Method and apparatus for adaptive feedforward correction of output current ripple in an onboard charging system

Abstract

The charging system comprises an AC-DC converter for connecting to an AC mains power supply; a DC-link connected to the output of the AC-DC converter; and a DC-DC converter having an input, a control input, and an output coupled to the output of the AC-DC converter. The DC-DC converter includes a driving network for controlling the DC-DC converter. The controller has a feedforward input for receiving a signal corresponding to a voltage across the DC-link, a feedback input for receiving a signal corresponding to an output current provided by the DC-DC converter, and an output coupled to the control input of the DC-DC converter. The controller generates a control signal that controls the driving network based on the positive half-cycle and negative half-cycle of the ripple voltage in the DC-link, and the ripple current amplitude at the output of the DC-DC converter during at least one of the positive half-cycle or negative half-cycle.

Description

Technology Field

[0001] The present invention generally relates to onboard charging for automobiles, specifically to a vehicle onboard charging method and system in which feedforward control is used to reduce output current ripple. Background Technology

[0002] Regulatory standards such as IEC61000-3-2 require a device that draws high power from the AC mains to implement power factor correction (PFC). PFC regulates the current drawn from the AC mains in proportion to the AC voltage, thereby reducing distortion of the AC sine wave under high load conditions. This inevitably defines the input power waveform over time as a sine wave. Figure 1 illustrates the voltage (V), current (I), and power (P) at the input of a PFC circuit. However, DC-DC converters, such as those used in automotive onboard charging applications, require a nearly constant power output. A common method for buffering the sine power input to provide a constant power output is to have a large capacitance bank between the PFC and the DC-DC stage of the onboard charging system, commonly referred to as a DC-link. The capacitor provides energy storage during periods of low input power and is recharged during periods of higher input power in the input power cycle.

[0003] Since providing a constant voltage in the DC-link would require infinite capacitance, some AC ripple will actually always be present, and the ripple amplitude is inversely proportional to the capacitance of the DC-link. Figure 2 illustrates the voltage ripple of the DC-link for 1mF, 2mF, and 3mF of the DC-link. Therefore, the DC-DC converter must also provide ripple removal within its control loop to attenuate the remaining DC-link ripple and prevent the ripple from causing excessive output current ripple.

[0004] Since high-voltage capacitors are expensive and bulky, reducing the capacitance value to the minimum, or otherwise to the smallest possible capacitance, is a competitive advantage. This allows for a maximum ripple limited only by the component rated voltage, not the output current ripple. Subsequently, the DC-DC converter will eliminate the remaining voltage ripple with sufficient attenuation to meet the output ripple current requirements.

[0005] Implementing a DC-DC converter for an onboard charging system with appropriate attenuation of such DC-link ripple amplitude presents a challenge for control design. A control loop design capable of achieving stability and the necessary attenuation of DC-link ripple may not be possible through conventional closed-loop control of the output current.

[0006] One technique to improve damping is to inject the DC-link voltage directly into the control unit using a method commonly known as "feedforward." This method bypasses the delay inherent in the control loop and cancels out output current ripple in proportion to the input voltage. While the output current ripple is canceled out by applying a precisely accurate amount of correction through the precise design of feedforward control coefficients, it must be noted that the output current ripple does not increase as a result of reversing polarity or overcompensation.

[0007] Conventional methods to achieve this involve characterizing and / or calculating precise coefficient values ​​used as fixed constants in control design. However, the response of typical DC-DC converters is often nonlinear and may require different coefficients at different operating points (e.g., output voltage). Furthermore, component tolerances and drift can cause individual DC-DC converters to deviate from the characterized / calculated model, thereby reducing the effectiveness of feed-forward compensation.

[0008] An exemplary embodiment satisfies the significant need for a charging system and method that overcomes the defects of known onboard charging systems for vehicles and effectively reduces or otherwise eliminates output current ripple.

