIN2|.

[0091] When the value of |V1-V2| is greater than Vrs, the voltage level will flip.

[0092] When the value of |VIN1-VIN2| is greater than VRS, the voltage level will flip.

[0093] Figure 6 The waveform diagram shown illustrates an ideal scenario where there is no interference in the communication signal. However, in actual communication, there are many sources of interference, making it impossible for interference to occur. Figure 7 The waveform in the image.

[0094] in, Figure 6 The upper dashed line represents +Vrs, and the lower dashed line represents -Vrs.

[0095] Actual communication scenarios are far more complex than ideal ones. Adhering to the principle of simplifying complexity, this section focuses on the connections on the communication bus... Figure 1 The nodes of the 160 indoor units and 40 outdoor units were simplified.

[0096] The 200 communication nodes are simplified into a first transceiver system 1000 and a second transceiver system 2000.

[0097] For example, the first transceiver system 1000 is an indoor unit system used for receiving messages, and the second transceiver system 2000 is an outdoor unit system used for sending messages.

[0098] See Figure 3 The communication chip of outdoor unit 300 sends bus data through pins 9 and 10, while the communication chip MM1192 of indoor unit 200 receives data through pins 15 and 16.

[0099] When the signal flows only inside the outdoor unit system, there is no corresponding interference because there is only one ground GND2 (not shown, which is the ground connected to the emitter of NPN transistor Q7 in the bus drive circuit 240 of the outdoor unit 300).

[0100] However, since the indoor unit 200 needs to receive signals, if the level of the first differential bus from the outdoor unit 300 is high, this level must be transmitted not only within the outdoor unit system but also to the indoor unit system.

[0101] See Figure 5 The communication chip of indoor unit 200 has a ground GND1, while outdoor unit 300 and indoor unit 200 do not share a ground.

[0102] The outdoor unit system and the indoor unit system do not share a ground, but the signal needs to flow between the two systems. The communication chip is generally based on CMOS architecture, which has a very high input impedance. Even a small interference on the bus can disturb pins 15 and 16 of the communication chip, causing poor communication.

[0103] See Figure 7 It shows a waveform diagram of poor communication caused by interference.

[0104] Figure 7 The middle circle A shows that pins 15 and 16 of the communication chip MM1192 can cause differential malfunctions due to excessive overshoot and undershoot. Figure 7 The middle circle B indicates a malfunction caused by the superposition of differential noise; Figure 7 The middle circle C indicates a malfunction caused by the attenuation of the AMI signal on the bus.

[0105] Figure 8 The waveform of poor communication during actual testing is shown in the image. Figure 8 As can be seen, there is significant interference at pins 15 and 16 of the communication chip MM1192. The red circle indicates the area with poor communication, and the red waveform line represents the differential waveform of pins 15 and 16, which was synthesized on an oscilloscope.

[0106] See Figure 9 Even without communication, pins 15 and 16 of the communication chip MM1192 will experience significant interference under normal conditions.

[0107] To address the above issues, considering that the communication system involves 200 nodes, a 1000m communication line, and the communication chip is a high-impedance CMOS architecture, some embodiments of this application include reference circuits at pins 15 and 16 of the communication chip MM1192, which can filter out interference caused by other substrates.

[0108] In some embodiments of this application, each communication node can serve as a receiving communication node. Therefore, a reference circuit needs to be set up for the receiving side of each communication node.

[0109] Figure 10 A simplified block diagram showing communication between an indoor unit 200 and an outdoor unit 300 is shown.

[0110] The indoor unit 200 includes an indoor main controller 210 and an indoor communication chip 220, and the outdoor unit 300 includes an outdoor main controller 310 and an outdoor communication chip 320.

[0111] A first reference circuit 260 is provided on the receiving side of the indoor communication chip 220, and a second reference circuit 330 is provided on the receiving side of the outdoor communication chip 320.

[0112] The first reference circuit 260 and the second reference circuit 330 have the same structure.

[0113] In some embodiments of this application, the reference circuit includes a first reference branch and a second reference branch.

