Cascaded high-voltage frequency conversion system load braking system and braking method

Abstract

The invention discloses a cascade type high-voltage frequency conversion system load braking system and a braking method. The cascade type high-voltage frequency conversion system load braking system comprises a braking control panel, a braking resistor interface of the braking control panel is connected with a braking resistor, positive and negative busbar interfaces of a terminal of the braking control panel are connected with a direct-current bus of a frequency converter power module, and a power input interface of the braking control panel is connected with a 15V power supply. According to the braking circuit, the problem of control lag caused by a strategy of sacrificing speed response in order to restrain bus rising in an existing method is solved.

Description

Technical Field

[0001] The present invention belongs to the technical field of drilling rig electric drive, and particularly relates to a load braking system for a cascaded high-voltage frequency conversion system, and also relates to a braking method for the load braking system of the cascaded high-voltage frequency conversion system. Background Art

[0002] During the upgrading process of chain drive type oil drilling rigs, there is a mode of replacing diesel engine drive with a high-voltage frequency conversion drive system, which not only achieves energy-saving effects, but also realizes noise reduction and reduces carbon emission indicators.

[0003] During the deceleration operation of the potential energy load frequency conversion speed regulation system in the hoisting and lowering operation conditions, due to the influence of load inertia, the actual reduction rate of the motor speed may be lower than the reduction rate of the output frequency. At this time, the motor will feedback electric energy to the frequency conversion speed regulation system, causing the bus voltage of the frequency conversion speed regulation system to rise. If no measures are taken, it will cause the bus voltage to rise and cause overvoltage faults in the frequency conversion speed regulation system and shut down.

[0004] Common treatment methods include the following measures: 1. Activate Vdc control to reduce the braking torque so that the DC bus voltage is maintained within the allowable range. When activating Vdc control, the drive automatically extends the ramp-down time; 2. A voltage stabilization strategy that delays the speed control effect. The essence of both measures is a voltage stabilization strategy that sacrifices the speed control effect: that is, in order to suppress voltage rise, the time of speed drop is adaptively limited to avoid continuous voltage rise caused by too fast speed drop. Summary of the Invention

[0005] The purpose of the present invention is to provide a load braking system for a cascaded high-voltage frequency conversion system, which solves the problem of control lag caused by the strategy of sacrificing speed response in the existing method to suppress bus rise.

[0006] Another purpose of the present invention is to provide a braking method for the load braking system of the cascaded high-voltage frequency conversion system.

[0007] The technical solution adopted by the present invention is that a load braking system for a cascaded high-voltage frequency conversion system includes a braking control board. The braking resistor interface of the braking control board is connected to a braking resistor, the positive and negative busbar interfaces of the terminals of the braking control board are connected to the DC bus of the inverter power module, and the power input interface of the braking control board is connected to a 15V power supply.

[0008] The characteristics of the present invention also lie in

[0009] The braking control board includes a control board body. An operational amplifier is arranged on the control board body. The inverting input terminals of the operational amplifier are respectively connected to one ends of a resistor R7 and a resistor R9. The other end of the resistor R7 is connected to a 15V power supply. The other end of the resistor R9 is connected to one end of a resistor R10, and the other end of the resistor R10 is grounded. The non-inverting input terminals of the operational amplifier are respectively connected to one ends of a resistor R4 and a resistor R5. The other end of the resistor R4 is successively connected in series with a resistor R8, a resistor R2, and a resistor R1. The other end of the resistor R5 is connected to one end of a resistor R6. The output terminal of the operational amplifier is connected to one end of a resistor R11. The other end of the resistor R11 is respectively connected to one end of a resistor R12 and the base of a triode. The other end of the resistor R12 is grounded. The collector of the triode is connected to one end of a resistor R13, and the other end of the resistor R13 is connected to a 15V power supply. The emitter of the triode is connected to the anode of a diode D2. The cathode of the diode D2 is respectively connected to one end of a resistor R15 and the gate of a field effect power transistor Q2. The other end of the resistor R15 is grounded. The drain of the field effect power transistor Q2 is successively connected to a resistor R14 and the anode of a diode D1. The cathode of the diode D1 is respectively connected to one end of a braking resistor and the resistor R1. After the cathode of the diode D1 is connected to the resistor R1, it is connected to the positive DC bus bar of the inverter power module. The other end of the braking resistor is connected to the end of the resistor R14 far from the diode D1. The source of the field effect power transistor Q2 is respectively connected to one end of a resistor R17 and the other end of the resistor R6. The other end of the resistor R17 is connected to one end of a resistor R16, and the other end of the resistor R16 is connected to the drain of the field effect power transistor Q2. After the source of the field effect power transistor Q2 is connected to the resistor R16, it is connected to the negative DC bus bar of the inverter power module.

