阅读说明：本技术 一种变压器变比可调的宽范围恒功率输出切换电路 (Transformer transformation ratio adjustable wide-range constant power output switching circuit ) 是由 张逾良 杨志民 王哲 冀哲 胡晓阳 李金洁 陈超飞 徐艳超 李维旭 张现民 李铎 于 2020-04-01 设计创作，主要内容包括：一种变压器变比可调的宽范围恒功率输出切换电路及方法。其是将高频电压输入一个变压器的初级,使该变压器的次级两端通过一个整流桥整流并经滤波电容滤波并输出,在次级线圈中间设有一个抽头使次级线圈分为上下两个绕组,且使上下绕组圈数不同,而使所述滤波电容由具有两个电容串接而成,且具有一个串接中点,将所述抽头通过一个控制开关与所述串接中点连接,通过控制开关K的通断使整流电路处于桥式整流状态或成倍压整流状态输出。实现了输出无级调压,在全范围内恒功率输出,且相比于业界流行的利用开关调节变压器变比的方案,在少用两只整流二极管的前提下,采用倍压整流方式使整流模块保持最优工作特性的显著效果及其突出的优越性。(A transformer transformation ratio adjustable wide-range constant power output switching circuit and a method. The high-frequency voltage is input into the primary of a transformer, so that two ends of the secondary of the transformer are rectified through a rectifier bridge, filtered and output through a filter capacitor, a tap is arranged in the middle of the secondary coil to divide the secondary coil into an upper winding and a lower winding, the number of turns of the upper winding and the lower winding is different, the filter capacitor is formed by connecting two capacitors in series and is provided with a series midpoint, the tap is connected with the series midpoint through a control switch, and the rectifier circuit is in a bridge type rectification state or a voltage-multiplying rectification state and output through the on-off of a control switch K. The output stepless voltage regulation is realized, the constant power output is realized in the whole range, and compared with the scheme of utilizing a switch to regulate the transformer transformation ratio, which is popular in the industry, the remarkable effect and the outstanding superiority of the optimal working characteristic of the rectifier module are kept by adopting a voltage-multiplying rectification mode on the premise of using less two rectifier diodes.)

1. The utility model provides a transformer transformation ratio adjustable wide region constant power output switching circuit which characterized in that contains:

a transformer having a primary winding (Np) for receiving a high frequency input and a secondary winding (Np) having two secondary output terminals (3, 5), and a tap (4), the tap (4) causing the secondary winding between the two secondary output terminals to be divided into upper and lower windings (Ns1, Ns2) with unequal numbers of turns of said upper and lower windings; the two secondary output terminals (3 and 5) output voltage (U0) to a load through a rectifier bridge, the output end of the rectifier bridge is provided with two capacitors (CD1 and CD2) connected in series as an output filter capacitor, the tap is connected to the series connection midpoint of the output filter capacitor through a control switch (K), and the rectification mode can be changed through the on-off of the control switch (K) so as to realize full-range constant power output.

2. The wide-range constant power output switching circuit with the adjustable transformer transformation ratio as claimed in claim 1, wherein the number of turns between the upper and lower windings (Ns1, Ns2) should satisfy the following formula:

(Vs/V2)≤(2*Ns1)/(Ns1+Ns2)<1

v1 and V2 are the end values of the target voltage range, and Vs is the switching point.

3. The transformer ratio adjustable wide-range constant power output switching circuit of claim 1, wherein the capacitors in series have the same capacitance.

4. The wide-range constant-power-output switching circuit with the adjustable transformer transformation ratio as claimed in claim 1, wherein: the control switch is MOS or IGBT.

