A frequency conversion control method for achieving low total harmonic content of input current of SWISS rectifier

Abstract

The present invention discloses a variable frequency control method for realizing low input current total harmonic content of a SWISS rectifier, which includes the following steps: Step 1, within a high-frequency switching cycle time T s , the SWISS rectifier first transfers energy by the output voltage u H of the first high-frequency bridge, and then transfers energy by the output voltage u L of the second high-frequency bridge, and then enters the freewheeling stage; Step 2, when the leakage inductance current drops to 0, that is, when the freewheeling stage ends, the forward magnetization of the transformer ends, and the SWISS rectifier immediately enters the negative magnetization stage; Step 3, in the negative magnetization stage, energy is transferred by the output voltage u H of the first high-frequency bridge, and then energy is transferred by the output voltage u L of the second high-frequency bridge, and then enters the freewheeling stage. When the leakage inductance current drops to 0, the rectifier starts to enter the next switching cycle for operation. The present invention can effectively reduce the input current THD, reduce the volume of magnetic components, and improve the power density.

Description

Technical Field

[0001] The invention relates to the technical field of three-phase AC / DC converters, in particular to a frequency conversion control method for realizing low total harmonic content of input current of a SWISS rectifier. Background Art

[0002] The three-phase pulse width modulation (PWM) rectifier uses fully controlled power devices, which can well control the input current waveform and phase, and can achieve high power factor. It has been widely studied and applied. SWISS rectifier is a new type of step-down three-phase PWM rectifier with high efficiency, high power factor, no input current impact, single-stage isolated step-down conversion and wide output voltage range. It has good application prospects in a wide range of fields such as uninterruptible power supply, variable frequency speed regulation, electric vehicle charging, high-power lighting, aviation power supply, etc.

[0003] In order to solve the problems of duty cycle loss, high input current THD, low power density, etc. caused by the DC filter inductor of the SWISS rectifier output, some literatures have proposed a SWISS rectifier without DC filter inductor. The rectifier operates in leakage current discontinuous mode (DCM). In this mode, the high-frequency switching cycle must be greater than the modulation time of the rectifier high-frequency switch tube when running at full load. Since the rectifier operates at a constant switching frequency, the modulation time accounts for a smaller proportion of the switching cycle when operating at medium and low power levels than when fully loaded. Especially under low power level operating conditions, the transformer leakage inductance current is "narrow and sharp", which will affect the quality of the input current waveform and is not conducive to reducing the rectifier input current THD. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a frequency conversion control method for achieving low total harmonic content of input current of SWISS rectifier, which can effectively reduce input current THD, reduce the volume of magnetic components and improve power density.

[0005] In order to solve the above technical problems, the present invention provides a frequency conversion control method for realizing low total harmonic content of input current of SWISS rectifier, comprising the following steps:

[0006] Step 1: In a high-frequency switching cycle time T s The SWISS rectifier first outputs the voltage u H The energy is transferred, and then the second high-frequency bridge outputs the voltage u L Transfer energy and then enter the freewheeling phase;

[0007] Step 2: When the leakage inductance current drops to 0, that is, the freewheeling stage ends, the transformer forward magnetization ends, and the SWISS rectifier immediately enters the negative magnetization stage;

[0008] Step 3: In the negative magnetization stage, the first high-frequency bridge outputs a voltage u H The energy is transferred, and then the second high-frequency bridge outputs the voltage u L Energy is transferred and then the freewheeling stage is entered. When the leakage inductance current drops to 0, the rectifier starts to work in the next switching cycle.

[0009] Preferably, in step 2, the SWISS rectifier operates in a critical discontinuous state of the leakage inductance current, that is, the next magnetization stage starts immediately when the leakage inductance current drops to 0, and operates in a variable frequency control mode, and the ideal switching frequency f of each switching cycle is s_cal It is calculated that within half a switching cycle, u H The energy transfer time is t H ,u L The energy transfer time is t L The follow-up phase time is t D , and satisfy: t H +t L +t D =T s_cal / 2.

