CN101902139B - Modularized multiple constant current output converter - Google Patents

Abstract

The invention relates to a multi-channel output electric energy converter, and aims to provide a modular multi-channel constant current output converter. The converter includes N sub-modules, and each sub-module includes a transformer T2N, an Nth rectifier, and an output DC filter capacitor CON, and the primary windings of the transformers in each sub-module are connected in series; the converter has a two-stage structure: the first The first stage includes the first transformer T1 and the controllable high-frequency AC source Vac connected in parallel at both ends of the primary winding of the first transformer T1; the second stage includes the aforementioned N sub-modules; the two ends of the secondary winding of T1 are respectively connected to the The first and last ends of the primary winding of the sub-module transformer. In the present invention, the excitation inductance of the first-stage transformer is not affected by the short circuit or open circuit of the load, the design of the main circuit parameters is simple, and it is not necessary to consider the influence on the main circuit parameters under abnormal conditions. Sub-module circuits can be standardized and flexibly combined to obtain any desired output, reducing production costs.

Description

Modular multi-channel constant current output converter

technical field

The invention relates to a multi-channel output power converter, in particular to a modular multi-channel constant current output converter.

Background technique

Many applications of power conversion require converters to be able to achieve DC constant current output, such as battery chargers, LED drive power supplies, etc. In addition to the need for multiple outputs, high-voltage isolation is also required to meet safety regulations and high-strength electrical insulation.

In order to obtain an isolated multi-output DC current source, a two-stage DC-DC scheme is generally used. The front stage uses an isolated DC-DC to obtain a constant voltage source, and then follows multiple non-isolated DC-DCs to achieve multiple channels. Independent constant current output. The scheme is flexible and has high reliability. However, since multiple independent post-stage DC-DCs are required, independent control chips and switching devices are required, which greatly increases the cost.

In order to reduce the cost, there are many ways to carry out multi-channel constant current in a passive way, and can realize more accurate current sharing among multiple currents. In Fig. 1, the method of coupling inductance in series in the rectifier diode of the isolated high-frequency AC source is used to realize the current sharing of the current of the two DC outputs. Moreover, by using the mutual coupling of multiple coupled inductors, it can be extended to multiple constant DC outputs. However, since the diode is connected in series with the coupled inductor, and there are many multi-channel coupled inductor windings, the interfaces of these windings must be connected in series with the secondary side rectifier diode, which leads to complicated PCB wiring on the secondary side and increases the high-frequency AC loss of a lot of PCBs.

In Figure 2, using the charge balance principle of capacitors, a DC blocking capacitor C _B is connected in series between the AC power supply and the rectifier circuit to achieve the balance of positive and negative charges, thereby obtaining the equalization of the DC side current. Although the cost of the capacitor is low and the implementation is simple, when this method is used for more outputs, it needs to cooperate with the technical implementation of the coupled inductor.

Another technique (Figure 3) is to connect multiple high-frequency transformer primary side windings in series, and the secondary side uses capacitor rectification to obtain DC, and realize the same load current for multiple channels. This technology utilizes the principle that the current of the primary and secondary sides of an ideal transformer depends on the turn ratio, and under the condition of ensuring the same turn ratio of multiple transformers, the average current of the secondary side is equal. Although this technique is simple, it has some disadvantages that seriously limit its application range. Mainly include: 1) Since each transformer bears high insulation requirements, each transformer must meet safety requirements, which greatly increases the cost, reduces window utilization, and affects the efficiency of the converter. 2) Since the excitation current of the primary side in series does not reflect to the secondary side circuit, when the topology structure with relatively large excitation current, such as series and parallel resonant converters, the ratio of the excitation current of the transformer to the load current is relatively close, consider The dispersion to the excitation inductance is large, so the current sharing degree of multiple output currents is affected. 3) Since the excitation current has a large proportion in the total current of the primary side of the transformer, the final output current must be sampled and compared with the current reference. To precisely control the output current, it is impossible to control the current of each channel by sampling the primary current. 4) When a certain load is short-circuited, since only the capacitor is filtered, the corresponding transformer of this road is equivalent to a short-circuit, resulting in a change in the total excitation inductance connected in series on the primary side, thereby affecting the steady-state gain of the converter and increasing the control difficulty. Especially for series-parallel resonant converters, the total equivalent excitation inductance has a great influence on the steady-state control of the converter, which will seriously reduce the reliability of the converter.

