Power converter, power converter controller, and method of controlling power converter

Abstract

The invention relates to a power converter, a power converter controller and a method of controlling the power converter. The power converter includes a half-bridge or full-bridge switching network, an LLC resonant tank electrically coupled to the switching network, a rectifier circuit configured to provide a DC output voltage electrically coupled to a filter capacitor, a transformer inductively coupling the rectifier circuit to the LLC resonant tank, and a control circuit coupled to the transformer. And a controller configured to determine a reference voltage to which the DC output voltage is adjusted and adjust a switching frequency of the switching network based on a difference between the DC output voltage and the reference voltage. The controller is configured to determine a reference voltage based on an input voltage feedback and / or an output current feedback for the power converter, and / or to determine a variable switching frequency or a variable switching period of the switching network based on an input voltage magnitude and an output current magnitude.

Description

Background Art

[0001] Resonant power converters are widely adopted due to their inherent soft-switching ability, high efficiency, low EMI (electromagnetic interference), and high power density. Common resonant power converter topologies include series resonant converters, parallel resonant converters, and series-parallel resonant converters such as LCC and LLC converters.

[0002] The LLC power converter is a resonant converter in which a DC input voltage is converted into a square wave by a switching network arranged as a half-bridge or full-bridge. The switching network powers a resonant LLC loop that filters out harmonics and provides a sinusoidal-like voltage and current waveform to the transformer. A rectifier circuit on the secondary side of the transformer converts the transformer AC current into a DC current that charges a filter capacitor, which in turn provides a DC output voltage. By modulating the square wave frequency (i.e., the switching frequency) relative to the resonance of the LLC loop, the converter power flow can be controlled. The resonant power converter provides high conversion efficiency when operating near resonance, but it is difficult to provide the required line (input) regulation and load (output) regulation over a wide operating range.

[0003] An unregulated LLC power converter operates simply at a fixed frequency where the efficiency is maximized, but it does not provide line (input) regulation and load (output) regulation. Without line regulation, there is no suppression of input ripple except for output voltage tracking the input voltage, and the input impedance is inherently negative, which poses stability problems for the input filter.

[0004] A fixed-output regulated LLC power converter provides line regulation and load regulation by keeping the output voltage substantially constant regardless of the input voltage and output load, but it requires a large deviation in the switching frequency to maintain closed-loop regulation. The fixed-output regulated LLC power converter also has poor stability at the operating corners and may require a large resonant inductor to achieve a wide operating range.

[0005] Therefore, there is a need for an improved LLC power converter, an LLC power converter controller, and a method for controlling an LLC power converter. Summary of the Invention

[0006] According to an embodiment of a power converter, the power converter includes: a half-bridge or full-bridge switching network; an LLC resonant circuit electrically coupled to the switching network; a rectifier circuit configured to provide a DC output voltage and electrically coupled to a filter capacitor; a transformer inductively coupling the rectifier circuit to the LLC resonant circuit; and a controller configured to determine a reference voltage to which the DC output voltage is regulated and adjust a switching frequency of the switching network based on a difference between the DC output voltage and the reference voltage, wherein the controller is configured to determine the reference voltage based on input voltage feedback and / or output current feedback for the power converter such that the adjustment of the switching frequency is limited according to the input voltage and / or output current of the power converter.

[0007] According to an embodiment of a method for controlling a power converter, the power converter includes a half-bridge or full-bridge switching network, an LLC resonant circuit electrically coupled to the switching network, a rectifier circuit configured to provide a DC output voltage and electrically coupled to a filter capacitor, and a transformer inductively coupling the rectifier circuit to the LLC resonant circuit. The method includes: adjusting a switching frequency of the switching network based on a difference between the DC output voltage and a reference voltage to which the DC output voltage is regulated; and determining the reference voltage based on input voltage feedback and / or output current feedback for the power converter such that the adjustment of the switching frequency is limited according to the input voltage and / or output current of the power converter.

[0008] According to another embodiment of a power converter, the power converter includes: a half-bridge or full-bridge switching network; an LLC resonant circuit electrically coupled to the switching network; a rectifier circuit configured to provide a DC output voltage and electrically coupled to a filter capacitor; a transformer inductively coupling the rectifier circuit to the LLC resonant circuit; and a controller configured to determine a variable switching frequency or variable switching period of the switching network based on input voltage magnitude and output current magnitude.

[0009] According to another embodiment of a method for controlling a power converter, the power converter includes a half-bridge or full-bridge switching network, an LLC resonant circuit electrically coupled to the switching network, a rectifier circuit configured to provide a DC output voltage and electrically coupled to a filter capacitor, and a transformer inductively coupling the rectifier circuit to the LLC resonant circuit. The method includes: receiving input voltage feedback and / or output current feedback for the power converter; and determining a variable switching frequency or variable switching period of the switching network based on input voltage magnitude and output current magnitude.

[0010] Those skilled in the art will be able to recognize additional features and advantages after reading the following detailed description and viewing the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The elements in the accompanying drawings are not necessarily drawn to scale relative to each other. Identical reference numerals denote corresponding like parts. The features of the various illustrated embodiments may be combined unless mutually exclusive. The embodiments are shown in the drawings and described in detail in the following description.