[0114] The first reference branch and the second reference branch are connected in parallel and are respectively connected to the same reference ground GND.

[0115] The first output terminal of the first reference branch is connected to the location where the first receiving terminal IN(2) is connected to the AC coupling circuit on the receiving side, and the second output terminal of the second reference branch is connected to the location where the second receiving terminal IN(1) is connected to the AC coupling circuit on the receiving side.

[0116] In this way, interference from the bus is converted into common-mode interference to the reference ground GND and filtered out. At the same time, the resistance values ​​between the first output terminal and the reference ground GND and the second output terminal and the reference ground GND are determined based on the resistance values ​​of the built-in resistors of the communication chip, so that the normal communication of the communication chip will not be affected by adding a reference circuit.

[0117] The following explanation uses only the structure of the first reference circuit 260 as an example.

[0118] See Figure 11 It shows the arrangement of the first reference circuit 260.

[0119] The first reference branch includes resistor R2, and the resistance between the first output terminal OUT1 and the reference ground GND is the value of R2; the second reference branch includes resistor R4, and the resistance between the second output terminal OUT2 and the reference ground GND is the value of R4.

[0120] During communication, the signals from points A and B on the communication bus need to be differentially calculated within the comparator of the indoor communication chip 220. Since the voltage at pins 15 and 16 of the indoor communication chip 220 needs to be maintained at 2.5V when idle, R2 = R4.

[0121] According to the specifications of the communication chip, the built-in Rin range is between 25KΩ and 46KΩ.

[0122] See Figure 11 Resistor R2 is equivalent to being connected in parallel with Rin1. Therefore, the parallel resistance should be between 25KΩ and 46KΩ. In this case, R2 > 103.125KΩ.

[0123] The larger the resistance, the greater the interference. Based on actual testing, R2=120KΩ was selected.

[0124] See Figure 12 This shows another circuit diagram of the first reference circuit 260.

[0125] When the indoor communication chip 220 is idle, the voltage levels at pins 15 and 16 are 2.5V. This 2.5V is converted internally by the chip and is not strictly 2.5V because it is connected through two 33KΩ resistors. During communication, the voltage levels at pins 15 and 16 will change.

[0126] Therefore, in some embodiments of this application, when idle, the voltage levels of pins 15 and 16 must be clamped at 2.5V to avoid interference. During communication, it can perform differential operations with signals from points A and B within the comparator.

[0127] See Figure 12 The first reference circuit 260 is powered by a DC power supply of +5V.

[0128] The first reference branch includes a first pull-up resistor R1 and a first pull-down resistor R2 connected in series. The connection point between the first pull-up resistor R1 and the first pull-down resistor R2 forms the first output terminal OUT1. The first pull-up resistor R1 is connected between the first output terminal OUT1 and the DC power supply +5V, and the first pull-down resistor R2 is connected between the first output terminal OUT1 and the reference ground GND.

[0129] The second reference branch includes a second pull-up resistor R3 and a second pull-down resistor R4 connected in series. The connection point between the second pull-up resistor R3 and the second pull-down resistor R4 forms the second output terminal OUT2. The second pull-up resistor R3 is connected between the second output terminal OUT2 and the DC power supply +5V, and the second pull-down resistor R4 is connected between the second output terminal OUT2 and the reference ground GND.

[0130] In idle state, to ensure that the voltage levels at the first output terminal OUT1 and the second output terminal OUT2 are 2.5V respectively, the resistance values ​​of the first pull-up resistor R1, the second pull-up resistor R3, the first pull-down resistor R2, and the second pull-down resistor R4 must be equal.

[0131] That is, R1=R2=R3=R4.

[0132] After checking the specifications of the communication chip, the built-in Rin range is between 25KΩ and 46KΩ. Therefore, see... Figure 12 Resistor R2 is equivalent to being connected in parallel with Rin1. Therefore, the parallel resistance should be between 25KΩ and 46KΩ. In this case, R2 > 103.125KΩ.

