CN114499212A - A current stress-optimized extended phase-shift control method for dual active full-bridge DC-DC converters - Google Patents

Abstract

The invention relates to the technology of a DC-DC converter and discloses a current stress optimization expansion phase-shift control method of a double-active full-bridge DC-DC converter. The method calculates the per unit values of the average transmission power and the current stress of the converter under two modes during the expansion phase-shift control, then searches for the optimal phase-shift ratio combination through a Lagrange extreme value method, converts the obtained optimal phase-shift amount into the driving pulse through the expansion phase-shift modulator to act on the converter to realize the optimization of the current stress, reduces the circuit conduction loss, and thus improves the efficiency of the whole system.

Description

A current stress-optimized extended phase-shift control method for dual active full-bridge DC-DC converters

1Technical field

The invention relates to a DC-DC converter technology, in particular to a current stress optimized extended phase-shift control method of a dual active full-bridge DC-DC converter.

2 Background technology

Dual active full-bridge DC-DC converters are widely used in electric vehicles, photovoltaic power generation, uninterruptible power supplies and energy storage due to their advantages of high power density, electrical isolation, bidirectional energy flow and easy soft switching. technical field.

At present, there are two commonly used control methods for dual active full-bridge DC-DC converters: (1) PWM control, this method is simple and easy to implement, but because the effective value of the output AC voltage of the full-bridge inverter can only be low Because of the input DC voltage, its voltage regulation range is limited. Moreover, the dynamic characteristics of the converter are poor. (2) Phase-shift control, under this control method, the inverter system has small inertia, fast dynamic response and easy soft switching. But in single-phase shift control, since the control amount is only the phase shift amount between the square wave voltages output by the two H bridges, the converter mainly transmits energy through the transformer leakage inductance (or series auxiliary inductance). Therefore, when the input voltage does not match the output voltage, the inductor current stress of the converter will increase greatly. Excessive current stress will lead to increased converter losses, decreased efficiency and even damage to switching devices. In order to reduce the current stress, a current stress optimization extended phase-shift control method for dual active full-bridge DC-DC converters is proposed. Stress optimization.

3 Contents of the invention

The purpose of the present invention is to provide a current stress optimized expansion phase-shift control method of a dual active full bridge DC-DC converter, which can reduce the effective value of the inductor current of the dual active full bridge circuit, reduce the circuit conduction loss, and thereby improve the efficiency of the entire system. The technical solution is as follows:

S1: A current stress optimization extended phase shift control method for a dual active full bridge DC-DC converter, comprising: the circuit topology of the dual active full bridge DC-DC converter involved in the optimization control method includes a primary side full bridge Circuit, secondary full bridge circuit, input voltage U ₁ , auxiliary inductor L, high frequency transformer T, input filter capacitor C ₁ , output filter capacitor C ₂ and load resistor R; switch tube S ₁ , switch tube S ₂ , switch tube S ₃ , switch tube S ₄ , switch tubes S ₁ to S ₄ are all connected in anti-parallel with a diode D ₁ to D ₄ , switch tube S ₅ , switch tube S ₆ , switch tube S ₇ , switch tube S ₈ , switch tube S ₅ ~ _S8 are also connected in anti _- parallel with _a diode _D5 ~ _D8 ; the switch tubes S1~S4, the input voltage U1, the auxiliary inductor L, the input filter capacitor _C1 , and the high _- frequency transformer T constitute a primary side full-bridge circuit, The switch tubes S ₅ - S ₈ together with the load resistor R, the output filter capacitor C ₂ , and the high-frequency transformer T form a secondary side full-bridge circuit.

The extended phase-shift control of the dual active full-bridge DC-DC converter has two degrees of freedom for phase-shift control, which are the inner-shift comparison and the outer-shift comparison. Among them, the internal shift comparison D ₁ is defined as the ratio of the phase difference between the first switch tube S ₁ and the fourth switch tube S ₄ in the primary side full-bridge circuit to π; the internal shift ratio D ₂ is defined as the primary side full-bridge circuit _The ratio of the phase difference between the _first switch S1 and the fourth switch S5 in the bridge circuit. According to the magnitude relationship between the internal shift and the external shift, it can be divided into the following two modes: the phase-shift relationship corresponding to mode 1 is 0≤D ₁ ≤D ₂ ≤1; for mode 2, the corresponding shift-correlation is 0≤D ₂ ≤D ₁ ≤1.