5. A transformer transformation ratio adjustable wide-range constant power output switching method is characterized in that high-frequency voltage is input into a primary of a transformer, two ends of a secondary of the transformer are rectified through a rectifier bridge and filtered through a filter capacitor and output, a tap is arranged in the middle of the secondary coil to enable the secondary coil to be divided into an upper winding and a lower winding, the number of turns of the upper winding and the lower winding is different, the filter capacitor is formed by two capacitors which are connected in series and is provided with a series connection midpoint, the tap is connected with the series connection midpoint through a control switch, and full-range constant power output is achieved through the on-off of a control switch K;

when low-voltage constant power output is required, the switch is switched off, so that the rectifying circuit is in a bridge rectifying state; when high-voltage constant-power output is needed, the switch is closed, the tap is connected with the series connection midpoint, the two series connection capacitors are charged by the windings with a large number of turns, and the output end is output in a voltage-multiplying and current-regulating state.

Technical Field

The invention relates to a power output circuit, in particular to a wide-range constant-power output switching circuit with an adjustable transformer transformation ratio.

Background

The constant power switching power supply is characterized in that when the output voltage UO is reduced, the output current IO is increased instead, so that the product IOUO of the output voltage UO and the output current PO is kept constant. The switching power supply can be used as a high-efficiency, quick and safe switching power supply. With the development of science and technology, the variety of products applied to a high-power conversion device is more and more, and a constant-power supply with continuously adjustable output wide range is a special application in a plurality of application fields of a switching power supply. Among them, the problem that prior art exists:

⑴ in wide range constant power modules, its output is difficult to cover the full range;

⑵ have the disadvantage of switching delay;

⑶, the required driving circuit is complicated and the cost is high;

these problems and drawbacks are problems that those skilled in the art are faced with.

For this reason, for wide-range output, it is generally necessary to reduce the transformer primary stress by winding switching, and to achieve a wider output voltage range with the same duty cycle or frequency regulation range.

As shown in fig. 1, assuming that the switching frequency adjustment range is between F1 and F2, when SS1 is closed, the adjustment range of the output voltage is from Vmin to Vmax, when SS1 is open, it can be calculated according to the turn ratio, and under the condition that the frequency adjustment range is not changed, the adjustment range of the output voltage is from Vmin Ns1/(Ns1+ Ns2) to Vmax Ns1/(Ns1+ Ns 2). Therefore, by reasonably designing the turn ratio, the output voltage range of the whole topology can be expanded to be Vmin × Ns1/(Ns1+ Ns2) to Vmax by a winding switching mode under the condition that the frequency regulation range is not changed.

When SS1 is closed, if the output power is constant at P, the maximum value of the output current at Vmin is Imax, and the primary current at this time is calculated as Ipmax ═ Imax (Ns1+ Ns 2)/Np. When ss1 is turned off, the minimum output voltage is Vmin × Ns1/(Ns1+ Ns2), and when the output power is still constant at P, the maximum output current is P/(Vmin × Ns1/(Ns1+ Ns2)) -Imax (Ns1+ Ns2)/Ns1, and the primary current is Imax (Ns1+ Ns2)/Ns1 Ns1/Np, it can be seen that the maximum value of the primary current is constant.

That is to say, by means of winding switching, the output voltage range can be widened and the constant power output capability can be improved under the condition that the primary maximum current is not changed and the duty ratio or the switching frequency regulation range is not changed.

When the output voltage range is from V1 to V2, if the range is too wide, it needs to be realized by the switching of the secondary winding of the transformer.

For the conventional switching method, the switching point Vs should be selected when designing so that V1< Vs < V2, and the transformer turn ratio should be designed so that Vs/Ns2 is V2/(Ns1+ Ns 2).

Disclosure of Invention

In order to solve the above problems, the present invention provides a wide-range constant power output switching circuit with an adjustable transformer transformation ratio, which can output stepless voltage regulation and output constant power in a full range. Another objective is to provide a technical solution that can keep the optimal operating characteristics of the rectifier module with the help of lower component requirements.

