Low frequency high power transmitter

Abstract

A low-frequency high-power transmitter includes N controllable high-voltage DC power supplies, N inverter modules, a tuning unit, and an antenna. Each controllable high-voltage DC power supply is a power conversion device isolated from the mains input. The DC voltage output terminals of the N controllable high-voltage DC power supplies are respectively connected to the DC input terminals of the N inverter modules. The bipolar symmetrical square wave output terminals of the N inverter modules are cascaded and connected to the input terminal of the tuning unit. The output terminal of the tuning unit is connected to the antenna. The phases of the excitation signals of the N inverter modules differ sequentially by π / N, where N is a natural number greater than 1. This invention superimposes the bipolar symmetrical square waves output by the N inverter modules with sequentially phase-differenced excitation signals (π / N) to obtain a bipolar symmetrical stepped waveform with 2N-1 levels, greatly reducing the odd harmonic content of the transmitted signal and thus effectively improving the output quality of the low-frequency high-power transmitter.

Description

Technical Field

[0001] This utility model relates to a high-power low-frequency transmitter with low odd harmonic content and high output quality, belonging to the field of communication technology. Background Technology

[0002] With the rapid development of defense technology and the background of military-civilian integration, the field of transmitters has also made significant progress. There are many types of transmitters, among which low-frequency long-wave transmitters have wavelengths of several kilometers, frequency ranges from tens to hundreds of kilohertz, and a sine wave carrier with an amplitude of 1 kilovolt to tens of kilovolts. Low-frequency transmitters have advantages such as stable signal propagation, strong diffraction capability, strong anti-interference capability, and good penetration capability. A block diagram of a traditional low-frequency transmitter is shown below. Figure 1 As shown, it consists of a controllable high-voltage DC power supply, an excitation signal, a power amplifier module, a tuning unit, and an antenna. The excitation signal is the control signal of the transmitter. The controllable high-voltage DC power supply has a high-frequency switching power supply, which converts the mains power into high-quality DC high voltage. The power amplifier module amplifies the power of the excitation signal. The tuning unit adjusts the power amplifier output to match the antenna (impedance).

[0003] The working principle of a traditional high-power transmitter is that the mains power input is converted into a controllable high-voltage DC power supply to power the power amplifier module. The excitation signal (a sine wave signal of 30KHz to 300KHz) is controlled by the power drive circuit inside the power amplifier module to amplify the power of the excitation signal so that its voltage reaches a certain amplitude. Then it is connected to the tuning unit. By adjusting the parameters of the tuning unit, the power signal is matched with the antenna impedance, and the communication signal is transmitted through the antenna.

[0004] The conversion efficiency of the controllable high-voltage DC power supply and power amplifier module is a key factor determining the operating efficiency of low-frequency transmitters. Currently, controllable high-voltage DC power supplies are implemented through high-frequency switching power supplies. There are many topologies for high-frequency switching power supplies, including hard-switching topologies such as forward topologies, push-pull topologies, and half-bridge (full-bridge) topologies, and soft-switching topologies such as phase-shifted full-bridge soft-switching topologies and LLC half-bridge (full-bridge) topologies. Currently, controllable high-voltage DC power conversion mostly adopts soft-switching topologies. With the development of materials science, the main power devices of controllable high-voltage DC power supplies adopt new power switching transistors such as silicon carbide MOS and gallium nitride MOS. These new power switching transistors have advantages such as low on-resistance, fast switching speed, simple driving, and short reverse recovery time of the body diode, enabling controllable high-voltage DC power supplies to achieve high frequency, miniaturization, and high conversion efficiency.

[0005] Low-frequency transmitters require high-voltage controllable DC power supplies, reaching several kilovolts, which complicates their design, makes power device selection difficult, and necessitates high safety protection levels for high-voltage outputs. Furthermore, the low conversion efficiency of power amplifier modules means that in high-power transmitters, power loss necessitates enhanced heat dissipation capabilities, such as forced air cooling or liquid cooling, resulting in a larger overall size for low-frequency transmitters.

