Patent Description:
This section provides background information related to the present disclosure. The document <CIT> discloses a technique of determining input power and current, for energy consumption measurement, by adjusting Power Factor Correction (PFC) input current value to compensate phase shift in current sense circuit. The document <CIT> discloses a technique for power factor correction including selectively coupling bit reactive loads with a load having dynamic reactive properties to dynamically correct a power factor. The document <CIT> discloses a system and method for measuring power in a power factor converter and <CIT> discloses a power factor correction system with an EMI line filter at the input includes circuitry to sense the capacitor current of the EMI filter to improve the accuracy of the power factor enhancement.

An AC-DC switched mode power supply (SMPS) commonly includes a filter, a power factor correction (PFC) circuit, and a control circuit. The control circuit may calculate an input current, an input voltage, an input power, etc. of the SMPS based on sensed parameters. Typically, the SMPS employs a power-metering chip for measuring input current and input voltage, calculating input power, etc..

The invention is disclosed by the appended claim <NUM>.

Further aspects and areas of applicability will become apparent from the description provided herein. It should be understood that various aspects of this disclosure may be implemented individually or in combination with one or more other aspects. It should also be understood that the description and specific examples herein are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.

Corresponding reference numerals indicate corresponding (but not necessarily identical) parts and/or features throughout the several views of the drawings.

A method for determining an AC input current of a SMPS including a filter and a PFC circuit according to one example embodiment of the present disclosure is illustrated in <FIG> and indicated generally by reference number <NUM>. As shown in <FIG>, the method <NUM> includes generating an analog signal representing a difference between an AC line voltage and an AC neutral voltage in the SMPS in block <NUM>, comparing the analog signal and a defined threshold to determine zero crossings of the analog signal in block <NUM>, determining a power line frequency (e.g., a frequency of an AC input voltage and/or an AC input current) based on at least two of the zero crossings of the analog signal in block <NUM>, determining a reactive current flowing in the filter based on the determined frequency in block <NUM>, and determining the AC input current of the SMPS based on the determined reactive current and a PFC AC current in block <NUM>.

By identifying zero crossings of the analog signal, the power line frequency of the SMPS may be accurately calculated. This power line frequency is used in determining the AC input current, as further explained below. As such, precisely determining the power line frequency ensures the determined input current is accurate. Because the input current is accurately determined, current sensing devices such as conventional power-metering devices (e.g., power meter chips) used to monitor input parameters such as an AC input current are unnecessary.

As explained above, the AC input current is determined based on the PFC AC current and the reactive current. For example, <FIG> illustrates a SMPS <NUM> including a line rail L, a neutral rail N, a filter <NUM> coupled between the line rail L and the neutral rail N for receiving an AC input current i_in, and a PFC circuit <NUM> coupled to an output of the filter <NUM>. The filter <NUM> (e.g., an electromagnetic interference (EMI) filter) includes one or more X-capacitors coupled between the line rail L and the neutral rail N. For purposes of calculations, the one or more X-capacitors may be combined into an equivalent X-capacitance C_eq of the filter <NUM>. These X-capacitors provide a path for a reactive current i_c to flow between the line rail L and the neutral rail N. As such, a current i_pfc provided to the PFC circuit <NUM> is not necessary equal to the AC input current i_in. Therefore, when determining the AC input current i_in, compensation should be made for the reactive current i_c flowing through the filter's X-capacitors.

Referring back to <FIG>, the power line frequency may be determined based on at least two zero crossings of the analog signal representing a difference between the AC line voltage and the AC neutral voltage. For example, <FIG> illustrates a graph <NUM> including an analog signal <NUM> and a square wave signal <NUM>. The analog signal <NUM> represents a difference between the AC line voltage and the AC neutral voltage as explained above. In some examples, the analog signal <NUM> may be generated with a single differential amplifier, as further explained below.

The square wave signal <NUM> may be generated based on a comparison between the analog signal <NUM> and a defined threshold. For example, a comparator may be used to generate the square wave signal <NUM>. In such examples, the comparator may output a high or low signal when the analog signal <NUM> equals the defined threshold, is greater than the defined threshold, is less than the defined threshold, etc. After which, the comparator may be reset. This creates various rising edges and falling edges of the square wave signal <NUM>.

The defined threshold may be a zero crossing of the analog signal <NUM>. For example, the defined threshold may equal zero. In other examples, the defined threshold may be another suitable positive value if the analog signal is shifted to prevent the signal from falling below zero. This may be necessary if a digital controller (e.g., digital signal processor (DSP)) is used to process the information and calculate the power line frequency. In the particular example of <FIG>, the analog signal is shifted <NUM> V (e.g., half of the <NUM> DSP voltage), and therefore the defined threshold is <NUM> V.

The rising edges and/or falling edges of the square wave signal <NUM> may correspond to the zero crossings of the analog signal. For example, in the particular example of <FIG>, each rising edge and each falling edge of the square wave signal <NUM> correspond to one zero crossing (e.g., <NUM> V) of the analog signal. In other examples, only the rising edges or only the falling edges may correspond to the zero crossings.

