Method and circuit for measuring properties of an alternating primary voltage through a galvanic isolation barrier

Abstract

The invention relates to a method for measuring properties of an alternating primary voltage (PRV) with a primary frequency (PRf) at a first side of a galvanic isolation barrier (GAB) at a second side of the latter. It includes generating a primary signal (PRS) from the primary voltage (PRV) with at least partial rectification, and generating, using an operational amplifier (25) of a modulator (20), a pulse width modulated signal (PWMS) from the primary signal (PRS) using a carrier signal (CAS). A duty cycle ratio of the pulse width modulated signal (PWMS) varies in accordance with a time-varying voltage value (PRS(t)) of the primary signal (PRS). An optocoupler (44) transmits the pulse width modulated signal (PWMS) to the second side. The method includes a zero cross signal generation step (S60) and / or an amplitude signal generation step (S70). For reliability and cost-efficiency, a pulse width modulation switching frequency (PWMf) of the pulse width modulated signal (PWMS) exceeds 10 times the primary frequency (PRf). The modulator (20) uses an oscillating circuit for generating the carrier signal (CAS). The operational amplifier (25) forms part of the oscillating circuit. The invention further relates to an electric circuit (1, 1A, 100) and a control unit (200) for a refrigerant compressor (300).

Description

[0001] Method and circuit for measuring properties of an alternating primary voltage through a galvanic isolation barrier

[0002] The present invention relates to a method for measuring, at a second side of a galvanic isolation barrier, properties of an alternating primary voltage, which is provided at a first side of the galvanic isolation barrier.

[0003] An electric power consumer like a refrigerant compressor, in more detail an electric motor thereof, can be supplied with electric power by at least one alternating primary voltage. The electric power consumers can be damaged when an amplitude of the primary voltage becomes too high, e.g. due to disturbances in a power grid. It is desired to detect when the amplitude of the primary voltage exceeds a critical maximum and, when this occurs, stop supplying the primary voltage to the electric power consumer to shut the latter off.

[0004] Similarly, the electric power consumer may not operate properly or even become damaged if it is running while the amplitude of the primary voltage becomes too low. Accordingly, it is desired to detect when the amplitude of the primary voltage becomes lower than a critical minimum and, when this occurs, stop supplying the primary voltage to the electric power consumer to shut the latter off.

[0005] The supply of the primary voltage to the electric power consumer can be controlled by at least one relay. By switching the at least one relay, the suppl of the primary voltage to the electric power consumer can be started and stopped.

[0006] However, when the at least one relay is switched while a time-varying voltage value of the primary voltage has a high absolute value, for example while the tinevarying voltage is just at its positive or negative peak value, there is an increased risk that the electric power consumer and / or the relay itself are damaged by switching of the at least one relay. Further, there is a risk of generating disturbances in the power grid by switching of the at least one delay at arbitrary times.

[0007] It has been proposed to switch the at least one relay at zero cross times of the primary voltage only, i.e. just when the primary voltage crosses 0 V. This decreases the risks mentioned above.

[0008] A conventional electric power consumer, especially a conventional control unit for controlling a refrigerant compressor, often includes a transformer adapted to a frequency of the primary voltage (referred to as a primary frequency). The primary frequency is typically 50 Hz or 60 Hz. The transformer provides galvanic isolation between the power grid and inner parts of the electric power consumer, e.g. a control unit for controlling operation of the motor of the refrigerant compressor.

[0009] Such a conventional grid-frequency transformer transforms the primary voltage to a consumer-side voltage. By nature, an amplitude of the consumer-side voltage follows an amplitude of the primary voltage power by a factor. As the transformer does not change the frequency, the consumer-side voltage (after having passed the transformer) is still alternating with the primary frequency (e.g. with the comparatively low 50 Hz or 60 Hz). On other words, the consumer-side voltage has the same frequency as the primary voltage, i.e. the primary frequency.

[0010] Therefore, the amplitude and the zero-crossings of the primary voltage can be detected directly based upon the consumer-side voltage. The consumer-side voltage can be measured easily, and the zero cross times of the consumer-side voltage can be determined. Further, it is simple to measure the amplitude of the consumer-side voltage amplitude (i.e. at the second side of the galvanic isolation barrier). Accordingly, it is not necessary for a controller for the electric power consumer to measure properties of the alternating primary voltage, especially its amplitude and / or its zero cross times, directly at the primary voltage, i.e. "through the galvanic isolation barrier at a grid-side of the transformer.

[0011] However, newer electrical power devices often employ switch mode power supplies (SPMS) instead of conventional grid-frequency transformers. In such a switch mode power supply, at first, the primary voltage is converted to a high frequency signal. A secondary side is stabilized to a fixed direct current (DC) voltage. Therefore, neither the amplitude nor the zero crossings of the primary voltage can be detected based on measurements at the secondary side of the SMPS.

[0012] The problem underlying the invention is to provide a particularly simple and costefficient solution for measuring properties of an alternating primary voltage through a galvanic isolation barrier.

[0013] This problem is solved by a method with the features according to claim 1.

[0014] It is a method for measuring, at a second side of a galvanic isolation barrier, properties of an alternating primary voltage, which is provided at a first side of the galvanic isolation barrier.

[0015] The method includes the following steps: an adaptation step for generating a primary signal from the primary voltage, wherein the adaption step includes at least partially rectifying the primary voltage; a modulation step for generating a pulse width modulated signal based on a carrier signal, wherein the modulation step includes modulating the primary signal with the carrier signal, wherein a typical characteristic (e.g. a duty cycle ratio) of the pulse width modulated signal varies in accordance with a time-varying voltage value of the primary signal; a transmission step for generating a transmitted signal at the second side of the galvanic isolation barrier from the pulse width modulated signal, wherein the transmission step includes using an optocoupler for transmitting the pulse width modulated signal from the first side of the galvanic isolation barrier to the second side of the galvanic isolation barrier; and at least one of the following:

[0016] - a zero cross signal generation step including generating a zero cross signal from the transmitted signal with an envelope detector; and

[0017] - an amplitude signal generation step including generating an amplitude signal from the transmitted signal with an integrator.

[0018] The method allows to pass information about the alternating primary voltage through the galvanic isolation barrier, especially information about a zero cross timing of the primary voltage and / or about an amplitude of the primary voltage.

[0019] The zero cross times of the primary voltage can be the times when the primary voltage crosses a certain voltage value, such as 0 V, e.g. with respect to a (first) reference potential, for example, e.g. a (first) neutral point potential and / or a (first) ground potential at the first side of the galvanic isolation barrier.

[0020] The present invention is cost-efficient, simple, and reliable. Only very few components are needed. Especially, the invention can operate with only one single unidirectional "transmission channel" through the galvanic isolation barrier, namely the optocoupler.

[0021] The pulse width modulated signal controls ("drives") the optocoupler. The working principle is to generate the pulse width modulated signal that carries the information to be passed through the galvanic isolation barrier. The modulation is performed such that the pulse width modulated signal

[0022] - varies in a frequency range and / or

[0023] - has an amplitude, typical voltage values and / or a shape adapted to the optocoupler's transfer characteristics. This allows for particularly efficient and reliable transfer of the relevant information (about the primary voltage) through the galvanic isolation barrier by the optocoupler.

[0024] The transmitted signal at the second side of the galvanic isolation barrier is pulse width modulated in accordance with the pulse width modulated signal at the first side of the galvanic isolation barrier. In particular, a typical characteristic (e.g. a duty cycle ratio such as a pulse-time fraction) of the transmitted signal can correspond to the typical characteristic (e.g. the duty cycle ratio such as the pulse-time fraction) of the pulse width modulated signal and hence varies in accordance with the time-varying voltage value of the primary signal.

[0025] The zero cross signal includes information about the zero cross timing of the primary voltage. The zero cross signal may include distinctive signal features (e.g. sharp increases and / or sharp decreases) that indicate zero crosses of the primary voltage. For example, some type of zero crosses of the primary voltage (e.g. when the primary voltage changes from negative to positive) may lead to a sharp increase of the zero crosses signal and / or some (other) kind of zero crosses of the primary voltage may lead to a sharp decrease of the zero cross signal (e.g. when the primary voltage changes from positive to negative). The distinctive signal features may be (at least substantially) coincident with the corresponding zero crosses, e.g. occurring with a time difference of less than 1 ms about an actual time of the zero cross, maybe of less than 0,5 ms or even of less than 0,2 ms. In one example, the signal features follow the corresponding actual zero cross times with a time delay of in the range of 0,01 ms to 0,2 ms.

