CN101814752A - Control system and method of UPS (Uninterrupted Power System) - Google Patents

Abstract

The invention discloses a UPS control system, which performs double-closed-loop control on the UPS. The double-closed loops include a current loop as an inner loop and a voltage loop as an outer loop. In the current loop, the inverter current given value and inverter The feedback value of the current takes the difference, and the control amount of the inverter voltage is obtained through the proportional adjustment of the current loop proportional coefficient; the control system includes a current loop proportional coefficient adjustment module, which includes a detection unit and a coefficient given unit. The detection unit is used for Detect whether the UPS satisfies the bus overvoltage control condition. The coefficient setting unit is used to set the current loop proportional coefficient to the smaller value of the two preset current loop proportional coefficients when the bus overvoltage control condition is satisfied. When the voltage control condition is not satisfied, the current loop proportional coefficient is taken as the larger value of the two preset current loop proportional coefficients. Also disclosed is a UPS control method. The invention can solve the overvoltage problem of the bus bar at a lower cost, and reliably enhance the capacity of the UPS system with inductive loads.

Description

UPS control system and method

technical field

The present invention relates to an uninterruptible power supply (Uninterruptable Power Supply, UPS), in particular to a UPS control system and method.

Background technique

At present, many UPSs are not capable of carrying inductive loads due to the limitation of their own topology. For example, they cannot carry inductive loads with large power factors, such as motors. As shown in Figure 1, a general double-conversion UPS with single input and single output includes a rectification part and an inverter part. The rectification part adopts a BOOST converter, and the inverter part adopts a three-level topology. When the inductive load L3 is suddenly added, a large current DC component will be generated instantaneously. When the inverter voltage is positive and the inverter current flowing through the inverter inductor L2 is negative, as shown in the direction of the dotted arrow in Figure 1, The inverter current will continuously charge the positive bus capacitor C1 through the body diode of the upper supervisor Q3. Because the DC component of the current flowing through the inverter inductance L2 is large, the current cannot flow through the diode D3 due to the reverse blocking effect of the diode D3, so the energy poured into the positive bus capacitor C1 is greater than the energy consumed by the inductive load L3. Finally, the positive bus voltage will become higher and higher, which will lead to overvoltage of the positive bus capacitor C1 after several power frequency cycles. Similarly, when the inverter current is reversed, the negative bus capacitor C2 will also experience overvoltage.

As mentioned above, if the rectification part of the UPS adopts a BOOST converter or a similar topology, the bus overvoltage problem will occur when the UPS has an inductive load with a relatively large power factor (close to an ideal inductor). In order to solve the bus overvoltage problem, a known solution is to use a capacitor with a higher withstand voltage as the positive bus capacitor, but this solution that relies on hardware modification requires a lot of extra cost.

Contents of the invention

The main purpose of the present invention is to provide a UPS control system and method to solve the problem of busbar overvoltage at relatively low cost.

To achieve the above object, the present invention adopts the following technical solutions:

A control system of UPS, said UPS includes a rectification part and an inverter part sequentially connected between an AC power supply and a load, and is characterized in that:

The control system includes a PID controller, which is used to perform double closed-loop control on the UPS. The double closed loop includes a current loop as an inner loop and a voltage loop as an outer loop. In the voltage loop, the inverter The difference between the given voltage value and the feedback value of the inverter voltage is taken, and the given value of the inverter current is obtained through proportional integral adjustment. In the current loop, the feedback of the given value of the inverter current and the inverter current The difference is taken as the value, and the control amount about the inverter voltage is obtained through the proportional adjustment of the proportional coefficient of the current loop, wherein the inverter voltage is the output voltage of the inverter part, and the inverter current is the inverter The output current of the changing part;

The control system also includes a current loop proportional coefficient adjustment module, which includes a detection unit and a coefficient setting unit, the detection unit is used to detect whether the UPS meets the bus overvoltage control condition, and the coefficient setting unit is used for When the bus overvoltage control condition is satisfied, the current loop proportional coefficient is taken as the smaller value of the two preset current loop proportional coefficients; when the bus overvoltage control condition is not satisfied, the current loop proportional coefficient is set to The loop proportional coefficient is taken as the larger value among the two preset current loop proportional coefficients.

