Method for dc under- and / or overvoltage regulation of an electric power converter, electric power converter and dc microgrid

Abstract

The present invention relates to a method for DC undervoltage regulation and / or DC overvoltage regulation for an electric power converter (100). The method includes: monitoring (410) a DC voltage (41) by the electric power converter (100) and comparing the DC voltage (41) with undervoltage regulation limits (42, 43) and / or overvoltage regulation limits (420), wherein when DC undervoltage regulation or DC overvoltage regulation is disabled, the undervoltage regulation limits (42, 43) and / or overvoltage regulation limits are at least partially, preferably completely, reduced to compensate. The method further includes: activating (430) DC undervoltage regulation or DC overvoltage regulation in response to the DC voltage (41) reaching the undervoltage regulation limits (42, 43) or the overvoltage regulation limits, respectively, and adjusting (440) the DC voltage (41) based on the undervoltage load regulation coefficient or the overvoltage load regulation coefficient, respectively, and finally disabling (450).

Description

Technical Field

[0001] This invention generally relates to DC undervoltage and DC overvoltage regulation functions used in power converters such as inverters and rectifiers. In particular, but not exclusively, this invention relates to DC undervoltage and DC overvoltage regulation in DC microgrids, such as regulation used in marine power systems. Background Technology

[0002] If needed, known power converters can have undervoltage and overvoltage regulator functionality by enabling the converter to support the system's DC voltage, such as its common DC link or bus voltage. Enabling these functions is not mandatory, and in some cases, they can even be harmful. For example, in electric motor applications (such as marine main propulsion), overvoltage regulators are typically disabled because when activated, they will begin to increase motor power by increasing its speed to limit the rise in DC voltage, which is clearly undesirable.

[0003] In a DC microgrid, the balance between power generation and consumption can be observed through the DC voltage. If the DC voltage rises, more energy is generated than consumed, and vice versa. When the voltage drops, the more aggressive the voltage change, the greater the imbalance. For example, without an balance between production and consumption, the power system will collapse due to excessively high or low voltage rises, and equipment will trip based on undervoltage and overvoltage protection functions. However, undervoltage and overvoltage protection functions differ from undervoltage and overvoltage regulator functions.

[0004] Since the undervoltage and overvoltage regulator functions are used to regulate DC voltage, the activation of the regulator essentially changes the operating mode of the power converter to that of a voltage source. This leads to another important aspect of microgrid control: how to enable the parallel operation of multiple devices.

[0005] In theory, the two voltage sources in the system can continuously generate and accurately measure the same voltage, so the system works well. However, in the real world, the system does not work that way, and there are always defects in equipment and measurement errors, etc., and the end result is that the voltage sources measure slightly different voltages, for example. To solve this problem, a DC voltage drop is used to run multiple voltage sources in parallel, where the voltage reference of the source is adjusted based on the load of the source. The drop can usually be based on the following equation (1):

[0006] ,

[0007] Among them, U DC,ref It is a DC voltage reference that has undergone a drop, U DC,NOM It is the nominal voltage of the voltage source, I S It is the current of the voltage source, I NOMLet be the nominal current of the voltage source, and ζ be the drop factor. It can be seen that if the current is zero, the DC voltage reference can be equal to the nominal voltage. On the other hand, if the current is equal to the nominal current, the DC voltage reference has a predetermined DC voltage drop relative to the nominal voltage defined by the drop factor. The drop factor is dimensionless and is typically significantly less than 1.

[0008] The aforementioned drop has also been included in the undervoltage and overvoltage regulator functions, causing the regulator's activation limit to change according to the load. However, this introduces the practical possibility that the regulator may be activated at inconvenient times, where the DC voltage is not near the desired voltage level, because the activation limit changes according to the load due to the drop. Therefore, there remains a need to develop DC undervoltage and DC overvoltage regulators for use in DC power converters connected to systems such as DC microgrids. Summary of the Invention

[0009] The object of this invention is to provide a method for DC undervoltage regulation and / or DC overvoltage regulation of an electric power converter, an electric power converter, and a DC microgrid. Another object of this invention is that the method, electric power converter, and DC microgrid provide a solution for more selectively activating and correctly operating the DC undervoltage and DC overvoltage regulators when regulating the DC voltage of a system in which the electric power converter operates.

[0010] The objectives of this invention are achieved through the methods for DC undervoltage regulation and / or DC overvoltage regulation of power converters, power converters, and DC microgrids as defined in the respective independent claims.

