Resonant inverter and conversion method

Abstract

A resonant inverter for a resonant converter includes a switching network and a resonant tank circuit. The switching network is controlled by a control circuit that responds to a sampled electrical feedback parameter provided by the resonant tank circuit. The value of the sampled electrical feedback parameter or the time at which the electrical feedback parameter is sampled is modified in response to a measured time delay between the control circuit indicating a desired change in the switching state of the switching network and the output of the switching network responding to the desired change.

Description

Technical Field

[0001] The present invention relates to the field of resonant inverters, and in particular to a resonant inverter for use in a resonant converter. Background Art

[0002] The resonant inverter is the main component of a resonant converter. Although the typical use of a resonant converter is to perform DC-DC conversion, there is an increasing interest in adapting the resonant converter to perform AC-DC or even AC-AC conversion.

[0003] US 2014 / 0091718 A1 proposes using an LLC DC / DC converter as a PFC circuit after the rectifier. This actually provides a resonant converter for performing AC-DC conversion. In this document, it is described how to use an oscillator to control the frequency of the resonant converter. The control value of the feedback control system is the switching frequency of the resonant inverter.

[0004] EP 3414824 A1 describes how to use electrical feedback parameters to control the operation of a resonant converter. The electrical feedback parameters may include the voltage across a capacitor of an LLC circuit (i.e. a resonant tank circuit). The electrical feedback parameters may be obtained at the switching instant of a gate drive signal that controls the switch operation.

[0005] It is therefore known to provide a self-oscillating resonant converter which utilizes internal components to form a resonant tank and uses a signal value (eg a voltage level occurring in the circuit) to control the switching operation.

[0006] There is a continuing desire to improve the operation of resonant converters, in particular, to improve the power factor of resonant converters when the resonant converter is used as a power factor corrector (PFC). Summary of the invention

[0007] The invention is defined by the claims.

[0008] According to an example of one aspect of the present invention, a resonant inverter is provided. The resonant inverter includes: an input node for receiving an input for conversion; a switch network connected to the input node, the switch network including at least a first switch and a second switch, wherein a first switch output is defined by a node located between the first switch and the second switch; a resonant tank circuit coupled to the first switch output, wherein an electrical feedback parameter is provided by the resonant tank circuit; a sampling circuit adapted to sample the electrical feedback parameter provided by the resonant tank circuit at a sampling time; a control circuit adapted to generate a switch drive signal according to the sampled electrical feedback parameter, the switch drive signal indicating the desired switch state of the first switch and the second switch; a switch driver adapted to control the switch state of the first switch and the second switch in response to a gate drive signal, wherein a change in the switch state of the first switch and the second switch causes a change in the first switch output; and a timing module adapted to monitor one or more other components of the resonant inverter to determine a time delay between a change in the switch drive signal and a corresponding change in the first switch output, wherein the sampling time depends on the change in the switch drive signal, and the sampling circuit is adapted to adjust the sampling time and / or the value of the sampled electrical feedback parameter according to the time delay.

[0009] The inventors have recognized that (propagation) time delays in the switch driver and / or in the switch network itself cause a delay between the switch drive signal indicating the desired switching and the actual switching of the output of the switch network. This means that the sampled electrical feedback parameter (which is usually sampled at the time when the switch drive signal changes) cannot accurately reflect the electrical feedback parameter at the more desired time when the first switch output changes. This reduces the PFC performance of the resonant inverter. Therefore, it is necessary to obtain a desired sampled value, which is a sample of the electrical feedback parameter at the time when the first switch output changes.

[0010] The inventors have also identified that the length of this time delay varies depending on the characteristics of the resonant inverter, in particular, the input voltage received. Therefore, the inventors have realized that in order to accurately obtain the desired sample of the electrical feedback parameter (at the time when the switch actually changes switching state), it is necessary to accurately determine the length of the time delay.

[0011] The inventors have overcome this problem by using a timing module to monitor components of the resonant inverter to determine the length of this time delay, and modifying the characteristics of the sampling (e.g. the sampling time or the value of the sample) accordingly to actually obtain the desired sample of the electrical feedback parameter.

[0012] The timing module can be adapted to directly measure the time delay between a change in the switch drive signal and a corresponding change in the first switch output, for example by directly monitoring the switch drive signal and the first switch output. In other embodiments, the timing module can infer the timing delay, for example, based on an input voltage received at an input node and / or an output voltage (e.g., at a sampling time).

[0013] The electrical feedback parameter may include a voltage across a capacitor of the resonant tank circuit. The resonant tank circuit typically includes at least one capacitor and at least one inductor, and the inventors have recognized that the voltage across the capacitor may be used to appropriately control the resonant tank circuit. Examples of suitable resonant tank circuits include LC resonant tank circuits, LLC resonant tank circuits, LLCC resonant tank circuits, and the like.

[0014] The sampling circuit may be adapted to set the sampling time equal to the sum of the time at which the switch drive signal changes and the time delay.

[0015] Preferably, the sampling time depends on the falling edge of the gate driving signal.

[0016] The resonant inverter may further comprise a peak measurement module adapted to determine a peak value of the electric feedback parameter, wherein the sampling circuit is adapted to adjust the value of the sampled electric feedback parameter in dependence on the time delay and the determined peak value of the magnitude of the electric feedback parameter.

