Active load for reconstructing a phase angle

Abstract

The present invention relates to an active load (10) for reconstructing a phase angle of an alternating voltage output by a device under test (14) having at least one DUT switching unit, the active load comprising: a measuring device (16) for measuring the alternating voltage output by the device under test (14); a reconstruction device (24) which is designed to reconstruct a phase angle of the alternating voltage; a switching device (20); and a control device which is signal-connected to the reconstruction device (24) and is designed to regulate, via the switching device (20), a load point of the device under test (14) in phase depending on the reconstructed phase angle of the alternating voltage.

Description

[0001] AVL SET GmbH

[0002] Active load for reconstructing a phase angle

[0003] The present invention relates to an active load for reconstructing a phase angle of an alternating voltage output by a test object, as well as a test device with such an active load and a method for testing a power electronic test object with such an active load.

[0004] The present invention is based on the use of active loads for testing power electronics, in particular for testing converters or inverters, or even just their power sections. Active loads essentially replicate the electrical behavior of passive three-phase chokes / inductors or electric motors, or, as a multi-phase current source, allow a load current to be applied to an electrical device under test.

[0005] Multiphase systems are typically three-phase, but can in principle also have other phase numbers. For the sake of readability, the discussion of the invention often refers only to converters or inverters, and not both, although in these cases the other case is always implied. Other well-known synonyms for converters and inverters are converters, inverters, and pulse inverters.

[0006] Tests using active loads aim to validate the electrical and thermal behavior of inverters and / or inverter power sections as early as possible in the development process, by operating at various, mostly steady-state, AC-side load points. These load points can be defined by parameters such as voltage, current, frequency, power factor, and / or the cosine of the phase shift angle between current and voltage (cos(cp)). At a fixed operating point, the phase shift angle <p konstant und definiert bei sinusförmigen Größen über cos(cp) den Leistungsfaktor. Üblicherweise wird der Lastpunkt durch eine Benutzereingabe vorgegeben. AVL SET GmbH

[0007] However, particularly in the early stages of development, some functions of finished inverters are often not yet available. One example is current control. This means that only the voltage can be set, but the phase current cannot be actively regulated. At earlier stages of the development process, an interface for rotor position detection, which can be provided by a resolver or encoder, for example, is also frequently not yet present for an electric machine that will later be operated.

[0008] However, with the current state of the art, the task of testing the converter at different operating points, possibly with missing phase current control and rotor position detection, is only possible to a limited extent:

[0009] Active loads based on the emulation of chokes or other inductors can only absorb reactive and active power, not supply it. Their operating range is therefore limited exclusively to the motor-inductive quadrant of the four operating ranges. The generator-based and capacitive quadrants are thus inaccessible.

[0010] Active loads based on machine emulation, such as permanent magnet synchronous machines, can indeed deliver active power; however, even with these, controlling an operating range with a capacitive load is only possible to a very limited extent. Furthermore, it is necessary that at least a rotor position evaluation already exists in the inverter under test, since the inverter must apply a phase-correct voltage to achieve a desired operating point.

[0011] A further disadvantage of both of the aforementioned active loads is that the parameters of the emulated choke or machine, corresponding to the desired load point (defined by current, voltage, frequency, and power factor), must be calculated manually. While this problem could be circumvented by directly specifying the desired current and frequency to the active load, even in this case, the phase angle of the applied current must first be transmitted to the inverter (AVL SET GmbH) via rotor position emulation. The inverter then applies the desired voltage in phase with the desired power factor.

[0012] In principle, it would be conceivable for the inverter to transmit the phase angle to the active load. However, this solution is also disadvantageous, as it requires an additional real-time interface, which is unnecessary in the finished inverter.

[0013] The object of the present invention is to eliminate, at least partially, the disadvantages described above in a cost-effective and simple manner.

[0014] In particular, one of the aims of the invention is to test a converter that is still under development in a cost-effective and efficient manner.

[0015] Furthermore, it is an object of the present invention to provide an active load in a cost-effective and simple manner, which eliminates the aforementioned disadvantages of the solutions mentioned above.

[0016] Furthermore, it is an object of the invention to provide an active load in a cost-effective and simple manner with which any stationary operating points, defined by a free choice of voltage, current, frequency and power factor within the electrical limits, can be operated, whereby neither a current control in the converter under test nor a separate transmission of the phase angle is required.