Preferably, the detection unit includes a current calculation unit and a first judgment unit, the current calculation unit is used to calculate the reactive current in the load current on the load, and the first judgment unit is used to convert the reactive current The power current is compared with the set threshold value, and when the reactive current is greater than the threshold value, it is judged that the bus overvoltage control condition is satisfied, otherwise it is judged that the bus overvoltage control condition is not satisfied.

Preferably, the reactive current is obtained by calculating the reactive components of the load current at multiple sampling points within one power frequency cycle by the current calculation unit and taking an average value.

Preferably, the detection unit includes a second judging unit, which is used to compare the bus voltage with a set voltage reference value, and compare the inverter current with a set current reference value, when the bus When the voltage is greater than the voltage reference value and the inverter current is greater than the current reference value, it is determined that the bus overvoltage control condition is satisfied; otherwise, it is determined that the bus overvoltage control condition is not satisfied.

Preferably, the control amount related to the inverter voltage is a control amount for generating SPWM, and the inverter voltage is generated by the SPWM.

A control method for UPS, characterized in that:

The control method includes performing double-closed-loop control on the UPS. The double-closed-loop includes a current loop as an inner loop and a voltage loop as an outer loop. In the voltage loop, the inverter voltage given value and inverter The feedback value of the voltage takes the difference, and after proportional integral adjustment, the given value of the inverter current is obtained. In the current loop, the difference between the given value of the inverter current and the feedback value of the inverter current is taken, and the current The proportional adjustment of the loop proportional coefficient obtains the control amount about the inverter voltage; wherein, the current loop proportional coefficient is adjusted through the following steps:

A. Detect whether the UPS satisfies the busbar overvoltage control condition;

B. When the busbar overvoltage control condition is satisfied, the current loop proportional coefficient is taken as the smaller value of the two preset current loop proportional coefficients;

C. When the busbar overvoltage control condition is not satisfied, the current loop proportional coefficient is taken as the larger value of the two preset current loop proportional coefficients.

Preferably, step A comprises the following steps:

A11. Calculate the reactive current in the load current;

A12. Comparing the reactive current with the set threshold value, when the reactive current is greater than the threshold value, it is judged that the busbar overvoltage control condition is satisfied, otherwise it is judged that the busbar overvoltage control condition is not satisfied .

Preferably, in step A11, the reactive current is obtained by calculating the reactive components of the load current at multiple sampling points within one power frequency cycle and taking an average value.

Preferably, the calculation of the reactive component adopts Fourier transform, which is obtained by multiplying the cosine value of the angle between the inverter current and the inverter voltage corresponding to the power frequency cycle by the instantaneous value of the load current.

Preferably, step A comprises the following steps:

A21. Detect bus voltage and inverter current; and

A22. Compare the bus voltage with the set voltage reference value, and compare the inverter current with the set current reference value. When the bus voltage is greater than the voltage reference value and the inverter current is greater than If the current reference value is equal to the current reference value, it is judged that the bus overvoltage control condition is satisfied; otherwise, it is judged that the bus overvoltage control condition is not satisfied.

The beneficial technical effect of the present invention is:

The control system according to the present invention adopts PID double closed-loop control. In the current loop as the inner loop, the difference between the given value of the inverter current and the feedback value of the inverter current is taken, and the ratio of the proportional coefficient of the current loop is adjusted to obtain about The control amount of the inverter voltage. In the above closed-loop control system, by using a small current loop proportional coefficient, the bus voltage rise can be effectively suppressed, mainly because the small current loop proportional coefficient makes the inverter voltage obtain a relatively large overshoot, which increases the The loss of bus energy, so as to avoid bus overvoltage. However, for system indicators with non-inductive loads, typical system indicators such as resistive loads and rectifier loads in terms of THD (total harmonic distortion, total harmonic distortion), a relatively large current loop proportional coefficient is required to be able to meet the requirements. Therefore, in the present invention, it is first detected whether the UPS satisfies the bus overvoltage control condition, and when the bus overvoltage control condition is satisfied, the smaller current loop proportional coefficient among the two preset current loop proportional coefficients is adopted; otherwise, the larger current loop proportional coefficient is adopted. Ring proportional coefficient, so as to be able to take into account the system indicators. For example, according to the nature of the system load, it is judged whether the busbar overvoltage control condition is satisfied, and only a small current loop proportional coefficient is used when it is judged to be an inductive load, so as to avoid the problem that the inductive load is likely to cause the busbar overvoltage, and increase the system with inductive load. Ability. Compared with the traditional solution, the present invention can fundamentally avoid the problem of bus overvoltage and can take into account other indicators when the UPS has a non-inductive load, without additionally using high-cost high-voltage-resistant capacitors as bus capacitance, thus reducing the cost of the system.

