Power conversion device having active filter

Abstract

Disclosed is a power conversion device equipped with an active filter, the device comprising: a primary circuit unit for converting input AC power to AC power of a predetermined frequency; a transformer having a primary coil that receives the AC power converted by the primary circuit unit, and a secondary coil magnetically coupled to the primary coil to transform the magnitude of the voltage of the primary coil and output the resulting voltage; a secondary circuit unit configured to convert the voltage of the secondary coil into direct current and output the resulting voltage; and an active filter circuit unit comprising a capacitor having one end connected to a center tap of the secondary coil, and two switches that are connected in series to output terminals of the secondary circuit unit and have a connection node therebetween connected to the other end of the capacitor.

Description

Power conversion device with active filter

[0001] The present invention relates to a power conversion device, and more specifically, to a power conversion device having an active filter capable of blocking low-frequency ripples, etc. included in direct current current during the process of converting input alternating current power into direct current power for purposes such as battery charging.

[0002] Recently, with the rapid expansion of electric vehicle distribution along with the advancement of electric vehicle-related technology, the need for high-density / low-cost on-board chargers (OBCs), which are the core power conversion devices equipped in electric vehicles, is increasing.

[0003] Conventional onboard chargers primarily utilize a two-stage approach, converting AC grid power to DC and then converting the converted DC power using an insulated DC-DC converter. These conventional two-stage onboard chargers primarily utilize bulky, short-lived electrolytic capacitors for AC-DC conversion, resulting in a shorter lifespan and larger size for the charger itself, making them unsuitable for in-vehicle installation.

[0004] To overcome the shortcomings of these two-stage chargers, a one-stage charger has been developed that includes a primary switching circuit that converts AC grid power to AC, and a secondary switching circuit that converts AC to DC electrically insulated and coupled to the primary switching circuit through a transformer. This one-stage technology has the advantage of eliminating electrolytic capacitors and simplifying the circuit, thereby extending the lifespan and miniaturizing the charger, and increasing efficiency by reducing the number of power conversion stages.

[0005] However, since the 1-stage charger generates low-frequency ripples in the DC current output as the battery's charging current, an active filter is required as a decoupling circuit to remove them. Conventionally known active filters use the topology of a buck-boost DC-DC converter consisting of a switch, an inductor, and a capacitor, which increases volume and price. In particular, the DC decoupling method active filter using the topology of a buck-boost DC-DC converter has the problem of high capacitor voltage ratings and low-order harmonics in the ripple.

[0006] The matters described as background technology above are only intended to enhance understanding of the background of the present invention, and should not be taken as an admission that they correspond to prior art already known to those skilled in the art.

[0007] Accordingly, the present invention aims to solve a technical problem of providing a power conversion device having an active filter capable of blocking low-frequency ripples, etc. included in direct current current during the process of converting alternating current power into direct current power for purposes such as battery charging.

[0008] The problems to be solved by the present invention are not limited to those described above. Other problems and advantages of the present invention not mentioned above can be understood through the following description and will be more clearly understood through the embodiments of the present invention. Furthermore, those skilled in the art will readily appreciate that the problems and advantages of the present invention can be realized by the means and combinations thereof set forth in the claims.

[0009] As a means for solving the above technical problem, the present invention,

[0010] A primary circuit that converts input AC power into AC power of a preset frequency;

[0011] A transformer having a primary coil that receives AC power converted by the primary circuit section and a secondary coil that is magnetically coupled to the primary coil and converts and outputs the magnitude of the voltage of the primary coil;

[0012] A secondary circuit unit that converts the voltage of the secondary coil into direct current and outputs it; and

[0013] An active filter circuit including a capacitor having one end connected to the center tap of the secondary coil and two switches connected in series to the output terminal of the secondary circuit, the serially connected connection node being connected to the other end of the capacitor;

[0014] A power conversion device having an active filter including a

[0015] In an embodiment of the present invention, the secondary circuit section includes a first leg formed of a first switch and a second switch, each connected to one end of the secondary coil, and a second leg formed of a third switch and a fourth switch, each connected to the other end of the secondary coil, wherein the first leg and the second leg are connected in parallel with each other such that one end of the first switch is connected to one end of the third switch and one end of the second switch is connected to one end of the fourth switch, and the connection node of the first switch and the third switch and the connection node of the second switch and the fourth switch can constitute the output terminal.

[0016] In an embodiment of the present invention, the first switch and the third switch are turned on / off with a preset phase difference, the first switch and the second switch are turned on / off in a complementary relationship, the third switch and the fourth switch are turned on / off in a complementary relationship, and the first to fourth switches can be turned on / off with a constant duty of 0.5.