[0133] The larger the resistance, the greater the interference. Through actual testing, R1=R2=R3=R4=120KΩ was selected.

[0134] In some embodiments of this application, although Figure 12R1 / R2 / R3 / R4 shown is a single resistor, but R1 can also be designed to include multiple sub-resistors connected in series, with the total resistance value of these multiple sub-resistors designed to be 120KΩ.

[0135] See Figure 13 It shows the use of Figure 13 The actual waveforms tested are shown in the reference circuit.

[0136] pass Figure 13 The communication waveforms given are relatively smooth, with almost no interference, whether they are differential signals or communication signals received at the RXD end.

[0137] See Figure 14 It shows the use of Figure 12 The reference circuit shown is used to test the waveforms of pins 15 and 16 of the communication chip separately.

[0138] Figure 14 and Figure 8 The image shows a comparison of the differential signals between pins 15 and 16. Figure 14 The differential signal shown is essentially free of interference.

[0139] In some embodiments of this application, a reference circuit is added to the receiving side of the communication chip to convert interference generated on the bus into a common-mode signal to the reference ground, thereby filtering out the interference signal through the reference ground.

[0140] There are many factors that affect the communication waveform on the bus. In some embodiments of this application, in order to find the key factors affecting the communication waveform on the bus, the nodes of, for example, 160 indoor units and 40 outdoor units connected to the communication bus are simplified.

[0141] See the simplified diagram. Figure 15 Only the key components affecting the communication section are drawn separately, including (1) the communication chip MM1192; (2) the DC blocking capacitors C6 and C7 on the communication bus; (3) the switching transistors Q6 and Q7 that form the bus drive circuit; and (4) the communication line 400.

[0142] exist Figure 15 Based on this, a simplified communication loop analysis is performed on multiple communication nodes (e.g., 200 communication nodes, including 40 outdoor units and 160 indoor units).

[0143] With outdoor unit 300 transmitting while indoor unit 200 remains silent, and the communication distance less than 20 meters (i.e., ignoring the resistance and inductance parameters on the bus), simulations were performed. The simulation results for bus voltage and bus current are shown below. Figure 6 .

[0144] Figure 16As can be seen, there is a relatively large current spike on the bus. Although the simulated waveform has very little distortion, the actual test bus communication waveform can be found in [reference needed]. Figure 7 It can be seen that the bus communication waveform exhibits significant oscillations (see...). Figure 17 (The part circled in red).

[0145] Therefore, it is necessary to suppress large current surges on the bus to avoid oscillations in the bus communication waveform.

[0146] In some embodiments of this application, a common-mode inductor 410 with a differential-mode component is provided on the communication bus (see...). Figure 15 This is used to reduce differential-mode interference and common-mode interference on the communication bus and improve the quality of bus communication.

[0147] See Figure 15 The common-mode inductor 410 has two windings, denoted as: the first winding and the second winding.

[0148] The first winding is set on the first differential bus of the communication bus, and the second winding is set on the second differential bus of the communication bus.

[0149] The communication between the two transceiver systems will be explained using the indoor unit 200 in the first transceiver system 1000 as an example and the outdoor unit 300 in the second transceiver system 2000 as an example.

[0150] Since differential signals are transmitted on the communication bus, the receiving side includes two differential terminals, referred to as the first receiving terminal and the second receiving terminal, and the transmitting side also includes two differential terminals, referred to as the first transmitting terminal and the second transmitting terminal.

[0151] For example, see Figure 15 When the second transceiver system 2000 sends a message, the first sending end is OUT(A) and the second sending end is OUT(B). When the first transceiver system 1000 receives a message, the first receiving end is IN(2) and the second receiving end is IN(1).

