High-voltage frequency transformer energy feeding braking device
Technical field
The present invention relates to the control technology of the high voltage converter in the electrical system, specifically is a kind of high-voltage frequency transformer energy feeding braking device.
Background technology
Along with the development of power electronic technology, frequency converter is widely used in industries such as iron and steel, petrochemical industry, running water, electric power as the product of Development of Power Electronic Technology, and particularly the application of high voltage converter is increasingly extensive.
At present high voltage converter mainly is divided into two types of voltage-source type and current source types, and current-mode converter exists power factor low, and its application scenarios of shortcoming such as the harmonic pollution of electrical network is big are very limited.The voltage-source type high voltage converter mainly contains following several types:
1, height mode high voltage converter: the voltage of electrical network is converted into low pressure by transformer, utilizes the combination of low voltage frequency converter and low voltage motor to realize frequency conversion
2, low high mode high voltage converter: different with above-mentioned frequency converter is has increased by a transformer again at the outlet side of low voltage frequency converter, can use high-voltage motor to carry out speed governing.
3, three level mode high voltage converters: he utilizes the series connection of high tension apparatus to solve problem of withstand voltage.
4, power unit cascade multilevel electrical level formula high voltage converter: it utilizes the series connection of low pressure and low power unit to realize high pressure, utilizes the harmonic pollution of phase shifting transformer technology solution to electrical network simultaneously, adopts diode rectification, makes the power factor height of grid side.
Above-mentioned the 1st kind and the 2nd kind of high voltage converter belong to transitional technology to be eliminated, because cost hangs down in the small-power occasion and still has application.Though the 3rd kind is newer technology, limited by device, ceiling voltage can only arrive 4160 volts, and for domestic 6KV and 10KV main flow electrical network, application is restricted.It is simple that the 4th type voltage-source type frequency converter belongs to technology, the technical scheme of superior performance, but its topmost topic in the process of using is: when load is braked, can produce very big energy, how to handle or utilize this part energy, be the problem of a difficulty always.
The mode of braking of existing frequency converter generally can be divided into following three kinds:
(1) DC injection braking, promptly the perfectly straight stream electric current of asynchronous motor stator is realized dynamic braking; Mainly need in the DC injection braking design to determine two parameter DC injection braking frequency f and DC injection braking electric current I, and determining and all very big relation of operating mode of motor of these two parameters had relatively high expectations to operating personnel.
(2) dynamic braking is dissipated in braking energy on the brake resistance in parallel with the intermediate dc loop; Dynamic braking is made of brake unit and brake resistance.After the energy that electricity takes place the motor that is in on-position was again sent the intermediate dc loop back to, its energy was consumed in the resistance heating mode by brake unit by the brake resistance that is connected in parallel on the storage capacitor two ends.Be all the energy consumption type, the difference of it and DC injection braking be with energy consumption on the brake resistance outside the motor, motor can be not overheated, thereby can work more continually.But because each power cell volume is less, it is inconsistent respectively to organize current potential simultaneously, and each is organized between the resistance also will keep certain insulation distance, and resistance also will have cooling measure, the less employing in the many level of formula so this mode is established ties and propagated the significance simultaneously.
(3) regenerative braking is sent the braking energy that feeds back to the intermediate dc loop back to electrical network by feedback unit.The frequency converter network side rectifying part of the regenerative braking of energy feedback type is reversible, generally adopts the PWM controlled rectification.When regenerated energy produced, rectifying part worked in inverter mode, gave electrical network with Way of Regenerating Energy Feedback, and regenerated energy is fully exploited.But this method is higher to the stability requirement of power supply, in case have a power failure suddenly, inversion will take place overturn.
This mode need increase the complexity of system configuration and control algolithm with energy by the anti-electrical network of sending back to of input isolating transformer, in three level formula high-pressure frequency-conversions this application is arranged, but basic not application in multiple-level serially connected.
(4) double frequency braking, basic principle is when needs are braked, and a harmonic voltage is superimposed upon on the normal output voltage, thereby the kinetic energy of load is converted into thermal energy consumption in motor, is referred to as the double frequency braking.Frequency converter can not exceed rated current by the volitional check output current when braking.The harmonic frequency that superposes during braking can be provided with, and occurs the situation of resonance when avoiding braking.Be converted into thermal energy consumption in motor because double frequency braking is the kinetic energy with load and motor, so the double frequency braking not needing to be suitable for the occasion and the complex structure of frequent braking.
Summary of the invention
Technical problem to be solved by this invention is, provide one to can be used in many level of power unit cascade formula high voltage converter, and circuit structure is simple, loss is little, cost is low, power factor is high, to the high-voltage frequency transformer energy feeding braking device of electrical network no-harmonic wave pollution.
High-voltage frequency transformer energy feeding braking device of the present invention includes a plurality of energy feedback control circuits, and the quantity of energy feedback control circuit is consistent with the quantity of the power cell that constitutes frequency converter.Described energy feedback control circuit includes the current direction detection circuit that is used for detection power unit output current direction and is used for being in the energy feedback operating mode decision circuitry that normal operating conditions still is in the energy regenerating condition in energy feedback power controlling unit inverter bridge, also include the feedback circuits for triggering that are used for triggering high voltage transducer power unit inverter bridge break-over of device, current direction detection circuit and energy feedback operating mode decision circuitry are connected to the control input end of feedback circuits for triggering, and four road outputs of feedback circuits for triggering link to each other with the inverter bridge device of power cell respectively.