Contents of the invention

The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a modular multi-channel constant current output converter.

In order to solve the above problems, the present invention provides a converter that can be modularized and obtain the required multi-channel constant current output through flexible combination.

The modular multi-channel constant current output converter in the present invention includes N sub-modules, and each sub-module includes: a transformer T2N, an Nth rectifier and an output DC filter capacitor CON, and the transformers in each sub-module The primary windings are connected in series in sequence; the converter has a two-stage structure: the first stage includes the first transformer T1 and the controllable high-frequency AC source Vac connected in parallel at both ends of the primary winding of the first transformer T1; the second stage includes the aforementioned N two sub-modules; the two ends of the T1 secondary winding are respectively connected to the first and last ends of the primary windings of the sub-module transformers connected in series.

As an improvement, in each of the sub-modules, the secondary winding of the transformer T2N is connected to the input of the Nth rectifier, the output of the Nth rectifier is connected to both ends of the output DC filter capacitor CON, and the DC constant current load is connected to the said The output DC filter capacitor CON is connected in parallel.

As an improvement, in each of the sub-modules, the secondary side of the transformer T2N can be a single winding structure, or a multi-winding rectification structure, such as a center-tapped winding structure.

As an improvement, in each of the sub-modules, the Nth rectifier can be a half-wave rectifier circuit, or a full-bridge rectifier circuit, or a center-tap rectifier circuit, or a voltage doubler rectifier circuit, and other suitable for output capacitor Filtered rectifier circuit.

As an improvement, the sub-modules are packaged into mutually independent AC-DC modules with high-frequency AC input and DC output, and are connected to the first stage through movable joints or fixed joints.

As an improvement, the turn ratio of the transformer T2N in each sub-module is determined according to the requirement of the output current of the channel.

As an improvement, the outputs of the sub-modules are connected in parallel or in series to adjust the output current or voltage.

As an improvement, a current sensor is provided on the intermediate AC busbar at one end of the secondary winding of the first transformer T1, and the current sensor is sequentially connected to the sampling filter circuit, the current error amplifier, and the control circuit of the controllable high-frequency AC source Vac.

As an improvement, a capacitor C _B is connected in series with one end of the secondary winding of the first transformer T1.

As an improvement, the controllable high-frequency AC source Vac is a high-frequency inverter circuit with the characteristics of an AC current source.

Compared with the scheme in which the primary transformer is connected in series to realize the current sharing on the secondary side, the beneficial effects of the present invention are:

(1) The series transformer does not need to consider the insulation strength of safety regulations, which greatly reduces the production cost, improves the window utilization rate of the second-stage transformer core, and improves the conversion efficiency of the transformer;

(2) Simplifying the design of the second-stage transformer can make full use of the large excitation inductance of the transformer itself, reduce the influence of the excitation current on the current sharing accuracy, and improve the current sharing degree of multiple outputs.

(3) Sub-module circuits can be standardized, and can be flexibly combined to obtain any desired output, reducing production costs.

(4) The excitation inductance of the first-stage transformer is not affected by the short circuit or open circuit of the load, the design of the main circuit parameters is simple, and there is no need to consider the influence on the main circuit parameters under abnormal conditions.

(5) Modularization enables more specifications of multi-channel constant current output converters, which can be obtained only by flexible assembly of the first-stage circuit and the sub-modules of the subsequent stage, without separate design, avoiding cumbersome product materials and specifications .

(6) The constant current control strategy of the intermediate bus sampling avoids the current sampling of the output DC side. Using the centralized sampling of the intermediate bus makes modularization easier. Only the connection of the main power circuit is required during assembly, and there is no need to consider the connection of the control line.

Description of drawings

Figure 1: Current sharing technology of diode series coupled inductors;

Figure 2: A circuit in which DC blocking capacitors are connected in series on the secondary side of the transformer to achieve two-way current sharing;

Figure 3: The existing technology of connecting multiple transformers in series to realize current sharing on the secondary side;

Figure 4: The two-stage scheme proposed by the present invention realizes the scheme of multi-channel constant current output;

Figure 5: Intermediate AC bus current sampling feedback scheme;

Figure 6: The solution for eliminating the DC component of transformer excitation by connecting DC blocking capacitors in series in the intermediate busbar;

Fig. 7: the embodiment that the present invention realizes three-way output in series-parallel resonance (LLC) high-frequency inverter half-bridge circuit;

Figure 8: The present invention realizes the embodiment of three-way DC constant current output in the flyback inverter circuit;

Fig. 9: An embodiment of the present invention realizing three-way DC constant current output in a current source type full-bridge inverter circuit.

specific embodiment

Embodiments of the present invention will be described in detail below in conjunction with the accompanying drawings.