[0011] According to a first aspect, a method for DC undervoltage regulation and / or DC overvoltage regulation for an electric power converter. The method includes monitoring a DC voltage by the electric power converter. The method further includes comparing the DC voltage with undervoltage regulation limits and / or overvoltage regulation limits, which are defined at least by user-specified or process-specified undervoltage limits and / or user-specified or process-specified overvoltage limits, respectively, wherein when DC undervoltage regulation or DC overvoltage regulation is disabled, the undervoltage regulation limits and / or overvoltage regulation limits are at least partially, preferably completely, compensated for for voltage drop using an undervoltage drop factor or an overvoltage drop factor, respectively.

[0012] The method further includes: activating DC undervoltage regulation or DC overvoltage regulation in response to the DC voltage reaching the undervoltage regulation limit or the overvoltage regulation limit, respectively, to change DC undervoltage regulation or DC overvoltage regulation to an active state. When DC undervoltage regulation or DC overvoltage regulation is in an active state, the undervoltage regulation limit and / or overvoltage regulation may preferably not be degraded.

[0013] The method further includes: when DC undervoltage regulation or DC overvoltage regulation is active, adjusting the DC voltage by adjusting the load of the power converter based on the undervoltage load regulation coefficient or the overvoltage load regulation coefficient, respectively, wherein the undervoltage load regulation coefficient and / or the overvoltage load regulation coefficient are based on the voltage difference between the undervoltage regulation limit or the overvoltage regulation limit and the DC voltage, and based on the undervoltage drop coefficient or the overvoltage drop coefficient.

[0014] In addition, the method includes disabling DC undervoltage regulation or DC overvoltage regulation when the DC voltage becomes higher than the user-specified or process-specified undervoltage limit or the user-specified or process-specified overvoltage limit, respectively.

[0015] Preferably, after deactivation, the DC undervoltage regulation or DC overvoltage regulation returns to the deactivated state. Therefore, the power converter can continue to monitor the DC voltage and compare it against (multiple) undervoltage and / or overvoltage regulation limits.

[0016] The droop compensation is preferably related to the adjustment of the reference DC voltage, which depends on the undervoltage droop factor or the overvoltage droop factor and the load of the power converter.

[0017] User-specified limits refer to limits that can be defined as constant by the user or that can be changed by the user as needed. For example, a user can define limits directly via the user interface of the power converter. Alternatively, a user can define limits through the control system associated with the power converter. Process-specified limits can refer to another device or controller in the system, where the power converter is configured to operate to define limits, for example, defining limits under certain conditions that satisfy criteria used to change the limits. This can occur without direct user action.

[0018] In addition, when DC undervoltage regulation or DC overvoltage regulation is disabled, the load of the power converter can be adjusted based on the load reference of the power converter.

[0019] Load adjustment may include: adjusting the load to a lower level relative to a load reference when DC undervoltage regulation is active, and / or adjusting the load to a higher level relative to a load reference when DC overvoltage regulation is active.

[0020] When DC undervoltage regulation or DC overvoltage regulation is disabled, the undervoltage drop factor and / or overvoltage drop factor can be defined based on a predetermined DC voltage drop at the nominal load associated with the undervoltage regulation limit and / or overvoltage regulation limit, respectively.

[0021] Furthermore, when DC undervoltage regulation or DC overvoltage regulation is disabled, the undervoltage regulation limit and / or overvoltage regulation limit can be configured to include, respectively, a user-specified or process-specified undervoltage limit and / or a user-specified or process-specified overvoltage limit, as well as a descent compensation term as a function of the load.

[0022] The undervoltage load regulation factor and / or overvoltage load regulation factor can be the ratio of the voltage difference to the product of the following: the ratio is the product of the "undervoltage drop factor or overvoltage drop factor" and the "user-specified limit or process-specified undervoltage limit and / or user-specified or process-specified overvoltage limit".

[0023] The undervoltage regulation limit may have a lower limit based on the DC undervoltage regulation limit when DC undervoltage regulation is active, and the product of the load reference and the undervoltage drop factor; and / or the overvoltage regulation limit may have an upper limit based on the overvoltage regulation limit when overvoltage regulation is active, and the product of the load reference and the overvoltage drop factor.

[0024] This method may include: when DC undervoltage regulation or DC overvoltage regulation is active, requiring the DC voltage to be below or equal to the undervoltage regulation limit, and / or requiring the DC voltage to be equal to or higher than the overvoltage regulation limit. Therefore, when these requirements are not met, DC undervoltage regulation or DC overvoltage regulation can be disabled.

[0025] A load reference can be defined as the ratio of the reference current to the nominal current. Therefore, a load reference can be dimensionless.

