Method for controlling a high-voltage heater and high-voltage heater

Abstract

To provide a method for controlling a high-voltage heater with which EMC limits can be observed and ripple currents kept within the permissible limits, a method (100) for controlling a high-voltage heater (200) is proposed, wherein the high-voltage heater (200) comprises several heating circuits (10, 11, 12) and several power switches (13, 14, 15), wherein each of the heating circuits (10, 11, 12) is associated with a power switch (13, 14, 15), wherein at least one first of the power switches (13) is clocked with a first clock frequency, and wherein at least one second of the power switches (14) is clocked with a second clock frequency, and wherein the first clock frequency is higher than the second clock frequency.

Description

[0001] The present invention relates to a method for controlling a high-voltage heater, wherein the high-voltage heater comprises several heating circuits and several power switches, each of the heating circuits being assigned a power switch, wherein at least one first power switch is clocked at a first clock frequency, and wherein at least one second power switch is clocked at a second clock frequency. The present invention further relates to a high-voltage heater and a motor vehicle with a high-voltage heater.

[0002] In battery-electric vehicles, high-voltage heaters are used to regulate the coolant temperature. These heaters are particularly useful in cold temperatures to quickly heat the coolant. The coolant is then used to heat the drive battery and, depending on the thermal management system, also the vehicle interior to the desired temperature.

[0003] High-voltage heaters, especially those used in battery-electric vehicles, must meet a multitude of requirements. Firstly, they must provide the necessary power. Secondly, electromagnetic compatibility (EMC) limits must be observed, and ripple currents must not exceed permissible limits. A significant portion of the manufacturing costs for such high-voltage heaters is attributable to the required EMC filters and power switches. These components also require considerable installation space, creating a conflict between cost and space constraints. If sufficiently large EMC filters cannot be installed, derating must be performed in certain operating conditions to comply with limits and prevent thermal overheating of the power components.Furthermore, the transfer of known 400-volt solutions to 800-volt systems is not readily possible, as there are greater power losses in the power switches at the same clock frequency and the input stage in the form of the EMC filter also becomes larger due to higher potential differences.

[0004] From CN 116909331 A, an electric heating device is known which comprises a plurality of sensors and further includes a plurality of independent heating loops, each heating loop corresponding to an independent control system. The control system receives signals collected from the sensor and controls the switching on, switching off, and thus the power output of the heating loop.

[0005] The present invention is based on the objective of providing a method for controlling a high-voltage heater and a high-voltage heater with which EMC limits can be met and ripple currents can be kept within the permissible limits.

[0006] To solve the problem underlying the invention, a method for controlling a high-voltage heater is proposed, wherein the high-voltage heater comprises several heating circuits and several power switches, wherein each of the heating circuits is assigned a power switch, wherein at least one first of the power switches is clocked with a first clock frequency, and wherein at least one second of the power switches is clocked with a second clock frequency, wherein it is provided that the first clock frequency is higher than the second clock frequency.

[0007] The method can also be described as a method for the asymmetrical control of heating circuits of a high-voltage heater.

[0008] According to the invention, the at least one first circuit breaker and the at least one second circuit breaker are clocked at different switching frequencies, and thus the heating circuits assigned to the respective circuit breakers are operated at different switching frequencies. In particular, a combination of at least one fast circuit breaker with the first switching frequency and at least one slow circuit breaker with the second switching frequency is operated within the framework of the method.

[0009] By switching the at least one first, particularly fast, circuit breaker at the first higher switching frequency, EMC requirements can be met and ripple currents kept low. Switching the at least one second, particularly slow, circuit breaker ensures that the total power of the high-voltage heater can be supplied.

[0010] The at least one first circuit breaker with the higher first switching frequency serves for current / power control. Furthermore, since the at least one first, particularly fast, circuit breaker is switched simultaneously with the at least one second, particularly slow, circuit breaker, it is not necessary to design an EMC filter, preferably encompassed by the high-voltage heater, to match the switching frequency of the at least one, particularly slow, circuit breaker. The EMC filter can therefore be smaller, thus reducing the space required for the high-voltage heater.