[0010] Preferably, in step 3, in order to realize the rectifier variable frequency control, the zero-crossing state of the leakage inductance current is detected to assist in indicating the start of the high-frequency switching cycle, which specifically includes the following steps:

[0011] Step 31, the control unit includes a threshold comparator hardware circuit, FPGA and MCU, the leakage inductance current obtained by sampling passes through the threshold comparator to obtain the leakage inductance current zero crossing flag Zreoc, and the zero crossing flag is connected to the FPGA; a counter is set in the FPGA to increase every 10ns, the counter output value is Cnt, and the counter output value Cnt is set to zero when the zero crossing flag Zreoc is set high;

[0012] Step 32: When the counter output value Cnt is 0, enable the MCU to perform sampling and calculation, and respectively calculate the three-phase input voltage u of the SWISS rectifier. a 、u b 、u c , DC output voltage u o Sampling is performed and the sampled voltage u a 、u b 、u c The input voltage peak value U is calculated by the phase-locked loop m and phase θ; according to the DC output voltage u obtained by sampling o The DC output voltage converted to the transformer primary voltage u is calculated by using the transformer ratio N. s =Nu o ;

[0013] Step 33: According to the input voltage peak value Um The output voltage u of the first high-frequency bridge in this control cycle is calculated by using the phase θ H The second high-frequency bridge output voltage u L , according to the three-phase input current peak reference value I m * The first current modulation target i of the bus in this control cycle is calculated by using the phase θ H With the second current modulation target i L ;

[0014] Step 34: According to the transformer leakage inductance L r , switching cycle T s , the first high-frequency bridge output voltage u H The second high-frequency bridge output voltage u L and the first current modulation target i H With the second current modulation target i L , calculate the auxiliary variable temp H With temp L , and then calculate the ideal switching frequency f of this cycle s_cal ;

[0015] Step 35: According to the auxiliary variable temp H 、temp L , and the ideal switching frequency f s_cal The first modulation time t of the high-frequency power tube can be calculated H With the second modulation time t L ;

[0016] Step 36: set the first modulation time t of the high frequency power tube H With the second modulation time t L For 10 8 Multiply to obtain the first modulation comparison value Cnt H Compare with the second modulation value Cnt L , the first modulation comparison value Cnt H Compare with the second modulation value Cnt L The signal is transmitted to FPGA and compared with the counter output value Cnt to generate a high-frequency power tube control signal to control the operation of the high-frequency power tube of the SWISS rectifier.

[0017] Preferably, in step 33, the first current modulation target i of the bus within the control period is calculated. H With the second current modulation target i L for:

[0018]

[0019] Preferably, in step 34, the auxiliary variable temp is calculatedH With temp L , and then calculate the ideal switching frequency f of this cycle s_cal for:

[0020]

[0021] Preferably, in step 35, the first modulation time t of the high-frequency power tube is calculated. H With the second modulation time t L for:

[0022]

[0023] The beneficial effects of the present invention are as follows: in the present invention, the rectifier operates in the critical discontinuous mode of the leakage current, and the total modulation duration of the high-frequency switch tube accounts for 100% of the switching period, which can effectively reduce the input current THD; compared with the current discontinuous mode, when the average current value is constant, the leakage current peak value working in the critical discontinuous mode of the leakage current is smaller; under variable frequency control, the switching frequency of the high-frequency switch tube is relatively high, which can reduce the volume of magnetic components and improve power density. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a circuit structure diagram of the SWISS rectifier of the present invention.

[0025] FIG. 2( a ) is a waveform diagram of the input voltage expansion circuit of the SWISS rectifier of the present invention.

[0026] FIG. 2( b ) is a diagram showing an ideal current waveform of a SWISS rectifier busbar according to the present invention.

[0027] Figure 3 This is a schematic diagram of the modulation method of the present invention.

[0028] Figure 4 (a) shows the forward magnetization u of the transformer of the present invention H Schematic diagram of working status during power transfer stage.

[0029] Figure 4(b) shows the forward magnetization u of the transformer of the present invention. L Schematic diagram of working status during power transfer stage.

[0030] FIG4( c ) is a schematic diagram of the working state of the transformer of the present invention in the forward magnetization freewheeling stage.

[0031] Figure 4(d) shows the negative magnetization u of the transformer of the present invention. H Schematic diagram of working status during power transfer stage.

[0032] Figure 4(e) shows the negative magnetization u of the transformer of the present invention. L Schematic diagram of working status during power transfer stage.

[0033] FIG4( f ) is a schematic diagram of the working state of the transformer of the present invention during the negative magnetization freewheeling stage.

[0034] Figure 5 This is a flow chart of the frequency conversion control method of the present invention.

