Leakage current compensator circuit

Abstract

The invention relates to a leakage current compensator circuit (10; 50; 60) comprising:-a plurality of current-carrying wires electrically coupled to a power source and to an electrical load (12), each of the power source and the electrical load (12) comprising a protective ground terminal; -a protective ground conductor (20) electrically coupled to a protective ground terminal of the power source and to a protective ground terminal of the electrical load (12); -a measurement circuit for measuring leakage currents in the plurality of current-carrying conductors; and-a current injector (22) electrically coupled to the plurality of current-carrying conductors, where the current injector (22) is configured to actively cancel a leakage current in the plurality of current-carrying conductors by injecting a compensation current into the protective ground conductor (20) based on an output of the measurement circuit.

Description

Technical Field

[0001] This invention relates to a leakage current compensation circuit for grid-connected devices, such as charging equipment for electric vehicles. Background Technology

[0002] Grid-connected devices are electrical installations that are directly connected to the power grid. For example, grid-connected charging stations for electric vehicles (EVs) enable EV owners to charge their vehicles directly from the grid. These charging stations can be installed in homes, businesses, or public places and can help manage electricity demand and grid stability by allowing controlled charging during peak and off-peak hours.

[0003] A typical grid-connected system in a three-phase system includes active current-carrying power lines (L1, L2, and L3), a neutral (N) conductor, and a protective earth (PE) conductor. Other systems include fewer current-carrying lines, such as US-phase electrical systems (L1 and L2) and single-phase electrical systems (L1). For these and other systems, leakage current is the current flowing in an undesirable current path under normal operating conditions. Leakage current is sometimes referred to as residual current and can occur, for example, from one of the current-carrying power lines to the protective earth conductor. The peak and root mean square (RMS) values ​​of this leakage current are regulated by various standards for buildings and grid-connected electric vehicles.

[0004] Especially in electric vehicle charging applications, electric vehicles are charged via cables connected to an Electric Vehicle Service Equipment (EVSE). To meet electrical safety standards, EVSEs typically include residual current monitoring devices that measure the level of residual current flowing into the protective earth conductor. If this residual current exceeds a threshold determined by the relevant standard, it will actively disconnect power to the grid-connected electric vehicle via an EVSE relay.

[0005] However, despite their existence, there remains a persistent need for improved systems and methods for compensating for leakage currents. In particular, there remains a persistent need for improved systems and methods for detecting and compensating for leakage currents found in grid-connected devices, especially in applications involving non-isolated electronic power converters, including, for example, electric vehicle service equipment systems, or other technologies such as heat pumps, air conditioning, etc. Summary of the Invention

[0006] A leakage current compensator (LCC) circuit is provided. The LCC circuit includes a first residual current coil, a second residual current coil, and a current injector. The first residual current coil serves as an open-loop measuring coil, while the second residual current coil serves as a closed-loop measuring coil. Between these two residual current coils, the current injector injects a compensating current into the protective grounding conductor. Both residual current coils can be configured as current transformers, summing all AC input line and neutral line currents and transforming them to the measuring windings according to the winding ratio, the measuring windings being wound around the same magnetic core. The open-loop measuring coil measures any leakage current generated by the grid-connected device, while the closed-loop measuring coil measures the actual leakage current remaining after compensation. The current injector allows the LCC circuit to actively cancel leakage current by first injecting the current measured by the open-loop measuring coil, and then injecting an additional or modified current determined by the closed-loop gain from the closed-loop measuring coil.

[0007] A current injector is a dynamic current source used to inject compensating current into the protective earth conductor. The current injector is connected between the dummy ground and the protective earth conductor. The dummy ground is connected to the grid conductor between the closed-loop and open-loop measurement coils. This configuration allows leakage current compensation to have a complete loop, enabling the leakage current compensator circuit to actively offset leakage current in the protective earth conductor by providing an alternative path for the leakage current, rather than allowing it to enter the grid infrastructure. The leakage current compensator circuit may include four grid configuration relays for switching between three-phase and single-phase or two-phase operation. The grid configuration relays ensure compatibility with virtually any grid-connected application, including three-phase Y-type electrical systems, three-phase delta electrical systems, US-phase electrical systems, and single-phase electrical systems.

