WO2007076702A1 - Convertisseur continu-continu auto-oscillant et son procede de commande - Google Patents

Convertisseur continu-continu auto-oscillant et son procede de commande Download PDF

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Publication number
WO2007076702A1
WO2007076702A1 PCT/CN2006/003697 CN2006003697W WO2007076702A1 WO 2007076702 A1 WO2007076702 A1 WO 2007076702A1 CN 2006003697 W CN2006003697 W CN 2006003697W WO 2007076702 A1 WO2007076702 A1 WO 2007076702A1
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WIPO (PCT)
Prior art keywords
signal
circuit
load
pulse
frequency
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PCT/CN2006/003697
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English (en)
French (fr)
Inventor
Zhiyu Liu
Chunhui Zhu
Haizhou Zhao
Original Assignee
Emerson Network Power Energy Systems Ab
Emerson Network Power Co., Ltd.
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Publication date
Application filed by Emerson Network Power Energy Systems Ab, Emerson Network Power Co., Ltd. filed Critical Emerson Network Power Energy Systems Ab
Priority to EP06840727.9A priority Critical patent/EP1973220B1/en
Priority to US12/087,278 priority patent/US8406014B2/en
Publication of WO2007076702A1 publication Critical patent/WO2007076702A1/zh

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Classifications

    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M3/00—Conversion of dc power input into dc power output
    • H02M3/22—Conversion of dc power input into dc power output with intermediate conversion into ac
    • H02M3/24—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters
    • H02M3/28—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac
    • H02M3/325—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal
    • H02M3/335—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only
    • H02M3/337—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only in push-pull configuration
    • H02M3/3376—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only in push-pull configuration with automatic control of output voltage or current
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M1/00—Details of apparatus for conversion
    • H02M1/42—Circuits or arrangements for compensating for or adjusting power factor in converters or inverters
    • H02M1/4208—Arrangements for improving power factor of AC input
    • H02M1/4241—Arrangements for improving power factor of AC input using a resonant converter
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M3/00—Conversion of dc power input into dc power output
    • H02M3/01—Resonant DC/DC converters
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M1/00—Details of apparatus for conversion
    • H02M1/0048—Circuits or arrangements for reducing losses
    • H02M1/0054—Transistor switching losses
    • H02M1/0058—Transistor switching losses by employing soft switching techniques, i.e. commutation of transistors when applied voltage is zero or when current flow is zero
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M3/00—Conversion of dc power input into dc power output
    • H02M3/22—Conversion of dc power input into dc power output with intermediate conversion into ac
    • H02M3/24—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters
    • H02M3/28—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac
    • H02M3/325—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal
    • H02M3/335—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only
    • H02M3/33569—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only having several active switching elements
    • H02M3/33571—Half-bridge at primary side of an isolation transformer
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02B—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
    • Y02B70/00—Technologies for an efficient end-user side electric power management and consumption
    • Y02B70/10—Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes

Definitions

  • the invention relates to a DC power conversion technology, and in particular to a control method and device for a resonant DC/DC converter.
  • a series resonant DC/DC converter adopts a resonant conversion technique. Since the resonant element operates in a sinusoidal resonant state, the voltage on the switching transistor naturally crosses zero, and zero voltage turn-on can be realized. The loss is small.
  • This topology usually uses the Pulse Frequency Modulation (PFM) method to stabilize the output voltage by changing the operating frequency.
  • Figure 1 shows the basic form of a half-bridge SRC series resonant DC/DC converter. When PFM control is applied to the circuit, the two bypass tubes S1 and S2 are driven symmetrically and symmetrically, each conducting 50% (this is an ideal value, such as Consider the dead zone setting should be slightly less than 50% of the switching period.
  • the relationship between the power supply output voltage gain M and the operating frequency f is -
  • V. And V in are the output and input voltage
  • f is the operating frequency
  • f r f r is the resonant frequency
  • L r is the resonant inductance value
  • C r is
  • simple frequency conversion control will lead to wide or even failure of the operating frequency range, which is difficult to optimize the magnetic components and excessive circuit loss, and the problem that the feedback control is difficult to design. Therefore, the simple FM control cannot meet the light load or no load. The output voltage is required.
  • the half bridge digital resonant circuit is taken as an example to illustrate the shortcomings of the FM control mode. Similarly, the phenomenon of the full bridge series resonant circuit is exactly the same as the half bridge series resonance phenomenon. In theory, all resonant control circuits have similar problems.
  • the object of the present invention is to provide a control method and device for a resonant DC/DC converter, which solves the problem that in the prior art, when the load is operated at a light load or a no load, the use of the frequency modulation control is difficult to optimize the magnetic component, and it is difficult to stabilize the voltage and the circuit. The problem of excessive loss.
  • the technical solution adopted by the present invention is: A control method of a resonant DC/DC converter, which adjusts the output voltage by changing the conduction frequency of the input switching tube of the resonant circuit, and also according to the feedback of the load circuit.
  • the signal adjusts the duty cycle of the switching transistor such that the voltage output range of the resonant circuit is expanded.
  • the resonant circuit input switch tube can be controlled by a driving pulse through a driving circuit, and the obtaining of the driving pulse includes the following steps,
  • the pulse signal whose frequency and duty ratio are adjusted together with the feedback signal is used as the driving pulse of the driving circuit, so that the resonant circuit operates in PWM (Pulse width modulation). Modulation) control and PFM control mixing mode; otherwise, the pulse signal whose duty cycle is stable and the frequency changes with the feedback signal is used as the driving pulse of the driving circuit, so that the resonant circuit operates in the PFM control mode.
  • PWM Pulse width modulation
  • Modulation Pulse width modulation
  • PFM control mixing mode otherwise, the pulse signal whose duty cycle is stable and the frequency changes with the feedback signal is used as the driving pulse of the driving circuit, so that the resonant circuit operates in the PFM control mode.
  • the step 1) may include the following steps: La) sampling the feedback voltage from the load circuit;
  • the selection of the PFM control and the PFM+PWM control in the above control method is preferably implemented by the following process: in the step 2), the feedback signal is respectively subjected to an arithmetic processing to obtain a frequency conversion control signal and a pulse width modulation signal; the pulse width modulation signal
  • the operation processing process includes the steps of comparing with the reference signal to determine whether the load operates in a light load or no load state, the reference signal is determined according to the electrical characteristics of the load; and the load is operated in the step 3) In the light load or no-load state, a drive pulse that is commonly adjusted by the variable frequency control signal and the pulse width modulation signal is generated; otherwise, a drive pulse whose duty cycle is stable and which is separately adjusted by the variable frequency control signal is generated.
