CN102468748A - Constant current charging device for energy storage capacitor by PWM (Pulse-Width Modulation) control - Google Patents

Abstract

The invention discloses a constant current charging method and device for an energy storage capacitor by PWM (Pulse-Width Modulation) control, which are suitable for the technical field required for quick energy storage of a capacitor, such as the application field of generating a pulse electric field, a pulse magnetic field, a pulse laser, a pulse microwave, flash light and the like in the manner of quickly charging the energy storage capacitor and then instantaneously discharging the energy storage capacitor. The constant current charging device comprises a converter (302), a PWM generator (310), a current controller (311), a voltage controller (312), an inductor (304) and an energy storage capacitor (306). By using an open-loop PWM control method with a preset charging curve, the constant current charging device is capable of charging approaching to an ideal constant current in the charging process so as to reduce the current impact of the charging process, decrease the inductance of a charging inductor and reduce the making difficulty of an inductor project.

Description

Storage capacitor open loop PWM controls constant current charger

Technical field

The invention discloses a kind of storage capacitor open loop PWM control constant current charge method and device; Needing to be suitable for the technical field of electric capacity fast energy storage, as with the storage capacitor quick charge then the mode of instantaneous discharge produce the application of impulse electric field, pulsed magnetic field, pulse laser, pulse microwave, flash of light etc.

Background technology

To the storage capacitor charging, again with the electric capacity repid discharge, this method can produce very strong pulse power, is a kind of practicable method that produces impulse magnetic field, pulse laser, pulse microwave, flash of light etc.Improve pulse repetition frequency, can be through the control charge and discharge process time, reducing the charging interval is main means.Desirable charging modes is hoped charge power supply to the storage capacitor constant current charge, can make storage capacitor charging voltage fast rise, shortens the charging interval, also can reduce charging process improves power supply to the rush of current of switching device generation current utilization rate.

Existing constant current charge method has closed loop PWM constant current charge method and serial-resonant constant current charge method.Closed loop PWM control mode is that real-time current sampling and given continuous current are compared, and the size of controlling duty ratio then makes current constant, and disclosed patent CN101013850 disclosed this method in 2006.This method charging inductance is smaller, but because the closed-loop control time is long, is adapted to the above long-time constant-current charing system of charge cycle hundreds of millisecond.

Serial-resonant constant current charge method is to make charging inductance and storage capacitor generation series resonance, and in resonant process, the charging current of electric capacity reduces the charging interval that resonance frequency just can reduce electric capacity near constant current in this process.This method charging interval is very fast, but the charging interval is uncontrollable; And the charging inductance that resonance need be very big takes place, and being unfavorable for reducing the weight and volume of charging device, the inductance of simultaneously big electric current big inductance quantity also brings great difficulty to manufacturing process.

Open loop PWM control is exactly not control the charging current constant current through feedback, but charging process is undertaken by predefined charging PWM curve, makes charging current constant through preferred curve.Open loop control is applicable to all indeclinable occasion of power source loads and circuit parameter; The equivalent load of charge power supply does not change in the storage capacitor charging process; The main element parameters such as capacitor and inductor that charging process is relevant are constant, and this provides to open loop control maybe.

Storage capacitor charging circuit schematic diagram such as Fig. 1 of open loop PWM control, direct voltage square wave pulse E (t) charges to storage capacitor through inductance, and its magnitude of voltage and pulse duration can produce through switching power converters.Like Fig. 2 (a), establish its high voltage and hold time and be t _On, voltage is that the zero time is t _Off, this voltage charges to storage capacitor through inductance.The crest voltage duration is being provided, and the rising of inductive current is calculated as follows:

${\mathrm{\Δi}}_{\mathrm{Lup}}=\frac{u_0-u_c}{L}\·t_{\mathrm{on}}\left(j\right)---\left(1\right)$

When the square wave crest voltage that provides finishes, because inductive current need be continuously, diode continuousing flow conducting this moment, inductive current descends in time, and following formula is arranged:

${\mathrm{\Δi}}_{\mathrm{Ldown}}=-\frac{u_c}{L}\·t_{\mathrm{off}}---\left(2\right)$

Fig. 2 (b) is the waveform that a PWM cycle internal inductance electric current rises and descends.Through last surface analysis, can draw to draw a conclusion:

(1). square wave charges to storage capacitor through inductance, and control square wave duty ratio width can be controlled the size of charging current climbing and charging current under open loop situations.

(2). as long as do not change with the relevant component parameter of control in the storage capacitor charging process, just can make charging process can carry out the open loop control of stable repetition.

(3) open loop PWM control can make charging current constant, reduces charging current and impacts, and charging inductance is reduced.