[0017] By modifying the previously sampled voltage in this way, the electrical feedback parameter is sampled by the sampling circuit at a moment when no switching action is currently occurring in the resonant inverter. Therefore, there is no interference (e.g., noise or current injection) that may affect the value of the electrical feedback parameter. This improves the accuracy of the sampled voltage.

[0018] The timing module may include: a slope detection circuit adapted to detect a slope of the first switch output; and a timer adapted to time a difference between a change in the switch drive signal and a corresponding slope of the first switch output.

[0019] In other embodiments, the timing module includes an input monitoring circuit adapted to determine an input voltage received at an input node and to calculate a time delay based on the determined input voltage.

[0020] According to some embodiments, the first switch is a first high-side switch, the second switch is a first low-side switch, and the first switch and the second switch are connected in series between the input node and a ground or reference voltage.

[0021] The resonant inverter may be adapted such that: the switch network further comprises: a third switch and a fourth switch, the third switch being a second high-side switch, the fourth switch being a second low-side switch, the third switch and the fourth switch being connected in series between the input node and the ground or reference voltage, wherein the second switch output is defined by a node between the third switch and the fourth switch; and the resonant tank is connected between the first switch output and the second switch output. Therefore, the switch network may be a full-bridge (FB) switch network.

[0022] An AC / DC PFC resonant inverter is proposed herein, comprising: an AC input; an AC rectifier adapted to rectify the AC input to provide an input for conversion; and any resonant inverter described herein.

[0023] The present invention also provides an LED driver, comprising: any previously claimed resonant inverter, and an isolation transformer at a first switch output of the resonant tank circuit, wherein a secondary side of the isolation transformer is used to drive an LED load.

[0024] As is known in the art, the primary side of the isolation transformer may be used as the inductor of the resonant tank circuit.

[0025] The present invention also proposes a conversion method, comprising: receiving an input for conversion at an input node; operating a switch network connected to the input node, the switch network comprising at least a first switch and a second switch, wherein the first switch output is defined by a node located between the first switch and the second switch; providing an electrical feedback parameter from a resonant tank circuit coupled to the first switch output; sampling the electrical feedback parameter provided by the resonant tank circuit at a sampling time; generating a switch drive signal according to the sampled electrical feedback parameter, the switch drive signal indicating the desired switching state of the first switch and the second switch; controlling the switching state of the first switch and the second switch in response to a gate drive signal, wherein a change in the switching state of the first switch and the second switch causes a change in the first switch output; and determining a time delay between a change in the switch drive signal and a corresponding change in the first switch output, wherein the sampling time depends on the change in the switch drive signal, and the step of sampling the electrical feedback parameter comprises: adjusting the sampling time and / or the value of the sampled electrical feedback parameter according to the time delay.

[0026] In an embodiment, the electrical feedback parameter comprises a voltage across a capacitor of the resonant tank circuit.

[0027] The step of sampling preferably includes setting the sampling time equal to the sum of the time at which the switch drive signal changes and the time delay.

[0028] The method may further comprise determining a peak value of the electrical feedback parameter, wherein the step of sampling comprises adjusting the value of the sampled electrical feedback parameter as a function of the time delay and the determined peak value of the electrical feedback parameter magnitude.

[0029] These and other aspects of the invention will be apparent from and elucidated with reference to the embodiment(s) described hereinafter. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] For a better understanding of the invention, and in order to more clearly show how the same may be carried into effect, reference will now be made, by way of example only, to the accompanying drawings, in which:

[0031] Figure 1 A resonant inverter according to an embodiment of the present invention is shown;

[0032] Figure 2 A resonant inverter for a resonant converter according to an embodiment of the present invention is shown;

[0033] Figure 3 An AC switch network for a resonant inverter according to an embodiment of the present invention is shown;

[0034] Figure 4 illustrates, in component form, a delay between a change in a switch drive signal and a response of the output of the switching network to the change in the switch drive signal;

[0035] Figure 5 graphically illustrating a delay between a change in a switch drive signal and a response of an output of a switching network to the change in the switch drive signal;

[0036] Figure 6 shows the relationship between the input voltage to a resonant inverter and the length of the delay between indicating a change in switch configuration and the output responding to the command;

[0037] Figure 7 Components of a resonant inverter are shown, including a timing module for determining a delay length; and

[0038] Figure 8 A method according to an embodiment of the present invention is shown. DETAILED DESCRIPTION

[0039] The present invention will be described with reference to the accompanying drawings.

[0040] It should be understood that the detailed description and specific examples, although indicating exemplary embodiments of the device, system and method, are only for illustrative purposes and are not intended to limit the scope of the invention. These and other features, aspects and advantages of the device, system and method of the present invention will become better understood from the following description, the appended claims and the accompanying drawings. It should be understood that the drawings are only schematic and are not drawn to scale. It should also be understood that the same reference numerals are used throughout the drawings to indicate the same or similar parts.

[0041] The present invention provides a resonant inverter for a resonant converter, comprising a switch network and a resonant tank circuit. The switch network is controlled by a control circuit, which responds to a sampled electrical feedback parameter provided by the resonant tank circuit. In response to a measured time delay between the control circuit indicating a desired switch state of the changing switch network and the output of the desired switch network in response to the change, the value of the sampled electrical feedback parameter or the time at which the electrical feedback parameter is sampled is modified.

