Power converter, power converter control and method for controlling a power converter

Abstract

A power converter, a power converter controller, and a method for controlling a power converter are described. 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 electrically coupled to a filter capacitor configured to provide a DC output voltage; a transformer inductively coupling the rectifier circuit to the LLC resonant tank; 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.The controller is configured to determine the reference voltage based on input voltage and / or output current feedback for the power converter and / or 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.

Description

[0001] Resonant power converters are widely used for their inherent soft switching capability, 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 the DC input voltage is converted to a square wave by a switching network arranged as either a half-bridge or full-bridge. The switching network feeds a resonant LLC tank, which filters out harmonics and provides a sinusoidal voltage and current waveform to a transformer. A rectifier circuit on the secondary side of the transformer converts the transformer AC current to a DC current, which charges a filter capacitor, which in turn provides a DC output voltage. The converter power flow is controlled by modulating the square wave frequency (i.e., switching frequency) with respect to the resonance of the LLC tank.Resonant power converters provide high conversion efficiency when operating near resonance, but struggle to provide the required line (input) and load (output) regulation over a wide operating range.

[0003] Unregulated LLC power converters have simple operation at a fixed frequency where efficiency is maximized, but they do not provide line regulation (input regulation) or load regulation (output regulation). Without line regulation, in addition to the output voltage following the input voltage, there is no input ripple rejection, and the input impedance is inherently negative, introducing stability issues with the input filter.

[0004] LLC power converters with fixed output regulation provide line regulation and load regulation by keeping the output voltage essentially constant regardless of the input voltage and output load, but require large switching frequency variations to maintain closed-loop regulation. LLC power converters with fixed output regulation also suffer from poor stability at operating corners and may require large resonant inductances to achieve a wide operating range.

[0005] Thus, there is a need for an improved LLC power converter, an improved LLC power converter controller, and an improved method for controlling an LLC power converter.

[0006] The object of the present invention is to provide power converters and methods for controlling a power converter with improved characteristics.

[0007] This object is achieved by power converters according to claims 1 and 25 and methods according to claims 13 and 29.

[0008] According to one embodiment of a power converter, the power converter comprises: a half-bridge or full-bridge switching network; an LLC resonant tank electrically coupled to the switching network; a rectifier circuit electrically coupled to a filter capacitor configured to provide a DC output voltage; a transformer inductively coupling the rectifier circuit to the LLC resonant tank;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 and / or output current feedback for the power converter such that adjustment of the switching frequency is constrained as a function of an input voltage and / or an output current of the power converter.;

[0009] According to one embodiment of a method for controlling a power converter comprising a half-bridge or full-bridge switching network, an LLC resonant tank electrically coupled to the switching network, a rectifier circuit electrically coupled to a filter capacitor configured to provide a DC output voltage, and a transformer inductively coupling the rectifier circuit to the LLC resonant tank, the method comprises: 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 and / or output current feedback for the power converter such that the adjustment of the switching frequency is limited as a function of an input voltage and / or an output current of the power converter.;

[0010] According to another embodiment of a 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 electrically coupled to a filter capacitor configured to provide a DC output voltage; a transformer inductively coupling the rectifier circuit to the LLC resonant tank; and a controller configured to determine a variable switching frequency or a variable switching period for the switching network based on a magnitude of the input voltage and a magnitude of the output current.

[0011] According to another embodiment of a method for controlling a power converter comprising a half-bridge or full-bridge switching network, an LLC resonant tank electrically coupled to the switching network, a rectifier circuit electrically coupled to a filter capacitor configured to provide a DC output voltage, and a transformer inductively coupling the rectifier circuit to the LLC resonant tank, the method comprises the steps of: receiving input voltage and / or output current feedback for the power converter; and determining a variable switching frequency or a variable switching period for the switching network based on a magnitude of the input voltage and a magnitude of the output current.

[0012] Those skilled in the art will recognize additional features and advantages upon reading the following detailed description and examining the accompanying drawings.

[0013] The elements of the drawings are not necessarily to scale relative to one another. Like reference numerals indicate correspondingly similar parts. The features of the various illustrated embodiments may be combined, provided they are not mutually exclusive.

[0014] Preferred embodiments of the present invention will be discussed in more detail below with reference to the accompanying drawings, in which: Fig. 1A illustrates a schematic diagram of a switch-mode DC / DC power converter according to an embodiment; Fig. Figure 1B illustrates a more detailed view of both the switching network and the LLC resonant tank of the power converter; Fig. Figure 1C illustrates a gain curve for the power converter as a function of frequency (F) and load current for different quality factor (Q) values; Fig. Figure 1D illustrates an equivalent resonant circuit for LLC resonant tank amplification; Fig. 2 illustrates a schematic diagram of the switch-mode DC / DC power converter according to another embodiment; Fig. 3 illustrates a schematic diagram of the switch-mode DC / DC power converter according to another embodiment; Fig. 4 illustrates an embodiment for modifying a target voltage control setpoint for the power converter; Fig. 5 illustrates another embodiment for modifying a target voltage regulation setpoint for the power converter; Fig. 6 illustrates another embodiment for modifying a target voltage regulation setpoint for the power converter; Fig. 7 illustrates another embodiment for modifying a target voltage regulation setpoint for the power converter; Fig. 8 illustrates an embodiment of a control methodology according to which a variable switching frequency is implemented for the switching network of the power converter over the entire normal operating range of the power converter; Fig. 9 illustrates an embodiment of a control methodology according to which a variable switching frequency is implemented for the switching network of the power converter outside a predetermined range of error voltages and a fixed switching frequency at resonance is implemented for the switching network within the predetermined range of error voltages; Fig. 10 illustrates an embodiment of a feedforward control implemented by the power converter controller; and Fig. 11 illustrates another embodiment of a feedforward control implemented by the power converter controller.

