Power converter and method for operating a power converter

Abstract

A power converter (10) comprising at least three booster modules for transferring power from an AC input side (2) to a DC output side (3). Each booster module has an input and an output which are separated in potential and can operate as a power factor correction module. The input of a first booster module (11) is connected to the input side (2) and its output is connected to the output side (3) to provide a first output current to the output side (3); the input of a second booster module (12) is connected to the input side (2) and its output is connected to a buffer capacitor (15) to provide a second output current to the buffer capacitor (15); the input of a third booster module (13) is connected to the buffer capacitor (15) and its output is connected to the output side (3) to provide a third output current to the output side (3).

Description

Technical Field

[0001] This invention relates to the field of electronic power converters. Specifically, it relates to power converters and methods for operating power converters. Background Technology

[0002] For example, an AC-DC converter for an on-board charger (OBC) used in electric vehicles typically includes two stages:

[0003] • Three power factor correction (PFC) modules, each controlling its corresponding input current in a sinusoidal manner and in phase with its corresponding input voltage, are embedded in a slow control loop to regulate the PFC output voltage; and

[0004] • Electrically isolated DC-DC converter with a slow control loop that regulates the output current, for example, for charging a battery, or regulates the output voltage, for example, when the battery is not connected.

[0005] The current design has the following drawbacks:

[0006] • Hardware complexity: On top of the three PFC modules, a DC-DC module with transformers must be designed. All these components must also be driven by signals, which must be generated and their levels regulated.

[0007] • Software complexity: A total of three different control loops must be designed and optimized to keep the entire system stable, which increases the difficulty of interaction between the control loops.

[0008] • Electrical and thermal losses: Each switching stage has at least 3% losses, so adding a DC-DC converter after PFC means the losses will be 6% or worse.

[0009] • Cost and failure risk: The material expenditure is enormous compared to the simplicity of the task to be accomplished (i.e., just a battery charger).

[0010] US 2012 / 0120697 A1 discloses a three-phase isolated rectifier with PFC, wherein a separate PFC module is connected to a three-phase AC power supply and its DC side is connected in parallel.

[0011] US 2015 / 0162823 A1 illustrates a PFC circuit with low total harmonic distortion.

[0012] WO 2018 / 002852 A1 discloses a converter with three conversion modules that can operate in both three-phase and single-phase modes. The outputs of the three conversion modules are connected in parallel. Each conversion module includes an indirect matrix converter, a transformer, a coupling inductor, and an H-bridge switching device. In single-phase mode, two conversion modules are operated to generate output current, while in the third conversion module, the indirect matrix converter is disabled, and the H-bridge switching device is used as an active filter on the output side. When in single-phase mode, the converter is complex and cannot effectively utilize the capabilities of the components. Summary of the Invention

[0013] Therefore, the object of the present invention is to provide a power converter and a method for operating a power converter of the above type, which overcomes at least one or more of the above-mentioned disadvantages.

[0014] A power converter is used to transfer power from at least the AC input side to the DC output side, the power converter including at least three power factor correction (PFC) modules: a first boost module, a second boost module, and a third boost module.

[0015] Each boost converter module has corresponding input and output terminals, which are voltage-separated.

[0016] in

[0017] Each boost module can operate as a power factor correction (PFC) module, drawing sinusoidal current at its respective module input.

[0018] In a configuration referred to as a series configuration,

[0019] • The input terminal of the first boost module is connected to the input side, and the output terminal of the first boost module is connected to the output side to provide a first output current to the output side;

[0020] • The input terminal of the second boost module is connected to the input side, and the output terminal of the second boost module is connected to a buffer capacitor to provide a second output current to the buffer capacitor;

[0021] • The input terminal of the third boost module is connected to a buffer capacitor, and the output terminal of the third boost module is connected to the output side to provide a third output current to the output side.

[0022] Using this topology, ripple in the total current on the output side can be compensated by using a relatively small buffer capacitor. This can also be done by almost completely discharging the buffer capacitor and then fully or almost fully charging it.

[0023] In this embodiment, the buffer capacitor is not an electrolytic capacitor. In this embodiment, it is a thin-film dielectric capacitor.

