An improved three-phase bridge full-controlled rectifier power supply

Abstract

This invention relates to an improved three-phase bridge fully controlled rectifier power supply, comprising a three-phase AC transformer T, a three-phase full-bridge phase-controlled rectifier circuit based on thyristors or diodes, and a DC filter inductor L disposed on the DC bus. d and filter capacitor C d It also includes an auxiliary circuit connected in parallel with the DC filter inductor Ld, the auxiliary circuit having a resistor R. h Diode D h and switching devices G h diode D h With resistance R h Connected in parallel and then with switching device G h Series connection; when switching device G h When turned on, the output current of the phase-controlled rectifier circuit can pass through resistor R h and switching device G h Flow to filter capacitor C d ; and the switching device G h When turned off, resistor R h Through diode D h This invention enables the power supply to meet the requirements of a high power factor and low current harmonics on the AC side, as well as a low output DC ripple voltage, while also meeting the requirements of low output DC voltage fluctuation under high power surges or fluctuating loads.

Description

Technical Field

[0001] This invention relates to electrical drives or power supplies, and more particularly to an improved three-phase bridge fully controlled rectifier power supply and its control method. Background Technology

[0002] Industrial inverters typically use rectifiers composed of diodes or thyristors as their DC power supply. When the mains voltage fluctuates within the normal range, the DC power supply using diode rectification will fluctuate with the input voltage. For high-power applications requiring a relatively constant DC output voltage, and considering cost-effectiveness, a phase-controlled rectifier circuit composed of thyristors is generally used to achieve a regulated DC power supply. To reduce the ripple of the output voltage or current and limit it to a given allowable range, a filter is needed at the output of the rectified power supply. For voltage-source inverters, capacitor filtering is required. Furthermore, to improve the power factor at the AC input of the rectifier, an inductor is usually connected in series between the rectifier and the DC filter capacitor.

[0003] Thyristor-based single-phase rectifier circuits are relatively simple, have lower requirements for triggering circuits, and are easy to adjust as phase synchronization is straightforward. However, their output DC voltage ripple is relatively large. Because they are connected to only one phase of the power grid, they can easily cause load imbalance, so they are generally only used in small to medium capacity equipment below 4kW. For larger loads, three-phase circuits are typically used. When the rectifier capacity is large, and low DC voltage ripple is required, with special requirements for speed, a three-phase bridge fully controlled rectifier circuit should be considered. This is because this circuit has balanced three phases, resulting in low output DC voltage and current ripple, minimal impact on the power grid, and short control lag time. Figure 1 This is a typical three-phase bridge fully controlled rectifier and voltage regulator circuit structure using thyristor control, consisting of three functional parts: transformer, phase-controlled rectification, and filter. The transformer section uses a three-phase AC transformer T to match the appropriate AC input voltage. The phase-controlled rectification section converts the AC voltage to DC voltage, and it consists of three bridge arms, each with two thyristors, using six thyristor switches (T1 to T6 as shown in the diagram). The three bridge arms form a six-pulse rectification, and the conduction angle of the input AC voltage is controlled by coordinating the triggering time of each thyristor to achieve the regulation and stabilization of the rectified DC output power supply. The filter section consists of a DC filter inductor L. d and filter capacitor C d This is a component used to reduce output DC power supply ripple. The DC filter inductor L... d It also helps reduce harmonics in the three-phase AC input current of the rectifier and improves the input power factor. The rectified output voltage, after filtering, serves the external load R. L Provide DC power U d .

