Ac-dc converter and controller thereof

Abstract

The application provides an AC-DC converter and a controller thereof, and relates to the technical field of AC-DC converters. The controller for the AC-DC converter comprises a rectifier circuit for converting an AC input voltage into a DC output voltage, and the controller uses control logic to control the rectifier circuit according to two or more operating modes. Each operating mode of the rectifier circuit has a voltage gain, and each operating mode determines the gain of the rectifier circuit. The controller selects one operating mode from the two or more operating modes based on at least one of an AC input voltage value and a required DC output voltage value. The AC-DC converter provides a wide range of DC output voltage and power factor correction. The controller can be used with AC-DC converter topologies such as boost converters, isolated boost converters, PWM converters, LLC resonant converters and LCC resonant converters. Through the controller, the AC-DC converter can achieve optimal performance within a wide voltage variation range.

Description

[0001] Related applications

[0002] This application claims priority to U.S. Provisional Patent Application No. 63 / 272,154, filed October 26, 2021, the disclosure of which is incorporated herein by reference in its entirety. Technical Field

[0003] This invention relates to the field of AC-DC converter technology, and more particularly to an AC-DC converter and its controller for implementing two or more operating modes, wherein each operating mode determines the gain of the converter rectifier circuit with power factor correction and provides a wide range of DC output voltages. Background Technology

[0004] Boost converters are typically used as AC-DC rectifiers to achieve power factor correction. The output voltage of a boost converter will be higher than the peak value of the input AC voltage. For typical applications, the AC voltage is changed from 90V to 264V to cover AC systems of 120V (60Hz) and 220V (50Hz). Therefore, the output voltage of the boost converter is typically regulated to 400V. Since (1) the load typically requires a voltage different from the boost output voltage (e.g., 400V) and (2) the load needs to be electrically isolated from the AC voltage, another DC-DC converter is needed to convert the 400V boost output voltage to the output voltage Vout. Figure 1 A typical circuit diagram is shown to achieve this goal using existing methods. The capacitor CBST is used as an energy storage capacitor to store energy to buffer pulsating input power from an AC power source. It contains an average voltage (DC voltage) of approximately 400V plus a frequency doubling ripple (120Hz for a 60Hz AC line and 100Hz for a 50Hz line). The peak value of the frequency doubling ripple voltage is typically around 10 to 20V, depending on the design requirements.

[0005] In some applications, the AC input voltage varies significantly, for example, from 90V to 264V, a ratio of 3:1. The output voltage also varies considerably. For example, if using… Figure 1The circuit charges the battery of an electric vehicle (EV), changing the battery voltage from 250V (when the battery is fully discharged) to 430V (when the battery is fully charged). Therefore, when the input voltage is at its lowest level (e.g., 90V) and the output voltage is at its highest level (e.g., 430V), the voltage gain is calculated as Vgain_max = 430V / 90V = 4.8. When the input voltage is at its highest level (e.g., 264V) and the output voltage is at its lowest level (e.g., 250V), the voltage gain is calculated as Vgain_min = 250V / 264V = 0.95. To meet the charging requirements of the EV battery, the voltage gain of the EV charger will vary within a range of 4.8 / 0.95 = 5, which is a very large range. Existing methods can only achieve optimal performance within a very narrow range. For example, the power supply will operate at its highest efficiency when the input voltage is 220V and the output battery voltage is between 330V and 380V. When the input voltage and battery voltage exceed this range, the efficiency of the EV charger will significantly decrease. Therefore, as mentioned above, when the input and output voltages have large variations, existing AC-DC converters cannot achieve optimal performance over a wide voltage variation range. Summary of the Invention

[0006] (a) Technical problems to be solved

[0007] To address the shortcomings of existing technologies, this invention provides an AC-DC converter and its controller, which solves the technical problem that existing AC-DC converters cannot achieve optimal performance over a wide voltage variation range.

[0008] (II) Technical Solution

[0009] To achieve the above objectives, the present invention provides the following technical solution:

[0010] In a first aspect, the present invention provides a controller for an AC-DC converter, comprising a rectifier circuit for converting an AC input voltage into a DC output voltage, the controller comprising:

[0011] Control logic that controls the rectifier circuit based on two or more operating modes;

[0012] Each of the two or more operating modes determines the gain of the rectifier circuit;

[0013] The controller selects an operating mode from two or more operating modes based on at least one of the AC input voltage value and the required DC output voltage value;

[0014] The AC-DC converter provides a wide range of DC output voltages with power factor correction.

[0015] Preferably, the operating modes include high-gain mode, low-gain mode, and zero-gain mode.

[0016] Preferably, the high-gain mode, low-gain mode, and zero-gain mode are alternately controlled by the controller.

[0017] Preferably, the controller controls the rectifier circuit to operate in the first and second modes;

[0018] In the first mode, the rectifier circuit operates for the first integer value of half a cycle of the AC input voltage, and in the second mode, the rectifier circuit operates for the second integer value of half a cycle of the AC input voltage.

[0019] Preferably, the DC output voltage includes a ripple voltage with a ripple frequency lower than the AC line frequency.

[0020] Preferably, the rectifier circuit uses an LLC converter;

[0021] in,

[0022] The controller controls the rectifier circuit in full-bridge operating mode, half-bridge operating mode, and non-operating mode.

[0023] The rectifier circuit operates in full-bridge mode during the first integer value of the AC power frequency half-cycle of the AC input voltage;

[0024] The rectifier circuit operates in half-bridge mode during the second integer value of the AC power frequency half-cycle of the AC input line voltage.

[0025] The rectifier circuit is in non-operating mode during the third integer value of the AC power frequency half-cycle of the AC input voltage.

[0026] Preferably, the DC output voltage of the AC-DC converter includes a low-frequency ripple voltage;

[0027] Among them, the frequency of the low-frequency ripple voltage is related to the frequency of the AC input line voltage.

[0028] Preferred,

[0029] When the input AC voltage is in the low voltage range, the rectifier circuit operates in full-bridge mode;

[0030] When the input AC voltage is in the high voltage range, the rectifier circuit operates in half-bridge mode;

[0031] When the input AC voltage is in a low voltage range, the output DC voltage can be adjusted to the required DC value by changing the gain of the rectifier circuit in full-bridge mode.

[0032] When the input AC voltage is in the high voltage range, the output DC voltage can be adjusted to the required DC value by changing the gain of the rectifier circuit in half-bridge mode.

[0033] Preferably, when the input AC voltage is between a low range and a high range, the rectifier circuit adjusts the output DC voltage to the desired value by alternating between full-bridge mode and half-bridge mode.

[0034] Preferably, the rectifier circuit operates in full-bridge mode during one integer value of the AC power frequency half-cycle of the AC input voltage, and ceases operation during another integer value of the AC power frequency half-cycle of the AC input voltage.

[0035] Preferably, when the rectifier circuit operates in full-bridge mode, the output DC voltage is adjusted to the desired value by changing the gain of the rectifier circuit.

[0036] Preferably, the output DC voltage is adjusted to the desired value by changing the ratio of the first integer value to the second integer value.

[0037] Preferably, the output DC voltage is adjusted to the desired value by changing the combination of changing the gain of the rectifier circuit and changing the ratio of the first and second integer values.

[0038] Preferably, the rectifier circuit operates in half-bridge mode during a first integer value of the AC power frequency half-cycle of the AC input voltage, and stops operating during a second integer value of the AC power frequency half-cycle of the AC input voltage.

[0039] Preferably, the output DC voltage is adjusted to the desired value by changing the gain of the rectifier circuit in half-bridge operating mode.

[0040] Preferably, the controller controls the rectifier circuit so that the rectifier circuit operates during the first part of the AC input voltage AC power frequency half-cycle, and does not operate during the second part of the AC input voltage AC power frequency cycle.

[0041] Preferably, the rectifier circuit operates when the instantaneous AC input voltage is at its peak value or within ±45 degrees of its peak value, and does not operate when the instantaneous AC input voltage is at the zero-crossing point or within ±30 degrees of the zero-crossing point.

[0042] Preferably, the output DC voltage is regulated by controlling the AC input power of the rectifier circuit during the time interval of the rectifier circuit's operation.

[0043] Preferably, the output DC voltage is adjusted by controlling the duration of the time interval during the operation of the rectifier circuit.

[0044] Preferably, during the AC power frequency half-cycle, the rectifier circuit operates during the first part of the AC input voltage half-cycle and does not operate during the other part of the AC power frequency half-cycle.

[0045] In a second aspect, the present invention provides an AC-DC converter, including the controller described above.

[0046] Preferably, the AC-DC converter is any one of a Boost converter, an isolated Boost converter, a PWM converter, an LLC resonant converter, and an LCC resonant converter.

[0047] (III) Beneficial Effects

[0048] This invention provides an AC-DC converter and its controller. Compared with the prior art, it has the following advantages:

[0049] The controller for an AC-DC converter in this invention includes a rectifier circuit that converts an AC input voltage to a DC output voltage. The controller uses control logic to control the rectifier circuit based on two or more operating modes. Each operating mode of the rectifier circuit has a voltage gain, and each operating mode determines the gain of the rectifier circuit. The controller selects an operating mode from the two or more operating modes based on at least one of the AC input voltage value and the desired DC output voltage value. The AC-DC converter provides a wide range of DC output voltage and power factor correction. This controller can be used with AC-DC converter topologies such as boost converters, isolated boost converters, PWM converters, LLC resonant converters, and LCC resonant converters. This controller enables the AC-DC converter to achieve optimal performance over a wide voltage range. Attached Figure Description

[0050] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0051] Figure 1 This is a circuit diagram of a Boost converter followed by an LLC converter for AC-DC power supplies, based on existing technology.

[0052] Figure 2 It is a circuit diagram of a boost converter with a voltage multiplier based on existing technology;

[0053] Figure 3 Circuit diagram of a full-bridge pulse width modulation (PWM) converter based on existing technology;

[0054] Figure 4 Based on the circuit diagram of the existing full-bridge LLC DC-DC converter;

[0055] Figure 5 The waveforms of AC input voltage, AC input current, and output voltage of an AC-to-DC converter with power factor correction (PFC) based on existing technology are shown.

[0056] Figure 6 This is a general circuit block diagram of an AC-DC rectifier with power factor correction according to one embodiment, showing the output energy storage capacitor and constant current load;

[0057] Figure 7A and 7B The simulated waveforms are for the embodiment operating normally in high-gain mode (Vo_avg=400V, Vo_rip_pp=16V, Pout=2,000W) and low-gain mode (Vo_avg=200V, Vo_rip_pp=16V, Pout=1000W), respectively.

[0058] Figure 8 A simulated waveform for sub-power frequency modulation according to one embodiment is shown, where N_high = 5, N_low = 2, Vo_avg = 342.7V, Vo_rip_pp = 92V, Pout = 1721W;

[0059] Figure 9 Simulated waveforms for sub-line frequency modulation with N_high=7, N_low=1, Vo_avg=375V, Vo_rip_pp=60V, Pout=1,876W are shown according to one embodiment.

[0060] Figure 10 Simulated waveforms for sub-power frequency modulation with N_high=2, N_low=2, Vo_avg=300V, Vo_rip_pp=78V, Pout=1500W are shown according to one embodiment;

[0061] Figure 11 Simulated waveforms for sub-power frequency modulation with N_high=2, N_low=5, Vo_avg=257V, Vo_rip_pp=112V, Pout=1,302W are shown according to one embodiment;

[0062] Figure 12Simulated waveforms of sub-power frequency modulation according to one embodiment are shown, with N_high=5, N_low=2, Gain_high=2, Gain_low=1.04, Vo_avg=345V, Vo_rip_pp=88.8V, and Pout=1732W.

