CN114884186A

CN114884186A - Low-voltage low-power ACDC power supply with pre-charging device

Info

Publication number: CN114884186A
Application number: CN202210667643.6A
Authority: CN
Inventors: 廖晓斌; 詹柏青; 王正云; 李小锋; 罗万里
Original assignee: Guangdong Fullde Electronics Co Ltd
Current assignee: Guangdong Fullde Electronics Co Ltd
Priority date: 2022-06-14
Filing date: 2022-06-14
Publication date: 2022-08-09

Abstract

The invention relates to a low-voltage low-power ACDC power supply with a pre-charging device, wherein an auxiliary power supply of the ACDC power supply is provided with a transformer, the pre-charging device comprises a secondary winding N4 on the transformer and a one-way conducting element connected in series with the same-name end side of the secondary winding N4, the same-name end of the secondary winding N4 is connected to a direct-current positive bus of the ACDC power supply through the one-way conducting element, a direct-current negative bus is connected with the other end of the secondary winding N4, and the conducting direction of the one-way conducting element is that the same-name end flows to the positive bus. The invention can reduce the volume of the pre-charging loop, reduce the cost of the pre-charging loop, improve the pre-charging efficiency and improve the reliability of the system.

Description

Low-voltage low-power ACDC power supply with pre-charging device

Technical Field

The invention relates to the field of power supplies, in particular to a low-voltage low-power ACDC power supply with a pre-charging device.

Background

A low-voltage low-power ACDC bidirectional isolation power supply module is basically composed of an AC/DC circuit, a DC/DC circuit, a voltage and current detection circuit, a switching tube driving circuit, a control circuit, a cooling fan, an auxiliary power supply and the like, wherein the auxiliary power supply supplies power (direct current) to each driving circuit, the detection circuit, the fan and the control circuit, and if the control circuit needs the auxiliary power supply to provide a 12V power supply, the control circuit needs the auxiliary power supply to provide a 24V power supply and the like. The low-voltage low-power ACDC bidirectional isolation power supply module can convert alternating current of AC220V into direct current to charge a battery (the highest battery voltage is 30V), and can convert the battery voltage into alternating current AC220V to supply power to alternating current equipment. The principle of the bidirectional isolation power supply (ACDC) is generally to rectify ac power into dc power by PWM to obtain a dc bus, then invert the dc bus voltage into high-frequency ac power, isolate the dc power by a transformer, and then rectify the dc power at the secondary side of the transformer to obtain dc power. In the ACDC power supply, a large capacitor is provided in each dc bus for smoothing and reliable dc bus voltage.

In addition, the power supply products with the battery voltage generally less than 30V and the power less than 2000W have AC-DC, DC-DC and DC-AC level conversion, and the level conversion can avoid the voltage of a direct current bus because the direct current bus is provided with a large-capacity capacitor, so that the voltage at two ends of the capacitor can not change suddenly, but the current at two ends of the capacitor can change suddenly. If the capacitor is not provided with the pre-charging circuit, the two ends of the capacitor are equivalent to short circuit at the moment of power-on, and very large current can be generated, which is determined by the working principle of the capacitor. Transient peak currents can exceed device limits and cause circuit operation anomalies (blow-out).

Therefore, the pre-charging device plays a role in limiting the charging current of the capacitor at the moment of power-on of the power supply so as to ensure that circuit components cannot be burnt out due to overlarge charging circuit of the capacitor. And after the direct current bus capacitor finishes the charging work, the pre-charging device needs to be bypassed (opened), so that the good working performance of the power supply is ensured (if the pre-charging loop is not opened, the pre-charging device can cause energy loss).

In a low voltage (AC220V) low power supply (less than 2000W), a common pre-charge principle is shown in fig. 1, in which a dc power supply charges a dc bus capacitor through a current limiting resistor, and a switch opens or bypasses the current limiting resistor after the charging voltage reaches a predetermined voltage. The method has two types of parallel connection and series connection of the current limiting resistor and the switch. The switch may be a relay or a transistor.

The following is a specific precharge device structure commonly used in circuit design, in which the advantages and disadvantages are as follows.

