Modular multilevel converter pre-charge

Abstract

According to the embodiments described herein, the modular multilevel converter (MMC) is precharged by: driving a bypass current from the auxiliary power supply through multiple bypass switches included in the corresponding multiple batteries; driving an insertion current through multiple insertion switches included in the multiple batteries in response to the sum of voltages across multiple battery capacitors included in the multiple batteries satisfying a drive threshold; and disconnecting circuit breakers connecting the auxiliary power supply to the multiple batteries and the generator to external power rails in response to the voltage across the DC link capacitors satisfying the precharge threshold when driving the insertion current, with the DC link capacitors connected between each external power rail.

Description

Technical Field

[0001] The embodiments presented in this disclosure generally relate to modular multilevel converters (MMCs) and the capacitors contained therein. Specific embodiments described herein depict pre-charging schemes for the capacitors. Background Technology

[0002] Wind turbine generators (WTGs) are an increasingly popular source of power generation, which can be deployed individually or comprised of several wind turbines, often referred to as a wind farm. In WTGs and other power generation or consumption systems connected to the grid or distribution lines, millimeter-scale converters (MMCs) can be used to electrically connect two powered systems operating with different voltage / current schemes. When initiating a connection between two powered systems, the MMC equalizes the voltage / current differences between the two systems to reduce power surges (e.g., inrush currents from the high-voltage side to the low-voltage side) and other anomalous effects. For example, in a WTG, the MMC can equalize these differences via a DC (direct current) link located between the machine-side converter (MSC) and the line-side converter (LSC), which is charged to a predefined level before contacting via a series of charging components (e.g., one or more transformers, diode bridges, current-limiting resistors, fuses, circuit breakers, switches, etc.). Summary of the Invention

[0003] One embodiment of this disclosure is a method comprising: driving a bypass current from an auxiliary power source through a plurality of bypass switches included in a plurality of corresponding batteries; driving an insertion current through a plurality of insertion switches included in the plurality of batteries in response to the sum of voltages across a plurality of battery capacitors included in the plurality of batteries satisfying a drive threshold; and disconnecting a circuit breaker connecting the auxiliary power source to the plurality of batteries and connecting a generator to an external power rail in response to the voltage across a DC link capacitor satisfying a pre-charge threshold when driving the insertion current, the DC link capacitor being connected between each external power rail, wherein driving the bypass current includes tuning (525) the switching rate of a single bypass switch during battery capacitor charging to make the charge in the plurality of battery capacitors equal; and wherein driving the insertion current includes tuning (545) the switching rate of a single insertion switch during battery capacitor discharging to make the charge in the plurality of battery capacitors equal.

[0004] In one embodiment, in conjunction with any of the methods described above or below, the drive current includes tuning the switching rate of a single bypass switch during battery capacitor charging to make the charges in the plurality of battery capacitors equal; and the drive insertion current includes tuning the switching rate of a single insertion switch during battery capacitor discharging to make the charges in the plurality of battery capacitors equal.

[0005] In one embodiment, in conjunction with any of the methods described above or below, the method further includes measuring the difference in voltage levels of each of the plurality of battery capacitors while driving at least one of the bypass current and the insertion current; and, in response to the difference exceeding a difference threshold, stopping the auxiliary power supply from charging the battery capacitors and stopping the battery capacitors from charging the DC link capacitors.

[0006] In one embodiment, in conjunction with any of the methods described above or below, the method further includes, before driving the bypass current: closing a circuit breaker to link the auxiliary power supply to the positive and negative rails via a rectifier, with a DC link capacitor and the plurality of batteries connected between the positive and negative rails; and allowing an initial current to circulate through the plurality of batteries until a switching threshold voltage is reached in the plurality of battery capacitors.

[0007] In one implementation, in conjunction with any of the methods described above or below, the driving threshold exceeds the peak rectified voltage of the auxiliary power supply.

[0008] In one implementation, in conjunction with any of the methods described above or below, the auxiliary power supply is a multiphase power supply, wherein each phase provided by the auxiliary power supply simultaneously charges the plurality of battery capacitors while driving bypass current.

[0009] In one implementation, in conjunction with any of the methods described above or below, a bypass switch is connected in parallel with a first current diode, and an insertion switch is connected in parallel with a second current diode, wherein the insertion current flows through the first current diode and the bypass current flows through the second current diode.

[0010] One embodiment of this disclosure is a controller for a modular multilevel converter (MMC) including a plurality of batteries connected in series between a positive rail and a negative rail, wherein each of the plurality of batteries includes a bypass switch, a plug-in switch, and a battery capacitor, wherein the plurality of batteries are connected in parallel with a DC link capacitor, the controller being configured to perform the following operations: driving a bypass current from an auxiliary power supply through the bypass switch; driving a plug-in current from the battery capacitor through the plug-in switch in response to the sum of voltages across the battery capacitors satisfying a drive threshold; and disconnecting a circuit breaker that connects the auxiliary power supply to a rectifier and a wind turbine generator to an external power line via the positive and negative rails in response to the voltage across the DC link capacitors satisfying a pre-charge threshold, wherein driving the bypass current includes tuning (525) the switching rate of a single bypass switch during battery capacitor charging to make the charges in the plurality of battery capacitors equal; and wherein driving the plug-in current includes tuning (545) the switching rate of a single plug-in switch during battery capacitor discharging to make the charges in the plurality of battery capacitors equal.

