Balancing device and method for balancing an ungrounded power supply system and enhanced insulation monitoring device

Abstract

The invention relates to a balancing device (10) and a method for balancing an ungrounded power supply system (2). The balancing device (10) is multipole switched between the respective active conductor (L1, L2) and the ground potential (PE) and comprises a voltage measuring device (12) for each active conductor (L1, L2) for detecting the conductor-to-ground voltage (U L1‑PE , U L2‑PE ); a microcontroller (14) for evaluating the conductor-to-ground voltage (U L1‑PE , U L2‑PE ); a PFC controller (16) for each active conductor (L1, L2), which brings about a voltage balance between the active conductors (L1, L2) by means of a control impedance which is reproduced; an intermediate circuit (18) for storing the energy converted in the control impedance; and a converter (20) for outputting the energy stored in the intermediate circuit (18) to the power supply system (2).

Description

Technical Field

[0001] The present invention relates to a balancing device and method for balancing an ungrounded power supply system having at least two active conductors, and also to an enhanced insulation monitoring device comprising the balancing device according to the present invention. Background Technology

[0002] When higher requirements are placed on the operational safety, fire safety, and contact safety of electrical systems, ungrounded power supply systems are used. These systems are also known as isolated networks (French: "Isolé Terre"—IT) or IT power supply systems. In these systems, the active components of the power supply system are isolated from the ground potential (i.e., the earth), and the exposed conductive parts of the connected electrical equipment are grounded individually or collectively. The advantage of this type of network is that the operation of the connected electrical equipment is not affected when an initial insulation fault occurs. Therefore, even with an insulation fault, the system can continue to operate because there is an ideally infinite resistance (insulation resistance) between the corresponding active conductors of the network and the ground potential, preventing the formation of a closed loop.

[0003] To ensure the electrical safety of ungrounded power supply systems, insulation monitoring devices (IMDs) must be used in accordance with the IEC 61557-8 standard. These devices can detect and report critical system conditions, such as insufficient insulation levels or excessive capacitance to ground. If necessary, upon receiving an alarm message from the insulation monitoring device (IMD), the faulty branch will be disconnected.

[0004] Similarly, the balance state of line voltage relative to ground potential (i.e., conductor-to-ground voltage) can be used as a monitoring and alarm parameter. The balance state of conductor-to-ground voltage, like insulation resistance, plays a crucial role. According to the formula... (To ground) leakage capacitance C e The energy stored in a capacitor increases with the square of the applied voltage. If, at the rated operating voltage, the voltage between the active conductor and ground is completely unbalanced, the total energy stored in the capacitor will double. Simultaneously, this doubling of the conductor-to-ground voltage significantly increases the risk to personal safety and property upon contact with the active conductor.

[0005] To control the energy stored in a system, one can reduce leakage capacitance or design capacitor capacity according to worst-case operating conditions; however, this approach is not always feasible depending on the scale of the power supply system. In DC ungrounded networks, the problem of increased energy in capacitors due to conductor-to-ground voltage imbalance is particularly prominent. In this case, even a high impedance imbalance in the insulation level of the active conductor to ground can lead to significant voltage shifts and associated energy increases. In AC networks, capacitors not only act as energy storage devices but also possess reactive characteristics. In many cases, especially in large industrial networks, the reactance of leakage impedance is lower than the effective resistance. Therefore, even an imbalance in the configuration of leakage capacitance to ground can cause related voltage shifts, leading to dangerous voltage surges.

[0006] In AC networks with voltage imbalances, alternating voltage becomes more important than stored energy for the varistor loads applied to insulation materials and electromagnetic compatibility (EMC) protection circuits. With prolonged voltage imbalances, these components may experience excessive unilateral losses, potentially impacting their lifespan.

[0007] When voltage imbalance occurs in the AC power grid, the alternating voltage will cause varistor loads to be applied to the insulation materials and electromagnetic compatibility (EMC) protection circuits, which are more important than energy storage elements.

[0008] Limiting leakage capacitance to ground is advantageous in both AC and DC networks, but it is not always technically feasible.

[0009] Another alternative approach is to actively or passively balance the conductor-to-ground voltage, which is significantly more efficient due to the square relationship between energy and voltage.