[0026] The amplitude signal includes information about the amplitude of the primary voltage. For example, an amplitude of the amplitude signal may depend on the amplitude of the primary voltage. Especially, the amplitude of the amplitude signal can be (at least substantially) proportional to the amplitude of the primary voltage. In one embodiment, the primary voltage has a primary frequency, wherein a pulse width modulation switching frequency of the pulse width modulated signal exceeds 10 times the primary frequency. Often, the primary frequency is comparatively low, e.g. in range from 10 Hz to 70 Hz (e.g. 16,7 Hz, 50 Hz, or 60 Hz). Accordingly, the time-varying voltage value of the primary signal changes comparatively slowly over time. The transfer characteristics of common optocouplers that are easily available and cost-efficient are not particularly good for precisely forwarding the primary signal (or even the primary voltage). With the present invention, the good transfer characteristics of the optocoupler for the pulse width modulated signal are exploited in a simple, reliable, and cost-efficient manner. This ensures good forwarding of the relevant information about the primary voltage through the galvanic isolation barrier. The relevant information, such as about the zero cross timing and / or the amplitude can be extracted easily from the transmitted signal.

[0027] The primary voltage can have a sinusoidal shape.

[0028] Generating the primary signal from the primary voltage may include half-wave rectification. Moreover, generating the primary signal from the primary voltage can include full-wave rectification. The primary signal can include waves corresponding (at least substantially) to positive half-waves and / or waves corresponding (at least substantially) to negative half-waves of the primary voltage.

[0029] The adaption step may include adding a voltage offset to the primary voltage and / or to the primary signal. This can, for example, reduce a time delay between the actual time of the zero cross of the primary signal and the corresponding indication in the zero cross signal. The offset can be a reason for the primary signal wave corresponding to the half-waves of the primary voltage only substantially. The carrier signal may include sawtooth shapes (at least in some time sections).

[0030] A typical characteristic of the carrier signal may vary depending on the time-varying voltage value of the primary signal. The typical characteristic of the carrier signal may include one of, several of, or all of the following:

[0031] - A cycle length of the respective single sawtooth (e.g. measured in ps or ms).

[0032] - A duration of a falling edge of the respective single sawtooth (e.g. measured in ps or ms).

[0033] - A duration of a rising edge of the respective single sawtooth (e.g. measured in ps or ms).

[0034] - A ratio between the duration of the falling edge and cycle length of the respective single sawtooth (e.g. measured in % of the cycle length).

[0035] The pulse width modulated signal may be a pulse-pause signal. Such a modulation allows for good efficiency and proper transmission of the relevant information by the optocoupler.

[0036] The pulse width modulated signal can be cycled. Each cycle may include a pulse and a pause.

[0037] The pulse width modulated signal can be a substantially square wave signal (during on-time intervals).

[0038] The generation of the pulse width modulated signal is influenced by the primary signal (and hence by the primary voltage). Especially, the pulse width modulated signal reflects the information about the primary voltage that shall be passed through the galvanic isolation barrier. For example, a typical characteristic of the pulse width modulated signal may vary depending on the time-varying voltage value of the primary signal. It may be hence indicative of the time-varying voltage value of the primary signal. Hence, it is indicative of the time-varying voltage value of the primary voltage as well (at least during on-time intervals of the pulse width modulated signal).

[0039] For example, the typical characteristic of the pulse width modulated signal may include one of, several of, or all of the following:

[0040] - A cycle length of a respective single cycle of the pulse width modulated signal (e.g. measured in ps or ms). It may correspond to the cycle length of the corresponding cycle of the carrier signal.

[0041] - A pulse width over the respective single cycle of the pulse width modulated signal (e.g. measured in ps or ms). It may correspond to one of

[0042] • the duration of the falling edge and

[0043] • the duration of rising edge of the respective single sawtooth (e.g. measured in ps or ms) of the corresponding cycle of the carrier signal.

[0044] - A pause width over the respective single cycle of the pulse width modulated signal (e.g. measured in ps or ms, for example the respective time between two subsequent pulses). It may correspond to the other one of

[0045] • the duration of the falling edge and

[0046] • the duration of rising edge of the respective single sawtooth (e.g. measured in ps or ms) of the corresponding cycle of the carrier signal.

[0047] - A pulse-time fraction (e.g. measured in % of the cycle length of the respective single cycle of the pulse width modulated signal). It may correspond to the ratio between the duration of the falling edge and the cycle length of the corresponding single sawtooth in the carrier signal.

[0048] For example, the "duty cycle ratio" of the pulse width modulated signal mentioned above can include or consist of the pulse-time fraction. Further, said "duty cycle ratio" may include or consist of a ratio between the pulse width and the pause width of the respective single cycle of the pulse width modulated signal. According to an aspect, the "duty cycle ratio" can include or consist of the pulse width of the individual pulse as such; it can be understood as ratio compared to a fixed time period, e.g. 0,01 ms, in this specific context).

[0049] Correspondingly, a typical characteristic of the transmitted signal may vary depending on the time-varying voltage value of the primary signal. The different possibilities described with respect to the typical characteristic of the pulse width modulated signal apply accordingly.

[0050] In one embodiment, a maximum pulse width (i.e. a maximum value of the pulse width) and / or a maximum pulse-time fraction (i.e. a maximum value the pulsetime fraction) may relate to a maximum voltage and / or an amplitude of the primary signal (and hence of a maximum voltage and / or the amplitude of the primary voltage).

[0051] According to one aspect, the modulation step can include generating the pulse width modulated signal based on (at least) positive half-waves and / or (at least on) negative half-waves of the primary voltage (e.g. depending on whether the adaption step includes half-wave rectification or full-wave rectification).

[0052] In one embodiment, an operational amplifier is used for modulating the primary signal with the carrier signal. Operational amplifiers are easily available and costefficient solution for this functionality. Additionally or alternatively, the operational amplifier is used for generating the carrier signal. Employing the same operational amplifier both in the course of generating the carrier signal and in modulating the primary signal with the carrier signal yields a synergistic effect.

[0053] According to one aspect, the integrator includes a low pass filter. In other words, the amplitude signal generation step may include low pass filtering of the transmitted signal. The method may further include switching of at least one relay, e.g. with a microcontroller, based on the zero count signal and / or the amplitude signal received by the microcontroller.

[0054] The microcontroller may be directly electrically coupled to the envelope detector and / or the integrator.

[0055] The at least one relay may (be configured to) switch supply of the primary voltage to an electric power consumer (e.g. like a refrigerant compressor or parts thereof, e.g. an electric motor). Switching the at least one relay at the time when the primary voltage crosses zero (i.e. in accordance with the zero cross timing of the primary voltage) reduces a risk of failure of the at least one relay. In other words, this feature helps to improve the reliability and lifetime of the at least one relay and of the electric power consuming device.

[0056] The zero cross timing of the primary voltage can be determined based on the zero cross signal and / or the amplitude signal.

[0057] According to one aspect, the zero cross timing can be determined based on a periodic time of the amplitude signal and a peak timing of the amplitude signal. The peak timing is when the amplitude signal has its maximum value. The expected zero cross timing of the primary voltage can be determined based on the peak timing plus a quarter (and / or three quarters) of the periodic time of the amplitude signal. An amplitude time delay of the amplitude signal with regard to the primary voltage can be considered by an amplitude time offset. The amplitude time offset may be predetermined. For example, the amplitude time offset may be stored in a memory. The memory may be included in the microcontroller. Additionally or alternatively, the memory may be external to the microcontroller and accessible by the microcontroller.

[0058] According to one aspect, the zero cross timing can be determined based on checking when the zero cross signal breaks through (rises above / starts to exceed) a rise threshold. Additionally or alternatively, the zero cross timing can be determined based on checking when the zero cross signal falls below (starts to be smaller than) a drop threshold. The rise threshold and the drop threshold can be the same or different. For example, the rise threshold and / or the drop threshold can be in a range from 20 % to 80 % of a maximum value of the zero cross signal (e.g. a maximum voltage of the zero cross signal), may be in a range from 35 % to 65 %. In one example, the zero cross signal increases sharply from a low level (e.g. at 0 V or higher) to a high level (higher than the low level, e.g. in a range from 2 V to 8 V) when the primary voltage rises above zero. Additionally or alternatively, the zero cross signal falls sharply from the high level when the primary voltage falls below zero. In this regard, the zero cross signal being at its high level at least substantially indicates when the primary voltage is in its positive halfwave. Main rising and falling edges of the zero cross signal indicate the zero cross times of the primary voltage and can be easily detected, e.g. by the microcontroller.

