Harmonic suppression circuit of switching power supply and switching power supply

Abstract

The invention relates to the technical field of switching power supplies, and discloses a harmonic suppression circuit of a switching power supply and the switching power supply, the circuit comprises an active power factor correction circuit connected between a rectification circuit and a PWM switching circuit, two alternating current ends of the rectification circuit are connected to a power grid alternating current, and the rectification circuit rectifies the alternating current into a half-wave pulsating direct current; the PWM switching circuit converts the input voltage into power supply voltage to supply power to a load; the active power factor correction circuit controls an input current envelope line to follow an input voltage waveform and stabilizes an output voltage to the PWM switching circuit, so that the power factor is effectively improved, and harmonic noise caused by current waveform distortion is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of switching power supplies, and in particular to a harmonic suppression circuit of a switching power supply and a switching power supply. Background Art

[0002] Switching power supplies are usually used as power supplies for various types of electrical equipment to convert unregulated AC or DC input voltages into regulated AC or DC output voltages. Switching power supplies are generally composed of rectifier circuits and DC-DC circuits, in which the DC side of the rectifier circuit is often connected in parallel with one or more large-capacity power frequency filter capacitors as DC voltage support. However, due to the presence of power frequency filter capacitors, the load characteristics of the circuit are capacitive, that is, the filter capacitor is actually a nonlinear load. The presence of nonlinear loads will cause voltage and current waveforms to be distorted.

[0003] Rectifier circuits often use rectifier diodes to form rectifier bridges. Rectifier diodes have unidirectional conductivity, so they are only turned on in each half cycle of the AC input voltage. At the same time, due to the presence of filter capacitors, the rectifier diodes will only be turned on near the peak value of each half cycle of the AC input voltage. The AC input voltage still generally maintains a sinusoidal waveform, but the AC input current presents a high-amplitude spike pulse waveform, such as Figure 1 As shown in the figure, this severely distorted current waveform contains a large amount of harmonic components, which will not only cause a serious drop in the line power factor, but also seriously affect the entire power supply network and interfere with other electrical equipment on the same power supply network. Summary of the invention

[0004] In view of this, the present invention provides a harmonic suppression circuit of a switching power supply and a switching power supply to solve the problem of how to suppress harmonics of the switching power supply.

[0005] In a first aspect, the present invention provides a harmonic suppression circuit for a switching power supply, the switching power supply includes a rectifier circuit and a PWM switching circuit, the harmonic suppression circuit includes: an active power factor correction circuit, the first input end of the active power factor correction circuit is connected to the first DC end of the rectifier circuit, the second input end of the active power factor correction circuit is connected to the second DC end of the rectifier circuit, the first output end of the active power factor correction circuit is connected to the first input end of the PWM switching circuit, and the second output end of the active power factor correction circuit is connected to the second input end of the PWM switching circuit; two AC ends of the rectifier circuit are connected to AC power of a power grid, the built-in filter capacitors of the rectifier circuit are connected in parallel, and the rectifier circuit rectifies the AC power into half-wave pulsating DC power; the first output end of the PWM switching circuit is connected to the first power supply end of the load, the second output end of the PWM switching circuit is connected to the second power supply end of the load, and the PWM switching circuit converts the input voltage into the power supply voltage to supply power to the load; the active power factor correction circuit is used to control the input current envelope to follow the input voltage waveform and stabilize the output voltage to the PWM switching circuit.

[0006] The present invention adds an active power factor correction circuit between the rectifier circuit and the PWM switch circuit, so that the load end is purely resistive. The active power factor correction circuit is used to compensate for the current waveform distortion caused by the capacitive load in the switching power supply by controlling the input current envelope to follow the input voltage waveform, thereby effectively improving the power factor, reducing multiple harmonic noise caused by the current waveform distortion, and reducing the power frequency harmonic interference.

[0007] In an optional implementation, the active power factor correction circuit is a BOOST type power factor correction circuit; by controlling the on-time of the power switch device inside the BOOST type power factor correction circuit, the input current envelope is controlled to follow the input voltage waveform.

[0008] In an optional embodiment, a BOOST-type power factor correction circuit includes: a first inductor, a first transistor, a first resistor and a first diode, wherein the first end of the first inductor is connected to the first DC end of the rectifier circuit, the second end of the first inductor is connected to the first end of the first transistor and the anode of the first diode; the cathode of the first diode is connected to the first power supply end of the load; the second end of the first transistor is connected to the second DC end of the rectifier circuit and the second power supply end of the load through the first resistor, and the control end of the first transistor receives a drive signal; the drive signal is used to control the conduction time of the first transistor.

