Three-level brake chopper and method for controlling a three-level brake chopper

Abstract

The invention relates to a three-level brake chopper comprising a first controllable semiconductor switch (T1) connected between a positive direct current pole (dc+) and a first connection point, a second controllable semiconductor switch (T2) connected between the first connection point and a neutral direct current pole (NP), a third controllable semiconductor switch (T3) connected between the neutral direct current pole (NP) and a second connection point, a fourth controllable semiconductor switch (T4) connected between the second connection point and a negative direct current pole (dc-), a resistance arrangement (Rbrk) connected between the first connection point and the second connection point, and a control arrangement (11) configured to, in response to detecting a fault in the resistance arrangement (Rbrk), control the second controllable semiconductor switch (T2) and the third controllable semiconductor switch (T3) into a conducting state.

Description

TECHNICAL FIELD

[0001] The present invention relates to a three-level brake chopper and a method for controlling a three-level brake chopper. BACKGROUND

[0002] A brake chopper or braking chopper can be used in connection with electrical systems and devices, such as power converter devices, for dissipating regenerative energy that cannot be fed back to a power supply network, for example. As an example, in case an electrical machine controlled by a frequency converter having a DC (direct current) voltage intermediate circuit is rotated by a load connected to the electrical machine, the electrical machine can act as a generator and feed power back to the frequency converter. If the rectifier of the frequency converter is not configured or cannot feed the regenerative energy back to the network that powers the frequency converter, the voltage of the intermediate circuit starts to increase. When the voltage of the intermediate circuit has increased to a predetermined limit, such as above a nominal voltage of the intermediate circuit, a brake chopper connected to the frequency converter can be activated and used for converting the excess electrical energy into heat in its braking resistors to reduce the voltage of the intermediate circuit. The brake chopper can be used to reduce the voltage, for example, until the voltage is within an acceptable range of the nominal voltage.

[0003] Three-level devices, such as three-level converter devices, are devices having three DC poles. In addition to a positive DC pole and a negative DC pole, they have a neutral DC pole. A brake chopper for use in connection with such three-level converters or other devices can be provided as a three-level brake chopper also having corresponding positive and negative DC poles and a neutral DC pole.

[0004] Protection against a fault in the braking resistors of a three-level brake chopper, such as a braking resistor ground fault or short circuit, can be based on a fuse, for example.

[0005] A problem associated with the above-described solution is that the fuses are bulky and expensive, thus resulting in additional costs and requiring more space. Furthermore, the fuses can cause further losses in the system. SUMMARY

[0006] It is therefore an object of the present invention to provide a method and means for implementing the method to overcome or at least alleviate the above problems. The object of the present invention is achieved by a method and a three-level brake chopper.

[0007] The present invention is based on the idea of connecting a terminal of the braking resistors to the neutral point in response to detecting a fault in the braking resistors by means of controllable semiconductor switches of the brake chopper.

[0008] The solution of the application is advantageous in that protection against a fault in the braking resistor of a three-level braking chopper can be arranged without a fuse or similar additional component, and thus potentially reduce costs. In addition, the protection reaction time to a fault can be improved. BRIEF DESCRIPTION OF DRAWINGS

[0009] In the following, the application will be described in more detail by means of exemplary embodiments with reference to the attached drawings, in which:

[0010] Figure 1 An example of a three-level braking chopper according to an embodiment is shown;

[0011] Figure 2 An example of a three-level braking chopper according to an embodiment is shown;

[0012] Figure 3 An example of the operation of a three-level braking chopper according to an embodiment is shown; and

[0013] Figure 4 An example of a three-phase three-level converter according to an embodiment is shown. DETAILED DESCRIPTION

[0014] The following embodiments are exemplary. Although the description can refer to "an" or "one" implementation, it will be understood by those skilled in the art that the description applies equally to "one or more" or "at least one" implementations. There can be many apparatuses that have the same general

