Filter apparatus and power supply system

A filter apparatus, which includes a feedback active common-mode filter and a feed-forward active common-mode filter, the feedback active common-mode filter includes a common-mode noise detection component and a first filter circuit, and the feed-forward active common-mode filter includes the common-mode noise detection component and a second filter circuit, where the first filter circuit is connected between the common-mode noise detection component and the device, and performs feedback filtering on a first common-mode noise signal, to obtain a second common-mode noise signal; the common-mode noise detection component is connected between the first filter circuit and the second filter circuit, detects the second common-mode noise signal, and provides the second filter circuit with the second common-mode noise signal; and the second filter circuit is connected between an external power source and the common-mode noise detection component, and performs feed-forward filtering on the second common-mode noise signal.

TECHNICAL FIELD

Embodiments of the present application relate to the field of circuits, and in particular, to a filter apparatus and a power supply system.

BACKGROUND

With a growing quantity of electronic devices, an electromagnetic interference (EMI) phenomenon is increasingly severe. EMI conducted interference includes common-mode interference. To resolve an EMI common-mode interference problem, a conventional method is to add a passive EMI common-mode filter (including a common-mode inductor and a Y capacitor) to a system to suppress noise. However, the passive common-mode filter has disadvantages such as a large size and high costs. In recent years, some scholars use an active filtering technology to resolve the EMI common-mode interference problem, and a new active common-mode EMI filter emerge. According to an active common-mode EMI filter in the prior art, it is generally difficult to balance a conflict between filtering performance and circuit costs.

SUMMARY

Embodiments of the present disclosure provide a filter apparatus and a power supply system, so that filtering performance for common-mode noise can be effectively improved to some degree.

A first aspect provides a filter apparatus, where the filter apparatus is connected between an external power source and a device, the filter apparatus is configured to perform filtering processing on a noise signal from the device, the filter apparatus includes a feedback active common-mode filter and a feed-forward active common-mode filter, the feedback active common-mode filter includes a common-mode noise detection component and a first filter circuit, and the feed-forward active common-mode filter includes the common-mode noise detection component and a second filter circuit, where

the first filter circuit is connected between the common-mode noise detection component and the device, and the first filter circuit is configured to perform feedback filtering processing on a first common-mode noise signal from the device, to obtain a second common-mode noise signal;

the common-mode noise detection component is connected between the first filter circuit and the second filter circuit, and the common-mode noise detection component is configured to detect the second common-mode noise signal, and provide the second filter circuit with the second common-mode noise signal; and

the second filter circuit is connected between the external power source and the common-mode noise detection component, and the second filter circuit is configured to perform feed-forward filtering processing on the second common-mode noise signal.

With reference to the first aspect, in a first possible implementation manner of the first aspect, the common-mode noise detection component is further configured to provide the first filter circuit with the second common-mode noise signal; and

the first filter circuit is further configured to perform feedback filtering processing on the second common-mode noise signal.

With reference to the first possible implementation manner of the first aspect, in a second possible implementation manner of the first aspect, the common-mode noise detection component includes:

a primary side, configured to detect the second common-mode noise signal; and

a first secondary side, where an output end of the first secondary side is connected to an input end of the first filter circuit, and the output end of the first secondary side is further connected to an input end of the second filter circuit, to separately provide the first filter circuit and the second filter circuit with the second common-mode noise signal detected by the primary side.

With reference to the first possible implementation manner of the first aspect, in a third possible implementation manner of the first aspect, the common-mode noise detection component includes:

a primary side, configured to detect the second common-mode noise signal; and

a second secondary side, where an output end of the second secondary side is connected to an input end of the first filter circuit, to provide the first filter circuit with the second common-mode noise signal detected by the primary side; and

a third secondary side, where an output end of the third secondary side is connected to an input end of the second filter circuit, to provide the second filter circuit with the second common-mode noise signal detected by the primary side.

With reference to the second or the third possible implementation manner of the first aspect, in a fourth possible implementation manner of the first aspect, the external power source is a power grid, the power grid is connected to the device by using a power cable, and the power cable includes a phase wire and a neutral line; and

the primary side includes:

a first sub-primary side, connected in series on the phase wire; and

a second sub-primary side, connected in series on the neutral line.