[0010] Regardless of the specific design, balancing typically consumes energy. This means that energy must either be extracted from the side with increased voltage, for example, through components such as ohmic resistors, and converted into heat, or it must be replenished as power on the other side. Especially in ungrounded AC networks with low leakage impedance, reactive power in the range of kilovolt-amperes (kVA) may be required to achieve balancing.

[0011] The purpose of this invention is to provide an energy-neutral active voltage balancing method.

[0012] According to existing technology, the energy limitation of ground leakage capacitance in ungrounded power supply networks is achieved through application-specific specifications for permissible capacitance values. However, due to the physical system characteristics of devices such as photovoltaic (PV) systems, it is often impossible to impose any limits on permissible capacitance values.

[0013] Furthermore, existing technologies know that conductor-to-ground voltage can be actively or passively balanced. One passive solution is to use a balancing voltage divider with a center tap connected to the ground potential. However, since the resistors in these long-term connected systems cannot be designed to be sufficiently low, this method can only partially address the problem of reduced insulation resistance due to imbalance. Well-known insulation monitoring devices (IMDs), with their technology of incorporating balanced network coupling, already meet this requirement.

[0014] Active methods can assess voltage imbalances and respond appropriately.

[0015] Patent application DE 10 2020 006 919 A1 describes a method for determining unbalanced loads by compensating for any voltage imbalances by switching discrete resistance values ​​between an active conductor and ground.

[0016] Active correction of unbalanced loads can also be achieved through voltage and power supply circuits. Patent application WO2023 / 007253A1 illustrates such a design integrated into an enhanced insulation monitoring device; Patent specification DE 10 2018 116 055 B3 further describes a method and insulation monitor for resistance adaptive insulation monitoring, describing a classic three-voltmeter method in which two operating points are observed; however, instead of switching discrete resistors, the combination of semiconductor switches and resistors is modulated to maintain a constant coupling resistance over a specific integration time. Patent application DE 10 2020 211 760 A1 discloses a balancing resistor device that is also used for discharging safety capacitors.

[0017] All of the above methods are for ungrounded DC power supply systems, while there are no existing methods or devices for balancing ungrounded AC power supply systems, and in particular, there are no related measures to achieve energy neutrality balance. Summary of the Invention

[0018] Therefore, the purpose of this invention is to design an electrical switching device and method that can balance the conductor-to-ground voltage in an energy-neutral manner in an ungrounded power supply system (especially an ungrounded AC power supply system) while minimizing power loss.

[0019] This objective is achieved by a balancing device that switches between the corresponding active conductor and ground potential in multiple stages and has the following characteristics.

[0020] The balancing device includes a voltage measuring device for detecting the corresponding conductor-to-ground voltage generated by each active conductor; a microcontroller for evaluating the measured conductor-to-ground voltage and controlling a power factor correction (PFC) controller, with each active conductor equipped with such a PFC controller. The microcontroller sets the conductor-to-ground voltage required to achieve balance as a target value. The corresponding PFC controller controls current consumption in such a way that it individually reproduces a control impedance for each active conductor. The magnitude of this control impedance, by providing reactive power, achieves the desired balance of the conductor-to-ground voltage. Furthermore, the balancing device includes an intermediate circuit for storing the energy converted in the control impedance; and a converter for feeding the energy stored in the intermediate circuit back to the power supply system at a frequency adapted to the power supply system.

[0021] Therefore, this balancing device can counteract voltage surges to ground by controlling the load in the form of impedance. Unlike traditional voltage balancing methods that use (controllable) balancing resistors, the energy converted in the reproduced control impedance is not converted into heat (power loss), but is fed back to the power supply system as electrical energy between the active conductors.

[0022] The balancing device described in this invention is designed to achieve a roughly energy-neutral balance relative to the ungrounded power supply system to be balanced, that is, the balancing task can be completed without extracting energy and utilizing heat, or without additional energy replenishment.

[0023] In a further design, a data circuit is provided between the balancing device and the insulation monitoring device (IMD), through which the set control impedance information can be transmitted to the insulation monitoring device (IMD).