[0009] In an optional embodiment, the harmonic suppression circuit of the switching power supply also includes: an active harmonic regulator, wherein the input end of the active harmonic regulator is connected to the power grid, and the output end of the active harmonic regulator is connected to two AC ends of the rectifier circuit; the active harmonic regulator is used to sample, analyze, and establish a spectrum diagram for the harmonics generated by the nonlinear load, and inject a harmonic opposite to the harmonic generated by the nonlinear load into the AC side of the rectifier circuit based on the spectrum diagram.

[0010] In an optional embodiment, the active harmonic regulator includes: a second resistor, a first control switch, a second inductor, a converter, and a control module, wherein the first end of the second resistor is connected to the power grid, the second end of the second resistor is connected to the first end of the second inductor, and the second resistor is connected in parallel with the first control switch; the second end of the second inductor is connected to the input end of the converter; the input end of the converter is also connected to the power grid, and the output end of the converter is connected to two AC ends of the rectifier circuit; the control module is used to collect the voltage and current at the load end, and based on the voltage and current at the load end, analyze the harmonics generated by the nonlinear load, and establish a harmonic spectrum diagram generated by the nonlinear load, and based on the spectrum diagram, by controlling the operating state of the converter, inject a harmonic opposite to the harmonic generated by the nonlinear load into the AC side of the rectifier circuit.

[0011] The present invention adds an active harmonic regulator on the basis of an active power factor correction circuit. The active harmonic regulator suppresses harmonics generated by a nonlinear load by means of harmonic injection, thereby improving the defect of the power factor correction circuit in suppressing harmonics.

[0012] In an optional embodiment, the harmonic suppression circuit of the switching power supply also includes: a high-frequency filter, wherein the input end of the high-frequency filter is connected to the power grid, the output end of the high-frequency filter is connected to the input end of the active harmonic regulator, and the high-frequency filter is used to suppress the conducted noise in a preset frequency band.

[0013] In an optional implementation, the high-frequency filter includes: a first X capacitor, a second X capacitor, a third X capacitor, a first Y capacitor, a second Y capacitor, a first common-mode inductor, and a second common-mode inductor, wherein a first end of the first common-mode inductor is connected to a first end of the first X capacitor and a live wire of a power grid, a second end of the first common-mode inductor is connected to a second end of the first X capacitor and a neutral wire of a power grid, a third end of the first common-mode inductor is connected to a first end of the second X capacitor and a first end of the first Y capacitor, and a fourth end of the first common-mode inductor is connected to a second end of the second X capacitor and a first end of the second Y capacitor; a first end of the second common-mode inductor is connected to a third end of the first common-mode inductor, a second end of the second common-mode inductor is connected to a fourth end of the first common-mode inductor, a third end of the second common-mode inductor is connected to an input end of an active harmonic regulator and a first end of a third X capacitor, and a fourth end of the second common-mode inductor is connected to an input end of the active harmonic regulator and a second end of the third X capacitor; and a second end of the first Y capacitor and a second end of the second Y capacitor are both connected to a ground wire of a power grid.

[0014] In a second aspect, the present invention provides a switching power supply, comprising: a rectifier circuit, a PWM switch circuit and a harmonic suppression circuit of the first aspect and any optional implementation manner thereof, wherein a first input end of the active power factor correction circuit is connected to a first DC end of the rectifier circuit, a second input end of the active power factor correction circuit is connected to a second DC end of the rectifier circuit, a first output end of the active power factor correction circuit is connected to a first input end of the PWM switch circuit, and a second output end of the active power factor correction circuit is connected to a second input end of the PWM switch circuit; two AC ends of the rectifier circuit are connected to AC power of a power grid, a built-in filter capacitor of the rectifier circuit is connected in parallel, and the rectifier circuit rectifies the AC power into half-wave pulsating DC power; a first output end of the PWM switch circuit is connected to a first power supply end of a load, a second output end of the PWM switch circuit is connected to a second power supply end of the load, and the PWM switch circuit converts an input voltage into a power supply voltage to supply power to the load; the active power factor correction circuit is used to control the input current envelope to follow the input voltage waveform and stabilize the output voltage to the PWM switch circuit.

[0015] In an optional embodiment, the rectifier circuit includes: a rectifier bridge and a filter capacitor, wherein the AC side of the rectifier bridge is connected to AC power, the DC side of the rectifier bridge is connected in parallel with the filter capacitor, the DC side of the rectifier bridge is connected to the first input terminal and the second input terminal of the active power factor correction circuit, and the rectifier bridge is used to rectify the AC power into half-wave pulsating DC power.

