CN103595304B - Variable Frequency Drives powers on and braking circuit - Google Patents

Abstract

The invention discloses a power-on and brake circuit of a variable-frequency transmission system, which includes a power-on brake circuit, a rectifier circuit and a transmission system. The power-on brake circuit is combined with a soft power-on circuit and a brake circuit, and its two input terminals are respectively connected to the two output positive poles and negative poles of the rectifier circuit, and its two output terminals are respectively connected to the two input positive poles and the two input poles of the transmission system. The negative pole is connected, the two input ends of the rectifier circuit are respectively connected to the live wire and the neutral wire of the single-phase AC power supply, and the transmission system is a frequency conversion speed regulation system. The invention can realize soft power-on of the rectifier and fast braking of the motor, has small power-on current impact, has reliable braking function, and has a simple circuit structure without manual control, and is suitable for frequency conversion speed regulation systems powered by AC power.

Description

Power-on and braking circuit of frequency conversion drive system

technical field

The invention relates to a device in the field of AC frequency conversion and speed regulation using power electronic conversion technology, in particular to a power-on and braking circuit for a frequency conversion drive system.

Background technique

The power-on current limiting circuit and fast braking circuit are important components of the variable frequency drive system, and their application fields include industrial sewing machines, CNC machine tools, etc.

In a large power system, the energy storage capacitor on the output side of the rectifier circuit has a large capacity and its initial voltage is zero, so the energy storage capacitor will cause a high-amplitude inrush current during the power-on stage, causing damage to power devices, pollution Power grid and other adverse consequences, so power-on current limiting measures must be taken. Up to now, the power-on current-limiting circuit has a variety of solutions, including: (1) For higher power levels, the current-limiting resistor or PTC is connected in series on the DC side or the AC live wire, and the relay or power switch is used to automatically cut off the power after power-on. ; (2) NTC thermistors connected in series, using its negative temperature characteristics, limit the current during power-on, but keep it after power-on; (3) Connect the current limiting device in series to curb the rate of change of current. Each program has a variety of specific measures. The above various power-on current limiting circuits have their own advantages and disadvantages. Generally, active solutions are used, which require DSP or MCU control, and the cost is high and complicated. For low-power frequency conversion drive systems, the proportion of cost is too large. After searching the existing technology, it was found that two traditional soft-start circuits were summarized in the article "A Starting Inrush Current Suppression Circuit" ("Journal of Electrical Machinery and Control", No. 6, 2011), and a three-stage soft-start circuit was proposed. Inrush current suppression circuit, this circuit can effectively suppress the primary inrush current and the secondary inrush current at start-up, but there is still an inrush current, the structure is complex, the number of components is large, and the control is not easy.

When the transmission system is decelerating, braking or reversing, it will feed back electric energy, which will cause the voltage of the electrolytic capacitor in the DC circuit to rise, threatening the life of the electrolytic capacitor, power devices and switching power supply connected to the DC side. For this reason, braking measures must be adopted , to consume the excess energy of the DC circuit. Industrial sewing machines (500W) powered by single-phase AC power supply, CNC machine tools (below 5.0kW) and other power electronic converters that require fast positioning have higher and higher requirements for fast braking technology that enables the motor to stop quickly and accurately. The energy consumption braking method is commonly used at present. When the DC back circuit voltage rises to a certain value, the energy consumption braking circuit is activated to reduce the DC circuit voltage. So far, there is only one energy-consumption braking scheme adopted in practice, that is, to install a seventh power device and a power resistor in the DC loop, and consume the DC loop voltage by controlling its duty cycle. This kind of energy consumption braking circuit generally adopts an active scheme, which requires DSP or MCU control, and the cost is high and complicated. For low-power frequency conversion drive systems, the proportion of cost is too large. After searching the existing technology, it was found that the article "A Design of Rapid Braking and Accurate Positioning Control Scheme for Brushless DC Motor" ("Industrial and Mine Automation", 2010 No. A rotating magnetic field that is opposite to the direction of inertial rotation is generated inside to accelerate the motor to brake. This method has complex control and high cost, and the braking energy is consumed inside the motor, so it is not suitable for frequent braking applications.

Based on the above analysis, for low-power frequency conversion speed regulation applications, it is necessary to introduce a simple, safe, reliable and low-cost integrated circuit that integrates soft power-on and energy-consuming braking.

Contents of the invention

In view of the above-mentioned defects of the prior art, the technical problem to be solved by the present invention is to provide a power-on and braking circuit in a variable frequency transmission system, which can realize small power-on impact, reliable braking, simple circuit, easy control, and low cost. Etc.