[0009] In an exemplary embodiment, the charging system comprises: an AC-DC converter having an input terminal for connecting to an AC mains power supply; a DC-link having a terminal connected to an output terminal of the AC-DC converter, comprising at least one capacitor; and a DC-DC converter having an input terminal coupled to an output terminal of the AC-DC converter, a control input terminal, and an output terminal coupled to a load to be charged. The DC-DC converter comprises a driving network for controlling the DC-DC converter. A controller having at least one feedforward input terminal is coupled to a DC-link for receiving a signal corresponding to a voltage across the DC-link, at least one feedback input terminal for receiving at least one signal corresponding to an output current provided by the DC-DC converter at an output terminal, and at least one output terminal coupled to a control input terminal of the DC-DC converter. The controller generates a control signal at at least one output terminal for controlling the driving network of the DC-DC converter. The control signal generated by the controller is based on the positive half-cycle and negative half-cycle of the ripple voltage in the DC-link, and the amplitude of the ripple current at the output terminal of the DC-DC converter during at least one of the positive half-cycle and negative half-cycle.

[0010] In one aspect, the controller adjusts the control signal based on the amplitude of the ripple current at the output terminal of the DC-DC converter during both the positive half-cycle and the negative half-cycle of the ripple voltage in the DC-link for each cycle of the ripple voltage in the DC-link over a plurality of cycles.

[0011] In another aspect, the controller determines a plurality of error values ​​associated with the ripple current at the output terminal of the DC-DC converter during at least one of the positive half-cycle or negative half-cycle in each of the plurality of cycles of the ripple voltage in the DC-link, adjusts the feedforward coefficients based on the plurality of error values, and the control signal generated by the controller is based on the adjusted feedforward coefficients. Each error value associated with the ripple current at the output terminal of the DC-DC converter is based on the instantaneous current and the set current value at the output terminal of the DC-DC converter. For each of at least one of the positive half-cycle or negative half-cycle, the controller integrates the error value throughout at least one of the positive half-cycle or negative half-cycle in each of the plurality of cycles.

[0012] For each cycle of the ripple voltage in the DC-link in a plurality of cycles, the controller adjusts the control signal based on both the positive half-cycle and the negative half-cycle of the ripple voltage in the DC-link. During each positive half-cycle of the plurality of cycles, the error value associated with the current ripple at the output terminal of the DC-DC converter includes an instantaneous value of the ripple current at the output terminal of the DC-DC converter that is less than a set current value. During each negative half-cycle of the plurality of cycles, the error value associated with the current ripple at the output terminal of the DC-DC converter includes a set current value that is less than an instantaneous value of the ripple current at the output terminal of the DC-DC converter.

[0013] Based on the integrated error value, the controller adjusts the feedforward coefficient by adding to or subtracting from the previously adjusted version of the feedforward coefficient.

[0014] The controller includes a feedforward path from the DC-link and a feedback path from the output terminal of the DC-DC converter. The feedforward path generates a feedforward control signal, and the feedback path generates a feedback control signal; the control signal is based on the feedforward control signal and the feedback control signal. The controller combines the feedforward control signal and the feedback control signal to generate a combined control signal. Based on the combined control signal, the controller generates a control signal that controls the driving network of the DC-DC converter.

[0015] Based on the combined control signal, the control signal controls the switching frequency, duty cycle, or phase shift of the switching device of the driving circuit network.

[0016] A method for controlling a DC-DC converter of a charging system comprising a DC-link coupled to the input of a DC-DC converter comprises: receiving at least one signal representing a current at the output of the DC-DC converter and a voltage at the DC-link; and, for a plurality of cycles of ripple voltage, determining a positive half-cycle and a negative half-cycle of ripple voltage at the DC-link based on the received DC-link voltage. The method further comprises: determining a plurality of error values ​​associated with a ripple current at the output terminal of the DC-DC converter during at least one of a positive half-cycle or a negative half-cycle for each of the plurality of cycles of ripple voltage at the DC-link; and adjusting a feedforward factor based on the plurality of error values ​​associated with a ripple current at the output terminal of the DC-DC converter. A control signal is generated based on the adjusted feedforward factor, and controlling the DC-DC converter comprises using the control signal.