[0015] According to an embodiment and as Figure 1 and Figure 2As shown, the three-level brake chopper 10 comprises a positive direct current pole dc+, a negative direct current pole dc- and a neutral direct current pole NP. The three-level brake chopper 10 further comprises a first controllable semiconductor switch T1 connected between the positive direct current pole dc+ and a first connection point PI and a second controllable semiconductor switch T2 connected between the first connection point PI and the neutral direct current pole NP. The three-level brake chopper 10 further comprises a third controllable semiconductor switch T3 connected between the neutral direct current pole NP and a second connection point P2 and a fourth controllable semiconductor switch T4 connected between the second connection point P2 and the negative direct current pole dc-. In Figure 1 and Figure 2 the example, the collector / emitter terminals of the controllable semiconductor switches T1, T2, T3, T4 are directed towards the positive direct current pole dc+ and the emitter / collector terminals of the controllable semiconductor switches T1, T2, T3, T4 are directed towards the negative direct current pole dc-. The controllable semiconductor switches T1, T2, T3, T4 can be, for example, IGBTs (Insulated Gate Bipolar Transistors) or FETs (Field Effect Transistors) or any suitable controllable semiconductor switch. The three-level brake chopper 10 further comprises a resistive means Rbrk; Rbrk1, Rbrk2 connected between the first connection point and the second connection point. The resistive means Rbrk; Rbrk1, Rbrk2 can comprise one resistor or two or more resistors connected in series and / or in parallel with each other. According to an embodiment and as shown in Figure 1 , the resistive means Rbrk can be connected only to the first connection point PI and to the second connection point P2 in the main circuit of the brake chopper 10. According to another embodiment and as shown in Figure 2 , the resistive means comprises two parts Rbrk1, Rbrk2 connected in series between the first connection point PI and the second connection point P2, such that the connection point P3 between the two parts Rbrk1, Rbrk2 is connected to the neutral direct current pole NP. Each of the parts Rbrk1 and Rbrk2 can be one resistor or two or more resistors connected in series and / or in parallel with each other. According to an embodiment, the three-level brake chopper 10 can further comprise a first diode D1 connected in parallel with the second controllable semiconductor switch T2 and a second diode D2 connected in parallel with the third controllable semiconductor switch T3. The first diode D1 and the second diode D2 enable, for example, the energy possibly stored in the stray inductance of the cable or wiring of the resistive means to be released. According to an embodiment, the three-level brake chopper 10 can further comprise a third diode D3 connected in parallel with the first controllable semiconductor switch T1 and a fourth diode D4 connected in parallel with the fourth controllable semiconductor switch T4. In Figure 1 and Figure 2 the example, the cathode terminals of the possible diodes D1, D2, D3, D4 are directed towards the positive direct current pole dc+ and the anode terminals of the possible diodes D1, D2, D3, D4 are directed towards the negative direct current pole dc-.

[0016] Figure 1 and Figure 2 The exemplary brake chopper 10 also comprises a control device 11 configured to control, for example, the operation of the brake chopper 10. For the sake of clarity, the internal control connections between the control device 11 and other components of the brake chopper 10, such as the controllable semiconductor switches T1-T4, are not shown in the figure. The control device 11 and its functions can also be implemented at least partly by means of a control device of another device, such as a power converter device, to which the brake chopper 10 is connected or included, for example.

[0017] According to an embodiment, the three-level brake chopper 10 can be used and configured to release electrical energy from a capacitor circuit comprising the capacitors C1 and C2, which can be a capacitor circuit of a power converter or a capacitor circuit related to a power converter, such as an intermediate circuit thereof. Thus, Figure 1 and Figure 2 The capacitors C1 and C2 in the exemplary three-level brake chopper 10 can typically represent a three-level DC voltage capacitor circuit in which the capacitors C1 and C2 are connected between the positive DC pole, the negative DC pole and the neutral DC pole of such a capacitor circuit. The full DC voltage of the exemplary capacitor circuit is u dc and it comprises the partial voltages u C1 and u C2 on the capacitors C1 and C2, respectively. Figure 3 An example of the operation of a three-level brake chopper according to an embodiment is shown. According to an embodiment and as Figure 3As shown, the three-level brake chopper 10 can be used to discharge electrical energy from only one half C1 or C2 of the DC voltage capacitor circuit at a time, or from both halves C1 + C2 at the same time. For example, by controlling only the first controllable semiconductor switch T1 to be conductive, i.e. ON, current flows through the first controllable semiconductor switch T1, the brake resistor Rbrk and the second diode D2 from the positive DC pole dc+ to the neutral DC pole NP. Thus, energy from the first half C1 of the DC voltage capacitor circuit is discharged. On the other hand, by controlling only the fourth controllable semiconductor switch T4 to be conductive, i.e. ON, current flows through the first diode D1, the brake resistor Rbrk and the fourth controllable semiconductor switch T4 from the neutral DC pole NP to the negative DC pole dc-. Thus, energy from the second half C2 of the DC voltage capacitor circuit is discharged. The first diode D1 and the second diode D2 thus enable non-simultaneous discharge of energy from the first half C1 and the second half C2 of the DC voltage capacitor circuit. Furthermore, by controlling both the first controllable semiconductor switch T1 and the fourth controllable semiconductor switch T4 to be conductive, i.e. ON, current flows through the first controllable semiconductor switch T1, the brake resistor Rbrk and the fourth controllable semiconductor switch T4 from the positive DC pole dc+ to the negative DC pole dc-. Thus, energy is discharged from the entire DC voltage capacitor circuit C1 + C2.