[0063] Figure 13 Simulated waveforms of sub-double-line frequency modulation according to one embodiment are shown, with N_half_high = 5, N_half_low = 2, Vo_avg = 342.7V, Vo_rip_pp = 55V and Pout = 1716W;

[0064] Figure 14 The simulated waveform of sub-harmonic modulation according to one embodiment is shown, with N_half_high = 7, N_half_low = 1, Vo_avg = 375V, Vo_rip_pp = 38V and Pout = 1875W;

[0065] Figure 15 The simulated waveform of sub-harmonic modulation according to one embodiment is shown, with N_half_high = 2, N_half_low = 2, Vo_avg = 300V, Vo_rip_pp = 38V and Pout = 1502W;

[0066] Figure 16 The simulated waveform of sub-harmonic modulation according to one embodiment is shown, with N_half_high = 2, N_half_low = 5, Vo_avg = 275V, Vo_rip_pp = 66V and Pout = 1290W;

[0067] Figure 17 The simulated waveform of sub-power frequency modulation according to one embodiment is shown, with N_half_low = 6, N_half_zero = 2, Vo_avg = 150V, Vo_rip_pp = 55V and Pin_avg = 750W;

[0068] Figure 18 The simulated waveform of subharmonic modulation according to one embodiment is shown, with N_half_high = 4, N_half_low = 4, Vin = 100V, Vo_avg = 150V, Vo_rip_pp = 39V, Pin_avg = 750W and R_load = 30Ω;

[0069] Figure 19The simulated waveform of sub-double-line frequency modulation according to one embodiment is shown, where N_half_high = 2, N_half_low = 6, Vin = 120V, Vo_avg = 150V, Vo_rip_pp = 35V, Pin_avg = 750W and R_load = 30Ω;

[0070] Figure 20 A simulated waveform for subharmonic modulation according to one embodiment is shown, where N_half_low = 6, N_half_zero = 2, Vin = 200V, Vo_avg = 150V, Vo_rip_pp = 55V, Pin_avg = 750W, and R_load = 30Ω.

[0071] Figure 21A This is a circuit diagram of an LLC converter that can be used as an AC-DC rectifier with power factor correction, based on existing technology.

[0072] Figure 21B This is a control block diagram used to control LLC converters to achieve PFC operation;

[0073] Figure 22 This is a control block diagram of an AC-DC rectifier according to one embodiment;

[0074] Figure 23 The waveforms of the LLC converter under conventional control according to existing technology are displayed in PFC mode, where the x-axis is in degrees, and the waveforms of the rectified input voltage (top), current (middle), and input power (bottom) are also shown.

[0075] Figure 24 The waveform of the inner line frequency modulation implemented for an LLC converter according to one embodiment is shown, wherein the converter is turned on from 50 degrees to 130 degrees.

[0076] Figure 25 The waveform of the inner line frequency modulation implemented for an LLC converter according to one embodiment is shown;

[0077] Figure 26 The waveform of an inner line frequency modulation implemented for an LLC converter according to one embodiment is shown, wherein the converter is turned on from 60 degrees to 120 degrees.

[0078] Figure 27 The waveform of the inner line frequency modulation is shown according to one embodiment when the current is controlled to be constant;

[0079] Figure 28 The waveform shown is for inner line frequency modulation of a peak current of 1A, decreasing from 1.4A, according to one embodiment;

[0080] Figure 29 This is a control block diagram of an internal frequency modulation control strategy according to one embodiment. Detailed Implementation

[0081] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are described clearly and completely. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0082] Switching converters with two or more operating modes:

[0083] The embodiments of the present invention describe an AC-DC converter and its controller with a wide input and output voltage variation range, wherein the AC-DC converter has two or more voltage gains and achieves optimal operating conditions throughout the entire input and output voltage variation range.

[0084] Therefore, embodiments provide a power converter having two or more operating modes and producing two or more voltage gains, both or all of which achieve optimal operating conditions (e.g., high-efficiency operation), and a method for controlling the input power of the power converter so as to control the output power over a wide range, and the power converter always operating in an optimal state, i.e., in a high-efficiency or most efficient state when the converter produces different (e.g., high or low) output powers. According to embodiments, the control method is applied to an AC input and the input AC current follows the shape of the AC voltage to achieve power factor correction. The control method can be used to select operating modes to achieve power factor correction over a wide range of input voltage variations and output voltage variations, as well as at different power levels, thereby allowing the power converter to maintain high-efficiency operation in two or more operating modes. The output DC voltage contains a low-frequency ripple of approximately twice the AC voltage frequency. The input AC side and the output DC side are electrically isolated. The input voltage variation range can be at least a 2:1 ratio. For example, in one embodiment, the input voltage variation range can be a 3:1 ratio, for example from approximately 90V to approximately 264V.

[0085] As used in embodiments of the present invention, the terms “converter,” “switching converter,” “power converter,” “AC-DC converter,” “rectifier,” and “AC-DC rectifier” are used interchangeably and refer to topology-based converters such as, but not limited to, boost, PWM converters, full-bridge, half-bridge, LLC, LCL, and resonant converters. When the input of the converter is an AC voltage, the terms “rectifier” and “AC-DC rectifier” may be used.

[0086] As used in embodiments of the present invention, the terms “control” and “controller” are used interchangeably and can refer to control algorithms (e.g., logic, computer software stored on a non-transient computer-readable medium) and / or circuits (e.g., logic circuits, electronic hardware).

[0087] As used in embodiments of the invention, the term "substantially" in relation to values ​​or conditions refers to values ​​or conditions that are the same as or close to the desired or selected values ​​or conditions, such as those achievable within the tolerances of circuit components, control parameters, etc. By using the term "substantially," it is understood that it is not necessary to precisely achieve the listed characteristics, parameters, and / or values, but rather deviations or variations, including, for example, tolerances, measurement errors, limitations known to those skilled in the art regarding measurement accuracy, and other factors, may occur in quantities that do not preclude the effects that the characteristics, parameters, and / or values ​​are intended to provide. Features, parameters, and / or values ​​that are substantially absent (e.g., substantially removed, substantially zero) can be significant features that are within noise, below background, below the detection limit, or a small fraction (e.g., <1%, <0.1%, <0.01%, <0.001%, <0.00001%, <0.000001%, <0.0000001%). It should be understood that, in the embodiments of the present invention, a characteristic, parameter, and / or value referred to as "same as" another characteristic, parameter, and / or value may be substantially the same as another characteristic, parameter, and / or value.

[0088] The simulation described in this embodiment of the invention was performed using PSIM Professional version 2021b.1.7 (Powersim Inc., Troy, MI, USA).

[0089] A controller may be implemented to control the operation of the converter, and may include implementing a gain modulation strategy as described in embodiments of the present invention. The controller may perform one or more functions, such as, but not limited to, voltage and / or current sensing, generating voltage and / or current reference signals, power factor correction, and generating gate drive signals for switches (e.g., MOSFETs, IGBTs, etc.).

[0090] The controller may include an electronic processor and memory. The processor may be, for example, a computer or digital controller, such as a microcontroller unit (MCU), a field-programmable gate array (FPGA), etc. The processor may include processing power and an input / output (I / O) interface through which it can receive multiple input signals (e.g., voltage and / or current sensing signals, voltage and / or current reference signals) and generate multiple output signals (e.g., gate drive signals for switches). Memory is provided for storing data and instructions or code (i.e., algorithms such as controller algorithms, controller logic, software, etc.) that can be executed by the processor. Memory may include various forms of non-volatile (i.e., non-transient) memory, including flash memory or read-only memory (ROM), including various forms of programmable read-only memory (e.g., PROM, EPROM, EEPROM), and / or volatile memory including random access memory (RAM), including static random access memory (SRAM), dynamic random access memory (DRAM), and synchronous dynamic random access memory (SDRAM). Converters may include driver circuitry or devices to interface between the controller's output and the control (e.g., gate) terminals of semiconductor switches.

[0091] The memory stores executable code including control logic configured to control the overall operation of the converter according to a desired control strategy (e.g., the converter gain modulation strategy described in embodiments of the invention). For example, when executed by a processor, the control logic is configured to generate various gate drive signals for switching the converter in response to one or more input signals. The control logic may include programmable logic blocks to implement specific functions, such as, but not limited to, zero-crossing detection, error amplifiers, pulse width modulation (PWM), power factor correction (PFC), zero-voltage switching (ZVS), RMS voltage and / or current calculators, operating mode control logic, and startup and / or shutdown strategies. The memory may also store features, such as lookup tables accessible by the control logic. Non-limiting examples of control strategies or portions thereof that may be implemented individually or in various combinations in the controller of the embodiments described in the invention are provided. Figure 1 and Figure 2 As shown in the image. Figure 21B , 22 29 and / or strategies for controlling the rectifier circuit to achieve performance characteristics, such as, but not limited to, Figure 21B , 22 The waveform examples shown in 29 are examples of those. See also... Figure 7A , 7B 8~20 and 24~28.

[0092] The control method described in this invention can implement at least one modulation strategy. In one embodiment, the modulation strategy includes varying the voltage gain from one value in one AC cycle to another value in the next AC cycle, referred to herein as sub-power frequency modulation or sub-F-line modulation. This may include changing the converter's operating mode at a frequency below the line frequency (or AC line frequency, 50 Hz in Asia and Europe, and 60 Hz in North America). Operating modes may include high voltage gain, low voltage gain, and zero voltage gain. The sub-F-line modulation frequency (F-lineM) is below the AC frequency, for example, 10 Hz or 20 Hz.

[0093] In another embodiment, the modulation strategy includes changing the voltage gain from a value in the previous half-AC cycle to another value in the next half-AC cycle, referred to here as sub-frequency modulation.

[0094] In another embodiment, the modulation strategy includes changing the voltage gain over half an AC cycle, referred to here as inside-line frequency modulation.

[0095] In another embodiment, referred to as sub-switching frequency modulation or sub-Fs modulation, the converter's operating mode changes at a frequency below the switching frequency but above the power frequency. For example, the power frequency could be 50 Hz or 60 Hz, and the switching frequency could be 500 kHz. The sub-Fs modulation frequency (F_SM) could be, for example, approximately 20 kHz. During the sub-switching frequency modulation period T_SM, the converter operates according to one of three possible modes: high voltage gain, low voltage gain, and zero voltage gain.

[0096] According to an embodiment, the energy storage component can be used to maintain the output voltage at a selected DC level. The energy storage element, such as a capacitor, delivers additional power to the load when the instantaneous input power is lower than the load power, and stores the additional power when the instantaneous input power is greater than the load power.

[0097] AC-DC rectifiers are widely used in industrial applications. When the output power exceeds 75W, power factor correction (PFC) is required. In PFC, the input AC current is controlled to have the same shape and phase as the input AC voltage. In practical applications, the AC voltage is a sinusoidal waveform. Therefore, the AC current is also a sinusoidal waveform.

[0098] A conventional boost converter with a voltage multiplier, such as Figure 2 As shown. When capacitor C 12 When MOSFET S2 is short-circuited, the output voltage of the Boost converter is:

[0099] V_gain_low=Vboost_low / Vin=1 / (1–D) (1)

[0100] Where D is the duty cycle of switch S1. When MOSFET S2 is off (not conducting), the Boost converter operates in voltage doubler mode. The output voltage of the Boost converter is:

[0101] V_gain_high=Vboost_high / Vin=2 / (1–D) (2)

[0102] By controlling the on and off states of S2, the voltage doubler boost converter can produce two voltage gains at the same duty cycle. Note that in the example above, the voltage doubler boost converter has two possible operating modes.

[0103] Operating mode #1: When S2 is turned on and the voltage doubler Boost converter generates a voltage gain gain_low as shown in formula (1), the duty cycle is D.

[0104] Operating mode #2: When S2 is off and the voltage doubler Boost converter produces the voltage gain as shown in formula (2), with the same duty cycle as operating mode #1, gain_high = 2 * gain_low.

[0105] Boost converters are not intended to operate at very small duty cycles (e.g., less than about 30%) or very large duty cycles (e.g., greater than about 70%). Therefore, by turning S2 on and off in the voltage doubler Boost converter, as... Figure 2 As shown, a very wide range of operating gains can be achieved while maintaining the duty cycle within the desired range (between approximately 30% and approximately 70%).

[0106] For example, for a conventional boost converter, when D is between 30% and 70%, the voltage gain is from

[0107] Gain1=1 / (1–0.3)=1.43 (3.1)

[0108] to

[0109] Gain2=1 / (1–0.7)=3.33 (3.2)

[0110] The voltage gain variation range is:

[0111] Gain_range1=3.33 / 1.43=2.33 (3.3)

[0112] Using a voltage doubler converter, the voltage gain increases from [value missing] in both operating modes.

