Patent Description:
An power factor (PF) is an important energy-saving indicator for various drivers, which not only affects a conversion efficiency of a driver, but also cause the driver to pollute a power grid of an entire power supply system in a case that the PF of said driver is low. Therefore, requirements for power factor correction (PFC) circuits are increasing.

In the conventional Boost PFC circuits, a bandwidth of a control loop is limited by an industrial frequency, resulting in a slow dynamic response speed of the control loop.

<CIT> discloses circuits and methods for use with a power supply that provides a main output including a main DC voltage having a first AC voltage ripple, or a main DC current having a first AC current ripple. A ripple cancellation converter provides a second AC voltage ripple connected in series with the main output, such that the first AC voltage ripple is substantially cancelled; or a second AC current ripple connected in parallel with the main output, such that the first AC current ripple is substantially cancelled.

<CIT> discloses that a predicted ripple in the feedback voltage of a switching converter is generated, based on the ripple over a certain number of recent switching cycles. The DC portion of the feedback voltage is filtered out. This predicted feedback voltage ripple is then added to a fixed reference voltage to create a compensated reference voltage. The compensated reference voltage is applied to the non-inverting input of an error amplifier, and the feedback voltage (having a DC component and ripple) is applied to the inverting input of the error amplifier.

<CIT> discloses that a DC-DC converter control circuit has an inductor configured to be interposed between a first node which is set to a first direct current voltage or a second direct current voltage and a second node which outputs an output voltage at a predetermined direct current voltage level, an error signal generator configured to generate an error signal depending on a voltage difference between a reference voltage and a voltage correlating with the output voltage, a ripple extractor configured to extract and output ripple components contained in the voltage of the first node, a single-ended signal generator configured to generate a single-ended signal based on the error signal and an output signal from the ripple extractor, and a switch drive unit configured to drive and control, based on the single-ended signal, a switch circuit which sets the first node to the first direct current voltage or the second direct current voltage.

<CIT> discloses that the power factor improvement circuit, having step-up conversion means <NUM>, includes: voltage ripple extraction means <NUM> that extracts, as an output voltage ripple, a difference between an output voltage and a DC target voltage of the output voltage; reference signal generation means 16a that generates, as a reference signal, a cosine wave and a sine wave with a frequency of an integral multiplication of an input voltage waveform; steady voltage ripple generation means 16b that generates a voltage ripple under a steady state, using the voltage ripple and the reference signal; and input current command value generation means <NUM> that creates an input current command value for controlling an input current using the voltage ripple under the steady state.

In view of the above, a control circuit and an AC-DC power supply applying the control circuit are provided according to the present disclosure, to solve the problem of slow dynamic response speed of the conventional loop.

According to claim <NUM>, a control circuit applied to an AC-DC power supply is provided. The control circuit includes a ripple reference signal generation circuit and an error compensation circuit. The ripple reference signal generation circuit is configured to generate a ripple reference signal characterizing an industrial frequency ripple of an output voltage of the AC-DC power supply. The error compensation circuit is configured to compare a sum of a reference signal characterizing a desired output voltage of the AC-DC power supply and the ripple reference signal with a feedback signal characterizing the output voltage of the AC-DC power supply, to generate a voltage compensation signal. The control circuit is configured to generate a control signal for controlling a main power tube of the AC-DC power supply based on the voltage compensation signal. The ripple reference signal generation circuit performs low-pass filtering on an inductive current sampling signal characterizing a current flowing through an inductor in the AC-DC power supply to obtain a first inductive current sampling signal characterizing the industrial frequency ripple component of the output voltage. The ripple reference signal generation circuit is further configured to shift a phase of the first inductive current sampling signal and change an amplitude of the first inductive current sampling signal to obtain an estimated industrial frequency ripple component of the output voltage The ripple reference signal is proportional to the estimated industrial frequency ripple component, and both depend on a capacitive reactance of an output capacitor of the AC-DC power supply.

