Communication system, slave unit used for communication system, and communication method

A communication system includes a master unit; and a plurality of slave units including a slave unit to which a termination resistance is set, the plurality of slave units connected to the master unit via a communication line. In the communication system, the master unit includes a master communication control unit that normally sets a communication rate of communication performed with the plurality of slave units to a high baud rate, switches the high baud rate to a low baud rate after detecting that communication with the slave unit to which the termination resistance is set is disabled, transmits an instruction for switching the low baud rate to the high baud rate to the plurality of slave units after detecting that the communication with the slave unit to which the termination resistance is set is restored, and switches setting of the master unit itself to the high baud rate.

TECHNICAL FIELD

An embodiment of the present disclosure relates to a communication system, a slave unit used for the communication system, and a communication method.

BACKGROUND ART

JP 2000-165568 A discloses communication systems in which a plurality of slave units are bus-connected to a master unit via communication lines. In the case of an air conditioning system installed in a large building, a plurality of indoor units usually serve as slave units and an outdoor unit or a central control unit serves as a master unit, for example.

In this kind of air conditioning system, the master unit sequentially acquires and collectively manages information on the operation of each connected indoor unit (for example, set temperature information, sensor information, and the like). Further, in the air conditioning system, the master unit can collectively control the operation of the plurality of indoor units.

If the communication rate is increased in this kind of communication system, the signal waveform may be disturbed due to reflection of the communication signal at the end of the communication line. If the communication line is long, the influence thereof is particularly large. To cope with the above problem, by setting a termination resistance in the communication line, reflection of signals is suppressed and disturbance of signal waveforms can be suppressed to enable communication.

SUMMARY

In this kind of communication system, it is desirable to set termination resistances to units located at both ends of the communication line. The following is conceivable: a master unit located at one end of the communication line automatically searches for a slave unit estimated to be located at the most distant position, the master unit transmits an instruction for setting a termination resistance to the slave unit, and accordingly, the slave unit automatically sets the termination resistance. The exchange of information between the master unit and the slave unit before the setting of the termination resistance is performed by means of a low-speed communication that enables communication even if the termination resistance is not present.

However, if such automatic setting of the termination resistance is performed, a relay or the like to be connected to the communication line is required in order to cause a resistance in the slave unit to function as the termination resistance. Normally, an open relay is used as the relay. Therefore, if a power source of a slave unit to which a termination resistance should be set is turned off, there will be no termination resistance for the slave unit on the communication line. Accordingly, it is assumed that there will arise a problem that high-speed communication between the master unit and all slave units will be disabled.

In a communication system, a plurality of slave units are connected to a master unit via communication lines and a termination resistance is set to a slave unit. The present disclosure has been devised in view of the above-described problems, and an object of the present disclosure is to provide a communication system, a master unit and a slave unit used for the communication system, and a communication method that enable, in the above communication system, appropriate communication between the master unit and other slave units even if communication between the master unit and the slave unit to which a termination resistance is set is disabled.

In order to achieve the above object, a communication system of the present disclosure includes: a master unit; and a plurality of slave units including a slave unit to which a termination resistance is set, the plurality of slave units being connected to the master unit via a communication line, in which the master unit includes a master communication control unit that normally sets a communication rate of communication performed with the plurality of slave units to a high baud rate, switches the high baud rate to a low baud rate after detecting that communication with the slave unit to which the termination resistance is set is disabled, transmits an instruction for switching the low baud rate to the high baud rate to the plurality of slave units after detecting that the communication with the slave unit to which the termination resistance is set is restored, and switches setting of the master unit itself to the high baud rate, and each of the plurality of slave units includes a slave communication control unit that normally sets a communication rate of communication performed with the master unit to a high baud rate, switches the high baud rate to a low baud rate after detecting that the communication with the master unit is disabled, and switches the low baud rate to the high baud rate after receiving, from the master unit, an instruction for switching the low baud rate to the high baud rate.

