Power converter system and method of operating a power converter system to reduce losses

Abstract

The invention relates to a power converter system comprising one or more input converters having an input converter topology, one or more output converters having an output converter topology, and a DC link comprising one or more energy storages, wherein the DC link is connected between the input converters and the output converters. The power converter system comprises a controller configured to adjust an operating point defined by an output frequency and an output angle to minimize operation at one or more predetermined undesired operating point ranges to reduce losses in the DC link. The one or more predetermined undesired operating point ranges are determined based on the input converter topology, the output converter topology, an angle difference between the output angle and an input angle, and a frequency difference between the output frequency and an input frequency.

Description

Technical Field

[0001] This invention generally relates to power converter systems. In particular, but not exclusively, this invention relates to reducing or minimizing DC link losses in power converter systems such as frequency converters. Background Technology

[0002] A typical frequency converter includes a rectifier circuit and an inverter circuit. The rectifier circuit, which may be referred to as, for example, a line bridge, network bridge, or rectifier bridge, is used to convert electrical energy from alternating current (AC) to direct current (DC). The inverter circuit, which may be referred to as, for example, a motor bridge, inverter bridge, or load bridge, is used to convert from DC to AC. It is well known that some rectifier and inverter circuits are bidirectional because they are capable of transmitting power in both directions. Frequency converters also include a DC link, or DC bus, or DC intermediate circuit, which typically includes one or more DC link capacitors, wherein the DC link is connected between the rectifier and inverter circuits.

[0003] Even though most of the electrical power is converted, some energy is lost as power losses. One of the components where these losses occur is in the DC link, specifically in one or more of its capacitors. Losses in capacitors are undesirable and reduce capacitor lifespan. Furthermore, stress in the DC link increases when the low-frequency components of the rectifier align with the low-frequency components of the inverter. Therefore, solutions are needed to reduce or minimize the losses and stress induced in the DC link, such as improving the efficiency of the frequency converter and extending the lifespan of the capacitor(s) in the DC link. Summary of the Invention

[0004] The object of this invention is to provide a power converter system and a method for operating the power converter system to reduce DC link losses in the power converter system. Another object of this invention is that the power converter system and method reduce or minimize DC link losses in the power converter system.

[0005] The objectives of the invention are achieved by a power converter system and a method for operating the power converter system, the power converter system being used to reduce losses in the DC link of the power converter system as defined in the respective independent claims.

[0006] According to a first aspect, a power converter system is provided, such as a power converter system including a frequency converter. The power converter system includes one or more input converters having an input converter topology and one or more output converters having an output converter topology. The power converter system also includes a DC link including one or more energy storage devices, wherein the DC link is connected between the one or more input converters and the one or more output converters. The power converter system also includes a controller configured to control the one or more output converters to generate one or more output waveforms having an output frequency and an output angle, and to determine the input frequency and input angle of the one or more input converters.

[0007] The controller is configured to adjust the operating point defined by the output frequency and the output angle to minimize operation at one or more predetermined undesirable operating point ranges in order to reduce losses in the DC link, wherein the one or more predetermined undesirable operating point ranges are determined based on: (i) the input converter topology, (ii) the output converter topology, (iii) the angular difference between the output angle and the input angle, and (iv) the frequency difference between the output frequency and the input frequency.

[0008] The determinations based on (i) to (iv) listed above may refer to: determining the input converter topology and output converter topology of the converter in question, and subsequently determining the losses occurring in the DC link at different operating points based on the angular and frequency differences of the determined topologies, and ultimately determining one or more predetermined undesirable operating point ranges.

[0009] The determination of losses occurring in the DC link may include, for example, modeling, performing calculations, using one or more tables (which have pre-stored data on losses occurring at different operating points in the DC link), or using pre-recorded operating data of a converter (which has the topology).

[0010] Additionally, alternatively, in addition to (i) to (iv), the relative load in the power converter system may also be considered in the determination. Thus, one or more predetermined undesirable operating point ranges can be determined for the topology in question based on (iii) angle difference, (iv) frequency difference, and (v) relative load.

[0011] Therefore, one or more predetermined undesirable operating point ranges can be defined by a combination of one or more values ​​of the output frequency relative to one or more values ​​of the input frequency and one or more values ​​of the output angle relative to one or more values ​​of the input angle.

[0012] A power converter system can be configured to have a nominal operating range, which is defined by a combination of one or more values ​​of the output frequency and one or more values ​​of the output angle.

[0013] The nominal operating range may include one or more acceptable operating point ranges in a non-overlapping manner and one or more predetermined undesired operating point ranges.

[0014] Furthermore, in a DC link, operation at one or more predetermined undesirable operating point ranges causes higher losses than operation at acceptable operating point ranges.

[0015] The nominal operating range may also include one or more preferred operating point ranges. One or more preferred operating point ranges may be predefined such that operation within these ranges results in lower losses in the DC link than operation within the acceptable operating point range. One or more preferred operating point ranges may be included within the acceptable operating point range, in which case operation within them results in lower losses than operation within adjacent acceptable operating point ranges. Alternatively, one or more preferred operating point ranges may be non-overlapping relative to the acceptable operating point ranges, and of course, non-overlapping relative to one or more predetermined undesired operating point ranges.