[0113] Gain1 = 1 / (1–0.3) = 1.43, when switch S2 is open (3.4)

[0114] to

[0115] Gain3 = 2 / (1–0.7) = 6.67. When switch S2 is off, (3.5)

[0116] Therefore, the voltage gain variation range is

[0117] Gain_range2=6.67 / 1.43=4.67 (3.6)

[0118] It is important to note that, such as Figure 2 The switching converter shown can provide two voltage gains with the same operating conditions in two operating modes, such as the same duty cycle in this case. In some cases, the term "same operating conditions" means similar switching frequencies of the resonant converter.

[0119] Figure 3 This is a circuit diagram of a traditional full-bridge PWM converter. In the circuit, capacitor C... b Used to block any possible DC voltage from the full-bridge output. When all four switches Q1, Q2, Q3, and Q4 are switched based on PWM control, the voltage gain is calculated as follows:

[0120] Gain_FB_PWM1=Vo / Vin=D*Ns / Np (4)

[0121] Where Np is the number of turns in the primary winding of the transformer, Ns is the number of turns in the secondary winding, and D is the duty cycle.

[0122] Figure 3 Another operating mode of the full-bridge PWM converter shown is where Q3 and Q4 are switched via PWM control, Q1 is always off, and Q2 is always on (no switching). Equivalently, under this control, the converter operates in half-bridge mode. The voltage gain calculation formula is: Gain_FB_PWM2=Gain_HB_PWM=Vo /

[0123] Vin=0.5*D*Ns / Np (5)

[0124] As can be seen from equations (4) and (5), with the same duty cycle D, the full-bridge PWM converter can produce two different voltage gains in two different operating modes.

[0125] Figure 4 This is a circuit diagram of a full-bridge LLC converter based on existing technology. In the diagram, C... r L r L pThe resonant elements are Q1, Q2, Q3, and Q4, which are switches in a full-bridge configuration. The secondary side is a full-wave rectifier with a diode bridge. Alternatively, a half-wave rectifier with a center-tapped transformer can be used. Furthermore, a synchronous rectifier (SR) can be used instead of diodes to reduce losses in the secondary circuit. Different secondary-side configurations do not affect the control strategy described in the embodiments of this invention.

[0126] According to the fundamental frequency analysis method (FHA), the approximate output voltage of a full-bridge LLC converter can be expressed by the following equation:

[0127]

[0128] Where n is the transformer turns ratio, f r f is the series resonant frequency. n The normalized frequency is K, the inductance ratio is Q, and the quality factor is Q.

[0129]

[0130] Similarly, another operating mode of the full-bridge LLC converter is when Q3 and Q4 operate under switching frequency modulation control. Q1 is always off, and Q2 is always on (no switching). This converter operates in half-bridge mode. Therefore, the voltage gain calculation formula is:

[0131]

[0132] From equations (6) and (7), it can be seen that the full-bridge LLC converter, such as Figure 4 As shown, the same switching frequency can be used to generate two voltage gains in different operating modes (full bridge and half bridge). One mode operates the LLC converter in full bridge mode, and the other operates the LLC converter in half bridge mode.

[0133] 1. Two voltage gains

[0134] The analysis above notes that some switching power supply converters, such as Figure 2 , 3 As shown in Figure 4, two voltage gains can be generated. More specifically, these converters have the following characteristics:

[0135] They have two operating modes, using the same control parameter values ​​to produce two different voltage gains, such as the same duty cycle (for PWM converters, Figure 2 , 3 or the same switching frequency (for resonant converters, Figure 4 Under the same input voltage and the same control parameters, they can produce two different output voltage values.

[0136] They operate near their optimal operating conditions in both operating modes. The term "optimal" means that the converter will operate at high efficiency or low voltage or current stress.

[0137] For example, if the duty cycle of a boost converter is about 50%, it can be considered to be in optimal operating condition. However, if the duty cycle is about 90%, it cannot be considered to be in optimal operating condition because the voltage and current stress on the switches would be very high.

[0138] Similarly, if the switching frequency of an LLC converter is close to its resonant frequency, it can be considered to be in optimal operating condition. However, if the switching frequency of an LLC converter is much higher than its resonant frequency, for example, two or three times the resonant frequency, it cannot be considered to be in optimal operating condition.

[0139] Additionally, for full-bridge PWM converters and full-bridge LLC converters, if all MOSFETs are always off, the converter does not operate, and the output voltage is zero. This operating mode is considered zero-gain mode. For boost converters, if the MOSFETs are always off, the output voltage will equal the input voltage, and the gain will be 1.

[0140] 1.1 Sub-power frequency control strategy

[0141] As is well known, for AC-DC rectifiers with power factor correction (PFC), the AC input current follows the AC input voltage, having the same phase and shape, such as... Figure 5 As shown. Since the input power varies with time, but the output load consumes a constant power, an energy storage element is required. This energy storage element is typically a large capacitor. For Figure 1 The Boost converter shown has an energy storage capacitor of C. BST Because of C BST Typically very large, C BST The voltage across the terminals is a DC value (Vo_avg) with a small low-frequency voltage ripple (Vo_rip_pp). The ripple frequency is twice the power frequency (100Hz or 120Hz). The value of Vo_avg is much larger than the value of Vo_rip_pp. For example, Vo_avg might be approximately 400V, while Vo_rip_pp might be approximately 10V to 20V. To adjust the output voltage over a wide range and eliminate low-frequency voltage ripple, a second-stage DC-DC converter (LLC converter, such as...) can be added. Figure 1 (As shown). Since the output voltage of the boost converter is always higher than the peak value of the input AC voltage, and the voltage gain variation of the LLC is usually limited, therefore, as Figure 1 The output voltage variation range Vo shown is finite.

[0142] This article describes a control technique called variable gain modulation control to achieve a very wide range of output voltage variations while ensuring that the switching converter (or rectifier) ​​operates at or near its optimal operating state.

[0143] The characteristics of variable gain modulation include:

[0144] (1) A switching power converter that operates in two or more voltage gain modes, such as a high-gain operating mode (gain value Gain_high) and a low-gain operating mode (gain value Gain_low), for converting AC voltage to DC voltage. The switching converter can also implement power factor correction (PFC).

[0145] (2) The energy storage capacitor at the output of the switching power converter is used to maintain the approximate DC voltage across the load.

[0146] (3) For both high-gain and low-gain operation, the switching power supply converter operates under optimal or near-optimal conditions (e.g., high-efficiency operation).

[0147] (4) The switching power supply converter can operate alternately in high-gain mode and low-gain mode according to the AC voltage cycle, for example, 20ms for a 50Hz system and 16.67ms for a 60Hz system. For example, the converter can run in high-gain mode for N_high AC cycles, then in low-gain mode for N_low AC cycles (where N_high and N_low are integers), and then return to high-gain operation mode.

[0148] (5) The output DC voltage contains a DC component and a low-frequency ripple component. The frequency of the low-frequency component depends on N_high and N_low, as well as the period of the AC voltage (T_line). For a 50Hz AC system, T_line = 20ms. If the converter operates for two AC line cycles in high-gain mode (N_high = 2) and three AC line cycles in low-gain mode (N_low = 3), the output voltage ripple will contain a low-frequency ripple AC component with a period of T_rip_low = 2 x 20ms + 3 x 20ms = 100ms. The low-frequency ripple frequency is F_rip_low = 1 / T_rip_low = 10Hz. Therefore, the output voltage ripple contains a low ripple frequency of 10Hz and a dual-frequency ripple of 100Hz.

[0149] (6) Since the output voltage generated by the converter in low-gain mode is lower than that in high-gain mode, for the same input AC voltage, the AC power supply operating in low-gain mode draws less power from the AC input voltage than that operating in high-gain mode. In other words, when the input AC voltage is the same, the power drawn from the AC power supply is different in different operating modes (high-gain mode and low-gain mode).

[0150] (7) Since the input AC voltage is the same, the switching power supply converter can absorb a smaller AC sinusoidal current in low-gain mode compared to high-gain mode operation. Corresponding to different operating modes, there may be AC ​​sinusoidal currents with different peak values.

[0151] (8) To achieve a wider range of output voltage variation, the values ​​of Gain_high and Gain_low may differ significantly. For example, if Gain_high is twice Gain_low, the output voltage can vary at a ratio of 2:1 with the same control parameter values. If Gain_high = 1.1 * Gain_low, the output voltage may only vary at a ratio of 1.1:1, which is less than ideal.

[0152] (9) In addition to high-gain and low-gain operating modes, a zero-gain operating mode can also be achieved. Zero-gain operating mode can be defined as the power converter essentially not using power from the AC power supply; therefore, when the converter operates in steady state, the output voltage is essentially zero when operating in zero-gain mode. The output voltage is typically zero when the converter is not switching. However, boost converters are an exception. For boost converters, when the boost switch is not switching, the output voltage is essentially equal to the peak value of the AC voltage. Under normal operating conditions, the output voltage of the boost converter is higher than the input voltage. Therefore, if the boost switch (e.g., a MOSFET) is not switching, the boost diode will be reverse-biased, and no energy will be transferred from the input to the output.

[0153] (10) Includes zero-gain mode. The switching power converter can operate in three modes to achieve a specific output voltage level. Zero-gain mode operation is not specifically emphasized in the following description because all topologies can operate in zero-gain mode.

[0154] In some embodiments, the time interval for the switching power converter to operate in high-gain mode or low-gain mode can be selected such that the output voltage rises during high-gain mode operation and falls during low-gain mode operation, for example, as... Figure 8 and Figure 9 The simulation waveform is shown in the figure.

[0155] 1.2 Sub-power frequency control strategy

[0156] Figure 6 This is a block diagram of an AC-DC rectifier with two voltage gains, Gain_high and Gain_low, according to one embodiment, featuring power factor correction (PFC). For PFC operation, a relatively large capacitor (e.g., ...) is used at the load. Figure 6 The Co value is shown, therefore the output voltage is essentially a DC voltage with low-frequency ripple. For example, Co = 1,000uF is used in analysis and simulation, but other values ​​can also be used. Ripple voltage (V) o_rip_pp The value of ripple voltage is smaller than its DC value (Vo_avg), typically less than 20% of the DC value. The frequency of ripple voltage is related to the line frequency.

[0157] In the following description of the control strategy, the following assumptions are made:

[0158] Assumption 1.1: AC-DC rectifiers with power factor correction have two operating modes: (1) high-gain operating mode and (2) low-gain operating mode.

[0159] Assumption 1.2: The voltage gain (Gain_high) in high-gain operating mode is twice the voltage gain (Gain_low) in low-gain operating mode, Gain_high = 2 * Gain_low. For example, Gain_high = 2 and Gain_low = 1. Voltage gain is defined as the ratio of the output DC voltage value to the root mean square (rms) value of the input AC voltage, as shown in formulas (8) and (9) below.

[0160] Assumption 1.3: The input AC voltage remains constant. The analysis uses Vac = 200V rms and a frequency of 50Hz as an example, with the converter operating in PFC mode.

[0161] Assumption 1.4: The maximum output voltage is 400V DC (200V rms*2), the DC load current is 5A, and the maximum output power is 2000W.

[0162] Assumption 1.5: The load current is always 5A for different output voltage values.

[0163] Assumption 1.6: The switching frequency (e.g., typically in the range of 100–200 kHz) is much higher than the line frequency (50 Hz or 60 Hz), and the switching frequency ripple is ignored.

[0164] Assumption 1.7: The value of the output capacitor is very large, so that the low-frequency ripple voltage across the output capacitor (which is the same as the output voltage) is much smaller than its average value (or DC value).

[0165] It's important to note that Gain_high is defined as the ratio of the output DC voltage (average voltage) to the AC voltage (rms) when the AC-DC rectifier is operating in high-gain mode. Gain_low is defined as the ratio of the output DC voltage (average voltage) to the AC voltage (rms) when the AC-DC rectifier is operating in low-gain mode. Therefore:

[0166] Gain_high = Vo_avg / Vac = 2, operating in high gain mode (8)

[0167] Gain_low = Vo_avg / Vac = 1, operating in low gain mode (9)

[0168] Where Vac is the RMS value of the input AC line voltage.

[0169] Figure 7A The simulation results are shown when the converter is operating in high-gain mode. In this case, the output voltage (top) is 400V. The average value is 400V, and the low-frequency ripple peak-to-peak value is approximately 16V. The second waveform (starting from the top) is the AC input voltage. The third waveform (starting from the top) is the input AC current. The bottom waveforms are the input power Pinput and the output power Pout. The input power is a sine wave. The output power is almost a DC value with small ripple.