[0012] Figure 1A A schematic diagram of a switched-mode DC / DC power converter according to an embodiment is illustrated;

[0013] Figure 1B A more detailed view of both the switching network and the LLC resonant tank of the power converter is illustrated;

[0014] Figure 1C The gain curves of the power converter according to frequency (F) and load current for different quality factor (Q) values are illustrated;

[0015] Figure 1D An equivalent resonant circuit for the LLC resonant tank gain is illustrated;

[0016] Figure 2 A schematic diagram of a switched-mode DC / DC power converter according to another embodiment is illustrated;

[0017] Figure 3 A schematic diagram of a switched-mode DC / DC power converter according to another embodiment is illustrated;

[0018] Figure 4 An embodiment of modifying the target voltage regulation set point of the power converter is illustrated;

[0019] Figure 5 Another embodiment of modifying the target voltage regulation set point of the power converter is illustrated;

[0020] Figure 6 Another embodiment of modifying the target voltage regulation set point of the power converter is illustrated;

[0021] Figure 7 Another embodiment of modifying the target voltage regulation set point of the power converter is illustrated;

[0022] Figure 8 An embodiment of a control method is illustrated, according to which a variable switching frequency is achieved for the switching network of the power converter over the entire normal operating range of the power converter;

[0023] Figure 9 An embodiment of a control method is illustrated, according to which a variable switching frequency is achieved for the switching network of the power converter outside a predetermined error voltage range, while a fixed switching frequency at resonance is achieved for the switching network within the predetermined error voltage range;

[0024] Figure 10 Illustrates an embodiment of feedforward control implemented by a power converter controller; and

[0025] Figure 11 Illustrates another embodiment of feedforward control implemented by a power converter controller. DETAILED DESCRIPTION

[0026] Power converters, power converter controllers, and power converter control embodiments for improving the availability of regulated and unregulated LLC power converters are described herein. Line (input) regulation and / or load (output) regulation objectives can be controlled in such a way that the resulting reference voltage's dependence on the input voltage magnitude and the output (load) current magnitude limits the operating frequency range for maintaining regulation. This approach results in a system-defined adjustment performance with quantified performance bounds and a narrower operating frequency range for higher efficiency and more constrained operation. Individually or in combination, feedforward control determined based on the input voltage magnitude and the output current magnitude can be used to determine the variable switching frequency or variable switching period of the switching network on the input (primary) side of the power converter. Feedforward control can be used for both regulated and unregulated LLC power converters.

[0027] By defining a reference voltage within the operating range and allowing closed-loop operation within a narrower (constrained) operating frequency range, the operating efficiency of the power converter is closer to the resonant frequency operation while allowing line regulation and / or load regulation objectives to be met. If output voltage regulation is desired, the control methods described herein allow regulation of the power converter output voltage. For example, output voltage feedback can be used to generate an error voltage relative to the reference voltage. A compensator such as a PID (Proportional Integral Derivative) controller can be used to drive the switching frequency of the switching network in a manner that regulates the output voltage to match the reference voltage.

[0028] Individually or in combination, the control methods described herein can implement a block to calculate a reference voltage or an incremental target voltage that takes into account the dependence on the input voltage magnitude and the output current magnitude. For example, an uncompensated target voltage regulation setpoint specified at a nominal input voltage and output current can be modified by a voltage adjustment magnitude such that the resulting reference voltage is related to the voltage regulation setpoint, the output current magnitude, and / or the input voltage magnitude, and reduces the frequency deviation from the resonant frequency for closed-loop operation. This can be achieved using a relationship that relates the input voltage magnitude and / or the output current magnitude to the voltage adjustment magnitude for the target voltage regulation setpoint as needed to achieve the desired line and / or load voltage regulation and a constrained frequency operating range.

[0029] Compared with a conventional fixed-output voltage regulated power converter, the control method described herein provides a reduced frequency range to maintain regulation within a desired input voltage range and output current range, improves efficiency and power density by the reduced frequency range requirement, provides the ability to adjust line and load regulation according to application requirements, improves the transient response to load current by matching the voltage-drop load line to the output impedance, improves the overvoltage and overcurrent threshold tracking operating range, and improves anomaly detection through voltage correlation in a multi-power system.

[0030] Compared with a conventional fixed-frequency unregulated power converter, the control method described herein reduces the output voltage deviation due to line and load regulation, suppresses input voltage ripple, has flexibility in trading off efficiency, line regulation, load regulation, input voltage range, output voltage range, and operating frequency range, and increases the (negative) input impedance, system stability, and simplifies the input filter design. Other advantages will become apparent as various embodiments are described in more detail below.

[0031] Next, exemplary embodiments of a power converter, a power converter controller, and a power converter control embodiment are described with reference to the accompanying drawings.

[0032] Figure 1A A schematic diagram of a switched-mode DC / DC power converter 100 according to an embodiment is illustrated. The power converter 100 can be regulated or unregulated and can be used in various power electronics applications that require high efficiency, a wide input voltage range, and high power density, such as, for example, PC power supplies, server power supplies, telecom power supplies, flat-panel TV and flat-panel display power supplies, AC-DC adapters, electric vehicle charging, etc.

[0033] The power converter 100 includes a switching network 102 and an LLC resonant tank 104 electrically coupled to the switching network 102. Figure 1A The switching network 102, the LLC resonant tank 104, and other associated circuitry, such as drivers, switches, transformers, etc., are generally illustrated. Figure 1B A more detailed view of both the switching network 102 and the LLC resonant tank 104 is provided.

[0034] The switching network 102 can be as Figure 1BThe full - bridge switching network implemented using four switching devices S1 to S4 as shown, or the half - bridge switching network in which two of the switching devices (e.g., S1 and S2) are replaced by capacitors. The LLC resonant circuit 104 includes two inductors Lm, Lr and a capacitor Cr. The primary inductor Lm is magnetically coupled to the secondary inductor Lr through a transformer 106, and the capacitor Cr of the LLC resonant circuit 104 is in series with the secondary inductor Lr. The LLC resonant circuit 104 oscillates at a specific frequency called resonance.