[0026] According to a second aspect, an electric power converter is provided. The electric power converter includes: a DC voltage bus; conversion circuitry connected to the DC voltage bus for providing DC / AC, AC / DC, or DC / DC voltage conversion; voltage determination means, such as one or more voltage sensors, for determining the DC voltage of the DC voltage bus; current determination means, such as one or more current sensors, for determining the load current of the electric power converter; and a controller configured to perform the method according to the first aspect.

[0027] The controller can be configured to control the load of the power converter based on the load reference of the power converter when DC undervoltage regulation or DC overvoltage regulation is disabled.

[0028] An electric power converter may include a capacitor or capacitor bank connected to a DC voltage bus, or a battery or battery bank.

[0029] An electric power converter can be an inverter or a rectifier.

[0030] According to a third aspect, a DC microgrid is provided. The DC microgrid includes a common DC bus having a DC voltage, one or more DC voltage sources connected to the common DC bus, and one or more power converters according to a second aspect connected to the common DC bus. The DC microgrid can be arranged as a shipboard power system.

[0031] This invention provides a method for DC undervoltage regulation and / or DC overvoltage regulation of an electric power converter, the electric power converter itself, and a DC microgrid. This invention offers advantages over known solutions because DC undervoltage regulation and / or DC overvoltage regulation are activated at the correct time and deactivated when no longer needed. The electric power converter can operate in a network, such as in a DC microgrid on a ship, to regulate its DC voltage based on monitoring the DC voltage, and therefore does not require complex centralized control of all devices in the network.

[0032] Based on the following detailed description, those skilled in the art will understand a variety of other advantages.

[0033] The terms “first” and “second” are used in this document to distinguish one element from another, and unless otherwise explicitly stated, they are not specifically prioritized or ordered.

[0034] The exemplary embodiments of the invention presented herein should not be construed as limiting the applicability of the appended claims. The verb "comprising" is used herein as an open-ended limitation, which does not exclude the presence of additional unrecited features. Unless otherwise expressly stated, the features recited in the appended claims may be freely combined with each other.

[0035] The novel features considered characteristic of the invention are specifically 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 when read in conjunction with the accompanying drawings and from the following description of specific embodiments. Attached Figure Description

[0036] The accompanying drawings illustrate some embodiments of the invention by way of example and not limitation.

[0037] Figure 1 An electric power converter is schematically shown.

[0038] Figure 2 An electric power converter is schematically shown.

[0039] Figure 3 A DC microgrid is schematically illustrated.

[0040] Figure 4A flowchart is shown of a method for DC undervoltage regulation and / or DC overvoltage regulation for an electric power converter.

[0041] Figure 5 The operation of an electric power converter configured with DC undervoltage regulation and / or DC overvoltage regulation is shown. Detailed Implementation

[0042] Figure 1 A power converter 100 is schematically shown, including a DC voltage bus 10, a conversion circuit 12 connected to the DC voltage bus 10 for providing DC / AC, AC / DC, or DC / DC voltage conversion, a voltage determining device 14 (such as one or more voltage sensors) for determining the DC voltage U_DC of the DC voltage bus 10, and a current determining device 16 (such as one or more current sensors) for determining the load current of the power converter 10. The power converter 100 also includes a controller 20. The controller 20 can be configured to perform the following combined... Figure 4 Describe some or all of the method steps.

[0043] The controller 20 can be arranged to receive voltage measurement data from the voltage determining device 14 and current measurement data from the current determining device 16. For example, Figure 1 The power converter 100 may be an inverter that converts DC at its input to AC at its output, and optionally to operate a motor 110 connected to the output.

[0044] Furthermore, controller 20 can be configured to provide multiple control signals to conversion circuit 12, for example, to switch semiconductor power switches to produce a desired output waveform. This may include the use of pulse width modulation (PWM) technology.

[0045] The controller 20 can be configured to perform current control and / or voltage control (not shown). Current control and / or voltage control may include scalar control or vector control known to those skilled in the art.

[0046] When DC undervoltage or DC overvoltage regulation is disabled, controller 20 can be configured to control the load of power converter 100 based on a load reference. The load reference can be user-specified or process-specified. The load reference can be defined as the ratio of a reference current to the nominal current. For example, the reference current at a given moment could be 15 amps, and the nominal current of power converter 100 could be 100 amps, thus providing a load reference of 0.15.

[0047] The power converter 100 may include a capacitor 11 or capacitor bank, or a battery 11 or battery bank connected to the DC voltage bus 10. The capacitor 11 or capacitor bank, or the battery 11 or battery bank, may be used as an energy storage and / or filtering device for smoothing the DC voltage of the DC voltage bus 10.

