CN114785157A - An AC-DC-AC converter for on-line UPS and its control method - Google Patents

Abstract

An AC-DC-AC converter for an online UPS, comprising an AC input voltage source Vin, a first power switch tube S ₁ , a second power switch tube S ₂ , a third power switch tube S ₃ , a fourth power switch tube S 3 , and a fourth power switch tube S 1 . Power switch tube S ₄ , fifth power switch tube S ₅ , sixth power switch tube S ₆ , seventh power switch tube S ₇ , eighth power switch tube S ₈ , input inductance L _in , output inductance L _out , bus capacitance C _bus ; according to the polarity of the input voltage, the rectification stage works in the boost mode or the buck-boost mode; when in the positive half cycle of the input voltage, the rectification stage keeps the _third power switch S3 turned on and allows the The _fourth power switch S4 is kept disconnected, and at the same time, the _first power switch S1 and the _second power switch S2 are switched with a high switching frequency. At this time, the rectification stage works in the boost mode; Soft switching and high frequency operation are allowed, reducing the size of the input inductor.

Description

An AC-DC-AC converter for on-line UPS and its control method

technical field

The invention relates to an AC-DC-AC converter for an on-line UPS and a control strategy thereof, belonging to the technical field of power electronic converters, in particular to the technical field of high power density uninterruptible power supplies (UPS).

Background technique

An uninterruptible power supply (UPS) can provide backup power for critical loads during grid outages and disturbances. UPS can be divided into three categories, namely backup UPS, online interactive UPS, and online UPS. The backup UPS uses a static switch to directly connect the input to the output during normal operation of the grid, while charging the battery. When the grid fails, the static switch is disconnected, and the battery supplies power to the load through the inverter. Since the inverter operates only in standby mode, the switching time is long and the protection against input disturbances is small during normal operation. In industrial environments, line-interactive UPSs are more popular. During normal operation, they are connected to the load through a passive regulation stage, which filters out most of the line disturbances. In the event of a grid failure, a series switch is used to disconnect before the inverter runs. Grid, switching time is a few milliseconds. The online UPS type first converts the grid voltage to the DC voltage on the intermediate DC bus, and then converts the DC bus voltage to the AC voltage of the amplitude and frequency required by the output load, and the load is always provided by the inverter stage to ensure the load. uninterrupted on the AC voltage. Online UPS is often used in the field of safe and continuous operation of electronic equipment, which has high requirements on the power density of UPS.

In the prior art, a transformer isolation topology and a single DC bus have been proposed, in which an isolated PFC rectification stage is usually used to meet the isolation requirements, and a three-stage isolated on-line UPS has been proposed, which uses an additional DC rectification stage before the PFC rectification stage. -DC conversion stage to meet isolation requirements. In the above technologies, the peak rated transformer limits its efficiency and adversely affects power density. For non-isolated on-line UPSs, topologies have been proposed that have a common neutral between the input and output anxiety ports. These topologies use four-quadrant switches to limit their operating frequency and have a split DC bus. Capacitor requirements can be doubled, limiting their overall power density or increasing the complexity of their control.

SUMMARY OF THE INVENTION

In order to overcome the above-mentioned deficiencies of the prior art, the purpose of the present invention is to provide an AC-DC-AC converter for an on-line UPS and a control method thereof, which has the advantages of realizing soft switching, allowing high-frequency operation, and reducing the need for Enter the volume characteristics of the inductor.

For achieving the above object, the technical scheme adopted in the present invention is:

An AC-DC-AC converter for on-line UPS includes an AC input voltage source Vin, a first power switch tube S ₁ , a second power switch tube S ₂ , a third power switch tube S ₃ , and a fourth power switch tube S 3 . Power switch S ₄ , fifth power switch S ₅ , sixth power switch S ₆ , seventh power switch S ₇ , eighth power switch S ₈ , input inductance L _in , output inductance L _out , bus capacitance C _bus ;

The first end of the AC input voltage source Vin is connected to the source of the _third power switch S3, the second end of the AC input voltage source Vin, the source of the _first power switch S1, and the bus capacitor _Cbus The second end of the power switch S6 and the source of the _sixth power switch S6 are connected to the second end of the output end; the drain of the _third power switch S3 and the source of the _fourth power switch S4 are connected to the input inductor L _in The first end of the input inductor L _in and the source of the _second power switch tube S2 are both connected to the drain of the first power switch tube S1 _; the drain of the _fourth power switch tube S4 and the drain of the _second power switch S2 is connected to the first end of the bus capacitor C _bus ; the drain of the _fifth power switch S5 is connected to the drain of the _seventh power switch S7; the fifth power switch _The source of the tube S5 and the drain of the _sixth power switch tube S6 are connected to the first end of the output inductor L _out ; the source of the _seventh power switch tube S7 and the drain of the _eighth power switch tube S8 are connected to the first end of the output inductor L out. The second ends of the output inductor L _out are all connected; the source of the _eighth power switch tube S8 is connected to the first end of the output end.

