EP4674043A1

EP4674043A1 - A circuit for providing power factor correction for an ac/dc converter

Info

Publication number: EP4674043A1
Application number: EP24727824.5A
Authority: EP
Inventors: Andrei BLINOV; Ievgen VERBYTSKYI; Andrii Chub; Dmitri VINNIKOV
Original assignee: Tallinn University of Technology
Current assignee: Tallinn University of Technology
Priority date: 2023-03-01
Filing date: 2024-03-01
Publication date: 2026-01-07
Also published as: WO2024180529A1; EE05886B1; EE202300007A

Abstract

A power converter with at least one inductor on the input and rectifier system that transform AC voltage to a unipolar DC pulse voltage that filtered with output capacitor. The PTC DC-DC unit can provide PTC and galvanic isolation in one conversion stage. The power converter can implement FET, IGBT, GAN, BIT, ITO and diodes as solid-state switches and solid-state rectifiers to enable the required current consumption. AC current and voltage as well as output voltage are measured by analog to digital converter. AC voltage further is used for forming reference current with PEL block and sine block. For reconfigurable converters a mode selector block defines feedforward gain according to current operation mode.

Description

A circuit for providing power factor correction for an AC/DC converter

Technical field

This invention relates to the field of control of active rectifiers with AC/DC converters with power factor correction (PFC) and, more particularly, to the field of one- or bidirectional soft- switching active rectifiers. The main areas of application of this invention are charging systems for electric vehicles and power supply systems for electronic devices.

State of the art

The PFC requirements for AC loads are specified in the European standard EN61000-3-2. This standard requires power factor close to one at power levels greater than 100 W. The PFC function is an integral part of most active rectifiers. It can be implemented as an additional module or as an integrated function built into a one stage active rectifier. Conventional power factor correction algorithms are based on Proportional-Integral fPI) controllers, which are simple in design but do not always allow the required Total Harmonic Distortion (THD) value to be achieved, causing significant current distortion, especially in zero crossing region. This drawback is caused by both the limited gain factor of the controller, as well as by the delay caused by the sampling step. It is known that the sampling delay can be reduced by increasing the switching frequency, but with it, switching power losses also increase. US9054597B2, 9.06.2015, Silergy Semiconductor Technology (CN) describes a boost PFC controller that uses variable frequency modulation to control the sampling delay. The boost PFC controller comprises an off signal generator for comparing an inductor current sample signal against a first control signal, an on signal generator for comparing a peak value of a second control signal having a first coefficient of proportionality to an off time of said power switch against a third control signal having a second coefficient of proportionality to an off duty cycle of said power switch, and a logic circuit connected to the signal generator and the off signal generator, wherein the logic circuit is turning on the power switch when the on signal is active, and turning off the power switch when the off signal is active. Simultaneously with the sampling delay, the PFC input current shape has distortions because of limited static gain value of the PI controller, the evaluation of which is not included in the description of the control method. In addition, reference signals are generated based on analog component’s values that additionally distort shape of current and complicate digital realization of PFC controller.

These distortions may be mitigated with post processing of PI controller signal in microprocessor unit as proposed in US patent No US7,821,237B2, 26.10.2010, Cirrus Logic, Inc., where a coupling, a switch and an inductor are connected together to form a switch-mode boost stage for receiving a rectified line input voltage and providing a link output voltage; a sensed current is observed from the switch-mode boost stage, a target current is generated proportionate to the rectified line input voltage, and a target current value of the target current and a sensed current value of the sensed current are compared, in response to the comparing, output is a two-level current comparison result signal and in response to the two-level current comparison result signal, is generated a switch control signal that has a cycle which is adjusted for controlling the switch so that the sensed current is approximately proportionate to the rectified line input voltage. The idea of invention to use finite-state machine for PFC control realization is equivalent to relay control, but due to such digital realization significant response delay is introduced and at the same time, it does not allow to flexibly change the control algorithm, which is potentially possible with microprocessor systems.