[0004] In addition to high voltage regulation accuracy, rectified power supplies typically require high AC power factor, low DC power ripple coefficient, and a small output voltage dynamic fluctuation range. This is achieved by adding a DC filter inductor L between the rectified output and the filter capacitor. d Besides reducing AC input current harmonics and decreasing DC output voltage ripple, another benefit of this filter inductor is that it improves the power factor at the AC input. (Filter inductor L) d The larger the value, the higher the power factor. However, the introduction of the filter inductor will affect the dynamic adjustment response of the DC output voltage, increasing the fluctuation range of the output DC voltage during sudden load changes. Here, we analyze a design case of a DC regulated power supply with a rated power of 2000kW and a rated output voltage of 1800V. The design requires a power factor greater than 0.86, while under a sudden 50% increase in rated load, the output voltage fluctuation range should be less than 3% of the rated output voltage. The DC voltage ripple factor should be less than 0.5%. Figure 1 The conventional circuit design achieves a power factor of approximately 87% at full load, and the output voltage ripple factor also meets the requirements. However, when a 50% rated load is suddenly applied, the output voltage fluctuation remains excessive and does not meet the requirements. Figure 2 This is a simulation scenario. From top to bottom, the waveforms are the power supply output DC voltage V_out (unit: V) and the output current I(R_Load) (unit: A). The rectifier power supply has a stable output voltage of 1800V under no-load conditions. At 0.3 seconds, a 1000kW power load is suddenly applied, causing transient fluctuations in the output voltage, ranging from a minimum of approximately 1650V to a maximum of approximately 2000V. The maximum voltage fluctuation is 200V, exceeding 10%. Further analysis revealed that the large voltage fluctuations were primarily caused by the sudden load application exciting the inductor L in the filter circuit. d With capacitor C d The low-frequency oscillations and resonances cause their initial resonant voltage to be too large, and the filter inductor L... d The larger the parameter, the greater the voltage fluctuation amplitude. Since the dynamic response capability of thyristors using phase control is inherently weak, therefore... Figure 1 The circuit structure cannot guarantee a small voltage fluctuation range under large impact loads.

[0005] To achieve a high input power factor, low three-phase AC input harmonics, and low output DC ripple voltage, while also minimizing output voltage fluctuations under high-power surges or fluctuating loads, it is necessary to... Figure 1 The traditional three-phase bridge fully controlled rectifier power supply main circuit shown is improved. Summary of the Invention

[0006] The purpose of this invention is to improve the traditional three-phase AC fully controlled rectifier and regulated power supply based on thyristors, and to propose a corresponding control method so that the power supply can meet the requirements of high power factor and current harmonics on the AC side, low output DC ripple voltage, and low output DC voltage fluctuation amplitude under high power impact or fluctuating load conditions.

[0007] To achieve the above objectives, an improved three-phase bridge fully controlled rectifier power supply is provided, including:

[0008] A three-phase AC transformer T is used to transform and match the appropriate AC input voltage.

[0009] The phase-controlled rectifier circuit has three bridge arms, each of which consists of two thyristors or diodes, and the three bridge arms form a six-pulse rectification.

[0010] The filter circuit includes a DC filter inductor Ld and a filter capacitor C. d The DC filter inductor L d The DC filter inductor L is connected in series on the positive bus of the DC bus at the output of the phase-controlled rectifier circuit. d The end furthest from the phase-controlled rectifier circuit is used to connect to the negative bus of the DC bus via an external load, thereby supplying power to the load. The filter capacitor C... d One end is connected to the DC filter inductor L d One end is the contact point between the load and the other end, which is connected to the negative busbar.

[0011] Also includes DC filter inductor L d A parallel auxiliary circuit, wherein the auxiliary circuit includes a resistor R h Diode D h and switching devices G h The diode D h With resistance R h Connected in parallel, and then with the switching device G h Series;

[0012] When switching device G h When turned on, the output current of the phase-controlled rectifier circuit can pass through resistor R h and switching device G h Flow to filter capacitor C d ; and the switching device G h When turned off, resistor R h Through diode D h To continue streaming.

[0013] Furthermore, the switching device G h It is configured as a self-turn-off switching device. The self-turn-off switching device includes, but is not limited to, IGBT, GTO, or IEGT.

[0014] The control method for the auxiliary circuit further includes:

[0015] The target control voltage U of the rectifier power supply d *The output DC voltage U of the DC bus obtained from actual sampling and detection d The difference, minus the set constant M Udmin Afterwards, the output range is limited by a limiter after PI regulation to obtain the modulated wave;

[0016] The modulated wave is compared with the triangular carrier wave Tri, and the resulting PWM pulse is used to control the switching device G in the auxiliary circuit. h To take control.

