Patent Description:
Currently, in a photovoltaic power generation system, an RS485 or controller area network (CAN, Controller Area Network) communication manner is usually used between an inverter and a direct-current-side device. However, the direct-current-side device such as a power converter is usually far away from the inverter. In this case, if RS485 or CAN communication is used, a long trench needs to be dug or a communication cable needs to be routed overhead additionally during construction. The construction is complex and the communication cable costs much. In addition, if a port of the communication cable is used for a long time, the port may be corroded, the cable may be damaged, or other problems may occur. Consequently, communication quality deteriorates or communication is interrupted, affecting normal running of the system. <CIT> discloses a method and system that includes a solar panel. A power bus is coupled to the solar panel. The power bus supports transmission of AC communication signals. A slave node, coupled to the power bus, transmits information regarding solar panel performance. A master node, remotely coupled to the slave node over the power bus, receives the information regarding solar panel performance from the slave node.

The present invention is defined by the attached independent claims. Other preferred embodiments may be found in the dependent claims. The present application discloses a power generation system (<NUM>), comprising a plurality of power converters (<NUM>, 102a) and an inverter (<NUM>, 110a), an input end of each power converter (<NUM>, 102a) configured to being connected to at least one solar panel or at least one battery, an output end of each power converter (<NUM>, 102a) connected to an input end of the inverter (<NUM>, 110a) in series and in parallel, the inverter (<NUM>, 110a) being configured to convert a direct current that is input from the converters (<NUM>, 104a) into an alternating current for power supply, and the inverter (<NUM>, 110a) comprises:a control apparatus (<NUM>), configured to control the inverter (<NUM>, 110a) to convert the direct current that is input from the power converters (<NUM>, 102a) into the alternating current for power supply; and a communications apparatus (<NUM>), coupled to the control apparatus (<NUM>), and configured to: send a networking information request signal to the power converters (<NUM>, 102a) in the power generation system (<NUM>) through a direct-current power line (<NUM>) that transmits the direct current in the power generation system (<NUM>), wherein a frequency of the networking information request signal is within a first frequency band, and the networking information request signal is used to request networking information required for networking between the inverter (<NUM>, 110a) and the power converters (<NUM>, 102a);receive the networking information from the power converters (<NUM>, 102a) through the direct-current power line (<NUM>); and send a control signal to the power converters (<NUM>, 102a) through the direct-current power line (<NUM>), wherein a frequency of the control signal is within a second frequency band, and the control signal is used to control an operating parameter of the power converters (<NUM>, 102a) and the first frequency band is lower than the second frequency band. The present application discloses a method for an inverter (<NUM>, 110a) in a power generation system (<NUM>), comprising:Generating (S401) a networking information request signal, and sending the networking information request signal to a power converters (<NUM>, 102a) in the power generation system (<NUM>) through a direct-current power line (<NUM>) that is used to transmit electric energy in the power generation system (<NUM>), wherein a frequency of the networking information request signal is within a first frequency band, and the networking information request signal is used to request networking information required for networking between the inverter (<NUM>, 110a) and the power converters (<NUM>, 102a);receiving (S402) the networking information from the power converters (<NUM>, 102a) through the direct-current power line (<NUM>), and performing networking with the power converters (<NUM>, 102a) based on the networking information; and generating (S403) a control signal, and sending the control signal to the power converters (<NUM>, 102a) through the direct-current power line (<NUM>), wherein a frequency of the control signal is within a second frequency band, and the control signal is used to control an operating parameter of the power converters (<NUM>, 102a); wherein the first frequency band is lower than the second frequency band. The present application discloses a method for power converters (<NUM>, 102a) in a power generation system (<NUM>), comprising:receiving (S501) a networking information request signal from an inverter (<NUM>, 110a) through a direct-current power line (<NUM>) that transmits electric energy in the power generation system (<NUM>), wherein a frequency of the networking information request signal is within a first frequency band, and the networking information request signal is used to request networking information required for networking between the inverter (<NUM>, 110a) and the power converters (<NUM>, 102a);sending (S502) the networking information to the inverter (<NUM>, 110a) through the direct-current power line (<NUM>); and receiving (S503) a control signal from the inverter (<NUM>, 110a) through the direct-current power line (<NUM>), wherein a frequency of the control signal is within a second frequency band, and the control signal is used to control (S504) an operating parameter of the power converters (<NUM>, 102a); wherein the first frequency band is lower than the second frequency band.

The following further describes this application with reference to specific embodiments and accompanying drawings. It may be understood that the specific embodiments described herein are merely intended to explain this application, but not to limit this application. In addition, for ease of description, the accompanying drawings show only some rather than all structures or processes related to this application. It should be noted that, in this specification, reference numerals and letters in the following accompanying drawings represent similar items. Therefore, once an item is defined in an accompanying drawing, the item does not need to be further defined or interpreted in subsequent accompanying drawings.

In the descriptions of this application, it should be further noted that, unless otherwise specified and limited, the terms "setting", "connecting", and "connected" should be understood in a broad sense, for example, may be a fixed connection, a detachable connection, or an integrated connection; may be a mechanical connection or an electrical connection; may be directly connected, or may be indirectly connected by using an intermediate medium, or may be internally connected between two components. The specific meanings about the foregoing terms in the embodiments may be understood by a person of ordinary skill in the art based on specific circumstances.

It should be understood that although terms "first", "second", and the like may be used in this specification to describe features, the features should not be limited by these terms. These terms are used only for distinction and cannot be understood as an indication or implication of relative importance. For example, without departing from the scope of the example embodiments, the first feature may be referred to as a second feature, and similarly, the second feature may be referred to as a first feature.

Some example embodiments are described as processing or methods depicted as flowcharts. Although the flowchart describes the operations as sequential processing, many of these operations can be implemented in parallel, concurrently, or simultaneously. In addition, the sequence of the operations may be rearranged. The processing may be terminated when the operation is completed, but may further have additional blocks that are not included in the figures. The processing may correspond to a method, a function, a procedure, a subroutine, a subprogram, or the like. The following describes some terms appearing in the specification of this application.

Power converter: It is configured to perform voltage conversion on an input direct current. In some embodiments of this application, for example, the power converter may implement a direct current (DC)/direct current (DC) voltage boosting function, to convert a low-voltage direct current from a direct-current power supply (for example, a solar panel) into a high-voltage direct current for output. For example, in a photovoltaic power generation system, the power converter may convert a low-voltage direct current into a direct current voltage output that meets an input direct current voltage requirement of an inverter, to track a maximum power of a solar panel, so that the solar panel outputs the maximum power.

