Power supply circuit of an active EMI filter powered by power supply harmonics

Abstract

The present invention discloses a power supply circuit for an active EMI filter that extracts energy from power harmonics, comprising a harmonic inductor, which is sequentially connected to a booster, a filter voltage regulator, and a single-pole to double-pole circuit. A battery is connected between the filter voltage regulator and the single-pole to double-pole circuit. The circuit of the present invention extracts the energy generated by the harmonics of the switched-mode power converter from the power line of the switched-mode power converter to be filtered and supplies it for use by the active EMI filter.

Description

Technical Field

[0001] The present invention belongs to the technical field of electromagnetic interference suppression, and relates to a power supply circuit for an active EMI filter that extracts energy from power supply harmonics. Background Art

[0002] Since a switching power converter realizes the change of electric energy by using switching devices, there will be a dynamic change between the presence and absence states of voltage and current during the process of electric energy change, and this dynamic change process will introduce high-frequency electromagnetic interference. These electromagnetic interferences will affect the working states of other electronic devices in the surrounding power supply environment. Therefore, it is necessary to suppress the electromagnetic interference generated by the switching power converter. In the electromagnetic interference suppression technology, the suppression technology with small volume and light weight is the active EMI filter.

[0003] The active EMI filter must be powered by an external power supply, and the external power supply is used to provide the energy to cancel the electromagnetic interference generated by the switching power converter and the electric energy for the normal filtering operation of the active EMI filter. Generally, there is no suitable external power supply for the active EMI filter around the object to be filtered, namely the switching power converter, and it needs to be developed separately. The active EMI filter generally has high requirements for the external power supply. It not only requires a separate power supply source, but also requires electrical isolation measures between the output and the input, and the power supply ripple should be very small. These requirements will increase the volume and weight of the external power supply, and will seriously reduce the advantages of the active EMI filter in terms of small volume and light weight. Summary of the Invention

[0004] The purpose of the present invention is to provide a power supply circuit for an active EMI filter that extracts energy from power supply harmonics. This circuit extracts the energy generated by the harmonics of the switching power converter from the power line of the switching power converter to be filtered and supplies it for use by the active EMI filter.

[0005] The technical solution adopted by the present invention is that the power supply circuit for an active EMI filter that extracts energy from power supply harmonics includes a harmonic inductor, and the harmonic inductor is sequentially connected to a booster, a filter voltage regulator and a single-pole to double-pole circuit. A battery is connected between the filter voltage regulator and the single-pole to double-pole circuit.

[0006] The features of the present invention also lie in that:

[0007] The harmonic inductor includes a magnetic core, a secondary coil and m groups of resonators. Each group of resonators is composed of a capacitor and an inductor with different values connected in series. One end of each group of resonators is connected to the power line, and the other end is connected to the N line; the secondary coil and the inductors in each group of resonators are wound around the magnetic core.

[0008] The booster includes n diodes connected in parallel, and a capacitor is connected between adjacent two diodes. There are n diodes and n capacitors.

[0009] The filter voltage regulator includes a capacitor C, a zener diode VD, and an inductor L connected in parallel.

[0010] The single-pole to double-pole circuit includes voltage-dividing resistors R1 and R2. Filter capacitors C q1 , C q2 are respectively connected in parallel across both ends of the voltage-dividing resistor R1; filter capacitors C q3 , C q4 are respectively connected in parallel across both ends of the voltage-dividing resistor R2.

[0011] In each group of resonators, the maximum operating frequency f max of the magnetic core is designed by formula (1).

[0012] f max = f0·(m + 1) (1);

[0013] where f0 is the operating frequency of the equipment to be filtered;

[0014] The magnetic path length L e of the magnetic core is designed by formula (2).

[0015]

[0016] The cross-sectional area A e of the magnetic core is designed by formula (3).

[0017]

[0018] where D is the outer diameter of the magnetic core and d is the inner diameter of the magnetic core.

[0019] The capacitance value C of the filter voltage regulator is designed by formula (4).

[0020]

[0021] where f k is the resonance frequency corresponding to the maximum harmonic power; U k is the harmonic voltage corresponding to the maximum harmonic power, I k is the harmonic current corresponding to the maximum harmonic power; A cv is the ripple factor of the active EMI filter;

[0022] The inductance value L of the filter voltage regulator is designed by formula (5).