In order to achieve the above object, the present invention provides a power-on and braking circuit of a variable frequency transmission system, including a rectifier circuit, a power-on braking circuit and a transmission system. The input end of the power-on braking circuit is connected to the output end of the rectification circuit, and the output end of the power-on braking circuit is connected to the input end of the transmission system.

The rectifier circuit includes an input filter inductor and a rectifier bridge, wherein one end of the input filter inductor is connected to the live line of the single-phase AC power supply; the input end of the rectifier bridge is respectively connected to the other end of the input filter inductor and the neutral line of the single-phase AC power supply.

The power-on braking circuit includes six resistors, five AC capacitors, an electrolytic capacitor, two relays, a transistor, and a Zener diode, wherein: the first relay includes a set of first primary coils and a second A normally open contact, the second relay includes a set of second primary coils, second normally open and first normally closed secondary contacts. After the first normally open contact, the first AC capacitor and the first resistor are connected in parallel, one common terminal is connected to the output positive pole of the rectifier circuit, and the other common terminal is connected in parallel with the first normally closed secondary contact and the second AC capacitor The other common end after the first normally closed secondary contact is connected in parallel with the second AC capacitor is connected to the positive pole of the electrolytic capacitor, one end of the second resistor, one end of the third resistor, one end of the fourth resistor, and the sixth One end of the resistor is connected to form the first output end; the negative pole of the electrolytic capacitor, the other end of the second resistor, one end of the second normally open contact, one end of the fifth resistor, the anode of the Zener diode, one end of the third AC capacitor, and the emitter of the transistor It is connected to the output negative pole of the rectifier circuit and forms the second output terminal; the other end of the third resistor is connected to the other end of the second normally open contact; after the other end of the fifth resistor, the cathode of the Zener diode, and the other end of the third AC capacitor are connected It is connected with the base of the transistor and the other end of the fourth resistor; the other end of the sixth resistor is connected with one end of the fourth AC capacitor, one end of the first primary coil and the cathode of the first diode, and the other end of the fourth AC capacitor and the first primary coil The other end is connected to the anode of the first diode and then connected to one end of the fifth AC capacitor, one end of the second primary coil and the cathode of the second diode, and the other end of the fifth AC capacitor, the other end of the second primary coil and the second diode The anode of the tube is connected to the collector of the transistor.

The drive system includes a voltage source inverter and a motor drive system.

In the present invention, the main innovation point is the power-on braking circuit, which includes a soft power-on circuit (mainly composed of the first normally open contact, the first AC capacitor, the second AC capacitor, the electrolytic capacitor, the first normally closed contact , the second resistor), which can realize the RC composed of the first resistor and the electrolytic capacitor to be powered on in series, so that the electrolytic capacitor rises slowly, the first resistor is the power-on resistor; Normally open contact, fourth resistor, fifth resistor, Zener diode, third AC capacitor, transistor, sixth resistor, fourth AC capacitor, first primary coil, first diode), can realize power-on voltage When approaching the peak value of the single-phase AC power supply, the first normally open contact is used to short-circuit the first resistor. The brake circuit it contains (mainly composed of the first normally closed secondary contact, the second AC capacitor, transistor, the sixth resistor, the fifth AC capacitor, the second primary coil, the second diode, the second normally open contact head, the third resistor), it can be realized that when the DC voltage exceeds the specified value, the third resistor is connected by the second normally open contact, so that the electrolytic capacitor drops below the specified value. The rectification circuit can be a controllable or non-controllable rectification circuit, and the transmission system generally refers to the motor-mechanical load system.

Compared with the prior art, the present invention has the following beneficial effects: the present invention can realize soft power-on of the rectifier and rapid braking of the motor, has a small power-on current impact, has a reliable braking function, and has a simple circuit structure without human control. The utility model has good safety, strong versatility and low cost, and is suitable for frequency conversion and speed regulation systems powered by AC power.

Description of drawings

Other characteristics, objects and advantages of the present invention will become more apparent by reading the detailed description of non-limiting embodiments made with reference to the following drawings:

Fig. 1 is a schematic diagram of the power-on and braking circuit of the frequency conversion drive system of the present invention.

detailed description

The present invention will be described in detail below in conjunction with specific embodiments. The following examples will help those skilled in the art to further understand the present invention, but do not limit the present invention in any form. It should be noted that those skilled in the art can make several modifications and improvements without departing from the concept of the present invention. These all belong to the protection scope of the present invention.