A master unit used for a communication system of the present disclosure normally performs communication at a high baud rate via a communication line, switches the high baud rate to a low baud rate after detecting that the communication is disabled, and is connected to a plurality of slave units via a communication line, the plurality of slave units including a slave unit to which a termination resistance is set, and the master unit includes a master communication control unit that normally sets a communication rate of communication performed with the plurality of slave units to the high baud rate, switches the high baud rate to the low baud rate after detecting that communication with the slave unit to which the termination resistance is set is disabled, transmits, to the plurality of slave units, an instruction for switching the low baud rate to the high baud rate after detecting that communication with the slave unit is restored, and switches setting of the master unit thereof to the high baud rate.

A slave unit used for a communication system of the present disclosure is connected to, through a communication line, a master unit that sets a communication rate of communication performed with a plurality of slave units including a slave unit to which a termination resistance is normally set to a high baud rate, switches the high baud rate to a low baud rate after detecting that communication with the slave unit to which the termination resistance is set is disabled, transmits an instruction for switching the low baud rate to the high baud rate to the plurality of slave units after detecting that the communication with the slave unit is restored, and switches setting of the master unit itself to the high baud rate, and the slave unit includes a slave communication control unit that normally sets a communication rate of communication preformed with the master unit to the high baud rate, switches the high baud rate to the low baud rate after detecting that the communication with the master unit is disabled, and switches the low baud rate to the high baud rate after receiving an instruction for switching the low baud rate to the high baud rate from the master unit.

A communication method of the present disclosure includes: performing communication normally at a high baud rate via a communication line by means of a master unit and a plurality of slave units including a slave unit to which a termination resistance is set, and switching the high baud rate to a low baud rate by means of the master unit after communication between the master unit and the slave unit to which the termination resistance is set is disabled; switching a communication rate to the low baud rate by means of a slave unit that is unable to communicate with the master unit due to the master unit switching the high baud rate to the low baud rate; after the communication between the master unit and the slave unit to which the termination resistance is set is restored, transmitting, by means of the master unit, an instruction for switching the low baud rate to the high baud rate to the plurality of slave units, and switching setting of the master unit itself to the high baud rate; and switching the low baud rate to the high baud rate by means of the slave units that receive the instruction for switching the low baud rate to the high baud rate from the master unit.

DESCRIPTION OF EMBODIMENTS

Hereinafter, an air conditioning system configured as an embodiment of a communication system of the present disclosure will be described with reference to the drawings.

Configuration of Air Conditioning System According to One Embodiment

A configuration of an air conditioning system according to the present embodiment will be described with reference toFIG.1. An air conditioning system1is installed in a large building such as an office building or a commercial facility, for example. The air conditioning system1includes an outdoor unit10as a master unit and a plurality of indoor units20-1,20-2, and20-3as slave units which are bus-connected to the outdoor unit10by using a communication line30or refrigerant piping (not shown). The air conditioning system1is what is called a multi-type air conditioning system. The communication line30is a two-wire bus communication line. Remote controllers7-1to7-3are connected to the indoor units20-1to20-3respectively by wire. The operation modes of operation/shutdown and cooling/heating, the set temperature, and the like of the indoor units20-1to20-3are set by means of the remote controllers7-1to7-3respectively. The outdoor unit10is connected to a three-phase power source2with a breaker3therebetween. The indoor units20-1to20-3are connected to single-phase power sources4-1to4-3with breakers5-1to5-3therebetween, respectively. That is, each of the outdoor unit10and the indoor units20-1to20-3is independently connected to a power source. In general, it is assumed that the power sources of the air conditioning system1are not shut off after installation of the air conditioning system1. However, in some cases, the power sources of the indoor units20-1to20-3may be individually shut off by means of the operations of the breakers5-1to5-3respectively.

