Carrier communication system applied to cascaded H-bridge converter

Abstract

The invention provides a carrier communication system applied to a cascaded H-bridge converter, and belongs to a carrier communication technology in the field of electrical engineering. The carrier communication system is composed of a communication master node and N communication slave nodes, each communication slave node comprises a high-frequency noise filter, a coupling coil, a slave node modulation circuit and a slave node demodulation circuit, and the communication master node comprises a master node signal coupling loop, a master node modulation circuit and a master node demodulation circuit. By means of the structure, a low-impedance communication signal channel is constructed on the cascade output side through the main node signal coupling loop, and an annular carrier channel is constructed by the high-frequency noise filter and the coupling coil of each communication slave node, the main node signal coupling loop in the communication main node and the cascade cables between the H bridges. According to the invention, the signal-to-noise ratio of the carrier channel is improved, the communication reliability is ensured, and the power line carrier communication mode can be applied to the cascaded H-bridge converter.

Description

Technical Field

[0001] This invention pertains to carrier communication technology in the field of electrical engineering, specifically relating to a carrier communication system applied to a cascaded H-bridge converter. Background Technology

[0002] Cascaded H-bridge converters are widely used in power systems, especially in STATCOM, solid-state transformers (SST), PV grid-connected inverters (PVGI), and transformerless energy storage systems (TESS), due to their advantages over traditional converters, such as easy modular expansion, low switching frequency, high conversion efficiency, and low current harmonic content.

[0003] Due to its modular nature, the control of a cascaded H-bridge converter is based on communication. The main controller sends control commands to each cascaded unit via communication. Therefore, the communication system requires high speed, fixed and minimal communication latency, and high reliability. Traditionally, communication in cascaded multilevel inverters typically uses wired communication such as fiber optics, CAN, or RS-485, requiring dedicated communication cables, which increases construction complexity and cost. Power line communication (PLC) is widely used in power systems because it does not require additional communication cables. Therefore, introducing PLC communication has significant engineering implications.

[0004] Recent research on the application of PLC communication in power electronics has mainly focused on integrating the monitoring and control of PLCs with power electronic converters. This includes both in-depth theoretical analysis in academic papers and practical engineering applications, such as the invention patent applications "A Synchronous Transmission System for Energy and Information" (CN 102624427 B), "A Centralized Photovoltaic Power Generation System Capable of Distributed MPPT" (CN 106941263 B), "A Cascaded Multilevel Inverter System" (CN 105827130 B), and "Communication Circuit and Communication System Applied to Cascaded Multilevel Inverters" (CN 108847871 B).

[0005] Chinese invention patent application CN 102624427 B, authorized on December 11, 2013, entitled "A Synchronous Transmission System for Energy and Information," utilizes the switching subharmonics of a Boost converter as a carrier wave. While maintaining a constant duty cycle (ensuring a constant output power of the Boost converter), information modulation is achieved by changing the switching frequency of the Boost converter. Different switching frequencies correspond to data 0 and data 1, respectively. Therefore, it can be said that the inherent signal-to-noise ratio (SNR) during information transmission is very high. Furthermore, Chinese invention patent application CN106941263 B, authorized on April 23, 2019, entitled "A Centralized Photovoltaic Power Generation System Capable of Distributed MPPT," still uses a DC power line as the carrier communication channel, but integrates the modulation process into the control of the power converter, superimposing the modulated signal of the information onto the control setpoint of the Buck converter to achieve information transmission. Because the modulation signal of the information is achieved through control loop perturbation, the communication frequency is much lower than the switching frequency of the Buck converter. The switching frequencies and higher harmonic components of the Buck converter output, after low-pass filtering, are significantly attenuated. Therefore, the inherent channel SNR is very high. However, the implementation of these PLC communications is still limited to high-SNR power flow lines. For low-SNR channels, the above scheme still has the following shortcomings:

[0006] 1. For cascaded H-bridge converter systems, where the noise band covers the communication band, complex modulation and coding methods are needed to combat the effects of noise in the communication band, resulting in limited communication rate and large communication delay.

[0007] 2. Since the communication carrier is the subharmonic of the switch, the system communication rate is limited by the switching frequency of the converter, which is not suitable for applications with high communication rate requirements; while the scheme of using disturbances superimposed on the control loop to achieve information modulation has an even lower communication rate.