  • the operation processing process of the frequency conversion control signal in the step 2) includes comparing with the reference signal two to determine whether the load operates in an approximately no-load state, The reference signal 2 is determined according to the electrical characteristics of the load, and the reference signal 2 is satisfied. If the load works according to the judgment of the reference signal 2 in an approximate no-load state, the reference signal 1 must work according to the judgment of the reference signal 1 to work at light load or empty.
  • the step 3 when the load operates in an approximately no-load state, a drive pulse whose frequency is stable and is separately adjusted by the pulse width modulation signal is generated.
  • a resonant DC/DC converter is also provided, including
  • the driving circuit controls an input switch of the resonant circuit according to the input driving pulse, and the resonant circuit supplies the converted power to the load circuit under the control of the driving circuit, and
  • the negative feedback compensation regulator obtains a feedback signal by performing a negative feedback compensation operation on the feedback voltage sampled in the load circuit
  • a discriminator judging a load state of the load circuit according to the input feedback signal, and outputting a drive pulse modulation signal
  • Driving the pulse generator to modulate and output the driving pulse according to the input driving pulse modulation signal If the load operates in a light load or no load state, the frequency and duty ratio of the output driving pulse are adjusted together with the feedback signal; otherwise, the output The duty cycle of the drive pulse is stable and the frequency varies with the feedback signal.
  • the dynamic pulse generator comprises a frequency conversion control circuit and a frequency conversion control + pulse width modulation circuit; if the discriminator judges that the load works in a light load or no load state, the drive pulse modulation signal is output to the frequency conversion control + pulse width modulation circuit, and the control is controlled The output pulse and the duty ratio are adjusted together with the feedback signal to change the drive pulse; otherwise, the drive pulse modulation signal is output to the variable frequency control circuit to control the drive pulse whose output duty ratio is stable and the frequency changes with the change of the feedback signal.
  • a preferred scheme for performing PFM control and PFM+PWM control of the above resonant DC/DC converter can use only one driving signal generating circuit module: the discriminator includes arithmetic circuits one and two, and the arithmetic circuit is set There is a reference signal, the driving pulse modulation signal comprises a frequency conversion control signal and a pulse width modulation signal; the feedback signal is calculated by the operation circuit, and compared with the reference signal, the output is a pulse width modulation signal; the feedback signal The operation circuit 2 outputs an inverter control signal; the reference signal is determined according to the electrical characteristics of the load, so that when the load operates in a light load or no load state, the output pulse width modulation signal changes with the feedback signal.
  • the driving pulse generator includes a frequency conversion control circuit and a pulse width modulation circuit
  • the frequency conversion control circuit generates a frequency conversion pulse whose frequency is controlled by a frequency conversion control signal
  • the pulse width modulation circuit is modulated according to pulse width
  • the signal pulse-width modulates the variable frequency pulse and outputs a drive pulse.
  • the pulse width modulation circuit may be configured to compare the pulse width modulation signal with the variable frequency pulse and output the driving pulse.
  • variable frequency pulse may be input to the synchronizing terminal of the pulse width modulation circuit, and the pulse width modulation circuit may pulse-width modulate the input variable frequency pulse according to the pulse width modulation signal to output a driving pulse.
  • the operation circuit 2 is configured with a reference signal 2; the feedback signal is calculated by the operation circuit 2, compared with the reference signal 2, and the output is converted into a frequency conversion.
  • a control signal; the reference signal 2 is determined according to an electrical characteristic of the load, such that when the load operates in an approximately no-load state, the output variable frequency control signal remains stable; otherwise, changes with the feedback signal; and the reference signal Second, if the load works according to the judgment of the reference signal 2 in the approximate no-load state, it will work in the light load or no-load state according to the judgment of the reference signal one;
  • the frequency conversion control circuit may adopt a structure including a voltage-frequency oscillator and a triangular wave generator which are sequentially connected; the frequency conversion control signal is input to a voltage-frequency oscillator to control an oscillation frequency thereof, and the triangular wave generator outputs a frequency-controlled frequency conversion pulse.
  • the PWM control mode is introduced to realize the two control modes of PFM and PFM + PWM.
  • the PFM control is used.
  • the power supply frequency is too high, the PFM is introduced. +PWM control mode. It is also possible to fix the frequency at a higher frequency and enter the PWM control mode, thereby solving the difficult problem of the resonant converter, that is, the problem that the operating frequency is too high and the circuit loss is too large at light load and no load, and the resonant circuit is greatly increased.
  • the output voltage regulation capability effectively extends the voltage output range.
  • PFM control and PFM + PWM control are logically optional parallel relationships, but can be implemented by using a preferred inverter control circuit and pulse width modulation circuit in series.
  • the circuit avoids many logic gating.
  • the device and the multi-channel negative feedback compensation regulator are used in a simple circuit, and the two control modes are switched smoothly, and the reliability and dynamic characteristics are very good.
  • the invention is applicable to the deformation topology of the full bridge series, the parallel resonant circuit, the half bridge string, the parallel resonant circuit and the resonant circuit such as LLC, and has strong engineering significance.
  • FIG. 1 is a schematic diagram of a typical half bridge series resonant circuit in the prior art.
  • Figure 2 is a graph showing the output characteristics of the circuit in the PFM control mode of Figure 1.
  • Fig. 3 is a comparison diagram of the output characteristic curve of the circuit of Fig. 1 after the control method of the present invention is employed.
  • Figure 4 is a block diagram showing the principle of a DC/DC converter of the present invention.
  • FIG. 5 is a detailed block diagram of the circuit in the dashed box of Figure 4.
  • Fig. 6 is a schematic diagram showing the relationship between the feedback signal of the DC/DC converter and the frequency and duty ratio in Fig. 4.
  • Figure 7 is a waveform diagram of the drive pulse.
  • Fig. 8 is a block diagram showing another principle of the DC/DC converter of the present invention. ⁇ detailed description ⁇
  • a control method of a resonant DC/DC converter is to adjust an output voltage by changing a conduction frequency of a switching circuit of a resonant circuit thereof, and is also adjusted according to a feedback signal of a load circuit
  • the duty cycle of the switching transistor extends the voltage output range of the resonant circuit.
  • the curves A1 to A3 in FIG. 3 are characteristic curves of the output voltage Vo and the frequency f with a duty ratio of 50% using a separate PFM control mode under different load conditions. It can be seen that as the load is reduced, Vo tends to be flat and difficult to stabilize by increasing the operating frequency.
  • the curves B1, B2, and B3 in Fig. 3 are characteristic curves of the output voltage Vo and the duty ratio D and the frequency f in the integrated mode after the switching frequency of the curves A1 to A3 is raised to fa in the PFM control mode. Schematic; Control of duty cycle D starts from 50% until it reaches zero.