[0017] In an embodiment of the present invention, the capacitance value (C) of the capacitor is expressed by the formula

[0018]

[0019] (P bat : Required power of the battery connected to the above output terminal, V bat : It can be determined as the minimum value that satisfies the required voltage of the battery connected to the above output terminal, ω: angular frequency of the input AC power.

[0020] In an embodiment of the present invention, the voltage rating of the capacitor is given by

[0021]

[0022] (v C,peak : Voltage rating of the above capacitor, V M : Peak value of input AC voltage, I M : Peak value of input AC current, P bat : The required power of the battery connected to the above output terminal, ω: angular frequency of the input AC power, C: capacitance of the capacitor can be determined as follows.

[0023] An embodiment of the present invention may further include an active filter control unit including a calculator for calculating a target voltage of the capacitor, a PR controller for generating a control duty value for reducing an error between the target voltage and the measured actual voltage of the capacitor, a duty generator for generating an actual duty signal corresponding to the control duty value, and a switching signal generator for generating a gate signal for controlling two switches of the active filter circuit unit using the duty signal generated by the duty generator.

[0024] In an embodiment of the present invention, the active filter circuit may further include an inductor having one end connected to the other end of the capacitor and the other end connected to the connection node of the two switches.

[0025] According to the power conversion device having the above active filter, a filter of the AC decoupling method can be implemented using a smaller number of active and passive elements compared to the conventional one, thereby optimizing the ripple reduction effect along with a reduction in production cost and circuit size.

[0026] In addition, according to the power conversion device having the above active filter, circuit control and active filter control are possible through simple control, so the reliability of operation can be increased.

[0027] The effects that can be obtained from the present invention are not limited to the effects mentioned above, and other effects not mentioned can be clearly understood by a person having ordinary skill in the art to which the present invention belongs from the description below.

[0028] The following drawings attached to this specification illustrate preferred embodiments of the present invention, and together with the detailed description of the invention described below, serve to facilitate a better understanding of the technical idea of ​​the present invention. Therefore, the present invention should not be interpreted as being limited to the matters described in the following drawings.

[0029] FIG. 1 is a circuit diagram illustrating a power conversion device having an active filter according to one embodiment of the present invention.

[0030] Fig. 2 is a waveform diagram showing the operation of the secondary circuit in the embodiment of Fig. 1.

[0031] FIG. 3 and FIG. 4 are diagrams showing waveforms of voltage and current in each part of the circuit in the embodiment of FIG. 1.

[0032] Fig. 5 is a control block diagram explaining switch control of the active filter circuit in the embodiment of Fig. 1.

[0033] FIG. 6 is a circuit diagram illustrating a power conversion device having an active filter according to another embodiment of the present invention.

[0034] It may include a transformer (20) having a primary coil (21) that receives AC power converted by a circuit unit (10) and a secondary coil (22) that is magnetically coupled to the primary coil (21) and converts and outputs the magnitude of the voltage of the primary coil (21), a secondary circuit unit (30) that converts the voltage of the secondary coil (22) into DC and outputs it, and an active filter circuit unit (40) including a capacitor (C) that has one end connected to the center tap of the secondary coil (22) and two switches (S5, S6) that are connected in series to the output terminal of the secondary circuit unit (30) and whose serially connected connection nodes are connected to the other end of the capacitor (C).

[0035] The primary circuit unit (10) can be implemented with various types of conversion circuits that convert AC power transmitted from the grid into AC power of a preset frequency through switching. For example, the primary circuit unit (10) can employ various types of conversion circuits that convert grid power into AC in a 1-stage structure, such as a conventional full-bridge circuit, an interleaved totem pole-based conversion circuit, an unfolding full-bridge-based conversion circuit, a half-bridge matrix-based conversion circuit, and a full-bridge matrix-based conversion circuit.

[0036] The transformer (20) may include a primary coil (21) and a secondary coil (22). As in the operating principle of a typical transformer, the primary coil (21) and the secondary coil (22) are magnetically coupled to each other, so that the magnitude of the voltage of the primary coil (21) can be converted and induced in the secondary coil (22) according to the turns ratio of the primary coil (21) and the secondary coil (22). Accordingly, the output voltage of the primary circuit unit (10) is applied to both ends of the primary coil (21), and the voltage at both ends of the secondary coil (22) can be provided as the input voltage of the secondary circuit unit (30).