[0008] 3. For example, the invention patent application "A Synchronous Transmission System for Energy and Information" (CN 102624427 B) uses frequency modulation to transmit information, so the channel utilization is not as good as amplitude modulation and phase modulation.

[0009] Chinese invention patent application CN 105827130 B, granted on April 9, 2019, entitled "A Cascaded Multilevel Inverter System," utilizes the cascaded cable of a cascaded multilevel inverter as a carrier communication channel, and uses inductors and capacitors connected in parallel to construct low-frequency power flow loops and high-frequency signal flow loops respectively. Although this communication scheme utilizes the wideband noise channel of the cascaded cable, it still has the following shortcomings:

[0010] 1. The high and low frequency signals are split using only inductors and capacitors in parallel without any processing of high frequency noise. Therefore, complex modulation and coding methods are still needed to combat the effects of noise in the communication band, resulting in limited communication speed and large communication delay.

[0011] 2. Since the inductor is connected in series in the cascaded circuit, the inductance value is relatively limited and cannot be too large, so the shunting effect between high and low frequencies is not ideal;

[0012] 3. The actual impedance of a low-impedance communication band loop constructed using only one capacitor at a cascaded output port is not ideal;

[0013] 4. The parallel coupling of inductors and capacitors used in the second communication module on the inverter side (the slave node in this application) results in a relatively large channel impedance and severe signal attenuation.

[0014] Chinese invention patent application CN 108847871 B, authorized on June 11, 2021, entitled "Communication Circuit and Communication System Applied to Cascaded Multilevel Inverters," also utilizes the cascaded cable of the cascaded multilevel inverter as a carrier communication channel. This invention employs a balanced bridge structure constructed by connecting two symmetrical low-pass filter circuits in parallel on the output side of the inverter unit. The two low-pass filter circuits are used to suppress high-frequency noise output from the inverter unit connected in parallel, reducing the influence of the inverter unit on the communication channel. The receiving end at the node eliminates the influence of high-frequency noise output from the inverter unit connected in parallel on its own received signal by taking the differential signal from the midpoint of the two symmetrical low-pass filter balanced bridges. Although this communication scheme solves the impact of the wide noise bandwidth of the cascaded multilevel inverter system on communication, it still has the following shortcomings:

[0015] 1. The symmetrical bridge circuit composed of two low-pass filter circuits introduces a large number of passive components, which increases the system cost;

[0016] 2. Since it is necessary to take the differential signal at the midpoint of the two low-pass filter bridge arms to eliminate noise, the consistency requirements of the component parameters of the two low-pass bridge arms are high. Errors in passive components will lead to the deterioration of the system SNR.

[0017] 3. The main node coupling circuit uses the magnetizing inductance of the coupling transformer as the inductance of the LC series resonance. When the required resonant inductance is small, the design requirements of the coupling transformer are high, and the consistency of the inductance is not easy to control. Summary of the Invention

[0018] The technical problem to be solved by this invention is the aforementioned deficiency. The purpose is to provide a carrier communication system for cascaded H-bridge converters, so as to solve the technical problem that power line carrier communication technology cannot be applied to cascaded H-bridge converters.

[0019] The objective of this invention is achieved by providing a carrier communication system for a cascaded H-bridge converter. This system comprises one master communication node and N slave communication nodes, with each slave node corresponding to one H-bridge converter unit within the cascaded H-bridge converter. Each slave node includes a high-frequency noise filter, a coupling coil, a slave node modulation circuit, and a slave node demodulation circuit. The master communication node includes a master node signal coupling loop, a master node modulation circuit, and a master node demodulation circuit. A cascaded slave node string formed by multiple cascaded slave nodes is connected in parallel with the master node signal coupling loop. The master communication node is connected to the power grid through a main power filter. The carrier frequency in the carrier communication system is f. c .