[0035] The transformer 106 includes a primary - side winding Tps electrically coupled to the LLC resonant circuit 104 and a secondary - side winding Tss electrically coupled to the rectifier circuit 108. The switching network 102 generates a square wave to excite the LLC resonant circuit 104, which in turn outputs a resonant sinusoidal current scaled and rectified by the transformer 106 and the rectifier circuit 108. The output capacitor Cout on the secondary side filters the rectified AC current and outputs a DC voltage Vout to one or more loads 110. In Figure 1B it, the rectifier circuit 108 is implemented using a passive full - bridge diode rectifier. However, the rectifier circuit 108 can also be actively controlled. For example, the rectifier circuit 108 can be a synchronous rectifier with actively controlled switching devices. In each case, the rectifier circuit 108 is electrically coupled to the filter capacitor Cout that provides the DC output voltage Vout, and the transformer 106 inductively couples the rectifier circuit 108 to the LLC resonant circuit 104.

[0036] Figure 1C Illustrated are the gain curves of the power converter 100 according to frequency (F) and load current for different quality factor (Q) values. Operation at the resonant frequency of the LLC resonant circuit 104 allows for fixed gain and high efficiency through zero - voltage switching (ZVS) and zero - current switching (ZCS). Operation at a frequency above the resonant frequency allows for changing the resonant circuit gain (K), so frequency modulation can be used to achieve closed - loop regulation of the output voltage Vout.

[0037] The converter gain is equal to the gain of the switching network 102 multiplied by the gain of the LLC resonant circuit 104 multiplied by the transformer turns ratio (Tps / Tss). The gain of the switching network 102 is 1 for a full - bridge switching network and 0.5 for a half - bridge switching network. The LLC resonant circuit gain K can be derived by analyzing Figure 1D the equivalent resonant circuit shown. The LLC resonant circuit gain K is the magnitude of its transfer function and is given by:

[0038]

[0039] where Q is the quality factor and is given by:

[0040]

[0041] Rac is the reflected load resistance and is given by:

[0042]

[0043] Fx is the normalized switching frequency and is given by:

[0044]

[0045] fr is the resonant frequency and is given by:

[0046]

[0047] m is the ratio of the total primary inductance to the resonant inductance and is given by:

[0048]

[0049] As Figure 1C shown, as the load resistance decreases with an increase in the output current, the low-Q curve corresponds to lighter load operation while the high-Q curve corresponds to heavier loads. All Q curves (load conditions) intersect at the resonant frequency point (Fx = 1 or fs = fr) and are normalized to unity gain for reference in Figure 1C .

[0050] The power converter 100 can operate based on the concepts of ZVS and ZCS, which helps to minimize switching losses and improve efficiency. ZVS ensures that when the switching devices S1 to S4 are turned on, the voltage across the switching devices S1 to S4 is zero. ZCS ensures that when the switching devices S1 to S4 are turned off, the current flowing through the switching devices S1 to S4 is zero.

[0051] When the switching frequency of the power converter 100 is higher than the resonant frequency Fx of the LLC resonant tank 104, the power converter 100 operates in ZVS and provides efficient voltage conversion. When the switching frequency of the power converter 100 is lower than the resonant frequency Fx of the LLC resonant tank 104, the power converter 100 operates in ZCS with improved overall efficiency. The control method of the LLC resonant power converter generally involves adjusting the switching frequency to regulate the output voltage Vout. This method maintains high efficiency over a wide range of input voltage and load conditions, but requires a large deviation in the switching frequency to maintain closed-loop regulation, has poor stability at the operating corners, and may require a large resonant inductor to achieve a wide operating range.

[0052] The control method described herein provides a systematic and flexible method that allows for balancing efficiency, operating frequency range, wide input range, and stable operation over a full load current range. In the case where the power converter 100 operates as a regulated converter, the control method allows for adjusting the line (input) and load (output) regulation capabilities of the LLC power converter to achieve the desired frequency operating range. In the case where the power converter 100 operates as a regulated or unregulated converter, the control method provides a feedforward control term that is calculated based on the input voltage magnitude and output current magnitude and is used to determine the variable switching frequency or variable switching period of the switching network 102 on the input (primary) side of the power converter 100.

[0053] For regulated power converter operation, the converter controller 112 determines the reference voltage Vref to which the DC output voltage Vout is regulated, and adjusts the switching frequency Fctl of the switching network 102 based on the difference Verr between the DC output voltage Vout and the reference voltage Vref. In Figure 1A this example, the controller 112 is a digital controller implemented using digital circuitry and firmware. The controller 112 can be, for example, a microcontroller.

[0054] The controller 112 includes a voltage difference calculator block 114 for calculating Verr based on the difference between Vout and Vref. A control loop mechanism 116, such as a PID (Proportional Integral Derivative) controller, applies a correction PIDout to the error voltage Verr based on proportional, integral, and derivative terms. Other types of control loop mechanisms can be used.

[0055] The frequency adjustment block 118 adjusts the switching frequency Fctl of the switching network 102 based on the correction PIDout to the error voltage Verr. The switching frequency Fctl is provided to a clock generator 120, such as a voltage controlled oscillator (VCO), numerically controlled oscillator (NCO), etc. If the clock generator 120 is digital, the clock generator 120 can be part of the controller 112. The clock generator 120 provides a timing signal to the switching network 102 that synchronizes the operation of the switching devices S1 to S4 at the switching frequency Fctl.

[0056] The controller 112 also includes line (input) and load (output) regulation logic 122 for determining the reference voltage Vref based on input voltage feedback and / or output current feedback (‘Vin feedback’, ‘Iout feedback’) for the power converter 100. Thus, the adjustment of the switching frequency Fctl is limited according to the DC input voltage Vin and / or output current Iout of the power converter 100.