[0152] When setting the common-mode inductor 410, see [link / reference]. Figure 15 One end of the first winding is connected to the common connection point of the first differential bus of the communication bus, the first receiving terminal IN(2) and the first transmitting terminal OUT(A) of the first transceiver system 1000, and the other end of the first winding is connected to the common connection point of the first differential bus of the communication bus, the first receiving terminal IN(2) and the first transmitting terminal OUT(A) of the second transceiver system 2000. One end of the second winding is connected to the common connection point of the second differential bus of the communication bus, the second receiving terminal IN(1) and the second transmitting terminal OUT(B) of the first transceiver system 1000, and the other end of the second winding is connected to the common connection point of the second differential bus of the communication bus, the second receiving terminal IN(1) and the second transmitting terminal OUT(B) of the second transceiver system 2000.

[0153] The selection of common mode inductor 410 should meet the requirements of signal transmission distance. This invention requires a communication distance of 0 to 1000 meters. Considering the design margin, the design requires a communication distance of 1200 meters.

[0154] In communication principles, when the length of the communication cable exceeds 1 / 4 of the wavelength, the communication line 400 can no longer be considered as lossless transmission. At this point, the parasitic effect becomes significant. Therefore, the length of the communication line 400 must be less than 1 / 4 of the wavelength.

[0155] Therefore, in some embodiments of this application, if the communication distance is considered to be 1200 meters, then 1200m = λ / 4, and the cutoff frequency f = c / λ, where c = 300000km / s is the speed of light in a vacuum, and therefore f = 62.5KHz.

[0156] Therefore, it is necessary to consider that the common-mode inductor 410 has a high attenuation effect at its cutoff frequency and also has a differential-mode component.

[0157] The greater the attenuation effect, the better the effect, but the size of the inductor will also be larger. Therefore, taking into account both the attenuation effect and long-distance communication transmission, in some embodiments of this application, the attenuation of the common mode inductor 410 is required to reach 12dB or more.

[0158] In some embodiments of this application, the common-mode inductor 410 can be a small surface-mount common-mode inductor 410, such as a Würth 744222 small common-mode inductor 410, based on the inductance and attenuation relationship curve. Figure 19 It can be seen that it has a 16.5dB attenuation at a frequency of 62.5KHz, and according to the data, the common mode inductor 410 also has a 90nH differential mode component, which meets the selection requirements of this application for the common mode inductor 410.

[0159] When the common-mode inductor 410 selected above is applied to the communication line 400, the waveforms of the bus voltage and bus current obtained from the simulation test are shown below. Figure 19 As shown.

[0160] In some embodiments of this application, when considering high-speed (e.g., 48kHz) communication, impedance matching between the transmitting and receiving sides also needs to be considered.

[0161] Furthermore, considering that the length of the communication bus is also a factor affecting the signal or energy, the concept of characteristic impedance is introduced.

[0162] When selecting cables, the characteristic impedance will vary depending on the type of cable.

[0163] In a multi-split air conditioning system, if the Homebus bus cable is selected as the communication cable VCTF05, then the characteristic impedance Z0 is 75Ω.

[0164] For multi-split air conditioners, after considering the load impedance and characteristic impedance, a system can be established as follows: Figure 20 The impedance matching circuit model is shown.

[0165] See Figure 20 If we take the outdoor unit as the signal source in the outdoor unit system, that is, the outdoor unit system is the transmitting side system, then the reflection coefficient of the impedance matching circuit is (ZL-Z0) / (ZL+Z0).

[0166] If the indoor unit in the indoor unit system is taken as the signal source, that is, the indoor unit system is the transmitting side system, then the reflection coefficient of the impedance matching circuit is (ZS-Z0) / (ZS+R0).

[0167] Where ZL represents the indoor unit system-side terminal impedance, and ZS represents the outdoor unit system-side terminal impedance.

[0168] As mentioned above, see Figure 20 Let ZS be the first terminating impedance set on the transceiver side of the first transceiver system 1000, and ZL be the second terminating impedance set on the transceiver side of the second transceiver system 2000.