Description of drawings

Figure 1 is a circuit structure diagram of a single-input single-output double-conversion UPS;

Fig. 2 is a control schematic diagram of an embodiment of the present invention;

Fig. 3 is the structural block diagram of the current loop proportional coefficient adjustment module in the control system of the present invention;

Fig. 4 is a structural block diagram of a current loop proportional coefficient adjustment module of an embodiment;

Fig. 5 is the structural block diagram of the current loop proportional coefficient adjustment module of another embodiment;

Fig. 6 is the basic flowchart of adjusting the current loop proportional coefficient in the control method of the present invention;

Fig. 7 is a flow chart of an embodiment judging whether the UPS satisfies the busbar overvoltage control condition;

Fig. 8 is a specific flow chart corresponding to the embodiment of Fig. 7 for adjusting the proportional coefficient of the current loop;

Fig. 9 is a flow chart of another embodiment for judging whether the UPS satisfies the bus overvoltage control condition.

Detailed ways

The present invention will be further described in detail below through embodiments in conjunction with the accompanying drawings.

In one embodiment, as shown in Figure 1, the UPS includes a rectification part and an inverter part connected in sequence between the AC power supply and the load, and the control system of the present invention is used to carry out PID (proportional integral derivative) to the UPS Double closed-loop control. Figure 2 shows the control schematic diagram of the UPS. This double closed loop includes an outer loop and an inner loop, the outer loop is a voltage loop, which adopts proportional integral regulation, and the inner loop is a current loop, which adopts proportional regulation. In the voltage loop, take the difference between the given inverter voltage Vref and the feedback value Vinv of the inverter voltage, and adjust the proportional integral link Upi to obtain the given value of the inverter current; in the current loop, the inverter current given The difference between the fixed value and the feedback value Il of the inverter current is obtained to obtain the current loop error. After the current loop error is adjusted at least through the ratio of the current loop proportional coefficient Ip, the control amount about the inverter voltage is obtained, preferably SPWM (sinusoidal Pulse Width Modulation) wave to get the control amount of the corresponding inverter voltage. In the present invention, the inverter voltage refers to the output voltage of the inverter part, and the inverter current refers to the output current of the inverter part (ie, the front-end current of the load).

(包括一个比例环节和一个延时环节)，控制对象是逆变电感L2。In the above double closed loop, the proportional coefficient Ip of the current loop plays the role of small overshoot and good following performance in the control. Specifically, the current loop transfer function can be expressed as

(including a proportional link and a delay link), the control object is the inverter inductance L2.

In addition to the PID digital controller for the above-mentioned PID double closed-loop control, the control system also includes a current loop proportional coefficient adjustment module. Please refer to Figure 3. The current loop proportional coefficient adjustment module includes a detection unit and a coefficient setting unit. Given current loop proportional coefficient Ip. The present invention pre-sets a current loop proportional coefficient with a small value and a current loop proportional coefficient with a relatively large value. When the busbar overvoltage control condition is satisfied, the coefficient setting unit takes the current loop proportional coefficient Ip as the preset The smaller value of the busbar overvoltage control is realized. When the busbar overvoltage control condition is not satisfied, the coefficient setting unit takes the current loop proportional coefficient Ip as a preset larger value, so as to meet the requirements of the larger current loop It is a system index with better performance under the proportional coefficient. Such system indicators include both dynamic and steady-state indicators, and the steady-state indicators include THD system indicators.

In the present invention, the larger value can be defined as the value that the current loop proportional coefficient also ensures that the relevant system indicators are in the normal range when the UPS has a non-inductive load, and the smaller value is compared with the larger value. The value depends on the specific requirements of busbar overvoltage control when the UPS has an inductive load.

