Inverter and method for operating an inverter

Abstract

Inverter for supplying power to an electric motor in a system, wherein the converter comprises signal electronics (3) and power electronics (4), wherein the signal electronics (3) comprises such a computer unit (1), in particular also software executed thereon, such that at regular time intervals, in particular for a respective time interval, new values ​​for physical quantities of the motor and / or new values ​​for output signal voltage for outputs (5, 6), in particular second outputs (5), for controlling actuators of the system can be determined, wherein the second outputs (5) are implemented digitally, in particular always assuming one of two signal states, in particular one of two output signal voltage values, wherein the signal electronics (3) includes a timer compare unit (2), a first output (6) is electrically connected or operatively connected to the output of the timer-compare unit (2), in particular the timer-compare unit (2) controls the first output (6), wherein a data line is provided between an input of the timer compare unit (2) and the computer unit (1) of the signal electronics (3) for transmitting information regarding the time of a signal voltage change of the first output (6), in particular of a next signal voltage change, wherein the timer compare unit (2) has a higher clock frequency than the frequency associated with the regular time intervals, in particular the time interval, wherein the frequency of the timer compare unit (2) has a frequency at least two, in particular at least three or four, orders of magnitude higher than the frequency associated with the time interval, wherein the output of the timer compare unit (2) drives an amplifier stage which generates the voltage for the first output (6).

Description

[0001] The invention relates to a converter and a method for operating a converter.

[0002] It is known that inverters whose signal electronics include a microcontroller execute a control procedure digitally. In this process, calculation steps are performed depending on a predefined clock signal. This allows the values ​​of physical quantities to be determined at this clock signal and thus at simultaneously defined points in time. It should be noted that the computational effort can vary across different clock cycles. Therefore, depending on the operating state and the influence of disturbances, there are periods in which the calculation requires the entire time interval defined by the clock signal, and other periods in which the calculation does not require the entire time interval defined by the clock signal. Consequently, the microcontroller's processing power is not fully utilized in every clock cycle.The faster the values ​​of the quantities are determined, the more accurately the determined values ​​follow the desired trend or correspond more closely to the actual physical value. However, the described clocking simplifies the entire software programming for the control procedure installed in the computer unit.

[0003] Camshafts are generally known. Cam tracks, in particular, are also well-known. Here, the angular dependence of the radius of a surface area at an axial point on a shaft generates a signal voltage profile that is absolutely synchronous with the rotation of the shaft, since the radius profile is geometrically defined.

[0004] From DE 29 41 287 C2, a digital ignition control device for converter valves is known as the closest prior art.

[0005] An electronic cam control unit is known from DE 103 42 561 A1.

[0006] A cam switch is known from the manual “Digital Cam Switch CamCon DC51”; Digitronics Automationsanlagen GmbH; edition dated 14.6.2006.

[0007] The invention is therefore based on the objective of replicating mechanical systems using electrical systems, with the least possible effort required.

[0008] According to the invention, the problem is solved in the converter according to the features specified in claim 1 and in the method for operating a converter according to the features specified in claim 4.

[0009] Key features of the invention for the inverter are that it is designed to supply an electric motor, the inverter includes signal electronics and power electronics, wherein the signal electronics comprise a computer unit designed in such a way that new values ​​for physical quantities of the motor and / or new values ​​for output signal voltage for outputs, in particular second outputs, can be determined at regular time intervals, in particular for a respective time interval, where the output is digital, in particular always assuming one of two signal states, wherein a first output is electrically connected or electrically functionally connected to the output of a timer compare unit, wherein a data line is provided between an input of the timer-compare unit and a computer unit of the signal electronics, in particular for transmitting information regarding the time of a signal voltage change of the output, especially of a next signal voltage change, wherein the timer-compare unit has a higher clock frequency than the frequency associated with the regular time intervals, in particular the time interval, and in particular the reciprocal of the time interval.

[0010] The advantage here is that the voltage waveform generated at the output exhibits a quantization error that is orders of magnitude smaller. This is because, despite the relatively slow clock speed used to calculate the values ​​of the control parameters, the higher-frequency timer-compare unit achieves high accuracy in inducing the voltage change at the desired time. The voltage timing changes are thus not synchronized with the clock speed of the computer unit, but rather with the much faster clock speed of the timer-compare unit, resulting in a significantly smaller error due to temporal quantization.

[0011] The term "electrically interconnected" also includes a device in which the timer-compare unit uses its own output signal to control an amplifier stage, which then provides the signal voltage for the first output at its associated output.