Energy storage converter: It has a bidirectional DC/DC conversion function. In some embodiments of this application, the energy storage converter may be connected to a direct-current power supply (for example, a battery) and implement a function of charging and discharging the direct-current power supply.

Inverter: It converts an input direct current into an alternating current through direct current (DC)/alternating current (AC) conversion for output.

Direct-current-side device: It is a device that is connected to a direct current input end of an inverter through a direct-current power line configured for direct current transmission, for example, a device that is connected to a direct current input end of an inverter through a direct-current power line and that provides the inverter with a direct current that meets a specific operating parameter requirement. Examples of the direct-current-side device include, but are not limited to, any one or more of a power converter, an energy storage converter, a battery cabinet, a direct current optimizer, a combiner box, and the like, or may include another direct-current-side device. The operating parameter includes, but is not limited to, any one or more of an output power, an output voltage, an output current, and the like, or may include another operating parameter.

<FIG> shows an example of a power generation system according to some implementations of this application.

As shown in <FIG>, according to some embodiments of this application, a power generation system <NUM> is provided. The system <NUM> includes at least one power converter <NUM> (for example, n power converters 102a,. , and 102n) and at least one inverter <NUM> (for example, p inverters 110a,. , and 110p). An input end of the power converter <NUM> is connected to at least one solar panel string <NUM>. Each solar panel string may include one or more solar panels. In some implementations, each power converter may be connected in series to one solar panel string. For example, the power converter 102a may be connected in series to a solar panel string 101a. In some other implementations, each power converter may be connected in series to a plurality of solar panel strings. As a DC/DC converter with a voltage boosting function, the power converter <NUM> may convert a low-voltage direct current that is output by the solar panel string <NUM> into a direct current voltage output that meets an input direct current voltage requirement of the inverter. An output of the power converter <NUM> is connected to an input of the inverter <NUM> through a direct-current power line <NUM>. After the direct current output by the solar panel string <NUM> passes through the power converter <NUM>, the direct current is transmitted to the inverter <NUM> through the direct-current power line <NUM>. The inverter <NUM> converts the received direct current into an alternating current for output, for example, output to a power grid. When there are a plurality of power converters <NUM> or inverters <NUM>, output ends of the power converters may be connected in parallel, and input ends of the inverters may be connected in parallel. As shown in <FIG>, output ends of the power converters 102a,. , and 102n are connected in parallel, and input ends of the inverters 110a,. , and 110p are connected in parallel. The parallel-connected output ends of the power converter 102a,. , and 102n are connected to the parallel-connected input ends of the inverter 110a,. , and 110p through the direct-current power line <NUM>.

In some implementations, the system <NUM> may further be connected in parallel to an energy storage unit shown by a dashed-line box in <FIG>, to store excess electric energy of the solar panel string <NUM> in the power generation system <NUM>, and supplement power supply at any time when necessary. The energy storage unit may include at least one energy storage converter <NUM> (for example, m energy storage converters 104a,. , and <NUM>) and at least one battery <NUM> (for example, k batteries 103a,. , and <NUM>) connected to the energy storage converter <NUM>. Each energy storage converter <NUM> may be connected to one or more batteries. An example of the battery <NUM> may include, but is not limited to, a battery cabinet. In some embodiments of this application, the energy storage converter <NUM> may have a bidirectional DC/DC conversion function, to charge and discharge electric energy of the battery <NUM>. When there are a plurality of energy storage converters <NUM>, output ends of the plurality of energy storage converters <NUM> are also connected to the direct-current power line <NUM> in a parallel manner. For example, as shown in <FIG>, the energy storage converters 104a,. , and <NUM> are connected in parallel and then connected to the direct-current power line <NUM>.

In some implementations of this application, when a voltage of the battery <NUM> is sufficient, the battery <NUM> may not be connected to the inverter <NUM> through the energy storage converter <NUM>, but instead, the battery <NUM> is directly connected to the inverter <NUM>. In other words, the energy storage unit includes only the battery <NUM>, and does not include the energy storage converter <NUM>. In some embodiments of this application, an example of the battery <NUM> includes, but is not limited to, a battery cabinet. After connected in parallel to the power converter <NUM>, the battery <NUM> is also connected to the input end of the inverter <NUM> through the direct-current power line. In some embodiments of this application, devices such as the power converter <NUM>, the energy storage converter <NUM>, or the battery <NUM> that are connected to the inverter through the direct-current power line <NUM> may be collectively referred to as a direct-current-side device.

According to some implementations of this application, a communication signal may be injected into the direct-current power line <NUM> that transmits electric energy between the direct-current-side device and the inverter <NUM>, to implement information transmission and control between the direct-current-side device and the inverter <NUM>. For example, the direct-current power line <NUM> that transmits electricity in the power generation system is also used as a signal transmission line for information transmission and control. In this way, it is unnecessary to dig a long trench or route a communication cable overhead additionally for communication between the direct-current-side device (i.e., the power converter <NUM>, and optional the energy storage converter <NUM>, or the battery <NUM>) and the inverter <NUM> in the power generation system, thereby reducing costs of construction and communication cables.

<FIG> shows examples of internal structures of a direct-current-side device <NUM> and an inverter <NUM> according to an embodiment of this application. To implement communication between the direct-current-side device (i.e., the power converter <NUM>, and optional the energy storage converter <NUM>, or the battery <NUM>) and the inverter <NUM>, a communications apparatus may be disposed at each of the direct-current-side device <NUM> (for example, the power converter <NUM>, the energy storage converter <NUM>, or the battery <NUM>) and the inverter <NUM> to receive and send information. The direct-current-side device <NUM> includes the power converter <NUM>, and optional the energy storage converter <NUM>, the battery <NUM>, and the like.

As shown in <FIG>, according to some embodiments of this application, the inverter <NUM> may include a control apparatus <NUM> and a communications apparatus <NUM>. The control apparatus <NUM> is configured to control an operation of the inverter <NUM>, for example, control the inverter <NUM> to convert a direct current that is input from the direct-current-side device into an alternating current for power supply. For example, the controller <NUM> generates a signal for requesting networking information required for networking between the inverter <NUM> and the direct-current-side device <NUM>, a control signal for controlling an operating parameter of the direct-current-side device <NUM>, or another control signal used to control networking with the direct-current-side device <NUM> and convert a direct current from the direct-current-side device <NUM> into an alternating current.