Experiments have proved that if the PID digital controller adopts a small current loop proportional coefficient Ip, it is very effective in suppressing the rise of the bus voltage. Large overshoot increases the loss of bus energy. However, the UPS system may have inductive loads or non-inductive loads. For example, when the system has resistive loads and rectifier loads, the system index of THD should be considered, and this index requires a larger current loop. ratio factor to meet the requirements. By adopting the above technical solutions, the present invention can not only ensure the suppression of bus voltage rise, but also take into account the index requirements including THD.

Detecting whether the UPS satisfies the bus overvoltage control conditions can be determined according to the nature of the load. If the nature of the identified load is inductive load, it can be determined that the bus overvoltage control condition is met, and a smaller current loop proportional coefficient is used at this time; if the nature of the identified load is capacitive or resistive load, it can be determined that the bus overvoltage control is not satisfied Conditions, at this time, a larger current loop proportional coefficient is used, so as to increase the system's ability to carry inductive loads under the premise of taking into account other system indicators.

Since the power factor of the inductive load and the magnitude of the reactive current of the current are different from those of the non-inductive load, it can be identified whether it is an inductive load or not according to the magnitude of the reactive current of the load current. As shown in Figure 4, preferably, the detection unit includes a current calculation unit and a first judgment unit, wherein the current calculation unit is used to calculate the reactive current in the load current IL, and the first judgment unit is used to compare the reactive current with the set Compared with the predetermined threshold M, when the reactive current is greater than the threshold M, it is judged that the bus overvoltage control condition is satisfied, otherwise it is judged that the bus overvoltage control condition is not satisfied. According to the judgment result of the first judging unit, the coefficient setting unit will provide the current loop proportional coefficient of corresponding size.

When calculating reactive current, the waveform of load current IL can be decomposed into discrete Fourier in a power frequency cycle with multiple sampling points to decompose the reactive component Iq cos wt, and expand it into a discrete Fourier series as :

${\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; N</span>}}\underset{\mathrm{<span\; class="notranslate">\; 0</span>}}{\overset{\mathrm{<span\; class="notranslate">\; N</span>}}{<span\; class="notranslate">\; \&Integral;</span>}}\mathrm{<span\; class="notranslate">\; Iq</span>}\mathrm{<span\; class="notranslate">\; cos</span>}\frac{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; P.I.</span>}}{\mathrm{<span\; class="notranslate">\; N</span>}}\mathrm{<span\; class="notranslate">\; j</span>}$

The reactive current of the load current is represented by the variable Iq, and the inductive load, capacitive load and resistive load can be properly distinguished according to the size and positive or negative of the corresponding component. For inductive loads, Iq is positive (positive means that voltage leads current), for resistive loads, Iq is a small positive number, and for capacitive loads, Iq is negative (negative means that current leads voltage), so according to Iq Distinguish between inductive loads, capacitive loads, and resistive loads. Therefore, a threshold value can be set, and when Iq is greater than the threshold value, it is considered as an inductive load. The threshold value is based on the size of the reactive current, which can roughly divide the loaded load into inductive load and non-inductive load. The specific value can be changed according to the actual application situation.

Therefore, in a preferred embodiment, the current calculation unit respectively calculates the reactive components of the load current at multiple sampling points within one power frequency cycle, and takes the average value as the reactive current. The reactive component can preferably be calculated by Fourier transform, which is obtained by multiplying the instantaneous value of the load current and the cosine value of the angle between the inverter current and the inverter voltage.

Detecting whether the UPS satisfies the busbar overvoltage control condition can also be judged according to the magnitude of the busbar voltage and inverter current.

As shown in Figure 5, in another embodiment, the detection unit includes a second judging unit, the second judging unit is used to compare the bus voltage V with the set voltage reference value Vr, and compare the inverter current I with The set current reference value Ir is compared. When the bus voltage is greater than the voltage reference value and the inverter current is greater than the current reference value, it is judged that the bus overvoltage control condition is satisfied, otherwise it is judged that the bus overvoltage control condition is not satisfied. For example, when the second judging unit judges that the voltage of the positive bus or the negative bus is greater than a certain value (such as 10% of the voltage value, that is, when there is a risk of bus overvoltage), if the inverter current is judged to be greater than a certain value at the same time, it is judged that the bus is overvoltage The control conditions are met. At this time, quickly adjust to the set smaller current loop proportional coefficient Ip to reduce the bus voltage. And when the bus voltage decreases, it will gradually return to the original current loop proportional coefficient Ip.