As shown in FIG. 1 , a power-on and braking circuit of a variable frequency transmission system includes a power-on braking circuit 1 , a rectifier circuit 2 and a transmission system 3 . Wherein, the power-on braking circuit is combined with a soft power-on circuit and a braking circuit, and its two input terminals are respectively connected to the two output positive poles and negative poles of the rectifier circuit 2, and its two output terminals are respectively connected to the two output terminals of the transmission system 3. Only the input positive pole is connected to the negative pole, and the two input ends of the rectifier circuit 2 are respectively connected to the live line and the neutral line of the single-phase AC power supply.

The specific circuit structure is described in detail below.

The rectifier circuit includes an input filter inductor and a rectifier bridge, wherein one end of the input filter inductor is connected to the live line of the single-phase AC power supply; the input end of the rectifier bridge is respectively connected to the other end of the input filter inductor and the neutral line of the single-phase AC power supply.

The power-on braking circuit includes six resistors, five AC capacitors, one electrolytic capacitor E1, two relays, one transistor TR1, and one Zener diode ZD1, wherein: the first relay includes a set of first primary Coil W1 and first normally open contact K1, the second relay includes a set of second primary coil W2, second normally open contact K21 and first normally closed secondary contact K22. After the first normally open contact K1, the first AC capacitor C1 and the first resistor R1 are connected in parallel, one common end thereof is connected to the output positive pole of the rectifier circuit 2, and the other common end thereof is connected to the first normally closed secondary contact K22 and the first normally closed secondary contact K22. One common end of the parallel connection of the second AC capacitor C2 is connected, and the other common end of the parallel connection of the first normally closed secondary contact K22 and the second AC capacitor C2 is connected to the positive electrode of the electrolytic capacitor E1, one end of the second resistor R2, and the third One end of the resistor R3, one end of the fourth resistor R4, and one end of the sixth resistor R6 are connected to form the first output end; the negative pole of the electrolytic capacitor E1, the other end of the second resistor R2, one end of the second normally open contact K21, and the fifth resistor R5 One end, the anode of the Zener diode ZD1, one end of the third AC capacitor C3, and the emitter of the transistor TR1 are connected to the output cathode of the rectifier circuit 2 to form a second output end; the other end of the third resistor R3 is connected to the second normally open contact K21 The other end is connected; the other end of the fifth resistor R5, the cathode of the Zener diode ZD1, and the other end of the third AC capacitor C3 are connected to the base of the transistor TR1 and the other end of the fourth resistor R4; the other end of the sixth resistor R6 is connected to the fourth One end of the AC capacitor C4, one end of the first primary coil is connected to the cathode of the first diode D1, the other end of the fourth AC capacitor C4, the other end of the first primary coil is connected to the anode of the first diode D1, and then connected to the fifth AC capacitor C5 One end, one end of the second primary coil W2 is connected to the cathode of the second diode D2, the other end of the fifth AC capacitor C5, the other end of the second primary coil W2 is connected to the anode of the second diode D2, and then connected to the collector of the transistor TR1 .

The transmission system 3 includes a voltage source inverter and a motor transmission system connected thereto.

Specifically, in this embodiment, the parameters of each device used are as follows:

Considering the standard single-phase AC voltage 220V power supply, when the DC circuit voltage is 300V, the first normally open secondary contact K1 acts to attract the first normally open contact K1. When the DC circuit voltage is 350V, the second relay acts to close the second normally open contact K21 and disconnect the first normally closed secondary contact K22.

Relay W1/K1: primary action current 3.0mA;

Relay W2/K21/K22: primary action current 3.5mA;

AC capacitors C1, C2, C4, C5: 0.1μF, 1.2kV;

AC capacitor C3: 0.1μF, 50V;

Electrolytic capacitor E1: 4x680μF, with a withstand voltage of 400V.

Power resistor R1: 50Ω, 50W;

Power resistor R2: 100kΩ, 2W;

Power resistor R3: 5kΩ, 50W;

Diode D1, D2: 1N4148;

Zener diode ZD1: voltage regulator 5.1V;

Resistor R4: 360kΩ+20kΩ;

Resistor R5: 5.1kΩ; when the DC voltage is 300V, the divided voltage is close to 3.9V. When the DC voltage is 385V, the divided voltage is about 5.0V;

Resistor R6: 100kΩ/2W.

