Bus automatic discharge circuit for frequency converter

Abstract

The utility model provides an automatic bus discharge circuit for a frequency converter. The bus automatic discharge circuit for the frequency converter comprises a normally closed switch element, an input loop of which is connected with a controlled power supply, an output loop of which is connected between a bus and a discharge common end, and a normally closed contact arranged in the output loop and configured to open the normally closed contact after the input loop is driven by the controlled power supply; and the controlled power supply is provided with a voltage detection end connected with the bus and is configured to send a power supply signal to the input loop under the condition that the detection voltage of the voltage detection end is higher than a set value. According to the mode, the normally-closed switching element can be automatically switched on and off according to the power signal, so that the output loop is connected to discharge residual voltage under the condition that the input loop is disconnected, and normal use of elements in the circuit and safety of maintenance personnel are guaranteed.

Description

Technical Field

[0001] The utility model relates to the technical field of discharge circuits, in particular to a busbar automatic discharge circuit for a frequency converter. Background Art

[0002] Most of the current inverter designs include a filter side, a rectifier side, and an inverter side. Electrolytic capacitors, as rectifier and filter capacitors of inverters / inverters, play a vital role in the circuit. When the inverter is running, it starts to charge the capacitors connected in parallel between the positive and negative poles of the bus, making the DC bus more stable. When the inverter is out of operation, the bus voltage loses its discharge circuit due to the loss of load, and the parasitic resistance of the capacitor itself is very small, so there is often a certain amount of residual charge on the capacitor. When these residual charges exist, powering on again may generate a large closing inrush current and a high overvoltage, which may lead to the breakdown of the power capacitor and even explosion, and also have a certain impact on the life of the capacitor. In addition, if the discharge is not timely, maintenance personnel may be electrocuted when touching the inverter board, which may endanger human life in serious cases. Utility Model Content

[0003] One purpose of the utility model is to provide a bus automatic discharge circuit for a frequency converter.

[0004] A further object of the present invention is to be able to automatically perform the discharge process without active control.

[0005] In particular, the utility model provides a bus automatic discharge circuit for a frequency converter, comprising:

[0006] A normally closed switch element, whose input circuit is connected to a controlled power source, and whose output circuit is connected between a busbar and a discharge common terminal, wherein the output circuit has a normally closed contact and is configured to open the normally closed contact after the input circuit is driven by the controlled power source;

[0007] The controlled power supply has a voltage detection terminal connected to the bus and is configured to send a power signal to an input circuit when the detection voltage of the voltage detection terminal is higher than a set value.

[0008] Optionally, the discharge common terminal includes: a discharge resistor, which is connected in series with the output circuit and is used to discharge the residual charge in the bus after the normally closed contact is closed.

[0009] Optionally, the normally closed switch element includes: a normally closed relay, the input circuit is a coil circuit of the normally closed relay, and the output circuit is a contact circuit of the normally closed relay.

[0010] Optionally, a freewheeling diode is connected in parallel with the normally closed switch element to protect the elements in the busbar automatic discharge circuit from being damaged.

[0011] Optionally, an indicating component is connected to the controlled power supply and in parallel with the normally closed switch element, and is used to indicate the voltage level of the controlled power supply.

[0012] Optionally, the indicating component includes:

[0013] The light emitting diode is connected to a controlled power source and configured to change light intensity according to the controlled power source.

[0014] Optionally, the indicating component further includes:

[0015] The current limiting resistor is connected between the controlled power supply and the light emitting diode to protect the light emitting diode and stabilize the current.

[0016] Optionally, a capacitor is connected to the bus bar and is used to store the electric energy released by the bus bar.

[0017] Optionally, the controlled power supply is further configured to: stop sending the power signal when the detection voltage of the voltage detection terminal is lower than a set value;

[0018] The output circuit is further configured to close the normally closed contact when the input circuit detects no power signal.