[0011] Preferably, the high-voltage heater comprises at least three heating circuits and at least three power switches, and at least one third of the power switches is clocked with a third clock frequency, and the first clock frequency is higher than the third clock frequency, preferably the third clock frequency being equal to the second clock frequency.

[0012] By using a third circuit breaker and a third heating circuit assigned to the third circuit breaker, the second and third heating circuits can be switched on in stages to provide the required power.

[0013] Advantageously, the first power switch is provided that it is a silicon carbide field-effect transistor (SIC-FET), and / or that the second power switch is an insulated-gate bipolar transistor (IGBT), and / or that the third power switch is an insulated-gate bipolar transistor (IGBT), and / or that the first power switch and / or the second power switch and / or the third power switch is clocked using a pulse-width modulation (PWM) method, and / or that the heating circuits have the same ohmic resistance, and / or that the heating circuits have the same rated power, preferably about 2 kW.

[0014] If three heating circuits with a nominal output of 2 kW each are provided, the total nominal output is therefore 6 kW.

[0015] It is advantageous to provide that the first clock frequency is at least one, preferably at least two, and more preferably at least three orders of magnitude higher than the second clock frequency and / or the third clock frequency.

[0016] It is particularly provided that the first clock frequency is at least 10 kHz, preferably at least 50 kHz, and more preferably at least 100 kHz, and / or that the second clock frequency and / or the third clock frequency is at most 1 kHz, preferably at most 100 Hz, more preferably at most 50 Hz, and more preferably at most 30 Hz.

[0017] Since the first circuit breaker switches at a minimum of 10 kHz, the EMC filter can be significantly smaller, thus reducing the required installation space. The higher switching frequency also allows the use of smaller inductors, thereby limiting ripple currents.

[0018] It is particularly preferred that the first clock frequency is 100 kHz ± 10 kHz and that the second clock frequency and / or the third clock frequency is 30 Hz ± 3 Hz.

[0019] Furthermore, it may be provided that the first circuit breaker is switched off when the second circuit breaker and / or the third circuit breaker is switched on, and / or that the first circuit breaker is switched on when the second circuit breaker and / or the third circuit breaker is switched off.

[0020] Thus, when the second (especially slower) and / or third circuit breaker is switched on, the first (especially faster) circuit breaker is switched off simultaneously, thereby reducing or eliminating ripple currents at the input of the high-voltage heater. When the second (especially slower) and / or third circuit breaker is switched off, the first (especially faster) circuit breaker is switched on simultaneously.

[0021] Furthermore, it may be provided that the first clock frequency is increased during the switching on and off of the second circuit breaker and / or third circuit breaker in such a way that the first circuit breaker is switched several times during the switching on and off process of the second circuit breaker and / or third circuit breaker.

[0022] The second and / or third circuit breaker exhibit turn-on and turn-off edges in the time-current diagram during the turn-on and turn-off processes, over which the current rises and falls, respectively. The first circuit breaker, with the higher initial switching frequency, is preferably configured to turn on and off multiple times within the time interval of the turn-on and / or turn-off edges of the second and / or third circuit breaker. This can advantageously result in less fluctuation in the overall current demand on a high-voltage network.

[0023] Preferably, the duration of the switching-on and switching-off processes of the second and / or third circuit breaker is between 2 and 3 µs. The period of the first circuit breaker is further preferably in the range of 1 µs or less, so that multiple switching on and off cycles are possible during the switching-on and switching-off processes of the second and / or third circuit breaker.

[0024] Furthermore, it may be provided that the switching operations of the second circuit breaker and the third circuit breaker are offset from each other in time.

[0025] The staggered switching operations of the second and third power switches result in a stepwise activation of the second and third heating circuits, thus providing a control cascade by means of which current and ripple voltages in the high-voltage heater can be maintained and power control is provided.

[0026] It is also preferable to provide that the switching operations of the circuit breakers are controlled by an input current control.

[0027] In particular, an indirect automatic current control is preferably used, which regulates the current at the input of the high-voltage heater. The significantly faster switching and cycle times of the first circuit breaker allow the switching-off and switching-on processes of the slower second and third circuit breakers to be compensated for by planned feedforward control.

[0028] Alternatively, instead of current regulation, a corresponding coordinated control can be implemented.