Since the gain coefficients of the proportional k_p and integral fa are dependent on the output power of PFC convertor, in the US patent No US8,797,004B2, 5.08.2014, TDK -Lambda UK Limited has proposed to adjust the operation of the regulator experimentally and save the mode parameters in look-up table for further its implementation in real operation. Because of nonconstant reference of PFC applications integral term of PI controller has limited efficiency and, as result, in common feedback configuration PFC applications have relatively large distortion that may effectively reduced with feedforward control. Here, redefining of controller parameters is performed iteratively, with a long transition process that worsens the PFC dynamics changes in operating conditions.

For instance, in the US patent application No US2005/0270814A1, 8.12.2005, In-Hwan Oh a feedforward control is used for correction of duty cycle value with sudden changes of input voltage. Such controller realization is tightly related to specifics of microcontroller FMS7401, feedforward block only claimed but is not described, PI controller parameters are fixed and their values are not estimated.

Pure feedforward control is proposed in the US patent application No US2009/0015214A1, 15.01.2009, Hung-Chi Chen, but is not so effective because requires an accurate model of PFC converter that is not always possible, moreover, any distortion and noise in measured values may cause a large error. The closest solution is described in US 7359224 B2, 15.04.2008, International Rectifier Corporation and is depicted in fig. 1 of said patent. The PFC converter consists of a boost converter circuit having a boost inductance and a power factor correction switch coupled in series with the boost inductance, the boost inductance and power factor correction Switch being coupled across the output of a rectifier being supplied with AC power from an AC line, the boost converter circuit further comprising a boost diode coupled to a junction between the inductor and the switch, an output of the boost diode coupled to an output capacitor, a DC bus voltage being provided across the output capacitor, further comprising a control circuit receiving as inputs a rectified AC input voltage from the rectifier, a signal proportional to current through the inductor and the DC bus voltage across the capacitor, and wherein the control circuit provides a pulse width modulated signal to control the on time of the power factor correction switch, the control circuit further comprising: a voltage regulator providing a regulated voltage signal based on a reference voltage and the DC bus voltage; a multiplier operable to multiply the regulated voltage signal by the rectified AC input voltage to provide a current reference signal; a current regulator receiving the current reference signal and the signal proportional to the inductor current, wherein the current regulator further comprises: a difference device operable to subtract the signal proportional to the inductor current from the current reference signal, a PI controller adapted to receive the output of the difference device and provide a first control signal; a feedforward device operable to receive the rectified AC input voltage and to provide a second control signal, wherein the second control signal has a smaller dynamic range than the AC input voltage; an adder operable to add the first control signal to the second control signal to provide a PWM reference signal; and a pulse width modulated signal generator operable to provide the pulse width modulated signal to control the on time of the PFC circuit, wherein the pulse width modulated signal generator utilizes the PWM reference signal to generate the pulse width modulated signal.

The above solution describes an aggregated feedback-forward communication control method used to amplify a PFC converter by improving the dynamics of the converter and reducing the THD value of the input current.

Common control solutions of PFC converters based on PI controllers have significant inertia because of the error reducing does not begin immediately after the appearance of the disturbance, but only after it causes a significant deviation of the current from the reference value. Additionally, integral term because of its inertia has limited impact to error mitigation for non-constant reference signal. In prototype of US7,359,224B2 is taken into account that the main disturbing factor is the change in the input voltage v_m according to the law v_m = dsinfoi/), which is easy to predict for designing of feedforward link. This allows to calculate feedforward value of duty cycle DFF as function of input voltage v_m and output voltage v_out, which, usually, may be considered as constant value Vout'. (1) that allows significantly reduce the error.

The residual error was eliminated by a conventional PI controller but it is not explained how to adjust the gain factors of P and I terms k_p and fa respectively. It is known that parameters k_p and fa have restrictions that defined by converter stability conditions and dynamics. Therefore, their nominal values k_P(_nom) and fa(_nom) that satisfy a minimum error are function of converter topology, its parameters value, and environment conditions. So, if converter operates with dynamically changed conditions, as PFC converter, values k_P(_nom) are also changed and should be dynamically estimated. Therefore, PI controller implementation with fixed gain, for PFC converters has mediocre results.