[0016] The nominal operating range can be further defined by the relative load of the power converter system.

[0017] The nominal operating range may include one or more predetermined undesirable operating point ranges, which are values ​​only for relative loads exceeding 0.7 (or 70%), or more preferably 0.6 (or 60%), or optionally exceeding 0.5 (or 50%).

[0018] A power converter system can be configured to have or receive information about the input converter topology and the output converter topology, and to define one or more predetermined undesired operating point ranges based on the received input converter topology and the received output converter topology. This information can be set by the person installing and configuring the power converter system, or it can be preset during the manufacture of the power converter system.

[0019] The power converter system can be configured to receive information about modulation techniques and further define one or more predetermined undesired operating point ranges based on those modulation techniques.

[0020] The controller can be configured to synchronize the output frequency and output angle with the input frequency and input angle, respectively. The output angle can then be adjusted to have a predetermined angular offset relative to the input angle to avoid operation at one or more unwanted phase angles associated with one or more predetermined unwanted operating point ranges.

[0021] The controller can be configured to adjust the output angle to change through one or more undesired phase angles associated with one or more predetermined undesired operating point ranges faster than when operating around one or more predetermined undesired operating point ranges. Optionally, the adjustment of the output angle can be based on a control reference that provides a higher rate of angle change at one or more undesired phase angles compared to phase angles around one or more undesired phase angles. The control reference can be a chirp-like signal arranged at one or more undesired phase angles to produce a higher rate of angle change. The purpose of the control reference can be to compensate for the motor frequency, thereby enabling faster transitions through the undesired phase angles.

[0022] The controller can be configured to adjust the output frequency to a predetermined frequency offset from the input frequency to ensure a faster transition through one or more unwanted phase angles associated with one or more predetermined unwanted operating point ranges.

[0023] The power converter system may include multiple output converters, preferably more than one of which are connected in parallel with respect to each other to the DC link. The controller may be configured to adjust the output angles of the multiple output converters relative to each other and relative to the power converter system to reduce losses in the DC link.

[0024] According to a second aspect, a method is provided for operating a power converter system to reduce losses in the DC link of the power converter system. The power converter system includes one or more input converters having an input converter topology and one or more output converters having an output converter topology. The DC link includes one or more energy storage devices, such as one or more capacitors and / or one or more batteries, and the DC link is connected between the one or more input converters and the one or more output converters.

[0025] The method includes determining the input frequency and input angle of the power converter system.

[0026] The method further includes: adjusting the output frequency and output angle of one or more output converters to minimize operation at one or more predetermined undesirable operating point ranges to reduce losses in the DC link, wherein the one or more predetermined undesirable operating point ranges are determined based on: (i) the input converter topology, (ii) the output converter topology, (iii) the angular difference between the output angle and the input angle, and (iv) the frequency difference between the output frequency and the input frequency.

[0027] The determination based on (i) to (iv) listed above may refer to: determining the input converter topology and output converter topology of the converter under discussion, and for said topology, determining the loss in the DC link at different operating points as a function of angle difference and frequency difference, and finally determining one or more predetermined undesirable operating point ranges.

[0028] The determination of losses occurring in the DC link may include, for example, modeling, performing calculations, using one or more tables (which have pre-stored data on losses occurring at different operating points in the DC link), or using pre-recorded operating data of a converter (which has the topology).

[0029] Additionally, alternatively, in addition to (i) to (iv), the relative load in the power converter system may also be considered in the determination. Thus, one or more predetermined undesirable operating point ranges can be determined for the topology in question based on (iii) angle difference, (iv) frequency difference, and (v) relative load.

[0030] For example, two of (iii) to (v) can be used as variables for fixing one of (iii) to (v). In some examples, the frequency difference can be fixed to a certain value, and then the angle difference and relative load can be used to define one or more predetermined undesired operating point ranges for the fixed frequency difference. Of course, other options for fixing one of (iii) to (v) are also possible.

[0031] The method may include: synchronizing the output frequency and output angle with the input frequency and input angle, respectively, and subsequently adjusting the output angle to have a predetermined angular offset relative to the input angle to avoid operation at one or more undesirable phase angles (the one or more undesirable phase angles being related to one or more predetermined undesirable operating point ranges).

[0032] As a supplement or alternative to the above synchronization, the method may include: adjusting the output angle to change, more quickly than, one or more undesirable phase angles around one or more predetermined undesirable operating point ranges, said undesirable phase angles being related to one or more predetermined undesirable operating point ranges.

[0033] The adjustment of the output angle can be based on a control reference (such as a nonlinear control reference) that provides a higher rate of angle change at one or more undesirable phase angles compared to phase angles around one or more undesirable phase angles.

[0034] The control reference can be a chirped signal, which is arranged to produce a higher rate of angular change at one or more undesired phase angles.

[0035] The method may include: adjusting the output frequency to differ from the input frequency by a predetermined frequency offset to ensure a faster transition through one or more unwanted phase angles associated with one or more predetermined unwanted operating point ranges.

