inverter

Abstract

Inverter (1), comprising: - an intermediate circuit connection (2) for connecting the inverter (1) to a DC intermediate circuit (3), - a power section (4) designed to generate a number of alternating voltages (u, v, w) for controlling an electric motor (5) from a direct voltage (UG) present at the DC intermediate circuit (3), and - a protective circuit (6) which is inserted between the intermediate circuit connection (2) and the power section (4), characterized in that - the protection circuit (6) is designed to - in one current direction (IMOT) from the DC link (3) to the inverter (1), to disconnect the DC link connection (2) from the power section (4) as soon as a first maximum load is exceeded, and - in one current direction (IGEN) from the inverter (1) to the DC intermediate circuit (3) to disconnect the intermediate circuit connection (2) from the power section (4) as soon as a second maximum load is exceeded, whereby the first maximum load differs from the second maximum load.

Description

[0001] The invention relates to an inverter.

[0002] The invention is based on the objective of providing an inverter that can be operated as reliably as possible.

[0003] WO 2019 / 197 459 A2 shows a mobile application with an energy storage device and an electrical load, wherein the energy storage device and the electrical load are selectively coupled electrically via a power bus.

[0004] DE 10 2012 110 236 A1 discloses a disconnecting device for a power supply unit of an industrial truck with an electrically switchable disconnect switch, wherein a current sensor for measuring a current in a main line switched by the disconnect switch and evaluation electronics are provided, wherein the evaluation electronics can open the disconnect switch depending on the current measured by the current sensor and the disconnect switch can be opened or closed by a vehicle control system of the industrial truck via a switching connection of the evaluation electronics.

[0005] US 2010 / 0 127 663 A1 shows a battery system with a fuse whose tripping current is changed depending on the condition.

[0006] The inverter has a conventional, for example two-pole, intermediate circuit connection for connecting the inverter to a DC intermediate circuit (also known as an intermediate circuit network or DC bus). Reference is made to the relevant technical literature in this regard.

[0007] The inverter further comprises a conventional power section designed to generate, for example, three, alternating voltages from a DC voltage present at the DC link for controlling an electric motor, such as a three-phase motor. The power section may, for example, include three half-bridges formed from semiconductor circuitry, etc. Reference is made to the relevant technical literature in this regard.

[0008] The inverter also has a protective circuit that is connected between the DC link connection and the power section.

[0009] The protection circuit is designed to disconnect the DC link connection from the power section in the case of a current direction IMOT from the DC link to / into the inverter as soon as a first maximum load is exceeded, and in the case of a current direction IGEN from the inverter to the DC link to disconnect the DC link connection from the power section as soon as a second maximum load is exceeded, whereby the first maximum load differs from the second maximum load.

[0010] Inverters supplied via the DC link connection should not fail in the event of a short circuit in the supplying DC link or DC network. The short circuit can be caused, for example, by a wiring fault, damage to the supply lines, or the failure of another component in the DC link network. In this case, the inverter feeds both the electrical energy stored in its own capacitors and the mechanical (rotational) energy stored in any connected electric motor into the short circuit.

[0011] Traditionally, protective devices are designed to trip in this case, even if the inverter itself is not defective. This is because the protective devices used are dimensioned for the opposite current direction (from the DC link into the inverter) and, for example, trip regardless of the current direction even at a DC current higher than the device's maximum current, in order to prevent a fire in the device. Such a fire could occur if the inverter itself has a short circuit, for example due to defective power semiconductors, and "unlimited" energy is fed into the inverter from the DC link or DC link network, or if the inverter is short-circuited at its DC link connection.

[0012] According to the invention, a single- or double-pole direction-sensitive protection circuit is arranged in the inverter directly behind the DC link connection. This can be implemented, for example, using fast-switching, low-loss power semiconductors (SiC or GaN). The special feature of this protection circuit is its design for a known maximum load (current waveform, i 2 (t-value, total energy), which occurs precisely when the inverter is short-circuited at its DC link connection. The protection circuit is designed so that it will not trip in this case. This assumes that the connection technology, conductor tracks, and components (especially the DC link capacitors and the inverter diodes) in the inverter are designed to withstand this fault condition at least a few times during its life cycle.