Compared with the previous embodiment, it is not easy to distinguish inductive loads in this embodiment, so there will be certain risks.

In the above embodiments, the load current, the bus voltage and the inverter current can be detected by setting relevant measurement circuits, and these measurement circuits can adopt various conventional designs.

As shown in FIG. 6, according to an embodiment of the present invention, the UPS control method includes a step of adjusting the current loop proportional coefficient, which is described as follows:

Step A. Detect whether the UPS satisfies the busbar overvoltage control condition;

Step B. When the busbar overvoltage control condition is satisfied, the current loop proportional coefficient is set to a smaller value; and

Step C. When the busbar overvoltage control condition is not satisfied, the current loop proportional coefficient is set to a larger value.

It can be judged whether the bus overvoltage control condition is satisfied according to the nature of the load. As shown in Figure 7, in one embodiment, the step A includes the following steps:

Step A11. Calculate the reactive current in the load current according to the load current value; and

Step A12. Comparing the reactive current with the set threshold value, judging that the bus overvoltage control condition is satisfied when the reactive current is greater than the threshold value, otherwise judging that the bus overvoltage control condition is not satisfied.

As shown in Figure 8, in a more preferred embodiment, the process of adjusting the proportional coefficient of the current loop is as follows:

Step 201, for the load current value IL flowing through the load, use fast Fourier transform to calculate the instantaneous value of the load current Iout_0 and the cosine value CosQ0 of the angle between the inverter current and the inverter voltage at one sampling point in the current power frequency cycle, and set Iout_0 is multiplied by CosQ0, accumulated with the calculation results of the previous sampling points, and assigned to the variable IqSumM_0;

Step 202, after the calculation of the previous sampling point in the current power frequency cycle is completed, it is judged whether the calculation of all the sampling points in the current power frequency cycle is finished, if not finished, return to step 201, if finished, enter step 203;

Step 203, divide IqSumM_0 by the number of sampling points of the output voltage cycle to obtain the reactive current Iq;

Step 204, comparing the reactive current Iq with the set threshold value, if it is judged that Iq is greater than the threshold value, go to step 205, if it is judged that Iq is smaller than the threshold value, go to step 206;

Step 205, taking the current loop proportional coefficient Ip as a set smaller value;

In step 206, the current loop proportional coefficient Ip is set to a larger value.

For the above steps 204-206, the threshold condition is used to distinguish the inductive load from other loads, so that different current loop proportional coefficients are used for different loads. The threshold value can be a digital value after calibration conversion, for example, 500 (per unit rated current corresponds to 4096), and taking 500 can effectively distinguish resistive loads. After the system is running, if the load is an inductive load, it will enter step 205, while the resistive load and rectifying load current can only enter step 206 when the load is steady-state (ignoring dynamic and very small inductive loads).

Whether the bus overvoltage control condition is satisfied can also be judged according to the bus voltage and inverter current. As shown in Figure 9, in another embodiment, the step A includes the following steps:

Step A21. Detect bus voltage and inverter current; and

Step A22. Compare the bus voltage and inverter current with the set voltage and current reference values respectively. When the bus voltage is greater than the voltage reference value and the inverter current is greater than the current reference value, it is judged that the bus overvoltage control condition is satisfied, otherwise it is judged The bus overvoltage control condition is not satisfied.

The above content is a further detailed description of the present invention in conjunction with specific preferred embodiments, and it cannot be assumed that the specific implementation of the present invention is limited to these descriptions. For those of ordinary skill in the technical field of the present invention, without departing from the concept of the present invention, some simple deduction or replacement can be made, which should be regarded as belonging to the protection scope of the present invention.