[0008] In another embodiment, a method for actively canceling leakage current is provided. This method typically includes:

[0009] (a) Measure the leakage current generated at the open-loop measurement coil by the grid-connected device and its (one or more) loads;

[0010] (b) Inject compensation current based on the measured leakage current;

[0011] (c) Measure the actual leakage current remaining after the compensation current is applied to the protective grounding conductor; and

[0012] (d) Modify the compensation current based on the closed-loop gain from the closed-loop measurement coil.

[0013] A measurement of the leakage current generated by the grid-connected device is performed at the open-loop measurement coil. A first transimpedance amplifier converts the input current signal from the open-loop measurement coil into a proportional output voltage signal. A current injector includes an operational amplifier closed-loop gain function to provide appropriate compensation current to the protective ground conductor. The measurement of the compensated leakage current is performed at the closed-loop measurement coil. A second transimpedance amplifier converts the input current signal from the closed-loop measurement coil into a proportional output voltage signal. The compensation current is then modified by the current injector based on the output of a bandpass summator amplifier, which has separate gain factors for open-loop and closed-loop compensation. The bandpass summator amplifier includes a first input terminal coupled to the sum of the outputs of the first and second transimpedance amplifiers, while a second input terminal is coupled to a dummy ground node. The current injector includes a first terminal coupled to the output of the bandpass summator amplifier and a second terminal coupled to the dummy ground node. The current injector injects the modified compensation current according to a closed-loop control function to reduce the leakage current. The modified compensation current further reduces the leakage current, optionally to less than a predetermined threshold, such as 2mARMS (root mean square amperes).

[0014] As discussed herein, embodiments of the invention include open-loop reduction and closed-loop reduction of leakage current. Open-loop reduction involves continuously measuring the leakage current in the current-carrying conductor for output to a bandpass summing amplifier. Closed-loop reduction involves summing the open-loop feedback of a first transimpedance amplifier with the closed-loop feedback of a second transimpedance amplifier. The summed current measurement, multiplied by the open-loop and closed-loop gains, is output to a current injector for injecting compensation current into the protective grounding conductor. By providing initial open-loop reduction, the leakage current compensator circuit reduces noise in the current-carrying conductor without relying solely on the closed-loop gain of the bandpass summing amplifier / functional block.

[0015] In other embodiments, the leakage current compensator circuit includes one of an open-loop measurement coil and a closed-loop measurement coil, rather than both. These embodiments are well-suited for use with grid-connected devices that generate little noise, while offering cost savings compared to embodiments with both closed-loop and open-loop measurements of leakage current.

[0016] For example, a leakage current compensator circuit may consist only of a closed-loop current coil that winds around all active and neutral grid lines (L1, L2, L3, N) except for the protective ground conductor. Alternatively, a leakage current compensator circuit may consist only of an open-loop current coil. The leakage current compensator circuit also includes a virtual ground control circuit and a current injector. The current injector is a dynamic current source used to inject compensating current into the protective ground conductor and is connected between the protective ground conductor and the virtual ground. In operation, a transimpedance amplifier converts the current signal from the appropriate measuring coil into a proportional output voltage signal. The output voltage signal is then processed by a bandpass amplifier. The bandpass amplifier includes a differential amplifier that allows mid-band frequency components to pass while attenuating very low and very high frequencies. Specifically, the bandpass amplifier includes a first input terminal coupled to the output of the transimpedance amplifier, while a second terminal is coupled to the virtual ground node (V). gnd The current injector then modifies the compensation current based on the output of the bandpass summing amplifier. The current injector comprises a first terminal coupled to the output of the bandpass amplifier and a second terminal coupled to a virtual ground node (V). gnd The second terminal of the current injector injects a modified compensation current based on either the open-loop or closed-loop gain function to reduce leakage current. The modified compensation current reduces leakage current, optionally reducing it to below a predetermined threshold.

[0017] Other embodiments include systems for open-loop and / or closed-loop compensation of leakage current, the system including one or more digital signal processors (DSPs), microcontrollers, and / or other digital processors. For example, the system may include a DSP for performing open-loop and / or closed-loop compensation of measured leakage current. The system also includes a first analog-to-digital converter (ADC) electrically coupled to the output of an open-loop measurement circuit and a second ADC electrically coupled to the output of a closed-loop measurement circuit. Each ADC converts an analog input (such as received from a transimpedance amplifier) ​​into a digital signal for the DSP. The DSP then performs open-loop and / or closed-loop reduction of the leakage current. That is, the DSP, according to open-loop and / or closed-loop control functions, causes a current injector to inject a modified compensation current into the protective ground conductor to reduce the leakage current in the current-carrying line, optionally reducing it to below a predetermined threshold.

