A current-free sampling DC power supply parallel current sharing topology and a control method thereof

Abstract

The application discloses a currentless sampling DC power parallel current sharing topology, and the current sharing topology comprises a first switch tube Q1, a second switch tube Q2, an inductor L, a freewheeling diode D and a filter capacitor C; the first switch tube Q1 and the ground form a first input port, the second switch tube Q2 and the ground form a second input port, the filter capacitor C forms an output port at both ends, the source stage of the first switch tube Q1, the source stage of the second switch tube Q2 and the cathode of the freewheeling diode D are connected with one end of the inductor L, the other end of the inductor L is connected with the positive electrode of the filter capacitor C, and the negative electrode of the filter capacitor C is grounded. The current sharing topology realizes parallel current sharing of two DC power supplies through the maintaining effect of the inductor on current, has no current sampling or additional control loop, and improves the reliability of the parallel power supply; the topology can be used to form a parallel system by using two common DC power supplies without current sharing function, reduces the cost of the parallel power supply, and expands the application range.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of power electronic applications, and particularly relates to a current-free sampling DC power supply parallel current sharing topology and a control method thereof. BACKGROUND

[0002] Power supply parallel power supply is a relatively simple and convenient method to provide higher output power. Due to the voltage stabilizing characteristics of the DC power supply, the output impedance of the common DC regulated switching power supply is usually very low, usually about 10 mΩ. If two power supplies are directly connected in parallel, a very small output voltage error or output impedance difference will cause a significant output current error, resulting in unbalanced load of the two power supplies, and even circulating current between the power supplies. The output series diode of the power supply or the use of MOSFET and the controller to form an ideal diode can avoid circulating current, but cannot solve the problem of unbalanced load. Therefore, when the DC power supply is connected in parallel, the power supply needs to have a current sharing function.

[0003] The existing parallel current sharing schemes include external characteristic droop method, active current sharing method, etc. The external characteristic droop method reduces load imbalance by making the output characteristic of the power supply present a certain equivalent series resistance. The active current sharing method needs to sample the output current of the power supply, and requires signal transmission between the power supplies. The relatively inexpensive general DC power supply does not have these functions and cannot form a parallel power supply system. In the face of the low-cost requirement of the low-voltage DC power supply system, it has strong practical significance to use inexpensive DC power supplies to form a parallel power supply system. SUMMARY

[0004] To solve the problems in the above applications, the present application proposes a circuit topology for two-way power supply parallel connection: the two-way input of the parallel current sharing circuit connects the same type of power supply, and has an output port. The current sharing circuit works independently of the parallel connected power supply, and the two parallel connected power supplies work independently. The current sharing circuit topology is suitable for low-voltage DC power supply below 100V, allows a certain voltage difference between the two power supplies, and realizes two-way DC power supply parallel current sharing without current sampling, current sharing control loop and inter-module communication. While keeping the low cost of the power supply system, the application range of DC power supply parallel power supply is expanded.

[0005] The object of the present application can be achieved by the following technical solutions:

[0006] A current-free sampling DC power supply parallel current sharing topology, the current sharing topology comprising a first switch tube Q1, a second switch tube Q2, an inductor L, a freewheeling diode D and a filter capacitor C.

[0007] The first switch tube Q1 and the ground constitute a first input port, the second switch tube Q2 and the ground constitute a second input port, the filter capacitor C constitutes an output port, the source level of the first switch tube Q1, the source level of the second switch tube Q2 and the cathode of the freewheeling diode D are connected with one end of the inductor L, the other end of the inductor L is connected with the positive pole of the filter capacitor C, and the negative pole of the filter capacitor C is grounded.

[0008] Further, the first input port and the second input port are additionally connected with bypass capacitors in parallel;

[0009] Further, the first input port and the second input port are additionally connected with filters in parallel, and the filter is composed of a bypass capacitor and a filter inductor in series.

[0010] Further, the freewheeling diode D is a Schottky diode.

[0011] Further, the first switch tube Q1 and the second switch tube Q2 are MOSFET switch tubes.

[0012] The control method of the above-mentioned current sampling-free DC power supply parallel current sharing topology is as follows:

[0013] In the current sharing topology, the first switch tube Q1 and the second switch tube Q2 are alternately turned on and work complementarily, and the turn-on time of the first switch tube Q1 and the second switch tube Q2 does not overlap.