Disclosure of invention

The invention is a circuit for providing a power factor correction to AC/DC converters, with the circuit connected to an AC voltage source. The circuit comprises a power converter that is connected to an output capacitor and a current sensor. The circuit comprises a control circuit, an input of which is a rectified signal from the AC input voltage rectifier of the inductor current sensor, which is proportional to the current. The signals are fed to an analog-to-digital converter connected to a phase lock module in which an initial phase to a reference module is formed. The reference module is connected to a first input of a first output multiplier. A signal from an output of the first PI controller is fed to a second input of the first output multiplier, which forms a control voltage signal and is based on the difference between the output voltage and the setting voltage obtained by a first differential device and a ramp module, with the output signal of the setting current of the first output multiplier being separated from the measured current by a second differential device and is fed to the second PI controller. In the second PI controller, the first control signal is formed, which is driven to the first input of the summator. In the forward communication module, a second control signal is formed based on the input voltage, which is directed to the second input of the adder, and then the control signal is fed to the modulator, where a control signal to the transistors of the power converter is formed. The power converter shall include at least one transistor and one inductor. The signal from the second differential device is connected to the model unit, which, based on the parameters of the converter, has a gain factor of the proportional and integral parts of the second PI controller and is limited to the input control signal, input voltage, output voltage and input current of the input of the second PI controller. In the forward communication block, a second control signal is additionally formed using the output voltage and input current, and in the modulator, depending on the input signal, a sequence of high or low pulses is formed.

According to one embodiment of the invention, the signal from the first output multiplier, depending on the ambient temperature, is corrected by the second multiplier.

According to one embodiment of the invention, the transition function of the forward communication module is a defined model with a selection module.

According to one embodiment of the invention, the setting current is defined just by the signal Zre/.

In the proposed solution, which is based on a mathematical model and measured currents, the voltages and environmental parameters of the PFC converters dynamically determined the maximum value of the proportional part, since when using a variable setting size, this period had the greatest impact on reducing the error: (2) where kp(nom) is the nominal gain of the proportional part,

Vin is the input voltage,

Vout is the output voltage, iin is the input current,

L inductance,

R resistance,

C capacitance and

T temperature,

Whereas the gain factor Ki of the integral part is intended to eliminate residual error caused by temperature fluctuations, measurement error and other secondary factors. For example, a conventional boost converter as PFC converter can be described by a basic finite differential equation [7]: where v_g(n) is the voltage,

T_s is the temperature,

D(n) filling factor, and current i_rej(n) denotes inductor current IL.

A minor improvement of (3) that introduces the measured current value ZL(H) allows for a more robust combined feedforward-feedback control strategy:

First component of (4) is a feedforward block that corresponds to duty cycle of ideal boost converter and defines a feedforward estimation of duty cycle DFF, while the second component appears as modification of common proportional term of the PID controller. The difference of reference current i_rej{n+l) and the inductor current //.(//) in the second term may be defined as control error e(n+l): and other factors are denoted as nominal gain kp(_nOm) of proportional term

Then (4) may be simplified:

Actually, the proportional term gain may differ from the nominal value k_P(nom) thus generalized expression of controller is follow:

The embodiment of the invention is shown in Fig. 2 and comprises a power converter with at least one inductor on its input and a rectifier system that transforms AC voltage to a unipolar DC pulse voltage that is filtered with an output capacitor. The PFC DC/DC provides both PFC and galvanic isolation in a single conversion stage. The power converter can implement FET, IGBT, GAN, BJT, JTO and diodes as solid-state switches and solid-state rectifiers to enable the required current consumption. Both the AC current and voltage as well as the output voltage are measured by analog to digital converter 5. AC voltage is further used for forming a reference current with a PLL module 6 and a sine module 16. Also, the AC current, AC voltage and the output voltage are used in feedforward module 13 for utilizing basic equation of converter mathematical model (1) and (2). Additionally, the AC current and the output voltage are used to calculate proportional gain k_p and integral gain k, in model unit 18 for the second PI controller 12. For protecting against overheating, the current reference signal is scaled by temperature controlled amplifier 17. For reconfigurable converters mode selector module 19 defines feedforward gain according to current operation mode.