[0037] The secondary circuit unit (30) can convert AC power output from the secondary coil (22) of the transformer (20) into DC power and output it. In the case where the power conversion device equipped with an active filter according to one embodiment of the present invention is an onboard charger, a battery (50) can be connected to the output terminal of the secondary circuit unit (30).

[0038] The secondary circuit unit (30) may include a first leg (L1) formed of a first switch (S1) and a second switch (S2), each connected to one end of the secondary coil (22) of the transformer (20), and a second leg (L2) formed of a third switch (S3) and a fourth switch (S4), each connected to the other end of the secondary coil (22). The first leg (L1) and the second leg (L2) may be connected in parallel with each other, such that one end of the first switch (S1) may be connected to one end of the third switch (S3), and one end of the second switch (S2) may be connected to one end of the fourth switch (S4). The connection nodes of the first switch (S1) and the third switch (S3) and the connection nodes of the second switch (S2) and the fourth switch (S4) may constitute output terminals, each of which may be connected to two terminals of the battery (50).

[0039] The active filter circuit (40) may include a fifth switch (S5) and a sixth switch (S6), which are two switches that are connected in series between a capacitor (C) whose one end is connected to the center tap of the secondary coil (22) of the transformer (20) and an output terminal of the secondary circuit (30), and whose serially connected connection node is connected to the other end of the capacitor (C). The fifth switch (S5) and the sixth switch (S6) may be controlled to be in an on / off state in a complementary relationship, and the fifth switch (S5) or the sixth switch (S6) may be controlled by a carrier signal in the form of a triangle wave with a preset cycle and a modulation index (m p ) can be determined through comparison.

[0040] Hereinafter, the operation of a power conversion device equipped with an active filter according to an embodiment of the present invention having the configuration described above will be described in detail. However, in the embodiment of the present invention, since known techniques in the art can be applied to the primary circuit unit (10) and the transformer (20), a detailed description thereof will be omitted, and the secondary circuit unit (30) and the active filter circuit unit (40) will be described in detail.

[0041] Fig. 2 is a waveform diagram showing the operation of the secondary circuit in the embodiment of Fig. 1.

[0042] Referring to FIG. 2, in the embodiment of the present invention, the secondary circuit unit (30) is controlled so that the first leg (L1) and the second leg (L2) have a phase difference of θ, and the two switches in each leg can operate in a complementary relationship. That is, the first switch (S1) and the third switch (S3) are turned on / off with a phase difference of θ, the first switch (S1) and the second switch (S2) can be turned on / off in a complementary relationship, and the third switch (S3) and the fourth switch (S4) can also be turned on / off in a complementary relationship. In addition, all the switches (S1-S4) of the secondary circuit unit (30) have a constant duty (d) of 0.5. s ) can be turned on / off.

[0043] On / off control of each switch (S1-S4) is performed at a preset cycle (T s ) with a triangular wave-shaped carrier signal (C1, C3) and a duty (d) of 0.5 s ) can be achieved by a switch control signal generated by comparing the reference voltages corresponding to each other. Since this switch control signal generation technology is a known technology in the art, further detailed description will be omitted.

[0044] In addition, the power conversion device according to an embodiment of the present invention may have a separate control unit (controller) for switching control as described above. This control unit may be implemented using a technique known in the art for generating a gate signal for switch control, and therefore a more detailed description thereof will be omitted.

[0045] By this control, the voltage (v) between the connection node (a) of the first switch (S1) and the second switch (S2) and the connection node (b) of the third switch (S3) and the fourth switch (S4) ab ) and the voltage (v) of the connection node (a) of the first switch (S1) and the second switch (S2) a ) and the voltage (v) of the connection node (b) of the third switch (S3) and the fourth switch (S4) b ) 1 / 2 of the agreement( ) can be determined as shown in Fig. 2.

[0046] Here, the voltage (v) of the connection node (a) of the first switch (S1) and the second switch (S2) a ) and the voltage (v) of the connection node (b) of the third switch (S3) and the fourth switch (S4) b ) 1 / 2 of the agreement( ) can be expressed as in the following equation 1.

[0047] [Formula 1]

[0048]

[0049] FIG. 3 and FIG. 4 are diagrams showing waveforms of voltage and current in each part of the circuit in the embodiment of FIG. 1.

[0050] Referring to FIGS. 3 and 4, the main factors in a power conversion device having an active filter according to an embodiment of the present invention are explained using formulas.

