CN107968571B - A three-phase-shift control method for dual active bridge converters - Google Patents

Abstract

The invention relates to a control method of a dual active bridge converter, and aims to provide a three-phase-shift control method for a dual active bridge converter. The output voltage controller used to adjust the output voltage is set in the dual active bridge DC converter of the bidirectional topology. The input signal of the output voltage controller is the difference between the given value of the secondary side DC voltage and the actual measured value. The output signal is the control signal α, which is used to adjust the duty ratios D1 and D2 of the midpoint voltage of the primary side bridge arm and the midpoint voltage of the secondary side bridge arm and their phase difference D3. The present invention solves the problem of the optimal solution of the current stress of the dual active bridge and the control complexity: obtain the D1, D2 and D3 corresponding to the minimum value of the inductance current stress at each power point, and solve the relationship between the three Based on the relationship, a simple control method is proposed, and only one PI controller can realize the operation of the converter on the track with the least current stress.

Description

A three-phase-shift control method for dual active bridge converters

technical field

The invention relates to a control method of a single-phase or multi-phase double active bridge converter, which belongs to the direction of a bidirectional direct current isolation switching power supply in the field of power electronics.

Background technique

Converters with isolation and bidirectional energy flow have a wide range of application requirements, such as microgrids, solid-state transformers, electric vehicle charging piles, etc. Whether it is an AC or DC bidirectional converter, its core part is a medium and high frequency isolated bidirectional DC-DC converter. In practical applications, in order to reduce energy loss, cost and volume, efficiency and power density are important indicators for evaluating isolated bidirectional DC-DC converters.

Among many isolated bidirectional DC-DC converter topologies, dual active bridge has been widely studied and applied because of its symmetrical structure, flexible control, and easy zero-voltage turn-on. The topology of the commonly used single-phase dual-active bridge is shown in Figure 1. This topology is a symmetrical structure. Both the primary side and the secondary side of the transformer are composed of switching tubes to form a full bridge circuit. V _ab and V _cd are the primary and secondary sides respectively. The midpoint voltage of the secondary side bridge arm, i _L is the inductor current. The two full-bridge circuits are connected through a medium-high frequency transformer.

The commonly used single-phase dual-active bridge has four bridge arms, and phase differences can be generated between each bridge arm, so there are three control variables, including the duty ratios D ₁ and D ₂ of V _ab and V _cd , and Vab and Vcd The phase difference φ between them. The traditional phase-shift modulation method only adjusts φ while keeping D ₁ and D ₂ at 50%. This method is simple to control and the switching tube can automatically realize the characteristics of zero-voltage turn-on (ZVS-on), but the range of zero-voltage turn-on is limited and There is a large current stress, which will increase the conduction loss. Scholars from various countries have carried out a lot of research on this, and the focus of the research is to try to adjust D ₁ , D ₂ and φ at the same time, so as to reduce the conduction loss with a smaller current stress. In the article "Current-stress-optimized switching strategy of isolated bidirectional DC–DC converter with dual-phase-shift control" published in IEEE Transaction on Industrial Electronics [Journal of Power Electronics] in 2013, it is proposed to simultaneously adjust D ₁ , D ₂ and φ to reduce the current stress, but because D1 and D2 are kept equal, this control method essentially only adjusts two dimensions, and the obtained minimum value of current stress is only a local optimum; in 2012, IEEE Transaction on In the article "Closed form solution for minimum conduction lossmodulation of DAB converters" published by Power Electronics [Journal of Power Electronics], the conduction loss is reduced by changing the decoupling adjustment of the three dimensions of D ₁ , D ₂ and φ, but this method expresses The formula is complex, and there is no closed-loop design at the middle power level, and the complex control method makes it unsuitable for engineering practice. "Unified Triple-Phase-Shift Control to Minimize Current Stress and Achieve Full Soft-Switching of Isolated Bidirectional DC–DC Converter" published in IEEE Transaction on Industrial Electronics [Journal of Power Electronics] in 2016 proposed the use of Karush–Kuhn–Tucker The conditional method obtains the minimum value of the current stress at each power point by freely adjusting the three dimensions, but this method needs to know the size of the output power when adjusting D ₁ , D ₂ and Df, so it is necessary to add a current sensor to The output current is sampled in real time, but the high-frequency current is difficult to accurately sample, which increases the cost and control difficulty of the controller.