[0042] The present invention relies on the recognition that, in order to improve power factor correction, it is desirable for the control circuit to respond to changes in the output of the switching network. However, the inventors have recognized that, for example with low voltage rails, it is difficult to measure and respond to changes in the output of the switching network because the changes may be extremely small. It will be appreciated herein that the desired sample (value) may be obtained by modifying the response of the sampling circuit (e.g., the sampling time or the value of the sample) based on the measured time delay.

[0043] For example, embodiments may be used to drive LED devices or any other element where a consistent DC output with good power factor properties from an AC source is desired.

[0044] Figure 1 is a block diagram showing a resonant inverter 1 according to an embodiment of the present invention.

[0045] The resonant inverter 1 includes a switch network 11 and a resonant tank circuit 12. The switch network 11 and the resonant tank circuit 12 receive an input V for conversion. in , and generates an AC output V out The resonant tank circuit 12 also provides an electrical feedback parameter V fb , such as feedback voltage. The electrical feedback parameter provides information about the AC output V out information, and may include the voltage across the capacitor of the resonant circuit 12.

[0046] Suitable embodiments of the switching network 11 and the resonant tank converter 12 are well known in the art, although suitable embodiments will be described later.

[0047] Generally speaking, the switch network 11 provides an output 11a at a first switch output node SN1 to the resonant tank converter 12, which is used by the resonant tank converter to generate an alternating current (AC) output V out The switch network is connected to the input V in The output 11a at the first switching output node SN1 is switched between the voltage at the switching node SN1 and the ground or reference voltage GND.

[0048] Similarly, a resonant tank converter typically includes an LLC circuit and may otherwise be referred to as an LLC tank converter.

[0049] The sampling circuit 13 obtains the electrical feedback parameter V fb (“sampled feedback parameter”) cs This is performed at the time of sampling. Methods of obtaining samples of the feedback parameters are well known to the skilled person, as are components or circuits capable of obtaining such samples.

[0050] The sampling circuit 13 may be designed to repeatedly sample the electrical feedback parameter V whenever a switch of the switching network moves from a closed state to an open state or from an open state to a closed state, for example. fb Take samples.

[0051] The resonant inverter further includes a control circuit 14, which controls the operation of the switch network 11 (ie, the switches in the switch network). The control circuit 14 controls the electrical feedback parameter V obtained by the sampling circuit 13. fb Sample V cs The control circuit 14 generates a switch drive signal S for controlling the operation of the switch network 11. dr .

[0052] Switch drive signal S dr controllably between a "high" state and a "low" state (eg, 5V / 3.3V and 0V, respectively, although other values ​​are contemplated). The low state indicates that the output at the first switch output node is expected to be equal to the input V in , while a high state indicates that it is desired that the output at the first switch output node SN1 is equal to the ground / reference voltage (or vice versa).

[0053] As an example, the electrical feedback parameter V fb Can be compared with the reference feedback parameter V ref (such as a reference voltage) and used to control the switch drive signal S dr The frequency or time period of the switching (and therefore the frequency or time period of the switching performed by the switching network 11) is controlled. As known to the skilled person, the frequency of the switching controls the voltage / current supplied to the load driven by the resonant converter including the resonant inverter, i.e., the AC output Vout Parameters.

[0054] Other methods of controlling the switch network 11 in response to an electrical feedback parameter such as the voltage across a capacitor of the resonant tank circuit 12 are well known in the art. EP3414824A1 is an example of a document describing a suitable control method.

[0055] Because the sampling circuit 13 can repeatedly or iteratively sample the electrical feedback parameter, the control circuit can repeatedly or iteratively control the operation of the switching network (ie, provide a feedback loop system).

[0056] The control circuit 14 controls the operation of the switch network via the switch driver 15. Specifically, the control circuit 14 controls the conductivity of the switches of the switch network so as to define the switching cycle of the switch network. The switch driver 15 includes the necessary components to drive the switching of the switches within the switch network. The switch driver 15 may include, for example, a level shifter and a gate driver.

[0057] Sampling time (i.e., sampling circuit 13 for electrical feedback parameter V fb The sampling time depends on the switch drive signal S dr As an example, the sampling circuit 13 may detect a change in the switch drive signal S dr The electrical feedback parameters are sampled based on the edge of the

[0058] More specifically, when the switch driving signal instructs the switch network to switch the voltage at the first switch output node from the ground / reference voltage GND to the input voltage V in When the sampling circuit 13 detects the switch drive signal S dr The edge of the electrical feedback parameter V fb Take samples.

[0059] In another example, when the switch driving signal instructs the switch network to change the voltage at the first switch output node from the input voltage V in When the sampling circuit 13 detects the switch driving signal S dr The electrical feedback parameters are sampled based on the edge of the

[0060] However, the present inventors have recognized that it is desirable to obtain an electrical feedback parameter V in response to a change in the output of the switching network (ie, a change in the voltage at the first switching output node SN1). fb This enables the control circuit to dynamically adjust the switching frequency of the switching network on a cycle-by-cycle basis. This improves the power factor of the entire resonant inverter.

[0061] In particular, the control circuit may be adapted to control the switch network so that the (corrected) sampled V cs The curve of voltage over time produces a perfect (positive) sinusoidal waveform. This can be performed with reference to the mains AC input, for example such that the frequency of the curve of the sampled Vcs voltage matches the frequency of the mains input. Since these sampled feedback parameters represent the amplitude of the energy (current) extracted from the mains, this in turn means a sinusoidal input current, as desired, to meet the PF requirement.

