Harmonic improvement control circuit

Abstract

The utility model relates to the technical field of harmonic improvement, in particular to a harmonic improvement control circuit, which comprises a filter rectifier module, a bus voltage detection module, a filter capacitor E2, a switch control module, a switch power supply module and a load module. The bus voltage detection module is electrically connected with the filter rectifier module, one end of the filter capacitor E2, the switch control module and the switch power supply module, the switch power supply module is electrically connected with the load module, the other end of the filter capacitor E2 is electrically connected with the switch control module, and the filter rectifier module is connected with commercial power. The magnitude of the valley voltage after rectification is controlled by limiting the charging voltage of the filter capacitor E2, namely the magnitude of the stored energy, so that the conduction angle of the input current is controlled; meanwhile, the voltage and current following degree is increased, the power factor is improved, and the purpose of improving harmonic waves is achieved.

Description

Technical Field

[0001] The utility model relates to the technical field of harmonic improvement, in particular to a harmonic improvement control circuit. Background Art

[0002] As people's requirements for energy utilization are getting higher and higher, countries have higher and higher requirements for the power factor harmonics of electrical and electronic equipment; and the number of LED lights used is increasing, so the restrictions on LED harmonics in various countries are getting higher and higher, and all countries have promulgated legal and regulatory requirements; in addition, as people's requirements for light quality increase, flicker-free lighting has gradually become a consideration for people.

[0003] However, the existing control circuits on the market that need to meet the above requirements have the following disadvantages:

[0004] 1. Narrow input voltage range and short life:

[0005] Due to the reduction of the filter capacitor capacity after rectification, the capacitor size is either small, with poor ripple current resistance and short life, or large in size and high in cost, with low valley voltage and small input voltage range;

[0006] 2. The circuit is complex and the cost is high:

[0007] Generally, a boost circuit is combined with a buck circuit, which has a complex circuit structure and high cost;

[0008] 3. Low efficiency, can not achieve completely no flicker:

[0009] Generally, a power factor correction (PFC) solution is used, and the output has industrial frequency ripple. To eliminate it, a flash elimination circuit needs to be added, which increases losses and reduces efficiency. Utility Model Content

[0010] The technical problem to be solved by the utility model is to provide a harmonic improvement control circuit, which can ensure the stable operation of the switching power supply module within a wider input voltage range, and can achieve LED light without flicker in LED lighting applications.

[0011] In order to solve the above technical problems, the technical solution adopted by the utility model is:

[0012] A harmonic improvement control circuit comprises a filtering and rectifying module, a bus voltage detection module, a filtering capacitor E2, a switch control module, a switching power supply module and a load module, wherein the bus voltage detection module is electrically connected to the filtering and rectifying module, one end of the filtering capacitor E2, the switch control module and the switching power supply module respectively, the switching power supply module is electrically connected to the load module, the other end of the filtering capacitor E2 is electrically connected to the switch control module, and the filtering and rectifying module is connected to the mains.

[0013] Furthermore, the bus voltage detection module includes a comparator U2A, a first voltage divider unit and a second voltage divider unit, the non-phase input end of the comparator U2A is electrically connected to the first voltage divider unit, the inverting input end of the comparator U2A is electrically connected to the second voltage divider unit, the output ends of the first voltage divider unit and the comparator U2A are both electrically connected to the switch control module, and the second voltage divider unit is respectively electrically connected to the filter rectifier module, one end of the filter capacitor E2 and the switching power supply module.

[0014] Furthermore, the first voltage divider unit includes a resistor R11 and a resistor R12, one end of the resistor R11 is electrically connected to the non-phase input end of the comparator U2A and one end of the resistor R12, respectively, the other end of the resistor R11 is electrically connected to the switch control module, the other end of the resistor R12 is electrically connected to the second voltage divider unit and the switch control module, respectively, and the second voltage divider unit is electrically connected to the filter rectifier module.