In the example of <FIG>, the power line frequency may be determined based on two consecutive zero crossings. For example, when two consecutive zero crossings are used to determine the frequency f, a time interval (t) between the two consecutive zero crossing points may be half of the period (T) of main power supply, as shown below in equation (<NUM>). Equation (<NUM>) may be rearranged into equation (<NUM>) to solve for the frequency (f). In equation (<NUM>) above, the time interval (t) may be measured, determined, etc. by, for example, an edge interruption mechanism in a control circuit (e.g., any one of the control circuit disclosed herein). <MAT> <MAT>.

In some examples, the power line frequency of a power supply may vary from <NUM> to <NUM>. This variation in the frequency may have a large impact on impedances in the power supply, such as on the X-capacitance C_eq of the filter <NUM> in <FIG>. For example, the capacitive reactance of the X-capacitance C_eq of <FIG> is <NUM> / (<NUM>*pi*f*C). This capacitive reactance affects the reactive current i_c. As such, by determining the precise value of the power line frequency (f), the reactive current i_c may be accurately calculated (as further explained below). As a result, the input current i_in may be determined with precision.

Additionally, the power line frequency (f) determination explained above is adaptive to frequency variations. For example, if the unknown power line frequency (f) of the input voltage varies, zero crossings of the analog signal will change accordingly. In turn, the time interval (t) between the two consecutive zero crossing points changes. Thus, even if the power line frequency (f) varies (e.g., between <NUM> and <NUM>), the frequency determination scheme explained above may precisely determine the value of the frequency (f).

The determined input current may be used in a variety of ways. For example, the determined input current may be used to calculate other electrical parameters (e.g., input power, etc.) of the SMPS. In such examples, conventional power-metering devices (e.g., power meter chips) that calculate input parameters are unnecessary. Additionally, the determined input current may be periodically, randomly or continuously reported to an external device for monitoring purposes. In other examples, the determined input current may be used for controlling one or more power switches in the PFC circuit and/or other power conversion circuitry in the SMPS. In such examples, the determined input current may be used to increase the power factor of the SMPS.

The above methods for determining an AC input current may be implemented in any suitable control circuit including, for example, any one of the control circuits disclosed herein. For example, and as shown in <FIG>, the SMPS <NUM> includes a control circuit <NUM> coupled to the PFC circuit <NUM> for controlling at least one power switch <NUM> in the PFC circuit <NUM>. As shown in <FIG>, the control circuit <NUM> receives sensed signals <NUM>, <NUM> representing the AC line voltage and the AC neutral voltage, respectively. In some examples, the control circuit <NUM> may generate an analog signal (e.g., the analog signal <NUM> of <FIG>) representing a difference between the AC line voltage and the AC neutral voltage, and determine an AC input voltage of the SMPS <NUM> and/or a power line frequency based on the analog signal. In some instances, the control circuit <NUM> may compare the analog signal and a defined threshold to determine zero crossings of the analog signal, and then determine the power line frequency based on at least two of the zero crossings of the analog signal. In some examples, the control circuit may determine the reactive current i_c flowing through the X-capacitance C_eq based on the determined frequency, and determine the AC input current of the SMPS <NUM> based on the determined reactive current i_c and the PFC AC current i_pfc, as explained above.

The control circuit <NUM> may include various components for determining the power line frequency, the AC input voltage, the AC input current i_in, etc. In some examples, the control circuit <NUM> may include one or more amplifiers, comparators, filters, controllers, etc. for determining the AC input current i_in. For example, <FIG> illustrates an AC-DC SMPS <NUM> including a control circuit <NUM> having differential amplifiers <NUM>, <NUM>, a comparator <NUM>, filters <NUM>, <NUM> (e.g., RC filters, etc.) and a digital controller <NUM> (e.g., a DSP). In other examples, the control circuit <NUM> may include more or less components than is shown in <FIG>. The control circuit <NUM> of <FIG> is one example implementation of the control circuit <NUM> of <FIG>.

In some examples, the differential amplifier <NUM> may generate an analog signal representing a difference between an AC line voltage and an AC neutral voltage. In such examples, the digital controller <NUM> may determine an AC input voltage Vin_ac and a power line frequency (e.g., the frequency of the AC input voltage Vin_ac and/or an AC input current i_in) based on the analog signal. In some examples, the control circuit <NUM> (e.g., the digital controller <NUM>) may then determine a reactive current i_c, the AC input current i_in, an input power of the SMPS <NUM>, etc..

As shown in <FIG>, the SMPS <NUM> further includes a filter <NUM> and an active PFC circuit <NUM> coupled to the output of the filter <NUM>. As shown, the filter <NUM> is represented by an equivalent X-capacitance C_eq coupled across between a line rail L and a neutral rail N. In the particular example of <FIG>, the PFC circuit <NUM> has a boost topology. As such, the PFC circuit <NUM> includes an inductor L, a power switch Q, and a diode D arranged in a boost configuration. As shown, the power switch Q is an N-channel MOSFET. In other examples, another suitable topology and/or suitable switching device may be employed if desired.

