Capacitance protection in power converters

Abstract

The invention provides capacitance protection in a power converter. A system includes a DC bus electrically configured to be connected to one or more of a rectifier and an inverter, the DC bus including a positive bus and a negative bus; and a DC link electrically connected to the DC bus. The DC link comprises: an energy storage device comprising at least two energy storage elements; and a fuse assembly electrically connected to the energy storage device and electrically connected to one of the positive bus bar and the negative bus bar.

Description

Technical Field

[0001] The present disclosure relates to capacitor protection in power converters. Background Art

[0002] A power converter, such as a variable speed drive, an adjustable speed drive, or an uninterruptible power supply, can be connected to an alternating current (AC) high power electrical distribution system, such as a power grid. The power converter can drive, power, and / or control, for example, a motor or a power electronic load. Electrical equipment includes an electrical network that converts AC power to direct current (DC) power or converts DC power to AC power. Summary of the invention

[0003] In one aspect, a system includes: a DC bus electrically configured to be connected to one or more of a rectifier and an inverter, the DC bus including a positive bus and a negative bus; and a DC link electrically connected to the DC bus. The DC link includes: an energy storage device including at least two energy storage elements; and a fuse assembly electrically connected to the energy storage device and electrically connected to one of the positive bus and the negative bus.

[0004] Implementations may include one or more of the following features.

[0005] The energy storage device may include at least two energy storage elements connected in series.

[0006] The energy storage device may include at least two energy storage elements connected in parallel, each of which includes a film capacitor.

[0007] The fuse assembly may include a fuse element connected in parallel with a capacitive element.

[0008] The energy storage device may be electrically connected to the positive bus, and the fuse assembly may be electrically connected to the energy storage device and the negative bus.

[0009] The energy storage device may be electrically connected to the negative bus, and the fuse assembly may be electrically connected to the energy storage device and the positive bus.

[0010] The energy storage device may include two or more capacitor strings connected in parallel with each other, and each of the two or more capacitor strings may include at least two capacitors connected in series.

[0011] The system may further include a discharge circuit. The discharge circuit may include a discharge resistor and a controllable switch, and the controllable switch may be configured to be turned on in response to a short circuit in one of the at least two energy storage elements.

[0012] In another aspect, a protection device for a drive system includes: a fuse assembly configured to be electrically connected between (i) a capacitor bank in the drive system and (ii) one of a positive bus and a negative bus of the drive system. The fuse assembly includes: a fuse element connected in parallel with a capacitor element, the fuse element being configured to disconnect in response to a short circuit in one of the capacitors in the capacitor bank, so that the capacitor element provides an impedance and a current path to another capacitor in the capacitor bank that is not short-circuited.

[0013] In some embodiments, the protection device further includes a discharge circuit configured to be electrically connected to a positive bus and a negative bus of the drive system.

[0014] On the other hand, a drive device includes: a rectifier; an inverter; and a DC link electrically connected to the rectifier and the inverter. The DC link includes: a positive bus; a negative bus; an energy storage device including at least two capacitor banks; and a fuse assembly electrically connected to each capacitor bank and one of the positive bus and the negative bus.

[0015] Implementations may include one or more of the following features.

[0016] Each capacitor group may include two capacitors connected in parallel.

[0017] Each capacitor group may include at least two capacitor strings, and each string may include at least two capacitors electrically connected in series.

[0018] Each fuse assembly may have the same fuse rating.

[0019] Each fuse assembly may be connected to one of the capacitor banks and the positive bus.

[0020] Each fuse assembly may be connected to one of the capacitor banks and the negative bus.

[0021] Each capacitor group may include the same number of capacitors in the same configuration, and each capacitor group may include the same nominal capacitance.

[0022] Implementations of any technology described herein may include devices, apparatus, systems and / or methods. The details of one or more implementations are set forth in the accompanying drawings and the following description. Other features will be apparent from the description and drawings, and from the claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 is a block diagram of an example of a power converter.

[0024] Figure 2 is a schematic diagram of an example of a system including a power converter.

[0025] Figure 3is a schematic diagram of another example of a system including a power converter.

[0026] Figure 4 is a schematic diagram of another example of a system including a power converter.

[0027] Figures 5A-5D Shown from Figure 4 Simulated data of the power converter.