[0048] Figure 2 A power converter 100 is schematically shown, including a DC voltage bus 10, a conversion circuit 12 connected to the DC voltage bus 10 for providing DC / AC, AC / DC, or DC / DC voltage conversion, a voltage determining device 14 (such as one or more voltage sensors) for determining the DC voltage U_DC of the DC voltage bus 10, and a current determining device 16 (such as one or more current sensors) for determining the load current of the power converter 10. The power converter 100 also includes a controller 20. The controller 20 may be arranged to receive voltage measurement data from the voltage determining device 14 and current measurement data from the current determining device 16. For example, Figure 1 The power converter 100 may be a rectifier that converts AC at its input to DC at its output, and optionally may be operated by a generator 120 connected to the output. Figure 2 The controller 20 in the middle can be basically similar to the combination Figure 1 The controller described.

[0049] As can be recognized, Figure 1 The inverter can be structurally similar to Figure 2 The rectifier, however, has different main directions of power flow. In some embodiments, the power converter 100 can be bidirectional, as it can selectively allow power to flow in either direction.

[0050] Figure 3 A DC microgrid 200 is schematically illustrated. The DC microgrid 200 includes a common DC bus 210 with DC voltage, one or more DC voltage sources 102A-102D connected to the common DC bus 210, and one or more power converters 100 connected to the common DC bus 210. However, the DC microgrid 200 may not necessarily be arranged as a shipboard power system. Although four DC voltage sources 102A-102D and only one power converter 100 are shown, these numbers can vary depending on the DC microgrid 200.

[0051] As can be seen, the DC voltage of the common DC bus 210 is connected to each device, namely (one) or more DC voltage sources 102A-102D and one (or more) power converters 100. Therefore, they are arranged to operate in parallel with each other. In the event that the DC voltage becomes too high or too low, one or more power converters 100 can begin to regulate the DC voltage of the common DC bus 210 by activating overvoltage or undervoltage regulation functions, respectively.

[0052] Figure 4 A flowchart is shown of a method for DC undervoltage regulation and / or DC overvoltage regulation for an electric power converter 100, such as combining Figure 1 and Figure 2 The methods shown and described.

[0053] Item or step 400 refers to an optional initiation phase of the method. Suitable equipment and components are obtained, and the system is assembled and configured for operation, if these have not been previously set up.

[0054] As described above, at least some (if not all) of the method steps can be executed by the controller 20 of the power converter 100.

[0055] Step 410 of the method or procedure refers to monitoring the DC voltage by the power converter 100. For example, monitoring 410 may be performed continuously or at certain intervals. Monitoring 410, such as that including measurements, may be performed during the time when DC undervoltage regulation and / or DC overvoltage regulation are in a disabled or active state.

[0056] Step 420 of the item or method refers to comparing the DC voltage with an undervoltage regulation limit and / or an overvoltage regulation limit defined by at least a user-specified or process-specified undervoltage limit and / or a user-specified or process-specified overvoltage limit, wherein when DC undervoltage regulation or DC overvoltage regulation is disabled, the undervoltage regulation limit and / or overvoltage regulation limit are at least partially, preferably completely, compensated for the descent using an undervoltage descent factor or an overvoltage descent factor, respectively.

[0057] In some embodiments, droop compensation may be related to an adjustment of the reference DC voltage, which depends on the undervoltage droop factor or the overvoltage droop factor and the load of the power converter.

[0058] Furthermore, when DC undervoltage regulation or DC overvoltage regulation is disabled, the undervoltage regulation limit and / or overvoltage regulation limit can be configured to include a user-specified or process-specified undervoltage limit and / or user-specified or process-specified overvoltage limit, as well as a descent compensation term as a function of the load. For example, the undervoltage regulation limit can be configured to be defined as follows:

[0059]

[0060] Among them, U UV_LIM It is the undervoltage regulation limit, U UV_USER It is the user-specified or process-specified undervoltage limit, and I is the load current or reference current of the power converter 100. NOM It is the nominal current of the power converter 100, and ζ UV This is the undervoltage descent factor. The part in parentheses represents the descent compensation term, which is a function of the load (i.e., the ratio of the load current or reference current to the nominal current). A similar equation can also be defined for the overvoltage regulation limit, i.e.,

[0061]

[0062] Among them, U OV_LIM It is the overvoltage regulation limit, U OV_USER This is the user-specified or process-specified overvoltage limit, where I is the load current or reference current of the power converter 100. NOM It is the nominal current of the power converter 100, and ζ OV This is the undervoltage drop factor. The drop compensation term can partially or preferably completely eliminate the effect of the drop.