The power switch Q of the PFC circuit <NUM> may be controlled with a PFC current loop control. For example, the control circuit <NUM> may receive a bulk voltage of the PFC circuit <NUM> via a voltage divider <NUM>, and an inductor current iL via the differential amplifier <NUM> and the filter <NUM>. The control circuit <NUM> may then generate a control signal with a driver <NUM> for controlling the power switch Q.

Additionally, the SMPS <NUM> includes a DC/DC power converter <NUM> (e.g., a DC/DC power circuit) coupled to the output of the PFC circuit <NUM>. The DC/DC power converter <NUM> may include any suitable converter topology including, for example, a flyback converter, a forward converter (e.g., a two transistor forward converter), a buck converter, a boost converter, a bridge converter (e.g., full bridge, half bridge, etc.), a resonant converter (e.g., an LLC converter, etc.), etc. Additionally, the DC/DC power converter <NUM> may include an isolated converter topology (e.g., having a transformer), or a non-isolated converter topology. In some examples, the DC/DC power converter <NUM> may include synchronous rectifiers on the secondary side of an isolation transformer.

Further, the SMPS <NUM> may include a rectification circuit for rectifying the AC input. For example, and as shown in <FIG>, the SMPS <NUM> includes a diode bridge rectifier <NUM> coupled between the filter <NUM> and the PFC circuit <NUM>. In some examples, a high frequency filter capacitor C may be coupled between the rectifier <NUM> and the PRC circuit <NUM>, as shown in <FIG>. In other embodiments, other suitable rectification circuits may be employed if desired.

The input current i_in may be determined based on the inductor current iL provided to the PFC circuit <NUM> and the reactive current i_c in the filter <NUM>. The input current i_in is expressed as shown in equation (<NUM>) below.

As shown in <FIG>, an instantaneous value (e.g., an RMS value) of the inductor current iL may be measured based on a voltage drop across a shunt resistor R1. This voltage drop signal is amplified by the single differential amplifier <NUM>. Next, the amplified signal is fed to a pin of an ADC in the digital controller <NUM> via the filter <NUM>. In the particular example of <FIG>, the differential amplifier <NUM> includes an offset. For example, the differential amplifier <NUM> may include a voltage divider for shifting (e.g., offsetting) the amplifier's output to ensure the output is positive.

In such examples, the inductor current iL may be determined based on a voltage (Vil. ADC) sampled by the ADC (e.g., the ADC counter value), and provided by the differential amplifier <NUM>. For example, the value of the ADC after converting the output of the differential amplifier <NUM> may be determined using equation (<NUM>) below.

In equation (<NUM>), R1 is the value of the shunt resistor, Gi is the gain of the differential amplifier <NUM>, Voffset is the offset in the differential amplifier <NUM> as explained above, and ADCi is the ADC's interrupt bit. The interrupt bit ADCi may be expressed as equation (<NUM>) below, where N is the number of bits of the ADC, and Vref is the reference voltage provided to the ADC.

The inductor current iL may be calculated by rearranging equation (<NUM>), as shown below in equation (<NUM>).

In equation (<NUM>), values of the Vref, N, R1, Gi and Voffset are known based on the design of the SMPS <NUM>. In such examples, if the ADC is a <NUM> bit ADC (as is typical), the reference voltage Vref is <NUM>. 5V, and Voffset / (R1xGi) equals loffset, equation (<NUM>) may be simplified to equation (<NUM>) below.

Equation (<NUM>) may be further simplified into equation (<NUM>) below. In equation (<NUM>), Ki equals <NUM> / <NUM>^<NUM> * <NUM> / Rs * Gi, A equals ViL. ADC, and B equals loffset. In such examples, the inductor current iL can be derived once the ADC counter value ViL. ADC is obtained by the digital controller <NUM>.

The reactive current i_c may be determined based on the equivalent X-capacitance C_eq, as shown in equation (<NUM>) below.

In equation (<NUM>), Vc is the voltage across the equivalent X-capacitance C_eq, and is determined based on equation (<NUM>) below. In equation (<NUM>), Vac(t) is the AC main input voltage, Vac is a measured value of the AC input voltage, and w equals <NUM> x π (pi) x f (frequency).

When equations (<NUM>) and (<NUM>) are combined, the reactive current i_c may be expressed as equation (<NUM>) below.

For example, <FIG> and <FIG> illustrate graphs <NUM>, <NUM> including various waveforms of simulated current in the SMPS <NUM>. Specifically, the graph <NUM> of <FIG> includes a current waveform <NUM> representing the inductor current iL(t), and a current waveform <NUM> representing the input current i_in(t). The graph <NUM> of <FIG> includes a current waveform <NUM> representing the reactive current i_c(t), and a current waveform <NUM> representing the input current i_in(t).

The graph <NUM> shows the impact of the reactive current i_c at a light load. For example, at a light load (e.g., <NUM>% load and below, etc.), the input current i_in(t) (waveform <NUM>) and the inductor current iL(t) (e.g. the PFC current) are small. As such, the reactive current i_c(t) (waveform <NUM>) may have a larger impact on the input current i_in(t) than as compared to a larger load, a full load, etc. Thus, if the reactive current i_c(t) cannot be accurately calculated at, for example, a light load, the input current i_in(t) (determined based on the reactive current) may not meet desired accuracy standards.

