Passive low-harmonic frequency converter special for rail transit air conditioner

Abstract

The utility model belongs to the technical field of electronic circuit, especially relates to a passive low harmonic frequency converter special for rail transit air conditioner. The frequency converter includes: passive filter module, rectifier module, precharge module, voltage-sharing filter module, inverter module and control module. The input end of passive filter module is connected to the output end of alternating -current source, and the output end is connected to the input end of rectifier module, and the output end of rectifier module is connected to the input end of precharge module, the output end of precharge module is connected to the input end of voltage-sharing filter module, the output end of voltage-sharing filter module is connected to the input end of inverter module, and the output end of inverter module is the voltage output end of passive low harmonic frequency converter special for rail transit air conditioner, and inverter module and control module are connected through inverter control and protection circuit. The utility model can reduce the harmonic interference of frequency converter inverter to input power grid, protects the electrical equipment on power grid, and improves the security of operation.

Description

Technical Field

[0001] This utility model relates to the field of electronic component packaging technology, and in particular to a passive low harmonic frequency converter for rail transit air conditioning. Background Technology

[0002] The main circuit of a frequency converter is typically an AC-DC-AC structure. External power frequency is uncontrolled rectified into DC voltage by a three-phase bridge circuit, then filtered by capacitors and inverted into AC voltage with a variable frequency by high-power transistor switching elements. During rectification and inversion, the high-frequency switching of the power modules distorts the input and output current and voltage waveforms, generating harmonic components with frequencies that are integer multiples of the fundamental frequency. These harmonics interfere with the power quality of the grid, causing various negative impacts on the power system.

[0003] To prevent electrical equipment on the power grid from being damaged by harmonics from frequency converters, it is necessary to reduce the harmonics.

[0004] Current research progress in harmonic suppression technology for frequency converters mainly focuses on aspects such as reactor installation, PWM optimization, and AI algorithm application. Utility Model Content

[0005] In view of this, the present invention provides a passive low-harmonic frequency converter for rail transit air conditioning, which is used to solve the technical problem of excessive harmonics in the existing frequency converter, which interferes with the power grid and power system.

[0006] The technical solution adopted in this utility model is:

[0007] This utility model provides a passive low-harmonic frequency converter specifically for rail transit air conditioning, comprising:

[0008] Passive filter module, rectifier module, precharge module, voltage equalization filter module, inverter module and control module;

[0009] The input terminal of the passive filter module is connected to the voltage output terminal of the circuit, and the output terminal is connected to the input terminal of the rectifier module. The passive filter module is used to filter the input voltage.

[0010] The output terminal of the rectifier module is connected to the input terminal of the pre-charge module. The rectifier module is used to rectify the AC voltage and output DC voltage.

[0011] The output terminal of the pre-charge module is connected to the input terminal of the voltage equalization filter module. The pre-charge module is used to limit the inrush current when the system is powered on to prevent the capacitor from overcharging.

[0012] The output terminal of the voltage equalization filter module is connected to the input terminal of the inverter module, and the voltage equalization filter module is used to filter the input DC voltage.

[0013] The output terminal of the inverter module is the voltage output terminal of the passive low harmonic frequency converter for rail transit air conditioning. The inverter module is used to convert AC voltage to DC voltage.

[0014] The control module and the inverter module are connected via inverter control and protection circuits.

[0015] Preferably, the passive filtering module is used to filter the input voltage, including inductors L1 and L2 connected in parallel to the three-phase power supply, resistors R1, R3, R11, R4, R5, and R6 connected in parallel to the three-phase power supply, and capacitors C1, C2, C3, C4, C5, and C6, as well as safety capacitors CY1, CY2, CY3, CY4, CY5, and CY6.

[0016] Preferably, the passive filter module includes a two-stage LC filter circuit. In the first-stage LC filter circuit, the two ends of resistor R1 are connected in parallel with capacitor C1. One end of resistor R1 is connected to the R-phase voltage output terminal and to the first end of inductor L1 on the R-phase line. The other end of resistor R1 is connected to the first end of inductor L1 on the S-phase line via resistor R3. The two ends of resistor R3 are connected in parallel with capacitor C2. One end of resistor R3 is connected to the S-phase voltage output terminal and to the first end of inductor L1 on the S-phase line. The other end of resistor R3 is connected to the first end of inductor L1 on the T-phase line via resistor R11. The two ends of resistor R11 are connected in parallel with capacitor C3. One end of resistor R11 is connected to the T-phase voltage output terminal and to the first end of inductor L1 on the T-phase line. The other end of resistor R11 is connected to the first end of inductor L1 on the R-phase line via resistor R1.