The first power switch S ₁ , the second power switch S ₂ , the third power switch S ₃ , the fourth power switch S ₄ , the fifth power switch S ₅ , and the sixth power switch S ₆ , the seventh power switch tube S ₇ , and the eighth power switch tube S ₈ are both SiCMOSFET switch tubes.

The first power switch S ₁ , the second power switch S ₂ , the third power switch S ₃ , the fourth power switch S ₄ , the fifth power switch S ₅ , and the sixth power switch S ₆ , the seventh power switch tube S ₇ , and the eighth power switch tube S ₈ are all provided with diodes connected in parallel.

The first power switch S ₁ , the second power switch S ₂ , the third power switch S ₃ , the fourth power switch S ₄ , the fifth power switch S ₅ , and the sixth power switch S ₆ , the seventh power switch tube S ₇ , and the eighth power switch tube S ₈ are driven by complementary pulses.

The first power switch S ₁ , the second power switch S ₂ , the third power switch S ₃ , and the fourth power switch S ₄ form a rectifier stage of the converter.

The first power switch tube S ₁ , the second power switch tube S ₂ , the third power switch tube S ₃ , and the fourth power switch tube S ₄ can all implement zero-voltage turn-on soft switching.

The fourth power switch tube S ₄ , the fifth power switch tube S ₅ , the sixth power switch tube S ₆ , and the seventh power switch tube S ₇ constitute the inverter stage of the converter.

A control method for an AC-DC-AC converter of an online UPS, comprising the following steps:

For the rectification stage control, the rectification stage of the converter works in two operating modes: boost and buck-boost. In order to reduce the size of the input inductor, it operates at high frequency; in order to maintain high efficiency at high switching frequency, the rectification stage works Operates in boundary conduction mode, so that the power switch tube is turned on at zero voltage;

During the positive half cycle of the input voltage, the rectifier stage operates in boost mode, and the instantaneous value of the input voltage is less than half of the DC bus voltage; when the instantaneous value of the input voltage is greater than half of the DC bus voltage, only at the end of each switching cycle The zero-voltage turn-on can be realized only when the inductor current of the PWM is less than a certain negative value i _boostmin ; C _OSS is the parasitic capacitance of the _first power switch S1 and the _second power switch S2; the _second power switch S2 is in the inductor After the current crosses zero, it remains on for a period of time to establish the required negative inductor current, so as to ensure the zero-voltage turn-on of the _first power switch S1;

During the negative half cycle of the input voltage, the rectifier stage operates in buck-boost mode, and the _third power switch S3 and the _fourth power switch S4 naturally realize zero-voltage turn-on. When the instantaneous value of the input voltage is less than the bus voltage , the buck-boost converter composed of the _third power switch S3 and the _fourth power switch S4 always works in the boost mode. In this mode, the _third power switch S3 does not need the _fourth power switch S4 Turn on for a period of time to achieve zero voltage turn-on.

In the control of the entire rectification stage, the rectification stage works in the boundary conduction mode, and controls the first power switch S ₁ , the second power switch S ₂ , and the third power switch S ₃ by sensing the polarity of the input voltage , the drive signal of the gate of the _fourth power switch tube S4; when the input voltage is greater than zero, the first power switch tube S1 is turned on _{t onboost} first, and then the _second power switch tube S2 is turned on until the inductor current drops to i _boostmin The following; when the input voltage is less than zero, the _third power switch S3 turns on t _onbuck-boost first, and then the _fourth power switch S4 turns on until the inductor current reaches zero; a zero current detection circuit is required in the whole control, The zero current detection circuit senses the inductor current and utilizes two hysteresis comparators, one for each half input cycle; when the inductor current drops below i _boostmin during the positive half cycle of the input voltage, the hysteresis comparator generates a trigger signal , in the negative half cycle of the input voltage, when the inductor current reaches zero, the hysteresis trigger generates a trigger signal, and the controller resets the PWM counter and starts the next switching cycle by detecting the trigger signal in each half cycle; The output voltage of the rectifier stage is adjusted through the low bandwidth voltage loop of the PI controller to control the conduction time of the _first power switch S1 and the _third power switch S3;

