A medium frequency power supply rectification soft start circuit

Abstract

The utility model discloses a kind of medium-frequency power supply rectification soft-start circuit, including the three-phase fully-controlled rectifier bridge of six SCR, still including synchronous transformer, controller and electric reactor, three-phase ac incoming line provides three-phase ac for three-phase fully-controlled rectifier bridge;Synchronous transformer collects the phase sequence and voltage signal of three-phase ac incoming line, and each signal is sent to controller;Controller generates thyristor control pulse according to the signal of synchronous transformer, separately controls the conduction angle of two SCRs, makes the direct current output voltage of three-phase fully-controlled rectifier bridge gradually rise in multiple steps.This medium-frequency power supply rectification soft-start circuit of the utility model, in starting process, realize that direct current voltage is ladder type slowly rises, direct current is small amplitude pulse type fluctuation, avoid the impact of rectification starting process to entire medium-frequency power supply, also avoid the so-called "blasting" sound of direct current current-limiting reactor CLR, also avoid the malfunction of protection circuit.

Description

Technical Field

[0001] This utility model belongs to the technical field of rectifier circuits in medium-frequency induction power supplies, specifically relating to a medium-frequency power supply rectifier soft-start circuit. Background Technology

[0002] The rectifier circuit in the intermediate frequency induction power supply is very important. It receives electrical energy from the power grid and provides DC power to the entire intermediate frequency induction power supply.

[0003] Please see Figure 1 and Figure 2 In a conventional hard-triggered three-phase bridge rectifier circuit (three-phase fully controlled rectifier bridge), the triggering of the six SCRs (Semiconductors Rectifiers) is not differentiated or uniformly controlled. As a result, when the rectification starts, the DC voltage will rise rapidly to the rated voltage. During this process, the DC current will also rise rapidly because the DC capacitor needs to be charged. The rising DC current will cause the DC current-limiting reactor CLR to be instantly magnetized. The instantly magnetized DC current-limiting reactor CLR may attract the nearby metal cabinet and make a so-called "bang" sound.

[0004] Such a rapid increase in DC voltage and current is harmful to intermediate frequency power supplies, as it can damage some components and, in extreme cases, even cause malfunctions in protection circuits. Utility Model Content

[0005] The purpose of this utility model is to overcome the defects of the prior art and provide a medium frequency power supply rectifier soft start circuit. During the start-up process, the DC voltage rises slowly in a step-like manner and the DC current fluctuates in a small-amplitude pulse-like manner, which avoids the impact of the rectifier start-up process on the entire medium frequency power supply, avoids the so-called "explosion" sound of the DC current limiting reactor CLR, and avoids the malfunction of the protection circuit.

[0006] The technical solution to achieve the above objective is: a medium-frequency power supply rectifier soft-start circuit, comprising a three-phase fully controlled rectifier bridge composed of six SCRs, and further comprising a synchronous transformer, a controller, and a reactor, wherein:

[0007] The three-phase AC incoming line provides three-phase AC power to the three-phase fully controlled rectifier bridge;

[0008] The synchronous transformer collects the phase sequence and voltage signals of the three-phase AC input lines and sends each signal to the controller;

[0009] The controller generates thyristor control pulses based on the signal from the synchronous transformer, and individually controls the conduction angle of two of the SCRs, so that the DC output voltage of the three-phase fully controlled rectifier bridge increases step by step in multiple stages.

[0010] The reactor is connected to the output terminal of the three-phase fully controlled rectifier bridge to limit the current surge during startup.

[0011] In the aforementioned medium-frequency power supply rectifier soft-start circuit, the controller is connected to the output terminal of the three-phase fully controlled rectifier bridge. After each boost step, the controller synchronously detects the actual DC output voltage of the three-phase fully controlled rectifier bridge and compares it with the built-in voltage setting value corresponding to each boost step. If the actual DC output voltage reaches the voltage setting value corresponding to each stage, it proceeds to the next boost step. If the actual DC output voltage is higher or lower than the voltage setting value corresponding to each stage, the boost is stopped or the rectification is turned off. After several boost steps, the DC output voltage reaches the rated value, and the soft start is completed.

[0012] The medium-frequency power supply rectifier soft-start circuit of this utility model incorporates a synchronous transformer to collect the phase sequence of the three-phase AC input power supply. In addition, two SCRs are individually controlled. During the startup process, the DC voltage rises slowly in a step-like manner, and the DC current fluctuates in a small-amplitude pulse-like manner. This avoids the impact of the rectification startup process on the entire medium-frequency power supply, avoids the so-called "backfiring" sound of the DC current limiting reactor (CLR), and avoids the malfunction of the protection circuit. Attached Figure Description

[0013] Figure 1 This is a diagram showing the output voltage of a conventional hard-triggered rectifier.

[0014] Figure 2 The output current diagram for a conventional hard-triggered rectifier;

[0015] Figure 3 This is a circuit diagram of the medium-frequency power supply rectifier soft-start circuit of this utility model;

[0016] Figure 4 This is a schematic diagram showing the individual control of two of the SCRs;

[0017] Figure 5 This is a diagram showing the output voltage of the medium-frequency power supply rectifier soft-start circuit of this utility model;

[0018] Figure 6 This is a diagram showing the output current of the medium-frequency power supply rectifier soft-start circuit of this utility model. Detailed Implementation

[0019] To enable those skilled in the art to better understand the technical solution of this utility model, its specific embodiments are described in detail below with reference to the accompanying drawings:

[0020] Please see Figures 3 to 6 The preferred embodiment of this utility model is a medium-frequency power supply rectifier soft-start circuit, which includes a synchronous transformer 20, a controller 30, a reactor CLR, and a three-phase fully controlled rectifier bridge 10 composed of six SCRs.