In order to achieve the above object, the present invention provides a wide-range constant power output switching circuit with an adjustable transformer transformation ratio, comprising:

a transformer having a primary winding (Np) for receiving a high frequency input and a secondary winding (Np) having two secondary output terminals (3, 5), and a tap (4), the tap (4) causing the secondary winding between the two secondary output terminals to be divided into upper and lower windings (Ns1, Ns2) with unequal numbers of turns of said upper and lower windings; the two secondary output terminals (3 and 5) output voltage (U0) to a load through a rectifier bridge, the output end of the output of the rectifier bridge is provided with two capacitors (CD1 and CD2) connected in series to serve as output filter capacitors, the tap is connected to the series connection midpoint of the output filter capacitors through a control switch (K), and the rectification mode can be changed through the on-off of the control switch (K) so as to achieve full-range constant power output.

The invention also provides a wide-range constant power output switching method with adjustable transformer transformation ratio, which is characterized in that high-frequency voltage is input into the primary of a transformer, so that the two ends of the secondary of the transformer are rectified by a rectifier bridge, filtered by a filter capacitor and output, a tap is arranged in the middle of the secondary coil to divide the secondary coil into an upper winding and a lower winding, the number of turns of the upper winding and the lower winding is different, so that the filter capacitor is formed by connecting two capacitors in series and is provided with a series connection midpoint, the tap is connected with the series connection midpoint through a control switch, and the full-range constant power output is realized by controlling the on-off of a switch K;

when low-voltage constant power output is required, the switch is switched off, so that the rectifying circuit is in a bridge rectifying state; when high-voltage constant-power output is needed, the switch is closed, the tap is connected with the series connection midpoint, the two series connection capacitors are charged by the windings with a large number of turns, and the output end is output in a voltage-multiplying and current-regulating state.

Preferably, for the case of the target voltage range V1 to V2, the switching point Vs should be selected such that V1< Vs < V2, while the transformer turns ratio should be designed such that: (Vs/V2) ≦ (2 × Ns1)/(Ns1+ Ns2) < 1.

Preferably, the switch is an electronic switch, and can be switched by a MOS or IGBT tube under the control of a signal.

The invention has the advantages that by means of the technical scheme, the invention realizes output stepless voltage regulation and constant power output in the whole range, and compared with the scheme of utilizing a switch to regulate the transformation ratio of a transformer, which is popular in the industry, the invention adopts the obvious effect of maintaining the optimal working characteristic of a rectifier module by adopting a voltage-multiplying rectification mode on the premise of using less two rectifier diodes and the outstanding advantages thereof.

Drawings

Fig. 1 is a circuit diagram of a transformer for reducing primary stress by winding switching.

Fig. 2 is a schematic diagram of a transformer ratio adjustable wide-range constant power output switching circuit according to the present invention.

Fig. 3 is a circuit diagram of an embodiment of a wide-range constant-power output switching circuit with an adjustable transformer transformation ratio according to the present invention.

Detailed Description

In order to embody the above effects and show the advantages thereof, the technical solution of the present invention is further specifically described below by way of embodiments and with reference to the accompanying drawings.

For the occasion of wide-range output, the primary stress of the transformer needs to be reduced by adopting a winding switching mode, and meanwhile, a wider output voltage range is realized under the condition of the same duty ratio or frequency regulation range.

The invention adopts a novel method to realize winding switching, and obtains better device stress and cost under the condition of having the advantages of the original switching circuit.

Fig. 2 is a schematic diagram of the circuit of the present invention. The main technical concept of the invention is that on the basis of a conventional circuit, a tap is added to a transformer, and the number of turns of upper and lower windings of the tap is not equal, so that for the sake of easier clarification, it is assumed that Ns1 is more than Ns 2; then, a switch K is connected in series to the tap to the midpoint of the output filter capacitor, and the full-range constant power output is realized by controlling the on-off of the K.

The following examples are intended to illustrate the invention but are not intended to limit the scope of the invention.