[0063] Furthermore, when DC undervoltage regulation or DC overvoltage regulation is disabled, the load on the power converter can be adjusted based on a load reference (e.g., the relationship or ratio between the reference current and the nominal current of the power converter 100). This can actually depend on the power requirements of the devices or processes connected to the power converter 100, such as those including the motor 110.

[0064] Step 430 of the item or method refers to activating DC undervoltage regulation or DC overvoltage regulation in response to the DC voltage reaching the undervoltage regulation limit or the overvoltage regulation limit, so as to change DC undervoltage regulation or DC overvoltage regulation to an active state.

[0065] Therefore, in various embodiments, activation occurs at a set voltage value (such as a user-specified or process-specified undervoltage or overvoltage limit) because this limit is compensated for during the period when DC undervoltage regulation or DC overvoltage regulation is disabled. Thus, the user can rely on activation occurring at the correct time.

[0066] When DC undervoltage regulation or DC overvoltage regulation is active, the undervoltage regulation limit and / or overvoltage regulation may preferably not be reduced.

[0067] Item or method step 440 refers to adjusting the DC voltage by adjusting the load of the power converter based on the undervoltage load adjustment coefficient or the overvoltage load adjustment coefficient when the DC undervoltage regulation or DC overvoltage regulation is active, wherein the undervoltage load adjustment coefficient and / or the overvoltage load adjustment coefficient are based on the voltage difference between the undervoltage regulation limit or the overvoltage regulation limit and the DC voltage, and are based on the undervoltage drop coefficient or the overvoltage drop coefficient.

[0068] The undervoltage drop factor and / or overvoltage drop factor can be defined based on a predetermined DC voltage drop at the nominal load that is associated with the undervoltage regulation limit and / or the overvoltage regulation limit, respectively.

[0069] For example, when DC undervoltage is activated, the load of the power converter 100 can be reduced relative to a load reference that the power converter 100 would otherwise follow or a corresponding load that the converter 100 would attempt to provide. When DC overvoltage is activated, the load of the power converter 100 can be increased relative to a load reference that the power converter 100 would otherwise follow or a corresponding load that the converter 100 would attempt to provide. In this way, the DC voltage can be regulated by improving the power balance condition (i.e., the balance between power generation and power consumption).

[0070] Therefore, load adjustment may include: adjusting the load to a lower level relative to a load reference when DC undervoltage regulation is active, and / or adjusting the load to a higher level relative to a load reference when DC overvoltage regulation is active.

[0071] The undervoltage load regulation factor and / or overvoltage load regulation factor can be configured to determine the contribution of the power converter 100 to regulate the DC voltage when DC undervoltage regulation or DC overvoltage regulation is active. Therefore, the higher the voltage difference, the greater the contribution to a particular undervoltage drop factor or overvoltage drop factor.

[0072] In some embodiments, when DC undervoltage regulation or DC overvoltage regulation is active, the undervoltage load regulation coefficient and / or overvoltage load regulation coefficient can be ratios of the voltage difference to the product of the undervoltage drop coefficient or overvoltage drop coefficient and a user-specified limit or a process-specified undervoltage or overvoltage limit, respectively. Therefore, they can be configured to be defined as follows:

[0073]

[0074]

[0075] Among them, Γ UV It is the undervoltage load adjustment value, Γ OV It is the overvoltage load adjustment value, U UV_LIM and UOV_LIM These are the undervoltage regulation limit and the overvoltage regulation limit, U DC It is the DC voltage of the power converter 100, and ζ UV and ζ OV These are the undervoltage reduction coefficient and the overvoltage reduction coefficient, respectively. In this case, when DC undervoltage regulation or DC overvoltage regulation is active, the undervoltage regulation limit and the overvoltage regulation limit are not reduced and compensated.

[0076] Furthermore, when DC undervoltage regulation or DC overvoltage regulation is active, the undervoltage regulation limit may have a lower limit based on the DC undervoltage regulation limit when DC undervoltage regulation is active, and the product of the load reference and the undervoltage drop factor, and / or the overvoltage regulation limit may have an upper limit based on the overvoltage regulation limit when overvoltage regulation is active, and the product of the load reference and the overvoltage drop factor.

[0077] In some embodiments, the lower limit and / or upper limit can be configured to be defined as follows:

[0078]

[0079]

[0080] Among them, U UV_LIM_MIN and U OV_LIM_MAX These are the lower and upper limits, and K is the load reference. The load reference K can be defined as the ratio of the reference current to the nominal current.