[0020] Preferably, the coupling coil is a current transformer structure; the high-frequency noise filter includes an LC parallel resonant network and an LCR series resonant network, wherein the LC parallel resonant network is an inductor L p and capacitor C p The parallel structure, with its two ends denoted as points A and C respectively, the LCR series resonant network consists of inductors L connected in series. s Resistance R s Capacitor C s Composition, inductor L s The other end is connected to point C, capacitor C s The other end is connected to one end of the coupling coil, and the connection point is denoted as point I; points A and I form the input terminal of the communication slave node and are connected in parallel with the H-bridge converter unit;

[0021] The slave node modulation circuit includes a slave node controller and a slave node signal modulation bridge. The slave node demodulation circuit includes a bandpass filter, a precision detector circuit, a comparison decision circuit, and a Universal Asynchronous Transceiver Interface (UART) connected in sequence. That is, the slave node demodulation circuit uses the UART to complete the synchronization of the demodulated signal. The bandpass filter and the slave node signal modulation bridge are both connected in parallel to the secondary side of the coupling coil.

[0022] Preferably, the resonant frequencies of both the LC parallel resonant network and the LCR series resonant network are set to the carrier frequency f. c Capacitor C s The capacitance value C s0 and inductor L s The value of L s0 Capacitor C D The capacitance value Cp0 and inductor L p The value of L p0 They respectively satisfy:

[0023]

[0024] The resistor R s The Q value of the LCR series resonant network is used to adjust the bandwidth BW requirement. Let Q1 be the Q value of the LCR series resonant network. Q1 satisfies the following condition:

[0025]

[0026] Among them, R s0 For resistor R s The resistance value.

[0027] Preferably, the LC parallel resonant network and the LCR series resonant network are connected to form a low-pass filter structure, that is, the connection point C of the LC parallel resonant network and the LCR series resonant network is one end of the output port of the high-frequency noise filter, and the cutoff frequency of the low-pass filter is denoted as f. d f d <1 / 5f c And ensure that at carrier frequency f c The attenuation at that location is higher than 20 dB.

[0028] Preferably, the master node signal coupling loop includes a master node coupling capacitor C. m , main node coupling inductor L m Coupling bandwidth adjustment resistor R m Master node signal receiving transformer T Rx and master node signal transmission transformer T Tx The main node coupling capacitor C m Coupling bandwidth adjustment resistor R m , main node coupling inductor L m Master node signal transmission transformer T Tx The primary side is connected in series, and the main node signal receiving transformer T Rx The primary side is connected in parallel with the coupling inductor L at the main node. m The two ends of the main node signal coupling loop are connected in parallel to the input port of the main power filter to realize the connection between the communication main node and the main power filter.

[0029] The master node modulation circuit includes a master node controller and a master node signal modulation bridge. The master node demodulation circuit includes a bandpass filter, a precision detector circuit, a comparison and decision circuit, and a Universal Asynchronous Receiver / Transmitter (UART) interface connected in sequence. That is, the master node demodulation circuit uses the UART interface to synchronize the demodulated signal. The master node signal modulation bridge is connected in parallel to the master node signal transmitting transformer T. Tx The secondary side; the bandpass filter is connected in parallel to the main node signal receiving transformer T. Rx The secondary side.

[0030] Preferably, the main node coupling capacitor C m Coupling bandwidth adjustment resistor R m Coupled with the main node inductor L m The circuit obtained by series connection is called a master node series resonant network, and the frequency of this master node series resonant network is set as the carrier frequency f. c ; Master node coupling capacitor C m The capacitance value C m0 Coupled with the main node inductor L m The value of L m0 Conditions met:

[0031]

[0032] The coupling bandwidth adjustment resistor Rm is used to adjust the Q value of the master node series resonant network to meet the bandwidth BW requirement. The Q value of the master node series resonant network is denoted as Q2, and Q2 satisfies the following condition:

[0033]

[0034] Among them, R m0 Adjusting resistor R for coupling bandwidth m The resistance value.

[0035] Preferably, the master node signal transmitting transformer T Tx A tightly coupled transformer structure is adopted, and the leakage inductance value of this tightly coupled transformer structure is denoted as L1, where L1 < 1 / 100L. m0 L m0 Main node coupled inductor L m The sensing value; the master node signal receiving transformer T Rx Designed as a high-excitation inductance structure, let the high-excitation inductance structure at the carrier frequency f be... c The magnetizing inductance at that point is L2, and L2 > 100L m0 The excitation inductance value L2 avoids the main node signal receiving transformer T Rx Coupled with the main node inductor L m The resonant frequency shift caused by parallel connection.