[0006] Utility model patent application CN201320009579.9 discloses a very low frequency (VLF) high-power transmitter, comprising several series-connected unit inverter bridges; the outputs of the series-connected unit inverter bridges are connected to a VLF antenna through a tuning matching network; each unit inverter bridge includes multiple insulated gate bipolar transistors (IGBTs). This VLF high-power transmitter has advantages such as small size, high power, and reliable operation. However, its power amplification module uses IGBTs to form an inverter H-bridge, which is a traditional power amplification method. Its operating frequency is VLF, with a frequency range of 300Hz to 3000Hz. IGBTs can adapt to this frequency band. Furthermore, in this patent, several power amplification units receive the same excitation signal, achieving power expansion. However, the output of the power amplification unit is a square wave. The optimal symmetrical bipolar duty cycle output of 50% is calculated to be 48.3%, indicating a large amount of odd harmonic content, and the output quality needs improvement. Utility Model Content

[0007] The purpose of this invention is to address the shortcomings of existing technologies by providing a low-frequency, high-power transmitter that reduces odd harmonic content and improves the transmitter's output quality.

[0008] The problem described in this utility model is solved by the following technical solution: A low-frequency high-power transmitter includes N controllable high-voltage DC power supplies, N inverter modules, a tuning unit TX, and an antenna An. Each controllable high-voltage DC power supply is a power conversion device isolated from the mains input. The DC voltage output terminals of the N controllable high-voltage DC power supplies are respectively connected to the DC input terminals of the N inverter modules. The bipolar symmetrical square wave output terminals of the N inverter modules are cascaded and connected to the input terminal of the tuning unit TX. The output terminal of the tuning unit TX is connected to the antenna An. The phase difference of the excitation signals of the N inverter modules is π / N, where N is a natural number greater than 1.

[0009] In the aforementioned low-frequency high-power transmitter, each inverter module includes four power switching transistors and four drive circuits. The drains of the first power switching transistor Q1 and the third power switching transistor Q3 are connected to the positive terminal of the power supply. The drains of the second power switching transistor Q2 and the fourth power switching transistor Q4 are connected to the sources of the first power switching transistor Q1 and the third power switching transistor Q3, respectively. The sources of the second power switching transistor Q2 and the fourth power switching transistor Q4 are connected to the negative terminal of the power supply. The gates of the four power switching transistors are connected to the output terminals of the four drive circuits, respectively. The voltage signal between the sources of the first power switching transistor Q1 and the third power switching transistor Q3 is the output signal of the inverter module.

[0010] In the aforementioned low-frequency high-power transmitter, the excitation signals for the four drive circuits of each inverter module are provided by the control unit. The input port of the control unit is connected to the excitation signal, and the input terminals of the excitation signals of the four drive circuits are respectively connected to different output ports of the control unit.

[0011] The aforementioned low-frequency high-power transmitter includes a controllable high-voltage DC power supply comprising a three-phase active power factor correction circuit and a switching power supply. The input terminal of the three-phase active power factor correction circuit is connected to the three-phase mains power, and the output terminal is connected to the input terminal of the switching power supply. The power switching transistors of the switching power supply and the four power switching transistors of the inverter module are all silicon carbide MOSFETs.

[0012] In the aforementioned low-frequency high-power transmitter, the duty cycle of the excitation signal of the inverter module is 50%.

[0013] This invention superimposes the bipolar symmetrical square waves output by N inverter modules whose phases differ by π / N sequentially to obtain a bipolar symmetrical stepped waveform with 2N-1 levels, which greatly reduces the odd harmonic content of the transmitted signal and thus effectively improves the output quality of the low-frequency high-power transmitter.

[0014] The power switching transistor of this invention is a silicon carbide MOSFET, which can improve the conversion efficiency of the controllable high voltage DC power supply and inverter module. Attached Figure Description

[0015] The present invention will now be described in further detail with reference to the accompanying drawings.

[0016] Figure 1 This is a block diagram of a traditional low-frequency transmitter. Figure 2 This is a block diagram of the electrical principle of this utility model; Figure 3 This is the electrical schematic of the inverter module; Figure 4 This is a waveform diagram of the inverter module's output voltage. Figure 5 Electrical schematic diagram of this utility model; Figure 6 This is the electrical schematic diagram of a low-frequency high-power transmitter with three sets of cascaded inverter modules; Figure 7 It is the output waveform of a low-frequency high-power transmitter with three cascaded inverter modules.