Summary of the invention

1. the technical problem that will solve

Open loop PWM control charging process speed is fast, and the charging process rush of current is little.At first be how to design charging device, comprise converter design, pwm control signal produces the design of circuit, and the sampling of charging voltage charging current, comparison, mistake are limit the design of control circuit.Be open loop PWM control method then, its core is how to obtain the duty ratio curve, and how to produce pwm control signal by curve.

2. the design of storage capacitor open loop PWM control constant current charger

Charging device such as Fig. 3, the input direct voltage 301 of converter 302, the size of this direct voltage directly influences the maximum of storage capacitor charging voltage.This converter is a pulsed dc voltage 303 with this dc voltage conversion, gives storage capacitor 306 chargings through inductance 304 then.

The function of PWM generator 310 is to produce Series P WM signal 309, the size of the pulse duration of the output dc voltage 303 of this signal controlling converter 302 according to the duty cycle parameters curve.

The size of current sensor 308 sampling charging currents 305; When storage capacitor charging current or charging current climbing during greater than their set point; Current Control 311 produces control signal 313, and control PWM generator 310 reduces duty ratio or makes duty ratio is zero.

Voltage control 312 sampling storage capacitor voltages 307, when the storage capacitor charging voltage equaled set point, it was zero that generation control signal 314 control PWM generators 310 make duty ratio.

3. open loop PWM controls constant current charge process duty ratio curve

Open loop PWM control is exactly to provide the PWM parameter in advance, just provides the change in duty cycle curve, and the pwm control signal that PWM generator produces changes with the change in duty cycle curve, thereby controls whole charging process.

Change in duty cycle curve such as Fig. 4 (a), the corresponding waveform of the charging current of storage capacitor such as Fig. 4 (b), the corresponding waveform of the charging voltage of storage capacitor such as Fig. 4 (c).Complete PWM open loop control charging process is divided into following three phases:

(1) the T1 stage, adopt the duty ratio work that increases fast, inductive current is climbed to the constant current charge current value.This stage hopes that current-rising-rate is fast, and just the T1 time will lack.

(2) the T2 stage is the constant current charge stage.In this stage, charging current reaches constant current value, and it is constant to require the control duty ratio that charging current is kept.Constant-current phase shared ratio in whole charging process is big more, and charging process is unreasonable to be thought.

(3) the T3 stage, the electric current decline stage, this stage be for capacitance voltage more and more near the peak value of switch power source output voltage, can improve the voltage utilization of converter.

4. use the advantage of these apparatus and method

The charging method of open loop PWM control can reduce the charging interval.Be that it is few that electric current rises to constant current value institute's time spent because the T1 stage duty ratio of charging process is big on the one hand; On the other hand, in the T2 stage of charging process, can make electric current very stable through PWM control, charging process is near desirable constant current charge.

Another advantage of the charging method of open loop PWM control is the inductance value that can reduce charging inductance.The storage capacitor constant current charge of relative resonance control mode, the mode inductance of open loop PWM control wants little of below 1/3rd, if select for use the littler PWM cycle, then inductance can further reduce.

Description of drawings

Fig. 1 is a storage capacitor quick-charging circuit sketch map;

Fig. 2 (a) is a PWM waveform sketch map, a PWM of Fig. 2 (b) cycle inductive current rise and fall sketch map;

Fig. 3 is a storage capacitor open loop PWM control constant current charger sketch map;

Fig. 4 (a) is in the charging process, and the duty ratio curve of storage capacitor open loop PWM control, Fig. 4 (b) are the corresponding triphasic charging current curves of storage capacitor, the corresponding triphasic voltage curve of Fig. 4 (c) storage capacitor.

Fig. 5 is several kinds of circuit forms of converter, and Fig. 5 (a) is the Buck converter, and Fig. 5 (b) is isolated push-pull converter, and Fig. 5 (c) is the bridge converter of isolating;

Fig. 6 is two kinds of method sketch mapes that are converted into the output pwm control signal from the duty ratio table;

Fig. 7 is a storage capacitor open loop PWM control constant current charge modular design sketch map.

Embodiment

1. converter specifically designs

Converter 302 inputs are direct voltages 301, and output is pulsed dc voltage 303, and the duty specific energy of this voltage is by 309 meters controls of output signal of PWM generator 310.Require the change in duty cycle scope big, can adopt the buck converter, perhaps adopt the push-pull converter of isolating, the full-bridge converter of isolation, these converter duty ratio controlled range all can reach 5%-95%.

Fig. 5 (a) is the buck converter, and occupancy controller output makes the switching element T break-make through drive circuit, charges to storage capacitor through inductance then.