[0017] Preferably, the passive filtering module includes a two-stage LC filter circuit. In the second-stage LC filter circuit, one end of capacitor C7 is connected to the second end of inductor L1 on the R-phase line, and the other end is connected to the second end of inductor L1 on the S-phase line; one end of capacitor C8 is connected to the second end of inductor L1 on the S-phase line, and the other end is connected to the second end of inductor L1 on the T-phase line; one end of capacitor C9 is connected to the second end of inductor L1 on the R-phase line, and the other end is connected to the second end of inductor L1 on the T-phase line; the first end of inductor L2 on the R-phase line is connected to the second end of inductor L1 on the R-phase line, and the first end of inductor L2 on the S-phase line is connected to the second end of inductor L1 on the S-phase line. The inductor L2 is connected to the first end of the T-phase line and the second end of the inductor L1 is connected to the T-phase line. One end of the safety capacitor CY1 is connected to the second end of the inductor L1 on the T-phase line, and the other end of the safety capacitor CY1 is grounded. One end of the safety capacitor CY2 is connected to the second end of the inductor L1 on the S-phase line, and the other end of the safety capacitor CY2 is grounded. One end of the safety capacitor CY3 is connected to the second end of the inductor L1 on the R-phase line, and the other end of the safety capacitor CY3 is grounded. The second end of the inductor L2 on the R-phase line is connected to the R-phase voltage output terminal. The second end of the inductor L2 on the S-phase line is connected to the S-phase voltage output terminal. The second end of the inductor L2 on the T-phase line is connected to the T-phase voltage output terminal.

[0018] Preferably, in the second-stage LC filter circuit, one end of the safety capacitor CY4 is connected to the second end of the inductor L2 on the R-phase line, and the other end of the safety capacitor CY4 is grounded; one end of the safety capacitor CY5 is connected to the second end of the inductor L2 on the S-phase line, and the other end of the safety capacitor CY5 is grounded; one end of the safety capacitor CY6 is connected to the second end of the inductor L2 on the T-phase line, and the other end of the safety capacitor CY6 is grounded; the two ends of the resistor R4 are connected in parallel with the capacitor C4, one end of the resistor R4 is connected to the R-phase voltage output terminal, and the other end of the resistor R4 is connected to the S-phase voltage output terminal through the resistor R5; the two ends of the resistor R5 are connected in parallel with the capacitor C5, one end of the resistor R5 is connected to the S-phase voltage output terminal, and the other end of the resistor R5 is connected to the T-phase voltage output terminal through the resistor R6; the two ends of the resistor R6 are connected in parallel with the capacitor C6, one end of the resistor R6 is connected to the T-phase voltage output terminal, and the other end of the resistor R6 is connected to the R-phase voltage output terminal through the resistor R4.

[0019] Preferably, the rectifier module is a three-phase half-wave rectifier module or a three-phase full-wave rectifier module, used to rectify a three-phase 380VAC AC power supply into a 540V DC power supply. The three-phase full-wave rectifier module includes six diodes VD1, VD2, VD3, VD4, VD5, and VD6. These six diodes are divided into two groups: VD1, VD3, and VD5 form a common cathode group, with their cathodes connected together to form the positive DC output; VD2, VD4, and VD6 form a common anode group, with their anodes connected together to form the negative DC output. The anode of VD1 is connected to the R phase of the three-phase AC power supply, the anode of VD3 is connected to the S phase of the three-phase AC power supply, and the anode of VD5 is connected to the... The cathodes of VD2, VD4, and VD6 are connected to the T phase of the three-phase AC power supply. The cathodes of VD2, VD4, and VD6 are connected to the S phase of the three-phase AC power supply. The three-phase half-wave rectifier module includes three diodes: VD7, VD8, and VD9. The cathodes of the three diodes are connected together to form the positive DC output. The anode of VD7 is connected to the R phase of the three-phase AC power supply, the anode of VD8 is connected to the S phase of the three-phase AC power supply, and the anode of VD9 is connected to the T phase of the three-phase AC power supply.

[0020] Preferably, the pre-charge module includes a current-limiting resistor and a power electronic switching device to reduce the inrush current during power-on; wherein the number of the current-limiting resistors is one or more; the power electronic switching device is a relay, contactor, or high-voltage isolated electronic switch; the current-limiting resistor and the power electronic switching device are connected in parallel and then connected in series with other modules, with the input terminal connected to the output terminal of the rectifier module and the output terminal connected to the input terminal of the voltage equalization filter module.

[0021] Preferably, the voltage equalization filter module includes two or more filter electrolytic capacitors and two or more voltage equalization resistors, wherein the voltage equalization resistors have equal resistance values, the voltage equalization resistors are connected in parallel across the two ends of the multiple series capacitors, the positive terminal of the capacitor is connected to the DC voltage output terminal, and the negative terminal of the capacitor is connected to the DC voltage input terminal.

[0022] Preferably, the inverter module includes six IGBT electronic switching elements and their peripheral circuitry for converting DC voltage into AC voltage with variable frequency and voltage. The six IGBT electronic switching elements are Q1, Q2, Q3, Q4, Q5, and Q6, with Q1, Q3, and Q5 forming the upper bridge arm and Q2, Q4, and Q6 forming the lower bridge arm. The collectors of Q1, Q3, and Q5 are connected to the positive terminal of the DC power supply, and the emitters of Q2, Q4, and Q6 are connected to the negative terminal of the DC power supply. The emitter of Q1 is connected to the emitter of Q2... The collectors of Q1, Q2, Q3, Q4, Q5, and Q6 are connected to form an R-phase bridge arm, the emitter of Q3 is connected to the collector of Q4 to form an S-phase bridge arm, and the emitter of Q5 is connected to the collector of Q6 to form a T-phase bridge arm. Any point in the R-phase bridge arm is connected to the load R terminal, any point in the S-phase bridge arm is connected to the load S terminal, and any point in the T-phase bridge arm is connected to the load T terminal. The gates of Q1, Q2, Q3, Q4, Q5, and Q6 are respectively connected to the output terminals of the corresponding drive circuits. The drive circuits receive PWM control signals to control the on and off states of the IGBTs.