[0017] The auxiliary circuit is connected in parallel with the filter inductor and then in series with the positive bus of the three-phase full-bridge rectifier power supply, or the auxiliary circuit is connected in parallel with the filter inductor and then in series with the negative bus of the three-phase full-bridge rectifier power supply.

[0018] The PWM pulse affects the switching device G. h The control is further configured such that when the PWM pulse value is positive, the switching device G... h When the switching device G is turned on and the value is negative, it is in conduction mode. h Turn off.

[0019] The rated power of the three-phase bridge fully controlled rectifier power supply is configured to be 4kW or higher. The rated power of the three-phase bridge fully controlled rectifier power supply is configured to be 2000kW, and the rated output voltage is 1800V. The resistor R... h For 0.1 ohms, M Udmin The constant is 10, the switching frequency of the triangular carrier is 1000Hz, the peak-to-peak value is 10, and the minimum value is 0.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] 1) By employing the technical method proposed in this paper, the thyristor-based rectifier power supply can simultaneously meet the requirements of high power factor, low current harmonics, and low output DC voltage ripple on the AC side, while also maintaining a very small output DC voltage fluctuation range under high-power surge or fluctuating load conditions. This makes this low-cost, high-power rectifier and regulated power supply based on thyristors suitable for load power supply applications with very stringent requirements for DC power supply performance.

[0022] 2) The improved main circuit architecture is simple, the improvement cost is small, and the added control method is relatively simple to implement and will not affect the normal operation efficiency.

[0023] 3) The essential advantage of the improvement scheme and control method proposed in this patent is that it avoids the low-frequency large-amplitude oscillation of the filter inductor and filter capacitor under sudden large load conditions, thereby suppressing the large fluctuation of DC output voltage. Although this method is proposed for three-phase thyristor rectifier circuits, the auxiliary circuit and control method mentioned can also be applied to three-phase full-bridge diode rectifier power supplies. Attached Figure Description

[0024] Figure 1 A schematic diagram of the main circuit of a three-phase bridge fully controlled rectifier power supply is shown.

[0025] Figure 2 The output voltage and current waveforms are shown when a 50% rated load is suddenly applied.

[0026] Figure 3 A schematic diagram of the main circuit of the improved three-phase bridge fully controlled rectifier power supply is shown.

[0027] Figure 4 The control principle block diagram of the auxiliary circuit is shown.

[0028] Figure 5 The simulated waveforms are shown under the condition of a sudden increase of 50% of the rated load.

[0029] Figure 6 A schematic diagram of an improved three-phase full-bridge diode rectifier power supply is shown.

[0030] Figure 7 The diagram shows the case where the auxiliary circuit and the filter inductor are connected in parallel and then in series on the negative bus of a three-phase full-bridge rectifier power supply. Detailed Implementation

[0031] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0032] Figure 3 This is a schematic diagram of the main circuit of the proposed improved three-phase bridge fully controlled rectifier power supply. Figure 1 As can be seen from the structural comparison shown, only one additional element, the same as the original filter inductor L, was added to the original filter section. d The auxiliary circuit is connected in parallel, with all other parts and parameters remaining unchanged. This auxiliary circuit consists of resistor R. h Diode D h and G h This fast-switching device is composed of an IGBT (or other self-turn-off switching devices such as GTO, IEGT, etc.). The diode D... h With resistance R h The three-phase bridge rectifier is connected in parallel, and then in series with the IGBT. When the IGBT is turned on, the three-phase bridge rectifier output current can flow through resistor R. h The current flows to the filter capacitor side of the IGBT. When the IGBT is turned off, the resistor R...h Since it is practically difficult to achieve zero inductance, it can be achieved through diode D. h Freewheeling current prevents instantaneous overvoltage caused by shutdown.

[0033] (1) Control methods

[0034] Figure 3 The improved three-phase bridge fully controlled rectifier power supply shown only requires... Figure 1 The traditional control method shown adds control to the auxiliary circuit section, because Figure 1 Traditional control methods for circuits are very mature and have been described in relevant literature, so they will not be elaborated here. Figure 4 This is a block diagram illustrating the control principle for controlling the auxiliary circuit.