With reference to the first aspect or any possible implementation manner of the first to the fourth possible implementation manners of the first aspect, in a fifth possible implementation manner of the first aspect, the first filter circuit includes a loop compensation circuit, a first current injection circuit, and a first external power supply circuit, where

an input end of the loop compensation circuit is connected to the common-mode noise detection component, and an output end of the loop compensation circuit is connected to an input end of the first current injection circuit, to provide the first current injection circuit with a current signal;

an output end of the first current injection circuit is connected to protection ground, to inject, into the protection ground, the current signal output by the loop compensation circuit; and

the first external power supply circuit is configured to provide the loop compensation circuit with a working voltage.

With reference to the fifth possible implementation manner of the first aspect, in a sixth possible implementation manner of the first aspect, the second filter circuit includes: a voltage/current conversion circuit, a second current injection circuit, and a second external power supply circuit, where

an input end of the voltage/current conversion circuit is connected to the common-mode noise detection component, an output end of the voltage/current conversion circuit is connected to an input end of the second current injection circuit, and the voltage/current conversion circuit is configured to provide the second current injection circuit with a current signal;

an output end of the second current injection circuit is connected to the protection ground, to inject, into the protection ground, the current signal output by the voltage/current conversion circuit; and

the second external power supply circuit is configured to provide the voltage/current conversion circuit with a working voltage.

With reference to the first aspect or any possible implementation manner of the first to the sixth possible implementation manners of the first aspect, in a seventh possible implementation manner of the first aspect, the filter apparatus further includes a differential-mode filter, where

the differential-mode filter is connected between the external power source and the second filter circuit, and the differential-mode filter is configured to perform filtering processing on a differential-mode noise signal from the device.

With reference to the first aspect or any possible implementation manner of the first to the seventh possible implementation manners of the first aspect, in an eighth possible implementation manner of the first aspect, the filter apparatus further includes a high frequency passive common-mode filter, where

the high frequency passive common-mode filter is connected between the first filter circuit and the device, and the high frequency passive common-mode filter performs filtering processing on an initial common-mode noise signal from the device, where

the first noise signal processed by the first filter circuit is a common-mode noise signal obtained after the initial common-mode noise signal is processed by the high frequency passive common-mode filter.

A second aspect provides a power supply system, including the filter apparatus provided in the first aspect, an external power source, and a device, where the filter apparatus, the external power source, and the device form a loop by using a line, when the device runs, a common-mode noise signal is generated on the line, and the filter apparatus is configured to filter the common-mode noise signal.

Based on the foregoing technical solutions, in the filter apparatus provided in the embodiments of the present disclosure, a feedback active common-mode filter and a feed-forward active common-mode filter are sequentially connected in a direction from a device to an external power source, and filtering performance can be effectively improved by means of two stages of filtering. In addition, the two filters share one common-mode noise detection component, which can effectively reduce circuit costs, complying with a high density and miniaturization trend of current power supply products and having a wide application prospect.

DESCRIPTION OF EMBODIMENTS

For ease of comprehension of solutions provided in the embodiments of the present disclosure, the following concepts are first described.

(1) Electromagnetic interference refers to an interference phenomenon generated after an electromagnetic wave interferes with an electronic element, and includes conducted interference and radiated interference. The conducted interference refers to that a signal on one electrical network is coupled to (interferes with) another electrical network by using conductive medium.

In terms of categories, propagation manners of electromagnetic noise may be classified into conducted emission (CE) and radiated emission (RE). The conducted emission refers to a process of propagating electromagnetic noise energy by using one or more conductors (for example, a power cable, a signal line, a control line, or another metal body).

The power cable is a major path through which the conducted interference is transmitted into and out of a device. Through the power cable, interference in the power grid may be transmitted to a device, interfering with normal operation of the device. Similarly, interference generated by the device may also be transmitted to the power grid through the power cable, interfering with normal operation of another device.

(2) Common-mode interference refers to a potential difference between a power cable and the earth, or between a neutral line and the earth. For a three-phase circuit, the common-mode interference exists between any phase and the earth. The common-mode interference may also be construed as common signal interference simultaneously loaded at each input signal interface end. The common-mode interference is transmitted between a signal line and the earth, and is asymmetric interference.

(3) Differential-mode interference refers to a potential difference between a power cable and a neutral line. For example, interference between a neutral line and a live line of a power grid is referred to as the differential-mode interference.