In summary, the existing dual active bridge control methods cannot balance the optimal solution of current stress and control complexity.

Contents of the invention

The technical problem to be solved by the present invention is to overcome the deficiencies in the prior art and provide a three-phase-shift control method for a dual active bridge converter. This method adjusts D ₁ , D ₂ and D ₃ through a three-phase shift control method, so that the inductive current stress of the dual active bridge reaches the minimum value, and finds the internal relationship of the three dimensions, which simplifies the control method, is simple and easy, and is suitable for engineering practice.

For solving technical problem, solution of the present invention is:

A three-phase-shift control method for a dual active bridge converter is provided, which is to set an output voltage controller for adjusting the output voltage in a dual active bridge DC converter with a bidirectional topology, and the input signal of the output voltage controller is The difference between the given value of the DC voltage on the secondary side and the actual measured value, and its output signal is the control signal α, which is used to adjust the duty ratio D ₁ of the midpoint voltage of the primary side bridge arm and the midpoint voltage of the secondary side bridge arm and D ₂ and its phase difference D ₃ ;

The duty ratios D ₁ and D ₂ of the midpoint voltages of the bridge arms on the primary side and the secondary side and the phase difference D ₃ between them are calculated by the following formula:

In the above formula, α is the control signal output by the output voltage controller, and its value range is [0,1]; V ₁ and V ₂ are the DC voltages of the primary side and the secondary side respectively, and n is the primary side to the secondary side The transformation ratio of the side is n:1, the value range of n is not limited, and d is the voltage gain ratio nV ₂ /V ₁ of the converter.

In the present invention, the primary side and the secondary side of the dual active bridge DC converter can be interchanged; the dual active bridge DC converter is any one of the following: single-phase dual active bridge DC converter, multiple phase dual active bridge DC converter, two level dual active bridge DC converter, multilevel dual active bridge DC converter, or a modular multilevel circuit based on dual active bridge.

In the present invention, the dual active bridge DC converter is a single-phase dual active bridge converter, and its primary side and secondary side have a total of eight switching tubes, which are respectively the first switching tube S1 and the second switching tube S1 on the primary side The tube S2, the third switch tube S3 and the fourth switch tube S4, and the fifth switch tube S5, the sixth switch tube S6, the seventh switch tube S7 and the eighth switch tube S8 on the secondary side; the first switch tube in series The switch tube S1 and the second switch tube S2 are connected in parallel with the third switch tube S3 and the fourth switch tube S4 in series, and the fifth switch tube S5 and the sixth switch tube S6 in series are connected with the seventh switch tube S7 and the eighth switch tube in series. The switch tube S8 is connected in parallel;

The driving signals of all switching tubes are 50% square wave signals, which are generated according to the phase difference D ₃ , and the duty ratios D ₁ and D ₂ of the primary side and secondary side bridge arm midpoint voltages; among them, the first switch The signals of the tube S1 and the second switching tube S2 are complementary, the signals of the third switching tube S3 and the fourth switching tube S4 are complementary, the signals of the fifth switching tube S5 and the sixth switching tube S6 are complementary, and the signals of the seventh switching tube S7 and the eighth switching tube are complementary. The signals of the switching tube S8 are complementary; the time when the switching tube S1 is ahead of the S3 is controlled by the duty ratio D1, the time when the fifth switching tube S5 is ahead of the seventh switching tube S7 is controlled by the duty cycle _D2 , and the _first switching tube S1 and the phase difference _D3 between the fifth switching tube S5 is controlled.

In the present invention, the output voltage controller is controlled by proportional integral PI.

In the present invention, the output voltage controller includes a voltage difference comparator, a PI controller and a limiter connected in sequence; wherein, the input signal of the voltage difference comparator is the given value of the secondary side DC voltage and the actual The difference between the measured values, the PI controller controls the control signal α, and the limiter limits the control signal α to [0,1], so that the output power and the control signal α have a monotonic relationship, and the duty cycle D is obtained by calculation. ₁ and _D2 are constrained to be in the range [0,1] and D3 is constrained to be in the range [0,0.5].