[0017] The labels in the diagram are as follows: DC1~DCN, first controllable high-voltage DC power supply~Nth controllable high-voltage DC power supply; NB, inverter module; NB1~NBN, first inverter module~Nth inverter module; QD1~QD4, first drive circuit~fourth drive circuit; Q1~Q4, first power switch transistor~fourth power switch transistor; TX, tuning unit; An, antenna; MCU, control unit; RL, load. Detailed Implementation

[0018] This invention provides a solution for a low-harmonic, high-efficiency, miniaturized low-frequency high-power transmitter that addresses the shortcomings of existing technologies.

[0019] See Figures 2-5 Let N represent a natural number greater than 1. This utility model includes N controllable high-voltage DC power supplies (i.e., the first controllable high-voltage DC power supply DC1 to the Nth controllable high-voltage DC power supply DCN), N inverter modules (i.e., the first inverter module NB1 to the Nth inverter module NBN), a tuning unit TX, and an antenna An. Each controllable high-voltage DC power supply is a power conversion device isolated from the mains input. The DC voltage output terminals of the N controllable high-voltage DC power supplies are respectively connected to the DC input terminals of the N inverter modules. The bipolar symmetrical square wave output terminals of the N inverter modules are cascaded (i.e., connected in series) and then connected to the input terminal of the tuning unit TX. The output terminal of the tuning unit TX is connected to the antenna An. The excitation signal input terminals of the N inverter modules are connected to the control unit, and the phases of the excitation signals of the N inverter modules differ by π / N sequentially.

[0020] Its working principle is as follows: the mains power input is divided into N groups, which respectively power N controllable high-voltage DC power supplies. Each controllable high-voltage DC power supply is an independent power conversion device, isolated from the mains power input. The N controllable high-voltage DC power supplies power N inverter modules respectively. The excitation signal is processed by the control unit MCU to form N sets of drive signals, which drive the N inverter modules respectively. The output signals of the N inverter modules are superimposed and combined to form a power-amplified transmission signal. This transmission signal is connected to the input terminal of the tuning unit. By adjusting the parameters of the tuning unit to achieve impedance matching with the antenna, the antenna transmits and outputs the transmission signal.

[0021] Controllable high-voltage DC power supplies are generally high-power switching power supplies, using three-phase AC mains input. The front-end is a three-phase active power factor correction (PFC) circuit, which brings the input power factor close to 1 and significantly reduces input current harmonics. The output voltage of the three-phase active power factor correction circuit is typically 800Vdc DC. The input voltage of the controllable high-voltage DC power supply is the output voltage of the three-phase active power factor correction circuit. The power conversion of the controllable high-voltage DC power supply adopts a soft-switching topology (phase-shifted full-bridge soft-switching topology, full-bridge LLC soft-switching topology, etc.). The power switching transistors are silicon carbide MOSFETs. Each controllable high-voltage DC power supply has an internal microcontroller, which can set the output voltage via communication, making the output voltage adjustable between several hundred volts and one thousand volts. The upper limit of the output voltage of the controllable high-voltage DC power supply is one thousand volts. At present, silicon carbide MOSFET technology is relatively mature, and its 1200V withstand voltage series is widely used, making it very suitable for high-power controllable high-voltage DC power supplies. The use of soft-switching technology and new silicon carbide MOSFETs results in high conversion efficiency for the controllable high-voltage DC power supply.