For the inverter stage control, the inverter stage is mainly used to generate the sinusoidal AC voltage at the output, and the inverter stage also works in two working modes of boost and buck-boost; the inverter stage works in a continuous conduction mode with a fixed switching frequency;

In the whole inverter stage control, the voltage error signal is generated by comparing the sinusoidal reference voltage with the detected output voltage, and the voltage error signal is sent to the controller of the inverter stage, which includes two There are two controllers G _cbuck and G _cbuck-boost ; when the output voltage is greater than zero, the buck controller G _cbuck controls the duty cycle of the _fifth power switch S5, and the output of the buck-boost controller G _cbuck-boost is Ignored, the eighth power switch remains on; when the output voltage is less than zero, the buck-boost controller G _cbuck-boost controls the duty cycle of the seventh power switch, the output of the buck controller G _cbuck is ignored, and the first The six power switches remain on.

A single DC bus is used between the rectifier stage and the inverter stage.

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

The described AC-DC-AC converter for on-line UPS uses a single DC bus between the rectifier stage and the inverter stage. Capacitor requirements are reduced by 50%. The rectifier stage at the input of the converter operates in BCM mode, enabling soft switching and allowing high frequency operation, reducing the size of the input inductor. The output inverter stage operates in CCM mode, and the controller regulates the output voltage of the converter through resistors and reactive loads. The converter is suitable for integrating the charging and discharging interface of the battery, the battery interface utilizes the main power stage in the discharging phase, and does not need the peak power rated discharging phase, and uses a buck converter with a lower rated power when charging. Thus achieving high efficiency and high power density.

A single DC bus is used between the rectifier stage and the inverter stage, which reduces the capacitance requirement of the DC bus by 50% compared with the traditional online UPS with discrete DC bus; the rectifier stage of the input of the converter is in BCM mode operation, soft switching is achieved, and high frequency operation is allowed, reducing the size of the input inductor. The output inverter stage operates in CCM mode, and the controller adjusts the output voltage of the converter through resistance and reactive load; the converter is suitable for integrating the charging and discharging interface of the battery, and the battery interface utilizes the main power stage during the discharge phase without peaking In the power rated discharge stage, when charging, a buck converter with a lower rated power is used to achieve high efficiency and high power density.

Description of drawings

Fig. 1 is the topology structure diagram of the AC-DC-AC converter that is used for on-line UPS of the present invention;

Fig. 2 is the working mode diagram of the positive half cycle of the input voltage in the rectification stage of the present invention;

Fig. 3 is the working mode diagram of the negative half cycle of the input voltage in the rectification stage of the present invention;

4 is a working mode diagram of the positive half cycle of the output voltage in the inverter stage of the present invention;

Fig. 5 is the working mode diagram of the negative half cycle of the output voltage in the inverter stage of the present invention;

FIG. 6 is a time-enlarged graph of the inductor current, a waveform graph of the average value of the inductor current, and a waveform graph of the input voltage. Among them, the sine solid line is the waveform diagram of the input voltage, the sawtooth solid line is the time magnification diagram of the inductor current, and the sine dotted line is the waveform diagram of the average value of the inductor current;

Fig. 7 is the controller block diagram of the rectification stage;

8 is a control block diagram of a zero-current detection circuit for the rectification stage;

Fig. 9 is the controller block diagram of the inverter stage;

Figure 10 is the battery charging path in the normal operation mode of the battery interface architecture diagram;

Figure 11 is the battery discharge path in the standby operation mode of the battery interface architecture diagram;

Wherein: Vin is the input voltage source; S1 is the first power switch; S2 is the second power switch; S3 is the third power switch; S4 is the fourth power switch; S5 is the fifth power switch; S6 is the The sixth power switch tube; S7 is the seventh power switch tube; S8 is the eighth power switch tube; C _bus is the bus capacitor; C _in is the input capacitor; C _out is the output capacitor; L _in is the input inductance; L _out is the output Inductance; L _bat is the battery side inductance; S _b1 is the first power switch tube on the battery side; S _b2 is the second power switch tube on the battery side; S _R1 is the first fast relay; S _R2 is the second fast relay; Vout is the output Voltage.

Detailed ways

In order to make those skilled in the art better understand the solutions of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only Embodiments are part of the present invention, but not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

It should be noted that the terms "first", "second" and the like in the description and claims of the present invention and the above drawings are used to distinguish similar objects, and are not necessarily used to describe a specific sequence or sequence. It is to be understood that the data so used may be interchanged under appropriate circumstances such that the embodiments of the invention described herein can be practiced in sequences other than those illustrated or described herein. Furthermore, the terms "comprising" and "having" and any variations thereof, are intended to cover non-exclusive inclusion, for example, a process, method, system, product or device comprising a series of steps or units is not necessarily limited to those expressly listed Rather, those steps or units may include other steps or units not expressly listed or inherent to these processes, methods, products or devices.

