CN118112345A - A common-mode interference analysis method for four-switch buck-boost converter - Google Patents

Abstract

The invention discloses a common mode interference analysis method for a four-switch buck-boost converter, which comprises the steps of designing a FSBB converter common mode interference model scheme, and specifically dividing the scheme into a FSBB converter circuit model with LISN (LINE IMPEDANCE Stabilization Network, line impedance stabilizing network), a common mode conduction coupling path model and a common mode interference equivalent circuit model; secondly, a simplified common-mode voltage calculation method is provided, operation data are provided by interference sources V2 and V4 for calculation, and a normalized common-mode voltage calculation formula is obtained; finally, the common mode interference of different shift ratios and duty ratios is calculated, analyzed and realized aiming at the quadrilateral modulation strategy of FSBB converters, and the common mode interference of the peak value/secondary peak value current fixed frequency control scheme under different power levels is calculated, analyzed and realized. The method has the characteristics of low calculation complexity, rapidness, simplicity, convenience, strong applicability and high engineering application value.

Description

A common-mode interference analysis method for four-switch buck-boost converter

Technical Field

The invention belongs to the technical field of electromagnetic compatibility, and in particular relates to a common mode interference analysis method for a four-switch buck-boost converter.

Background technique

Four Switch Buck-Boost (FSBB) converter has the characteristics of buck-boost function and bidirectional power transmission, and is suitable for a variety of occasions, such as photovoltaic power generation system, battery energy storage system, microgrid system, etc. In related application occasions, electromagnetic safety issues cannot be ignored. In order to adapt to the complex electromagnetic environment of the space, the designed and produced converter equipment and systems must comply with the relevant standards of electromagnetic compatibility (EMC). The implementation of electromagnetic interference modeling prediction, problem analysis and evaluation and selection of rectification plans in the equipment and system design stage will help shorten the development cycle and reduce costs. In recent years, with the further development of power converter research and development towards high power and high integration, as well as the large-scale commercial use of wide bandgap (WBG) semiconductor devices, the switching noise caused by the high voltage change rate (dv/dt) and high current change rate (di/dt) caused by the higher switching frequency characteristics has brought more serious electromagnetic interference (EMI) challenges, among which the common mode (CM) conducted interference problem is the most significant. The above puts forward the need for analyzing and predicting the common-mode voltage of the FSBB converter.

The traditional control strategy of FSBB converter is called multi-mode control, which mainly distinguishes the working mode according to the relationship between the input and output voltage of the converter. The working modes include Buck mode, Boost mode, Buck-Boost mode, etc. However, under multi-mode control, as the load increases, the FSBB converter will work in a hard switching state, limiting the switching frequency and efficiency. Therefore, some scholars have proposed a unified mode inductor current quadrilateral modulation strategy. Quadrilateral modulation can achieve zero voltage switching (Zero Voltage Switching, ZVS) of all switches, which is beneficial to improve the switching frequency and efficiency of FSBB converter. Based on the quadrilateral modulation strategy, some scholars have proposed peak current fixed frequency control schemes, sub-peak current fixed frequency control schemes, etc., but the above control schemes are relatively complex, increasing the number of working states of the FSBB converter, making its common-mode interference analysis and calculation more complex and computationally intensive than traditional multi-mode control. Therefore, a simple common-mode interference analysis and prediction method is urgently needed.

Common common-mode interference analysis methods for FSBB converters include: mathematical model method, circuit simulation method, and actual measurement method.

The mathematical model method is a theoretical calculation method. By establishing a mathematical model of the power converter, it uses the relevant EMC theories for analysis, including circuit analysis, electromagnetic field analysis, and transmission line theory. This method requires deep electromagnetic knowledge and mathematical skills, and is usually used in the early stages of theoretical research and system design. Its disadvantage is that solving its precise mathematical model may be very complicated, especially when considering nonlinear components, electromagnetic coupling, and actual environmental conditions. The analysis of the model is complex, parameter uncertain, and abstract, and it requires a lot of time and effort for large systems or systems containing multiple components, making it difficult to apply in practice.

The circuit simulation method uses electromagnetic field simulation software, such as SPICE (Simulation Program with Integrated Circuit Emphasis), to model and simulate the power converter. By introducing common-mode interference sources in the simulation, the response of the system can be observed and the level of common-mode interference can be evaluated. This method is a powerful tool for system designers to perform preliminary electromagnetic compatibility analysis before actual manufacturing. The disadvantage is that complex power converter systems may require a lot of computing resources for accurate simulation, especially when accurate simulation is performed in the high-frequency range, the computational complexity and calculation time will increase significantly.

