DC speed regulator maintenance: D DC speed regulator is a thyristor converter DC transmission system given by the product manufacturer of the group company. It is also widely used in the field of DC speed regulation in my country, almost as much as the European DC speed regulator. The whole circuit of the highly intelligent DC speed regulation device using a microcontroller (three-phase all-air bridge, excitation output circuit) consists of three The circuit boards are composed of main board power supply/driver board and excitation trigger board. The power supply/drive board and the excitation trigger board have the highest failure rate. In response to maintenance needs, the circuit schematic diagrams of these two circuit boards have been mapped
D DC speed regulator power supply/drive board includes the armature main circuit, excitation output circuit, It is composed of switching power supply circuit and terminal trigger circuit.
.D DC speed regulator armature main circuit and excitation main circuit
The typical structure of the armature main circuit is a three-phase all-air bridge, which is composed of three dual one-way thyristor modules on the power input side and rectifier A r\series spike voltage absorption network is connected in parallel between the positive and negative output terminals to eliminate harmful voltage glitches entering from the power grid. Two current transformers are used to collect three-phase current signals and send them to the subsequent main board to form a current loop closed-loop control and extract over-current protection signals. A shunt is connected in series to the positive end of the rectified output voltage for an external ammeter to display the operating current. The power supply of the thyristor module cooling fan is introduced through the terminal.
The excitation main circuit of D DC speed regulator is different from other DC speed regulators. It uses chopper current to rectify the six-pulse voltage obtained by three-phase rectification through chopper stage and circuit filtering to form a smoother and smoother voltage. The stable (higher quality) DC adjustable voltage is also widened by the use of a chopper circuit, which eliminates the need to switch the input power supply voltage (sum) and directly inputs the three-phase power supply. The control signal is a width-modulated pulse, and the maximum output DC voltage value can be set according to the parameter setting requirements. The main excitation circuit adopts a modular package and contains a three-phase bridge rectifier circuit, switches and other power devices. The lead-out terminals can be connected in series with reactors or short-circuited. The required pulse width adjustment signal is provided by the excitation trigger board.
The output voltage is supplied to the excitation winding of the DC motor through capacitors and filtering. A modular excitation overvoltage protection component is also connected to the excitation power supply to simplify the excitation circuit. Let’s take a look at the action process of the overvoltage protection component: < br/> Figure D is a simplified circuit of the DC speed regulator excitation circuit
In the figure, the switching tube is the excitation coil D, the freewheeling diode D, and the rectifier filter circuit of the power supply. D, \, r form an overvoltage protection circuit. When the peak voltage value in the rectified voltage reaches the breakdown voltage value of the voltage regulator tube D, the peak component of the D reverse breakdown conduction triggering thyristor conduction voltage is absorbed by charging. When the upper voltage is established, the charging current gradually decreases and is only less than the holding current of the thyristor) and the shutdown charging is terminated early, so that the overvoltage protection circuit selectively absorbs only the part of the voltage spike that exceeds the voltage spike stored by the capacitor. And then consumed by the resistor r.
The induced voltage (excitation current detection signal) of the coil connected in parallel on the reactor (green dam) is introduced through the pin of the terminal into the pin of the front-stage excitation current control signal terminal (from the main board) to the input excitation current. The fixed signal is synthesized into a new excitation current control signal and enters the subsequent stage control circuit (see the figure below) to form a current loop control signal. The induced current signal (excitation current detection signal) obtained from the current transformer is also introduced into the front-stage excitation current control circuit through the terminal to form an over-excitation under-current or over-current fault protection signal (see the figure below).
.D DC speed regulator switching power supply circuit
The power entering from the terminal is introduced into the bridge rectifier circuit through two current limiting resistors and filtered by the circuit as the DC power supply of the switching power supply. The switching power supply circuit generally includes the following loops:
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oscillating loop. It consists of a resistor, a resistor, and a voltage stabilizing tube connected in series to form the starting circuit pin of the power supply. The internal and external circuits of the pin constitute the oscillation circuit. The internal related circuits, the switching tube, the primary winding of the switching transformer, the self-power winding, etc. form the entire oscillation circuit and then self-power supply after controlled conduction. The induced voltage generated by the winding is rectified and filtered as the working power supply. The oscillation loop is the main link in the circuit that forms oscillation and starts working after it is powered on.
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Voltage stabilizing circuit. After the circuit starts to oscillate, the voltage stabilizing circuit then functions to accurately control the duty cycle of the pulse signal output by the pin, causing the energy storage of the pulse transformer to change to maintain a stable voltage value output by the secondary winding. The circuit link that automatically implements voltage stabilization control on the output voltage is called a voltage stabilizing loop. It is generally composed of an external error amplifier, an internal error amplifier, and a control circuit formed by a voltage feedback circuit, a reference voltage, and an optocoupler circuit. This circuit is composed of external circuits and peripheral circuits. The voltage feedback signal is processed to control the input current of the optocoupler D to change the on-resistance of the phototransistor on the output side of D, and then the voltage change of the input pin of the controlled feedback signal causes the internal pulse processing circuit to change the duty of the output pulse of the pin. ratio to achieve the purpose of stabilizing the output voltage. The voltage stabilizing loop is also an important link to ensure the normal operation of the circuit, affecting the level and stability of the output voltage.