[0023] Preferably, the control module includes a DSP chip and its peripheral circuitry, used to control the on and off of the power switching devices in the inverter module.

[0024] In summary, this utility model relates to a passive low-harmonic frequency converter specifically designed for rail transit air conditioning. The passive filter module effectively removes high-frequency noise and stray signals, ensuring stable operation of subsequent circuit modules. The rectifier module converts three-phase 380VAC AC power into 540V DC power. The pre-charge module reduces the inrush current, preventing large current surges on the filter capacitors and rectifier bridge, protecting the components in the circuit. The voltage equalization filter module effectively suppresses high-frequency noise, harmonics, and other interference signals in the power supply or circuit, resulting in a smoother and more stable output signal and a relatively pure DC voltage. The inverter module converts the DC input voltage into an AC output voltage with a specific frequency and waveform. The control module synchronously manages multi-dimensional data such as current, voltage, and temperature, coordinating the operation of each functional module. Attached Figure Description

[0025] To more clearly illustrate the technical solutions of the embodiments of this utility model, the drawings used in the embodiments of this utility model will be briefly introduced below. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort, and these are all within the protection scope of this utility model.

[0026] Figure 1 This is the main block diagram of the passive low harmonic frequency converter for rail transit air conditioning of this utility model;

[0027] Figure 2 This is a schematic diagram of the passive filtering module in an embodiment of the present invention;

[0028] Figure 3 This is a schematic diagram of the rectifier module in an embodiment of the present invention;

[0029] Figure 4 This is a schematic diagram of the pre-charging module in an embodiment of the present invention.

[0030] Figure 5 This is a schematic diagram of the voltage equalization filter module in an embodiment of this utility model.

[0031] Figure 6 This is a schematic diagram of the control module in an embodiment of the present invention. Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of the embodiments of this utility model clearer, the technical solutions of the embodiments of this utility model will be clearly and completely described below with reference to the accompanying drawings. It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. In the description of this utility model, it should be understood that the terms "center," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicating orientation or positional relationships, are based on the orientation or positional relationships shown in the accompanying drawings, and are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this utility model. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element. Unless otherwise specified, embodiments of the present invention and the various features thereof can be combined with each other, all within the protection scope of the present invention.

[0033] Example 1

[0034] like Figure 1As shown, this utility model provides a passive low-harmonic frequency converter specifically for rail transit air conditioning. This utility model provides a passive low-harmonic frequency converter specifically for rail transit air conditioning, comprising: a passive filter module, a rectifier module, a pre-charge module, a voltage equalization filter module, an inverter module, and a control module. The input terminal of the passive filter module is connected to the voltage output terminal of the circuit, and its output terminal is connected to the input terminal of the rectifier module. The output terminal of the rectifier module is connected to the input terminal of the pre-charge module; the output terminal of the pre-charge module is connected to the input terminal of the voltage equalization filter module; the output terminal of the voltage equalization filter module is connected to the input terminal of the inverter module; the output terminal of the inverter module is the voltage output terminal of the passive low-harmonic frequency converter specifically for rail transit air conditioning; the inverter module and the control module are connected through an inverter control and protection circuit.

[0035] In one embodiment, please refer to Figure 2 The passive filtering module includes two layers of LC filtering modules, including inductors L1 and L2 connected in parallel to the three-phase power supply, and resistors R1, R3, R11, R4, R5, and R6 connected in parallel to the three-phase power supply, and capacitors C1, C2, C3, C4, C5, and C6, as well as safety capacitors CY1, CY2, CY3, CY4, CY5, and CY6.

[0036] Specifically, the three-phase AC voltage input enters the first-layer LC filter circuit. In the R-phase line, capacitor C1 is connected in parallel with damping resistor R1; in the S-phase line, capacitor C2 is connected in parallel with damping resistor R3; in the T-phase line, capacitor C3 is connected in parallel with damping resistor R11. Each set of resistors and capacitors is connected in parallel between the three-phase lines (RS, ST, TR) to suppress differential-mode interference. Capacitors C1, C2, and C3 provide a low-impedance path for differential-mode high-frequency noise, while damping resistors R1, R3, and R11 are used to suppress the self-excited oscillation of the LC network, reduce the equivalent Q value of the capacitors (increase system damping), and improve the stability of the filter. L1 is a three-phase common-mode inductor, connected in series on the R, S, and T lines respectively, used to filter out common-mode interference current in the three-phase lines; C7, C8, and C9 are Y capacitors, providing a discharge path for common-mode current, helping to guide noise to ground, thereby protecting the load equipment. Inductors present high impedance to high-frequency AC components, hindering the passage of high-frequency current and making it difficult for the current to continue propagating, thus attenuating high-frequency interference between phases. Capacitors present low impedance to high-frequency AC components, providing a low-impedance path for the high-frequency current, allowing more of it to flow to ground, thereby filtering out most high-frequency harmonics. For low-frequency and fundamental components, the inductor's hindering effect is smaller, and the capacitor's bypassing effect is also weaker; these components can pass relatively smoothly through the first-layer LC filter circuit. After the first layer of filtering, the three-phase voltage still retains some high-frequency harmonics and other noise.