[0011] In one embodiment, in conjunction with any controller described above or below, operation further includes: driving a bypass current to tune the switching rate of a single bypass switch during battery capacitor charging to make the charge in each battery capacitor equal; and driving an insertion current to tune the switching rate of a single insertion switch during battery capacitor discharging to make the charge in each battery capacitor equal.

[0012] In one implementation, in conjunction with any controller described above or below, operation further includes: measuring the difference in voltage levels of each battery capacitor while driving at least one of the bypass current and the insertion current; and, in response to the difference exceeding a difference threshold, stopping the auxiliary power supply from charging the battery capacitor and stopping the battery capacitor from charging the DC link capacitor.

[0013] In one implementation, in conjunction with any controller described above or below, the operation further includes, before driving the bypass current: closing the circuit breaker to link the auxiliary power supply to the positive and negative rails via the rectifier; and allowing the initial current to circulate through the battery until the switching threshold voltage is reached in the battery capacitor.

[0014] In one implementation, in conjunction with any controller described above or below, the drive threshold exceeds the nominal voltage of the plurality of batteries.

[0015] In one implementation, in conjunction with any controller described above or below, the auxiliary power supply is a multiphase power supply, each phase of which simultaneously charges the respective battery capacitors while driving the bypass current.

[0016] In one implementation, in conjunction with any controller described above or below, a bypass switch is connected in parallel with a first-current diode, and a plug switch is connected in parallel with a second-current diode.

[0017] One embodiment of this disclosure is a modular multilevel converter (MMC) comprising: a positive rail; a negative rail; a DC link including a DC link capacitor connected between the positive and negative rails; a rectifier connected between the positive and negative rails and selectively connected to an auxiliary power supply of a wind turbine generator (WTG), wherein the rectifier supplies DC power from the auxiliary power supply on the positive and negative rails, the peak voltage of which after rectification is below a pre-charge threshold of the DC link capacitor; and a plurality of batteries connected in series between the positive and negative rails, each of the plurality of batteries including: a battery capacitor connected between a first node and a second node; a plug-in switch connected to the first node and a third node; a bypass switch connected to the third node and the second node; and a first current diode configured to allow current to flow from the third node to the first node and prevent current from flowing from the third node to the first node. The current flows from the first node to the third node; a second current diode is configured to allow current to flow from the second node to the third node and prevent current from flowing from the third node to the second node; and a gate controller is configured to control the voltage across the DC link capacitor and the battery capacitor by switching the first switch open and the second switch closed to charge the battery capacitor beyond its nominal voltage, and then switch the first switch open and the second switch closed to discharge the battery capacitor to charge the DC link capacitor to a precharge threshold, to drive the bypass switch current including tuning (525) the rate of switching of a single bypass switch during battery capacitor charging to make the charge in the plurality of battery capacitors equal, and to drive the insertion switch current including tuning (545) the rate of switching of a single insertion switch during battery capacitor discharge to make the charge in the plurality of battery capacitors equal. Attached Figure Description

[0018] To gain a more detailed understanding of the features of this disclosure, the disclosure briefly summarized above can be described in more detail with reference to embodiments, some of which are illustrated in the accompanying drawings. However, it should be noted that the accompanying drawings only show typical embodiments of this disclosure and should not be construed as limiting its scope, as other equally effective embodiments are permissible with respect to this disclosure.

[0019] Figure 1 A schematic diagram of a wind turbine according to an embodiment described in this disclosure is shown.

[0020] Figure 2 A schematic diagram showing the components inside the nacelle and tower of a wind turbine according to an embodiment described in this disclosure.

[0021] Figure 3A and 3B The present disclosure illustrates the component layout and circuit diagram in a modular multilevel converter according to embodiments thereof.

[0022] Figure 4 This invention demonstrates components of a battery according to an embodiment of the present disclosure.

[0023] Figure 5 This is a flowchart of a method for pre-charging a modular multilevel converter according to embodiments of the present disclosure.

[0024] Figure 6 This is a block diagram of a controller unit that can be used as a gate controller according to one or more embodiments of the present disclosure.

[0025] For ease of understanding, the same reference numerals are used to denote common elements in the figures where possible. It is conceivable that elements disclosed in one embodiment may be usefully utilized in other embodiments without specific description. Detailed Implementation

[0026] This paper presents a Modular Multilevel Converter (MMC) and its novel control scheme, which eliminates the need for additional charging components in the DC link. This results in fewer points of failure in the MMC, a smaller operational and deployment footprint, simplified maintenance, and improved system reliability. Instead of being charged via transformers and rectifiers supplied from the grid, the DC link capacitors in the MMC are charged using auxiliary power from an WTG (Wind Turbine Generator) or other power generation system intended for grid connection. The auxiliary power overcharges the battery capacitors in the MMC to precharge the DC link capacitors, providing nominal voltage in both the DC link capacitors and the battery capacitors for connecting the WTF to the grid via the MMC.