[0057] In one embodiment, the controller 112 includes output control, startup, and shutdown logic 124 for providing a target voltage regulation setpoint Vtarg to the line and load regulation logic 122. According to this embodiment, the line and load regulation logic 122 determines a reference voltage Vref by modifying the target voltage regulation setpoint Vtarg based on input voltage feedback and / or output current feedback. This allows the reference voltage Vref to be determined at a switching frequency Fctl that is closer to the resonance of the LLC resonant circuit 104. The line and load regulation logic 122 or other controller logic may also determine a variable switching frequency Fnom_var or a variable switching period Tnom_var of the switching network 102 based on the input voltage magnitude and the output current magnitude.

[0058] The input voltage and output current feedback provided to the controller 112 indicate the input voltage magnitude and the output current magnitude. The input voltage and output current feedback may be sensed or measured Vin and Iout values, respectively. In another embodiment, the input voltage and output current feedback may be related to the input voltage magnitude and the output current magnitude, respectively. In Figure 1A and Figure 1B , the controller 112 implements line (input) and load (output) regulation via the reference voltage Vref that limits the switching frequency adjustment amount, and also implements feedforward control via the variable switching frequency Fnom_var or the variable switching period Tnom_var of the switching network 102. The controller 112 may also include adjustment mode control logic 126 for determining whether the power converter 100 should operate in a regulated state or an unregulated state. The controller 112 may also include protection logic 128 for implementing one or more converter protection schemes such as overvoltage protection (OVP), overcurrent protection (OCP), and overheat protection (OTP).

[0059] Figure 2 FIG. illustrates a schematic diagram of a switched-mode DC / DC power converter 100 according to another embodiment. In Figure 2 , the controller 112 implements line (input) and load (output) adjustment via the reference voltage Vref that limits the switching frequency adjustment amount, but does not implement feedforward control. Instead, Figure 2 the illustrated embodiment of the controller 112 implements a fixed (resonant) switching frequency Fnom_fix or a fixed (resonant) switching period Tnom_nom of the switching network 102. The fixed switching frequency Fnom_fix (or the fixed switching period Tnom_nom) matches or is slightly higher than the resonant frequency (or resonant period) of the LLC resonant loop 104. According to Figure 2In the illustrated embodiment, the controller 112 adjusts the fixed switching frequency Fnom_fix or the fixed switching period Tnom_nom based on the difference Verr between the DC output voltage Vout and the reference voltage Vref to adjust the switching frequency Fctl of the switching network 102.

[0060] Figure 3 FIG. illustrates a schematic diagram of a switched-mode DC / DC power converter 100 according to another embodiment. In Figure 3 this case, the controller 112 implements feed-forward control but does not implement line (input) or load (output) regulation. According to this embodiment, the power converter 100 operates in an unregulated mode but tracks the output voltage Vout. In Figure 3 this case, the controller 112 determines the variable switching frequency Fnom_var or the variable switching period Tnom_var of the switching network 102 based on the input voltage magnitude and the output current magnitude, where the input voltage magnitude and the output current magnitude are indicated by the input voltage and output current feedback provided to the controller 112.

[0061] As explained earlier herein, for the case of a regulated power converter, the controller 112 can determine the reference voltage Vref by modifying the target voltage regulation setpoint Vtarg based on the input voltage feedback and / or the output current feedback. This allows the reference voltage Vref to be determined at a switching frequency Fctl that is closer to the resonance of the LLC resonant circuit 104.

[0062] Figure 4 FIG. illustrates an embodiment of the controller 112 that modifies the target voltage regulation setpoint Vtarg based on the relationship 200 that relates the magnitude of the output current (Iout) to the magnitude of the voltage adjustment (δVtarg) of the target voltage regulation setpoint Vtarg. In Figure 4 this case, the relationship 200 is linear and has a negative slope. According to this embodiment, the magnitude of the adjustment δVtarg of the target voltage regulation setpoint Vtarg decreases linearly as the magnitude of Iout increases and increases linearly as the magnitude of Iout decreases.

[0063] Figure 5 FIG. illustrates another embodiment of the controller 112 that modifies the target voltage regulation setpoint Vtarg based on the relationship 300 that relates the magnitude of the output current (Iout) to the magnitude of the voltage adjustment (δVtarg) of the target voltage regulation setpoint Vtarg. In Figure 5 this case, the relationship 300 is a piecewise linear function defined by two or more straight line segments 302 having different negative slopes that increase as the magnitude of the output current increases. As an example, Figure 5Four (4) straight line segments 302_1 to 302_4 are shown. In Figure 5 , the gradient (slope) of δVtarg increases for higher Iout thresholds Iout_th and decreases for lower Iout thresholds Iout_th. The piecewise linear function can have a zero slope for negative output current values, as Figure 5 shown, or can have a non-zero slope for negative output current values.

[0064] Figure 6 FIG. illustrates another embodiment of a controller 112 that modifies a target voltage regulation setpoint Vtarg based on a relationship 400 that relates the magnitude (Vin) of an input voltage (Vin) to a voltage adjustment (δVtarg) of the target voltage regulation setpoint Vtarg. In Figure 6 , the relationship 400 is linear and has a positive slope. A line (input) regulation with a slope equal to the output / input voltage ratio is equal to 0%. A slope of 0 is equal to 100% line regulation. The slope between these two extremes is proportional to the line regulation achieved, where the magnitude of the voltage adjustment δVtarg increases linearly with an increase in the magnitude of Vin and decreases linearly with a decrease in the magnitude of Vin.