[0022] The low-frequency transmitter has N inverter modules NB. Figure 3 The circuit diagram of the inverter module NB shows that each inverter module NB includes four power switches and four drive circuits. The four power switches are designated as first power switch Q1 to fourth power switch Q4, and the four drive circuits are designated as first drive circuit QD1 to fourth drive circuit QD4. The drains of the first power switch Q1 and the third power switch Q3 are connected to the positive terminal of the power supply +VH. The drains of the second power switch Q2 and the fourth power switch Q4 are connected to the sources of the first power switch Q1 and the third power switch Q3, respectively. The sources of the second power switch Q2 and the fourth power switch Q4 are connected to the negative terminal of the power supply GND. The gates of the first power switch Q1 to the fourth power switch Q4 are connected to the output terminals of the first drive circuit QD1 to the fourth drive circuit QD4, respectively. The excitation signal input terminals of the four drive circuits are connected to different output ports of the control unit MCU, and the input ports of the control unit MCU are connected to the excitation signal. The source of the first power switch Q1 is called the first load terminal S1, and the source of the third power switch Q3 is called the second load terminal S2. A load RL is connected between the first load terminal S1 and the second load terminal S2. In other words, the voltage signal between the sources of the first power switch Q1 and the third power switch Q3 is the output signal of the inverter module, which is a bipolar symmetrical square wave. The four power switches are connected to form an inverter H-bridge.

[0023] The operation of the inverter module includes the following steps: a. The first power switch Q1 and the fourth power switch Q4 are simultaneously turned on, while the second power switch Q2 and the third power switch Q3 are turned off. The current flows from the positive terminal of the power supply +VH through the first power switch Q1, the load RL, and the fourth power switch Q4 to the negative terminal of the power supply GND. At this time, the voltage at the first load terminal S1 is +VH, the voltage at the second load terminal S2 is 0, and the output voltage of the inverter module (i.e., the voltage at the first load terminal S1 - the voltage at the second load terminal S2) is +VH. b. The first power switch Q1 is turned off and the second power switch Q2 is turned on. That is, the first power switch Q1 and the third power switch Q3 are turned off and the second power switch Q2 and the fourth power switch Q4 are turned on. The first load terminal S1 and the second load terminal S2 are short-circuited to ground through the second power switch Q2 and the fourth power switch Q4, respectively. At this time, the output voltage of the inverter module is 0. c. When the fourth power switch Q4 is turned off and the third power switch Q3 is turned on, the current flows from the positive terminal of the power supply +VH through the third power switch Q3, the load RL, and the second power switch Q2 to the negative terminal of the power supply GND. At this time, the voltage at the second load terminal S2 is +VH, the voltage at the first load terminal S1 is GND, the voltage at the load RL terminal is reversed, and the output voltage of the inverter module is -VH. d. The third power switch Q3 is turned off, and the fourth power switch Q4 is turned on. The first load terminal S1 and the second load terminal S2 are short-circuited to ground through the second power switch Q2 and the fourth power switch Q4, respectively. The output voltage of the inverter module is 0, completing one complete conversion cycle.

[0024] The inverter module has three output voltage values: +VH, 0, and -VH. The output of the H-bridge inverter is an AC output based on the alternating switching of these three voltage values. When the duty cycle of the drive waveforms of the first power switch Q1 and the third power switch Q3 is fixed at 50%, the output waveform of the H-bridge inverter is as follows: Figure 4 As shown. Under these conditions, the output is a bipolar square wave with equal amplitude. The symmetrical bipolar square wave output with a 50% duty cycle is closest to a sine wave, containing only odd harmonics. The carrier wave of the low-frequency transmitter is a sine wave. When the excitation signal is a sine wave, it is amplified by a controllable high-voltage DC power supply and an inverter module, then converted into a bipolar symmetrical square wave. This wave is then connected to a tuning unit. The tuning unit adjusts the parameters of its internal variable inductor and capacitor to match the filtered bipolar symmetrical square wave output with the antenna impedance. Simultaneously, due to the variable inductor and capacitor within the tuning unit, the bipolar symmetrical square wave is filtered into a quasi-sine wave.