Fig. 2 shows a solid-state switching series type pre-charging device, which uses a power switch tube Q1 to control the output of the pre-charging device. The method has the advantages that the pre-charging device is disconnected after the direct current bus is charged; there is no contact discharge (the common contact switch has the problem of arc drawing at the closing or opening moment). The disadvantage is that the power switch tube and the power switch tube driving circuit are high in cost, and the instantaneous overcurrent problem (heat dissipation) of the power switch is also required to be considered.

Fig. 3 shows a relay switch series type precharge device, i.e. a relay is used to control the output of the precharge device, which is a scheme of using more precharge devices in the power supply design. The advantages are low cost; the control method is simple. The relay K1 has the disadvantages that the possibility of arc pulling exists at the moment of disconnection of the relay K1 (the relay contacts are fused together and the disconnection function is lost due to the arc pulling or long-time large-current operation); the volume is large, and the energy density is not large.

Fig. 4 shows a switch parallel type precharge device, in which a current limiting resistor is connected in parallel to both ends of a main input relay/contactor, the relay/contactor does not operate when the power is on, an input source charges a direct current bus through the current limiting resistors R1 and R2, when a charging voltage reaches a design value, the relay/contactor is closed (K1), the precharge device is bypassed, and a circuit operates normally. The scheme of the pre-charging device is also a scheme of using more pre-charging devices in the power supply design. The advantage is the lowest cost; the volume is minimum; the control method is simple. The disadvantage is that the pre-charging device is not completely disconnected with the main circuit, and the design of partial circuit has problems.

In high-voltage and high-power supply equipment, a direct-current bus needs to be provided with a special transformer for charging a direct-current bus capacitor. The principle of the method is that alternating current is transformed by a transformer to obtain lower voltage, the voltage is regulated by a soft starter circuit or limited by a resistor, then direct current is obtained by rectification of a rectifying circuit, then a direct current bus capacitor is charged, and after charging is finished, a charging loop needs to be switched off by a switch. That is, the high-voltage high-power supply pre-charging device is complicated, and not only needs a special high-power transformer, but also needs a large rectifying circuit and a disconnecting switch, because the voltage of the capacitor cannot suddenly change, a pre-charging soft start circuit or a current-limiting resistor is also needed to prevent the capacitor and a charging loop from being damaged due to overlarge charging current.

The above conventional pre-charging schemes do not have to open resistors or soft start current limiting, switching, or even dedicated rectifying circuits. The resistor plays a role in limiting current, and the soft starter is mainly used for limiting current in the soft starter although being voltage regulating equipment, so that the voltage of the capacitor is slowly raised; the switch has the function of bypassing or disconnecting after the charging is finished; the rectified current rectifies the alternating current to direct current, since the direct current bus is direct current.

These two precharging schemes have many disadvantages:

1. the pre-charging device is complex and has poor reliability

The pre-charging schemes can not be used for resistance or soft start current limiting, the pre-charging schemes need to be matched with a switch, a special rectifying circuit and the like, and direct-current voltage sampling is needed so as to control the switch to be disconnected or bypass a pre-charging loop in real time. With such a complicated charging loop, the entire power supply system cannot operate normally as long as there is a problem in one place.

2. The pre-charging loop is large in size, and the optical current-limiting power supply or the soft starter occupies a large space.

The pre-charging device needs to select a pre-charging resistor or a soft starter with a larger power grade, and even if the pre-charging time is prolonged, the resistor or the soft starter with the larger power grade needs to be selected. If resistor current-limiting pre-charging is selected, the resistor is large in size and power level. Taking ACDC power supply of AC220V, 2000W as an example, the current-limiting resistor is 100 Ω, and the DC bus capacitor voltage needs to be charged from 0V to DC300V according to the power formula P _R ＝U ² /R，P _R U is the voltage drop across resistor R for power consumption of the resistor. It can be seen from the formula that the voltage across the capacitor is 0V before the bus capacitor is charged, and after the precharge voltage is suddenly applied, since the voltage across the capacitor cannot suddenly change, the voltage (DC300V, DC voltage rectified by AC220V) is applied to the current-limiting resistor, and then the precharge voltage is applied to the current-limiting resistorInstantaneous power P across charging resistor R _R ＝U ² The charging current 300/100 is 3A, which is also the current on the limiting resistor, with/R900W. It can be seen that the pre-charge resistor has a power level of 900W, and the resistor is selected to be at least about 225W according to engineering application experience.