[0065] Figure 7 FIG. illustrates another embodiment of a controller 112 that modifies a target voltage regulation setpoint Vtarg based on a relationship 500 that relates the magnitude of an input voltage (Vin) to a voltage adjustment (δVtarg) of the target voltage regulation setpoint Vtarg. In Figure 7 , the relationship 500 is a piecewise linear function defined by two or more straight line segments 502 having different positive slopes. As an example, Figure 7 FIG. illustrates three (3) straight line segments 502_1 to 502_3. In Figure 7 , the positive slope of the straight line segment 502_2 that includes the nominal input voltage value 'Vnom' is less steep than the positive slope of each of the straight line segments 502_1, 502_3 that do not include the nominal input voltage value Vnom. For example, the positive slopes of both the straight line segment 502_1 that includes the minimum input voltage value 'Vmin' and the straight line segment 502_3 that includes the maximum input voltage value 'Vmax' can be steeper than the positive slope of the straight line segment 502_2 that includes the nominal input voltage value Vnom. This allows for a greater degree of adjustment of the target voltage regulation setpoint Vtarg for input voltage magnitudes that are farther from the nominal input voltage value Vnom and a smaller degree of adjustment of the target voltage regulation setpoint Vtarg for input voltage magnitudes that are closer to the nominal input voltage value Vnoms.

[0066] Figure 8An embodiment of the control method is illustrated. According to this embodiment, the controller 112 adjusts the switching frequency Fctl of the switching network 102 for the difference (Vref - Vout) between the DC output voltage Vout and the reference voltage Vref within the entire normal operating range of the power converter 100. According to this embodiment, the controller 112 always operates the power converter in a regulated mode.

[0067] Figure 9 An embodiment of the control method is illustrated. According to this embodiment, the controller 112 adjusts the switching frequency Fctl of the switching network 102 for the difference (Vref - Vout) between the DC output voltage Vout and the reference voltage Vref that falls outside the predetermined range 600. For the difference (Vref - Vout) between the DC output voltage Vout and the reference voltage Vref that falls within the predetermined range 600, the controller 112 uses a fixed frequency Fnom_fix or a fixed switching period Tnom_fix tuned to the resonance of the LLC resonant circuit 104 as the switching frequency Fctl of the switching network. According to this embodiment, for the Vref - Vout difference outside the predetermined range 600, the controller 112 operates the power converter in a regulated mode, while for the Vref - Vout difference within the predetermined range 600, the controller 112 operates the power converter in an unregulated mode.

[0068] The controller 112 can adopt a similar method for feed - forward control. For example, the controller 112 can use a dead - zone when calculating the feed - forward control, such that the power converter 100 has a frequency - dependence on the difference Verr between the DC output voltage Vout and the reference voltage Vref, without the need for a compensator to drive the control loop. Instead, if desired, the controller 112 can generate a frequency based on Verr (and optionally Iout and / or Vout).

[0069] Figure 10 An embodiment of the feed - forward control implemented by the controller 112 is illustrated. According to this embodiment, the controller 112 determines a variable switching frequency Fnom_var of the switching network 102 based on the magnitude of the input voltage (Vin) and the magnitude of the output current (Iout). If the power converter 100 is operated in a regulated mode, the controller 112 also adjusts the variable switching frequency Fnom_var based on the difference between the DC output voltage Vout and the reference voltage Vref to adjust the switching frequency Fctl of the switching network 102.

[0070] In Figure 10In this case, the variable switching frequency Fnom_var is calculated based on Vin and Iout. The range of Vmin is from a minimum value Vin(min) to a maximum value Vin(max). The range of Iout is from 0 to a maximum value Iout(max). The controller 112 can select Fnom_var(Vin, Iout) in a manner that minimizes the output voltage variation. For example, to reduce the LLC gain and keep the output voltage increase within the target range, the controller 112 can increase the variable switching frequency Fnom_var to increase the input voltage (Vin) magnitude and decrease the output current (Iout) magnitude.

[0071] Figure 11 FIG. illustrates another embodiment of the feed-forward control implemented by the controller 112. According to this embodiment, the controller 112 determines the variable switching period Tnom_var of the switching network 102 based on the input voltage (Vin) magnitude and the output current (Iout) magnitude. If the power converter 100 is operating in the regulated mode, the controller 112 also adjusts the variable switching period Tnom_var based on the difference between the DC output voltage Vout and the reference voltage Vref to adjust the switching period of the switching network 102.

[0072] In Figure 11 this case, the controller calculates the variable switching period Tnom_var instead of the variable switching frequency Fnom_var, which may be more suitable for Figure 1C the non-linearity in the gain curve shown. The controller 112 can select Tnom_var(Vin, Iout) in a manner that minimizes the output voltage variation. For example, to reduce the LLC gain and keep the output voltage increase within the target range, the controller 112 can decrease the variable switching period Tnom_var to increase the input voltage (Vin) magnitude and decrease the output current (Iout) magnitude.

[0073] For the variable switching frequency Fnom_var and variable switching period Tnom_var embodiments, the controller 112 can use piecewise linear approximation, where the breakpoints are determined based on Vin and Iout. The piecewise linear approximation is represented by the parallel slanted dashed lines in Figure 10 and Figure 11 and the breakpoints are represented by the lateral space between the parallel slanted dash-dotted lines. Alternatively, the controller 112 can implement a look-up table with interpolation between the table points to determine Fnom_var or Tnom_var based on Vin and Iout.

[0074] The present disclosure is not limited thereto, and the following numbered examples illustrate one or more aspects of the present disclosure.

[0075] Example 1. A power converter, comprising: a half-bridge or full-bridge switching network; an LLC resonant circuit electrically coupled to the switching network; a rectifier circuit electrically coupled to a filter capacitor, the rectifier circuit being configured to provide a DC output voltage; a transformer inductively coupling the rectifier circuit to the LLC resonant circuit; and a controller configured to determine a reference voltage to which the DC output voltage is regulated and to adjust a switching frequency of the switching network based on a difference between the DC output voltage and the reference voltage, wherein the controller is configured to determine the reference voltage based on input voltage feedback and / or output current feedback for the power converter such that the adjustment of the switching frequency is in accordance with input voltage and / or output current limits of the power converter.