[0036] Preferably, the bandwidth BW is set to twice the baseband data bandwidth.

[0037] Preferably, the signal modulation of the slave node is completed inside the slave node controller. When the slave node sends a signal, the slave node controller controls the enable of the triangular carrier of the PWM controller according to bit0 and bit1 of the baseband data to be sent to realize the modulation of the triangular carrier. Then, the triangular carrier is compared with the reference level corresponding to 50% duty cycle to realize the output of the PWM drive signal with fundamental frequency fc and duty cycle of 50%.

[0038] Preferably, the signal modulation of the master node is completed inside the master node controller. When the master node sends a signal, the master node controller controls the enable of the triangular carrier of the PWM controller according to bit0 and bit1 of the baseband data to be sent to realize the modulation of the triangular carrier. Then, the triangular carrier is compared with the reference level corresponding to 50% duty cycle to realize the output of the PWM drive signal with fundamental frequency fc and duty cycle of 50%.

[0039] Compared with the prior art, the beneficial effects of the present invention are specifically reflected in:

[0040] (1) The output switching noise component of the H-bridge converter unit, which is fully suppressed by the high-frequency noise filter at the node, is reduced in the communication frequency band, thereby improving the SNR of the channel.

[0041] (2) The coupling coil is placed outside the high-frequency noise filter at the slave node and connected in series with it to avoid the influence of the switching noise component of the H-bridge converter unit on the signal received by its corresponding slave node in the communication frequency band.

[0042] (3) By adopting unbalanced coupling, a symmetrical low-pass filter circuit is reduced, which lowers the cost of the system and avoids the deterioration of the system SNR caused by component inconsistency issues when using a balanced structure.

[0043] (4) The resonant points of both the LCR series resonant network in the high-frequency noise filter at the slave node and the LCR series resonant network in the signal coupling circuit at the master node are set at the carrier frequency f. c Together, they constructed a low-impedance channel under the carrier frequency band, which significantly reduced signal attenuation during transmission.

[0044] (5) The LCR series resonant network in the high-frequency noise filter of the slave node is used as the output filter of the signal modulation bridge in the slave node modulation circuit, and the LCR series resonant network in the signal coupling circuit of the master node is used as the output filter of the signal modulation bridge in the master node modulation circuit, which further saves system cost.

[0045] (6) The inductor in the LCR series resonant network of the main node signal coupling circuit adopts an independent inductor and a parallel structure with the signal receiving transformer, which reduces the design difficulty of the signal receiving transformer and improves the coupling efficiency, especially when the resonant inductance is small.

[0046] (7) By improving the SNR of the system, simpler modulation and demodulation schemes (such as 0OK modulation and envelope detection demodulation) can be applied, which improves the communication rate and reduces the communication delay. Attached Figure Description

[0047] Figure 1 This is a structural block diagram of the present invention.

[0048] Figure 2 This is a block diagram of the communication slave node circuit in an embodiment of the present invention.

[0049] Figure 3 This is a block diagram of the slave node modulation principle in an embodiment of the present invention.

[0050] Figure 4 This is a block diagram of the slave node demodulation circuit in an embodiment of the present invention.

[0051] Figure 5 This is a block diagram of the communication master node circuit in an embodiment of the present invention.

[0052] Figure 6 This is a block diagram of the slave node modulation principle in an embodiment of the present invention.

[0053] Figure 7 This is a block diagram of the slave node demodulation circuit in an embodiment of the present invention. Detailed Implementation

[0054] The technical solution of the present invention will now be clearly and completely described in conjunction with the accompanying drawings.

[0055] Figure 1 This is a structural block diagram of the present invention. As shown in the figure, the present invention provides a carrier communication system applied to a cascaded H-bridge converter. The carrier communication system consists of one communication master node and N communication slave nodes. Each communication slave node corresponds to one H-bridge converter unit in the cascaded H-bridge converter. Each communication slave node includes a high-frequency noise filter, a coupling coil, a slave node modulation circuit, and a slave node demodulation circuit. The communication master node includes a master node signal coupling loop, a master node modulation circuit, and a master node demodulation circuit. The cascaded communication slave node string formed by multiple cascaded communication slave nodes is connected in parallel with the master node signal coupling loop. The communication master node is connected to the power grid through a main power filter. The carrier frequency in the carrier communication system is f. c .