In addition to providing the working power of the oscillation chip, the self-powered winding also rectifies the induced voltage of the self-powered winding and sends it out to the pin to form a voltage negative feedback signal. The negative feedback voltage signal is essentially the synthesis of the above-mentioned optocoupler return signal and the induced voltage signal of the self-powered winding, which together regulate the output voltage of the secondary winding (including the power supply of the oscillation chip).
Figure D DC speed regulator switching power supply circuit
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Protection circuit. The resistor-capacitance components, diodes and voltage regulator components connected in parallel on the primary winding of the switching transformer play the role of providing a reverse current path for the switch tube and suppressing the reverse voltage peak. They are the current sampling of the series connection of the switch tube source of the voltage protection circuit. The resistor converts the current change flowing through the switch tube into a voltage signal input current detection signal input pin to form a current closed-loop control circuit that can respond quickly to current changes. The current detection signal is also added to the gate of the field effect transistor. When a sharply changing current jump signal is generated in the switch tube, it is instantly turned on and the voltage of the gate of the switch tube is quickly lowered to quickly suppress the transient rising current. When the protection loop starts to take control, the circuit may be in a stopped oscillation state. In a sense, the protection loop can also form oscillation conditions and form a link of the oscillation loop.
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Load circuit. The rectified and filtered output of the secondary winding is used as the power supply output of the final trigger circuit as the power supply for the digital control terminals and the power supply for the control board relay coil + as the power supply for the main board unit. The + and - two-way power supplies provide power for the mainboard control circuit. The status of each load circuit is closely related to the switching power supply. In particular, the overload and short-circuit status of the load circuit will cause intermittent oscillation of the switching power supply or cause the work to stop. The control mechanism is as follows: the overload or short-circuit status of the load circuit triggers the protection circuit of the switching power supply. The starting control takes overcurrent protection action to cause the switching circuit circuit to stop oscillating or be in an intermittent oscillation state. Abnormalities in the external circuit load circuit of the switching power supply will cause abnormal performance of the switching power supply (it is easy to misjudge that the switching power supply circuit itself is faulty). This is something that should be paid attention to during maintenance.
.D DC speed regulator’s final trigger circuit
The power supply/driver board is generally installed with a trigger pulse circuit and also reserves another final trigger pulse circuit. The module mounting holes on the radiator are also reserved. The installation position of a thyristor is reserved to realize the compatibility of the two-quadrant or four-quadrant operation of the speed controller controlling the load motor (from software to hardware). The final trigger circuit is two parts of the same circuit. Each part of the circuit is composed of six trigger circuits. The upper arm and the lower bridge correspond to the +- trigger circuits in a parallel relationship. This connection method allows each output to be connected to logic. The algorithm controls the output to form a double trigger pulse output of the wooden bridge arm trigger pulse and the complementary pulse sent from the corresponding bridge arm to form a three-phase fully controlled bridge output current path. Since the circuit board uses chip components, the current-limiting resistor in series in the primary winding of the pulse transformer is connected in parallel with the resistor and a bypass capacitor is connected in parallel to the resistor to provide an AC path, which can reduce DC losses and increase the amplitude of the AC signal. .
Figure D DC speed regulator final trigger circuit
, D DC speed regulator excitation plate circuit
Figure D DC speed regulator excitation plate circuit? ：= ：--：/
The signal test terminals of the local circuit and the terminals of the connecting signal cable between the two circuit boards are all marked with terminals (according to serial numbers), but some terminals such as current transformer terminals are among them. One is an empty terminal, and the other terminals are independent terminals. Only one lead terminal is also a test point. It will be clearer where each terminal goes if compared with the actual circuit board.
The current detection signal from the transformer is introduced into the three-phase bridge rectifier circuit on the power supply/driver board through the terminals, and is rectified into a DC signal through the terminals and input into the mainboard circuit for operating current display, overload alarm and shutdown protection. The input three-phase voltage is divided and current-limited by r, r, r (semi-variable resistors) and three resistors, and then sent to the mainboard circuit through the cable terminal as the power grid reference synchronization signal and the three-phase input voltage detection signal. , Introduce the output voltage of the three-phase fully controlled bridge into the circuit board, and then send it to the main board through the cable terminals after r and r are adjusted to form the internal voltage loop control and form the output voltage detection (alarm) signal.
(Excitation current control circuit) Two switching power supply oscillation chips and an optical coupler
The composition and function of the excitation current control circuit are different from the conventional phase-shift trigger circuit, which is called a pulse width modulation circuit. more appropriate.