  • the control of the input and output of the resonant circuit is performed by the driving pulse through the driving circuit. Therefore, the switching from PFM to PFM+PWM is realized by the change of the driving pulse. Since the switching of the control mode is directly related to the load, the driving pulse is The following methods are used to obtain -
  • the judging process is performed by calculating the feedback signal and comparing with the reference signal: the feedback signal is respectively processed to obtain the variable frequency control signal and the pulse width modulation signal.
  • the operation process of the pulse width modulation signal is to compare the feedback signal by a proportional or addition and subtraction operation, and compare it with the set reference signal. If it is lower than the reference signal (or higher than the reference signal, it is determined according to the logic characteristic of the circuit, It is assumed here that the feedback signal is proportional to the load voltage, and the lower the feedback signal, the lighter the load, the direct output of the calculated feedback signal as a pulse width modulated signal.
  • the stable reference signal 1 is output as the pulse width modulation signal, and since the pulse width modulation signal does not change at this time, it corresponds to the case of pure PFM control.
  • the reference signal one needs to be determined according to the electrical characteristics of the load, so that the comparison based on the reference signal one judges whether the substantially correct response load operates in a light load state.
  • the operation process of the variable frequency control signal can be carried out in two ways.
  • One is to directly convert the feedback signal into a frequency conversion control signal after proportional or addition and subtraction, so that the variable frequency control signal always changes with the change of the feedback signal, so the resonant circuit Always have PFM control mode.
  • the other is to follow the operation mode of the pulse width modulation signal described above, and compare the result with the set reference signal two after the operation of proportional or addition and subtraction, if it is higher than the reference signal two (or lower than the reference signal, according to the circuit
  • the logic characteristics are determined. It is assumed that the feedback signal is proportional to the load voltage, and the lower the feedback signal, the lighter the load.
  • the feedback signal after the operation is directly output as the variable frequency control signal.
  • the stable reference signal 2 is output as the frequency conversion control signal, and since the frequency conversion control signal does not change at this time, it corresponds to the case of pure PWM control.
  • the reference signal 2 also needs to be determined based on the electrical characteristics of the load such that the comparison based on the reference signal two determines whether the substantially correct reaction load is operating in an approximately no-load state.
  • the load operates in an approximate no-load state according to the judgment of the reference signal 2
  • it is determined to work in a light load state according to the judgment of the reference signal one, which also It is ensured that in any case, at least one of the pulse width modulation signal and the variable frequency control signal changes with the change of the feedback signal.
  • step 2) if the load works in the non-light load state, the pulse width modulation signal is stabilized as the reference signal one, and the frequency conversion control signal changes with the change of the feedback signal, so under the control of the two signals
  • the output is a driving pulse whose duty cycle is stable and the frequency changes with the feedback signal.
  • the resonant circuit operates in the PFM control mode; if the load operates in a light load state, both the pulse width modulation signal and the variable frequency control signal change with the feedback signal.
  • the resonant circuit works in PFM+PWM control mode; if the load works at approximately no load State, the pulse width modulation signal changes with the change of the feedback signal, and the frequency conversion control signal is stabilized as the reference signal two, so under the control of the two signals, the output is a driving pulse whose frequency is stable and the duty ratio changes with the feedback signal.
  • the resonant circuit operates in the PWM control mode; the following describes in detail a method using the above control method.
  • Resonant DC/DC converter combined with Figure 4 and Figure 5, including
  • the driving circuit controls an input switch of the resonant circuit according to the input driving pulse, and the resonant circuit supplies the converted power to the load circuit under the control of the driving circuit, and
  • Negative feedback compensation regulator acted upon by the PI regulator, will be sampled from the load circuit
  • the feedback voltage is obtained after the feed voltage and the set voltage are set to perform a negative feedback compensation operation
  • the discriminator includes the arithmetic circuits one and two, and the arithmetic circuits one and two are respectively set with reference signals one and two
  • the feedback signal is passed through the operation circuit After performing an operation and comparing with the reference signal, the output is a pulse width modulation signal
  • the feedback signal is calculated by the operation circuit 2, and compared with the reference signal 2, and then output as an inverter control signal
  • the reference signals 1 and 2 are based on the electrical characteristics of the load.
  • the discriminator When the load works in an approximate no-load state, the discriminator outputs a stable variable frequency control signal (ie, reference signal 2) and a pulse width modulation signal that varies with the feedback signal; when the load operates in a light load state, the discriminator output is The pulse width modulation signal and the frequency conversion control signal that change with the feedback signal change; in addition, the discriminator outputs a variable frequency control signal that changes with the feedback signal and a stable pulse width modulation signal (ie, reference signal one).
  • a stable variable frequency control signal ie, reference signal 2
  • a pulse width modulation signal that varies with the feedback signal
  • the discriminator output when the load operates in a light load state, the discriminator output is The pulse width modulation signal and the frequency conversion control signal that change with the feedback signal change; in addition, the discriminator outputs a variable frequency control signal that changes with the feedback signal and a stable pulse width modulation signal (ie, reference signal one).
  • the drive pulse generator includes a frequency conversion control circuit and a pulse width modulation circuit.
  • the frequency conversion control circuit includes a voltage frequency oscillator and a triangular wave generator which are sequentially connected; the pulse width modulation circuit is
  • the frequency conversion control signal input voltage frequency oscillator controls the oscillation frequency thereof, and the voltage frequency oscillator changes the voltage signal of the frequency conversion control signal into a square wave signal whose output frequency changes, and the triangular wave generator receives the square wave signal of the frequency change to generate a triangular wave of frequency variation.
  • the signal is output to the synchronous end of the PWM generating circuit; the PWM generating circuit pulse-width modulates the input frequency-converted triangular wave signal according to the pulse width modulation signal V ⁇ mp input from the comp terminal, and outputs a driving pulse.
  • the duty cycle of the drive pulse does not change any more, only the frequency changes, that is, enters the PFM control; when V ⁇ mp and the variable frequency control signal both change the output, the duty cycle of the drive pulse
  • the frequency changes at the same time, that is, enters the PFM+PWM control; when the stable output of the variable frequency control signal is the reference signal two, the frequency of the driving pulse does not change any more, and only the duty cycle changes, that is, enters the PWM control.
  • the reference signal is one-half of the peak value of the triangular wave, so that the driving pulse outputted in the PFM control mode has a duty ratio of 50%.
  • the separate PWM control mode can also be disabled, so that the output frequency of the drive pulse is always related to the feedback signal, which is equivalent to setting the reference signal two to zero.