[0170] Figure 7B The simulation results are shown when the converter is operating in low-gain mode. In this case, the output voltage (top) is 200V, and the low-frequency ripple is approximately 16V peak-to-peak.

[0171] Figure 8 The simulation results for sub-power frequency modulation are shown when N_high = 5 and N_low = 2. In this case, the converter operates for five AC cycles in high-gain mode and two AC cycles in low-gain mode. With this control method, the average output voltage (top) is approximately 343V, and the low-frequency ripple peak-to-peak value is Vo_rip_pp = 92V. The output power is 1,721W. From time T1 (T1 = approximately 2.1 seconds) to time T2 (T2 = approximately 2.2 seconds), the converter operates in high-gain mode, and the output voltage rises. During this period, the input current is high. From time T2 to T3 (T3 = approximately 2.24 seconds), the converter operates in low-gain mode, and the output voltage drops. The time interval from T1 to T3 is 140ms, which is equal to (N_high + N_low) * T_line = (5 + 2) * 20ms = 140ms.

[0172] Under sub-power frequency modulation, the average output voltage decreases from 400V to 343V. The converter operates alternately between high-gain and low-gain modes. These two modes provide optimal operating conditions and high efficiency.

[0173] It should also be noted that the input power is higher during high-gain mode operation (peak 4000W), while the input power is lower during low-gain mode operation (peak 2000W).

[0174] Another observation is that under sub-power frequency modulation control, the output voltage does not reach a steady state in either high-gain or low-gain operating mode. For example, at the end of high-gain operation, at T2( Figure 8 If high-gain mode continues to operate, the output voltage will continue to increase. Similarly, at the end of low-gain mode operation, at T3( Figure 8 If the low-gain mode continues, the output voltage will continue to decrease. Since this is a low-frequency variation or low-frequency ripple, another DC-DC converter can be used as a second stage to eliminate this low-frequency ripple.

[0175] It is important to note that sub-power frequency modulation will alter the DC value of the output voltage of a converter with power factor correction. It will not eliminate the converter's low-frequency ripple voltage. An additional DC-DC converter is required to eliminate the low-frequency ripple voltage and produce a pure DC voltage.

[0176] Figure 9 The simulation results for sub-power frequency modulation are shown when N_high = 7 (high-gain mode operation for seven AC cycles) and N_low = 1 (low-gain mode operation for one AC cycle). In this case, Vo_avg = 375V, Vo_rip_pp = 60V, and the output power is Pout = 1876W.

[0177] Figure 10 The simulation results for sub-power frequency modulation are shown under N_high = 2 (high-gain mode operation for two AC cycles) and N_low = 2 (low-gain mode operation for two AC cycles). In this case, Vo_avg = 300V, Vo_rip_pp = 78V, and the output power is Pout = 1500W.

[0178] Figure 11 The simulation results for sub-power frequency modulation are shown when N_high = 2 (high-gain mode operation for two AC cycles) and N_low = 5 (low-gain mode operation for five AC cycles). In this case, Vo_avg = 257V, Vo_rip_pp = 112V, and the output power is Pout = 1302W.

[0179] The analysis above shows that by changing the number of AC cycles in high-gain mode (N_high) and low-gain mode (N_low), sub-power frequency modulation can be used to change the output voltage of the AC-DC rectifier. Sub-power frequency modulation refers to a control period that is an integer multiple of the AC power frequency cycle. For example... Figure 8 and 11 As shown, the control cycle is 7 times the AC cycle (N_high + N_low = 7). Figure 9 In the case shown, the control cycle is 8 times the AC power frequency cycle. Figure 10 In the case shown, the control cycle is four times the AC power frequency cycle. Sub-power frequency modulation will produce a low-frequency ripple below the AC power frequency.

[0180] 1.3 Continuous adjustment of output voltage DC value

[0181] As the above analysis shows, the gain values ​​in high-gain mode (Gain_high) and low-gain mode (Gain_low) are fixed, and the number of AC line cycles (N_high) in high-gain mode is an integer value for low-gain mode (N_low). Therefore, the DC output voltage value will be a discrete value. Under these conditions, the DC output voltage value cannot be continuously adjusted.

[0182] In practical implementation, optimal operating conditions, such as high efficiency, will be maintained within a limited gain range. For example, using an LLC converter, high-efficiency operation can be maintained within a voltage gain range of 1.8 to 2.2, or a variation of ±10%. Therefore, by changing the actual gain of the converter, the DC value of the converter's output voltage can be precisely adjusted to the desired value.

[0183] For example, Figure 12 The simulation results are shown for N_high=5, N_low=2, Gain_high=2, and Gain_low=1.04. In this case, the DC output voltage is 345V, slightly higher than the 342.7V for N_high=5, N_low=2, Gain_high=2, and Gain_low=1. Figure 8 As shown.

[0184] Because the gain of an AC-DC switching converter can be continuously adjusted, the DC value of the output voltage can also be adjusted to any desired value. This can be achieved through feedback control. In the case of a PWM converter embodiment, the gain can be adjusted by changing the duty cycle. In the case of a resonant converter embodiment, the gain can be adjusted by changing the switching frequency.

[0185] Similarly, the gain value (Gain_high) in high-gain mode can be adjusted to achieve precise output voltage regulation. This will not be elaborated further here.

[0186] Therefore, the converter's output voltage can be adjusted according to the following relationship:

[0187] (1) A larger N_high value will increase the output voltage.

[0188] (2) A larger N_low value will reduce the output voltage.

[0189] (3) A larger Gain_high will increase the output voltage.

[0190] (4) A larger Gain_low will increase the output voltage.

[0191] (5) A higher N_high / N_low ratio will increase the output voltage.

[0192] All four parameters, N_high, N_low, Gain_high, and Gain_low, can be used to control the output voltage. Below is an example of a strategy to achieve the ideal combination.

[0193] (1) To reduce low-frequency output voltage ripple, smaller N_high and N_low values ​​can be used.

[0194] (2) To maintain selected operating conditions, such as high efficiency, the converter parameters can be selected to minimize voltage gain variation. For example, in high-gain operating mode, the gain variation is 1.8 to 2.2, and in low-gain operating mode, the gain variation is 0.9 to 1.1. A wide range of DC output voltage variations can be achieved through sub-power frequency modulation.

[0195] As an example of point (1) above, the operating mode of N_high=5 and N_low=5 (Mode A) will produce the same DC output voltage value as the operating mode of N_high=1 and N_low=1 (Mode B). In Mode A, the period of the low-frequency ripple will be 10 times the AC power frequency period (5+5), i.e., Trip_low = (5+5) x 20ms = 200ms (for a 50Hz AC system). For Mode B, the period of the low-frequency ripple is twice the AC power frequency (1+1), i.e., Trip_low = (1+1) x 20ms = 40ms. Therefore, the output voltage ripple is smaller in Mode B, which is ideal.

[0196] Regarding point (2) above, it is generally observed that the wider the required voltage gain, the greater the design loss of the converter. Therefore, the converter will achieve worse performance. For example, consider two designs using LLC converters. Designing LLC_A requires a voltage gain variation of 2 to 3, while designing LLC_B requires a voltage gain variation of 2 to 2.2, with all other requirements being the same. Designing LLC_B will achieve better performance than designing LLC_A, such as higher efficiency. Therefore, designing LLC_B would be the preferred choice.

[0197] Therefore, by employing sub-power frequency modulation technology, the converter can operate in different gain modes, achieving a wider range of output voltage variations, while the gain variation of the converter itself is very small.

[0198] 1.4 Sub-octave frequency modulation

[0199] To reduce low-frequency output voltage ripple, sub-power frequency modulation can be extended to sub-harmonic modulation. In this case, high-gain mode operation and low-gain mode operation can be determined based on half a cycle of the AC power frequency period, for example, 10ms for a 50Hz system and 8.33ms for a 60Hz system. For example, the converter operates in high-gain mode for N_half_high AC power frequency half-cycles and in low-gain mode for N_half_low AC power frequency half-cycles (where N_half_high and N_half_low are integers), alternating between high-gain and low-gain modes. For example, assuming the AC power frequency is 50Hz, the converter operates in high-gain mode for 3 AC power frequency half-cycles, or 3 * 10ms = 30ms, and then in low-gain mode for 2 AC power frequency half-cycles, or 2 * 10ms = 20ms.

[0200] The difference between sub-power frequency modulation and sub-harmonic modulation lies in the minimum time interval. With sub-harmonic modulation, the minimum time interval is half the AC power frequency cycle. For a 50Hz AC system, the minimum time interval is 10ms. For a 60Hz AC system, the minimum time interval is 8.33ms.

[0201] Figure 13The simulation results are shown when N_half_high = 5 and N_half_low = 2 under subharmonic modulation. In this case, the converter operates for 5 AC power frequency half-cycles (5 * 10 ms = 50 ms) in high-gain mode and 2 AC power frequency half-cycles (2 * 10 ms = 20 ms) in low-gain mode. With this control method, the average output voltage is approximately 342.7V, and the low-frequency ripple peak-to-peak value is Vo_rip_pp = 55V. The output power is 1717W. From time T1 (approximately 2.1 seconds) to time T2 (approximately 2.15 seconds), the converter operates in high-gain mode, and the output voltage rises. During this period, the input current is high. From time T2 to T3 (approximately 2.17 seconds), the converter operates in low-gain mode, and the output voltage decreases. The time interval from T1 to T3 is 70ms, which is equal to (N_half_high + N_half_low) * T_half_line = (5 + 2) * 10ms = 70ms. T_half_line is the time of half a cycle of the AC power frequency. T_half_line = T_line / 2 = 10 milliseconds.

[0202] By comparison Figure 8 and Figure 13 The simulation results shown yield the following conclusions:

[0203] (1) The DC output voltage values ​​are basically the same. This is because the relative proportions of high-gain mode operation and low-gain mode operation are the same.

[0204] (2) Figure 13 The ripple voltage is 55V (Vo_rip_pp=55V), while Figure 8 The ripple voltage is 92V (Vo_rip_pp = 92V). Using sub-frequency modulation, the ripple is reduced by about half.

[0205] (3) The low-frequency ripple period of the sub-harmonic modulation is 70ms. Figure 13 The low-frequency ripple period of sub-power frequency modulation is 140ms. Figure 8 ).

[0206] Figure 14 The simulation results for subharmonic modulation are shown with N_half_high = 7 (high-gain mode operation for seven AC power frequency half-cycles, 7 * 10 ms = 70 ms) and N_half_low = 1 (low-gain mode operation for one AC power frequency half-cycle, 1 * 10 ms = 10 ms). In this case, Vo_avg = 375V, Vo_rip_pp = 38V, and the output power is Pout = 1875W.

[0207] Figure 15The simulation results of subharmonic modulation with N_half_high = 2 (high-gain mode operation for two AC power frequency half-cycles, 2 * 10 ms = 20 ms) and N_half_low = 2 (low-gain mode operation for two AC power frequency half-cycles, line period, 2 * 10 ms = 20 ms) are shown. In this case, Vo_avg = 300V, Vo_rip_pp = 38V, and the output power is Pout = 1500W.

[0208] Figure 16 The simulation results for subharmonic modulation with N_half_high = 2 (high-gain mode operation for two AC power frequency half-cycles, 2 * 10 ms = 20 ms) and N_half_low = 5 (low-gain mode operation for five AC power frequency half-cycles, 5 * 10 ms = 70 ms) are shown. In this case, Vo_avg = 257V, Vo_rip_pp = 66V, and the output power is Pout = 1290W.

[0209] contrast Figure 8 and 13 , Figure 9 and 14 , Figure 10 and 15 , Figure 11 and 16 Simulation results show that sub-harmonic modulation exhibits characteristics of sub-power frequency modulation while achieving significantly lower (almost halved) low-frequency ripple voltage. Therefore, sub-harmonic modulation is the preferred implementation method. The remainder of this description will focus solely on the sub-harmonic modulation method.

[0210] It should also be noted that in the above analysis, the switching between high-gain mode and low-gain mode operation occurred at the zero-crossing point of the AC input voltage. However, the switching can occur at any AC input voltage. One advantage of switching at the zero-crossing point is that the transition between high-gain and low-gain mode operation will be smooth. Therefore, switching at the zero-crossing point may be advantageous during steady-state operation. During dynamic operation, switching when the instantaneous input voltage is not zero may be advantageous to improve dynamic performance.