Claims (10)

1. the control system of a UPS, described UPS comprises rectifying part and the inversion part that is connected in turn between AC power and the load, it is characterized in that:

Described control system comprises the PID controller, it is used for described UPS is carried out two closed-loop controls, the described pair of closed loop comprises as the electric current loop of interior ring with as the Voltage loop of outer shroud, in described Voltage loop, value of feedback to inverter voltage set-point and inverter voltage is got difference, regulate through proportional integral, obtain the inverter current set-point, in described electric current loop, value of feedback to described inverter current set-point and inverter current is got difference, regulates through the ratio of electric current loop proportionality coefficient, obtains the controlled quentity controlled variable about described inverter voltage, wherein said inverter voltage is the output voltage of described inversion part, and described inverter current is the output current of described inversion part;

Described control system also comprises electric current loop proportionality coefficient adjusting module, it comprises detecting unit and coefficient unit, described detecting unit is used to detect described UPS and whether satisfies bus overvoltage controlled condition, described coefficient unit is used for when described bus overvoltage controlled condition satisfies, described electric current loop proportionality coefficient is taken as less value in two default electric current loop proportionality coefficients, when described bus overvoltage controlled condition does not satisfy, described electric current loop proportionality coefficient is taken as bigger value in two default electric current loop proportionality coefficients.

2. the control system of UPS as claimed in claim 1 is characterized in that, described detecting unit comprises the current calculation unit and first judging unit, and wherein, described current calculation unit is used for calculating the reactive current of the load current in the described load; Described first judging unit is used for the threshold values of described reactive current and setting is compared, and judges described bus overvoltage controlled condition during greater than described threshold values when described reactive current and satisfies, otherwise judge that described bus overvoltage controlled condition does not satisfy.

3. the control system of UPS as claimed in claim 2 is characterized in that, described reactive current is the idle component that calculates the load current of a plurality of sampled points in the power frequency period by described current calculation unit, averages and obtains.

4. the control system of UPS as claimed in claim 1, it is characterized in that, described detecting unit comprises second judging unit, described second judging unit is used for the voltage reference value of busbar voltage and setting is compared, and the current reference value of described inverter current and setting compared, when described busbar voltage greater than described voltage reference value and described inverter current during greater than described current reference value, judge that described bus overvoltage controlled condition satisfies, otherwise judge that described bus overvoltage controlled condition does not satisfy.

5. as the control system of each described UPS in the claim 1 to 4, it is characterized in that described controlled quentity controlled variable about inverter voltage is the controlled quentity controlled variable that SPWM takes place, described inverter voltage generates by described SPWM.

6. the control method of a UPS is characterized in that:

Described control method comprises carries out two closed-loop controls to described UPS, the described pair of closed loop comprises as the electric current loop of interior ring with as the Voltage loop of outer shroud, in described Voltage loop, value of feedback to inverter voltage set-point and inverter voltage is got difference, regulates through proportional integral, obtains the inverter current set-point, in described electric current loop, value of feedback to described inverter current set-point and inverter current is got difference, regulates through the ratio of electric current loop proportionality coefficient, obtains the controlled quentity controlled variable about inverter voltage; Wherein, described electric current loop proportionality coefficient is by the following steps adjustment:

A. detect described UPS and whether satisfy bus overvoltage controlled condition;

B. when described bus overvoltage controlled condition satisfies, described electric current loop proportionality coefficient is taken as less value in two default electric current loop proportionality coefficients;

C. when described bus overvoltage controlled condition does not satisfy, described electric current loop proportionality coefficient is taken as bigger value in two default electric current loop proportionality coefficients.

7. as the control method of UPS as described in the claim 6, it is characterized in that: steps A may further comprise the steps:

A11. the reactive current in the computational load electric current;

A12. the threshold values with described reactive current and setting compares, and judges described bus overvoltage controlled condition during greater than described threshold values when described reactive current and satisfies, otherwise judge that described bus overvoltage controlled condition does not satisfy.

8. the control method of UPS as claimed in claim 7 is characterized in that, in the steps A 11, described reactive current is by calculating the idle component of the load current of a plurality of sampled points in the power frequency period respectively, averages and obtains.

9. the control method of UPS as claimed in claim 8 is characterized in that, Fourier transform is adopted in the calculating of described idle component, by obtaining with the load current instantaneous value the included angle cosine of the inverter current of corresponding power frequency period and inverter voltage is on duty.

10. the control method of UPS as claimed in claim 6 is characterized in that, steps A may further comprise the steps:

A21. detect busbar voltage and inverter current; With

A22. the voltage reference value with busbar voltage and setting compares, and the current reference value of described inverter current and setting compared, when described busbar voltage greater than described voltage reference value and described inverter current during greater than described current reference value, judge that described bus overvoltage controlled condition satisfies, otherwise judge that described bus overvoltage controlled condition does not satisfy.

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