  • Modules capable of implementing the functions of the variable frequency control circuit and the pulse width modulation circuit are usually integrated in one chip. Depending on the internal functional architecture of the chip used, there may be more specific circuit relationships between them, such as a pulse width modulation circuit. It may be that the pulse width modulation signal is 1 ⁇ 4. ⁇ Compared with the frequency conversion triangle wave signal, the output drive pulse is synthesized. But simplified, The variable frequency control circuit and the pulse width modulation circuit can be summarized as a series circuit relationship, that is, the frequency conversion control circuit generates a pulse signal and controls its frequency, and the pulse width modulation circuit further determines the duty ratio of the pulse signal.
  • the control frequency changes simultaneously with the duty cycle:
  • the duty cycle changes from D0% to 50% full pulse width (without dead band), causing the output voltage to continue to rise;
  • the frequency is also reduced from finax to f0. This change also causes the output voltage to rise.
  • the duty cycle reaches a maximum of 50%, and the output voltage rises to V2.
  • the operation mode is PFM+PWM control.
  • Waveform A is the drive pulse waveform with a 50% duty cycle under PFM control.
  • Waveform B is the drive pulse waveform under PFM+PWM control. The aspect ratio width and frequency are adjusted as the output voltage changes until the duty cycle is zero.
  • the above resonant DC/DC converter adopts a frequency conversion control circuit and a pulse width modulation circuit structure connected in series on the circuit to realize logic parallel juxtaposition of PFM control and PFM+PWM control scheme, and actually another alternative scheme can be adopted.
  • the discriminator selectively controls one of the output to meet the control pulse of the control according to the load judgment condition, that is: If the discriminator determines that the load is operating in a light load or no load state, outputting a drive pulse modulation signal to the variable frequency control + pulse width modulation circuit, and controlling a drive pulse whose output frequency and duty ratio are jointly adjusted according to a change of the feedback signal; Otherwise, the drive pulse modulation signal is output to the variable frequency control circuit to control the drive pulse whose output duty ratio is stable and the frequency changes with the change of the feedback signal.
  • This alternative also achieves the object of the invention, but with a more complex
  • the value of the reference signal determines the timing of switching the control mode.
  • the choice of pointcut for most resonant circuits, it is determined according to the condition of the load, generally light load, no load or almost no load, because the control ability of PFM is weak in this area.
  • the control method of the present invention is applicable to a circuit working using a resonance principle, including series resonance, parallel resonance, series-parallel resonance, etc., and the circuit topology may be a full bridge, a half bridge, or the like.
