Abstract: Proposed one kind of novel bidirectional DC/DC converter. This transformation clamour uses entire numerical control, and the application synchronization rectification technology, enables the entire design to have the high efficiency, the high control performance, the energy to be possible characteristics and so on two-way flow. This converter’s control core is PHILIPS Corporation produces based on ARM7 the essence LPC2119 micro controller. Introduced system’s basic constitution, has analyzed electric circuit’s principle of work and the main primary device’s selection method, and has given the final experimental result.
Key word: Numerical control; DC/DC converter; Pulse-duration modulation; Synchronized rectification
O introduction
In order to realize the direct-current energy two-way transmission, the bidirectional DC/DC converter is widely applied in situations and so on UPS system, space power system, electric automobile actuation and accumulator cell charging and discharging maintenance.
Time these applications, are many requests the switching power supply not only to be able to control the energy the two-way flow, but must be able to realize the low pressure, the big electric current output. In the turn-on frequency not too high situation, reduced, output current increase along with the output voltage, the rectification loses has become the influence switching power supply efficiency main post element. Therefore, to raise switching power supply’s efficiency, must try to reduce the rectification loss. But uses in this paper the synchronized rectification technology is one kind the effective measure which reduces the rectification to lose.
Middle the former power source design, the analogue control technology because of its dynamic response quick, non-merits and so on quantized error, low in price widespread should collapse; But numerical control technology as a result of its aspect and so on cost and technology factors but little obtains the application. In recent years, along with Semiconductor Technology’s unceasing development, the digital micro controller’s cost obviously reduced, the performance enhanced unceasingly, this caused the high frequency switching power supply’s entire digitization into possible. Because the numerical control has can simplify the system hardware not to count, the reduction discrete component’s quantity, the improvement system reliable and so on many merits, therefore it will certainly to obtain more and more widespread application in present’s switching power supply design.
l system introduction
1.1 system basic statements
System’s whole constitution as shown in Figure 1. Figure in 1 dashed line for system’s control section. Other primarily electric circuit part. Main circuit’s principle of work in the behind multianalysis.
In system’s control circuit, its core processor is PHILIPS (Phillips) the company produces based on ARM7 the essence LPC2119 micro controller. LPC2119 has the high performance, the low cost, the low power loss and so on many merits, very suitable to apply in has the strict request industrial control domain to the cost and the performance. Those who are responsible for A/D transform is 24 high accuracy A/D switch CS5460A, it has the low cost, the high performance characteristic similarly, formerly has the widespread application in each kind of product.
When the control circuit works, CS5460A after obtaining the system output voltage, the amperage simulated signal, transforms them into the digital quantity, and passes to LPC2119 through the special-purpose main line. LPC2119 will obtain these information later first to carry on software processing and so on digital filtering to it, will then take it as the feedback quantity again, will use in the control algorithm the operation, will obtain the control quantity and the corresponding driving signal. Controls the main circuit switching valve’s movement finally.
1.2 bidirectional DC/DC entire numerical control’s software realizes
As mentioned above, stemming from the simplification control circuit structure, increases aspect and so on system reliability considerations, the system uses take ARM chip LPC2119 as the control system core entire digitized design. Must realize the control function which we expected, except outside basic loop which introduced in above, the consummation, the reliable control software and the appropriate control policy is also indispensable.
In the control software aspect, the author in line with each level clearly demarcated, the succession graduation, the overall situation considered that the written standard’s design general rule has carried on the systems control software’s development. According to the electric power electron software’s actual need, in the procedure whole divides into 3 levels, respectively is the master control level, the algorithm level and the connection level. And the connection level is a first floor, the master control level is the top layer, the algorithm level has the connection master control level and the connection level middle bridge role. Specifically speaking, the master control level does not involve the concrete operation, is only responsible for each duty the dispatch, the interrupt arrangement, the time and priority processing and so on. The master control level has a document, including the main function and interrupt function. Transfers the algorithm level in the main function and the interrupt function the function to realize system’s function. But the algorithm level is responsible for the specific target the execution, control algorithm’s realization, system’s major function all manifests in the algorithm level. The connection level is responsible with hardware’s connection, possesses carries on processing with the peripheral device related operation in this level.
In the control policy aspect, this article has chosen the increase type digit PI algorithm. The increase type PI algorithm’s principal advantage is
(1) increase type algorithm does not need to make the accumulation, the control quantity determination only with the recent several erroneous sampling value related, namely its error does not accumulate.
what (2) it each time outputs is controls the quantity the increase, the misoperation affects is small.
In the PI algorithm, the proportional part can improve system’s dynamic property, but the integral part can reduce system’s static error, theoretically may realize not static difference output. After the discretization digital PI algorithm expression is
In the formula: KP is the scale-up factor;
K1 is the integral coefficient;
e(k) is this error;
u(k) is this control quantity output.