[0017] The foregoing problem is solved by an active load with the features of claim 1, a method with the features of claim 13, and a test device with the features of claim 16. Further features and details of the invention will become apparent from the dependent claims, the description, and the drawings. Features and details described in connection with the active load according to the invention naturally also apply in connection with the method and the test device according to the invention, and vice versa, so that the disclosure of the individual aspects of the invention always refers, or can refer, to each other. AVL SET GmbH

[0018] According to the invention, an active load is intended to enable the reconstruction of the phase angle of an alternating voltage output by a device under test (DUT) with at least one DUT switching device. Furthermore, the active load is intended to enable the phase-correct application of a load current. Such an active load is characterized by the following features: The active load comprises a measuring device for measuring the alternating voltage output by the DUT, a reconstruction device configured to reconstruct the phase angle of the alternating voltage, a switching device, and a control device that is in signal communication with the reconstruction device.The control device is designed to determine, among other things, its phase shift angle. <p definierten Lastpunkt des Prüflings in Abhängigkeit des rekonstruierten Phasenwinkels der Wechselspannung über die Schalteinrichtung phasenrichtig einzuregeln und Regelung eines durch unter anderem diesen Phasenwinkel definierten Arbeitspunkts.

[0019] The core concept of an active load according to the invention is that the device under test applies a voltage of any desired frequency and amplitude to the active load. The active load measures this voltage and reconstructs the phase angle from it. Thus, no separate transmission of the phase angle is necessary. With such an active load, the load point can be freely adjusted by parameterizing the active load with the desired current or power and the desired power factor or phase shift angle. <p zwischen Strom und Spannung möglich. Da die aktive Last über eine Stromregelung verfügt und den Phasenwinkel rückermittelt, kann sie den gewünschten Lastpunkt durch Ansteuerung der Schalteinrichtung über die Schalteinrichtung phasenrichtig einregeln.

[0020] An active load is an electronic component or circuit that controls and / or maintains a variable or fixed current or voltage in the circuit, independent of the applied voltage. Unlike passive loads, which merely influence current flow through their resistive, capacitive, or inductive properties, an active load can actively adapt its characteristics to simulate and optimize the load for testing purposes or for controlling circuits. To solve the technical problem underlying the invention, the active load can be electrically and / or signal-wise connected to the device under test (DUT). The DUT is an electronic component, in particular a power electronic component, that has at least one DUT switching device and outputs at least one alternating voltage.The device under test is preferably an electrical transducer, also referred to as a converter, or an inverter, or a power section of a transducer or inverter. The switching device of the device under test is an electrical component or group of electrical components with which an electrical line can be switched, wherein the switching device of the device under test is, in particular, an electrical switch, a transistor, a half-bridge, a full bridge, or a three-phase bridge. The switching device of the device under test switches, in particular, an output voltage of the device under test, i.e., the alternating voltage. An alternating voltage is an electrical voltage whose polarity changes at regular intervals, but whose time-averaged value is generally zero. The waveform of the voltage is irrelevant, but for the purposes of the invention, it should contain a significant fundamental wave that forms the basis for the phase angle to be reconstructed.The alternating voltage can be single-phase or multi-phase, particularly three-phase. The measuring device is, for example, a voltage sensing device that converts the measured voltage from analog to digital and makes it available to the downstream system. Advantageously, for cost reasons, it can comprise a simple comparator circuit that compares the alternating voltage with the DC link voltage of the device under test, since, in the case of switching two-point converters, knowledge of the switching state of the half-bridge is sufficient to perform the phase angle reconstruction. In the case of multi-phase devices under test, the measuring device is preferably configured to measure the alternating voltage emanating from the device under test in each phase. The reconstruction device serves to reconstruct the phase angle of the alternating voltage.The control device serves to regulate an output current of the active load, whereby the output current is preferably selected such that a load point of the device under test is regulated in phase and with the desired amplitude. The control device can, in particular, be a voltage control device and / or a current control device. The control device can include additional components, in particular a current measuring device, the values ​​of which are required for a setpoint / actual value comparison of a controller. If the control device is a voltage control device, a current measuring device is not necessary. The load point AVL SET GmbH is a specific point in the characteristic curve of the device under test, which is occupied due to the system properties of the device under test and the external influences and parameters acting on the device under test.The load point can be defined by several of the parameters voltage, current, frequency, power factor, phase shift angle cp and / or a cosine of the phase shift angle cos(cp) between current and voltage.

