Method for operating a converter

Abstract

The invention relates to a method for operating an inverter (10) of an electric machine, in particular of an electrically powered vehicle, wherein the inverter (10) has at least three half-bridges (30, 32, 34) each with at least one upper semiconductor switch (11, 12, 13) and at least one lower semiconductor switch (11, 12, 13, 14, 15, 16). In the method, the inverter (10) is used at least intermittently for heat generation by operating at least one upper semiconductor switch (11, 12, 13) or one lower semiconductor switch (14, 15, 16) of at least one half-bridge (30, 32, 34) in linear operation.

Description

[0001] The invention relates to a method for operating a converter of an electrical machine, in particular of an electrically powered vehicle.

[0002] In winter, electrically powered vehicles require more heat than the usual waste heat, particularly for interior air conditioning and rapid charging of the traction battery. Additional heating elements or heating functions are required to provide this heat.

[0003] The necessary heat can be provided via several paths. One possibility is the use of PTC heating elements. In this case, a high-voltage heater is installed in the vehicle that serves only as a heating element. Another possibility is inefficient operation of the electric drive. In this case, the electric machine's inverters feed a current into the electric machine that does not generate any torque in order to utilize heat via the electric machine's stator resistance and the inverter's main switch. Alternatively, high-frequency currents can also be introduced into the electric machine. Both methods via the electric drive have the disadvantage that torque safety must be observed. Furthermore, the switched-mode inverters lead to electromagnetic excitation of the high-voltage network.This is particularly critical with regard to electromagnetic compatibility (EMC) and the steep switching edges of modern inverters at fast charging stations.

[0004] DE 10 2011 083 945A1 discloses a control device for controlling a semiconductor switch of an inverter, comprising a switching signal amplification device configured to amplify a switching signal generated by a control of the inverter and to generate a first switching control signal that controls the semiconductor switch in a switching mode. Furthermore, the control device comprises a current control device coupled to a current sensor output of the semiconductor switch and configured to generate a second switching control signal that controls the semiconductor switch in a linear mode.Furthermore, the control device comprises a selection device which is coupled to the switching signal amplification device and the current control device and which is designed to output either the first switching control signal or the second switching control signal for controlling a control terminal of the semiconductor switch as a function of at least one operating selection signal.

[0005] An object of the invention is to provide an improved method for operating a converter of an electrical machine, in particular of an electrically powered vehicle.

[0006] The above-mentioned problem is solved by the features of the independent claim.

[0007] Advantageous embodiments and advantages of the invention emerge from the further claims, the description and the drawing.

[0008] According to one aspect of the invention, a method for operating a converter of an electrical machine, in particular of an electrically powered vehicle, is proposed, wherein the converter has at least three half-bridges, each with at least one upper semiconductor switch and at least one lower semiconductor switch. In the method, the converter is used at least temporarily to generate heat by operating at least one upper semiconductor switch or one lower semiconductor switch of at least one half-bridge in linear mode.

[0009] According to the proposed method, the semiconductor switches of the two half-bridges of the converter are controlled in such a way that the desired heat generation is possible. The semiconductor switches, typically SiC MOSFETs, of the traction converter are put into linear operation. This allows an adjustable current to flow through the semiconductor switches. For example, either only the upper semiconductor switch, only the lower semiconductor switch, or both semiconductor switches can be used in linear operation for each half-bridge. Since the entire battery voltage is dropped across one or both semiconductor switches of a half-bridge, high heating output is achieved even at low currents. The converter is operated in a type of controlled bridge short circuit, i.e. no currents flow in the electrical machine.

[0010] The proposed method saves components compared to separate auxiliary heaters. Compared to variants that supply current to the electric motor, there is no impact on torque generation and no EMC excitation due to high currents from fast-switching components.

[0011] The application of the method is particularly advantageous for converters with high rated power, since only a part of the rated power can be dissipated as heat.