[0017] The method further comprises the step of integrating an error value associated with current ripple at the output terminal of a DC-DC converter throughout at least one of the positive half-cycle or negative half-cycle in each of the plurality of cycles. The error value associated with current ripple at the output terminal of the DC-DC converter is based on the instantaneous value of current ripple at the output terminal of the DC-DC converter and the average current at the output terminal of the DC-DC converter.

[0018] Determining multiple error values ​​involves determining multiple error values ​​associated with the ripple current at the output terminal of the DC-DC converter during each of the positive half-cycle and negative half-cycle of each of the multiple cycles of the ripple voltage in the DC-link. During each of the positive half-cycles of the multiple cycles, the error value associated with the current ripple at the output terminal of the DC-DC converter includes an instantaneous value of the ripple current at the output terminal of the DC-DC converter that is less than the average current. During each of the negative half-cycles of the multiple cycles, the error value associated with the current ripple at the output terminal of the DC-DC converter includes an average current that is less than the instantaneous value of the ripple current at the output terminal of the DC-DC converter.

[0019] Adjusting the feedforward coefficient involves adding to or subtracting from the integrated error value and the previously adjusted version of the feedforward coefficient.

[0020] The method further includes the step of determining a feedforward control signal based on adjusted coefficients and determining a feedback control signal based on electrical characteristics at the output of a DC-DC converter. The control signal is based on the feedforward signal and the feedback control signal.

[0021] The control signal regulates the switching frequency, duty cycle, or phase shift of the switching device in the driving network. Brief explanation of the drawing

[0022] Aspects of the present invention will be described in detail below with reference to exemplary embodiments in conjunction with the drawings, and in the drawings: FIG. 1 is a diagram showing a set of waveforms illustrating the relationship between voltage, current, and power appearing at the input of a PFC block of an onboard charging system; FIG. 2 is a diagram showing a set of waveforms illustrating the effect of DC-link capacitance on DC ripple voltage in the link; FIG. 3 is a block diagram of a vehicle onboard charging system according to an exemplary embodiment; FIG. 4 is a diagram illustrating waveforms representing the relationship between feedforward-controlled output current ripple and voltage ripple in the DC-link of a vehicle onboard charging system at different levels of feedforward control; FIG. 5 is a drawing illustrating a waveform during a first case of feedforward control of a vehicle onboard charging system of FIG. 2 according to an exemplary embodiment; FIG. 6 is a drawing illustrating a waveform during a second case of feedforward control of a vehicle onboard charging system of FIG. 2 according to an exemplary embodiment; and FIG. 7 is a flowchart illustrating the operation of the vehicle onboard charging system of FIG. 3 according to an exemplary embodiment. Specific details for implementing the invention

[0023] The following description of exemplary embodiment(s) is merely illustrative in nature and is by no means intended to limit the invention, its application, or use. In the drawings and throughout the detailed description, the same reference numerals are used to identify identical or similar components. For clarity, components are not drawn to scale unless otherwise specified.

[0024] An exemplary embodiment relates to an apparatus and method utilizing feedforward control to reduce ripple current appearing at the output of a charging system utilizing a DC-DC converter, such as an onboard charging (OBC) system for automobiles. The apparatus adaptively changes at least one feedforward factor by measuring and processing the output current of the DC-DC converter and by comparing its phase relationship with the input ripple voltage of the DC-DC converter. The apparatus continuously updates the feedforward factor toward an ideal value or a range thereof. The necessary inputs for the proposed feedforward control scheme, namely the DC-link voltage and output current of the DC-DC converter, are already available in the OBC system and therefore require no or minimal additional hardware. The measurement and processing of the current signal at the output of the DC-DC converter is also simple, non-process-intensive, and therefore very low in implementation cost.

[0025] FIG. 3 is a charging system (10) according to an exemplary embodiment. The charging system (10) receives an AC voltage from an AC source (10), such as an AC mains power source, and delivers a DC current to a load (12) to be charged. The load (12) may be one or more batteries, capacitors, or other devices that store or retain electric charge. When used as an OBC system for an electric vehicle, the load (12) may be multiple batteries, particularly used to provide propulsion to the vehicle.