The actual measurement method is to use actual measurement equipment and technology, such as oscilloscopes, spectrum analyzers, network analyzers, EMI test receivers, etc., to directly measure the common-mode interference level of the power converter. This method directly reflects the common-mode interference in the actual system and is an important means of evaluating the electromagnetic compatibility of power converters. Its disadvantages are that it needs to be measured based on the actual converter system, and it is impossible to model and predict the common-mode interference in the design phase to shorten the development cycle and reduce costs; second, establishing an appropriate measurement environment may also require dedicated laboratory equipment, which increases cost and complexity.

Therefore, in response to the common-mode voltage prediction needs of FSBB converters, especially for the common-mode voltage prediction needs of FSBB converters under the peak/sub-peak current fixed-frequency control scheme based on quadrilateral modulation, how to simplify the common-mode interference analysis and calculation methods and quickly predict the common-mode voltage is an urgent problem that researchers in this field need to solve.

Summary of the invention

In order to overcome the shortcomings of the prior art, the present invention provides a common-mode interference analysis method for a four-switch buck-boost converter, including a common-mode interference model scheme, a simplified common-mode voltage calculation method, a common-mode interference analysis implementation under a quadrilateral modulation strategy, and a common-mode interference analysis implementation for a peak/sub-peak current fixed frequency control scheme. First, a common-mode interference model scheme for a FSBB converter is designed, which is specifically divided into a FSBB converter circuit model with a LISN (Line Impedance Stabilization Network), a common-mode conduction coupling path model, and a common-mode interference equivalent circuit model; secondly, a simplified common-mode voltage calculation method is proposed, and the interference sources V2 and V4 provide operation data for calculation to obtain a normalized common-mode voltage calculation formula; finally, the common-mode interference of different shift ratios and duty cycles is calculated and analyzed for the quadrilateral modulation strategy of the FSBB converter, and the common-mode interference of the peak/sub-peak current fixed frequency control scheme at different power levels is calculated and analyzed. The method of the present invention has the characteristics of low computational complexity, fast and simple, strong applicability, and high engineering application value.

The technical solution adopted by the present invention to solve the technical problem is as follows:

Step 1: Design a common-mode interference model scheme for the FSBB converter, which is specifically divided into a FSBB converter circuit model with a line impedance stabilization network LISN, a common-mode conduction coupling path model, and a common-mode interference equivalent circuit model;

Step 2: Use a simplified common-mode voltage calculation method, with interference sources _V2 and _V4 providing operation data for calculation, to obtain a normalized common-mode voltage calculation formula;

Step 3: Calculate and analyze the common-mode interference of different shift ratios and duty cycles for the quadrilateral modulation strategy of the FSBB converter, and calculate and analyze the common-mode interference of the peak/sub-peak current fixed-frequency control scheme at different power levels.

Preferably, the FSBB converter circuit model with line impedance stabilization network LISN is used to describe the circuit structure of the FSBB converter, including switching devices, inductors, and capacitors. The line impedance stabilization network LISN represents the EMI test network inserted on the power line; the common-mode conduction coupling path model is used to describe the flow path of the common-mode current in the circuit and analyze how the common-mode current is formed and propagated; the common-mode interference equivalent circuit model is used to represent the equivalent circuit of the common-mode interference in the circuit, and intuitively feedback the generation and propagation mechanism of the common-mode interference.

Preferably, the simplified common-mode voltage calculation method is to normalize the parasitic capacitance, whose magnitude is the sum of the interference sources _V2 and _V4 , that is:

V _cm (ω) = C _norm (ω)·(V ₂ (ω) + V ₄ (ω))

Wherein, V _cm (ω) represents the common mode voltage amplitude, C _norm (ω) represents the normalized value of parasitic capacitance, and ω represents the angular frequency;

Preferably, the quadrilateral modulation strategy is to calculate and analyze the common mode interference of the quadrilateral modulation strategy of the FSBB converter under different shift ratios and duty cycles, and give corresponding mathematical expressions and image drawing;

Mathematical expressions contain:

(1) The harmonic amplitude of the common-mode interference of interference sources _V2 and _V4 in the frequency domain:

In the formula represents the amplitude of the interference voltage source _V2 ,/> represents the amplitude of the interference voltage source _V4 , D represents the duty cycle, _d1 represents the duty cycle of the switch tube _Q1 , _d4 represents the duty cycle of the switch tube _Q4 , T represents the control period, G represents the voltage gain, /> represents the phase shift, n is the harmonic order, V _in represents the input voltage, j represents the imaginary unit, and t represents the time;

(2) The harmonic amplitude of the common-mode interference obtained after simplified merging under the quadrilateral modulation strategy is:

Preferably, the peak/sub-peak current constant frequency control scheme is to calculate and analyze the common mode interference of the FSBB converter at different power levels, and provide corresponding mathematical expressions and image drawing.