According to some embodiments of this application, the communications apparatus <NUM> is coupled to the control apparatus <NUM>, and configured to implement communication with the direct-current-side device <NUM>. For example, the networking information request signal is sent from the inverter <NUM> to the direct-current-side device <NUM>, or the requested networking information is received from the direct-current-side device <NUM>, to complete networking. An example of the networking information includes, but is not limited to, any one or more of a physical address, a logical address, a serial number, a device identification code, and the like of the direct-current-side device. The communications apparatus <NUM> may send the control signal from the inverter <NUM> to the direct-current-side device <NUM>, to control the operating parameter of the direct-current-side device <NUM>. The operating parameter may include, but is not limited to, an output voltage, an output current, an output power, and the like of the direct-current-side device <NUM>. A frequency band within which a frequency of the networking information request signal is located may be relatively low, to prevent crosstalk during networking. A frequency band within which a frequency of the control signal is located may be relatively high, for example, higher than the frequency band within which the networking information request signal is located, to implement high-speed information transmission.

In this application, that one frequency band is higher than another frequency band may mean that a highest frequency and a lowest frequency of the one frequency band are respectively higher than a highest frequency and a lowest frequency of the another frequency band. To be specific, if a second frequency band is higher than a first frequency band, a highest frequency within the second frequency band is higher than a highest frequency within the first frequency band, and a lowest frequency within the second frequency band is higher than a lowest frequency within the first frequency band. Likewise, that one frequency band is lower than another frequency band may mean that a highest frequency and a lowest frequency of the one frequency band are respectively lower than a highest frequency and a lowest frequency of the another frequency band.

For example, according to some embodiments of this application, that the frequency band within which the frequency of the control signal is located is higher than the frequency band within which the networking information request signal is located may mean that a highest frequency of the frequency band within which the frequency of the control signal is located is higher than a highest frequency of the frequency band within which the networking information request signal is located, and a lowest frequency of the frequency band within which the frequency of the control signal is located is higher than a lowest frequency of the frequency band within which the networking information request signal is located. According to some embodiments of this application, the frequency band within which the frequency of the networking information request signal is located may not overlap the frequency band within which the frequency of the control signal is located. For example, the networking information request signal may be a low-frequency signal whose frequency is lower than <NUM>, and the control signal may be a high-frequency signal whose frequency is higher than <NUM>. In some other implementations, the frequency band within which the frequency of the networking information request signal is located may partially overlap the frequency band within which the frequency of the control signal is located. For example, the frequency of the networking information request signal may be within a low frequency band of <NUM> to <NUM>, and the frequency of the control signal may be within a high frequency band of <NUM> to <NUM>.

According to some embodiments of this application, the communications apparatus <NUM> may further control a frequency of a to-be-sent signal (for example, the networking information request signal, the networking message, or the control signal) based on information related to the to-be-sent signal. The message related to the to-be-sent signal includes, but is not limited to, an amount of data of the signal, a delay of the signal, a distance over which the signal is to be sent, and the like. For example, when an amount of to-be-transmitted data is relatively small, a signal with a relatively low frequency may be used for transmission. When the amount of data is relatively large, a signal with a relatively high frequency may be used for transmission. For another example, when a delay requirement of a to-be-transmitted signal is relatively low (that is, a high delay), a signal with a relatively low frequency may be used for transmission. When the delay requirement is relatively high (that is, a low delay), a signal with a relatively high frequency may be used for transmission. For another example, when a communication distance of the to-be-sent signal is relatively short, a signal with a relatively high frequency may be used. When a communication distance is relatively long, a signal with a relatively low frequency is used for communication, to be transmitted over a longer distance. A manner of controlling, by the communications apparatus <NUM>, the frequency of the to-be-sent signal based on the information related to the to-be-sent signal is described in detail below.

In some implementations, the control signal sent by the inverter <NUM> to the direct-current-side device <NUM> through the direct-current power line by using the communications apparatus <NUM> may be classified into a general control signal and a special control signal. The two signals have different signal amplitudes. The general control signal is used to control the operating parameter of the direct-current-side device <NUM> in a normal case. In other words, in general cases, the general control signal is used for communication. The special control signal is used to control the operating parameter of the direct-current-side device <NUM> in a special case. For example, in a high voltage ride-through case or a low voltage ride-through case, an amplitude of the control signal is increased or decreased, so that the direct-current-side device <NUM> can quickly detect that the signal amplitude is abnormal, and quickly perform a predetermined action to quickly adjust the operating parameter of the direct-current-side device <NUM>. For example, in a normal case, an amplitude of the general control signal may be, for example, <NUM> to <NUM> mV. If the high voltage ride-through case or the low voltage ride-through case occurs, the amplitude of the control signal is quickly changed, for example, to <NUM> mV. In some implementations, a response may be made only to one of the high voltage ride-through case and the low voltage ride-through case by changing the amplitude of the control signal to be different from the amplitude of the general control signal. In some other implementations, both cases need responses. Then, amplitudes of control signals sent in the two cases may be set to be different from each other, so that the direct-current-side device <NUM> can quickly determine an action that needs to be performed based on a detected signal amplitude.

In some other implementations, the communications apparatus <NUM> may also be configured to send or receive other information.

The direct-current-side device <NUM> may include a communications apparatus <NUM> and a control apparatus <NUM>. The communications apparatus <NUM> may be the same as or similar to the communications apparatus <NUM> in the inverter, and is configured to implement communication with the inverter <NUM>.

For example, in some implementations, the communications apparatus <NUM> may receive the networking information request signal from the inverter <NUM> in the power generation system, for example, filter out the networking information request signal from the direct-current power line, and obtain networking information request information through demodulation; and send the networking information to the inverter <NUM> based on the networking information request through the direct-current power line, for example, may send any one or more of the physical address, the logical address, the serial number, the device identification code, and the like of the direct-current-side device, to complete networking with the inverter <NUM>. After the networking, the communications apparatus <NUM> receives the control signal or another signal from the inverter <NUM>, or send other information to the inverter <NUM>. For example, the communications apparatus <NUM> may send an operating information transmission signal to the inverter <NUM> through the direct-current power line. The operating information transmission signal may include, but is not limited to, operating status information, an operating log, alarm information, and the like of the direct-current-side device <NUM>. According to some embodiments of this application, similar to the communications apparatus <NUM>, the communications apparatus <NUM> may also control a frequency of a to-be-sent signal (for example, the networking information request signal, the networking message, or the control signal) based on information related to the to-be-sent signal, as described in detail below.