[0211] The selection of control parameters such as N_half_high, N_half_low, Gain_high, and Gain_low is the same for both sub-harmonic modulation and sub-power frequency modulation.

[0212] 1.5 Extended to output voltage lower than the value achieved in low-gain mode.

[0213] The above analysis assumes a high gain of 2, a low gain of 1, and an input voltage of 200V rms. Therefore, the steady-state output voltage in high-gain mode is 400V (200V*2), and the steady-state output voltage in low-gain mode is 200V (200V*1). Through sub-power frequency and sub-harmonic modulation, the output voltage can be adjusted between 200V and 400V, or between the steady-state output voltage values ​​in high-gain and low-gain modes.

[0214] If the required output voltage is below 200V, such as 150V, a zero-gain operating mode can be introduced, and the converter operates between low-gain mode and zero-gain mode. In zero-gain mode, the steady-state output voltage is zero.

[0215] In the example above, if the converter's output voltage needs to be adjusted to around 150V, while the converter's output is 200V when operating at low gain, then one possible operation would be as follows:

[0216] (1) The converter operates in low gain mode, N_low AC power frequency cycle, or N_half_low AC power frequency half cycle.

[0217] (2) Then the converter runs in zero-gain mode for N_zero AC power frequency cycles, or N_half_zero AC power frequency half cycles;

[0218] (3) The converter repeats the above operation.

[0219] N_zero is the number of AC power frequency cycles during converter operation in zero-gain mode. The steady-state output voltage is zero when there is no energy transfer from input to output. N_half_zero is the number of AC power frequency half-cycles when the AC-DC rectifier operates in zero-gain mode.

[0220] In the above example and control strategy, the output voltage of the AC-DC rectifier can be adjusted to around 150V. The following points should be noted:

[0221] (1) Use smaller N_low and N_zero values ​​to reduce low-frequency ripple in the output voltage.

[0222] (2) When using different N_low and N_zero, the output voltage can be adjusted between 0V and 200V.

[0223] (3) Subharmonic modulation can also be used. In this case, the converter operates in low-gain mode for N_half_low AC power frequency half-cycles and N_half_zero AC power frequency half-cycles.

[0224] (4) The values ​​of N_low, N_zero and N_half_low, N_half_zero can be small enough that the output voltage of the AC-DC rectifier is a DC value (Vo_avg) with low-frequency ripple (Vo_rip_pp). For example, these values ​​can be chosen to keep Vo_rip_pp less than 10% to 50% of Vo_avg.

[0225] Figure 17 The simulation results are shown for Vac = 200V, N_half_low = 6, and N_half_zero = 2. Under these operating conditions, the output voltage is Vo_avg = 150V. The peak-to-peak value of the low-frequency ripple is 55V.

[0226] 2. Input voltage variation control strategy

[0227] The above analysis shows that the output voltage can be changed using variable gain modulation methods (sub-power frequency modulation and sub-harmonic modulation). This section demonstrates that the output voltage can remain approximately the same when the input voltage varies over a wide range.

[0228] The following assumptions are made in the following analysis:

[0229] Assumption 2.1: The converter with power factor correction has two operating modes: (1) high gain operating mode and (2) low gain operating mode.

[0230] Assumption 2.2: The voltage gain (Gain_high) in high-gain operating mode is twice the voltage gain (Gain_low) in low-gain operating mode, where Gain_high = 2 * Gain_low. For example, assume Gain_high = 2 and Gain_low = 1. Note that the gain is defined as Vo_avg and Vac.

[0231] Assumption 2.3: The input AC voltage will vary between Vac1 = 100Vrms and Vac2 = 200Vrms, with a ratio of 2:1. In this analysis, the 50Hz AC line frequency is used for illustrative purposes. The AC-DC rectifier operates in PFC mode.

[0232] Assumption 2.4: The output voltage is regulated to 150V DC, and the DC load current is 5A within the aforementioned input voltage variation range (between 100Vrms and 200Vrms). Therefore, the output power is 750W. The load resistance is 30Ω.

[0233] Assumption 2.5: The load current is always 5A for different input voltage levels.

[0234] Assumption 2.6: The switching frequency (typically in the range of 100–500kHz) is much higher than the line frequency (50Hz or 60Hz), and the switching frequency ripple is ignored.

[0235] Assumption 2.7: Using sub-harmonic modulation, the operation of sub-power frequency modulation will be the same.

[0236] For example, when the input AC voltage changes from 100V to 200V, the average value of the output voltage is adjusted to 150V.

[0237] When the input AC voltage is 100V Figure 18 Simulation waveforms show that when the converter operates in high-gain mode (Gain_high = 2) for four AC power frequency half-cycles (N_half_high = 4, or 4 * 10 ms = 40 ms), it then operates in low-gain mode (Gain_low = 1) for the next four AC power frequency half-cycles (N_half_low = 4, or 4 * 10 ms = 40 ms), and the output voltage can be adjusted to 150V. If the converter operates in high-gain mode for an extended period, such as 10 to 50 line cycles, the output voltage will be 2 * 100 = 200V. Conversely, if the converter operates in low-gain mode for an extended period, the output voltage will be 1 * 100 = 100V. Therefore, by switching between high-gain and low-gain modes, the output voltage can be adjusted to 150V.

[0238] When the input AC voltage becomes 120V, the steady-state output voltage adjustment range is from 120V (low gain mode) to 120V*2=240V (high gain mode). Figure 19 The computer simulation waveforms are displayed. In this configuration, the converter operates in high-gain mode for two AC half-cycles (N_half_high = 2) and in low-gain mode for six AC half-cycles (N_half_low = 6). The average output voltage is regulated to 150V.

[0239] When the input AC voltage is 150V, the converter always operates in low gain mode, and the average value of the output voltage is always 150V.

[0240] When the input AC voltage is 200V, even if the converter operates in low-gain mode (Gain_low = 1), the steady-state output voltage will still be 200V, higher than the required 150V. Therefore, the converter should operate in both low-gain and zero-gain modes. Figure 20The simulation results are shown when the converter operates in low-gain mode for 6 AC half-cycles (N_half_low = 6) and in zero-gain mode for 2 AC half-cycles (N_half_zero = 2). The output voltage is adjustable to 150V.

[0241] It should be noted that the converter can also operate in high-gain mode and zero-gain mode to generate 150V, but this will increase the converter's voltage and / or current.

[0242] In the example above, the parameters are: Vin_min = 100V, Vin_max = 200V, Gain_low = 1, and Gain_high = 2. With an input AC voltage of Vin_min, the maximum possible output voltage is Vin_min * Gain_high = 200V. The output voltage can then be adjusted to any value between 200V and 0V. If a higher output voltage is required, a larger Gain_high is needed.

[0243] 3. Combination of simultaneous changes in input voltage and output voltage

[0244] The above embodiments use variable gain modulation at sub-power frequency and sub-harmonic frequency modulation for converters with power factor rectification to achieve (1) a wide range of output voltage variation when the input AC voltage is fixed; and (2) a fixed output voltage when the input AC voltage varies over a wide range. There are three operating modes: (1) high gain mode, (2) low gain mode, and (3) zero gain mode.

[0245] As demonstrated above, the output voltage can be continuously adjusted by changing the gain value of high-gain mode, low-gain mode, or both.

[0246] In practical applications, the input AC voltage can have a wide range of variation, and the output voltage can also have a wide range of adjustment. The control method described in this embodiment can also achieve this objective.

[0247] The following assumptions are for illustrative purposes only, for example:

[0248] Assumption 3.1: Use sub-frequency modulation because it produces lower output voltage ripple.

[0249] Assumption 3.2: The input AC voltage may vary from 100Vrms to 200Vrms, and the line frequency is 50Hz.

[0250] Assumption 3.3: The output voltage can be adjusted to any value between 100VDC and 200VDC.

[0251] Assumption 3.4: The load current is 5A under all output voltages. The analysis results are the same for different load currents.

[0252] Assumption 3.5: It can be changed from 1.8 to 2.2 (±10%) while maintaining high performance.

[0253] Assumption 3.6: The low gain value is Gain_low = 1, which can be changed from 0.9 to 1.1 (±10% change) while maintaining high performance.

[0254] Based on computer simulations, the table below provides the operating conditions for achieving the above design requirements.

[0255] Table 1: Operating conditions for a required output voltage Vo_avg = 100V

[0256]

[0257] Remark:

[0258] • Assume the error is less than 0.5V (0.5% of 100V). When the output voltage is between 99.5V and 100.5V, it is considered to have reached 100V.

[0259] • In Case 1.4, a voltage gain of 0.97 is required in low gain mode to fine-tune the output voltage to 100V.

[0260] Comparing Case 1.3 and Case 1.6, when the input voltage increases from 150V to 155V, the output voltage is fine-tuned to 100V in low-gain mode using a voltage gain of 0.99. The values ​​of N_half_low and N_zero remain unchanged.

[0261] • In all cases, with Vo_avg = 100V and Vin = 100V to 200V, only low-gain mode and zero-gain mode are required. High-gain mode is not activated.

[0262] • NO indicates that this working mode was not used.

[0263] For Case 1.4, the converter operates for 4 AC half-cycles in low-gain mode (N_half_low = 4) and 3 AC half-cycles in zero-gain mode (N_half_zero = 3). The actual gain value in low-gain mode is 0.97. Therefore, the output DC voltage is 100.1V. The converter is not operating in high-gain mode.

[0264] Table 2: Operating conditions for a required output voltage Vo_avg = 200V

[0265]

[0266] Remark:

[0267] In the above simulation, it is assumed that the error is less than 1.0V (0.5% of 200V). When the output voltage is between 199V and 201V, it is considered to have reached 200V.

[0268] Between Case 2.3 and Case 2.6, N_half_low and N_half_high are the same in both cases, and Gain_high for a 155V input is changed to 1.88 so that the output voltage can be adjusted to 200V.

[0269] • When the input voltage is 100V, the rectifier operates continuously in high-gain mode. When the input is between 100V and 110V, the rectifier operates continuously in high-gain mode. The output voltage can be adjusted to 200V by changing the rectifier's gain (from 1.8 to 2).

[0270] • When the input voltage is 120V, the rectifier operates for 2 half-cycles of AC power frequency in low-gain mode and 4 half-cycles of AC power frequency in high-gain mode.

[0271] • When the input voltage is 200V, the rectifier operates continuously in low-gain mode. When the input voltage is between 180V and 200V, the output voltage can be adjusted to 200V by changing the rectifier gain (from 0.9 to 1.0).

[0272] • When the input voltage is 180V, the rectifier outputs 200V when operating in low-gain mode for 9 half-cycles of AC power frequency and in high-gain mode for 1 half-cycle of AC power frequency.

[0273] Table 3: Operating conditions for a required output voltage Vo_avg = 150V

[0274]

[0275]

[0276] Remark:

[0277] In the above simulation, it is assumed that the error is less than 0.75V (0.5% of 150V). When the output voltage is between 149.25V and 150.75V, it is considered to have reached 150V.

[0278] • When the input voltage is higher than 150V, the high-gain mode is not selected. The AC-DC rectifier operates between low-gain mode and zero-gain mode.

[0279] In Case 3.6, the rectifier output voltage is adjusted by changing the Gain_low value to 0.97 while continuously operating in low-gain mode.

[0280] Based on the above analysis and simulation results, when the input voltage varies between 100V and 200V (ratio 2:1), the output voltage of the AC-DC rectifier can be adjusted to any value between 100V and 200V (ratio 2:1) through sub-frequency variable gain modulation, operating in both high-gain and low-gain modes. For the low-gain operating mode (between 0.9 and 1.1) and the high-gain operating mode (between 1.8 and 2.2), the gain variation is less than 10%. The total voltage gain variation is 4:1. The lowest voltage gain is achieved when Vin = 200Vrms and Vo = 100V (gain of 0.5). The highest voltage gain is achieved when Vin = 100Vrms and Vo = 200V (gain of 2). Therefore, a 4:1 input-to-output voltage variation has been achieved with an actual gain variation of only ±10% for the AC-DC converter.

[0281] 4. Implementation

[0282] The preceding sections detailed the working principle of variable gain modulation in AC-DC rectifiers. This section uses subharmonic modulation as an example to illustrate the implementation details of variable gain modulation.