As shown in Figure 4, the modular multi-channel constant current output converter in the present invention includes N sub-modules with the same structure, and each sub-module includes: a transformer T2N, an Nth rectifier and an output DC filter The capacitor CON is connected in series with the primary windings of the transformers in each sub-module in sequence. That is: the other end of the primary side of the transformer T21 is connected to one end of the primary side of T22, and the other end of the primary side of T22 is connected to one end of the primary winding of the transformer in the next sub-module at one time, and is connected to the other end of T2N in turn; the converter It has a two-stage structure: the first stage includes the first transformer T1, a controllable high-frequency AC source Vac connected in parallel at both ends of the primary winding of the first transformer T1; the second stage includes the aforementioned N sub-modules; the secondary winding of the T1 The two ends are respectively connected to the first and last ends of the primary windings of the sub-module transformers connected in series.

In each sub-module, the secondary winding of the transformer T2N is connected to the input of the Nth rectifier, the output of the Nth rectifier is connected to both ends of the output DC filter capacitor CON, and the DC constant current load is connected in parallel with the output DC filter capacitor CON. The turns ratio of the transformer T2N is determined according to the requirement of the output current of this circuit.

In order to obtain precise control of the output current, feedback control can be performed by sampling the DC current signal in a certain path on the output side. Considering that the DC currents of each channel are equal, the DC output side can also be connected to a common ground or a common positive terminal, and the total output current can be sampled for feedback, and the precise control of each current can be obtained through the current sharing characteristics of the sub-module itself. Another simpler control method is to sample the current in the intermediate AC bus, and obtain the average current value after filtering, and then perform feedback control (as shown in Figure 5). The current signal on the secondary side of the transformer T1 passes through the current sensor and enters the sampling filter circuit to obtain the DC average signal and output the current error amplifier. The output signal of the error amplifier enters the control circuit of the high-frequency AC source, and then controls the high-frequency AC source to obtain The desired AC source signal, forming a feedback adjustment.

In order to avoid the large DC excitation component that may appear in the first-stage transformer in some applications (such as when the AC source is asymmetrical), the transformer will be saturated. By connecting the DC blocking capacitor C _B in series with the secondary winding of the transformer T1 (as shown in Figure 6), the volt-second balance of the primary and secondary windings of T1 can be balanced, and the DC component of the excitation current can be eliminated. In the DC excitation current elimination circuit, a capacitor C _B is connected in series at one end of the secondary side of the first transformer (T1), and the other end of C _B is connected to the end after multiple transformers in the second stage are connected in series, and the connection modes of the remaining circuits are different. Change.

FIG. 7 is a specific embodiment of the present invention applied in an LLC resonant half-bridge inverter circuit, through a center-tap rectification structure, to realize three-way constant current output. The positive end of the input DC power supply Vin is connected to one end of the switch tube S1, the other end of S1 is connected to S2 and one end of the series resonant inductor Lr, and the other end of S2 is connected to the input ground. The control terminals of S1 and S2 are respectively connected to the two output terminals of the resonant half-bridge drive circuit. The other end of the inductor Lr is connected to one end of the primary winding Np of the first transformer T1, wherein the parallel resonant inductor Lm can be an independent inductor connected in parallel with the primary side of the transformer T1, or can be the excitation inductance of the primary side of the T1. The other end of the primary winding of the transformer T1 is connected to one end of the series resonant capacitor Cr, and the other end of Cr is connected to the input ground. One end of the secondary winding Ns of the transformer is connected to one end of the primary winding of the transformer T21, the other end of the primary winding of T21 is connected to one end of the primary winding of T22, and one end of the primary winding of T22 is connected to one end of the primary winding of T23. The other end of the secondary winding of T1 is connected to one end of the DC blocking capacitor CB, and the other end of CB is connected to the other end of the primary winding of T23. One end of the first end of the secondary winding of the transformer T21 is connected to the anode of the diode D1, the middle end is connected to the negative end of the output capacitor CO1, and the third end is connected to the anode of the diode D2. The cathodes of diodes D1 and D2 are connected to the positive terminal of output capacitor CO1. The positive terminal and the negative terminal of CO1 are respectively connected to the two ends of the DC constant current load. The current signal in the secondary winding Ns of the first transformer is input to the current sampling filter circuit after passing through the current sensor Cs, the average value of the current is obtained and then output, and then enters the current error amplifier circuit, and the output signal of the error amplifier is input to the resonant half-bridge control and The driving circuit controls the switching frequency of the half-bridge so as to obtain a constant output current on the DC side.