[0036] Furthermore, the power converter system includes multiple output converters connected to a DC link, and the method may include: adjusting the output angles of the multiple output converters relative to each other (e.g., to avoid similar angles), and optionally, adjusting the output angles of the multiple output converters relative to the input angle of the power converter system (e.g., to avoid lower input angles) to reduce losses in the DC link.

[0037] This invention provides a power converter system and a method for operating the power converter system to reduce losses in the DC link of the power converter system. This invention offers advantages over known solutions because avoiding or minimizing operating time within one or more predetermined undesirable operating point ranges reduces losses and stress in the DC link and increases the lifespan of DC link components.

[0038] Based on the following "detailed implementation", various other advantages will become apparent to those skilled in the art.

[0039] In this paper, the expression “multiple” can refer to any positive integer starting from one (1).

[0040] The expression “multiple” can refer to any positive integers starting from two (2).

[0041] In this document, the terms “first,” “second,” and “third” are used to distinguish one element from others, and unless otherwise explicitly stated, they are not specifically prioritized or ordered.

[0042] The exemplary embodiments of the invention presented herein should not be construed as limiting the applicability of the appended claims. In this document, the verbs “comprising” and “including” are used as open-ended restrictions, and do not exclude the presence of features not described. Unless otherwise expressly stated, the features recited in the appended claims can be freely combined with each other.

[0043] The novel features considered characteristic of the invention are particularly set forth in the appended claims. However, the invention itself (its construction and operation, as well as its additional objects and advantages) will be best understood by reading in conjunction with the accompanying drawings and by the following description of specific embodiments. Attached Figure Description

[0044] The accompanying drawings illustrate some embodiments of the invention by way of example and not limitation.

[0045] Figure 1 A power converter system is schematically illustrated.

[0046] Figure 2 An example of the nominal operating range of a power converter system is shown.

[0047] Figure 3 Another example of the nominal operating range of a power converter system is shown.

[0048] Figure 4 A flowchart is shown for a method of operating a power converter system to reduce losses in the DC link of the power converter system.

[0049] Figure 5 The loss in the DC link of the power converter system according to the first example is shown.

[0050] Figure 6 The loss in the DC link of the power converter system according to the second example is shown.

[0051] Figure 7 The loss in the DC link of the power converter system according to the third example is shown.

[0052] Figures 8 to 10 Examples of frequency difference as a function of time, angle difference as a function of time, and motor speed difference as a function of time are shown.

[0053] Figures 11A to 11CAn example of the effect of angle difference on the DC link current of a power converter system with an input converter and an output converter is shown.

[0054] Figures 12A to 12C An example is shown illustrating the effect of phase offset in the angle of the output converter on the DC link current of a power converter system having one input converter and two output converters. Detailed Implementation

[0055] Figure 1 A power converter system 100 is schematically illustrated. The power converter system 100 includes one or more input converters 10 having an input converter topology and one or more output converters 12 having an output converter topology. The power converter system 100 also includes a DC link 14 comprising one or more energy storage devices 15, such as, but not limited to, one or more capacitors and / or batteries, wherein the DC link 14 is connected between the one or more input converters 10 and the one or more output converters 12. Furthermore, the power converter system 100 includes a controller 20 configured to control the one or more output converters 12 to generate one or more output waveforms having an output frequency 102F and an output angle 102A, and to determine the input frequency 101F and input angle 101A of the one or more input converters 10.

[0056] The controller 100 is configured to adjust the operating point defined by the output frequency 102F and the output angle 102A to minimize operation at one or more predetermined undesirable operating point ranges, thereby reducing losses in the DC link 14. One or more predetermined undesirable operating point ranges are determined based on the input converter topology, the output converter topology, the angular difference between the output angle 102A and the input angle 101A, and the frequency difference between the output frequency 102F and the input frequency 101F.

[0057] The determination based on the input converter topology, output converter topology, angle difference, and frequency difference may refer to: first, determining the input converter topology and output converter topology of the converter in question; then, determining the losses occurring in the DC link at different operating points based on the determined angle and frequency differences of the topologies; and finally, determining one or more predetermined undesirable operating point ranges. These one or more predetermined undesirable operating point ranges can then be stored in the memory (device) of the power converter system 100 for use during operation of the system 100.

[0058] The controller 20 can also be configured to control other functions of the power converter system 100, as well as functions related to safety or power quality.

[0059] The frequency converter 100 may optionally include an input filter 16, such as including one or more inductors and / or one or more capacitors, such as through each input phase. Figure 1 Multiple power sources 30 (e.g., the power grid or a power source connected to the power grid) and multiple loads 40 (such as an electric motor or a load connected to the electric motor) are also shown.

[0060] Figure 2 An example of the nominal operating range 129 of the frequency converter 100 is shown. The horizontal axis represents the angular difference 111. The vertical axis represents the frequency difference 112.

[0061] The nominal operating range 129 includes at least one or more predetermined undesirable operating point ranges 122 and other operating point ranges. These other operating point ranges may be, or may include at least one or more acceptable operating point ranges 124, preferably in a non-overlapping manner relative to the one or more predetermined undesirable operating point ranges 122. Therefore, one or more predetermined undesirable operating point ranges 122 (e.g., within the nominal operating range 129) can be defined by one or more values ​​of the output frequency 102F and one or more values ​​of the output angle 102A relative to a combination or function of the input frequency 101F and the input angle 101A. For example, a specific angular difference may be within or outside one or more predetermined undesirable operating point ranges 122 for the value of the frequency difference 112. In a DC link, operation at one or more predetermined undesirable operating point ranges 122 results in higher losses than operation at acceptable operating point ranges 124. Therefore, avoiding or minimizing operation within one or more predetermined undesirable operating point ranges 122 reduces losses in the DC link 14.