[0029] Preferably, the high-voltage heater has an EMC filter, wherein the EMC filter is designed for the first clock frequency.

[0030] The EMC filter can also be called an input filter.

[0031] Therefore, the EMC filter is preferably designed for a switching frequency of approximately 100 kHz.

[0032] A further advantage is that an IGBT can be used in amplifier operation to charge an intermediate circuit capacitor.

[0033] The IGBT is preferably an additional IGBT besides the at least one second power switch and / or the at least one third power switch, which serves to safely shut down the high-voltage heater. This IGBT is used at the moment the high-voltage heater is started up in amplifier mode to slowly charge an intermediate circuit capacitor with reduced current flow.

[0034] Furthermore, it may be provided that voltage measurement is carried out via a passive discharge of capacitors, wherein the voltage measurement is preferably carried out by using discharge resistors.

[0035] Another solution to the problem underlying the invention is provided by providing a high-voltage heater for carrying out a previously described method.

[0036] Another solution to the problem underlying the invention consists of a motor vehicle comprising a high-voltage heater as described above.

[0037] All the aforementioned features and designs of the above-explained procedure can be applied analogously to the high-voltage heater and the motor vehicle.

[0038] The invention is explained in more detail below with reference to the accompanying figures. These show: Fig. 1 a schematic representation of a high-voltage heater, Fig. 2. a time-flow diagram, and Fig. 3 a motor vehicle with a high-voltage heater.

[0039] A method 100 for controlling a high-voltage heater 200 is described using the in Fig. The high-voltage heater 200 shown in Figure 1 is explained. The high-voltage heater 200 has a first heating circuit 10, a second heating circuit 11, and a third heating circuit 12. A first power switch 13, designed as a SiC FET 13a, is assigned to the first heating circuit 10. A second power switch 14 and a third power switch 15 are assigned to the second heating circuit 11 and the third heating circuit 12, respectively. The second power switch 14 and the third power switch 15 are designed as IGBTs 14a and 15a, respectively. Each of the power switches 13, 14, and 15 is controlled by an associated driver circuit 16a, 16b, and 16c, respectively.

[0040] The high-voltage heater 200 also features an EMC filter 17 and another IGBT 18, which is operated in amplifier mode. A driver circuit 16d is also associated with the additional IGBT 18.

[0041] The first circuit breaker 13 is clocked at a first clock frequency. Similarly, the second circuit breaker 14 is clocked at a second clock frequency, and the third circuit breaker 15 at a third clock frequency. The first clock frequency is at least three orders of magnitude higher than the second and third clock frequencies. The clock frequency of the first circuit breaker 13 is approximately 100 kHz. The second and third clock frequencies of the second circuit breaker 14 and the third circuit breaker 15 are the same and are approximately 30 Hz.

[0042] The time-flow diagram of Fig. Figure 2 shows a first current profile 19 in the first heating circuit 10 and, by way of example, a second current profile 20 in the second heating circuit 11. As can be seen in the comparison of the first current profile 19 in the first heating circuit 10 with the second current profile 20 in the second heating circuit 11, the first power switch 13 is operated with a first switching frequency which is significantly higher than the second switching frequency of the second power switch 14.

[0043] This allows EMC requirements to be met and ripple currents to be reduced.

[0044] During the switch-on and switch-off processes, the current waveform 20 in the second heating circuit 11 exhibits a switch-on edge 21 and a switch-off edge 22. During the switch-on edge 21 and the switch-off edge 22, the first circuit breaker 13 is operated with an increased initial switching rate, so that the first circuit breaker 13 is switched on and off several times. This reduces fluctuations in the total current demand of the high-voltage heater.

[0045] The first circuit breaker 13 is also switched off when the second circuit breaker 14 is switched on and switched on again when the second circuit breaker 14 is switched off, so that while the current 20 in the second heating circuit 11 is at its maximum, the first circuit breaker 13 is switched off and the current 19 in the first heating circuit 10 is zero. This switching of the first circuit breaker 13 and the second circuit breaker 14 reduces ripple currents at the input of the high-voltage heater 200.