3. The pre-charging loop is an energy consuming circuit or a harmonic generation loop.

If the soft starter is used for pre-charging, the principle of the soft starter is a chopping principle, and the sine wave of the power grid is regulated in a chopping mode, so that the power grid is influenced greatly.

By adopting the resistance current-limiting charging method, although the influence on the power grid is not generated, the method is an energy-consuming charging mode, the energy for charging the bus capacitor is less than the energy consumed by a pre-charging loop (a resistor and a switch), and much energy is consumed on the resistor. In addition, the charging efficiency is low, and the charging current becomes smaller and smaller as the voltage of the capacitor to be precharged increases, so that it takes a long time to complete the precharging operation. In addition, the heat emitted by the circuit in the pre-charging process can cause the internal temperature of the equipment to rise, and the system is unstable.

4. The precharge circuit is too costly.

Such a precharge circuit is costly due to its complexity.

Disclosure of Invention

The invention aims to: the volume of the pre-charging loop is reduced, the cost of the pre-charging loop is reduced, the pre-charging efficiency is improved, and the reliability of the system is improved.

Therefore, the low-voltage low-power ACDC power supply with the pre-charging device is provided, and comprises an AC/DC circuit, a switching tube driving circuit for driving each switching tube in the AC/DC circuit to be opened and closed, a control circuit electrically connected with the switching tube driving circuit, an auxiliary power supply for supplying power to the driving circuit and the control circuit, and the pre-charging device for pre-charging a capacitor of a direct current bus on the AC/DC circuit; the auxiliary power supply has a transformer T100; the pre-charging device comprises a secondary winding N4 on the transformer T100 and a one-way conduction element D101 connected in series with the same-name end side of the secondary winding N4, the same-name end of the secondary winding N4 is connected to a positive BUS V _ BUS + of the direct current BUS through the one-way conduction element D101, a negative BUS V _ BUS-of the direct current BUS is connected with the other end of the secondary winding N4, wherein the conduction direction of the one-way conduction element D101 is from the same-name end of the secondary winding N4 to flow to the positive BUS V _ BUS +.

Compared with the prior art, the structure has the following advantages:

1. a winding and a one-way conduction element are independently added on the basis of an auxiliary power transformer, and a new direct-current power supply is formed by utilizing the capacitance on the bus and is completely isolated from other electric loops, thereby being safe and reliable.

2. The one-way winding is additionally arranged on the transformer, the size of the original transformer is not changed, for the whole system, the one-way conduction element is equivalently arranged, the capacitance is arranged on the bus, the capacitance is not additionally arranged, the volume space is not increased, and the one-way conduction element only has current flowing in the pre-charging process, so that the size of the one-way conduction element is small, and the one-way conduction element can be completed by adopting a patch one-way conduction element.

3. The realization cost is low, only one unidirectional conducting element and one transformer winding are needed, and the transformer winding is not just a little copper wire.

4. The charging conversion efficiency is high, the energy is directly burned off in a heating mode unlike a current-limiting resistor, and the working efficiency is at least over 80 percent when the charging conversion efficiency is used as a switching power supply.

Drawings

FIG. 1 is a logic diagram of a conventional precharge control principle.

Fig. 2 shows a solid-state switching series type precharge device.

Fig. 3 shows a relay switch series type precharge device.

Fig. 4 shows a switching parallel type precharge device.

Fig. 5 is a diagram showing the structure of the precharge circuit according to the present invention.

Detailed Description

The technical solution of the present invention is further explained with reference to the accompanying drawings and specific embodiments.

The low-voltage low-power ACDC power supply of the embodiment is an AC/DC and DC/DC bidirectional isolation power supply below 2000W. The AC/DC and DC/DC bidirectional isolation power supply comprises an AC/DC circuit, a DC/DC circuit, a pre-charging device, a voltage and current detection circuit, a switching tube driving circuit, a control circuit, a cooling fan, an auxiliary power supply and the like. The auxiliary power supply supplies power (direct current) to each of the driving circuit, the detection circuit, the fan and the control circuit, and if the control circuit needs the auxiliary power supply to provide 12V power, the fan is provided with 24V power, and the like.