Diagram of the simplified principle diagram of the excitation current control circuit
The excitation detection signal input from the terminal is input to the mainboard circuit through a terminal for excitation current display and loss of excitation shutdown protection. The current detection signal input pin is sent all the way. The pin is used to protect the circuit from oscillation during overload.
The working process of the excitation current control circuit can be analyzed by the simplified diagram:
The oscillation chip and the peripheral circuit together form a pulse width control circuit. The pin output pulse width depends on the pin input voltage value. The high and low output pulse frequency depends on is the time constant r between feet. The excitation current control signal input by the pin is a composite signal of the voltage input by the terminal and the pin. The excitation given signal from the main board is input by the pin. The pin input is the excitation current detection signal from the terminal in the figure. Under the action of two combined (subtraction/current negative feedback) signals, when the chip pin voltage rises, the pin output pulse duty cycle decreases and the excitation main circuit outputs after chopping. When the DC voltage decreases, the foot output pulse duty cycle increases, and the rectified voltage (current) output by the excitation main circuit rises to achieve the purpose of controlling and stabilizing the output excitation current.
For the adjustable pulse width output controller, under the action of the pin input control signal, the pin output pulse width controlled pulse signal is added to the input side of the optocoupler to form the input current of the light-emitting diode on its input side. The power supply of the output side circuit is supplied from the terminal (from the motherboard), converted into an isolated AC power supply by an oscillation chip and a pulse transformer, and then rectified and filtered by D to provide a DC voltage. Under the action of the input signal, the output side transistor (push-pull circuit) turns on the output adjustable pulse width signal drive (switching tube) to maintain the voltage value at both ends of the excitation line diagram at the amplitude given by the control signal.
Optocoupler devices are used for potential isolation and signal transmission between control loops and main power (weak current and strong current). They have several levels of voltage isolation and ampere-level current output capabilities, which can be directly used to drive the following The module is also called a driver or driver optocoupler for this purpose.
(Fault list) The radio operation panel of a D DC speed controller displays a fault code of magnetic field undercurrent and refuses to accept the operating signal. Detect the excitation main circuit (the three-phase rectifier bridge and tube in the module). The fast-blow fuse connected in series with the normal input power supply does not blow. Determine whether the fault circuit is in the excitation current control circuit or the excitation current signal detection circuit.
When the machine is powered on, it displays a fault code for magnetic field undercurrent. The first step is to solve the alarm signal caused by insufficient excitation current. Connect the output end of the excitation circuit to the load resistor and call up the rated current and magnetic field rating of the motor from the operation display panel. The current prevents the detection circuit from operating and reporting a fault.
Detect the signal voltage on the input side and between the pins of the tube photocoupler driven by the D DC speed regulator excitation board circuit (see picture). However, the voltage value of the power supply pin and pin of the photocoupler is measured. It means that the main excitation circuit stopped working due to the loss of the power supply of the optocoupler, and the excitation current detection circuit reported a fault code of magnetic field undercurrent. Check that the pin of the oscillation circuit has the supply voltage introduced but the pin does not output pulse voltage. Poor judgment.
After replacing the power supply on the output side of the optocoupler, the entire machine returned to normal operation.
An optocoupler is an electrical/optical conversion and signal transmission component that requires an isolated power supply circuit on the input side and the output side. If a set of power supply signal transmission is lost, the signal transmission will be terminated. This circuit is formed by a power supply oscillation chip), a pulse transformer and other components. The inverter isolated power supply is used to supply power to the output side of the optocoupler. When this power supply is damaged, the main excitation circuit stops working and reports a magnetic field undercurrent fault. In actual maintenance, the author has encountered many cases of magnetic field undercurrent failure reported after damage. This may be a weak link in the circuit design of this type of machine and should be noted.
(Example of faults) After powering on a D DC speed regulator, the operation panel displays a fault code of magnetic field undercurrent and refuses to accept the running signal added to the pin of the excitation main circuit (see the figure to observe the output of the excitation main circuit module) Deformation and cracks determine the module and damage. The module model is D. It is difficult to buy such accessories on the market. Users require emergency repair. Considering that the internal circuit of the module is a simple three-phase rectifier circuit and only a tube and two diodes (retaining freewheeling The other diode can be omitted) and the outer tower circuit can be used to repair the fault. Remove the original module and use D) One single-phase rectifier bridge and two tubes, one of which is used for the chopper tube and one of which uses its integrated stage and emitter The diodes connected in parallel serve as freewheeling diodes (it is quite difficult to find such a high-power and high-speed diode, so I simply replaced it with a tube). Place the two tubes on an insulating sheet and fix the rectifier bridge on the heat sink. At the optocoupler A resistor is connected in series to the output end of the test machine. The output excitation voltage of the test machine is normal and the fault is repaired.
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