[0056] In this embodiment, the master node signal modulation bridge in the master node modulation circuit and the slave node signal modulation bridge in the slave node modulation circuit are any one of the following types: full bridge, half bridge, or other single-phase inverter bridge topologies.

[0057] Figure 2 This is a block diagram of the communication slave node circuit in an embodiment of the present invention. Figure 3 This is a block diagram of the slave node modulation principle in an embodiment of the present invention. Figure 4 This is a block diagram of the slave node demodulation circuit in an embodiment of the present invention. Figure 2 , Figure 3 and Figure 4 The specific structure of the communication node is as follows. In this embodiment, the coupling coil is a current transformer structure; the high-frequency noise filter includes an LC parallel resonant network and an LCR series resonant network, wherein the LC parallel resonant network is an inductor L... p and capacitor C p The parallel structure, with its two ends denoted as points A and C respectively, the LCR series resonant network consists of inductors L connected in series. s Resistance R s Capacitor C s Composition, inductor L s The other end is connected to point C, capacitor C s The other end is connected to one end of the coupling coil, and the connection point is denoted as point I; points A and I form the input terminal of the communication slave node and are connected in parallel with the H-bridge converter unit.

[0058] The slave node modulation circuit includes a slave node controller and a slave node signal modulation bridge. The slave node demodulation circuit includes a bandpass filter, a precision detector circuit, a comparison decision circuit, and a Universal Asynchronous Transceiver Interface (UART) connected in series. That is, the slave node demodulation circuit uses the UART to synchronize the demodulated signal. The bandpass filter and the slave node signal modulation bridge are both connected in parallel to the secondary side of the coupling coil.

[0059] exist Figure 2 In the diagram, point B is one endpoint where the cable from point I to the H-bridge side connects to the output terminal of the H-bridge, and point D is the other end of the coupling coil. Additionally, from... Figure 1 As can be seen, point C of the first H-bridge converter unit and point D of the Nth H-bridge converter unit constitute the output of the cascaded communication slave node string.

[0060] In this embodiment, the resonant frequencies of both the LC parallel resonant network and the LCR series resonant network are set to the carrier frequency f. c Capacitor C s The capacitance value C s0 and inductor L s The value of L s0 Capacitor Cp The capacitance value C p0 and inductor L p The value of L p0 They respectively satisfy:

[0061]

[0062] The resistor R s The Q value of the LCR series resonant network is used to adjust the bandwidth BW requirement. Let Q1 be the Q value of the LCR series resonant network. Q1 satisfies the following condition:

[0063]

[0064] Among them, R s0 For resistor R s The resistance value.

[0065] In this embodiment, the bandwidth BW is set to twice the baseband data bandwidth.

[0066] In this embodiment, the LC parallel resonant network and the LCR series resonant network are connected to form a low-pass filter structure. That is, the connection point C of the LC parallel resonant network and the LCR series resonant network is one end of the output port of the high-frequency noise filter. Let the cutoff frequency of this low-pass filter be f. d f d <1 / 5f c And ensure that at carrier frequency f c The attenuation at that location is higher than 20 dB.

[0067] In this embodiment, the signal modulation of the slave node is completed inside the slave node controller. When the slave node sends a signal, the slave node controller controls the enable of the triangular carrier of the PWM controller according to bit0 and bit1 of the baseband data to be sent to achieve triangular carrier modulation. Then, the triangular carrier is compared with the reference level corresponding to 50% duty cycle to achieve the output of a PWM drive signal with a fundamental frequency of fc and a duty cycle of 50%. This drive signal drives the slave node signal modulation bridge to achieve power amplification, and then injects it into the power circuit of the cascaded H-bridge converter through the coupling coil. After being filtered by the LCR series resonant network in the high-frequency noise filter, it is converted into a sinusoidal modulated wave and transmitted in the power circuit of the cascaded H-bridge converter. When receiving a signal, the slave node controller controls all the switches of the control signal modulation bridge to be turned off, outputting a high impedance state to avoid its influence on the received signal. At this time, the slave node controller is the control chip of the H-bridge converter unit, which performs power control of the H-bridge converter unit and also takes into account the modulation and demodulation functions of carrier communication.

