A LCL resonant type current source DC-DC converter topology

Abstract

This invention discloses an LCL resonant current-source DC-DC converter topology, comprising a voltage-source inverter bridge, a high-frequency isolation transformer, an LCL resonant cavity, an uncontrolled rectifier bridge, and an output inductor. Based on the current-source phase-shifted full-bridge DC-DC converter topology, an LCL resonant cavity is connected in series between the secondary side of the high-frequency isolation transformer and the input side of the uncontrolled rectifier bridge. Fixed-frequency phase-shifting control is employed, effectively improving the output current and input voltage gain of the current-source phase-shifted full-bridge DC-DC converter, reducing the output current ripple coefficient, eliminating the backflow power problem of the current-source phase-shifted full-bridge converter over a wide range, and improving the stability of the converter during operation.

Description

Technical Field

[0001] This invention relates to the field of power supply technology, and in particular to an LCL resonant current source DC-DC converter topology. Background Technology

[0002] With the development of power electronics technology and the application demands in fields such as new energy electric vehicles and DC microgrids, the application range of high-frequency isolated DC-DC converters is becoming increasingly wide. Currently, the most commonly used high-frequency isolated DC-DC converters are voltage source type, capable of outputting stable DC voltage. However, this type of topology suffers from problems such as high current stress and large DC-side current ripple, making it unsuitable for applications requiring high output current, such as electrolytic hydrogen production, energy storage, and electromagnetic detection transmitters. In contrast, current source type phase-shifted full-bridge DC-DC converters, in addition to their wide output voltage and current range, simple structure, and convenient control, also feature low output current ripple due to the large series inductor on the output side. Therefore, they have high application value in medium-to-high power applications and applications with high current requirements.

[0003] However, existing current-source phase-shifted full-bridge DC-DC converters suffer from problems such as secondary-side duty cycle loss and power backflow due to transformer leakage inductance, thus reducing converter efficiency. Therefore, the performance of current-source phase-shifted full-bridge DC-DC converters needs further improvement to enhance efficiency and stability during energy conversion. Summary of the Invention

[0004] Purpose of the invention: To address the above problems, the purpose of this invention is to provide an LCL resonant current source DC-DC converter topology that eliminates the backflow power problem of current source phase-shifted full-bridge converters over a wide range, thereby improving the stability of the converter during operation.

[0005] Technical Solution: The present invention discloses an LCL resonant current source DC-DC converter topology, comprising a voltage source inverter bridge, a high-frequency isolation transformer, an LCL resonant cavity, an uncontrolled rectifier bridge, and an output inductor. The voltage source inverter bridge consists of two half-bridges connected in parallel, each half-bridge including an upper arm and a lower arm, both of which include a switching transistor. The midpoint of the two half-bridges serves as the output terminal of the voltage source inverter bridge. The output terminal of the voltage source inverter bridge is connected to the primary side of the high-frequency isolation transformer, and the secondary side of the high-frequency isolation transformer is connected to one end of the LCL resonant cavity. The other end of the LCL resonant cavity is connected to the input terminal of the uncontrolled rectifier bridge. The uncontrolled rectifier bridge consists of two half-bridges connected in parallel, each half-bridge including an upper arm and a lower arm, both of which include a diode. The midpoint of the two half-bridges serves as the input terminal of the uncontrolled rectifier bridge, and the output terminal of the uncontrolled rectifier bridge is connected to the output inductor.

[0006] Furthermore, the two half-bridges of the voltage source inverter bridge are respectively referred to as the first half-bridge and the second half-bridge. The two switches in the first half-bridge are referred to as S1 and S2, and the two switches in the second half-bridge are referred to as S3 and S4. Switches S1 and S3 are complementary to S2 and S4 respectively. The ratio of the phase difference of the drive signals of S1 and S3 to half a working cycle is the phase shift D.

[0007] Furthermore, the DC-DC converter control strategy adopts fixed-frequency phase-shift control, and the voltage source inverter bridge adopts phase-shift control.

[0008] Furthermore, the conduction angle of the uncontrolled rectifier bridge is calculated, as shown in the following expression:

[0009]

[0010] In the formula, Q = Z o / R is the quality factor, R is the load resistance, and Z is the load resistance. o =ω s L k The characteristic impedance is ω. s L is the resonant angular frequency. k This represents the inductance value on the right side of the LCL resonant cavity.

[0011] Furthermore, the output current and input voltage gain of the DC-DC converter are calculated, and the expressions are as follows:

[0012]

[0013] In the formula, I o V represents the output current value. in Where is the input voltage value, D is the shift ratio, and n is the turns ratio of the high-frequency isolation transformer.