[0015] Described herein are embodiments of a power converter, a power converter controller, and a power converter controller for improving the usability of regulated and unregulated LLC power converters. Line regulation (input regulation) and / or load regulation (output regulation) objectives can be controlled in such a way that the resulting reference voltage dependence on the magnitude of the input voltage and the magnitude of the output current (load current magnitude) limits the frequency range of operation used to maintain regulation. This approach results in systematically defined regulation performance with quantified performance limits and a narrower operating frequency range for higher efficiency and more constrained operation.Separately or in combination, feedforward control, determined based on the magnitude of the input voltage and the magnitude of the output current, can be used to determine a variable switching frequency or a variable switching period for a switching network on the input (primary) side of the power converter. Feedforward control can be used in both regulated and unregulated LLC power converters.

[0016] By defining the reference voltage across the operating range and in a manner that enables closed-loop operation over a narrower (constrained) operating frequency range, the power converter operates closer to the efficiency achieved with resonant frequency operation while allowing line regulation and / or load regulation objectives to be met. The control methodology described herein allows the power converter output voltage to be regulated when output voltage regulation is desired. For example, output voltage feedback can be used to generate an error voltage relative to the reference voltage. A compensator, such as a proportional-integral-derivative (PID) 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.

[0017] Separately or in combination, the control methodology described herein may implement a block to calculate the reference voltage or delta target voltage, which takes into account a dependence on the input voltage magnitude and the output current magnitude. For example, an uncompensated target voltage control setpoint specified at a nominal input voltage and a nominal output current may be modified by a voltage adjustment variable such that the resulting reference voltage is a function of the voltage control setpoint, the output current magnitude, and / or the input voltage magnitude, and reduces the frequency deviation from the resonant frequency to achieve closed-loop operation.This can be achieved, as required, using a relationship that relates the magnitude of the input voltage and / or the magnitude of the output current to the voltage setting value for the target voltage regulation setpoint to achieve the desired line and / or load voltage regulation and the restricted frequency operating range.

[0018] Compared to conventional fixed output voltage power converters, the control methodology described herein provides a reduced frequency range to maintain regulation over a desired input voltage range and a desired output current range, improves efficiency and power density through reduced frequency range requirements, provides the ability to tailor line and load regulation to application requirements, results in improved transient response to load current through matched voltage drop between load line and output impedance, has an improved overvoltage and overcurrent threshold tracking operating range, and improves anomaly detection through voltage correlation in multiple supply systems.

[0019] Compared to conventional fixed-frequency, unregulated power converters, the control methodology described herein reduces output voltage variation due to line and load regulation, suppresses input voltage ripple, has flexibility to balance efficiency, line regulation, load regulation, input voltage range, output voltage range, and operating frequency range, and has improved (negative) input impedance, system stability, and simplified input filter design. Other advantages will become apparent as the various embodiments are described in more detail below.

[0020] Next, embodiments of the power converter, the power converter controller, and the power converter control embodiments will be described with reference to the figures.

[0021] Fig. Figure 1A illustrates a schematic diagram of a switched-mode DC / DC power converter 100 according to one embodiment. The power converter 100 may be regulated or unregulated and may be used in various power electronics applications requiring high efficiency, a wide input voltage range, and high power density, such as 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.

[0022] The power converter 100 includes a switching network 102 and an LLC resonant tank 104 electrically coupled to the switching network 102. Fig. 1A generally illustrates the switching network 102, the LLC resonant tank 104, and other associated circuitry, such as drivers, switches, transformers, etc., where Fig. 1B provides a more detailed view of both the switching network 102 and the LLC resonant tank 104.

[0023] The switching network 102 may be a full-bridge switching network implemented using four switching devices S1 to S4, as shown in Fig. 1B, or a half-bridge switching network in which two of the switching devices (e.g., S1 and S2) are replaced by capacitors. The LLC resonant tank 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, while the capacitor Cr of the LLC resonant tank 104 is connected in series with the secondary inductor Lr. The LLC resonant tank 104 oscillates at a specific frequency, referred to as resonance.