[0019] In another aspect of the utility model, a frequency converter is provided, comprising any one of the above bus automatic discharge circuits for the frequency converter.

[0020] The utility model of the bus automatic discharge circuit for the frequency converter includes a normally closed switch element, whose input circuit is connected to a controlled power supply, and whose output circuit is connected between the bus and the discharge common terminal, wherein the output circuit has a normally closed contact, and is configured to open the normally closed contact after the input circuit is driven by the controlled power supply; the controlled power supply has a voltage detection terminal connected to the bus, and is configured to send a power signal to the input circuit when the detection voltage of the voltage detection terminal is higher than the set value. In this way, the normally closed switch element can automatically switch according to the power signal, so that when the input circuit is disconnected, the output circuit is connected to discharge the residual voltage, thereby ensuring the normal use of the components in the circuit and the safety of the maintenance personnel.

[0021] Based on the detailed description of the specific embodiments of the present invention in combination with the accompanying drawings below, those skilled in the art will become more aware of the above and other purposes, advantages and features of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Hereinafter, some specific embodiments of the present invention will be described in detail in an exemplary and non-limiting manner with reference to the accompanying drawings. The same reference numerals in the accompanying drawings indicate the same or similar components or parts. It should be understood by those skilled in the art that these drawings are not necessarily drawn to scale. In the accompanying drawings:

[0023] Figure 1 is a schematic diagram of a discharge circuit of an embodiment;

[0024] Figure 2 The utility model is a schematic diagram of a bus automatic discharge circuit for a frequency converter according to an embodiment of the utility model. DETAILED DESCRIPTION

[0025] It should be understood by those skilled in the art that the embodiments described below are only a part of the embodiments of the present invention, rather than all the embodiments of the present invention, and the embodiments are intended to explain the technical principles of the present invention, rather than to limit the protection scope of the present invention. Based on the embodiments provided by the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should still fall within the protection scope of the present invention.

[0026] In the description of the present invention, it should be understood that the terms "longitudinal", "lateral", "upper", "lower", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc. indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present invention.

[0027] Furthermore, it should be noted that in the description of the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a direct connection, an indirect connection through an intermediate medium, or the internal communication of two components. For those skilled in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0028] Figure 1 is a schematic diagram of a discharge circuit of an embodiment. Figure 1 The circuit design shown is a usable discharge circuit.

[0029] Most of the current inverter designs include a filter side, a rectifier side, and an inverter side. Electrolytic capacitors, as rectifier and filter capacitors of inverters / inverters, play a vital role in the circuit. When the inverter is running, it starts to charge the capacitors connected in parallel between the positive and negative poles of the bus, making the DC bus more stable. When the inverter is out of operation, the bus voltage loses its discharge circuit due to the loss of load, and the parasitic resistance of the capacitor itself is very small, so there is often a certain amount of residual charge on the capacitor. When these residual charges exist, powering on again may generate a large closing inrush current and a high overvoltage, which may lead to the breakdown of the power capacitor and even explosion, and also have a certain impact on the life of the capacitor. In addition, if the discharge is not timely, maintenance personnel may be electrocuted when touching the inverter board, which may endanger human life in serious cases.

[0030] Usually, the discharge circuit of the inverter is to connect resistors in parallel at both ends of the bus voltage to achieve discharge. Although this method can consume the residual voltage of the bus voltage after power failure, it also has additional power loss during the operation of the inverter.

[0031] In addition, there is another way to Figure 1 The discharge circuit shown is connected to the busbar via resistors R1, R2, R3 and R5, and the discharge circuit is controlled by a microcontroller unit (MCU) during this process.

[0032] MCU is an integrated circuit, also often called a single-chip microcomputer or microprocessor, designed for embedded systems and IoT devices. Figure 1 In the discharge circuit shown, when the circuit operates normally, the switch 10 is kept in an open state under the control of the MCU, so that the circuit where the resistor R6 is located is in a disconnected state.