  • the inverter When the operating frequency of the resonant circuit is low, the inverter is operated in the frequency conversion control mode; when the operating frequency is high, the converter is operated in the frequency conversion control + pulse width modulation control mode, thereby avoiding no load and light load. Under the condition, the switching frequency is too high, which is conducive to the stability of the output voltage at light load.
  • the invention can be realized by a simple circuit structure. When the circuit is switched between states of different control modes, the switching is smooth, and the reliability of the circuit operation is ensured.
  • the frequency conversion control + pulse width modulation, frequency conversion control and discriminating circuit of the invention can be constructed by using a hardware circuit or by programming a chip having a corresponding function module according to the control method of the present invention, and this part of the work is Those of ordinary skill in the art will readily derive from the above-described technical solutions.

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  • Power Engineering (AREA)
  • Dc-Dc Converters (AREA)

Description

一种谐振直流 /直流变换器及其控制方法
【技术领域】
本发明涉及直流电源变换技术， 具体是涉及一种谐振直流 /直流变 换器的控制方法及装置。
【背景技术】
小型化和高频化是当今电源发展的趋势， 但是开关频率的升高带 来了开关管损耗过大的问题， 这是传统 BUCK变换器无法解决的， 而 谐振变换器则可以较好的解决这个问题。
以串联谐振变换器为例， 串联谐振直流 /直流 （DC/DC) 变换器采 用谐振变换技术， 由于谐振元件工作在正弦谐振状态， 开关管上的电 压自然过零， 可以实现零电压开通， 电源损耗很小。 这种拓扑通常采 用变频调制 （Pulse frequency modulation, 简称 PFM) 方式， 通过改变 工作频率来稳定输出电压。 图 1为半桥 SRC串联谐振 DC/DC变换器 的基本形式， 在对该电路采用 PFM控制时， 两个幵关管 Sl、 S2互补 对称驱动， 各导通 50% (此为理想值， 如考虑死区的设置应为略小于 50%) 的开关周期。 电源输出电压增益 M与工作频率 f的关系为-
Figure imgf000003_0001
其中， V。与 Vin分别为输出、 输入电压， f 为工作频率， fr fr为谐振频率， Lr为谐振电感值， Cr为
Figure imgf000003_0002
谐振电容值， p。为输出功率。
从式 （1 ) 中可以发现， 当工作频率 f大于谐振频率 &时， 工作频 率越高， 电压增益 M越低； 同理， 当工作频率 f小于谐振频率 时， 工作频率越低， 电压增益 M越低。 串联谐振拓扑控制频率 f与输出电 压 V。的关系曲线如图 2所示。 由图 2可以发现， 串联谐振变换器一个 主要的难点问题在于轻载和空载条件下输出电压难以稳定。 当控制频 率大于谐振频率 fr， 串联谐振拓扑的输出电压随着控制频率的升高而 降低， 当负载减小至轻载状态时， 输出电压趋于平缓， 这样为了稳定 电压， 工作频率需要升得很高， 但是工作频率范围过宽会带来磁性器 件难以优化的问题， 而且工作频率越高， 电路损耗也越大； 此外， 当 负载接近空载， 输出电压反而有可能会上升， 导致无法进行负反馈控 制。 因此在电源行业中， 有人在输出端加上固定的负载， 利用这种方 法在轻载和空载条件下稳定输出电压， 但这样会增加空载损耗， 降低 电源效率。
总之， 单纯的变频控制会导致工作频率范围过宽甚至失效， 带来 磁性元件难以优化和电路损耗过大的问题， 以及反馈控制难以设计的 问题， 所以简单的调频控制无法满足轻载或空载时输出稳压的要求。
上面以半桥串联谐振电路为例说明了调频控制方式存在的缺陷， 同样的， 全桥串联谐振电路的现象与半桥串联谐振现象是完全相同的。 从理论上讲， 所有的调频控制的谐振电路都存在类似的问题。
【发明内容】
本发明的目的在于提供一种谐振直流 /直流变换器的控制方法及其 装置， 以解决现有技术中负载工作在轻载或空载时采用调频控制存在 磁性元件难以优化、 难以稳压和电路损耗过大的问题。
为了实现上述目的， 本发明所采取的技术方案是： 一种谐振直流 / 直流变换器的控制方法， 是通过改变其谐振电路输入开关管的导通频 率来调节输出电压， 还根据负载电路的反馈信号调整所述开关管的占 空比， 使得谐振电路的电压输出范围扩展。
所述谐振电路输入开关管可由驱动脉冲经驱动电路进行控制， 所 述驱动脉冲的获得包括如下步骤，
1 ) 获取负载电路的反馈信号；
2) 根据所述反馈信号判断负载是否工作在轻载或空载状态；
3 )如果负载工作在轻载或空载状态， 则将频率与占空比随反馈信 号变化而共同调节的脉冲信号作为驱动电路的驱动脉冲， 使谐振电路 工作在 PWM (Pulse width modulation, 脉宽调制）控制与 PFM控制混 合模式； 否则， 将占空比稳定而频率随反馈信号变化的脉冲信号作为 驱动电路的驱动脉冲， 使谐振电路工作在 PFM控制模式。
所述步骤 1 ) 可包括如下步骤： la) 从负载电路中采样反馈电压；
lb) 将所述反馈电压进行负反馈补偿运算获得反馈信号。
上述控制方法中 PFM控制与 PFM+PWM控制的选择优选由下述 过程实现： 所述步骤 2)中将反馈信号分别经运算处理后得到变频控制 信号和脉宽调制信号； 所述脉宽调制信号的运算处理过程包括与参考 信号一进行比较来判断负载是否工作在轻载或空载状态的步骤， 所述 参考信号一根据所述负载的电气特性确定； 所述步骤 3 )中当负载工作 在轻载或空载状态时， 即产生由变频控制信号和脉宽调制信号共同调 节的驱动脉冲； 否则， 产生占空比稳定而由变频控制信号单独调节的 驱动脉冲。
