LC passive pfc resonant control circuit

Abstract

The utility model provides a kind of LC passive PFC resonance control circuit, comprising: current sampling module, for sampling load current, output sampling signal;Comparator, the comparator has first input port, second input port and output port;First input port is connected to the sampling signal, second input port is connected to reference signal, and output port exports control signal;Three-phase LC passive PFC module, including resonant inductance network, resonant capacitance network and rectifier network connected in turn;Resonant inductance network receives three-phase power supply voltage;Resonant capacitance network includes three capacitor branches between three phase lines, and each capacitor branch includes filter capacitor and corresponding relay switch connected in series;The control end of relay switch is connected to control signal.The utility model can meet harmonic control standard when standby state, avoid the problem that bus voltage is too high, and also can meet the effect of PFC modulation when working state.

Description

Technical Field

[0001] This utility model belongs to the field of power electronics technology, and in particular relates to an LC passive PFC resonant control circuit. Background Technology

[0002] In the field of power electronic equipment, to meet the mandatory control standards for harmonic current in different countries or regions, electrical equipment with a rated current of less than 16A must ensure that the harmonic content of its input current is within the regulatory limits. Taking variable frequency air conditioning products as an example, in order to suppress harmonic pollution on the grid side, passive power factor correction (PFC) technology is often used in conventional technical solutions. Among them, the LC type passive PFC circuit is widely used in the inverter design of three-phase variable frequency air conditioners due to its simple structure and low cost.

[0003] like Figure 1 and 2 Both circuits shown are three-phase LC resonant PFC circuit topologies, in which Figure 1 This is a circuit with a delta connection. Figure 2 Both circuits are star-connected and can suppress harmonic content, meeting the requirements of national standards.

[0004] However, in such Figure 1 and 2 In the circuit shown, if the power supply contains a high level of harmonics, these harmonics will resonate with the LC resonant circuit in standby mode when they enter the circuit. This will cause the inductors L1, L2, and L3 to resonate with the capacitors C1, C2, and C3. Consequently, a high voltage will be generated across the downstream capacitor C7. For example, at the normal rated voltage of 380Vac, without considering the harmonics, the downstream bus voltage, i.e., the voltage across capacitor C7, would be approximately 540V. However, due to the introduction of harmonics, the downstream bus voltage can even reach over 1200V, far exceeding the withstand voltage of diodes D1-D6 and the downstream capacitor C7. This overvoltage condition not only accelerates component aging but may also lead to electrical safety risks such as insulation breakdown and capacitor explosion, directly affecting equipment reliability and user safety.

[0005] It is evident that while existing LC passive PFC circuits can meet harmonic suppression requirements under operating conditions, they lack effective means to suppress resonant overvoltage in standby mode, becoming a key technical bottleneck restricting the safety design of three-phase inverter air conditioners. Therefore, there is an urgent need to propose a resonant control circuit for LC passive PFC. Utility Model Content

[0006] To address the shortcomings of existing technologies, this utility model aims to provide an LC passive PFC circuit that can meet harmonic control standards in standby mode to avoid excessive bus voltage, and can also achieve PFC modulation effects in operating mode.

[0007] The present invention adopts the following technical solution.

[0008] This utility model provides an LC passive PFC resonant control circuit, comprising: The current sampling module is used to sample the load current and output a sampling signal; A comparator having a first input port, a second input port, and an output port; the first input port is connected to the sampled signal, the second input port is connected to the reference signal, and the output port outputs a control signal; A three-phase LC passive PFC module includes a resonant inductor network, a resonant capacitor network, and a rectifier network connected in sequence. The resonant inductor network receives the three-phase power supply voltage. The resonant capacitor network includes three capacitor branches disposed between the three phase lines. Each capacitor branch includes a filter capacitor connected in series and a corresponding relay switch. The control terminal of the relay switch is connected to the control signal.

[0009] Preferably, the current sampling module includes a sampling resistor connected in series in the load circuit.

[0010] Preferably, the current sampling module includes a sampling resistor connected in series in the load circuit and a TVS diode connected in parallel across the sampling resistor.

[0011] Preferably, the LC passive PFC resonant control circuit further includes an amplifier and a filter, which are connected in sequence between the current sampling module and the first input port of the comparator.

[0012] Preferably, the comparator is configured as follows: When the sampled signal is greater than or equal to the reference signal, a control signal is output to close the relay switch. When the sampled signal is less than the reference signal, a control signal is output to disconnect the relay switch.