According to the input voltage U ₁ , the output voltage U ₂ , the ratio n of the high frequency transformer T, the switching frequency f, the auxiliary inductance L, the internal shift ratio D ₁ and the external shift ratio D ₂ , it can be obtained that the converter is under extended phase shift control. The per-unit values of the average transmission power and current stress in the two modes are:

i _L =2[k(1-D ₁ )+2D ₂ -1] (2)

In the formula, k is the voltage conversion ratio, and k=U ₁ /nU ₂ .

S2: According to the average transmission power p and the current stress i _L obtained above, the relationship between the transmission power and the current stress of the converter under the extended phase shift control is constructed by defining the Lagrangian function. The Lagrangian function can be defined for

E=i _L +λ(pp ^* ) (3)

In the formula, E is the Lagrangian function; λ is the Lagrange multiplier; p ^* is the given transmission power of the converter. Taking the derivation of the Lagrangian function, the relationship between k and p can be obtained between the optimal phase shifts D ₁ and D ₂ , which minimize the current stress of the dual active full-bridge DC-DC converter under the extended phase shift control. Mode.

S3: Optimizing the extended phase-shift control method based on the current stress may be performed by the following steps: sampling the input voltage, output voltage and output current information of the dual active full-bridge DC-DC converter converter. Then, the voltage conversion ratio k and the per-unit value p of the given transmission power are calculated, and the power range of the converter is judged. The optimized phase shifts D 1 and D 2 are calculated by the above formulas (4) and (5), and the obtained optimized phase shifts D ₁ and D ₂ are calculated. The phase shift amount is converted into drive pulses by the extended phase shift modulator and acts on the converter. Finally, the simulation model of the dual active full-bridge DC-DC converter is built in Simulink of MATLAB.

4 Description of drawings

Figure 1 is a topology diagram of a dual active full bridge DC-DC converter;

Fig. 2-Fig. 3 are the working waveform diagrams of the dual active full-bridge DC-DC converter under the extended phase-shift control under the two modes of the converter;

Fig. 4 is the current stress optimization control block diagram of the dual active full bridge DC-DC converter;

Figure 5 is a current stress simulation diagram of a dual active full-bridge DC-DC converter under single phase-shift control;

FIG. 6 is a current stress simulation diagram of a dual active full-bridge DC-DC converter under the current stress optimization extended phase-shift control;

5 specific implementations

The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. According to the topology diagram of the dual active full bridge DC-DC converter shown in FIG. 1 , this embodiment describes in detail the current stress optimized extended phase shift control method for the dual active full bridge DC-DC converter.

S1: FIG. 1 is a topological structure diagram of the dual active full-bridge DC-DC converter involved in the present invention, including a primary-side full-bridge circuit, a secondary-side full-bridge circuit, an input voltage U ₁ , an auxiliary inductor L, a high-frequency transformer T, input filter capacitor C ₁ , output filter capacitor C ₂ and load resistance R; switch tube S ₁ , switch tube S ₂ , switch tube S ₃ , switch tube S ₄ , switch tubes S ₁ to S ₄ are all connected in anti-parallel with a diode D ₁ ～ D ₄ , switch tubes S ₅ , switch tubes S ₆ , switch tubes S ₇ , switch tubes S ₈ , switch tubes S ₅ ～ S ₈ are also connected in anti-parallel with a diode D ₅ ～ D ₆ ; switch tubes S ₁ ～ S ₄ and input voltage U ₁ , auxiliary inductor L, input filter capacitor C ₁ , and high-frequency transformer T form a primary full-bridge circuit. Switch tubes S ₅ to S ₈ and load resistor R, output filter capacitor C ₂ , high The frequency transformer T constitutes a secondary full-bridge circuit.