[0068] Figure 5This is a block diagram of the communication master node circuit in an embodiment of the present invention. Figure 6 This is a block diagram of the master node modulation principle in an embodiment of the present invention. Figure 7 This is a block diagram of the master node demodulation circuit in an embodiment of the present invention. Figure 5 , Figure 6 and Figure 7 The specific structure of the communication master node is thus visible. In this embodiment, the master node signal coupling loop includes the master node coupling capacitor C. m , main node coupling inductor L n Coupling bandwidth adjustment resistor R m Master node signal receiving transformer T Rx and master node signal transmission transformer T Tx The main node coupling capacitor C m Coupling bandwidth adjustment resistor R m , main node coupling inductor L m Master node signal transmission transformer T Tx The primary side is connected in series, and the main node signal receiving transformer T Rx The primary side is connected in parallel with the coupling inductor L at the main node. m The two ends of the main node signal coupling loop are connected in parallel to the input port of the main power filter to realize the connection between the communication main node and the main power filter.

[0069] The master node modulation circuit includes a master node controller and a master node signal modulation bridge. The master node demodulation circuit includes a bandpass filter, a precision detector circuit, a comparison and decision circuit, and a Universal Asynchronous Receiver / Transmitter (UART) interface connected in series. That is, the master node demodulation circuit uses the UART interface to synchronize the demodulated signal. The master node signal modulation bridge is connected in parallel to the master node signal transmitting transformer T. Tx The secondary side; the bandpass filter is connected in parallel to the main node signal receiving transformer T. Rx The secondary side.

[0070] exist Figure 5 Above, E and F are the two endpoints of the signal coupling loop of the master node. These two endpoints constitute the port of the communication master node. This port is connected in parallel with the output of the cascaded communication slave node string and the master power filter, respectively.

[0071] In this embodiment, the main node coupling capacitor C is... m Coupling bandwidth adjustment resistor R m Coupled with the main node inductor L m The circuit obtained by series connection is called a master node series resonant network, and the frequency of this master node series resonant network is set as the carrier frequency f. c ; Master node coupling capacitor C m The capacitance value C m0 Coupled with the main node inductor Lm The value of L m0 Conditions met:

[0072]

[0073] The coupling bandwidth adjustment resistor R m The Q value of the master node series resonant network is used to adjust the bandwidth BW requirement. Let Q2 be the Q value of the master node series resonant network. Q2 satisfies the following condition:

[0074]

[0075] Among them, R m0 Adjusting resistor R for coupling bandwidth m The resistance value.

[0076] In this embodiment, the master node signal transmitting transformer T Tx A tightly coupled transformer structure is adopted, and the leakage inductance value of this tightly coupled transformer structure is denoted as L1, where L1 < 1 / 100L. m0 L m0 Main node coupled inductor L m The sensing value; the master node signal receiving transformer T Rx Designed as a high-excitation inductance structure, let the high-excitation inductance structure at the carrier frequency f be... c The magnetizing inductance at that point is L2, and L2 > 100L. m0 The excitation inductance value L2 avoids the main node signal receiving transformer T Rx Coupled with the main node inductor L m The resonant frequency shift caused by parallel connection.

[0077] In this embodiment, the signal modulation of the master node is completed inside the master node controller. When the master node sends a signal, the master node controller controls the enable of the triangular carrier of the PWM controller according to bit 0 and bit 1 of the baseband data to be sent to achieve triangular carrier modulation. Then, the triangular carrier is compared with the reference level corresponding to 50% duty cycle to achieve the output of a PWM drive signal with a fundamental frequency of fc and a duty cycle of 50%. This drive signal drives the signal modulation bridge to achieve power amplification. At this time, the master node signal coupling circuit is equivalent to the coupling capacitor C of the master node. m The main node coupling inductor L m and coupling bandwidth adjustment resistor R m A series resonant network, composed of multiple series components, filters the amplified square wave power signal, converting it into a sinusoidal modulated wave for transmission in the cascaded power loop. When receiving a signal, the master node controller activates the two lower transistors of the signal modulation bridge, outputting a 0 level, and transmits the master node signal to the transformer T.Tx The secondary side short circuit, i.e., the primary node signal transmitting transformer T Tx Externally, this manifests as leakage inductance. At this time, the main node coupling circuit operates in a series resonant state, and the signal is received through the main node signal receiving transformer T. Rx Coupled inductor L from the main node m The maximum communication signal can be obtained from this. The master node controller is the control chip for the entire cascaded H-bridge system, which not only controls the entire cascaded H-bridge system but also performs some modulation and demodulation functions for carrier communication.