[0018] Embodiments of the present invention are not limited to the foregoing description, as the present invention may include digital circuitry systems for current injectors and / or virtual grounding circuits. For example, a current injector may include a Class D amplifier for converting a low-voltage DC input to a high-voltage DC output. Instead of using analog amplifiers (e.g., Class A, Class B, and Class AB amplifiers) to continuously change the compensation current, the Class D amplifier modulates the duty cycle of a pulse-width modulation (PWM) waveform based on the input voltage and the desired output voltage. By controlling the duty cycle, the Class D amplifier regulates the compensation current while minimizing power losses. Furthermore, the virtual grounding circuit may include a second DSP combined with an ADC and a digital-to-analog converter (DAC). For example, the second DSP (which may be identical to the first DSP) may actively maintain the DC average value of the virtual grounding at the same potential as the protective grounding conductor. In particular, the second DSP may amplify the potential of the protective grounding conductor relative to the virtual grounding node (V0). gnd The voltage difference between the two inputs is calculated, while discarding any signals common to both inputs, such as noise or interference. The DSP then generates a supply current for the current injector, which allows the compensation system to operate on a wider range of virtual ground nodes.

[0019] These and other embodiments are well-suited for a wide range of applications, including non-isolated on-board chargers for electric vehicles. Because non-isolated on-board chargers generate noise, such as noise from the electric vehicle or other loads, the leakage current compensator circuit is uniquely suited to compensate for noise current in the protective grounding conductor. While the following description is primarily in conjunction with non-isolated on-board chargers, the invention is also well-suited for use with on-board chargers that have isolation transformers.

[0020] These and other features and advantages of the invention will become apparent from the following description of the invention when viewed in conjunction with the accompanying drawings and appended claims. It should be understood that any preferred and / or optional features of the invention may be combined individually or in suitable combinations in embodiments of the invention while still falling within the scope of claim 1, even if such combinations are not expressly required in the appended claims. Attached Figure Description

[0021] Figure 1 This is a circuit diagram of a leakage current compensator circuit coupled to an on-board charger according to an embodiment of the present invention.

[0022] Figure 2 yes Figure 1 The circuit diagram of the leakage current compensator circuit.

[0023] Figure 3 It is used for Figure 1 The logic table of the leakage current compensator circuit.

[0024] Figure 4 yes Figure 1The circuit diagram of the car charger.

[0025] Figure 5 The circuit diagram is based on the leakage current compensator circuit of the second embodiment, which has closed-loop compensation for leakage current.

[0026] Figure 6 The circuit diagram of the leakage current compensator circuit according to the third embodiment has open-loop compensation for leakage current.

[0027] Figure 7 This is a schematic block diagram of a system for compensating leakage current according to a fourth embodiment of the present invention. Detailed Implementation

[0028] refer to Figure 1 The diagram illustrates a leakage current compensator (LCC) circuit according to a first embodiment, and is generally designated 10. The leakage current compensator circuit 10 is coupled to an on-board charger 12 for providing a regulated DC voltage to a vehicle 14. More specifically, the leakage current compensator circuit 10 includes a first residual current coil 16 and a second residual current coil 18, which surround all active and neutral grid lines (L1, L2, L3, N) except for the protective ground conductor 20. Under normal operating conditions, the vector sum of the currents in all active phases is zero. However, if the grid-connected device is generating leakage current, the sum of the currents in the active phases is not equal to zero, indicating the presence of a non-zero current in the protective ground conductor. It is worth noting that the invention is not limited to residual current coils (sometimes referred to as current sensing coils or current transformers) used for measuring current, as other current sensors / sensing circuits can be used in other embodiments, whether now known or developed later.

[0029] To detect and compensate for leakage current, a first residual current coil 16 is used as an open-loop measuring coil, while a second residual current coil 18 is used as a closed-loop measuring coil. The open-loop measuring coil 16 measures any leakage current generated by the grid-connected devices 12, 14, while the closed-loop measuring coil 18 measures the actual leakage current remaining after compensation. The leakage current can be measured in other ways, optionally using a digital signal processor. Between these two residual current coils, a current injector 22 injects compensation current into the protective ground conductor 20. The current injector 22 allows the leakage current compensator circuit 10 to actively cancel the leakage current by first injecting the current measured by the open-loop measuring coil 16, and then injecting an additional current determined by the closed-loop gain from the closed-loop measuring coil 18. The virtual ground control circuit 24 actively maintains the DC average value of the virtual ground to be the same as the potential in the protective ground conductor 20, thereby allowing the use of a low-voltage current injector. Each of these aspects of the leakage current compensator circuit 10 will be discussed in more detail below.