Recursion may obtain by type (1)
Type (1) subtracts type (2) to be possible to obtain the increase type digit PI control algorithm expression to be as follows:
Type (3) △u(k) namely the control quantity increase which outputs for the digital regulator. Therefore, the control algorithm outputs finally the control quantity is:
Middle installment practical work, if the load is the lead-acid battery, then works as when energy to flowing (charge), the system may according to need separately using the voltage closed loop or the electric current closed loop control device output voltage and the output current. The voltage, the electric current closed loop use are the increase type PI algorithms which this article states; When energy reverse flowing, stemming from practical application’s need, the system only (accumulator cell) the side carries on the constant flow control to the load.
2 electric circuit work process analysis
This article proposed main circuit analysis situs as shown in Figure 2, mainly includes: Power source input side filter electric capacity C1; The main switch manages S1 as well as the S1 SNUBBER electric circuit which by R1, C2, D2 is composed; Transformer T as well as carries on magnetism replacement for its primary side the third winding and carries on magnetism replacement for its nearby the clamp which by R2, C3, D3 is composed; Electric valve S2, the after flow manage S3 and output filter link L and C4 and so on several parts.
2.1 energies to flowing when work process analysis
In order to be advantageous for the analysis, the supposition this time the load is an accumulator cell. When electric circuit control energy to flowing, the main circuit the time work generally speaking may divide into two stages every week, namely forward flowing stage and after flow stage. But to prevent electric valve S2 and the after flow manages at the same time S3 the breakover to create the transformer vice-side the penetration short circuit, two supplementary pulses need to join the dead area, thus the final electric circuit’s work process may divide into 4 parts. Is in charge of S1, electric valve S2, the after flow to manage S3 driving signal as shown in Figure 3, Figure 3 l to 4 namely has corresponded the electric circuit work 4 stages separately.
When energy to flowing, if the output current is winding through the tube pressure drop big M0S tube parasitism body diode, will then bring the very big rectification loss and the after flow loss. Therefore, we have applied the synchronized rectification technology, causes the electric current to wind through breakover resistance only then 6mΩ the MOS tube, reduced the loss, to raise the efficiency greatly. The following is the energy to the flowing when 4 working stage multianalysis.
Stage l (energy when to flowing) this stage is starting, is in charge of S1 and electric valve S2 is triggered the breakover. The input current inflow transformer primary side winding’s end of the same name, the output current flows out nearby the transformer time winding’s end of the same name. This time the energy is stirring up the converter by the input lateral load side transmission’s way same tradition’s single end basically consistent, its electric current flows to like in chart 4(a) to show. Figure 4(a) i1 represents the transformer primary side electric current, i2 represents the transformer vice-side electric current (similarly hereinafter). This process until responsible shutdown when only will then finish.
When the stage 2 (dead time 1) this stage just started, is in charge of S2 and electric valve S2 shuts off, the after flow managed S3 still not the breakover but his/her body diode already the breakover. As a result of the transformer leakage inductance’s limit, the transformer vice-side electric current reduces gradually by the output current, but winds through the after flow body diode’s electric current to start by zero to increase gradually. In this stage, the output current in transforms by the rectification return route to the after flow return route. In this process direction of current like chart 4(b) shows. In chart (b) i2a, i2b expressed separately the load current flows through the electric valve and the after flow tube’s two parts.
Stage 3 (after flow stage) when this stage starts, the after flow manages S3 to trigger the breakover, therefore output current mainly by way of the S3 after flow, thus loses to reduce greatly. This stage will continue manages when the S3 shutdown to the after flow only then to end, its electric current flows to as shown in Figure 4(c).
When the stage 4 (dead time 2) this stage just started, the after flow manages S3 to shut off, but his/her body diode still breakover after flow. The output current carries on the after flow completely by way of the after flow tube’s body diode. This stage only will then later stop until the responsible breakover. This process direction of current as shown in Figure 4(d). Hence, main circuit one cycle’s work already ended. When electric circuit next time movement, is in charge of S1 and electric valve S2 meets the breakover, the electric circuit enters stage 1 when the active status.
when 2.2 energy reverse flowing work process analysis
When energy reverse flowing, electric circuit’s work process with the BOOST electric circuit basic consistent, may divide into two stages roughly.
Stage l (after flow) in the middle of this stage, the after flow tube breakover, the electric valve shut off, battery discharge electric current i1 winds through inductance coil L, the electric current linearity increases, electrical energy by magnetic energy form Chu in inductance coil L. This process direction of current as shown in Figure 5(a).
The stage 2 (back discharge) in the middle of this stage, the after flow tube shuts off, the electric valve breakover. Inductance L will store up the magnetic energy transforms as the electrical energy and the accumulator cell together to the input side electric discharge. Its electric current flows to like in chart 5(b) to show.