[0062] Figure 3 Another example of the nominal operating range 129 of the frequency converter 100 is shown. The horizontal axis represents the angular difference 111. The vertical axis represents the relative load 113 of the frequency converter 100. Therefore, in Figure 3 In this context, a nominal operating range 129 is defined for a single value of frequency difference 112 and / or output frequency 102F. This nominal operating range 129 includes a predetermined undesirable operating point range 122 and multiple other operating point ranges, i.e., multiple acceptable operating point ranges 124. The relative load 113 ranges from 0 to 100% (or 1). The angular difference 111 ranges from 0° to 120° (0 radians to 2π / 3 radians). Figure 3The terms “highest,” “high,” “medium,” and “low” refer to the relative amount of loss in DC link 14.

[0063] exist Figure 3 In the example, there exists a predetermined undesirable operating point range 122 centered on a value of approximately 80° angular difference 111. The range 122 of relative load 113 at lower values ​​is narrower (on the horizontal axis) compared to the value of relative load 113 at higher values. Range 122 is widest (on the horizontal axis) at 100% relative load.

[0064] Furthermore, the nominal operating range 129 may also include one or more preferred operating point ranges 126. One or more preferred operating point ranges 126 may be predetermined such that operation in one or more preferred operating point ranges 126 results in lower losses in the DC link 14 than operation in the acceptable operating point range 124. One or more preferred operating point ranges 126 may be included within the acceptable operating point range 124, in which case operation therein results in lower losses than operation in adjacent acceptable operating point ranges 124. Alternatively, one or more preferred operating point ranges 126 may be non-overlapping with respect to the acceptable operating point range 124, and of course, non-overlapping with respect to one or more predetermined undesirable operating point ranges 122.

[0065] exist Figure 3 In the example, there exists a preferred operating point range 126 centered on an angular difference 111 of approximately 0° to 30°, and another preferred operating point range at 120°. The preferred operating point range 126 is narrower at the relative load 113 value compared to the value at the higher value. The preferred operating point range 126 is widest at 100% relative load.

[0066] Figure 3 A nominal operating range 129 is shown, which includes a predetermined undesirable operating point range 122 only for values ​​of relative load exceeding approximately 0.6 (or 60%). Therefore, the nominal operating range 129 may consist only of an acceptable operating point range 124, which is substantially independent of the value of the angle difference 111 and / or certain values ​​of the output angle 102A relative to the load. In many cases, when the relative load is sufficiently low, the losses occurring in the DC link 14 may be substantially the same for all values ​​of the angle difference 111 and / or the output angle 102A. However, for higher values ​​of the relative load 113, the losses in the DC link 14 can actually vary depending on the angle difference 111 and / or the output angle 102A, as illustrated.

[0067] Generally, it should be noted that in DC link 14, various combinations of input and output converter topologies exhibit varying power losses, particularly under higher relative loads, for example, such as Figures 5 to 7 As shown. The power loss in DC link 14 varies depending on the frequency 112 and the angle difference 111, as well as the topology of the converter under discussion. Modulation techniques can also have some effect on the loss.

[0068] Figure 4 A flowchart is shown of a method for operating a power converter system 100 to reduce losses in the DC link 14 of the power converter system 100. The method steps can be executed using a controller 20. Therefore, the controller 20 can be configured to execute the method steps and / or cause some other(multiple) means(s) of the system 100 to execute them.

[0069] Project 400 or method step 400 refers to the optional initiation phase of a method.

[0070] Item 410 or method step 410 refers to: determining the input frequency 101F and input angle 101A of the frequency converter 100. The input frequency 101F and input angle 101A can be determined using voltage and / or current measuring devices (such as (multiple) voltage and / or current sensors). Alternatively, the input frequency 101F and input angle 101A can be provided to the power converter system 100 by another device (communicatingly connected to the power converter system 100). In some embodiments, the input frequency 101A can be predetermined / assumed to be the nominal frequency of the power supply 30 (such as the mains). Therefore, for the frequency difference 112, only the output frequency 102F needs to be determined.

[0071] In various embodiments, the input frequency 101F may refer to the frequency of the power grid, for example, 50 Hz or 60 Hz (close to 50 Hz). A determined input angle 101A may be selected as a reference for determining the output angle 102A and / or angle difference 111. For example, the input phase voltage may be used as a reference value to determine the output angle 102A and / or angle difference 111.

[0072] Item 420 or method step 420 refers to: adjusting the output frequency 102F and output angle 102A of one or more output converters 10 to minimize operation at one or more predetermined undesirable operating point ranges 122, thereby reducing losses in the DC link 14, wherein the one or more predetermined undesirable operating point ranges 122 are determined based on the following: input converter topology, output converter topology, angular difference 111 between output angle 102A and input angle 101A, and frequency difference 112 between output frequency 102F and input frequency 101F.