[0059] A time delay of the zero cross signal with regard to the primary voltage can be considered by a cross time offset. The zero cross time offset may be predetermined. For example, the cross time offset may be stored in the microcontroller and / or provided by the software.

[0060] As generating the zero cross signal from the transmitted signal is (different from generating the amplitude signal) not based on integration of the transmitted signal, the cross time offset is typically much smaller than the amplitude time offset and might be even neglected.

[0061] According to one aspect, the method may include controlling the at least one relay with compensating for a relay activation time of the at least one relay. The control signal is sent with a time difference corresponding to the relay activation time before an estimated time for the zero cross at which the at least one relay shall be switched. In order to switch the supply of the primary voltage via the at least one relay more exactly at the zero cross(es) of the primary voltage, the relay activation time can be compensated for. Especially, the method may include controlling a switching time of the at least one relay based at least on the relay activation time and at least one of the zero cross signal and the amplitude signal. The relay activation time be a time interval from sending a control signal for switching the at least one relay until the at least one relay has actually switched (opened / closed electric contact for supply of the primary voltage) in response to said control signal.

[0062] The method may include measuring the relay activation time of the at least one relay, e.g. with the microcontroller. Additionally or alternatively, the relay activation time can be measured in advance (or calculated) and is stored in the memory.

[0063] The problem mentioned above is further solved by an electric circuit with the features according to claim 6.

[0064] It is an electric circuit, with a galvanic isolation barrier, for measuring, at a second side of the galvanic isolation barrier, properties of an alternating primary voltage, which is provided at a first side of the galvanic isolation barrier, wherein the electric circuit comprises: an adaptor that is configured to generate a primary signal from the primary voltage, wherein the adaptor at least partially rectifies the primary voltage; a modulator that is connected to the adaptor and is configured for generating a pulse width modulated signal based on the primary signal by modulating the primary signal with a carrier signal, wherein a typical characteristic (e.g. a duty cycle ratio, for example a pulse-time fraction) of the pulse width modulated signal varies in accordance with a time-varying voltage value of the primary signal; a barrier transmitter that is connected to the modulator and is configured for generating a transmitted signal at the second side of the galvanic isolation barrier from the pulse width modulated signal, wherein the barrier transmitter includes an optocoupler for transmitting the pulse width modulated signal from the first side of the galvanic isolation barrier to the second side of the galvanic isolation barrier; and at least one of the following: an envelope detector that is connected to the barrier transmitter at the second side of the galvanic isolation barrier and is configured for generating a zero cross signal from the transmitted signal; and an integrator that is connected to the barrier transmitter at the second side of the galvanic isolation barrier and is configured for generating an amplitude signal.

[0065] The features, embodiments, modifications, and advantages described with regard to the method apply correspondingly with regard to the electric circuit and vice versa.

[0066] The modulator is arranged on a grid-side (a power input-side) of the electric circuit with respect to the galvanic isolation barrier. The envelope detector and / or the integrator is / are arranged on a consumer-side of the electric circuit with respect to the galvanic isolation barrier.

[0067] The adaptor may include a rectifier, e.g. a half-wave rectifier or a full-wave rectifier (such as a diode bridge). In one embodiment, the adaptor includes a voltage offset adder. The voltage offset adder causes a voltage offset of the primary voltage, of the primary signal, and / or of an intermediate signal that is generated from the primary voltage and from which the primary signal is generated. This can help to reduce a time delay of the carrier signal and the pulse width modulated signal to the zero cross timing.

[0068] In one embodiment, the modulator comprises an oscillating circuit for generating the carrier signal. Thus, the carrier signal can be generated directly within the electric circuit with a cost-efficient implementation.

[0069] According to one aspect, the modulator can comprise an operational amplifier for modulating the primary signal with the carrier signal. Operational amplifiers are easy to integrate, easily available, cost-efficient in view of this functionality and small.

[0070] The operational amplifier can form part of the oscillating circuit. It is hence used in a synergistical manner.

[0071] In one embodiment, the integrator includes a low pass filter circuit. A low pass filter is a simple and efficient way to integrate the transmitted signal at least partly. For example, as the pulse-time fraction of the pulse width modulated signal is indicative of the time-varying voltage value of the primary voltage (at least during time intervals), integration of the pulse-width signal leads to the amplitude signal, wherein the amplitude of the amplitude signal scales in accordance with the amplitude of the primary signal (and hence of the primary voltage).

[0072] A time constant of the integrator (e.g. the low pass filter circuit) may be longer than the cycle lengths of the pulse width modulated signal (and hence of the transmitted signal). The time constant may be less than 1 / (4*PRF), wherein PRF is the primary frequency. For example, the time constant may be in the range of 0,2 ms to 5 ms.

[0073] According to one aspect, the electric circuit comprises a controller, wherein the controller is connected to the envelope detector and the integrator and configured to receive the zero cross signal and / or the amplitude signal. The controller hence can retrieve the relevant information (about the primary voltage) from the zero cross signal and / or the amplitude signal.

[0074] In one embodiment, the electric circuit comprises at least one relay and the controller is configured to switch the relay based on the zero cross signal and / or the amplitude signal. The controller may be electrically connected to the at least one relay for forwarding control signals to the at least one relay. The at least one relay may be connected to the primary voltage and configured to switch supply of the primary voltage to an electric power consumer on and off (under control of the controller).

[0075] According to one aspect, the controller can be configured to measure a mechanical relay activation time of the at least one relay and to control a switching time of the relay at least based on the zero cross signal and the mechanical relay activation time. Hence, the controller can compensate for the mechanical relay activation time.

[0076] The controller can include a microcontroller. This also covers the case the controller consists of the microcontroller. A microcontroller allows for receiving the zero cross signal and / or the amplitude signal as input and to evaluate the input in order to estimate the zero cross timing of the primary voltage. Further, the microcontrollers allows for controlling the at least one relay based on the esteemed zero cross timing of the primary voltage (optionally also considering the relay activation time). The microcontroller can include a processor. The microcontroller may detect the zero cross timing (e.g. "upward" zero cross times when the primary voltage changes from negative to positive voltage and / or "downward" zero cross times when the primary voltage changes from positive voltage to negative voltage) by evaluating the zero cross signal and / or the amplitude signal.

[0077] The microcontroller may detect, by evaluating the zero cross signal and / or the amplitude signal, when the amplitude of the primary voltage exceeds a critical maximum. The microcontroller can be configured to control the at least one relay to switch off the supply of the primary voltage (e.g. to the electric consumer) in this case, especially such that the supply stops at a zero cross time of the primary voltage.

[0078] Additionally or alternatively, the microcontroller may detect, by evaluating the zero cross signal and / or the amplitude signal, when the amplitude of the primary voltage does not exceed a critical minimum. The microcontroller can be configured to control the at least one relay to switch off the supply of the primary voltage (e.g. to the electric consumer) in this case, especially such that the supply stops at a zero cross time of the primary voltage.

[0079] In one embodiment, the microcontroller detects, based on the zero cross signal and / or the amplitude signal, when the primary frequency exceeds a critical maximum frequency. The microcontroller can be configured to control the relay to switch off the supply of the primary voltage (e.g. to the electric consumer) in this case, especially such that the supply stops at a zero cross time of the primary voltage.

[0080] Additionally or alternatively, the microcontroller may detect, based on the zero cross signal and / or the amplitude signal, when the primary frequency falls below a critical minimum frequency. The microcontroller can be configured to control the relay to switch off the supply of the primary voltage (e.g. to the electric consumer) in this case, especially such that the supply stops at a zero cross time of the primary voltage.

[0081] In one embodiment, the microcontroller determines the primary frequency based on the zero cross signal and / or the amplitude signal.

[0082] According to one aspect, the microcontroller can be configured to match switching on the supply of the primary voltage via the at least one relay with the zero cross time of the primary voltage.

[0083] The problem mentioned above is further solved by a control unit for controlling a refrigerant compressor, wherein the control unit includes the electric circuit according to the present invention. The embodiments, modifications, and advantages described with respect to the electric circuit and the method according to the present invention apply accordingly with respect to the control unit, respectively, and vice versa.

[0084] For example, the problem mentioned above may be solved by the following aspects:

[0085] Aspect 1 : Method for measuring, at a second side of a galvanic isolation barrier, properties of an alternating primary voltage, which is provided at a first side of the galvanic isolation barrier, wherein the method includes the following steps: an adaptation step for generating a primary signal from the primary voltage, wherein the adaption step includes at least partially rectifying the primary voltage; a modulation step for generating a pulse width modulated signal based on a carrier signal, wherein the modulation step includes modulating the primary signal with the carrier signal, wherein a duty cycle ratio of the pulse width modulated signal varies in accordance with a time-varying voltage value of the primary signal; a transmission step for generating a transmitted signal at the second side of the galvanic isolation barrier from the pulse width modulated signal, wherein the transmission step includes using an optocoupler for transmitting the pulse width modulated signal from the first side of the galvanic isolation barrier to the second side of the galvanic isolation barrier; and at least one of the following: a zero cross signal generation step including generating a zero cross signal from the transmitted signal with an envelope detector; and an amplitude signal generation step including generating an amplitude signal from the transmitted signal with an integrator.