上述控制方法中还可进一步增加单独采用 PWM控制的选择： 所 述步骤 2)中所述变频控制信号的运算处理过程包括与参考信号二进行 比较来判断负载是否工作在近似空载状态的步骤， 所述参考信号二根 据所述负载的电气特性确定， 并且所述参考信号二满足， 若负载根据 参考信号二的判断工作在近似空载状态则根据参考信号一的判断必然 工作在轻载或空载状态;所述步骤 3)中当负载工作在近似空载状态时， 即产生频率稳定而由脉宽调制信号单独调节的驱动脉冲。
为本发明的目的， 还提供一种谐振 DC/DC变换器， 包括
驱动电路和谐振电路， 所述驱动电路根据输入的驱动脉冲控制谐 振电路的输入幵关管， 谐振电路在所述驱动电路的控制下将变换后的 电源提供给负载电路， 以及
负反馈补偿调节器， 将从负载电路中采样的反馈电压进行负反馈 补偿运算后获得反馈信号；
甄别器， 根据输入的反馈信号判断负载电路的负载状态， 输出驱 动脉冲调制信号；
驱动脉冲发生器， 根据输入的驱动脉冲调制信号调制并输出驱动 脉冲： 如果负载工作在轻载或空载状态， 输出的驱动脉冲的频率与占 空比随反馈信号变化而共同调节； 否则， 输出的驱动脉冲的占空比稳 定而频率随反馈信号的变化而变化。
上述谐振 DC/DC变换器进行 PFM控制与 PFM+PWM控制的一种 可选方案是采用两个相对独立的驱动信号发生电路模块， gp , 所述驱 动脉冲发生器包括变频控制电路和变频控制 +脉宽调制电路；若所述甄 别器判断负载工作在轻载或空载状态， 则向变频控制 +脉宽调制电路输 出驱动脉冲调制信号， 控制其输出频率和占空比随反馈信号变化而共 同调节的驱动脉冲； 否则， 则向变频控制电路输出驱动脉冲调制信号， 控制其输出占空比稳定而频率随反馈信号的变化而变化的驱动脉冲。
上述谐振 DC/DC变换器进行 PFM控制与 PFM+PWM控制的一种 优选方案则可只釆用一个驱动信号发生电路模块： 所述甄别器包括运 算电路一和二， 所述运算电路一设定有参考信号一， 所述驱动脉冲调 制信号包括变频控制信号和脉宽调制信号； 所述反馈信号经运算电路 一进行运算、 与参考信号一比较后， 输出为脉宽调制信号； 所述反馈 信号经运算电路二进行运算后输出为变频控制信号； 所述参考信号一 根据负载的电气特性确定， 使得当负载工作在轻载或空载状态时， 输 出的脉宽调制信号随反馈信号的变化而变化； 反之， 则保持稳定； 所 述驱动脉冲发生器包括变频控制电路和脉宽调制电路， 所述变频控制 电路产生频率由变频控制信号控制的变频脉冲， 所述脉宽调制电路根 据脉宽调制信号将所述变频脉冲进行脉宽调制后输出驱动脉冲。
所述脉宽调制电路可以是将脉宽调制信号与变频脉冲比较合成后 输出驱动脉冲。
也可以是， 将所述变频脉冲输入所述脉宽调制电路的同步端， 所 述脉宽调制电路根据脉宽调制信号对输入的变频脉冲进行脉宽调制后 输出驱动脉冲。
为实现近似空载状态下的纯 PWM控制， 进一步优选的是， 所述 运算电路二设定有参考信号二； 所述反馈信号经运算电路二进行运算、 与参考信号二比较后， 输出为变频控制信号； 所述参考信号二根据负 载的电气特性确定， 使得当负载工作在近似空载状态时， 输出的变频 控制信号保持稳定； 反之， 则随反馈信号的变化而变化； 并且所述参 考信号二满足， 若负载根据参考信号二的判断工作在近似空载状态则 根据参考信号一的判断必然工作在轻载或空载状态；
所述变频控制电路可采用这样的结构， 包括依次连接的压频振荡 器和三角波发生器； 所述变频控制信号输入压频振荡器控制其振荡频 率， 所述三角波发生器输出频率受控的变频脉冲。 釆用上述技术方案， 本发明有益的技术效果在于：
1 ) 在谐振 DC/DC变换器的控制方式中， 引入 PWM控制方式， 实现 PFM与 PFM +PWM两种控制方式， 在电源工作频率较低时釆用 PFM控制， 电源工作频率过高时引入 PFM +PWM控制方式。 还可在 频率更高时固定频率， 进入 PWM控制方式， 从而解决了谐振变换器 的难点问题， 即轻载和空载时工作频率太高和电路损耗过大的问题， 极大地增加了谐振电路的输出电压调节能力， 有效扩展电压输出范围。
2) PFM控制与 PFM +PWM控制两种方式在逻辑上是可选的并联 关系， 但可以采用优选的变频控制电路和脉宽调制电路串联的方式来 实现， 优选实现电路避免了许多逻辑选通器件和多路负反馈补偿调节 器的使用， 电路简单， 并且两种控制方式切换平滑， 其可靠性和动态 特性非常好。
本发明对全桥串、 并联谐振电路、 半桥串、 并联谐振电路和 LLC 等谐振电路的变形拓扑都适用， 有较强的工程意义。
下面结合附图和具体实施方式对本发明作进一步的详细说明：
【附图说明】
图 1是一种现有典型的半桥串联谐振电路示意图
图 2是图 1中电路 PFM控制方式下的输出特性曲线图。
图 3是图 1 中电路采用本发明控制方法后的输出特性曲线比较示 意图。
图 4是一种本发明 DC/DC变换器的原理框图。
图 5是图 4虚线框中电路的细化框图。
图 6是图 4中 DC/DC变换器反馈信号与频率及占空比的关系示意 图。
图 7是驱动脉冲波形图。
图 8是另一种本发明直流 /直流变换器的原理框图。 【具体实施方式】
一种谐振 DC/DC变换器的控制方法，是通过改变其谐振电路输入 开关管的导通频率来调节输出电压， 还根据负载电路的反馈信号调整 所述开关管的占空比， 使得谐振电路的电压输出范围扩展。
仍以图 1中的半桥串联谐振电路为例， 图 3中的曲线 A1〜A3是不 同负载状况下采用单独 PFM控制方式， 占空比为 50%的输出电压 Vo 与频率 f的特性曲线示意图， 可以看出， 随着负载的减轻， Vo趋于平 缓， 难于通过提高工作频率的方式来稳定。 图 3中的曲线 Bl、 B2、 B3 分别是曲线 A1〜A3 的开关频率升高到 fa时在 PFM控制方式中切入 PWM后综合制方式下输出电压 Vo与占空比 D和频率 f的特性曲线示 意图； 对占空比 D的控制从 50%开始直到降低到 0为止。 由曲线 Bl、 B2、 B3可以看出， 在引入了 PFM+PWM控制后， 输出电压能够在控 制频率大于 fa开始，至控制频率 fb迅速衰减到 0，与单纯的 PFM控制 方式相比输出特性得到了很大的改善。
对谐振电路输入开关管的控制是由驱动脉冲经驱动电路来进行 的， 因此从 PFM到 PFM+PWM的切换靠驱动脉冲的变化来实现， 由 于控制方式的切换与负载情况直接相关， 因此驱动脉冲的获得釆用如 下方法-
1 )获取负载电路的反馈信号， 所述反馈信号由从负载电路中采样 的反馈电压经过负反馈补偿运算获得；
2)根据所述反馈信号判断负载的工作状态， 此判断过程通过对反 馈信号的运算和与参考信号的比较来进行： 将反馈信号分别经运算处 理后得到变频控制信号和脉宽调制信号。 脉宽调制信号的运算处理过 程是将反馈信号进行比例或加减等运算后与设定的参考信号一进行比 较， 若低于参考信号 （或高于参考信号， 根据电路的逻辑特性来确定， 这里假定反馈信号与负载电压成正比， 反馈信号越低， 负载越轻） 则 直接输出运算后的反馈信号作为脉宽调制信号。 否则输出稳定的参考 信号一作为脉宽调制信号， 由于此时的脉宽调制信号不发生变化， 因 此对应于单纯 PFM控制的情形。参考信号一需要根据所述负载的电气 特性来确定， 使得基于参考信号一进行的比较判断能够基本正确的反 应负载是否工作在轻载状态。