In the embodiment of the invention, the high-frequency input transformer comprises a transformer with two input terminals (1, 2) and a primary winding Np for receiving high-frequency input, the secondary of the transformer is additionally provided with a tap 4 besides two secondary output terminals (3, 5), and in the embodiment, the turns of upper and lower windings (Ns1, Ns2) of the tap 4 are not equal, and Ns1 is more than Ns 2; the two secondary output terminals (3 and 5) output voltage U0 to a load through a rectifier bridge, the output end of the rectifier bridge is provided with two capacitors (CD1 and CD2) connected in series as an output filter capacitor, the tap is connected in series with a switch K to the midpoint of the output filter capacitor, and full-range constant power output can be realized by controlling the on-off of the switch K.

The working process of the device is as follows:

(1) when low-voltage constant-power output is needed, the switch K is switched off, at the moment, two ends of a secondary winding of the transformer are added to two arms of the rectifier bridge, the rectifier bridge works in a conventional mode, and high voltage is output from two ends of filter capacitors CD1 and CD2 which are connected in series; at the moment, the current of the two arms of the diode is half of the output current;

(2) when high-voltage constant-power output is required, the switch K is closed, and at the moment, the voltage at the two ends of the upper winding and the lower winding is Vs1 to Vs2 because the number of turns Ns1 to Ns2 of the upper winding and the lower winding is greater.

In the positive half cycle, the output of the winding Ns1 on the transformer charges a first filter capacitor CD1 through a diode D1, a first capacitor CD1 and a transformer tap, and V_CD1＝V_s1(ii) a Meanwhile, the lower winding Ns2 charges a second filter capacitor CD2 through a switch K and a diode D4, and V_CD2＝V_s2；

In the negative half cycle, the upper winding Ns1 charges the second filter capacitor CD2 through the switch K and the diode D2, and V_CD2＝V_s1(ii) a The lower winding Ns2 charges the CD1 through a diode D3 and a switch K, and the voltage is V_s1＞V_s2Obviously, the lower winding Ns2 cannot charge the first filter capacitor CD 1;

similarly, in a steady state condition, the lower winding Ns2 cannot charge the second filter capacitor CD 2; that is, in the steady state, in the positive and negative half cycles, only the upper winding Ns1 is shown to charge the filter capacitors CD1 and CD 2.

Obviously, in the steady state situation, the output voltage V₀Satisfies the following equation: v₀＝V_CD1+V_CD2＝2V_s1，

Thereby realizing voltage-doubling rectification.

The circuit analysis shows that:

when the circuit is in a low-voltage constant-power mode, a conventional bridge rectification mode can be adopted; the current born by the diode is half of the output current; the diode withstand voltage is based on outputting a low voltage.

In a high-voltage constant-power mode, a circuit is switched into a voltage-multiplying rectification mode by switching on a switch K, and the current of a rectifier diode is still half of the output current at the moment; and its voltage clamp is at half the output voltage.

In operation, as shown in fig. 2, when k is closed, the output voltage range is Vmin to Vmax, and when k is open, the output voltage range changes as: vmin (2 × Ns1)/(Ns1+ Ns2) to Vmax (2 × Ns1)/(Ns1+ Ns 2). If the turn ratio is designed reasonably, the output voltage range can be expanded to Vmin (2 × Ns1)/(Ns1+ Ns2) to Vmax by opening and closing k, and the primary current is unchanged.

The traditional switching circuit selects 6 diodes, and the maximum reverse voltage borne by each diode is Vmax, while the circuit of the invention only needs 4 diodes, and the maximum reverse voltages of D1 and D2 are Vmax 0.5(1+ Ns2/Ns 1). In the case of low voltage, the advantage of relative compactness of the circuit is obtained, since the current carried by the single diode of the circuit according to the invention is greater compared with that of the conventional circuit. However, when the highest output voltage reaches 600V to 1000V, in a switching power supply with a frequency of 100kHz or higher, if the conventional scheme is adopted, because the 1200V ultrafast recovery Si diode has poor high-frequency performance and a small selection margin, the 1200V SiC diode must be selected, but the circuit of the invention only needs to select the 600V fast recovery diode, and has a great cost advantage.