The beneficial effects of the present invention are as follows:

1. Fast and simple. Through the designed model scheme, only the operation data provided by the interference sources _V2 and _V4 are used, eliminating the detailed device parameters and circuit parameters such as inductance, capacitance, resistance, etc. in the converter system, avoiding tedious differential equations or simulations, and reducing the complexity of calculations;

2. Strong applicability. The simplified common-mode interference analysis method proposed is applicable to the application scenarios of various modulation strategies or control schemes of FSBB converters. It can more quickly perform parameter modification and calculation analysis for different control schemes, different shift ratios and duty cycles, and different power level requirements;

3. High engineering application value. In the early stages of design, when system parameters may not be fully determined, this simplified common-mode interference analysis method can provide sufficient information to make reasonable decisions in the preliminary stages of design.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a flow chart of the method of the present invention.

FIG. 2 is a circuit diagram of a FSBB converter with a LISN according to the present invention.

FIG3 is a common-mode interference equivalent circuit of the present invention.

FIG. 4 shows the common mode conductive coupling path of the present invention, (a) the conductive coupling path of the node SW ₁ , (b) the conductive coupling path of the node SW ₂

FIG5 is an equivalent common mode interference model of the present invention.

FIG6 shows the common mode interference of the quadrilateral modulation strategy under different shift ratios and duty cycles _according to an embodiment of the present invention, (a) Vin ₌ 18V, (b) Vin ₌ 28V, (c) Vin = 36V.

Figure 7 is a common-mode interference of the sub-peak current fixed-frequency control scheme under different power levels according to an embodiment of the present invention, (a) a schematic diagram of parameters corresponding to different powers of Vin ₌ 18V, (b) a relationship diagram between the power level of Vin ₌ 18V and the normalized common-mode voltage, (c) a schematic diagram of parameters corresponding to different powers of Vin ₌ 28V, (d) a relationship diagram between the power level of Vin ₌ 28V and the normalized common-mode voltage, (e) a schematic diagram of parameters corresponding to different powers of Vin ₌ 36V, and (f) a relationship diagram between the power level of _Vin = 36V and the normalized common-mode voltage.

Detailed ways

The present invention is further described below in conjunction with the accompanying drawings and embodiments.

After comparing the traditional common-mode interference analysis method for a four-switch buck-boost (FSBB) converter, the present invention further simplifies the common-mode interference model scheme and the common-mode voltage calculation method, so that the common-mode interference analysis method of the present invention has the characteristics of low calculation complexity, fast and simple, strong applicability, and high engineering application value.

To achieve the above object, the present invention adopts the following technical solution:

A common-mode interference analysis method for a four-switch buck-boost converter includes a common-mode interference model scheme, a simplified common-mode voltage calculation method, and common-mode interference analysis implementation under different modulation strategies.

The common-mode interference model scheme includes the FSBB converter circuit model with LISN, the common-mode interference equivalent circuit model, and the common-mode conduction coupling path model. The FSBB converter circuit model with LISN is used to describe the circuit structure of the FSBB converter, including switching devices, inductors, capacitors and other components, while LISN represents a network inserted in the power line, which is usually used to standardize the EMI of the device under test, and is used here to measure the EMI of the FSBB converter. The common-mode conduction coupling path model is used to describe the flow path of the common-mode current in the circuit. This model helps to analyze how the common-mode current is formed and propagated. The common-mode interference equivalent circuit model is used to represent an equivalent circuit abstracted from the common-mode interference in the circuit. This model can intuitively feedback the generation and propagation mechanism of common-mode interference, providing a basis for further analysis and calculation.

A simplified common-mode voltage calculation method is used. Based on the common-mode voltage formula of the FSBB converter obtained by the equivalent common-mode interference model, the parasitic capacitance in the formula is normalized, and the common-mode voltage calculation formula is further simplified. Its size is the sum of the interference sources _V2 and _V4 , forming a simplified normalized common-mode voltage calculation method.