[0046] The EMC filter 17 of the high-voltage heater 200 is designed for the first clock frequency of the first power switch 13. Furthermore, the additional IGBT 18 serves to safely switch off the high-voltage heater 200, whereby the IGBT 18 is used at the moment of commissioning of the high-voltage heater 200 in amplifier operation to slowly charge an intermediate circuit capacitor with reduced current flow.

[0047] Fig. Figure 3 shows a motor vehicle 300 with a high-voltage heater 200 according to Fig. 1. Reference symbol list 100 procedures 200 high-voltage heaters 10 First heating circuit 11 Second heating circuit 12 Third heating circuit 13 First circuit breaker 13a SiC-FET 14 Second circuit breaker 14a IGBT 15 Third circuit breaker 15a IGBT 16a Driver circuit 16b Driver circuit 16c driver circuit 16d driver circuit 17 EMC filters 18 IGBT 19 First current path 20 Second current path 21 Turn-on edge 22 Turn-off edge QUOTES INCLUDED IN THE DESCRIPTION

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

[0000] CN 116909331 A

[0004]

Claims

[1] Method (100) for controlling a high-voltage heater (200), wherein the high-voltage heater (200) comprises several heating circuits (10, 11, 12) and several power switches (13, 14, 15), wherein each of the heating circuits (10, 11, 12) is assigned a power switch (13, 14, 15), wherein at least one first of the power switches (13) is clocked at a first clock frequency, and wherein at least one second of the power switches (14) is clocked at a second clock frequency, characterized by , that the first clock frequency is higher than the second clock frequency. [2] Method (100) according to claim 1, characterized by, that the high-voltage heater (200) comprises at least three heating circuits (10, 11, 12), and at least three power switches (13, 14, 15), and that at least one third of the power switches (15) is clocked with a third clock frequency, and that the first clock frequency is higher than the third clock frequency, preferably the third clock frequency being equal to the second clock frequency. [3] Method (100) according to claim 1 or 2, characterized by, that the first power switch (13) is a SiC-FET (13a), and / or that the second power switch (14) is an IGBT (14a), and / or that the third power switch (15) is an IGBT (14a), and / or that the first power switch (13) and / or the second power switch (14) and / or the third power switch (15) is clocked with a PWM, and / or that the heating circuits (10, 11, 12) have the same ohmic resistance, and / or that the heating circuits (10, 11, 12) have the same rated power, preferably about 2 kW. [4] Method (100) according to any of the aforementioned claims, characterized by, that the first clock frequency is at least one, preferably at least two, further preferably at least three, orders of magnitude higher than the second clock frequency and / or the third clock frequency, and / or that the first clock frequency is at least 10 kHz, preferably at least 50 kHz, in particular preferably at least 100 kHz, and / or that the second clock frequency and / or the third clock frequency is at most 1 kHz, preferably at most 100 Hz, further preferably at most 50 Hz, in particular preferably at most 30 Hz, and / or that the first clock frequency is 100 kHz ± 10 kHz, and that the second clock frequency and / or the third clock frequency is 30 Hz ± 3 Hz. [5] Method (100) according to any of the aforementioned claims, characterized by, that the first circuit breaker (13) is switched off when the second circuit breaker (14) and / or the third circuit breaker (15) is switched on, and / or that the first circuit breaker (13) is switched on when the second circuit breaker (14) and / or the third circuit breaker (15) is switched off. [6] Method (100) according to any of the aforementioned claims, characterized by , that the first clock frequency is increased during the switching on and off of the second power switch (14) and / or third power switch (15) such that the first power switch (13) is switched several times during the switching on and off process of the second power switch (14) and / or third power switch (15). [7] Method (100) according to any of the aforementioned claims, characterized by , that the switching operations of the second circuit breaker (14) and the third circuit breaker (15) are offset from each other in time. [8] Method (100) according to any of the aforementioned claims, characterized by , that the switching operations of the power switches (13, 14, 15) are carried out by an input current control, and / or that the high-voltage heater (200) has an EMC filter (17) wherein the EMC filter (17) is designed for the first clock frequency, and / or that an IGBT (18) is used in amplifier operation to charge an intermediate circuit capacitor with a current flow. [9] High-voltage heater (200) configured to carry out a method (100) according to one of the preceding claims. [10] Motor vehicle (300) comprising a high-voltage heater (200) according to claim 9.

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