[0076] Example 2. The power converter according to Example 1, wherein the controller is configured to determine the reference voltage by modifying a target voltage regulation set point based on the input voltage feedback and / or the output current feedback.

[0077] Example 3. The power converter according to Example 2, wherein the controller is configured to modify the target voltage regulation set point based on a relationship that correlates a magnitude of the output current with a magnitude of a voltage adjustment for the target voltage regulation set point.

[0078] Example 4. The power converter according to Example 3, wherein the relationship is a linear function defined by a straight line having a negative slope.

[0079] Example 5. The power converter according to Example 3, wherein the relationship is a piecewise linear function defined by two or more straight line segments having different negative slopes that increase as the magnitude of the output current increases.

[0080] Example 6. The power converter according to any one of Examples 2 to 5, wherein the controller is configured to modify the target voltage regulation set point based on a relationship that correlates a magnitude of the input voltage with a magnitude of a voltage adjustment for the target voltage regulation set point.

[0081] Example 7. The power converter according to Example 6, wherein the relationship is linear and has a positive slope.

[0082] Example 8. The power converter according to Example 6, wherein the relationship is piecewise linear and has two or more straight line segments having different positive slopes.

[0083] Example 9. The power converter according to Example 8, wherein a positive slope of a straight line segment that includes a nominal input voltage value is less steep than a positive slope of a straight line segment that does not include the nominal input voltage value.

[0084] Example 10. The power converter according to Example 8 or 9, wherein the piecewise linear function has a zero slope for negative output current values.

[0085] Example 11. The power converter according to Example 8 or 9, wherein the piecewise linear function has a non-zero slope for negative output current values.

[0086] Example 12. The power converter according to any one of Examples 1 to 11, wherein the controller is configured to adjust the switching frequency of the switching network for a difference between the DC output voltage and the reference voltage that falls outside a predetermined range, and wherein the controller is configured to use a fixed frequency tuned to the resonance of the LLC resonant circuit as the switching frequency of the switching network for a difference between the DC output voltage and the reference voltage that falls within the predetermined range.

[0087] Example 13. The power converter according to any one of Examples 1 to 12, wherein the controller is configured to determine a variable switching frequency or a variable switching period for the switching network based on an input voltage magnitude and an output current magnitude, and wherein the controller is configured to adjust the variable switching frequency or the variable switching period based on the difference between the DC output voltage and the reference voltage to adjust the switching frequency of the switching network.

[0088] Example 14. The power converter according to Example 13, wherein the controller is configured to increase the variable switching frequency or decrease the variable switching period to increase the input voltage magnitude and decrease the output current magnitude.

[0089] Example 15. A method of controlling a power converter, the power converter including a half-bridge or full-bridge switching network, an LLC resonant circuit electrically coupled to the switching network, a rectifier circuit electrically coupled to a filter capacitor and configured to provide a DC output voltage, and a transformer inductively coupling the rectifier circuit to the LLC resonant circuit, the method including: adjusting a switching frequency of the switching network based on a difference between the DC output voltage and a reference voltage to which the DC output voltage is regulated; and determining the reference voltage based on an input voltage feedback and / or an output current feedback for the power converter such that the adjustment of the switching frequency is in accordance with input voltage and / or output current limits of the power converter.

[0090] Example 16. The method according to Example 15, wherein determining the reference voltage includes modifying a target voltage regulation set point based on the input voltage feedback and / or the output current feedback.

[0091] Example 17. The method according to Example 16, wherein modifying the target voltage regulation setpoint comprises: modifying the target voltage regulation setpoint based on a relationship that relates the magnitude of the output current to the magnitude of the voltage adjustment for the target voltage regulation setpoint.

[0092] Example 18. The method according to Example 17, wherein the relationship is a linear function defined by a straight line with a negative slope.

[0093] Example 19. The method according to Example 17, wherein the relationship is a piecewise linear function defined by two or more straight line segments having different negative slopes that increase as the magnitude of the output current increases.

[0094] Example 20. The method according to any one of Examples 16 to 19, wherein modifying the target voltage regulation setpoint comprises: modifying the target voltage regulation setpoint based on a relationship that relates the magnitude of the input voltage to the magnitude of the voltage adjustment for the target voltage regulation setpoint.

[0095] Example 21. The method according to Example 20, wherein the relationship is linear and has a positive slope.

[0096] Example 22. The method according to Example 20, wherein the relationship is piecewise linear and has two or more straight line segments having different positive slopes.

[0097] Example 23. The method according to Example 22, wherein the positive slope of the straight line segment that includes the nominal input voltage value is less steep than the positive slope of the straight line segments that do not include the nominal input voltage value.

[0098] Example 24. The method according to any one of Examples 15 to 23, wherein adjusting the switching frequency of the switching network comprises: adjusting the switching frequency of the switching network for a difference between the DC output voltage and the reference voltage that falls outside a predetermined range; using a fixed frequency tuned to the resonance of the LLC resonant circuit as the switching frequency of the switching network for a difference between the DC output voltage and the reference voltage that falls within the predetermined range.

[0099] Example 25. The method according to any one of Examples 15 to 24, further comprising: determining a variable switching frequency or a variable switching period of the switching network based on the magnitude of the input voltage and the magnitude of the output current; and adjusting the variable switching frequency or the variable switching period based on the difference between the DC output voltage and the reference voltage to adjust the switching frequency of the switching network.

[0100] Example 26. The method according to Example 25, wherein determining the variable switching frequency or the variable switching period based on the input voltage magnitude and the output current magnitude includes: increasing the variable switching frequency or decreasing the variable switching period to increase the input voltage magnitude and decrease the output current magnitude.