[0014] Furthermore, the output power of the DC-DC converter is calculated, as shown in the following expression:

[0015]

[0016] Furthermore, the output current ripple coefficient of the DC-DC converter is calculated, and the expression is as follows:

[0017]

[0018] Furthermore, during the commutation process, the resonant capacitance C inside the LCL resonant cavity... k The pre-stage inductor L r The voltage is clamped to the negative value of the resonant capacitor voltage, so that the polarity of the primary current of the high-frequency isolation transformer is made the same as the polarity of the primary voltage in the next operating stage in advance, thus eliminating the power backflow problem. The calculation expression for the no-backflow operating range of the high-frequency isolation transformer is as follows:

[0019]

[0020] In the formula, T s β is the switching period, and β is the voltage v of the LCL resonant cavity capacitor. Ck With the primary voltage v of the high-frequency isolation transformer ab The phase difference between them, L r This is the inductance value on the left side of the LCL resonant cavity.

[0021] Furthermore, the design process for the resonant groove parameters of the LCL resonant cavity is as follows:

[0022] Step 1: Determine the appropriate Q value for the output current and input voltage gain range based on the actual usage requirements of the high-frequency isolation transformer;

[0023] Step 2: Calculate the turns ratio of the high-frequency isolation transformer. The calculation expression is as follows:

[0024]

[0025] Step 3: Calculate the characteristic impedance value. The calculation expression is as follows:

[0026]

[0027] Step 4: Calculate the LCL resonant cavity parameters. The calculation expression is as follows:

[0028]

[0029]

[0030] In the formula, f s It is the resonant frequency.

[0031] Beneficial effects: Compared with the prior art, the significant advantages of this invention are:

[0032] Based on the current-source phase-shifted full-bridge DC-DC converter topology, this invention connects an LCL resonant cavity in series between the secondary side of the high-frequency isolation transformer and the input side of the uncontrolled rectifier bridge. This improves the output current and input voltage gain of the current-source phase-shifted full-bridge DC-DC converter, reduces the current ripple coefficient, and eliminates the power backflow problem of the converter over a wide range. It also achieves zero-voltage turn-on or zero-current turn-off of the switching transistors on the voltage-source inverter bridge side across the entire power range, reducing converter power loss and improving the reliability and safety of the converter during operation. Attached Figure Description

[0033] Figure 1 This is a topology diagram of the LCL resonant current source DC-DC converter in the embodiment;

[0034] Figure 2This is a schematic diagram of the operating waveforms of the LCL resonant current source DC-DC converter in the embodiment;

[0035] Figure 3 This is a diagram showing the operating modes of the LCL resonant current source DC-DC converter in the embodiment;

[0036] Figure 4 This is the equivalent circuit diagram of the LCL resonant current source DC-DC converter in the embodiment;

[0037] Figure 5 The graph shows the relationship between the output current and input voltage gain H, the quality factor Q, and the shift ratio D when the transformer turns ratio and load resistance are fixed.

[0038] Explanation of symbols and labels in the attached drawings: L r —Left-side inductor of the LCL resonant cavity; C k —Resonant capacitor; L k —Inductance on the right side of the LCL resonant cavity; L o —Output-side energy storage inductor; R o —Equivalent load on the output side; C in —Input-side filter capacitor; v ab —Voltage at the midpoint of the two half-bridges in a voltage source type full-bridge; v cd —The midpoint voltage of the two half-bridges in a current-source type full-bridge; r —Transformer primary current; v Lr —Inductor voltage on the left side of the LCL resonant cavity; v Lk —Inductor voltage on the right side of the LCL resonant cavity; v Ck —LCL resonant capacitor voltage; i Lr —LCL resonant cavity pre-stage inductor current; i Lk —LCL resonant cavity stage inductor current; i Ck —Resonant capacitor current; I o —Output current; V in —Input voltage; D—Ratio of the phase difference between S1 and S3 drive signals to half a switching cycle; T s —Switching cycle; T d —Dead time of the switching transistors on the voltage source type full bridge. Detailed Implementation

[0039] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments.