[0033] When the inverter stops running, the circuits where resistors R1, R2, R3 and R5 are located stop working. At this time, the MCU controls the switch 10 to close, causing the circuit where resistor R6 is located to be connected, thereby achieving the discharge of the bus voltage.

[0034] By adding a control method to the parallel resistor, that is, the discharge circuit is turned on and off by the MCU. However, this method requires the detection circuit to detect the external power supply and transmit the signal to the MCU module. After receiving the signal, the MCU opens the discharge circuit through the control switch to discharge the residual bus voltage. The execution is slow, the circuit redundancy is complex, and the cost is relatively high.

[0035] In order to solve the above problems, the utility model proposes a bus automatic discharge circuit for a frequency converter, such as Figure 2 shown.

[0036] Figure 2 This is a schematic diagram of a busbar automatic discharge circuit for a frequency converter according to an embodiment of the utility model. In this embodiment, it generally includes:

[0037] A normally closed switch element, whose input circuit is connected to a controlled power source P, and whose output circuit is connected between a bus and a common discharge terminal, wherein the output circuit has a normally closed contact, and is configured to open the normally closed contact after the input circuit is driven by the controlled power source P; the controlled power source P has a voltage detection terminal connected to the bus, and is configured to send a power signal to the input circuit when the detection voltage of the voltage detection terminal is higher than a set value. The output circuit can only be connected when the normally closed contact of the normally closed switch element is closed.

[0038] In some optional embodiments, a normally closed switch element is an electrical or electronic component characterized in that the contacts are closed in normal state (i.e., when not activated or without external force), allowing current to pass. When external conditions change, such as applied force, electromagnetic field effects, electrical signals, or mechanical movement, the normally closed contacts will open, interrupting the circuit and preventing current from flowing. This component is commonly used in circuit design for safety, control logic, fault protection, or signal switching scenarios.

[0039] Optionally, the controlled power supply P can also be generally configured to stop sending the power signal when the detection voltage of the voltage detection terminal is lower than a set value.

[0040] The output circuit can also be generally configured to close the normally closed contact when the input circuit detects no power signal.

[0041] When the detection voltage at the voltage detection end is lower than the set value, the controlled power supply P is disconnected, and there is no power signal on its output side. At this time, no power signal can be detected in the input circuit, and the normally closed switch element will close its normally closed contacts, thereby connecting the output circuit.

[0042] In some optional embodiments, the execution logic of the normally closed switch element is that when there is a power signal in its input circuit, its switch is in an open state, that is, the output circuit is in a disconnected state; when there is no power signal in its input circuit, its switch will become a closed state, so that the output circuit is in a connected state.

[0043] P+ and N- respectively represent the positive and negative ends of the bus voltage, and the controlled power supply P is configured to send out a power signal only when the conditions are met. For example, when the bus voltage of the bus is greater than the set value, the controlled power supply P will send out a power signal, and the input circuit in the normally closed switch element is connected to the controlled power supply P. When the controlled power supply P sends out a power signal, the normally closed contact in its output circuit is in an open state, and the circuit used for discharge is in a disconnected state. Those skilled in the art can determine the specific size of the set value according to actual conditions.

[0044] In some optional embodiments, the normally closed switch element may generally include: a normally closed relay K1 , an input circuit being a coil circuit of the normally closed relay K1 , and an output circuit being a contact circuit of the normally closed relay K1 .

[0045] Among them, the normally closed relay K1 is an electrical control component, which is characterized by the fact that when there is no external excitation (such as no power), the contacts (contact points) of the relay are closed, forming a path state, allowing current to pass. Once the external excitation signal is applied to the coil of the relay (usually an electromagnetic coil), the generated magnetic field will cause mechanical action to disconnect the contacts, disconnect the circuit, and prevent current from flowing.

[0046] The working principle of the normally closed relay K1 can generally include:

[0047] Static State: When there is no current flowing through the relay coil, the normally closed contacts remain closed, allowing current to flow through the contacts to the load.