[0035] FIG. 6( a ) is a simulation waveform diagram of the input and output of the rectifier when the present invention is operating at 5 kW.

[0036] FIG. 6( b ) is a diagram showing the voltage and current simulation waveforms of the transformer when the present invention is running at 5 kW.

[0037] FIG. 7( a ) is a diagram showing the simulated waveforms of the rectifier input and output when the present invention is operating at 2.5 kW.

[0038] FIG. 7( b ) is a simulation waveform of transformer voltage and current when the present invention is running at 2.5 kW. DETAILED DESCRIPTION

[0039] A frequency conversion control method for realizing low total harmonic content of input current of a SWISS rectifier comprises the following steps:

[0040] Step 1: In a high-frequency switching cycle time T s The SWISS rectifier first outputs the voltage u H The energy is transferred, and then the second high-frequency bridge outputs the voltage u L Transfer energy and then enter the freewheeling phase;

[0041] Step 2: When the leakage inductance current drops to 0, that is, the freewheeling stage ends, the transformer forward magnetization ends, and the SWISS rectifier immediately enters the negative magnetization stage;

[0042] Step 3: In the negative magnetization stage, the first high-frequency bridge outputs a voltage u H The energy is transferred, and then the second high-frequency bridge outputs the voltage u L Energy is transferred and then the freewheeling stage is entered. When the leakage inductance current drops to 0, the rectifier starts to work in the next switching cycle.

[0043] Figure 1 The topological structure diagram of the SWISS rectifier is composed of a three-phase input filter, a voltage expansion circuit, and a high-frequency isolation conversion circuit. The corresponding nodes of the three buses at the output end of the voltage expansion circuit are defined as x, y, and z, respectively, and the current flowing through is i x 、i y 、i z The present invention sets the appropriate high-frequency tube switch timing and conduction time to make the high-frequency bridge output voltage u ab The first high-frequency bridge output voltage u appears in sequence H , the second high-frequency bridge output voltage uL , 0 three levels, the secondary amplitude of the high-frequency isolation transformer is an alternating square wave of the DC output voltage value, realizing the transformer leakage inductance L r The left end is the "high-low-zero" three-level voltage, and the right end is the transformer secondary voltage u cd The voltage converted to the primary side is u s The voltage difference across the leakage inductor causes the leakage inductor current to increase or decrease, thereby achieving the purpose of controlling the transferred energy.

[0044] As shown in Figure 2(a), the bidirectional switch of the voltage expansion circuit switches on according to the three-phase voltage phase θ. A grid cycle can be divided into 12 sectors, and the voltage u xy with u yz It is a triangular wave. Through the alternating conduction of the bidirectional switch tube, the three-phase input current flows into the three buses of the expansion circuit respectively. Taking sector 1 as an example, the bus current i x 、i y 、i z Corresponding to the three-phase current i a 、i b 、i c Therefore, the bus current can be controlled with the three-phase input current as the modulation target. The ideal bus current waveform of the SWISS rectifier is shown in Figure 2(b).

[0045] According to the different conduction combinations of the power tubes in the high-frequency isolation conversion circuit, the output voltage u of the high-frequency bridge ab There are three voltage combinations: (1) a and b are connected to x and z respectively, and the transformer is positively magnetized; a and b are connected to z and x respectively, and the transformer is negatively magnetized. The voltage across a and b in this combination is defined as the output voltage u of the first high-frequency bridge H ; (2) a and b are connected to x and y respectively, the transformer is positively magnetized, a and b are connected to y and x respectively, the transformer is negatively magnetized; or a and b are connected to y and z respectively, the transformer is positively magnetized, a and b are connected to z and y respectively, the transformer is negatively magnetized. The voltage across a and b in this combination is defined as the output voltage u of the second high-frequency bridge L ; (3) a and b are connected, the transformer leakage current continues to flow, and the voltage between a and b is 0. cd The voltage converted to the primary side is defined as u s ,u s The amplitude is Nu o square wave.