[0081] Step 450 of the item or method refers to disabling DC undervoltage regulation or DC overvoltage regulation when the DC voltage becomes higher than the user-specified or process-specified undervoltage limit or lower than the user-specified or process-specified overvoltage limit, respectively.

[0082] The disabling criteria can also be configured to be defined as follows:

[0083]

[0084] Therefore, when DC undervoltage regulation or DC overvoltage regulation is active, and subsequently the load reference K becomes lower than the undervoltage load adjustment value Γ. UV Or higher than the overvoltage load adjustment value Γ OV When necessary, DC undervoltage regulation or DC overvoltage regulation can be disabled.

[0085] Preferably, after being deactivated, the DC undervoltage regulation or DC overvoltage regulation returns to the deactivated state.

[0086] This method can stop at item 499.

[0087] Figure 5The operation of a power converter 100 configured with DC undervoltage regulation and / or DC overvoltage regulation as disclosed herein is illustrated. The vertical axis on the left side of the figure represents current in amperes. The vertical axis on the right side of the figure represents DC voltage in volts. The invention is not limited to the stated current and / or voltage range or level, but may be used for other current and voltage ranges or levels. The horizontal axis represents time, such as seconds.

[0088] Figure 5 The example illustrates the operation of a power converter 100 in a DC microgrid with one source and two loads, both of which include the power converter 100 as described above (see also...). Figure 3 (Another configuration is provided for reference). Reference numeral 51 indicates the current supplied by the source, i.e., source current 51. Reference numeral 52 indicates the current of the first load, i.e., first load current 52, which is configured with DC undervoltage regulation and / or DC overvoltage regulation as described above. Reference numeral 53 indicates the current of the second load, i.e., second load current 53, which is configured with DC undervoltage regulation and / or DC overvoltage regulation as described above. The load currents are shown as negative currents, and the source currents are shown as positive currents. The maximum source current 51 is 100 amperes.

[0089] DC voltage, denoted by reference numeral 41, refers to, for example, the DC voltage of a common DC bus. When the power converter 100 is connected to a common DC bus, the power converter 100 is configured to monitor the DC voltage, for example, through its voltage measurement or voltage sensor. The activation state of the first load is denoted by 71, while the activation state of the second load is denoted by 72.

[0090] Furthermore, when DC undervoltage regulation is disabled, reference numeral 42 indicates the undervoltage regulation limit 42 for the first load, i.e., the first undervoltage regulation limit, and reference numeral 43 indicates the undervoltage regulation limit 43 for the second load, i.e., the second undervoltage regulation limit. When DC undervoltage regulation and / or DC overvoltage regulation are disabled, the undervoltage regulation limits 42 and 43 are reduced and compensated, thus remaining essentially constant at 684V and 686V respectively. Figure 5 As shown. Even as the load currents 52 and 53 change, the undervoltage regulation limits 42 and 43 remain essentially unchanged. The undervoltage regulation limits 42 and 43 can actually be user-specified or process-specified values.

[0091] Furthermore, the reference current of the first load is marked with 62, i.e., the first reference current 62, and the reference current of the second load is marked with 63, i.e., the second reference current 63. It can be seen that when the DC undervoltage regulation is disabled, the first load current 52 follows the first reference current 62. Furthermore, when the DC undervoltage regulation is disabled, the second load current 53 follows the second reference current 63. In this case, when the DC undervoltage regulation is disabled, the load currents 52 and 53 are shown to precisely follow the reference currents 62 and 63; however, in some cases, due to the characteristics of the control method used in said cases, some deviations may exist.

[0092] Now describing Figure 5 The operation of DC undervoltage regulation is described. Initially, DC undervoltage regulation (and DC overvoltage regulation) is disabled. DC voltage 41 increases until the source current 51 begins to increase primarily due to the increase in the second load current 53. As the source current 51 increases, DC voltage 41 continues to decrease, but remains above the first undervoltage regulation limit 42 and the second undervoltage regulation limit 43.

[0093] After a period of decreasing DC voltage 41, DC voltage 41 reaches the second undervoltage regulation limit 43, and therefore, DC undervoltage regulation of the second load is activated. The second load current 53 begins to deviate from the second reference current 63, i.e., it falls below the second reference current 63, in order to regulate DC voltage 41 so that it does not decrease. It can be seen that DC voltage 41 continues to decrease, but no longer as rapidly.

[0094] The DC voltage is regulated by the power converter 100 of the second load through an undervoltage load regulation coefficient Γ based on the power converter 100 of the second load. UV_2 This is performed by adjusting the load of the power converter 100, wherein the undervoltage load adjustment coefficient Γ UV_2 The coefficient is based on the voltage difference between the second undervoltage regulation limit 43 and the DC voltage 41, and is based on the undervoltage drop coefficient ζ. UV_2, For example, as defined by equation (3A).