This embodiment works through the following steps:

Consider the standard single-phase AC voltage 220V power supply situation. When the single-phase AC voltage is non-standard power supply, the following parameters need to be adjusted appropriately, but the changes are small, and only the values of the action current and release current of the first and second relays need to be changed. In the power-on braking circuit of this embodiment:

Soft power-on circuit: composed of the first normally open contact, the first AC capacitor C1, the second AC capacitor C2, the electrolytic capacitor E1, the first normally closed contact, and the second resistor R2, which can realize the combination of the first resistor R1 and the second resistor R2. The RC composed of electrolytic capacitor E1 is powered on in series, so that the electrolytic capacitor E1 rises slowly, and the first resistor R1 is the power-on resistor; no matter the single-phase AC voltage is powered on at any phase angle, the electrolytic capacitor E1 is charged through the power resistor R1, and the electrolytic capacitor The voltage at the E1 terminal rises from zero volts according to the command law;

Cutting off the circuit after power-on: the first normally open contact K1, the fourth resistor R4, the fifth resistor R5, the Zener diode ZD1, the third AC capacitor C3, the transistor TR1, the sixth resistor R6, and the fourth AC capacitor C4 , the first primary coil, and the first diode D1, which can realize that when the power-on voltage is close to the peak value of the single-phase AC power supply, the first normally open contact K1 short-circuits the first resistor R1; when the voltage at the terminal of the electrolytic capacitor E1 rises to 300V When left or right, resistors R4 and R5 divide the voltage to obtain a voltage of 3.9V, which does not exceed the operating value of the Zener diode ZD1. After being filtered by the AC capacitor C3, it is applied to the base of the transistor TR1TR1, and the transistor TR1TR1 is turned on, so that the coil W1 generates about 3.0mA The primary current pulls in the first normally open contact K1, shorts the regular resistor R1, cancels the soft power-on process, enters the weak hard power-on process, and charges the DC circuit voltage to the peak value of the single-phase AC voltage of 310V;

Braking circuit: composed of the first normally closed secondary contact K22, the second AC capacitor C2, the transistor TR1, the sixth resistor R6, the fifth AC capacitor C5, the second primary coil W2, the second diode D2, the second The normally open contact K21 and the third resistor R3 can realize that when the DC voltage exceeds the specified value, the second normally open contact K21 connects the third resistor R3, so that the electrolytic capacitor E1 drops below the specified value; when the transmission system decelerates , When braking or flipping over, the voltage at the E1 terminal of the electrolytic capacitor rises. If it exceeds about 350V, the second relay operates, the second normally open contact K21 is connected, the power resistor R3 consumes the energy stored in the electrolytic capacitor E1, and the electrolytic capacitor E1 drops , and at the same time the first normally closed contact is disconnected to prevent the rectifier circuit from replenishing energy. When the voltage of the electrolytic capacitor E1 is lower than a certain value, the second relay is reset, the second normally open contact K21 is disconnected, the first normally closed contact is connected, and the circuit enters a normal state;

The first and second relays themselves have hysteresis characteristics. Their action voltages are 300V and 350V respectively, but the release voltage is lower than a value of 300V and 350V. The optional release voltages are 250V and 300V respectively, that is, the release current is 2.5mA. and 3.0mA. For the second relay, you can choose a lower release current, which can realize fast braking, that is, when the braking voltage is lower than 300V, the braking process will be accelerated.

The role of AC capacitors C1-C2 is to suppress the sparks caused by the contacts, the role of AC capacitors C3-C5 is to filter, the role of diodes D1-D2 is to continue the coil, and the role of resistor R2 is to release the electrolytic capacitor E1 after power off energy of. The function of the resistors R4 and R5 is to divide the voltage.

In this embodiment, the rectification circuit may be a controllable or non-controllable rectification circuit, and the transmission system may be a frequency conversion speed regulation system. Of course, in other embodiments, other motor-mechanical load systems may also be used.

The invention realizes the on-off of the current-limiting resistance and the on-off of the energy-consumption braking resistance by adopting the relay, so that the frequency conversion transmission system realizes the functions of safe power-on and fast braking. Strong, low cost and other advantages.

Specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art may make various changes or modifications within the scope of the claims, which do not affect the essence of the present invention.