FIG. 1is a schematic block diagram of a filter apparatus100according to an embodiment of the present disclosure. As shown inFIG. 1, the filter apparatus100is connected between an external power source200and a device300, the filter apparatus100is configured to perform filtering processing on a noise signal from the device300, the filter apparatus100includes a feedback active common-mode filter110and a feed-forward active common-mode filter120, the feedback active common-mode filter110includes a common-mode noise detection component130and a first filter circuit140, and the feed-forward active common-mode filter120includes the common-mode noise detection component130and a second filter circuit150, where

the first filter circuit140is connected between the common-mode noise detection component130and the device300, and the first filter circuit140is configured to perform feedback filtering processing on a first common-mode noise signal from the device300, to obtain a second common-mode noise signal;

the common-mode noise detection component130is connected between the first filter circuit140and the second filter circuit150, and the common-mode noise detection component130is configured to detect the second common-mode noise signal, and provide the second filter circuit150with the second common-mode noise signal; and

the second filter circuit150is connected between the external power source200and the common-mode noise detection component130, and the second filter circuit150is configured to perform feed-forward filtering processing on the second common-mode noise signal.

In this embodiment of the present disclosure, the device300may be a load taking power from the external power source200, or the device300may be a device, such as an inverter, that supplies power to the external device200. The external power source is, for example, a power grid or a battery. It should be understood that, the external power source200is connected to the device300by using a power cable, and during operation, the device300generates a noise signal, such as a common-mode noise signal, on the power cable. In this embodiment of the present disclosure, the feedback active common-mode filter110and the feed-forward active common-mode filter120sequentially perform filtering processing on the noise signal from the device before the noise signal reaches the external power source200, which can effectively reduce impact of the noise signal on the external power source, and also indirectly reduces impact of the noise signal on another device connected to the external power source.

In addition, in this embodiment of the present disclosure, in a direction from a noise generator (corresponding to the device300inFIG. 1) to the external power source, the feedback active common-mode filter110is in front of the feed-forward active common-mode filter120, and the feedback active common-mode filter110and the feed-forward active common-mode filter120share one common-mode noise detection component130, so that the filter110and the filter120detect a same signal-to-noise ratio of the noise signal, which is equivalent to using a feed-forward active common-mode filter or a feedback active common-mode filter to detect a signal-to-noise ratio of a noise signal in the conventional technology, helping improve a filtering effect. In addition, the feedback active common-mode filter110and the feed-forward active common-mode filter120share one common-mode noise detection component130, which significantly reduces circuit costs and complies with a high density and miniaturization trend of current power supply products.

Therefore, in the filter apparatus provided in this embodiment of the present disclosure, a feedback active common-mode filter and a feed-forward active common-mode filter are sequentially connected in a direction from a noise generator (corresponding to the device inFIG. 1) to an external power source, and the two filters share one common-mode noise detection component, which can effectively improve an overall filtering effect of a filter circuit on one hand, and effectively reduce circuit costs on the other hand, complying with a high density and miniaturization trend of current power supply products, and having a wide application prospect.

In this embodiment of the present disclosure, for ease of understanding and description, the device300shown inFIG. 1is also referred to as a noise generator.

Optionally, in this embodiment of the present disclosure, the common-mode noise detection component130is further configured to provide the first filter circuit140with the second common-mode noise signal.

The first filter circuit140is further configured to perform feedback filtering processing on the second common-mode noise signal.

Specifically, the common-mode noise detection component130separately provides the first filter circuit140and the second filter circuit150with the detected second common-mode noise signal. The second filter circuit performs feed-forward filtering processing on the second common-mode noise signal, and the first filter circuit140performs feedback filtering processing on the second common-mode noise signal.

It should be understood that, assuming that the first filter circuit140performs feedback filtering processing on the second common-mode noise signal and obtains a third common-mode noise signal, the common-mode noise detection component130may detect the third common-mode noise signal during next detection, and separately provides the third common-mode noise signal for the first filter circuit140and the second filter circuit150, so that the second filter circuit150performs feed-forward filtering processing on the third common-mode noise signal, and the first filter circuit140performs feedback filtering processing on the third common-mode noise signal, to obtain a fourth common-mode noise signal. This process is repeated.

It should be understood that, in a working process of a feedback common-mode filter, a noise signal detected by a noise detection component is a noise signal on which filtering processing has been performed by the feedback common-mode filter. In a working process of a feed-forward common-mode filter, a noise detection component first detects a noise signal, and then performs filtering on the noise signal. In this embodiment of the present disclosure, the feedback active common-mode filter110and the feed-forward active common-mode filter120are sequentially connected in a direction from the device300to the external power source200, and it can be understood that the feedback filtering processing of the feedback active common-mode filter110and the feed-forward filtering processing of the feed-forward active common-mode filter120are sequentially performed on common-mode noise from the device300, that is, the common-mode noise signal processed by the feed-forward active common-mode filter120is a common-mode noise signal that has been processed by the feedback active common-mode filter110.