[0013] Due to current sensing, current direction detection, and dedicated switch control, the protection circuit can be designed to activate even at such high currents / 2 This triggers t-value limits / total energies that are only slightly above the values ​​permitted by the device during operation in both current directions and in the generator direction in the event of a fault ("device is short-circuited at the DC link connection"). This not only prevents a fire in the event of a short circuit ("device is defective"), but also allows the inverter to be switched off in the event of an overload (load requires too high a motor current) before an integrated component is overloaded.

[0014] The protection circuit integrated into the inverter therefore distinguishes between external and internal fault cases by measuring current and triggers both in a current direction-sensitive and overload-dependent manner.

[0015] Another embodiment dynamically considers the current flowing from the inverter to the DC link and / or from the DC link to the inverter. This current can be calculated from the output level and the DC link voltage, or measured directly in the inverter. The system then compares this current with the DC link current for plausibility. Depending on the magnitude of the power or current difference detected during the plausibility check, a warning can be issued or a shutdown triggered. Such a difference between input and output power can be caused, for example, by a high-impedance ground fault or short circuit. The sign of the difference indicates the location of the fault.

[0016] In this context, an inverter is defined as a drive control device that has at least one intermediate circuit (DC) connection as a power / supply connection. This can be a control cabinet device, a field device, a device mounted on the motor, or a device integrated into the motor. The inverter may also have an AC connection with active or passive input, although this is irrelevant for the required functionality.

[0017] An external fault is defined as a fault (especially a short circuit) in the supplying intermediate circuit or DC network. An internal fault is defined as a fault (especially a short circuit) within the device itself.

[0018] In one embodiment, the first maximum load is assigned a predetermined current profile of a current from the DC intermediate circuit to the inverter, and / or an I 2t-value of the current from the DC link to the inverter assigned, and / or a total energy assigned that is delivered from the DC link to the inverter.

[0019] In one embodiment, the second maximum load is assigned a predetermined current profile of a current from the inverter to the DC link, and / or an I 2 t-value of the current from the inverter to the DC link assigned, and / or a total energy assigned that is delivered by the inverter to the DC link.

[0020] In one embodiment, the protection circuit comprises: a current sensor configured to measure the current intensity and direction of a current flowing between the DC link and the inverter, a number of controllable switching devices, for example semiconductor switching devices and / or relays, which are inserted between the DC link connection and the power section, and a control device coupled to the current sensor and the switching devices, which controls the switching devices depending on the current direction and intensity.

[0021] In one embodiment, the protection circuit includes: a voltage sensor designed to measure a voltage at the DC link terminal.

[0022] In one embodiment, the inverter has a DC link capacitor, and the protection circuit is configured to pre-charge the DC link capacitor. In other words, the protection circuit also forms a pre-charging circuit for pre-charging the DC link capacitor when the inverter is switched on.

[0023] In one embodiment, the protection circuit is designed to galvanically isolate the inverter from the DC link when maintenance is required.

[0024] In one embodiment, the inverter has an actuating device by means of which a user can trigger the maintenance request.

[0025] In one embodiment, the inverter has a fieldbus interface via which, for example, status information, sensor values, etc. can be transmitted to another fieldbus participant and / or maintenance requests can be received.

[0026] The protection circuit is integrated into the inverter, so that it can be directly connected to and operated in an open DC network.

[0027] The protection circuit has the following functions.

[0028] The inverter is protected, for example in the event of a grid fault, and the DC link is protected, for example in the event of an inverter fault. Protection is achieved by detecting and disconnecting / disconnecting the inverter. Detection can be dynamically adapted during operation via an interface to the inverter's control system. Positive and negative deviations can be evaluated differently.

[0029] The device's internal DC link can be pre-charged. This pre-charging can be achieved when the inverter is switched on under voltage using standard pre-charging devices of the protection circuit, passively via a resistor or PTC thermistor, or actively using semiconductor switches and an inductor.

[0030] Current and voltage can be measured. Current and voltage can be measured using standard methods, such as resistance, shunt, or sensors. Rapid current changes (short circuit, di / dt) can be detected using UCE-SAT monitoring (IGBT saturation). The measured values ​​can be made available via an interface.