[0016] In an optional embodiment, the rectifier bridge includes: a first rectifier diode, a second rectifier diode, a third rectifier diode, and a fourth rectifier diode, wherein the cathode of the first rectifier diode is connected to the anode of the second rectifier diode, and the anode of the first rectifier diode is connected to the anode of the third rectifier diode; the cathode of the third rectifier diode is connected to the anode of the fourth rectifier diode; the cathode of the fourth rectifier diode is connected to the cathode of the second rectifier diode; the cathode of the first rectifier diode and the cathode of the third rectifier diode are led to two AC ends of the rectifier circuit; the anode of the first rectifier diode and the cathode of the second rectifier diode are led to two DC ends of the rectifier circuit. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0018] Figure 1 It is the current waveform distortion diagram;

[0019] Figure 2 is a composition diagram of a harmonic suppression circuit according to an embodiment of the present invention;

[0020] Figure 3 is a composition diagram of another harmonic suppression circuit according to an embodiment of the present invention;

[0021] Figure 4 is a composition diagram of another harmonic suppression circuit according to an embodiment of the present invention;

[0022] Figure 5 is a specific structural diagram of an active harmonic regulator according to an embodiment of the present invention;

[0023] Figure 6 4 is a specific structural diagram of a high frequency filter according to an embodiment of the present invention. DETAILED DESCRIPTION

[0024] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present invention.

[0025] In the description of the present invention, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc., indicating the orientation or positional relationship, are based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first", "second", and "third" are used for descriptive purposes only, and cannot be understood as indicating or implying relative importance.

[0026] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, it can also be the internal connection of two components, it can be a wireless connection, or it can be a wired connection. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0027] In addition, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0028] When the switching power supply is working normally, its internal power frequency filter capacitor will charge and discharge frequently, and the voltage across the power frequency filter capacitor will show a sawtooth-like ripple, and the minimum value of the voltage on the capacitor is much greater than zero, and is not much different from the maximum ripple peak. Due to the unidirectional conductivity of the rectifier diode in the rectifier circuit, the rectifier diode will only conduct forward when the instantaneous voltage of the AC input is higher than the voltage on the filter capacitor, and the rectifier diode will be reverse biased and cut off when the instantaneous voltage of the AC input is lower than the voltage on the filter capacitor. Therefore, the rectifier diode will only conduct near the peak value of each half cycle of the AC input voltage. The AC input voltage still generally maintains a sinusoidal waveform, but the AC input current presents a high-amplitude spike pulse waveform, such as Figure 1 As shown in the figure, this severely distorted current waveform contains a large amount of harmonic components, which will not only cause a serious drop in the line power factor, but also seriously affect the entire power supply network and interfere with other electrical equipment on the same power supply network.

[0029] For the above problems, there are two main technologies for switching power supply harmonic suppression:

[0030] The first solution is to use an active power factor correction circuit (Power Factor Correction, referred to as PFC). The power factor is an important indicator to measure the efficiency of the power supply system, which indicates the ratio of the active power to the apparent power in the power supply system. The basic working principle is the BOOST boost PFC integrated circuit, which uses a pulse width modulation strategy to control the waveform of the input current to synchronize it with the input voltage waveform, reduce the harmonic content, and reduce the electromagnetic interference caused by the severe distortion of the current waveform caused by the capacitive load. The BOOST boost PFC circuit has a current continuous mode (CCM) working mode. In this mode, the peak current stress flowing through the power switch components is small, so that the electrical stress of the power switch components and related components is small, the input ripple current is also small, and it works in a constant frequency control mode and the filter circuit is easy to design, so it has been widely promoted in practical applications.

[0031] However, solution one will seriously aggravate the high-frequency EMI interference of the EMI switching power supply itself and increase the difficulty of filter design.

[0032] The second solution is to use a harmonic suppressor, connect a reactor in series in the capacitor circuit, and form a filtering circuit for specific harmonics by accurately adjusting the parameter values ​​of the capacitor and the reactor, so that the capacitor reactance branch presents a zero impedance characteristic at a specific harmonic frequency point. When the harmonic current in the power grid flows through this circuit, the harmonic current is guided to flow mainly through this branch, thereby effectively filtering and suppressing the harmonics, significantly improving the purity and stability of the power system, and avoiding interference with the power grid and other equipment. This solution is mainly suitable for power systems and equipment environments with significant harmonic pollution problems, such as industrial production lines containing a large number of power electronic equipment, data centers, and motor drive systems using variable frequency speed regulation technology.

[0033] However, in Solution 2, since the harmonic suppressor filter circuit uses capacitors plus inductors, such as silicon steel sheet inductors or large-capacity capacitors, the harmonic suppressor has the disadvantages of being large in size, heavy in weight, and high in cost. It will also increase the power loss of the transmission line, which is not conducive to reducing costs and increasing efficiency of the product.