[0051] Grid voltage (v) g ) and system current (i g ) is expressed as in the following equation 2, the system power (pg ) can be expressed as in Equation 3, and the system power (p) transferred from the primary side to the secondary side g ) is the power (p) delivered to the battery (50). bat ) and the power (p) transmitted to the capacitor (C) of the activity filter circuit (40) c ) can be expressed as Equation 4.

[0052] [Formula 2]

[0053]

[0054]

[0055] (V M , I M are the peak values ​​of grid voltage and grid current, respectively, t is time, and ω is the angular frequency of grid power.

[0056] [Formula 3]

[0057]

[0058] [Formula 4]

[0059]

[0060] Here, the power (p) delivered to the battery (50) bat ) and the power (p) transmitted to the capacitor (C) of the active filter circuit (40) c ) are set as in Equation 5 and Equation 6, respectively, and through the same process as Equation 7, the capacitor voltage (v) of the activity filter circuit (40) is set as in Equation 8. C ) can be determined.

[0061] [Formula 5]

[0062]

[0063] [Formula 6]

[0064]

[0065] [Formula 7]

[0066]

[0067] [Formula 8]

[0068]

[0069] The voltage (v1) of the secondary coil center tap connection terminal of the capacitor (C) of the active filter circuit (40) can be expressed as in the following equation 9. In addition, the modulation index (m) of the fifth switch (S5) and the sixth switch (S6) of the active filter circuit (40) p , -1< m p <1) When defining as in Equation 10, the voltage (v2) of the connection node of the capacitor (C) of the active filter circuit (40) and the fifth and sixth switches (S5, S6) can be determined as in Equation 11. As shown in Fig. 4, the modulation index (m p ) and a carrier signal (C5) in the form of a triangle wave having a preset period can be compared to determine the on / off of the fifth switch (S5), and the on / off state of the sixth switch (S6) can be determined in a complementary relationship with the fifth switch (S5).

[0070] [Formula 9]

[0071]

[0072] In Equation 9, the inductor voltage (v) across the secondary coil La , v Lb ) can be omitted because the average voltage is 0 V in the normal state.

[0073] [Formula 10]

[0074]

[0075] [Formula 11]

[0076]

[0077] Therefore, the voltage of the capacitor (v C ) can be determined as shown in the following equation 12.

[0078] [Formula 12]

[0079]

[0080] From equations 7 and 12, equation 13 can be derived, and from equations 5 and 13, equation 14 can be derived.

[0081] [Formula 13]

[0082]

[0083] [Formula 14]

[0084]

[0085] From the above equation 14, the capacitance value of the capacitor (C) can be determined as in the following equation 15.

[0086] [Formula 15]

[0087]

[0088] Here M p is the modulation index (m) of the fifth switch (S5) and the sixth switch (S6). p ) as the peak value of '-1 <M p Since it has a range of <1', the capacitance value of the capacitor (C) can be determined as a value that satisfies the range of the following equation 16.

[0089] [Formula 16]

[0090]

[0091] That is, the value of the capacitor (C) of the active filter circuit (40) is the required power (P) required to charge the battery connected to the output terminal of the secondary circuit (30). bat ) and required voltage (V bat ) and the primary circuit (10) can be determined by the frequency (ω=2πf, about 377 when f=60Hz) of the AC system power input.

[0092] Also, the voltage rating of the capacitor (C) is v C Since it is equal to the maximum value of , it can be determined as Equation 17 below from Equations 5 and 8.

[0093] [Formula 17]

[0094]

[0095] In this way, since the value and rated voltage of the capacitor (C) of the active filter circuit (40) can be obtained, the capacitor (C) having the minimum capacitance and rated voltage can be selected by considering the electrical characteristics required by the battery (50), thereby enabling selection of the optimal capacitor.

[0096] Meanwhile, the control of the fifth switch (S5) and the sixth switch (S6) of the active filter circuit (40) is performed by the actual voltage (v) of the capacitor (C). C ) and target voltage (v C * ) can be achieved through comparison.

[0097] Fig. 5 is a control block diagram explaining switch control of the active filter circuit in the embodiment of Fig. 1.

[0098] Referring to Fig. 5, the switching control of the active filter circuit (40) is performed by controlling the capacitor target voltage (v C *) and the target voltage (v) of the operator (110) and capacitor (C) that generates C *) and the measured capacitor voltage (v C ) to generate a control duty value to reduce the error of the PR (Proportional Resonant) controller (120), a duty generator (130) to generate an actual duty signal corresponding to the control duty value generated by the PR controller (120), and a switching signal generator (140) to generate a signal (gate signal) for controlling the switches (S5, S6) of the active filter circuit (40) using the duty signal generated by the duty generator (130). The active filter control unit of FIG. 5 may be included as a part of the control unit of the power conversion device according to an embodiment of the present invention.