[0028] Figure 6 is a schematic diagram of another example of a system including a power converter.

[0029] Figure 7 is a schematic diagram of another example of a system including a power converter.

[0030] Figure 8 is a schematic diagram of another example of a system including a power converter.

[0031] Fig. 9 is a schematic diagram of another example of a system including a power converter.

[0032] Fig.10 is a schematic diagram of another example of a system including a power converter. DETAILED DESCRIPTION

[0033] Figure 1 1 is a block diagram of an example of a power converter 110. The power converter 110 includes an input node 111, a filter system 170, a rectifier 117, and a DC link 118. Figure 1 In the example shown, the filter system 170 is located between the input node 111 and the intermediate node 114. However, the filter system 170 may be located in a different portion of the power converter 110, or may be omitted.

[0034] Rectifier 117 includes electronic components that are arranged and / or controlled to convert alternating current (AC) or time-varying power from power distribution network 101 into direct current (DC) power that is provided to DC link 118. Rectifier 117 is any type of arrangement of electrical components that converts AC current into DC current. For example, rectifier 117 may be a diode bridge rectifier. Power converter 110 may include additional components and assemblies. For example, power converter 110 may include an inverter, such as inverter 219 ( Figure 2 ). The power converter 110 may be a drive device. For example, the power converter 110 may be a variable frequency drive (VFD), an adjustable speed drive (ASD), or a variable speed drive (VSD).

[0035] The DC link 118 includes a positive bus 112a and a negative bus 112b. In operational use of the power converter 110, the voltage across the DC link 118 is Vdc, and the positive bus 112a is at a potential greater than the negative bus 112b by Vdc volts. The DC link 118 also includes an energy storage device 140 that stores electrical potential energy in the form of voltage.

[0036] Energy storage device 140 includes one or more capacitor banks 142. Although power converter 110 may include more than one capacitor bank 142, Figure 1 Only one capacitor bank 142 is shown in the figure. Each capacitor bank 142 may include, for example, two or more capacitors connected in series, capacitors connected in parallel to each other, or two or more series capacitor strings connected in parallel, wherein each string includes at least two capacitors connected in series. The capacitor may be an electrolytic capacitor and / or a film capacitor. The fuse assembly 150 is electrically connected to the capacitor bank 142. The fuse assembly 150 is also electrically connected to the positive bus 112a or the negative bus 112b.

[0037] When a capacitor in one of the groups 142 experiences a short circuit, the potential energy stored in the capacitor is suddenly released. This released energy can cause component failure and can ignite items near the power converter 110. For example, the power converter 110 may need to pass a component failure test. As part of the component failure test, the energy storage device 240 is subjected to a short circuit and a flammability test is performed. The flammability test includes wrapping the power converter 110 in a cotton blanket and short-circuiting the capacitor through an external stimulus. If the protection of the energy storage device 240 is insufficient, the cotton blanket will catch fire, and the converter 110 is considered to have failed the component failure test.

[0038] Furthermore, when one of the capacitors in bank 142 is shorted, the other capacitor in bank 142 is suddenly subjected to twice the voltage. This causes high currents to flow in DC link 118 and other components in power converter 110 and may cause the entire power converter 110 to malfunction or become significantly damaged.

[0039] On the other hand, the configuration and placement of the fuse assembly 150 protects the capacitors in the capacitor bank 142 from being damaged in an event that causes one or more capacitors to short-circuit. The fuse assembly 150 also helps to effectively manage surge currents that may occur during a brown-in event. In addition, the configuration and placement of the fuse assembly 150 also ensures that the power converter 110 can comply with component failure test requirements.

[0040] Figure 22 is a schematic diagram of a system 200. The system 200 includes a power converter 210 connected to a load 202 and a three-phase AC power distribution network 201. The power converter 210 can be, for example, a variable speed drive (VSD), an adjustable speed drive (ASD), or a variable frequency drive (VFD). The load 202 can be, for example, an induction motor or a permanent magnet synchronous machine. The dashed lines are used to show the grouping of components, and the dashed lines do not necessarily represent physical objects. However, the power converter 210 can be in a housing or casing, such as a rack-mount box or cabinet.