[0013] Preferably, the reference signal is set according to a load current threshold; when the sampled signal is greater than or equal to the reference signal, it indicates that the load current is greater than or equal to the load current threshold; when the sampled signal is less than the reference signal, it indicates that the load current is less than the load current threshold.

[0014] Preferably, of the three capacitor branches, the first capacitor branch is connected between the phase lines corresponding to AB, the second capacitor branch is connected between the phase lines corresponding to BC, and the third capacitor branch is connected between the phase lines corresponding to AC.

[0015] Preferably, the first ends of the three capacitor branches are respectively connected to the corresponding phase lines of A, B, and C, and the second ends of the three capacitor branches are connected together.

[0016] Preferably, the resonant inductor network includes filter inductors respectively disposed on the three phase lines.

[0017] Preferably, the rectifier network includes a first diode to a sixth diode; The connection point between the positive terminal of the first diode and the negative terminal of the second diode is connected to the phase line of phase A; The connection point between the positive terminal of the third diode and the negative terminal of the fourth diode is connected to the phase line of phase B. The connection point between the positive terminal of the fifth diode and the negative terminal of the sixth diode is connected to the C-phase line; The negative terminals of the first diode, the third diode, and the fifth diode are connected together as the positive output terminal; The positive terminals of the second diode, the fourth diode, and the sixth diode are connected together as the negative terminal of the output.

[0018] Preferably, the three-phase LC passive PFC module further includes a filter capacitor disposed between the output positive terminal and the output negative terminal.

[0019] The beneficial effects of this invention are as follows: Compared with the prior art, by connecting three relays in series in the three-phase LC passive PFC module, and combining the current sampling module and comparator to orderly control the energizing state of the relays, the operating time of the inductors and capacitors in the circuit can be controlled. Specifically, in standby mode, the load current does not exceed the load current threshold, and the sampling signal does not exceed the reference signal. Therefore, the control signal output by the comparator keeps the relays in the open state, and the inductors and capacitors in the three-phase LC passive PFC module do not participate in LC resonance, thus avoiding the problem of excessively high resonant voltage in the subsequent stage. In the unit's normal operating state, if the load current is greater than or equal to the load current threshold, the sampling signal is greater than or equal to the reference signal. Therefore, the control signal output by the comparator initiates the relay operation, and the inductors and capacitors in the three-phase LC passive PFC module participate in LC resonance, achieving the effect of PFC correction. Therefore, through the above control, this invention not only avoids the problem of excessively high bus voltage in standby mode, but also satisfies the effect of PFC modulation in operating mode. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the topology of a three-phase LC passive PFC delta circuit in the prior art; Figure 2 This is a schematic diagram of the topology of a three-phase LC passive PFC star circuit in the prior art; Figure 3 This is a schematic diagram of an LC passive PFC resonant control circuit in one embodiment of the present invention, wherein the three-phase LC passive PFC modules are connected in a delta topology. Figure 4 This is a schematic diagram of an LC passive PFC resonant control circuit in another embodiment of the present invention, wherein the three-phase LC passive PFC modules are connected in a star topology. Figure 5 This is the working logic diagram of the relay switch in this utility model. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of this utility model clearer, the technical solutions of this utility model will be clearly and completely described below with reference to the accompanying drawings of the embodiments. The embodiments described in this application are merely some embodiments of this utility model, not all embodiments. Based on the spirit of this utility model, other embodiments obtained by those skilled in the art without creative effort are all within the protection scope of this utility model.

[0022] In the following description, references are made to “some embodiments,” which describe a subset of all possible embodiments. However, it is understood that “some embodiments” may be the same subset or different subsets of all possible embodiments and may be combined with each other without conflict.

[0023] In the following description, the terms "first, second, third" are used merely to distinguish similar objects and do not represent a specific ordering of objects. It is understood that "first, second, third" may be interchanged in a specific order or sequence where permitted, so that the embodiments of this application described herein can be implemented in an order other than that illustrated or described herein.

[0024] Unless otherwise defined, all technical and scientific terms used in the embodiments of this application have the same meaning as commonly understood by one of ordinary skill in the art. The terminology used in the embodiments of this application is for the purpose of describing the embodiments of this application only and is not intended to limit this application.

[0025] In existing LC-type passive PFC circuits, due to the presence of inductors and capacitors, harmonics of different frequencies cause resonance in the inductors and capacitors during standby, resulting in excessively high bus voltage in the downstream stage, which exceeds the range that the components can withstand.

[0026] The present invention provides an LC passive PFC resonant control circuit that not only avoids the problem of excessive bus voltage in standby mode, but also satisfies the effect of PFC modulation in working mode.