[0021] It can be advantageous if, in the case of an active load according to the invention, the device under test is an electrical converter with a multiphase output, in particular a DC / AC converter. The active load is especially suitable for testing electrical converters with a multiphase output. If the device under test is a DC / AC converter, i.e., it has a DC input, the active load can preferably have a DC output with which it can be connected to the device under test. In this way, the power that, for example, is supplied to the active load on the AC side by the device under test can be extracted again on the DC side and made available to the device under test again. This way, a large portion of the power remains in the test setup, while the power supply only has to cover the resulting losses.

[0022] It is advantageous if at least one of the switching devices under test incorporates a half-bridge. A half-bridge consists of two electronic switches, typically transistors such as MOSFETs or IGBTs, and two freewheeling diodes, each arranged antiparallel to the electronic switches. The two electronic switches are usually connected in series, with the junction of the two switches serving as the output. The first electronic switch connects this output to a positive supply voltage, while the second connects the output to a negative supply voltage or ground. The switching device of the active load can also exhibit these characteristics.

[0023] Furthermore, the switching device of the active load, particularly in three-phase and multi-phase applications, can be a two-level inverter, a three-level inverter, or a multi-level inverter. The three-level inverter and the multi-level inverter can consist of several individual cells connected in series, and the multi-level inverter can also consist of several two-level or three-level inverters connected in parallel (suitable for AVL SET GmbH). The achievable accuracy of the phase angle reconstruction increases with the complexity of the switching device of the active load.

[0024] Further advantages are achieved when the alternating voltage is multi-phase, particularly three-phase. In this case, it is preferably provided that the measuring device measures the voltage in each of the phases. Alternatively, if the phase relationship is known, it is also possible for the measuring device to measure the alternating voltage in only one or in fewer than one of the phases.

[0025] In particular, the measuring device may include a comparator. A comparator comprises an electronic circuit that compares two values. The comparator may preferably be configured to output a binary signal, especially with respect to each phase separately.

[0026] Furthermore, it is advantageous if the device under test includes a signal generation device for generating an alternating voltage. The signal generation device can include a PWM signal generator configured to output a pulse-width modulated (PWM) electrical signal. For this purpose, the signal generation device can be configured to perform the following steps: a1) defining a fundamental frequency f and a voltage amplitude U; a2) calculating a time signal of the phase angle y according to y(t) = 2TT * f * t; a3) calculating target voltages for phases of the device under test, in particular according to

[0027] Uu, set = t / *cos(Y(t)), Uv, set = t / *cos(Y(t)- 2TT / 3) and Uw, set = t / *cos(Y(t)- 4TT / 3); and a4) Calculate control signals for the phases. a5) Generate the AC voltage by switching the test object's switching devices with the control signals calculated in step a4.

[0028] The optional feature in step a3) is intended for a three-phase AC voltage with phases U, V, W. The control signal can generally be a pulse-width modulated signal or a signal for pulse-width modulation, preferably a PWM measurement signal. Step a4) can be implemented by using a suitable AVL SET GmbH

[0029] Modulation methods, such as sine-triangle modulation, are used, in which the target voltage is compared with a triangular reference signal and the control signals for the power switches of the device under test are calculated accordingly.

[0030] Further advantages are achieved if, in a further particular embodiment of the invention, the reconstruction device is configured to reconstruct the phase angle of the AC voltage via the following steps: b1) measuring phase voltages of the AC voltage, preferably by determining the values ​​of the phase voltages as a function of the voltage value of the AC voltage relative to the DC voltage by a comparator and thus a switch position of the switching device of the device under test; b2) calculating two transformed phase voltages by projecting the binary signals using Clarke transformation; b3) normalizing the transformed phase voltages, in particular to values ​​from -1 to +1; b4) reconstructing a PLL phase angle from the normalized transformed phase voltages using a phase-locked loop; and b5) adjusting a load point of the device under test as a function of the reconstructed PLL phase angle.

[0031] The comparator can, in particular, be the comparator according to claim 5. If the alternating voltage is single-phase, the expression "the phases" is to be understood as "the one phase". A phase-locked loop (PLL) is a control loop with a controlled oscillator whose phase is tracked to that of an external signal. In phase-locked loops, the dependence of the manipulated variable on the control deviation—the phase shift—is periodic. The control can therefore "lock" on various relative phase positions that differ by whole multiples of 2TT. In the locked state, the frequency of the oscillator is that of the reference signal. With a suitable implementation, the phase angle of the oscillator is also that of the reference signal. AVL SET GmbH

[0032] Steps a1) to a5) are performed by the test subject. Steps b1) to b5) are performed by the active load.