[0034] Based on this, in order to solve the limitation that active (active) power factor correction circuits alone cannot meet the requirements of harmonic disturbance in special fields, improve the adaptability of switching power supplies, and solve the shortcomings of passive harmonic suppressors, such as large size, heavy weight, high cost and power loss. In this embodiment, a harmonic suppression circuit of a switching power supply is provided, and the switching power supply includes a rectifier circuit and a PWM switch circuit, such as Figure 2 As shown, the harmonic suppression circuit includes: an active power factor correction circuit.

[0035] like Figure 2As shown, the first input end of the active power factor correction circuit is connected to the first DC end of the rectifier circuit, the second input end of the active power factor correction circuit is connected to the second DC end of the rectifier circuit, the first output end of the active power factor correction circuit is connected to the first input end of the PWM switch circuit, and the second output end of the active power factor correction circuit is connected to the second input end of the PWM switch circuit. The active power factor correction circuit is used to control the input current envelope to follow the input voltage waveform and stabilize the output voltage to the PWM switch circuit.

[0036] like Figure 2 As shown, the two AC ends of the rectifier circuit are connected to the AC power of the power grid, and the built-in filter capacitors of the rectifier circuit are connected in parallel. The rectifier circuit rectifies the AC power into half-wave pulsating DC power.

[0037] like Figure 2 As shown, the first output end of the PWM switch circuit is connected to the first power supply end of the load, and the second output end of the PWM switch circuit is connected to the second power supply end of the load. The PWM switch circuit converts the input voltage into the power supply voltage to supply power to the load.

[0038] Specifically, the basic idea of ​​the active power factor correction circuit is to add a PFC circuit at the input end of the PWM switching circuit, that is, the filter capacitor in the rectifier circuit is not directly connected to the PWM switching circuit, so it presents a pure resistive load to the load end, avoiding current waveform distortion caused by capacitive load.

[0039] Optionally, the active power factor correction circuit mostly adopts a DC-DC circuit, and the working principle is similar to that of a switching power supply. Although the output current waveform of the active power factor correction circuit is intermittent, the output current envelope is the same as the voltage waveform, and the input current envelope of the active power factor correction circuit and the rectifier circuit voltage waveform (i.e., the grid voltage waveform) are in the same phase.

[0040] Optionally, the controller of the active power factor correction circuit includes: a reference voltage ref and a voltage error amplifier VA, a multiplier M, a current error amplifier CA, a pulse width modulator and a driver, etc. The load can be a switching power supply. The working principle of the controller of the active power factor correction circuit is as follows:

[0041] After the output voltage of the rectifier circuit is compared with the reference voltage value, it is input to the voltage error amplifier. The output of the voltage error amplifier and the rectified input voltage are added to the multiplier together. The output of the multiplier is used as the reference value of the current feedback control. After being compared with the detected input current signal, it is input to the current error amplifier and added to the PWM and driver to control the on and off of the switch tube of the active power factor correction circuit, so that the input current and the input voltage waveform of the rectifier circuit are basically in phase, which greatly reduces the current harmonics, improves the input power factor, and keeps the output voltage stable.

[0042] This embodiment uses an active power factor correction circuit to achieve that the AC voltage and current of the switching power supply are in phase and that the voltage waveform and current waveform both conform to a sinusoidal waveform, which not only solves the power factor compensation problem but also reduces low-frequency harmonic conduction disturbance. In some optional implementations, the active power factor correction circuit is a BOOST-type power factor correction circuit; by controlling the on-time of the power switch device inside the BOOST-type power factor correction circuit, the input current envelope is controlled to follow the envelope of the half-wave pulsating DC power.

[0043] Specifically, in principle, any DC / DC converter topology can be used as the main circuit of a power factor correction circuit. However, due to the special advantages of the BOOST converter, it is more widely used in power factor correction circuits.

[0044] The main advantages of BOOST type power factor correction circuit are summarized as follows:

[0045] (1) Input inductance can reduce the requirements for input filters and prevent high-frequency transient impacts from the power grid on the main circuit;

[0046] (2) The output voltage is greater than the peak input voltage. If the input is 90 to 132V AC, the output DC voltage will be approximately 200V; if the input is 95 to 240V AC, the DC output will be approximately 400V;

[0047] (3) The maximum voltage stress of the switching device is the output voltage value;

[0048] (4) It is easy to drive the power switch, and the potential of the switch source is 0V;

[0049] (5) It can maintain normal operation within the wide range of input voltage and frequency specified by international standards.

[0050] In some optional embodiments, such as Figure 3 As shown, the BOOST type power factor correction circuit includes: a first inductor L1, a first transistor Q1, a first resistor R1 and a first diode D5.