[0012] According to an advantageous embodiment of the method, in the linear operation of the at least one upper or lower semiconductor switch, a control terminal of the at least one upper or lower semiconductor switch can be controlled at a voltage value that lies between a voltage value for switching on and a voltage value for switching off the at least one upper or lower semiconductor switch. Alternatively, in the linear operation, the control terminal can be raised to the voltage value for switching on for a predetermined period of time and then lowered again to the voltage value for switching off before the at least one upper or lower semiconductor switch has achieved its full conductivity. In this way, the at least one upper or lower semiconductor switch can advantageously be operated in the linear operation in order to achieve the desired heat generation.

[0013] According to an advantageous embodiment of the method, all lower or all upper semiconductor switches of the converter, in which at least one upper or one lower semiconductor switch is operated in linear mode, can be short-circuited. The upper semiconductor switches are short-circuited when a lower semiconductor switch is operated in linear mode, and vice versa. This ensures that the electric machine is not driven and no torque is generated.

[0014] According to an advantageous embodiment of the method, linear operation can be limited to a continuous thermal power of the at least one upper or lower semiconductor switch. This advantageously prevents permanent impairment of the at least one upper or lower semiconductor switch.

[0015] According to an advantageous embodiment of the method, a predetermined current can be set in the at least one upper or lower semiconductor switch during linear operation. This allows the desired heating power to be advantageously generated by the at least one upper or lower semiconductor switch.

[0016] According to an advantageous embodiment of the method, when the linear operation is clocked, a low supply voltage and / or an increased capacitance at the control terminal and / or a high resistance of the control terminal of the at least one upper or lower semiconductor switch can be set. This advantageously allows the desired heat generation in the at least one semiconductor switch to be achieved.

[0017] According to an advantageous embodiment of the method, a duration of linear operation and / or a current in the at least one upper or lower semiconductor switch can be adjusted based on a model. In particular, the model can take into account a maximum duty cycle during clocked operation of the at least one semiconductor switch at a given intermediate circuit voltage, cooling water flow, and / or cooling water temperature. This advantageously prevents overloading, since measuring the current with conventional current sensors is not possible in a bridge short circuit.

[0018] According to an advantageous embodiment of the method, the upper and lower semiconductor switches of a half-bridge can be operated alternately in linear mode. A uniform load on the semiconductor switches can be achieved by distributing the power across the individual phases.

[0019] According to an advantageous embodiment of the method, at least one semiconductor switch of a half-bridge can be operated alternately with a semiconductor switch of another of the half-bridges in linear mode. Alternating activation of the phases is advantageous for ensuring a uniform load on the semiconductor switches.

[0020] According to an advantageous embodiment of the method, the desired heat output can be controlled via a duty cycle of the individual phases of the clocked linear operation of the at least one upper or lower semiconductor switch. Advantageously, the total power can be controlled by activating and deactivating the phases and via the duty cycle of the individual phases.

[0021] Further advantages will become apparent from the following description of the drawings. The drawings illustrate an exemplary embodiment of the invention. The drawings, the description, and the claims contain numerous features in combination. Those skilled in the art will also expediently consider the features individually and combine them into useful further combinations.

[0022] It shows: Fig. 1 a system overview of a converter of an electrical machine for operation with a method according to an embodiment of the invention.

[0023] In the figure, identical or similar components are numbered with the same reference numerals. The figure shows only an example and is not to be understood as limiting.

[0024] Fig. 1 shows a system overview of a converter 10 of an electrical machine for operation with a method according to an embodiment of the invention.

[0025] The converter 10 has three half-bridges 30, 32, 34, each with an upper semiconductor switch 11, 12, 13 and a lower semiconductor switch 14, 15, 16. The converter 10 is electrically supplied with an input voltage 50, for example, a voltage from a high-voltage battery, and an input current 60 via the capacitor 18. The semiconductor switches 11, 12, 13, 14, 15, 16 of the half-bridges 30, 32, 34 generate three phase voltages 40, 42, 44, often referred to as U, V, W.

[0026] According to the proposed method, the converter 10 is used at least temporarily to generate heat by operating at least one upper semiconductor switch 11, 12, 13 or a lower semiconductor switch 14, 15, 16 of at least one half-bridge 30, 32, 34 in a linear mode.