[0062] In contrast, if the control circuit relies on switching the switch drive signal S dr If the electrical feedback parameter sampling value at the time of the control circuit is incorrect, the operation of the control circuit will be based on the wrong feedback parameter. By accurately determining the feedback parameter at the time when the actual value output of the control circuit switches, the power factor of the resonant inverter can be improved by appropriate control via the control circuit.

[0063] It is not desirable to sample the electrical feedback parameter in direct response to changes in the output of the control circuit because the input V in may be close to zero (for example, if the input signal V in This will make it difficult to detect when the output of the control circuit changes from ground to V in The slope of the change (because when the input signal V in Close to zero the change may be imperceptible).

[0064] There are several reasons why it is desirable to sample the electrical feedback parameter to reflect its value when a change in the output of the switching network is executed (at SN1).

[0065] Firstly, a change in the output of the switching network marks an internal resonant tank state transition, which relates to the energy transferred by the resonant tank circuit to its output. Thus, by obtaining a feedback parameter value reflecting the time of the change in node SN1, a better and more precise control of the energy transfer is obtained, which translates into better tracking of the mains input of the improved PFC (i.e., control thereof) (e.g., compared to obtaining the value of the switch drive signal S when the switch drive signal S is changed). dr The value of the feedback parameter is compared when it changes).

[0066] In addition, compared with the time when the value at the node SN1 changes, when the switch drive signal S dr When V changes fb The signal amplitude may be low. Specifically, near the zero crossing point of the mains, when the switch drive signal changes, V fb The voltage is so close to zero, and can even go negative at times, which makes the measurement more difficult. You can add V fbThe offset in the sensing / measuring circuit is used to be able to measure negative values. Therefore, more errors can be expected, such as measurement errors due to low-amplitude interference / due to offset, etc. The value change at the node SN1 (i.e. the switching element's response to the switch drive signal S dr Sampling at the time of responding) has fewer of the aforementioned disadvantages, namely, V fb The signal amplitude is larger, will not become negative, and will likely be higher than the switch drive signal S dr Sampling the same signal at varying times is a more accurate measurement of the input signal that is fed to the controller.

[0067] Therefore, the problem is how to accurately obtain the output switching of the control circuit (for example, switching from the ground voltage GND to the input voltage V in ) time.

[0068] The present inventors have solved this problem by determining the value of the time delay during operation of the resonant inverter.This enables a cycle-by-cycle correction of the sampled feedback parameters, thereby providing more accurate feedback parameters for controlling the operation of the switching network.

[0069] The inventors have also recognized that the delay time Tdelay as the electrical feedback parameter V fb varies as a function of the magnitude of , which in turn depends on the input voltage V supplied to the resonant inverter in For lower input voltage V in , which delay is smaller than for higher input voltages. By determining the time delay during operation of the resonant inverter, the current (variable) value of the time delay can be obtained and thereby used to more accurately control the switching of the switching network.

[0070] The timing module 16 is adapted to determine the output switch drive signal S dr The control circuit 14 and the switch network 11 respond to the switch drive signal S dr The delay is caused by, for example, propagation delays through the switch driver 15 and / or the (parasitic) capacitance in the switch network 11 or the resonant circuit 12, which slows down the output provided by the switch network to the switch driver signal S. dr These delays are explained in more detail later.

[0071] The timing module 16 monitors components or parameters of the resonant inverter in order to determine the time delay, suitable embodiments of which will also be described later. An example of a parameter of the resonant inverter is the voltage present at the node SN1.

[0072] The sampling circuit 13 is adapted to modify the value of the sample obtained or the sampling time in response to the value of the time delay determined by the timing module. This is to modify the value of the sample obtained or the sampling time after the output of the switching network 11 has been subjected to the switch drive signal S dr The step is performed by obtaining a value equivalent to or representative of the value of the electrical feedback parameter at a time when the change in the electrical feedback parameter is responded to (ie, taking into account the time delay).

[0073] In other words, it will be appreciated that the time delay may be variable such that the sampling circuit may be dynamically adapted to respond to changes in the time delay.

[0074] In a simple embodiment, the sampling time can be delayed by the determined time delay so that when the switch drive signal S dr The switch drive signal S dr The electrical feedback parameters are sampled in response to changes in the

[0075] In another embodiment, the sampled feedback parameter V cs The value of the voltage change dV cs modified (eg, they are summed) to obtain a value representing the switch drive signal S at the output of the switching network. dr The value of the electrical feedback parameter value at the time when the voltage change dV is responded to. cs Respond to time delays.

[0076] The voltage change dV can be calculated using the following formula: cs :

[0077]

[0078] Where T delay represents the determined time delay, V cs_peak represents the peak value of the electrical feedback parameter, and T s_ctrl represents the switching cycle of the switching network (which is controlled by the control circuit 14).

[0079] The inverter 1 may further comprise a peak measurement module 17 adapted to determine a peak value (ie a maximum value) of the electrical feedback parameter. Suitable examples of peak measurement modules will be well known to the skilled person.