[0030] It is worth noting that, Figures 1 to 2The power grid conductors depicted include four current-carrying conductors L1, L2, L3, and N for a three-phase Y connection. However, in other embodiments, the power grid conductors may include fewer current-carrying conductors suitable for three-phase delta electrical systems, US-phase electrical systems, and / or single-phase electrical systems.

[0031] like Figure 2 As best shown, the open-loop measuring coil 16 is a current transformer with a toroidal core made of magnetic material, through which the charged conductors (L1, L2, L3) and the neutral conductor (N) pass. The conductors (L1, L2, L3, N) each form a coupled primary winding with one turn, while a single coupled secondary winding with more turns is connected to a first transimpedance amplifier 26, which converts the secondary winding current into a voltage. The closed-loop measuring coil 18 is also a current transformer with a toroidal core made of magnetic material, through which the charged conductors (L1, L2, L3) and the neutral conductor (N) pass. The conductors (L1, L2, L3, N) each form a coupled primary winding with one turn, while a single coupled secondary winding with more turns is connected to a second transimpedance amplifier 28, which converts the secondary winding current into a voltage. As explained below, the open-loop measuring coil 16 measures the voltage generated by the grid-connected device 12 ( Figure 1 ) and its electrical load 14 ( Figure 2 The leakage current generated is measured by the closed-loop measuring coil 18, which measures the difference between the charged conductor and the neutral conductor, and measures the actual leakage current remaining after open-loop compensation.

[0032] As noted above, the leakage current compensator circuit 10 includes a virtual grounding control circuit 24. The virtual grounding control circuit 24 includes a differential amplifier 30, which amplifies the connection between the protective grounding conductor 20 and the virtual grounding node (V...). gnd The voltage difference between the two inputs is filtered out, discarding any signals common to both inputs, such as noise or interference. A symmetrical filter processes the output of the differential amplifier 30 to extract the symmetrical component while suppressing the asymmetrical component. A grid-supplied current source 32 then generates a variable, controlled current during US phase-by-phase (two-phase) or three-phase operation. The virtual ground control circuit 24 also includes a full-wave rectifier 34 to generate the supply current for the virtual ground control circuit 32, which allows the leakage current compensator circuit 10 to operate over a wider range of virtual ground nodes. The current injector 22 is a dynamic current source for injecting compensating current into the protective ground conductor 20. The power supply for the current injector 22 is not shown, but it can be powered by a bipolar low-voltage power supply with an amplitude less than + / -60V and grounded to the virtual ground node and isolated from the protective ground. Also as Figure 2As shown, the current injector 22 is connected between the protective ground conductor 20 and the dummy ground 36, which is coupled to the active phase. This configuration allows the leakage current compensation to have a complete loop, thereby allowing the leakage current compensator circuit 10 to actively offset the leakage current in the protective ground conductor by providing an alternative path for the leakage current to flow rather than returning to the grid infrastructure.

[0033] For example Figure 2 As shown, the leakage current compensator circuit 10 optionally includes four grid configuration relays S1, S2, S3, and S4 for switching between three-phase operation and single-phase or two-phase operation. Specifically, when closed, the first relay S1 couples the neutral conductor (N) to the virtual ground node (V). gnd When closed, the second relay S2 couples the first current-carrying conductor (L1) to the virtual ground node (V). gnd Furthermore, when the third relay S3 is closed, it couples the first current-carrying conductor (L1) to the third current-carrying conductor (L3), while when the fourth relay S4 is closed, it couples the first current-carrying conductor (L1) to the second current-carrying conductor (L2). The virtual grounding network includes multiple capacitors 38 that act as an averaging circuit, such that the virtual grounding node (V gnd The potential of the protective grounding conductor 20 is close to that of the protective grounding conductor 20, thereby allowing a low voltage to be injected into the protective grounding conductor 20.