Another embodiment of invention is shown in Fig. 3. In this embodiment, the voltage control loop with the ramp 7, the first differential device 8 and the first PI controller 9 are eliminated and instead them a reference current is defined by signal i_ref. Such embodiment is applied for charging devices where output voltage for implementing constant current mode or constant current voltage of charging. The proper charging mode is defined in mode selector 19.

List of drawings

The invention is described in more detail below, with reference to the drawings, where:

Fig. 1 shows a schematic diagram of a boost PFC converter with combined feedforward and feedback control loop based on a PI controller (background art).

Fig. 2 is a schematic diagram of unified PFC converter with combined feedforward and feedback control loop based on model unit.

Fig. 3 is a schematic diagram of unified PFC converter without feedback voltage control loop based on model unit.

Fig. 4 describes timing diagrams of PFC converter.

Fig. 5 describes shapes of grid current.

Examples of carrying out the invention The proposed invention operation mode is considered on example of boost converter shown in Fig. 2.

A circuit for providing power factor correction 100 comprises a connection to an AC voltage source 1, the circuit includes a power converter 2 connected to an output capacitor 3 and a current sensor 4. The circuit for providing power factor correction (PFC) 100 further comprises a control circuit that receives as inputs a rectified AC input voltage from a rectifier, a signal proportional to current through the inductor from the current sensor 4. These inputs are all transmitted to an analog to digital converter 5 which is connected to a phase locked loop 6 that forms an initial phase for a reference block 16 connected to a first input of a first multiplier 10, to a second input of the first multiplier 10 the signal is supplied from an output of a first PI controller 9 that forms control voltage signal based on difference of output voltage and reference voltage provided with a first difference device 8 and a ramp module 7. The output signal of a reference current of the first multiplier 10 is subtracted to measured current with a second difference device 11 and is fed to a second PI controller 12 where a first control signal formed is delivered to a first input of an adder 13 and a second control signal is formed in a feedforward module 14 based on input voltage and is fed to a second input of an adder 13, thereafter a total control signal is fed to a modulator 15 that forms a control signal for transistors of the power converter 2.

The circuit for providing a power factor correction is characterized in that the power converter 2 comprises at least one transistor and one inductor, a signal from a second differential device 11 is connected to a model unit 18 that is defining gains of proportional and integral terms of a second PI controller 12 based on parameters of converter and limits the input control signal of the second PI controller 12, input, output voltages and input current, the feedforward module

14 forms a second control signal with output voltage and input current additionally, a modulator

15 forms sequence of high or low pulses depending on input signal.

The signal from the first output multiplier 10 is corrected with a second multiplier 17 depending the ambient temperature. The transfer function of the feedforward block 14 is defined by a model selector block 19, and the voltage control loop with the ramp 7, the first difference device 8 and the first PI controller 9 are eliminated and instead them reference current is defined by signal i_ref.