[0095] Even though the second load has DC undervoltage regulation in the active state, the DC voltage 41 continues to decrease in this example case, but more slowly than before. After another period of time, the DC voltage 41 reaches the first undervoltage regulation limit 42, and therefore, the DC undervoltage regulation of the first load is activated. The first load current 52 begins to deviate from the first reference current 62, i.e., it falls below the first reference current 62, in order to regulate the DC voltage 41 so that it does not decrease. The regulation of the DC voltage is achieved by the power converter 100 of the first load through an undervoltage load regulation coefficient Γ based on the first load. UV_1This is performed by adjusting the load on the power converter 100, where the undervoltage load adjustment factor Γ is... UV_1 The coefficient is based on the voltage difference between the first undervoltage regulation limit 42 and the DC voltage 41, and is based on the undervoltage drop coefficient ζ. UV_1 For example, as defined by equation (3A).

[0096] It can be seen that the DC voltage 41 reaches or is set to a constant value of 684V, which is equal to the first undervoltage regulation limit 42. During this period, both power converters 100 have DC undervoltage regulation that is active based on activation signals 71 and 72, and for both loads, the load currents 52 and 53 are less than the corresponding reference currents 62 and 63.

[0097] After a certain period of time, it can be seen that the second reference current 63 begins to decrease, i.e., becomes more negative. Simultaneously, the load current 53 begins to decrease because the decreasing second reference current 63 affects the lower limit of the undervoltage regulation voltage, for example, as defined in equation (4A), while the first current reference 63 and the first load current 53 increase (become more negative) based on the first reference current 62 affecting the lower limit of the undervoltage regulation voltage, for example, as defined in equation (4A). This continues until the DC voltage 41 begins to increase from the first undervoltage regulation limit 42, meaning that the DC undervoltage regulation of the first load is deactivated and changes to an inactive state. When the DC voltage 41 becomes higher than the user-specified or process-specified undervoltage limit of 684V, the load reference of the power converter 100 (the load reference K can be defined, for example, as the ratio of the reference current to the nominal current) (in this case, relative to the first reference current 62) becomes lower than the undervoltage load adjustment value Γ. UV_1 At this time, DC undervoltage regulation is disabled. It can be seen that the first load current 52 becomes equal to the first reference current 62.

[0098] When DC voltage 41 becomes higher than the second undervoltage regulation limit 43, the deactivation of DC undervoltage regulation of the power converter 100 of the second load occurs later. When DC voltage 41 becomes higher than the user-specified or process-specified undervoltage limit of 686V, the load reference of the power converter 100 (load reference K can be defined, for example, as the ratio of reference current to nominal current) (in this case, relative to the second reference current 63) becomes lower than the undervoltage load adjustment value Γ. UV_2 At this time, DC undervoltage regulation is disabled. It can be seen that the second load current 53 becomes equal to the second reference current 63.

[0099] Figure 5The DC undervoltage regulation of the power converter 100 is shown to be activated at a user-specified or process-specified undervoltage level (42 or 43). Drop compensation ensures activation does not occur at the wrong time. However, DC overvoltage regulation will operate in the same way, as the DC voltage becomes too high rather than too low.

[0100] In some embodiments, the power converter 100 may be additionally configured with undervoltage and overvoltage protection functions. These protection functions deactivate the converter 100 if the DC voltage 41 becomes too low to operate or dangerously high. However, these protection functions do not correspond to the DC undervoltage regulation and DC overvoltage regulation functions disclosed herein.

Claims

1. A method for DC undervoltage regulation and / or DC overvoltage regulation in an electric power converter (100), the method comprising: DC voltage (41) is monitored (410) by power converter (100); The DC voltage (41) is compared (420) with undervoltage regulation limits (42, 43) and / or overvoltage regulation limits defined by at least user-specified or process-specified undervoltage limits and / or user-specified or process-specified overvoltage limits, wherein when the DC undervoltage regulation or the DC overvoltage regulation is disabled, the undervoltage regulation limits (42, 43) and / or the overvoltage regulation limits are respectively compensated for at least partially, preferably completely, by using an undervoltage drop factor or an overvoltage drop factor; In response to the DC voltage (41) reaching the undervoltage regulation limit (42, 43) or the overvoltage regulation limit respectively, the DC undervoltage regulation or DC overvoltage regulation is activated (430) to change the DC undervoltage regulation or DC overvoltage regulation to the active state. When the DC undervoltage regulation or the DC overvoltage regulation is in the active state, the DC voltage (41) is regulated (440) by adjusting the load of the power converter (100) based on the undervoltage load regulation coefficient or the overvoltage load regulation coefficient, respectively, wherein the undervoltage load regulation coefficient and / or the overvoltage load regulation coefficient is based on the voltage difference between the undervoltage regulation limit (42, 43) or the overvoltage regulation limit and the DC voltage (41), and is based on the undervoltage drop coefficient or the overvoltage drop coefficient; and When the DC voltage (41) becomes higher than the user-specified or process-specified undervoltage limit (42, 43) or lower than the user-specified or process-specified overvoltage limit, the DC undervoltage regulation (450) or DC overvoltage regulation is disabled.