In an example, the voltage compensation signal excludes an industrial frequency ripple component of the output voltage, so that a control loop is not limited by an industrial frequency and a dynamic response speed of the control loop is improved.

In an example, the ripple reference signal generation circuit is further configured to multiply the estimated industrial frequency ripple component of the output voltage by a voltage division coefficient corresponding to the feedback signal of the output voltage to generate the ripple reference signal. The voltage division coefficient is a ratio of the feedback signal of the output voltage to the output voltage.

In an example, the ripple reference signal generation circuit shifts the phase of the first inductive current sampling signal to cause a lag of <NUM> degrees.

In an example, the ripple reference signal generation circuit changes an amplitude of the first inductive current sampling signal, to cause amplitude of the estimated industrial frequency ripple component of the output voltage to be directly proportional to a capacitive reactance of an output capacitor of the AC-DC power supply.

In an example, the capacitive reactance of the output capacitor of the AC-DC power supply is a capacitive reactance at a frequency close to twice of the industrial frequency.

In an example, the ripple reference signal generation circuit changes an amplitude of the first inductive current sampling signal, to cause amplitude of the estimated industrial frequency ripple component of the output voltage to be inversely proportional to an impedance of an inductive current sampling resistor.

In an example, the inductive current sampling resistor is connected in series in a current loop flowing through the inductor in the AC-DC power supply.

In an example, the control circuit further includes a current reference generation circuit and a pulse width modulation (PWM) generation circuit. The current reference generation circuit is configured to generate a current reference signal based on the voltage compensation signal. The PWM generation circuit is configured to compare a current sampling signal characterizing a current flowing through the main power tube with the current reference signal to generate a PWM signal. The PWM signal serves as a control signal for controlling the main power tube of the AC-DC power supply.

According to a second aspect, an AC-DC power supply is provided. The AC-DC power supply includes a power stage circuit and the control circuit described above.

With the technical solutions of the present disclosure, the ripple reference signal characterizing the industrial frequency ripple component of the output voltage is added to the reference voltage of the desired output voltage, so that the reference and the feedback voltage of the output voltage are almost the same at the industrial frequency band. In addition, the voltage compensation signal outputted by the error compensation circuit does not include the industrial frequency ripple component, and the voltage compensation signal without the industrial frequency ripple component does not affect the tracking reference of the current loop. Therefore, the loop can be designed without considering limit of the industrial frequency on the cut-off frequency of the loop, thereby effectively increasing the cut-off frequency of the loop and improving the dynamic response speed of the loop.

In order to more clearly describe the technical solutions in the embodiments of the present disclosure or the technical solutions in the conventional technology, drawings to be used in the description of the embodiments of the present disclosure or the conventional technology are briefly described hereinafter. It is apparent that the drawings described below are merely used for describing the embodiments of the present disclosure, and those skilled in the art may obtain other drawings according to the provided drawings without any creative effort. <FIG> is a structural block diagram of an AC-DC power supply according to an embodiment of the present disclosure.

The present disclosure is described on the basis of the embodiments hereinafter, but is not limited to these embodiments. In the detailed description of the present disclosure hereinafter, numerous specific details are set forth. Those skilled in the art can understand the present disclosure without these specific details. To avoid obscuring the substance of the present disclosure, well-known methods, procedures, processes, elements and circuits are not described in detail herein.

In addition, those skilled in the art should understand that the drawings are provided herein for illustration, and are not necessarily drawn to scale.

In addition, it should be understood that in the following description, the term "circuit" indicates a conductive loop formed by at least one element or sub-circuit through electrical connections or electromagnetic connections. When an element or a circuit is described as being "connected to" another element or an element or a circuit is described as being "connected between" two nodes, the element or the circuit is coupled or connected to another element directly or via other element. The elements may be connected physically, logically, or a combination thereof. In addition, when an element is described as being "directly coupled" or "directly connected" to another element, it indicates that there is no element between the two elements.