[0073] Optionally, the relative load 113 of the power converter system 100 may be considered in the determination of one or more predetermined undesirable operating point ranges 122. The relative load 113 may also be considered in addition to the input converter topology, output converter topology, angle difference 111, and frequency difference 112. Therefore, one or more predetermined undesirable operating point ranges 122 can be determined for the topology in question based on angle difference, frequency difference, and relative load.

[0074] The method may include: determining the input converter topology and output converter topology of the converter in question, and then, optionally for said topology, determining the losses occurring at different operating points of the DC link as functions of angle and frequency differences at different relative loads 113, and finally determining one or more predetermined undesirable operating point ranges 122. The determined predetermined undesirable operating point ranges 122 may be stored in the storage device of the power converter system 100 for use during its operation.

[0075] For example, such as Figure 3 As shown, depending on the combination of topologies, one or more operating point ranges may exist, as will be explained in further detail below, where losses in DC link 14 (such as in its capacitors) are higher than losses in other surrounding operating point ranges. These can be predefined and stored in the controller 20 of the power converter system 100. Therefore, the controller 20 can be configured to at least minimize operation in such a predetermined undesirable operating point range 122. For example, the method may include synchronizing the output frequency 102F and output angle 102A with the input frequency 101F and input angle 101A, respectively, so as to... Figure 3 The preferred operating point range 126 on the left side is used to prevent the relative load 113 from being at a high value or increasing to a high value (in this case, above about 75%).

[0076] The method can stop at item 499 or method step 499.

[0077] Figure 5The losses in the DC link 14 of a power converter system 100 according to the first example are shown. The input converter 10 is arranged with a topology called a six-pulse diode rectifier. Furthermore, the output converter 12 is arranged with a topology called a half-bridge. The horizontal axis represents the output angle 102A or angle difference 111. The vertical axis represents the relative load 103 in watts. It can be seen that for the value of the relative load 103 below 50% (or 0.5), the power profile is essentially horizontal. However, there are two operating point ranges around the output angle 102A or the angle difference 111 of approximately 20° and 80°, which cause fewer losses in the DC link 14 compared to operating in other operating point ranges adjacent to them. Operating in these operating point ranges (i.e., acceptable operating point range 124 or preferred operating point range 126) results in less loss in the DC link 14 than operating near, for example, 45° or 100°, which can be predefined as a predetermined undesirable operating point range 122.

[0078] Figure 6 The losses in the DC link 14 of the power converter system 100 according to the second example are shown. The input converter 10 is arranged with a topology called a six-pulse diode rectifier. Furthermore, the output converter 12 is arranged with a topology called a T-type inverter. The horizontal axis represents the output angle 102A or angle difference 111. The vertical axis represents the relative load 103 in watts. In this case, the power profile is essentially horizontal for a relative load 103 value less than 60% (or 0.6). However, there are two distinct operating point ranges around the values ​​of the output angle 102A or angle difference 111, approximately 22° and 82°. Operating near or at 22° causes less loss in the DC link 14 compared to operating in other operating point ranges adjacent to 22°. This can be predefined as a predetermined undesirable operating point range 122. On the other hand, operating near or at 82° causes less loss in the DC link 14 than operating in other adjacent operating point ranges. This can be predefined as the preferred operating point range 126. Other operating points in the preferred operating point range 126 can be included in the acceptable operating point range(s) 124.

[0079] Figure 7The losses in the DC link 14 of the power converter system 100 according to the third example are shown. The input converter 10 is arranged with a topology called a T-type rectifier. Furthermore, the output converter 12 is arranged with a topology called a T-type inverter. The horizontal axis represents the output angle 102A or angle difference 111. The vertical axis represents the relative load 103 in watts. Again, in this case, the power profile is essentially horizontal for the value of the relative load 103 being less than 50% (or 0.5). However, there are two distinct operating point ranges around the value of the output angle 102A or angle difference 111: approximately 10° and 80°. Operating closer to or at 10° causes fewer losses in the DC link 14 compared to operating in other operating point ranges adjacent to 10°. This can be predefined as the preferred operating point range 126. On the other hand, operating closer to or at 80° causes more losses in the DC link 14 than operating in other adjacent operating point ranges. This can be predefined as a predetermined undesirable operating point range 122. Other operating points can be included in the multiple acceptable operating point ranges 124. Optionally, operating ranges close to or at 10° can be included in the multiple acceptable operating point ranges 124. Furthermore, operating ranges close to or at 120° can be considered another preferred operating point range 126 or included in the multiple acceptable operating point ranges 124. This is similar to... Figure 3 The situation is shown.

[0080] Therefore, returning to the combination Figure 4 The methods shown and discussed, and especially given that Figure 5 and Figure 7 It may be advantageous that the method may include: synchronizing the output frequency 102F and the output angle 102A with the input frequency 101F and the input angle 101A, respectively, and subsequently adjusting the output angle 102A to have a predetermined angular offset relative to the input angle 101A to avoid operation at one or more undesirable phase angles (the one or more undesirable phase angles being related to one or more predetermined undesirable operating point ranges 122). Therefore, as... Figure 3 As shown, the angle difference 111 can be initially adjusted to zero, and then slightly (if any) adjusted to have a predetermined angle offset, for example, within the range of 10° to 20°. For example, when the motor setpoint is close to the mains frequency, the motor frequency is synchronized with the mains frequency, and the motor angle and the mains angle are synchronized. Then, a small angle offset value is applied to pursue or even ensure continuous operation at some other points besides the predetermined undesirable operating point range 122. On the other hand, for in Figure 6 This may not be beneficial in terms of the topology used in the case shown.