The control apparatus <NUM> of the direct-current-side device <NUM> is coupled to the communications apparatus <NUM>, and configured to adjust the operating parameter of the direct-current-side device <NUM> according to an instruction of the inverter <NUM>. The operating parameter may include, but is not limited to, the output voltage, the output current, the output power, or the like of the direct-current-side device <NUM>. In some implementations, the direct-current-side device <NUM> (for example, the power converter <NUM>) may have two operating states: one is a power-limited output state, and the other is a normal power output state. Before the direct-current-side device <NUM> is networked with the inverter <NUM>, the control apparatus <NUM> may control the direct-current-side device <NUM> to operate in the power-limited output state, that is, an operating state in which the output voltage, current, or power or the like of the direct-current-side device <NUM> is limited to be relatively low. Based on an indication that the direct-current-side device has been networked with the inverter, for example, the control signal received from the inverter <NUM> after the networking is completed, the control apparatus <NUM> controls the direct-current-side device <NUM> to enter a normal operating state. In the power-limited output state, the output voltage, current, or power or the like of the direct-current-side device <NUM> is limited, to avoid a problem such as an electric shock or line overload caused by a construction problem such as incorrect cable connection or cable damage, thereby improving safety of a power station.

By respectively adding the communications apparatuses <NUM> and <NUM> to the direct-current-side device <NUM> and the inverter <NUM>, in the power generation system <NUM> shown in <FIG>, the direct-current power line <NUM> between the direct-current-side device (for example, the power converter <NUM>) and the inverter <NUM> may be configured to transmit direct current energy from the direct-current-side device to the inverter <NUM>, and implement communication between the direct-current-side device <NUM> and the inverter <NUM>. During communication, device identification and networking in the system may be first implemented between the direct-current-side device and the inverter <NUM> by using a signal with a relatively low frequency, to resolve a problem that the inverter cannot identify a direct-current-side device connected to the inverter due to crosstalk during high-frequency networking. Then, information transmission and control may be performed by switching to a relatively high frequency band. For example, networking may be first implemented by using a signal with a low frequency lower than <NUM>, and then information transmission and control are performed by switching to a signal with a high frequency higher than <NUM>. It should be noted that, the "lower than <NUM>" and the "higher than <NUM>" in this application are merely examples for description, and are not intended to limit this application. In various implementations, signals with different frequencies may be selected based on different communication distances, weather conditions, transmission requirements, or the like.

In some implementations, after the networking is implemented between the direct-current-side device <NUM> and the inverter <NUM> at a relatively low frequency, a high frequency may be switched to for communication in an adaptive manner. For example, a communication frequency is gradually increased, to finally reach a highest frequency that can be implemented under a current condition, for example, reach a highest transmit frequency while ensuring a specific bit error rate condition, and communicate at the highest frequency, to achieve a fastest transmission speed.

According to some implementations of this application, a frequency of a signal to be transmitted between the inverter <NUM> and the direct-current-side device <NUM> through the direct-current power line that transmits electric energy may be further adjusted or determined based on other information related to the to-be-sent signal. The related information may include, but is not limited to, an amount of data, a delay requirement, a transmission distance, and the like.

For example, according to an embodiment of this application, when an amount of data to be transmitted between the inverter <NUM> and the direct-current-side device <NUM> is relatively small, a signal with a relatively low frequency may be used for transmission. When the amount of data is relatively large, a signal with a relatively high frequency may be used for transmission. For example, when a data amount range is lower than an amount of several k, for example, lower than <NUM>, a signal with a relatively low frequency may be used to transmit data. The relatively low frequency may be within a same frequency band as the frequency of the networking information request signal, or may be the same as the frequency of the networking information request signal. When the data amount range is higher than the amount of several k, for example, higher than <NUM>, a signal with a relatively high frequency may be used to transmit data.

According to another embodiment of this application, a frequency of a signal to be transmitted through the power line may be further related to a delay requirement. The delay refers to a time required for transmitting a data packet or the like from one end of a network to another end. When a delay requirement of a signal to be transmitted between the inverter <NUM> and the direct-current-side device <NUM> is relatively low (that is, a high delay), a signal with a relatively low frequency may be used for transmission. When the delay requirement is relatively high (that is, a low delay), a signal with a relatively high frequency may be used for transmission. For example, when a to-be-transmitted signal is a signal with a high delay, for example, a delay higher than <NUM>, a signal with a relatively low frequency may be used to transmit the signal to implement low-speed communication. The relatively low frequency may be within a same frequency band as the frequency of the networking information request signal, or may be the same as the frequency of the networking information request signal. When the to-be-transmitted signal requires a low delay, for example, the delay needs to be lower than <NUM>, a signal with a relatively high frequency may be used to transmit data, to implement high-speed communication.

According to another embodiment of this application, a communication distance between the inverter <NUM> and the direct-current-side device <NUM> may also be used as one of factors that affect a frequency of a to-be-sent signal. For example, for a relatively short communication distance, a signal with a relatively high frequency may be used, and for a relatively long communication distance, a signal with a relatively low frequency is used for communication, to be transmitted over a longer distance. For each communication distance, two communication frequency bands may coexist, to implement low-speed communication and high-speed communication respectively, for example, to implement low-frequency networking and high-frequency control between the inverter <NUM> and the direct-current-side device <NUM>. For example, when the inverter <NUM> is relatively close to the direct-current-side device <NUM>, the frequency of the low-frequency networking request signal transmitted between the two may be <NUM>, and the frequency of the control signal may be <NUM>. When the inverter <NUM> is relatively far away from the direct-current-side device <NUM>, the frequency of the low-frequency networking request signal transmitted between the two may be <NUM>, and the frequency of the control signal is <NUM>.

According to some implementations of this application, the communications apparatuses <NUM> and <NUM> may be same apparatuses, and are respectively disposed at the direct-current-side device <NUM> and the inverter <NUM> to implement communication between the two. A structure of the communications apparatus may be shown in <FIG>.

As shown in <FIG>, the communications apparatus <NUM>/<NUM> may include a controller <NUM> and a transceiver <NUM>.