[0040] like Figure 1The diagram shown illustrates the topology of an LCL resonant current source DC-DC converter as described in this embodiment. It includes a voltage source inverter bridge, a high-frequency isolation transformer, an LCL resonant cavity, an uncontrolled rectifier bridge, and an output inductor. The voltage source inverter bridge consists of two half-bridges connected in parallel. Each half-bridge includes an upper arm and a lower arm, and each arm includes a switching transistor, denoted as S1-S4. The midpoints a and b of the two half-bridges serve as the output terminals of the voltage source inverter bridge. The output terminal of the voltage source inverter bridge is connected to the primary side of the high-frequency isolation transformer. The secondary side of the high-frequency isolation transformer is connected to one end of the LCL resonant cavity, and the other end of the LCL resonant cavity is connected to the input terminal of the uncontrolled rectifier bridge. The uncontrolled rectifier bridge also consists of two half-bridges connected in parallel. Each half-bridge includes an upper arm and a lower arm, and each arm includes a diode, denoted as D1-D4. The midpoints c and d of the two half-bridges serve as the input terminals of the uncontrolled rectifier bridge, and the output terminal of the uncontrolled rectifier bridge is connected to the output inductor L. o .

[0041] The LCL resonant cavity includes two inductors and one resonant capacitor C. k The secondary side of the high-frequency isolation transformer is connected to the left inductor L. r One end, left inductor L r The other end is connected to the right inductor L. k One end and resonant capacitor C k On one side, the resonant capacitor C k The other side is connected to the secondary side of the high-frequency isolation transformer and the midpoint d of the half-bridge of the uncontrolled rectifier bridge, respectively, with the right inductor L... k The other end is connected to the midpoint c of the half-bridge of the uncontrolled rectifier bridge.

[0042] In one example, the two half-bridges of the voltage source inverter bridge are referred to as the first half-bridge and the second half-bridge, respectively. The two switches in the first half-bridge are referred to as S1 and S2, and the two switches in the second half-bridge are referred to as S3 and S4. The duty cycle of the drive signals of the four switches S1-S4 is 50%. Switches S1 and S3 are complementary to S2 and S4 respectively. The ratio of the phase difference between the drive signals of S1 and S3 to half a working cycle is the phase shift D.

[0043] In one example, the DC-DC converter control strategy employs fixed-frequency phase-shift control, while the voltage source inverter bridge uses phase-shift control.

[0044] In one example, the conduction angle of an uncontrolled rectifier bridge is calculated using the following expression:

[0045]

[0046] In the formula, Q = Z o / R is the quality factor, R is the load resistance, and Z is the load resistance. o =ω s Lk The characteristic impedance is ω. s L is the resonant angular frequency. k This represents the inductance value on the right side of the LCL resonant cavity.

[0047] In one example, the output current and input voltage gain of this DC-DC converter are calculated using the following expression:

[0048]

[0049] In the formula, I o V represents the output current value. in Where is the input voltage value, D is the shift ratio, and n is the turns ratio of the high-frequency isolation transformer.

[0050] In one example, the output power of the DC-DC converter is calculated using the following expression:

[0051]

[0052] The output current ripple coefficient of this DC-DC converter is calculated using the following expression:

[0053]

[0054] In one example, during the commutation process, the resonant capacitance C inside the LCL resonant cavity... k The pre-stage inductor L r The voltage is clamped to the negative value of the resonant capacitor voltage, so that the polarity of the primary current of the high-frequency isolation transformer is made the same as the polarity of the primary voltage in the next operating stage in advance, thus eliminating the power backflow problem. The calculation expression for the no-backflow operating range of the high-frequency isolation transformer is as follows:

[0055]

[0056] In the formula, T s β is the switching period, and β is the voltage v of the LCL resonant cavity capacitor. Ck With the primary voltage v of the high-frequency isolation transformer ab The phase difference between them, L r This is the inductance value on the left side of the LCL resonant cavity.

[0057] In one example, the design process for the resonant groove parameters of the LCL resonant cavity is as follows:

[0058] Step 1: Determine the appropriate Q value for the output current and input voltage gain range based on the actual usage requirements of the high-frequency isolation transformer;

[0059] Step 2: Calculate the turns ratio of the high-frequency isolation transformer. The calculation expression is as follows:

[0060]

[0061] Step 3: Calculate the characteristic impedance value. The calculation expression is as follows:

[0062]

[0063] Step 4: Calculate the LCL resonant cavity parameters. The calculation expression is as follows:

[0064]

[0065]

[0066] In the formula, f s It is the resonant frequency.

[0067] The schematic diagram of the drive signals and related operating waveforms of the switching transistors S1-S4 are as follows: Figure 2 As shown, in order to prevent shoot-through of the upper and lower switching transistors on the voltage source inverter bridge side during actual operation, Figure 2 The drive signal diagram takes dead time into account. Under this control strategy, the operating mode of the output current source type high-frequency isolated full-bridge DC-DC converter during the positive half-cycle is as follows: Figure 3 As shown.