[0026] As illustrated in FIG. 3, the charging system (10) includes an AC-DC converter (14) having an input terminal for connecting to a terminal of an AC power source (11). The AC-DC converter (14) converts the AC voltage and current received at its input terminal and generates a DC voltage and current at its output terminal. The AC-DC converter (14) may have one of a plurality of known embodiments and may include an input filter circuit, a rectifier circuit, and a transformer for reducing input noise. The AC-DC converter (14) may be considered as a power factor correction circuit, as the AC-DC converter (14) uses power factor correction to correct the relative phase of current versus voltage to provide an optimal or otherwise improved power factor.

[0027] A DC-link (16) is coupled across the output terminal of an AC-DC converter (14). In the illustrated exemplary embodiment, the DC-link (16) is at least one capacitor. The DC-link (16) provides energy storage during a lower input power period and is recharged during a higher power input power period of the input power cycle.

[0028] The DC-DC converter (18) primarily converts the DC output of the AC-DC converter (14) and delivers DC power to the load (12). As illustrated in FIG. 3, the DC-DC converter (18) includes an input terminal coupled to the output terminal of the AC-DC converter (14). The output terminal of the DC-DC converter (18) is coupled to the load (12). The DC-DC converter (14) converts the DC output of the AC-DC converter (14) to a desired DC output level at its output. Since the charging system (10) is an onboard charging system for a vehicle, the DC-DC converter (18) is a boost or step-up type converter that provides an increased voltage compared to the voltage appearing at the input terminal of the DC-DC converter (18). In other applications, the DC-DC converter (18) is a buck or step-down type converter that provides a reduced voltage compared to the voltage appearing at its input terminal. The DC-DC converter (18) may have any one of a plurality of known DC-DC converter embodiments. A DC-DC converter (18) comprises at least one switching component, such as a transistor, that controls the operation of the converter, and a driving circuit having an input terminal that receives a control signal appearing at an input control terminal of the converter and an output terminal that drives the control terminal of the switching component. In one embodiment, the DC-DC converter (18) comprises an inductor, a diode, and a capacitor, the switching component is connected in parallel with a series combination of the diode and the capacitor, and the inductor is coupled between the switching component and the input terminal of the converter.

[0029] Referring further to FIG. 3, the charging system (10) further includes a controller (20) that provides feedforward control used to control the output of a DC-DC converter (18). The controller (20) includes at least one input terminal coupled across the DC-link (16) to receive a voltage (Vdc-link) appearing across the DC-link as part of a feedforward control path; one or more input terminals coupled to the output of the DC-DC converter (18) as part of a feedback control path; and an output terminal coupled to the input terminal of the driving circuit of the DC-DC converter (18) to provide a control signal. The feedforward path changes the control signal generated by the feedback control path to set the switching frequency of the driving circuit of the DC-DC converter (18).

[0030] In an exemplary embodiment, the feedback control path of the controller (20) is exemplified as a feedback control circuit or block (24). The feedback control circuit (24) receives a signal appearing across a sensing resistor (26) connected in series with the load (12), and thereby the feedback control circuit (24) determines the output current (Idc-out) of the DC-DC converter (18). The feedback control circuit (24) may, for example, compare the output current (Idc-out) of the DC-DC converter (18) and / or its ripple current with a predetermined current threshold value and generate an error signal (28) based on the comparison at the output terminal of the feedback control circuit (24). The feedback control circuit (24) may be implemented in hardware and may include a voltage comparator circuit. Alternatively, the feedback control circuit (24) may be implemented as a field programmable gate array (FPGA), as a state machine, etc., as software instructions executed by a microcontroller.

[0031] In an exemplary embodiment, the feedforward control path of the controller (20) is exemplified as a feedforward control circuit or block (22) comprising at least one input terminal coupled to the DC-link (16) to receive a voltage across the DC-link (16). The feedforward control circuit (22) also comprises an input terminal connected across a voltage across a sensing resistor (26) to determine an output current from the DC-DC converter (18). The feedforward control circuit (22) may be implemented as a software instruction stored in memory that generates a feedforward control signal (32) when executed by a microcontroller or the like. Alternatively, the feedforward control circuit (22) may be implemented as an FPGA or a state machine. In an embodiment, the feedforward control circuit (22) and the feedback control circuit (24) are implemented or otherwise controlled by the same microcontroller forming at least a part of the controller (20).