[0048] Active state: When the coil receives a voltage or current signal, the coil generates a magnetic field, attracting the armature or yoke iron, causing mechanical movement, thereby disconnecting the contacts and separating the contacts.

[0049] Reset: When the coil is de-energized, the magnetic field disappears and a spring or reset device returns the contacts to their original closed state.

[0050] Specifically, in this embodiment, interface 1 and interface 2 represent the coil circuit where the input circuit is located, and interface 3 and interface 4 represent the contact circuit where the output circuit is located. The output circuit can be automatically connected through the normally closed relay K1, thereby realizing the discharge of the bus voltage by the output circuit.

[0051] In some optional embodiments, the discharge common terminal may also generally include: a discharge resistor R1, which is connected in series with the output circuit and is used to discharge the residual charge in the bus after the normally closed contact is closed. The discharge resistor R1 is mainly used in circuit design to control the charge release process in the capacitor (especially a large-capacity capacitor, such as an electrolytic capacitor) to ensure that the capacitor is safely discharged to a safe voltage level when not in use or under maintenance.

[0052] The main function of the discharge resistor R1 in the circuit is to safely release the electrical energy stored in the capacitor (such as capacitors, coils, etc.). When the circuit is disconnected or the equipment is turned off, a large amount of charge may still be stored in the capacitor, which may cause electrical breakdown, equipment damage or safety risks if not properly released. The discharge resistor R1 forms a low-resistance path, allowing the charge to discharge to a safe level at a controlled rate, generally combined across the capacitor, to ensure personal safety during circuit operation and maintenance.

[0053] The selection of discharge resistor R1 generally needs to consider factors such as the capacity of the capacitor, initial voltage, target discharge time, and safe voltage, and calculate the resistance value and power to ensure effectiveness without overheating. In the design, components such as thermistors and indicator lights are sometimes added to monitor the discharge process or warning status. In high-voltage systems, the discharge resistor R1 may need to be specially designed to withstand high voltage, be non-inductive, and have good heat dissipation to ensure fast and stable discharge. Technicians in this field can select a qualified discharge resistor R1 based on actual conditions.

[0054] Optionally, the circuit of the present invention may also generally include a freewheeling diode D1 connected in parallel with the normally closed switch element to protect the elements in the busbar automatic discharge circuit from being damaged.

[0055] In some optional embodiments, the freewheeling diode D1 may also be called a flyback diode, which is a special electronic component whose main function is to provide a low-resistance path in the circuit so that the current can flow smoothly, especially when the inductive load (such as the electromagnetic core coil, motor, transformer, etc.) is powered off, to prevent damage or voltage spikes caused by reverse voltage (induced electromotive force). The freewheeling diode D1 is usually used in parallel with the inductive load to ensure the continuity of the current and avoid excessive induced voltage when the current is suddenly interrupted.

[0056] In the scheme of the utility model, the freewheeling diode D1 is connected in parallel to both ends of the normally closed relay K1 to protect the components from being broken down or burned out by the induced voltage, and forms a loop with it so that the high electromotive force generated by it is consumed in the loop in the form of freewheeling current, thereby protecting the components in the circuit from being damaged.

[0057] Optionally, the circuit of the present invention may generally further include an indicating component, which is connected to the controlled power source P and in parallel with the normally closed switch element K1 , and is used to indicate whether the voltage of the controlled power source P is high or low.

[0058] In some optional embodiments, the indicating component may generally include: a light emitting diode LED1 connected to a controlled power source P and configured to change light intensity according to the controlled power source P.