[0041] The power distribution network 201 distributes AC power having a fundamental frequency of, for example, 50 or 60 Hertz (Hz). The distribution network 201 may include, for example, one or more transmission lines, distribution lines, cables, and / or any other mechanism for transmitting power. The distribution network 201 includes three phases, referred to as a, b, and c. Each phase a, b, c has a corresponding grid voltage Va, Vb, Vc. The power converter 210 includes input nodes 211a, 211b, 211c, each of which is electrically coupled to one of the three phases (a, b, c) of the distribution network 201. The power converter 210 also includes intermediate nodes 214a, 214b, 214c.

[0042] The power converter 210 may also include a filter system ( Figure 2 214a, 214b, 214c). The filter system may be, for example, an inductor or LCL filter between each input node 211a, 211b, 211c and the corresponding intermediate node 214a, 214b, 214c. Other implementations of the filter system are also possible. For example, the filter system may be implemented as a DC link choke between the rectifier 217 and the DC link 218.

[0043] The power converter 210 includes a rectifier 217, a DC link 218, and an inverter 219. The rectifier 217 includes electronic switches that are arranged and / or controllable to convert AC currents ia, ib, ic at nodes 214a, 214b, 214c into a DC current Idc flowing to the DC link 218. Figure 2 In the example of , the rectifier 217 is a diode bridge rectifier including diodes D1 to D6. Diode D1 and diode D4 are electrically connected to the intermediate node 214a, diode D1 is electrically connected to the positive bus 212a of the DC link 218, and diode D4 is electrically connected to the negative bus 212b of the DC link 218. Diode D3 and diode D6 are electrically connected to the intermediate node 214b, diode D3 is electrically connected to the positive bus 212a, and diode D6 is electrically connected to the negative bus 212b. Diode D5 and diode D2 are electrically connected to the intermediate node 214c, diode D5 is electrically connected to the positive bus 212a, and diode D2 is electrically connected to the negative bus 212b.

[0044] The DC link 218 includes an energy storage device 240. The energy storage device 240 includes capacitor sections or capacitor groups 242a and 242b. Each group 242a and 242b includes two parallel capacitor strings, each string including two series capacitors. Group 242a includes a first string having series capacitors C1 and C2 and a second string having series capacitors C3 and C4. The first string and the second string are connected in parallel to each other. Group 242b is identical and includes a third string having series capacitors C5 and C6 and a fourth string having series capacitors C7 and C8. The third and fourth strings are connected in parallel to each other. Groups 242a and 242b have the same number of capacitors arranged in the same manner, and groups 242a and 242b have the same nominal capacitance.

[0045] The midpoints of the strings are not electrically connected. For example, the node between capacitors C1 and C2 is not electrically connected to the node between capacitors C3 and C4. In addition, capacitors C1 to C8 are not individually fused, and there is not necessarily a fuse in the energy storage device 240 itself.

[0046] The group 242a is electrically connected to the fuse assembly 250a and the negative bus 212b of the DC link 218. Figure 2 As shown, capacitors C1 and C3 are directly connected to fuse assembly 250a. Fuse assembly 250a is also electrically connected to positive bus 212a of DC link 218. Group 242b is electrically connected to fuse assembly 250b and negative bus 212b. Figure 2 As shown, capacitors C5 and C7 are directly connected to fuse assembly 250a. Fuse assembly 250b is also electrically connected to positive bus 212a.

[0047] Fuse assembly 250a includes fuse FS1 and buffer capacitor Cs1 connected in parallel with fuse FS1. Fuse assembly 250b includes fuse FS2 and buffer capacitor Cs2 connected in parallel with fuse FS2. The rated operating voltage of fuses FS1 and FS2 is a DC voltage equal to or greater than Vdc. The current rating of each fuse FS1 and FS2 is at least 15% to 20% greater than the current rating of the capacitor in the corresponding group 242a and 242b. Each fuse FS1 and FS2 includes a corresponding fuse element, and when a current that generates enough heat energy to melt the fuse element flows through the fuse, the fuse element is disconnected. The current that disconnects each fuse FS1 and FS2 depends on the value and duration of the current flowing through the fuse. The parameter related to the current that disconnects each fuse FS1 and FS2 can be called i2T rating. The i2T rating is obtained from the fuse current-time curve provided by the fuse manufacturer. When open, current cannot flow in fuses FS1 and FS2. When closed, current can flow in fuses FS1 and FS2.