[0031] The protective circuit enables safe galvanic isolation, for example for maintenance purposes. Galvanic isolation can be achieved, for example, by a mechanically isolating element, such as a relay contact. This can be designed and controlled safely.

[0032] The protective circuit can be directly operated or activated by a user, e.g., via pushbuttons / switches, with feedback, for example, via indicator lights. Operation can be similar to a maintenance switch on decentralized AC devices. Operation can be performed using a pushbutton.

[0033] In case of faults in the DC link network or internal inverter faults, the inverter can automatically disconnect itself from the DC link network and thus be protected.

[0034] In case of maintenance, the inverter can be disconnected from the "running" intermediate circuit and reconnected.

[0035] The inverter's internal protection circuit can react to both an overcurrent in the event of a fault (monitoring the rise time) and to an excessively high continuous current (monitoring the average value).

[0036] The inverter's internal protection circuit (unlike all external monitoring elements) can dynamically adjust to the current operating state and react accordingly in a "sensitive" manner, because the current output current in the inverter and the inverter's internal losses are known.

[0037] The inverter's internal protection circuit can perform monitoring of the grid symmetry (measuring the voltages +UZK against PE and -UZK against PE at the Y capacitors).

[0038] The inverter or its internal capacitors can be pre-charged.

[0039] The inverter may contain a "control unit" or a maintenance switch.

[0040] This allows the inverter to be operated directly on an open DC network or intermediate circuit.

[0041] The invention is described in detail below with reference to the drawing. The drawing shows: Fig. 1 an inverter according to the invention. Fig. Figure 1 shows an inverter according to the invention.

[0042] The inverter 1 has a two-pole intermediate circuit connection 2 for connecting the inverter 1 to a DC intermediate circuit or intermediate circuit assembly 3.

[0043] The inverter 1 further comprises a power section 4, which, for example, includes an exemplary H6 bridge 15 and is designed to generate three AC voltages u, v, w from a DC voltage UG present at the DC intermediate circuit 3 for controlling an electric motor 5. Reference is also made to the relevant technical literature in this respect.

[0044] The inverter 1 further comprises a protection circuit 6, which is inserted between the DC link terminal 2 and the power section 4 and is configured to disconnect the DC link terminal 2 from the power section 4 in at least one power path when a first maximum load is exceeded, and when a current flows from the DC link 3 to the inverter 1, to disconnect the DC link terminal 2 from the power section 4 when a second maximum load is exceeded, wherein the first maximum load differs from the second maximum load. The second maximum load can, for example, be greater than the first maximum load or vice versa.

[0045] The first maximum load can be assigned a predefined current profile of a current IMOT from the DC intermediate circuit 3 to the inverter 1, and / or an I2 The t-value of the current IMOT from the DC link 3 to the inverter 1 is assigned, and / or a maximum total energy is assigned that is delivered from the DC link 3 to the inverter 1.

[0046] The second maximum load can be assigned a predefined current profile of a current IGEN from inverter 1 to the DC intermediate circuit 3, and / or an I 2 The t-value of the current IGEN from inverter 1 to the DC intermediate circuit 3 is assigned, and / or a maximum total energy is assigned that is delivered from inverter 1 to the DC intermediate circuit 3.

[0047] The protection circuit 6 has a current sensor 8 which is designed to measure the current intensity and direction of a current IDC+, IDC- flowing between DC intermediate circuit 3 and inverter 1.

[0048] The protection circuit 6 further comprises four controllable switching devices S1-S4 in the illustrated circuit configuration, wherein the switching devices S1 and S2 are connected in series in an upper branch between the DC link terminal 2 and the power section 4, and wherein the switching devices S3 and S4 are connected in series in a lower branch between the DC link terminal 2 and the power section 4.

[0049] The protection circuit 6 further includes a control device 9 which is coupled to the current sensor 8 and the switching devices S1-S4 and which controls the switching devices S1-S4 depending on the current direction and current intensity.

[0050] The protection circuit 6 further includes a voltage sensor 11, which is designed to measure the voltage UG at the intermediate circuit connection.