[0023]

[0024] where k2 is the cut-off frequency control factor.

[0025] The capacity W of the battery is designed by formula (6).

[0026] W = t·(PEMI -k3·k in ·P in ) (6).

[0027] The beneficial effects of the present invention are as follows: The electric energy of the power supply circuit comes from the harmonic energy generated by the filtered switching power converter, without providing any external power supply, solving the industry problem of difficult external power supply configuration for active EMI filters. In addition, a rechargeable battery is provided in the power supply circuit of the active EMI filter for extracting power from power supply harmonics proposed by the present invention, solving the problem of insufficient power energy during the operation of the active EMI filter due to insufficient harmonic energy extraction. Moreover, since no external power supply device is introduced, the absolute advantages of small volume and light weight of the active EMI filter are greatly guaranteed. Description of the Drawings

[0028] Figure 1 is a schematic structural diagram of the power supply circuit of the active EMI filter for extracting power from power supply harmonics of the present invention. Detailed Embodiments

[0029] The present invention will be described in detail below with reference to the drawings and specific embodiments.

[0030] The power supply circuit of the active EMI filter for extracting power from power supply harmonics of the present invention, the input energy of this power supply circuit comes from the switching power converter itself that is filtered, obtains the harmonic energy generated by the switching power converter through induction, realizes the matching of the power supply voltage for the active EMI filter through a step-up transformer design, realizes the conversion of a unipolar power supply to a bipolar power supply through a unipolar-to-bipolar circuit, and solves the problem of insufficient power energy during the operation of the active EMI filter due to insufficient harmonic energy extraction by setting a rechargeable battery. Since no external power supply device is added, the absolute advantages of small volume and light weight of the active EMI filter are greatly guaranteed.

[0031] The power supply circuit of the active EMI filter for extracting power from power supply harmonics of the present invention has a structure as Figure 1 shown, and this power supply circuit consists of five parts: a harmonic inductor, a step-up transformer, a filter voltage regulator, a battery, and a unipolar-to-bipolar circuit.

[0032] The harmonic inductor includes m groups of resonators, a magnetic core, and a secondary coil. Each group of resonators is composed of a capacitor C and an inductor L with different resistances connected in series. One end of each group of resonators is connected to the power line, and the other end is connected to the N line; the inductor of the resonator and the secondary coil are both wound around the magnetic core. Among each group of resonators, capacitor C2 and inductor L2 resonate with the second harmonic, capacitor C3 and inductor L3 resonate with the third harmonic,..., capacitor C m+1 and inductor L m+1 resonate with the (m + 1)th harmonic;

[0033] The boost converter consists of capacitors (C b1 , C b2 ,..., C bn ) and diodes (VD1, VD2,..., VD n ). It can convert AC harmonics into DC.

[0034] The filter voltage regulator consists of an inductor L, a capacitor C, and a zener diode VD, and can stabilize the DC voltage of the rectifier within the operating voltage range of the active EMI filter.

[0035] The battery is a rechargeable battery. When there is sufficient harmonic energy on the line, the battery can store energy. When there is insufficient harmonic energy on the line, the battery can supply power to the active EMI filter.

[0036] The single-pole to bipolar circuit is provided with voltage-dividing resistors R1, R2 and filter capacitors C q1 , C q2 , C q3 , C q4 , providing a stable bipolar voltage for the active EMI filter.

[0037] The design method of the power supply circuit of the active EMI filter for extracting harmonic energy of the present invention specifically includes the following process:

[0038] Set the effective value of the line voltage of the switched power converter as U, and the effective value of the voltage of the i-th harmonic is denoted as U i , and the effective value of the current is denoted as I i (i = 2, 3...n).

[0039] Step 1, design the harmonic inductor;

[0040] Step 1.1, design the number m of resonators in the harmonic inductor;

[0041] The number m of resonators in the harmonic inductor is designed according to the harmonic power. Starting from the 2nd harmonic, calculate the power of each harmonic in turn (the power of the i-th harmonic is denoted as P i , P i = U i × I i ). When the power P j of the j-th harmonic is greater than 1 mW; and the power P j+1 of the j + 1-th harmonic is less than 1 mW, take j - 1 as the value of m.