[0024] The transformer 106 includes a primary winding Tps electrically coupled to the LLC resonant tank 104 and a secondary winding Tss electrically coupled to a rectifier circuit 108. The switching network 102 generates a square wave to excite the LLC resonant tank 104, which in turn outputs a sinusoidal resonant current that is scaled and rectified by the transformer 106 and the rectifier circuit 108. An 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 Fig. 1B, the rectifier circuit 108 is implemented using a passive full-bridge diode rectifier. However, the rectifier circuit 108 may instead be actively controlled. For example, the rectifier circuit 108 may be a synchronous rectifier with actively controlled switching devices. In either case, the rectifier circuit 108 is electrically coupled to the filter capacitor Cout, which provides the DC output voltage Vout, and the transformer 106 inductively couples the rectifier circuit 108 to the LLC resonant tank 104.

[0025] Fig. Figure 1C illustrates the gain curve for power converter 100 as a function of frequency (F) and load current for various quality factor (Q) values. Operation at the resonant frequency of LLC tank 104 allows fixed gain and high efficiency to be achieved through zero-voltage switching (ZVS) and zero-current switching (ZCS). Operation at frequencies beyond the resonant frequency allows the resonant tank gain (K) to be changed so that frequency modulation can be used to achieve closed-loop regulation of the output voltage Vout.

[0026] The converter gain is equal to the gain of the switching network 102 times the gain of the LLC resonant tank 104 times the transformer turns ratio (Tps / Tss). The gain of the switching network 102 is 1 for a full-bridge switching network implementation and 0.5 for a half-bridge switching network implementation. The LLC resonant tank gain K can be determined by analyzing the Fig. 1D. The LLC resonant tank gain K is the magnitude of its transfer function as given by: K(Q,m,Fx)=|Vo_ac(s)Vin_ac(s)|=Fx2(m−1)(m∗Fx2−1)2+Fx2∗(Fx2−1)2∗(m−1)2∗Q2 where Q is the quality factor and is given by: Q=LrCrRac,

[0027] Rac is the reflected load resistance and is given by: Rac=8π2∗Tps2Tss2∗Ro,

[0028] Fx is the normalized switching frequency and is given by: Fx=fsfr, for the resonance frequency and is given by: fr=12πLr∗Cr, and m is the ratio of the total primary inductance to the resonant inductance and is given by: m=Lr+LmLr

[0029] As in Fig. As shown in Figure 1C, low Q curves correspond to lighter load operation, while higher Q curves correspond to heavier loads as the load resistance decreases with increased output current. All Q curves (load conditions) cross at the resonant frequency point (at Fx = 1 or fs = fr) and are shown for reference in Fig. 1C normalized to a gain of one.

[0030] The power converter 100 can be operated based on the concept of ZVS and ZCS, which helps minimize switching losses and improve efficiency. ZVS ensures that the voltage across switching devices S1 to S4 is zero when switching devices S1 to S4 are turned on. ZCS ensures that the current flowing through switching devices S1 to S4 is zero when switching devices S1 to S4 are turned off.

[0031] When the switching frequency of power converter 100 is above the resonant frequency Fx of LLC resonant tank 104, power converter 100 operates in ZVS mode, providing efficient voltage conversion. When the switching frequency of power converter 100 is below the resonant frequency Fx of LLC resonant tank 104, power converter 100 operates in ZCS mode with improved overall efficiency. The control method of an LLC resonant power converter typically involves adjusting the switching frequency to regulate the output voltage Vout. Such an approach maintains high efficiency over a wide range of input voltages and load conditions, but requires large deviations in the switching frequency to maintain closed-loop regulation, suffers from poor stability at operating corners, and may require large resonant inductances to achieve a wide operating range.

[0032] The control methodology described herein provides a systematic, flexible approach that enables balancing efficiency, operating frequency range, wide input range, and stable operation over the full load current range. In the case where the power converter 100 is operated as a regulated converter, the control methodology enables adjusting the line (input) and load (output) regulation capability of the power converter LLC to achieve the required frequency operating range.In the case where the power converter 100 is operated as a regulated or unregulated converter, the control methodology provides a feedforward control term that is calculated based on the magnitude of the input voltage and the magnitude of the output current and is used to determine a variable switching frequency or a variable switching period for the switching network 102 on the input (primary) side of the power converter 100.

[0033] For regulated power converter operation, the converter controller 112 determines a reference voltage Vref to which the DC output voltage Vout is regulated and sets the switching frequency Fctl of the switching network 102 based on a difference Verr between the DC output voltage Vout and the reference voltage Vref. Fig. 1A, the controller 112 is a digital controller implemented using digital circuitry and firmware. The controller 112 may be, for example, a microcontroller.

[0034] 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 may be used.

[0035] A 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), a numerically controlled oscillator (NCO), etc. If the clock generator 120 is digital, the clock generator 120 may be part of the controller 112. The clock generator 120 provides the switching network 102 with a timing signal that synchronizes the operation of the switching devices S1 to S4 at the switching frequency Fctl.

[0036] The controller 112 also includes line (input) and load (output) control logic 122 for determining the reference voltage Vref based on input voltage and / or output current feedback (“Vin feedback”, “lout feedback”) for the power converter 100. Accordingly, the adjustment is limited to the switching frequency Fctl as a function of the DC input voltage Vin and / or the output current lout of the power converter 100.