[0169] In some embodiments of this application, see reference 1. Figure 15 One end of the first terminating impedance ZS is connected to the common connection point of one end of the first winding, the first receiving terminal IN (2) and the first transmitting terminal OUT (A) of the first transceiver system 1000, and the other end of the first terminating impedance ZS is connected to the common connection point of one end of the second winding, the second receiving terminal IN (1) and the second transmitting terminal OUT (B) of the first transceiver system 1000.

[0170] One end of the second terminating impedance ZL is connected to the common connection point of the other end of the first winding, the first receiving terminal IN(2) and the first transmitting terminal OUT(A) of the second transceiver system 2000, and the other end of the second terminating impedance ZL is connected to the common connection point of the other end of the second winding, the second receiving terminal IN(1) and the second transmitting terminal OUT(B) of the second transceiver system 2000.

[0171] When testing the waveform of the communication signal, it was found that the following conditions were met when the settings of the first terminal impedance ZS and the second terminal impedance ZL were different.

[0172] That is, the first terminal impedance ZS is located on the transceiver side of the communication node between the two ends of the first transceiver system 1000, and the second terminal impedance ZL is located on the transceiver side of the communication node between the two ends of the second transceiver system 2000.

[0173] See back Figure 1 In some embodiments of this application, the first transceiver system 1000 is an indoor unit system, and the indoor unit system includes 160 indoor units connected in sequence, which are numbered IDU1, IDU2, ..., IDU160 in sequence according to the direction of communication signal transmission.

[0174] When the corresponding indoor unit system receives signals, the outdoor unit is the transmitting communication node and the indoor unit is the receiving communication node, that is, the communication signal transmission direction is from the outdoor unit to the indoor unit.

[0175] At this point, the indoor unit at the free end is the tail of the indoor unit system (i.e., the indoor unit is the tail indoor unit), and the indoor unit at the other end of the multiple indoor units in the indoor unit system is the head of the indoor unit system (i.e., the indoor unit is the head indoor unit).

[0176] At this time, the head indoor unit of the indoor unit system is IDU1, and the tail indoor unit of the indoor unit system is IDU160.

[0177] The second transceiver system 2000 is an outdoor unit system, which includes forty outdoor units connected in sequence, numbered ODU1, ODU2, ..., ODU40 according to the direction of communication signal transmission.

[0178] In some embodiments of this application, when the second transceiver system 2000 transmits a message, the outdoor unit at the free end is the head of the outdoor unit system (i.e., the outdoor unit is the head outdoor unit), and the outdoor unit located at the other end of the multiple outdoor units in the outdoor unit system is the tail of the outdoor unit system (i.e., the outdoor unit is the tail outdoor unit).

[0179] At this time, the head outdoor unit of the outdoor unit system is ODU1, and the tail outdoor unit of the outdoor unit system is ODU40.

[0180] In some embodiments of this application, the outdoor units at both ends of the outdoor unit system include a head outdoor unit and a tail outdoor unit, and the indoor units at both ends of the indoor unit system include a head indoor unit and a tail indoor unit, with the head and tail being relative terms.

[0181] In some embodiments of this application, the following conditions are met when the positions of the first terminating impedance ZS and the second terminating impedance ZL are not the same: The first terminating impedance ZS is located on any of the transceiver sides of IDU2 to ODU159, and the second terminating impedance ZL is located on any of the transceiver sides of ODU2 to ODU39.

[0182] The following provides various arrangements of the first terminating impedance ZS and the second terminating impedance ZL.

[0183] In some embodiments of this application, the second terminal impedance ZL is set on the transceiver side of the outdoor unit located at the end of the plurality of outdoor units. For example, the second terminal impedance ZL is set on the transceiver side of ODU1 or the transceiver side of ODU40.

[0184] The first terminating impedance ZS is set on the transceiver side of any indoor unit. For example, the second terminating impedance ZL is set on the transceiver side of any one of IDU1 to IDU160.

[0185] In some embodiments of this application, the second terminal impedance ZL is set on the transceiver side of any outdoor unit. For example, the second terminal impedance ZL is set on the transceiver side of any one of ODU1 to ODU40.