[0059] Light-Emitting Diode (LED) is a semiconductor electronic component that can directly convert electrical energy into light energy. Unlike traditional incandescent bulbs or fluorescent lamps, LED emits light by electronically exciting semiconductor materials rather than heating filaments or gases, which makes LED have significant advantages in energy efficiency, life and environmental protection. Therefore, when the detection voltage of the voltage detection end is higher than the set value, the controlled power supply P has a signal, that is, the input circuit is operating normally. At this time, the light-emitting diode LED1 is connected to the controlled power supply P and will also be in a state of constant light. At this time, the working state of the input circuit can be determined by the light-emitting state of the light-emitting diode LED1. When the detection voltage of the voltage detection end is lower than the set value, the controlled power supply P is disconnected, and the light of the light-emitting diode LED1 will become weak in a short time, and gradually dim as the voltage in the circuit decreases. Those skilled in the art can determine the operating state of the circuit where the controlled power supply P is located by the brightness change of the light-emitting diode LED1, and can also determine whether the inverter where it is located is powered off and the voltage level, so as to facilitate the safety of subsequent maintenance.

[0060] Optionally, the indicating component may also generally include: a current limiting resistor R2, connected between the controlled power supply P and the light-emitting diode LED1, for protecting the light-emitting diode LED1 and stabilizing the current. The main function of the current limiting resistor R2 in circuit design is to limit the current passing through the circuit or a certain component to protect the circuit from damage caused by excessive current and ensure the circuit is stable and operates safely. In addition, it can also be used in combination with capacitors in signal processing to form a low-pass filter to filter out high-frequency noise and improve signal quality.

[0061] Optionally, the circuit of the utility model may also generally include a capacitor connected to the busbar to store the electric energy released by the busbar. In the inverter, capacitors play a vital role, which is mainly reflected in the following aspects:

[0062] 1. Filtering: The main function of the DC bus capacitor of the inverter is filtering, smoothing the pulsating DC voltage output by the rectifier circuit, reducing the AC component, and providing the inverter with a nearly pure DC voltage. This can reduce the distortion of the AC voltage waveform output by the inverter and improve the current quality of the motor drive.

[0063] 2. Energy storage: The capacitor is connected in parallel in the DC link of the inverter to play the role of energy storage. When the current demand is peak, the capacitor releases energy to replenish, and vice versa, it charges to help smooth the DC bus voltage, cope with dynamic load changes, and reduce the impact on the power grid.

[0064] 3. Compensation: In complex systems, capacitors may also be used for power factor correction, improving grid quality, or compensating for harmonic waveforms, reducing high-frequency harmonics entering the grid, and improving energy efficiency.

[0065] 4. Demagnetization: During emergency shutdown, the capacitor can absorb the motor demagnetization energy to prevent overvoltage damage to the inverter and motor components and protect the system.

[0066] 5. Switching frequency input current: Provides input current for the inverter switching frequency. The capacitor helps maintain a stable inverter process and reduce switching frequency current harmonics.

[0067] In some optional embodiments, an optional capacitor is an electrolytic capacitor E1, which is a capacitor using an electrolyte as a dielectric medium. Compared with other types of capacitors, such as ceramic, film or thin film capacitors, it has unique properties and application characteristics.

[0068] In some optional embodiments, the utility model also includes a frequency converter, including the above-mentioned bus automatic discharge circuit. Most of the current frequency converter designs include a filter side, a rectifier side and an inverter side. Electrolytic capacitors, as rectifier filter capacitors of frequency converters / inverters, play a vital role in the circuit. When the frequency converter is running, the capacitors connected in parallel between the positive and negative poles of the bus begin to be charged, making the DC bus more stable. When the frequency converter exits operation, the bus voltage loses the discharge circuit due to the loss of load, and the parasitic resistance of the capacitor itself is very small, so there is often a certain residual charge on the capacitor, and when these residual charges exist, powering on again may generate a large closing surge current and a very high overvoltage, which may lead to the breakdown of the power capacitor, and even explosion, and also have a certain impact on the life of the capacitor; in addition, if the discharge is not timely, the maintenance personnel may be electrocuted when touching the frequency conversion board at this time, which may endanger people's lives in serious cases. Therefore, by applying the above-mentioned bus automatic discharge circuit to the inverter, the residual charge can be automatically discharged through the automatic discharge circuit when the inverter stops, thereby reducing the danger of artificial discharge and improving the efficiency of maintenance.