[0034] Figure 3 The diagram further illustrates the operation of power grid configuration relays S1, S2, S3, and S4. In single-phase normal operation, relays S1, S3, and S4 are on (conducting), while relay S2 is off (not conducting). In single-phase reversed operation, relay S1 is off (not conducting), while relays S2, S3, and S4 are on (conducting). For two-phase (US) operation, relays S1 and S2 are off (not conducting), while relays S3 and S4 are on (conducting). For three-phase Y-type and three-phase delta-type electrical systems, relay S1 is on (conducting), while the remaining relays S2, S3, and S4 are off (not conducting).

[0035] Turning to the operating method, the leakage current compensator circuit 10 includes a circuit system (analog and / or digital) for actively canceling leakage current according to the following method steps:

[0036] (a) Measure the leakage current generated at the open-loop measurement coil by the grid-connected device and its (one or more) loads;

[0037] (b) Inject compensation current based on the measured leakage current;

[0038] (c) Measure the actual leakage current remaining after the compensation current is applied to the protective grounding conductor; and

[0039] (d) Modify the injection current based on the closed-loop gain from the closed-loop measurement coil. Each such step is discussed separately below.

[0040] A measurement of the leakage current generated by the grid-connected device is performed at the open-loop measuring coil 16. A first transimpedance amplifier 26 converts the input current signal from the open-loop measuring coil 16 into a proportional output voltage signal. This voltage signal represents the leakage current generated by the grid-connected device (optionally an on-board charger 12 or an electric vehicle 14). The leakage current is carried by conductors (L1, L2, L3, N) that electrically connect the grid voltage 42 to the grid-connected device.

[0041] Injecting compensation current based on measured leakage current involves applying a compensation current to the protective grounding conductor 20. The current injector 22 includes an operational amplifier closed-loop gain function for providing the injected current to the protective grounding conductor 20. For example, for a mains frequency of 50 / 60 Hz, the compensation current may comprise a sinusoidal waveform with a frequency between 5 Hz and 20 kHz.

[0042] The step of measuring the compensated leakage current is performed at the closed-loop measurement coil 18. This step involves converting the input current signal from the closed-loop measurement coil 18 into a proportional output voltage signal. This step is performed by a second transimpedance amplifier 28, which includes a first input coupled to an operational amplifier and a second input grounded to a reference voltage. The second transimpedance amplifier 28 also includes a transimpedance resistor coupled between the output of the operational amplifier and its inverting input. The output of the second transimpedance amplifier 28 is then processed by a bandpass summing amplifier 40. The bandpass summing amplifier 40 includes a differential amplifier with a non-inverting input and an inverting input, thereby allowing mid-band frequency components to pass through while attenuating very low frequencies and very high frequencies.

[0043] The current injector 22 then performs the modification of the compensation current based on the output of the bandpass summing amplifier 40. Specifically, the bandpass summing amplifier 40 includes a first input terminal coupled to the sum of the outputs of the first transimpedance amplifier 26 and the second transimpedance amplifier 28, while a second terminal is coupled to a virtual ground node (V0). gnd The current injector 22 includes a first terminal coupled to the output of the bandpass summing amplifier 40 and a virtual ground node (V). gnd The second terminal of the current injector 22 injects a modified compensation current according to a closed-loop control function to reduce leakage current. The modified compensation current reduces leakage current, optionally reducing it to less than a predetermined threshold, such as 2mARMS.

[0044] To reiterate, the system and method of the present invention include open-loop reduction and closed-loop reduction of leakage current. Open-loop reduction involves continuously measuring the leakage current in the current-carrying conductors (L1, L2, L3, N) for output to a bandpass summing amplifier 40. Closed-loop reduction involves summing the open-loop feedback (which is relatively constant) of a first transimpedance amplifier 26 with the closed-loop feedback of a second transimpedance amplifier 28. The summed current measurement, multiplied by separate gain factors for open-loop and closed-loop compensation, is output to a current injector 22 to inject compensation current into the protective grounding conductor 20. By providing initial open-loop reduction, the leakage current compensator circuit 10 reduces noise in the current-carrying conductors without relying solely on the closed-loop gain of the bandpass summing amplifier 40.

[0045] This invention is well-suited for a wide range of applications, including on-board chargers for electric vehicles, thereby preventing the danger of electric shock to people and equipment. Figure 4 The invention depicts an on-board charger 12, which includes a power factor correction (PFC) circuit system and a non-isolated DC / DC converter for providing regulated DC output to a vehicle 14. Because the non-isolated DC / DC converter generates noise, for example, from the vehicle 14 or other loads, a leakage current compensator circuit 10 is uniquely suited to compensate for noise currents (i.e., leakage currents from 5 Hz to 20 kHz) in the protective ground conductor. Although illustrated as a non-isolated DC / DC converter, the invention is also well-suited for use with on-board chargers that have isolated DC / DC converters. Furthermore, the invention is applicable to any grid-connected application, including three-phase Y-type electrical systems, three-phase delta electrical systems, US-phase electrical systems, and single-phase electrical systems.