[0012] Alternatively, the expert could have used the unused computing time based on the described state of the art, but this would not have yielded significantly better results.

[0013] In an advantageous embodiment, the frequency of the timer-compare unit is at least two, and in particular at least three or four, orders of magnitude higher than the frequency at which the values ​​of the state variables are updated by the processing unit for the corresponding time interval. The advantage here is that the timer-compare unit has a very simple, less complex structure compared to a microcontroller, and precisely for this reason, highly precise generation of the desired voltage waveform is possible. This is because the timer-compare unit only needs to have a counter that is clocked at the high frequency and thus increments a counter value for each corresponding period.This counter value then only needs to be compared by the compare unit, i.e. a comparator, with the value transmitted by the computer unit, i.e. with the information about the time, and thus the output voltage change is caused when the transmitted value is reached.

[0014] In an advantageous embodiment, the output of a timer-compare unit controls an amplifier stage that generates the voltage for the first output. A key advantage is that the timer-compare unit can be implemented as an integrated circuit and does not need to generate high output voltages or currents. Important features of the method include its suitability for operating a converter to power an electric motor. the inverter includes signal electronics and power electronics, wherein the signal electronics comprise a computer unit operated in such a way that new values ​​for physical quantities of the motor and / or new values ​​for output signal voltage for outputs, in particular second outputs, are determined at regular time intervals, in particular for a respective time interval, where outputs are implemented digitally, in particular always assuming one of two signal states, where a timer-compare unit controls a first output, wherein the computer unit of the timer-compare unit transmits information regarding the time of a signal voltage change of the output for a subsequent time period, in particular of a next signal voltage change, wherein the timer-compare unit has a higher clock frequency than the frequency associated with the regular time intervals, in particular the time interval, and in particular the reciprocal of the time interval.

[0015] The advantage here is that a complex control procedure can be implemented, whereby only updated values ​​of state variables are determined at each time interval of the computer unit's clock cycle. Nevertheless, the generation of output voltages with very high temporal accuracy is possible through the use of a timer-compare unit. In this way, it is possible to determine a future time at which a change in the output voltage can be effected.

[0016] Key features of the alternative method are that at least one first output is analog and not digital, in particular providing an analog voltage signal. wherein the computer unit provides information regarding the delay and the signal voltage curve to a delay unit, wherein the delay unit controls the voltage signal at the first output, in particular wherein the delay unit comprises a memory for intermediate storage of the voltage curve, in particular wherein the delay unit has a higher clock frequency than the frequency associated with the regular time intervals, in particular the time interval, in particular that is, in particular, than the reciprocal of the time interval.

[0017] An advantage of this approach is that, at each clock cycle (which doesn't necessarily have to be regular), values ​​of the electric motor's physical parameters are determined according to a machine model embedded in the control procedure executed on the computer unit. This allows for the determination of new values ​​for these state variables, at least approximately synchronously, within a sufficiently short timeframe. From the determined state variables, their actual and target values, values ​​for manipulated variables, such as the motor voltage space vector, are calculated, and the corresponding pulse-width modulated control signals for the output stage are then generated. Similarly, the voltage values ​​of the second outputs are also determined at each clock cycle. To determine the voltage values ​​of the first outputs, only information regarding the voltage value and the respective time is generated and transmitted to the timer-compare unit.In this way, the generation of the desired output signal voltage is effected at the desired time, whereby this time may also lie within a time interval, so that the computer unit would not be able to control, in particular change, the voltage value at the desired time in the clock signal specified to it by the software and its own quartz crystal.

[0018] In an advantageous embodiment, the timer-compare unit comprises a ramp-up counter whose value is compared with a second value corresponding to the time information. When the second value is exceeded, a comparator transmits a change in the voltage value at the first unit by altering its output signal, particularly in a preceding time interval. The advantage here is that high temporal precision can be achieved with very little effort. The timer-compare unit can be implemented as either hardware or software.

[0019] In an advantageous embodiment, the motor is regulated to a constant speed by the inverter. A benefit here is that the determined and transmitted time for the output voltage change corresponds to a proportional angular interval, thus allowing the simulation of a mechanically generated cam track signal with very small deviations.

[0020] Further advantages arise from the sub-claims.

[0021] The invention will now be explained in more detail with the help of illustrations: In Fig. Figure 1 describes an embodiment of the invention in more detail. Here, an electric motor M is powered by a converter comprising signal electronics 3 and power electronics 4, which includes a power stage consisting of three half-bridges. Each half-bridge comprises at least one electronic power semiconductor switch in its upper branch and another in its lower branch. The half-bridges are supplied from a DC voltage source. The power switches are controlled by pulse-width modulation, with the control signals being generated by the signal electronics.