[0027] The at least one upper or lower semiconductor switch 11, 12, 13, 14, 15, 16 can be operated in linear mode by controlling a control terminal 21, 22, 23, 24, 25, 26 of the at least one upper or lower semiconductor switch 11, 12, 13, 14, 15, 16, for example a gate electrode if the semiconductor switch 11, 12, 13, 14, 15, 16 is a MOSFET, at a voltage value which lies between a voltage value for switching on and a voltage value for switching off the at least one upper or lower semiconductor switch 11, 12, 13, 14, 15, 16. Alternatively, for linear operation, it is also possible for the control terminal to be raised to the voltage value for switching on for a predetermined period of time and then lowered again to the voltage value for switching off before the at least one upper or lower semiconductor switch 11, 12, 13, 14, 15, 16 has achieved its full conductivity.

[0028] Either all of the lower or all of the upper semiconductor switches 14, 15, 16, 11, 12, 13 of the converter 10, in which at least one of the upper or lower semiconductor switches 11, 12, 13, 14, 15, 16 is operated in linear mode, can be short-circuited. This ensures that no torque is applied to the electric machine. The on-state resistance can be in the range of milliohms.

[0029] For example, the upper semiconductor switch 13 of half-bridge 34 can be operated in linear mode, while the lower semiconductor switches 14, 15, and 16 of half-bridges 30, 32, and 34 are operated in short circuit mode. Heat can be generated in one to all three of the upper semiconductor switches 11 to 13.

[0030] Alternatively, it is also possible for the lower semiconductor switch 16 of half-bridge 34 to be operated in linear mode, while the upper semiconductor switches 11, 12, 13 of half-bridges 30, 32, 34 are operated in short circuit mode. Heat can be generated in one to all three of the lower semiconductor switches 14 to 16.

[0031] For a uniform load of the semiconductor switches 11, 12, 13, 14, 15, 16, the upper and lower semiconductor switches 11, 12, 13, 14, 15, 16 of a half-bridge 30, 32, 34 can each be operated alternately in linear mode.

[0032] At least one semiconductor switch 11, 12, 13, 14, 15, 16 of a half-bridge 30, 32, 34 can also be operated alternately in linear mode with a semiconductor switch 11, 12, 13, 14, 15, 16 of another of the half-bridges 30, 32, 34. This allows the load to be evenly distributed across the half-bridges 30, 32, 34.

[0033] In a further embodiment, it is also possible for both the upper and lower semiconductor switches 11, 14; 12, 15; and 13, 16 of a half-bridge 30, 32, 34 to be operated in linear mode. The heat can be generated in two to all six of the semiconductor switches 11, 12, 13, 14, 15, 16.

[0034] Advantageously, in at least one upper or lower semiconductor switch 11, 12, 13, 14, 15, 16, the linear operation can be limited to a continuous thermal power of the semiconductor switch 11, 12, 13, 14, 15, 16 so that the semiconductor switch 11, 12, 13, 14, 15, 16 is not overloaded and damaged.

[0035] Thus, in linear operation, a predetermined current can be set in at least one upper or lower semiconductor switch 11, 12, 13, 14, 15, 16.

[0036] If the linear operation is clocked, a low supply voltage and / or an increased capacitance at the control terminal 21, 22, 23, 24, 25, 26 and / or a high resistance of the control terminal 21, 22, 23, 24, 25, 26 of the at least one upper or lower semiconductor switch 11, 12, 13, 14, 15, 16 can advantageously be set.

[0037] In order to avoid overloading the semiconductor switch 11, 12, 13, 14, 15, 16 during linear operation, a duration of linear operation and / or a current in the at least one semiconductor switch 11, 12, 13, 14, 15, 16 can advantageously be set based on a model. In particular, during clocked operation of the at least one upper or lower semiconductor switch 11, 12, 13, 14, 15, 16, the model can take into account a maximum duty cycle for a given intermediate circuit voltage, and / or cooling water temperature, and / or given cooling water flow rate.

[0038] For a uniform load of the upper and lower semiconductor switches 11, 12, 13, 14, 15, 16, the upper and lower semiconductor switches 11, 12, 13, 14, 15, 16 of a half-bridge 30, 32, 34 can each be operated alternately in linear mode.

