CN1545194A - Cascaded Bidirectional DC-DC Converter - Google Patents

Abstract

The invention relates to a cascade two-way DC-DC converter, composed of two parts: nonisolated two-way DC-DC converter and high-frequency DC transformer, where the former includes circuittopologies such as two-way boost, two-way buck, two-way boost-buck, etc. and the latter is composed of high-frequency inverter/rectifier, high-frequency transformer, and high-frequency rectifier/inverter unit, where the first and fourth ones include push-pull circuit, half-bridge circuit, full-bridge circuit, push-pull forward circuit, double-tube forward circuit, active clamped forward circuit, nonsymmetrical half-bridge circuit, and other circuits. It implements two-way energy flow and electrical isolation, where all its switch tubes are zero-voltage switches, and has the advantage of relatively independent two parts, convenience for control, high conversion efficiency and power density, and simple circuit structure, etc.

Description

Cascaded Bidirectional DC-DC Converter

technical field

The cascaded bidirectional DC-DC converter of the invention belongs to a power electronic converter.

Background technique

There are three traditional solutions for isolated bidirectional DC-DC converters:

1. Phase-shifting bidirectional conversion technology

This technology uses transformer leakage inductance (or external inductance) to complete bidirectional energy transmission through bridge arm phase shifting. It uses leakage inductance to transfer energy, limiting the application of this technology in high-power applications.

2. Voltage type-current type combined bidirectional conversion technology

This technology is the combined voltage mode-current mode topology, and its main drawback is that the voltage spikes on the switching devices caused by the leakage inductance of the transformer are large. This drawback is due to the current mode topology involved in this technology, which limits the application of this technology.

3. Flyback bidirectional conversion technology

This technology uses a single-ended flyback converter as the main topology. Its main defect is that it uses a coupled inductor (flyback transformer) to transmit energy, which limits its application in high-power applications.

Contents of the invention

The purpose of the present invention is to aim at the above-mentioned defects in the prior art, and develop a method that can overcome the existing defects, realize zero-voltage switching and electrical isolation of all switching tubes, have two parts that are relatively independent, can independently realize control, and have a simple circuit cascaded bidirectional DC-DC converter.

The cascaded bidirectional DC-DC converter of the present invention is composed of a relatively independent non-isolated bidirectional DC-DC converter and a high-frequency DC transformer connected to each other to form a cascaded structural circuit. Among them, the non-isolated bidirectional DC-DC converter can be a bidirectional step-up (Boost) converter, a bidirectional step-down (Buck) converter, a bidirectional step-down (Buck/Boost) converter and other topologies; the DC transformer consists of The high-frequency inverter/rectifier circuit is connected to the primary side of the high-frequency transformer, and its secondary side is connected to the high-frequency rectifier/inverter circuit. The high-frequency rectifier/inverter unit can be full-wave rectifier/push-pull inverter, full-bridge rectifier /Full-bridge inverter, half-bridge rectifier/half-bridge inverter, push-pull forward rectification/push-pull forward inverter and other structures, the same high-frequency inverter/rectifier unit can also be push-pull inverter/full-wave rectifier , Full-bridge inverter/full-bridge rectifier, half-bridge inverter/half-bridge rectifier, push-pull forward inverter/push-pull forward rectifier and other structures.

Description of drawings

Figure 1. Block diagram of a cascaded bidirectional DC-DC converter. Among them, figure (a) is a cascaded connection of a non-isolated bidirectional converter and a high-frequency DC transformer, and figure (b) is a cascaded connection of a high-frequency DC transformer and a non-isolated bidirectional converter.

Figure 2. Schematic diagram of the main circuit of three typical circuit structures of non-isolated bidirectional DC-DC converters. Figure (c) is a schematic diagram of the main circuit of a bidirectional boost converter, Figure (d) is a schematic diagram of the main circuit of a bidirectional buck converter, and Figure (e) is a schematic diagram of the main circuit of a bidirectional buck converter.

Figure 3. Schematic diagram of the main circuit composed of a high-frequency DC transformer.

Figure 4. Schematic diagram of the constituent units of a DC transformer. Among them, picture (f) is a push-pull circuit, picture (g) is a half-bridge circuit, picture (h) is a full-bridge circuit, picture (i) is a push-pull forward circuit, picture (j) is a two-tube forward circuit, Figure (k) is an active clamp forward circuit, and Figure (1) is an asymmetrical half-bridge circuit.