Compared with the prior art, the present invention has the following beneficial technical effects:

The dual active bridge three-phase-shift control method of the present invention solves the problem of the optimal solution of the current stress of the dual active bridge and the control complexity: obtain the corresponding D ₁ , D ₂ and D ₃ , and solve the relationship between the three, and put forward a simple control method, and only use a PI controller to realize the operation of the converter on the track with the least current stress.

Description of drawings

Figure 1 shows the topology of a commonly used dual active bridge bidirectional DC-DC converter;

Figure 2 is a schematic diagram of the voltage waveform and phase relationship at the midpoint of the original secondary bridge arm;

Fig. 3 is a control block diagram of the present invention;

Figure 4 is a waveform diagram of the midpoint voltage of the primary and secondary bridge arms under different load conditions when V ₁ ≥ nV ₂ ;

Fig. 5 is a waveform diagram of the midpoint voltage of the primary and secondary bridge arms under different load conditions when V ₁ <nV ₂ .

Detailed ways

The present invention will be described in detail below in conjunction with accompanying drawing and embodiment, also describe the technical problem and beneficial effect that technical solution of the present invention solves simultaneously, it should be pointed out that described embodiment is only intended to facilitate the understanding of the present invention, and to It does not have any limiting effect.

The topology of the single-phase dual active bridge bidirectional DC-DC converter circuit is shown in Figure 1. The primary side is composed of four switch tubes S1-S4, two bridge arms form a full bridge circuit, and the midpoints of the two bridge arms are points a and b respectively. Points a and b are connected to the primary side winding of the transformer. The secondary side is composed of four switching tubes S5-S8, two bridge arms form a full bridge circuit, and the midpoints of the two bridge arms are points c and d respectively. Points c and d are connected to the secondary side winding of the transformer. L _k is the transformer leakage inductance or external inductance. V _ab is the voltage difference between point a and point b; V _cd is the voltage difference between point c and point d; i _L is the inductor current; i ₁ and i ₂ are the input and output currents respectively; V ₁ is the primary The DC voltage of the side; V ₂ is the DC voltage of the secondary side.

The main working waveforms of the single-phase dual active bridge bidirectional DC-DC converter are shown in Figure 2. D ₁ and D ₂ represent the duty ratios of the midpoint voltages of the primary and secondary side bridge arms respectively, and D ₃ represents the duty ratio between the two. phase difference between them.

The control block diagram used in this embodiment is shown in Figure 3, including a voltage difference comparator, a PI controller, a limiter, a duty cycle and phase difference calculation module, and a drive signal generation module connected in sequence. Among them, the input signal of the voltage difference comparator is the difference between the given value V _2ref of the secondary side DC voltage and the actual measured value V ₂ ; the signal is controlled by PI to obtain the control signal α; the purpose of the limiter is to convert α It is limited between 0 and 1, which is easy to realize the post-stage control, so that the output power and α have a monotonically increasing relationship. When V ₂ is less than V _2ref , the difference is positive, and the control signal α gradually becomes larger, increasing the output power, so that V ₂ increases; when V ₂ is greater than V _2ref , the difference is negative, the control signal α gradually decreases, and the output power is reduced, so that V ₂ decreases; through the duty cycle and phase difference calculation module, according to the control signal α Obtain the primary and secondary side duty cycle D ₁ , D ₂ and its phase difference D ₃ , the calculation formula is as follows:

Where V ₁ and V ₂ are the primary side and secondary side DC voltages respectively, n is the transformation ratio n:1 of the primary side to the secondary side of the transformer, and d is the voltage gain ratio nV ₂ /V ₁ of the converter, because the output power It has a monotonically increasing relationship with α. Figure 4 and Figure 5 respectively show the waveform diagrams of the midpoint voltage of the primary and secondary bridge arms that vary with power under the conditions of V ₁ ≥ nV ₂ and V ₁ < nV ₂ . increases, α increases gradually, and D ₁ , D ₂ , D ₃ change according to the above relationship to reach the required output power.