[0021] The six SCRs are SCR1, SCR2, SCR3, SCR4, SCR5 and SCR6.

[0022] The three-phase AC incoming line 40 provides three-phase AC power to the three-phase fully controlled rectifier bridge 10.

[0023] Synchronous transformer 20 collects the phase sequence and voltage signals of the three-phase AC incoming line 40 and sends each signal to controller 30.

[0024] The controller 30 generates thyristor control pulses based on the signal from the synchronous transformer 20, and individually controls the conduction angles of SCR1 and SCR5 to achieve stepped voltage boost. The controller 30 is connected to the output terminal of the three-phase fully controlled rectifier bridge 10 to detect the actual DC output voltage of the three-phase fully controlled rectifier bridge 10.

[0025] The reactor CLR is connected to the output of the three-phase fully controlled rectifier bridge 10 to limit the current surge during startup.

[0026] The working principle of the medium-frequency power supply rectifier soft-start circuit of this utility model is as follows:

[0027] (1) Step-by-step boost: When starting up, the controller 30 gradually increases the conduction angle of SCR1 and SCR5, so that the DC output voltage rises step by step in multiple steps (instead of reaching full voltage at once); after each boost step, the controller 30 will synchronously detect the actual DC output voltage of the three-phase fully controlled rectifier bridge 10 and compare it with the voltage setting value corresponding to the built-in boost step.

[0028] (2) Closed-loop control: If the voltage meets the standard (the actual DC output voltage is equal to the corresponding voltage setting value), then proceed to the next boost step; if it does not meet the standard (the actual DC output voltage is less than or greater than the corresponding voltage setting value), then stop boosting or shut down rectification to achieve protection; after several boost steps, the output voltage reaches the rated value and soft start is completed.

[0029] (3) Output characteristics: The output voltage rises slowly in a step-like manner; the output current fluctuates in a small-amplitude pulse-like manner, avoiding large current surges.

[0030] The core advantages and protection functions of this utility model's medium-frequency power supply rectifier soft-start circuit are as follows:

[0031] (1) Suppressing startup shock: By stepping up the voltage, the current and voltage stress on the power grid and internal components of the power supply (such as SCR and reactor) is greatly reduced;

[0032] (2) Fault protection: The output voltage is continuously monitored throughout the soft start process; if a fault occurs in the downstream part of the intermediate frequency power supply (such as the inverter) causing rectification failure (such as abnormal voltage), the system can stop in time to prevent the fault from spreading and protect the main body of the intermediate frequency power supply.

[0033] (3) Improved reliability: The smooth startup process extends the lifespan of power components such as SCR and improves the overall stability of the system.

[0034] This utility model's medium-frequency power supply rectifier soft-start circuit achieves a smooth establishment of the rectified DC voltage through a closed-loop strategy of "synchronous sampling → stepped trigger control → voltage detection feedback." It not only eliminates the electrical shock caused by traditional direct starting but also integrates process fault diagnosis and protection functions, making it a medium-frequency power supply rectifier starting solution that balances smooth start-up and system safety.

[0035] The intermediate frequency power supply rectifier soft-start circuit of this utility model gradually increases the DC voltage in a step-by-step manner during the rectification start-up process. After several steps, the DC voltage is detected and compared. If the DC voltage meets the standard, the step-by-step rectification continues until the rated DC voltage is reached. Only then is the soft-start rectification considered complete. In this way, if there is a fault in the intermediate frequency power supply during the entire soft-start rectification process, it will cause rectification failure, thus avoiding damage to the intermediate frequency power supply.

[0036] In summary, the intermediate frequency power supply rectifier soft-start circuit of this utility model achieves a gradual increase in DC voltage and a small-amplitude pulse fluctuation in DC current during the startup process. This avoids the impact of the rectification startup process on the entire intermediate frequency power supply, avoids the so-called "backfiring" sound of the DC current limiting reactor CLR, and avoids the malfunction of the protection circuit.

[0037] Those skilled in the art should recognize that the above embodiments are only used to illustrate the present utility model and are not intended to limit the present utility model. Any changes or modifications to the above embodiments within the scope of the essential spirit of the present utility model will fall within the scope of the claims of the present utility model.

Claims

1. A medium-frequency power supply rectifier soft-start circuit, comprising a three-phase fully controlled rectifier bridge composed of six SCRs, characterized in that, It also includes synchronous transformers, controllers, and reactors, among which: The three-phase AC incoming line provides three-phase AC power to the three-phase fully controlled rectifier bridge; The synchronous transformer collects the phase sequence and voltage signals of the three-phase AC input lines and sends each signal to the controller; The controller generates thyristor control pulses based on the signal from the synchronous transformer, and individually controls the conduction angle of two of the SCRs, so that the DC output voltage of the three-phase fully controlled rectifier bridge increases step by step in multiple stages. The reactor is connected to the output terminal of the three-phase fully controlled rectifier bridge to limit the current surge during startup.

2. The medium-frequency power supply rectifier soft-start circuit according to claim 1, characterized in that, The controller is connected to the output terminal of the three-phase fully controlled rectifier bridge. After each boost step, the controller synchronously detects the actual DC output voltage of the three-phase fully controlled rectifier bridge and compares it with the voltage setting value corresponding to each boost step. If the actual DC output voltage reaches the voltage setting value corresponding to each stage, it enters the next boost step. If the actual DC output voltage is higher or lower than the voltage setting value corresponding to each stage, it stops boosting or turns off rectification. After several boost steps, the DC output voltage reaches the rated value, and the soft start is completed.

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