[0186] The first terminating impedance ZS is set on the transceiver side of the indoor unit located at the end of the multiple indoor units. For example, the second terminating impedance ZL is set on the transceiver side of IDU1 or IDU160.

[0187] For long-distance communication, it is also necessary to consider setting distributed capacitance to eliminate the effect of distributed inductance on impedance matching on the Homebus bus.

[0188] The key component in a cable is the distributed inductance on the signal line. According to the conjugate principle, since there is inductance on the signal line, its impedance matching circuit needs to use a capacitor to eliminate the influence of the inductance. That is, the inductive reactance of the inductor and the capacitive reactance of the capacitor are equal.

[0189] The inductive reactance of the inductor is 2πfL, where f is the communication frequency and L is the inductance.

[0190] The capacitive reactance of the capacitor is 1 / (2πfc), where c is the capacitance.

[0191] In some embodiments of this application, the high-speed communication frequency f can be selected as a communication frequency greater than 20KHz, for example, the communication frequency f is selected as 48KHz.

[0192] Choose a cable length of 1000 meters.

[0193] Based on the communication cable model mentioned above, the total distributed inductance L on the cable can be calculated: for example, 1000 * 0.32 = 320 (uH); Let 2πfL = 1 / (2πfc), then the total distributed capacitance c on the cable is calculated to be 34.4nF.

[0194] This distributed capacitance is placed on the Homebus bus to eliminate the effect of the distributed inductance L on impedance matching in the cable.

[0195] As mentioned above, the terminating impedance is calculated considering the characteristic impedance of the signal line, and the distributed capacitance is calculated considering the communication frequency and cable length. Therefore, an impedance matching circuit that considers the terminating impedance and distributed capacitance can improve the impedance matching when the communication signal is transmitted over a long distance, thereby improving the communication quality.

[0196] As described above, the multi-split air conditioning communication system can reduce the oscillation and attenuation of the communication bus waveform under both high-speed and low-speed communication, thus meeting the requirements for high-quality communication compatible with both high-speed and low-speed conditions.

[0197] In the description of the above embodiments, specific features, structures, materials, or characteristics may be combined in any suitable manner in one or more embodiments or examples.

[0198] The above are merely specific embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A multi-split air conditioning communication system, characterized in that, This includes multiple indoor units and multiple outdoor units connected to the Homebus bus, where each outdoor unit and indoor unit is a communication node. The communication node includes: The master controller is used to control the communication nodes; A communication chip, which is communicatively connected to the main controller, is used to receive communication signals from the Homebus bus and transmit the communication signals sent by the main controller to the Homebus bus; The receiving-side AC coupling circuit is connected to the receiving end of the communication chip and is used to receive communication signals from the Homebus bus. The reference circuit includes a first reference branch and a second reference branch, which are respectively connected to the same reference ground. The first output terminal of the first reference branch is connected to the location where the first receiving terminal is connected to the receiving-side AC coupling circuit in the receiving terminal, and the second output terminal of the second reference branch is connected to the location where the second receiving terminal is connected to the receiving-side AC coupling circuit in the receiving terminal. The resistance value between the first output terminal and the reference ground is equal to the resistance value between the second output terminal and the reference ground, and the resistance value is determined based on the resistance value of the built-in resistor of the communication chip.

2. The multi-split air conditioning communication system according to claim 1, characterized in that, The first reference branch is a first pull-down resistor, one end of which is connected to the reference ground, and the other end forms the first output terminal; The second reference branch is a second pull-down resistor, one end of which is connected to the reference ground, and the other end forms the second output terminal.

3. The multi-split air conditioning communication system according to claim 1, characterized in that, The reference circuit is powered by a DC power supply of +5V. The first reference branch includes a first pull-up resistor and a first pull-down resistor connected in series. The connection point between the first pull-up resistor and the first pull-down resistor forms the first output terminal. The first pull-up resistor is connected between the first output terminal and the DC power supply, and the first pull-down resistor is connected between the first output terminal and the reference ground. The second reference branch includes a second pull-up resistor and a second pull-down resistor connected in series. The connection point between the second pull-up resistor and the second pull-down resistor forms the second output terminal. The second pull-up resistor is connected between the second output terminal and the DC power supply, and the second pull-down resistor is connected between the second output terminal and the reference ground. The resistance values ​​of the first pull-up resistor, the second pull-up resistor, the first pull-down resistor, and the second pull-up resistor are equal.

