CN110148944B - High-power-density island interactive UPS and comprehensive control method thereof - Google Patents

Abstract

The invention discloses a high-power density island interactive UPS and a comprehensive control method thereof. The UPS rectifier is used for controlling charging and discharging of the battery and simultaneously used for improving the problems of harmonic pollution and reactive injection of a power grid caused by nonlinear load access. When the power supply of the island fails, the energy storage battery pack supplies power, and the two converters output power supply voltage together to provide continuous and reliable voltage for the load. Under such conditions, the power density is higher than that of a conventional UPS because the current stress experienced by each converter is reduced by half as the outputs of the two converters are connected in parallel. The invention can reduce the capacity and volume of the UPS device, and can be widely applied to occasions with large harmonic pollution and high requirement on the reliability of the power supply.

Description

A high power density island interactive UPS and its comprehensive control method

technical field

The present invention is in the technical field of UPS control, in particular to a high-power density sea-island interactive UPS comprehensive control method.

Background technique

With the further development of modern network technology and information industry, the losses caused by the interruption of the power supply of many important loads of electronic equipment have become more and more serious. Uninterruptible Power Supply (UPS) can provide continuous, high-quality, high-efficiency and reliable AC power to the load, and has protection and detection functions. Applications.

As more and more nonlinear loads are connected to the island power system, the harmonic pollution of the island power system is becoming more and more serious. Traditional UPS seldom considers harmonics and reactive power pollution caused by nonlinear loads, as well as reasonable switching between charging and discharging of energy storage batteries and controlling the DC side voltage. Considering that the UPS of the online interactive structure is normally powered by the mains, one side charges the battery through the mains, and the other side controls and compensates the mains supply voltage. Therefore, it is considered that the mains is charging and discharging the battery through the converter at the same time. , Additional power grid harmonic and reactive current compensation control, improve power quality, and after the mains fault bypass, the two converter outputs of the UPS are connected in parallel to supply power, which reduces the design capacity of the UPS and improves the power density. Therefore, based on the online interactive UPS structure, a reasonable control method is required to ensure that when the mains power fluctuates, the inverter compensates for the quality of the island power supply voltage, and the rectifier compensates for the power quality of the grid; after the mains failure, the inverter and rectifier are connected in parallel. When outputting the supply voltage, the current stress of each converter is reduced by half, and the power density is improved.

SUMMARY OF THE INVENTION

The invention aims to provide a high power density island interactive UPS and a comprehensive control method thereof. When the mains power fluctuates, the inverter compensates for the quality of the island power supply voltage, and the rectifier compensates for the power quality of the grid; after the mains failure, the inverter, The rectifiers are connected in parallel to output the supply voltage, the current stress of each converter is reduced by half, and the power density is improved.

In order to solve the above-mentioned technical problems, the technical scheme adopted in the present invention is: a high power density island interactive UPS, which includes a filter, a static switch, a transformer, an inverter, a rectifier, an energy storage battery pack and a controller; The filter is connected to the mains output end, the static switch is connected between the filter output end and the transformer input end; the inverter and the rectifier are respectively connected to the two isolated ports of the transformer, and the energy storage battery is connected to On the DC bus lines of the two converters; the controller is connected to the sampling circuit and drives the inverter and the rectifier through the drive protection circuit.

The comprehensive control method of the present invention includes an inverter control part and a rectifier control part:

The inverter control part includes:

1) Detect mains output voltage u _s , load current i _L , inverter input current i _inv and output voltage u _inv , rectifier input current i _rec and output voltage u _rec , DC side voltage u _dc ;

2) Calculate the synchronous phase angle θ _s by calculating the mains output voltage u _s through the phase-locked loop, and detect whether the mains is faulty;