The common mode interference analysis under the quadrilateral modulation strategy is realized by calculating and analyzing the common mode interference of the quadrilateral modulation strategy of the FSBB converter under different shift ratios and duty cycles. The switch tubes of the two bridge arms are all in action in one cycle, and the interference sources _V2 and _V4 exist at the same time. The switching signal of the modulation strategy in the time domain is Fourier decomposed, the size of the common mode interference source in the frequency domain is derived, the corresponding mathematical expression is given, and the relationship between the shift ratio, duty cycle and normalized common mode voltage is plotted.

The common-mode interference analysis of the peak/sub-peak current fixed-frequency control scheme is implemented by calculating and analyzing the common-mode interference of the FSBB converter at different power levels. The switching signal in the time domain is Fourier decomposed, and the characteristic parameters corresponding to the control scheme involved, that is, the shift ratio and duty cycle parameters at different power levels are substituted into the calculation, the size of the common-mode interference source in the frequency domain is derived, the corresponding mathematical expression is given, and the relationship between the converter power level and the normalized common-mode voltage is plotted.

Example:

The present invention proposes a simplified common-mode interference analysis method for a four-switch buck-boost (FSBB) converter, including a common-mode interference model scheme, a simplified common-mode voltage calculation method, a common-mode interference analysis implementation under a quadrilateral modulation strategy, and a common-mode interference analysis implementation for a peak/sub-peak current constant-frequency control scheme. The flow chart is shown in FIG1 .

The FSBB converter consists of two bridge arms. When the upper tube and the lower tube are switched, the potential of the switch nodes SW ₁ and SW ₂ jumps, which is the source of EMI. The equivalent circuit of LISN consists of two 50Ω resistors and passive devices. Its function is to capture the conducted interference generated by the circuit and then send the interference signal to the EMI test receiver for measurement and recording. The circuit diagram of the FSBB converter with LISN is shown in Figure 2. The ground is usually a heat sink. C _pin is the parasitic capacitance of the converter input positive line to the ground; C _pout is the parasitic capacitance of the converter output positive line to the heat sink; C _pe is the parasitic capacitance of the converter negative line to the ground; C _p is the parasitic capacitance of the switch nodes SW ₁ and SW ₂ to the ground.

Common-mode interference flows from the positive and negative lines of the FSBB converter to the LISN, with equal magnitude and direction. According to the substitution theory, the switch nodes _SW1 and _SW2 are equivalent to interference voltage sources and interference current sources: the interference current flowing through the switch tube _Q1 is _I1 , and the interference current flowing through the switch tube _Q3 is _I2 , so the switch tubes _Q1 and _Q3 are replaced by interference current sources _I1 and _I2 ; the interference voltage at the switch node _SW1 is _V2 , and the interference voltage at the switch node _SW2 is _V4 , so the switch tubes _Q2 and _Q4 are replaced by interference voltage sources V2 and _V4 . The equivalent circuit of common-mode interference is shown in Figure 3. The common-mode current flows out from the positive poles of the interference voltage sources _V2 and _V4 , flows to the ground through _Cp , _and then flows back to the negative pole of the interference source through _Cpin , _Cpe , _Cp , _Cpout and LISN. The common-mode conduction coupling path is shown in Figure 4.

The common mode voltage collected by LISN is:

Wherein, _Call = _Cpin + _Cpe + _Cp + _Cpout . The equivalent common-mode interference model of the FSBB converter is established, as shown in FIG5.

According to the above analysis, the common-mode voltage of the FSBB converter is calculated by _V2 , _V4 and the parasitic capacitance in the circuit. By normalizing the parasitic capacitance, the common-mode voltage calculation formula is further simplified, and its magnitude is the sum of the interference sources _V2 and _V4 , that is:

V _cm (ω) = C _norm (ω)·(V ₂ (ω) + V ₄ (ω))

Where C _norm (ω) is the normalization coefficient.

The common-mode interference sources _V2 and _V4 are analyzed separately. It is stipulated that A is the amplitude of the interference voltage source, D is the duty cycle, _d1 is the duty cycle of the switch tube _Q1 , and _d4 is the duty cycle of the switch tube _Q4 . It is easy to know that: A = _Vin , D = _d1 when stepping down, A = _Vout , D = 1- _d4 when stepping up. The common-mode interference source in the time domain is decomposed by Fourier, and the harmonic amplitude of the common-mode interference in the frequency domain is further derived:

Where T is the control period, n is the harmonic order, and n≥2.

Under the quadrilateral modulation strategy, the switch tubes of the two bridge arms are all in action within one cycle, so the interference sources _V2 and _V4 exist at the same time. The switching signal of the modulation strategy in the time domain is decomposed by Fourier, and the harmonic amplitude of the common mode interference in the frequency domain is derived:

Where T is the control period, G is the voltage gain, is the shift ratio, n is the harmonic order, and n≥2.