[0027] like Figure 3 and 4 The present invention discloses an LC passive PFC resonant control circuit, comprising: a current sampling module, a comparator, and a three-phase LC passive PFC module.

[0028] The current sampling module is used to sample the load current and output a sampling signal; The comparator has a first input port, a second input port, and an output port; the first input port is connected to the sampled signal, the second input port is connected to the reference signal Ref, and the output port outputs a control signal Ctrl; A three-phase LC passive PFC module includes a resonant inductor network, a resonant capacitor network, and a rectifier network connected in sequence. The resonant inductor network receives the three-phase power supply voltage. The resonant capacitor network includes three capacitor branches disposed between the three phase lines. Each capacitor branch includes a filter capacitor connected in series and a corresponding relay switch. The control terminal of the relay switch is connected to the control signal Ctrl.

[0029] In this invention, relays are connected in series in each capacitor branch of the resonant capacitor network of the three-phase LC passive PFC module. By combining the current sampling module and the comparator to control the energizing state of the relays in an orderly manner, the resonant operating time of the inductor and capacitor in the circuit can be controlled. This avoids the problem of excessive bus voltage in the standby state and satisfies the effect of PFC modulation in the working state.

[0030] In this utility model, the three-phase power supply is equivalent to Figure 3 and 4 The AC power sources X, Y, and Z are provided. Specifically, AC power sources X, Y, and Z provide AC power to the three phases A, B, and C, respectively.

[0031] In a preferred embodiment, the current sampling module may include a sampling resistor connected in series in the load circuit and a TVS (Transient Voltage Suppressor) diode connected in parallel across the sampling resistor.

[0032] The sampling resistor is preferably a low-resistance precision resistor (e.g., 0.1Ω / 1% accuracy). Since the voltage across the sampling resistor is proportional to the load current flowing through it, the sampling signal can be obtained by measuring the voltage drop across the sampling resistor, thus enabling sampling of the load current. This sampling method is suitable for low to medium current scenarios (e.g., load current less than 10A).

[0033] The function of a TVS diode is to protect the circuit from electrostatic discharge (ESD) or surge voltage.

[0034] It should be noted that the use of a sampling resistor in the current sampling module is merely an example and not a limitation. In other embodiments, such as when the load current is high, the current sampling module can also be implemented using a current transformer or other methods.

[0035] In a preferred embodiment, the LC passive PFC resonant control circuit further includes an amplifier and a filter.

[0036] The amplifier and filter are connected sequentially between the current sampling module and the first input port of the comparator.

[0037] An operational amplifier can be used to amplify the sampled signal. Generally, an operational amplifier is an electronic integrated circuit containing multiple stages of amplification circuitry. Its input stage is a differential amplifier circuit, which has high input resistance and zero-point drift suppression capability; the intermediate stage mainly performs voltage amplification, with high voltage amplification factor, and is generally composed of a common-emitter amplifier circuit; the output stage outputs the amplified sampled signal.

[0038] For example, an RC low-pass filter can be used to filter the amplified sampled signal to eliminate high-frequency noise, smooth the signal, and improve signal stability.

[0039] In a preferred embodiment, the comparator is configured as follows: When the sampled signal is greater than or equal to the reference signal Ref, a control signal Ctrl is output to close the relay switch; When the sampled signal is less than the reference signal Ref, a control signal Ctrl is output to disconnect the relay switch.

[0040] Furthermore, the reference signal Ref is set according to the load current threshold; when the sampled signal is greater than or equal to the reference signal Ref, it indicates that the load current is greater than or equal to the load current threshold; when the sampled signal is less than the reference signal Ref, it indicates that the load current is less than the load current threshold.

[0041] In this way, during standby mode, the load current does not exceed the load current threshold, and the sampled signal does not exceed the reference signal Ref. Therefore, the control signal Ctrl output by the comparator keeps the relay in the off state, and the inductors and capacitors in the three-phase LC passive PFC module do not participate in the LC resonance operation, thus avoiding the problem of excessively high resonant voltage in the subsequent stage. During the unit's normal operating state, if the load current is greater than or equal to the load current threshold, the sampled signal is greater than or equal to the reference signal Ref. Therefore, the control signal Ctrl output by the comparator switches the relay to work, and the inductors and capacitors in the three-phase LC passive PFC module participate in the LC resonance operation, achieving the effect of PFC correction.

[0042] In a preferred embodiment, such as Figure 3 As shown, of the three capacitor branches, the first capacitor branch is connected between the phase lines corresponding to AB, the second capacitor branch is connected between the phase lines corresponding to BC, and the third capacitor branch is connected between the phase lines corresponding to AC.