[0032] It is understood that the controller (20) generates an additional control signal not shown in FIG. 3 for controlling the operation of the charging system (10), including a control signal connected to control the input terminal of the AC-DC converter (14) for controlling its operation.

[0033] As illustrated in FIG. 3, the feedforward control circuit (22) generates a feedforward control signal (32) that is combined with a feedback control signal (28). In the illustrated exemplary embodiment, the feedforward control signal (32) is added to the feedback control signal (28) to generate a combined control signal (34). The combined control signal (34) is provided to the input terminal of a controlled oscillator circuit (36), e.g., a voltage-controlled oscillator circuit. The controlled oscillator circuit (36) may be implemented as any one of a plurality of well-known voltage-controlled oscillator embodiments. The output of the oscillator circuit (36) is connected to the input terminal of the driving circuit of the DC-DC converter (18), so that the control signal (38) generated by the controlled oscillator circuit (36) controls the driving circuit. In this manner, the combined control signal (34) of the controller (20) controls the frequency of the output of the controlled oscillator circuit (36) and thereby controls the switching frequency of the DC-DC converter (18). Instead of controlling and / or modulating the switching frequency, the controller (20) may use the combined control signal (34) to modulate the duty cycle or phase shift of the switching device of the driving circuit of the DC-DC converter (18) using a well-known technique.

[0034] For a conventional control loop that performs insufficient ripple removal, the output current ripple is nearly in phase and proportional to the DC-link voltage ripple (Fig. 4), that is, as the input voltage increases, the output current also increases. Conversely, when a very large amount of feedforward is applied, the output ripple current will change and be inversely proportional to the DC-link ripple voltage (i.e., as the input voltage increases, the output current decreases). This relationship is used to determine whether the feedforward factor (Kff) of the feedforward control circuit (22) should be increased or decreased.

[0035] Additionally, the amplitude of the output ripple current of the DC-DC converter (18) is used to determine how much the feedforward factor (Kff) should be increased or decreased. A large in-phase current ripple will require a large increase in the feedforward factor (Kff), a small in-phase current ripple will require a small increase in the factor (Kff), a small inverse current ripple will require a small decrease in the factor (Kff), and a large inverse current ripple will require a large decrease in the factor (Kff).

[0036] The feedforward control circuit (22) determines the polarity of the voltage ripple in the DC-link (16) by comparing the instantaneous voltage in the DC-link (16) with its average voltage. Since the control loop of the AC-DC converter (14) has infinite gain in DC, the average voltage and the set value voltage are the same and therefore do not need to be calculated. The voltage in the DC-link (16) may simply be compared to the set value voltage.

[0037] The duration of half a cycle and / or the positive portion of the ripple voltage in the DC-link (16) is determined as the time period during which the voltage across the DC-link (16) exceeds the DC-link setpoint voltage. Similarly, the duration of half a cycle and / or the negative portion of the ripple voltage in the DC-link (16) is determined as the time period during which the voltage across the DC-link (16) is less than the DC-link setpoint voltage. During the positive half cycle of the ripple voltage in the DC-link (16), the measured instantaneous output current (Idc-out) of the DC-DC converter (18) is measured against the setpoint current (which is equal to the average current) to generate a current error signal (I_error_pos).

[0038]

[0039] The current error signal (I_error_pos) is integrated over half a cycle of the positive ripple voltage across the DC-link (16) by adding each successive measurement to the sum of the previous measurements. The result of the integration is the integrated current (I_int_pos) used to proportionally adjust or update the coefficient (Kff) of the feedforward control circuit (22) as follows.