Below in conjunction with accompanying drawing, the present invention is described in further detail:

Referring to FIG. 1 , it is a topological structure diagram of an AC-DC-AC converter used in an online UPS according to the present invention, including an AC input voltage source Vin, a first power switch S ₁ , a second power switch S ₂ , a first power switch S 2 , and a second power switch S 2 . Three power switch tubes S ₃ , fourth power switch tube S ₄ , fifth power switch tube S ₅ , sixth power switch tube S ₆ , seventh power switch tube S ₇ , eighth power switch tube S ₈ , input inductance L _in , output inductance L _out , bus capacitance C _bus ;

The first end of the AC input voltage source Vin is connected to the source of the _third power switch S3, the second end of the AC input voltage source Vin and the source of the _first power switch S1 are connected to the second end of the bus capacitor _Cbus . terminal and the source of the _sixth power switch tube S6 are connected to the second terminal of the output terminal; the drain of the _third power switch tube S3 is connected to the source of the _fourth power switch tube S4 and the first terminal of the input inductor L _in terminals are connected; the second terminal of the input inductor L _in is connected to the source of the _second power switch tube S2 and the drain of the first power switch tube S1 _; the drain of the _fourth power switch tube S4 is connected to the second power switch tube S2 _The drain of the power switch S2 is connected to the first end of the bus capacitor C _bus and the drain of the _fifth power switch S5 is connected to the drain of the _seventh power switch S7; the drain of the _fifth power switch S5 The source is connected to the drain of the _sixth power switch S6 and the first end of the output inductor L _out ; the source of the _seventh power switch S7 is connected to the drain of the _eighth power switch S8 and the output inductor L The second ends of _out are all connected; the source of the _eighth power switch tube S8 is connected to the first end of the output end.

Referring to FIG. 2 , it is a working mode diagram of the positive half cycle of the input voltage in the rectification stage of the present invention. According to the polarity of the input voltage, the rectification stage works in the boost mode or the buck-boost mode. During the positive half cycle of the input voltage, the rectifier stage switches the third power switch S3 on by keeping the _third power switch S3 on and the _fourth power switch S4 off, while switching the third power switch S4 with a high switching frequency. A power switch tube S ₁ and the second power switch tube S ₂ , at this time, the rectification stage works in the boost mode.

Referring to FIG. 3, it is a working mode diagram of the present invention in the negative half cycle of the input voltage in the rectification stage. When in the negative half cycle of the input voltage, the rectifier stage keeps the _first power switch S1 turned on and the The _second power switch S2 is kept disconnected, and at the same time, the _third power switch S3 and the _fourth power switch S4 are switched with a high switching frequency. At this time, the rectification stage works in a buck-boost mode. For low-power applications, the second power switch and the fourth power switch can be replaced by power diodes, which can reduce the complexity of gate driving. The boost mode and buck-boost mode of the rectifier stage are controlled during their respective half-cycles, thereby regulating the DC bus voltage while drawing a sinusoidal current from the input with unity power factor.

Referring to FIG. 4 , it is a working mode diagram of the positive half-cycle of the output voltage in the inverter stage of the present invention. In order to generate a positive output voltage at the output end, the inverter stage keeps the _eighth power switch S8 on and allows the eighth power switch S8 to be turned on. The _seventh power switch S7 is kept disconnected, while the _fifth power switch S5 and the sixth power switch _S6 are switched with a high switching frequency. At this time, the inverter stage works in the buck mode.

Referring to FIG. 5 , it is a working mode diagram of the negative half cycle of the output voltage in the inverter stage of the present invention. In order to generate a negative output voltage at the output end, the inverter stage keeps the _sixth power switch S6 turned on and allows the sixth power switch S6 to be turned on. The _fifth power switch S5 is kept disconnected, and at the same time, the _seventh power switch S7 and the eighth power switch _S8 are switched with a high switching frequency. At this time, the inverter stage works at buck-boost model. The boost mode and buck-boost mode of the inverter stage are controlled in their respective half cycles to generate the required sinusoidal AC voltage at the output port.