[0037] Upon entering the second-layer LC filter circuit, the characteristics of inductors and capacitors are used again for filtering. L2 is also a three-phase common-mode inductor, connected in series after L1. Inductor L2 continues to block residual high-frequency components. Safety capacitors CY1, CY2, CY3, CY4, CY5, and CY6 further bypass these high-frequency components to ground. This layer of filtering further reduces the harmonic content in the voltage, making the output three-phase voltage closer to the ideal sine wave. Finally, the output is filtered / damped by the output filter network, which is shown below. Figure 2 The capacitor C4 and damping resistor R4 are connected in parallel. In the passive filter module, the two-stage common-mode filter enhances high-frequency suppression capability; reduces common-mode interference that the first-stage LC filter fails to fully suppress; and the multi-stage common-mode filter improves common-mode interference suppression capability. The capacitor and damping resistor are connected in parallel to improve differential-mode interference suppression capability and prevent resonance. The damping resistor R4 and capacitor C4 are connected in parallel to form the first output RC module, which is connected between the R phase and the S phase. The damping resistor R5 and capacitor C5 are connected in parallel to form the second output RC module, which is connected between the S phase and the T phase. The damping resistor R6 and capacitor C6 are connected in parallel to form the third output RC module, which is connected between the T phase and the R phase. The first, second, and third output RC modules absorb high-frequency differential-mode interference while suppressing resonance generated by the capacitor itself, suppressing self-excited oscillation or resonance spikes in the system at certain frequencies, and protecting the components in the circuit.

[0038] A three-phase rectifier circuit is used to rectify a three-phase 380VAC AC power supply into a 540V DC power supply. The operation of the three-phase rectifier circuit is based on the unidirectional conductivity of diodes. Utilizing the 120° phase difference between the three-phase AC power, continuous DC output is achieved within one cycle. When a large-capacity filter capacitor is connected after the rectifier circuit and the load is light, the capacitor will charge when the diode is conducting and slowly discharge through the load when it is cut off. Ideally, the capacitor can stabilize the voltage near the peak line voltage. When the three-phase 380VAC AC power supply is rectified into a 540V DC power supply, the charging of the filter capacitor at the moment of power-on will generate a surge several times the rated current, requiring the selection of surge-resistant diodes.

[0039] In one embodiment, please refer to Figure 3The rectifier module includes six impact-resistant diodes VD1, VD2, VD3, VD4, VD5, and VD6. These six diodes are divided into two groups: VD1, VD3, and VD5 form a common cathode group, with their cathodes connected together to form the positive DC output; VD2, VD4, and VD6 form a common anode group, with their anodes connected together to form the negative DC output. The anode of VD1 is connected to the R phase of the three-phase AC power supply; the anode of VD3 is connected to the S phase; the anode of VD5 is connected to the T phase; the cathode of VD2 is connected to the R phase; the cathode of VD4 is connected to the S phase; and the cathode of VD6 is connected to the... In phase T of the power supply, during the positive half-cycle of the three-phase AC power supply, the diode connected to the phase with the highest anode potential in the common cathode group conducts, and the diode connected to the phase with the lowest cathode potential in the common anode group conducts as the phase of the three-phase AC power supply changes. When the voltage of a certain phase is the highest among the three phases, the positive diode of that phase conducts, and when the voltage of a certain phase is the lowest among the three phases, the negative diode of that phase conducts. At any given moment, there must be one positive diode and one negative diode conducting simultaneously, forming a current loop. The diodes conduct sequentially in the order of VD1 and VD6, VD1 and VD2, VD3 and VD2, VD3 and VD4, VD5 and VD4, and VD5 and VD6. Each diode conducts for 120° in each cycle. Current flow: One phase of the power supply (high potential) → common cathode diode group → load or capacitor → common anode diode group → another phase of the power supply (low potential). The output DC voltage is the instantaneous value of the two-phase line voltage. For example, when phase R and phase S are conducting, the output voltage is URS = UR − US. Through the orderly conduction of 6 diodes, the positive and negative half-cycle voltages of the three-phase AC power supply are rectified into a 540V DC power supply.

[0040] The pre-charge module is a key component in power electronic systems used to protect circuits and prevent power-on surges. Its function is to reduce inrush current, prevent large current surges on filter capacitors and rectifier bridges, and protect components in the circuit. The pre-charge module includes current-limiting resistors and power electronic switching devices, such as operating relays, contactors, or high-voltage isolated electronic switches (e.g., solid-state relays). The current-limiting resistor typically has a resistance value of tens to hundreds of ohms, and its power rating must match the charging energy to limit the charging current and prevent surges. The current-limiting resistor and the power electronic switching device are connected in parallel and then in series in the circuit. When the power electronic switching device is in the open state, the current flows through the current-limiting resistor and then into the subsequent modules in the circuit. When the power electronic switching device is in the closed state, the current does not flow through the current-limiting resistor and flows directly into the subsequent modules in the circuit.