[0081] Alternatively or additionally, the method may, for example, include: adjusting the output angle 102A to change through one or more undesirable phase angles (the one or more undesirable phase angles being associated with one or more predetermined undesirable operating point ranges 122) more quickly at operating points around one or more predetermined undesirable operating point ranges 122. This may refer to the controller 20 changing the operating point passing through the one or more undesirable phase angles faster than other operating points. This can be performed, for example, by adjusting the output angle 102A based on a control reference, such as for or in the controller 20 for controlling the output value, wherein the control reference provides a higher rate of angle change at one or more undesirable phase angles compared to phase angles around one or more undesirable phase angles. Thus, at or near one or more undesirable phase angles, the operating time is minimized. The control reference may be non-linear so as to provide a higher rate of angle change at one or more undesirable phase angles 122 than at phase angles around one or more undesirable phase angles 122. As an example, the control reference is a chirped signal arranged to produce a higher rate of angle change at one or more undesirable phase angles. As will be described later below Figures 8 to 10 The example shown is an illustration of the effect of a comparative reference, as mentioned in this article.

[0082] As another example, the method may include adjusting the output frequency 102F to differ from the input frequency 101F by a predetermined frequency offset to ensure a faster transition through one or more undesired phase angles, said undesired phase angles being associated with one or more predetermined undesired operating point ranges 122. For example, with the motor setpoint frequency at 49.5 Hz (close to, for example, the mains frequency of 50 Hz), a reduction in motor speed to, for example, 49 Hz increases the frequency difference 112. This would ensure a transition twice as fast through the undesired operating point range 122, resulting in lower stress on the DC link capacitor 15.

[0083] Given the examples disclosed above, it becomes clear that controller 20 can be configured to use one or more predetermined undesired operating point ranges 122, which are determined by a combination of topology, angle differences 111, frequency differences 112, and optionally relative load 113. A specific frequency (at which speed and angle adjustments are performed) depends on the combination of topologies.

[0084] For example, for a diode rectifier and a three-stage converter, the worst-case scenario is a combination of a 50Hz grid frequency as the power supply (30Hz) and a 100Hz motor frequency as the load (40Hz). For a three-stage grid converter and a three-stage inverter, the worst-case scenario is at close frequencies, meaning, for example, a 50Hz grid and a 50.1Hz motor.

[0085] Figures 8 to 10 Examples of frequency difference 112 as a function of time, angle difference 111 as a function of time, and motor speed difference as a function of time are shown, in which the motor is load 40. These figures illustrate the effect of a control reference, including a chirped signal arranged to produce a higher rate of angular change at one or more undesired phase angles.

[0086] Figure 8 A first frequency difference 51 with a linear reference signal, a second frequency difference 52 with a first control reference (with a first gain value), a third frequency difference 53 with a second control reference (with a second gain value), and a fourth frequency difference 54 with a third control reference (with a third gain value) are shown. The third gain value is the highest, the second gain value is the second highest, and the first gain value is the lowest. In the cases of 52 to 54, the control reference may be nonlinear, or due to its shape or otherwise, provide a higher rate of angular change at one or more undesired phase angles 122 than at phase angles around one or more undesired phase angles 122.

[0087] Figure 9 A first angular difference 61 with a linear reference signal, a second angular difference 62 with a first linear control reference, a third angular difference 63 with a second reference, and a fourth angular difference 64 with a third control reference are shown. In the cases of 62 to 64, the control reference may be nonlinear, or due to its shape or otherwise, provide a higher rate of angular change at one or more undesired phase angles 122 than at phase angles around one or more undesired phase angles 122.

[0088] Figure 10 A first motor speed difference 71 with a linear reference signal, a second motor speed difference 72 with a first control reference, a third motor speed difference 73 with a second control reference, and a fourth motor speed difference 74 with a third control reference are shown. In the cases of 72 to 74, the control reference may be nonlinear, or due to its shape or otherwise, provide a higher rate of angular change at one or more undesired phase angles 122 than at phase angles around one or more undesired phase angles 122.

[0089] Figures 8 to 10 An example with a predetermined undesirable operating point range 122 is shown, which is located at an angular phase difference of 180° or approximately 180° (or π), representing the phase angle difference between the motor and the power grid phases. As described above, different gains are used to apply compensation using a control reference (i.e., including chirp-like signals) to illustrate the differences in angular slope around the undesirable operating point range 122.

[0090] For a typical two-pole pair 50Hz motor operating at a nominal speed of 1500rpm, Figure 10 The diagram illustrates the effect of control references (such as chirp-like signals) on motor speed. The most aggressive use of compensation via the reference signal results in a peak difference of less than 3 rpm, meaning that less than 0.2% speed difference is introduced as a disturbance. This disturbance will only slightly affect motors above 300kW; however, for lower rated power motors, the disturbance will be negligible.