Referring to FIG. 6, it is a time magnified graph of the inductor current, a waveform graph of the average value of the inductor current, and a waveform graph of the input voltage. Among them, the sine solid line is the waveform diagram of the input voltage, the sawtooth solid line is the time magnification diagram of the inductor current, and the dashed sine line is the waveform diagram of the average value of the inductor current. During the positive half cycle of the input voltage, when the instantaneous value of the input voltage is less than half the voltage of the DC bus, the rectification stage works in boost mode. When the instantaneous value of the input voltage is greater than half of the bus voltage, zero-voltage turn-on can be achieved only when the inductor current at the end of each switching cycle is less than i _boostmin . Therefore, the _second power switch S2 remains on for a period of time after the inductor current crosses zero to establish the required negative inductor current, thereby ensuring that the _first power switch S1 and the second power switch S1 Zero voltage turn _- on of S2. During the negative half cycle of the input voltage, the rectification stage works in a buck-boost mode, and the _third power switch S3 and the _fourth power switch S4 naturally realize zero-voltage turn-on. When the input voltage is less than the bus voltage, it works in the boost mode in the buck-boost mode. In this mode, the _third power switch S3 does not need the _fourth power switch S4 to be turned on for an additional period of time to achieve this. Zero voltage turn-on.

Referring to FIG. 7 , it is a block diagram of the controller in the rectification stage. In the proposed control, the rectification stage works in the BCM mode. By sensing the polarity of the input voltage, the controller is the first power switch S ₁ and the second power switch S 1 . S ₂ , the third power switch S ₃ , and the fourth power switch S ₄ generate gate driving signals. During the positive half cycle of the input voltage, the first power switch S ₁ is turned on t _onboost , and then the second power switch S ₂ is turned on until the inductor current drops below i _boostmin . During the negative half cycle of the input voltage, the third power switch S ₃ is turned on t _onbuck-boost , and then the fourth power switch S ₄ is turned on until the inductor current reaches zero.

Referring to FIG. 8, it is a control block diagram of a zero current detection circuit for the rectification stage. The zero current detection circuit senses the inductor current and utilizes two hysteretic comparators, one for each half input cycle. For the positive half cycle of the input voltage, when the inductor current falls below i _boostmin , the hysteresis comparator generates a trigger signal, similarly during the negative half cycle of the input voltage, when the inductor current reaches zero, the hysteresis trigger will A trigger signal is generated and the controller resets the PWM counter and starts the next switching cycle by detecting the trigger signal in every half cycle. The output voltage of the rectifier stage is adjusted through the low bandwidth voltage loop of the PI controller to output the on-time of the _first power switch S1 and the _third power switch S3.

Referring to Fig. 9, it is a block diagram of the controller of the inverter stage. For the inverter stage control, the inverter stage is mainly used to generate a sinusoidal AC voltage at the output, and the inverter stage also works in two working modes of boost and buck-boost. The inverter stage operates in continuous conduction mode (CCM) with a fixed switching frequency. For the control of the entire inverter stage, the voltage error signal is generated by comparing the sinusoidal reference voltage with the detected output voltage and sent to the controller of the inverter stage. The controller of the inverter stage includes two controllers and G cbuck and G _cbuck and G _cbuck-boost . For a positive output voltage half-cycle, the buck controller G _cbuck generates a duty cycle that controls the _fifth power switch S5, the output of the buck-boost controller G _cbuck-boost is ignored, and the eighth The power switch tube _S8 remains on. For a negative output voltage half cycle, the buck-boost controller G _cbuck-boost generates a duty cycle that controls the _seventh power switch S7, the output of the buck controller G _cbuck is ignored, and the sixth The power switch tube _S6 remains on.

Referring to FIG. 10 , it is the battery charging path in the normal operation mode of the battery interface architecture diagram. The battery interface includes a DC-DC converter, which is composed of the first power switch tube S _b1 on the battery side and the second power switch on the battery side. It consists of a tube S _b2 , a battery side inductance L _bat , the first fast relay S _R1 and the second fast relay S _R2 . In the normal operation mode, the battery is charged, the first fast relay S _R1 is turned on, the second fast relay S _R2 is turned off, and both the rectifier stage and the inverter stage are operating normally. In this mode, through the DC-DC conversion to charge the battery from the DC bus.

Referring to FIG. 11, it is the battery discharge path in the standby operation mode of the battery interface architecture diagram. When the power grid fails, the DC-DC converter is not used to supply power to the load. In this case, the first fast relay S _R1 is turned off. On, the second fast relay S _R2 is turned on, the battery is connected to the input end of the boost converter, and the boost converter is composed of a first power switch tube, a second power switch tube and an input inductor. The boost converter in the rectifier stage sets the rating for the output power of the system, delivering the power to the DC bus, thus ensuring continuous power output to the load through the inverter stage.