For the mainstream electric automobile charging pile in the industry at present, when the constant power output voltage range is 300-750V, if a traditional circuit is adopted, the constant power output voltage range can be realized by switching the number of secondary turns from 3 turns (450V-750V) to 2 turns (300V-500V), the highest withstand voltage of a corresponding secondary diode is 750V, and a 1200V SiC diode is usually selected in consideration of transient spike and derating;

in one embodiment of the invention: the circuit shown in fig. 2 can be implemented by designing Ns1 to be 3 and Ns2 to be 1, where the maximum withstand voltage borne by the diode is 750 × 0.5(1+1/3) ═ 500V, and the performance of the ultrafast recovery Si diode of 600V is still sufficient in the range of 100k to 300k, so that the ultrafast recovery Si diode of 600V is only needed.

In summary, the invention can realize the stepless switching from the bridge rectification to the voltage-doubling rectification by the tap and switch switching of the transformer, and can realize the constant power output of the product in the whole output range by only adding one switch and one control circuit; meanwhile, because the required rectifying and switching devices have lower voltage and current stress, the cost can be reduced without sacrificing the efficiency. And because the output is constant power output, the output current is correspondingly reduced when the high section is switched, so that the voltage-multiplying rectifying circuit can be adopted to work.

In this specific embodiment, the parameter selection of the switching manner is realized, as shown in fig. 2, when k is closed, the theoretical output voltage range is Vmin to Vmax, and when k is open, the theoretical output voltage range is changed as follows: vmin (2 × Ns1)/(Ns1+ Ns2) to Vmax (2 × Ns1)/(Ns1+ Ns 2).

In order to ensure that the output range is widened, the following requirements are met:

vmin > Vmin (2 × Ns1)/(Ns1+ Ns2), i.e., (2 × Ns1)/(Ns1+ Ns2) < 1.

In order to ensure that the output range should satisfy continuously:

vmax (2 Ns1)/(Ns1+ Ns2) is not less than Vmin, namely (2 Ns1)/(Ns1+ Ns2) is not less than Vmin/Vmax.

In summary, for the case of the target voltage ranges V1 to V2, the switching point Vs should be selected such that V1< Vs < V2,

meanwhile, the turn ratio of the transformer is designed as follows: (Vs/V2) ≦ (2 × Ns1)/(Ns1+ Ns2) < 1.

For example: the output voltage range is 300V-750V, and V1-300V and V2-750V can be set;

if Vs is 500V, Vs/V2 is 2/3, that is, Ns1 is 1, Ns2 is 2, (2 × Ns1)/(Ns1+ Ns2) is 2/3, so as to satisfy the requirement that (2 × Ns1)/(Ns1+ Ns2) should be between 2/3 and 1. Similarly, Ns1 may be selected to be 2, Ns2 may be 3, and (2 × Ns1)/(Ns1+ Ns2) may be 4/5, which also satisfies the requirement that (2 × Ns1)/(Ns1+ Ns2) should be between 2/3 and 1.

Therefore, as long as two conditions of V1< Vs < V2 and (Vs/V2) ≦ (2 × Ns1)/(Ns1+ Ns2) <1 are met, the turn ratio of the transformer can be designed according to the actual requirement and the withstand voltage value of the actual commonly-used power diode.

Fig. 3 is a circuit diagram of an embodiment of a wide-range constant-power output switching circuit with an adjustable transformer transformation ratio according to the present invention. The circuit adopts an electronic switch tube to control the on-off of the switch.

Although the present invention has been described in detail with reference to the above embodiments, it should be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the spirit and scope of the invention.