CN102013810A - Double-circuit double-tube forward shock combined converter with output midpoint - Google Patents

Abstract

Half-bridge inverters are widely used in low-voltage inverter applications, but their power supply voltage needs to provide a midpoint. The secondary side of the traditional dual-circuit dual-transistor forward combination converter cannot output positive and negative polarity voltages, and the secondary rectifier diodes and freewheeling diodes are subjected to relatively large current stress, making device selection difficult. This patent proposes a dual-transistor forward DC combined converter with an output midpoint with a simple structure—a dual-circuit dual-transistor forward combined converter with an output midpoint, which solves the problem of being unable to output positive and negative polarity voltages and secondary The single-channel current rating of the edge is too large, and the problem of device selection is difficult. Its circuit features are as follows: the main circuit is two sets of double-tube forward converters connected in parallel on the primary side, the transformer has two secondary sides, and the secondary side is connected in parallel with the corresponding transformer secondary side to form two outputs, and the two outputs are connected in series to form Output the midpoint structure. It ensures that the voltage output has positive and negative poles, and at the same time reduces the power rating of a single transformer and the current rating of the secondary rectifier and freewheeling tube.

Description

Dual-channel dual-transistor forward combined converter with output midpoint

technical field

The invention relates to a double-channel double-tube forward combination converter with a midpoint output band, which belongs to the DC conversion technology in power conversion.

Background technique

In the case where the input and output of the circuit require isolation, the DC converter usually uses a high-frequency isolation transformer to achieve electrical isolation. The loss and volume of high-frequency isolation transformers occupy a large proportion in high-power DC transformers, so how to optimize the design to reduce the loss and volume of high-frequency isolation transformers is very important.

At present, half-bridge inverters are widely used in low-voltage inverter applications, but their power supply voltage needs to provide a midpoint. Therefore, it is necessary for the direct-to-direct conversion circuit of the previous stage to provide a midpoint. The secondary side of the traditional dual-circuit dual-transistor forward combination converter cannot output positive and negative polarity voltages, and cannot provide the required midpoint, and the secondary side rectifier diodes and freewheeling diodes are subjected to large current stress, making it difficult to select components . The dual-tube forward converter has the advantages of low voltage stress of the primary switching tube, no bridge arm through-circuit, high reliability, etc., and the output is interleaved, the output equivalent duty cycle is twice that of the input, and the size of the filter inductor is reduced , but in applications where high power and reliability are required and the output is required to have positive and negative poles, since the circuit has a single polarity output and the rectified current rating of the secondary side is large, it is difficult to select the device. This patent proposes a topological structure of a DC converter - a dual-channel dual-transistor forward combined converter with an output midpoint. It not only inherits the original advantages of dual-channel dual-tube forward excitation, but also provides convenience for subsequent circuits because the output voltage is positive and negative. At the same time, the transformer series structure reduces the power rating of a single transformer and the current rating of the secondary side, thereby The volume and weight are reduced, and the selection of secondary side rectification devices is also facilitated.

Contents of the invention

The invention aims at proposing a new type of forward topology on the basis of the traditional forward converter and combining the characteristics of the DC transformer to solve the power conversion problem in the occasion of high-power high-voltage input, low-voltage and high-current output.

The main circuit of the converter is characterized in that: a converter combination with an output midpoint structure is adopted, the secondary sides are connected in parallel with corresponding transformer secondary sides to form two outputs, and the two outputs are connected in series to form an output midpoint. The combined structure is as follows: the primary sides of the two sets of dual-tube forward converters are connected in parallel, and the corresponding secondary sides of the two dual-tube forward converters are rectified and then interleaved and connected in parallel to form two outputs and then connected in series. The output midpoint is grounded, that is, it does not belong to The output voltage polarity is only positive or the polarity is only negative. The transformer has two secondary sides, and the corresponding secondary sides are rectified and connected in parallel, and share one output filter circuit (output filter inductor and capacitor). Each dual-transistor forward converter topology includes a switching tube, a diode, a power transformer with two secondary sides, an output filter inductor, and an output filter capacitor.

This patent adopts a DC converter whose output midpoint is grounded, uses an isolated DC converter topology and utilizes a high-frequency isolation transformer to realize the isolation function. The advantages of this high power DC converter are:

(1) The DC transformer retains the advantages of low voltage stress of the primary switch tube of the traditional dual-tube forward converter, no bridge arm straight-through, and high reliability;

(2) The topological characteristic of the DC transformer is that the output midpoint is grounded, and the output voltage has positive and negative poles;

(3) The design idea that the two primary sides of the DC converter work synchronously and interleaved in parallel at the same frequency reduces the size of the input and output filters, reducing the volume and weight of the system;

(4) The DC converter with multiple outputs increases the output current, so that the current rating of a single channel is reduced, which provides convenience for device selection. Therefore, the DC converter with this structure is very suitable for large current output occasions and the situation where the selected current of the secondary side rectifier device is limited.

Description of drawings

Fig. 1 is a schematic diagram of the circuit topology of the present invention.

FIG. 2 is a control block diagram of a control circuit of the converter.

Figure 3 is a waveform diagram of the output current when the circuit is interleaved.

Figure 1——The main symbol names of Figure 3: (1) U _in , U _dc , u _dc , u _ref —respectively, the input voltage, output voltage, voltage sampling at the output terminal, and reference voltage of the output voltage regulator. (2) i ₁ , I _Lf1 —— sampling the current flowing through the inductor in the DC converter, and outputting the current on the inductor L _f1 . (3) Q ₁ , Q ₂ , Q ₃ , Q ₄ —— respectively, the primary switching tubes of the DC converter. (4) D ₁ -D ₄ —— respectively, the freewheeling diodes of the primary side of the DC converter. (5) D ₅ -D ₈ —respectively, the secondary side rectifier diodes of the DC converter. (6) D ₉ -D ₁₀ —— respectively, the freewheeling diodes of the secondary side circuit of the DC converter. (7) L _f1 -L _f2 ——respectively the secondary filter inductance of the DC converter (8) C _f1 -C _f2 ——respectively the output capacitance of the DC converter (9) T ₁ -T ₂ ——isolating transformer.