InFIG.1, the number of indoor units connected to the outdoor unit10is three. However, the number of indoor units is not limited to three, and a large number of indoor units such as four or more indoor units may be connected to the outdoor unit. Hereinafter, if it is not necessary to specify which indoor unit among the above indoor units is used, an indoor unit is referred to as an indoor unit20.

The outdoor unit10has a master controller11for controlling the operation of a plurality of indoor units20. The master controller11includes a communication circuit111, a microcomputer112serving as a master communication control unit, and a resistance113functioning as a termination resistance as shown inFIG.2.

The communication circuit111is connected to communication lines30. The communication circuit111has a function of performing communication at a high baud rate via the communication lines30and a function of performing communication at a low baud rate which is relatively lower in rate than the high baud rate via the communication lines30. The high baud rate is 20 kHz and the low baud rate is 10 kHz, which is half of the high baud rate, for example. Hereinafter, communication performed at a high baud rate is referred to as high-speed communication and communication performed at a low baud rate is referred to as low-speed communication. Under the control of the microcomputer112, the communication circuit111transmits, to the indoor units20, an operation status information request and operation control information. The communication circuit111also acquires information on the operation status such as set temperature information and sensor information transmitted from the indoor units20, and performs processes and stores data.

The microcomputer112normally sets the rate of communication performed by the communication circuit111with the indoor units20to a high baud rate. Alternatively, the microcomputer112switches the rate to a low baud rate after detecting that communication is disabled with the indoor units20to which termination resistances are set, in other words, in which resistances212are connected to communication lines30, as described later. Further, after the microcomputer112detects that the communication performed with the indoor units20to which the termination resistances are set has been restored, the microcomputer112transmits, to each indoor unit20, an instruction for switching the speed to a high baud rate, and switches the rate of communication performed by the communication circuit111with each indoor unit20to a high baud rate.

The resistance113in the master controller11is set up so as to function as a termination resistance while always being connected to the communication lines30. The resistance113suppresses the reflection of signals transmitted through the communication lines30and ensures that the communication in the air conditioning system1is appropriately performed at a high baud rate.

The indoor unit20has a slave controller21for controlling the operation of the indoor unit20itself in accordance with instructions transmitted from the outdoor unit10and a remote controller7. The slave controller21has a communication circuit211connected to communication lines30, a resistance212, a switching circuit213, a microcomputer214serving as a slave communication control unit, and a nonvolatile memory215as shown inFIG.3.

Similar to the communication circuit111, the communication circuit211has a function of performing high-speed communication and a function of performing low-speed communication. Under the control of the microcomputer214, the communication circuit211transmits information on an operation status such as the set temperature information and sensor information of the indoor unit20thereof to the master controller11, namely the outdoor unit10, in response to a request transmitted from the outdoor unit10.

The switching circuit213is composed of a relay, a semiconductor switch, and the like which are operated by using an electric signal. The switching circuit213electrically switches the parallel connection/non-connection of the resistance212to the communication lines30by switching the conduction/non-conduction of the resistance212to the communication lines30. Suppose that the resistance212is connected in parallel to the communication lines30by means of the switching circuit213. In the above case, the resistance212functions as a termination resistance. The termination resistance suppresses the reflection of signals transmitted through the communication lines30and ensures that the communication in the air conditioning system1is appropriately performed at a high baud rate.

The microcomputer214controls the switching operation of the switching circuit213by supplying an electric signal to the switching circuit213based on information stored in the nonvolatile memory215, which will be described later. Further, the microcomputer214sets the rate of communication performed by the communication circuit211with the outdoor unit10through the communication lines30to a high baud rate in a normal state. Alternatively, the microcomputer214switches the communication rate to a low baud rate after detecting that the communication with the outdoor unit10is disabled. After the microcomputer214receives an instruction for switching the speed to a high baud rate from the outdoor unit10, the microcomputer214switches the rate of communication performed by the communication circuit211with the outdoor unit10to a high baud rate.