Figure 5. Two typical main circuit schematics of cascaded bidirectional DC-DC converters. Among them, the figure (m) is a cascaded type composed of non-isolated step-down (Buck) bidirectional DC-DC converter + full-bridge inverter/full-bridge rectifier and full-bridge rectifier/full-bridge inverter composed of cascaded DC transformers Schematic diagram of the main circuit of the bidirectional DC-DC converter; Figure (n) is a non-isolated boost (Boost) bidirectional DC-DC converter + push-pull inverter/full-wave rectifier and full-bridge rectifier/full-bridge inverter. Schematic diagram of the main circuit of the cascaded bidirectional DC-DC converter composed of cascaded DC transformers.

Figure 6. Schematic diagram of the main circuit of the non-isolated bidirectional step-up DC-DC converter.

Figure 7. Non-isolated bidirectional boost (Boost) DC-DC converter inductor current and other current and voltage waveforms.

Figure 8. Equivalent modal diagram of a bidirectional step-up DC-DC converter (using the alternating working mode of inductor current iLIII).

Figure 9. Schematic diagram of the main circuit of a DC transformer composed of a push-pull circuit and a full-bridge circuit.

Figure 10. DC transformer working principle waveform.

Figure 11. Schematic diagram of the main circuit of the series-parallel structure of the cascaded bidirectional DC-DC converter.

Detailed ways

Figure 1 is a structural block diagram of a cascaded bidirectional DC-DC converter. It can be seen from Figure 1 that the cascaded bidirectional DC-DC converter is formed by connecting a non-isolated bidirectional DC-DC converter and a high-frequency DC transformer. That is, the non-isolated bidirectional converter is cascaded with the high-frequency DC transformer, or conversely, the high-frequency DC transformer is cascaded with the non-isolated bidirectional converter.

The non-isolated bidirectional DC-DC converter can be a bidirectional boost converter shown in Figure (c) in Figure 2, a bidirectional buck converter circuit shown in Figure (d) and a bidirectional buck converter circuit shown in Figure (e) Bidirectional conversion topologies such as bidirectional buck-boost converters.

The composition of the high-frequency DC transformer is shown in Figure 3, that is, the high-frequency inverter/rectifier circuit is connected to the primary side of the high-frequency transformer, and the secondary side of the high-frequency transformer is connected to the high-frequency rectifier/inverter circuit. Among them, the high-frequency inverter/rectifier unit and the high-frequency rectifier/inverter unit can adopt circuits of several structural forms as shown in FIG. 4 . The coupling relationship between the high-frequency inverter/rectifier unit and the high-frequency transformer connected to the high-frequency rectifier/inverter unit can be arbitrarily selected and coordinated as required.

Using the structural block diagram shown in Figure 1, several non-isolated bidirectional DC-DC conversion topologies shown in Figure 2, the schematic diagram of the high-frequency DC transformer shown in Figure 3 and the DC transformer components shown in Figure 4, it can be constructed Cascaded bidirectional DC-DC converter topologies with different structures. Figure 5 shows the topology diagrams of the two forms. Among them, the figure (m) is a cascaded type composed of non-isolated step-down (Buck) bidirectional DC-DC converter + full-bridge inverter/full-bridge rectifier and full-bridge rectifier/full-bridge inverter composed of cascaded DC transformers Schematic diagram of a bidirectional DC-DC converter; Figure (n) is a DC transformer stage composed of a non-isolated boost (Boost) bidirectional DC-DC converter + push-pull inverter/full-wave rectifier and full-bridge rectifier/full-bridge inverter A schematic diagram of a cascaded bidirectional DC-DC converter composed of cascades. Take the topology shown in Figure (n) as an example to illustrate its working principle.

Working principle of non-isolated boost (Boost) bidirectional DC-DC converter

The cascaded bidirectional DC-DC converter consists of two parts, and the control circuits of these two parts can be independent of each other, so their working principles can be explained separately.

A boost bidirectional DC-DC converter is formed by replacing the unidirectional switch of the boost converter with a bidirectional switch. Figure 6 is a non-isolated boost (Boost) bidirectional DC-DC converter, in which a power MOSFET is used to represent a bidirectional switch. The bidirectional switch is an active controllable switch with bidirectional current flow capability, including Power MOSFET, IGBT, CoolMOS, or a similar switch invented in the future, or a composite switch structure with the same function. V ₁ and V ₂ are DC voltage sources or DC active loads. In the boost type (Boost) bidirectional DC-DC converter, the inductor L has three working modes. Figure 7 shows the control signal of the switching tube and the waveform of the inductor current.