[0091] Figures 11A to 11C An example of the effect of the angle difference 111 on the DC link current 16C of a power converter system 100 is shown, which has an input converter 10 and an output converter 12. Figure 11A A power converter system 100 is schematically shown. It will be understood that a power supply 30 connected to the input of the power converter system 100 and a load 40 connected to the output of the power converter system 100 may be present. Figure 11A The input current 16I, output current 16O, and capacitor current 16C of DC link 14 are shown.

[0092] like Figure 11B and Figure 11C As shown, with Figure 11C Compared to the smaller angle difference 111 and its capacitor current 16C, Figure 11B The large angular difference 111 in the DC link 14 resulted in a higher amplitude of the capacitor current 16C. Figure 11B The angular difference in 111 is 180°, however Figure 11C The angle difference is approximately 40°. Therefore, the controller 20 of the power converter system 100 (or in the method described above) can be configured to change the angle difference 111 or perform a phase shift when operating at or near 180° in order to reduce losses in the DC link 14.

[0093] Figures 12A to 12CAn example is shown illustrating the effect of the phase offset in the angles of the output converters 12, 12B on the DC link current of the power converter system 100 (which has one input converter 10 and two output converters 12, 12B). It is understood that a power supply 30 connected to the input of the power converter system 100 and a load 40 connected to the output of the power converter system 100 may exist. The power converter system 100 may include a plurality of output converters 12, 12B, which are preferably more than one output converter connected in parallel with respect to each other to the DC link 14. More than two output converters 12, 12B may exist. Optionally, there may be two or more input converters 10, 10B connected to the DC link 14, which are preferably connected in parallel with respect to each other, such as... Figure 1 As shown.

[0094] Figure 12A The diagram illustrates the input current 16I in DC link 14, the first output current 16O_1 in DC link 14 toward the output converter 12 (such as the first output converter), the second output current 16O_2 in DC link 14 toward the second output converter 12B, and the capacitor current 16C in DC link 14. Optionally, each output power converter 12, 12B may have a local DC link capacitor (not shown) with a relatively small capacitance value.

[0095] from Figure 12B and Figure 12C It can be seen from this that when with Figure 12C Compared to the smaller phase shift and its capacitor current of 16C, Figure 12B The small phase offset between the angles of the output converters 12 and 12B in the DC link 14 results in a higher amplitude in the capacitor current 16C. Figure 12B The phase shift in the middle is approximately 40°, however Figure 12C The phase offset is 180°. Therefore, the controller 20 of the power converter system 100 can be configured to change or execute the phase offset of the angle to change the angle of at least one of the output converters 12, 12B away from a similar angle relative to the angle of the other output converter 12, 12B in order to reduce losses in the DC link 14.

[0096] Therefore, in various embodiments, the controller 20 can be configured to adjust the output angles of the plurality of output converters 12, 12B relative to each other to reduce losses in the DC link 14.

[0097] exist Figures 12A to 12CIn this case, if possible, the angles of the output currents 16O_1 and 16O_2 can be phase-shifted (e.g., the two output converters 12 and 12B are 180° relative to each other), thus avoiding the simultaneous extraction of peak current (or power) from the DC link 14.

[0098] Additionally, the controller 20 can be configured to adjust the output angles of the multiple output converters 12, 12B relative to the input angle of the power converter system 100, thereby avoiding the extraction of peak current (or power) from the DC link 14 when the input current 16I is low (or exhibits a trough).

[0099] Preferably, the two output converters 12, 12B can be configured to allow simultaneous power extraction when the input current 16I is at its peak, meaning that the DC link 15 (such as one or more of its capacitors) is charging. By doing so, DC link ripple and power loss are reduced, while the lifespan of the DC link capacitors 15 is increased.

[0100] Each output power converter 12, 12B can be configured to control its own phase offset or current angle based on the voltage ripple in the DC link 14, such that it draws current / power, for example, near the top of the voltage ripple.

[0101] Alternatively, the output converters 12, 12B can be controlled to operate by using a unique ID in system 100 (e.g., inverter 3 in N), and (if necessary) to perform phase shifting based on that unique ID (e.g., (3-1)*360° / n).

[0102] In some embodiments, control may be communication-based, wherein a central controller (such as controller 20) sets an ideal phase offset for each converter 12, 12B based on parameters such as the number of working units, power, and unit load.

Claims

1. A power converter system (100), comprising: One or more input converters (10), the one or more input converters (10) having an input converter topology; One or more output converters (12, 12B) having an output converter topology; DC link (14), the DC link (14) including one or more energy storage units (15), wherein the DC link (14) is connected between the one or more input converters (10) and the one or more output converters (12, 12B); as well as A controller (20) is configured to control the one or more output converters (12, 12B) to generate one or more output waveforms having an output frequency and an output angle, and to determine the input frequency and input angle of the one or more input converters (10). The controller (100) is configured to adjust the operating point defined by the output frequency and the output angle to minimize operation at one or more predetermined undesirable operating point ranges (122) to reduce losses in the DC link (14), wherein the one or more predetermined undesirable operating point ranges (122) are determined based on: - The input converter topology - The output converter topology - The angle difference between the output angle and the input angle, and - The frequency difference between the output frequency and the input frequency.