[0046] Figure 3 The modulation method schematic diagram shows that in a high-frequency switching cycle time T s The SWISS rectifier first outputs the voltage u H The energy is transferred, and then the second high-frequency bridge outputs the voltage uL Energy is transferred, and then the freewheeling stage is entered. When the leakage inductance current drops to 0, that is, the freewheeling stage ends, the transformer forward magnetization ends, and the SWISS rectifier immediately enters the negative magnetization stage; in the negative magnetization stage, the first high-frequency bridge outputs a voltage u H The energy is transferred, and then the second high-frequency bridge outputs the voltage u L Energy is transferred, and then the freewheeling stage is entered. When the leakage current drops to 0, the rectifier starts to work in the next switching cycle. The output voltage u H The average current flowing from the transformer leakage inductance into the busbar during the energy transfer period is the first modulation current i H ; The second high-frequency bridge output voltage u L The average current flowing into the busbar from the transformer leakage inductance during the energy transfer period is the second modulation current i L .

[0047] The SWISS rectifier operates in the critical discontinuous state of the high-frequency AC tank circuit (transformer primary side) current (also the transformer leakage current), that is, when the leakage current drops to 0, the next magnetization stage begins immediately, and operates in the variable frequency control mode. The ideal switching frequency f s_cal It is calculated that within half a switching cycle, u H The energy transfer time is t H ,u L The energy transfer time is t L The follow-up phase time is t D , and satisfy: t H +t L +t D =T s_cal / 2.

[0048] It should be pointed out that due to the y bus current i y The direction is determined each time the energy is transferred, so in a complete power transfer cycle, u L Voltage u during energy transfer ab Only the x and y busbars or the y and z busbars bear the load. The detailed working process of the SWISS rectifier under the modulation method of the present invention when the y busbar current is positive is as follows Figure 4(a)-Figure 4(f) shown.

[0049] Taking the three-phase voltage phase θ∈[π / 6,π / 3] and the transformer forward magnetization (as shown in FIG. 4(a)-(c)) as an example, the working process of the SWISS rectifier under the modulation method of the present invention is analyzed:

[0050] (c1)u H Transfer energy: As shown in Figure 4(a), the power transfer time in this mode is the first modulation time t H , we can get the average current i flowing into the bus in this modeH for:

[0051]

[0052] (c2)u L Transfer energy: As shown in Figure 4(b), the power transfer time in this mode is the second modulation time t L , we can get the average current i flowing into the bus in this mode L for:

[0053]

[0054] (c3) Freewheeling stage: As shown in Figure 4(c), the power transfer time in this mode is t D , we can get the average transformer leakage inductance current i in this mode D for:

[0055]

[0056] Taking the negative magnetization of the transformer (as shown in FIG. 4( d )-( f )) as an example, the working process of the SWISS rectifier under the modulation method of the present invention is analyzed:

[0057] (c4)u H Transfer energy: As shown in Figure 4(d), the power transfer time in this mode is the first modulation time t H , we can get the average current i flowing into the bus in this mode H for:

[0058]

[0059] (c5)u L Transfer energy: As shown in Figure 4(e), the power transfer time in this mode is the second modulation time t L , we can get the average current i flowing into the bus in this mode L for:

[0060]

[0061] (c6) Freewheeling stage: As shown in Figure 4(f), the power transfer time in this mode is t D , we can get the average transformer leakage inductance current i in this mode D for:

[0062]

[0063] The modulation method of the present invention uses the three-phase input current as the modulation target to control the bus current. When θ∈[π / 6,π / 3], the current i L Through the y busbar into the b phase, i HThe current i flows into phase a through the x bus, that is, the ideal current of phase b is used as the reference to modulate the current i L , taking the ideal current of phase a as the reference, the modulation current i H . Then the ideal modulation target can be expressed as:

[0064]

[0065] During the switching period T s , Transformer leakage inductance value L r When the control period u is determined, the combination of equations (4)-(6) can be calculated to obtain H with u L The modulation time is:

[0066]

[0067] The same is true when θ is in other intervals. Therefore, the modulation method of the present invention only needs to obtain the three-phase input voltage peak value U m And phase θ, and then calculate u within a control cycle H 、u L 、i H * with i L * , then combined with the known switching period T s and transformer leakage inductance L r The modulation time t in the control cycle can be obtained H With t L .

[0068] Figure 5 The flow chart of the modulation method of the present invention is shown, and the details are as follows:

[0069] 1) The control unit consists of a threshold comparator hardware circuit, FPGA and MCU. The sampled leakage inductance current passes through the threshold comparator to obtain the leakage inductance current zero-crossing flag Zreoc, and the zero-crossing flag is connected to the FPGA; a counter that increases every 10ns is set in the FPGA to control the high-frequency switching cycle. The output value of the counter is Cnt. When the zero-crossing flag Zreoc is set high, the counter output value Cnt can be set to zero.