[0037] In one embodiment, controller 112 includes output control, startup, and shutdown logic 124 that provides a target voltage regulation setpoint Vtarg to line and load regulation logic 122. According to this embodiment, line and load regulation logic 122 determines reference voltage Vref by modifying target voltage regulation setpoint Vtarg based on input voltage and / or output current feedback. This allows reference voltage Vref to be determined at a switching frequency Fctl that is closer to the resonance of LLC tank 104. Line and load regulation logic 122 or other control logic may also determine a variable switching frequency Fnom_var or a variable switching period Tnom_var for switching network 102 based on the magnitude of the input voltage and the magnitude of the output current.

[0038] The input voltage and output current feedback provided to controller 112 indicates the magnitude of the input voltage and the magnitude of the output current. The input voltage and output current feedback may be sensed or measured Vin and lout values, respectively. In another embodiment, the input voltage and output current feedback may be related to the magnitude of the input voltage and the magnitude of the output current, respectively. Fig. 1A and Fig. 1B, the controller 112 implements line (input) and load (output) regulation via the reference voltage Vref, which constrains the amount of switching frequency adjustment, and also implements feedforward control via the variable switching frequency Fnom_var or the variable switching period Tnom_var for the switching network 102. The controller 112 may also include regulation mode control logic 126 for determining whether the power converter 100 should operate in a regulated or unregulated state. The controller 112 may further include protection logic 128 for implementing one or more converter protection schemes, such as overvoltage protection (OVP), overcurrent protection (OCP), and overtemperature protection (OTP).

[0039] Fig. 2 illustrates a schematic diagram of the switch-mode DC / DC power converter 100 according to another embodiment. Fig. 2, the controller 112 implements line (input) and load (output) regulation via the reference voltage Vref, which limits the amount of switching frequency adjustment, but does not implement feedforward control. Instead, the Fig. 2, the controller 112 determines a fixed (resonant) switching frequency Fnom_fix or a fixed (resonant) switching period Tnom_nom for the switching network 102. The fixed switching frequency Fnom_fix (or the fixed switching period Tnom_nom) is equal to or slightly higher than the resonant frequency (or resonant period) of the LLC resonant tank 104. According to the Fig. 2, the controller 112 sets 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 set the switching frequency Fctl of the switching network 102.

[0040] Fig. 3 illustrates a schematic diagram of the switch-mode DC / DC power converter 100 according to another embodiment. Fig. 3, controller 112 implements feedforward control, but no line (input) or load (output) regulation. According to this embodiment, power converter 100 operates in an unregulated mode, but with tracking of the output voltage Vout. Fig. 3, the controller 112 determines a variable switching frequency Fnom_var or a variable switching period Tnom_var of the switching network 102 based on the magnitude of the input voltage and the magnitude of the output current, where the magnitude of the input voltage and the magnitude of the output current are indicated by the input voltage and output current feedback provided to the controller 112.

[0041] As previously explained herein, the controller 112 for the regulated power converter package may determine the reference voltage Vref by modifying a target voltage regulation setpoint Vtarg based on the input voltage 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 tank 104.

[0042] Fig. 4 illustrates an embodiment of the controller 112 modifying the target voltage regulation setpoint Vtarg based on a relationship 200 relating the magnitude of the output current (Iout) to the magnitude of the voltage adjustment (δVtarg) for the target voltage regulation setpoint Vtarg. In Fig. 4, the relationship 200 is linear and has a negative slope. According to this embodiment, the magnitude of the adjustment δVtarg to the target voltage control setpoint Vtarg decreases linearly with increasing magnitude of lout and increases linearly with decreasing magnitude of lout.

[0043] Fig. 5 illustrates another embodiment of the controller 112 that modifies the target voltage regulation setpoint Vtarg based on a relationship 300 that relates the magnitude of the output current (Iout) to the magnitude of the voltage adjustment (δVtarg) for the target voltage regulation setpoint Vtarg. In Fig. 5, the relationship 300 is a piecewise linear function defined by two or more straight-line segments 302 having different negative slopes that increase with increasing magnitude of the output current. Four (4) straight-line segments 302_1 through 302_4 are shown in Fig. 5 is shown as an example. In Fig. 5, the gradient (slope) for δVtarg increases for higher lout threshold values lout_th and decreases for lower lout threshold values lout_th. The piecewise linear function can have a zero slope for negative output current values, as in Fig. 5, or have a non-zero slope for negative output current values.

[0044] Fig. 6 illustrates another embodiment of the controller 112 that modifies the target voltage regulation setpoint Vtarg based on a relationship 400 that relates the magnitude of the input voltage (Vin) (Vin) to the magnitude of the voltage adjustment (δVtarg) for the target voltage regulation setpoint Vtarg. In Fig. 6, the relationship 400 is linear and has a positive slope. A slope equal to the output / input voltage ratio equals 0% line (input) regulation. A slope of 0 equals 100% line regulation. A slope between these two extremes is proportional to the achieved line regulation, with the magnitude of the voltage adjustment δVtarg increasing linearly with increasing magnitude of Vin and decreasing linearly with decreasing magnitude of Vin.