The nonvolatile memory215stores termination resistance setting information if the indoor unit20thereof is a target to which the termination resistance is to be set. The master controller11of the outdoor unit10automatically identifies an indoor unit20located as far away as possible by means of communication at the time of construction of the facility. The master controller11transmits a command for setting the termination resistance to the identified indoor unit20. Accordingly, the microcomputer214of the indoor unit20that has received the command operates the switching circuit213by itself and may store the setting information in the nonvolatile memory215when the resistance212is input to the communication lines30. Further, the following is also possible: an installation worker selects an indoor unit20located at a distance based on the wiring state of the communication lines30at the time of installation of each unit, and implements setting of the selected indoor unit20by using the remote controller7, and the termination resistance setting information may thereby be directly input to the indoor unit20. In this case, the termination resistance setting information is not stored in an indoor unit20for which setting is not implemented by using the remote controller7, and this kind of indoor unit is an indoor unit20to which the termination resistance is not set.

Operation of Air Conditioning System According to One Embodiment

The operation of the air conditioning system1according to the present embodiment will be described with reference toFIGS.4to8. In the sequence diagrams ofFIGS.4to6, thick arrows indicate high-speed communication and thin arrows indicate low-speed communication.

In the air conditioning system1, the rate of communication performed between the outdoor unit10and each indoor unit20is normally set to a high baud rate, and communication at a high baud rate is performed between these units. When communication is performed at a high baud rate, the influence of the reflection of communication signals at the ends of each communication line30increases, and the signal waveforms may be disturbed. In order to cope with the above problems, by setting termination resistances to the units at both ends of each communication line30, in other words, the outdoor unit10and an indoor unit20far from the outdoor unit10, the reflection of the signals is suppressed and the disturbance of the signal waveforms can be prevented. An indoor unit20to which the termination resistance is set (in which the resistance212is connected to the communication lines30) is preferably located at a position farthest from the outdoor unit10. However, even if the indoor unit20is not located at a position farthest from the outdoor unit, if the indoor unit20is located relatively far from the outdoor unit among the connected indoor units20, the reflection of the signals can be suppressed to some extent and the disturbance of the signal waveforms can be prevented. This enables the communication to be performed at a high baud rate. Here, the meaning of the term “far” between the outdoor unit10and each indoor unit20does not refer to the distance between the installation positions of the outdoor unit and the indoor unit, but the term “far” is used based on the length of each communication line30connecting both units.

The nonvolatile memory215of the indoor unit20that is a target to which a termination resistance is to be set stores termination resistance setting information indicating that the indoor unit20itself is a target to which a termination resistance is to be set. In the present embodiment, a nonvolatile memory215-3of an indoor unit20-3which is located at a position farthest from the outdoor unit10stores termination resistance setting information indicating that the indoor unit20-3is a target to which a termination resistance is to be set.

After the air conditioning system1is started, that is, after the power sources of units in the air conditioning system1are turned on, the microcomputer214acquires information in the nonvolatile memory215in each indoor unit20as shown in the control flow ofFIG.8. If the termination resistance setting information is acquired (“YES” in S21), the microcomputer214switches the switching circuit213to the closed state (S22).

Here, a microcomputer214-3of the indoor unit20-3acquires the termination resistance setting information from the nonvolatile memory215-3, switches a switching circuit213-3to the closed state, and a resistance212-3is connected to the communication lines30(S1inFIG.4). That is, the termination resistance is set to the indoor unit20-3. Further, in the indoor units20-1and20-2, the nonvolatile memories215-1and215-2do not store the termination resistance setting information. Therefore, the switching circuits213-1and213-2are maintained in an open state, and the resistances212-1and212-2are maintained in a non-connected state. That is, no termination resistance is set to the indoor units20-1and20-2.