In this embodiment, the switching tube driving circuit is used for driving each switching tube in the AC/DC circuit and/or the DC/DC circuit to be turned on and off. The control circuit is electrically connected with the switching tube driving circuit. The pre-charging device pre-charges a capacitor of a direct current bus on the AC/DC circuit.

As shown in fig. 5, the auxiliary power supply of this embodiment has a transformer T100, the pre-charging device includes a secondary winding N4 on the transformer T100, and a unidirectional conducting element D101 connected in series to the end of the secondary winding N4 at the same name, the end of the secondary winding N4 at the same name is connected to a positive BUS V _ BUS + of the dc BUS via the unidirectional conducting element D101, and a negative BUS V _ BUS-of the dc BUS is connected to the other end of the secondary winding N4, wherein the conducting direction of the unidirectional conducting element D101 is from the end of the secondary winding N4 at the same name to the positive BUS V _ BUS +.

Further, a switching tube Q20 is connected in series on the primary side of the transformer T100 for electric control, and a switching tube Q20 is connected with a control circuit; the transformer T100 is further provided with another secondary winding N3, and the control circuit regulates the output voltage of the secondary winding N4 through feedback control with the output voltage of the secondary winding N3 as a voltage control reference.

Referring to fig. 5, when the switch Q20 is turned on, the power DC +, DC-is applied to the two ends of the transformer winding N1, the current flows out from the pin 1 of the dotted terminal of the N1 winding, and according to the principle of magnetic field coupling of the transformer, the current flows into the

pins

2, 8, 9 of the dotted terminals of the other windings N2, N3, N4 of the transformer, but because of the direction cut-off effect of the unidirectional conducting element, no current flows in the windings N2, N3, N4 at this time; when the switch Q20 is turned off, because the current in the coil N1 cannot flow continuously, at this time, the current starts to flow out from the

pins

2, 8 and 9 of the windings N2, N3 and N4, and flows to the respective capacitors through the unidirectional conducting element, the current in the winding N3 flows into the capacitor C110 through the unidirectional conducting element D102, and the current in the winding N4 flows into the capacitors C100-C102 in the dc bus through the unidirectional conducting element D101, so as to maintain the direction of the magnetic field in the transformer. After the magnetic field energy is completely converted into the electric energy and the electric energy is output from the secondary side of the transformer, the switching tube Q20 is switched on again, the electric energy on the primary side of the transformer is converted into the magnetic energy, then the switching tube Q20 is switched off, and the magnetic energy is converted into the electric energy again and the electric energy is output from the secondary side of the transformer. And repeating the steps, and continuously conducting and stopping to transfer the primary side of the energy charging transformer to the secondary side.

After the energy is continuously transferred to the secondary side, the voltage on the capacitor gradually rises. The auxiliary power supply takes 12V as feedback, the high voltage and 12V are output by the winding N3, the conduction time of the auxiliary power supply chip for controlling the Q20 to be conducted is shorter, and the transmitted energy is smaller; when the voltage on the capacitor of the N3 winding is lower than 12V, the Q20 is turned on for a longer time, and more energy is transferred from the primary side of the transformer to the secondary side. Since the winding N4 and the winding N2 are secondary windings, but the turn ratios are different, the turn ratios of the N4 and the N2 are determined according to the required ratio of the direct-current bus voltage to 12V. When the N2 winding outputs energy, the N4 winding also outputs energy to charge the bus power supply.

The invention uses auxiliary power supply, and adds a coil winding N4 and one-way conduction element in the transformer to complete pre-charging. As shown in fig. 5, coil N4(9-7) is an added coil winding in transformer T100 and D101 is an added unidirectional conducting element. In the system working power supply, 12V, GND1 power supply is feedback power supply, the rest of power supplies are based on 12V, GND1 power supplies, if the number of turns of the 12V, GND1 power supplies corresponding to the coil N3(8-6) of the transformer is 3, the number of turns of the 24V, GND2 power supplies corresponding to the coil N2(2-4) of the transformer is 6. If the dc bus needs 180V, the transformer N4(9-7) coil needs 45 turns. After a pre-charging coil is added in the transformer, the volume of the transformer is unchanged.