[0051] like Figure 3As shown, the first end of the first inductor L1 is connected to the first DC end of the rectifier circuit, the second end of the first inductor L1 is connected to the first end of the first transistor Q1 and the anode of the first diode D5; the cathode of the first diode D5 is connected to the first power supply end of the load; the second end of the first transistor Q1 is connected to the second DC end of the rectifier circuit and the second power supply end of the load through the first resistor R1, and the control end of the first transistor Q1 receives a driving signal; the driving signal is used to control the conduction time of the first transistor Q1.

[0052] Optionally, after the sinusoidal AC is input to the rectifier, the rectifier circuit rectifies it into a positive half-cycle pulsating voltage. The BOOST type power factor correction circuit mainly involves controlling the phase and waveform of the input current and voltage to achieve a high power factor. The voltage closed loop and current closed loop can be added to achieve the correction of the power factor, as follows:

[0053] (1) Voltage closed-loop control: used to stabilize the output voltage. The voltage controller generates a control command (the output of the voltage controller is called the voltage control command).

[0054] (2) Current closed-loop control: In order to make the inductor current track the "mantou wave" waveform (i.e., the positive half-cycle pulsating voltage waveform) output by the rectifier circuit, the input current can become a sine wave and be in phase with the input voltage. Among them, the current closed-loop control multiplies the voltage control command with the output voltage sampling of the rectifier bridge to form a "mantou wave" control command as the reference given value of the current controller.

[0055] (3) Current controller: The control instruction it outputs is the duty cycle of the switch tube, which is driven by the switch tube to control the on and off of the switch tube to control the inductor current to track the reference given value and stabilize the output voltage.

[0056] (4) Control the inductor current: By controlling the inductor current to track the reference given value, the inductor current is made to circle around the reference given value, and the inductor current is approximately a "mantou wave".

[0057] (5) Control of input current and voltage: After PFC control, the input current presents a sine wave with a burr shape and is basically in phase with the input voltage, thus achieving the purpose of power factor correction.

[0058] In short, the BOOST power factor correction circuit improves the power factor of the power supply and reduces harmonic distortion by adjusting the waveform and phase of the input current and voltage to make them as close to a sine wave as possible and keep them in phase.

[0059] In some optional embodiments, such as Figure 4As shown, the harmonic suppression circuit of the switching power supply also includes: an active harmonic regulator, wherein the input end of the active harmonic regulator is connected to the power grid, and the output end of the active harmonic regulator is connected to the two AC ends of the rectifier circuit; the active harmonic regulator is used to sample, analyze, and establish a spectrum diagram for the harmonics generated by the nonlinear load, and inject a harmonic opposite to the harmonic generated by the nonlinear load into the AC side of the rectifier circuit based on the spectrum diagram.

[0060] Specifically, since the active power factor correction circuit cannot completely suppress the power frequency harmonics, an active harmonic control circuit is added to the front end of the rectifier circuit to sample, analyze and establish a spectrum diagram for the harmonics generated by the nonlinear load. Based on this spectrum diagram, a harmonic opposite to the harmonic generated by the nonlinear load is sent to the grid side, thereby achieving the effect of harmonic suppression. The principle block diagram is shown in the figure. Figure 5 shown.

[0061] Specifically, the active harmonic control circuit can adjust the phase angle of the voltage and current waveform according to the situation of the power supply end, correct the current waveform, improve the power factor, and effectively suppress harmonic interference. Optionally, the active harmonic controller has a standard serial port debugging interface. The host computer can capture harmonics in real time through the debugging software, set it through the visual interface, and feed back the actual working state of the switching power supply to the active harmonic controller, so as to comprehensively and effectively suppress the harmonics in the power grid.

[0062] In some optional embodiments, such as Figure 5 As shown, the active harmonic regulator includes: a second resistor R2, a first control switch S1, a second inductor L2, a converter, and a control module, wherein: Figure 5 The inductor Lf and capacitor Cf in the circuit form a high-frequency filter. In fact, the active harmonic regulator can be directly connected to the power grid.

[0063] like Figure 5 As shown, the first end of the second resistor R2 is connected to the power grid, the second end of the second resistor R2 is connected to the first end of the second inductor L2, and the second resistor R2 is connected in parallel with the first control switch S1; the second end of the second inductor L2 is connected to the input end of the converter; the input end of the converter is also connected to the power grid, and the output end of the converter is connected to the two AC ends of the rectifier circuit; the control module is used to collect the voltage and current at the load end, and based on the voltage and current at the load end, analyze the harmonics generated by the nonlinear load, and establish a harmonic spectrum diagram generated by the nonlinear load, and based on the spectrum diagram, by controlling the operating state of the converter, inject a harmonic opposite to the harmonic generated by the nonlinear load into the AC side of the rectifier circuit.