Fig. 5 (b) is the push-pull converter of isolating, and occupancy controller output makes switching element T 1, T2 break-make through drive circuit, after transformer isolation, charges to storage capacitor through inductance.

Fig. 5 (a) is a bridge converter, and occupancy controller output makes switching device Q1, Q2, Q3, Q4 break-make through drive circuit, after transformer isolation, charges to storage capacitor through inductance.

2. the calculating of charging process duty cycle parameters table

As can beappreciated from fig. 1 inductive current is exactly a charging current, the controlled target of constant current charge be the ratio that makes the constant current time account for whole charging process try one's best big, it is very fast that this requires that T1 stage electric current rises, the T3 time in stage is short; Simultaneously, also will control the stable repetition of continuous current, this requires the constant current control stabilization, and current ripples is little.

The T1 stage, adopt the duty ratio work that increases fast, inductive current is climbed to the constant current charge current value.The perfect condition in this stage is that electric current rises in a period of time internal linear.Like Fig. 1 (b), can know by formula 1, in Ton electric current rising in the time; Can know that by formula 2 Toff time internal inductance electric current does not descend when capacitance voltage is low.This stage can be regarded as inductive current only to rise not descend.

If there be n PWM cycle in the T1 stage, each cycle ON time is Ton (j), and then inductive current was progressively accumulated through each cycle, and its value is:

$i_L=\frac{u_0}{L}\underset{j=1}{\overset{n}{\mathrm{\Σ}}}{t}_{\mathrm{on}}\left(j\right)---\left(3\right)$

If duty cycle alpha, if this stage duty ratio is constant, then current-rising-rate is:

$\frac{{\mathrm{\Δi}}_L}{\mathrm{\Δt}}=\frac{u_0}{L}\mathrm{\α}---\left(4\right)$

In the T1 stage, the relation between duty ratio size, T1 time length, the charging current size when T1 finishes can obtain according to (4) (5) two formulas.

The T2 stage is the constant current charge stage.In this stage, charging current has reached constant current value, requires the control duty ratio, and it is constant that charging current is kept, i.e. dynamic equilibrium is kept in the rising and the decline of a PWM cycle internal inductance electric current.Both satisfied following equality:

$\frac{u_0-u_c}{L}{t}_{\mathrm{on}}=\frac{u_c}{L}{t}_{\mathrm{off}}---\left(5\right)$

Then can derive:

$\mathrm{\α}=\frac{u_c}{u_0}---\left(6\right)$

Be this stage, duty cycle parameters by formula 6 provides, and keeping current constant only needs duty ratio to be directly proportional with capacitance voltage.At the initial stage in constant current charge stage, capacitance voltage is very low, and keeping the needed square-wave voltage duty ratio of current constant can be smaller, and along with the rising of capacitance voltage, keeping the needed square-wave voltage duty ratio of current constant can progressively increase.Constant current charge latter stage, switch power source output voltage duty ratio very great talent is enough to keep constant current.

In the T3 stage, the electric current decline stage, more and more near the peak value of switch power source output voltage, this moment, the duty ratio maximum can not be kept constant current charge to this stage capacitance voltage.When charging current is more and more littler, it is more and more slower that capacitance voltage rises.In order to improve the supply voltage switch utilance, it is necessary continuing to keep a period of time charging.When pressure reduction near zero the time, to not contribution of capacitance energy storage.In order to make capacitance voltage reach required value fast, shorten the required time in this stage, the crest voltage of design Switching Power Supply output must be a little more than the capacitance voltage of mission requirements.

Obtain the duty cycle parameters of three phases according to top theory, carry out emulation on computers.Artificial circuit figure such as Fig. 1 (a), the duty ratio of E (t) provides by Fig. 3 (a) curve.It is made up of a series of duty ratio, in simulation process, can adjust each duty ratio size, makes charging current near Fig. 3 (b).Because this charging device belongs to power electronic circuit, the waveform that simulation waveform and real work are measured has difference, so in order to make charging current more near constant current charge, duty cycle parameters also will be adjusted according to the current waveform of actual measurement in the working control process.

3.PWM the concrete design of controller

Pwm signal can be the switch periods of fixing, the PWM pattern that ON time changes; Perhaps fixing ON time makes the PWM pattern that the turn-off time changes; Perhaps fixing turn-off time, the PWM pattern that ON time is changed.

Like Fig. 6, produce pwm control signal by the duty cycle parameters curve, typical method has two kinds.

A kind of like Fig. 6 (a), MCU through D/A, through PWM special integrated circuit such as chips such as TL494 or SG3525, produces one or more pwm control signal with duty cycle parameters again.

Another kind of MCU produces needed pwm signal with the duty cycle parameters table through the PWM timer like Fig. 6 (b), and MCU chips such as PIC, Cortex, MSP all carry these PWM timers at present.