[0080] By modifying the previously sampled voltage in this way, the electrical feedback parameter is sampled by the sampling circuit at a moment when no switching action is currently occurring in the resonant inverter. Therefore, there is no interference / only negligible interference (e.g., noise or current injection) that may affect the value of the electrical feedback parameter. The sampled feedback parameter can then be compensated using additional inputs (e.g., the peak value and switching period of the electrical feedback parameter), thereby modifying the sampled value so that it reflects the value of the electrical feedback parameter as if it were sampled at a delayed target moment that coincides with the rising edge at the first switch input node SN1 (which may have interference). In this way, a clean feedback parameter for the target moment and with the correct level is obtained.

[0081] In other words, the proposed method provides a sampled feedback parameter reflecting a sample of the electrical feedback parameter at the point where the output of the switching network changes.

[0082] The sampling circuit 13 and the control circuit 14 may be integrated into the same component (eg, a microcontroller or a microprocessor).

[0083] The timing module 16 may not be able to determine the time delay between the most recent change in the switch drive signal and the change in the output of the switch network. in This may occur when the voltage amplitude is very low or zero (which will cause the output of the switching network to also be very low or zero) and the slope detection of the output of the switching network fails.

[0084] In this case, the most recently obtained time delay (eg, in a previous cycle of switching) may be used to modify the sampling time or the value of the sampled electrical feedback parameter.

[0085] Although not shown, the resonant converter 1 may also include an AC input and an AC rectifier. The AC input may, for example, include a connection for connecting to a mains power supply. The AC rectifier rectifies the signal provided by the AC input to supply as an input V to the resonant inverter in .

[0086] Figure 2 is a circuit diagram showing a switching network 21 and a resonant tank circuit 22 in the context of a resonant converter 20 for use in an embodiment of the present invention. Figure 2 shows an AC output V for using the resonant tank circuit 22 out To provide DC output V bus Other components of the resonant converter 20.

[0087] Although the operation of the resonant converter 20 will be readily understood by a skilled person, a brief description will be provided below for the sake of clarity.

[0088] The switch network 21 includes a switch connected in series to the input voltage V (provided at the input node N1). in The first switch S1 and the second switch S2 are connected to the ground or reference voltage GND. Therefore, the first switch S1 is a first high-side switch and the second switch S2 is a first low-side switch. The first switch output node SN1 provides the output of the resonant tank circuit.

[0089] The operation of the first switch S1 and the second switch S2 is controlled by a control circuit (not shown), for example via a switch driver (also not shown), as is well known to the skilled person.

[0090] The resonant tank circuit 22 is an LLC tank circuit, although other examples are also contemplated. The resonant tank circuit here includes a resonant inductor Ls and a resonant capacitor Cs connected in series to form a series resonant tank Ls, Cs. The resonant tank circuit 22 also includes a transformer formed by a first / primary side inductor Lm (connected in series with the resonant inductor Ls and the resonant capacitor Cs) and a second / secondary side inductor (formed as two sub-inductors L21, L22). The resonant inductor Ls, the resonant capacitor Cs and the first side inductor Lm form an LLC circuit of an LLC tank circuit, as is well known in the art. As the skilled person will appreciate, the term "inductor" is used synonymously with the term "winding" herein.

[0091] The current induced by the first side inductor Lm in the second side inductor L21, L22 (i.e., the alternating signal output by the resonant tank circuit) is rectified by the output rectifier D1, D2. Here, the output rectifier is a center-tapped output rectifier with full-wave rectification, although this can be replaced by a bridge rectifier (for which a center tap is not required, i.e., the second side inductor L21, L22 can be a continuous inductor).

[0092] The rectified output is smoothed by capacitor C bus smoothing, thus providing for the load R load The basic DC voltage of the power supply. Load R load It may for example comprise an LED arrangement, for example formed of one or more strings or one or more LEDs.

[0093] It should be noted that the load R load It may be resistive (as shown). However, the skilled person will appreciate that other load types may be used as the load R load , for example, a second switch mode converter connected to another resistive load (such as a buck converter with an LED load connected to its output), which in effect acts as a constant power load. Other load types may include constant current loads or constant voltage loads.

[0094] The skilled person will appreciate that the switching network 21, the resonant tank circuit 22, the output rectifiers D1, D2 and the smoothing capacitor C bus The configuration means that the series resonant tank Ls, Cs and the load R load (Connect to V bus ) together actually act as a voltage divider.

[0095] The impedance of the resonant tank Ls, Cs will change in response to the frequency change of the signal provided at the first switch output node SN1, which itself responds to the switching frequency of the first switch S1 and the second switch S2. Therefore, the control circuit (not shown) can control the output to the load R by adjusting the switching frequency of the switching network (i.e., the first switch and the second switch). load voltage / current.

[0096] Typically, the switch network 21 is operated so that the duty cycle of the signal at the first switch output node SN1 is approximately 50%. It is also known that the control circuit introduces a predetermined delay (otherwise known as "non-overlap time" or "dead time") between switching the first switch and switching the second switch (when changing the value at the first switch output node SN1) to prevent the input V in Short to ground / reference voltage GND.

[0097] In fact, Figure 2 A typical or known example of a half-bridge series resonant inverter is shown. Other suitable resonant inverters are known to the skilled person, such as a full-bridge series resonant inverter, a half-bridge parallel resonant inverter and a full-bridge parallel resonant inverter.

[0098] The voltage across the resonant capacitor Cs of the resonant tank circuit 22 can be used as the electrical feedback parameter V fb The control circuit may track this voltage in order to provide a smooth oscillating current through the resonant tank circuit, for example matching the mains current, to improve the power factor of the overall resonant converter. Such steps will be known to the skilled person.