[0025] Figure 5The electrical schematic of this utility model shows that the input of the low-frequency high-power transmitter is three-phase AC 380VAC mains power. The mains power outputs N sets of DC high voltage VH1, VH2...VHN through N controllable high voltage DC power supplies (i.e., the first controllable high voltage DC power supply DC1 to the Nth controllable high voltage DC power supply DCN). The outputs of the N controllable high voltage DC power supplies are isolated from each other and supply power to the N inverter modules respectively. The excitation signal is processed by the MCU and outputs N sets of control signals with the same frequency as the excitation signal and a fixed duty cycle of 50% (adjustable). These control signals correspond to the N inverter modules respectively. At the same time, the MCU phase-shifts the N sets of control signals so that the phase difference between the control signals of adjacent inverter modules is π / N. Each set of phase-shifted control signals is sent to the input terminals of the four drive circuits (i.e., the first drive circuit QD1 to the fourth drive circuit QD4) of the corresponding inverter module. The four drive circuits control the four power switching transistors of the corresponding inverter module. The output signals of the N inverter modules are superimposed sequentially to obtain a bipolar symmetrical stepped waveform with an amplitude of VH1+VH2+……+VHN, where VH1 to VHN are the output voltages of the N controllable high-voltage DC power supplies, i.e., the supply voltages of the N inverter modules.

[0026] from Figure 5 As can be seen, the bipolar symmetrical square wave output terminals of the N inverter modules are cascaded sequentially as follows: the first load terminal S1 of the first inverter module NB1 and the second load terminal S2 of the Nth inverter module NBN are connected to the input terminal of the tuning unit TX. For any two adjacent inverter modules, the second load terminal S2 of the preceding inverter module is connected to the first load terminal S1 of the following inverter module. Alternatively, it can be described as: the source of the first power switch Q1 of the first inverter module NB1 and the source of the third power switch Q3 of the Nth inverter module NBN are connected to the input terminal of the tuning unit TX. For any two adjacent inverter modules, the source of the third power switch Q3 of the preceding inverter module is connected to the source of the first power switch Q1 of the following inverter module.

[0027] The following explanation uses N=3 as an example.

[0028] See Figure 6 and Figure 7 Taking N=3, the 380VAC three-phase AC mains power is converted into three sets of mutually isolated DC high voltages by three controllable high-voltage DC power supplies (i.e., the first controllable high-voltage DC power supply DC1 to the third controllable high-voltage DC power supply DC3). The voltage values ​​of the three sets of DC high voltages are VH1, VH2, and VH3, respectively. Assuming the voltage values ​​of the three sets of DC high voltages are equal, i.e., VH1=VH2=VH3, the excitation signal is processed by the MCU, which outputs three sets of control signals with the same frequency as the excitation signal and a fixed duty cycle of 50% (adjustable). These control signals control the inverter module through the drive circuit. The output voltage waveform of the first inverter module NB1 is as follows: Figure 4As shown (VH1=VH), since this example involves cascading three inverter modules, the phase difference of the control signals of adjacent inverter modules is π / 3 = 60°. Therefore, the control signals of the second inverter module NB2 and the third inverter module NB3 are shifted by 60°. The output waveform of the cascaded low-frequency high-power transmitter is as follows: Figure 7 As shown.

[0029] In practical engineering design, based on the actual needs of current high-power low-frequency transmitters, the operating transmission frequency of low-frequency transmitters is generally tens to hundreds of kilohertz, the amplitude of the transmitted waveform is hundreds to thousands of volts, and the transmitted waveform is a sine wave. The power devices used in the controllable high-voltage DC power supply and inverter module involved in this utility model are silicon carbide devices, which are a new material at present. These devices have advantages such as fast switching speed, good switching characteristics, low on-resistance, high withstand voltage, and suitability for high-power conversion. Devices with withstand voltage of 1200V and 1700V have been widely used. Among them, devices with withstand voltage of 1200V are very suitable for the application of the high-power low-frequency transmitter proposed in this utility model. After using silicon carbide devices in the power switching devices of the controllable high-voltage DC power supply and inverter module, the conversion efficiency can be improved and the overall heat generation of the high-power low-frequency transmitter can be reduced.

[0030] The power conversion section of the controllable high voltage DC power supply adopts a full-bridge LLC soft-switching topology, the power switching device uses low on-resistance silicon carbide MOSFETs, and the output rectification uses silicon carbide diodes, which enables the controllable high voltage DC power supply to have high conversion efficiency. In this embodiment, the output voltage of the controllable high voltage DC power supply is controllable and adjustable, with an adjustment range of 600 to 1000VDC.