Finally, according to the values of D ₁ , D ₂ and D ₃ , eight driving signals are generated by the driving signal generation module: all driving signals are 50% square wave signals; S1 and S2 are complementary, S3 and S4 are complementary, S5 and S6 Complementary, S7 and S8 are complementary _; the time of S1 ahead of S3 is controlled by D1, the time _of S5 ahead of S7 is controlled by D2, and the phase difference between S1 and S5 is controlled by _D3 .

Claims (5)

1. a kind of double active bridge converter three phase-shifting control method, it is characterized in that, be to be provided with the output voltage controller for regulating output voltage in the double active bridge DC converter of bidirectional topological structure, this output voltage control The input signal of the converter is the given value and the actual measured value of the DC voltage of the secondary side, and its output signal is the control signal α, which is used to adjust the duty ratio of the midpoint voltage of the primary side bridge arm and the midpoint voltage of the secondary side bridge arm D ₁ and D ₂ and their phase difference D ₃ ; The duty ratios D ₁ and D ₂ of the midpoint voltages of the bridge arms on the primary side and the secondary side and the phase difference D ₃ between them are calculated by the following formula: In the above formula, α is the control signal output by the output voltage controller, and its value range is [0, 1]; V ₁ and V ₂ are the DC voltages of the primary side and the secondary side respectively, and n is the primary side to the secondary side The transformation ratio of the side is n:1, the value range of n is not limited, and d is the voltage gain ratio nV ₂ /V ₁ of the converter. 2. The method according to claim 1, wherein the primary side and the secondary side of the dual active bridge DC converter are interchangeable; the dual active bridge DC converter is any one of the following: Single phase dual active bridge DC converter, multiphase dual active bridge DC converter, two level dual active bridge DC converter, multilevel dual active bridge DC converter, or dual active bridge based Modular multilevel circuits. 3. The method according to claim 1, wherein the dual-active-bridge DC converter is a single-phase dual-active-bridge converter, and its primary side and secondary side have eight switch tubes in total, which are respectively primary and secondary. The first switching tube S1, the second switching tube S2, the third switching tube S3 and the fourth switching tube S4 on the side, and the fifth switching tube S5, the sixth switching tube S6, the seventh switching tube S7 and the second switching tube on the secondary side Eight switching tubes S8; the first switching tube S1 and the second switching tube S2 of the series switching tubes are connected in parallel with the third switching tube S3 and the fourth switching tube S4 connected in series, and the fifth switching tube S5 and the sixth switching tube S6 are connected in series connected in parallel with the seventh switching tube S7 and the eighth switching tube S8 connected in series; The driving signals of all switching tubes are 50% square wave signals, which are generated according to the phase difference D ₃ , and the duty ratios D ₁ and D ₂ of the primary side and secondary side bridge arm midpoint voltages; among them, the first switch The signals of the tube S1 and the second switching tube S2 are complementary, the signals of the third switching tube S3 and the fourth switching tube S4 are complementary, the signals of the fifth switching tube S5 and the sixth switching tube S6 are complementary, and the signals of the seventh switching tube S7 and the eighth switching tube are complementary. The signals of the switching tube S8 are complementary; the time when the switching tube S1 is ahead of the S3 is controlled by the duty ratio D1, the time when the fifth switching tube S5 is ahead of the seventh switching tube S7 is controlled by the duty cycle _D2 , and the _first switching tube S1 and the phase difference _D3 between the fifth switching tube S5 is controlled. 4. The method according to claim 1, wherein the output voltage controller is controlled by proportional-integral PI. 5. method according to claim 1, is characterized in that, described output voltage controller comprises voltage difference comparator, PI controller and limiter connected in sequence; Wherein, the input signal of voltage difference comparator is The given value and the actual measured value of the DC voltage on the secondary side are controlled by the PI controller to obtain the control signal α, and the limiter limits the control signal α to [0, 1], so that the output power and the control signal α have a monotonic relationship. And through calculation, the duty ratios D ₁ and D ₂ are limited within the range of [0, 1], and D3 is limited within the range of [0, 0.5].