2. The power converter system (100) of claim 1, wherein the one or more predetermined undesirable operating point ranges are defined by one or more values ​​of the output frequency and the output angle relative to a combination of the input frequency and the input angle.

3. The power converter system (100) as claimed in claim 1 or 2, wherein the power converter system (100) is configured to have a nominal operating range defined by a combination of one or more values ​​of the output frequency and one or more values ​​of the output angle. The nominal operating range includes one or more acceptable operating point ranges in a non-overlapping manner and one or more predetermined undesirable operating point ranges. In the DC link, operation at one or more predetermined undesirable operating point ranges causes higher losses than operation at acceptable operating point ranges.

4. The power converter system (100) as claimed in any one of claims 1 to 3, wherein the nominal operating range further includes one or more preferred operating point ranges.

5. The power converter system (100) as claimed in any one of claims 1 to 4, wherein the nominal operating range is further defined by the relative load of the power converter system (100).

6. The power converter system (100) of any one of claims 1 to 5, wherein the controller is configured to synchronize the output frequency and the output angle with the input frequency and the input angle, respectively, and The output angle is then adjusted to have a predetermined angular offset relative to the input angle to avoid one or more unwanted phase angle operations associated with one or more predetermined unwanted operating point ranges.

7. The power converter system (100) of any one of claims 1 to 6, wherein the controller is configured to: adjust the output angle to change, more quickly than, through one or more undesirable phase angles associated with the one or more predetermined undesirable operating point ranges around the operating points around the one or more predetermined undesirable operating point ranges.

8. The power converter system (100) of claim 7, wherein adjusting the output angle is based on a control reference. The control reference provides a higher rate of angular change at the one or more undesirable phase angles compared to phase angles around the one or more undesirable phase angles.

9. The power converter system (100) of claim 8, wherein the control reference is a chirped signal arranged to produce the higher rate of angular change at the one or more undesired phase angles.

10. The power converter system (100) of any one of claims 1 to 5, wherein the controller is configured to adjust the output frequency to differ from the input frequency by a predetermined frequency offset to ensure faster transition through one or more undesired phase angles associated with the one or more predetermined undesired operating point ranges.

11. The power converter system (100) of any one of claims 1 to 10, the power converter system (100) comprising a plurality of output converters (12, 12B) connected to the DC link (14), wherein the controller (20) is configured to adjust the output angle of the plurality of output converters (12, 12B) relative to each other to reduce losses in the DC link (14).

12. The power converter system (100) of claim 11, wherein the controller (20) is configured to adjust the output angle of the plurality of output converters (12, 12B) relative to the input angle of the power converter system (100) to reduce losses in the DC link (14).

13. A method for operating a power converter system (100) to reduce losses in a DC link (14) of the power converter system (100), the power converter system (100) including one or more input converters (10) having an input converter topology and one or more output converters (12) having an output converter topology, wherein the DC link (14) includes one or more energy storage devices (15), and the DC link (14) is connected between the one or more input converters (10) and the one or more output converters (12), the method comprising: - Determine the input frequency and input angle of the power converter system (100), and - Adjust the output frequency and output angle of the one or more output converters (10) to minimize operation at one or more predetermined undesirable operating point ranges (122) to reduce losses in the DC link (14), wherein the one or more predetermined undesirable operating point ranges (122) are determined based on the input converter topology, the output converter topology, the angle difference (111) between the output angle (102A) and the input angle (101A), and the frequency difference (112) between the output frequency (102F) and the input frequency (101F).

14. The method of claim 13, comprising: To synchronize the output frequency and the output angle with the input frequency and the input angle, respectively. The output angle is then adjusted to have a predetermined angular offset relative to the input angle to avoid one or more unwanted phase angle operations associated with one or more predetermined unwanted operating point ranges.

15. The method of claim 13 or 14, wherein the method comprises: The output angle is adjusted to change, in the case of operating points around the one or more predetermined undesirable operating point ranges, to pass through one or more undesirable phase angles associated with the one or more predetermined undesirable operating point ranges faster than at operating points around the one or more predetermined undesirable operating point ranges.

16. The method of claim 15, wherein adjusting the output angle is based on a control reference. The control reference provides a higher rate of angular change at the one or more undesirable phase angles compared to phase angles around the one or more undesirable phase angles.

17. The method of claim 16, wherein the control reference is a chirped signal arranged to produce the higher rate of angular change at the one or more undesired phase angles.

18. The method of claim 13, wherein the method comprises: The output frequency is adjusted to differ from the input frequency by a predetermined frequency offset to ensure a faster transition through one or more unwanted phase angles associated with one or more predetermined unwanted operating point ranges.

19. The method of any one of claims 13 to 18, wherein the power converter system (100) includes a plurality of output converters (12, 12B) connected to the DC link (14), the method comprising: Adjust the output angles of the plurality of output converters (12, 12B) relative to each other, and Optionally, the output angles of the plurality of output converters (12, 12B) can be adjusted relative to the input angle of the power converter system (100) to reduce losses in the DC link (14).

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