The extended phase-shift control of the dual active full-bridge DC-DC converter has two degrees of freedom for phase-shift control, which are the inner-shift comparison and the outer-shift comparison. Among them, the internal shift comparison D ₁ is defined as the ratio of the phase difference between the first switch tube S ₁ and the fourth switch tube S ₄ in the primary side full-bridge circuit; the internal shift comparison D ₂ is defined as the primary side full-bridge circuit _The ratio of the phase difference between the _first switch S1 and the fourth switch S5 in the bridge circuit. According to the size relationship between the internal shift and external shift, the working waveforms under the two modes under extended phase shift control are shown in Figure 2 and Figure 3: Figure 2 is Mode 1, and the corresponding phase shift relationship is 0 ≤D ₁ ≤D ₂ ≤1; Figure 3 shows mode 2, and the corresponding phase shift relationship is 0≤D ₂ ≤D ₁ ≤1. Among them, U _ab is the output voltage of the H bridge on the U ₁ side; U _cd is the output voltage of the H bridge on the U ₂ side; T _hs is half a switching cycle.

According to the input voltage U ₁ , the output voltage U ₂ , the high frequency transformer T transformation ratio n, the switching frequency f, the auxiliary inductance L, the internal shift ratio D ₁ and the external shift ratio D ₂ , it is obtained that the converter is in the extended phase shift control. The average transmission power P in the two modes is:

The per-unit transmission power of the converter is per-unitized, and the per-unitized transmission power p in the two modes under extended phase-shift control is obtained:

where _PN is the maximum transmission power, _PN =nU ₁ U ₂ /8fL;

Thus, the per-unitized current stress i _L is obtained:

i _L =2[k(1-D ₁ )+2D ₂ -1] (3)

k is the voltage conversion ratio, k=U ₁ /nU ₂ .

S2: According to the per-unit value p of the average transmission power and the per-unit value of the current stress i _L obtained above, the relationship between the transmission power and the current stress of the converter under the extended phase shift control is constructed by defining a Lagrangian function, The Grange function can be defined as

E=i _L +λ(pp ^* ) (4)

In the formula, E is the Lagrangian function; λ is the Lagrange multiplier; p ^* is the given transmission power of the converter.

In order to obtain the relationship between the optimal phase shift amounts D ₁ and D ₂ to minimize the converter current stress, the per-unit value of transmission power and the per-unit value of current stress expressed by equations (2) and (3) are substituted into equation ( 4), and take the derivative of the Lagrangian function,

The relationship between k and p between the optimal phase shifts D ₁ and D ₂ , which minimizes the current stress of the dual active full-bridge DC-DC converter under the extended phase shift control, can be obtained.

S3: Optimizing the extended phase-shift control method based on current stress can be performed through the following steps, and the optimization strategy process is shown in Figure 4: Sampling the input voltage, output voltage and output current information of the dual active full-bridge DC-DC converter. After the difference between the reference voltage U _ref and the sampled output voltage, the transmission power P is obtained by multiplying the output current I ₀ by the PI regulator, and then divided by P _N to obtain the per-unit p, which is obtained according to the size of p and the calculation The corresponding power interval is determined by the voltage transfer ratio _{k of} the The drive pulses act on the converter.

Finally, the simulation model of the dual active full-bridge DC-DC converter is built in Simulink of MATLAB. The design indicators of the converter are as follows: the input side voltage is 150V, and the resistive load R=20Ω replaces the output side power supply, so that the output voltage is 50V; the specific simulation parameters are switching frequency f=10kHz, transformer ratio n=1:1, auxiliary inductance L=183.3uH, input side filter capacitor _C1 =2200uF, output side filter capacitor _C2 =1100uF. Under the simulation results of the same input voltage U _ab and output voltage U _cd of 150V and 50V, it can be clearly seen from Figure 5 and Figure 6 that the current stress under the optimized extended phase-shift control has a significant decrease. By calculating the efficiency of the converter under the single phase-shift control and the current-optimized extended phase-shift control are 92% and 96%, respectively, and the converter efficiency has a certain improvement under the optimized extended phase-shift control.