[0027] Example Implementation

[0028] Figure 1 This diagram illustrates a horizontal axis WTG 100. A WTG 100 typically includes a tower 102 and a wind turbine nacelle 104 positioned at the top of the tower 102. A wind turbine rotor 106 is connected to the nacelle 104 via a low-speed shaft extending outside the nacelle 104. The wind turbine rotor 106 includes three rotor blades 108 mounted on a common hub 110, rotating in the rotor plane, but may include any suitable number of blades, such as one, two, four, five, or more. Each blade 108 (or wing) typically has an aerodynamic shape, with a leading edge 112 facing the wind, a trailing edge 114 located at the opposite end of the chord of the blade 108, a tip 116, and a root 118 for connection to the hub 110 in any suitable manner.

[0029] In some implementations, blades 108 may be connected to hub 110 using pitch bearings 120, such that each blade 108 can rotate about its longitudinal axis to adjust the blade pitch. The pitch angle of the blades 108 relative to the rotor plane can be controlled, for example, by a linear actuator, hydraulic actuator, or stepper motor connected between hub 110 and blades 108.

[0030] Figure 2 A schematic diagram showing typical components within the nacelle 104 and tower 102 of the WTG 100. When wind 200 drives the blades 108, the rotor 106 rotates, causing the low-speed shaft 202 to rotate. Gears in the gearbox 204 mechanically convert the low speed of the low-speed shaft 202 into the relatively high speed of the high-speed shaft 208, suitable for generating electricity using the generator 206.

[0031] The controller 210 can sense the rotational speed of one or both shafts 202, 208. If the controller determines that the shaft is rotating too fast, it can signal a braking system 212 to slow the rotation of the shaft, thereby slowing the rotation of the rotor 106—that is, reducing the revolutions per minute (RPM). The braking system 212 can prevent damage to the components of the WTG 100. The controller 210 can also receive input from an anemometer 214 (providing wind speed) and / or a wind vane 216 (providing wind direction). Based on the received information, the controller 210 can send control signals to one or more blades 108 to attempt to adjust the blade pitch 218. By adjusting the blade pitch 218 relative to the wind direction, the rotational speed of the rotor (and therefore the shafts 202, 208) can be increased or decreased. For example, based on wind direction, controller 210 can send control signals to components including yaw motor 220 and yaw drive 222 to rotate nacelle 104 relative to tower 102, thereby allowing rotor 106 to be positioned more (or in some cases less) upwind.

[0032] Figure 3A and 3B This illustration shows the component layout in the MMC 300 according to an embodiment of the present disclosure. Although illustrated as a single-phase layout, those skilled in the art will understand that the MMC 300 can be applied to multi-phase layouts, such as when used with a three-phase WTG 100 or other systems that generate or consume power from a linked three-phase power grid or distribution line. Regardless of the number of phases, the MMC 300 includes a common DC link 315.

[0033] An MMC 300 typically includes multiple batteries 310a-h (collectively referred to as batteries 310) connected in series as part of a phase leg coupled to a DC link 315. The batteries 310 included in a given MMC 300 are modular, and manufacturers can include more or fewer batteries depending on the needs of a specific application. Each battery 310 may include (or may be included in) one or more separate power modules that comprise some or all of the circuitry of the battery 310. Figure 4 The circuitry of battery 310 will be discussed in more detail. Battery 310 is modular in nature; each battery 310 can have the same or substantially the same physical footprint or input / output interface as other batteries 310 in the MMC 300. Therefore, modules can be replaced or interchanged to meet the needs of a specific deployment and can be repaired or replaced independently as needed.

[0034] The grid controller 320 (including its various sub-controllers) controls the operation of the battery 310 and the circuit breaker 360 (or other switches). The grid controller 320 drives various powered switching components in the battery 310 and the circuit breaker 360, which connects an auxiliary power supply 365 to the rectifier 350 to precharge one or more DC link capacitors 330a-b (collectively referred to as DC link capacitors 330). The grid controller 320 monitors various probes 325a-b (e.g., current probe 325a on the rectifier 250, voltage probe 325b across the DC link capacitors 330, and voltage probes across the capacitors in the battery 310) to adjust the charging and discharging of the various capacitors during the precharging of the MMC 300.

[0035] A DC link 315 is provided between two voltage rails 380, referred to as positive voltage rail 380a and negative voltage rail 380b, respectively. Some batteries 310 are typically connected to the mains or distribution lines (e.g., Figure 3B The line-side converter (LSC) 375a of the batteries 310a-b) and the other battery 310 (e.g., Figure 3B The batteries 310c-d) are connected to a machine-side converter (MSC) 375b of a generator such as a WTG 100 when the MMC 300 is in an operational state (e.g., not pre-charged). When the DC link capacitor 330 is being pre-charged, rail 380 can be disconnected from the power distribution line and generator to isolate the battery 310 from the grid or power distribution line and control how the auxiliary power supply 365 charges the DC link capacitor 330. In other words, when the DC link capacitor 330 is being pre-charged, LSC 375a is disconnected from the grid and MSC 375b is disconnected from the generator. Figure 3AAs shown, the DC link 315 may include a central node 385 between the rails 380. Furthermore, the MMC 300 can conceptually be divided into "upper" and "lower" arms and elements based on the fact that components are connected from the phase (output) terminals of the MMC 300 to either the positive rail 380a (e.g., as the "upper" battery 310) or the negative rail 380b (e.g., as the "lower" battery).