[0010] The braking resistor includes resistors R18, R19, R20, and R21 connected in parallel. One end of the resistor 18 is connected to the cathode of the diode D1, and the other end of the resistor 18 is connected to the end of the resistor R14 far from the diode D1.

[0011] The control board body is arranged on the outer wall of the power module housing of the inverter and is arranged in the air duct on the back of the power cabinet. The braking resistors are arranged side by side on the control board body. A field effect power transistor Q2 is arranged below the braking resistors on the control board body. A hot air diversion radiator is arranged on the back of the control board body corresponding to the braking resistors. There are inlet and outlet holes on the power module housing, and the braking control board is connected to the power module through the inlet and outlet holes.

[0012] The field effect power transistor Q2 uses NMOS.

[0013] Another technical solution adopted by the present invention is a braking method for the load braking system of a cascaded high-voltage frequency conversion system. The above-mentioned cascaded high-voltage frequency conversion system load braking system is adopted, and the specific process is as follows: When the voltage of the P+ DC bus is 1050V, the resistance R5 is 5V voltage, and the voltage sampling circuit is input to the non-inverting input terminal of the operational amplifier via R5. The 5V sampling voltage is input to the inverting input terminal of the operational amplifier via R9. The supply voltage of the operational amplifier is +15V. When it is detected that the voltage at the non-inverting input terminal of the operational amplifier is higher than 5V, the voltage at the output terminal of the operational amplifier follows the output and is input to the base of the triode Q1 via the current-limiting resistor R11. +15V is input to the collector of the triode Q1 via the current-limiting resistor R13. After the output terminal of the operational amplifier outputs and triggers the gate of the triode Q1 to turn on, the emitter of the triode outputs to the field-effect power tube Q2 via the diode D2. When the collector of the triode Q1 is turned on and the emitter outputs, after the gate of the field-effect power tube Q2 obtains a voltage of 13.5V, it turns on the external braking resistor to absorb the energy of the voltage higher than 1050V on the P+ bus. When the voltage of the P+ bus is lower than 1050V and at the same time the voltage at the non-inverting input terminal of the operational amplifier is lower than 5V, the field-effect power tube Q2 is turned off and the braking resistor stops absorbing energy. At the moment when the field-effect power tube Q2 is turned off, in order to prevent the leakage inductance of the braking resistor from causing a relatively high drain voltage of the field-effect power tube Q2, the method of dividing the voltage by the resistors R16 and R17 is adopted to pull down the drain voltage of the field-effect power tube Q2. If the drain voltage of the field-effect power tube is still higher than the voltage of the P+ bus, it is released to the bus via the resistor R14 and the diode D1 to protect the field-effect tube Q2. The functions of R12 and R15 are to release the interference voltage at the base of the triode.

[0014] The beneficial effects of the present invention are as follows: The load braking system of the cascaded high-voltage frequency conversion system of the present invention directly uses 10kV as the system power supply, eliminates the large-power transformer device required by the conventional low-voltage frequency conversion system, and does not require a compensation device. And when the bus voltage reaches the requirement for starting braking of the system, the power module outputs a signal to trigger the gate of the MOSFET, and the positive and negative busbars of the DC bus are connected to the braking resistor through the MOSFET switch. The energy fed back to the DC bus is absorbed in the form of intermittent heating of the resistor, which not only achieves a fast response for speed control, but also can reduce the bus voltage to an acceptable range. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 The circuit diagram of adding the load braking circuit of the present invention to the power module;

[0016] Figure 2 The circuit diagram of the braking control board in the present invention;

[0017] Figure 3 The schematic diagram of the main circuit topology structure of the 10kV cascaded high-voltage high-power frequency converter;

[0018] Figure 4 is the schematic diagram of the power module of the frequency converter;

[0019] Figure 5 is the installation schematic diagram of the load braking circuit of the present invention.

[0020] In the figure, 1. control board body, 2. braking resistor, 3. hot air diversion radiator, 4. power module housing, 5. inlet and outlet holes, 6. field effect power transistor Q2. Specific implementation manner

[0021] The present invention will be described in detail below in conjunction with the accompanying drawings and specific implementation manners.

[0022] Embodiment 1

[0023] The load braking system of the cascaded high-voltage frequency conversion system of the present invention, as Figure 1 shown, includes a braking control board. The braking resistor interface of the braking control board is connected to the braking resistor, the positive and negative busbar interfaces of the terminals of the braking control board are connected to the DC bus of the frequency converter power module, and the power input interface of the braking control board is connected to a 15V power supply.