Claims (6)

1. A power-on and braking circuit for a variable frequency transmission system, characterized in that it includes a rectifier circuit, a power-on braking circuit and a transmission system, the input end of the power-on braking circuit is connected to the output end of the rectifier circuit, and the power-on braking circuit The output of the circuit is connected to the input of the transmission system, where: The power-on braking circuit includes six resistors, five AC capacitors, an electrolytic capacitor, two relays, a transistor, and a Zener diode, wherein: the first relay includes a set of first primary coils and a second One normally open contact, the second relay includes a group of second primary coils, second normally open and first normally closed secondary contacts, after the first normally open contact, the first AC capacitor and the first resistor are connected in parallel, the One common terminal is connected to the output positive pole of the rectifier circuit, and the other common terminal is connected to a common terminal after the first normally closed secondary contact and the second AC capacitor are connected in parallel, the first normally closed secondary contact and the second AC capacitor The other common end of the capacitor connected in parallel is connected to the positive pole of the electrolytic capacitor, one end of the second resistor, one end of the third resistor, one end of the fourth resistor, and one end of the sixth resistor to form the first output end; the negative pole of the electrolytic capacitor, the second resistor The other end, one end of the second normally open contact, one end of the fifth resistor, the anode of the Zener diode, one end of the third AC capacitor, and the emitter of the transistor are connected to the output negative pole of the rectifier circuit to form the second output end; the third resistor is another One end is connected to the other end of the second normally open contact; the other end of the fifth resistor, the cathode of the Zener diode, and the other end of the third AC capacitor are connected to the base of the transistor and the other end of the fourth resistor; the other end of the sixth resistor is connected to One end of the fourth AC capacitor and one end of the first primary coil are connected to the cathode of the first diode, and the other end of the fourth AC capacitor and the other end of the first primary coil are connected to the anode of the first diode and then connected to one end of the fifth AC capacitor and the first end of the first diode. One end of the second primary coil is connected to the cathode of the second diode, and the other end of the fifth AC capacitor and the other end of the second primary coil are connected to the anode of the second diode and then connected to the collector of the transistor. 2. The power-on and braking circuit of the variable frequency transmission system according to claim 1, characterized in that: the first normally open contact, the first AC capacitor, the second AC capacitor, the electrolytic capacitor, the first normally closed The contact and the second resistor form a soft power-on circuit. The soft power-on circuit realizes the power-on of the RC series composed of the first resistor and the electrolytic capacitor, so that the electrolytic capacitor rises slowly. The first resistor is the power-on resistor; regardless of single-phase AC When the voltage is powered on at any phase angle, the electrolytic capacitor is charged through the power resistor, and the terminal voltage of the electrolytic capacitor rises exponentially from zero volts. 3. The power-on and braking circuit of the variable frequency transmission system according to claim 1, characterized in that: the first normally open contact, the fourth resistor, the fifth resistor, the Zener diode, the third AC capacitor, The transistor, the sixth resistor, the fourth AC capacitor, the first primary coil, and the first diode constitute a cut-off circuit after power-on, and the circuit realizes that when the power-on voltage is close to the peak value of the single-phase AC power supply, the first normally open contact short-circuits Connect the first resistor. 4. The power-on and braking circuit of the variable frequency transmission system according to claim 1, characterized in that: the first normally closed secondary contact, the second AC capacitor, the transistor, the sixth resistor, and the fifth AC capacitor , the second primary coil, the second diode, the second normally open contact, and the third resistor form a brake circuit, which realizes that when the DC voltage exceeds a specified value, the second normally open contact connects the third resistor, Make the electrolytic capacitor drop below the specified value; when the transmission system decelerates, brakes or reverses, the voltage at the electrolytic capacitor terminal rises. If it exceeds the set value, the second relay acts, the second normally open contact is connected, and the third The resistance consumes the energy stored in the electrolytic capacitor, the terminal voltage of the electrolytic capacitor drops, and at the same time the first normally closed contact is disconnected to prevent the rectifier circuit from replenishing energy; when the voltage of the electrolytic capacitor is lower than a certain value, the second relay resets and the second normally open contact disconnected, the first normally closed contact is connected, and the circuit enters a normal state. 5. The power-on and braking circuit of the variable frequency transmission system according to any one of claims 1-4, characterized in that: the rectifier circuit includes an input filter inductor and a rectifier bridge, wherein one end of the input filter inductor is connected to a single-phase AC The live wire of the power supply is connected; the input end of the rectifier bridge is respectively connected with the other end of the input filter inductor and the neutral wire of the single-phase AC power supply. 6. The power-on and braking circuit of the variable frequency drive system according to any one of claims 1-4, characterized in that the drive system includes a voltage source inverter and a motor drive system connected thereto.