[0070] 2) When the counter output value Cnt is 0, the MCU is enabled to sample and calculate the three-phase input voltage u of the SWISS rectifier. a 、u b 、u c , DC output voltage u o Sampling is performed and the sampled voltage u a 、u b 、u cThe input voltage peak value U is calculated by the phase-locked loop m and phase θ; according to the DC output voltage u obtained by sampling o The DC output voltage converted to the transformer primary voltage u is calculated by using the transformer ratio N. s =Nu o ;

[0071] 3) According to the input voltage peak value U m The output voltage u of the first high-frequency bridge in this control cycle is calculated by using the phase θ H The second high-frequency bridge output voltage u L , according to the three-phase input current peak reference value I m * The first current modulation target i of the bus in this control cycle is calculated by using the phase θ H With the second current modulation target i L :

[0072]

[0073] 4) According to the transformer leakage inductance L r , switching cycle T s , the first high-frequency bridge output voltage u H The second high-frequency bridge output voltage u L and the first current modulation target i H With the second current modulation target i L , calculate the auxiliary variable temp H With temp L , and then calculate the ideal switching frequency f of this cycle s_cal for:

[0074]

[0075] 5) According to the auxiliary variable temp H 、temp L , and the ideal switching frequency f s_cal The first modulation time t of the high-frequency power tube can be calculated H With the second modulation time t L for:

[0076]

[0077] 6) Set the first modulation time t of the high frequency power tube H With the second modulation time t L For 10 8 Multiply to obtain the first modulation comparison value Cnt H Compare with the second modulation value Cnt L , the first modulation comparison value CntH Compare with the second modulation value Cnt L The signals are transmitted to FPGA and compared with the counter output value Cnt to generate eight high-frequency power tube control signals to control the operation of the high-frequency power tube of the SWISS rectifier.

[0078] The high-frequency switch modulation duration calculation requires the switching period T s , and in the frequency conversion control process T s is a variable, so the switching cycle duration must be obtained before the modulation duration is calculated. From formula (8), it can be seen that the total working time of the SWISS rectifier without DC filter inductor in half a switching cycle is t s It can be expressed as:

[0079]

[0080] Where D y is the ratio of the working time to the switching period. At the same time, the modulation time t H With t L The calculation formula can be obtained:

[0081]

[0082] In the formula, temp H With temp L They are all independent of the switching cycle and can be expressed as:

[0083]

[0084] Combining equations (12) and (13), we can obtain:

[0085]

[0086] D y = 0.5 Substituting into the above formula, we can get the ideal switching frequency f when the rectifier works in the critical discontinuous mode of leakage inductance current. s_cal , expressed as:

[0087]

[0088] Combined with formula (13), the high-frequency switch modulation duration under the ideal switching cycle can be obtained:

[0089]

[0090] Through equations (14)-(17), when the three-phase input voltage, three-phase input current reference, and leakage inductance value are known, temp is first calculated H With temp L, further calculations are performed to obtain the ideal switching frequency f that enables the rectifier to operate in the critical discontinuous mode of leakage inductance current. s_cal , and finally according to temp H 、temp L With f s_cal The modulation duration of the high-frequency switch tube is calculated.

[0091] It can be seen from Figure 6(a) that the switching frequency varies between 43k and 60kHz when running at full load (5kW), and the input current THD is 2.19% when running at full load; it can be seen from Figure 7(a) that the switching frequency varies between 90k and 120kHz when running at half load (2.5kW), and the input current THD is 0.80% when running at half load. It can be seen from Figure 6(b) and Figure 7(b) that the leakage inductance current increases or decreases through the voltage difference across the leakage inductance, and the voltage u ab with u s The rising edges coincide and the leakage inductance current works in critical discontinuous mode, which meets the design requirements of the variable frequency control method.