[0024] The braking circuit of the present invention is applicable to cascaded high-voltage high-power frequency converters. Cascaded high-voltage high-power frequency converters are a type of frequency converter that is widely used in various industries. They achieve high-voltage output by directly cascading the output ends of several low-voltage power units. As Figure 3 shown, it is the schematic diagram of the main circuit topology of an 8-unit series high-voltage frequency converter. The 10kV power supply is input to a 48-pulse phase-shifted rectifier transformer, and the phase-shifted rectifier transformer is connected to each power module of the H-type structure (8 in series per phase, a total of 24). The output voltage of each power unit is superimposed in series to form the output voltage of the multilevel converter; as Figure 4 shown, each power module is an uncontrolled rectifier bridge + single-phase H-bridge structure.

[0025] As Figure 2As shown in the figure, the braking control board includes a control board body 1. An operational amplifier IM358 is provided on the control board body 1. The inverting input terminal of the operational amplifier IM358 is respectively connected to one end of a resistor R7 and a resistor R9. The other end of the resistor R7 is connected to a 15V power supply. The other end of the resistor R9 is connected to one end of a resistor R10. The other end of the resistor R10 is grounded. The non-inverting input terminal of the operational amplifier IM358 is respectively connected to one end of a resistor R4 and a resistor R5. The other end of the resistor R4 is successively connected in series with a resistor R8, a resistor R2, and a resistor R1. The other end of the resistor R5 is connected to one end of a resistor R6. The output terminal of the operational amplifier IM358 is connected to one end of a resistor R11. The other end of the resistor R11 is respectively connected to one end of a resistor R12 and the base of a triode. The other end of the resistor R12 is grounded. The collector of the triode is connected to one end of a resistor R13. The other end of the resistor R13 is connected to a 15V power supply. The emitter of the triode is connected to the anode of a diode D2. The cathode of the diode D2 is respectively connected to one end of a resistor R15 and the gate of a field effect power transistor Q2. The field effect power transistor Q2 is an NMOS, and the specific model is 2SK1317. The other end of the resistor R15 is grounded. The drain of the field effect power transistor Q2 is successively connected to a resistor R14 and the anode of a diode D1. The cathode of the diode D1 is respectively connected to one end of a braking resistor and the resistor R1. After the cathode of the diode D1 is connected to the resistor R1, it is connected to the positive DC bus bar of the frequency converter power module. The other end of the braking resistor is connected to the end of the resistor R14 far from the diode D1. The source of the field effect power transistor Q2 is respectively connected to one end of a resistor R17 and the other end of the resistor R6. The other end of the resistor R17 is connected to one end of a resistor R16. The other end of the resistor R16 is connected to the drain of the field effect power transistor Q2. After the source of the field effect power transistor Q2 is connected to the resistor R16, it is connected to the negative DC bus bar of the frequency converter power module.

[0026] Among them, the resistors R1, R2, R8, R4, R5, and R6 constitute a voltage sampling circuit. The resistors R7, R9, and R10 constitute a voltage sampling circuit. The resistors R16 and R17 constitute a protection circuit.

[0027] The braking resistor includes resistors R18, R19, R20, and R21 connected in parallel. One end of the resistor 18 is connected to the cathode of the diode D1, and the other end of the resistor 18 is connected to the end of the resistor R14 far from the diode D1.

[0028] The models of the diodes D1 and D2 are EM520, and the triode is an NPN type with the model 2SC2073.

[0029] Embodiment 2

[0030] On the basis of Embodiment 1, as Figure 5As shown in the figure, the control board 1 is arranged on the outer wall of the power module housing 4 of the frequency converter and is located in the air duct at the back of the power cabinet. The braking resistors 2 (resistors R18, R19, R20, R21) are arranged in parallel on the control board 1. A field-effect power transistor Q26 is arranged on the control board 1 below the braking resistors 2. A hot air diversion radiator 3 is arranged on the back of the control board 1 corresponding to the braking resistors 2. An inlet and outlet hole 5 is arranged on the power module housing 4. The braking control board is connected to the power module through the inlet and outlet hole 5. The heat generated by the resistors R18, R19, R20, and R21 is extracted by the axial flow fan at the top of the power cabinet.