4. The multi-split air conditioning communication system according to claim 1, characterized in that, The receiving-side AC coupling circuit includes: The first RC circuit has one end connected to the first differential bus of the Homebus bus and the other end connected to the common connection point of the first output terminal and the first transceiver terminal. The second RC circuit has one end connected to the second differential bus of the Homebus bus, and the other end connected to the common connection point of the second output terminal and the second transceiver terminal; The first RC circuit and the second RC circuit have the same structure.

5. The multi-split air conditioning communication system according to claim 1, characterized in that, Multiple outdoor units form a first transceiver system, and multiple indoor units form a second transceiver system. The multi-split air conditioning communication system includes: A common-mode inductor having a differential-mode component, the common-mode inductor having a first winding and a second winding, one end of the first winding being connected to the common connection point of the first differential bus of the Homebus bus, the first receiving terminal and the first transmitting terminal of the first transceiver system, and the other end of the first winding being connected to the common connection point of the first differential bus, the first receiving terminal and the first transmitting terminal of the second transceiver system, one end of the second winding being connected to the common connection point of the second differential bus of the Homebus bus, the second receiving terminal and the second transmitting terminal of the first transceiver system, and the other end of the second winding being connected to the common connection point of the second differential bus, the second receiving terminal and the second transmitting terminal of the second transceiver system; The common-mode inductor is used to suppress differential-mode interference and common-mode interference on the communication bus, and the cutoff frequency of the common-mode inductor is determined based on the length of the communication bus and the attenuation is 12dB or more.

6. The multi-split air conditioning communication system according to claim 5, characterized in that, The common-mode inductor is a surface-mount inductor.

7. The multi-split air conditioning communication system according to claim 5, characterized in that, The multi-split air conditioning system further includes an impedance matching circuit, which is used to match the impedance during communication signal transmission. The impedance matching circuit includes: The first terminating impedance has one end connected to the common connection point of one end of the first winding, the first receiving end and the first transmitting end of the first transceiver system, and the other end connected to the common connection point of one end of the second winding, the second receiving end and the second transmitting end of the first transceiver system. The second terminating impedance has one end connected to the common connection point of the other end of the first winding, the first receiving end and the first transmitting end of the second transceiver system, and the other end connected to the common connection point of the other end of the second winding, the second receiving end and the second transmitting end of the second transceiver system. Distributed capacitance, which is disposed on the communication bus, is used to eliminate the effect of distributed inductance on impedance matching on the communication bus; Wherein, the resistance values ​​of the first terminal impedance, the second terminal impedance, and the characteristic impedance of the cable used in the communication bus are all equal, and When the first terminating impedance and the second terminating impedance are set at different positions, the following condition must be met: The first terminal impedance is located on the transceiver side of the communication node between the two ends of the first transceiver system, and the second terminal impedance is located on the transceiver side of the communication node between the two ends of the second transceiver system.

8. The multi-split air conditioning communication system according to claim 7, characterized in that, The first terminal impedance is set on the transceiver side of the communication node located at the end of the multiple communication nodes in the first transceiver system. The second terminal impedance is set on the transceiver side of any one of the multiple communication nodes in the second transceiver system.

9. The multi-split air conditioning communication system according to claim 8, characterized in that, The second terminal impedance is set on the transceiver side of the communication node located at the end of the multiple communication nodes in the second transceiver system. The first terminal impedance is set on the transceiver side of any one of the multiple communication nodes in the first transceiver system.

10. The multi-split air conditioning communication system according to claim 7, characterized in that, The distributed capacitance is calculated based on the cable type, maximum distance, and communication frequency used.

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