Claims

1. A frequency conversion control method for achieving low total harmonic content of input current of a SWISS rectifier, characterized in that: The steps include: Step 1: In a high-frequency switching cycle time T s The SWISS rectifier first outputs the voltage u H The energy is transferred, and then the second high-frequency bridge outputs the voltage u L Transfer energy and then enter the freewheeling phase; Step 2: When the leakage current drops to 0, that is, the freewheeling stage ends, the transformer forward magnetization ends, and the SWISS rectifier immediately enters the negative magnetization stage; the SWISS rectifier works in the critical discontinuous state of the leakage current, that is, when the leakage current drops to 0, the next magnetization stage begins immediately, and works in the variable frequency control mode. The ideal switching frequency f of each high-frequency switching cycle is s_cal It is calculated that within half a high-frequency switching cycle, u H The energy transfer time is t H ,u L The energy transfer time is t L , the follow-up phase time is t D , high frequency switching cycle ideal switching frequency f s_cal The reciprocal of s_cal , and satisfy: t H +t L +t D =T s_cal / 2; Step 3: In the negative magnetization stage, the first high-frequency bridge outputs a voltage u H The energy is transferred, and then the second high-frequency bridge outputs the voltage u L Energy is transferred and then the freewheeling stage is entered. When the leakage inductance current drops to 0, the rectifier starts to enter the next high-frequency switching cycle.

2. The frequency conversion control method for realizing low total harmonic content of input current of SWISS rectifier according to claim 1, characterized in that: In step 2 and step 3, in order to realize the rectifier variable frequency control, the zero-crossing state of the leakage inductance current is detected to assist in indicating the start of the high-frequency switching cycle, which specifically includes the following steps: Step 31, the control unit includes a threshold comparator hardware circuit, FPGA and MCU, the leakage inductance current obtained by sampling passes through the threshold comparator to obtain the leakage inductance current zero crossing flag Zreoc, and the zero crossing flag is connected to the FPGA; a counter is set in the FPGA to increase every 10ns, the counter output value is Cnt, and the counter output value Cnt is set to zero when the zero crossing flag Zreoc is set high; Step 32: When the counter output value Cnt is 0, enable the MCU to perform sampling and calculation, and respectively calculate the three-phase input voltage u of the SWISS rectifier. a 、u b 、u c , DC output voltage u o Sampling is performed and the sampled voltage u a 、u b 、u c The input voltage peak value U is calculated by the phase-locked loop m and phase θ; according to the DC output voltage u obtained by sampling o The DC output voltage converted to the transformer primary voltage u is calculated by using the transformer ratio N. s =Nu o ; Step 33: According to the input voltage peak value U m The output voltage u of the first high-frequency bridge in the high-frequency switching cycle is calculated and the phase θ is controlled. H The second high-frequency bridge output voltage u L , according to the three-phase input current peak reference value I m * The first current modulation target i of the bus in the high-frequency switching cycle is calculated and the phase θ is used to control the first current modulation target i of the bus in the high-frequency switching cycle. H With the second current modulation target i L ; Step 34: According to the transformer leakage inductance L r , high frequency switching period T s , the first high-frequency bridge output voltage u H The second high-frequency bridge output voltage u L and the first current modulation target i H With the second current modulation target i L , calculate the auxiliary variable temp H With temp L , and then calculate the ideal switching frequency f of the high-frequency switching cycle s_cal ; Step 35: According to the auxiliary variable temp H 、temp L , and the ideal switching frequency f s_cal The first modulation time t of the high-frequency power tube can be calculated H With the second modulation time t L ; Step 36: set the first modulation time t of the high frequency power tube H With the second modulation time t L For 10 8 Multiply to get the first modulation comparison value Cnt H Compare with the second modulation value Cnt L , the first modulation comparison value Cnt H Compare with the second modulation value Cnt L The signal is transmitted to FPGA and compared with the counter output value Cnt to generate a high-frequency power tube control signal to control the operation of the high-frequency power tube of the SWISS rectifier.

3. The frequency conversion control method for realizing low total harmonic content of input current of SWISS rectifier according to claim 2, characterized in that: In step 33, the first current modulation target i of the bus in the high-frequency switching cycle is calculated and obtained. H With the second current modulation target i L for:

4. The frequency conversion control method for realizing low total harmonic content of input current of SWISS rectifier according to claim 2, characterized in that: In step 34, the auxiliary variable temp is calculated H With temp L , and then calculate the ideal switching frequency f of the high-frequency switching cycle s_cal for:

5. The frequency conversion control method for realizing low total harmonic content of input current of SWISS rectifier according to claim 2, characterized in that: In step 35, the first modulation time t of the high-frequency power tube is calculated. H With the second modulation time t L for:

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