[0024] Because the balancing device introduces a control impedance into the power supply system, and the independent insulation monitoring device (IMD) measures and displays this impedance, it inevitably leads to misjudgments of the system status. Therefore, it is necessary to correct the displayed value of the insulation monitoring device (IMD). To this end, the set control impedance information is transmitted from the balancing device to the insulation monitoring device (IMD) via a data circuit, and calculations are performed using the known current-voltage relationship (parallel resistance circuit).

[0025] The object of the present invention is also achieved by an enhanced insulation monitoring device that integrates the balancing device according to the present invention and forms a structural unit with the balancing device.

[0026] This enhanced insulation monitoring equipment mainly complies with relevant standards. In addition to realizing the insulation monitoring function, it can also balance and regulate the ungrounded power supply system being monitored, which effectively realizes the shared use of electrical (such as power supply) and structural (such as shell) resources, and is both economical and efficient.

[0027] The aforementioned balancing device is based on the implementation of the method according to the present invention, and therefore the aforementioned technical effects are also reflected in the characteristic advantages of the method.

[0028] In particular, this method is characterized by achieving near-zero power loss balance regulation.

[0029] In addition, this balancing device can be used to test the operability of insulation monitoring equipment.

[0030] Users can use balancing devices to inject (control) impedance into the power supply system, thereby simulating various system scenarios and the response of insulation monitoring equipment.

[0031] The balancing device can also be used to generate common-mode current, which is crucial for fault location in ungrounded power supply systems via insulation fault location system (IFLS). Attached Figure Description

[0032] Other advantageous design features can be derived from the following description and accompanying drawings, which illustrate a preferred embodiment of the invention in detail by way of example.

[0033] Figure 1 This illustrates an ungrounded single-phase power supply system with a balancing device according to the present invention. Figure 2 : A functional schematic diagram of the balancing device according to the present invention is shown; Figure 3 This illustrates an ungrounded single-phase power supply system with a balancing device according to the present invention and a data circuit between the system and an insulation monitoring device. Detailed Implementation

[0034] Figure 1 An ungrounded single-phase power supply system 2 is shown, which has a balancing device 10 according to the present invention.

[0035] The power supply system 2 is exemplarily designed as a single-phase AC network with active conductors L1 and L2, and is powered by an isolation transformer 4.

[0036] Insulation resistance R f1 R f2 and leakage capacitance C e1 C e2 This forms a composite leakage impedance to ground (ground potential PE). Load resistance R L It is connected to the power supply system 2 as an electrical device.

[0037] According to the present invention, the balancing device 10 is connected in multiple poles between the corresponding active conductors L1, L2 and the ground potential PE.

[0038] The total insulation resistance is composed of the insulation resistance R f1 R f2 The parallel connection is determined by an insulation monitoring device (IMD) with the same number of poles connected between the corresponding active conductors L1 and L2 and the ground potential PE.

[0039] The power supply system 2 and the (non-enhanced) insulation monitoring device (IMD) constitute the application environment of this invention, but are not part of this invention.

[0040] Figure 2 The balancing device 10 according to the present invention is shown in the form of a functional block diagram.

[0041] The voltage U to ground of each active conductor L1 and L2 is measured using voltage measuring device 12. L1-PE U L2-PE This data is then transmitted to microcontroller 14 for evaluation. Microcontroller 14 uses the corresponding conductor-to-ground voltage U. L1-PE U L2-PE As the target value, the PFC controller 16 configured for each active conductor L1 and L2 is controlled. The PFC controller 16, as the final control element in the control loop, is the core component of the balancing device 10.

[0042] The PFC controller 16 is known in the field of power supply units. Each PFC controller acts as an energy absorber and maps the control impedance required for balanced regulation. The PFC controller 16 is an active power electronic circuit group, particularly suitable for electrical devices with nonlinear power consumption. In this context, the PFC controller 16 controls current consumption in such a way that the current consumption under sinusoidal voltage exhibits a sinusoidal purely resistive characteristic. In principle, the PFC controller 16 can be considered as a circuit group for providing controlled impedance, a characteristic necessary for reproducing the (control) impedance composed of effective resistance and reactance.

