Partially parallel dual active bridge converter

Abstract

The invention belongs to the technical field of switching power supplies, and particularly relates to a partially parallel dual-active bridge converter. The converter comprises a high-voltage-side full-bridge circuit, an inductor and at least two low-voltage-side full-bridge circuits connected in parallel, each full-bridge circuit is connected with a filter capacitor in parallel, the high-voltage-side full-bridge circuit is connected with the two low-voltage-side full-bridge circuits through two transformers, and primary sides of the two transformers are connected in series; when the voltage required by the low-voltage side is lower and the current is larger, the number of the full-bridge circuits connected in parallel at the low-voltage side is larger. The high transformation ratio is realized by the two transformers, and the two transformers are connected in series at the high-voltage side, so that the currents at the high-voltage side of the transformers are equal, and the two active full bridges at the low-voltage side are automatically equalized in a steady state.

Description

Technical Field

[0001] The invention belongs to the technical field of switch power supplies, in particular to a partially parallel dual active bridge converter. Background Art

[0002] The DAB (Dual Active Bridge) converter is a highly efficient, bidirectional power conversion device that has received extensive attention in the field of power electronics in recent years. With the rapid development of applications such as renewable energy, energy storage, and electric vehicles, the demand for efficient, high-power-density power converters is increasing. The DAB converter has become an ideal choice for these applications due to its ability to flow energy in both directions, low switching losses, high power density, and good electrical isolation characteristics. One of its core features is the bidirectional energy transmission achieved through phase shift control technology, which gives it great flexibility in applications such as battery charging and discharging, inversion, and conversion. In addition, with the continuous advancement of high-frequency transformer technology, the size and weight of the DAB converter have been effectively reduced, further enhancing its application potential in portable devices and new energy vehicles.

[0003] However, despite the obvious performance advantages of DAB converters, they still face technical challenges such as high-frequency switching losses, magnetic losses, and system stability. Therefore, issues such as topology optimization, control strategy improvement, and loss management of DAB converters have become a hot topic in current research. Through continuous technological innovation and optimization, the advantages of DAB converters in terms of high efficiency, low loss, and flexibility will be further demonstrated, promoting their application in a wider range of fields.

[0004] Due to the irregularity and unpredictability of renewable energy, the large-scale access to renewable energy in the power grid will reduce the reliability and stability of the power grid operation. As mentioned above, the voltage on the bus side of the energy storage system is large, and the current on the energy storage system side is large. This requires that the active devices on the energy storage system side of the DC / DC converter have a large rated current, and a transformer with a large transformation ratio is required. Therefore, the present invention is based on the DAB converter, and through reasonable design, a partially parallel dual active bridge converter is obtained. Summary of the invention

[0005] In view of the shortcomings of the prior art, the present invention intends to solve the technical problem and provide a partially parallel dual active bridge converter. The converter has the advantages of high transformation ratio, automatic current sharing, simple structure, convenient control, modular expansion, etc. The high transformation ratio is achieved by two transformers. The high-voltage side windings of the two transformers are connected in series and then connected to the active full bridge on the high-voltage side; the low-voltage side windings of the two transformers are respectively connected to two external inductors, and then respectively connected to two active full bridges, and the DC sides of the two low-voltage side active full bridges are connected in parallel. Since the high-voltage side windings of the transformers are connected in series, the low-voltage side automatically shares the current.

[0006] The present invention solves the technical problem by adopting the following technical solution:

[0007] A partially parallel dual active bridge converter, characterized in that it includes a full bridge circuit on the high voltage side, an inductor and at least two parallel full bridge circuits on the low voltage side, each full bridge circuit is connected in parallel with a filter capacitor, the full bridge circuit on the high voltage side and the two full bridge circuits on the low voltage side are respectively connected through two transformers, and the primary sides of the two transformers are connected in series; when the voltage required on the low voltage side is lower and the current is larger, the number of parallel full bridge circuits on the low voltage side is more.