[0015] Furthermore, the second voltage-dividing unit includes a resistor R2, a resistor R3 and a resistor R4, one end of the resistor R3 is electrically connected to one end of the resistor R4 and the inverting input end of the comparator U2A, the other end of the resistor R3 is electrically connected to one end of the resistor R2, the other end of the resistor R2 is electrically connected to the filtering and rectifying module, one end of the filtering capacitor E2 and the switching power supply module, and the other end of the resistor R4 is electrically connected to the first voltage-dividing unit and the switching control module.

[0016] Furthermore, the bus voltage detection module also includes a diode D4, an anode of the diode D4 is electrically connected to the second voltage divider unit and the filter rectifier module respectively, and a cathode of the diode D4 is electrically connected to one end of the filter capacitor E2 and the switch power supply module respectively.

[0017] Furthermore, the switch control module includes a MOS tube Q1 and a diode D1, the gate of the MOS tube Q1 is electrically connected to the bus voltage detection module, the drain of the MOS tube Q1 is electrically connected to the other end of the filter capacitor E2 and the cathode of the diode D1, respectively, the source of the MOS tube Q1 is electrically connected to the anode of the diode D1 and the switching power supply module, and the source of the MOS tube Q1, the anode of the diode D1 and the switching power supply module are all grounded.

[0018] Furthermore, the switch control module also includes a resistor R13, a resistor R14 and a resistor R15, one end of the resistor R15 is electrically connected to one end of the resistor R14 and the gate of the MOS tube Q1, respectively, the other end of the resistor R15 is electrically connected to the bus voltage detection module, the other end of the resistor R14 is electrically connected to the bus voltage detection module, one end of the resistor R13 and the switching power supply module, and the other end of the resistor R14 and one end of the resistor R13 are both grounded, and the other end of the resistor R13 is electrically connected to the source of the MOS tube Q1.

[0019] Furthermore, it also includes an auxiliary power supply module, which is electrically connected to the bus voltage detection module.

[0020] The beneficial effects of the utility model are:

[0021] This solution detects the input voltage through the bus voltage detection module, and can control whether the filter capacitor E2 is involved; when the bus voltage is higher than the set value, the filter capacitor E2 is disconnected and no longer charged, and the switch control module is cut off because the voltage of the filter capacitor E2 is lower than the bus voltage; when the bus voltage is lower than the voltage of the filter capacitor E2, the switch control module works to smooth the input voltage of the switch power supply module; when the bus voltage is higher than the voltage of the filter capacitor E2 again, and lower than the voltage set by the switch control module, the AC power is rectified to provide energy for the switch power supply module and charge the filter capacitor E2; this solution controls The voltage of the filter capacitor E2, that is, the amount of energy storage, is controlled to achieve the conduction phase of the filter rectifier module (that is, the phase angle when the bus voltage is higher than the voltage of the filter capacitor E2 again and lower than the voltage set by the switch control module), that is, the valley value of the bus voltage is limited, thereby achieving the purpose of advancing the conduction angle and reducing harmonics; when the input voltage is lower than the voltage set by the switch control module throughout the process, the filter capacitor E2 is fully turned on, and the valley voltage is not too low due to the existence of the filter capacitor E2, so the switching power supply module can be guaranteed to work stably within a wider input voltage range. In LED lighting applications, LED lights can be achieved without flicker. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a module connection block diagram of the harmonic improvement control circuit of the utility model;

[0023] Figure 2 It is a circuit principle diagram of the harmonic improvement control circuit of the utility model;

[0024] Figure 3 It is a circuit schematic diagram of the auxiliary power supply module of the harmonic improvement control circuit of the utility model;

[0025] Description of labels:

[0026] 1. Filter and rectifier module; 2. Bus voltage detection module; 3. Switch control module; 4. Switch power supply module; 5. Load module; 6. Auxiliary power supply module. DETAILED DESCRIPTION

[0027] In order to explain the technical content, achieved objectives and effects of the present invention in detail, the following is an explanation in conjunction with the implementation modes and the accompanying drawings.