According to some implementations of this application, the transceiver <NUM> is configured to send a to-be-sent signal from a transmit end to a receive end through a power line. For example, according to some implementations of this application, the transceiver <NUM> may include a coupler and a filter. The two may be integrated into one circuit, or may be spatially separated as a coupler and a filter. The coupler is configured to couple the to-be-sent signal to the power line, to transmit the to-be-sent signal through the power line. The filter is configured to filter out, from the power line, a signal received through the power line. The coupling herein may be performed in a plurality of manners, for example, magnetic ring coupling and capacitive coupling.

In some implementations, the power line herein may be a direct-current power line, the transmit end may be the inverter <NUM> in the power generation system, and the receiving end is the direct-current-side device <NUM> connected to the inverter <NUM> through the direct-current power line. Alternatively, the transmit end may be the direct-current-side device <NUM> in the power generation system, and the receiving end is the inverter <NUM>.

According to some implementations of this application, the controller <NUM> is configured to control a frequency of the to-be-sent signal based on information related to the to-be-sent signal. The information related to the to-be-sent signal may include, but is not limited to, information about networking between the transmit end and the receive end of the to-be-sent signal, an amount of data of the to-be-sent signal, a delay of the to-be-sent signal, a distance over which the to-be-sent signal is to be sent, and the like.

For example, the information related to the to-be-sent signal may be information about whether the transmit end has been networked with the receive end. Before the transmit end is networked with the receive end, the controller <NUM> may control the frequency of the to-be-sent signal to be within a first frequency band with a relatively low frequency. After the transmit end is networked with the receive end, the controller <NUM> may control the frequency of the to-be-sent signal to be within a second frequency band with a relatively high frequency. For example, if it is determined that the to-be-sent signal is the foregoing networking information request signal, the to-be-sent signal is controlled to be on the first frequency band, for example, the foregoing low frequency band lower than <NUM>, to prevent crosstalk during the networking between the inverter and the direct-current-side device. If it is determined that the to-be-sent signal is the control signal used to control the operating parameter of the direct-current-side device or is the operating information transmission signal that carries at least one of operating status information, an operating log, and alarm information of the direct-current-side device, the to-be-sent signal is controlled to be on the second frequency band, for example, the foregoing high frequency band higher than <NUM>.

In different implementations, signals with different frequencies may be selected based on different communication distances, weather conditions, transmission requirements, or the like. For example, the controller <NUM> in the communications apparatus may be configured to change at least one of frequency values of the first frequency band and the second frequency band based on a length of the connected power line. For example, when a communication distance (that is, the distance over which the to-be-sent signal is to be sent) is relatively short, or in other words, the distance over which the to-be-sent signal is to be sent is relatively short, a signal with a relatively high frequency may be used. When a communication distance (that is, the distance over which the to-be-sent signal is to be sent) is relatively long, a signal with a relatively low frequency is used for communication, to be transmitted over a longer distance. For each communication distance, two communication frequency bands may coexist, to implement low-speed communication and high-speed communication respectively. For example, the communications apparatus is disposed in each of the inverter <NUM> and the direct-current-side device <NUM>, to implement low-frequency networking and high-frequency control between the two. For example, when the inverter <NUM> is relatively close to the direct-current-side device <NUM>, the frequency of the low-frequency networking request signal transmitted between the two may be <NUM>, and the frequency of the control signal may be <NUM>. When the inverter <NUM> is relatively far away from the direct-current-side device <NUM>, the frequency of the low-frequency networking request signal transmitted between the two may be <NUM>, and the frequency of the control signal is <NUM>.

According to some implementations of this application, a frequency of a signal to be sent by the communications apparatus may be further adjusted or determined based on other information related to the to-be-sent signal. The related information may include, but is not limited to, an amount of data, a delay requirement, and the like.

For example, according to an embodiment of this application, the controller <NUM> in the communications apparatus may be configured to: when an amount of to-be-transmitted data is relatively small, control a signal with a relatively low frequency to be used for transmission, and when the amount of to-be-transmitted data is relatively large, control a signal with a relatively high frequency to be used for transmission. For example, when a data amount range is lower than an amount of several k, for example, lower than <NUM>, a signal with a relatively low frequency may be used to transmit data. The relatively low frequency may be within a same frequency band as the frequency of the networking information request signal, or may be the same as the frequency of the networking information request signal. When the data amount range is higher than the amount of several k, for example, higher than <NUM>, a signal with a relatively high frequency may be used to transmit data.

According to another embodiment of this application, the controller <NUM> in the communications apparatus may be configured to: when a delay requirement of a to-be-transmitted signal is relatively low (that is, a high delay), control a signal with a relatively low frequency to be used for transmission, and when the delay requirement is relatively high (that is, a low delay), control a signal with a relatively high frequency to be used for transmission. For example, when a to-be-transmitted signal is a signal with a high delay, for example, a delay higher than <NUM>, a signal with a relatively low frequency may be used to transmit the signal to implement low-speed communication. The relatively low frequency may be within a same frequency band as the frequency of the networking information request signal, or may be the same as the frequency of the networking information request signal. When the to-be-transmitted signal requires a low delay, for example, the delay needs to be lower than <NUM>, a signal with a relatively high frequency may be used to transmit data, to implement high-speed communication.

In some implementations, the communications apparatus may be configured to adaptively adjust a frequency. In the power generation system, after networking is implemented by using a relatively low first frequency band, the communication frequency is gradually increased, to finally reach a highest frequency that can be implemented under a current condition, for example, reach a highest transmit frequency while ensuring a specific bit error rate condition, and use the frequency as a second frequency band for information transmission and control, to achieve a fastest transmission speed.

In addition, in the communications apparatus, a system for modulation to the first frequency band and a system for modulation to the second frequency band may be integrated or may be discrete. To be specific, the communications apparatus may include a separate integrated apparatus, and the separate integrated apparatus may generate signals located on two different frequency bands. The communications apparatus may alternatively include two subsystems or two sub-apparatuses. One of the two subsystems (or the two sub-apparatuses) is configured to generate a signal with a relatively low frequency (for example, lower than <NUM>), and the other is configured to generate a signal with a relatively high frequency (for example, higher than <NUM>).