[0048] The inverter 219 converts the DC voltage across the energy storage device 240 into a three-phase AC voltage, which is then injected into the load 202. The output voltage level and the output fundamental frequency are controlled by the controller 230, and the output of the controller 230 controls the inverter switches in the inverter 219. The inverter 219 includes output terminals 205u, 205v, 205w, each of which is connected to one of the three phases of the load 202. The inverter 219 includes a network of electronic switches (e.g., power transistors) arranged to generate a desired AC voltage.

[0049] The inverter 219 may be controlled based on a pulse width modulation (PWM) control scheme, such as a space vector PWM control scheme. The control of the inverter 219 may be implemented by a control system 230. The control system 230 includes an electronic processor, an electronic memory, and an input / output interface. The control system 230 may be a microcontroller.

[0050] The above discussion relates to a power converter that generates and provides an AC drive signal 204 to a load 202. However, other configurations and applications are possible. For example, the power converter 210 may be implemented without an inverter 219 and configured to drive a DC load.

[0051] Next, the operation of the power converter 210 during the capacitor short circuit event is discussed using capacitor C4 as an example. Before the capacitor short circuit event, the power converter 210 operates normally. The DC link 218 is normal, and none of the capacitors C1 to C8 are short-circuited. The voltage across the DC link 218 is Vdc, and the controller 230 controls the amplitude and frequency of the output voltage injected into the load 202.

[0052] A capacitor short circuit event occurs, and capacitor C4 is short circuited. The energy stored in capacitor C4 is suddenly released, and a high current flows from capacitors C1 and C2 into capacitor C3 and the short circuited capacitor C4. This causes the voltage across capacitor C3 (which is in series with the short circuited capacitor C4) to increase from Vdc / 2 to Vdc. Current also flows from rectifier 217 and other adjacent branches ( Figure 2 The high current causes the fuse FS1 to open, making the snubber capacitor Cs1 part of the group 242a.

[0053] Once fuse FS1 is disconnected, snubber capacitor Cs1 provides a high impedance path, thereby preventing current from flowing or greatly reducing the current flowing into capacitor C3. By reducing or eliminating the current flowing into capacitor C3, capacitor C3 will not fail, and the short circuit current will not ignite items near power converter 210 (e.g., cotton blankets during flammability testing). Power converter 210 is able to continue to operate despite having a smaller capacitance. Depending on load 202, power converter 210 may trip or may continue to operate. In any case, fuse assembly 250a prevents the high current flowing due to the short circuit event from igniting components near power converter 210 (e.g., cotton blankets during flammability testing) and / or causing a failure of power converter 210.

[0054] The rated operating voltage of fuses FS1 and FS2 is a DC voltage corresponding to Vdc or higher. The current rating of fuses FS1 and FS2 has a safety margin to accommodate a situation that is at least 15% to 25% greater than the ripple current rating of the capacitors in the corresponding groups 242a and 242b. The ripple current rating of the capacitors is calculated based on the required load-side inductive current and the source-side inductive current, which in turn depends on whether a DC link or input AC reactor is used. Any known method can be used to determine the ripple current rating.

[0055] Figure 3 is a schematic diagram of a system 300 including a power converter 310. Power converter 310 is the same as power converter 210, except that power converter 310 includes a DC link 318 instead of DC link 218. DC link 318 is similar to DC link 218, except that in DC link 318, fuse assemblies 250a and 250b are electrically connected to negative bus 212b instead of positive bus 212a. Capacitor bank 242a is electrically connected to fuse assembly 250a and positive bus 212a. Capacitor bank 242b is electrically connected to fuse assembly 250b and positive bus 212a.

[0056] Figure 3 The fuse assemblies 250a and 250b in the illustrated arrangement provide for the same as they are placed on the positive bus 212a side ( Figure 2 Fuse assemblies 250a and 250b may be electrically connected to negative bus 212b, for example, in situations where disconnecting positive bus 212a from energy storage device 240 may be challenging.

[0057] Figure 4is a schematic diagram of a system 400 including a power converter 410. Power converter 410 is the same as power converter 310, except that power converter 410 includes DC link choke inductors 470a and 470b. DC link choke inductor 470a is in positive bus 212a between rectifier 217 and DC link 218. DC link choke 470b is in negative bus 212b between rectifier 217 and DC link 218.