[0045] Fig. 7 illustrates another embodiment of the controller 112 modifying the target voltage regulation setpoint Vtarg based on a relationship 500 relating the magnitude of the input voltage (Vin) to the magnitude of the voltage adjustment (δVtarg) for the target voltage regulation setpoint Vtarg. In Fig. 7, the relationship 500 is a piecewise linear function defined by two or more straight-line segments 502 having different positive slopes. Three (3) straight-line segments 502_1 to 502_3 are Fig. 7 is shown as an example. In Fig. 7, the positive slope of a straight-line segment 502_2 containing a nominal input voltage value 'Vnom' is shallower than the positive slope of each straight-line segment 502_1, 502_3 that does not contain the nominal input voltage value 'Vnom'. For example, the positive slope of a straight-line segment 502_1 containing a minimum input voltage value 'Vmin' and the positive slope of a straight-line segment 502_3 containing a maximum input voltage value 'Vmax' may both be steeper than the positive slope of the straight-line segment 502_2 containing the nominal input voltage value 'Vnom'. This allows a greater degree of adaptation to the target voltage control setpoint Vtarg for input voltage magnitudes further away from the nominal input voltage value 'Vnom' and less adaptation for input voltage magnitudes closer to the nominal input voltage value 'Vnom'.

[0046] Fig. Figure 8 illustrates one embodiment of the control methodology according to which the controller 112 adjusts the switching frequency Fctl of the switching network 102 for differences (Vref-Vout) between the DC output voltage Vout and the reference voltage Vref throughout the normal operating range of the power converter 100. According to this embodiment, the controller 112 always operates the power converter in a regulated mode.

[0047] Fig. 9 illustrates one embodiment of the control methodology according to which the controller 112 adjusts the switching frequency Fctl of the switching network 102 for differences (Vref-Vout) between the DC output voltage Vout and the reference voltage Vref that fall outside a 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 tank 104 as the switching frequency Fctl of the switching network for differences (Vref-Vout) between the DC output voltage Vout and the reference voltage Vref that fall within the predetermined range 600. According to this embodiment, the controller 112 operates the power converter in a regulated mode for Vref-Vout differences outside the predetermined range 600 and in an unregulated mode for Vref-Vout differences within the predetermined range 600.

[0048] Controller 112 may employ a similar approach for feedforward control. For example, controller 112 may use a deadband when calculating feedforward control, so that power converter 100 exhibits a frequency dependence on the difference Verr between the DC output voltage Vout and the reference voltage Vref without requiring a compensator to drive a control loop. Instead, controller 112 may generate a frequency based on Verr (and optionally lout and / or Vout), if desired.

[0049] Fig. 10 illustrates one embodiment of feedforward control implemented by controller 112. According to this embodiment, controller 112 determines a variable switching frequency Fnom_var for switching network 102 based on the magnitude of the input voltage (Vin) and the magnitude of the output current (lout). If power converter 100 is operating in regulated mode, controller 112 also adjusts 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 switching network 102.

[0050] In Fig. 10, the variable switching frequency Fnom_var is calculated as a function of Vin and lout. Vmin ranges from a minimum value Vin(min) to a maximum value Vin(max). lout ranges from 0 to a maximum value lout(max). The controller 112 can select Fnom_var(Vin, lout) in a manner that minimizes the output voltage variation. For example, to reduce the LLC gain and keep the output voltage increase within a target range, the controller 112 can increase the variable switching frequency Fnom_var to increase the magnitude of the input voltage (Vin) and decrease the magnitude of the output current (Iout).

[0051] Fig. Figure 11 illustrates another embodiment of feedforward control implemented by controller 112. According to this embodiment, controller 112 determines a variable switching period Tnom_var for switching network 102 based on the magnitude of the input voltage (Vin) and the magnitude of the output current (lout). If power converter 100 is operating in regulated mode, 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 switching network 102.

[0052] In Fig. 11, the controller calculates the variable switching period Tnom_var instead of a variable switching frequency Fnom_var, which provides a better adaptation to the non-linearity in the Fig. 1C. Controller 112 may select Tnom_var(Vin, I-out) in a manner that minimizes the output voltage variation. For example, to reduce the LLC gain and maintain the output voltage increase within a target range, controller 112 may decrease the variable switching period Tnom_var for increasing the magnitude of the input voltage (Vin) and decreasing the magnitude of the output current (Iout).

[0053] For the embodiments of the variable switching frequency Fnom_var and the variable switching period Tnom_var, the controller 112 may use piecewise linear approximations in which the breakpoints are made as a function of Vin and lout. The piecewise linear approximations are shown in Fig. 10 and Fig.11 are indicated by the parallel sloping dashed lines, and the breakpoints are indicated by the lateral spaces between the parallel sloping dashed lines. Alternatively, the controller 112 may implement a lookup table with interpolation between table points to determine Fnom_var or Tnom_var as a function of Vin and lout.

[0054] Although the present disclosure is not so limited, the following numbered examples illustrate one or more aspects of the disclosure.