[0068] Figure 3 The working principles of each mode are as follows:

[0069] Mode 1 [t0-t1]: Before time t0, the resonant capacitance C k Voltage applied to inductor L k Two ends, output inductor L o Charging the load, inductor L k The current on the primary side begins to decrease, and the current in the secondary diodes D2 and D3 begins to decrease, while current begins to appear in D1 and D4. At time t0, S1 is turned on, and the converter begins to operate in the energy transfer stage. At this time, v ab =V in Since the voltage across the resonant capacitor cannot change abruptly, the inductor L... r The voltage increases by V in Resonant capacitor C k Current equals inductance L r and inductor L k The sum of the currents. The circuit's operating state is as follows: Figure 3 As shown in (a).

[0070] Mode 2 [t1-t2]: At time t1, the inductance L r As the voltage polarity becomes negative, the current begins to gradually decrease. The circuit's operating state is as follows: Figure 3 As shown in (b).

[0071] Mode 3 [t2-t3]: At time t2, the inductance L kThe current becomes positive and continues to increase within the range of t2-t3, and the inductance L... r Current equals resonant capacitance C k and inductor L k The sum of the currents. The circuit's operating state is as follows: Figure 3 As shown in (c).

[0072] Mode 4 [t3-t4]: Within t3-t4, the inductance L k The current increases to the output current value I o And remain constant, therefore the inductance L k When the voltage drop is zero, the current through the secondary diodes D2 and D3 decreases to zero, while the current through D1 and D4 increases to the output current I. o The circuit's operating state is as follows: Figure 3 As shown in (d).

[0073] Mode 5 [t4-t5]: At time t4, S4 is turned off, and the primary current i r The system begins discharging the parallel equivalent capacitor of S3 and charging the parallel equivalent capacitor of S4. When the voltage across switch S3 drops to zero, the anti-parallel diode of S3 conducts, and the primary current freewheels through the anti-parallel diodes of S1 and S3. At this time, v ab =0, inductance L r Voltage decreases by V in The circuit's operating state is as follows: Figure 3 As shown in (e).

[0074] Mode 6 [t5-t6]: At time t5, S3 is turned on, and the circuit operates as follows: Figure 3 As shown in (f).

[0075] Mode 7 [t6-t7]: At time t6, the resonant capacitance C k Current reverses direction, capacitor voltage v Ck Reaching peak value, inductance L k The current is equal to the inductance L r and capacitor C k The sum of the currents. The circuit's operating state is as follows: Figure 3 As shown in (g).

[0076] Mode 8 [t7-t8]: At time t7, the inductance L r The current on the upper side becomes negative, and the primary current i r It also becomes negative, S3 achieves zero-voltage turn-on, and the current freewheels through the anti-parallel diodes S3 and S1, and the resonant capacitor C... k Current equals inductance L r and inductor L k The sum of the currents. Within t7-t8, the resonant capacitor supplies power to the inductor L. r Charging, inductor L rThe current begins to increase in the reverse direction. The circuit operation state is as follows: Figure 3 As shown in (h).

[0077] Mode 9 [t8-t9]: At time t8, S1 is turned off. Since the voltage across it is zero, S1 can achieve zero-voltage turn-off. The circuit operation state is as follows: Figure 3 As shown in (i).

[0078] Mode 10[t9-t 10 At time t9, capacitor C k and inductor L r The voltage polarity becomes negative, and the output inductance L o Inductor L supplies power to the load. k The current on the primary side begins to decrease, and the current in the secondary diodes D2 and D3 begins to decrease, while current begins to appear in D1 and D4. The circuit operation is as follows. Figure 3 As shown in (l).

[0079] Based on the above modal analysis and Figure 2 It can be seen that during one operating cycle of the converter, the current flowing through the transformer has the same polarity as the primary side voltage, and there is no stage where the polarity of the transmitted power is opposite to the average transmitted power. During operation, the resonant capacitor in the LCL resonant cavity charges the preceding inductor, causing the primary side current i... L The direction changes to be the same as the polarity of the primary voltage in the next working stage, thereby eliminating the return power.

[0080] Figure 4 The equivalent circuit diagram of the LCL resonant current source DC-DC converter is given, and the equivalent load is:

[0081]

[0082] In the formula, R is the output resistance, α is the conduction angle of the uncontrolled rectifier bridge, and ω s This is the resonant angular frequency. It can be seen that, due to the large inductor connected in series on the output side, the equivalent load exhibits inductive behavior.

[0083] Simultaneously, frequency domain analysis can yield the LCL resonant capacitor voltage v. Ck With the transformer primary voltage v ab The phase difference β between them is:

[0084]

[0085] In the formula, Q is the quality factor and α is the conduction angle of the uncontrolled rectifier bridge.