Example 1

An AC-DC-AC converter for an online UPS includes an AC input voltage source, a first power switch S ₁ , a second power switch S ₂ , a third power switch S ₃ , and a fourth power switch S ₄ , the fifth power switch tube S ₅ , the sixth power switch tube S ₆ , the seventh power switch tube S ₇ , the eighth power switch tube S ₈ , the input inductance, the output inductance, and the bus capacitance;

The first end of the AC input voltage source is connected to the source of the _third power switch S3, the second end of the AC input voltage source and the source of the _first power switch S1 are connected to the second and sixth ends of the bus capacitor. The source of the power switch _S6 is connected to the second end of the output end; the drain of the _third power switch S3 is connected to the source of the _fourth power switch S4 and the first end of the input inductor; the input inductor The second end of the power switch S2 is connected to the source of the _second power switch S2 and the drain of the first power switch S1 _; the drain of the _fourth power switch S4 and the drain of the _second power switch S2 It is connected to the first end of the bus capacitor and the drain of the _fifth power switch S5 and the drain of the _seventh power switch S7; the source of the _fifth power switch S5 is connected to the sixth power switch _S6 The drain of the output inductor is connected to the first end of the output inductor; the source of the _seventh power switch S7 is connected to the drain of the _eighth power switch S8 and the second end of the output inductor; the eighth power switch S7 The source of ₈ is connected to the first terminal of the output terminal.

The first power switch S ₁ , the second power switch S ₂ , the third power switch S ₃ , the fourth power switch S ₄ , the fifth power switch S ₅ , and the sixth power switch S ₆ , the seventh power switch tube S ₇ , and the eighth power switch tube S ₈ are both SiCMOSFET switch tubes.

The first power switch S ₁ , the second power switch S ₂ , the third power switch S ₃ , the fourth power switch S ₄ , the fifth power switch S ₅ , and the sixth power switch S ₆ , the seventh power switch tube S ₇ , and the eighth power switch tube S ₈ are all provided with diodes connected in parallel.

The first power switch S ₁ and the second power switch S ₂ are driven by complementary pulses.

The third power switch tube S ₃ and the fourth power switch tube S ₄ are driven by complementary pulses.

The fifth power switch S ₅ and the sixth power switch S ₆ are driven by complementary pulses.

The seventh power switch S ₇ and the eighth power switch S ₈ are driven by complementary pulses.

The first power switch S ₁ , the second power switch S ₂ , the third power switch S ₃ , and the fourth power switch S ₄ form a rectifier stage of the converter.

The first power switch tube S ₁ , the second power switch tube S ₂ , the third power switch tube S ₃ , and the fourth power switch tube S ₄ can all implement zero-voltage turn-on soft switching.

The fourth power switch tube S ₄ , the fifth power switch tube S ₅ , the sixth power switch tube S ₆ , and the seventh power switch tube S ₇ constitute the inverter stage of the converter.

A control method for an AC-DC-AC converter for an on-line UPS is: for the rectification stage control, the rectification stage of the converter works in two working modes of boost and buck-boost, in order to reduce the input inductance. size, operating at high frequencies. In order to maintain high efficiency at high switching frequency, the rectification stage operates in boundary conduction mode (BCM), thereby realizing zero-voltage turn-on (ZVS) of the power switch. During the positive half cycle of the input voltage, the rectifier stage operates in boost mode, the instantaneous value of the input voltage is less than half the DC bus voltage, when the instantaneous value of the input voltage is greater than half the DC bus voltage, only at the end of each switching cycle ZVS can only be realized when the inductance current is less than a certain negative value i _boostmin ; C _OSS is the parasitic capacitance of the _first power switch S1 and the _second power switch S2; the _second power switch S2 crosses zero when the inductor current crosses After that, it must be kept on for a period of time to establish the required negative inductor current to ensure the zero-voltage turn-on (ZVS) of the _first power switch S1; in the negative half cycle of the input voltage, the rectifier stage operates in buck-boost mode , the _third power switch S3 and the _fourth power switch S4 naturally realize zero voltage turn-on (ZVS), when the instantaneous value of the input voltage is less than the bus voltage, the _third power switch S3 and the fourth power switch S The buck-boost converter composed of ₄ always works in the boost mode. In this mode, the _third power switch S3 does not need the _fourth power switch S4 to be turned on for a period of time to achieve zero voltage turn-on (ZVS). In the control of the whole rectification stage, the rectification stage works in the BCM mode, and the first power switch S 1 , the second power switch S 2 , the third power switch S 3 , the first power switch S ₁ , the second power switch S ₂ , the third power switch S ₃ , The _fourth power switch S4 generates a gate drive signal; for a positive input voltage, the _first power switch S1 is _{turned on} for a long time, and then the _second power switch S2 is turned on until the inductor current drops to i _{boostmin is} below; for negative input voltage, the _third power switch S3 is turned on t _onbuck-boost for such a long time, and then the _fourth power switch S4 is turned on until the inductor current reaches zero; a zero is required in the whole control A current sense (ZCD) circuit that senses the inductor current and utilizes two hysteretic comparators, one for each half input cycle. For the positive half cycle of the input voltage, when the inductor current falls below i _boostmin , the hysteresis comparator generates a trigger signal, similarly during the negative half cycle of the input voltage, when the inductor current reaches zero, the hysteresis trigger will A trigger signal is generated, the controller resets the PWM counter and starts the next switching cycle by detecting the trigger signal in each half cycle; the output voltage of the rectifier stage is regulated by the low bandwidth voltage loop of the PI controller to output the first Turn-on time _of the power switch S1 and the _third power switch S3; for the inverter stage control, the inverter stage is mainly used to generate the sinusoidal AC voltage at the output, and the inverter stage also works in boost and buck-boost Operating mode. The inverter stage operates in continuous conduction mode (CCM) with a fixed switching frequency. For the control of the entire inverter stage, the voltage error signal is generated by comparing the sinusoidal reference voltage with the detected output voltage and sent to the controller of the inverter stage. The controller of the inverter stage includes two controllers and G cbuck and G _cbuck and G _cbuck-boost ; for a positive output voltage half cycle, the buck controller G _cbuck generates a duty cycle that controls the fifth power switch, and the output of the buck-boost controller G _cbuck-boost is ignored, so The eighth power switch tube is kept on; for a negative half cycle of the output voltage, the buck-boost controller G _cbuck-boost generates a duty cycle that controls the seventh power switch tube S ₇ , and the output of the buck controller G _cbuck If ignored, the sixth power switch tube _S6 remains on.