[0064] Specifically, Figure 5 Taking the active harmonic regulator directly connected to the grid as an example, if it is connected to the switching power supply, the converter is connected to the rectifier circuit at the rear stage, and the load is as shown in Figure 5. Figure 2 The load in Figure 2 The rectifier circuit, active power factor correction circuit, and PWM switch circuit are all added Figure 5 .

[0065] Specifically, the main principle of the active harmonic regulator is to transmit a harmonic opposite to the harmonic generated by the nonlinear load to the grid side and superimpose it on the harmonic to achieve the purpose of suppressing harmonics. Based on this concept, the active harmonic regulator was launched, which can effectively suppress the 2nd to 25th harmonics, adjust the phase angle of the voltage and current waveforms according to the actual situation of the grid, correct the current waveform, and improve the power factor, thereby effectively suppressing the interference of harmonics on the grid. Its working principle diagram is shown in the figure below. Figure 5 shown.

[0066] Optionally, the active harmonic regulator mainly suppresses harmonics based on the harmonic injection method, and its specific structure is not limited to Figure 5 , other structures with harmonic analysis and injection can also be used, which are not limited here.

[0067] Optionally, the active harmonic regulator has a very friendly user interface, which can be set on site through the dialogue window of the user interface, and the actual status of the user site can be truly fed back to the active harmonic regulator, and then the real-time harmonic capture can be performed through the sampling picker, so that the harmonics in the power grid can be fully and effectively suppressed. This regulator also includes a standard RS232 interface, which allows the harmonic information to be connected to the real-time computer in real time.

[0068] In some optional embodiments, such as Figure 3 As shown, the harmonic suppression circuit of the switching power supply also includes: a high-frequency filter, wherein the input end of the high-frequency filter is connected to the power grid, the output end of the high-frequency filter is connected to the input end of the active harmonic regulator, and the high-frequency filter is used to suppress the conducted noise in the preset frequency band.

[0069] Specifically, the active power factor correction circuit is the basis for suppressing power frequency harmonic interference, but since it is also a switching circuit, it is inevitable that its switching noise will be transmitted outward, and a high-frequency filtering circuit needs to be added to suppress the switching conduction noise.

[0070] Optionally, the high frequency filter mainly suppresses conducted noise in a frequency band of 10kHz to 30MHz.

[0071] In some optional embodiments, such as Figure 6As shown, the high-frequency filter includes: a first X capacitor CX1, a second X capacitor CX2, a third X capacitor CX3, a first Y capacitor CY1, a second Y capacitor CY2, a first common-mode inductor L3, and a second common-mode inductor L4, wherein a first end of the first common-mode inductor L3 is connected to a first end of the first X capacitor CX1 and a live wire of a power grid, a second end of the first common-mode inductor L3 is connected to a second end of the first X capacitor CX1 and a neutral wire of a power grid, a third end of the first common-mode inductor L3 is connected to a first end of the second X capacitor CX2 and a first end of the first Y capacitor CY1, and a fourth end of the first common-mode inductor L3 is connected to a first end of the second X capacitor CX2 and a first end of the first Y capacitor CY1. The first end of the second common-mode inductor L4 is connected to the third end of the first common-mode inductor L3, the second end of the second common-mode inductor L4 is connected to the fourth end of the first common-mode inductor L3, the third end of the second common-mode inductor L4 is connected to the input end of the active harmonic regulator and the first end of the third X capacitor CX3, the fourth end of the second common-mode inductor L4 is connected to the input end of the active harmonic regulator and the second end of the third X capacitor CX3; the second end of the first Y capacitor CY1 and the second end of the second Y capacitor CY2 are both connected to the ground line of the power grid.

[0072] In some optional implementations, the harmonic suppression circuit further includes a digital power meter, which is used to detect the harmonic waveform at the input end of the switching power supply and record the harmonic abnormal value, which is used to compare with the national standard.

[0073] Optionally, the harmonic suppression circuit and the switching power supply are placed in a shielded room, and a harmonic disturbance test is performed, so that the final multiple harmonic interference values ​​of the switching power supply under the dual effects of the active power factor correction circuit and the active harmonic controller can be accurately obtained, thereby adding effective suppression measures for foreseeable risks, reducing the repeated verification time of EMC tests, reducing the risks caused by EMC test failures, and reducing R&D costs, EMC testing costs, and project start-up cycles.

[0074] In this embodiment, a switching power supply is provided. Figure 2 As shown, it includes: a rectifier circuit, a PWM switch circuit and a harmonic suppression circuit (ie, an active power factor correction circuit) of the above embodiment and any optional implementation manner thereof.