[0041] In one embodiment, see Figure 4The pre-charge module includes a current-limiting resistor R1 and an electronic switch K1A. The current-limiting resistor R1 and the electronic switch K1A are connected in parallel and then connected in series to the circuit. Its input terminal is connected to the output terminal of the rectifier module, and its output terminal is connected to the input terminal of the voltage equalization filter module.

[0042] Specifically, when the system is powered on, electronic switch K1A is in the open state. The power supply first slowly charges the energy storage capacitor in the main circuit through the current-limiting resistor R1. Due to the current-limiting effect of the current-limiting resistor, the charging current is limited to a safe range, and the capacitor voltage gradually rises to close to the power supply voltage. After power-on, electronic switch K1A closes, cutting off the pre-charging circuit. The electronic switch K1A can also be replaced by a relay or a contactor, and the current-limiting resistor R1 can be replaced by multiple current-limiting resistors.

[0043] When multiple electronic components (such as IGBTs and capacitors) are connected in series, the voltage distribution across each component can be uneven due to the discreteness of component parameters and various imbalances in the circuit. A voltage equalization filter module includes two or more filter electrolytic capacitors and two or more voltage equalization resistors. By connecting voltage equalization resistors or capacitors in parallel across each component, or using other voltage equalization circuit structures, the current can be distributed according to a certain pattern, thereby achieving a balanced voltage distribution across each component. Since capacitors in AC circuits have the characteristic of passing high frequencies and blocking low frequencies, while inductors have the characteristic of passing low frequencies and blocking high frequencies, combining them into a filter circuit can effectively suppress high-frequency noise, harmonics, and other interference signals in the power supply or circuit, making the output signal smoother and more stable, and producing a relatively pure DC voltage.

[0044] In one embodiment, see Figure 5 The voltage equalization filter module includes two filter electrolytic capacitors C1 and C2 and two voltage equalization resistors RA and RB for filtering AC voltage. The voltage equalization resistors make the DC voltage evenly distributed across capacitors C1 and C2, avoiding voltage deviation on C1 and C2 and preventing damage to the electrolytic capacitors due to voltage deviation.

[0045] Specifically, C1 and C2 are connected in series between the positive and negative terminals of the DC power supply, RA is connected in parallel with C1, and RB is connected in parallel with C2. During the initial power-on phase of the circuit, the DC power supply charges C1 and C2 respectively through the voltage equalization resistors RA and RB. The current flow is: DC power supply positive terminal → RA → C1 → RB → DC power supply negative terminal. Since the resistance values ​​of RA and RB are equal, the charging time constants of C1 and C2 are the same, and the voltages across them rise synchronously with time. When the circuit reaches a steady state, the voltages across C1 and C2 are equal, and the sum of their voltages is equal to the DC power supply voltage. If the voltages of C1 and C2 deviate due to differences in capacitor parameters, for example, VC1 > VC2, then the current IR1 = VC1 / RA on RA increases, and the current IR2 = VC2 / RB on RB decreases. The excess current is diverted through RA, C1 discharges, and C2 charges until the voltage is rebalanced. This voltage equalization process is dynamic and continuous, ensuring that the voltages across C1 and C2 remain equal under any operating condition, effectively preventing damage to the electrolytic capacitors due to voltage deviation.

[0046] Inverter modules are the core components in power electronic systems that convert DC power into AC power. They convert DC input voltage into AC output voltage with a specific frequency and waveform through the periodic switching of power switching devices.

[0047] In one embodiment, see Figure 6 The inverter module includes six IGBT electronic switching elements and their peripheral circuits, used to convert DC voltage into AC power with variable frequency and voltage. The six IGBT electronic switching elements are Q1, Q2, Q3, Q4, Q5, and Q6. Q1, Q3, and Q5 form the upper bridge arm, and Q2, Q4, and Q6 form the lower bridge arm. Q1 and Q2 are connected in series between the positive and negative terminals of the DC power supply to form the R-phase bridge arm. Q3 and Q4 are connected in series between the positive and negative terminals of the DC power supply to form the S-phase bridge arm. Q5 and Q6 are connected in series between the positive and negative terminals of the DC power supply to form the T-phase bridge arm. Any point in the R-phase bridge arm is connected to the load terminal R, any point in the S-phase bridge arm is connected to the load terminal S, and any point in the T-phase bridge arm is connected to the load terminal C.

[0048] The IGBT (Insulated Gate Bipolar Transistor) decomposes the three-phase sinusoidal voltage signal into a space voltage vector through a space vector pulse width modulation (SVPWM) or sinusoidal pulse width modulation (SPWM) control strategy. Within one PWM cycle, the two IGBTs on the same bridge arm conduct complementaryly (such as Q1 and Q2), and different bridge arms conduct sequentially with a 120° phase difference.