Described energy feedback operating mode decision circuitry comprises the power cell capacitance voltage testing circuit that is used to obtain the capacitance voltage peak value, power cell DC bus-bar voltage testing circuit and the comparison/decision circuitry that is used for the voltage between detection power unit dc bus P, the N; Capacitance voltage testing circuit and DC bus-bar voltage testing circuit are connected two inputs of comparison/decision circuitry respectively; The output of comparison/decision circuitry is by the conducting or the shutoff of above-mentioned feedback circuits for triggering power controlling unit inverter bridge.
Because the present invention adopts above technical scheme, promptly at each power cell an energy feedback control circuit is arranged all, does not only increase any device, and has realized the consumption of braking energy feedback.Because the utility model energy feedback control circuit is made of the low-voltage device that satisfies power cell builtin voltage standard, so cost is low; In addition, the realization of control section is also very convenient, only needs additional correspondent voltage to detect link, current direction detection link and voltage comparator and gets final product, and technical feasibility is good; In control, saved complicated PWM calculating etc., made full use of inverter bridge, improved utilization rate.
Description of drawings
Fig. 1 is the circuit block diagram of energy feedback control circuit of the present invention;
Fig. 2 is the circuit block diagram of the energy feedback operating mode decision circuitry in the embodiment of the invention;
Fig. 3 is the circuit diagram of the feedback circuits for triggering in the embodiment of the invention;
Fig. 4 implements to make the circuit diagram of energy feedback operating mode decision circuitry in the middle energy back feed device for the utility model in the embodiment of the invention;
Fig. 5 is the circuit diagram of the power cell inverter bridge circuit of the use embodiment of the invention.
Embodiment
Embodiments of the invention comprise the corresponding to a plurality of energy feedback control circuits of quantity with the power cell that constitutes frequency converter.
As shown in Figure 1, energy feedback control circuit comprises the testing circuit that is used for detection power unit output current direction and is used for being in the feedback circuits for triggering that normal operating conditions still is in the energy feedback operating mode decision circuitry of energy regenerating condition and is used to trigger the inverter bridge break-over of device in energy feedback control inverter bridge that four road outputs of feedback circuits for triggering link to each other with the inverter bridge device respectively.
When frequency converter normally moved, energy feedback control circuit was idle, and the work of circuit other parts is the same when not having this energy feedback control circuit.When motor braking moves, energy feeds back in the dc-link capacitance by the inverter bridge of power cell, cause capacitance voltage to raise, when capacitance voltage is higher than the setting peak value that allows capacitance voltage, can selectively make the break-over of device of inverter bridge this moment, the energy in the capacitor fed back in the motor by inverter bridge consume.Suppose the output current direction as shown in Figure 5, the IGBT2 conducting in the inverter bridge at this moment, also conducting of corresponding IGBT3, the energy on the electric capacity feeds back in the motor and consumes.
As shown in Figure 2, energy feedback operating mode decision circuitry mainly is made of power cell capacitance voltage testing circuit, power cell DC bus-bar voltage testing circuit and comparison/decision circuitry; The capacitance voltage testing circuit is used to obtain the peak value of capacitance voltage, and as a comparison/and an input of decision circuitry; The DC bus-bar voltage testing circuit is used for the voltage between detection power unit dc bus P, the N, and as a comparison/and another input of decision circuitry; Comparison/decision circuitry detects voltage to these two and compares, judges, according to the direction output control signal of power cell output current, controls the conducting or the shutoff of inverter bridge again.Circuits for triggering when described feedback circuits for triggering can adopt common high voltage converter operate as normal so just can save circuits for triggering, simplify the structure, and have reduced the complexity of control.
Current direction detection circuit among Fig. 1 mainly is to be used for the direction of detection power unit output current, control the conducting and the shutoff of upper and lower bridge arm according to the sense of current of power cell output, the electric current that flows through the conducting brachium pontis is consistent with the sense of current that detected power cell is exported.
In order to make inverter bridge be operated in energy feedback operating state, the present invention is provided with the feedback circuits for triggering, these circuits for triggering adopt 4 pulse control modes, as shown in Figure 3, any moment only provides the conducting control signal of two inverter bridge devices, two signals of two other control signal and this are opposite, avoided upper and lower bridge arm conducting simultaneously.Allow on earth wherein any two break-over of device this depend on power cell output current direction, regardless of power cell output current direction, the sense of current that flows through conduction device is consistent with the direction of power cell output current, and the energy that produces in the time of only in this way just making braking feeds back in the motor and consumes.Feedback circuits for triggering shown in Figure 3 comprise several and door or the door and the logical circuit of not gate.The DICT signal is the current direction signal that is obtained by power cell output current direction testing circuit among the figure, the fiber-optic signal when the RD signal is operate as normal.When detecting GAOYA1 and be 0, block the DICT signal, the inverter bridge operate as normal.When detecting GAOYA2 and be 0, block the RD signal, inverter bridge is in the feedback energy operating state, and at this moment the DICT signal works, and produces conducting and the shutoff that RD10 and RD11 come IGBT in the Control and Feedback circuit according to the DICT signal.
Fig. 4 is the physical circuit figure of the energy feedback operating mode decision circuitry in the embodiment of the invention.As shown in the figure, circuit obtains DC bus-bar voltage V2 and obtains circuit voltage V1 by the capacitance voltage testing circuit by voltage transformer earlier.Through comparator comparison/judgement, when V2>V1, the output control signal allows the work of energy feedback control circuit.Otherwise energy feedback control circuit is in closed condition.