[0040]

[0041] (Kff_new) is the adjusted or updated coefficient (Kff) of the feedforward control circuit (22), (Kff_prev) is the previously adjusted / updated coefficient (Kff), and (Kadj) is a fixed predetermined value. FIG. 5 illustrates the positive half cycle and negative half cycle of the ripple voltage appearing across the DC-link (16), during which the instantaneous output current (Idc-out) of the DC-DC converter (18) is largely in phase with the ripple voltage across the DC-link (16), indicating that very little feedforward is applied. Integrating the instantaneous current from the positive half cycle results in the integrated current (I_int_pos) being multiplied by the ratio (Kadj), and the result is added to the previously determined coefficient (Kff(Kff_prev)) to obtain the adjusted, updated feedforward coefficient (Kff_new).

[0042] Additionally, during the negative half cycle of the ripple voltage across the DC-link (16), the measured instantaneous output current (Idc-out) of the DC-DC converter (18) is measured against the set value current to generate the following current error signal (I_error_neg):

[0043]

[0044] Integrating the current error signal (I_error_neg) during the negative half cycle of the ripple voltage in the DC-link (16) generates an integrated current (I_int_neg), from which the feedforward coefficient (Kff) of the feedforward control circuit (22) is adjusted and / or updated by:

[0045]

[0046] As illustrated in FIG. 5, integrating the instantaneous current from the negative half-cycle results in the integrated current (I_int_neg) being multiplied by the ratio (Kadj), and the product is added to the previously determined coefficient (Kff(Kff_prev)) to obtain an updated coefficient (Kff_new) that is adjusted. In this way, the coefficient (Kff) of the feedforward control circuit (22) is corrected based on each positive and negative half-cycle of the ripple voltage in the DC-link (16) until the ripple current of the output current (Idc-out) at the output of the DC-DC converter (18) is largely minimized.

[0047] FIG. 6 illustrates the positive and negative half cycles of the ripple voltage appearing across the DC-link (16), and indicates that during this time, the instantaneous output current (Idc-out) of the DC-DC converter (18) is out of phase with the ripple voltage across the DC-link (16), so that a very large amount of feedforward is applied. The integrated current ((I_int_pos) (during the positive half cycle of the ripple voltage in the DC-link (16)) and (I_int_neg) (during the negative half cycle)), respectively, causes a reduction in the updated feedforward factor (Kff), which is adjusted compared to the corresponding previously determined feedforward factor (Kff(Kff_prev)).

[0048] FIG. 7 illustrates a flowchart of the operation of a feedforward control circuit (22) according to an exemplary embodiment. Initially, the voltage signal across the sensing resistor (26) as well as the ripple voltage across the DC-link (16) is received in (200). The ripple voltage in the DC-link (176) and the ripple current at the output of the DC-DC converter (18) are determined in (220). Half-cycles of the ripple voltage across the DC-link (16) are identified in (222), and together with this, the duration of each positive and negative half-cycle is determined in (224). After deducting the setpoint current (I_setpoint), the instantaneous ripple current (Idc-out) at the output of the DC-DC converter (18) is integrated in (226) over the corresponding half-cycle of the ripple voltage in the DC-link (16). For each half cycle of the ripple voltage in the DC-link (16), the integrated current is multiplied by the ratio (Kadj) and added to the previously determined feedforward coefficient (Kff_prev) (or effectively subtracted from the case where the integrated current is a negative value) to produce a newly adjusted, updated feedforward coefficient (Keff_new) in (228). The feedforward output control value (32) is determined based on the newly updated feedforward coefficient (Keff_new) in (230). The feedforward output control value (32) may also be determined by _____. In (232), the feedforward output control signal (32) is combined with the feedback output control signal (28), which produces a combined control signal (34) used as an input to the controlled oscillator circuit (36). The controlled oscillator circuit (36) generates a control signal (38) at its output terminal that is provided to the input terminal of the driving circuit of the DC-DC controller (18) in (234).