[0014] In each switching cycle, the turn-on time of the first switch tube Q1 and the second switch tube Q2 is equal, and is t on ; in the process from the turn-off of the first switch tube Q1 to the turn-on of the second switch tube Q2 and from the turn-off of the second switch tube Q2 to the turn-on of the first switch tube Q1, there is a fixed dead time t d .

[0015] When the first switch tube Q1 is turned on and the second switch tube Q2 is turned off, the current of the inductor L rises or falls according to the voltage relationship between the first input port and the second output port.

[0016] When the second switch tube Q2 is turned on and the first switch tube Q1 is turned off, the current of the inductor L rises or falls according to the voltage relationship between the second input port and the output port; when the first switch tube Q1 and the second switch tube Q2 are both turned off, the inductor L is freewheeling by the freewheeling diode D, and the current of the inductor L falls; when the load is rated, the current of the inductor L is always greater than zero.

[0017] The beneficial effects of the present application are as follows:

[0018] 1. The application realizes automatic current sharing without current sampling through the hardware characteristics of the current sharing circuit topology, and there is no signal transmission between the power supplies and between the power supplies and the current sharing module, and the power supplies do not need to have the current sharing function, thereby reducing the cost of parallel power supply and widening the application range of parallel power supply.

[0019] 2. The application proposes an automatic current sharing method using the hardware characteristics of the current sharing circuit topology, and compared with the traditional parallel current sharing scheme, the current sharing control loop is not needed, and the stability of the parallel power supply system is improved. BRIEF DESCRIPTION OF DRAWINGS

[0020] In order to more clearly illustrate the technical solutions in the embodiments of the application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or the prior art description, and obviously, other drawings can be obtained by those skilled in the art without creative labor on the premise of not paying the creative labor.

[0021] Figure 1 It is a schematic diagram of the current sharing topology of the application;

[0022] Figure 2 It is a basic working waveform diagram of the current sharing topology of the application;

[0023] Figure 3 It is a working waveform diagram of the current sharing topology of the application under light load;

[0024] Figure 4 It is a schematic diagram of the variant structure of the current sharing topology of the application;

[0025] Figure 5 It is a schematic diagram of the variant structure of the current sharing topology of the application;

[0026] Figure 6 It is the simulation result of the current sharing error of the current sharing topology of the application;

[0027] Figure 7 It is the test result of the output voltage and efficiency of the test prototype;

[0028] Figure 8 It is the test result of the current sharing accuracy of the test prototype. DETAILED DESCRIPTION

[0029] The technical solutions in the embodiments of the application will be described clearly and completely below with reference to the drawings in the embodiments of the application, and obviously, the described embodiments are only part of the embodiments of the application, not all the embodiments. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative labor are within the protection scope of the application.

[0030] A current-free sampling DC power supply parallel current sharing topology, as shown in Figure 1 The current sharing topology comprises a first switch tube Q1, a second switch tube Q2, an inductor L, a freewheeling diode D and a filter capacitor C.

[0031] The first switch tube Q1 and the ground constitute a first input port, the second switch tube Q2 and the ground constitute a second input port, the filter capacitor C constitutes an output port, the source level of the first switch tube Q1, the source level of the second switch tube Q2 and the cathode of the freewheeling diode D are connected with one end of the inductor L, the other end of the inductor L is connected with the anode of the filter capacitor C, and the cathode of the filter capacitor C is grounded.

[0032] The freewheeling diode D can be a Schottky diode.

[0033] As shown in Figure 2 The control method of the topology is as follows:

[0034] 1) Before t0 moment, the first switch tube Q1 and the second switch tube Q2 are both off, and the inductor L is freewheeled by the freewheeling diode D;

[0035] 2) At t0 moment, the first switch tube Q1 is turned on, the second switch tube Q2 is turned off, and the current of the inductor L is determined according to the voltage relationship between the first input port and the output port, and rises or falls;

[0036] 3) At t1 moment, the first switch tube Q1 and the second switch tube Q2 are both off, and the inductor L is freewheeled by the freewheeling diode D, and the current of the inductor L falls;

[0037] 4) At t2 moment, the second switch tube Q2 is turned on, the first switch tube Q1 is turned off, and the current of the inductor L is determined according to the voltage relationship between the second input port and the output port, and rises or falls;

[0038] 5) At t3 moment, the first switch tube Q1 and the second switch tube Q2 are both off, and the inductor L is freewheeled by the freewheeling diode D, and the current of the inductor L falls.