For example, when the device300runs, a common-mode noise signal a is generated on a power cable, the feedback filtering processing of the feedback active common-mode filter110and the feed-forward filtering processing of the feed-forward active common-mode filter120are sequentially performed on the common-mode noise signal when the common-mode noise signal a is transmitted to the external power source200, and a common-mode noise signal b finally reaching a side of the external power source200is a common-mode noise signal after two stages of filtering processing. Compared with the common-mode noise signal a originally generated by the device300, impact on the external power source200is significantly reduced. For example, the common-mode noise signal a originally generated by the device300is quantized as 1, and it is assumed that filtering performance of the feedback active common-mode filter110and filtering performance of the feed-forward active common-mode filter120are both 1/10. In this case, a common-mode noise signal al is obtained after the common-mode noise signal a is processed by the feedback active common-mode filter110, where a quantized value of the common-mode noise signal al is 1/10. The common-mode noise signal al is further processed by the feed-forward active common-mode filter120, to obtain a common-mode noise signal b, where a quantized value of the common-mode noise signal b is 1/100. It can be known that the common-mode noise signal b (for example, the quantized value is 1/100) finally reaching the side of the external power source200is a common-mode noise signal after two stages of filtering processing. Compared with the common-mode noise signal a (for example, the quantized value is 1) originally generated by the device300, the common-mode noise signal b is significantly attenuated, which reduces a degree of interference to the external power source200, and also indirectly reduces a risk of common-mode interference caused by the external power source200to another device (other than the device300) connected to the external power source200.

It can be known from above that, in this embodiment of the present disclosure, two stages of filtering are implemented by using a feedback active common-mode filter and a feed-forward active common-mode filter, which can effectively improve filtering performance for a common-mode noise signal from a device.

Optionally, as shown inFIG. 2, in this embodiment of the present disclosure, the common-mode noise detection component130includes:

a primary side Np, configured to detect the second common-mode noise signal;

a second secondary side Ns1, where an output end of the second secondary side Ns1is connected to an input end of the first filter circuit140, to provide the first filter circuit140with the second common-mode noise signal detected by the primary side Np; and

a third secondary side Ns2, where an output end of the third secondary side Ns2is connected to an input end of the second filter circuit150, to provide the second filter circuit150with the second common-mode noise signal detected by the primary side Np.

Specifically, as shown inFIG. 2, the first filter circuit140performs feedback filtering processing on a first common-mode noise signal {circle around (1)} from the device300. Specifically, for example, a reverse cancellation signal {circle around (2)} (which is reverse relative to the first common-mode noise signal {circle around (1)}) is generated to weaken the first common-mode noise signal {circle around (1)}. In this case, the second common-mode noise signal detected by the common-mode noise detection component130is a noise signal shown by {circle around (3)} inFIG. 2. For example, strength of the second common-mode noise signal {circle around (3)} may be considered as a strength difference between the first common-mode noise signal {circle around (1)} and the cancellation signal {circle around (2)}. The common-mode noise detection component130provides the second common-mode noise signal {circle around (3)} for the second filter circuit150, and the second filter circuit150performs filtering processing on the second common-mode noise signal {circle around (3)}, to generate a cancellation signal {circle around (4)}. In this case, strength of a noise signal {circle around (5)} that has been processed by the second filter circuit150and that flows to the side of the external power source200may be construed as a strength difference between the second common-mode noise signal {circle around (3)} and the cancellation signal {circle around (4)}. That is, the noise signal {circle around (5)} shown inFIG. 2is already weak compared with the first common-mode noise signal {circle around (1)} from the device300. Therefore, noise interference with an external power source can be significantly reduced.

Therefore, in the filter apparatus provided in this embodiment of the present disclosure, a feedback active common-mode filter and a feed-forward active common-mode filter are sequentially connected in a direction from a noise generator (corresponding to the device inFIG. 1) to an external power source, overall filtering performance of a circuit can be effectively improved by means of two stages of filtering, and two filters share one common-mode noise detection component, which effectively reduces circuit costs.

It should be understood that a specific form of the common-mode noise detection component130is provided inFIG. 2illustratively but not restrictively. In an actual application, another feasible manner may be used, as long as the common-mode noise detection component130can detect a common-mode noise signal in a circuit, and can separately provide the first filter circuit140and the second filter circuit150with the detected common-mode noise signal, which is not limited in this embodiment of the present disclosure.