变频控制信号的运算处理过程可以采用两种方式， 一是直接将反 馈信号进行比例或加减等运算后输出作为变频控制信号， 这样， 变频 控制信号始终随反馈信号的变化而变化， 因此谐振电路始终保持有 PFM控制方式。 另一是仿照上述脉宽调制信号的运算方式， 在比例或 加减等运算后还将结果与设定的参考信号二进行比较， 若高于参考信 号二 （或低于参考信号， 根据电路的逻辑特性来确定， 这里假定反馈 信号与负载电压成正比， 反馈信号越低， 负载越轻） 则直接输出运算 后的反馈信号作为变频控制信号。 否则输出稳定的参考信号二作为变 频控制信号， 由于此时的变频控制信号不发生变化， 因此对应于单纯 PWM控制的情形。参考信号二同样需要根据所述负载的电气特性来确 定， 使得基于参考信号二进行的比较判断能够基本正确的反应负载是 否工作在近似空载状态。 并且， 为了保证从 PFM控制到 PFM+PWM 控制再到 PWM控制的平滑切换， 若负载根据参考信号二的判断工作 在近似空载状态则根据参考信号一的判断必然工作在轻载状态， 这也 就保证了在任意情况下， 脉宽调制信号与变频控制信号中至少有一个 是随反馈信号的变化而变化的。
3 ) 根据步骤 2) 的判断结果， 如果负载工作在非轻载状态， 脉宽 调制信号稳定为参考信号一， 而变频控制信号随反馈信号的变化而变 化， 因此在这两个信号的控制下输出的是占空比稳定而频率随反馈信 号变化的驱动脉冲， 此时谐振电路工作在 PFM控制模式； 如果负载工 作在轻载状态， 脉宽调制信号与变频控制信号均随反馈信号的变化而 变化， 因此在这两个信号的控制下输出的是频率与占空比均随反馈信 号变化而共同调节的驱动脉冲， 此时谐振电路工作在 PFM+PWM控制 模式； 如果负载工作在近似空载状态， 脉宽调制信号随反馈信号的变 化而变化， 而变频控制信号稳定为参考信号二， 因此在这两个信号的 控制下输出的是频率稳定而占空比随反馈信号变化的驱动脉冲， 此时 谐振电路工作在 PWM控制模式； 下面详细介绍一种采用上述控制方法的谐振 DC/DC变换器， 结合 图 4和图 5， 包括
驱动电路和谐振电路， 所述驱动电路根据输入的驱动脉冲控制谐 振电路的输入幵关管， 谐振电路在所述驱动电路的控制下将变换后的 电源提供给负载电路， 以及
负反馈补偿调节器， 由 PI调节器充当， 将从负载电路中采样的反 馈电压以及设置的给定电压进行负反馈补偿运算后获得反馈信号； 甄别器， 包括运算电路一和二， 所述运算电路一和二分别设定有 参考信号一和二； 反馈信号经运算电路一进行运算、 与参考信号一比 较后， 输出为脉宽调制信号； 反馈信号经运算电路二进行运算、 与参 考信号二比较后输出为变频控制信号； 参考信号一和二均根据负载的 电气特性确定， 其设定原则与前述控制方法中的描述相同， 在此不再 赘述。 当负载工作在近似空载状态时， 甄别器输出稳定的变频控制信 号 （即参考信号二） 和随反馈信号变化而变化的脉宽调制信号； 当负 载工作在轻载状态时， 甄别器输出均随反馈信号变化而变化的脉宽调 制信号和变频控制信号； 此外， 甄别器输出随反馈信号变化而变化的 变频控制信号和稳定的脉宽调制信号 （即参考信号一）。
驱动脉冲发生器， 包括变频控制电路和脉宽调制电路。 变频控制 电路包括依次连接的压频振荡器和三角波发生器； 脉宽调制电路为
F M产生电路。变频控制信号输入压频振荡器控制其振荡频率， 压频 振荡器将变频控制信号的电压信号变为输出频率变化的方波信号， 三 角波发生器接收该频率变化的方波信号产生频率变化的三角波信号并 输出到 PWM产生电路的同步端； PWM产生电路根据从 comp端输入 的脉宽调制信号 V∞mp对输入的变频三角波信号进行脉宽调制后输出驱 动脉冲。 当 V∞mp稳定输出为参考信号一时， 驱动脉冲的占空比不再变 化， 只有频率变化， 即进入 PFM控制； 当 V∞mp与变频控制信号均变 化输出时， 驱动脉冲的占空比和频率同时变化， 即进入 PFM+PWM控 制； 当变频控制信号稳定输出为参考信号二时， 驱动脉冲的频率不再 变化， 只有占空比变化， 即进入 PWM控制。
一般使参考信号一为三角波峰值的一半， 这样在 PFM控制模式时 输出的驱动脉冲具有 50%的占空比。 当然， 根据应用需要， 也可以取 消单独的 PWM控制方式， 使驱动脉冲的输出频率始终与反馈信号相 关， 这就相当于将参考信号二设置为 0。
能够实现变频控制电路和脉宽调制电路功能的模块通常集成在一 块芯片中， 根据所使用芯片内部功能架构的区别， 它们之间的具体电 路关系可以有更多的情况， 例如脉宽调制电路也可以是将脉宽调制信 号¼。^与变频三角波信号比较合成后输出驱动脉冲。不过简化的看来， 变频控制电路和脉宽调制电路总可以概括为串联的电路关系， 即变频 控制电路产生脉冲信号并控制其频率， 而脉宽调制电路则进一步确定 脉冲信号的占空比。 如图 6所示， 是上述谐振 DC/DC变换器的负反馈补偿调节器输出 的反馈信号 Vf与谐振电路工作频率 f及谐振电路输出 V的函数关系， 其中， 横轴代表负反馈补偿调节器输出的反馈信号 Vf， 并假定负反 馈补偿调节器最高输出 12v。 上述谐振 DC/DC变换器的工作状态描述 如下：
1.当反馈信号从 a~b变化时， 控制频率不变， 为 f=fmax， 占空比 从 0%变化到 D0%;谐振电路输出 V从 0变化到 VI；工作模式为 PWM 控制。
2.当反馈信号从 b〜c变化时， 控制频率与占空比同时变化： 占空比 从 D0%变化到 50%满脉宽 （未含死区）， 导致输出电压继续上升； 同 时， 控制频率也从 finax减小到 f0， 该变化也导致输出电压的上升； 当 环路电压上升到 b时， 占空比达到最大值 50%， 输出电压上升为 V2; 工作方式为 PFM+PWM控制。
3.当反馈信号从 b〜12V变化时， 占空比不变， 控制频率从 fO继续 下降到 fmin， 输出电压继续上升， 直至 f=fmin时， 输出电压达到最大 值 V3; 工作模式为 PFM控制。
从图 6 中可以看出， 反馈信号升高， 输出电压也升高， 所以能够 做闭环控制。 图 6中 c对应确定运算电路一的参考信号一， b对应确定 运算电路二的参考信号二； 当控制系统不包括纯 PWM控制模式时， b=0 o
不同控制模式下驱动脉冲的波形如图 7所示，波形 A是 PFM控制 下的稳定为 50%占空比的驱动脉冲波形，波形 B是 PFM+PWM控制下 的驱动脉冲波形， 驱动脉冲的占空比宽度和频率随输出电压变化而调 节， 直到占空比为零。
上述谐振 DC/DC变换器采用了电路上串联的变频控制电路与脉宽 调制电路结构来实现逻辑上并列可选的 PFM控制与 PFM+PWM控制 方案， 实际上也可以采用另一种可选方案， 如图 8所示， 即采用两个 相对独立的驱动信号发生电路模块， 分别组建变频控制电路和变频控 制 +脉宽调制电路；然后使甄别器根据负载判断情况选择性的控制其中 之一输出满足本发明控制要求的驱动脉冲， 即： 若所述甄别器判断负 载工作在轻载或空载状态， 则向变频控制 +脉宽调制电路输出驱动脉冲 调制信号， 控制其输出频率和占空比随反馈信号变化而共同调节的驱 动脉冲； 否则， 则向变频控制电路输出驱动脉冲调制信号， 控制其输 出占空比稳定而频率随反馈信号的变化而变化的驱动脉冲。 此可选方 案同样能实现本发明目的， 只不过与前述优选方案相比具有更为复杂 的形式。