Unless otherwise stated, the terms "include", "comprise" or any other variations in the specification are intended to be inclusive, rather than exclusive or exhaustive. That is, the terms indicate "including but not limited to".

In the description of the present disclosure, it should be understood that terms "first", "second" and the like are used only for description and cannot be understood as indicating or implying relative importance. In addition, in the description of the present disclosure, "multiple" means two or more unless otherwise stated.

<FIG> is a structural block diagram of an alternating current-direct current (AC-DC) power supply according to an embodiment of the present disclosure. In this embodiment, the AC-DC power supply serving as a power factor correction (PFC) circuit is taken as an example. As shown in <FIG>, the PFC circuit includes a rectifier circuit <NUM>, a power stage circuit <NUM> and a control circuit <NUM>.

Specifically, the rectifier circuit <NUM> receives an alternating current input voltage AC, rectifies the alternating current input voltage AC, and outputs a direct current input voltage VIN. The rectifier circuit <NUM> may be a full-bridge rectifier bridge or a half-bridge rectifier bridge. The output of the rectifier circuit <NUM> may be equivalent to a direct current voltage source.

The power stage circuit <NUM> includes an inductor (or a transformer), a power switch, a diode and the like. The power stage circuit <NUM> directly receives the direct current input voltage VIN outputted by the rectifier circuit. By controlling a conduction state of the power switch, an input current and an input voltage of the power stage circuit basically have consistent waveforms and an output voltage of the power stage circuit is basically constant. Here, the power stage circuit <NUM> is a boost topology. The power stage circuit <NUM> includes an inductor Lε connected with an input terminal of the power stage circuit, a main power switch Q coupled with the inductor Lε, a diode D coupled with a common terminal of the inductor Lε and the main power switch Q, and an output capacitor Cε connected with an output terminal of the power stage circuit to generate an output voltage Vε across the output capacitor Cε. The output voltage Vε serves as an input voltage of a converter at a later stage, or directly provides energy for a load.

The control circuit <NUM> generates a switch control signal based on feedback signals of the output voltage and the inductive current in the power stage circuit <NUM>, to control switch on/off of the power switch in the power stage circuit <NUM>, so that the output voltage Vε is maintained to be closed to an expected value, and the input current and the input voltage of the power stage circuit <NUM> basically have consistent waveforms.

Compared with the conventional technology, the control circuit <NUM> estimates an industrial frequency ripple component ΔVo of the output voltage Vf by sampling an industrial frequency ripple of the output voltage Vε or based on an industrial frequency inductive current and the like, to obtain a ripple reference signal VREF1, and adds the ripple reference signal VREF1 to a reference signal VREF characterizing the desired output voltage of the PFC circuit, so that in a case that a bandwidth of a voltage loop in the control loop is greater than a certain frequency (e.g. <NUM>), the industrial frequency ripple component ΔVO of the output voltage Vε is no longer included in a voltage compensation signal VCOMP of the voltage loop and the output voltage Vε still includes the industrial frequency ripple component ΔVo. Therefore, the loop of the voltage loop can be designed based on the switching frequency without considering the industrial frequency. In addition, a closed-loop cut-off frequency may be used to characterize a dynamic response speed of the closed-loop system, and a high closed-loop cut-off frequency leads to a fast dynamic response speed. Therefore, the control circuit according to the present disclosure improves the dynamic response speed of the control loop.

In the embodiments of the present disclosure, the control circuit <NUM> includes a ripple reference signal generation circuit <NUM>, a feedback circuit <NUM>, an error compensation circuit <NUM>, a current reference generation circuit <NUM> and a pulse width modulation (PWM) generation circuit <NUM>.