[0033] Step b1) may preferably also include the step: b1.1) Generating a binary signal for each of the phases, in particular by determining the values ​​of the binary signal as a function of the voltage value of the AC voltage with respect to the DC voltage by a comparator and thus the switch position of the switching device under test.

[0034] The Clarke transform is used to convert multiphase quantities into a simpler two-axis coordinate system with axes a and β that are 90° apart, thus representing the sine and cosine input signals required for the phase-locked loop. The Clarke transform describes one of several possible space vector representations. The fundamental frequency is the lowest frequency of an alternating current generated by the load. The switching frequency is the frequency at which the switching device under test switches the device under test.

[0035] It is particularly advantageous if the reconstruction device is also configured to verify the validity of the reconstructed phase angle, especially by analyzing switching signals from the device under test. This validity check can eliminate certain errors and overall increases the accuracy of the active load's operation.

[0036] Further advantages are achieved if the active load also has an input device for receiving user input, where the user input includes an expected fundamental frequency. With at least an approximately correct input of the fundamental frequency, the reconstruction device can be optimally initialized, and the active load can approach the load points of the test specimen more quickly, which can shorten test durations.

[0037] Furthermore, it is advantageous if the reconstruction device is configured to automatically determine the fundamental frequency of the test specimen. This automatic determination can be provided as an alternative or additional measure to the previously described embodiment of the invention. Automatic determination of the fundamental frequency can lead to faster testing if the fundamental frequency of the test specimen is unknown. AVL SET GmbH

[0038] A further object of the present invention is a method for testing a power electronic device under test with a device switching device configured to output a multiphase alternating voltage, comprising the steps: a) connecting an active load according to any one of claims 1 to 11 to the device under test; a) defining a fundamental frequency f and a voltage amplitude U; a) calculating a time signal of the phase angle y, in particular according to Y(t) = 2 TT * f * t; a) calculating target voltages for each of the phases of the device under test, in particular for three phases U, V and W according to

[0039] Uu, set = t / *cos(Y(t)), Uv, set = t / *cos(Y(t)- 2TT / 3) and Uw, set = t / *cos(Y(t)- 4TT / 3); a4) Calculating control signals for the phases; a5) Generating the AC voltage by switching the test object's switching devices with the control signals calculated in step a4; b1) Measuring phase voltages of the AC voltage for each of the phases, preferably by determining the values ​​of the phase voltages as a function of the voltage value of the AC voltage with respect to a DC intermediate circuit voltage by a comparator and thus a switch position of the test object's switching device; b2) Calculating two transformed phase voltages by projecting the binary signals using Clarke transformation; b3) Normalizing the transformed phase voltages, in particular to values ​​from -1 to +1; b4) Reconstructing a PLL phase angle from the normalized transformed phase voltages using a phase-locked loop;and b5) Adjusting a load point of the test specimen depending on the reconstructed PLL phase angle. AVL SET GmbH;

[0040] In this procedure, the device under test is controlled via the output of the active load. Accordingly, one output of the device under test is connected to an input of the active load, and another output of the active load is connected to an input of the device under test.

[0041] The method may preferably include the further step: b1 .1 ) Normalizing the phase voltages of the alternating voltage, wherein the phase voltages in the subsequent method step are the normalized phase voltages.

[0042] Preferably, the method further comprises the step: b2.1) filtering the transformed phase voltages with a filter frequency that lies, in particular, between the fundamental frequency and a switching frequency of the load. In this filtering, the phase error introduced by such filtering is known to a person skilled in the art or at least derivable. Accordingly, the phase error of the filtered transformed phase voltages can be corrected as a function of the filtering in step b2.1).

[0043] Another object of the present invention is a test device for testing a power electronic test object with an active load according to one of claims 1 to 11.

[0044] In a particular embodiment of the invention, the term "comprise" and / or the term "have" can also mean "to be".

[0045] Further advantages, features, and details of the invention will become apparent from the following description, in which exemplary embodiments of the invention are described in detail with reference to the drawings. The drawings schematically show:

[0046] Fig. 1 shows a test device with an active load according to a particular embodiment of the invention;

[0047] Fig. 2 shows a time signal of the reference phase angle of the test object to be reconstructed;

[0048] Fig. 3 Target voltages of three phases U, V and W, based on the reference phase angle from Fig. 2; AVL SET GmbH

[0049] Fig. 4 shows the target voltage UU.SET and a reference signal of phase U, for generating a control signal, using sine-triangle modulation;

[0050] Fig. 5 shows an alternating voltage of phase U generated from the signals of Fig. 4;

[0051] Fig. 6 shows a binary signal generated from the alternating voltage of Fig. 5;

[0052] Fig. 7 two transformed phase voltages after a Clarke transformation of the alternating voltages of three phases U, V and W;

[0053] Fig. 8 shows the transformed phase voltages of Fig. 7 after filtering;

[0054] Fig. 9 shows the filtered transformed phase voltages of Fig. 8 after normalization;

[0055] Fig. 10 shows the phase angles calculated from the normalized filtered transformed phase voltages of Fig. 9;

[0056] Fig. 11 Course of correction of a phase error; and

[0057] Fig. 12 shows a flowchart for a method for reconstructing the

[0058] Phase angle.