In some implementations, the controller <NUM> may further control an amplitude of the to-be-sent signal based on the information related to the to-be-sent signal. For example, one or more cases may be predetermined, and when the one or more predetermined cases occur, the to-be-sent signal is modulated to different amplitudes. For example, if it is determined that the communications apparatus is in a normal communication state, the amplitude of the to-be-sent signal is controlled to be a relatively low amplitude, for example, <NUM> to <NUM> mV. If as described above, a high-voltage ride-through case or a low-voltage ride-through case occurs, and a control signal needs to be sent, an amplitude of the control signal is controlled to be a relatively high amplitude, for example, <NUM> mV. In some implementations, a response may be made only to one of the high voltage ride-through case and the low voltage ride-through case. In some other implementations, both cases need responses. Then, amplitudes of control signals sent in the two cases may be different from each other. According to some implementations of this application, optionally, in the communications apparatus, a system for modulation to a first amplitude and a system for modulation to a second amplitude may be integrated or may be discrete. To be specific, the communications apparatus may include a separate integrated apparatus, and the separate integrated apparatus may generate signals with two different amplitudes. The communications apparatus may alternatively include two subsystems or two sub-apparatuses that are respectively configured to generate signals with different amplitudes. One of the two subsystems (or the two sub-apparatuses) is configured to generate a signal with a relatively low amplitude (for example, lower than <NUM> mV), and the other is configured to generate a signal with a relatively high amplitude (for example, <NUM> mV).

In some implementations, the controller <NUM> in this specification may include a modem, configured to modulate an original to-be-sent signal received from the control apparatus <NUM> of the inverter <NUM> or the control apparatus <NUM> of the direct-current-side device <NUM> to different frequency bands, to generate a to-be-sent signal. For example, the original to-be-sent signal may be modulated to the first frequency band or the second frequency band, or modulated to different amplitudes, to meet different communication requirements. A specific modulation/demodulation circuit may be implemented in various existing or future manners, for example, OFDM and FSK.

It should be noted that the communications apparatus described above with reference to <FIG> may be applied to direct-current power line carrier communication shown in <FIG> in this application, and may also be similarly applied to alternating-current power line carrier communication.

A specific method for communication between the direct-current-side device <NUM> and the inverter <NUM> is described in detail below with reference to <FIG>.

<FIG> shows an example of communication between the direct-current-side device <NUM> and the inverter <NUM> according to an embodiment of this application. As shown in <FIG>, when the direct-current-side device <NUM> and the inverter <NUM> communicate with each other by using the direct-current power line that transmits electricity in the power generation system as a direct-current bus, first, the inverter <NUM> generates a networking information request signal, for example, may send the networking information request signal to the direct-current-side device through the direct-current bus by using the communications apparatus <NUM> (<NUM>). The networking information request signal is used to request networking information required for networking between the inverter <NUM> and the direct-current-side device <NUM>, for example, request any one or more of a physical address, a logical address, a serial number, a device identification code, and the like of the direct-current-side device. For example, the communications apparatus <NUM> may modulate a frequency of the networking information request signal to a first frequency band, for example, the foregoing low frequency band lower than <NUM>, and then couple the modulated networking information request signal to the direct-current power line, to transmit the modulated networking information request signal to the direct-current-side device <NUM> through the direct-current power line.

The direct-current-side device <NUM> filters out the networking information request signal from the direct-current power line, and obtains networking information request information through demodulation. Based on the networking information request, the direct-current-side device <NUM> may send the networking information to the inverter <NUM> by using the communications apparatus <NUM> (<NUM>). For example, if the networking information request signal is a request for obtaining the device identification code of the direct-current-side device, the networking information may be the device identification code of the direct-current-side device. A signal that is sent by the direct-current-side device <NUM> and that carries the networking information may be modulated to a frequency band that is the same as the frequency band within which the received networking information request signal is located.

After receiving the networking information sent by the direct-current-side device <NUM>, for example, filtering out the signal carrying the networking information from the direct-current power line, and obtaining the networking information through demodulation, the inverter <NUM> may perform networking with the direct-current-side device based on the received networking information, to facilitate subsequent information transmission and control. Then, the inverter <NUM> may generate a control signal whose frequency is higher than a frequency of the networking information request signal, for example, modulate the frequency of the control signal to a second frequency band higher than the first frequency band, for example, the foregoing high frequency band higher than <NUM>, and then couple the control signal to the direct-current power line to send the control signal to the direct-current-side device <NUM>, where the control signal is used to control an operating parameter of the direct-current-side device (<NUM>). After receiving the control signal, the direct-current-side device <NUM> may adjust the operating parameter based on the received control signal, for example, adjust any one or more of an output power, an output voltage, an output current, and the like based on a requirement in the control signal.

In addition to receiving the control signal of the inverter to adjust the operating parameter of the direct-current-side device <NUM>, the direct-current-side device <NUM> may further send an operating information transmission signal to the inverter through the direct-current power line in a similar manner (<NUM>). The operating information transmission signal may carry, for example, at least one of operating status information, an operating log, and alarm information of the direct-current-side device. That the direct-current-side device <NUM> sends an operating information transmission signal to the inverter (<NUM>) may be: The inverter first sends an operating information request to the direct-current-side device <NUM>, and then the direct-current-side device <NUM> sends the operating information transmission signal based on the request received from the inverter <NUM>. Alternatively, the direct-current-side device <NUM> may actively send the operating information transmission signal based on a requirement, for example, send the operating information transmission signal to the inverter <NUM> at a specified time. A frequency of the operating information transmission signal may be the same or belong to the same frequency band as the frequency of the control signal. For example, both are signals whose frequencies are higher than the frequency of the networking information request signal.

By implementing system networking at a relatively low frequency, and then switching to a signal with a relatively high frequency for information transmission and control, a problem that when a high-frequency signal is used for networking between an inverter and a power converter, the high-frequency signal easily causes crosstalk on an adjacent direct-current bus, and consequently, the inverter cannot identify power converters connected to the inverter can be effectively avoided. In some implementations, after the networking is implemented at a relatively low frequency, a high frequency may be switched to for communication in an adaptive manner. For example, a communication frequency is gradually increased, to finally reach a highest frequency that can be implemented under a current condition, for example, reach a highest transmit frequency while ensuring a specific bit error rate condition, and communicate at the highest frequency, to achieve a fastest transmission speed.