[0075] A first input end of the active power factor correction circuit is connected to a first DC end of the rectifier circuit, a second input end of the active power factor correction circuit is connected to a second DC end of the rectifier circuit, a first output end of the active power factor correction circuit is connected to a first input end of the PWM switch circuit, and a second output end of the active power factor correction circuit is connected to a second input end of the PWM switch circuit;

[0076] The two AC terminals of the rectifier circuit are connected to the AC power of the power grid, and the built-in filter capacitors of the rectifier circuit are connected in parallel. The rectifier circuit rectifies the AC power into half-wave pulsating DC power;

[0077] The first output end of the PWM switch circuit is connected to the first power supply end of the load, the second output end of the PWM switch circuit is connected to the second power supply end of the load, and the PWM switch circuit converts the input voltage into the power supply voltage to supply power to the load;

[0078] The active power factor correction circuit is used to control the input current envelope to follow the input voltage waveform and stabilize the output voltage to the PWM switching circuit.

[0079] In some optional implementations, the rectifier circuit includes: a rectifier bridge and a filter capacitor C1, wherein:

[0080] The AC side of the rectifier bridge is connected to AC power, the DC side of the rectifier bridge is connected in parallel with the filter capacitor C1, and the DC side of the rectifier bridge is connected to the first input terminal and the second input terminal of the active power factor correction circuit. The rectifier bridge is used to rectify the AC power into half-wave pulsating DC power.

[0081] In some optional embodiments, such as Figure 3 As shown, the rectifier bridge includes: a first rectifier diode D1, a second rectifier diode D2, a third rectifier diode D3, and a fourth rectifier diode D4, wherein:

[0082] The cathode of the first rectifier diode D1 is connected to the anode of the second rectifier diode D2, and the anode of the first rectifier diode D1 is connected to the anode of the third rectifier diode D3; the cathode of the third rectifier diode D3 is connected to the anode of the fourth rectifier diode D4; the cathode of the fourth rectifier diode D4 is connected to the cathode of the second rectifier diode D2; the cathode of the first rectifier diode D1 and the cathode of the third rectifier diode D3 are led to the two AC ends of the rectifier circuit; the anode of the first rectifier diode D1 and the cathode of the second rectifier diode D2 are led to the two DC ends of the rectifier circuit.

[0083] Although the embodiments of the present invention have been described in conjunction with the accompanying drawings, those skilled in the art may make various modifications and variations without departing from the spirit and scope of the present invention, and such modifications and variations are all within the scope defined by the appended claims.

Claims

1. A harmonic suppression circuit for a switching power supply, characterized in that: The switching power supply includes a rectifier circuit and a PWM switch circuit, and the harmonic suppression circuit includes: an active power factor correction circuit, The first input end of the active power factor correction circuit is connected to the first DC end of the rectifier circuit, the second input end of the active power factor correction circuit is connected to the second DC end of the rectifier circuit, the first output end of the active power factor correction circuit is connected to the first input end of the PWM switch circuit, and the second output end of the active power factor correction circuit is connected to the second input end of the PWM switch circuit; The two AC terminals of the rectifier circuit are connected to the AC power of the power grid, the built-in filter capacitors of the rectifier circuit are connected in parallel, and the rectifier circuit rectifies the AC power into half-wave pulsating DC power; The first output end of the PWM switch circuit is connected to the first power supply end of the load, the second output end of the PWM switch circuit is connected to the second power supply end of the load, and the PWM switch circuit converts the input voltage into the power supply voltage to supply power to the load; The active power factor correction circuit is used to control the input current envelope to follow the input voltage waveform and stabilize the output voltage to the PWM switch circuit.

2. The harmonic suppression circuit of the switching power supply according to claim 1, characterized in that: The active power factor correction circuit is a BOOST type power factor correction circuit; By controlling the on-time of the power switch device inside the BOOST type power factor correction circuit, the input current envelope is controlled to follow the input voltage waveform.

3. The harmonic suppression circuit of the switching power supply according to claim 2, characterized in that: The BOOST type power factor correction circuit includes: a first inductor, a first transistor, a first resistor and a first diode, wherein: The first end of the first inductor is connected to the first DC end of the rectifier circuit, and the second end of the first inductor is connected to the first end of the first transistor and the anode of the first diode; The cathode of the first diode is connected to the first power supply terminal of the load; The second end of the first transistor is connected to the second DC end of the rectifier circuit and the second power supply end of the load through the first resistor, and the control end of the first transistor receives a driving signal; The driving signal is used to control the conduction time of the first transistor.

4. The harmonic suppression circuit of the switching power supply according to claim 1, characterized in that: Also includes: Active harmonic regulator, where The input end of the active harmonic regulator is connected to the power grid, and the output end of the active harmonic regulator is connected to two AC ends of the rectifier circuit; The active harmonic regulator is used to sample, analyze and establish a spectrum diagram of the harmonics generated by the nonlinear load, and inject a harmonic opposite to the harmonic generated by the nonlinear load into the AC side of the rectifier circuit based on the spectrum diagram.