[0043] The first capacitor branch includes capacitor C1 and relay switch K1; the second capacitor branch includes capacitor C2 and relay switch K2; and the third capacitor branch includes capacitor C3 and relay switch K3.

[0044] In this way, the three-phase LC passive PFC module is connected in a delta topology.

[0045] In a preferred embodiment, such as Figure 4 As shown, the first ends of the three capacitor branches are respectively connected to the corresponding phase lines of A, B, and C, and the second ends of the three capacitor branches are connected together.

[0046] The first capacitor branch also includes capacitor C1 and relay switch K1; the second capacitor branch also includes capacitor C2 and relay switch K2; and the third capacitor branch also includes capacitor C3 and relay switch K3.

[0047] In this way, the three-phase LC passive PFC module is connected in a star topology.

[0048] In a preferred embodiment, the resonant inductor network includes resonant inductors respectively disposed on three phase lines. Specifically, a resonant inductor L1 is disposed on phase line A; a resonant inductor L2 is disposed on phase line B; and a resonant inductor L3 is disposed on phase line C.

[0049] In a PFC module, by setting up a resonant inductor network and a resonant capacitor network, the current waveform can be adjusted to be closer to a sine wave when the PFC module is in operation, reducing current distortion. The inductor smooths current fluctuations by storing and releasing energy, while the capacitor balances voltage fluctuations through charging and discharging. Together, they reduce grid harmonic content and improve the power factor (PF value close to 1). Simultaneously, the resonant characteristics of the capacitor and inductor can reduce electromagnetic interference (EMI) problems caused by sudden current changes, ensuring stable equipment operation and reducing interference to other electronic equipment.

[0050] In a preferred embodiment, the rectifier network includes a first diode D1 to a sixth diode D6; The connection point between the positive terminal of the first diode D1 and the negative terminal of the second diode D2 is connected to the phase line of phase A; The connection point between the positive terminal of the third diode D3 and the negative terminal of the fourth diode D4 is connected to the phase line of phase B. The connection point between the positive terminal of the fifth diode D5 and the negative terminal of the sixth diode D6 is connected to the C-phase line. The negative terminals of the first diode D1, the third diode D3, and the fifth diode D5 are connected together as the positive output terminal; The positive terminals of the second diode D2, the fourth diode D4, and the sixth diode D6 are connected together as the negative terminal of the output.

[0051] This topological connection of diodes D1 to D6 enables rectification, converting three-phase AC voltage into DC voltage, which is then output via an output terminal that includes both positive and negative terminals.

[0052] In a preferred embodiment, the three-phase LC passive PFC module further includes a filter capacitor C7 disposed between the output positive terminal and the output negative terminal.

[0053] The rectifier network converts alternating current into pulsating direct current, resulting in periodic fluctuations in the output voltage. By connecting a filter capacitor C7 in parallel at the output of the rectifier network, energy is stored and charged during voltage peaks, and discharged during voltage troughs, thus mitigating voltage fluctuations and making the output voltage closer to constant DC.

[0054] As can be seen, the core concept of this utility model lies in controlling the operating state of the LC resonant network by introducing a switching device (relay) into the LC resonant network formed by the resonant inductor network and the resonant capacitor network. Specifically, by connecting a normally open relay in series at one end of each of the capacitors C1, C2, and C3, the relays can disconnect the circuit between the inductors L1, L2, and L3 and the capacitors C1, C2, and C3 when there is no control command from the unit, thus preventing resonance between the inductors and capacitors.

[0055] The overall control logic is as follows Figure 5 As shown, when the unit is powered on, the inductor and capacitor in the LC resonant network are in an open state because a normally open relay is used, so resonance cannot occur; however, in order to ensure that the unit still meets the national requirements for harmonic suppression during normal operation, the relay switch needs to be switched on under certain conditions.

[0056] At this time, the unit awaits the start-up command. Upon receiving the start-up command, the load (compressor, etc.) starts running. When the load current reaches the current load threshold, a comparator can control relays K1, K2, and K3 to switch on, thus enabling the inductor and capacitor to enter the working state during start-up operation. The current load threshold can be set empirically; for example, a load current of 3-6A is typically sufficient to control the relay switches to close during the start-up phase.

[0057] If the unit receives a shutdown command or a unit malfunctions, the unit will enter standby mode. To prevent the inductor and capacitor from entering a state with a high resonant voltage during standby, the relay switches K1, K2 and K3 can be opened by controlling the comparator. The unit will then enter a state waiting for a power-on command, or a state where the customer shuts down the power and does not use the unit, and will re-enter the power-on state when there is a demand again.