[0058] Figures 5A-5D shows the power converter 410 ( Figure 4 ). In the simulation, the input voltage at nodes 211a, 211b, 211c is 480 volts AC; the rating of power converter 410 is 480V, 103 amperes (A), and 55 kilowatts (kW); each DC link choke inductor 470a, 470b is 530 microhenries (μH), the DC bus capacitor is 3600 microfarads (μF), and the capacitance of each capacitor C1 to C8 is 1800 μF.

[0059] Figure 5A shows the voltage of the buffer capacitor Cs1 as a function of time, Figure 5B shows the voltage across capacitor C3 (VC3) as a function of time, Figure 5C shows the voltage across capacitor C4 (VC4) as a function of time, Figure 5D The voltage across the DC bus (Vdc) is shown as a function of time. Figures 5A-5D Have the same time scale in seconds.

[0060] In the simulation, the power converter 410 operates in a steady state with a load of 0.1 pu (per unit). At time t=2s, the capacitor C3 is short-circuited, and a high current flows into the local short circuit involving the capacitor C3. Figure 5B As shown in Figure 1, just after time t=2s, the voltage across capacitor C3 (VC3) drops rapidly to zero. Also at time t=2s, the voltage across capacitor C4 (VC4) increases from half of the DC bus voltage (Vdc) to the instantaneous DC bus voltage (Vdc) because capacitor C3 is experiencing a short circuit. Therefore, the voltage across capacitor C4 undergoes a step change, and a high surge current follows.

[0061] The surge current spike in capacitor C4 is injected from adjacent capacitor sections, including capacitors C1 and C2 and capacitors C5, C6, C7 and C8. The charging current flowing from capacitors C1 and C2 into capacitor C4 returns to capacitors C1 and C2 and does not flow through fuse FS1 and negative bus 212b. This is because negative bus 212b does not provide a preferred path for the current circulating between capacitors C1, C2 and C4. However, for the current flowing from the capacitors in group 242b (capacitors C5 to C8) into capacitor C4, the return path includes fuse FS1, negative bus 212b and fuse FS2. Fuses FS1 and FS2 are connected in series and experience the same high current amplitude. The fault current path starts from the input AC power supply 201, passes through the diode in the rectifier 217, the DC link choke 470a, the short-circuited capacitor C3, and finally enters capacitor C4. The fault current returns to the source 201 only through fuse FS1. Therefore, the thermal stress on fuse FS1 is slightly higher than the thermal stress on fuse FS2, and fuse FS1 may open before fuse FS2.

[0062] After the i2T rating of fuse FS1 is reached, fuse FS1 opens, merging snubber capacitor CS1 into capacitor bank 242a. Snubber capacitor CS1 forms a high impedance path between the capacitor combination formed by bank 242a (capacitors C1, C2, C3, C4) and negative bus 212b. Shortly after time t=2s, the voltage across capacitor C4 (VC4) begins to partially circulate and dissipate in the small loop formed between itself and the C1-C2 branch. Source 201 also provides charging energy to snubber capacitor CS1 through C1 and C2. Figure 5A As shown in Figure 1, the voltage across CS1 (VCS1) begins to increase. Figure 5C As shown, just around time t=2s, capacitor C4 experiences a high voltage state for at least 0.5 seconds. The overvoltage rating of capacitor C4 allows capacitor C4 to withstand a higher voltage for a relatively short period of time without being damaged.

[0063] Figure 6 6 is a schematic diagram of system 600. System 600 includes power converter 610. Power converter 610 is similar to power converter 310, except that power converter 610 includes DC link 618. DC link 618 is similar to DC link 318, except that DC link 618 includes capacitor bank 642 instead of bank 242b. Capacitor bank 642 is a single string of two series capacitors: capacitors C5 and C6. Therefore, power converter 610 includes an odd number of capacitor strings or branches. Specifically, power converter 610 includes three capacitor branches, two in bank 242a and one in bank 642.

[0064] Group 242a is electrically connected to fuse assembly 250a and positive bus 212a. Fuse assembly 250a is electrically connected to negative bus 212b. Group 642 is electrically connected to fuse assembly 250b and positive bus 212a. Fuse assembly 250b is electrically connected to negative bus 212b.