In the first working mode, the inductor current (i _LI ) is always greater than zero, and the energy flows from the voltage source V ₁ to the voltage V ₂ side, which is a conventional boost converter. During the conduction period of the switch tube _S1 , the voltage _V1 is applied to the inductor _L1 , and the inductor current increases. After the switch tube _S1 is turned off, the diode _D2 conducts freewheeling, and the voltage on the inductor _L1 is: V ₂ -V ₁ , the inductor current decreases. Assuming that the conduction duty cycle of the switch tube _S1 is D, the positive and negative "volt-second" areas on the inductor _L1 are equal in steady state operation:

${\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; D.</span>}}$

In the second working mode, the inductor current (i _LII ) is always less than zero, and the energy flows from the voltage source V ₂ to the voltage V ₁ side, which is a conventional step-down (Buck) converter. During the conduction period of the switch tube S ₂ , the voltage on the inductor L ₁ is: V ₂ -V ₁ , and the inductor current increases. After the switch tube S _{2 is turned off, the diode D 1 conducts freewheeling, and the voltage V 1 is added} to the inductor L ₁ , the inductor current decreases. Assuming that the conduction duty cycle of the switching tube _S2 is (1-D), the positive and negative "volt-second" areas on _L1 are equal in steady state operation:

V ₁ =(1-D)V ₂

In the third working mode, the inductor current crosses zero. When the average value of the inductor current is greater than 0, the energy flows from the voltage source V ₁ to the voltage V ₂ source. When the average value of the inductor current is less than 0, the energy flows from the voltage source V ₂ flow to voltage source V ₁ . There are 6 working modes when energy flows from voltage source V ₁ to voltage source V ₂ . The equivalent circuit is shown in Figure 8.

[t ₀ -t ₁ ] Before time t ₀ , diode D ₁ conducts freewheeling, and at time t ₀ , switching tube S ₁ conducts with zero voltage. i _L increases under the action of voltage _V1 .

[t ₁ -t ₂ ] At time t ₁ , the inductor current crosses zero and increases through the switch tube S ₁ , and the inductor current i _L reaches the maximum value i _Lmax at time _{t 2} .

[t ₂ -t ₃ ] At time t ₂ , the switch tube S ₁ is turned off, the diode D ₂ continues to flow naturally, and the inductor current i _L decreases under the action of the voltage V ₂ -V ₁ .

[t ₃ -t ₄ ] At time t ₃ , switch tube S ₂ is turned on with zero voltage, and S ₂ is in synchronous rectification mode. The inductor current provides energy to the capacitor C and the load through _S2 .

[t ₄ -t ₅ ] At time t ₄ , the inductor current crosses zero under the action of the voltage V ₂ -V ₁ and flows in reverse through the switch tube S ₂ .

[t ₅ -t ₆ ] At time t ₅ , switch S ₂ is turned off, and the inductor current reaches the minimum value i _Lmin , after which diode D ₁ freewheels, and at time t ₆ S ₁ is turned on with zero voltage to start the next switching cycle.

When the power flow is reversed, the working mode is similar, which is omitted here.

In this mode of operation, assuming that the conduction duty cycle of the switch tube _S1 is D, the positive and negative "volt-second" areas on the inductor _L1 during steady-state operation are equal, which can also be obtained: V ₁ =(1-D )V ₂ .

In this working mode, the switch tubes S ₁ and S ₂ are zero-voltage turn-on (ZVS), and the switching loss is small; the diodes D ₁ and D ₂ are naturally turned on and off, and there is no reverse recovery problem. Therefore, by rationally designing the inductor to make the circuit work in the third working mode, reliable and efficient operation of the circuit can be realized.

Working principle of DC transformer

A DC transformer can transform a DC voltage into another or more DC voltages proportional to it. Usually, the switching tube of the DC transformer works under a fixed duty ratio to complete the voltage conversion function without voltage regulation control. Including one-way and two-way two types. In the bidirectional DC transformer, the switching tubes used are bidirectional switches. The following uses the topology shown in FIG. 9 as an example to illustrate its working principle. In Fig. 9, L _lk is the equivalent leakage inductance of the transformer, and V ₁ and V ₂ are DC voltage sources or DC active loads.