[0101] Example 27. A power converter, comprising: a half-bridge or full-bridge switching network; an LLC resonant circuit electrically coupled to the switching network; a rectifier circuit electrically coupled to a filter capacitor, the rectifier circuit being configured to provide a DC output voltage; a transformer inductively coupling the rectifier circuit to the LLC resonant circuit; and a controller configured to determine a variable switching frequency or a variable switching period of the switching network based on the input voltage magnitude and the output current magnitude.

[0102] Example 28. The power converter according to Example 27, wherein the controller is configured to adjust the variable switching frequency or the variable switching period based on a difference between the DC output voltage and a reference voltage, thereby adjusting the DC output voltage.

[0103] Example 29. The power converter according to Example 28, wherein the controller is configured to determine the reference voltage based on the input voltage feedback and / or the output current feedback such that the adjustment of the variable switching frequency or the variable switching period is in accordance with the input voltage and / or output current limits of the power converter.

[0104] Example 30. The power converter according to any one of Examples 27 to 29, wherein the controller is configured to increase the variable switching frequency or decrease the variable switching period to increase the input voltage magnitude and decrease the output current magnitude.

[0105] Example 31. A method of controlling a power converter, the power converter comprising a half-bridge or full-bridge switching network, an LLC resonant circuit electrically coupled to the switching network, a rectifier circuit electrically coupled to a filter capacitor and configured to provide a DC output voltage, and a transformer inductively coupling the rectifier circuit to the LLC resonant circuit, the method comprising: receiving input voltage feedback and / or output current feedback of the power converter; and determining a variable switching frequency or a variable switching period of the switching network based on the input voltage magnitude and the output current magnitude.

[0106] Example 32. The method according to Example 31, further comprising: adjusting the variable switching frequency or the variable switching period based on a difference between the DC output voltage and a reference voltage, thereby adjusting the DC output voltage.

[0107] Example 33. The method according to Example 32 further includes: determining the reference voltage based on the input voltage feedback and / or the output current feedback, so as to adjust the variable switching frequency or the variable switching period according to the input voltage and / or the output current limit of the power converter.

[0108] Example 34. The method according to any one of Examples 31 to 33, wherein determining the variable switching frequency or the variable switching period based on the input voltage magnitude and the output current magnitude includes: increasing the variable switching frequency or decreasing the variable switching period to increase the input voltage magnitude and decrease the output current magnitude.

[0109] Terms such as "first", "second", etc. are used to describe various elements, regions, parts, etc., and are not intended to be limiting. Throughout the description, the same terms refer to the same elements.

[0110] As used herein, the terms "having", "including", "including (including)", "comprising", etc. are open-ended terms indicating the presence of the element or feature, but not excluding other elements or features. Unless the context clearly indicates otherwise, the articles "a", "an", "the", and "said" are intended to include both plural and singular.

[0111] Unless otherwise clearly stated, the expression "and / or" should be interpreted to cover all possible conjunctive and disjunctive combinations. For example, the expression "A and / or B" should be interpreted to refer to only A, only B, or both A and B. Unless otherwise clearly stated, the expression "at least one of..." should be interpreted in the same way as "and / or". For example, the expression "at least one of A and B" should be interpreted to mean only A, only B, or both A and B.

[0112] It should be understood that the features of the various embodiments described herein can be combined with each other unless otherwise specifically stated.

[0113] Although specific embodiments have been shown and described herein, those of ordinary skill in the art will understand that various alternative and / or equivalent implementations can be used in place of the specific embodiments shown and described without departing from the scope of the present invention. This application is intended to cover any adaptations or variations of the specific embodiments discussed herein. Therefore, the present invention is limited only by the claims and their equivalents.

Claims

1. A power converter, comprising: A half - bridge or full - bridge switching network; An LLC resonant circuit, electrically coupled to the switching network; A rectifier circuit, electrically coupled to a filter capacitor, the rectifier circuit being configured to provide a DC output voltage; A transformer, inductively coupling the rectifier circuit to the LLC resonant circuit; And A controller, configured to determine a reference voltage to which the DC output voltage is regulated, and to adjust a switching frequency of the switching network based on a difference between the DC output voltage and the reference voltage, Wherein the controller is configured to determine the reference voltage based on input voltage feedback and / or output current feedback for the power converter, such that the adjustment of the switching frequency is limited according to the input voltage and / or output current of the power converter.

2. The power converter according to claim 1, wherein the controller is configured to: determine the reference voltage by modifying a target voltage regulation set - point based on the input voltage feedback and / or the output current feedback.

3. The power converter according to claim 2, wherein the controller is configured to: modify the target voltage regulation set - point based on a relationship that correlates the magnitude of the output current with the magnitude of the voltage adjustment for the target voltage regulation set - point.

4. The power converter according to claim 3, wherein the relationship is a linear function defined by a straight line with a negative slope.

5. The power converter according to claim 3, wherein the relationship is a piece - wise linear function defined by two or more straight line segments having different negative slopes that increase as the magnitude of the output current increases.

6. The power converter according to claim 2, wherein the controller is configured to: modify the target voltage regulation set - point based on a relationship that correlates the magnitude of the input voltage with the magnitude of the voltage adjustment for the target voltage regulation set - point.

7. The power converter according to claim 6, wherein the relationship is linear and has a positive slope.

8. The power converter according to claim 6, wherein the relationship is piece - wise linear and has two or more straight line segments with different positive slopes.

9. The power converter according to claim 8, wherein the positive slope of the straight line segment including the nominal input voltage value is less steep than the positive slope of the straight line segment not including the nominal input voltage value.