Next, the microcomputer112of the outdoor unit10transmits, to each indoor unit20, information for inquiring whether a termination resistance is set (S2, S4, and S6). When the air conditioning system1is started, the rate of communication performed between the outdoor unit10and each indoor unit20is set to a high baud rate, and the communication between these units is performed at a high speed.

After receiving an inquiry transmitted from the outdoor unit10, each indoor unit20transmits information indicating the setting state of the termination resistance to the outdoor unit10as a response to the inquiry (S3, S5, and S7). The outdoor unit10recognizes the indoor unit20to which the termination resistance is set based on the information transmitted from each indoor unit20(S8). Here, the outdoor unit10recognizes that the termination resistance is set to the indoor unit20-3.

After these processes are performed when a power source of each unit of the air conditioning system1is turned on, air conditioning communication is sequentially performed at predetermined time intervals (times t0, t1, t2. . . inFIG.5) between the outdoor unit10and each indoor unit20. In the air conditioning communication, an operation status information request and an operation command are transmitted from the outdoor unit10to each indoor unit20, for example. In response to the request and command, each indoor unit20transmits, to the outdoor unit10, operation/shutdown information, set temperature information, detection data information of various sensors, and the like. At this time, the rate of communication performed between the outdoor unit and each indoor unit20is set to a high baud rate (S11inFIG.7and S23inFIG.8). Therefore, the exchange of requests, commands, and information is performed by means of high-speed communication (thick arrows of S101to S110inFIG.5, S12inFIG.7, and S24inFIG.8).

Suppose that, immediately after time t4, a failure state occurs in which the indoor unit20-3is in a power-off state or the microcomputer112stops operating. In the above case, the switching circuit213-3of the indoor unit20-3, which has been electrically operated, is automatically set to the open state, and the resistance212-3functioning as the termination resistance is disconnected from the communication lines30. This disables the high-speed communication performed between the outdoor unit10and each indoor unit20. Therefore, the indoor unit20-3is not able to receive the information that has been transmitted from the outdoor unit10to the indoor unit20-3at time t5(S111inFIG.5). At this time, the microcomputer112of the outdoor unit10recognizes that communication with the indoor unit20-3to which the termination resistance is set is disabled (“YES” in S13ofFIG.7). After the microcomputer112recognizes that communication with the indoor unit20-3is disabled, the microcomputer112switches the communication rate of the communication circuit111to a low baud rate (S14inFIG.7).

Then, at time t6, the outdoor unit10transmits information to an indoor unit20-1by means of low-speed communication. However, since the rate of the indoor unit20-1is set to a high baud rate, the baud rate setting does not match. Therefore, the indoor unit20-1is not able to receive the transmitted information (S112inFIG.5).

The indoor unit20-1does not receive information from the outdoor unit10when a predetermined time elapses from the time t3at which the information from the outdoor unit10was last received, more specifically, when a period of time set between time t3and time t9elapses from time t3, time t9being the reception timing two cycles after time t3. Therefore, the microcomputer214-1recognizes that communication with the outdoor unit10is disabled (“YES” in S25ofFIG.8). After the microcomputer214-1recognizes that communication with the outdoor unit10is disabled, the microcomputer214-1switches the communication rate of the communication circuit211-1to a low baud rate (S26inFIG.8).

Similarly, before time t10, the microcomputer214-2of the indoor unit20-2recognizes that communication with the outdoor unit10has been disabled, and the communication rate of the communication circuit211-2is switched to a low baud rate.

This enables communication to be performed between the outdoor unit10and the indoor units20-1and20-2because the baud rate setting between the outdoor unit10and the indoor units20-1and20-2can be matched at a low baud rate. Thereafter, the exchange of pieces of information on air conditioning is sequentially performed at predetermined time intervals (times t9, t10, . . . ) by means of low-speed communication (thin arrows of S115to S123inFIGS.5and6, S15inFIG.7, and S27inFIG.8). Since low-speed communication is performed at a low baud rate, communication between each unit is possible regardless of whether a termination resistance is connected. At time t11, the outdoor unit10performs low-speed communication with the indoor unit20-3. However, the indoor unit20-3is not able to receive information because the indoor unit20-3is still in the power-off state (S119inFIG.6).