The control signal sent by the inverter <NUM> to the direct-current-side device <NUM> through the direct-current power line may be classified into a general control signal and a special control signal. The two signals have different signal amplitudes. The general control signal is used to control the operating parameter of the direct-current-side device in a normal case. In other words, in general cases, the general control signal is used for communication. The special control signal is used to control the operating parameter of the direct-current-side device in a special case. For example, in a high voltage ride-through case or a low voltage ride-through case, an amplitude of the control signal is increased or decreased, so that the direct-current-side device quickly detects that the signal amplitude is abnormal, and can quickly perform a predetermined action to quickly adjust the operating parameter of the direct-current-side device. For example, in a normal case, an amplitude of the general control signal may be, for example, <NUM> to <NUM> mV. If the high voltage ride-through case or the low voltage ride-through case occurs, the special control signal needs to be sent. An amplitude of the special control signal may be, for example, <NUM> mV.

In some implementations, the direct-current-side device <NUM> (for example, the power converter <NUM>) may have two operating states: one is a power-limited output state, and the other is a normal power output state. Before the direct-current-side device <NUM> is networked with the inverter <NUM>, the direct-current-side device <NUM> may operate in the power-limited output state. Based on an indication that the direct-current-side device has been networked with the inverter, for example, once a control signal from the inverter <NUM> is received, the direct-current-side device <NUM> may enter a normal operating state. In the power-limited output state, the output voltage, current, or power or the like of the direct-current-side device <NUM> is limited, to avoid a problem such as an electric shock or line overload caused by a construction problem such as incorrect cable connection or cable damage or accidental contact, thereby improving safety of a power station.

In a communication process, processing performed by the inverter <NUM> and the direct-current-side device <NUM> may be shown in <FIG> and <FIG> respectively.

<FIG> is a flowchart of a method for the inverter <NUM> in the power generation system according to an embodiment of this application. First, block S401: The inverter <NUM> generates a networking information request signal, and sends the networking information request signal to the direct-current-side device <NUM> in the power generation system through a direct-current bus. A frequency of the networking information request signal may be modulated to a first frequency band, for example, the foregoing low frequency band lower than <NUM>. The networking information request signal is used to request networking information required for networking between the inverter and the direct-current-side device, for example, any one or more of a physical address, a logical address, a serial number, and a device identification code of the direct-current-side device. Then, block S402: Receive networking information from the direct-current-side device <NUM> through the direct-current bus, and perform networking with the direct-current-side device based on the networking information. Then, block S403: Generate a control signal, and send the control signal to the direct-current-side device <NUM> through the direct-current bus. A frequency of the control signal may be set within a second frequency band higher than the first frequency band, for example, the foregoing high frequency band higher than <NUM>, to implement high-speed communication. The control signal may be used to control an operating parameter of the direct-current-side device <NUM>. In some implementations, the inverter <NUM> may further receive an operating information transmission signal from the direct-current-side device through the direct-current bus, that is, block S404. The operating information transmission signal carries at least one of operating status information, an operating log, and alarm information of the direct-current-side device <NUM>. The operating information transmission signal may be actively sent by the direct-current-side device <NUM>, or may be received from the direct-current-side device <NUM> after an operating information request is sent to the direct-current-side device <NUM>.

<FIG> is a flowchart of a method for the direct-current-side device <NUM> in the power generation system according to an embodiment of this application. As shown in <FIG>, first, block S501: Receive a networking information request signal from the inverter <NUM> through a direct-current bus. A frequency of the networking information request signal is within a first frequency band, for example, the foregoing low frequency band lower than <NUM>. Then, block S502: Send networking information to the inverter <NUM> based on the received networking information request signal through the direct-current bus. In this embodiment, a frequency of a signal carrying the networking information may also be set within the first frequency band. Alternatively, in some implementations, the frequency of the signal carrying the networking information may be different from the frequency of the networking information request signal. Then, block S503: Receive a control signal from the inverter. A frequency of the control signal may be within a second frequency band, for example, the foregoing high frequency band higher than <NUM>. Then, block S504: The control apparatus in the direct-current-side device <NUM> may adjust an operating parameter, for example, an output voltage, an output current, or an output power, of the direct-current-side device based on the received control signal. In some implementations, the direct-current-side device <NUM> may further send, actively or based on a request of the inverter <NUM>, an operating information transmission signal that carries at least one of operating status information, an operating log, and alarm information of the direct-current-side device <NUM> to the inverter <NUM> through the direct-current bus, that is, block S505. In this embodiment, a frequency of the operating information transmission signal may be within the second frequency band. In another implementation, the operating information transmission signal may alternatively be modulated to another frequency band.

The foregoing communication content is merely an example for description. In various implementations, the inverter <NUM> and the direct-current-side device <NUM> may perform communication that includes various types of information.

In some cases, some or all of the embodiments disclosed in <FIG> may be implemented by hardware, firmware, software, or any combination thereof. The disclosed embodiments may be further implemented as instructions carried or stored on one or more transitory or non-transitory machine-readable (for example, computer-readable) storage media. The instructions may be read and executed by one or more processors in a machine, to enable the machine to perform one or more features in the methods described above with reference to <FIG>. The machine-readable medium may include any mechanism for storing or transmitting information in a machine (for example, a computer)-readable form, but is not limited to a floppy disk, an optical disc, a compact disc read-only memory (CD-ROMs), a magnetic disk, a read-only memory (ROM), a random access memory (RAM), an erasable programmable read only memory (EPROM), an electrically erasable programmable read only memory (EEPROM), a magnetic card or an optical card, a flash memory, or a tangible machine-readable memory that transmits information through a network by using a signal (for example, a carrier, an infrared signal, or a digital signal) that is propagated through electricity, light, sound, or another form. Therefore, the machine-readable medium includes any type of machine-readable medium suitable for storing or transmitting an electronic instruction or information in a machine (for example, a computer)-readable form.

Therefore, according to an embodiment of this application, a machine-readable medium may be provided. The machine-readable medium stores an instruction. When the instruction is run on a machine, the machine performs some or all of the methods described above with reference to <FIG>.

The methods disclosed in the foregoing embodiments of this application may be applied to a processor, or implemented by a processor. The processor may be an integrated circuit chip and has a signal processing capability. In an implementation process, steps in the foregoing methods can be implemented by using a hardware integrated logical circuit in the processor, or by using instructions in a form of software. The processor may be a general purpose processor, a digital signal processor (DSP), an application-specific integrated circuit (ASIC), a field programmable gate array (FPGA) or another programmable logic device, a discrete gate or transistor logic device, or a discrete hardware component, and may implement or execute various methods, blocks, and logical block diagrams disclosed in the embodiments of this application. The general purpose processor may be a microprocessor, or the processor may be any conventional processor or the like. Steps of the methods disclosed with reference to the embodiments of this application may be directly executed and accomplished by means of a hardware decoding processor, or may be executed and accomplished by using a combination of hardware and software modules in a decoding processor. A software module may be located in a mature storage medium in the art, such as a random access memory, a flash memory, a read-only memory, a programmable read-only memory, an electrically erasable programmable memory, or a register. The storage medium is located in the memory, and the processor reads information in the memory and completes the steps in the foregoing methods in combination with hardware of the processor.