[0099] Figure 3 An alternative embodiment of the switch network 31 is shown, for example, instead of Figure 2 The switching network 21 is shown in FIG.

[0100] The switch network is different from the previously described switch network in that it also includes a switch connected in series at the input node N1 (providing the input voltage V in ) and a ground or reference voltage GND, a third switch S3 as a second high-side switch and a fourth switch S4 as a second low-side switch. The second switch output SN2 is defined by a node between the third switch and the fourth switch.

[0101] The resonant tank circuit 22 is then connected between the first switching output SN1 and the second switching output SN2. The voltage across the resonant capacitor Cs can still be used as the electrical feedback parameter V fb .

[0102] In fact, Figure 3 A typical or known example of a full-bridge series resonant inverter is shown.

[0103] Figure 4 The control circuit 44, the switch driver 45 and the switch network 41 are shown for better understanding the switch drive signal S dr The output V of the switching network 41 changes with SN1 The reason for the time delay between responses.

[0104] The switch network 41 here comprises a first switch S1 and a second switch S2 connected in series between an input node N1 and a ground or reference voltage GND. A first switch output node SN1 is defined between the first switch and the second switch.

[0105] Switch drive signal S dr There is a propagation delay path from the output of the control circuit through the switch driver and switch S2 to the first switch output node SN1. Therefore, the response at the first switch output node is delayed compared to the output of the instruction to perform the switching action "open" depending on the resonant tank current I according to the following formula SN1 The instantaneous magnitude of and the (parasitic) capacitance value C of any (multiple) capacitors connected to node SN1 SN1 :

[0106]

[0107] C SN1 The capacitance value may be partially parasitic (eg, as part of the drain-source capacitance of both S1 and S2 ) and / or partially physically present as a capacitor placed (externally) at node SN1 (not shown and not required).

[0108] Because V sn1 The slope of is therefore not constant over time (due to the resonant tank current I SN1 's instantaneous amplitude), so different "latencies" can be observed, e.g. for a "steep slope" this delay is smaller compared to a more "flat slope".

[0109] An additional intentional delay may be introduced by introducing a delay between the control signal for the first switch S1 and the control signal for the second switch S2. This delay may be provided to prevent the input V inis connected to the ground / reference voltage GND via the first switch and the second switch. However, it should be noted that if the switch drive signal S dr After the corresponding control signal for another switch is generated, the switch drive signal S dr There will be no such delay between that and the corresponding change in the output.

[0110] As mentioned above, in response to the change in the desired conductivity of the switch of the switching network, that is, the switch drive signal S dr The change of the electrical feedback parameter V fb of sampling.

[0111] Figure 5 shows the switch drive signal S dr The change of the signal S at the first switch output node SN1 SN1 The time delay between changes in T delay . Figure 5 The electrical feedback parameter V during this time period is also plotted. fb curve.

[0112] It can be seen that the switch drive signal S dr At time t 1 and the voltage at the first switch output node SN1 changes at a later time t 2 (This change is defined as occurring at 50% of the slope). Therefore, there exists a value equal to t 2 -t 1 Time delay T delay This results in the signal S SN1 The electrical feedback parameter at the time of the change is related to the instruction S of changing the first switch output node dr There is a significant difference dVcs between the electrical feedback parameters at the time. The difference dVcs is when the signal S SN1 The electrical feedback parameter V at the point where the change fb The voltage V 2 And when the switch drive signal S dr The electrical feedback parameter V at the point where the change fb The voltage V 1 The difference between.

[0113] It has been explained previously how the delay time Tdelay can be used as an electrical feedback parameter V fb varies as a function of the magnitude of , which in turn depends on the input voltage V supplied to the resonant inverter in For lower input voltage V in , the delay is smaller than for higher input voltages.

[0114] Input voltage V inIt may not be a constant voltage source. For example, the input voltage V in It can be the rectified mains voltage (ie, varies as a function of time). Therefore, the input voltage V in The value of can vary as a function of time (synchronized with the mains voltage). This means that for V in For different values ​​of , the delay time Tdelay will change over time. Therefore, the embodiment preferably continuously updates the calculated delay time.

[0115] Figure 6 is the input voltage V in The magnitude of (x-axis, measured in volts) versus the time delay T delay ) and the length of the input voltage (y-axis, measured in seconds). It can be seen that at low input voltages, the time delay is initially high, drops at mid-range voltages, and then increases again at high-range voltages.

[0116] It will be appreciated that if the relationship between the magnitude of the input voltage and the length of the time delay is known, then the time delay T delay The length can be measured directly by the input voltage V in The amplitude of the signal is determined by applying a function to the measured amplitude.

[0117] Thus, although not shown, the timing module may include an input monitoring circuit adapted to determine an input voltage received at an input node and calculate a time delay based on the determined input voltage.

[0118] Figure 7 A timing module 76 is shown for use in an embodiment of the present invention. The timing module 76 is shown in the context of other components of a resonant inverter.

[0119] The timing module 76 includes a slope detection circuit 76a adapted to detect the slope of the voltage at the first switch output node SN1 and generate a slope signal S in response to the detected slope. slope .

[0120] The timing module 76 also includes a timer 76b, which is adapted to time the difference between the time when the switch drive signal indicates a change (generated by the control circuit 14) and the time when the detected slope is detected. The time when the switch drive signal indicates a change in the first switch output node will be known from the control circuit 14. For example, the control circuit may change the switch drive signal S dr A trigger for timer 76b is generated at the point in time.