[0039] In a clocked linear operation, the desired heat output can be controlled via a duty cycle of the individual phases of the clocked linear operation of at least one upper or lower semiconductor switch 11, 12, 13, 14, 15, 16. List of reference symbols 10 inverters 11 semiconductor switches 12 semiconductor switches 13 semiconductor switches 14 semiconductor switches 15 semiconductor switches 16 semiconductor switches 18 capacity 21 Control connection 22 Control connection 23 Control connection 24 control connection 25 Control connection 26 Control connection 30 Half Bridge 32 Half Bridge 34 Half Bridge 40 Phase voltage U 42 Phase voltage V 44 Phase voltage W 50 input voltage 60 input current QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] DE 10 2011 083 945A1

[0004]

Claims

[1] Method for operating a converter (10) of an electrical machine, in particular of an electrically operated vehicle, wherein the converter (10) has at least three half-bridges (30, 32, 34), each with at least one upper semiconductor switch (11, 12, 13) and at least one lower semiconductor switch (14, 15, 16), wherein the converter (10) is used at least temporarily to generate heat by operating at least one upper semiconductor switch (11, 12, 13) or a lower semiconductor switch (14, 15, 16) of at least one half-bridge (30, 32, 34) in a linear mode. [2] Method according to claim 1, wherein in the linear operation of the at least one upper or lower semiconductor switch (11, 12, 13, 14, 15, 16), a control terminal (21, 22, 23, 24, 25, 26) of the at least one upper or lower semiconductor switch (11, 12, 13, 14, 15, 16) is controlled at a voltage value which lies between a voltage value for switching on and a voltage value for switching off the at least one upper or lower semiconductor switch (11, 12, 13, 14, 15, 16), or wherein in the linear operation, the control terminal (21, 22, 23, 24, 25, 26) is raised to the voltage value for switching on for a predetermined period of time and is then lowered again to the voltage value for switching off before the at least one upper or lower semiconductor switch (11, 12, 13, 14, 15, 16) has reached its full conductivity. [3] Method according to claim 1 or 2, wherein all lower or all upper semiconductor switches (14, 15, 16, 11, 12, 13) of the converter (10), in which at least one upper or one lower semiconductor switch (11, 12, 13, 14, 15, 16) is operated in linear mode, are switched into a short circuit. [4] Method according to one of the preceding claims, wherein the linear operation is limited to a continuous thermal power of the at least one upper or lower semiconductor switch (11, 12, 13, 14, 15, 16). [5] Method according to one of the preceding claims, wherein in linear operation a predetermined current is set in the at least one upper or lower semiconductor switch (11, 12, 13, 14, 15, 16). [6] Method according to one of the preceding claims, wherein, when the linear operation is operated in a clocked manner, a low supply voltage, and / or an increased capacitance at the control terminal (21, 22, 23, 24, 25, 26), and / or a high resistance of the control terminal (21, 22, 23, 24, 25, 26) of the at least one upper or lower semiconductor switch (11, 12, 13, 14, 15, 16) is set. [7] Method according to one of the preceding claims, wherein a duration of the linear operation and / or a current in the at least one semiconductor switch (11, 12, 13, 14, 15, 16) is set based on a model, in particular wherein the model takes into account a maximum duty cycle in a clocked operation of the at least one upper or lower semiconductor switch (11, 12, 13, 14, 15, 16) at a given intermediate circuit voltage, and / or cooling water flow, and / or cooling water temperature. [8] Method according to one of the preceding claims, wherein the upper and lower semiconductor switches (11, 12, 13, 14, 15, 16) of a half-bridge (30, 32, 34) are each operated alternately in linear mode. [9] Method according to one of the preceding claims, wherein at least one semiconductor switch (11, 12, 13, 14, 15, 16) of a half-bridge (30, 32, 34) is alternately operated in linear mode with a semiconductor switch (11, 12, 13, 14, 15, 16) of another of the half-bridges (30, 32, 34). [10] Method according to one of the preceding claims, wherein the desired heat output is controlled via a duty cycle of the individual phases of the clocked linear operation of the at least one upper or lower semiconductor switch (11, 12, 13, 14, 15, 16).

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