In this embodiment of the present disclosure, the primary side Np is connected in series on a power cable, and is configured to collect a common-mode noise signal on the power cable. Both secondary sides, that is, the second secondary side Ns1and the third secondary side Ns2, may obtain, by means of electromagnetic induction, the second common-mode noise signal detected by the primary side. The second secondary side Ns1is configured to provide the first filter circuit140with the second common-mode noise signal, and the third secondary side Ns2is configured to provide the second filter circuit150with the second common-mode noise signal.

Optionally, in this embodiment of the present disclosure, the external power source200is a power grid, the power grid is connected to the device300by using a power cable, and the power cable includes a phase wire and a neutral line; and

the primary side Np includes:

a first sub-primary side Np1, connected in series on the phase wire; and

a second sub-primary side Np2, connected in series on the neutral line.

Specifically, as shown inFIG. 3, the power cable includes a live line L line and a neutral line N line. Specifically, the common-mode noise detection component130includes two primary sides (Np) and two secondary sides (the second secondary side Ns1and the third secondary side Ns2), where one primary side Np is connected in series on the L line of the power grid, and the other primary side Np is connected in series on the N line of the power grid, to detect a common-mode noise signal on the L line and the N line. Based on an electromagnetic induction principle, the secondary side Ns1and the secondary side Ns2separately provide the detected common-mode noise signal to the first filter circuit140of the feedback active common-mode filter110and the second filter circuit150of the feed-forward active common-mode filter120.

Optionally, as shown inFIG. 3, an output end of the second secondary side is connected in parallel to a resistor R2, an output end of the third secondary side is connected in parallel to a resistor R1, and the two resistors are configured to convert a common-mode noise current signal sampled by the primary side Np into a voltage signal. The resistor R1may be considered as, for example, an output resistance of a common-mode current transformer, where a resistance value is generally between several ohms and dozens of ohms, or may be considered as an input resistance of the first filter circuit140, which is not limited in this embodiment of the present disclosure. The resistor R2generally has a resistance value of thousands of ohms, and may be considered herein as an input resistance of the second filter circuit150.

Optionally, as shown inFIG. 3, in this embodiment of the present disclosure, the first filter circuit140includes: a loop compensation circuit141, a first current injection circuit142, and a first external power supply circuit143, where

an input end of the loop compensation circuit141is connected to the common-mode noise detection component130, and an output end of the loop compensation circuit141is connected to an input end of the first current injection circuit142, to provide the first current injection circuit142with a current signal;

an output end of the first current injection circuit142is connected to protection ground, to inject, into the protection ground, the current signal output by the loop compensation circuit141; and

the first external power supply circuit143is configured to provide the loop compensation circuit141with a working voltage.

Specifically, the input end of the loop compensation circuit141is connected to an output end of the second secondary side Ns1of the common-mode noise detection component130.

It should be understood that the current signal output by the loop compensation circuit141is a signal used to cancel the first common-mode noise signal. In this case, the first current injection circuit142injects, into the protection ground, the current signal output by the loop compensation circuit141, that is, the current signal is used to cancel the first common-mode noise signal from the device300. It should be further understood that an event of reducing strength of the first common-mode noise signal {circle around (1)} by the cancellation signal {circle around (2)} shown inFIG. 2may be construed as an effect generated by injecting, by the first current injection circuit142into the protection ground, the current signal output by the loop compensation circuit141shown inFIG. 3.

In this embodiment of the present disclosure, specifically, the resistor R1connected in parallel to the output end of the second secondary side Ns1may be considered as an input resistance of the loop compensation circuit141.

Optionally, the loop compensation circuit141may be built by an operational amplifier, specifically, as shown inFIG. 4.

It should be understood that the device300shown inFIG. 4is specifically an inverter.

It should be understood that,FIG. 3andFIG. 4illustratively but not restrictively provide schematic structural diagrams of the first filter circuit140in the feedback active common-mode filter110. In an actual application, another feasible form in the prior art may also be used for the first filter circuit140, as long as the first filter circuit140can implement feedback filtering in cooperation with the common-mode noise detection component130, which is not limited in this embodiment of the present disclosure.

Optionally, as shown inFIG. 3, in this embodiment of the present disclosure, the second filter circuit150includes: a voltage/current conversion circuit151, a second current injection circuit152, and a second external power supply circuit153, where

an input end of the voltage/current conversion circuit151is connected to the common-mode noise detection component130, an output end of the voltage/current conversion circuit151is connected to an input end of the second current injection circuit152, and the voltage/current conversion circuit151is configured to provide the second current injection circuit152with a current signal;

an output end of the second current injection circuit152is connected to the protection ground, to inject, into the protection ground, the current signal output by the voltage/current conversion circuit151; and

the second external power supply circuit153is configured to provide the voltage/current conversion circuit151with a working voltage.