[0121] The timing module 76 thus actually determines the time delay by direct measurement.

[0122] Figure 7 Also shown is a peak measurement module 17 for capturing the maximum value of the electrical feedback parameter.

[0123] In a simple example, where the electrical feedback parameter is a voltage signal, the peak measurement module may include a diode and a large capacitor (e.g., ~100 pf) connected in series between the electrical feedback parameter and the ground / reference voltage. The anode of the diode may be connected to the electrical feedback parameter, while the cathode is connected to one side of the large capacitor. Thus, the voltage across the capacitor will be equal to the peak value of the electrical feedback parameter.

[0124] Other suitable examples will be apparent to the skilled person, for example the processor is adapted to iteratively sample the electrical feedback parameter and select the maximum sampled value of the electrical feedback parameter as the maximum value of the electrical feedback parameter. This approach may be preferred for improved accuracy.

[0125] Thus, the peak measurement module 17 may be implemented using analog or digital components.

[0126] In any of the foregoing embodiments, different elements may be distributed or implemented using different components of the resonant converter / inverter. For example, a single microprocessor may contain some or all elements of the control circuit, sampling circuit, and timing module.

[0127] Figure 8 A conversion method 800 according to an embodiment is shown.

[0128] The conversion method 800 comprises a first step 801 of receiving an input for conversion at an input node.

[0129] The conversion method 800 further comprises a second step 802 of operating a switch network connected to the input node, the switch network comprising at least a first switch and a second switch, wherein a first switch output is defined by a node located between the first switch and the second switch.

[0130] The conversion method 800 further comprises a second step 802 of providing an electrical feedback parameter from a resonant tank circuit coupled to the first switch output.

[0131] The conversion method 800 further comprises a third step 803 of sampling an electrical feedback parameter provided by the resonant tank circuit at a sampling time.

[0132] The conversion method 800 further comprises a fourth step 804 of generating a switch drive signal in accordance with the sampled electrical feedback parameter, the switch drive signal being indicative of a desired switch state of the first switch and the second switch.

[0133] The conversion method 800 further includes a fifth step 805 of controlling the switching states of the first switch and the second switch in response to the gate drive signal, wherein changes in the switching states of the first switch and the second switch cause changes in the output of the first switch.

[0134] The conversion method 800 also includes a sixth step 806 of determining a time delay between a change in the switch drive signal and a corresponding change in the first switch output.

[0135] The sampling time depends on the variation of the switch drive signal, and the step of sampling the electrical feedback parameter includes adjusting the sampling time and / or the value of the sampled electrical feedback parameter according to the time delay.

[0136] A skilled person will be able to readily adapt the above method to appropriately perform the conversion to implement any of the concepts described herein, such as with reference to Figures 1 to 7 As described.

[0137] A skilled person will be able to easily develop a processing system for executing any of the methods described herein. Therefore, each step of the flowchart may represent a different action performed by a processing system and may be performed by a corresponding module of the processing system.

[0138] Thus, embodiments may utilize a processing system. A processing system may be implemented in many ways using software and / or hardware to perform the various functions desired. A processor is an example of a processing system that employs one or more microprocessors that may be programmed using software (e.g., microcode) to perform the desired functions. However, a processing system may be implemented with or without a processor, and may also be implemented as a combination of dedicated hardware that performs some functions and a processor (e.g., one or more programmed microprocessors and associated circuits) that performs other functions.

[0139] Examples of processing system components that may be employed in various embodiments of the invention include, but are not limited to, conventional microprocessors, application specific integrated circuits (ASICs), and field programmable gate arrays (FPGAs).

[0140] In various implementations, a processor or processing system may be associated with one or more storage media such as volatile and non-volatile computer memory (such as RAM, PROM, EPROM, and EEPROM). The storage media may be encoded with one or more programs that perform the desired functions when run on one or more processors and / or processing systems. The various storage media may be fixed within the processor or processing system, or may be transportable so that one or more programs stored thereon can be loaded into the processor or processing system.

[0141] It will be understood that the disclosed method is preferably a computer-implemented method. Therefore, the concept of a computer program is also proposed herein, and the computer program includes a code module for realizing any described method when the program is run on a processing system such as a computer. Therefore, the different parts, rows or blocks of the code of the computer program according to the embodiment can be run by a processing system or a computer to perform any described method herein. In some alternative implementations, the function pointed out in the frame may not occur in the order pointed out in the figure. For example, according to the function involved, the two frames shown in succession can actually be run substantially simultaneously, or these frames can sometimes be run in reverse order.

[0142] By studying the drawings, the specification and the appended claims, those skilled in the art can understand and implement variations of the disclosed embodiments when practicing the claimed invention. In the claims, the word "comprising" does not exclude other elements or steps, and the word "one" or "an" does not exclude multiple. A single processor or other unit can implement the functions of several items recorded in the claims. The mere fact that certain measures are recorded in mutually different dependent claims does not indicate that the combination of these measures cannot be used advantageously. If a computer program is discussed above, it can be stored / distributed on an appropriate medium, such as an optical storage medium or solid-state medium provided with or as part of other hardware, but can also be distributed in other forms, such as via the Internet or other wired or wireless telecommunications systems. If the term "suitable for" is used in the claims or the specification, it should be noted that the term "suitable for" is intended to be equivalent to the term "configured to". Any figure mark in the claims should not be interpreted as limiting the scope.