2.3 transformers, inductance, electric capacity parameter selections
The comprehensive power source volume, the system efficiency, the control precision, the component pressure resistance and so on many factor’s considerations, this article selects operating frequency f=55 kHz, T=1/f, biggest dutyfactor Dmax is 0.4, is in charge of S1 biggest breakover time toNmax is
2.3.1 transformer’s computations
Transformer vice-side voltage Vs according to type (6) computation.
In the formula: Vo on behalf of output voltage;
Vf on behalf of transformer vice-side tube pressure drop and output filter inductance pressure drop.
Then the transformer vice-side most low voltage should be
If the input voltage Vp minimum value is VPmin, therefore may obtain changes compares n is
In the formula: Bm is iron core’s biggest work magnetic-flux density;
S is the transformer magnetic core’s effective cross-sectional area.
Therefore, may obtain transformer primary side winding number of windings N1 is:
When calculates the third winding, first should accumulate balanced principle computation resetting voltage Vr according to the volt-second is
In the formula: tDFFmin is in charge of S1 the shortest turn-off time;
VPmax is the biggest input voltage.
Then may obtain is responsible for the transformer primary side magnetic flux replacement third winding’s number of windings N3 is
2.3.2 output filter inductance L computation
Must calculate the output filter inductance the inductance quantity, first should determine that flows through the inductance the electric current △IL size. From aspects and so on inductance coil’s external dimensions, cost, indicial response considered that △IL takes output current Io 10%~30% to be quite appropriate. In this paper, to limit in the output current well the ripple content, takes △IL for output current Io 10%. In the synthesis, may obtain inductance L by type (13) the size.
2.3.3 output capacity C4 computation
Output capacity’s size abundant needs the limiting value which suppresses by the output ripple voltage to determine, is also by △IL as well as output capacity’s equivalent series resistance ESR determination. Usually the output ripple voltage takes for the output voltage 0.3%~O.5%, in this paper the ripple voltage takes 0.3%. Therefore, may obtain
After extracting ESR, may product handbook selection appropriate filter electric capacity which provides according to the factory.
3 experimental results
Tests prototype’s main primary device shaping and the design variable is as follows: The main power component is HITACHI (Hitachi) 2SKl317, what the electric valve and the after flow tube use is IRL3803, two manifesto tubes which in the transformer primary side magnetism reset circuit uses is PHILIPS (Phillips) BYV26G. What here must point out that when carries on the electric valve and the after flow tube’s shaping, besides must consider the power component’s pressure resistance, the discharge current capability, but should also the special attention breakover resistance value size. This article chooses IRL3803 is IR Corporation promotes uses in the synchronized rectification specially the MOS tube, the breakover resistance only then 6mΩ, can the greatest degree reduce the breakover loss and, thus reduces gives off heat. Computation may result in the transformer primary side by the type (5)~ type (14), vice-side, the third winding changes the ratio is 170:3:255; Output filter inductance for 14.72μH; The electric capacity is 9900μF. The load is the monomer lead-acid battery.
The experiment major technique condition is as follows: The turn-on frequency is 55kHz. When forward work, the input voltage Vi for 400(1±5%)V, specified output voltage Vo is 2V, the output current is 20A; When reverse work, input voltage for 2(1±10%)V.
After measures, when system work the constant voltage, the stationary stream precision may achieve are smaller than O.5% design requirements; The installment peak efficiency is 86.7%. Main experiment profile like chart 6~ shown in Figure 8; When energy/reverse flowing, system’s efficiency curve as shown in Figure 9.
Figure 6 is gives when the battery charging the electric valve, the after flow tube driving signal actual profile. This time the primary side manager profile and the electric valve are synchronous. Figure 6 channel l is the rectification power component’s actuation profile, the channel 2 for the after flow power component’s actuation profile. When Figure 7 is the energy reverse flowing, the rectification power component, the after flow power component’s driving signal actual profile, this time the primary side main power component does not act. Figure 7 channel 1 actuates the profile for the rectification power component, the channel 2 to actuate the profile for the after flow power component. When Figure 8 is the energy to the flowing, the DC/DC converter is outputting the 2V voltage the experiment profile. May see from Figure 8, the output constant voltage precision is high, the voltage ripple is very small.
4 conclusions
This article proposed one kind based on the micro controller LPC2119 entire digital bidirectional DC/DC converter. Its principal characteristic includes:
(1) uses the entire numerical control, the hardware design is succinct, the reliability is high;
(2) application synchronization rectification falls the low pass condition loss effectively, the system efficiency is high;
(3) output constant voltage, the stationary stream precision are high, the systems control performance is good;
(4) system cost is low.
The experiment proved that this converter principle is correct, the job safety is reliable, and has the good control performance, may apply in the monomer accumulator cell sufficient/electric discharge and so on many kinds of both must output the low pressure big electric current and to control the energy two-way flow the situation, has the broad market prospect.