[0059] Figure 1 schematically shows a test setup 12 for testing a power electronic device under test 14 with an active load 10. The active load is configured to reconstruct a phase angle. The device under test 14 is a DC / AC converter, also referred to as an inverter 14a, and thus outputs an alternating voltage. Its output is connected to the active load 10. As a DC / AC converter, the device under test 14 has several switching devices (not explicitly shown) for regulating the alternating voltage, which are not shown in detail. The device under test 14 is supplied with voltage via a power supply 13 and a DC link 21. AVL SET GmbH

[0060] The active load 10 includes a measuring device 16 for measuring the alternating voltage output by the device under test 14 in the three phases U, V, W of the connecting line 17. The measuring device 16 is a voltage measuring device, preferably with a comparator and / or can alternatively also comprise a voltage detection device with an analog-to-digital converter. In this embodiment of the invention, the measuring device 16 measures whether the voltage at the output of the device under test 14 is above or below a reference value, which preferably corresponds to half the DC link voltage of the device under test 14. The voltage measurement is performed for each phase of the connecting line 17. Accordingly, the measuring device 16 only measures whether the output voltage of the device under test 14 is "above" or "below" at any given time.

[0061] The output of the device under test 14 is connected via the measuring device 16 and an inductor 18 to the input of a switching device 20, which is configured as an AC / DC converter. The DC terminal of the switching device 20 is connected to the DC terminal of the device under test 14 in order to circulate the power within the test apparatus 12.

[0062] Furthermore, the active load 10 has a control device 22 with a reconstruction device 24 for reconstructing a phase angle and a drive device 26. The reconstruction device 24 is configured to calculate an uncorrected reconstructed phase angle and to correct the phase angle of the test specimen 14.

[0063] To control and / or regulate the test specimen, the reconstruction device 24 is connected to a control device 26. The reconstruction device 24 is configured to reconstruct and / or calculate a corrected phase angle ycomp. In particular, the reconstruction device 24 is configured to reconstruct a corrected phase angle ycomp from transformed phase voltages Ua, Uß.

[0064] During operation, the control unit 26 sends a control signal to the switching unit 20 based on the corrected phase angle ycomp, which in turn controls the device under test 14. The control unit 26 uses current control methods as its current control device, comparing one or more current setpoints with one or more measured current values ​​obtained from the current measuring device 19. The current setpoint(s) are calculated based on the desired load point and the reconstructed phase angle.

[0065] Here, l corresponds to the phase current amplitude desired by the user. <p dem vom Benutzer gewünschten Phasenverschiebungswinkel und Ycomp(t) dem Zeitverlauf des rekonstruierten Phasenwinkels der Spannung des Prüflings. Sollen alternativ andere Größen wie etwa Leistung und Leistungsfaktor vorgegeben werden, können gemäß allgemein bekanntem Fachwissen die Parameter l und <p berechnet werden.

[0066] The inductor 18 acts as a current control loop in the control engineering sense. The control device 26 calculates an output voltage for the switching device 20, which causes the desired current flow through the inductor 18 and thus into the device under test 14. Various control devices can be used as the control device 26, such as a PI controller, a state controller, or a deadbeat controller. The control device 26 can also be a voltage control device.

[0067] The method for phase angle recovery with an active load 10 according to the invention is described in detail with reference to Figures 2 to 11. It starts with the test situation shown in Figure 1, in which a DC / AC converter under test generates a three-phase alternating voltage system. Figures 2 to 5 and steps a1 to a5 relate to the generation of an alternating voltage by the device under test 14 using pulse width modulation (PWM). Figures 6 to 11 and the related steps b1 to b5 relate to phase angle reconstruction (PR) and the correction of a phase error of the PLL phase angle. In a first step a1, the fundamental frequency f and the voltage amplitude U of the alternating voltage to be generated by the device under test 14 are initially determined. Subsequently, in a second step a2, the AVL SET GmbH

[0068] For alternating current, a phase angle time signal is calculated internally from the fundamental frequency f of the device under test. The fundamental frequency f corresponds to a predefined value, which can be, for example, a manual input from a user or an automated input from a test cycle. The predefined phase angle time signal is calculated as follows: y(t) = f 2TT ■ f ■ t

[0069] The signal of the specified phase angle with a period of 1 ms or a frequency f of 1 kHz is shown in Fig. 2.