3) If the mains fails, turn off the static switch, synthesize and calculate the load reference voltage amplitude U ^* _L and the synchronous phase angle θ _s , and obtain u ^* _L as the output voltage command of the inverter, the output voltage command and its actual output. The difference of the voltage u _inv is sent to the PI controller to obtain the inner loop reference current i _invr , and then through the proportional resonance control to achieve no static error tracking; when the mains fails, the rectifier switches to V/F control, and the output voltage is controlled by PI. Obtain the inner loop current command i _rec1 ; if the mains is normal, lag the mains output voltage u _s by 90° to obtain the voltage component corresponding to the β axis, and then through αβ/dq transformation to obtain the voltage components _ud , u in the rotating coordinate system _q , calculate the q-axis component u _ql of the load reference voltage according to the load reference voltage amplitude U ^* _L ;

再与输出电压u_s相减最终得到逆变器的输出电压指令，输出电压指令与实际输出电压u_inv做差送入PI控制器，得到内环参考电流i_invr，内环参考电流i_invr经过比例谐振控制得到逆变器的驱动信号；4) Transform u _d and u _ql to αβ coordinates to obtain the load reference output voltage

Then subtract the output voltage u _s to finally obtain the output voltage command of the inverter. The difference between the output voltage command and the actual output voltage u _inv is sent to the PI controller to obtain the inner loop reference current i _invr , and the inner loop reference current i _invr passes through The proportional resonance control obtains the drive signal of the inverter;

The rectifier control part includes:

1) Multiply the load current i _L and the mains voltage synchronization signal sinθ _s , and the product is multiplied by a low-pass filter and a coefficient 2 to obtain the peak value of the active current of the load; the peak value of the active current of the load is used to obtain the compensation current that the UPS needs to compensate for reference quantity i _p ;

2) Subtract the DC side voltage u _dc and the DC voltage reference value u _dcn , the obtained error signal is multiplied by the grid voltage synchronization signal sinθ _s after passing through the PI controller, superimposed on the compensation current reference value _ip , and finally the UPS is obtained. Rectifier input current reference value i _recr2 ;

3) Difference between the UPS rectifier input current reference value i _recr2 and the rectifier input current i _rec , obtain the inverter modulated wave through the proportional resonance and harmonic compensation controller, and then compare it with the carrier to obtain the rectifier drive signal.

After the mains failure, if the battery has been discharged so that the DC side voltage u _dc <0.6u _dcn , the quality of the UPS output voltage will deteriorate, so turn off the UPS output and wait for the mains to return to normal.

In the present invention, the expressions of the voltage components _ud and u _q in the rotating coordinate system are:

The q-axis component u _ql of the load reference voltage is expressed as:

In the present invention, the process of using the load active current peak value to obtain the compensation current reference value ip to be compensated by the _UPS includes: using the load active current peak value to calculate the DC part of the h-th harmonic current, filtering and extracting the DC part and multiplying the Taking the power grid voltage synchronization signals _{sinθ s} and 2, and then subtracting it from the load current, the reference amount ip of the compensation current that the UPS needs to compensate when the mains is normal can be obtained.

The transfer function after the combination of proportional resonance and harmonic compensation controller is:

Among them, K _p is the proportional coefficient, K _r is the fundamental wave resonance coefficient, K _rh is the resonance coefficient of the h-th harmonic, h is the characteristic harmonic of the load, and ω is the grid angular frequency.