Specifically, the input end of the voltage/current conversion circuit151is connected to an output end of the third secondary side Ns2of the common-mode noise detection component130.

It should be understood that the current signal output by the voltage/current conversion circuit151is a signal used to cancel the second common-mode noise signal. The second current injection circuit152injects, into the protection ground, the current signal output by the voltage/current conversion circuit151, that is, the current signal is used to cancel the second common-mode noise signal detected by the common-mode noise detection component130. It should be further understood that an event of reducing strength of the second common-mode noise signal {circle around (3)} by the cancellation signal {circle around (4)} shown inFIG. 2may be construed as an effect generated by injecting, into the protection ground by the second current injection circuit152, the current signal output by the voltage/current conversion circuit151shown inFIG. 3.

In this embodiment of the present disclosure, specifically, the resistor R2connected in parallel to the output end of the third secondary side Ns2may be considered as an input resistance of the voltage/current conversion circuit151.

Optionally, the voltage/current conversion circuit151may be built by an operational amplifier, specifically, as shown inFIG. 4.

It should be understood that,FIG. 3andFIG. 4illustratively but not restrictively provide schematic structural diagrams of the second filter circuit150in the feed-forward active common-mode filter120. In an actual application, another feasible form in the prior art may also be used for the second filter circuit150, as long as the second filter circuit150can implement feed-forward filtering in cooperation with the common-mode noise detection component130, which is not limited in this embodiment of the present disclosure.

In the filter apparatus in this embodiment of the present disclosure, mixed use of a feedback active common-mode filter and a feed-forward active common-mode filter combines advantages of feedback filtering, that is, a simple circuit, a variable loop gain, and insensitivity to phase variations, and advantages of feed-forward filtering, that is, strong universality, desirable stability (self-excited oscillation does not occur easily), not oscillating easily, and a high signal-to-noise ratio of a picked up noise signal.

Therefore, in the filter apparatus provided in this embodiment of the present disclosure, a feedback active common-mode filter and a feed-forward active common-mode filter are sequentially connected in series in a direction from a noise generator to an external power source, a detected signal-to-noise ratio of overall noise of a filter circuit may be equivalent to a signal-to-noise ratio detected by a conventional one-stage feedback active common-mode filter, and a relatively strong anti-interference capability and relatively good filtering performance are achieved. Specifically, a relatively high low-frequency insertion loss can be implemented. For example, an insertion loss of a low frequency 150 KHz may be higher than 40 dB. Moreover, filtering performance can be effectively improved by means of two stages of filtering. In addition, the feedback active common-mode filter and the feed-forward active common-mode filter share one common-mode noise detection component, reducing a quantity of noise detection components to be used and reducing circuit costs.

Optionally, as shown inFIG. 5, in this embodiment of the present disclosure, the common-mode noise detection component130includes:

a primary side Np, configured to detect the second common-mode noise signal; and

a first secondary side Ns, where an output end of the first secondary side Ns is connected to an input end of the first filter circuit140, and the output end of the first secondary side is further connected to an input end of the second filter circuit150, to separately provide the first filter circuit140and the second filter circuit150with the second common-mode noise signal detected by the primary side.

Specifically, as shown inFIG. 5, the first filter circuit140performs feedback filtering processing on a first common-mode noise signal {circle around (1)} from the device300. Specifically, for example, a reverse cancellation signal {circle around (2)} (which is reverse relative to the first common-mode noise signal {circle around (1)}) is generated to weaken the first common-mode noise signal {circle around (1)}. In this case, the second common-mode noise signal detected by the common-mode noise detection component130is a noise signal shown by {circle around (3)} inFIG. 2. For example, strength of the second common-mode noise signal {circle around (3)} may be considered as a strength difference between the first common-mode noise signal {circle around (1)} and the cancellation signal {circle around (2)}. The common-mode noise detection component130provides the second common-mode noise signal {circle around (3)} for the second filter circuit150, and the second filter circuit150performs filtering processing on the second common-mode noise signal {circle around (3)}, to generate a cancellation signal {circle around (4)}. In this case, strength of a noise signal {circle around (5)} that has been processed by the second filter circuit150and that flows to the side of the external power source200may be construed as a strength difference between the second common-mode noise signal {circle around (3)} and the cancellation signal {circle around (4)}. That is, the noise signal {circle around (5)} shown inFIG. 2is already weak compared with the first common-mode noise signal {circle around (1)} from the device300. Therefore, noise interference with an external power source can be significantly reduced.