[0070] From the specified time-dependent phase angle y(t) and a voltage amplitude U selected by the user, the target voltages USET of the three phases U, V and W are calculated in a third step a3, according to:

[0071] UU,SET = U ■ cos (y(t))

[0072] _ 2TT

[0073] UV, SET = U ■ cos (y(t) — )

[0074] _ 4TT

[0075] Uw, SET = U ■ cos (y(t) — )

[0076] In this example, the calculated target voltages of the three phases are each phase-shifted by 2TT / 3 relative to each other and are shown in Figure 3.

[0077] In a fourth step, to calculate the control signals Uu and OUT for the phases, the target voltages referenced to half the DC link voltage are compared with a triangular carrier signal (sine-triangle modulation). If the referenced target voltage is above the carrier signal, the half-bridge of the device under test 14 switches the positive DC link voltage potential; if it is below, it switches the negative DC link voltage potential. For clarity, Figure 4 shows only the target voltage signal Uu and OUT, and the higher-frequency carrier signal Uref for phase U. The signals for phases V and W are equivalent. AVL SET GmbH

[0078] In a fifth step a5, the comparison signal calculated in step a4 is applied to one or more test object switching devices of the test object 14, whereupon the latter generates the alternating voltage or the three-phase voltage system from Figure 5.

[0079] For the reconstruction of the phase angle, the AC voltage or the three-phase voltage system from Figure 5 output by the device under test 14 must be detected by the reconstruction device 24 of the active load 10. This is preferably done by measuring the phase voltages of the device under test 14 with a measuring device 16, which is configured as a comparator, wherein the reference voltage of the comparator is half the DC link voltage. In a first step of the phase reconstruction b1, a binary signal llu is therefore generated, which is either 0 when the corresponding half-bridge of the converter 14a switches the negative DC link potential and 1 when it switches the positive DC link potential. Alternatively, a continuous-value or higher-level discretized measurement can be performed by means of a conventional voltage measurement, for example by means of commercially available analog-to-digital converters, and this signal can be further processed, i.e., the AC voltage orThe rotating voltage system from Figure 5 is present as a signal.

[0080] The binary signal Uu, binary is shown in Figure 6. In a second step of the phase reconstruction b2, two transformed phase voltages Ua and Uß are calculated and / or generated from the binary signals in Figure 6 or the signals in Figure 5 using a Clarke transform. The Clarke transform converts the three phase voltages Uu, binary, Uv, binary, and Uw, binary into two equivalent transformed phase voltages Ua and Uß, according to:

[0081] The transformed phase voltages generated in this way from three phases to two mutually orthogonally equivalent phases are shown in Fig. 7.

[0082] The transformed phase voltages are then, in an optional

[0083] Step b2.1 of the phase reconstruction filtered to eliminate the influence of harmonics by AVL SET GmbH

[0084] To reduce the switching operations of the inverter 14a, the filter frequency is preferably chosen between the expected fundamental frequency f of the voltage (see above) and the switching frequency of the inverter 14a in order to preserve as much of the fundamental information as possible while simultaneously suppressing the interfering switching. Filtering inevitably leads to errors in both amplitude and phase. Both errors are eliminated, compensated, and / or corrected in the following steps. The filtered signals Ua, f and Uß, f are shown in Figure 8. They now exhibit a strong resemblance to a sine wave and a cosine wave, which is advantageous for phase reconstruction. They also contain (damped) harmonics caused by the switching of the device under test 14. Figure 8 also shows the signal of a hypotenuse U. hypot + Uß fn is shown, which is used for normalization is calculated.

[0085] In phase reconstruction, the signal amplitude is generally irrelevant. The signal amplitude is influenced at this point by the set voltage amplitude U, the DC link voltage, the filter type, and the filtering coefficients from the previous step. For the following steps, in a third step of phase reconstruction (b3), the two filtered phase voltages Ua, f and Uß, f are normalized to Ua, f, n and Uß, f, . n so that they can serve as input signals for the subsequent phase-locked loop (PLL). Due to normalization, the signals always lie within the range of -1 to +1. If the optional step b2.1 is omitted, the two unfiltered phase voltages Ua and Uß are normalized to Ua, n and Uß, respectively. nThe same applies if a continuous-value or higher-level discretized voltage measurement is used instead of a comparator-based voltage measurement. The subsequent procedure is otherwise identical in every case. For the sake of readability, all options will not be listed repeatedly below.