[0049] In an exemplary embodiment, the charging system (10) is configured such that limits are set for the range of increase and decrease of the feedforward coefficient (Kff), thereby preventing the operation of the feedforward control circuit (22) from using extreme values ​​of the feedforward coefficient (Kff) determined during unexpected transitions, AC grid disturbances, and / or other fault conditions. Additionally, if an excessive output current error (I_error_pos or I_error_neg) is detected, the charging system (10) may utilize a reset that serves as a safety mechanism for the feedforward coefficient (Kff) to become a fault value. Furthermore, a "deadband" for the integrated current values ​​(I_int_pos and I_int_neg) may be implemented so that values ​​below a specific threshold are ignored and no adjustment or update of the feedforward coefficient (Kff) is made. This effectively disables feedforward operation once the ripple current (Idc_out) is within an acceptable limit.

[0050] The feedforward control circuit (22) is described above as integrating a current error signal at the output of the DC-DC converter (18) and thus adjusting and / or updating the feedforward factor (Kff) based on both the positive and negative half-cycles of the ripple voltage in the DC-link (16). In an alternative embodiment, the feedforward control circuit (22) integrates the current error signal and adjusts the feedforward factor based on only the positive half-cycle or only the negative half-cycle of the ripple voltage in the DC-link (16), rather than both the positive and negative half-cycles. In yet another alternative embodiment, the feedforward control circuit (22) integrates the current error signal and adjusts the feedforward factor (Kff) based on both the positive and negative half-cycles of the ripple voltage, rather than all cycles of the ripple voltage in the DC-link (16).

[0051] It is understood that exemplary embodiments have been described herein in an illustrative manner, and that the terms used are intended to be descriptive rather than limiting. Clearly, many modifications and variations of the invention are possible in light of the foregoing teachings. Since the foregoing description is by no means illustrative, variations may be made without departing from the spirit and scope of the invention as defined in the appended claims.