[0049] Specifically, the conduction sequence is as follows:

[0050] When Q1 receives a high-level conduction signal at its gate, Q1 turns on. Assuming that Q6 also turns on at the same time, that is, when Q1 and Q6 are on, the current flows out from the positive terminal of the DC power supply, through the collector of Q1 to the load R terminal, then out from the load C terminal, and back to the negative terminal of the DC power supply through the emitter of Q6. The current path is: positive terminal of DC power supply → collector of Q1 → emitter of Q1 → phase R of load → phase T of load → emitter of Q6 → collector of Q6 → negative terminal of DC power supply.

[0051] When Q3 receives a high-level conduction signal at its gate, Q3 turns on. Assuming that Q2 also turns on at the same time, that is, when Q3 and Q2 are on, the current flows out from the positive terminal of the DC power supply, through the collector of Q3 to the load R terminal, then out from the load C terminal, through the emitter of Q2 back to the negative terminal of the DC power supply. The current path is: positive terminal of DC power supply → collector of Q3 → emitter of Q3 → phase S of load → phase R of load → emitter of Q2 → collector of Q2 → negative terminal of DC power supply.

[0052] When Q5 receives a high-level turn-on signal at its gate, Q5 turns on. Assuming that Q4 also turns on at the same time, when both Q5 and Q4 are on, the current flows out from the positive terminal of the DC power supply, through the collector of Q5 to the load terminal C, then out from the load terminal S, and back to the negative terminal of the DC power supply through the emitter of Q4. The current path is: positive terminal of DC power supply → collector of Q5 → emitter of Q5 → phase R of load → phase T of load → emitter of Q4 → collector of Q4 → negative terminal of DC power supply. By controlling the on-time ratio of each IGBT, the output voltage and frequency can be continuously adjusted.

[0053] The control module is used to synchronously manage multi-dimensional data such as current, voltage, and temperature, and coordinate the work of various functional modules. It includes a DSP chip and its peripheral circuits, including: current detection section, voltage detection section, temperature detection section, keyboard display section, external interface and communication section, and inverter control section.

[0054] The specific DSP chip (Digital Signal Processor) serves as the core control unit, possessing high-speed data processing capabilities and acting as a communication hub for real-time computation and logic coordination. The current detection section includes a current sensor and signal conditioning circuitry, used for real-time monitoring of the main circuit current and overcurrent protection. When the detected current exceeds the threshold, it immediately triggers a DSP interrupt, blocking the inverter circuit's drive signals to prevent device damage; it also provides control algorithm feedback, supplying current feedback for closed-loop control and enabling dynamic adjustment. The voltage detection section includes a voltage sensor and signal processing circuitry, used for input / output voltage monitoring, overvoltage / undervoltage protection, and closed-loop control feedback. Specifically, the voltage detection section can detect three-phase AC input voltage or DC bus voltage to determine grid status or DC-side stability, monitoring the inverter's output AC voltage to ensure output waveform quality; when the voltage exceeds the safe range, it triggers a protection mechanism to prevent capacitor or power device breakdown; it also provides feedback for voltage loop control. The temperature detection section includes a temperature sensor and signal conditioning, where the temperature sensor can be contact or non-contact, converting the temperature signal into a voltage signal, which is then filtered and input to the DSP's ADC channel. The keyboard and display section is used for human-machine interaction, including input devices, display devices, and drive circuits, enabling parameter setting, status display, and operation control. Specifically, system parameters are modified by inputting and modifying them via the input device buttons; operating data (such as output voltage, current, frequency, temperature, and fault codes) is displayed in real time on the LCD screen or LED digital tube; and operation control is achieved through button functions such as start, stop, forward / reverse, and mode switching (e.g., manual / automatic), facilitating on-site debugging and maintenance.

[0055] The external interfaces and communication components include electrical connection interfaces and communication interfaces. The electrical connection interfaces can perform analog input / output (AI / AO), connecting external sensors or actuators to expand system functionality, and can also perform digital input / output (DI / DO), receiving external switch signals or outputting control signals. Communication interfaces include serial ports, CAN bus, and Ethernet. The serial port (UART / RS485) enables point-to-point communication with host computers (such as PLCs, industrial PCs) or other devices, transmitting control commands or status data (such as the Modbus protocol). The CAN bus is suitable for multi-device networking (such as distributed motor control systems), supporting high-speed, interference-resistant communication. Ethernet (EtherCAT, Profinet) meets the needs of the Industrial Internet of Things (IIoT), enabling remote monitoring and big data analysis.

[0056] The inverter control section includes drive circuits, etc., wherein the inverter control section includes: current detection section, voltage detection section, temperature detection section, keyboard display section, external interface and communication section, and the inverter section control. In one embodiment, an optocoupler isolation drive chip (such as HCPL-316J) is used to amplify the DSP control signal and achieve electrical isolation. PWM signal generation: The DSP generates a pulse width modulation signal according to the control algorithm (such as SPWM, SVPWM) to drive the power switching devices (such as IGBT, MOSFET) of the inverter.