[0283] Make the following assumptions:

[0284] Assumption 4.1: The range of the input AC rms voltage variation is from Vin_min to Vin_max.

[0285] Assumption 4.2: The output voltage variation range is from Vo_avg_min to Vo_avg_max.

[0286] Assumption 4.3: Implement an AC-DC rectifier according to the above requirements, so that the average output voltage Vo_avg can be adjusted to any value between Vo_avg_min and Vo_avg_max over the entire input voltage variation range from Vin_min to Vin_max.

[0287] Assumption 4.4: The design gain value in high-gain mode is Gain_high. Gain_high can be adjusted from Gain_high_min to Gain_high_max. Further assuming that Gain_high_min is 10% lower than Gain_high and Gain_high_max is 10% higher than Gain_high, the gain variation is ±10%.

[0288] Assumption 4.5: The design gain value in low-gain mode is Gain_low. Gain_low can be adjusted from Gain_low_min to Gain_low_max. Further, assume that Gain_low_min is 10% lower than Gain_low, and Gain_low_max is 10% higher than Gain_low, resulting in a gain variation of ±10%.

[0289] Assumption 4.6: Voltage gain is defined as the ratio of the average value of the DC output voltage to the RMS value of the AC input voltage.

[0290] Assumption 4.7: Subharmonic modulation is used. The operating mode of the AC-DC rectifier depends on the AC power frequency half-cycle T_half_line. Within T_half_line, the rectifier will not change its operating mode. It will remain in zero-gain mode, low-gain mode, or high-gain mode. For a 50Hz system, T_half_line = 10ms. For a 60Hz system, T_half_line = 8.33ms.

[0291] Assumption 4.8: N_L refers to the AC half-cycle number T_half_line when the AC-DC rectifier operates in low-gain mode. N_H refers to the AC half-cycle number T_half_line when the AC-DC rectifier operates in high-gain mode. N_Z refers to the AC half-cycle number T_half_line when the AC-DC rectifier operates in zero-gain mode.

[0292] Assumption 4.9: To simplify the analysis, assume that the AC-DC rectifier changes its operating mode when the AC input voltage crosses zero. It should be noted that the rectifier can change its operating mode at any time.

[0293] In one embodiment, the selection of Gain_high satisfies the following requirements:

[0294] Vo_avg_max≤Gain_high*Vin_min (10)

[0295] Based on this requirement, the AC-DC rectifier may be able to produce the maximum output voltage at the minimum input voltage.

[0296] The implementation may be at least partially implemented as an algorithm in the controller of the converter. According to one embodiment, key steps of the algorithm may include the following:

[0297] Step 1: Detect the actual input AC voltage Vin. Vin is between Vin_min and Vin_max.

[0298] Step 2: Determine the required output voltage Vo_avg. Vo_avg is between Vo_avg_min and Vo_avg_max.

[0299] Step 3: Calculate the two threshold voltage levels:

[0300] Vo_th1=Vin*Gain_low (11.1)

[0301] Vo_th2 ​​= Vin * Gain_high (11.2)

[0302] Step 4: Determine the operating mode: modulation between zero-gain mode and low-gain mode, and modulation between low-gain mode and high-gain mode.

[0303] Condition 1: Vo_avg≤Vo_th1 (12.1)

[0304] Condition 2: Vo_th1 <Vo_avg≤Vo_th2 (12.2)

[0305] Step 5: If condition 1 shown in equation (12.1) is satisfied, then step 6 can be used to determine the control parameters. If condition 2 shown in equation (12.2) is satisfied, then step 7 can be used to determine the control parameters.

[0306] Step 6: If condition 1 is met, the AC-DC rectifier can modulate between low-gain and zero-gain modes. N_L, N_Z, and Gain_low can be determined to adjust the average output voltage to Vo_avg.

[0307] Step 6.1: Determine N_L and N_Z (e.g., based on a lookup table with measured Vin and desired Vo_avg values) to make the output voltage close to the desired output voltage Vo_avg. The lookup table can be generated based on design requirements and low gain values.

[0308] Step 6.2: Using the N_L and N_Z obtained in Step 6.1, change the low gain value of the AC-DC rectifier to produce the desired output voltage Vo_avg. This can be done by the feedback circuit.

[0309] Note 6.1: The general principle is to select the minimum possible values ​​of N_L and N_Z to produce an output voltage close to the desired output voltage Vo_avg, thereby minimizing the low-frequency ripple of the output voltage.

[0310] Note 6.2: The lookup table method is an example of step 6.1. Other methods can also be used to determine N_L and N_Z, such as feedforward, feedback, and logic circuits with digital control.

[0311] Note 6.3: Determining the low gain value Gain_low to generate the required output voltage Vo_avg can be done by the feedback circuit.

[0312] Note 6.4: Under condition 1, the period of the low-frequency ripple of the output voltage can be calculated as follows:

[0313] T_rip1=T_half_line*(N_L+N_Z) (13)

[0314] Step 7: With condition 2 met, the AC-DC rectifier can modulate between low-gain and high-gain modes. N_H, N_L, Gain_low, and Gain_high can be determined to adjust the average output voltage to Vo_avg.

[0315] Step 7.1: Determine N_H and N_L based on the measured Vin and the required Vo_avg value using a lookup table to make the output voltage close to the required output voltage Vo_avg. The lookup table can be generated based on design requirements and low-gain or high-gain values.

[0316] Step 7.2: Using N_H and N_L obtained in Step 7.1, change the low gain value (when the rectifier is operating in low gain mode), or the high gain value (when the rectifier is operating in high gain mode), or both, so that the AC-DC rectifier generates the desired output voltage Vo_avg. This can be performed by a feedback circuit.

[0317] Note 7.1: In one embodiment, the minimum possible values ​​of N_L and N_H can be selected to produce an output voltage close to the desired output voltage Vo_avg, thereby minimizing low-frequency ripple of the output voltage. N_L and N_H can be obtained by looking up a table based on the measured input voltage Vin, the desired output voltage Vo_avg, and the known values ​​of Gain_low and Gain_high after the design is completed. Other methods, such as feedforward, feedback, or logic circuitry, can also be used to determine N_L and N_H.

[0318] Note 7.2: Steps 7.1 and 7.2 can be repeated two or more times to optimize N_L, N_H and low gain value Gain_low, high gain value Gain_high to produce the desired output voltage Vo_avg.

[0319] Note 7.3: Under condition 2, the period of the low-frequency ripple of the output voltage can be calculated as follows:

[0320] T_rip2=T_half_line*(N_L+N_H) (14)

[0321] Note 7.4: T_rip1 and T_rip2 may be several times larger than the AC power frequency half-cycle. Therefore, the control circuit needs a time period equal to several T_rip1 or T_rip2 to generate the required output voltage Vo_avg. For example, the control circuit may need 5 to 20 AC power frequency half-cycles to reach a steady state and generate a stable output voltage Vo_avg.

[0322] Note 7.5: In one operating mode, an AC-DC rectifier can always operate in high-gain mode and never in low-gain mode. This can happen when the input voltage is low and the required output voltage is high. By changing the value of Gain_high, the output voltage can be adjusted to the design value.

[0323] Note 7.6: In another operating mode, the AC-DC rectifier may always operate in low-gain mode and never in high-gain mode. This can happen when the input voltage is high and the required output voltage is low. By changing the value of Gain_low, the output voltage can be adjusted to the desired value.

[0324] Special case 1

[0325] This section discusses a special case. If the input AC voltage is 110V or 220V, and the output voltage of the AC-DC rectifier is a fixed voltage, such as 50V, then the variable gain modulation strategy can be simplified as follows:

[0326] Assumption 4.1.1: The input voltage varies between 100V and 140V or between 190V and 240V.

[0327] Assumption 4.1.2: The output voltage is fixed at Vo_avg = 50V.

[0328] Assumption 4.1.3: The high gain value Gain_high is twice the low gain value Gain_low. Gain_high = 2 * Gain_low.

[0329] The variable gain modulation strategy can achieve the following:

[0330] Step 7.4.1: When the input voltage is between 100V and 140V, the AC-DC rectifier operates only in high-gain mode. The output voltage can be controlled by changing the Gain_high value.

[0331] Step 7.4.2: The gain range can be designed as follows:

[0332] Gain_high_req_min=50V / 140V=0.36 (15.1)

[0333] Gain_high_req_max=50V / 100V=0.50 (15.2)

[0334] Under these conditions, if the gain of the AC-DC rectifier can be adjusted from 0.36 to 0.50 when the rectifier is operating in high-gain mode, then when the input voltage changes from 100V to 140V, the output voltage can be adjusted to 50V.

[0335] Step 7.4.3: When the input voltage is between 190V and 240V, the AC-DC rectifier operates only in low-gain mode. The output voltage can be controlled by changing the Gain_low value.

[0336] Step 7.4.4: The gain range should be designed as follows:

[0337] Gain_low_req_min=50V / 240V=0.21 (16.1)

[0338] Gain_low_req_max=50V / 190V=0.26 (16.2)

[0339] When the rectifier operates in low-gain mode, the gain of the AC-DC rectifier can be adjusted from 0.21 to 0.26. Therefore, when the input voltage changes from 190V to 240V, the output voltage can be stabilized at 50V.

[0340] Step 7.4.5: The actual high gain value of the AC-DC rectifier can be designed within the following range:

[0341] Gain_high_act_min=0.36 (17.1)

[0342] Gain_high_act_max=0.52 (17.2)

[0343] or

[0344] Gain_high_act=0.44±18% (17.3)

[0345] Therefore, the actual low gain value of the AC-DC rectifier might be (based on assumption 4.1.3):

[0346] Gain_low_act_min=0.36 / 2=0.18 (18.1)

[0347] Gain_low_act_max=0.52 / 2=0.26 (18.2)

[0348] or

[0349] Gain_low_act=0.22±18% (18.3)

[0350] Step 7.4.6: Using the design obtained in step 7.4.5, the AC-DC rectifier operates in high-gain mode when the input voltage is low (100–140V) and in low-gain mode (190–240V) when the input voltage is high, and produces the desired output voltage (50V) by changing the voltage gain value of the rectifier.

[0351] Special case 2

[0352] For example, if the output voltage is required to be adjusted to 50V when the input voltage is between 140V and 190V, or if the output voltage is required to be maintained at 50V when the input voltage is between 100V and 240V, the following control strategy can be adopted:

[0353] Condition #1: When the input voltage is between 100V and 140V, the AC-DC rectifier operates in high-gain mode, and the high-gain value is used to regulate the output voltage to the design value of 50V.

[0354] Condition #2: When the input voltage is between 190V and 240V, the AC-DC rectifier operates in low-gain mode, and the low-gain value is used to regulate the output voltage to the design value of 50V.

[0355] Condition #3: Sub-frequency modulation can be used when the input voltage is between 140V and 190V. The AC-DC rectifier operates alternately between high-gain and low-gain modes. The N_L and N_H values, as well as the high-gain and low-gain values, are used to regulate the output voltage to the design value of 50V. Detailed control methods are as described above.

[0356] 5. Example: LLC converter implementation of the above control strategy

[0357] Typically, the above control strategies can be implemented in different converter topologies. As mentioned above, various topologies, such as full-bridge PWM converters and full-bridge LLC resonant converters, operate in full-bridge mode (high-gain mode) and half-bridge mode (low-gain mode). Operation at both voltage gains can be optimized for the specific converter topology used. This section describes the implementation of a variable gain modulation control strategy for LLC converters.

[0358] When the resonant parameters, transformer turns ratio, and load resistance are the same, the voltage gain of the full-bridge operation is twice that of the half-bridge operation.

[0359] Gain_LLC_FB=2*Gain_LLC_HB (19)

[0360] Zero-gain mode operation of the LLC AC-DC rectifier can be achieved when all four switches are turned off (i.e., the switches are off).

[0361] LLC resonant converters can be used as AC-DC rectifiers and achieve power factor correction (PFC).