The one-way conduction element has the function of one-way conduction, and can charge the energy of the transformer to the direct current bus so as to prevent the voltage (energy) of the direct current bus from returning to the transformer. After the direct current bus capacitor is charged, the direct current bus capacitor is powered by the main loop, at the moment, the bus capacitor can rise a little, but the pre-charging loop cannot fill the auxiliary power supply system due to the existence of the one-way conduction element. Meanwhile, because the bus voltage is higher than the voltage output by the auxiliary power supply N4 at the moment, the electric energy of the auxiliary power supply can not be charged into the bus capacitor any more, and even if the electric energy is charged, the electric energy is not concerned.

According to the invention, only one winding N4 is added on the auxiliary power supply, the volume of the transformer of the auxiliary power supply is basically unchanged, because the diameter of the enameled wire of the winding is 0.1mm, and a small one-way conduction element can be used as FR157, the cost is low, the reliability is high, the occupied volume is small, and the transformer is energy-saving and environment-friendly.

In summary, the pre-charging device of the present invention is designed in a bidirectional isolated power supply with AC/DC and DC/DC power below 2000W. The bidirectional isolation power supply comprises an AC/DC, a DC/DC, a system working power supply, a control center, a pre-charging device and the like, can invert battery energy into alternating current, can rectify the energy at an alternating current end into direct current to charge a battery, and can be carried out bidirectionally. Since the bidirectional power supply needs a dc bus, a capacitor having a large capacity is required to stabilize the dc bus voltage. It is known that the capacitor voltage cannot be abruptly changed, needs to be slowly charged, and needs to be charged to a voltage close to the required dc bus voltage. In many precharging schemes, a resistor or a soft starter is used for limiting current and a switch is matched with operations of disconnection, precharging and the like, so that not only is a circuit complex, unreliable and uneconomical, but also no energy is wasted, and more importantly, a precharging circuit occupies a large amount of space in the modern pursuit of higher energy density and better energy density, and is very cost-effective.

The low-voltage low-power supply (ACDC) does not need a special pre-charging device, and only needs to add a coil winding and an additional low-power one-way conduction element in a transformer in an auxiliary working power supply in the conventional ACDC power supply. The cost is reduced, the reliability is enhanced, and the energy density of the bidirectional energy storage power supply is improved.

As an improvement, the auxiliary power supply of this embodiment is preferably a flyback operating power supply, in which the primary side is operated, the secondary side is not operated, and the two sides are independently operated in a coupled inductor manner, and after the switching tube is turned off, the secondary side can provide a reset voltage to the magnetic core without additionally adding a magnetic flux reset winding.

In addition, the load is increased for the secondary winding N3 in the process of precharging the capacitance of the DC bus provided in the AC/DC circuit. Therefore, the precharging can be completed more quickly by utilizing the coupling principle. Specifically, only the power of the feedback power supply 12V needs to be increased during operation, for example, in the pre-charging process, the control system can increase the 12V load by starting a device (such as a fan) or connecting a resistor, and according to the transformer coupling relationship, the pre-charging end transformer winding can also output more electric energy, so that the voltage of the bus capacitor can be rapidly increased.

In this embodiment, the secondary winding N2 is used to supply power to the cooling fan, the secondary winding N4 is used to supply power to the control circuit, the control circuit controls the on/off of the cooling fan, and the manner of increasing the load for the secondary winding N3 is set to control the control circuit to start the cooling fan, so that resource integration and utilization are achieved.

Furthermore, a unidirectional conducting element D103 and a unidirectional conducting element D102 are respectively connected in series to the terminals of the secondary winding N2 and the secondary winding N3, wherein the conducting direction of the unidirectional conducting element D102 flows out from the terminal of the secondary winding N3, and the conducting direction of the unidirectional conducting element D103 flows out from the terminal of the secondary winding N2. The arrangement of D102 and D103 prevents the primary side or N4 from being affected by voltage fluctuations caused when the power of the feedback power supply 12V is increased/when the fan is supplied with power.