[0028] Please refer to Figure 1, the technical solution adopted by the utility model is:

[0029] A harmonic improvement control circuit comprises a filtering and rectifying module, a bus voltage detection module, a filtering capacitor E2, a switch control module, a switching power supply module and a load module, wherein the bus voltage detection module is electrically connected to the filtering and rectifying module, one end of the filtering capacitor E2, the switch control module and the switching power supply module respectively, the switching power supply module is electrically connected to the load module, the other end of the filtering capacitor E2 is electrically connected to the switch control module, and the filtering and rectifying module is connected to the mains.

[0030] From the above description, it can be seen that the beneficial effects of the utility model are:

[0031] This solution detects the input voltage through the bus voltage detection module, and can control whether the filter capacitor E2 is involved; when the bus voltage is higher than the set value, the filter capacitor E2 is disconnected and no longer charged, and the switch control module is cut off because the voltage of the filter capacitor E2 is lower than the bus voltage; when the bus voltage is lower than the voltage of the filter capacitor E2, the switch control module works to smooth the input voltage of the switch power supply module; when the bus voltage is higher than the voltage of the filter capacitor E2 again, and lower than the voltage set by the switch control module, the AC power is rectified to provide energy for the switch power supply module and charge the filter capacitor E2; this solution controls The voltage of the filter capacitor E2, that is, the amount of energy storage, is controlled to achieve the conduction phase of the filter rectifier module (that is, the phase angle when the bus voltage is higher than the voltage of the filter capacitor E2 again and lower than the voltage set by the switch control module), that is, the valley value of the bus voltage is limited, thereby achieving the purpose of advancing the conduction angle and reducing harmonics; when the input voltage is lower than the voltage set by the switch control module throughout the process, the filter capacitor E2 is fully turned on, and the valley voltage is not too low due to the existence of the filter capacitor E2, so the switching power supply module can be guaranteed to work stably within a wider input voltage range. In LED lighting applications, LED lights can be achieved without flicker.

[0032] Furthermore, the bus voltage detection module includes a comparator U2A, a first voltage divider unit and a second voltage divider unit, the non-phase input end of the comparator U2A is electrically connected to the first voltage divider unit, the inverting input end of the comparator U2A is electrically connected to the second voltage divider unit, the output ends of the first voltage divider unit and the comparator U2A are both electrically connected to the switch control module, and the second voltage divider unit is respectively electrically connected to the filter rectifier module, one end of the filter capacitor E2 and the switching power supply module.

[0033] Furthermore, the first voltage divider unit includes a resistor R11 and a resistor R12, one end of the resistor R11 is electrically connected to the non-phase input end of the comparator U2A and one end of the resistor R12, respectively, the other end of the resistor R11 is electrically connected to the switch control module, the other end of the resistor R12 is electrically connected to the second voltage divider unit and the switch control module, respectively, and the second voltage divider unit is electrically connected to the filter rectifier module.

[0034] Furthermore, the second voltage-dividing unit includes a resistor R2, a resistor R3 and a resistor R4, one end of the resistor R3 is electrically connected to one end of the resistor R4 and the inverting input end of the comparator U2A, the other end of the resistor R3 is electrically connected to one end of the resistor R2, the other end of the resistor R2 is electrically connected to the filtering and rectifying module, one end of the filtering capacitor E2 and the switching power supply module, and the other end of the resistor R4 is electrically connected to the first voltage-dividing unit and the switching control module.

[0035] Furthermore, the bus voltage detection module also includes a diode D4, an anode of the diode D4 is electrically connected to the second voltage divider unit and the filter rectifier module respectively, and a cathode of the diode D4 is electrically connected to one end of the filter capacitor E2 and the switch power supply module respectively.

[0036] It can be seen from the above description that the diode D4 serves to separate the bus voltage from the filtered voltage.

[0037] Furthermore, the switch control module includes a MOS tube Q1 and a diode D1, the gate of the MOS tube Q1 is electrically connected to the bus voltage detection module, the drain of the MOS tube Q1 is electrically connected to the other end of the filter capacitor E2 and the cathode of the diode D1, respectively, the source of the MOS tube Q1 is electrically connected to the anode of the diode D1 and the switching power supply module, and the source of the MOS tube Q1, the anode of the diode D1 and the switching power supply module are all grounded.