2. The method of claim 1, wherein the drop compensation relates to an adjustment of a reference DC voltage, the adjustment of which depends on the undervoltage drop factor or the overvoltage drop factor and the load of the power converter (100).

3. The method of claim 1 or 2, wherein, When the DC undervoltage regulation or the DC overvoltage regulation is disabled, the load of the power converter (100) is adjusted based on the load reference of the power converter (100).

4. The method of any one of claims 2-3, wherein the load adjustment comprises: When the DC undervoltage regulation is in the active state, the load is adjusted to be at a lower level relative to the load reference of the power converter (100), and / or When the DC overvoltage regulation is in the active state, the load is adjusted to be at a higher level relative to the load reference of the power converter (100).

5. The method of any one of claims 1-4, wherein, When the DC undervoltage regulation or the DC overvoltage regulation is disabled, the undervoltage drop factor and / or the overvoltage drop factor are defined based on a predetermined DC voltage drop at the nominal load relative to the undervoltage regulation limit (42, 43) and / or the overvoltage regulation limit, respectively.

6. The method of any one of claims 1-5, wherein, When the DC undervoltage regulation or the DC overvoltage regulation is disabled, the undervoltage regulation limit (42, 43) and / or the overvoltage regulation limit are configured to include the user-specified or process-specified undervoltage limit and / or the user-specified or process-specified overvoltage limit, respectively, and a descent compensation term as a function of the load.

7. The method of claim 6, wherein the undervoltage load adjustment coefficient and / or the overvoltage load adjustment coefficient are respectively ratios of the voltage difference to a product of "the undervoltage drop coefficient or the overvoltage drop coefficient" and "the user-specified or process-specified undervoltage limit or the user-specified or process-specified overvoltage limit".

8. The method according to any one of claims 1-7, wherein, The undervoltage regulation limits (42, 43) have a lower limit, which is based on the undervoltage regulation limits (42, 43) when the DC undervoltage regulation is in the active state, and the product of the load reference of the power converter (100) and the undervoltage drop coefficient, and / or The overvoltage regulation limit has an upper limit, which is based on the overvoltage regulation limit when the DC overvoltage regulation is in the active state, and the product of the load reference of the power converter (100) and the overvoltage drop coefficient.

9. The method of any one of claims 1-8, wherein the load reference of the power converter (100) is defined as the ratio of the reference current (52, 53) to the nominal current.

10. The method of any one of claims 1-9, comprising: When the DC undervoltage regulation or the DC overvoltage regulation is in the active state The DC voltage (41) needs to be lower than or equal to the undervoltage regulation limits (42, 43), and / or The DC voltage (41) needs to be higher than or equal to the overvoltage regulation limit.

11. An electric power converter (100), comprising: DC voltage bus (10). Conversion circuit (12), connected to the DC voltage bus, for providing DC / AC, AC / DC, or DC / DC voltage conversion. Voltage determining device (14), which is used to determine the DC voltage (41) of the DC voltage bus (10). Current determining device (16), the current determining device being used to determine the load current of the power converter (100); and A controller (20) is configured to perform the method according to any one of claims 1-10.

12. The power converter (100) of claim 11, wherein the controller (20) is configured to control the load of the power converter (100) based on a load reference of the power converter (100) when the DC undervoltage regulation or the DC overvoltage regulation is disabled.

13. The power converter (100) as claimed in claim 11 or 12, comprising: A capacitor (11) or capacitor bank, or a battery (11) or battery bank connected to the DC voltage bus (10).

14. A DC microgrid (200), comprising: A common DC bus (210) with DC voltage (41). One or more DC voltage sources (102A-102D) connected to a common DC bus (210), and One or more power converters (100) as described in any one of claims 10-13 are connected to the common DC bus (210).

15. The DC microgrid (200) as described in claim 14 is arranged as a shipboard power system.

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