[0039] Wherein, t0-t1 and t2-t3 are equal, and both are t on ; t1-t2 and t3-t4 are equal, and both are dead time t d .

[0040] It is assumed that the inductor current change amounts in the Q1, Q2 conduction time and the dead time are ΔI1, ΔI2 and ΔI d The instantaneous value of the inductor L current is unchanged before and after each switching cycle, and it can be known that:

[0041] ΔI1+ΔI2+2×ΔI d= 0 (1)

[0042] In the time period of t0~t1, t2~t3, let the average current of inductor L be I1, I2 respectively, since the voltage across inductor L is constant in these time periods, the slope of the current change of inductor L is constant in these time periods, then the instantaneous current of inductor L at the midpoint of t0, t1 and t2, t3 is I1, I2 respectively. It can be known that:

[0043]

[0044] I1= I2 (3)

[0045] The average input current of the first input port and the second input port is:

[0046]

[0047] It can be known that the average input current of the first input port and the second input port is equal.

[0048] According to the volt-second balance of inductor L, the output voltage of the current-sharing topology can be derived as:

[0049] U in1 ×t on +U in2 ×t on = U o ×2×(t on +t d ) (5)

[0050]

[0051] It can be known that the change value of inductor current in t0~t1, t2~t3 and dead time is respectively:

[0052]

[0053] Since ΔI d <0, it can be known that the peak-to-peak value of inductor ripple current is:

[0054] ΔI L(pp) = max(ΔI1, ΔI2) (8)

[0055] When the load current is low, the working waveform diagram of the current-sharing topology is shown in Figure 3 Since in the dead time, the current of inductor L drops to 0 in the process of freewheeling of freewheeling diode D, formula (1), (2), (3) no longer holds.

[0056] From Figure 3The current waveforms of the first switch Q1 and the second switch Q2 are known, and the average currents of the first input port and the second input port are not equal at this time. Meanwhile, due to the dead time, the current of the inductor L drops to 0, and the voltage across the inductor L is equal, so formulas (5) and (6) are no longer valid.

[0057] According to Figure 3 The voltage waveform at the left end of the inductor L is known, and the output voltage of the current sharing topology is higher than the result derived in formula (6), but lower than the voltage of any one of the first input port and the second input port.

[0058] If the input current of the current sharing topology is further reduced, the output voltage of the current sharing topology rises above the lower voltage of the first input port and the second input port, and the average current of the input port with the lower voltage is 0.

[0059] Since the switching power supply usually does not have the ability of reverse power transmission, the output voltage of the power supply connected to the input port rises to equal the output voltage of the current sharing topology, and the power supply is in an idle state, which does not cause problems. When the current sharing topology is in an idle state, the output voltage is equal to the higher voltage of the first input port and the second input port.

[0060] In view of the above characteristics of the current sharing topology, the following design requirements are made:

[0061] 1) Try to reduce the proportion of the dead time in a switching cycle, so that the output voltage of the current sharing topology changes less when the current sharing topology is fully loaded than when the current sharing topology is idle.

[0062] 2) According to the switching frequency and the designed input voltage range, select the value of the inductor L, so that the unbalanced input current of the current sharing topology only occurs when the load is light, and at the same time, avoid using too large inductance to cause the increase of volume and cost. It can be allowed that ΔI L(pp) is 1 / 3-1 / 5 of the full load output current of the current sharing topology.

[0063] The first switch Q1 and the second switch Q2 can both be MOSFET switches. Since MOSFET switches have parasitic body diodes, in order to prevent the body diode from being turned on and causing circulating current, the absolute value of the voltage difference between the first input port and the second input port cannot exceed the forward conduction voltage drop of the MOSFET body diode, which is about 0.6V-0.7V, and decreases to about 0.5V with the increase of temperature. Therefore, in actual application, the absolute value of the voltage difference between the first input port and the second input port should be lower than 0.5V.