5. The harmonic suppression circuit of the switching power supply according to claim 4, characterized in that: The active harmonic regulator includes: a second resistor, a first control switch, a second inductor, a converter, and a control module, wherein: The first end of the second resistor is connected to the power grid, the second end of the second resistor is connected to the first end of the second inductor, and the second resistor is connected in parallel to the first control switch; The second end of the second inductor is connected to the input end of the converter; The input end of the converter is also connected to the power grid, and the output end of the converter is connected to two AC ends of the rectifier circuit; The control module is used to collect the voltage and current at the load end, and based on the voltage and current at the load end, analyze the harmonics generated by the nonlinear load, and establish a harmonic spectrum diagram generated by the nonlinear load. Based on the spectrum diagram, by controlling the operating state of the converter, a harmonic opposite to the harmonic generated by the nonlinear load is injected into the AC side of the rectifier circuit.

6. The harmonic suppression circuit of the switching power supply according to claim 4, characterized in that: Also includes: High frequency filter, where The input end of the high-frequency filter is connected to the power grid, the output end of the high-frequency filter is connected to the input end of the active harmonic regulator, and the high-frequency filter is used to suppress conducted noise in a preset frequency band.

7. The harmonic suppression circuit of the switching power supply according to claim 6, characterized in that: The high frequency filter comprises: a first X capacitor, a second X capacitor, a third X capacitor, a first Y capacitor, a second Y capacitor, a first common mode inductor, and a second common mode inductor, wherein: A first end of the first common-mode inductor is connected to a first end of the first X capacitor and a live line of a power grid, a second end of the first common-mode inductor is connected to a second end of the first X capacitor and a neutral line of a power grid, a third end of the first common-mode inductor is connected to a first end of the second X capacitor and a first end of a first Y capacitor, and a fourth end of the first common-mode inductor is connected to a second end of the second X capacitor and a first end of a second Y capacitor; The first end of the second common-mode inductor is connected to the third end of the first common-mode inductor, the second end of the second common-mode inductor is connected to the fourth end of the first common-mode inductor, the third end of the second common-mode inductor is connected to the input end of the active harmonic regulator and the first end of the third X capacitor, and the fourth end of the second common-mode inductor is connected to the input end of the active harmonic regulator and the second end of the third X capacitor; The second end of the first Y capacitor and the second end of the second Y capacitor are both connected to the ground line of the power grid.

8. A switching power supply, characterized in that: include: A rectifier circuit, a PWM switch circuit, and a harmonic suppression circuit as described in any one of claims 1 to 7, wherein: A first input end of the active power factor correction circuit is connected to a first DC end of the rectifier circuit, a second input end of the active power factor correction circuit is connected to a second DC end of the rectifier circuit, a first output end of the active power factor correction circuit is connected to a first input end of the PWM switch circuit, and a second output end of the active power factor correction circuit is connected to a second input end of the PWM switch circuit; The two AC terminals of the rectifier circuit are connected to the AC power of the power grid, the built-in filter capacitors of the rectifier circuit are connected in parallel, and the rectifier circuit rectifies the AC power into half-wave pulsating DC power; The first output end of the PWM switch circuit is connected to the first power supply end of the load, the second output end of the PWM switch circuit is connected to the second power supply end of the load, and the PWM switch circuit converts the input voltage into the power supply voltage to supply power to the load; The active power factor correction circuit is used to control the input current envelope to follow the input voltage waveform and stabilize the output voltage to the PWM switch circuit.

9. The switching power supply according to claim 8, characterized in that: The rectifier circuit includes: a rectifier bridge and a filter capacitor, wherein: The AC side of the rectifier bridge is connected to AC power, the DC side of the rectifier bridge is connected in parallel with the filter capacitor, the DC side of the rectifier bridge is connected to the first input terminal and the second input terminal of the active power factor correction circuit, and the rectifier bridge is used to rectify the AC power into half-wave pulsating DC power.

10. The switching power supply according to claim 9, characterized in that: The rectifier bridge comprises: a first rectifier diode, a second rectifier diode, a third rectifier diode, and a fourth rectifier diode, wherein: The cathode of the first rectifier diode is connected to the anode of the second rectifier diode, and the anode of the first rectifier diode is connected to the anode of the third rectifier diode; The cathode of the third rectifier diode is connected to the anode of the fourth rectifier diode; The cathode of the fourth rectifier diode is connected to the cathode of the second rectifier diode; The cathode of the first rectifier diode and the cathode of the third rectifier diode lead out two AC ends of the rectifier circuit; The anode of the first rectifier diode and the cathode of the second rectifier diode lead out two DC ends of the rectifier circuit.

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