[0022] The signal electronics 3 comprise a computer unit 1 with a microcontroller, which is connected to a timer-compare unit 2 for generating signals for a first output 6 or several first outputs. The computer unit 1 also generates the signals for second outputs 5.

[0023] The computer unit also performs a control procedure for the motor M, whereby the values ​​of a manipulated variable, such as the motor voltage vector, are determined taking into account setpoints and corresponding actual values ​​of quantities, such as the motor current vector and / or winding values. This procedure is executed digitally. This means that at regular intervals, for example, every millisecond, new values ​​for such or other physical quantities of the motor and / or new values ​​for output signals are determined. The values ​​determined in this way are then implemented using the appropriate means. For example, the determined motor voltage is supplied to the output stage in the form of pulse-width modulation ratios for each power switch. The value of the previously measured supply DC voltage, i.e., the intermediate circuit voltage, is also taken into account.The pulse-width modulated signals thus generate the motor voltage, i.e., the motor voltage space vector, with the help of the voltage-generating means, i.e., the output stage, to whose input the pulse-width modulated signals are supplied to control the output stage.

[0024] Signals are generated at the outputs in a corresponding manner by controlling an electronic switch assigned to each output in such a way that either a HIGH or a LOW state is present. The HIGH state preferably lasts 24 seconds. The signal voltage values ​​of the second outputs 6 are therefore updated at the beginning of each time interval.

[0025] It is therefore important that the processing unit and the software running on it are designed in such a way that the values ​​of the motor's state variables, such as the motor voltage space vector, are determined only once per time interval, i.e., clock cycle. The same applies to the signal states, i.e., signal voltage values, of the second outputs. The clock cycle is, for example, 1 millisecond. However, clock cycle durations between 0.1 and 10 ms are also possible.

[0026] Advantageously, according to the invention, to generate the signal voltage values ​​of the first outputs 5, information is supplied to the timer-compare unit 2 at the beginning of a time interval, which corresponds to a time at which the new signal voltage value should be available at the output.

[0027] The Timer-Compare Unit 2 comprises a ramp-up counter and a comparator to determine the timing. This comparator compares the counter value with the predefined value, i.e., the input information. The ramp-up counter is clocked at a high frequency, for example, 40 MHz. Thus, the counter value is incremented by 1 every 25 ns. In this way, quantization errors can be reduced by orders of magnitude, and the signal voltage value at the first output corresponds exactly to the desired time with an error of less than 25 ns.

[0028] It is important that the clock frequency of the ramp-up counter, i.e., the Timer Compare Unit 2, is at least one or more orders of magnitude higher than the frequency corresponding to the update time interval. In the example above, a factor of more than 1000 is used.

[0029] The desired target voltage curve at the first output can be achieved with a much smaller quantization error using the Timer-Compare unit 2 than if the voltage curve were output directly from the computer unit via the second outputs.

[0030] Thus, cam track signals, for example, can be generated very precisely. The motor M is controlled or regulated by the inverter in such a way that the rotational speed of the motor M's rotor reaches a predetermined value, particularly within the smallest possible tolerance band around this value.

[0031] As a cam track signal, a periodic signal is now provided at at least one respective second output, whereby, similar to a mechanical camshaft, the state HIGH is output at the first output for one or more angular sections per revolution of the rotor shaft of the motor, and otherwise LOW.

[0032] As described above, the information about the time of the state change is output from the computer unit 1 to the timer-compare unit 2. This time is calculated assuming a constant rotational speed.

[0033] If an electric motor drives an object at approximately 10 m / s at the desired target speed, the quantization error in the above example, i.e., at an update frequency of 1 kHz, is 10 mm. With the timer-compare unit operating at 40 MHz, a quantization error of 0.25 µm is therefore achievable.

[0034] The signal voltages applied to the outputs are used to control actuators. Actuators with a dead time can also be used; that is, they can only be activated after a delay following a change in the signal voltage applied to the first output. This dead time can be taken into account when determining the aforementioned time. Thus, the invention not only allows for highly accurate determination of the signal voltage change time, but also compensates for dead time by including the delay time in the prediction. In a first embodiment of the invention, a constant movement speed is always assumed.

[0035] In further embodiments of the invention, an arbitrary target speed profile is specified. The motor is controlled by the inverter and influenced by the controller implemented in the inverter in such a way that the target profile is maintained as closely as possible. The determination of the timing and the consideration of the dead time of an actuator are then carried out taking the target profile into account.