[0065] Although fuse FS2 can be a lower value because it only supports one capacitor branch, the fuse ratings of fuse FS2 and FS1 should be the same. In addition, the fuse ratings of fuse FS1 and FS2 are sufficient to protect corresponding groups 242a and 642. When the capacitor (e.g., capacitor C4) in group 242a is short-circuited, the short-circuit current circulates in a small loop formed by other capacitors (capacitors C1, C2 and C3) in group 242a. The capacitor C3 that is not short-circuited connected to C4 experiences a high voltage, and a charging current flows into capacitor C3 from capacitors C1 and C2. The short-circuit current also flows from adjacent groups 642 and source 201. The fuse FS1 connected in series with group 242a is finally disconnected and the buffer capacitor Cs1 is charged. The charged buffer capacitor provides high impedance, thereby suppressing the current in the short-circuit branch.

[0066] If a capacitor in group 642 is shorted, a similar series of events occurs and a short circuit current will flow through fuse FS2. This short circuit current causes fuse FS2 to open and places snubber capacitor Cs2 in group 642. Snubber capacitor Cs2 provides a high impedance path and prevents or reduces short circuit current in the short circuit capacitor.

[0067] Figure 7 7 is a schematic diagram of a system 700 including a power converter 710. The power converter 710 is the same as the power converter 310, except that the power converter 710 includes a DC link 718 instead of the DC link 318. The DC link 718 is similar to the DC link 318, but the DC link 718 includes three capacitor groups 742a, 742b, 742c. Each group 742a, 742b, 742c includes three parallel capacitor strings, each string including two series capacitors. Group 742a includes a first series capacitor string C1 and C2, a second series capacitor string C3 and C4, and a third series capacitor string C5 and C6. Group 742b includes a first series capacitor string C7 and C8, a second series capacitor string C9 and C10, and a third series capacitor string C11 and C12. Group 742c includes a first series capacitor string C13 and C14, a second series capacitor string C15 and C16, and a third series capacitor string C17 and C18.

[0068] Each group 742a, 742b, 742c is electrically connected to the positive bus 212a and a corresponding fuse assembly 750a, 750b, 750c. The fuse assemblies 750a, 750b, 750c are electrically connected to the negative bus 212b. Each fuse assembly 750a, 750b, 750c includes a corresponding fuse FS1, FS2, FS3 connected in parallel with a corresponding snubber capacitor Cs1, Cs2, Cs3.

[0069] A short circuit event in one of the groups 742a, 742b, 742c causes the fuse of the corresponding fuse assembly 750a, 750b, 750c to open, so that the corresponding buffer capacitor Cs1, Cs2, Cs3 provides a high impedance path to the affected string. For example, if capacitor C18 experiences a short circuit event, the short circuit current flows into capacitor C18 and returns via fuse FS3. When fuse FS3 is opened, buffer capacitor Cs3 provides a high impedance path to capacitor C17.

[0070] Figure 7 The configuration of the power converter 710 shown is an example, and other configurations are also possible. For example, fuse assemblies 750a, 750b, and 750c can be electrically connected to the positive bus 212a, rather than the negative bus 212b. In addition, the power converter 710 can be implemented with filters such as DC link choke inductors 470a and 470b and / or filters between intermediate nodes 214a, 214b, 214c and input nodes 211a, 211b, 211c. In another example, the power converter 710 can include more than or less than three capacitor groups, each group having a corresponding fuse assembly.

[0071] Figure 8 8 is a schematic diagram of a system 800 including a power converter 810. The power converter 810 includes three capacitor groups 842a, 842b, and 842c. Each group 842a, 842b, and 842c includes a capacitor string, and each string has two capacitors connected in series. Group 842a includes series capacitors C1 and C2, group 842b includes series capacitors C3 and C4, and group 842c includes series capacitors C5 and C6.

[0072] Group 842a is electrically connected to fuse assembly 850a and positive bus 212a, group 842b is electrically connected to fuse assembly 850b and positive bus 212a, and group 842c is electrically connected to fuse assembly 850b and positive bus 212a. Fuse assemblies 850a, 850b and 850c are electrically connected to negative bus 212b. Each fuse assembly 850a, 850b, 850c includes a corresponding fuse FS1, FS2, FS3 connected in parallel with a corresponding snubber capacitor Cs1, Cs2, Cs3. Fuses FS1, FS2, FS3 have the same i2T rating, and snubber capacitors Cs1, Cs2, Cs3 have the same capacitance.