[0035] The control of the auxiliary circuit is actually the timely control of the switching device IGBT's turn-on and turn-off, such as... Figure 4 As shown, the target control voltage U of the power supply d *The output DC voltage U obtained from actual sampling and detection d The difference, minus the set constant M Udmin Afterwards, the output range is limited by a PI (proportional-integral) circuit and then by a limiter to obtain a modulated wave. This modulated wave is compared with a triangular carrier wave Tri, and the resulting PWM pulse is used to control the IGBT in the auxiliary circuit. When the PWM pulse value is positive, the IGBT is turned on; when it is negative, the IGBT is turned off.

[0036] (2) Simulation verification of the proposed method

[0037] Regarding the 2000kW / 1800V rectifier power supply case mentioned earlier, Figure 3 The circuit was improved and, according to Figure 4 The control method is improved, in which the auxiliary resistor R h Designed to be 0.1 ohms. Referring to the design performance requirements, M... Udmin The constant is set to 10, the switching frequency of the triangular carrier is set to 1000Hz, the peak-to-peak value is set to 10, and the minimum value is 0.

[0038] Figure 5 The simulated waveforms under a sudden 50% applied rated load are shown from top to bottom as follows: the power supply output DC voltage waveform V_out (unit: V), the output current waveform I(R_Load) (unit: A), and the resistor R in the auxiliary circuit. h The current waveform I(Rh).

[0039] Simulation results show that when a 50% rated load is suddenly applied, the output voltage experiences transient fluctuations, but the lowest voltage is greater than 1765V and the maximum is less than 1810V. This indicates a maximum fluctuation amplitude of 35V, which is less than 2% compared to the rated 1800V. This is also significant compared to the circuit before the improvement. Figure 1 Under the same impact load, the output DC voltage fluctuation amplitude decreased from more than 10% to less than 2%, meeting the technical design requirement of no more than 3%. (Comparison) Figure 5 and Figure 2 It can be seen that under heavy load shocks, the improved circuit is also beneficial in shortening the DC output voltage fluctuation recovery time. Furthermore, it can be seen that although the auxiliary circuit helps the system output suppress large fluctuations in DC output voltage caused by heavy load shocks or fluctuations, as mentioned earlier, M... Udmin The value is set to 10, so the IGBT is turned off once the fluctuation amplitude is less than 10V. The auxiliary resistor R... h No current flows through it anymore, so when the power supply is under normal and stable load or small fluctuation load, the resistance R h It will not generate heat loss, meaning it will not affect normal operating efficiency. Figure 5 When the load is 50% full-load impact, the actual conduction time of Rh is within two power frequency cycles.

[0040] The essential advantage of the improved scheme and control method proposed in this patent is that it avoids low-frequency large-amplitude oscillations of the filter inductor and filter capacitor under sudden increases in load, thereby suppressing large fluctuations in the DC output voltage. Although this method is proposed for three-phase thyristor rectifier circuits, the auxiliary circuits and control methods mentioned can also be applied to other circuits such as... Figure 6 In the three-phase full-bridge diode rectifier power supply shown, it is the one that... Figure 3 The thyristors from T1 to T6 in the main circuit shown are replaced with Figure 6 The thyristors D1 to D6 in the main circuit shown are equivalent to the thyristors in a thyristor-based three-phase full-bridge rectifier power supply operating in a fully conducting state. This allows the three-phase full-bridge diode rectifier power supply to achieve extremely low output DC voltage fluctuation amplitude and fluctuation time even under high-power impact loads, thereby improving the performance of the rectifier power supply.

[0041] Figure 6 The control principle of the auxiliary circuit of the three-phase full-bridge diode rectifier power supply is completely the same as... Figure 4 The control principle block diagram of the auxiliary circuit shown is the same, so it will not be described again here.

[0042] Figure 7 The auxiliary circuit and the filter inductor are connected in parallel and then in series on the negative bus of the three-phase full-bridge rectifier power supply. Their essential effect is the same as... Figure 6The situation is the same as when they are connected in series on the DC positive bus, and the control principle is completely the same. Figure 4 The control principle block diagram of the auxiliary circuit shown is the same, so it will not be described again here.