[0036] In further embodiments of the invention, analog outputs are provided as first and / or second outputs instead of such digital outputs. In this case, the desired predicted signal waveform is transmitted to a short-term memory instead of a timer-compare unit, which then outputs the predicted signal waveform, in particular executing a respective signal voltage change at the transmitted discrete time points. Reference symbol list 1 computer unit with microcontroller 2 Timer-Compare Unit 3 Signal electronics 4 Power Electronics 5 second exits 6 first exit M electric motor

Claims

[1] Inverter for supplying an electric motor in a plant, wherein the converter comprises signal electronics (3) and power electronics (4), wherein the signal electronics (3) comprises such a computer unit (1), in particular also software executed thereon, such that at regular time intervals, in particular for a respective time interval, new values ​​for physical quantities of the motor and / or new values ​​for output signal voltage for outputs (5, 6), in particular second outputs (5), for controlling actuators of the system can be determined, wherein the second outputs (5) are implemented digitally, in particular always assuming one of two signal states, in particular one of two output signal voltage values, wherein the signal electronics (3) includes a timer compare unit (2), a first output (6) is electrically connected or operatively connected to the output of the timer-compare unit (2), in particular the timer-compare unit (2) controls the first output (6), wherein a data line is provided between an input of the timer-compare unit (2) and the computer unit (1) of the signal electronics (3) for transmitting information regarding the time of a signal voltage change of the first output (6), in particular of a next signal voltage change, wherein the timer compare unit (2) has a higher clock frequency than the frequency associated with the regular time intervals, in particular the time interval, wherein the frequency of the timer compare unit (2) has a frequency at least two, in particular at least three or four, orders of magnitude higher than the frequency associated with the time interval, wherein the output of the timer compare unit (2) drives an amplifier stage which generates the voltage for the first output (6). [2] Method for operating an inverter to supply an electric motor in a plant, wherein the converter comprises signal electronics (3) and power electronics (4), wherein the signal electronics (3) comprises a computer unit (1) operated in such a manner, in particular also with software to be executed in such a manner, such that at regular time intervals, in particular for a respective time interval, new values ​​for physical quantities of the motor and / or new values ​​for output signal voltage for outputs (5, 6), in particular second outputs (5), for controlling actuators of the system are determined, wherein the second outputs (5) are implemented digitally, in particular always assuming one of two signal states, where a timer compare unit (2) controls a first output (6), wherein the computing unit (1) transmits information to the timer-compare unit (2) regarding the time of a signal voltage change of the first output (6) for a subsequent time period, in particular of a next signal voltage change, wherein the timer compare unit (2) has a higher clock frequency than the frequency associated with the regular time intervals, in particular the time interval, in particular the reciprocal of the time interval, wherein the frequency of the timer compare unit (2) has a frequency at least two, in particular at least three or four, orders of magnitude higher than the frequency associated with the time interval, wherein the output of the timer compare unit (2) drives an amplifier stage which generates the voltage for the first output (6). [3] Method for operating an inverter to supply an electric motor in a plant, wherein the converter generates a cam track signal which is supplied from an output of the converter (4) to an actuator of the system, and the converter regulates the motor to a constant speed, wherein the converter comprises signal electronics (3) and power electronics (4), wherein the signal electronics (3) comprises a computer unit (1) operated in such a way that new values ​​for physical quantities of the motor and / or new values ​​for output signal voltages for outputs (5, 6) for controlling the actuators of the system, in particular second outputs (5), are determined at regular time intervals, in particular for a respective time interval, wherein a first output (6) is electrically connected or electrically operatively connected to the output of a timer-compare unit (2), in particular the timer-compare unit (2) controls the first output (6), wherein the computing unit (1) provides information regarding the delay and the signal voltage profile to a delay unit, wherein the delay unit controls the voltage signal at the first output (6), in particular wherein the delay unit comprises a memory for temporarily storing the voltage curve, in particular wherein the delay unit has a higher clock frequency than the frequency associated with the regular time intervals, in particular the time interval, in particular that is, than the reciprocal of the time interval, wherein the timer-compare unit (2) comprises a ramp-up counter whose value is compared with a second value corresponding to the information about the time, wherein a comparator, upon exceeding the second value, causes a change in the voltage value at the first output (6) by changing its output signal, wherein the second value is transmitted from the computer unit (1) to the timer-compare unit (2), in particular in a preceding time interval.

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