10. The power converter according to claim 1, wherein the controller is configured to: adjust the switching frequency of the switching network for a difference between the DC output voltage and the reference voltage that falls outside a predetermined range, and wherein the controller is configured to: use a fixed frequency tuned to the resonance of the LLC resonant circuit as the switching frequency of the switching network for a difference between the DC output voltage and the reference voltage that falls within the predetermined range.

11. The power converter according to claim 1, wherein the controller is configured to: determine a variable switching frequency or a variable switching period for the switching network based on the magnitude of the input voltage and the magnitude of the output current, and wherein the controller is configured to: adjust the variable switching frequency or the variable switching period based on the difference between the DC output voltage and the reference voltage to adjust the switching frequency of the switching network.

12. The power converter according to claim 11, wherein the controller is configured to: increase the variable switching frequency or decrease the variable switching period to increase the magnitude of the input voltage and decrease the magnitude of the output current.

13. A method of controlling a power converter, the power converter including a half-bridge or full-bridge switching network, an LLC resonant circuit electrically coupled to the switching network, a rectifier circuit electrically coupled to a filter capacitor and configured to provide a DC output voltage, and a transformer inductively coupling the rectifier circuit to the LLC resonant circuit, the method including: Adjusting the switching frequency of the switching network based on the difference between the DC output voltage and the reference voltage to which the DC output voltage is adjusted; And Determining the reference voltage based on input voltage feedback and / or output current feedback for the power converter such that the adjustment of the switching frequency is limited according to the input voltage and / or output current of the power converter.

14. The method according to claim 13, wherein determining the reference voltage includes: Modifying a target voltage regulation set point based on the input voltage feedback and / or the output current feedback.

15. The method according to claim 14, wherein modifying the target voltage regulation set point includes: Modifying the target voltage regulation set point based on a relationship that correlates the magnitude of the output current with the magnitude of the voltage adjustment for the target voltage regulation set point.

16. The method according to claim 15, wherein the relationship is a linear function defined by a straight line with a negative slope.

17. The method according to claim 15, wherein the relationship is a piecewise linear function defined by two or more straight line segments having different negative slopes that increase as the magnitude of the output current increases.

18. The method according to claim 14, wherein modifying the target voltage regulation set point includes: Modifying the target voltage regulation set point based on a relationship that correlates the magnitude of the input voltage with the magnitude of the voltage adjustment for the target voltage regulation set point.

19. The method according to claim 18, wherein the relationship is linear and has a positive slope.

20. The method according to claim 18, wherein the relationship is piecewise linear and has two or more straight line segments having different positive slopes.

21. The method according to claim 20, wherein the positive slope of the straight line segment including the nominal input voltage value is shallower than the positive slope of the straight line segments not including the nominal input voltage value.

22. The method according to claim 13, wherein adjusting the switching frequency of the switching network includes: adjusting the switching frequency of the switching network for a difference between the DC output voltage and the reference voltage that falls outside a predetermined range; and using a fixed frequency tuned to the resonance of the LLC resonant circuit as the switching frequency of the switching network for a difference between the DC output voltage and the reference voltage that falls within the predetermined range.

23. The method according to claim 13, further comprising: determining a variable switching frequency or a variable switching period for the switching network based on the magnitude of the input voltage and the magnitude of the output current; and adjusting the variable switching frequency or the variable switching period based on the difference between the DC output voltage and the reference voltage to regulate the switching frequency of the switching network.

24. The method according to claim 23, wherein determining the variable switching frequency or the variable switching period based on the magnitude of the input voltage and the magnitude of the output current includes: increasing the variable switching frequency or decreasing the variable switching period to increase the magnitude of the input voltage and decrease the magnitude of the output current.

25. A power converter, comprising: a half-bridge or full-bridge switching network; an LLC resonant circuit electrically coupled to the switching network; a rectifier circuit electrically coupled to a filter capacitor, the rectifier circuit being configured to provide a DC output voltage; a transformer inductively coupling the rectifier circuit to the LLC resonant circuit; and a controller configured to determine a variable switching frequency or a variable switching period for the switching network based on the magnitude of the input voltage and the magnitude of the output current.

26. The power converter according to claim 25, wherein the controller is configured to: adjust the variable switching frequency or the variable switching period based on a difference between the DC output voltage and a reference voltage such that the DC output voltage is regulated.

27. The power converter according to claim 26, wherein the controller is configured to: determine the reference voltage based on the input voltage feedback and / or the output current feedback such that the adjustment of the variable switching frequency or the variable switching period is limited according to the input voltage and / or the output current of the power converter.

28. The power converter according to claim 25, wherein the controller is configured to increase the variable switching frequency or decrease the variable switching period to increase the magnitude of the input voltage and decrease the magnitude of the output current.

29. A method of controlling a power converter, the power converter including a half-bridge or full-bridge switching network, an LLC resonant circuit electrically coupled to the switching network, a rectifier circuit electrically coupled to a filter capacitor and configured to provide a DC output voltage, and a transformer inductively coupling the rectifier circuit to the LLC resonant circuit, the method including: receiving input voltage feedback and / or output current feedback for the power converter; and Determine a variable switching frequency or a variable switching period for feeding back the switching network based on the magnitude of the input voltage and the magnitude of the output current.

30. The method according to claim 29, further comprising: Adjust the variable switching frequency or the variable switching period based on the difference between the DC output voltage and a reference voltage such that the DC output voltage is regulated.

31. The method according to claim 30, further comprising: Determine the reference voltage based on the input voltage feedback and / or the output current feedback such that the adjustment of the variable switching frequency or the variable switching period is restricted according to the input voltage and / or the output current of the power converter.

32. The method according to claim 29, wherein determining the variable switching frequency or the variable switching period based on the magnitude of the input voltage and the magnitude of the output current comprises: Increase the variable switching frequency or decrease the variable switching period to increase the magnitude of the input voltage and decrease the magnitude of the output current.

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