Referring back to <FIG>, the control circuit <NUM> uses the single differential amplifier <NUM> to determine the AC main input voltage and the frequency (f). For example, and as shown in <FIG>, the differential amplifier <NUM> generates an analog signal representing a difference between the AC line voltage and the AC neutral voltage, as explained herein. This analog signal is provided to the digital controller <NUM> for obtaining the AC main input voltage. For example, an instantaneous value (e.g., an RMS value) of the AC main input voltage Vac may be determined based on equation (<NUM>) below.

In equation (<NUM>), Vac. ADC represent a voltage (e.g., the analog signal) sampled by the ADC and provided by the differential amplifier <NUM>, R2 / (R1 + R2) represents a voltage divider for scaling down the main voltage to an acceptable voltage level for the digital controller <NUM>, N is the number of bits of the ADC, and Vref is the reference voltage provided to the ADC. Additionally, Z represents a voltage shift (e.g., <NUM>. 25V) to accommodate the ADC voltage range (e.g., <NUM>.

The control circuit <NUM> may determine the frequency (f) when obtaining the AC main input voltage. For example, and as shown in <FIG>, the analog signal generated by the differential amplifier <NUM> is provided to the comparator <NUM>. The comparator <NUM> compares the analog signal (e.g., the analog signal <NUM> of <FIG>) to a defined threshold, and generates a square wave signal (e.g., the square wave signal <NUM> of <FIG>) for the digital controller <NUM> based on the comparison, as explained above. The defined threshold is selected to ensure rising edges and/or falling edges of the square wave signal correspond to the zero crossings of the analog signal (and therefore the AC main input voltage). The ADC in the digital controller <NUM> then calculates the power line frequency (f) based on the rising edges and falling edges (zero crossings) of the analog signal, as explained above.

By developing the analog signal (the AC main input voltage) with the single differential amplifier <NUM> and determining precise zero crossings with the comparator <NUM>, the power line frequency (f) may be accurately calculated. For example, and as explained herein, the frequency (f) is determined based on zero crossing points of the analog signal (a single waveform) generated by the differential amplifier <NUM>. In contrast, conventional approaches determined frequency based on multiple waveforms. Specifically, conventional approaches determined zero crossing points of a line voltage signal and zero crossing points of a neutral voltage signal, and then determined the frequency based on both sets of zero crossing points. As such, any delay between when the line voltage signal and the neutral voltage signal crosses zero may cause inaccuracies in the determined frequency. However, in the present disclosure, the power line frequency (f) may be accurately determined without this delay. In turn, the precise power line frequency (f) may be used to accurately determine the reactive current i_c, as explained above.

Additionally, in the particular example of <FIG>, the AC main input voltage and the frequency (f) are determined by using the single differential amplifier <NUM> (e.g., a high impedance differential amplifier). In such examples, only one port of the ADC in the digital controller <NUM> may be required to obtain the frequency (f) as compared to traditional control schemes that measure the AC line voltage and the AC neutral voltage, and require two or more ADC ports.

In some embodiments, the control circuit <NUM> may determine the input power provided to the SMPS <NUM>. For example, the digital controller <NUM> may determine an input power Pin of the SMPS <NUM> based on the analog signal and the AC input current. More specifically, the digital controller <NUM> may calculate the input power Pin by multiplying an RMS value of the AC main input voltage Vac calculated in equation (<NUM>) above, and an RMS value of the AC input current i_in calculated in equation (<NUM>) above. In such examples, the power factor is assumed to be a value near unity (<NUM>), such as <NUM>.

The calculated input power Pin may be used to calibrate the SMPS <NUM> based on the actual input power. For example, <FIG> illustrates a graph <NUM> including multiple values PM1-<NUM> of the calculated input power Pin and multiple values P1-<NUM> of the actual input power at different loads. Specifically, the values PM1, P1 correspond to a <NUM>% load, the values PM2, P2 correspond to a <NUM>% load, the values PM3, P3 correspond to a <NUM>% load (half load), and the values PM4, P4 correspond to a <NUM>% load (full load).

Based on the points of intersection between each corresponding calculated value and actual value, offset errors and gain errors of the ADC in the digital controller <NUM> may be determined at various loads. For example, the offset error and the gain error may be calculated based on the values PM1-<NUM>, P1-<NUM> corresponding to the <NUM>% load, the <NUM>% load, the <NUM>% load, and the <NUM>% load. For instance, equations (<NUM>) and (<NUM>) below may be used to determine the offset error and the gain error, respectively, between the <NUM>% load and the <NUM>% load. <MAT> <MAT>.

Additionally, equations (<NUM>) and (<NUM>) below may be used to determine the offset error and the gain error, respectively, between the <NUM>% load and the <NUM>% load. <MAT> <MAT>.

The offset error and the gain error calculations may also be applicable to output power of the SMPS <NUM>. For example, a calculated output power of the SMPS <NUM> may be used to calibrate the SMPS <NUM> based on the actual output power. In such examples, equations similar to equations (<NUM>)-(<NUM>) may be employed to determine the offset error and the gain error at various loads.