Compared with the prior art, the present invention has the beneficial effects as follows: the present invention can supply power to the load through a filter, a static switch and a transformer when the commercial power is normally supplied, and in order to maintain the stability of the power supply voltage, the UPS inverter compensates the load. At the same time, in order to improve the power quality problems caused by nonlinear load access, the rectifier outputs compensation current to offset harmonics and reactive currents; when the power supply is powered off, the energy storage battery pack supplies power, and the two converters are connected in parallel Output power supply voltage. At this time, the two converters work in the V/f control mode at the same time, providing continuous and reliable voltage for the load and improving the UPS power density (when the island power supply fails, the energy storage battery pack is used to supply power, and the two converters are powered by the energy storage battery pack. Common output supply voltage to provide continuous and reliable voltage for the load. In this case, due to the parallel connection of two converters, the current stress of each converter is reduced by half, so the power density is higher than that of traditional UPS). On the basis of improving the quality of the power supply voltage, the invention realizes compensation for harmonics and reactive power pollution caused by the non-linear load of the island to the power system. The circuit is simple, the cost is low, and the efficiency is high. In occasions, it is especially suitable for the power supply of isolated electrical equipment. The invention can reduce the capacity and volume of the UPS device, and can be widely used in the occasions where the harmonic pollution is large and the reliability of the power supply is high.

Description of drawings

FIG. 1 is a schematic structural diagram of a high-power-density sea-island interactive UPS according to an embodiment of the present invention;

FIG. 2 is a control block diagram of a high power density island interactive UPS inverter according to an embodiment of the present invention;

FIG. 3 is a control block diagram of a high power density sea-island interactive UPS rectifier according to an embodiment of the present invention;

FIG. 4 is a schematic diagram of a working mode switching process of a high power density sea-island interactive UPS according to an embodiment of the present invention.

Detailed ways

1 is a schematic structural diagram of a high power density island interactive UPS according to an embodiment of the present invention, including a filter, a static switch, an inverter, a rectifier, a transformer, an energy storage battery pack and a controller; the filter is connected to the mains output The static switch is connected between the output end of the filter and the input end of the transformer; the inverter and the rectifier are connected to the two isolated ports of the transformer, and the energy storage battery pack is connected to the DC bus of the two converters The controller is connected to the sampling circuit and the drive protection circuit of the converter; the two converters both adopt an H-bridge structure composed of IGBTs. The control system includes a controller, a sampling circuit and a drive protection circuit.

2 and 3 are control block diagrams of a high-power-density sea-island interactive UPS according to an embodiment of the present invention, which are mainly composed of a fault detection module, a phase-locked loop module, an inverter compensation voltage calculation module, a load supply voltage control module, and a rectifier compensation current calculation module. module, DC side voltage regulation control module, proportional resonance and harmonic compensation control module, the specific control strategy includes the following steps:

1) Detect mains output voltage u _s , load current i _L , inverter input current i _inv and output voltage u _inv , rectifier input current i _rec and output voltage u _rec , DC side voltage u _dc ;

2) Calculate the synchronous phase angle θ _s by calculating the mains output voltage u _s through the phase-locked loop, and detect whether the mains is faulty;

3) If the mains fails, turn off the static switch, and synthesize the load reference voltage amplitude U ^* _L and the synchronous phase angle θ _s to obtain u ^* _L as the output voltage command of the inverter, and make the difference with the actual output voltage u _inv It is sent to the PI controller, and the PI output obtains the inner loop reference current i _invr , which is then controlled by proportional resonance to achieve no static error tracking; when the mains fails, the rectifier is also switched to V/F control, and the output voltage is controlled by PI to obtain the internal The loop current command i _rec1 , because its output voltage command and voltage outer loop current inner loop control mode are the same as those of the inverter, the outputs of the two converters are connected in parallel, so the current stress suffered is reduced by half, and the power density is improved;

4) If the mains is normal, lag the power supply voltage u _s sampled in step 1) by 90° to obtain the voltage component corresponding to the β-axis, and then undergo αβ/dq transformation to obtain the voltage components _ud , u _q in the rotating coordinate system, Its formula is:

Then calculate the q-axis component u _ql of the load reference voltage according to the load reference voltage amplitude U ^* _L , the formula is as follows:

再与供电电压u_s相减最终得到逆变器的输出电压指令，再将其与实际输出电压u_inv做差送入PI控制器，输出得到内环参考电流i_invr，经过比例谐振控制得到逆变器的驱动信号；Transform u _d and u _ql to αβ coordinates to get the load reference output voltage