Figure 8 shows the application of the present invention in the flyback inverter circuit, including the flyback inverter circuit in the first stage, and the transformer in the second stage sub-module adopts a half-wave rectification structure output by a single winding, and after capacitor filtering, a direct current is obtained Constant current output. The positive end of the input DC power supply is connected to the end of the same name of the primary winding Np of the first transformer, and at the same time connected to one end of the resistor Rc and the capacitor Cc, the other end of the capacitor Cc is connected to the other end of the resistor Rc, and then connected to the diode Dc The cathodes are connected together. The anode of the diode Dc is connected with the opposite end of the primary winding of T1, and then connected to one end of S1, and the other end of S1 is connected to the input ground. The control terminal of S1 is connected to the output of the flyback control drive circuit. The opposite end of the secondary winding of T1 is connected to the same end of the primary winding of the second stage transformer T21, the opposite end of the primary winding of T21 is connected to the same end of the primary winding of T22, and the opposite end of the primary winding of T22 Connect to the terminal with the same name of the primary winding of T23. The end of the same name of the secondary winding of T1 is connected to one end of the DC blocking capacitor CB, and the other end of CB is connected to the end of the same name of the primary winding of T23. The terminal with the same name of the secondary winding of the transformer T21 is connected to the anode of the diode D1, and the cathode of the diode D1 is connected to the positive terminal of the output filter capacitor CO1. The opposite end of the secondary winding of the transformer T21 is connected to the negative end of the output DC filter capacitor CO1, and the output DC constant current load is connected in parallel to both ends of CO1. The same-named end of the secondary winding of transformer T22 is connected to the anode of diode D2, the cathode of diode D2 is connected to the positive end of capacitor CO2, the opposite-named end of the secondary winding of T22 is connected to the negative end of output capacitor CO2, and the output constant current load Parallel to both ends of CO2. The same terminal of the secondary winding of the transformer T23 is connected to the anode of the diode D3, the anode of the diode D3 is connected to the positive terminal of the output filter capacitor CO3, and the opposite terminal of the secondary winding of T23 is connected to the negative terminal of the output capacitor CO3. The constant current load is connected in parallel at both ends of CO3. After the current signal in the secondary winding Ns of the first transformer passes through the current sensor Cs, it is input to the current sampling filter circuit, the average value of the current is obtained and then output, and then enters the current error amplifier circuit, and the output signal of the error amplifier is input to the control of the flyback circuit With the drive circuit, the main circuit is controlled so that a constant output current on the DC side can be obtained.

Fig. 9 is the application of the present invention in the current source type full-bridge inverter circuit. The input inductance Lin is regarded as a current source in the switching cycle, and the full-bridge switching inverter circuit chops the current source and inputs it to generate an AC source to the first transformer. The positive end of the input DC source Vin is connected to one end of the inductor Lin, the other end of the Lin inductor is connected to one end of the switch tubes S1 and S3, the other end of the switch S1 is connected to one end of the switch tube S2, and the other end of S2 is connected to the input ground . The other end of switch S3 is connected to one end of switch S4, and the other end of S4 is connected to the input ground. The controls of the switch tubes S1, S2, S3, and S4 are respectively connected to the four output terminals of the control circuit. One end of the primary winding of the transformer T1 is connected to the connection point of the switches S1 and S2, and the other end is connected to the connection point of the switches S3 and S4. The current sensor Cs transmits the current signal in the secondary winding of the transformer T1 to the input terminal of the sampling and filtering circuit, the output terminal of the filtering circuit is connected to the input terminal of the current error amplifier, and the output terminal of the amplifier is connected to the feedback terminal of the controller. The circuit in the second stage is the same as the embodiment in FIG. 7 , and will not be repeated here.