The ripple reference signal generation circuit <NUM> is configured to generate the ripple reference signal VREF1 characterizing the industrial frequency ripple of the output voltage of the AC-DC power supply. The ripple reference signal generation circuit <NUM> aims to superimpose the generated ripple reference signal VREF1 to the reference signal VREF characterizing the desired output voltage of the AC-DC power supply, to cause the voltage compensation signal VCOMP not to include the industrial frequency ripple component ΔVo of the output voltage Vf, so that the control loop is not limited by the industrial frequency, thereby improving the dynamic response speed of the control loop. Here, the output voltage Vε includes the industrial frequency ripple component ΔVO and a sum VO of ripple components at other frequencies and an average value of the output voltage, that is, Vf=ΔVO+VO.

In an embodiment, the ripple reference signal generation circuit <NUM> performs low-pass filtering on an inductive current sampling signal VRS characterizing the current flowing through the inductor Lε in the power stage circuit <NUM> to obtain a first inductive current sampling signal VRS1 characterizing the industrial frequency ripple component of the output voltage. Then, a phase of the first inductive current sampling signal VRS1 is shifted and an amplitude of the first inductive current sampling signal VRS1 is changed to obtain the ripple reference signal VREF1 characterizing the estimated industrial frequency ripple component VREF2 of the output voltage.

Referring to <FIG>, the estimated industrial frequency ripple component VREF2 of the output voltage is expressed as: <MAT>.

Here, VRS1 represents the first inductive current sampling signal VRS1 obtained by performing low-pass filtering on the inductive current sampling signal VRS, RS represents an inductive current sampling resistance, and f represents a frequency.

After the estimated industrial frequency ripple component VREF2 of the output voltage is obtained, a product of the estimated industrial frequency ripple component VREF2 of the output voltage and a voltage division coefficient K (K=R<NUM>/(R<NUM>+R<NUM>)) in the output voltage feedback circuit <NUM> serves as the ripple reference signal VREF1. Here, the estimated industrial frequency ripple component is superimposed into the reference signal of the desired output voltage in a proportion the same as the voltage division coefficient K in the output voltage feedback circuit <NUM>, so as to match the feedback signal inputted to the error compensation circuit in the voltage loop and the reference signal, thereby obtaining an accurate voltage compensation signal. The voltage division coefficient K is a ratio of the feedback signal of the output voltage to the output voltage. Based on this, the ripple reference signal VREF1 is expressed as: <MAT> <MAT>.

According to the above equations, an amplitude adjustment coefficient K<NUM> of obtaining the ripple reference signal VREF1 from the first inductive current sampling signal VRS1 may further be obtained.

In an example, in the above equations, f is equal to or close to <NUM>. The frequency of the alternating current input voltage AC (i.e., industrial frequency) is equal to <NUM> and the input current of the PFC circuit is required to track the waveform of the input voltage, so that the frequency of the input current of the PFC circuit is also equal to <NUM>. Therefore, the ripple at the output terminal has a frequency of <NUM>. Based on this, a capacitive reactance of the output capacitor Cf is mainly considered here in a case of <NUM>.

Based on the above analysis, in an embodiment, the ripple reference signal generation circuit <NUM> may include a low-pass filter <NUM> and a phase shift and amplitude adjustment circuit <NUM>.

Specifically, the low-pass filter <NUM> is an electronic filtering device that allows a signal having a frequency below a cut-off frequency to pass, and does not allow a signal having a frequency higher than the cut-off frequency. The low-pass filter <NUM> performs low-pass filtering on the inductive current sampling signal VRS characterizing the current flowing through the inductor Lε in the power stage circuit <NUM>, to obtain the first inductive current sampling signal VRS1 characterizing the industrial frequency ripple component of the output voltage. Here, a circuit structure of the low-pass filter <NUM> is not limited, as long as low-pass filter at a predetermined cut-off frequency can be realized.