[0038] From the above description, it can be known that the MOS tube Q1 is a switch device for controlling the charging of the filter capacitor E2, and the diode D1 provides a loop for the reverse discharge of the filter capacitor E2.

[0039] Furthermore, the switch control module also includes a resistor R13, a resistor R14 and a resistor R15, one end of the resistor R15 is electrically connected to one end of the resistor R14 and the gate of the MOS tube Q1, respectively, the other end of the resistor R15 is electrically connected to the bus voltage detection module, the other end of the resistor R14 is electrically connected to the bus voltage detection module, one end of the resistor R13 and the switching power supply module, and the other end of the resistor R14 and one end of the resistor R13 are both grounded, and the other end of the resistor R13 is electrically connected to the source of the MOS tube Q1.

[0040] From the above description, it can be seen that the resistor R15 is a pull-up resistor that can improve the driving capability, the resistor R13 is a current limiting resistor that can protect the MOS tube Q1, and the resistor R14 is the gate-drain resistor of the MOS tube Q1 to protect the MOS tube Q1 from breakdown.

[0041] Furthermore, it also includes an auxiliary power supply module, which is electrically connected to the bus voltage detection module.

[0042] From the above description, it can be seen that providing an auxiliary power supply module can provide a stable DC power supply for the bus voltage detection module.

[0043] Please refer to Figures 1 to 3 As shown, the first embodiment of the utility model is:

[0044] Please refer to Figure 1 A harmonic improvement control circuit includes a filter rectifier module 1, a bus voltage detection module 2, a filter capacitor E2, a switch control module 3, a switch power supply module 4 and a load module 5. The bus voltage detection module 2 is electrically connected to the filter rectifier module 1, one end of the filter capacitor E2, the switch control module 3 and the switch power supply module 4 respectively, the switch power supply module 4 is electrically connected to the load module 5, the other end of the filter capacitor E2 is electrically connected to the switch control module 3, and the filter rectifier module 1 is connected to the mains.

[0045] The rectifier and filter module rectifies the AC power of the mains into DC power;

[0046] The filter capacitor E2 filters the rectified steamed bun wave into a relatively smooth DC voltage;

[0047] The switching power supply module 4 provides a constant voltage / constant current source for the load module 5;

[0048] The load module 5 may be an electrical load, an LED light source, or an MCU, etc. In this embodiment, the load module 5 includes a plurality of light emitting diodes connected in series.

[0049] The bus voltage detection module 2 is used to detect the input voltage and output it to the switch control module 3. When the detected voltage is higher than the set voltage, the filter capacitor E2 is disconnected, and the power supply of the switch power supply module 4 is directly provided by the AC mains after rectification. When the detected voltage is lower than the set voltage, the switch control module 3 is turned on to charge the filter capacitor E2. The switch control module 3 provides a circuit for the filter capacitor E2 and the switch power supply module 4.

[0050] Please refer to Figure 2The bus voltage detection module 2 includes a comparator U2A (model LM393), a first voltage divider unit and a second voltage divider unit. The positive input terminal of the comparator U2A is electrically connected to the first voltage divider unit, and the negative input terminal of the comparator U2A is electrically connected to the second voltage divider unit. The output terminals of the first voltage divider unit and the comparator U2A are both electrically connected to the switch control module 3, and the second voltage divider unit is respectively electrically connected to the filter rectifier module 1, one end of the filter capacitor E2 and the switch power supply module 4.

[0051] Please refer to Figure 2 The first voltage-dividing unit includes a resistor R11 (resistance value is 10kΩ) and a resistor R12 (resistance value is 2kΩ), one end of the resistor R11 is electrically connected to the non-inverting input end of the comparator U2A and one end of the resistor R12 respectively, the other end of the resistor R11 is electrically connected to the switch control module 3, the other end of the resistor R12 is electrically connected to the second voltage-dividing unit and the switch control module 3 respectively, and the second voltage-dividing unit is electrically connected to the filter rectifier module 1.