[0086] Aspect 2: Method according to aspect 1 , wherein the primary voltage has a primary frequency, wherein a pulse width modulation switching frequency of the pulse width modulated signal exceeds 10 times the primary frequency.

[0087] Aspect 3: Method according to any one of the aspects 1 to 3, wherein an operational amplifier is used for modulating the primary signal with the carrier signal.

[0088] Aspect 4: Method according to any one of the aspects 1 to 3, wherein the integrator includes a low pass filter.

[0089] Aspect 5: Method according to any one of the aspects 1 to 4, wherein the method includes the following step: switching of at least one relay with a microcontroller based on the zero cross signal and / or the amplitude signal received by the microcontroller.

[0090] Aspect 6: Electric circuit, with a galvanic isolation barrier, for measuring, at a second side of the galvanic isolation barrier, properties of an alternating primary voltage, which is provided at a first side of the galvanic isolation barrier, wherein the electric circuit comprises: an adaptor that is configured to generate a primary signal from the primary voltage, wherein the adaptor at least partially rectifies the primary voltage; a modulator that is connected to the adaptor and is configured for generating a pulse width modulated signal based on the primary signal by modulating the primary signal with a carrier signal, wherein a duty cycle ratio of the pulse width modulated signal varies in accordance with a time-varying voltage value of the primary signal; a barrier transmitter that is connected to the modulator and is configured for generating a transmitted signal at the second side of the galvanic isolation barrier from the pulse width modulated signal, wherein the barrier transmitter includes an optocoupler for transmitting the pulse width modulated signal from the first side of the galvanic isolation barrier to the second side of the galvanic isolation barrier; and at least one of the following: an envelope detector that is connected to the barrier transmitter at the second side of the galvanic isolation barrier and is configured for generating a zero cross signal from the transmitted signal; and an integrator that is connected to the barrier transmitter at the second side of the galvanic isolation barrier and is configured for generating an amplitude signal.

[0091] Aspect 7: Electric circuit according to aspect 6, wherein the modulator comprises an oscillating circuit for generating the carrier signal.

[0092] Aspect 8: Electric circuit according to aspect 6 or 7, wherein the modulator comprises an operational amplifier for modulating the primary signal with the carrier signal.

[0093] Aspect 9: Electric circuit according to aspect 7 and 8, wherein the operational amplifier forms part of the oscillating circuit. Aspect 10: Electric circuit according to any one of the aspects 6 to 9, wherein the integrator includes a low pass filter circuit.

[0094] Aspect 11 : Electric circuit according to any one of the aspects 6 to 10, wherein the electric circuit comprises a controller, wherein the controller is connected to the envelope detector and the integrator and configured to receive the zero cross signal and / or the amplitude signal.

[0095] Aspect 12: Electric circuit according to aspect 11 , wherein the electric circuit comprises at least one relay and wherein the controller is configured to switch the relay based on the zero cross signal and / or the amplitude signal.

[0096] Aspect 13: Electric circuit according to aspects 11 and 12, wherein the controller is configured to measure a mechanical relay activation time of the at least one relay and to control a switching time of the relay at least based on the zero cross signal and the mechanical relay activation time.

[0097] Aspect 14: Electric circuit according to any one of the aspects 11 to 13, wherein the controller includes a microcontroller.

[0098] Aspect 15: Control unit for controlling a refrigerant compressor, wherein the control unit includes the electric circuit according to any one of the preceding aspects.

[0099] Additional features, advantages, and possible applications of the invention result from the following description of exemplary embodiments and the drawings. All the features described and / or illustrated graphically here form the subject matter of the invention, either alone or in any desired combination, regardless of how they are combined in the claims or in their references back to preceding claims.

[0100] Preferred embodiments of the invention will now be described with reference to the drawings, in which:

[0101] Fig. 1 schematically illustrates a method and an electric circuit for measuring properties of an alternating voltage through a galvanic isolation barrier and controlling a relay in accordance with the present invention;

[0102] Fig. 2 shows a part of the electric circuit of Fig. 1 in more detail;

[0103] Fig. 3 shows the primary voltage and different signals that are generated in

[0104] Fig. 1 in response to the primary voltage if using the electric circuit of Fig. 2;

[0105] Fig. 4 shows an enlarged section of Fig. 3 around an upward zero cross of the primary voltage from negative voltage values to positive voltage values;

[0106] Fig. 5 schematically illustrates how a bump in an electric current through a relay coil of the relay in Fig. 1 is used to measure a relay activation time in the course of switching the relay;

[0107] Fig. 6 schematically illustrates how the relay in Fig. 1 is controlled to switch supply of the primary voltage to an electric power consumer on or off exactly at a time of a downward zero cross of the primary voltage based on the measurement of a time of the previous upward zero cross of the primary voltage through the galvanic isolation barrier, further considering the relay activation time; Fig. 7 shows a control unit for controlling the operation of a refrigerant compressor, wherein the control unit includes the electric circuit according to Figs. 1 and 2; and

[0108] Fig. 8 show a modification of the electric circuit of Fig. 1 without a voltage offset adder in an adaptor of the electric circuit.

[0109] Fig. 1 schematically illustrates a method for measuring properties of an alternating primary voltage PRV. The primary voltage PRV is provided at a first side of the galvanic isolation barrier GAB, but the properties are measured at a second side of the galvanic isolation barrier GAB, hence "through" the galvanic isolation barrier GAB. Fig. 1 schematically illustrates an extended electric circuit 100 with an electric circuit 1 (see Fig. 2) or electric circuit 1A (see Fig. 8) that is configured for performing such a method as well.

[0110] The primary voltage PRV is an alternating voltage (also referred to as "AC voltage" for "alternating current voltage") having, for example, a frequency of 50 Hz or 60 Hz and a root mean square voltage (RMS voltage) in the range from 100 V to 250 V, e.g. 230 V. An example for a time-varying voltage value PRV(t) of the primary voltage PRV is shown in Fig. 3.

[0111] The electric circuit 1 , 1 A shown in Fig. 1 comprises an adaptor 10, a modulator 20 connected to the adaptor 10, a barrier transmitter 40 connected to the modulator 20, an envelope detector 60 connected to the barrier transmitter 40, and an integrator 70 connected to the barrier transmitter 40.

[0112] Fig. 2 shows an exemplary embodiment of the electric circuit 1 in more detail and Fig. 8 shows a modification of the electric circuit 1. The only difference between the electric circuit 1 (in Fig. 2) and the electric circuit 1A (in Fig. 8) is that the adaptor 10 of the electric circuit 1 includes an additional voltage offset adder 15, 16 which is omitted in the electric circuit 1A. Hence, all descriptions made with respect to the electric circuit 1 apply accordingly with respect to the electric circuit 1A except with regard to this difference.

[0113] The extended electric circuit 100 depicted in Fig. 1 comprises the electric circuit 1 (or the electric circuit 1A). Hence, descriptions made with respect to the electric circuit 1 (and 1A) naturally also apply to the electric circuit 100 accordingly.

[0114] The extended electric circuit 100 in Fig. 1 includes further elements. In more detail, the extended electric circuit 100 additionally comprises a microcontroller 80 that is connected to the envelope detector 60 and to the integrator 70. It also comprises at least one relay 90 that is connected to the microcontroller 80. The microcontroller 80 controls switching of the relay 90. A control output 83 sends control signals to the relay 90 for switching the relay 90.