[0042] Step 1.2, design the resonant frequency f i (i = 2, 3,..., m + 1) of the i-th resonator in the harmonic inductor;

[0043] The resonant frequency f iDesigned by the formula f i = i·f0.

[0044] Where f0 is the operating frequency of the device to be filtered. When the device to be filtered is powered by connecting to an AC 50Hz power grid, f0 takes 50Hz; otherwise, f0 takes the switching frequency of the device to be filtered, with the unit of Hz.

[0045] Step 1.3, design the maximum operating frequency f of the magnetic core in the harmonic inductor max ;

[0046] The maximum operating frequency of the magnetic core is designed by f max = f0·(m + 1);

[0047] Step 1.4, design the material of the magnetic core in the harmonic inductor;

[0048] The material of the magnetic core in the harmonic inductor ensures that its relative permeability μ r is greater than 1000 within 0Hz to f max and nanocrystalline material is recommended.

[0049] Step 1.5, design the inner diameter d and outer diameter D of the magnetic core in the harmonic inductor;

[0050] The inner diameter d of the magnetic core in the harmonic inductor is designed according to the line voltage level.

[0051] When the line voltage U is less than 36V, the inner diameter d of the magnetic core is designed by the following formula:

[0052] Unit: cm;

[0053] When the line voltage U is 36 to 100V, the inner diameter d of the magnetic core is designed by the following formula:

[0054] Unit: cm;

[0055] When the line voltage U is above 100V, the inner diameter d of the magnetic core is selected as 1.8cm;

[0056] The outer diameter D of the magnetic core in the harmonic inductor is obtained by the formula D = 1.2d + 0.8, with the unit of cm.

[0057] Step 1.6, design the magnetic path length L of the magnetic core in the harmonic inductor e ;

[0058] The magnetic path length L of the magnetic core in the harmonic inductor e is designed by the formula ;

[0059] Step 1.7, design the cross-sectional area A of the magnetic core in the harmonic inductor e;

[0060] The cross-sectional area A of the magnetic ring in the harmonic inductor e From the formula Design.

[0061] Step 1.8, design the inductance L in the i-th resonator of the harmonic inductor i The internal resistance R of the inductance i ;

[0062] The inductance L in the i-th resonator of the harmonic inductor i The internal resistance R of the inductance i From the formula Design.

[0063] Step 1.9, design the capacitance value C of the i-th resonator of the harmonic inductor i ;

[0064] The capacitance value of the i-th resonator of the harmonic inductor is designed by the formula Design;

[0065] Where Q is the quality factor of the resonator, take 12; R i Is the internal resistance of the inductance L in the i-th resonator i Of the inductance.

[0066] Step 1.10, design the inductance value L of the i-th resonator of the harmonic inductor i ;

[0067] The inductance value L of the i-th resonator i From the formula Design.

[0068] Where Q is the quality factor of the resonator, take 12, R i Is the internal resistance of the inductance L in the i-th resonator i Of the inductance.

[0069] Step 1.11, design the number of turns n of the inductance coil of the i-th resonator of the harmonic inductor i ;

[0070] The number of turns n of the inductance coil of the i-th resonator of the harmonic inductor i From the formula Design;

[0071] Where L i Is the inductance value of the i-th resonator; L e Is the magnetic path length of the magnetic ring; u0 is the vacuum permeability; u r Is the relative permeability of the magnetic ring; A e Is the cross-sectional area of the magnetic ring.

[0072] Step 1.12, determine the harmonic order K corresponding to the maximum harmonic power in the circuit;

[0073] Calculate the power of the harmonics from the 2nd to the (m + 1)th in sequence. When the power of the kth harmonic is the maximum, record: P k as the maximum harmonic power; U k as the harmonic voltage corresponding to the maximum harmonic power, I k as the harmonic current corresponding to the maximum harmonic power, f k as the resonance frequency corresponding to the maximum harmonic power, n k as the number of turns of the inductor coil L corresponding to the kth harmonic K .

[0074] Step 1.13, design the number of turns n of the secondary coil in the harmonic inductor.

[0075] Design the number of turns n of the secondary coil in the harmonic inductor to be equal to n k .

[0076] Step 2, design the booster;

[0077] Step 2.1, design the supply voltage U AEF of the active EMI filter.