[0052] Please refer to Figure 2 The second voltage-dividing unit includes a resistor R2 (resistance value is 240 kΩ), a resistor R3 (resistance value is 240 kΩ) and a resistor R4 (resistance value is 3.6 kΩ), one end of the resistor R3 is electrically connected to one end of the resistor R4 and the inverting input end of the comparator U2A, the other end of the resistor R3 is electrically connected to one end of the resistor R2, the other end of the resistor R2 is electrically connected to the filtering and rectifying module 1, one end of the filtering capacitor E2 and the switching power supply module 4, and the other end of the resistor R4 is electrically connected to the first voltage-dividing unit and the switching control module 3.

[0053] Please refer to Figure 2 The bus voltage detection module 2 also includes a diode D4 (model M7), the anode of the diode D4 is electrically connected to the second voltage divider unit and the filter rectifier module 1 respectively, and the cathode of the diode D4 is electrically connected to one end of the filter capacitor E2 and the switch power supply module 4 respectively.

[0054] Please refer to Figure 2 The switch control module 3 includes a MOS tube Q1 (model SVF2N60F) and a diode D1 (model ES1J), the gate of the MOS tube Q1 is electrically connected to the bus voltage detection module 2, the drain of the MOS tube Q1 is electrically connected to the other end of the filter capacitor E2 and the cathode of the diode D1, the source of the MOS tube Q1 is electrically connected to the anode of the diode D1 and the switch power module 4, and the source of the MOS tube Q1, the anode of the diode D1 and the switch power module 4 are all grounded.

[0055] Please refer to Figure 2The switch control module 3 also includes a resistor R13 (resistance value is 10Ω), a resistor R14 (resistance value is 100kΩ) and a resistor R15 (resistance value is 3kΩ), one end of the resistor R15 is electrically connected to one end of the resistor R14 and the gate of the MOS tube Q1 respectively, the other end of the resistor R15 is electrically connected to the bus voltage detection module 2, the other end of the resistor R14 is electrically connected to the bus voltage detection module 2, one end of the resistor R13 and the switch power supply module 4 respectively, and the other end of the resistor R14 and one end of the resistor R13 are both grounded, and the other end of the resistor R13 is electrically connected to the source of the MOS tube Q1.

[0056] Please refer to Figure 1 , also includes an auxiliary power supply module 6, and the auxiliary power supply module 6 is electrically connected to the bus voltage detection module 2.

[0057] The filter rectifier module 1 includes a fuse resistor F1 (resistance value is 22Ω), a capacitor C1 (capacitance value is 47nF), a varistor RV1 (rated voltage value is 470V), a resistor R1 (resistance value is 4.7kΩ), an inductor L1 (inductance value is 2mH) and a rectifier bridge BR1 (model MB10F). For the specific connection relationship between the components, please refer to Figure 2 When the high voltage generated by lightning is introduced into the power supply through the power grid, it is protected by the fuse resistor F1 and the varistor RV1. When the voltage applied to the two ends of the varistor RV1 exceeds its working voltage, its resistance value decreases, so that the high-voltage energy is consumed on the varistor RV1. If the current is too large, the fuse resistor F1 will burn to protect the subsequent circuit. The capacitor C1, the inductor L1 and the resistor R1 form an LC filter network, which mainly suppresses the electromagnetic noise and clutter signals of the input power supply to prevent interference with the power supply. At the same time, it also prevents the high-frequency clutter generated by the power supply itself from interfering with the power grid. The rectifier bridge BR1 converts the AC power into DC power.

[0058] The switching power supply module 4 includes a resistor R7 (resistance value is 9.1 kΩ), a chip U1 (model KP107A), a diode D2 (a freewheeling diode, model ES1J), an electromagnetic winding T1A (an energy storage inductor, the inductance value is 2 mH), a resistor R9 (resistance value is 4.3 Ω), a resistor R8 (resistance value is 4.3 Ω) and a resistor R10 (resistance value is 300 kΩ). For the specific connection relationship between the components, please refer to Figure 2 , the electromagnetic winding T1A is an energy storage inductor, the diode D2 is a freewheeling diode, the resistor R7 is an open circuit protection setting resistor, and the resistors R8 and R9 are current sampling resistors;