In some examples, the control circuits disclosed herein may report one or more electrical parameters to an external device. For example, <FIG> illustrates an AC-DC SMPS <NUM> including a control circuit <NUM> having an interface for communicating with an external device. In the particular example of <FIG>, the interface includes a power management bus (PMBus). In other examples, the interface may additionally and/or alternatively include an I-squared-C bus, a universal serial bus (USB), a wire, a connector, a terminal, etc..

As shown in <FIG>, the SMPS <NUM> includes the filter <NUM>, the bridge rectifier <NUM>, the PFC circuit <NUM>, and the DC/DC power converter <NUM> of <FIG>. For example, the DC/DC power converter <NUM> may include at least one power switch <NUM> and a transformer <NUM> coupled to the power switch <NUM>. Although the power switch <NUM> is shown coupled along a high DC rail and to a primary winding of the transformer <NUM>, it should be apparent to those skilled in the art that the power switch <NUM> and/or the transformer <NUM> may be coupled in another suitable manner depending on, for example, the topology of the DC/DC power converter <NUM>.

The control circuit <NUM> of <FIG> is similar to the control circuit <NUM> of <FIG>, but includes additional components for controlling the power switch <NUM> of the DC/DC power converter <NUM> along with the power switch Q of the PFC circuit <NUM>. For example, the control circuit <NUM> includes a main voltage conditioning circuit <NUM>, the digital controller <NUM> of <FIG> (e.g., a primary side digital controller), a secondary side digital controller <NUM>, and an opto-coupler <NUM> coupled between the primary side digital controller <NUM> and the secondary side digital controller <NUM>. The main voltage conditioning circuit <NUM> may include a differential amplifier (e.g., the differential amplifier <NUM> of <FIG>), a comparator (e.g., the comparator <NUM> of <FIG>), etc. for developing a signal based on the line and neutral voltages and the power line frequency, as explained above. Additionally, the digital controller <NUM> may determine the power line frequency, a reactive current in the filter <NUM>, an AC input current lin of the SMPS <NUM>, an AC main voltage Vac, an input power Pin, etc., as explained above.

The digital controller <NUM> controls one or more power switches in the DC/DC power converter <NUM>. For example, the digital controller <NUM> receives signals representing an output voltage Vout and an output current lout of the DC/DC power converter <NUM>, and then generates one or more control signals based on the received signals for controlling the power switch(es) in the DC/DC power converter <NUM>.

Additionally, the digital controller <NUM> may calculate an output power Pout of the SMPS <NUM> if desired. In some examples, and as shown in <FIG>, the control circuit <NUM> may pass the calculated output power Pout from the secondary side digital controller <NUM> to the primary side digital controller <NUM>. In such examples, the primary side digital controller <NUM> may use the output power Pout to estimate the input power Pin (as further explained below), control the power switch Q in the PFC circuit, etc. In other examples, secondary side digital controller <NUM> may estimate the input power Pin if desired.

The opto-coupler <NUM> provides isolation in the control circuit <NUM> between primary side control components and secondary side control components. As shown, signals representing input parameters (e.g., the AC main voltage Vac, the AC input current lin, the input power Pin, etc.) may be passed from the primary side controller <NUM> to the secondary side digital controller <NUM> via the opto-coupler <NUM>, and signals representing output parameters (the output power Pout, etc.) may be passed from the secondary side controller <NUM> to the primary side digital controller <NUM> via the opto-coupler <NUM>. In some examples, the input and output parameters may be passed through the opto-coupler <NUM> via a universal asynchronous receiver-transmitter (UART).

One or more of the input and output parameters may be reported to the external device via the communication interface. For example, in the particular example of <FIG>, one or more of the AC main voltage Vac, the AC input current lin, the input power Pin, the output voltage Vout, the output current lout, the output power Pout, etc. may be sent by the secondary side digital controller <NUM> to the external device via the PMBus. This allows a user to review and confirm the input and output parameters of the SMPS <NUM> are at desired levels, and confirm the accuracy of calculated values of the parameters. In other examples, the primary side digital controller <NUM> may report any one or more of the input and output parameters to the external device via a communication interface.

In other embodiments, it may be desirable to report calculated values of one or more electrical parameters depending on the accuracy of the calculated value. For example, <FIG> illustrates a method <NUM> for reporting an AC input electrical parameter of a SMPS including a filter and a PFC circuit. As shown in <FIG>, the method <NUM> includes calculating a value of the AC input electrical parameter of the SMPS in block <NUM>. For example, and as further explained below, the AC input electrical parameter may be determined based on, e.g., a reactive current in the filter, a PFC input current, etc..

The method <NUM> further includes estimating a value of the AC input electrical parameter of the SMPS in block <NUM>. The estimated value of the AC input electrical parameter may be determined based on known characteristics such as the efficiency, the output power, etc. of the SMPS.