[0073] Figure 8 The configuration of the power converter 810 shown is an example, and other configurations are also possible. For example, fuse assemblies 850a, 850b, and 850c can be electrically connected to the positive bus 212a instead of the negative bus 212b. In addition, the power converter 810 can be implemented with filters such as DC link choke inductors 470a and 470b and / or filters between intermediate nodes 214a, 214b, 214c and input nodes 211a, 211b, 211c. The power converter 810 can include more or less than three series capacitor groups, each group having a corresponding fuse assembly.

[0074] Fig. 9 9 is a schematic diagram of a system 900 including a power converter 910. In addition to the power converter 910 including a DC link 918, the power converter 910 is similar to the power converter 310 ( Figure 3 ). The DC link 918 includes capacitor banks 242a and 242b and fuse assemblies 250a and 250b, and also includes discharge charging circuits 945a and 945b. The discharge circuits 945a and 945b help the capacitors in series with the short-circuit capacitors to discharge faster. Increasing the discharge speed reduces the amount of time that the surviving capacitors are exposed to high voltages, and also allows the buffer capacitors in the fuse assemblies associated with the short-circuit capacitors to charge faster.

[0075] The discharge circuit 945a includes a discharge resistor 946a and a controllable switch 947a electrically connected to the discharge resistor 946a. The discharge resistor 946a is electrically connected to the positive bus 212a. The controllable switch 947a can be, for example, a silicon controlled rectifier (SCR). The controllable switch 947a includes a control node (gate of the SCR) electrically connected to the voltage divider. The control node is used to control the state of the switch 947a. The controllable switch 947a is electrically connected to the relay coil M1, and the relay coil M1 is electrically connected to the negative bus 212b.

[0076] The discharge circuit 945b is configured in the same manner. The discharge circuit 945b includes a discharge resistor 946b and a controllable switch 947b electrically connected to the discharge resistor 946b. The discharge resistor 946b is electrically connected to the positive bus 212a. The controllable switch 947b can be, for example, an SCR. The controllable switch 947b includes a control node (gate of the SCR) electrically connected to the voltage divider. The controllable switch 947b is electrically connected to the relay coil M2, and the relay coil M2 is electrically connected to the negative bus 212b.

[0077] The operation of the power converter 910 is discussed by taking the case of a short circuit of capacitor C2 as an example. After the short circuit of capacitor C2, the voltage on capacitor C1 (which is electrically connected in series with capacitor C2) increases from half of the DC bus voltage to the full DC bus voltage (Vdc). Shortly after the short circuit event occurs, fuse FS1 opens. After fuse FS1 opens, the voltage across the buffer capacitor Cs1 begins to increase, and the voltage across the capacitor C1 begins to drop from Vdc. The discharge circuit 945a helps to quickly discharge the surviving capacitor (capacitor C1 in this example) and promotes the rapid charging of the buffer capacitor Cs1.

[0078] During steady-state operation of the power converter 910, the voltage across the relay coils M1 and M2 is zero, and the SCRs 947a and 947b are in the off state. Continuing with the above example, when the capacitor C2 is short-circuited, the voltage across the buffer capacitor Cs1 begins to increase. When the voltage across the buffer capacitor Cs1 causes the relay M1 to turn on, the SCR 947a also turns on and allows the capacitor C1 to discharge quickly. The operation of the SCR 947a is limited to the short-circuited branch (group 242a in this example) and does not affect the operation of the adjacent capacitor branch (group 242b in this example). The capacitance of the DC bus is reduced, but as long as the ripple caused by the reduced DC bus capacitance does not cause a drive fault, the power converter 910 can continue to operate.

[0079] A discharge circuit having the configuration of discharge circuit 945a can be used with any of the DC links and power converters discussed above. For example, DC link 218 ( Figure 2 ) may include two instances of discharge circuit 945a, one instance being associated with capacitor group 242a and the other instance being associated with capacitor group 242b.