其中C_oss为功率开关管的寄生电容。Further, i _boostmin is less than or equal to

Among them, C _oss is the parasitic capacitance of the power switch tube.

The above content is only to illustrate the technical idea of the present invention, and cannot limit the protection scope of the present invention. Any changes made on the basis of the technical solution according to the technical idea proposed by the present invention all fall within the scope of the claims of the present invention. within the scope of protection.

Claims (9)

1. The AC-DC-AC converter for online UPS includes AC input voltage source Vin, the first power switch tube S₁A second power switch tube S₂Third powerSwitch tube S₃Fourth power switch tube S₄The fifth power switch tube S₅Sixth power switch tube S₆Seventh power switch tube S₇The eighth power switch tube S₈An input inductor L_inAn output inductor L_outBus capacitor C_bus；

The first end of the AC input voltage source Vin and the third power switch tube S₃Is connected with the second end of the AC input voltage source Vin and the first power switch tube S₁Source electrode and bus capacitor C_busSecond terminal and sixth power switch tube S₆The source electrodes of the first and second transistors are connected with the second end of the output end; third power switch tube S₃And a fourth power switch tube S₄Source and input inductance L of_inAre all connected; input inductance L_inAnd a second terminal of the second power switch tube S₂Source electrode and first power switch tube S₁The drain electrodes of the two are all connected; fourth power switch tube S₄And a second power switch tube S₂Drain electrode and bus capacitor C_busAre all connected; fifth power switch tube S₅Drain electrode of and seventh power switch tube S₇Is connected with the drain electrode of the transistor; fifth power switch tube S₅Source electrode of and sixth power switch tube S₆Drain of and output inductor L_outIs connected with the first end of the first connecting pipe; seventh power switch tube S₇Source electrode of and eighth power switch tube S₈Drain of and output inductor L_outThe second ends of the two are connected; eighth power switch tube S₈Is connected to the first end of the output terminal.

2. An AC-DC-AC converter for an online UPS as defined in claim 1 in which the first power switch S is a single transistor₁A second power switch tube S₂The third power switch tube S₃Fourth power switch tube S₄The fifth power switch tube S₅Sixth power switch tube S₆Seventh power switch tube S₇The eighth power switch tube S₈Are all SiCMOS switch tubes.

3. An AC-DC-AC converter for an online UPS as defined in claim 1 in which the first power switch S is a single transistor₁A second power switch tube S₂The third power switch tube S₃The fourth power switch tube S₄The fifth power switch tube S₅Sixth power switch tube S₆Seventh power switch tube S₇The eighth power switch tube S₈Are provided with diodes connected in parallel.

4. An AC-DC-AC converter for an online UPS as defined in claim 1 wherein the first power switch S₁A second power switch tube S₂The third power switch tube S₃The fourth power switch tube S₄The fifth power switch tube S₅Sixth power switch tube S₆Seventh power switch tube S₇The eighth power switch tube S₈Driven by complementary pulses.