The phase shift and amplitude adjustment circuit <NUM> shifts the phase of the first inductive current sampling signal VRS1 and change the amplitude of the first inductive current sampling signal VRS1 to obtain the ripple reference signal VREF1 characterizing the estimated industrial frequency ripple component VREF2 of the output voltage. It can be seen from the above equations <NUM> and <NUM> that the amplitude adjustment coefficient K<NUM> of obtaining the ripple reference signal VREF1 from the first inductive current sampling signal VRS1 is obtained, and the phase shift and amplitude adjustment circuit <NUM> multiplies the first inductive current sampling signal VRS1 by the amplitude adjustment coefficient K<NUM> to obtain the amplitude of the ripple reference signal VREF1. Specifically, the amplitude of the estimated industrial frequency ripple component VREF2 of the output voltage is directly proportional to the capacitive reactance of the output capacitor Cε of the AC-DC power supply and inversely proportional to the impedance of the inductive current sampling resistance RS. Further, the capacitive reactance of the output capacitor Cε refers to a capacitive reactance of the output capacitor Cε at a frequency close to twice of the industrial frequency.

Further, due to an expression feature of the capacitive reactance of the capacitor, the phase shift and amplitude adjustment circuit <NUM> adjusts the phase of the ripple reference signal VREF1 to be <NUM> degrees behind the first inductive current sampling signal. It should be understood that the phase shift and amplitude adjustment circuit <NUM> may perform the phase shift and the amplitude adjustment simultaneously, that is, perform the phase shift prior to the amplitude adjustment, or perform the amplitude adjustment prior to the phase shift.

The above embodiment only gives a method for obtaining the ripple reference signal VREF1. Any other method with which the ripple reference signal VREF1 is obtained and added to the reference signal VREF of the desired output voltage to improve the loop bandwidth of the voltage loop is within the protection scope of the present disclosure.

For example, in another embodiment, the ripple reference signal generation circuit <NUM> filters the output voltage Vf to obtain an industrial frequency ripple sampling signal VREF3 characterizing the industrial frequency ripple component ΔVO of the output voltage, and multiplies the industrial frequency ripple sampling signal VREF3 by the voltage division coefficient K in the output voltage feedback circuit <NUM> as the ripple reference signal VREF1.

Specifically, the ripple reference signal generation circuit <NUM> obtains a real-time value of the output voltage by filtering the output voltage Vε through a first filter with a first cut-off frequency, obtains an average value of the output voltage by filtering the output voltage Vε through a second filter with a second cut-off frequency, and subtracts the average value from the real-time value to obtain the industrial frequency ripple sampling signal VREF3. The second cut-off frequency is much less than the first cut-off frequency.

The feedback circuit <NUM> is configured to input the output voltage Vε subjected to proportional conversion to the error compensation circuit <NUM>. Specifically, the feedback circuit <NUM> includes resistors R<NUM> and R<NUM> that are connected in series. A terminal of the resistor R<NUM> is grounded. A non-grounded terminal of the feedback circuit <NUM> receives the output voltage Vf, and a feedback voltage VFB is outputted at a common node of the resistors R<NUM> and R<NUM>, that is, VFB=K*(ΔVO+VO), and the voltage division coefficient is K (K=R<NUM>/(R<NUM>+R<NUM>)).

The error compensation circuit <NUM> is configured to compare the feedback signal VFB characterizing the output voltage Vε of the AC-DC power supply with a sum of the reference signal VREF characterizing the desired output voltage Vε of the AC-DC power supply and the ripple reference signal VREF1, that is, VREF+VREF1, to generate the voltage compensation signal VCOMP. The control circuit <NUM> generates a control signal for controlling the main power switch Q of the AC-DC power supply based on the voltage compensation signal VCOMP, to improve the dynamic response speed of the control loop. The error compensation circuit <NUM> includes an error amplifier EA. A positive input terminal of the error amplifier EA receives the sum of the reference signal VREF of the desired output voltage Vε and the ripple reference signal VREF1, that is, VREF+VREF1, a negative input terminal of the error amplifier EA receives the feedback signal VFB of the output voltage Vf and an output terminal of the error amplifier EA outputs the voltage compensation signal VCOMP. The output terminal of the error amplifier EA is provided with a compensation capacitor.