[0051] The protection circuit 6 also includes conventional interference suppression chokes 14 in the circuit shown.

[0052] The inverter 1 further comprises a DC link capacitor 7, wherein the protection circuit 6 is designed to pre-charge the DC link capacitor 7 upon switch-on. A PTC element 10 is provided for this purpose as an example.

[0053] The protective circuit 6 is designed to galvanically isolate the inverter 1 from the DC link 3 when a maintenance request is triggered. For this purpose, the inverter 1 has an actuating device 12 by means of which a user can trigger the maintenance request.

[0054] Inverter 1 has a fieldbus interface 13 for data exchange with external devices.

Claims

[1] Inverter (1) comprising: - an intermediate circuit connection (2) for connecting the inverter (1) to a DC intermediate circuit (3), - a power section (4) designed to generate a number of alternating voltages (u, v, w) for controlling an electric motor (5) from a direct voltage (UG) present at the DC intermediate circuit (3), and - a protection circuit (6) which is inserted between the intermediate circuit connection (2) and the power section (4), characterized by , that - the protection circuit (6) is designed to - in one current direction (IMOT) from the DC link (3) to the inverter (1), to disconnect the DC link connection (2) from the power section (4) as soon as a first maximum load is exceeded, and - in one current direction (IGEN) from the inverter (1) to the DC intermediate circuit (3) to disconnect the intermediate circuit connection (2) from the power section (4) as soon as a second maximum load is exceeded, whereby the first maximum load differs from the second maximum load. [2] Inverter (1) according to claim 1, characterized by , that - the first maximum load is assigned a predetermined current profile of a current (IMOT) from the DC intermediate circuit (3) to the inverter (1), or an I 2 t-value of the current (IMOT) from the DC intermediate circuit (3) to the inverter (1) is assigned, or a total energy is assigned which is delivered from the DC intermediate circuit (3) to the inverter (1). [3] Inverter (1) according to claim 1 or 2, characterized by , that - the second maximum load is assigned a predetermined current profile of a current (IGEN) from the inverter (1) to the DC intermediate circuit (3), or an I 2 t-value of the current (IGEN) from the inverter (1) to the DC intermediate circuit (3) is assigned, or a total energy is assigned which is delivered from the inverter (1) to the DC intermediate circuit (3). [4] Inverter (1) according to any of the preceding claims, characterized by , that - the inverter (1) is designed to adapt the first maximum load and / or the second maximum load as dynamically variable limits depending on a current operating state of the inverter, in particular depending on an output power and / or an output current of the inverter. [5] Inverter (1) according to any of the preceding claims, characterized by , that - the inverter (1) is designed to issue a warning before reaching the first maximum load and / or before reaching the second maximum load. [6] Inverter (1) according to any of the preceding claims, characterized by , that - the protection circuit (6) has: - a current sensor (8) designed to measure the current intensity and direction of a current (IDC+, IDC-) flowing between the DC intermediate circuit (3) and the inverter (1), - a number of controllable switching devices (S1-S4) which are inserted between the DC link connection (2) and the power section (4), and - a control unit (9) which is coupled to the current sensor (8) and the switching devices (S1 - S4) and which controls the switching devices (S1-S4) depending on the current direction and current intensity. [7] Inverter (1) according to claim 6, characterized by , that - the protection circuit (6) has: - a voltage sensor (11) designed to measure a voltage (UG) at the intermediate circuit connection (2). [8] Inverter (1) according to any of the preceding claims, characterized by , that - the inverter (1) has an intermediate circuit capacitor (7), - wherein the protection circuit (6) is designed to precharge the intermediate circuit capacitor (7). [9] Inverter (1) according to any of the preceding claims, characterized by , that - the protection circuit (6) is designed to galvanically isolate the inverter from the DC intermediate circuit (3) in the event of a maintenance request. [10] Inverter (1) according to claim 9, characterized by , that - the inverter (1) has an actuating device (12) by means of which a user can trigger the maintenance request. [11] Inverter (1) according to any of the preceding claims, characterized by , that - the inverter (1) has a fieldbus interface (13).

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