[0018] According to embodiments, in response to detecting a fault in the resistance arrangement Rbrk; Rbrk1, Rbrk2, the second controllable semiconductor switch T2 and the third controllable semiconductor switch T3 are controlled to the conductive state, i.e. ON. Thus, the terminals of the resistance arrangement Rbrk; Rbrk1, Rbrk2 are connected to the neutral point NP and thus essentially no voltage is applied across the resistance arrangement. According to embodiments, in response to detecting a fault in the resistance arrangement, the first controllable semiconductor switch T1 and the fourth controllable semiconductor switch T4 are additionally controlled to the non-conductive state, i.e. OFF. If the first controllable semiconductor switch T1 and / or the fourth controllable semiconductor switch T4 are already in the non-conductive state, they can be controlled to remain in the non-conductive state. According to embodiments, controlling the first controllable semiconductor switch T1 and the fourth controllable semiconductor switch T4 to the non-conductive state can be performed before controlling the second controllable semiconductor switch T2 and the third controllable semiconductor switch T3 to the conductive state. Thus, the second controllable semiconductor switch T2 and the third controllable semiconductor switch T3 can only be controlled to the conductive state after a predetermined delay, e.g. a few microseconds later, from when the first controllable semiconductor switch T1 and the fourth controllable semiconductor switch T4 were controlled to the non-conductive state. For example, in the case of a ground fault in the resistance arrangement, the solution according to the above-described embodiments effectively grounds the neutral point NP, and in the case of a short circuit fault in the resistance arrangement, the solution according to the above-described embodiments effectively prevents current from flowing through the resistance arrangement.

[0019] According to embodiments, the fault in the resistance arrangement can for example be any type of fault, such as a brake resistor ground fault and / or a short circuit. According to embodiments, detecting the fault in the resistance arrangement Rbrk; Rbrk1, Rbrk2may for example be performed based on one or more current and / or voltage quantities related to the three-level brake chopper 10 and / or based on one or more received signals. To this end, the control arrangement 11may for example be configured to monitor one or more current and / or voltage quantities related to the three-level brake chopper 10. As an example, detecting the fault in the resistance arrangement Rbrk; Rbrk1, Rbrk2may be based on brake chopper 10 and / or resistance arrangement Rbrk; Rbrk1, Rbrk2current information, preferably in combination with control signal information of one or more of the controllable semiconductor switches T1-T4. As another example, detecting the fault in the resistance arrangement Rbrk; Rbrk1, Rbrk2may be based on collector-emitter (or drain-source) voltage information of one or more of the controllable semiconductor switches T1-T4, preferably in combination with control signal information of one or more of the controllable semiconductor switches T1-T4. As yet another example, detecting the fault in the resistance arrangement Rbrk; Rbrk1, Rbrk2may be based on monitoring the output voltage of the three-level brake chopper 10, preferably in combination with monitoring control signal information of one or more of the controllable semiconductor switches T1-T4. As yet another example, detecting the fault in the resistance arrangement Rbrk; Rbrk1, Rbrk2may be based on monitoring the DC voltage u dc or a partial voltage u C1 and u C2 of the capacitor circuit, preferably in combination with monitoring control signal information of one or more of the controllable semiconductor switches T1-T4. Furthermore, one or more separate or external sensors, such as temperature sensors or optical sensors, can be used for detecting the fault in the resistance arrangement Rbrk; Rbrk1, Rbrk2. Such sensors can then for example provide a signal to the control arrangement 11indicative of a fault. Furthermore, any combination of the above-mentioned alternatives for fault detection can also be used. According to embodiments, the solutions according to the above-mentioned embodiments can also be combined with fuses or other types of protection, for example if needed for some reason.