Then subtract it from the power supply voltage u _s to finally get the output voltage command of the inverter, and then send it to the PI controller to make a difference with the actual output voltage u _inv , and output the inner loop reference current i _invr , which is obtained through proportional resonance control. The drive signal of the inverter;

5) Multiply the load current i _L detected in step 1) and the mains voltage synchronization signal sinθ _s detected in step 2), and then pass through the low-pass filter and multiply by the coefficient 2 to obtain the peak value of the load active current. The calculation formula as follows:

Among them, I _mh and φ _h are the amplitude and power factor angle of the h-th harmonic current respectively (h=1, 2, ...). It can be seen that the DC part is half of the peak value of the active current of the load. After multiplying by the grid voltage synchronization signal _{sinθ s} and 2, and then subtracting it from the load current, the reactive power and harmonic reference quantities ip to be compensated by the UPS when the mains is normal can be obtained;

6) Subtract the DC side voltage u _dc sampled in step 1) from the DC voltage reference value u _dcn to obtain an error signal, which is multiplied by the grid voltage synchronization signal sinθ _s after passing through the PI controller, and superimposed on the result obtained in step 5). Compensation current reference value i _p , and finally obtains the UPS rectifier input current reference value i _recr2 ;

7) Difference between the rectifier current reference command value obtained in step 3) or step 6) and the current value i _rec obtained by sampling, obtain the inverter modulated wave through the proportional resonance and harmonic compensation controller (PR+HC), and then Comparing with the carrier to get the drive signal of the converter, the transfer function of the controller is as follows:

where K _p is the proportional coefficient, K _r is the fundamental wave resonance coefficient, K _rh is the resonance coefficient of the h-th harmonic, h is the characteristic harmonic of the load, and ω is the grid angular frequency;

8) After the mains failure, if the battery has been discharged so that the DC side voltage u _dc <0.6u _dcn , the UPS output voltage quality has deteriorated, and the UPS output needs to be turned off to wait for the mains to return to normal.

4 is a schematic diagram of a working mode switching process of a high-power-density sea-island interactive UPS according to an embodiment of the present invention, which specifically includes the following steps:

Step 1: Determine whether the mains is faulty. If the mains is normal, the UPS rectifier will absorb the active power from the mains to charge the battery, stabilize the DC side voltage, and control the output compensation current to improve the power quality of the mains; the UPS inverter outputs Compensate for mains voltage fluctuations and improve power supply voltage quality;

Step 2: If the mains fails, judge whether the DC side voltage is less than 0.6 times the rated value, if it is less than, turn off the UPS and wait for the mains to recover. If it is greater than, go to step 3;

Step 3: Powered by the energy storage battery, the two converters are isolated and output in parallel through the transformer to provide a stable voltage for the load.

Claims (6)

1. A comprehensive control method for a high power density island interactive UPS, the high power density island interactive UPS comprises a filter, a static switch, a transformer, an inverter, a rectifier, an energy storage battery pack and a controller; the filter Connected to the mains output end, the static switch is connected between the filter output end and the transformer input end; the inverter and the rectifier are respectively connected to the two isolated ports of the transformer, and the energy storage battery pack is connected to the two on the DC bus of the converter; the controller is connected to the sampling circuit and drives the inverter and the rectifier through the drive protection circuit; it is characterized in that it includes: 1) Detect mains output voltage u _s , load current i _L , inverter input current i _inv and output voltage u _inv , rectifier input current i _rec and output voltage u _rec , DC side voltage u _dc ; 2) Calculate the synchronous phase angle θ _s by calculating the mains output voltage u _s through the phase-locked loop, and detect whether the mains is faulty; 3) If the mains is normal, in the UPS inverter control, take the mains output voltage u _s as the voltage component u _α of the α axis, and lag it by 90° to obtain the voltage component u _β corresponding to the β axis, and then pass through αβ. /dq transformation to obtain the voltage components _ud and u _q in the rotating coordinate system, and calculate the q-axis component u _ql of the load reference voltage according to the load reference voltage amplitude U ^* _L ; 4) Transform u _d and u _ql to αβ coordinates to obtain the load reference output voltage