[0008] Further, when there are two full-bridge circuits connected in parallel on the low-voltage side, assuming that the full-bridge circuit on the high-voltage side includes a switch S 1 ~S 4 , a full-bridge circuit on the low-voltage side includes MOS tube Q 1 ~Q 4 , another full-bridge circuit on the low-voltage side includes MOS tube Q 5 ~Q 8 ; The process of using APS phase shift modulation is as follows:

[0009] t 0 ~t 1 Phase: Switch S 2 , S 3 Conducting, MOS tube Q 1 , Q 4 , Q 5 , Q 8 The inductor is turned on. At this time, the voltage on both sides of the inductor is calculated according to formula (1), and t is calculated according to formula (2). 1 The inductor current at the moment;

[0010] V Lac =V in +2nV out (1)

[0011]

[0012] Where V Lac Represents the voltage across the inductor, V in represents the input voltage of the transformer, n represents the transformer transformation ratio, V out represents the output voltage of the transformer, i Lac (t 0 ),i Lac (t 1 ) represent t 0 ,t 1 The inductor current at the moment, L ac Indicates the inductance value, It indicates the multiple of the phase shift angle of a full-bridge circuit on the low voltage side in the entire switching period;

[0013] t 1 ~t 2 Phase: Switch S 2 , S 3 Conducting, MOS tube Q 1 , Q 4 Turn off, MOS tube Q 2 , Q 3 , Q 5 , Q 8 If the 2 The inductor current at the moment is expressed as:

[0014]

[0015] In the formula, i Lac (t 2 ) indicates t 2 The inductor current at time It indicates the multiple of the phase shift angle of a full-bridge circuit on the low voltage side in the entire switching period;

[0016] t 2 ~t 3 Phase: Switch S 2 , S 3 Conducting, MOS tube Q 5 , Q 8 Turn off, MOS tube Q 2 , Q 3 , Q 6 , Q 7 The inductor is turned on. At this time, the voltage on both sides of the inductor is calculated according to formula (4), and t is calculated according to formula (5). 3 The inductor current i at the moment Lac (t 3 );

[0017] V Lac =V in -2nV out (4)

[0018]

[0019] t 3 ~t 4 Phase: Switch S 2 , S 3 Shutdown, S 1 , S 4 Conducting, MOS tube Q 2 , Q 3 , Q 6 , Q 7 The inductor is turned on. At this time, the voltage on both sides of the inductor is calculated according to formula (6), and t is calculated according to formula (7). 4 The inductor current i at the momentLac (t 4 );

[0020] V Lac =-V in -2nV out (6)

[0021]

[0022] t 4 ~t 5 Phase: Switch S 1 , S 4 Conducting, MOS tube Q 2 , Q 3 Shutdown, Q 1 , Q 4 conduction, and the rest remain unchanged, then t 5 The inductor current i at the moment Lac (t 5 ) is expressed as:

[0023]

[0024] t 5 ~t 6 Phase: Switch S 1 , S 4 Conducting, MOS tube Q 6 , Q 7 Shutdown, Q 5 , Q 8 The inductor is turned on. At this time, the voltage on both sides of the inductor is calculated according to formula (9), and t is calculated according to formula (10). 6 The inductor current i at the moment Lac (t 6 );

[0025] V Lac =-V in +2nV out (9)

[0026]

[0027] Furthermore, the inductor current at each moment in half a switching cycle is calculated by the following formula:

[0028]

[0029] The average value of the inductor current in half a switching cycle is:

[0030]

[0031] The output power expression of the converter is:

[0032]

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] 1. In this topology, the high transformation ratio of the converter is realized by two transformers, so a higher transformation ratio can be achieved.

[0035] 2. Since the two transformers are connected in series on the high-voltage side, the currents on the high-voltage side of the transformers are equal, so the two active full-bridges on the low-voltage side automatically share the current in steady state.

[0036] 3. The voltage at the energy storage side of the converter is small and the current is large, so the current stress of the low-voltage side switching devices can be reduced in high-power situations.

[0037] 4. The number of full-bridge circuits connected in parallel on the low-voltage side is not fixed. When the voltage required on the low-voltage side is lower and the current is larger, more full-bridge circuits can be connected in parallel to reduce the current stress on the low-voltage side. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 is a topological diagram of the present invention;

[0039] Figure 2 This is the APS phase shift modulation waveform;

[0040] Figure 3 It is the switching mode under APS phase shift modulation. DETAILED DESCRIPTION

[0041] Specific embodiments are given below in conjunction with the accompanying drawings. The specific embodiments are only used to introduce the technical solutions of the present invention in detail and are not intended to limit the protection scope of the present application.

[0042] The present invention provides a partially parallel dual active bridge converter (PPDAB for short), including a full-bridge circuit on the high-voltage side, an inductor, and at least two full-bridge circuits in parallel on the low-voltage side, each full-bridge circuit is connected in parallel with a filter capacitor, and the full-bridge circuit on the high-voltage side and the two full-bridge circuits on the low-voltage side are respectively connected through two transformers, and the primary sides of the two transformers are connected in series, so when the parameters of the two transformers are the same, the secondary currents will be exactly the same, thus avoiding the current sharing problem. The number of full-bridge circuits in parallel on the low-voltage side is not fixed. When the voltage required on the low-voltage side is lower and the current is larger, more full-bridge circuits can be connected in parallel to reduce the current stress on the low-voltage side.