[0080] Fig.101 is a schematic diagram of a system 1000 including a power converter 1010. The power converter 1010 includes a DC link 1018, which includes capacitor groups 1042a, 1042b, 1042c, each capacitor group including two capacitors in parallel. Group 1042a includes parallel capacitors C1 and C2. Group 1042b includes parallel capacitors C3 and C4. Group 1042c includes parallel capacitors C5 and C6. Capacitors C1 and C6 can be film capacitors. Each capacitor group 1042a, 1042b, 1042c is electrically connected to a positive bus 212a and a corresponding fuse assembly 1050a, 1050b, 1050c. Fuse assemblies 1050a, 1050b, 1050c are electrically connected to a negative bus 212b. Each fuse assembly 1050a, 1050b, 1050c includes a respective fuse FS1, FS2, FS3 connected in parallel with a respective snubber capacitor Cs1, Cs2, Cs3.

[0081] An example of a short circuit event in the DC link 1018 is provided using a short circuit event in capacitor C1. Capacitor C1 is shorted, and fuse FS1 opens almost immediately and before FS2 or FS2. By opening FS1, snubber capacitor Cs1 is placed in series with capacitor C2, reducing the amount of voltage across capacitor C2 and avoiding failure of the DC link 1018 and / or power converter 1010.

[0082] Power converter 1010 is shown as an example, and other implementations are possible.For example, DC link 1018 may include more or less than three capacitor banks and associated fuse assemblies.

[0083] These and other implementations are within the scope of the following claims.

Claims

1. A system comprising: a DC bus electrically configured to be connected to one or more of a rectifier and an inverter, the DC bus comprising a positive bus and a negative bus; as well as a DC link electrically connected to the DC bus, the DC link comprising: An energy storage device comprising at least two energy storage elements; as well as A fuse assembly is electrically connected to the energy storage device and to one of the positive bus and the negative bus.

2. The system according to claim 1, wherein the energy storage device comprises at least two energy storage elements connected in series.

3. The system of claim 1, wherein the energy storage device comprises at least two energy storage elements connected in parallel.

4. The system of claim 3, wherein each energy storage element comprises a film capacitor.

5. The system of claim 1, wherein the fuse assembly includes a fuse element connected in parallel with a capacitive element.

6. The system of claim 1, wherein the energy storage device is electrically connected to the positive bus, and the fuse assembly is electrically connected to the energy storage device and the negative bus.

7. The system of claim 1, wherein the energy storage device is electrically connected to the negative bus, and the fuse assembly is electrically connected to the energy storage device and the positive bus.

8. The system of claim 1, wherein the energy storage device comprises two or more capacitor strings connected in parallel.

9. The system of claim 8, wherein each of the two or more capacitor strings comprises at least two capacitors connected in series.

10. The system of claim 1 further comprising a discharge circuit.

11. The system of claim 10, wherein the discharge circuit comprises a discharge resistor and a controllable switch, and wherein the controllable switch is configured to be turned on in response to a short circuit in one of the at least two energy storage elements.

12. A protection device for a drive system, the protection device comprising: A fuse assembly configured to be electrically connected between (i) a capacitor bank in the drive system and (ii) one of a positive bus and a negative bus of the drive system, and wherein: The fuse assembly includes: a fuse element connected in parallel with a capacitor element, the fuse element being configured to open in response to a short circuit in one of the capacitors in the capacitor group so that the capacitor element provides an impedance and a current path to another capacitor in the capacitor group that is not short-circuited. 13 . The protection device of claim 12 , further comprising a discharge circuit configured to be electrically connected to the positive bus and the negative bus of the drive system.

14. A driving device comprising: Rectifier; Inverter; as well as a DC link electrically connected to the rectifier and the inverter, the DC link comprising: positive busbar; Negative busbar; An energy storage device comprising at least two capacitor banks; as well as A fuse assembly is electrically connected to each capacitor bank and one of the positive bus and the negative bus.

15. The driving device according to claim 14, wherein each capacitor group comprises two capacitors connected in parallel. 16 . The driving device according to claim 14 , wherein each capacitor group comprises at least two capacitor strings, and each string comprises at least two capacitors electrically connected in series.

17. The drive device of claim 14, wherein each fuse assembly has the same fuse rating.

18. The drive device of claim 14, wherein each fuse assembly is connected to one of the capacitor banks and the positive bus.

19. The drive device of claim 14, wherein each fuse assembly is connected to one of the capacitor banks and the negative bus.

20. The driving apparatus of claim 14, wherein each capacitor group includes a same number of capacitors in a same configuration, and each capacitor group includes a same nominal capacitance.

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