[0043] (3) Improvement effect

[0044] 1) By employing the technical method proposed in this paper, the thyristor-based rectifier power supply can simultaneously meet the requirements of high power factor, low current harmonics, and low output DC voltage ripple on the AC side, while also maintaining a very small output DC voltage fluctuation range under high-power surge or fluctuating load conditions. This makes this low-cost, high-power rectifier and regulated power supply based on thyristors suitable for load power supply applications with very stringent requirements for DC power supply performance.

[0045] 2) The improved main circuit architecture is simple, the improvement cost is small, and the added control method is relatively simple to implement and will not affect the normal operation efficiency.

[0046] 3) The essential advantage of the improvement scheme and control method proposed in this patent is that it avoids the low-frequency large-amplitude oscillation of the filter inductor and filter capacitor under sudden large load conditions, thereby suppressing the large fluctuation of DC output voltage. Although this method is proposed for three-phase thyristor rectifier circuits, the auxiliary circuit and control method mentioned can also be applied to three-phase full-bridge diode rectifier power supplies.

[0047] The above specific embodiments are merely preferred embodiments of the present invention. Based on the technical solutions of the present invention and the relevant teachings of the above embodiments, those skilled in the art can make various alternative improvements and combinations to the above specific embodiments.

Claims

1. An improved three-phase bridge fully controlled rectifier power supply, comprising: A three-phase AC transformer T is used to transform and match the AC input voltage. The phase-controlled rectifier circuit has three bridge arms, each of which consists of two thyristors or diodes, and the three bridge arms form a six-pulse rectification. The filter circuit includes a DC filter inductor L. d and filter capacitor C d The DC filter inductor L d On one of the DC busbars connected in series at the output of the phase-controlled rectifier circuit, the DC filter inductor L d The end furthest from the phase-controlled rectifier circuit is used to connect to the other bus of the DC bus via an external load, thereby supplying power to the load. The filter capacitor C... d One end is connected to the DC filter inductor L d The connection between the load and the other end is connected to the other busbar; Its features are: Also includes DC filter inductor L d A parallel auxiliary circuit, wherein the auxiliary circuit includes a resistor R h Diode D h and switching devices G h The diode D h With resistance R h Connected in parallel, and then with the switching device G h Series; When switching device G h When turned on, the output current of the phase-controlled rectifier circuit flows through resistor R h and switching device G h Flow to filter capacitor C d ; and the switching device G h When turned off, resistor R h Through diode D h Continue streaming; The control method for the auxiliary circuit includes: The target control voltage U of the rectifier power supply d *The output DC voltage U of the DC bus obtained from actual sampling and detection d The difference, minus the set constant M Udmin Afterwards, the output range is limited by a limiter after PI regulation to obtain the modulated wave; The modulated wave is compared with the triangular carrier wave Tri, and the resulting PWM pulse is used to control the switching device G in the auxiliary circuit. h To take control.

2. The three-phase bridge fully controlled rectifier power supply according to claim 1, characterized in that: The switching device G h It is configured as a self-turn-off switching device.

3. The three-phase bridge fully controlled rectifier power supply according to claim 2, characterized in that: The self-turn-off switching devices include, but are not limited to, IGBTs, GTOs, or IEGTs.

4. The three-phase bridge fully controlled rectifier power supply according to claim 1, characterized in that, The PWM pulse affects the switching device G. h The control is configured such that when the PWM pulse value is positive, the switching device G... h When the switching device G is turned on and the value is negative, it is in conduction mode. h Turn off.

5. The three-phase bridge fully controlled rectifier power supply according to claim 1, characterized in that: The auxiliary circuit is connected in parallel with the filter inductor and then in series with the positive bus of the three-phase full-bridge rectifier power supply, or the auxiliary circuit is connected in parallel with the filter inductor and then in series with the negative bus of the three-phase full-bridge rectifier power supply.

6. The three-phase bridge fully controlled rectifier power supply according to claim 4, characterized in that: The rated power of the three-phase bridge fully controlled rectifier power supply is configured to be above 4kW.

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