[0031] Taking the potential winch load of an oil drilling rig as an example for calculation, the parameters of each device in the braking control board are as follows:

[0032] (1) Calculation of the braking group parameters generated by the execution of deceleration:

[0033]

[0034] According to the moment of inertia of the mechanical load, calculate the kinetic energy of the load: where, J is the moment of inertia of the load (Kmg2); ω is the angular velocity (radian value / second);

[0035]

[0036] Substitute Equivalent to the gravity borne on the drum:

[0037] G m = mg (3)

[0038] The equivalent load torque converted to the motor shaft is:

[0039]

[0040] where R is the radius of the drum wound with the wire rope and j is the total transmission ratio.

[0041] The torque lost in the mechanism when lifting the heavy object is:

[0042]

[0043] The torque when lowering the heavy object:

[0044]

[0045] The load drives the motor, so this part of the energy is transferred to the motor side. Also, since the motor is an inductive load and the current cannot change suddenly, the energy fed back by the motor to the bus will cause the DC bus voltage to rise. Then, to prevent the DC bus voltage of a single power module from rising beyond the permitted range, the deceleration time, the fastest deceleration time, must be determined.

[0046]

[0047] Among them, n is the set speed of the frequency converter, and M b is the rated power of the motor. The deceleration time we determined is t = 1.5tb.

[0048] When the deceleration time is t, the required braking torque:

[0049]

[0050] Braking power:

[0051]

[0052] Braking resistor:

[0053]

[0054] Set the braking resistor turn-on voltage to 1050V. After system calculation, P B is 288kW. This system has two 1000kW 10000V frequency converters, and each has 24 H-structured cascaded frequency conversion modules. According to the 1 / 4 intermittent braking duty system, the continuous power of the resistors R18, R19, R20, and R21 installed on each braking control board is 3kW, and the resistance is 320Ω. Then each resistor is 800W, 1.3K. Select the rated current of the field effect power transistor Q2 to be 10A, and the diode D2 to be 10A.

[0055] Embodiment 3

[0056] The braking method of the load braking system of the cascade high-voltage frequency conversion system of the present invention adopts the above-mentioned load braking system of the cascade high-voltage frequency conversion system. The specific process is as follows: When the voltage of the P+ DC bus is 1050V, the voltage of the resistor R5 is 5V. The voltage sampling circuit is input to the non-inverting input terminal 3 of the operational amplifier via R5, and the 5V sampling voltage is input to the inverting input terminal 2 of the operational amplifier via R9. The supply voltage of the operational amplifier is +15V. When it is detected that the voltage of the non-inverting input terminal 3 of the operational amplifier is higher than 5V (that is, the P+ voltage is higher than 1050V), the voltage of the output terminal 1 of the operational amplifier follows and outputs, and is input to the base of the triode Q1 via the current-limiting resistor R11; +15V is input to the collector of the triode Q1 via the current-limiting resistor R13. After the output terminal 1 of the operational amplifier outputs to trigger the gate of the triode Q1 to turn on, the emitter of the triode outputs via the diode D2 to the field-effect power transistor Q2. After the collector of the triode Q1 is turned on and the emitter outputs, after the gate of the field-effect power transistor Q2 obtains a voltage of 13.5V, it turns on the external braking resistor to work and absorbs the energy of the voltage higher than 1050V on the P+ bus; when the voltage of the P+ bus is lower than 1050V and at the same time the voltage of the non-inverting input terminal 3 of the operational amplifier is lower than 5V, the field-effect power transistor Q2 turns off and the braking resistor stops absorbing energy; at the moment when the field-effect power transistor Q2 turns off, in order to prevent the leakage inductance of the braking resistor from causing a relatively high drain voltage of the field-effect power transistor Q2, the method of dividing the voltage by the resistor R16 and the resistor R17 is adopted to pull down the drain voltage of the field-effect power transistor Q2. If the drain voltage of the field-effect power transistor is still higher than the voltage of the P+ bus, it is released to the bus via the resistor R14 and the diode D1 to protect the field-effect transistor Q2. The functions of R12 and R15 are to release the interference voltage of the base of the triode.

Claims

1. Load braking system for cascaded high-voltage frequency conversion system, characterized in that, It includes a brake control board, a brake resistor interface of the brake control board is connected to a brake resistor, a positive and negative busbar interface of a terminal of the brake control board is connected to a DC busbar of a frequency converter power module, and a power input interface of the brake control board is connected to a 15V power supply.