[0020] According to embodiments, a three-level converter device, such as an NPC (neutral point clamped) converter or an ANPC (active neutral point clamped) converter, can comprise a three-level braking chopper 10 according to any of the embodiments described herein. The three-level braking chopper 10 can be connected to the main circuit of the three-level converter by connecting the positive direct current pole dc+ of the three-level braking chopper together with the three-level converter, connecting the negative direct current pole dc- of the three-level braking chopper together with the three-level converter, and connecting the neutral direct current pole NP of the three-level braking chopper together with the three-level converter. Figure 4 An example of a three-phase three-level NPC converter main circuit provided with a three-level braking chopper 10 is shown. The three alternating current poles of the converter are denoted as ACa, ACb and ACc. The exemplary converter can for example operate as an inverter and / or as a rectifier.

[0021] According to any of the embodiments described herein, the control device 11 or other device controlling the operation of the braking chopper 10 or a combination thereof can be implemented as one physical unit or two or more separate physical units configured to implement the functionality of the various embodiments. In this document, the term "unit" generally refers to a physical or logical entity, such as a physical device or a part thereof, or a software routine. The control device 11 according to any of the embodiments can for example be implemented at least partly by means of one or more computers or corresponding digital signal processing (DSP) equipment provided with suitable software. Such a computer or digital signal processing equipment preferably comprises at least a working memory (RAM) providing a storage area for arithmetic operations, and a central processing unit (CPU), such as a general purpose digital signal processor. The CPU can comprise a set of registers, an arithmetic logic unit, and a control unit. The CPU control unit is controlled by a sequence of program instructions transferred to the CPU from the RAM. The CPU control unit can contain a number of microinstructions for basic operations. The implementation of the microinstructions can vary depending on the CPU design. The program instructions can be coded by a programming language, which can be a high-level programming language, such as C, Java, etc., or a low-level programming language, such as a machine language or an assembler. The computer can also have an operating system, which can provide system services to computer programs written in a programing language. The computer or other device or a part thereof implementing the various embodiments can also include suitable input means for receiving, for example, measurement data and / or control data, and output means for outputting, for example, control data or other data. At least a part of the functionality according to any of the embodiments can also be implemented using one or more specific integrated circuits or discrete electrical components and devices.

[0022] For example, the current power converter system and components thereof can include processors and memories that can be used to implement functionality in accordance with the various embodiments described herein. Accordingly, at least some modifications and configurations that can be required for implementing the embodiments can be performed as software routines that can be implemented as added or updated software routines. If at least a portion of the functionality of any of the embodiments is implemented by software, such software can be provided as a computer program product including a computer program code, which, when run on a computer, causes the computer or a corresponding device to perform the functionality in accordance with the embodiments as described herein. Such computer program code can be stored on or typically embodied in a computer-readable medium, such as a suitable memory (e.g., a flash memory or an optical memory), from which the computer program code can be loaded into one or more units that execute the program code. In addition, such computer program code implementing any of the embodiments can be loaded, e.g., via a suitable data network, to one or more units that execute the computer program code, and such computer program code can replace or update program code that can be present.

[0023] It will be obvious to those skilled in the art that, as technology advances, the inventive concept can be implemented in various ways. The application and its embodiments are not limited to the examples described above but can vary within the scope of the claims.

Claims

1. A method for controlling a three-level brake chopper, the three-level brake chopper comprising: a positive direct current pole (dc+), a negative direct current pole (dc-) and a neutral direct current pole (NP); a first controllable semiconductor switch (T1) connected between the positive direct current pole (dc+) and a first connection point (P1); a second controllable semiconductor switch (T2) connected between the first connection point (P1) and the neutral direct current pole (NP); a third controllable semiconductor switch (T3) connected between the neutral direct current pole (NP) and a second connection point (P2); a fourth controllable semiconductor switch (T4) connected between the second connection point (P2) and the negative direct current pole (dc-); and a resistance arrangement (Rbrk; Rbrk1, Rbrk2) connected between the first connection point (P1) and the second connection point (P2), the method comprising: controlling the second controllable semiconductor switch (T2) and the third controllable semiconductor switch (T3) to a conducting state in response to detecting a fault in the resistance arrangement (Rbrk; Rbrk1, Rbrk2).