It may be understood that the embodiments described in this specification may be implemented by hardware, software, firmware, middleware, microcode or a combination thereof. Hardware implementations may include at least one of the following implementations, for example but not limited to, one or more application-specific integrated circuits (ASICs), electronic circuits, digital signal processors (DSPs), programmable logic devices (PLDs), field programmable gate arrays (FPGAs), general purpose processors, dedicated processors, microprocessors, other electronic units configured to perform the functions described in this application, or a combination thereof.

For software implementation, the technology described in this specification may be implemented by using modules for executing the functions (for example, a process or a function) described in this specification. Software code may be stored in the memory and executed by the processor. The memory may be implemented in the processor or outside the processor.

Therefore, according to another embodiment of this application, a system may be provided, including a processor and a memory. The memory stores an instruction, and the processor is configured to read the instruction stored in the memory, to perform some or all of the methods described above with reference to <FIG>.

In the power generation system in this application, the direct-current-side device <NUM> may be any one or more of a power converter, an energy storage converter, a battery cabinet, a direct current optimizer, a combiner box, and the like. <FIG> respectively show schematic diagrams of communicative connections between an inverter and different examples of the direct-current-side device <NUM>. <FIG> is a schematic diagram of communication between only a power converter and an inverter according to an embodiment of this application. <FIG> is a schematic diagram of communication between only an energy storage converter and an inverter according to an embodiment of this application. <FIG> is a schematic diagram of communication between only a battery cabinet and an inverter according to an embodiment of this application. Other direct-current-side devices such as the direct current optimizer and the combiner box may also communicate with the inverter in a similar manner.

In a system shown in <FIG>, at least one power converter <NUM> is connected to at least one inverter <NUM>, and an input end of the power converter <NUM> is connected to at least one solar panel string. When there are a plurality of power converters <NUM> and inverters <NUM>, outputs of the power converters <NUM> are connected in parallel, inputs of the inverters <NUM> are connected in parallel, and the outputs of the power converters <NUM> are connected to the inputs of the inverter <NUM> through a direct-current bus constituted by a direct-current power line. Communication apparatuses in the power converter <NUM> and the inverter <NUM> couple the foregoing low-frequency signals to the direct-current bus, to implement system networking at a relatively low frequency; and then switch to a relatively high frequency, and couple signals to the direct-current bus, to implement high-speed information transmission and control between the power converter <NUM> and the inverter <NUM>.

In a system shown in <FIG>, at least one energy storage converter <NUM> is connected to at least one inverter <NUM>, and an input end of the energy storage converter <NUM> is connected to a battery to implement battery charging and discharging. When there are a plurality of energy storage converters <NUM> and inverters <NUM>, outputs of the energy storage converter <NUM> are connected in parallel, inputs of the inverters <NUM> are connected in parallel, the outputs of the energy storage converter <NUM> are connected to the inputs of the inverter <NUM> through a direct-current bus constituted by a direct-current power line. Communication apparatuses in the energy storage converter <NUM> and the inverter <NUM> couple low-frequency or high-frequency signals to the direct-current bus, to implement information transmission and control between the energy storage converter <NUM> and the inverter <NUM>.

<FIG> shows a system in which the battery <NUM> is directly connected to the inverter <NUM> without the energy storage converter. For example, the battery <NUM> may be in a form of a battery cabinet. The battery cabinet may include a battery pack, a battery control apparatus, and a communications apparatus. There may be one or more batteries <NUM> and one or more inverters <NUM>. When there are a plurality of batteries <NUM> and inverters <NUM>, outputs of the batteries <NUM> are connected in parallel, inputs of the inverters <NUM> are connected in parallel, and the outputs of the battery cabinets and the inputs of the inverters <NUM> are connected through a direct-current bus constituted by a direct-current power line. Communication apparatus in the battery cabinet and the inverter <NUM> couple low-frequency or high-frequency signals to the direct-current bus, so that the battery control apparatus in the battery cabinet may communicate with the inverter, to implement information transmission and control between the inverter <NUM> and the battery cabinet.

The systems shown in <FIG> may be applied to various power generation systems, and are not limited to a photovoltaic power generation system. <FIG> show cases in which one type of direct-current-side device communicates with an inverter. In another implementation, the system may alternatively include a plurality of types of direct-current-side devices that separately communicate with the inverter, for example, the system shown in <FIG>.

Claim 1:
A power generation system (<NUM>), comprising a plurality of power converters (<NUM>, 102a) and an inverter (<NUM>, 110a), an input end of each power converter (<NUM>, 102a) configured to being connected to at least one solar panel or at least one battery, an output end of each power converter (<NUM>, 102a) connected to an input end of the inverter (<NUM>, 110a) in series and in parallel, the inverter (<NUM>, 110a) being configured to convert a direct current that is input from the converters (<NUM>, 104a) into an alternating current for power supply, and the inverter (<NUM>, 110a) comprises:
a control apparatus (<NUM>), configured to control the inverter (<NUM>, 110a) to convert the direct current that is input from the power converters (<NUM>, 102a) into the alternating current for power supply; and
a communications apparatus (<NUM>), coupled to the control apparatus (<NUM>), and configured to:
send a networking information request signal to the power converters (<NUM>, 102a) in the power generation system (<NUM>) through a direct-current power line (<NUM>) that transmits the direct current in the power generation system (<NUM>), wherein a frequency of the networking information request signal is within a first frequency band, and the networking information request signal is used to request networking information required for networking between the inverter (<NUM>, 110a) and the power converters (<NUM>, 102a);
receive the networking information from the power converters (<NUM>, 102a) through the direct-current power line (<NUM>); and
send a control signal to the power converters (<NUM>, 102a) through the direct-current power line (<NUM>), wherein a frequency of the control signal is within a second frequency band, and the control signal is used to control an operating parameter of the power converters (<NUM>, 102a) and the first frequency band is lower than the second frequency band.