[0058] In summary, the beneficial effects of this invention are as follows: Compared with the prior art, by connecting three relays in series in the three-phase LC passive PFC module, and combining the current sampling module and comparator to orderly control the relay's activation state, the operating time of the inductor and capacitor in the circuit can be controlled. Specifically, in standby mode, the load current does not exceed the load current threshold, and the sampling signal does not exceed the reference signal Ref. Therefore, the control signal output by the comparator keeps the relay in the open state, and the inductor and capacitor in the three-phase LC passive PFC module do not participate in LC resonance, thus avoiding the problem of excessively high resonant voltage in the subsequent stage. In the unit's normal operating state, if the load current is greater than or equal to the load current threshold, the sampling signal is greater than or equal to the reference signal Ref. Therefore, the control signal output by the comparator initiates relay operation, and the inductor and capacitor in the three-phase LC passive PFC module participate in LC resonance, achieving the PFC correction effect. Therefore, through the above control, this invention not only avoids the problem of excessively high bus voltage in standby mode but also satisfies the PFC modulation effect in operating mode.

[0059] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of this utility model and not to limit it. Although the utility model has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of this utility model. Any modifications or equivalent substitutions that do not depart from the spirit and scope of this utility model should be covered within the protection scope of the claims of this utility model.

Claims

1. An LC passive PFC resonant control circuit, characterized in that, include: The current sampling module is used to sample the load current and output a sampling signal; A comparator having a first input port, a second input port, and an output port; the first input port is connected to the sampled signal, the second input port is connected to a reference signal, and the output port outputs a control signal. A three-phase LC passive PFC module includes a resonant inductor network, a resonant capacitor network, and a rectifier network connected in sequence. The resonant inductor network receives the three-phase power supply voltage. The resonant capacitor network includes three capacitor branches disposed between the three phase lines. Each capacitor branch includes a filter capacitor connected in series and a corresponding relay switch. The control terminal of the relay switch is connected to the control signal.

2. The LC passive PFC resonant control circuit according to claim 1, characterized in that, The current sampling module includes a sampling resistor connected in series in the load circuit and a TVS diode connected in parallel across the sampling resistor.

3. The LC passive PFC resonant control circuit according to claim 1, characterized in that, Also includes: An amplifier and a filter are connected sequentially between the current sampling module and the first input port of the comparator.

4. The LC passive PFC resonant control circuit according to claim 1, characterized in that, The comparator is configured as follows: When the sampled signal is greater than or equal to the reference signal, a control signal is output to close the relay switch. When the sampled signal is less than the reference signal, a control signal is output to disconnect the relay switch.

5. The LC passive PFC resonant control circuit according to claim 4, characterized in that, The reference signal is set according to the load current threshold; when the sampled signal is greater than or equal to the reference signal, it indicates that the load current is greater than or equal to the load current threshold; when the sampled signal is less than the reference signal, it indicates that the load current is less than the load current threshold.

6. The LC passive PFC resonant control circuit according to claim 1, characterized in that, Of the three capacitor branches, the first capacitor branch is connected between the phase lines corresponding to AB, the second capacitor branch is connected between the phase lines corresponding to BC, and the third capacitor branch is connected between the phase lines corresponding to AC.

7. The LC passive PFC resonant control circuit according to claim 1, characterized in that, The first ends of the three capacitor branches are respectively connected to the corresponding phase lines of A, B, and C, and the second ends of the three capacitor branches are connected together.

8. The LC passive PFC resonant control circuit according to claim 1, characterized in that, The resonant inductor network includes filter inductors respectively disposed on the three phase lines.

9. The LC passive PFC resonant control circuit according to claim 1, characterized in that, The rectifier network includes a first diode, a second diode, a third diode, a fourth diode, a fifth diode, and a sixth diode; The connection point between the positive terminal of the first diode and the negative terminal of the second diode is connected to the phase line of phase A; The connection point between the positive terminal of the third diode and the negative terminal of the fourth diode is connected to the phase line of phase B. The connection point between the positive terminal of the fifth diode and the negative terminal of the sixth diode is connected to the C-phase line; The negative terminals of the first diode, the third diode, and the fifth diode are connected together as the positive output terminal; The positive terminals of the second diode, the fourth diode, and the sixth diode are connected together as the negative terminal of the output.

10. The LC passive PFC resonant control circuit according to claim 9, characterized in that, The three-phase LC passive PFC module also includes a filter capacitor disposed between the output positive terminal and the output negative terminal.

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