[0078] The master node demodulation circuit and the slave node demodulation circuit adopt the same circuit structure, and their working principle is as follows: After the signal is obtained from the secondary side of the signal coupling coil of the slave node or the secondary side of the receiving transformer of the master node, it is sent to the bandpass filter. The center frequency of the bandpass filter is set to the carrier frequency f. c The bandwidth is set to BW. After filtering out out-of-band noise, the data is sent to a precision detection circuit to achieve envelope detection and restore the envelope of the baseband data. Then, the data is compared with the reference threshold value through a comparison decision circuit to obtain the preliminary baseband data. The data is then sent to the UART port of the master node or slave node controller. The final demodulation is completed by using the controller's UART port to complete the bit synchronization of the demodulated signal.

[0079] The present invention provides a communication slave node for a cascaded H-bridge converter, wherein one communication slave node corresponds one-to-one with an H-bridge converter unit. A low-impedance communication signal path is constructed on the cascaded output side using the master node signal coupling loop. On the H-bridge side, the high-frequency noise filter of the communication slave node sufficiently attenuates the high-frequency components of the switching noise at the H-bridge output. Since the LC parallel resonant network in the high-frequency noise filter exhibits high impedance for the communication signal, and the LCR series resonant network exhibits low impedance, the LCR series resonant network in the high-frequency noise filter of each communication slave node, the coupling coil, the master node signal coupling loop in the master node, and the cascaded cables between each H-bridge construct a ring carrier channel.

Claims

1. A carrier communication system applied to a cascaded H-bridge converter, characterized in that, The carrier communication system consists of one master communication node and N slave communication nodes. Each slave communication node corresponds to one H-bridge converter unit in the cascaded H-bridge converter. Each slave communication node includes a high-frequency noise filter, a coupling coil, a slave node modulation circuit, and a slave node demodulation circuit. The master communication node includes a master node signal coupling loop, a master node modulation circuit, and a master node demodulation circuit. A cascaded slave communication node string formed by multiple cascaded slave communication nodes is connected in parallel with the master node signal coupling loop. The master communication node is connected to the power grid through a main power filter. The carrier frequency in the carrier communication system is f. c .

2. The carrier communication system applied to a cascaded H-bridge converter according to claim 1, characterized in that, The coupling coil is a current transformer structure; the high-frequency noise filter includes an LC parallel resonant network and an LCR series resonant network, the LC parallel resonant network being an inductor L p and capacitor C p The parallel structure, with its two ends denoted as points A and C respectively, the LCR series resonant network consists of inductors L connected in series. s Resistance R s Capacitor C s Composition, inductor L s The other end is connected to point C, capacitor C s The other end is connected to one end of the coupling coil, and the connection point is denoted as point I; points A and I form the input terminal of the communication slave node and are connected in parallel with the H-bridge converter unit; The slave node modulation circuit includes a slave node controller and a slave node signal modulation bridge. The slave node demodulation circuit includes a bandpass filter, a precision detector circuit, a comparison decision circuit, and a Universal Asynchronous Transceiver Interface (UART) connected in sequence. That is, the slave node demodulation circuit uses the UART to complete the synchronization of the demodulated signal. The bandpass filter and the slave node signal modulation bridge are both connected in parallel to the secondary side of the coupling coil.

3. A carrier communication system applied to a cascaded H-bridge converter according to claim 2, characterized in that, The resonant frequencies of both the LC parallel resonant network and the LCR series resonant network are set to the carrier frequency f. c Capacitor C s The capacitance value C s0 and inductor L s The value of L s0 Capacitor C p The capacitance value C p0 and inductor L p The value of L p0 They respectively satisfy: The resistor R s The Q value of the LCR series resonant network is used to adjust the bandwidth BW requirement. Let Q1 be the Q value of the LCR series resonant network. Q1 satisfies the following condition: Among them, R s0 For resistor R s The resistance value.