[0057] Among them, SPWM simulates a sine wave by adjusting the pulse width to achieve amplitude and frequency regulation of AC output voltage (such as variable frequency speed control); SVPWM optimizes voltage vector distribution, improves DC bus voltage utilization, and reduces output current harmonics; commutation logic control in the three-phase inverter circuit coordinates the turn-on / turn-off sequence of 6 power devices to ensure smooth motor operation and avoid phase-to-phase short circuits; and in conjunction with the current and voltage detection module, it quickly blocks the PWM output and cuts off the power circuit in the event of overcurrent, overvoltage, or overheating.

[0058] Example 2

[0059] The present invention relates to a rail transit air conditioning equipment, including the rail transit air conditioning dedicated passive low harmonic frequency converter described in Embodiment 1.

[0060] For more information on each module, component, or circuit, please refer to the relevant descriptions in Example 1.

[0061] The above description is merely a specific embodiment of this utility model. Those skilled in the art will understand that, for the sake of convenience and brevity, the specific working processes of the systems, modules, and units described above can be referred to the corresponding processes in the foregoing method embodiments, and will not be repeated here. It should be understood that the protection scope of this utility model is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in this utility model, and these modifications or substitutions should all be covered within the protection scope of this utility model.

Claims

1. A passive low-harmonic frequency converter specifically for rail transit air conditioning, characterized in that, include: Passive filter module, rectifier module, precharge module, voltage equalization filter module, inverter module and control module; The input terminal of the passive filter module is connected to the output terminal of the AC power supply, and the output terminal of the passive filter module is connected to the input terminal of the rectifier module. The passive filter module is used to filter the input voltage of the AC power supply. The output terminal of the rectifier module is connected to the input terminal of the pre-charge module. The rectifier module is used to rectify the AC voltage and output DC voltage. The output terminal of the pre-charge module is connected to the input terminal of the voltage equalization filter module. The pre-charge module is used to limit the inrush current when the system is powered on to prevent the capacitor from overcharging. The output terminal of the voltage equalization filter module is connected to the input terminal of the inverter module, and the voltage equalization filter module is used to filter the input DC voltage. The output terminal of the inverter module is the voltage output terminal of the passive low harmonic frequency converter for rail transit air conditioning. The inverter module is used to convert AC voltage and output AC voltage. The control module and the inverter module are connected via inverter control and protection circuits.

2. The passive low-harmonic frequency converter for rail transit air conditioning as described in claim 1, characterized in that, The passive filtering module is used to filter the input voltage, including inductors L1 and L2 connected in parallel to the three-phase power supply, resistors R1, R3, R11, R4, R5, and R6 connected in parallel to the three-phase power supply, and capacitors C1, C2, C3, C4, C5, and C6, as well as safety capacitors CY1, CY2, CY3, CY4, CY5, and CY6.

3. The passive low-harmonic frequency converter for rail transit air conditioning as described in claim 2, characterized in that, The passive filter module includes a two-stage LC filter circuit. In the first-stage LC filter circuit, the two ends of resistor R1 are connected in parallel with capacitor C1. One end of resistor R1 is connected to the R-phase voltage output terminal and to the first end of inductor L1 on the R-phase line. The other end of resistor R1 is connected to the first end of inductor L1 on the S-phase line via resistor R3. The two ends of resistor R3 are connected in parallel with capacitor C2. One end of resistor R3 is connected to the S-phase voltage output terminal and to the first end of inductor L1 on the S-phase line. The other end of resistor R3 is connected to the first end of inductor L1 on the T-phase line via resistor R11. The two ends of resistor R11 are connected in parallel with capacitor C3. One end of resistor R11 is connected to the T-phase voltage output terminal and to the first end of inductor L1 on the T-phase line. The other end of resistor R11 is connected to the first end of inductor L1 on the R-phase line via resistor R1.

4. The passive low-harmonic frequency converter for rail transit air conditioning as described in claim 2, characterized in that, The passive filtering module includes a two-stage LC filter circuit. In the second-stage LC filter circuit, one end of capacitor C7 is connected to the second end of inductor L1 on the R-phase line, and the other end is connected to the second end of inductor L1 on the S-phase line; one end of capacitor C8 is connected to the second end of inductor L1 on the S-phase line, and the other end is connected to the second end of inductor L1 on the T-phase line; one end of capacitor C9 is connected to the second end of inductor L1 on the R-phase line, and the other end is connected to the second end of inductor L1 on the T-phase line; the first end of inductor L2 on the R-phase line is connected to the second end of inductor L1 on the R-phase line, and the first end of inductor L2 on the S-phase line is connected to the second end of inductor L1 on the S-phase line. The inductors are connected as follows: the first end of the T-phase line of inductor L2 is connected to the second end of the T-phase line of inductor L1; one end of the safety capacitor CY1 is connected to the second end of the T-phase line of inductor L1, and the other end of the safety capacitor CY1 is grounded; one end of the safety capacitor CY2 is connected to the second end of the S-phase line of inductor L1, and the other end of the safety capacitor CY2 is grounded; one end of the safety capacitor CY3 is connected to the second end of the R-phase line of inductor L1, and the other end of the safety capacitor CY3 is grounded; the second end of the R-phase line of inductor L2 is connected to the R-phase output terminal; the second end of the S-phase line of inductor L2 is connected to the S-phase output terminal; and the second end of the T-phase line of inductor L2 is connected to the T-phase output terminal.