In this embodiment of the present disclosure, the second common-mode noise signal detected by the primary side can be provided for the first filter circuit140and the second filter circuit150by using one secondary side, reducing circuit costs.

Optionally, as shown inFIG. 6, in this embodiment of the present disclosure, the filter apparatus100further includes a differential-mode filter160, where

the differential-mode filter160is connected between the external power source200and the second filter circuit150, and the differential-mode filter160is configured to perform filtering processing on a differential-mode noise signal from the device300.

Specifically, as shown inFIG. 8, the differential-mode filter140may be connected in series on only a live line L line, or the differential-mode filter140may be connected in series on only an N line, or the differential-mode filter140is connected in series on both the N line and the L line, which is not limited in this embodiment of the present disclosure.

In a direction from a noise generator (corresponding to the device300in this embodiment of the present disclosure) to the external power source200, the differential-mode filter140is connected in series behind the feedback active common-mode filter110and the feed-forward active common-mode filter120, the feedback active common-mode filter110and the feed-forward active common-mode filter120process most common-mode noise signals, and the differential-mode filter140is configured to process a differential-mode noise signal in the circuit. It should be understood that, in addition to an original differential-mode noise signal from the device300, the differential-mode noise signal may further include a differential-mode noise signal generated due to unbalanced common-mode noise signals of the L line and the N line. It should be understood that, when common-mode noise has an imbalance problem on the N line and the L line of the external power source, original common-mode noise may be converted into differential-mode noise. In this embodiment of the present disclosure, the differential-mode filter140is connected in series behind the feed-forward active common-mode filter120(seen in the direction from the noise generator to the external power source), which can effectively resolve the foregoing problem of conversion from common-mode noise into differential-mode noise. That is, the common-mode noise is first filtered, and then the differential-mode noise is filtered, resolving a problem that it is difficult to filter low frequency noise.

Therefore, in this embodiment of the present disclosure, a feedback active common-mode filter, a feed-forward active common-mode filter, and a differential-mode filter are sequentially connected in series in a direction from a noise generator to an external power source, which can desirably filter low frequency noise (including common-mode noise and differential-mode noise). In addition, the feedback active common-mode filter and the feed-forward active common-mode filter share one common-mode noise detection component, which can effectively reduce circuit costs, complying with a high density and miniaturization trend of power supply products in the prior art and having a wide application prospect.

Preferably, considering that bandwidth of an amplifying circuit is limited, to better process a noise current whose frequency is 1 MHz or higher, one stage of passive common-mode filtering may further be inserted between the noise generator and the feedback active common-mode filter.

Optionally, as shown inFIG. 7, in this embodiment of the present disclosure, the filter apparatus100further includes a high frequency passive common-mode filter170, where

the high frequency passive common-mode filter170is connected between the first filter circuit140and the device300, and the high frequency passive common-mode filter170performs filtering processing on an initial common-mode noise signal from the device300, where

the first noise signal processed by the first filter circuit140is a common-mode noise signal obtained after the initial common-mode noise signal is processed by the high frequency passive common-mode filter170.

Specifically, as shown inFIG. 7, in a direction from a noise generator to an external power source, a first stage is high frequency passive common-mode filtering, a second stage is feedback active common-mode filtering, a third stage is feed-forward active common-mode filtering, and a fourth stage is differential-mode filtering. A connection method of the high frequency passive common-mode filter170in a circuit is specifically shown inFIG. 8, which belongs to the prior art, and details are not described herein.

It should be understood that, a filtering effect of a passive filter on a frequency of 1 MHz or higher is obvious. For example, the high frequency passive common-mode filter150may be used to process a noise signal whose frequency is 1 MHz or higher.

In this embodiment of the present disclosure, by means of a combination of feed-forward and feedback filtering, it is implemented that two stages of active filters share one common-mode current detection component, reducing a quantity of detection components to be used. In addition, a common-mode filter includes the two stages of active common-mode filters and one stage of high frequency passive filter has an extremely desirable filtering effect over a full band, and a signal-to-noise ratio is the same as that of one-stage feedback active filtering, achieving a relatively strong anti-interference capability. In addition, impact of a sequence of a differential-mode filter and a common-mode filter on overall EMI performance is considered. Common-mode noise has a problem of being unbalanced on the L line and the N line, and the common-mode noise may be converted into differential-mode noise. Therefore, a differential-mode inductor needs to be added to the L line or the N line, to resolve a problem that it is difficult to filter low frequency noise. An optimal structure is that the differential-mode filter is disposed behind an active filter. Common-mode noise is first filtered, and then differential-mode noise is filtered.