Additionally, the method <NUM> includes determining an average value of the calculated AC input electrical parameter in block <NUM>. For example, the AC input electrical parameter may be averaged over a number of samples for a number of AC cycles. Averaging the calculated AC input electrical parameter may increase the accuracy of the electrical parameter. In some examples, this step is performed if a difference between the calculated value of the AC input electrical parameter and the estimated value of the AC input electrical parameter is less than a defined tolerance threshold.

The method <NUM> further includes determining an accuracy of the calculated value of the AC input electrical parameter in block <NUM>, and reporting the calculated value of the input electrical parameter to an external device in block <NUM>. The accuracy of the calculated AC input electrical parameter may be based on, for example, the average value of the AC input electrical parameter. Additionally, in some examples the calculated value of the input electrical parameter is reported if the accuracy of the calculated value of the AC input electrical parameter is less than a defined accuracy threshold.

The AC input electrical parameter of <FIG> may be any suitable electrical parameter in the SMPS such as the AC input current, the input power, etc. of the SMPS. For example, <FIG> illustrates a method <NUM> for calibrating (or recalibrating) and reporting the input power of the SMPS.

As shown in <FIG>, the method <NUM> includes calculating an AC input power Pin. cal of the SMPS in block <NUM> and a DC output power Pout. cal of the SMPS in block <NUM>. For example, the AC input power Pin. cal may be determined based on the calculated AC input current (e.g., an RMS value of the AC input current) and AC input voltage (e.g., an RMS value of the AC input voltage) as explained above relative to equations (<NUM>) and (<NUM>). In such examples, the calculated AC input current may be based on a reactive current in a filter, a PFC current, a power line frequency, etc. as explained above. The DC output power Pout. cal may be determined based on a sensed output voltage Vout and output current lout of a DC/DC power converter, as explained above relative to <FIG>.

Next, the method <NUM> includes querying a table in block <NUM>, and estimating an AC input power Pin. est in block <NUM>. For example, the table may include various known efficiency curves based on actual measurements. The table may be a lookup table stored in, for example, a control circuit implementing the method <NUM>. The estimated AC input power Pin. est may be calculated based on the calculated output power Pout. cal (which is typically more accurate than the calculated input power Pin. cal), and the efficiency curves. For example, the estimated AC input power Pin. est may be calculated based on equation (<NUM>) below. In equation (<NUM>), η represents an efficiency of the SMPS, ηPFC represents an efficiency of the PFC circuit, ηDC/DC represents an efficiency of the DC/DC power converter, etc. at the calculated output power Pout.

The method <NUM> further includes determining whether a difference ΔPin between the calculated AC input power Pin. cal and the estimated AC input power Pin. est is less than a defined tolerance threshold ε in block <NUM>. The defined tolerance threshold ε may be any suitable value depending on, for example, the estimated AC input power Pin. est and a desired accuracy of the AC input power Pin. For example, if it is desirable to have an accuracy within a particular value, the defined tolerance threshold ε may be equal to the estimated AC input power Pin. est multiplied by the particular value. For instance, if the estimated AC input power Pin. est is 869W and it is desirable to have an accuracy within <NUM>%, the defined tolerance threshold ε may be equal to about 17W (869W*<NUM>%).

If it is determined that the difference ΔPin between the calculated AC input power Pin. cal and the estimated AC input power Pin. est is greater than or equal to the defined tolerance threshold ε in block <NUM>, the method <NUM> returns to calculating the AC input power Pin. cal of the SMPS in block <NUM>. In such examples, the AC input power Pin. cal may be recalculated in the attempt to determine a more accurate value of the AC input power Pin. For example, any one of the various parameters used in calculating the AC input power Pin. cal may change. For instance, parameters such as the reactive current, the AC input current, the power line frequency, etc. may be recalculated to determine values that are more accurate. As a result, the AC input current may be determined, and the AC input power Pin. cal may become more accurate. As such, the AC input power Pin. cal may be calibrated (or recalibrated) to obtain a more accurate value.

If it is determined that the difference ΔPin between the calculated AC input power Pin. cal and the estimated AC input power Pin. est is less than the defined tolerance threshold ε in block <NUM>, an average value of the AC input power Pin. avg is calculated in block <NUM>. In some examples, averaging the value of the AC input power Pin. cal may improve the accuracy. For example, the average value of the AC input power Pin. avg may be calculated based on equation (<NUM>) below. In equation (<NUM>), N may represent any suitable value including, for example, the number of samples for a number of AC cycles. In some examples, it is desirable to increase the value of N to achieve a more accurate averaged value of the AC input power Pin.

Next, the method <NUM> includes determining whether an accuracy of the calculated AC input power Pin. cal is less than a defined accuracy threshold Acc_threshold in block <NUM>. This determination may be made based on the averaged AC input power Pin. avg, as shown in equation (<NUM>) below.

The defined accuracy threshold Acc_threshold may be any suitable value based on, for example, design parameters, etc. In some examples, the defined accuracy threshold Acc_threshold may depend on the load coupled to the SMPS. For example, the defined accuracy threshold Acc_threshold may be <NUM>% for loads ranging between <NUM>-<NUM>% load, etc. In other examples, the defined accuracy threshold Acc_threshold may be <NUM>% for lighter loads (e.g., loads ranging between <NUM>-<NUM>% load, etc.).