Detailed ways

The main circuit of the dual-circuit dual-transistor forward combined converter with output midpoint is shown in Figure 1. Two sets of dual-transistor forward converters are used to connect the primary sides in parallel, the transformer has two secondary sides, and the corresponding secondary sides of the two sets of converters are The sides are staggered in parallel and then connected in series, and the output midpoint is grounded, that is, the secondary sides that do not belong to the same transformer are connected in parallel, and share one output filter circuit (output filter inductor and capacitor).

The specific main circuit topology is shown in Figure 1. The main body is composed of two parallel-connected double-tube forward converters with two secondary sides. The primary sides of the two forward circuits are connected in parallel, and the corresponding windings of the secondary sides are connected in parallel. Each dual-transistor forward module includes two switch tubes, two primary-side freewheeling diodes, two secondary-side rectifier diodes, one secondary-side freewheeling diode, an output filter inductor and an output capacitor. The connection method is: the source of the switch tube _Q1 is connected to the cathode of the diode _D1 , the drain is connected to the positive output terminal of the input DC power supply U _in , and the anode of the diode _D1 is connected to the negative output terminal of U _in . Similarly, The drain of the switch tube _Q2 is connected to the anode of the diode _D2 , the source is connected to the negative output terminal of U _in , and the cathode of the diode _D2 is connected to the positive output terminal of the input DC power supply U _in ; similarly, the switch tube Q The source of diode _D3 is connected to the cathode of diode _D3 , the drain is connected to the positive output terminal of U _in , the anode of diode _D3 is connected to the negative output terminal of input DC power supply U _in , similarly, the switch tube _Q4 The drain is connected to the anode of the diode _D4 , the source is connected to the negative output terminal of the input DC power supply _Uin , and the cathode of _D4 is connected to the positive output terminal of the input DC power supply _Uin (that is, the primary side is connected in parallel); from _Q1 The source of Q2 leads to the same-named terminal of transformer _T1 (the same-named terminal is shown in the figure), and the drain of _Q2 leads to the same-named terminal of transformer _T1 ; similarly, the source of _Q3 leads to the same-named terminal of transformer _T2 . The drain of Q ₄ leads to the opposite end of the transformer _T2 ; the same end of the secondary side of the transformer _T1 is connected to the anodes of the secondary rectifier diodes _D5 and _D6 , and the same end of the secondary side of the transformer _T2 is connected to the secondary rectifier diode _D7 , the anode of D ₈ ; the opposite end of the secondary side of a group of T ₁ transformers (including D ₅ ) is connected to the opposite end of the secondary side of a group of T ₂ transformers (including D ₇ ) and grounded; D ₅ is connected to the cathode of D ₇ Together (i.e. to achieve staggered parallel connection), the anode of D ₉ is grounded, the cathode is connected to the cathode of D ₅ and D ₇ ; similarly, the cathode of D ₆ and D ₈ are connected together, the anode of D ₁₀ is connected to the -U _dc terminal, The cathode is connected to the cathodes of D ₆ and D ₈ ; the opposite end of the secondary side of a group of T ₁ transformers (including D ₆ ) is connected to the opposite end of the secondary side of a group of T ₂ transformers (including D ₈ ) and connected to -U _dc ; Both ends of L _f1 are respectively connected to the +U _dc terminal of the output DC voltage and the cathodes of D ₅ , D ₇ , and D ₉ , one end of C _f1 is connected to the +U _dc end, and the other end is grounded; the other end of L _f2 is connected to Ground, the other end is connected to the cathodes of D ₆ , D ₈ , and D ₁₀ , one end of C _f2 is connected to the -U _dc end, and the other end is grounded; the secondary side DC voltage output is connected in series between the two forward converters.

The two forward converters in the converter work interleavedly, that is, the control signals of (Q ₁ , Q ₂ ) and (Q ₃ , Q ₄ ) differ by 180°. The multi-output high-current output DC converter adopts a double-loop control scheme. The control block diagram of the double closed-loop control scheme is shown in Figure 2: the reference voltage u _ref of the output terminal is connected to the non-inverting input terminal of the voltage loop regulator, the sampling voltage u _o of the output terminal is connected to the inverting input terminal of the voltage loop regulator, and the voltage loop The output of the regulator and the sample _i1 of the output filter inductor current are respectively connected to the non-inverting input terminal and the inverting input terminal of the current inner loop regulator. The output of the current inner loop regulator is intersected with the triangular wave carrier adjusted by the synchronous signal to generate a PWM wave. The PWM wave controls the switching tubes (Q ₁ , Q ₂ ) of the DC converter module to adjust the output voltage. Similarly, the other positive The switching tubes (Q ₃ , Q ₄ ) of the excitation circuit are also controlled in the same way, and will not be described here. In actual work, the two-way driver can be completed with one driver chip, and the required functions can be realized.

Claims (1)

1. One kind with output mid point two-way double tube positive exciting combined converter, converter is by two groups of two-transistor forward converter former limit parallel connections, transformer belt two-way secondary, secondary adopts corresponding transformer secondary crisscross parallel to form two-way output, two-way output series connection forms the structure of exporting mid point, and circuit feature is a transformer belt two-way secondary, the secondary rectification crisscross parallel of corresponding transformer forms two-way output, forms output neutral earthing structure.

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