[0069] The utility model provides a low-loss bus voltage automatic discharge circuit for a frequency converter. The circuit includes a discharge control part and a safety indication part. The discharge control circuit uses the working principle of a switching power supply. When the voltage drops to the moment when the switching power supply is turned off, the discharge control part automatically releases the residual voltage of the bus after power failure, thereby reducing the danger of manual discharge and improving the efficiency of maintenance. When the bus voltage is working normally, the discharge control part disconnects the bus voltage discharge to reduce power consumption.

[0070] The indicator light of the safety indication part, that is, the light emitting diode LED1, is bright when the bus voltage is operating normally, and is turned off when the voltage drops to start the discharge mode. As the voltage drops, the light gradually dims, which serves as a warning and improves safety.

[0071] The present invention is fully described for a clearer disclosure, and the prior art will not be listed one by one.

[0072] At this point, those skilled in the art should recognize that, although multiple exemplary embodiments of the present invention have been shown and described in detail herein, many other variations or modifications that conform to the principles of the present invention can still be directly determined or derived from the contents disclosed in the present invention without departing from the spirit and scope of the present invention. Therefore, the scope of the present invention should be understood and recognized as covering all such other variations or modifications.

Claims

1. A bus automatic discharge circuit for a frequency converter, characterized in that: include: A normally closed switch element, whose input circuit is connected to a controlled power source, and whose output circuit is connected between the busbar and a discharge common terminal, wherein the output circuit has a normally closed contact and is configured to open the normally closed contact after the input circuit is driven by the controlled power source; The controlled power supply has a voltage detection terminal connected to the bus bar and is configured to send a power signal to the input circuit when the detection voltage of the voltage detection terminal is higher than a set value.

2. The bus automatic discharge circuit for a frequency converter according to claim 1, characterized in that: The discharge common terminal includes: a discharge resistor connected in series with the output circuit, and used for discharging the residual charge in the bus after the normally closed contact is closed.

3. The bus automatic discharge circuit for a frequency converter according to claim 1, characterized in that: The normally closed switch element includes: a normally closed relay, the input circuit is a coil circuit of the normally closed relay, and the output circuit is a contact circuit of the normally closed relay.

4. The bus automatic discharge circuit for a frequency converter according to claim 1, characterized in that: Also includes: A freewheeling diode is connected in parallel with the normally closed switch element and is used to protect the elements in the busbar automatic discharge circuit from being damaged.

5. The bus automatic discharge circuit for a frequency converter according to claim 1, characterized in that: Also includes: An indicating component is connected to the controlled power supply and in parallel with the normally closed switch element, and is used to indicate the voltage level of the controlled power supply.

6. The bus automatic discharge circuit for a frequency converter according to claim 5, characterized in that: The indicating component comprises: A light emitting diode is connected to the controlled power source and configured to change light intensity according to the controlled power source.

7. The bus automatic discharge circuit for a frequency converter according to claim 6, characterized in that: The indicating component also includes: A current limiting resistor is connected between the controlled power supply and the light emitting diode, and is used to protect the light emitting diode and stabilize the current.

8. The bus automatic discharge circuit for a frequency converter according to claim 1, characterized in that: Also includes: The capacitor is connected to the bus and is used to store the electric energy released by the bus.

9. The bus automatic discharge circuit for a frequency converter according to claim 1, characterized in that: The controlled power supply is further configured to: stop sending the power signal when the detection voltage of the voltage detection terminal is lower than the set value; The output circuit is further configured to close the normally closed contact when the input circuit fails to detect the power signal.

10. A frequency converter, characterized in that: The invention comprises a bus automatic discharge circuit as claimed in any one of claims 1 to 9.

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