In the topology shown in Figure 9, the switching tubes S ₃ (S ₅ , S ₈ ) and the switching tubes S ₄ (S ₆ , S ₇ ) are turned on complementary (with a dead zone to avoid direct connection), and half of the The switching cycle, so the equivalent duty cycle is 1, so the transformation ratio of the DC transformer is equal to the transformation ratio of the high frequency transformer. Figure 10 is the waveform of the working principle, where V _gs3 (V _gs5 , V _gs8 ), V _gs4 (V _gs6 , V _gs7 ) are the switching tube control signals, and V ₄ and V ₅ are the voltages added to both sides of the equivalent leakage inductance L _lk Voltage waveform, V _Llk is the voltage waveform added to the equivalent leakage inductance, and i _Llk is the current in the equivalent leakage inductance. There are 6 switching modes in the whole switching cycle, and its working principle is explained in detail below.

[t ₀ -t ₁ ] Before time t ₀ , transformer T _r is magnetically reset, diode D ₃ is in freewheeling state, and diode D ₅ (D ₈ ) and diode D ₆ (D ₇ ) are turned on and commutated at the same time. At time t ₀ , switch S ₃ is turned on with zero voltage (ZVS), and the leakage inductance current continues to increase at the slope of V _m /L _lk (assuming that the amplitude of V _Llk is V _m ), and switch S ₅ (S ₈ ) also Due to the diode D ₅ (D ₈ ) freewheeling can conduct at zero voltage (ZVS).

[t ₁ -t ₂ ] At time t ₁ , the leakage inductance current i _Llk reaches the load current value, the voltage applied to the inductor L _lk is 0, and the power is transmitted to the voltage V ₃ side until the switch tube S ₃ is turned off at time t ₂ .

[t ₂ -t ₃ ] At time t ₂ , the switch tube S ₃ is softly turned off under the buffer of its output junction capacitance, and at the same time D ₄ starts conducting to reset the transformer magnetically. Diode D ₆ (D ₇ ) and diode D ₅ (D ₈ ) conduct commutation at the same time, so switch tube S ₅ (S ₈ ) is softly turned off. At time _t3 , S ₄ is turned on at zero voltage (ZVS) when diode D ₄ is freewheeling, and switch S ₆ (S ₇ ) is also turned on at zero voltage (ZVS) when diode D ₆ (D ₇ ) is freewheeling, and the converter enters the second half of the switching cycle. The work of the second half cycle is symmetrical to that of the first half cycle, which is omitted here.

FIG. 11 is a block diagram of a cascaded bidirectional DC-DC converter with a series-parallel structure according to the present invention. Among them, non-isolated bidirectional DC-DC converters can be composed of parallel or interleaved parallel structures; high-frequency DC transformers can be composed of parallel, series or multiple output/input structures; as shown in Figure 11 (o), Figure (p) and Figure (q) shown.

Claims (4)

1. a tandem type bidirectional DC-DC converter is characterized in that, does not isolate bidirectional DC-DC converter and high frequency commutator transformer two parts are interconnected to constitute by relatively independent.

2. according to the described tandem type bidirectional DC-DC converter of claim 1, it is characterized in that not isolating bidirectional DC-DC converter and comprise bidirectional voltage boosting formula (Boost) DC-DC converter, two-way step down formula (Buck) DC-DC converter, two-way step-down/up type (Buck/Boost) DC-DC converter, two-way two level or multilevel topologys such as two-way mound gram (Cuk) DC-DC converter.

3. according to the described tandem type bidirectional DC-DC converter of claim 1, it is characterized in that the high frequency commutator transformer is connected in the former limit of high frequency transformer by high-frequency inversion/rectification circuit, the high frequency transformer secondary is connected in high-frequency rectification/inverter circuit and constitutes.Wherein high-frequency inversion/rectification unit and high-frequency rectification/inversion unit can adopt push-pull circuit, half-bridge circuit, full-bridge circuit, push-pull ortho-exciting circuit, double tube positive exciting circuit, active clamp forward circuit, asymmetry half-bridge circuit etc.

4. a tandem type bidirectional DC-DC converter is characterized in that, will not isolate parallel connection that bidirectional DC-DC converter forms parallel connection or crisscross parallel form and high frequency commutator transformer composition, connect or the multichannel output form is interconnected to constitute.

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