[0036] Figure 3A This exhibit showcases a variety of resistors and inductors, which may be inherent to the wiring and circuit layout, or intentionally calibrated to known values ​​via the installed resistors and inductors. Figure 3B An idealized circuit layout is shown, in which resistors (except for the 355mm pre-charge current limiting resistor) and inductors are omitted for ease of understanding. Figure 3A As shown, DC link resistors 335a-b (resistors 335 on the positive rail 380a and the negative rail 380b, respectively) are shown on DC link 315, while converter internal resistors 340a-b and arm inductors 345a-b are shown between each battery 310d-e. Figure 3A and 3B All embodiments show a current-limiting resistor 355 between the circuit breaker 360 and the rectifier 350, which is provided to limit the current and voltage levels supplied to the rail 380 through the rectifier 350. In various embodiments, the negative rail 380b is connected to ground, although in other embodiments, the negative rail 380b may be isolated from the ground for voltage insulation purposes.

[0037] When circuit breaker 360 is closed, auxiliary power supply 365 is connected to a rectifier line including current-limiting resistor 355 and rectifier 350 (which can be connected to the rectifier line via transformer 370, as shown below). Figure 3B The auxiliary power supply 365 used to precharge the MMC 300 can be the auxiliary power supply of the WTG 100 or another AC power source (e.g., an external diesel generator, solar panel array, uninterruptible power supply). By connecting the auxiliary power supply 365 from the grid side of the MMC 300 and precharging the capacitors as described herein, a lower voltage level compared to the grid voltage (e.g., a low-voltage 220V AC power supply 365 compared to a 1kV AC or higher grid voltage) can be used to prepare the MMC 300 for operation. The rectifier 350 converts the AC power generated by the auxiliary power supply 365 into DC power on rail 380, which precharges the various capacitors in the battery 310 and the DC link capacitors 330 under the management of the grid controller 320.

[0038] Figure 4 The components of the battery 310 are shown according to an embodiment of the present disclosure. Figure 4 Can be with Figure 3A and 3B To understand this in combination, each battery 310 includes a battery capacitor 410, a first switch 420a (collectively referred to as switch 420), and a second switch 420b. Each switch 420 is arranged in parallel with a corresponding current diode 430 (first current diode 430a and second current diode 430b, respectively), allowing current to flow through the battery 310 in a specific direction when the corresponding switch 420 is open. The paired switches 420 and current diodes 430 can be included in a single package or integrated component 425 (first component 425a and second component 425b, respectively). In various embodiments, the switch 420 can be included in an insulated-gate bipolar transistor (IGBT) or other power semiconductor device (e.g., a power metal-oxide-semiconductor field-effect transistor (MOSFET) or bipolar junction transistor (BJT)). Therefore, a gate controller 320 (not shown) can control whether a given switch 420 is open or closed by controlling the gate of the associated power semiconductor device.

[0039] In embodiments using power semiconductor devices, the current-carrying diode 430 can be mounted as an anti-parallel diode, allowing current to flow from the emitter side to the collector side of the switch 420 and preventing current from flowing from the collector side to the emitter side. Considering that the battery 310 has a first node 440a and a second node 440b, and the battery capacitor 410 is connected in parallel with the switch 420 between the first node and the second node, the first switch 420a will be connected between the first node 440a and the third node 440c, while the second switch 420b will be connected between the third node 440c and the second node 440b. The corresponding current-carrying diode 430 allows current to flow from the second node 440b to the third node 440c and from the third node 440c to the first node 440a, and prevents current from flowing from the first node 440a to the third node 440c and from the third node 440c to the second node 440b.

[0040] A voltage probe 450 spanning the battery capacitor 410 (e.g., connected to the first node 440a and the second node 440b) measures the state of charge of the battery capacitor 410. The gate controller 320 uses the state of charge of individual batteries 310 as well as the aggregated or summed state of charge of all batteries 310 to manage when and at what frequency the switches 420 in the batteries 310 are opened and closed to precharge the DC link capacitor 330 (not shown) and the battery capacitor 410.

[0041] When will Figure 4 When the battery 310 shown is used as a single capacitor battery 310, each battery 310 can be connected in series with other batteries between rails 380. (See reference...) Figure 3AThe first battery 310a can be connected to the positive rail 380a via the third node 440c, and to the second battery 310b via the second node 440b (at the corresponding third node 440c). Similarly, the second node 440b of the second battery 310b is connected to the third node 440c of the third battery 310c, the second node 440b of the third battery 310c is connected to the third node 440c of the fourth battery 310d, and so on, until the second node 440b of the fourth battery 310d is connected to the upper arm reactor 345a (or according to...). Figure 3A Representative resistor 340a). The lower arm connection is similarly connected to the lower arm reactor 345b via interlocking second node 440b and third node 440c (or according to Figure 3A The representative resistor 340b is located between the negative rail 380b and the negative rail 380b. In this example arrangement, the second switch 420b acts as a bypass switch to carry bypass current to charge the battery capacitor 410, and the first switch 420a acts as a plug switch to discharge the battery capacitor 410 and charge the DC link capacitor 330.