[0059] The auxiliary power supply module 6 includes an electromagnetic winding T1B (an auxiliary winding of the electromagnetic winding T1A), a diode D3 (model ES1J), a capacitor E3 (capacitance value is 100μF), a resistor R16 (resistance value is 10kΩ), a capacitor C3 (capacitance value is 100nF), a capacitor C4 (capacitance value is 10μF) and a chip U3 (a 12V LDO linear voltage regulator chip). For the specific connection relationship between the various components, please refer to Figure 3 The coupled energy of electromagnetic winding T1B is rectified by diode D3, filtered by capacitor C3 and capacitor E3, and then stabilized and filtered by chip U3 and capacitor C4 to output a stable 12V DC voltage source.

[0060] The working principle of the above wave improvement control circuit is:

[0061] The resistor R11 and the resistor R12 divide the voltage to provide a stable reference voltage to the in-phase terminal IN1+ of the comparator U2A. The resistors R2, R3 and R4 divide the voltage, and the input comparator U2A's reverse terminal IN1- is compared with the reference voltage of the in-phase terminal IN1+ of the comparator U2A. When the resistor R4 divided voltage is lower than the reference voltage, it is determined that the bus voltage does not exceed the set value. The OUT1 pin of the comparator U2A outputs a high level, and VCC drives the MOS tube Q1 to turn on through the resistor R15, and the filter capacitor E2 is charged to store energy. When the resistor R4 divided voltage is higher than the reference voltage, it is determined that the bus voltage exceeds the set value, and the OUT1 pin of the comparator U2A outputs a low voltage, pulling down the gate of the MOS tube Q1, the MOS tube Q1 is not turned on, and the filter capacitor E2 is no longer charged. When the bus voltage is lower than the voltage of the filter capacitor E2, the diode D1 (reverse freewheeling diode) is not conducting. When the bus voltage is lower than the voltage of the filter capacitor E2, the diode D1 is conducting, the filter capacitor E2 supplies power to the load module 5, and the voltage of the filter capacitor E2 gradually decreases. The MOS tube Q1 is conducting until the input voltage is higher than the voltage of the filter capacitor E2 again, and the rectifier bridge BR1 is conducting, that is, there is input current; the AC mains ACL / ACN charges the filter capacitor E2 and supplies power to the switching power supply module 4; when the voltage of the bus voltage throughout the entire cycle is lower than the set value, the MOS tube Q1 is conducting during the entire cycle, the filter capacitor E2 is large enough, and the valley value of the voltage after passing through the filter capacitor E2 is not too low, so the normal operation of the switching power supply module 4 can be guaranteed.

[0062] This solution controls the valley voltage after rectification by limiting the charging voltage of the filter capacitor E2, that is, the amount of stored energy, and thus controls the conduction angle of the input current; at the same time, it increases the degree of voltage and current following, improves the power factor, and achieves the purpose of improving harmonics.

[0063] In summary, the utility model provides a harmonic improvement control circuit, which detects the input voltage through the bus voltage detection module, and can control whether the filter capacitor E2 is involved; when the bus voltage is higher than the set value, the filter capacitor E2 is disconnected and no longer charged, and at the same time, the switch control module is cut off because the voltage of the filter capacitor E2 is lower than the bus voltage; when the bus voltage is lower than the voltage of the filter capacitor E2, the switch control module works to smooth the input voltage of the switch power supply module; when the bus voltage is higher than the voltage of the filter capacitor E2 again, and lower than the voltage set by the switch control module, the mains rectifier provides energy for the switch power supply module, and the filter capacitor E2 is charged. 2 Charging; This solution controls the voltage of the filter capacitor E2, that is, the amount of energy storage, to achieve the conduction phase of the filter rectifier module (that is, the phase angle when the bus voltage is higher than the voltage of the filter capacitor E2 again and lower than the voltage set by the switch control module), that is, to limit the valley value of the bus voltage, thereby achieving the purpose of advancing the conduction angle and reducing harmonics; when the input voltage is lower than the voltage set by the switch control module throughout the process, the filter capacitor E2 is fully turned on, and the valley voltage is not too low due to the existence of the filter capacitor E2, so the switching power supply module can be guaranteed to work stably within a wider input voltage range. In LED lighting applications, LED lights can be made flicker-free.