2. The load braking system for cascaded high-voltage frequency conversion system according to claim 1, characterized in that, The brake control board comprises a control board body (1), on which an operational amplifier is arranged, wherein the reverse input end of the operational amplifier is respectively connected to one end of a resistor R7 and a resistor R9, the other end of the resistor R7 is connected to a 15V power supply, the other end of the resistor R9 is connected to one end of a resistor R10, the other end of the resistor R10 is signal-grounded, the positive input end of the operational amplifier is respectively connected to one end of a resistor R4 and a resistor R5, the other end of the resistor R4 is connected in series with a resistor R8, a resistor R2, and a resistor R1 in sequence, the other end of the resistor R5 is connected to one end of a resistor R6, the output end of the operational amplifier is connected to one end of a resistor R11, the other end of the resistor R11 is respectively connected to one end of a resistor R12 and a base of a triode, the other end of the resistor R12 is signal-grounded, the collector of the triode is connected to one end of a resistor R13, the other end of the resistor R13 is connected to a 15V power supply, The emitter of the triode is connected to the anode of the diode D2, the cathode of the diode D2 is respectively connected to one end of the resistor R15 and the gate of the field effect power tube Q2, the other end of the resistor R15 is signal-grounded, the drain of the field effect power tube Q2 is sequentially connected to the resistor R14 and the anode of the diode D1, the cathode of the diode D1 is respectively connected to one end of the braking resistor and the resistor R1, the cathode of the diode D1 is connected to the resistor R1 and then connected to the positive DC busbar of the inverter power module, the other end of the braking resistor is connected to the end of the resistor R14 away from the diode D1, the source of the field effect power tube Q2 is respectively connected to one end of the resistor R17 and the other end of the resistor R6, the other end of the resistor R17 is connected to one end of the resistor R16, the other end of the resistor R16 is connected to the drain of the field effect power tube Q2, and the source of the field effect power tube Q2 is connected to the resistor R16 and then connected to the negative DC busbar of the inverter power module.

3. The load braking system for cascaded high-voltage frequency conversion system according to claim 2, characterized in that, The brake resistor includes resistors R18, R19, R20 and R21 which are arranged in parallel. One end of the resistor 18 is connected to the cathode of the diode D1, and the other end of the resistor 18 is connected to an end of the resistor R14 away from the diode D1.

4. The load braking system for cascaded high-voltage frequency conversion system according to claim 3, characterized in that, The control board body (1) is arranged on the outer wall of the power module housing (4) of the frequency converter and the control board body (1) is arranged in the air duct at the back of the power cabinet; the brake resistor (2) is arranged in parallel on the control board body (1); a field effect power tube Q2 (6) is arranged on the control board body (1) and below the brake resistor (2); a hot air deflection radiator (3) is arranged at the back of the control board body (1) and at a position corresponding to the brake resistor (2); an inlet and outlet hole (5) is arranged on the power module housing (4); and the brake control board is connected to the power module through the inlet and outlet hole (5).

5. The load braking system for cascaded high-voltage frequency conversion system according to claim 2, characterized in that, The field effect power transistor Q2 uses an NMOS.

6. The braking method for the load braking system of the cascaded high-voltage frequency conversion system according to any one of claims 2 to 5, characterized in that, The specific process is as follows: When the P+ DC bus voltage is 1050V, the resistor R5 has a voltage of 5V. The voltage sampling circuit is input to the non-inverting input terminal of the operational amplifier via R5, and the 5V sampling voltage is input to the inverting input terminal of the operational amplifier via R9. The supply voltage of the operational amplifier is +15V. When it is detected that the voltage at the non-inverting input terminal of the operational amplifier is higher than 5V, the voltage at the output terminal of the operational amplifier follows the output and is input to the base of the triode Q1 via the current-limiting resistor R11. +15V is input to the collector of the triode Q1 via the current-limiting resistor R13. After the output terminal of the operational amplifier outputs to trigger the gate of the triode Q1 to turn on, the emitter of the triode outputs via the diode D2 to the field effect power transistor Q2. When the collector of the triode Q1 is turned on and the emitter outputs, after the gate of the field effect power transistor Q2 obtains a voltage of 13.5V, it turns on the external braking resistor to work and absorb the energy of the voltage higher than 1050V on the P+ bus. When the P+ bus voltage is lower than 1050V and at the same time the voltage at the non-inverting input terminal of the operational amplifier is lower than 5V, the field effect power transistor Q2 turns off and the braking resistor stops absorbing energy. At the moment when the field effect power transistor Q2 turns off, in order to prevent the leakage inductance of the braking resistor from causing a relatively high drain voltage of the field effect power transistor Q2, the method of dividing the voltage by the resistor R16 and the resistor R17 is used to pull down the drain voltage of the field effect power transistor Q2. If the drain voltage of the field effect power transistor is still higher than the voltage of the P+ bus, it is released to the bus via the resistor R14 and the diode D1 to protect the field effect transistor Q2. The functions of R12 and R15 are to release the interference voltage at the base of the triode.

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