[0042] When arranged in Figure 4 The battery 310 shown is configured to form a dual-cell arrangement (where each battery 310 includes two capacitors, and each battery 310 can be connected in series with other batteries 310 between rails 380). (See reference...) Figure 3A The first battery 310a can be connected to the positive rail 380a via the corresponding third node 440c, and connected to the first node 440a of the second battery 310b via the second node 440b of the first battery 310a. The second battery 310b is then connected to the third battery 310c via the corresponding third node 440c. In this example, the third battery 310c can be connected to the fourth battery 310d via the second node 440b of the third battery 310c and the first node 440a of the fourth battery 410d. Therefore, the batteries 310 can be alternately connected in various connection schemes (third to third node or second to first node) until the fourth / final battery 310d of the upper arm is connected to the upper reactor 345a and / or resistor 340a. Similarly, the batteries 310e-h of the lower arm are connected to the lower arm reactor 345b via an alternating connection scheme (or according to...). Figure 3AThe representative resistor 340b is located between the negative rail 380b and the negative rail. In this example arrangement, in one half of the battery 310, the first switch 420a acts as a bypass switch to carry bypass current to charge the battery capacitor 410, and the second switch 420b acts as a plug-in switch to discharge the battery capacitor 410 to charge the DC link capacitor 330. In the other half of the battery in the example arrangement, the second switch 420b acts as a bypass switch to carry bypass current to charge the battery capacitor 410, and the first switch 420a acts as a plug-in switch to discharge the battery capacitor 410 to charge the DC link capacitor 330. Those skilled in the art will understand that more or fewer than eight batteries 310 can be used in the MMC 300.

[0043] In some embodiments, a discharge line is defined between the first node 440a and the second node 440b, which includes a discharge switch 460 and a discharge resistor 470. The discharge switch 460 may include various power semiconductor devices controlled by the gate controller 320 to selectively open and close. When the discharge switch 460 is closed, the discharge line forms a loop with the battery capacitor 410 and the discharge resistor 470, allowing energy stored in the battery capacitor 410 to be released within the battery 310 (also referred to as "discharge"). A freewheeling diode 480 is included in parallel with the discharge resistor 470 to reduce voltage overshoot after the discharge switch 460 is closed when discharging the battery capacitor 410. When preparing for maintenance or inspection of the battery 310, the gate controller 320 may discharge the battery capacitor 410 via the discharge resistor 470 when the voltage across the battery capacitor 410 exceeds a predefined threshold, so that the charge in the battery capacitor 410 of one battery 310 is equal to the charge in another battery 310, etc.

[0044] Figure 5 This is a flowchart of a method 500 for pre-charging an MMC 300 according to an embodiment of this disclosure. Method 500 begins at block 505, where a gate controller 320 closes a circuit breaker (CB) 360 to contact an auxiliary power supply 365 and a rectifier 350. Connecting the auxiliary power supply 365 and the rectifier 350 to rail 380 generates a DC voltage, and (according to block 510) a DC current circulates through the MMC 300 to pre-charge the DC link capacitor 330.

[0045] The gate controller 320 monitors the voltage (V) across the DC link capacitor 330. lc When the voltage V at block 515 lcIf the switching threshold is exceeded, method 500 continues to block 520. Otherwise, method 500 returns to block 510 to allow current to continue circulating through DC link capacitor 330. In various embodiments, the switching threshold is equal to the rectified peak voltage of auxiliary power supply 365, and in other embodiments, it can be a predefined value of the rectified peak voltage (e.g., x% of the peak). The rectified peak voltage is typically less than the nominal voltage of MMC 300, and the charge level in DC link capacitor 330 should exceed the rectified peak voltage to avoid current surges and other anomalous effects when establishing a connection between the two systems via MMC 300. Because the DC voltage on rail 380 is based on the rectified peak voltage of auxiliary power supply 365, the charge level in DC link capacitor 330 cannot exceed the rectified peak voltage unless a boost action is performed. Therefore, once the voltage V across DC link capacitor 330... lc If the switching threshold is exceeded, method 500 proceeds to block 520 to begin the boost operation.

[0046] At block 520, the gate controller 320 drives the bypass switch 420 in the battery 310 to charge the battery capacitor 410 therein. The frequency at which the gate controller 320 drives the bypass switch 420 (i.e., cycles between open and closed states) is based on the RLC (resistor, inductor, capacitor) characteristics of the MMC 300 and the required charging speed. When the bypass switch 420 is closed, bypass current flows through the battery 310 and charges the arm inductor / reactor 345. When the bypass switch 420 is open, the reactance current stored in the arm inductor 345 decays and flows through the current diode 430 to charge the battery capacitor 410. The gate controller 320 can vary the duty cycle and the frequency of the open / close cycle to optimize charging speed and charge level requirements. When used in a multiphase MMC 300, the grid controller 320 can drive the bypass switch 420 of each phase according to the relevant phase of the power supplied from the auxiliary power supply 365, so as to charge the battery capacitors 410 of all phases simultaneously.

[0047] In one embodiment, the gate controller 320 monitors the charge in individual battery capacitors 410 and (optionally) tunes the switching rates of various individual bypass switches 420 at block 525 to control the charging rate of the battery capacitors 410. In various embodiments, the gate controller 320 may keep bypass switches 420 open for a longer period of time for battery capacitors 410 that are charging too fast, or may keep bypass switches 420 closed for a longer period of time for battery capacitors 410 that are charging too slowly, or both. Therefore, the gate controller 320 can compensate for any charging imbalances that may occur in the battery capacitors 410 due to different tolerances in circuit components such as the capacitance of the battery capacitors 410, the resistance in the switches 420, and parasitic resistance.

