Abstract: Introduced based on two port network switching power supply input flat wave circuit design general principle and the method. This method through to the flat wave electric circuit input admittance and output impedance’s design, can guarantee the flat wave electric circuit while has good flat wave effect to the high frequency component, reduces as far as possible to the low frequency component weaken, moreover does not affect power source’s elevating capacity while flat wave. Based on this principle design’s fourth-order direct-current line flat wave application project reality, the movement result had indicated that this principle has the good project practicality.< ?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" />
Key word: Input flat wave electric circuit; Input admittance; Output impedance
Introduction
Electronic technology’s rapidly expand, set a higher request to the electronic instrumentation and the equipment. In performance, safer reliable; In the function, increases unceasingly; Uses, the automaticity is getting higher and higher; In the volume, miniaturizes day by day. This enabled to have the numerous merit switching power supplies in aspects and so on computer, correspondence, astronautics, color television to obtain day by day the widespread application. But, because in the switch voltage-stabilized source, the switching valve work in on-off state, its alternating voltage and the electric current will have the very strong peak disturbance and the resonant disturbance through electric circuit’s primary device. These disturbance serious pollution city electricity electrical network, has affected the neighbor electronic instrumentation and equipment’s normal work; At the same time, as a result of this shortcoming, causes the switching power supply to be unable to apply in some precise electronic instrumentation, therefore, reduces switching power supply’s electromagnetic interference as far as possible, enhances its use scope, is engaged in the question which the switching power supply design must consider.
This article author has applied two port network principle, the flat wave electric circuit has carried on the analysis to the switching power supply, has given the input flat wave circuit design general method and the related parameter computational method.
1 based on two port network input flat wave electric circuit’s design
At present widely uses switching power supply, regardless of the single-valve type, the push-pull type, the semi-bridge system, entire bridge-type may induce the form which for as shown in Figure 1 (take single-phase as example).
May see by Figure 1: Through to inputs the flat wave electric circuit’s disposition, may change electric circuit’s equivalent impedance, then achieves the anticipated flat wave effect.
1. 1 input flat wave electric circuit twin port network model establishment
General schematic diagram which based on shown in Figure 1, may establish the input flat wave electric circuit twin port network model which as shown in Figure 2.
Its hybrid parameter equation is as follows:
In the formula: g11 is the input admittance; g22 is the output impedance; g12 is the reverse electrical current gain; g21 is the direct voltage gain. May transform the equivalent circuit diagram which by type (1) for as shown in Figure 3.
1. 2 input flat wave circuit design general principle
In switching power supply’s design, the input flat wave electric circuit must satisfy the following several requests:
①Must guarantee that the flat wave electric circuit while flat wave, does not affect power source’s elevating capacity;
②Regarding the input low frequency component, the request flat wave electric circuit does not create the weaken as far as possible;
③Regarding the high frequency harmonic component, the flat wave electric circuit must have the good flat wave effect.
Convolution (1) shows the hybrid parameter equation and shown in Figure 3 equivalent schematic diagram, by request①May obtain: The flat wave electric circuit’s input admittance and the output impedance must be as far as possible small, is also g11 = g22 = 0; By request②May obtain: Regarding the low frequency component, the reverse electrical current increases g12 and the direct voltage increases the g21 design value to be 1 as far as possible, but the input admittance and the output impedance must be as far as possible small, is also g12 = g21 = 1, g11 = g22 = 0;
By request③May obtain: Regarding the high frequency component, g11, g12, g21, g22 must small as far as possible. Synthesizes the above analysis conclusion, this is inputs the flat wave circuit design the general method and the flat wave effect judgment standard.
2 example analyses
The LC flat wave electric circuit and the fourth-order direct-current line flat wave is the project actual commonly used flat wave electric circuit, below we analyzes its flat wave effect by the above conclusion. Figure 4 is the LC flat wave electric circuit.
Its hybrid parameter equation is:
Regarding direct component:
Because f tends to 0, the correspondence has w = 2πf to tend to 0;
Obviously g11 = g22 = 0; g12 = g21 = 1
Regarding high frequency harmonic component:
When consideration wl > 10, obviously has g11 = g12 = g21 = g22≈0, the analysis system’s input admittance and the output impedance are as follows: Must guarantee that input admittance g11 tends to 0, causes the L value to be very big inevitably; Must guarantee that output impedance g22 tends to 0, causes the C value to be similarly very big inevitably, this has brought the limitation for the project practical application, this is also precisely the LC flat wave electric circuit’s shortcoming. The following analyzes again in the project actual widespread application fourth-order direct-current line flat wave, its schematic diagram as shown in Figure 5.
Its hybrid parameter equation is as follows:
In the formula:
If command:
, then may obtain the corresponding parameter to be as follows: g11 = gz; g12 = g21 = z; g22 = - l1 sz
Below we analyze this flat wave voltage transfer function the amplitude-frequency characteristic, this flat wave’s voltage transfer function is:
The g parameter substitution, makes its logarithm amplitude frequency characteristic using MATLAB as follows to show:
Obviously: Is small in the low frequency band output voltage’s weaken, the high frequency band’s flat wave effect is quite obvious.
May see by the above analysis: Because this electric circuit device parameter’s choice scope is wide, therefore easy to design satisfies the design requirements, and is suitable for the project actual flat wave. The author has applied this electric circuit in the switching power supply which designs for Changsha some company.
The design requirements are:
①Inputs 1 000 V peak voltage, produces 20 A electric currents most greatly.
②When flat wave output current from 0~25 A changes, causes 513 V voltage huntings not to surpass 2%.
According to the above the design requirements may obtain the design permissible value:
Input admittance: 20/1000 = 0. 02
Output impedance: (1 ± 2%) = 20. 93~20. 11
The author designated finally the parameter value is:
L 1 = 500μH; L 2 = 140μH; R0 = 0. 3 OMEGA; C1 = 470μf; C2 = 40μf
Obtains this group of parameter value substitution type (3):
g = 5; z = 0. 003;
g11 = gz = 0. 015;
g12 = g21 = 0. 003;
g22 = 0. 2
Joins around this flat wave switching power supply output wave shape to be as follows:
Obviously, after joining the fourth-order direct-current line flat wave, the output voltage ripple reduced greatly.
3 conclusions
In the switching power supply widespread application, the voltage hunting which created in on-off state has limited switching power supply’s use scope day by day as a result of the switching valve work, therefore needed to suppress the harmonic interference which created as a result of the voltage hunting. This article applies two port network theorem, has carried on the analysis summary to the switching power supply input flat wave electric circuit’s design requirements, has obtained three principles of design. It suits in any flat wave design. Embarks from this principle of design, may also carry on the analysis to the existing switching power supply input flat wave performance. This article has given one fourth-order direct-current line flat wave which applies this principle to design, and used in the project reality, the movement result had indicated: This principle theoretical and the practicality are good, have the versatility.