[0115] Turning now to Fig. 1 for an introductory overview, in an adaptation step S10, the adaptor 10 generates a primary signal PRS from the primary voltage PRV. In a modulation step S20, the modulator 20 generates a pulse width modulated signal PWMS from the primary signal PRS, wherein the modulator 20 modulates the primary signal PRS with a pulse width modulation. In this example, the primary signal PRS is modulated using a carrier signal CAS (see Figs. 3 and 4) that is generated within the modulator 20 from the primary signal PRS. In a transmission step S40, the barrier transmitter 40 generates a transmitted signal TRS at the second side of the galvanic isolation barrier GAB. The transmitted signal TRS at least substantially corresponds to the pulse width modulation signal PWMS. In other words, the transmitted signal TRS is the pulse width modulation signal PWMS as it is forwarded through the galvanic isolation barrier GAB by the barrier transmitter 40. In a zero cross signal generation step S60, the envelope detector 60 generates a zero cross signal ZCS from the transmitted signal TRS. The zero cross signal ZCS highlights zero cross times of the primary voltage PW, in the exemplary embodiment particularly "upward" zero cross times tZCu of the primary voltage PRV from negative voltage to positive voltage (see Figs. 3 and 4). The zero crosses of the primary voltage PRV from negative voltage to positive voltage can be referred to as "upward zero crosses". Similarly, the zero crosses of the primary voltage PRV from positive voltage to negative voltage can be referred to as "downward zero crosses" and the corresponding zero cross times tZCd can be referred to as "downward zero cross times".

[0116] In an amplitude signal generation step S70, the integrator 70 generates an amplitude signal AMS from the transmitted signal TRS. The amplitude signal AMS scales with an amplitude of the primary voltage PRV.

[0117] The microcontroller 80 receives the zero cross signal ZCS and determines, based on the zero cross signal ZCS, the next (or an even later) upward zero cross time tZCu and / or the next (or an even later) downward zero cross time.

[0118] The primary voltage PRV is received by the adaptor 10 in an input step S11.

[0119] The adaptor 10 can include a voltage divider for reducing a voltage of the primary signal PRS compared to the primary voltage PRV, see resistors 12, 13, and 14 in Fig. 2. Accordingly, the adaption step S10 may include voltage division.

[0120] The primary signal PRS is generated from the primary voltage PRV in the adaption step S10 including at least partial rectification (step S12). Accordingly, the adaptor 10 of the electric circuit 1 includes a rectifier. In Figs. 2 and 8, the rectifier includes a diode 15 (in this embodiment, more specifically a Schottky diode). In the adaptor 10 shown in Fig. 8, a first resistor 12, a second resistor 13, and a third resistor 14 are connected in series between an input 11 of the adaptor 10 and a reference potential at the first side of the galvanic isolation barrier GAB, here shown as first reference potential Gnd1 (e.g. a first ground potential). The diode 15 is connected between the first resistor 12 and the first ground Gnd1. Hence, the second resistor 13 and the diode 15 are connected to the first resistor 12 in parallel. Further, an output 19 of the adaptor 10 and the third resistor 14 are connected in parallel to the second resistor 13. Accordingly, an absolute voltage of the primary signal PRS (i.e. between the output 19 of the adaptor 10 and the first reference potential Gnd1 ) cannot exceed a maximum of an absolute value of F (Ri2 + R13 + Ri4)*PRV(t), wherein R12 is the resistance of the first resistor 12, R13 is the resistance of the second resistor 13, and R14 is the resistance of the third resistor 14.

[0121] In the exemplary electric circuit 1A shown in Fig. 8, the primary signal PRS and its time-varying voltage value PRS(t) result from voltage division and half-wave rectification of the primary voltage PRV.

[0122] As noted above, the electric circuit 1 shown in Fig. 1 additionally includes the voltage offset adder 15, 16. The voltage offset adder includes an input 15 for a positive supply voltage VCC and a fourth resistor 16. This VCC input 15 is connected to in-between the resistor 12 and the resistor 13 via the fourth resistor 16. A cathode of the diode 15 is connected in parallel

[0123] - to the input 11 (for the primary voltage PRV) via the first resistor 12,

[0124] - to the VCC input 15 via the fourth resistor 16,

[0125] - to the output 19 of the adaptor 10 via the second resistor 13, and

[0126] - to the first reference potential (Gnd1 ) via the second resistor 13 and the third resister 14.

[0127] An anode of the diode 15 is connected to the first reference potential Gnd1. In the electric circuit 1 shown in Fig. 2, the primary signal PRS and its time-varying voltage value PRS(t) also basically result from voltage division and half-wave rectification of the primary voltage PRV. Figs. 3 and 4 show the primary voltage PRV and the signals when using the electric circuit 1 of Fig. 2. Due to the voltage offset adder 15, 16, the time-varying voltage value PRS(t) of the primary signal PRS starts to deviate from zero at a time tP shortly before the upward zero crossing time tZCu. Hence, the carrier signal CAS shown in Fig. 4 is activated shortly before the upward zero crossing time tZCu as well. This helps to reduce a time delay dtZCu from the upward zero crossing tZCu until a leading pulse of the pulse width modulation signal PWMS starts (see Fig. 4). For example, the time tP can be in the range from 0 ms to 0,4 ms before the upward zero crossing time tZCu. The resistances of the resistors 12, 13, 14, 16 are adapted accordingly.

[0128] With the electric circuit 1A shown in Fig. 8, the time-varying voltage value PRS(t) is zero during the complete negative half-waves of the primary voltage PRV.

[0129] In any case, the time-varying voltage value PRS(t) (at least substantially) scales with the time-varying voltage value PRV(t) during the positive half-waves of the primary voltage PRV.

[0130] Other modifications are possible. For example, in one modification (not shown), the adaptor 10 includes a full-wave rectifier, for example a diode bridge. In another modification, the primary signal PRS scales with the negative half-waves of the primary voltage.

[0131] The modulation step S20 includes modulating the primary signal PRS with the carrier signal CAS (see step S22 in Fig. 1 ). The electric circuits 1 includes the modulator 20 for performing the modulation step S20. In the exemplary embodiment, the modulator 20 comprises an oscillating circuit for generating the carrier signal CAS from the primary signal PRS (see step S21 in Fig. 1 ). The oscillating circuit is shown on the left side of the modulator 20 in Fig. 2 and comprises an operational amplifier 25. A positive power supply input of the operational amplifier 25 is connected to an input 24 for the positive supply voltage VCC. A negative power supply input of the operational amplifier 25 is connected to the first reference potential Gnd1. A non-inverting input of the operational amplifier 25 is connected to the input 21 of the modulator 20 and hence receives the primary signal PRS. An inverting input of the operational amplifier 25 is connected to an output of the operational amplifier 25 via a resistor 27. A reference input 23 of the modulator 20 is connected to the inverting input in parallel with the resistor 27. The reference input 23 is coupled to the first reference potential Gnd1 via a capacitor 22. The capacitor 22 can form part of the modulator 20 and the oscillating circuit. In addition, the output of the operational amplifier 25 is connected with the input 21 of the modulator 20 (and hence with the non-inverting input) via a resistor 26.

[0132] Fig. 2 shows a connection point 28 that is electrically connected with the output of the operational amplifier 25, the resister 26, and the resistor 27. Furthermore, it is electrically connected to a barrier-side (a side at the galvanic isolation barrier GAB) of the modulator 20 to forward the output of the operational amplifier 25 towards the galvanic isolation barrier GAB.

[0133] As soon as the time-dependent voltage value PRS(t) deviates from zero, the oscillating circuit starts to generate the carrier signal CAS. The carrier signal CAS then exhibits a sawtooth shape. This is illustrated in Figs. 3 and 4.

[0134] The carrier signal CAS varies depending on the time-varying voltage value PRS(t) of the primary signal PRS. It hence shows a typical characteristic varying with the time-varying voltage value PRS(t) of the primary signal PRS(t) - and thus finally with the time-varying voltage value PRV(t) of the primary voltage PRV at least during time intervals (in more detail at least during the positive half-waves of the primary voltage PRV).

[0135] The individual sawtooth differ. Each sawtooth has falling edge and a rising edge. The higher PRS(t) is at the of the individual sawtooth, the longer is a duration of the falling edge of this sawtooth but the shorter are a duration of the rising edge and a cycle length (corresponding to sum of the durations of the falling edge and the rising edge) of this sawtooth. A ratio between the duration of the falling edge and the cycle length of the sawtooth increases with increasing PRS(t). The carrier signal CAS thus includes information about an amplitude of the primary signal PRS (and hence of an amplitude of the primary voltage PRV).

[0136] This is particularly evident in Fig. 4 showing an enlarged section of Fig. 3 around the a zero cross of the primary voltage, in more detail when its time-varying voltage value PRV(t) changes from negative to positive. A time scale tSC in Fig. 4 can be, for example, 4 ms.

[0137] The operational amplifier 25 modulates the primary signal PRS, which is applied to the non-inverting input, with the carrier signal CAS provided at the inverting input. The pulse width modulated signal PWMS is provided by the output of the operational amplifier 25.