5. An AC-DC-AC converter for an online UPS as defined in claim 1 wherein the first power switch S₁A second power switch tube S₂The third power switch tube S₃Fourth power switch tube S₄Constituting the rectifier stage of the converter.

6. An AC-DC-AC converter for an online UPS as defined in claim 1 in which the first power switch S is a single transistor₁A second power switch tube S₂The third power switch tube S₃The fourth power switch tube S₄The soft switch can realize zero voltage switching.

7. An AC-DC-AC converter for an online UPS as defined in claim 1 in which the fourth power switch S₄The fifth power switch tube S₅Sixth power switch tube S₆Seventh power switch tube S₇Forming the inverter stage of the transformer.

8. A method of controlling an AC-DC-AC converter for an online UPS according to claim 1, comprising the steps of:

for the control of the rectification stage, the rectification stage of the converter works in two working modes of boost and buck-boost, and in order to reduce the size of input inductance, the converter operates at high frequency; in order to keep high efficiency under high switching frequency, the rectification stage works in a boundary conduction mode to operate, so that the power switching tube is switched on at zero voltage;

in the positive half period of the input voltage, the rectification stage operates in a boost mode, and the instantaneous value of the input voltage is less than half of the voltage of the direct current bus; when the instantaneous value of the input voltage is greater than half the dc bus voltage, only the inductor current at the end of each switching cycle is less than a negative value i_boostminWhen the voltage is zero, zero voltage switching-on can be realized; c_OSSIs a first power switch tube S₁And a second power switch tube S₂The parasitic capacitance of (2); second power switch tube S₂The first power switch tube S can be ensured to be switched on for a period of time to establish the required negative inductive current after the inductive current is zero-crossed₁Zero voltage of (2) is turned on;

during the negative half-cycle of the input voltage, the rectifier stage operates in buck-boost mode, the third power switch S₃And a fourth power switch tube S₄Naturally realizing zero voltage switching-on, and when the instantaneous value of the input voltage is less than the bus voltage, the third power switch tube S₃And a fourth power switch tube S₄The buck-boost converter is always operated in boost mode, and in the boost mode, the third power switch tube S₃Does not need a fourth power switch tube S₄Switching on for a period of time to achieve zero voltage turn-on;

in the control of the whole rectification stage, the rectification stage works in a boundary conduction mode, and the first power switch tube S is controlled by sensing the polarity of the input voltage₁A second power switch tube S₂The third power switch tube S₃The fourth power switch tube S₄A drive signal of the gate; when the input voltage is greater than zero, the first power switch tube S₁First turn on t_onboostThen the second power switch tube S₂Is turned on until the inductor current drops to i_boostminThe following; when the input voltage is less than zero, the third power switch tube S₃First on t_onbuck-boostThen the fourth power switch tube S₄Switching on until the inductor current reaches zero; a zero current detection circuit is needed in the whole control, the zero current detection circuit induces an inductive current, and two hysteresis comparators are utilized, and each half input period corresponds to one hysteresis comparator; in the positive half period of the input voltage, the inductor current drops to i_boostminWhen the inductive current reaches zero in the negative half cycle of the input voltage, the hysteresis trigger generates a trigger signal, and the controller resets the PWM counter and starts the next switching cycle by detecting the trigger signal in each half cycle; the output voltage of the rectifier stage is regulated by the low-bandwidth voltage loop of the PI controller to control the first power switch tube S₁And a third power switch tube S₃On-time of (d);

for the control of the inversion stage, the inversion stage is mainly used for generating sine alternating-current voltage of an output end, and the inversion stage also works in two working modes of boost and buck-boost; the inverter stage works in a continuous conduction mode with fixed switching frequency;

in the whole inversion stage control, a voltage error signal is generated by comparing a sinusoidal reference voltage with a detected output voltage and is sent to a controller of an inversion stage, wherein the controller of the inversion stage comprises two controllers G_cbuckAnd G_cbuck-boost(ii) a When the output voltage is greater than zero, the controller G of buck_cbuckControlling a fifth power switch transistor S₅Duty cycle of (3), buck-boost controller G_cbuck-boostThe output of the eighth power switch tube is ignored, and the eighth power switch tube is kept on; when the output voltage is less than zero, buck-boost controller G_cbuck-boostController G for controlling duty ratio and buck of seventh power switch tube_cbuckThe output of the sixth power switch tube is ignored, and the sixth power switch tube is kept on.

9. An AC-DC-AC converter and control strategy for an online UPS according to claim 8 where a single DC bus is used between the rectification and inverter stages.

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