[0055] Example 1. A power converter comprising: a half-bridge or full-bridge switching network; an LLC resonant tank electrically coupled to the switching network; a rectifier circuit electrically coupled to a filter capacitor configured to provide a DC output voltage; a transformer inductively coupling the rectifier circuit to the LLC resonant tank;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 and / or output current feedback for the power converter such that adjustment of the switching frequency is constrained as a function of an input voltage and / or an output current of the power converter.;

[0056] Example 2. The power converter of example 1, wherein the controller is configured to determine the reference voltage by modifying a target voltage regulation setpoint based on the input voltage and / or output current feedback.

[0057] Example 3. The power converter of example 2, wherein the controller is configured to modify the target voltage regulation setpoint based on a relationship relating the magnitude of the output current to the magnitude of the voltage adjustment for the target voltage regulation setpoint.

[0058] 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.

[0059] Example 5. The power converter of example 3, wherein the relationship is a piecewise linear function defined by two or more straight-line segments having different negative slopes that increase with increasing magnitude of the output current.

[0060] Example 6. The power converter of any one of examples 2 to 5, wherein the controller is configured to modify the target voltage regulation setpoint based on a relationship relating the magnitude of the input voltage to the magnitude of the voltage adjustment for the target voltage regulation setpoint.

[0061] Example 7. The power converter according to Example 6, wherein the relationship is linear and has a positive slope.

[0062] Example 8. The power converter of example 6, wherein the relationship is piecewise linear and includes two or more straight line segments having different positive slopes.

[0063] Example 9. The power converter of Example 8, wherein the positive slope of a straight-line segment containing a nominal input voltage value is shallower than the positive slope of a straight-line segment not containing the nominal input voltage value.

[0064] 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.

[0065] 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.

[0066] Example 12. The power converter of any one of examples 1 to 11, wherein the controller is configured to adjust the switching frequency of the switching network for differences between the DC output voltage and the reference voltage that fall outside a predetermined range, and wherein the controller is configured to use a fixed frequency tuned to a resonance of the LLC resonant tank as the switching frequency of the switching network for differences between the DC output voltage and the reference voltage that fall within the predetermined range.

[0067] Example 13. The power converter of 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 a magnitude of the input voltage and a 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.

[0068] Example 14. The power converter of example 13, 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 to decrease the magnitude of the output current.

[0069] Example 15. A method for controlling a power converter comprising a half-bridge or full-bridge switching network, an LLC resonant tank electrically coupled to the switching network, a rectifier circuit electrically coupled to a filter capacitor configured to provide a DC output voltage, and a transformer inductively coupling the rectifier circuit to the LLC resonant tank, the method comprises the steps of: 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 and / or output current feedback for the power converter such that adjustment of the switching frequency is constrained as a function of an input voltage and / or an output current of the power converter.

[0070] Example 16. The method of example 15, wherein determining the reference voltage comprises modifying a target voltage control setpoint based on the input voltage and / or output current feedback.

[0071] Example 17. The method of example 16, wherein modifying the target voltage control setpoint comprises: modifying the target voltage control setpoint based on a relationship relating the magnitude of the output current to the magnitude of the voltage adjustment for the target voltage control setpoint.

[0072] Example 18. The method of Example 17, wherein the relationship is a linear function defined by a straight line having a negative slope.

[0073] Example 19. The method of Example 17, wherein the relationship is a piecewise linear function defined by two or more straight-line segments having different negative slopes that increase with increasing magnitude of the output current.

[0074] Example 20. The method of any one of examples 16 to 19, wherein modifying the target voltage control setpoint comprises: modifying the target voltage control setpoint based on a relationship relating the magnitude of the input voltage to the magnitude of the voltage adjustment for the target voltage control setpoint.

[0075] Example 21. The method of Example 20, wherein the relationship is linear and has a positive slope.

[0076] Example 22. The method of Example 20, wherein the relationship is piecewise linear and comprises two or more straight line segments having different positive slopes.

[0077] Example 23. The method of Example 22, wherein the positive slope of a straight-line segment containing a nominal input voltage value is shallower than the positive slope of a straight-line segment not containing the nominal input voltage value.

[0078] Example 24. The method of 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 differences between the DC output voltage and the reference voltage that fall outside a predetermined range; using a fixed frequency tuned to a resonance of the LLC resonant tank as the switching frequency of the switching network for differences between the DC output voltage and the reference voltage that fall within the predetermined range.

[0079] Example 25. The method of any one of examples 15 to 24, further comprising: determining a variable switching frequency or a variable switching period for the switching network based on a magnitude of the input voltage and a 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.

[0080] Example 26. The method of example 25, 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 increasing the variable switching frequency or decreasing the variable switching period to increase the magnitude of the input voltage and to decrease the magnitude of the output current.

[0081] Example 27. A power converter comprising: a half-bridge or full-bridge switching network; an LLC resonant tank electrically coupled to the switching network; a rectifier circuit electrically coupled to a filter capacitor configured to provide a DC output voltage; a transformer inductively coupling the rectifier circuit to the LLC resonant tank; and a controller configured to determine a variable switching frequency or a variable switching period for the switching network based on a magnitude of the input voltage and a magnitude of the output current.