4. Current Control and voltage control specifically design

Current sensor adopts the Hall current instrument transformer or uses resistance sampling to amplify then.

The current value of sampling and magnitude of voltage can be through the A/D conversions; Carry out the comparison of charging current climbing, charging current comparison, charging voltage relatively by MCU; When storage capacitor charging current or charging current climbing during greater than their set point, MCU reduces duty ratio through program or makes duty ratio is zero; To make duty ratio be zero to MCU when the storage capacitor charging voltage reaches set point.

Current Control and voltage control also can adopt analog comparator, and current-rising-rate comparison, charging current comparison, charging voltage and corresponding set-point are compared, and result relatively is sent to MCU and controls that to reduce duty ratio or make duty ratio be zero.

The set point of current-rising-rate, continuous current, electric capacity charging voltage etc. can be given by potentiometer, also can be given by button.

5. storage capacitor open loop PWM controls a design example of constant current charge circuit

Fig. 7 is a design example of storage capacitor open loop PWM control constant current charge.Converter can adopt the buck converter, and perhaps adopting the push-pull converter of isolating, the full-bridge converter of isolation, input voltage can be to exchange or direct current.This instance adopts bridge converter, and input is a three-phase alternating current.

Like Fig. 7, three-phase alternating-current supply voltage 711, through controllable silicon phase control rectifier 701,703 filtering of inductance 702 electric capacity, the bridge converter of process power device 704 compositions is to the former limit of transformer 705 again; There are two windings on the inferior limit of this transformer, and through rectification circuit 706,2 couples of storage capacitor C2 charge through inductance L.

Charging duty ratio profile memory is inner at MCU, is tabled look-up through the PWM timer output of inside by MCU.The duty cycle signals 709 of output is complementary two-way, and duty ratio is identical with frequency, phase phasic difference 180 degree.Control logic circuit is a logic gates, can make this two-way duty cycle signals wherein one the tunnel give driving 1 and drive 4, and driving 2 and driving 3 are given in another road; Control logic circuit can also make this two-way duty cycle signals controlled signal 708 turn-off.

Charging current is obtained by Hall current sensor HL, through importing MCU into after modulus converter A/D 1 digitlization; Storage capacitor voltage imports MCU by 709 dividing potential drops into through after other modulus converter A/D 2 digitlizations.Current-rising-rate, Constant Electric Current flow valuve, electric capacity charging voltage value are provided by parameter control point adjustment 710, import MCU into through after other modulus converter A/D 3 digitlizations.MCU calculates current-rising-rate; Current-rising-rate, Constant Electric Current flow valuve, electric capacity charging voltage value are compared with given set point respectively; If sampled value has reached set point, MCU produces control signal 708, and being reduced duty ratio or made duty ratio by control logic circuit is zero.

Claims (8)

1. a storage capacitor constant current charger comprises converter (302), PWM generator (310), Current Control (311), voltage control (312), inductance (304), storage capacitor (306); This device adopts open loop PWM control method.

2. according to the converter described in the claim 1, can be push-pull converter, the bridge converter of buck converter, isolation; It is characterized in that direct voltage (301) is transformed to dc pulse voltage (303), and this dc pulse voltage charges to storage capacitor (306) through inductance (304); This dc pulse voltage duty ratio receives pwm control signal (309) control.

3. according to PWM generator described in the claim 1, it is characterized in that producing pwm control signal (309) according to the change in duty cycle curve comes control change device (302).

4. according to Current Control described in the claim 1 (311), the charging current (305) of the storage capacitor that it is characterized in that sampling, output control signal (313) when this electric current exceeds set point, this control signal control PWM generator (310) reduces duty ratio.

5. according to voltage control described in the claim 1 (312), the charging voltage (307) of the storage capacitor that it is characterized in that sampling, output control signal (314) when this charging voltage value exceeds set point, this control signal control PWM generator (310) reduces duty ratio.

6. according to the open loop PWM control method described in the claim 1, it is characterized in that producing pwm signal rice control change device according to the change in duty cycle curve.

7. according to the curve of change in duty cycle described in the claim 6, comprise electric current ascent stage T1, constant current charge stage T2, electric current decline stage T3; The characteristic of this three phases is:

Electric current ascent stage T1 adopts big space rate work that charging current is risen; At constant current charge stage T2, duty ratio progressively increases from little, and charging current is kept constant; At electric current decline stage T3, duty ratio is kept maximum.

8. according to the curve of change in duty cycle described in the claim 7, its producing method is that this curve is stored in the data storage with forms mode, by the program generation of tabling look-up; Perhaps this curve program of directly enrolling produces.

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