[0099] As shown in Fig. 5, a power conversion device having an active filter according to an embodiment of the present invention is configured to operate two switches (S5, S6) constituting an active filter circuit (40) to determine a target voltage (v) of a capacitor (C) through an operation of a predetermined formula. C *) and the voltage (v) of the measured capacitor (C) C ) and can control the active filter through simple control that can minimize the error. That is, the power conversion device equipped with the active filter according to the embodiment of the present invention can help improve the operational reliability and reduce the overall size by simplifying the control structure of the active filter.

[0100] FIG. 6 is a circuit diagram illustrating a power conversion device having an active filter according to another embodiment of the present invention.

[0101] The embodiment illustrated in Fig. 6 has a structure in which an inductor (L) is additionally provided between the capacitor (C) of the active filter circuit (40) and the switches (S5, S6). By adding the inductor (L), the peak current of the series inductor connected to each end of the secondary coil (22) of the transformer (20) can be reduced, thereby reducing the rating of the switch.

[0102] As described above, the power conversion device equipped with an active filter according to various embodiments of the present invention can optimize the ripple reduction effect while reducing the production cost and circuit size by implementing an AC decoupling type filter using a smaller number of active and passive components compared to the prior art. In addition, the power conversion device equipped with an active filter according to various embodiments of the present invention can increase the reliability of operation because circuit control and active filter control are possible through simple control.

[0103] - Explanation of symbols -

[0104] 10: Primary circuit 20: Transformer

[0105] 21: Primary coil 22: Secondary coil

[0106] 30: Secondary circuit 40: Active filter circuit

[0107] 50: Battery

Claims

1. Primary circuit section that converts input AC power into AC power of a preset frequency; A transformer having a primary coil that receives AC power converted by the primary circuit section and a secondary coil that is magnetically coupled to the primary coil and converts and outputs the magnitude of the voltage of the primary coil; A secondary circuit that converts the voltage of the secondary coil into direct current and outputs it; and An active filter circuit including a capacitor having one end connected to the center tap of the secondary coil and two switches connected in series to the output terminal of the secondary circuit, the serially connected connection node being connected to the other end of the capacitor; A power conversion device having an active filter including:

2. In claim 1, the secondary circuit part, It includes a first leg composed of a first switch and a second switch, each connected to one end of the secondary coil, and a second leg composed of a third switch and a fourth switch, each connected to the other end of the secondary coil. The first leg and the second leg are connected in parallel with each other, such that one end of the first switch is connected to one end of the third switch, and one end of the second switch is connected to one end of the fourth switch. A power conversion device having an active filter, characterized in that the connection nodes of the first switch and the third switch and the connection nodes of the second switch and the fourth switch constitute the output terminal.

3. In claim 2, A power conversion device having an active filter, characterized in that the first switch and the third switch are turned on / off with a preset phase difference, the first switch and the second switch are turned on / off in a complementary relationship, the third switch and the fourth switch are turned on / off in a complementary relationship, and the first to fourth switches are turned on / off with a constant duty of 0.

5.

4. In claim 1, The capacitance value (C) of the above capacitor is given by the formula (P bat : Required power of the battery connected to the above output terminal, V bat : A power conversion device having an active filter, characterized in that the voltage required by the battery connected to the output terminal is determined as the minimum value satisfying ω: angular frequency of the input AC power.

5. In claim 1, The voltage rating of the above capacitor is given by (v C,peak : Voltage rating of the above capacitor, V M : Peak value of input AC voltage, I M : Peak value of input AC current, P bat : A power conversion device having an active filter, characterized in that the power required by the battery connected to the output terminal is determined as follows: ω: angular frequency of the input AC power, C: capacitance of the capacitor.

6. In claim 1, A power conversion device having an active filter, characterized in that it further comprises an active filter control unit including a calculator for calculating a target voltage of the capacitor, a PR controller for generating a control duty value for reducing an error between the target voltage and the measured actual voltage of the capacitor, a duty generator for generating an actual duty signal corresponding to the control duty value, and a switching signal generator for generating a gate signal for controlling two switches of the active filter circuit unit using the duty signal generated by the duty generator.

7. In claim 1, the active filter circuit part, A power conversion device having an active filter, characterized in that it further includes an inductor whose one end is connected to the other end of the capacitor and whose other end is connected to the connection node of the two switches.

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