The relationship between the time shift ratio and the duty cycle of quadrilateral modulation is: After simplification and merging, the harmonic amplitude of common mode interference is obtained:

It is a periodic function:

According to the above calculation method, the size of the normalized common-mode voltage under the quadrilateral modulation strategy at different input voltages can be obtained. _Vin takes 18V, 28V and 36V respectively, _Vout takes 28V, n takes 2, and the relationship between the shift ratio, duty cycle and normalized common-mode voltage is plotted, as shown in Figure 6.

For the FSBB converter based on the peak/sub-peak current fixed frequency control scheme, the sub-peak current fixed frequency control scheme is analyzed. This control scheme needs to determine the T _2max corresponding to the PI controller output time T _PI and the DCM power limit P _DCMmax . When T _PI ≤T _2max , the FSBB converter operates in DCM mode:

Otherwise, run in CCM mode:

V _in is 18V, 28V and 36V respectively, V _out is 28V, and n is 2. Compare the calculated shift ratios at different power levels such as 50W, 100W, 200W, 300W, 400W, and 500W By substituting the duty cycle _d1 parameter into the calculation, the common-mode voltage of the FSBB converter based on the sub-peak current fixed-frequency control scheme at different power levels can be obtained, and the relationship between the converter power level and the normalized common-mode voltage can be plotted, as shown in Figure 7.

Claims (5)

1. A common mode interference analysis method for a four-switch buck-boost converter, comprising the following steps: Step 1: Design a common-mode interference model scheme for the FSBB converter, which is specifically divided into a FSBB converter circuit model with a line impedance stabilization network LISN, a common-mode conduction coupling path model, and a common-mode interference equivalent circuit model; Step 2: Use a simplified common-mode voltage calculation method, with interference sources _V2 and _V4 providing operation data for calculation, to obtain a normalized common-mode voltage calculation formula; Step 3: Calculate and analyze the common-mode interference of different shift ratios and duty cycles for the quadrilateral modulation strategy of the FSBB converter, and calculate and analyze the common-mode interference of the peak/sub-peak current fixed-frequency control scheme at different power levels. 2. A common-mode interference analysis method for a four-switch buck-boost converter according to claim 1, characterized in that the FSBB converter circuit model with a line impedance stabilization network LISN is used to describe the circuit structure of the FSBB converter, including switching devices, inductors, and capacitors, and the line impedance stabilization network LISN represents an EMI test network inserted on the power line; the common-mode conduction coupling path model is used to describe the flow path of the common-mode current in the circuit and analyze how the common-mode current is formed and propagated; the common-mode interference equivalent circuit model is used to represent the equivalent circuit of the common-mode interference in the circuit, and intuitively feedback the generation and propagation mechanism of the common-mode interference. 3. A common-mode interference analysis method for a four-switch buck-boost converter according to claim 1, characterized in that the simplified common-mode voltage calculation method is to normalize the parasitic capacitance, and its size is the sum of the interference sources _V2 and _V4 , that is: V _cm (ω) = C _norm (ω)·(V ₂ (ω) + V ₄ (ω)) Wherein, V _cm (ω) represents the common mode voltage amplitude, C _norm (ω) represents the normalized value of parasitic capacitance, and ω represents the angular frequency. 4. A common mode interference analysis method for a four-switch buck-boost converter according to claim 3, characterized in that the quadrilateral modulation strategy is to calculate and analyze the common mode interference of the quadrilateral modulation strategy of the FSBB converter under different shift ratios and duty cycles, and give corresponding mathematical expressions and image drawing; Mathematical expressions contain: (1) The harmonic amplitude of the common-mode interference of interference sources _V2 and _V4 in the frequency domain: In the formula represents the amplitude of the interference voltage source _V2 ,/> represents the amplitude of the interference voltage source _V4 , D represents the duty cycle, _d1 represents the duty cycle of the switch tube _Q1 , _d4 represents the duty cycle of the switch tube _Q4 , T represents the control period, G represents the voltage gain, /> represents the phase shift, n represents the harmonic order, V _in represents the input voltage, j represents the imaginary unit, and t represents the time; (2) The harmonic amplitude of the common-mode interference obtained after simplified merging under the quadrilateral modulation strategy is: 5. A common-mode interference analysis method for a four-switch buck-boost converter according to claim 1, characterized in that the peak/sub-peak current constant-frequency control scheme is to calculate and analyze the common-mode interference of the FSBB converter at different power levels, and give corresponding mathematical expressions and image drawing.