[0078] Step 2.2, design the boosting multiple b of the booster;

[0079] The boosting multiple b of the booster is designed by the maximum harmonic voltage U k and the supply voltage U AEF of the active EMI filter (AEF). The boosting multiple b is calculated by U AEF / U k . When the calculated value is a non-integer, then by rounding up, expand the calculated value to the minimum value that is an integer multiple of 2, which is the value of b. For example: calculating U AEF / U k gives a ratio of 13.2. Expand the value of 13.2 to the minimum value that is an integer multiple of 2, which is 14.

[0080] Step 2.3, design the diodes of the booster;

[0081] The total number of diodes of the booster is set to b; low on-state voltage drop diodes are selected for the diodes of the booster, and the on-state voltage drop is selected as 0.2V.

[0082] Step 2.4, design the capacitors of the booster;

[0083] The total number of capacitors of the booster is set to b; the capacitance value of the capacitors of the booster is selected as 10uF.

[0084] Step 3, design the filter voltage regulator;

[0085] Step 3.1, design the ripple coefficient A of the power supply for the active EMI filter cv ;

[0086] The ripple coefficient A of the power supply for the active EMI filter cv is set to 1%.

[0087] Step 3.2, design the capacitance value C of the filter voltage regulator;

[0088] The capacitance value of the filter voltage regulator is designed according to the following formula:

[0089]

[0090] where f k is the resonance frequency corresponding to the maximum harmonic power; U k is the harmonic voltage corresponding to the maximum harmonic power, and I k is the harmonic current corresponding to the maximum harmonic power; A cv is the ripple coefficient of the active EMI filter.

[0091] Step 3.2, design the inductance L of the filter voltage regulator;

[0092] The inductance value L of the filter voltage regulator is designed according to the following formula:

[0093]

[0094] where: f k is the resonance frequency corresponding to the maximum harmonic power; k2 is the cut-off frequency control factor, taking 0.6.

[0095] Step 3.3, design the regulated voltage value U VD ;

[0096] Design the regulated voltage value U VD of the zener diode to be U AEF .

[0097] Step 4, design the battery;

[0098] Step 4.1, design the total harmonic input power P in ;

[0099] Calculate the power of the harmonics from the 2nd to the m+1th in sequence. The total harmonic input power is designed by the formula P in = P2 + P3 +... + P m+1 .

[0100] Step 4.2, design the capacity W of the battery;

[0101] The battery is a rechargeable battery. When the harmonic energy harvesting is insufficient to enable the active EMI filter to operate, the battery supplies supplementary energy. The capacity is designed by the formula W = t·(P EMI -k3·k in ·P in ).

[0102] Where: t is the rated usage time of the battery; P EMI is the rated power of the active EMI filter; k3 is the conversion efficiency of the power supply device, taking 0.85; k in is the harmonic conversion efficiency, taking 0.75; P in is the total harmonic input power.

[0103] Step 5, design a single-pole to double-pole circuit;

[0104] For the single-pole to double-pole circuit, the resistors R1 and R2 satisfy R1 = R2. Select high-value and high-precision resistors. The recommended resistance value is 100K and the precision is 0.1%; the voltage-stabilizing capacitors C q1 , C q2 satisfy C q1 = C q2 . Select electrolytic capacitors, taking 4.7 - 10uF; the voltage-stabilizing capacitors C q3 , C q4 satisfy C q3 = C q4 , select non-polar capacitors, and the capacitance value of C q3 is taken as 100 times the capacitance value of C q1 .