[0043] Intermediate circuit 18 absorbs the energy generated by the effective resistance, or provides the energy required for the reactance of PFC controller 16.

[0044] The converter 20 transfers the energy from the intermediate circuit 18 to the power supply system 2.

[0045] If necessary, energy can also be fed back from the converter to the intermediate circuit.

[0046] All planned power electronic components can be considered to be nearly lossless.

[0047] Figure 3 exist Figure 1Based on this, an ungrounded single-phase power supply system 2 with the balancing device 10 described in this invention and the data circuit 22 between the device and the insulation monitoring device (IMD) is further shown.

[0048] The insulation monitoring device (IMD) acquires control impedance information introduced by the balancing device 10 according to conductor specificity via data circuit 22. Since these control impedances affect the measurement results of the insulation monitoring device (IMD), the insulation monitoring device (IMD) takes them into account when determining the insulation resistance, thereby achieving active contextual balancing adjustment and preventing the insulation monitoring device (IMD) from displaying incorrect measurement results.

[0049] In principle, for three-phase AC power supply systems, a three-phase balancing device 10, which is coupled in a three-phase configuration and corresponds to the balancing device of this invention, can also be used.

[0050] The balancing device 10 is suitable for both ungrounded AC power supply system 2 and ungrounded DC power supply system 2.

Claims

1. A balancing device (10) for balancing an ungrounded power supply system (2) having at least two active conductors (L1, L2), characterized in that: The balancing device (10) switches between the corresponding active conductors (L1, L2) and the ground potential (PE) in multiple stages. The balancing device (10) includes a voltage measuring device (12) for detecting the conductor-to-ground voltage (U) of the corresponding active conductors (L1, L2). L1-PE U L2-PE ); microcontroller (14), the microcontroller (14) being used to evaluate the conductor-to-ground voltage (U L1-PE U L2-PE ); Power factor correction (PFC) controller (16), each of the active conductors (L1, L2) is provided with the PFC controller (16), the microcontroller (14) is based on the conductor-to-ground voltage (U) in a balanced state. L1-PE U L2-PE The PFC controller (16) is controlled as a target value and the control impedance is reproduced for each active conductor (L1, L2) to achieve voltage balance between the active conductors (L1, L2); an intermediate circuit (18) is used to store the energy converted in the control impedance; and a converter (20) is used to output the energy stored in the intermediate circuit (18) to the power supply system (2).

2. The balancing device (10) according to claim 1, characterized in that: A data circuit (22) is provided between the balancing device (10) and the insulation monitoring device (IMD), the data circuit (22) being used to transmit the set control impedance related information to the insulation monitoring device (IMD).

3. An enhanced insulation monitoring device, characterized in that: Includes the balancing device (10) according to claim 1 or 2, used to form structural units.

4. A method for balancing an ungrounded power supply system (2) having at least two active conductors (L1, L2), characterized in that: The method includes the following steps to be performed in a balancing device (10) that performs multiple switching between the respective active conductors (L1, L2) and ground potential (PE): The corresponding conductor-to-ground voltage (U) is detected by the voltage measuring device (12). L1-PE U L2-PE ); The conductor-to-ground voltage (U) is evaluated using a microcontroller (14). L1-PE U L2-PE ); The microcontroller (14) sets the conductor-to-ground voltage (U) in a balanced state for each of the active conductors (L1, L2) by the PFC controller (16). L1-PE U L2-PE ) as the target value, The control impedance is reproduced for each of the active conductors (L1, L2) by the corresponding PFC controller (16) so that voltage balance is achieved between the active conductors (L1, L2); The energy converted from the control impedance is stored in the intermediate circuit (18). The energy stored in the intermediate circuit (18) is output to the power supply system (2) via the converter (20).

5. The method according to claim 4, characterized in that: The set control impedance related information is transmitted to the insulation monitoring device (IMD) through the data circuit (22) set between the balancing device (10) and the insulation monitoring device (IMD).

6. Use of the balancing device (10) according to claim 1 or 2 for testing the operability of an insulation monitoring device (IMD).

7. Use of a balancing device (10) according to claim 1 or 2 for generating a common-mode current for fault location in an ungrounded power supply system (2) via an insulation fault location system.

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