[0048] The gate controller 320 also monitors the relative difference (ΔV) between the charge level of a single cell capacitor 410 and the average (median or intermediate) charge level of all cell capacitors 410. cc At block 530, when any battery 310 exhibits a charge in its associated battery capacitor 410 that is higher or lower than a threshold difference from the average (e.g., x% higher than the average charge), method 500 proceeds to block 555, where the gate controller 320 stops driving the bypass switch 420. Otherwise, method 500 proceeds to block 535, where the gate controller 320 also monitors the collective or summative charge level (ΣV) of the battery capacitors 410. cc At block 535, when the collective charge level ΣV cc When the charge level is below the drive threshold, method 500 returns to block 520 so that the gate controller 320 can continue to drive the bypass switch 420 to charge the battery capacitor 410. The gate controller 320 continues to drive the bypass switch 420 (according to block 520) until the collective charge level ΣV cc The drive threshold is met. The drive threshold is set based on the total charge of the battery capacitor 410 relative to the DC link capacitor 330. In a single-phase MMC 300, the drive threshold can be set to be 2-5% higher than the nominal charge voltage of the battery capacitor 410, depending on the ratio of the equivalent capacitance of the DC link capacitor 330 to the equivalent capacitance of all battery capacitors 410. In a multi-phase MMC 300, which typically includes more battery capacitors 410 than a single-phase MMC 300, the drive threshold can be set accordingly lower than in a single-phase MMC 300.

[0049] When the collective charge level ΣV ccWhen the drive threshold is met, method 500 proceeds from block 535 to block 540, where gate controller 320 begins driving insertion switch 420 to charge DC link capacitor 330 from battery capacitor 410. At block 540, gate controller 320 drives insertion switch 420 in battery 310 to discharge battery capacitor 410 therein, pre-charging DC link capacitor 330 to above the rectified peak voltage. The frequency at which gate controller 320 drives insertion switch 420 (i.e., cycling between open and closed states) is based on the RLC characteristics of MMC 300 and the desired charge / discharge rate. When insertion switch 420 is closed, insertion current flows from battery 310 and charges DC link capacitor 330. When insertion switch 420 is open, battery capacitor 410 retains its charge. Gate controller 320 can vary the duty cycle and the frequency of the open / close cycle to optimize the discharge rate and the current generated on rail 380. When used in a multiphase MMC 300, the gate controller 320 can simultaneously drive the insertion switch 420 of each phase to charge the DC link capacitor 330.

[0050] The gate controller 320 monitors the charge in the individual battery capacitors 410 and (optionally) tunes the duty cycles of various individual plug-in switches 420 at block 545 to control the discharge rate of the battery capacitors 410. In various embodiments, the gate controller 320 may keep the plug-in switch 420 open for a longer period of time for battery capacitors 410 that are discharging too quickly, or may keep the bypass switch 420 closed for a longer period of time for battery capacitors 410 that are discharging too slowly, or both.

[0051] At block 550, the gate controller 320 also monitors the relative difference (ΔV) between the charge level of a single battery capacitor 410 and the average (median or intermediate) charge level of all battery capacitors 410. cc In some implementations, the difference threshold used in block 550 is the same as the difference threshold used in block 535, but may differ in other implementations. When any battery 310 exhibits a charge in its associated battery capacitor 410 that is higher or lower than the difference threshold from the average (e.g., x% higher than the average charge), method 500 proceeds to block 555, where the gate controller 320 stops driving the insertion switch. Otherwise, method 500 proceeds to block 560, where the gate controller 320 monitors the charge level V of the DC link capacitor 330 while driving the insertion switch 420. lc .

[0052] At block 560, when the charge level V of DC link capacitor 330... lcIf the charge level is below the pre-charge threshold, method 500 returns to block 540 so that the gate controller 320 continues to drive the insertion switch 420 to charge the DC link capacitor 330 from the battery capacitor 410. The gate controller 320 continues to drive the insertion switch 420 (according to block 540) until the charge level V of the DC link capacitor 330 reaches a certain threshold. lc The pre-charge threshold must be met. In a three-phase MMC 300, the sum of the voltages of the battery capacitors 410 across all phases must be at least twice the pre-charge threshold. Otherwise, when the charge level V of the DC link capacitor 330 is... lc When the pre-charge threshold is met, method 500 proceeds from block 560 to block 565 so that the gate controller 320 ends the pre-charge action and disconnects the circuit breaker 360 to disconnect the auxiliary power supply 365 from the rail 380.

[0053] At block 555, in response to the detection that a charge imbalance during the charging (according to block 530) or discharging (according to block 550) of battery capacitor 410 exceeds a difference threshold that gate controller 320 can compensate for by changing the switching rate, gate controller 320 stops driving switches 420 in battery 310; allowing all switches 420 to open. Additionally, gate controller 320 generates an alarm or maintenance message and optionally activates a discharge line to discharge battery capacitor 410. Method 500 then proceeds to block 565 to ensure that circuit breaker 360 is open and auxiliary power supply 365 is disconnected from MMC 300. Method 500 can then terminate.

[0054] In various embodiments, the gate controller 320 may execute block 565 to disconnect the circuit breaker 360 at any time after the battery capacitor 410 has been fully charged (e.g., after the positive determination of block 535).