In the present embodiment, it is also provided that the coil turn ratio between the secondary winding N4 and the secondary winding N3 is configured to a specific ratio that enables the output voltage of the secondary winding N4 to approach or be equal to the voltage of the dc bus when the output voltage of the secondary winding N3 reaches a predetermined reference. Therefore, after the capacitor voltage is charged, the unidirectional conducting element does not need to be disconnected, and when the output voltage of the bus and the output voltage of the transformer winding are close, the charging current does not exist basically.

The unidirectional conducting element of the embodiment may be a diode or other device with unidirectional current-carrying capacity formed by a PN junction.

Compared with the prior art, the precharge device of the embodiment has the following advantages:

5. After the capacitor voltage is charged, the unidirectional conducting element does not need to be disconnected, because when the output voltage of the bus and the transformer winding is close, the charging current does not exist basically.

The above embodiments are merely some preferred embodiments of the present invention, and those skilled in the art can make various alternative modifications and combinations of the above embodiments based on the technical solution of the present invention and the related teaching of the above embodiments.

Claims

1. A low-voltage low-power ACDC power supply with a pre-charging device,

the ACDC power supply comprises an AC/DC circuit, a switching tube driving circuit for driving each switching tube in the AC/DC circuit to be opened and closed, a control circuit electrically connected with the switching tube driving circuit, an auxiliary power supply for supplying power to the driving circuit and the control circuit, and a pre-charging device for pre-charging a capacitor of a direct current bus on the AC/DC circuit;

the method is characterized in that:

the auxiliary power supply has a transformer T100;

the pre-charging device comprises a secondary winding N4 on the transformer T100 and a one-way conduction element D101 connected in series with the same-name end side of the secondary winding N4, the same-name end of the secondary winding N4 is connected to a positive BUS V _ BUS + of the direct current BUS through the one-way conduction element D101, a negative BUS V _ BUS-of the direct current BUS is connected with the other end of the secondary winding N4, wherein the conduction direction of the one-way conduction element D101 is from the same-name end of the secondary winding N4 to flow to the positive BUS V _ BUS +.

2. The precharge apparatus according to claim 1, wherein: the primary side of the transformer T100 is connected in series with a switching tube Q20 for electric control, and the switching tube Q20 is connected with the control circuit; the transformer T100 is further provided with another secondary winding N3, and the control circuit regulates the output voltage of the secondary winding N4 through feedback control by taking the output voltage of the secondary winding N3 as a voltage control reference.

3. The precharge apparatus according to claim 2, wherein: the auxiliary power supply is a flyback working power supply.

4. A pre-charging apparatus according to claim 3, wherein: during the pre-charging of the capacitance of the DC bus on the AC/DC circuit, a load is added to the secondary winding N3.

5. A pre-charging device according to claim 4, wherein: the homonymous end of the secondary winding N3 is connected in series with a one-way conducting element D102, and the conducting direction of the one-way conducting element D102 flows out from the homonymous end of the secondary winding N3.

6. A pre-charging device according to claim 4 or 5, wherein: the ACDC power supply further comprises a cooling fan for cooling the circuit, the transformer T100 is further provided with another secondary winding N2, the secondary winding N2 is used for supplying power to the cooling fan, the secondary winding N4 is used for supplying power to the control circuit, the control circuit controls the opening and closing of the cooling fan, and the mode of increasing the load of the secondary winding N3 further comprises controlling the control circuit to start the cooling fan.

7. The precharge apparatus according to claim 6, wherein: the homonymous end of the secondary winding N2 is connected in series with a unidirectional conducting element D103, and the conducting direction of the unidirectional conducting element D103 flows out from the homonymous end of the secondary winding N2.

8. A precharge device according to any one of claims 2 to 5, wherein: the coil turn ratio between the secondary winding N4 and the secondary winding N3 is configured to be a certain ratio that enables the output voltage of the secondary winding N4 to approach or be equal to the voltage of the DC bus when the output voltage of the secondary winding N3 reaches a predetermined reference.

9. The precharge apparatus according to claim 1, wherein: the unidirectional conducting element is a diode.