5. The passive low-harmonic frequency converter for rail transit air conditioning as described in claim 4, characterized in that, In the second-stage LC filter circuit, one end of the safety capacitor CY4 is connected to the second end of the inductor L2 on the R-phase line, and the other end of the safety capacitor CY4 is grounded. One end of the safety capacitor CY5 is connected to the second end of the inductor L2 on the S-phase line, and the other end of the safety capacitor CY5 is grounded. One end of the safety capacitor CY6 is connected to the second end of the inductor L2 on the T-phase line, and the other end of the safety capacitor CY6 is grounded. The two ends of the resistor R4 are connected in parallel with the capacitor C4. One end of the resistor R4 is connected to the R-phase output terminal, and the other end of the resistor R4 is connected to the S-phase output terminal through the resistor R5. The two ends of the resistor R5 are connected in parallel with the capacitor C5. One end of the resistor R5 is connected to the S-phase output terminal, and the other end of the resistor R5 is connected to the T-phase output terminal through the resistor R6. The two ends of the resistor R6 are connected in parallel with the capacitor C6. One end of the resistor R6 is connected to the T-phase output terminal, and the other end of the resistor R6 is connected to the R-phase output terminal through the resistor R4.

6. The passive low-harmonic frequency converter for rail transit air conditioning as described in claim 1, characterized in that, The rectifier module is a three-phase half-wave rectifier module or a three-phase full-wave rectifier module, used to rectify a three-phase 380VAC AC power supply into a 540V DC power supply. The three-phase full-wave rectifier module includes six diodes: VD1, VD2, VD3, VD4, VD5, and VD6. These six diodes are divided into two groups: VD1, VD3, and VD5 form a common cathode group, with their cathodes connected together to form the positive DC output; VD2, VD4, and VD6 form a common anode group, with their anodes connected together to form the negative DC output. The anode of VD1 is connected to the R phase of the three-phase AC power supply, and the anode of VD3 is connected to the S phase of the three-phase AC power supply. The three-phase half-wave rectifier module includes three diodes: VD7, VD8, and VD9. The cathodes of the three diodes are connected together to form the positive DC output. The anode of VD7 is connected to the R phase of the three-phase AC power supply, the anode of VD8 is connected to the S phase of the three-phase AC power supply, and the anode of VD9 is connected to the T phase of the three-phase AC power supply.

7. The passive low-harmonic frequency converter for rail transit air conditioning as described in claim 1, characterized in that, The pre-charge module includes a current-limiting resistor and a power electronic switching device to reduce the inrush current during power-on; wherein the number of the current-limiting resistors is one or more; the power electronic switching device is a relay, contactor, or high-voltage isolated electronic switch; the current-limiting resistor and the power electronic switching device are connected in parallel and then connected in series with other modules, with the input terminal connected to the output terminal of the rectifier module and the output terminal connected to the input terminal of the voltage equalization filter module.

8. The passive low-harmonic frequency converter for rail transit air conditioning as described in claim 1, characterized in that, The voltage equalization filter module includes two or more filter electrolytic capacitors and two or more voltage equalization resistors, wherein the voltage equalization resistors have equal resistance values, and the voltage equalization resistors are connected in parallel across the two ends of the multiple filter electrolytic capacitors connected in series. The positive terminal of each capacitor is connected to the DC voltage output terminal, and the negative terminal of each capacitor is connected to the DC voltage output terminal.

9. The passive low-harmonic frequency converter for rail transit air conditioning as described in claim 1, characterized in that, The inverter module includes six IGBT electronic switching elements and their peripheral circuitry, used to convert DC voltage into AC power with variable frequency and voltage. The six IGBT electronic switching elements are Q1, Q2, Q3, Q4, Q5, and Q6, with Q1, Q3, and Q5 forming the upper bridge arm and Q2, Q4, and Q6 forming the lower bridge arm. The collectors of Q1, Q3, and Q5 are connected to the positive terminal of the DC power supply, and the emitters of Q2, Q4, and Q6 are connected to the negative terminal of the DC power supply. The emitter of Q1 is connected to the emitter of Q2... The collectors of Q1, Q2, Q3, Q4, Q5, and Q6 are connected to form an R-phase bridge arm. The emitter of Q3 is connected to the collector of Q4 to form an S-phase bridge arm. The emitter of Q5 is connected to the collector of Q6 to form a T-phase bridge arm in between. Any point in the R-phase bridge arm is connected to the load R terminal. Any point in the S-phase bridge arm is connected to the load S terminal. Any point in the T-phase bridge arm is connected to the load T terminal. The gates of Q1, Q2, Q3, Q4, Q5, and Q6 are respectively connected to the output terminals of the corresponding drive circuits. The drive circuits receive PWM control signals to control the on and off states of the IGBTs.

10. The passive low-harmonic frequency converter for rail transit air conditioning as described in claim 1, characterized in that, The control module includes a DSP chip and its peripheral circuitry, used to control the on and off of the power switching devices in the inverter module.

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