[0064] Considering that the current of the input port is intermittent when the current sharing topology is working, a bypass capacitor or a combination of a bypass capacitor and a filtering inductor can be added to the first input port and the first input port to improve this problem. The changed circuit is as follows Figure 4 ,Figure 5 As shown.

[0065] In order to verify the principle of the circuit topology and its control method, the parallel current sharing circuit topology and its control method are simulated and verified. Figure 6 As shown, the current sharing topology has good current sharing effect when the output current is sufficient and the input voltage deviation is within the allowable range.

[0066] In order to further verify the performance of the circuit topology, a prototype is made and tested. The test uses two voltage 20V ordinary regulated DC power supplies that can be fine-tuned, each with a maximum current of 3A, and the current sharing module has a maximum output current of 6A. Figure 7 、 Figure 8 The test results show that the voltage fluctuation of the prototype is about 2% from no load to full load; when the load is higher than 25% of the rated value, the efficiency of the prototype is about 99%; when full load, the current sharing accuracy of the prototype is higher than 2% within the entire allowable voltage difference range.

[0067] The present application proposes a circuit topology suitable for parallel connection of DC power supplies below 100V. The present application eliminates the dependence of traditional parallel current sharing methods on current sampling, inter-module communication or modification of power supply loops. Compared with traditional parallel current sharing methods, it has the advantages of simple structure, high reliability and low cost.

[0068] In the description of the present application, the description of the terms "one embodiment", "example", "specific example" and the like means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. In the present application, the illustrative description of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0069] The basic principles, main features and advantages of the present application are shown and described above. It should be understood by those skilled in the art that the present application is not limited by the above embodiments, and the above embodiments and descriptions in the specification are only illustrative of the principles of the present application. Without departing from the spirit and scope of the present application, various changes and improvements can be made to the present application, and these changes and improvements all fall within the scope of the claimed present application.

Claims

1. A control method of a current-sampling-free DC power supply parallel current sharing topology, characterized in that, The current-sharing topology comprises a first switch Q1, a second switch Q2, an inductor L, a freewheeling diode D and a filter capacitor C. The first switch Q1 and the ground form a first input port, the second switch Q2 and the ground form a second input port, the filter capacitor C forms an output port, the source of the first switch Q1, the source of the second switch Q2 and the cathode of the freewheeling diode D are connected to one end of the inductor L, the other end of the inductor L is connected to the positive electrode of the filter capacitor C, and the negative electrode of the filter capacitor C is grounded. The control method is as follows: In the current-sharing topology, the first switch Q1 and the second switch Q2 are alternately turned on and work complementarily, and the turn-on time of the first switch Q1 and the second switch Q2 does not overlap. In each switching cycle, the turn-on time of the first switch Q1 and the second switch Q2 is equal, both being t on ; in the process of the first switch Q1 being turned off to the second switch Q2 being turned on and the second switch Q2 being turned off to the first switch Q1 being turned on, there is a fixed dead time t d ; When the first switch Q1 is turned on and the second switch Q2 is turned off, the current of the inductor L rises or falls according to the voltage relationship between the first input port and the second output port. When the second switch Q2 is turned on and the first switch Q1 is turned off, the current of the inductor L rises or falls according to the voltage relationship between the second input port and the output port; when the first switch Q1 and the second switch Q2 are both turned off, the inductor L is freewheeling by the freewheeling diode D, and the current of the inductor L falls; under the rated load, the current of the inductor L is always greater than zero.

2. The control method of the current sampling-free DC power supply parallel current sharing topology according to claim 1, characterized in that, The first input port and the second input port are both additionally connected in parallel with a bypass capacitor.

3. The control method of the current sampling-free DC power supply parallel current sharing topology of claim 1, wherein, The first input port and the second input port are both additionally connected in parallel with a filter, which is composed of a bypass capacitor and a filter inductor in series.

4. The control method of the current sampling-free DC power supply parallel current sharing topology of claim 1, wherein, The freewheeling diode D is a Schottky diode.

5. The control method of the current sampling-free DC power supply parallel current sharing topology of claim 1, wherein, The first switch Q1 and the second switch Q2 are both MOSFET switches.

Images