[0138] The electric circuit 1 shown in Fig. 2 includes an optional signal refiner for refining the pulse width modulating signal PWMS. The signal refiner includes further elements between the output of the operational amplifier 25 and an output 39 of the modulator 20. Said optional elements include a further input 29 for the positive supply voltage VCC, resistors 30, 31 , 32, a transistor 33, and connections to the first reference potential Gnd1. The resistors 30, 31 , and 32 are connected in series between the input 29 for the positive supply voltage VCC and the first reference potential Gnd1. The electrical connection point 28 (and hence the output of the operational amplifier 25) are connected to in-between the resistors 30 and 31 . A base of the transistor 33 is connected to in-between the resistor 31 and the resistor 32. Hence, the base of the transistor 33 is in electrical connection with the output of the operational amplifier 25 via the resistor 31. An emitter of the transistor 33 is connected to the first reference potential Gnd1. Finally, a collector of the transistor 33 is connected to (or constitutes) an output 39 of the modulator 20. The transistor 33 can draw off current from an input side of an optocoupler 44 of the barrier transmitter 40. The transistor 33 is non-essential. In other embodiments, the operational amplifier 25 itself could be able to draw off current from the input side of the optocoupler 44.

[0139] An example of the pulse width modulated signal is shown in Figs. 3 and 4. It is (at least substantially) a pulse-pause signal and / or square wave signal during on- time intervals Tonand constant (in this example constantly zero) during off-time intervals Toff. The on-time intervals Tonsubstantially match (substantially co-oc- cur) with the positive half-waves of the primary voltage PRV and the off-time intervals TOff substantially match (substantially co-occur) with the negative halfwaves of the primary voltage PRV.

[0140] During each on-time interval Ton(i.e. while the pulse width modulated signal PWMS is "active") a plurality of pulse-pause cycles occurs. In this regard, "pause" may mean the time between two subsequent pulses, especially while the pulse width modulated signal PWMS is active.

[0141] As the pulse width modulated signal PWMS results from the modulation of the primary signal PRS with the carrier signal CAS, it includes - similar to the carrier signal CAS - a typical characteristic, which depends on and changes in accordance with the time-varying voltage value PRS(t) and hence with the time-varying voltage value PRV(t). As can be seen best in Fig. 4, a pulse width TPL during the respective single cycle of the pulse width modulated signal PWMS increases with increasing time-varying voltage value PRS(t) of the primary signal PRS. The pulse width TPL is the same as the duration of the falling edge of the corresponding individual sawtooth of the carrier signal CAS. A pause width TPA during the respective single cycle of the pulse width modulated signal PWMS instead decreases with increasing time-varying voltage value PRS(t) of the primary signal PRS. The pause width TPA is the same as the duration of the rising edge of the corresponding individual sawtooth of the carrier signal CAS.

[0142] One cycle of the pulse width modulated signal PWMS includes one pulse and one adjacent (e.g. subsequent) pause. A cycle length of the individual cycle of the pulse width modulated signal PWMS corresponds to the pulse width TPL plus the pause width TPA of the respective individual cycle. The cycle length of one pulsepause combination is the same as the cycle length of the corresponding individual sawtooth in the carrier signal CAS.

[0143] Especially, the higher the time-varying voltage value PRS(t) is during the individual pulse-pause cycle of the pulse width modulated signal, the higher is a pulsetime fraction in this pulse-pause cycle. The pulse-time fraction may be measured in % over the respective single pulse-pause cycle of the pulse width modulated signal PWM. For example, it might be calculated as follows: pulse-time fraction = TPL / (TPL + TPA) * 100 %. The pulse-time fraction is the same as the ratio between the duration of the falling edge and the cycle length of the corresponding individual sawtooth in the carrier signal CAS. The pulse-time fraction is larger than zero only during the on-time intervals (Ton). It is an example for a "duty cycle ratio".

[0144] The pulse width modulated signal PWMS is free of pulses during the off-time interval Toff. So to say, the pulse width and the pulse-time fraction of the pulse width modulated signal PWMS are zero during the off-time interval TOff. The non-occur- rence of pulses for longer than a certain time threshold can indicate the presence of the off-time interval TOff. This corresponds to the pause width exceeding a certain time threshold and the cycle length exceeding a certain time threshold.

[0145] The pulse width modulated signal PWMS includes information about the timevarying voltage PRS(t) and hence about the time-varying voltage PRV(t) during the positive half-waves, especially in the form of the changing pulse-time fraction. Furthermore, the modulator 20 ensures that a very significant and very steep increase of the pulse width modulated signal PWMS occurs in response to the upward zero cross of the primary voltage PRV, substantially at same time as the upward zero cross.

[0146] Fig. 4 shows the upward zero cross of the primary voltage PRV at the upward zero cross time tZCu. Very shortly thereafter, a leading pulse of the pulse width modulated signal PWMS occurs. The pulse width modulated signal PWMS sharply rises from zero to a maximum (PuMax) for the first time during this on- time interval Ton. The time delay dtZCu from the upward zero crossing tZCu until said leading pulse occurs is very short, in this example less than 0,1 ms (see Fig. 4). It cannot even be properly seen in Fig. 3 without magnification. As an example, PuMax might be in a range from 5 V to 20 V.

[0147] The barrier transmitter 40 receives the pulse width modulated signal PWMS at the first side of the galvanic isolation barrier GAB and generates from it the transmitted signal TRS at the second side of the galvanic isolation barrier GAB. In this manner, the barrier transmitter 40 forwards the information included in pulse width modulated signal PWMS through the galvanic isolation barrier GAB.

[0148] For this purpose, the barrier transmitter 40 include the optocoupler 44. The optocoupler 44 forms part of the galvanic isolation barrier GAB. In this exemplary embodiment, at the first side of the galvanic isolation barrier GAB, an anode of the optocoupler 44 is connected to an input 42 of the barrier transmitter 40 for the positive supply voltage VCC. A cathode of the optocoupler 44 (at the first side of the galvanic isolation barrier GAB) is connected with (or constitutes) an input 41 for the barrier transmitter 40 for the pulse width modulated signal PWMS. At the second side of the galvanic isolation barrier GAB, a collector of the optocoupler 44 is connected, via a resistor 45, to an input 46 for a second side supply voltage VCCJSO, and an emitter of the optocoupler 44 is connected to a second reference potential Gnd2, e.g. a second ground potential.

[0149] The barrier transmitter 40 may further include a transistor 47 as shown in Figs. 2 and 8. In this example, the transistor 47 is a pnp-transistor and its emitter is connected to the input 46 for the second side supply voltage VCCJSO (in parallel to the resistor 45). A base of the transistor 47 is connected to the collector of the optocoupler 44. A collector of the transistor 47 is connected with an output 49 of the barrier transmitter 40 and in parallel, via a resistor 48, with the second reference potential Gnd2. The transistor 47 additionally sharpens the transmitted signal TRS that is provided to the output 49 of the barrier transmitter 40.

[0150] The transmitted signal TRS can have the same shape and / or timing as the pulse width modulated signal PWMS shown in Figs. 3 and 4.

[0151] As the barrier transmitter 40 generates the transmitted signal TRS from the pulse width modulated signal PWMS such that the transmitted signal TRS is of at least substantially the same shape as the pulse width modulated signal PWMS and as the barrier transmitter 40 does not cause substantial delay of the transmitted signal TRS with regard to the pulse width modulated signal PWMS, the relevant information (included in the pulse width modulated signal PWMS) about the zero cross timing and the amplitude of the primary voltage PRV is forwarded accurately through the galvanic isolation barrier GAB and hence to the envelope detector 60 and the integrator 70.

[0152] Since the cycle lengths and the pulse widths of the pulse width modulated signal PWMS vary during the on-time intervals Ton, a frequency PWMf of the pulsepause signal is not constant but varies.

[0153] The pulse width modulated signal PWMS varies during the on-time intervals Tonin a frequency range well above the primary frequency PRF and with an (at least substantially) constant amplitude PuMax. Hence, it can be transmitted more efficiently, more precisely, and more reliably by the optocoupler 44 than the primary voltage PRV or the primary signal PRS as such. In particular, the included information about the zero crosses and the amplitude of the primary voltage PRV is transmitted efficiently, precisely, and reliably by the optocoupler 44 and hence transferred through the galvanic isolation barrier GAB.

[0154] An input 61 of the envelope detector 60 and an input 71 of the integrator 70 are connected in parallel to the output 49 of the barrier transmitter 40. Hence, the transmitted signal TRS is provided to both the envelope detector 60 and the integrator 70.

[0155] The envelope detector 60 is a simple analogue circuit. An output 65 of the envelope detector 60 is connected with the input 61 of the envelope detector 60 via a Schottky diode 62, a cathode of the Schottky diode 62 being at the side of the output 65. The second reference potential Gnd2 is coupled to the cathode of the Schottky diode 62 in parallel to the output 65 via a capacitor 63 and, additionally in parallel, via a resistor 64.