[0086] Since the signals Ua, f and Uß, f are orthogonal to each other, they can be normalized over the hypotenuse to: AVL SET GmbH

[0087] Figure 9 shows the filtered transformed phase voltages from Fig. 8 after such normalization.

[0088] In signal processing, it is known that a phase can be recovered from (distorted) sine / cosine signals using a phase-locked loop (PLL) or an angle-tracking observer (ATO). Internally, this involves observing the angle y of the phase-locked loop. PLLThe calculated angle is then fed back to the input, where the error relative to the input signal is calculated and adjusted to zero. In this way, the internally observed angle becomes the reconstructed angle, which is used as the output signal. The observed fundamental frequency of the phase-locked loop, fpn, is also calculated and used as an output signal.

[0089] The filter from step b2.1 of the phase reconstruction introduces a phase error due to its operating principle. Since the filter topology and the fundamental frequency of the angle signal are known thanks to the PLL, the frequency-dependent phase error of the filter is also known and can be compensated for, for example, using a lookup table or an analytical equation. The error between the specified phase angle YSET and the PLL phase angle YPLL of the phase-locked loop is the difference between the curves in Fig. 10.

[0090] To correct the error, the PLL phase angle YPLL is corrected to a corrected phase angle Ycomp. A result of the phase error correction performed in a fifth step of the phase reconstruction b5 is shown in Figure 11.

[0091] The target angle of the phase angle y SET deviates from the determined PLL phase angle y PLL ab. Through error correction, in particular with the help of a look-up table or AVL SET GmbH an analytical equation, this error is corrected so that the compensated phase angle curve y comp their progression from the determined phase angle to the target angle of the phase angle y SET The adjustment process takes approximately 1.5 periods or 1.5 ms in the example shown. Various mathematical functions can be used for compensation, which reduce the difference in the curves, particularly by continuously reducing it.

[0092] Figure 12 shows a flowchart for a method for generating an alternating voltage and reconstructing the phase angle, summarizing the steps of Figures 2 to 11. The steps and the quantities calculated and passed in each step are also indicated. It should be noted that steps b1.1 and b2.1 are optional and do not necessarily have to be performed.

[0093] The preceding explanations of the embodiments describe the present invention exclusively by way of examples.

[0094] AVL SET GmbH

[0095] Reference symbol list

[0096] 10 active load

[0097] 12 Test device

[0098] 13 Power supply

[0099] 14 examinees

[0100] 14a Inverter

[0101] 16 Measuring device

[0102] 17 Connecting line

[0103] 18 Inductance

[0104] 19 Current measuring device

[0105] 20 Switching device

[0106] 21 DC link

[0107] 22 Control unit

[0108] 24 Reconstruction facility

[0109] 26 Control unit

[0110] YSET target angle of the phase angle f fundamental frequency u voltage amplitude

[0111] Uli, set target voltage of phase U

[0112] Uli, out control signal of phase U, phase voltage

[0113] Uu, binary binary signal of phase U

[0114] Ua, Uß transformed phase voltages

[0115] Ua, f, Uß, f filtered transformed phase voltages

[0116] Ua, f, n, Uß, f, n normalized filtered transformed phase voltages

[0117] YPLL determined phase angle

[0118] Ycomp compensated phase angle fPLL determined frequency P phase shift angle

Claims

AVL SET GmbH Patent claims 1. Active load (10) for reconstructing a phase angle of an alternating voltage output by a device under test (14) with at least one switching device of the device under test, comprising a measuring device (16) for measuring the alternating voltage output by the device under test (14), a reconstruction device (24) configured to reconstruct a phase angle of the alternating voltage, a switching device (20), and a control device (26) which is in signal communication with the reconstruction device (24) and is configured to adjust a load point of the device under test (14) in phase as a function of the reconstructed phase angle of the alternating voltage via the switching device (20).

2. Active load (10) according to claim 1, wherein the test object (14) is an electrical converter (14a) with a multiphase output, in particular a DC / AC converter.

3. Active load (10) according to one of the preceding claims, wherein the at least one test specimen switching device has a half-bridge.