2. The method according to claim 1, comprising: controlling the first controllable semiconductor switch (T1) and the fourth controllable semiconductor switch (T4) to a non-conducting state in response to detecting a fault in the resistance arrangement (Rbrk; Rbrk1, Rbrk2). controlling the first controllable semiconductor switch (T1) and the fourth controllable semiconductor switch (T4) to the non-conducting state is performed before controlling the second controllable semiconductor switch (T2) and the third controllable semiconductor switch (T3) to the conducting state. detecting the fault in the resistance arrangement (Rbrk; Rbrk1, Rbrk2) based on one or more current and / or voltage quantities related to the three-level brake chopper, and / or based on one or more signals received.

5. A three-level brake chopper, comprising:

3. The method of claim 2, wherein, a positive direct current pole (dc+), a negative direct current pole (dc-) and a neutral direct current pole (NP); 4. The method of claim 1 or 2 or 3, comprising: a first controllable semiconductor switch (T1) connected between the positive direct current pole (dc+) and a first connection point; a second controllable semiconductor switch (T2) connected between the first connection point and the neutral direct current pole (NP); a third controllable semiconductor switch (T3) connected between the neutral direct current pole (NP) and a second connection point; a fourth controllable semiconductor switch (T4) connected between the second connection point and the negative direct current pole (dc-); a resistance arrangement (Rbrk; Rbrk1, Rbrk2) connected between the first connection point and the second connection point; and a control arrangement (11) configured to control the second controllable semiconductor switch (T2) and the third controllable semiconductor switch (T3) to a conducting state in response to detecting a fault in the resistance arrangement (Rbrk; Rbrk1, Rbrk2). ​ ​ ​ ​ ​ ​ 6. The three-level brake chopper of claim 5, wherein, The control device (11) is configured to control the first controllable semiconductor switch (T1) and the fourth controllable semiconductor switch (T4) into a non-conductive state in response to detecting a fault in the resistance arrangement (Rbrk; Rbrk1, Rbrk2). The control device (11) is configured to control the first controllable semiconductor switch (T1) and the fourth controllable semiconductor switch (T4) into the non-conductive state before controlling the second controllable semiconductor switch (T2) and the third controllable semiconductor switch (T3) into the conductive state.

7. The three-level brake chopper of claim 6, wherein, The control device (11) is configured to detect a fault in the resistance arrangement (Rbrk; Rbrk1, Rbrk2) based on one or more current and / or voltage quantities related to the three-level brake chopper and / or based on one or more received signals.

8. The three-level brake chopper according to claim 5 or 6 or 7, wherein, The control device (11) is configured to monitor one or more current and / or voltage quantities related to the three-level brake chopper. The resistance arrangement (Rbrk; Rbrk1, Rbrk2) comprises at least one resistor.

9. The three-level brake chopper of claim 8, wherein, The resistance arrangement (Rbrk; Rbrk1, Rbrk2) comprises two or more resistors connected in series and / or in parallel with each other.

10. The three-level brake chopper of any one of claims 5 to 9, wherein, The resistance arrangement comprises two parts (Rbrk1, Rbrk2) connected in series between the first connection point (P1) and the second connection point (P2), wherein a connection point (P3) between the two parts (Rbrk1, Rbrk2) is connected to the neutral DC pole (NP).

11. The three-level brake chopper of claim 10, wherein, A first diode (D1) connected in parallel with the second controllable semiconductor switch (T2), and a second diode (D2) connected in parallel with the third controllable semiconductor switch (T3).

12. The three-level brake chopper of claim 10, wherein, A third diode (D3) connected in parallel with the first controllable semiconductor switch (T1), and a fourth diode (D4) connected in parallel with the fourth controllable semiconductor switch (T4).

13. The three-level brake chopper of any one of claims 5 to 12, comprising: The controllable semiconductor switches (T1, T2, T3, T4) are insulated gate bipolar transistors or field effect transistors.

14. The three-level brake chopper of claim 13, comprising: The three-level brake chopper (10) according to any one of claims 5-15.

15. The three-level brake chopper of any one of claims 5 to 14, wherein, The three-level brake chopper (10) according to any one of claims 5-15.

16. A three-level converter apparatus comprising: ​

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