Claims

1. A resonant inverter (1), comprising: Input node (N1) for receiving the input voltage (V in ); A switch network (11) is connected to the input node, the switch network comprising at least a first switch (S1) and a second switch (S2) coupled in series, wherein the first switch output (S SN1 ) is defined by a node (SN1) located between the first switch and the second switch; A resonant tank circuit (12, 22) coupled to the first switch output and adapted to output an alternating signal (V out ), where the electrical feedback parameter (V fb ) is provided by the resonant tank circuit; A sampling circuit (13) adapted to sample the electrical feedback parameter provided by the resonant tank circuit at a sampling time; A control circuit (14) for generating a switch drive signal (S) according to the sampled electrical feedback parameter dr ), the switch drive signal indicates a desired switch state of the first switch and the second switch; a switch driver (15) adapted to control the switch states of the first switch and the second switch in response to a gate drive signal, wherein a change in the switch states of the first switch and the second switch causes a change in the output of the first switch; as well as a timing module (16) adapted to monitor at least the voltage at the node (SN1) of the resonant inverter to determine a time delay between a change in the switch drive signal and a corresponding change in the first switch output, The sampling time depends on the variation of the switch driving signal, and the sampling circuit is adapted to adjust the sampling time and / or the sampled value of the electrical feedback parameter according to the time delay.

2. The resonant inverter (1) according to claim 1, wherein the electrical feedback parameter comprises the voltage across a capacitor (Cs) of the resonant tank circuit.

3. The resonant inverter (1) according to claim 1 or 2, wherein the sampling circuit (13) is suitable for setting the sampling time to be equal to the sum of the time when the switch drive signal changes and the time delay.

4. The resonant inverter according to any one of claims 1 to 3, wherein the sampling time depends on the gate drive signal (S dr )’s falling edge.

5. The resonant inverter according to any one of claims 1 to 2, further comprising a peak measurement module (17), the peak measurement module being adapted to determine a peak value of the electrical feedback parameter, wherein the sampling circuit is adapted to adjust the value of the sampled electrical feedback parameter according to the determined peak value of the time delay and the amplitude of the electrical feedback parameter.

6. A resonant inverter according to any one of claims 1 to 5, wherein the timing module (76) comprises a slope detection circuit (76a) and a timer (76b), the slope detection circuit being suitable for detecting the slope of the first switch output, and the timer being suitable for timing the difference between the change of the switch drive signal and the corresponding slope of the first switch output.

7. The resonant inverter of any one of claims 1 to 5, wherein the timing module comprises an input monitoring circuit adapted to determine an input voltage received at the input node and to calculate a time delay based on the determined input voltage.

8. A resonant inverter according to any one of claims 1 to 7, wherein the first switch (S1) is a first high-side switch, the second switch (S2) is a first low-side switch, and the first switch and the second switch are connected in series between the input node and ground or a reference voltage (GND).

9. The resonant inverter according to claim 8, wherein: The switch network (31) further comprises a third switch (S3) and a fourth switch (S4), the third switch being a second high-side switch and the fourth switch being a second low-side switch, the third switch and the fourth switch being connected in series between the input node and the ground or reference voltage (GND), wherein a second switch output is defined by a node located between the third switch and the fourth switch; and The resonant tank circuit (22) is connected between the first switch output and the second switch output.

10. An AC / DC PFC resonant inverter, comprising: AC input; an AC rectifier adapted to rectify the AC input to provide an input for conversion; as well as A resonant inverter (1) as claimed in any one of the preceding claims.

11. A resonant converter, comprising: A resonant inverter (1) according to any one of the preceding claims; as well as An output rectifier (D1, D2) is adapted to rectify the alternating signal output by the resonant tank circuit.

12. A conversion method (800), comprising: Receiving (801) input for conversion at an input node; Operate (802) a switch network connected to the input node, the switch network comprising at least a first switch and a second switch, wherein a first switch output is defined by a node located between the first switch and the second switch; providing (803) an electrical feedback parameter from a resonant tank circuit coupled to the first switch output; sampling the electrical feedback parameter provided by the resonant tank circuit at a sampling time (804); generating (805) a switch drive signal according to the sampled electrical feedback parameter, the switch drive signal indicating a desired switch state of the first switch and the second switch; controlling (806) the switch states of the first switch and the second switch in response to a gate drive signal, wherein changes in the switch states of the first switch and the second switch cause changes in the output of the first switch; and determining (807) a time delay between a change in the switch drive signal and a corresponding change in the first switch output, The sampling time depends on the change of the switch driving signal, and the step of sampling the electrical feedback parameter includes: adjusting the sampling time and / or the sampled value of the electrical feedback parameter according to the time delay.

13. The method of claim 12, wherein the electrical feedback parameter comprises a voltage across a capacitor of the resonant tank circuit.

14. The method according to claim 12 or 13, wherein the step of sampling comprises: The sampling time is set to be equal to the sum of the time when the switch driving signal changes and the time delay.

15. The method according to any one of claims 12 to 13, further comprising: determining a peak value of the electrical feedback parameter, The sampling step includes adjusting the sampled value of the electrical feedback parameter according to the time delay and the determined peak value of the amplitude of the electrical feedback parameter.

Images