[0046] Now for reference Figure 5 The diagram illustrates a leakage current compensator circuit according to another embodiment, and is generally labeled 50. Figure 5 Leakage current compensator circuit 50 and Figure 2 The difference between the leakage current compensator circuit 10 and the circuit is that... Figure 5 The leakage current compensator circuit 50 includes only closed-loop measurement of leakage current. This embodiment is well-suited for use with grid-connected devices that generate little noise, while offering cost savings compared to embodiments that perform both closed-loop and open-loop measurements of leakage current generated by the grid-connected device.

[0047] Specifically, the leakage current compensator circuit 50 includes only the second residual current coil 18, which surrounds all active and neutral grid lines (L1, L2, L3, N) except for the protective ground conductor 20. Figure 2 Similar to the previous embodiment, the residual current coil includes a current transformer that sums all AC input line and neutral line currents and transforms them to a measuring winding according to the winding ratio, the measuring winding being wound around the same magnetic core. Figure 5 The leakage current compensator circuit 50 is otherwise structurally and functionally similar to Figure 2 The leakage current compensator circuit 50 is the same as that of the leakage current compensator circuit 10. For example, the leakage current compensator circuit 50 includes a virtual ground control circuit 24 and a current injector 22. The current injector 22 is a dynamic current source for injecting compensating current into the protective ground conductor 20. The current injector 22 is connected between the protective ground conductor 20 and the virtual ground 36, which is coupled to the active phase.

[0048] In operation, the transimpedance amplifier 28 converts the current signal from the closed-loop measurement coil 18 into a proportional output voltage signal. The output of the transimpedance amplifier 28 is then processed by the bandpass summing amplifier 40. The bandpass summing amplifier 40 includes a differential amplifier with non-inverting and inverting inputs, allowing mid-band frequency components to pass while attenuating very low and very high frequencies. The current injector 22 then performs a modification of the compensation current based on the output of the bandpass summing amplifier 40. Specifically, the bandpass amplifier 40 includes a first input terminal coupled to the output of the transimpedance amplifier 28, while a second terminal is coupled to a virtual ground node (V0). gnd The current injector 22 includes a first terminal coupled to the output of the bandpass summing amplifier 40 and a virtual ground node (V). gnd The second terminal of the current injector 22 injects a modified compensation current according to a closed-loop control function to reduce leakage current. The modified compensation current reduces leakage current, optionally reducing it to below a predetermined threshold.

[0049] Now for reference Figure 6 The diagram illustrates a leakage current compensator circuit according to another embodiment, and is generally labeled 60. Figure 6 Leakage current compensator circuit 60 and Figure 2 The difference between the leakage current compensator circuit 10 and the circuit is that... Figure 6 The leakage current compensator circuit 60 only includes open-loop measurement of leakage current. Similar to... Figure 5 Implementation examples, Figure 6 The embodiments are well-suited for use with grid-connected devices that generate very little noise, while offering cost savings compared to embodiments involving closed-loop and open-loop measurements of leakage current.

[0050] Specifically, the leakage current compensator circuit 60 includes only a first residual current coil 16, which surrounds all active and neutral grid lines (L1, L2, L3, N) except for the protective ground conductor 20. Figure 2 As in the previous embodiment, the first residual current coil includes a current transformer that sums all AC input line and neutral line currents and transforms them to a measuring winding according to the winding ratio, the measuring winding being wound around the same magnetic core. Figure 6The leakage current compensator circuit 60 is otherwise structurally and functionally similar to Figure 2 The leakage current compensator circuit is the same. For example, the leakage current compensator circuit 60 includes a virtual grounding control circuit 24 with a full-wave rectifier 34 to generate a supply current for the virtual grounding control circuit 32. The current injector 22 is a dynamic current source for injecting compensation current into the protective grounding conductor 20. Also, Figure 6 As shown, the current injector 22 is connected between the protective ground conductor 20 and the virtual ground 36, which is coupled to the active phase.