Suppose that the power source of the indoor unit20-3is restored or the state is recovered from the failure state immediately after time t11. In the above case, the indoor unit20-3is started while the communication rate is set to a high baud rate. At the same time, the indoor unit20-3acquires the termination resistance setting information from the nonvolatile memory215-3by using the microcomputer214-3. Further, the indoor unit20-3switches the switching circuit213-3to the closed state, connects the resistance212-3to the communication lines30, and sets the resistance as a termination resistance (“YES” in S21and S22ofFIG.8).

Then, at time t14, the outdoor unit10transmits information to the indoor unit20-3by means of low-speed communication. However, the baud rate setting does not match because the baud rate of the indoor unit20-3is set to a high baud rate. Therefore, the indoor unit20-3is not able to receive the transmitted information (step S124inFIG.6).

When a predetermined time elapses from when the indoor unit20-3is started (from the start of the indoor unit to time t17), the indoor unit20-3does not receive information from the outdoor unit10. Therefore, the microcomputer214-3recognizes that communication with the outdoor unit10is disabled (“YES” in S25ofFIG.8). After the microcomputer214-3recognizes that communication with the outdoor unit10is disabled, the microcomputer214-3switches the communication rate of the communication circuit211-3to a low baud rate (S26inFIG.8).

As a result, the baud rate setting matches at a low baud rate between the outdoor unit10and the indoor unit20-3, and communication between the outdoor unit10and the indoor unit20-3becomes possible. The indoor unit20-3receives information transmitted from the outdoor unit10to the indoor unit20-3at a low speed at time t17(S129inFIG.6), and transmits the response to the information to the outdoor unit10(S130inFIG.6).

After receiving the response from the indoor unit20-3, the outdoor unit10recognizes that communication with the indoor unit20-3is restored (“YES” in S16ofFIG.7). At time t18, the microcomputer112of the outdoor unit10broadcast-transmits an instruction for switching the speed to a high baud rate to each indoor unit20at a low speed (S131inFIG.6). Subsequently, the microcomputer112switches the communication rate of the communication circuit111to a high baud rate (S17inFIG.7).

After the indoor units20-1to20-3receive an instruction for switching the speed to a high baud rate from the outdoor unit10(“YES” in S28ofFIG.8), the indoor units use the microcomputers214-1to214-3to switch the communication rates of the communication circuits211-1to211-3to a high baud rate (S29inFIG.8).

As a result, the baud rate setting matches at a high baud rate between the outdoor unit10and the indoor units20-1to20-3. Thereafter, the exchange of information on air conditioning is sequentially performed at predetermined time intervals (time t19, t20, . . . ) by means of high-speed communication (S12ofFIGS.7and S24ofFIG.8).

According to the above-described embodiment, an air conditioning system includes an outdoor unit and a plurality of indoor units connected by means of a bus-type communication line and in which a termination resistance is set to a communication line of an indoor unit. In the air conditioning system, normally high-speed communication is performed, and when communication between the outdoor unit and the indoor units becomes disabled, the high-speed communication is switched to low-speed communication so that communication can be continued. Accordingly, it is possible to prevent interruption of communication in the air conditioning system as much as possible while performing communication efficiently. If communication with the indoor units becomes possible, communication efficiency is enhanced by quickly returning the low-speed communication to the high-speed communication.

In the present embodiment, a description has been given using an example where an outdoor unit is a master unit and a termination resistance which is supposed to be provided at one end of a communication line is preset to the outdoor unit. However suppose that a centralized management device or the like is located farther away than the outdoor unit on the communication line. In the above case, a termination resistance may be set to the centralized management device without setting a termination resistance to the outdoor unit.