Claims

1. The power supply circuit of an active EMI filter for extracting energy from power harmonics, characterized in that: It includes a harmonic inductor, which is sequentially connected to a step-up transformer, a filter voltage regulator, and a single-pole to double-pole circuit. A battery is connected between the filter voltage regulator and the single-pole to double-pole circuit; The harmonic inductor includes a magnetic ring, a secondary coil, and m groups of resonators. Each group of resonators is composed of a capacitor and an inductor with different values connected in series. One end of each group of resonators is connected to the power line, and the other end is connected to the N line; the inductor and the secondary coil in each group of resonators are wound around the magnetic ring; The step-up transformer includes n diodes connected in parallel, and a capacitor is connected between adjacent two diodes. There are n diodes and n capacitors; The design process of the harmonic inductor is as follows: Design the number m of resonators in the harmonic inductor, specifically: The number m of resonators in the harmonic inductor is designed according to the harmonic power. Starting from the second harmonic, the power of each harmonic is calculated in turn. The power of the i-th harmonic is denoted as P i , P i =U i ×I i . When the power P j of the j-th harmonic is greater than 1 mW; and the power P j+1 of the (j + 1)-th harmonic is less than 1 mW, then j - 1 is taken as the value of m; Design the resonant frequency f of the i-th resonator in the harmonic inductor i , where i = 2, 3,..., m + 1; The resonant frequency f of the i-th resonator i is designed by the formula design; Where f0 is the operating frequency of the filtered device. When the filtered device is powered by an AC 50Hz power grid, f0 takes 50Hz; otherwise, f0 takes the switching frequency of the filtered device, with the unit of Hz; The maximum operating frequency f of the magnetic ring in the designed harmonic inductor max ; The maximum operating frequency of the magnetic ring is determined by Design; Design the inner diameter d and outer diameter D of the magnetic ring in the harmonic inductor; the inner diameter d of the magnetic ring in the harmonic inductor is designed according to the line voltage level: When the line voltage U is less than 36V, the inner diameter d of the magnetic ring is designed by the following formula: , unit: cm; (1) When the line voltage U is between 36V and 100V, the inner diameter d of the magnetic ring is designed by the following formula: , unit: cm (2) The outer diameter D of the magnetic ring in the harmonic inductor is obtained from the formula and the unit is cm. Design the capacitance value C of the i-th resonator in the harmonic inductor i ; The capacitance value of the ith resonator in the harmonic inductor is given by the formula Design; where Q is the quality factor of the resonator, taking 12; R i is the internal resistance of the inductor L i in the i-th resonator; Design the inductance value L of the i-th resonator in the harmonic inductor i , the inductance value L of the i-th resonator i is designed by the formula ; where Q is the quality factor of the resonator, and R i is the internal resistance of the inductor L i in the i-th resonator; Design the number of turns n of the inductor coil of the i-th resonator in the harmonic inductor i ; The number of turns n of the inductance coil of the i-th resonator in the harmonic inductor i From the formula Design; where L i is the inductance value of the i-th resonator; L e is the magnetic path length of the magnetic core; u0 is the permeability of free space; u r is the relative permeability of the magnetic core; A e is the cross-sectional area of the magnetic core; The design process of the step-up transformer is as follows: Supply voltage U for designing an active EMI filter AEF ; Design the step-up multiple b of the step-up transformer; The boost multiple b of the boost converter is determined by the maximum harmonic voltage U k and the supply voltage U AEF of the active EMI filter; the boost multiple b is designed as a non-integer value calculated from U AEF / U k and then, through rounding, the calculated value is expanded to the minimum value that is an integer multiple of 2, which is the value of b.

2. The power supply circuit of the active EMI filter for power supply harmonic energy extraction according to claim 1, characterized in that: The filter voltage regulator includes a capacitor C, a zener diode VD, and an inductor L connected in parallel.

3. The power supply circuit of the active EMI filter for power supply harmonic energy harvesting according to claim 1, characterized in that: The single-pole to bipolar circuit includes voltage-dividing resistors R1 and R2, and filter capacitors C are respectively connected in parallel across both ends of the voltage-dividing resistor R1 q1 , C q2 ; filter capacitors C are respectively connected in parallel across both ends of the voltage-dividing resistor R2 q3 , C q4 .

4. The power supply circuit of the active EMI filter for power supply harmonic energy harvesting according to claim 1, wherein: The capacitance value C of the filter voltage regulator is designed by formula (3): （3）； where: f k is the resonant frequency corresponding to the maximum harmonic power; U k is the harmonic voltage corresponding to the maximum harmonic power, I k is the harmonic current corresponding to the maximum harmonic power; A cv is the ripple coefficient of the active EMI filter; The inductance value L of the filter voltage regulator is designed by formula (4): （4）； Where k2 is the cut-off frequency control factor.

5. The power supply circuit of the active EMI filter for power supply harmonic energy extraction according to claim 1, characterized in that: The capacity of the battery is designed by the following formula (5): （5） Wherein, W is the capacity of the battery, t is the rated usage time of the battery; P EMI is the rated power of the active EMI filter; k3 is the conversion efficiency of the power supply device, k in is the harmonic conversion efficiency, P in is the total harmonic input power.

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