[0024] In an embodiment, the power converter, particularly the controller of the power converter, is configured to discharge the buffer capacitor to a voltage less than 30%, 50%, or 70% of the DC output voltage on the output side, particularly at each pulse of the third output current.

[0025] In the context of this application, the boost module can be understood as a general-purpose boost module that can operate as a PFC with the AC input and as a boost converter with the DC input. Various topologies can be used, such as flyback converters, H-bridge converters, etc.

[0026] A power accelerator (PFC) can present an adjustable resistive load to the AC input side while directly transferring the power drawn from the AC input side to the potentially electrically isolated DC output side. "Direct" power transfer means that the PFC does not compensate for, filter, or smooth power ripple that occurs at the input side at twice the AC input base frequency. Therefore, the PFC, and in this case, the boost module, does not include a smoothing capacitor that has a relevant effect at that frequency.

[0027] In this embodiment, the at least three boost modules lack power storage elements, specifically capacitors, designed to smooth current pulses occurring at twice the fundamental frequency of the AC source to which the power converter is designed to be connected. In other words, the boost modules do not contain any filter capacitors at all, or if filter capacitors are present, their capacitance should be such that they block current components at twice the fundamental frequency of the AC source to which the power converter is designed to be connected. Therefore, such capacitors do not exchange power and are not used to store power at such frequencies.

[0028] In this embodiment, the at least three booster modules have similar or particularly identical parameters.

[0029] In one embodiment, the power converter includes a controller configured to...

[0030] • Control the first boost converter module to draw sinusoidal current from its input terminal;

[0031] • Control the second boost converter module to draw sinusoidal current from its input terminal;

[0032] • Control the third boost module to provide a third output current to supplement the first output current, so that the sum of the third output current and the first output current is at least approximately constant.

[0033] This can be achieved by controlling the third boost module to minimize the deviation between the sum of the third output current and the first output current and a predetermined setpoint. "Predetermined" means, for example, that the setpoint is stored in the controller or determined by another monitoring and control loop.

[0034] Therefore, the controller can be configured to operate at least one boost module (or a general-purpose boost module) as a PFC and operate another boost module as an output current generator that compensates for the output ripple of the other boost module operating as a PFC.

[0035] In this embodiment, the power converter is reconfigurable, meaning it includes switchable connections between boost modules, resulting in different topologies for the power converter. In addition to the topologies described above, it can also be reconfigured to have the following configurations:

[0036] • The inputs of the three boost modules are separate from each other, and their outputs are connected in parallel to the output side.

[0037] In this configuration, known as a three-phase parallel configuration, the power converter can operate in three-phase mode, transferring power from a three-phase AC power supply to the DC output side. The three input terminals can be connected to the three-phase AC source in either a Delta (triangle) or Y configuration.

[0038] In this embodiment, the power converter can be reconfigured to have the following configuration:

[0039] • The inputs of the three boost modules are connected in parallel to each other, and their outputs are connected in parallel to the output side.

[0040] In this configuration, known as a single-phase parallel configuration, the power converter can operate in single-phase mode, that is, transfer power from a single-phase AC power supply to the DC output side.

[0041] In one embodiment, the power converter includes a controller configured to operate based on a charging current limit I. lim Charging current setpoint value I set The maximum rated current I of the power converter max The power converter switches the connections between the boost modules based on the power supply configuration (single-phase or three-phase) it operates on.

[0042] • When the power converter is connected to the three-phase AC input side, it is connected in a three-phase parallel configuration;

[0043] • When the power converter is connected to the single-phase AC input side, if the charging current limit I lim Less than the charging current setpoint value I setTwice the maximum rated current I and if the charging current limit is less than the maximum rated current I max Four-thirds are connected in series; and

[0044] • Otherwise, connect in single-phase parallel configuration.

[0045] This enables the converter to operate automatically at the highest permissible charging power, depending on the situation.

[0046] A method for controlling a power converter includes the following steps:

[0047] • Control the first boost converter module to draw sinusoidal current at its input terminal;

[0048] • Control the second boost module to draw sinusoidal current at its input terminal;

[0049] • Control the third boost module to provide a third output current to supplement the first output current, so that the sum of the third output current and the first output current is at least approximately constant.