Claims

Claim 1 As a charging system, an AC-DC converter having an input terminal for connecting to an AC main power source; a DC-link having a terminal connected to an output terminal of the AC-DC converter, the DC-link comprising at least one capacitor; and a DC-DC converter having an input terminal coupled to the output terminal of the AC-DC converter, a control input terminal, and an output terminal coupled to a load to be charged, the DC-DC converter comprising a driving network for controlling the DC-DC converter.A controller comprising at least one feedforward input terminal coupled to the DC-link to receive a signal corresponding to a voltage across the DC-link, at least one feedback input terminal for receiving at least one signal corresponding to an output current provided by the DC-DC converter at the output terminal, and at least one output terminal coupled to the control input terminal of the DC-DC converter, wherein the controller generates a control signal at the at least one output terminal to control the driving network of the DC-DC converter, wherein the control signal generated by the controller is based on the amplitude of the ripple current at the output terminal of the DC-DC converter during at least one of the positive half cycle and the negative half cycle of the ripple voltage in the DC-link, and the controller determines a plurality of error values ​​associated with the ripple current at the output terminal of the DC-DC converter during at least one of the positive half cycle or the negative half cycle in each of the plurality of cycles of the ripple voltage in the DC-link, adjusts a feedforward coefficient based on the plurality of error values, and the controller generates A charging system wherein the control signal is based on an adjusted feedforward coefficient, and each error value associated with the ripple current at the output terminal of the DC-DC converter is based on the instantaneous current and set current value at the output terminal of the DC-DC converter, and for each of at least one of the positive half cycle or the negative half cycle, the controller integrates the error value throughout at least one of the positive half cycle or the negative half cycle in each of the plurality of cycles. Claim 2 A charging system according to claim 1, wherein the controller adjusts the control signal based on the amplitude of the ripple current at the output terminal of the DC-DC converter during both the positive half cycle and the negative half cycle of the ripple voltage in the DC-link for each cycle of the ripple voltage in the DC-link in a plurality of cycles. Claim 3 delete Claim 4 delete Claim 5 delete Claim 6 A charging system according to claim 1, wherein the controller adjusts the control signal based on both the positive half cycle and the negative half cycle of the ripple voltage in the DC-link for each cycle of the ripple voltage in the DC-link in a plurality of cycles, and during each of the positive half cycles of the plurality of cycles, the error value associated with the ripple current at the output terminal of the DC-DC converter includes an instantaneous value of the ripple current at the output terminal of the DC-DC converter that is less than the set current value, and during each of the negative half cycles of the plurality of cycles, the error value associated with the ripple current at the output terminal of the DC-DC converter includes a set current value that is less than the instantaneous value of the ripple current at the output terminal of the DC-DC converter. Claim 7 A charging system according to claim 1, wherein, based on an integrated error value, the controller adjusts the feedforward coefficient by adding to or subtracting from a previously adjusted version of the feedforward coefficient. Claim 8 A charging system according to claim 1, wherein the controller includes a feedforward path from the DC-link and a feedback path from the output terminal of the DC-DC converter, the feedforward path generates a feedforward control signal and the feedback path generates a feedback control signal, and the control signal is based on the feedforward control signal and the feedback control signal. Claim 9 In claim 8, the controller combines the feedforward control signal and the feedback control signal to generate a combined control signal, and the control signal controlling the driving network of the DC-DC converter is based on the combined control signal, in a charging system. Claim 10 In claim 9, a charging system wherein, based on the combined control signal, the control signal controls the switching frequency, duty cycle, or phase shift of the switching device of the driving circuit network. Claim 11 A charging system according to claim 1, wherein the control signal controls the switching frequency, duty cycle, or phase shift of the switching device of the driving circuit network. Claim 12 A method for controlling a DC-DC converter of a charging system comprising a DC-link coupled to the input of a DC-DC converter, the method comprising: receiving at least one signal representing a current at an output terminal of the DC-DC converter and a voltage at the DC-link; determining a positive half-cycle and a negative half-cycle of the ripple voltage at the DC-link based on the received DC-link voltage for a plurality of cycles of the ripple voltage; determining a plurality of error values ​​associated with a ripple current at the output terminal of the DC-DC converter for at least one of a positive half-cycle or a negative half-cycle in each of the plurality of cycles of the ripple voltage at the DC-link; and adjusting a feedforward coefficient based on the plurality of error values ​​associated with the ripple current at the output terminal of the DC-DC converter. A method for controlling a DC-DC converter, comprising the steps of generating a control signal based on an adjusted feedforward coefficient and controlling the DC-DC converter using the control signal, and further comprising the step of integrating the error value associated with the ripple current at the output terminal of the DC-DC converter throughout at least one of the positive half cycle or the negative half cycle for each of at least one of the plurality of cycles, wherein the error value associated with the ripple current at the output terminal of the DC-DC converter is based on the instantaneous value of the ripple current at the output terminal of the DC-DC converter and the average current at the output terminal of the DC-DC converter. Claim 13 delete Claim 14 delete Claim 15 A method for controlling a DC-DC converter, wherein determining a plurality of error values ​​comprises determining the plurality of error values ​​associated with the ripple current at the output terminal of the DC-DC converter during each of the positive half cycle and the negative half cycle of each of the plurality of cycles of the ripple voltage in the DC-link, wherein during each of the positive half cycles of the plurality of cycles, the error value associated with the ripple current at the output terminal of the DC-DC converter comprises the instantaneous value of the ripple current at the output terminal of the DC-DC converter which is less than the average current, and during each of the negative half cycles of the plurality of cycles, the error value associated with the ripple current at the output terminal of the DC-DC converter comprises the average current which is less than the instantaneous value of the ripple current at the output terminal of the DC-DC converter. Claim 16 A method for controlling a DC-DC converter according to claim 12, wherein adjusting the feedforward coefficient comprises adding to or subtracting from the integrated error value and a previously adjusted version of the feedforward coefficient. Claim 17 A method for controlling a DC-DC converter according to claim 16, further comprising the step of determining a feedforward control signal based on adjusted coefficients and determining a feedback control signal based on electrical characteristics at the output terminal of the DC-DC converter, wherein the control signals are based on the feedforward control signal and the feedback control signal. Claim 18 In claim 12, the method of controlling a DC-DC converter wherein the control signal controls the switching frequency, duty cycle, or phase shift of the switching device of the DC-DC converter.

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