[0086] Figure 5The graph shows the relationship between the output current and input voltage gain H, the quality factor Q, and the shift ratio D when the transformer turns ratio n = 1 and the fixed load resistance R = 5Ω. It can be seen that the output current and input voltage gain H increase as the quality factor Q decreases, and increase as the shift ratio D increases.

[0087] The LCL resonant current-source DC-DC converter topology described in this invention, based on the current-source phase-shifted full-bridge DC-DC converter topology, connects an LCL resonant cavity in series between the secondary side of the high-frequency isolation transformer and the input side of the uncontrolled rectifier bridge. This improves the output current and input voltage gain of the current-source phase-shifted full-bridge DC-DC converter, reduces the current ripple coefficient, and eliminates the power backflow problem over a wide range. It achieves zero-voltage turn-on or zero-current turn-off of the voltage-source inverter bridge-side switches across the entire power range, reducing converter power loss and improving the reliability and safety of the converter during operation.

Claims

1. A topology for an LCL resonant current source DC-DC converter, characterized in that, The system includes a voltage source inverter bridge, a high-frequency isolation transformer, an LCL resonant cavity, an uncontrolled rectifier bridge, and an output inductor. The voltage source inverter bridge consists of two half-bridges connected in parallel, each half-bridge including an upper arm and a lower arm, both of which include a switching transistor. The midpoint of the two half-bridges serves as the output terminal of the voltage source inverter bridge. The output terminal of the voltage source inverter bridge is connected to the primary side of the high-frequency isolation transformer, and the secondary side of the high-frequency isolation transformer is connected to one end of the LCL resonant cavity. The other end of the LCL resonant cavity is connected to the input terminal of the uncontrolled rectifier bridge. The uncontrolled rectifier bridge also consists of two half-bridges connected in parallel, each half-bridge including an upper arm and a lower arm, both of which include a diode. The midpoint of the two half-bridges serves as the input terminal of the uncontrolled rectifier bridge, and the output terminal of the uncontrolled rectifier bridge is connected to the output inductor. The conduction angle of the uncontrolled rectifier bridge is calculated using the following expression: ； where Q = Z o R is the quality factor, R is the load resistance, Z o = ω s L k is the characteristic impedance, ω s is the resonant angular frequency, L k is the inductance value on the right side of the LCL resonant cavity; The output current and input voltage gain of this DC-DC converter are calculated using the following expressions: ； In the formula, I o V represents the output current value. in Where D is the input voltage value, n is the shift ratio, and n is the turns ratio of the high-frequency isolation transformer. The output power of this DC-DC converter can be calculated using the following expression: ； The output current ripple coefficient of this DC-DC converter is calculated using the following expression: ； In the formula, L o For output-side energy storage inductor; During the commutation process, the resonant capacitance C inside the LCL resonant cavity... k The pre-stage inductor L r The voltage is clamped to the negative value of the resonant capacitor voltage, so that the polarity of the primary current of the high-frequency isolation transformer is made the same as the polarity of the primary voltage in the next operating stage in advance, thus eliminating the power backflow problem. The calculation expression for the no-backflow operating range of the high-frequency isolation transformer is as follows: ； In the formula, T s β is the switching period, and β is the voltage v of the LCL resonant cavity capacitor. Ck With the primary voltage v of the high-frequency isolation transformer ab The phase difference between them, L r The inductance value on the left side of the LCL resonant cavity; The design process for the resonant slot parameters of the LCL resonant cavity is as follows: Step 1: Determine the appropriate Q value for the output current and input voltage gain range based on the actual usage requirements of the high-frequency isolation transformer; Step 2: Calculate the turns ratio of the high-frequency isolation transformer. The calculation expression is as follows: ； Step 3: Calculate the characteristic impedance value. The calculation expression is as follows: ； Step 4: Calculate the LCL resonant cavity parameters. The calculation expression is as follows: ； In the formula, f s C is the resonant frequency. k It is a resonant capacitor.

2. The LCL resonant current source DC-DC converter topology according to claim 1, characterized in that, The two half-bridges of the voltage source inverter bridge are designated as the first half-bridge and the second half-bridge, respectively. The two switches in the first half-bridge are designated as S1 and S2, and the two switches in the second half-bridge are designated as S3 and S4. Switches S1 and S3 are complementary to S2 and S4, respectively. The ratio of the phase difference between the drive signals of S1 and S3 to half a working cycle is called the phase shift ratio D.

3. The LCL resonant current source DC-DC converter topology according to claim 1, characterized in that, The DC-DC converter control strategy adopts fixed-frequency phase-shift control, and the voltage source inverter bridge adopts phase-shift control.

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