[0156] In the exemplary embodiments, the barrier transmitter 40 adds no significant transmission time delay. This is evident from Fig. 4. The envelope detector 60 generates the zero crossing signal ZCS from the transmitted signal TRS. The zero cross signal ZCS (see Figs. 3 and 4) substantially corresponds to an "envelope" of the transmitted signal TRS. The transmitted signal TRS is not shown but of similar or the same shape as the pulse width modulated signal PWMS, maybe with another (e.g. lower) amplitude. At the beginning of the each on-time interval Ton, the zero cross signal ZCS exhibits a sharp main rise edge. This is caused by a "counterpart" (in the transmitted signal TRS) to the leading pulse of the pulse width modulated signal PWMS (e.g. by a corresponding leading pulse of the transmitted signal TRS for the respective on-time interval Ton). The sharp main rise edge of the zero cross signal ZCS in Fig. 4 occurs at the same time tZCB as a rising edge of the leading pulse of the pulse width modulated signal PWMS. No transmission time delay of the zero cross signal ZCS relative to the pulse width modulated signal PWMS can be seen in Fig. 4.

[0157] Hence, the zero cross signal ZCS signal suddenly breaks through (rises above / starts to exceed) a rise threshold ZCT at tZCB as well. As the time delay dtZCu is very small, it can be neglected. With sufficient precision, it can be assumed that tZCB « tZCu. In other words, the time tZCB (when the zero cross signal breaks through the rise threshold ZCT) is indicative of the upward zero cross time tZCu. Optionally, the microcontroller 80 can even consider the time delay dtZCu. For example, a value of dtZCu can be pre-stored in the memory and can be used to calculate tZCu = tZCB - dtZCu.

[0158] The memory can include an internal memory of the microcontroller 80. Additionally or alternatively, the memory can include a memory external to the microcontroller 80 that is accessible by the microcontroller 80.

[0159] An input 81 of the microcontroller 80 (see Fig. 1 ) receives the zero cross signal ZCS, see step S79 in Fig. 1 . The microcontroller 80 detects when the zero cross signal ZCS breaks through the rise threshold ZCT. The rise threshold ZCT can be in the range from 20 % to 80 % of a maximum value ZCSMax of the zero cross signal ZCS, e.g. 50 %. The microcontroller 80 detects the time tZCB (the breakthrough time) which is indicative of the zero cross time tZCu. As the primary frequency PRF is pre-stored, e.g. in the memory, and / or as the microcontroller 80 detects the primary frequency PRF, the microcontroller 80 can estimate the next downward zero cross time tZCd and / or the next upward zero cross time tZCu'. Naturally, instead of the primary frequency PRF, a corresponding periodic time PRT (=1 / PRF) can be stored and / or measured instead of the primary frequency PRF. Hence, storing and / or measuring the primary frequency PRF can include or consist of storing and / or measuring the periodic time PRT. For example, the microcontroller 80 can determine the periodic time PRT by measuring a time span that passes between two subsequent times tZCB and / or a time span that passes between two subsequent maximums of the amplitude signal AMS. The next upward zero crossing time tZCu' can be estimated based on the detected zero crossing time tZCu, for example as follows: tZCu' = tZCu + PRT = tZCu + 1 / PRF. The next downward zero crossing time tZCd can be estimated accordingly as follows: tZCd = tZCu + PRT / 2. As explained above, tZCB or (tZCB - dtZCu) may be used as tZCu.

[0160] In more general, the transmission time delay caused by the barrier transmitter 40 is preferably less than 0,1 ms. Apart from that, if there is any known significant transmission time delay tTD in embodiments not shown, it can be compensated for. For example, a value of the transmission time delay tTD can be stored in the memory and considered when calculating the expected next downward zero cross time tZCd, e.g. as tZCd = tZCu + PRT / 2 - tTD and / or the expected next upward zero cross time tZCu', e.g. as TZCu' = tZCu + PRT - tTD. As explained above, tZCB or (tZCB - dtZCu) may be used as tZCu. The integrator 70 is a convenient analogue RC low pass filter circuit. It is simple, reliable, and cost-efficient. An output 74 of the integrator 70 is connected with the input 71 via a resistor 72. The second reference potential Gnd2 is connected to the resistor 72 via a capacitor 73 in parallel with the output 72.

[0161] An input 81 of the microcontroller 80 receives the amplitude signal AMS (see step S79 in Fig. 1 ).

[0162] As explained above, the pulse-time fraction of the pulse width modulated signal PWMS increases with increasing time-varying voltage values PRS(t) and hence, during the on-time intervals Ton, with increasing time-varying voltages PRV(t).

[0163] Since the transmitted signal TRS is (at least substantially) of the same shape as the pulse width modulated signal PWMS, the same holds for the transmitted signal TRS: A pulse-time fraction of the transmitted signal TRS during the on-time intervals Ton increases with increasing time-varying voltage values PRS(t) and hence with increasing time-varying voltages PRV(t). Therefore, a maximum of the amplitude signal AMS for the individual on-time interval Tonscales with the amplitudes of the primary signal PRS and hence with the amplitude of the primary voltage PRV during the corresponding positive half-wave. Similarly, an area under the peak of the amplitude signal for one half-wave of the primary voltage PRV scales with the amplitude of the primary voltage PRV during said positive halfwave.

[0164] The microcontroller 80 detects based on the amplitude of the amplitude signal AMS and / or based on the area below the amplitude signal AMS when the amplitude of the primary voltage PRV exceeds a critical maximum. In this case, the microcontroller 80 operates the relay 90 to switch of supply of the primary voltage PRV to the electric power consumer, e.g. an electric motor 301 shown in Fig. 7, exactly at the next downward zero crossing time tZCd or at the next upward zero crossing time tZCu. The critical maximum may be adjustable.

[0165] Additionally or alternatively, the microcontroller 80 detects based on the amplitude of the amplitude signal AMS and / or based on the area below the amplitude signal AMS when the amplitude of the primary voltage PRV does not reach a critical minimum. In this case, the microcontroller 80 operates the relay 90 to switch of supply of the primary voltage PRV to the electric power consumer, e.g. the electric motor 301 shown in Fig. 7, exactly at the next downward zero crossing time tZCd or at the next upward zero crossing time tZCu. The critical minimum may be adjustable.

[0166] In order to match an actual time tSW of switching off the supply of the primary voltage PRV particularly exactly with the zero crossing time tZCd I tZCu, the microcontroller can also measure and consider a relay activation time RAT. This is explained with regard to Figs. 1 , 5, and 6.

[0167] In step S91 (see Fig. 1 ), the microcontroller 80 sends the control signal 91 (see Figs. 1 and 5) for switching the relay 90. The control signal 91 can be a digital output of the microcontroller 80.

[0168] Fig. 5 shows the control signal 91 and a current iC flowing through a relay coil of the relay 90 over time. A switching operation of the relay 90 starts in response of receiving the control signal 91. The current iC through the relay coil raises until it reaches a maximum. This behavior is caused by the relay coil's induction. The actual switching of the supply of the primary voltage PRV to the electric power consumer does not happen instantly in response to receiving the control signal 91 but after the relay activation time RAT, i.e. at the actual switching time tSW. The induction in the relay coil is changing depending on a relay contact position. When the relay contacts hit each other, this gives a small "bump" iCB in the curve of the current iC.

[0169] In step S92, the microcontroller 80 measures the current iC, e.g. using a resistor connected in series with the relay coil, and detects the bump iCB in the rising current iC. The microcontroller 80 determines the relay activation time RAT as the time difference between tRC (e.g. the time of issuing the control signal 91 ) and the time tSW when the bump iCB appears.

[0170] The microcontroller 80 saves the relay activation time RAT in the memory. When the supply of the primary voltage PRW to the electric power consumer shall be switched on or off at the downward zero crossing time tZCd, the microcontroller 80 outputs the control signal 91 for switching the relay 90 at the time tRC, which is shifted by the relay activation time RAT to before the downward zero crossing time tZDd (see Fig. 6). For example, tRC can be calculated as follows: tRC = tZCu + PRT / 2 - RAT. As explained above, tZCB or (tZCB - dtZCu) may be used as tZCu. As explained above, tTD could be optionally considered if present.