4. Active load (10) according to one of the preceding claims, wherein the alternating voltage is a multi-phase alternating voltage, in particular a three-phase alternating voltage.

5. Active load (10) according to one of the preceding claims, wherein the measuring device (16) comprises a comparator. AVL SET GmbH 6. Active load (10) according to one of the preceding claims, wherein the reconstruction device (24) is configured to reconstruct the phase angle of the AC voltage via the following steps: b1) Measuring phase voltages of the AC voltage, preferably by determining the values ​​of the phase voltages as a function of the voltage value of the AC voltage with respect to a DC intermediate circuit voltage by a comparator and thus the switch position of the switching device under test; b2) Calculating two transformed phase voltages (u a a) by projecting the phase voltages (Uu, out, Uv, out, Uw, out) using Clarke transformation. b3) Normalizing the transformed phase voltages (Ua, Uß), in particular to values ​​from -1 to +1; b4) Reconstructing a PLL phase angle (YPLL) from the normalized transformed phase voltages (Ua, t, n, Uß, t, n) with a phase-locked loop; and b5) adjusting a load point of the test specimen (14) as a function of the reconstructed PLL phase angle.

7. Active load (10) according to claim 6, further comprising the step: b1.1 ) normalizing the phase voltages of the alternating voltage, wherein the phase voltages (Uu. out, Uv, out, Uw, out) in the subsequent process step are the normalized phase voltages (Uu, binary, Uv, binary, Uw, binary).

8. Active load (10) according to claim 6 or 7, further comprising the step: b2.1 ) filtering the transformed phase voltages (u a , Uß) with a filter frequency which lies in particular between the fundamental frequency (f) and a switching frequency of the load. AVL SET GmbH 9. Active load (10) according to any of the preceding claims, further comprising the step: b2.2) Correcting a phase error of the PLL phase angle.

10. Active load (10) according to one of the preceding claims, wherein the reconstruction device (24) is further configured to check whether the reconstructed phase angle is valid, in particular by analyzing switching signals of the device under test (14).

11. Active load (10) according to one of the preceding claims, further comprising an input device for receiving user input, wherein the user input comprises an expected fundamental frequency.

12. Active load (10) according to one of the preceding claims, wherein the reconstruction device (24) is configured to automatically determine a fundamental frequency of the test specimen (14).

13. Method for testing a power electronic device under test (14) with a device switching device configured to output a multiphase alternating voltage, comprising the steps: a) connecting an active load (10) according to one of the preceding claims to the device under test (14); a) defining a fundamental frequency f and a voltage amplitude U; a) calculating a time signal of the phase angle y, in particular according to Y(t) = 2TT * f * t; a) calculating target voltages for each of the phases of the device under test (14), in particular according to Uu, set = t / *cos(Y(t)), Uv, set = t / *cos(Y(t)- 2TT / 3 and Uw, set = t / *cos(Y(t)- 4TT / 3; a4) Calculating control signals for the phases; AVL SET GmbH a5) Generating the AC voltage by switching the test object's switching devices with the control signals calculated in step a4; b1) Measuring phase voltages of the AC voltage, preferably by determining the phase voltage values ​​as a function of the AC voltage value relative to a DC intermediate circuit voltage using a comparator and thus the switch position of the test object's switching device; b2) Calculating two transformed phase voltages (u a , Uß) by projecting the phase voltages (Uu. out, Uv, out, Uw, out) using Clarke transformation; b3) normalizing the filtered transformed phase voltages (Ua, t, Uß, t), in particular to values ​​from -1 to +1; b4) reconstructing a PLL phase angle (YPLL) from the normalized filtered transformed phase voltages (Ua, t, n, Uß, t, n) with a phase-locked loop; and b5) adjusting a load point of the test specimen (14) as a function of the reconstructed PLL phase angle.

14. Method according to claim 13, further comprising the step: b1 .1 ) Normalizing the phase voltages of the alternating voltage wherein the phase voltages (Uu. out, Uv, out, Uw, out) in the subsequent method step are the normalized phase voltages (Uu, binary, Uv, binary, Uw, binary).

15. Method according to claim 13 or 14, further comprising the steps: b2.1) Filtering the transformed phase voltages (u a , Uß) with a filter frequency which lies in particular between the fundamental frequency (f) and a switching frequency of the load and AVL SET GmbH b2.2) Correcting a phase error of the filtered transformed phase voltages (u a , Uß) depending on the filtering in step b2.1 ).

16. Test device (12) for testing a power electronic test object (14) with an active load (10) according to one of claims 1 to 12.

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