In such configuration analog to digital converter reads input voltage V_m, input current I_m and output voltage Vdc. Digital value of output voltage Vdcjdb is compared with reference voltage Vdc _ref generated with ramp generator 7 as shown in Fig. 4 a). After comparing of these signals, voltage error signal AU* is formed and goes to the first PI controller 9. Input voltage V_m is used as reference for phase locked loop (PLL) 6 for generating synchronized pulses of input voltage Vm. Unlike of prior art invention addition reference block 16 of generating pure normalized sinus wave inarm synchronized with input voltage that allows get ideal reference signal of grid current, Fig. 4 b). This synchronized sinus wave is multiplied with output signal of the first PI controller 9 VAout that defines of grid current amplitude and as result a reference grid current IrefPFC is formed, Fig. 4 c). If power converter 2 is overheated in the proposed invention the block 17 limits the reference current on level Irefjim, Fig. 4 c). This current is compared with input current I_m by second difference device 11 and current error MAout is formed that comes to input of model unit (MU) 18, Fig. 4 d). MU limits error MAout on levels M_max and M_mm, defines gain of proportional k_p and fa integral terms based on values of input current I_m and output voltage Vout as well as parameters of power converter frequency/ inductance /.i and capacitance Ci that provides flexible operation of converter and eliminates unstable operation during transients. The processed signal is coming to the second PI controller 12 together with tuned coefficients k_p and fa. After integration and amplification output signal of second PI controller 12 CAout forms first component of duty cycle D signal, Fig. 4 e) whereas second component is formed by feedforward (FFD) block CFFD 14 based on power converter regulation law Fig. 4 f). Main advantage of the proposed invention is that FFD block may change regulation parameters based on mode selection block (MS) 19 for reconfigurable and bidirectional power converter structures as well as smoothly change regulation parameters under changing environmental conditions, for instance temperature. A total signal of sum CAout and CFFD is connected to input of modulator M 15 that form control signal u_c of the power converter, which unlike of state of art device may have varied frequency, Fig. 4 j).

Fig. 5 illustrates timing diagrams for V_m = 230 V, Vout = 415 V, Zi = 700 pH, Ci = 440 pF,/= 80 kHz, k_p = 0.09; & = 0.016.

The invention proposes a control system for a PFC converter based on feedback control loop of output voltage and combined feedback and feedforward control loops of input current. Feedforward control loop has a reconfigurable structure, whereas feedback current control loop is realized with model unit defining the gain of integral and proportional terms of PI controller. As a result, the control system provides for mitigating of the current distortion, improving the dynamics and increasing the stability margin.

List of reference numbers

1 - an AC voltage source 2 - a power converter

3 - an output capacitor

4 - a current sensor

100 - a circuit for providing power factor correction (PFC) 5 - an analog to digital converter

6 - a phase locked loop

7 - a ramp module

8 - a first differential device

9 - first PI controller 10 - a first output multiplier

11 - a second differential device

12 - a second PI controller

13 - an adder

14 - a feedforward module 15 - a modulator

16 - a reference module

17 - a second multiplier

18 - a model unit

19 - a model selector module

Claims

1. A circuit for providing power factor correction to an AC/DC converter, said circuit is connected to an AC voltage source (1) and the circuit comprises a power converter (2) connected to an output capacitor (3) and a current sensor (4), said circuit further comprises a control circuit that receives as inputs a rectified AC input voltage from the rectifier, a signal proportional to current through the inductor from current sensor (4), all these signals are transmitted to analog to digital converter (5) which is connected to a phase locked loop (6) that form an initial phase for reference module (16), connected to a first input of a first output multiplier (10) and to a second input of the first output multiplier (10) is a signal from an output of the first PI controller (9) that forms a control voltage signal based on a difference of the output voltage and the reference voltage provided with a first differential device (8) and ramp module (7), whereas the output signal of the reference current of the first output multiplier (10) is subtracted from measured current with a second difference device (11) and is fed to a second PI controller (12) where the first control signal formed that is delivered to first input of adder (13), and the second control signal is formed in feedforward block (14) based on input voltage and is delivered to second input of adder (13), thereafter a total control signal goes to modulator (15) that forms a control signal to transistors of the power converter (2) characterized in that the power converter (2) comprises at least one transistor and one inductor, the signal from the second difference device (11) is connected to a model unit (18) that is defining gains of proportional and integral terms of the second PI controller (12) based on parameters of converter and limits the input control signal of second PI controller (12), input voltage, output voltage and input current, the feedforward module (14) forms a second control signal with output voltage and input current additionally, a modulator (15) forms sequence of high or low pulses, depending on input signal.

2. The circuit according to claim 1, characterized by that the signal from the first output multiplier (10) is corrected with the second multiplier (17), depending on the ambient temperature.

3. The circuit according to claims 1 and 2, characterized in that transition function of the forward communication module (14) is a defined model with the selector module (19).

4. The circuit according to claims 1, 2 and 3, characterized in that the device current is defined by the signal i_ref