4. A carrier communication system applied to a cascaded H-bridge converter according to claim 2 or 3, characterized in that, The LC parallel resonant network and the LCR series resonant network are connected to form a low-pass filter structure. Specifically, the connection point C between the LC parallel resonant network and the LCR series resonant network is one end of the output port of the high-frequency noise filter. The cutoff frequency of this low-pass filter is f. d f d <1 / 5f c And ensure that at carrier frequency f c The attenuation at that location is higher than 20 dB.

5. A carrier communication system applied to a cascaded H-bridge converter according to claim 1, characterized in that, The master node signal coupling circuit includes the master node coupling capacitor C. m , main node coupling inductor L m Coupling bandwidth adjustment resistor R m Master node signal receiving transformer T Rx and master node signal transmission transformer T Tx The main node coupling capacitor C m Coupling bandwidth adjustment resistor R m , main node coupling inductor L m Master node signal transmission transformer T Tx The primary side is connected in series, and the main node signal receiving transformer T Rx The primary side is connected in parallel with the coupling inductor L at the main node. m The two ends of the main node signal coupling loop are connected in parallel to the input port of the main power filter to realize the connection between the communication main node and the main power filter. The master node modulation circuit includes a master node controller and a master node signal modulation bridge. The master node demodulation circuit includes a bandpass filter, a precision detector circuit, a comparison and decision circuit, and a Universal Asynchronous Receiver / Transmitter (UART) interface connected in sequence. That is, the master node demodulation circuit uses the UART interface to synchronize the demodulated signal. The master node signal modulation bridge is connected in parallel to the master node signal transmitting transformer T. Tx The secondary side; the bandpass filter is connected in parallel to the main node signal receiving transformer T. Rx The secondary side.

6. A carrier communication system applied to a cascaded H-bridge converter according to claim 5, characterized in that, The main node coupling capacitor C m Coupling bandwidth adjustment resistor R m Coupled with the main node inductor L m The circuit obtained by series connection is called a master node series resonant network, and the frequency of this master node series resonant network is set as the carrier frequency f. c ; Master node coupling capacitor C m The capacitance value C m0 Coupled with the main node inductor L m The value of L m0 Conditions met: The coupling bandwidth adjustment resistor R m The Q value of the master node series resonant network is used to adjust the bandwidth BW requirement. Let Q2 be the Q value of the master node series resonant network. Q2 satisfies the following condition: Among them, R m0 Adjusting resistor R for coupling bandwidth m The resistance value.

7. A carrier communication system applied to a cascaded H-bridge converter according to claim 5 or 6, characterized in that, The master node signal transmitting transformer T Tx A tightly coupled transformer structure is adopted. The leakage inductance value of this tightly coupled transformer is denoted as L1, where L1 < 1 / 100L. m0 L m0 Main node coupled inductor L m The sensing value; the master node signal receiving transformer T Rx Designed as a high-excitation inductance structure, let the high-excitation inductance structure at the carrier frequency f be... c The magnetizing inductance at that point is L2, and L2 > 100L m0 The excitation inductance value L2 avoids the main node signal receiving transformer T Rx Coupled with the main node inductor L m The resonant frequency shift caused by parallel connection.

8. A carrier communication system applied to a cascaded H-bridge converter according to claim 3 or 6, characterized in that, The bandwidth BW is set to twice the baseband data bandwidth.

9. A carrier communication system applied to a cascaded H-bridge converter according to claim 2, characterized in that, The signal modulation of the slave node is completed inside the slave node controller. When the slave node sends a signal, the slave node controller controls the enable of the triangular carrier of the PWM controller according to bit0 and bit1 of the baseband data to be sent to realize the modulation of the triangular carrier. Then, the triangular carrier is compared with the reference level corresponding to 50% duty cycle to realize the output of the PWM drive signal with fundamental frequency fc and duty cycle of 50%.

10. A carrier communication system applied to a cascaded H-bridge converter according to claim 5, characterized in that, The signal modulation of the master node is completed inside the master node controller. When the master node sends a signal, the master node controller controls the enable of the triangular carrier of the PWM controller according to bit0 and bit1 of the baseband data to be sent to realize the modulation of the triangular carrier. Then, the triangular carrier is compared with the reference level corresponding to 50% duty cycle to realize the output of the PWM drive signal with fundamental frequency fc and duty cycle of 50%.

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