If it is determined that the accuracy of the calculated AC input power Pin. cal is greater than or equal to the defined accuracy threshold in block <NUM>, the method <NUM> returns to calculating (or recalculating) the AC input power Pin. cal of the SMPS in block <NUM> in the attempt to determine a more accurate value of the AC input power Pin. cal, as explained above. In such examples, the AC input power Pin. cal may be calibrated (or recalibrated) to obtain a more accurate value. If, however, the determined accuracy of the calculated AC input power Pin. cal is less than the defined accuracy threshold in block <NUM>, the calculated AC input power Pin. cal may be reported to an external device in block <NUM>. For example, the calculated AC input power Pin. cal may be reported via a PMBus as explained above.

In other examples, the AC input electrical parameter of <FIG> may be the AC input current. For example, <FIG> illustrates a method <NUM> for calibrating (or recalibrating) and reporting the AC input current of the SMPS. The method <NUM> of <FIG> is substantially similar to the method <NUM> of <FIG>, but refers to the AC input current.

For example, and as shown in <FIG>, the method <NUM> includes calculating an AC input current lin. cal of the SMPS in block <NUM> and a DC output power Pout. cal of the SMPS in block <NUM>. The AC input current lin. cal may be determined based on a reactive current, a PFC current, a power line frequency, etc. as explained above.

The method <NUM> then includes querying a table in block <NUM>, and estimating an AC input current lin. est in block <NUM>. As explained above, the table (e.g., a stored lookup table) may include various known efficiency curves based on actual measurements. The estimated AC input current lin. est in <FIG> may be calculated based on the calculated output power Pout. cal, the efficiency curves, and an AC main voltage Vac. For example, the estimated AC input current lin. est may be calculated based on equation (<NUM>) below.

Next, the method <NUM> includes determining whether a difference ΔIin between the calculated AC input current lin. cal and the estimated AC input current lin. est is less than a defined tolerance threshold ε in block <NUM>. For example, the defined tolerance threshold ε may be determined in a similar manner as explained above relative to the input power's tolerance threshold ε.

If it is determined that the difference ΔIin between the calculated AC input current lin. cal and the estimated AC input current lin. est is greater than or equal to the defined tolerance threshold ε in block <NUM>, the method <NUM> returns to calculating (or recalculating) the AC input current lin. cal in block <NUM> in the attempt to determine a more accurate value of the AC input current lin. In such examples, the AC input current lin. cal may be calibrated (or recalibrated) and/or determined to obtain a more accurate value if more accurate values of the reactive current, the PFC current, the power line frequency, etc. are obtained. If, however, it is determined that the difference ΔIin between the calculated AC input current lin. cal and the estimated AC input current lin. est is less than the defined tolerance threshold ε in block <NUM>, an average value of the AC input current lin. avg is calculated in block <NUM>. This may improve the accuracy of the AC input current lin. For example, the average value of the AC input current lin. avg may be calculated based on equation (<NUM>) below. In equation (<NUM>), N may represent the number of samples for a number of AC cycles, as explained above.

The method <NUM> further includes determining whether an accuracy of the calculated AC input current lin. cal is less than a defined accuracy threshold Acc_threshold in block <NUM>. The defined accuracy threshold Acc_threshold relating to the calculated AC input current lin. cal may be any suitable value such as <NUM>%, <NUM>%, etc., as explained above relative to the defined accuracy threshold relating to the AC input power. The accuracy of the calculated AC input current lin. cal is determined based on the averaged AC input power lin. avg, as shown in equation (<NUM>) below.

If the accuracy of the calculated AC input current lin. cal is greater than or equal to the defined accuracy threshold in block <NUM>, the method <NUM> returns to calculating (or recalculating) the AC input current lin. cal in block <NUM> in the attempt to determine a more accurate value of the AC input current lin. cal (e.g., recalibration), as explained above. If, however, the determined accuracy of the calculated AC input current lin. cal is less than the defined accuracy threshold in block <NUM>, the calculated AC input power lin. cal may be reported to an external device in block <NUM> via, for example, a PMBus as explained above.

The methods <NUM>, <NUM>, <NUM> for calibrating (or recalibrating) and/or reporting an AC input electrical parameter may be implemented by any suitable control circuit including, for example, any one of the control circuits disclosed herein. In some examples, some or all portions of the methods may be implemented with one or more of the digital controllers disclosed herein (e.g., the primary side digital controller, the secondary side digital controller, etc.) may be used. Additionally, the methods for calibrating (or recalibrating) and/or reporting an AC input electrical parameter may be implemented in the control circuit in conjunction with the methods for determining an AC input current. In other examples, the methods for recalibrating and/or reporting an AC input electrical parameter (and not the methods for determining an AC input current) may be implemented in the control circuit, or vice-versa.

The control circuits disclosed herein may include an analog control circuit, a digital control circuit, or a hybrid control circuit (e.g., a digital control unit and an analog circuit). The digital control circuits may be implemented with one or more types of digital control circuitry. For example, the digital control circuits each may include a digital controller such as a digital signal controller (DSC), a DSP, a microcontroller unit (MCU), a field-programmable gate array (FPGA), an application-specific IC (ASIC), etc. As such, any one of the control methods disclosed herein may be at least partially (and sometimes entirely) performed by a digital controller.