[0051] In operation, the transimpedance amplifier 26 converts the current signal from the open-loop measurement coil 16 into a proportional output voltage signal. The output of the transimpedance amplifier 26 is then processed by the bandpass summing amplifier 40. The bandpass summing amplifier 40 includes a differential amplifier with non-inverting and inverting inputs, allowing mid-band frequency components to pass while attenuating very low and very high frequencies. The current injector 22 then performs a modification of the compensation current based on the output of the bandpass summing amplifier 40. Specifically, the bandpass amplifier 40 includes a first input terminal coupled to the output of the transimpedance amplifier 28, while a second terminal is coupled to a virtual ground node (V). gnd The current injector 22 includes a first terminal coupled to the output of the bandpass summing amplifier 40 and a virtual ground node (V). gnd The second terminal of the current injector 22 injects a modified compensation current to optionally reduce the leakage current to less than a predetermined threshold, according to the open-loop control function.

[0052] Now for reference Figure 7 The diagram illustrates a system for compensating for leakage current, and is generally designated 70. System 70 is functionally similar to... Figure 2 The implementation is the same, except that Figure 2 All or part of the analog circuitry includes one or more digital signal processors (DSPs), microcontrollers, and / or other digital processors.

[0053] By way of non-restrictive examples, Figure 7System 70 includes a DSP 72 for open-loop and / or closed-loop compensation of the measured leakage current. System 70 also includes a first analog-to-digital converter (ADC) 74 electrically coupled to the output of the open-loop measurement circuitry and a second ADC 76 electrically coupled to the output of the closed-loop measurement circuitry. Each ADC 74, 76 converts an analog input (such as received from transimpedance amplifiers 26, 28) into a digital signal for use by DSP 72. DSP 72 then performs open-loop and / or closed-loop reduction of the leakage current. Closed-loop reduction involves summing the open-loop feedback (which is relatively constant) of the first transimpedance amplifier 26 with the closed-loop feedback of the second transimpedance amplifier 28. The summed current measurement is output to a current injector 22 for injecting a compensation current into the protective ground conductor 20. At this point, DSP 72 causes the current injector 22 to inject a modified compensation current to reduce the leakage current according to a closed-loop control function, optionally reducing it to below a predetermined threshold.

[0054] Embodiments of the present invention are not limited to the foregoing, as the invention may include digital alternatives to either or both of the current injector 22 and the virtual ground circuit 24. For example, the current injector 22 may include a Class D amplifier for converting a low-voltage DC input to a high-voltage DC output. Instead of using analog amplifiers (e.g., Class A, Class B, and Class AB amplifiers) to continuously change the compensation current, the Class D amplifier modulates the duty cycle of a pulse-width modulation (PWM) waveform based on the input voltage (from DSP 72) and the desired output voltage. By controlling the duty cycle, the Class D amplifier regulates the compensation current while minimizing power losses. Also as... Figure 7 As shown, the virtual grounding circuit 24 may include a second DSP combined with an ADC and a digital-to-analog converter (DAC). For example, the second DSP may actively maintain the DC average value of the virtual grounding at the same potential as that in the protective grounding conductor 20. In particular, the second DSP may amplify the potential of the protective grounding conductor 20 relative to the virtual grounding node (V0). gnd The voltage difference between the two inputs is calculated, while discarding any signals common to both inputs, such as noise or interference. The DSP then generates a supply current for the current injector 22, which allows the leakage current compensator circuit 70 to operate on a wider range of virtual ground nodes.

[0055] The above description describes the present embodiments of the present invention. Various changes and modifications can be made without departing from the spirit and broader aspects of the invention. This disclosure is presented for illustrative purposes and should not be construed as an exhaustive description of all embodiments of the invention or as limiting the scope of the claims to the specific elements incorporated into these embodiments or descriptions. For example, any reference to an element using the articles “a,” “an,” “the,” or “the” in the singular should not be construed as limiting the element to the singular.

Claims

1. A leakage current compensator circuit (10; 50; 60), including: - Multiple current-carrying conductors electrically coupled to a power source and an electrical load (12), each of the power source and the electrical load (12) including a protective grounding terminal; - A protective grounding conductor (20) electrically coupled to the protective grounding terminal of the power supply and the protective grounding terminal of the electrical load (12); - A measurement circuit, said measurement circuit being used to measure the leakage current in the plurality of current-carrying wires; and - Current injector (22), the current injector (22) being configured to apply a dynamic compensation current to the protective grounding conductor (20), the current injector (22) being electrically coupled to a plurality of current-carrying conductors, wherein the current injector (22) is configured to actively counteract leakage current in the plurality of current-carrying conductors by injecting compensation current into the protective grounding conductor (20) based on the output of the measurement circuit.