Then subtract the output voltage u _s to finally obtain the output voltage command of the inverter. The difference between the output voltage command and the actual output voltage u _inv is sent to the PI controller to obtain the inner loop reference current i _invr , and the inner loop reference current i _invr passes through The proportional resonance control realizes tracking without static error, and then the output of the proportional resonance controller is compared with the carrier wave to obtain the drive signal of the inverter; 5) In the UPS rectifier control, the load current i _L is multiplied by the mains voltage synchronous signal sinθ _s , and the product passes through the low-pass filter and is multiplied by the coefficient 2 to obtain the load active current peak value; use the load active current peak value to obtain Compensation current reference ip to be compensated by the _UPS ; 6) Subtract the DC side voltage u _dc and the DC voltage reference value u _dcn , the obtained error signal is multiplied by the grid voltage synchronization signal sinθ _s after passing through the PI controller, and superimposed on the compensation current reference value _ip , and finally the UPS is obtained. Rectifier input current reference value i _recr2 ; 7) Make a difference between the UPS rectifier input current reference value i _recr2 and the rectifier input current i _rec , obtain the rectifier modulation wave through the proportional resonance and harmonic compensation controller, and then compare with the carrier to obtain the rectifier drive signal; 8) If the mains fails, turn off the static switch, synthesize and calculate the load reference voltage amplitude U ^* _L and the synchronous phase angle θ _s , and obtain the common output voltage command u ^* _L of the inverter and the rectifier; 9) In the UPS inverter control, the difference between u ^* _L and the actual output voltage u _inv of the inverter is sent to the PI controller, and the inner loop reference current i _invr is obtained. The inner loop reference current i _invr is controlled by proportional resonance and generated. After comparing with the carrier, the inverter drive signal is obtained; 10) In the UPS rectifier control, the rectifier is switched to V/F control, and the difference between u ^* _L and the actual output voltage u _rec of the rectifier is sent to the PI controller to obtain the rectifier inner loop current command i _rec1 , and then through proportional resonance control and The rectifier drive signal is obtained after comparing with the carrier. 2. The comprehensive control method of the sea-island interactive UPS according to claim 1, characterized in that, after a mains failure, if the battery is always discharged so that the DC side voltage u _dc <0.6u _dcn , the quality of the UPS output voltage becomes worse , turn off the UPS output and wait for the utility power to return to normal. 3. the comprehensive control method of high power density sea-island interactive UPS according to claim 1, is characterized in that, the expression of voltage component _ud under the rotating coordinate system, u _q is:

4. the comprehensive control method of high power density sea-island interactive UPS according to claim 1, is characterized in that, the q-axis component u _ql expression of load reference voltage is:

5. The comprehensive control method of the high power density sea-island interactive UPS according to claim 1, wherein the process of obtaining the compensation current reference value i _p that the UPS needs to compensate by utilizing the load active current peak value comprises: utilizing the load active current peak value Calculate the DC part of the hth harmonic current from the peak current value, filter and extract the DC part, multiply it by the grid voltage synchronization signal sinθ _s and 2, and then subtract it from the load current to obtain the compensation that the UPS needs to compensate when the mains is normal. Current reference quantity i _p . 6. the comprehensive control method of high power density sea-island interactive UPS according to claim 1, is characterized in that, the transfer function after proportional resonance and harmonic compensation controller are combined is:

Among them, K _p is the proportional coefficient, K _r is the fundamental wave resonance coefficient, K _rh is the resonance coefficient of the h-th harmonic, h is the characteristic harmonic of the load, and ω is the grid angular frequency.

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