[0050] The features of a method can be combined with the features of a device, and vice versa. Attached Figure Description

[0051] The subject matter of the invention will now be explained in more detail with reference to exemplary embodiments shown in the accompanying drawings, which schematically illustrate:

[0052] Figure 1 This is a possible topology for PFC to achieve electrical isolation;

[0053] Figure 2 This is another possible topology for PFC to achieve electrical isolation;

[0054] Figure 3 This is the output current of the boost converter module when operating in single-phase mode.

[0055] Figure 4 It is used to supplement Figure 3 The output current of the boost converter module;

[0056] Figure 5 It is the structure of an electrically isolated power converter configured for single-phase operation;

[0057] Figure 6 It is the structure of an electrically isolated power converter configured for three-phase operation; and

[0058] Figure 7 This refers to the charging current used for different configurations of the converter. Detailed Implementation

[0059] The reference numerals used in the figures and their meanings are listed in summary form in the reference numeral list. In principle, the same reference numerals are used for the same parts in the figures.

[0060] Figure 1 and Figure 2 Possible topologies for a three-phase PFC to achieve electrical isolation are shown. These are merely examples of a large number of possible topologies that include boost converter modules. Figure 1 In this topology, there are three PFC boost inductors Tr0, Tr1, and Tr2, each with two coils, so that the PFC function and current isolation are implemented in the same stage. Therefore, this topology contains three identical electrically isolated PFC circuits. As long as this circuit operates with a three-phase AC mains input, the output ripple will be very small, and the battery can be charged directly without cascading additional stages.

[0061] Figure 2 The circuit clearly refers to only one phase, so for three-phase operation, three such PFC modules will be used.

[0062] exist Figure 1 and Figure 2 In this circuit, the output capacitor has a very small capacitance because it only suppresses high-frequency noise, not smooths the output or charging voltage and / or current. If three modules are used in three-phase operation with their outputs connected in parallel, large electrolytic capacitors are not required.

[0063] The purpose of these two examples is to illustrate some of the many possible ways to implement a power converter that operates as an electrically isolated three-phase PFC, which can be directly connected to the battery without the need for an additional second stage.

[0064] about Figure 1 and Figure 2 The drawback of the described topologies is that, when operating in single-phase AC input mode, their output current will have a sinusoidal square curve waveform, resulting in 100% ripple. Figure 3 As shown.

[0065] Figure 3 The output current of the boost module in single-phase operation is shown. The boost module acts as a resistive load on input side 2, drawing a sinusoidal current in phase with the voltage on input side 2. Therefore, the power delivered by the PFC follows a squared sine signal.

[0066] With DC voltage on output side 3, power pulsation will generate current, and its pulse is twice the AC input base frequency.

[0067] While most batteries would withstand such a charging current, most OEMs would not accept it. In traditional solutions, a large capacitor must be used to eliminate the ripple valleys, and then a second stage (i.e., a DC-DC converter) after PFC is inevitably used again to further smooth and control the charging current.

[0068] According to the present invention, the topology of the power converter 10 is modified to use boost modules 11, 12, and 13 in different ways. For example... Figure 3 As shown, one is arranged to provide a first output current, while the other is arranged to provide a complementary output current, which, when added to the first output current, produces at least a nearly constant current, i.e., a current with very small or negligible ripple. Figure 4 A supplement is shown Figure 3 The complementary output current of the boost converter module.

[0069] Figure 5 and Figure 6 Two different configurations of an electrically isolated, reconfigurable power converter 10 are shown, comprising three boost modules: a first boost module 11, a second boost module 12, and a third boost module 13. The power converter 10 transfers power from input side 2 to output side 3. Depending on the configuration, input side 2, or the AC side, includes one or three pairs of power converter input terminals. Depending on the configuration, they can be individually connected to the first AC input phase 21, or they can be connected to the second AC input phase 22 and the third AC input phase 23. If three pairs of power converter input terminals are present, they can be connected in a delta or star (or Y) configuration. Output side 3, or the DC side, includes a pair of power converter output terminals. An output capacitor 16 is shown connected in parallel with output side 3. The output capacitor 16 has a relatively small capacitance because it will only need to filter out small defects in the output current and voltage, preventing the circuit from generating high-frequency components. More specifically, its capacitance allows it to block current components that are twice the fundamental frequency of the AC frequency at which the power converter is designed to operate. Therefore, the output capacitor 16 does not exchange power and is not used to store power at this frequency.