[0055] In various embodiments, after successfully charging the DC link capacitor 330 and ensuring that the circuit breaker 360 is open (according to block 565), the gate controller 320 or another control device may cause various circuit breakers or switches to connect the generator (e.g., WTG 100) to the battery 310 including the MSC and to connect an external power line to the battery 310 including the LSC to link the generator to the power grid or distribution line via rail 380. Method 500 can then end.

[0056] Figure 6This is a block diagram of a controller unit 600 according to one or more embodiments, which can be used as a gate controller 320. The controller unit 600 includes one or more computer processors 610 and memory 620. The one or more processors 610 represent any number of processing elements, each of which may include any number of processing cores. The memory 620 may include volatile memory elements (such as random access memory), non-volatile memory elements (such as solid-state, magnetic, optical, or flash-based memory), and combinations thereof. Furthermore, the memory 620 may be distributed across different media (such as network storage or external hard drives).

[0057] As shown in the figure, the one or more processors 610 are communicatively coupled to the communication system 630 to send / receive communications with various probes 325 / 450 and other controller units 600 associated with the WTG 100 or auxiliary power supply 365 via optical fiber, wire and / or radio signals.

[0058] The memory 620 may include multiple “modules” for performing the various functions described herein. In one embodiment, each module includes program code executable by one or more processors 610. However, other embodiments may include some or all of the modules implemented in hardware (i.e., circuitry) or firmware. The memory 620 includes precharge control logic 640, which enables the controller unit 600 to optimize the charging of the DC-link capacitor 330 via auxiliary power supply 365, as described herein. In some embodiments, the precharge control logic 640 is pre-loaded with setpoints and thresholds for various control schemes, such as those combined by way of example. Figure 5 Described.

[0059] The embodiments proposed in this disclosure have been mentioned above. However, the scope of this disclosure is not limited to the specifically described embodiments. Rather, any combination of the features and elements provided above, whether or not related to different embodiments, is contemplated for implementing and carrying out the contemplated embodiments. Furthermore, although the embodiments disclosed herein may achieve advantages over other possible solutions or over the prior art, whether a particular advantage is achieved by a given embodiment does not limit the scope of this disclosure. Therefore, the aspects, features, embodiments, and advantages described herein are merely illustrative and should not be considered as elements or limitations of the appended claims unless expressly mentioned in the claims.

[0060] As those skilled in the art will understand, the embodiments disclosed herein can be embodied as systems, methods, or computer program articles. Therefore, aspects can take the form of entirely hardware implementations, entirely software implementations (including firmware, resident software, microcode, etc.), or implementations combining software and hardware aspects, all of which can be referred to herein as “circuit,” “module,” or “system.” Furthermore, aspects can take the form of computer program articles embodied in one or more computer-readable media having computer-readable program code thereon.

[0061] This invention can be a system, a method, and / or a computer program article. The computer program article may include a computer-readable storage medium (or medium) having computer-readable program instructions thereon (e.g., a portable computer floppy disk, hard disk, random access memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM or flash memory), optical fiber, portable optical disc read-only memory (CD-ROM), optical storage device, magnetic storage device, or any suitable combination thereof) for causing a processor to execute various aspects of the invention.

[0062] Various aspects of this disclosure are described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program articles according to embodiments presented herein. It will be understood that each block in the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, or other programmable data processing apparatus to create a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions / behaviors specified in one or more blocks of the flowchart illustrations and / or block diagrams.

[0063] The flowcharts and block diagrams in the figures illustrate the possible structures, functions, and operations of systems, methods, and computer program articles according to various embodiments. In this regard, each block in a flowchart or block diagram may represent a module, segment, or portion of code, comprising one or more executable instructions for implementing a specified logical function. It should also be noted that in some alternative implementations, the functions indicated in the blocks may not appear in the order shown in the figures. For example, two blocks shown consecutively may actually be executed substantially simultaneously, or these blocks may sometimes be executed in reverse order, depending on the functions involved. It should also be noted that each block in the block diagrams and / or flowchart descriptions, and combinations of blocks in the block diagrams and / or flowchart descriptions, may be implemented by a special-purpose hardware system to perform the specified function or behavior, or a combination of special-purpose hardware and computer instructions.

[0064] In view of the foregoing, the scope of this disclosure is defined by the following claims.

Claims

1. A method for pre-charging a modular multilevel converter, comprising: The bypass current driven from the auxiliary power supply (365) passes through multiple bypass switches (420b) included in the corresponding multiple batteries (310). In response to the sum of voltages across a plurality of battery capacitors (410) included in the plurality of batteries satisfying a drive threshold, an insertion current is driven through a plurality of insertion switches (420a) included in the plurality of batteries to charge a DC link capacitor (330) by discharging the plurality of battery capacitors (410), wherein the drive threshold exceeds the peak rectified voltage for the auxiliary power supply (365). as well as In response to the voltage across the DC link capacitor (330) satisfying the pre-charge threshold when driving the insertion current, the circuit breaker (360) connecting the auxiliary power supply to the plurality of batteries and the generator to the external power rails (380) is disconnected, and the DC link capacitor is connected between each external power rail (380). The drive bypass current includes tuning the switching rate of a single bypass switch during battery capacitor charging to ensure that the charge in the plurality of battery capacitors is equal. as well as The drive insertion current includes tuning the switching rate of a single insertion switch during the discharge of the battery capacitors to make the charges in the plurality of battery capacitors equal.