[0043] The following is an example of a topology of two full-bridge circuits in parallel. The full-bridge circuit on the high-voltage side includes a switch S 1 ~S 4 , a full-bridge circuit on the low-voltage side includes MOS tube Q 1 ~Q 4 , another full-bridge circuit on the low-voltage side includes MOS tube Q5 ~Q 8 ; The working principle of PPDAB converter under APS phase-shift modulation is introduced.

[0044] When APS phase shift modulation is used, the output power of the converter can be controlled by adjusting the two phase shift angles between the two parallel full-bridge circuits on the low-voltage side and the full-bridge circuit on the high-voltage side. When the current reaches a steady state, the modulation waveform is as follows Figure 2 As shown, and are the multiples of the phase shift angle of the two full-bridge circuits on the low-voltage side in the entire switching cycle. When the converter outputs power from the high-voltage side to the low-voltage side, the range of these two values ​​should be 0 to 0.25. For the convenience of analysis, the ratio of the number of turns of the primary and secondary sides of the transformer is n:1, the switching cycle is T, and the input end is a constant voltage source with a fixed voltage value of V in The output end is a constant voltage load, and its voltage value is fixed at V out , the inductance value is L ac , the inductor current is i Lac , the voltage across the inductor is V Lac , and ignore the dead time and the switch drain-source voltage V gs Taking into account the factors such as the rise and fall time, and assuming that the switch tubes, transformers and other devices used are ideal devices with zero loss, the entire switching cycle can be divided into 6 modes, such as Figure 3 As shown, the inductor current under different modes is analyzed as follows:

[0045] Mode a(t 0 ~t 1 Stage): High voltage side S 2 , S 3 On, low voltage side Q 1 , Q 4 , Q 5 , Q 8 The output voltage is superimposed on the input voltage through the two transformers and applied to the inductor. The inductor current increases in a positive direction and has the largest slope. The voltage calculation formula across the inductor is shown in formula (1). Assuming t 0 The inductor current at this moment is i Lac (t 0 ), then t 1 The calculation formula of the inductor current at the moment is shown in formula (2):

[0046] V Lac =V in +2nV out (1)

[0047]

[0048] Mode b(t1 ~t 2 Stage): High voltage side S 2 , S 3 Still conducting, low voltage side Q 1 , Q 4 Shutdown, Q 2 , Q 3 , Q 5 , Q 8 The output voltages are coupled by two transformers and cancel each other out on the primary side. Therefore, the voltage across the inductor is V in , then t 2 The inductor current at this moment is shown in formula (3):

[0049]

[0050] Mode c(t 2 ~t 3 Stage): High voltage side S 2 , S 3 On, low voltage side Q 5 , Q 8 Shutdown, Q 2 , Q 3 , Q 6 , Q 7 The voltage V across the inductor is Lac The calculation formula is (4), then t 3 The inductor current at this moment is shown in formula (5);

[0051] V Lac =V in -2nV out (4)

[0052]

[0053] Mode d(t 3 ~t 4 Stage): High voltage side S 2 , S 3 Shutdown, S 1 , S 4 On, low voltage side Q 2 , Q 3 , Q 6 , Q 7 Still conducting, the inductor current first decreases in the positive direction and then increases in the negative direction. The voltage V Lac The calculation formula is (6), t 4 The inductor current at the moment is shown in formula (7);

[0054] V Lac =-V in -2nVout (6)

[0055]

[0056] Mode e(t 4 ~t 5 Stage): High voltage side S 1 , S 4 On, low voltage side Q 2 , Q 3 Shutdown, Q 1 , Q 4 The inductor voltage is similar to that of mode b but in the opposite direction, which is -V in , t 5 The calculation formula of the inductor current at the moment is shown in formula (8);

[0057]

[0058] Mode f(t 5 ~t 6 Stage): High voltage side S 1 , S 4 On, low voltage side Q 6 , Q 7 Shutdown, Q 5 , Q 8 When the inductor is turned on, the calculation formula of the inductor voltage is as shown in formula (9), t 6 The calculation formula of the inductor current at the moment is shown in formula (10);

[0059] V Lac =-V in +2nV out (9)

[0060]