[0070] Each boost converter module includes a module input terminal and a module output terminal. Each module input terminal consists of a pair of corresponding input terminals. Each module output terminal consists of a pair of corresponding output terminals.

[0071] The controller 50 is configured to measure the current and / or voltage in the power converter 10 and control the switching of the boost module. It can also be configured to control a configuration switch (not shown) to reconfigure the topology of the power converter 10.

[0072] Figure 5The structure of an electrically isolated power converter in a configuration for single-phase operation is shown to achieve the aforementioned current increase. A first boost module 11 is connected to the power converter input side 2 at its module input and to the output side 3 at its module output. A second boost module 12 is also connected to the input side 2 at its module input, in parallel with the first boost module 11, and to a buffer capacitor 15 at its module output. A third boost module 13 is connected to the buffer capacitor 15 at its module input and to the power converter output side 3 at its module output.

[0073] like Figure 3 As shown, the upper branch of the first boost module 11 generates the first output current. The lower branches, including the second boost module 12 and the third boost module 13, operate as follows:

[0074] • The second boost module 12 is controlled to draw sinusoidal current from its input and charge the buffer capacitor 15, and

[0075] • The third booster module 13 is controlled to produce a voltage with Figure 4 The complementary waveform of the output current causes the buffer capacitor 15 to discharge.

[0076] Ideally, the sum of the output currents of the first boost module 11 and the third boost module 13 will be perfectly flat, i.e., without ripple.

[0077] The size of the buffer capacitor 15 allows it to store only a sufficient amount of energy so that the third boost module 13 can generate a complementary current without fully discharging. The voltage waveform at the buffer capacitor 15 can have any amount of ripple, limiting the capability of the third boost module 13 to approximately 80% to 95% of its nominal capability. However, the capacitance of the buffer capacitor 15 can be significantly smaller than that required in a conventional two-stage converter. Therefore, the buffer capacitor 15 can be implemented not as an electrolytic capacitor, but as, for example, a thin-film dielectric capacitor.

[0078] Figure 6 The structure of the same electrically isolated power converter in a configuration for three-phase operation is shown. The module inputs are connected to the corresponding AC input phases 21, 22, and 23. The module outputs are connected in parallel to output side 3.

[0079] When charging a lithium-ion battery, the charging current must be limited to a value that does not exceed the battery's maximum charging voltage. This is represented by I. lim The charging current limit is a function of the state of charge. As the state of charge increases, it decreases until it reaches zero at 100% charge.

[0080] Based on the charging current limit I lim Charging current setpoint value I set The maximum rated current I of the charger max The power converter 10 operates under a power supply configuration (single-phase or three-phase), such as the PFC module. Figure 6 As shown, connect all three in parallel, or as... Figure 5 As shown, connect the two connected in series with the third in parallel.

[0081] • In the case of a three-phase power supply, the PFC modules are always connected in parallel, and the charging current is set to min(I lim ,I set ).

[0082] • In the case of a single-phase power supply, if 2I set >I lim and If so, the PFC modules are configured in series; otherwise, they are connected in parallel.

[0083] Therefore, the charger can operate at its maximum rated power when using single-phase and three-phase power supplies in parallel configurations.

[0084] Figure 7 The maximum charging current is shown in the three-phase configuration (solid line), single-phase parallel configuration (dashed line), and single-phase series configuration (dotted line) of the same power converter 10. However, the charging current is constant in three-phase operation (solid line), while an inherent ripple exists in the single-phase parallel configuration (dashed line). The AC component of this current can be used to monitor the battery's health and state of charge. However, if the peak value of the ripple charging current exceeds the charging current limit, the single-phase series configuration is used instead, resulting in the constant charging current being limited to 2 / 3 of the rated value (dotted line).

[0085] Although the invention has been described in this embodiment, it should be clearly understood that the invention is not limited thereto, but may be embodied and practiced differently in other ways within the scope of the claims.