Therefore, in the filter apparatus provided in this embodiment of the present disclosure, a first stage is feedback cancellation, and a second stage is feed-forward cancellation, and advantages of a feedback active filter and a feed-forward active filter are combined, which can effectively improve a cancellation effect on a noise signal, that is, a filtering effect is improved. In addition, because a common-mode current detection component detects a common-mode current signal after one stage of feedback active filtering processing, an anti-interference capability of the filter circuit is relatively strong, which is equivalent to improving a filtering effect while keeping a relatively high signal-to-noise ratio. In addition, a feedback active filtering module and a feed-forward active filtering module share one common-mode current detection component, which can significantly reduce circuit costs.

In this embodiment of the present disclosure, the feedback active common-mode filter and the feed-forward active common-mode filter are combined to process a common-mode noise signal in the circuit. It should be understood that performance of an active filter can replace a conventional passive common-mode filter. Active filtering is used in the present disclosure, it is unnecessary to pay special attention to a problem of mismatching between impedance of a noise generator and impedance of a load, and the present disclosure is applicable to common-mode EMI noise filtering of all switch mode power supplies. In addition, in this embodiment of the present disclosure, the high frequency passive common-mode filter150needs to only filter high frequency noise, the high frequency passive common-mode filter150occupies a small area on a board. In addition, in this embodiment of the present disclosure, in each active common-mode filter, a semiconductor component is used to replace an inductor that has a large volume, which significantly reduces an occupied area on the board. Therefore, the filter apparatus provided in this embodiment of the present disclosure can resolve a problem that a conventional EMI filter occupies a large area on the board. In addition, because a volume of a common-mode inductor is greatly reduced, usage of copper and iron cores is reduced, and a weight reduction purpose is also implemented.

In addition, in this embodiment of the present disclosure, a high frequency passive filter, a feedback active common-mode filter, a feed-forward active common-mode filter, and a differential-mode filter are sequentially connected in series in a direction from a noise generator to an external power source, common-mode noise is first filtered, and then differential-mode noise is filtered, which can prevent a problem that the differential-mode noise, which is converted from the common-mode noise due to unbalanced impedance, flows to the external power source and results in insufficient filtering performance.

The filter apparatus provided in this embodiment of the present disclosure may be applied to all power supply products or power supply systems. For example, the filter apparatus may be connected in series between an external power source and an inverter, or may be connected in series between an external power source and an electric device. For example, the filter apparatus may be applied to a solar grid-tied PV power generating system. Electrical energy may be delivered in a form of a single-phase AC power, which is referred to as single-phase power for short, or may be delivered in a form of three-phase AC power. Specifically, as shown inFIG. 9, the filter apparatus provided in this embodiment of the present disclosure is connected in series in a three-phase AC power scenario.

Therefore, in the filter apparatus provided in this embodiment of the present disclosure, a feedback active common-mode filter and a feed-forward active common-mode filter are sequentially connected in a direction from a noise generator (corresponding to the device inFIG. 1) to an external power source, and the two filters share one common-mode noise detection component, which can effectively improve an overall filtering effect of a filter circuit on one hand, and effectively reduce circuit costs on the other hand, complying with a high density and miniaturization trend of current power supply products, and having a wide application prospect.

FIG. 10shows a power supply system400according to an embodiment of the present disclosure. As shown inFIG. 10, the power supply system includes a filter apparatus410, an external power source420, and a device430, where the filter apparatus410, the external power source420, and the device430form a loop by using a line, when the device430runs, a common-mode noise signal is generated on the line, and the filter apparatus410is configured to filter the common-mode noise signal. The filter apparatus410may be the filter apparatus100provided in the foregoing embodiment.

Therefore, in the power supply system400provided in this embodiment of the present disclosure, a feedback active common-mode filter and a feed-forward active common-mode filter are sequentially connected in a direction from a noise generator to an external power source, and the two filters share one common-mode noise detection component, which can effectively improve an overall filtering effect of a filter circuit on one hand, and effectively reduce circuit costs on the other hand, complying with a high density and miniaturization trend of current power supply products, and having a wide application prospect.