The invention utilizes the series connection of a plurality of primary windings of the transformer to realize the characteristic that the average currents of multiple outputs of the secondary side are equal or proportional. By inserting a first-stage isolation transformer between the high-frequency AC source and multiple series-connected transformers, the problem existing in only one-stage multiple-transformer series circuits is solved. The first-stage transformer converts the high-frequency AC source on the input side into the amplitude required by the subsequent stage. The primary sides of the sub-modules in the second stage are connected in series in sequence, and then connected in parallel to the secondary output winding of the first-stage transformer. Since the primary sides of the transformer are connected in series, the primary currents are the same. By designing the excitation inductance of the transformer as large as possible, the excitation current can be ignored, so the current of the primary side in the second-stage transformer basically has a turn ratio relationship with the conversion current of the secondary side, so that a better secondary current can be obtained. Average flow. After the AC current is rectified and filtered by a capacitor, a stable DC current is obtained and supplied to a DC constant current load.

Because the transformer in the second stage only needs to bear the required turn ratio design and meet the rated volt-second parameters of the magnetic core, the influence of the excitation current can be minimized, thereby obtaining better output-side accuracy.

It should be noted that special terms used in describing certain features or solutions of the present invention should not be used to indicate that the terms are redefined here to limit some specific features, features or solutions of the present invention related to the terms. In conclusion, the terms used in the following claims should not be construed to limit the invention to the particular embodiments disclosed in the specification, unless the above detailed description expressly defines those terms. Accordingly, the actual scope of the invention includes not only the disclosed embodiments, but also all equivalent arrangements which practice or perform the invention under the claims.

Claims (10)

1. A modular multi-channel constant current output converter, including N sub-modules, each sub-module includes: a transformer T2N, an Nth rectifier and an output DC filter capacitor CON, the transformer in each sub-module The primary windings are connected in series sequentially; it is characterized in that the converter has a two-stage structure: the first stage includes a first transformer T1, and a controllable high-frequency AC source Vac connected in parallel at both ends of the primary winding of the first transformer T1; The stage includes the aforementioned N sub-modules; the two ends of the T1 secondary winding are respectively connected to the first and last ends of the sub-module transformer primary windings in series; the constant current output is obtained by sampling one end of the secondary winding of the first transformer T1 The current on the intermediate AC bus is used as the input of the output constant current control circuit to control the input AC source Vac, thereby realizing the control of each output current. 2. The converter according to claim 1, characterized in that, in each of the sub-modules, the secondary winding of the transformer T2N is connected to the input of the Nth rectifier, and the output of the Nth rectifier is connected to the output DC filter capacitor CON The two ends of the DC constant current load are connected in parallel with the output DC filter capacitor CON. 3 . The converter according to claim 1 , wherein in each of the sub-modules, the secondary side of the transformer T2N has a single-winding structure or a multi-winding rectification structure. 4 . 4. The converter according to claim 1, characterized in that, in each of the sub-modules, the Nth rectifier is any one of the following rectifier circuits suitable for output capacitor filtering: a half-wave rectifier circuit , full bridge rectifier circuit, center tap rectifier circuit or voltage doubler rectifier circuit. 5. The converter according to claim 1, characterized in that, the sub-modules are packaged into AC-DC modules with high-frequency AC input and DC output independent of each other, and are connected to the first module through movable joints or fixed joints First level connection. 6. The converter according to claim 1, characterized in that, the turn ratio of the transformer T2N in each sub-module is determined according to the requirement of the output current of the channel. 7. The converter according to claim 1, characterized in that, the outputs of the sub-modules can also be connected in parallel or in series to adjust the output current or voltage. 8. The converter according to claim 1, characterized in that, the first stage of the indirect current sampling and constant current control circuit is a current transformer, and then sequentially connected with a sampling filter circuit, a current error amplifier, a controllable Control circuit of high frequency AC source Vac. 9. The converter according to any one of claims 1 to 6, wherein a capacitor CB is connected in series with one end of the secondary winding of the first transformer T1. 10. The converter according to any one of claims 1 to 6, wherein the controllable high-frequency AC source Vac is a high-frequency inverter circuit with characteristics of an AC current source.

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