2. The circuit (10; 50; 60) according to claim 1, wherein the measurement circuit includes an open-loop measurement coil (16) or a closed-loop measurement coil (18).

3. The circuit (10) according to claim 1, wherein: The measurement circuit includes each of an open-loop measurement coil (16) and a closed-loop measurement coil (18); and each of the open-loop measurement coil (16) and the closed-loop measurement coil (18) includes a current transformer having an annular element extending around the plurality of current-carrying conductors.

4. The circuit (10) according to claim 3, wherein, The current injector (22) is electrically coupled to the multiple current-carrying wires between the open-loop measurement coil (16) and the closed-loop measurement coil (18).

5. The circuit (10) according to claim 4, wherein, The output of the open-loop measurement coil (16) is coupled to the first transimpedance amplifier (26); and the output of the closed-loop measurement coil (18) is coupled to the second transimpedance amplifier (28).

6. The circuit (10) according to claim 5, wherein, Each of the first transimpedance amplifier (26) and the second transimpedance amplifier (28) provides an output to the input terminal of a bandpass summing amplifier (40), the bandpass summing amplifier (40) including a connection to a virtual ground node (V). gnd The second input terminal of ).

7. The circuit (10) of claim 6, wherein the current injector (22) includes a first input terminal coupled to the output of the bandpass summing amplifier (40) and coupled to a virtual ground node (V). gnd The second input terminal of ).

8. The circuit (10) according to claim 5 further includes a function for regulating the virtual ground node (V). gnd The virtual grounding control circuit (24) is used.

9. A method for compensating leakage current in a grid-connected device (12) electrically connected to a plurality of current-carrying conductors and a protective grounding conductor (20), the method comprising: - Measure the first leakage current in multiple current-carrying wires based on the output of an open-loop measurement circuit; -Based on the measured first leakage current, a first compensation current is injected into the protective grounding conductor (20) to provide open-loop leakage current reduction; - Measure the second leakage current in multiple current-carrying wires based on the output of a closed-loop measurement circuit; as well as -Based on the measured second leakage current, a second compensation current is injected into the protective grounding conductor (20) to provide closed-loop leakage current reduction.

10. A system (70) for compensating leakage current, the system comprising: - Measurement circuit, which is configured to measure leakage current in multiple current-carrying wires electrically connected between the power supply and the electrical load (12); - Current injector (22), the current injector being configured to apply a compensation current to a protective grounding conductor (20) electrically connected between the power source and the electrical load (12); as well as - A processor (72) electrically connected to the measurement circuit and the current injector (22), the processor (72) being configured to determine the compensation current based on at least one of an open-loop gain function and a closed-loop gain function, the processor (72) being further configured to cause the current injector (22) to apply the compensation current to the protective grounding conductor (20).

11. The system (70) according to claim 10, wherein, The measurement circuit includes at least one current transformer (16, 18) having an annular element extending around the plurality of current-carrying conductors for output to the processor (72), the processor (72) including at least one analog-to-digital converter (74, 76).

12. The system (70) according to claim 10, wherein, The measurement circuit includes each of an open-loop measurement coil (16) and a closed-loop measurement coil (18), wherein the processor (72) is configured to determine the compensation current based on each of the open-loop gain function and the closed-loop gain function, the open-loop gain function being based on the output of the open-loop measurement coil (16) and the closed-loop gain function being based on the output of the closed-loop measurement coil (18).

13. The system (70) of claim 10, wherein the current injector (22) includes a first input terminal coupled to the output of the processor (72) and coupled to a virtual ground node (V). gnd The second input terminal of ).

14. The system (70) of claim 13, wherein the processor (72) is configured to connect the virtual ground node (V) gnd The DC average value of ) is maintained at the same level as that of the protective grounding conductor (20).

15. The system (70) of claim 13 further includes an electrical connection between the plurality of current-carrying conductors and the virtual grounding node (V). gnd Multiple grid configuration relays (S1, S2, S3, S4) between the processor (72), wherein the multiple grid configuration relays (S1, S2, S3, S4) are responsive to the processor (72) for use with a three-phase power supply, a split-phase power supply or a single-phase power supply.

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