Claims

1. A power converter (10) for transmitting power from an AC input side (2) to a DC output side (3), the power converter (10) comprising at least three boost modules: a first boost module (11), a second boost module (12) and a third boost module (13). Each boost converter module has a corresponding input terminal and an output terminal, which are electrically separated. Each boost module can operate as a power factor correction (PFC) module, drawing sinusoidal current at its respective module input. in, In a configuration known as a cascaded configuration, • The input terminal of the first boost module (11) is connected to the input side (2), and the output terminal of the first boost module (11) is connected to the output side (3) to provide a first output current to the output side (3); • The input terminal of the second boost module (12) is connected to the input side (2), and the output terminal of the second boost module (12) is connected to the buffer capacitor (15) to provide a second output current to the buffer capacitor (15); • The input terminal of the third boost module (13) is connected to the buffer capacitor (15), and the output terminal of the third boost module (13) is connected to the output side (3) to provide a third output current to the output side (3); as well as The power converter (10) includes switchable connections between boost modules (11, 12, 13), resulting in different topologies for the power converter (10), which can thus be reconfigured into a configuration known as a three-phase parallel configuration. • The inputs of the three boost converter modules (11, 12, 13) are separate from each other, and their outputs are connected in parallel to the output side (3); and The power converter (10) can be reconfigured to a configuration known as a single-phase parallel configuration, wherein • The inputs of the three boost converter modules (11, 12, 13) are connected in parallel, and their outputs are connected in parallel to the output side (3); and The power converter (10) includes a controller (50) configured to operate based on a charging current limit I. lim Charging current setpoint value I set The maximum rated current I of the power converter max The power converter (10) switches the connections between the boost modules (11, 12, 13) according to the power supply configuration in operation. • When the power converter (10) is connected to the three-phase AC input side (2), the three-phase parallel configuration is used for connection; • When the power converter (10) is connected to the single-phase AC input side (2) and the charging current limit I lim Less than the charging current setpoint value I set Twice that of the maximum rated current I and the charging current limit is less than the maximum rated current I max In four-thirds of the cases, the connection is made in the aforementioned series configuration; and • Otherwise, connect in the single-phase parallel configuration.

2. The power converter (10) according to claim 1, wherein, The at least three boost modules have no power storage element, which is designed to smooth current pulses that occur at twice the base frequency of the AC source to which the power converter (10) is connected.

3. The power converter (10) according to claim 2, wherein, The power storage element is a capacitor.

4. The power converter (10) according to claim 1, wherein, The at least three booster modules have the same parameters.

5. The power converter (10) according to claim 1, comprising a controller (50) configured to: • Control the first boost module (11) to draw sinusoidal current at its input; • Control the second boost module (12) to draw sinusoidal current at its input; • Control the third boost module (13) to provide the third output current to supplement the first output current, so that the sum of the third output current and the first output current is at least approximately constant.

6. The power converter (10) according to claim 5, wherein, The controller is configured to discharge the buffer capacitor (15) to a voltage less than 50% or less than 70% of the DC output voltage on the output side.

7. The power converter (10) according to claim 5, wherein, The controller is configured to discharge the buffer capacitor (15) to a voltage less than 50% or less than 70% of the DC output voltage on the output side at each pulse of the third output current.

8. A method for controlling a power converter (10) according to any one of claims 1-7, comprising the following steps: • Control the first boost module (11) to draw sinusoidal current at its input; • Control the second boost module (12) to draw sinusoidal current at its input; • Control the third boost module (13) to provide the third output current to supplement the first output current, so that the sum of the third output current and the first output current is at least approximately constant; The method further includes the following steps: based on the charging current limit I lim Charging current setpoint value I set The maximum rated current I of the power converter max The power converter (10) switches the connections between the boost modules (11, 12, 13) according to the power supply configuration in operation. • When the power converter (10) is connected to the three-phase AC input side (2), the three-phase parallel configuration is used for connection; • When the power converter (10) is connected to the single-phase AC input side (2) and the charging current limit I lim Less than the charging current setpoint value I set Twice that of the maximum rated current I and the charging current limit is less than the maximum rated current I max In four-thirds of the cases, the connection is made in the aforementioned series configuration; and • Otherwise, connect in the single-phase parallel configuration.

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