If, for example, the control circuit is a digital control circuit, the control circuit may be implemented with one or more hardware components and/or software. For example, instructions for performing any one or more of the features disclosed herein may be stored in and/or transferred from a non-transitory computer readable medium, etc. to one or more existing digital control circuits, new digital control circuits, etc. In such examples, one or more of the instructions may be stored in volatile memory, nonvolatile memory, ROM, RAM, one or more hard disks, magnetic disk drives, optical disk drives, removable memory, non-removable memory, magnetic tape cassettes, flash memory cards, CD-ROM, DVDs, cloud storage, etc..

Portions of the control circuits may be on the secondary side of an isolation barrier if, for example, the corresponding power circuit includes an isolation transformer. In such cases, control signal(s) from the control circuits may cross the isolation barrier (e.g., via one or more isolation devices such as isolation transformers, opto-couplers, etc.) to control power switches on the primary side of the power circuit, as shown in <FIG>.

In addition, the control methods disclosed herein may be repeated as desired. For example, the control circuits may be able to successively perform the methods as desired and/or if applicable.

The teachings disclosed herein may be applicable in any suitable SMPS having one or more power circuits. In some examples, the teachings may be implemented in at least part of a front-end AC-DC distributed power supply. In such examples, the power supply may receive an AC input voltage ranging between <NUM>-264VAC at power line frequency ranging between <NUM>-<NUM>, and provide a regulated 12VDC output or another suitable output voltage. For example, the power supply may have an output power rating of 800W at 12V/<NUM>. 7A, 1800W at 12V/<NUM>. 5A, 2000W at 12V/<NUM>. 9A, 2400W at 12V/<NUM>. 7A, and/or another suitable power rating. In some examples, the power supply may include redundant architectures, and provide a single output. The power supply may be particularly useful in server applications, storage applications (e.g., database applications, cloud hosting applications, etc.), networking applications, etc..

By employing the control methods disclosed herein, an AC main voltage may be developed to include precise zero crossings without a delay that is typically seen in conventional approaches when sampling line and neutral voltages. As a result, an accurate value of the power line frequency may be obtained from the zero crossings, and an accurate input current determination may be achieved based on the power line frequency. In some examples, the AC main voltage may be developed using a single differential amplifier. In such examples, only one port of an ADC in a digital controller (if employed) may be required as compared to multiple ports in conventional approaches.

Additionally, the control methods may provide a solution for measuring input power without relying on power-metering devices (e.g., power meter chips) as in conventional approaches. As a result, costs are reduced, board space is increased, etc. as compared to conventional approaches. Thus, the teachings disclosed herein may provide a low cost, compact SMPS design.

Further, the control methods may provide a solution for calibrating (or recalibrating) input parameters such as an AC input current, input power, etc. to improve accuracy of the parameters. If the accuracy of a parameter is adequate, the parameter may be reported to an external device if desired. The calibrating (or recalibrating) of input parameters may be performed while the SMPS is operating (e.g., on-line). As such, calibrations may be based on real-time calculations.

Claim 1:
A switched mode power supply, SMPS, (<NUM>, <NUM>, <NUM>) comprising:
a line rail (L) and a neutral rail (N);
a filter (<NUM>, <NUM>) coupled between the line rail and the neutral rail, the filter including an input for receiving an AC input voltage (Vin_ac) and an AC input current (i_in), an X-capacitance (C_eq), and an output;
a power factor correction, PFC, circuit (<NUM>) coupled to the output of the filter (<NUM>), the PFC circuit (<NUM>) including an input for receiving a PFC AC current (i_pfc); and
a control circuit (<NUM>, <NUM>, <NUM>) coupled to the PFC circuit (<NUM>), the control circuit (<NUM>) configured to:
generate an analog signal (<NUM>) representing a difference between an AC line voltage (<NUM>) and an AC neutral voltage (<NUM>),
compare the analog signal and a defined threshold to determine zero crossings of the analog signal,
determine a frequency of the AC input voltage or the AC input current based on at least two of the zero crossings of the analog signal,
determine a reactive current (i_c) flowing through the X-capacitance (C_eq) in the filter based on the determined frequency,
determine a calculated AC input current (Iin_cal) of the SMPS based on the determined reactive current (i_c) and the PFC AC current (i_pfc), and
characterized by the control circuit (<NUM>) further configured to:
determine an estimated AC input current (Iin_est) of the SMPS based on a defined efficiency, an output power (Pout_cal.) of the SMPS and an AC main voltage (Vac),
determine a difference (ΔIin) between the calculated AC input current (Iin_cal) and the estimated AC input current (Iin_est),
determine an average value of the AC input current (Iin_avg) when the difference (ΔIin) is less than a defined tolerance threshold (E),
determine an accuracy of the determined AC input current (Iin_cal) based on the average value of the AC input current, and
report the determined AC input current to an external device if the accuracy is less than a defined accuracy threshold (Acc_threshold).