[0031] The inverter module is composed of silicon carbide power switching devices. The power supply for each inverter module is a corresponding controllable high-voltage DC power supply. In this embodiment, the output range of the controllable high-voltage DC power supply is 600-1000VDC. The power switching devices of the inverter module can be mature 1200V silicon carbide MOS single tubes in parallel (silicon carbide module). The excellent characteristics of silicon carbide material can improve the conversion efficiency of the inverter module.

[0032] In this embodiment, the output range of the controllable high-voltage DC power supply is 600–1000 Vdc. Silicon carbide power devices form the inverter module. The excitation signal is processed by the MCU, which outputs three sets of inverter module control signals with phase shifts of 60° sequentially. These signals control the inverter module through various drive circuits, and the output waveform is as follows: Figure 7As shown, the output frequency of the cascaded inverter modules perfectly tracks the frequency of the excitation signal. When the output of the controllable high-voltage DC power supply is 1000V, the peak output voltage of the cascaded inverter modules is 6000V. When the output voltage of the controllable high-voltage DC power supply is 600V, the peak output voltage of the cascaded inverter modules is 3600V. The output power of the cascaded inverter modules is the sum of the output power of the three controllable high-voltage DC power supplies.

[0033] like Figure 7 As shown, the cascaded inverter module outputs produce a 7-level stepped waveform. When the number of cascaded modules is N, the number of output levels is 2N+1. The more levels the cascaded inverter module outputs produce, the closer the waveform is to a sine wave, and the lower the harmonics. After the cascaded inverter module outputs are filtered by the inductors and capacitors inside the tuning unit, a high-quality sine wave can be obtained. The excitation signal is matched to the antenna impedance after being amplified by a controllable high-voltage DC power supply and adjusted by the inverter module power amplifier and tuning unit, and then transmitted through the antenna.

Claims

1. A low frequency high power transmitter, characterized in that, It includes N controllable high-voltage DC power supplies, N inverter modules, a tuning unit (TX), and an antenna (An). Each controllable high-voltage DC power supply is a power conversion device isolated from the mains input. The DC voltage output terminals of the N controllable high-voltage DC power supplies are respectively connected to the DC input terminals of the N inverter modules. The bipolar symmetrical square wave output terminals of the N inverter modules are cascaded and connected to the input terminal of the tuning unit (TX). The output terminal of the tuning unit (TX) is connected to the antenna (An). The phase difference of the excitation signals of the N inverter modules is π / N, where N is a natural number greater than 1.

2. A low frequency high power transmitter according to claim 1, characterized in that Each inverter module includes four power switching transistors and four drive circuits. The drains of the first power switching transistor (Q1) and the third power switching transistor (Q3) are connected to the positive terminal of the power supply. The drains of the second power switching transistor (Q2) and the fourth power switching transistor (Q4) are connected to the sources of the first power switching transistor (Q1) and the third power switching transistor (Q3), respectively. The sources of the second power switching transistor (Q2) and the fourth power switching transistor (Q4) are connected to the negative terminal of the power supply. The gates of the four power switching transistors are connected to the output terminals of the four drive circuits, respectively. The voltage signal between the sources of the first power switching transistor (Q1) and the third power switching transistor (Q3) is the output signal of the inverter module.

3. A low frequency high power transmitter according to claim 2, characterized in that The excitation signals for the four drive circuits of each inverter module are provided by the control unit. The input port of the control unit is connected to the excitation signal, and the input terminals of the excitation signals of the four drive circuits are respectively connected to different output ports of the control unit.

4. A low frequency high power transmitter according to claim 3, characterized in that The controllable high-voltage DC power supply includes a three-phase active power factor correction circuit and a switching power supply. The input terminal of the three-phase active power factor correction circuit is connected to the three-phase mains power, and the output terminal is connected to the input terminal of the switching power supply. The power switching transistors of the switching power supply and the four power switching transistors of the inverter module are all silicon carbide MOSFETs.

5. A low frequency high power transmitter according to any one of claims 1-4, characterized in that The duty cycle of the excitation signal of the inverter module is 50%.

Images