[0362] Figure 21A This is a circuit diagram of an LLC converter used as an AC-DC rectifier with power factor correction. The AC input voltage is rectified by a diode bridge. The rectified AC voltage (Vrec) is applied to the input of the LLC converter. Figure 21B This is a controller block diagram used to control the LLC converter to achieve PFC operation. The output of the voltage error amplifier serves as the current reference for the input LLC current. Changing the switching frequency of the LLC converter makes the LLC input current a rectified sine wave with the desired peak value, determined by Iref. By controlling the input current of the LLC converter (Irec) to be a sine wave, the AC input current can be controlled to be a sine wave, achieving power factor correction. By selecting the resonant parameters and transformer turns ratio, the output voltage can be adjusted to the desired value. Note that the input capacitor Cin (e.g., ...) Figure 21A (As shown) is a small capacitor used to filter out switching frequency ripple.

[0363] The LLC converter operates in full-bridge mode when all four switches Q1, Q2, Q3, and Q4 are on. When Q1 and Q2 are on, Q3 is off, and Q4 is on, the LLC converter operates in half-bridge mode. The gain in full-bridge mode is twice that in half-bridge mode.

[0364] 5.1 Fixed output voltage, wide input voltage range

[0365] In this analysis, it is assumed that a large energy storage capacitor is connected to the output of the LLC AC-DC rectifier, so that the output voltage is a low-frequency DC voltage with small ripple.

[0366] Assumption 5.11: The input AC voltage changes from 100V to 240V.

[0367] Assumption 5.12: The output voltage of the LLC AC-DC rectifier is regulated to 50V.

[0368] In one embodiment, the control strategy may be as follows:

[0369] Step 5.11: When the input voltage is between 100V and 140V, the LLCAC-DC rectifier operates in full-bridge mode. The output voltage is controlled by changing the gain Gain_LLC_FB of the full-bridge LLC rectifier.

[0370] Step 5.12: The required gain range can be designed as follows:

[0371] Gain_LLC_FB_req_min=50V / 140V=0.36 (20.1)

[0372] Gain_LLC_FB_req_max=50V / 100V=0.50 (20.2)

[0373] This means that the gain of the LLC AC-DC rectifier should be designed between 0.36 and 0.50 when operating in full-bridge mode. In this case, the output voltage can be stabilized at 50V when the input voltage changes from 100V to 140V.

[0374] Step 5.13: When the input voltage is between 190V and 240V, the LLCAC-DC rectifier operates in half-bridge mode. The output voltage is controlled by changing the gain value Gain_LLC_HB of the half-bridge LLC rectifier.

[0375] Step 5.14: The required gain value can be designed as follows:

[0376] Gain_LLC_HB_req_min=50V / 240V=0.21 (21.1)

[0377] Gain_LLC_HB_req_max=50V / 190V=0.26 (21.2)

[0378] This means that the gain of the LLC AC-DC rectifier should be designed between 0.21 and 0.26 when operating in half-bridge mode. When the input voltage changes from 190V to 240V, the output voltage is controlled by changing the gain value of the LLC rectifier, Gain_LLC_HB.

[0379] Step 5.15: Since Gain_LLC_FB = 2 * Gain_LLC_HB, the actual gain of the LLC AC-DC rectifier operating in full-bridge mode can be designed to be within the following range:

[0380] Gain_LLC_FB_act_min=0.36 (22.1)

[0381] Gain_LLC_FB_act_max=0.52 (22.2)

[0382] or

[0383] Gain_LLC_FB_act=0.44±18% (22.3)

[0384] In this case, the actual gain range of the LLC AC-DC rectifier in half-bridge mode is as follows:

[0385] Gain_LLC_HB_act_min=0.18 (23.1)

[0386] Gain_LLC_HB_act_max=0.26 (23.2)

[0387] or

[0388] Gain _LLC_HB_act = 0.22 ± 18% (23.3)

[0389] Using sub-frequency modulation, the LLC AC-DC rectifier operates alternately between full-bridge and half-bridge modes.

[0390] For example, if Vin = 150V, then the output of the LLC AC-DC rectifier can be maintained under the following operating conditions:

[0391] Gain _LLC_FB = 0.45 (24.1)

[0392] Gain_LLC_HB=0.21 (24.2)

[0393] N_half_FB = 2 and N_half_HB = 2 (24.3)

[0394] Where N_half_FB = 2 indicates that the LLC AC-DC rectifier operates in full-bridge mode for two AC power frequency half-cycles. N_half_HB = 2 indicates that the LLC AC-DC rectifier operates in half-bridge mode for two AC power frequency half-cycles. It should also be noted that Gain_LLC_FB = 0.45 and Gain_LLC_HB = 0.21 are within the design gain range.

[0395] For other input AC voltages between 140V and 190V, N_half_FB and N_half_HB can be determined first using a lookup table, and then the desired gain values ​​for Gain_LLC_HB and Gain_LLC_FB can be determined using a feedback circuit, as described above.

[0396] Using the above control strategy, it has been demonstrated that with a gain variation range of ±18%, the LLC AC-DC rectifier can maintain the output voltage at 50V when the input voltage varies from 100V to 240V, or with a variation range of 2.4:1, or 170V±41%.

[0397] It is important to note that an LLC converter with a gain variation range of ±18% will exhibit better performance than an LLC converter with a gain range of ±41%. This demonstrates the benefits of subharmonic modulation.

[0398] 5.2 Simultaneous wide range variation of output and input voltage

[0399] For the LLC AC-DC rectifier described in Section 5.1, if the output voltage needs to be regulated to any value between 40V and 60V, and the gain range is close to ±10%, the gain of the LLC AC-DC rectifier can be designed as follows:

[0400] Step 5.21: To achieve Vo = 60V at an input voltage of Vac = 100V, the maximum gain of the LLC AC-DC rectifier operating in full-bridge mode is:

[0401] Gain_LLC_FB_max=60V / 100V=0.6 (25.1)

[0402] Gain_LLC_FB_nom=0.6 / (1+0.1)=0.55 (25.2)

[0403] Gain_LLC_FB_min=0.55*(1–0.1)=0.5 (25.3)

[0404] Gain_LLC_FB=0.55±10% (25.4)

[0405] The gain range of the half-bridge operation is:

[0406] Gain_LLC_HB_max = 0.3 (26.1)

[0407] Gain_LLC_HB_nom=0.275 (26.2)

[0408] Gain_LLC_HB_min = 0.25 (26.3)

[0409] Gain_LLC_HB=0.275±10% (26.4)

[0410] The table below provides examples of control strategies to achieve the above design requirements.

[0411] Table 5.21: The required output voltage is Vo = 50V

[0412]

[0413]

[0414] Table 5.22: The required output voltage is Vo = 40V

[0415]

[0416] Table 5.23: The required output voltage is Vo = 60V

[0417]

[0418] Therefore, sub-frequency modulation control is adopted, switching between three modes: full-bridge, half-bridge, and zero-gain. When the input voltage changes from 100V to 240V, the output voltage can be arbitrarily adjusted between 40V and 60V, while the required gain change of the LLC AC-DC rectifier is ±10%.

[0419] Generally, when the input voltage varies widely from Vin_min to Vin_max, if an LLC AC-DC rectifier is required to produce an output voltage ranging from Vo_avg_min to Vo_avg_max, the following guidelines are recommended:

[0420] Rule 5.1: When the input voltage is close to Vin_min and the required output voltage is close to Vo_avg_max, full-bridge mode can be used. The output voltage is controlled by the switching frequency of the full-bridge LLC converter.

[0421] Guideline 5.2: When the input voltage is close to Vin_max and the required output voltage is close to Vo_avg_min, half-bridge mode can be used. The output voltage is controlled by the switching frequency of the half-bridge LLC converter. If the output voltage cannot be adjusted to Vo_avg_min by operating in half-bridge mode, sub-frequency modulation (a combination of half-bridge mode and zero-gain mode) can be used to adjust the output voltage to Vo_avg_min.

[0422] Guideline 5.3: When the input voltage is close to Vin_max and the required output voltage is close to Vo_avg_max, full-bridge mode and half-bridge mode can be used alternately. The output voltage is determined by the switching frequency of the full-bridge mode, the switching frequency of the half-bridge mode, and the time interval between the converter operating in half-bridge mode and full-bridge mode, N_LLC_FB / N_LLC_HB.

[0423] Guideline 5.4: When the input voltage is close to Vin_min and the required output voltage is close to Vo_avg_min, full-bridge mode and half-bridge mode can be used alternately. The output voltage is determined by the switching frequency of the full-bridge mode, the switching frequency of the half-bridge mode, and the time interval between the converter operating in half-bridge mode and full-bridge mode, N_LLC_FB / N_LLC_HB.

[0424] Guideline 5.5: For other input voltage values ​​and other desired output voltage values, a more detailed analysis can be performed to find the optimal values ​​for N_LLC_FB, N_LLC_HB, Gain_LLC_FB, and Gain_LLC_HB.

[0425] Guideline 5.6: N_LLC_FB and N_LLC_HB can be obtained, for example, through a lookup table based on input voltage Vin, output voltage Vo_avg, Gain_LLC_FB, and Gain_LLC_HB. Vin can be obtained from the input measurement, Vo_avg can be obtained from the system, and Gain_LLC_FB and Gain_LLC_HB are known after the design is completed.

[0426] Guideline 5.7: Closed-loop control circuits can be used to change the switching frequency of an LLCAC-DC rectifier to obtain the desired output voltage Vo_avg.

[0427] Figure 22 This is a block diagram of a controller according to one embodiment, which can be implemented for an LLC AC-DC rectifier over a wide input voltage variation range to achieve the above control strategy.

[0428] The input AC voltage Vac, output voltage Vo, and output reference voltage Vref are fed to the mode selection module 2210. Based on Vac, Vref, and Vo, and using the method described above, the mode selection module determines which of the five possible operating modes should be selected: (1) half-bridge mode, (2) full-bridge operation (also known as single-mode operation), and (3) half-bridge + full-bridge (HB + FB), (4) half-bridge + zero gain (HB + ZG), or (5) full-bridge + zero gain (FB + ZG) (also known as dual-mode operation). When a mode is selected ( Figure 22 In block 2220), the corresponding mode control signal (dashed line) is sent to the gate driver block 2230 of the controller to generate gate drive signals G1 to G4 for the converter switches to achieve operation in this mode. Figure 22 In the diagram, the five modes of the gate driver block are shown as controller 1 to controller 5. However, it should be understood that in actual implementation, only one controller receives the corresponding mode control signal.

[0429] When operating in half-bridge mode, controller 1 determines the switching frequency based on the output voltage and reference voltage to regulate the output voltage Vo to the reference voltage VREF. The input voltage can be continuously monitored. The controller generates four gate drive signals (e.g., ...) for the switches (MOSFETs) of the LLC AC-DC rectifier. Figure 21A (As shown). Fs_HB is the switching frequency of the LLC converter when it operates in half-bridge mode.

[0430] When operating in full-bridge mode, controller 2 determines the switching frequency based on the output voltage and reference voltage to regulate the output voltage Vo to the reference voltage VREF. The input voltage can be continuously monitored. The controller generates gate drive signals for the MOSFETs of the LLC AC-DC rectifier, such as... Figure 21A As shown. Fs_FB is the switching frequency of the LLC converter when it operates in full-bridge mode.

[0431] When operating in a combination of half-bridge and full-bridge modes (sub-frequency modulation), controller 3 determines N_HB, N_FB, Fs_FB, and Fs_HB based on the output voltage and reference voltage, thereby regulating the output voltage Vo to the reference voltage Vref. The input voltage can be continuously monitored. Controller 3 generates gate drive signals for the MOSFETs of the LLCAC-DC rectifier, such as... Figure 21A As shown. N_HB is the number of AC power frequency half-cycles when the LLC converter operates in half-bridge mode. N_FB is the number of AC power frequency half-cycles when the LLC converter operates in full-bridge mode.

[0432] When operating in a combination of half-bridge and zero-gain mode (sub-hybridization), controller 4 determines N_HB, N_ZG, and Fs_HB based on the output voltage and reference voltage, thereby regulating the output voltage Vo to the reference voltage Vref. The input voltage can be continuously monitored. Controller 4 generates four gate drive signals for the MOSFETs of the LLC AC-DC rectifier, such as... Figure 21A As shown. N_ZG is the AC power frequency half-cycle number when the LLC converter operates in zero-gain mode, which is determined by making all four switches (e.g., as shown)... Figure 21A This is achieved by turning off Q1, Q2, Q3 and Q4 shown in the diagram.