[0082] Example 28. The power converter of 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 such that the DC output voltage is regulated.

[0083] Example 29. The power converter of example 28, wherein the controller is configured to determine the reference voltage based on the input voltage and / or output current feedback such that the adjustment is limited to the variable switching frequency or the variable switching period as a function of an input voltage and / or an output current of the power converter.

[0084] Example 30. The power converter of 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 magnitude of the input voltage and to decrease the magnitude of the output current.

[0085] Example 31. A method for controlling a power converter comprising a half-bridge or full-bridge switching network, an LLC resonant tank electrically coupled to the switching network, a rectifier circuit electrically coupled to a filter capacitor configured to provide a DC output voltage, and a transformer inductively coupling the rectifier circuit to the LLC resonant tank, the method comprising: receiving input voltage and / or output current feedback for the power converter; and determining a variable switching frequency or a variable switching period for the switching network based on a magnitude of the input voltage and a magnitude of the output current.

[0086] Example 32. The method of example 31, further comprising the steps of: adjusting 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.

[0087] Example 33. The method of example 32, further comprising the step of: determining the reference voltage based on the input voltage and / or output current feedback such that the adjustment is limited to the variable switching frequency or the variable switching period as a function of an input voltage and / or an output current of the power converter.

[0088] Example 34. The method of any one of examples 31 to 33, 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 increasing the variable switching frequency or decreasing the variable switching period to increase the magnitude of the input voltage and to decrease the magnitude of the output current.

[0089] Terms such as "first," "second," and the like are used to describe various elements, regions, sections, etc., and are also not intended to be limiting. Like terms refer to like elements throughout the specification.

[0090] As used herein, the terms "have," "include," "comprise," "have," and the like are open-ended terms that indicate the presence of specified elements or features but do not preclude additional elements or features. The articles "a," "an," and "the" are intended to include both the plural and singular unless the context clearly indicates otherwise.

[0091] The expression "and / or" should be interpreted to cover all possible conjunctive and disjunctive combinations, unless explicitly stated otherwise. For example, the expression "A and / or B" should be interpreted to mean only A, only B, or both A and B. The expression "at least one of" should be interpreted in the same way as "and / or" unless explicitly stated otherwise. 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.

[0092] It is understood that the features of the various embodiments described herein may be combined with one another unless expressly stated otherwise.

[0093] Although specific embodiments have been illustrated and described herein, it will be apparent to those skilled in the art that a variety of alternative and / or equivalent implementations may be substituted for 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, it is intended that this invention be limited only by the claims and their equivalents.