2. The method according to claim 1, further comprising: While driving at least one of the bypass current and the insertion current, the difference in voltage level of each of the plurality of battery capacitors is measured; as well as In response to the difference exceeding the difference threshold (530, 550), the auxiliary power supply stops charging the battery capacitor and the battery capacitor stops charging the DC link capacitor.

3. The method according to claim 1 or 2, further comprising, before driving the bypass current: The circuit breaker is closed to link the auxiliary power supply to the positive rail (380a) and the negative rail (380b) via a rectifier (350), the DC link capacitor and the plurality of batteries being connected between the positive rail and the negative rail; and The initial current is circulated through the plurality of batteries until the switching threshold voltage is reached in the plurality of battery capacitors.

4. The method according to claim 1 or 2, wherein the auxiliary power supply is a multiphase power supply, and each phase provided by the auxiliary power supply simultaneously charges the plurality of battery capacitors while driving the bypass current.

5. The method according to claim 1 or 2, wherein the bypass switch is connected in parallel with the first current diode (430b), and the insertion switch is connected in parallel with the second current diode (430a).

6. A controller (600) for a modular multilevel converter (300), the modular multilevel converter including a plurality of batteries (310) connected in series between a positive rail (380a) and a negative rail (380b), each of the plurality of batteries including a bypass switch (420b), a plug-in switch (420a) and a battery capacitor (410), wherein the plurality of batteries are connected in parallel to a DC link capacitor (330), the controller being configured to perform the following operations: The bypass current from the auxiliary power supply (365) is driven through the bypass switch; In response to the sum of voltages across the battery capacitors satisfying a drive threshold, an insertion current from the battery capacitors is driven (540) through an insertion switch to charge the DC link capacitor (330) by discharging the battery capacitors (410), wherein the drive threshold exceeds the nominal voltage for the plurality of batteries (310). as well as In response to the voltage across the DC link capacitor meeting the pre-charge threshold, the circuit breaker (360) connecting the auxiliary power supply to the rectifier (350) and the wind turbine generator (100) to the external power line via the positive and negative rails is disconnected. The drive bypass current includes tuning the switching rate of a single bypass switch during battery capacitor charging to ensure that the charge in the plurality of battery capacitors is equal. as well as The drive insertion current includes tuning the switching rate of a single insertion switch during the discharge of the battery capacitors to make the charges in the plurality of battery capacitors equal.

7. The controller of claim 6, wherein the operation further comprises: While driving at least one of the bypass current and the insertion current, the difference in voltage level of each battery capacitor is measured; as well as In response to the difference exceeding the difference threshold (530, 550), the auxiliary power supply stops charging the battery capacitor and the battery capacitor stops charging the DC link capacitor.

8. The controller according to claim 6 or 7, wherein the operation further comprises, before driving the bypass current: Close the circuit breaker to link the auxiliary power supply to the positive and negative rails via a rectifier; and The initial current is circulated through the battery until the switching threshold voltage is reached in the battery capacitor.

9. The controller according to claim 6 or 7, wherein the auxiliary power supply is a multiphase power supply, each phase provided by the auxiliary power supply simultaneously charges each battery capacitor while driving the bypass current.

10. The controller according to claim 6 or 7, wherein the bypass switch is connected in parallel with the first current diode (430b), the insertion switch is connected in parallel with the second current diode (430a), wherein the insertion current flows through the first current diode, and wherein the bypass current flows through the second current diode.

11. A modular multilevel converter (300), comprising: Positive polar orbital (380a); Negative polar orbit (380b); DC link (315), which includes a DC link capacitor (330) connected between the positive rail and the negative rail. A rectifier (350) is connected between the positive and negative rails and selectively connected to an auxiliary power supply (365) in a wind turbine generator (100), wherein the rectifier supplies DC power from the auxiliary power supply of the wind turbine generator on the positive and negative rails, the peak voltage of which is rectified is below the pre-charge threshold of the DC link capacitor. Multiple batteries (310) are connected in series between the positive and negative electrode rails, each of the multiple batteries comprising: A battery capacitor (410) is connected between a first node (440a) and a second node (440b); Insert a switch (420a) which is connected to the first node and the third node (440c); A bypass switch (420b) is connected to the third and second nodes; The first current diode (430a) is configured to allow current to flow from the third node to the first node and to prevent current from flowing from the first node to the third node; The second current diode (430b) is configured to allow current to flow from the second node to the third node and to prevent current from flowing from the third node to the second node; and The gate controller (320) is configured as follows: The voltage across the DC link capacitor and the battery capacitor is controlled by switching the bypass switch (420b) open and closed to charge the battery capacitor to a drive threshold exceeding the nominal voltage for the battery capacitor (410), and then the plug switch (420a) and bypass switch (420b) are switched open and closed to discharge the battery capacitor to charge the DC link capacitor to a pre-charge threshold, and The drive bypass current includes tuning the switching rate of a single bypass switch (420b) during battery capacitor charging to ensure equal charge in the plurality of battery capacitors; and The drive insertion current includes tuning the switching rate of a single insertion switch (420a) during the discharge of the battery capacitors to make the charges in the plurality of battery capacitors equal.

Images