[0433] When operating in a combination of full-bridge and zero-gain modes (sub-frequency modulation), controller 5 determines N_FB, N_ZG, and Fs_FB based on the output voltage and reference voltage, thereby regulating the output voltage Vo to the reference voltage Vref. The input voltage can be continuously monitored. Controller 5 generates four gate drive signals for the MOSFETs of the LLCAC-DC rectifier, such as... Figure 21A As shown. It should be noted that in most cases, the combination of half-bridge and zero-gain mode operation is superior to the combination of full-bridge and zero-gain mode operation, because the output voltage is lower than that required in the half-bridge operation mode in this case.

[0434] In one embodiment, for dual-mode operation (subharmonic modulation operation), N_FB, N_HB, and N_ZG can be selected by looking up a table based on Vac, Vref, and Vo. The actual output voltage Vo can be adjusted by the switching frequencies Fs_FB and Fs_HB through a feedback loop.

[0435] When the input and output voltages change, the mode selection module switches from one operating mode to another. The mode change can occur at the zero-crossing point of the input AC voltage.

[0436] It should be understood that, Figure 22 The control diagram shown can also be used for any AC-DC rectifier based on other circuit topologies.

[0437] In-line frequency modulation of 6LLC converter

[0438] Sub-harmonic modulation produces low-frequency ripple below the power frequency, such as 25Hz in a 50Hz AC power system. Using the line frequency modulation described in this section, the output voltage can be reduced while keeping the low-frequency ripple at the power frequency.

[0439] Figure 23 The waveforms of the LLC converter under conventional control are shown. In the graph, the x-axis represents degrees, from 0 to 359 degrees, representing one complete AC line cycle. The waveforms of the rectified input voltage (top), current (middle), and input power (bottom) are displayed. Using conventional control, the LLC converter operates from 0 to 180 degrees, as shown... Figure 23 As shown. Using the parameters used in the waveform, the average input power is P51 = 220W.

[0440] Based on the inner line frequency modulation, the LLC converter operates (i.e., turns on) for a time interval shorter than half a cycle. The LLC converter stops operating (or turns off) for the remainder of the half cycle.

[0441] Figure 24 This displays a waveform example of line frequency modulation within a complete line cycle. The rectified input voltage (top), current (middle), and input power (bottom) waveforms are shown. Reference Figure 24 In the first half of the AC power frequency cycle:

[0442] The LLC converter stops operating between 0 and 49 degrees.

[0443] The LLC converter stopped operating between 131 degrees and 179 degrees.

[0444] The LLC converter operates between 50 degrees and 130 degrees.

[0445] In the second half of the AC power frequency cycle:

[0446] The LLC converter stops operating between 180 degrees (0+180) and 229 degrees (49+180).

[0447] · The LLC converter stops operating between 311 degrees (131 + 180) and 359 degrees (179 + 180).

[0448] · The LLC converter operates between 230 degrees (50 + 180) and 310 degrees (130 + 180).

[0449] When the LLC converter is operating, it can operate in full - bridge or half - bridge mode. In Figure 24 the example shown, the average input power is P52 = 168W. Since P52 is lower than P51, so Figure 24 the output voltage in this case is lower than Figure 23 the output voltage in that case. This can be expressed as follows:

[0450] Assume the load current is the same at Io and losses are ignored. Then, Pin = Pout = Vo * Io. So,

[0451] V51 = P51 / Io and V52 = P52 / Io

[0452] Since P52 < P51, then V52 < V51. Therefore, the output voltage can be reduced by in - line frequency modulation.

[0453] It should be noted that the start - up operation of the LLC AC - DC rectifier does not need to be symmetric about the 90 - degree point (the peak of the AC voltage). For example, it can be asymmetric up to the 90 - degree point, such as operating between 50 degrees and 110 degrees, or between 70 degrees and 140 degrees.

[0454] Figure 25 Another example showing in - line frequency modulation is when the LLC converter operates (turns on) between 0 degrees and 60 degrees and does not operate (turns off) between 61 degrees and 179 degrees. Using the parameters used in the figure, the average input power is approximately P53 = 44W. The output voltage (V53) will be lower than the above two cases.

[0455] In the above analysis, when the LLC converter is on (operating), the input current is controlled to follow the input voltage waveform. It is part of a sine wave. When the LLC converter is off (not operating), the input current is zero.​​​​​​​It should be noted that when the LLC converter is turned on, the input current can be controlled to any waveform. Figure 27 This illustrates an example of line frequency modulation when the input current is controlled to a constant value when the LLC converter is turned on. In this case, the average input power is P54 = 129 W.

[0458] The output voltage, determined by the input power, can also be controlled by the peak current when the LLC converter is turned on. For example, Figure 28 This shows that when the peak current is controlled to 1A ( Figure 24 The waveform shown is when the input power is P56 = 119W (reduced from 1.4A).

[0459] In some applications, it may be preferable to turn on the LLC converter when the instantaneous input voltage is high, such as in the approximately 90-degree region.

[0460] Figure 29 An embodiment of the control circuit for implementing line frequency modulation is shown. A voltage error amplifier uses the output voltage Vo, the reference voltage Vref, and the rectified AC voltage Vrec as inputs and generates a reference current Iref as the input to the current loop. The current error amplifier forces the rectified input current Irec to equal the reference current Iref by changing the switching frequency Fs. Gate drivers and logic circuitry generate gate drive signals for the four primary switches in the LLC converter. Zero-crossing of the AC input voltage needs to be detected. Theta_start is the starting angle at which the LLC converter begins operation. Theta_stop is the stopping angle at which the LLC converter stops operating (turns off). The difference between Theta_stop and Theta_start is the conduction angle of the LLC converter (representing the conduction time). By changing the conduction angle, the output voltage can be changed. In one embodiment, the values ​​of Theta_start and Theta_stop can be predetermined, which simplifies the control logic.

[0461] It's important to note that the inner-line frequency modulation method can also be applied to other AC-DC converter topologies, such as Boost converters, isolated Boost converters, and LCC resonant converters. It's also crucial to understand that when a Boost converter operates on an AC-DC rectifier, the output voltage is higher than the peak AC line voltage. Therefore, when the Boost MOSFET is turned off, the boost diode is reverse-biased, and no energy is transferred from the AC side to the output DC side. A subtle difference between Boost and LLC converters is that the inductance of the Boost inductor is significantly larger than that of the resonant inductor in an LLC converter. During the transition between turn-on and turn-off operation, energy stored in the boost inductor is transferred to the output DC side.

[0462] In summary, the output voltage of an AC-DC rectifier with internal frequency control can be adjusted in the following ways:

[0463] • The peak current of the rectifier input current, or equivalent to the input power when the rectifier is turned on.

[0464] • The conduction angle of the rectifier during the half-cycle of AC power frequency.

[0465] • The position of the rectifier relative to the half-cycle of the AC power frequency when it is turned on, such as near the zero crossing point (0 degrees to 60 degrees) or near the peak value of the AC voltage (around 90 degrees).

[0466] It should be noted that, in the embodiments of the present invention, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0467] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A controller for an AC-DC converter, characterized in that, Includes a rectifier circuit that converts AC input voltage to DC output voltage; the controller includes: Control logic that controls the rectifier circuit based on two or more operating modes; Each of the two or more operating modes determines the gain of the rectifier circuit; The controller selects an operating mode from two or more operating modes based on at least one of the AC input voltage value and the required DC output voltage value; The AC-DC converter provides a wide range of DC output voltages with power factor correction; The controller controls the rectifier circuit to operate in the first and second modes; The rectifier circuit operates in the first working mode for a duration of a first integer number of AC power frequency half-cycles, and operates in the second working mode for a duration of a second integer number of AC power frequency half-cycles.

2. The controller as described in claim 1, characterized in that, The operating modes include high-gain mode, low-gain mode, and zero-gain mode.

3. The controller as described in claim 2, characterized in that, The high-gain mode, low-gain mode, and zero-gain mode are alternately controlled by the controller.

4. The controller as described in claim 1, characterized in that, The DC output voltage includes a ripple voltage with a ripple frequency lower than the AC line frequency. The ripple frequency is determined by the alternation period of the two or more operating modes, and the alternation period is an integer multiple of the AC power frequency period or the AC power frequency half-cycle.

5. The controller as described in claim 1, characterized in that, The rectifier circuit uses an LLC converter; in, The controller controls the rectifier circuit in full-bridge, half-bridge, and non-operating modes. The rectifier circuit operates in full-bridge mode during the first integer number of AC power frequency half-cycles of the AC input voltage; The rectifier circuit operates in half-bridge mode during the second integer half-cycle of the AC power frequency of the AC input line voltage; The rectifier circuit is in non-operating mode during the third integer half-cycle of the AC power frequency of the AC input voltage.

6. The controller as described in claim 5, characterized in that, The DC output voltage of the AC-DC converter includes low-frequency ripple voltage; Among them, the frequency of the low-frequency ripple voltage is related to the frequency of the AC input line voltage.

7. The controller as described in claim 5, characterized in that, When the input AC voltage is in the low voltage range, the rectifier circuit operates in full-bridge mode; When the input AC voltage is in the high voltage range, the rectifier circuit operates in half-bridge mode; When the input AC voltage is in a low voltage range, the output DC voltage can be adjusted to the required DC value by changing the gain of the rectifier circuit in full-bridge mode. When the input AC voltage is in the high voltage range, the output DC voltage can be adjusted to the required DC value by changing the gain of the rectifier circuit in half-bridge mode.

8. The controller as claimed in claim 7, characterized in that, When the input AC voltage is between the low and high ranges, the rectifier circuit adjusts the DC output voltage to the desired value by alternating between full-bridge and half-bridge modes.

9. The controller as described in claim 5, characterized in that, The rectifier circuit operates in full-bridge mode during an integer number of AC power frequency half-cycles of the AC input voltage and stops operating during another integer number of AC power frequency half-cycles of the AC input voltage.

10. The controller as claimed in claim 5, characterized in that, When the rectifier circuit operates in full-bridge mode, the DC output voltage is adjusted to the desired value by changing the gain of the rectifier circuit.

11. The controller as claimed in claim 5, characterized in that, The DC output voltage is adjusted to the desired value by changing the ratio of the first integer to the second integer.

12. The controller as claimed in claim 5, characterized in that, The DC output voltage is adjusted to the desired value by changing the combination of the gain of the rectifier circuit and the ratio of the first and second integers.

13. The controller as described in claim 5, characterized in that, The rectifier circuit operates in half-bridge mode during the first integer number of AC power frequency half-cycles of the AC input voltage, and stops operating during the second integer number of AC power frequency half-cycles of the AC input voltage.

14. The controller as claimed in claim 5, characterized in that, The DC output voltage can be adjusted to the desired value by changing the gain of the rectifier circuit in half-bridge operation mode.

15. The controller as claimed in claim 1, characterized in that, The controller controls the rectifier circuit so that the rectifier circuit operates during the first part of the AC input voltage AC power frequency half-cycle and does not operate during the second part of the AC input voltage AC power frequency cycle.

16. The controller as claimed in claim 15, characterized in that, The rectifier circuit operates when the instantaneous AC input voltage is at its peak value or within ±45 degrees of its peak value, and does not operate when the instantaneous AC input voltage is at the zero-crossing point or within ±30 degrees of the zero-crossing point.

17. The controller as claimed in claim 15, characterized in that, The DC output voltage is adjusted by controlling the AC input power of the rectifier circuit during the time interval of the rectifier circuit's operation.

18. The controller as claimed in claim 15, characterized in that, The DC output voltage is adjusted by controlling the duration of the time interval when the rectifier circuit is operating.

19. The controller as claimed in claim 15, characterized in that, During the AC power frequency half-cycle, the rectifier circuit operates during the first part of the AC input voltage half-cycle and does not operate during the other part of the AC power frequency half-cycle.

20. An AC-DC converter, characterized in that, Includes the controller as described in claim 1.

21. The AC-DC converter as claimed in claim 20, characterized in that, The AC-DC converter is any one of the following: Boost converter, isolated Boost converter, PWM converter, LLC resonant converter, and LCC resonant converter.

22. An AC-DC converter, characterized in that, Includes the controller as described in claim 5.

23. An AC-DC converter, characterized in that, Includes the controller as described in claim 15.

24. The AC-DC converter as claimed in claim 23, characterized in that, The AC-DC converter is any one of the following: Boost converter, isolated Boost converter, PWM converter, LLC resonant converter, and LCC resonant converter.

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