Since here the PFC circuit is taken as an example, the current reference generation circuit <NUM> is configured to multiply the direct current input voltage VIN by the voltage compensation signal VCOMP to obtain the current reference signal Vi, so that the current sampling signal Is tracks the waveform of the input voltage VIN. In an example, the current reference generation circuit <NUM> is a multiplier for multiplying the direct current input voltage VIN by the voltage compensation signal VCOMP to obtain the current reference signal Vi.

The PWM generation circuit <NUM> is configured to compare the current sampling signal Is characterizing the current flowing through the main power switch Q with the current reference signal Vi to generate a PWM signal. The PWM signal serves as a control signal for controlling the main power switch Q of the AC-DC power supply. The PWM generation circuit <NUM> includes a comparator CMP. A non-inverting input terminal of the comparator CMP receives the current reference signal Vi. An inverting input terminal of the comparator CMP receives the current sampling signal Is. An output terminal of the comparator CMP outputs a PWM signal. Here, the current sampling signal Is is obtained through a switch current sampling resistor Rsi, which is connected between a terminal of the main power switch Q and the ground potential.

According to the present disclosure, the control circuit can improve the cut-off frequency of the control loop by adding the ripple reference signal VREF1 characterizing the industrial frequency ripple component ΔVo of the output voltage to the reference voltage VREF characterizing the desired output voltage, so that the reference of the voltage loop is expressed as VREF+VREF1. In this way, the reference and the feedback voltage VFB=K*(ΔVO+VO) of the output voltage are almost the same at the industrial frequency band. In addition, the voltage compensation signal VCOMP outputted by the error compensation circuit does not include the industrial frequency ripple component, and the voltage compensation signal VCOMP without the industrial frequency ripple component does not affect the tracking reference of the current loop. Therefore, the loop can be designed without considering limit of the industrial frequency on the cut-off frequency of the loop, thereby effectively increasing the cut-off frequency of the loop and improving the dynamic response speed of the loop.

Claim 1:
A control circuit (<NUM>) configured to be applied to an alternating current-direct current, AC-DC, power supply, the control circuit (<NUM>) comprising:
a ripple reference signal generation circuit (<NUM>), configured to generate a ripple reference signal (VREF1) characterizing an industrial frequency ripple component (ΔVo) of an output voltage (Vf) of the AC-DC power supply; and
an error compensation circuit (<NUM>), configured to compare a sum (VREF+VREF1) of a reference signal (VREF) characterizing a desired output voltage of the AC-DC power supply and the ripple reference signal (VREF1) with a feedback signal (VFB) characterizing the output voltage of the AC-DC power supply, to generate a voltage compensation signal (VCOMP);
wherein the control circuit (<NUM>) is configured to generate a control signal for controlling a main power switch (Q) of the AC-DC power supply based on the voltage compensation signal:
characterized in that: the ripple reference signal generation circuit (<NUM>) is configured to perform low-pass filtering on an inductive current sampling signal (VRS) characterizing a current flowing through an inductor in the AC-DC power supply to obtain a first inductive current sampling signal (VRS1) characterizing
an industrial frequency ripple component of the output voltage; and
wherein the ripple reference signal generation circuit (<NUM>) is further configured to shift a phase of the first inductive current sampling signal (VRS1) and change an amplitude of the first inductive current sampling signal (VRS1) to obtain an estimated (VREF2) industrial frequency ripple component of the output voltage,
wherein the ripple reference signal (VREF1) is proportional to the estimated industrial frequency ripple component (VREF2) and both depend on a capacitive reactance of an output capacitor (Cf) of the AC-DC power supply.