上述控制方法中， 参考信号的取值决定了控制方式切换的时机。 至 于切入点的选择， 对于大部分谐振电路而言， 是根据负载的状况来确 定， 一般为轻载、 空载或近似空载的区域， 因为在该区域中， PFM的 控制能力较弱。 特别的， 对于某些电路， 例如低压大电流电路， 有时 并不是只有在常规意义的 "轻载"等情况下才需要使用上述控制方法 (因为在这种电路中， 一般意义上的 "轻载"状态无法完整概括电路 输出特性发生变化的区域）， 这时可根据对电路输出特性的整体评价确 定切入点，即参考信号的取值，使得能够在 PFM控制能力减弱的区段， 适时切入 PWM控制方式来增强或补充 PFM控制的效果。 因此， 在本 发明中 "轻载 "等概念应广义的理解为 PFM控制能力减弱的负载状态， 而不是局限于常规的 "小电流、 低电压" 的负载状态。
本发明控制方式适用于使用谐振原理工作的电路， 包括串联谐振、 并联谐振、 串并联谐振等， 电路拓扑可以是全桥、 半桥等。 在谐振电 路的工作频率较低时， 使变换器工作在变频控制方式； 而在工作频率 较高时， 使变换器工作在变频控制 +脉宽调制控制方式， 这样就避免了 空载和轻载条件下， 开关频率太高的问题， 有利于轻载时输出电压的 稳定。 本发明可由简单的电路结构实现， 电路在不同控制方式的状态 之间切换时， 切换是平滑的，保证了电路工作的可靠性。
本发明的变频控制 +脉宽调制、 变频控制和甄别电路等既可以采用 硬件电路来搭建也可以通过对具有相应功能模块的芯片按照本发明控 制方法进行编程来用软件实现， 这部分工作是本领域的普通技术人员 根据上述的技术方案所容易推导出来的。

Claims

权利要求书
1、 一种谐振直流 /直流变换器的控制方法， 是通过改变其谐振电路 输入开关管的导通频率来调节输出电压， 其特征在于： 还根据负载电 路的反馈信号调整所述开关管的占空比， 使得谐振电路的电压输出范 围扩展。
2、 根据权利要求 1 所述的谐振直流 /直流变换器的控制方法， 其特 征在于： 所述谐振电路输入幵关管由驱动脉冲经驱动电路进行控制， 所述驱动脉冲的获得包括如下步骤，
1 ) 获取负载电路的反馈信号；
2) 根据所述反馈信号判断负载是否工作在轻载或空载状态；
3 )如果负载工作在轻载或空载状态， 则将频率与占空比随反馈信 号变化而共同调节的脉冲信号作为驱动电路的驱动脉冲， 使谐振电路 工作在脉宽调制控制与变频控制混合模式； 否则， 将占空比稳定而频 率随反馈信号变化的脉冲信号作为驱动电路的驱动脉冲， 使谐振电路 工作在变频控制模式。
3、 根据权利要求 2所述的谐振直流 /直流变换器的控制方法， 其特 征在于： 所述步骤 1 ) 包括
la) 从负载电路中采样反馈电压；
lb ) 将所述反馈电压进行负反馈补偿运算获得反馈信号。
4、 根据权利要求 3 所述的谐振直流 /直流变换器的控制方法， 其特 征在于：
所述步骤 2)中将反馈信号分别经运算处理后得到变频控制信号和 脉宽调制信号； 所述脉宽调制信号的运算处理过程包括与参考信号一 进行比较来判断负载是否工作在轻载或空载状态的步骤， 所述参考信 号一根据所述负载的电气特性确定；
所述步骤 3 )中当负载工作在轻载或空载状态时， 即产生由变频控 制信号和脉宽调制信号共同调节的驱动脉冲； 否则， 产生占空比稳定 而由变频控制信号单独调节的驱动脉冲。
5、 根据权利要求 4所述的谐振直流 /直流变换器的控制方法， 其特 征在于- 所述步骤 2)中所述变频控制信号的运算处理过程包括与参考信号 二进行比较来判断负载是否工作在近似空载状态的步骤， 所述参考信 号二根据所述负载的电气特性确定， 并且所述参考信号二满足， 若负 载根据参考信号二的判断工作在近似空载状态则根据参考信号一的判 断必然工作在轻载或空载状态；
所述步骤 3 )中当负载工作在近似空载状态时， 即产生频率稳定而 由脉宽调制信号单独调节的驱动脉冲。
6、 一种谐振直流 /直流变换器， 包括驱动电路和谐振电路， 所述驱 动电路根据输入的驱动脉冲控制谐振电路的输入开关管， 谐振电路在 所述驱动电路的控制下将变换后的电源提供给负载电路， 其特征在于： 还包括
负反馈补偿调节器， 将从负载电路中采样的反馈电压进行负反馈 补偿运算后获得反馈信号；
甄别器， 根据输入的反馈信号判断负载电路的负载状态， 输出驱 动脉冲调制信号；
驱动脉冲发生器， 根据输入的驱动脉冲调制信号调制并输出驱动 脉冲： 如果负载工作在轻载或空载状态， 输出频率与占空比随反馈信 号变化而共同调节的驱动脉冲； 否则， 输出占空比稳定而频率随反馈 信号的变化而变化的驱动脉冲。
7、 根据权利要求 6所述的谐振直流 /直流变换器， 其特征在于： 所 述驱动脉冲发生器包括变频控制电路和变频控制 +脉宽调制电路；
若所述甄别器判断负载工作在轻载或空载状态， 则向变频控制 +脉 宽调制电路输出驱动脉冲调制信号， 控制其输出频率和占空比随反馈 信号变化而共同调节的驱动脉冲； 否则， 则向变频控制电路输出驱动 脉冲调制信号， 控制其输出占空比稳定而频率随反馈信号的变化而变 化的驱动脉冲。
8、 根据权利要求 6所述的谐振直流 /直流变换器， 其特征在于： 所 述甄别器包括运算电路一和二， 所述运算电路一设定有参考信号一， 所述驱动脉冲调制信号包括变频控制信号和脉宽调制信号； 所述反馈 信号经运算电路一进行运算、 与参考信号一比较后， 输出为脉宽调制 信号； 所述反馈信号经运算电路二进行运算后输出为变频控制信号； 所述参考信号一根据负载的电气特性确定， 使得当负载工作在轻载或 空载状态时， 输出的脉宽调制信号随反馈信号的变化而变化； 反之， 所 驱动脉冲发生器包括变频控制电路和脉宽调制电路， 所述变 频控制电路产生频率由变频控制信号控制的变频脉冲， 所述脉宽调制 电路根据脉宽调制信号将所述变频脉冲进行脉宽调制后输出驱动脉 冲。
9、 根据权利要求 8所述的谐振直流 /直流变换器， 其特征在于： 所 述脉宽调制电路是将脉宽调制信号与变频脉冲比较合成后输出驱动脉 冲。
10、 根据权利要求 8所述的谐振直流 /直流变换器， 其特征在于： 所 述变频脉冲输入所述脉宽调制电路的同步端， 所述脉宽调制电路根据 脉宽调制信号对输入的变频脉冲进行脉宽调制后输出驱动脉冲。
11、 根据权利要求 8~10任意一项所述的谐振直流 /直流变换器， 其特 征在于： 所述运算电路二设定有参考信号二； 所述反馈信号经运算电 路二进行运算、 与参考信号二比较后， 输出为变频控制信号； 所述参 考信号二根据负载的电气特性确定， 使得当负载工作在近似空载状态 时， 输出的变频控制信号保持稳定； 反之， 则随反馈信号的变化而变 化； 并且所述参考信号二满足， 若负载根据参考信号二的判断工作在 近似空载状态则根据参考信号一的判断必然工作在轻载或空载状态；
12、 根据权利要求 8〜10任意一项所述的谐振直流 /直流变换器， 其特 征在于： 所述变频控制电路包括依次连接的压频振荡器和三角波发生 器； 所述变频控制信号输入压频振荡器控制其振荡频率， 所述三角波 发生器输出频率受控的变频脉冲。
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