[0064] The above description is only an embodiment of the present invention, and does not limit the patent scope of the present invention. Any equivalent transformations made using the contents of the specification and drawings of the present invention, or directly or indirectly applied in the relevant technical field, are also included in the patent protection scope of the present invention.

Claims

1. A harmonic improvement control circuit, characterized in that: It includes a filtering and rectifying module, a bus voltage detection module, a filtering capacitor E2, a switch control module, a switching power supply module and a load module. The bus voltage detection module is electrically connected to the filtering and rectifying module, one end of the filtering capacitor E2, the switch control module and the switching power supply module respectively. The switching power supply module is electrically connected to the load module, the other end of the filtering capacitor E2 is electrically connected to the switch control module, and the filtering and rectifying module is connected to the mains.

2. The harmonic improvement control circuit according to claim 1, characterized in that: The bus voltage detection module includes a comparator U2A, a first voltage divider unit and a second voltage divider unit. The positive input end of the comparator U2A is electrically connected to the first voltage divider unit, and the negative input end of the comparator U2A is electrically connected to the second voltage divider unit. The output ends of the first voltage divider unit and the comparator U2A are both electrically connected to the switch control module, and the second voltage divider unit is respectively electrically connected to the filter rectifier module, one end of the filter capacitor E2 and the switch power supply module.

3. The harmonic improvement control circuit according to claim 2, characterized in that: The first voltage divider unit includes a resistor R11 and a resistor R12, one end of the resistor R11 is electrically connected to the non-phase input end of the comparator U2A and one end of the resistor R12, the other end of the resistor R11 is electrically connected to the switch control module, the other end of the resistor R12 is electrically connected to the second voltage divider unit and the switch control module, and the second voltage divider unit is electrically connected to the filter rectifier module.

4. The harmonic improvement control circuit according to claim 2, characterized in that: The second voltage-dividing unit includes a resistor R2, a resistor R3 and a resistor R4, one end of the resistor R3 is electrically connected to one end of the resistor R4 and the inverting input end of the comparator U2A, the other end of the resistor R3 is electrically connected to one end of the resistor R2, the other end of the resistor R2 is electrically connected to the filtering and rectifying module, one end of the filtering capacitor E2 and the switching power supply module, and the other end of the resistor R4 is electrically connected to the first voltage-dividing unit and the switching control module.

5. The harmonic improvement control circuit according to claim 2, characterized in that: The bus voltage detection module further includes a diode D4, an anode of which is electrically connected to the second voltage divider unit and the filter rectifier module respectively, and a cathode of which is electrically connected to one end of the filter capacitor E2 and the switch power supply module respectively.

6. The harmonic improvement control circuit according to claim 1, characterized in that: The switch control module includes a MOS tube Q1 and a diode D1, the gate of the MOS tube Q1 is electrically connected to the bus voltage detection module, the drain of the MOS tube Q1 is electrically connected to the other end of the filter capacitor E2 and the cathode of the diode D1 respectively, the source of the MOS tube Q1 is electrically connected to the anode of the diode D1 and the switching power supply module respectively, and the source of the MOS tube Q1, the anode of the diode D1 and the switching power supply module are all grounded.

7. The harmonic improvement control circuit according to claim 6, characterized in that: The switch control module also includes a resistor R13, a resistor R14 and a resistor R15, one end of the resistor R15 is electrically connected to one end of the resistor R14 and the gate of the MOS tube Q1 respectively, the other end of the resistor R15 is electrically connected to the bus voltage detection module, the other end of the resistor R14 is electrically connected to the bus voltage detection module, one end of the resistor R13 and the switch power supply module respectively, and the other end of the resistor R14 and one end of the resistor R13 are both grounded, and the other end of the resistor R13 is electrically connected to the source of the MOS tube Q1.

8. The harmonic improvement control circuit according to claim 1, characterized in that: It also includes an auxiliary power supply module, which is electrically connected to the bus voltage detection module.

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