Claims

[1] A power converter (100) having the following features: a half-bridge or full-bridge switching network (102); an LLC resonant tank (104) electrically coupled to the switching network (102); a rectifier circuit (108) electrically coupled to a filter capacitor configured to provide a DC output voltage; a transformer (106) inductively coupling the rectifier circuit (108) to the LLC resonant tank (104); and a controller (112) configured to determine a reference voltage to which the DC output voltage is regulated and to set a switching frequency of the switching network (102) based on a difference between the DC output voltage and the reference voltage, wherein the controller (112) is configured to determine the reference voltage based on input voltage and / or output current feedback for the power converter (100) such that the adjustment is limited to the switching frequency as a function of an input voltage and / or an output current of the power converter (100). [2] The power converter (100) of claim 1, wherein the controller (112) is configured to determine the reference voltage by modifying a target voltage regulation setpoint based on the input voltage and / or output current feedback. [3] The power converter (100) of claim 2, wherein the controller (112) is configured to modify the target voltage regulation setpoint based on a relationship relating the magnitude of the output current to the magnitude of the voltage adjustment for the target voltage regulation setpoint. [4] The power converter (100) of claim 3, wherein the relationship is a linear function defined by a straight line having a negative slope. [5] The power converter (100) of claim 3, wherein the relationship is a piecewise linear function defined by two or more straight line segments having different negative slopes that increase with increasing magnitude of the output current. [6] The power converter (100) of any one of claims 2 to 5, wherein the controller (112) is configured to modify the target voltage regulation setpoint based on a relationship relating the magnitude of the input voltage to the magnitude of the voltage adjustment for the target voltage regulation setpoint. [7] The power converter (100) of claim 6, wherein the relationship is linear and has a positive slope. [8] The power converter (100) of claim 6, wherein the relationship is piecewise linear and comprises two or more straight line segments having different positive slopes. [9] The power converter (100) of claim 8, wherein the positive slope of a straight line segment containing a nominal input voltage value is shallower than the positive slope of a straight line segment not containing the nominal input voltage value. [10] The power converter (100) according to any one of claims 1 to 9, wherein the controller (112) is configured to adjust the switching frequency of the switching network (102) for differences between the DC output voltage and the reference voltage that fall outside a predetermined range, and wherein the controller (112) is configured to use a fixed frequency tuned to a resonance of the LLC resonant tank (104) as the switching frequency of the switching network (102) for differences between the DC output voltage and the reference voltage that fall within the predetermined range. [11] The power converter (100) according to any one of claims 1 to 10, wherein the controller (112) is configured to determine a variable switching frequency or a variable switching period for the switching network (102) based on a magnitude of the input voltage and a magnitude of the output current, and wherein the controller (112) 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 (102). [12] The power converter (100) of claim 11, wherein the controller (112) is configured to increase the variable switching frequency or decrease the variable switching period to increase the magnitude of the input voltage and to decrease the magnitude of the output current. [13] A method for controlling a power converter (100) comprising a half-bridge or full-bridge switching network (102), an LLC resonant tank (104) electrically coupled to the switching network (102), a rectifier circuit (108) electrically coupled to a filter capacitor configured to provide a DC output voltage, and a transformer (106) inductively coupling the rectifier circuit (108) to the LLC resonant tank (104), the method comprising the steps of: Setting a switching frequency of the switching network (102) 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 and / or output current feedback for the power converter (100) such that the adjustment is limited to the switching frequency as a function of an input voltage and / or an output current of the power converter (100). [14] The method according to claim 13, wherein determining the reference voltage comprises the step of: Modify a target voltage control setpoint based on input voltage and / or output current feedback. [15] The method of claim 14, wherein modifying the target voltage control setpoint comprises the step of: Modifying the target voltage control setpoint based on a relationship that relates the magnitude of the output current to the magnitude of the voltage adjustment for the target voltage control setpoint. [16] The method of claim 15, wherein the relationship is a linear function defined by a straight line having a negative slope. [17] The method of claim 15, wherein the relationship is a piecewise linear function defined by two or more straight line segments having different negative slopes that increase with increasing magnitude of the output current. [18] The method according to any one of claims 14 to 17, wherein modifying the target voltage control setpoint comprises the step of: Modifying the target voltage control setpoint based on a relationship that relates the magnitude of the input voltage to the magnitude of the voltage adjustment for the target voltage control setpoint. [19] The method of claim 18, wherein the relationship is linear and has a positive slope. [20] The method of claim 18, wherein the relationship is piecewise linear and comprises two or more straight line segments having different positive slopes. [21] The method of claim 20, wherein the positive slope of a straight line segment containing a nominal input voltage value is shallower than the positive slope of a straight line segment not containing the nominal input voltage value. [22] The method according to any one of claims 13 to 21, wherein adjusting the switching frequency of the switching network (102) comprises the step of: Adjusting the switching frequency of the switching network (102) for differences between the DC output voltage and the reference voltage that fall outside a predetermined range; and Using a fixed frequency tuned to a resonance of the LLC resonant tank (104) as the switching frequency of the switching network (102) for differences between the DC output voltage and the reference voltage that fall within the predetermined range. [23] The method according to any one of claims 13 to 22, further comprising the step of: Determining a variable switching frequency or a variable switching period for the switching network (102) based on the magnitude of the input voltage and the magnitude of the output current; and Setting the variable switching frequency or the variable switching period based on the difference between the DC output voltage and the reference voltage to set the switching frequency of the switching network (102). [24] The method of 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 comprises the steps of: 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 (100) having the following features: a half-bridge or full-bridge switching network (102); an LLC resonant tank (104) electrically coupled to the switching network (102); a rectifier circuit (108) electrically coupled to a filter capacitor configured to provide a DC output voltage; a transformer (106) inductively coupling the rectifier circuit (108) to the LLC resonant tank (104); and a controller (112) configured to determine a variable switching frequency or a variable switching period for the switching network (102) based on the magnitude of the input voltage and the magnitude of the output current. [26] The power converter (100) of claim 25, wherein the controller (112) 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 so that the DC output voltage is regulated. [27] The power converter (100) of claim 26, wherein the controller (112) is configured to determine the reference voltage based on the input voltage and / or output current feedback such that the adjustment is limited to the variable switching frequency or the variable switching period as a function of an input voltage and / or an output current of the power converter (100). [28] The power converter (100) according to any one of claims 25 to 27, wherein the controller (112) is configured to increase the variable switching frequency or decrease the variable switching period to increase the magnitude of the input voltage and to decrease the magnitude of the output current. [29] A method for controlling a power converter (100) comprising a half-bridge or full-bridge switching network (102), an LLC resonant tank (104) electrically coupled to the switching network (102), a rectifier circuit (108) electrically coupled to a filter capacitor configured to provide a DC output voltage, and a transformer (106) inductively coupling the rectifier circuit (108) to the LLC resonant tank (104), the method comprises the following steps: Receiving input voltage and / or output current feedback for the power converter (100); and Determining a variable switching frequency or a variable switching period for the switching network (102) based on the magnitude of the input voltage and the magnitude of the output current. [30] The method of claim 29, further comprising the step of: Setting the variable switching frequency or the variable switching period based on a difference between the output DC voltage and a reference voltage so that the output DC voltage is regulated. [31] The method according to claim 30, further comprising the step of: Determining the reference voltage based on the input voltage and / or output current feedback such that the adjustment is limited to the variable switching frequency or the variable switching period as a function of an input voltage and / or an output current of the power converter (100). [32] The method according to any one of claims 29 to 31, 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 the following steps: 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.

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