Claims (3)

1. A current stress optimization expansion phase-shifting control method of a double-active full-bridge DC-DC converter can reduce the effective value of the inductive current of a double-active full-bridge circuit and reduce the conduction loss of the circuit, thereby improving the efficiency of the whole system. The technical scheme is as follows:

a current stress optimization extension phase shift control method of a double-active full-bridge DC-DC converter comprises the following steps: the circuit topology of the double-active full-bridge DC-DC converter related to the optimization control method comprises a primary full-bridge circuit, a secondary full-bridge circuit and an input voltage U₁Auxiliary inductor L, high-frequency transformer T and input filter capacitor C₁An output filter capacitor C₂And a load resistance R; switch tube S₁Switch tube S₂Switch tube S₃Switch tube S₄Switching tube S₁～S₄Are all connected in anti-parallel with a diode D₁～D₄Switching tube S₅Switch tube S₆Switch tube S₇Switch tube S₈Switching tube S₅～S₈Are also all connected in anti-parallel with a diode D₅～D₈(ii) a Switch tube S₁～S₄And an input voltage U₁Auxiliary inductor L and input filter capacitor C₁The high-frequency transformer T forms a primary side full-bridge circuit and a switching tube S₅～S₈AND load resistor R and output filter capacitor C₂The high-frequency transformer T forms a secondary side full bridge circuit.

The expansion phase-shift control of the double-active full-bridge DC-DC converter has two degrees of freedom of phase-shift control, namely an inner-shift phase-shift control. Wherein the internal shift phase ratio is D₁Is defined as the first switch tube S in the primary side full bridge circuit₁And a fourth switching tube S₄The ratio of the phase difference of (d) to pi; internal shift phase ratio D₂Is defined as the first switch tube S in the primary side full bridge circuit₁And a fourth switching tube S₅The phase difference of (d) to pi. According to the magnitude relation between the inward shift ratio and the outward shift ratio, the two modes can be divided into the following two modes: the phase shift relation corresponding to the mode 1 is D which is more than or equal to 0₁≤D₂Less than or equal to 1; mode 2, corresponding to a phase shift relationship of 0. ltoreq.D₂≤D₁≤1。

According to input voltage U₁Output voltage U₂High-frequency transformer T transformation ratio n, switching frequency f, auxiliary inductance L and internal shift ratio D₁Comparison with outward Shift₂The per unit values of the average transmission power and the current stress under two modes of the converter under the extended phase-shift control can be obtained as follows:

i_L＝2[k(1-D₁)+2D₂-1] (2)

wherein k is the voltage conversion ratio, and k is U₁/nU₂。

2. The method of claim 1, wherein the average transmission power p and the current stress i are obtained according to the current stress-optimized spread phase-shift control method of the dual-active full-bridge DC-DC converter_LThe relationship between extended phase shift control down-converter transmission power and current stress is constructed by defining a lagrangian function, which can be defined as

E＝i_L+λ(p-p^*) (3)

Wherein E is a Lagrangian function; λ is lagrange multiplier; p is a radical of^*For a given transmission power of the converter. And derivation is carried out on the Lagrange function, so that the optimized phase shift D for minimizing the current stress of the dual-active full-bridge DC-DC converter under the control of the extended phase shift can be obtained₁And D₂And k and p.

3. The current stress-optimized extended phase-shift control method of the dual-active full-bridge DC-DC converter according to claim 1, wherein the current stress-optimized extended phase-shift control method can be performed by the following steps: and sampling input voltage, output voltage and output current information of the double-active full-bridge DC-DC converter. Then, the voltage conversion ratio k and the given per unit value p of the transmission power are calculated, the power range of the converter is judged, and the optimized phase shift quantity D is calculated through the formula₁And D₂And converting the obtained optimized phase shift amount into a driving pulse through an extended phase shift modulator to be applied to the converter. And finally, building a simulation model of the double-active full-bridge DC-DC converter in Simulink of MATLAB.

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