[0061] When the circuit reaches a steady state, according to the symmetry of the inductor current, we can obtain equation (11):

[0062] i Lac (t 3 )=-i Lac (t 0 ) (11)

[0063] By combining the above expressions of the inductor current, we can solve the expression of the inductor current at each moment in half a switching cycle, as shown in equation (12);

[0064]

[0065] According to the above formula, the average value of the inductor current in half a cycle can be solved, as shown in formula (13);

[0066]

[0067] Then, the expression of the converter output power can be obtained from the symmetry of the inductor current, as shown in equation (14);

[0068]

[0069] The calculation formula of the square of the effective value of the inductor current can also be derived from formula (12), as shown in formula (15);

[0070]

[0071] The effective value of the inductor current is used as the evaluation standard of the current stress on the PPDAB converter. That is, it is believed that the larger the effective value of the inductor current is, the greater the current stress on the devices in the converter is.

[0072] Any matters not described in the present invention are applicable to the prior art.

Claims

1. A partially parallel dual active bridge converter, characterized in that: It includes a full-bridge circuit on the high-voltage side, an inductor and at least two parallel full-bridge circuits on the low-voltage side. Each full-bridge circuit is connected in parallel with a filter capacitor. The full-bridge circuit on the high-voltage side and the two full-bridge circuits on the low-voltage side are connected through two transformers respectively, and the primary sides of the two transformers are connected in series. When the voltage required on the low-voltage side is lower and the current is larger, the number of parallel full-bridge circuits on the low-voltage side is more.

2. The partially parallel dual active bridge converter according to claim 1, characterized in that: When there are two full-bridge circuits connected in parallel on the low-voltage side, assuming that the full-bridge circuit on the high-voltage side includes switches S1 to S4, one full-bridge circuit on the low-voltage side includes MOS tubes Q1 to Q4, and the other full-bridge circuit on the low-voltage side includes MOS tubes Q5 to Q8; the process of using APS phase shift modulation is as follows: Stage t0~t1: switches S2 and S3 are turned on, and MOS tubes Q1, Q4, Q5, and Q8 are turned on. At this time, the voltage on both sides of the inductor is calculated according to formula (1), and the inductor current at time t1 is calculated according to formula (2); IN Lac =V in +2nV out (1) Where V Lac Represents the voltage across the inductor, V in represents the input voltage of the transformer, n represents the transformer transformation ratio, V out represents the output voltage of the transformer, i Lac (t0),i Lac (t1) represents the inductor current at t0 and t1 respectively, L ac Indicates the inductance value, It indicates the multiple of the phase shift angle of a full-bridge circuit on the low voltage side in the entire switching period; In the stage of t1-t2: switches S2 and S3 are turned on, MOS tubes Q1 and Q4 are turned off, and MOS tubes Q2, Q3, Q5, and Q8 are turned on. The inductor current at time t2 is expressed as: In the formula, i Lac (t2) represents the inductor current at time t2, It indicates the multiple of the phase shift angle of a full-bridge circuit on the low voltage side in the entire switching period; Stage t2-t3: switches S2 and S3 are turned on, MOS tubes Q5 and Q8 are turned off, and MOS tubes Q2, Q3, Q6, and Q7 are turned on. At this time, the currents on both sides of the inductor are calculated according to formula (4), and the inductor current i at time t3 is calculated according to formula (5). Lac (t3); IN Lac =V in -2nV out (4) Stage t3-t4: switches S2 and S3 are turned off, S1 and S4 are turned on, and MOS tubes Q2, Q3, Q6, and Q7 are turned on. At this time, the voltage on both sides of the inductor is calculated according to formula (6), and the inductor current i at time t4 is calculated according to formula (7): Lac (t4); IN Lac =-V in -2nV out (6) In the stage of t4-t5: switches S1 and S4 are turned on, MOS tubes Q2 and Q3 are turned off, Q1 and Q4 are turned on, and the rest remain unchanged. Then the inductor current i at time t5 is Lac (t5) is expressed as: Stage t5-t6: switches S1 and S4 are turned on, MOS tubes Q6 and Q7 are turned off, and Q5 and Q8 are turned on. At this time, the voltage on both sides of the inductor is calculated according to formula (9), and the inductor current i at time t6 is calculated according to formula (10): Lac (t6); IN Lac =-V in +2nV out (9) 。 3. The partially parallel dual active bridge converter according to claim 2, characterized in that: The inductor current at each moment in half a switching cycle is calculated by the following formula: The average value of the inductor current in half a switching cycle is: The output power expression of the converter is: 。

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