[0171] Fig. 7 shows a refrigerant compressor 300 and a control unit 200 for controlling an operation of a refrigerant compressor 300. The refrigerant compressor 300 comprises a refrigerant input 304, a refrigerant output 305, and a compressing means 302 (such as a piston assembly, a scroll compressor assembly, or the like) arranged between the refrigerant input 304 and the refrigerant output 305. The refrigerant compressor 300 further comprises the electric motor 301 for driving the compressing means 302. The control unit 100 controls the supply of the primary voltage PRV from a voltage source 210, e.g. a power grid, to the electric motor 301 via the relay 90. As explained above, the supply of the primary voltage PRV to the electric motor 301 can be switched on and off by the relay 90. The control unit 200 includes the electric circuit 100 according to Fig. 1. As the actual switching tSW of the relay 90 for switching the supply of the primary voltage PRV to the electric motor 301 is matched to the zero cross timing of the primary voltage PRV, the risk of failure of the relay 90 is reduced. Moreover, the control unit 200 prevents damage of the refrigerant compressor 300 by switching the relay 90 to stop the supply of the primary voltage PRV to the electric motor 301 when the amplitude of the primary voltage PRV becomes excessive or too low as described above. The microcontroller 80 is protected by the galvanic isolation barrier GAB. The relay 90 or the whole control unit 200 can also be integrated into the refrigerant compressor 300. The control unit 200 may also be configured to interrupt supply of the primary voltage PRV to the electric motor 301 when the primary frequency PRF (in other words the periodic time PRT) is without a tolerable range.

[0172] For multi-phase electric power supplies, the electric circuit 100 (and hence the control unit 200) can comprise an individual electronic circuit 1 or 1A for each phase and at least one relay 90 for each phase. The electric circuit 100 may have a common microcontroller 80 for all phases or several microcontrollers 80 for different phases.

[0173] In the case of a multi-phase electric power supply, the microcontroller(s) 80 may be also configured to monitor a phase shift between respective different phases, e.g. by comparing the time offsets between the zero offsets tZCd, tZCu, and / or the times tZCB of the respective different phases. The microcontroller(s) 80 can automatically switch off the corresponding relay 90 at respective zero crossings of the individual phases if at least one phase shift is outside a tolerated range.

Claims

Claims:

1. Method for measuring, at a second side of a galvanic isolation barrier (GAB), properties of an alternating primary voltage (PRV), which is provided at a first side of the galvanic isolation barrier (GAB), wherein the primary voltage (PRV) has a primary frequency (PRf), wherein the method includes the following steps: an adaptation step (S10) for generating a primary signal (PRS) from the primary voltage (PRV), wherein the adaption step (S10) includes at least partially rectifying the primary voltage (PRV); a modulation step (S20) for generating, with a modulator (20), a pulse width modulated signal (PWMS) based on a carrier signal (CAS), wherein the modulation step (S20) includes modulating the primary signal (PRS) with the carrier signal (CAS), wherein a duty cycle ratio of the pulse width modulated signal (PWMS) varies in accordance with a time-varying voltage value (PRS(t)) of the primary signal (PRS), wherein an operational amplifier (25) is used for modulating the primary signal (PRS) with the carrier signal (CAS); a transmission step (S40) for generating a transmitted signal (TRS) at the second side of the galvanic isolation barrier (GAB) from the pulse width modulated signal (PWMS), wherein the transmission step (S40) includes using an optocoupler (44) for transmitting the pulse width modulated signal (PWMS) from the first side of the galvanic isolation barrier (GAB) to the second side of the galvanic isolation barrier (GAB); and at least one of the following: a zero cross signal generation step (S60) including generating a zero cross signal (ZCS) from the transmitted signal (TRS) with an envelope detector (60); and an amplitude signal generation step (S70) including generating an amplitude signal (AMS) from the transmitted signal (TRS) with an integrator (70),characterized in that a pulse width modulation switching frequency (PWMf) of the pulse width modulated signal (PWMS) exceeds 10 times the primary frequency (PRf) and that the modulator (20) comprises an oscillating circuit and uses the oscillating circuit for generating the carrier signal (CAS), wherein the operational amplifier (25) forms part of the oscillating circuit.

2. Method according to claim 1 , wherein the integrator includes a low pass filter (70).

3. Method according to any one of the preceding claims, wherein the method includes the following step:- switching of at least one relay (90) with a microcontroller (80) based on the zero cross signal (ZCS) and / or the amplitude signal (AMS) received by the microcontroller (80).

4. Method according to claim 3, wherein microcontroller (80) measures a mechanical relay activation time (RAT) of the at least one relay (90) and controls a switching time of the relay (90) at least based on the zero cross signal (ZCS) and the mechanical relay activation time (RAT).

5. Method according to claim 3 or 4, wherein the at least one relay switches supply of the primary voltage (PRV) to an electric power consumer (301 ), wherein the method includes switching the at least one relay at a time (tZCd, tZCu, tZCu') when the primary voltage (PRV) crosses zero.

6. Method according to any one of the preceding claims, wherein the carrier signal (CAS) includes sawtooth shapes.

7. Electric circuit (1 , 1A, 100), with a galvanic isolation barrier (GAB), for measuring, at a second side of the galvanic isolation barrier (GAB), properties of an alternating primary voltage (PRV), which is provided at a first side of the galvanic isolation barrier (GAB), wherein the electric circuit (1 , 1A, 100) comprises: an adaptor (10) that is configured to generate a primary signal (PRS) from the primary voltage (PRV), wherein the adaptor (10) at least partially rectifies the primary voltage (PRV); a modulator (20) that is connected to the adaptor (10) and is configured for generating a pulse width modulated signal (PWMS) based on the primary signal (PRS) by modulating the primary signal (PRS) with a carrier signal (CAS), wherein a duty cycle ratio of the pulse width modulated signal (PWMS) varies in accordance with a time-varying voltage value of the primary signal (PRS), wherein the modulator (20) comprises an operational amplifier (25) for modulating the primary signal (PRS) with the carrier signal (CAS); a barrier transmitter (40) that is connected to the modulator (20) and is configured for generating a transmitted signal (TRS) at the second side of the galvanic isolation barrier (GAB) from the pulse width modulated signal (PWMS), wherein the barrier transmitter (40) includes an optocoupler (44) for transmitting the pulse width modulated signal (PWMS) from the first side of the galvanic isolation barrier (GAB) to the second side of the galvanic isolation barrier (GAB); and at least one of the following: an envelope detector (60) that is connected to the barrier transmitter (40) at the second side of the galvanic isolation barrier (GAB) and is configured for generating a zero cross signal (ZCS) from the transmitted signal (TRS); and an integrator (70) that is connected to the barrier transmitter (40) at the second side of the galvanic isolation barrier (GAB) and is configured for generating an amplitude signal (AMS),characterized in that the electric circuit (1 , 1 A, 100) is configured such that a pulse width modulation switching frequency (PWMf) of the pulse width modulated signal (PWMS) exceeds 10 times the primary frequency (PRf) and that the modulator (20) comprises an oscillating circuit for generating the carrier signal (CAS), wherein the operational amplifier (25) forms part of the oscillating circuit.

8. Electric circuit (1 , 1A, 100) according to claim 7, wherein the integrator includes a low pass filter circuit (70).

9. Electric circuit (100) according to claim 7 or 8, wherein the electric circuit (100) comprises a controller (80), wherein the controller (80) is connected to the envelope detector (60) and the integrator (70) and configured to receive the zero cross signal (ZCS) and / or the amplitude signal (AMS).

10. Electric circuit (100) according to claim 9, wherein the electric circuit (100) comprises at least one relay (90) and wherein the controller (80) is configured to switch the relay (90) based on the zero cross signal (ZCS) and / or the amplitude signal (AMS).

11. Electric circuit (100) according to claims 9 and 10, wherein the controller (80) is configured to measure a mechanical relay activation time (RAT) of the at least one relay (90) and to control a switching time of the relay (90) at least based on the zero cross signal (ZCS) and the mechanical relay activation time (RAT).

12. Electric circuit (100) according to claim 10 or 11 , wherein the at least one relay (90) is connected to the primary voltage (PRV) and configured to switch supply of the primary voltage (PRV) to an electric consumer (301 ) on and off.

13. Electric circuit (100) according to any one of the claims 9 to 12, wherein the controller includes a microcontroller (80).

14. Electric circuit (100) according to claims 12 and 13, wherein the microcon- troller (80) is configured to match switching on the supply of the primary voltage (PRV) via the at least one relay (90) with a zero cross time (tZCd, tZCu, tZCu') of the primary voltage (PRV).

15. Control unit (200) for controlling a refrigerant compressor (300), wherein the control unit (200) includes the electric circuit (1 , 1A, 100) according to any one of the claims 7 to 14.

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